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COMPARATIVE ZOOLOGY, 


AT HARVARD COLLEGE, CAMBRIDGE, MASS. 


Sounded by private subscription, in 1861. 


Deposited by ALEX. AGASSIZ. 


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LISP 
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QUARTERLY JOURNAL 


OF 


MICROSCOPICAL SCIENCE: 


EDITED BY 


E. RAY LANKESTER, M.A., LL.D., F.R.S., 


Fellow of Exeter College, Oxford, and Jodrell Professor of Zoology in University 
College, London ; 


WITH THE CO-OPERATION OF 


W. T. THISELTON DYER, M.A., C.M.G., F.R.S., 
Assistant Director of the Royal Gardens, Kew ; 


E. KLEIN, M.D., F.R.S., 


Joint-Lecturer on General Anatomy and Physiology in the Medical School of 
St. Bartholomew’s Hospital, London ; 


H. N. MOSELEY, M.A., LL.D., F.R.S., 
Linacre Professor of Human and Comparative Anatomy in the University of Oxford, 
AND 


ADAM SEDGWICK, M.A., F.BS., 
Fellow and Assistant-Lecturer of Trinity College, Cambridge. 


VOLUME XXVII.—NeEw Sertrs. 
ith Arthographic Plates and Engrabings on Wood, 


LONDON: 
J. & A. CHURCHILL, 11, NEW BURLINGTON STREET. 
1887. 


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CONTENTS. 


CONTENTS: OF No: CVON.S. 7 AUGUST, 1886. 
MEMOIRS : 


The Anatomy of the Madreporaria: Il. By G. Herspert Fow rr, 
B.A., Keble College, Oxon., Berkeley Fellow of the Owens 
College, Manchester. (With Plate 1) : : 

On the Formation of the Germinal Layers in Chelonia. By K. 
Mirsuxuri, Ph.D., Professor of Zoology, and C. Isurkawa, 
Assistant in Zoology, University of Tokyo, Japan. (With Plates 
TET LV; and) V) 

On the Structure and Development of the ‘peteanane Hlerients 
in Myxine glutinosa, L. By J. T. Cunninenam, B.A., 
Fellow of University College, Oxford, and Superintendent of the 
Scottish Marine Station. (With Plates VI and VIT) 

Studies on Earthworms. No. II. By Witiiam Braxtanp Ben- 


HAM, B.Sc., Demonstrator in the Zoological Laboratory of 


University College, London. (With Plates VIII and IX) 

On Dinophilus Gigas. By W. F. R. Wetnoy, M.A., Fellow of St. 
John’s College, Cambridge; Lecturer on Invertebrate Morpho- 
logy to the University. (With Plate X) 


CONTENTS OF No. CVI, N.S., OCTOBER, 1886. 
MEMOIRS: 


The Development of the Mole (Talpa Europea). Stages E to 
J. By Watrer Hearn, M.A., Resident Superintendent of the 


Plymouth Laboratory of the Marine Biological Association of 


the United Kingdom. (With Plates XI, XII and XIII) 


On the Presence and Structure of the Pineal Eye in Lacertilia. 
By W. Batpwin Spencer, B.A., Fellow of Lincoln College; 


Assistant to the Linacre Pro‘essor of Human and Comparative 
Anatomy in the University of Oxford. (With Plates XLV, XV, 
XVI, XVII, XVIII, XIX and XX) 


PAGE 


17 


49 


77 


109 


123 


165 


lv CONTENTS. 


On the Life-History of Pedicellina. By Srpyey F. Harmer, B.A., 
B.Sc., Fellow of King’s College, Cambridge, and of University 
College, London. (With Plates XXI and XXII) : 

Dr. Dohrn’s Inquiries into the Evolution of Organs in the Chordata. 
By J. T. Cunnineuam, B.A., F.R.S.E. . 

REVIEW : 
Patten on the Eyes of Molluses and Arthropods 


CONTENTS OF No. CVII, N.S., JANUARY, 1887. 


MEMOIRS : 

The Anatomy of the Madreporarian Coral Fungia. By GrLBert 
C. Bourne, B.A., F.L.S., New College, Oxford. (With Plates 
XXIII, XXIV “al XXV) 3 

On Some Points in the Development of Petuaneen aba: 
By Artuur E. Suiptzy, B.A., Christ’s College, Cambridge, 
Demonstrator of Comparative Anatomy in the University. (With 
Plates XXVI, XXVIJ, XXVIIT and XXIX) 

The Ammoniacal Decomposition of Urine. By Wm. Rosert 
Smitu, M.D., D.Sc., F.R.S.Ep., Examiner in Chemistry and 
Forensic Medicine, University of Aberdeen. (With Plate XXX, 
figs. 1 and 2) 

Notes on Echinoderm Morphology, No. x. On the Sipneea 
Presence of Symbiotic Alge in Antedon rosacea. By P. 
HERBERT CaRventer, D.Sc., F.R.S., F.L.S., Assistant Master 
at Eton College. (With Plate XXX, fig. 3) : : 

The Function of Nettlecells. By R. von Lenprenretp, Pu.D., 
F.L.S., Assistant in the Zoological Laboratory of University Col- 
lege, London. (With Plate XXX, fig. 4) : 

Some New Methods of Using the Aniline Dyes for akin 
Bacteria. By E. Hanpury Hankin : 

Illustrations of the Structure and Life-History of Phytophekoee 
infestans, the Fungus causing the Potato Disease. By H. 
MarsHatt Warp, M.A., F.L.S., Fellow of Christ’s College, 
Cambridge, and Professor of Botany in the Forestry School, Royal 
Indian College, Cooper’s Hill. (With Plates XXXI and XXXII) 

On the Formation and Liberation of the Zoospores in the Sapro- 
legniee. By Marcus M. Harroe, D.Sc., M.A.,, F.R.U.L. 


PAGE 


239 


265 


285 


293 


325 


371 


379 


393 


401 


413 


427 


CONTENTS. 


CONTENTS OF No. CVIII, N.S., MARCH, 1887. 


MEMOIRS : 

The Termination of Nerves in the Liver. By A. B. Macatium, 
B.A., Fellow of University College, Toronto, Canada. (With 
Plate XXXIII, figs. 1 to 6) : 

On the Nuclei of the Striated Muscle- Fibre i in Mananis (Meno- 
branchus) lateralis. By A. B. Macatuum, B.A., Fellow of 
University College, Toronto, Canada. (With Plate XXXIII, 
figs. A and B) : : : 

The Development of the Cape Speties of Penuarae: Part III. 
On the Changes from Stage a to Stage Fr. By Apam Sepewicx, 
M.A., F.R.S., Fellow of Trinity College, Cambridge. (With 
Plates XXXIV, XXXV, XXXVI and XXXVII) ; 

Morphological and Biological Observations on Criodrilus lacuum, 
Hoffmeister. By Dr. L. Ortsy, Zoolog. Instit. University of 
Budapest. (With Plate XXXVIII, figs. 1 to 8) 

Studies on Earthworms. No. III. Criodrilus lacuum, Hof. 
meister. By Witttam Braxtanp Benuam, B.Sc., Demonstrator 
in the Zoological Laboratory of University College, London. 
(With Plate XXXVIII, figs. 9 to 19) : : 5 

Notes on the Chromatology of Antheacereus. By C. A. 
Mac Muny, M.A., M.D. (With Plates XXXIX and XL) 

On Ctenodrilus parvulus, nov. spec. By Ropert ScHarrr, 
B.Sc., Po.D. (With Plate XLI) ; , 

The Relation of the Nemertea to the Wertsrata: By A. A. W. 
Husrecut, Professor in Utrecht. (With Plate XLII) 


InDEX 


PAGE 


439 


461 


467 


551 


561 


573 


591 


605 
645 


The Anatomy of the Madreporaria: II. 
By 


G. Herbert Fowler, B.A., 
Keble College, Oxon., Berkeley Fellow of the Owens College, Manchester. 


With Plate I. 


In a previous paper (4), I have described the anatomy of a 
solitary Imperforate coral, Flabellum; and of a branching 
Perforate, Rhodopsammia. The present memoir treats of two 
examples of colonial Perforate forms, Madrepora Durvillei 
and M. aspera. 


Maprerora Durvitier (Milne-Edw. and Haime). 


Two fragments of this perforate Madreporarian were kindly 
entrusted to me for study by Professor H. N. Moseley, who 
had obtained them during the voyage of H.M.S. “Challenger.” 

The species was founded by Milne-Edwards (1) from a part 
of the M. rosea of Esper, but as his account is very incom- 
plete, Mr. J. J. Quelch, of the British Museum, has furnished 
the following description of the coral. I am glad to be able to 
take occasion to thank him for this and many other courtesies. 

A. “Corallum arborescent, spreading, and remotely ra- 
mose, or occasionally sub-prostrate, and almost destitute of 
branchlets on the under surface. Branches often nearly 2 
em. thick, becoming very thin towards their extremity, sub- 
terete, elongated, covered irregularly with crowded capillary 
polyp-bearing branchlets, which generally give to the branches 
a sub-cylindrical outline of about 3—5 mm. in diameter. 


VOL, XXVII, PART 1,—NEW SER, A 


2 G. HERBERT FOWLER. 


Branchlets small and short, about 1—2 cm. in length, con- 
sisting generally of a few thin and long tubiform calicles ; 
towards the apical parts of the branches they become much 
less elongated and often quite short. Surface slightly 
porous, very distinctly costulated throughout, and marked with 
fine echinulations which are very distinctly arranged on the 
calicles. Calicles generally tubiform, about 15 mm. wide 
and 1: cm. long, except towards the apical parts of the branches, 
where they are shorter and smaller, and sometimes tubo- 
nariform; a few short tubonariform calicles are generally 
placed on the surface of the branches between the branchlets. 
Star distinct, of six more or less lamelli-spiniform septa, two 
of which, the distal and the proximal, are usually much 
enlarged, and meet one another, often deep down in the fossa ; 
while occasionally, as in the terminal calicles, the six septa are 
subequal, and coalesce at the centre.” 

«This species seems to be distinguishable from the M. 
echinata (Dana) simply by the costulations of the surface, 
which in the latter is smooth or finely granulated. It is 
doubtful, however, whether this character will prove to be 
sufficiently constant to separate the two species, when a larger 
number of forms has been examined.” 

Figs. 1 and 2 represent the dorsal and ventral aspects of a 
fragment of a branch, and show most of the characteristics 
mentioned in the above description. 

In a transverse section of the corallum (fig. 3), the peri- 
pheral ring of polyp cavities is cut somewhat obliquely (a a.), 
owing to the inclination of branchlets and calicles to the 
branch; while the more central ones, cut at a lower level and 
more transversely, are approximately circular in outline (a’ 
a’.). They lie, roughly speaking, on three sides of the branch, 
none are apparent on the fourth. The shorter radius of the 
latter seems to imply that the growth in diameter of the 
branch depends upon the outward growth of the polyps. 

In the axis of the branch is a central cavity (c. c.), into 
which project six septum-like ridges ; this probably represents 
a cavity previously inhabited by the now apical polyp. The 


THE ANATOMY OF THE MADREPORARIA. 3 


tops of both my specimens having been broken off, I have not 
been able to prove this; nor again to investigate the method of 
budding; but in M. aspera is such another central cavity with 
six septa, which is continuous with that of the apical polyp. 
All other polyp cavities converge towards, and, by means of 
canals, eventually open into, this central cavity, but no more 
definite connection is traceable. Tissues not unlike mesenteries 
are sometimes visible in it, but the alcohol in which the speci- 
mens were killed did not penetrate sufficiently rapidly to 
preserve the central parts in good histological condition. In 
some sections the six septa are not recognisable, and the axis 
of the branch is occupied by a wide-meshed network of coral ; 
this is probably due to reabsorption of part of the skeleton. 

In transverse section are also seen concentric series of lon- 
gitudinal canals (c*.) permeating the corallum; their 
arrangement appears to indicate that the radial growth of the 
branch is effected in the following manner. Directly beneath 
the external body wall of the colony a series of longitudinal 
canals runs between the cost (fig. 4, c') ; and it is probable 
that, for increase in the diameter of the branch, the costz grow 
outwards, and then, bulging laterally, fuse over these canals, so 
as to enclose them entirely in corallum (cf. fig. 10, v.). Thus 
there results a series of internal longitudinal canals, concen- 
trically arranged, with radi of coral between them which 
represent former cost. Not only does the appearance of such 
a transverse section as fig. 3 suggest that this is the mode of 
growth, but also “ dark lines of growth” (fig. 5) run radially 
from each costa towards the centre, so continuously as to indi- 
cate that what was a costa when the diameter of the branch 
was very small, has continued to grow as such, and to be still 
such, when the diameter is very much larger. New coste, 
when required owing to the increased circumference of the 
branch, appear to take their origin from the point of fusion of 
previous costz. 

More minutely, growth is effected, presumably by the 
activity of calycoblast cells, through the addition to and for- 
mation of crystalline ellipsoids, similar to those described 


A G. HERBERT FOWLER. 


by v. Koch in Stylophora (2). These ellipsoids have a distinct 
sweep from one “ line of growth” to the next. 

The calyces are all of approximately the same size, and 
that so minute as to render investigation of the anatomy 
difficult. 

The septa are very irregular of occurrence; the complete 
number appears to be six, but three are rarely to be seen in 
one section, often none at all. They are not constant through 
the whole depth of the polyp cavity, but occur as discontinuous 
ridges (fig. 6, Ad.). In every polyp, however, either an axial or 
abaxial septum is present, which enables the orientation of the 
polyp to be effected as in the Alcyonaria. (These terms, axial 
and abaxial, are used in preference to the ordinary and mis- 
leading “dorsal”? and “ ventral,” and were suggested originally 
by Professor Milnes Marshall, ‘Trans. Roy. Soc. Edin.,’ 
1883.) 

There is no columella, but often the axial and abaxial septa 
fuse, low down in the polyp cavity, so as to divide it into two 
equal halves (fig. 3, a’), in a manner suggestive of the 
“median plate” in Pocillopora and Seriatopora figured by 
Professor Moseley (3). 

The costz bear apparently no relation to the septa in the 
well-grown colony, whatever may have been the case in the 
founder-polyp. Not only is no connection traceable between 
them in a transverse section of the branch, but even in a single 
polyp standing off from the stem, where the number of septa 
is under the most favorable conditions but six, about twenty 
costz surround the calicle. 

sp. Anatomy.—The whole of the corallum is covered exter- 
nally by a definite body wall of ectoderm, mesoderm, and 
endoderm (fig. 6, ext. b. w., fig. 4, ect. me. en.), immediately 
beneath which lie, as in Rhodopsammia, external longitu- 
dinal canals parallel to the long axis of the corallum (figs. 
3, 4, 6, c'). These, however, are not the result of the same 
anatomical relations in both cases ; in Rhodopsammia, lamellee 
of mesoderm with a layer of endoderm on each side are given 
off from the external body wall, and unite with the endoderm 


THE ANATOMY OF THE MADREPORARIA. 5 


and mesoderm which clothe the exterior surface of the theca ; 
and into the canals thus formed project the costa. In 
M. Durvillei, the layer of endoderm and mesoderm which 
is immediately apposed to the exterior surface of the corallum, 
rises in a ridge towards the external body wall; and at the 
points where these layers meet and fuse are formed the coste, 
i.e. in the angle of the mesoderm ; and therefore between the 
cost lie the canals. A comparison of fig. 4 with (4) fig. 17 
will make clear the anatomical difference. 

There is thus no trace of any structure resembling the “ peri- 
pheral continuations of the mesenteries of v. Koch.” 

These canals appear to open over the lip of the calyces into 
the polyp cavities ; they are connected with each other trans- 
versely between the spikes (echinulations) of the costz (figs. 
6,7); and further, by radial canals (figs. 3, 4, c3.) they open 
into the internal longitudinal canals, which I believe, as above 
stated, to have, at an earlier period in the history of the branch, 
occupied a position similarly external to the corallum. The 
whole system which thus perforates the corallum, and allows 
free current of fluid to even the most remote parts of the 
colony, is lined by endoderm and mesoderm throughout, and 
opens into similarly lined polyp cavities. 

The general structure of the colony is, therefore, (1) an 
external body wall, under which and between the cost 
lies (2) a series of external longitudinal canals opening 
into each other, and also through the corallum, into (3) the 
internal canals, mainly longitudinal, with radial and trans- 
verse connections, communicating in their turn with (4) the 
celentera of the polyps. Into the last the external 
longitudinal canals also open directly, through the theca. The 
whole system is of course merely a complication of the primi- 
tive coelenteron. 

Of the polyps there are at least two distinct types, which 
are full of interest as constituting the first record of marked 
dimorphism among the Madreporaria. Both are Actinian in 


structure. 
Type A has in the highest sections twelve perfectly normal 


6 G. HERBERT FOWLER. 


mesenteries, and a stomatodeum which is a simple invagina- 
tion of the external body wall. A little way down in the 
polyp, six of the mesenteries, in every case the same six, 
assume a curious modification of structure, which wil] be 
described first as seen in a series of transverse sections. Fig. 8 
represents the characteristic features of a polyp of this type; 
the mesenteries numbered 2, 4, 6, 7,9, 11 are those which 
undergo modification, and are diagrams of a series of drawings 
made from the same mesentery with camera lucida at different 
heights. 

There appears first (fig. 8.2) an involution of the stomato- 
deeum directed towards the mesentery, on the floor of which 
the ectodermic cells are long, but shorter at the sides. By 
fusion of the mesoderm and obliteration of the ectoderm on 
each side of this involution, a small canal with a definite 
lumen is found to be pinched off, and to lie enclosed in the 
mesoderm lamella of the mesentery (fig. 8.4). In the neigh- 
bourhood of this involution, the endodermic cells lining the 
mesenterial chamber become enormously lengthened and vacuo- 
lated, though the layer is still apparently only one cell deep. 

Some sections lower down in the polyp (fig. 8 ), another 
similar involution appears in the stomatodzum, in which the 
ectodermic cells are short on the floor, but pass into deeper 
ones at the sides; this similarly results in the enclosure of 
what appears to be a second canal in the centre of the mesen- 
tery (fig. 8.7). In the first canal, as is shown in the diagram, 
the longer ectoderm cells face towards the stomatodzum ; in 
the second away from it. 

Further down yet, where the stomatodzeum ceases, the free 
edge of the mesentery is enlarged into a perfectly normal 
filament (fig. 8.9); and finally (fig. 8.11), the whole modifica- 
tion disappears suddenly, the two canals meeting below; the 
mesentery then presents a perfectly normal appearance, namely, 
a mesoderm lamella with a layer of small endodermic cubical 
cells on each side of it, and bearing the usual filament. 

The compilation of these sections, which I have attempted 
to express in fig. 6 M, shows that on an ordinary mesentery 


THE ANATOMY OF THE MADREPORARIA. 7 


occurs a swelling due to elongation of the endoderm cells, 
through which runs, in the mesoderm, a canal lined by ecto- 
derm, doubled back on itself, and opening at both ends into 
the stomatodzeum, with the ectoderm of which its lining is 
continuous. 

Of twenty-one polyps examined, seven present this modifi- 
cation of six (and in all cases of the same six) mesenteries, 
namely, those numbered 2, 4, 6, 7, 9, 11, according to the 
method employed in the diagram ; the other six mesenteries, 
1, 3, 5, 8, 10, 12, and all the twelve mesenteries of the other 
polyps, are perfectly normal, and show no tendency to such a 
modification. Were it possible to explain the sectional appear- 
ances by a contortion of the mesentery, the regularity with 
which it occurs would be sufficient proof that it is a definite 
modification of structure, the parallel of which has yet to be 
sought in the Anthozoa. 

The unmodified mesenteries in Type A, generally die out 
before the plane of the opening of stomatodzeum into celen- 
teron is reached, in transverse sections. If they present a fila- 
ment, which is seldom the case, it is of the same character as 
that figured (fig. 8.11), i.e. identical with that of a modified 
mesentery ; more frequently none is present, or at most a 
slight endodermal swelling on the free edge. 

The mesenteries 4, 9, run very much deeper into the corallum 
than the others. 

Type B, of about the same diameter as A, is of the normal 
Actinian structure. The twelve mesenteries are simple, and 
exactly like those unmodified in Type A. Most of them die out 
after a very short course, but those numbered 2, 4, 6, 7, 9, 11, 
on the same notation as in fig. 8, present a more developed fila- 
ment than the other six, and extend further down into the 
corallum, and of these 4, 9, have by far the longest course, and 
are the only ones that bear ova. 

We have thus two distinct types of polyp, the one distin- 
guished only for entire normality ; the other with a hitherto 
undescribed form of mesentery. In both is observable a differ- 
entiation affecting the same six mesenteries, exhibited in the 


8 G. HERBERT FOWLER. 


one case as a tendency to a longer course, and to the more 
complete development of the filament; im the other as the 
peculiar modification described above ; and in both types two 
of these six have of all the longest course, and are, so far as I 
have observed, the only ones that bear reproductive organs. 

Neither type is confined to certain areas of the branch, but 
both appear to be irregularly distributed. 

Tentacles are not recognisable in my specimens, but it is 
probable that in the living animal they occur as slight evagina- 
tions of the chambers, and have shrunk under the action of the 
alcohol in which the polyps were killed. 

Muscles are obviously present on the mesoderm lamella of 
the mesenteries, but owing to their minute size it is impossible 
to detect how they are arranged. I see no reason to doubt 
that they agree with Actinia. So far as it is possible to judge 
without this clue, the septa are entoceelic. 

c. Histology.—There is but little to be said under this head, 
except as regards the modified mesentery, an almost transverse 
section of which is represented in fig. 9. ‘The state of the 
specimens did not allow of an exhaustive study of cell structure, 
but those cells, the elongation of which causes the peculiar 
swelling on both surfaces of the mesentery, are apparently 
simply lengthened, much vacuolated, and ameceboid at their free 
ends. No food particles were detected in them, or indeed in 
any other part, but many zooxanthellz are embedded amongst 
them. ‘These cells pass gradually into the ordinary endoderm, 
and their appearance suggests strongly that their condition is 
merely an exaggeration of that of the “ Flimmerstreifen”’ of 
the brothers Hertwig, i.e. of the two lateral lobes of the 
mesenterial filament. 

In a recent paper (5) Dr. Wilson has suggested that these 
lateral lobes are ectodermic in origin, circulatory in function, 
and homologous with the “ectodermic bands” described by 
him on the axial mesenteries of certain Alcyonaria. I may 
here state that, so far as histological evidence from the adult 
is valuable, it points, in all the Madreporaria that I have yet 
examined, distinctly in the other direction. The central 


THE ANATOMY OF THE MADREPORARIA. 9 


“ Nesseldriisenstreifen” have precisely the same microscopic 
appearance as the stomatodzeal ectoderm; while the “ Flim- 
merstreifen,” im the unbroken gradation by which they pass 
into the endoderm, and by their characteristic staining, seem to 
be much more nearly connected with that layer than with the 
ectoderm, and to exhibit an intermediate condition between the 
ordinary cubical or pavement cells of the endoderm and the 
enormously lengthened cells of M. Durvillei. v. Heider (6), 
on the same grounds, had previously come to the same con- 
clusion with regard to Cerianthus. 

The ova, which in my specimens were few in number, are 
surrounded by a mesodermal capsule, and possess the ordinary 
structure. In the one case, in which an ovum was observed 
on a modified mesentery, it was borne on the neck between the 
endodermic swelling and the mesenterial filament. 

p. General Conclusions. — This form has four interesting 
features in common with the Alcyonaria (Octactiniz) : 

1. The marked tendency to an absence of polyps on one (the 
ventral) side of the branch and branchlets. 

2. The very definite orientation of the polyps by a stronger 
development of axial and abaxial septa; and the concomitant 
bilateral symmetry, the plane of bisection being at right angles 
to the long axis of the branch or branchlet. 

3. The differentiation of mesenteries, which, confined in the 
Alcyonaria to two, is here extended to six, and more particu- 
larly to two of these, though not the same two as in the other 
group. 

4. The distinct dimorphism. 

Of the true significance of this dimorphism no certain 
explanation can be gathered from this form studied merely by 
itself; it can only be resolved by a comparative study of allied 
species. Differentiation of function appears to be incomplete ; 
both forms are reproductive, both apparently digestive. The 
most that can be said is that A is, perhaps, more digestive and 
less reproductive than B, for the filaments are more deve- 
loped than in the latter form, and I have only once observed 
an ovum on a modified mesentery. Should the modification 


10 G. HERBERT FOWLER. 


be digestive in function, as is probably the case, A might 
certainly be termed a “‘ gastrozooid.” 

But at present any explanation of the function of the struc- 
ture above described, cannot be other than a mere speculation. 
It cannot be regarded as a necessary result of the colonial 
habit, since nothing similar occurs in the next species to be 
described—M. aspera. It can hardly be connected with re- 
production, as ova are of rarer occurrence in the modified than 
in the unmodified polyps; and an excretory apparatus is not 
required by an organism whose cells are capable of amceboid 
activity, egestion as well as ingestion. 

The only evidence on the point is derived from the distribu- 
tion of the zooxanthelle. These are most plentiful, firstly, in 
the external canals just under the body wall; and secondly, 
among the elongated cells of the mesentery. Assuming, as we 
may fairly do, that nutriment and aération were the determin- 
ing factors of such distribution, it would seem that, in the first 
case, there must be a strong current of nutritive “ chyle- 
aqueous fluid” (to use a word of the older zoologists) in these 
external canals, and that aération was effected by diffusion of 
oxygen through the body wall from the surrounding medium ; 
and in the second place, that the elongated vacuolated cells of 
the mesentery were in some way assimilative, while oxygenation 
of the tissues for these special digestive processes (and there- 
fore secondarily and accidentally to the benefit of these 
symbiotic alge), resulted from a constant stream of water 
flowing through the central ectodermal canal of the 
mesentery. 

That such a stream does pass through this canal is extremely 
probable, for the longer ectodermic cells are all morphologi- 
cally on the same side of the canal; a wave of ciliary action 
must therefore result in a current through the canal from one 
of the apertures into the stomatodeum towards the other. 
A comparison of fig. 8.7 with fig. 6 mw will explain this arrange- 
ment of the cells. 

It is interesting to note that in M. Durvillei, as in 
Alcyonaria and Antipatharia, two mesenteries are distinguished 


THE ANATOMY OF THE MADREPORARIA. 11 


from the rest by running far deeper into the corallum or 
rachis. This may be a specialisation for circulatory purposes, 
as has been shown by Dr. Wilson to be true for certain Alcyo- 
naria, or connected with production of the generative elements, 
as is the case in Antipatharia; in M. Durvillei certainly the 
latter, perhaps also the former, holds good. 


Maprepora AsPEeRA (Dana). 


For a fragment of this coral, fortunately the upper part of a 
branch, I am again indebted to Professor Moseley. 

The species was founded by Dana (7), who gives a good 
figure of the colony. 

A. Corallum.—A transvers esection of the corallum (fig. 10) 
shows that the polyp cavities (a a’) are arranged in a definite 
ring, and not merely confined to three sides as in M. Durvillei, 
round a central cavity into which project six septa, more or 
less fused together at their free edges. This central cavity 
(c. c.) is continuous with that of the apical polyp of the branch. 
The arrangement of the internal longitudinal canals is not so 
definitely concentric as in M. Durvillei, but the method of 
circumferential growth of the corallum appears to be similar 
in both species, since the costz appear to fuse over the external 
longitudinal canals (v. fig. 10, z, and p. 3). 

In the apical polyps are found six distinct entoccelic septa, 
and six smaller exoccelic, of which all are not always present ; 
in the others generally only an axial or abaxial septum. A 
similar difference between them was observed by v. Koch (8) 
in M. variabilis, where both exosepta and entosepta were 
present in the apical polyps, but entosepta only in the rest. 

In this form, as in the former species, there appears to be 
no relation in number and position between cost and septa, 
the former being by far the most numerous. 

The cost are apparently formed as in M. Durvillei, 
that is, at the points where the endoderm and mesoderm 
apposed to the exterior surface of the corallum touch the 
external body wall (v. p. 5 and fig. 4), but in both species, 
owing to alcoholic contraction, the latter has so shrunk on to 


12 G. HERBERT FOWLER. 


the corallum that the cost project through it, and the exact 
conditions are difficult to determine with certainty. 

B. Anatomy.—The general anatomy of the colony, as regards 
the relations of canals, body wall, polyp cavities, &c., agrees 
with that of M. Durvillei. Beyond the fact that in M. 
aspera the polyp cavities are placed closer together, and that 
therefore there are fewer canals in the corallum, there is little 
or no difference between them. As regards the polyps, how- 
ever, there is no dimorphism; all the polyps, except those 
which are obviously immature buds, are identical in structure. 

A typical polyp possesses twelve perfectly normal mesen- 
teries, and a stomatodeum which is a simple invagination of 
the external body wall. When numbered on the same system 
as in M. Durvillei, it is found that those mesenteries marked 
1, 2, 4, 6,7, 9, 11, 12, are the ones which develop mesen- 
terial filaments, that is, the same mesenteries as in M. 
Durvillei, with the addition of the abaxial “ directives ;” 
while the others, 3, 5, 8, 10, generally have no filament, and 
do not extend to the bottom of the stomatodeum. 

The apical polyps are about twice the size of the others, 
but, except for their possession of more septa, are identical 
in structure with them. 

The muscles in both apical and lateral polyps are arranged 
on the mesenteries just as in Actinia, and present nothing 
unusual in structure. 

Tentacles I was unable to recognise, macroscopically or 
by sections, but a figure by Dana shows that they are present, 
and twelve in number. In this, as in the species last described, 
they have shrunk into insignificance, owing to the action of 
the spirit in which the specimens were preserved. They agree 
with M. variabilis, in which, according to v. Koch, they are 
also exoccelic and entoccelic. 

The histology calls for no remark, agreeing with that of 
forms already described. Calycoblasts were very distinctly 
present in the growing parts of the colony. 

c. Method of Budding.—With regard to this, I have been 
able to gléan but little information ; since the immature polyps 


THE ANATOMY OF THE MADREPORARIA. 13 


are so crowded with zooxanthellz, owing presumably to the 
amount of nutriment supplied to them, that the tissues are 
much obscured. 

The stomatodzeum is invaginated to a considerable depth 
into the future polyp cavity before it is perforated for com- 
munication between the ceelenteron and the exterior, and also 
apparently before any mesenteries are formed. The cavity 
into which it is invaginated is already of considerable diameter, 
and larger than the ordinary canals of the colony; though 
smaller than that of a fully formed polyp, at that point it is 
probably never enlarged by reabsorption of coral, but its con- 
tinuation upwards by future growth of the polyp possesses a 
gradually increasing diameter. 

In a young polyp in which the stomatodeum was invagi- 
nated, but not yet perforated below, the latter appeared to be 
supported by tissue surrounding the future septa, just as the 
external body wall is supported by tissue enclosing the costz. 
In sections below the stomatodzum, and unconnected with it, 
were seen two small mesenteries with filaments, which appeared 
to be growing upwards towards the stomatodzum, and to have 
not yet joined it. It is therefore possible that these grow 
upwards from the canal system, and are formed quite inde- 
pendently of the rest of the polyp. This view is further 
supported by the observation that, in sections quite at the top 
of a branch, above the plane of any lateral polyps, occur in 
the canals one, sometimes two, little mesenteries with fila- 
ments, which I believe to be growing upwards towards the 
sites of future polyps. They appear to take rise, near the 
cavity of the apical polyp, from the wall of the canals. 

In the only other stage of development from which any 
observations could be made six mesenteries had appeared ; of 
these the two furthest from the axis carried muscles on the 
outer faces, though it does not necessarily follow that they 
were the abaxial “directives” of the adult. The muscles of 
the other two pairs were not sufficiently developed to allow of 
their arrangement being recognised. 

Conclusion—From M,. Durvillei, the present species is 


14 G. HERBERT FOWLER. 


widely separated by a strong morphological distinction, the 
absence of dimorphism; since the difference between the 
apical and lateral polyps in M. aspera is hardly strong enough 
to be reckoned as such. That such a distinction should exist 
between two species of a genus is very remarkable; but, con- 
sidering the great antiquity of these forms, the similar struc- 
ture of the colony in both, and the fact that they exhibit a 
similar differentiation of certain mesenteries, it is not to be 
inferred that their systematic relations are unsound. 


Nore. 

For microscopic sections through both hard and soft parts 
of the coral, such as are figured in (4) Pl. XLI, figs. 14, 15, I 
have found the method, originally applied by v. Koch to these 
forms, extremely useful. The coral, having been left in borax 
carmine for three days, and treated with acidulated alcohol for 
six hours, is transferred to absolute alcohol, and from this to 
ether; into the ether is dropped absolutely dry powdered 
Canada balsam in small quantities at a time, till enough is dis- 
solved to make a block, rather larger when dry than the speci- 
men. The ether is driven off by a gentle heat, leaving the 
coral permeated throughout by balsam. About a week should 
be devoted to this part of the process. 

Sections are then cut with a lapidary wheel, or, if this is not 
procurable, with afret saw ; and ground like geological sections 
on a slate, then polished on a water of Ayr stone. Oil and 
emery powder should be avoided, water alone being used for 
the stones. 

One surface of the section having been ground and polished, 
it should be affixed permanently by that surface to a glass 
slide, on to which some dry Canada balsam has been melted, 
and not again be moved. When the other surface has been 
similarly ground and polished to the required thinness, it 
should be brushed lightly, first with absolute alcohol, then 
immediately with oil of cloves; this removes all dirt from the 
surface. A drop of balsam in benzole is then placed on the 
section, and the cover glass lightly dropped on it. 


THE ANATOMY OF THE MADREPORARIA. 15 


ERRATUM. 


In my previous paper (4) Pl. XL, fig. 1°, the septa were 
wrongly numbered ; they should have been marked 1, 4, 3, 4, 
2, 4, 3, 4, 1, reckoning on each side from the central “ direc- 
tive’ septum, D. 


LITERATURE. 


1. Mitnz-Epwarps.—‘ Hist. Nat. d. Coralliaires,’ iii, p. 148. 
2. von Kocu.—‘ Jen. Zeitschr.,’ Bd. xi. 
3. MospetEy.—‘ Quart. Journ. Mier. Sci.,’ Oct., 1882. 
4, FowLer.—‘ Quart. Journ. Mier. Sci.,’ Oct., 1885. 
5. Witson.—‘ Mitth. Zool. Sta. Neap.,’ Bd. v. 

6. von Herppr.—‘ Sitz. k. Akad. Wissench.,’ 1879. 

7. Dana.— Zoophytes of the Wilkes Expedition.’ 

8. v. Kocu.—‘ Morph. Jahrb.,’ Bd. vi. 


DESCRIPTION OF PLATE I, 


Illustrating Mr. G. Herbert Fowler’s Paper on “ The Anatomy 
of the Madreporaria.” 


a. Polyp cavities, cut obliquely. a’. Polyp cavities, cut transversely. 4d. 
Abaxial (ventral) septum. 4. Axial (dorsal) septum. C. Coste. c.c. Cen- 
tral cavity, continuous with the apical polyp. _c!. External longitudinal canals 
between the coste. c*. Internal longitudinal canals. c*. Radial and trans- 
verse connecting canals. Co. Corallum of the main branch. d. Cut edges of 
the endoderm and mesoderm lining the celenteron. ect. Ectoderm. ex. En- 
doderm. ext. b. w. External body wall of ectoderm, mesoderm, and endoderm. 
M. Mesentery, showing the endodermal swelling. me. Mesoderm lamella. 
S. Septum. S.C. Septal Columella-plate. St. Stomatodeum. 7%. Theca 
of polyp. Z. Zooxanthelle. 2. Fusion of coste over ext. long. canals. 
All except Fig. 10 are from Madrepora Durvillei. 


Fie. 1.—Dorsal view of the corallum of two fragments of a branch, 
bearing calicles, and branchlets formed of other calicles. 

Fie. 2.—Ventral view of the same specimens ; one of which is entirely 
bare of calicles on this side, and on the other ouly a few are present. 

Fic. 3.—Transverse section of a branch, showing the polyp cavities, the 
central cavity, and the canals running in various directions. The concentric 


16 G. HERBERT FOWLER. 


arrangement of the latter is well shown. Into the central cavity project the 
six septa. In two of the innermost ring of polyps, the axial and abaxial 
septa have fused into the septal columella-plate. 

Fic. 4.—Diagram of a transverse section of a polyp and of part of the 
branch. The external body wall is shown to be supported on the cost, as 
its mesoderm and endoderm are continuous with those lying on the outer face 
of the corallum. The polyp cavity shows at this point twelve mesenteries 
supporting the stomatodeum. (In nature the mesoderm lies closely apposed 
to the surface of the corallum, and there is no space between them, such as is 
introduced into the diagram for clearness.) 

Fic. 5.—Transverse section of a portion of the branch, to show the lines 

of growth, running between the canals radially and terminating each in a 
costa. 
Fic. 6.—Diagram of a longitudinal section of a polyp along the dotted line 
in Fig. 8. The tentacles are omitted, as they were not recognisable in my 
specimens ; the canal system in the corallum is also omitted. On the left the 
section passes between the axial septum and mesentery No. 7, and above the 
polyp down an external longitudinal canal; on the right, through the abaxial 
septum and down a costa, of which the echinulations and the canals between 
them are shown. The numbers indicate the same mesenteries as in Fig. 8. 
On the mesentery 7 is figured the endodermal swelling, with the bent canal 
indicated by dotted lines. In the stomatodum are shown the two openings 
of the canals of mesenteries 7, 9, 11; and below the stomatodeum the free 
edges of these three mesenteries alone appear, the others dying out before 
this plane is reached. The dotted line indicates the junction of theca and 
septa, and the discontinuous character of the septum (42.) is clearly shown. 

Fic. 7.—The external body wall viewed from the exterior; the lighter spots 
are the places where the echinulations of the costs have pierced the body 
wall on account of its shrinkage. This drawing shows the arrangement of the 
external longitudinal canals, and their connections between the spikes of the 
costee. (Camera lucida.) 

Fic. 8.—Diagram of the various forms and conditions of the mesenteries 
in a polyp of Type A. Those numbered 1], 3, 5, 8, 10, 12 are unmodified and 
normal. The others, 2, 4, 6, 7,9, 11, are modified in all the polyps of this 
type; they are from camera lucida drawings of the same mesentery at different 
heights. The arrows and Roman numerals in Fig. 8 show the planes in which 
the successive sections are taken.—2 shows the endodermal swelling, and the 
upper opening of the canal; 6 shows the lower opening; 9 is below the 
stomatodeeum, and bears a filament; and in 11] no trace of the modification 
remains, the mesentery being normal, and similar to those of Type B. 

Fic. 9.—Transverse section of a modified mesentery, passing through both 
arms of the canal. 

Fic. 10.—Transverse section of the corallum of a branch of M. aspera. 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 17 


On the Formation of the Germinal Layers in 
Chelonia. 


By 


K. Mitsukuri, Ph.D., 
Professor of Zoology, 


and 


Cc. Ishikawa, 
Assistant in Zoology, University of Tokyo, Japan. 


With Plates II, III, IV, and V. 


In the spring of 1884 we made the acquaintance of Mr. 
Hattori, the proprietor of a large fish-hatching establishment in 
Honjo, a suburb of Tokyo. His father before him, and he, had 
succeeded in making the snapping turtle—Trionyx Japo- 
nicus, Schlegel—breed freely and naturally in captivity, and 
thus in furnishing the market with a constant and large supply 
of its delicate flesh. In his farm hundreds of these turtles are 
annually hatched, and if the eggs are marked as they are laid 
the exact age of any given deposit can be determined with 
great precision, even to minutes in many cases. Such an 
opportunity for the investigation of Reptilian development 
seemed to us too good to be thrown away, especially as nobody 
had, so far as we were aware at the time, worked on the em- 
bryology of Chelonia since the days of Agassiz and Clark, and 
therefore with modern methods of investigation. Mr. Hattori 
kindly consenting, we went to his farm daily during the 
breeding season of 1884 and of 1885, and succeeded in collect- 
ing a fairly complete series of the Tryonix embryos, beginning 

VOL, XXVIJ, PART ].—NEW SER, B 


18 K. MITSUKURI AND C. ISHIKAWA. 


with the time when the eggs are deposited, and ending with 
their hatching out. The present paper gives the results of our 
study on the formation of the germinal layers. Papers on 
other points and later stages of development will follow from 
time to time since the investigation is being continued, as the 
pressure of other duties permit us. 

We wish to return our warmest thanks to Mr. Hattori for 
cheerfully acceding to our numerous demands on his good 
nature, and for furthering greatly our work with his intelli- 
gent assistance. Thanks are also due to the authorities of the 
University of Tokyo for the payment of necessary expenses 
attending the investigation, and for the use of instruments, 
reagents, &c. Finally, we wish to express our deep obligations 
to Dr. Isao Jijima for valuable suggestions in regard to the 
methods of investigation. 

We made many interesting observations on the breeding 
habits of Trionyx, but we reserve these for some other occasion, 
as foreign to the purpose of this paper. We simply mention 
that the Trionyx eggs are nearly spherical in shape, and have 
a hard brittle shell like that of the fowl, and not leathery, as 
in some Chelonia. Their size is very variable, the smallest we 
measured being 10 mm., the largest 23 mm., the most usual 
size about 21—22 mm. in diameter. This difference in size 
seems to be due mostly to the size of the parent. With this 
we pass on at once to the consideration of the subject proper 
of the present communication. 

The earliest stage of which we will give a detailed description 
is taken from an egg opened directly after its deposition. Our 
attempts to obtain still earlier stages by opening pregnant 
females have proved but partially successful. In almost every 
case, with only some doubtful exceptions, the eggs we found 
in the oviduct were unfortunately fully as much advanced as 
those just laid. 

On opening an egg directly after its deposition the blasto- 
derm is always found at the pole turned above. The embryonic 
shield, with the pellucid area around it, stands out conspicuously 
as a small, nearly circular spot, on the yellow surface of the 


FORMATION OF GERMINAL LAYERS IN OCHELONIA. 19 


yolk. The general appearance of the embryonic shield at this 
stage is represented in fig. 1 @ and 34, enlarged about thirty 
diameters. Fig. 1 a, shows it as seen from the dorsal side, 
and fig. 1 6, as seen from the ventral side after the removal of 
the shield from the egg. The embryonic shield does not lie in 
the centre of the area pellucida (a. p.), but is placed excentri- 
cally nearer its hind end, so that here it is continuous with the 
area opaca (a. 0.). The ectoblast has already spread itself over 
a large part of the egg, although we did not determine its exact 
limits (see fig. 16). On the dorsal view the blastopore (d/., 
fig. 1 a) forms the most conspicuous feature ; it is seen as a 
wide transverse slit across the posterior part of the embryonic 
shield, occupying considerably more than one third of the 
breadth across. From the blastopore a passage leads obliquely 
forward and ventralward, and opens about in the centre of the 
ventral surface with a circular opening (v. 0.). The walls of 
the ventral opening are posteriorly quite high, but become 
gradually lower and lower toward the front, until they sink to 
the general level of the ventral surface. For the sake of 
brevity this passage, leading from the blastopore dorsally and 
opening below, we shall hereafter call the blastoporic passage. 
It becomes eventually the neurenteric canal. Returning to 
the dorsal surface, the shield in front of the blastopore presents 
a broad flat expanse, in which are seen indistinctly three opaque 
lines radiating from behind forward, like the prongs of a 
trident. On referring to the ventral side we see that the two 
lateral opaque lines correspond to the thickenings which form 
the walls of the inferior opening of the blastoporic passage. 
Accordingly they are thickest posteriorly, and gradually thin 
out toward the front. The middle prong of the trident cor- 
responds to the roof of the blastoporic passage, and its con- 
tinuation to the front edge of the embryonic shield. It is, in 
fact, the chorda entoblast, which is still in the process of 
formation in front, as will be made clear by sections. The 
remaining parts of the ventral surface not taken up by these 
three thickenings present the appearance of a honeycomb. 
Of this we shall speak later on. Coming back to the dorsal 


20 K. MITSUKURI AND C. ISHIKAWA. 


surface again, the area behind the blastopore, especially the 
median longitudinal space, is on a lower level than the parts in 
front. This, the sections show us, is the line of the primitive 
streak. At the part where the embryonic shield posteriorly 
joins the area opaca there is a considerable transverse thicken- 
ing (s/.), shown both in the dorsal and ventral views—in the 
latter covered with yolk matter. This undoubtedly corresponds 
to the “sichel” or “sickle” which Kupffer describes in a 
similar Lacerta embryo (No. 5, Taf. i, fig. 1, s/.). We should 
add that these differences in level become much more con- 
spicuous after the embryonic shield has been removed and 
treated in reagents than when it is stretched over the yolk, 
and also that the embryos of this stage vary considerably in 
their surface views, especially when they are hardened. 

Figs. 7—15 are selected from the series of transverse sec- 
tions obtained from the embryo represented in figs. 1 @ and 6. 
The figures are arranged in order from behind forward. Figs. 
7—9 pass through the part behind the blastopore, figs. 10, 11 
through the blastoporic passage, and figs. 12—15 through the 
part in front of the blastopore. 

In fig. 7, the most posterior section represented, the ecto- 
blast extends over the whole, being two or three layers of cells 
thick in the embryonic shield, but gradually thinning out to a 
single layer of flat cells toward both sides. The yolk occupies 
the entire lower stratum. Nuclei (n.7.) are visiblein it. The 
space between the ectoblast and the yolk is occupied by a mass 
of mesoblast cells which is here distinctly separate from both 
the ectoblast and the yolk. 

In fig. 8 (which by the way is taken from another embryo of 
the same deposit, as the section corresponding to this in the 
first series is unfortunately injured) the ectoblast is continuous 
in the median line with the mesoblast, i. e. it is very actively 
proliferating and giving off cells abundantly to the mesoblast. 

Fig. 9 passes through the region directly behind the blasto- 
pore. The ectoblast is distinct laterally, but toward the 
median line, and at some distance from it, passes gradually into 
a mass of cells in which no layers can be distinguished. Dif- 


FORMATION OF GERMINAL LAYERS IN CHELONIA, 21 


ferent from fig. 8 where the ectoblast cells, although con- 
tinuous in the median line with the mass below, still maintain 
their columnar shape over the whole dorsal surface and thus 
give an impression of the ectoblast extending entirely across ; 
the ectoblast is in this section fused into the median mass 
without retaining the slightest trace of the columnar arrange- 
ment, and the median mass of cells thus expose their surface 
to the exterior for a short space in the axial line (yk. p.). We 
wish to emphasise the fact that this part directly behind the 
blastopore is neither at this nor at any subsequent time until 
considerably later (if ever at all), covered by the ectoblast of 
the general surface of the body. This area we consider to 
be the remnant of the yolk-plug of Rusconi found in 
the Amphibian embryos. This will become clear in the 
later stages. rom the axial mass, where the layers are indis- 
tinguishable, there extends toward each side a thick meso- 
blastic wing under the ectoblast. The yolk seems to be dis- 
tinct from the mass above, although, throughout this region, 
protoplasmic threads seem to connect the two. 

Fig. 10 passes just in front of the dorsal lip of the blastopore 
where the ectoblast reflects downward and forward to become 
continuous with the axial strip of the entoblast or chorda- 
entoblast (compare fig. 16). The blastoporic passage (dl. p.) 
seen as a transverse space is still open on the left to the 
exterior. The floor of the passage is formed by a mass of cells 
continuous with the yolk-plug ; in fact we may consider this a 
part of the plug. At a lower level the mesoblast (mes.) 
stretches out laterally as two wings from the median mass. 
The relations of the yolk are the same as in fig. 9. 

So far the sections seem to have passed through the part 
known as the “ sickle.” 

The next section represented (fig. 11) evidently passes 
through what may be called the neck or isthmus, i.e. the point 
from which the three prongs of the trident referred to in the 
surface view radiate (compare fig. 1 6). Accordingly, the 
entoblast is found only in the median line as a thickening con- 
stituting the walls of the blastoporic passage (6/. p.), which is 


22 K. MITSUKURI AND C. ISHIKAWA. 


now irregularly circular in section. The roof and the sides of 
the passage are formed by a columnar epithelium two or three 
cells thick (enc.). This is continuous with the ectoblast at the 
dorsal lip of the blastopore (compare figs. 16 and 10). It is 
the chorda-entoblast of Hertwig (No. 6). The floor of the 
passage and the lower part in general is made up of irregularly 
scattered cells. This is not only the continuation of the yolk- 
plug but also of the yolk itself, which occupied the lowest 
stratum in figs. 7—10. and which has been in the last two or 
three sections gradually merging itself into the floor of the 
blastoporic passage. Thus, although it does not appear in any 
single transverse section, the three germinal layers are fused 
in the region behind the blastopore. Laterally the entoblast 
is very thin and passes gradually into the yolk. The section 
is out of the region of the “ sickle,”’ and there is no longer a 
mesoblastic wing on each side. 

Fig. 12 passes through the posterior part of the lower open- 
ing of the blastoporic passage. The thickenings which form 
the lateral walls of the opening are therefore still quite thick 
(compare fig. 1 4). The columnar chorda-entoblast is found 
as before forming the roof and the sides of the passage, which 
is now open below. Towards the lower part of the side walls 
the columnar arrangement is lost and the cells are irregularly 
scattered. Further out at the sides the cells form a loose 
network, and then at the edge of the embryonic shield passes 
into the yolk. 

Fig. 13 passes through the anterior part of the ventral open- 
ing of the blastoporic passage, which has now flattened itself 
out into a shallow groove in the median line. Its roof is still 
formed by the distinctly columnar chorda-entoblast. Later- 
ally, the chorda-entoblast gradually passes into a mass of cells 
arranged in an irregular loose network, which in its turn is 
replaced by the yolk at the edge of the embryonic shield. 

Passing forward, the chorda-entoblast begins gradually to con- 
fine itself more and more to the ventral median surface, until in 
the seventh section from fig. 13 it has the appearance, presented 
in fig. 14. Here the columnar shape is confined to a few cells 


FORMATION OF GERMINAL LAYERS IN CHELONTA. 23 


in the ventral median line. They pass above gradually into the 
loose network of cells which has now extended itself entirely 
across. The meshes of the network have also become larger 
than in the previous sections. It is evidently this loose network 
that produced the appearance of a honeycomb in fig. 1 0. 

Fig. 14 passes in front of the ventral opening of the blasto- 
poric passage, and indicates that the loosely scattered lower 
layer cells are here arranging themselves into the chorda- 
entoblast in the ventral median line of this region, i.e. along 
the front part of the middle prong of the trident apparent in 
the surface views (figs. 1 @ and 4). 

Fig. 15 passes near the front end of the embryonic shield. 
There is no longer any trace of the chorda-entoblast ; the 
entire entoblast is an irregular stratum of stellate cells not 
thick enough to form a network. It passes into the yolk at 
the sides. 

We may here call attention to the appearances which are 
seen in some embryos of this stage. Round the edge of the 
lower opening of the blastoporic passage, especially toward the 
front, there is a shelf-like extension of the entoblast into the 
archenteric cavity somewhat like the velum of a hydromedusa. 
Fig. 14a, Pl. III, represents such an appearance. The section 
is well in front, so that the shelf-like extension is continuous 
across and divides a small space above from the main digestive 
cavity below. In sections posterior to this, the small space 
opens below. We do not know what the significance of this is, 
unless we suppose that the embryo is younger than that given 
in fig. 1, and therefore the ventral opening of the blastoporic 
passage is not yet entirely clear. 

Fig. J6 is the median longitudinal section of an embryo 
taken from the same lot as that represented in fig. 1. The 
blastoporic passage is very distinct. On its dorsal lip, the 
ectoblast is reflected forwards and downwards and becomes 
continuous with the chorda-entoblast which passes in front into 
a loose network of cells with wide meshes, and finally, into the 
yolk at the edge of the embryonic shield. At the posterior 
wall of the blastoporic passage, the three layers, the ectoblast, 


24 K. MITSUKURI AND C. ISHIKAWA. 


the mesoblast, and the yolk (i.e. the entoblast) are merged 
into one another; in other words, the ectoblast and the ento- 
blast are here fused and from the fused place a mass of 
mesoblast cells extends posteriorly. The three layers are inde- 
pendent a short distance behind the blastopore. As the cross- 
sections of this region (figs. 8, 9, and 10) show that the 
mesoblastic mass is similarly extending to each side, we may 
conclude that, in addition to the primitive streak (fig. 8), the 
mesoblast is being given off from the posterior wall of the 
blastoporic passage, or at least from its upper part in all 
posterior directions for an arc of 180°, somewhat in the shape 
of an open fan; and this posterior unpaired mesoblastic mass 
causes the swelling known as the “sickle.” Examining the 
ectoblast of the posterior part more in detail, we find it 
gradually losing its columnar character as we approach the 
blastopore from behind, but the space where the fused median 
mass of cells is dorsally exposed to the exterior, viz. the yolk- 
plug (compare fig. 9) is not as conspicuous in the longitudinal 
section as in the later stages. The entoblastic part of this 
fused mass extends quite forward. This corresponds to the 
cells seen in the floor of the blastoporic passage in fig. 11. A 
slight projection from its extreme tip is, we imagine, the 
remnant of the shelf-like structure mentioned in reference to 
fig. 14 a. 

The principal facts brought out by the study of this stage 
may be summed up as follows : 

J. There is a passage which, beginning with the blastopore 
on the posterior part of the dorsal surface, takes a forward 
aud downward course to the ventral surface, opening in about 
the middle part of the latter by a circular opening. 

2. At the dorsal lip of the blastopore the ectoblast is re 
flected and becomes continuous with the chorda-entoblast. 

3. In front of the blastopore there are as yet only two 
primary layers, the ectoblast and the entoblast. 

4. The entoblast is having its axial part arranged into a 
columnar epithelium to form the chorda-entoblast. This 
process proceeds from behind forward. 


FORMATION OF GERMINAL LAYERS IN OHELONIA. 25 


5. At the posterior wall (i.e. floor) of the blastoporic pas- 
sage the ectoblast and the entoblast are fused, and from the 
point of fusion the mesoblast is being given off posteriorly in 
all directions for the space of 180°. 

6. Also, behind the place where the two primary layers are 
thus fused, the ectoblast is giving off cells to the mesoblast 
along the median line (fig. 8). This is the line of the primi- 
tive streak. It is very short and is present in only two or 
three sections. 

7. The mesoblastic mass derived from the two sources men- 
tioned in (5) and (6) is unpaired and constitutes the transverse 
swelling in the posterior part of the embryonic shield, “the 
sickle.” This is the only place where the mesoblast is present 
at this stage. 

8. The median mass formed by the fusion of the three 
layers at the posterior wall of the blastoporic passage appears 
for a short space on the dorsal surface (fig. 9)—the remnant of 
the yolk-plug of Rusconi. 


Formation of the Mesoblast and of the Chorda 
Dorsalis. 


In the previous stage, the mesoblast was found only in the 
region behind the blastoporee We may now proceed to 
describe its formation in front of the blastopore. We call atten- 
tion first to the embryo represented in figs. 2 a and b. It was 
taken out exactly forty-eight hours after the deposition, but as 
the weather was unusually cold for the season during the 
interval, it has made very little progress in development, and 
is not as far advanced as many thirty-six hours old. As before, 
a dorsal and a ventral view of the embryonic shield is given, 
although these are not taken in this case from the same 
embryo. The shape of the shield has not changed materially 
from the previous stage. In the dorsal view (fig. 2a) the 
blastopore has assumed a horseshoe shape, and is more of a 
slit than before. Occupying the concavity of the horseshoe 
is the rudimentary yolk-plug. Round the blastopore, and 


26 K. MITSUKURI AND C. ISHIKAWA. 


along the median line in front of it, there is an opacity. This 
seems to be due simply to the fact that the cell layers are 
thicker in this region than elsewhere. In the middle of this 
opacity in front of the blastopore and apparently starting from 
the latter there is a shallow median groove, which probably 
corresponds to the “ Primitivrinne” or “ Rickenrinne” 
described by Hertwig in the Triton embryo (No. 6). On the 
ventral side (fig. 24), we wish to call especial attention to the 
ventral opening of the blastoporic passage (v.0.). In the 
previous stage, it was acircular opening without definite limits. 
In this stage it has acquired well-defined limits on all sides ex- 
cept towards the front, where it is only faintly bounded. Along 
the median line of the roof of the recess thus formed, a wide 
low ridge is visible and is continued in some specimens in 
front of this area. This is undoubtedly the chorda-entoblast. 
In the ventral view, the posterior part is concealed by 
a mass of yolk which has accumulated here in the process of 
removing the shield from the egy. 

As we are going to describe somewhat in detail the next 
stage, we may omit the description of the sections of this, 
except one through the ventral opening of the blastoporic 
passage. Fig. 17 is such a section. It passes through the front 
part of the lower opening. There is in the median line a 
slight notch in the ectoblast which corresponds to the groove 
seen in the surface view. In the entcblast we see the axial 
chorda-entoblast formed as usual of columnar cells. Late- 
rally, it passes on each side into a mass of polygonal cells— 
the darm-entoblast of Hertwig (No. 6)—which becomes in 
its turn continuous with the yolk at the edge of the em- 
bryonic shield. At the point where the chorda-entoblast 
and the darm-entoblast meet each other, the darm-entoblast 
projects as a ridge into the digestive cavity and thus con- 
stitutes one of the lateral edges which bound the ventral 
opening of the blastoporic passage (compare fig. 2 4). Con- 
forming to the groove in the ectoblast, the chorda-entoblast 
projects downwards in the median line. This corresponds no 
doubt to the ridge seen in the surface view within the lower 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 27. 


opening of the blastoporic passage. This section also shows 
that the roof of the well-defined area which forms the lower 
opening of the blastoporic passage is formed by the chorda- 
entoblast and that the latter thus occupies by itself a special 
recess of the digestive cavity. From just where the 
chorda-entoblast and the darm-entoblast join each 
other, there goes out laterally on each sidea string 
of cells (mes.) placed dorsally to the darm-entoblast 
and ventrally to the ectoblast and distinct from 
both. This is the commencing mesoblast. The meso- 
blast is therefore not continuous from the first across the 
median line. . 

The surface view of the next stage is represented in fig. 3. 
The embryonic shield has become pear-shaped, the broader 
end being the front end. The blastopore is horseshoe shaped, 
as in figs. 2 a and 4, and occupying its concavity is the yolk- 
plug. The head-fold has just begun, and is seen as the pos- 
terior of the two semilunar curves found near the front end of 
the embryonic shield. The anterior curve is probably the 
commencing amniotic fold. Between the head-fold and the 
blastopore there is seen in the median line an opaque streak, 
which is narrowest in the middle, and becomes broader ante- 
riorly and posteriorly. This is the chorda, which is nearly 
completed in the middle, but still unfinished toward each end. 
The area pellucida is, as before, found only toward the front 
and the sides. The pear-shape of the embryonic shield seems 
to have been produced mainly by its posterior part having 
lengthened. 

Figs. 18—23 are selected from a series of cross-sections 
obtained from an embryo of this stage, and are arranged from 
behind forwards. 

Fig. 18, the most posterior section represented, goes through 
the lateral hmbs of the horseshoe-shaped blastopore and the 
yolk-plug occupying its concavity. The ectoblast, which con- 
sists of only a single layer of cells at the sides, becomes gra- 
dually thicker towards the median line, which it does not, 
however, reach. Ata short distance from the latter, and at 


28 K. MITSUKURI AND C. ISHIKAWA. 


the lips of the blastopore, the ectoblast turns ventralward, and 
becomes lost in the mass of cells found in the axial line. It 
retains, however, its columnar character for some distance 
downwards. The considerable space between the two lateral 
lips of the blastopore is filled almost entirely by a plug (y4. p.) 
of considerable size, which projects upwards from the axial mass 
of cells as far as the level of the general surface of the embryo. 
The difference between the ectoblast and this plug is at once 
unmistakeable and striking. While the cells in the ectoblast 
are columnar and always arranged perpendicularly to the sur- 
face, the cells in the plug are polygonal and without any defi- 
nite arrangement. We shall return to the discussion of this 
structure directly. 

As just stated, the ectoblast turns downwards near the median 
line, and loses itself in the axial mass. All the germinal layers 
are, in fact, fused here, for the entoblast, although it has some 
appearances of being differentiated, is not entirely distinct, and 
the mesoblast also stretches away from this mass on each side. 
Toward the sides the entoblast is yet undifferentiated ; it con- 
sists of an abundant protoplasmic network with numerous nuclei, 
and is full of yolk-spheres and granules. There is no question 
whatever that laterally the mesoblast receives cells from the 
entoblast or yolk. Especially along one line (a, figs. 18 and 
20) nuclei are heaped in a special mass, from which cells are 
being given off to the mesoblast. This contribution to the 
mesoblast from the germinal wall is only in the posterior part, 
as it is no longer observable in fig. 23, and as the germinal 
wall itself, even in a more advanced stage, is found only round 
the posterior part as a horseshoe-shaped ridge (fig. 5). 

Having gone over the description of the various parts of this 
section, let us return to the discussion of the plug (yA. p.) 
which sticks out to the external surface between the lateral 
lips of the blastopore. When we compare our figure 18 with 
the frontal section through the yolk-plug of a Triton em- 
bryo, which Hertwig (No. 6) gives in his fig. 9, Taf. ii, we 
think nobody will hesitate long before concluding that the 
plug in our figure is homologous with the yolk-plug of 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 29 


Rusconi found in the Amphibian eggs. Allowing for the 
differences between a holoblastic and a meroblastic egg, the 
relations in the two figures are almost exactly alike, part for 
part. If the slits between the plug and the lateral lips of the 
blastopore extended in our figure a little more into the midst 
of each mesoblastic mass the resemblance would be compiete ; 
but even for the Amphibian eggs the slits do not always extend 
as far as represented in fig. 9, as Hertwig himself mentions 
(No. 6, p. 14). At any rate, in each case there is an axial 
mass of cells, (1) into which the ectoblast turns down at the 
lateral lips of the blastopore, (2) in which the entoblast is not 
to be distinguished, (3) from which the mesoblastic masses 
start away toward each side, and (4) which sends a plug upwards 
between the lips of the blastopore. If we compare the longi- 
tudinal section of the plug in Trionyx (fig. 24, y/. p.) with the 
sagittal section of the Amphibian yolk-plug (Hertwig, No. 6, 
Taf. ii, fig. 4), we see again that the relations of different parts 
are alike. It is true that the plug in Trionyx is not bounded 
posteriorly by a groove, and passes directly into the ectoblast 
of the primitive streak, but when we consider that the plug in 
Trionyx is only rudimentary this is not to be wondered at, and 
is of little significance. . 

We think we are justified, on these grounds, in concluding 
that we have in the mentioned structure of Trionyx the rem- 
nant of the yolk-plug, which appears conspicuously in the 
Amphibian egg. Strahl describes the same structure (compare 
No. 13, ser. iii, figs. 0, 0.1, 0.2; ser. iv, figs. 0, 0.1; ser. v, 
figs. 0, 0.1, 0.2, 0.3; ser. vi, figs. 0, 0.1; ser. vii, fig.0.1, also 
No. 9, Taf. i, figs. 6, 7, 14, and 15; and No. 10, figs. 2 and 38), 
but, so far as known to us, has never explained its nature. 
Kupffer describes the “ Zapfen” occupying the horseshoe- 
shaped blastopore of Lacerta (No. 5, Taf. i, figs. 2 and 3, 2), 
but does not state its homology. He mentions that in Coluber 
Aesculapii the plug is sometimes divided into two parts by a 
median fissure (No. 5, Taf. iv, fig. 40, f and g). We have 
also observed a similar appearance in some of the earlier em- 
bryos of Trionyx, but we are satisfied that there is no true 


30 K. MITSUKURI AND C. ISHIKAWA. 


median fissure. What appears to be such is the optical ex- 
pression of the primitive streak, along which the ectoblast is 
proliferating, and giving cells to the mesoblast below. Even 
in the earliest embryos with this appearance it is doubtful if 
it ever extends to the extreme tip of the plug. As far as we 
are aware, the only author who mentions what seems to be the 
yolk-plug in an amniotic Vertebrate is Gasser, who observed 
it in an abnormal fowl embryo (No. 4, Taf. x, figs.4—7). The 
reason why the yolk-plug in Trionyx is more conspicuous at 
this stage than earlier stands, we think, in close connection 
with the fact that the blastopore has become a much better 
defined horseshoe-shaped slit. 

We return now from this long digression to the description 
of the embryo before us. The sections behind fig. 18 show 
that immediately behind the yolk-plug, which persists distinctly 
in only one more section after fig. 18, the ectoblast extends 
over the whole surface as shown by the characteristic columnar 
cells. For ashort space, however, the ectoblast is proliferating 
in the median line and is continuous with the mesoblast below. 
This is seen in only three sections after which the ectoblast 
becomes independent. The entoblast seems, however, to be 
connected with the mesoblast for a greater length and to be 
actively contributing cells to the latter. This is the region 
where the germinal wall makes a horseshoe-shaped bend round 
the posterior part of the embryo (fig. 5). Except in this last 
detail, the relations of the various parts behind the blastopore 
exactly as in the stage represented in fig. 1. 

Going forward, fig. 19 passes through the blastoporic passage. 
As it is directly in front of the dorsal lip of the blastopore, the 
ectoblast is still continuous for a little space with the chorda- 
entoblast, which as usual vaults over the passage. The columnar 
cells extend to the sides also, but on the floor of the passage 
the cells are polygonal, so that this part which is the continua- 
tion of the yolk-plug differs in its appearance from the roof 
and the sides. To this part, too, the darm-entoblast (end.) is 
attached. From the entire side of the axial mass the meso- 
blastic sheet goes out on each side. 


FORMATION OF GERMINAL LAYERS IN CHELONIA. dl 


Fig. 20 passes slightly in front of the ventral opening of 
the blastoporic passage. In the median line the chorda-ento- 
blast (enc.) forms directly the roof of the digestive cavity, 
without the intervention of the darm-entoblast (end.) which 
stops at a short distance from the axial line. On the left side 
of the section, more clearly than on the right, the darm-ento- 
blast is seen to make a fold at its innermost point where it 
abuts against the chorda-entoblast and then to turn outside 
again to be lost in the mesoblast. The mesoblast is therefore 
partly continuous with the chorda-entoblast and partly with 
the darm-entoblast. In other words, it starts from the point 
where the chorda- and the darm-entoblast meet each other. The 
mesoblast cells in this region show a peculiar arrangement. 
Those cells next the ectoblast are columnar and look like the 
continuation of the chorda-entoblast. The cells placed ven- 
trally to these are polygonal and without any definite arrange- 
ment. Laterally cells are being added to the mesoblast in the 
whole region of the germinal wall, but especially at a ; proli- 
feration seems to take place in the posterior region even from 
the outer part of the darm-entoblast, as in this section. This 
is, however, confined to the part which still consists of two or 
three layers of cells, and never extends to the inner part which 
has only a single layer of cells, and constitutes the well 
differentiated darm-entoblast. 

We pass over for the present figs. 2] and 22, and come to 
the most anterior section represented (fig. 23). It is in the 
region of the head-fold as shown by a notch (h.f.) on one side 
in the ectoblast. The darm-entoblast, which is laterally quite 
thick and consists of columnar cells, is internally very thin and 
becomes continuous with the chorda-entoblast near the median 
line. From the point of junction as well as from the sides of 
the chorda-entoblast mesoblastic cells are budding off on each 
side. There is in this section a small mass of mesoblast cells 
outside of the head-fold which is distinct from the main mass. 
This isolation has been brought about by the ectoblast folding 
downward as the head-fold; more posteriorly the lateral mass 
fuses with the main mass. In this section the germinal wall 


32 K. MITSUKURI AND C, ISHIKAWA. 


is absent, and thus no additions are made laterally to the meso- 
blast from the entoblast. 

Returning to the middle region of the body, figs. 21 and 22 
serve to show the first steps in the formation of the notochord. 
The chorda-entoblast which in fig. 20 passed laterally without 
any interruption into the mesoblast, is in fig. 21 marked off 
from the mesoblast, at least in the upper part. The cells at the 
border between the two are turned away from one another ; 
thus the cells of the chorda are directed inwards and down- 
wards, while the contiguous cells of the mesoblast are directed 
outwards and downwards. The mesoblast is still united with 
the darm-entoblast. As yet, the chorda is only a mass of 
columnar cells. In fig. 22, five sections in front of fig. 21, the 
chorda has become rounded in outline and considerably smaller 
in section. The most dorsal and median cells alone are 
columnar, and the remaining cells are arranged as if the more 
lateral cells have folded inwards and downwards from the two 
sides and met in the median line. The mesoblast is now dis- 
tinctly separated from both the chorda and the darm-entoblast. 
The last abuts against the chorda, but seems separate from it. 
This is as far as the formation of the chorda has advanced in 
this stage. In front of fig. 22 the chorda becomes wider again, 
until in the region of the head-fold it is as represented in 
fig. 23; a similar arrangement is found at the posterior end of 
the embryo. 

Fig. 24 is a longitudinal section of another embryo from the 
same deposit of eggs as the one represented in fig. 3. It 
passes very nearly in the median line. The blastoporic 
passage is considerably narrower than in fig. 16. Its angle of 
inclination to the surface of the ectoblast is now greater, 
approaching more nearly a right angle; hence it has become 
also much shorter than before. At the dorsal lip of the blas- 
topore the ectoblast is reflected and becomes continuous with 
the chorda-entoblast. Owing to the fact that the chorda is 
most developed and therefore narrower in the middle region of 
the embryo than in front or behind, and perhaps also to the 
fact that the section is slightly oblique, the mesoblast (mes.) 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 35 


appears for a short space ( *—c.) in this section. The 
entoblast, which is very thick in front, especially in the 
head-fold (h. f. marked by a notch in the ectoblast), becomes 
suddenly reduced at the point ¢ into a thin ventral layer 
(end.) which stretches posteriorly as far as the point marked 
with a +, where it seems to unite with the chorda-entoblast. 
From the point of junction and also continued forward from 
the chorda-entoblast, the mesoblast sheet stretches forwards as 
far as c, above the darm-entoblast (end.) and beneath the ecto- 
blast. Behind the blastoporic passage there is a large mass of 
cells projecting downward (the Endwulst). On the dorsal 
surface, directly behind the passage, columnar cells are absent 
for a short space. This is the longitudinal section of the yolk- 
plug. Following it, the ectoblast cells appear, but cannot at 
first be separated from the large mesoblastic mass, for this is the 
region of the primitive streak where the ectoblast is giving off 
cells below. Very soon, however, it becomes an independent 
sheet. The continuation downwards of the yolk-plug forms the 
whole posterior wall of the blastoporic passage, and is there- 
fore seen as its floor in cross-sections. The entoblast is con- 
tinuous with it at the extreme front of the “ Endwulst,” but 
becomes a distinct layer on the ventral surface. The meso- 
blast, utterly indistinguishable from the yolk-plug, stretches 
away posteriorly. Behind the blastopore the three germinal 
layers are thus fused. The mesoblast, which is separate from 
the entoblast on the ventral surface of the ‘‘ Endwulst,” is 
receiving more posteriorly additions from the yolk or germinal 
wall. 

In the next stage which we figure (figs. 4 @ and 4), the 
head-fold has considerably advanced, and the amnion (am.) 
covers it already so that it is not visible from the dorsal side. 
The medullary folds have touched each other. At the poste- 
rior end the yolk plug is included between the diverging 
medullary folds. 

The sections through the head region of this stage show 
beautifully, and in an unmistakeable and conclusive manner, the 
mode of the formation of the mesoblast and of the chorda 

VOL. XXVII, PART 1,—NEW SER. Cc 


34 K. MITSUKURI AND C. ISHIKAWA. 


dorsalis. Figs. 25—28 are selected to illustrate these 
points. 

Fig. 25 is the most anterior section represented. It goes 
through the posterior part of the head. The amnion is closed 
over it, but the digestive cavity is still widely open below. The 
darm-entoblast formed by columnar cells does not reach the 
chorda-entoblast, but is separated from it by an interval 
where cells are most actively proliferating and 
giving rise to the mesoblastic mass. Fig. 29 is a 
similar section from another embryo of the same stage. Here 
also the chorda-entoblast, instead of passing directly into the 
darm-entoblast, is separated from it on each side by a space 
where cells are actively dividing and giving rise to the meso- 
blast. This figure shows also more naturally than fig. 25 that 
the mesoblastic mass consists of spindle-shaped and stellate 
cells arranged in such a way as to give an impression of having 
radiated from their origin. 

Figs. 26—28 show clearly the mode of the formation of the 
notochord. Fig. 26 is two sections behind fig. 25. The 
mesoblastic masses have separated from the chorda- and darm- 
entoblast. The chorda-entoblast is arcuate. The darm-ento- 
blast abuts against it but is distinctly separate from it. In 
fig. 27, the third section behind fig. 26, the chorda-entoblast 
has become a cord-like mass, against the more ventral side of 
which the darm-entoblast of both sides is applied. This cor- 
responds to fig. 22 of the previous stage. In fig. 28, the third 
section behind fig. 27, the darm-entoblast has passed under the 
notochord from both sides, and united so as to form a continuous 
sheet across. ‘The formation of the notochord is thus com- 
pleted. 

As in the previous stage, the notochord is finished only in 
the middle region of the embryo. Toward the posterior 
region, in front of the ventral opening of the blastoporic pas- 
sage, the chorda is in the process of formation. The mode of 
formation is exactly as at the front end. Figs. 30—34 from 
an embryo of nearly the same stage as that represented in figs. 
4 a and 4, are introduced to illustrate this process. 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 35 


Fig. 30 is the most posterior section given. It is slightly in 
front of the ventral opening of the blastoporic passage, which 
is still visible as a groove in the median line. The darm- 
entoblast (end.), which is distinct laterally, does not reach the 
chorda-entoblast, but passes into a zone from which the meso- 
blastic sheet spreads away laterally, and which in its turn 
becomes continuous with the chorda-entoblast. This corre- 
sponds to fig. 25 or fig. 29 of the anterior region, or to fig. 20 
of the previous stage. 

In fig. 81 the chorda-entoblast is beginning to be marked 
off from the mesoblast, which is, however, still united with the 
darm-entoblast, at least on the left side. This corresponds to 
fig. 21 of the previous stage. 

In fig. 32 the mesoblast has become entirely separated from 
both the chorda- and the darm-entoblast (excepting a little 
spot on the left). The chorda-entoblast is now a compact 
mass by itself, against the sides of which the darm-entoblast is 
applied. This is more clearly shown on the right side than on 
the left. This corresponds to fig. 26 of the anterior region, and 
to fig. 22 of the previous stage. 

In fig. 33 the darm-entoblast has passed some way under 
the chorda which has almost the appearance of the finished 
structure. This corresponds to fig. 27. 

In fig. 34 the darm-entoblast has passed completely under 
the chorda and forms a continuous sheet across, and the for- 
mation of the notochord is finished. This corresponds to 
fig. 28. 

The formation of the chorda at the anterior region comes to 
an end much earlier than in the posterior region, where it is 
continued on until considerably later, and where the growth in 
length of the embryo seems mainly to take place. 

It remains now to state the fate of the blastoporic passage. 
In an embryo taken out two days later than that given in 
figs. 4 a and 3b, from the same deposit of eggs, in an 
embryo, therefore, five days old with five or six mesoblastic 
somites, the passage is no longer dorsally open. The medul- 
lary canal has completely closed over it and the blastoporic 


36 K. MITSUKURI AND C. ISHIKAWA. 


passage has been changed to the neurenteric canal. Figs. 35 
a—d, will show the relations of the germinal layers round the 
passage. In a, the most anterior section given, the darm- 
entoblast, the notochord, the mesoblast, and the medullary 
canal are all separate. In 6 the chorda has fused above with 
the walls of the medullary canal, appears for a little space in 
the median line on the roof of the digestive cavity, and divides 
the darm-entoblast of the two sides which seem to rest against 
it. In ¢ the canal opens below into the digestive cavity. 
The mesoblast is now continuous with the darm-entoblast and 
the walls of the neurenteric canal at the junction of the two. 
In d the posterior part of the neurenteric canal has been cut. 
In the next section (not figured), the cells in the axial region 
are only more compact than elsewhere, and show that the 
posterior wall of the canal is reached. Thus from the mass 
behind the blastoporic passage (i.e. the “‘ Endwulst’’), the 
posterior wall of the neurenteric canal seems to have been 
developed in siti. From this mass the mesoblast is extend- 
ing laterally on each side. It is not possible for us to state 
exactly how the yolk-plug disappears. A part of it which 
formed the posterior wall of the blastoporic passage is no 
doubt changed into the posterior wall of the neurenteric canal. 
A part placed more dorsally is perhaps changed directly to the 
ectoblast of the general surface of the embryo. 

In an embryo six days old, i. e. one day older than that of 
fig. 35, the neurenteric canal still persists. In an embryo 
seven days old it is no longer found. We are not in a position 
to state how its disappearance is brought about. 

To state briefly the principal facts brought out by our observa- 
tions on the formation of the mesoblast and of the notochord : 

In the embryo represented in figs. 1 @ and 4, the mesoblast 
was found only in the region behind the blastoporic passage, 
radiating in the shape of an open fan from the posterior wall 
of the passage, as well as from the ectoblast along the primi- 
tive steak, and constituting the structure called the “sickle.” 
In further course of development the mesoblast becomes ex- 
tended into the region in front of the blastoporic passage. 


FORMATION OF GERMINAL LAYERS IN OHELONIA. 37 


Here it arises as a paired mass, and its point of origin 
is invariably at the junction of the chorda-entoblast 
with the darm-entoblast. In other words, one part 
of the mesoblast is always continuous with the 
chorda-entoblast, while the other part passes into 
the darm-entoblast. 

Besides this source the mesoblast receives large contributions 
of cells from the germinal wall, and even from the outermost 
part of the darm-entoblast contiguous with the germinal 
wall. 

The notochord is formed out of the chorda-entoblast. It is 
completed first in the middle, and then extends both backward 
and forward. Its mode of formation is the same, both in front 
and behind. First, at the point of the origin of the mesoblast 
the connection of the three structures that meet there, viz. 
the mesoblast, the chorda-, and the darm-entoblast, is loosened. 
The mesoblast is then found as two separate masses, one on 
each side of the median line. The darm-entoblast rests with 
its free edges against the sides of the chorda-entoblast ; it, how- 
ever, passes gradually under the chorda-entoblast, until finally 
the darm-entoblast of two sides fuses in the median line, and 
forms a continuous sheet over the digestive cavity. In the 
meantime the chorda-entoblast has arranged itself into the 
finished chorda-dorsalis. 


The formation of the Blastoporic Passage. 


There are differences of opinion among previous writers on 
the subject in regard to the formation of the blastoporic 
passage in Reptilia. Balfour (No. 2, p. 424-5) says: “ After 
the segmentation and the formation of the embryonic shield 
(area pellucida) the blastoderm becomes distinctly divided into 
epiblast and hypoblast. At the hind end of the shield a some- 
what triangular primitive streak is formed by the fusion of 
the epiblast and hypoblast, with a number of cells between 
them, which are probably derived from the lower rows of the 
segmentation cells. At the front end of the streak a passage 
arises, open at both extremities, leading obliquely forwards 


38 K. MITSUKURI AND C. ISHIKAWA. 


through the epiblast to the space below the hypoblast.” Here 
Balfour does not say how this passage arises. In his ‘Com- 
parative Embryology’ (vol. ii, p. 168) he says: “At the front 
end of the primitive streak an epiblastic involution appears, 
which soon becomes extended into a passage open at both 
extremities, leading obliquely forwards through the epiblast to 
the space below the hypoblast.” Kupffer (No. 5) is of sub- 
stantially the same view. Weldon (No. 14, p. 136) says: “ At 
a point (dp.), however, the position of the future blastopore, 
these layers are replaced by a mass of closely-packed cells 
(pr.), exhibiting no division into layers, and forming the 
primitive streak, which may, in some cases at least, extend 
backwards as far as the commencement of the area opaca. The 
blastopore commences at the anterior end of this streak as a 
pit, open above and closed below. ... . The floor of this pit 
presently breaks up, and the blastopore assumes its normal 
condition, forming a communication between the archenteron 
and the exterior, its anterior wall forming a communication 
between the epiblast and the lower layer cells. From this time 
a change in the character of the lower layer cells takes place, 
beginning from the anterior wall of the blastopore, where they 
pass into the epiblast, and proceeding forwards. Instead of 
being large, irregular, full of yolk, as in the previous stages, 
they become columuar, lose their yolk, arrange themselves in 
a definite layer several cells deep, and take on the characters 
of normal hypoblast..... This process is evidently an in- 
vagination comparable to that which takes place in an Elasmo- 
branch. It especially resembles the process described by 
Scott and Osborne in the newt.” Strahl gave his views first 
in an article published in 1882 (No. 8), and again in a later 
writing (No. 13, p. 55). His views, as expressed in the latter, 
are briefly as follows :—Before the neurenteric canal is present 
the germinal disc consists throughout only of ectoblast and 
entoblast, except in the region of the primitive streak, which 
is oval or pear-shaped, or nearly triangular in form. In such 


a disc three processes, which may be independent of one 
another, now take place. 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 39 


1. Under the primitive streak the entoblast is differentiated, 
so far as it has not done so already. 

2. Inthe middle of the primitive streak the canalis neuren- 
tericus is sunk, at first perpendicularly below and then hori- 
zoutally forward. 

3. In the region of the primitive streak the ectoblast differen- 
tiates from the mesoblast.” This differs in the regions before 
and behind the neurenteric canal. In front of the canal the 
whole mass is differentiated into the ectoblast and the meso- 
blast (i. e. mesoblast according to his views: we would call it 
the chorda-entoblast). In the region behind the canal, only 
the epidermal layer of the ectoblast is differentiated, the 
differentiation of the remaining cells into the structures for 
which they are destined: viz. the extreme end of the medullary 
canal, of the chorda, &c., takes place at a much later date. 

As we stated before, we did not succeed in obtaining the 
stages earlier than fig. 1. We will try, however, to reason back 
from our earliest stages and to deduce what processes have given 
rise to such a form. Of course, such a priori reasoning is 
liable to mistakes, and we offer the following remarks merely as 
suggestions which need verification by future investigations. 
If the blastoporic passage really commences as an epiblastic 
invagination, it seems to us that Kupffer is quite right in con- 
sidering the invaginated sac as the gastrula cavity much reduced 
in size (No.5, p. 2). But apart from the inherent improba- 
bility that the bottom of the archenteron should after- 
ward give way and the archenteron should become counected 
with some cavity beyond itself, we think we have another 
sufficient reason in rejecting the view of an epiblastic invagi- 
nation in this fact that directly behind the passage, when 
it is established, there is an area which is not covered by the 
ectoblast, 1. e. the yolk-plug. We think then that what really 
takes place must be very much as Weldon and Strahl describe 
it, for these two writers differ after all, when we leave out 
minor points, only in this, that the former thinks the passage 
arises at the front end, and the latter at the middle of the 
primitive streak. Our views, then, on these earliest stages 
are as follows : 


40 K. MITSUKURI AND C. ISHIKAWA. 


At the end of the segmentation the blastoderm becomes 
divided into two primary layers, the ectoblast above consist- 
ing of columnar cells, and the entoblast below consisting 
of irregularly shaped cells without any definite arrangement. 
At the region of the future blastopore and primitive streak, 
this process of differentiation is somewhat modified from what 
takes place elsewhere. When the differentiation of the ectoblast 
has proceeded backward and come to the future dorsal lip of the 
blastopore, it does not extend further in the median line over the 
blastodermic surface, but becomes reflected downward and con- 
tinuous with the axial strip of the lower layer cells which acquire 
the columnar character from this point forward in the median line 
of the future embryo, and arranged themselves into the chorda- 
entobiast. This process has proceeded to the front end of 
the embryonic shield in the embryo represented in fig. 1. 
Whether there is any actual invagination of cells from the 
dorsal lip of the blastopore we cannot tell, but this is of no 
moment so long as the ectoblast becomes continuous with the 
axial strip of the entoblast at the dorsal lip, and the arrange- 
ment of the lower layer cells into the chorda-entoblast pro- 
ceeds from here towards the front. We can conceive the blas- 
toporic passage itself arising in this way. As the cells arrange 
themselves into the chorda-entoblast, these columnar cells 
separate from the cells directly behind them and thus a fissure 
or canal is produced just at the same rate as the cells arrange 
themselves into the chorda-entoblast. The posterior wall of 
this canal would thus be composed of undifferentiated cells, as 
it actually is. 

While the differentiation of the ectoblast thus stops, in the 
median line, at the dorsal lip of the blastopore, and the above- 
mentioned changes leading to the formation of the blastoporic 
passage are going on, we can suppose that the differentiation of 
the ectoblast is at the same time proceeding actively in the more 
lateral parts and is extending backwards and meeting in the 
median line again slightly behind the blastopore (see fig. 6). 
There would thus be left behind the blastopore a small space not 
covered by the ectoblast. This is the yolk-plug, which is of course 


FORMATION OF GERMINAL LAYERS IN CHELONIA, 4] 


continuous with the undifferentiated cells forming the’posterior 
wall of the blastoporic passage. From the ectoblast in the 
median line behind the yolk-plug, cells begin to proliferate and 
constitute the primitive streak. This may happen before the 
blastoporic passage is completed (see Strahl, No. 8, Taf. xiv, 
fig. 11). Proliferation begins also from the posterior wall of 
the blastoporic passage. We shall then have a stage exactly 
like that given in figs. 1 a and 6. When we make a careful 
study of the latter embryo, some such series of changes as we 
have sketched out will become an absolute necessity. Our 
views are in the main like those of Weldon and of Strahl, 
but we think we have filled in more details. Strahl, it is 
true, says that the passage begins in the middle of the primi- 
tive streak. We are inclined to think that in his figs. 8 and 9, 
Taf. xiv (No. 8), he has stages in which the differentiation of 
the ectoblast from the entoblast has not proceeded as far as the 
dorsal lip of the blastopore. In our view, the 2nd and 8rd 
processes given in his account have the closest relations to each 
other. Our hypothesis also makes what takes place in Reptilia 
harmonise well with the development of lower forms, especially 
of the Amphibia. 


Discussion of the Results of our Observations. 


In an article published as early as 1875 Balfour (No. 1, 
p- 208) states that “ Amphioxus is the Vertebrate whose mode- 
of development in its earliest stages is the simplest, and the 
modes of development of other Vertebrates are to be looked 
upon as modifications of this, due to the presence of food ma- 
terial in their ova.” In the same article, as well as in several 
subsequent publications (Nos. 2 and 3), he endeavoured to 
work out the comparison of the vertebrate development with 
the idea given in the above quotation for its foundation. Above 
all, he has insisted that the mesoblast always arises as paired 
masses, one on each side of the median line, and that these 
two masses are to be regarded as paired diverticula of the ali- 
mentary canal. Recently O. Hertwig (No. 6), in connection 
with the ‘‘ Coelomtheorie”’ of himself and his brother, has worked 


42 K. MITSUKURI AND OC. ISHIKAWA. 


out this idea very completely in Amphibia, and has also shown, 
from the investigations of other workers, how the same idea 
could be carried out through other classes of Vertebrata. We 
need hardly say that our investigations most completely bear 
out Balfour’s and Hertwig’s view. In fact, the agreement 
between the development of Amphioxus and Amphibia on one 
side, and of Reptilia on the other, as shown by our work, is as 
complete as could be desired, when we make due allowance for 
the fact that on one side is a holoblastic and on the other a 
meroblastic egg. Let us examine more in detail. 

When we compare our fig. 16 with Hertwig’s fig. 4 (Taf. 1, 
No. 6) of Triton, we are at once struck with the close similarity 
between the two, allowing for the fact that the latter represents 
a whole egg, and the former only a small part of it. ‘There is 
in both a passage connecting the cavity which becomes the 
future alimentary canal with the exterior. This is, according to 
Hertwig’s nomenclature, “die enger Theil der Darmhohle 
(dh.),”’ according to ours “the blastoporic passage.” At the 
dorsal lip of this passage the ectoblast in both is reflected, and 
becomes continuous with the chorda-entoblast. In the region 
in front of the passage the embryo consists of only the ectoblast 
and entoblast. In both there is the yolk-plug behind the 
passage, and contiguous with it the two primary layers are 
fused, and from the fused point there stretches backward an 
unpaired mesoblastic mass. Hertwig’s fig. 11, Taf. v, and 
figs. 7 and 10, Taf. vi, of Rana, are essentially alike. 

Hertwig’s fig. 17 (Taf. iv) is the frontal section through the 
line a—d of fig. 4, Taf. 11. It passes through the beginning of 
the unpaired mass of mesoblast. It presents an appearance 
very similar to our fig. 8 of the corresponding region. The 
ectoblast is proliferating in the median line, and giving cells 
to the mesoblast. 

In our figure the entoblast and mesoblast are separate, but 
we have shown already that they become continuous further 
forward. Hence exactly the same relations hold in this region 
in Triton and Trionyx. Compare also fig. 2, Taf. vi, and fig. 5, 
Taf. viii, given by Hertwig of the corresponding region in Rana. 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 43 


Hertwig’s fig. 9, Taf. 11, is the frontal section through the 
line c—d of fig. 4, Taf. 11. It is substantially the same as our 
fig. 9, although there is a closer resemblance between it and our 
fig. 18, as we have already shown. 

Unfortunately Hertwig does not give a cross section of the 
front region of an embryo which has not yet developed the 
mesoblast; but we are sure it will be essentially like our 
figs. 13 and 14, although we cannot expect to find the lateral 
parts composed of a network of cells. 

Now, as to the origin of the mesoblast, our results agree with 
Hertwig’s account as completely as could be desired. In the 
region behind the blastopore he says the mesoblast arises as an 
unpaired mass in the Amphibia. Such is the case with 
Trionyx, as shown in our figs. 7, 8,16, and 24. In front of the 
blastopore the mesoblast arises as paired masses separated from 
each other in the median line by the chorda-entoblast. For 
this point compare our figs. 17 and 20, or, best of all, figs. 25 
and 29, with Hertwig’s figs. 1 and 2 (Taf. ui) of Triton. In 
the latter the chorda-entoblast passes into the parietal layer 
of the mesoblast, while the darm-entoblast is reflected just 
where it abuts against the chorda-entoblast, and passes into 
the visceral layer of the mesoblast, thus constituting what 
amounts to a pair of diverticula from the alimentary canal, one 
on each side of the chorda, repeating what is seen in Amphioxus. 
Hertwig has marked the entrance to these rudimentary diverti- 
cula with a star (*) in his figures. We have also marked in 
our figures what we consider to be the corresponding spots 
with the same mark (*). We think that morphologists will 
not find any difficulty in recognising in Trionyx the relations 
closely similar to those in Amphibia. In Trionyx the meso- 
blastic mass becomes continuous on each side with the ento- 
blast, just at the point where the chorda- and the darm- 
entoblast meet each other. The cells being much smaller in 
Trionyx than in Triton, it is not possible to distinguish the 
parietal from the visceral layer of the mesoblast; but if both 
the chorda- and the darm-entoblast pass into the mesoblastic 
mass, the relations found here amount to the same thing as 


44 K. MITSUKURI AND OC. ISHIKAWA. 


found in Triton and in Amphioxus. We think our figs. 25 
and 29 ought to convince the most sceptical on this point. It is 
significant that at one time (fig. 17) the chorda-entoblast occu- 
pies a recess of the alimentary canal by itself, and from the 
two sides of this recess the mesoblastic masses stretch out—a 
relation which recalls vividly the development of Amphioxus. 

Our fig. 19 may prove a stumbling block to some in the way 
of comparison with Amphibia. But we think this figure is 
soon reduced to the general rule. We have already pointed 
out that the cells forming the floor of the blastoporic passage 
in this figure are different from those of the roof and the sides. 
If we consider the chorda-entoblast as extending on each side 
to the spot marked with the star, and this spot as corresponding 
with the similarly marked spot in fig. 15, Taf. iv, of Hertwig, 
which passes through the corresponding part of Triton, the 
comparison will become easy. ‘The apparent difficulty is 
brought about by the cells of the floor being many layered in 
Trionyx. 

There is another point on which we wish to touch. Although 
there is no doubt that the mesoblastic masses arise as what 
morphologically amount to diverticula of the alimentary canal, 
the development in Trionyx has so far changed from the primi- 
tive method that the masses no longer form an epithelium as 
in Amphioxus or Triton or even compact masses throughout, 
but at places only loose masses of spindle and stellate cells 
(figs. 25 and 29). This fact will, we think, answer Kolliker’s 
objection, based upon the shape of cells in the mesoblast, 
against the epithelial origin of the mesoblast. (We have 
not access to Kolliker’s original paper but take his views as 
given in Hertwig’s paper, No. 6,p.105). Kolliker is no doubt 
correct in supposing that such forms are due to very rapid 
proliferation. 

As to the formation of the chorda, it is only necessary to 
compare our figs. 25—28 with Hertwig’s figs. 3—6 (Taf. i) 
of Triton, and figs. 8—11 (Taf. viii) of Rana, in order to be 
convinced of the similarity of the process in Reptilia and 
Amphibia. Our figs. 25 and 29 correspond with figs. 1 or 2 


ia 


FORMATION OF GERMINAL LAYERS IN CHELONIA. 45 


(Taf. iii, Hertwig) of Triton. Our fig. 26 with fig. 4 (Taf. iii) 
of Triton, our fig. 27 with fig. 5 (Triton), and, finally, our 
fig. 28 with fig. 6 (Triton). 

As to the contribution to the mesoblast from the germinal 
wall, there is of course no equivalent in the holoblastic egg of 
Amphioxus or Amphibia. It seems to us that phylogenetically 
this source is not of much significance and is brought about 
wholly by adaptation. Sarasin’s (No. 15) researches on the 
Reptilian egg have brought out the fact that new cells are 
added on from the yolk to the blastoderm by a process very 
similar to budding. Why could we not suppose that this 
process goes on until considerably later, and that the addition 
of cells to the mesoblast from the germinal wall is but the 
continuation of this process? 

We should like to add another suggestion. In Trionyx the 
primitive streak is continuous with the lateral edges of the 
blastopore, enclosing the yolk-plug (see fig. 6). Have we not 
here a case where a part of the original blastopore lips has 
met in the median line and formed the primitive streak, while 
the rest of the edge of the blastopore has retained its original 
condition ? 

We think we have succeeded in showing that the develop- 
ment of Reptilia harmonises completely with that of Amphibia. 
Our observations confirm the conclusions which Hertwig 
formed in regard to the Reptilian development, basing his 
judgment on the observations of other workers (No. 6, Theil ii), 
but we hope we have filled in many details not before noticed. 
We dissent strongly from Strahl, who in two separate publica- 
tions (Nos. 11 and 13) oppose Hertwig’s views. We think 
Strahl is singularly unfortunate in the interpretation of his 
sections. 

We think it hardly necessary to go over other papers on the 
germinal layers of Reptilia (Strahl, Nos. 7, 8,9, 10,11, 12,13; 
Kupffer, No. 5; Weldon, No. 14; Hoffmann, No. 16), and 
point out the points of similarity and dissimilarity between 
those workers and ourselves. The reader must refer to the 
original papers themselves. 


46 K. MITSUKURI AND C. ISHIKAWA. 


We conclude, expressing the hope that our investigations 
will furnish a necessary intermediate step in establishing firmly 
the views of Balfour and Hertwig in higher Vertebrates. 


BIBLIOGRAPHY. 


1. F. M. Batrour.—“ A Comparison of the Early Stages in the Develop- 
ment of Vertebrates,” ‘Quart. Journ. Micr. Sci.,’ 1875. 


2. F. M. Batrour.—“ On the Early Development of the Lacertilia, together 
with,” &e., ‘Quart. Journ. Mier. Sci.,’ 1879. 


3. F. M. Batrour.—‘ Comparative Embryology,’ vol. ii, 1881. 


& 


GassEr.—‘ Der Primitivstreifen bei Vogelembryonen,’ Cassel, 1879. 


5. C. Kurrrer.— Die Gastrulation an den meroblastischen Hiern der Wir- 
belthiere u. die Bedeutung des Primitivstreifs,’ ‘Arch. f. Anat. u. 
Physiol.,’ Anat. Abth., 1882 and 1883. 

6. O. Hertwic.—‘ Die Entwicklung des Mittleren Keimblattes der Wirbel- 
thiere,’ Jena, 1883. Also found in ‘ Jen. Zeit.,’ Bd. xv, p. 287, et seq. 
and Bd. xvi, p. 247, et seq. Taf. xii—xv of Bd. xv correspond to Taf. 
i—iv of the separate publication, and Taf. xiv—xviii of Bd. xvi to Taf. 
v—ix. We refer only to the separate publication. 

7. H. Srrant.— Ueber die Entwicklung des Canalis myelo-entericus u. der 
Allantois der Eidechse,” ‘ Arch. f. Anat. u. Physiol.,’ Anat. Abth., 1881. 

8. H. Srrant.—* Beitrage zur Entwicklung von Lacerta agilis,” ‘Arch. 
f. Anat. u. Physiol.,”? Anat. Abth., 1882. 


9, H. Srraut.— Beitrage zur Entwicklung der Reptilien,” ‘ Arch. f. Anat. 
u. Physiol.,’ Anat. Abth., 1883. 
10. H. Strant.— Ueber Canalis neurentericus und Allantois bei Lacerta 
viridis,” ‘Arch. f. Anat. u. Physiol.,? Anat. Abth., 1883. 


11. H. Srrant.— Ueber frithe Entwicklungsstadien von Lacerta agilis,” 
‘Zool. Anz.,’ No. 142. 


12. H. Srrant.— Ueber Entwicklungsvorgange am Vorderende des Embryo 
von Lacerta agilis,” ‘ Arch. f. Anat. u. Physiol.,’ Anat. Abth., 1884. 

13. H. Srrant.— Ueber Wachsthumsvorgange am Embryonen von Lacerta 
agilis,” Separatabdruck aus den ‘ Abhandlung der Tenckenbergischen 
naturforschenden Gesellschaft,’ Frankfurt, 1884. 

14. F. R. Weitpon.—*‘ Note on the Early Development of Lacerta mura- 
lis,” ‘Quart. Journ. Micr. Sci.,’ 1888; also ‘Studies from the 
Morph. Laboratory in the University of Cambridge,’ vol. ii, pt. 1, 1884. 


FORMATION OF GERMINAL LAYERS IN CHELONTA. 47 


15. C. F. Sarastn.— Reifung u. Furchung der Reptilieneier,” ‘ Arb. aus d. 
Zool.-Zoot. Inst. Wiirzburg,’ Bd. vi, 1883. 


16. C. K. Horrmann.—“ Beitrage zur Entwicklungsgeschichte der Repti- 
lien,” ‘ Zeit. f. Wiss. Zool.,’ 1884. 


EXPLANATION OF PLATES II, III, IV, and V, 


Illustrating Mr. K. Mitsukuri’s Paper on “The Formation of 
the Germinal Layers in Chelonia.” 


List of Reference Letters. 


a.o. Area opaca. a. p. Area pellucida. am. Amnion. a. Line along which 
nuclei are specially heaped up in the germinal wall. Figs. 18 and 20.—d/. 
Blastopore. 4/. p. Blastoporic passage. ch. Notochord. ect. Hctoblast. 
en. Entoblast. exc. Chorda entoblast. exd. Darm entoblast. g. w. Ger- 
minal wall. 4%.f. Head-fold. mes. Mesoblast. x. Nuclei in the yolk. 
sl. “Sickle.” v. 0. Ventral opening of the blastoporic passage. yh. Yolk. 
yk. c. Yolk-corpuscles. yt. p. Yolk-plug. 2. Shelf-like extension into the 
archenteron. 

All the figures, excepting Figs. 5, 6, 14a, 16, and 35, have been drawn by 
C. Ishikawa. Figs. 1—6 and 35 have been re-drawn by M. Indo. 

Figs. 1—4 have been drawn with Zeiss’s A A, x 2; Figs. 7—17 with 
Zeiss’s CC, x 2; Figs. 18—34 with Zeiss’s DD, x 2; Fig. 35 with 
Zeiss’s B B, x 2; Fig. 5 not drawn to scale; Fig. 6 is.a diagram. 


Fic. 1a.—Dorsal view of the embryonic shield from an egg just deposited. 

Fic. 14.— Ventral view of the same. 

Fic. 2@.—Dorsal view of the embryonic shield from an egg laid forty-eight 
hours. 

Fic. 26.—Ventral view of another embryonic shield of the same age from 
the same deposit. 

Fie. 3.—Dorsal view of the embryonic shield from an egg laid thirty-six 
hours. 

Fie. 4a.—Dorsal view of an embryo from an egg laid three days. 

Fic. 44.—Ventral view of the same. 

Fic. 5.—Ventral view of an embryo from an egg laid five days. 

Fig. 6.—Diagram of the embryonic shield. 

Fries. 7—15.—Series of transverse sections of the embryonic shield given 
in Figs. 1a and 4, arranged from behind forward. 


48 K. MITSUKURI AND OC. ISHIKAWA. 


Fig. 7. Section of the region where the three germinal layers are free 
from one another. 

Fig. 8. Section of the primitive streak. 

Fig. 9. Section passing directly behind the blastopore. 

Fig. 10. Section passing just in front of the dorsal lip of the blastopore 

Fig. 11. Section through the blastoporic passage. 

Fig. 12. Section passing through the posterior part of the ventral opening 
of the blastoporic passage. 

Fig. 13. Section passing through the anterior part of the ventral opening 
of the blastoporic passage. 

Figs. 14 and 15. Sections passing in front of the ventral opening of the 
blastoporic passage. 

Fig. 14a. Section showing the shelf-like extension into the archenteron. 

Fig. 16. Median longitudinal section of an embryo closely similar to Fig. 
la and 6, and from the same deposit. 

Fic. 17. Section passing through the ventral opening of the blastoporic 
passage of the embryonic shield, similar to that given in Fig. 2@ and 4, and 
from the same deposit. 

Fics. 18—23.—Series of transverse sections of an embryonic shield, 
closely like that given in Fig. 3, and from the same deposit. Arranged from 
behind forward. 

Fig. 18. Section passing through the lateral limbs of the horseshoe 
shaped blastopore. 

Fig. 19. Section through the blastoporic passage. 

Fig. 20. Section passing slightly in front of the ventral opening of the 
blastoporic passage. 

Figs. 21 and 22. Sections passing through the middle region of the 
shield. 

Fig. 23. Section passing through the region of the head-fold. 

Fic. 24.—Median longitudinal section of an embryonic shield, closely like 
Fig. 3, and from the same deposit. 

Fies. 25—28.—Series of transverse sections through the head region of 
the embryo represented in Figs. 4a and 4, illustrating the mode of the forma- 
tion of the notochord. Arranged from before backward. 

Fic. 29.—Transverse section through the head region of another embryo, 
closely like Figs. 4 and 4, from the same deposit. 

Fics. 30—84.—Series of transverse sections from the posterior region of 
an embryo, very much like that given in Fig. 4a and 4, illustrating the mode 
of the formation of the notochord in that region. Arranged from behind 
forward. 

Fic. 35.—Series of transverse sections from the posterior region of an 
embryo, with five or six mesoblastic somites, showing the neurenteric canal. 
Arranged from before backward. 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 49 


On the Structure and Development of the Repro- 
ductive Elements in Myxine glutinosa, L. 


By 


J.T. Cunningham, B.A., 


Fellow of University College, Oxford, and Superintendent of the Scottish 
Marine Station. 


With Plates VI and VII. 


Historical.—The first zoologist who investigated the minute 
structure of the generative organs and their products in the 
Myxinoida was Johannes Miiller. Between the years 1835 and 
1845 the great Berlin naturalist published a monograph on the 
‘Comparative Anatomy of the Myxinoids,’ the parts of which 
were first read before the Academy of Sciences of Berlin, and 
subsequently published separately in three folio volumes. The 
description of the reproductive system occurs in the last volume, 
published in 1845; the contents of this volume were com- 
municated to the Academy in 1842. The description is brief, 
but as far as it goes I have found it in most respects correct. 
I shall here quote it almost completely. 

“The sexual organs hang in a long peritoneal fold on the 
right side of the mesentery. The structure in Bdellostoma 
and Myxine is exactly the same. The structure in the two 
sexes is also completely similar, and it is very difficult to dis- 
tinguish testis and ovary. 

«The testes consist of a number of round and roundish 
long grains (kérner), which resemble the eggs; each has an 
external skin like the egg skin, and a content somewhat similar 

VOL. XXVII, PART 1,—NEW SER. D 


50 J. T. CUNNINGHAM. 


to the yolk of the egg; the substance within the testicular 
vesicles consists of granules of various sizes, but all smaller than 
the yolk granules. Spermatozoa at the time when the Myxine 
were examined in the fresh condition (August) were not present ; 
they are apparently only to be observed at the breeding season. 
The most important difference between the testicular vesicles 
(hodenbliischen = kérner, mentioned above) and the eggs seems 
to lie in the fact that in the former the germinal vesicle is 
wanting. 

“The eggs are, when small, round; later they become much 
elongated, and the ripe ones are very large. I have seen 
them in specimens preserved in spirit as long as 6” (13 mm.). 
At the time when I examined the Myxine alive the eggs were 
not large. In all young eggs, besides the yolk granules, is 
seen the germinal vesicle, which is very distinct; it contains, 
besides smaller granula, two or three cells with nuclei which 
form the germinal spot. When the eggs have become elon- 
gated the germinal! vesicle lies always at one of the thin ends 
of the eggs. The yolk granules are differently constructed to 
the granula of the testicular vesicles ; the granula of the latter 
are much smaller and round; the yolk granules are, on the 
contrary, ellipsoidal, and quite similar to the yolk granules of 
the Elasmobranchs, i.e. they have transverse lines on the sur- 
face which indicate a differentiation of substance and recall 
the amylon bodies. ‘These lines are present in the fresh con- 
dition, as in Sharks and Rays.” 

The following figures are given: 

Taf. i, fig. 1—The right side of the abdominal cavity of a 
male Myxine; the testis exposed ; natural size. 

Taf. u, fig. 3.--Testicular vesicles in the mesorchium of 
Bdellostoma Forsteri, natural size; the vesicles are here 
large and distinct, and project from the edge of the mesorchium ; 
in the former figure the separate vesicles cannot be distin- 
guished. 

Taf. ii, fig. 6.—Young round egg of Myxine fresh magni- 
fied. 


Taf. ii, fig. 7—Young egg slightly elongated. 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 51 


Taf. u, fig. 8.—Yolk granules from ripe egg of Myxine; 
some are free, but some contained in a spherical capsule. 

Taf. ii, fig. 5.—Ripe egg from ovary of Bdellostoma 
Forsteri, natural size ; it is 3°1 cm. in length. 

The description of Miiller is the only one which has ever 
been given of the male generative organ of Myxine, and it 
agrees in the main with the structure of the young testis, 
which I shall describe in this paper; but Miller did not under- 
stand completely the more minute structure of the organ, nor 
recognise the significance of what he saw. At the time 
when Miiller’s account of the female organ was written only 
the ovarian egg was known, and his description of it is correct 
except that part which refers to the structure of the germinal 
vesicle. He says nothing of the development of the egg or of 
its relation to the ovary. His figures have the same qualities 
as his description ; they represent correctly what can be seen 
by ordinary dissection without minute investigation. 

The next addition to our knowledge on this subject was 
made by Dr. Allen Thomson, in 1859. In the article “ Ovum,” 
in ‘Todd’s Cyclopedia of Anatomy and Physiology,’ that author 
gives the following very scanty account of the mature ovum 
of Myxine :—“ I have found that in the Myxine glutinosa 
the globular yolk is enclosed in a horny capsule of similar 
consistence and structure (he has been describing the ovum of 
Elasmobranchs), but of a simple elongated ellipsoidal shape ; 
and in place of four terminal angular tubes there are a number 
of trumpet-shaped tubular processes projecting from the middle 
of the two ends, which probably serve the same purpose as the 
differently shaped appendages of the ova of the shark and 
skate.” 

He gives a figure of the egg which has been copied in most 
of the recent text-books and works on Ichthyology. It is 
correct in shape, but it represents in outline the globular 
ovum contained within the capsule, the former being much 
smaller than the latter. It is evident, from both description 
and figure, that Dr. Thomson was under the impression that 
the capsule of the ovum of Myxine, with its polar processes, 


52 J. T. CUNNINGHAM. 


bore the same relation to the ovum as the egg capsule of ovi- 
parous Elasmobranchs, and that the two protective structures 
were homologous. This view has been adopted on Thomson’s 
authority by recent authors; Balfour, for example (‘ Comp. 
Emb.’), simply refers to Thomson’s description. I have not 
been able to ascertain whence Thomson obtained the specimen 
on which his description is founded. It is evident, as will be 
seen later, that he only examined the egg externally. 

In 1862, the Academy of Sciences of Copenhagen offered a 
prize for an investigation which should solve the problem of the 
reproduction and development of Myxine. The prize was never 
awarded, no one having undertaken the work, but in 18638 Pro- 
fessor J. Steenstrup published, as a guide to any who might 
attempt the research, an account of a specimen of Myxine which 
contained ripe eggs. Professor Steenstrup began by remarking 
that no one seemed to have seen males, and of females only 
those which had young or slightly developed eggs, and that the 
very young and undeveloped females were as unknown as the 
males; that in the literature there seemed to be no record 
that naturalists had seen individuals of less than 8 or 9 inches 
long, whilst those large egg-bearing females which had pre- 
viously been investigated were generally 10 to 13 inches in 
length. The work of Miller and Allen Thomson had appa- 
rently not come under Steenstrup’s notice. The rest of 
Steenstrup’s short paper is in substance as follows : 

The females of 10 to 15 inches in length have generally 
been regarded as females with fully developed sexual products, 
not without some reason. They have had not only a large 
number of eggs which were larger than the ripe egg of Petro- 
myzon, but most of them have had in addition from twelve to 
twenty eggs which were } to ; inch long, and 2 to 2} lines 
broad, and these eggs, which have been situated in moniliform 
fashion along the margin of the ovary, have been so loosely 
embedded in its folds that they easily fell out into the body 
cavity. On account of the interest attaching to the question I 
made a point of collecting as far as possible all the specimens 
of Myxine which I could obtain, for the Zoological Museum, 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 53 


and the number was not inconsiderable. In most of the 
female specimens which came to hand the large eggs were like 
cucumbers in shape, tapering to both ends, but in a few speci- 
mens the eggs were much thicker in proportion to their length, 
and not pointed at the ends; these, like the other kind, were 
arranged in a long series enclosed in the mesoarium, and 
easily fell out into the body cavity. Lastly, in September, 
1862, a specimen was found amongst a number sent to the 
museum, in which some of the eggs not only had the same 
great thickness and ellipsoidal form, but were surrounded 
externally by a firmer, almost horny shell which at the ends 
was provided with a number of slightly curved or S-shaped 
horny threads. Each thread ends in a head with three or four 
projecting lobes or hooks, and thus has a certain resemblance 
to a ship’s anchor. The threads remind one of those which 
project from the eggs of Sharks and Rays, just as the shell itself 
reminds one of the egg capsule in those forms. The figure 
here given shows both the appearance of the capsules and also 
the manner in which they hang in the mesoarium, together 
with large unripe eggs and a large number of small ones. The 
eggs provided with threads were entangled by means of these 
in the edge of the mesoarium, and with one another. Two 
conclusions may be drawn from this specimen ; one, that the 
eggs must be destined to be attached by means of their 
threads to foreign objects or to one another ; and second, that 
the females hitherto obtained have not been in the last stage 
of sexual activity. It follows from the last conclusion that the 
fish’s known mode of life as a devourer of carcasses must be 
short and temporary even for the females, and is perhaps only 
needful until the eggs have obtained a certain stage of deve- 
lopment, when the animals probably pass into another mode of 
existence. 

Steenstrup’s account agrees with Thomson’s except in two 
features: first, that the former does not describe or represent a 
globular ovum inside the capsule, and second, that he figures 
one end of the capsule, forming about one fifth of the whole, 
detached as a kind of operculum. With reference to the 


54. J. T. CUNNINGHAM. 


concluding part of the above account, I have to point out 
here that Myxine is not nearly so completely parasitic in its 
habits as has generally been believed. I have found that it 
lives for the most part concealed in soft mud, and is found in 
very large numbers on muddy areas of the sea-bottom. There 
is no direct evidence that it penetrates the bodies of living fish, 
and although it is often brought to the surface in the bodies of 
cod and haddocks which have been hooked, it is far more 
frequently taken on the hooks themselves. It frequently 
happens, as I have myself witnessed, that when a long line set 
for haddocks, and baited with mussel or herring, is hauled up 
near the mouth of the Firth of Forth, as many Myxine as 
haddocks are hooked, sometimes fifty specimens of the former 
being taken at one haul. I am in the habit of taking large 
numbers of Myxine in eel-pots set on muddy ground at a 
depth of thirty to forty fathoms off the coast of Haddington- 
shire, and baited with dead herrings, cod, or haddock. Thus, 
whatever the reason may be why so few perfectly ripe females 
are taken, it is not because the animals in this condition no 
longer bore into the bodies of fish; though the fact might be 
explained by the ripe females ceasing to feed altogether. 

The accounts of the egg of Myxine given by Dr. Gunther 
in his “Study of Fishes,” in the ‘ British Museum Catalogue,’ 
and in his article “ Ichthyology” in the ‘ Encyclopedia 
Britannica,’ 9th edition, are derived from the paper of Steen- 
strup above quoted. 

In Robert Collett’s ‘ Norges Fiske,’ which forms the supple- 
mentary volume to the ‘ Vidensk. Selsk. Forh.’ of Christiania for 
1874, and was itself published in 1875, mention was made of 
the distribution of Myxine, and the occurrence of its eggs. 
Of the latter the author says that they have been obtained by 
Professor Esmarck in the Christiania Fjord, and that they are 
often taken on soft ground off the coast of Finmark, or found 
in the stomachs of cod. Thinking that the eggs here referred 
to were eggs naturally deposited, | wrote to Mr. Collett on the 
subject, and in a very courteous reply he informed me that all 
the eggs he had seen, and to which he referred, were destitute 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 55 


of the characteristic polar threads; those obtained by Professor 
Esmarck having been taken from the ovary of the female, and 
those he himself obtained from Finmark having been given to 
him by Mr. Buck, of Oxfjord, and also probably coming from 
immature females. On applying to Mr. Buck himself I was 
informed by him that he had only obtained the eggs from the 
ovary of the female. 

The only specimens of the ripe egg in the hands of natural- 
ists are those obtained by Professor Steenstrup, as above 
described, which are now in the Copenhagen Museum, and a 
single specimen, which is in the Anatomical Museum of Edin- 
burgh University. By the kindness of Professor Sir William 
Turner I have had the privilege of examining the latter, but 
as it is a unique specimen I was not able to cut it so as 
to examine its structure. The specimen is represented in 
Plate VI, fig 1, of the natural size. Externally it agrees 
with the figures of Thomson and Steenstrup, except that it has 
no indication of any separation of a part of the capsule to form 
such an operculum as shown in the figure given by the latter 
author. The length of the ovum is 25 mm., of the threads 
about 5 mm. ‘The capsule or membrane enclosing the ovum is 
thicker at the poles than elsewhere, and the thickened portion 
can be seen to be transparent, as shown in the figure. At each 
pole of the ovum there is a slight conical projection, to which 
the polar threads are attached. One of these projections, the 
upper in the figure, is larger than the other, and it is beneath 
this larger projection that the protoplasmic disc is situated—a 
fact which I infer from my study of the unripe eggs. I was 
allowed to cut off a couple of threads for microscopic examina- 
tion. One of these is represented in fig, 1,7. The thread is 
solid, and not tubular ; its structure, as seen under a low power, 
appears homogeneous, and in my investigation of the develop- 
ment of the threads I have found no indication that they are 
tubular in any stage of growth. The statement of Allen Thom- 
son on this point is therefore erroneous, and doubtless due to 
his preconceived opinion that the threads were homologous with 
the processes of the egg capsule in Elasmobranchs, 


56 J. T. CUNNINGHAM. 


The history of the specimen of the ripe ovum in Professor 
Turner’s museum cannot, unfortunately, now be traced. It is 
described in the catalogue as “egg of Myxine, enclosed in its 
horny capsule, with its terminal openings surrounded by pro- 
cesses.” This entry was made by Dr. Spencer Cobbold, but 
that gentleman informed me that he received no account from 
Professor Goodsir of the history of the specimen. The ter- 
minal openings mentioned do not exist. Though there is a micro- 
pyle at the protoplasmic pole it is doubtful if this had been seen 
by Professor Goodsir. Tradition says that the specimen was 
obtained by Mr. Shirley, formerly assistant in the Anatomical 
Museum, and was by him dredged up from the sea-bottom. It 
is certain that it was brought to the museum in the time of 
Professor John Goodsir, but no record of its origin is now to 
be discovered. Itis possible that Dr. Allen Thomson’s account 
was founded on this Edinburgh specimen, as I have not been 
able to find any indication that mature ova of Myxine ever 
existed in Glasgow, where Thomson was professor. 

It is much to be deplored that Dr. Thomson did not give a 
complete account of the sources of his knowledge of the Myxme 
ovum. I am inclined to think that the Edinburgh specimen 
was taken from a mature female, like Steenstrup’s, as I have 
vainly dredged for the deposited eggs with much perseverance 
in places where the animals were extremely abundant. 

The portions of the literature on the subject in Danish and 
Norwegian were translated for me by my friend Mr. W. E. 
Hoyle, M.A., of the “ Challenger” Commission Office, and to 
him, as well as to Professor Turner and the several zoologists 
who have given most courteous attention to inquiries concern- 
ing Myxine which I addressed to them, I have much pleasure 
in expressing here my heartiest thanks. 

Course of the Research.—Since last June I have made 
systematic efforts to obtain the ripe generative products of 
Myxine, and as the animals were obtained with considerable ease 
in large numbers in the neighbourhood of the Firth of Forth I 
had some reason to hope for success. I have conveyed a 
number of living and well-grown specimens to the aquarium of 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 57 


the Scottish Marine Station, and some of these have lived there 
for six months; but they refused to feed, and probably in con- 
sequence of this their sexual organs have not developed to the 
mature condition. I was able to observe the normal mode of 
life of the creatures when at rest and not seeking food. They 
lie with their bodies entirely buried in soft mud, with the ex- 
ception of the extreme tip of the snout, and in this condition 
respiration is carried on by means of a current of water, which 
enters at the nostril, passes into the pharynx, and after tra- 
versing the gill-sacs escapes by the two branchial apertures 
situated immediately in front of the liver. This current is 
rendered evident by the movement of the particles of mud 
caused on the escape of the water from the latter openings. I 
have also obtained a large number of specimens of Myxine 
from fishermen and by means of my own excursions, and as I 
failed to obtain ripe eggs or ripe spermatozoa I set myself to 
try and elucidate the nature and development of the ova and 
spermatozoa by the minute investigation of the immature 
organs. 

Female Organs.—To deal with the ovaries first, careful 
examination shows that the largest ovarian eggs are situated 
nearest to the attached border of the mesoarium. The ovary 
of Myxine agrees in structure and relations with that of other 
fishes very closely ; its chief peculiarities are two in number. 
Firstly, it is extremely thin from side to side, the edge where 
the eggs are produced, forming a border only slightly thicker 
than the mesoarium with which it is continuous: there is no 
distinct boundary between ovary and mesoarium. Secondly, 
the mesoarium is attached, not to the back of the body cavity, 
but along the line of attachment of the mesentery with the 
straight intestine. The eggs are produced at the free edge of 
the ovary, which is covered by a thin epithelium; and the eggs 
are produced from this germinal epithelium in the same way 
as in other Vertebrates, and are surrounded after their separa- 
tion by a follicle consisting of a connective-tissue capsule, and 
a follicular epithelium. I have not attempted to ascertain 
whether the cells of the follicular epithelium are derived from 


58 Je T. CUNNINGHAM. 


the germinal epithelium or produced otherwise; the former 
method is that believed to obtain by the best authorities in all 
Vertebrates, and I have no evidence against its occurrence in 
Myxine. As the eggs grow larger by the accumulation of yolk 
they pass inwards towards the attached border of the mesoarium, 
the largest and oldest being always the most internal. These 
large eggs appear when a specimen is first opened to hang from 
the edge of the ovary, but examination of the organ in liquid 
shows at once their true relations. ‘The mesoarium is con- 
tinuous with the connective-tissue sheath of the follicle in the 
largest ovarian egg, as well as in the small ones, along a line 
which passes round the longest circumference of the ellipsoid 
formed by the follicle, and the transition between the two 
structures is abrupt ; the mesoarium in the immediate neigh- 
bourhood of its attachment to the follicle is as thin as else- 
where and is easily torn, so that the larger eggs are easily 
separated, follicle and all, from the ovary when the animal is 
roughly handled. The weight of the large egg causes the 
mesoarium to be stretched, and each egg hangs down beyond 
the edge of the ovary, seeming at first sight to be enclosed ina 
bag formed by part of the mesoarium. But the relation of the 
two is always as I have described above ; and it does not differ 
from the relation between egg follicle and ovarian stroma in 
Elasmobranchs and other Vertebrates except in the contrast in 
thickness between the ovarian egg and the surrounding portion 
of the ovary. In order to ascertain the structure of the fol- 
licle and egg membranes I cut series of sections through the 
polar portions of the largest ovarian eggs I could find. Fig. 2 
represents the appearance of one of these sections passing 
exactly through the pole of the egg. The egg from which the 
section was taken was 16 mm. in length, and neither by external 
examination nor from the sections could any trace of the polar 
threads be discovered. In the section the thickest and most 
external layer is the connective-tissue capsule (a), composed of 
very thin interlaced fibrils with numerous small nuclei. This 
layer is disposed in laminz parallel to the surface of the follicle, 
and in it are numerous small elongated spaces, some of which 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 59 


are blood-vessels. The connective-tissue layer passes off into 
the thin flat mesoarium (me.). On the surfaces of the latter, 
as well as on the outer surface of the follicle, there is doubtless 
a thin flat epithelium, but this is so indistinctly differentiated 
from the connective tissue that it does not show itself in 
sections except by its nuclei. Within the connective-tissue 
layer is the epithelium of the follicle (6). This epithelium is 
composed of elongated cells disposed with their axes perpendi- 
cular to the surface of the epithelium. There are several | 
layers of these cells as shown in the figure, but the layers are 
not regularly arranged, in some places three, in others four or 
five nuclei succeeding one another in a radial direction. At 
the exact pole of the egg there is a differentiated portion of 
epithelium, where a proliferation of the latter has taken place. 
This portion is composed of polygonal cells which are little or 
not at all elongated, and towards the egg it runs out into a 
thin cylindrical process which penetrates the next layer, as 
shown at e.p. Thenext layer (c) is thin and membranous. In 
the living egg it is doubtless in contact with the epithelium, 
and the separation between the two shown in the figure has 
been produced by the action of the hardening reagents em- 
ployed in the preparation of the egg. This layer as shown in 
the figure appears under a low power single and homogeneous, 
‘and it is Im immediate contact with the substance of the ovum 
proper, or, as it is sometimes called, the vitellus. The polar 
portion of the vitellus which is in immediate contact with the 
membrane (c) is granular in structure, stains well, and is proto- 
plasmic in nature. In this protoplasmic cap is found the 
germinal vesicle, shown in some of the other figures. Beneath 
the membrane (c) at other parts of the ovum there is no separate 
protoplasmic layer, the yolk-discs extending to the inner 
surface of the membrane. The protoplasmic cap with its 
germinal vesicle forms thus a germinal disc similar to that 
found in the bird’s ovum, and other meroblastic vertebrate 
ova. The rest of the ovum is composed principally of yolk 
elements, the elliptical vitelline discs show in the figure. The 
nature of the membrane (c) must here be particularly consi- 


60 J. T. CUNNINGHAM. 


dered ; we can obtain some probable conclusions concerning it 
by referring to what is known concerning the egg membranes 
in other Vertebrata. The account which Balfour gives in his 
‘Comp. Emb.,’ vol. i, of the egg membranes in Craniata, is as 
follows. There are three membranes which may all coexist, 
or one or two only may be present. These are: 

1. An outermost homogeneous membrane without striz or 
fine pores, by most authors regarded as a chorion (i. e. as pro- 
duced by the follicular epithelium), but by Balfour as a vitelline 
membrane (i.e. as produced by the ovum itself). 

2. A radiately striated membrane, internal to the former 
when the two coexist, which can be broken up into a series of 
separate columns. These give to the membrane its radiate 
striation, but it is probable that there are fine pores between 
the columns. This membrane is the zona radiata of most 
authors. It is a differentiation of the outermost layer of 
the yolk. 

3. Within the zona radiata a third and delicate membrane 
is occasionally found, especially when the ovum is approaching 
maturity. 

According to Balfour, the first membrane to be formed in 
Elasmobranchs is the vitelline membrane, the first of the three 
above defined ; this appears in some instances before the forma- 
tion of the follicle, a fact which appears to show that it is 
really formed as a differentiation of the protoplasm of the egg. 
In Elasmobranchs this membrane attains a very considerable 
development. A zona radiata is generally if not always present 
in Elasmobranchii, but arises later than the vitelline mem- 
brane. The zona radiata always disappears long before the 
ovum isripe. The vitelline membrane also gradually atrophies 
though it lasts much longer than the zona radiata. When the 
egg is taken up by the oviduct, all trace of both membranes 
has disappeared. 

Is there any evidence to show whether the membrane (c) in 
the Myxine ovum owes its existence to the ovum itself or to the 
follicular epithelium? The only evidence to which I will point 
at present is that the follicular epithelium is very much thicker 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 61 


at the poles of the follicle than in the equatorial region, and 
the membrane in question varies in thickness with the epithe- 
lium. I shall recur to the question of the nature and origin 
of the membrane further on. In this paper I shall call the 
membrane the vitelline membrane, using that term to include 
the whole of the primary egg membranes produced within the 
follicle. The term chorion will not be used, as its application 
in the case of mammals to a membrane which is partly derived 
from the blastoderm renders it unsuitable in connection with 
primary egg membranes. The term vitelline membrane, as 
used in this paper, implies no assertion as to derivation from 
follicular epithelium on the one hand, or ovum on the other. 
In Myxine, as will be conclusively shown in the course of what 
follows, the vitelline membrane forms the sole protective covering 
of the deposited ovum. 
It is now necessary to trace the destiny and elucidate the 
significance of the process from the follicular epithelium above 
described. In the sections succeeding the one shown in fig. 2 
this cylindrical process is seen to penetrate the vitelline mem- 
brane, occupying a tubular cavity in the latter, and passing 
through it to form a hemispherical projection on its inner sur- 
face. This tubular aperture in the vitelline membrane, with 
its contained epithelial cells, is shown in fig. 3, as seen under a 
high power. The section lies almost in the plane of the canal, 
and so exposes nearly the whole of its cellular contents, in- 
cluding the hemispherical projection surrounded by the proto- 
plasm of the germinal disc. ‘This cellular projection is covered 
by a thin membrane continuous with the vitelline membrane, 
and is not in immediate contact with the germinal disc. In 
fig. 3 the outer end of the canal, that towards the follicular 
epithelium, is closed, owing to the direction of the plane of the 
section, but in previous sections, as stated above, the cellular 
cylinder filling up the canal is seen to be continuous with the 
process projecting from the surface of the follicular epithelium. 
The structures now described, as I have convinced myself by 
a series of sections from more than one egg, exist only at one 
pole of the ovarian ovum, There is thus at one pole of the 


62 J. T. CUNNINGHAM. 


nearly ripe ovum a tubular canal extending through the chorion, 
but not open internally, filled up by a cylinder of cells project- 
ing from the follicular epithelium. It is evident, on considera- 
tion of the above facts, that this aperture is to form the micro- 
pyle in the ripe ovum, and we have here, as will be explained 
more fully below, the explanation of the process of fertilisation 
in the ovum of Myxine. It is very improbable that sperma- 
tozoa could penetrate such a thick dense capsule as is formed 
by the vitellime membrane in the ripe ovum, and thus the 
presence of a micropyle is necessary. Another point of some 
interest in this connection is that we have here for the first 
time the complete history of the origin and formation of the 
micropyle in a vertebrate ovum. A micropyle is known to 
exist in many Teleostean ova, but little investigation has been 
made as to how the structure is produced in the course of the 
ovarian development of the ovum. 

In a paper which has recently come into my hands (‘‘ Studien 
uber das Hi,” ‘Mémoires del’Acad. Imp. St. Peters.,’ 1885), Ph. 
Owsjannikow describes some observations on the micropyle in 
the ovum of Osmerus eperlanus, the comparison of which 
with my description and figures is very interesting. The eggs 
studied by Owsjannikow were not naturally shed, but taken 
when almost ripe from the ovary. In this condition the layer 
of follicular epithelium, or granulosa, as the Russian investi- 
gator calls it, is frequently found attached to the egg mem- 
brane. The egg membrane consists of two layers, called zona 
radiata externa and zona radiata interna. A micropyle 
pierces both of these layers, and is expanded like a funnel 
externally. A conical projection from the granulosa was seen 
to extend into the micropyle. This conical projection was not 
solid as in the case of Myxine, but hollow, forming a lining to 
the micropyle. A thin thread was seen to extend from the end 
of the funnel-shaped opening in the external zona, through the 
internal micropyle, which was a narrow canal in the internal 
zona. <A row of granules was also seen to extend from the 
inner end of the internal micropyle into the vitellus. Con- 
cerning the thread and row of granules Owsjannikow gives no 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 63 


conclusion as to their nature ; he describes the projection from 
the granulosa as extending only through the external micro- 
pyle as far as the inner surface of the external zona. But it 
seems to me extremely probable that the thin thread and row 
of granules above mentioned belong to the follicular epithe- 
lium, and are originally continuous with the conical projection 
of the granulosa. Thus the differences between the condition 
in the egg of the smelt and in that of Myxine, are two: first 
the projection from the follicular epithelium into the micro- 
pyle in the smelt is a hollow cone, not a solid one as in 
Myxine; secondly, the inner end of the micropyle in the smelt 
is open. With regard to the latter point, the micropyle is 
completely open in the later stages of the egg of Myxine, and 
whether the micropyle is at first closed internally in Osmerus 
is not known. It is probable that careful investigation would 
show that in all Teleosteans whose ova possess a micropyle 
that structure is produced by a projection of cells from the 
follicular epithelium. 

It is at least possible that in all Vertebrates the micropyle 
will be found on investigation to be produced in the same way 
as in Myxine, namely, by the growth of a cellular process 
from the follicular epithelium towards the vitellus while the 
vitelline membrane is being formed. 

Amongst some specimens of Myxine sent to me in December 
last I found some in which the ovarian eggs appeared older 
than any I had examined before, the poles being more obtuse 
and the transverse diameter greater thau usual. These eggs 
were 20 mm. in length. I cut series of sections through the 
polar regions of some of these eggs, and one of these sections 
passing through the protoplasmic pole is shown in fig. 4. 
Several differences are seen from this figure to exist between 
the follicle of these older eggs and that shown in fig. 2. The 
connective-tissue envelope is thinner; the follicular epithelium 
has its cells arranged somewhat differently, the nuclei being 
crowded towards the deeper surface. But the greatest difference 
of all is the presence in the epithelium of deep pits expanded 
at the bottom, and corresponding to these, processes from the 


64 J. T. CUNNINGHAM. 


vitelline membrane. In the figure a wide interval is shown 
between the vitelline membrane with its processes and the 
epithelium with its pits, but as in the former case, there can be 
no doubt that this is merely a result of the process of prepara- 
tion; in the natural condition the membrane was in .contact 
with the epithelium, and its processes filled up completely 
the pits in the latter. It is rather curious that the epithelium 
thins out very much over the tops of the processes, and this 
would seem to be in opposition to the belief that the vitelline 
membrane, processes and all, is due to the secretory activity of 
the epithelium ; but it is probable that the formation of the 
processes takes place at the sides where the epithelium is very 
thick, and that they are pushed up by growth at the base. In 
these processes, rudimentary as they are, it is not difficult to 
recognise the early stages of the polar threads which distin- 
guish the ripe deposited egg of Myxine. Here, then, at last 
we have the explanation of these processes, which have hitherto 
received no interpretation except the erroneous one of Allen 
Thomson. The capsule enclosing the ripe ovum is undoubtedly 
the vitelline membrane, and the polar threads are processes 
from this. I have already pointed out that I have ascertained 
by actual examination that these processes are not tubular, as 
Allen Thomson supposed, but solid. Thus, there is no homo- 
logy or comparison possible between the capsule of the egg of 
Myxine with its polar threads, and the horny capsule in which 
the eggs of oviparous Elasmobranchs are enclosed. The 
Elasmobranch capsule is produced by a special gland in the 
oviduct, and the fact that Myxine has no oviduct might alone 
have prevented the comparison which was instituted by Dr. 
Thomson, and which so many authors have repeated. lefer- 
ring, again, to fig. 4, it is seen that the vitelline membrane 
has much increased in thickness since the stage shown in 
fig. 2. The proliferation and differentiation of cells at the pole 
in the follicular epithelium has disappeared, but the cylinder 
of cells, though reduced in size, still remains in the micropyle, 
and is evidently destined to keep the latter open until the 
maturation of the ovum is complete. Close beneath the 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 65 


micropyle, in the section passing actually through the pole, is 
seen the germinal vesicle, which is large and spherical in shape, 
and therefore circular in section. It is composed of a thin 
membrane containing fibrils and granules, but no conspicuous 
germinal spot. Its position and appearance are seen in the 
figure. 

On January 29th of the present year I obtained specimens 
of Myxine in which the development of the eggs had proceeded 
so far that the growth of the polar threads produced an effect 
on the external appearance of the follicle. At each end of the 
follicle was a slight protuberance, which was considerably 
larger at one end than the other. On the surface of the pro- 
tuberance were minute rounded elevations, evidently due to 
the presence of the threads beneath. One of these eggs con- 
tained in its follicle is represented of the natural size in fig. 
11. Its length is about 21 mm., breadth 7 mm. Fig. 12 
shows a section through the pole of that end of the ovum dis- 
tinguished by the larger protuberance. The protuberance is 
seen to consist of the connective-tissue layer, the processes, 
and the thickened follicular epithelium and vitelline membrane 
in their neighbourhood. The thickness of the membrane close 
to the base of one of the threads is ‘29 mm., of the follicular 
epithelium at its thickest parts°30 mm. The connective-tissue 
layer is thinner than at the stages already described, and is 
especially reduced above the terminations of the polar pro- 
cesses ; at the point marked z this layer was only ‘(02 mm. in 
thickness; at the pole y it was ‘5 mm. thick. The germinal 
vesicle and germinal disc are not altered in structure. The 
micropyle is somewhat narrower, and the cells present in it at 
previous stages have disappeared almost completely, only a 
little débris remaining. The micropyle seemed also in these 
ova to be open internally, though of this point I am not abso- 
lutely certain. If there is a membrane closing the inner end 
it is an extremely thin one. The vitelline membrane and the 
follicular epithelium are both much increased in thickness, as 
will be evident from a comparison between figs. 12 and 4; the 
latter is magnified fifty times, the former only thirty-five 

VOL, XXVII, PART 1.—NEW SER. E 


66 J. T. CUNNINGHAM. 


This increased thickness is more pronounced at the polar 
region of the egg than elsewhere, but the two layers are thick- 
ened to some degree over the whole surface of the ovum. The 
structure of the prominence at the opposite pole of the ovum 
is similar except that the growth of the threads is not so far 
advanced, and of course micropyle, germinal vesicle, and 
germinal disc are absent. At the germinal pole a circular 
depression is present in the external surface of the vitelline 
membrane, above the micropyle, as shown in fig. 12. For the 
sake of absolute accuracy of statement I must mention that in 
the section from which fig. 12 was drawn the same separation 
between chorion and follicular epithelium, due to the action of 
the hardening reagents, was present, as is shown in figs. 2 and 
4. The length of the specimen from which the eggs I have 
described were taken was about 15 inches. It was taken with 
several others on haddock lines twenty-four miles south-south- 
east of the Isle of May. There were a few other specimens in 
the same lot in which the largest ovarian eggs showed polar 
protuberances due to the presence of the chorionic processes, 
but the description I have given is taken from the specimen in 
which the protuberances were most developed. 

It is necessary now to consider more minutely the structure 
of the vitelline membrane, and to determine, if possible, its 
mode of formation and its homologies. As seen under a low 
power it appears, as I have said, homogeneous and structure- 
less. In the preparations from ova hardened with chromic 
acid and stained with borax carmine I was unable to find any 
structure, even with the highest powers; but in sections from 
ova hardened with Perennyi’s fluid (chromic and nitric acid 
mixed) under a high power striz perpendicular to the surface 
of the membrane are plainly seen. The structure thus brought 
to view is shown in fig. 4, a, taken from a preparation of the 
same series as fig. 4. The striz are more deeply stained than 
the rest of the membrane; they are for the most part parallel 
to one another, but sometimes they branch into two. Several 
of them are moniliform. In some cases I have traced them at 
the external surface of the membrane, where the latter was 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 67 


separated from the epithelium, into continuity with proto- 
plasmic fibrils outside the membrane. These fibrils I believe 
to be in the natural condition continuous with the cells of the 
epithelium, and I conclude that the strize are really pores in 
the membrane, which are filled up by protoplasmic processes 
from the cells of the follicular epithelium. A similar condition 
of things exists, and has been described by many authors in 
Teleostean ova, and has been very completely elucidated by 
Owsyannikow in the paper already cited. Owsyannikow ob- 
tained his most satisfactory results from examination of the 
egg of Perca fluviatilis. In this species the vitelline mem- 
brane consists of two layers, both of which contain pores, and 
are therefore called by him zona radiata externa and in- 
terna. The zona externa is in the ripe ovum gelatinous, 
and causes the adhesiveness of the egg membrane. I have 
myself examined sections of the vitelline membrane of the 
ovum of the cod after deposition. The pores here are quite 
straight and never branched, and they are somewhat further 
apart than those in the egg of Myxine. In the cod I could 
discover no separation of the membrane into two layers. It 
seems evident to me that the vitelline membrane in the ovum 
of Myxine, which is a zona radiata in the usual sense of the 
term, is homologous with the zona radiata in Teleostean 
ova. When there are two zone radiate, as in Perca 
fluviatilis and Osmerus eperlanus, according to Ows- 
gannikow, these seem to be simply parts of one membrane 
differentiated in physical properties, but essentially similar in 
structure. Balfour regards the zona radiata in vertebrate 
ova as a differentiation of the outermost layer of the yolk. It 
seems to me much more probable that it is produced by the folli- 
cular epithelium. It is concluded by most authorities that the 
pores in the zona radiata are occupied by processes from the 
cells of the follicular epithelium, and that the function of these 
processes is to convey nutriment tothe ovum. In Myxine such 
processes exist. The manner in which the membrane arises I 
conclude is as follows :—The deeper part of the elongated epi- 
thelium cells is gradually changed into the zona radiata, the 


68 J. T. CUNNINGHAM. 


substance of the cells being partly transformed into the sub- 
stance of the membrane, while threads of protoplasm, at more 
or less regular intervals, remain unchanged, and thus give rise 
to the pores of the membrane. On this hypothesis—for it is 
little more—any membrane which may be formed by the ovum 
itself is to be sought on the inner side of the zona radiata. 
In Myxine I have found no such membrane. I have not 
hitherto had an opportunity of comparing the structure of the 
egg follicle in Petromyzon with that in Myxine. According 
to Calberla the ovum in Petromyzon is surrounded by a zona 
radiata in two layers, both radiately striated. According to 
Kupffer and Benecke the outer layer is not striated. Calberla 
asserts the existence of a micropyle, while Kupffer and Benecke 
have thrown doubts on the presence of such an aperture. 
Judging from what I have seen in Myxine I am inclined to 
think that Calberla is correct, and that the condition of things 
in Petromyzon is exactly similar to that in Myxine, except 
that the zona radiata in the former is, as in Perea, divided 
into two layers. In the ovum of Myxine I have observed in 
some sections a very faint trace of a separation into two layers, 
and have indicated this in fig. 12, but I do not think this (in 
the absence of any difference in character in the two layers, 
and in view of the fact that the line of separation can never 
be traced continuously for any distance) indicates difference of 
origin of the two strata of the membrane. The membrane is 
not developed till a late stage in the growth of the ovum. 

In fig. 13 is shown a section through the pole of an ovarian 
ovum 11 mm. in length. The germinal disc is seen to have the 
same characters as it has in the more mature ova, except that 
the germinal vesicle is elliptical in section. This latter pecu- 
liarity is probably an accident caused by the action of reagents. 
Under a system magnifying 50 diameters, the follicular epithe- 
lium at this stage can scarcely be distinguished, while the con- 
nective-tissue layer is very thick. On applying a higher 
magnifying power it is seen that no membrane of any kind 
exists at this stage between the follicular epithelium and the 
vitellus, The epithelium itself is only one cell thick, and the 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 69 


cells vary in size, so that the deeper surface of the epithelium 
is irregular (vide fig. 13a). Amongst the specimens obtained 
on January 29th, I recognised for the first time a female which 
had recently discharged its ova. In place of the 19—25 large 
ova which are usually present there were a corresponding 
number of collapsed follicles; each of these had a slit-like 
aperture at one end, through which the ovum had been ex- 
pelled. I found afterwards that similar “spent” specimens were 
present among a lot obtained on December 24th, 1885, and I 
have obtained them on several occasions since. Thus it is 
proved that the deposition of ova occurs in Myxine in the 
neighbourhood of the Firth of Forth during the months of 
December, January, February, and March. In spite of this 
discovery, and many zealous attempts, I have hitherto com- 
pletely failed to obtain a single deposited and fertilized ovum. 

Before recognising the specimens which had quite recently 
discharged their ova, I had frequently found corpora lutea in 
the ovaries of old females; and I have since observed various 
intermediate stages in the process of absorption of the follicles 
from which the ova have escaped ; the last stage being that of 
minute yellow nodules in the mesoarium. 

It is obvious from the above that the eggs described by 
Steenstrup had escaped from the follicles and remained in the 
body cavity entangled by their polar processes. The eggs may 
have been expelled from the follicles naturally, and not yet 
discharged from the body cavity; but it is more probable that 
the eggs were very near perfect maturity in the follicles when 
the animal was captured, and that the follicles were ruptured 
by the rough handling the specimen received from the 
fishermen. 

The yolk-elements are of two kinds; flat, elliptical, trans- 
parent and highly refringent discs such as were described by 
Johannes Miller, which are doubtless albuminous, and clear 
spherical-lobed which are probably of a fatty nature (fig. 5). 
In the very young eggs these yolk-elements are not present, 
but only fine granules which make the ovum when viewed by 
transmitted light black and opaque. In still younger eggs, 


70 J. IT. CUNNINGHAM. 


such as are found in very small females, the eggs in the fresh 
state are spherical and quite clear, showing the germinal vesicle 
somewhat eccentric in position, and clear protoplasm all round. 
Fig. 6 represents a stained preparation from the ovary of a 
specimen only six inches in length, which was taken in an eel- 
trap, July, 1885. The free edge is marked 2, the attached y ; 
the eggs extend almost up to the attached border, the meso- 
arium not being yet developed. 

Male Organs.—We pass now to the consideration of the 
male sex. It is a curious and hitherto unexplained fact that 
the male Myxine is very seldom taken. Among the hundreds 
of specimens which have passed through my hands I have 
only succeeded in identifying eight males, and these are all 
very immature. It is a matter of some difficulty to recognise 
the immature testes in these young males, and some few young 
male specimens may have escaped my recognition, as the matter 
requires careful examination with the microscope. But it is 
certain that the vast majority of the specimens which I have 
obtained have been females with large eggs in the ovary, eggs 
varying from 1 to 20 mm. in length. The same experience 
has been recorded by others who have occupied themselves with 
the subject, and until I engaged in the research no one had seen 
the ripe spermatozoa of Myxine. My examination of the 
young male convinced me that Johannes Muller was dealing 
in his description with specimens in a similar condition to my 
own, but his account of the minute structure of the testes is 
inadequate. His figure of the male reproductive organ in its 
natural size and in situ is perfectly correct, and on this point 
I must be content with a reference to his figure. The organ 
is similar in general arrangement to the ovary: it les along 
the right side of the body, the organ of the left side not being 
developed, and it consists of an extremely thin flat mesor- 
chium, with a slightly thickened free border. In this border 
the male elements of reproduction are produced. When a 
piece of the border is cut out and examined under a low power 
of the microscope in the fresh state the thickened border is 
seen to consist of connective tissue containing a number of 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 71 


more or less spherical capsules, varying very much in size. 
By careful compression, the contents of these capsules can be 
brought into view, but the structure is not very distinct. 
When a capsule is burst by compression spherical cells are 
seen to escape from it. These cells have a very delicate outline ; 
they are very transparent, and the nucleus is only to be dis- 
tinguished by careful focussing. These cells vary slightly in 
size, the average diameter being 17 » ; their appearance in the 
fresh state is represented in fig. H. 7 

The interior of the capsules is completely filled up by 
these cells, which in the fresh state are spherical while still 
within the capsule, but become more or less polygonal after 
hardening. The structure is brought out more distinctly by 
preparing a piece of the tissue with hardening reagents, e.g. 
corrosive sublimate or chromic acid, staining it, and then 
mounting in a transparent medium. Fig. 7 shows the appear- 
ance of such a preparation when magnified 50 diameters. The 
capsules in the thickened border of the testis are seen to be 
crowded with nuclei, but nothing further can be distinguished. 
Under a higher power, if the preparation has been compressed, 
the separate nucleated cells in the capsules can be distin- 
guished. By cutting sections transverse to the thickened 
border the structure is brought clearly into view. Fig. 8 
shows the appearance of such a prepared and stained section 
magnified 70 times. The outlines of the cells are not distinct, 
but they can be followed under a higher power. I concluded 
from the above facts that the cells in the capsules, after sub« 
division, were converted directly into spermatozoa, which by 
rupture of the capsules escaped into the body cavity of the 
animal. There is every reason to believe that the fertilisation 
in Myxine takes place outside the body. 

After identifying the male organ and investigating its 
structure, | was surprised to find that in nearly all specimens 
with very immature eggs the posterior portion of the sexual 
organ had the same structure as the testis. This testicular 
portion occupies about 2 inches of the posterior end of the 


ie. J. T. CUNNINGHAM. 


sexual organ, and I have only found it in specimens in which 
the eggs were very small, that is, less than 4 mm. in length. 

Fig. 10 shows a prepared and stained section of the male 
portion of the organ in such a hermaphrodite specimen, under 
a magnifying power of 100, and it will be seen that it agrees 
in all respects with the figure of a section of the testis. 

In one of the hermaphrodite specimens obtained on January 
29th last, I discovered, on teasing up a portion of the testicular 
portion of the generative organ, a number of spermatozoa, and 
stages of spermatogenesis. The various structures as seen in the 
fresh state are shown in fig. 14. The spermatozoa possess a pear- 
shaped head, which is very highly refringent, and has a distinct 
outline ; round the posterior thicker end of the head is a trans- 
lucent protoplasmic body, which is produced into a long tail. 
These spermatozoa were not moving, and were not present in 
vast numbers as is usually the case. The specimen from which 
they were taken had been dead a few hours. I have not been 
able to obtain a sufficient supply of material to make a com- 
plete study of the spermatogenesis ; the few stages I could make 
out are shown in fig. 14. In some cases two spermatozoa were 
connected by their tails, and on the connecting thread thus 
produced were slight dilatations composed of clear protoplasm. 
In other cases a cell somewhat spherical in shape gave off two 
processes, one of which was the tail of a spermatozoon, while 
the other terminated in a point, the head of the spermatozoon 
belonging to the process having probably become detached in 
the operation of teasing. There were also seen cells in which 
were present one or more structures resembling the heads of 
the spermatozoa. These structures and the heads of the 
spermatozoa stain deeply in carmine; they doubtless consist 
of nuclear substance, but I have not been able to trace their 
origin from the nuclei of the cells in which they occur. It is 
evident that the cells and spermatozoa described were derived 
from the spherical cells of the testicular capsules. These cells 
apparently develope the heads of the spermatozoa which then 
grow out from the cells, trailing a thread of protoplasm which 
forms the tail. The curious thing about the spermatogenesis 


REPRODUOTIVE ELEMENTS IN MYXINE GLUTINOSA. 73 


observed in Myxine is that the spermatozoa are attached to 
the spermatoblast by the tails, and not by their heads, as usually 
occurs. I found no cases in which large numbers of sperma- 
tozoa were united in bundles such as occur in most animals ; 
there were never more than two spermatozoa connected with 
one another or with a spermatoblast. The spermatozoa were 
contained in the capsules of the testicular tissue, and it is thus 
proved conclusively that the spherical cells usually found in 
these capsules are really spermatoblasts. In the fresh prepara- 
tion from which fig. 15 was drawn, although none of the 
spermatozoa showed any motion, the protoplasm of the cell 
represented at a was slowly vibrating. In two other herma- 
phrodite specimens, one obtained in March, I have found a 
few spermatozoa, which in one case exhibited a slow vibratory 
movement of the tail. But I have found no more satisfactory 
evidence of the process of spermatogenesis. In all the cases 
the number of spermatozoa was not large, and it is difficult to 
believe that fertilisation is effected by such a meagre produc- 
tion of spermatozoa as was seen in the specimens I have 
mentioned. In no case have I discovered any trace of sperma- 
togenesis in a specimen which was completely masculine. 

In all specimens of Myxine with well-developed ovarian 
eggs which I have examined, with one exception, no testicular 
portion was present in the sexual organ. The only conclusion 
I can draw is that in the young state the females are nearly, 
but not quite always hermaphrodite, and that the testicular 
portion normally disappears as the eggs become more mature. 
It seems probable that fertilization is normally effected by 
hermaphrodites, since true males are so rare. 

In the exceptional instance above mentioned, I found, to- 
gether with large ovarian eggs in the anterior part of the 
sexual organ, the posterior portion, two inches in length, 
much thicker at the free border than either the true testis or 
the male part of the immature hermaphrodites. But in this 
portion, when examined by means of prepared and stained 
sections, I found, instead of the structure already described in 
the testis, a general cellular structure in which no definite 


74 J. 1. CUNNINGHAM. 


capsules were visible. There was a stroma of connective tissue 
in which were large irregular spaces containing nucleated 
cells, and I concluded that this was an abnormal case in 
which cellular hypertrophy of the testicular portion had taken 
place. It was a case probably in which the testicular portion 
present normally in the young state, had, instead of being 
absorbed, undergone a kind of cellular degeneration accom- 
panied by hypertrophy. 


SUMMARY. 


The firm membrane enclosing the ripe deposited ovum of 
Myxine is a primary egg membrane produced within the 
follicle. 

The polar threads are processes from this membrane. 

The membrane is single and not differentiated into layers : 
it possesses minute pores perpendicular to its surface, and is 
therefore a zona radiata. 

The zona radiata in Myxine is homologous with the single 
or double zona radiata of Teleosteans and of Petromyzon. 

The membrane at one pole of the ovum, that at which the 
protoplasmic germinal disc is situated, is perforated by a 
micropyle. 

The micropyle is produced by a process from the follicular 
epithelium. 

The immature testis in Myxine consists of a thickened 
border of the mesorchium containing more or less spherical 
capsules, which are filled with hyaline nucleated spermatoblasts. 

A large proportion of immature Myxine are hermaphro- 
dite, the posterior portion of the reproductive organ containing 
testicular capsules which have the same structure as those 
found in the male. 

Spermatozoa have been found in the testicular portion of 
the hermaphrodite organ, but not in the males. 


REPRODUCTIVE ELEMENTS IN MYXINE GLUTINOSA. 75 


CaTALOGUE OF LITERATURE CONCERNING THE REPRODUCTIVE 
OrGaANs oF Myxine. 


1845. Jonannes Miuier.—‘ Untersuchungen wtber die Hingeweide der 
Fische,’ ‘Schluss der Vergleichenden Anatomie der Myxinoiden,’ 
Berlin, 1845, pp. 4 and 5, Taf. i, Fig. 1, Taf. ii, Figs. 3, 4, 5, 6, 7, 8. 

1859. Dr. Atten Tomson, Professor of Anatomy in the University of 
Glasgow —Art. “Ovum,” ‘Todd’s Cyclopedia of Anat. and Phys.,’ 
vol. v, 1859, two figures in woodcut. 

1863. Pror. SreenstRuP.—“ Oversigt. Dansk. Vidensk. Selsk. Forhandl.” 
Kjbenhavn, 1863, p. 233, woodcuts. 

1875. Rospert Cottert.—‘ Norges Fiske,’ published as Supplement to the 
‘ Vidensk. Selsk. Forh.’ of 1874, Christiania, 1875. 


DESCRIPTION OF PLATES VI ann VII, 


Illustrating Mr. J. T. Cunningham’s Paper on the ‘ Repro- 
ductive Elements in Myxine glutinosa, L. 


Fie. 1.—Specimen of the mature deposited ovum of Myxine in the Ana- 
tomical Museum of the University of Edinburgh. Nat. size. 

Fig. 1, a.—Oue of the polar threads of the same specimen. Magnified 30 
diam. 

Fie. 2.—Section through protoplasmic pole of ovarian egg of Myxine. 
Length of the entire ovum, 16 mm. Plane of the section passes through 
longer axis of the ovum, and is perpendicular to the mesoarium. a. Sheath of 
vascular connective tissue. 46. Follicular epithelium. c. The vitelline mem- 
brane. d. The protoplasmic dise. ep. The process of the follicular epithelium 
which passes into the micropyle. me. The mesoarium. Magnified 50 diam. 


Fig. 3.—The micropyle in section: from an ovum of the same ovary as 
Fig. 2. c,d, as in preceding figure. ep. point to the hemispherical 
termination of the cellular process. Magnified 280 diam. 

Fic. 4.—Sectiou through protoplasmic pole of ovarian egg 20 mm, in 
length. Plane of the section as in Fig. 2. a, 6, ¢, d. asin Fig. 2. mi. The 
micropyle, with contained cellular thread. P. Pits in the follicular epithelium, 
in which the polar processes are contained. yp. The polar processes of tle 


76 J. T. CUNNINGHAM. 


vitelline membrane, corresponding to the pits. g.v. The germinal vesicle. 
Magnified 50 diam. 

Fie. 4¢.—Follicular epithelium and vitelline membrane, as seen in a section 
of same series as Fig. 4, to show the canals in the vitelline membrane. Mag- 
nified 350 diam. 

Fic. 5.—Yolk-elements from ovarian egg in fresh condition. a. Vitelline 
dises contained in spherical capsules. 8. Similar discs free. y. Spherical 
bodies, probably composed of fat. 

Fic. 6.—Portion of ovary of young Myxine 6 inches long, stained with 
borax-carmine. .. The free, y. the attached border. Magnified 100 diam. 

Fic. 7.—Stained preparation from testis of immature male Myxine. a. 
Capsules full of nucleated cells (spermatoblasts). me. Mesorchium. J/. 
Blood-vessels. Magnified 50 diam. 


Fic. 8.—Section of testis from same specimen as Fig. 7. The plane of the 
section is perpendicular to the thickened border of the testis. ca. Capsules. 
me. Mesorchium. co. Connective tissue. Magnified 70 diam. 


Fie. 9.—Spermatoblasts of immature male Myxine, as seen in the fresh 
state after escape from the ruptured testicular capsules. Magnified 280 
diam. 


Fic. 10.—Section of testicular portion of reproductive organ of immature 
hermaphrodite Myxine. ca. and co. as in Fig. 8. Magnified 100 diam. 

Fic. 11.—Ovarian ovum of Myxine contained in its follicle, having a pro- 
jection at each pole caused by the development of the polar processes of the 
vitelline membrane, Natural size. 

Fie. 12.—Section through the protoplasmic pole of an ovum, similar to 
that shown in Fig. 11. a, 4, ¢, d,g. v., p., as in Fig. 4. Magnified 35 diam. 

Fic. 13.—Section through protoplasmic pole of young ovarian ovum of 
Myxine. Length of ovum, 1] mm. a, 4, ¢, d, g. v.,as in Fig. 12. Magnified 
50 diam. 

Fie. 13 a.—Follicular epithelium and neighbouring parts from same section 
as Fig. 13. a, 4, d, as before. Magnified 200 diam. 

Fic. 14.—Spermatozoa, and stages of spermatogenesis, from testicular por- 
tion of reproductive organ in a hermaphrodite Myxine. Magnified 250 diam. 


STUDIES ON EARTHWORMS. rey 


Studies on Earthworms. No. II. 
By 


William Blaxland Benham, B.Sc., 
Demonstrator in the Zoological Laboratory of University College, London. 


With Plates VIII and IX. 


In continuation of Part II of my previous paper on this 
subject,! I shall describe three new genera belonging to 
Perrier’s group of Intraclitelliani. Although Beddard has 
shown? that the grouping of Earthworms according to the rela- 
tive position of the male pore and the clitellum, does not hold 
good even within the limits of one genus, yet it isa convenient 
classification, and, [ think, may be used at present till a more 
satisfactory system is introduced. The genus Acanthodrilus 
to which I refer is post-clitellian in most of its species, but 
Beddard describes A. nove-zelandiz and other species as 
having the male pore situated in the clitellum. 

I have received all the worms which I am about to describe 
from Prof. Ray Lankester, who has for many years taken every 
opportunity of procuring exotic specimens. The new genera 
show interesting combinations in one worm of characters which 
have been regarded as of generic value for different worms: 
thus Urobenus possesses intestinal glands known hitherto 
only in Uroche ta, and also ceca similar to those which are 
known only in Pericheta, Again Trigaster combines an 
alimentary tract somewhat like that of Digaster, with the 
four prostates and male pores of Acanthodrilus. 

Since writing my previous paper on Microcheta I have 


1 This Journal, February, 1886, p. 213. 
* * Proc. Zool. Soc.,’ 1885, p. 810. 


78 WILLIAM BLAXLAND BENHAM. 


received some more Earthworms from Professor Lankester 
which belong to this genus, but differ in several points from the 
species there described: to the new form I have given the specific 
name Beddardi, as it was he who gave the name of the 
genus to a worm described by Rapp! as Lumbricus micro- 
chetus. These worms were none of them in a good condition 
for histological study, so that many gaps will appear in the 
description of their minute structures. 


Microcheta Beddardi, nov. sp. 


These worms were sent to Professor Lankester from Natal 
by Mrs. Saunders. In a preserved condition they are dark 
coloured, with a slightly greenish tinge and with a brown clitel- 
lum; they are rather longer but narrower than a large-sized 
Lumbricus agricola, being 14 or 15 inches in length, and 
about 4+ inch in breadth ; the number of somites, 365, is easily 
counted owing to the soft and extended condition of the worms. 
They are nearly cylindrical, slightly wider anteriorly than pos- 
teriorly, with an obtuse aural region. 

The prostomium is represented by a portion separated from 
somite 1 by a shallow groove, and with its anterior free edge 
crenated (figs. 1 and 2). : 

In the clitellum the intersegmental grooves are less con- 
spicuous than elsewhere, while the nephridiopores are much 
more evident. The extent of the clitellum varies slightly in 
the six specimens in my possession, but usually cccupies somites 
x to xx1I, and in one case somite xx11isincluded. (M. Rappi 
has a clitellum extending through somites x11I to xxv.) 

The somites 111 to vil inclusive are biannulated, but the 
remaining somites of the worm are simple. 

The sete and nephridiopores have the same arrangement 
as in M. Rappi, Bedd., but the relation between them is more 
clearly seen than in the previous species, as the sete are extruded 
from the body, and the nephridiopores are now seen to be in a 
line with the lower setz of the lateral couples. 

There are no dorsal pores. 

1 «Wurtemb, Naturwiss. Jahresb.,’ vol, iv, 1848. 


STUDIES ON EARTHWORMS. 79 


I could find no male pores, but, curiously enough, the 
pores of the oviduct are fairly evident. These are placed in 
the groove between somites x11 and x111, oue on each side of 
the middle line. By means of a series of transverse sections I 
found they were the external openings of the funnel-shaped 
organ described and figured by me (“‘ Studies on Earthworms,” 
No. I, Pl. XVI, fig. 7) for M. Rappi, of the function of which 
I was then doubtful. I believe now that this organ is the ovi- 
duct, and that these pores are their apertures (PI. VIII, fig, 3, e). 

The pores of the spermathece differ in position from those 
of the former species. They lie ina line with the nephridiopores, 
usually one on each side, on the anterior edges of somites x1 
and x11; these pores I could see by the aid of a lens, after I had 
found the spermathecee (fig. 3, 6). 

The Internal Anatomy.—The general anatomy agrees 
with that of M. Rappi, but one or two noteworthy differences 
are presented. 

In the alimentary tract the only difference is in the shape 
and extent of the intestinal glands. In M. Rappi, the 
gland on each side has the appearance of a rounded swelling 
on the side of the intestine, which it partly covers dorsally, 
and into the lumen of which the cavity of the gland opens by 
a wide aperture. The gland occupies the whole length of 
somite 1x, and only a small portion of it lies in the preceding 
somite (fig. 9). But in this new species the gland is bilobed, 
being nipped, as it were, by the septum, which divides it into 
two very nearly equal parts ; the larger lobe lies in somite v111, 
the smaller lobe in somite rx. Moreover the gland is greatly 
constricted off from the intestine (fig. 8) so that the commu- 
nication between the two cavities is reduced to a small aperture. 

The genital organs present several important differences. 
Instead of two pairs of seminal reservoirs and of ciliated 
rosettes, there is only one pair of each in this new species. 
The seminal reservoirs lie in somite x, and the ciliated rosettes 
in somite 1x. Inthe three specimens opened the reservoirs 
are small, looser in structure, and more irregular than in M. 
Rappi; in one case only is the ciliated rosette not enclosed in 


80 WILLIAM BLAXLAND BENHAM. 


the reservoir. I think, therefore, that the worms are not 
quite genitally mature. 

The ovaries have the same position as before,—on the 
posterior face of the anterior septum of somite x11. On the 
opposite face of this septum, and lying therefore in the pre- 
ceding somite, is the funnel of the oviduct; this is the organ 
marked “ #” in the figures illustrating my paper on M. Rappi.! 

It seems at first sight somewhat peculiar that this should be 
the case ; the same sort of arrangement has, however, been men- 
tioned by Beddard for Megascolex (Pleurocheta).* And 
in many sections an appearance is presented which, I think, 
allows no doubt that this interpretation is correct. 

The oviduct has not such a folded appearance, nor is the 
edge fringed by narrow lobes as in M. Rappi. By following 
the duct through a continuous series of transverse sections I 
was able to trace it from its external pore up to its internal 
expanded funnel, which is closely attached to the septum 
xlI—x111, which is itself perforated (fig. 10). The appearance 
represented in the figure was repeated in several sections; the 
ovary is seen on one side of the septum lying in somite x111, 
and the edge of funnel, formed of columnar cells (doubtless 
ciliated, though the sections do not show this) on the other 
side of the septum in somite x11. There is a perforation in the 
septum, or rather the septum is here incomplete, allowing ova 
to pass through it into the duct. 

I was unable to find the structure which is marked “‘y” in 
my previous paper. Beddard has noticed a structure in a 
similar position in Ac. dissimilis and other species® re- 
peated in the two somites in front of the true ovary, and he 
suggests that they may be remnants of two pairs of ovaries; 
indeed in one specimen one of these structures contained ova. 

The spermathece show a remarkable and interesting 
difference from the arrangement seen in M. Rappi. In that 
species they consist of four rows of from one to four small 

1 This Journal, February, 1886, Pl. XV, fig. 4; Pl. XVI, figs. 7 and 14. 


2 «Trans. Royal Soc. Edinb.,’ xxx, 1883, p, 481. 
3 ¢Proc, Zool. Soc.,’ 1885, p. 827. 


STUDIES ON EARTHWORMS. 81 


horse-shoe shaped bodies in the anterior region of somites x11, 
XI11, xIv, xv. In the present species, as a rule, only four 
spermathece are present ; a pair in each of the somites x1 and 
x11, and each is an elongated pyriform sac (fig. 6) ; but in one 
specimen an asymmetrical condition obtains, for here there 
are, on one side, two pyriform sacs in each of the somites x1, 
x11, while on the other side there is only one spermatheca in 
each somite, one of which is crozier shaped (fig. 7). The 
wall of the spermatheca is thick and muscular ; its internal 
lining consists of tall columnar cells. In these two species 
then we have a difference corresponding to that shown in 
Pericheta aspergillum, EH. P.,! where there are numerous 
small sacs (which, however, surround a larger one), and in P. 
elongata, which has a simple large sac. It may be that as 
the worm becomes more mature a larger number of sperma- 
thecz will appear, for these specimens are apparently not quite 
mature. If this were so it would certainly militate against the 
theory of the homology between the spermathece and a portion 
of the nephridium. 

The nephridia closely resemble those of M. Rappi, but 
their tubular portion is less developed, except in the case of the 
first pair, where the coiled portion has a glandular appearance, 
as in so many Harthworms, and may perhaps serve in some 
way as a salivary gland though it has the usual nephridial 
structure and an external aperture (see Darwin, ‘ Vegetable 
Mould and Harthworms,’ p. 42). The external pore of this pair 
is situated, not on the anterior edge of somite 11, to which it 
belongs, but on a slight prominence in somite 1 (fig. 2). 

In the vascular system of M. Rappi, the dorsal vessel is 
doubled in somites Iv, V, VI, VII, VIII, in the last of which the 
walls are much thickened, so as to give a heart-shaped appear- 
ance to the vessel. In M. Beddardi, there is the same con- 
dition, but limited to somites vi, vi1, viii. Beddard has noticed 
a similar difference in the extent of doubling of the dorsal vessel 
in specimens of Ac. nove-zelandiz,’ where usually the 

1 ¢Nouy. Arch. de Mus. d’hist. nat. de Paris,’ viii, 1872. 
2 «Proc. Zool. Soc.,’ 1885, p. 821. 
VOL, XXVII, PART 1,—NEW SER. F 


82 WILLIAM BLAXLAND BENHAM. 


vessel is doubled throughout the body, except at its passage 


through the septa, but in one specimen it was a single tube 
throughout. 


Urobenus brasiliensis, nov. gen. et sp. 


I have named this worm after my friend Dr. A. G. Bourne, 
of the Presidency College, Madras, the name being formed by 
transliteration. Its specific name refers to its habitat. It came, 
together with a species of Titanus, from Pedza acu, and was 
given to Prof. Lankester by Prof. Edouard van Beneden of Liége. 

External Characters.—The worm is 6 inches in length, 
and about 4rd of an inch in breadth ; it consists of ninety-two 
somites, which are of nearly equal size throughout the body. 
The worm is cylindrical, and tapers gradually anteriorly, where 
it ends in a well-marked though narrow prostomium (PI. 
VIII, fig. 11) which is embedded in the buccal somite only 
to a slight extent. The worm was soft and not much con- 
tracted, so that the somites have not the annulated appearance 
so frequently noticeable in Harthworms. 

The clitellum is fairly well developed and does not extend 
completely around the body, in this respect resembling Lum- 
bricus, Microcheta and others. The latero-ventral edge is 
placed between the ventral and lateral rows of sete; the cli- 
tellum extends through somites xiv to xxv (PI. VIII, fig. 12). 
The sets are arranged in four couples in each somite—a 
ventral couple on each side, and a more lateral couple on each 
side (figs. 12 and 20); this condition holds throughout the 
body. The sete themselves have the ordinary shape of an 
elongated /; the free extremity, however, is slightly more 
hooked than in Lumbricus; there is the usual thickening 
about midway along the setz (fig 138, a). The sete from the 
ventral series of the clitellum have their embedded portion more 
distinctly curved than the ordinary sete (fig. 13, a: The length 
of the sete is 65 mm. 

The nephridiopores are placed in the auterior region of 


the somites in a line with the outermost setz of the lateral 
couples (fig. 12, c). 


STUDIES ON EARTHWORMS. 83 


I was unable to see either the pores of the sperm-ducts or 
those of the spermathecz, but on dissection I found that the 
sperm-duct opened to the exterior in the anterior region of 
somite xx slightly dorsad of the ventral couple of setz on each 
side (fig. 12, d). 

The spermathecz open close to the nephridiopores in the 
anterior region of somites VII, VIII, rx, on each side. 

Internal Anatomy—All the septa are thin and easily 
torn ; the nephridia are delicate, but the spermathece are very 
prominent (fig. 14). 

The alimentary canal (fig. 14) consists of six well-marked 
regions. The thin-walled buccal region occupies two somites, 
and leads into the pharynx, which extends very nearly up to 
the end of somite v. There is nothing specially noticeable 
about these parts; the muscular wall of the pharynx does not 
extend so far backwards on the ventral as it does on the 
dorsal surface. This seems a more or less usual condition m 
Earthworms. The cesophagus, which follows, is somewhat sac- 
culated and is bent forwards upon itself in somite v1, and after 
another bend back again, enlarges in somite vir to form a 
proventriculus, such as is found in Lumbricus, but which 
is not so well marked in other Earthworms. Owing to the in- 
fundibulate septa, the cesophagus appears to extend through 
more somites than it actually does, but by carefully tracing 
the nephridia (for the septa are very thin and easily broken 
and therefore not reliable for the purpose) it is found that the 
gizzard (e) occupies somite vi11. This has the ordinary 
structure with the chitinous lining within and the nacreous 
muscular appearance without. Behind the gizzard commences 
the tubular intestine (g), which is continued through somites 
1x to xv; this is narrower than the cesophagus and quite 
straight ; it is hidden by the seminal reservoirs in the somites 
in which these structures lie. In each of the somites 1x, x, and 
XI is a pair of intestinal glands (fig. 14, f), similar im shape 
to those figured by Perrier for his genus Urocheta,’ and 
called by him “glandes de Morren.” Lach of these six 


1 < Arch. de Zool. Experim. et gener.,’ iii, 1874. 


84. WE fee BLAXLAND BENHAM. 


glands is a reddish, ovoid body opening into the intestine by 
means of a short, narrow stalk, and constricted near its free ex- 
tremity in such a way that this portion has the appearance of 
a short cone, inverted on the end of the ovoid portion. 

The structure of these glands resembles mainly that of the 
calciferous cesophageal glands of Lumbricus; they appear in 
transverse sections to be made up of a number of tubules cut 
across, lined by an epithelium (the nature of which could not 
satisfactorily be made out, owing to the condition of the worm), 
resting upon a basement membrane (PI. IX, fig. 43). Between 
and around the tubules are large irregular blood spaces, com- 
municating with an abundant vascular network on the surface 
of the gland. In the lumina of the tubules I observed oily- 
looking globules (a) of various sizes. Masses of these were 
found in the alimentary canal itself in the region of these 
glands. These globules appear to be the secretion of these 
glands, and from analogy with what is known in Lumbricus 
and Microchzta one may consider them as carbonate of 
lime, though I did not use any tests in this case. Similar 
glands occur also in Acanthodrilus; and Beddard, in his de- 
scription of them,! says that they are made up of lamelle of 
connective tissue carrying blood-vessels, which dip into the 
lumen of the gland. He does not say whether these lamelle 
anastomose, so as to give the appearance of tubules, and from his 
description it would appear that in that genus they do not do so. 

In somite xvi the intestine suddenly changes its character ; 
it becomes about three times its previous size, and is deeply 
constricted as it passes through the septa. These constrictions 
of the pouched intestine (figs. 14, 16) are not merely 
caused by the septa, as in the sacculated region, but are due 
to a series of ten pairs of short and wide-mouthed pouches or 
ceeca from the axial lumen of the intestine. There is a thicken- 
ing (? glandular) along the vertical wall between two consecu- 
tive ceca (fig. 16, ¢). This pouched region extends through 
somites XVI to XXv. 

Behind the last pouch is a rather deeper constriction, after 

1 «Proc, Zool. Soc.’ 


STUDIES ON HARTHWORMS. 85 


which the canal gradually widens out again to form the typhlo- 
solar region or sacculated intestine (fig. 14,7). This 
commences in somite xxvi, and extends for a considerable dis- 
tance backwards. The wall is much thinner than in the pre- 
ceding region, and it is only slightly constricted as it passes 
through the septa. The typhlosole commences and ends con- 
currently with this division of the intestine. In somite xxv1 
there are seen two small elongated cxca, the end of one appear- 
ing on each side of the intestine (fig. 14, k). These spring 
close together from the ventral wall of the intestine, near the 
middle line, just at the junction of the pouched intestine with 
the sacculated region, and pass outwards upwards (fig. 15, 0). 
They resemble the characteristic intestinal ceca found in 
Pericheta, being narrow, cylindrical, with the free end 
rounded. This is the first time, I believe, that these ceca 
have been found in Intraclitellian worms, or, indeed, in other 
genera than Pericheta. 

It is interesting to find a worm combining the two sets of 
intestinal outgrowths—the “glandes de Morren” found in 
Urocheta and these intestinal ceca of Pericheta. It 
would be interesting to ascertain the structure of these out- 
growths, in order to compare them with that of the already 
known outgrowths of the alimentary tract of various Earth- 
worms; but my specimens are not well enough preserved to 
show their structure satisfactorily. The typhlosole is a 
simple dependent fold, containing the usual blood-vessel, and is 
not a cylindrical valve, as in Lumbricus, Microcheta, &e. 

The Genital Organs.—Of these I was able to find only 
some of the male organs (not the testes) and the spermathece ; 
no ovaries nor oviducts were distinguishable. The seminal 
reservoirs are four in number, one pair lying in somite xII 
and x11, and the second pair in somite xiv (fig. 17, 9); they 
have a looser structure than those of Lumbricus, and a much 
more irregular outline; they are not so intimately connected 
with the septa as in the latter form, and so are easily displaced 
and broken. 

The ciliated rosettes are, similarly, four in number, are 


86 WILLIAM BLAXLAND BENHAM. 


comparatively large, and lie quite freely in their somites. One 
pair lies in somite x11, the other pair in somite x11 (fig. 17, 
h, j). Apparently, therefore, the posterior ciliated rosette on 
each side lies in front of its seminal reservoir. Perrier has 
described a similar condition in Pontodrilus, and Beddard 
for Acanthodrilus dissimilis, but in these cases the first 
rosette is in front of the seminal reservoir. It seems to me 
that, at any rate in Urobenus, this condition is due to the 
immaturity of the worm; for in Lumbricus agricola the 
seminal reservoirs appear at first as outgrowths from the septa 
anteriorly and posteriorly in the case of the first pair, or pos- 
teriorly only in the case of the second pair, without any con- 
nection between those of the two sides in the somite in which 
the ciliated rosettes lie, so that if the worm be dissected in an 
immature condition it would present somewhat the appearance 
seen in Urobenus. 

Similarly, the freedom of the ciliated rosettes seems to have 
the same explanation, since these also are free in Lumbricus 
in the above-mentioned condition, but, as is well known, become, 
in the fully mature worm, completely enclosed in the seminal 
reservoirs. I have mentioned the same condition in Micro- 
cheta Beddardi. 

A sperm-duct passes from each of the ciliated rosettes to 
the body wall; here it turns backwards, and the two sperm- 
ducts on each side unite in somite x11, and the common duct 
thus formed runs along the body wall to somite xx, where it 
opens to the exterior in the anterior region of the somite, 
between the ventral and lateral couples of setz. 

There are no accessory glands on the sperm-duct, nor copu- 
latory papillz on the exterior. 

The only female organs which I could find are the three 
pairs of spermathece (fig. 17,7). Each spermatheca is a 
white, elongated, pyriform sac, the free extremity of which is 
rounded, while the opposite extremity gradually narrows to 
form a delicate duct; it is bent upon itself once or twice in its 
course, and opens to the exterior in the anterior region of the 
somite, quite close to, but distinctly separated from, the 


STUDIES ON EARTHWORMS. 87 


nephridiopore. These spermathece are placed in the somites 
VII, VIII, and 1x. 

The nephridia occur in every somite behind the second 
(fig. 17, n, n’). Those of the seven anterior somites differ 
slightly from those in the rest of the somites. An ordinary 
nephridium, taken from a somite behind somite 1x, consists of 
a delicate, loosely-coiled, short tubule, containing two, or in 
some parts three, parallel lumina; the lumen communicates, on 
the one hand, with the coelom by means of the funnel, and on 
the other with a vesicular diverticulum, which opens to the ex- 
terior (fig. 18). This vesicle is a long, thin-walled sac, the free 
blind extremity of which, directed dorsally, is rounded ; while 
the narrow duct, after receiving the tubule of the nephridium, 
dips into the body wall and opens to the exterior by the ne- 
phridiopore, placed in a line with the lateral setze (fig. 20, 0). 
In the preserved condition each of these vesicles contained, at 
their blind end, a mass of white granular substance, rendering 
the vesicles very conspicuous on opening the worm. ‘The 
structure of the tubule and the shape of the funnel (fig. 19) 
closely resemble those of Lumbricus. 

The nephridia behind somite xx are smaller, and the tubules 
even less coiled than in the one just described. 

The nephridia in somites 111 to 1x present a somewhat dif- 
ferent arrangement of their parts (fig. 17 n'—n’). The tubule 
is less developed than in the posterior nephridia, and instead 
of opening into the neck of the vesicle near the external pore 
it enters the enlarged portion of the vesicle near its blind end. 
These seven nephridia have very long narrow vesicles, since 
the tubular portion is carried far back, and lies (as shown in 
fig. 14,2) alongside of, and partly above, the cesophagus and 
gizzard. A similar difference between the most anterior and 
the following nephridia is seen in the case of Microcheta 
Rappi. 

Pyriform Sacs.—In each of the somites behind the ninth, 
i. e. behind the last pair of spermathecz, there is a pair of 
small pyriform sacs (fig. 17, p) placed between the nerve-cord 
and the ventral sete. Each of these has its enlarged free end 


88 WILLIAM BLAXLAND BENHAM. 


filled with a white granular substance similar to that found in 
the nephridial vesicles ; this rounded end is directed outwards, 
whilst the narrow duct passes at first inwards, then bends back- 
wards and pierces the body wall. By means of transverse 
sections the external aperture of these organs is found to be 
situated between the nerve-cord and the ventral couple of 
sete on each side (fig. 20, 6). They were not sufficiently well 
preserved to make out any details of their structure, but, so far 
as I could make out, their general structure is as follows :— 
A delicate membrane surrounds the sac (fig. 21, @) and forms its 
wall, within which is a granular substance (0) which was stained 
only slightly by borax-carmine. In the centre of this substance 
is an irregular lumen (d) lined by short columnar cells (c) 
whose nuclei stained deeply ; whether these are ciliated or not 
I was unable to determine. 

The diagram (fig. 20) shows the position in relation to the 
sete of this pyriform sac and its pore on one side, and the 
nephridiopore on the other side. 

These pyriform sacs seem quite similar in shape and position 
to those found only in the posterior region of the body in 
Urocheta; what their function may be seems quite impos- 
sible to say at present. 

The vascular system was not followed to any great ex- 
tent. The dorsal trunk (fig. 14, p) is ampullate posteriorly and 
becomes wider in the region of the pouched intestine ; passing 
forwards this character becomes more marked in somites xtII 
and forwards. In the intestinal region a pair of vessels is 
given off in each somite to the intestine. In each of the 
somites x11 and x111 is a pair of moniliform lateral hearts, 
but anteriorly to these somites these hearts are very thin and no 
longer moniliform ; they pass from the dorsal to the ventral 
trunk. Beside the dorsal and ventral trunks both a typhlosolar 
and a subneural trunk are present. 

The nervous system exhibits no essential difference from 
that of Lumbricus. The cerebral ganglia are distinct and 
placed in somite 111. 

Thus Urobenus resembles Urocheta in two remarkable 


STUDIES ON EARTHWORMS. 89 


points viz. in the possession of similar intestinal glands, and 
of pyriform sacs. These led me at first to think that I had to 
deal with an Urocheta, but the various points of difference 
—e. g. the sete, which in Perrier’s form are notched at the 
free extremity, the nephridia, the character of the seminal 
reservoirs, which are elongated and tongue shaped in Uro- 
cheta, the presence of a distinct prostomium, which is not 
the case in Perrier’s worm, and the general character of the 
alimentary tract,—all these lead me to form a new genus for the 
worm under consideration. 


Diacheta Thomasii, nov. gen. et. sp. 


In a bottle containing several small worms from St. Thomas 
(West Indies) some were very noticeable on account of their 
stoutness and of the arrangemeut of the sete ; this latter pecu- 
liarity suggested to me the name Diacheta, since the sete are 
far removed from each other as in Plutellus and Ac. mul- 
tiporus, and moreover alternate from somite to somite, as in 
the posterior region of Urocheta, and in Schmarda’s genus 
Pontoscolex. 

External Anatomy.—The worm is cylindrical with very 
obtuse rounded extremities and is greatly swollen anteriorly, 
instead of narrowing towards the prostomium (Pl. VIII, fig. 
22). Its length is about 8 inches, and its breadth about 3rd 
inch, but the worm was very much contracted so that these 
measurements will not represent its size when living. The 
body consists of 335 somites, of which those behind the clitellum 
are very short, whilst in the preclitellar region they are of 
much greater length ; some of these anterior ones are traversed 
by two grooves with a slight ridge between them, on which 
the sete are placed (fig. 22). 

The prostomium is absent, and the anterior border of the 
buccal somite is not much narrower than the clitellum. It is 
marked by numerous longitudinal grooves extending back- 
wards for about half the length of the somite. 

The clitellum extends through somites xx to xxxi11, and 
completely surrounds the body (fig. 24), asin Pericheta, 


90 WILLIAM BLAXLAND BENHAM. 


Digaster, &c. The intersegmental grooves in this region are 
very deep and wide, and the sete, except those of the ventral 
row, are not very evident. 

Behind the clitellum the body of the worm becomes much 
narrower and retains this diameter to the end of the body. 
The five somites immediately in front of the clitellum are very 
short, and the diameter of the worm is here much smaller, but 
in front of these it increases and retains the size of the clitellum 
up to somite 11. Somites x, xI, XII, XIII are very conspicuous, 
and are not annulated as are those immediately anterior to them. 

The setz are eight in each somite and are not in couples, 
but they are arranged in such a way as to form fourteen rows 
along the body. In describing this arrangement it will be 
convenient to adopt M. Perrier’s plan which he used in the 
case of Plutellus,! of numbering the sete on each side. The 
most ventral seta on each side will be called “ seta 1,” whilst 
the most dorsal will be called “seta 7.” The series of “ seta 
1” form a continuous line on each side of the ventral mid-line 
throughout the body, but the remaining three sete (“ 2, 4, 6,”) 
on each side of one somite alternate with the three sete (“ 3, 
5, 7”) of the somite in front and of that behind (fig. 23). In 
this way we get the fourteen rows of sete. 

As will be best seen from the figures (23 and 24) the sete 
of the two sides of one somite are themselves not symmetrical. 
The sete 1 and 2 of one somite, or 1 and 3 of the next somite, 
correspond to the ventral couple of Lum bricus, &c., and sete 4 
and 6, or 5 and 7 to the lateral couple of the same Earthworm. 
The sete are very small, being only about °55 mm. in length ; 
they have the usual shape, but the distal and proximal regions 
differ in length; the distal (free) region is much shorter than 
the proximal (embedded) region, and its extremity is more 
strongly curved than in the ordinary sete of Lumbricus 
(fig. 25). 

External Apertures.—I could find no apertures what- 
ever, except the terminal mouth and anus. But by dissec- 
tion I find that the nephridia open to the exterior by 


1 « Arch. de Zool. Exper. et gen.,’ t. ii, 1873, p. 245. 


STUDIES ON EARTHWORMS. 91 


pores place slightly ventrad of and anterior to the line of 
“seta 4” (fig. 23, a), i. e. the lower seta of the lateral couple, 
as in Urocheta, Microcheta, &c. These pores do not 
follow the setz in their alternation, but form a continuous 
line ; the two male pores were also by dissection found to be 
situated very far back, viz. in somite xx11. Each is placed a 
little dorsad of and anterior to the line of “ seta 3,” which is 
present on one side of this somite, but absent on the other side 
(fig. 24, 6). The spermathecz open at the posterior edges of 
somites vi, vil, and vii1, in the same line with the nephridio- 
pores (fig. 23, c). 

Internal Anatomy.—There are five strong infundibuli- 
form septa behind somites vi to x, hiding the cesophagus and 
gizzard, such as are seen in Titanus, Anteus, Urocheta, 
&c.; the next ten septa behind these are much thinner, and 
behind somite xx they are exceedingly delicate. The elongated 
seminal reservoirs are very conspicuous (fig. 26). 

The alimentary tract presents no remarkable points. The 
cesophagus occupies somite v and part of somite vi. The 
gizzard occupies the rest of somite vi. Then follows the tubular 
intestine, which is very narrow; it passes through the five 
strong septa, and in somite x1 becomes enlarged; its walls 
become thin, and are constricted as the tube passes through 
the septa; this is the sacculated or typhlosolar intestine. The 
typhlosole is a simple laterally-compressed fold, carrying the 
usual blood-vessel. 

There are no glands nor ceca opening into the cesophagus 
or intestine. 

The only genital organs which I was able to find are a 
pair of seminal reservoirs with their rosettes and ducts, and 
three pairs of spermathece. : 

The seminal reservoirs consist of a pair of very long 
tongue-shaped sacs (as in Titanus and Urocheta), starting 
from somite x11, and reaching as far backwards as somite 
XxxvilI (fig. 26, g). This is a most exceptional length for the 
seminal reservoir, for in Urocheta the elongated sacs only 
occupy three somites, and in Titanus fourteen somites. As 


92 WILLIAM BLAXLAND BENHAM. 


they pass through the septa the sacs are greatly constricted ; 
so much so in one specimen that the reservoir on one side is 
cut in two, as not unfrequently happens in Lumbricus. 

In another specimen the reservoirs are present, but are empty, 
and are not of so great an extent as in the one figured. 

The ciliated rosettes (f) lie in somite x1, one on each 
side of the intestine ; they are not enclosed in the reservoirs 
in front of which they are placed. This arrangement is very 
similar to the condition found in Urocheta. 

The single sperm-duct on each side is very delicate; it 
passes backwards along the body wall to its aperture in 
somite xx11, without having any accessory glands in connection 
with it. 

I could find no testes, nor ovaries nor oviducts. The sper- 
mathece are six in number (d), a pair lying in each of the 
somites VI, VII, vil1, and having their apertures in the posterior 
region of these somites. ach is a simple elongated pyriform 
sac (fig. 29), bent twice upon itself. 

The nephridia occur in each somite behind the second. 
Each consists of a coiled tubule (fig. 27), which is of much 
greater extent than in Urobenus, and contans parallel lumina 
within it, having the usual structure. The tubule opens into 
the ccelom by means of a funnel similar to that of Urobenus; 
the proximal end of the tubule alters its character before pass- 
ing to the exterior, the lumen becoming wider and the walls 
muscular, as in Lumbricus; but here this vesicular region 
is more highly developed than in that form, which, however, it 
resembles in that the vesicle is a continuation of the tubule, 
and not a diverticulum from it, asin Urobenus and Micro- 
cheta. The nephridiopores have already been mentioned as 
being in a line with seta 4. 

As is so frequently the case, the most anterior nephridium 
is greatly modified. Resting against the hinder part of the 
pharynx in somites rv and v is a large, compact, glandular- 
looking organ (fig. 26, c), the slightly-coiled duct of which opens 
to the exterior on the anterior edge of somite 111. The glan- 
dular-looking portion of this modified nephridium is made up 


STUDIES ON EARTHWORMS. 93 


of a compact mass of tubules (fig. 28), or rather of a single 
very greatly folded tubule (a), the folds of which are pressed 
close against one another, and contain parallel lumina, which 
in some regions appear to be ciliated. From the outer side 
of this mass arises the vesicular portion or duct (4), which is 
irregular in diameter, bends upon itself three or four times, and 
then passes forwards as a narrow, straight duct, lying alongside 
the pharynx, to its external pore. The structure of this ne- 
phridium is quite similar to the unmodified posterior ones. In 
Urocheta Perrier describes “ glandes 4 mucosité,” which 
have the same position, and Beddard describes a modified 
nephridium in Ac. multiporus, which opens, not to the 
exterior, but into the buccal cavity. It seems probable that 
all these glandular bodies in the anterior region of the body 
may be modified nephridia. 

The vascular system consists of the usual longitudinal 
vessels, viz. dorsal, ventral, and typhosolar trunks, together 
with a series of lateral hearts. I could see no lateral longitu- 
dinal (“intestino-tegumentary”’) trunks. The dorsal trunk in 
the posterior region of the body is only slightly moniliform, 
but as it passes forwards this condition becomes more marked, 
especially in somites xvi to x11. In somite xr a pair of monili- 
form lateral hearts are given off, and similar ones are found 
in somites x, 1x, and vii1, each being smaller than that behind 
it. In the next two anterior somites the ‘ commissural vessels” 
are no longer moniliform, and are very much more delicate 
than the posterior vessels. 

The nervous system consists of the usual cerebral ganglia, 
which are here well marked, and lie in somite 111 and a series 
of ventral ganglia. These lie quite close together, so that the 
intervening cord is very short (fig. 30). This is doubtless due 
to the greatly contracted state of the worm. Three or four 
pairs of lateral nerves are given off from each ganglion, but 
none from the short cord. Probably if the contraction were 
less and the ganglia longer some of the lateral nerves would 
appear to come off from the cord. 

Just as Urobenus has certain resemblances to Urocheta, 


94 WILLIAM BLAXLAND BENHAM. 


so also there are several points in which Diacheta shows a 
resemblance to Perrier’s genus, viz. in the similarly modified 
first nephridium, in the single elongated pair of seminal reser- 
voirs (though they are in Diacheta very much longer than in 
the other worm), and the single pair of “ free”’ ciliated rosettes, 
and in the position of the nephridiopores. But there are note- 
worthy differences between the two worms. In Diacheta 
the body wall is thick, and not transparent. The anterior 
extremity is not pointed, as in Urocheta, but much swollen 
and obtuse. There are neither calciferous glands (“ glandes 
de Morren”’) on the intestine, nor the pyriform sacs on the 
body wall, nor “ intestinal hearts.” The nephridia differ con- 
siderably. The clitellum is longer than the area supposed by 
Perrier to represent this structure in Urocheta (but certainly 
this may differ in the same genus). 

The sete are all simple, and have not the bifid form charac- 
teristic of Urocheta; they alternate throughout the body,! 
except the ventralmost, which remain in line. In Urocheta 
these last alternate as the rest do; but this happens only in 
the posterior part of the body. It seems, then, that this new 
worm is very closely allied to Urocheta, and in any classifi- 
cation would have to be placed very near to it among the 
Intraclitelliani. 


Trigaster Lankesteri, nov. gen. et sp. 


This worm, like Diacheta, comes from St. Thomas and 
belongs to the group Intraclitelliani. The single speci- 
men was incomplete, as the hinder part was wanting. Professor 
Ray Lankester had opened it and made sketches of it. 

The most striking point externally is the presence of a deep 
median ventral fossa, situated in the anterior region of the 
clitellum ; this fossa is bounded on each side by a couple of 
papille ; the whole arrangement is doubtless used in copulation. 

This worm possesses three distinct gizzards, separated from 
one another by cesophageal regions; it is this character that 


‘In the genera Pontoscolex, Schm., and Geogenia, Kinb., a similar 
alternation of the sete is present in certain regions of the body. 


STUDIES ON EARTHWORMS. 95 


suggested its generic name. Here then we have a condition 
intermediate between Digaster (HE. P.) and Moniligaster! 
(E. P.), but whereas the former is post-clitellian, and the latter 
aclitellian, Trigaster has its male genital pores situated within 
the clitellum. 

External Anatomy.—The size and number of somites is 
necessarily unknown, as the only specimen that I have had 
the opportunity of examining is incomplete. 

The setz are arranged in four couples in each somite 
(fig. 31); the ventral and lateral couples on one side are 
nearer to one another than are the ventral couples of the 
two sides ; the eight setz are all on the ventral surface. The 
sete are very small and difficult to see owing to the greatly 
contracted state of the worm. As seen in a transverse section 
they are *2 mm. long, and are less curved than in Lum- 
bricus. The preclitellar somites are quadriannulated, and 
the third annulus forms a very distinct ridge (a in fig. 32); 
the setz are placed in the second annulus (fig. 32). 

The prostomium is broad, and occupies the whole dorsal 
border of the anterior extremity; it is not embedded in 
somite 1. The setz commence in somite 11. 

The clitellum commences behind somite x111, and occupies 
twenty-seven somites, extending as far as somite xu. This is 
an exceptional length for the clitellum, the nearest approach 
being Titanus with fifteen somites. Theclitellum is incomplete, 
there being a groove in the mid-ventral line, in which the two 
ventral couples of setz are placed (fig. 31). In the anterior 
part of this groove is the fossa (yg) above mentioned. 

There are no dorsal pores, nor could I find any nephridio- 
pores. 

The male pores are four in number, and although not 
visible externally are indicated by the fossa, and are easily 
seen in transverse sections. This fossa appears to extend 
through somites XVII, XVIII, XIX, and xx and part of somite xv1, 
but the somites are so short in this region and the sete so 
difficult to see that the actual number of somites may be less, 

t €Nouvelles Arch. de Mus. d’hist. nat. de Paris,’ viii, 1872. 


96 WILLIAM BLAXLAND BENHAM. 


as I may have counted annuli by mistake for somites. The 
side of the fossa is formed partly by two rather prominent 
papillee (f,/’), one of which is formed on somite xvii and part of 
somite xvi ; the other is formed by somites x1x and xx; between 
the two papillz the side of the fossa is formed by somite xvuit, 
which dips down into the fossa at a level with the base of the 
papille. 

The papille are in a line with the ventral couple of sete, 
though I could see no setz on the papille themselves, and 
there are no special or “penial’’ sete connected with this 
region. Each male pore lies at the base of a papilla, giving 
four male pores as in Acanthodrilus. 

The pores of the spermathece, though not visible externally, 
lie in somites vir and viir in a line with the ventral sete in the 
posterior region of the somites. 

Internal Anatomy.—None of the septa are particularly 
thick, but those in the anterior region are slightly stronger 
than the more posterior ones, and tend to hide the gizzard. 

The alimentary tract (fig. 33) consists of a short buccal 
mass, a pharynx which passes through five somites, esophagus, 
three gizzards and the intestine. A short csophagus leaves 
the pharynx and passes through somite vi; in somite v1 it 
widens out and enters the first gizzard, in somite vir the 
anterior region of the somite is occupied by a thin-walled 
cesophageal portion, and the posterior region by a second 
gizzard. The same arrangement is repeated in somite 1x. 
Behind each of the gizzards is placed a slightly thicker septum ; 
each gizzard has the usual structure and is quite separated 
from the neighbouring gizzards. The tubular intestine com- 
mences in somite x, and extends through this and the two fol- 
lowing somites. In somite xn the intestine becomes rather 
larger and as it passes through the septa is slightly constricted. 
This forms the sacculated intestine. There are no cesophageal 
nor intestine glands such as are found in Lumbricus, 
Microcheta, Urobenus, &c., but there are three pairs of 
“‘gyape-like glands”? around the pharynx and cesophagus, a 
pair in each of the somites rv, v, and vi. These organs are 


STUDIES ON EARTHWORMS. 97 


shown in situ in fig. 33 and enlarged in figs. 35 and 36. 
Whether these structures are “ salivary glands” and open into 
the alimentary canal I am unable to say. I could not find any 
opening though they were embedded in the muscular wall of 
the pharynx, nor on the other hand could I find any external 
opening as the alimentary tract had been removed from the 
body before I received it. Each of these structures is 
made up of a much branched tubule, each branch ending 
in a tuft of elongated processes, each of which contains a 
lumen (fig. 35). The lumen bends round on itself at the 
apex of the process (fig. 36), and probably is continuous up 
and down each of the processes; this lumen is intracellular 
and in transverse section (fig. 37) has an appearance quite 
similar to that of a nephridium. ‘There is a very abundant 
vascular supply to these structures and the capillary loops have 
numerous dilatations on their course, as in the capillaries on 
the nephridium of Lumbricus, but here they are larger and 
much more numerous ; these dilatations are filled with a granu- 
lar material (figs. 36, 37) which is probably due to the remains 
of the blood-corpuscles. I think that there is no doubt that 
these structures, though apparently in connection with the 
alimentary canal, are really modified nephridia; even if they 
do open into the alimentary canal we have the same thing 
occurring in Ac. multiporus. Tke nephridia in the rest of 
the body are extremely minute, and this may have some relation 
to the great development of these anterior ones. Perrier remarks 
on the great development of the glandular appendages of the 
alimentary canal of Pericheta Houlleti! and the small 
development of the nephridia, and suggests that these appen- 
dages may take on an excretory function, the products being 
used for digestive purposes. 

The Genital System.—Of the male organs I could find 
neither testes, nor seminal reservoirs, nor ciliated rosettes, nor 
sperm-ducts; but in each of the somites xvi and xvi is a pair 
of whitish convoluted tubes, having the shape and appearance 
of the “‘ prostates” of Acanthodrilus (fig. 34, d, da’). Each 

1 ©Nouv. Arch.,’ &c., viii. 
VOL. XXVII, PART ],—NEW SER. G 


98 WILLIAM BLAXLAND BENHAM. 


of these prostates consists of two regions traversed by a lumen. 
The distal blind extremity has a looser structure and a more 
granular appearance, whilst the proximal portion, near the 
external pore, has a nacreous aspect. 

The distal portion is coiled, and has a layer of columnar 
cells (fig. 42, 0) surrounding the lumen. Beyond this layer is a 
deeper one of club-shaped granular cells (a), very similar to the 
cells in the epidermis of the clitellum of Lumbricus, &c., 
and as in that region there are capillary blood-vessels traversing 
this glandular layer. The outer wall of this region is formed 
by thin but firm membrane. 

The epithelium of the lumen in the proximal region (fig. 41) 
consists of tall, narrow, columnar cells, with a highly refracting 
cuticle, and, instead of a deep layer of granular cells, there is a 
muscular layer, consisting of oblique fibres, as well as circular 
and longitudinal fibres. In this region, too, the capillary blood- 
vessels ramify amongst the epithelial cells. Outside the mus- 
cular layer is a thin membrane, as in the glandular region. 

I could find no spermatozoa or other contents in these 
organs. Their proximal portion is probably extrusible, and 
represents the penial region of the duct in Pericheta, whilst 
the slightly coiled portion will correspond to the greatly coiled, 
compact, glandular “ prostate” of that genus. The external 
pores of these “‘ prostates” lie at the base of the papille, which 
form the boundaries of the ventral “ copulatory fossa ;” a pore 
being at the base of each papilla. 

The two ovaries lie in somite x11 (fig. 34), one on each side. 
The ovary is a grape-like mass of lobules, and is attached to 
the anterior septum of the somite (fig. 39). Each lobule is 
supplied by a blood-vessel, around the branches of which are 
set the ova, embedded in the ccelomic epithelial cells (fig. 40). 
Each ovum has the characteristic structure. 

In each of the somites vir and viir there is a pair of sub- 
globular white sacs (fig. 34, a, a’), opening to the exterior in 
the posterior region of the somite, close to the nerve-cord, in a 
line with the ventral sete (fig. 31, e, e’). When I examined these 
sacs by teasing them I could find no spermatozoa in them, but 


STUDIES ON EARTHWORMS. 99 


merely a mass of granular, oily-looking granules. But by 
means of sections I was able to identify these sacs as sperma- 
thecz. The spermatozoa were now seen in bundles, chiefly 
in the neck of the sack, while in the sack itself they were less 
numerous, and mixed with the granular globules. The wall of 
the spermatheca is muscular, and the cavity is lined by tall 
columnar epithelial cells. 

The nephridia are represented in each somite by numerous 
vascular tufts on the body wall; more numerous in the genital 
somites than elsewhere. These are apparently independent of 
one another, and consist of a slightly-coiled tubule containing a 
narrow, intracellular lumen. Surrounding each tuft is a net- 
work of capillaries (fig. 38) without dilatations. As for their 
communication, either internally or externally, I am unable to 
say anything. Though I cut sections through the body wall I 
could not trace the nephridia through it, owing to the badly 
preserved condition of the worm, nor could I make out any 
detail of their structure. 

I have already described the glandular structures in the 
anterior somites, which I take to be modified nephridia. 

As for the fact of there being a large number of small 
nephridia in each somite, several Harthworms are now known 
to possess more than two nephridia to each somite. Beddard 
has described Ac. multiporus with eight, and I have sections 
through a Pericheta in which there are very numerous, small 
nephridia in each somite—a condition also found by Beddard 
in this genus, who has seen their external pores. 


Kinberg’s Genera. 


In my previous paper I gave the characters of eleven 
Earthworms, as described, though very inadequately, and, 
as it now appears, wrongly, by Kinberg’ in 1866. In the 
April number of the ‘Comptes Rendus” for the present 
year M. E. Perrier, in a short note, corrects some of Kin- 
berg’s descriptions, as observed by himself after examination 

1 *Ofversigt af. Kongl. Vetensk. Acad. Forhandlgr,’ Stockholm, xxiii. 

2 «Comptes rendus,’ cii, 1886, p. 875. 


100 WILLIAM BLAXLAND BENHAM. 


of Kinberg’s type specimens. He comes to the conclusion 
that the only good genera are Tritogenia, which has 
eight set in each somite, and not six, as Kinberg stated; 
Geogenia, with the clitellum occupying somites x111 to xviu, 
and carrying modified sete; and Eurydame, which has four 
sete, and not eight, in a somite. These have a quincuncial 
arrangement in the posterior region of the body, and are bifur- 
cated, as in Urocheta (E. P.). In other respects Kinberg’s 
descriptions are correct. The remainder of Kinberg’s worms 
belong to other genera. Mandane and Hegesipyle are 
species of Perrier’s Acanthodrilus. Alyattes is a species 
of Lumbricus. Hypogeon remains indeterminate; whilst 
the remainder, as mentioned in my previous paper, Perrier 
considers to be species of Perichzta, Schm. (= Megascolex, 
Templeton). 


Recent Appitions to EartHworm LITERATURE. 


Since my previous paper! was published, several additions 
have been made to the literature of Karthworms, some treating 
of the histology of known species and others being descrip- 
tions of new forms. 

Professor F, Vejdovsky’s beautiful work on the Oligochzta 
(‘ Systeme und Morphologie der Oligochaeten’) contains a com- 
paratively slight reference to terricolous forms, so far as new 
anatomical details are concerned. Amongst these are drawings 
of the structure of the clitellum, details as to the development 
of the sete, structure of body wall, the spermatophors, &c., in 
Dendrobena, Allolobophora, Allurus, Lumbricus, 
as well as some reference to and drawings of Criodrilus 
lacuum, Hoffmeister. 

In regard to the classification of the group, he puts aside 
Perrier’s arrangement, founded on the relation between the 
sperm pore and the clitellum, and divides the whole of the Oli- 
gocheta into seventeen families (p. 63). Many reasons can 
be adduced for this plan in preference to the more hard-and- 


1 This Journal, 1886, pp. 213—292. 


STUDIES ON EARTHWORMS. 101 


fast arrangement previously adopted, e. g. species of Acan- 
thodrilus have been described by Beddard (‘ Proc. Zool. Soc.,’ 
1885, p. 814), and by Horst (‘ Notes of Leyden Museum,’ vi), 
in which the male pores are not posterior to the clitellum, as 
in the three species described by Perrier, but are within the 
area of the clitellum. Again, Beddard has described a species 
of Megascolex (Pleurocheta, ‘Trans. Roy. Soc. Edin.,’ 
xxx, 1883), in which the genital pore has also this position, 
instead of the usual post-clitellian position of the remaining 
species of Megascolex and Pericheta. 

It seems better, therefore, to use in the future Vejdovsky’s 
plan, and form the following families for the Terricolous 
Oligocheeta : 

1. Pontodrilide. 
. Criodrilidee. 
. Lumbricide (= Preclitelliani). 
. Eudrilide (= Intraclitelliani). 
. Acanthodrilide. 
. Perichzetidee (+ Pleurochetide of Vejdovsky). 
. Plutellide. 
. Moniligasteride. 

In February of this year Mr. F. HE. Beddard published 
(‘Ann. Mag. Nat. Hist.,’ p. 89) a description of a new 
species of Pericheta, and of Moniligaster, together 
with some notes on Pericheta Houlleti, E. P., and P. 
posthuma, Vaillant. P. Ceylonica, Beddard, differs from 
all other species of this genus with the exception of P. 
armata, Beddard,' in possessing a sac, containing one or 
more penial setz, on each side of somite xviii, in which lie 
the male pores—an arrangement found, too, in Acantho- 
drilus. 

Moniligaster Barwelli, Beddard, agrees with Perrier’s 
M. Deshayesii in having no clitellum, although the genital 
organs are mature in both species. 

In the new species only the posterior pair of “testes” in 
somite 1x are present. The sperm duct, which appears to have 


1 © Ann. Mag. Nat. Hist.,’ xii, 1883. 


ont mS orb © wo 


102 WILLIAM BLAXLAND BENHAM. 


no funnel, opens to the exterior at the hinder region of the 
same somite. In somite vi1I is a pair of spermathece, occu- 
pying the position of the anterior pair of testes of Perrier’s 
form. 

In the ‘ Zool. Anzeiger,’ 1886, p 342, Beddard discusses the 
relation of the ovary to the spermatheca in Eudrilus, as de- 
scribed by Perrier (‘ Nouv. Arch. Mus. d’Hist. Nat.,’ 1872, 
viii), from whose figures and description it appears that the 
ovary is grafted on to the spermatheca, from the opposite side 
of which springs a coiled diverticulum. 

Beddard comes to the conclusion that the ovary is in con- 
tinuity with the oviduct—Perrier’s coiled ‘ diverticulum ”— 
and, moreover, that the ovary has a very different structure 
from that of Oligocheta in general, in that it is surrounded by 
a fibrous tunic, continuous with the wall of the oviduct, and 
the cavity is divided by trabecule into chambers, in which lie 
ova in different stages of development. 

At a recent meeting of the Zoological Society of London, 
Beddard pointed out certain variations in the position of the 
genital pores of Perionyx excavatus, E. P., as seen in a 
large number of specimens. 

The development of the seminal reservoirs in Lumbricus 
is described by Dr. R.S. Bergh (‘ Zool. Anzeiger,’ 1886, p. 
231) in a preliminary note. 

It consists essentially of a bulging of the septa of the 
somites x and x1, so as to give rise to the anterior and posterior 
sacs on each side of the first, and a posterior sac on each side 
of the second of these somites [as mentioned in a footnote on 
p- 259, of my previous paper]. There isa similar arrangement 
in connection with the ovaries—“ receptacula ovorum ”—which 
consists of small backward, saclike protrusions of the posterior 
septum of somite x11. Hach spermatheca is developed as an in- 
vagination of the epidermis, forming a sac which is surrounded 
by the muscular layers of the body wall. 

A memoir by Hermann Ude (‘ Zeit. fiir wiss. Zool.,’ xlvi, 
pp. 85—142) on the dorsal pore of Karthworms, deals chiefly 
with the structure of the body wall; unfortunately figures are 


STUDIES ON EARTHWORMS. 103 


not very freely given. The various layers of the body wall are 
considered, and a discussion of the opinions of previous authors 
with respect to each of the layers, forms a great part of the 
paper. Inthe epidermis he describes the columnar cells and 
the goblet-cells; but in the latter he figures no branched 
base, which, however, I find to exist: the structure of the 
clitellum is not described. 

Below the epidermis he finds a “basal membrane.” In the 
muscular layers he notes an appearance presented in sections 
across the fibres, which shows the fibre to be made up of 
fibrille. The fibre consists of a denser peripheral portion, in 
which lies the nucleus, and a less dense central portion. The 
bundles of muscle-fibres are surrounded by finely granular 
connective tissue, the perimysium, in which are found small 
nuclei, whilst the larger nuclei belong to the muscle-fibres. 

He draws attention to the fact that the arrangement of the 
longitudinal muscles in Lumbricus agricola, Hoffm., is 
not universal in the genus. 

The dorsal pore lies on the anterior edge of the somites in 
which it occurs, and appears in the intersegmental groove. It 
is absent in the most anterior somites, but the position of the 
first pore is constant for a given species, e. g. in L. agricola, 
between somites vii and 1x, in Allolobophora turgida, 
Eisen, between somites x and x1. In Typheus orientalis, 
Beddard, the pore commences only behind the clitellum. It 
has not been noticed in Anteus, Titanus, Urocheta, or 
Microcheta. 

Vejdovsky states that it is generally absent in the Limi- 
cole. 

In a fully-developed clitellum the pores become closed by 
a development of cuticular substance around the edge, which 
gradually increases and fills the pore. In Allol. mucosa, 
Eisen, however, it remains visible in the clitellum. 

Claparéde described the epidermis as being invaginated at 
the dorsal pore, as it is at the seta-follicle; but Ude finds 
that such is not the case. The dorsal pore is a perforation 
through the epidermis and muscular layers, and the celomic 


104 WILLIAM BLAXLAND BENHAM. 


epithelium passes across these layers and meets the cuticle 
round the edge of the pore. There is a special set of muscle- 
bundles, forming a sphincter muscle for the pore. 

As to the physiology of the pore, Ude considers that 
there is not the slightest connection between the dorsal 
pore and the nephridia, although the former is, to a certain - 
extent, excretory, since the ccelomic fluid can be extruded 
through it, either in drops, as in Lumbricus, or may be even 
squirted through the pore to a distance of about a foot, as 
has been noticed in species of Megascolex and Pericheta 
by Vordermann (‘ Natwork. Tijdsche-Nederl. Indie,’ vol. 11, 
p-i11). 

The following experiments were undertaken to ascertain 
whether or not any liquid was taken in through the pore. A 
worm was dried by lying on blotting paper for some hours; the 
anterior and posterior extremities were then tied with string 
and the worm was immersed for fifteen minutes in water. On 
removal it was found to be greatly swollen, and Ude was led to 
think, from this, that water was taken in through the pore. 
But the following experiment caused him'to doubt the truth 
of this opinion. Instead of employing pure water he dissolved 
some iron oxide in the water, and after the worm had remained 
in this for some time (after previously being dried) it was 
killed and the ccelomic fluid was tested for iron by means of 
cyanide of potassium. No red colour was produced, and hence 
Ude concludes that no water was taken in through the dorsal 
pore. The swelling of the worm must therefore have been due 
to the intaking of water by the genital ducts, nephridia, and 
mouth. The worm was carefully weighed before and after the 
various stages of the experiment, and it was found that it 
weighed about 0°2 grams more (on the average) after immer- 
sion than before. 

Accompanying this memoir is a bibliography of the subject, 
and a useful table for determining the species of the genera 
Lumbricus and Allolobophora is given. The position of 
the first dorsal pore is given in each species, and appears to 
furnish a useful specific character. 


STUDIES ON EARTHWORMS. 105 


Two new species are described, Allolobophora longa and 
A. hispanica. 

Rosa (‘ Bull. Mus. Zool., &c.,’ Torino, vol. i) has added a 
new species, A. celtica, to his previously described forms. 


EXPLANATION OF PLATES VIII & IX, 


Illustrating Mr. Benham’s “ Studies on Earthworms.” 


Microcheta Beddardi. 


Fic. 1.—The anterior extremity of the worm, showing three somites from 
above. (x 13.) 

Fic. 2.—The three anterior somites from the side. (x 13.) a,a. The second 
and third nephridiopores on the intersegmental grooves. 0. The first nephri- 
diopore, situated on a slight prominence in somite 1. c. The lateral sete. 
d. The ventral sete. 

Fic. 3.—Four somites of the clitellum from below. (x 2.) a. The 
nephridiopores. 4%. The spermathecal pores. ¢. The lateral sete. 4. The 
ventral sete. e. The pores of the oviducts. 

Fic. 4.—One of the lateral setee from a preclitellar somite. Nat. size, 
0:39 mm. : 

Fic. 5.—One of the ventral sete from somite xrx. Nat. size, 0°715 mm. 

Fic. 6.—A spermatheca. 

Fic. 7.—Two somites of another specimen, showing the asymmetrical dis- 
position of the spermathece. © 

Fie. 8.—A portion of the intestine, with the intestinal glands. 

Fig. 9.—A portion of the intestine, with the intestinal glands, of M. 
Rappi. : 

Fie. 10.—A portion of one of a series of transverse sections of M. Bed- 
dardi, showing the relative positions of the ovary and its duct: one on each 
side of the septum x1i—xur._ a. Portion of the funnel of the oviduct. 4. 


Blood-vessel in septum. f Colomic epithelial cells, forming the ovary. 
o. Ova amongst these cells. s. Septum. 


Urobenus brasiliensis. 


Fic. 11.—The anterior extremity of the worm (nat. size). @ Prostomium 
Fic. 12.—Ventral view of the clitellum and neighbouring somites. (x 2.) 


106 WILLIAM BLAXLAND BENHAM. 


a. Ventral sete. &. Lateral sete. c. The nephridiopores. d. The pores of 
the sperm-ducts. 

Fic. 13.—Setz. Nat. size, 0°65 mm. a. From the preclitellar region. 
6. One of the ventral setz from the clitellum. 

Fie. 14.—The worm opened along the dorsal surface to show its general 
anatomy. (X 13.) a. Prostomium. 6. Pharynx. c. @sophagus. d. Pro- 
ventriculus. e. Gizzard. f Intestinal glands. g. Tubular intestine. 4. 
Pouched intestine. 7. Sacculated intestine. &. Ventral cca, at the 
junction of the pouched with the sacculated intestines. /,/. Nephridia. m, m. 
Spermathece. x, 2’. Seminal reservoirs. p. Dorsal blood-trunk. 

Fic. 15.—The junction of (a) the pouched with (c) the sacculated intes- 
tine, seen from the ventral surface in order to show the origin of the ventral 
ceca (5). 

Fic. 16.—A portion of the pouched intestine, the dorsal wall of which 
has been removed, seen from above. a. The ventral wall of the axial lumen 
of the intestine. 9%. A pouch. c. The glandular (?) ridge at the junction of 
a pouch with the axial portion. 

Fic. 17.—The alimentary tract has been removed to show the genital 
organs, nephridia, &c. (x 2.) The seminal reservoirs have been removed 
from the left side; the anterior nephridia have been drawn aside to show 
more clearly the somites to which they belong. ‘The posterior nephridia are 
also somewhat displaced. a. Prostomium. 4. Cerebral or supra-pharyngeal 
ganglia. c. First ventral ganglion. d. Ventral nerve-cord. /,f. The sper- 
mathece (there should be lines separating the spermathece from the nephridia 
where they dip into the body wall, on the right side). g,g. The seminal 
reservoirs of the right side. 4, 7. The anterior and posterior ciliated rosettes. 
k. The sperm-duct. 7. Position of the sperm-pore. 2, a!, x7. The nephridia, 
of which x!—n7 are somewhat different from the following ones. p. The 
pyriform vesicles. g, r. Interruptions in the muscular coat of the body wall 
for the ventral and lateral sets respectively. 

Fie. 18.—One of the posterior nephridia. a@. The vesicular diverticulum. 
b. The tubule. c. The entrance of the tubule into the neck of the vesicle. 
d. The duct leading to the nephridiopore. e. Nephridial funnel. 

Fie. 19.—A nephridial funnel. 

Fic. 20.—A diagrammatic transverse section through the body to show the 
relative positions on one side of the pyriform vesicle, and on the other of the 
nephridiopore with the sete. 1,2. The ventral couple of sete. 3, 4. The 
lateral couple of sete. a. Pyriform vesicle. 6. Its external pore. x. 
Nephridial vesicle. o. Nephridiopore. 

Fic. 21.—A transverse section through a pyriform vesicle. a. Membrane 
forming the outer wall. 4. Granular substance. c. Columnar epithelium 
lining the lumen. d. lumen. 


STUDIES ON EARTHWORMS. 107 


Diacheta Thomasii. 


Fic, 22.—Dorsal view of the first thirty-nine somites, showing the scattered 
and alternating arrangement of the sete. (x 3.) cl. Clitellum, occupying 
somites xx to xxx. 7. Ridge in the somites anteriorly to somite x. 

Fic. 23.—View, from below, of a portion of the body wall which has been 
cut along the dorsal mid-line and pinned out, so as to show the alternating and 
asymmetrical arrangement of the sete, which are numbered 1 to 7. (x 10.) 
a. The nephridiopores. ¢. The spermathecal pores. d. Sete, 1, 2, 3, corre- 
sponding to the ventral couple of Lumbricus. e. The sete, 4, 5, 6, 7, 
corresponding to the lateral couple. 

Fie. 24.—Ventral view of three somites of the clitellum, which has been 
cut along the dorsal mid-line and spread out. a. The nephridiopores. 4. 
The pores of the sperm-duct. d. The ventral sete. e. The lateral sete. 

Fic. 25.—A seta; nat. size 0°25 mm. 

Fie. 26.—General view of the worm, when opened from the dorsal surface ; 
the spermathece have been straightened out in order to show their position ; 
the gizzard, &c., are hidden by the strong septa. (Xx 38.) a. The supra- 
pharyngeal ganglia. 4. The pharynx. c. The modified first nephridium. 
d, d. The spermathece. e, e. The strong septa behind the somites vi to x. 

J. The ciliated rosette. g. The seminal reservoir. 4%. The dorsal blood- 
trunk. 7,7. Nephridia. . The sacculated intestine. 7. A lateral heart. 

Fie. 27.—A nephridium. a. The coiled tubule. 4. Vesicular portion or 
duct, being a continuation of the tubule. c. The portion of the duct leading 
to the nephridiopore. / The funnel. 

Fic. 28.—One of the first pair of nephridia (“glandes & mucosité” of 
Perrier). a. The glandular-looking mass of tubules. 4. The vesicular 
portion or duct. c. The external aperture which is placed on the anterior 
edge of somite II. 

Fie. 29.—A spermatheca. 

Fie. 30.—A portion of the nerve-cord, showing four closely placed ganglia, 
with the lateral nerves. 


Trigaster Lankesteri. 


Fic. 31.—Ventral view of the first fifty somites; the body wall has been 
cut along the dorsal mid-line and pinned out. (xX 2.) a@. The prostomium. 
6. The mouth. c. The lateral sete. d. The ventral sete. e, e’. The sper- 
mathecal pores. f,/’. The papilla forming the sides of the median fossa. g. 
The median genital fossa. 4. The clitellum occupying somites xiv to x1. 

Fic. 32.—Two somites further enlarged, to show the three grooves whica 
surround the somites. a. A more or less prominent ridge in the anterior 
somites. c. The lateral, and d. the ventral sete. 

Fie. 33.—The alimentary tract, together with the septa, removed from the 
body. (xX 4.) a@. The buccal region. 4. The pharynx. ¢, d, e. The three 


108 WILLIAM BLAXLAND BENHAM. 


pairs of glandular-looking, modified nephridia. ff, /. Gsophageal regions, 
separated by the three gizzards, g, 9’, g". 4h, h. The septa. j’. The tubular 
intestine. k. The sacculated intestine. 

Fie. 34.—The contents of the somites vi to xx after the removal of the 
alimentary tract. (x 3.) a, a’. The two pairs of spermathece. 0. The 
ovary. c,c’. Vascular tufts, probably nephridia, attached to the body wall. 
d, d'. The two pairs of prostates. e. The ventral nerve-cord. 

Fic. 35.—A group of tubules from one of the modified nephridia of somite 
vi. a. The base from which the tubules arise. 4, 4. The capillary blood- 
vessels with their dilatations on the tubules. c,c. The branched processes 
springing from @. 

Fic. 36.—The free extremity of one of the tubules of a modified nephridium 
from somite vI. a. Connective-tissue wall of the tubule. 4. Capillary 
blood-vessel in the wall. d. A dilatation of the blood-vessel. 7. Lumen of 
the tubule. 


Fic. 37.—A transverse section of a tubule of one of the modified nephridia. 
a. A dilatation of one of the capillaries. 4, 4. Capillary blood-vessels. c. 
Connective tissue forming the wall of the tubule. d. Perforated cell of the 
nephridium. J. Intracellular lumen. 2. Nucleus of perforated cell. 

Fic. 38.—A portion of one of the vascular tufts, indicated at c. in Fig. 34. 
a. Connective tissue. 6. blood-vessel. 7, Intracellular lumen. 

Fic. 39.—The ovary attached to the septum xi—xi1. (xX 10.) 

Fic. 40.—A lobule of the ovary, with the blood-vessel, 4, branching 
amongst the coelomic epithelial cells, c, amongst which are the ova, a. 
(Slightly diagrammatic.) 

Fic. 41.—A portion of a section through the prostate, near its external 
aperture. a. Cuticular lining. 4. Columnar epithelial cells. ce. Muscular 
coat. d. Membrane forming outer wall of prostate. e¢. Blood-vessels lying 
in this coat, and branching amongst the epithelial cells. 

Fic. 42.—A portion of a section through the prostate near its free extremity. 
a. Deep-lying, club-shaped granular cells. 4. Columnar epithelial cells. e. 
Blood-vessels ramifying amongst the club-shaped cells. d. A membrane 
forming the external coat of the prostate. 

Fre. 43.—A portion of a transverse section through one of the intestinal 
glands of Urobenus. a. Various-sized, oily-looking globules ( ? calcareous) 
lying in the lumen of the tubules. 6. Large blood-sinuses surrounding the 
tubules. e. Epithelial cells lining the lumen. /. The lumen. m. Basement 
membrane to the epithelium, forming the wall of the blood-sinus. 


ON DINOPHILUS GIGAS. 109 


On Dinophilus Gigas. 
By 


Ww. Fr. R. Weldon, M.A., 
Fellow of St. John’s College, Cambridge; Lecturer on Invertebrate 
Morphology to the University. 


With Plate X. 


In the spring of last year Mr. Shipley brought to Cambridge 
a few specimens of a Dinophilus, which he had found in 
Mount’s Bay, near Penzance. These he was kind enough to 
place at my disposal; and in April last I was able myself to 
procure a larger number of specimens from the same locality. 

The animals were found in considerable numbers on red 
seaweeds, &c., in pools, near spring-tide low water mark, on 
the rocks to the west of St. Michael’s Mount. The weeds were 
placed in shallow white basins, with plenty of sea-water, for 
from twelve to twenty-four hours, when the Dinophilus left the 
weed, and were easily seen against the white wall of the vessel, 
on the side turned towards the light. 

The length of the body varied greatly, the smallest specimens 
found being about 0°75 mm., while the largest were nearly two 
millimetres in length. The colour was a brilliant orange, uni- 
formly distributed in granules through the skin, and more 
intensely developed in the stomach. 

The body consists of a head or pre-oral lobe, seven post- 
oral segments, and a ventral unsegmented tail. 

The head is somewhat broader than the segment immediately 
behind it ; its form is that of a truucated cone, and it is covered 


110 W. F. BR. WELDON. 


with fine cilia, and with stiff sense hairs, the latter being 
especially prominent in a pair of patches at the anterior end 
(fig. 1, s. h.). On the dorsal aspect of the head are two bright 
red, kidney-shaped eyes. A small pair of ciliated pits, such as 
are described by Korschelt, M‘Intosh, and Hallez was observed 
(fig. 1 e2p:). 

The second segment bears on its ventral surface the mouth, 
which is an elongated slit, bounded by a number of slight folds, 
which are richly ciliated. 

The six following segments are tolerably uniform in diameter, 
each in the extended condition being slightly dilated in the 
centre, and separated from its neighbour by an exceedingly 
shallow constriction. 

Behind the last segment the body narrows suddenly, forming 
the tail. 

The ‘‘ segmentation” of the body is only conspicuous in the 
fully extended condition. By contraction the whole of the 
dorsal and ventral surfaces become uniform, and the very 
slightest indication on the sides alone remains to indicate the 
series of swellings and constrictions referred to. Fig. 2, drawn 
from a specimen which had contracted under the influence of 
corrosive sublimate, but which was not in any way otherwise 
distorted, shows this.! 

The prz-oral lobe, the ventral surface of the body, and the 
tail are uniformly covered with short vibratile cilia, and in each 
segment the cilia are continued into a band which surrounds 
the animal, while behind the cilia of each segmental ring is a 
circlet of fine sense hairs (fig. 1, s. #.). Sensory hairs were 
also specially conspicuous on the tail. 

The pigment granules and numerous oil-globules in the skin 
rendered the creature so opaque that little could be made out 
in the living state, except the outline of the highly-coloured 
stomach (fig. 1, s¢.) and the mouth (m.). 

The three species of Dinophilus, possessing a brilliant yellow 
pigment, which have hitherto been described, are D. vorti- 

1 Only six post-oral ciliated rings are visible in this figure. I have noticed 
the absence of the seventh in one or two preserved specimens. 


ON DINOPHILUS GIGAS. LI 


coides (= D.capitata), D. metameroides, and D. cau- 
data. From each of these the Cornish species differs in some 
respect. From D. vorticoides it is distinguished by the 
absence of a general coating of cilia on the dorsal surface, and 
by the presence of definite ‘‘ segmental” ciliated bands ; from 
D. metameroides it differs in the entirely superficial nature 
of the apparent “segmentation,” adjacent segments not being 
separated by infoldings of the body wall. 

I have not been able to consult Levinsen’s recent description 
of D. caudata,! but, so far as I can gather, it resembles D. 
vorticoides rather than the present form. 

It will be seen from what follows that a further character is 
presented by the present species, which has not been recognised 
in others—the possession of a well-marked nervous system. In 
the absence of any detailed information as to the structure of 
other forms it would be premature to regard this as a specific 
character, but even without it there seems to be sufficient 
warrant for establishing a new species, which I propose to 
call D. gigas, from the large size of the sexually mature 
individuals. 


IT.—ANATomy. 


In its general structure D. gigas agrees closely with the 
D. apatris of Korschelt, differing from it chiefly in the pre- 
sence of a nervous system and in the histological structure 
of the ectoderm. The paper of Korschelt? is so complete, and 
contains so full an account of the previous observations on the 
genus, that it is unnecessary to do more than refer the reader 
to it before passing on to a detailed description of the present 
species. 

The ectoderm, as has already been seen, varies in charac- 
ter in different parts of the body. In the head a transverse 
section (fig. 3) shows a well-marked difference between the 
dorsal and ventral portions. On the ventral side are seen cells 


1 «Viddensk. Meddel. fra den naturh. Foren. in Kjobenhavn,’ 1879-80. 
2 «Zeitschr. f. w. Zoologie,’ Bd. xxxvii, Hft. 3. 


112 W. F. R. WELDON. 


of three kinds ; the most numerous (fig. 3, gv.) are columnar, 
staining moderately deeply, and crowded with granules; 
wedged in between these are certain cells, the peripheral ex- 
tremities of which are conical (m. ep.), but which send inwards 
fine processes, some of which are probably muscular, while 
others are nervous. The cells of the third kind (fig. 3, x) are 
pale, with deeply staining nuclei. Immediately below the 
ectoderm, on the ventral side, is a delicate layer of transverse 
muscles (7. m.), the fibres of which are, I believe, continuous 
with many of the processes of the cells marked m. ep., though 
this connection is not so easily seen in the head as it is in the 
trunk (cf. fig. 10). 

The dorsal ectoderm of the head is composed of an indiffer- 
ent epithelium several cells thick (cf. fig. 8, where, however, 
the curvature of the head has caused this portion to be cut 
tangentially, so that the thickness of the ectoderm appears too 
great). 

Passing backwards, the dorsal and lateral surfaces of the 
body are uniformly covered, between the head and the anus, ' 
with a more or less cylindrical epithelium, one cell thick (cf. 
figs. 4, 5, 6, 8), which is ciliated only in the region of the trans- 
verse rings already referred to. 

The ventral ectoderm, in the region of the mouth and lips, 
is a simple columnar epithelium with narrow, elongated cells 
(figs. 46), but behind the mouth, on the whole ventral sur- 
face of the trunk, it has much the same structure as on the 
corresponding side of the head. The myo-epithelial cells, with 
their processes, are, however, much better marked (figs. 8 and 
10, m. ep.), and their connection with the circular muscles is 
more easily seen (fig. 10), while the cells lying between them 
are all of one kind—large, finely granular, and paler, with 
rounded nuclei (figs. 8 and 10, gr.). In the figures the whole 
of the conical ectoderm elements with processes are labelled 
m. ep.; it is, however, obviously probable that many are 
nervous in nature. 

In the tail the ectoderm is throughout of the same charac- 
ter as that on the ventral side of the trunk, except that the 


ON DINOPHILUS GIGAS. 115 


granular interstitial cells are replaced by elements secreting a 
more or less sticky mucus. By means of this secretion the 
animal can attach itself with some degree of firmness to foreign 
objects. 

Closely attached to the ectoderm is the central nervous 
system, which consists of a brain and a pair of lateral ventral 
nerve-cords. 

The brain (fig. 8, ». f. + 2. ¢.) entirely fills the pre-oral 
lobe. It consists of a central mass of nerve-fibres (n. f.) sur- 
rounded by ganglion cells (n. c.). Embedded in its substance 
are the two eyes (xr), each consisting of one or two cells loaded 
with granules of deep red pigment, surmounted by a small 
cuticular lens. 

The lateral nerve-cords (figs. 4, 5, 6,8) are everywhere 
in close contact with the skin. Large anteriorly, they grow 
gradually smaller in passing backwards (ef. figs. 4 and 8) till 
in the last segment they altogether disappear. Each cord con- 
sists of a mass of fibres (fig. 4, ”. f.), which is in the anterior 
region more or less completely separated from the skin by 
nerve-cells (n. ¢.) ; in passing backwards, however, the nerve- 
cells almost entirely disappear, and it is to this that the dimi- 
nution in size of the cord is chiefly due. 

No trace of commissures between the cords, nor of any 
branches, could be found, though the presence of well-deve- 
loped regions of sense hairs, already referred to, makes it cer- 
tain that some kind of peripheral nervous plexus exists. 

Just above the nerve-cords, throughout the whole length of 
the trunk, runs a small bundle of longitudinal muscle-fibres 
(1. m.). These, and the ventral circular fibres already men- 
tioned, are the only traces of a muscular system which could 
be found. The walls of the alimentary canal, except a small 
part of the pharynx, and apparently the whole dorsal region 
of the body, are entirely destitute of muscles. 

The space between the body wall and the alimentary canal is 
everywhere traversed by strands of connective tissue, which 
forms a network with large spaces between the meshes. There 
is no trace of an epithelial boundary to the spaces thus formed, 

VOL. XXVII, PART 1.—NEW SER. H 


114 W. F. R. WELDON. 


neither is there any sign of a division of the cavity by trans- 
verse septa. 

In certain of the connective-tissue cells which thus traverse 
the body cavity are “flame cells” belonging to an excretory 
system of the ordinary platyelminth type. The granular and 
opaque character of the ectoderm made it extremely difficult to 
observe these organs in the living animal, and I did not succeed 
in finding them in sections. I can only say that there is cer- 
tainly a group of “flame cells” at the points marked ne. in 
feral: 

The alimentary canal presents all the well-known 
characters distinctive of the genus. The mouth (fig. 1, m) is 
an elongated slit bounded by curved, ciliated lips. It leads 
into an upwardly-directed pharynx, which communicates ante- 
riorly by a narrow opening with the esophagus. The ceso- 
phagus itself passes horizontally backwards. The section 
represented in fig. 4 is taken immediately behind the point of 
communication between these two structures, so that the ceso- 
phagus (@.) is here entirely shut off from the pharynx (v. ph.). 
The pharynx itself is seen to be a bounded vertical wall, com- 
posed of pale, columnar, ciliated cells ; outside these lie masses 
of gland-cells (m. g.), which are in places closely attached to 
the pharyngeal epithelium; other similar gland-cells (e. gl.) 
lie at the base of the ectoderm of the lip. 

A section or two further backwards (fig. 5) the pharynx is 
seen to be composed of two portions—a main vertical portion, 
the same as that seen in front, and a horizontal portion (A. ph.), 
in the form of a lateral pouch on each side. In this, as in the 
preceding section, groups of gland-cells are seen, attached both 
to the pharynx and to the cesophagus. 

Passing on to the region behind the mouth, the epithelium 
of the vertical portion of the pharynx becomes darker and 
streaked with bands of mucus thrown into it by the glands, 
which still surround it (fig.6). The ventral pouches have now 
united to form a horizontal limb below the main body of the 
organ, so that its lumen becomes j-shaped. Finally, still 
further backwards, the vertical portion ends in a large muscular 


ON DINOPHILUS GIGAS. 115 


bulb (fig. 7, m. ph.), lying ventral to the commencing stomach, 
while the horizontal portion closes and in section disappears. 

From a consideration of these sections, and from the dia- 
grammatic longitudinal section given in fig. 11, it is obvious 
that the pharynx of this Dinophilus has the same structure as 
that described by Korschelt, Hallez, and others, in the better 
known species of the genus. 

I have, however, been unable to make the animal evert its 
pharynx, as some species are said to do. Irritation with fresh 
water, acetic acid, &c., or stimulation by pressing the cover- 
slip, were equally useless in this respect. Further, im no case 
did my preserved specimens evert the pharynx in dying. 

The esophagus has already been seen; it is a narrow tube 
lined by a ciliated epithelium (figs. 4—6), which opens, at 
about the beginning of the second segment, into the large, 
wide stomach (figs. 1, 2, and 8, s¢.), distinguished by its wide 
lumen and its granular, brilliantly pigmented epithelium. The 
cilia of the stomach are very long, and during life their action 
produces a most violent agitation of the contents of the organ. 

In the sixth segment the stomach bears on its ventral side 
a small pyloric opening (fig. 9), leading into an intestine, 
which is also ciliated. The stomach is prolonged, as a kind of 
cecum, for a short distance behind the pylorus. The intestine 
passes backwards through the seventh segment, diminishing 
gradually in diameter, till at last it narrows suddenly and opens 
to the exterior in the dorsal middle line. 

The reproductive organs are in both sexes similar to those 
described by Korschelt! in the female of D. apatris; that is, 
they each consist of a Y-shaped mass of cells, the anterior 
limbs of which lie under the posterior half of the stomach 
(fig. 8, t,), while the posterior unpaired limb lies under the 
intestine, or else, as is more generally the case (fig. 9, me.), 
pushes this latter organ to oneside. The two sexes are similar 
externally, until the ripening of the reproductive cells renders 
the ova or spermatozoa distinguishable through the skin. At 
the time of sexual maturity the gonads enlarge, so as to com- 


' Loe. cit. 


116 WwW. F. R. WELDON. 


pletely fill the body cavity, the alimentary canal becomes much 
reduced in size, and it and the ectoderm appear to undergo a 
kind of fatty degeneration. I could find no ducts of any kind 
for the generative products, and from the condition of the 
tissues of ripe individuals, I have no doubt that, when the 
generative products are mature, the animals rupture their body 
wall and die. If this be true, it explains the sudden disap- 
pearance of Dinophilus at the end of spring, which has been 
noticed by Hallez' and others. In the case of D. gigas, 
all the individuals collected at Mount’s Bay on April 22nd had 
undergone so much degeneration that they were quite useless 
for histological purposes, while the absolute number of indi- 
viduals collected between the 16th and 23rd of April was so 
small compared with the number obtained in the same time a 
fortnight earlier, as to show that the process of disappearance 
was beginning. 


IIJ.—On tue Systematic Position oF DINOPHILUS. 


It is hardly necessary to indicate the points of resemblance 
between Dinophilus and a fairly late Cheetopod larva. The 
ciliated rings and the ventral plate of ciliated ectoderm, asso- 
ciated with a pair of unsegmented lateral nerve-cords; the ciliated 
alimentary canal, with its large stomach, its narrow cesophagus 
with a muscular pharynx, and its intestine; these are features 
in which all species agree with a late Polygordius larva, while 
in D. gyrociliatus Ed. Meyer finds that the excretory sys- 
tem is “almost identical with that of a Nereis larva.”’? The only 
point of difference between Dinophilus and the Archiannelids 
is the absence of an epithelial body cavity, and this character, 
in spite of the importance given to it by many observers, 
seems to be, in this case at least, of secondary importance. 
For in the first place the body cavity of Saccocirrus seems to 
be devoid of any definite epithelium ;* while in the second place 

1 © Histoire naturelle des Turbellariés,’ Lille, 1879. 

2 Quoted by Lang, ‘Monographie der Polycladen,’ p. 679. 


3 Compare the figures given by Fraipont, ‘ Archives de Biologie,’ Tome v, 
Pl. xiv, which are confirmed by sections in the Cambridge Laboratory, 


ON DINOPHILUS GIGAS. REZ 


the head cavity of Criodrilus and of many Polycheets is, at 
an early stage,! exactly in the condition which is permanent in 
Dinophilus; it is a cavity, not bounded by any definite 
“celomic” epithelium, but traversed by mesodermic fibres, 
which form a plexus running through it. 

From these considerations it may plausibly be argued that 
we have in Dinophilus a form representing in its main features 
a stage in the evolution of Chetopods which is in the existing 
members of that group repeated only in the larval condition— 
a form in which the only archiannelid character which is not 
developed is the epithelial and segmented character of the 
body cavity. 

That the epithelial character of the body cavity may be 
acquired within the limits of a group, Saccocirrus, as already 
pointed out, seems to prove; while the acquisition ef segmen- 
tation is well seen in the various species of Dinophilus itself. 
Thus, in D. vorticoides? we find the whole body unseg- 
mented, with a uniform covering of cilia; in D. apatris® we 
have an external segmentation which is not shared by the ex- 
cretory system; while in D. gyrociliatus we find the ne- 
phridia composed of ‘simple, intracellular, segmental organs, 
terminating in flame cells;’* and lastly, in D. metame- 
roides we have the appearance of a commencing segmenta- 
tation of the body cavity.’ 

But the anatomy of Dinophilus seems to show that from its 
near connection with the Trochozoon ® it is related to other 
forms besides Chetopods. The pharynx seems especially to 
show this. Comparing the longitudinal section (fig. 11) with 
a similar section through the pharynx of Histriobdella 
(fig. 13) we see that the pharyngeal apparatus is obviously 

1 Cf. Hatschek, “Stud. tib. Entw. d. Anneliden,” ‘ Arb. a. d. Zool. Inst, 
Wien,’ 1878, and others. 

2 EH. van Beneden, ‘ Bull. Acad. Roy. Belg.,’ Tome xviii. 

3 Korschelt, loc. cit. 

4 Hd. Meyer, quoted by Lang, loc. cit. 

> Hallez, loc. cit. 


6 T use this term to imply simply the type, whatever that may have been, 
which is now ontogenetically represented by the trochospheres. 


118 WwW. F. BR. WELDON. 


homologous in the two cases. But the pharyngeal appendix 
of Histriobdella carries three chitinous teeth, showing that this 
organ may in some cases develope skeletal structures; and 
when once this is ascertained the resemblance to the Molluscan 
odontophore becomes obvious. Further, in Terebella, and 
other Polycheets, the pharyngeal armature is developed from a 
ventral and posterior diverticulum of the stomodzeum 
(fig. 14), which is apparently homologous with the correspond- 
ing diverticulum of the Archiannelid pharynx. The wide dis- 
tribution which some organ of this kind had among the Tro- 
chozoa is evident from its persistence in the larve of such 
creatures as Sipunculus and many others. 

It sems, therefore, legitimate to conclude that in the pha- 
ryngeal appendix of Dinophilus and the Archiannelids we have 
a persistent record of some ancestral organ from which deve- 
loped the stomodeal armature of least the Molluscs and 
Cheetopods, and probably also of Rotifers and Crustacea. 

As for the derivation of Dinophilus and the forms which it 
represents from simpler types, there are, as Korschelt has 
already pointed out, many features which connect it with the 
Rhabdoceel Turbellarians. The body cavity and excretory 
system especially are in exactly the same condition as those of 
a Rhabdoceel with well-developed ccelomic spaces, such, for 
example, as Mesostoma. 

It is commonly stated that myo-epithelial cells are absent 
from the ectoderm of Rhabdoceels, and that the muscle-fibres 
are in this group devoid of nuclei. I hope, however, shortly 
to show that, in Convoluta at least, certain of the ectoderm 
cells have a structure practically identical with that just 
described in Dinophilus. 

The only characters of importance which separate Dino- 
philus from the Rhabdoceels are, the possession of an anus, 
and the metameric repetition of ciliated bands. Of these, the 
second may very possibly have arisen within the limits of the 
genus, since D. vorticoides is uniformly ciliated; but in 
any case we havein Allostoma!? a precisely similar formation 

' Graff, ‘ Monographie der Turbellarien,’ Bd. i, Taf. 19. 


ON DINOPHILUS GIGAS. 119 


of a single ciliated ring in an undoubted Rhabdocel. The 
assumption of a pelagic life might easily cause in any Rhab- 
doceel a hypertrophy of the cilia in certain definite regions and 
the consequent appearance of ciliated bands; and it seems safe 
to predict that a more thorough investigation of the pelagic 
inhabitants of those warm seas which are most favorable to 
the development of surface faunas will reveal the existence of 
genera in which this character has been developed. 

The researches of Lang on Oligocladus and Cyclo- 
porus? have shown that at least in Polyclads there is no diffi- 
culty in the temporary establishment of an anus in any region 
of the body, and when this is once recognised the passage from 
a temporary to a permanent condition is easy. 

The pharynx of Dinophilus and of the lower Chetopods 
offers another strong proof of Turbellarian affinities. Oncom- 
paring the diagrams given in figs. 11 to 16 we see that the 
stomodeum of Dinophilus, Polygordius, and Histriob- 
della possesses a posterior muscular thickening lying in the 
wall of a lateral outgrowth from the pharynx, which is in all 
cases conceivably, and in Dinophilus certainly, eversible. In 
the embryo Terebella (fig. 14) a similar posterior outgrowth 
from the stomodzum exists, which subsequently” envelopes 
the whole circumference of the pharynx, and constitutes the 
rudiment of the pharyngeal armature. In Nais (fig. 15) we 
have a similar muscular thickening on the anterior wall of 
the stomodeum. 

These facts receive at least a plausible explanation, if we 
suppose that the various forms of pharyngeal apparatus just 
mentioned are derived from a structure which primitively sur- 
rounded the whole organ, persistence in the posterior region 
only being in such forms as Polygordius, perhaps associated 
with the filling up of the prz-oral lobe by the brain, while the 
existence of an elongated proboscidiform prostomium in Nais 
renders it most convenient to preserve the musculature in 
front. But such a circumeesophageal apparatus as is here in- 


1 Lang, op. cit., pp. 155, et seq. 
2 Salensky, ‘ Archives de Biologie,’ t. iv. 


120 WwW. F. BR. WELDON. 


dicated is exactly furnished by the Rhabdoccl pharynx 
(fig. 16). 

We seem, therefore, to have in Dinophilus a form which, 
related on the one hand to the Archiannelids, retains on the 
other many features characteristic of the ancestor common to 
those groups (especially Cheetopods, Gephyreans, Mollusca, 
Rotifers, and Crustacea) which possess a more or less modified 
trochosphere larva ; and of these the relations of the body cavity, 
of the excretory system, and of the pharynx, seem to point 
unmistakeably to a Turbellarian origin. 


EXPLANATION OF PLATE X, 


Illustrating Mr. W. F. R. Weldon’s Paper ona “Species of 
Dinophilus Gigas.” 


List of Reference Letters. 


aa. Anus. c.p. Cephalic ciliated pits. cz. Transverse ciliated bands. 
BE. Hye. e. gi. Gland cells of lips. gv. Granular cells of ectoderm. 4%. ph. 
Horizontal diverticulum of pharynx. Zz. Intestine. /.m. Longitudinal muscle- 
fibres. J. Mouth. m. ph. Muscular appendix of pharynx. m. ep. Myo- 
epithelial cells of ectoderm. MMe. Median lobe of gonad. we. Position of 
observed nephridia. x. 7. Nerve-fibres. 2. g. Nerve-cells. 2.7. Lateral 
nerve-cord. «@. Csophagus. 7. m. Circular muscles. s¢. Stomach. s. A. 
Cephalic sense hairs. sh'. Post-cephalic rings of sense hairs. w. Deep cells 
of cephalic ectoderm. Sr. Brain. S¢. Stomodeal musculature. 


Fies. 1—10.—Dinophilus gigas. 

Fig. 1. The live animul extended, seen by transmitted light. 

Fig. 2. A specimen contracted by treatment with corrosive sublimate 
solution, but not otherwise distorted. This figure shows fairly well the 
shape assumed on irritation by the live creature. 

Fig. 3. A transverse section through the pre-oral lobe. 

Figs. 4—6. Transverse sections through the pharyngeal region. 


ON DINOPHILUS GIGAS. 121 


Fig. 7. The muscular bulb of the pharynx, in transverse section. 
Fig. 8. Section through the middle of the trunk. 
Fig. 9. Section through junction of stomach and intestine. 
Fig. 10. Section of ventral ectoderm. Zeiss’s im., oc. 2. 
Figs. 11—16.—Diagrams of various forms of pharyngeal apparatus, as 
seen in longitudinal sections of the head. 


Fig. 11. 
Fig. 12. 
Fig. 13. 
Fig, 14. 
Fig. 15. 
Fig. 16. 


Dinophilus (original). 

Polygordius (schematised from Uhljanin). 
Histriobdella (schematised from Foettinger). 
Terebella larva (schematised from Saleusky). 
Navis (schematised from Vejdovsky). 

Vortex (schematised from von Graff ). 


VOL. XXVIII, PART 1.—NEW SER. I 


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The Development of the Mole (Talpa Europea). 
STAGES E to J. 


By 


Walter Heape, M.A., 
Resident Superintendent of the Plymouth Laboratory of the Marine Biological 
Association of the United Kingdom. 


With Plates XI, XII, and XIII. 


Durine the preparation of the following paper I have been 
conscious that a considerable proportion of the matter included 
is of little special interest; at the same time it has appeared 
to me that the course of the development of certain organs in 
the Mole deserves to be recorded, and in order to do so satis- 
factorily I have been compelled to mention much which is not 
different from embryological phenomena already observed in 
other Vertebrates. 

I have further been led to hope that a somewhat complete’ 
account of the development of one of the Insectivora will not 
be without value. 

To facilitate reference I have described the development of 
the embryo in stages, which, in continuance with the stages of 
growth described in a former paper (No. 8), will be called 
Stages E, F,G, H,and y. A summary of the various sections of 
this paper will be found on p. 150. 


EXTERNAL FEATURES. 


Stage E—The youngest embryo which I have figured (fig. 1) 
lies flat upon the surface of the blastodermic vesicle. The 
embryo is ‘76 mm. long, and is narrow in the centre and wider 

VOL, XXVII, PART 2.—NEW SER. K 


124 WALTER HEAPE. 


at eachend. A shallow medullary groove runs down the centre 
of the long axis of the embryo, which in its turn is narrow in 
the centre and wider at either end. On each side the medul- 
lary groove in the central narrow portion of the embryo, three 
protovertebre may be seen already formed. 

The hinder end of the embryo is thickened owing to the 
growth of the mesoblast of the primitive streak, while anteriorly 
it is flattened out to form the cephalic plate. The shaded 
portion surrounding the embryo (a.p.) is the extent of the 
area pellucida at this age. 

Fig. 2 represents a slightly older embryo of the same stage 
of growth (1°82 mm. long). The medullary folds have here 
begun to form, they are raised somewhat, and in the centre of 
the embryo are already approximated. At the anterior end the 
floor of the medullary groove, on either side, is swollen, and on 
the outer and anterior edge of the two masses so formed a deep 
narrow groove indicates the commencement of the formation 
of the optic organs and will be referred to as the “ optic 
grooves.” 

This early appearance of the organ of sight 1s, so far as I am 
aware, peculiar, and is worthy of notice; even at this age the 
grooves are directed outwards and downwards, and have their 
origin from the most anterior portion of the medullary groove. 
The curved condition of this embryo is due to careless manipu- 
lation whilst it was in a fresh and soft state. 


Stage F. — Fig. 3 represents an embryo of this stage of 
growth ; it is 1:96 mm. long. The medullary folds have met, 
although they have not yet coalesced, in the middle of the 
embryo, and have extended thence forwards. 

The anterior end of the medullary canal is, however, still 
widely open, and the two thickenings of the floor and sides of 
this portion are shown. The optic grooves are also indicated 
in the same manner as they were in the previous figure. 

It will be observed that the sides of the medullary canal at 
the anterior end have grown forwards in advance of the floor. 
At the hind end the medullary canal is widely open, forming 


THE DEVELOPMENT OF THE MOLE. 125 


the sinus rhomboidalis. On either side of the embryo, just 
behind the widely open anterior end of the medullary canal, a 
ridge extends backwards and onwards over the blastodermic 
vesicle ; these ridges are the first traces of the two tubes which 
will eventually form the heart (compare fig. 5, hi.). 

Figs. 4 and 5 are two drawings of an embryo of about 
the same age as that last described (Stage r). The length of 
the latter is, however, greater than that of the former embryo, 
being 2°12 mm., while the medullary groove is not so far ad- 
vanced in development. My object in drawing fig. 4 is not 
only to show these points but to represent the amnion, which 
is as yet developed only at the hind end of the embryo, 
and has already grown nearly half way over the back of the 
embryo. 

Fig. 5 is a transparent view of the same embryo, and indi- 
cates the position of the first five protovertebre, and of the 
commencing tubes (At., ht.) which eventually will form the heart. 
The blind lateral prolongations of the medullary groove at the 
cephalic end are the optic grooves. In this figure also the 
floor of the sinus rhomboidalis at its posterior end is seen to 
contain a much thickened, forwardly projective knot, which, as 
will be shown in sections, is the anterior end of the primitive 
streak. The medullary folds may therefore be described as 
extending posteriorly behind the front end of the primitive 
streak. 


Stage G.—Stage a is represented by the embryo drawn in 
fig. 6. The hinder portion of the medullary canal is much 
the same as before; anteriorly, however, development has pro- 
gressed, and the edges of the medullary folds have come 
together and partially fused up at the anterior end of the 
embryo. At the extreme end, however, a pore is left, owing 
to the more rapid growth of the sides than of the floor of the 
canal as pointed out above. At this stage, therefore, the 
neural canal is still open to the exterior, both anteriorly and 
posteriorly. 

The optic grooves are now closed, and have given rise to the 


126 WALTER HEAPE. 


optic vesicles ; these are shown as two bud-like vesicles pro- 
jecting outwards and backwards, and slightly downwards from 
the front end of the neural tube ; behind them the swelling of 
the fore-brain is discernible, while still further backwards and 
at the edge of the body of the embryo the two tubes of the 
heart are indicated. 

The folding off of the embryo from the yolk-sac has at this 
stage made some progress, and, indeed, the whole of the head 
of the embryo as far back as the line so. pl. now lies projected 
freely above the blastodermic vesicle. 


Stages H and J.—These stages are depicted in figs. 7 and 9, 
the embryo represented in the former figure being 2:2 mm. 
long, that in the latter figure 3°06 mm. long. The more com- 
plete closure of the medullary canal and the constriction of its 
anterior region into fore-, mid-, and hind-brains is to be noticed. 
The optic vesicles are still seen in fig. 9; in fig. 7 they are 
barely noticeable, owing to the curved position of the embryo 
when drawn. 

The increase of the protovertebrz and the gradual reduction 
of the sinus rhomboidalis is also seen, while the thickened 
anterior end of the primitive streak is now enclosed within 
the posterior walls of the medullary canal, and projects up- 
wards as a rounded knob at its hinder end. 

The direction of the increase of the protovertebre is a 
difficult matter to determine, but a careful examination and 
measurement of figs. 5, 7, and 9 leads me to believe that in all 
probability the increase is almost altogether posteriorwards 
during those stages. The embryo (fig. 7) of Stage u has, 
however, apparently one protovertebree more anteriorly than 
the embryo of Stage F (fig. 5), and the embryo (fig. 9) of 
Stage s one more than that of Stage u (fig. 7). The embryos 
of Stages & and F are more difficult to compare (figs. 1 and 
5), but I think it is highly probable the increased number in 
the latter is due to a backward growth. 

The amnion at Stage n completely covers the embryo (fig. 
7), an anterior limb having grown over the head as the 


THE DEVELOPMENT OF THE MOLD. 127 


posterior limb grew over the tail at an earlier period (Stage r, 
’ fig. 4). 

The anterior fold of the amnion (vide p. 146) is the so-called 
pro-amnion of Beneden and Julin (No. 2). It must be noted 
that up to the close of Stage s no signs of a folding off of the 
tail end of the embryo can be observed, and, indeed it is not 
until considerably later that this process takes place. 

The first junction of the two tubes to form the heart takes 
place during Stage u, and is shown in fig. 8; while the side 
view of the head of the embryo drawn in fig. 10 (Stage J) 
shows the relation of the heart to the visceral arches, and the 
arrangement of the latter. 

There are at this stage five visceral arches. Faint grooves 
indicating the partial formation of two and even three visceral 
arches may be discerned during Stage u, but it is not until 
Stage 5 is reached that they can be satisfactorily outlined. 

For the comparison of these figures with figures of other 
mammalian embryos I would refer to papers Nos. 3, 4, 5, 6, 7, 
9, and 10. 


Tue EPrisiast. 


Soon after the epiblast is first definitely produced it is in the 
form of a plate of columnar cells of uniform thickness over the 
whole embryonic area, and passing abruptly at the edge into 
the flattened epiblast cells which cover the remainder of the 
embryonic vesicle. This stage is figured in a former paper, 
No. 8, fig. 30. 

During the primitive streak stage of growth and the early 
formation of the medullary groove, the lateral epiblast becomes 
reduced in thickness and at the edge of the area the cells 
gradually assume a flattened condition and blend without 
a break with those of the vesicle (l.c. figs. 32—36, and 
43—46). 

The appearance of protovertebre and the deepening of the 
medullary groove is attended by a further modification of the 
epiblast of the embryo. 

During Stages & to c the median portion becomes thickened 


128 WALTER HEAPE. 


and forms the medullary plate (fig. 15) while the lateral por- 
tions become gradually still more reduced in thickness, until in 
those portions of the embryo where the medullary groove has 
attained its greatest depth prior to its conversion into a canal 
the lateral epiblast is formed for the most part of a single row 
of somewhat cubical cells, continuous, without modification, 
either over the vesicle or across the embryo as the inner fold 
of the amnion (fig. 17). 

Where the lateral epiblast joins the wall of the medullary 
groove there is now an abrupt transition from the columnar 
cells lining the latter to the cubical cells of the former. 

Subsequently, Stages H.J., in that portion of the embryo 
where the neural canal is formed, the closure of the medullary 
groove causes the approximation of the lateral portions of the 
epiblast, which fuse, and thus form a continuous layer across 
the embryo. The cubical epiblast cells at the same time become 
much flattened on the dorsal surface of the embryo (figs. 26, 29, 
and 47), while (1) in the trunk, the cells of that portion of epi- 
blast which overlies the somatic mesoblast remain cubical 
(figs. 26, 27, 29, and 47); and (2) in the anterior region, the 
cells of certain portions which either give rise to sensory 
structures (figs. 25 and 46), or which surround externally the 
visceral arches (figs. 23 and 46) assume again a columnar 
form. 

In that region of the trunk where the medullary canal is 
still open the lateral epiblast cells remain as before, cubical. 

The Medullary Groove.—At the commencement of Stage E 
a deep medullary groove exists about the middle of the embryo ; 
anteriorly and posteriorly it is shallower however, finally ter- 
minating in the latter direction upon reaching the anterior end 
of the primitive streak, while in the former direction all trace 
of the groove is lost some considerable distance behind the front 
end of the embryo. 

Beyond the anterior end of the medullary groove the epiblast 
is thickened to form the “ cephalic plate.” 

Fig. 1 is a transparent view of an embryo with three proto- 
vertebr, and shows the relations above mentioned; I have 


THE DEVELOPMENT OF THE MOLE. 129 


also figured three transverse sections, which indicate the struc- 
ture and form of (1) the cephalic plate (fig. 12) ; (2) the groove 
in its anterior portion (fig. 14); and (3) the groove in its 
posterior portion (fig. 15). 

In fig. 12 the thick cephalic plate is shown, becoming folded 
off from the yolk-sac; fig. 14 is taken from the region in front 
of the protovertebre, and depicts the wide and shallow groove, 
the wall at the bottom of which is considerably thinner than 
at the edge of the groove ; and in fig. 15, taken from the region 
of the second protovertebra the medullary groove is V-shaped, 
and the columnar cells of which it is formed pass abruptly into 
the lateral epiblast cells, thus indicating the extent of the 
“medullary plate.” 

At the hind end the wide and shallow medullary groove 
forms the so-called “sinus rhomboidalis.” <A section through 
this region of an embryo during Stage Fr is shown in fig. 18. 

At the close of Stage & the groove has considerably increased 
in length, and during Stage F it reaches to the anterior end 
of the embryo (figs. 3 and 16). The latter figure is a trans- 
verse section through the anterior end, and shows— 

(1) The median medullary groove. 

(2) The commencement of the curvature upwards of the 
lateral portions of the cephalic plate and the formation of the 
two “optic grooves” (op. gr.), seen in surface view in fig. 4, 
which give rise when the neural canal is closed, to the optic 
vesicles. 

The Medullary Canal.—The medullary plate is now sharply 
marked off from the lateral epiblast from a considerable dis- 
tance in front of the first protovertebra backwards to the pos- 
terior end of the embryo, and the groove itself commences to 
close in the region of the protovertebrez. 

The closure is effected by the approximation of the peri- 
pheral edges of the medullary plate, a sharp angle being thus 
formed at the junction of the lateral epiblast with the edge of 
the plate (fig. 17). 

The closure commences at a late period of Stage e¢ in the 
region of the first provertebra, extending thence forwards and 


130 WALTER HEAPE. 


backwards ; it proceeds very rapidly, being at the end of this 
stage, although open at its immediate anterior end (fig. 6), 
closed from there posteriorly until the fourth protovertebra is 
reached, after which point it gradually widens out into the 
sinus rhomboidalis (figs. 28 to 33). 

At the close of Stage 4 a narrow slit-like pore is all that 
remains open at the anterior end (fig. 20), while posteriorly it 
is closed as far back as the eighth protovertebra; and at the 
end of Stage s the whole groove is converted into a canal until 
the last, the fourteenth, protovertebra is reached. 

The sinus rhomboidalis is now narrow and shallow (figs. 48 
and 50). The swelling in the floor at the hind end of the 
sinus rhomboidalis is caused by the mesoblast of the front end 
of the primitive streak (figs. 33 and 35 ; 48 and 50). 

When the canal is first formed, its lumen—except in the 
anterior region which is described below—is a narrow slit and 
its walls are thicker at the sides than they are dorsally and 
ventrally (fig. 28) ; soon afterwards, however, during Stage u, 
the middle portion of the lateral walls thickens still more and 
projects into the narrow lumen of the canal, thus converting it 
into an hour-glass form (fig. 29). 

The cells of the cord are much elongated, and their nuclei, in 
‘general, oval (fig. 43). 

I may in this place mention there appears to me to be great 
likelihood of the migration of mesoblast cells into the walls of 
the medullary canal during Stages n and gs. Sections of an 
embryo belonging to the former stage present strong evidence 
of this process (fig. 43). Two masses of mesoblast cells are to 
be seen in very close connection with the lateral walls of the 
canal in the region of the neck, and from these masses I feel 
inclined to believe certain cells grow into the tissue of the 
nervous system. 

As I will show below, these masses of cells are in connection 
with two blood-vessels, which are in process of formation, and 
it would appear highly probable that these ingrowing meso- 
blast cells give rise to the blood-vessels of the spinal cord. 

The Brain.— When the medullary groove first closes in 


THE DEVELOPMENT OF THE MOLE. 131 


(Stage e) it is wider in front of the first protovertebra than it 
is in the latter and posterior regions, and faint indications of a 
division of the brain into portions may be discerned in section, 
and to some extent also in the surface view of this stage; the 
hind-brain, with its somewhat thinner roof, is of considerable 
length and blends into an anterior portion in which the roof is 
thicker. Stage uo shows some little advance upon this; the 
cranial flexure has begun (fig. 34) and the cavity of the brain 
has increased in size, the roof of the hind-brain also is thinner 
and wider than before (fig. 23). 

At the close of Stage s three divisions of the brain are indi- 
cated (fig. 49). There is a well-marked cranial flexure, and at 
what is now the anterior end of the animal the mid-brain is 
situated. The cavity of the mid-brain is partially separated 
from that of the fore-brain by a constriction of the walls at the 
junction of the two, but the structure of the wall is very 
similar in both portions. The hind- and mid-brains pass into 
one another without any such constriction, but the thin roof of 
the former distinguishes it from the latter. The lower wall of 
the hind-brain at the posterior end is now much folded. The 
lower wall of the fore-brain is curved downwards, forming a 
short and wide diverticulum which marks the first appearance 
of the infundibulum. The apex of the infundibulum comes 
into close connection with the anterior end of the alimentary 
tract and with the notochord overlying it (fig. 49). 

The Optic Vesicles—The optic grooves seen in the head in 
surface view in figs. 2 and 5 are the rudiments of the optic 
vesicles ; they are shown in section in fig. 16. Later (Stage 
H), when the medullary groove forms a closed canal in the 
head region, these grooves become wide lateral diverticula pro- 
jecting from the anterior portion of the brain, and constitute 
the optic vesicles (fig. 20). They are situated dorsally on 
each side the middle line, and are projected outward and 
somewhat downwards and backwards. 

Such a condition is clearly shown in surface view in fig. 9, 
Sections of this stage show a very similar condition as regards 
the development of the vesicles; they merely extend slightly 


132 WALTER HEAPE. 


further outwards, but do not at this stage fuse with the 
external epiblast (fig. 21). 

The wall of the optic vesicles is similar in structure to the 
wall of the remainder of the fore-brain. 

It is interesting to note that for a considerable period after 
Stage 3 the optic vesicles show but very slight advancement on 
the condition then attained; their growth appears now to be 
retarded in as marked a degree as it was advanced in the early 
stages. The early appearance of the optic grooves will probably 
be recognised as a mammalian distinction when the embryo- 
logy of more species of Mammalia has been worked, but the 
sudden checking of the development in the Mole we may 
expect is due to the specialisation of this species. Any modi- 
fication of an important sensory organ would doubtless rapidly 
affect the development of the organ, but such an extended 
modification as is apparent here says much for the primitive 
nature of the habits of the animal. 

The Ear.—The first indication of the ear arises during Stage 
H as a thickening of the external epithelium on each side the 
hind-brain (fig. 25). The thickening extends along a great 
portion of the hinder half of the hind-brain, and during Stage 
J increases in thickness and becomes grooved along the greater 
part of its length (fig. 46). 

The Cranial and Spinal Nerves.—I do not propose to describe 
the development of the cranial and spinal nerves in this paper. 
I hope to make a separate communication upon this portion 
of the development at some future time. 


Tue Hyposuast. 


The hypoblast in the earliest condition of Stage & is similar 
to what it was in Stage p (described in my former paper, No. 
8), and is composed of a single layer of flattened cells extending 
on all sides over the embryonic area (figs. 13, 14, and 15). 

The cells in the median line give rise to the notochord, and 
the changes they undergo will be described in detail in another 
section of this paper. 

The formation of the deep medullary groove in Stage p and 


THE DEVELOPMENT OF THE MOLE. 133 


the thickening of the vertebral portions of the mesoblast 
causes the hypoblast cells underlying those structures to be 
stretched out as it were and flattened (No. 8, fig. 45). 

In Stages & and F this condition may still be seen where the 
groove is deepest in front of the protovertebre (fig. 13) ; 
anteriorly the groove becomes shallower and the hypoblast 
cells more rounded in consequence (fig. 14), while posteriorly 
the formation of protovertebre forces the lateral hypoblast 
downwards, and the axial hypoblast cells are again thickened 
(figs. 15 and 17). 

In the region of the sinus rhomboidalis the medullary groove 
again projects considerably below the level of the peripheral 
body wall, and, forcmg the hypoblast cells downwards also, 
flattens them. 

This condition in the anterior region and posteriorly below 
the sinus rhomboidalis is, however, soon modified; the thick- 
ening of the peripheral mesoblast and the gradual depression 
of the body wall brings the lateral portions of the hypoblast 
on a level with the axial portion throughout the length of the 
embryo, and at the close of Stage s the cells of the whole 
layer, wherever it is not converted into the alimentary canal, 
become rounded. 

The Alimentary Canal.—The first trace of the alimentary 
canal appears during Stage pv (vide No. 8, fig. 46) at the 
anterior end of the embryo as a short tubular diverticulum. 
In the paper referred to I described this tube as the noto- 
chord, an error which I have corrected here and in more detail 
in p. 136 of the present paper in the section devoted to that 
organ. 

This structure is indicated in figs. 1] and 12, Stage zr. The 
diverticulum has but a small lumen, and is situated close 
against the cephalic plate; the cells of which it is formed are 
columnar. 

Stages c and H witness further changes ; the fore-gut is now 
considerably longer (fig. 34). It is rounded anteriorly (fig. 
- 22), but farther backwards is widened out laterally (fig. 19) 
and becomes flattened and crescent shaped, the lateral horns 


134 WALTER HEAPE. 


of the crescent being projected upwards and somewhat closely 
approximated to the lateral epiblast of the embryo (figs. 19, 
23, and 24). 

The epithelium of the dorsal border of the sac is thinner 
than that of the ventral border, the difference being more 
apparent in the hinder portion than in the front portion of 
the sac. The points of the lateral horns are lined with 
cylindrical cells. 

There is no distinct evidence at this stage (H) of outgrowths 
of the fore-gut in the position of the future visceral arches, 
but slight indications of the invagination of the epiblast may 
be seen corresponding to the grooves mentioned in the descrip- 
tion of the surface view of an embryo of Stage u. 

On the ventral surface at the anterior end of the fore-gut in 
Stages c and u (figs. 19 and 22) two slight invaginations of 
the epiblast may be seen one on either side of the middle line, 
and a few sections further backwards the epiblast and hypo- 
blast are closely applied in the middle line, and there is a deep 
median groove in the epiblast (fig. 23). 

At the close of Stage s there is a still further change in these 
relations. The lateral outgrowths of the fore-gut are now 
directed towards invaginations of the epiblast which corre- 
spond to the grooves mentioned in the description of a surface 
view of an embryo of this stage (Stage J). 

The outgrowths are directed outwards and downwards from 
the lateral portions of the lumen of the canal (fig. 46). 

The hypoblast and epiblast have met and are partially fused 
in the case of the anterior diverticula, although there is as yet 
no perforation constituting a definite cleft, but in the more 
posterior diverticula the hypoblast does not meet the epiblastic 
involution. Now also the fore-gut is a little longer, and the 
fusion of epiblast and hypoblast on the ventral surface near the 
front end is closer, although the perforation to form the mouth 
has not yet taken place (fig. 49). 

This invagination of the epiblast is clearly seen in an embryo 
of this stage to be in the form, anteriorly, of two shallow 
grooves which converge posteriorly, these forming a deep 


THE DEVELOPMENT OF THE MOLE. 135 


median invagination (figs. 44, 45). These grooves are formed 
along the anterior border of the first visceral arch. The epi- 
blast and hypoblast are in close contact along the whole of the 
V-shaped groove, but become actually fused posteriorly at the 
apex, where the mouth will eventually be formed (compare 
figs. 44, 45, and 49). 

It will be seen by the foregoing description that the mouth 
is formed somewhat behind the anterior end of the fore-gut at 
the apex of a V-shaped groove on the ventral surface of the head, 
the diverging limbs of which groove are directed forwards. 
The section of the gut which is placed anteriorly to the 
mouth is identical with the blind tube first formed by the 
folding-off of the embryo from the yolk-sac, and this anterior 
diverticulum exists for some time after the ventral enlargement 
of the gut towards the external groove. 

These facts appear to indicate that a more primitive mouth, 
the terminal position of which is indicated by the primary 
anterior diverticulum of the fore-gut, has been replaced by a 
secondary formation, the paired origin of which is rendered 
possible by the two converging grooves in the epiblast of the 
ventral surface. 

If these observations are correct, they must be considered to 
some extent confirmatory of Dr. Dohrn’s theory of the paired 
origin of the existing mouth of the Vertebrata, but I would 
suggest that such evidence cannot be used as argument for the 
paired formation of the primitive Vertebrata mouth, the 
terminal position of such being exceedingly probable. 

As in the earlier stage, the cells forming the dorsal wall of 
the fore-gut are throughout thinner than those lining the 
remainder of the cavity, and in the posterior section of its 
length are much flattened ; on the other hand the cells of the 
ventral wall, the lateral horns, and the outgrowths to form the 
visceral clefts, are cubical or even columuar in form. 

The Notochord.—The notochord, as I have before described 
(No. 8, figs. 37—48), is a hypoblastic structure and is primi- 
tively in connection with the hypoblast and the lateral plates 
of mesoblast of the embryo. During Stage p it becomes first 


136 WALTER HEAPE. 


separated from the lateral mesoblast, then reduced in thickness, 
and finally converted (1) in the anterior region into an arc 
formed of a single row of columnar cells; (2) towards the 
central deepest portion of the medullary groove into a single 
row of considerably flattened cells; while (3) in the hinder 
region it remains thickened and forms posteriorly the 
anterior wall of the neurenteric canal, thus joining the 
epiblast. 

During this stage (Stage p), the notochord is, throughout 
its whole length, never actually isolated from the hypoblast, 
but remains a portion of that layer, although an obviously 
specialised portion; it is in fact the remnant of the primitive 
hypoblast (1. c.). 

In this same paper (l.c. fig. 46) I described as a portion of 
the notochord a short tube formed of columnar cells lying 
below the medullary plate at the anterior end of the embryo. 
I must here correct that error. This tube does not represent 
the notochord solely, but constitutes the anterior end of the 
alimentary tract (figs 11 and 12), and, as I shall show below, 
the cells only of the dorsal portion of this tube give rise 
eventually to the anterior end of the notochord. 

During Stages © and F the relations of the notochord 
remain very much the same as they were during Stage p (figs. 
14,15, and 17) ; it is noticeable, however, at the close of Stage Fr, 
that in the trunk of the embryo, where the medullary groove 
is deep, the axial hypoblast has increased in thickness 
(fig. 17). 

The deepening of the medullary groove towards the anterior 
region which occurs during Stage G causes the notochord cells 
situated there to be reduced in the same manner as they were 
reduced in the central region during Stage p. Similarly the 
axial hypoblast is reduced in bulk in the posterior region of 
th eembryo, while in the central region, where the protovertebrz 
are forming, there is a further increase in the size of the 
notochord. 

At this stage of growth (Stage e) the notochord exhibits a 
tendency to become separated from the hypoblast layer in the 


THE DEVELOPMENT OF THE MOLE. 137 


same manner, although not with precisely the same result, as 
when the neurenteric canal was formed in Stage p. 

The process in the latter stage involved the ingrowth of the 
lateral portions of hypoblast and the conversion of the axial 
portion, containing the neurenteric canal, first into an arc and 
then into a complete tube. Now the lateral hypoblast grows 
inwards below the axial portion of primitive hypoblast and 
unites to form a continuous layer, merely causing the isolation 
of the axial portion as either a solid rod or band of cells which 
lies freely between the hypoblast and the medullary canal. It 
is, however, true that a lumen may appear in some of the por- 
tions of the notochord which are rod like, although its conver- 
sion thus into a tube is, so far as I can determine, a secondary 
matter, and is not connected with the method of isolation. 

The isolation of the notochord first occurs in the region of 
the first protovertebra during Stage Gc, and extends during 
Stages Hw and J anteriorly and posteriorly. The separation 
does not, however, appear to be a continuous process, and the 
shape of the isolated notochcrd is very various. To demon- 
strate these facts I have figured several sections of an embryo 
with nine protovertebre (Stage u, figs. 24 and 36 to 42). 

In this embryo, in front of the first protovertebra, the noto- 
chord is isolated for some distance as a rod or thickened band 
(figs. 24 and 37), in which a lumen may occasionally be seen 
(fig. 86: compare also figs. 23 and 25, which are drawings of 
sections through another embryo of this stage). 

In the region of the first protovertebra, it is in the form of 
a flattened band consisting of a single row of cells (fig. 38), 
and this condition persists, except here and there, where the 
notochord is not completely isolated (fig. 39), until the fourth 
protovertebra is reached ; here it increases in size. From this 
point it is more frequently attached to the hypoblast (fig. 40), 
and posterior to the seventh protovertebra is not isolated at all. 
Immediately behind the seventh protovertebra it is in the form 
of an are (fig. 41), which further backwards flattens out, and 
the mass, increasing in size, joins the front end of the primitive 
streak (fig. 42). 


138 WALTER HEAPE. 


Such is the condition of the notochord during Stage H. At 
the close of Stage 5s, however, the whole of the notochord, 
except at the immediate anterior end, backwards to the ninth 
protovertebra, is isolated as a rod of varying size and shape 
(figs. 46 and 47). Behind the ninth protovertebra it becomes 
band shaped and continues in this form, still distinct from the 
hypoblast, for some distance behind the last (fourteenth) proto- 
vertebra. It then again assumes the form of a rod, although 
of much larger size than in the anterior region, in the centre 
of which a lumen may here and there be seen, and joins the 
anterior end of the primitive streak becoming thus connected 
there with the epiblast, hypoblast, and lateral mesoblast 
(fig. 50). 

The phenomena I have here described, viz.: (1) the presence 
of a mass of primitive undifferentiated hypoblast in the 
median line (Stage p) ; (2) its reduction to a thin, even single 
layer of cells (Stages p, £, and F), and (3) the conversion of 
those cells into the notochord (Stages c, H, and 3); these 
phenomena, in my opinion, indicate without doubt that this 
organ is of hypoblastic and not of mesoblastic origin. 

Further, during the isolation of the notochord, (a) the 
appearance, vague though it be, of an are of notochordal cells ; 
(6) the fact that the isolation of the solid rod or band com- 
mences at the two sides and gradually extends across the 
median line (figs. 39—42); and (c) the occasional appearance 
of a lumen in this rod,—these appearances indicate that it is 
formed in the same manner as the notochord of Amphioxus, 
that is to say by the ingrowth of the Jateral hypoblast and the 
constriction of the axial mass of primitive hypoblast cells. 

I have already discussed the views of other observers upon 
this subject (No. 8) and need not again refer to them. 

Figs. 39 and 40 are especially interesting in regard to the 
isolation of the notochord. In both these drawings the 
process of isolation is shown taking place; in both the noto- 
chordal tissue is in the form of a pair of knobs connected by a 
median more slender portion; and in both cases when the 
notochord is actually isolated it will be isolated as a band of 


THE DEVELOPMENT OF THE MOLE. 139 


greater or less substantiality. It will be noticed the knobs 
are more or less free from the underlying flattened hypoblast 
cells, while in the median line there are no flattened cells, thus 
showing the process of the growth of the lateral hypoblast 
below the axial primitive hypoblast. 

The relation of the notochord at the front end of the embryo 
requires special notice ; it will be best understood by a reference 
to figures of longitudinal sections through embryos of Stage 
E (fig. 11), Stage u (fig. 34), and Stage 5 (fig. 49). In 
fig. 11 the notochord is not separated from the roof of the 
fore-gut; in fig. 34 it remains attached to the anterior wall 
of the fore-gut, although isolated posteriorly ; but in fig. 49 the 
notochord, although joined at its anterior extremity to the 
hypoblast, is separated from it throughout its extent posteriorly. 

The hooked anterior end of the notochord, so characteristic 
of this organ, is seen to be due, in the Mole, to the fact that it 
is derived from the anterior wall of the alimentary tract after 
the cranial flexure has commenced. 

At the close of Stage s, therefore, the notochord is continu- 
ous with the epiblast at the front end of the embryo, by means 
of the front wall of the fore-gut, which is fused with the 
epiblast at the point where the mouth will eventually be 
formed ; and posteriorly, at the anterior end of the primitive 
streak, where epiblast, hypoblast, and mesoblast are all joined 
together (compare figs. 49 and 50). 

The close relation of the fore-brain to the notochord, a rela- 
tion brought about not so much by the cranial flexure as by 
the ventral enlargement of the brain at this point, will be 
referred to in another communication, which I hope shortly to 
make, upon the pituitary body of the Mole. 

There is one other point of interest in the growth of the 
notochord in the Mole, and that is its size compared with the 
nervous system. The relative size of the notochord compared 
with the nervous system is less in the higher than it is in the 
lower Vertebrate embryos. In the Mole the notochord is rela- 
tively smaller than it is in any other Vertebrate embryo I am 
acquainted with, and it appears to me the reduction in size is 

VOL. XXVII, PART 2.—NEW SER. I 


140 WALTER HEAPE. 


due to the comparatively early development of the nervous 
system. During the early part of Stage p there is a consider- 
able mass of primitive hypoblast along the axial line of the 
embryo, but the rapidly forming medullary groove pressing on 
to this mass before it has become formed into a rod capable of 
resisting much pressure, causes it to bulge inwards and thus 
flattens out its cells, administering an effective check to the 
development of the organ. Such a check occurs during Stages 
p and £. Subsequently the thickening of the lateral meso- 
blast plates and the consequent depression of the lateral hypo- 
blast, removes the strain from the axial cells and admits of the 
isolation of the slender rod or band which exists for the 
greater portion of the length of an embryo Mole at the close 
of Stage s. 


Tue MeEsos.3ast. 


At the close of Stage p the mesoblast in front of the 
primitive streak is in the form of two lateral plates which are 
connected together across the middle line by means of a mass 
of undifferentiated hypoblast, except during a short space 
where they are separated by the deep portion of the medullary 
groove. 

At the periphery these mesoblastic plates are split into two 
layers, an upper somatic and a lower splanchnic layer, along 
the whole of their extent posterior to the cephalic plate. The 
split is entirely peripheral, however, and does not extend into 
the embryonic area (vide former paper No. 8). 

The Mesoblastic Somites and the Body Cavity During 
Stage E the spiitting of the mesoblast extends further forwards, 
and also inwards towards the medullary groove. I have never 
been able completely to satisfy myself that this splitting ever 
extends to the innermost portion of the mesoblastic plates ; 
but, as I have before explained, the small size of the embryo 
and the dense compact nature of the middle layer renders it 
exceedingly difficult accurately to determine such a point. 

The nearest approach to a continuous split of the mesoblast 
from the axial portion to the periphery which I have seen. is 


THE DEVELOPMENT OF THE MOLE. 141 


represented in fig. 13; and here it will be seen, although there 
is No positive division into somatic and splanchnic layers, yet 
such a division is indicated in the section by the arrangement 
of the nuclei of the cells on each side a line, which is repre- 
sented by a narrow band of a lighter shade than the surrounding 
tissue. 

In sections of three other embryos which I have examined, 
about the centre of the medullary groove there is similarly an 
indication of the splitting of the mesoblast from the periphery 
to the axial portion, the cells being arranged in two parallel 
rows along the inner edges of the two layers of mesoblast, 
although no cavity is actually formed. Thus, although it 
cannot be said that a split actually occurs through the whole 
plate of lateral mesoblast in the Mole, yet there is without 
doubt a tendency to such splitting in embryos of Stage = about 
the centre of their body. 

In the same stage of growth (Stage £) is to be observed : 

(1) The separation of the axial and peripheral portions of the 
mesoblastic plates, these two portions being connected by a 
narrow neck of cells, the intermediate cell mass; and (2) 
the formation of protovertebre by means of clefts in the 
axial mesoblast at right angles to the long axis of the embryo, 
which divide this portion into cubical masses. The indication 
of the splitting of the mesoblast at the same time becomes 
more definite, and results in a cavity (fig. 15) within both the 
protovertebre and the peripheral mesoblast, a cavity which 
does not, however, extend through the intermediate cell mass 
(compare also fig. 17, Stage F). 

The cells of the protovertebre are radially arranged round a 
narrow elongated cavity, and form in a transverse section through 
the middle of a somite a triangular mass, the apex of which is 
situated at the base of the medullary groove. 

The cells of the peripheral mesoblast in the region of the 
protovertebre are columnar on their inner side and border, a 
narrow slit extending to the periphery. At the edge of the 
area the cells become flattened, and form a thin somatic and 
thicker splanchnic layer, extending over the yolk-sac, 


142 WALTER HEAPE. 


An examination of consecutive sections reveals, in front of 
the protovertebr, the axial and peripheral mesoblast in the 
form of a continuous solid plate, with no cavity in the axial 
portion ; while in the peripheral portion the cavity gradually 
recedes outwards (fig. 14) until it no longer exists within the 
limits of the embryonic area. 

Behind the protovertebre the cavity in both axial and peri- 
pheral mesoblast becomes at once and simultaneously oblite- 
rated, and two thick solid lateral plates of mesoblast extend 
backwards, and join the mesoblast of the primitive streak. 

As the medullary groove closes in, the protovertebree become 
more cubical and compact (compare sections of Stage u, show- 
ing these points (figs. 31, 30, and 28) ), and the narrow slit re- 
duced to a small central pore, which about this time becomes 
very generally partially filled up by a core of cells derived from 
the lower and inner portion of the protovertebra. 

The protovertebre then (Stage H) commence, first in the 
anterior region, and gradually assuming in subsequent stages the 
same relation posteriorly, to divide into two portions, an outer 
and dorsal arched portion composed of columnar cells, and a 
lower and inner portion formed of irregularly rounded cells (fig. 
29; compare also fig. 52 of Stage 3), the former giving rise 
mainly to the muscle-plates, the latter to the bodies of the 
vertebre and the connective tissue surrounding them. It will 
be shown subsequently, however, that the inner portion also 
participates in the formation of the muscle-plate. 

A very marked cavity exists between the two portions on 
the outer side of the somite (fig. 29), and the vertebral portion 
of the mesoblast is continued ventrally below the neural canal 
towards the notochord. 

The cavity is derived from the small cavity present in the 
earlier stage (Stage £) ; and it is worthy of notice it is not first 
obliterated and then again formed, as has been stated by some 
observers to be the case in the Chick, nor does it entirely dis- 
appear, as has been supposed to be its fate in Mammalia 
(vide No. 1, p. 553). 

Anterior to the protovertebre scattered mesoblast cells 


THE DEVELOPMENT OF THE MOLE. 143 


exist below the neural canal, closely approximated to the slight 
rod-like notochord (figs. 24 and 26), while in the region of the 
protovertébre the mesoblast is more compact, and does not 
extend so far beneath the medullary canal (fig. 28). 

In Stage s the anterior protovertebre exhibit still further 
changes :—(1) The vertebral portion of the somite has increased 
very considerably in depth ; (2) the cavity has almost entirely 
disappeared, remaining only as a mere slit (fig. 47) within; (3) 
the muscle-plate, which is now formed of two rows of columnar 
cells. The second row lies inside the first, close beside and 
parallel to it. It is formed from the cells of the vertebral por- 
tion of the somite, which have hitherto occupied this position. 
The two rows are continuous with each other at their dorsal 
and ventral ends, and the cavity before spoken of lies between 
them, reduced to a narrow slit. 

Posterior to the three anterior protovertebre the muscle- 
plate consists of only a single layer of columnar cells, as was 
the case in the earlier stage (H). 

The muscle-plates are therefore first formed anteriorly. 

When examining this stage my attention was drawn to the 
histological characters of the cells of the outer layer of the 
muscle-plate in the anterior protovertebre. 

These cells were observed with an ordinary Zeiss D lens 
to be continued outwards into more or less fine processes, and 
upon examining sections with a high power (Powell and Lea- 
land’s ;,th oil immersion and Reichert’s ;4,th oil immersion) 
it was found that these fine processes were branched or simple 
prolongations of the mesoderm cells, which on the one hand 
joined with the ectoderm cells, and on the other formed a 
fine network immediately below the ectoderm. 

These processes are voluntary muscular fibres, which are thus 
early developed from the outer portion of the muscle-plate. 
This structure is fairly satisfactorily represented in fig. 51. 

The fact being observed that these mesoderm cells actually 
joined the ectoderm cells led me to make a renewed exami- 
nation of my sections of earlier stages, and I found that from 
the time the hypoblastic mesoblast was formed in Stage c 


144 WALTER HEAPE. 


(No. 8) it was always possible to trace processes from meso- 
derm cells into the overlying epiblast cells. 

The elongated mesoblast cells shown in fig. 51° are more 
extended in Stage s than they hitherto have been. 

In Stage u (figs. 27—-29) a tendency to elongate may be 
observed in these cells and so also in Stages e and F (fig. 17), 
but it is not until Stage s is reached they can actually be 
described as muscular processes. Further, this condition in 
Stage 5 only exists in a marked degree in the first few anterior 
protovertebre ; further backwards these processes gradually 
decrease in length. 

With regard to the inner layer of the muscle-plate, certain 
of the cells already show a differentiation into elongated 
muscular fibres, but they are not all of them as yet so meta- 
morphosed. 

The protovertebre remain at the close of Stage s still 
separated from one another throughout their depth, and 
between each short blood-vessels run, which are dorso-lateral 
branches from the dorsal aorta (fig. 52). 

The mesoblast at the front end of the embryo now extends 
between the notochord and the floor of the neural canal (figs. 
44, 45, and 49), the embryo having increased dorso-ventrally. 

I find no trace of the body cavity in the head. As was 
stated above, the splitting of the mesoblast never extends to 
the axial portion of this part of the mesoblast, and no cavity, 
as far as I have been able to see, makes its appearance 
secondarily. 

Pericardial Cavity.—The separation of the pericardial cavity 
from the remainder of the body cavity has only commenced 
during Stage 5, and at the close of that stage the mesenteries 
in which the ductus Cuvieri run from the body wall to the 
sinus venosus, divide the body cavity into two dorsal sections, 
one on each side the pleuro-peritoneal cavities, and one median 
ventral section, the pericardial cavity. 

These three sections are all continuous at the anterior end 
into a single cavity surrounding the heart, which is prolonged 
a. considerable distance further forwards. 


THE DEVELOPMENT OF THE MOLE. 145 


Posteriorly the pleuro-peritoneal cavities are each continuous 
with the body cavity contained between the diverging folds of 
the somatopleure and splanchnopleure. 

The Primitive Streak.—During Stages & and F the relations 
of the primitive streak are almost exactly similar to those 
described for Stage p (No. 8), the only difference being the 
extension of the medullary folds backwards round the front 
end of the primitive streak (fig. 18). The lumen of the 
neurenteric canal disappears, but the point where it originally 
existed is shown by the fusion of the epiblast, hypoblast, noto- 
chord, and primitive streak mesoblast at the front end of the 
latter (Stage s, fig. 50). 

In my paper, No. 8, I endeavoured to prove the mesoblast 
of the primitive streak did not extend beyond the point where 
the neurenteric canal was situated, and I showed that over the 
whole of that part of the embryo situated anterior to the 
primitive streak, mesoblast was formed from the hypoblast 
(“hypoblastic mesoblast ”’). 

Now if this be true, it follows that the mesoblast of the primi- 
tive streak takes no part in the formation of the body of the 
embryo anterior to the neurenteric canal, and that the growth 
of the embryo is caused by a multiplication of cells anterior 
to the primitive streak. 

The mesoblast of the primitive streak is, however, a con- 
siderable and hitherto a constantly increasing mass, and it 
extends backwards and outwards beyond the embryonic area. 
It thus occupies the position where eventually the allantois is 
formed, and it is, in fact, the primitive streak mesoblast which 
forms the walls of that organ. 

During the stages now under discussion (e—s) the primitive 
streak becomes partially—almost entirely—divided into two 
portions, an anterior and a posterior portion. The division is 
caused by the formation of two pits—(1) a dorsal pit which 
eventually gives rise to the anus, and (2) a ventral pit which 
projects upwards and backwards into the primitive streak, and 
forms the cavity of the allantois (figs. 35 and 50). 

These two pits constrict the blastoderm and partially divide 


146 WALTER HEAPE. 


the primitive streak into a short anterior portion which projects 
upwards along the floor of the medullary groove at its hind 
end, and into a larger posterior portion which forms the wall 
of the allantois (figs. 33 and 35, Stage u, and figs. 48 and 50, 
Stage J). 

The dorsal pit I have mentioned gives rise to the anus; this 
structure is therefore formed in the middle of the primitive 
streak in the Mole, in the same position as Weldon (No. 11) 
pointed out the anus of Lacertilia is formed. 

The Amnion.—The amnion is first formed, as I have before 
described (p. 127), at the hind end of the embryo; extending 
thence forwards, and being met by the lateral folds of the 
amnion. which also grow, in the first place, from behind forwards 
(figs. 26,28, 35, and 50). This portion of the amnion is formed 
as in the Chick of a double fold of somatopleure. Immediately 
upon the junction of the two lateral folds and the formation 
of true and false amnion, the epiblast of the false amnion, 
which is shown in fig. 28, unites eventually with the neigh- 
bouring uterine tissue, and the thin sheet of somatic mesoblast 
alone remains between the uterine wall externally and the 
splanchnic mesoblast within. 

At the front end of the embryo a different structure is found 
to exist. The lateral folds in this region are similar to the 
posterior portion of these folds, but the median anterior fold 
of the amnion is different inasmuch as it is formed solely of 
epiblast and hypoblast (fig. 34). Although the amnion at the 
anterior end is not formed until some considerable time after 
the mesoblast of the embryo has extended to the front end of 
the embryonic area, and although this mesoblast has ex- 
tended laterally over the vesicle throughout the whole length 
of the embryonic area, it only extends forwards for a very 
short distance, and does not grow between that portion of the 
epiblast and hypoblast which gives rise to the anterior fold of 
the amnion. Consequently, when the head of the embryo 
becomes projected anteriorly over the yolk-sac, as it does 
first in Stage c (fig. 6), and then bends downwards, forming 
for itself a pit on the surface of the yolk-sac, the walls of this 


THE DEVELOPMENT OF THE MOLE. 147 


pit constitute the anterior fold of the amnion, and are formed 
solely of epiblast and hypoblast. This portion of the amnion 
does not come in contact with the wall of the uterus. 

The relations of these parts have recently been very fully 
described by Beneden and Julin in Rabbit and Bat embryos 
(No. 2). These authors have named this anterior fold of the 
amnion the “pro-amnion,” and have most ingeniously, and as 
it appears to me correctly, compared it with the internal stalk 
of the “‘ trager” of inverted types of mammalian embryos. 

I should mention that the mesoblast present in the median 
line in the longitudinal section of an embryo of Stage ug 
(fig. 11) is concerned in the production of the heart, the 
anterior fold of the amnion having its origin in front of 
this mesoblast (compare figs. 11 and 34). 

The Allantois.—The allantois is, in an embryo of Stage F, a 
short wide diverticulum of the hypoblast projecting into the 
posterior portion of the primitive streak mesoblast behind the 
point where the epiblast and mesoblast curve over to form the 
amnion, and therefore also behind the point where the anal 
pit is forming. 

This diverticulum increases in size during Stages a, H, and J, 
and forms at the latter stage a very considerable vesicular 
cavity opening by a narrow neck into the (future hind-gut) 
yolk-sac beneath. The hypoblast diverticulum is formed of 
rounded cells, and is surrounded by a mass of mesoblast through 
which blood-vessels already ramify. The relation of these 
parts is shown in figs. 35 and 50. 

The Vascular System.—In the earliest embryo I have examined 
of Stage x, viz. one with only a single protovertebra, the posi- 
tion of the heart is already indicated, and vessels are already 
formed in the splanchnic mesoblast of the blastoderm outside 
the embryonic area. Blood-corpuscles are, moreover, to be 
seen within these vessels even at this early age. 

At the close of Stage r, the rudiments of the dorsal aorta 
are present, lying some distance on each side the notochord 
and extending from a point on a level with the front end of 
the heart backwards to the last protovertebra (fig. 17). They 


148 WALTER HEAPE. 


do not, however, as yet form continuous tubes. From the front 
end of the aorta on each side a short vessel is given off which 
lies dorsal to the aorta and immediately below the nervous 
system ; it does not, however, extend far. Thereis no commu- 
nication between the aorte and the heart tubes at this stage. 

At the commencement of Stage H the two tubes of the heart 
have met at their anterior end, and form a single wide tube for 
a short distance (figs. 24 and 25), a single pair of aortic arches 
are formed and the dorsal aorte extend backwards as two 
separate tubes some distance beyond the last protovertebra ; 
just before they terminate they give off two vitelline arteries. 

A series of short diverticula project from the aorta dorso- 
laterally between the somites, and ventrally, below them at 
this stage and during Stage J (compare figs. 2731 and 52). 

From near the front end of the aortz, a little posterior to 
the point where the aortic arch runs into it, two internal carotid 
arteries are projected forwards and extend to the under surface 
of the optic lobes (fig. 21, ¢.¢. a.) ; while from about the same 
point two vessels run backwards joined at intervals with the 
aorte (fig. 24, v. a.) on each side of, and closely applied to, the 
now closed neural canal. These vessels run back to a point 
just in front of the first protovertebra and are doubtless the 
vertebral arteries. 

Stage 5 shows little alteration ; the heart is still in the form 
of a straight tube somewhat longer than in Stage u, but without 
curvature or any sign of a division into chambers; there is still 
also only one pair of aortic arches, and two separate aorte are 
still present throughout the extent of their course. 

A number of small vessels are now given off from the internal 
carotid arteries, and the aorte in their anterior portion also 
send short branches into the surrounding tissue. The vessels 
which I have before described, running backwards on each side 
the nervous system, are frequently in communication with the 
aorte, and it is these vessels which appear at this stage to 
project diverticula into the substance of the walls of the spinal 
canal (vide above) (fig. 43). 

The vitelline arteries are given off about on a level with the 


THE DEVELOPMENT OF THE MOLE. _ 149 


ninth and tenth protovertebre as a series of branches, after 
which the aortz immediately become reduced to very minute 
proportions. 

The venous system, which is barely distinguishable in Stage 
H, is very slightly developed in Stage y. The vitelline veins 
run in the converging folds of the splanchnopleure to the 
posterior end of the heart on a level with the second and third 
protovertebree. 

The only veins in the trunk of the embryo are two slightly 
developed anterior cardinal veins which are situated on the 
outer edge of the anterior protovertebre (fig. 47, a. c. v.). 
They communicate with the ductus Cuvieri where the vitelline 
veins run into the heart between the second and third proto- 
vertebree, and run forwards as far as the first protovertebra. 

Traces of a posterior cardinal vein may be seen for some 
little distance behind the ductus Cuvieri; but as a vessel it 
exists only for a few sections, and is situated at the point 
where the somatopleure commences to turn upwards to form 
the amnion. 

Thus it may be observed the arterial system is in a far more 
advanced condition than is the venous system in the body of 
the embryo. 

The Structure of the Heart—In Stage rz the heart merely 
consists of a small tube in the thickened splanchnic mesoblast 
on either side, in front of the protovertebre (fig. 14). Then 
(Stage ¥) the thickened portion is bulged outwards into the 
body cavity and splits up into two layers. The outer layer 
bounding the body cavity forms the wall of the heart itself, the 
inner the flattened epithelial lining of the cavity of the heart. 
The space between these two layers increases and in Stage u 
(fig. 25) is considerable. In this figure the epithelial layer is 
connected with the outer layer of the heart by long proto- 
plasmic processes stretching from cell to cell across the space. 
In Stage s the wall of the heart has increased in size more in 
proportion than has the inner epithelial layer. The latter is 
now an elongated bag within the space contained by the outer 
wall and connected with the latter by marvellously delicate 


150 WALTER HEAPE. 


simple or branched cell processes (fig. 47). At the points 
where the cavity of the heart is continuous with the vessels 
entering into and emanating from the heart, the epithelial 
layer is continuous with the wall of these vessels. As I have 
stated above, the heart shows no indication of curvature or of 
division into chambers. 

The Blood-Corpuscles are formed from stellate mesoderm 
cells. The nuclei of these cells become darker, the stellate 
processes are then withdrawn and a meagre coating of proto- 
plasm surrounds the now rounded nucleus. Such conditions 
and changes are shown in many of the figures I have drawn ; 
notably in fig. 25 in the heart, and in fig. 28 in the vitelline 
vessels. 


SUMMARY. 


External Features.— The early appearance of the optic 
grooves (Stage £) which give rise to the optic vesicles; the 
existence of five visceral arches in Stage 3; the formation of 
the amnion first at the hind end of the embryo; and the 
folding off of the head end of the embryo only, are the chief 
points to be noted. The enclosure of the front end of the 
primitive streak within the medullary fold; the formation of 
protovertebrz, chiefly from before backwards; the closure of 
the medullary groove; the appearance of three divisions of the 
brain, and the formation of the heart are also detailed. 

The Epiblast.—The epiblast of the embryo (Stages r—e) 
becomes formed into a median thickened portion, the medul- 
lary plate, and into lateral portions which are formed of 
cubical cells and are continuous with the flattened epiblast 
cells which cover the vesicle. The closure of the medullary 
groove (Stages H and J) causes the union of the lateral epiblast 
which thus forms a continuous layer across the embryo. The 
medullary groove commences about the centre of the embryo, 
widening out into the sinus rhomboidalis behind and into the 
cephalic plate anteriorly. The optic grooves are formed one 
on each side of the middle line in the cephalic plate (figs. 4 
and 16). 


THE DEVELOPMENT OF THE MOLE. Bot 


The Medullary Canal.—The closure of the medullary groove 
commences in the region of the first protovertebra during 
Stage e and proceeds anteriorly and posteriorly, and at the 
close of Stage 5 a complete canal is formed as far back as the 
last (fourteenth) protovertebra. The lateral walls of the canal 
thicken, and are converted into an hour-glass form in places. 
The migration of mesoblast (nutritive) cells into the walls of 
the canal is noted in Stages H and J. 

The Brain.—The three divisions of the brain are indicated in 
Stage 3, and a well-marked cranial flexure is then present. 
The infundibulum is just apparent at this stage in close con- 
nection with the front end of the alimentary canal and noto- 
chord (fig. 49). 

The Optic Vesicles are formed from the optic grooves by the 
closure of the medullary canal. These organs first appear 
extremely early, but their development is soon checked, doubt- 
less in consequence of the habits of the adult animal. 

The Ear in Stage y is merely indicated as a deep groove in 
a thickened mass of mesoblast on either side of the hind-brain. 

The Cranial and Spinal Nerves are not described. 

The Hypoblast may be divided into axial and peripheral 
portions. The peripheral hypoblast, a single layer of flattened 
cells, extends on all sides over the embryonic area during 
Stage x. The deepening of the medullary groove stretches 
these cells and flattens them still more, but the thickening of 
the lateral mesoblast forces the lateral hypoblast down, removes 
the strain, and its cells become rounded. 

The Notochord is formed of axial hypoblast cells. In Stage 
c a mass of axial hypoblast cells are continuous with two 
lateral masses of mesoblast—derived from lateral hypoblast— 
and with the lateral hypoblast layer also. In Stages p and & 
the axial mass becomes isolated from the lateral mesoblast 
plates, and gradually decreases in size below the deepening 
medullary groove until in that portion where the groove is 
deepest, 1. e. near the centre, a single layer of flattened cells is 
all that exist. 

It does not, however, become reduced to this extent through- 


152 WALTER HEAPE. 


out its length ; at the posterior end it remains thickened, and 
by the ingrowth of the lateral portions the axial cells first 
form an arch and then a complete tube, which is the neuren- 
teric canal and which communicates dorsally with the exterior 
and ventrally with the yolk-sac. 

This tube is the homologue of the median dorsal diverticulum 
of the alimentary tract in Amphioxus, i. e. the structure which 
gives rise to the notochord of that animal, and it is noteworthy 
that in the Mole it disappears almost entirely before the noto- 
chord is formed. 

The single layer of cells to which the greater part of the 
axial hypoblast is reduced at the close of Stage p (No. 8) again 
increases in bulk during Stages £ to J, and gives rise to the 
notochord. 

As was the case with the lateral hypoblast, the flattening 
of these cells and their increase in bulk appears to be due, first 
to the stretching effect of the rapidly deepening medullary 
groove, and secondly to the release from that strain caused by 
the depression of the lateral portions of the embryo. 

The isolation of the notochord first occurs in the region of 
the first protovertebra during Stage G, and extends anteriorly 
and posteriorly during Stages u and J. 

The isolation is caused by the ingrowth of the lateral hypo- 
blast below the axial cells, and the latter are isolated either 
as a solid band or rod, although a lumen may here and 
there appear in it afterwards. 

At the close of Stage s the notochord is completely separated 
from the hypoblast, except at two points, viz. at the anterior 
end, where it is connected with the hypoblast and epiblast, 
where these two layers fuse to form the mouth, and posteriorly 
where it is joined to both epiblast, hypoblast, and mesoblast, 
at the front end of the primitive streak (figs. 49 and 50). 

The origin of the notochord and the manner of its isolation 
appear to be sufficient reason to regard it as entirely homolo- 
gous with the notochord of Amphioxus. 

For a review of other opinions on this point I would refer to 
a discussion in my former paper (No. 8), 


THE DEVELOPMENT OF THE MOLE. 158 


The hooked anterior end of the notochord is due to its origin 
from the front wall of the fore-gut. Its close approximation 
to the fore-brain is noted. 

The relatively small size of the notochord to the nervous 
system in the Mole is pointed out, and it is suggested the early 
development of the latter is the cause of the check adminis- 
tered to the growth of the former, a check from which it appears 
never entirely to recover. 

The Alimentary Canal first appears in Stage p as a short 
tubular diverticulum, projecting below the cephalic plate nearly 
to the anterior end of the embryo. 

The tube enlarges and extends backwards during the pro- 
gress of the folding off of the embryo during Stages & to 4g, 
and the cranial flexure causes a ventral enlargement, which 
is somewhat posterior to the original anterior diverti- 
culum. 

The mouth and the visceral clefts are not formed at the close 
of Stage 3, but the epiblast and hypoblast have fused at the 
point where the mouth will eventually be formed, and several 
lateral outgrowths from the now widened fore-gut exist ; in the 
case of one of these, the anterior one, the hypoblast has reached 
the epiblast, and the two layers are partially fused at that 
point. 

The mouth is formed at the apex of a Y-shaped groove, the 
diverging limbs of which are directed forwards; these grooves 
are the anterior border of the first visceral arch. 

The primary anterior diverticulum would indicate the 
existence primitively of a terminal mouth, while the two 
grooves, at the junction of which the mouth is formed, 
would suggest a paired origin for the existing mouth of the 
animal. 

The Mesoblastic Somites and Body Cavity.—The lateral plates 
of mesoblast are split horizontally into somatic and splanchnic 
layers, but the split is not actually carried through both peri- 
pheral and axial portions of the plates, being merely indicated 
in Stage © in the axial portion. The mesoblast of the head 
also is not split, and no cavity is formed there, 


154 WALTER HEAPE. 


Protovertebre are formed and the axial and _ peripheral 
portions of the mesoblast plates are separated from one another 
by the intermediate cell mass. : 

A cavity appears in the protovertebre, Stage £, which still 
exists at the close of Stage J. 

The formation of the muscle-plate commences at Stage H 
from the outer layer of cells of the protovertebra, but during 
Stage s, in the three anterior protovertebrz, a second row of 
cells derived from the inner (vertebral) portion of the somite, 
takes part in its formation, the two rows being continuous with 
one another at their dorsal and ventral ends. 

The muscle-plates are first formed anteriorly. The outer 
cells of the muscle-plate in Stage J are prolonged into fine pro- 
cesses, which are connected with the overlying epiblast cells, 
and constitute voluntary muscular fibres (fig. 51). Certain of 
the cells of the inner layer are also differentiated into elongated 
muscular fibres. 

I would further remark the mesoblast and epiblast cells in 
front of the primitive streak appear always to be connected 
together by processes. 

The Pericardial Cavity only commences to form during 
Stage s, and is not at the close of that stage entirely separated 
from the remainder of the body cavity. 

The Primitive Streak has the same relations in Stages E and F 
as in Stage p, except that the medullary folds grow backwards 
round its front end. The neurenteric canal disappears, but its 
original position is indicated by the fusion of the germinal 
layers at the front end of the primitive streak. 

The mesoblast of the primitive streak does not give rise to 
the mesoblast of the body of the embryo in front of the primi- 
tive streak, in my opinion, but extends backwards and outwards 
and forms the wall of the allantois. The anus is formed in the 
middle of the primitive streak. 

The Amnion is first formed at the hind end and from thence 
extends forwards. This portion of the amnion is formed of a 
double fold of somatopleure; the epiblast of the outer fold 
unites with the epithelium of the uterus. The anterior fold 


THE DEVELOPMENT OF THE MOLE. 155 


of the amnion, however, is formed only of epiblast and hypo- 
blast, and has been called by van Beneden and Ch. Julin, who 
first described this structure, the “ pro-amnion.” 

The Allantois commences in Stage F as a short wide diverti- 
culum projecting upwards and backwards into the primitive 
streak. This diverticulum enlarges during Stages c to 5; it 
is lined with hypoblast cells (figs. 35 and 50). 

The Arterial System.—The dorsal aortze commence in Stage r, 
and remain double until after Stage 5; they are connected with 
the heart by a single pair of aortic arches during Stages H 
and Js, and give off vitelline arteries at their posterior end. 
Internal carotid arteries and vertebral arteries are formed, and 
it is from the latter of these vessels the mesoblast cells are 
derived which migrate into the walls of the neural canal. 

The Venous System is very slightly developed. Vessels are 
to be seen in the splanchnopleure over the yolk-sac at an early 
date, but vitelline veins connected with the heart are not seen 
until Stage H. Two short anterior cardinal veins are present 
in Stage J, and traces of two posterior cardinals, but nothing 
more. 

The Heart, which is formed of two tubes widely asunder in 
Stage £, is composed of a single tube for a short distance in 
Stage H, and is somewhat longer, but still straight and without 
sign of division into chambers at the close of Stage 3. The 
thickened splanchnic mesoblast which gives rise to the heart, 
splits into two layers at an early age. The outer of these 
layers forms the outer wall of the heart, the inner the flattened 
epithelium of the cavity of the heart. 

When the heart enlarges, as it does rapidly, a wide space 
exists between these two layers, but they are connected together 
by exceedingly fine processes of their cells which stretch across 
the space. 

The Blood-Corpuscles appear to be formed from stellate 
mesoblast cells directly. 

In conclusion, I may mention that I propose eventually to 
follow the further development of the organs of the Mole, one 
by one, and in doing so, to pay more attention to the researches 

VOL. XXVI1, PART 2,—NEW SER, M 


156 WALTER HEAPE. 


of other investigators than has appeared to me advisable in the 
present paper. 


LITERATURE. 


1. F. M. Batrour.—‘ Comparative Embryology,’ vol. ii, 1881. 
2. Ep. van BENEDEN AND Cuas. Jutin.—“ Recherches sur la formation 
des annexes fcetales chez les mammiféres,”’ ‘ Archives de Biologie,’ 
vol. v, 1884. 
3. To. L. W.. Biscuorr.—‘ Entwicklungsgeschichte des Kaninchens-eies,’ 
1842. 
. Tu. L. W. Biscporr.—‘ Entwicklungsgeschichte des Hunde-eies,’ 1845. 
. Tu. L. W. Biscoorr.— Entwicklungsgeschichte des Meerschweinschens,’ 
1852. 
6. Tu. L. W. Biscuorr.—‘ Entwicklungsgeschichte des Rehes,’ 1854. 
. W. F. Havsmann.—‘ Ueber die Zeugung und Entstehung des wahren 
weiblichen eies bei den Saugethieren und Menschens,’ 1840. 
8. W. Hrarz.— Development of the Mole,” ‘Quart. Journ. of Mier. 
Sci.,’ 1883. 
9. v. Henson.— Beobachtungen iiber die Befruchtung und Entwicklung 
des Kaninchens und Meerschweinschens,” ‘ Zeit. f. Anat. und Ent- 
wickelungsgeschichte,’ vol. i, 1876. 


ne 


~_ 


10. A. Korrrker.—‘ Entwicklungsgeschichte des Menschens und der Hoheren 
Thiere, 1879. 


ll. W. F. R. Wetpon.—“ Note on the Early Development of Lacerta 
muralis,’” ‘Quart. Journ. Micr. Sci.,’ 1883. 


THE DEVELOPMENT OF THE MOLE, 157 


DESCRIPTION OF PLATES XI, XII, & XIII, 


Illustrating Mr. Walter Heape’s Paper on “ The Development 
of the Mole (Talpa Europea),” Stages E to J. 


List of Reference Letters. 


a.arc. Aortic arch. a.c.v. Anterior cardinal vein. al. c. Alimentary 
canal. ali. Allantois. all. v. Allantoic vessels. am. Amnion. am. fl. False 
amnion. az.p. Anal pit. a.p. Area pellucida. aud. ep. Auditory epithelium. 
aud. inv. Auditory involution. 06.c. Body cavity. c. pl. Cephalic plate. 
d. a. Dorsal aorta. ep. Epiblast. fdr. Fore-brain. 4. dr. Hind-brain. 
At. Heart. hy. Hypoblast. 7. ¢. a. Internal carotid artery. 7. c. m. Inter- 
mediate cell mass. m. Mesoblast. m. dr. Mid-brain. m. gr. Medullary 
groove. m.pl. Medullary plate. msc. pl. Muscle-plate. x. c. Neural canal, 
ach. Notochord. op. gr. Optic grooves. op. v. Optic vesicles. p.c. Peri- 
cardial cavity. pro. am. pro-amnion. p. st. Primitive streak. =p. v. Proto- 
vertebra. Si. rh. Sinus rhomboidalis. so. m. Somatic mesoblast. so. pl. 
Somatopleure. sp. m. Splanchnic mesoblast. sp. p/. Splanchnopleure. v. a, 
Vertebral artery. vs. ach. Visceral arch. v¢.a. Vitelline artery. vt. v. Vi- 
telline vessels. v¢. vz. Vitelline vein. 


Figs. 1—10 were sketched with Zeiss’s a* lens and eye-piece 2 by myself, 
and were most carefully shaded by Mr. H. A. Chapman under my supervision. 

Figs. 11—35, 44—50, and 52 were sketched with Zeiss’s B lens and eye- 
piece 2. 

Figs. 36—43 and 51 were sketched with Zeiss’s D lens and eye-piece 2. 


Fie. 1, Stage E.—Transparent view of embryo ‘76 mm. long. It has three 
protovertebre. The medullary groove is narrow in the middle of the body, 
widening out at either end. The anterior end of the primitive streak projects 
as a dark knob into the wide sinus rhomboidalis. The flattened cephalic plate 
(c. pl.) and the area pellucida (a. p.) are to be observed. 

Fic. 2, Stage E.—Surface view of embryo 1°82 mm. long. The cephalic 
plate has now two deep lateral grooves, the optic grooves (op.gr.). The 
curved condition of the embryo is due to careless manipulation. 

Fic. 3, Stage F.—Surface view of embryo 1:96 mm. long. The medullary 
groove has commenced to close in the region of the protovertebre (which are 
not shown in this drawing), but the edges of the groove have not yet 
coalesced. The optic grooves are seen at either side of the cephalic plate. 

Kie. 4, Stage F.—Surface view of embryo 2°12 mm, long. Although some- 


158 WALTER HEAPE. 


what bigger than the embryo drawn in Fig. 3, the medullary folds have not 
advanced so far along the body of the embryo as they have in the latter 
embryo. At the anterior end, however, they are slightly more advanced, and 
where the folds meet in front a narrow slit is to be seen. The amnion is 
shown covering the posterior half of the embryo, and the wide sinus rhom- 
boidalis is indicated below it. 

Fic. 5, Stage F.—Transparent view of the same embryo, seen from below. 
Four fully formed protovertebre are present, and a fifth is indicated behind 
the posterior one. The primitive streak projects into the sinus rhomboidalis. 
The optic grooves appear as narrow lateral prolongations of the medullary 
groove at its anterior end. The heart (A¢.) commences to form at this stage, 
and is indicated by a thickening of the blastoderm on either side the embryo 
just behind and outside the optic grooves. 

Fic. 6, Stage G.—Surface view of embryo 2°33 mm. long. The medullary 
groove is closed up to the anterior end, where a small pore remains connecting 
the medullary canal with the exterior. The sinus rhomboidalis is still widely 
open behind. The head has now been folded off from the yolk-sac as far as 
the line so. pl., which shows the point of divergence of the folds of somatopleure. 
Faint indications of the divisions of the brain are shown, and the laterally 
projecting optic vesicles are very distinct (op. v.). 

Fie. 7, Stage H.—Surface view of embryo 2°2 mm. long. Ten proto- 
vertebra are present. The closure of the medullary groove has advanced. 
The sinus rhomboidalis is narrowed, and the primitive streak forced upwards 
as a rounded knob at the posterior end of the latter. The head is more 
rounded, and shows partial division into fore-, mid-, and hind-brains. The 
amnion has been torn away, and the jagged edge of the somatopleure sur- 
rounds the body of the embryo. 

Fic. 8, Stage H.—View of the under surface of the head of the same 
embryo, showing the heart and the diverging folds of somatopleure and 
splanchnopleure. 

Fic. 9, Stage J.—Surface view of an embryo 3°06 mm. long. The sinus 
rhomboidalis is much narrowed, and the medullary groove closed for the 
greater portion of its length. The optic vesicles and fore-, mid-, and hind-brains 
are well shown. Thirteen protovertebre are present. The primitive streak is 
in the same condition as described for Fig. 7, also the amnion has been torn 
away as it was in that figure. 

Fie. 10.—Lateral view of the head of the same embryo, showing the heart 
and five visceral arches. 

Fic. 11, Stage E.—Median longitudinal section of the anterior end of an 
embryo with three protovertebre. The cephalic plate projects slightly over 
the blastoderm in front, the folding-off process having already begun in this 
embryo. The commencement of the fore-gut is indicated at a/.c. A small 
portion of mesoblast exists between the epiblast and hypoblast of the blasto- 


THE DEVELOPMEN’T OF THE MOLE. 159 


derm at the front end of the embryo; beyond that point no mesoblast is 
present in the middle line. 


Fie. 12, Stage H.—Transverse section through the cephalic plate of an 
embryo with three protovertebre. At the point where this section is taken 
the flat cephalic plate is completely folded off from the yolk-sac. The narrow 
fore-gut is shown as a tube (a/. c.) immediately below the cephalic plate. A 
few scattered mesoblast cells extend between the two layers of epiblast. 


Fie. 13, Stage E.—Transverse section through an embryo 1:97 mm. long, 
with only a single protovertebra. The section is taken in front of the proto- 
vertebra, and shows the indication of a split of the mesoblast into somatic and 
splanchnic layers throughout its whole depth. The medullary groove is wide 
and deep. The notochord is formed of flattened cells. 


Figs. 14 and 15, Stage E.—Tranverse sections through the same embryo 
which is drawn in Fig. 1. 
Fig. 14 is taken in front of the protovertebra, where the mesoblast is 
split into somatic and splanchnic layers only at the periphery. 
Fig. 15 passes through a protovertebra. The body cavity extends in- 
wards as far as the intermediate cell mass (¢.c. m.) in the peripheral 
mesoblast, and a small cavity is also present within the protovertebra. 


Fies. 16, 17, and 18, Stage F.—Transverse sections through embryos with 
five protovertebre. 


Fig. 16 is a section through the head. The cephalic plate is grooved in 
the middle line and at either side where the wide optic grooves are 
situated. When the external edges meet in the middle line these optic 
grooves will be converted into vesicles communicating by a wide aper- 
ture with the central canal. The notochord is not yet separated from 
the hypoblast. 

Fig. 17 is through the trunk ; the medullary groove is narrower, and the 
notochord more defined than in Fig. 15, which is a section through a 
similar region of an embryo of Stage E. 

Fig. 18 is a section through the sinus rhomboidalis, and shows the 
anterior end of the primitive streak and the amnion. 


Fic. 19, Stage G.—Transverse section through the head of an embryo with 
eight protovertebre, 2°49 mm. long. The head at this point is completely 
folded off, and the medullary groove (still open) will at this point give rise to 
the mid-brain, A few sections further forward the optic vesicles are cut, 
projecting outwards from the central canal, and it is on account of the 
proximity of these structures that the wide space between the external 
epiblast and the walls of the medullary canal is present here. This space is 
here filled with stellate mesoblast cells. The two grooves in the epiblast on 
the under surface on either side the middle line converge posteriorly, and 
where they meet the mouth will eventually be formed. 


160 WALTER HEAPE. 


Fies. 20—33. Stage H.—Transverse sections through three embryos of this 
stage. 

Fig. 20 is a section through the front of the head; it passes through the 
point of origin of the optic vesicles, and shows at the same time the 
pore through which the neural canal is open to the exterior at this 
stage. 

Fig. 21 passes through both the mid- and fore-brains and through the 
centre of the optic vesicles, which are here seen to be directed out- 
wards, downwards, and backwards. 

Fig. 22 passes through the hind-brain and the front end of the fore-gut 
(al. c.). The notochord is not yet separated from the axial hypoblast 
here. The front edge of the first aortic arch is shown. This vessel is 
very wide, and may be seen for many sections. 

Fig. 23 is also a section through the hind-brain, but at its posterior end. 
The notochord is here isolated from the hypoblast. The two grooves 
in the ventral epiblast on either side the middle line, which were seen 
in Fig. 22, have met in this figure and form a single deep groove 
closely in contact with the ventral wall of the fore-gut, and here the 
mouth will be formed. These grooves define the anterior border of the 
first visceral arch (vs. ach.). The alimentary canal in this figure is 
very considerably wider than in Fig. 22. In Figs. 20 to 23, the head 
of the embryo is folded off from the yolk-sac. 

Fig. 24 is taken from a different embryo from what Figs. 20—23, and 25 
are taken. The front end of the heart is shown. ‘The section is not 
quite transverse, and the first aortic arch is shown on the right side 
and not on the left side. The extremely wide fore-gut and the separa- 
tion of the heart into two portions, shown here, is also due to this fact. 

Fig. 25. The alimentary canal is here open ventrally. In Fig. 24 the 
splanchnopleure had formed a complete layer, but the somatopleure had 
not met below the gut. In this figure the splanchnopleure as well as 
the somatopleure are still divergent. The heart is here in the form of 
two tubes, and the two layers of which it is formed may here be seen. 
The formation of blood-corpuscles from stellate mesoblast cells also 
may be observed. The thickened epiblast on either side the neural 
canal is the commencement of the auditory organ. 

Fig. 26. A section immediately in front of the first protovertebra. The 
vitelline vein is seen in the splanchnopleure, branching out over the 
yolk-sac. The fold of the somatopleure to form the amnion is also 
indicated (am.). 

Fig. 27. A section through the anterior protovertebra. 

Fig. 28. A section through the middle of the embryo. The large vitel- 
line vessels are shown in the splanchnic layer of mesoblast over the 
yolk-sac. The true (am.) and false (am. fis.) amnion are both shown 


THE DEVELOPMENT OF THE MOLE. 161 


here. The false amnion is formed of flattened somatic mesoblast and 
columnar epiblast cells, the latter will eventually fuse with the 
uterine epithelium. 

Fig. 29 is also a section through the middle of the embryo. The cells of 
the protovertebre are here seen to be somewhat elongated on the right 
side of the section, while on the left the cavity of the protovertebra is 
shown partially filled by a cove of mesoblast cells. This was also 
shown in Fig. 28. The hour-glass shape of the neural canal at this 
point is also to be observed. 

Figs. 30 aud 31 are from the hinder portion of the trunk of the embryo. 
The neural canal is not closed, the protovertebre are not so com- 
pletely isolated from the neighbouring mesoblast, and the notochord, 
which is larger than in former sections of this stage, is not at all 
isolated from the hypoblast in Fig. 31. In both these sections the two 
dorsal aortz, which were present in all the sections from Fig. 23 to 
Fig. 29, are here giving off branches to the yolk-sac. The vitelline 
arteries (v¢. a.), and posterior to this point, the aorte themselves, no 
longer exist. 

Fig. 32 is a section behind the former sections, and just in front of the 
primitive streak. ‘The widely open medullary groove is here called the 
sinus rhomboidalis. 

Fig. 33 is a section through the primitive streak; the medullary folds are 
growing round it and will shortly completely enclose its front end. 

Fie. 34, Stage H.—A median longitudinal section through the head of an 
embryo, in which the following points are shown :—The cranial flexure; the 
fore-, mid-, and hind-brains; the notochord separated from the hypoblast, 
except along the front wall of the alimentary canal ; the ventral prolongation 
from the primitively straight fore-gut (a/. c.), and the pro-amnion formed of 
epiblast and hypoblast only (pro. am.). 

Fic. 35, Stage H.—Median longitudinal section through the hind end of an 
embryo. ‘The dorsal pit (anal pit) and the ventral pit (allantoic pit) separate 
the anterior from the posterior portions of the primitive streak. 

Fies. 36—42, Stage H.—Transverse sections through various regions of an 
embryo, to show the formation of the notochord. 

Fig. 36 in the anterior region shows a lumen within the notochord. 

Fig. 37. In the anterior region: notochord is rod like, and is separated 
from the hypoblast. 

Fig. 38. In the anterior region: notochord is a flattened band-like struc- 
ture ; it is separated from the hypoblast. 

Fig. 39. In the middle region : the notochord is not yet separated from 
the hypoblast in the middle line, although it is so separated at either 
edge. The lateral ingrowth of the hypoblast is shown. 

Fig. 40, from the posterior region, shows relations similar to those seen 


162 WALTER HEAPE. 


in Fig. 39, only the notochordal mass is itself considerably larger the 
lateral ingrowth of the hypoblast is here also indicated. 

Fig. 41. From still further posteriorwards: the notochord is not yet 
isolated from the hypoblast, but formed into an arc. 

Fig. 42. From the hind end of the embryo, immediately in front of the 
primitive streak : the notochord is a large thickened axial mass, with 
no indication of the growth of the hypoblast below it. 

Fig. 43, Stage H.—A transverse section through the medullary cord of 
an embryo with eleven protovertebre, from the region in front of the first 
protovertebra and behind the hind-brain. Between the lateral mesoblast 
plate and the cord is a small space, in which several nuclei are seen. The 
space is continuous with blood-vessels in process of formation, and the nuclei 


show a tendency to pass into the medullary cord. One such nucleus is shown 
in the drawing. 


Fies. 44 and 45, Stage J.—Transverse sections through the hind-brain of 
an embryo with fourteen protovertebree. The alimentary canal is narrow in 
front (Fig. 44), and wider posteriorly (Fig. 45). The two grooves in the 
epiblast on the under surface in the anterior section converge in a single deeper 
groove in the posterior section, where the fusion of the epiblast and hypoblast 
takes place, and where the mouth will eventually be formed. The dorso- 
ventral elongation of the fore-gut and the notochord is due to the plane in 
which the section was cut, caused by the cranial flexure. The presence of 
mesoblast cells between the notochord and the floor of the brain is to be 
noticed. 

Fic. 46, Stage J, is a section, not completely transverse, through an embryo 
with fourteen protovertebre, passing through the hind-brain and the auditory 
mvolution. The first aortic arch is shown on one side, and a lateral prolonga- 
tion of the fore-gut to form the first visceral cleft on the other side. 

Fic. 47, Stage J.—Transverse section through an embryo with thirteen 
protovertebre in the region of the second protovertebra. Fore-gut crescent 
shaped. Anterior cardinal veins and dorsal aorte present. Embryo is com- 
pletely folded off from the yolk-sac. The heart is enclosed in the peri- 
cardium. The thick outer wall and flattened epithelial layer of the heart are 
here seen to be connected by fine processes of the cells forming one or other 
of these layers. 


Fic. 48, Stage J.—A transverse section through the primitive streak of an 
embryo with fourteen protovertebre. The thickened lateral mesoblast will be 
seen, by comparing this section with that drawn in Fig. 50, to be concerned in 
the formation of the allantois. Allantoic vessels (a//. v.) are to be seen in this 
section. 


Fic. 49, Stage J.—A median longitudinal section through the head of an 


embryo with fourteen protovertebre. The division between the fore- and 
mid-brains and the folded floor and thin roof of the hind-brain is shown. The 


THE DEVELOPMENT OF THE MOLE. 163 


cranial flexure, ventral prolongation of the anterior end of the fore-gut, and 
the hooked anterior end of the notochord is also indicated. The notochord is 
seen to be continuous at its anterior end with the hypoblast and epiblast at 
the point where the mouth will eventually be formed. The existence of 
mesoblast cells between the notochord and the floor of the brain is to be 
noticed. 

Fic. 50, Stage J—A median longitudinal section through the hind end of 
an embryo with fourteen protovertebre. The allantoic cavity has increased 
in size, and numerous blood-vessels are seen in its walls. The mesoblast 
surrounding the allantoic cavity is derived from the primitive streak meso- 
blast. The relation of the epiblast, hypoblast, notochord, and mesoblast at 
the front end of the primitive streak is seen to be precisely the same as I 
indicated in a diagram (Fig. 50) of my former paper (No. 8). The neurenteric 
canal is obliterated. 

Fig. 51, Stage J.—A transverse section of a portion of the muscle-plate of 
an embryo with fourteen protovertebre. The cells of the muscle-plate 
(msc. pl.) are extended into long processes which are continuous with the 
epiblast cells (ep.) lying above them. These processes are commencing 
muscular fibres. 

Fie. 52, Stage J.— Longitudinal section through an embryo with fourteen 
protovertebre. The section is taken through a line about half way between 
a perpendicular and horizontal longitudinal line, and bisects the muscle-plates 
and aorta of one side of the body. The hypoblast lining the alimentary canal 
is cut through slightly to one side of the middle line, and the notochord 
therefore is not shown. The arched muscle-plate and muscular processes of 
its cells, the aorta and its dorso-lateral prolongations between the proto- 
vertebr are shown. 


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PINEAL EYE IN LACERTILIA. 165 


On the Presence and Structure of the Pineal 
Eye in Lacertilia. 


By 
W. Baldwin Spencer, B.A., 


Fellow of Lincoln College, Assistant to the Linacre Professor of Human and 
Comparative Anatomy in the University of Oxford. 


With Plates XIV, XV, XVI, XVII, XVIII, XIX and XX. 


Tue following work has been carried on in the morphological 
laboratory of the University of Oxford. It has been made 
possible solely through the kindness of Professor Moseley, 
whose invaluable assistance in various ways, especially in 
procuring from different sources the necessary specimens, I 
here desire to acknowledge with sincere thanks. 

Historical Account.—Though it was impossible for the 
external indication of the important organ which forms the 
subject of the following pages to escape the notice of naturalists 
and more especially of those dealing with the classification of 
the group, consisting as it does in the modification of a median 
scale upon the dorsal surface of the head, yet it is strange that 
only within a very recent period has there been any thorough 
investigation of the structures lying beneath. This is perhaps 
chiefly to be accounted for by the fact that the structure in 
question lies usually within the parietal foramen, enclosed 
tightly by bone and connective tissue, and is thus left intact 
within the skull on removal either of the skin from the external 
or the brain from the internal surface. 

Brandt,’ writing in 1829, uses the following words when 
describing the skull of Lacerta agilis. ‘ Hinterhaupts- 


1 © Medizinisch Zoologie,’ 1829, Bd. i, p. 160. 


166 W. BALDWIN SPENCER. 


schilder 4; selten nur 3; die beiden mittelsten hintereinander 
stehenden, die kleinsten, das obere, grdssere regelmassig 
5-eckig, meist mitten, mit einer runden, vertieften stelle,” and 
he adds in a foot-note, “ Eine eigne Driisenstelle bezeichnend.” 
The external marking on the surface of the head is not repre- 
sented in the drawing of L. agilis (fig. a, Tf. xix), but his 
description shows that he recognised the presence of an internal 
modification corresponding to the specialised scale. 

Milne Edwards! and Dugés? both figure the external modi- 
fication in certain lizards, but neither, strangely, make the 
slightest mention of it in their descriptions of the animals. 

Leydig,® writing more than forty years later, is apparently 
the first to point out with any clearness the presence of the 
organ, and to give some account of its structure and of the 
development of the epiphysis, though he entirely failed to dis- 
cover the relationship existing between the two. Under a 
high power, he says, the body in question which lies ‘‘ above 
the thalamencephalon or the region of the third ventricle,” is 
seen to consist of long cells similar to those of a cylindrical 
epithelium, so arranged that they form altogether a shallow pit 
with a circular outline; the rim of the pit is turned upward, 
and has a thick black girdle of pigment; “ welcher schon fiir 
das freie Auge das Organ sehr bemerklich macht.” After stating 
that it has a special blood supply, he goes on to say: “ Das 
Organ ist keineswegs, woran Man zuniichst denken konnte, 
die embryonale Zirbel, dem diese folgt erst darunter und ist 
von ganz anderer Beschaffenheit.”’ 

“ Fragliches Gebilde entspricht ferner der Stelle, wo sich am 
skeletirten Schadel des fertigen Thieres im spateren scheitel- 
beine, das oben schon erwahnte kreis runde Loch befindet.” 

He examined the organ in Lacerta agilis, L. muralis, 
L. vivipara, and Anguis fragilis. On pl. xii (fig. 159) he 

1 « Recherches Zoologiques pour servir a Vhistoire des Lézards,” ‘ An. Sci. 
Nat.,? 1829, tom. xvi, p. 50. 


2 « Mémoire sur les especes indigenes du genre Lacerta,” ‘ An. Sci. Nat.,’ 
1829, tom. xvi, p. 337. 


3 «Die Arten der Saurier,’ 1872, p. 72, Taf. 12. 


PINEAL EYE IN LAOCERTILIA. 167 


draws asection at right angles to the long axis of the head in L. 
agilis, passing through the organ in question, which he calls the 
“ Stirn Organ,” and the pineal gland. Speaking of this section 
he says: “ Man gewinnt dadurch die Ueberzeugung das es 
sich um eine innerhalb der Epidermis besonders abgegrenzte 
Partie handelt ; und zwar einer solchen, welche von kugeligen 
Umriss und zelliger Zusammensetzung tber der Oeffnung im 
Scheitelbein ruht. Unmittelbar unter dem Knochen in der 
gleichen senkrechten Linie steht die Zirbeldriise. Sollen etwa 
die Lagen des Schnittes genauer aufgezahlt werden, so folgt 
von aussen nach innen zuerst die Hornschicht der Epidermis ; 
dan die Schleimschicht und das kugelige zellige, Organ in ihr ; 
darauf die nicht ossificirte, stark schwarz pigmentirte Theil 
der Lederhaut ; alsdann der Knochen mit seinen Markratimen, 
welche gegen die Oberflache gedffnet sind. Unterhalb des 
Knochens kommt die wieder stark gefarbte harte Hirnhaut, 
und unter dieser, ihr angeheftet die Zirbel; sie verbindet sich. 
durch zwei nervése‘Schenkel mit dem Gehirn.” 

He describes also the presence of the organ in Anguis 
frygeélis; it is present as a small dark spot on the thalamen- 
cephalon of very young embryos (cf. Tf. xii, fig. 160), whilst 
in somewhat older embryos (fig. 162), in addition to the spot, 
a dark streak is present lying above the unpigmented part, 
which he recognises as the true pineal gland as well as “ ein 
kleiner unpigmentirter Korper, wie ein winziger Higel bemerk- 
bar ” (fig. 163, c). 

These three parts are distinct from the epiphysis itself, and 
can be seen on removal of the skin from the head. Further, 
it is evident that the black spot and the black streak are of a 
similar structure, the walls of each are composed of long 
cylindrical cells so arranged in the streak as to bound a clear 
space (see fig. 163), whilst at the black spot they enclose a pit 
“die vielleicht als Ausgang jener Lichtung zu deuten ist.’ . 
The cells of both structures have pigment at their inner ends 
bounding the cavities, the pigment in those of the “spot” 
being much deeper than in those of the “streak.” With 
regard to the epiphysis, he says: “ Die Zirbel deren Stiel aus 


168 W. BALDWIN SPENCER. 


zwei Schenkeln besteht, liegt unterhalb des ‘ Punctes’ und 
‘Streifens,’ und zeigt sich als etwas von beiden wohl verschie- 
denes. Ihre Oberflache hat das schon gedachte, faltige Aus- 
sehen, das ich auf eine Zusammensetzung aus gewundenen 
Schlatichen bezog. Doch erhielt ich auch den Eindruck, als 
ob es sich um eine blasige Bildung mit Faltung der Oberflache 
handle. Die Zirbel ist vollig unpigmentirt.” As to the nature 
and function of the structure, he says: ‘“‘ Wie das Organ zu 
deuten sie, wird im Augenblick wohl Niemand zu sagen sich 
im Stande fiihlen. Doch kann ich nicht umhin, einstweilen 
an die ‘ Stirndriise’ der Batrachier zu denken und etwas dieser 
Bildung verwandter zu vermuthen.” 

In 1882 Rabl Riickhard,! dealing with the development of 
the epiphysis in the Trout, stated that the pineal gland appears 
early in the median line on the dorsal surface of the brain, 
between the first and second brain vesicles, as an outgrowth 
which admits of close comparison with that of the primary optic 
vesicles. This resemblance led him to the idea of the pos- 
sibility, supposing certain secondary developments of epiblast 
(to form a lens) and of mesoblast took place, that the pineal 
gland might become transformed into an eye just as are the 
optic vesicles. This result—the formation of an eye more or 
less closely similar to the paired eyes—is of course precisely 
that which does not obtain in Lacertilia, where no such secon- 
dary development from epiblast and mesoblast takes place. 

He says: “ Allein wahrend diese unter Mitmirkung des sich 
zur Linse einstiilpenden Ectoderms und des Mesoderms com- 
plicirte Veranderungen eingehen, die schliesslich zur Ent- 
wickelung des héchst entwickelten Sinnesorganes, des Auges, 
fiihren, sehen wir an der Zirbeldriise trotz der giinstigen Lage 
ihres distalen Endes dicht unter dem Ectoderm nichts der- 
gleichen. Mann denke sich eme ahnliche Wucherung und 
ihre Folgen, wie an dem die Augenblasen bedeckenden Kcto- 
derm, das Auftreten von Pigment im sich betheiligenden 
Mesoderm und nichts steht der Vorstellung im Wege, dass 

1 “Zur Deutung und Entwickelung des Gehirns der Knockenfische,” ‘ Arch, 
f, Nat, und Phys.,’ 1882, p. 111, 


+ 


PINEAL EYE IN LACERTILIA. 169 


sich aus der Zirbel ein den Augen ahnliches unpaares Sinnes- 
organ entwickelt. Interessant ist, dass diese Gegend in einen 
bestimmten embryonstadium bei Reptilien (Lacerta, Anguis) 
eine ahnliche Entwickelung wenigstens andeutungsweise zeigt 
und dass hier am Scheitelbeine des fertigen Thieres sich ein 
kreisrundes Loch befindet.” 

In a subsequent paper, which I have not had the opportunity 
of seeing, but a quotation from which is given by the author ina 
recent note to the ‘Zoologischer Aunzeiger,”! he apparently makes 
a further suggestion with regard to the pineal gland, and says 
“ Das Schadeldach der riesigen fossilen enaliosaurier des Lias 
des Ichthyosaurus und Plesiosaurus besitzt ein unpaares Loch, 
welches seiner Lage nach mit dem Loch in Scheitelbein der 
Saurier tibereinzustimmen scheint. Vielleicht lag auch hier 
das viel entwickeltere Zirbelorgan mit seinem distalen Endtheil 
zu Tage, und man konnte sich vorstellen, das seine Leistung 
nicht sowohl die eines Sehorgans als die eines Organs des 
Warmesinnes war, dazu bestimmt, seine Trager vor der zu 
ntensiven LEinwirkung der tropischen Sonnenstrahlen zu 
warnen, wenn sie in trager Ruh, nach Art ihrer noch lebenden 
Vettern der Crocodile, sich am Strande und auf den Sand- 
binken der Liassee sonnten.” 

Ahlborn? has described carefully the structure of the epi- 
physis in Petromyzon, giving a series of drawings to illustrate 
the histology of the part and its attachment to the brain. 

He follows Scott in saying that it arises as a glove-finger- 
shaped outgrowth on the hinder part of the roof of the thala- 
mencephalon in front of the posterior commissure and behind 
the ganglion habenule. 

In the adult, according to Ahlborn, the basal proximal part 
is reduced to a mere rudiment, whilst the most distal portion 
of the pineal gland has acquired a secondary fusion with the 


1 ‘Zool. Anzeig.,’ 21st June, 1886, “ Zur Deutung der Zirbeldrise.” The 
paper referred to here was, of course, published subsequently to Ahlborn’s 
paper, “ Ueber die Bedeutung der Zirbeldrise,” published in 1884. 

2 «Untersuchungen tiber das Gehirn der Petromyzon,”’ ‘ Zeit. f. Wiss,,’ 
1883, p. 230, Tf. 13 and 16, 


170 W. BALDWIN SPENOER. 


terminal division of the left ganglion habenule, whereby is 
simulated the existence of a primitive genetic connection of the 
epiphysis with the anterior roof of the thalamencephalon. 

In the epiphysis Ahlborn states that three parts can be dis- 
tinguished clearly separated off from each other. 

(1) A hinder thread-like stalk. 

(2) Two anterior vesicles lying upon one another (Taf. xiii, 
fig. 2, and Taf. xvi, figs. 43, 44, 46, and 47). The latter form, 
the “ Weisse kuchenartige Masse,”’ which Wiedersheim recog- 
nised as the primitive pineal gland, and lie above the point of 
the beak-shaped roof of the thalamencephalon. The thread- 
like stalk is attached to the upper vesicle, and corresponds to 
the proximal and median part of the epiphysis of Selachians 
and Amphibians (and we may now add to the stalk connecting 
the “eye” with the dorsal surface of the thalamencephalon of 
Lacertilia). 

The distal portion of the epiphysis consists of two vesicles, of 
which the upper is the larger ; their cavities, save in rare cases, 
do not communicate with each other. Ahlborn describes the 
upper vesicle as being a delicate hollow structure, flattened 
out dorso-ventrally, and placed close to the skeletogenous roof 
of the cranial cavity. The cells of the lower wall are always 
much thicker and deeper than those of the upper, and in his 
figures (Taf. xvi, figs. 44, 46, and 47), though he does not 
describe them minutely, are seen to have their long rod-like 
ends free from nuclei, and turned towards the cavity, whilst the 
nuclei are all placed close to their external extremities. These 
rod-like structures, however, are quite devoid of pigment, and, 
moreover, have a thin but well-marked layer of nervous matter 
present between them and the cavity of the vesicle, which is 
itself apparently occupied by strands of nervous tissue passing 
from the posterior to the thin anterior wall. There is nothing 
comparable to a lens. 

The under vesicle is attached on its ventral surface to the 
left ganglion habenule (the whole organ is placed asymmetri- 
cally, and lies on the left side), whilst its upper wall is fused 
with the larger upper vesicle. This secondary fusion with 


PINEAL EYE IN LACERTILIA. 171 


the brain roof necessitating the closure of the epiphysis within 
the cranial cavity. 

Ahlborn!? has also, in a separate article, discussed the nature 
of the pineal gland. He does not agree with Van Wijhe, who, 
following Goette’s work on Amphibia, had regarded the pineal 
gland as “ Ein Umbildungsprodukt einer letzten Verbindungs 
des Hirns mit der Oberhaut” (a mistake corrected later by 
Van Wijhe (see infra). He agrees, on the other hand, with 
Balfour,? who stated that the epiphysis arose as an outgrowth 
from the dorsal surface of the thalamencephalon, and says, 
himself: ‘ Das Neuralrohr is relativ lange vor dem Auftreten 
der ersten epiphysenanlage vollstandig geschlossen, der Porus 
ist nicht mehr vorhanden.” He states, further, that the cavity 
of the primitive pineal gland is a new structure formed as an 
outgrowth of the neural canal, and “ ist also nicht ein Rest der 
vorderen Verschlusséffnung des Gehirns ;” hence it cannot be 
compared with the anterior neuropore of Ascidians and Am- 
phioxus ; but he says: “‘ Durch den Vergleich der Epiphysis 
cerebri mit einer primitiven Augenblase glaube ich nun eine 
Reihe sehr gewichtiger Griinde fiir eine neue und wie es scheint 
richtige Deutung der Zirbeldriise gefunden zu haben.” He 
then draws attention to the fact that both the pineal gland 
and the optic vesicles agree in origin as hollow outgrowths, the 
only difference between the two being that the optic vesicles 
are large and laterally placed, whilst the pineal vesicle is small, 
dorsal, and median. After giving in detail other reasons, he 
says, Alles zusammengenommen komme ich nun aus folgenden 
griinden : 

(1) Nach mit dem Augenblasen tibereinstimmenden Ent- 
stehung der Epiphysis durch eine hohle Austilpung der 
Hirnwand ; 

(2) nach dem Ursprung und der Verkntipfung der Epiphysis 
mit der optischen Hirnregion, speciell mit dem Thalamus 
opticus ; 

1 “ Ueber die Bedeutung der Zirbeldriise,” ‘ Zeit. f. Wiss.,’ 1884, Bd. xl, 


p. 331. 
2 «Klasm. Fishes,’ p. 177. 


VOL. XXVII, PART 2,—NEW SER. N 


172 W. BALDWIN SPENCER. 


(3) nach der morphologischen Aehnlichkeit des Organs mit 
einer primitiven Augenblase (Blischen und Stiel) ; 

(4) nach der angenahert peripherischen Lage des Blaschens 
bei den Selachiern, Ganoiden und Petromyzonten und nach 
einer volkommen peripherischen Lage bei den Amphibien 
(ausserhalb des Schidels auf gleicher hohe mit den Augen ; 

(5) nach dem ursprunglichen zusammenhang der Epiphysis 
mit der Nervenleiste (van Wijhe); zu der Vermuthung, das 
die glandula pinealis als das Rudiment einer un- 
paaren Augenanlage anzusehen ist. Wenn dieser 
Schluss richtig ist, so besitzt die Epiphysis als Rudimentares 
Stirnauge, wie mir scheint, noch jetzt ein funktionirendes 
Analogon in dem unpaaren Auge der Tunicaten und vielleicht 
auch des Amphioxus.” 

Van Wijhe, dealing with the development of Selachians, 
stated first that the anterior neuropore (the spot at which the 
brain remained last in connection with the epidermis during 
closure of the neural canal) corresponded to the pineal gland 
as was stated by Goette to hold true for Amphibia. In his 
more recent paper,’ wherein he describes the results arrived at 
by working with duck embryos, he corrects his first mistake, 
and states that in birds, though the neuropore exists till the 
stage with twenty-eight somites, it then completely disappears, 
whilst when twenty-nine somites are present, the earliest 
rudiment of the epiphysis appears. 

Hoffmann? states that in representatives of nearly all classes 
of Vertebrates it has been proved that the epiphysis arises as 
an evagination of the roof of the thalamencephalon, and figures 
its earliest stages in various reptilian embryos (Tropidona- 
tus natrix and Lacerta); showing also that it is perfectly 
distinct from, though present at the same time as, the anterior 
neuropore. The latter, he says, indicates the position where the 
“ Vorderhirn ” joins the “ Zwichenhirn”’ whilst the epiphysial 

1 “Ueber den vorderen Neuroporus und die phylogenetische Function des 
Canalis Neurentericus der Wirbelthiere,” ‘ Zool. Anzeig.,’ 1884, p. 683. 


2 « Weitere Untersuchungen zur Entwickelungsgeschichte der Reptilien,’ 
‘Morph. Jahr.,’ Bd. xi, 1885, p. 192, 


PINEAL EYE IN LACERTILIA. 173 


rudiment is situated where the “ Zwichenhirn” and the “ Mittel- 
hirn” unite. He states further: ‘‘ Die vordere Ausbruch- 
tung der Epiphysis schnirt sich volstandinge von den Hirndach 
ab; sie bildet eine kleine, runde, selbstandige Blase von platt- 
gedruckter Form und stellt die Anlage des sogenannten Ley- 
digschen Organes/von Strahl hat dieses zuerst erkannt und 
ich kann seinen Befund bestatigen.” 

The most recent, as well as most interesting work upon the 
pineal gland is that of de Graaf,’ to whom is certainly due the 
merit of having first clearly shown that in one particular 
animal (Anguis fragilis) the pineal gland actually is 
modified into a structure comparable to an Inverte- 
brate eye. He says: “Dem zufolge gleicht bei Anguis 
fragilis das ganze abgeschnirte Stiick etwa dem Auge eines 
hoher entwickelten wirbellosen Thieres, wie uns z. B. Cephalo- 
poden, Pteropoden und Heteropoden bekannt ist.” 

According to de Graaf the Epiphysis, in Amphibia and 
Reptiles (Lacertilia), arises as a hollow outgrowth of the 
thalamencephalon,”? never passing much beyond this stage in 
Urodeles (Pl. 2, figs. 13—18), but in Anura and Lacertilia 
becoming divided into two parts. In the former, growth 
results in the formation of a distal bladder-shaped portion and 
a solid stalk connecting this with the brain-roof (Pl. 2, figs. 
22—29) ; the distal part is gradually constricted off from the 
stalk and comes to lie excerebrally and finally without the 
cranium and close beneath the skin; the stalk, on the other 
hand, lies permanently within the brain membranes and thus 
enclosed in the skull cavity. 

In the adult, he says, the cut-off portion of the epiphysis 
(‘ Stieda’s gland”) lies embedded in the cutis close beneath 
the epidermis, is surrounded by a specially close-woven case, 


1 (a) “Zur Anatomie und Entwickelung der Epiphyse bei Amphibien 
und Reptilien,” ‘ Zool. Anzeig.,’ 29th March, 1886. (4) ‘ Bijdrage tot de 
kennis van den bouw en de ontwickkeling der epiphyse bij Amphibién en 
Reptilién,’ van Henri W. de Graaf, Leiden, 1886. 

2 He thus differs from Goette in regarding the epiphysis as a secondary 
outgrowth, having nothing to do with the neuropore. 


174 W. BALDWIN SPENCER. 


‘ and shows retrogressive metamorphosis, undergoing fatty 
degeneration. What Goette regarded as the epiphysial stalk 
is, according to Graaf, nothing more than a branch of the 
Ramus supra-maxillaris of the fifth nerve, and always 
terminates in the connective-tissue case, never in the organ 
itself. The extra-cranial part, though present in the adult 
Rana esculenta, R. temporaria, Alytes obstetricans, 
Bombinator ingens, and Bufo cinerea, is completely 
wanting in the full-grown Hyla arborea. In Reptilia the 
development of the epiphysis takes place as in Amphibia, the 
distal portion being, according to de Graaf, completely 
cut off from the proximal stalk; it lies between the 
brain membranes and has the form of a small, roundish, more 
or less flattened out vesicle, and shows cellular structure. The 
wall lying in contact with the parietal foramen is thickened and 
lens shaped, whilst the hinder wall is pigmented on its inner side. 

De Graaf describes in some detail and figures (Pl. 4, figs. 
32—34) the organ in Anguis fragilis. Reference to this 
description will be made later on. 


Results of the present investigation. 


I desire in the first place to acknowledge the kindness of 
Dr. Ginther, to whom I am indebted for the gift of examples 
of different genera (indicated by an asterisk in the list below) 
from the duplicate specimens of the British Museum; my 
thanks are also due to Professor Stewart for the opportunity 
of examining specimens of Iguana and Varanus from the. 
collection of the Royal College of Surgeons. 

To E. B. Poulton, Esq., of Keble College, and to F. Beddard, 
Esq., of the Zoological Society, I am indebted for specimens of 
Hatteria. 

My thanks also are due to Professor Westwood for the gift 
of a fine Chameleo vulgaris, and for the opportunity of 
examining C. bifurcatus; and to G. C. Bourne, Esq., of New 
College, for a specimen of Gecko mauritanicus. 


PINEAL EYE IN LACERTILIA. 175 


I have also to acknowledge gratefully the gift of various 
species of Lacertilia, prepared especially and sent to me from 
the Bahamas by J. Gardiner, Esq.; they arrived too late for 
the results of their examination to be included in the present 
article, but I hope to be able to publish an account of the 
structure of the organ in these forms in a short time. 

The forms investigated have been the following : 


‘Hatteria punctata. Lyriocephalus scutatus. 


‘“*Varanus giganteus. **Calotes versicola. 
me bengalensis. ae ophiomaca. 
-Monitor (sp. ?). -*Agama hispida. 
- Ameiva corvina. & *Stellio cordylina. 
»-Chameleo vulgaris. * *Grammatophora barbata. 
* s bifurcatus. <~*Moloch horridus. 
-Gecko verus. Leiodera nitida. 
»  Mauritanicus. x Anguis fragilis. 
~-Anolis (various species). « Cyclodus gigas. 
Leiolemus tenuis. » Lacerta ocellata. 
*Uraniscodon (Plica) umbra. 4 viridis. 
**Iguana tuberculata. 3 (Zootoca) vivipara. 
«* Draco volans. ««Seps chalcidica. 


-*Ceratophora aspera. 


The material has, in the great majority of cases, consisted of 
spirit specimens in a better or worse state of preservation so 
far as histological structure was concerned, so that in many 
instances it has been impossible to do much more than ascer- 
tain the presence or absence of the organ, its connection or 
separation from the proximal part of the epiphysis, and perhaps 
a few details with regard to its histological structure. Even in 
‘fresh specimens the organ lies so deeply embedded in connec- 
tive tissue and so closely shut in by bone, which must be 
removed along with it to prevent injury to the structure, that 
there is great difficulty in rapidly reaching it with reagents. 
Of two of the most important forms—Hatteria punctata 
and Varanus giganteus—I have had the great advantage, 
through Professor Moseley’s kindness, of examining fresh 
specimens, and have thus been able to investigate more care- 
fully the structure of the retina. 


176 W. BALDWIN SPENCER. 


In the account which follows the structure of the organ is 
described separately in the different forms examined; this 
structure, as might have been expected to be the case in an 
organ of this kind (which must be regarded as in a more or 
less rudimentary condition), shows considerable variation, even 
amongst species of the same genus. I hope on a future occa- 
sion to describe the organ in other forms of Lacertilia. 


Hatteria punctata, Pl. XIV, figs. 2, 3,4, and 5; Pl. XV, 
figs. 7 and 8; Pl X Xo as. 7: 


(1) External Appearance.—There is in Hatteria but 
very little external trace of the eye, no special scale being 
modified into a “ cornea ;” an absence of pigment, however, in 
the skin of the median line, slightly posterior to the level of the 
paired eyes, indicates the position of the parietal foramen ; this 
external indication being more evident in some than in others. 

(2) Position of the Eye.—The foramen itself is filled 
up by a plug of connective tissue, which, notwithstanding the 
absence of pigment, must effectually prevent the organ lying 
beneath from functioning as an eye in the ordinary sense of 
the word; light would more easily penetrate the skin at this 
than at any other portion of the surface of the head, but yet it 
is perfectly impossible for an image to be formed upon the 
retina. The fibres of the connective tissue in the foramen 
may be divided into two sets—(1) an outer set (Pl. XV, fig. 7, 
Cf) arranged on the whole at right angles to the surface of 
the head, and which on the inner side of the foramen are con- 
nected with (2) an inner set lying immediately in front of the 
eye, and arranged so as practically to form a hemisphere, part 
of the internal surface of which forms the anterior boundary of 
a capsule enclosing the eye (figs. 2, 7, and 8, Ci). The 
hinder half of the capsule which thus lies in the lower part of 
the foramen is formed of somewhat loosely aggregated fibres 
with well-marked nuclei scattered irregularly amongst them, 
and is drawn out in the direction of the optic stalk, which, 
together with a blood-vessel, pierces the capsule wall at its 


PINEAL EYE IN LACERTILIA. 177 


most posterior point (fig. 2); the extreme length of the cap- 
sule is 1*4 mm. Special fibres cross from the capsule wall to 
the edge of the lens, and, being connected with the tissue 
immediately surrounding the retina, may serve the purpose of 
keeping the eye in position, and thus represent the rudiment 
of a structure of importance when the eye was fully func- 
tional. The capsule in its hinder part contains much irre- 
gularly scattered connective tissue with nuclei, its anterior 
part, however, being free from them. Within the capsule 
breaks up an artery (figs. 2 and 7, B.v.) whose branches ramify 
-amongst the fibres behind the eye; this special blood supply 
is a prominent feature in connection with the organ in all the 
forms examined. 

The eye lies with its long axis directed upwards and for- 
wards in the most anterior part of the capsule; figs. 7 and 8 
show the relative position of the eye in its capsule with regard 
to the brain and the parietal foramen. 

Structure of the Eye.—Through the kindness of Prof. 
Moseley I have been able to examine the structure in a fresh 
specimen, and, notwithstanding. the fact that the organ cannot 
now be fully functional, the retina is fairly well developed. 

The eye has, roughly speaking, the shape in section (PI. 
XIV, fig. 2) of a cone, the base of which lies turned towards 
the surface, whilst the pineal stalk is connected with the apex. 
The walls of the optic vesicle are divided into two parts, (1) 
an anterior; (2) a posterior; of which the former forms the 
lens, and the latter the sensitive structures. 

(1) Lens.—The lens of the pineal thus differs markedly 
from that of the paired eyes, where it originates as a secondary 
structure by invagination of the epiblast, whilst in the former 
it is apparently directly the product of the brain wall itself, 
and equivalent in position to that part of the paired optic 
vesicles which after invagination forms the retinal elements. 

De Graaf has likened the eye to that of such Invertebrates 
as Cephalopods and Pteropods ; but, apart from other differ- 
ences which exist between the two in regard to both develop- 
ment and structure, the lens is not in the least degree com- 


178 W. BALDWIN SPENCER. 


parable in the two cases, being in the Invertebrates mentioned 
formed as a cuticular secretion. 

In Hatteria as in all forms examined it is distinctly cellular, 
the nuclei being prominent and numerous (fig. 2). The 
median cells are elongate so as to give the lens a curious cone 
shape, the base corresponding to the front of the eye and the 
apex lying in the optic axis; the cells are further arranged in 
a definite manner as shown in fig. 2, and are, as the latter 
indicates, directly continuous with those of the retina. 

(2) Retina.— The retinal elements are arranged in the 
manner typical of Invertebrates, i.e. the rods lie on the inner 
side bounding the cavity of the optic vesicle, the nerve enter- 
ing posteriorly and not spreading out in front of the rods. 

Within the same vertebrate animal we thus find 
eyes developed on both vertebrate and invertebrate 
types, both being also formed fromthe modification 
of the walls of hollow outgrowths of the brain. 

The retina consists of the following elements (Pl. XIV, figs. 
2, 3, 4, and 5): 

(1) A layer of rod-like bodies (R) enveloped in deep pig- 
ment, which when the rods are separated (fig. 5) is seen to be 
so deposited upon them as to produce a striated appearance. 
The pigment is specially densely deposited around the margin 
of the retina in contact with the lens, extending here through 
the whole thickness of the wall. A curious specialisation 
takes place in connection with the rods lying in the optic axis, 
which also obtains in the pineal eye of many other forms. 
The rods in this portion are elongated (R') to at least twice the 
length of the ordinary ones, and are in connection at their 
outer ends with a special group of nucleated cells (n*) which 
lie enclosed by a somewhat definite membrane in the pineal 
stalk, with the fibres of which they are directly connected 
(fig. 4). 

(2) A double and, in parts, triple row of spherical nucleated 
elements (n!), which appear to be connected by processes, on 
the one hand with the rods, and on the other with the layers 
external tothem. They surround posteriorly the elongate rods, 


PINEAL EYE IN LACERTILIA. 179 


and their processes in this region run in many cases (n*) 
directly into connection with the fibres of the optic stalk. 
The layer gradually thins out anteriorly until that part is 
reached where, in the neighbourhood of the lens, the pigment 
is present through the whole breadth of the wall. In its 
thickest part the whole layer (consisting of the double or triple 
row of elements) is about the same breadth as the layer of 
rods. 

(3) External to the spherical elements lies a thin layer con- 
sisting of a fine punctated material, which takes the stain 
(heematoxylin) with difficulty but contains numerous scattered 
fine pigment granules. Into this, which may be called the 
Molecular layer,' pass processes from the retinal elements 
on either side (fig. 2, mo.). The layer in question is a very 
thin one in Hatteria punctata, but forms, when seen in 
section (fig. 2), a definite boundary line separating the retinal 
elements into an internal and an external division. Poste- 
riorly the layer spreads out and surrounds the specially 
elongated rods in the optic axis, anteriorly it reaches as far 
forwards as the ring of pigment surrounding the lens. It is 
possible that this layer and many of the processes passing into 
it may be of the nature of supporting structures. 

(4) A layer of nucleated spherical elements (fig. 3, n”) lying 
close to the molecular layer, and distinguished from those on 
the inner side by their greater size; they are arranged so as to 
alternate (the alternate arrangement is, however, by no means 
perfectly constant) with ‘ 

(5) A layer of cone-shaped bodies (Co.) in which no nuclei 
can be detected. They lie with their broad ends externally, 
and gradually taper internally till their pointed ends are 
closely in contact with the molecular layer into which pro- 
cessses from them run (fig. 3). 

(6) Between the bases of the above are a series of spindle- 
shaped elements with nuclei, from which processes pass off 
internally, which may either run directly into the molecular 
layer or into the spherical bodies on its external side. At the 

' Cf. de Graaf, Pl. 4, fig. 34, g/. 


180 W. BALDWIN SPENOER. 


posterior part (i.e. near the pineal stalk) the cone-shaped 
elements seem to be absent, and their place to be taken by 
large nucleated spindles (Co), which, as it were, bend round 
internally (fig. 5) and give off processes running directly into 
the fibres of the stalk. 

Connection with the Brain.—It has hitherto been 
stated by all writers that the distal part of the epiphysis 
becomes separated from the proximal which forms the pineal 
gland of the adult, and that the former comes to lie (as shown 
by de Graaf in Anguis fragilis) external to the cranial cavity 
in the parietal foramen. De Graaf! figures in Anguis the 
eye as fitted closely into the parietal foramen encased by con- 
nective tissue, but separated by a considerable interval from 
the proximal hollow epiphysial stalk from which in develop- 
ment it has been cut off. 

In Hatteria, as also in several other forms to be 
described below, longitudinal vertical sections show 
clearly that the highly developed eye is connected 
with the epiphysis by a solid and well-marked stalk, 
which may be called the pineal stalk. 

This runs in the median line backwards and slightly down- 
wards ; it enters the eye at the posterior end, the walls of the 
optic vesicle being here (fig. 2) drawn out somewhat back- 
wards. The relationship of the elongated rods to the stalk 
has been already described ; passing backwards from the eye 
the stalk makes a decided bend upwards, then pierces the wall 
of the eye capsule at its most posterior point and runs straight 
back to the epiphysis; its fibres enter the latter, being appa- 
rently connected with the cells of the apex and the under 
surface. The pineal stalk contains elements which have much 
the appearance of those found at an early stage in the deve- 
loping nerve of the paired eyes, that is, they much resemble 
cells which are undergoing a process of elongation so as to 
form long fibres (figs. 2 and 4); some having undergone 
considerable elongation, others being yet spindle shaped. 

There can be little doubt that this median, azygos, nerve 

1 Pl. 4, figs. 31, 32, 33, and 34. 


PINEAL EYE IN LACERTILIA. 181 


represents the originally hollow process uniting the proximal 
with the distal portion of the epiphysis, and which, losing its 
connection with the optic vesicle in some forms (e.g. Anguis), 
is in others (e.g. Hatteria) transformed into a solid stalk 
serving as the nerve of the pineal eye. It has been sufficiently 
‘demonstrated that the latter is the distal portion of the epi- 
physis, and we are thus presented with a new sensory structure 
—the pineal eye—agreeing precisely with the paired eyes in 
(1) its development as an outgrowth from the walls of the neural 
canal, and (2) the formation of its nerve by the gradual solidifi- 
cation of the primitively hollow tube connecting the distal 
vesicle with the proximal portion of the outgrowth. In the 
case of the paired eyes the whole of the outgrowth save the 
vesicle is transformed into a nerve; in the pineal eye only the 
median part of the outgrowth is thus metamorphosed, the 
proximal part retaining its originally hollow nature. 


VWaranus cicantews, Pl XPV fie 1) figs Ger PEK; 
fig. 10; Pl. XIX, fig. 34. 


External Appearance.—In a large specimen of this 
animal, measuring six feet one inch from the snout to the tip 
of the tail, which I was enabled to examine in the fresh state 
through Professor Moseley’s kindness, the external indication 
of the eye is so clear that it is remarkable that no one has 
hitherto examined the organ lying beneath. The head is 
covered with small, deeply-pigmented tubercle-like scales, save 
in the median line, where, somewhat posterior to the paired 
eyes, a single large scale is present, standing out prominently 
by reason of its creamy whiteness (fig. 10). 

The scale is roughly hexagonal in shape, measuring 5 mm. 
across, and has upon it a slightly-raised circular rim, the area 
within which has the appearance of a transparent membrane 
drawn tensely over a cavity beneath. A dark circular spot in 
the middle, visible in the living animal, indicates the position 
of the eye, and is, as will subsequently be shown, due to the 
presence of a mass of pigment in the lens. In the matter of 


182 W. BALDWIN SPENCER. 


external indication of the structure Varanus thus differs 
much from Hatteria in the possession of this scale, modified 
to form a cornea. 

Position of the Eye.—The cornea thus formed lies imme- 
mediately above the parietal foramen, the space in which is 
tightly filled by connective tissue, in the midst of which again 
lies the pineal eye. There is thus no real cavity beneath the 
cornea, but the pigment, which elsewhere is abundantly present 
in the skin, is here entirely absent, so that by this means the 
passage of light to the organ is much facilitated. Beneath the 
epidermis and the rete mucosum the connective-tissue fibres 
of the cutis vera are arranged in two definite sets, as in 
Hatteria: (1) a series running parallel to the anterior surface 
of the eye from side to side of the foramen (PI. XIV, fig. 1, 
Ct”), interlacing with each other, and thus forming a dome- 
shaped structure above the eye; and (2) a series of bundles 
(Ct) at right angles to the former, upon which they spread out 
at their internal ends, whilst externally they run outwards 
to the rete mucosum. Obliquely directed strands pass from 
one bundle to another, and the irregular spaces thus left are 
filled up by a meshwork of indefinitely arranged fibres. 

Immediately below the level of the first series of fibres is 
placed the eye itself, but, instead of lying, as in Hatteria, ina 
capsule, the connective tissue closely invests it. The tissue 
within the parietal foramen may be divided into three parts: 
(1) a series (Ct*) bounding the sides of the parietal foramen, 
and continuous with the upper series (C7¢'); these follow in their 
course the outline of the bone; (2) irregularly arranged fibres 
(Cz*), filling up the greater part of the foramen; (8) a series 
forming a special encasement for the eye, to the sides of which 
their long axes are parallel (C¢*, the arrangement of these is 
scarcely made sufficiently prominent in the figure). 

In Hatteria is found a special capsule in the space within 
which the eye is situate. Even in this form a certain amount 
of connective tissue les within the capsule, whilst a still greater 
development of the tissue would lead to the condition which 
obtains in Varanus giganteus. 


PINEAL EYE IN LACERTILIA. 183 


In addition: to the connective tissue within the foramen a 
large blood-vessel is present, which, accompanying the optic 
stalk till the foramen is reached, breaks up in this into nume- 
rous branches ramifying in the connective tissue (B.v.), a branch 
finally passing from either side in front of the eye (fig. 1), 
whilst one pierces the connective-tissue dome. 

Structure of the Hye.—The eye is, though the size of 
the two specimens of Hatteria and Varanus are so dif- 
ferent (Hatteria under 2 ft., Varanus 6 ft.), as nearly as 
possible precisely the same size in both, measuring, in the 
line of the optic axis, °4 mm., but in Varanus the eye is 
compressed somewhat in this direction, so that it is broader 
from side to side slightly than in Hatteria (cf. figs. 1 and 2). 

Lens.—The lens is distinctly cellular in structure, the cells 
being elongated in the direction of the optic axis, and having 
the appearance of stretching the whole breadth of the lens, 
their nuclei, which are very prominent, being situated so that 
in section (fig. 1) they form a well-marked line across the lens 
from side to side somewhat nearer to the inner than the outer 
surface. The whole lens has the appearance represented in 
fig. 1, being thickest in the median line and thinning away 
rapidly at each side where it joins the retina. 

Right in its very middle is present a large, more or less 
globular mass of small spherical cells, deeply pigmented (fig. 1, 
pig.), and lying directly in the optic axis. The presence of these 
must of necessity interfere with the action of the organ as an 
eye, in fact, the whole structure is characterised by the presence 
of a great amount of pigment deposited in every part. It is 
this pigment in the lens which causes the eye seen through the 
transparent cornea to appear like a black spot, and its presence, 
which must be regarded as due to degeneracy in the tissues, 
indicates that the organ is now in a rudimentary condition. 

Structure of Retina.—The rods line the cavity of the 
vesicle and form a very definite layer, being deeply embedded 
in pigment, which renders it difficult to distinguish their out- 
lines. Processes pass from them, often accompanied by pig- 
ment granules, into the external-lying layers. Asin Hatteria 


184 W. BALDWIN SPENCER. 


certain of the rods become elongated ; this lengthening is con 
fined in the former to those lying in the optic axis;but in 
Varanus takes place at two points, one of which, the most 
prominent, lies in the optic axis, whilst the other lies to the 
anterior side, each being connected with the entrance of a 
separate nervous strand into the eye. 

Amongst the rods are scattered numerous spherical masses 
of pigment. There is not the slightest indication of any struc- 
tures lying internal to the rods embedded in pigment, such as 
are described by de Graaf in Anguis; on the other hand, the 
internal limit of the layer of rods is so well marked as to 
present the appearance of a definite membrane lining the 
cavity. The latter was most probably filled during life by a 
fluid, the coagulated remains of which are seen attached as an 
irregular structureless coagulum to the inner ends of the rods. 
External to the rods is a layer of finely punctated material 
(Mo) apparently corresponding to the much narrower layer in 
Hatteria. This layer, together with the rods, occupies as 
nearly as possible one half of the breadth of the retina. In 
this layer are situated spherical elements (n!), which in some 
cases can be traced into connection with the rods; no arrange- 
ment in two or more rows, asin Hatteria, can be detected, 
but they appear to be placed somewhat irregularly. External 
to the molecular layer, the outer limit of which is somewhat 
sharply defined, lie a series of spherical-shaped elements (n2). 
The appearance of these as seen in section is given in fig. 6. 
Some of the elements resemble those lying within the mole- 
cular layer (n'), others have processes passing straight through 
to the rods on the internal and the nerve-fibres on the external 
side, whilst others again are connected with one another and 
with the layers on either side by irregularly branching pro- 
cesses. 

Certain of the nerve-fibres pass round behind the vesicle 
and then enter the retinal elements, but apparently the greater 
number are directly connected with the two above-described 
bundles of elongated rods. 

Within the external layers of the retina are many large 


PINEAL EYE IN LACERTILIA. 185 


spherical masses of deep brown pigment (pzg.'), connected in 
some cases with the pigment enclosing the rods ; beyond this, 
again, a certain amount of pigment in minute granules is 
scattered irregularly amongst the external spherical elements, 
and completely external to the optic vesicle posteriorly is 
massed around the entrance of the nerve a great amount of 


pigment deposited in branchial cells (pig.’). 


Nerve.—The pineal stalk is well marked in Varanus 
giganteus and differs moreover from anything met with 
amongst other forms (even other genera of Varanus).' 
Instead of being single there are three distinct nervous strands 
entering the vesicle posteriorly ; two of these are more promi- 
nent than the third, which appears to be in connection with 
the anterior of the former; the single posteriorly placed nerve 
entering very nearly but not quite in the line of the optic 
axis. The larger and smaller anterior strands join together, 
and then, after a marked curve, shared in by the posterior 
one, they join the latter and run back as the solid pineal stalk 
to the proximal part of the epiphysis. 

At first it seemed possible that the appearance described 
might be due to the cutting im longitudinal section of the walls 
of a hollow stalk distorted somewhat by reagents, but an 
examination of a continuous series soon showed that this was 
not the case, and that the pineal stalk, single proxi- 
mally, broke up distally into two, and finally into 
three separate nerves entering the optic vesicle. 


The most noticeable features in the eye of Varanus are: 

(1) The great development of pigment in all parts, and 
more especially in the lens. 

(2) The curious nature of the retina, which has really the 
form of a cellular network ; the cells being in connection with 
one another by branched processes, the nuclei being scattered 
somewhat irregularly and giving rise, together with the proto- 
plasm around them, to the spherical elements of the retina. 


‘ The only other lizard as yet examined, in which anything comparable to 
this is found, is Lacerta ocellata, to be described Jater on. 


186 W. BALDWIN SPENCER. ‘ 


Reference to this structure of the retina will be made again 
when dealing with the epiphysis in Cyclodus. 
(3) The triple nature of the pineal stalk. 


Varanus bengalensis, Pl. XV, fig. 12; Pl. XVI, fig. 17; 
Pl. XIX, figs. 37 and 41. 


External Indication.—In the several specimens of V ara- 
nus examined (in addition to V. giganteus) the external in- 
dication of the eye was very clear indeed, consisting of a large, 
modified, median scale (Pl. XIX, fig. 37), lying somewhat 
posterior to the level of the paired eyes, and having at its 
centre a circular dark space, surrounded at a short distance by 
a dark circular line. The central part, which is to a certain 
extent transparent, acts as a cornea for the eye placed beneath. 

Position of the Eye.—In small specimens of Varanus, 
when the skin is removed from the head, the pineal eye is 
removed with it and may be examined whole. Fig. 12 repre- 
sents a portion of the skull roof of a very young specimen of 
V. bengalensis viewed from the under surface, the bone 
being very thin indeed. The portion surrounding the parietal 
foramen is represented in the figure, together with the pineal 
eye, lying in the latter and viewed as a solid object. The 
foramen has a somewhat oval shape and backwards from it 
leads a groove in the median line. The specimen from which 
this is taken was not in good histological preservation, and no 
connection with the brain can be traced. The eye is circular 
in outline and depressed from above downwards, and shows, 
when viewed by transmitted light, the rods embedded in pig- 
ment and forming a very definite layer. Since they line a 
space within the vesicle, circular in outline, those at the sides, 
when the object is viewed from above or below, form a circle (R), 
external to which lie the other elements of the retina. In the 
optic axis posteriorly lies a prominent mass of rods more deeply 
pigmented than elsewhere, and which indicate most probably a 
series of elongated rods connected with the union of the pineal 
stalk; the latter may have been pulled away along with the 


PINEAL BYE IN LACERTILIA. 187 
‘ 
brain membranes when the surface of the skull was removed 


from above the brain. 

The connective tissue lying external to the eye is quite 
transparent, and being placed as it is immediately beneath the 
skin, the entrance of light is thus made possible ; in fact, it is 
impossible to prevent the light from entering, not only in this 
but in the case of the pineal eyes of all other Lacertilia, when 
they are placed so near to the skin. 

In section, the eye of a somewhat larger V. bengalensis 
shows the following structure differing much from that of 
V. gigauteus, a difference the more noticeable since it exists 
between members of the same genus. 

Fig. 41 represents a longitudinal section along the median 
line of the head passing through the parietal foramen; the 
results are represented somewhat diagrammatically. The eye 
hes within the foramen tightly enclosed again within connec- 
tive tissue, no special capsule being present. A very notice- 
able feature is the entire absence of pigment above the eye, 
though this is present in abundance in the skin elsewhere 
(Ct, pig.) in the connective tissue of the cutis vera. The eye 
itself is depressed dorso-ventrally, so that but comparatively 
little space remains within the vesicle; the latter lies directly 
above the anterior extremity of the proximal part of the 
epiphysis, which runs right up into the foramen from the dorsal 
wall of the thalamencephalon lying some distance posteriorly. 

Fig. 17 gives a more detailed representation of the foramen 
with its contents. Beneath the cuticle (cu.) the epidermis is 
seen (ep.), then the rete mucosum, the nucleated cells of which 
are in this part somewhat longer than those elsewhere ; beneath 
this lies the connective tissue of the cutis vera (Ct). On either 
side of the foramen are numerous pigment cells (Ct¢, pzg.), and the 
fibres as before may be divided into two series—(1) a set running 
at right angles to the long axis of the head, and (2) others form- 
ing a roof for the foramen, and connected with those lying within 
the latter, which form a close investment for the eye (C?*). 

Within the foramenalso isamuch branched blood-vessel which 
enters along with the epiphysial stalk; a small branch passes for- 

VOL, XXVII, RART 2,—NEW SER, 0 


188 W. BALDWIN SPENCER. 


ward on either side in front of the eye just asin V. giganteus. 
The figure shows the specialisation in the connective tissue above 
the eye, and the entire absence of pigment-bearing cells in the 
same position, though they are present on both sides in the section. 

Lens.—The lens has very much the same structure as in V. 
giganteus, being distinctly cellular with well-marked nuclei, 
forming in section a double or triple row from side to side, the 
cells appearing to run the whole breadth, whilst in the middle of 
the lens a great mass of pigment is deposited in the line of the 
optic axis. The pigment masses are spherical on the external, 
and more rod-like on the internal surface. 

Structure of Retina.—The specimen being preserved in 
spirits without special reference to histological work, it was 
somewhat difficult to make out many points with regard to the 
structure of the retina. The rods are well developed and pro- 
minent, lining the cavity of the vesicle, and having their long 
axes arranged as indicated in the figure, those in the optic axis 
being at right angles to the external surface, the eye itself being 
immovably fixed, so as to look directly upwards. They are em- 
bedded in pigment, and none amongst them appear to be specially 
elongated (associated, doubtless, with the absence of connection 
with any nerve, suchasis present in V. giganteus or Hatteria). 
No trace of any definite structure internal to the rods can be seen. 

External to the rods lie a series of spherical-shaped elements 
(n'), corresponding, presumably, to the same in Hatteria and 
V. giganteus, and at intervals amongst these can be detected 
spindle-shaped bodies, which, together with the former, stain 
easily (with hematoxylin and borax-carmine). Both these he 
within a layer, consisting, as in V. giganteus, of finely-punc- 
tated material, whose external limit is well defined. It is difficult 
to ascertain precisely the structure of this particular layer, which 
in these two (as well as in other forms) has the appearance of a 
ground substance, in which lie the external ends of the rods and 
the spherical elements, but its constant presence and character 
renders it unlikely that it is the result simply of reagents ; it is 
here called the molecular layer, but may, perhaps, differ in nature 
from the layer to which the same name is applied in Hatteria, 


PINEAL EYE IN LACERTILIA. 189 


External to this lies a series of cone-shaped bodies (Co.), the 
pointed internal ends of which abut against the molecular layer, 
their broader external extremities being placed against the 
limiting membrane of the eye, where a certain amount of 
pigment (pig.') is deposited in the form of fine granules. 

In some cases a connection (not well drawn in the figure) can be 
traced between the cones and the rods, or, in other cases, the spheri- 
cal elements. This connection is best developed in the optic axis. 

Epiphysis.—In a preliminary communication to the Royal 
Society! the eye of one specimen of V. bengalensis was de- 
scribed as connected with the brain by a hollow epiphysial 
stalk. Further investigations have shown that this statement 
must be modified. It is by no means easy to determine the 
point, and possibly with a fresh specimen a connection between 
the eye and the proximal portion of the epiphysis may be shown | 
to exist. The two come very close together (closer than is 
represented in fig. 17), and there is a decided appearance of a 
connection between them. Further study of my sections has 
failed to establish the poimt, and fig. 17 represents, as far as 
can at present be ascertained, the actual state. 

The epiphysis (fig. 41) may be divided into three parts: (1) 
the distal, separated off as the pineal eye; (2) a short, hollow, 
proximal portion, arising from the roof of the thalamencephalon, 
and running at right angles to this; and (3) a median portion 
running forward from the end of the latter along the roof of 
the cranial cavity enclosed in the brain membranes. This part 
also is hollow, and its walls consist of a single layer of distinctly 
nucleated columnar cells. Its distal extremity lies immediately 
beneath the pineal eye, and is swollen out and filled with blood- 
corpuscles, the cells in the wall of this part being somewhat 
cubical in shape. Passing backward the walls approach one 
another until they come into contact, and for a short distance 
a solid stalk is formed; further back, again, the walls part 
from each other, and in this region the cells lengthen out very 
much until they pass into the proximal part (fig. 41). 


1 «Proc. R.8.,’ ‘* Preliminary Communication on the Structure and Pre- 
sence in Sphenodon and other Lizards of the Median Eye, described by de 
Graaf in Anguis fragilis,” June 10th, 1886. 


190 W. BALDWIN SPENCER. 


Monitor (sp. ?).—In the Monitor examined there was no 
external trace of the organ to be discerned, though when the 
skin was removed from the dorsal surface of the head and 
viewed by transmitted light, an absence of pigment and 
general transparency in the spot overlying the parietal foramen 
indicated the position of the eye. The latter could be easily 
distinguished as a small black spot lying within the foramen, 
which was itself. in the form examined, extremely small. 
Unfortunately the specimen was in a bad state of preservation 
histologically, and the tissues very dry, so that it was again 
impossible to make out the details of the structure. The 
eye, which is deeply pigmented save anteriorly, where is the 
lens, appears to be placed at the distal extremity of a pineal 
stalk which, as in Varanus giganteus, runs up vertically 
through the foramen, accompanied as usual by a large artery. 


Chameleo vulgaris, Pl. XVI, fig. 21; Pl. XIX, fig. 40 ; 
Pl. XX, fig. 6. 


In this form a curious modification takes place, an optic 
vesicle being formed but not reaching any high degree of 
development. In the short account written in ‘ Nature,’! it 
was stated in a note that the organ was present in Chameleo 
vulgaris—a statement of which de Graaf has subsequently 
denied the truth. He says that though the parietal foramen 
is open in the young form it becomes closed as the adult state 
is reached, and that there can be thus no organ remaining in 
connection with the proximal part of the epiphysis. Before 
reading his note, and subsequently to the publication in 
‘Nature,’ three more adult specimens were cut in section 
(the first note was based upon a dissection), with the result 
that each one has fully confirmed the statement that the organ 
is present in Chameleo, and moreover remains in connection 
with the proximal part of the epiphysis, though it certainly is 
in a comparatively low state of development. 

External Indication.—The presence of the organ is 
indicated in both Chameleo vulgaris and Chameleo 

1 ©Nature,’ May 13th, 1886. 


PINEAL BYE IN LACERTILIA. 191 


bifurcatus by a tubercle slightly depressed below the level 
of the surrounding ones, and having a very transparent appear- 
ance ;! it lies in the median line just in front of the anterior 
end of the strongly marked ridge, which occupies the dorsal 
surface of the head posteriorly. 

Fig. 40 gives a diagrammatic view of the relationship of the 
different parts; the parietal foramen is not large but is still 
clearly present, and very easily distinguishable in sections. 
Within it and lying immediately beneath the modified tubercle 
is the optic vesicle ; elsewhere as usual the skin is deeply pig- 
mented, but the pigment cells are entirely wanting above the 
vesicle, a fact which is especially noticeable in sections of this 
animal, the cells having long processes and being closely 
packed together (fig. 21). It is this absence of pigment which 
produces the transparent effect in the tubercle. The surface 
of the latter is very convex, and beneath it the layers of the 
skin are arranged as usual, a series of special connective-tissue 
fibres forming an encasement for the vesicle. Within the 
foramen there is the customary well-marked and branching 
blood-vessel (6.v.), which accompanies the pineal stalk. 

Structure of Vesicle-—In Chameleo the structure of 
the vesicle is very simple. It has the form of a hollow sphere 
whose walls have been compressed dorso-ventrally, so that its 
greatest length lies in the line of the long axis of the head. 
Its walls are formed of elongated distinctly nucleated cells, 
those facing into the cavity bearing long cilia; no pigment is 
present and there is no differentiation into lens and retina, the 
cells of the anterior and posterior walls of the vesicle being 
alike. Posteriorly the imner wall of the vesicle is, as it were, 
drawn downwards (fig. 21), a small horn-like space being thus 
formed, turned somewhat towards the pineal stalk ; its general 
appearance conveys the idea of the vesicle having at first had 
the relationship to the then open pineal stalk which is at 
present shown by the swollen distal extremity to the epiphysial 
tube in Cyclodus.. By the meeting of the walls of the epi- 
physial tube the vesicle would become closed, and the solid 


1 The external indication is much clearer in some than in other specimens, 


192 W. BALDWIN SPENCER. 


pineal stalk formed; this would be attached primitively to the 
posterior end, and the bending of the cells of the vesicle wall 
(fig. 21) make it appear as if a subsequent drawing down of 
the stalk to the ventral surface had taken place. In the 
specimens examined the stalk is seen to end anteriorly some- 
what sharply against the under surface of the vesicle, at any 
rate, in this part none of its fibres could be traced into the 
cells above, though, as the specimens examined were not 
specially preserved for histological purposes, it is quite possible 
that with fresh ones a connection might be demonstrated. 
Posteriorly, however, where the drawing down of the wall 
occurs the fibres and cells are in connection with each other. 
The pineal stalk itself is avery definite structure, running from 
the under surface of the vesicle downwardsand slightly backwards, 
till just without the parietal foramen, where it joins the hollow 
epiyhysial stalk running backward to the roof of the thalamence- 
phalon. In structure it resembles closely that of Hatteria. 


Gecko verus. 


Neither in the adult nor in the embryo is there the slightest 
external trace of the organ, the skin being tuberculated and 
capable of being lifted up from the head without remaining 
attached in the position of the parietal foramen. There is no 
discernible trace of the latter: in lizards in which it is present 
the skin cannot be removed wholly from the surface of the head. 

Sections show that the epiphysis is a well-marked structure 
in Platydactylus arising from the roof of the thalamence- 
phalon and running straight upwards till it comes into contact 
with the roof of the cranial cavity. This portion corresponds 
to the proximal part of the structure in other forms, and appa- 
rently the pineal stalk, which usually runs forward from this 
along the dura mater, as well as the distal portion modified into 
the pineal eye, are both absent in Gecko. The epiphysis is hollow 
and its cavity gradually increases in size as it passes further from 
the roof of the brain and approaches the skull, against which 
it ends blindly ; there is no differentiation in its walls, so far as 
could be discerned, to form an optic vesicle. 


PINEAL EYE IN LACERTILIA. 193 


The same structure is present in Gecko verus and Gecko 
mauritanicus. 


Ameiva corvina. 


Ameiva externally agrees with Platydactylus in the 
absence of a modified scale to function as a cornea; the skin 
of the head is also easily removable, not being attached in the 
position of the foramen, which is also wanting in this species. 
I have not yet examined it by means of sections, but as far as 
can be told it agrees with Gecko. 


Anolis, Pl. XV, fig. 11; Pl. XVII, fig: 24. 


It is not my intention in this paper to describe the structure 
of the eye of Anolis in any great detail, as before long I hope, 
by the kindness of Mr. J. Gardiner, to be enabled to describe, 
by means of specimens prepared carefully by him, the eyes of 
several species of Anolis from the Bahamas. The eye of one 
specimen has, however, been figured viewed as a solid object 
from beneath (fig. 11). The brain membranes are represented, 
the dura mater having branched pigment-cells scattered over it, 
and having a specially dark ring around the margin of the 
parietal foramen in which lies the eye. The latter is somewhat 
elliptical in shape, its long axis lying in the same line with 
that of the head: the eye is compressed dorso-ventrally, and 
when compared with the organin Varanus bengalensis (fig. 
12), placed by its side, the rods are seen to be much larger than 
in the latter ; the cavity within the optic vesicle, whose size is in- 
dicated by the circular space bounded by the inner ends of the 
rods, being hence considerably less in Anolis than in Varanus. 

Fig. 24 (Pl. XVIT) is a drawing of the eye of another species 
of Anolis from the West Indies. The organ lies in the 
foramen with its upper surface close beneath the surface of 
the head. Its shape is unlike that of any form described 
hitherto, being elongated in a dorso-ventral direction. The 
lens is cellular and its hinder border is deeply convex towards 
the cavity of the vesicle, calling to mind somewhat the shape 
of the structure n Hatteria; in the optic axis certain of the 


194 W. BALDWIN SPENCER. 


cells are apparently undergoing degeneration, pigment being 
deposited in them. 

Retina.—The hinder wall of the vesicle forming the retina 
is thinnest where it joins the lens and thickest posteriorly. 
The whole is noticeable by reason of a great development of 
pigment, which appears to surround all the elements. The rods 
(R.) are very well marked and in some cases, especially in the 
line of the optic axis, present the appearance of being striated ; 
in the latter position also they are especially elongated. At 
their external ends they seem to be connected with spherical 
elements (n), also embedded in pigment; these are united by 
means of processes, rendered evident again by pigment deposited 
upon them, with a layer of elements apparently corresponding to 
the cone-shaped bodies of other retinas (Co.). In its most pos- 
terior region theelements seem to be inconnection with the fibres 
of the optic stalk (Op. s.), which runs downwards and backwards 
within the vacuolate tissue filling up the parietal foramen. 


Leiolemus tenuis. 


The external indication of the eye is very clear in the specimen; 
the scale is in the usual position and surrounded by a series ar- 
ranged in a circular manner around it as a centre, the two pos- 
terior ones being larger than the other four. In the middle of the 
eye-scale itself lies the circular cornea, white and dome-shaped. 
Sections show that the eye is present beneath, the walls of the 
vesicle being differentiated into a transparent cellular lens an- 
teriorly and a retina posteriorly ; the rods are enveloped in pig- 
ment, and the latter is deposited also through the whole thickness 
of the retina. The whole organ had shrunk so much that it was 
impossible again to do more than recognise the presence of the 
structure, and the fact that it was differentiated into an eye; the 
proximal part of the epiphysis stretches, in the dura mater, very 
nearly to the eye, but whether there is or is not any connection 
between the two could not be determined. In this form also 
pigment is present in great abundance in the skin, and its 
absence above the eye is a marked feature in sections. 


PINEAL BYE IN LACERTILIA. 195 


Plica (Uraniscodon) umbra. 


In this the external indication is particularly clear. The 
scales on the dorsal surface of the head are small, save one 
whose great size renders it prominent; in the centre of this a 
small, white, slightly dome-shaped structure indicates the 
position of the eye beneath. 

Position of the eye.—The organ lies very far forward on 
the dorsal surface, being placed (Pl. XIX, fig. 35) over the 
anterior region of the cerebral hemispheres; it is situated 
within the parietal foramen, the size of which is far greater 
than that of the eye itself, which lies embedded in connective 
tissue. The usual absence of pigment immediately above it is 
to be noted. 

Structure.—The organ was not in a good enough state of 
preservation histologically to render any detailed examination 
of its structure possible. So far as could be discerned the con- 
nection of the eye with the epiphysis is retained, the solid pineal 
stalk (Op. s.) running backward immediately within the skull 
cavity. Attention may be drawn to one curious point—close 
to the eye is a small secondary and deeply pigmented vesicle 
(op!.). It may be possible that in the specimen examined this 
is merely due to a shrinkage of the walls of the whole optic 
vesicle, whereby the anterior and posterior have come into close 
contact, and thus simulated the appearance of two vesicles, but, 
as far as could be ascertained, this was not the case. The deep 
pigmentation of the anterior as well as the posterior wall is 
strong evidence against this view. 


Iguana tuberculata, Pl. XV, figs. 15 and 16; Pl. XXVII, 
fig. 23. 

The full description of the organ, which is present highly 
developed in Iguana is not given in this paper. I hope before 
long to have the opportunity of examining its structure in a 
living specimen. 

External Indication.—The usual modified scale is present 
and in large specimens is very conspicuous. In smaller ones 
(Pl. XV, fig. 16) a shghtly raised central portion is present, 


196 W. BALDWIN SPENCER. 


which is devoid of pigment, and transparent enough to allow of 
the eye beneath being seen as a dark spot. In larger speci- 
mens (fig. 15) the central part is still more raised, and forms a 
dome-shaped structure. In the figure, which is twice the size 
of the original, the scales from the dorsal surface of the head 
are represented, and the prominence of the scale with its 
modification to form a cornea can be seen. The only wonder 
again is that long before this a careful examination of the 
structure has not been made. 

Structure.—The eye lies within the parietal foramen, which 
is well developed in Iguana, surrounded closely by connective 
tissue, there being no capsule present. The eye is so placed 
that its optic axis is as nearly as possible in the vertical line. 
In shape it simply resembles an inverted cup with the lens, 
which has a flattened external surface, occupying the anterior 
end. The organ is usually more cup-shaped and symmetrical 
than the one figured (Pl. XVII, fig. 23) ; but this, which is 
drawn without any of its surroundings, will serve to demon- 
strate the structure as far as it will be described in the present 
communication. 

Lens.—The lens is convex posteriorly, and almost—due to 
its anterior surface being flattened—plano-convex in shape ; it 
is distinctly cellular, with well-marked nuclei scattered irregu- 
larly in section. On either side it thins out to join the walls of 
the posterior part, in which, at the line of union, a specially 
deep circular ring of pigment is deposited. 

Retina.—The rods (R) are well marked and embedded in 
deep pigment. In the line of the optic axis is a bundle of 
specially elongated ones (R') ; externally they are in contact 
with spherical elements (n!), which are as usual of, roughly 
speaking, the same size as the nuclei of the lens cells. These 
elements, together with the external ends of the rods, appear 
to be surrounded by a molecular layer of punctated material, 
clearly distinguishable, but yet not so well marked as in 
Varanus giganteus. Most externally is a layer of cone- 
shaped bodies (Co.), the internal ends of which taper off into 
processes connecting them either with the spherical elements 


PINEAL BYE IN LACERTILIA. 197 


or with the rods. Their flattened bases rest upon the connec- 
tive-tissue investment of the eye. 

At its posterior extremity enters the pineal stalk. The 
appearance of this in one form examined is given in fig. 23, 
where it had the form of a simple nervous strand, much as in 
Hatteria, the specialised rods running down into it, though 
there was no group of nucleated bodies to be seen at their 
external ends. 

Draco volans. 


The eye is present in Draco volans, though the specimens 
examined did not make it possible to investigate the structure in 
detail, the vesicle walls having apparently shrunk and come to 
lie close together, so as to obliterate the internal cavity. The 
whole is in a condition, as far as could be ascertained, which 
resembles that seen in- Chameleo or Lyriocephalus. 

The vesicle is ovoid in shape, and placed with its long axis 
in the median line of the head within the parietal foramen ; its 
walls are composed of cells with very distinct nuclei, but no 
further differentiation to form retina or lens could be distin- 
guished, and the vesicle itself was remarkable for the absence 
of pigment in its walls, a feature already noticed in Chameleo 
and Lyriocephalus. The only pigment present lay in the 
dura mater, and surrounded the very posterior extremity of 
the vesicle in the position in which the pineal stalk would 
enter, though it was not possible to determine the existence of 
this. 

Externally specimens of Draco differed somewhat in their 
indication of the organ, its position being in most cases easily 
determined by the presence of a specially modified scale in the 
usual position, and bearing a cornea-like space. 


Ceratophora aspera. 


The organ is indicated externally in the usual manner by a 
scale modified to form acornea. Thestructure of the epiphysis 
is interesting, being unlike that met with before. In the 
specimen examined, though the external indication was present, 
the parietal foramen was seen, when sections through the head 


198 W. BALDWIN SPENCER. 


were cut, to be closed. Its position is indicated by a large 
blood-vessel which branches on the internal surface of the skull 
as it enters the bone exactly as the vessel accompanying the 
pineal stalk branches on entering the parietal foramen, the two 
branches thus formed pass through to the external surface. 
The parietal foramen appears simply to have closed up, the 
blood-vessel remaining and piercing the bone. 

In many forms such as Leiolemus the optic vesicle is 
placed quite on the internal side of the foramen; in such a 
form as this were the bone to grow and close up the foramen 
the vesicle would be left on the internal surface ; this is exactly 
what appears to have taken place in Ceratophora aspera. 
The epiphysis has the usual form, being well developed and con- 
sisting of a proximal portion at right angles to the roof of the 
thalamencephalon, whilst, from the further end, the distal 
portion runs forward along the under surface of the dura mater 
as the pineal stalk until it ends in a slightly swollen portion 
immediately beneath the parietal foramen. This corresponds 
to the optic vesicle of other forms ; in structure it appears to be 
solid and to consist of rounded elements, resembling very closely 
those present and figured by de Graaf in Rana esculenta. 

There is this important difference, however, between Amphi- 
bia and Lacertilia, that in the former the distal portion of the 
epiphysis becomes completely cut off from the proximal and is 
placed externally to the skull, whilst in Lacertilia, on the other 
hand, the distal part not only remains in connection with the 
proximal but is permanently closed within the skull cavity 
after closure of the parietal foramen. 


Lyriocephalus scutatus. 


The usual external indication is present though not so pro- 
minent as in many other forms, the scale being somewhat 
smaller than those by which it is enclosed posteriorly, which 
form a v-shaped ridge behind it, the point of the v being di- 
rected backward ; on the scale a circular, slightly raised, trans- 
parent part is modified to form a cornea. 

Internally the structure of the optic vesicle resembles more 


PINEAL EYE IN LACERTILIA. 199 


that of Chameleo than any other, there being no differentia- 
tion of the walls to form a lens and retina. The shape of the 
vesicle is, however, unlike that of Chameleo, being elongated 
dorso-ventrally. Its walls consist of nucleated columnar cells, 
and are thicker anteriorly than posteriorly, where there is 
present a small amount of pigment on the external surface of 
the cells. 

The whole structure lies in the parietal foramen, and has the 
form, viewed as a solid object, of a small ovoid body whose 
anterior end is closely apposed to the connective-tissue, forming 
a roof to the parietal foramen, between which and the cuticle 
no pigment is present. The pineal stalk is a prominent struc- 
ture, entering the posterior end of the vesicle where it unites 
with the cells; unfortunately, in the specimen examined the 
part with the optic vesicle and portion of the pineal stalk 
attached to it was torn away from the underlying structures, 
but their can be little doubt from the similarity between this 
form and such as Chameleo, that the stalk simply passes back 
to join the proximal portion of the epiphysis, the upper part of 
which is seen running forward in the dura mater directly 
towards the optic vesicle. 


Calotes, Pl. XV, figs. 13 and 14; Pl. XVIII, figs. 31 and 
S03 Pl. XX fig: 8; 


In smaller species of Calotes the external indication of 
the eye is most clear. A large median scale is so modified 
(fig. 13) as to present precisely the appearance of an eye. In 
its centre is a circular black space, within which lies a white 
ring enclosing a dark space resembling exactly the pupil. This 
effect is produced by reason of the central part of the scale 
being transparent and slightly raised into a dome-shaped cornea, 
while beneath it lies the pineal eye which, on removal of the 
scale, is seen to have a globular form. The external surface is 
covered with a glistening white substance, save anteriorly, where 
the transparent lens is placed; the internal cavity is lined by 
the rods embedded in deep pigment, and hence appears in- 
tensely dark when seen through the lens, the whole eye having 


200 W. BALDWIN SPENCER. 


thus the appearance, viewed from above, of a white rim sur- 
rounding a dark circular space, and lying immediately beneath 
the scale, is easily visible on the dorsal surface of the head. 

Calotes ophiomaca and C. versicola.—In both these 
species the external indication is very clear, the modified scale 
with its corneal, central part forming a prominent object on 
the surface of the head : internally the structure is practically 
the same in both forms, and the description which follows is 
that of the first mentioned of the two species. 

Position of the Eye.—The organ is considerably smaller 
than the foramen in which it lies, and is enclosed in connective 
tissue ; the inner fibres of the cutis vera are so arranged as to 
form a dome-shaped structure above the eye (Ct.*) whilst there is 
the usual marked absence of pigment between the latter and 
the external surface, which is also dome-shaped. The cells of 
the rete mucosum are noticeably elongated and columnar im- 
mediately above the eye (R.M.). 

Structure.—The whole organ is considerably compressed, 
in the dorso-ventral line, its longest axis (Pl. XVIII, fig. 33) 
lying in the same line with that of the head. 

Lens.—The lens is distinctly cellular though the nuclei of 
the component cells are not clearly visible (fig. 33, Le.) as in 
other form such as Seps (fig. 32). The structure is concavo- 
convex in shape, its anterior surface being convex outwards, 
whilst certain of the cells on the inner side have become pig- 
mented (pig.) and thereby assumed a striking similarity to 
the rods. 

Retina.—The rods (R.) are very well developed, facing into 
the cavity of the optic vesicle; from their external ends pro- 
minently marked processes pass to an outer layer of cone-shaped 
bodies (Co.), the broad bases of which le upon the external 
limiting structure of the eye. There is an absence of any 
spherical elements such as are seen in other forms. As before 
said, no nuclei can be recognised in the lens, and the failure to 
detect both may very probably be due to the fact that the 
specimen was not in a very good state of histological preserva- 
tion rather than to their being absent. 


PINEAL EYE IN LACERTILIA. 201 


In connection with the eye a large blood-vessel (B. v.) is 
developed which runs up by the side of the epiphysial process 
to the foramen. 

Epiphysis.—The eye is, as far as could be told, completely 
separated off from the brain; the proximal part of the epi- 
physis runs, as usual, at right angles to the dorsal surface of 
the brain, whilst the median part corresponding to the pineal 
stalk of other forms runs forward from the former along the 
upper surface of the cranial cavity, ending blindly before the 
foramen is reached (fig. 31, Hp'., Op. s.). 


Agama hispida, Pl. XIX, fig. 39. 

The external indication of the eye is very clear in this form, 
consisting, in a specially large scale placed medianly on the 
head posteriorly to the paired eyes, in a slight depression and 
surrounded by small tubercle-like scales. A raised white rim 
encloses a circular space marked by a curious hour-glass 
shaped, dark looking patch. 

Sections show that the organ lies within the parietal fora- 
men and is almost spherical in shape ; above it the connective 
tissue of the cutis vera is modified as in other forms (e.g. 
Varanus bengalensis), and is entirely free from pigment, 
the cells of the rete mucosum being also somewhat elongated 
above the eye; the latter is surrounded immediately by vacuo- 
late tissue as in Cyclodus or Anolis (figs. 18 and 24). It 
is difficult to determine the structure of the eye owing to the 
fact that not only the rods, which are long and well marked, 
but also the external part of the retina is deeply pigmented ; 
it appears as if nearly all the elements lying external to the 
rods had degenerated into pigment-bearing cells, amongst 
which at intervals spherical elements corresponding to those 
of other forms can with difficulty be distinguished. In many 
cases processes, also pigmented, pass from the rods to the pig- 
ment masses lying external to them. 

The lens is distinctly cellular and forms the transparent 
anterior boundary to the optic vesicle, though as the walls of 
the latter are comparatively thick the cavity is small; even in 


202 W. BALDWIN SPENCER. 


some of the cells of the lens pigment is deposited. It is 
difficult to determine whether the organ is or is not yet con- 
nected with the proximal part of the epiphysis, owing to the 
great development of pigment in the dura mater surrounding 
the upper part of the epiphysis, and leading from this to the 
eye; it was not possible to say definitely whether in the 
specimen examined this did or did not contain a process from 
the proximal part of the epiphysis. 


Grammatophora barbata. 


The scale modified to act as a cornea is present and promi- 
nent on the surface of the head. 

The eye is present beneath and has apparently (having been 
only examined as a solid object) the form of a bulb, very 
similar indeed to that already described in Calotes ; in fact, the 
figures of this as a solid object (fig. 14) would serve also for 
that of Grammatophora. Externally the bulb is covered 
with a glistening white substance, whilst internally it is lined 
by deep pigment in which the rods are embedded. Above the 
eye, which does not appear to be connected with the epiphysial 
stalk, pigment is, as usual, entirely wanting in the skin. 


Moloch horridus, Pl. XIX, fig. 36. 


External Appearance.—In the specimen examined the 
external indication was very well marked, consisting of a cir- 
cular dark space, surrounded again at a short distance by a 
dark circular line, and lying upon a small smooth space in the 
median line dorsally amongst the stiff horn-like processes 
covering the head. 

Position of Eye.—Longitudinal sections at once showed 
(Pl. XIX, fig. 36) that this space corresponded roughly in 
extent to that of the parietal foramen, and that within this and 
close beneath the surface lay the eye. Unfortunately like 
many others this specimen was in too bad a state of pre- 
servation to do more than enable me to ascertain with 
certainty the presence and general outline of the organ. It is 
remarkable for its spherical shape, deep pigment, and com- 


PINEAL EYE IN LACERTILIA. 203 


parative size. These points are indicated in fig. 36 where the 
eye is drawn as a solid object. It will be seen that it lies 
close beneath the surface, the skin being here completely 
devoid of pigment and quite smooth, forming in fact a cornea 
(Cor.). As far as could be ascertained, though the point could 
not be determined with certainty owing to the state of preser- 
vation of the specimen, the eye is connected, as represented 
diagrammatically with the proximal part of the epiphysis by 
the solid pineal stalk (Op. s. ?). 


Leiodera nitida, Pl. XVII, fig. 22; Pl. XIX, fig. 38. 


External Appearance.—The specialised scale (Pl. XIX, 
fig. 38) forms a prominent feature in the median dorsal line of 
the head, bearing in its centre a small dome-shaped structure 
perfectly white, and hence standing out in clear contrast to 
the deeply-pigmented scale, of which it is a_ specialised 
portion. 

Position of the Eye.—The organ lies closely embedded 
in connective tissue, and not really filling up the parietal 
foramen, than which it is considerably smaller. The layers of 
the skin above it are so modified as to form the external dome- 
shaped structure already noticed, whilst pigment is markedly 
absent from this part, though present on either side (fig. 22, 
Ct. pig.). A very striking feature in section is the peculiar 
elongation of the cells of the rete mucosum (R. M.), whose in- 
ternal ends appear in many cases to be prolonged downwards, 
each cell being so placed that its long axis is at right angles to 
the surface at that particular spot. The connective tissue, 
further, very closely invests the eye, whilst no such well- 
developed blood-vessel is to be recognised as is met with in 
most Cases. 

Structure.—The organ has a very definite shape shown in 
fig. 22, being depressed dorso-ventrally, as a result of which the 
cavity of the vesicle is very small. 

Lens.—The lens is well developed, and, as usual, cellular, 
the nuclei of its cells being prominent in section, and so 
arranged that they form in the main a line from side to side. 

VOL, XXVII, PART 2.—NEW SER. P 


204 W. BALDWIN SPENCER. 


It is thickest in the line of the optic axis, and thins off to each 
side, where it joins the retina. The lens is, in fact, doubly 
convex, its anterior surface being in close contact with the 
investing connective tissue, and parallel to the surface of the 
dome-shaped cornea above. 

Retina.—The retina, owing to the compression of the eye, 
may be likened in shape to the walls of an oblong box, the 
lid of which is formed by the lens. The rods line the internal 
surface, and are very clearly marked ; none appear to be espe- 
cially elongated ; their external ends are in connection with a 
layer of spherical-shaped elements (n'), as in other forms these 
elements being also of the same size as the nuclei of the lens. 
Most externally lie a layer of cone-shaped bodies (Co.), whose 
inner ends taper off into processes passing to the spherical or 
rod elements, whilst their broad bases lie upon the external 
limiting membrane of the eye. 

Epiphysis.—The eye appears to be completely separated 
off from the proximal part of the epiphysis, which consists of 
(1) a proximal part with walls of distinctly nucleated cells, 
which extends vertically from the thalamencephalon to the roof 
of the brain cavity ; and (2) of a solid thin part running for- 
ward along the brain roof from the proximal part towards, but 
not reaching as far as, the parietal foramen; it is enveloped 


in pigment, and, being very thin, is somewhat difficult to 
trace. 


Anguis fragilis, Pl. XVII, fig. 25. 

This form has been described and figured in detail by de 
Graaf,! but in certain important points I am unable to agree 
with him. 

Fig. 25 represents, somewhat diagrammatically, a longitu- 
dinal vertical section through the foramen, the eye, and the 
epiphysis. The eye in the specimen figured was considerably 
smaller than the foramen, and the epiphysis was remarkable 
for running forward until very close to the eye, whilst its distal 
rounded extremity was invested by pigment cells (Ep. pig.). 


1 Op. cit., pl. 4, fig. 34. 


PINEAL EYE IN LACERTILIA. 205 


As described by de Graaf, the eye is separated off from the 
epiphysis. In his figure the lens is shown completely separated 
off from the retina, which overlaps it anteriorly. This does 
not appear to be the case; but, on the contrary, the eye, as 
far as could be told, agreed with all other forms examined in 
having the lens directly continuous with the posterior walls of 
the vesicle.! 

The most important point of difference, however, is concerned 
with the retina. De Graaf figures this (Pl. 4, fig. 34) as 
having a layer of unpigmented rods (s/.)—his “ Staafjeslaag”— 
together with a layer of unpigmented cells (cep.)—his “ Cyilin- 
dercellenlaag”—lying internal to the pigmented rods. 
Of neither of these two layers can I succeed in finding any 
trace, either in Anguis fragilis, or in any of the forms yet 
examined. In every instance all that can be discerned within 
the rods is merely the remains of what may be supposed to have 
been during life the fluid contents of the vesicle. In coagu- 
lating this does in some instances appear to attach itself to the 
parts of the rods facing into the cavity, but never forms, in any 
specimen examined hitherto, any structures so definite as to be 
interpreted into the “ Staafjeslaag” or “ Cyllindercellenlaag” 
of de Graaf. 


Cyclodus gigas, Pl. XV, fig. 9; Pl. XVI, figs. 18, 19, and 
20); Pl XVITT; figs 29); Plt XX, fig? 5. 


In Cyclodus the epiphysis is not developed into an eye, 
but the structure is nevertheless in an interesting state, showing 
most probably a stage passed through during the development 
of the eye in other forms. 

External Appearance.—lIn fig. 9 is represented a portion 
of the scale specially modified in connection with the organ. 
It lies, as in all other forms, in the median line posterior to 


1 In my first communication to ‘ Nature,’ the lens of Hatteria was described 
as separated from the retina, but examination of a fresh specimen showed at 
once this was a result due to slight post-mortem degeneration of the tissues, 
and that in reality the two were perfectly continuous, a result which subse. 
quent investigations of many forms has fully confirmed, 


206 W. BALDWIN SPENCER. 


the paired eyes, and is easily discernible in the living animal, 
one of which I was enabled to examine. It consists of a dark 
patch, having again the appearance of a membrane stretched 
tensely over a cavity, surrounded by an irregular, slightly- 
raised, white border, represented in the figure, in which is 
drawn only the central part of the scale. 

Thus the modification to form a ‘ cornea” is, as reference to 
the figure will show, in a rudimentary state, and foreshadows 
the similarly rudimentary condition of the organ beneath. In 
fig. 29 is represented a solid side view of the brain, showing 
the position of the pineal gland; it lies enclosed in the brain 
membranes, and fitting closely into the parietal foramen, out 
of which it is easily removed along with the dura mater. The 
epiphysis is very long, and stretches far forward beyond the 
roof of the thalamencephalon, almost to the anterior extremity 
of the cerebral hemispheres, its distal extremity being deeply 
embedded in pigment in the dura mater, and having the 
appearance, as in fig. 29, of a dark, swollen mass. 

In section it is seen that the epiphysis is hollow throughout 
its whole course, the cavity being in direct communication 
with the third ventricle; the cells composing its walls are all 
columnar in nature and distinctly nucleated, cilia also being 
easily distinguished in most parts. 

The whole may be divided into two parts: (1) a proximal 
portion, stretching from the roof of the thalamencephalon in 
the form of a tube to the parietal foramen ; and (2) a swollen 
distal extremity lying in the latter, and closely invested by 
vacuolate tissue. In other words, the epiphysis in Cyclodus 
has the form of a vesicle attached to the brain by a 
hollow stalk. The vesicle may be regarded as homologous 
with the eye of other lizards in a rudimentary state,! and the 
hollow connecting process with the solid pineal stalk and 
proximal part of the epiphysis of such a form as Hatteria. 

In figs. 19 and 20 is represented, on a larger scale, the 
structure of the anterior and posterior walls of the vesicle (by 
the anterior wall is meant that nearest the external surface). 


1 It may also be closely compared with the condition in adult Hlasmobranchs. 


PINEAL EYE IN LACERTILIA. 207 


In both, the cells are seen to be much elongated with very dis- 
tinct nuclei; in the case of the anterior ones, save for the 
presence of well-marked cilia, they differ but little from those 
of a lens. An elongation of those lying in the middle would, 
in fact, transform this into the lens of such a form as Lacerta 
ocellata (Pl. XVIII, fig. 30). 

Passing to the posterior surface, however, a curious but 
interesting modification takes place (cf. figs. 19 and 20), the 
nuclei all pass to the external surface, whilst the 
ends of the cells, which are left facing into the cavity 
of the vesicle, bear a close resemblance to the rod- 
like structures of the retina of other forms. 

It is possible that we have here a stage in the development 
of the retina. The internal portion of the cell forms the 
“vod,” the nucleus passes to the external end, and with the 
protoplasm lying around it forms the spherical-shaped element 
of the retina, still retaining its connection with the rod. Other 
cells, lying on the opposite side (supposing the wall of the 
vesicle, as in Cyclodus, to be more than one cell thick), 
become transformed into the external-lying elements of the 
retina, their protoplasm becoming in part drawn out into pro- 
cesses, which enter into connection with those of other cells, 
in part remaining around the nuclei, forming thus the external 
spherical elements and the processes connecting these with each 
other. This development would give exactly such a structure 
as has been already described in Varanus giganteus. In 
this form it is noticeable that the spherical elements of the 
retina consist of nuclei with a small amount of protoplasm 
around them, the nuclei being identical in size with those of 
the lens, the greater part of the protoplasm of the cells seeming 
to be developed into processes connecting the various elements. 
By this means is developed a network of branched cells, con- 
nected on the one hand with rods, and on the other with nerve- 
fibres. 

In Cyclodus the stage is reached and retained in which the 
rods have begun to be formed by a removal of the nuclei to 
the outer ends of the cells, where they form, together with 


208 W. BALDWIN SPENCER. 


those of the external-lying cells, a prominent layer (figs. 18 
and 20, n.). 
Lacerta. 
Two species of this genus have been examined. 


(1) Lacerta viridis, Pl. XVII, fig. 26. 

In this form the external indication, though recognisable, is 
not at all prominent, consisting merely in a dark circular space 
upon a median scale. 

The organ lies immediately beneath this within the foramen ; 
it is flattened out dorso-ventrally and embedded in deep pig- 
ment, as represented in fig. 26, where it is drawn as a solid 
object. Its smallness and the great deposition of pigment 
rendered it very difficult to examine the structure in detail, 
and the backward extension of the pigment towards the epi- 
physis made it also difficult to distinguish any pineal stalk, 
though in parts there were indications of its existence (Hp. 7) ; 
this pigment may, however, be a deposition in the brain mem- 
branes which must once have surrounded the stalk connecting 
the vesicle with the epiphysis, and which persist after the 
separation of the two has taken place. 


(2) Lacerta ocellata, Pl. XVIII, figs. 27, 28, and 30. 

In this the external indication of the organ is far more con- 
spicuous than in L. viridis; the scale with its dark central 
circular space, surrounded by a slightly raised light-coloured 
rim, forming a well-marked feature on the dorsal surface of the 
head. 

Position of the Eye.—This differs somewhat from that of 
other forms inasmuch as it lies closer to the external surface ; 
the connective tissue in which it lies completely fills up the 
foramen, and when the brain, together with its membranes, are 
pulled away internally from the skull, the eye is brought away 
with them (Pl. XVIII, fig. 28). The position within the 
foramen is represented in fig. 27, where the eye is drawn as a 
solid object surrounded by a great number of branched pig- 
ment cells. The foramen is supposed to be cut in half longitu- 
dinally and vertically, one side being removed to show the 


PINEAL EYE IN LACERTILIA. 209 


eye; the connective tissue enclosing it being omitted for the 
sake of clearness. 

Structure.—In shape the eye resembles more than any- 
thing else a hemisphere, the equatorial plane being occupied 
by the lens, which is, in shape, almost concavo-convex, its 
outer, anterior surface being flattened. The bulb is encased 
closely by the connective tissue of the dura mater (D. M.), a 
thin layer passing in front of the lens, whilst all the posterior 
surface is surrounded by,branched pigment cells (pig.*). 

Lens.—The lens has the usual cellular structure, being 
thinnest round the margin where it is continuous with the 
retina; the nuclei of its component cells form a well-marked 
layer running across it in section from side to side. 

Retina.— Within the retina a considerable deposition of 
pigment in various parts indicates, to a certain extent, degen- 
eracy, and at the same time renders the examination of its 
structure difficult. 

The rods (R) are well marked, and in places present the 
appearance of being striated. Two bundles of rods are slightly 
elongated (R'), being in connection with two distinct nervous 
strands entering the retina posteriorly. External to the rods 
lie spherical nucleated elements arranged in two layers, an 
inner (v!) and an outer (n”), whilst amongst them much 
pigment is scattered in small granules, rendering their detec- 
tion difficult; in parts still larger masses of pigment are 
present, which may perhaps be due to the degeneracy of the 
spherical elements into pigment-bearing cells. 

Epiphysis.—As before said, two distinct nervous strands 
may be seen entering the retina posteriorly and close together 
(ne), one being larger than the other; back from these two, 
which soon unite, may be traced a single nervous strand which 
it is extremely difficult to follow, owing to its close investment 
by connective tissue of the dura mater, but which J believe 
runs downwards and backwards until it joins the proximal 
part of the epiphysis (p.), which is considerably swollen and 
has a curious development of pigment in its walls. | 

Along with the pineal stalk runs the usual blood-vessel, 


210 W. BALDWIN SPENCER. 


which on nearing the eye bulb breaks up into numerous 
branches which ramify (figs. 27 and 30, B. v.) amongst the 
pigment cells encasing the eye. 


Zootoca vivipara. 


The presence and structure of the eye in this form has been 
described to a certain extent by Leydig, though he failed to 
recognise its connection with the epiphysis, and did not apply 
to it the name of eye. The presence of deep pigment in the 
specimen examined makes it impossible to describe in detail 
the structure of the retina. Pigment is also thickly deposited 
in the skin, but it is seen in section to end abruptly on each 
side of the parietal foramen; so thick is the layer of pigment 
that no light, save for this provision, could possibly reach the 
pineal eye. 

The eye has the usual form of a hollow vesicle with the lens 
anteriorly, lying immediately beneath the specialised scale. 
Pigment runs from the proximal part of the epiphysis to the 
eye, but, as far as could be told, the latter is separated from the 
brain. 

The eye is present in early stages, before any definite indi- 
cation of the parietals can be distinguished ; in an embryo 
whose head measured 6 mm. in length, the eye is a prominent 
object on the dorsal surface of the head, immediately beneath 
the skin. It is flattened in the dorso-ventral line so that the 
cavity is small; anteriorly the lens is differentiated and its 
cells are perfectly continuous with those of the vesicle behind, 
which are being transformed into the retinal elements, though 
the fine pigment granules already deposited throughout their 
substance (and absent from those of the lens) render it dif- 
ficult to distinguish the different elements; facing into the 
vesicle, however, the rods can be seen around which the pig- 
ment granules are thickest; external to these lie spherical 
elements massed closely together and not yet separated into 
definite layers. These may very probably be regarded as the 
nuclei of the cells whose internal parts are becoming trans- 
formed into rods. The eye appears to be connected with the 


PINEAL EYE IN LACERTILIA. 211 


proximal portion of the epiphysis by a fibrous strand, such as 
is represented by De Graaf as connecting the distal with the 
proximal portion of the epiphysis in Bufo cinerea. 


Seps chalcidica, Pl. XVIII, fig. 32; Pl. XX, fig. 5. 


External Appearance.—The external modification is not 
so evident in this form as in some others. If one of the 
median scales posterior to the paired eyes on the dorsal surface 
of the head be examined it will be found to have upon it a 
dark-coloured oval patch (hence distinguishable from the 
yellow-brown surface of the scale) ; this, which has the charac- 
teristic appearance of a membrane stretched over a space 
beneath, indicates the position of the eye lying beneath it. 

Position of the Eye.—The eye lies somewhat on the inner 
side of the foramen (Pl. XVIII, fig. 32), there being as usual 
no pigment between it and the external surface. It is remark- 
able in being the only one in the forms yet examined, which is 
larger than the foramen ; its relation to this is shown in the 
figure, where it is seen that the parietal bones overlap it on each 
side to a small extent; if by any reason the foramen became 
closed then the eye would be situated intracranially, whilst in 
Amphibia the position is always extracranial, when the distal 
vesicle of the epiphysis becomes, as in Anura, separated off 
from the proximal. The eye is surrounded immediately by a 
great development of pigment bearing tissue which fills up 
what part of the foramen is not occupied by the organ itself. 

Structure.—The whole eye is, in longitudinal vertical 
section, seen to be elliptical in shape, the long axis correspond- 
ing in position with that of the head and hence forming a strong 
contrast to such an eye as that of Anolis (Pl. XVIII, fig. 24). 

Lens.—The lens is distinctly cellular, the nuclei of the 
constituent cells forming a line prominent in section across 
from side to side, slightly nearer to the inner than to the 
outer surface; the whole is doubly convex in shape, thickest 
in the line of the optic axis, and thinnest where it is continuous 
with the retina. 

Retina.—The specimen not being in very good order histo- 


ZrZ W. BALDWIN SPENCER. 


logically, the structure of the retina could not be determined 
with any great amount of accuracy. The rods as usual formed 
the most prominent feature; at their external ends in certain 
parts spherical elements could be distinguished (n!), whilst, most 
externally, elements corresponding doubtless to the cone-shaped 
ones of other eyes were present (Co.). In many parts external 
to the rods masses of pigment (pig.”), indicating doubtless 
degeneracy in the tissues of the retina, were present. 

Connection with the brain.—The eye is apparently 
completely separated off from the brain, no pineal stalk being 
recognisable. 


General Account of the Structure in Lacertilia. 


The above account reveals the epiphysis within the group 
Lacertilia as a structure of very varied development, in 
some forms presenting merely the appearance of a hollow 
process from the roof of the thalamencephalon, in others being 
modified into a well-marked eye, whilst between these two 
extremes various intermediate forms are found. In taking a 
short general review of the results detailed above we may deal 
with them under the four following heads : 

(1) General Formof the Epiphysis.'—The simplest form 
seen isin Platydactylus, where it has merely the structure of 
a hollow outgrowth running at right angles to the surface of the 
thalamencephalon until it reaches the dura mater lining the 
cranial cavity. In Hatteria, on the other hand, we have a form 
in which specialisation is carried to its furthest extent, with the 
result that the epiphysis becomes modified into three parts—(1) 
a proximal part, still hollow, and connected with the brain roof, 
(2) a median, solid pineal stalk, serving to connect the former with 
(3) the distal portion differentiated into an optic organ. These 
forms may be taken as two extremes, the gap between which is 
filled up by various modifications : thus in Cyclodus the epi- 
physis instead of running straight upwards turns forwards, and at 
the distal end swells out into a vesicle whose walls show a trace 


1 Compare the diagram showing the development of the epiphysis in various 
forms on Pl. XX. 


PINEAL EYE IN LAOERTILIA. 2138 


of differentiation into lens anteriorly and retina posteriorly ; the 
hollow connection with the brain persisting through life. In 
such forms again as Calotes, Seps, or Leiodera the same 
differentiation into an optic organ with retinal elements takes 
place as in Hatteria, but the connection with the brain is 
lost. In a few forms further, such as Chameleo vulgaris 
and Lyriocephalus scutatus, the development of the epi- 
physis is carried to a great extent, resulting in a division into 
three parts, as in Hatteria, but the distal vesicle is not 
differentiated into an eye, its walls retaining their primitive 
structure. 

In Varanus giganteus a peculiar modification takes 
place, seen in no other form examined ; the pineal stalk, which 
is well developed, breaking up into three divisions before 
the eye is reached, whilst in V. bengalensis the eye is 
apparently separated from the proximal portion of the epi- 
physis, and the part equivalent to the pineal stalk of the other 
species is hollow and ends beneath the optic vesicle in a slight 
swelling. 

(2) State of Retinal Elements.—Dealing with the 
state of development of the retinal elements, the eyes are found 
to differ to no little extent in this respect; thus in Hatteria 
it is better developed than in any other form examined: im 
Varanus, on the other hand, while the elements can be dis- 
tinguished the whole eye is marked by a great deposition of 
pigment ; even in the centre of the lens a large globular mass 
is present which must effectually prevent the entrance of light 
to the vesicle in the line of the optic axis, whilst, in addition 
to this, many of the retinal elements degenerate into pigment- 
bearing cells. In others, such as Anolis, almost all the 
elements are enveloped in pigment, whilst in others,as Agama 
hispida, so great is the deposition that it is not possible to 
distinguish any elements save the rods. In contrast to this we 
find in some genera, such as Chameleo and Lyriocephalus 
that no pigment is present at all, and, accompanying this 
absence of pigment, it is found that the vesicle is 
not developed into an eye, its walls retaining their 


214 W. BALDWIN SPENCER. 


primitive structure of columnar cells, ciliated in- 
ternally. In Cyclodus again we find another modification 
present, the epiphysis having apparently reached a stage passed 
through in the development of the eye of other Lacertilia; 
a vesicle is formed distally, but the pineal stalk remains widely 
open, very little pigment is present amongst the cells, and no 
true eye is found. In Ceratophora, lastly, the distal 
extremity of the epiphysis is placed within the cranial cavity 
beneath the spot, corresponding in position to the parietal 
foramen of other forms; the portion equivalent to the optic 
vesicle is present, forming a slightly swollen mass at the distal 
extremity of the pineal stalk (?), consisting of rounded elements 
very similar to those present in the extracranial part of the 
epiphysis of Bufo cinerea. 

(3) External Modification.— When we come to deal with 
the external modification it is very remarkable to notice that a 
high development in this is by no means necessarily accom- 
panied by, or the index of, a highly-developed sense-organ 
beneath. In Varanus giganteus the external indication is 
extremely well marked, whilst the eye beneath is also well 
developed, and connected with the pineal stalk ; in Hatteria, 
on the other hand, the eye is still better developed, the retinal 
elements being more clearly differentiated, whilst there is quite 
absent that great development of pigment which must indicate 
to a certain extent degeneracy in the eye of Varanus. Despite 
this there isin Hatteria no external modification, or, at all 
events, only a very slight one present indicating the position of 
the eye beneath ; the latter also lies deeply embedded in connec- 
tive tissue—deeper still than in the case of Varanus—though, as 
in every other form, there is a marked absence of pigment 
between the eye and the surface of the head. Thus, in the one 
of these two forms in which the organ is most highly de- 
veloped, we find that the external modification is much the 
least evident. If, again, such genera as Calotes, Seps, 
Leiodera, and Anolis be taken, in these the modified scale 
is so prominent as to form the most noticeable feature on the 
dorsal surface of the head, and to resemble a cornea; below it 


PINEAL EYE IN LACERTILIA. 215 


the eye is in a more or less highly developed state, its elements 
often obscured by deposition of pigment, but revealing in all 
cases, even when best developed, its rudimentary nature by the 
absence of any nervous connection with the brain. 

(4) Position of the Eye.—With regard to the position 
of the eye considerable variation is seen. In such forms as 
Calotes, Leiodera, Anolis, or Agama, for example, the 
eye is close beneath the external surface, lying in the upper 
part of the well-marked parietal foramen. In Varanus the 
eye lies somewhat deeper, whilst in Hatteria it is placed 
deeper still on the inner side of the foramen, and in both forms 
a great development of connective tissue takes place, the latter 
being in every instance arranged in a definite manner. In 
Lacerta ocellata and Cyclodus the eye is placed within the 
parietal foramen, fitting it closely, the foramen having the 
form (see Pl. XVIII, fig. 27) of a truncated cone, whose apex 
hes externally. In Ceratophora aspera finally, the parietal 
foramen is closed, and the modified distal portion of the epi- 
physis hes quite within the skull cavity. The connective-tissue 
encasements of the eye also show some variations. In Hat- 
teria is seen the highest development in this respect, the eye 
lying in a definite capsule, and having special supporting fibres 
stretching across to it from the walls in the anterior part. In 
Varanus the arrangement of the connective-tissue fibres 
appear to indicate the fact that a capsule formerly enclosing 
the eye, as in Hatteria, has become filled up with fibres, so 
that the eye is now immovably fixed. In other forms, again, 
such as Cyclodus, Anolis, or Anguis, it lies surrounded 
by vacuolate tissue, whilst in others, as Chameleo, Lacerta 
ocellata, Leiodera, Monitor, Uraniscodon, Calotes, 
and various other genera, the connective tissue, without any 
trace of capsule, closely invests the eye, no space being left 
within the parietal foramen. 


If now we take typical examples from amongst the Lacertilia, 
and consider the state of development in each with regard to 
the above four points, it is seen that no one form shows a high 


216 W. BALDWIN SPENCER. 


state in all, some being well developed in one and some in 
another respect, but each being degenerate in at least one of 
the four features. 

Referring to the latter under the numbers (1), (2), (3), and 
(4), and taking first Hatteria, we find that it shows in (1) 
and (2) a high, in (3) a low, and in (4) a somewhat low state. 

Varanus giganteus shows in (]) a high, in (2) a con- 
siderably degenerate, in (3) a high, and in (4) a somewhat low 
state. 

Calotes shows in (1) a degenerate (i.e. connection with 
brain lost), in (2) a somewhat degenerate, in (3) a very high, 
and in (4:) a high state of development. 

Chameleo vulgaris shows in (1) a high, in (2) a low, in 
(3) a fairly high, and in (4) a somewhat low state. 

The same result exactly is obtained when each form is tested 
in the same way, showing that the organ is never present 
in a perfectly functional state, but always presents 
some one feature, at least, in which it is more or less 
imperfect. 

We are thus brought to the conclusion that the pineal eye 
in Lacertilia is a rudimentary structure—that at the 
present time it is not so highly developed as it must have been 
at some previous period when fully functional. 

It is, indeed, difficult to ascertain whether the structure is 
now functional at all. In lizards, whose paired eyes are closed, 
no result is obtained by rapidly focussing a strong beam of 
light on to the modified eye scale, and thus on to the pineal 
eye; in fact, strong light suddenly focussed into one of the 
paired eyes merely causes the lid to be drawn down without 
any further apparent result, whilst in the pineal eye there is no 
protecting lid, and no movement whatever takes place to remove 
the eye from the direction in which the light is coming. 

Wiedersheim has, since the greater part of this paper was 
written and the preliminary communication to the Royal 
Society published, attempted to show that the organ is func- 
tional and not rudimentary ; he bases his conclusions upon the 
study of several forms such as Varanus, in which, as pre- 


PINEAL EYE IN LACERTILIA. 217 


viously described by myself, a most noticeable feature is the 
absence of pigment between the eye and the exterior. This is 
certainly very clearly marked and, further, is perfectly constant ; 
but there can be no doubt, in face of the descriptions given 
above, that, if we use the term “rudimentary organs” to 
include such as are now from change in their structure less 
capable of fulfilling their function than they have been at 
some previous time, then within this category must certainly 
be included the pineal eye of Lacertilia. Such features as the 
great development of pigment in, for example, Varanus, or 
the loss of connection with the brain in many, such as 
Calotes, are surely only capable of explanation on the suppo- 
sition that the organ is rudimentary. 


One of the most prominent features in connection with the 
organ is its Invertebrate structure. This was pointed 
out by de Graaf in Angius fragilis, but in none of the 
forms examined have any structures equivalent to the rod-like 
bodies placed internally to those embedded in deep pigment, 
described and figured by him as present in the above-men- 
tioned species, been found. There is often, however, a struc- 
tureless substance resembling a coagulum present within the 
vesicle, which doubtless represents the remains of a humour 
which was fluid during life; in certain cases it appears to have 
attached itself to the inner ends of the rods and thus simulates 
to a certain extent elements lying internal to and connected 
with them. Further, there seems to be but little ground for 
likening the eye to that of Cephalopods and Pteropods, as is 
done by de Graaf; the structure of the retina is different, and 
that of the lens essentially so, being formed as a cuticular se- 
cretion in Mollusca, whilst in Lacertilia it is distinctly cellular 
and formed directly from the cells of the neural canal. 

As before! pointed out the development and structure ot 
this organ is extremely interesting, as showing that out of 
the walls of a vesicle originating as a hollow out- 
growth from the neural canal, may be formed an optic 

1 “Nature,” May, 1886. 


218 W. BALDWIN SPENCER. 


organ of the Invertebrate type, whilst from the walls 
of a precisely similar vesicle, and within the same 
animal, may be formed an eye of the Vertebrate 
ty pe. 

In both cases the nerve-fibres enter into connection with 
the retinal elements lying on the side remote from the rods ; 
in one case, however, important secondary developments take 
place which are wanting in the other, and to which are further 
entirely due the differences existing between the two types of 
eyes. 

In the case of the pineal eye, first, we have a vesicle, the 
anterior portion of the walls of which are transformed into the 
lens ; of the cells forming the walls of the posterior half, those 
facing into the cavity give rise to the rods, whilst external to 
these are formed the other retinal elements, into connection 
with which enter the fibres of the pineal stalk ; the primary 
optic vesicle persists, and there is thus formed an eye on what 
is usually spoken of as “ the Invertebrate type,” i.e. the rods 
facing directly into the cavity of the vesicle, and the nerve 
entering into connection with the external lying elements. 

In the case of the paired eye, however, we find that, whilst 
up to a certain point it agrees in development precisely with 
the pineal eye, after that point is reached secondary struc- 
tures appear which have an important influence on its final 
form. The retinal elements are formed out of the cells of the 
vesicle wall; the lens, however, is not, but arises as an invagi- 
nation which pushes before it the external wall; whilst there is 
this difference between the lenses of the two forms, we see at 
once, when dealing with the retinal elements, that they are 
formed in a similar position to that in which they are present 
in the pineal eye—that is, the cells facing into the optic 
vesicle give rise to the rod-elements, whilst the external 
lying cells give rise to what are really the outer layers of the 
retina (nuclear and molecular layers, &c.). It is simply the 
formation of the lens as an invagination which causes the rods 
to assume what appears to be an external position, but is 
external only when regarded in connection with a secondarily 


PINEAL EYE IN LACERTILIA. 219 


formed cavity, the primary optic cavity which persists in the 
pineal eye entirely disappearing in the paired eyes. 

There is, however, this difference, that in the pineal eye the 
posterior portion of the vesicle wall forms the retina, in the 
paired eyes the anterior; the lens of the pineal eye being a 
structure totally distinct from that of the paired eyes. 

In the pineal eye both light transmitting and 
light receiving structures are formed out of the 
walls of the neural canal; the absence of this in the 
paired eye does not perhaps constitute so great a difference as 
appears at first sight, for though the lens is not formed out of 
the neural wall it is formed out of epiblast cells exactly as this 
is, and in such forms as the Amphibia, where the epiblast is 
divided into two layers, nervous and epidermic, then the lens 
is formed solely by the cells of the nervous layer. 

In both cases, finally, the nerve-fibres are in connection 
with the external lying elements and retain this connection 
throughout life, to do which, after invagination has taken 
place in the paired eyes, they must pierce the walls of the 
secondary vesicle; there is thus produced the phenomenon of 
the nerve-fibres spreading out “in front of” (as it is called), 
and internal to, the retinal elements, though, morphologically 
speaking, they are behind and external to them, exactly as in the 
pineal eye. 

Significance of the Organ. 

In all forms of Vertebrates the epiphysis arises at an early 
stage as a hollow outgrowth from the roof of the thalamen- 
cephalon. Goette stated that the epiphysis was identical in posi- 
tion with the anterior neuropore—the part at which the walls of 
the neural canal remained longest in connection with the epiblast 
—but there seems to be no doubt whatever that this is not the 
case and that the rudiment of the epiphysis is formed at an early 
period in a position some little way posterior to that of the an- 
terior neuropore. There can thus be no connection between 
the persistent anterior neuropore of Amphioxus and the epi- 
physis of other animals, supposing the former to be equivalent 
to the neuropore of remaining Chordata, which cannot be 

VOL. XXVII, PART 2,—NEW SER. Q 


220 W. BALDWIN SPENCER. 


regarded as perfectly certain when its relationship to the 
anterior end of the notochord is considered. 

In Petromyzon, according to Ahlborn,' the epiphysis 
arises as a hollow outgrowth from the roof of the thalamen- 
cephalon, which in subsequent development becomes divided 
into three parts, (a) a proximal solid stalk, (b) two distal vesi- 
cles of which the larger is the uppermost, whilst the smaller 
acquires a secondary connection with the left ganglion habe- 
nulz. The whole lies within the cartilages enclosing the brain, 
and though a certain rod-like appearance is subsequently pro- 
duced in the cells, particularly those of the upper vesicle, still 
no pigment is developed and no differentiation into retina or 
lens takes place. 

In Elasmobranchs? the epiphysis stretches forward as a 
hollow outgrowth with a dilated end, which may 
remain within the skull cavity or be enclosed in the cartilage 
of the roof. 

In Amphibia’ the same development takes place in early 
stages, the organ remaining in Urodeles as a mushroom-shaped 
structure, whilst in Anura it is differentiated into a vesicle 
distally and a solid fibrous stalk proximally, the former being 
afterwards cut off and occupying an extracranial position im- 
mediately beneath the skin. 

In Reptilia it arises in all forms as a hollow, forwardly 
directed outgrowth, which becomes most highly differentiated 
in Lacertilia, where, in many forms, its distal vesicular por- 
tion forms an optic organ. 

In Aves the structure also stretches forward, originating as 
a hollow outgrowth, and being subsequently divided into a 
distal part which becomes vascular and a proximal solid stalk. 

In Mammalia, finally, the structure.is much less developed, 
the process being shorter than in the lower forms and directed 
backwards. 


1 « Untersuchungen iiber das Gehirn der Petromyzon,” ‘ Zeit. f. Wiss.,’ 
Bd. xxxix, p. 230, Tf. 13 and 16. 

2 Balfour, ‘ Elasm. Fishes,’ p. 17. 

3 Henri de Graaf, op. cit., p. 23 (Urodeles) and p. 27 (Anura). 


PINEAL BYE IN LACERTILIA. 7p | 


Taking thus the animal kingdom as a whole, we see that the 
epiphysis presents in all forms below mammals the following 
two points in common with regard to its structure. 

(1) It originates as a hollow vesicular outgrowth stretching 
forward from the roof of the thalamencephalon. 

(2) It becomes divided during development into two main 
divisions. 

(a) A distal vesicle. 

(6) A stalk (hollow or solid) connecting (a) with the 
brain roof. 

In Mammalia the first of these two points obtains (except 
that the structure stretches backwards instead of forwards), 
but degeneration of the tissues sets in at an early period and 
secretion of solid material takes place in the part corresponding 
to the hollow vesicle of other forms. 

In Aves both points obtain, but in course of development 
the distal vesicle becomes solid and highly vascular. Below 
Aves it apparently remains vesicular throughout life save in 
the Anura where the distal division separates off, becomes 
solid, and lies extracranially. 

So far as is known to us at present the distal portion becomes 
most highly modified in Lacertilia ; further investigations into 
its structure in other groups is needed, but, as far as our present 
knowledge goes, we are justified in saying that in Lacertilia 
alone, amongst living forms, the distal part of the epiphysis is 
modified into an eye and the tissues between it and the external 
surface are modified so as to allow of the easy transmission of 
rays of light to the organ. 

In Petromyzon certainly the structure of the organ as 
figured by Ahlborn resembles somewhat an eye, but closer ex- 
amination reveals considerable differences between it and the 
eye of any Lacertilian. 

(1) Its division into two vesicles, one above the other, is a 
point of some importance, indicating that in this case develop- 
ment takes place along another line from that pursued in 
Lacertilia, where the vesicle always remains single. 

(2) The absence of true retinal elements or lens is remark- 


Doe, W. BALDWIN SPENCER. 


able. At first sight Ahlborn’s figures of the organ, especially 
of the walls of the upper vesicle, call to mind the rod elements 
of other forms, but a closer examination again reveals important 
points of difference; they do not, as in Lacertilia, face into 
the cavity, being bounded internally as well as externally by 
nervous matter, and, more important still, there is an entire 
absence of pigment, which is the prominent feature possessed 
in common by the rods ofall Lacertilian eyes. Further, again, 
the cavity of the optic vesicle is traversed by strands of nervous 
matter passing from the anterior to the posterior wall, a feature 
entirely wanting in any pineal eye, however degenerate, amongst 
Lacertilia. 

On the other hand, these rod-like structures occupy the 
hinder wall of the vesicle, the proper position, supposing them 
to be true but degenerate retinal elements; and it may be 
remembered that amongst Lacertilia, which must be regarded 
as descended from ancestors possessed of pineal eyes, we do 
know of one form (Cyclodus) in which the eye now stops at 
a stage of development in which the cells of the posterior wall 
much resemble those of Petromyzon, and are devoid of 
pigment. The absence of lens also is paralleled in the case of 
Cyclodus. 

(3) The organ is completely enclosed within the cartilaginous 
cranium, and acquires a secondary connection with the brain 
(its lower vesicle fusing with the left ganglion habenule) 
which is quite unknown amongst any Lacertilian. 

The conclusion to be drawn from ‘these facts! is that at the 
present time the epiphysis of Petromyzon certainly does not 
become modified into a pineal eye at all comparable to that of 


1 For our knowledge of the structure of the epiphysis of Petromyzon we 
must rely on Ahlborn’s description here quoted ; it is, of course, possible that, 
viewed in the light of recent work, the structures described by him might be 
found to bear another interpretation. I have not at present been able to study 
the structure, but would suggest the possibility of what Ahlborn figures as 
nervous material lying internal to the rod-like structures, and as strands of 
tissue crossing from the anterior to the posterior wall of the vesicle, being in 
reality only the coagulated remains of the fluid contents of the vesicle. 


PINEAL EYE IN LACERTILIA. 923 


Lacertilia, in which its double nature and secondary fusion 
with the brain are quite unparalleled. At the same time it is of 
course possible, though we have no direct evidence of the fact, 
that the epiphysis is in a rudimentary state, and may be the 
degenerate representative of a once well-developed pineal eye. 
The general structure of the organ—a distal vesicular part with 
a solid proximal stalk—being in favour of this view, as is also 
the resemblance—upon which, however, too much stress must 
not be laid, between the walls of the upper vesicle and those of 
the swollen extremity of the epiphysis in Cyclodus. 

Further investigations into the structure of the epiphysis are 
much needed amongst Pisces. At present it is known that 
amongst Elasmobranchs the structure developes as a hollow 
outgrowth from the roof of the thalamencephalon. This, as 
figured by Balfour in Scyllium,! stretches forward right over 
the cerebral hemisphere, and comes finally to consist of (1) a 
swollen distal extremity, and (2) a hollow stalk connecting (1) 
with the brain roof. The swollen extremity may further remain, 
as in Raja, external to the cranium, or become embedded 
within the cartilage,asin Acanthias. There is thus a striking 
similarity between this and the epiphysis at a certain stage of 
development in Lacertilia and the final stage persistent in 
Cyclodus. 

When, however, we come to the Amphibia we find that 
amongst these the epiphysis passes through precisely the same 
forms in development, but (1) remains very rudimentary indeed 
in Urodela, and (2) after reaching a considerably higher stage 
of development in Anura undergoes great degeneration. The 
structure in the latter becomes differentiated into a distal 
vesicle, connected by a solid pineal stalk with the brain; the 
stalk soon, however, disappears, and the distal portion lies com- 
pletely separated extracranially, its constituent cells undergoing 
degeneration. Never at any period does it become developed 
in any living Amphibian into an eye. 

The word living is used and emphasised, because it is by 
no means certain that the same remark can be applied to all 


' «Comp. Embryology,’ vol. ii, p. 355. 


224 W. BALDWIN SPENCER. 


the extensive group of extinct forms classed together as 
Labyrinthodonta, and usually regarded as the extinct repre- 
sentatives of the class Amphibia. On the contrary, one of 
the most interesting features in the cranial skeleton of these 
is the possession of an extremely well-marked and prominent 
parietal foramen,! which is proportionately quite as large, and 
in many cases larger, in comparison to the size of the skull 
than in living Lacertilia. 

There is no doubt that the presence of a parietal 

foramen is intimately associated witha high state of 
development of the epiphysis, and we are thus brought 
without hesitation to the conclusion that, whilst amongst living 
Amphibians the epiphysis is present only in a rudimentary and 
degenerate condition, in extinct Amphibia (Labyrintho- 
donta) the epiphysis was in a high state of spe- 
cialisation. Further, the only group of living animals in 
which, as before said, a parietal foramen is present, is Lacer- 
tilia. Within this group, though various degenerate forms 
are seen, yet, inasmuch as 
The organ is found in genera of every family, ancient and recent alike (in 
Hatteria, in Calotes, in Agama, in Moloch, in Anolis, in Iguana, in Anguis, 
in Varanus, in Seps, in Lacerta), in which a foramen is developed ; whilst 
again, in such as Gecko, Ameiva, and Ceratophora, where uo foramen persists, 
the organ is absent, 
It may be further said that the presence of a parietal 
foramen, as a structure typical of the skulls of a 
group of animals indicates the presence of a pineal 
eye within that group. 

It is quite true that in three forms described—Cyclodus, 
Chameleo, and Lyriocephalus—the foramen is present, 
and though the epiphysis is, in certain respects, highly deve- 
loped in each case, the distal portion retaining its connection 
with the brain roof, yet no true eye is formed. This, however, 
need present no difficulty in the way of acceptance of the 
above statement. Regarding the present families of Lacer- 

1 See especially the drawings of Fritsch in‘ Fauna der Gaskoble und der 
Kalkstein,’ Prag., 1885. 


PINEAL EYE IN LACERTILIA. 225) 


tilia as descendants of some common ancestor, we can come 
to no other conclusion, inasmuch as the more primitive and 
specialised forms agree at the present time in the possession of 
a parietal foramen occupied by a pineal eye, and that this is, 
further, a characteristic of the nearest allies of the forms 
mentioned, than that the ancestral form possessed both these 
structures, and that the condition seen in Chameleo, Cy- 
clodus, and Lyriocephalus is not typical but secondary ; 
they possess a parietal foramen simply because their ancestors 
possessed a pineal eye, which in them is in a rudimentary con- 
dition, as indeed the external modification in Cyclodus 
(Pl. XV, fig. 9) seems to show in the case of this form in 
particular. | 

When, therefore, we find the parietal foramen exceedingly 
well developed throughout all the group Labyrinthodonta, 
we are justified in concluding that in them a pineal eye 
was in all probability present, even though we may grant 
the possibility (an unlikely one under the circumstances) of its 
occasional presence, as in Lacertilia, in a low state of 
development. 

In living Reptilia the presence of the foramen is confined 
to one group, but amongst the extinct forms, which may be 
regarded as the ancestors of the Reptilia now living, whilst 
some, at all events, may further be regarded as intimately 
connected with the ancestors of living birds, we find that the 
foramen is a well-developed structure. Judging from its 
present condition in the relatively small Lacertilia of the 
present day, we may imagine that in the huge extinct forms of 
Mesozoic periods—in such as Ichthyosaurus and Plesio- 
saurus, the walls of whose foramina even present rugosities 
as if for the insertion of muscles—the pineal eye attained a 
development and importance quite disproportionate to that 
with which we are now acquainted in any living form. 


1 T am indebted to Professor Moseley for calling my attention to the paper 
upon “ The Brain of a Theromorphous Reptile of the Permian Epoch,” by Cope, 
in which is figured a cast of the brain of one of the Diadectide. Perhaps 
the most remarkable feature is the huge comparative size of the cavity within 


226 W. BALDWIN SPENCER. 


The walls of the foramina are lifted above the level of the 
parietal bones, and it is perfectly possible, if not certain, that 
the organ itself, enclosed in the eye capsule, projected con- 
siderably beyond the surface. 

With the gradual extinction of these forms and of the 
Deinosauria (i. e. Iguanodon, &c.), after the Cretaceous period 
was passed, the organ, we may suppose, began with the rapidly 
dwindling size of the specialised tertiary and later Reptilia and 
Aves to lose its importance, until, degenerating in various de- 
grees in different groups, it retained traces of its original eye-like 
structure in the only groups in which, amongst living reptiles, 
the parietal foramen persists ; its preservation being intimately 
connected with and dependent upon the presence of this struc- 
ture. The foramen is preserved amongst no group whatever 
of existing Aves, and hence in these the epiphysis undergoes 
considerable degeneration, though in its development it still 
reaches a stage when, asin Reptilia, it consists of a distal 
vesicle connected with the brain roof by a solid stalk. 

In Mammalia the degeneration is far more complete, and 
all trace of the ancestral importance is completely lost. 

There now remains for consideration the two classes, Uro- 
chorda and Cephalochorda; with regard to the latter it is 
very difficult, if not impossible, to homologise any part of its 
nervous system with the epiphysis of higher forms; the per- 
sistent anterior neuropore described by Hatscheck may perhaps 
be homologous with that of other forms of Chordata which 
closes during development, though even this must be regarded 
as extremely doubtful owing to its position considerably 
posterior to the anterior end of the notochord ; neither can it 
for the same region be considered the homologue of the epi- 
physis, which again lies posterior to the neuropore. The 
azygos pigment spot described as an “eye” has no apparent 


the parietal foramen, presumably filled during life by the epiphysis. In addi- 
tion to this, Professor Cope points out a large posterior process leading “back 
towards the optic lobes and roof of the thalamencephalon, and which recent 
work on living forms can scarcely leave room to doubt represents the flattened 
pineal stalk. 


PINEAL EYE IN LACERTILIA. 227 


resemblance in position or structure to the pineal eye of 
Lacertilia. 

As figured by Langerhans! and Niisslin,? it is a pigment 
spot within the walls of the neural canal, and lies anterior to 
the part shown subsequently by Hatschek to be the anterior 
neuropore ; whereas if it were the homologue of the azygos eye 
of Tunicata it must lie posteriorly to this. 

Turning to the Urochorda a structure is at once met with 
which naturally suggests comparison with the pineal eye. 
Yet, however tempting it may be to homologise the azygos 
Tunicate eye with the latter, it cannot be too clearly pointed 
out that the two organs differ fundamentally in 
structure and position, and we have not the slightest 
reason for supposing that the pineal eye is the direct repre- 
sentative of the Tunicate eye. In the first place, the internal 
position of the latter clearly distinguishes it from the pineal 
eye; even supposing the tunicate organ to, in some way, undergo 
evagination there still remains the difficulty that the retina cor- 
responds in position to the part which after evagination would 
give rise to the lens, whilst the latter structure is perfectly 
distinct in nature and formation from that of the pineal eye. 

The curious formation of the lens in Tunicates from the 
union of two or more separate parts, differing in shape and quite 
distinct from that of Lacertilia in their relationship to the 
retina, is an important point of difference, and renders it quite 
impossible, whatever may be the case with the retina, to homo- 
logise the lens in the two forms. At the same time there is 
considerable analogy between the two lenses, inasmuch as each 
is formed directly out of the walls of the neural canal, 
a point in which they at once agree with one another, and differ 
from every other Vertebrate. Notwithstanding this it must, I 
think, be admitted that the vesicular nature of the eye in 
Lacertilia and the formation of the lens out of a portion of 
the vesicle, constitutes a difference of fundamental importance 
between the two eyes in their fully-developed condition. 


1 « Arch. f. Mikr. Anat.,’ Bd. xii, Tf. 12, fig. 17. 
2 «Zur Kritik des Amphioxusauges,’ Otto Nisslin, Tubingen, 1877. 


228 W. BALDWIN SPENCER. 


Whilst it must be admitted that we are without evidence 
sufficient to warrant us in regarding the pineal as the direct 
representative of the azygos Tunicate eye, it is, perhaps, 
worth suggesting that there may be some connection between 
the larval eye of Tunicata and the epiphysis of higher 
forms. It may be pointed out, first of all, that the position 
of the eye and that of the rudiment of the epiphysis is the 
same with regard to the anterior end of the notochord, both, 
further, being situated on the dorsal surface of the “ brain,” 
applying this term to the anterior vesicle of the neural canal 
in Tunicata. It must, however, be also noticed that the eye 
of the latter is placed not exactly medianly, but slightly to the 
right side! There still remains the great difficulty of the 
transformation of the internally placed eye into an external 
hollow process of the brain roof. 

According to Kowalewsky,’ the Tunicate eye first appears as 
a thickening of the dorsal wall of the brain cavity, in 
one particular portion the cells becoming cylin- 
drical and much elongated, and pigment appearing at 
theirinternalends. The refractive structures forming the 
lens are produced subsequently, so that at first the eye is 
merely a specially thickened part of the roof of the brain 
cavity, and only at a later period appears to assume its dis- 
tinctly internal position, bulging out into the cavity (ef. figs. 
32, 34). 

Turning now to the epiphysis, we find that it arises as a 
hollow outgrowth from the brain roof, presenting, as a rule, 
nothing comparable to the structure of the Tunicate eye. In 
one form, however, amongst Amphibia, it is just possible 
that we meet with an indication of a connection existing be- 
tween the two. A further examination in other forms, par- 
ticularly those of Pisces, might possibly reveal a similar 


1 Ahlborn draws attention to the slightly asymmetrical position of the 
epiphysis in Petromyzon, where it becomes, by secondary growth, united to 
the left ganglion habenule ; but since the eye of Tunicates is on the right 
side, it is difficult to imagine any connection between the two. 

2 ‘Arch. f. Mikr. Anat.,’ Bd. vii, 1871, pl. xii, figs. 32 and 34. 


PINEAL EYE IN LACERTILIA. 229 


method of development; at any rate, without laying undue 
stress upon the example to be quoted, it is worth while drawing 
attention to it, inasmuch as it reveals to us the possible path 
by which the epiphysis of higher forms has been developed out 
of a structure similar to the larval Tunicate eye at an early 
stage. De Graaf, in his recent memoir,' figures and describes 
the development of the epiphysis in Bufo cinerea. His 
figures are, unfortunately, not drawn with such regard to his- 
tological detail as could be desired in the present instance, but, 
so far as they go, they indicate the possible existence of a con- 
nection between the epiphysis of Bufo and the azygos eye of 
the embryo Tunicate. He shows the epiphysis as arising at 
first as a thickening of the roof of the thalamence- 
phalon, which soon assumes the form of a slight 
hollow outgrowth. Onthe inner surface of the cells, 
sharing in the thickening and subsequent outgrowth, 
isa small but well-defined mass of pigment. This pig- 
ment very soon entirely disappears, and a hollow process—the 
epiphysis—is formed, which gradually increases in size, and 
becomes differentiated into a vesicular distal portion and a 
solid stalk, the former gradually becoming constricted off. Is 
it not possible that in these phenomena we have an indication 
of the change from the internally situated Tunicate eye into an 
externally placed hollow process? As before said, the Tunicate 
eye arises as a distinct thickening of the brain-roof, the cells 
forming the thickened portion bearing pigment on their in- 
ternal ends. Just the same phenomena are witnessed in the 
case of the epiphysis of Bufo cinerea, but, instead of develop- 
ing into an eye internally placed, the cells, whose external 
ends already form a bulging on the outer surface, form into 
a well-defined evagination, the internally placed pigment dis- 
appears, and the epiphysis, as present in all the higher groups 
of the Chordata, is developed. 

Whether we are here presented with an epitome of the steps 
passed through during transformation of the internally-placed 
eye of a transparent organism into the externally-lying evagina- 

1 Op. cit., pl. iii, figs. 22 and 23, p. 27. 


230 W. BALDWIN SPENCER. 


tion of a creature whose skin has become opaque, and to whom 
an eye within the brain has become useless, it would be ex- 
tremely difficult to say with certainty;! it is, however, worth 
while calling attention to the fact that the epiphysis in very 
early stages in its development in Bufo cinerea resembles 
the Tunicate eye before the appearance of refractive elements, 
whilst subsequent loss of pigment and evagination transforms 
it into the epiphysis of the adult. 

If there be any truth in the above hypothesis it follows that 
we must start with a form which may be regarded as the 
common ancestor of present Tunicata and the higher Chor- 
data; in this, which closely resembles an embryonic Tunicate, 
certain cells of the dorsal wall of the neural cavity are 
specially elongated and bear pigment at their internal ends, 
just as in the embryo Tunicate eye and Anuran epiphysis. 
From this point development leads in two directions—(1) to 
the highly developed internal eye of present Tunicata with 
its secondarily developed refractive structures, and (2) by 
evagination and loss of pigment to the epiphysis of higher 
Chordata. Subsequent differentiation in the latter results 
in the formation of a distal vesicle united to the brain roof by 
a stalk, at first hollow and afterwards solid, whilst finally the 
distal vesicle becomes modified into the pineal eye. 

The evolution of the epiphysisis represented diagrammatically 


1 Tt will be seen that this differs from the suggestion of Professor Lankester 
that the internal eye of Tunicates by evagination forms the Vertebrate eye. 
In the first place I suppose the evagination to give rise to the epiphysis, 
subsequent differentiation of the distal vesicle of which gives origin to the 
pineal eye. Secondly, I assume the development of the Tunicate eye and the 
epiphysis out of an ancestral form common to Tunicata and the higher 
Chordata, development taking place along two different lines and being possibly 
connected with the transparency of the one and the opacity of the other form. 
At the same time it may be pointed out that it is possible that the paired eyes 
may be formed by evagination of paired internal eyes similar to the one which 
becomes transformed into the epiphysis. The vesicles giving rise to the 
paired and pineal eyes are precisely similar to each other, and may have 
originated in the same way, the two types of eyes being aoe the result of 
the es of secondary structures. 


PINEAL EYE IN LACERTILIA. Folk 


in the figures on Pl. XX, which show the various stages passed 
through before the highest form of development is reached, 
and also the various forms as the result of degeneration. Each 
stage save the earliest ones (1, 2, and 3) which are found in 
the development of Tunicata and Bufo cinerea, represent 
the permanent condition of the epiphysis in some living form. 
The question now arises, is it possible to determine at what 
period or rather within what group of animals the distal vesicle 
first became differentiated into a pineal eye. There must 
clearly have been a period during which the hollow epiphysial 
evagination was not functioning as an eye, precisely in the 
same way in which the primary optic vesicles must have existed 
as hollow outgrowths of the brain before they, in like manner, 
were differentiated into optic organs ; in fact, the three distinct 
stages of (1), a hollow bladder-like evagination (fig. 4) ; of (2), 
a distal vesicle connected by a hollow stalk (fig. 5) to the 
brain ; of (3), a vesicle connected with a solid stalk (fig. 6), 
must necessarily all have intervened before the final stage 
(fig. 7) wasreached. When in any particular form we find one 
of these three stages are we to assume that in that given form, 
and hence in the closely allied members of the same group, the 
epiphysis has never in its philogenetic history reached a higher 
stage of development than the one in which it is now present ? 
Suppose, for example, that we find an animal in which the 
epiphysis has the form represented in fig. 5, must we take it 
for granted that in that animal and its ancestors no higher 
stage of differentiation has ever been reached. Taking the 
animals in which this particular stage is permanent, we find 
that they include certain Elasmobranchs together with 
Cyclodus gigas amongst Lacertilia. Now we have clear 
evidence that, in the forms from which we must suppose 
Cyclodus in common with all other lizards to be descended, 
as well as in its nearest living allies, the epiphysis is developed 
into a pineal eye. To what conclusion must we come in the 
case of Elasmobranchs; certainly the non-development of 
a pineal eye in living examples is no proof whatever that such 
a structure was not present in its ancestors. It must at once 


252 W. BALDWIN SPENCER. 


be granted that an Elasmobranch, such as Raja or Acan- 
thias, differs from Cyclodus inasmuch as none of its living 
allies have the organ more highly developed, whilst in forms 
allied to Cyclodus it isin a high state of development; yet 
even this is by no means of so great importance, as to make us 
conclude that living forms present us with the highest stage 
yet reached in Elasmobranchs. If we turn to the Am- 
phibia we finda group of animals amongst whom in no living 
form is there a pineal eye present, and yet we may feel per- 
fectly sure that in the great group of extinct Amphibia 
(Labyrinthodonta) one was not only present but most probably 
developed to its highest pomt. It must be admitted that we 
have at present no direct evidence of the existence of pineal 
eye within the group Pisces : until our knowledge is far greater 
with regard to the development of the structure in, more 
especially Dipnoi and Ganoidei, it will be impossible to 
determine the question of the presence or absence of the 
structure within the group. Meanwhile, the varied state of 
development seen in such forms as Petromyzon on the one 
hand, and Acanthias, Raja, and Scyllium on the other, 
may perhaps be taken as evidence tending in favour of the 
view that in its present form the organ is rudimentary. All 
that may now be rightly insisted upon is that the absence of 
the eye in living forms, either of this or of any other class, is 
no proof that one has not been present at some period in the 
phylogenetic history of the group. 


The conclusions, finally, to which we are brought are the 
following : 

(1) Our present knowledge is not great enough to 
allow us, in Amphioxus, to homologise any structure 
either with the Tunicate azygos eye or with the 
epiphysis. 

(2) The epiphysis of higher Chordata is the homo- 
logue of the larval Tunicate eye. 

(3) The pineal eye is produced as a secondary 
differentiation of the distal part of the epiphysis. 


PINEAL EYE IN LACERTILIA. 233 


(4) There is not sufficient evidence to prove or 
disprove the existence of the organ within the 
group Pisces; it was present in extinct Amphibia, 
and is found amongst living forms only in Lacertilia. 

(5) In all forms at present existing it is in a 
rudimentary state, and though its structure is 
better developed in some than in others, it is per- 
fectly functional in none. 

(6) It was present most highly developed in 

(1) Extinct Amphibia (Labyrinthodonta), and 

(2) The large group of extinct forms (as Ich- 
thyosaurus, Plesiosaurus, Iguanodon, &c.) which 
may be regarded as ancestors alike of living 
Reptilia and Aves. 

(7) The pineal eye may probably be most rightly 
considered, as peculiarly a sense organ of pre-Ter- 
tiary periods. 


234 W. BALDWIN SPENCER. 


EXPLANATION OF PLATES XIV, XV, XVI, XVII, 
XVIII, XIX, & XX, 


Illustrating Mr. Baldwin Spencer’s Paper on “ The Presence 
and Structure of the Pineal Eye in Lacertilia.” 


List of Reference Letters. 


Ant. (Le). Cells of anterior wall of distal vesicle of epiphysis. C. Cilia of 
cells lining epiphysis. Ca. Capsule of connective tissue enclosing the pineal 
eye. Car. Cartilage within skull in Hatteria. Cd. Cerebellum. C. H. Cere- 
bral hemispheres. Co, Cone-shaped bodies of pineal eye. Co. Modified 
cone-shaped bodies lying near the pineal stalk. Cor. Cornea. C¢#., Ct.!, Ct.2, 
Ct3, Ct.4, Ct.°, Ct. Connective tissue in various positions in connection with 
the parietal foramen and pineal eye. Ct. pig. Pigment in the cutis vera. 
Cut. Cuticle. De. Dermis. D. M. Dura mater. Hp. Hpidermis. Lp., Ep.! 
Epiphysis. Zp. 1. Swollen distal end of epiphysis. £p.! (ops.) Portion of 
epiphysis equivalent to the pineal stalk. Hum. Humour of eye. Inf. Infun- 
dibulum. Ze. Lens. Md. Medulla oblongata. Mes. Mesencephalon. Mo. 
Molecular layer of eye. WV. Nuclei of cells of epiphysis walls. V.}, 2.1 In- 
ternal row of nuclei in retina. .?, V.? External row of nuclei in retina. 
n> Specialised nucleated elements in pineal stalk of Hatteria. ze. Nerve- 
fibres. WV. ct. Nuclei of connective tissue. O// Olfactory nerve. Op., Op. v. 
Optic vesicle. Op. S. Pineal stalk. Op. L. Optic lobe of brain. Pa. for. 
Parietal foramen. Pa., Par. Parietal bones. Post. (R.) Cells of posterior 
wall of swollen end of epiphysis in Cyclodus. pig., pig.', pig.?, pig.3, pig.t 
Pigment developed in various positions in connection with the eye. Proc. 
Processes uniting various retinal elements in Varanus. Ae. Retina of pineal 
eye. &.,7. Rods of retina. £.! Specialised rods in connection with entrance 
of nerve-fibres. &. Mp. Rete mucosum. SS. Spindle-shaped elements of 
retina. hl., Th. 3rd vent. Thalamencephalon and 3rd ventricle. Vent.3 3rd 
ventricle. 


PLATE XIV. 


Fic. 1.—Longitudinal vertical section through the parietal foramen of 
Varanus giganteus. The right side lies posteriorly, the left anteriorly, 
and the parietal bone enclosing the foramen is shaded yellow. The connective 
tissue is seen forming a dome to the foramen and filling up the latter. The 
pineal eye is cut through in the median line, showing the lens with its special 
development of pigment in the optic axis and the retina with the elongated 
rods where the nerves enter the vesicle. The nerves are three in number, two 


PINEAL EYE IN LACERTILIA. 235 


joining into one and the two main strands then uniting to form the solid pineal 
stalk. The large blood-vessel accompanying the stalk enters the foramen, 
together with the latter. 


Fic. 2.—Longitudinal vertical section through the connective tissue capsule 
containing the pineal eye of Hatteria punctata. The right side is the 
anterior, the left the posterior, the external surface of the head being parallel 
to the breadth of the plate. The capsule is formed anteriorly by the con- 
nective tissue filling up the parietal foramen. Into the capsule passes a 
blood-vessel, which ramifies amongst loosely scattered connective-tissue fibres. 
The anterior part of the capsule is comparatively empty, but special fibres 
pass from the walls to the sides of the lens. The optic vesicle is cut through 
in the median line, showing the cone-shaped lens and the elements of the retina 
together with the pineal stalk entering posteriorly. 


Fic. 3.—Section through the retina of Hatteria punctata. The left is 
the internal, the right the external surface. Internally the shade indicates 
the fluid within the vesicle, bounding the cavity of which are the rods lying 
in pigment. External to the rods lie the inner spherical-shaped elements, 
then the molecular layer, and external to the latter larger spherical bodies 
together with conical and spindle-shaped bodies, the latter two being in con- 
nection with nerve-fibres. (In the figure the nerve-layer has been drawn so 
as to appear more prominent than it is in reality.) 


Fig. 4.—Section through the portion where the pineal stalk enters the walls 
of the vesicle. The specialised bundle of rods lying in the optic axis, with 
the nuclei in connection with them, are seen together with the retinal elements 
around the entrance of the nerve-fibres of the stalk. The fibres run round 
in front of the capsular-like structure which contains the specialised nucleated 
elements, sending some to these on either side, the remainder passing on and 
either (1) entering into connection with the elements nearest to the pineal 
stalk, or (2) passing farther on to form a layer of nerve-fibres on the external 
surface of the vesicle. 


Fig. 5.—Separated rods from the retina of the pineal eye of Hatteria 
punctata. The pigment is so deposited as to produce the effect of 
striations. 

Kic. 6.—Section through the retina of Varanus giganteus. The rods 
lie embedded in pigment on the internal surface, passing into the cavity of 
the vesicle; the shade on the left indicates the humour within the latter. The 
reticular nature of the retina external to the rods is seen, the nuclei of the 
spherical elements being coloured red. The internal spherical elements are 
situated within the molecular layer; amongst the external ones are large 
masses of pigment; more external still is a thin layer of nerve-fibres, and 
outside this the connective-tissue fibres enclosing the optic vesicle. 


VOL. XXVII, PART 2,—NEW SER. K 


236 W. BALDWIN SPENCER. 


PLATE XV. 


Fic, 7.—Longitudinal vertical section through the median line of the head 
in Hatteria punctata in the region of the parietal foramen. ‘The relative 
positions of the epiphysis, the pineal stalk, and pineal eye, are seen together 
with the plug of connective tissue filling up the foramen. In front of the 
epiphysis is the vascular roof of the thalamencephalon. 


Fic. 8.—Diagrammatic side view of the brain of Hatteria punctata. 
The brain is lying in its cartilaginous case. From the thalamencephalon 
between the cerebral hemispheres and the optic lobes arises the epiphysis, 
which at first running almost directly upward, turns forwards on reaching the 
cartilaginous roof as far as the parietal foramen, where the pineal stalk pierces 
the cartilage and enters the optic vesicle, which is seen lying in its capsule. 


Fic. 9.—External view of the modified eye-scale of Cyclodus, showing 
the modification to form a cornea. 


Fic. 10.—External view of the scales in the median line of the head of 
Varanus giganteus, showing the scale modified as a cornea. 

Fic. 11.—The pineal eye of Anolis (sp.?) removed, together with the 
brain membranes, and viewed as a solid object by transmitted light. 

Fic. 12.—The pineal eye of a small specimen of Varanus bengalensis, 
ying within the parietal foramen and viewed from the under surface. 


Fic. 13.—The modified eye-scale of a small Calotes (sp. ?), with the trans- 
parent cornea in the middle through which the eye is seen. 


Fic. 14.—The pineal eye of the same Calotes, whose scale is figured in 
Fig. 13, removed with the dura mater and viewed as a solid object. 


Fie. 15.—Scales from median line on head of a large specimen of Iguana 
tuberculata, showing the modified eye-scale with cornea. 


Fic. 16.—Modified eye-scale of a young Iguana, showing the transparent 
central portion with the eye beneath as a dark spot. 


PLATE XVI. 


Fie. 17.—Longitudinal vertical section through the parietal foramen of 
Varanus bengalensis, showing the pineal eve and the hollow epiphysial 
stalk immediately beneath. The yellow shade indicates bone. p.! Hollow 
epiphysial stalk. 

Fie. 18.—J.ongitudinal vertical section through the distal part of the 
epiphysis of Cyclodus, showing the swollen extremity and the hollow epi- 
physial stalk connecting this with the brain. Zp. 1. Swollen extremity, 
Ep. Epiphysial stalk, 


PINEAL EYE IN LACEHRTILIA. 237 


Fic. 19.—Section through a part of the upper wall of the swollen extremity 
of the epiphysis in Cyclodus. @. Cilia of cells bounding the cavity of the 
epiphysis. Aut. (Le) The elongate cells, equivalent to those forming the 
lens of the parietal eye in other forms. . Oval nuclei of the cells. 

Ftc. 20.—Section through portion of the under wall of the same. Post. (2.) 
Ends of the cells facing into the cavity in the position of the rods of other 
forms. . Circular nuclei of the cells. 

Fie, 21.—Longitudinal vertical section through the parietal foramen of 
Chameleo vulgaris, showing the optic vesicle, pineal stalk, and epiphysis. 
The yellow shade indicates the parietal bone. 


PLATE XVII. 


Fie. 22.—Longitudinal vertical section through the parietal foramen and 
pineal eye of Leiodera nitida. The great elongation of the cells of the 
rete mucosum is drawn, and the entire absence of pigment from the cutis vera 
above the eye indicated. 

Fig. 23.—Pineal eye of Iguana tuberculata, cut in section and re- 
moved from the parietal foramen. When in position the optic axis looks 
directly upwards. 

Fic. 24.—Longitudinal vertical section through the parietal foramen of 
Anolis (sp.?), showing the pineal eye lying within the vacuolate tissue, to- 
gether with the pineal stalk. 

Fic. 25.—Longitudinal vertical section through the parietal foramen of 
Anguis fragilis, showing the pineal eye separated from the proximal portion 
of the epiphysis and the forward extension of the latter. 

Fic. 26.—The eye of Lacerta viridis, viewed as a solid object lying 
within the parietal foramen. 


PLATE XVIII. 


Fic. 27.—The pineal eye of Lacerta ocellata, viewed as a solid object 
lying within the parietal foramen, one half of which has beencut away. The 
eye lies within a mass of branched pigment cells, amongst which ramify the 
branches of the blood-vessel which accompanies the pineal stalk. 

Fic. 28.—The brain of Lacerta ocellata, with the pineal eye lying in 
the dura mater, viewed from the side. 

Fie. 29.—The brain of Cyclodus gigas, viewed from the side, with the 
epiphysis stretching forwards and upwards and ending in a swollen part within 
the parietal foramen surrounded by pigment. (The foramen should not be 
closed above.) 


238 W. BALDWIN SPENCER, 


Fic. 30.—Longitudinal vertical section through the pineal eye of Lacerta 
ocellata, showing the double nature of the nerve. 

Fic. 31.—Diagrammatic longitudinal vertical section through the brain of 
Calotes ophiomaca, to show the pineal eye lying within the parietal 
foramen and its relationship to the epiphysis, and of this to the brain. 

Fig. 32.—Longitudinal vertical section through the pineal eye of Seps 
chalcidica, showing its relationship to the foramen and its surrounding of 
deep pigment. 

Fic. 33.—Longitudinal vertical section through the pineal eye of Calotes 
ophiomaca, showing its meltionsp to the parietal foramen and the blood- 
vessel within the latter. 

PLATE XIX. 

Fic. 34.—Diagrammatic longitudinal vertical section through the parietal 
foramen of Varanus giganteus, showing the eye within the parietal fora- 
men and the pineal stalk. 

Fig. 35.—Diagrammatic longitudinal vertical section through the median 
line of the brain of Plica umbra, to show the eye and its relationship to 
the pineal stalk and epiphysis. 

Fig. 36.—Diagrammatic side view of the brain and pineal eye of Moloch 
horridus, viewed as a solid object, the eye lying within the parietal foramen. 

Fic. 37.—Modified median eye-scale of a small Varanus bengalensis. 

Fic. 38.—Modified median eye-scale of Leiodera nitida. 

Fre. 39.—Modified median eye-scale of Agama hispida. 

Fic. 40.—Diagrammatic longitudinal vertical section through the brain of 
Chameleo vulgaris, to show the distal vesicle with the pineal stalk. 

Fic. 41,—Diagrammatic longitudinal vertical section through the brain of 
Varanus bengalensis, showing the eye lying in the parietal foramen, and 
the pineal stalk with its swollen extremity beneath the eye. 


PLATE XX. 


Diagram illustrating the development of the epiphysis from an internally 
placed eye in the “brain” of an ancestor common to Tunicata and higher 
Chordata. Figs. 1—7 illustrate the evolution of the organ till its highest 
stage of development is reached. Figs. 2 and 3 are diagrammatised from 
those of two stages in the development of the epiphysis in Bufo cinerea, 
as given by de Graaf. Fig. 1 represents an early stage of development, accord- 
ing to Kowalevsky, in Tunicates, before the formation of a lens. In higher 
Chordata loss of pigment and evagination produce the epiphysis, which may 
in various forms reach different stages shown in the figures. The cross-line 
shading indicates the parietal bone. Figs. 9—12 representing various stages 
of degeneration in forms in which the parietal foramen becomes closed. Alk 
the figures are, of course, perfectly diagrammatical. 


ON THE LIFE-HISTORY OF PEDICELLINA. 239 


On the Life-History of Pedicellina. 
By 


Sidney F. Harmer, B.A., B.Sc., 
Fellow of King’s College, Cambridge, and of University College, London. 


With Plates XXI aud XXII. 


Durine the summer of 1885, spent in Rocquaine Bay, 
Guernsey, I succeeded in obtaining material for the study of 
the metamorphosis of Pedicellina echinata, a form which 
occurs in great abundance (in Rocquaine Bay) on Coralline 
growing under the shade of other seaweeds in tide-pools. 

The larve of Pedicellina invariably refused to fix them- 
selves when kept in a small quantity of water, and I therefore 
ultimately adopted the following method for procuring the 
various stages necessary for the investigation. 

Adult colonies were placed, after the removal of all super- 
fluous parts of the Coralline on which they were growing, in a 
small vessel, the mouth of which was closed by a piece of linen. 
The vessel was then left for a day or more in a tide-pool, after 
which a careful search (with the aid of a low power) over the 
Coralline was generally rewarded by the discovery of several 
young Pedicellina, which had resulted from larve hatched in 
the tide-pool, and which, owing to their inability to escape 
from the vessel in which they were confined, had been obliged 
to fix on the Coralline. After preservation with corrosive 
sublimate and decalcification of the Alga, sections were easily 
prepared. In this manner, I succeeded in obtaining numerous 
individuals of various ages, fixed under perfectly normal con- 
ditions. 


240 SIDNEY F. HARMER. 


My study of the metamorphosis of Pedicellina has led me 
in the main to a complete confirmation of the account already 
given by Barrois (No. 3), and summarized on pp. 312 and 313 
of my previous paper on Loxosoma (No. 4), where I have 
ventured on a criticism of Barrois’ conclusions which I do not 
find to be justified by my own investigation of the subject. 
In opposition to my previous opinion, I must now conclude 
that the post-larval changes consist in a remarkable metamor- 
phosis, and that the first bud is formed after the primary 
individual has acquired its adult characters. Barrois has 
published no figures illustrative of his statements, the actual 
details of the process being difficult to understand from his 
very short description, whilst the morphological nature of the 
changes remains entirely obscure. The subject appears to me, 
therefore, to deserve further consideration. 

The structure of the larva is well known from the researches 
of Hatschek,' and it will be unnecessary to describe it in more 
than a few of its details. 

In the swimming attitude of the larva, the ciliated ring is 
everted to the exterior, whilst from the oral face project two 
prominent structures ;—the epistome, with its tuft of long cilia, 
and the anal cone, on which opens the anus. During the re- 
tracted condition, however, the ciliated ring is reflected to the 
interior of the large vestibular cavity, whose outer walls are 
formed by the fold of skin which bears the ciliated ring itself 
(cf. Pl. XXI, fig. 1). The floor of the vestibule is constituted 
by the ventral or oral surface of the larva, being specially de- 
pressed between the base of the epistome and the anal cone, 
and at the sides of the latter. 

As Barrois has correctly stated, fixation takes place by the 
oral surface, the larva being meanwhile in its ‘‘retracted” condi- 
tion. Pl. XXI, fig. 1, a median longitudinal section, will 
serve to illustrate the method of fixation. It will be noticed 
that the long axis of the stomach is approximately parallel 
to the surface of attachment. 


1 Vide the summary of Hatschek’s results in Balfour, ‘ Comp. Emb..,’ vol. 
i, pp. 242—246. 


ON THE LIFE-HISTORY OF PEDICELLINA. 241 


Fig. 3 represents a horizontal section of a larva not long 
after its fixation: the occurrence of brain (= “ dorsal organ,” 
v. No. 4), cesophagus, and rectum in the figure sufficiently de- 
fines the level of the section. The epistome is cut in the region 
of its greatest thickness, whilst at the summit of the anal 
cone is seen the depression into which opens the anus. By 
comparing this with fig. 1, it will be observed that the anus 
has already altered its position, since it is now directed some- 
what forwards, the rectum being more nearly parallel to the 
stomach than before. The cells of the vestibular epithelium 
are very high at the sides of the anal cone, and are character- 
ized by the special readiness with which they take up colouring 
matters. 

Fig. 5 represents a horizontal section through the apices of 
the epistome and anal cone of another individual of the same 
age. The epistome is here seen to be continuous, at each side, 
with a fold of vestibular epithelium; epistome and folds 
together forming (as seen in this section) a horseshoe-shaped 
ridge partially embracing the sides of the anal cone, in which 
region the two lateral folds become evanescent. The result of 
this arrangement is the formation of a somewhat deep ciliated 
groove (0.g.) running round the greater part of the vestibule, 
and passing in front into the transversely elongated, funnel- 
shaped mouth. Posteriorly, however, owing to the disappear- 
ance of the lateral folds, the oral grooves fade away at the 
sides of the anus, where vestibule and oral grooves conse- 
quently appear continuous in such a section as that represented 
in fig. 5. The relations of these structures will become more 
clear on reference to fig. 4, a larva somewhat older than those 
previously described, the section passing transversely through 
the region of the anal cone, in the plane a B in fig. 1. At the 
sides of the anal cone are the two lateral portions of the vesti- 
bule (J. v.), these structures being separated from the oral 
grooves by the folds already mentioned. Inthe more anterior 
sections of the series, the lateral folds become continuous with 
the epistome, and the oral grooves with the mouth. Further 
back, on the contrary, the folds become lower, and finally dis- 


242 SIDNEY F. HARMEK. 


appear, so that the oral grooves are not distinguishable in the 
post-anal region of the vestibule. The above description, 
together with a reference to fig. 5, will thus show that the deep 
post-anal groove (m.v.) of fig. 1 is continuous equally with the 
oral grooves and with the general vestibular cavity. For 
further clearness, dotted lines in the same figure indicate the 
position and relations of the right lateral fold as it would appear 
by looking at the wall of the vestibule from the inside of the 
latter. The relations of half of the ciliated ring and of the 
right oral groove are also shown in the figure. 

. Fig. 2 represents a longitudinal section of a recently-fixed 
larva, passing in the direction of the line cp in figs. 3 and 4. 
One of the lateral folds, owing to its projection inwards into 
the vestibule, separates the latter into two portions, containing 
respectively the mouth (and oral groove) and part of the epis- 
tome. The latter portion obviously corresponds to one of the 
lateral regions of the vestibule (/. v.) in fig. 3. Fig. 2 further 
explains the continuity of the tip of the epistome with the 
lateral folds (cf. figs. 1 and 5). In more median sections of 
the same series the latter are not seen, the epistome being per- 
fectly free at its apex, whilst the separation of the vestibular 
cavity into two parts is not apparent. 

A considerable portion of the base of the epistome and of 
the sides of the anal cone is formed of a remarkable tissue, 
composed of large cells, with transparent contents, hardly 
staining with colouring matters (fig. 2, 7). The nature of 
this tissue (which atrophies during the metamorphosis) is 
unknown to me. 

The revolution (about to be described) of the alimentary 
canal was obviously well understood by Barrois, although I 
did not formerly succeed in making out his exceedingly con- 
cise statements on this head. 

Figs. 8 and 9 represent two sections of an obliquely longitu- 
dinal series through a more advanced stage. Fig. 9 involves 
the rectum, whilst fig. 8 shows the mouth and cesophagus. In 
the latter figure is seen one of the deep portions of the vesti- 
bule lying at the sides of the rectum, which is itself of course 


ON THE LIFE-HISTORY OF PEDICELLINA. 243 


not visible. The dorsal organ and the sucker have both dege- 
nerated, and are represented merely by the “ globules” de- 
scribed by Barrois in various parts of the larva after its 
metamorphosis. These ‘ globules” are rounded nucleated 
cells, which do not stain readily with reagents, their general 
form being shown in fig. 8, &c. 

It is obvious, from an inspection of the two sections figured, 
that the stomach has now taken up a position inclined to the 
surface of attachment, the concavity of the alimentary canal 
being directed somewhat backwards. 

Remarkable changes, already described in part by Barrois, 
have by this time occurred.! 

Fig. 9 shows that the aperture of the vestibule has closed, 
so that this cavity has no longer any communication with the 
exterior. The vestibule is partially divided into three por- 
tions, which do not, however, quite correspond with those 
described by Barrois. The most ventral portion (v. v. in 
fig. 9) corresponds to the region near the previous vestibular 
aperture, and is destined to atrophy completely. The next 
portion (v. or.) is in connection with the mouth (fig. 8), whilst 
the most dorsal portion (v. an.) contains the anal cone, and is 
at this stage and later the largest and most important part of 
the vestibule. The second or oral division still communicates 
with the ventral portion, whilst it is almost separated from the 
dorsal or anal division by the growth of the epistome and of 
the lateral folds. 

In another section of the series it is seen that the oral and 
anal divisions of the vestibule still communicate by a small 
aperture, as in the diagram, fig. 16 (a. v. v.). 

The anal portion of the vestibule is very large, and is grow- 
ing, at the previously posterior end of the larva, away from 
the surface of attachment. The cells lining this part of the 
vestibule are obviously engaged in active growth and multi- 


1 The following statements will be more readily understood with the 
assistance of Pl. XXII, fig. 16, representing in a diagrammatic form a 
median longitudinal section through an individual of the same age as figs. 
8 and 9, 


244, SIDNEY F. HARMER. 


plication, their protoplasm being finely granular and staining 
readily with colouring matters. The backward growth of the 
vestibule occurs first in the regions at the two sides of the anal 
cone (cf. fig. 3), but soon extends to the median portion be- 
hind the cone (fig. 9), so that this part of the vestibule grows 
towards the free end of the fixed larva, during the rotation of 
the alimentary canal, as a single actively extending diverticu- 
lum, in which the primary differentiation of median and lateral 
regions is no longer marked. 

Fig. 6 will serve to explain more clearly the relations of the 
oral grooves and neighbouring structures at a stage very slightly 
earlier than that of figs. 8 and 9. The section passes in a direc- 
tion corresponding to the line xk L in fig. 16, and consequently 
involves the apex of the epistome, the lateral folds, and the 
oral grooves. The anal cone, visible in fig. 5, is, of course, not 
involved by the section, which in other respects differs from the 
former figure mainly in the facts that the diameter of this por- 
tion of the vestibule has become lessened, and that by the par- 
tial rotation of the alimentary canal the apex of the epistome 
has come nearly into contact with the posterior wall of the 
vestibule (the manner in which this happens will be understood 
by comparing fig. 1 with fig. 16), the form of the lateral folds 
being at the same time altered (cf. fig. 6 with fig. 5). By this 
change of position of epistome and lateral folds, the oral and 
anal sections of the vestibule communicate merely by a com- 
paratively small round aperture. The oral grooves are no 
longer continuous posteriorly with the anal portion of the 
vestibule, although on the left side of the section at least, a trace 
of the former continuity is distinguishable. During later stages 
the growth of epistome and lateral folds completely separates 
the oral from the anal division of the vestibule, the aperture 
a.v.v. in fig. 6 being gradually constricted until it finally 
disappears. 

At the stage of figs. 8 and 9 a considerable amount of his- 
tolysis is taking place. This process affects specially the 
stomach, the epistome, the anal cone, and the ventral portion 
of the vestibule. In the case of the stomach, portions of the 


ON THE LIFE-HISTORY OF PEDICELLINA. 245 


epithelial cells and some of their nuclei pass bodily into the 
lumen of the organ (cf. figs. 8 and 9), where they are found 
quite free at later stages. The more projecting parts of the 
epistome and of the anal cone lose most of their component 
cells. The cilia of the latter become indistinct, the cell-sub- 
stance itself obviously degenerating (fig. 9). Ultimately ciliated 
portions of the cells are thrown off into the vestibule (figs. 9 
and 12), in which they can be discovered until a very late stage 
in the metamorphosis. They no doubt leave the vestibule 
either by the mouth or by the (adult) vestibular aperture, 
when the latter is formed. 

The histolysis of the ventral portion of the vestibule (fig. 9, 
v. v.) similarly results in the passage of fragments of cells into 
its own cavity. 

This process is again illustrated by fig. 12, a section passing 
in the plane of the line EF in fig. 9. The permanent vestibule 
is in this section (cf. fig. 16) completely separated from the 
degenerating portion, its lumen, like that of the latter, con- 
taining fragments of degenerating cells. 

The ventral division of the vestibule (v. v.) in fig. 9 occupies 
the position of the future stalk, and in later stages its cavity 
becomes more and more reduced until it finally atrophies. 
During this process, the cells previously found in its lumen 
disappear. In sections parallel to the plane of attachment the 
cavity (just before its atrophy) appears as a fine tube surrounded 
by a series of elongated cells radiating from it towards the 
body wall. It is very tempting to assume that these cells are 
phagocytes, engaged in the destruction of the vestrbule. After 
the atrophy of the latter, its place is occupied by numerous 
“ globules” (fig. 10), which will themselves be replaced by 
ordinary connective-tissue corpuscles (fig. 13). 

The same assertion may be made of other parts of the 
“primary body cavity,” which is at the stage of fig. 9 almost 
completely filled with “ globules,” resulting from the histolysis 
of the brain, the sucker, the tissue at the base of the epistome 
and anal cone, and other larval structures. When the primary 
individual is mature the ‘‘ globules” have disappeared, and are 


246 SIDNEY F. HARMER. 


replaced by a gelatinous matrix, in which lie connective-tissue 
corpuscles. Are we not justified im assuming that the 
“ slobules” are the active agents in the histolysis, and that 
they are in fact typical phagocytes ? 

During the histolysis of portions of the anal cone, the latter 
structure itself becomes much depressed. This feature of the 
metamorphosis, although already obvious in fig. 9, may be 
further illustrated by means of fig. 7, a section passing in a 
plane corresponding to the line 1 g in fig. 16. 

Owing to the further depression (occurring at a slightly later 
stage) of the anal cone, the marked bilateral arrangement of 
this part of the vestibule is, in part at least, lost. At the stage 
of figs. 8 and 9, as cau be easily seen from these figures them- 
selves, the posterior portion of the vestibule is no longer re- 
duced in the median plane to a small slit between anal cone 
and vestibular wall (as in fig. 1), but is, in this position also, 
a spacious cavity lined by a columnar epithelium (fig. 9). 

After the anal cone has reached the condition of the latter 
figure the vestibule, in sections parallel to the long axis of the 
stomach, will usually appear bounded posteriorly by a simple 
uniformly curved wall, whilst its oesophageal side is floored by 
the degenerating tissue of the epistome (fig. 7). In later 
stages, however, the well-developed epithelium of the sides of 
the vestibule extends inwards, so that the cavity is then en- 
tirely bounded by its permanent, partially regenerated epi- 
thelium. 

In the next stage represented very considerable changes 
have occurred, whereby the alimentary canal has taken up a 
position not unlike that which it will ultimately retain. 
Fig. 10 represents an actual section which passes in the median 
longitudinal plane of a larva at this stage. Whereas in 
fig. 16 the axis of the stomach is but slightly inclined to the 
surface of attachment, in the present instance it has assumed 
a position almost at right angles to this plane, and the con- 
cavity of the gut is now directed towards the primitively pos- 
terior end of the fixed larva. In the course of this rotation 
of the alimentary canal the vestibule, owing to atrophy of one 


ON THE LIFE-HISTORY OF PEDIOELLINA. 247 


at least of the portions described in the last stage, has become 
somewhat simplified. All the more ventral regions (situ- 
ated in the neighbourhood of the surface of attachment) have 
completely disappeared, and in their place is found a mass of 
cells filling a cylindrical stalk, which obviously corresponds to 
that of the adult Pedicellina. The anal division of the ves- 
tibule has continued its backward growth and now lies almost 
at the free end of the young animal. At about this stage it 
acquires a secondary opening to the exterior on the side corre- 
sponding to the posterior surface of the larva. This opening 
is formed by a simple concrescence between the vestibular 
epithelium and the external ectoderm of the body, accompa- 
nied by a linear perforation formed at the point of junction 
of these two distinct portions of ectoderm. My sections have 
given me no indication of the occurrence of a ‘labial invagi- 
nation” (Barrois, q. v.) placing the above portion of the ves- 
tibule in connection with the exterior. 

The character of the vestibular aperture, immediately after 
its formation, may be seen from fig. 1], a section passing in a 
plane corresponding to cH 1n fig. 10. The vestibular aperture, 
at the sides of which tentacles (¢.) are already developing, is 
shown, by an examination of the remaining sections of the 
series, to have the form of a slit elongated in the direction of 
the median plane of the animal. Immediately before the for- 
mation of the aperture the vestibular epithelium would appear, 
in a section of this kind, quite unconnected with the external 
ectoderm, but already extending towards it in the form of a 
median groove, similar in appearance to the portion gy. v. in 
fig Ll: 

The mouth in fig. 10 has, at first sight, the appearance of 
being closed. By a comparison, however, of fig. 10 with 
fig. 16, it would seem that the apex of the epistome is really 
represented (in the former) by the ectoderm closing the (per- 
manent) mouth, and it is thus probable that the commence- 
ment of the digestive tube in fig. 10 (v. or.) is a part of the 
oral division of the vestibule. This impression is strongly 
confirmed by a section (uot figured) similar to, but later than, 


248 SIDNEY F. HARMER. 


fig. 9. In the individual referred to, the stalk portion of the 
vestibule is still present, but is small, and is connected with 
the cesophagus very much as in the diagram fig. 16; i.e. at 
some distance from the point where the apex of the epistome 
ultimately meets the vestibular wall. 

In somewhat later stages the permanent mouth is formed by 
the perforation of the septum between the two portions of the 
vestibule in fig. 10, and probably in the position of the aper- 
ture a. v. v. in fig. 16. 

In living individuals of the same age could usually be dis- 
covered a small projection of the surface of the body in the 
region marked ?s. in fig. 10. This represents the larval 
“sucker,” which, as Barrois has correctly stated, disappears 
during the metamorphosis. The region of the “ dorsal organ” 
or brain of the larva is doubtless indicated by the marked angle 
on the left side of the stalk of the individual just referred to. 
None of the previous histological peculiarities of the organ re- 
main at this stage, and it is in fact already almost impossible to 
distinguish with certainty its position. 

It appears to me that Barrois has suggested the real expla- 
nation of the metamorphosis of Pedicellina, although he has 
confined himself to one or two short statements, which are 
given without any indication of the manner in which they are 
to be interpreted. I quote below one or two passages from 
Barrois’ note so many times referred to (3), the given quota- 
tions reproducing, so far as I am aware, the whole of Barrois’ 
explanation of this complicated subject. 

(i) ‘La premiére position” [corresponding, from the de- 
scription, with my own fig. 10] “représente un état tout a 
fait analogue au Loxosoma, avec anus en haut et csophage 
en bas.” 

(ii) “ L’inférieure”? [portion du vestibule] ‘‘ qui porte la 
couronne, et dont les éléments viennent former la glande du 


pied.” 
(iii) “‘ Les deux organes énigmatiques de l’exoderme”’ [i. e. 
sucker and dorsal organ] . . . . “ne sont, suivant moi, que 


des organes provisoires; tous deux sont rejetés sur la face 


ON THE LIFE-HISTORY OF PEDICELLINA. 249 


dorsale, ov ils finissent par disparaitre, peu a peu. Sans doute 
il faut voir, dans les deux soies décrites par Salensky sur la 
face dorsale du Loxosoma crassicauda, le reste de l’organe 
des sens antérieur”’ [i. e. the dorsal organ] “ qui, d’apres mes 
recherches, vient occuper cette place.” 

I have already (4) explained my reasons for the belief that 
the dorsal organ at any rate, and perhaps the sucker, are im- 
portant organs, which throw considerable light upon the mor 
phology of the Polyzoa, so that I cannot accept Barrois’ con- 
clusion that these structures have no particular significance. 

It is obvious that, however accurate Barrois’ conclusions 
(quoted above) may be, they need further explanation. The 
similarity between larva and adult in the Entoprocta, even 
in the position of the buds in Loxosoma, is so striking that 
some means of comparing the two stages is necessary. I 
therefore suggest the following explanation of the relation 
between larva and adult. 

It does not seem to me that Caldwell’s theory of the sur- 
faces of the Polyzoa receives any support from the metamor- 
phosis of Pedicellina. The short line between mouth and 
anus remains unchanged throughout the metamorphosis, and 
in order to prove that it is not ventral, it still remains neces- 
sary to show that the dorsal organ of the larva is not a brain, 
and that the larval surfaces do not correspond with those of a 
Trochosphere. 

Figs. 17—19 (Pl. XXII) are diagrams representing a pos- 
sible explanation of the metamorphosis of the Entoprocta, 
but although founded on the history of Pedicellina, Loxo- 
soma is the form which is actually (hypothetically) repre- 
sented. 

Fig. 17 explains a possible conception of one of the earlier 
stages in the acquirement of the sessile habit by the free- 
swimming Polyzoon ancestors. The form is, however, to all 
intents and purposes, a Loxosoma larva, with brain, sub- 
cesophageal ganglion (not discovered in Pedicellina until a 
stage later than fig. 10), and a pair of buds, one of which is 
shown, I believe there are no authentic instances of the fixa- 


250 SIDNEY F. HARMER. 


tion of a Polyzoon larva by any other than its oral surface, 
and it may therefore be assumed that this method of fixation 
was acquired at a very early stage in the phylogeny of the 
group. Let us suppose, however, that this ‘“Archi-Loxo- 
soma,” on fixing itself by the edge of its vestibule, left an 
aperture (for the entrance of food), surrounded by the ciliated 
ring (vide fig. 17), leading from the exterior into the otherwise 
closed vestibule, and situated behind the anus. 

Subsequent development may be imagined to give rise to a 

form like fig. 18, in which the vestibular opening is an elon- 
gated slit, extending along the whole of the region formerly 
occupied by the posterior side, and still surrounded by the 
ciliated ring. The mouth, in order to obtain its food as con- 
veniently as possible, now faces the posterior side (of the 
former stage), and this has entailed a rotation of the entire 
alimentary canal, in the manner shown in fig. 18. 
_ By the growth of the proximal end of the Polyzoon, the 
mouth would be thrust away from the point of support, and 
the animal might thereby obtain an advantage in procuring 
food by means of its ciliary currents. But during this process, 
the proximal portions of the ciliated ring would become far 
less efficient for obtaining food than the distal portions, and 
would tend to atrophy. The final result would be the acquire- 
ment of a form like fig. 19, representing in a very slightly 
diagrammatic form, an adult Loxosoma. The ciliated ring is 
here represented as consisting of two disconnected portions, cor- 
responding (1) to the ring of tentacles ; (2) to the foot-gland (ef. 
the second of Barrois’ conclusions quoted on p. 248). The foot- 
gland has remained practically as an open groove, a series of 
ciliated tentacles having been developed round the margin of 
the permanent vestibule. 

The position of the buds in the larval Loxosoma appears at 
first sight fatal to the above hypothesis. That this larva does 
actually develop buds normally can hardly be doubted, since 
I have shown not only that these structures are developed 
twenty-four hours after hatching (which might, however, be an 
abnormal circumstance, due to the want of proper conditions 


ON THE LIFE-HISTORY OF PEDICELLINA. 251 


for fixation), but also that ectodermic thickenings, the com- 
mencements of the buds, are to be detected some time before 
the embryo is ready to leave the maternal vestibule, the possi- 
bility of the development having been influenced by abnormal 
conditions being here out of the question. 

In figs. 17,18, and 19, the position of the dorsal organ is 
represented as not having been much altered during the rota- 
tion of the alimentary canal, which has, so to speak, been 
pulled through the loop formed by the dorsal organ and the 
somewhat hypothetical subcesophageal ganglion. Assuming for 
the moment this position for the dorsal organ, we find that 
throughout the metamorphosis the buds retain their original 
situation (in Loxosoma) between the dorsal organ and the 
ciliated ring, and that their position with regard to the ceso- 
phagus is practically the same as that which characterised them 
at their first appearance. 

Is there, however, any reason for believing that the position 
of the dorsal organ is correctly indicated in the diagrams? It 
seems to me that this question must be answered in the affirma- 
tive. In the first place, the degenerating dorsal organ of 
Pedicellina does in reality occupy this position, and in the 
second place (vide No. 3 of Barrois’ conclusions on p. 248), 
the circumcesophageal commissures may be represented by the 
strong ganglionated nerves passing from the ganglion to the 
“posterior sense-organs”” in L. crassicauda, as originally 
described by Salensky (see also No. 4, Pl. xix, fig.1). Should 
the metamorphosis of Loxosoma be proved to bear out this 
suggestion of Barrois’, we must assume either that the whole 
brain has atrophied, or that the adult possesses at most a small 
portion of the brain at the ends of the two widely separated 
cesophageal commissures. 

With regard to the actual metamorphosis of Pedicellina, 
I have to point out that Ihave not succeeded in demonstrating 
the presence either of cesophageal commissures or of a sub- 
cesophageal ganglion. The latter structure becomes distinct 
only at a stage later than fig. 10, and it then has the position 
which characterises the adult ganglion. 

VOL, XXVII, PART 2.—NEW SEK 8 


bo 


Pe SIDNEY F. HARMER. 


No. 1 of Barrois’ conclusions quoted on p. 248, appears to 
me perfectly just. It is impossible in fact not to be struck 
with the great resemblance between the solitary Pedicellina 
shown in fig. 10 and an adult Loxosoma, and this similarity 
is quite conspicuous even at much later stages. The obliquity 
of the lophophore in Loxosoma is hence, on the view already 
explained, another of the archaic features of this genus, the 
lophophore having still a marked inclination to the “ anterior” 
side of the animal (fig. 19). 

It is unfortunate that the metamorphosis of Loxosoma, 
which possesses a foot-gland, should be unknown, but we are 
able to make certain inferences from the phenomena of budding. 
Both vestibule and foot-gland originate as longitudinal groove- 
like invaginations of the ectoderm of the “ anterior” face of 
the bud. Fig. 15 is a reproduction of a drawing from Oscar 
Schmidt, in which the foot-gland is represented as originating 
from the two proximal cells of the ectoderm of the “ anterior” 
side of the bud, and in which it is further seen that these cells 
are not in the least marked off from those which are taking 
part in the formation of the vestibule. The relations of lopho- 
phore and foot-gland in this figure are indeed exactly those of 
the ciliated ring in the diagram (fig. 18). 


The Metamorphosis of Pedicellina viewed in its 
relation to the above Hypothesis. 


I have no reason to believe that the position of the ciliated 
ring shown in fig 1] is in any way altered during the subsequent 
metamorphosis. This structure in all probability degenerates 
in situ. 

The ciliary apparatus of an ordinary Trochosphere is not, 
however, constituted entirely by the preoral circlet. In the 
neighbourhood of the latter there occurs in Polygordius, 
e. g., (cf. Hatschek, No. 2) a series of smaller cilia forming a 
postoral circlet, whilst a third part of the apparatus is con- 
stituted by “‘a ciliated groove running between the two ciliated 
rings, and prolonging itself into the ciliated mouth,” This 


ON THE LIFE-HISTORY OF PEDICELLINA. 253 


last portion is obviously represented in Pedicellina by the 
ciliated oral grooves, continuous, as in Polygordius, with 
the mouth. The relations of these grooves during the meta- 
morphosis appear to me to deserve further consideration. 

We have found that the median postanal portion of the 
vestibule is continuous with the oral grooves, of which it may, 
indeed, be said to form a part. Acccording to Hatschek 
(1) it is, like other portions of the vestibule, lined by ciliated 
cells. 

If we are justified in assuming that the oral groove—a part 
of the typical Trochospheral ciliary apparatus—extends, poten- 
tially at least, from the mouth completely round the vestibule 
to the postanal region, it seems to me that considerable light 
is thrown on the metamorphosis. The morphological position 
of the oral groove will be in no way altered during the rotation 
of the alimentary canal, and in fig. 16 it will continue to pass 
from the mouth round the ab-anal side of the altered lateral 
folds to the median post-anal portion of the vestibule, even 
though it is no longer distinguishable in the persisting division 
of the latter structure. In figs. 16 and 6 we observe, however, 
the commencement of a separation of the oral groove into two 
parts—one continuous with, and becoming indistinguishable 
from, the “ oral” section of the vestibule (v. or. in fig. 16), and 
the other potentially passing from the free apex of the epistome 
in fig. 16 to the end of the reference line m. v. in the same 
figure. The position of this latter portion will be the median 
line passing from a.v.v. to m.v. Owing to the fact that it 
is situated behind the anal cone it is, of course, unpaired (cf. 
fig. 5), and it appears to me that its situation may be very 
fairly considered to be represented by the linear groove which 
in fig. 11 has formed the permanent vestibular aperture. From 
the margins of this groove are developed the tentacles, which, 
if the above reasoning is legitimate, are formed from the region 
of the oral groove. 

The fact that the tentacles of the adult lophophore of the 
oral side are on the ab-anal side of the mouth appears to me 


254 SIDNEY F. HARMER. 


to prove that the lophophore itself is developed from a mor- 
phologically preoral portion of the oral groove. 

The relation between the velum proper and the oral cilia has 
become, in the Entoprocta, considerably complicated by the 
formation of a fold of integument (vestibular wall), carrying 
the former to some distance from the latter. When the 
Pedicellina larva attaches itself, the distance between the two 
structures becomes increased. The velar portion maintains its 
position at fixation, and soon atrophies ; the oral groove, on 
the contrary, growing away from the degenerated velum. Even 
during the phylogenetic history of the process we may suppose 
that the velum atrophied at fixation. This is par excellence 
a locomotive structure, and would be useless in an attached 
condition. The oral cilia would, however, continue (in the 
hypothetical stage of fig. 18) to convey food to the mouth, and 
the cells bearing them would, after a time, become prolonged 
into tentacles, by which their range of activity would be 
extended. 

During the abbreviated metamorphosis of Pedicellina it 
has hence resulted (if the above be true) that the velum takes 
no part in the change of position involved in the passage to the 
adult condition. 

Summarizing the above, I may express my conviction (1) 
that the metamorphosis of Pedicellina is a simple modifica- 
tion of a more archaic process, due to abbreviation of develop- 
ment, (2) that the oral groove persists in part as the adult 
lophophore, (3) that the vestibule closes at fixation, and under- 
goes the whole of its alterations in the interior of the larva, 
opening secondarily only when the adult condition is practi- 
cally attained. 

The adult form is reached by the elongation of the stalk of 
fig. 10, and by the replacement of its contained “ globules ” by 
characteristic connective-tissue and muscle-cells ; by the for- 
mation of a stolon and a diaphragm, and by various alterations 
in the calyx. The more important of these consist in the 
complete (or almost complete) loss of the obliquity of the 
lophophore, in the development of the permanent ganglion 


ON THE LIFE-HISTORY OF PEDICELLINA. 955 


and generative organs (if these are formed in the primary 
individual, as is probably the case) and in the complete forma- 
tion of the vestibular aperture and tentacles. I have made no 
special observations on most of the above points, although on 
the important question of the origin of the colony from the 
primary individual, I am able to throw some light. 

In the first place, it may be stated that adult colonies are 
by no means restricted to one growing point, as stated by 
Hatschek (1). Of very common occurrence is the develop- 
ment of two growing points, one at each end of the unbranched 
stolon: I have noticed this even before the formation of a 
single secondary calyx. A third growing point may be deve- 
loped as a lateral branch of the main stolon; the amount of 
branching is, however, always slight in P. echinata, and 
apparently in all cases the cesophagus of each calyx is on the 
side directed to the growing point to which this calyx properly 
belongs, as already indicated by Hatschek. 

The formation of the stolon is shown in fig. 13, a longi- 
tudinal section of the stalk of a completely developed but 
still solitary individual. The young stolon, which is cut 
medianly, is developed on the cesophageal side of the Pedicel- 
lina. The base of the stalk (which is alone represented) con- 
sists of a thick cuticle, underneath which occurs a layer of 
ectoderm, surrounding a gelatinous matrix in which lie con- 
nective-tissue and muscle-cells. The section, however,—an 
extremely good preparation—is contradictory to the theory of 
Hatschek, according to which the apex of the stolon is pro- 
vided with a hypoblastic vesicle derived from the dorsal organ, 
and engaged in the formation of the mid-gut of the secondary 
calyces. I may at once state that I have entirely failed to 
convince myself of the occurrence of any such vesicle, at any 
period, in the stolon, and I am forced to believe that Hatschek 
has been mistaken in assuming its existence. Neither in 
sections nor in entire specimens (whether living or treated 
with reagents) could I discover the slightest evidence of the 
presence of Hatschek’s vesicle, although I have investigated 
both adult and young stolons in this connection. 


256 SIDNEY F. HARMER. 


It appears to me probable that the growing point of the 
stolon of Pedicellina (vide fig. 13) consists solely of an ecto- 
dermic layer secreting a cuticle and of a mass of indifferent 
mesodermic connective-tissue cells, embedded in a structure- 
less jelly. If this is the case, the only organ derived from the 
hypoblast of the embryo would appear to be the mesenteron of 
the primary individual, all other parts of the colony being 
devoid of any derivatives of hypoblast cells. 

This conclusion can hardly be avoided unless we assume that 
some of the stellate cells of fig. 16 are really hypoblastic in 
nature, although indistinguishable from the mesoderm cells in 
their appearance. Owing to the nature of the process by 
which the dorsal organ degenerates, it is impossible to assert 
that some of its cells do not become ameboid wandering cells 
which migrate into the growing point. It can, however, be 
safely stated that no hypoblastic vesicle is formed from the 
degenerating dorsal organ. It may further be pointed out that 
the conclusion arrived at on a previous occasion as to the 
nervous (epiblastic) nature of the dorsal organ, in Pedicellina 
as in Loxosoma, is in opposition to the view that this struc- 
ture plays any part in the budding. 

The well-known fact that calyces of Pedicellina may fall 
from their stalks, which thereupon develop new calyces, appears 
to me in direct contradiction to Hatschek’s view of the bud- 
ding. The loss of the calyces is probably a normal, periodically 
occurring process, which is perhaps to be regarded as a means 
of rejuvenescence, and which is at least analogous to the forma- 
tion of the “ brown bodies ” in the Ectoprocta. Itis exceed- 
ingly easy to discover individuals in healthy colonies in which 
the calyx has been lost, and a new “ bud” (easily recognised 
by its small size and immature condition) is being developed 
just below the scar. Specimens kept in captivity seem inva- 
riably to lose their calyces if the quantity of water is not very 
large, the calyx falling off at the “diaphragm.” This struc- 
ture, which is merely a constriction at the base of the calyx, 
filled by a row of flat cells, is perhaps a special arrangement 
by which the calyx can break away from the stalk, without 


ON THE LIFE-HISTORY OF PEDICELLINA. 257 


injury to the latter. I have been unable to show that calyces 
which have thus left their stalks are able to become the starting- 
points of fresh colonies. The specimens under observation have 
invariably died after a day or two, even if kept in a tide-pool. 

Calyces formed at the scars produced in the manner above 
indicated, seem to me (from superficial examination of entire 
specimens) to develop in exactly the same manner as those 
produced at the true growing point. The occurrence of this 
phenomenon is undoubtedly adverse to Hatschek’s theory of 
budding ; the whole of the stomach falls away with the calyx, 
whilst the existence of a plug of cells filling up the diaphragm 
appears to preclude the possibility of the migration of any 
cells derived from the stomach to the proximal side of the 
diaphragm. Unless, indeed, it is assumed that some of the 
“‘ connective-tissue ” cells of the stalks as well as of the stolon 
are endodermic in nature, it must be concluded that none of 
the cells of the bud are descendants of any of the cells belong- 
ing to the embryonic hypoblast. 

With regard to the further history of the budding (whether 
at the growing point or at the apex of an old stalk) I have very 
little to say. The free end of the stolon (or stalk) before long 
develops an ectodermic invagination (fig. 14) destined to give 
rise to the lophophore and, according to my view, to the whole 
of the alimentary canal of the bud. The latter is from the 
first continuous with the lophophoral rudiment, and in other 
sections of the series to which fig. 14 belongs, the stomach and 
vestibular cavity are separated from one another by means of a 
septum. The latter does not, however, cut off the whole of 
the deepest part of the invagination, but, since it is not deve- 
loped in the position of the cesophagus the vestibule and stomach 
remain continuous with one another (as in fig. 14). By the 
formation of a diaphragm and by other processes already 
described by Hatschek, the bud attains its adult condition. 
The continuation of the stolon is formed by a lateral outgrowth 
from that region in the young bud which afterwards becomes 
the base of its stalk, precisely as in fig. 13 with the exception of 
the fact that the new growing point is formed long before the 


958 SIDNEY F. HARMER. 


bud is itself mature. It is worthy of remark that the young 
vestibular invagination does not occur accurately at the apex 
of the stolon, but on the side of the apex turned towards the 
growing point. In this respect it exactly agrees with the 
position of the vestibular invagination formed near the apex 
of a stalk which has lost its calyx, and again with that of the 
incompletely rotated vestibule in intermediate stages of the 
metamorphosis. It may indeed be said that the young 
vestibule of all the buds is inclined towards the growing point, 
and that in all cases it subsequently undergoes a rotation in 
the same direction (but to a less marked degree) as that occur- 
ing at the metamorphosis. 

The history of the Pedicellina-larva appears to me to point 
to the existence of a fixation-period in Loxosoma also. In 
this case, the buds observed by me in the larva of L. Lepto- 
clini would probably have to undergo a change of position, 
during the metamorphosis, similar to that represented in figs. 
17—19. I am inclined to believe that the degeneration of the 
larval stomach observed in the same species, after a free life of 
one or two days, was abnormal, and was due to the absence of 
the conditions necessary for fixation. 


On the Nature of the “Brown Bodies” of the 
Ecetoprocta. 


The above statements with regard to the life-history of the 
Entoprocta may, perhaps, give some indication of the manner 
in which the “ brown bodies” of the Ectoprocta have origi- 
nated. There can probably be no longer any doubt whatever 
that these structures are degenerated polypides, which are 
subsequently replaced by new ones budded off from the walls 
of the zccecia. 

In the metamorphosis of Pedicellina the purely larval 
organs degenerate and form a mass of cells, which subsequently 
become connective-tissue cells. The degeneration is here 
slight, and has not yet acquired sufficient importance to give 
rise to a characteristic “ brown body.” 


ON THE LIFE-HISTORY OF PEDICELLINA. 259 


Whilst in the adult Loxosoma nothing comparable to the 
formation of “ brown bodies” is known, the adnlt Pedicel- 
lina has developed a special arrangement—the constriction at 
the base of the calyx—by which the latter may be lost without 
material injury to the remainder of the colony. 

In the adult Ectoprocta there seems to be the same 
necessity for the rejuvenescence of some of the organs, but 
here the occurrence of a thick ectocyst, usually intimately con- 
nected with that of neighbouring individuals, in general pre- 
vents the loss of any part of the body wall, asin Pedicellina. 
In some of the stoloniferous Ctenostomata, however, the 
entire zocecium is deciduous. 

But even in Pedicellina one may almost speak of a 
“‘zocecium” in the same sense as in the Ectoprocta. It isa 
well-known fact that septa occur at intervals across the stolon 
of Pedicellina, and in most cases are developed in such a 
manner that a piece of the stolon, connected with the base of 
each stalk, is cut off from the remainder of the stolon by a pair 
of symmetricaliy-placed septa. There are thus typically two 
septa between the bases of each two stalks, and stalk-bearing 
and stalkless sections of the stolon alternate regularly with one 
another. 

It is thus possible to consider stalk plus portion of stolon 
connected with it, the representative of a zocecium. The distal 
end of the zocecium is from time to time segmented off, carry- 
ing with it the whole of the alimentary apparatus, whilst a new 
polypide is developed within the remaining portion by a process 
of budding. By the formation of a new constriction the distal 
part of the zocecium—the calyx—becomes again differentiated 
from the proximal part—the stalk. 

In the Ectoprocta the occurrence of the same process is 
usually obviously impossible, and the polypide alone degenerates, 
forming a ‘“ brown body” which subsequently passes into the 
new stomach, and is ejected by the anus. The occurrence of 
this circumstance is already foreshadowed in two particulars in 
Pedicellina. We find, in the first place, that a new polypide 
is actually budded off by the ectoderm of the zocecium at or 


260 SIDNEY F. HARMER. 


before the loss of the calyx; and, in the second place, that the 
tissues have already acquired, at the metamorphosis, the power 
of disposing of degenerated structures. 

In the Ectoprocta one may hence suppose that, owing 
to the inconvenience of losing a portion of the zocecium at each 
rejuvenescence, the new polypide is budded off near the pre- 
ceding one, instead of from an entirely different part of the 
zocecium, as in Pedicellina (below the diaphragm). The 
degenerating alimentary canal and other structures are then 
worked up by the “ Parenchymgewebe” (Vigelius), which has 
inherited this kind of power from the larval tissues, into the 
condition of a “brown body,” which passes into the new 
stomach, and reaches the exterior by means of the anus. 

In the development of the Ectoprocta an archenteron is 
formed, in a large number of cases at least. The embryo is, 
however, richly supplied with yolk; it develops within the in- 
terior of the parent, and its alimentary canal is hence, in many 
cases, functionless. 

At its metamorphosis this larva possesses no functional ali- 
mentary canal, and must hence form a new one. But since in 
its previous phylogenetic history our Polyzoon has acquired 
the power of developing new “ polypides” from various parts 
of its ectoderm, a fresh gut could without difficulty be formed 
within the bedy wall of the metamorphosed larva; since the 
latter is now in the same condition as an adulJt zocecium whose 
polypide has just become a “ brown body.” 

This, indeed, is what actually happens. The larva passes at 
once into the condition of a zocecium containing a “ brown 
body,” the remains of its larval organs. The complicated me- 
tamorphosis of Pedicellina has been given up, the larval 
structures now degenerating by the method employed during 
the atrophy of the polypides in adult individuals, and finally 
leaving the zocecium by passing as the first ‘‘ brown body” 
into the alimentary tract of the primary polypide, and thence 
to the exterior. 

The metamorphosing Ectoproctan larva is probably in 
the same condition (irrespective of the difference pointed out 


ON THE LIFE-HISTORY OF PEDICELLINA. 261 


in the methods by which the alimentary canal is lost in the 
two cases) as the primary individual of a Pedicellina colony 
would be immediately after the loss of its calyx, supposing that 
it had not meanwhile developed a stolon and secondary 
calyces. 

Unless I am mistaken in my views with regard to the meta- 
morphosis of Pedicellina, it appears to me necessary to con- 
clude that in the Hntoprocta the ventral line of the body 
extends from a.v.* in figs. 10 and 19, down the right sides of 
the figures, as far as a. v.! The median dorsal line will in con- 
sequence be represented by the entire left sides from a.v.! to 
a.v.” These surfaces are most clearly expressed in the young 
Loxosoma bud, in which the whole of the surface turned 
away from the parent (characterised by the possession of ves- 
tibule and foot-gland) is ventral, whilst the opposite surface of 
the bud is, conversely, dorsal. 

I hope to be able before long to publish some account of the 
development and metamorphosis of the Ectoprocta. Till that 
time I prefer to withhold any further expression of opinion 
with regard to the surfaces and relations of the larve of this 
group of the Polyzoa. 


List oF Papers REFERRED TO. 


1. B. Hatscnex.— Embryonalentwicklung und Knospung der Pedicellina 
echinata,” ‘ Zeits. f. wiss. Zool.,’ Bd. xxix, 1877, 8. 502. 

2. B. Harscorx.— Studien zur Entwicklungsgeschichte der Anneliden,”’ 
© Arb. a. d. Zool. Inst. zu Wien,’ Bd. i, 1878, S. 277. 

3. J. Barrots.—“ Métamorphose de la Pédicelline.” ‘Comptes rendus de 
PAcad. des Sci.,’ T. xcii, 1881, p. 1527. 

4. 8. FE. Harmer.—“ On the Structure and Development of Loxosoma,” 
‘Quart. Journ. Mic. Sci.,’ vol. xxv, 1885, p. 261. 


262 SIDNEY F. HARMER. 


EXPLANATION OF PLATES XXI & XXII, 


Illustrating Mr. S. F. Harmer’s Paper on “ The Life-history 
of Pedicellina.” 


Reference Letters. 


an. Anus. an.c. Analcone. a.v.tand a.v.? Hypothetical morphologically 
anterior and posterior ends, respectively, of the vestibular aperture. a. v. v. 
Aperture between oral and anal divisions of vestibule (in position of permanent 
mouth). d. Bud. 4ér. Brain (= “dorsal organ”). c.c. Fragments of 
ciliated cells. c.p. Ciliated pit of brain. c. 7. Cihated ring. d.s. Dorsal 
sense-organ (of Loxosoma). epst. Epistome. / dr. Fibrous part of brain. 
fg. Foot-gland. ga. Ganglion of adult. g.p. Growing point of stolon. 
g.v. Median groove of permanent vestibule, ultimately becoming the vesti- 
bular aperture (in position of part of oral groove of larva?). zé. Intestine. 
1.7. Lateral fold of vestibular wall. 7. v. Lateral portions of anal division of 
vestibule. m. Mouth. mes. Mesoderm. m.v. Median postanal portion of 
the anal division of the vestibule. @. Csophagus. o.g. Oral groove. 
rec. Rectum. s. Sucker. s¢. Stomach. ¢. Tentacle. v. Vestibule. v. a. 
Its aperture. v. an. “ Anal” division of vestibule. v. or. “Oral” division. 
v. v. Ventral division. z. Large-celled tissue at base of epistome and anal 
cone. 


PLATE XXI. 
Pedicellina echinata. 

Fic. 1.—Median longitudinal section of a larva quite recently fixed (on 
. Coralline). 

Fic. 2.—Obliquely longitudinal section (in the plane C D in figs 3 and 4?) 
of a similar larva. 

Fic. 3.—Horizontal section of a slightly older larva, passing through brain 
(= dorsal organ), esophagus, epistome, and anal cone. 

Fic. 4.—Obliquely transverse section (in the plane A B in fig. 1), at a stage 
very soon after fixation. 


1 In describing one section as passing in a plane indicated in the figure of 
another, it is to be understood that the details in the two individuals do not 
always exactly correspond. This is due, partly to a difference in age between 
the two larve figured, and partly to variations in the position of the internal 
structures, owing to varying conditions of muscular contraction. 


ON THE LIFE-HISTORY OF PEDICELLINA. 263 


Fic. 5.—Horizontal section, at an early stage in the metamorphosis, passing 
through the tip of the epistome, the lateral folds and oral grooves, and the 
apex of the anal cone. 


Fics. 6 and 7.—Two sections of a considerably older individual, passing 
respectively in the planes K L and I J in Fig. 16. 

Fies. 8 and 9.—Two sections of an individual of the age of Fig. 16, passing 
in an obliquely longitudinal direction. Fig. 8 cuts the mouth and one of the 
lateral portions of the permanent vestibule, Fig. 9 passing through the rectum 
and the degenerating vestibule of the stalk. In another section of the same 
series the two parts of the vestibule are continuous, exactly as in the diagram, 
Fig. 16. 

Fic. 10.—Median longitudinal section of an advanced, but still solitary, 
individual. 

Fic. 11.—Horizontal section (in the plane GH in Fig. 10) through a 
similar specimen. 

Fie. 12.—Section of an individual of the age of Figs. 8 and 9, passing in 
the plane E F in the latter figure. 

Fie. 13.—Median longitudinal section through the stalk of a solitary 
individual with commencing primary stolon. The arrow indicates the position 
of the oral side of the calyx. 

Fic. 14.—Obliquely transverse section of a young bud, developed at the 
growing point. 


PLATE XXII. 


Fic. 15.—Young bud of Loxosoma, from the ventral side. Copied from 
O. Schmidt, ‘ Arch. f. mik. Anat.,’ Bd. xii, 1876, Pl. ITI, fig. 17. 

Fie. 16.—Diagrammatic longitudinal section of a metamorphosing Pedi- 
cellina at the stage of Figs. 8, 9, &c. 

Fies. 17—19.—Diagrams illustrating the supposed morphological nature of 


the metamorphosis of the Entoprocta, A full explanation is given in the 
text. 


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EVOLUTION OF ORGANS IN THE CHORDATA. 265 


Dr. Dohrn’s Inquiries into the Evolution of 
Organs in the Chordata. 


By 
J.T. Cunningham, B.A., F.R.S.E. 


SEVEN years elapsed from the publication of the ‘ Ursprung 
der Wirbelthiere’ before the appearance of the first of Dohrn’s 
‘Studien zur Urgeschichte des Wirbelthierkorpes,’ that on 
the mouth of Teleosteans. As he points out in a short preface 
to that paper the three chief peculiar articles of faith in his 
previous essay, in comparison with the views current at the 
time, were that the ancestors of Vertebrates closely resembled 
Annelids, that the principle of change of function was the 
safest guide in tracing morphological histories, and that the 
extent to which degeneration might proceed was unlimited. 

In the attempt to reconstruct the Vertebrate ancestor, Dohrn 
has concentrated his attention almost exclusively on the 
actual structure and development of the organs of existing 
Vertebrates, convinced that a great deal of what was generally 
believed concerning the relation of the organs was inaccurate, 
and that no light could be thrown on the question by hasty 
conclusions drawn from superficial resemblances of the organs 
of Vertebrate and other embryos, until the organisation of 
the Vertebrates themselves was more thoroughly investigated. 

The following is a list of the studies with the dates of pub- 
lication : 

1882. I. “ Der Mund der Knochenfische.” 
II. “Die Entstehung und Bedeutung der Hypophysis bei den 
Teleostiern.” 


1883. III. “ Die Entstehung und Bedeutung der Hypophysis bei Petro- 
myzon Planeri.” 


266 J. T. CUNNINGHAM. 


1884. IV. “Die Entwicklung und Differenzirung der Kiemenbogen der 
Selachier.” 
V. “Zur Entstehung und Differenzirung der Visceralbogen bei Pe- 
tromyzon Planeri.” 
VI. “Die paarigen und unpaaren Flossen der Selachier.” 
1885. VII. “ Entstehung und Differenzirung des Zungenbein und Kiefer 
Apparates der Selachier.” ' 
VIII. “Die Thyreoidea bei Petromyzon, Amphioxus, und den Tuni- |: | 
caten.” 

IX. “Die Bedeutung der Unpaaren Flosse fiir die Beurtheilung der 
genealogischen Stellung der Tunicaten und des Amphioxus, 
und die Reste der Beckenflosse bei Petromyzon.” 

X. “ Zur Phylogenese des Wirbelthierauges.” 


Ancestral Mouth—TIn the first of these studies reference is 
made to the question of the position of the ancestral mouth, 
which in the‘ Ursprung der Wirbelthiere’ was located between 
the crura cerebelli in the fourth ventricle. Professor Fritsch 
and Mr. Sanders argued that this was an untenable supposition, 
because it would be impossible to accept the consequence of 
it, namely, that all the cerebral nerves belonged to a supra- 
cesophageal ganglion. Dohrn acknowledges the justice of the 
objection, and provisionally abandons the quest of the ancestral 
mouth. He has never since resumed the inquiry. He deals 
with investigations of the development of the actual mouth, the 
results of which confirm his view that the aperture represents 
a united pair of gill-clefts. Im embryos of Teleosteans he found 
that there was no stomodzeum, and that the mouth arose as a 
pair of enteric outgrowths which at first opened to the exterior, 
one on each side, the apertures only subsequently meeting in 
the middle ventral line. 


Hypophysis of Teleosteans and Petromyzon. 


The hypophysis also in Teleosteans, according to the second 
paper of the series, does not arise from an ectodermal oral 
invagination or stomodeum, but from a pair of endodermal 
evaginations in front of those which form the mouth. The 
organ therefore represents a pair of przoral gill-clefts (i. e. it 
is derived in the Teleosteans from the endodermal parts of 


EVOLUTION OF ORGANS IN THE CHORDATA, 267 


such a pair) which in the actual development of Teleosteans 
never acquire an opening to the exterior. In a postscript to 
this paper Dohrn mentions Hatschek’s results concerning the 
origin of the ciliated pit in Amphioxus. This pit is the left of 
a pair of anterior evaginations of the endoderm, which opens 
to the exterior while the other remains closed. According to 
Dohrn these two diverticula are homologous with the hypo- 
physis in the Teleostean, and the opening in Amphioxus is 
the persistent branchial opening. The ciliated pit of the 
Ascidians is also homologous with that of Amphioxus. Ac- 
cording to Bateson the proboscis cavity with its pore in Balano- 
glossus is homologous with the ciliated pit in Amphioxus, 
but whether the body cavity of the proboscis in Balanoglossus 
can be derived from a pair of gill-clefts is a question which 
seems to threaten to do away with the possibility of the diagno- 
sis of organs according to their embryological origin. 

The hypophysis in Petromyzon has a unique history in the 
individual, and this forms the subject of the third member of 
the series. The examination of the embryos of Petromyzon 
was undertaken by Dohrn in order to prove that the funda- 
mental difference generally supposed to exist between the 
branchial cartilages of Selachians and of Petromyzon was 
entirely imaginary, but the discussion of this subject is post- 
poned till the hypophysis has been considered. Scott! had 
stated that the hypophysis of the Lamprey arose as an ecto- 
dermal invagination connected with the nasal pit. 

Balfour had doubted this result, but Dohrn entirely confirmed 
it, except that he found the hypophysial invagination to be at first 
separate, lying between the commencing mouth and nasal cavity, 
and that he pointed out that the whole long nasal duct of the 
adult which runs back beneath the brain is as much part of the 
hypophysis as the follicular organ formed from its inner ex- 
tremity.2. The nasal duct is in fact a fused pair of ectodermal 


1 *Morph. Jahrb.,’ vii. 

2 It seems extremely probable, although I am not aware that it has been 
suggested before, that the nasal duct which in Myxine opens into the pharynx, 
is homologous with the so-called nasal duct of Petromyzon. If this be so, of 


VOL, XXVII, PART 2,—NEW SER, T 


268 J. T. CUNNINGHAM. 


pits originally belonging to the pair of gill-clefts which has been 
transformed into the hypophysis. The function of the nasal 
duct in the adult is apparently to draw in water in order 
that it may reach the olfactory organ and then expel it; it is 
probably, to use an undignified word, a sniffing organ, neces- 
sitated by the disconnection of the mouth from the function of 
respiration. This new function of the hypophysial gill-clett 
could easily be derived from its original one. 


Visceral Arches of Elasmobranchs. 


In order to demonstrate the fallacy of the argument that 
the external branchial cartilages of Selachians were the repre- 
sentatives of a primitive “ external” branchial skeleton retained 
in the existing Cyclostomata, it would have been sufficient, says 
the beginning of the fourth study, to describe the development 
of these two cartilages (two to each arch) in Selachians and 
compare it with the quite different history of the branchial 
skeleton in the Lamprey. But it seemed advisable to give a 
complete account of the development of the Elasmobranch 
gill-arch, as previous results were fragmentary. 

It is to be understood that a typical arch such as the first, 
second, or third branchial, is under consideration, not the hyoid 
or the posterior, which are either modified or reduced. In a 
horizontal section of the arch towards its middle the cavity of 
the arch surrounded by its epithelial cells (head-cavity of 
course the connection between the pharynx and the nasal pits in Myxine is 
formed by the hypophysis and not by a nostril properly so named. The hypo- 
physial invagination in the embryo of Petromyzon comes into very close 
relation with the pharynx as well as with the infundibulum, and on the hypo- 
thesis which I have supported in my paper on Kupffer’s vesicle, &c., that the 
infundibulum represents the original mouth, it is easy to understand how a 
separation between infundibulum and pharynx might occur in either of two 
ways, by leaving the hypophysis connected only with the infundibulum as 
in Petromyzon, or by leaving the communication between hypophysis and 
pharynx still open as in Myxine. In other Vertebrates again the hypophysial 
invagination has been absorbed inte the stomodzum, and reaches from thence 
to the infundibulum, but has not retained a connection with the pharynx. 
These speculations can of course only be tested by examination of the deve- 
lopment of Myxine, 


EVOLUTION OF ORGANS IN THE CHORDATA. 269 


Balfour and his school) is seen in the centre dividing the 
section into an anterior and posterior half. This cavity is 
continuous below with the pericardium. The artery of the 
arch is on the posterior side of the cavity, or as it is better to 
call it, from the destination of its walls, of the muscle tube of 
the arch. The branchial processes grow out first on the pos- 
terior side, and along their base appears a vein which opens 
dorsally into the artery. Similarly on the anterior side appear 
branchial processes with an anterior vein, also opening into 
the artery. The two veins become connected by two hori- 
zontal commissures. In the adult the posterior vein becomes 
disconnected from the anterior and unites with the anterior vein 
of the arch behind it. 

The cartilaginous arch arises as a condensation of mesoderm 
cells posterior to the muscle-plate. Between the upper and 
lower venous commissures, where the muscle-tube is already 
diminished in thickness, condensation of mesoderm cells takes 
place also on the anterior side, and the two condensed masses 
uniting, eliminate the muscle-tube between them. This separa- 
tion of the muscle-tube does not take place dorsally and ven- 
trally, because the cartilaginous arch bends inwards in those 
regions. A central part of the muscle-tube is thus separated 
and lies on the inner side of the arch; it becomes the adductor 
arcus visceralis. Both Gegenbauer and Vetter believe the 
adductor mandibule to be homodynamous with the adductor 
arcus, but this is an error, the former is homodynamous with 
the whole musculature of one (or more) arch. The external 
middle portions of the tubes form the musculi interbranchiales ; 
the dorsal, externally the constrictor superficialis, internally the 
interarcuales. Other muscles come from the ventral portions, 
The coracohyoid is a true body muscle, and has nothing to 
do with visceral arches. 

The cartilage already described, the middle portion first 
developed, forms the two middle internodes of the adult arch. 
Above these dorsally is the basale, below the copulare. The 
cartilage separates the adductor from the interarcualis above, 
from the coracobranchialis below. The cartilage is internal to 


270 J. T. CUNNINGHAM. 


the artery ; and the artery is at first posterior to the muscle- 
tube. The branchial cartilaginous rays arise as condensations 
of mesoderm cells separate from the arch, and between the 
artery and posterior vein. The so-called external cartilages 
are simply the most dorsal and the most ventral of the series 
of rays altered somewhat in position, and therefore have no 
similarity with the arches in Petromyzon, which are true arches. 

Branchial lamelle are never developed on the anterior side 
of the hyoid arch, or of the spiracular arch. The external 
filaments of the embryo arise as simple elongations of the 
posterior lamelle of each arch, the anterior not elongating 
at all. A curious suggestion is made concerning the function 
of these elongated filaments, namely, that they serve to absorb 
yolk ; how the yolk gets into them could not be discovered, 
but yolk is present in the filaments and in their veins, in the 
posterior branchial vein, and the efferent arteries, never in the 
branchial artery or in the heart. 


Thymus of Elasmobranchs. 


At the time when the external filaments have attained to 
about half their length, but when the branchial rays are not 
differentiated, a proliferation of epithelium takes place in the 
upper angle of the first gill-cleft, forming a kind of bud. 
Similar buds are formed in the four posterior gill-clefts, but 
the fifth bud disappears again entirely in the Sharks, but 
persists in the Rays. These buds form the thymus of the 
adult. The cause of the separation of these portions of the 
branchial epithelium is the shortening of the clefts. The 
upper portion of the original clefts is obliterated by a coales- 
cence of the arches, accompanied by processes of growth which 
alter the original position of the terminal rays of each series, 
and so produce the extra-branchial cartilages. The epithelial 
nodules of the thymus after they have sunk into the mesoderm 
become associated with mesodermic cells, a process which 
ought not to excite surprise, since the epithelium in question 
originally no doubt formed branchial laminz into which meso- 
derm extended. The bending of the arches above described is 


EVOLUTION OF ORGANS IN THE CHORDATA. 271 


connected with the formation of the united portions of the 
musculus constrictor superficialis, but the original cause of the 
whole process is to be explained only after further investiga- 
tions have been described. Lcker first definitely described the 
thymus of fishes in his article ‘‘ Blood-vessel Glands,” in Wag- 
ner’s ‘ Dictionary of Physiology,’ Bd. iv, but could find no such 
organ in the Sturgeon, in Cyclostomata, or in Teleosteans. 
In a foot-note Dohrn points out that the thymus of Teleosteans 
exists in the position already accurately defined by Leydig in 
his ‘ Anat. histol. Untersuchungen tiber Fische und Reptilien.’ 
In this note also emphatic contradiction is made of Gegen- 
baur’s generally accepted view that the pseudobranchia of 
Teleosteans is the reduced gill of the hyoid arch, and therefore 
not homologous with the pseudobranchia or spiracular gill of 
Elasmobranchs. Dohrn maintains that Johann Miller was 
quite right in asserting that the pseudobranchia of Teleosteans 
was homologous with the spiracular gill of Elasmobranchs, 
and that Balfour, who has been followed by Hoffmann, was 
mistaken in supposing that in the Teleosteans the choroid 
gland represents the spiracular gill. Stieda found that the 
thymus of mammals arose from only one gill-cleft, the last, or 
last but one ; Dohrn states that the carotid gland may possibly 
represent a rudimentary thymus derived from another cleft. 


Branchial Skeleton and Arches of Petromyzon. 


After showing that the extra-branchial cartilages of Elasmo- 
branchs are really displaced gill rays, the next point in arguing 
that the branchial skeleton of Petromyzon is composed of 
true branchial arches, is to demonstrate the development of 
this skeleton, and this is the object of the fifth paper. It is 
known from the researches of Scott and Balfour that the 
first trace of the visceral arches appears in the form of 
head-cavities, rounded cell-tubes between the diverticula of 
the gut, which afterwards form the gill-clefts. The question 
of correspondence between the head-cavities and the dorsal 
myotomes is left for a future period. There is a difference 
between the embryonic gill arches of Petromyzon and those 


272, J. T. CUNNINGHAM. 


of Elasmobranchs in the position of the original vessel of the 
arch. This vessel in the latter forms lies near the outer bor- 
der of the arch; in Petromyzon it lies as near as possible to 
the inner surface. The arch elongates and becomes flattened 
antero-posteriorly ; the muscle-tube undergoes a correspond- 
ing compression. The cartilaginous arch arises anterior to the 
muscle-tube, but soon divides this tube in the middle of the 
arch completely, separating an adductor on the inner side from 
a constrictor on the outer, as in Selachians, The cells of the 
anterior wall of the muscle-tube have a remarkable peculiarity. 
They persist, in embryonic form, as long tubes, which run the 
whole length of the arch, and show a transverse striation only 
on the exterior. All the muscles run the whole length of the 
arch and unite, dorsally as well as ventrally, with those of the 
other side ; the important point about this is that if the carti- 
laginous rods were to disappear the condition would be the 
same as that which actually exists in Myxine. The chief dif- 
ference between the gill lamine of the adult Petromyzon and 
those of Selachians is that the former are directed towards the 
exterior, the latter towards the interior, and this difference 
appears at their first origin in the embryo. It is probable 
that the adductors serve as inspiratory muscles by lifting up 
the ventral side of the branchial region, and so expanding the 
branchial cavities, while the constrictors are expiratory, their 
contraction driving the water out. 

Thus it is shown that the branchial skeleton of Petromyzon 
is composed of true cartilaginous branchial arches. It is true 
that these arches in the Cyclostomata are not segmented, nor 
are they in the Teleostean ; and this shows that Petromyzon is 
derived from a form more premature than the Selachian, in 
which the segmentation had not yet occurred. The same truth 
is indicated by the homology of the hypophysis with the nasal 
duct, an homology which, as Dohrn frankly acknowledges, was 
first asserted by Goette in his ‘Entwicklung der Unke.’ 
Petromyzon must have branched off from a condition in which 
the hypophysis was still an independent preoral pair of gill- 
clefts. That the gills of Petromyzon are homologous with 


EVOLUTION OF ORGANS IN THE CHORDATA. 273 


those of Selachians has been suggested by Huxley and P. 
Fiirbringer, and is by Dohrn’s results fully established. 
Myxine is a further modification of Petromyzon, and shows a 
remnant of the branchial skeleton in the cartilage of its ductus 
cesophageo-cutaneus. The internal position of the branchial 
artery in the embryo Petromyzon is simply explicable as a 
consequence of the displacement of the branchial lamelle to- 
wards the interior, and this change of position has been 
brought about by the necessity of protecting the gills which 
arose when the present habits of the animal (either burrowing 
in mud or attaching itself to other animals) were acquired.! 
Thus the theory that the branchial cartilages of Petromyzon 
represent an archaic system not elsewhere present except in 
the extra branchial cartilages of Selachians falls to the ground, 
and with it disappear the consequences which Gegenbaur 
formerly deduced from it. The Cyclostomata had no jaws it 
was said because their ancestors had no true gill arches from 
which jaws might be derived, whereas the truth is probably 
they have lost the jaws through the conversion of the biting 


1 In my paper on Myxine, in the previous number of this Journal, I have 
described the habits of Myxine from actual observation. There can be no 
doubt that during far the greater portion of its time the animal lies motion- 
less, buried in mud, with only the extremity of its snout protruding. In this 
condition the method of respiration, unique among fishes, namely, the constant 
passage of a current of water through the nostril to the gill-pouches, is the 
only method possible. Doubtless this method is also the most convenient 
when the animal is boring into the body of a fish, or when its whole body has 
penetrated into the flesh of its prey; and it is difficult to say which of its 
habits, burrowing or boring into its prey, was the prior cause in producing 
the existing condition of the respiratory organs. I have not yet ascertained 
whether the respiratory current is maintained by ciliary action, or by internal 
muscular action, or by both combined. No muscular respiratory movements 
are visible externally. Ammoccetes, it is true, burrows, although it has a 
branchial skeleton; and I do not know how the Ammoccetes, when buried, 
can carry on the method of respiration which is seen in Petromyzon. Petro- 
myzon never burrows, it conceals itself beneath stones and in crevices, but it 
could not take in water by all its branchial apertures as it does unless it 
were surrounded by water free from sediment. The comparison of the habits 
of Petromyzon and Myxine illustrates the diversity of functions performed by 


274, Jj. T. CUNNINGHAM. 


into a sucking mouth. It was said that they had no lhmbs 
because the skeleton of a limb was derived from an arch of 
the branchial skeleton, and no true branchial arches were 
present; the truth is that the limbs are not derived from 
branchial arches, as is now generally acknowledged, and there 
is a rudiment of the pelvic fin in Petromyzon, to be after- 
wards described. 


The Origin of the Fins of Fishes. 


The true history of the origin of the limbs of fishes, paired 
and unpaired fins, as Dohrn reads it, is set forth in the sixth 
Study. Inthe original ancestral condition the Vertebrate body 
was similar in most respects to that of an Annelid. The medul- 
lary tube was an open plate, the intestine extended through 
the whole length of the body to a terminal anus, and on each 
segment were two pairs of appendages, processes of the body 
wall provided with processes of the body musculature, in fact, 
dorsal and ventral parapodia. The nerve plate was, of course, 
ventral, when the animal was reversed in position and the plate 
folded into a tube, the two series of ventral parapodia were 
brought together in the median dorsal line and coalesced both 
laterally and longitudinally, forming the dorsal fin, which was 
originally continuous along the whole length of the body. 
Another change which took place was that a new anus was 
formed out of the fusion of two gill-slits, and in consequence 


one organ, and the contrast between the functions of homologous organs in 
two forms. An important function of the sucker-mouth of Petromyzon is to 
adhere to stones in the bed of a river, and without this power the animal 
would immediately lose control of its own movements, and be carried away at 
the mercy of the currents in which it habitually lives. This function is 
entirely wanting in Myxine, whose mouth is not truly a sucker at all, but a 
boring apparatus, I have never seen a Myxine use its mouth to attach itself, 
while Petromyzon never leaves its mouth attachment at one place, except to 
immediately secure it again at another. Yet the mouth of Myxine can take 
in food without boring, as is demonstrated every day in the North Sea when 
the fisherman finds on his lines numbers of Myxine which have taken the 
baited hook far down into the intestine without using their teeth upon the 
bait at all. 


EVOLUTION OF ORGANS IN THE CHORDATA. 275 


the postanal gut disappeared ; the degeneration of the postanal 
gut is actually repeated in ontogeny. The contraction of the 
ventral part of the tail thus brought about caused the series of 
dorsal parapodia behind the anus to coalesce in the same manner 
as the ventral parapodia, and thus the median anal fin was 
produced. The przanal dorsal parapodia were never approxi- 
mated laterally, but partly disappeared, partly coalesced longi- 
tudinally to form the existing pelvic and pectoral fins. The 
fins therefore have nothing to do with gills, either in the way 
supposed in Gegenbaur’s Archipterygium theory, or in the 
way originally suggested by Dohrn in the ‘ Ursprung der 
Wirbelthiere. In the theory now taught by Dohrn the 
metameric external gills of Annelids are left out of considera- 
tion; the ancestor, it is to be presumed, had none. The facts 
on which the theory is based, and which are important results 
of investigation however explained, are as follows :—The mus- 
culature of the pectoral fin is derived in embryos of Elasmo- 
branchs (Pristiurus) from a series of muscle buds separated 
from the ventral end of each myotome. Each bud divides 
into four pieces, two above and two below. The same is true 
of the pelvic fin. That these fins cannot be serially homo- 
logous with any parts of the gill arches is proved by the fact 
that the musculature of the gill arches is derived from the 
head cavities, and these are ventral to the myotomes. So also 
the gill cartilages are not homodynamous (serially homologous) 
with the ribs, for the ribs are between the myotomes, the series 
of which is continued anteriorly above the gill arches. A 
large number of myotomes contribute to form each fin. Behind 
the anus on each side muscle buds are given off from the 
ventral ends of the myotomes ; these are serially homologous 
with those already described, and in all probability, although 
the transformation was not traced, they form the musculature 
of the anal fin. The musculature of the dorsal fins arises from 
buds given off dorsally exactly as those belonging to the paired 
fins are given off ventrally. The fin rays in the dorsal fins 
arise as median cartilaginous rays, at first quite unconnected 
with any other part of the skeletou. One would have expected 


276 J. T. CUNNINGHAM. 


to find, if the theory be true, that these rays were originally 
double ; but Dohrn says nothing of this difficulty, attaching the 
greatest importance to the musculature. It has been objected to 
Dohrn’s theory by myself and Professor Carl Vogt that in Teleos- 
tean embryosthere is a preanal median fin in addition to the pre- 
anal paired fins ; to which Dohrn has replied that it has not been 
proved that this fin has any musculature, and therefore it is pro- 
bably a new development peculiar to the class in which it occurs. 


Morphology of the Mandibular and Hyoid Arches of Selachians. 


We come next to a discussion of one of the most compli- 
cated chapters in Vertebrate morphology, the question of the 
mandibular and hyoid arches in Selachians. We will take a 
rapid survey of the facts as they exist according to Dohrn’s 
investigations, and then consider the deductions he draws 
from them. In embryos of Pristiurus, Scyllium, Mustelus, 
Centrina, Torpedo, and Raja the conus arteriosus at its terminal 
bifurcation forms the hyoid arteries, the arteries of the hyoid 
arch. From each of these arteries near its origin arises 
another artery which runs parallel to and anterior to the hyoid 
artery. Between the bases of these two lies the thyroid gland, 
and the arteries are to be called the thyroid arteries. The 
hyoid artery supplies only one series of branchial laminz, the 
posterior. There is also but one branchial hyoid vein, the 
posterior. There is only one venous commissure from the 
hyoid vein instead of two as in the posterior arches, and 
this commissure opens into the thyroid artery. The art. 
thyroidea has hitherto been called the art. mandibularis. 
The thyroid artery, after receiving the venous commissure, is 
continued into the spiracular artery. The hyoid vein divides 
dorsally into two branches, one of which runs back and joins 
the dorsa] aorta system, the other runs forward as the carotis 
posterior, joins for a short distance behind the hypophysis 
with the same vein of the other side, then separates running 
one each side of the hypophysis, the vein of each side receiving 
a large vein from the spiracular gill. 


EVOLUTION OF ORGANS IN THE CHORDATA. 207 


The musculature of the hyoid arch is peculiar in this respect, 
that no internal portion of the muscle-tube is segmented off 
by the cartilage, and accordingly no adductor is formed. The 
musculi interarcuales are also absent, and there is a complicated 
system of ligaments fastening the hyomandibular cartilage. 
The ventral muscles, on the other hand, are similar to those of 
the posterior arches. 

With regard to the cartilage of the hyoid arch, development 
shows that in the Sharks the upper middle internode, dorsal to 
the venous commissure forms the hyomandibular, no separate 
basale or dorsal internode is formed; but, as the hyomandi- 
bular carries a number of branchial cartilage rays, and also a 
dorsal ray, which is homodynamous with the upper extra- 
branchial (so-called) cartilage of the gill arches, it follows that 
the hyomandibular contains the basale (dorsal internode) of 
the hyoid arch. 

In the Sharks the first rudiment of the mandibular arch 
appears at the level where the hyoid vein joins the spiracular 
artery, but unlike the posterior rudiments it consists from 
the first of two cartilaginous centres: the under becomes the 
mandible, the upper the upper jaw, the so-called palato-quad- 
rate. No adductor is formed in the mandibular arch. It has 
been generally taught that the masticatory muscle of the jaws 
is the homologue of the adductor, but this is not so; no homo- 
logue of the adductor is present. 

There are no cartilaginous rays on the mandibular arch. 
The doctrine, therefore, of Gegenbauer and his followers, that 
the lower and upper jaw are parts of a single cartilage arch 
equivalent to a posterior gill arch is unfounded. 

In the Rays the development of the cartilages of the hyoid 
arch is quite different to that described for the Sharks. 

There are two cartilage-centres, one near the posterior edge 
of the arch, the other near the anterior side, behind the spira- 
cular cleft; each cartilage has its own muscle system. The 
first cartilage is separated into a dorsal and ventral part by the 
venous commissure, and each part bears gill rays. The second 
cartilage becomes the hyomandibular, it has its own muscle 


278 j. T. CUNNINGHAM. 


system which forms the mus. levator. The conclusion which 
must be drawn is that the hyomandibular in the Rays is a 
remnant of an arch anterior to and entirely distinct from the 
hyoid arch, while in the Sharks the dorsal part of the hyoid 
arch with its raysis fused with the hyomandibular. According 
to Gegenbaur the hyomandibular in the Rays represents only 
the mandibular process of the hyomandibular of the Sharks ; if 
this were true there would be no rays dorsal to the venous 
commissure in the Rays, whereas the fact is that these dorsal 
rays exist, but the cartilage they belong to is separate from 
the hyomandibular. Dohrn finally suggests that the upper 
jaw is also an independent gill arch, and the mandible another, 
but for the present leaves the further tracing of the transfor- 
mations for more profound investigations. He concludes the 
section on the hyoid arch in the Rays with the remark that he 
is satisfied to dispel the illusion that we already know what we 
want to ascertain. 

The spiracular cartilage is next taken in hand. Dohrn has 
investigated its origin in Scyllium canicula and catulus, Pris- 
tiurus, Mustelus, Raja and Torpedo. He found it always a 
single cartilage, and states that there is no foundation for the 
theory that it is either an enlarged single ray, or a combina- 
tion of rays. It is probably a portion of an independent 
arch, but what relation this arch bears to others it is at present 
impossible to say. ‘The adductor mandibulz is developed from 
the whole of the walls of the mandibular head cavity, no 
portion being separated off as an adductor; only one differen- 
tiation of a portion occurs, namely, the formation of the levator 
maxille superioris from the part lying nearest to the spiracle. 

When it has been postulated that the hyoid arch is really 
double and contains two arches fused together, it becomes 
necessary to inquire what has become of the cleft originally 
existing between these two arches. Has the cleft disappeared 
without leaving a trace, or has it merely undergone a meta- 
morphosis? Dohrn answers that the pair of clefts, i.e. the 
endodermal parts of them, have united in the median ventral 
line and formed the thyroid gland. This organ arises in the 


EVOLUTION OF ORGANS IN THE OHORDATA. 279 


embryo in the middle line very far forward as an outgrowth of 
endoderm cells close behind the mouth, and subsequently 
passes backwards losing its connection with the pharynx. In 
a note Dohrn promises in a future study to discuss the spira- 
cular cleft of the Selachians and Ganoids, and the pseudobranch 
of Teleosteans, and to show that between the mandible and 
the hyoid in Teleostean embryos on each side a deep invagina- 
tion of the ectoderm occurs, which is to be regarded as the 
ectodermal part of the cleft represented by the thyroid. (It is 
probable that this invagination is the same as that observed by 
other embryologists and diagnosed as the Teleostean represen- 
tative of the spiracle.) In another note it is stated that 
evidence will at a future time be adduced to show that in the 
jaw and hyoid system of Teleosteans five independent visceral 
arches are combined : 1, upper jaw; 2, lower jaw; 3, spiracular 
cartilage ; 4, hyomandibular ; 5, hyoid. 


The Thyroid of Petromyzon. 


The subject discussed in Study VIII is the thyroid in 
Petromyzon and its homologue in Amphioxus and the Tuni- 
cata. In the larval Ammoceetes the first trace of the thyroid 
appears at the time when the most anterior branchial diver- 
ticula of the endoderm grow out. Its first rudiment is a 
diverticulum directed downwards and somewhat forwards, close 
beneath the median part of the first pair of branchial diver- 
ticula, which is homologous with the spiracular clefts of Sela- 
chians and the pseudobranchize of Teleosteans. Between the 
stomodzum and enteron on each side runs the most anterior 
branchial artery, homologous with the spiracular artery of the 
Selachians ; it opens into the cephalic aorta of its own side, 
Petromyzon possessing two cephalic aorta one on each side of 
the notochord. The growth backwards of the mesoderm of 
the velum causes the opening of the thyroid diverticulum to be 
pushed farther back, so that it soon comes to lie at the level of 
the second pair of branchial sacs, and later between the second 
and third. A sagittal ingrowth of mesoderm now divides the 
thyroid anteriorly into two halves. On each side another 


280 J. T. CUNNINGHAM. 


pushing in forms the glandular lamella, the uninvaginated part 
forming the cover-lamella. In the glandular lamella a differ- 
entiation takes places into conical masses of gland-cells, the 
apex of the cone turned to the cavity of the gland, and 
ordinary ciliated cells. In the advanced larva of Ammoceetes 
two ciliated grooves run transversely in the wall of the 
pharynx, in front of the gill-sacs, and converge on the median 
ventral line to meet in the opening of the thyroid. These 
grooves Dohrn has ascertained to be derived from the endo- 
dermal sacs which represent the spiracular clefts, and which in 
Ammoceetes never acquire an opening to the exterior. 

Now the endostyle or hypobranchial groove of Ascidians, 
e.g. Cione intestinalis or Salpa, is closely similar in histo- 
logical structure to the thyroid of Ammoceetes. There is the 
same differentiation into bulbous agglomerations of gland- 
cells, and a more even layer of ciliated cells. Moreover, in the 
Ascidian there is a pair of ciliated grooves immediately behind 
the mouth, which ventrally converge to the hypobranchial 
groove, dorsally to the ciliated pit (hypophysis). These 
grooves of the Ascidian must be homologous with those of 
Ammoceetes, and must therefore represent in the Ascidian the 
spiracular clefts. And it follows that Tunicates must be 
derived from fishes, not vice versa. The reason suggested 
for the transformation is that the thyroid and spiracular clefts 
have been converted into mucous-secreting organs to aid in 
the conveyance of nourishment to the cesophagus. 

In Amphioxus there is not a hypobranchial groove, but a 
hypobranchial ridge, but this ridge has the same histological 
character as the thyroid in Ammoccetes and the hypobranchial 
groove in Ascidians. A homologue of the peripharyngeal 
ciliated grooves is not mentioned as occurring in Amphioxus, 
and the development of the hypobranchial ridge has not been 
studied. 

The conclusion drawn from all this is that both Tunicates 
and Amphioxus are degenerate fishes derived from ancestors 
more or less similar to the Cyclostomata. A difficulty which 
arises in considering Dohrn’s arguments is that no reason 1s 


EVOLUTION OF ORGANS IN THE CHORDATA. 281 


given why the spiracular endoderm sac should open into the 
thyroid endoderm sac, since these were presumably originally 
separate; the spiracle being anterior to the hyomandibular, 
the thyroid between hyomandibular and hyoid. Dohrn does 
not mention this question, being satisfied so far to show that 
the condition of the ciliated grooves in Tunicates is directly 
derivable from the condition in Ammoccetes. The derivation 
of the arrangement in the latter from that in Selachians is not 
discussed. 


Rudiments of Paired Fins in Petromyzon. 


In the ninth Study Dohrn returns again to the question of 
the fins. How, he demands, could an animal of the size and 
complication of the Cyclostomata obtain for itself organs of 
such fundamental effect on the whole organisation as pectoral 
and pelvic fins ? The question is perhaps not so convincing as he 
thinks ; for, on his own hypothesis, the neural and ventral para- 
podia must at one time have arisen, and the theory of the evo- 
lution of organs is not at present in such a state as to make it 
any more easy to understand how these organs arose than how 
limbs could arise in the Cyclostome, unless, indeed, it were 
postulated that the segmented vertebrate ancestor, with its 
dorsal and ventral parapodia, was a creation into whose pre- 
vious origin it were impious to inquire. But what is more to 
the point is that, although Gegenbaur believed no rudiment of 
fins could be discovered in the Cyclostomata, Dohrn has dis- 
covered in Ammoccetes rudiments of muscle-buds similar to 
those which in other fishes form the muscles of the unpaired 
fins. These buds, however, remain as indifferent cells during 
the Ammoceetes stage, and are only differentiated into the fin 
muscles when the metamorphosis into Petromyzon takes 
place. The buds are given off ventrally as well as dorsally, 
and as the dorsal series forms the muscles of the dorsal fin, 
the przanal ventral ones must at one time have formed mus- 
cles of then existing paired fins. Moreover, there is, accord- 
ing to Dohrn, a rudiment of the pelvic fins in Petromyzon, 
namely, the longitudinal folds bordering the anus, Below 


282 J. T. CUNNINGHAM. 


these folds are a pair of muscles, called by Schneider, in his 
‘ Beitrage zur vergl. Anatomie der Wirbelthiere,’ the anal fin 
muscles. According to Dohrn, these muscles serve to pro- 
trude the so-called penis of the male Lamprey. Dohrn raises 
the question of the possibility of copulation in the Lamprey, a 
possibility which does not really exist, for in the female there 
is a protrusible tube at the abdominal pore, which is shorter 
but otherwise exactly similar to that of the male. Dohrn 
suggests that the anal fin muscles of Schneider are homologous 
with the muscles of the pelvic fin in other fishes (Selachians 
especially). 


Origin of the Vertebrate Paired Eyes. 


The most recent study deals with the embryology and phy- 
logeny of the Vertebrate eye. It was obvious to previous 
embryologists that the nervous part of the eye was originally 
in the wall of the brain. Lankester suggested that the an- 
cestor was at this time transparent, while Balfour believed that 
though the tissues may have been transparent, the original 
cause of the outgrowth of the optic vesicle was the covering of 
the original superficial eye by the formation of the medullary 
tube. But the starting-point of Dohrn’s inquiry is the deve- 
lopment of the eye-muscles. Balfour indicated briefly the 
origin of these muscles from the most anterior head-cavity. 
Marshall (this Journal, vol. xxi) ascertained that only the 
rectus internus superior, inferior, and obliquus inferior arose 
from the pre-mandibular cavity, while the obliquus superior 
arose from the mandibular, the rectus externus from the 
hyoid. But Marshall believed that the dorsal parts of the 
head cavities from which the eye-muscles were formed were 
homologous with myotomes, and not with the ventral celom 
in the trunk. Dohrn does not agree with this, and holds that 
the dorsal parts, like the ventral, are not homologous with the 
myotomes in the trunk, but only with the ventral walls of the 
body cavity. As a consequence of this it follows that the eye- 
muscles are true muscles of visceral arches, and must have 
been originally branchial muscles. The reason why branchial 


EVOLUTION OF ORGANS IN THE CHORDATA, 283 


muscles came into relation with the eye is that the light 
reached the latter, when the medullary tube began to close, 
through the ectodermal pit of a preoral gill-cleft. This ecto- 
dermal branchial pit is now the lens of the eye, whose peculiar 
mode of formation is thus explained. The vascular part of the 
same gill arch is retained in the choroid gland of Teleosteans, 
which receives its blood supply from the pseudobranchial vein, 
and the arteria centralis retinee, which is the efferent artery of 
the lens branchia. This hypothesis explains the vessels of the 
campanula Halleri, of the pecten of Reptiles and Birds, the em- 
bryonic lens vessels of Mammals, as remnants of the blood- 
vessels of the branchia represented by the lens. Leaving the 
eye, Dohrn next goes on to support his view that aimost the 
whole of the head except the brain represents visceral or ven- 
tral structures, just as the tail contains only dorsal structures, 
and asserts his belief that attempts to estimate the number of 
myotomes in the head are all in vain. In his opinion the 
cerebral nerves have lost those branches which innervated 
myotomes and their derivatives, and have, in consequence of 
the extraordinary enlargement and complication of the ventral 
region, increased to a corresponding degree their visceral 
branches, at the same time having undergone great alterations 
in distribution on account of the changes of relative position 
among the gill arches. Thus, the attempts of Van Wighe and 
others to diagnose dorsal branches of the cranial nerves are 
founded in mistaken views. A ramus dorsalis of a spinal nerve 
never innervates a mucous tube, any more than the ramus 
dorsalis, so called, of a cranial nerve innervates myotomes and 
muscles of a dorsal fin. Again, Dohrn points out how necessary 
it is to understand more accurately the anatomy and develop- 
ment of the vertebrate organs before constructing complete 
and simple schemes which reduce the head to a number of 
myotomes as formerly to a certain number of vertebre. A 
great anatomist once said that if he wished to read romances 
he knew better specimens than histories of creation where- 
with to amuse himself, 4 propos of which Dohrn points out 
that if phylogenies are to be compared with romances it is as 
VOL, XXVII, PART 2,—NEW SER, U 


284. J. T. CUNNINGHAM. 


well to remember that the most sensational are not always the 
best works of art. 

We have thus given a summary of Dohrn’s results and indi- 
cated the point of view from which he regards the problem of 
vertebrate phylogeny. The speculations formulated in the 
‘Ursprung der Wirbelthiere’ have been in some cases sup- 
ported in others overthrown by his later researches, but he 
still holds strongly to the fundamental thesis that the original 
ancestor was a segmented animal more or less similar to an 
Annelid, and that the organisation of Cyclostomata, Amphioxus, 
and Tunicata can only be explained by profound degeneration. 
Whatever the fate of his various theories may be in the future 
of morphology, it is certain that his studies form a massive 

contribution to the really scientific study of organogeny, and 
that his independent attitude and stimulating suggestiveness 


of thought are worthy of his favorite motto, ‘“‘ Was fruchtbar 
ist allein ist wahr.” 


REVIEW. 


Patten on the Eyes of Molluscs and Arthropods. 


In the last number of the ‘ Mittheilungen’ of the Zoological 
Station of Naples appears an extensive article by Dr. William 
Patten on the “ Eyes of Molluscs and Arthropods.” The article 
contains the record of a number of observations on the structure 
of the eye in these animals, which appear to be of considerable 
value and importance. Accompanying the record of facts is a variety 
of theoretical and speculative statements, which are so extraor- 
dinary as not only to call for special notice, but are even likely to 
lead some readers to underestimate the value of the observations. 
Indeed, the attitude taken by this young and inexperienced 
naturalist in criticising the work of his predecessors, and in the 
enunciation of astounding general propositions, of the eccentricity 
and inadmissibility of which he appears to be altogether uncon- 
scious, is one which is greatly to be regretted as likely to diminish 
the weight which would otherwise be attached to his statements of 
fact, obviously the outcome of industrious investigation. 

A large portion of the memoir deals with the eyes of Mollusca, 
of which we shall not here say anything further. The most im- 
portant new result recorded in the memoir is that relating to the 
essential structure of the compound eyeof Arthropoda. Dr. Patten 
appears to have discovered that Grenacher is wrong in supposing 
that the cells of the crystalline cones are the matrix cells of the 
corneal lenses. He has found a distinct layer of epidermic matrix 
cells, which produce the cuticular lenses, and were entirely missed 
by Grenacher. This new layer is therefore the equivalent of 
the vitreous layer of the monomeniscous Arthropod eye. The 
crystalline cone cells are, on the other hand, according to Patten, 
part of the retinal apparatus, and the rhabdom of Grenacher, which 
forms a sort of stalk to the group of crystalline cone cells, is really 
formed by them, and is not a cuticular product of the retinula cells 
of Grenacher, which surround it, and, according to that observer, 
produce it. Dr. Patten’s observations on these points require con- 
firmation, but appear to be likely to prove correct. As to nerve- 
endings, his observations are more doubtful, since he has committed 
himself in a somewhat over-confident manner to a series of specula- 
tive generalisations on the subject of nerve-endings, for the formu- 
lation of which it is only too obvious that neither his knowledge of 
facts nor his acquaintance with the work of contemporary histolo- 
gists qualify him. He objects altogether to the term “nerve-end 
cell,” and holds that all the cells of the Arthropod ommateum are sup- 
plied with nerve-fibres, the chief of which are those which, according 


286 REVIEW. 


to him, form a meshwork in the crystalline cone cells, being derived 
from an axial nerve-fibre, which runs up the rhabdom in order to 
spread itself out in those cells. It certainly cannot be at once ad- 
mitted that the fibres which Patten has thus traced in so many 
directions are nerve-fibres, though possibly they are so. On the 
other hand, contrary to his assertions in reference to the Arthropod 
eye, Patten lays down the law in a dogmatic fashion in regard to 
the Molluscan hypodermis. “The nerves,” he says, “must termi- 
nate between the cells, and probably extend to their very outer 
ends.’ The “must’’ of the foregoing assertion depends on the cor- 
rectness of a speculative account of the phylogenetic development 
of a nervous system, for many of the details of which Dr. Patten has 
no conclusive grounds to urge. At present, it may be remarked, 
histologists have been led, by the observations of Ranvier and others, 
to admit that nerve-fibres do in some regions terminate between the 
cells of the epidermis of Vertebrata, but it is also very generally 
held that nerve-fibres of organs of special sense terminate in the 
substance of special nerve-end cells. 

Dr. Patten’s observations are possibly correct, but he does not 
strengthen the confidence likely to be placed in them by dogmatism 
of the kind in which he indulges. Our knowledge of the relation 
of nerve-fibres to nerve-end cells is admittedly very unsatisfactory, 
and will require observations over aud above those of Dr. Patten 
to put it on a satisfactory footing. 

Such being the main facts of importance which Dr. Patten seeks 
to establish, we may pass to a brief notice of some of his more 
astonishing theoretical statements. In the course of the extensive 
memoir (over 200 pages) which Dr, Patten has devoted to this 
subject, it is very seldom that we find a continuous straightforward 
and intelligible account of the facts, with a sober discussion of pro- 
babilities as to matters in which his own observations are im con- 
flict with those of other observers, or are incomplete. Dr. Patten 
is continually introducing into his record, with an unbecoming 
assumption of wisdom and authority, speculations or statements of 
a theoretical nature, which are so extravagant and betray so 
much ignorance as to make the reader regret very heartily that 
they have been allowed to disfigure a treatise which must on other 
grounds command attention. For instance:—1l. On p. 625 the 
description of the eye of Penzus is introduced with the following 
utterance :—‘“‘ The great impetus that modern zoological science 
has received from comparative anatomy has not been due so much to 
more subtle or able comparisons as to a more perfect knowledge of 
the structure of single forms.” How there is to be comparative 
anatomy without comparison, or how comparison is to proceed 
without an increased knowledge of the single forms compared, is not 
explained by Dr. Patten. The sentence, so far as it means any- 
thing, appears to be a negation of the value of scientific morphology 
altogether. This, however, is a trifle compared with what follows, 


REVIEW. 287 


and we quote it merely to show Dr. Patten’s appreciation of the 
scope and tendency of morphological research. 

2. A few lines below the passage above quoted we find the follow- 
ing dictum. ‘“ We must expect a certain amount of structural 
uniformity in those organs which have to carry by the same means 
the same forms of energy to similar perceptive centres.” This 
seems to be almost a truism; if the ‘same means” are employed 
for such a purpose we certainly must expect uniformity. But 
what does our author mean by “ carrying the same forms of energy 
to similar perceptive centres?” He is speaking of the eye; what 
is the form of energy which he imagines to be carried by means of 
the eye and optic nerves to a perceptive centre? A perusal of his 
final chapter explains this paradoxical allusion. Our readers will 
hardly credit the statement in the first instance, but it is actually 
true that Dr. Patten supposes that the energy of sunlight is 
carried with quantitative significance by nerves from the eye to 
nerve centres. He writes (p. 712): “In plants this sun energy is 
used in the chlorophyll grains, for in them the production of 
organic matter takes place. But in animals it is probable that the 
pigment granules are only the receivers of energy—the heliophags, 
as we shall call them—while this energy is transmitted by nerve- 
fibres to centres where it is consumed in the production of proto- 
plasmic compounds.” ‘This astounding theory of “ heliophags ” is 
only part of a general theory of ‘“ dynamophagy,’’ which is deve- 
loped at great length by Dr. Patten in his final chapter. 

“ Living bodies,” he says, “are distinguished by their power to 
absorb matter and energy, and from them produce high compounds 
by whose disintegration force is liberated as motion. This se- 
quence of events is vitality. .... We have only to deal with the 
second of these processes, the absorption of energy or dynamo- 
phagy, and more especially with the absorption of solar energy or 
heliophagy.”” Eyes then are primarily not organs of sight but 
heliophags, organs for the absorption of solar energy, and only 
secondarily acquire a sensory significance! Similarly auditory 
organs are declared to be absorbers of the energy of sound vibra- 
tions, whilst “the energy of coarser vibrations, of pressure, contact, 
or movement ’’ is “‘absorbed” by tactile hairs and “ that of gases, 
solutions or chemical compounds,” by means of taste-cells! 

It is thus coolly proposed by Dr. Patten to revolutionise all the 
established conclusions of modern physiology in regard to the 
nervous system, of which conclusions he, it is only fair to say, 
appears to be entirely ignorant. He actualiy imagines that the 
energy received from external bodies is quantitatively transmitted 
from the surface of an animal by its nerves to the nerve-centres and 
there made use of. It is hardly necessary to point out that such a 
notion is simply preposterous, and that to speak of “ the absorption 
of energy” as he does, betrays not only a fundamental ignorance 
of physiology but also of physics. The energy of the nervous 


288 REVIEW. 


system and of the animal body generally, is, it is scarcely necessary 
to say, taken into the body in the form of potential energy of 
food-stuffs, and exists there as the potential energy of the proteids 
or higher chemical combinations which constitute protoplasm. 
All that the sense organs do in the way of bringing the ‘actual’ 
energy external to the animal body into relation with the nerve- 
centres, is to furnish special trains of explosive substance (i.e. 
of substances whose potential is suddenly convertible into actual 
energy), so that energy of various forms external to the body is 
able to initiate at appropriate points, and by means of special 
apparatus the conversion within the body of potential into actual 
energy, the amount of which has no relation whatever to the 
amount of the incident energy by which the explosion was started. 
Precisely as the energy liberated in a gun barrel is not the energy 
of the fall of the hammer which explodes the detonator, nor pro- 
portional to it, so is the energy of the animal body entirely distinct 
from the energy which sets its various sense organs in operation. 
The sense organs of the animal body may be compared to the 
detonating apparatus ; and Dr. Patten might as well tell us that 
the purpose of a gun’s trigger is to absorb energy and transmit it 
to the ball, whilst ignoring altogether the gunpowder, as to talk 
about sense organs being ‘“ dynamophags ” and eyes being “ absor- 
bers ” of the “ beneficial effects of the sunlight.” 

3. In elaborating his doctrine Dr. Patten commits himself to 
many erronous statements, which show how little he is qualified to 
deal with the subject. We may notea few of these. Onp. 709 Dr. 
Patten writes of the “animal pigment, especially that of colourless 
plastids.” Animal pigment is declared to be “a living sub- 
stance!” It is further stated, without the slightest attempt to sup- 
port so startling a conclusion, that the “ pigment granules of animal 
tissues are modified chlorophyll granules!” Dr. Patten not only 
expresses new ideas but also has invented a new chemical termino- 
logy. He writes of “waste products, such as carbonic acid gas, 
sulphides, ammoniates and ureates.’’ His knowledge of chlorophyll 
and of the steps by which animal pigment granules are to be derived 
from chlorophyll granules may be judged of by the following: 
‘Chlorophyll, as is well known, is extremely unstable and soluble 
in many fluids, even in water.” 

4, The statement that “it is well known that pigment, like chlo- 
rophyll, is dependent for its existence upon the sunlight,” is totally 
at variance with fact. Instances of the formation of chlorophyll in 
plants which are excluded from sunlight are known, and still more 
numerous instances of animals which develop brilliant pigment 
although living in what is relatively to ordinary daylight, darkness. 
No doubt in the race, pigment must havea direct dependence on the 
access of sunlight; in the absence of light it cannot be of service to 
the organism. But there is no evidence to show either that chloro- 
phyll or pigment are dependent for their existence upon sunlight. 


REVIEW. 289 


5. In green plants, according to Patten, “ chlorophyll is without 
doubt the substance affected by sunlight,” and ‘the only rational 
supposition is that pigment is the substance in animals directly 
affected by the sunlight.”” Itis somewhat impertinent of Dr. Patten 
to accuse those who may not assent to his crude theories of enter- 
taining irrational suppositions. Most physiologists will remember 
that there are not a few simple experiments which demonstrate 
that protoplasm devoid of pigment is affected by sunlight and by 
its visible as opposed to its thermal factors. For instance, Engel- 
mann has shown that the colourless Protozoon Pelomyxa contracts 
when exposed suddenly to sunlight, and the retina of albinoes is 
“directly affected ” by sunlight. 

6. It is a matter for regret that Dr. Patten has not made himself 
acquainted with the facts as to the action of light on protoplasm. One 
of the most important lines of inquiry in the minute study of the eyes 
of Arthropods, Molluscs, and other Invertebrates, is to be found in 
an exact determination of the presence or absence of pigment in the 
nerve-end cells and of the distribution of pigment granules in those 
cells. The question is a difficult one to investigate, because the 
observer generally is compelled to dissolve the pigment present in 
an ommateum before a satisfactory study of the cells can be made. 
Dr. Patten, in the more valuable portion of his memoir containing the 
record of his observation, has not given so much attention to this 
matter as we could wish. It is remarkable that whilst he indulges 
in such “tall talk’ with regard to pigment and heliophagy and the 
fundamental relation of pigment to this newly discovered function, 
yet he himself professes (we do not throw doubt on his observa- 
tion) to have traced the chief optic nerve-fibres of the Arthropod 
polymeniscous eye to the colourless transparent cells of the 
erystal cones. It is evidently a subject which does not trouble 
him much since he quite recklessly attributes to other authorities 
on Arthropod eyes, statements with regard to the presence or 
absence of pigment in nerve-end cells which are the reverse of 
those made by the gentlemen in question. Thus at p. 670 he says: 
“‘ Let us take for instance one of the lateral eyes of Scorpio and 
it will be found, according to Graber and Lankester, that the om- 
mateum consists of ommatidia each one composed of five central 
colourless cells or retinophore.” The reader who has followed 
us so far will not be surprised to learn that the particular cells in 
question were described and figured by Lankester as pigmented 
and not colourless, and were made by him the text of a discussion 
as to the significance of pigment in nerve-erd cells. 

7. It is not, however, of any use to expect accuracy of observa- 
tion as to the contents of books and contemporary memoirs from 
Dr. Patten. He is far too much engrossed with laying down new 
principles of physiology and expounding to a benighted world the 
results of his philosophic meditations. As he himself says (p. 672), 
since doctors disagree, he intends to choose his own course, picking 


290 REVIEW. 


out such facts as suit his theories and denying the existence of 
those which do not. 

It is not to be expected that a writer who openly professes such 
principles should quote accurately the observations of other people. 
At the same time this incapacity for accurate observation of books 
and the neglect to observe at all such books as a text-book 
of physiology, and one also of physics, must lead Dr. Patten’s 
reader to consider the possibility that his incapacity for correct 
observation extends also to other matters. 

8. To continue our notes. On p. 685 we read: ‘“ We must admit 
that the possibility of regarding the phaosphere found in Euscor- 
pius italicus by Lankester as an aborted nucleus is not so 
remote as he would have us believe.” Whether the phaosphere can 
possibly be an aborted nucleus or not may be an open question ; it 
is but another instance of Patten’s extraordinary inaccuracy when 
he states that Lankester “ would have us believe’ anything on the 
subject. The matter was not discussed by Lankester at all. 

9. On p. 717, Dr. Patten declares that he often hears “it said of 
any pigmented spot that it is not an eye, but simply a meaningless 
collection of pigment,’ and also alludes to “those who believe that 
pigment is a waste product.” We trust that it is not in the excel- 
lent Zoological Station of Naples, where Dr. Patten has recently 
been pursuinghis studies, that he has heard the above quoted remark. 
Was it made by a fellow student at Trieste or in the laboratory of 
Leuckart at Leipzig? In any case it seems to be a pity that 
Dr. Patten should have repeated these disparaging remarks con- 
cerning pigment spots, because no sensible person attaches any 
importance to them, and it is scarcely worth while to adduce, as Dr. 
Patten does, the well-known facts which render them unjustifiable. 

10. On p. 716 we find it stated that “an organ most perfectly 
adapted for the condensation and absorption of the greatest amount 
of (solar) energy is likewise perfectly constructed for the perception 
of objects.”” The concentration of light is stated to be the condi- 
tion essential for the most perfect “ heliophagous organ,” and it is 
declared that ‘‘ the amount of energy absorbed weuld depend upon 
the most perfect condensation of light upon a given area.” One 
surely would expect a writer on the theory of eyes to make himself 
acquainted with the simpler facts known as to the properties of 
lenses! But it seems that Dr. Patten has not found time to do 
this. The rays of light concentrated by a lens are, it is hardly 
necessary to say, merely those rays which fall upon the surface of 
the lens. Hence if the mere absorption of the energy of these 
rays is all that is needed, there is no advantage whatever in the 
provision of a lens. The naked epidermic surface of an area equal 
to that of a lens would present a perfect instrument for the “ absorp- 
tion” of solar energy, and, indeed, would ‘“‘ absorb” more than can 
the retina with the lens intervening between it and the surrounding 
medium. In plants accordingly we find no lenses but a simple 


REVIEW. 291 


exposure of green surface to the solar rays. On the other hand if, 
as is the case according to received theories, the process which goes 
on in the retina is not important as an absorption or (to use a 
better term) a conversion of energy quantitatively, but only quali- 
tatively, that is to say, in respect of initiating active changes in 
the nerve-end cells with the subsequent consequences of which the 
amount of energy converted has not so much to do as has its quality, 
then we can understand that a lens which disposes the solar rays on 
the retinal surface in a manner conducive to the localisation of their 
differing quality, has importance and value. 

11. A melancholy instance of the extent to which Dr. Patten acts 
upon the principle of bending facts to theory, even at the risk of 
the grossest disrespect to contemporary authors of acknowledged 
competency, is found in his treatment of Sars’s observations on the 
luminous organs of Euphausia. Patten wishes to consider these 
organs as eyes, and instances of his hypothetical ‘“ heliophags ;”’ 
accordingly he suggests that Sars was misled by flashings of reflected 
light when he stated that they gave out light at intervals. Ina 
note at the end of Patten’s paper the editor of the ‘ Mittheil- 
ungen ’ very honestly states that Messrs. Paul Miyer and Giesbrecht 
have in consequence examined three living specimens of Euphausia, 
and entirely confirm Sars’s observations and refute the unjust 
insinuations made by Dr. Patten. 

12. A similar unwarrantable adhesion to theory, in the face of 
opposing facts, is seen in Dr. Patten’s attempt to evade the conse- 
quences of the observations of Lankester and Bourne on the lateral 
eyes of Scorpions and Limulus, in regard to the latter of which 
animals they have the confirmatory evidence of Grenacher. Dr. 
Patten has propounded a theory of the Arthropod eye, to the effect 
that itis in all cases derived from a vesicle formed by invagi- 
nation of the epidermis, and consists, therefore, of three layers of 
cells, viz. the two layers of the flattened vesicle and the epidermic 
layer which grows in front of it during its nipping off and detach- 
ment from the point of invagination. It is probably true that this 
is the structure and the ancestral! history of the ordinary compound 
eyes of Crustacea and Insects: but there is no justification in the 
small area of facts observed by Dr. Patten himself for including 
all Arthropod eyes, all ocelli wherever situated and however 
constructed under this type. It is not clear why Dr. Patten 
insists on the universality of his generalisation, applying it to 
groups of Arthropods which he knows nothing about, and pre- 
suming to deny the accuracy of observations which he has not 
taken the trouble to test. Lankester and Bourne described the 
ommateum of the lateral eyes of Scorpions as being “ mono- 
stichous,”’ like the great lateral eyes of Limulus. They figured sec- 
tions of the lateral eyes of both Kuscorpius italicus and of 
Androctonus funestus. Their sections are in existence, and 
leave not the slightest doubt as to the accuracy of the statement 

VOL. XXVII, PART 2,—NEW SER. x 


292 REVIEW. 


that these lateral eyes consist of simple depressions of the epi- 
dermis, there being no folding in of the edges of the depression so 
as to form a vesicle, and consequently no duplication or triplication 
of the layers. The fact thus established, that there is no vitreous 
layer in certain Arthropod eyes intervening between the cuticle and 
the nerve-end cells, naturally enough is an obstacle to Dr. Patten’s 
sweeping generalisation. After citing the observations in question 
he dismisses them with the cool remark : “ For theoretical reasons I 
am obliged to assume that this layer (the vitreous) is always present.” 

Were Dr, Patten not dominated by theories, one more extrava- 
gant than another, he would not have “assumed”’ anything about 
such an important matter, but would simply have taken a Scor- 
pion (common enough at Naples), and cut some sections of its 
lateral eyes. Dr. Patten, however, openly professes that he has 
made it his habit in constructing his views on the structure of eyes 
to “choose his own course, picking out those facts which seem to 
point in the right direction ;” that is to say, which support a favourite 
theory or amplify a startling generalisation, and ignoring or flatly 
denying, without troubling to bring them to the only test recognised 
by loyal students of nature, those which cannot be thus used. 

18. Finally, we must point out that, in expressing his opinions, Dr. 
Patten often shows as great a want of manners as of fundamental 
knowledge. He objects to the supposition that in more complex 
eyes some of the pigmentiferous cells are due to intrusive connective 
tissue which has penetrated between the cells of epidermic origin. 
One author, he states, “has carried this supposition to an absurd 
degree.’ There is nothing “absurd” in the supposition, as Dr. 
Patten would recognise were he acquainted with the histology of 
the epidermis. In Lumbricus, Hirudo, and even in some Verte- 
brates, the occurrence of such intrusive connective tissue is a de- 
monstrable and admitted fact; and in relation to the eye of 
Arthropoda it appears to have been actually observed taking place, 
according to Kingsley’s recent account of his investigation of the 
development of the eye of Crangon (‘ Zoolog. Anzeiger,’ No. 234). 
But in any case it ill becomes a novice to charge his masters and 
teachers with “ absurdity.’’ It should be enough for him to demon- 
strate an error (if he can) and to employ respectful language in 
doing so. 

Grenacher is subjected by Dr. Patten to even more objectionable 
treatment. On p.728, this young American, after citing an opinion 
published by Grenacher, says: “This he knows is absurd, and 
cannot be true.” The expression is offensive and discreditable. 

On the whole we cannot congratulate Dr. Dohrn on his con- 
tributor. There are, no doubt, some laborious observations con- 
tained in this ill-regulated production ; but it is a question whether 
their value will counterbalance the effect on the author’s reputation 
of the evidence which it bears of his want of both scientific and 
social education. 


The Anatomy of the Madreporarian Coral 
Fungia. 


By 


Gilbert C. Bourne, B.A., F.L.S., 
New College, Oxford. 


With Plates XXIII, XXIV and XXV. 


DurRinG a visit, extending from the middle of September, 
1885, to the middle of January, 1886, to the island of Diego 
Garcia, an atoll lying in S. lat. 7° 13’, E. long. 72° 23’, I 
was able to collect and preserve a large number of specimens 
of Fungia dentata, which form the subject of the present 
memoir. 

The Fungize were very abundant within the lagoon, espe- 
cially among the knolls and banks of growing coral on its east 
side, where, at low spring tides, they could be collected by 
scores from depths ranging from three to ten feet. They 
occur singly, more usually in groups of five or six, among the 
massive Astreids and Madrepores of which the knolls are 
chiefly composed, usually lying in a hollow or basin, or half 
hidden beneath the spreading branches of some large Madre- 
pora, and are thus protected from being swept away by the 
tides which set strongly across the knolls. 

Specimens of a diameter of three inches and more were 
extremely common, but it was very rarely that I could find 
any of smaller size; the smallest that I was able to procure 
measures as much as ‘two inches across, and a prolonged 
search failed to reward me with a single smaller specimen, or 


VOL. XXVII, PART 3.—NEW SER. Y 


294 GILBERT C. BOURNE. 


with an example of the nurse-stock.! In this I was very much 
disappointed, for Professor Moseley succeeded in finding a 
specimen at Tahiti in the course of a few hours’ search, whilst 
I was unsuccessful day after day. Although the Fungi at 
Tahiti lay in only three inches of water, and the search was 
an easy one, he mentions the great difficulty he had in finding 
the nurse-mass among the numerous adult forms on the reef ; 
and in my case, where they lay in three feet or more of water, 
it is possible that I may have overlooked the small nurse-stock 
and the smaller recently detached Fungiz; this is the more 
likely since both the nurse-stocks and the young forms would 
probably remain hidden beneath the great flat plates of dead 
Madrepore which form the basis of the mounds of living coral. 
Yet I can scarcely believe this to be the case, for not only did 
I search very closely by wading and diving among the corals, 
but I frequently turned over the above-mentioned flat plates 
of coral-rock and examined their under surfaces without ever 
finding a single example, nor did I ever meet with a group of 
very small forms, nor with anything like the group of nurse- 
stocks attached to the corallum of an old and dead Fungia, as 
figured by Stutchbury (39). I am inclined to believe that 
sexual reproduction followed by asexual reproduction by 
budding from a nurse-stock takes place in Fungia only 
at certain seasons of the year, and that it was not in 
progress during my stay at Diego Garcia. This seems the 
more probable because I have found no trace either of ova or 
of spermatozoa in any of the large specimens which I have 
brought home for examination. Reproduction in Fungia 
appears to be effected also by budding and by simple fission. 
In the British Museum there are several examples of the 
former process, in which indubitable buds can be seen growing 
from the base of a large Fungia. The buds always arise from 


1 Semper (38) calls the nurse-stock of Fungia a Strobila, but as this 
name was originally applied to the dividing parent-stock of Aurelia, which is 
essentially different from the bud-producing parent-stock of Fungia, and since 
it is objectionable to use the same name for two very different phenomena, I 
use the word nurse-stock for the fixed parent of Fungia. 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 295 


the base, and it is not unlikely that they may be formed only 
when, by some accident, the coral has been overturned. 
Examples of fission are rare, but I have in my possession a 
dead corallum which is nearly divided into two separate 
Fungi, and in which the axial fosses are already completely 
separated from one another and form mouths excentrically 
placed on peristomial discs inclined towards one another at a 
wide angie. There is a similar specimen in the British 
Museum. In the same collection there is a very good specimen 
of a nurse-stock brought by H.M.S. Alert from the Seychelles, 
found on March 5th, 1883. This is a young specimen from 
which the first bud has not yet been detached, and the soft 
tissues still extend down over the outside of the corallum to 
the basal disc ; unfortunately the spirit in which it was con- 
tained has been allowed to evaporate, and the soft tissues are 
unfit forexamination. But since it was found only two months 
later than the date of my search at Diego Garcia and in the 
Same seas, it may be taken as an objection to my opinion 
given above, that there is a special season of sexual followed 
by asexual reproduction from a nurse-stock in Fungia. It is 
quite possible that sexual reproduction may be very much 
economised in these corals and is of rare occurrence, the 
maintenance of the numbers of a species being ensured firstly 
by the budding off of an indefinite number of forms from the 
sexually produced nurse-stock, and secondly, by the simple 
asexual processes of budding and fission above described. 
The whole history of the reproduction of these forms is very 
imperfectly understood, although it presents many problems 
of the greatest interest. A naturalist travelling in coral-seas 
should not fail to try and secure some specimens of the nurse- 
stocks carefully preserved in spirit, as well as specimens of the 
young free forms recently separated from the parent-stock. To 
this should be added any observations that may be possible on 
the relative frequency of the nurse-stocks, on the frequency of 
budding or fission, and on the rate of growth. I was unable 
to carry out an extended series of observations on the Fungize 
at Diego Garcia, for the knolls on which they were found lay 


296 GILBERT C. BOURNE. 


“in the lagoon at some distance from my hut, and want of space 
and appliances prevented me from constructing proper aquaria 
in which to study them at leisure. Such as I tried to keep 
alive in buckets and tubs full of sea water soon perished, the 
water rapidly becoming foul in the hot climate unless a 
constant stream is kept through it. As for placing any indi- 
viduals of Fungia or masses of any other coral in a particular 
spot on the beach where they might be readily accessible for 
study, a short experience showed me the impracticability of 
the suggestion. Placed on the lagoonward beech in smooth 
water they were quickly covered with and destroyed by the 
sand ; on the external shores they were at once rolled over and 
over and destroyed by the great waves which are capable of 
moving masses weighing 2 cwt. and more, and throwing them 
up in a sort of low wall all round the island. 

The specimens which I brought home for examination were 
killed with hot corrosive sublimate, and afterwards treated 
with picric acid and preserved in 70 per cent. spirit. In 
this way I was able to preserve several specimens with the 
short stumpy tentacles fully expanded, as is shown in fig. 1. 

Although the general features of the corallum of Fungia 
have been well known for a long time, and have more recently 
been carefully described by Professor Martin Duncan (5), 
the arrangement of the soft tissues, and their relation to the 
corallum has not yet been studied. G. von Koch, it is true, 
has recently published a few remarks on the subject (23) and 
gives a figure, but the latter is incorrect in details, and the 
description merely amounts to a statement that the general 
anatomy of Fungia corresponds with that of the other Madre- 
poraria; he does not attempt to give a detailed description of 
the internal structure. As any attempt to remodel the classi- 
fication of the Madreporaria must depend on an intimate know- 
ledge of the relation of the soft parts to the corallum, I shall 
give in the following pages as detailed a description of the 
anatomy as circumstances will permit. 

The family Fungidz was estabiished by Dana in 1846. 
In his splendidly illustrated work on the ‘ Zoophytes of the 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 297 


Wilkes’ Exploring Expedition,’ he gives descriptions of several 
species, with drawings of the hard parts and the living animals. 
To the latter I shall have occasion to refer further on. The 
family thus established was made the subject of a memoir by 
Milne-Edwards and Haime, in which many new species were 
described, and the characteristic features of the corallum were 
noted. The same authors give a full description of the family 
in the ‘ Histoire des Coralliaires, but confine themselves to 
the study of the corallum throughout. Professor Martin 
Duncan has lately published a memoir on the same family, 
dealing especially with the hard structures, and to his account 
I have little or nothing to add. The following description of 
the corallum is taken principally from his paper (5). 

The corallum is simple and discoidal, the base usually rather 
concave, and the upper surface convex. The theea is distinct 
and confined to the basal surface ; it is continuous in the cen- 
tral part of the disc, but in its more peripheral parts it is per- 
forated by numerous apertures, which lead through it into the 
interseptal loculi. The septa are numerous, arranged in seven 
cycles in the moderately large forms, and are continuous; the 
free margins of the septa are dentate. The theca is orna- 
mented with radiating rows of spines, each row corresponding 
in position with a septum above, and representing a costa. 
The axial fossa is elongate and shallow. The columella is tra- 
beculate and rudimentary. Special structures named synap- 
ticula are characteristic of the Fungidz ; they consist of nearly 
vertical or curved rows of bars, bridging over the space between 
and connecting the lower portions of two contiguous septa. 
By them the lower parts of the interseptal loculi are divided 
up into nearly vertical channels, bounded on two sides by 
synapticula, and on the other two by the septa. Excellent 
figures of the synapticula are given by Professor Duncan. 

The flat discoid shape of Fungia is not a characteristic of 
the genus, but occurs in other groups of the Madreporaria, 
e.g. Deltocyathus among the Turbinolide, Stephano- 
phyllia and Leptopenus among the Eupsammide. The 
flat shape is a secondary effect produced by the mode of 


298 GILBERT C. BOURNE. 


growth, for in its youngest stage the corallum of the nurse- 
stock of Fungia is cup-shaped and resembles a Caryophyllia, 
having a distinct lateral theca, and a basal disc by which it is 
attached. In the course of subsequent growth the peristome 
expands laterally, so that the nurse-stock already shows traces 
of the discoid shape before any young forms are set free; this 
is very well seen in the specimen dredged by the “Alert,” re- 
ferred to above. The separation of the young Fungia from 
the nurse-stock takes place at a short distance below the edge 
of the peristome, so that only a small portion of the lateral 
theca of the nurse-stock passes into the free form. As growth 
proceeds the peripheral ends of the septa are the seats of the 
greatest activity in the deposition of calcareous matter, each 
septum at once growing outwards and sending off calcareous 
processes from its lower edge, which meet and fuse with those 
of adjoining septa to form the perforate theca. Thus, the in- 
crease in size of the coral proceeds almost entirely in a hori- 
zontal direction, bringing about the discoid shape of the adult. 
The corallum of a young Fungia just set free from the nurse- 
stalk has a circular opening beneath, which leads into the 
interseptal loculi and marks the point of former attachment ; 
this hole is soon filled up by the deposition of calcareous 
tissue, which remains as a small boss in the centre of the base 
of the disc, marking the space which represents the basal disc 
of the attached coral. The remainder of the under surface isa 
thecal structure, the more central imperforate part of which is 
probably that portion of the lateral theca of the nurse-stalk 
above the line of detachment, the outer and perforate part 
being derived from a fusion of the lower ends of the septa, and 
not intimately connected with the synapticula, as I think after 
a careful examination of the fresh corallum,though on this point 
I am at variance with Professor Duncan. The series of figures 
3—8 show how the discoid shape is derived from the cup- 
shaped coral by lateral growth. The theca of Fungia, although 
entirely confined to the basal surface, and perforated by nume- 
rous apertures leading into the interseptal loculi, is quite homo- 
logous with the theca of other Madreporaria, and bears similar 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 299 


relations to the mesenteries and the ceelenteron, as I shall 
describe further on. It is important to notice that the theca 
is formed, in the course of outward growth, from the fused 
ends of contiguous septa, as is stated by G. von Koch 
‘to be the case in the lateral thece of other cup-shaped 
Madreporaria. 

I shall use throughout the same terminology as Fowler in 
in his admirable paper on “‘Coral Anatomy” (9); but since 
the flattened form of Fungia makes it a little difficult to dis- 
tinguish “ base” from ‘ basal disc” in a general description, 
I shall make use of the terms ‘oral surface”? and “ aboral 
surface,” the former including the mouth and peristome, the 
latter the theca and basal disc. 

Drawings of living Fungiz have been given by Eschscholtz, 
Quoy and Gaimard, and Dana. ‘The first of these gives a 
tolerably correct figure, but only four cycles of tentacles are 
represented, the more peripheral cycles not being noticed. 
Quoy and Gaimard (33) figure two species of Fungia under 
the name of Fongies a grosses tentacules (Fungia 
crassitentaculata). These are remarkable for the great 
length of the tentacles, which are represented as scattered 
irregularly over the disc. Milne-Edwards and Haime, not 
noticing the regular arrangement of the tentacles in Esch- 
scholtz’s figure, say: ‘‘ Toute la partie supérieure du corps de 
Vanimal, correspondante a la partie lamellifere du polypier, est 
garnie des tentacules épais qui ne sont pas groupés en forme de 
couronne comme chez la plupart des Zoanthaires.” Dana’s 
figure of Fungia lacera in the ‘ Zoophytes of the Wilkes’ 
Exploring Expedition’ is reproduced in his book on ‘ Corals 
and Coral Islands,’ and he says in the latter work: “ The ten- 
tacles are scattered over the disc instead of being arranged in 
regular circles. It is evident from the figure that the appa- 
rent circles, where there is more than one, in Actiniz, arise 
from the crowding of the series of tentacles together, and also 
that the inner row of tentacles in polyps is the older. It will 
be noticed also that each of the tentacles stands where a new 
ridge or calcareous septum in the coral begins.” That the 


300 GILBERT C. BOURNE. 


circles of tentacles in Actinic do not arise in the manner here 
suggested is sufficiently proved by the researches of Lacaze 
Duthiers and the Hertwigs, but I have not seen it contradicted 
of Fungia that the tentacles are scattered irregularly over the 
disc. Yet so far is this from being the case, that on first 
taking the living animal out of the sea I was immediately 
struck with the arrangement of the tentacles in definite cycles. 
Fig. 1 is a drawing of F. dentata, somewhat contracted by 
spirit, but with the short stumpy tentacles still expanded. 
Their arrangement will be at once understood by a comparison 
of the drawing with the diagram (fig. 2). 

Each tentacle is placed, not, as Dana says, on the innermost 
extremity of each septum, but on a slight elevation of the 
upper edge of each septum near its innermost extremity ; from 
the point of attachment of the tentacle the septum is con- 
tinued obliquely downwards and inwards towards the axial 
fossa, none but the last two cycles ending at any great dis- 
tance from it. Since the tentacles correspond exactly in 
position with the septa, what is stated of the arrangement of 
the one holds equally good of the other. 

There are twelve primary septa, of which ten reach the 
mouth, two being rather shorter than the others and placed 
opposite each end of the long axis of the mouth. The ten- 
tacles placed on the inner extremities of these septa overhang 
the mouth, but are small and degenerate. 

Both Lacaze Duthiers (7) and von Koch (21) describe 
twelve septa as rising simultaneously in the first cycle, making 
the prime number of septa twelve instead of six. According 
to the latter six alternate septa grow faster than the others, 
giving the appearance of two cycles of six each; this is appa- 
rently not the case in Fungia whose twelve septa of the first 
order are, with the exception above mentioned, of equal size. 

There are twelve septa of the second order alternating with 
those of the first ; they reach very nearly to the mouth and are 
all of equal length; the tentacles corresponding with them 
form, with those of the first cycle, a ring surrounding the 
mouth. 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 301 


There are twelve pairs of septa of the third order. Each 
pair of this order embraces a septum of the first order. The 
fourth order contains twenty-four pairs of septa, each pair 
embracing alternately a septum of the first and a septum of 
the second order. 

The fifth and sixth orders also contain twenty-four pairs of 
septa each. Those of the fifth order are the longer, and each 
pair embraces a septum of the first and second orders alter- 
nately ; those of the sixth order are much shorter, and each 
pair embraces a septum of the third order. 

These last two orders, the fifth and sixth, very possibly 
represent only one complete cycle of septa and tentacles. But 
since the difference in the length of the septa shows a differ- 
ence in their time of origin I have thought it better to keep 
them separate. 

The seventh order contains ninety-six pairs of septa, with 
their corresponding tentacles. The septa are extremely short 
and rudimentary ; the tentacles are minute and placed close to 
the circumference of the disc. 

The sequence of the septa is 1, 7, 5, 7, 4, 7, 
Beni, OF i eth Oy 0 Ay F530; V5) 05 1, O05 05 45,05 
system. 

The tentacles are arranged in six tolerably definite circles at 
different distances from the mouth, as may be seen in figs. 1 
and 2. The arrangement both of tentacles and septa is very 
regular and easily made out at each end of the long axis of the 
mouth, but it becomes more irregular and obscure at the sides. 
Thus, contrary to previous statements, Fungia is perfectly 
regular, and agrees with other Madreporaria in the arrange- 
ment of tentacles and septa. The tentacles, which are small 
and club shaped in most species, are correctly figured by 
Dana. The remaining external features do not call for special 
notice and may be understood by reference to fig. 1. 

To examine the internal structure, I decalcified some speci- 
mens in nitric acid solution, and afterwards stained and cut 
sections from them in the usual way. Another specimen I 
half decalcified and dissected, and further made use of the 


Gifeoncte Os te 
5, 7, 1; in each 


302 GILBERT C. BOURNE. 


method invented by G. von Koch, to study the relations of the 
hard and soft parts in situ. This method, which is described 
in the ‘ Proceedings of the Zoological Society,’ 1880, p. 41, 
yields valuable results with smaller corals, but requires con- 
siderable experience, and is not wholly satisfactory when so 
large a coral as Fungia is dealt with. 

Von Koch, in a sbort note on the anatomy of Fungia and 
other Madreporaria, published in the beginning of this year, 
rightly says that its structure is essentially the same as that of 
other Madreporaria, but he makes no mention of the peculi- 
arities which obtain from the relation of the soft parts to the 
synapticula, and his diagram is incorrect in some particulars 
(23). 

The Mesenteries.—It is obvious that, since the lower 
parts of the interseptal loculi are broken up by synapticula, 
there must be some corresponding modification of structure in 
the mesenteries, if the latter structures are present in Fungia. 
Professor Duncan was so much struck with this in his studies 
on the corallum that he was led to express a doubt whether 
mesenteries could exist at all (5). Transverse sections show 
that mesenteries do exist, and that in all their essential charac- 
ters they have the arrangement typical of Hexactinian 
Actinaria. They are arranged in pairs, each pair being dis- 
tinguished by the arrangement of its longitudinal muscle-fibres, 
which are placed on the adjacent faces of the two mesenteries 
composing the pair, except in the case of the two pairs of 
directive mesenteries, one pair at each end of the long axis of 
the mouth, in which the longitudinal muscle-fibres are placed 
on the reverse sides. The space included between each pair 
of mesenteries is an entocele (Fowler, 9) and in each entocele 
there is a septum. There are seven orders of mesenteries in 
the Fungia which I am describing, corresponding to the 
seven orders of septa. 

The primary and secondary mesenteries are attached to the 
stomodzeum, and in their upper parts traverse the whole space 
from the mouth to the periphery of the disc. The tertiaries 
are not attached to the stomodzum, but reach nearly to it. 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 803 


The remaining orders are of constantly decreasing length, the 
septenaries being very minute. All the mesenteries are firmly 
attached by their upper border to the peristome. 

In the upper portions of the interseptal loculi there are no 
synapticula; here the mesenteries are free to radiate across 
the whole space between the mouth and the periphery of the 
disc, and show in this part the ordinary structure, viz. a central 
structureless supporting lamina, the Mesoglea,! bearing a 
layer of endoderm on each face. On one face are borne the 
longitudinal, or retractor muscles, bundles of stout muscular 
fibres developed from the endoderm, supported by and appear- 
ing as if intimately connected with, supporting offsets of the 
mesogloea. On the opposite side to the longitudinal muscles 
are the transverse muscle-fibres, much more feebly developed 
than the former, and having a general arrangement at right 
angles to them ; they are not easy to see in Fungia. 

In the lower portions of the interseptal loculi the continuity 
of the mesenteries is broken by the synapticula, and they 
present special modifications of structure which can only be 
understood by a careful comparison of figs. 10, 13, and 15. 
Fig. 10 represents a mesentery of the third order dissected out 
from a decalcified specimen, and viewed from the side. The 
upper portion is seen to be complete, and exhibits the charac- 
teristic arrangement of muscle-fibres, but it will be noticed 
the longitudinal muscles are gathered into more distinct bundles 
than is usually the case in Actinaria. Each face is covered 
with a layer of endoderm, as may be seen by reference to figs. 
13 and 15. The lower portion of the mesentery is necessarily 
discontinuous owing to the intervention of the synapticula. 
Here the mesogloea is seen to be continued into a number of 
strong bands or ligaments to which the separate bundles of 
longitudinal muscles are attached, these ligaments passing 
down through the intersynapticular spaces to be fastened, 


1 [ have coined this term as a substitute for the term ‘‘ mesoderm ” in the 
Ceelenterata, and use it as the equivalent of the “‘ Stiitzlamelle ” or ‘“ Gallert- 
substanz”’ of German authors, for reasons which are stated at the end of the 


paper. 


304, GILBERT C. BOURNE. 


according to their position, either to the aboral body wall, or 
to thickened lines of the mesoglea of the skeletotrophic invest- 
ment shortly to be described. In sections these ligaments 
may be seen as thickenings of the tissue surrounding each in- 
tersynapticular passage, more rarely as complete partitions 
dividing such a chamber intwo. The endoderm covering each 
face of the mesentery becomes continuous, where the latter is 
divided by the synapticulum, with the endoderm of the skeleto- 
trophic investment. The theca being perforate in all but its 
most central portions, the ligaments of the mesenteries pass 
through the perforations and are continued outside the theca, 
to be fastened to the aboral body wall (see fig. 15). The theca 
or aboral surface of Fungia is completely covered with soft 
tissues which do not closely invest the corallum, but are 
separated from the latter by a portion of the cclenteron. It 
is important to observe that this extra-thecal portion of the 
ceelenteron is, partially at least, divided into chambers by mesen- 
teries in the manner described above. 

The free edges of the primary and secondary mesenteries 
below their insertion into the stomodzum, and the free edges 
of the remaining mesenteries in their entire length, are fur- 
nished with the thickenings known as mesenterial filaments. 
In the primaries and secondaries the mesenterial filaments are 
very thick ; their epithelial cells are very long, attenuated, and 
crowded close together, showing an abundance of deeply- 
staining nuclei. Nematocysts are scanty; but I was able to 
distinguish a number of cells, which seemed to be of the same 
character as the gland-cells described by the Hertwigs in 
Actinia and Sagartia (15). In the other mesenteries the fila- 
ments are not so thick, and gland-cells are less abundant, 
nematocysts more so; in other respects their structure re- 
sembles that of the filaments of the primaries and secondaries. 
At the lower end of the free border of each mesentery is a 
bundle of much-coiled filaments, forming the structure known 
as an acontium.’ These structures in Fungia are strictly 


1 Professor Moseley has pointed out to me that the name acontium is 
used by Gosse and the Hertwigs to describe only those structures at the base 


ANATOMY OF THE MADREPORARIAN OCORAL FUNGIA. 305 


comparable with the mesenterial filaments, of which they 
appear to be a continuation. The lower free edge of the me- 
sentery appears to be prolonged into a long lamellar offset, 
which is much plicated, and surrounded along its free edge 
with the thickening which forms the main body of the acon- 
tium. This thickening has a similar histological structure to 
that of a mesenterial filament, differing from it only in the 
larger size of the epithelial cells of which it is composed, in the 
abundance of nematocysts, and the corresponding poverty of 
gland-cells. Fowler describes acontia of similar structure in 
Flabellum patagonichum, and states that they are pro- 
truded through cinclides in the peristome (9, p.14). Although 
I handled some hundreds of living Fungia I never saw the 
acontia protruded, either through the cinclides or through the 
mouth, but in some species of Mandrina, acontia of exactly 
similar structure to those above described were protruded 
through large cinclides on the peristome when the animal was 
irritated. 

According to Gosse (11) and the Hertwigs the acontia in 
Sagartia have the form of bunches of long filaments developed 
at the lower free edge of each mesentery, each filament being 
ribbon shaped, with one of its borders much thickened. Such 
acontia are protruded through cinclides in the body wall. The 
acontia observed by Fowler and myself are protruded in Fla- 
bellum and Meandrina through cinclides in the peristome, and 
appear to be more simple in structure, consisting of a much 
plicated off-set or prolongation of the lower free border of the 
mesentery, the edge of which is thickened in continuation with 
the thickening which forms the mesenterial filament above, 


of the mesentery which are in the form of a bunch of filaments. I have fol- 
lowed Fowler in extending the name to that mass of contorted filaments, 
which is generally known as the contorted mesenterial filaments. This I have 
done because (1) they differ in histological detail from the filament on the 
upper part of the mesentery in exactly the same manner that Gosse’s acontia 
differ. (2) They may be protruded through cinclides. (8) They are clearly 
a less differentiated condition of Gosse’s acontia, but not morphologically 
distinct from them. To those who adhere to Gosse’s original definition, the 
name as I use it in the text, would be incorrect. 


306 GILBERT C. BOURNE. 


but differing from this in histological detail. The more com- 
plicated and effective acontia of Sagartia are probably de- 
veloped from a simpler form, such as this. 

In Fungia the mesoglea appears to break up dendritically 
in the swelling of the acontium, instead of ending in a T-shaped 
swelling, as in other forms (vide fig. 12). 

The acontia of the tertiary and succeeding mesenteries lie 
coiled up in the exocceles at the bases of those mesenteries, and 
in section appear to fill up the greater part of those spaces 
(vide figs. 13 and 15). 

Since the septa are large compared with the interseptal 
loculi, and since the septa are always in the entocceles, it fol- 
lows that the two mesenteries forming a pair are pushed apart 
from one another, whilst the adjacent mesenteries of contiguous 
pairs lie close together. So much is this the case, that when 
a decalcified animal is cut across transversely the adjacent me- 
senteries of contiguous pairs appear from their position to form 
pairs, and in old specimens they may become fused together at 
a little distance from the periphery, as is shown in fig. 11. 

The Celenteron.—The celenteron is represented by the 
axial space lying below the stomodeum, the peripheral cham- 
bers known as exocceles and endocceles, and the extra-thecal 
space lying on the aboral surface between the theca and the 
external body wall. 

The axial portion of the celenteron is not definitely cireum- 
scribed. Above, it opens freely into the stomodzal invagina- 
tion; below, it is limited by the investments of the trabecular 
columella; at the sides it is partially limited by the thickened 
borders of the mesenteries above described. So far as it can 
be considered as a definite cavity it is no doubt the cavity in 
which digestion is chiefly effected, the process being carried 
out by the secretions of the gland-cells of the mesenterial 
filaments. 

The relations of the peripheral parts of the ccelenteron are 
difficult to understand in this, as in all other Madreporarian 
corals, but are further complicated in Fungia by the presence 
of synapticula. The ccelenteron is composed of all those 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 307 


chambers which are lined with endoderm, and if a cast be 
made of all those chambers it will represent the space occupied 
by the celenteron. Such a cast I have attempted to represent 
in fig. 16. The peripheral chambers of the ccelenteron are 
divided by the mesenteries into exoceles and entocceles ; in 
those corals in which, as in Fungia, all the septa are entoccelic, 
the entoceles are almost obliterated by the septa which rise 
up within them, but morphologically lie wholly outside them, 
since every part of the corallum is invested with its proper 
layers [viz. a layer of cells lying next to the calcareous sub- 
stance from which the latter is secreted (the calycoblasts of 
von Heider), a very thin layer of mesogloea, and a layer of 
endoderm], and is thus separated from the ccelenteron by 
the three layers of tissue which limit every part of the body. 
Thus, in a cast of the celenteron, the latter is seen to he 
broken up into wedges by the spaces which are occupied by 
the septa (vide fig. 16), and in Fungia these wedges are 
further perforated by the apertures through which pass the 
synapticula connecting adjacent septa. 

Further than this, outside the theca (which is basal and also 
perforate in Fungia), there lies a portion of the cclenteron, 
communicating with the intra-thecal chambers by canals which 
pass through the perforations in the theca, and, like the intra- 
thecal chambers, divided by the continuations of the mesen- 
teries into exocceles and entocceles (vide figs. 15 and 16, cw/.). 
These complicated relations cannot, I conceive, admit of rational 
explanation unless the theory of von Koch be admitted, namely, 
that the corallum is derived primitively from the basal ecto- 
derm, and that the theca is formed by the fused peripheral 
parts of the septa, which in fusing divide the mesenteries, and 
leave a portion of the coelenteron external to the theca. From 
his account of the development of Astroides calycularis 
(21) it appears that the skeleton first makes its appearance as 
a ring of calcareous nodules situated between the ecto- 
derm of the basal disc and the surface of attach- 
ment. As development proceeds radial folds of the ectoderm 
and mesoglea (mesoderm) are formed, beneath which are 


308 GILBERT C. BOURNE. 


lines of calcareous crystals; these are the first rudiments of 
the septa. Ata later stage the septa form proportionally high 
plates, over which the ectoderm is bent in the form of a fold, 
the septa begin to branch at their peripheral ends, and 
eventually these branches meet and fuse with one another to 
form the theca, which cuts the mesenteries in two portions 
and isolates the more peripheral part of the ccelenteron from 
the more central, the former being limited externally by the 
soft body wall, which at first extends down to the base of the 
theca. One might almost speak of the corallum as being 
pushed in from below, all the three body layers being invagi- 
nated to receive it. Eventually the ectoderm which is bent 
over the corallum, having the sole function of secreting cal- 
careous matter, comes to be represented by that layer of cells 
lying between the mesogloea and the corallum, to which von 
Heider has given the name of calycoblasts. In old specimens 
the external body wall becomes atrophied around the lower 
part of the calyx, where it is physiologically replaced by the 
theca, but it still holds its place as an investment of the upper 
part of the calyx (Randplatte of von Heider) (14). The young 
nurse-stock of Fungia, so long as it remains cup shaped, has 
all the characters of a Caryophyllia, and may be compared 
strictly with the young Astroides. Stutchbury (39) says of 
it, ‘So long as the young Fungia retains the form of a Caryo- 
phyllia it is entirely enveloped by the soft parts of the animal, 
but as the upper disc of the coral spreads out and assumes its 
characteristic form, the pedicle is left naked and the soft parts 
extend only to the line where the separation afterwards takes 
place.” In the “ Alert ” specimen in the British Museum the 
soft parts still extend to the base of the nurse-stalk, although 
the upper disc has begun to widen out. When the young 
Fungia separates from the nurse-stock a clean scar is left at 
the point of detachment, through which there is for a short 
time free communication to the interior. But the deposition 
of calcareous matter round the central ends of the septa soon 
blocks up this passage, and immediately afterwards the soft 
parts covering the theca (which is now nearly confined to the 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 309 


basal surface as in the adult) meet in the centre and fuse 
together, so that the primitively external corallum is now 
entirely covered over by soft tissues, and one can only predi- 
cate its origin from the fact that it is everywhere covered with 
three investing tissues, the ectoderm, now represented by the 
calycoblastic layer, the mesoglea, and the endoderm, to which 
I have above referred under the name of the skeletotrophic 
investments. That part of the coelenteron which in Fungia lies 
external to the theca on the aboral surface, is the same mor- 
‘phologically as the extra-thecal part of the ccelenteron described 
as existing around the upper part of the calyx in other corals 
by von Koch, von Heider, and Fowler. For further information 
on this interesting subject I must refer the reader to the 
published works of these three authors. 

The Stomodeum.—This is extremely short in Fungia. I 
was unable to trace the existence of gonidial grooves (siphono- 
glyphes) at its ends, though they no doubt exist. When alive 
the animal constantly closes the middle portion of its mouth, 
leaving small apertures at the extreme ends through which 
currents of water pass in and out. I did not determine 
whether these currents are constant in direction. 

Histology.—This is simple in character and does not differ 
in any essential from the Actinian type. 

The ectoderm of the peristome is composed of long columnar 
epithelial cells, whose inner ends are drawn out into fine pro- 
cesses which rest on the mesogloea ; each ectoderm cell has a 
distinct oval nucleus which stains deeply in borax carmine. 
Numerous smaller interstitial cells lie between the processes 
of the inner ends of the epithelial cells. Large nematocysts 
are embedded in the ectoderm ; they are especially abundant 
on the ectoderm of the tentacles, but excepting for this the 
histology of the tentacles is quite similar to that of the rest of 
the peristome. I could not distinguish more than one kind of 
nematocyst in Fungia. In every case the lower part of the 
thread is armed with a spiral line of spines ; when inverted the 
terminal end of the thread is coiled obliquely round the basal 
portion. The ectoderm of the aboral surface differs slightly 

VOL, XXVII, PART 3.—NEW SER. Z 


310 GILBERT C. BOURNE. 


from that of the peristome in that the epithelial cells compos- 
ing it are less columnar and more cubical, and it is scantily 
provided with nematocysts. 

Between the corallum and the mesoglcea there is invariably 
a layer of rounded, granular, soft-looking cells which do not 
stain easily; their nucleus is tolerably large and stains but 
faintly in borax carmine. From their position these are 
clearly equivalent to ectoderm cells; they are the calycoblasts 
(vide fig. 17, cy.}.. They are simple rounded cells, as described 
by their discoverer, von Heider ; I could find no trace of stria- 
tion in them as Sclater did in Stephanotrochus, nor does 
their shape agree with his account. 

Between the ectoderm and endoderm of the body wall, and 
between the two layers of endoderm which form each septum, 
lies a sheet of homogeneous tissue called by German authors 
“ Stutzlamelle,” by Englishmen “ mesoderm,” or sometimes 
“the supporting lamina.” I have called it the Mesoglea 
for reasons which are more conveniently given at the end of 
this paper. I could find no trace of structure in this layer in 
Fungia, though it is possible that the use of proper reagents in 
the fresh condition might have disclosed a fibrillar structure. It 
stains slightly with hematoxylin, not at all with borax carmine. 

The endoderm is composed throughout of a single layer of 
cubical cells with a tolerably large nucleus and a nucleolus. 
Presumably these cells bear cilia in the living animal. In 
many parts of the body, but particularly in the region of the 
insertion of the mesenteries, the endoderm is crowded with 
masses of rounded nucleated cells of peculiar appearance ; at 
first sight they might easily be mistaken for endoderm cells 
forming a layer several cells deep. When treated with iodine 
they give a blue colouration, so that there can be no doubt 
that they are symbiotic alge, which occur so plentifully in the 
endoderm of many Actiniz. I was unable to find any trace 
of gonads in the specimens which | examined. 

The study of the anatomy of Fungia justifies the position 
which has always been assigned to it, between the perforate 
and imperforate Madreporarians. The theca, it has been 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 311 


shown, is perforate in its more peripheral portions, imperforate 
in its central portion, and as age increases the imperforate 
area increases largely. The canals passing through the per- 
forate portion, and putting the intra-thecal in communication 
with the extra-thecal coelenteron are, no doubt, homologous 
with the system of canals described by Fowler in Rhodo- 
psammia parallela. I can offer no explanation of the 
origin and significance of the synapticula. Physiologically 
they seem to serve as stays or buttresses, giving solidity and 
coherence to the corallum. 

The most important result of my researches seems to me to 
be the strong evidence furnished in favour of von Koch’s 
theory of the formation of the skeleton in the Madreporaria, 
the evidence in favour of the existence of extra-thecal ccelen- 
teron being, as I think, particularly conclusive. 


The Mesoglea, Mesoderm, or Stitzlamelle in 
Celenterata. 


Throughout my paper I have used the name Mesoglea 
for the (structureless) supporting membrane which separates 
the ectoderm from the endoderm in Fungia, as in all the 
Ceelenterata. 

The names given to this layer by German authors are 
Stiitzlamelle, Zwischensubstanz, Gallertschichte, or Mesoderm. 
Among English authors the use of the name mesoderm has 
become general in describing it. Whilst the exact significance 
of this layer in the Coelenterata and its homology with the 
mesoblast of the higher Metazoa are, to say the least of it, far 
from being settled, it seems to me that the use of the name 
mesoderm is highly productive of confusion and error. 

The names ectoderm and endoderm, meaning simply outer 
and inner skin, were first given by Allmann to the outer and 
inner cell layers of the Ceelenterata (G. J. Allmann, “On the 
Anatomy and Physiology of Cordylophora,” ‘ Phil. Trans.,’ 
exlili, 1853), and had they always retained this their original 
signification there could have been no objection to the use of 


312 GILBERT C. BOURNE. 


the name mesoderm for the median layer of the Celenterate 
body. But, as the Hertwigs have pointed out very clearly, 
from the time that the primary germinal layers, the epiblast 
and hypoblast, of the higher Metazoa were first compared 
and homologised with the ectoderm and endoderm of the 
Ceelenterata, there has been an increasing tendency to use the 
names ectoderm and endoderm as the equivalents of epiblast 
and hypoblast ; and this is especially the case among German 
authors, with whom the use of the names epiblast, mesoblast, 
hypoblast for the germ layers of the embryo, has not found 
general acceptance. It followed that the name mesoderm 
came to be used in the same sense, or very nearly so, as meso- 
blast, instances being numerous among German authors, and 
not infrequent even among English authors, where the meso- 
derm of the germ or embryo is spoken of. The difficulty 
arising from the identical use of these two names was appre- 
ciated by the Hertwigs and by F. E. Schulze, who treated 
the subject at some length, each in their own way. F. E. 
Schulze asks the very pertinent question whether the name 
mesoderm can only be used in those cases in which a special 
layer of cells arises early, that is, before the development of 
tissues and organs, as a special germ layer; or whether one 
can speak of a mesoderm when a differentiation of a special 
middle layer of tissue from the outer or inner epithelial layer 
arises later and without the formation of a special germ layer. 
He concludes by drawing a distinction between triple-walled 
animals, such as the Celenterata, and those which have three 
germinal layers (viz. the higher Metazoa (Triploblastica) but 
not the Coelenterata), admitting at the same time that the 
Celenterates have not a mesoderm in the sense of a distinct 
layer of cells derived from either or both of the two primary 
germ layers before the latter show any differentiation into 
tissues or organs. He speaks of them as being “ dreischich- 
tige”’ but “ zweiblattrige.” The Hertwigs, in dealing with the 
difficulty, proposed to limit the use of the words ectoblast and 
entoblast (i.e. epiblast and hypoblast) to the germinal layers 
of the embryo, and to use the names ectoderm and endoderm 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 313 


to denote the outer and inner limiting layers of the adult 
body, whilst the name mesoderm should include all those tis- 
sues which lie between the two limiting layers above men- 
tioned. This nomenclature is very objectionable, and indeed 
has not met with very general acceptance. If limited to the 
Coelenterata it would be sufficiently expressive and consistent, 
but when applied to the higher groups of the Metazoa it be- 
comes utterly impossible of application. To begin with, it is 
hard to draw any sharp line between the external and internal 
limiting membranes in the higher Metazoa; in forms where 
the stomodeum and proctodzeum are derived from epiblastic 
invaginations, and form no inconsiderable part of the digestive 
tract, the confusion becomes complete. In the Isoyoda, for 
instance, nearly the whole of the digestive tract is formed from 
the stomodezum and proctodzeum ; thus, according to the Hert- 
wigs, this clearly epiblastic internal limiting layer would be 
called endoderm. In the Vertebrate phylum, also, the adult 
nervous system, clearly derived as it is from the epiblast, 
would, because it lies between the two limiting layers, come 
under the name of mesoderm. Moreover, it is an altogether 
unscientific and confusing method to classify tissues by their 
position in the adult rather than by their derivation from the 
primitive germ layers. 

The words ectoderm, mesoderm, endoderm, have become so 
universally used as the equivalents of epiblast, mesoblast, hy- 
poblast, that there is very little hope of their being now 
limited to the group of Coelenterata to which they were origi- 
nally applied, and this being the case we ought to consider 
how far the median supporting lamella of that phylum, the 
Stutzlamelle or Gallertschichte of German authors, is homolo- 
gous with the mesoblast of the higher Metazoa before apply- 
ing the name mesoderm to it. If it is not homologous, but is 
of a different nature, then some other name than mesoderm 
should be found for it, otherwise it will be confused with the 
true mesoblast. 

This opens two questions (1) What do we mean when we 
speak of a true mesoblast? (2) What are the characters of the 


314 GILBERT C. BOURNE. 


median lamella, and what is its origin in the Celenterate 
phylum ? 

This is not the place to enter into a discussion of the whole 
subject of the origin and significance of the germinal layers, 
which the first question introduces, but it may shortly be 
stated, without going very far wrong, that by mesoblast is 
meant a layer of undifferentiated cells, developed in the embryo 
before the differentiation of other organs or tissues, from either 
one or the other or both of the primary germ layers, the epi- 
blast and hypoblast. By mesoderm, or its adjective meso- 
dermic, are meant all such tissues in the adult as are clearly 
derived from the mesoblast. This is not the sense in which 
I should like to use the term, but a sense which has become 
inevitable from the usage of other authors. 

To this idea of mesoblast receut theories on the origin of 
metameric segmentation have added another highly important 
signification, and one which is of especial importance to the 
present question. In the majority of the higher Metazoa 
(Triploblastica) the mesoblast is understood, in part, to denote 
the limiting layer of the celom. The Platyhelminthes offer a 
difficulty to this conception in that they are not known to 
possess a true ceelom, and it is a question whether they ances- 
traily possessed one, or whether they are the surviving repre- 
sentatives of the triploblastic Metazoon in which the celom 
was not developed. From the analogy of the Discophora, and 
from other considerations, I am inclined to think it probable 
that future researches will prove that all the Triploblastica are 
ancestrally Coelomata, the presence of mesoblast implying the 
(ancestral) presence of a celom.! However this may be, in 


1 Tn the embryo of Leptoplana, the cells which will form the mesoblast are 
marked out very early, before the hypoblast and epiblast are definitely estab- 
lished. But it is noticeable that the mesoblast cells are split off from the 
four large cells which afterwards form the hypoblast, the epiblast having been 
already marked out by four smaller cells, which eventually increase in number 
and surround the mesoblast and hypoblast. I think that in this case the 
mesoblast may fairly be said to have a hypoblastic origin. I can see no 
objection to the view that this may be a very much abbreviated development, 
derived from a type in which the mesoblast arose as (hypoblastic) outgrowths 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 315 


all those forms in which a ccelom is recognised the division 
of the mesoblast into splanchnopleure and somatopleure, and 
its relation to the ccelom in limiting it, must enter largely into 
our conception of what is meant by the term mesoblast. 

The origin of the mesoblast is very various ; for information 
on this point I must refer the reader to Balfour’s ‘Comparative 
Embryology,’ vol. ii, p. 290, where a tabular account of its 
various modes of origin is given. From this table it will be 
seen that while instances of a mixed derivation of the meso- 
blast are not common, a purely epiblastic derivation is still 
more uncommon, occurring in fact only in the larva of Desor, 
Bonellia, and perhaps in Lumbricus trapezoides. A 
purely hypoblastic derivation is of frequent occurrence. It 
is generally admitted that part of the mesoblast, at any rate, 
was primitively derived from the epiblast ; that in many forms 
all traces of this derivation are lost has been explained by 
Lankester (26 and 27) by his theory of precocious segregation. 
On the other hand there is much evidence in favour of the view 
that the coelom is derived from archenteric diverticula, and 
that the limiting walls of the ceelom are in consequence de- 
rived from hypoblast. This is clearly the case in several 
groups; in others there is reason to believe that the origin of 
the mesoblast as ingrowths from the lips of the blastopore is 
an abbreviation of development, and that in the ancestors of 
the groups in which this occurs the mesoblast took its rise 
from the walls of outgrowths of the archenteron. 

It is assumed that the triploblastic Metazoa took their origin 
from the diploblastic Metazoa, as the Ccelenterates have been 
called (I leave the Dicyemidz and Orthonectide out of the 
question). The Celenterate, represented by an Actinia, already 
in the elongation of its mouth and the arrangement of its 
mesenteries, shows a tendency to bilateral symmetry. It is 
supposed that this tendency is further increased, that the radial 
symmetry of the peripheral chambers is replaced by a bilateral 
symmetry, metamerically repeated along the long axis formed 
of the archenteron. If this were admitted it would admit the Turbellaria 
among the Coelomata. 


316 GILBERT ©. BOURNE. 


by the mouth; and, finally, it is supposed that these chambers 
are the equivalents of the paired archenteric diverticula seen 
in the embryo of Amphioxus, outgrowths which are eventually 
nipped off to form the mesoblastic somites, the walls of which 
constitute the mesoblast, the cavities the celom. If the facts 
adduced in support of this theory are not numerous enough to 
warrant our giving unqualified consent to it, there is at least a 
great deal to be said in its favour. What is important to the 
present purpose is, that if it be accepted as a probability, and 
if further it be admitted as a general statement that, throughout 
the Triploblastica this is the origin of the ccelom, then by far 
the greater part of what we understand by mesoblast in 
the Triploblastica is homologous, not with the supporting 
lamina, the Stiitzlamelle, of the Coelenterata, but with the 
endoderm lining the cavities of the entoceles and exocceles. 

If we seek for an explanation of the supporting lamina in its 
origin we do not get a very satisfactory answer. Kowalevsky 
(25) describes the development of a jelly-like interstitial tissue 
between the cells of the inner layer of the thickened ectoderm 
of the larve of certain Alcyonarians. The inner cells eventu- 
ally lose their primitive shape, become star shaped or spindle 
shaped, and are separated from one another by an interstitial, 
jelly-like substance. The outer ectoderm cells form a plaster 
epithelium, which bounds the external surface of the animal. 
In this case there is no doubt that the interstitial tissue, usually 
called the mesoderm of the adult, is derived from the epiblast. 
We have not so exact an account of the development of the 
supporting lamina in any other group of the Ccelenterata. 
Fol (10) describes the appearance of a clear transparent jelly 
between the two primary layers in Geryonia, but is unable to 
state which layer it is derived from. Claus (2) is no more 
explicit on the same subject in his work on Charybdea 
marsupialis. Metschnikoff (‘Studien ber die Entwicklung 
der Medusen und Siphonophoren’) speaks of a similar jelly- 
like substance making its appearance, but he does not say 
how. Chun gives no further account of the origin of the jelly- 
like substance in Ctenophora ; but, according to a recent paper 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 317 


oy Metschnikoff (29), mesoblast cells are marked off in the 
embryo of Callianira bialata before any tissues are de- 
veloped, but after the complete separation of ectoderm from 
endoderm. He says, further, that the case is the same in 
Beroe and Cydippe. From the account given the segmentation 
appears to be very peculiar. If the formation of mesoderm is 
correctly described it would mark off the Ctenophora very 
sharply from the remainder of the Coelenterata. Metschnikoff, 
however, for reasons which are not quite clear to me, refuses 
to this layer the name of mesoderm. 

No account is given of the origin of the supporting lamina 
in the Hydrozoa, nor in the Actinaria. 

The only certain knowledge, then, that we have about the 
origin of the jelly-like layer is that in the Aleyonarians Sym- 
podium coralloides and Clavularia crassa the inter- 
stitial substance is derived from the epiblast, and the cells in 
it are epiblast cells. Thus the origin of the jelly-like support- 
ing lamina of Ccelenterata gives no direct evidence of its 
homology with the mesoblast of the Triploblastica, but rather 
the contrary, for the latter is, as we have seen, rather connected 
with the hypoblast than with the epiblast. 

The characters of the supporting lamina in the Ceelenterata 
are as follows : 

In the Hydromeduse it is a fine, apparently structureless 
membrane, interposed between ectoderm and endoderm. When 
treated with suitable reagents it exhibits a fibrillar arrange- 
ment; it contains no cells. 

In the Siphonophora it is a structureless jelly-like substance. 

In the Scyphomeduse (Charybdea) the jelly-like substance 
is abundant, forming the bulk of the umbrella; it contains no 
cells, but has a fibrillar arrangement. 

In the Discomedusz (Aurelia) the gelatinous matrix contains 
a number of oval or star-shaped cells, anastomosing with one 
another, and mainly derived from the hypoblast. 

In the Ctenophora it contains muscular stellate cells, mostly 
of epiblastic origin, though some are stated by Chun to come 
from the hypoblast. 


318 GILBERT C. BOURNE. 


According to Metschnikoff, in certain forms these cells are 
marked out early in the embryo. 

In Alcyonaria cells in which the calcareous spicules forming 
the skeleton are developed lie embedded in a gelatinous 
matrix. 

In Actinaria and Madreporaria the supporting lamina is 
fibrillar, and contains a few connective-tissue cells. Some- 
times muscular fibres are embedded in it (Hertwigs, 15). 

It is obvious that in none of these cases (except the doubtful 
case of the Ctenophora, as described by Metschuikoff) is there 
anything like a true mesoblast, in the sense of a cellular layer 
marked out early in the embryo. But there is a third layer 
of tissue in the body, interposed between the ectoderm and 
endoderm, which in some cases does and in others does not 
contain cells, but the bulk of which in all cases is a gelatinous 
matrix. This third layer assumes immense development in 
some forms, e. g. the Discomedusz and Alcyonaria, so that it 
is wholly misleading to call Ceelenterates two-layered animals. 
They are certainly three-layered—anyone can see that by 
cutting a section across any one of them—but the question is, 
Can they possibly be called triploblastic ? Can they be said to 
possess a third germinal layer—a mesoblast? - 

It is sometimes argued that the mesoblast is, after all, 
nothing more than a layer of cells developed from one or both 
of the two primary layers; that the middle layer of the 
Coelenterata contains cells in many instances; that these cells 
differ from the mesoblast cells of other forms only in the date 
of their taking up their position in the third layer, the former 
being separated off from -the primary layers in the embryo, the 
latter in the adult ; that this difference in time is not essential ; 
and that therefore the cell-containing middle layer in the 
Alcyonaria, for example, has as much right to be called a 
mesoblast as that of any other animal. 

I cannot but think that this style of argument leads to a 
want of precision of ideas, and to a vagueness in the definition 
of the thing signified. In a great number of forms the middle 
layer contains no cellular element; it is a nearly structureless 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 319 


gelatinous matter, poured in, as it were, between the ecto- 
derm and endoderm to serve as a support for those tissues and 
to give coherence and consistency to the body of the animal. 
Where no cells are present (Hydromeduse, Charybdcea), a 
third cell layer, a mesoblast, obviously cannot be spoken of. 
In other forms we find cells derived from one or other of the 
primary layers wandering into the gelatinous substance after 
the formation of the latter, and retaining a constant position 
there (Discomeduse, Actinaria). ‘These cells ought to be con- 
sidered epiblastic or hypoblastic according to their origin, just 
as much as the central nervous system of the Vertebrata, 
entirely surrounded by mesoblastic structures, is considered as 
part of the epiblast. 

In the Alcyonaria the separation of the epiblast cells which 
are destined to become the skeletogenous cells takes place 
contemporaneously with the secretion of the gelatinous matrix 
in which they are embedded. None the more is the layer thus 
formed entitled to be called a germinal layer, or even a 
separate cell layer, though a step has been made towards the 
latter. The cells forming the skeleton are clearly epiblastic in 
origin, are derived from the epiblast after its demarcation, and 
are properly considered as its derivatives. The Alcyonarian 
skeleton is really of epiblastic origin. 

In a further stage the cells which, in Ctenophora, are 
destined to become stellate muscular cells embedded in the 
gelatinous matrix of the supporting lamina, are, according to 
Metschnikoff, marked out early in the embryo, at a period 
when the endoderm is scarcely covered in by the ectoderm. 
This is nearly the same thing as the formation of embryonic 
mesoblast, and foreshadows it, but the ultimate history of the 
cells ought to preclude our calling them mesoblastic. 

I do not wish to assert that the supporting lamina of Ce- 
lenterata is not represented in the mesoblast of Coelomata; it 
is highly probable that it is. The Aleyonaria and Ctenophora 
are good examples of the tendency which muscular and con- 
nective-tissue cells, primitively belonging to the external and 
internal limiting layers, have to separate themselves from their 


320 GILBERT C. BOURNE. 


original position and to become more deeply situated. When 
such cells form a layer situated between epiblast and hypo- 
blast they constitute a third layer, a mesoblast. But in point 
of fact we have no positive evidence that such a simple third 
layer exists without the ancestral coexistence of a celom. I 
have already given reasons for believing that such a simple me- 
soblast does not obtain in the Platyhelminthes. The nearest 
approach to it is in the Ctenophora, and in them the stellate 
cells are homologous, not with the whole of the mesoblast of 
the Celomata, but only with a part of it, viz. that part which 
may be supposed to have originated independently of the 
celom, but of the origin of which the traces are, in the 
majority of cases, suppressed. 

The part is not the whole, nor should the name denoting the 
whole be given to the part, for which reason I object to 
giving the name mesoblast, or its equivalent mesoderm, to the 
supporting lamina of Ccelenterata. I have proposed for it the 
name Mesogloa, a name which was suggested to me by 
Professor Lankester in the course of a conversation on this 
subject, and which corresponds exactly to the Gallertlage of 
German authors. Its meaning, “ middle jelly,” has particular 
reference to the Medusze, of whose bodies it forms the greater 
part. 

Before concluding this paper I have to express my obliga- 
tions to Professor Moseley, who kindly permitted me to use 
the Oxford laboratory during my studies, and assisted me with 
much valuable advice. Also to my friends Mr. Hatchett 
Jackson, and Mr. W. Baldwin Spencer of Oxford, who helped 
me in many ways. 


ANATOMY OF THE MADREPORARIAN CORAL FUNGIA. 321 


List oF Works REFERRED TO. 


1. F. M. Batrour.—‘ Comparative Embryology,’ 1880, 2 vols. 


2. C. Craus.—* Untersuchungen tiber Charybdca marsupialis,” ‘ Ar- 


beit. aus. Zool. Instit. Wien,’ Bd. i, p. 221. 


. J. D. Dana.—‘ Report on Zoophytes of the Wilkes’ Exploring Expedi- 


tion,’ 1846. 


4, J. D. Dana.—‘ Corals and Coral Islands,’ 1872. 


18. 


20. 


21 


. 


. P. Martin Duncay.— Observations on the Madreporarian Family the 


Fungide,” ‘Journ. Linn, Soc.,’ xvii, p. 187. 


. H. ve Lacaze Dututers.—“ Développement des Coralliaires,” ‘ Arch. de 


Zool. Exper. et gén.,’ tom. i, 1872. 


. H. pe Lacaze Duruters.—“ Développement des Coralliaires,” ‘ Arch. 


de Zool. Exper. et gén.,’ tom. ii, 1873. 


. Escuscnoi1z.— Isis,’ 1825, p. 476, pl. 5, fig. 19. 
. G. H. FowLrrer.—“ The Anatomy of the Madreporaria,” I, ‘ Quart. Journ. 


Micr. Sci.,’ 1885, p. 577. 


. H. Fou.—“ Die erste Entwicklung der Geryonideneies,” ‘ Jenaische 


Zeitschrift,’ vii, p. 471. 


. P. H. Gossr.—‘ Actinologia Britannica,’ 1860. 
. Haacnze.—* Blastologie der Korallen,” ‘Jenaische Zeitschrift,’ 1879. 


. A. von Hemper.—“ Sagartia troglodytes,” ‘Sitz. der Kais. Akad. 


zum Wien,’ lxxv, Abth. i, p. 367. 


. A. von Hurprr.— Die Gattung Cladocora,” ‘Sitz. der Kais. Akad. 


Wiss.,’ 1881. 


. O. anp R. Herrwie.— Die Actinien,’ Jena, 1879. 
. HoLttarp.—‘ These de la faculté des Sciences de Paris,’ Sorbonne, 1848. 
. G. von Kocu.— Bemerkungen iiber das Skelet der Korallen,” ‘ Morph. 


Jahrb.,’ v, p. 316; Extract in ‘ Proc. Zool. Soc.,’ 1880, p. 24. 

G. von Kocu.—* Notizen iiber Korallen,’ ‘Morph. Jahrb.,’ vi, p. 355. 

G. von Kocu.— Mittheilungen iiber Coelenteraten,” ‘Jenaische Zeit- 
schrift,’ xi. 

G. von Kocu.—“ Mittheilungen tiber das Kalkskelet der Madreporarien,” 
‘Morph. Jahrb.,’ viii, p. 85; Abstract in ‘Journ. Roy. Micr. Soc.’ 
(2), ii, p. 795. 

G. von Kocu.—“ Ueber die Entwicklung der Kalkskelettes von As- 


troides calycularis,” ‘Mitth. aus der Stat. Zool. Neapel,’ iii, 
1882, p. 284. 


322 GILBERT C. BOURNE. 


22. 
23. 


24 


G. von Kocu.—‘ Biol. Centralblatt,’ ii, 1882. 


G. von Kocu.—‘ Ueber das Verhaltniss von Skelet und Weichtheile be 
den Madreporen,” ‘ Morph. Jahrb.,’ xii, p. 154, 1886. 


. A. KonitKer.—‘ Jeones Histologie,’ 2te Abth., Heft i, p. 116. 


25. A. Kowatevsky.—* Zur Entwicklungsgeschichte der Alcyoniden,” ‘ Zool. 


Anzeig.,’ 2te Jahrg., No. 38. 


96. E. Ray LANKEsTER.—‘ Ann. Mag. Nat. Hist.,’ xi, p. 321, 1873. 
27. HE. Ray Lanxester.—‘ Quart. Journ. Micr. Sci.,’ New Series, xvii, 


28 


29 


30 
3l 


32. 


33 
34 


35 


36 
37 


p. 399. 

. Ex. MetscunrKorr.— Spongeologische Studien,” ‘ Zeit. fiir wiss. Zool., 
xxxil, 1879. 

. Ev. Metscunixorr.— Vergleichend Embryologische Studien,” ‘Zeit. 
fur wiss. Zool.,’ xlii, 1885. 

. Mitnr-Epwarps anp Haimre.—‘ Histoire des Coralliaires,’ Paris, 1860. 


. H. N. Mosrtry.—‘‘ On Seriatopora and Pocillopora,” ‘Quart. Journ. 
Micr. Sci.,” New Series, 1882, p. 391. 


H. N. Mosetry.— “ Challenger ” Reports,’ “ Zoology,” vol. ii, “ Report 
on the Deep Sea Madreporaria.” 


. Quoy anp Garmard.—‘ Voyage de l’Astrolabe,’ vol. ii, pl. xiv. 


. F. E. Scuvutze.— Entwickelung der Sycandra raphanus,” ‘Zeit. 
fiir wiss. Zool.,’ xxv, 1875, Suppl. 


. FE. E. Scnvrze.— Untersuchungen tiber den Bau und die Entwicklung 
der Spongien,” ‘ Zeit. fiir wiss. Zool.,’ Bd. xxxi, p. 262. 


. SCHNEIDER AND RottrEKEN.—‘ Ann. Mag. Nat. Hist.,’ vii, 1871. 


. W. L. Sctater.— On a Madreporarian Coral of the genus Stephano- 
trochus,” ‘ Proc. Zool. Soc.,’ 1866. 


38. C. Semper.— Generationswechsel bei Steinkorallen,” ‘Zeit. fiir wiss 


39 


Zool.,’ xxii, p. 235. 
. SturcHBuRY.— Trans. Linn. Soe.,’ vol. xvi, 1830, p. 494. 


40. ALLEN THomson.— Report Brit. Assoc., 1877, ‘ President’s Address.’” 


4] 


1G. H. Fow.er.— Anatomy of the Madreporatia,” ii, ‘Quart. Journ. 
Micr. Sci.,’ xxvii. 


1 Received since this paper was sent up to the press. 


ANATOMY OF TRE MADREPORARIAN CORAL FUNGIA. 3239 


DESCRIPTION OF PLATES XXIII, XXIV, & XXV. 


Illustrating Mr. Gilbert C. Bourne’s Paper on ‘‘ The Anatomy 
of the Madreporarian Coral Fungia.” 


Fie. 1. Ad naturam.—General view of Fungia dentata, showing the ar- 
rangement of the tentacles and their relation to the septa. 

Fie. 2.—Diagram in illustration to Fig. 1. m. Mouth. ¢. Tentacles. 
1, 2, 3, 4, 5, 6. Septa (or tentacles) of the first, second, third order, &c. 
Primary septa coloured red, secondary blue, tertiary green, quaternary yellow, 
quinary, &c., black. 

Fics. 3—8.—Diagrammatic, from Stutchbury, Semper, and Moseley. 

Fig. 3 is a young nurse-stock of Fungia immediately after fixation. 
p. Peristome. ¢h. Theca. 4. Base. 

Fig. 4. The same, in which the’peristome has commenced to widen out 
and assume its characteristic form. 

Fig. 5. Nurse-stock of Fungia; an absorption of calcareous matter has 
taken place along the line £ where the young Fungia will separate from 
the nurse-stock. 

Fig. 6. Young Fungia shortly after separation from the nurse-stock. 
The peristome has grown greatly in excess of the theca. 

Fig. 7. The same more advanced, showing the increasing size of the 
peristome. 

Fig. 8. The adult Fungia. 

Fic. 9.—Diagram showing a pair of mesenteries and their relation to the 
investing tissues of the corallum. The mesentery to the left is seen to be 
divided by a synapticulum into a central and a peripheral portion. ec. Kcto- 
derm. m. Mesogloea of the body wall. ed. Endoderm of the body wall. 
m'. Mesoglea of the mesenteries. m’. Mesoglaea of the skeletotrophic 
tissues. ed’. Endoderm of the mesenteries. ed’. Endoderm of the skeleto- 
trophic tissues. ms. Muscles. cy. Calycoblasts. ed. Nematocysts. m./. 
Mesenterial filaments. sb. a. Symbiotic alge. syz. Perforation through 
which a synapticulum passes. 

Fic. 10. Ad naturam.—A mesentery of Fungia dentata. ac. Acontia. 
y. m. s. Longitudinal muscle-fibres, the remainder of the lettering as before. 
The shaded part represents that part of the mesentery which is formed of 
mesoderm and its overlying muscular fibres. The dotted lines show the 
tubes (parts of the ccelenteron) bounded by endoderm of the skeletotrophic 
investment which run down between the synapticula, to the mesogloea of 
which thickened prolongations of the mesoglcea of the mesenteries are attached, 
as shown in 2. 


324 GILBERT ©. BOURNE. 


Fic. 1]. Ad naturam.—Two contiguous mesenteries not belonging to the 
same pair, from an adult Fungia, showing their tendency to fuse together in 
old specimens. Lettering as before. 

Fie. 12. Ad naturam.—Section through an acontium, showing the dendritic 
branching of the mesoderm in the acontium, the large nematocysts ed., and 
the gland-cells gd. 

Fic. 13.—Diagrammatic horizontal section through the corallum and soft 
parts of Fungia dentata. The corallum is shaded, the mesoglcea is repre- 
sented by a black line. The calycoblasts are omitted for simplicity’s sake. 
The septa are seen to lie in the entoceles, the cclenteron being broken up 
by the synapticula into a number of parallel tubes, in each of which are seen 
the mesoglea thickenings 2, which give attachment to the vertical muscle- 
fibres. The acontia of the lower orders of mesenteries are seen coiled up in 
the celenteron. m¢. Mesenteries. syz. Synapticula. 

Fic. 14. Ad naturam.—Section through the body wall of F. dentata. 
ed. Endoderm. m. Mesogloea. ec. Ectoderm. z. Interstitial cells. 

Fic. 15.—Diagrammatic vertical section through the peripheral part of F. 
dentata. ec. p. Ectoderm of the peristome. ec. 6. Ectoderm of the base. 
The shading and lettering as in Fig. 13. ¢h. Theca. ev. Exoceele. ent. Ento- 
ccele external to theca. 

Fic. 16.—Diagram illustrating the relations of the celenteron to the 
corallum. The drawing may be considered as a cast of all the cavities lined 
by endoderm. At sp. are shown the spaces occupied by the septa, by which 
the body is broken up into a number of wedge-shaped masses. The rows of 
parallel elongate perforations show the position of the synapticula. At c@l. is 
seen that part of the body cavity which lies outside the perforate theca. 
th. Perforations for theca. syz. Perforations for synapticula. 

Fic. 17.—A portion of the skeletotrophic investment highly magnified. 
ed. Endoderm. m. Mesoglea. cy. Calycoblasts 


bo 
Or 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 8 


On Some Points in the Development of 
Petromyzon fluviatilis.! 


By 
Arthur E. Shipley, B.A., 


Christ’s College, Cambridge, Demonstrator of Comparative Anatomy in the 
University. 


With Plates XXVI, XXVII, XXVIII, and XXIX. 


Tue development of the Lamprey has occupied the attention 
of many embryologists during the last fifty years. Of these we 
owe the most complete accounts of the changes through which 
the egg passes to Max Schultze, Owsjannikow, Calberla, 
Scott, Balfour, and Dohrn. I have recently worked through 
the development of Petromyzon again, and worked out the 
origin of several organs which have hitherto been incompletely 
known. In many of the most important points my researches 
confirm those of the earlier observers, and to these I have only 
referred at such length as would make the account intelli- 
gible; in others, such as the persistence of the blastopore, the 
origin of the ventral mesoblast, &c., I differ from previous 
descriptions; and some points, such as the development of the 
heart, of the parts of the brain and cranial nerves, are worked 
out for the first time. 

The material for this article was obtained by artificially 

1 The differences between Petromyzon planeri and fluviatilis are so 
slight, and the intermediate forms so common, that I am disposed to follow 
Anton Schneider, and to consider them as varieties of the same species. This 


species may conveniently retain the name fluviatilis, as opposed to the 
larger form Petromyzon marinus. 


VOL, XXVII, PART 3 ——NEW SER. AA 


326 ARTHUR E. SHIPLEY. 


fertilising the eggs of the ripe female Lampern, hatching the 
larve out, and rearing them in confinement. The breeding 
time is during the latter half of April and the beginning of 
May. 

The generative products of both male and female were 
squeezed into glass vessels containing fresh water, and the 
contents slightly stirred. The eggs at once adhered to the 
bottom and sides of the vessel, and were left undisturbed for 
three or four hours. The water was then poured off and a 
fresh supply added. This was kept thoroughly aerated by 
means of Semper’s aerating apparatus. The number of eggs 
fertilised were about 70 per cent. of the total, though some 
hatches were much more successful than others, The rate of 
segmentation and development also varied greatly, being 
influenced by the temperature and manner of aeration. The 
unfertilised eggs very soon could be distinguished from the 
fertilized ; they developed great cavities or craters and were 
soon attacked by fungi. The fungus, however, rarely affected 
the developing eggs. 

The spermatozoa have elongated heads, pointed at their free 
end, but thicker at the end from which the tail arises (fig. 1). 
Their length is from 35 to 40 micro. mm., of which the head 
forms 8 micro.mm. They move actively about in the water, 
until they come into contact with an ovum. They enter the 
egg through a micropyle, and Calberla states that the head 
only enters the protoplasm of the ovum, the tail remaining 
fixed in the micropyle, thus hindering the entrance of other 
spermatozoa. 

The eggs are almost spherical, with a diameter of about a 
millimetre. On contact with water the outer cell-membrane 
swells up and forms a gelatinous coating, by means of which 
the eggs adhere to the bottom and sides of the vessel. This 
gelatinous envelope is of considerable thickness ; it ultimately 
disappears shortly before the embryo is hatched. Sections 
through unfertilised eggs show the protoplasm crowded with 
oval yolk granules, which stain deeply. These yolk granules 
vary in size, and this is very evident in the segmenting eggs, 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. S27 


where the yolk granules in the more quickly dividing upper 
pole are much smaller than those in the more inert lower pole. 
An attempt has been made to show that those parts of the 
unsegmented egg containing the smaller granules is destined 
to form the epiblastic parts of the embryo (16).! This view 
seems to me to need confirmation. The small size of the yolk 
granules in the epiblast might be due to the more rapid 
division of these cells, causing a more rapid consumption of the 
food-yolk. 

The unusually deep staining which the yolk granules assume 
very materially increases the difficulty of observation. EHspe- 
cially in the earlier stages of development the cell limits and 
nuclei were rendered obscure by the masses of deeply stained 
yolk granules. 

As previous observers have stated, there are two polar bodies 
extruded one after the other. After fertilization the egg con- 
tracts, leaving a cavity between it and the egg membrane. 

The first furrow appears about the fourth hour; it appears 
first in the upper pole and spreads round the egg on each side. 
Calberla states that the micropyle becomes at first oval, then 
slit like, and finally passes over into the primary furrow. I 
have not been able to observe this process in my eggs. He 
further states that the first furrow divides the egg into two 
unequal parts, a large epiblastic and a small hypoblastic ; the 
smaller of these divides subsequently more rapidly than the 
latter. Thus, according to him, the first furrow would cor- 
respond with the first equatorial one in the Frog’s ovum. 
Scott, although he had no fresh material to work with, was 
able to correct this, and, as the latter suggests, Calberla was 
probably misled by cases of abnormal segmentation. Many 
of the eggs which apparently had not been fertilized divided 
by one, two, and sometimes three furrows, and when this 
took place the furrows were nearly always abnormal in 
position. 

The second furrow is vertical and at right angles to the 
first, and also appears first in the upper pole. The third is 


1 The figures in brackets refer to the list of papers at the end. 


328 ARTHUR E. SHIPLEY. 


equatorial, but nearer the upper than the lower pole. After 
its appearance the epiblastic half is separated from the hypo- 
blastic or yolk-bearing half (fig. 2). 

The external phenomena of segmentation have been accu- 
rately described by Max Schultze, with the exception of 
the next stage. After the first equatorial furrow he describes 
two more in the same plane, but in my eggs the equatorial 
furrow was followed by two vertical lines, which appear at 
first in the upper pole exactly as they do in the Frog’s ovum 
(fig. 3). These are followed by two more equatorial furrows 
which divide the egg into thirty-two segments. After this the 
segments of the epiblastic pole divide more rapidly than those 
of the lower. 

Fig. 5 represents a transverse section through an egg thirty- 
six hours after fertilisation. In this stage it is a_blasto- 
sphere, with a segmentation cavity enclosed by a single layer 
of cells except along the line where the epiblastic and hypo- 
blastic cells join. Here the layer is two cells thick. The 
nuclei of the large cells appear small, but it must be recollected 
that the amount of protoplasm is very small compared to the 
yolk. The latter has been omitted for the sake of clearness. 
Fig. 6 is taken from an egg twelve hours later. Here both 
the roof and floor of the segmentation cavity are many cells 
thick. A similar stage is found in the Frog’s ovum, but there 
is this difference between the two. In the Frog’s egg the 
whole of the roof of the segmentation cavity forms epiblast ; 
in the Lamprey it is only the outermost layer. The following 
stages are accompanied by a thinning out of the roof of the 
segmentation cavity, and are represented in figs. 7 and 8. 
On this point my observations tend to confirm those of 
Calberla, and are opposed to those of Schultze, who found 
a many-layered roof to the segmentation cavity just before 
invagination. The thinning out appears to be brought about 
by the inner cells of the roof passing round to the sides and 
floor of the segmentation cavity. Just before the invagination 
which forms the gastrula the roof of the segmentation cavity 
consists of a single layer of cells; the segmentation cavity is 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 329 


large and occupies the whole of the upper hemisphere, whilst 
the lower hemisphere is solid and consists of larger cells, which 
we may speak of as yolk-cells. The most external layer of 
these consists of rather columnar cells. These latter cells 
socn become smaller than the inner yolk-cells, and about the 
time of invagination the whole egg is enclosed by a layer of 
small columnar cells, the epiblast. This is brought about by 
the conversion of the outermost row of yolk-cells into small 
columnar cells. As Balfour has shown, this takes place 
latest in the region of the blastopore. 

The invagination which forms the mesenteron commences 
about 180 hours after fertilisation ; it commences at one side 
of the equator of the egg, in the region where the single layer 
of epiblast cells passes into the yolk-cells (fig. 9). The invagi- 
nation at first has a wide-arched slit-like opening, but this 
soon narrows into a small circular pore (fig. 4). The segmen- 
tation cavity is gradually obliterated by the invaginated cells. 
These from the first enclose a cavity, the mesenteron. In this 
respect the formation of the gastrula is like that of Amphioxus, 
and differs from that of the Amphibia, where the mesenteron 
appears later as a splitting underneath the invaginated cells. 
The presence of a large amount of food-yolk causes the invagi- 
nated cells to be pushed dorsalwards. The mesenteron 
extends as a tubular cavity about two thirds round the 
embryo. Its dorsal wall is composed of columnar cells resem- 
bling those of the general epiblast ; the cells forming the floor 
have the same characters as the yolk-cells (fig. 12). The 
dorsal side of the mesenteron lies in immediate contact with 
the under surface of the epiblast throughcut its entire length. 
In this respect again the Lamprey differs from the Frog, where 
the invaginated hypoblast cuts off a mass of cells on its dorsal 
side, which subsequently forms the mesoblast. 

The mesoblast now appears by the differentiation of two 
bands of these yolk-cells, which lie in the angles formed by 
the mesenteron and the epiblast (fig. 12). This differentiation 
commences in front and is continued backward. The two 
bands of mesoblast are separated dorsally by the juxtaposition 


300 ARTHUR E. SHIPLEY. 


of the dorsal wall of the mesenteron and the epiblast, and 
ventrally by the hypoblastic yolk-cells which are in contact 
with the epiblast over two thirds of the embryo. Subse- 
quently, but at a much later date, the mesoblast is completed 
ventrally by the downgrowth on each side of these mesoblastic 
plates. This takes place at a comparatively early stage in the 
head and that part of the trunk lying in front of the liver. 
In the posterior part, which remains swollen with yolk, the 
ventral completion of the mesoblast is delayed. 

The first formation of the mesoblastic plates appears to 
take place by a differentiation of the hypoblastic yolk-cells in 
situ, and not from invaginated cells (figs. 12 and 13). The 
subsequent downward growth is brought about by the cells 
proliferating along the free ventral edge of the mesoblast, 
these cells then growing ventralwards, pushing their way 
between the yolk-cells and epiblast (fig. 11). 

This account of the origin of the mesoblast differs from that 
given by Scott. He describes the mesoblast as arising from 
two sources—(1) cells which are derived from the invagina- 
tion of the blastoderm, (2) the outermost layer of the hypo- 
blastic yolk-cells, which, according to Scott, split off from 
the remainder, and form a ventral sheet which completes the 
mesoblast in that side of the body. The mesoblast in the 
head is derived only from the first source, as by the time it is 
completed ventrally the head is raised above the yolk-con- 
taining parts. 

Shortly before the development of the head fold raises the 
head from the yolk-bearing part of the embryo, the neural 
plate becomes evident in the exterior. It extends as alow 
ridge from the anterior lip of the blastopore to just in front of 
the blind anterior end of the mesenteron, over two thirds of 
the circumference of the embryo. 

The blastopore is always visible at the posterior end of the 
neural plate. Schultze has given a very complete set of figures 
of the exterior of the embryo. As his figures show, with the 
elongation of the embryo the anterior end curves round and 
overlaps the posterior, thus obscuring the blastopore. Fig. 10 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 331 


is a section taken through the blastopore and the head soon 
after the head is raised above the general level of the egg. 

From his observations of the embryo as a whole, Schultze 
came to the conclusion that the blastopore persisted and gave 
rise to the anus, and he was supported in this view by Calberla. 
Later observers, however, who have studied the development 
of the Lamprey by means of sections, have maintained 
Benecke’s view that the blastopore disappears. Scott 
describes the neural canal enclosing the blastopore and figures 
the neurenteric canal thus formed. He describes the formation 
of the anus, from a protuberance of the alimentary canal 
which approaches the epidermis and breaks through about the 
twentieth day. Balfour also states that the blastopore closes 
and does not form the permanent anus. 

My observations of the embryo as an opaque object lead me 
to the belief that the blastopore remained open. In this I 
have been confirmed by sections taken through a series of 
embryos preserved at intervals of a few hours. Primarily the 
blastopore hes at the posterior dorsal end of the embryo 
(fig. 4), but by the growth of the dorsal surface and the forma- 
tion of the tail it comes to occupy a position in the ventral 
surface. What was the anterior lip in the first position comes 
to be the posterior in the latter. 

Fig. 4 is a view of the embryo twelve days old, as an opaque 
object, showing the blastopore at the posterior end of the 
neural ridge. Fig. 16 is an oblique section through an embryo 
about two days older, showing the nervous cord just separated 
from the skin, and the notochord both continuing behind the 
blastopore. 

Scott was of opinion that the lumen of the invaginated 
mesenteron persisted only in the fore-gut. Soon after the in- 
vagination is completed this part of the alimentary canal lying 
in the head and neck becomes raised from the rest of the 
embryo. It is thus separated off from the yolk-cells, and the 
hypoblastic cells in this region soon assume a definite columnar 
appearance, though they continue to contain yolk granules for 
some days. This region extends to where the liver appears 


302 ARTHUR E. SHIPLEY. 


in older embryos. A similar change in the cells lining the 
mesenteron takes place at its posterior end. The cells lining 
the blastopore and extending for some distance into the ali- 
mentary canal assume very early a columnar appearance and 
appear perfectly continuous with the columnar epiblast (figs. 
10, 14, and 16.) The cells lining the hind-gut retain the 
character of the yolk-cells for a long time, but the lumen of 
the mesenteron in this region never disappears, as Scott and 
Calberla thought. The lumen of the alimentary canal, with 
the exception of the mouth, is derived directly from the inva- 
gination which forms the gastrula, and no part of it is ever 
obliterated in the course of development. 

A similar persistence of the blastopore to form the anus appears 
to be common in the Amphibia. It has been shown to occur 
in the Newt by Miss Johnson, in the Frog by Spencer, 
and in Alytes by Gasser. Its occurrence in the Cyclos- 
tomata seems to point to the fact that it is a primitive 
feature retained in those eggs whose development is not greatly 
modified by the presence of a large mass of yolk. Renewed 
observations in the development of Amphioxus would pro- 
bably throw some light on this point. 


The Central Nervous System. 


The early development of the central nervous system has 
been so fully described by Calberla, Balfour, and Scott, 
that little is left to be added to their account. But the origin of 
the neural canal, the relationship of the posterior end of the neural 
cord to the blastopore, and the later development of the parts 
of the brain and the cranial nerves present points of interest. 

Calberla was the first to show that the central nervous 
system of the Lamprey arises by a delamination and not by 
an involution of the epiblast. He described a similar origin for 
the nervous system of the Teleostei, and Balfour and 
Parker found the same to be the case in Lepidosteus. 

The first trace of theneural plate appears about the eighth day 
after fertilization, just after the invagination is completed. A 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 330 


shallow groove is seen running forward from the blastopore, 
round about two thirds of the embryo and passing a little in 
front of the blind end of the mesenteron. The groove is a very 
temporary structure and is soon replaced by a ridge. This 
arises by the epiblastic cells lining the groove, which are of a 
columnar shape, budding off cells from their under surface. 
The result of this is that a keel of cells is formed which forms 
the neural ridge externally (fig. 12), and internally presses in 
between the mesoblastic plates. The keel arises solely by the 
epiblast cells budding off cells in their under surface only. It 
is much deeper in the anterior third of its course, which region 
ultimately forms the brain. 

The keel in the course of two or three days loses its connec- 
tion with the epidermis ; this occurs at first anteriorly and ex- 
tends backward, and as Scott has pointed out, it does this of 
itself and not by an ingrowth of the mesoderm in each side as 
Calberla described. 

Figs. 13, 15, and 16 show the solid neural cord lying above 
the notochord, which by this time is separated off from the 
hypoblast. It is important to notice that the neural canal 
does not arise until after the connection between the neural 
cord and epidermis is severed. It is about the origin of this 
neural canal that my observations and those of Calberla and 
Scott are at variance. They described the epidermic layer 
of epiblast passing down into the nervous, in such a way that 
the canal, when it does appear, is lined by this layer. I have 
not been able to see any trace of this. The cells forming the 
nervous system appear to me to be all split off from the under 
surface of the epidermis in the dorsal middle line, and the 
continuity of the epidermis in this region never seems to be 
broken by any such invagination as they suggest. Balfour 
was also doubtful on this point; but in his and Parker’s 
work on the development of Lepidosteus, they state that 
there is no evidence of the epidermic layer being concerned in 
the formation of the canal. 

The canal seems to arise as a split between the cells in the 
axis of the solid cord, and not by the absorption of the central 


304 ARTHUR E. SHIPLEY. 


cells, as has been suggested in the case of the Teleostei. It 
appears at first anteriorly and extends backward, and for some 
little time the walls of the lumen are by no means sharply 
defined. Processes from the cells lining the canal project into 
its cavity and suggest the idea that they have been torn out 
from between the cells of the other side. 

The neural cord remains solid at its posterior end for some 
time, and here it becomes fused with the surrounding struc- 
tures in a somewhat remarkable way. It does not fuse round 
the blastopore as Scott describes, indeed it is not easy, con- 
sidering its mode of origin, to see how it could; and there is 
no hollow neurenteric canal. Figs. 14 and 15 represent two 
sections taken through a larva just after hatching. Fig. 14 is 
through the region of the blastopore. It shows the neural 
cord with its canal already formed; beneath this lies the noto- 
chord, and beneath this again asolid rod of cells which is con- 
tinuous with the subnotochordal rod and the dorsal hypoblast. 
This latter structure is the solid postanal gut. The mesoblastic 
plates are seen separating off from the hypoblast yolk-cells 
which occupy the remaining space with the epidermis. Dor- 
sally this is produced to form the dorsal fin. Fig. 15 repre- 
sents a section through the tail a little posterior to the blasto- 
pore. Here the neural cord, notochord, and postanal gut have 
fused into a rod-like mass of tissue which is ventrally con- 
tinuous with the hypoblast cells; a few sections posterior to 
this none of the three embryonic layers are distinguishable 
except the epidermal portion of the epiblast. A longitudinal 
median section through the tail is represented in fig. 20. This 
shows the mass of indifferent tissue which lies in the tail and 
which by internal differentiation gives rise, as the tail grows, 
to mesoblastic somites, neural cord and postanal gut. This 
mass of tissue, which in many respects reminds one: of the 
growing point in a plant, may be called the primitive streak. 
It is perhaps worth while to point out that it lies at what was 
originally the anterior lip of the blastopore. 

A similar mass of tissue formed by the fusion of the pri- 
mary layers has been described by Balfour and Parker in 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 300 


Lepidosteus, Spencer in the Frog, and Miss Johnson 
in the Newt. 

The further development of the central nervous system will 
be described later after some of the details connected with the 
mesoblast and hypoblast have been considered. 


The Mesoblast. 


The origin of this layer from the yolk-cells situated in the 
angle between the epiblast and the invaginated endoderm has 
been described above. For some little time the mesoblast re- 
mains in the condition of two triangular masses of cells, 
separated from one another dorsally by the notochord and ner- 
vous system, ventrally by the yolk-cells which lie in contact with 
the ventral epiblast. In the anterior end of the embryo the 
mesoblast soon unites ventrally by lateral downgrowths; in 
the trunk, however, which remains crowded with yolk-cells for 
a week or ten days after hatching, this takes place much 
later. 

Scott has described the formation of the muscle-plates very 
accurately, and it will therefore be unnecessary to give more 
than a short résumé in order to make the following account 
intelligible. About the twelfth or thirteenth day the meso- 
blastic somites appear by the segmentation of the dorsal part 
of the lateral mesoblastic plates. These appear at first ante- 
riorly, and the segmentation extends backwards. The most 
anterior one lies close behind the auditory sac. The ventral 
unsegmented mesoblast has split into the splanchopleure and 
the somatopleure on each side, and in the region just behind the 
posterior gill-cleft these have met ventrally, forming a ventral 
mesentery, connecting the alimentary canal with the ventral 
body wall. 

The mesoblast somites are shown in fig. 17, which repre- 
sents a horizontal section through an embryo fourteen days 
old. They are cubical masses of cells enclosing a small cavity, 
often entirely obliterated, which represents part of the body 
cavity. The cells surrounding this are at first uniform in size, 
and each side is only one cell thick. Like the other cells of 


306 ARTHUR HE. SHIPLEY. 


the embryo they contain yolk granules, which are gradually 
absorbed. In the tail region these mesoblastic somites con- 
tinue to be segmented off from the primitive streak till five 
or six days after the larva is hatched. 

In transverse sections the mesoblastic somites appear trian- 
cular, having a median side against the nervous system and 
notochord, an external one against the epididymis and a ventral 
one. Besides these there are the anterior and posterior sides. 
The cells composing all these, except those of the external 
layer, develope into longitudinal muscles. Whilst this is taking 
place the dorsal surface of the embryo has become raised above 
the general level, so that the embryo in section is no longer 
round but pear-shaped. 

As Stannius, Grenacher, and Langerhans _ have 
shown, the muscles of the Lamprey fall into two groups, which 
differ in structure as well as in their disposition. The first of 
these form the myomeres, and are derived directly from the 
mesoblastic somites ; the second comprise the muscles of the 
eye, those belonging to the respiratory system, and those con- 
nected with the upper and lower lip and mouth generally. 
These seem to arise exclusively from the ventral unsegmented 
parts of the mesoblast, and perhaps, in some cases, from wan- 
dering mesoblast cells. The muscles of the heart resemble the 
latter in many points. 

Each myomere in the Lamprey or Ammoccete consists of a 
number of plates of muscle-substance, lying one on the top of 
another. Each plate is flat, and more less square in outline. 
It is bounded anteriorly and posteriorly by the myotomes ex- 
ternally by a connective-tissue layer closely connected with the 
skin, and internally by a similar layer. Above and below, or 
dorsally and ventrally, it is in contact with a similar muscle- 
plate. In some myomeres which have become modified, such 
as the anterior one which extends far forward over the ear, the 
shape of the muscle-plate has lost its square outline and be- 
come oblong, but in one of the myomeres of the trunk they 
are almost square in longitudinal section. 

From the above description it will be seen that each muscle- 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 337 


plate or “ Kastchen” of Stannius occupies the horizontal 
space between two myotomes, and that they lie one on another, 
so that in a horizontal section we see only one, in a transverse 
or vertical section we see one lying on another like sheets of 
paper. Each “ muscle-plate” contains several nuclei, which 
stain more deeply than the muscle-substance. It is trans- 
versely striated, and faint longitudinal striz can also be de- 
tected ; these correspond with fibrillz, into which the muscle- 
substance easily breaks up. These latter are especially large, 
and can be easily recognised in transverse sections near the 
most external part of the ‘‘ muscle-plate.”’ 

The development of these muscle-plates is as follows :— 
The outermost layer of cells forming the mesoblastic somite 
does not appear to be converted into muscles. For along time 
it persists as a definite layer of cubical cells with large nuclei 
lying between the skin and the myomere; this is the case till 
long after the other cells of the mesoblastic somite have deve- 
loped into muscles. Finally, this layer seems to disappear, 
but remains of it can still be distinguished lying just within 
the skin, even when the myomere has assumed the appearance 
characteristic of the full-grown Ammocete. This view that 
the somatic layer does not take part in the formation of the 
myomeres, is not in agreement with what Balfour has de- 
scribed in the Elasmobranchs, where both the inner and 
outer layer become muscular; but, on the other hand, the 
muscles of the myomeres in Amphioxus appear to be de- 
rived from the splanchnic layer only, and the same view is 
supported by Gotte and the Hertwigs. 

The remaining cells of the mesoblastic somite begin to 
grow in between one another, and between each neighbouring 
somite an intermuscular septum is deposited. The process of 
growing in between one another is carried on until each cell 
occupies the whole length from one myotome to the next, and 
at the same time, each cell becomes somewhat flattened, so 
that their transverse section, which was at first round, become 
oval (fig. 24). At the same time longitudinal thickenings 
occur in the cortical part of the cell, the medullary portion 


308 ARTHUR E. SHIPLEY. 


remaining clear and staining very slightly. The nucleus lies 
in this medullary portion. The longitudinal thickenings occur 
at intervals, so that in transverse section the cortex of the cell 
appears beaded ; these fine fibrille stain fairly well so that 
they can easily be distinguished from the medulla. The flat- 
tening of the cell goes on until the cell occupies the whole 
space between two myotomes, not only longitudinally but also 
transversely (fig. 25). The original nucleus of each cell 
divides into two or three, so that in each of these plates of 
muscle-substance two or three nuclei can be seen and an occa- 
sional yolk granule, which is, however, soon absorbed. In 
addition to the longitudinal striation caused by the thread-like 
thickenings in the cortex, a transverse striation appears. Each 
plate of muscle-substance remains in this condition, with a 
clear unstained medulla containing two or three deeply stained, 
large, flat, oval nuclei (fig. 18), with a well-marked nucleolus ; 
enclosed by a cortex, for about two weeks after hatching. The 
cortex consists chiefly of its dorsal and ventral walls, and each 
of these is thickened at regular intervals by the above-men- 
tioned fibrille. Each fibrilla runs the whole length of the 
myomere and is inserted into the intermuscular septa behind 
and in front. About a fortnight after the young Ammoceete 
is hatched, the substance of the fibrille increases at the 
expense of the medullary part, and this goes on until each 
plate of muscle-substance consists exclusively of fibrillar sub- 
stance. The nuclei have increased in number, but instead 
of lying loose in medulla they become squeezed in be- 
tween the fibrille, lose their regular shape and can only 
be recognised as small flattened bodies which stain deeply. 
The whole plate of muscle-substance now consists of fibrillar 
substance which stains uniformly with here and there a more 
deeply stained nucleus (fig. 29). The whole appears homo- 
geneous, the fibrille cannot as a rule be recognised, though in 
some cases they are seen in transverse section as dots. Each 
<‘ Kastchen ”? now resembles fundamentally the muscle-plate of 
the adult Lamprey ; and it will be noticed that each is a deve- 
lopment of what was a single cell. 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 339 


The second variety of muscle-fibre met with in the Lamprey 
seems to be exclusively derived from the ventral unsegmented 
mesoblastic plate, and from the walls of the head cavities. 
The muscles with this origin are those which serve to move the 
lips, the velum and the other structures of the mouth, and 
certain muscles connected with the gill apparatus, and prob- 
ably the muscles of the eye. These latter have the same 
histological structure, but owing to the fact that the eye does 
not develope until the Lamprey stage, no eye muscies appear 
till very late in the life of the Ammoccete and I have conse- 
quently been unable to follow their development. 

The muscle-fibres of this second variety of muscle tissue, 
consist of long tubular cells, cylindrical in shape, with a 
medulla of clear substance which does not stain, and a cortex 
which is thickened at intervals by longitudinal rods. These 
give the cortex a beaded appearance in transverse section. 
The medulla contains the nucleus, which stains deeply. This 
is at first single, but subsequently divides until a row of nuclei 
occupy the axis of the muscle-fibre, in some cases so closely 
packed as almost to touch. It will be noticed that these 
muscle-fibres resemble in the minute structure the first stage 
in the development of the muscles forming the myomeres. 
These muscle-fibres are transverse striated. 

The fibres of the heart belong to this second variety, and are 
developed from the same part of the mesoblast. They, however, 
possess certain peculiarities. which will be described after the 
formation of the heart has been considered. 

The Heart. 

The first appearance of the body cavity as a space takes 
place in the region behind the posterior gill-cleft and in front 
of the liver. The part of the embryo lying in front of this 
region is at an early stage raised from the posterior half by the 
backward growth of the head fold, and the embryo lies within 
the egg-shell bent in half, the angle of the bend being just in 
that region where the heart is subsequently formed. By this 
means all those parts in front of the liver are free from the 
yolk-bearing cells, and the lining cells of the mesenteron all 


340 ARTHUR HK. SHIPLEY. 


become columnar. In this anterior region the mesoblast soon 
unites ventrally. In the posterior region the ventral union of 
the mesoblast is delayed, the lateral plates of mesoblast lying 
between the yolk-cells and the epiblast end in a free edge, and 
until these edges unite, the yolk-cells are in contact with the 
epidermis ventrally. 

In the region between the liver and the last gill-slit the 
mesoblast splits at about the fifteenth day into a somatic and a 
splanchnic layer; between the two a well-developed body 
cavity appears. The former layer lines the body wall, the 
latter envelopes the alimentary canal. It forms a dorsal mesen- 
tery supporting that structure, and a well-marked ventral 
mesentery of considerable depth connecting the ventral wall of 
the intestine with the body wall. It is in this ventral mesen- 
tery that the heart is developed. The two layers forming the 
mesentery fuse dorsally and ventrally, but separate from one 
another in their middle, forming a cavity which is the lu- 
men of the heart (fig. 24). Subsequently both the mesentery 
connecting the heart with the alimentary canal—the meso- 
cardium—and the ventral one connecting the heart with the 
ventral body wall, atrophy and the heart lies as a tube uncon- 
nected with the surrounding structures (fig. 25). 

From the fact mentioned above that the mesoblast behind 
the heart has not split into somatic and splanchnic layers nor 
united ventrally, it will be seen that the cavity of the heart 
communicates posteriorly with the space between the veutral 
yolk-cells and the epidermis. Such a space would be equiva- 
lent to part of the segmentation cavity. Soon after the heart 
is formed such a space arises, and at once becomes crowded 
with cells destined to form blood-corpuscles (fig. 26). At first 
I was inclined to think that these cells were budded off from 
the yolk-cells, but more careful observation has led me to 
believe that they originate from the free edge of the lateral 
plates of the mesoblast, which as I mentioned above are 
growing down between the yolk-cells and the epiblast. These 
corpuscles are oval with large nuclei, and they usually contain 
at first one or two yolk granules which they soon absorb. 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 341 


The cavity in which the corpuscles lie in great numbers is subse- 
quently shut off by the mesoblast as it grows downwards and 
becomes the subintestinal vein. It is from the first continuous 
with the posterior end of the heart, and the corpuscles soon 
pass from it into that organ. From the first appearance of 
the heart in the ventral mesentery its walls have been double ; 
the splanchnopleure having split into two layers, of these the 
outer is at first much the thicker consisting of cubical cells ; 
the inner layer is composed of comparatively flattened cells. 
The heart at first is a straight tube of the same length as the 
section of the body cavity in which it lies. Very soon, how- 
ever, it increases in length, and thus becomes slightly twisted ; 
at the same time two constrictions appear, dividing it into three 
chambers. The most posterior of these is the sinus venosus ; 
it is directly continuous with the space in which the corpuscles 
are developing. By this time this space has acquired definite 
walls by the downgrowth of the mesoblast in this region, and 
it may now be spoken of as the subintestinal vein. 

The liver which developes as a ventral outgrowth of the 
intestine first makes its appearance in this space, and when the 
latter gets closed off as a vein, the liver has become a branched 
gland projecting into it, so that the blood returning from the 
alimentary canal passes between the tubuliof the liver. Thus, 
from the very first an hepatic portal system is present. The 
tubuli of the liver do not appear to have any continuous meso- 
blastic coating, though here and there a flattened cell can be 
distinguished in the outside of a tubule. 

The venous sinus communicates by a narrow opening with 
the auricle or second chamber of the heart. This in its turn 
opens by a similar narrow opening into the ventricle. This 
latter opening is guarded by a pair of valves, which appear by 
the tenth day after hatching; they effectually prevent any 
regurgitation of the blood into the auricle. The walls of the 
ventricle have undergone a considerable change. From the 
cells of the inner lining a number of branched muscle-cells 
have been developed (fig. 36). These cells stretch across the 
cavity of the ventricle from side to side, and fuse and anas- 

VOL, XXVII, PART 3.— NEW SER. B B 


342 ARTHUR BE. SHIPLEY. 


tomose with one another in a very complex manner. They 
contain numerous nuclei, and show a longitudinal striation 
though not a transverse one. The centre of the ventricle is 
comparatively free from them, but at the sides they form a 
spongy reticulum in the meshes of which corpuscles abound. 

The ventricle passes anteriorly into the ventral aorta, and 
at the point where the aorta passes into the solid tissue 
between the gills there is another pair of valves resembling 
the auriculo-ventricular ones. The ventral aorta, like the 
other vessels, arises by a split in the mesoblast which subse- 
quently acquires a definite wall. It passes forward as a single 
vessel in the ventral median line until it reaches the thyroid 
gland, and here it splits in two branches. Each branch then 
passes forward on one side of this body, and ends in the most 
anterior gill vessel. From the single part of the ventral aorta 
three pairs of vessels are given off, passing in front of the 
fifth, sixth, and seventh gill-slits respectively. The posterior 
wali of the seventh cleft bears no gill filaments, and has no 
vessel. From each side of the double part of the ventral aorta 
five vessels are given off, the four posterior of these pass in 
front of the first, second, third, and fourth gill-slits. The 
most anterior is the vessel which in the earlier stages passes in 
front of a gill-slit which subsequently disappears. In the 
older embryos, when the mouth is fully formed it runs along 
the base of the velum. 

The vessels after traversing the gills unite in the dorsal 
middle line to form the dorsal aorta; this runs backward to 
the posterior end of the body, lying just underneath the noto- 
chord. From its first appearance it gives off two transverse 
vessels in the neighbourhood of the pronephros; these supply 
the glomerulus. Anteriorly it gives off a pair of vessels to 
supply the upper lip, the carotids. In the older larvz the 
aorta gives off a vessel which passes dorsally up one myotome, 
then along the dorsal surface of the myomere behind it, and 
hence the blood is collected by a vein which returns it to the 
posterior cardinal down the next myomere. The larve are 
fairly transparent, and in each myotome these two opposite 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 343 


currents can be seen, and along the top of each myomere a 
backwardly directed stream. In the tail the aorta splits, and 
one branch passes each side of the cloaca; they unite ventrally, 
and are continued forwards as the subintestinal vein. Before 
it splits it gives off a vessel which runs back along the base of 
the notochord to supply the tail; this may be termed the 
caudal artery. The blood from this is returned by a caudal 
vein which soon splits into the two posterior cardinal veins. 
These large veins run forward, one each side of the aorta: 
the duct of the pronephros runs in their wall. Anteriorly 
they unite with the anterior cardinals, and form two ducts of 
Cuvier which open into the sinus venosus. The anterior 
cardinals bring back blood from the head. The tubuli of the 
pronephros lie in their cavity, so that the pronephros, like the 
kidney of the Amphibia, has a double blood supply. The car- 
dinal veins do not appear till after the subintestinal vein, which 
for some little time is the only vein in the body. Later still a 
vessel appears in the right side of the intestine, opposite the 
subintestinal vein in the spinal fold; this, like the last named, 
passes through the liver. In my latest stages also there is 
an impaired vessel bringing blood back to the heart from the 
ventral region of the gills; this is mentioned by Balfour. 
The blood-corpuscles are of only one kind, large oval disc-like 
structures, with a well-marked nucleus. The protoplasm 
scarcely stains, but the nucleus assumes a deep colour. 

Owing to the transparency of the larva, the circulation can 
be watched with great ease. The walls of the vessels at first 
possess no elasticity, hence great regurgitation takes place, 
and the blood advances by a series of jerks. The valves at the 
anterior end of the ventricle and between the auricle and the 
ventricle prevent this affecting the blood in the heart. 

The heart begins to beat long before the cells exhibit any 
histological differentiation into muscles. 


The Pronephros. 


The first origin of the larval excretory system is by no means 
easy to make out, as it arises at a period when the embryo is 


344 ARTHUR E. SHIPLEY. 


crowded with yolk. Scott has described it fully, and in most 
respects my observations confirm his. As he describes, the 
first structure to appear is the segmental duct which is at first 
solid. The cells forming this are derived from the mesoblast 
cells which lie between the already segmented dorsal part of 
the mesoderm and the ventral unsegmented portion. These 
cells form a solid cord lying between the mesoblast and the 
epiblast ; the cord continues to grow backward by a differen- 
tiation of the cells in situ. A few hours later a lumen appears 
in the centre of the cord by the separation of the cells; this 
soon becomes elliptical in section (fig. 11). It opens into 
the posterior part of the alimentary canal. 

From this account it will be seen that at first the segmental 
duct is between the mesoblast and epiblast; it, however, soon 
comes to occupy a deeper position by the growth of the sur- 
rounding tissue. So far we have only considered the duct in 
that part of its coufse where the body cavity is not yet deve- 
loped; but in the region of the heart, where the body cavity 
has already appeared, its origin seems to be somewhat different. 
The lumen of the segmental duct here becomes continuous 
with a groove in the parietal peritoneum, lying near the angle 
where the somatopleure and splanchnopleure diverge. When 
this groove closes it leaves four or five openings which persist 
as the openings of the ciliated funnels. This account of the 
origin of the ciliated funnels agrees with that of Fiirbringer, 
but differs from Scott’s, who describes the funnels arising 
as blind projections of the segmental duct which acquire an 
opening into the body cavity. Each funnel soon acquires 
cilia, which extend for some distance down its lumen, and are 
usually directed downwards towards the tubuli. The funnel 
is composed of large cubical cells with a large nucleus, at its 
lip it passes suddenly over into the flat cells of the peritoneal 
epithelium. At its base it is continuous with a duct which 
soon becomes elongated and coiled, and ultimately joins the 
segmental duct. The walls of the tubuli are composed. of 
large clear glandular cells. The posterior end of the seg- 
mental duct opens into the cloaca 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 345 


The segmental duct throughout its course runs in close 
connection with the post-cardinal vein, lying in contact with 
it, almost in its wall in the under and inner side. In 
the anterior region this vein has so grown round the pro- 
nephros that the tubuli really le inside it (fig. 29). The 
tubuli are covered by a few flattened cells whose presence 
becomes more obvious about the twenty-fifth day by a deposit 
of dark brown pigment. The tubuli have thus a venous 
blood supply. The glomerulus on the other hand is supplied 
from the aorta. There is only one glomerulus on each side, 
stretching each side of the alimentary canal and extending 
through about the same space as the glandular part of the 
kidney. Hach glomerulus is a diverticulum of the peritoneum, 
which generally becomes sacculated ; it receives its blood by a 
single vessel on each side directly from the aorta. 

Since the time of Bowman it has been known that the 
kidneys of Fishes, Frogs, and Snakes have a double blood 
supply, the tubuli uriniferi being surrounded by a capillary net- 
work of vessels which receive their blood from the renal portal 
veins, and the glomerulus which is supplied with blood from 
the aorta by the renal artery. It is an interesting fact to find 
that a similar blood supply is present from the very first in 
such a temporary organ as the pronephros of the Lamprey. 

In the great majority of cases I found fine ciliated funnels 
in each pronephros. The whole gland did not extend over a 
greater space than that occupied by three myomeres, although 
in some cases the ciliated funnels, which were of some length, 
overlapped into a fourth myomere, but I was unable to coufirm 
the relationship alleged to exist between the number of ciliated 
funnels and the number of somites through which the pro- 
nephros extended. . 


The Skeleton. 

The skeletons of the oldest larva at my disposition consisted 
of the notochord derived from the endoderm, and of certain carti- 
Jages in the head and branchial region derived from the lateral 
mesoblast. The origin of the notochord has been completely 


346 ARTHUR E. SHIPLEY. 


described by Calberla, Scott, and others, and I have nothing 
to add to their account. In the histological differentiation of 
the chord from a solid string of more or less cubical cells, to 
the vacuolated cylinder which forms the permanent notochord, 
there is a stage which is perhaps worth mentioning. In the early 
stages a transverse section of the chord shows portions of three 
or four cells, a little later these cells have pushed their way 
between one another and arranged themselves in such a way 
that they occupy the whole room inside the sheath of the 
notochord. Whilst in this condition vacuoles appear in the 
substance of the cells and for a day or two the notochord pre- 
sents very much the same structure as the notochord of Amphi- 
oxus. This is, however, soon replaced by the vacuolated 
appearance characteristic of the notochordal tissue of the higher 
Vertebrata (figs. 18 and 23). 

The posterior end of the notochord passes into the indifferent 
mass of tissue described in the tail. The anterior end is 
slightly curved downwards apparently by the increased vertical 
height of the brain. It ends just behind the infundibulum, 
its end being in contact with the posterior end of the nasal in- 
vagination. There is no trace that it has ever passed in front 
of this point, although in the young stages it reaches relatively 
almost as far forward as the nervous system. The relation of 
its anterior end to the brain hence appears to be due to the 
overgrowth of the nervous system anteriorly. 

The cartilage which composes the rest of the skeleton is 
characterised by the small amount of intercellular substance. 
This stains very deeply. ‘The cells are large with usually only 
one nucleus, though sometimes two. I have endeavoured to 
represent this structure in fig. 19. The branchial bases are 
the first part of the skeleton to appear. They arise about the 
twenty-fourth day as straight bars of cartilage lying external 
and slightly posterior to the branchial vessel. In their relation 
to the vessel they correspond with the extrabranchial bars of 
the Tadpole, and the Sharks. The true branchial bars run 
internal to the branchial vessel. 

The bars run behind the gill-slit to which they belong, and 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 347 


there is no bar in front of the first persistent cleft. They are 
slightly curved inwards towards the median linein the middle part 
of their course where they bend round the external opening of 
the cleft. About the thirtieth day they fuse with one another 
ventrally and so two rods are formed which lie close together 
in the posterior half of their course but diverge round the 
thyroid. About the same time each bar sends forward two 
processes, one above and the other below the opening of the 
gill to which it belongs; these ultimately fuse with the pos- 
terior edge of the gill bar next in front. The processes of the 
most anterior bar fuse with each other. Dorsally the last six of 
the bars also become continuous (fig. 42), and form two longi- 
tudinal bars which run parallel and close to the notochord. 
The most anterior bar does not join this rod but sends a process 
inwards, serving to support the auditory capsule, which lies 
just in front of it directly over the first persistent gill-cleft. 

The first traces of the basi-cranial skeleton appear on the 
thirtieth day as two rods of cartilage, the trabecule (figs. 40). 
They he close against the notochord for their posterior two 
thirds, anteriorly, however, they diverge and surround the 
pituitary space. About six days after their first appearance 
the trabecule send out laterally a transverse bar of cartilage 
which passes out on each side in front of the auditory capsule, 
lying between the ganglia of the fifth and seventh nerves. Pro- 
fessor Parker has identified this as the rudiments of the pedicle 
and pterygoid. ‘They lie in the tissue of the bar which is in 
front of the first gill-cleft which has long ago disappeared. 

Immediately beneath the trabecule the carotid artery runs 
forward as an anterior continuation of the dorsal aorta. The 
trabeculz have become continuous with the dorsal end of the 
most anterior branchial bar, which is not united with the longi- 
tudinal bar formed from the fused dorsal end of the other six. 
The connection is very slight but is quite evident in sections. 
between this and the dorsal end of the second bar some little 
space exists, the latter when it commences lies at a slightly 
lower level than the trabecule. 

The above description represents the condition in my oldest 


348 ARTHUR E. SHIPLEY. 


larva, fifty-two days (fig. 43). The further development of 
the Lamprey’s skull has been deseribed by Professor Parker in 
his great work on ‘The Skeleton of the Massipobranch 
Fishes,’ 


The Mesenteron. 


The cavity of the alimentary is formed by the invagination 
of the endoderm described in the first section of this article, 
when once found it does not disappear again, although in the 
region of the intestine it may be reduced to a slit by the 
pressure of the surrounding yolk-cells. 

The most anterior section, including the branchial region 
_ and that part of the intestine in front of the liver, is now 
separated from the rest by the raising of the head and neck 
from the remaining part of the embryo. The lining cells of 
this portion at once assume a columnar character ; the hypo- 
blastic cells in the region of the blastopore, or as it may now 
be termed the anus, also assume a similar form. But the cells 
in the middle part of the intestine still retain the features 
of the yolk-cells, those forming the roof of the enteron being 
however, rather more columnar than those of the floor and 
sides. 

In the head region almost the whole of the space inside the 
epiblast is taken up with the brain, which has a great depth, 
and with the notochord and the alimentary canal, which ends 
blindly in front. A small band of mesoblast lies on each side 
of the nervous system and notochord. This segments dorsally 
into a series of myomeres, the first lying close behind the ear. 
Ventrally the mesoblast has not grown down between the en- 
doderm, so that along the sides and under surface the hypoblast 
and epiblast are in contact. The first gill-slit appears, as Scott 
has described, about the twelfth or thirteenth day, the others 
arise eduring the next three or four days, the most posterior 
being the last formed. The gill-slits appear to me to be the 
result of the ventral downgrowth of mesoblast taking place 
only at certain places, these forming the gill-bars. Between 
each downgrowth the hypoblastic lining of the alimentary 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 349 


canal remains in contact with the epiblast, and here the 
gill opening subsequently appears about the twenty-second 
day. 

Huxley was the first to point out that the embryo 
Lamprey possesses eight gill-slits, and his account has been 
confirmed by Scott and Dohrn, who, however, point out 
that the first slit remains closed, and does not open to the ex- 
terior, as Huxley described. Dohrn has further shown that the 
first or rudimentary gill-slit becomes converted in the ciliated 
groove encircling the mouth, which was first described by 
Anton Schneider in Ammocetes. 

Fig. 27 represents a longitudinal horizontal section of the 
head of a twenty-one days’ old embryo. The eight primitive 
gill-slits are here shown lined by columnar epithelium, which 
in the posterior seven is most flattened at those points where 
the opening will subsequently appear. The corresponding area 
in the first cleft, however, will be seen to be lined with very 
high columnar cells. These cells afterwards acquire cilia and 
come to lie in a deep groove. 

The branchial vessels have only appeared in the first gill- 
bars, but the cells which will be converted into the cartilagi- 
nous gill arches have already become distinct (47. 6.). About 
the twenty-second day a process begins to grow backward from 
the middle of each gill-bar into the gill-slit behind. This re- 
duces the slit to a <-shaped opening. After the opening to 
the exterior has been established the gill-bars overlap each 
other, the passage from the cavity of the mouth to the exterior 
being directed outwards and backwards. Each gill-bar 
acquires a few gill filaments, into which the blood courses. 
The whole is covered by a layer of thick columnar epithelium 
continuous with that lining the rest of the mouth, except cer- 
tain small areas, mostly at the end of the short filaments, 
where the epithelium has become suddenly thin, thus putting 
the blood into closer communication with the surrounding 
water. 

The columnar glandular-looking cells which line so much of 
the cavity of the mouth contain a number of very fine gran- 


350 ARTHUR E. SHIPLEY. 


ules, which stain deeply with hematoxylin, giving the cell a 
very characteristic appearance. I have been unable to form 
any opinion as to the nature or fate of these granules. 

The ciliated ring mentioned above is shown in section 
in fig. 41, c.g. It lies close in front of the most anterior gill- 
bar; ventrally its two halves converge and run back as two 
parallel grooves to the opening of the thyroid gland in the 
ventral median line. The grooves here unite, and after receiv- 
ing the opening of the thyroid they continue as a single groove 
running in the ventral median line as far as the most posterior 
gill arch. Dorsally the grooves unite and become continuous 
with a median dorsal ridge, which is covered by high columnar 
cells, also ciliated. This ridge extends from the first gill arch 
to the commencement of the wsophagus. Anton Schneider 
describes a band of cilia running from this dorsal ridge on 
each side along each gill arch. This is not present in my 
oldest larva, but is no doubt formed later. 

Dohrn (23) has recently described the development of the 
thyroid so fully, and his paper is so beautifully illustrated, 
that it appears to me to be superfluous to describe again the 
origin of this organ. I can only confirm his results. He 
deals at length with the homology of the thyroid of Ammo- 
coetes, with the endostyle of Ascidians, and the hypobranchial 
ridge in Amphioxus. And the homology of the circumoral 
ciliated ring in Ammoceetes and Ascidians is also pointed 
out. To these homologies we may add, I think, that of the 
dorsal ciliated ridge of the young larval Lamprey to the dorsal 
lamella of Ascidians, and the hyperpharyngeal groove of 
Amphioxus. It isa curious fact, however, that in the last 
animal the form of the structure is reversed. We find ven- 
trally a ridge and dorsally a groove, whereas in Ammoccetes 
and Ascidians we have the ridge dorsal and the groove ventral. 
In spite of this, I think Dohrn’s arguments fully support the 
homology of the ventral organs, and the same reasoning holds 
good for the dorsal. 

The alimentary canal behind the branchial region may be 
divided into three sections. Langerhans has termed these 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 351 


the stomach, mid-gut, and hind-gut, but as the most anterior 
of these is the narrowest part of the whole intestine, it would 
perhaps be better to call it cesophagus. This part of the ali- 
mentary canal lies entirely in front of the yolk, and is, with 
the anterior region which subsequently bears the gills, raised 
from the rest of the egg when the head is folded off. In my 
later larvee it is composed of a single layer of very high co- 
lumnar cells, and is ciliated throughout. Round this is a thin 
layer of cells, which, I imagine, give rise to the muscular 
coats. The whole is supported by a dorsal mesentery, each 
side of which lies the head kidney (fig. 25). The ciliated 
columnar cells are directly continuous with those covering the 
dorsal ridge of the branchial region, but not with those of the 
ventral groove; this later connection must arise subsequently, 
as Anton Schneider describes it in the fully-grown 
Ammocete. 

The mid-gut which follows the cesophagus is, in the 
younger stages, crowded with yolk granules. The cells of the 
roof soon acquire a columnar shape, whilst the ventral part 
consists of a mass of cubical cells, each crowded with yolk. 
By degrees the yolk is absorbed, and the cells assume the same 
character as those lining the cesophagus. The lumen of the 
mid-gut is very much larger than that of the esophagus, the 
alimentary canal expanding suddenly at the commencement 
ofthe former. The absorption of yolk takes place from before 
backward, so that lumen and walls of the fore part of the mid- 
gut assume their permanent size and form, whilst the posterior 
half is choked with yolk. The lining high columnar cells are 
ciliated and quite continous with those of the cesophagus. 

By the time the yolk is all absorbed a longitudinal invagi- 
nation of the wall of the mid-gut takes piace. This occurs 
anteriorly on the left side, but twisting through a quarter of 
circle it comes to lie in the ventral side posteriorly. The 
ridge thus formed reduces the lumen of the alimentary canal 
from a round to a reniform shape in section. In this ridge or 
spiral valve runs the subintestinal vein, which has become 
quite small and has lost its median ventral position. Around 


aoe ARTHUR KEK. SHIPLEY. 


this vessel, filling up the space between the two sides of the 
spiral valve, is a quantity of fatty tissue. The cilia on the 
inner face of the spiral valve are very evident. 

The lumen of the mid-gut is so large that almost the whole 
of the body cavity in that region of the Ammoceete is taken 
up by this part of the intestine; consequently the liver, the 
only gland opening into the mid-gut, is pushed forward and 
lies on each side and below the esophagus. This gland has its 
origin at a very early stage, about the fourteenth day, as an 
evagination of the mid-gut, whilst the latter is still crowded 
with yolk. The diverticulum thus produced grows out in the 
ventral side of the alimentary canal into that space between 
the hypoblast and epiblast which was mentioned above as 
being crowded with blood-corpuscles. This space subsequently 
becomes enclosed by definite walls by the downgrowth of the 
mesoblast in this region. It becomes the subintestinal vein 
which still continues to supply the liver with venous blood. 
The single diverticulum soon begins to branch, and at an early 
stage one of the branches becomes differentiated from the 
others, acquires a large lumen, and forms the gall-bladder. 
The cells forming the liver are cubical with large nuclei, they 
do not appear to have a definite outer layer of flattened cells, 
though occasionally such a cell is present. In the older larve 
the gall-bladder has a great relative size. It lies embedded in 
the liver on the right side of the cesophagus. The bile-duct 
runs from it above the mid-gut, bending down to enter the 
mid-gut in the spiral valve on the left side. 

The hind-gut is smaller than the mid-gut, its anterior limit 
is marked by the termination of the spinal valve, which does 
not extend into this region. The two segmental ducts open 
into it just where it turns ventrally to open to the exterior by 
a median ventral anus. Its walls are in this region slightly 
puckered. The cells lining it are not so high as in the other 
parts of the intestine, but more cubical. 

Its lumen is from an early stage lined with cells which 
have lost their yolk, and it is in wide communication with the 
exterior from the first. This condition seems to be, as Scott 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 353 


suggests, connected with the openings of the ducts of the pro- 
nephros, for this gland is completed and seems capable of 
functioning long before any food could find its way through 
the mid-gut, or indeed before the stomodzeum has opened. 

The stomodzeum has a very early origin ; it commences on 
the fifteenth day as an invagination of ectoderm against the 
blind anterior end of the fore-gut. This gradually deepens 
and attains a very large size, partly due to great development 
of the upper lip, which grows forward and downward to con- 
stitute the large hooded structure which is so characteristic of 
the Ammocete. The greater part of this hood consists of 
simple muscle-fibres which interlace and cross one another in 
a diagonal direction. The lower lip does not reach so far for- 
ward as the upper (figs. 84 and 35). About the twentieth day 
the velum begins to appear in the posterior angle of the sto- 
modeum. This structure is formed by two grooves which 
gradually deepen and cut off a flap of tissue on each side of the 
middle line. These two grooves, shown in fig. 27, are not very 
deep. The tissue between them is broken through the next 
day so that the two lateral folds that remain are covered on 
their anterior face by epiblast, and on the greater part of their 
posterior face by hypoblast (fig. 28). Subsequently the meso- 
blast in these two flaps develope into muscle-fibres, and in the 
young larva a constant current is kept up by them, passing in 
at the mouth and out at the gill-clefts. This current is easily 
demonstrated by the aid of a little Indian ink suspended in 
the water. 

On the twenty-third day two tentacles begin to grow out 
from the under surface of the upper lip, one each side of the 
middle line; a little later two more appear on the sides, but 
placed more posteriorly ; later still two more appear behind the 
level of the last ; these are situated at the junction of the lower 
hip with the upper. Finally, a median tentacle appears in the 
ventral middle line. This last is far longer than the others 
and from its base a ridge, which is at first low, but increases in 
height posteriorly, extends back between the ventral portion of 
the ciliated ring (figs. 40 and 41). The number of tentacles 


B04 ARTHUR E. SHIPLEY. 


is afterwards increased by a pair of new ones arising between 
each of those already formed. The tentacles subsequently 
become branched (fig. 39). 

With regard to the mesoblast of the head I have little to 
add to the descriptions of Balfour and Scott. The area 
over which the gills extend at their first appearance extends to 
the posterior boundary of the sixth myomere. The most 
anterior myomere is situated close behind the ear, and the ear 
lies above the hyobranchial or first persistent gill-cleft. So 
that at their first appearance the six posterior gill-clefts cor- 
respond in their extent with the six anterior myomeres. As 
the larva grows the gill region appears to elongate with rela- 
tion to the muscular myomeres, so in my latest larva there are 
about nine myomeres over the area of the six gills (fig. 43). 
These anterior myomeres become V-shaped with the open 
angles directed forwards; turned the opposite way to those of 
Amphioxus, 

The mesoblast between the gills arranges itself into head 
cavities (fig. 21), and as Balfour and Scott have already 
shown, there are two head cavities in front of the hyomandi- 
bular cleft. These are at first continuous, but with the for- 
mation of the stomodzum they separate. One becomes pre- 
oral and obviously corresponding with the preemandibular 
head cavity of Elasmobranchs; the other with the mandi- 
bular (fig. 21). The walls of these cavities ultimately form 
the skeleton of the gill arches, the muscles of which are all 
of the tubular kind. Owing to the rudimentary condition of 
the eye in Ammoceetes, no eye-muscles are present and conse- 
quently it is impossible to say whether or no they are derived 
from the walls of the head cavities, but the researches of 
Stannius and Langerhans have shown that they possess 
the same histological characters as the muscles of the gills and 


upper lip. 
The Central Nervous System. 


The development of the central nervous system has been 
described above up to the stage when the central canal has 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 3855 


first appeared. The lumen is at first circular in outline, and 
the walls of the canal of uniform thickness (fig. 11). Ulti- 
mately in the region of the body the lumen becomes elon- 
gated and slit like (fig. 24); in the anterior end the Inmen 
widens into the variously shaped cavities which form the 
ventricles of the brain. The cells forming the walls of the 
canal are primarily more or less cubical, but they soon 
become spindle shaped, except those which form the roof 
and the floor of the central canal. These are formed of 
a single layer of short columnar cells. The canal is in 
the youngest stages proportionately very much larger than in 
the later; its size is diminished and its form altered by the 
thickenings which take place in different parts of the brain. 

The white matter first makes its appearance on the eighteenth 
day as two thin bands, one on each side of the brain and 
spinal cord (fig. 37). Later these unite in the ventral side 
and form an anterior commissure. After the appearance of 
the white matter the ganglion cells lose their spindle-shaped 
outline and become again circular. 

The cranial flexure is very slight; the anterior end of the 
brain is, however, slightly bent down, and with it the anterior 
end of the notochord (fig. 23). 

About the sixteenth day considerable changes take place in 
the brain; from the anterior and ventro-lateral angles of the 
fore-brain two diverticula are given off; these are the optic 
vesicles (fig. 30). They continue to grow upwards and back- 
wards till their blind end reaches a position behind and above 
the anterior end of the notochord. 

At the blind end of the diverticulum a knob is formed by 
the outer face proliferating cells, which form a multicellular 
retinal layer. The posterior face later on developes pigment 
in its cells. The lens is budded off from the inside of the 
single layer of epidermis, and lies as a flattened mass of cells 
close against the retinal layer (fig. 40). The stalk of the 
primary vesicle becomes solid by its walls coalescing on all 
sides, and forms the optic nerves. At their origin these nerves 
form a commissure projecting into the cavity of the fore-brain 


306 ARTHUR E,. SHIPLEY. 


on its ventral side; by the twenty-second day this optic 
chiasma is covered in by a single layer of ganglion cells. It is 
this body that Dohrn has by mistake figured as the Tuber 
cinereum (21). The commissure is shown in transverse 
section in fig. 39; the lumen of the infundibulum is seen 
below it, the cavity of the fore-brain above. 

About the same time that the optic vesicles commence to be 
given off from the anterior end of the brain a median dorsal 
evagination also appears. It was mentioned above that in the 
median line, both dorsally, ventrally, and in front, the central 
canal is enclosed by a single layer of more or less columnar 
cells, whilst the lateral walls are thick. This single layer is 
interrupted ventrally by the formation of the optic chiasma. 
Dorsally it is produced on the sixteenth day by the evagina- 
tion in question, which is the rudiment of the pineal gland 
(fig. 31). The walls of the pineal gland then consist at first 
of a single layer of cells forming a hollow sac which pushes its 
way between the brain and the epidermis, spreading out on all 
sides (fig. 31). At first its lumen is continuous with that of 
the fore-brain, but ultimately, by the folding of its walls, its 
cavity is obliterated and the communication with the lumen of 
the fore-brain is shut off. 

The eighteenth day, two days after the first appearance of 
the optic vesicles and the pineal gland, is the earliest date 
on which I have been able to recognise the appearance of any 
division into fore-, mid-, and hind-brain. On this day the 
single layer of cells roofing the central canal becomes folded in 
the manner indicated in fig. 23. This takes place at about 
the level of the attachment of the velum, a little in front of 
the ear. In larva of fifty-two days, this groove has not 
changed its form, but has become deeper. 

The division between the fore- and hind-brain is by no 
means so well marked; indeed, I have been unable to find any 
external groove, although it has been described by previous 
writers. Longitudinal horizontal sections through the brain 
show, however, that just behind the infundibulum and pineal 
gland the walls thin out so that the lumen appears diamond 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 857 


shaped. This thin wall I conclude makes the division between 
the optic thalami and the crura cerebri. 

The hind-brain and mid-brain resemble each other closely 
in structure, the mid-brain being only a trifle larger. Their 
cavity, which is at first slit like, becomes triangular by the 
lateral growth of the roof which pushes the side walls apart 
dorsally (figs. 40 and 41). This thin roof extends back as far 
as the second gill-cleft, after which it disappears and the 
nervous system has the structure represented in fig. 42. 

About the forty-fifth day a median longitudinal fold appears 
in the thin roof; this is the first of the numerous folds found 
in the roof of the mid- and hind-brain of the adult (fig. 41). 

The fore-brain still has its thick side walls, the optic thalami. 
Just in front of the stalk of the pineal gland a commissure of 
transverse fibres is found which runs from side to side on about 
the twenty-third day. This commissure corresponds with the 
Commissura tenuisima, described by Ahlborn in his 
exhaustive work on the brain of the adult Lamprey. It also 
probably corresponds with the commissure found by Balfour 
in Scyllium situated just in front of the base of the pineal 
gland. Osborn has recently described a similar commissure 
in the brain of the Amphibia, Menopoma, Meno- 
branchus, Amphiuma, and Rana, and I have adopted the 
name he proposes for it, the Superior Commissure. The com- 
missure of the pineal stalk in the Mammalian brain seems to 
occupy the same relative position. This superior commissure 
is at first covered with but a few ganglion cells, but these 
afterwards increase until two bodies are formed, the Ganglia 
Habenule. The left one is very small (fig. 39), but the right is 
a structure of considerable size, projecting downwards and back- 
wards, and reducing the lumen of the fore-brain to a Y-shaped 
slit. These bodies have been fully described by Ahlborn in 
the adult ; it is interesting to note that the curious asymmetry 
they possess is present from their first appearance. No other 
commissure has made its appearance by the fifty-second day. 

The cerebral hemispheres show some signs of appearing as 
lateral outgrowths in my oldest larvae, but no trace of paired 

VOL, XXVIT, PART 3,—NEW SER. Gc 


358 ARTHUR E. SHIPLEY. 

lateral ventricles are to be seen. The lateral outgrowths of 
the hemispheres embrace between them a mass of tissue formed 
at the back of the olfactory pit, which resembles in every way 
nerve matter. This structure is shown in figs. 33, 34, and 35, 
drawn from a series of sections taken through the head of a 
fifty-two days’ larva. This tissue in question appears to con- 
sist of ganglion cells. It is traversed by a canal which ends 
blindly behind and opens by the median nasal pit in front. 
Posteriorly it is continuous with a sheet of tissue which is de- 
scribed by Dohrn and Scott as giving rise to the pituitary 
body (fig. 39). Unfortunately my larve were not sufficiently 
old to enable me to determine whether this mass of tissue 
comes into closer relation with the brain and forms the olfac- 
tory lobes, or whether, as seems more probable from what we 
know of the development of these structures in other animals, it 
forms only the peripheral portion of the olfactory apparatus. 

About the twenty-fifth day some of the ganglion cells in the 
postero-lateral angle of the grey matter become much larger 
than the surrounding ones. These cells are particularly fre- 
quent in that part of the hind-brain lying between the audi- 
tory capsule. They probably develope into the “outer large 
cells” of Reissner. 

With regard to the development of the cranial nerves, I 
have no observations on the origin of the olfactory nerve, as 
this apparently does not arise till a much later stage than that 
attained by my oldest larvee. The origin of the optic nerve as 
an outgrowth of the brain has been described above. Owing 
to the rudimentary condition of the eye, the muscles of that 
organ are not developed, and consequently the third, fourth, 
and sixth nerves do not arise till a much later stage. This 
leaves the fifth, seventh, eighth, ninth, and tenth nerves to be 
considered. 

The origin of these nerves is much obscured by the yolk 
which crowds the cells of the embryo at the time they first 
appear. On the seventeenth day the first origin of the ganglia 
in the fifth and seventh nerve is seen. The ganglia arise as 
proliferations of the epiblast. By this means a knob of cells 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 309 


is formed, which arises at about the level of the notochord 
(fig. 32). This heap of cells arises close behind the lens of the 
eye, but seems to be distinct from it. It is divided into a 
larger anterior part, which belongs to the fifth nerve, and a 
smaller posterior portion, which forms the ganglion of the 
seventh. The roots of the nerves seem to me—though it is 
difficult to be certain on this point—to arise as outgrowths 
from a neural ridge in the lateral surface of the brain; these 
grow down and fuse with epiblastic thickening. This origin 
of the roots of the nerves corresponds with that described by 
Balfour, Marshall, Van Wijhe, and Beard, in the 
Elasmobranchs, and differs from what occurs in the Am- 
phibia as described by Spencer, where the nerve also is 
derived from the inner layer of epiblast. As Spencer sug- 
gests, this is probably due to the presence of a double layer of 
epiblast, the epidermic and nervous, in the Amphibia. 

By the nineteenth day the ganglion of the fifth nerve has 
completely separated off from the skin. It has now divided 
into two portions, which have, however, a common root taking 
its origin from the hind-brain just in front of the ear. The 
most anterior part forms a large ganglion on the root of a 
nerve which runs over the eye (fig. 22). This is the oph- 
thalmic ganglion, and the nerve is the ophthalmic branch of 
the trigeminus; it probably corresponds with the portio- 
profunda of the ophthalmicus superficialis of the Elasmobranchs. 
Immediately behind the ophthalmic ganglion, but quite dis- 
tinct from it, lies the ganglion of the other half of the fifth 
nerve. From this a mandibular nerve proceeds to run close 
behind the mouth, and later a maxillary branch appears pre- 
orally. In the angle between these ganglia the eye lies. The 
nerve connecting the ophthalmic with the main ganglion of 
the fifth nerve, described by Ahlborn in the adult, is not found 
at this stage, and both the ganglia are of approximately equal 
size. 

The seventh nerve arises behind the fifth and enters its 
ganglion, which, when separated off from the epiblast, lies close 
in front of the ear capsule (fig. 38). In early stages, 


360 ARTHUR E. SHIPLEY. 


whilst the most anterior gill-cleft—spiracle—is still present, 
the nerve can be seen passing from the ganglia between the 
rudimentary gill-cleft and the first persistent one—the hyo- 
branchial. Later on the ganglion increases in size, and ex- 
tends round the under and inner face of the auditory sac 
towards the ganglion of the ninth nerve, but it never quite 
reaches it, and the connection between the ganglion of the 
seventh and of the tenth nerves must be of: later origin. 
Neither does the ganglion of the seventh fuse with that of the 
fifth, though they are close together, and the root of the 
seventh does not enter the ear capsule to leave it again, as is 
the case in the adult. After the appearance of the ciliated 
ring in the place of the first gill-cleft, the seventh nerve sup- 
plies this structure. 

A few fibres from the brain enter the recessus labyrinthi 
of the ear; these arise close to the root of the seventh, and 
constitute the eighth nerve. 

The ganglia of the ninth and tenth nerves would seem to 
arise from a mass of cells split off from the epiblast close 
behind the ear. At a little later stage the ninth nerve has its 
ganglion lying close against the posterior boundary of the ear ; 
the nerve is continued along the posterior wall of the first 
persistent cleft, the hyobranchial. The ganglion seems to be 
still connected with the ganglion of the tenth nerve. This is 
a very large structure; it lies more dorsally than the others and 
it is in close connection with the mid-brain, having as yet deve- 
loped no root. Behind it and connected with it lies a ganglion 
which is situated dorsally above the second persistent gill-cleft ; 
from this chord the main branch of the vagus is continued 
backward, lying just external to the anterior cardinal vein 
(fig. 42). In front of each remaining cleft the chord bears a 
large ganglion, so that, counting the first, there are six distinct 
ganglia borne on the vagus. Ihave not been able to trace the 
fibres of this nerve beyond the last gill-cleft, but my friend 
Mr. Ransom, of Trinity College, tells me he has traced the 
vagus into the heart in the adult Petromyzon. Each of the 
ganglia in the vagus supplies the gill-cleft behind which it lies. 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 361 


There is no trace of the ramus lateralis of the vagus even in 
my oldest larve. 

The ganglion on the ninth nerve lies in front of the first 
myomere, between that and the ear, whilst that of the vagus 
lies between the first and second. The first dorsal root of the 
spinal nerves with its ganglion lies between the third and 
fourth myomere. Behind this there is a dorsal ganglion lying 
opposite each myotome. 

Sagemehl (17) has described very correctly the origin of 
the spinal nerves. The dorsal roots with their ganglia arise 
from a neural ridge which is at first of the same size all along. 
From this the ganglia begin to grow out about the eighteenth 
day, intersegmentally, that is opposite the myotomes. The- 
ganglia are in connection with one another for some time by a 
longitudinal commissure. This commissure appears to consist 
of the remains of the neural ridge; it ultimately disappears, as 
in Elasmobranchs. The dorsal nerves, after leaving the 
ganglia, run into the myotomes and eventually, I believe, reach 
the skin, though on this point I cannot be quite certain. On 
the other hand the ventral roots consist of nerve-fibres only, 
and run straight into the myomeres. They appear, according 
to Sagemehl, very soon after the first appearance of white 
matter in the chord, and they never have any connection with 
the dorsal roots. The resemblance between the distribution of 
the spinal nerves of this larva with those of Amphioxus as 
described by Rohon is very striking. 

The ear is formed, as Scott has described, from an invagina- 
tion of the epiblast. This appears very early about the four- 
teenth day. It soon deepens and becomes completely shut off, 
consisting then of an oval vesicle with a dorsally placed stalk, 
the recessus labyrinthi. This last is the remains of the duct 
leading to the exterior. The ear is in the same condition in 
my oldest larve. No signs of the semicircular canals have 
appeared. The epithelium lining the vesicle is high and 
columnar; about the twenty-second day certain patches of the 
epithelium become higher than the others and the cells develope 
each a very large cilium which projects into the cavity and 


362 ARTHUR E. SHIPLEY. 


bears a knob at its free end (fig. 41). About the same time a 
number of small concretions appear in the ear. These form 
the numerous spherical otoliths. 


Summary. 


I have now described the structure of the chief organs in 
my oldest larva, and I propose to conclude this paper by a brief 
summary of the results obtained. 

In the first place the mesoblast is not completed ventrally by 
a layer of cells split off from the hypoblastic yolk-cells, as 
Scott has described. But the ventral mesoblast is formed by 
the downgrowth of the mesoblastic plates, which ultimataly 
meet and unite in the ventral middle line. 

The blastopore does uot close up, as later observers have 
maintained, but, as Max Schultze described thirty years ago, 
it persists as the anus. There is no neurenteric canal, though 
a solid strand of tissue proceeds back from the alimentary 
canal and fuses with an indifferentiated mass of cells, into which 
the nervous system and mesoblast also pass. 

The lumen of the alimentary canal is that of the mesenteron ; 
it does not become obliterated during larval life. In its anterior 
end the hypoblast remains in connection with the epiblast at 
certain points, and here the gill-clefts arise ; between these the 
mesoblast grows down and forms the gill-bars. The origin of 
the ciliated ring and the hypopharyngeal groove and hyper- 
pharyngeal bar are also described, and the ciliated condition 
of the esophagus and stomach. 

The “ muscle- plates,” whose structure is so peculiar in the 
Lamprey, arise each from a single cell of the mesoblastic 
somites. This increases in size, slides in between the neigh- 
bouring cells, and ultimately occupies the whole of the space 
between two myotomes. Its nucleus divides until each cell 
contains several nuclei. Striated fibrils then appear and in- 
creases till the whole ‘ muscle-plate ” consists of little else be- 
sides these fibrils, squeezing between them a few nuclei. These 
“ muscle-plates ” arise from the segmental half of the meso- 
blast ; the muscles of the gills, lips, and probably of the eye, 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 363 


have a different structure and arise from the ventral unseg- 
mented part. 

The blood-corpuscles arise from the ventral free edges of the 
mesoblast, before they unite in the ventral middle line, they 
collect in a large sinus just behind the heart. The heart 
appears in the ventral mesentery, formed by the union of the 
lateral mesoblastic plates ; at first its lumen is continuous with 
the sinus just mentioned. This sinus lies between the hypo- 
blastic yolk-cells and the epiblast; it subsequently acquires 
walls and forms part of the subintestinal vein. 

The ciliated funnels of the pronephros are left as apertures 
by the segmental duct which in its anterior end is formed from 
agroove. The groove closes up at intervals, leaving four or five 
openings which become the funnels. They do not arise as 
blind projections from the duct, which subsequently, acquire 
ciliated openings. From the first the pronephros has a 
double blood supply, pure blood from the aorta passing to the 
glomerulus, and impure blood in the cardinal veins surrounding 
the tubuli. 

The early development of the skeleton is described up to the 
stage where Professor Parker commenced his researches. 

The canal of the central nervous system developes after the 
neural chord has separated off from the epidermis; it does not 
appear to be lined by any invaginated epidermis, as Calberla 
and Scott maintained. 

The first sign of differentiation of the parts of the brain is 
the formation on the sixteenth day of the optic vesicles and 
pineal gland. The division into fore-, mid-, and hind-brain 
appears soon after, but the fore- and mid-brain are not sepa- 
rated by any well-marked groove. The first transverse com- 
missure to appear is situated just in front of the stalk of the 
pineal gland. It forms the superior commissure of Osborn. 
Afterwards the ganglion cells thicken round it and form the 
asymmetrical ganglia habenule. 

The ganglia on the fifth, seventh, ninth, and tenth nerves 
are derived from epiblastic thickenings. Their roots probably 
arise as outgrowths from the neural ridge. The ganglion of the 


364 ARTHUR E. SHIPLEY. 


fifth divides into two parts, the ophthalmic and mandibular ; 
these have a common root. 

The seventh nerve at its first appearance supplies the first 
or spiracular gill-cleft ; when this is converted into the ciliated 
ring it continues to be supplied by the seventh nerve. 

The connection between the fifth, seventh, and tenth nerve 
ganglia does not exist and must be of later origin. 

The tenth nerve has a large ganglion on its root and bears a 
ganglion above each of the last six gill-clefts. No trace of the 
ramus lateralis is to be seen. 

The origin of the ganglia on the cranial nerves has no 
relation to the sense-organs of the skin; these have not 
appeared even in my oldest larva. 


LIveERATURE REFERRED TO. 


(1) 1836. Jon. Miitter.—‘ Vergleichende Anatomie der Myxinoiden, der 
Cyclostomen mit durchbohrten Gaumen,’ Berlin. 

(2) 1851. Srannrus.—“ Ueber den Bau den Muskeln bei Petromyzon 
fluviatilis,” ‘ Gottinger Nachrichten,’ 1851. 

(3) 1856. Aue. Mitier.—“ Ueber der Entwicklung der Neunaugen,” 
‘Miiller’s Archiv,’ 1856. 

(4) 1856. Max Scuuttz.—‘ Die Entwickelungsgeschichte von Petromy- 
zon Planeri,’ Haarlem. 

(5) 1864. Ave. Mijiter.—* Beobachtungen iiber die Befruchtungserschein- 
ungen im Ki der Neunaugen,” ‘ Verhandl. d. Konigsberger 
Phys.-dkonom. Gesellsch.’ 

(6) 1867. GrenAcHER.— Beitrage zur Erkenntniss der Muskeln der Cyclo- 
stomen und Leptocardier,” ‘ Zeit. f. wiss. Zool.,’ Bd. xvii. 

(7) 1870. Owssannixow.— The Development of Petromyzon fluvia- 
tilis’ (Russian). 

(8) 1878. Paut LancErnans.—“ Untersuchungen iiber Petromyzon 
Planeri,” Freilung, i B., 1873. 

(9) 1873. Witu. Mtrier.— Ueber die Hypobranchialrinne der Tunika- 
ten und deren Vorhandsein bei Amphioxus und den Cyelo- 
stomen,” ‘Jen. Zeit. f. Med. u. Naturwiss.,’ Bd. vii. 

(10) 1875. Witn. Mitter.—* Ueber das Urogenitalsystem des Amphioxus 
und der Cyklostomen,” ‘ Jen. Zeit. f. Med. u. Naturwiss.,’ Bd. ix. 


DEVELOPMENT OF PETROMYZON 


(11) 1877. 


(12) 1877. 
(13) 1878. 


(14) 1879. 
(15) 1880. 
(16) 1881. 
(17) 1882. 
(18) 1882. 
(19) 1883. 


(20) 1883. 


(21) 1883. 
(22) 1884. 


(23) 1885. 


FLUVIATILIS. 365 


E. Carpurta.—* Der Befruchtungsvorgang beim Petromyzon 
Planeri,” ‘ Zeit. f. wiss. Zool.,’ Bd. xxx. 

HE. Carperta.—* Zur Entwicklung des Medullarrohres u. der 
Chorda dorsalis der Teleostier und der Petromyzonten,”’ ‘Morph. 
Jahrbuch,’ Bd. iii. 

KuprrerR UND Brenecxe.— Der Vorgang der Befruchtung am 
Ki der Neunaugen,” ‘ Festschrift zur Feier von Th. Schwann,’ 
Konigsberg. 

Anton ScHNEIDER.—‘ Beitrage zur vergleichenden Anatomie und 
Entwicklungsgeschichte der Wirbelthiere,’ Berlin, 1879. 

W. B. Scorr.—* Vorlaufige Mittheilung. ib. d. Entwicklungs- 
geschichte d. Petromyzonten,” ‘ Zool. Anzeiger,’ Nos. 63 and 64. 

Nvrt.—“ Recherches sur le développement du Petromyzon 
planeri,” ‘Archives de Biologie,’ T. ii. 

SaceMenL.—‘ Untersuchungen iiber die Entwicklung der Spinal- 
nerven,’ Dorpat, 1882. 

W. B. Scort.—* Beitrage zur Entwicklungsgeschichte der Petro- 
myzonten,” ‘Morph. Jahrbuch,’ Bd. vii. 

W. K. Parker, “On the Skeleton of the Marsipobranch Fishes,” 
“ Phil) Trans; Part 1, 1883. 

AHNLBORN.—“ Untersuchungen tiber das Gehirn der Petromyzon- 
ten,” ‘Zeit. f. wiss. Zool.,’? Bd. xxxix. 

Doury.— Die Entstehung der Hypophysis bei Petromyzon 
Planeri,” ‘ Mitth. aus der Zool. Stat. zu Neapel.,’ Bd. iv. 
Autporn.—< Ueber den Ursprung und Austritt der Hirnnerven 

von Petromyzon,” ‘ Zeit. f. wiss. Zool.,’ Bd. xl. 

Dourn.— Die Thyroidea bei Petromyzon, Amphioxus und Tuni- 

caten,” ‘ Mitth. aus der Zool. Stat. zu Neapel., Bd. vi. 


366 ARTHUR E. SHTPLEY. 


EXPLANATION OF PLATES XXVI, XXVII, XXVIII, 
and XXIX, 


Illustrating Mr. Arthur E. Shipley’s Paper on “ Some Points 
in the Development of Petromyzon fluviatilis.” 


Reference Letters. 


a. Anus. a.c. Anterior cardinal. ao. Aorta. au. Ear. aur. Auricle. 
b.c. Body cavity. 4/. c. Blood-corpuscles. dp. Blastopore. 4Gr.'-dr.8 First 
to eighth gill-clefts. 67.4. Skeleton of branchial bars. 47.v. Vessels of bran- 
chial bars. c. Cerebral hemispheres. c.g. Ciliated groove. a. Dorsal fin. 
d. 1. Dorsal lamella. d.m. Dorsal mesentery. e. Hye. e.g. Egg membrane. 
ep. Epiblast. . 6. Fore-brain. fg. Fore-gut. g. Groove between mid- 
and hind-brain. g. 4. 2. Left ganglion habenule. g. 4. 7. Right ganglion ha- 
benule. g/. Glomerulus. g.z. Ganglion cells at base of olfactory invagination. 
Ah. Heart. Ad. Head. Ad. c. Head-cavities. 4.6. Hind-brain. hy. Hypo- 
blast. 7¢. Iter a tertio ad quartum venticulum. ¢zf Infundibulum. Ui. ¢. 
Liver tubules. 7.7/7. Lower lip. J. ¢. Lamina terminalis. m. Mesenteron. 
m.6. Mid-brain. m. br. Muscle of branchial bar. mes. Unsegmented mesoblast. 
mes. som. Mesoblastic somites. m./. Muscle-fibre of heart. m.g. Mid-gut. m. 
Muscle-plate. my. Myomere. x. Notochord. za. Olfactory invagination. 
n.r. Neural ridge. uw. Nucleus of muscle-plate. 0. e. Ciliated epithelium 
lining nasal invagination. op. ch. Optic chiasma. op. Ophthalmic ganglion. 
op. th. Optic thalami. op.v. Optic vesicle. p.g. Postanal gut. pix. Pineal 
gland. pit. Pituitary body. pr. Primitive streak. +. 7. Recessus labyrinthi. 
s. c. Segmentation cavity. s. cm. Superior commissure. s.d. Segmental duct. 
sm.pl. Somatopleure. sp.c. Spinal cord. sp. gl. Spinal ganglion. sp. pl. 
Splanchnopleure. st. Stomodeum. s.v. Sinus venosus. ¢. Tentacles. 7h. 
Thyroid gland. ¢. Trabecule. ¢ub. Tubule of pronephros. a. 7. Upper lip. 
v. Velum. v. ao. Ventral aorta. ven. Ventricle. v./f. 6. Cavity of fore- 
brain. v. 4. 6. Cavity of hind-brain. v.7. Ventral ridge in mouth. vv. 
Valves of the heart. y.c. Yolk-cells. V.g. Ganglion of fifth nerve. V.g.e. 
Fpiblastic ingrowth to form ganglion of fifth nerve. VJI. g. Ganglion of 
seventh nerve. X.g. Ganglion of tenth nerve. 


PLATE XXVI. 


Fic. 1.—Spermatozoa of Petromyzon fluviatilis. 

Fig. 2.—Segmenting ovum at the completion of the third or equatorial fur- 
row. e.g. Egg membrane. 

Fic. 3.—Segmenting ovum, showing the next two vertical furrows which 
have divided the upper cells and are extending into the lower. 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 367 


Fic. 4.—Ovum after the invagination is complete, twelve days old, showing 
the blastopore, dp., at posterior end of the neural ridge, x. r. 


Fic. 5.—Transverse section through ovum of thirty-six hours. ep. Epiblast. 
s.c. Segmentation cavity. y.c. Yolk-cells. 


Fie. 6.—Transverse section through ovum of forty-eight hours. s. ¢. Seg- 
mentation cavity. ep. Epiblast. y.c. Yolk-cells. 


Fic. 7.—Transverse section through ovum of sixty-seven hours. 


Fie. 8.—Transverse section through ovum of eighty-six hours, showing 
epiblast gradually thinning out. 
Fig. 9.—Longitudinal section through commencing gastrula, 136 hours. 


bp. Blastopore. hy. Hypoblast. y.c. Yolk-cells. m. Mesenteron. s.c. Seg- 
mentation cavity. 


Fic. 10.—Section through embryo of about the same stage as Fig. 4. 
bp. Blatsopore. y.c. Yolk-cells. Ad. Head. 


Fic. 11.—Transverse section through the body of an embryo just before 
hatching, seventeenth day. sp.c. Spinal cord. 2. Notochord. m. Me- 
senteron. mes. Mesoblast. s. d. Segmental duct.  Zeiss’s A, oc. 2, 
cam. luc. 


Fic. 12.—Transverse section through embryo of thirteenth day. sp. ¢. Spinal 
cord. 2. Notochord. mes. Mesoblast. m. Mesenteron. y.c. Yolk-cells. 
Zeiss’s A, oc. 2, cam. luc. 

Fic. 13.—Transverse section through embryo of fourteen days. Letters 
asin Fig. 12. Zeiss’s A, oc. 2, cam. luc. 

Fie. 14.—Transverse section through tail of larva twenty days old. Sp. C. 
Spinal cord. 2. Notochord. p.g. Solid postanal gut. mes. Mesoblast. dp. 
Blastopore. d./. Dorsal fin. Zeiss’s A, oc. 3, cam. luc. 

Fic. 15.—Transverse section from the same series as Fig. 14, but posterior 
to blastopore. d./f. Dorsal fin. mes. Mesoblast. pr. Fused tissue of noto- 
chord, spinal cord, and postanal gut, or primitive streak. Zeiss’s A, oc. 3, 
cam. luc. 

Fig. 16.—Transverse section of embryo just before hatching, seventeen 
days, through region of blastopore. dp. Blastopore. sp. c. Spinal cord. x. 
Notochord. y.c. Yolk-cells. 

Fie. 17.—Longitudinal section of embryo, showing formation of somites. 
n. Notochord. mes. som. Mesoblastic somites. sp.c. Spinal cord. d./, 
dorsal fin. 

Fic. 18.—Longitudinal section of embryo just before hatching. sp. c. Spinal 
cord. my. Myomere. sm. pl. Somatopleuric layer of somite. sp. p/. Splanch- 
nopleuric layer. 2. Notochord. Zeiss’s A, oc. 3, cam. luc. 

Fic. 19.—A piece of the cartilage of a branchial bar. 


Fic. 20.—A longitudinal vertical section through the tail of a larva twenty- 


368 ARTHUR E. SHIPLEY. 


one days old. a. Anus. p.g. Solid postanal gut. x. Notochord. sp. ¢. 
Spinal cord. pr. Primitive streak. y.c. Yolk-cells. 


- Fic. 21.—A longitudinal section through side of head of seventeen days’ 
embryo, showing the first three evaginations to form gill-clefts, and the true 
head-cavities. aw. Har. Ad. c’. aud hd. ec’. The first and second head-cavity. 
br., br?., and dr3, The first rudiments of gill-clefts. 7. v. The vessels of 
gills. s¢. Stomodzum. Zeiss’s A, oc. 3. 


PLATE XXVII. 


Fie. 22.—A longitudinal section through side of head of a larva twenty- 
one days old. au. Har. e. Hye. dr'., dr?., br’., br*. The first to fourth 
primary gill-clefts. 4.6. Hind-brain. ops. Ophthalmic ganglion. V. g. 
Ganglion in main branch of fifth nerve. 


Fic. 23.—A median longitudinal section through the head of a larva twenty- 
one days old. pin. Pineal gland. op.ch. Optic chiasma. if. Infundibulum. 
n. Notochord. st. Stomodeum. 477. Second primitive gill-cleft. ¢. Thyroid 
gland. za. Olfactory invagination. pi¢. Pituitary invagination. m. 6, Mid- 
brain. #%.%. Hind-brain. g. Groove between mid- and hind-brain. J. é. 
Lamina terminalis. 


Fic. 24.—Transverse section through the body of a larva of twenty days. 
sp.c. Spinal cord. fg. Fore-gut. . Notochord. som. pl. Somatopleure. 
sp.pl. Splanchnopleuric layers of myomeres. 0. ¢. Body cavity. 4%. Heart. 
c.f. Ciliated funnel. s. d. Segmental duct. Zeiss’s A, oc. 3, cam. luc. 


Fic. 25.—Transverse section through trunk of larva about twenty-four days. 
Letters as in Fig, 24, and ao. Aorta. a.c. Anterior cardinal. d.m. Dorsal 
mesentery. sp. gl. Spinal ganglion. g/. Glomerulus. Zeiss’s C, oc. 1, 
cam. luc. 

Fic. 26.—Section through embryo, one day before hatching, seventeen days 
old, cut whilst in the egg-shell. 4 Heart. sp.pl. Splanchnopleure. sm.pi. 
Somatopleure. 477. and ér*. Seventh and eighth gill-clefts. Ad. Head-cavities 
behind these. y.c. Yolk-cells. m.g. Mid-gut. 6. c¢. Body cavity. Zeiss’s 
A, oc. 3, cam. luc. 


Fic. 27.—Longitudinal horizontal section through a larva about twenty-two 
days. dr!.—dér*, The eight primary gill-clelts. dr. v. Vessels of gills. dr. 6. 
Branchial bars. jf. g. Fore-gut. ¢ub. Tubule of pronephros. s¢. Stomodeum. 
v. Velum. g.. Ganglion cells at base of nasal invagination. op. ch. Optic 
chiasma. iz/. Infundibulum. v./. 6. Cavity of fore-brain. x. Notochord. 
Zeiss’s B, oc. 1, cam. luc. 

Fic. 28.—Longitudinal horizontal section through larva of thirty-six days. 
u.l. Upper lip. v. Velum. 7. Thyroid gland. 2. ao. Ventral aorta. ven. 


DEVELOPMENT OF PETROMYZON FLUVIATILIS. 369 


Ventricle. aur. Auricle. vv. Valves. s.v. Sinus venosus. Ji. ¢. Liver 
tubules. m.g. Mid-gut. ér. 4. Branchial bars. v. r, Ventral ridge. my, 
Myomere. Zeiss’s A, oc. 1, cam. lue. 

Fig. 29.—Transverse section through pronephros of larva of forty-seven 
days. x. Notochord. m.p. Muscle-plates. xz. Nucleus. ao. Aorta. a. c. 
Anterior cardinal. g/. Glomerulus. ¢wd, Tubules. s. d. Segmental duct. 
bl. c. Blood-corpuscles. /. gy. Fore-gut. d.m. Dorsal mesentery. Zeiss’s D, 
oc. 1, cam. lue. 

Fic. 30.—Transverse section through fore-brain of embryo, seventeen days. 
na. Olfactory epithelium. op. v. Optic vesicle. ». fb. Cavity of fore-brain. 

Fig. 31.—Transverse section through thalamencephalon of larva of eighteen 
days. pin. Pineal gland. op. ¢h. Optic thalmi. v.f 4. Cavity of fore-brain. 
na. Olfactory epithelium. 

Fic. 32.—Transverse section through region of mid-brain of larva of sixteen 
days. st. Stomodial epithelium. V. g. e. Epiblastic origin of ganglion of fifth 
nerve. 2. Notochord. m.6. Mid-brain. 

Figs. 33, 34, and 35.—A series of sections through the anterior end of head 
of a larva fifty-two days old, to show the ganglia cells at base of olfactory 
epithelium, w. 7. Upper lip. 7. 7. Lower lip. ¢. Tentacles. gy. z. Ganglion 
cells at base of nasal invagination. o0.e. Ciliated epithelium lining nasal in- 
vagination. ec. Cerebral hemispheres. v./. b. Cavity of fore-brain. 


PLATE XXVIII. 


Fie. 36.—Branched muscle-fibres of heart of larva forty-nine days old. 
bl. c. Blood-corpuscles. m.f Muscle-fibre cut across. 

Fic. 37.—Transverse section through the hind-brain, showing appearance of 
white matter and ganglion of fifth nerve. 4.4. Hind-brain. s¢. Stomodeum. 
V. g. Ganglion of fifth nerve. This section is rather oblique. 

Fie. 38.—Transverse section through hind-brain, showing origin of ganglion 
of seventh nerve from epiblastic ingrowth. VZJJ. g. Ganglion of seventh 
nerve. az. Auditory vesicle. f. g. Fore-gut. 

Fie. 39.—Transverse section through fore-brain of larva forty-nine days 
old, toshow superior commissure. piz. Pineal gland. v./.6. Cavity of fore- 
brain. s. cm. Superior commissure. g. 4./. Left ganglion habenule. gy. 4.7. 
Right ganglion habenule. op. ch. Optic chiasma. pit. Pituitary body. inf. 
cavity of infundibulum. «7. Upper lip. /.¢. Lower lip. ¢. Tentacles. 
Zeiss’s C, oc. 1, cam. lue. 

Fic. 40.—Transverse section through mid-brain of larva of forty-nine days. 
t. Iter a tertio ad quartum ventriculum. e. Eye. ¢r. Trabecule. vv. r, 
Ventral ridge. Zeiss’s C, oc. 1, cam. luc. 


370 ARTHUR E. SHIPLEY. 


Fic. 41,—Transverse section through hind-brain of larva of fifty-two days. 
v. h. 6. Cavity of hind-brain. au. Har. r./. Recessus labyrinthi. VJ. g. 
Ganglion of seventh nerve. d./. Dorsal lamella. c.g. Ciliated groove. v.7r. 
Ventral ridge. v. Velum. ao. Aorta. Jdr.v. Branchial vessels. Zeiss’s A, 
oc. 3, cam. luc. 

Fic. 42.—Transverse section through region of sixth gill-bar of fifty-two 
days’ larva. Or®. Sixth gill-bar. sp. g/. Spinal ganglion. ao. Aorta. a. c. 
Anterior cardinal. ér.v. Branchial vessels. a@o.v. Ventral aorta. J. 9. 


Ganglion in tenth nerve. d.7. Dorsal lamella. dr. 6. Skeleton of branchial 
bars. m. 47. Branchial muscles. 


PLATE XXIX. 


Fic. 43.—Drawing of larva of fifty-two days. The notch in the liver, 
behind the heart, is due to the large gall-bladder, through whose walls the 


cesophagus is seen. This drawing was made by Mr. E. Wilson from the living 
specimen. 


THE AMMONIACAL DECOMPOSITION OF URINE. 371 


The Ammoniacal Decomposition of Urine. 
By 


Wim. Robert Smith, M.D., D.Se., F.R.S.Ed., 
Examiner in Chemistry and Forensic Medicine, University of Aberdeen. 


With Plate XXX, figs. 1 and 2. 


Wuen freshly voided, healthy urine, as is well known, is a 
clear, transparent, amber-coloured fluid, with a distinct acid 
reaction, and a peculiar aromatic odour. [If left to itself in an 
open vessel slight clouds of mucus soon appear which gradually 
sink to the bottom. After a time the acid reaction is noticed 
to be slightly increased, and crystals of uric acid and oxalate 
of lime are deposited. After a longer or shorter interval, de- 
pendent on the temperature of the surrounding media, this 
marked acidity begins to diminish and finally disappears, the 
urine becomes lighter in colour, a whitish scum forms on the 
surface, and the well-known ammoniacal odour indicates that 
it has become alkaline ; the uric acid crystals disappear, and 
whitish granules of urate of ammonia and prismatic crystals 
of urate of soda take their place, beautiful crystals of phosphate 
of magnesia and ammonia being subsequently thrown down. 

The increase of acidity is called by Scherer the acid fermen- 
tation, and is considered by him to be owing to the presence 
of the vesical mucus. The alkaline change is spoken of as the 
alkaline or ammoniacal fermentation, and is owing to the de- 
composition of the urea into carbonate of ammonia. 

These so-called fermentative changes are well known, and 
have long been recognised. So far back as 1682 Van Helmont 
spoke of the odour of urine as the effect of a putrefactive 


372 WILLIAM ROBERT SMITH. 


ferment, and later on Boerhaave, in a work published in London 
in 1732, makes direct mention of the presence of ammonia in 
urine as the result of decomposition. 

The source of the ammonia was, however, first clearly under- 
stood in 1799, when Cruickshank, Fourcroy, and Vauquelin 
discovered urea, the two latter observers showing that carbonate 
of ammonia was the principal product of its distillation, and 
they further pointed out the relationship between the conver- 
sion of urea in solution in water into carbonate of ammonia by 
heat, and the spontaneous “ fermentative” decomposition of 
urine. With a more accurate knowledge of the composition of 
urea the reason of its conversion into carbonate of ammonia 
became clearer, but the discovery of Proust that freshly voided 
urine could be kept for years in a well-stoppered flask without 
undergoing any change first led him to conclude that the action 
of air, especially of its oxygen, was necessary for its decompo- 
sition. Later authorities attributed the decomposition to the 
presence of a ferment, taking its origin in the putrid destruction 
of the mucus. 

Our ideas on the subject were, however, thoroughly changed 
by the work of Pasteur in 1860. He introduced fresh urine 
into a glass flask, boiled it for a few minutes, and then effectu- 
ally closed the flask by fusing its neck. He then found that 
urine thus treated remained fresh for an indefinite period. 
If, after the lapse of five or six weeks, he introduced into such 
urine pieces of asbestos which had been freely exposed to the 
air, decomposition speedily occurred, giving rise to the am- 
mouiacal smell and the development of numerous organisms, 
monads, vibriones, bacteria, &c. If, however, the asbestos, 
previous to its introduction, had been well heated in a blow- 
pipe flame, no change whatever took place in the urine. It 
was thus clearly shown that the ammoniacal change in urine 
was directly owing to the introduction of germs from the air, and 
subsequently Pasteur and Van Tieghem' showed that in every 
fermenting ammoniacal urine the presence of micro-organisms 


1 Recherches sur la fermentation de l’urée, etc.,’ ‘Comptes rendus,’ T. 
lviii, p. 210—264, 1864. 


THE AMMONIACAL DECOMPOSITION OF URINE. 373 


could be abundantly demonstrated, and to the presence of these 
the destruction of the urea was to be traced. 

The importance of these experiments was at once manifest, 
not only as giving a clearer explanation of the changes in 
urine, but also as indicative of the cause in fermentation gene- 
rally, and in the present day we all recognise the importance 
of Pasteur’s work as being the foundation of our methods of 
inquiry into the causes of infectious diseases. 

Two questions now naturally present themselves for con- 
sideration : 

1. Whether these organisms, which cause the alkaline fer- 
mentation, always gain admission from without, or whether 
freshly voided urine contains such germs, so that unboiled urine, 
carefully protected from contact with the air, may still de- 
compose; which would admit of the conclusion that the 
elements of fermentation do not always arise from without ? 

2. What particular organism causes the alkaline fermenta- 
tion, or are several kinds involved ? 

(1) As regards the entrance of the organism. It has been 
shown by Cazeneuve! and Livon, and Meissner? that perfectly 
fresh urine may be preserved free from any fermentative change 
by eliminating the possibility of the entrance of air and germs, 
and Professor Leube, by a series of ingenious experiments, has 
shown that normal urine, on its exit from the bladder, contains 
neither fungi nor germs, the development of which would cause 
decomposition of the urea. Further, by the exposure for a few 
minutes of nutrient gelatine in shallow glass vessels such as 
those used in plate cultivations, micro-organisms may be culti- 
vated from the air, which, when isolated, are found to be 
capable of giving rise to the decomposition of sterilised urine, 
and which, in form and general characters, are found to be 
identical with the organisms present in decomposed urine. 

(2) Is the ammoniacal change in urine due to the presence of 
one or more organisms? It is with the object particularly of 
dealing with this question that I have lately carried on an in- 


1 ¢Comptes rendus,’ T. Ixxxiv, p. 571, 1877. 
2 ¢ Deutsche Zeitschrift fiir Chirurgie,’ Bd. xiii, p. 344, 1880, 


VOL. XXVI1, PART 3.—NEW SER, DD 


374 WILLIAM ROBERT SMITH. 


vestigation under the direction of Dr. Klein at the Brown 
Institution. 

I would, however, in the first place call attention to a valuable 
paper published last year by Professor W. Leube, to which I 
am indebted for much information, in which he describes 
at some length a series of experiments undertaken by Dr. E. 
Graser and himself with the view of determining the particular 
organisms which produce the alkaline urinary fermentation. 
He mentions that, as the result of their experiments, they were 
able to isolate “ four well-described varieties” which possessed 
this property, two of them to a very great extent, and the re- 
maining two only in a feebler sense. 

The strongest influence he found to be exerted by small bacilli 
which he designated the Bacterium urex. These bacilli 
are described as being of a uniform size, ‘001 mm. in thickness, 
of an average length of ‘002 mm., with rounded ends. 

The second growth of most frequent occurrence is a micro- 
coccus of a globular form, and all of equal size, about °8 m. 
(008 mm.) in diameter. They are occasionally united to form 
diplococci, or two diplococci may join to form a square. 
They do not liquefy gelatine. 

The two remaining organisms which are said to possess a 
weaker and less constant action are: 

J, Small and thick bacilli of an oval shape with a varying 
length of 1:2 m. to 15 m., their greatest width being always 
‘7 or ‘8 m. 

2. Very minute bacilli with a length of from 1:2 to 1:4 m., 
and a thickness of °6 m. 

With the view of further investigating the life-history of the 
organisms producing this fermentation, I took a quantity of 
ordinary normal urine which had been recently voided and 
divided it into two parts; one part I placed aside in a sterilised 
beaker to allow of decomposition taking place in the ordinary 
way ; the other part I boiled in a sterilised flask for half an 
hour. I then filtered it into another sterilised flask, taking the 
ordinary precautions, and finally decanted it into a number of 
sterilised test-tubes which were subsequently steamed for 


THE AMMONIACAL DECOMPOSITION OF URINE. 370 


twenty minutes on two successive days in the steam of boiling 
water ; the tubes were then placed in an incubator, and after an 
interval of three weeks were still found to be sterile without 
the slightest trace of ammonia being present. 

Sterile neutral urine was prepared in the same way. 

In starting the cultivation of the organisms I adopted the 
plan described by Dr. Klein at a recent meeting of the 
Chemical Society. The fine end of a freshly made capillary 
pipette was placed in the ammoniacal urine, and a little 
allowed to ascend in the tube by capillarity ; a number of tubes 
containing nutrient gelatine were then inoculated by passing 
the pipette through the cotton-wool plug and allowing a drop- 
let of the urine to pass out; the tubes were then placed in 
water having a temperature of about 40° for the purpose of 
melting the gelatine; they were then gently shaken so that 
the droplet which had been introduced should be uniformly 
distributed, the gelatine being subsequently poured out, with 
the usual precautions, into the lower of the two dishes used in 
plate cultivations and allowed to reset. After this had oc- 
curred, the glasses were placed on a glass plate, covered with 
a Bell jar containing a piece of moist blotting paper and main- 
tained at a temperature of 20° C. in an incubator. 

By these means after the introduction of the smallest droplet 
a large number of organisms was obtained, and by the subse- 
quent processes of ‘ fractional cultivation’ and “ dilution ” 
these were isolated, and the tubes containing the acid and 
neutral sterile urine inoculated with them with the view of 
determining the particular organisms producing the ammo- 
niacal change. 

By these methods I was able to isolate about twenty dif- 
ferent organisms, both bacilli and micrococci, but after re- 
peated experiments I only found one organism—a micrococcus 
—able to decompose the urea into carbonate of ammonia. It 
would be tedious and serve no useful purpose to describe each 
of these organisms, and so I shall confine my remarks to a 
description of that one which induces the desired change. 

If a plate cultivation be made of this micrococcus, and kept 


376 WILLIAM ROBERT SMITH. 


at a temperature of 20° C., in twenty-four hours a number of 
small points are visible which by an ordinary magnifying glass 
are seen to have a faint outline, and to be scattered uniformly 
over the surface ; in two days they are very distinct and are 
seen as circular whitish spots of the size of a fine point. 
These spots do not increase much in size, and in a few days 
liquefaction of the gelatine commences. 

In tube cultivations, in which the solid gelatine is inocu- 
lated by means of a platinum wire inserted for some distance 
in the depth, the tubes being subsequently placed in an incu- 
bator at 20° C., in twenty-four hours the channel of inocu- 
lation is visible as a pale whitish streak made up of closely 
placed minute dots; these in a few days so enlarge that an 
appearance is presented of more or less parallel lines of small 
dots, at the same time that the growth spreads over the surface 
as a whitish film. In about three or four days the first trace 
of liquefaction is seen with slight depression of the surface ; 
this liquefaction gradually extends downwards from the sur- 
face, the liquefied part being thick and uniformly turbid. 

The accompanying drawings (Pl. XXX, figs. ] and 2) show 
these characteristics, and fig. 2 the amount of liquefaction which 
had taken place in eighteen days, the tube having been inoculated 
on the 12th July, and the sketch made on the 30th July. 

Microscopically, the micrococci are seen to be mostly single, 
or diplococci; there are, however, a few short chains and a few 
small groups of four, five, to eight. 

With this organism I inoculated both acid and neutral 
sterile urine, and in twenty-four to thirty-six hours the 
ammoniacal change took place. I also inoculated the fluid 
recommended by von Taksch, consisting of one litre of water, 
one eighth gramme of acid phosphate of potash, one sixteenth 
gramme of sulphate of magnesia, and three grammes of urea 
with a like result. 

Therefore, so far as my observations go, the ammoniacal 
decomposition of urine is brought about by the presence of a 
micrococcus which differs from that described by Professor W. 
Leube, inasmuch as it liquefies gelatine. Whether this organism 


THE AMMONIACAL DECOMPOSITION OF URINE. 377 


is identical with the organism known since Pasteur and Cohn 
(‘ Zeitsch. f. Biol.,’? A. Pfl. ii) as the Micrococcus uree I 
cannot say, because the characters of this latter had—at 
the time when Pasteur and Cohn investigated them—not been 
so studied by plate cultivation, &c., as they now are. 

I have not been able to detect any other organism having a 
like effect, although it is possible that there are such pos- 
sessing this quality in an inferior degree. 


DESCRIPTION OF PLATE XXX, figs. 1 and 2, 


I}lustrating Dr. Wm. Robert Smith’s Paper on “ The Ammo- 
niacal Decomposition of Urine.” 


Fie. 1.—Showing dotted appearance of the organism in the depth of gela- 
tine, with surface film, and commencing liquefaction at surface. 

Fic. 2.—Showing the amount of liquefaction which had taken place in 
eighteen days from the date of inoculation of a gelatine tube with the 
Micrococcus uree. 


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NOTES ON ECHINODERM MORPHOLOGY. 379 


Notes on Echinoderm Morphology, No. X. On 
the Supposed Presence of Symbiotic Alge in 
Antedon rosacea. 

By 


P. Herbert Carpenter, D.Sc., F.R.S., F.U.8., 
Assistant Master at Eton College. 


With Plate XXX, fig. 3. 


THE anatomical monograph on Antedon rosacea which 
has been recently published by Messrs. Vogt and Yung,! con- 
tains the exposition of a new theory as to the nature of the 
sacculi, those problematical structures which have hitherto so 
completely puzzled all the various naturalists who have devoted 
any attention to the Crinoidea. These vesicular bodies, to 
which the name sacculi was given by Dr. Carpenter,? were 
regarded by him as possibly sense-organs, by Edward Forbes 
- as ovaries, by Wyville Thomson as calcareous glands, and as 
possibly excretory organs by Perrier,® with whom Ludwig‘ was 
inclined to agree ; while Vogt and Yung describe them as sym- 
biotic algee.® 

Colourless, or nearly so during life, they become strongly 
tinged after death by the red pigment set free from the peri- 
some (antedonin?), and they then appear as the red spots 

1 ¢Traité d’Anatomie Comparée Pratique,’ Livr. 7, 8, pp. 519—572. 

2 « On the Structure, Physiology, and Development of Antedon (Coma- 
tula, Lamk.) rosaceus,” ‘Proc. Roy. Soc.,’ 1876, vol. xxiv, p. 227. 

3 “Recherches sur l’Anatomie et la Régénération des Bras de la Coma- 
tula rosacea,” ‘Arch. de Zool. exp. et géen.,’ 1873, T. ii, p. 67. 

4 « Beitrage zur Anatomie der Crinoideen,” ‘ Zeitschr. f. wiss. Zool.,’ 1877, 
Bd. xxviii, p. 305. 

* Op. cit., p. 570. 


380 P. HERBERT CARPENTER. 


which are so abundant at the sides of the ambulacra, especially 
in the pinnules. They occur in most, if not in all the species of 
Antedon, but are not always equally visible, being, as a rule, 
smaller and less darkly coloured in those from considerable 
depths. Their nature has been a constant puzzle to me ever 
since I began to make a special study of the Crinoids, eleven 
years ago; and any observations which would place their 
nature beyond a doubt would be an immense relief to my 
mind. Without desiring to express a decided opinion as yet, I 
find some difficulty in accepting the theory that they are sym- 
biotic algve, for reasons which will appear in the following pages. 

I will first quote the description which is given by the Swiss 
authors of these structures as they occur in Antedon 
rosacea. 


_ “Les spores amceboides de ces Zooxanthelles immigrent dans les larves, 
pendant que celles-ci nagent encore dans la mer. M. Goette les a décrites 
a cette époque comme des cellules contractiles, colorées en jaune, munies de 
noyaux, et ayant la forme de massues, dont le bout épaissi fait souvent encore 
saillie au-dessus de l’épiderme, ou on les trouve constamment. Ces cellules 
entrent plus profondément dans les tissus, elles deviennent rondes, dévelop- 
pent dans l’intérieur des masses colorées, une ou deux, qui se divisent en 
granules collés ensemble. Les paquets de granules réunis, ont, suivant M. 
Perrier, des queues trés longues et déliées, ce sont donc de véritables zoo- 
spores. Arrivées a cet état, les Zooxanthelles ont encore le mouvement 
amceboide di a leur protoplasme incolore, et sont entourées outre leur contour 
propre, d’une sorte de capsule formée par les tissus.” 


The structures which Vogt and Yung call amceboid spores 
are the pyriform oil-cells of Wyville Thomson,” who found 
them in the larva, “immediately after escaping from the 
vitelline membrane ;” and he further described how “the 
surface is dotted over with the wider ends of large pyriform 
lemon-coloured oil-cells immersed perpendicularly in the sar- 
code.” This fact appears to me to be a serious objection to 
Vogt and Yung’s theory that the lemon-coloured oil-cells are the 
migrating amceboid spores of symbiotic alge, which must lose 


1 Op. cit., p. 570. 
2“«QOn the Embryogeny of Antedon rosaceus, Linck (Comatula 


rosacea of Lamarck),” ‘ Phil. Trans.,’ 1865, pp. 521, 522, pl. xxiv, fig. 5. 


NOTES ON ECHINODERM MORPHOLOGY. 381 


no time in making their way into the ectoderm of the recently 
hatched larva. But unless I am greatly mistaken, these oil- 
cells are seen in Thomson’s figures of the larva while it is still 
within the vitelline membrane ;! and if this should really prove 
to be the case, it is a fatal argument to one part at least of 
Vogt and Yung’s theory. 

Goette” does not mention the exact time of their first 
appearance, but he describes them as follows: “ Zu einer 
gewissen Zeit treten in der sonst noch unverinderten Ober- 
haut zwischen ihrer Cylinderzellen keulenformige, tief gelb 
gefarbte, kernhaltige Zellen auf, deren dickeres Ende nach 
aussen gekehrt ist und nicht nur die Oberflache erreicht, son- 
dern bisweilen aus ihr hervortritt.” I cannot find, however, 
that Goette ever spoke of these yellow cells as contractile, 
as stated by Vogt and Yung; though lower down on the same 
page he described certain other cells in the epidermis which 
“sitzen mit dem dickeren kernhaltigen Ende fest an der 
inneren Cuticula;”’ and he proceeds to say of them “da sie 
ferner kontractil sind, so ziehen sie die letztere faltenformig 
ein, wodurch die Oberflache alterer Larven runzelig aussieht.” 
He also gave a figure illustrating this point, in which the 
yellow cells and the contractile cells are distinguished by 
separate letters ; and I do not know therefore why the former 
should be called contractile, and described as the amceboid 
spores of symbiotic alge by Messrs. Vogt and Yung. 

Goette prudently declined to give any opinion as to their 
nature, but described them as occurring in greatly increased 
numbers in the largest larvee which he examined ; while they 
are very abundant in the more advanced Pentacrinoid figured 
by Wyville Thomson,’ which has the bases of the arms appear- 
ing above the radial axillaries. They are equally abundant in 
the perisome of the mature Antedon, where they have been 


1 Phil, Trans.,’ 1865, p. 521, fig. c; pl. xxiv, fig. 4. 

2“ Vergleichende Entwickelungsgeschichte der Comatula mediter- 
ranee,” ‘Archiv f. Mikrosk. Anat.,’ Bd. xii, 1877, p. 596, Taf. xxvi, fig, 18. 

3 ¢Phil, Trans.,’ 1865, pl. xxvii, fig, 1. 


382 P, HERBERT CARPENTER. 


described by Perrier,! whose excellent account and figures of 
them seem, for a wonder, to have escaped the notice of 
Messrs. Vogt and Yung. He writes as follows: 

*Tmmédiatement au-dessous de la couche épithéliale se trouve un tissu par- 
ticulier formé d’éléments qui semblent relier entre elles la membrane cellu- 
laire qui forme le tégument externe et la membrane qui revét l’axe calcaire du 
bras. Ces éléments sont incolores, fusiformes, et les extrémités du fuseau, 
qui souvent se bifurquent, donnent naissance a des prolongements qui, aprés 
s’étre plus ou moins divisés, viennent s’attacher a |’une des deux membranes 
qui relient ces éléments. Dans la partie renflée de ces sortes de cellules 
étoilées on apergoit toujours un noyau trés-brillant.” 

The identity of these “éléments étoilées” with Goette’s 
contractile cells is evident from a comparison of the excellent 
figures given by both authors, and Perrier states expressly that 
he has not observed them perform amceboid movements or 
contractions of any kind, He regards them as “surtout des 
éléments du tissu conjonctif;’? and he proceeds to compare 
them with the yellow oil-cells of Wyville Thomson, “ corpus- 
cles jaune clair et trés-réfringents . . . quise retrouvent 
en plus ou moins grande abondance dans toutes les parties du 
corps de animal.” Finding what appear to be several inter- 
mediate stages between the two structures, he was led to the 
conclusion that ‘“‘les éléments étoilées et les gros éléments 
jaunes sont morphologiquement de méme nature, que ces 
derniers ne différent des autres que parce que la matiére jaune 
a envahi tout Vintérieur de la cellule et distend ses parois.” 
Now, however, we are told by Vogt and Yung that these 
yellow cells which Perrier found to be universally distributed 
in all parts of the mature Antedon rosacea, are really the 
ameeboid spores of symbiotic alge, and that the sacculi at the 
sides of the ambulacra and elsewhere are groups of “ véritables 
zoospores” of the same alge. According to their theory these 
zoospores are later developmental stages of the yellow cells, 
Perrier’s connective-tissue elements. 

The contents of the sacculi were described by . Professor 
Perrier ? in the following terms: 

1 Loc. cit., pp. 51—53, pl. iii, fig. 11. 
2 Loc. cit., p. 67; pl. ii, fig. 7. 


NOTES ON ECHINODERM MORPHOLOGY. 383 


‘*Chacune des masses en question se prolonge généralement en une sorte de 
queue trés-gréle, assez longue, souvent entortillée, continue avec la membrane 
propre de la masse d’owt elle dépend, et qui parait complétement anhiste. 
Dans cette membrane qui forme comme une sorte de sac et sur les parois de 
laquelle se montre presque toujours une sorte de petit noyau de couleur brune, 
on trouve un nombre variable de petites spheres incolores, trés-réfringentes, 
ressemblant a des goutelettes d’un liquide transparent, et probablement en- 
veloppées chacune d’une mince membrane qui l’empéche de se confondre avec 
ses voisines. Ce sont ces petites sphéres qui absorbent si rapidement les 
matiéres colorantes et qui, sous |’action du sublimé corrosif, prennent trés 
rapidement une couleur brune qui permet d’elles distinguer immédiatement.”’ 

When Messrs. Vogt and Yung have clearly demonstrated 
the mutual relations of the yellow (oil-) cells and the colourless 
contents of the sacculi, their theory as to the vegetable nature 
of both structures will have a more certain foundation than it 
possesses at present. 

Meanwhile let us inquire as to what is known concerning 
the development of the sacculi. Perrier has made a careful 
study of the mode of regeneration of the arms of Antedon 
rosacea, and he gives the following description of the changes 
which take place in the growing bud!:—“ Pendant que ces 
changements se produisent dans le cylindre intérieur, certains 
éléments du cylindre extérieur subissent une modification re- 
marquable ; ils se transforment en vésicules rondes remplies de 
ce liquide ou pour mieux dire de cette matiére jaune que nous 
avons déja rencontrée dans les éléments du tissu conjonctif des 
bras. Ainsi, soit dans le développement normal de l’embryon, 
soit dans la régénération des bras, ces corpuscules jaunes (oil- 
cells, Wyville Thomson) apparaissent de trés-bonne heure, ce 
qui semble indiquer que leur réle dans la vie de l’animal n’est 
pas sans quelque importance.” But, according to Vogt and 
Yung, the yellow cells are the amceboid spores of symbiotic 
alge! Perrier states that they appear before the new calca- 
reous elements are visible, just as is the case in the larva; but, 
according to the same observer,” the sacculi of the young arm, 
“ne se montrent que bien aprés les premiéres parties calcaires 

1 Loc. cit., p. 72. 
2 Loe. cit., p. 80. 


384 P. HERBERT CARPENTER. 


ont été déposées, et leur développement n’est pas encore com- 
plet que les divers articles de la pinnule sont déja_parfaite- 
ment distincts ;” while he described their development in the 
following terms : —‘‘ D’aprés ces observations, il semble que la 
premiére portion formée est le noyau de chaque vésicule ; 
toutefois, de trés-bonne heure, on peut distinguer une délicate 
membrane autour de ce noyau, membrane qui s’écarte de lui 
graduellement, et qui préexiste, en conséquence, a la plus 
grande partie du contenu de la vésicule.” It is difficult to 
believe that the groups of nuclei, which are the first indications 
of these structures, are really derived from the yellow cells. 
Their mutual relations, if existing, can hardly have escaped 
the notice of Perrier in the regenerating arm, or that of Wyville 
Thomson in the Pentacrinoid larva. The first indication of the 
sacculi noticed by the latter author! in the early larva is a 
minute vesicle containing a transparent fluid, which is imbedded 
in the tissue at the base of each of the azygos tentacles; but 
if this had been anything like the yellow oil-cells, which are 
abundant all over the Pentacrinoid, Thomson would surely 
have noticed the fact. 

The above, however, are not my only reasons for hesitating 
to accept this new doctrine of Vogt and Yung’s respecting the 
vegetable nature of the sacculi in Antedon rosacea. This 
species is the only Crinoid in which I have found these struc- 
tures in the interior of the body. Although they are very 
abundant on the pinnules of Antedon Eschrichti and its 
allied species, I have never found them anywhere else but at 
the sides of the ambulacra. They are usually more numerous 
on the arms than on the disc, but less so than on the pinnules, 
where they alternate very regularly with the groups of ten- 
tacles. Thus, for example, I can find none on the disc of an 
Antedon microdiscus from Cape York, and very few at the 
sides of the brachial ambulacra; but they are extraordinarily 
abundant on the pinnules. As a general rule, too, they are 
more numerous on the outer pinnules than on those nearer 
the disc, which are distended by the fertile portions of the 

1 © Phil, Trans.,’ 1865, p. 527. 


NOTES ON ECHINODERM MORPHOLOGY. 385 


genital glands. But when the glands are short, and do not 
extend over more than three or four pinnule segments, the 
distal ends of the genital pinnules are often abundantly pro- 
vided with sacculi, although there are few or none in their 
enlarged basal portions. I do not know how this will be 
explained by the supporters of the algal nature of the sacculi, 
and their relations in Antedon-species with plated ambulacra 
present still greater difficulties. I have sometimes failed to 
find them, even in Antedon, among the various plates sur- 
rounding the ambulacra ; but, as a general rule, they are fairly 
well developed in the pinnules, and occupy an extremely con- 
stant position with regard to the ambulacral plates. In those 
species which have the most highly differentiated pinnule- 
ambulacra the sacculi alternate with the tentacular groups, 
just as in Antedon rosacea, and the distal edges of the side 
plates are notched for their reception in the most regular way 
possible (Fig. 1,s). It does not appear probable to me that the 
calcareous elements of the skeleton would be so regularly 
modified for the reception of the sacculi if these structures 
were merely vegetable parasites; and the difficulties inherent 
in this view of their origin are increased by the fact that the 
side plates of Hyocrinus, Pentacrinus, and Metacrinus 
are not notched for the reception of sacculi, which do not occur 
at all in these genera, even when they are living side by side 
with Antedons in which sacculi are abundantly distributed 
at the sides of the pinnule-ambulacra. 

Sacculi occur in nearly all the species of Antedon, in 
Promachocrinus, Atelecrinus, and in three species of 
Eudiocrinus, though they are absent in the other two. 
They are sometimes to be found in Rhizocrinus and Bathy- 
crinus, though they are often so small and undeveloped as to 
be barely recognisable; but I have failed altogether to find 
them in Actinometra, Holopus, Hyocrinus, Meta- 
crinus, or Pentacrinus,' even when these genera have 

1 The structures which I formerly regarded as imperfect sacculi in Penta- 


crinus, so far as I could judge from the surface characters only, turn out to 
be of a different nature when seen in thin sections, 


386 P. HERBERT CARPENTER. 


been obtained at the same localities as Antedons which have 
abundant sacculi. 

Thus, for example, these red spots or sacculi are largely 
developed in Antedon abyssorum, A. remota, and in Pro- 
machocrinus abyssorum, all from adepth of 1600 fathoms 
in the Southern Ocean; but I have not seen one on the arms or 
pinnules of Hyocrinus bethellianus from the same locality ; 
while if they exist at all in Bathycrinus aldrichianus, of 
the same dredging, they are so scantily developed as to be 
almost unrecognisable. Here are some similar facts of the 
same kind. The “Challenger”? dredged eleven species of 
Antedon at a station near the Ki Islands, some with abundant 
sacculi, others in which they are almost entirely undeveloped ; 
while there is no sign of them at all in four species of Meta- 
crinus and in one of Actinometra from the same dredging, 
neither do they appear in two species of Pentacrinus or in 
four of Metacrinus from off the Meangis Islands, though 
abundant in six Antedon species from the same locality. 
The “ Challenger’s” dredgings at Cape York yielded nine 
species of Actinometra, in which there is no sign of sacculi; 
but they are enormously abundant on the pinnules of Antedon 
microdiscus and A. multiradiata, fairly so in A. irregu- 
laris, and scanty in A. bidentata—all from the same locality. 
They are very thick at the sides of the pinnule ambulacra in 
‘A. Dubeni and A. carinata, of which latter species over 100 
individuals were obtained at Bahia; but there is no trace of 
them in Actinometra lineata or Act. meridionalis, 
several examples of which were found living at the same place. 
I could name many similar cases from the dredgings of the 
“ Blake” in the Caribbean Sea. There are six different stations 
(near Barbadoes, Montserrat, Martinique, and St. Vincent) 
where Antedon species occur with abundant sacculi at the 
sides of the ambulacra, while none are to be found in the species 
of Actinometra and Pentacrinus which were obtained in 
the same dredgings. 

Antedon tenuis, dredged by the “Challenger” at Station 
170, has numerous sacculi on the outer pinnules, just as in the 


NOTES ON EOHINODERM MORPHOLOGY. 387 


other seven species of Antedon obtained at this station. 
They are also present on an example of this same species found 
at Station 169; but there is no sign of them in Eudiocrinus 
semperi, from the same station, nor in another individual of 
this latter type from Station 164, where they are present 
between the side plates of the ambulacra in Antedon 
acutiradia, five specimens of which were obtained by the 
“‘ Challenger.” 

The above facts seem to me to tell very decidedly against 
the supposed algal nature of the sacculi, which are so eminently 
characteristic of certain endocyclic Crinoids, and never occur 
in the exocylic Actinometra. They occur wherever An- 
tedon is found, from nearly 82° N. to below 52° S., and at all 
depths down to 2600 fathoms; but they are not to be found 
in species of Actinometra which live side by side with 
Antedon in the warmer parts of the world, and I pointed out 
in 1882! that this fact is one of considerable importance in 
the generic distinction of the two forms. I cannot think that 
Messrs. Vogt and Yung are aware of it, however, or they 
would hardly have committed themselves to the following 
statement :?—‘‘ Les Comatulides libres (Antedon, Actino- 
metra) offrent fort peu des différences anatomiques, et sauf 
quelques détails insignifiants, sont construites absolument sur 
le méme plan que notre espéce type.” The absence in Acti- 
nometra of the sacculi, which are almost always present in 
Antedon, may be a “ détail insignifiant ;” but it is, at any 
rate, one which may possibly turn out to be fatal to Messrs. 
Vogt and Yung’s theory of the vegetable nature of these 
structures. 

I cannot imagine any reason why the “ameeboid spores,” 
which have given rise to such abundant “ véritables zoospores” 
along the pimnule ambulacra of Antedon carinata and 
A. microdiscus at Bahia and at Cape York respectively, 
should not have had equal opportunities for developing in the 

1 «Preliminary Report on the ‘ Blake’ Comatule,” ‘Bull. Mus. Comp. 


Zool.,’ 1882, vol. ix, No. 4, p. 11. 
2 Op. cit., p. 571. 


388 P. HERBERT CARPENTER. 


pinnules of Actinometra meridionalis and Act. pauci- 
cirra, which occur at the same localities. The contrast 
between the pinnules of the two genera is so striking that 
there must be some reason for it, and I am altogether unable 
to understand why it should appear at all if the sacculi are 
only vegetable parasites. 

I much doubt, therefore, if we are any nearer to an under- 
standing of their real nature than we were before Vogt and 
Yung took up the subject. 

Since the above lines were written another view of the 
nature of the sacculi has been published by Walther,! who 
says: “Seine Function ist nach der mir zuginglichen Literatur 
noch unbekannt, doch vermuthe ich auf Grund folgender 
Beobachtungen: starke Lichtbrechung, starke Farbstoffauf- 
nahme, Mangel einer zelligen Structur, Aufbau aus poly- 
gonalen oder rundlichen Plattchen, Lage an den Punkten 
starkeren Wachsthums und eine gewisse fremdartige Hinla- 
gerung im Gewebe—dass es Reservematerial (Nahrungsdotter) 
ist; wahrend ich eine secretorische Function wegen der 
umgebenden undurchbrochenen Kapsel fur ausgeschlossen 
halte.”’ 

I have no remarks to offer respecting this suggestion of 
Walther’s ; but I will conclude by a few words upon Professor 
Perrier’s latest utterances upon the subject of the sacculi. He 
attributes the name to me,” being apparently unaware that it 
originated with my father, as did also the idea that they might 
be sensory organs.? The latter view is also attributed to me 
by Perrier in the following passage,* which refers to my first 
publication on the subject of the Crinoidea in 1876. “Les 

1 « Untersuchungen iiber den Bau der Crinoiden, &c.,” ‘ Paleeontographica,’ 
1886, Bd. xxxii, p.165. I propose at some future time to make some remarks 
upon this author’s application of ‘‘ Transcendental Morphology ” to the Cri- 
noidea. 

2 « Mémoire sur l’organisation et le Développement de la Comatule de la 
Mediterranée,” ‘ Nouv. Archiv. du Mus. Hist. Nat.,’ 1886, 2me Ser., T. ix, 
p. 154. 

2 «Proc. Roy. Soc.,’ 1876, vol. xxiv, p. 227. 

* Op. cit., p. 133. 


NOTES ON ECHINODERM MORPHOLOGY. 389 


corbeilles vibratiles du canal dorsal et les corps sphériques 
des bras lui paraissent étre des organes des sens.”” My only 
positive reference to the sacculi in this paper ! was in the expla- 
nation of fig. 1, which ran as follows.  s. Sacculi (‘ calcareous 
glands’ of Wyville Thomson) of doubtful (? sensory) nature.” 
I put in the “? sensory ” in accordance with my father’s sug- 
gestion made three months previously. But I cannot see that 
it at all justified Perrier in stating that the sacculi “lui par- 
aissent étre des organs des sens.” 

His assertion that I took the same view of the ciliated cups 
in the cceliac canal is entirely incorrect. All that I said of 
them? was that Ludwig had well compared them “to the 
ciliated funnels on the mesentery of the Synaptide.” Further 
on in the paper, however, I described how in certain pinnules 
of Actinometra armata the radiating branches of the axial 
cords “ enter into connection with peculiar cellular organs, of 
very similar construction to the groups of large epidermic 
cells described in the tactile papillz of the integument of the 
Synaptid, by Professor Semper. I am inclined to regard 
these organs also as sensory in function; their position upon 
the dorsal or most exposed side of the pinnules certainly 
favours this hypothesis.”” Here then Professor Perrier, misled 
by the double reference to the Synaptide, has confused 
together a variety of statements respecting entirely different 
structures. 1. The ciliated cups in the cceliac canals of the 
Comatule. 2. The ciliated funnels on the mesentery of 
the Synaptide. 38. The cell-groups in the tactile papille 
of the Synaptide. 4. The cellular organs on the dorsal side 
of the ungrooved pinnules of Actinometra armata. I 
attributed a sensory nature to the fourth of these, and he 
describes my views as applying to the first. 

But even this is not the full extent of his errors. For on 
the same page, in summarising my second paper of 1876, he 
says, “‘ Les corps sphériques (i. e. sacculi) y sont désignés sans 

1 « Remarks on the Anatomy of the Arms of the Crinoids,’’ ‘ Journ. Anat. 
and Physiol.,’ 1876, vol. x, p. 580. 

2 Thid., p. 579. 

VOL. XXVII, PART 3.—NEW SER. EF 


390 P. HERBERT CARPENTER. 


point de doute comme ‘ des organes des sens’ problématiques.” 
This statement is absolutely untrue. 

There is no mention whatever of the “corps sphériques ” of 
Antedon in the paper to which Perrier refers. But in 
describing the two kinds of arms of Actinometra armata, 
namely, those with and those without an ambulacral groove, I 
said :! “ Another difference between these two types of arms is 
that the curious problematical ‘sense organs’ which I have 
mentioned in a former paper are limited to the terminal pin- 
nules of the non-tentaculiferous arms. The three last seg- 
ments of these pinnules are very small, but the centre of the 
dorsal surface of each of the next seven or ten segments is 
occupied by one of these curious bodies, which when viewed 
from the exterior appears as a rounded brownish mass.” Per- 
rier, however, has confused these single, median, and antiam- 
bulacral structures of Actinometra with the double row of 
sacculi on the ambulacral side of the arms and pinnules in 
Antedon. 

It is really lamentable that the historical introduction to his 
elaborate and magnificently illustrated work, which will become 
a classic ere long, should be disfigured by errors like these. I 
could name others of the same kind, all of them alike due to 
sheer carelessness in consulting the works of his predecessors. 

Speaking of the sacculi on another page (154), Perrier says: 
“ Ces corps énigmatiques ont été récemment considérés comme 
des parasites et designés sous le nom de Zooxanthelles. 
Herbert Carpenter ne trouve pas qu’il y ait encore de raisons 
suffisantes pour se ranger a cette opinion.’ This statement is 
supported by no reference whatever to any of my published 
writings, for the very excellent reason that Professor Perrier 
has none to give. 

The section on the sacculi in the “ Challenger” Report was 
written in the summer of 1884. ‘This was the last occasion on 
which I referred to the nature of these structures in print; 
and it is impossible therefore that I could have expressed an 


1 « Remarks on the Anatomy of the Arms of the Canes Part II, 
‘Journ, Anat. and Physiol.,’ 1876, voi. xi, p. 92. 


NOTES ON ECHINODERM MORPHOLOGY. 391 


opinion adverse to the views of Messrs. Vogt and Yung 
respecting their vegetable nature, as these were not published 
till 1885, and I did not become aware of them till March, 
1886. 

On p. 154, after quoting from the “ Challenger ” report 
some facts respecting the distribution of the sacculi, Perrier 
adds : ‘‘ Cette inégale distribution montre que ce ne sont pas la 
des organes de quelque importance, si tant est que ce soient 
des organes; mais on ne peut rien conclure de ces données 
relativement a leur véritable nature.” I am by no means sure, 
however, that Perrier has drawn the right conclusion from the 
facts of their distribution. 

I have no means of knowing what is his own view of their 
nature ; but they are lettered z in his figures. The explana- 
tion of these has not yet appeared, and I am therefore uncer- 
tain whether z is explained as denoting “ zooxanthelles,” or 
whether it is used for some other descriptive term. 


DESCRIPTION OF PLATE XXX, fig. 3. 


Illustrating Mr. P. Herbert Carpenter’s Paper “ On the Sup- 
posed Presence of Symbiotic Alge in Antedon rosacea.” 


Fic. 3.—Portion of a pinnule of Antedon accela, with a very well- 
developed ambulacral skeleton. x 20. 

p. The pinnule joints. ¢.p. The covering plates of the ambulacra. s.p. The 
side plates. s. Notches in the distal edges of the side plates for the reception 
of the sacculi (Zooxanthelles, Vogt and Yung). 


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THE FUNCTION OF NETTLEOCELLS. 393 


The Function of Nettlecells. 
By 


R. von Lendenfeld, Ph.D., F.L.S., 
Assistant in the Zoological Laboratory of University College, London. 


With Plate XXX, fig. 4. 


MorPHo.oey. 

Both in the ectoderm and the entoderm of all Polypomedusze 
these elements are met with. They are never absent in the 
ectoderm in any species, and are generally also found in the 
entoderm. 

Their structure has been investigated by numerous authors ; 
particularly F, E. Schulze (1), O. Hamann (2), Korotneff (3), 
and the author (4) have studied their structure and action 
more closely. Also Jickeli (5) has dwelt on this subject. 

However different the animals may be on which these Nettle- 
cells are found, the latter nevertheless are always of the same 
structure, although they may vary very much in size. The 
large ones are fewer in number and more determinate in their 
position than the small ones. No Nettlecells of the large kind 
are found in the entoderm. 

The Nettlecells, or, as Schulze calls them, cnidoblasts, consist 
of a cell the greater portion of which is occupied by the well- 
known highly refracting vesicle, on the size of which the 
size of the whole cnidoblast depends. The granular proto- 
plasmatic portion of the Nettlecell is reduced in bulk so much 
that it only forms a thin coating over the surface of the vesicle. 
In one locality this plasmatic coat is slightly thickened, and here 
the flattened nucleus, closely attached to the vesicle, is situated. 


394 R. VON LENDENFELD. 


From the upper margin of this protoplasmatic sac which 
surrounds the vesicle, a conical, stout and pointed filament, the 
cnidocil, projects. This is about as long as the vesicle is 
broad, and is situated in such manner oblique to the surface as 
to form with it an angle of 45°. This angle is very constant. 
The cnidocil always points in a centrifugal direction, that is to 
say the cnidocils on the tentacles point towards the ends of the 
tentacles, those on the body point towards the mouth, and so 
on. The cnidocils invariably point in that direction from which 
a foreign body is most likely to approach the animal. 

The vesicle itself possesses a very distinct, tough, and appa- 
rently elastic membrane. It is closed on all sides except the 
anterior end, where a circular aperture, about a quarter as wide 
as the vesicle, is situated. This aperture leads into a very long 
tube, when the ecnidoblast has exploded. This tube is about 
twenty times as long as the cnidoblast and tapers towards the 
end, which appears pointed. It is surrounded by one or two 
spiral lines of minute hooks or bristles which are often very 
large and conspicuous at the base, but which rapidly decrease 
in size distally and become invisible even with the highest 
power near the end. The tube is probably closed at the end. 

This tube can be ejected with great force from the capsule of 
the cnidoblast, where it is coiled up very regularly before the 
explosion. The explosion inverts this tube hanging down 
from the orifice of the capsule into its interior, so that the 
external surface of the coiled-up tube becomes the internal 
surface of the ejected tube and vice versa. The well-known 
poisonous effect of these cnidoblasts is due to a poison which is 
contained in the interior of the coiled-up tube, and which, as 
the tube is inverted, comes to be situated on the outer surface. 
The tube penetrates, by the force of its ejection and in conse- 
quence of its small size, soft foreign bodies which may come in 
contact with the animal, and so the poison is transmitted into 
the body of the victim. Whilst Mébius and others have 
studied the tube and capsule, the discovery of the cnidocil was 
made by F. E. Schulze. 

After these facts had been made known, the question arose 


THE FUNOTION OF NETTLECELLS. 395 


whether the cnidoblast was in connection with the nervous 
system described particularly by the brothers Hertwig. Such 
a connection has been demonstrated in many cases by Jickeli, 
the author, and Korotneff. 

In the lower strata—subepithelium—of the dermis, ganglion 
cells are met with in those parts generally where cnidoblasts are 
situated. These ganglia cells are multipolar. Their processes 
are connected with slender nerve-fibres extending tangentially 
between the mesodermal jelly (the supporting membrane, 
Stiitzlamelle) and the outer epithelium. Some of these pro- 
cesses, however, extend in a radial, centrifugal direction, and 
these are connected with the large cnidoblasts. No con- 
nection has hitherto been observed with sufficient certainty 
between the ganglion cells and the small enidoblasts. 

The protoplasmatic outer portion of the cnidoblast is pro- 
longed into a process extending centripetally like a peduncle. 
This is composed of granular protoplasm and forms the 
connection between the cnidoblast and the ganglion cell below. 
Hamann found that these peduncles, in some cases at least, were 
not formed of granular protoplasm, but appeared as transparent 
and structureless peduncles formed of the same substance 
as the supporting mesodermal membrane. Subsequently I was 
able to demonstrate that the large cnidoblasts have two pedun- 
cles, one a transparent supporting rod as described by Hamann, 
and one a granular thread, which connects it with the ganglia 
cells of the subepithelium. Whilst the former is always quite 
straight, the latter generally appears more or less curved and 
irregular. 

These cnidoblasts are surrounded by high and slender cylins 
drical ciliated cells which form the outermost layer, or they 
penetrate the large cells of the outer epithelium. In those parts 
where the epithelium is formed by flat and low pavement cells, 
large cnidoblasts are never observed. 

The small cnidoblasts, however, are scattered over the surface 
more indiscriminately and occur in great abundance also in the 
pavement cell areas. In these areas a subepithelial layer of 
ganglion cells seems not to occur. 


396 R. VON LENDENFELD. 


PuHysIoLocy. 


F. E. Schulze, who discovered the cnidocil, was of opinion 
that any foreign body touching the cnidocil would cause an 
explosion of the Nettlecell, much in the same way as touch 
invariably causes a sting in the case of the stinging-nettle. To 
this end it appeared that the cnidocil was so placed as to point 
towards the ends of tentacles, that is, always in that direction 
whence an enemy would be most likely to approach. The 
position of the stinging hairs of Urtica is the same. 

Others who dwelt on the subject endorsed Schulze’s purely 
mechanical explanation, that direct pressure on the enidocil is 
transmitted to the cnidoblast and there causes the explosion of 
the capsule which is already in high tension. 

If this were so there would apparently be no reason for the 
connection of the cnidoblast with the nervous system of the 
animal. 

Now, it is a well-known fact that touch by no means invariably 
causes the explosion of the Nettlecells and the ejection of the 
tube. Ifa tentacle of an Actinia is viewed under the micro- 
scope in seawater under a cover-glass, and if fine grains of sand 
are placed in the water and a strong current produced by suction 
on one end, then the sand-grains are carried to and fro with 
great velocity by the moving water and continually come in 
contact with the surface of the tentacle. No explosion of a 
Nettlecell, however, can be observed. But if acetic acid be 
added to the water then the tubes will be seen shooting forth 
like rockets all over the surface. 

When the animals, as they often do, contract themselves and 
draw up their tentacles like the Medusze to one hundredth part 
of their length, or close them over the mouth like the Actiniz, 
there must be a very strong pressure, which according to the 
mechanical theory would immediately explode all the Nettle- 
cells. 

There are some species of Actinia which live in sand, as, for 
instance, the Cerianthus, Those which live in shallow water, 


THE FUNCTION OF NETTLECELLS. 397 


or between tide-marks, bury the body in the sand and expand 
their tentacles in the surface of the sand, the waves move the 
sand and it is evident that masses of sand must be continually 
falling on the tentacles. I have often observed a species of 
Actinia exceedingly abundant in the “ sands” of Port Phillip, 
Victoria, and I know that they do not retract their tentacles 
when the water moves and the sand drops on them. 

According to the mechanical theory, each sand-grain which 
came into contact with the tentacles would cause the explosion 
of a great number of Nettlecells. It is evident that this 
cannot be so. 

Further, there are Nettlecells embedded in the jelly of the 
umbrella of some Medusz (discovered by me, l. c., over the 
marginal bodies of Crambessa mosaica) which explode if 
the surface of the body is touched with acetic acid instan- 
taneously and long before the acid could have got to where 
they are situated. 

This will show that touch is by no means sufficient to cause 
the explosion of the Nettlecells; nor is it the only possible 
cause. 

It would now seem possible that the cnidoblasts were 
exploded at the will of the animal by a contraction caused 
consequent on a centrifugally acting nervous irritation in the 
plasmatic mantle surrounding the capsule. Chun (6) has 
observed muscular differentiations in this plasmatic mantle in 
Physalia, which is one of the severest stinging Ccelenterates. 
Others have been inclined to consider the peduncle as 
muscular and contractile. 

If we were to assume this we should not be able to see the 
use of the cnidocil. 

It seems, therefore, that there can be but one explanation of 
the mode of action of the cnidoblasts—of the large kind, at least 
—which is the following : 

1. The structureless peduncle is a support and may contract 
so as to withdraw the cnidoblast with its lid from the surface 
under certain circumstances, particularly when the parts where 
the Nettlecell is situated are to be contracted. The animal has 


898 R. VON LENDENTELD. 


control over these movements by means of the subepithelial 
nervous layer situated below the cnidoblasts. 

2. The granular peduncle is a nerve-fibre connecting the 
protoplasinatic mantle of the Nettlecell with the nervous system 
of the animal. 

3. By means of this the movements of the protoplasmatic 
mantle can be controlled. 

4. The explosion of the enidoblast is caused by the contraction 
of the plasmatic coat which surrounds the capsule, and which 
in Physalia (Chun, |. c.) has partly been converted into a 
network of muscular fibres. 

5. The plasmatic contractile coat of the cnidoblast is incited 
to action by the cnidocil. Ifanything touches the enidocil then 
the plasma mantle contracts and the tube is shot forth. 

6. The animal can, however, by its volition prevent this 
reflex action by means of the nerve-fibre connecting the cnido- 
blast with the ganglia cells below. In this way the explosion 
may be prevented even if the cnidocil be touched, if this be the 
wish of the animal. 

We find, accordingly, that the complicated machinery of 
nerve-centres controlling reflex actions of a low order in man 
and the higher animals is found also in these low forms of 
animal life, the Colentera. 

The Ctenophora, which are destitute of cnidoblasts, possess 
in their stead certain structures, the “ Klebezellen”’ of Chun and 
the “ Stiftzellen ”! of Hertwig, which appear homologous with 
these Nettlecells in the Ctenophora. Their action is very different 
and they do not explode like the cnidoblasts of Polypomeduse. 

It seems, however, probable that they are in a similar way 
subject to the control of the animal, as is the cnidoblast. 


' These are, according to my investigations of the histology of Nais cor- 
digera, Les., (7), not a sensitive apparatus, as the brothers Hertwig had 
assumed, but stinging hairs. 


THE FUNOTION OF NETTLECELLS. 399 


PAPERS REFERRED TO. 


1. F. E. Scuurze.—“ Ueber Syncoryne Sarsii, Lovén, und die zuge- 
horige Meduse Sarsia tubulosa.” 

2. O. Hamany.—“ Der Organismus der Hydroidpolypen.” ‘Jenaische 
Zeitschrift fiir Naturwissenschaft,’ 1881, Band 15. ‘‘ Ueber Nessel- 
kapselzellen,” |. c. 

3. Korotnerr.—* Ueber Siphonophoren.” Mittheilungen aus der zoolo- 
gischen Station in Neapel, 1884. 

4, R. v. Lenpsnretp.— Ueber Coelenteraten der Siidsee. iii., Ueber 
Webrthiere und Nesselzellen,”’ ‘ Zeitschrift fiir wissenschaftliche Zoo- 
logie,’ 1883, Band 388, p. 366. 

5. C. Jickeu1.—“ Ueber den Bau der Hydroidpolypen,” ‘ Morphologisches 
Jahrbuch,’ 1882. 

6. C. Cuun.—* Die Natur und Wirkungsweise der Nesselzellen bei Coe- 
lenteraten,” ‘ Zoologischer Anzeiger,’ Band 4, p. 646. 

7. R. v. Lenpenretp.— Nais cordigera, Les.,” ‘ Zeitschrift fiir wis- 
senschaftliche Zoologie,’ Band 41, p, 673. 


EXPLANATION OF PLATE XXX, fig. 4, 


Illustrating R. von Lendenfeld’s Paper on “‘ The Functions of 
Nettlecells.” 


Fic. 4.—Schematic representation of cnidoblast, &e.—a. Mesodermal sup- 
porting lamella. 6. Peduncle (Hamann’s) of cnidoblast. ¢. Ordinary cylin- 
drical epithelium cells. d@. Their nuclei. ¢. Longitudinal striated muscles. 
J: Subepithelial muscle-cells. gy. Their nuclei. /. Subepithelial ganglion cell. 
i. Tangential nerve-fibre. 4. Nucleus of the ganglion cell. 7. Epithelial sen- 
sitive cell. m. Its nucleus. x. Palpocil (Wright). 0. Cilia of the ordinary 
epithelium cells. y. Nerve connecting ganglion cell with cnidoblast. g. Pro- 
toplasmatic contractile mantle of cnidoblast. 7. Nucleus of enidoblast.  s. 
Nematocyst. ¢. Its aperture. w. Cnidocil (Schulze), v, Thread coiled up 
inside the cnidoblast, 


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NEW METHODS OF USING THE ANILINE DYES. 401 


Some New Methods of Using the Aniline Dyes 
for Staining Bacteria. 


By 
E. Hanbury Hankin. 


I nave lately been staining bacteria in tissues for Dr. Klein 
by some new methods that seem to offer certain advantages 
over those already in use. 

Dr. Klein has kindly supplied me with tissues containing 
various bacteria. But most of my results have been obtained 
with Bacillus anthracis. 

In the methods about to be described the hardening of the 
tissue that generally precedes section cutting must be care- 
fully attended to. It is always necessary to use Miiller’s 
fluid. The tissues must be cut into very small pieces, and the 
liquid frequently changed. If this is not done the nuclei will 
be found to show more affinity for the dye than the bacteria, 
and only those organisms that are placed near the margin of 
each section will be visible. 

Nearly equally good results are obtained with perfectly 
fresh material. 


Method a. Materials required: 

(1) A strong watery solution of methyl blue or Weigert’s 
aniline oil solution of the same dye. 

(2) A saturated alcoholic solution of eosin. This should 
be made simply by shaking up the dye with the alcohol and 
filtering. By heating the alcohol or letting the solid eosin 
remain for some days in contact with the liquid a stronger 
solution is obtained, which is undesirable for the present 


pur pose. 


402 BE. HANBURY HANKIN. 


(3) A pipette to hold the above. A test-tube fitted up as a 
wash bottle is very convenient for holding the eosin. 

(4) Absolute alcohol, which must be used in a capsule pro- 
vided with a cover, to prevent the access of watery vapour from 
the air. Every precaution should be taken to keep the alcohol 
as free from water as possible. 

(5) Benzine and clove-oil mixture, made by mixing equal 
volumes of benzine and oil of cloves, and adding sufficient abso- 
lute alcohol to dissolve the turbidity that appears on shaking 
together the above reagents. 

(6) Oil of cloves, which must be fresh and nearly colourless. 
By exposure for a few hours to light and air oil of cloves loses 
a great deal of its power of dissolving the aniline colours. 

(7) Benzine. This may be replaced by xylol or cedar oil. 

Modus Operandi.—The sections are taken from spirit 
and placed in the methyl blue solution. Immediately the 
eosin is dripped in from the pipette. About equal parts of the 
eosin and methyl blue solutions are employed. If too much 
eosin is used the background of the section will have a dull 
purplish tinge, contrasting badly with the blue-tinted bacteria ; 
while if too little eosin has been dropped in its red shade is 
scarcely visible. 

By adding eosin to the solution its power of dissolving 
methyl] blue is diminished. Part of the excess is precipitated 
in the form of a granular deposit; part of it combines with the 
tissue in the form of stain. The precipitate thus rapidly 
formed is readily dissolved by the alcohol used in dehydrating, 
and never spoils the appearance of the specimen. As soon as 
the eosin has been added the sections are removed one by one 
to absolute alcohol, shaken about in it for a few seconds, and 
then placed in the benzine and clove-oil mixture. 

The sections are washed in this till the effects of the eosin 
begin to be apparent, then washed rapidly in another capsule 
of the same mixture, spread out on a section lifter, placed in 
benzine, and mounted. If, however, they are not sufficiently 
decolorised they should be removed to oil of cloves, which will 
readily dissolve the excess of methyl blue. If the red tint of 


NEW METHODS OF USING THE ANILINE DYES. 4038 


the background is not sufficiently pronounced they may be 
treated for a minute or less with eosin dissolved in clove oil, 
afterwards washed in benzine and clove-oil mixture, lastly in 
benzine, and then mounted. 

The whole process does not take much more than a minute, 
of which about twenty seconds are occupied in adding the 
eosin solution to the methyl blue. The dehydrating in alcohol 
should be accomplished as rapidly as possible. 

Sections stained in this manner show the bacteria stained 
blue; the nuclei are similarly coloured, but of a lighter shade, 
the eosin has stained the red blood-corpuscles orange, and the 
background of the tissue is of a rose-red tint. 

Ganglion cells are stained purple if the section has not had 
too much of the colour removed. Besides the blood-corpuscles 
eosin can stain several other things of a yellow or orange tint, 
and if these structures have also an affinity for methyl! blue the 
two dyes combine, giving a bright green shade. Hemoglobin 
crystals and sometimes red blood-corpuscles are thus stained. 

In sections through the lung of a sheep which had suffered 
from foot-and-mouth disease this eosin and methyl blue method 
showed large amorphous caseous deposits of a bright emerald- 
green colour, while other methods of staining failed to 
differentiate them. 

Sections of the lung of another sheep, which contained 
encysted thread-worms, showed within their rose-red epidermis 
the protoplasm of the nematodes stained green, and their 
nuclei of a purple tint. 

Sections through a congested spleen showed orange-red 
blood-vessels on a background of blue and green nuclei almost 
as well as an injected specimen. 

While oil of cloves is generally used to help the alcohol in 
taking the excess of colour out of a section, I, on the contrary, 
use it for keeping the colour in, so far as the bacteria are con- 
cerned; for bacteria stained as here described would rapidly 
become invisible if left for long in the more powerful solvent, 
namely, the alcohol; and sections may often be kept inde- 
finitely in oil of cloves without the bacteria losing their stain, 


404, E. HANBURY HANKIN. 


although this solvent is quite capable of washing out all the 
colour from nuclei, connective tissue, &c. 

Not only clove oil, but also other clearing reagents, such as 
benzine, xylol, creosote, aniline, and cedar oil have a greater or 
less power of fixing the colour in the bacteria, though several 
of them ean dissolve the aniline dyes freely. 

Sections stained by any of these methods, quickly dehydrated 
and cleared, can then be washed for a longer time in alcohol, 
without the dye leaving the bacteria, than can sections which 
have been taken direct from the dye into spirit. I even found 
that clearing the tissue before staining, and then washing in 
alcohol, would slightly improve the result in some cases. 

Concerning this method of staining it may be remarked 
that, firstly, a mixture of methyl blue and eosin has scarcely 
any staining power. If the sections are put into the dye 
after the addition of the eosin no result is obtained, and 
consequently it is immaterial how long the sections are left in 
the mixed staining solution. Secondly, the eosin solution is 
much stronger than that in general use. If a section is 
stained in methyl blue, and then placed in a saturated alcoholic 
solution of eosin, as here used, in a very few seconds all the 
blue colour is turned out, and the section stained of a uniform 
red tint; but in this method the presence of the methyl blue 
in solution seems to protect the tissue from the eosin. Thirdly, 
when eosin and methyl blue solutions are mixed some of the 
methyl blue is precipitated, and after some time will be found 
sticking to the sides of the containing vessel. Fourthly, if a 
greater quantity of the eosin solution than that above men- 
tioned is employed, instead of a preponderance of red in the 
resulting stain, it will be found that the methyl blue has com- 
menced to stain the background besides the nuclei, and the 
whole section will have a purplish colour. Fifthly, if the con- 
ditions of solution of the dyes are reversed, and alcoholic 
methyl blue is added to watery solution of eosin, no staining 
effect is produced, unless the saturated eosin is diluted with 
about five times its bulk of water. By this method the bacteria 
are stained slightly better than in the manner above described, 


NEW METHODS OF USING THE ANILINE DYES. 405 


the only objection to its use being that the dilute eosin em- 
ployed (though stronger than the eosin solutions in general 
use) is incapable of staining the background of the tissue 
strongly. I have sections stained in this way showing dark blue 
bacilli on a nearly colourless background. 

Moreover, the eosin may be replaced by certain other 
reagents, which have the property of precipitating methyl 
blue ; for instance, by dilute alcoholic solution of picric acid 
and by a dilute alcoholic solution of tetrabromofluorescein. 
This last reagent is made from a strong watery solution of 
eosin by adding hydrochloric acid, filtering off, and washing 
the precipitate, and then dissolving it in alcohol.! 

In the former case I noticed that if the picric acid solution 
is too strong all the methyl] blue is precipitated in the solution, 
and no staining effect is produced. By diluting the picric 
acid the bacteria were stained, and by still further dilution of 
the picric acid no more effect was produced than in the first 
experiment. These facts seem to show that the precipitation 
of the methyl blue plays some part in producing the stain. 

Most of the aniline dyes in common use are more soluble in 
alcohol than in water. It occurred to me that if a saturated 
alcoholic solution was added to a strong watery solution of the 
same dye a precipitate would occur, and that possibly bacteria 
present would be stained. I first tried with Weigert’s aniline 
water solution of Spiller’s purple, and obtained very poor 


1 See ‘The Chemistry of the Coal Tar Colours,’ by Benedict and 
Knecht, published by Bell and Son. Since writing the above I have been 
looking over some of the first specimens that I made by the eosin and methyl 
blue method about six months ago. I find that some of them are faded, but 
in others the bacteria are still dark blue on a pink background. In the latter 
case, instead of using the eosin solution above described, I had used a mixture 
of three parts eosin saturated in alcohol, and one part of tetrabromo- 
fluorescein saturated in alcohol. When first made the bacteria were stained 
nearly black. 

The bacteria in question were small bacilli, which Dr. Klein found associated 
with some as yet undescribed disease of a sheep. They were not very easy to 
stain by this method. Scarcely any anthrax specimens stained in this way 
show any sign of fading. 

VOL. XXVIII, PART 3.—NEW SER. FF 


406 E. HANBURY HANKIN. 


results. On adding the alcoholic Spiller’s purple a whitish 
tinge was produced, as if milk had been added to the solution. 
This I found to be due to minute globules of aniline. I also 
found that these globules have a great affinity for the dye, for 
if aniline or any other oily liquid that can dissolve Spiller’s 
purple is shaken up in a test-tube with a watery solution of 
this dye nearly all the colouring matter is removed from the 
solution and dissolved in the oily liquid." 


I then tried with watery solutions of Spiller’s purple, and 
obtained successful results, in the following manner : 

Method s. The materials required are: 

(1) Saturated watery solution of Spiller’s purple. 

(2) Saturated alcoholic solution of the same dye. 

It is very important that both these solutions should be 
saturated. The best way to effect this result is to boil the 
dye with the solvent used in each case, allow the mixture to 
cool, and then filter. 

(3) Absolute alcohol, benzine and clove-oil mixture, and 
benzine as in Method a. 

(4) Eosin dissolved in oil of cloves made by mixing about as 
much eosin as can be lifted on the point of a penknife with a 
watch-glass full of oil of cloves. The mixture should be used 
fresh, as after standing a quantity of the eosin is precipitated 
in crystals, especially if any acid fumes or traces of picric and 
other acids are about. 

Modus operandi.—The sections are removed from spirit 
and placed in the watery Spiller’s purple. 

At once an equal bulk of alcoholic Spiller’s purple is dropped 
in from a pipette. The sections are then dehydrated in abso- 
lute alcohol as quickly as possible and removed to the benzine 
and clove-oil mixture. 

Sometimes it may be necessary to dehydrate, not in alcohol, 
but in alcohol saturated with Spiller’s purple. By this means 

1 All dyes that stain nuclei also stain the globules of an oil emulsion. 
Hence when staining—at any rate by these methods—care must be taken that 


_ no trace of oil of cloves or any other oil is introduced (on needles, section- 
lifters, &c.) into the staining solution. Mere traces will often spoil the result. 


NEW METHODS OF USING THE ANILINE DYES. 407 


the exit of the dye from the bacteria can be effectually pre- 
vented. 

When cleared the sections are removed from the benzine 
clove-oil mixture to oil of cloves containing eosin. The eosin 
stains the background red and at the same time turns out the 
excess of Spiller’s purple ; sometimes a few seconds, sometimes 
a few minutes, are required to do this. The sections are then 
washed in oil of cloves, passed through the benzine and clove- 
oil mixture to benzine and mounted. 

The removal of the excess of colour can be greatly hastened 
by moving the sections backwards and forwards between the 
oil of cloves and benzine and clove-oil mixture.! 

I attempted also to stain in this manner with fuchsin and 
gentian violet, but found that although the sections were left 
in the dyeing solution only for a few seconds they were hope- 
lessly overstained, and it was impossible to remove the excess 
of colour by means of oil of cloves. 

After some trouble I succeeded in finding out how to avoid 
this difficulty. The method is as follows: 

The sections are subjected to double treatment with fuchsin 
or gentian violet in the same way as above described for Spil- 
ler’s purple, then rapidly dehydrated in alcohol and placed 
in the benzine and clove-oil mixture. They are then removed 
to oil of cloves in which picric acid has been dissolved. This 
quickly turns out the excess of fuchsin or gentian violet and at 
the same time stains the background. The sections are then 
washed in pure oil of cloves, benzine and clove-oil mixture, 
placed in benzine and mounted. Or if a green background is 
preferred to the yellow tint of picric acid the sections may be 
contrast stained with a mixture of methyl blue snd picric acid 
dissolved in oil of cloves or aniline. They must then be washed 
rapidly in benzine clove-oil mixture and placed in benzine. 

The only objection to the use of gentian violet by this method 


1 This is really the reiteration of a “tip” kindly shown me by Mr. Lingard 
at the Brown Institution. He showed me that in staining by Gram’s method 
it is possible to turn out the excess of colour by moving the sectious from 
alcohol to oil of cloves, and back again repeatedly. 


408 E. HANBURY HANKIN. 


is that the bacteria, if at all easy to stain, are dyed black, which 
result, for obvious reasons, should generally be avoided. 

In all these methods of staining, advantage is taken of the 
well-known fact that benzine does not dissolve, and therefore 
fixes the aniline dyes. Sections when stained so feebly that 
prolonged washing in alcohol would render them quite colour- 
less, are placed in benzine after dehydration, and the loss of 
colour being thus checked, they are mounted as permanent 
sections. If, however, they were removed directly from the 
alcohol to the benzine, a precipitate of dye would probably be 
formed on the surface of the section, which would spoil the 
result. Hence the necessity for the benzine and oil of cloves 
mixture, which, refusing on the one hand to dissolve much 
more of the dye, and on the other to precipitate any, forms a 
link between the alcohol and the benzine. Sections should 
generally be piaced successively in two or three watch-glasses 
or capsules full of this mixture before removal to benzine; and 
in the last of the series they should only remain while they are 
being spread out on a lifter. By taking this precaution the 
last capsule will contain little dissolved dye, and all granular 
precipitate on the section is prevented. 

Another advantage in placing sections in benzine before 
mounting is that any residue of clove oil is removed. By this 
means the section is far more likely to be permanent than if 
the excess of clove oil is merely drained off with a piece of 
blotting paper, as is usually the case. 

In using these methods it is necessary to remember that 
fuchsin and other dyes which show such an affinity for nuclei 
when dissolved in water or alcohol, act quite differently when 
dissolved in oil of cloves. Under these conditions they are 
almost incapable of staining bacteria or nuclei, but the whole 
of the tissue becomes dyed of a uniform tint. This influence 
of the solvent in modifying the action of the dye is not of a 
chemical but rather of a physical nature, for the oil of cloves 
may be replaced by aniline, creosote, or any clearing agent, with 
scarcely any alteration in tke result. 

If a section is placed in water and some alcoholic fuchsin 


NEW METHODS OF USING THE ANILINE DYES. 409 


dropped in, the nuclei and bacteria will be found to have taken the 
dye. But if the section is placed in an alcoholic solution of 
fuchsin, and if the dye is precipitated by the addition of a consi- 
derable quantity of benzine, the whole of the tissue will be found 
to be strongly stained a uniform crimson tint. The dye has 
acted as a background stain. From these considerations it is 
evident that firstly, after the nuclei or bacteria in a section have 
been stained with Spiller’s purple, fuchsin, or gentian violet, if 
the excess of colour is being removed by means of oil of cloves, 
care must be taken to move the sections into a fresh quantity 
of the reagent as soon as it has become strongly tinted by the 
dye. And, secondly, after staining bacteria by double treat- 
ment with Spiller’s purple or methyl blue, they may be contrast 
stained with fuchsin dissolved in an oily medium. Aniline is 
the best for the purpose. After leaving in this reagent for 
about a minute they should be removed to picric acid and clove 
oil for a few seconds, then washed and mounted. If methyl 
blue was the dye previously used, the bacteria will be found to 
be stained green on a brick-red background. 

Another method of staining, which, though a little more 
complicated seems to offer certain advantages, is as follows: 

Sections are subjected to double treatment with fuchsin as 
above described, then washed for about five minutes in picric 
acid dissolved in oil of cloves; this last reagent is removed by 
washing in benzine and clove-oil mixture. They are then 
treated with methyl blue dissolved in aniline oil for about ten 
minutes. The effect of this is that every structure that was 
previously stained red with fuchsin is turned black, blue black, 
or dark purple. This, then, is the colour of the bacteria, and 
the background tint is green or blue. This can be changed to 
red by placing the section in oil of cloves aud eosin for a 
minute. The sections are then washed and mounted as in the 
other methods. Not only do sections stained in this way 
promise to be remarkably permanent, but the contrast between 
the dark blue of the micro-organism and the pale pink of the 
background is as strong as can be desired. 

The question arises whether sections stained by these methods 


410 E. HANBURY HANKIN. 


are likely to be permanent. It is well known that, ceteris 
paribus, bacteria that have been stained for six hours are more 
likely to retain their colour than those that have been in the 
staining solution for only a few minutes. Is it then likely that 
these methods will be permanent, where the whole process 
takes only a few minutes, and the bacteria are only exposed to 
the action of the dye for a few seconds? Though the only 
way to settle this question is to observe how long sections thus 
stained will last, I thought that some indication of their 
permanency or otherwise might be obtained by exposing them 
to the action of sunlight. Todo this I fixed up several sections 
in a window with a southern aspect on sunshiny days and 
observed the effect of the light at intervals. The results 
obtained were very different in different cases, but seemed to 
show that the permanency under these conditions depended 
rather on the amount of colour that had been washed out of 
the section after staining, than on the time that the section 
had been left in the staining solution. 

A section that had been stained in gentian violet for twenty- 
four hours in the ordinary manner was completely bleached by 
sunlight in three hours. A section stained by the eosin and 
methyl blue method, and in which all blue colour had been 
washed out of everything except the bacteria, faded in the 
same time, while other sections stained by the same method, 
but in which a trace of colour had been left in the nuclei, stood a 
whole day’s sunlight without much change, so far as the 
micro-organisms were concerned. Another section which had 
been stained in this method for histological purposes when 
exposed to six hours’ sunlight lost the colour previously 
adhering to the nuclei, but left the bacteria present still 
strongly dyed. It is thus clear that the fastness to light is due 
to the quantity of dye present in any stained part of the section ; 
and I employed this fact in differentiating out certain bacteria by 
means of light as follows. I had some sections of the liver of 
a mouse that had died of some form of septiczemia investigated 
by Dr. Klein. The sections when stained with Spiller’s purple 
and eosin showed here and there dark blue apparently homo- 


NEW METHODS OF USING THE ANILINE DYES. 411 


geneous masses plugging the smaller blood-vessels and expand- 
ing the capillaries. There was absolutely nothing to show 
whether or not these were masses of bacteria. But after I 
had exposed the mounted sections to sunlight for a day, the 
Spiller’s purple present in the interspaces between the bacilli 
was completely destroyed, and the masses that before seemed 
to be amorphous were now seen to consist of clusters of minute 
bacilli marked out with perfect distinctness. 

Some sections stained by the method last described were 
exposed to ten days’ sunlight during the hottest part of last 
July, without appreciable change, and they still show every- 
where the bacilli of a dark blue black tint, though the back- 
ground of the tissue has become so bleached as to be nearly 
invisible. This permanency of the stain produced by methyl 
blue and fuchsin in combination is remarkable, when it is 
remembered that manufacturers regard a dye as “ fast to light ” 
when a tissue stained by it is unchanged by three hours’ 
exposure. 

These methods of staining are generally inapplicable to 
coverslip specimens. But preparations of anthrax blood or 
pneumonia sputum, very excellent for demonstration purposes, 
can be made as follows: 

The films are stained with methyl blue or Spiller’s purple, 
washed and dried as usual, and then a drop of eosin dissolved 
in oil of cloves is placed on them for a few minutes; this is 
then washed off with clove oil and benzine mixture. This 
again is removed with benzine and the coverslips are then 
mounted. Bacteria are seen to be stained blue, red _ blood- 
corpuscles are red, pus-cells or leucocytes generally have purple 
nuclei, and the background has a pinkish tint. 

The method of staining by means of eosin and methyl blue 
gives very good results from a histological point of view, but 
will only succeed with bacteria that are easy to stain. 

The methods of double treatment with fuchsin and Spiller’s 
purple are successful with nearly all bacteria. 

Tubercle bacilli, however, cannot be satisfactorily stained 
by any of these methods. 


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ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 4138 


Illustrations of the Structure and Life-History 
of Phytophthora infestans, the Fungus 
causing the Potato Disease. 


By 


H. Marshall Ward, M.A., F.L.S., 


Fellow of Christ’s College, Cambridge, and Professor of Botany in the 
Forestry School, Royal Indian College, Cooper’s Hill. 


With Plates XXXI and XXXII. 


Some time ago I was commissioned to prepare for the 
Science and Art Department, South Kensington, a series of 
drawings illustrating the structure and life-histories of certain 
parasitic fungi; the intention being that these drawings should 
eventually be enlarged to form wall-diagrams suitable for 
museum and teaching purposes. I soon found that if the 
drawings were to be what I should wish them to be—i.e. to 
form a properly connected series, and to be taken from original 
preparations—the task promised to develope into one of greater 
magnitude than had been anticipated. In fact it became 
necessary to go over the entire field. 

On the completion of the drawings from which the diagrams 
illustrating the phenomena in the life of the potato disease 
fungus (Phytophthora infestans) were to be selected, it 
was suggested to me that they form in themselves a series 
which would probably be welcomed as bringing together facts 
about this fungus in a connected form, whereas what other 
original figures exist are scattered through various foreign 
periodicals, &c., or are not easily accessible to students. 

The text, it will be noticed, applies to the drawings through- 


414 H. MARSHALI WARD. 


out, any theoretical matters touched upon being referred to 
incidentally and in connection with points of structure, &c., in 
question. It has not been my intention to discuss hypothe- 
tical matters at any length, and hence the form of the descrip- 
tive letterpress. 


Fig. 1 was drawn from a preparation made by cutting off the 
epidermis of the leaf at the margin of a disease-spot, where the 
tissues are as yet green, and the white aérial hyphe of the 
fungus form the well-known velvety “bloom.” Two stomata 
are shown, and a number of intervening cells of the epidermis. 
The stomata are very wide open, and each guard-cell contains 
chlorophyll-corpuscles and a nucleus (see the stoma on the 
right). The vertical boundary walls of the epidermis-cells are 
sinuous. From each stoma emerge branched aérial hyphe of 
Phytophthora infestans, and their continuation into the 
leaf can be traced for a short distance. The aérial hyphe 
branch considerably and produce the ovoid “ conidia” at the 
tips of the branches, the tip often growing forwards and deve- 
loping another ‘conidium” before the first one has fallen, 
and so on repeatedly, as indicated by the peculiar joint-like 
swellings (see fig. 8 for further explanation of this process). 
Septa are found here and there below the joint-like swel- 
lings; otherwise the hyphe are not segmented. Conidia 
in various stages are still attached to the hyphe, others 
have fallen or been knocked off during manipulation; such 
a fallen conidium is seen lying on the epidermis. The pre- 
paration was made from a perfectly fresh leaf, and examined 
in water. 

Fig. 2.—This transverse section of a potato leaf was made 
across a similar part of the disease-spot, but passed somewhat 
closer to the dark brown part of the spot, where the cells are 
already dead; this is evident at the right hand of the drawing. 
The epidermis is very similar on both sides, the stomata being 
less numerous on the proper upper surface of the leaf. The 
mesophyll to the left of the preparation is still quite healthy 
and free from the mycelium of the fungus; the cells (seen in 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 415 


optical section and in plan) are turgid, and the chlorophyll- 
corpuscles bright green and sharply defined. A fibro-vascular 
bundle consisting of a few vessels, wood cells, and soft bast, 
and surrounded by a sheath, has been cut across transversely ; 
the palisade cells on its dorsal surface are arranged in a 
peculiar manner, and a depression in the epidermis of the 
upper side of the leaf corresponds with its course. To the 
right hand of the section the parasitic mycelium of Phyto- 
phthora infestans is rampant, though not as yet abundant 
in this younger portion of the disease-spot. The tubular, non- 
septate hyphe, are seen in the intercellular spaces, but not in 
the cells themselves. Many of the cells are already losing 
their turgescence and the chlorophyll-corpuscles are becoming 
discoloured and misshapen, the protoplasm and cell walls 
eventually turning brown and becoming disorganised. The 
hyphe in the intercellular spaces send branches through the 
stomata, especially on the lower side of the leaf, partly because 
that is more sheltered, and there is more moisture, and these 
branches become aérial hyphe which again ramify and produce 
the conidia, as seen in the centre of the figure. The stoma to the 
extreme right is cut through transversely, but not in the 
median plane, and the tip of a hypha is already protruding 
through it ; one hypha in the lacuna below has been cut across 
obliquely, and the extreme tip of another is just making its way 
outwards towards the orifice of the stoma. The stoma to the 
left of this is cut longitudinally, and the tips of two hyphe are 
about to protrude through to the exterior; the stoma to the 
left, again, is also in longitudinal section, and two branched 
conidiophores have passed through and developed their conidia 
outside. The details of these are similar to those in the 
preceding figure. To the left of this stoma is one of the 
numerous capitate hairs, with yellow, oily-looking contents; and 
still further to the left one of the longer pointed hairs, the outer 
cell walls of which are dotted with minute papille. Similar 
minute papillz exist on the outer walls of the epidermis-cells ; 
the enlarged epidermis-cells surrounding the base of the hair 
are often much larger than in the specimen drawn, A stray 


416 H. MARSHALL WARD. 


hypha is to be seen between the cells of the spongy mesophyll 
close to the epidermis at this part: it is cut through. The 
dark grey cell below the smaller hair is filled with fine 
granular particles of calcium oxalate. Below and to the right 
of this cell a hypha is making its way in the spaces between 
the palisade cells to the stoma (in oblique longitudinal sec- 
tion) on the morphologically upper surface of the leaf. It 
will be noticed that the cell walls of the epidermis turn brown 
over the badly infected portions, but, as elsewhere, the dis- 
colouration and disorganisation do not result immediately on 
the access of the mycelium; the process is accelerated or re- 
tarded by wet or dry weather—possibly apart from the mere 
quantity of mycelium, though certainly not independent of its 
presence. 

Fig. 3.—Portion of the tip of a branch of one of the conidio- 
phores which had grown out from a piece of potato-tuber, 
lying in a drop of water beneath the microscope. The order 
of development is from a to e; the conidium marked * is the 
same throughout. Ina the tip of the hypha is commencing 
to swell up, and soon becomes an ovoid body full of fine- 
grained protoplasm (6), still continuous with that of the coni- 
diophore. Soon afterwards the now larger conidium presents 
a more granular clouded appearance, and its proximal or basal 
end is cut off from the hypha below by aseptum, At its distal 
end a colourless papilla has appeared, due to the deliquescence 
and swelling of the cellulose wall at this point. In d this 
conidium is nearly ripe, and in e it has just fallen away by the 
rupture of the short, slender pedicle. Meanwhile, as the coni- 
dium referred to was approaching maturity, the hypha con- 
tinued to grow by bulging out below the septum in ¢, and (in 
this case) to the right. This pushed the point of union between 
the above conidium and its hypha over to the left, and thus 
caused the displacement of the conidium ind. In the latter 
figure the new growing point of the hypha has already swollen 
up to form a new terminal conidium, which was in its turn 
displaced (to the left also), as shown in e, by arenewed growth, 
and so on. In each case a flask-like dilation of the hypha 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 417 


marks the previous place of origin of a conidium, which had 
been thus developed and displaced. 

Fig. 4.—In this drawing the germination of the conidium 
and of the zoospores to which it gives origin are represented. 
The conidium (gy) was one of five which had been isolated in a 
drop of water, suspended in a damp chamber beneath the 
microscope. The sowing of conidia was taken from fresh, 
damp, diseased leaves, and made at 11.85 a.m., and the coni- 
dium (gy) wasthen drawn. The contents were densely granular, 
and looked dark grey. The cellulose wall was sharply marked, 
and the pale papilla at the anterior end distinct, but not promi- 
nent. The short, broken-off pedicel was also evident. The 
first changes of note occurred at about 2 p.m., when the con- 
tents appeared much more translucent and watery, the dark, 
coarse granules being no longer obvious. This seemed to be 
owing to their having altered in character and become more 
translucent. The cell wall was also paler, perhaps because the 
contrast between it and the closely fitting contents was less 
marked. The apical papilla was thicker, and slightly more 
prominent, During the next two hours or so (2 p.m. to 4 p.m.) 
the peculiar hyaline granular contents were obviously under- 
going changes, and very slow movements of the translucent 
granules occurred, producing variations in the faint cloudy 
markings shown in the drawings (A and 72). Towards 4 p.m. 
certain vacuoles appeared, and at length became sufficiently 
distinct to draw (7). There were about nine of these alto- 
gether. The papilla also became more prominent, as if it was 
swelling up. At 4.50 it was obvious that each of the vacuoles 
formed the centre of an angular block of protoplasm, as seen 
ink. These angular blocks were separated by thin, sharply 
marked plates, and the whole mass was no longer close to the 
outer wall of the conidium, but a pale, watery looking line lay 
between them. The apical papilla was still more gelatinous 
in appearance. That these angular blocks were incipient zoo- 
spores was proved by what followed. Their arrangement ap- 
peared to be as follows—one at the apex, three in the next tier 
(two visible in the drawing), four in the next tier (three visible 


418 H. MARSHALL WARD. 


in the drawing), and one at the base. The drawing was made 
at the higher focus. 

Four minutes after the drawing of k was completed the 
papilla at the apex gave way, and the zoospores glided out as 
shown at /. They appeared to be quite passive, as if being 
pushed out from behind. Special attention was paid to the 
fact that they were squeezed through the narrow aperture. 
On reaching the exterior the zoospores did not immediately 
move away, but remained some seconds, as if hesitating, as it 
were ; possibly the shock of meeting the water outside affected 
them. Two of the zoospores remained united for several 
seconds, presenting a superficial resemblance to conjugating 
amoebee; after slight ameeboid writhings they separated, but did 
not move out of the field. The zoospore (n) moved away briskly, 
but came to rest in less than a minute, and close to the now 
empty conidium, or zoosporangium, as it may be called. 

The movements and changes of the other zoospores could 
not be followed, as attention was devoted to the specimen n, 
the further fate of which was followed, and noted as accurately 
as possible (see o to z). Owing to its movements being nearly 
circular, and its coming to rest close to the empty zoosporan- 
gium, it was easy to see the two cilia and two vacuoles (0) as the 
movements ceased. The zoospore then became rounded off and 
seemed to throw off its cilia—at least I saw one detached (7, s), 
and lost sight of the other one. The two vacuoles became 
smaller and soon disappeared, as if the zoospore in diminishing 
its volume squeezed out water. As far as it was possible to 
judge, these processes occupied one minute, and the zoospore 
had then come to rest as a spherical mass (s), which soon 
clothed itself with a recognisable but thin membrane. 

It should be pointed out that the zoospore here followed 
moved for a very short time compared with others. I have 
frequently seen the zoospores still active twenty minutes or 
more after emergence, and they are said to move even longer. 
At the same time they often come to rest in from one to five 
minutes, and sometimes only give one little flirt and then come 
to rest. 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 419 


The spherical resting zoospore remained unaltered, to all 
appearance, from 4.56 till 6 o’clock, but soon after that was 
seen to be putting forth a protuberance (¢) (6.14 p.m.), which 
soon elongated into a hypha (v) (6.34) as long as the diameter 
of the zoospore. At 7.10 this germinal hypha was twice the 
diameter of the zoospore in length, and a large vacuole had 
formed in the rapidly emptying zoospore (w). This vacuole 
occupied nearly the whole of the cavity at 7.50—in other 
words, the protoplasm had nearly all passed into the develop- 
ing germinal hypha (#). A tiny protuberance on the hypha 
also indicated an incipient branch, which, however, did not 
attain any considerable length, and soon became emptied. At 
11.20 p.m. the state of affairs was as shown in the drawing (z). 
The whole of the protoplasm was in the apical one fourth or 
one fifth of the germinal tube, the rest being empty like the 
zoospore, and having three very thin septa across at pretty 
equal distances. Whether these septa are really cellulose walls 
it was impossible to determine. Next morning there was no 
appreciable change, and the protoplasm seemed to be dying © 
towards evening. 

The other four of the five conidia sown did not develope 
zoospores ; two of them germinated directly in the manner 
shown in fig. 7. The development of the zoospores is de- 
layed or even arrested by direct daylight, even if not very 
strong, and it is not improbable that in the present case the 
formation of the zoospores was arrested in the other conidia by 
the repeated and continued exposure of the preparation during 
the observations. 

Fig. 5.—In this drawing two zoospores are represented germi- 
nating on the epidermis of a potato leaf, and one has become 
rounded off, but has not yet put out a germinal tube. The 
preparation was obtained by painting the lower surface of a 
fresh leaf with a camel-hair pencil dipped in rainwater and 
then passed over freshly-developed conidia at the margins of 
disease-spots on other leaves. At the end of twenty hours the 
leaf was examined, and numerous zoospores were found on the 
epidermis, many of which had put forth germinal tubes which 


420 H. MARSHALL WARD. 


were entering the leaf. The drawing is combined from two 
preparations to save space, the zoospore which is putting forth 
a tube through the stoma having been observed on a different 
part from the other—in other words, instead of only one cell 
intervening between the stoma and the lower of the two germi- 
nating zoospores, there were very many. ‘The zoospore close 
to the stoma simply protrudes its tube into the orifice. The 
one lower down has germinated on an epidermis-cell, and the 
tip of the tube at once commenced to bore through the outer 
wall ; once inside, the germinal tube swells up and has in this 
case branched. The empty remains of the zoospore and part 
of the tube are left outside. The chlorophyll-corpuscles are 
shown in the guard-cells, but the nuclei are omitted. 

The germination of the conidia on the living leaf is often 
very rapid, and may certainly take place in two hours after the 
sowing was made. I could not satisfy myself that it is af- 
fected by light, as is that on glass slides. It is accomplished 
readily during the night, on leaves kept wet under bell-jars. 
The results seem to be more satisfactory if rainwater is em- 
ployed, in preference to well-water; and the same is true of 
experiments on glass slips. It is improbable that temperature 
was the important factor in these differences, possibly the 
oxygen present in the rainwater was of more significance. 

It occasionally happens that a zoospore germinates in an 
angle of the venation of the leaf, and sends its germinal hypha 
through the epidermal cells of the rib or “ vein” lying at its 
side; in such cases an optical section of the tube and zoospore 
can be obtained, but the best proof of the entry of the germi- 
nal tube through the wall of the epidermis-cell is obtained as 
follows. 

Fig. 6.—The preparation is part of a vertical longitudinal 
section of a young internode of the potato plant, and shows 
a stoma in longitudinal but not quite median section, and to 
the right a germinating zoospore, the germinal hypha of which 
has pierced the cuticle and cell-wall and is growing on inside 
the epidermis-cell. The method adopted was to sow large 
quantities of the conidia on one of the flat sides of the tetra- 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 421 


gonal, winged internodes of the potato plant; several such 
preparations were then laid with the sowings upwards, on 
damp blotting paper, in soup-plates covered with bell-jars, 
and the air kept damp. After twelve hours or longer, sections 
were cut longitudinally vertical to the flat places on which the 
sowings were made, and the section examined. It was not 
difficult to obtain evidence of the germination of the zoospores, 
and entry of the germinal hyphe, but it was only after many 
weeks that I succeeded in preparing the really satisfactory case 
here drawn. The razor had passed close to but not through 
the germinal tube; the empty zoospore and first part of its 
germinal hypha are seen lying close on the exterior of the 
cell wall—the zoospore had come to rest in a slight depression 
at the junction of two cells—the very fine hole through which 
the germinal tube passed was clearly visible on focussing. On 
reaching the anterior of the cell the hypha thickened con- 
siderably, and passed along the roof of the cell, and was just 
about to turn and run down the vertical wall (or possibly to 
bore through it) where the section was made. The sub-epi- 
dermal cells frequently contain a crimson-coloured sap, but 
none of the cells in the preparation were so coloured. 

Figs.7 and 8.—When the conidia of Phytophthora infes- 
tans are sown in water on glass slips, they frequently assume 
the appearances figured at figs. 4, gy, h, and 2, after a few hours, 
and then cease to develope further in the direction of producing 
zoospores. Instead of doing that, the cloudy, vacuolated condi- 
tion of the protoplasm which usually heralds the development of 
the zoospores (fig. 4, 2) is again replaced by the more uniformly 
hyaline appearance of the earlier stage (fig. 4, 2), and the papilla 
either commences to grow out as a hypha,or a protuberance from 
it (fig. 7) does so; occasionally, but rarely, this hypha branches, 
as in fig. 8. This germinal hypha, the development of which 
stamps the conidium as an ordinary spore (in contrast to its 
behaviour in other cases as a zoosporangium) elongates consi- 
derably, and in some specimens attains a length equal to ten 
times that of the conidium ; its apex then dilates into an ovoid 
body much like the conidium from which it originated (fig. 7). 

VOL, XXVII, PART 3, —NEW SER. GG 


422 H. MARSHALL WARD. 


Tn one instance (fig. 8) this took place at the end of each of 
the two branches. The protoplasm of the original conidium 
passed entirely into the hypha, and along it (fig. 7) wholly 
into the new or secondary conidium, which is usually somewhat 
smaller and sometimes much smaller (fig. 8) than the primary 
conidium. One or two fine transverse septa may be formed in 
the germinal hypha (fig. 7). As a very general rule the 
secondary conidium is oblique or misshapen ; fig. 7 was an ex- 
ceptionally symmetrical one. 

The conditions which determine this mode of germination, 
in preference to the formation of zoospores directly, are not 
quite clear ; but they seem to be connected with the nutrition 
of the germinating conidium. When the sowings of conidia 
are exposed to light these secondary conidia are often formed ; 
and I found it more difficult to obtain the zoospores in well-water 
than in rainwater. I here speak more especially of water from 
a particular well, which has proved to contain considerable 
quantities of organic matter. In large sowings, 1. e. where 
eighty to hundred or more conidia existed in the drop of water, 
by far the majority of the conidia germinated in this manner ; 
and wherever the germination was delayed from obscure causes 
beyond twelve hours, this was the prevalent form it assumed. 
Sowings in very dilute infusions of organic matter (jam and 
horsedung were tried) never yielded zoospores, whereas several 
conidia would germinate like this. When large quantities of 
the conidia were sown on a small area of the potato leaf or 
stem, a larger portion of them germinated thus (see fig. 9, 
below). ‘No connection was established between differences of 
temperature and of mode of germination. Putting all these 
facts together, it seems not improbable that the difference is 
due to nutrition, and possibly three factors were concerned in 
affecting this, (1) the amount of free oxygen available, (2) the 
comparative maturity of the conidia themselves, and (3) the 
intensity of the light. It is not inconceivable that direct sun- 
light increases the oxidizing processes during the early stages 
of the germination ; and I feel convinced that the presence of 
numerous competing conidia, or of organic matter generally, 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 423 


affects the germination by influencing the amount of oxygen 
available for any one conidium. I am satisfied that it is easier 
to obtain zoospores in dewdrops on the living leaf than in 
water on glass. Nevertheless, it must not be overlooked that 
the zoospores will develope on a wet leaf during the night, in- 
cluding the early hours of the morning. There can be little 
doubt that an interesting field of investigation in comparative 
physiology is here open. 

As to the significance of the secondary conidia and their 
formation, I have found them empty, as if they had developed 
zoospores which had escaped; but have never seen zoospores 
come from them. I have also seen a secondary conidium with 
what looked like a germinal hypha developed from it; but this 
died before developing very far, so that it was impossible to say 
whether a tertiary conidium could be developed. I have not 
seen these tubes enter a stoma. The secondary conidium 
would seem to be a second attempt on the part of the zoospore- 
producing protoplasm to prepare for the development of zoo- 
spores again ; there is a loss of substance from respiration, and 
the cellulose of the hypha has to be formed, and the energy 
expended is no doubt evolved at the expense of materials in the 
protoplasm, and not replaced by nutrition. 

Fig. 9.—This drawing was from a preparation of the epi- 
dermis of an internode on which several of the crowded 
conidia had germinated as above. The drawing is to scale. 
As usually happens in such cases as this, the germinal hypha 
is shorter than those developed in hanging drops, and the 
secondary conidium oblique. 

Fig. 10.—The preparation shows hyphe of the parasite in 
the cortical tissues of the internode three days after infection. 
The chief point of interest is the course of the hyphe, they 
run between the thin-walled, closely-fitting cells, in the middle 
lamellz, and even push aside the other layers of the cellulose 
walls; the diameter of the hypha is considerably greater than 
that of the walls they traverse. The same thing occurs in the 
tuber (see fig. 15, below). The hyphe branch often; they are 
devoid of septa and have very thin walls and abundant finely 


424, H. MARSHALL WARD. 


granular protoplasm. In the preparation drawn the hyphe 
are particularly luxuriant and thick, the diameter varying, 
however, in different parts of their course. Several interesting 
questions here suggest themselves. How are these hyphz 
nourished in the ‘‘ middle lamella”? Is any protoplasmic sub- 
stance preseut? -Processes are very rarely sent into the cells 
of the cortex; the branches in the upper part of the drawing 
are running over the cells and in the middle lamella, between 
the cell which is drawn and one that would have lain nearer 
the observer. The longitudinal hyphz often run for some 
distance in the line of junction between three cells. The cells 
contain pale chlorophyll-corpuscles; a nucleus is present in 
the one to the left, and a few crystals lie iu the large cell to 
the right of it. 

Fig. 11.—A potato-tuber was sliced across, and the mycelium 
of Phytophthora, from a diseased potato planted on the clean 
cut. The preparation was then put aside, and was not kept 
particularly damp. On examining the sections cut vertically 
to the cut surface, some time later, the mycelium was seen 
attacking the tuber, as in the drawing. The cut surface of the 
wound (at the top in the drawing) had undergone partial heal- 
ing by means of tangential divisions of the exposed cells (the 
rotten remnants of the cut cells were destroyed), and the two 
or three tiers of cells thus cut off had become cork-lke. The 
contents of the cells were removed to a large extent in making 
the preparation. The protoplasm or its remains turns coarsely 
granular, and eventually rusty brown; the starch-grains are 
dissolving, remains of the nuclei are found as opaque, coarsely 
granular masses, and here and there a crystal is noticed. The 
mycelium is strictly intercellular, the branches running between 
the cells in the narrow lacune, or in the substance of the walls. 
Eventually the cell walls soften and swell, and split apart, and 
finally turn rusty red and decay. 

Figs. 12 and 13.—Cells of a diseased potato in a somewhat 
more advanced condition. In addition to the changes above 
referred to the cell walls are now swelling, and the cells sepa- 
rating from one another at the middle lamella. In the pre- 


ILLUSTRATIONS OF PHYTOPHTHORA INFESTANS. 425 


paration from which fig. 13 was drawn it was easy to see the 
remains of the protoplasm as a sort of matrix in which the 
starch-grains (some partially eroded) were embedded. ‘The 
nucleus and proteid seem to be destroyed long before the 
starch, and it is even doubtful whether the starch is directly 
attacked at all until bacteria gain access, and hasten the de- 
composition. In fig. 13 starch grains are seen to be displaced 
from the matrix in which they were lying. 

Fig. 14.—Portion of mycelium from such a preparation as the 
last. The two branches running across from the vertical ones 
were passing along the surface of a cell, and a brownish tinge 
was given to the cell wall in the immediate neighbourhood. 
The same is seen in fig. 15, a and 6. The hypha corrodes the 
walls, as it were, in its immediate neighbourhood : the rest of 
these cell walls were as yet not coloured. 

Fig. 15.—Portions of hyphe in the middle lamella between 
the cells of the potato tuber. The corrosive action of the 
hyphe is indicated by the rusty hue which they cause the cell 
walls to assume. 


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ZOOSPORES IN THE SAPROLEGNIEA. 427 


On the Formation and Liberation of the 
Zoospores in the Saprolegniez. 


By 
Marcus M. Hartog, D.Sc., M.A., F.R.U.E. 


I. Tue ForMATION OF THE ZoosPoreEs. 


THE zoosporange of the Saprolegniee has long been a 
favourite object for the study of cell development; but only 
within the last few years has an insight been obtained into the 
great complexity of the phenomena attending the formation 
and the liberation of the zoospores. These were first described 
by Biisgen (“‘ Die Entwicklung der Phycomyceten-sporangien ” 
in ‘ Pringsheim’s Jahrbiicher,’ vol. xiii, 1882);' and, a little 
later, independently by Marshall Ward (‘Observations on 
Saprolegniez ” in ‘ Quarterly Journal of Microscopical Science,’ 
N.S., vol. xxiii, 1883). 

The following is an abstract of the nearly concurrent results 
obtained by these two observers. As is well known, the 
zoosporange is formed by the enlargement of the end of a 
hypha. The protoplasm streams into this enlargement and 
becomes dense, its transverse septum then isolates the zoo- 
sporange, which contains one large centre vacuole, or, in 
Achlya, often several small ones. A blunt beak-like enlarge- 
ment forms at an undetermined place (usually the apex), and 
through this the spores are finally emitted. 

In Achlya the following processes occur. There appears in 


1 This paper contains an excellent summary of the literature of the subject. 


428 MARCUS M. HARTOG. 


the protoplasm a network of lines, formed of fine granules, and 
marking out the protoplasm into polygonal areas. These lines 
broaden out, and become converted into clear bands, which 
slowly swell up “like transitory cell plates.” This we may 
term the first stage of preliminary division. 

The second or homogeneous stage consists essentially in 
the almost instantaneous disappearance of the clear bands ; the 
protoplasm becomes lighter and homogeneous; the central 
vacuole or vacuoles disappear at the same time that the basal 
septum, hitherto concave towards the sporange, now bulges in 
and becomes convex, showing that the turgescence of the 
sporange has diminished. This stage hardly lasts more than 
half a minute, and passes on to the 

Third stage, that of the shifting vacuoles. The proto- 
plasm loses its homogeneity owing to the appearance of a 
number of minute vacuoles, some of which would seem to 
occupy the centre of the meshes bounded by the network of 
the first stage, others to lie along the lines bounding them. 
These vacuoles come and go, fuse or disappear, and reappear. 
This stage gradually passes into the next. 

Fourth stage of finaldivision. Now, as the protoplasm 
shrinks from the wall, leaving a clear space interpreted by 
Biisgen and De Bary as a substance, new lines appear, 
clearly marked and more numerous than in the preliminary 
division. They are the optical expression of the planes 
separating the zoospores, which now contract, round off, and 
escape a little later. 

These are the facts as described by Biisgen and Ward, and 
as accepted by De Bary, their master, in his great work on 
Fungi. In the above summary I have alluded to the fact that 
Biisgen regards the lines of the preliminary division as rudi- 
mentary cell plates. Ward explains them as nuclear plates. 
Biisgen and De Bary seem to consider them to be the ultimate 
source of the expulsive substance lining the sporangial wall in 
the last stage, which, swelling in water, would determine the 
expulsion of the zoospores: they deny the existence of the 
flagella on the sporangial zoospore of Achlya as described by 


ZOOSPORES IN THE SAPROLEGNIEA. 429 


Cornu in his classical memoir, so that, for this genus, the exis- 
tence of an expulsive matter would be essential to liberate the 
zoospores. In Dictyuchus (genus), Saprolegnia, and 
Leptomitus the processes and stages differ only in minor 
details from the above. 

In July, 1884, I had the opportunity of going over this 
matter in Strasburg, under the direction of the same illustrious 
botanist, Prof. A. De Bary, and with the kind help of Dr. 
Biisgen. I had in hand a species of Saprolegnia which we 
were unable to determine, as during the intense heat it formed 
no sexual fruit. I anticipated nothing more than the confir- 
mation of my predecessors’ results, but to my surprise I found 
an undescribed phenomenon at the homogeneous stage. As 
soon as it came on, a crowd of bacteria swarmed from all parts 
to the neighbourhood of the sporange, and executed a vigorous 
dance there till the conclusion of the stage, when they 
dispersed. Inferring that some excretion must take place thus 
to attract the bacteria, I put in the eye-piece micrometer, and 
found indeed that the sporange narrowed greatly, by as much 
as one seventh of its previous calibre. This unexpected 
result set me thinking, and on my return to Cork I took up 
the study afresh. Here I have only obtained two species: 
Achlya polyandra, and a form with the constricted hyphz 
of a Leptomitus, but which seemed to be identical with 
Saprolegnia Thuretii,! sent to me recently by Prof. De 
Bary’s kindness. Though these forms were convenient for 
study and easily cultivated, they just failed to show the marked 
contraction so interesting in the undetermined Saprolegnia. 
I now proceed to describe the chief new points I have 
made out. 

In the Leptomitus form, and in starved sporanges of 
Achlya, where a narrow layer of parietal protoplasm sur- 
rounds an immense vacuole, it is easy to study the real signi- 

‘ T now think [ must have contaminated my culture of S. Thuretii with 
my Leptomitus form, which I hence regard as distinct, and define thus: 


Saprolegnia corcagiensis (n. sp.), diplanetica, habitu, constrictionibus, 
zoosporangiis que omnino Leptomiti lactei, polygama, oogoniis fenestratis. 


430 MARCUS M. HARTOG. 


ficance of the lines of preliminary division. They are the 
optical expression of thinnings of this parietal layer 
between prominences rounded towards the vacuole. 
These prominences enlarge, and the protoplasm aggregates 
more and more in them as they become nearly hemispherical ; 
and the intermediate protoplasm becomes thinner and thinner, 
so as to give the impression of clear spaces in surface view; but 
in optical section it is easy to assure oneself that the proto- 
plasm lining the sporange wall is everywhere continuous and 
closely applied thereto. Careful focussing everywhere shows 
the continuity of the clear bands and the vacuole. The 
granules which first marked out the lines of demarcation in 
Achlya do not disappear; they form a layer at the edge and 
over the free surface of each hemispherical prominence, and 
are seen as lines bounding it in plan and in optical section. 

When the sporange of Achlya is normal the central vacuole 
is replaced by several, owing to the abundance of protoplasm ; 
and these in the first stage become converted into a continuous 
system of lacune. The inner masses of protoplasm are all 
connected by thinner bands. 

In the narrower sporanges of Leptomitus there is no room 
for a double row of prominences; hence in section they pro- 
ject alternately, and the central vacuole becomes zigzag. 
Here it is easy to see that the lines or bands of the preliminary 
division are merely thinnings of the protoplasm. 

In the undetermined Saprolegnia the central vacuole per- 
sists, communicating, I think, with a lacunar system of spaces 
in the thick parietal layer of protoplasm, which includes several 
layers of prominences (or rather aggregations of protoplasm). 

The homogeneous stage consists essentially in the swelling 
up of the protoplasm and the loss of its resistance to 
osmosis. On examining a normal sporange of Achlya, and 
carefully focussing a lacuna with a high power (Zeiss E 4” for 
instance), we see at the onset of this stage that the margins of 
the lacuna advance and meet from the angles inwards until the 
space disappears completely, much in the same way as the con- 

1 As indeed figured by Biisgen (op. cit., T. xii, figs. 11, 12). 


ZOOSPORES IN THE SAPROLEGNIEA. 431 


tractile vacuole of an Amceba is seen to disappear. Inastarved 
sporange the protoplasm contracts into a bossed gut-like mass 
towards the centre of the sporange; for the cell wall is rather 
thickened and rigid, so that it cannot present the contraction so 
marked in the undetermined Saprolegnia and ina less degree 
in the Leptomitus form (which, however, is usually too 
narrow for easy measurements). I have tried to account for the 
causes of this curious phenomenon, of which I have just given 
the first complete description. It occurred to me that the 
following was a possible explanation. The protoplasm is acted 
upon in two ways: 1. The tendency of protoplasm to stick 
together into a single mass. 2. The tendency to aggregate 
around numerous centres (to form the prominences), aided by 
the turgescence of the sporange. If then the thinning 
at the intermediate bands went on to complete rupture at any 
one point, the turgescence would be lost; so the first force 
would overcome the second, now left unaided by the turgor 
lost for the moment, and would thus lead to homogeneity ; 
though the second force ultimately gain the upper hand in the 
next and last stage. In this case loss of turgescence should 
always bring on homogeneity. I tried to induce loss of 
turgescence by De Vries’s method of plasnolysis with solutions 
of cane sugar and of saltpetre. I found, however, that plasno- 
lysis to a very considerable extent was not sufficient to induce 
homogeneity. Hence the loss of turgescence must be a 
concomitant or follower of homogeneity, and not its 
cause. The explanation had seemed so simple that I was 
much disappointed at having to give it up; but the facts were 
too strong. 

I then experimented with the aqueous solution of eosin, 
which De Vries has shown does not diffuse readily through the 
**Hautschicht” or external layer of protoplasm, nor its internal 
layer, the “ vacuolar wall.” The protoplasm only stains readily 
at the stage of homogeneity ; whence we may conclude that at 
this stage the resistant layers do not exist, at least as continuous 
layers. I think it probable that the Hautschicht and 
vacuolar walls break up at this stage, and become re- 


432 MARCUS M. HARTOG. 


constituted later on, and that herein is the true essence of the 
homogeneous stage.1 Probably, also, the stage of shifting 
vacuoles is due to the reconstitution of these resistant layers. 

As to the nuclei which exist in the first stage (of preliminary 
division),? Biisgen adduces facts which make it probable that 
nuclear multiplication takes place during the homogeneous 
stage. The observation of the nuclei is extremely difficult, 
and I am still seeking a satisfactory technique for the pursuit 
and elucidation of this division of the subject. 


Il. Tue Liseration or THE ZoosPores. 


As already stated, the emission of the zoospores has been 
ascribed by previous observers to the secretion of an expulsive 
matter in the sporange, which swells up in the water to expel 
them. Now, if such a substance existed it should be visible 
by some difference of refrangibility or staining in the spo- 
range or outside. But there is no matter lining the sporangial 
wall that will stain in any reagent, or refract differently to 
the water of the preparation. I have tried aniline dyes, he- 
matoxylin, picrocarmine, before and after fixation by osmic 
acid, picric acid, absolute alcohol, and obtained no sign of its 
existence. There is no streakiness in the water (even on 
staining) at the emptying of the sporange. In this case we 
may fairly say, “ De non apparentibus et de non exsistentibus 
eadem est ratio.” But if we follow the process of expulsion 
fully and minutely, we shall be led to another explanation, 
admissible as involving a vera causa: acceptable, as cover- 
ing all the facts. To understand it we must review in detail 
the processes of the definitive separation and emission of the 
zoospores. 

The protoplasm which hitherto filled the beak usually forms 

1 I must here note that in Leptomitus the first lines of demarcation 
never wholly disappear ; the homogeneity is never absolute. 

? Whence Marshall Ward’s identification of the lines as nuclear plates is 
inadmissible. His words are rather ambiguous, “ A phenomenon of nuclear 


division in which the cell plate first formed becomes used up again” (I. c., 
p. 286). 


ZOOSPORES OF THE SAPROLEGNIE®. 433 


at least two zoospores, which, as they round off, become too 
large for the calibre of the beak and retire from it. The end 
wall ofthe beak, convex outwardly, is now seen in optic section 
to be menisciform, thickened in the middle and thinning off at 
the edges; and it presents that peculiar brilliant lustre which 
is so characteristic of diffluent or collenchymatised cell walls. 
And, indeed, it does shortly disappear, a phenomenon which De 
Bary ascribes with great plausibility to the secretion of some 
ferment. In some cases, especially in the undetermined 
Saprolegnia, we may actually perceive the disappearance, 
followed by the immediate outrush of the zoospores; but 
usually in Achlya and Leptomitus the foremost zoospore 
enters the beak, and closes up against its end wall, which, pos- 
sessing the same refractive index, ceases to be distinguishable. 
In this case the outrush ef the zoospores is the sole indication 
of the dissolution of the end wall of the beak. As soon as the 
way is clear, the zoospores crowd to the opening, closely serried, 
leaving a clear space along the side wall of the sporange, and 
giving at first sight the impression that they are indeed pushed 
by such a vis a latere as the expulsive matter of De Bary 
wouldexert. They force their way through the opening, often 
becoming constricted as they do so, and emerge obtusely pyri- 
form or of a stumpy “ biscuit shape,” with the anterior end the 
narrower, and possessing two flagella (tractella). The hinder 
ones in the sporange, as room is made for them, also lose their 
rounded or polygonal form, and assume this. In Achlya, as 
the zoospores emerge, they remain near the entrance, grouped 
in a hollow sphere, their narrower rounded ends turned in 
towards the centre. Hach new comer presses in between the 
others, so that the sphere grows in size till the zoospores have 
all settled there. 

The outrush of the spores, so rapid at first, is seen to slacken 
after some time, and then we can note more readily the real 
mode of procedure. A man up in a balloon, observing a crowd 
at the doors of a theatre, might well regard the inrush of sight- 
seers when the doors open as the expression of a vis a4 tergo; 
but he can correct his judgment by observing the behaviour of 


434 MARCUS M. HARTOG. 


the isolated later arrivals. We may often see in the half- 
emptied sporange a file of say eight or ten equidistant zoospores 
going towards the opening ; the hinder ones move leisurely 
enough, keeping their distance; the front ones quicken up their 
motion and lengthen their distance as they get to the mouth, 
and leave it with a run, like a late arrival when he is stimulated 
by coming in sight of the theatre. At length, when there are 
but two or three left in the sporange, they may be seen to move 
to and fro leisurely, as if careless of any goal, till when they 
happen as it were to get towards the apex ; then they too quicken 
speed and go out, but less fast than in the earlier stages of 
emission, and so finally leave the sporange empty. Only when 
the water is not well aerated a number of zoospores may remain 
inside. 

We now turn to those that have left the sporange in 
Achlya, grouped in a sphere outside. Each revolves on its 
long axis for a short time, then goes to rest, rounds off and 
becomes encysted in a cellulose wall, closely united with its 
neighbours. Sometimes, however, a few zoospores of Achlya 
may escape from the sphere and swim off a short distance to 
turn on themselves for a short time (sometimes becoming 
amceboid), round off, and encyst quite isolated. As these 
motions clearly indicated a motor organ, I used the usual reagent 
for cilia and flagella, iodine solution, which at once demonstrated 
the flagella in the moving zoospores, inside or outside the spo- 
range, as seen by Cornu and denied by Busgen and De Bary.1 


1 Cornu’s words are most explicit. “ Le trait d’union entre les Sapro- 
legnia et les Achlyaa cependant échappé jusqu’ici a tous les botanistes. 

“Les zoospores sont de deux sortes, comme chez les Saprolegnia 
[italicised in the original]. Les premiéres, au lieu de se mouvoir pendant 
plusieurs minutes ont juste assez d’agilite pour gagner Vouverture du 
sporange ; elles sont munies de deux cils antérieures, visibles dans les condi- 
tions favorables. Elles adhérent les unes aux autres en général par le moyen 
de ces cils. . . . Au bout de ce temps [three or four hours] elles présen- 
tent, soit le premier mode de germination, qui consiste a s’allonger en 
filaments, soit le deuxiéme, et émettent alors des zoospores de deuxiéme 
nature” (‘Monographie des Saprolegniées,’ p. 11). 

In the face of this clear and detailed statement by so trustworthy an inves- 


ZOOSPORES IN THE SAPROLEGNIEA. 435 


In Leptomitus and Saprolegnia the flagella are easily 
seen even in the sporange. In these forms the zoospores, 
instead of assembling in a hollow sphere at the mouth of the 
sporange, swim away freely in all directions for a few minutes, 
and then encyst after the fashion described for Achlya. In 
all these genera the cyst opens after a few hours and the 
zoospore leaves in a different form, kidney shaped, with two 
flagella diverging from the notch, one anterior (tractellum) and 
one posterior (pulsellum). This phenomenon of two distinct 
mobile conditions to the zoospore separated by an interval of 
rest, has received the name of Diplanetism. It is obvious 
that Achlya is also diplanetic. 

We have now to consider the full explanation of the outrush, 
which study has already led us to regard as really due to 
a vis a fronte, an attraction outside the sporange. No 
expulsive matter could produce the exit of the last few zoo- 
spores nor effect the acceleration of their movement near their 
mouth. Now, Engelmann and Pfeffer have by their brilliant 
researches familiarised us with the action of chemical 
stimuli. The swarming of the bacteria at one stage, evidently 
due to such a stimulus, led me to undertake this research, and 
I must invoke the theory again at this point. Saprolegniez ~ 
are among the most aerobic of plants; their culture only suc- 
ceeds when the water in which they grow is kept constantly 
oxygenated. When the oxygen is used up, the hyphe and 
young sporanges become deformed; the mature sporanges 
open by the disappearance of the end wall of the 
beak; but the zoospores remain inside; they encyst there 
and form the so-called “ Dictyuchus state,” which never 
occurs in well aerated cultures of the above three genera. 

It is obvious then that oxygen dissolved in the ambiant 
water exercises the stimulus which is the true source of the 
liberation of the zoospores. That such a stimulus is sufficient 
to account for the squeezing out is obvious from the observation 
tigator, it is astonishing that such excellent observers should have denied the 


existence of the flagella, without exhausting every means of ascertaining if 
they were there. 


436 MARCUS M. HARTOG. 


of Juranyi, cited elsewhere by Marshall Ward, that in Gidogo- 
nium the “ relatively large antherozooid forces its way through 
an aperture too small for it to reach the attracting oosphere.” 

The exit is so rapid at first because of the contrast between 
the external medium and the small amount of liquid within 
the sporange, vitiated by the close-packed thousands ofzoospores, 
and with its gases slowly changed through the sporangial wall, 
and because of the immense number of zoospores, all influenced 
at once by the stimulus. Later on the contrast is lessened, 
partly by the exit of so many zoospores, partly by the influx of 
aerated water from without to occupy the room left by their 
exit. Only near the very mouth of the sporange is the contrast 
marked enough to accelerate the pace of the foremost zoospores. 

But when the water is left unaerated there is no difference 
as regards oxygenation between the inside of the sporange and 
the surroundings; the beak may open, but the zoospores, 
feeling no attraction to without, stay where they are, and the 
Dictyuchus state is produced; or, if the aeration be imperfect, 
only some of the zoospores leave the sporange till those within 
are no longer attracted and remain inside. 

Finally, we may note that this is only one instance of the 
extraordinary susceptibility of this group to chemical stimuli. 
Others are well known, such as the growth of the hyphe of 
germinating zoospores (especially in the Dictyuchus condi- 
tion) towards food material, the germination of the oospores 
only in presence of food material, the growth of the 
antheridial branches towards the oogonium, &c: 

The following is an abstract of the chief points I claim to 
have established : 

1. The clear bands of the first stage of the zoosporange are 
neither cell plates nor nuclear plates, but thinner parts of the 
protoplasm due to the aggregation of the greater part thereof 
around distinct centres. 

2. At the homogeneous stage the protoplasm acquires an 
extreme perviousness to liquid; this is probably due to the 
temporary loss of the resistant layers (Hautschicht, vacuolar 
walls) as continuous layers. 


ZOOSPORES IN THE SAPROLEGNIEZ. 437 


3. The homogeneous stage is accompanied by a loss of 
turgescence, and in many cases by a marked contraction of the 
sporange. 

4, The clear spaces seen in the final separation are merely 
the watery liquid of the sporange between the contracting z0o- 
spores, and do not represent expulsive matter. Nosuch expul- 
sive matter exists. 

5. The sporangial zoospores of Achlya possess at their 
exit the two tractella described by Cornu, just like those of 
Saprolegnia and Leptomitus. Achlya is therefore dipla- 
netic. 

6. The escape of the zoospores is not due to any such expul- 
sive matter as has been assumed, but to the chemical stimulus 
of the oxygen in the medium acting on the auto-motile zoo- 
spores. 

It would seem probable that the escape of the protoplasm 
from gonidia of so many Peronosporez (Phytophthora and the 
plasmatoparous Peronospore, for instance) is due to the same 
chemical stimulus of well-aerated water. There is no evidence 
for the existence of an expulsive matter in the sporange or spore 
of any aquatic fungus. Sporangial walls being diffusible to 
water and gases it is obvious that the conditions of the constantly 
immersed sporange are totally different from those of the aerial 
ascus of the higher fungi, where such a material does certainly 
exist. 

The above observations were chiefly made on plants grown on 
mealworms in tumblers, and floated out on large glass slides for 
observation, seldom covered, and replaced in the tumblers after- 
wards. In some cases I have used small cultures in the hanging 
drop with the cardboard or blotting-paper moist chamber. 


P.S.—A suggestion as to the physiological value and 
the filiation of diplanetism, &c., may not be out of place. The 
zoospore on leaving the sporange has enough reserve material 
to carry it a certain distance, and to enable it to germinate. 
In the first swarming the zoospores get scattered; and then 
during the long stage of encystment the further work of dis- 

VOL, XXVII, PART 3,——-NEW SER. HH 


438 MARCUS M. HARTOG. 


semination is effected by the movements of the water at no 
cost to the organism. And we must bear in mind that a con- 
siderable amount of dissemination is needed, lest the zoospores 
should be uselessly attracted to the host on which their parent 
thallus is living. . 

In Achlya the limited first swarming forms a sort of 
zlobular colony of resting spores, easily broken away as a 
whole by a slight impact, as of a dead animal floating down 
stream. The swarmers when liberated form a host of invaders 
effecting rapid and complete infection, which isolated ones 
might fail to do. 

In Dictyuchus (gen.) the resting state of Achlya is 
reached without the expenditure of energy required to swim 
to the outlet of the sporange. A further economy is thus 
effected. 


The Termination of Nerves in the Liver. 
By 


A. B. Macallum, B.A., 
Fellow of University College, Toronto, Canada. 


With Plate XXXIII, figs, 1 to 6. 


oe 


Artrr the completion of my studies on the termination of 
nerves in the cutaneous epithelium of the tadpole, I began 
investigations on the distribution and arrangement of nerves in 
other organs, and have now arrived at what I consider important 
results, more especially in the case of liver. That of man was 
first employed at the outset of the investigation, but I soon 
perceived that on account of the small size of the cells here I 
would have to resort to some other Vertebrate for control pur- 
poses ; not that the liver of man does not yield definite results, 
but that these might always be open to doubt if taken alone. 
Fortunately at that time there were a number of Necturi in 
the Laboratory Aquarium, and to these I resorted, on the advice 
of Professor Wright, obtaining from them my most valuable 
preparations of the liver. The hepatic cells in these are from 
two to four times in diameter those in man. It is obvious, 
therefore, that for ascertaining the relations of nerves to the 
hepatic cells the liver of Necturus (=Menobranchus) is the 
most favorable that can be at the disposal of any histologist. 

I made preparations also from the livers of the dog, rabbit, 
and frog, which turned out to be of but indifferent value, and 
recognising that the narrower the field of investigation is the 
more could attention be bestowed on the necessary details of 
technical manipulation and of observation, I devoted nearly the 
whole of my time to winning successful results from the livers 

VOL, XXVII, PART 4.—NEW SER. Kt 


4.40 A. B. MACALLUM. 


of man and Necturus. There is besides another justification 
for narrowing the range of the work as I have done, namely, that 
one of the highest and one of the lowest Vertebrate types are 
embraced in the investigation. I do not wish to be understood 
as believing that the results which I here advance are typical 
of every Vertebrate liver. Indeed, the following pages show a 
not very close agreement of results from the two types, and it 
would be hazardous to say which presents the form of nerve 
termination which has the most general occurrence in other 
Vertebrate livers. 

I may be allowed to insist on one point about which the 
vaguest opinions are allowed to pass currently as correct: the 
hepatic cell and nerve-tissue are in close connection, not 
merely by contact, but by actual union. 

The literature on this subject, what little there is, is full of 
contradictions or negative statements. Pfliiger, the first 
observer in this line, came to definite conclusions, itis true, but 
although experimental physiology has partially confirmed his 
view, taken as a whole and not in detail, yet the workers since 
that time who have published descriptions of their researches on 
the nerves of the liver have found no such connection between 
these and the hepatic cells as he describes, or, in fact, none at 
all. The reason for these contradictory results partly is that 
in nearly every case the researches were based on the Mamma- 
lian liver, the cellular constituents of which are too small to 
admit of definitely deciding so difficult a question. 

I proceed now to give a résumé of the literature on the sub- 
ject, coupled with a description of the methods employed in each 
case. A reference to these methods is necessary in order that 
I may briefly outline their advantages and disadvantages. 

Pfliiger! used osmic acid to determine the course of the 
nerves. He found them rarely single, often in bundles, each 
single fibre dividing frequently and anastomosing, and finally 
penetrating the membrane of the liver-cells in order to termi- 
nate in the latter. The fibres retain their myeline investment 
up to the point of penetrating the cell. The fibres in the 

1 «Archiv fiir die ges. Physiologie,’ ii, 1869, also 1871. 


TERMINATION OF NERVES IN THE LIVER. 441 


interior of the cell terminate in a series of fine fibrils with 
regularly placed granules or swellings along the course of each. 

Hering! found a rich supply of nerve-fibres entering the 
portal canal and branching with the vessels running in Glisson’s 
capsule. Only a few were medullated, the finest bundles con- 
taining only non-medullated fibrils. Hering was unable to 
trace any nerves into the hepatic lobules. 

Nesterowsky” injected the vessels of the cat and dog with 
coloured glue, and left sections of the organ so treated in a 4 
per cent. solution of gold chloride for twenty to twenty-five 
minutes, after which he put them in a weak solution of glyce- 
rine acidified with acetic acid, till they took a violet colour, 
which usually happened in five to fifteen days. In some cases 
he added a little of a solution of ammonium sulphide in order 
to bring out the nerves more prominently. He found branches 
of the portal vein surrounded by a plexus of coarse and fine 
nerve-fibres. Out of the coarser plexus arise fine anastomosing 
fibres, forming loops; they enter the lobules and closely twine 
about the blood-capillaries. Nesterowsky never observed even 
a connection between these nerve-fibres and the hepatic cells. 
He could not determine whether the nerves were medullated or 
not, although he thought he saw in one case examples of the 
former. 

Kupffer® followed Nesterowsky’s methods, and came to the 
conclusion that the fibres considered by the latter as nerves are 
simply those of connective tissue. He treated sections of the 
liver obtained by means of a Valentine knife with weak chromic 
acid solution (0°05 per cent.) and then left them for several 
days ina 0:01 per cent. solution of gold chloride, when they 
attained a red or violet colour. By means of this method he 
demonstrated the so-called ‘stellate cells,’ and at the same 
time found that the tissues immediately about the central vein 
of the lobule acquired a violet tint, a fact which indicated, he 
first thought, the presence of nerve-fibres, but he afterwards 

‘ Stricker’s Handbuch,’ p. 452, Leipzig, 1871. 


1 
2 « Ueber die Nerven der Leber,” ‘ Virchow’s Archiv,’ Bd. 63, p. 412, 1875. 
3 “ Ueber Sternzellen der Leber,” £ Arch. fiir Mikr. Anat.,’ Bd, xii, p. 353. 


442, A. B. MACALLUM. 


considered the structures in question to belong to connective 
tissue, since they acted towards a solution of nickel oxide in 
ammonia like the latter, and as he found the same sort of fibrils 
directly entering the lobules from the hepatic serosa. 

Kolatschewsky! used two methods. In one, fine sections of 
the liver were pencilled out and treated for ten to twenty 
minutes with }—1 per cent. solution of gold chloride; these, 
put in water acidified with acetic acid, were left there for one or 
two weeks exposed to the light until they became coloured rose 
violet. According to the other method, sections of liver hardened 
with ,—;4, per cent. solution of ammonium bichromate were 
pencilled out and placed in a solution of the double chloride of 
gold and sodium of the strength recommended by Gerlach. 
The reduction is accomplished as in the first method. By these 
methods he found deeply coloured fibres running in the interlobu- 
lar spaces and entwining ultimately about the capillaries of the 
lobules. Some of the fibrils end in the nuclei on the capillary 
walls. The fibres branch, enter into the depth of the lobules, 
and form there plexuses of fibrils running parallel to and around 
the vascular channels. The smaller the capillaries the narrower 
are the meshes of the plexus. Kolatschewsky was not certain 
that these fibres are nerves, and he never saw their connection 
with the hepatic cells, if such occurred. His results agree in 
the main with those of Nesterowsky. 

Holbrook? made sections of the fresh liver when it was frozen, 
which he left in a 3 per cent. solution of gold chloride for thirty 
to forty minutes. The reduction of the gold was accomplished 
with formic acid. In some cases he hardened the tissue first 
of all with chromic acid, and then used the foregoing method. 
He found the nerves in the portal canal provided with a large 
number of nuclei and occurring usually in bundles of from 
three to five fibres, which enter the lobules and branch at acute 
angles along the capillary channels. The finest nerve-fibrille 


1 « Beitrage zur Histologie der Leber,” ‘Arch. fiir Mikr. Anat.,’ Bd. xiii, 
p- 415. 


9 


2 «The Termination of Nerves in the Liver,” ‘ Proceedings American So- 
ciety of Microscopists,’ p. 95, 1882. 


TERMINATION OF NERVES IN THE LIVER. 443 


are found running around the capillaries between these and the 
hepatic cells. They touch, pass between, but do not enter the 
latter as Pfliger maintains. Holbrook asserts that the fibrils 
are connected with the cement substance or protoplasmic bridges 
between the cells, and thereby with the outer portion of the cell 
reticulum. He also corroborates the results of Nesterowsky’s 
researches. 
Meruops. 

To demonstrate nerve-structures in the liver of Necturus 
the method employed was as follows: Pieces of the liver were 
hardened for a week or more in Erlicki’s fluid, or for several 
days in a +—+ per cent. solution of chromic acid. After the 
hardening was sufficiently completed in alcohol, sections of the 
frozen tissue were made with a Cathcart microtome. These, 
when the gum was carefully removed, were put in a weak solu- 
tion of formic acid (5 per cent.) for an hour, transferred to a 
1 per cent. solution of gold chloride for about twenty minutes, 
then washed in distilled water, and the gold afterwards reduced 
in the dark with a 10 per cent. solution of formic acid. About 
thirty hours sufficed for this reduction when the temperature of 
the room was 20° C. The sections then had a deep red colour, 
but sometimes the tinge was violet. The chromatine of the 
nuclei of the hepatic cells took a deep blue violet tint, the 
caryoplasma light violet, while the cytoplasma came out very 
distinct as a meshwork with a pink or light carmine colour, 
The nerve-fibres appeared deep violet, but the connective tissue 
of the interlobular spaces attained a light red, sometimes a 
deep red colour, 

When chromic acid was used as a hardening reagent the 
addition of any organic acid at the same time, such as acetic 
acid more especially, seemed to me to have the effect of robbing 
the nerve-fibres of their selective capacity for gold, while it 
increased the effect of the latter on the remaining constituents 
of the liver. 

I do not know whether chromic acid or Erlicki’s fluid offers 
in the method described more advantages. If there is any 
advantage at all it is to be obtained from the former reagent, 


AAA A. B. MACALLUM. 


as with it one is apt to get beautiful preparations of the liver in 
which the gall-capillaries, gall-ducts, blood-capillaries, the 
nerves, and the elements of the hepatic cells and their nuclei 
are demonstrated in a way that I have found equalled by no 
other method of manipulation. The value of chromic acid and 
gold chloride in this respect I shall refer to again in a subse- 
quent paper. 

Sections of the liver of Necturus are not of any value when 
they are of less than 0:020 m. in thickness, that being less than 
half the average diameter of the hepatic cell. 

In the case of the human liver chromic acid was the only 
reagent used in hardening. The sections were made with the 
paraffin method, and were subsequently treated in the manner 
already outlined. I found that uniformly thick or uniformly 
thin sections did not answer well, for in these either but short 
pieces of nerve-fibres or fibrils could be seen, or else they were 
obscured by the thickness of the section. I managed to obtain 
sections about half an inch square, which had a thickness at 
one edge two to three times greater than at the opposite one, 
so that the thickness decreased gradually from one edge to the 
other. With these sections I was able to see and follow a fibre 
in its full extent, together with its divisions or branchlets, and 
thereby gained all the advantages of a thick and a thin section, 
with the faults of neither so far as tracing the nerves is con- 
cerned. 

The success of the preparations of the human liver was the 
exception and not the rule. About 10 per cent. or at most 
20 per cent. of them only were valuable for all the purposes for 
which I made them. Sections from the same piece of liver, 
when treated under exactly like conditions but in different 
dishes, proved to be not equally successful, some being indif- 
ferent or worthless. Why this is I do not know. In the case 
of a very strong colouring with the gold so much as to obscure 
the structure, I used a } per cent. solution of potassic cyanide 
as recommended by Cybulsky.! By putting the over-stained 

tion in this solution the proper depth of colour is obtained 

1 «Zeit. fir wiss. Zool.,’ Bd. 39, 8. 657. 


TERMINATION. OF NERVES, IN THE LIVER. ALS 


by the solution of the excess of the fixed gold, this process of 
course being carefully watched. In this reagent one finds an 
additional advantage; the nerve-fibres are the last to part 
with the violet colour, thus being distinguished from connec- 
tive-tissue fibres. It, however, does not always operate in the 
latter way satisfactorily. 

The sections of the human liver received from the gold a dull 
violet or a dull red tint, while in other preparations a blue violet 
tint was found. In two cases I obtained preparations which to 
the eye appeared almost colourless, but which on examination 
demonstrated the nerve-fibres very distinctly. 

All the sections were cleared in oil of cloves, and mounted in 
balsam. 

In the study of the ultimate terminations of the nerves I 
have used the Leitz ;4, inch homogeneous immersion with special 
illumination. In the human liver, more especially, it was 
impossible to do anything with a less efficient objective. In 
the Necturus liver it was quite easy, however, to see the 
required structures with a system 7 of Leitz, but I have 
endeavoured in every case to verify my observations with the 
higher power objective. 

The value of gold chloride as a reagent for differentiating 
nerves is not admitted by all histologists. It has been urged 
also that the elements it selects in a fresh tissue and those it 
differentiates in a tissue hardened by a reagent such as chromic 
acid are not necessarily the same structures. This objection 
has a great deal of force, especially in view of the fact that gold 
chloride gives a violet tint to connective tissue which has been 
first hardened with chromic acid ; the corium of Necturus and 
the connective tissue around arteries are casesin point, More- 
over, the tendency of a hardened tissue is to reduce equally the 
gold so as to give to all the tissue elements a violet colour. Yet 
with all its faults the method of hardening with chromic acid 
and the subsequent treatment with gold chloride has many 
advantages over other micro-chemical and staining reagents, 
and so far as the demonstration by it of nerve-structures 
are concerned no greater suspicion should be attached to results 


446 A. B. MACCALLUM. 


obtained with it than to those of other histo-chemical reagents. 
Gold chloride employed in any way is not an infallible test for 
nerve-structures, for these have in the end to be determined by 
their intrinsic form and arrangement, by their origin and 
termination, or either separately. The violet colour given by 
gold chloride to fibres otherwise undemonstrable is therefore of 
accessory value only. 

It is not known definitely to what organic compound is due 
the capacity of nerve-fibres for fixing in themselves gold chloride. 
R. Gscheidlen,! after a series of experiments, came to the 
conclusion that the reduction is caused by a fatty substance. 
He treated pieces of the ischiadic nerve of a frog with ether, 
alcohol, and water respectively, and found that the extract 
obtained with ether reduces gold in a few hours, while that 
obtained with alcohol took longer to do the same, the aqueous 
extract, on the other hand, a very long time. As 90 per cent. 
of the solid extract obtained with ether is fatty in its nature 
Gscheidlen drew the inference that a constituent of this fat 
reduces the gold. I do not think that this explanation will 
suffice, for nearly all the fat of such an extract must come from 
the myeline investment of the fibres, and we find that no 
reduction usually occurs in the medulla. Fol? points out that 
the violet colour may have another explanation than a mere 
reduction of the gold, and calls attention to the fact demon- 
strated by Lindet that this reagent forms double salts with 
phosphorus compounds, especially the chlorides, which give 
aqueous solutions of a violet colour. Whether gold chloride 
undergoes reduction or enters into a more complicated condition 
it is outside the province of the histologist to determine. It is 
possible, however, without transgressing limits, to consider some 
aspects of this question and to suggest some points which may 
help in the solution It seems to me that the substance which 
favours the production of a violet colour with gold chloride is 
diffused through all forms of tissue, and that it is found in a 
concentrated condition in nerve-tissue only. If a section of 


1 ¢ Arch, fiir Mikr. Anat.,’ Bd. xiv, p. 225. 
* «Tehrbuch der Vergleichenden Microscopischen Anatomie,’ p. 175. 


TERMINATION OF NERVES IN THE LIVER, 44,7 


liver be treated with gold chloride, and the process of colouration 
be watched, it will be found that the first tinge which the 
nerve-fibres take is red, and afterwards they show all stages 
transitional between that colour and violet, while the other 
systems of tissue slowly pass through the same order of colours 
to the violet tint. The nuclear chromatine is an exception, 
being, like nerve-tissue, quick to attain a violet tint. Occa- 
sionally other structures act like nerve-fibres towards gold, and 
among these may be mentioned certain paranuclear bodies in 
the cutaneous epithelium of Necturus which are first coloured 
red, then rose violet, and finally deep violet. This appears to 
show that the substance which fixes the gold in a violet form 
is not confined to nerves, but is diffused to a small degree in 
other tissue elements. 

The finest nerve-fibrils being hardly thicker or less delicate 
than the trabeculz of the cytoplasma, it is wrong to suppose 
that a reagent which does not specially preserve and fix the 
latter will do this for the former. It is in this respect that I 
find the reason for the failure of Nesterowsky, Kolatschewsky, 
and others to resolve the finer nerve terminations, seeing that 
the reagents they used for hardening the tissue do not render 
the cytoplasma distinct and firm, and with it the finer nerve- 
fibrils. Ammonium bichromate is not a suitable reagent for 
this purpose, neither is the weak solution of chromic acid such 
as Kupffer used. The same objection can be urged against the 
method of freezing the fresh liver in order to obtain sections. 
The method of gold colouration must not be allowed to injure 
the cytoplasma. The test which I always exacted of the 
method employed was the distinct demonstration of the cell 
reticulum; that being in a good state of preservation, it was 
only a question of the number of trials with gold chloride in 
order to get the desired demonstration of the termination of 
the finest fibrils. I think also that the clearing up of fresh 
tissue with formic or acetic acid previous to steeping in goid 
chloride is apt to destroy both the cytoplasma and the finest 
nerve-fibrils. It is on this ground that I advocate the use of 
chromic acid to fix these before subjecting them to the action 


448 A. B. MACALLUM. 


of gold chloride, and to the subsequent treatment with formic 
or acetic acids. Osmic acid, although useful in the case of 
medullated nerve-fibres, is of no value for demonstrating the 
finest non-medullated fibrils. 

Here a few words are necessary concerning the structure of 
the cytoplasma. In figs. 3, 4, 5, 6 it is represented as a net- 
work with thickened nodal points. It must be admitted that 
it does not always appear in such a regular arrangement. The 
meshes are often much larger and round as if occupied by fat 
droplets. Often also the trabeculz thin out toward the peri- 
phery of the cell, so as to be nearly indistinguishable. The 
specimens of Necturus from which these preparations were 
made were caught early in March, 1885, and consequently 
there was but a small amount of fat in the hepatic cells. The 
appearance presented in the figures is a normal one, for 
chromic acid material with hematoxylin or aniline dyes show a 
similar arrangement. Flemming! believes in the arrangement 
of the cytoplasma in threads throughout the cell, but doubts if 
these form a network such as Klein? describes. Structures, 
however, like those drawn in figs. 5 and 6, leave hardly any 
doubt as to the occurrence of a reticulum. 


Tur NERVES oF THE Human Liver. 


In sections of the liver treated successfully with gold chloride 
the tissues immediately about the interlobular and central 
veins take a rose-violet or blue-violet colour. These strongly 
coloured fields, observed with a low-power objective, seem to 
consist wholly of violet-coloured fibres, but when more highly 
magnified the latter, which are commonly arranged in bundles, 
are seen to constitute but a small part of the interlobular 
tissue, or of that about the central vein, there being between 
the bundles a quantity of connective tissue coloured light violet 
orred. The thickest fibres are of about 0:0035 mm. in diameter. 
Each bundle is composed of a varying number of fibres, and is 


1 « Zellsubstanz, Kern, und Zelltheilung,’ Leipzig, 1882, p. 28. 
2 “ Observations on the Structure of Cells and Nuclei,” this Journal, vol. 
Xviil. 


TERMINATION OF NERVES IN THE LIVER. 449 


usually separated from its neighbour by a narrow interspace 
less in diameter than that of the bundle. The fibres when 
seen in transverse section are round, and possess nuclei which 
are closely applied, sometimes at definite intervals. The fibres 
are wavy in their course, and are clear and homogeneous. They 
branch frequently, the branches being of diminished size, 
round, and lacking the nuclei of the larger trunks. They 
appear in no way to be related to or derived from connective- 
tissue corpuscles, they do not anastomose with one another, 
and they nearly always have a parallel direction, decreasing in 
size as they pass into the smaller divisions of the interlobular 
canal, where their arrangement in bundles is not so common. 

The violet colour of the fibres render them remarkably 
distinct in contrast with the rose-violet connective tissue in 
which they lie scattered. Sometimes, however, the connective 
tissue is not coloured at all, but comes out as a granulo- 
fibrillar appearance which is apt to be overlooked in the 
presence of the deeply coloured fibres. In these cases the 
bundles are separated by the granulo-fibrillar substances which 
penetrates much less prominently between the individual 
fibres. 

Where connective tissue and nerve-fibres are coloured alike, 
it is useful to differentiate between the two with the aid of a 
weak solution of potassic cyanide. The section being placed 
on the slide a drop or two of this reagent is added to it and 
the decolouration watched with a moderately high power. 
When the interlobular tissue is deprived of its colour to the 
degree required the section is mounted in the usual way. 
Under the high power one now finds only a portion of the 
interlobular tissue retains its violet tint, and this portion is 
composed of the fibres above referred to. This does not neces- 
sarily show that the fibres so revealed are nerve-fibres, or 
definitely distinguish them from those of connective tissue. 
It, however, seems to agree with the experience of Cybulsky, 
that in tissue stained with gold chloride, and subsequently 


treated with potassic cyanide, the nerve-fibres retain their 
colour longest. 


450 A. B. MACALLUM. 


I have never seen the connection of these fibres with medul- 
lated nerves, having never found the latter in the liver, but the 
normal or abnormal occurrence of which in the interlobular 
canals I do not doubt. Medullated nerve-fibres are sometimes 
found in unusual places. For example, Cybulsky found a 
medullated nerve-fibre penetrating the cutaneous epithelium, 
and I also have seen the same thing in a preparation of epithe- 
lioma. One may be inclined to believe, therefore, that medul- 
lated nerve-fibres can and do occur in the liver. It is to be 
remembered too that gold chloride is not a good reagent for 
demonstrating the myeline investment of nerves, the occur- 
rence of which may escape the eye in preparations obtained 
with the one method. 

It is quite true, as Kupffer asserts, that in gold preparations 
violet-coloured tissue passes at places in from the serous 
covering of the liver between the hepatic cylinders. I gather 
from his statements that he supposes that no nerves can reach 
the hepatic tissue in this way. Such a supposition is ground- 
less, seeing that the serosa and the interlobular tissue are of 
one and the same origin, and one is as likely as the other to 
contain nerve-fibres. Where in my preparations the serosa 
was coloured violet throughout I added a drop of the solu- 
tion of potassic cyanide, and found, in consequence the same 
to be true here which I have described for the interlobular 
canals, namely, the presence of the two types of tissue— 
nerve and connective, the latter, however, very largely pre- 
dominating. 

There are at times interspersed between the bundles of large, 
violet-coloured fibres, fibrils in which the violet colour is not 
so distinct, and is more readily removable with potassic cyanide 
than that of the large fibres, but less so than that of connective 
tissue. I am doubtful of the significance of these, but they 
apparently answer to the smaller nerve-fibres of Nesterowsky. 
I have had no means of determining their connection with the 
larger fibres. 

Around the central vein of a lobule both the connective and 
the nerve-tissue are in small quantity. The nerve-tissue is 


TERMINATION OF NERVES IN THE LIVER. 451 


found absent frequently in otherwise successful preparations, 
aud the fibres usually are not more than half a dozen, each 
separated from the other by a considerable interval of space. 
For tracing the nerve-fibres further to their termination it is 
necessary to resort to the special sections which I have referred 
to, namely, those which decrease in thickness from one edge to 
the opposite one. Ina section of this sort, if the thick edge 
includes a longitudinal view of one of the interlobular canals, 
every facility is thereby afforded for following these fibres. <A. 
uniformly thin section is not of much value for this purpose, as 
in it the fibres can be followed but a short distance, on the 
average equal to the combined diameter of four or five cells, 
and the connection of the smaller with the larger fibres is diffi- 
cult to make out. Part of a section prepared in the manner 
described is drawn in fig. 1, which represents the border of a 
hepatic lobule. Atsuch a point are found medium-sized fibres 
coloured deep violet, always with a clearly defined border, quite 
different in this respect from connective-tissue fibres. One 
sees them arise from the large deep violet fibres of the inter- 
lobular canals, often as a direct continuation, without branching 
until after they enter the lobule. They are not numerous, 
there being usually two of them to each capillary channel, and 
they run between the capillary wall and the hepatic cells. 
They are easily distinguished with a low power objective. At 
first view they appear to form a network of anastomosing fibres, 
but a further examination shows that the branches of these 
fibres cross rather than join each other. Fibres of such a 
diameter are never found outside the capillary channels, that 
is, they do not penetrate between the liver-cells. These fibres 
belong to what I have denominated the coarse intralobular 
plexus. They possess no nuclei and branch at acute angles, 
the resulting branches being either quite as large as the original 
trunks or much finer. The large ones may be considered as 
belonging to the plexus just mentioned. The finer may be 
resolved into two classes: a perivascular plexus or network and 
an intercellular one. The perivascular network can be best 
seen when one looks from above into a capillary channel cut 


452 A. B. MACALLUM. 


longitudinally. The meshes of this network are irregular and 
greater or less in area than that of a hepatic cell, and the fibrils 
are very fine, without varicose swellings, and with a violet tint 
appearing quite distinct against the duller tint of the back- 
ground formed by the hepatic cells. This perivascular plexus 
is in direct continuation with the fibres of the coarse inter- 
lobular plexus, and is therefore of a nervous nature. Whether 
it belongs to the wails of the capillary channels or to the 
hepatic cells bordering on these, or to both, I do not know. 
Sometimes it appears to belong to one, sometimes to the other. 
I cannot even say whether it is distinct from the intercellular 
network. The latter, also, is formed of fine fibrils, which are 
commonly seen unconnected with each other, but which in good 
preparations show anastomoses enclosing a varying area and 
extending between the hepatic cells. The finest of these fibrils 
possess varicosities regularly arranged and observable only with 
homogeneous immersion lenses such as a +4; inch. 

All my efforts to find a further resolution of the fibrils of the 
perivascular plexus availed nothing inthe result. They might, 
as Kolatschewsky found in one or two cases, terminate in the 
nuclei of the capillary wall, but as to this I can bring no 
observations either for a negative or for an affirmative view, since 
in my preparations the capillary walls and their nuclei, unstained 
by gold chloride, appeared under high magnifying power as a 
hyaline refracting membrane. The perivascular plexus may, 
as I have already pointed out, serve as origin to the intercellular 
plexus. 

From the fibrils of the intercellular network ex- 
cessively minute twigs are given off which terminate 
each ina delicate bead in the interior of the hepatic 
cells near the nucleus. In asection such as that given in fig. 
1 one often suspects such intracellular terminations, but the use 
of homogeneous immersion objectives does not demonstrate them 
satisfactorily, and only a careful search of very thin sections 
gave in five or six cases results not at all doubtful. I found, 
indeed, in some specimens excessively fine fibrils of a violet 
colour passing from the capillary side of the hepatic cell to the 


TERMINATION OF NERVES 1N THE LIVER. 453 


neighbourhood of the nucleus and there end with the character- 
istic bead-like swelling; but I could not prove to my own 
satisfaction that they were other than prominently coloured 
trabeculz of the cell reticulum. A view of a specimen such as 
I have represented in fig. 2 lends itself easily to interpretation. 
Here a fine nerve-fibril running along the side of the hepatic 
cylinder gives a fine twig to each cell which reaches the vicinity 
of the nucleus. Sometimes a twig divides after it enters the 
cell, the divisions running to opposite sides of the nucleus. 
The terminal points of all the intracellular twigs are delicate 
beads. I was always compelled to believe that such twigs are 
really within the cell when I found their terminal beads to be 
on the same level as the nucleus in an optical view of the latter. 
It is, of course, impossible in the greater number of cases to say 
whether the fibrils which give rise to these intracellular twigs 
belong to the perivascular or to the intercellular network. In 
fig. 2 one finds great difficulty in determining to which network 
the nerve-fibril belongs, but in several cases the demonstration 
of the intercellular origin was quite distinct, and this has led 
me to conclude that only the intercellular fibrils give off intra- 
cellular twigs. 


Ture NERVES oF THE Liver IN NECTURUWS. 


The hepatic cells in Necturus measure 0:042—0'05 mm., 
and consequently in a given area of a thin section the number 
of cells is less correspondingly than in the human liver. From 
this one would expect to find a less rich supply of nerve-fibres, 
and results bear out this opinion. The nerve-fibres in the 
interlobular canals are few in number, and each has a diameter 
much narrower than that of the larger ones of the human liver ; 
their course is straighter till they enter the lobules, where they 
pass along the capillary channels to their termination. The 
small quautity of connective tissue in the interlobular canals 
usually takes a deep violet stain and then appears homogeneous 
and structureless. In such a case I have not found it necessary 
to remove the excess of the stain, for the nerve-fibres are clearly 
outlined against the connective tissue. Apart from the larger 


454 A. B. MACALLUM. 


interlobular canals the connective tissue also is not demonstrated 
by the gold, so that one finds no difficulty in tracing a nerve- 
fibre for a long distance, providing it lies in the plane of the 
section. 

Nuclei were rarely observed on the largest fibres, and whether 
these belonged to the sheath of the fibre or to nerve-corpuscles 
it was impossible to determine. The division of the fibres in 
the interlobular canals is not common, but branching occurs 
more frequently in the capillaries of the lobules. Here 
they give rise to fibrils of two sorts; those which form the 
perivascular plexus surrounding the capillary walls, and those 
which, few in number, apparently course between the hepatic 
cells. Iam unable to say whether there is any morphological 
or physiological difference between these kinds of fibres. I am 
inclined, however, to think they are one and the same, for they 
terminate in the majority of observed cases ina like way. The 
intercellular fibrils arise from fibres which serve as origins to 
the perivascular plexus; this also supports the conclusion 
already stated as to their physiological value. Ina thin section 
the intercellular fibrils are the most commonly visible. I have 
applied the term intercellular to them because, although they 
do not always run between the cells, they unquestionably lie 
outside the capillary channels for the greater part of their 
course. I have followed them in some cases for a distance equal 
to the combined diameters of over twenty of the cells and have 
found them to accommodate themselves but very little to the 
windings and tortuous course of the capillaries. In thin sec- 
tions, where the fragment of one cell is seen to lie over that of 
another, one of the fibrils in question has been again and again 
observed to pass between their contiguous walls. Part of their 
course is in the capillary channel, i.e. between the wall of the 
blood-capillary and the adjacent liver-cells. 

The meshes of the perivascular plexus vary much in size and 
form, being usually less than the area covered by a hepatic 
cel] and of an irregular quadrangular or triangular shape. The 
fibrils which form them are wavy in their course and apparently 
anastomose completely with one another. Now and then only 


TERMINATION OF NERVES IN THE LIVER. 455 


a longitudinal section of a capillary contains a view of this 
plexus in all its relations, onthe one hand with the hepatic 
cells, and on the other with the capillary wall. The latter 
appears closely embraced by the network which also, in well- 
preserved specimens, borders the hepatic cells. In this respect 
one has great difficulty, as in the human liver, in deciding to 
which the network belongs physiologically, if to the capillary 
wall or to the cells; the terminations of this network show that 
it belongs to the latter. Is it to be supposed, however, that 
nerves are not distributed to the capillaries themselves ? 

It was of course much easier to determine how the long 
intercellular fibrils terminate than to do the same thing for 
the fibrils of the perivascular plexus. My first conclusion, after 
some observation, was that both terminate in a like manner, 
but I soon perceived that it was rarely possible in thin sections 
to decide whether a fibril which runs in the capillary channel 
and gives off intracellular twigs belongs to the intercellular 
class or to perivascular network. Both class of fibrils are 
equally delicate. The intercellular ones I found again and 
again to terminate within the hepatic cells. I had therefore 
to guard against confusing the two sets of fibrils as to their ter- 
minations. One of the several cases where an absolute decision 
was possible is drawn in fig. 38. Here fibrils of the network 
are seen to give off twigs which penetrate the adjoining hepatic 
cells, while on the opposite edge of the capillary channel a fibril, 
apparently belonging to the intercellular order, terminates in a 
like way. 

The intercellular fibrils branch at certain intervals, each 
branch running at sharp angles with the main trunk. I believe 
several times to have detected a network of these branchlets. 
In such a case these intercellular fibrils would correspond to 
those of the intercellular network in the human liver. I must, 
however, leave this point in abeyance. If this network is 
usually present obstacles to its demonstration are certainly to 
be found in the deep tinting which the cell reticulum acquires 
from the gold method. ‘The perivascular network, on the other 
hand, is not obscured, for the capillary walls over against which 

VOL, XXVII, PART 4,— NEW SER. K K 


456 A. B. MACALLUM. 


it is usually seen are uncoloured, or nearlyso. The fibrils of the 
intercellular order are generally so delicate that it is difficult 
to arrest the removal of the colour of the overlying or under- 
lying cells with potassic cyanide at a point where the distinct- 
ness of the fibrils is retained. I had therefore no success in 
trying to determine definitely the common occurrence of an 
intercellular network. 

The simple intracellular nerve-twigs always termi- 
nate in the neighbourhood of the nucleus, either 
singly or after branching, each terminal point being 
a delicate bead. The unbranched twig may end on the 
side of the nucleus facing the point where the twig penetrates 
the cell, or after curving around the nucleus on the opposite 
or on one of the lateral sides. When a twig branches two 
or more of the branchlets may terminate in the positions 
mentioned. In many cases it is possible to trace a twig 
for a certain distance after it enters the cell, but not to 
determine how it ends, this being usually due to the deep 
colour which the nucleus and the dense cytoplasma immediately 
about it take from the gold. On the other hand, the cytoplasma 
may acquire such a deep stain relatively that the determination 
of the presence of intracellular nerve-twigs is almost impossible. 
Frequently also these have but a pink or red tint while the 
fibrils from which they arise are deep violet. 

All the forms of intracellular nerve terminations to be found 
in the liver of Necturus are not so simple as that just de- 
scribed. A form which I have several times met with having 
the intracellular twig branching dendritically is represented in 
fig. 4. A complicated mode of ending, a very common one 
in good preparations, appears to belong to the perivascular net- 
work. I am inclined, from reasons which I shall state further 
on, to regard it as a general one for the hepatic cells of 
Necturus. Fig. 5 shows how widely it differs from the other 
modes. Here a branch from the perivascular network pene- 
trates a cell and becomes continuous with the cell reticulum in 
such a way as to leave the impression at first that this reticulum 
belongs to the nerve-twig rather than to the cell itself, this 


TERMINATION OF NERVES IN THE LIVER. 457 


opinion being at the same time strengthened by the fact that 
the cell network is coloured deep violet. The trabecule of the 
reticulum in such cases as this are very much more slender 
than they are as ordinarily demonstrated, but an exception is 
to be made of cases like that in the figure, where the trabecule 
become thickened along two or more lines so as to give the 
intracellular nerve-twig the appearance of a branching which 
extends toward the nucleus. In fig. 6, however, the reticulum 
is formed of trabecule nearly as coarse as that usually observed 
in the cell. 

The demonstration of the simple intracellular termination 
occurring in the same cell with the more complicated form is 
apparently not possible. The former, if such is present when 
the other mode of termination is demonstrated, must necessarily 
be obscured by deep violet colour of the cell reticulum ; if this 
depth of tint be lacking it is possible to see the simpler termi- 
nations. Both forms are often demonstrated in the same 
section, and therefore one cannot consider that the method of 
hardening previous to treatment with gold chloride may account 
for the presence of the one or the other on the ground of their 
being artificially produced. 

It is probable that every hepatic cell in Necturus presents 
both forms of termination ; otherwise we ought to conclude 
that there are two kinds of specifically different glandular cells in 
the liver according to the doctrine of the physiological homo- 
dynamy of nerves. The simpler form of termination may be 
regarded as the same as that found in the cutaneous epithelium 
of the tadpole,! while the more complicated mode is apparently 
the glandularone. At present it is useless to discuss further the 
specific function of these, but I hope in a future paper on nerve 
terminations to treat more fully this aspect of the question. 


GENERAL. 


In the liver of Necturus there is a mode of nerve termina- 
tion which I have been unable to demonstrate in the human 


' This Journal, November, 1885, p. 53. 


458 A. B. MACALLUM. 


liver. In this mode the nerve fibril fuses or is continuous with 
the reticulum, but the fibril first penetrates the cell in order to 
accomplish this fusion, and in this way differs from the method 
of termination described by Holbrook by which the fibrils are 
connected with the intercellular bridges or cement substance. 
I thought at times to see with oil immersion objectives such a 
fusion of the nerve-fibrils with the cell reticulum in the human 
liver, but it was in every case impossible to obtain demonstra- 
tions as definite as those yielded by the liver of Necturus. 

This method of termination resembles to a certain extent that 
described by Pfliiger ; the resemblance would be a more complete 
one were the cell reticulum regarded as of nervous origin, and then 
the words of that observer would be applicable here also: “* Man 
kénnte demgemiss sagen, dass die Leberzelle eine Kernhaltige 
Anschwellung eines Nerven sei.” The points of difference 
between the method here described and that of Pfliger’s are, 
however, too many to permit the supposition that they are one 
and the same but viewed according to different modes of prepa- 
ration. When one compares the observations of Nesterowsky, 
Kolatschewsky, and Holbrook on the extreme fineness of the 
nerve-fibrils so far as they could trace’ them, the termination 
of medullated nerves in the hepatic cells appears exceedingly 
improbable except in pathological cases. 

With regard to the methods of technique employed by the 
other observers several objections may be urged ; these I have 
already put forward. The methods are no doubt useful in 
demonstrating the course but not the termination of the nerves. 
It must be thoroughly understood that the nerve terminations in 
the interior of liver-cells are as delicate, as easily injured, and as 
difficult of demonstration as the finer cell structure. If this 
point is admitted I do not apprehend that a confirmation of 
the description of the nerve terminations here given will be a 
tardy one. Of course there are reagents which preserve well 
the cell structure but which do not fix it in such a way as to 
permit the selective capacity of gold chloride full play, and one 
must then endeavour to find such reagents as will give with 
gold chloride the best results. I have found these in Erlicki’s 


TERMINATION OF NERVES IN THE LIVER. 459 


fluid and chromic acid, but it is possible that by varying the 
methods of the fixation of the gold some other reagent for 
hardening will give better results than I have obtained. 

In conclusion, I may state that I have demonstrated these 
terminations to several competent observers, and among these 
I may mention Professor Ramsay Wright and Professor Osler. 
To the former I owe my thanks for his having gone over and 
verified every point here advanced and for the advice of which 
I availed myself at various times during the research. 


4.60 A. B. MACALLUM. 


EXPLANATION OF PLATE XXXIII, figs. 1 to 6, 


Illustrating Mr. A. B. Macallum’s Paper on ‘‘ The Termination 
of Nerves in the Liver.” 


All the figures are representations, as exact as possible, of the structures 
drawn. 


Fic. 1—A section of the edge of a lobule of the human liver to show the 
course of the nerve-fibres. The clear spaces represent transverse and longi- 
tudinal sections of the radial capillaries where they are continuous with the 
interlobular capillaries. @. The coarse intralobular plexus. 4. The perivas- 
cular plexus. c. The intercellular fibrils. 4. The hepatic cells. The capil- 
lary walls are indistinguishable. Some of the larger nerve-fibres appear at 
places to run over the liver-celis, but at these points they actually follow the 
capillary pathways. Leitz, Oc. 3 and Obj. 7. The outlines of the cells, 
nuclei, and fibres were drawn with camera. 


Fic. 2.—Two cells of the human liver, showing the termination of nerve- 
fibrils in their interior. Leitz, Oc. 3, and oil immersion 54, inch. 


Fic. 3.—Shows the simple intracellular termination of nerves in the liver- 
cells of Necturus. a. A larger nerve-fibre. 4. An intercellular fibril, with 
ce, the perivascular plexus arising from a common fibre. LErlicki’s fluid, gold 
chloride, formic acid. Leitz, Oc. 3 and System 7. 


Fic. 4.—Shows the dendritic branching of a nerve-fibril in the interior of 
a single hepatic cell of Necturus. Erlicki’s fluid, gold chloride, formic 
acid. Leitz, Oc.3 and System 7. The branching of the fibril in the interior 
of the cell was drawn with hom. imm. 4; inch. 


Fic. 5.—Two hepatic cells of Necturus with nerve-fibrils of the peri- 
vascular plexus ; a fibril from the latter enters each of the cells and becomes 
continuous with the cell reticulum. LErlicki’s fluid, gold chloride, formic 
acid. Drawn to the scale of Leitz, Oc. 3. and System 7; but the course of 
the fibrils outlined as seen under hom. imm. -}; inch. 

Fic. 6.—A single hepatic cell of Necturus, showing the relations of nerve- 
fibrils and the cell reticulum. The optical plane is above the nucleus and near 
the upper surface of the cell. The nerve-fibril passes over the upper surface 
of the cell, and gives off a branch which divides into twigs to penetrate the 
cell and fuse with its reticulum. Lrlecki’s fluid, gold chloride, formic acid. 
Leitz, Oc. 3, and oil imm. =; inch. 


NUCLEI OF MUSCLE-FIBRE IN NECTURUS LATERALIS. 461 


On the Nuclei of the Striated Muscle-Fibre in 
Necturus (Menobranchus) lateralis. 


By 


A. 'B. Macailum, B.A., 
Fellow of University College, Toronto, Canada. 


With Plate XXXIII, figs. A and B. 


WHILE examining, several months ago, some preparations 
made for the purpose of demonstrating the mode of nerve 
termination in the striated muscle-fibre of Necturus, I found 
many of the isolated nuclei to possess on their surface furrows 
and striations hitherto undescribed, and which, I now believe, 
are of importance in determining the structure of the contractile 
element of muscle-substance. A careful study of these nuclei 
has further revealed other peculiarities which point to a conclu- 
sion as to the origin of the contractile element, the muscle 
reticulum. In view of this, I give a detailed description of the 
appearances presented by the nuclei, and refer them to their 
supposed causes. 

The best preparations were obtained with gold chloride and 
formic acid. This method is valuable for two reasons, the 
nuclei are completely isolated after a stay of thirty to forty 
hours in the acid, and the furrows on their surface take a deep 
violet tint, while the remaining portion of the nuclear membrane 
is coloured light, or rose violet. ‘The isolation of the nuclei from 
the muscle-substance prevents any confusion which might be 
caused by the striation of the muscle-fibre were one to examine 
them in situ. It is to be noted that the muscle-fibre in 


462 A. B. MACALLUM. 


Necturus macerates and disintegrates very easily in solutions 
of formic acid. 

The long diameter of the nuclei, the largest and the smallest, 
measures 0:037—0:053 mm., and the transverse diameter 0:010 
—-0'025 mm. The form of the nucleus varies somewhat, the oval 
being the most common; oblong and quadrate ones were occa- 
sionally observed. The membranes of old nuclei have apparently 
the capacity for attracting the reduced gold. In what might 
be considered as young nuclei, the membrane is not furrowed 
or but slightly so, and the chromatine is usually quite distinct, 
arranged in short, variously looped pieces along the long axis of 
the nucleus, or in the form of minute nodules (nucleoli) in 
different positions in the nuclear cavity (fig. 4,1 and 24). The 
reticulum of achromatine, or, better, caryoplasma, with the 
meaning attributed to that term by Carnoy, is very delicate 
with very narrow meshes in the nuclei just referred to. A very 
large number of the nuclei observed lacked chromatine while 
their caryoplasma was more prominent and its meshes larger. 
In a few, a further modification of the reticulum, to be described 
below, was observed. 

In view of Nicolaides’! work on the division of nuclei in the 
frog’s muscle, I made a careful search for like cases of division 
in Necturus, but the result was disappointing. Out of many 
hundred nuclei which I examined I found but one case of 
division, and that from the heart-muscle (fig. a, 11). Flemming? 
observed indirect division of the muscle nuclei in larval but not 
in adult Amphibia. My failure to findin Necturus what was 
observed by Nicolaides in the frog could not have been due to 
the reagent, gold chloride, for I found negative results when a 
mixture of chromic and acetic acids, or of these and osmic acid, 
was employed. 

Nine out of ten of the old nuclei, i.e. those in which there 
remains no trace of chromatine, have markings and furrowings 
on their surface. Sometimes, as in fig. a, 2, a series of parallel 

1“ Ueber die Karyokinetische Erscheinungen der Muskelkorper,” ‘ Arch. 


fiir Anat. und Phys., Phys. Abth., 1883, p. 441. 
2 ¢ Zellsubstanz Kern- und Zelltheilung,’ Leipzig, 1882, p. 337. 


NUCLEI OF MUSCLE-FIBRE IN NECTURUS LATERALIS. 463 


furrows occupy one part of the surface of the membrane, the 
remainder of which is possessed of a series running in a contrary 
direction. ‘hey may be arranged parallel to the length of 
the fibre, or, as in 8, perpendicular to the long axis of the 
nucleus, or, as in 7 and 9, oblique to the same. Often one 
finds a combination of the two last mentioned modes of 
arrangement as represented in 10. Cases were observed in 
which a furrow, followed a part of the way around the nucleus, 
was found to divide at an acute angle, the branches completing 
the rest of the nuclear circumference. Ifthe nucleus is flattened 
it is usual for the furrows to be confined to one surface. In 
7 and 9 the number of these is respectively three and two, 
and in 8 they are very numerous. The depths of the furrows 
vary with their breadth, the latter being estimated by the 
breadth of the violet line of reduced gold. The depth in some 
nuclei is such that when one takes an optical section of them 
the nuclear cavity is almost divided into a series of separate 
compartments (25). The distance of the furrows from each 
other is subject also to considerable variation (10, 12, 15). 

The cause of these furrows is in all probability the pressure 
exercised by the trabecule of the muscular reticulum described 
by Melland,! the transverse trabecule giving rise to the trans- 
verse furrows, the longitudinal ones to the furrows running 
parallel to the long axis of the nucleus. 

Here in passing I may refer to my own observations on this 
muscular reticulum. These were made on specimens obtained 
with gold chloride from the rabbit, frog, Necturus, crayfish, 
and grasshopper, and as a result I accept in full the views of 
Melland. In my preparations of the muscle-fibre obtained 
from the rabbit and Necturus this reticulum is in all its 
aspects splendidly demonstrated. Carnoy* apparently holds the 
same view as to the cause of the striation of the muscle-fibre 
in Hydrophilus piceus, for he describes it as due to a re- 
arrangement of the reticulum of the cell (cytoplasma of that 

1 «A Simplified View of the Histology of the Striped Muscle-fibre,” this 


Journal, July, 1885, p. 371. 
2 «La Biologie Cellulaire,’ Paris, 1884, pp. 192 and 193, fig. 38. 


464 A. B. MACALLUM. 


author) in longitudinal and transverse trabecule, the myosine 
arising from that part of the cellular contents enclosed in the 
meshes of the primitive reticulum of the cell. 

It is not too great an inference to draw that this reticulum 
is the true contractile element, while the myosine shifts and 
accommodates itself to the conditions of the latter. In support 
of this I refer to fig. a, 6 and 13, in which one sees that the 
furrowing takes the shape and arrangement of the meshes of 
the reticulum. 

Why the furrowing on the surface of some nuclei is longitu- 
dinal only, on others transverse, I cannot with certainty say. 
Of one thing I am sure: where one series of parallel furrows 
alone is visible, these are in by far the greater number of cases 
transverse to the long axis of the nucleus. The greater part of 
the muscle-fibre used in my preparations was in the uncon- 
tracted condition, and it is in this condition that the muscles 
are for the greater part of life. Following out the theory as to 
muscular contraction, given in the last paragraph, it is to be 
supposed that during rest the transverse trabecule of the muscle 
reticulum are contracted, but lengthened during contraction of 
the fibre, the conditions with regard to the longitudinal trabe- 
cule being in the reversed order. As now the contraction or 
shortening of the transverse trabecule must occur during the 
greater part of the life of the muscle, or during its resting 
periods, it is obvious that transverse furrows should be seen on 
the nucleus oftener and more prominent than longitudinal ones 
or than both combined. In this way we may explain away part 
of the difficulty of accounting for the occurrence of one or other 
series only of furrows. 

EK. Weber! found that the nuclei of the frog’s muscle are 
provided with longitudinal striz, which he thought due to the 
pressure exercised by the muscular fibrille. I endeavoured for 
the sake of comparing them with the nuclei in Necturus to 
isolate, after the manner already described, the nuclei of the 
frog’s muscle, but I met with a very indifferent success. In 


*“ Note sur les noyaux des muscles striés chez la grenouille adulte,” 
‘Archives de Physiologie,’ 1874, p. 489. 


NUCLE] OF MUSCLE-FIBRE 1N NECTURUS LATERALIS. 465 


the case of the few isolated, however, I could make out a cer- 
tain amount of transverse striation of the membrane. 

Further, as to the transverse furrows being often at acute 
angles with one another, an explanation for this may be found 
in the facts now to be described. 

A few nuclei presented other appearances than those men- 
tioned (fig. a, 9, 15, 16, 18, 19). Here the form of a oblong- 
meshed reticulum like that of the muscle-fibre was observed 
and considered by me at first to be caused by an impression pro- 
duced by the latter on the surface of the nuclear membrane. I 
found, however, in cases where it could admit of no doubt, that 
the reticulum was not on, but within the nucleus. In other 
words, there is in the interior of some nuclei a 
reticulum like in every respect to that found in 
the muscle-substance. In these cases no chromatine or 
caryoplasma could be observed. 

On the other hand, I observed a few nuclei in which the 
caryoplasma was approximately square meshed (fig. a, 23). The 
quadrangular form of the meshes is exhibited oftener and better 
in the nuclei from the heart muscle (fig. a, 20,21). ‘This form 
of the reticulum appears to be one of the stages transitional 
between the reticulum of the young nucleus and that referred 
to in the last paragraph. 

In view of these facts it is safe to infer, as Carnoy and 
Melland have done, that the muscle reticulum is simply the 
modified cytoplasma, the caryoplasma being derived from the 
latter.! 

Nuclei with such a modified caryoplasma as represented in 
fig. a, 20 and 21, must be capable of movement, or contraction 
and extension. This movement has been observed in the nuclei 
of vegetable cells by Hanstein,” and in the nuclei of white blood- 
corpuscles of Necturus by Gage,* and is amoeboid in character. 
But the possession of a square-meshed reticulum implies exten- 
sion and contraction in definite directions—the nucleus con- 

1 See Carnoy, op. cit., p. 250. 


2 © Bot. Zeit.’ 1872, p. 22. 
3 © Science,’ Jan. 8th, 1886. 


466 A. B. MACALLUM. 


tracts with the muscle-fibre and extends with it again, yet not 
passively. 

The possession of an irregularly meshed reticulum by the 
nucleus would imply on the part of the latter movements, if any 
at all, of an amceboid character. It is possible that this is just 
what occurred in the nuclei represented in fig. a, 10, 12, and 17, 
an unequal extension or contraction of all parts of the nucleus, 
resulting in a misplacemeut of the furrows and in their irregu- 
larity. 

Nicolaides suggests that all muscle nuclei take a more than 
passive share in muscular contraction. 

Some nuclei have part of their surface completely free from 
furrows (fig. 4,5). Ithink this is due to the fact that the whole 
of the nuclear body is not surrounded by the muscle-substance, 
a part of it lying between the latter and the sarcolemma. 


EXPLANATION OF PLATE XXXIII, figs. A and B. 


Illustrating Mr. Macallum’s Paper on the ‘Nuclei of the 
Muscle-fibre in Necturus lateralis,” 


Fie. a, 1—25.—Nuclei of striated muscle-fibre of Necturus lateralis, 
11, 20, 21, 22, representing some from the heart muscle. Mode of preparation : 
gold chloride, formic acid. 


Fic. B.—A part of a striated muscle-fibre with its nuclei, from Necturus. 
Gold chloride, formic acid. 

(Note.—In drawing these figures, Leitz obj. 7, and oc. 1 or 3 were 
employed.) 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 467 


The Development of the Cape Species of 
Peripatus. 


PART III. 
ON 'THE CHANGES FROM STAGE A TO STAGE F. 


By 


Adam Sedgwick, M.A., F.R.S., 
Fellow of Trinity College, Cambridge. 


With Plates XXXIV, XXXV, XXXVI, and XXXVII. 


THE early development of Peripatus capensis, as de- 
scribed in Parts I and II of this series, is apparently so 
different from that of the West Indian and New Zealand 
species, and at the same time our knowledge of the early 
stages of these species is still so incomplete, that it is difficult 
at present, and would indeed under the circumstances be 
waste of time, to attempt to institute any detailed comparison 
between them. With regard to the later stages, however, the 
matter stands otherwise; for not only do they seem to be 
alike in the three species, but in the case of the West Indian 
species at any rate we have in Dr. Kennel’s memoir, if not a 
complete still a detailed and coherent account of them. 

While able to speak, to this extent,’ favorably of Kennel’s 

1 In spite of Dr. Kennel’s objection, I must adhere to the view expressed 
in Part I of this series, that his account of the early stages of the Trinidad 
species presents internal evidence of the incompleteness of his observations. 
To particularise; his account of the relation of the embryo to the uterine 
wall, and of the origin of the so-called amnion and placenta, seems to me 


unsatisfactory. 
2 T am obliged to confess that Dr, Kennel has made some rather important 


468 ADAM SEDGWICK. 


scientific work, I regret to be obliged to take up an altogether 
different position with regard to the personal remarks directed 
against myself, with which he closes his memoir. 

He there devotes a considerable amount of space to a 
criticism of my first papers on the development of the Cape 
species. I do not desire to enter into a controversy with 
Dr. Kennel, nor do I intend to deal with his remarks in 
detail, but there are one or two points which require notice 
from me. 

His criticism has two main objects. In the first place 
he is anxious to prove that there is nothing new in my results: 
either they were known before, or he has already obtained 
them, or they are not true. With regard to this, 1 have only 
to say, if it please Dr. Kennel to take this view he is quite 
welcome to do so. His opinion is a matter of no interest to 
me. The second point is, however, more serious. Dr. Ken- 
nel’s object is apparently to impugn my personal honesty. 
He accuses me of trying to take credit for discoveries 
really made by another man. Not only is this charge 
false, but an examination of Dr. Kennel’s works on the de- 
velopment of Peripatus proves that he knew it to be false 
when he made it. 

He accuses me of unjustly laying claim to having proved 
that the mouth and anus of the Peripatus capensis are 
derived from the blastopore of the embryo. I may, perhaps, 
be allowed to state the facts concerning this matter. 

Balfour made the discovery that the blastopore of Peripatus 
capensis became closed in the middle so as to give rise to 
two openings. The question then arose—a question which 
was stated in Balfour’s memoir on Peripatus (No. 4, p. 255), 
and again in my paper on the “Origin of Metameric Segmen- 
tation” (No. 382, p. 55), both of which papers Dr. Kennel was 


blunders, which, however, are pardonable, inasmuch as they concern the points 
which are the most difficult—in fact the only points of any difficulty in the 
whole of the later stages, and at the same time are the points of the greatest 
interest—to follow. The blunders relate, as will be seen, to the fate of the 
ccelom and the origin of the various parts of the body cavity. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 469 


familiar with, as is shown by his constant reference to them— 
do these openings give rise to the mouth and anus of the 
adult, or do they become closed up, the mouth and anus being 
new formations? 

Balfour was unable to settle this, because he had no embryos 
between Stages B andr. The presumption was that they did 
not, both of them, persist, because Moseley (No. 23 a) had 
stated that he could find neither mouth nor anus in his 
youngest embryos (about my Stages p and £). Dr. Kennel 
was acquainted with this statement by Moseley, as is shown 
by his remarks on p. 195 of Part I of his work, where he 
actually uses it to cast doubt upon my view that the mouth 
and anus of the adult are derived from the blastopore of the 
embryo. There can be no doubt then that Kennel knew that 
Balfour had not proved the thesis that the mouth and anus of 
the adult were derived from the two parts of the blastopore. 
The intermediate stages which were necessary for its proof 
were obtained by me a year later, and I first announced the 
fact that the two parts of the blastopore persist into the adult, 
in my paper on the “Origin of Metameric Segmentation,” in 
a passage which reads as follows (p. 55): “In the paper referred 
to (Balfour’s memoir, edited by Moseley and myself) the ques- 
tion—Do these two openings become the mouth and anus of 
the adult ?—was left open. I am now in a position to state 
that they do become the mouth and anus of an embryo of an 
age equal to the oldest stage described by Moseley in his 
original paper, so that I think there can be no doubt that they 
do become the mouth and anus of the adult.” 

Dr. Kennel brings another charge against me of the same 
nature, equally baseless and wanton. 

I believe Dr. Kennel to be an honest worker, and I do not 
wish to speak of him in an unnecessarily harsh manner, but I 
am bound to confess that I do not understand his attitude of 
mind in bringing charges of this kind against me. I need 
only say with regard to them that the accusation of plagiarism 
in the matter of the mouth and anus may be taken as a fair 
sample of the kind of criticism, if criticism is the word 


470 ADAM SEDGWICK. 


to apply to such clumsy attacks, which he has throughout 
directed at my work on Peripatus. 


Tur EcropERM. 


During Stage a, the ectodermal or outer part of the embryo 
consists of a closely reticulated protoplasm, which contains a 
single layer of oval nuclei of fairly uniform size. At the lips of 
the blastopore this layer, with its contained nuclei, is prolonged 
inwards for a short distance to the more vacuolated endodermal 
part of the embryo. These nuclei, which are arranged in a 
layer immediately within the lips of the blastopore, resemble in 
their shape the ectodermal nuclei (Pl. XXXIV, figs. 2,3), and 
they may be regarded as ectodermal or endodermal according 
to the inclination of the observer. I am inclined to call them 
intermediate or undifferentiated nuclei, that is to say, nuclei 
which cannot be definitely assigned to the endoderm or ecto- 
derm, and in this capacity I shall have occasion to return 
to them when I come to speak of the later history of the 
mesoderm. 

The protoplasm surrounding these nuclei projects into the 
cavity of the blastopore and into the archenteron, in the form 
of delicate processes, which anastomose with other similar 
processes (Pl. XXXIV, fig. 3; Part II, fig. 26 3). 

When the mesodermal bands are formed, the nuclei of the 
ectoderm overlying them become slightly longer than elsewhere, 
and the ectoderm has the appearance of being composed of 
columnar cells. The nuclei are, however, still in a single 
layer. 

At the beginning of Stage c,a number of smaller, more 
rounded nuclei appear in the ectoderm within the outer layer 
of oval nuclei (Pl. XXXIV, fig. 6c). These nuclei are, in 
the next stage (Pl. XXXIV, fig. 9, v.n.), found along the inner 
i.e. ventral portion of the ectodermic thickening just men- 
tioned as overlying the somites. They constitute the rudi- 
ments of the central nervous system. 

The nuclei of the outer, i.e. latero-dorsal portions of the 
original ectodermal thickening (Pl. XXXIV, fig. 9), remain in 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 471 


a single layer, and the ectoderm containing them becomes 
pushed out by processes of the mesoblastic somites. These 
processes constitute the rudiments of the appendages. The 
latter are, as I have already mentioned in Part I, formed from 
before backwards, the first to appear being the appendages of the 
pre-oral somites—the later antenne—which exactly resemble 
in their development the other paired appendages of the body. 

After this general account I will now describe, in greater 
detail, the development of the ectoderm up to Stage £, under 
the following heads: 

1. The dorsal and ventral ectoderm which intervenes between 
the lateral thickenings. 

2. The lateral thickenings. 

3. The ectoderm of the proctodeum and stomodeum. 

It will be convenient to defer a description of the ectoderm 
of the primitive streak to the section of this paper on the 
history of the mesoderm. 

4, The slime-glands. 

1. Dorsal and Ventral Ectoderm.—During Stages a and B the 
ectoderm on the dorsal and ventral surfaces is composed of 
what may be called cubical cells with oval nuclei, but it must 
be remembered that these cells are not isolated from one 
another or from the endoderm. During Stage c, the nuclei of 
the dorsal ectoderm become spherical (Pl. XXXIV, fig. 6 ¢), as 
do also the nuclei of the ventral ectoderm on each side of the 
mouth (fig. 64). But the greater part of the ventral ectoderm, 
namely, that which intervenes between the mouth and anus 
(Pl. XXXIV, fig. 6 c), and that which is placed on each side 
of the anus, becomes reduced to an extremely thin layer 
(Pl. XXXIV, fig. 6 c, d), the character of which will be 
obvious from an inspection of the figures. In Stages p and zg, 
the ventral ectoderm retains the characters already described, 
but its width becomes less, the lateral thickenings having 
somewhat approached one another on the ventral surface (figs. 
9, 25). The dorsal ectoderm, on the other hand, becomes in 
Stage p somewhat reduced in thickness (figs. 9—13), though it 
never becomes as thin as the ventral portion, Subsequently, in 

VOL. XXVIT, PART 4,—NEW SER. EG 


472 ADAM SEDGWICK. 


Stage 5, it undergoes a striking change. It becomes much 
thickened. The thickening first appears in Stage p in the region 
of somites 7—10 (fig. 25), where indeed it lasts longer and is 
more marked than elsewhere, and gives rise to the prominence 
marked d in the figures of Pl. XXXII, Part I. The change 
begins at the sides and gradually extends dorsalwards. The ecto- 
dermal hump (d.) seems to retain until its disappearance indi- 
cations of this bilateral origin. The thickness of the dorsal 
ectoderm varies in different specimens, and no doubt depends 
to a certain extent on the amount of contraction which the 
protoplasm has undergone at death. 

This increase in thickness is mainly due to the appearance, out- 
side the nuclei, of a layer of vacuolated protoplasm. The vacuola- 
tion is not shown in my figures, but it is a very striking feature. 
The surface of the dorsal ectoderm, particularly of the hump, 
is very rough in these stages, and in the best-preserved em- 
bryos without a definite external boundary. It presents very 
much the appearance which a bath sponge would present in 
section, fraying out, as it were, into the surrounding fluid ; and 
one may fairly conclude that during life it possesses the power 
of sending out processes into the fluid surrounding the embryo, 
and that the superficial vacuoles open to the exterior. In 
short, I am inclined to think that this surface ectoderm during 
Stages r to F has a nutritive function, absorbing the fluid in 
which the embryo lies, and it seems to me conceivable that the 
placenta described by Kennel in the Trinidad species may be 
a more specialised organ of the same nature. During the pro- 
gress of Stage Fr the nuclei which have hitherto been placed in 
the deep parts of the layer (Pl. XX XV, figs. 23 a—e, 25) acquire 
a superficial position, excepting in the hump, where they retain 
their deep position until after Stage c. Contemporaneously 
with this change the deeper parts of the ectoderm become 
filled with very large vacuoles, so that the protoplasm is re- 
duced to fine cords, passing inwards from the superficial nucleated 
layer. This vacuolated deeper part of the dorsal ectoderm 
now becomes much reduced, so that in Stage rF the dorsal 
ectoderm consists mainly, if not entirely, of a thin layer of 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 473 


nucleated protoplasm derived from the superficial layer of the 
preceding stage. The hump, however, still persists, retaining 
the characters it had in Stage E. 

With regard to the internal boundary of the ectoderm, in 
the gastrula stage there was no line of demarcation between 
it and the endoderm. In Stage s the mesoderm appears, 
but causes no break in the continuity (Pl. XXXIV, fig. 
5 a—f). In Stages c and p, however, a definite separa- 
tion occurs, firstly by the appearance of the cavity in the 
somites, and secondly—and this happens later, in Stage 
p—by the dorsal and ventral separation of the endo- 
derm from the ectoderm. The endoderm is, however, still 
continuous with the splanchnic layer of mesoderm, and the 
ectoderm with the somatic. In the subsequent development 
this continuity seems to be retained and to be extended in 
consequence of the growth of the mesoderm over the internal 
surfaces of the at first uncovered parts of the two primary 
layers. At any rate I have never been able to see any well- 
defined boundary between the layers in question, even in the 
best-preserved embryos, if a careful examination was made 
with a high power. The defined line drawn in my figures has 
only an existence with a low power ; it is therefore extremely 
difficult to say whether or no nuclei pass in from the ectoderm 
to the mesoderm, and often not possible to settle for certain 
whether a given mass of nuclei belong to the ectoderm or 
somatic mesoderm. In the later stages (F) this absence of a 
defined line continues, so that it becomes difficult to decide 
whether the external transverse muscles of the body wall are 
ectodermal or mesodermal. To this point I shall return in 
Part IV of this series. 

2. The lateral thickenings, which give rise, amongst 
other things, to the nervous system, contain during Stages a 
and B a single layer of long oval nuclei (Pl. XXXIV, fig. 5 4). 
They are at first confined to the ectoderm immediately over- 
lying the mesoblastic somites, and constitute on each side a 
continuous band extending from the pre-oral region, where 
they are more ventrally placed and continuous with each other 


474, ADAM SEDGWICK. 


across the middle line, to the primitive streak behind. They 
diverge from one another as they pass backwards, and end in 
the ectoderm of the primitive streak. During Stages a 
and B they contain a single layer of oval nuclei, which rapidly 
increase in number, and become arranged in Stage c in parts 
in more than one layer. The latter fact is especially con- 
spicuous in the pre-oral portions, i. e. in the portions which 
will give rise to the cerebral ganglia (Pl. XXXIV, fig. 6 a). 

In Stage p the lateral thickenings have increased consider- 
ably in extent, occupying the whole of the sides of the body, 
and encroaching on the middle region of the body, where in 
the previous stages they were widely apart, somewhat on the 
ventral surface (Pl. XXXIV, figs. 9,11), so that the relation to 
the somites mentioned above (p. 473) is lost. The increase in 
the number of nuclei is now more marked, and is found to 
concern chiefly two regions: (a) nearly the whole of the pre- 
oral parts of the lateral thickenings (Pl. XXXIV, fig. 14) ; (4) 
the ventral (inner) portions only in the circumoral and postoral 
regions (Pl. XXXIV, figs. 9, 13). The increase has for its re- 
sults, as may be seen by reference to the figures, the production 
of some roundish nuclei lying internally to the oval nuclei. These 
round internally placed nuclei are much more numerous in 
Stage r, and eventually give rise to the whole of the cerebral 
ganglia and ventral nerve-cords. They remain up to the 
close of Stage © in close connection with the external layer of 
oval elements, though in some sections there are, in the post- 
oral region, indications of a commencing separation between 
them (Pl. XXXV, fig. 23 a—d). The manner of separation of 
the central nervous system from the superficial ectoderm will 
be described in Part IV. 

It is only necessary for me to point out here that in the 
region of the brain this separation does not occur, as the ecto- 
derm is invaginated, and remains in connection with the 
nervous tissue throughout life (Pl. XXXV, fig. 22a, and Pl. 
XXXVI, fig. 33). 

In Stage p a small amount of the so-called punctated tissue 
appears on the dorsal surface of this rudimentary central 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 475 


nervous system; this tissue, which is earlier and more largely 
developed in the cerebral rudiments than in the ventral cords, 
consists of a fine protoplasmic network, which stains but 
slightly and is almost entirely without nuclei. A similar 
network exists in the ventral nucleated parts of the nervous 
system, but is there obscured by the crowded nuclei. At first 
the whole central nervous system was similarly crowded with 
nuclei (Pl. XXXIV, figs. 15, 16 a, &c.), but in Stage p the 
latter began to withdraw from the dorsal part, thus allowing 
the non-staining protoplamsic network to stand out with great 
distinctness (Pl. XXXV, figs. 22, 23 a, &c.). At the boundary 
between this white matter and the nuclear mass there are, in 
Stages £, F, some nuclei which are somewhat larger than the 
rest, and more loosely arranged, so that they may be said to 
lie in the ventral part of the white matter (Pl. XXXVI, 
figs. 38, 39, &c.). Four such may generally be seen in each 
section of the ventral cords. 

I must now pass to describe the changes of the more dorsal 
parts of the lateral thickenings in the postoral region. In 
Stage p they contain a single layer of oval nuclei, and become 
at the same time pushed outwards by the outgrowths of the 
hinder part of the mesoblastic somites (Pl. XXXIV, fig. 9). 
These outgrowths are arranged in pairs, one pair from each 
pair of somites, and they constitute the rudiments of the 
postoral appendages. The first pair to be formed is the pair 
which will become the jaws; the next pair will form the oral 
papillz, and so on in order from before backwards. When 
the appendages are well established—in Stage n—it may be 
seen from an inspection of transverse sections that they are 
special developments of the posterior portion of lateral ridges 
of ectoderm which extend on each side for the whole length of 
a somite (Pl. XXXV, figs. 18 a, b, 21 a,/.7.). Immediately 
within these ridges there is a thickening of the somatic 
mesoderm (m. ¢.) which I shall speak of again later, and 
which is continuous with the thickened mesoderm of the 
appendage itself. The postoral appendages, therefore, may be 
described as special developments of longitudinal ridges, which, 


476 ADAM SEDGWICK. 


however, are not continuous up the whole length of the body, 
but are interrupted at the lines of segmental division. These 
limb-ridges in Stage z become separated from the appendages 
and continuous with one another dorsal to the appendages 
(Pl. XXXVI, fig. 36). They now, therefore, form one con- 
tinuous ridge on each side of the body, placed just dorsal to 
the insertion of the appendages. They eventually disappear. 

In Stage z the portions of the lateral thickenings dorsal to 
the line of insertion of the appendages, and the dorsal ecto- 
derm itself undergo a peculiar modification. The ectoderm 
here becomes thicker, and this increase in thickness is due, 
mainly, to an increase in the protoplasmic layer, elsewhere of 
extreme tenuity, on the outer side of the nuclei (Pl. XXXV, 
fig. 23 a—d). This modification, which has already been re- 
ferred to (p. 472), is seen first, and is always most conspicuous 
in the region of the seventh (Pl. XXXV, fig. 25) to about the 
tenth somite, where the nuclei become numerous and arranged 
in several layers. 

There is only one other portion of the postoral ectoderm 
which needs consideration, viz. the inner portion of the original 
lateral thickening—the parts which give rise to the nerve-cords. 

These are at first perfectly continuous from end to end of 
the body. They consist, in Stage z, when they first become 
well marked, of a number of oval nuclei with intermixed 
round nuclei in the deeper parts (Pl. XXXV, fig. 23 a—c). 
In Stage p they were wide apart, being separated by an area 
of extremely thin ectoderm (Pl. XXXIV, figs. 9—13). The 
latter, however, soon becomes of less extent (vide sections of 
Stage £), so that they approach one another until, in Stage F, 
they meet and coalesce in the middle line (Pl. XXXVI, figs. 388— 
41). They retain, however, always a trace of their paired origin. 
In late embryos of Stage F, the nerve-cords separate from them, 
and they become segmented in such a manner that they persist 
only between the appendages, the intervening portions having 
disappeared. In this condition they have been called by 
Kennel (No. 18) the ventral organs. The ventral organs, 
as Kennel has already described, persist into the adult, in 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 477 


which they are much more conspicuous in some species than 
in others. The ventral organs of the jaws and oral papille 
undergo special changes which have already been quite correctly 
described by Kennel, and which I shall have occasion only to 
refer to hereafter. 

It now only remains for me to describe the changes which 
take place in the pre-oral portions of the lateral thickenings. 
I have already stated that these are from the first continuous 
with one another in front and with the postoral portions behind 

_the mouth, that the internal rounded nuclei appear sooner in 
them than elsewhere, and in greater numbers. In fact, nearly 
the whole of the pre-oral lateral thickenings give rise to the 
internally placed rounded nuclei (Pl. XXXIV, fig. 16 a) which 
will form ultimately the cerebral ganglia. These rounded 
nuclei extend, though only in a thin layer, even across the 
middle line in front of the mouth, in which position they first 
appear in Stage c (Pl. XXXVI, fig. 28, com.), and rapidly in- 
creasing in number, remain in connection with the ectoderm 
until Stage nr, when they become detached (Pl. XXXV, fig. 
22 a, Pl. XXXVI, fig. 31, com.) though the cerebral rudi- 
ments themselves are still in connection with the ectoderm. 
It thus appears that the two cerebral ganglia and 
their connecting commissure are developed as a 
Single structure from the ectoderm. 

The ventral cords, beginning at the level of the jaws, are, as we 
have seen, continuous developments from the lateral thicken- 
ings; and the question arises: Does this continuity extend in 
front of the jaws to the preoral region, or is there a sharp separa~ 
tion between the cerebral rudiments and the ventral cords? 

There can be no doubt whatever that in Peripatus 
capensis there is no such break at any stage of develop- 
ment. A study of transverse sections of many different 
embryos from Stages c—x conclusively demonstrates that the 
ventral nerve-cords, which are developments of the inner 
portions only of the lateral thickenings, are continuous at 
all stages of their existence, both before and after their 
separation from the ectoderm, across the boundary between the 


478 ADAM SEDGWICK. 


first and second somites with the inner portion of the cerebral 
rudiment, which is a development of the whole surface of the 
pre-oral part of the lateral thickening. It is true that at first 
this part of the central nervous system is weaker than the parts 
in front and behind it, but long before the separation from the 
ectoderm occurs (Pl. XX XV, fig.190; Pl. XXXVL, fig. 35,c.o.n.), 
it forms a well-marked cord with a layer of white matter. 
The whole central nervous system of Peripatus 
capensis develops, therefore, as a continuous struc- 
ture from the ectoderm, and the independent origin and 
secondary connection of the cerebral ganglia and ventral 
chain, which has been asserted for some Arthropoda, e.g. 
for Spiders by Balfour (No. 3), for Annelida by Salensky 
(No. 27), Lumbricus by Kleinenberg (No. 15), and for Mol- 
luseca by various observers, does not hold for Peripatus.1 
Balfour held the same view with regard to this point in Peri- 
patus (No. 2 p. 337). 

I entirely agree with the remarks of Hattchek (No. 12, p. 8) 
on this subject. He holds, in opposition to Salensky, that the 
circumoral part of the nervous system in the annelid larve 
which he has investigated, develops fron the ectoderm in con- 
tinuity with the apical ganglion and ventral nerve-cords; and 
I am strongly inclined to think that a further and closer inves- 
tigation will show the same fact to hold for other Annelids and 
Molluscs. 

The Cerebral Grooves.—The cerebral ganglia gradually in- 
crease in size (Pls. XXXIV, XXXV, figs. 14, 16 a, 19 a) and 
their ventral surface becomes in Stage z markedly flattened (Pl. 
XXXV, fig. 22 a) and then invaginated (Part I, fig. 35), so as 
to form two grooves, which rapidly become narrower and deeper, 
until in Stage Fr they form two slits, longitudinally arranged, 
ending blindly in front, but opening behind into the buccal 
cavity (Part I, fig. 36, and Pl. XXXVI, fig. 33). Eventually, 
in old embryos of Stage r, they lose their external openings, 
become reduced in size, and form two vesicles in the ventral 


1 Kennel apparently holds the opposite view on this point. If he is right 
I can only suppose that P. Edwardsii differs in this respect from capensis. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 479 


portions of the cerebral ganglia. Owing to the relatively greater 
growth of the latter they appear to form, in the adult, small 
hollow appendages of the brain (No. 2, Pl. XVII, fig. D, d). 

The most important features which remain to be described 
in the development of the preoral part of the central nervous 
system, is the part which it takes in the formation of two 
organs—the eyes and the tentacular nerves. 

The eyes arise in Stage p as a pair of invaginations of the 
postero-lateral parts of the cerebral rudiments (Part I, fig. 29). 
The two pits so formed are placed immediately in front of the 
point of origin of the lip-folds from the pre-oral lobes (Part I, 
fig. 30). They are at first shallow, but soon become deeper, 
and eventually (by the end of Stage ©) constricted off from the 
surface, so as to form closed vesicles (Pls. XXXIV, XXXV, figs. 
16 a, 15, 19 a, 22 a). The eyes, therefore, are nothing 
more nor less than invaginations of the lateral por- 
tions of the rudiments of the cerebral ganglia, and of 
the surface ectoderm, which gave rise to and covers the latter. 
Two elements enter into their composition, (a) the surface 
ectoderm with its oval nuclei, and (4) the rounded nuclei of 
the cerebral rudiment. The columnar surface nuclei form the 
lining of the optic chamber, while the rounded elements which 
lie behind the inner wall give rise to part of the retina and 
optic nerve. Figs. 14, 15, 19 a, 22, show very clearly the 
method of development of the optic rudiment. In the later 
stages the connection between the posterior wall of the optic 
vesicle and the cerebral ganglion becomes somewhat con- 
stricted, but persists throughout life as the optic nerve. The 
eyes of Peripatus are, therefore, as I stated in my original 
paper (No. 33), cerebral eyes, and are from the very first in 
connection with the cerebral ganglia.! 


1 Kennel states that in P. Edwardsii the eye arises independently of the 
brain, and secondarily enters into connection with it. Not having examined 
the development of the eye in P. Edwardsii I am not in a position to 
affirm or deny the correctness of this statement. But there are certain other 
points in Kennel’s account, particularly those relative to the early stages and 
to the fate of the ccelom, which incline me to think that his material was not 
so good either in quality as might have been wished. 


480 ADAM SEDGWIOK. 


The tentacular nerves are to be regarded, from their method 
of development, as forward prolongations of the cerebral 
ganglia. 

In the outgrowths from the pre-oral lobes to form the 
tentacles the cerebral thickenings, which extend dorsalwards 
on to the anterior face of the former, participate in such a 
manner as to form the ventral surface of the developing ten- 
tacles (Pl. XXXIV, fig. 7). The deep rounded elements of these 
forward tentacular continuations of the cerebral rudiments 
eventually separate from the surface ectoderm, and become the 
tentacular nerves. 

The later stage of the cerebral ganglia will be considered in 
the next part of this series. By the stage reached (Stage F) 
they are in connection with the walls of the cerebral grooves. 

The latter are almost if not entirely constricted off from the 
surface, and are lined by the ectoderm which gave origin to 
the cerebral ganglia. Kennel regards this invaginated layer 
as the homologue of the ventral organs of the postoral region. 
It differs, however, from the latter in being invaginated. Not- 
withstanding this, the view seems to me a plausible one. 

The cerebral ganglia of Peripatus resemble, therefore, in their 
development and method of removal from the surface, the cen- 
tral nervous system of the Vertebrata, and the cavity of the 
ventral appendages of the adult brain corresponds! with the 
central canal of the latter. 

These cerebral grooves seem a fairly constant feature in 
Tracheate embryos. They do not, so far as I know, persist into 
the adult of any other Arthropod, but disappear in the course 
of development. In these cases their walls are said to become 
transformed into parts of the supracesophageal ganglia. Struc- 
tures of a similar nature are found in other animals. They 
have been described by Kowalevsky in the embryo of 
Dentalium (No. 16),in which animal the cerebral ganglia 
are formed from the walls of two invaginations of ectoderm 
at the apical pole of the body. They persist for some time, 
and then vanish. In Sipunculus Spengel (No. 35) has de- 


1 By this, of course, I do not mean that the two structures are homologous. 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 481 


scribed a single canal leading from the cerebral ganglion to 
open at the base ofa tentacle. In Nemertines, as is well known, 
canals opening on the surface penetrate into the cerebral 
ganglia, and in Balanoglossus a single canal traverses part of 
the central nervous system. Whether these canals leading to 
this important part of the central nervous system are homolo- 
gous it is difficult to say. Probably they are not, but are 
simply analogous, their function being, or having been, in 
some aquatic ancestor, respiratory. I have already (No. 31) 
suggested this as the probable genetic explanation of the 
central canal of the Vertebrate nervous system. 

Summary of the Early Development of Nervous System.—The 
lateral thickenings are from their origin continuous from 
somite to somite. They begin in front of the mouth, where 
they are connected with one another across the middle line, 
and they end behind in the ectoderm of the primitive streak. 

The rounded elements which give rise to the nervous system 
are derived from the ventral parts of these thickenings. They 
are formed first in the pre-oral region, and then in the lateral 
cords ; that is to say, the nervous system at its very first ap- 
pearance is a continuous structure beginning in front of the 
mouth, where it is continuous across the middle line, and ex- 
tending backwards on each side of the mouth. 

The portions of these two cords in front of the mouth become 
the cerebral ganglia, which give rise directly to the eyes and 
tentacular nerves ; the portions around the mouth become the 
circumoral commissures, while the portions behind the mouth 
are the rudiments of the ventral nerve-cords of the adult. The 
ectoderm from which the rounded elements arise remains 
thickened, and give rise to structures which have been called 
by Kennel the ventral organs. The ventral organs are at 
first placed at a little distance from the middle line. Eventually, 
however, they approach one another and meet, excepting in the 
region of the mouth and pre-oral lobes. 

On the pre-oral lobes the structures corresponding to the 
ventral organs of the posterior part of the body become invagi- 
nated and separated from the surface in such a manner as to 


482 ADAM SEDGWIOK. 


form the linings of the vesicles, which are attached throughout 
life to the ventral surface of the cerebral ganglia. 

3. The Stomodeal and Proctodeal Ingrowths—At the time 
when the blastopore is a continuous slit and traversed by strands 
of anastomosing protoplasm, i. e. during Stage a, the part of the 
endoderm which is continued into the ectoderm at the lips of 
the blastopore, resembles, in the small size and number of the 
vacuoles and the regular shape and arrangement of the 
nuclei, the ectoderm. In fact it is impossible to say whether 
this layer is really ectodermal or endodermal. By its position 
and development it resembles endoderm, by its characters 
ectoderm. 

When the blastopore closes in the middle these cells are left 
inside and form the median ventral wall of the mesenteron 
(Pl. XXXIV, figs. 5 6, 6 c, v. en.), and eventually assume the 
characters of endodermal nuclei. At the primitive mouth and 
anus, however, they still persist as rows of nuclei intervening 
between undoubted ectoderm and endoderm (Pl. XXXIV, fig. 
6 6,d), and they extend forwards for a short distance, forming 
the median ventral wall of a portion of the pre-oral enteron 
(Pl. XXXIV, fig. 4, and Pl. XXXVI, fig. 28). It is by the 
growth of this tissue that the lining of the stomodeum and 
proctodzum is formed. 

The details of the development of these structures will be 
best treated in the next section dealing with the alimentary 


canal. 
4. The slime-glands arise in Stage £ as hollow invaginations of 


the ectoderm of the oral papillz (Pl. XXXV, fig. 23 d, s. gl.). 
They gradually increase in length and project into the central 
compartment of the body cavity. Their further development 
will be described more conveniently in Part IV of this series. 
Kennel’s description of the origin of these organs agrees with 
my observations. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 483 


THe ENDeDERM. 


The endoderm during Stage a and earlier stages consists 
simply of the inner portion of the vacuolated protoplasmic 
wall of the embryo. Its vacuoles are somewhat larger and its 
nuclei fewer and more irregular in shape than those in the outer 
or ectodermal portion. But the two are perfectly continuous 
(vide figures on Pl. XIV, Part II). The vacuoles of the layer 
immediately within the ectodermal nuclei are larger than those 
in the innermost layer, i.e. in the layer next the gut cavity. 

Processes from the endoderm cells project into the enteron 
and anastomose with each other. This isa well-marked feature 
in embryos rather younger than Stage a, and indicates the 
origin of the gut asa vacuole or a concresence of vacuoles 
(Pl. XIV, fig. 23, Part II). 

These processes persist until Stage B at the blastopore, as I 
have already mentioned in Part II of this series (vide figs. 24 5, 
26 a, on Pl. XIV, Part II). At the hind end of the blastopore 
they become particularly well developed (Pl. XIV, fig. 25 a, 
Part IT), so much so that it is impossible to say in which section 
the blastopore ends and the primitive streak begins. In other 
words, the blastopore passes quite gradually into the primitive 
streak. Or again, to put it another way, the primitive streak 
only differs from the hind end of the blastopore in the fact that 
the anastomosing protoplasmic strands, which everywhere 
traverse the blastopore, contain nuclei in the former case, but 
not in the latter. On this view the primitive streak, in favour 
of which I may refer to Pl. XXXIV, fig. 1, which represents 
a section through the primitive streak of Stage a, and to 
Pl. XIV, fig. 25 a, Part II, which is a section through the hind 
end of the blastopore, is the hindermost portion of the blas- 
topore. 

The nuclei of the endoderm are large, and particularly 
remarkable for the irregularity of their shape. They do not, 
excepting those near the lips of the blastopore, ever present 
the karyokinetic figures characteristic of dividing nuclei; they 
appear to divide directly. Some of them are much branched 


484 ADAM SEDGWICK. 


like connective-tissue cells; a feature which is not at all 
exaggerated in the figures. 

The nuclei of the lips of the blastopore, which have already 
been described as intermediate between ectodermal and endo- 
dermal nuclei, constantly present the karyokinetic figures cha- 
racteristic of dividing nuclei (Pl. XXXIV, fig. 3, d.n., and 
Pl. XIV, fig. 26 5, Part IT). 

During Stages B and c, the endoderm, though diminishing 
somewhat in thickness, retains all the characteristics just 
described. 

During Stage s the blastopore, which has grown considerably 
in length, and markedly dumbbell-shaped in surface views closes 
in its middle portion (Pl. XXXII, figs. 28—25, Part I). This 
is effected simply by the approximation and fusion of its lips 
(Pl. XXXIV, fig. 56). The connection, which has hitherto 
existed between the latter by the anastomosing strands already 
mentioned, now becomes closer and they completely unite with 
oneanother. The result of their union is that the intermediate 
nuclei come to lie inside and form a definite part of the endo- 
derm, viz. the ventral endoderm in the median line between 
the mouth and the anus (Pl. XXXIV, fig. 6c). By their fate 
then these intermediate nuclei are endodermal, and so indeed 
I think we must regard them, unless indeed we are willing to 
take the view that the median ventral endoderm of the ali- 
mentary canal of Peripatus is ectodermal in origin. Up to the 
close of Stage c the endoderm has been in close contact and 
continuous with the ectoderm, excepting where the mesoblastic 
somites, which appear in Stage B, intervene. In Stage p, 
however, a remarkable change takes place, the endoderm 
separates ventrally and dorso-laterally from the ectoderm, and 
there is now a direct connection between the two only along 
the dorsal middle line (Pl. XXXIV, fig. 9). This is soon lost 
in Stage z, and henceforth the endoderm layer is only connected 
with the ectoderm through the walls and cells of the meso- 
blastic somites, and at the mouth and anus. 

This completes all I have to say about the endoderm till the 
close of Stage z, when it consists of a layer of vacuolated 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 485 


protoplasm which contains nuclei of irregular shape. But I 
still have to describe the development of the stomodzeum and 
proctodeum, and the change produced by it in the adjoining 
parts of the alimentary canal. 

The enteron at first reaches the front end of the body. 
Until the end of Stage c it has a considerable pre-oral extension 
(Pl. XXXVI, fig. 28). The anterior end of the body now 
becomes retracted, so that in Stage p the mouth lies at the very 
front end of the middle ventral line (Pl. XXXVI, fig. 29), 
though laterally the two pre-oral lobes project for a considerable 
distance (Pl. XXXVI, fig. 832). The result of this is that the 
intermediate nuclei, which in Stage c extended forwards from 
the mouth (Pl. XXXVI, fig. 28), now extend backwards and 
form the dorsal wall of the developing stomodeum. At the 
same time the lateral walls have appeared as special develop- 
ments of the same intermediate nuclei (Pl. XXXVI, fig. 32). 

The median ectoderm of the front end of the body so far 
has been in contact with the front end of the stomodeum 
(Pl. XXXVI, figs. 29 and 32). It now separates from it (cf. 
Part I, figs. 33, 34) and grows forward, so that a space 
becomes established between the dorsal wall of the stomodeum 
and the front end of the body (Pl. XXXVI, fig. 31). At the 
same time the dorsal wall of the stomodeum grows rapidly 
backwards, while the front end of the enteron maintains its 
position, or is, perhaps, thrown slightly forward. In this way 
a blind pocket of the enteron is established, lying on the 
dorsal side of the stomodzeum (Pl. XXXVI, fig. 31, p.p.). This 
anterior blind diverticulum persists for some time (late in 
Stage Fr) and then disappears without leaving a trace. It has 
been observed and described by Kennel. 

The stomodeum, the sides and roof of which are first 
developed (Pl. XXXVI, fig. 32, and Pl. XXXIV, fig. 16 a, 5), 
soon increases in extent, and by Stage F has acquired a well- 
developed floor (Pl. XX XVII, fig. 49). It is now definitely es- 
tablished, and has a thick lining of oval nuclei and a narrow 
lumen (Pl. XXXVI, fig. 36). It has also acquired a mesodermal 
covering from the splanchnic walls of the first and second so- 


486 ADAM SEDGWICK. 


mites (Pl. XXXVI, fig. 32, and Pl. XXXIV, figs. 14, 16a, 
&c.). Its further development will be followed in Part IV, 
but I may now state that it becomes the pharynx and 
cesophagus of the adult. 

Behind, the walls of the enteron extend to the hind end of 
the body below the primitive streak, and the anus not being 
terminal (Part I, fig. 25), there is at first a postanal gut. This state 
of things continues (Pl. XXXVI, figs. 28, 29) until the formation 
of the proctodzum, which happens when the anus has shifted to 
the hind end of the body, and the embryo has acquired its full 
complement of somites (Pl. XXXVI, fig. 30). The proctodeum 
is due to the growth of the intermediate nuclei. It eventually be- 
comes of considerable extent, acquires a mesodermal investment 
from the splanchnic walls of the adjoining somites, and finally 
constitutes the rectum of the adult (Pl. XX XVII, fig. 42). 

The nuclei of the embryonic endoderm of Peripatus are 
remarkable for being branched and angular. Nuclei of a 
similar character are found in other animals. Leydig (No. 19) 
has described branched nuclei in the Malpighian tubules and 
epithelium of the alimentary canal of Arthropoda, and Balfour 
(No. 3) speaks of large angular nuclei as occurring in the 
yolk-segment of Araneina. The angular shape is not 
retained in the adult Peripatus. 


Tue MeEsopERM. 


The early stages in the formation of the mesoderm, up to 
the end of Stage a, have been fully described in Part II of this 
series. 

The nuclei of the mesoderm, which arise from the nuclei of 
the primitive streak,extend laterally and grow forward on each 
side of the blastopore, at a little distance from it, as the 
lateral mesoblastic bands. ‘The mesoblastic bands are there- 
fore, primarily at any rate, outgrowths of the lateral portions 
of the primitive streak nuclei. This is shown clearly by 
fig. 26 a, b,c of Pl. XIV, Part II. In this embryo (Stage a) 
the mesoblastic bands (md.) had only a very small extension for- ~ 
wards (five sections in front of the blastopore). They consist of 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 487 


bands of nuclei placed in the vacuolated protoplasm inter- 
vening between the ectoderm and endoderm. 

The mesoblastic bands gradually acquire a greater extension 
forwards as the embryo and the blastopore increase in length. 
They very soon become segmented—before they have reached 
the level of the front end of the blastopore. This fact is 
clearly shown by Pl. XXXII, figs. 23 and 24, Part I. The seg- 
ments so formed do not at first (Pl. XXXII, fig. 23, Part I) 
possess any distinct central cavity around which the nuclei are 
arranged. By the stage figured in fig. 24, Part I, in which 
five mesoblastic somites are present, the cavities have appeared. 
The appearances presented by surface views are confirmed by 
an inspection of sections. I have sections of embryos, in 
which three solid somites could be made out on each side. 
Pl. XXXIV, fig. 2, represents a transverse section through a 
stage with one solid somite. The section is slightly oblique 
and passes through the somite of one side only ; on the other 
side the section passes in front of the mesoderm. Fig. 5 a—f 
represents sections through an embryo of the stage of fig. 25, 
Part I, in which the somites had reached the level of the 
anterior end of the blastopore. A distinct cavity, around which 
the nuclei of the somites are arranged, is present in the somites. 
By the close of Stage B (fig. 25, Part I) the somites of the 
anterior pair have reached their permanent position in front of 
the blastopore. They are separated from one another by the 
alimentary canal, which at this stage extends in front of the 
mouth (Pl. XXXIV, figs. 4, 6 a). 

With regard to this development the following questions, 
which can only be settled, if they can be settled at all, by a 
study of transverse sections, present themselves:—(1) How do 
the mesoblastic bands grow forward before they have aug- 
mented into the somites? and (2) How do the somites, which 
are established before the bands have reached the front end of 
the blastopore, reach their final position ? 

1. Do the bands grow forward independently of surrounding 
structures? or do they receive nuclei from the adjacent ecto- 

VOL, XXVII, PART 4.—-NEW SER, MM 


488 ADAM SEDGWICK. 


derm and endoderm? It must be remembered that the first 
somite is separated from the anterior end of the mesoblastic 
bands before the latter have reached the level of the middle of 
the blastopore, so that we are now only concerned with the old 
embryos of Stage a. After prolonged and careful study of 
a large number of embryos, I have come to the conclusion that 
this is a point which it is impossible to settle with certainty by 
a study of preserved specimens. Still there isa certain amount 
of evidence, which, on the whole, tends to show that the inter- 
mediate nuclei at the lips of the blastopore do contribute to 
the bands. ‘The evidence depends upon the appearances pre- 
sented by these nuclei at the lips of the blastopore. These 
are constantly met with in a state of division, i.e. present- 
ing the figures which are characteristic of binding nuclei. 
This is shown clearly in many of my figures, e.g. (Part II, 
fig. 266; and Pl. XXXIV, fig. 3, of this paper). Further, 
immediately within these intermediate nuclei, and lying be- 
tween the ectoderm and endoderm, there are often to be 
een nuclei, which may fairly be supposed to have been 
erived by division from the intermediate nuclei. These are 
present in sections through the young mesoblastic bands (Part 
II, fig. 26 6), and also in sections in front of the latter 
(Pl. XXXIV, fig. 3, close to d. n.); in the former case in- 
dicating that the nuclei in question are reinforcing the nuclei 
of the mesoblastic bands; in the latter that they are laying 
down the same structures. 

2. With regard to the second question, I can only state that 
the completed somites attain their final position by an altera- 
tion in the relative position of the structures in the anterior 
region of the embryo. 

Pl. XXXIV, figs. 4, 5 a—f, are illustrations of the structure 
of the embryo at the close of Stage B (Part I, fig. 25). Fig. 4 
is in front of the mouth, and is through the first pair of somites, 
now pre-oral. Fig. 5 @is through the mouth and second pair 
of somites; fig. 5 6 between the mouth and anus, through the 
region in which the blastopore lips have come together and 
fused ; fig. 5 c is through the anus; fig. 5 d, e, f, behind the 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 489 


anus through the primitive streak. The somites of this embryo 
differ from those of the earlier stages only in the fact that 
they contain a well-marked cavity. Their walls are still in 
continuous contact with the ectoderm and endoderm respectively. 
The primitive streak of this stage needs, however, more con- 
sideration. In the first place the primitive groove has become 
much more marked and extends over a greater distance than in 
the earlier stages (Part I, fig. 25, and Pl. XXXIV, fig.5 d—f). 
Immediately behind the blastopore the primitive streak con- 
sists of but few nuclei, which form a layer placed between the 
ectoderm and endoderm, and extending laterally as far as the 
mesoblastic bands. The latter structures here bend im towards 
the middle line, so that a few sections behind (fig. 5 e) they 
have reached and become indistinguishable from the primitive 
streak. The primitive streak in this region is much more 
bulky and consists of a large mass of nuclei. It extends 
back for about thirty sections behind the blastopore. There 
can be no doubt that the mesoderm of the developing hind end 
of the embryo, which now begins to grow forward so as to lie 
with its ventral side on the ventral side of the anterior part (vide 
Part I, figs. 26—31), is aerived from the continually proliferat- 
ing cells of the primitive streak. ‘The latter is indeed simply 
the growing point of the embryo, and in it the three layers of 
the embryo are united and indistinguishable from one another. 
It persists until the full complement of somites is obtained and 
then disappears. Some time before its disappearance it be- 
comes relatively of less extent, and the anus consequently 
comes to lie nearer the hind end of the body until, at its com- 
plete disappearance, the anus has gained its permanent position 
at the hind end of the body. Pl. XXXIV, fig. 6 d, illustrates 
the structure and appearance of the streak during Stage c. 
The section was taken at the hind end and cuts the embryo, 
the ventral flexure of which is beginning, at two points, viz. 
in the region of the primitive streak and in the region of the 
anus. ‘The later stages of the primitive streak are shown best 
in longitudinal vertical sections (Pl. XX XV, figs. 28—30). 
The large pole-cell of the primitive streak, visible during 


490 ADAM SEDGWICK. 


Stage a, and in the earlier embryos of Stage 3, vanishes later 
in Stage B. I do not know what becomes of it. 

Of the mesoblastic somites during Stage c there is but 
little to say. They maintain the same relations and struc- 
ture (Pl. XXXIV, fig. 6 a—d) as in the preceding stage, 
that is to say their walls are everywhere in contact with the 
adjacent ectoderm or endoderm. The cells of the somatic 
layer are thicker than those of the splanchnic layer. ‘This 
difference was observable in the previous stages (Pl. XXXIV, 
fig. 5 a), and becomes, as we shall see, much more marked 
in the subsequent stages. During Stage p, somites are still 
being formed at the hind end from the actively growing tissue 
of the primitive streak. This stage may be said to mark the 
close of the formation of new somites, i.e. by Stage » the 
embryo has acquired its full complement, though the posterior 
are so small and rudimentary that they are not visible from 
the exterior. 


SUMMARY oF THE DEVELOPMENT oF THE Bopy Cavity, 
NeEPHRIDIA, AND GENERATIVE OrGaANS. 


The elucidation of the further changes in the somites, and 
the development of the body cavity and heart, has presented 
some difficulties,—difficulties which have very much delayed 
the publication of my work, but which I am glad to say I 
have at length completely overcome. It will, I think, be 
convenient to explain the terms I shall use, and briefly to 
summarise the results I have obtained, before proceeding to a 
detailed description. 

The somites are obviously comparable to the somites of 
other animals. It is no less clear that the cavity in them is 
homologous with the cavities of the somites of other types, e. g. 
other Arthropoda and Annelida. I propose, therefore, 
to call the system of somite cavities and its derivates the 
ceelom or enterocele. 

The system of cavities, on the other hand, which arise partly 
in consequence of the withdrawal of the ectoderm from the 
endoderm, and partly secondarily in masses of mesoderm, is 


DEVELOPMENT OF THE CAPE SPEOIES OF PERIPATUS. 491 


what in other animals would be called a pseudocele. For this 
second system of cavities and its derivates I shall therefore use 
the words pseudocele or vascular space. 

My results can be summed up as follows : 

1. The adult body cavity comes entirely from pseudoccele. 
The enterocele has no part in its formation. 

2. This statement applies also to the heart and pericardium. 
These are both pseudoceelic, and have nothing to do with 
enteroceele. 

3. The only products of the enterocele cavity are :—(a) 
The nephridia. (0) The generative glands and their ducts. 

4. The nephridia do not open either in the embryo or in the 
adult into the body cavity proper (i.e. in Peripatus the 
pseudoccele), but into a vesicle in each appendage which has 
hitherto been unnoticed. 

These results, when taken in conjunction with the following 
peculiarities of Arthropod organisation, viz. the feeble deve- 
lopment of the somites, the apparent absence of nephridia, 
the vascular character of the pericardial cavity, and the posses- 
sion by the heart of lateral ostia opening into the pericardium,! 
will not be without interest to morphologists. 

Kennel (No. 13) was the first to point out that the median 
chamber of the body cavity and the pericardial chamber were 
not products of the enteroceele ; but Kennel erred in supposing 
that the cavities in the legs and the so-called lateral sinus 
(No. 13, p. 202) were derived from the somites. In his later 
memoir he apparently gives up this view so far as the lateral 
sinus is concerned, but still maintains that a portion of the 
ceelom becomes broken up by muscles, &c., and persists as the 
body cavity of the legs. In this, I think, he is mistaken, but 
it must be borne in mind that he has worked at a different 
species in which it is possible, though not likely, that the 
development of the structure in question may be different. 

Kennel’s observations of the fate of the so-called median 


1 This Arthropodan character was first pointed out to me by Professor 
Lankester. I have never seen attention called to it in any works or memoirs 
on this subject, 


4.92 ADAM SEDGWICK. 


divisions of the somites and of the origin of the generative 
tubes, pericardial cavity, and heart, differ, as will be seen, con- 
siderably from mine. His account, however, seems to me to 
lack precision, and I cannot help thinking, especially when I 
consider that he has altogether confounded the nephridial 
vesicles of the adult with the leg body cavity (see below), that 
he has erred here also. 

In my preliminary paper to the Royal Society (No. 33) I 
also made the mistake of supposing the leg cavities were 
ceelomic, but my account of the generative organs and their 
ducts was correct.- I expressly stated in that paper that I had 
not succeeded in following the later changes in the somites. 
My words were as follows: 


“So far the development of the somites is quite clear and easy to follow. 
But the changes by which the dorsal divisions of the somites are converted 
into their permanent form take place at a late period of development—during 
November—and are, in consequence of the thinness of the walls, extremely 
difficult to follow. Ihave not succeeded entirely in following them. I will 
content myself, therefore, with making the following statement, of the truth of 
which I am by no means confident. The dorsal divisions unite with each other 
transversely and longitudinally, and give rise to a continuous cavity—the 
pericardial cavity. ‘The portion of this cavity containing the generative cells 
become separated from the rest as two tubes which form the generative glands 
and part of their ducts, and come to lie ventral to the pericardium in the 
central compartment of the body cavity. The external parts of the generative 
ducts appear to be derived from the modified leg cavity of the anal papille.” 


With regard to previous observers of the adult anatomy, 
Balfour—the discoverer of the nephridia—overlooked the small 
vesicle in the leg cavity into which the funnel of the nephri- 
dium opens. This oversight is not to be wondered at in the 
case of the species (capensis) which he worked at, for the 
vesicle is extremely difficult to see in the adults of Peripatus 
capensis. Gaffron—the discoverer of the pericardial cavity 
and cardiac ostia—similarly overlooked the vesicle, though 
it is quite distinct and easy to see in the species—Peripatus 
Edwardsii—which he examined. 


DEVELOPMENT OF THE CAPK SPECIES OF PERIPATUS. 4938 


DESCRIPTION OF THE DEVELOPMENT OF THE MESODERM WITH 
Its CAVITIES FROM StTaGES D—F. 


It will facilitate matters if I begin by describing the deve- 
lopment of a particular pair of somites and of the mesodermal 
structures around them, and I will take for this purpose the 
third somite of the body (somite of the oral papille) as one 
which is typical of the rest and in which the changes are most 
easily followed. 

During Stage p, at the time when the ectoderm separates 
from the endoderm, the walls of the dorsal and ventral portions 
of each somite come together; the cavity is thus obliterated 
and a single layer of cells! lying in close contact with the ecto- 
derm results (cf. Pl. XXXIV, figs. 9 and 12, d. s., v. s.). 

At the same time some cells appear between the somatic 
wall of the somite and the ectoderm (Pl. XXXIV, fig. 10, me.). 
These cells, which are undoubtedly derived from the somatic 
mesoderm, extend the whole length of the somite. In the 
anterior part, i. e.in front of the limb outgrowth (Pl. XXXIV, 
fig. 10), they are less numerous than in the region of the 
latter, i.e. ia the posterior part of the somite (Pl. XXXIV, 
fiz. 9): 

The same arrangement is present in a more advanced state 
in the later embryos of Stage p (fig. 29, Part I), cf. Pl. XX XV, 
fig. 17, a—d. Fig. 17 a, me., shows the mass of cells in the 
front part of the somite, anterior to its connection with the 
somatic mesoderm. ‘The same section also shows the anterior 
part of the limb-ridge overlying this cell-mass. Fig 17 4 shows 
the connection with the mesoderm, while fig. 17 ¢ and d 
shows this mass in the posterior part of the somite in the 
region of the limb outgrowth. In the posterior part of the 
somite some of the cells of this mass project into the cavity of 
the somite in such a manner as to tend to separate the limb 
portion from the portion in the body, and at the same time a 


1 Tt is difficult to say whether these layers of cells arise in this manner or 
as outgrowths from the dorsal and ventral corners of the somites. 


494. ADAM SEDGWICK. 


cavity appears amongst the cells at the base of this rudimen- 
tary septum (fig. 17 d, 5. lat.). Both these latter features 
are more clearly shown at sep. and 6. Jat. in Pl. XXXIV, 
fig. 13. 

In a slightly more advanced stage (intermediate between p 
and ©) the cells of this parietal mass, as I may callit, are more 
numerous, and the contained cavity—9d. /at.—extends forwards 
to the anterior part of the somite (fig. 21 a, me., 6. lat.) ; while 
in the posterior part of the somite, in the region of the limb 
outgrowth, the rudimentary septum has become more marked 
(fig. 21 c, sep.), but the median portion of the celom still com- 
municates with the lateral or appendicular portion (Pl. XXXV, 
fig. 21 c). The latter (/.s. 3) has developed a ventral out- 
erowth, which lies along the outer side of the nerve-cord, and 
reaches the ectoderm. The ectoderm becomes slightly in- 
dented at the point of contact, where a perforation is soon 
formed. 

In the next stage (x) four changes are noticeable (Pl. 
XXXV, fig. 23 a—c) : 

(1) The dorsal or median part of the somite has extended 
itself dorsalwards (fig. 23 a). At the same time it does not 
extend so far backwards as the lateral part (i. e. the part in the 
appendage), so that the latter is overlapped by the median por- 
tion of the somite behind (4) (Pl. XXXV, fig. 23 d, 1.s.3, s. 4). 
(It must be remembered in this connection that the outgrowths 
into the developing appendage takes place at the hinder part of 
the somite.) 

(2) The space (4. Jat.) in the parietal mass of mesoderm 
(m. t.) has much increased (fig. 23 a), and has, at the same 
time, become partly divided by a tongue of cells, which 
eventually give rise to the muscles of the posterior internal 
projection of the jaw. 

(3) There exists a short, anteriorly directed, blind diverti- 
culum (or, may be, constricted-off groove), in the form of a 
tube, from the neck connecting the median portion with the 
lateral portion of the somite (fig. 23 6, c, a.v., and Z. s. 3). 

(4) The lateral portion of the somite has acquired an opening 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 495 


to the exterior (fig. 23 e). This happened ina slightly younger 
embryo. The opening is already covered over by the lip (L.), 
which is rapidly growing backwards (cf. Part I, fig. 35 ; embryo 
with commencing cerebral grooves). 

Briefly to recapitulate, the structure of the third somite at 
this stage is as follows:—In front it is dorsally placed and 
overlaps the second somite; its middle portion slopes ventral- 
wards and communicates with the posterior part, which is con- 
tained in the limb, and is peculiarly bent (fig. 23 c—e), and 
opens to the exterior. The middle portion further sends a 
narrow diverticulum forwards for a short distance (fig. 23 4, 
a.v.). The parietal mass of cells is larger than in the last 
stage, and contains several cavities, which are not derived from 
the ccelom, but arise independently in it. 

As in the earlier stages, there is a sheet of cells closely applied 
to the ectoderm, and extending from the dorsal end of the 
somite to the middle dorsal line (d.s.), and from the ventral 
corner (v.s.) along the parietal mass of mesoderm and the 
inner surface of the nerve-cord to the ventral ectoderm. Fur- 
ther, the endoderm has entirely separated from the ectoderm, 
so that two large spaces are left, the one a dorsal (0. /.), and the 
other ventral to the gut (0. dc.). These spaces contain a few 
scattered, more or less branched cells, which appear to be 
derived from the splanchnic walls of the somites, and are there- 
fore probably mesodermal in nature. 

There are therefore four distinct systems of spaces present 
in the embryo at this stage (£) : 

1. The cavity of the gut derived from a vacuolation ot the 
endoderm mass of the gastrula stage. 

2. The cavities of the somites, derived from a vacuolation of 
the protoplasm of the mesodermal bands. 

3. The spaces which appear independently of the other spaces 
in the parietal masses derived from the somatic walls of the 
somites. 

4. The spaces formed by the separation of the endoderm from 
the dorsal and ventral ectoderm, and derived in all probability 
from the vacuoles found in a corresponding position in the 


496 ADAM SEDGWICK. 


earlier stages (Part I, fig. 24 a—d). These latter spaces 
are comparable with blastoccele spaces of other embryos, so 
called because they present the relations of the segmentation 
cavity of the earlier stages. Such a name is, however, obviously 
out of place here, inasmuch as the segmentation cavity is never 
present. 

In the next stage (F) the dorsal division of the somite has 
entirely separated from the ventral, so that the two parts may 
be considered separately. 

The ventral division of the third somite presents the 
same parts as in the previous stage. These were, it will be 
remembered, (1) what I may call a vesicular internal part, ex- 
tending to the hind end of the appendage and forwards as an 
anterior diverticulum, and opening into (2) a tubular part, 
projecting ventrally and opening to the exterior. 

In Stage r the vesicular internal part (Pl. XXXVI, figs. 36, 
37, l.s.v. 3) has not only lost its vonnection with the dorsal 
(median) part of the somite, but its peripheral part—viz. that in 
the appendage—has become largely obliterated by the increase in 
the thickness of its mesodermal walls and by the growth of the 
slime-gland rudiment. At the same time the tubular part has 
become longer and more twisted (figs. 37, 38, /.s¢.3), and its 
external opening covered up by the lips, which have met on the 
ventral surface (Part I, fig. 836). The tubular part, therefore, 
no longer opens freely but into the posterior part of the buccal 
chamber. 

I will now describe more in detail the structure of the two 
parts. 

The inner walls of the internal vesicle retain (figs. 36, 37) 
the character presented by the walls of the anterior diverti- 
culum of the previous stage (a.v. Pl. XXXIV, fig. 23 4); i.e. 
the nuclei are relatively far apart, and separated by a slightly 
staining protoplasm. The outer wall, on the other hand, is 
reduced to a thin layer. 

The tubular portion I shall now call the nephridium. Its 
opening into the vesicle, shown in fig. 38, is a well-defined 
structure, which I shall call the funnel of the nephridium. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 497 


The external opening of the nephridium (fig. 37) is anterior to 
the funnel. The course of the tube at this stage will be under- 
stood by an inspection of figs. 37,38,38 a. It will be observed 
from these that the nephridium—the part marked J. s. ¢. 3 in 
fig. 38—projects back as a tube which ends blindly (fig. 38 a, 
l.s.t. 3 = sal. gl.). This backwardly projecting part gains an 
enormous extension in the later stages, and is known in the 
adult as the salivary gland. 

Kennel, who has correctly recognised the nephridial nature 
of the salivary gland, has made what I cannot but regard as 
one or two blunders in his description of its devevelopment. 

He says (No. 14, p. 38), “‘ Von allen Theilen der friiheren 
Segmentblase behilt nur der 3. Abschnitt, die blindsackartige 
Ausstiilpung, ihren Charakter, indem dort die Zellen als 
Epithel angeordnet sich erhalten; er wird zum Trichter des 
Segmentaiorgans.” Again, on p. 45, “ Man findet ihn (seg- 
mental trichter of salivary gland) an seiner alten Stelle, 
allenfalls ein wenig weiter nach hinten verschoben, als kurzen 
Blindsac, welcher von seiner Ansatzstelle aus schrag nach 
vorn dicht am eigentlichen Kanal der Speicheldriise hin 
verlauft, nun aber nicht mehr mit Raumen des Lateralsinus 
communicirt, sondern blind geschlossen ist ”’ (my italics). 

Combining these passages with a statement on p. 38 as to 
the breaking up of the Segmentblase of the oral papilla, it seems 
clear that Kennel imagines (1) that the third somite does not 
divide into a median and lateral part (though it does so in 
other somites). (2) That the somite itself breaks up entirely 
into a system of spaces, of which the lateral sinus is part. 
This is implied by the first of the above quotations, and the 
italicised parts of the second. It is also definitely stated on 
p. 176 of Th. 1 (No. 13) in the following words: ‘ Letzere 
(i.e. Segmentalhohle) werden spiter ganzlich in den Lateral- 
sinus und die Héhlung der Fiisschen umgewandelt und geben 
den Hohlorganen daselbst, besonders den Segmentalorganen 
z. Th. der Ursprung.’ (83) That the funnel of the salivary 
gland becomes closed and persists in life as a vesicle. (4) 
(from other statements on p. 39) that the funnel of the 


498 ADAM SEDGWICK. 


other nephridia are open throughout life into the broken-up 
space of the foot (or lateral sinus?). 

I admit it is rather difficult to make out his exact meaning, 
his account being somewhat confused and diffuse. But I 
think I am right in supposing that he maintains in the paper 
referred to the above four positions. Well, accepting his idea 
that the later stages resemble one another in the two species, 
I have no hesitation in saying that he has erred in each par- 
ticular. The third somite does divide into two parts. The 
ventral part does not break up into spaces nor does it become 
traversed by muscles and connective tissue, but persists through 
life as a vesicle with an epithelial lining. The lateral ramus 
has nothing to do with the cclom, but comes from the space 
marked 8. /at. in my sections. The funnel of the nephridium 
opens always into the lateral part of the somite, of which, 
indeed, it is a part, and does not become blindly closed. The 
funnels of the other nephridia do not open into the space 
of the feet, but into the lateral division of their proper 
somites exactly as do the salivary glands. 

Kennel further maintains that the funnel only of the adult 
nephridium is mesodermal. JI cannot accept this; it is an 
altogether fanciful view. It may be true, but it is a point quite 
impossible to settle by sections. With regard to it, I have 
only to say that the ectodermal ingrowth at the opening of the 
nephridum is so extremely inconspicuous that at the early 
stage, immediately before and after the establishment of the 
external opening, no such ectodermal part as Kennel describes 
is present. 

The dorsal divison of the third somite separates from 
the ventral in an embryo slightly older than that from which 
series fig. 23 was taken, viz. one in which the cerebral gooves 
were slightly more advanced than in fig. 22, but not so much 
developed as in fig. 33, Pl. XXXVI. After its separation, it 
becomes much reduced in size (fig. 36, d. s. 3), then still smaller 
(Pl. XXXVII, fig. 45, d. s.), and finally vanishes (fig. 46, d. s.). 

This completes what I have to say about the third somite 
up till Stage r, by which time the adult condition of the parts 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 499 


is practically attained. The remaining somites conform, on 
the whole, to the type described. They do, however, present 
certain differences, of which, perhaps, the most important are 
found in the posterior part of the body. In the posterior 
somites the dorsal divisions do not become obliterated, but 
persist and give rise to the generative glands (Pls. XXXVI, 
XXXVII, figs. 41, 43, d. s.=gen. o.). It will be more 
convenient, however, to defer the detailed consideration of 
this and other peculiar features of the remaining somites 
until after the description of the changes by which the adult 
body cavity, pericardial cavity, and heart are formed. 


Ture Bopy Cavity AND VASCULAR SYSTEM. 


I have already described the first appearance of the body 
cavity. It arises in Stage p as a space between the dorsal 
ectoderm and the endoderm (Pl. XXXIV, fig. 13 6.4.), and 
between the ventral ectoderm and the endoderm (0. dc.), There 
also appears at the same stage a space in the parietal thickening 
of the walls of the somites (Pl. XXXIV, fig. 13, d. dat.). In 
later embryos of Stage p (Pl. XXXV, figs. 17a2—d), these spaces 
are all more marked, and cells—apparently amoeboid war- 
derers from the walls of the somites—have made their appear- 
ance in the two former (Pl. XXXV, fig. 17 a—d.). These cells 
apply themselves to the ectodermal and endodermal walls of the 
chambers in which they are contained, and so form the founda- 
tion of the mesodermic investment by which the body cavity 
of the adult is lined. In the next stage the cavities 0. h., 5. bc, 
remain unchanged ; but the cavities in the parietal thickenings 
become definitely established (Pl. XXXV, fig. 21 a—e, 6. lat. 
The latter at this stage appear to be segmentally arranged ; 
each one beginning at the anterior end of asomite, and extend- 
ing backwards to the level of the appendage, in the mesoderm 
thickening of which it is lost. They are bounded internally 
by the septum which runs from the ventral border of the somites 
along the inner side of the nerve-cord to the ventral body wall, 
and externally by a mass of mesoderm cells which project into 
what I have called the limb-ridge (Pl. XXXV, fig. 21 a,/. r.), 


500 ADAM SEDGWICK. 


In the next stage (Stage rn, Pl. XXXV, figs. 23 a—c), the two 
median cavities, 0.A. and J. bc., present but little alteration, 
excepting that the dorsal one 6. h. has been encroached upon by 
the dorsal extension of the median division of the somite. 

The successive lateral spaces have now become continuous, 
extending through the region of the appendage immediately 
within the septum (v. s.). This is shown in Pl. XXXV, 
fig. 23 c—e, and more clearly by Pl. XXXV, fig. 25. (The 
tongue of cells in this space in figs. 23 a,b, 1 shall refer to 
later in describing the jaw somite.) 

Before proceeding, I may mention the fate of the three 
divisions of the pseudoceele or permanent body cavity which 
have so far appeared. The dorsal median cavity (d./.), which 
is from the first a continuous space, begins at the very front 
end of the body (Pl. XXXV, fig. 22 a, b.h.) and extends 
backwards as far as the ectoderm has separated from the endo- 
derm. It eventually reaches the hind end of the body, and 
becomes, i.e. all of it, except its very front and hind ends, the 
heart. The ventral (0.c.), which extends forwards as far as 
the mouth (Pl. XXXVI, fig. 31), will form the ventral portion 
of the median chamber of the body cavity of the adult. The 
lateral cavity, which is at first not a continuous cavity, but 
eventually becomes so, gives rise in the adult to the lateral 
chamber of the body cavity (lateral pinus)) which contains the 
nerve-cord and salivary gland. 

In Stage x, two new cavities appear amongst the nuclei of 
the ventral corners of the somites (Pl. XXXV, fig. 25, b. pe. 
and 6. bc’.). They are first seen at about the level of the seventh 
somite, and soon (in Stage F)increase in size and extend forwards 
to the level of the jaw somite, and backwards, eventually reaching 
the hind end of the body. Pl. XXXVI, fig. 39, shows the 
typical arrangement of these two additional cavities in Stage F. 
The dorsal of them (0. pe.) has extended dorsalwards as far as 
the median dorsal pseudoceele or rudimentary heart (0. h.), which 
has in this stage become much smaller. The ventral one (0. dc’.) 
also has extended dorsalwards as far as the ventral wall of the 
much reduced somite (d.s.). The somite, which in the previous 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 501 


stage extended ventrally as far as the dorsal insertion of the 
septum (v.s.) which separates the lateral chamber (0. dat.) from 
the ventral division of the median pseudoceele (0b. bc.) (vide 
Pl. XXXV, figs. 23 e, 24) has now shrunk, and its space is 
occupied by the ventral of the two new cavities (0. dc’,). This 
latter chamber, therefore, is bounded dorsally by the ventral 
wall of 6.py¢e and of the somite, internally by the splanchnic 
mesoderm of the gut wall, and ventrally by a septum separating 
it from the ventral division of the median pseudoceele (0. ac.). 

At the hind end of the same embryo the same relations are 
visible but in a less developed state. Here (Pl. XXXVI, fig. 41) 
the somites are almost in contact in the middle dorsal line, 
the heart space (b.4.) being very rudimentary. The dorsal 
division of the somites (d. s.) themselves are still well-developed 
structures with the generative nuclei in their floors. The two 
new chambers (0. pe., 6. dc’.) are present, but in a rudimentary 
form. It is by looking through a series of sections of an 
embryo of this age, such a series as that from which figs. 33 —41 
were selected, and comparing them with the previous stage, that 
it is possible to settle conclusively the fact that in figs. 38 and 
39 the space marked d.s. and s. 4 is the reduced somite—it can 
be followed backwards, gradually enlarging in successive seg- 
ments until at the hind end of the body (in figs. 41, 42) it has 
exactly the relations of the dorsal division of the somite of the 
earlier stage—and that the spaces marked 0. pe. and 0. dc’. are 
new formations in the walls of the dorsal divisions of the somites 
and have nothing to do with the true enterocele or cavities of 
the somites. They, like the spaces b. hand J. bc, are, from the 
first, continuous structures. . 

The determination of the relations of these cavities in suc- 
cessive stages has been one of considerable difficulty, for this 
reason, that the dorsal wall of the body often contracts at the 
death of the animal and obliterates all traces of the complex 
system of dorsal cavities. They then present merely the 
appearance, which has been seen by Kennel and has led him into 
error, of being an irregular system of spaces in the dorsal 
mesoderm. 


502 ADAM SEDGWICK. 


Kennel’s description of the origin of the heart and _peri- 
cardium from an irregular system of spaces in the dorsal 
mesoderm, derived from the broken-up dorsal divisions of the 
somites, is quite erroneous. 

Itis easy to see the arrangements which I have described, 
if embryos be used in which the dorsal ectoderm has not con- 
tracted. 

Corrosive sublimate solution with a few drops of acetic, or 
Perenyi’s fluid, or 70 per cent. spirit, seem to be the best 
reagents for obtaining this result, though their action is by no 
means certain. 

With regard to the fate of the two new cavities the dorsal 
of them (4. pc.) becomes the pericardium (Pl. XXXVII, figs. 
45, 46); the ventral (d. dc’.) enlarges, and by the withdrawal of 
the gut from the ventral wall of the dorsal division of the somite 
—which aborts, it will be remembered, in the anterior region 
(Pl. XXXVII, fig. 46) but gives rise to the generative organs 
in the posterior (Pl. XX XVII, fig. 43)—becomes continuous 
with its fellow. It remains for some time separated from the 
ventral median chamber (0. bc.) by the septum, which results 
from its method of origin. This septum eventually—Stage e— 
breaks down and the cavity 0b. bc’. becomes continuous with d. bc 
and the two form one chamber, the median chamber of the 
definite body cavity of the adult. 

I have now described the origin of all the parts of the adult 
body cavity except those in the legs. These arise in Stage F 
as spaces in the thickened mesoderm of the appendages 
(Pl. XXXVII, figs. 52, 58, 5. app). 

From the above account it is perfectly clear that, so far as its 
embryonic development is concerned, the body cavity of Peri- 
patus has, as I stated at the outset, nothing to do with the 
celom. It is a pseudoceele, a space which arises secondarily, 
i, e. subsequently to the ccelom, partly in the mesoderm masses 
produced from the walls of the somites and partly as spaces 
between the ectoderm and endoderm (cf. the vacuoles in the 
Same position in the gastrula stage), which soon become lined 
by mesoderm cells from the somites. The heart has an origin 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 503 


identically similar to that of the ventral part of the median 
chamber of the body cavity. The whole system is probably in 
communication and functions as a vascular space of which the 
heart is a specially marked off and contractile tract. The 
body cavity and pericardium of Peripatus, if comparable 
with anything in Annelida or Mollusca, must be looked 
upon as homologous with the vascular system. The peri- 
cardium of a Mollusc is, I think (but to these points I shall 
return later), from its development (Ziegler, No. 386) an 
enterocele, and as such has no communication—in this respect 
resembling the remains of the enterocele of Peripatus—with 
the pseudoceele represented by the heart and vascular system 
aud spaces. The chief difference, I take it, between the pseudo- 
ceele (body cavity) of Peripatus and the pseudoceele (vascular 
system and vascular spaces) of a Mollusc is that the latter is 
usually largely broken up by anastomosing strands of muscle 
and connective tissue, while in Peripatus the same space is, 
except in the legs, a fairly continuous and unbroken system. 

If the above suggestions are correct, and if at the same time 
the body cavity and heart of other Arthropoda develope in 
the same manner as in Peripatus (I shall examine this ques- 
tion later), then that peculiar Arthropod feature, viz. the paired 
ostia leading from the heart into the pericardium, receives a 
morphological explanation. 


FurtHer AccOUNT OF THE DEVELOPMENT OF THE SOMITES. 


After the foregoing description the various parts of the figures 
will be intelligible, and I may proceed to give an account of 
the changes which take place in the other somites. In doing 
this I shall refer to the changes in the mesodermic tissue 
generally. The somites, with regard to their development as 
far as Stage r, may be grouped under six heads :— 

1. The somites of the pre-oral lobes, or first pair. 

2. The somites of the jaws, or second pair. 

3. The somites of oral papille, or third pair. 

4. The somites of legs 1-—17, or fourth to twentieth pair. 

VOL, XXVIII, PART 4,—NEW SER. NN 


504 ADAM SEDGWICK. 


5. The somites of the anal papillz, or twenty-first pair. 

6. The rudimentary somites behind the twenty-first. 

The heading 4 will have to be further subdivided according 
as the dorsal divisions contain generative cells or not. 

The Somites of the First Pair (somites of pre-oral or an- 
tennal segment) take up a position in front of and at 
the sides of the mouth by the end of Stage B. This posi- 
tion they maintain during the whole of development. Their 
splanchnic walls are, at first, in close contact with the endoderm 
of the anterior part of the alimentary canal, and afterwards 
with the ectoderm of the stomodzeum when that is formed 
(Pl. XXXIV, fig. 8). They grow forward into the antenne 
when the latter appear in Stage p, so that the bases of the 
antenne are hollow (Pl. XXXIV, fig. 7). Soon—in old 
embryos of Stage p (Part I, fig. 29)—the cells of that portion 
of their inner wall which adjoins the ingrown ectoderm, pro- 
literate, and form a mass of cells (Pl. XXXV, figs. 16 a, 
19 6, ph. m.) which ultimately give rise to part of the muscu- 
lature of the pharyngeal wall and tongue. 

In Stage §, or possibly late in Stage p, the wall of the 
posterior external corner of the somite becomes markedly thick- 
ened (Pl. XXXV, fig. 19 6, S. 0.1) and pushed out ventrally 
into a short pouch. In the later embryos of Stage 5, and in 
young embryos of Stage r, this pouch, which is placed imme- 
diately behind the eye and at the level of the origin of the lip 
from the pre-oral somite, forms a distinct tube lying along the 
outer side of the nerve-cord (hind end of brain or beginning 
of ventral cord), and reaching to and fusing with the ventral 
ectoderm (Pl. XXXV, fig. 22 6, S. 0. 1) immediately in front 
of the jaw. So far as I can make out, an actual perforation is 
never formed at the point of contact. The tube persists until 
the later period of Stage r, being found in embryos in which 
the cerebral grooves are partly closed (Pl. XXXVII, fig. 5 o, 
S.o.1). It then vanishes without leaving a trace. 

There can, I think, be but little doubt that this structure is 
the rudimentary nephridium of the somite. It presents exactly 
the same relations as do the nephridia of posterior somites ; it 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 9005 


is a development of the posterior, external, ventral corner of 
the somite; is closely applied to the outer border of the central 
nervous system, where it fuses with the ventral ectoderm, and, 
as we shall see in a moment, the part of the somite into which 
it opens becomes separated from the remainder. With regard to 
the somite itself, it becomes much reduced in size in Stage E£, 
being encroached upon by the rapidly growing cerebral rudi- 
ments (Pl. XXXV, fig. 22a). In Stage r, in consequence of 
the same process, combined with the great development of the 
cerebral grooves, the first somite becomes much flattened out 
(Pl. XXXVI, fig. 33). It hes immediately over the white matter 
of the posterior lobes of the brain, and becomes divided into 
two parts posteriorly, viz. an external portion placed close 
to and immediately dorsal to the eye, and an internal or median 
portion (Pl. XXXVII, fig. 51, S. 1). 

The external portion, the walls of which are thicker than 
those of the median, is continuous with the rudimentary 
nephridial tube, of which indeed it forms the dorsal end. 

The first somite, therefore, behaves exactly as do the posterior 
somites. It becomes divided into two parts—a median part 
and a lateral part. The latter sends out a ventral diverticulum, 
which hugs the outer side of the nerve-cord and fuses with, if 
it does not open through, the ventral ectoderm. 

Kennel has seen the rudimentary nephridium, but he has 
not appreciated its significance or made out its exact relations 
to the lateral division of the somite on the one hand and the 
ventral ectoderm on the other. I should mention that by the 
time the lateral division of the somite has completely sepa- 
rated from the median, the nephridial tube has nearly vanished. 
This fact may account for Kennel’s omission to notice the con- 
nection between the two structures. The suggestion by the 
same author (No. 14, p. 49) that the eye may possibly be 
derived from the ectodermal part of the lost nephridium of 
the first somite, loses, after the discovery of the actual nephri- 
dium, any plausibility which it might at first sight have 
appeared to possess. It is obvious that the nephridium which 
possesses a rudiment of an external opening behind and ven- 


506 ADAM SEDGWICK. 


tral to the eye, and within the lip, can have nothing to do with 
the eye which is derived from the side of the cerebral rudiment. 

The Somites of the Second Pair (somites of the segment of 
the jaws) come to occupy in Stage B their permanent position 
at the sides of the mouth. In Stage p (the endoderm has 
separated from the ectoderm ventrally and on each side of the 
dorsal line, fig. 9) the rudiment of the jaw is laid down, and 
the somite is prolonged into it. (Pl. XXXIV, fig. 9, which, 
however, is through the oral papilla, represents quite accurately 
a section through the jaws at this stage.) The somatic wall of 
the somite becomes considerably thickened, particularly the 
ventral portion of it. This is very marked in Stage E (fig. 20, 
m.t.). The somite of the jaw segment is further in Stage E 
overlapped on the dorsal side by the somite behind (fig. 20). 
By the close of Stage x (stage of fig. 35, Part I) the portion 
of the cavity of the somite contained in the jaw has become 
almost obliterated by the growth of the cells above mentioned. 
The median portion persists for some time, and furnishes, from 
its splanchnic wall, cells which apply themselves to the develop- 
ing stomodzum and assist in forming the pharyngeal and 
cesophageal musculature. 

The median division of the jaw somite, which has from 
an early period a much less longitudinal extension than the 
median divisions of the other somites, coalesces in Stage F 
with the median division of the third somite. 

The walls of the ventral portion of the somite, which entirely 
fill up the jaw, form the muscles of the jaw and are prolonged 
backwards in the lateral compartment! of the body cavity as 
the tongue of cells, which has been already referred to and is 
shown in Pl. XXXV, fig. 23 a—c, at m. J. 

In the following Stage (r) the hind end of the jaws becomes 
enclosed by folds of the dorso-lateral walls of the buccal cavity 
and constitutes the rudiment (Pl. XXXVI, fig. 36, Je.) of the in- 
ternal backward continuation of the inner blade—the so-called 
lever of the jaw, which is so marked a feature in the adult. The 


1 The posterior end of this tongue of cells lies in the central compartment of 
the body cavity. 


DEVELOPMENT OF THE OAPE SPECIES OL PERIPATUS. 507 


further history of this structure, as well as that of the tongue 
of cells, which have been already described for Stage = and 
are shown in sections of Stage Fr at m./., Pl. XXXVI, figs. 36— 
39, will be described in Part IV. 

I have not been able to see any trace of even the rudiment 
of a nephridium of the jaw somite, unless, as Kennel has 
suggested, the internal prolongation of the jaw be regarded as 
such. 

The Somites of the Fourth to the Fifteenth Pairs,i.e. of the first 
to the twelfth legs, may be taken together. The development is 
essentially the same for all, and until Stage r almost exactly 
the same. The description of the changes of any one of them 
will therefore serve for all. Like the other parts of the body, 
they develope in order from before backwards. The dates given 
in the description below will refer to the anterior somites. 

The changes during Stage p are similar to those of the third 
somite, and the figures 1O—12, P]. XX XIV which were used to 
illustrate my description of the latter during Stage p, are 
really representations of these posterior somites. As a result 
of these changes the thickening of the somatic wall, the leg diver- 
ticulum, and the rudimentary septum, which partly separates 
the latter from the rest of the somites, are established. In 
Stage E, the somite has become divided into two parts by the 
completion of the septum,—into an anterior part placed dor- 
sally (fig. 24, S. 4) and a posterior part with a very small lumen 
contained in the leg (Pl. XXXV, fig. 25 J. s.7). These two 
portions do not overlap, as might be imagined from the earlier 
stage seen in figs. 13! or 21’ c, in which the septum is incomplete, 
the part of the somite in the body on a level with the leg 
having disappeared. The spaces in the parietal mass of me- 
soderm, the origin and history of which has already been 
described, have increased largely in size (fig. 25) and might 
easily be mistaken for a portion of the true celom. It must 
be carefully borne in mind—as I have already pointed out— 

1 These figures were not taken from the parts here referred to, but inasmuch 


as they precisely resemble in all particulars sections from these parts, they 
can be used as illustrations of the text. 


508 ADAM SEDGWICK. 


that these spaces are, so far as their development in this 
embryo is concerned, quite distinct from the cavity of the 
somites, which I regard as the true celom. I may, however, 
draw attention to the fact that the two sets of spaces arise in 
essentially the same manner, but not at the same stage; the 
coelomic spaces arise as vacuoles in the multinucleated bodies 
called mesoblastic somites, while the parietal spaces arise later 
as the result of the vacuolation of multinucleated masses de- 
rived from the walls of the somites. 

The development so far has only differed from that of the 
third somite in the much earlier separation of the median from 
the lateral portion of the somite. 

In Stage sr, the cavity of the lateral portions of the so- 
mites becomes extremely reduced in size, in consequence of 
the enormous thickening of their mesodermal walls (P]. XXXV, 
fig. 25, l.s. 7), and at the same time confined to the base of 
the appendage, the whole of the distal part of the latter being 
occupied by a mass of mesoderm cells. 

By the end of Stage £, the coelomic space of the fourth leg 
(seventh segment) has acquired an opening to the exterior in 
nearly the same position as the opening of the third somite, 1. e. 
immediately external to the nerve-cord, and by the same process, 
viz. a ventral outgrowth from the ceelom, which meets and fuses 
with the ectoderm (Pl. XXXV, fig. 25). The same process 
takes place in the three preceding legs (legs 1—3), I think, a 
little later. If this is so, we have an exception to the prevail- 
ing rule of development from before backwards. However 
this may be, the three preceding somites obviously possess 
their opening at a slightly later stage (early embryo of Stage 
Fr, P]. XXXVI, fig. 40, 7. s.v.6'). I should mention that even at 
this early stage the external openings of somites 7 and 8 
have not the same position as in the case of the other legs, but 
are nearer the periphery of the limb (cf. Pl. XXXV, fig. 25, 
o. s. 7, with Pl. XXXVi, fig. 40, o. 2. 6). 

To sum up, at the beginning of Stage F the lateral portions 


1 The apparent absence of a lumen in the passage in this figure is due to 
the contraction of the specimen. <7 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 509 


of the anterior somites are small spaces in the base of the legs 
with a ventral prolongation which lies along the outer edge of, 
and, except in the case of legs 4 and 5, opens to the exterior 
immediately outside the nerve-cord. In the case of these 
legs, the opening is a little removed from the nerve-cord and 
placed on the ventral surface of the leg itself. 

At the end of Stage F an important change takes place: the 
pseudoceele or body cavity of the leg makes its appearance. 
It arises simply as a space, which is from the first somewhat 
irregular and traversed by cells, in the mass of mesoderm 
which occupies the periphery of the appendage (Pl. XXXVII, 
figs. 52, 53 a, b, b.app). The space almost at once becomes 
much larger and more conspicuous than the lateral compart- 
ment of the celom, the outer wall of which—i.e. the wall 
which separates it from the new cavity—is extremely thin and 
delicate. So thin and delicate indeed, and so sudden the 
appearance of the leg pseudoccele, that I was for a long time 
inclined to the opinion that the latter was derived from a 
part of the lateral compartment of the celom. I have, how- 
ever, convinced myself, by prolonged and careful study of my 
sections, that this is not the case, but that the pseudoccele of 
the leg, both in its origin and subsequent history, has nothing 
to do with, and is entirely separate from, the lateral or 
nephridial compartment of the coelom. The extreme tenuity 
of the outer wall of the lateral ccelom of the legs is shared by 
the same structure in the oral papille (third somite) (vide figs. 
38, 38 a, l.s.v.3, Pl. XXXVI and description above, p. 449). 

By the close of Stage r we can distinguish, as in the case 
of somite 3, two parts in the lateral compartments of the 
somites, viz. (1) an internal vesicular part, with an internal 
and dorsal wall in which the nuclei are far apart and separated 
by a relatively large amount of little staining protoplasm, and 
an external wall of considerable tenuity separating it from the 
secondarily developed body cavity of the leg ; and (2) a tubular 
part which leads ventrally to the external opening; and even 
in this stage, except in the case of the first three legs (somites 
1v—vi), has begun to become convoluted. 


510 ADAM SEDGWICK. 


The tubular part, which in the case of the first three legs 
remains straight even in the adult, becomes the structure 
which was first described by Balfour (excepting (?) Saenger, 
whose paper I cannot procure) and called by him the nephri- 
dium ; while the internal vesicular part, which persists through- 
out life as a vesicle lying in the leg compartment of the body 
cavity (pseudoceele) and receiving the internal so-called funnel 
of the nephridium, has hitherto escaped notice. 

The fate of the median compartments of the body cavity of 
jaws, oral papille, and legs 1—15, I have already described. 
Except in the case of the second and third somites, which 
coalesce in Stage r, they retain their segmentation until their 
disappearance. This takes place in Stage F first at the level 
of about the fifth leg, proceeding backwards and forwards. It is 
preceded by the diminution in size of the cavity (Pl. XX XVII, 
fig. 45), and the development of the pericardium. 

An indication of the somites remains for a short time as a 
thickening in the floor of the pericardium, with which thickening 
the ventral wall of the heart is fused (Pl. XX XVII, fig. 46, d.s.). 
The floor of the pericardium soon, however, separates from 
the ventral wall of the heart, so that the two halves of the 
pericardial cavity become continuous. At the same time the 
dorsal wall of the heart separates from the dorsal body wall, 
and the heart then forms a tube lying quite freely in the peri- 
cardium. The cardiac ostia seem first to appear in Stage r, 
and are confined in the Cape Peripatus, at any rate, to the 
posterior part of the heart. 

The Development of Somites 16—20 differs from that just 
described only in so far as concerns the median divisions. The 
lateral divisions proceed in exactly the same way as in the 
anterior somites. The median divisions, however, contain in 
their splanchnic walls the germinal nuclei, and persist through- 
out life as the generative tubes. Their development therefore 
requires a special description. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 5dl1 


Tue GENERATIVE ORGANS. 


During Stage p a number of especially large (as large as the 
largest of the ordinary endoderm nuclei), round, granular 
nuclei appear in clusters in the dorsal endoderm of the hind 
end of the body. Their anterior limit is the sixteenth somite. 
They are not therefore seen until the sixteenth somite is 
formed. When they first appear they are crowded together in 
a mass in the endoderm at the hind end of the body; but they 
soon begin to acquire a relation to the cells of the splanchnic 
walls of the posterior somites. Some of them pass to the 
surface of the endoderm and project into the somites, pushing 
the mesoderm cells before them (Pl. XXXV, figs. 26 and 27, 
gen.). I think there can be no doubt that they give rise to the 
nuclei of the sexual cells of the adult, and I propose to call 
them the germinal nuclei. With regard to their disposition, 
I may give the following details :—In an embryo with eighteen 
somites they were present in the region of the last three, viz. 
of the sixteenth, seventeenth, aud eighteenth. They were 
placed in the endoderm near the layer of splanchnic mesoderm, 
but they did not project, except in one or two cases, into the 
cavity of the somite. 

In an embryo with twenty-one somites these nuclei were 
present in the region of the sixteenth to the twentieth somite 
inclusive. They were found in groups in the dorsal endoderm, 
and a considerable number of them projected into the somite, 
or, in other words, had migrated from the endoderm into the 
splanchnic mesoderm (Pl. XXXV, fig. 26). 

The same features were presented by an older embryo of 
Stage ©, with the full number of somites. Pl. XXXV, fig. 27, 
represents a section through the seventeenth somite of such an 
embryo, and shows very clearly the relations which these nuclei 
acquire to the splanchnic mesoderm. 

The cells of the latter form capsules surrounding the ger- 
minal nuclei, which possess but a very delicate (with difficulty 
visible) protoplasmic investment of their own. By the close of 
Stage E these germinal nuclei are present in the region of the 


512 ADAM SEDGWICK. 


sixteenth to the twentieth somite inclusive, lying partly in 
groups in the dorsal endoderm and partly in the splanchnic 
mesoderm, 

They are of the same size as the larger of the ordinary 
endodermal nuclei—'014 mm. in diameter. They differ, how- 
ever, from the latter in their evenly-rounded form, the outline 
being perfectly smooth, and in the fact that they lie together in 
groups of three or more. 

With regard to their origin, they come, as do all the tissues 
of the hind end of the body, from the primitive streak; and 
though there are in the primitive streak in Stage c large round 
nuclei of their aspect, it is not until Stage p that they can be 
distinguished in the endoderm with the above-mentioned 
characteristics. 

The median divisions of the somites in the generative region 
remain continuous with the lateral (nephridial) portions until 
the close of Stage r. Early in Stage r they have completely 
separated from the latter (Pl. XXXVI, fig. 41), and now rapidly 
become reduced in size, so that by the close of Stage F they have 
the form of somewhat triangular structures placed in the ventral 
wall of the heart and pericardium (Pl. XXXVII, fig. 43). 
Inasmuch as the gut has now completely separated from their 
ventral walls, the generative nuclei have entirely lost their con- 
nection with the endoderm—their place of origin. They still 
lie in the ventral walls of the somites,—a position which they 
maintain throughout life. 

In the next Stage (c, to be more fully described in Part IV 
of this series) the successive dorsal (generative) portions of 
the somites of the same side unite with one another, in con- 
sequence of the breaking down of the intervening segmental 
septa, so as to form two tubes (Pl. XXXVII, figs. 47, 48), 
which are the generative glands. The generative glands 
separate from the floor of the pericardium, except at their 
front end, where they remain connected throughout life. They 
thus have the form of two tubes closely applied together and 
placed in the dorsal region of the central compartment of the 


body cavity. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 513 


The Somites of the Twenty-first Pair, or somites of the anal 
papillee, never become divided into two parts. The median divi- 
sion remains in connection with the lateral(Pl. XXX VII, fig. 44), 
which, however, as in the case of the other somites, acquires 
aventral diverticulum. ‘This hugs the outer side of the nerve- 
cord, and acquires in late embryos of Stage F an external 
opening which, however, is much nearer the middle line than 
in the case of the anterior somites, and, indeed, may be 
described as being common with that of the opposite side. 
However this may be, the two openings soon become definitely 
united to form asingle opening,—the generative opening, while 
the tubes themselves persist as the generative ducts. Whether 
any large portion of the latter are ectodermal in origin, that is 
to say, derived from a growth of the lips of the opening at 
its first appearance, it is impossible to say. Kennel asserts 
that a large part of the generative duct is so derived, but it is 
obvious that such a statement, as in the case of the anterior 
segmental organs, cannot be regarded as anything more than 
an expression of probability. It is impossible to settle the 
question by sections, and [ know of no other method. 

From the above description of the origin of the generative 
organs and their ducts, which is in the essential points identical 
with that of my tentative preliminary account (No. 33), it is 
obvious that Kennel has failed to trace the origin of the 
germinal nuclei. He also differs from me as to the origin of 
the generative tubes themselves, which, he asserts, come from 
the dorsal divisions, not of a series of somites, but of one 
single pair. If his account is correct, which, seeing that he 
has not observed the origin of the germinal nuclei, I am 
inclined to doubt, it would appear that the generative tubes of 
the Cape species differ from those of the West Indian in this 
respect. He adopts my account of the derivation of the gene- 
rative ducts and their openings from the lateral divisions of a 
pair of somites, though, curiously enough, in another place he 
stigmatises my description as “ falsch.” 

It thus appears thatin Peripatus capensis the nephridial 
portion of the twenty-first somite does not separate from the 


514 ADAM SEDG WICK. 


median or generative portion, but remains in connection with 
the latter and forms the channel by which the generative part 
of the ceelom communicates with the exterior. The generative 
ducts are therefore modified nephridia, but it is important to 
notice that the connection between these structures is not to be 
compared with the so-called funnel of the normal nephridia. 
The latter is merely a special portion of the nephridial or 
lateral portion of the somite, and does not seem to be re- 
presented in the twenty-first somite. In the female of the 
West Indian and South American species, as described by 
Gaffron and Kennel, the case seems to be otherwise. Both 
these observers have found between the ovary and recepta- 
culum seminis a diverticulum of the oviduct, which ends in 
a thin-walled vesicle. This structure is called ‘“ Ovarian- 
trichter” by Gaffron, and “receptaculum ovorum” by Kennel; 
and the latter observer distinctly states that he does not regard 
it as homologous with the funnel of a nephridium (No. 14, 
p. 66), apparently because of the thin-walled vesicle (of which 
he was the discoverer) which closes up its free end. It seems 
to me, however, that it is this very thin-walled vesicle which 
renders it almost certain that the structure in question is 
homologous with the so-called funnels of the normal nephridia, 
all of which open into thin-walled vesicles of a nature pre- 
cisely similar to the receptaculum ovorum. Had the latter 
been absent and the diverticulum of the oviduct opened directly 
into the body cavity, as Gaffron at first supposed, then there 
would have been a very strong reason against regarding the 
diverticulum as homologous with the nephridial funnels. On 
my view, then, the receptaculum ovorum would correspond 
to a nephridial vesicle which had been drawn out of the leg 
portion of the body cavity and placed in the central com- 
partment. 

How comes it that this structure is absent from the oviduct 
of the South African species? In the neotropical species of 
Peripatus, in which the receptaculum ovorum is always 
present, the generative ducts open between a pair of fully- 
developed legs. Inthe South African Peripatus, on the other 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 515 


hand, they never open between a pair of fully-developed legs, 
but always behind the last pair of such; the legs correspond- 
ing to the generative nephridia being more or less completely 
rudimentary (anal papille, &c.); and it seems to me not un- 
reasonable to suppose that this abortion of the appendage has 
carried with it the abortion or non-development of the portion 
of the somite which, in the preceding legs, gives rise to the 
internal vesicle of the nephridia. 

It would be of interest in this connection to observe 
whether the oviduct of the New Zealand species, in which 
the generative ducts open between a pair of fully-developed 
legs, possesses a structure corresponding to the receptaculum 
ovorum. 

There are rudiments of two pairs of somites behind the 
somites of the anal papille in Stage rn. One of these is just 
visible in Stage r. They vanish completely at the end of 
Stage r. No appendages or rudiments of such are developed 
in connection with them. 


GENERAL CONSIDERATIONS. 


There are four points in the development of Peripatus 
capensis which appear to me to deserve a more detailed con- 
sideration and comparison, with corresponding processes in 
other types, than it is convenient to give them in a descriptive 
account. These are: (1) The incomplete segmentation, and 
syncytial nature of the embryo; (2) the development of the 
mesoderm ; (3) the development of the vascular system, body 
cavity and celom; and (4) the relation of the blastopore to 
the mouth and anus. 

The last point has already been sufficiently considered and 
its significance pointed out in my paper “On the Origin of 
Metameric Segmentation”? (No. 32). I see no reason to 
modify the views there set forth on this subject; on the con- 
trary, recent investigations seem to give them additional 
support. 

(1) I have already, in Part II of this series, dealt to 


516 ADAM SEDGWICK. 


a certain extent with the peculiarities in the segmentation 
of Peripatus capensis both intrinsically and in relation to 
other forms. I think, however, that the subject is of sufficient 
importance to deserve a more detailed treatment than it was 
possible to give it in that place. 

There can be but little doubt that the ovum of this species 
possessed, ata period relatively not very remote from the present, 
a large amount of good yolk; that it resembled in fact in this 
respect the ovum of the species now living in New Zealand, 
and the ova of Arthropoda generally. The large size, 
combined with the almost complete absence of food-yolk, 
can, it appears to me, only be accounted for by sup- 
posing that the ovum is passing from the large-yolked 
to the non-yolked condition, and is intermediate between 
the ovum of the New Zealand and that of the neotropical 
species. The ovum! of the latter species would on this view 
have been derived from the large-yolked ovum of some remote 
ancestor. 

There are other instances in the animal kingdom of small 
ova which there is strong ground for regarding as having 
been derived from large-yolked ova. The most conspicuous 
example of this is perhaps that of the Mammalia. Within this 
class we find both large-yolked and small ova; and the investi- 
gation of the former which is now being carried on by 
Caldwell has particular interest inasmuch as it will show 
more completely than has been possible hitherto how the 
development is modified by the loss of yolk. Caldwell’s 
investigations are not yet published, and we do not therefore 
know whether there is an ovum amongst the lower Mammalia 
with the property—unique so far as I know—of the ovum of 
Peripatus capensis, viz. the large size combined with 
the almost complete absence of yolk. 

It is this peculiarity which, while it gives the cleavage of 
the ovum of P. capensis a great interest, necessitates great 

1 The ovum of the Trinidad species which has been investigated by Kennel 
(Nos. 18, 14), and of a South American species which | have had an opportunity 
of examining, is relatively minute (diameter ‘04 mm.) and poor in food-yolk. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 517 


caution in dealing with the general importance of the phe- 
nomenon. 

I shall assume, then, to start with, that the ovum of the 
Cape species has only recently lost it yolk, and that it may 
be compared to an ovum of the New Zealand form from which 
the yolk has been almost completely dissolved out by some 
reagent. As a matter of fact, it is impossible, with our 
present methods, to effect this complete solution of yolk and 
leave its protoplasmic framework ; but what we cannot effect 
has been done by nature in the most complete manner, leaving 
an ovum which is little more than a loose protoplasmic sponge- 
work, excepting at one point where the protoplasm is more 
dense. It is at this point only that the cleavage takes place ; 
for the breaking up of the rest of the ovum into irregular 
masses cannot be regarded as a process! in any way related to 
cleavage, inasmuch as the nucleus takes no part in it. 

The cleavage would appear, therefore, to be meroblastic, and, 
as in meroblastic ova, the protoplasm round the nuclei at the 
periphery of the blastoderm is perfectly continuous with that 
of the main mass of the ovum in which the yolk is contained, 
but from which it is absent in this ovum; that is to say, we 
have round the periphery of the blastoderm, and lying in the 
part of it which corresponds to the yolk of large-yolked mero- 
blastic eggs, a number of yolk-nuclei, or rather of nuclei 
which correspond to the yolk-nuclei of such large-yolked eggs. 

But the cleavage is not only meroblastic, it takes place in 
the same manner as in centrolecithal ova, i.e. the furrows 
extend only a short distance into the ovum (vide Part II of 
this series, p. 179) ; the deeper parts of the segments are con- 
tinuous with each other. Very soon, however, the loosely 
reticulated protoplasm extends on to the contiguous surfaces 
of the segments, from which it was at first absent owing to the 
fact that the furrows are formed in the densely reticulated pro- 
toplasm only. It thus happens that each segment becomes 
continuous with all the contiguous segments near the surface, 


* This process is probably identical with the formation of the non-nucleate 
yolk-spheres found in many Arthropoda. 


518 ADAM SEDGWICK. 


as well as in the deeper parts (vide description of segmentation, 
p- 179, Part II). By the continued division of the nuclei at 
the edge of the blastoderm the embryo acquires an external 
layer of nuclei, which are absent only at one point—the future 
blastopore. 

Of all the forms of Arthropodan cleavage that I know of, this 
process seems to resemble most nearly that of the mite Tetrany- 
chus telarius, as described by Claparéde (No.6). In this form, 
as in Peripatus, the first segmentation nucleus divides at the 
periphery of the ovum, and not in its centre, as in most centro- 
lecithal ova. There is, however, the greatest possible variety 
in the position of the first segmentation nucleus in Arthropoda, 
and the matter does not seem immediately important. The 
same cannot, however, be said about the continuity between 
the segments. This seems to me a matter of the greatest 1m- 
portance at the present moment. It has long been known that 
the segments of many centrolecithal eggs are at first connected 
with oneanother. In proof of this I need only refer to Balfour’s 
summary of the cleavage of centrolecithal ova in vol. i of the 
‘Comparative Embryology,’ and to any of the recent works on 
Arthropod development (e.g. Patten, No. 25); that is to 
say, it has for some time been known that the segmentation of 
centrolecithal eggs is not a complete cleavage, and, indeed, 
sometimes does not deserve the name of cleavage at all (e. g. 
most Insecta). But it has generally been supposed that 
this continuity is soon lost, and that the final result of seg- 
mentation is in all cases a mass of completely separate cells 
(vide Patten, No. 25, pp. 565, 567). According to this 
view the connections which undoubtedly exist between the 
majority of cells of the adult is purely secondary (vide Flem- 
ming, No. 7, p. 74). 

Two questions now present themselves: (1) Is this view true 
in fact? (2) Is it genetically true? 

In other words, (1) Is it universally true that there is a stage 
in the embryonic development of the Metazoa in which all the 
cells of the body are isolated from one another? (2) Has 
there been such a stage in the evolution of the Metazoa, i.e. 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 519 


a stage in which the body of the common ancestor consisted of 
a mass of organically separate cells? 

The answer to the first question must be undoubtedly a nega- 
tative one. The cells arising from the segmentation in Peri- 
patus capensis are at no period of development completely 
isolated units, but retain a connection with one another 
throughout life. It is true that some of them break away from 
the rest, and form blood-corpuscles and generative cells, but 
the greater number present in the adult a connection with 
their neighbours—a connection which has been derived directly 
from the connections between the cells of the segmenting 
ovum. The same fact, as has been shown by Heathcote 
(No. 11), holds good for Julus; and it seems to me highly 
probable that the connections between the various adult cells 
of other Arthropoda with centrolecithal eggs will be found to 
be derived continuously from the connections between the cells 
of the segmenting ovum. 

But while we must admit that there are cases in which the 
cleavage is not complete, yet in a great many animals—in all 
cases of small holoblastic eggs—it seems to be quite certain 
that the cleavage is complete. It is true that the spheres 
always touch one another, and there may be an organic con- 
nection at the point of contact ; but assuming that there is no 
such connection, the question naturally arises: which of these 
two processes—the incomplete or the complete cleavage—is, 
from a phylogenetic point of view, the more correct ? 

It has generally been supposed that the complete cleavage is 
the most primitive process, and that the mass of organically 
distinct and similar cells, such as is found in the morula of a 
typical development, represents a colonial Protozoon-like 
ancestor of the whole of the Metazoa. In short, the general 
view seems to be that the immediate ancestor of the first 
Metazoon was a multicellular Protozoon, the separate cells of 
which were all distinct from one another. Can we find any 
justification in the animal kingdom, as we know it, for this 
view? Is there any living form constituted in this manner ? 
The answer is, it is hardly necessary to say, a negative one. 

VOL, XXVII, PART 4.—NEW SER. Om) 


520 ADAM SEDGWICK. 


There is no animal composed of a mass of separate and similar 
cells. All the colonial Protozoa consist of a number of cells 
connected with one another by protoplasmic filaments ; it may 
be by long contractile filaments, as in colonial Flagellates 
and Vorticellz, or it may be by short laterally springing 
filaments, as in Volvox; and it is by means of these connecting 
threads that the individuals of the colony effect the little co- 
ordination of which they are capable. 

Further, from an a priori point of view, it seems highly 
improbable that such a number of disconnected units could 
have formed a stage in the evolution of the Metazoa. Is it 
possible, then, that there has not been any such stage, and that 
the so-called colonial Protozoon stage in the Metazoon onto- 
geny is purely secondary, and has been produced by the 
mechanical requirements of individual development ? Answer- 
ing this question for the moment in the affirmative, we come 
to the alternative view, viz. that incomplete cleavage is the 
more primitive process. This view, though it possesses, accord- 
ing to our present knowledge, weaker embryological justifica- 
tion than the first, has a far stronger basis of facts derived 
from the anatomy of living forms. While amongst the Protozoa 
there is no counterpart of the fully segmented ovum, there is 
a comparatively large number of colonial forms in which the 
individuals are connected by irritable protoplasm, and of mul- 
tinucleate forms, in which the protoplasm, though more (some 
ciliated Infusoria) or less (some Rhizopoda) differentiated, is 
without that definite relation to the various nuclei which is 
characteristic of the colonial forms and of cells in general. 

Metschnikoff (No. 22, p. 132), in discussing this very ques- 
tion, contends that the preponderance of complete cleavage, 
especially in the lower forms, is a strong argument in favour 
of the colonial Protozoon origin of the Metazoa. Here I differ 
with him, for in all colonies that we know of the individuals 
are connected by protoplasmic filaments, which have arisen, not 
as the result of fusion, but as the result of the incomplete 
division of the common parent form. A mass of distinct cells, 
more or less closely applied to one another, is not a colony in 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 521 


the ordinary acceptation of the term, and it is such a form 
which, according to what I believe to be the view of Mets- 
chnikoff and most morphologists, represents the connecting link 
between the Protozoa and Metazoa. 

But perhaps it will be contended that I am wrong in 
ascribing this doctrine to them, and that they hold the view 
that the individuals composing that hypothetical ancestral 
Metazoon, which is suggested by the cleavage of the ovum, 
were not completely separate but connected as in living colonies 
of Protozoa. To this I would reply, that if such be their 
view, then they can find no justification for it from the de- 
velopment of forms in which complete cleavage occurs. It is 
rather in such a segmentation as we find in some Sponges 
(Marshall, No. 21; Sollas, No. 34), in Aleyonarians (Kowa- 
levsky and Marion, No. 17) and most Arthropoda that we 
shall have to seek the nearest embryological counterpart of the 
process by which the Metazoa arose from the Protozoa. 
If this is so, how are we to account for the frequency of the 
cases in which the furrows, dividing the ovum, completely 
separate the segments from each other? In the first place, I 
would ask, are the cases so numerous as is supposed? Itseems 
to me extremely probable that it will be found, on renewed 
investigation, that incomplete cleavage takes place in many 
forms in which it has been assumed that complete cleavage is 
the rule. The complete cleavage of small ova is such a striking 
phenomenon, and so readily lends itself to speculative sugges- 
tions, and has in this form so dominated the views of mor- 
phologists (vide especially Flemming’s remarks above referred 
to), that I cannot help feeling that it may, in some cases in 
which perhaps the observation was difficult, have been assumed 
to occur on insufficient evidence. And this feeling is rather 
confirmed by the well-known prevalence of the habit of as- 
suming cell boundaries when they cannot be seen. Almost 
every embryological memoir bears on its plates numerous 
examples of this habit. 

In the second place, it seems possible that the complete 
cleavage, found so conspicuously in small ova, may be sus- 


522 ADAM SEDGWICK. 


ceptible of a mechanical explanation. The clean rounded form 
of the spheres at the moment of division is unlike anything 
else in the animal kingdom, and is suggestive rather of an 
intensely active force in the centre of the cell, which compels 
for the moment the assumption of this form in the protoplasm 
over which it has dominion, than of a tendency inherited from 
an adult ancestor. I would refer in this connection to Brook’s 
observations on the total segmentation of Lucifer (No. 5). 
He describes how, at the moment of activity, the segments 
round themselves off, touching only at one point, while in the 
intervals of rest they flatten out against one another, and 
possibly become partly fused. The same phenomenon is found 
in other Crustacea (vide Balfour, No. 1, p. 112), and it 
seems fairly generally to happen that at the moments of 
activity the segments round themselves off, and in the intervals 
of rest flatten out against each other. These facts seem to me 
to indicate that it may be possible to find a purely mechanical 
explanation of complete cleavage. However this may be, it 
seems pretty clear that the holoblastic segmentation of small 
ova has not the phylogenetic significance usually ascribed to it. 

To sum up, the ancestral Metazoon has generally been 
assumed to be a colonial Protozoon, and when we examine the 
evidence for this view we find that the holoblastic segmenta- 
tion, which really suggested it, is totally opposed to it; and 
further, that the facts of incomplete cleavage which were 
thought to be opposed to it are somewhat in its favour, though 
much more suggestive of another view, which I will now 
consider. 

In Part II of this series I suggested that the ancestral 
Metazoon was not a colonial Protozoon, but a multinucleated 
Infusorian-like animal with possibly a mouth leading into a 
central vacuolated mass of protoplasm, and that evolution of 
the higher forms has consisted mainly in a definite arrange- 
ment of the nuclei and of the specialisation of certain of the 
vacuoles in the internal protoplasm into the cavities of 
organs, and of the protoplasmic strands between into the walls 
of the latter, and into nerves, muscles, &c, 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 528 


This is not a new view; it is the old view of the origin of 
the Metazoa, and has been held recently by Saville Kent 
(No. 28, vol. ii, p. 480) and others. It is entirely in 
accordance with the facts of the development of Peripatus 
capensis. 

With regard to this development, we have to observe that 
we cannot speak of cells till a comparatively late period 
(Stage B), and that the intimate structural change underlying 
the processes of growth of the young embryo is not an increase 
of cells, but a multiplication of nuclei. First of all a cortical 
layer of nuclei, lying in the peripheral layer and entirely sur- 
rounding, excepting at one point, the vacuolated spherical mass 
of protoplasm of which the embryo consists, is differentiated. 
The central protoplasm, which contains a few nuclei and a 
great number of large and small vacuoles to which the nuclei 
have at first no special relation, protrudes from the point at 
which the cortical nuclei are absent, as though to extend 
itself in an amoeboid manner in search of food. This is the 
solid gastrula stage (Part II, fig. 20). In it no cell outlines 
are distinguishable, the whole embryo differing only from, 
say Vorticella, in its large size, and the presence of a 
definitely arranged layer of nuclei round its periphery. 

From this stage the ccelo-gastrula is derived by the simple 
process of the confluence of the larger central vacuoles to form 
a single internal cavity, the establishment of the definite 
opening of this cavity to the exterior, and the arrangement of 
the central nuclei in the protoplasm lining it (Part II, figs. 23, 
24 6). Later the mesoderm appears. It is derived from 
some of the nuclei already present, which increase in number 
and arrange themselves in the protoplasm around some of the 
vacuoles which thus early become specialised into another 
organ, the celom. 

Metschnikoff, who has done such important service to 
biology in drawing attention to the physiological importance 
of ameeboid cells in the organism, has been one of the most 
prominent advocates of the view that the formation of the 
gastrula by invagination is a secondary process. He considers 


524 ADAM SEDGWICK. 


that the animal of which the gastrula is the embryonic repro: 
duction—if indeed it ever existed—was preceded by a form in 
which the endoderm consisted of a vacuolated mass of proto- 
plasm without any definite enteric cavity. So far most 
embryologists of the present day are with him. But he goes 
further ; he considers that this parenchymatous gastrula or 
blastula'—or as he calls it, Phagocytella—was preceded by 
a hollow blastula-like Protozoon form from which it arose by 
the migration inwards of certain of the cells of the wall of 
the blastula. This suggestion as to the origin of the gastrula 
and the form of the ancestral Protozoon has often been 
criticised, and it seems to me that the facts suggest, with 
equal strength, quite another view of the matter, viz. that 
which I have just hinted at. 

There are several ways suggested by embryology in which 
the passage from the Protozoa to the Metazoa may have 
been effected ; and a most admirable and profound analysis of 
each of these, and a critical review of our knowledge on this 
subject, is to be found in chap. xiii, vol. ii, of the ‘Comparative 
Embryology.’ I cannot do better than quote the words in 
which Balfour sums up this review of the facts—“ Considering 
the almost indisputable fact that both the processes above 
dealt with [delamination and invagination] have in many 
instances had a purely secondary origin, no valid arguments 
can be produced to show that either of them reproduces the 
mode of passage between the Protozoa and the ancestral two- 
layered Metazoa. These conclusions do not, however, throw 
any doubt upon the fact that the gastrula, however evolved, 
was a primitive form of the Metazoa; since this 
conclusion is founded upon the actual existence of 
adult gastrula forms independently of their occur- 
rence in development” (‘Comp. Emb.,’ vol. ii, p. 283; the 
italics are mine). 

These words seem to me to express as clearly now, as they 

1 Tam not quite sure whether he considers that the cortical layer (kyno- 


blast) of his Phagocytella was interrupted at any point for the protrusion 
of the central mass (phagocytoblast). 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 520 


did when they were written five years ago, the state of our 
knowledge on this subject, and in my opinion neither Metsch- 
nikofi’s view, nor that which I have just put forward as to the 
exact method of transition between the Protozoa and Metazoa, 
can be regarded as anything more than a more or less plausible 
suggestion without any strong basis of fact. 

The gastreea theory, in so far as it implies the existence of an 
ancestral two-layered organism, is still in accordance with 
known facts, and no discoveries have been made which deci- 
sively settle the mode of transition between the Protozoa and 
Metazoa. As, however, the subject is an interesting one it 
seems worth while contrasting Metschnikofi’s view with that 
which I have just put forward. But before doing so, am anxious 
to notice one or two points in which Metschnikoff seems to 
have misunderstood Balfour’s views on this subject. Bal- 
four, as is well known, was inclined to the view that 
the gastrea was preceded by a solid form, such a form as 
Metschnikoff terms parenchymella, and Metschnikoff himself 
quotes (No. 23) passages from the ‘Comp. Embryology’ 
which show this; and yet Metschnikoff represents Balfour as 
being opposed to the parenchymella theory. It is not quite 
clear to me what exactly Metschnikoff means by the paren- 
chymella theory; but if this theory merely postulates the 
existence of a beast with an outer ectodermal layer and an 
internal mass of amceboid cells, then I have no hesitation in 
saying that Metschnikoff is mistaken in regarding Balfour as 
having been actively opposed to it. It is true that Balfour 
thought that Metschnikoff’s view as to the method of origin 
of the parenchymella was improbable ; but surely one may 
accept the parenchymella without holding the precise views of 
Metschnikoff as to its origin, just as one may accept the 
gastrea theory without pinning one’s faith to any particular 
view of the mode of origin of the gastrea. It appears to me 
that Metschnikoff, in dealing with both the parenchymella and 
gastreea theories confuses two questions. 

(a) Was there an ancestral gastrula, with the characters 
attributed to it ? 


526 ADAM SEDGWICK. 


(0) If so, how did this ancestral form itself arise ? 

If the answer to the latter question falls within the province 
of the gastrea theory, Balfour did not accept that theory and 
Metschnikoff is wrong in saying that he was strongly inclined 
towards it. If, on the other hand, the gastrea theory simply 
generalises from a large number of anatomical and embryo- 
logical facts as to the past existence of an animal with a parti- 
cular structure, and leaves the question of origin out of consi- 
deration, then Balfour undoubtedly did accept the gastrea 
theory, but did not thereby, as Metschnikoff seems to think 
must necessarily have been the case, reject the Parenchymella. 
On the other hand, Balfour expressed himself distinctly in 
favour of the latter, though he did not call it by that title, 
for does not he say, and does not Metschnikoff quote him as 
saying (No. 28, p. 156), that he thought it probable that the 
ancestors of Ccelenterates possessed a solid endoderm of 
ameeboid cells ? 

This is not the only point in which Metschnikoff has mis- 
understood Balfour’s views. On p. 141 of No. 23, he ascribes 
to him the view that an amphiblastula form would represent 
more nearly than any other the transition between the Pro- 
tozoa and Metazoa. Balfour maintained no such position, as 
has been already pointed out by the translator of Metschnikoff’s 
paper on the ‘Intracellular Digestion of Invertebrates,” 
‘ Quarterly Journal of Microscopical Science,’ vol. xxiv, p. 107, 
note. 

But to resume: Metschnikoff supposes that the parenchy- 
matous ancestor was preceded by a hollow spherical form, the 
blastula, the cells of which were all alike ; and that the blastula 
became a parenchymatous gastrula by the migration inwards 
of cells from its external wall. 

I do not understand on what grounds Metschnikoff is so 
strongly disposed towards the view that the hollow blastula 
represents a primitive form. 

There are many cases, even amongst the Celenterates, in 
which a hollow blastula is not formed and segmentation gives 
rise to a solid planula, and in the rest of the animal kingdom, 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 527 


the cases, in which segmentation gives rise to a solid embryo 
are quite as numerous, if not more so, than those in which the 
reverse holds. 

I would even go further than this, and maintain that 
Metschnikoff’s view, that the ectoderm is primitive and the 
endoderm secondary—arising from the former by inwandering 
—is not more in accordance with the facts of embryology than 
the opposite view, viz. that the endoderm is primary, giving 
rise to the ectoderm by budding-off cells—outwandering as it 
may be called. In almost all Invertebrate groups there are 
instances of the latter process, in which the ovum, before or 
after division into two or more large cells, buds out a number 
of small cells which form the ectoderm; either itself, or the 
large cells produced by it, persisting, and eventually, after the 
appearance of a central cavity, forming the endoderm. 

I do not mean to say that the facts are more in favour of 
this view than in that of Metschnikoff, but I think they 
favour the one as much as the other. 

But granting the hollow blastula as a possible animal, I 
agree with Biitschli in thinking that there are great physio- 
logical difficulties in the way of accepting the process by which, 
according to Metschnikoff, it may have become transformed 
into a solid form. Surely a hollow sphere is in a much more 
advantageous position with regard to nutrition than a solid 
one; and yet Metschnikoff supposes that the transformation 
into the solid form was due to the migration of surface cells 
into the interior for nutritive purposes. The central part of 
the animal heing empty would require no nutriment, and even 
if it did, what more convenient arrangement could there be 
than a layer of cells to pass prepared nutritive substances into 
it? The ectoderm of Hydra or of Celenterates in general is 
not fed by the migration of cells from the endoderm, and in 
short we know of no instance in the animal kingdom of food 
being carried from one part of an organism to another in 
actively migrating cells. It seems to me much more likely, 
if the ancestral Protozoon was a hollow blastula, that the first 
differentiation would have been into locomotive sentient cells 


528 ADAM SEDGWICK. 


and cells for acquiring food, i.e. the differentiation supposed 
by the invaginate gastrula hypothesis. For it is clearly neces- 
sary on this view that the nutritive cells should be in direct 
contact with the external medium, and this they are not on 
Metschnikoff’s view. 

Then again, what justification do we find in the animal 
kingdom for the hollow blastula hypothesis? With the pos- 
sible exception of Volvox, I know of no form at all approach- 
ing a hollow blastula in structure. 

These difficulties are avoided by the hypothesis that the 
primitive form was solid, which also suits the facts quite as 
well. (1) It is no longer necessary to suppose the migration 
inwards of cells. (2) There are a considerable number of 
instances in the animal kingdom of lowly organised solid 
forms which give a certain amount of justification to the 
hypothesis of a solid ancestor. There is Trichoplax (No. 29), 
the Orthonectide, the whole of the Protozoa, the accelous 
Turbellaria, and finally the Sponges, or at least some of 
them under certain conditions. The latter case is of particular 
interest, and deserves a little attention here. 

Metschnikoff (No. 22, p. 372) states that Halisarca, when 
overfed with carmine, loses its canals and becomes a mass of 
ameeboid cells containing swallowed food, and surrounded by 
a common envelope of ectoderm. The same fact has been 
observed by Lieberkiihn in Spongilla (No. 20), in winter. 
From these observations, and others by Heckel and Carter 
(quoted by Metschnikoff, No. 22, p. 361), it appears that under 
certain nutritive conditions, the flagellated endoderm cells of 
sponges may lose their flagella and become ameeboid, and the 
whole sponge revert to the condition of the larva of Aplysina 
(Shulze, No. 30, Pl. 24, fig. 30) of a protoplasmic network 
with nuclei at the nodes, and a cortical layer of ectoderm. 

Metschnikoff (No. 22) has further observed that in many 
cases the food of the sponge passes directly into the paren- 
chyma and is not found in the collared endoderm cells; while 
in other cases it is found both in the cells of the endoderm 
and parenchyma. These facts, as Metschnikoff points out, seem 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 529 


to imply that the endoderm cells are not mainly nutritive, but 
that their main function is to cause the currents through the 
sponge body, and that the food brought by these currents 
passes into the parenchyma, through the walls of the passages, 
to be digested by the so-called mesoderm cells. 

The collared cells are thus inconstant, and appear to be 
merely parenchyma cells specially modified under certain 
conditions and capable of passing back into their original form 
when the need for them has passed away. When they vanish 
the canal system also goes and the sponge becomes solid so far 
as the latter isconcerned. Inasmuch as the parenchyma cells, 
and probably also the cells of the ectoderm, are all connected 
by their processes (except in the cases in which they break 
away and become ameeboid), it is clear that the sponge in this 
condition and in the case of Shulze’s larva already referred to, 
is a syncytium, and but little more than a multinucleated 
Protozoon. It differs from such a Protozoon simply in the 
greater development of the vacuoles (spaces between the 
cells) of the central portions, and in the presence of a distinct 
cortical layer of nuclei. 

In some cases this assumption by a sponge of the Protozoon 
form is much more marked than in the above cases. I refer 
to the case of the well-known form Haliphysema, described 
by Heckel (No. 10) as a sponge with an axial ciliated 
chamber traversing it, and by Lankester (No. 18) as a mul- 
tinucleated Rhizopod. It is difficult to believe that either 
of these distinguished naturalists can have made the mistake 
implied by these contradictory observations ; and the only way 
of reconciling the latter that I know of, is to be found in the 
above view, viz. that Haliphysema, like Spongilla and 
Halisarca possesses under certain conditions, the power of 
becoming solid: that in certain conditions in which it was found 
by Heckel, it approximates to the sponge, while under other 
conditions in which it has been found by Lankester and 
Saville-Kent it loses its sponge-like structure and comes to 
resemble a multinucleated Protozoon. There are certain 
points in Lankester’s description of the soft parts which favour 


530 ADAM SEDGWICK. 


this view, e.g. the obviously reticulated nature of the proto- 
plasm (see particularly fig. 9 in Lankester’s paper), the large 
number of nuclei, and, finally, the germ cells. 

These facts, though not in any sense proofs of the view of 
the origin of the Metazoa for which I am contending, are at 
any rate suggestive of it, and, so far as they go, in favour of 
it. That is to say, they suggest the view that there would be 
two courses open to a Protozoon after it had reached a size too 
great for the proper nutrition of its central portion, i.e. a size 
in which the ratio of surface to mass was unfavorable ; it would 
either divide, in which case it would remain a Protozoon, or 
it would develop from its vacuoles a system of connected and 
specialised channels with a definite communication to the 
exterior at one or more places. In the latter case it would 
constitute the first stage in the evolution of the Metazoa. 

There is no reason to suppose that the protoplasm of such a 
form, even though partially broken up into areas round the 
various nuclei, would thereby lose the power of taking in to 
itself foreign substances which were presented as nutriment ; 
in other words, would not prevent it from discharging the 
functions discharged by the protoplasm of all Protozoa, and 
by the parenchyma cells or phagocytoblasts of Metschnikoff. 

To sum up, while fully agreeing with Metschnikoff, that the 
formation of the endoderm by invagination of the wall of a 
hollow blastosphere is a secondary process, I cannot accept his 
position that the hollow blastula is a primitive form, or that the 
formation of the endoderm by migration inwards of the cells 
is a primary process. It seems extremely probable that the 
blastula has arisen to provide for the better nutrition of the 
growing embryo, and that the inwandering and invagination 
are alike secondary processes, the object of which is, when the 
proper stage is reached, to get the protoplasm back to its 
central position and ready for the development of the system of 
channels which render its maintenance in the inside possible. 

(2) The mesoderm in Peripatus arises from certain nuclei in 
the middle ventral line behind the blastopore. These nuclei 
may, as I have attempted to show above, fairly be regarded as 


DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 531 


corresponding with the nuclei in the lips of the blastopore> 
intermediate in character as well as in position, between the 
ectodermal and endodermal nuclei. The multiplication of these 
nuclei gives rise to a primitive streak, which, as in the Verte- 
brata, is entirely posterior to the blastopore, and is marked by 
a longitudinal groove—the primitive groove. 

This process resembles, in all essential points, the formation 
of the greater part of the mesoderm in other Tracheata from 
the walls of the germinal groove, differing only in this, that 
whereas in the latter the germinal or primitive streak occupies 
the greater part of the ventral surface, in Peripatus it is 
confined to the part of the ventral surface behind the anus. 

I have elsewhere (No. 32) stated my reasons for agreement 
with Balfour’s view, viz. that such a method of mesoderm 
formation is probably to be regarded as a modification of 
archenteric diverticula, such as are found in Amphioxus, &c. 
Whether the origin of mesoderm from the walls of archenteric 
diverticula is a primitive process or not is open to grave 
doubt. 

It seems to me there is a large body of embryological facts 
which suggest, at any rate, the view that the mesoderm arose 
as a result of the differentiation and rearrangement of certain 
of the nuclei of the amceboid central mass of the ancestral 
parenchymella or gastrula; that is to say, the facts seem 
to suggest the following as a possible general view of the origin 
of the three layers of the Triploblastica. 

(a) Starting with a large multinucleated Protozoon, the 
first advance consists in the differentiation of a cortical layer 
of nuclei and of the protoplasm governed by them into a 
peripheral layer or ectoderm. This layer was possibly of 
a plastic nature, and allowed the protrusion of the central 
mass at one or more points. The central mass would, in 
consequence of its large size, probably be capable of arrang- 
ing its vacuoles into a series of thoroughfares through itself 
from one opening on the surface to another, so that the intro- 
duction of nutritive matters to its deeper parts would be possible. 
On the analogy of the Platyhelminth excretory system we may 


532 ADAM SEDGWICK. 


imagine that the protoplasm of these tracts would acquire the 
property of throwing out vibratile processes into this system of 
channels for the purpose of assisting in an effective circulation 
of the external medium through the body. Such an animal 
would consist, then, of an ectoderm and a central multinucleate 
mass which, with Metschnikoff, we may call the meso-endoderm. 

(6) The next change would consist in the differentiation of 
the nuclei of the meso-endodermic mass into two kinds: 
(a) those governing the protoplasm lining the differentiated 
vacuoles ; and (4) the remainder, which would gradually dif- 
ferentiate into various kinds as evolution progressed. The 
differentiation of the protoplasm around the nuclei would 
proceed hand in hand with that of the nuclei; the result 
being a gradually increasing complexity in the tissues of the 
animal. 

The result would be, if the canal system remained complex, 
—a sponge; if, on the other hand, the canal system simplified 
and preserved only one opening, the ancestor of the other 
Metazoa. 

It is beyond the scope of this paper to discuss the evolution 
of the mesoderm. I merely throw this out as a suggestion, 
which is supported by the manner and order of development 
of the layers in many animals (a peeling off, so to speak, from 
the ovum: (1) of ectoderm; (2) of mesoderm; (3) leaving 
the endoderm as the remaining central mass), and as a com- 
pletion of the scheme which I have put forward in discuss- 
ing the manner of passage from the Protozoa to the 
Metazoa. , 

Finally, I would desire to draw attention to the fact (1) that 
the formation of mesoderm in Peripatus is essentially a forma- 
tion of nuclei, which pass to their respective positions and 
arrange themselves in the protoplasmic reticulum there present; 
and (2) that the primitive streak is the growing point of the 
animal, from which almost all the tissues of the body of the 
adult, viz. ectoderm, endoderm, and mesoderm are formed. 
This is an important point, to which sufficient attention has 
not been directed. Almost the whole of the embryo, behind 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 538 


the fifth or sixth somite—not merely the mesoderm, but all 
the layers—derives its nuclei from the primitive streak. The 
primitive streak nuelei are therefore not merely mesodermal, 
but ectodermal and endodermal as well. 

3. The last feature in the development of Peripatus 
capensis which I would desire to notice in its general bear- 
ings, is the development of the body cavity and the fate of 
the cclom. 

The coelom, as is well known, is the term applied to a body 
cavity with certain characters—characters which may be 
summed up in the following terms :—(1) The coelom does not 
communicate with the vascular system; (2) it communicates 
with the exterior by nephridial pores ; (3) its lining gives rise 
to the generative products; (4) it develops either as one or 
more diverticula from the primitive enteron, or as a space or 
spaces in the unsegmented or segmented mesoblastic bands (in 
the latter case called mesoblastic somites). 

The vascular space has none of these characters, and is 
known as a pseudoceelic space: it develops either from the 
blastocele or from asystem of channels hollowed out in the 
mesodermic tissue of the body. In the Annelida and Ver- 
tebrata these two spaces co-exist, and present a well-marked 
contrast to one another; while in the two other great groups 
of the animal kingdom—the Mollusca and Arthropoda— 
the relations of the two systems has not been thoroughly 
understood. We will first consider the case of the Arthro- 
poda. 

The body cavity in the Arthropoda has generally been 
regarded as ccelomic, in spite of the fact that it presents none 
of the ordinary celomic characters. It communicates with the 
vascular system, it does not open to the exterior by nephridial 
pores, its lining does not, so far as is known, develope the 
generative cells, for the generative glands are continuous with 
their ducts, and, so far asis known, have no connection with the 
body cavity. Neither has the body cavity been traced into 
connection with the undoubted ceelom of the embryo. In all 
the groups of the Arthropoda mesoblastic somites with a more 


534 ADAM SEDGWICK. 


or less well-marked cavity are formed in the embryo; but the 
fate of these structures has never been followed. We do not 
know whether their cavities enlarge and unite with one another 
and give rise to the body cavity and vascular system of the 
adult, or whether they shrivel up and disappear, their walls 
only remaining as part of the mesoderm. From what has 
been said it is also clear that it is impossible to say whether in 
the Arthropoda the vascular system is nipped off from the 
coelom, or whether it arises as a separate set of spaces in the 
mesoderm, as in Annelids and Vertebrates. 

Now, Peripatus is a true Arthropod so far as its body 
cavity is concerned: thus the heart drives the blood into 
it, and by means of the paired cardiac ostia sucks the blood 
out of it; it does not communicate with the exterior by nephri- 
dial pores, nor does its lining develope generative cells. We 
are therefore justified in regarding the body cavity of Peripatus 
as homologous with that of other Arthropoda. It results 
from this that the study of the development of the body 
cavity in Peripatus, which can be traced with comparative 
ease, must be of extreme interest, as tending to clear up the 
question of its celomic or non-ccelomic nature in Arthropoda 
generally. 

Kennel was the first to trace the body cavity of Peripatus. 
He showed that it was in part, at any rate, a pseudoceele, but 
his work was incomplete in that he failed to follow correctly 
the fate of the celom. He thought that the celom became 
merged into the body cavity. If this were correct, it would 
follow that in Peripatus the vascular system and ccelom would 
be in communication. 

As has been fully shown in the preceding pages, this is not 
the case. The celom of Peripatus can be traced through the 
whole development, as a system of spaces shut off at all stages 
of its growth from the system of body-cavity spaces. In the 
adult Peripatus the ccelom is in the following condition: (1) a 
series of nephridia ending internally in small thin-walled 
closed vesicles ; (2) two dorsal tubes—the generative glands 
and the ducts of these, which latter are derived from one pair 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 539 


of posterior somites. The pericardium, heart, whole of the 
body cavity (central, lateral, and leg compartments) are exclu- 
sively pseudoccelic in origin. 

In Peripatus, therefore, the gonads are cclomic, and their 
ducts what Lankester would call nephrodinic. 

The condition of the body cavity and cceelom of Peripatus 
will be best appreciated by comparing it with that of the same 
organs in an Annelid, suchas Lumbricus. 1. In Lumbricus 
the structures corresponding to the nephridial vesicles of 
Peripatus have swollen up and united with one another in pairs 
across the middle dorsal and ventral lines, and after some 
time have become united with one another longitudinally, 
though the separating walls between successive somites for the 
most part persist ; they constitute the coelomic body cavity of 
Lumbricus. 2. In Peripatus the vascular channels, excepting 
the heart, are swollen out to wide channels, more or less 
completely continuous with one another, so as to form four or 
five main vascular tracts, while in Lumbricus they are present 
as minute, branching, well-defined canals. 

On comparing Peripatus with other Arthropodain this con- 
nection we are at once met with these facts : (1) that in no other 
Arthropod are nephridia, recognisable as such, present ; (2) that 
the cavities of the somites cannot be traced beyond a compara- 
tively early stage of development; (3) that the early stages of 
the generative organs have not been thoroughly made out. 

We may, however, with fair probability predict, from what 
we know (1) of the development of Peripatus, and (2) of the 
resemblance of its body cavity to that of other Arthropods, 
that when the development of the latter has been fully worked 
out it will be found that the ccelom of the embryo persists as 
the generative tubes and their ducts, but for the most part 
vanishes (possibly giving rise to glands of a doubtful nephridial 
nature), and that the body cavity and vascular system has an 
exclusively pseudoccelic origin. 

In the Mollusca the ccelom and vascular space have not 
been generally sufficiently distinguished from one another. 
There seems, however, to be no doubt that the pericardial 


VOL. XXVII, PART 35.—NEW SER. PP 


539 ADAM SEDGWICK. 


cavity of the Lamellibranchiata and Gasteropoda repre- 
sents the entire celom. The reasons for this conclusion are 
(1) the pericardial cavity is always shut off from the vascular 
system; (2) it communicates with the exterior by a pair of 
nephridia. 

The generative organs have no relation to the ccelom, so 
far as is known, in either of the above Molluscan gronps; but 
in the Cephalopoda the generative cells are developed from 
the mesoderm lining a certain part of the celom. This gene- 
rative part of the ccelom seems, however, to be shut off in 
the adult from the viscero-pericardial sac. 

This fact, viz. the coelomic nature of the generative organs 
of the Cephalopoda, together with the fact that in other 
Molluscs the generative organs either dehisce into one of the 
nephridia, which morphologically are part of the cclom, or 
possess ducts which open close to or into the nephridial ducts, 
seems, to say the least of it, in favour of the view that the 
generative organs of all Molluscs were originally coelomic and 
that the present arrangement found in the majority is secondary. 
The question, of course, can only be settled definitely by em- 
bryological investigations, but, unfortunately, embryology does 
not speak clearly on the point. 

There can then, from the point of view of adult anatomy, be 
but little doubt that the pericardial cavity (and viscero-peri- 
cardial and generative sacs in Cephalopoda) alone is ccelomic 
in the Mollusca, and that the other system of spaces whether 
simulating a body cavity asin Chiton and other Gastero- 
poda, or forming a close meshwork of spaces as in Lamel- 
libranchs, are vascular and non-celomic spaces; and it is 
only necessary for embryology to bear out this conclusion to 
settle the matter definitely. Unfortunately, embryologists have 
not for the most part sufficiently regarded in their investigations 
the importance of the point, and, for the majority of Mollusca, 
we are in ignorance as to the exact method of development of 
the pericardium as opposed to the heart and vascular spaces. 

Rabl (No. 26), Patten (No. 25 a), and Ziegler (No. 36) have 
described mesoblastic bands in Planorbis, Patella, and 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 537 


Cyclas respectively, arising in the typically Annelidan manner; 
but Ziegler, so far as I am aware, has alone succeeded in ascer- 
taining what part these bands take in the formation of the peri- 
cardium, generative organs and kidney. The generative cells are 
derived from the mesoblastic bands. The pericardial cavity arises 
as two cavities—one in each band—which subsequently unite. 
The kidneys are hollowed out in certain masses of cells of the 
bands. These results, if generally applicable, appear to con- 
firm absolutely the anatomical proof of the celomic nature of 
the Molluscan pericardium. It is interesting to notice that in 
Ziegler’s figure (fig. 27) the developing pericardial vesicles have 
exactly the same relation to the primary body cavity or vas- 
cular space, i.e. they lie within it, as the nephridial vesicles of 
Peripatus have to the vascular cavity of the leg. 

There are certain animals to which the above general con- 
siderations as to the distinctness of the ccelom and vascular 
system do not apply. I refer more especially to the N ermer- 
tinea and Hirudinea. In the Nermertinea, according to 
Oudemans (No. 24), and in the Hirudinea, according to 
Bourne (No. 4a), structures which it is difficult to believe are 
not nephridia open into the vascular system. Ido not intend to 
discuss these cases now, because, on the one hand, this paper is 
already too long, and because, on the other, I do not think our 
present knowledge is sufficient to enable this to be done with 
profit. But I venture to submit with regard to them that 
it is not clear in either case that the vascular system into 
which the nephridia open is homologous with that of other 
types. The very fact that there is a communication with the 
exterior is a strong point in favour of the space being celomic ; 
and it should be remembered that very little is known with 
regard to its development in either group. 

In conclusion, I may point out, that whereas in most 
animals, e.g. Annelida, Mollusca, the vascular space or 
pseudoceele appears before the celom, in Peripatus the ceelom 
appears first, and that in Arthropods, at least, the vascular 
space is in the early stages very commonly occupied by yolk, 
while the celom is entirely free from yolk. ‘This latter 


5388 ADAM SEDGWICK. 


fact would seem to imply some connection between the vas- 
cular space and the enteric space; and I would also desire 
to point out that the ccelom, generative glands, and nephridia 
can, in all animals whose development is at all well known, be 
traced back to a very early embryonic structure, which appears 
at the very beginning of development, gives rise to no other 
structures, and itself arises in very different ways in different 
animals. ‘The embryonic structure [ refer to is in some cases 
the mesoblastic bands, and in others enteric diverticula. That 
these two kinds of coelomic rudiments, as I may call them, are 
homologous cannot be doubted, but which, if either, of the 
methods of origin is primitive, cannot in my opinion at present 
be settled. 

SUMMARY OF THE ABOVE REMARKS ON THE C@LOM AND 

Bopy Cavity. 

Tt is well known that the vascular system of the Arthropoda 
is in direct communication with the body cavity, and that the 
vessels are, for the most part, very rudimentary. In fact the 
blood is driven by the heart or dorsal vessel into the body 
cavity, and returned directly through the lateral cardiac ostia 
into the heart. In no other group of animals does this direct 
communication exist between the heart and the pericardium. 

It is therefore important to determine by the study of 
development, whether or no the blood-containing body and 
pericardial cavities of the Arthropoda are homologous with the 
corresponding structures of other types, in which they do not 
contain blood. 

The development of the Arthropodan heart and body cavity 
is in most cases extremely difficult to follow on account of the 
large amount of food yolk present in the embryos, and there 
is not, at present, any completely satisfactory history of it. 

The development of Peripatus capensis, which is a true 
Arthropod, so far as its body cavity and vascular system are 
concerned, is comparatively easy to follow. 

The coelom appears in the ordinary manner as a series of 
cavities, one in each mesoblastic somite. 

The somites, which are at first ventro-lateral in position, 


DEVELOPMENT OF THE CAPR SPECIES OF PERIPATUS. 539 


soon acquire a dorsal extension, and the cavity in each of them 
becomes divided into two parts—a ventral part which passes 
into the appendage, and a dorsal part which comes into contact 
but does not unite with its fellow of the opposite side on the 
dorsal wall of the enteron. 

The dorsal portions of the somites early become obliterated 
in the anterior part of the body, but posteriorly they persist, 
and those of the same side unite with each other so as to form 
two tubes which are the generative glands. 

The ventral or appendicular portions persist and retain their 
original isolation throughout life. They give rise to two 
structures : 

(1) To a coiled tube, which acquires an external opening 
through the ventral body wall at the base of the appendage 
and constitutes the nephridium of the adult ; 

(2) To a small vesicle, which is contained in the appendage 
and constitutes the internal blind end of the tubular or nephri- 
dial portion of the somite. (The opening of the nephridium 
into the vesicle is funnel shaped, and is commonly known as 
the internal funnel-shaped opening of the former.) 

From the above account it follows (1) that the ccelom of the 
embryo of Peripatus capensis gives rise to the nephridia 
and generative glands, but to no part of the body cavity of the 
adult ; (2) that the nephridia of the adult do not open into the 
body cavity. 

The body cavity of the adult consists, as is well known, of 
four divisions :—(a) the central compartment containing the 
intestine and generative organs, (4) the pericardial cavity, 
(c) the lateral compartments containing the nerve-cords and 
salivary glands, and (d) the portion in the appendage. 

Of these, without going into details, it may be said that a 
arises as a space between the ectoderm and the endoderm, 8, c, 
and d as spaces in the thickened somatic walls of the somites. 
The spaces are in communication with each other. 

The heart arises as a part of a@ which becomes separated 
from the rest. Posteriorly it acquires paired openings into 
the pericardium. It thus appears that the heart and various 


540 ADAM SEDGWICK. 


divisions of the body cavity of the adult form a series of spaces 
which have nothing to do with the celom. They all com- 
municate with each other and seem to form a series of enor- 
mously dilated vascular trunks, of which the heart is the 
narrowest and alone possesses the property of rhythmically 
contracting. 

To sum up it appears that the colom in Peripatus is an 
inconspicuous structure in the adult, and has no connection 
with the body cavity ; while, on the other hand, the spaces of 
the vascular system are but little subdivided, and form the 
heart and various divisions of the adult body cavity. 

Tf these results are applicable to the Arthropoda generally, 
and there is no reason, from the similarity of the adult anatomy, 
to doubt that they will be found to be so, the following mor- 
phological features may be added to those generally stated as 
appertaining to the group—ccelom inconspicuous, body 
cavity consisting entirely of vascular spaces. 

In Vertebrates and most Annelids, on the other hand, the 
parts in question are arranged as follows:—Body cavity 
entirely celomic; vascular spaces broken up into 
a complicated system of channels (arteries, veins, 
capillaries). 

In most Molluscs, finally, the pericardium alone is ccelomic ; 
the vascular spaces being represented by the heart and the 
more or less complicated system of spaces in the body. 


List oF PAPERS REFERRED TO. 

1. Baxrour, F. M.—‘ A Treatise on Comparative Embryology,’ vol. i, London, 
1885 (2nd ed.). 

2. Batrour, F. M.—‘A Treatise on Comparative Embryology,’ vol. ii, 
London, 1881. 

3. Ba.rour, F. M.—“ Notes on the Development of the Araneina,” ‘ Quart. 
Journ. of Mier. Sci.,’ vol. xx. 

4. Batrour, F. M.—‘‘ Anatomy and Development of Peripatus capen- 
sis,” ‘Quart. Journ. of Micro. Sci.,’ vol. xxiii. 

4a. Bournr, A. G.—‘‘ Contributions to the Anatomy of the Hirudinea,” 
© Quart. Journ. of Micro. Sci.,’ vol. xxiv. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. d41 


5. 


21. 


22. 


23. 


. Kennet, J.—“ Entwick. v. Peripatus Edwardsii u. torquatus,’ 


Brooxs, W. K.—“ Lucifer: a Study in Morphology,” ‘ Phil. Trans.,’ 
1882. 


. CraPaRbpE.—“ Studien iiber Acarinen,” ‘ Zeit. f. wiss. Zool., Bd. xviii. 
. Fremurne, W.— Zellsubstanz, Kern, und Zelltheilung,’ Leipzig, 1882. 
. Garrron, E.—“ Beitrige zur Anatomie u. Histologie von Peripatus,” 


Schneider’s ‘ Zoologische Beitrage,’ Bd. i, p. 33. 


. Garrron.— Beitrage zur Anatomie und Histologie von Peripatus,” 


ibid., p. 145. 


. Hacxet, E.—‘“‘ Die Physemarien (Haliphysema und Gastrophy- 


sema),” ‘Jena. Zeitschrift,’ 1877. 


. Heatucots, F. G.—‘ The Early Development of Julus terrestris,’’ 


‘Quart. Journ. of Mier. Sci.,’ vol. xxvi, p. 449. 


. Hatscuex, B.—“ Zur Entwick. des Kopfes von Polygordius,” ‘ Arbei- 


ten a. d. Zool. Inst. Wien,’ Bad. vi. 


. Kennet, J.—“ Entwickelungsgeschichte v. Peripatus Edwardsii und 


P. torquatus,” ‘Arbeiten a. d. Zool. Inst. Wirzburg,’ Bd. vii. 


2 


Theil ii, ‘ Arbeiten a. d. Zoo). Inst. Wurzburg,’ Bd. viii. 


. Kietvenserc, N.—“ The Development of the Earthworm Lumbricus 


trapezoides,” ‘Quart. Journ. of Micr. Sci.,’ vol. xix. 


3. Kowatrvsky, A.—‘ Etude sur ’Embryologie du Dentale,” ‘ Annales du 


Musée d’Histoire Naturelle de Marseille ’—‘ Zoologie,” vol. i. 


. Kowa.Evsky and Marron.—“ Documents pour l’Histoire embryogenique 


des Aleyonaire,” ibid. 


. LANKESTER, E, Ray.—‘‘The Structure of Haliphysema Tumano- 


> 


wiczii,” ‘Quart. Journ. of Micr. Sci.,’ vol. xix, p. 476. 


. Leypic, F.—‘ Zelle u. Gewebe,’ 1885. 
. LirperKtUHN.— Beitrage zur Entwickelungsgeschichte der Spongillen,’ 


’ 


‘ Miiller’s Arch.,’ 1856. 

MarsHaLt, W.—‘ Die Ontogoniev. Reniera filigrana,” ‘ Zeit. f. wiss, 
Zool.,’ Bd. 37. 

Metscunikorr, E.— Spongiologische Studien,” ‘Zeit. f. wiss. Zool.,’ 
Bd. 32. 

Metscunikxorr, E.—‘ Embryologische Studien an Medusen,’ Wien, 1886. 


23a. MoseLey, H. N.—“ On the Structure and Development of Peripatus 


24. 


capensis,” ‘ Phil. Trans.,’ 1874. 


OvuprEmans, A. C.—‘The Circulatory and Nephridial Apparatus of the 
Nemertea,” ‘ Quart. Journ. of Micr. Sci.,’ vol. xxv, Supplement, p. 1. 


25. Patten, W.—* The Development of Phryganids,” ‘Quart. Journ. of 


Mier. Sci.,’ vol. xxiv, 1884. 


542 ADAM SEDGWICK. 


25a. Patten, W.— The Embryology of Patella,” ‘ Arbeiten a. d. Zool. Inst. 
Wien,’ Bd. vi. 

26. Ras, C.— Ueber die Entwick. d. Tellerschnecken (Planorbis),” 
‘Morph, Jahrbuch,’ v, 1879. 

97. SALENSKy, W.—“ Etudes sur le developpement des Annélides,” ‘ Archives 
de Biologie,’ 3 and 4. 

98. Savinte-Kent.—‘ Manual of the Infusoria,’ London, 1881-82. 

29. Scnuizz, F. E.— Trichoplax adherens,” ‘ Zoologischer Anzeiger,’ 1883, 
p- 92. 

30. Scuutze, F. E.—“ Die Familie der Aplysinide,’ ‘ Zeit. f. wiss. Zool.,’ 
id xxx. 

31. Sepewick, A.A—“‘On the Original Function of the Canal of the Central 
Nervous System,” ‘Studies from the Morphological Laboratory, Cam- 
bridge,’ vol. ii, Pt. 1. 

82. Sepewick, A.---‘‘On the Origin of Metameric Segmentation,” ‘ Quart. 
Journ. of Micro. Sci.,’ vol. xxiv. 

33. Sepewick, A.—“ The Development of Peripatus capensis,” ‘ Proc. 
Roy. Soc.,’ 1885. 

33a. Sepewick, A.—“On the Development of the Cape Species of Peri- 
patus,” Pts. I and II, ‘Quart. Journ. of Micro. Sci.,’ vols. xxv 
and XXvi. 

34. Sottas, W. J.—“On the Development of Halisarca lobularis,” 
‘Quart. Journ. of Micro. Sci.,’ vol. xxiv. 

35. SpencEL.— Notes on Sipunculus,” ‘Tagebl. Naturf. Vers. Miinchen,’ 
1877. 

36. ZineterR, H. H.—* Die Entwick. v. Cyclas cornea,”’ ‘ Zeit. f. wiss. 
Zool.,’ Bd. xli, p. 525. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 543 


EXPLANATION OF PLATES XXXIV, XXXV, 
MXXVE & MXXVII, 


Illustrating Mr. A. Sedgwick’s Paper on “ The Development of 
the Cape Species of Peripatus.” 


List of Reference Letters. 


a. Anus. am. Amoeboid wandering cells in body cavity (pseudoccele). 
a. s. ph. Septum attaching anterior part of pharynx to dorsal body wall, 
at junction of somites 1 and 2. a. v. Anterior diverticulum of nephridium 
of oral papilla. &. Space formed by withdrawal of endoderm from ectoderm. 
b. Space formed in the parietal thickening of the somites. 4. app. Space 
formed in appendage. 4. dc. Space formed by separation of endoderm from 
ventral ectoderm. 0. dc\..The ventral of the two spaces formed in wall of 
somites at their ventral corner. 4. 4. Space formed by separation of endoderm 
from dorsal ectoderm. 4. /at. Space formed in parietal mesoderm. 0. pe. The 
dorsal of the two spaces formed in the wall of the somites at their ventral 
corner. Or. Brain. duc. cav. Buccal cavity. cc. c. Cords of cells projecting 
into pericardial cavity. c.g. Cerebral grooves. c.g. Groove in brain. com. 
Commissure between the two halves of the brain. c. 0. 2. Circumoral part 
of central nervous system. d. . Dividing nuclei of endoderm near the lip 
of the blastopore. d.s. Dorsal sheet of somatic mesoderm. d.s. 1, 2, &. 
Dorsal part of somites 1, 2, &c. e. Hye. ec. Hctoderm. ez. Endoderm. /. 
Funnel-shaped opening of tubular part of nephridium into internal vesicle. 
F.1, &. Legs. (f. dl. Line of obliterated blastopore between the mouth 
and anus. gez. Germinal nuclei. gez. d. Genital duct. gez. 0. Generative 
organ. g.andy.g. Alimentary canal. J. Jaw. 7. s. Ventral organ of jaw. 
I. Lips. /e. Internal backward projection of jaw. 7. 7. Limb-ridge. 7.8.1, 2. &. 
Lateral portions of somite contained in the legs. 7. s.¢. 1, 2, &c. Tubular 
portion of nephridial celom of appendages 1, 2, &c. (segmental organ). 
1. s.v.1, 2, &. Internal vesicular portion of nephridial ccelom of appendages 1, 
2, &c. M. Mouth. mé. Mesoblastic band. me. Anterior part of thickening 
of parietal mesoderm of the somites. m./. Muscles of internal projection 
of jaws. m.ph. Muscular wall of pharynx. mm. ¢. Posterior part of thickening 
of parietal mesoderm of the somites. 0.7.1, 2, &c. The external opening 
of nephridium of somites 1,2, &c. or. p. Oral papilla. 0. s. 3. Opening of 
somite 3. p.g. Primitive groove. pf. Pharynx. ph. m. Pharyngeal meso- 
derm from the splanchnic walls of the anterior somites. p. p. pre-oral 
pouch of alimentary canal. pr. Proctodeal lining. p. sf. Primitive streak. 


544 ADAM SEDGWICK. 


R. Rectum. 98. 1, 2, 3, &c. The first, second, and third somites, &c. 
sal. gl. Salivary gland. sep. Septum dividing the lateral portion of the 
somite from the dorsal. s/.g. Slime-gland. J. 0. 1. Rudimentary nephridial 
portion of somite. s¢. Stomodeum or its lining. 7. Tongue. v. ex. Ventral 
endoderm of alimentary canal derived from the cells intermediate between the 
ectoderm and endoderm when the blastopore was open along its whole length. 
v. 2. Ventral nerve-cord. v.0. Ventral organ. v.s. Ventral sheet of somatic 
mesoderm. v. sp. Vascular space. . White matter of central nervous 
system. 


All the figures are of Peripatus capensis, and drawn with Zeiss’s 
camera, ob. C, oc. 2, unless it is otherwise stated. 


Fic. 1.—Transverse section through a late embryo of Stage a (length 
*53 mm.), two sections behind the blastopore. The primitive groove is very 
deep and is hardly to be distinguished from the blastopore. The mesoblastic 
bands do not extend in front of the hind end of the blastopore. The primi- 
tive groove was confined to the front end of the streak. The latter extended 
through eighteen sections. ; 

Fics. 2 and 3.—Two transverse sections through an embryo of Stage B 
(length *65 mm.) with one somite, still solid, and separate from the front end of 
the mesoblastic band. Primitive streak extended through twenty-one sections. 

Fig. 2. Through the single somite which is present. (The section is 
slightly oblique, passing in front of the somite on the left side.) 

Fig. 3. Two sections in front of the anterior end of the somite. The 
endodermal nuclei at the lips of the blastopore were dividing actively. 
One such is shown at d. x. 


Fic. 4.—Section through a late embryo of Stage B (Stage of fig. 25, 
Pt. I) in front of the mouth. Reduced 3. 

Fic. 5, a—f—A series of sections through an embryo (length 1 mm.) 
of the same age as the last (Stage B, fig. 25, Pt. I). Reduced 3. Four 
separate somites could be distinctly made out on each side. Thirty sections 
were obtained through the streak. The groove extends the whole length of 
the streak. 

a. Through the mouth. 

b. Between the mouth and anus. The blastopore lips have fused ; their 
line of fusion is marked by a slight groove (f. 4/.). 

ec. Through the hind end of the anus. The mesoblastic bands in this 
region are not yet broken up into somites. 

d. Through the front end of the primitive streak, four sections behind 
the last. 


e. Through primitive streak, eight sections behind last. 
J. Through primitive streak, nine sections behind the last. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 9545 


Fic. 6, a—d.—A series of sections through an embryo of Stage c (fig. 26, 
Pt. 1). Reduced 3. 

a. In front of the mouth, through the pre-oral lobes. he anterior wall 
of the alimentary (ez.) just touched. 

6. Through the mouth. 

c. Between the mouth and anus. Wide separation of the somites. Very 
thin ventral ectoderm . 

d. Through the hind end of the body, in the region of the curvature. 
The embryo is cut in two places, through the anus and through the 
growing point (primitive streak and gr oove). 


Fics. 7—12 are from a young embryo of Stage p (fig. 28, Pt. I). The 
embryos of this age are always much narrower, both dorso-ventrally and 
laterally, than those older or younger. Reduced 3. 

Fig. 7. Section through the roots of the b udding antenne. 
Fig. 8. Through the anterior part of the mouth. 


Fig. 9. Through the posterior part of the third somite, in the region of 
the outgrowth of the oral papilla (or. p.). The sheets of cells extend- 
ing from the dorsal and ventral ends of the somites are present (d. s. 
and v.s.). The endoderm and ectoderm have separated from one 
another, excepting along the dorsal middle line. The cavity so formed 
is marked 4. 4. and 6. dc. 

Fig. 10. Through the anterior part of the fourth somite (in front of the 
region of the future leg), to show the anterior part of the thickening 
‘of the somatic mesoderm (me.). 

Fig. 11. Through the region of the future leg (posterior part of the 
somite), showing the position of the thickening on the ventral side of 
the outgrowth. 

Fig. 12. Through the fifth somite. The changes which have produced 
the parietal mass of cells from the somatic mesoderm have not yet 
occurred here. The somite is partly collapsed dorsally and ventrally. 

Fie. 13.—Through the third somite of an em bryo of Stage p, slightly older 
than the last. Reduced 3. On the left haud side the section passes through 
the posterior part of the somite, and shows the developing oral papilla and 
septum tending to divide the cavity of the somite into a part within the 
appendage and a part within the body. ‘The first trace of the third system of 
body cavity (4. dat.) is visible. 

Fic. 14.—Section through an embryo of Stage p, through the pre-oral 
somite, brain, and eye. The latter (e.) has the form of an open pit. Re- 
duced 3. 

Fie. 15.—Section through a slightly older embryo, showing a more ad- 
vanced stage in the brain and eye. Reduced 2. 


546 ADAM SEDGWICK. 


Fic. 16, a, 6.—Two sections through the mouth of a late embryo of Stage 
D (fig. 29, Pt. I). Reduced 3. 
ad. Through the anterior part in the region of the stomodeal in- 
growth. 
b. Through the posterior part. 


Fic. 17, a—d.—A series of sections through the region of the third somite 
of an embryo of same age as the last (fig. 29, Pt. 1). Reduced 4. 

a. Through the anterior part of the somite, in front of the attachment 
of the parietal thickening (me.). The parietal thickening always 
appears to be free in front; it is attached behind. 

6. Point of attachment of parietal thickening to somatic mesoderm. 

c. Two sections further back. 

d. Six sections further back through the region of the appendage 
(or. p.). 

Fie. 18, a—c.—Three sections through the seventh somite of the same 
embryo as that from which fig. 17 was taken. Reduced 4. 

a and & show the leg-ridge, which in fig. 18c—a section through the 
hinder part of the somite—is enlarged to form the developing fourth 
leg. 

A few sections behind Fig. 18 ¢ the cavity of the somite extends into the 
appendage. The anterior less developed part of the mesodermal 
thickening lies immediately within the leg-ridge, while the posterior 
larger part occupies the appendage itself. 


Fies. 19, a, 6; 20; 21, a—c are from sections through young embryos of 
Stage BE. Reduced 3. 

a. Through the head and first somite. The optic pit is closed. 

b. Through the mouth and first somite. This section shows the 
developing lip (Z.). In this and the previous section the mesoderm 
cells next the stomodzal ectoderm have proliferated to form the com- 
mencing pharyngeal and lingual musculature. 

Fig. 20. Through the second somite, with the third somite overlapping 
dorsally. 

Fig. 21 a. Through the anterior part of the third somite. The limb- 
ridge (/. 7.) and the mesodermal thickening with its cavity (0. Jat.) are 
well shown. 

6. Ten sections further back, through the anterior part of the appen- 
dage (oral papilla). The mesodermal thickening is much larger. 

c. Through the centre of the appendage. The somite is nearly divided 
into two parts by the septum (sep.). The portion in the appen- 
dage sends down a diverticulum, which lies against the outer border 
of the nerve-cord and reaches the ectoderm. 


Figs. 22—- 25 are through a late embryo of Stage ©. Reduced $. 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 54:7 


a. Through the pre-oral region, at the level of the cerebral commissure. 
The commencing cerebral groove (c. g.) is shown. 

b. Through the mouth and hind end of first somite, showing the 
rudimentary nephridium (s. 0. 1). One half of the section only is 
represented. (Drawn with Zeiss’s D, oc. 2). 

Fig. 23, a—e. A series through the third somite. 

a. The anterior part of the mesodermal thickening and its cavity (d’.) is 
much enlarged. The section passes through the hind end of the 
jaw (J.) and the lip (Z.). 

b. A few sections further back. A tube (a. v.) ending blindly in 
front, and opening behind into the limb portion of the somite, is 
present. 

c. Nine sections behind fig. 23 4, through the point of junction 
of the portion of the somite in the body (s. 3), the portion in the 
appendage (/. s. 3), and the anterior diverticulum (a. v. of Fig. 23 0). 

d. Through the centre of the appendage, seven sections behind the 
last. The anterior end of the fourth somite (s. 4) is visible, and 
rudiment of the slime-gland as an ectodermal ingrowth at the apex the 
of the oral papilla (s/. g.) is present. 

e. Nine sections behind the last. The external opening of the third 
somite covered over by the lip (Z.), which has grown back to this 
point, and the mesodermal thickening and its cavity (4. Jat.) of the 
wall of the fourth somite are present. 

Fig. 24. Between the oral papilla and first leg, through the fourth somite, 
twelve sections behind fig. 23 e. 

Fig. 25. Through the fourth leg. The eighth somite overlaps dorsally. 
The leg portion of the seventh somite opens to the exterior (0. s. 7). 
The great ectodermal thickening, which is so conspicuous in embryos 
of this stage, is cut through at d. 

Fic, 26.—Transverse section through the anus and twentieth somite of an 
embryo of Stage p. The rudiment of the proctodeum with its special lining 
(pr.) is present. The germinal nuclei (gez.) are present, both in the endoderm 
and splanchnic mesoderm. 


Fic. 27.—Transverse section through an embryo of Stage =, at the region 
of the seventeenth somite. The germinal nuclei are present in large numbers. 
The ccelom has not yet become divided into body and leg portions (see right 
hand side of section). 

Fic. 28.—Longitudinal vertical section through an embryo of Stage c. 
The section passes through mouth and anus. The hind end of the body 
is bent round and projects forward, bearing the primitive streak on its ventral 
surface. The alimentary canal reaches the anterior end of the body, and the 
transverse commissure (com.) connecting the two halves of the cerebral 
ganglion is visible in front of the mouth. The modified endoderm (s/.) or 


548 ADAM SEDGWICK. 


ingrown ectoderm—whichever view of its nature be taken—of the anterior 
(future dorsal) wall of the stomodeum is present. Zeiss’s A, oc, 2. 


Fic. 29.—Longitudinal vertical section through an embryo of Stage D. 
The hind end of the body has grown and become spirally coiled. The primi- 
tive streak is still present—but in a rudimentary form—on the ventral surface 
behind the anus. It is marked by a slight pit. A section to one side of the 
middle line of this embryo shows a considerable mass of nuclei in connection 
with it. The anterior end of the body has been drawn back in such a way 
that no part of the alimentary canal projects in front of the mouth. The 
anterior wall of the stomodeum is therefore now inclined dorsalwards and 
slightly backwards. Zeiss’s A, oc. 2. 


Fig. 30.—Longitudinal vertical section through the hind end of an embryo of 
Stage E. The anus is now practically terminal, and the primitive streak 
aborted. A rudiment of the latter still indeed exists, but there are no lateral 
masses of nuclei. The rudiment of the proctodeum is present (also in the 
last figure). Zeiss’s A, oc. 2. 

Fic. 31.—Longitudinal vertical section through the anterior end of an 
embryo of Stage EB. Zeiss’s C, oc. 2. Reduced 34. The anterior ectodermic 
wall of the body has grown forward in the middle line, and separated from the 
anterior wall of the alimentary canal (cf. fig. 34, Pt. I). The anterior wall 
of the stomodzum has now become its dorsal wall, and is directed backwards ; 
and an anterior pouch of the alimentary canal lies dorsal to it. The ventral 
wall of the stomodeeum has began to be formed. 


Fic. 32.—Longitudinal horizontal section through the anterior end of an 
embryo of Stage D. Zeiss’s A, oc. 2. 


Fics. 833—42 are transverse sections of an embryo of Stage F. 


Fig. 33. Through the first somite, brain and cerebral grooves. The 
section passes in front of the region where the two halves of the brain 
are connected, and the eye (e.) is just included in the section on the 
right side. Reduced 4. 

Fig. 34. The section is taken at the junction of somites 1 and 2, and 
passes through the posterior part of the brain, the anterior part of the 
permanent buccal cavity, and the anterior wall of the pharynx (pA.) 
The posterior part of the cerebral grooves (c. g.) are seen opening into 
the buccal cavity, the roof (Z.) of which becomes the so-called tongue 
of the adult. The jaw (J.) is visible on the right side. Reduced 3. 

Fig. 35. Through the mouth (m.) ; the opening which leads from the buccal 
cavity into the pharynx. In consequence of the contraction of the 
ectoderm, the second somite (s. 2) is hardly visible, and the median 
part of the space J. A. is obliterated. Reduced 3. 

Fig. 36. Behind the mouth, through the oral papille (07. .). The slime- 
gland (s/.g.) is cut through just behind its opening, and the anterior 


DEVELOPMENT OF THE CAPE SPECIES OF PERIPATUS. 549 


part of the ventral ccelom of the third som ite (internal vesicular por- 
tion, 7. s.3.) is shown. Reduced 3. 

Fig. 37. Immediately behind the junction of the pharynx and mesenteron, 
through the external opening of the salivary gland (ventral division of 
somite 3) into the hinder part of the buccal cavity (duc. cav.). 

Fig. 38. Through the dorsal division of somite 4 and the hind part of the 
ventral division of somite 3, the opening between the two parts (in- 
ternal vesicular portion, /. s. v. 3, and tubular portion, /. s. ¢.3) of which 
are shown. m./. Muscles of internal projection of jaws. 

Fig. 38 a. One side of a section, a little behind fig. 38, to show the com- 
mencing salivary gland (sal.g.). Zeiss’s D, oc. 2. Reduced 3. 

Fig. 39. Between the oral papilla and first leg. 

Fig. 40. Through the third leg, to show the ventral division of the sixth 
somite. The tubular portion of this (nephridium of third leg) isa 
straight tube (the lumen is not distinct, but this was probably due to 
the contraction of the specimen), opening externally at o. z. 6, and in- 
ternally into the internal vesicular portion (J. s. . 6). 

Fig. 41. Through the twentieth somite, in the region of the generative cells. 
The differentiation of the various divisions of the body cavity has hardly 
reached this part of the body, 4.4., d.pc., 6.dc'., being only present in 
a rudimentary form. The endoderm is slightly shrivelled up. The 
generative nuclei are still in the endoderm, though some of them project 
into the body cavity. Zeiss’s D, oc. 2. Reduced 3. 

Fig. 42. Through the rectum and anal papille (rudimentary eighteenth leg). 
The dorsal and ventral divisions of the somite are in communication. 

Fics. 43—46 are from old embryos of Stage F. Zeiss’s D, oc. 2. Re- 
duced 4. 

Fig. 43. Through the seventeenth somite, to show the dorsal division of the 
somite (d.s.), which may now be called the generative gland. The gut 
has separated from the latter, so that the two divisions of the part of 
the body cavity marked 4. dc’. communicate. The dorsal part of the 
section only is drawn. 

Fig. 44. Through the anal papilla (rudimentary eighteenth leg) and twenty- 
first somite. The two parts of the somite are in communication, and 
the ventral has almost acquired an opening to the exterior. This 
opening will be the generative opening. 

Figs. 45 and 46.—Dorsal parts of two transverse sections from the middle 
region of the body in front of the generative region ; 46 is the anterior. 
In 45 the dorsal division of the somite (d.s.) is not yet obliterated; in 
46 it has entirely vanished, and is represented only by the thickened 
layer of cells which form the veutral wall of the heart. 


Fies. 47 and 48.—Through the generative organs of an embryo of Stage «, 


550 ADAM SEDGWICK. 


in the region where they are detached from the pericardial floor. Zeiss’s F, 
oc. 2. 

Fic. 49.—Longitudinal vertical section through the anterior part of the 
body of an embryo of Stage r. Reduced 3. 

Fic. 50.—One side of a transverse section throngh a young embryo of Stage 
F. To show the latest stage of the rudimentary nephridium of the first somite 
(s. 0. 1), in close contact with the outer side of the hind part of the brain (a 
few nuclei of the latter are indicated). Zeiss’s D, oc. 2. Reduced 3. 

Fic. 51.—One side of a transverse section through the brain of a late em- 
bryo of Stage r. To show the two separate parts of the first somite. The 
cerebral grooves are closed. Reduced 3. 

Fic. 52.—Transverse section of the sixth leg of an old embryo of Stage Fr. 
To show the funnel-shaped opening (/.) of the tubular portion of the nephridium 
into the vesicular internal portion (/. s. v.), and the relation of the latter to the 
body cavity (pseudoccele) of the leg (4. app.). Zeiss’s D, oc. 2. Reduced 3. 

Fic. 53,@ and 6. Longitudinal horizontal sections of two contiguous legs 
of an embryo of same stage as last. Reduced 3. 


OBSERVATIONS ON OCRIODRILUS LAOUUM. Boul 


Morphological and Biological Observations on 
Criodrilus lacuum, Hoffmeister.’ 


By 


Dr. L. Orley. 
Zoolog. Instit. University of Budapest. 


With Plate XXXVIII, figs. 1 to 8. 


In Vejdovsky’s very complete work, ‘System und Mor- 
phologie der Oligocheten,” Prag., 1884, which bears the 
character of a useful text-book on the morphology of the 
Oligocheta, I find only a scanty and incomplete account of 
the very interesting terricolous form, Criodrilus. On pages 
16 and 58 he says: “ Lage der Hoden, Eierstécke, Samen- 
leiter und Samentaschen, sowie Gurtels unbekannt.” ‘ Leider 
weiss Man sehr wenig von dem Leben eines so merkwirdigen 
Oligocheeten.” I think that these assertions by this well- 
known investigator justify me in publishing my own observa- 
tions, incomplete though they are, relative to this worm. 

Criodrilus lacuum was discovered by the well-known 
German zoologist Fritz Miller, in 1844, in the so-called 
“Tegel-see,” near Berlin, and in the following year was de- 
scribed and figured by Hoffmeister.? It is almost incredible 
that fully thirty years should have elapsed since its discovery 
without its being found again. In 1876 this worm, found in 
a branch of the Danube near Linz, was again mentioned by 


1 Translated from the MS. by Wm. B. Benham, B.Sc. 
2 «Die bis jetzt bekannten Arten aus der Fam. der Regenwiirmer,’ Bruns- 
wick, 1845, p. 41. 


VOL, XXVII, PART 4,—NEW SER. QQ 


Soe DR. L. ORLEY. 


Hatschek! in his work, which furnishes contributions to the 
knowledge of the development and morphology of the 
Annelids. 

Two years later Hatschek® recognised this worm, described 
its development, and provided Vejdovsky with material for his 
researches.® 

Like Hatschek, I found Criodrilus in the neighbourhood of 
Buda-Pesth, and described it in a communication to the Hun- 
garian Academy of Science.* Recently it was found by Rosa’ 
in Italy, where it lives in the basin of the Po; somewhat 
earlier, too, it was noted by Panceri.® 

I have no doubt that it exists in other parts of Europe, and 
that only its habit of concealing itself has placed it amongst 
rare and hitherto little known Earthworms. The following 
description ought to lead to the discovery and to the better 
knowledge of it. 


Criodrilus lacuum. Hoffm. 


1845. ‘ Die bis jetzt bekannten Arten d. Faun. d. 
Regenwiirmer.’ 


A mudworm 4—12 cm. in length, and about 5—10 mm. in 
breadth, of a dark brown or greenish colour dorsally, with 
lighter, sometimes reddish colouration ventrally, with rusty- 


yellow areole, and milk-white, horn-like spermatophores near 
the male genital pore. 


The body is quadrangular (though this is less noticeable 


‘ *Sitzungsber. der Kais. Akad. d. Wiss. in Wien,’ Bd. 74, pp. 442—459. 

2 “Studien z. Entwick. d. Anneliden,” ‘ Art. Zool. Inst. Wien,’ Bd. 1. 

* (a) ‘ Monograph. d. Enchytreiden,’ Prag., 1879. (4) “ Ueber der Entwick. 
des Herzens bei Criodrilus,” ‘Sitzungsb. k. béhm. ges. der Wiss..’ Prag., 
1879. (¢) ‘System und Morphologie der Oligocheten,’ Prag., 1884. 

* (a) Amagyar. ‘ Oligochet. Fauna,’ Buda-Pesth, 1881. (4) ‘ Revisio et 
distributio specierum terricolarum regionis palarctice,’? Buda-Pesth, 1885. 

® ** Nota sui Lombrici del Veneto,”’ ‘ Atti del R. Inst. Ven. di Sci. lett. ed. 
atti, b: 1¥aiS.evie 


® “ Catalogo degli anellidi d’Italia,” ‘ Atti d. Soc. Ital. d. Sci. Nat.,’ 1875, 
xvii, p. 201. 


OBSERVATIONS ON CRIODRILUS LACUUM. 553 


anteriorly), gradually narrowing posteriorly, and ending in 
a pointed, yellowish, and often regenerated tail. When the 
worm is contracted the dorsal surface is usually depressed. 

The number of somites is 200—250, or more. The somites 
are well defined, obscurely triannulated, and somewhat pressed 
together towards the tail. There is no dorsal pore. The last 
or anal somite is longer than those just in front. The anus 
itself is dorsal. There are rounded swellings on the somites 
Xe Sa, XU, ANG, XII. 

The prostomium is moderately elongate and as long as the 
buccal somite, from which it is distinctly separated, without 
having a prolongation dorsally or a furrow ventrally (Hoff- 
meister’s description—“ Die Lippe ist mit dem Mundseg- 
ment verwachsen”—is incorrect). The prostomial pore is 
indistinct. 

The four rows of sete extend along the corners of the body. 
The distance between the rows is nearly equal. The setz of 
each pair are somewhat apart; they are not prominent, and 
are slightly curved with rough ends. 

The genital organs are on the same plan as in the Lum- 
bricinee, and present no peculiarities. The seminal reservoirs, 
with their lateral czeca, extend through the somites 1x to x11. 
The true testes last for only a short period, during which 
they early break up into spermatogonia, so that I could recog- 
nise the two pairs, which lie in the somites x1 and xu, only by 
the remnants. The two pairs of ciliated rosettes have an 
obscure plate-like structure ; those of the first pair lie on the 
septum between the somites x and x1; those of the hinder pair 
on that between xi and x11, so that they project into the somites 
x1 and xi respectively. The sperm ducts are spirally coiled 
at the base of the rosettes, unite with one another at the level 
of the somites x11 and x11, and thence a wider, tortuous, 
common canal extends on each side to the external pore on the 
ventral surface of somite xv, between the two couples of sete. 
The termination is simple; without an atrium there is only a 
large gland (“vulva’”’ of Hoffmeister), which probably serves 
for the construction of the cocoon. There are two pairs of 


554 DR. L. ORLEY. 


spermathece, which appear to open on the ventral surface 
between the somites 1x, x and x, x1 respectively. 

The ovaries lie in somite x11I, one on each side of the ventral 
blood-vessel, attached to the hinder face of the septum between 
the somites x11 and x111; they contain many ripe eggs, which 
are chiefly found at the free end of the ovary. I have not 
found a pointed prolongation at the distal end of the ovary. 
The oviducts lie opposite each ovary between the somites XIII 
and xiv; their plate-like funnels project into the former somite, 
and their very diminutive canal opens to the exterior on the 
ventral surface of somite xiv. 

I have not found separate yolk and cement glands. The 
horn-like spermatophores (Hoffmeister’s “ penis-formige 
Korpchen ”), 6 to 8 mm. in length, are found in the neighbour- 
hood of the male pore; their number is variable, and they are 
usually placed ventrally, although exceptionally they are to be 
met with on the dorsal surface. As a rule only two are situated 
on the neural side of somite x11, close to the ventral sete ; 
though very often they are some distance from them. They 
are always in pairs, from two to six in number ; only once have 
I found eight spermatophores, which were arranged irregularly 
round the male pore. These structures are products of copula- 
tion, and appear only during this operation ; whether they are 
formed in the sperm-duct, or by the swellings in front of the 
genital pore, I am unable to say with certainty. The spermato- 
phore, the shape of which is exactly rendered by fig. 7 (Pl. 
XXXVIII), consists of an homogeneous, hyaline, mucous sub- 
stance, in which are embedded numerous fine, enlongated fila- 
ments. The lumen is fairly wide and deep, open at the end, and 
filled with bundles of spermatozoa, which are massed together in 
a spiral fashion. The fibres in the wall can scarcely be the pro- 
duct of the epiderm cells; moreover, the spermatophores vary 
so much in number and position that one can scarcely admit 
that they are formed by the swellings. I think it more likely 
that they are formed in the spermathecz, there filled with sper- 
matozoa, and that they are then attached in position during 
mutual copulation. The broad basal portion clings fast to the 


OBSERVATIONS ON CRIODRILUS LACUUM. 55a 


cuticle, but never grows closely with it, so that the spermato- 
phore very easily falls away. That the great areola round the 
male pore and the swelling in front of it play an important part 
in copulation cannot be doubted, for, after the laying of the 
eggs, these structures immediately decrease in size. In speci- 
mens which I collected at the end of June I could find neither 
the swellings nor the areola, and in some even the male pore 
also had become indistinct. 

As to the time of sexual maturity of Criodrilus nothing 
positive is known. According to Vejdovsky the maturity 
seems to be attained in the months of June and July, since 
Hatschek found the cocoons with segmented eggs and embryos 
in the middle of June, whilst Hoffmeister mentions the worms 
furnished with ‘ pseudo-spermatophores ” at the beginning of 
July; Vejdovsky himself has not studied mature worms. My 
researches, however, extending over many years, show that the 
embryos escaping from the egg in summer may attain sexual 
maturity as early as February or March in the following year ; 
indeed, in the most favorable seasons copulation may even 
take place in these months. Copulation and egg laying take 
place almost certainly in June, since I have found at the 
beginning of July of this year no cocoons with embryos. The 
best sign of maturity are the large and very striking sperma- 
tophores, which are to be found regularly from March to the 
end of May, certainly not later. The embryos escape from the 
cocoons in May, June, and July; at the end. of the latter 
month I have collected only empty egg cases. At first the 
young worms are to be found amongst the thick roots of 
aquatic plants, only later in the mud, where they pass the 
winter and attain maturity. The clitellum, so very character- 
istic of the Lumbricinz, is, as Hoffmeister rightly insisted, 
absent. I have for many years collected these worms at all 
seasons, yet I have found no trace of a clitellum, nor of the 
so-called “ tubercula pubertatis ;” the great glandular areola 
of the male genital pore appears to replace the clitellum. 

The egg cases of the Lumbricine are known as roundish- 
oval chitinous capsules with pointed appendages, and are 


556 DR. L. ORLEY. 


presumably secreted by the clitellum. The cocoons of the 
Criodrilidz, however, are spindle-shaped, parchment like struc- 
tures with a colour that changes; they are about 5 cm. in 
length, rapidly diminishing towards each end. One end, 
drawn out into strongly fibrous threads, serves for attachment 
to the roots, or more rarely to the leaves and branches of 
water plants; the other end truncated, with a dentate edge, 
allows the embryos to escape. As is the form, so also is the 
colour different. The perfectly newly laid cocoons are nearly 
transparent, horny yellow in colour, but after a time they 
become darker, and towards the time of hatching of the 
embryos they are blackish in colour. This change in colour, 
which reminds me of the egg cases of Shark embryos,' may 
here too be traced to chemical changes. 

The substance of the egg cases is not wholly chitinous ; at 
any rate a large portion is dissolved in caustic potash ; on the 
contrary, a sort of coagulated yolk and mucus take a large 
share in their constitution. The substance itself is very easily 
wetted, so that liquids and gases can diffuse through it. 

The inside is filled with a fluid albuminous substance, allied 
in density to white of egg; in this from eight to twenty eggs 
are embedded, and in it are found the remains of the sub- 
stance of the spermatophores as well as innumerable sperma- 
tozoa, which are to be met with especially round the develop- 
ing eggs; their appearance is reproduced in fig. 8, Pl. XXX VIII. 
The number of eggs is very variable; usually only one third 
of the fertilised eggs develop; the largest number of embryos 
in a cocoon was eight, the smallest two. 

The structure of these egg cases is especially well shown, if 
freshly laid eggs, preserved in alcohol, are placed in water in 
order that they may swell up. When such cocoons are care- 
fully examined the swollen part is found to be banded; these 
bands appear to correspond with the somites of the anterior 
part of the body. This correspondence, as well as the fibrous 
structure of the outermost layer (fig. 2) and the remains of the 


1 LL. Orley, “Zur Physiol. der Haiembryonen,” ‘Termeszet. fiizetek,’ ix, 
1885, Buda-Pesth. 


* 
OBSERVATIONS ON CRIODRILUS LACUUM. 557 


spermatophores in the cocoon, allows one to suppose that the 
moulted skin of the anterior part of the body takes a share in 
the formation of the cocoon, just as in Lumbricine and Nephe- 
lide, the egg case probably owes its origin to the moulting of 
the clitellum. Since, however, the number of bands in this 
egg case exceeds twenty, it is probable that the somites lying 
behind the genital pores also take part in the formation of 
the cocoon.!' The tough secretion which builds up the chief 
portion of the cocoon, is probably furnished by the large swel- 
lings around and in front of the genital pores, and by the 
inner lining of the sperm duct. The process of formation of 
these egg cases, which alone would lead to positive results, I 
have unfortunately been unable to watch. Worms which I 
kept in my aquarium always hid themselves under cover of the 
roots of Sium latifolium, so that I was unable to overlook 
their operations. 

A transverse section through this cocoon shows three layers; 
an inner yellowish and homogeneous layer, an outer strongly 
fibrous, and a middle layer of interlaced strands (fig. 4). The 
fibrous layer is most easily seen at that end of the cocoon 
which is drawn out into threads (fig. 2), where they are col- 
lected together into strands and finally separate out into 
elastic fibres ; the latter serve for attachment to aquatic plants. 
Towards the swollen portion the fibrous layer becomes thinner 
at the expense of the middle layer. 

The middle layer (fig. 5) consists of innumerable interwoven 
bundles which are not separated into fibres. The network is 
densest below and becomes looser above. It looks so very 
much like a plant tissue, that a young botanist of this country 
at first disputed as to the substance of the tissue. Some 
thought it of vegetable origin. 

The lowermost or basal layer is made up of very many 
extremely delicate strata (fig. 6); these show a striated struc- 
ture, and contain here and there fibrous elements. This layer 
projects from the free end of the cocoon (fig. 3), is strongly 
folded, and serves to close the egg case. 


1 See the following paper, in which the Clitellum is described. —TRANSLATOR. 


558 DRG. ORLEY. 


The young are of a reddish colour, about 2—3 cm. in 
length, when they leave the cocoon. They escape from the 
free end of the egg case by the separation of the two “ lips,” 
which at first, owing to their elasticity, were closed. 

Hatschek supposes a Criodrilus to lay several cocoons, 
because the number of worms was very small in comparison 
with the cases which he found. I placed a Criodrilus amongst 
the roots of Sium latifolium, and in a few days found two 
quite transparent, and therefore fresh, cocoons. It appears to 
me, therefore, that a Criodrilus will lay two cocoons, in cor- 
respondence with the number of the sperm ducts. It is natural 
that more cocoons than worms should be found, since empty 
cocoons appear throughout the year attached amongst the 
roots; one sometimes finds old, black, very much frayed co- 
coons in certain places by thousands ; of freshly laid cocoons, 
on the contrary, I have never collected more than double the 
number relatively to the mature worms. 

Habits. — In isolated branches of large rivers, e.g. the 
Danube, as well as in flowing streams with muddy beds, there 
are places where the bottom is very nitrogenous owing to the 
decomposition of organic matter. In such places there are 
usually many aquatic plants with dense roots, which (at any rate 
here in Buda-Pesth, in the streams flowing into the Danube) 
are met with in great abundance. Amongst these plants I 
found a very large quantity of Sium latifolium, L., the 
favourite plant of Criodrilus. 

If these plants with their roots are taken out in the spring, 
and the “covert” carefully examined, one finds the long 
spindle-shaped cocoons and Criodrili engaged in egg-laying, 
so closely interlaced with the roots that they can only be 
separated with difficulty. The egg cases are at first sight so 
very like the Enteromorpha, that young botanists might dispute 
as to whether they are of vegetable or animal origin. It is 
only during the breeding season that the worms are to be 
found amongst the roots, where copulation and egg-laying 
takes place. After the completion of these operations they 
return to the mud, where their genital organs commence to 


OBSERVATIONS ON CRIODRILUS LACUUM. 559 
degenerate. I have never been able to study the copulation, 
though I have looked at many worms. The swellings, around 
and in front of the male genital pore, are, however, so very 
swollen during the breeding season, and secrete so much mucus, 
that I presume the copulation takes place as in the Lumbri- 
cine. The worms found in the mud are very active, they 
burrow deep into the mud; I have even met them at a clay 
bottom, wherever the penetration of the water through the 
deeper layers renders their passage possible. In very shallow 
water, areas regularly and finely perforated are to be seen at 
the sides and bottom of the channel, which disclose their 
presence ; these perforated places can frequently be used as a 
guide to their discovery. They only live scattered over a terri- 
tory: as they can swim in a peculiar serpentine way they wander 
to different places, and settle where the necessaries of their life 
are present. Their food consists of rotting and decaying 
vegetable matter, which they swallow mixed with mud. ‘Their 
size varies according to their habitat and local circumstances, 
as the statements of other observers affirm. However, even 
under the same circumstances, very great differences in size 
exist, so that, I think, in the first place individuality, and in 
the second place environment must be considered as factors 
in their varying size. . 

In the economy of nature they appear to do good service by 
their destruction of organic matter ; their feces, as in the case 
of Earthworms in general, increases the goodness of the mud, as 
is proved by the settlement of many plants in the places where 
Criodrilus lives. The mud of such a bottom is very rich, and 
on the overflowing of the stream it will be carried over the 
fields where it is of further use for the nourishment of plants. 

In winter these worms burrow very deep in the mud, so that 
one can dig them out only from very great depths. Their 
tenacity of life is great, yet after this season they are very much 
changed. In winter they soon perish in tanks with pure water, 
but in autumn they can be kept for aweek. In the tanks they 
twine themselves into a knot and are then very difficult to 
separate. Their power of regeneration is astonishing. A 


560 DR. L. ORLEY. 


worm, cut through the middle, forms a new tail with shortened 
somites. In autumn more worms with regenerated tails are 
found than in the spring. Once I found, in October, out of 
fifty specimens, thirty with regenerated tails. The tail is very 
brittle, and the reason is very likely to be found in the irregular 
arrangement of the muscle-bundles. 

In company with Criodrilus there lives a very interesting 
Earthworm, Allolobophora dubiosa, Orley, which has 
nearly the same habits. 

Amongst the Hirudinea, species of Aulostoma and 
Nephelis are their greatest enemies ; these swallow three or 
four Criodrili at a time. 

[For the explanation of figures 1 to 8, Plate XXXVIII, 
illustrating Dr. Orley’s paper, see p. 570.] 


STUDIES ON BARTHWORMS, 561 


Studies on Earthworms. 
No. III. Criodrilus lacuum, Hoffmeister. 


By 


William Blaxland Benham, B.Sc., 
Demonstrator in the Zoological Laboratory of University College, London. 


With Plate XXXVIII, figs. 9 to 19. 


Tnanxs to the kindness of Dr. Orley, who, at Professor Ray 
Lankester’s request, sent him a bottle containing a large 
number of Criodrilus preserved in spirit, and including both 
sexually mature and young specimens, as well as cocoons, I[ 
have been enabled to make a study of this interesting worm. 
The specimens are all in a good state of preservation, and I 
have been able to add several new facts concerning its anatomy. 
This is the first time that figures illustrating the general 
anatomy of Criodrilus have been published. Hoffmeister! gives 
a coloured figure of the worm, and of the cocoon, showing 
their natural size and appearance, but with no details as to 
sete, pores, &c.; Vejdovsky* has already published excellent 
figures of various portions or organs of the worm; e.g. the 
ovary, nephridial funnel, sete, transverse section of the body, 
so that I have not repeated these. Dr. Orley? added drawings 
of the prostomium, as well as of that of another worm which 
he described as Criodrilus dubiosus; but in his paper, 
published in the present number of this Journal, he makes no 

1 © Die bis jetzt bekannt. Art. aus d. Fam.d. Regenwiirmer,’ Brunswick, 1845. 


2 «Systeme und Morph. d. Oligocheten,’ Prag., 1884. 
3 * Mathemat.u.Termeszt.tudomanyi K6zlemenyek,’ Budapest, Bd. 16, 1881. 


562 WILLIAM BLAXLAND BENHAM. 


reference to this worm. He, however, mentions Allolobo- 
phora dubiosa as occurring with C. tacuum, so that, pre- 
sumably, they are one and the same animal. But with all 
these figures no general view of the worm has been given. 

My thanks are due to Professor Ray Lankester, not only for 
these worms, but also for allowing me to translate Dr. Orley’s 
paper, so that I could corroborate or comment on his observa- 
tions, and fill in details which he has left untouched. I am 
quite aware that a great deal more still remains to be done in 
reference to the anatomy and histology of Criodrilus, but I 
think the following, taken with the description of the previous 
observers, forms a fairly complete account of its anatomy. 

External Characters.—I have nothing to add to Orley’s 
statements as to the length and number of somites of the worm ; 
my specimens are all preserved in strong spirit, and are there- 
fore greatly contracted ; they are much coiled and twisted and 
had to be soaked in weak alcohol before they could be con- 
veniently dissected. A deep groove traverses the dorsal surface 
posterior to somite 1; the ventral surface is rounded, and the 
sides are more or less vertical (Pl. XX XVIII, fig. 12). 

The prostomium is distinct, and its terminal pore has 
been figured by Vejdovsky (loc. cit., pl. xin, fig. 12). The 
anterior somites are longer than the posterior ones, and are not 
so prominently quadrangular in section. On the ventral surface 
of somites 1X, X, XI, XII, and x11, there are prominent rounded 
papilla, in which the ventral sete are inserted. 

The structure of the epidermis is to a certain extent figured 
by Vejdovsky (loc. cit., pl. xiv, fig. 3). It consists of narrow 
columnar cells with oval nuclei; their inner ends seem to 
diverge and between them are seen small rounded cells with 
rounded nuclei (Pl. XXXVIII, fig. 17, c.), which Vejdovsky 
considers as young epiderm cells. Goblet cells are very rare; 
they are narrow cells filled with granular matter, with the 
protoplasm and nucleus at the imner ends. As the worm 
lives in water the necessity for secreting mucus would not be 
so great as in Harthworms, properly so-called, and hence the 
mucous cells are few and far between. The capillary loops of 


STUDIES ON EARTHWORMS. 563 


the blood-vessels pass between the cells of the epidermis 
(fig. 17, d), as in the Leech, and as Beddard has shown to be 
the case in Perionyx and in Pericheta. 

The longitudinal muscles are arranged irregularly, as in 
Microcheta, Allolobophora, and others. Connective 
tissue is abundant, and forms a fairly thick layer between 
the muscular layer and the coelomic epithelium. 

Previous writers have denied the existence of a clitellum ; 
even Orley, who expressly looked for it, says that he has found 
no trace of it; yet in all my specimens, which are sexually 
mature, a considerable difference in appearance is noticeable 
behind somite xv, and extending to about somite xtvi1. The 
worm is here nearly cylindrical, though slightly concave on the 
ventral surface, where the intersegmental grooves are not dis~ 
tinctly marked, but tend to run into one another across the 
middle line as shown in fig. 10. The colour, at any rate in 
spirit specimens, is rather darker over the dorsal and lateral 
surfaces of this region than elsewhere. Noticing this, I cut a 
series of transverse sections through the body, and I then 
found that behind the somite xv the epidermis gradually 
changed its character. 

In addition to the columnar cells forming the epidermis of the 
general surface, a layer of elongated, club-shaped cells, of 
various lengths, is present (fig. 18, c), so that the epidermis is 
here some four or five times deeper than elsewhere, and deeper 
at the sides than on the dorsal surface. These cells have avery 
similar appearance to those in the clitellum of Lumbricus 
aud Microcheta, though they differ slightly in detail. Each 
cell is filled with numerous highly refracting, small spherical 
globules, and the protoplasm with the nucleus is confined, 
apparently, to the inner, swollen end of the cell. As the cells 
vary in length, the appearance presented is that of three or 
four layers of such cells, as in Lumbricus; but in the latter 
worm these club-shaped cells contain a granular substance, 
and the rounded, refracting globules are confined to narrow, 
elongated cells, intermediate in length between the club- 
shaped and columnar cells and which are absent in Criodrilus, 


564 WILLIAM BLAXLAND BENHAM. 


Another point of difference is presented in the absence of the 
strands of connective tissue, which in Lumbricus separate the 
club-shaped cells into more or less distinct groups. I think that 
there can be no doubt that the clitellum is present; but as it 
commences and ends gradually, and since, from Orley’s remarks 
and from Hoffmeister’s drawing, there is no difference in 
colour in the living worm, it may easily be overlooked in this 
condition. 

The anus is situated quite dorsally (fig. 11), on an enlarged 
somite, which Vejdovsky considers as representing some seven 
or eight fused somites, as indicated by the ganglionic swellings 
figured in pl. x, fig. 21, of his work. 

The pore of the sperm-duct is placed on a large hemispherical 
papilla, or swelling, on somite xv, between the ventral and 
dorsal sete. which Orley speaks of as “ der Hof,” and which I 
have translated as “areola.” It is, in the sexually mature 
worm, very conspicuous, and has caused, in spirit specimens, 
the lateral swelling shown in Pl. XX XVIII, figs. 9, 10. 

The pore of the oviduct is similarly placed in somite xiv, 
but on a much less prominent papilla. Both these pores are 
visible from the side (fig. 13); and near them are usually one 
or more white spermatophores. These are fully described in 
the preceding paper, but whereas Orley states that they are 
generally fixed close to the ventral setz, the specimens exa- 
mined by me show them nearer the dorsal sete ; at the same 
time I do not intend by this, nor by my figure, that it should 
be inferred that Orley is in error: he has had much greater 
opportunity for observation than I have, and my figure was 
drawn some weeks before I saw his paper. 

I have been unable to see the nephridia pores, and there are 
no dorsal pores. 

The four couples of setz are set at the corners of the animal, as 
shown in fig. 11, and are perfectly evident throughout the body, 
including the clitellum. They are usually broken off short, so 
that I was unable to extract them; but in sections they are seen 
to have the ordinary shape (Vejdovsky, pl. xiii, fig. 13). 

Internal anatomy.—The alimentary tract differs from 


STUDIES ON EARTHWORMS. 565 


that of other earth-worms, with the exception of Pontodri- 
lus, in the absence of a gizzard. 

The pharynx extends to the hinder boundary of somite 1v 
(fig. 14), the walls are very muscular, and the usual radiating 
muscles pass to the body wall, some going as far back as somite 
vi. In transverse sections I found numerous glandular-looking 
cells amongst the muscles of the dorsal and lateral wall, but I 
was unable to find any duct leading to the lumen of the 
pharynx. There are similar groups of cells in the anterior 
somites, through which the cesophagus passes ; these lie on each 
side of the subintestinal blood-vessel, but I could find no duct. 
The cesophagus is a narrow, simple tube, the walls of which 
are fairly thick and very vascular. In somite x11 the ceso- 
phagus enlarges, and in somites x1v to xvi the diameter is 
some three or four times greater than in front. This “crop” 
has a whiter appearance, due to its thicker muscular walls, 
than the rest of the cesophagus; it is deeply constricted as it 
passes through the septa, and the wall is greatly folded in- 
ternally. I almost expected to find that this was a gizzard, 
but the structure is quite the same as that of the cesophagus. 
In the nineteenth somite the crop narrows and becomes the 
intestine, the walls of which are fairly thin, so that the dark 
food-material is seen through. 

Vejdovsky states that there is no typhlosole, but on slitting 
open the intestine along one side, and examining its interior, 
a moderate-sized typhlosole is seen on the dorsal wall. 
Series of sections confirmed this observation, and showed that 
the epithelium covering this in-pushed dorsal wall differs 
somewhat from the rest of the lining in that the cells are 
here longer and more regular in size. The typhlosole then 
is present, and init a small typhlosolar vessel or irregular 
blood space, into which vessels from the intestine wall enter, 
and from which small vessels pass vertically into the dorsal 
blood trunk, just as is the case with Lumbricus. How far 
back the typhlosole extends I am unable to say. 


' Perrier, “ Etudes sur l’organisation des Lomb. terrestres,” ‘ Arch. 
de Zool. Exper. et Gen.,’ ix, 1881. 


566 WILLIAM BLAXLAND BENHAM. 


The absence ofa gizzard, bothin Criodrilus and in Ponto- 
drilus, is probably related to the soft nature of their food- 
material. Both are aquatic in habit. Pontodrilus, as 
Perrier tells us, lives on the seashore, and its food consists of 
decaying vegetable matter thrown up by the sea. Criodrilus 
lives entirely in the water, and obtains its food, according to 
Orley, by swallowing the mud which contains decomposing 
vegetable matter. In both cases the food is soft, and already 
more or less finely divided, and can be easily digested, so that 
the necessity for a gizzard does not exist: in Lumbricus and 
other worms, however, which live on land and burrow and 
swallow the hard soil, some crushing apparatus is needed before 
the digestive fluid secreted by the wall of the intestine can act 
on the food. 

The vascular system I have not traced to any extent. 
The dorsal blood-trunk is large, and has the usual ampullate 
appearance up to somite xv. In the next preceding somite it 
is bent slightly to one side, and gradually gets narrower till it 
divides up on the wall of the pharynx. In each of the somites 
vil to x1 a pair of large and long moniliform hearts unite the 
dorsal to the ventral trunk; and there are lateral vessels in 
each of the somites posterior to the hearts. 

In the neighbourhood of the anus the dorsal trunk divides 
into two (Vejdovsky; pl. xiv). A subneural vessel is present 
and a typhlosolar vessel, but neither latero-neural nor intes- 
tino-tegumentary vessels exist. 

The nervous system presents no points of difference from 
the usual arrangement. The three “ great fibres” are present. 

The nephridia are not present in front of somite x11. 
A series of sections confirmed the results derived from 
dissection. In and behind this somite they are large and 
fairly conspicuous organs, having a slight muscular vesi- 
cular portion. Vejdovsky states that they open exteriorly 
in front of the ventral sete: he also figures a nephridial 
funnel (pl. xiii, 21), which somewhat resembles that of 
Lumbricus. 

Pontodrilus agrees with Criodrilus in that there are no 


STUDIES ON EARTHWORMS. 567 


nephridia in the anterior somites, the first nephridium being 
apparently in somite x1v, so that both these approach the 
Limicole in having no nephridia in those somites in which the 
spermathecze and ciliated rosettes lie, though they are present 
in the same somites with the oviduct and the posterior part of 
the sperm-duct. 

The Genital Organs.—I have succeeded in finding all the 
usual organs connected with the genital apparatus, with the 
exception of spermathece. The seminal reservoirs or sperm 
sacs are constructed on the plan of Allolobophora, and not 
on that of Lumbricus, as Orley seems to indicate, since there 
is no median portion connecting the sacs below the intestine 
(fig. 15). The worms which I dissected are sexually mature, 
one of them having spermatophores attached to somite XIV. 
There are four pairs of pouches, as in Allolobophora,' one 
on each side of each of the somites 1x, x, x1, and x11; they vary 
in size in these somites, and in different individuals. Each is 
an irregular loose mass, which is easily torn on opening the 
worm, and in sections the lobation is seen to be carried to a 
great extent, the cavity of the sac being subdivided by long, 
narrow inpushings of the wall of the sac, whilst loose separate 
masses of developing spermatozoa are seen in the somites in 
which the reservoirs lie. Those in somites 1x and x are formed 
as anteriorly directed saclike outpushings of the hinder septa 
of these somites, whilst those in somites x1 and x1I are pos- 
terior outgrowths of the anterior septa of these somites. Hach 
is connected to a septum by a short pedicle (Pl. XX XVIII, 
fig. 15, e! to e*). 

The testes (which Orley states lie in somites x1 and x11) 
are in reality in somites x and x1, attached to the anterior 
septa, very close to the ventral body wall, near the nerve cord 
(fig. 15, a). They have a digitate form, like the testis of 
A llolobophora turgida, figured by Bergh.’ (Pl. XXX VIII, 
fig. 16). Owing to their deep position they are very difficult to 

1 R.S. Bergh, “ Untersuch. iiberd. Bau u.d. Entwickl. d. Geschlectsorgane 
d. Regenwiirmer,” ‘Zeit. fiir wiss, Zool.,’ 1886, p, 303. 

2 Thid., fig. 1. 

VOL, XXVII, PART 4,——NEW SER. RR 


568 WILLIAM BLAXLAND BENHAM. 


find at first, but my dissections are confirmed by transverse 
sections. 

Close behind each testis is a ciliated rosette, lying, 
therefore, in somites x and x1, and close to the posterior 
septum of the somite. (Orley wrongly states that they are 
attached to the anterior septum of somites x1 and x11, into 
which they project.) 

The sperm-ducts from the two ciliated rosettes of one side 
unite at the level of the septum behind somite x1, and the 
single duct passes to somite xv, embedded in the connective 
tissue which exists between the coelomic epithelium and the 
longitudinal muscles of the body wall; hence it is practically 
impossible to trace it except by means of sections, unless it 
happen to be filled with spermatozoa, when it will appear 
whiter than the surrounding tissue. In somite xv is a large 
and conspicuous hemispherical gland, which may be called a 
prostate; the sperm-duct passes to the dorsal surface of this 
gland, dips down through its mass and opens to the exterior by 
the pore mentioned above, which is situated on a prominent 
rounded papilla, which seems to be merely the outer half of 
the prostate. This gland itself consists of cells similar to 
those forming the epidermis of the clitellum, and quite con- 
tinuous with them; the muscular layers of the body wall are 
here thin, and pass over the inner surface of the prostate, so 
that the gland appears to be formed merely by an hemispherical 
thickening of the epidermis over this area. 

The ovary is a flattened rounded disc attached to the 
anterior septum of somite x111, close to the nerve cord (fig. 15, 
f). It resembles the ovary of Perichzta in shape, and is 
without the tail-like prolongation of the ovary of Lumbricus 
(fig. 19). It is figured in Vejdovsky’s work,! but I have added 
a figure here, as he does not show the delicate membrane sur- 
rounding the organ. 

The ovisac (which seems to be a better name than Bergh’s 
“receptaculum ovorum,” since the word “ receptaculum ” 
has been applied to a spermatheca) is a botryoidal sac-like 


1 Loc. cit.; pl. xiii, fig. 23. 


STUDIES ON EARTHWORMS. 569 


protrusion of the posterior septum of somite x11, and thus hes 
in somite x1v. It is filled with ripe ova and has a goodly 
supply of blood capillaries on its wall. It is very conspicuous 
in the specimens dissected by me, much more so than the 
ovary, for which I should probably have mistaken it had not 
Bergh’s paper appeared ;! and it is curious that Orley makes 
10 mention of it. 

The funnel of the oviduct (fig. 15, g) projects into somite 
xu, close to the point where the ovisac is attached; and the 
edge of the funnel is more prominent than is usual. The 
external pore has already been mentioned, as being on somite 
xiv (fig. 10, c). 

Orley states that the spermathece “appear to open to the 
exterior between the somites 1x and x, and x and x1.” I can 
find no trace of spermathecze, though I have searched for them 
in some half a dozen specimens, of various stages of maturity ; 
nor is any trace of them presented in a series of sections 
through this region of the body. I must therefore conclude 
that this is an error of observation on his part; he says no 
more of them than the above quotation. Can he have mis- 
taken the ciliated rosettes for these organs, and mistaken the 
testes for the rosettes? It seems to me quite probable from 
his description of the relation of these structures that such is 
the case ; a portion of a ciliated rosette, removed, teased, and 
examined, would show mature spermatozoa, which might lead 
an observer to conclude that he was dealing with a sperma- 
theca. Again, the shape of the testes, as seen with a lens, 
might without difficulty be mistaken for ciliated rosettes, 
which he places in the position occupied by the testes, though 
he has placed these in the wrong somites. 

The cocoon and spermatophore are so fully described 
and figured by Orley, that I have nothing to add to his 
description of these structures. 

His interesting observations on the habits of Criodrilus 

‘ It is probable, as Mr. Beddard has remarked in a recent number of the 
‘Proc. Zool. Soc.,’ that the structure figured and described by me as the 


ovary of Microcheta (see this Journal, vols. xxvi and xxvii) is really 
the ‘‘ ovisac ;” and that I have overlooked the true gonad. 


570 WILLIAM BLAXLAND BENHAM. 


will, I hope, enable this form to be discovered in England 
and similar observations on the habits of other forms are a 
great desideratum. 

Parasites of Criodrilus.——My attention was first at- 
tracted to certain curious elongated structures attached to the 
ovary, and I found them afterwards in various parts of the 
body. These are narrow bodies, about one tenth of an inch in 
length, and of a white colour (in spirit). Each is invested by 
a well-defined cuticle, which encloses a very granular dark 
medullary protoplasm, in which is a clearer space, probably 
the nucleus. The shape varies to a great extent ; some consist 
of an elongated ovoid body drawn out at each end into a much 
narrower portion ; others are just the reverse, consisting of two 
ovoid swellings connected by a narrower portion. 

They are apparently Gregarine, which have been killed in 
various states of englenoid movement, such as is exhibited by 
Monocystis lumbrici; the worms had been killed in cor- 
rosive sublimate, judging from the white deposit on their 
surface, and this would cause the various states of movement 
to be fixed. At one end the cuticle is thickened and presents 
somewhat the appearance figured by Professor Lankester in 
vol. 3 of this Journal, Pl. VII, for M. aphrodite. 


EXPLANATION OF PLATE XXXVIII, 


Illustrating Dr. Orley’s Paper “ Observations on Criodrilus 
lacuum,” figs. 1 to 8, and Mr. Benham’s Paper “ Studies 
on Karthworms,” figs. 9 to 19. 


Criodrilus lacuum, Hoffmeister. 


Fic. 1.—Cocoon of Criodrilus lacuum. Natural size. a. The end by 
which it is attached. 4%. The free end. 


Fie. 2.—The attachable end more highly magnified. (x 300.) 


STUDIES ON BARTHWORMS. EL 


Fie. 3.—The free end more highly magnified. (x 300.) 


Fic. 4.—A transverse section through the middle portion of the wall of 
the cocoon. (xX 300.) a. Outer layer. 4. Middle layer. c. Inner layer. 


Fic. 5.—A detached piece of the middle layer. (x 800.) 
Fic, 6.—Strata of the inner layer. (x 300.) 

Fie. 7.—A spermatophore. (x 60.) 

Fic. 8.—Spermatozoa from the spermatophore. (x 500.) 


Fic. 9.—The anterior extremity of the worm viewed from above. (x 2, 
spirit specimen.) a. The prostomium. 4, The dorsal sete. c. Enlargement 
occupying somites xIv to xvitl, due to the large papille on the ventral sur- 
face. d. The clitellum., Behind somite xiv the quadrangular shape of the 
worm is shown. 


Fic. 10.—The same worm from below. a. The prostomium. 4%. The 
mouth. c¢. The pore of the oviduct. d. The pore of the sperm-duct, situated 
on a large rounded swelling causing the enlargement in this region. e. The 
ventral sete. /. The clitellum. 


Fic. 11.—The last few somites of the body, showing :—a. The anus, 
situated dorsally. 4. The region regarded by Vejdovsky as representing seven 
or eight fused somites. 

Fie. 12.—A diagrammatic outline of a section through the body in the 
posterior region of the body, showing its quadrangular shape, with the dorsal 
sete (a) and the ventral sete (4) placed at the corners. 


Fic. 18.—The side of the body, showing a spermatophore (a) attached to 
somite xIv. 4. dorsal sete. c. The ventral sete. d. The sperm-pore, on its 
enlarged papilla. e. The ovipore. 


Fie. 14.—General view of the anatomy of Criodrilus when opened in the 
usual way. (x 2.) a@. The pharynx. 4. The esophagus, swelling out at c 
to form a strong muscular crop. d. The intestine. e. The dorsal blood- 
vessel. ff. The lateral hearts. gy. g. The seminal reservoirs. /. The ovary. 
&. The ovisac (Bergh’s “receptaculum ovorum”). 7. The hemispherical 
glandular swelling or prostate around the terminal portion of the sperm-duct. 
m. Prostomium, 2. Suprapharyngeal ganglia. o. The nephridia. 


Fic. 15.—The genital organs of the left side greatly enlarged. A portion 
of the oesophagus is represented on the right of the figure. a@.a'. The two 
testes. 4, d’. The ciliated rosettes. c. The sperm-duct, which dips into the 
hemispherical prostate, d. The seminal reservoirs, ¢!, ¢°, ¢3, e4, are represented 
as relatively rather smaller than their true size; they are seen to be attached to 
the various septa. /. The ovary. The septum between the somites x11 and 
X1v is turned back so as to show the funnel of the oviduct, gy, and the nephri- 
dial funnel, 7. 4. The ovisac. 4%. Nephridium. 


Fic. 16.—A testis attached to the septum. 


bye STUDIES ON EARTHWORMS. 


Fic. 17.—A small portion of a section through the epidermis, to show a 
capillary loop, d, passing between the columnar cells, 2, and the small 
cells, c. a. The cuticle. e. The circular muscles. . 

Fic. 18.—A portion of the epidermis from somite xvIII, in order to show 
its clitellar structure. a. Cuticle. 6. Columnar epithelialcells. c. Hlongated 
club-shaped clitellar cells. d. Circular muscles. 


Fic. 19.—An ovary. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 573 


Notes on the Chromatology of Anthea cereus. 
By 


Cc. A. Mae Munn, M.A., M.D. 


With Plates XXXIX and XL. 


Tue colouring matters of Anthea cereus were first 
examined by Sorby,! who found several present in this 
Actinia. Among others he found chlorofucin, the bands 
of which had been observed by Mr. Charles Horner, and the 
position of which led Mr. Horner to think that the supposed 
chlorophyll was different to that of land plants. Sorby had 
previously found chlorofucin in fresh-water algze and sub- 
sequently in Fucus and other olive marine alge; and in 
his paper on “ Comparative Vegetable Chromatology” he 
gave directions for its separation from other pigments. Prof. 
Lankester, in the list of chlorophyll-containing animals in 
the English edition of Sachs’s ‘ Botany,’ includes Anthea 
cereus and puts “chlorofucin” after it, thus accepting 
Sorby’s statements. 

Among those animals which have been proved to contain 
symbiotic unicellular alge Anthea is now, I believe, included ;* 
and it becomes of interest to find out whether chlorofucin is 
due to the presence of these symbiotic algze or whether it is a 
pigment belonging intrinsically to the animal; whether, also, 
the other colouring matters associated with the chlorofucin 

1 «Proc. Roy. Soc.,”? No. 146, vol. xxi, 1873, p. 454. 

2 Hertwig, O. and R., “ Die Actinien,” ‘ Jena’ische Zeitschrift. f. Naturwis.,’ 


Bad. xiii, 1879, S. 495—500; and Geddes, ‘ Proc. Roy. Soc. Hdin.,’ vol. xi, 
188]—1882. 


574 Cc. A. MAC MUNN. 


belong to the animai or the alge. I have already! proved this 
point almost completely, as I found that in Anthea cereus, 
in Bunodes Ballii, and Sagartia Bellis, “yellow cells,” 
or symbiotic alge, are present, that these animals all contain 
chlorofucin, all contain the same accompanying colouring 
matters, and that these colouring matters are evidently due to 
the “yellow cells” with which the tentacles are stuffed ; for 
there is no essential difference in the spectra of the solutions of 
the tentacles in which the colouring matters are derived entirely 
from the “ yellow cells ” and those obtainable from other parts 
of the Actinia. 

Moreover, I have also proved that in anemones possessing 
yellow cells there is more or less suppression of the respiratory 
proteids found in other Actiniz. 

But I had not repeated Sorby’s experiments in which he 
applied Stokes’s “ fractional” method for the separation of the 
chlorofucin from the other colouring matters. In the present 
paper I have given the results of this examination, and, as 
will be seen, the statements of Sorby have been verified. This 
is of importance, as Krukenberg? has omitted to mention in the 
account of his experiments the results arrived -at by Sorby, 
although, as I shall show, he had evidently chlorofucin before 
him in some of the solutions whose spectra he has mapped. 

In the paper referred to above’ I haveshown that the mixture of 
colouring matters obtained from the Actiniz therein mentioned 
contain chlorofucin, and that the bands of this correspond to 
the chlorofucin bands in a similar solution of Fucus serratus. 
Sorby has figured in a diagram the bands of this pigment, but he 
does not give their wave-length measurements, and only figures 
the dominant bands of “ blue” and “ yellow chlorophyll” in 
the same diagram for the sake of comparison ; consequently 
some confusion is caused when one endeavours to find out what 


1<Proc. Roy. Soc.,’ No. 235, 1885, and ‘ Philos. Trans.,’ 1885, Part IT, 
641, and seq. 

* ¢Vergleichend-Physiol. Studien.,’ Iste Reihe, 5te Abth., 1881, 8. 38, 
and Ibid. 2te Reihe, 3tte Abth., 1882, 8. 72. 

3 © Philos. Trans.,” loc. cit. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 575 


Sorby means by “blue” and “yellow chlorophyll” and 
 chlorofucin,” and the object of this paper is to clear up this 
confusion as regards chlorofucin more especially, also to prove 
that the chlorofucin and its accompanying pigments are due 
entirely to the “ yellow cells.” 

It is necessary here to recall the experiment of Geddes! to 
mind. Geddes found that by exposing Anthea cereus to 
sunlight he got as much as 82—388 per cent. of oxygen, and he 
found starch and cellulose in the “ yellow cells.” He tries to 
reconcile this fact with the statement made by Krukenberg, 
who failed to get any evidence of the evolution of oxygen, by 
supposing that Krukenberg must have examined a different 
variety of Anthea; and he further observes: “Thus, then, 
the colouring matter of Anthea, described as chlorophyll by 
Lankester, has really been mainly derived from that of the 
endodermal alge of the variety plumosa, which predominates 
at Naples, while the Anthea-green of Krukenberg must mainly 
consist of the green pigment of the ectoderm, since the Trieste 
variety evidently does not contain alge in any great quantity. 
But since the Naples variety, contrary to the opinion of the 
brothers Hertwig,? does contain a certain amount of ordinary 
green pigment, and since the Trieste variety is tolerably sure 
to contain some alge, Heider having indeed shown the presence 
of yellow cells in Sagartia, both spectroscopists have then 
been operating on a mixture of two wholly distinct pigments— 
one vegetable, the other animal—diatom-yellow and Anthea- 
green.”’ In other words, Prof. Lankester’s pigment would be 
** diatom-yellow ” and Krukenberg’s “ Anthea-green.” But I 
believe this theory will not account for the above-mentioned 
discrepancy, as I find a chlorophyll as well as a 
chlorofucin in extracts of the “yellow cells,” and I 
shall endeavour to show that out of these yellow cells one extract 
may contain more of one coloured constituent, another more of 
another; and this result does not prove that one extract contains 

' ‘Nature,’ 26th Jan., 1882, pp. 8303—305, and ‘ Proc. Roy. Soc.,’ Edin,, 


vol. xi, 1881, 1882, p. 377—396. 
2 Loe. cit. 


576 C. A. MAC MUNN. 


an intrinsic Anthea pigment and another an algal pigment, 
but simply this: that the colouring matters of the alge are 
several, for we find at least one chlorophyll, one chlorofucin, and 
certain lipochromes, and perhaps other pigments, all of which 
belong to the “ yellow cells.” 

The Physiological Proof is not wholly reliable. 
The evolution of oxygen in the presence of sunlight in the 
case of Anthea must to a large extent at least depend on 
the situation of the ‘ yellow cells,” for it is evident that if in 
a given species these are shut up in the tentacles the oxygen 
given off has not much opportunity of escaping out of them so 
as to make itself evident in a vessel containing the anemone, 
moreover a large amount of the oxygen will in such a position 
be largely absorbed by the tissues of the animal, and the same 
manner in which the cells are packed, as shown in the accom- 
panying drawing, prevents the deeper lying cells from being 
acted upon by the rays of light. If on the other hand the 
ectoderm of the animal were studded with alge there would 
be a considerable development of oxygen perceptible, and there 
is certainly such a variation in the distribution of the “ yellow 
cells,” for insome Actinie I have observed rows of algeeembedded 
in the ectoderm, while in others they may be mostly confined 
to the tentacles. This point should not be lost sight of, and 
may account for the discrepancy to a great extent. 

The Morphological Proof that the “yellow cells ”’ are 
parasitic algze has been so well discussed that I need not here 
“treat of it,” but I may observe that Krukenberg’s ideaas to their 
hepatic function must, so far as their microscopic character is 
concerned, be completely negatived. In no invertebrate liver or 
answering organ are such bodies found. On the contrary, the 
microscopic characters of liver chlorophyll or entero- chlorophyll 
at once separate it from that of the ‘yellow cells;” for,in the case 
of entero-chlorophyll, it is easy enough to see that it occurs 
mostly dissolved in oil, or in granules, or diffused through the 
protoplasm of the lining cells of the liver tubes.1_ The spectro. 
scopic reasons for the same conclusion are considered below. 

1 «Proc. Roy. Soc.,’ No. 237, 1885, and ‘ Philos. Trans.,’ 1886, Part I. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 577 


The Chemical Proof is no less convincing, as the presence 
of starch within the “ yellow cells,’ and of a cellulose wall 
surrounding them, is easily proved, especially after, as Geddes 
has shown, the usual botanical precautions have been taken, 
namely, steeping the “ yellow cells ” in alcohol, then in caustic 
potash, and neutralising with acetic acid before applying the 
tests with iodine and with Schulze’s fluid. The same tests 
applied to liver chlorophyll entirely fail. 

It is not necessary here to describe the differences between 
the ‘yellow cells”? and the chlorophyll corpuscles of Hydra 
and Spongilla, as Professor Lankester’ has shown that the 
latter are not parasitic alge, and I have? lately studied the 
chlorophyll corpuscles of Stentor polymorphus, Para- 
mocecium, and Ophrydium, and compared their morphological 
characters with those of the ‘‘ yellow cells,” and have concluded 
that they too are not parasitic alge, although in some corpuscles 
T have found traces of an amyloid substance, and the presence 
of a cellulose wall. Miss Jessie Sallitt? has also studied the 
morphology of the chlorophyll corpuscles of certain Infu- 
sorians, but she has not found starch. This, however, 
is of no importance, for there is no reason why starch 
should not appear in the protoplasmic contents of an animal 
chlorophyll corpuscle containing chlorophyll. Nor would the 
absence of starch within such cells justify us in concluding 
that it is not formed there, as it may be, and probably is, 
rapidly removed elsewhere as soon as it is formed (Lankester). 
Granting that starch is built up by the agency of chlorophyll 
from carbon dioxide and water, we may not always meet with 
it, for botanists teach that some “ non-nitrogenous‘ organic 
substance is first formed in the chlorophyll corpuscle from 
carbon dioxide and water,’ which is “ not starch, but a sub- 


1 “On the Chlorophyll Corpuscles and Amyloid deposits of Spongilla and 
Hydra,” ‘ Quart. Journ. Mic. Sci.,’ vol. xxii, N.S., p. 229. 

* © Proc. Birm. Philos. Soc.,’ vol. v, Part I, pp. 177—218. 

3 “On the Chlorophyll Corpuscles of some Infusoria,” ‘ Quart. Journ. Mie. 
Sci.,’ vol. xxiv, 1884. 

* Vines, ‘Lectures on the Physiology of Plants,’ 1886, p. 145. 


578 O. A. MAC MUNN. 


stance (possibly allied to formic aldehyde) which goes to con- 
struct proteid, by combining either with the nitrogen and 
sulphur absorbed in the form of salts from the soil, or with the 
nitrogenous residues of previous decompositions of proteid. 
The starch deposited in the corpuscle is, however, the first 
visible product of the constructive metabolism going on 
within it; for, unless protoplasm is being formed, no starch can 
be produced : it may be regarded as a temporary reserve ma- 
terial.’ The fact that such “reserve material,” while, being 
of great service in a vegetable cell, and not being of much service 
in an animal cell, may lead to the metabolic process stopping 
short of its actual formation ; for it appears to me that the prin- 
cipal use of chlorophyll in the animal cell may be to supply the 
animal with oxygen by the decomposition of the animal’s waste 
carbon dioxide, and the formation of starch would be, to a great 
extent, a superfluous advantage. In that case the formation 
of starch would be more accidental than of actual necessity. 
This view of the function of animal chlorophyll is very much 
strengthened by the recent experiments of Regnard,! which, if 
confirmed, will tend to support the view that chlorophyll, even 
separated from the “chlorophyll corpuscles,” is of use in the 
respiratory processes of animals. Whatever the role of the 
intrinsic chlorophyll of the animal may be, there can be little 
doubt as to that of the “yellow cells” of Anthea, which all 
proofs, morphological, physiological, chemical, and spectro- 
scopic, point out as being distinct organisms, having an in- 
dependent life from the animal, although, of course, benefitting 
by their position not only themselves but their host. 

If sections of the tentacles are made after hardening in 
alcohol, it will be seen that the masses of yellow cells are 
packed in the tentacle at random as it were, and as the water 
is absorbed from them by the alcohol, radiating cracks appear 
in the mass of cells which are merely laid in apposition to each 
other, and not connected in any way as they would be if part 
of the animal’s structure. I have endeavoured to show this in 


1 ¢Compt. rend.,’? CI, 1293—1295, and ‘Journ, Chem. Soc.,’ March, 1886, 
p. 254. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 579 


the accompanying drawing, an inspection of which alone will 
convince most people that these bodies are not “secreting cells ” 
(Pl. XXXIX). 

Results of Spectroscopic Examination.—The chloro- 
phyllof Anthea differs from other chlorophylls in its remark- 
able instability towards caustic alkalies; this I have 
already described,! and the chlorofucin which accompanies it is 
. also remarkably unstable. I propose first to describe the 
results of an examination of the solutions of these pigments, and 
then to compare them with plant chlorophyll. 

In comparing my results with those of Krukenberg, the 
difficulty at once is encountered of attempting to find out what 
bands of his correspond with mine, as in all his early maps the 
Fraunhofer lines occupy the wrong position, and none of his 
measurements have been given in wave lengths. Still it is not 
difficult to see that the pigments met with by him do not differ 
from those here described, and if this be the case it is easy to 
say which are the bands of chlerofucin and which of chloro- 
phyll, &c., in his drawings, as I shall show further on. 

I now proceed to describe the results of an examination of 
the colouring matters of Anthea. All the specimens which I 
examined have been of a dull greenish colour and therefore are 
of the same colour as those examined by Sorby. 

The tentacles were removed from several specimens and put 
into absolute alcohol after washing with water, this I may call 
solution (1). The other parts without the tentacles were cut 
up small, washed with water, and also put into absolute alcohol ; 
this I may call solution (2). In both cases the absolute 
alcohol was left in contact with the parts for three days or 
longer in a dark place. 

The colour of solution (1) was greenish yellow, and it had 
a red fluorescence and gave in a certain depth sp. 1, while 
in a shallow layer a band became detached in the violet end of 
the spectrum, which I have tried to represent by sp. 2; but it 
must be remembered that this band may not be exactly repre- 
sented owing to the difficulty of seeing it, even by the help of 


1 © Philos, Trans.,’ loc. cit. 


580 C. A. MAC MUNN. 


good daylight. The presence of the second band (commencing 
from the red end) at once stamps this spectrum and distin- 
guishes it from the usual chlorophyll spectrum. These bands 
read approximately : 


Ist band) a. ® X6/74:5 to Node: 
Qng ane 5 Ae ONG oO GOS: 
Srd i) BSA 505 to O75. 


While the 4th band was guessed to be A 467 to A 443, but 
its edges were so ill-defined and it was so encroached upon by 
the general absorption of the violet end that this measure- 
ment may require to be corrected. 

The colour of solution (2) was a deep orange and it had also 
a red fluorescence, but not so well marked as that of the 
former solution. The spectrum is shown in sp. 3, and it is 
seen that while the same bands are present as those of sp. 1, 
yet the two first are of relatively different intensity 
of shading. ‘This points to the obvious conclusion that two 
colouring matters are present, the one indicated by the band 
in red, the other by the second band (and the third, as will be 
shown further on), there is more of the former present in the 
solution of the tentacles, of the latter in that of the other 
parts. The readings of these bands were the same as the last. 
In a thinner layer of this solution (2) there are two bands 
nearer the violet, that nearer the red being less shaded than 
the other. Sp. 4 is an attempt to show this, but it only 
approximately represents the position of these bands, of which 
one is coincident with the lipochrome band of sp.2. This dif- 
ference of spectrum explains the difference of colour of these 
solutions, for the latter solution probably contains an additional 
yellow colouring matter probably derived from the animal, 
but it is not an additional green but a yellow. 

Solution (1) (of the tentacles) was now agitated in a sepa- 
rating funnel, after dilution with water, with carbon bisul- 
phide, when the bisulphide fell to the bottom of a yellow-green 
colour leaving the alcohol layer orange. This bisulphide 
solution on separating possessed a red fluorescence and gave 
sp. 5, and the following readings : 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 0581 


Ist band . . . A685 tor 656. 
Onde ga iras slat NGA to, eGLIae (?) 
Bao! 5 ow oe ON DE ODS YG 


Two other bands in the green were also seen which doubt- 
less are obscured inthe alcohol solution by the shading 
produced by the yellow constituents absorbing the violet end ; 
and two others in the violet end were also visible, which, as far 
as I could judge, measured approximately from A 479 to A 460, 
and perhaps A 453 to X 436. 

A second bisulphide extract of the same solution, after the 
first had been removed, was not nearly as green as the first 
bisulphide extract, and contained less of the constituents 
giving the bands in the red half of the spectrum, but showed a 
dark band in the blue which was coincident with the A 479 to 
\ 460 band just mentioned. This spectrum is shown in sp. 6.1 
In every other respect the bands of sp. 5 and 6 agree. 

A third bisulphide extract of the same solution was hardly 
coloured, and gave traces of the same bands. The alcohol 
solution, which had been thrice extracted with bisulphide, was 
of an orange colour and contained a good deal of bisulphide, 
and now this solution no longer showed the first band 
in red, but did show the second and third bands of the original 
spectrum; these latter are evidently the bands of Sorby’s 
chlorofucin, as can be seen by a comparison with his dia- 
gram. They are shown in sp. 7; in a thinner layer there are 
other bands nearer the violet measuring approximately A 511 to 
\ 488, and \ 477 to \ 457, as shown in sp. 8. 

To see whether these two latter were the bands of Sorby’s 
fucoxanthin, a couple of drops of ammonia were added and a 
little water ; the bisulphide layer was now turbid and gave one 
broad band in green, the solution having an amber tint. (It 
is noticeable that in this and in a second similar bisulphide 
extract the dark bands in the blue and violet of sp. 6 and 8 
were not present ; but the blue colour with hydrochloric acid 

‘ Possibly the band may not belong to a lipochrome, as I found a pigment 


in Anthea’s tentacles soluble in glycerine, with a band in this part of the 
spectrum. See below. 


582 Cc. A. MAC MUNN. 


described by Sorby was not produced, because this pigment was 
not fucoxanthin.) The chlorofucin bands of sp. 7 after the bisul- 
phide had removed as much colouring matter as possible was 
(approximately) : 


Ist band . . . A644 tor 627°5. 
Ond ,, i. . . A595 tor 58. 


There were, however, other bands present—one in blue 
green and one in violet. This solution was a deep yellow 
colour, due, probably, partly to the incomplete separation of 
the yellow pigment giving the bands in the violet end. 

On evaporation of this solution some brown-yellow flocks 
separated out ; the residue was extracted with absolute alcohol. 
In this it formed a fine deep yellow solution, and gave sp. 7 
again, the bands reading : 


Ist band . . . A641 tor 627°5. 
Qn 3 we ww A UR MO NON: 


What the alcohol left undissolved was nearly all taken up by 
distilled water, forming a yellow solution, giving some shading 
at the blue end of green and absorbing the violet end. Hydro- 
chloric acid did not seem to affect this solution. 

According to Sorby,' the alcohol solution of chlorofucin is 
changed by hydrochloric acid, and on adding this reagent to 
its alcohol solution a new spectrum appears, namely, sp. 9, 
whose bands read approximately : 


Ist band . . . A 607°5 tov 597. 
9nd ;; 5s @ OA TON BY/G 


Hence there is no doubt that this colouring matter was 
chlorofucin. 

Solution (2) (i. e. the alcohol solution of the parts of Anthea 
without tentacles) also contained chlorofucin, as I proved, by a 
similar method. It was stated above that the solution (1), 
from which the bisulphide had removed as much of the colouring 
matter as it could take up, had been treated with ammonia 
(two drops) and agitated afresh with bisulphide, and that this 


1 Loc. cit., p. 455. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 5838 


bisulphide gave a band in the green; such a solution was 
evaporated to dryness, and the residue tested by the lipo- 
chrome tests. With iodine and iodide of potassium it re- 
mained unchanged, with nitric acid it gave a transient blue, 
with sulphuric acid a green and blue; hence it is a lipochrome. 

A second absolute alcohol extract having been made from 
the tentacles only was of a greenish-yellow colour with a 
red fluorescence, and gave the following bands: 


Ist band . . . A 681°5 to A 650 (dark part = A 678 to A 653). 
Qnd 5 «.. . A636 tod 601. 
3rd ,, . - - A593 toA573. - (See Sp. 10.) 


In a thin layer there may have been some shading between 
green and blue, and perhaps some in violet. To this solution 
water was added, and it was then agitated with carbon bisul- 
phide. On separating the latter it was greenish, leaving the 
alcohol yellow, and in both these solutions certain bands in 
the violet could now be seen, which were not visible in the 
original alcohol solution (before separation). I have tried 
to show all the bands in sp. 11 and 12. These read as 
follows : 


Ist band . . . A686 todA 656. 

DnGe ye en eae ACOA a FOP NONIe 5. 

Srdiy % pee bas ALO OORtOLAy oon 

4th ,, . . . (ashading before the next). 
Dini yy. « = « Deo bo W496, 

Cth” 3° we a NATION AGO: 


wih; 2. « « A 453:to X-496. 


Now, on comparing these bands with the bisulphide extract 
from the first alcohol extract of the tentacles, they are found 
to be practically almost the same. The yellow alcohol solution 
from which the bisulphide had removed the pigment giving 
these bands, no longer contained any chlorofucin, and showed 
hardly a trace of a band in red in a deep layer. It did show 
the shadow of a band in green, and perhaps another in the violet. 

If we compare a second absolute alcohol extract of the parts 
of Anthea free from tentacles with the second absolute extract 
of the tentacles, we find that no great difference exists between 

VOL, XXVII, PART 4,—NEW SER, ss 


584. CG, A. MAC MUNN. 


them. Such a solution was greenish yellow; it possessed a 
fine red fluorescence, and its bands read as follows: 


lst bande a. A Oslo torn O50; 
aal ~ 55 . 2 s A 6385 fo XN O05: 
Sra. Sey ADO Se mtolAmDilo. 


This solution, diluted with water, was agitated with bisul- 
phide ; the latter fell down of a yellow colour, and possessed 
a red fluorescence, and gave a spectrum the same as sp. I1, as 
will be seen by the following readings : 


list band*). = 9. Al68hb\ to X 656. 

QOnd ,, . . « A644 tor 619-5 (2). 
Sid, eS NGO ton a7 7: 

Ath ,, Sip daiy P 

5th 43, » 4) At APSO Ww 499: 
Giles a ee AAO TOWN AGO: 
theese + 2, oy APebe to o436: 


The alcohol solution from which this solution had been 
removed was of a yellow colour, and gave a feeble band at the 
end of green, and one in violet; on evaporation it left a dirty 
yellow residue, which gave no reaction with iodine and iodide 
of potassium, was slightly green with nitric acid, and brownish 
with sulphuric acid. 

A third absolute alcohol extract of the tentacles only, 
which had a green colour and a red fluorescence, gave sp. 13. The 
only difference between this and sp. 11 is in the shading of the 
second band, as in 13 it is one single band, whereas in 11] there 
is a distinct narrow part over the broad, less shaded one. The 
wave length readings, too, show a close agreement; thus the 
bands read: 

Ist band . . . A678 tod 647. 


Qnd ,, . . . 633 tod60L. 
Std h SeN MET to NSTI 


There was also a band at the blue end of green, and perhaps 
one in violet. 

A third extract of the parts of Anthea without the 
tentacles contained the same colouring matters. It was ofa 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 585 


greenish colour with a blood-red fluorescence, and gave the 
following bands : 


etebandeees NOV Stor Odze 
Qnd ,, 5 6 6 NBR To) 2s (BOIL, 
Srauss Set DON Coruonios 


There was also a band at the blue end of green, and perhaps 
one in violet. Hence,then,the third extract of the tentacles and 
the third extract of the parts without the tentacles contain the 
same colouring matters. Now, the colouring matter in these 
latter extracts, which gives the bands in the red end of the 
spectrum, is almost, if not altogether, free from chlorofucin ; 
at least the second and third bands of the spectrum give 
different measurements. So far as I can judge this, then, 
must be the pigment which Krukenberg would have belonging 
to Anthea, which he calls “Antheen,” although I cannot 
prove this assertion, owing to the way his spectra are repre- 
sented. Krukenberg says that the corresponding pigment 
withstands saponification, but in this case, as I have previously 
shown,! the addition of a little caustic soda alters the spectrum, 
as shown in sp. 14.2 

A fourth absolute alcohol extract of the tentacles gave the 
same spectrum, the bands reading : 


Ist band . . . A678 tor 650. 

Gad 5, S . . A 688to MEDI. 

0 . . « A591 torA573. Others uncertain. 
A fourth similar extract of parts without tentacles read : 

Ist band .. . A678 tor 650. 

ong = 42 6 AvlipR TOA GOL 

olan ., . + = A591 tor 573. Others uncertain, 


And a fifth and sixth alcohol extract of the tentacles, and a 
fifth and sixth of the parts without them, gave the same read- 
ings. Hence we have precisely the same colouring 
matters present in the tentacles asinthe rest of the 
animal, and as those in the tentacles are due to 

1 «Philos. Trans.,’ Part II, 1885. 


* NaHO causes precipitation, but after filtering, the solution is green, and 
gives sp. 14. 


586 ; C. A. MAC MUNN. 


“ vellow cells,” it is fair to conclude that those of the 
latter are also due to “yellow cells,” and do not 
belong intrinsically to the animal, which is the point 
to be proved. 

So far, then, there are several pigments present, three at 
least; one represented by a chlorophyll-like spectrum, charac- 
terised by the dominant band in red, and by others when the 
chlorofucin is separated out, chlorofucin represented by sp. 7, 
and a lipochrome, or lipochromes, represented by bands in the 
violet half of the spectrum. The chlorophyll is, however, 
more decomposable by caustic alkalies than is that of land 
plants ; and it is now necessary to see whether it agrees with 
Sorby’s “blue” or “yellow chlorophyll.” Sorby’s yellow 
chlorophyll is found in Ulva latissima.! 

In the following experiments it must be remembered that a 
relatively large quantity of chlorophyll was present, and that 
consequently the dominant chlorophyll band was much broader 
than that in any of the above spectra. I did not boil the 
Ulva, as Sorby directs, but merely extracted it in the cold 
with absolute alcohol for three days in the dark. The result- 
ing solution was a fine sap green colour with a blood-red 
fluorescence, and gave in a suitable depth the following 
measurements : 

Ist band . . . A 6815 tod 641. 


one ass 5 6 NOPE 1 NSPE 
BEd.) vse ie Ao ToAcbbG; 
4th = ,, oe ge ede! MOA Dee. 


There were also two other bands, one in blue green and one 
in violet. But in order to compare this solution with the 
chlorophyll constituent of Anthea’s colouring matters, it is 
necessary to agitate with bisulphide of carbon and examine the 
latter solution. Putting now the measurements of the bands 
of this solution, and those of the corresponding extract of 
Anthea side by side, we get: 

1 Sorby, loc. cit., p. 458. Besides the lipochromes there is in Anthea’s 
tentacles a pigment soluble in glycerine which gives bands in the violet, which 
T have described in my paper on the “ Chromatology of the Actinis,” loc. cit, 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 587 


Utva. | ANTHEA, 
Ist band . . A688'5 tor’ 659 and | Ist band . . A686 toA 656. 
shaded to A 641. 

Sikes) Miss sy cAOSoe tO mi Ollero: 2nd 5, 6s « NO44 to A625: 
SCOe yy rw 3 MDOT “torA57 1; Ord’ 5.) 6 wie ADO tO bbe 
Achy,  « « Uncertain. Ath ,y sy Wneertaim: 

Sth” y, » . A&D20 ‘to x 496: bth. 4, « oF ADeato A490: 
Gihy sy wee A 4Sbe Ton 466: 6th ,, . . A479 tor 460. 
We 50 a ee, to N48: (thier en sa AS45937 FO) Neos 


The discrepancy in the measurements of the 2nd band of 
Ulva and Anthea may be due to a trace of chlorofucin in 
the bisulphide extract of the latter. The bands in the violet 
may be neglected as they belong to the lipochrome constituents. 
Hence it would appear that the chlorophyll constituent in 
Anthea is closely related to, if not identical with, ‘ yellow 
chlorophyll.” A comparison of sp. 11 and 12 with sp. 15 and 
16, teaches that there is a remarkable resemblance between 
the pigments of Ulva and Anthea not only as regards the 
chlorophyll bands in the red half of the spectrum, but also 
as regards the lipochrome bands in the violet half. 

I have not here considered the identity of the chlorofucin 
of Anthea with that found in Fucus serratus, as I have 
done so already, but I may add that I have lately separated 
chlorofucin by Sorby’s method from otier olive algze, such as 
Fucus nodosus, and Laminaria digitata, and find that 
the bands are identical with those of the chlorofucin of Anthea. 

We may now conclude that the pigments of Anthea are 
the pigments of certain marine alge, and are there- 
fore the pigments of the “yellow cells,” which are 
known to be unicellular alge. 

With regard now to Krukenberg’s results ; taking his first 
paper! and examining the plate attached to it, we find that in 
the first spectrum he figures the double band in the red, the 
second of which I have shown to belong to chlorofucin; the 
second spectrum represents the effect of NaHO on “ Anthea- 
green,’ but it really represents the effect of NaHO on 


1 ¢Vergleichend. physiol. Studien.,’ lte Reihe, 5te Abth., 1881. 


588 GO. A. MAC MUNN, 


chlorofucin and yellow chlorophyll mixed; the third spectrum 
also evidently represents the bands of both pigments, and the 
fourth shows a chlorofucin spectrum. In his second paper, which 
deals with Anthea viridis var. plumosa, the plate (Tafel iv)! 
shows clearly enough the presence of the same colouring mat- 
ters, thus in sp. 2 the bands of chlorofucin are visible; in 
sp. 3 the chlorophyll constituent is present, perhaps mixed 
with the former, and so in all the others the presence of the 
same pigment with the lipochrome or lipochromes can be 
detected. Hence there is no essential difference between the 
pigments of Anthea plumosa and Anthea cereus, and 
doubtless, in the former, they are all due to the “ yellow cells ” 
also. Krukenberg seems to lean to the opinion that these 
colouring matters are allied to what he calls “ hepatochromates,” 
but such a theory is easily controverted, because (1) enterochlo- 
phyll is not nearly so easily decomposed as are the pigments of 
Anthea, and (2) the “fractional” method distinguishes them at 
once: in the case of enterochlorophyll, the bisulphide takes up 
more of the lipochrome, the alcohol retaining some chlorophyll. 
There are other reasons which I have given elsewhere, and 
the morphological differences are so well marked that it is no 
longer possible to maintain such a view. 

The present paper contains only a preliminary account of 
the subject, which I hope to study more thoroughly again. 

I have gone over most of Sorby’s experiments during the 
last ten years, and I am more and more convinced of the 
soundness of his deductions and the accuracy of his experi- 
ments; but owing to his diagrams not giving all the bands, and 
his bands not having all been described in wave-lengths, one 
has great difficulty sometimes in following the descriptions. 
This remark more especially applies to the chlorophylls, as lam 
unable yet to distinguish “ blue” from ‘ yellow chlorophyll,” 
aud I think one is safe in concluding with recent observers that 
the green constituent of chlorophyll gives four bands in the red 
half of the spectrum, and the yellow those in the violet half; 


1 Thid., 2te Reihe, 3tte Abth., 1882. 
* HK. g., the spectra are totally different. 


NOTES ON THE CHROMATOLOGY OF ANTHEA CEREUS. 589 


and hence I am inclined to think that the band represented in 
Sorby’s diagram in the case of “‘ blue” and “ yellow chloro- 
phyll” and chlorofucin occurring in the violet end, really 
belongs to the yellow constituent, which has been incompletely 
separated by the “ fractional”? method. 


EXPLANATION OF PLATES XXXIX and XL. 


Illustrating Dr. C. A. Mac Munn’s “ Noe. on the Chro- 
matology of Authea cereus.’ 


PLATE XXXIX. 

Transverse section of a tentacle of Anthea cereus which had been kept in 
alcohol for some time; it was stained with picrocarmine, and mounted in 
Canada balsam. The relationship of the “yellow cells” to the endodermal 
lining of the tentacle is well shown. The specimen is supposed to be mag- 
nified 80 diameters, and was drawn by means of Swift’s erecting camera 
lucida, the paper being fourteen inches distant from the eye-piece. 

The radiating cracks in the interior of the mass of ‘yellow cells” are 
clearly shown, as well as the absence of any connecting structure. 


PLATE XL. 
Spectra of the colouring matters of Anthea cereus, &c. 

Sp. 1.—Absolute alcohol extract of tentacles of Anthea, deep layer. 

Sp. 2.—The same shallow layer. 

Sp. 3.—Absolute alcohol extract of other parts without tentacles. 

Sp. 4.—The same shallow layer. 

Sr. 5.—The alcohol solution of tentacles was diluted with water and agitated 
with bisulphide of carbon, which gave this spectrum. 

Sp. 6.—Second bisulphide extract from the alcohol solution ; note the dark 
band in violet end, which does not belong to the pigment giving bands in the 
red end. 

Sp. 7.—The original alcohol solution after having been three times extracted 
with bisulphide ; these are the bands of Sorby’s chlorofucin. 


Sp. 8.—The same shallow depth. 


590 C. A. MAC MUNN. 


Sp. 9.—Action of hydrochloric acid on the same solution, showing changed 
chlorofucin as Sorby describes it. 

Sp. 10.—Second absolute alcohol extract of the tentacles; this shows mainly 
the chlorophyll bands, possibly the narrow band belongs to the chlorofucin ? 

Sp 11.—This was diluted with water and agitated with bisulphide of carbon 
which on separating gave this spectrum. 

Sp. 12.—The same shallow depth. 

Sp. 13.—Third absolute alcohol extract of tentacles (the second and third 
extract of the parts without the tentacles gave the same bands as the second 
and third extract of the tentacles, therefore they have not been mapped). 
Note in 13, the narrow (second) band is gone, showing that now the chloro- 
phyll constituent is probably alone present. 

Sp. 14.—Action of caustic soda on the last solution. 

Sp. 15.—For comparison with the chlorophyll bands of Anthea. An 
absolute alcohol extract of a green Ulva, was diluted with water and agitated 
with carbon bisulphide, which after separation gave this spectrum; this 
solution appears to contain Sorby’s ‘‘ yellow chlorophyll.” Compare with 5, 
1], and 138. 

Spr. 16.—Thin layer of the same. Compare with 12, and it will be seen 
that probably a similar lipochrome is present in Anthea and in Ulva. 


ON OTENODRILUS PARVULUS. 591 


On Ctenodrilus parvulus, nov. spec. 
By 


Robert Scharff, B.Sc., Ph.D. 


With Plate XLI. 


Tue genus Ctenodrilus, which was first established by 
Claparéde, is represented by two species, viz. Ct. pardalis and 
monostylos. 

A new species of this small and most interesting Annelid 
was recently discovered by Mr. Bolton, of Birmingham, in his 
seawater aquarium, and forwarded by him to Professor Ray 
Lankester for identification. Professor Lankester had the kind- 
ness to place the whole material at my disposal, and gave me 
the opportunity of pursuing my investigations at the zoological 
laboratory of University College. Mr. Bolton states that he does 
not know the exact locality whence the worm originally came. 
It is certain, however, that it was sent to him from some place 
along the British coast, where to my knowledge it has not been 
met with before. I kept abouta score of them in a small bottle 
for some weeks in November and December, 1884, in order to 
study their peculiar mode of fissiparous reproduction, and if 
possible to detect their sexual means of propagation. As regards 
the first item I was successful, but shared the same fate as my 
predecessors, Kennel and Zeppelin, in not finding any generative 
organs. 

The worms were at first not very lively, crawling slowly 
along the glass near the surface of the water, but soon began to 
divide rapidly. The new species, which I propose to name 
Ctenodrilus parvulus, differs in several respects from 


592 ROBERT SCHARFF. 


Ct. pardalis, and more so from Ct. monostylos. Its 
smaller size is the most striking feature, for while Ct. pardalis 
has from twelve to fourteen segments and a length of 6—7 
mm.,Ct. parvulus has only from seven to ten segments and 
averages about 4mm. in length. The most important differ- 
ence, however, lies in the nature of the bristles, which are not 
pectinated as in Ct. pardalis, but approach in shape one of 
the two kinds found in Ct. monostylos (fig. 2). 

In the anatomical details, as well as in all the other external 
characters, Ctenodrilus parvulus agrees very closely with 
Ct. pardalis. Ct. monostylos has characteristic distinguish- 
ing features in its peculiar tentacle and inthe form of the bristles. 
In that animal, recently described by Zeppelin,! two different 
kinds of bristles have been found, the one straight and needle 
like, the other slightly bent at the apex. Both occur in the same 
bundle except in the anterior segments. 

General Characters.—As already mentioned, Ct. par- 
vulus (fig. 1) agrees in general with Ct. pardalis, and 
exhibits the same characteristic dark green or violet spots in 
the skin, which are due to some colouring matter filling up 
part of the epidermal cells. The colour of the worm itself is of 
a greenish yellow, which sometimes allows of the internal 
arrangements being plainly visible in the living animal. On 
the other hand, very frequently the view is obscured to such an 
extent by the dark spots in the skin as to render its study very 
difficult. 

The segmentation of the body is clearly indicated. It is 
made up of a prostomium, with the head segment bearing 
the mouth, followed by a number of equal body segments and 
the tail segment with the anus. 

There are two rows of bristles on each side, and, as in 
Ct. pardalis, their number in the various metameres is 
subject to great variation. Sometimes I found only one bristle 
in the dorsal row and several in the ventral row of the same 


1 Max. Graf. Zeppelin, ‘‘Ueber den Bau und die Theilungsvorginge des 
Ctenodrilus monostylos,” ‘ Zeitschrift f. wissenschaftliche Zoologie,’ vol. 
RXXIX. 


ON CTENODRILUS PARVULUS. 593 


segment and vice vers’. In all probability the bristles become 
worn out in time and are then replaced by new ones. ‘This 
shows that we are not always justified in using the number of 
bristles for diagnostic purposes. 

Ctenodrilus parvulus is covered by a very thin cuticula 
and the under surface of the prostomium as well as the under 
part of the mouth segment are ciliated as in Aelosoma. The 
whole of the cesophageal cells and those of the intestine also 
bear cilia. Under the lens the animal has a reddish appear- 
ance, due to the bright red colour of the large stomach (fig. 1, 
st.), which will be dealt with later on. The cesophagus reaches 
to the commencement of the third segment, the stomach 
occupies generally three or four, and the remaining segments 
contain the intestine. 

With regard to segmental organs there is only one pair of 
them, viz. in the head segment (fig. 1, so.). In some of the 
more transparent specimens they are readily seen, but the 
study of their histological structure offers great difficulty. 

The vascular system, consisting of a dorsal (d. v.) and a 
ventral vessel (v. v.), is not always distinctly visible. The 
blood is colourless and does not contain any blood-corpus- 
cles. There is a dorsal vessel, existing only in the three 
anterior segments. It takes its origin at the junction of 
the oesophagus and stomach and its lumen is gradually 
narrowed down as it reaches the head segment. In the 
first segment it divides into two branches, which surround 
the cesophagus, and, joining again below into one, forming the 
ventral vessel. 

It now remains to say something about the movements of 
the animal. When isolated it quickly draws itself together and 
remains in a curved position for some time. It then protrudes 
the large bifid lower lip, which is no doubt used as a “ point 
d’appui,” in order to draw the body forward. But to do this 
the longitudinal muscles are gradually shortened, causing the 
body to swell up. The swelling is first seen near the hinder 
end, but soon travels towards the head, which is thus moved 
onward. Having hereby changed its position, before it ventures 


594, ROBERT SCHARFF. 


on anew move it feels its way first by means of the prosto- 
mium, which seems to act as a tactile organ, and then repeats 
the same performance. Sometimes it coils itself round in a 
snake-like fashion, continually using the thick lower lip, which, 
I believe, may also be useful in nutrition although I have not 
actually seen it taking up food with it. 

The Skin.—This is composed of an epidermis covered by a 
very thin homogeneous cuticula. The outlines of the compo- 
nent cells are not very readily made out in cross sections, and 
they vary in size according to the different parts of the skin in 
which they are found. At the sides of the body their height 
is about equal to their breadth, towards the ventral side. On 
the other hand, the cells increase in height and decrease in 
width. Their appearance here will be referred to again in con- 
nection with the nervous system, which lis in its entire length 
in the epidermis ; suffice it to say that it appears to consist of 
several layers in the ventral part of the body. 

I said before that the under surface of the head segment is 
ciliated. The same has likewise been noticed in the other two 
species of Ctenodrilus, as well as in a few more kindred forms. 

A surface view of the skin under very high power reveals a 
large number of the dark violet pigment spots, and among 
them a few much lighter ones. The intervening spaces are 
partly covered by exceedingly dark minute specks, contrasting 
with the light green or yellow ground. According to Kennel! 
the dark pigment is dissolved out by alcohol, a fact which I 
can testify by my own experience. The same author says, p. 
380, that if this fatty matter be withdrawn from the cells by 
the action of alcohol and turpentine, the colouring material 
remains behind in shape of irregular stains. The dark pigment 
lies in the epidermal cells, and appears to be of a fatty nature. 
In the prostomium and around the anus itis largely developed, 
and in these parts almost fills up the whole of the cells. This 
condition does not obtain towards the middle of the body, 
where the pigment only enters to a small extent into the 


+ J. Kennel, “Ueber Ctenodrilus pardalis,” ‘Arbeiten aus d. Zool. 
Institut, Wiirzburg,’ 1882, p. 380. 


ON CTENODRILUS PARVULUS. 595 


interior of the cell. Prof. Ray Lankester! makes mention of 
‘clear cells or vesicles”? as occurring in the skin of Cheto- 
gaster limnei, which appear to be identical structures. He 
tells us further that the clear vesicles in the integument of 
many Planarian worms likewise belong to the same order of 
structures. 

Projecting from the skin we have a certain number of 
bristle-bundles in every segment, viz. one pair in each. I have 
already called attention to the fact that the quantity of 
bristles in each bundles is not the same, but varies to a con- 
siderable extent. A characteristic structure of the Oligo- 
cheetes, the small involutions from the skin in which the 
bristles take their origin, is not present here. 

According to Zeppelin, Ctenodrilus monostylos has 
never less than two bristles in a bundle, while in parvulus I 
frequently found only one. The shape of the bristle in 
Ctenodrilus parvulus in distinction to the closely-related 
Ct. pardalis is that of a spear, the apical part being slightly 
bent (fig. 2). In the latter species the bristles are pectinated, 
and in Ct. monostylos there are two different kinds, one of 
them being long and slender, and the other somewhat resem- 
bling the one I just described as occurring in Ct. parvulus. 
Another point of difference in respect to the bristles of Ct. 
monostylos is that they project much further from the skin 
than in Ct. parvulus. 

The Muscles.—Beneath the epidermis we find one very thin 
muscular layer. There is no perceptible division into a trans- 
verse and longitudinal part, the layer consisting merely of the 
primitive longitudinal fibres, which stretch without intermission 
from head to tail. The few bristles in each bundle are moved 
by some fibres attached to the general body wall. 

A powerful muscle inserted at the front part of the ceso- 
phagus causes the protrusion of the lower lip. No special 
structure can be assigned to the muscular fibre, and, as Zeppelin 
has pointed out, Ctenodrilus shows great resemblance to the 


1 E. R. Lankester, “ A Contribution to the Knowledge of the Lower Amne- 
lids,” ‘ Trans. of the Linnean Soe.,’ vol. xxvi, p. 634. 


596 ROBERT SCHARFF. 


Polygordius group with regard to the muscular system. We also 
find in this group the same primitive arrangement of a simple 
longitudinal Jayer of muscles, and in this simple muscular 
structure we see no doubt represented the original condition 
among the Annelids. 

The Alimentary Canal.—Three parts may easily be dis- 
tinguished in the alimentary canal of Ctenodrilus parvulus. 
The ventral mouth, which has the form of a longitudinal slit, 
opens into the ciliated cesophagus. This, in its turn, is followed 
at the beginning of the third segment by the red stomach, and 
the intestine constitutes the remainder of the alimentary canal. 
The latter, like the cesophagus, is ciliated, and generally com- 
mences at the end of the sixth or the commencement of the 
seventh segment. In Ct. pardalis the cells of the whole of the 
alimentary canal are ciliated,! while in Ct. monostylos we find 
a similar condition as in Ct. parvulus, viz. ciliated cells in the 
cesophagus and intestine only. The cells of the ventral side of 
the alimentary canal are considerably higher than those of the 
lateral or dorsal sides, so as to cause that part to appear from 
two to three times as thick. The reddish cells of the stomach 
gradually merge into the ciliated cells of the intestine, that is 
to say, they become lighter and lighter in colour, and assume 
the ciliated condition on approaching that part of the alimen- 
tary canal. At the commencement of the stomach we do not 
see anything of that kind, but an abrupt change from the ciliated 
to the non-ciliated condition. 

The cesophagus (fig. 1, @) is much narrower than the stomach, 
and attains its smallest diameter close to the mouth, just above 
the hinder end of the lower lip (‘‘ Unterlippe” of Kennel, 
“ Russel ” of Zeppelin). 

This lower lip is situated beneath the mouth, and consists of 
a broad muscular plate, the anterior part of which being split. 
I mentioned before that a strong muscle, acting as protractor 
to this organ, is inserted into the lower portion of the ceso- 
phagus. 


' Kennel, loc. cit., p. 383. 


ON CTENODRILUS PARVULUS. 597 


Claparéde,! who gave the first description of Ct. pardalis, 
represented the lower lip of this form (pl. xv), as if it were the 
swollen front portion of the cesophagus, and described it as a 
“tonnenformiger muskuldser Schiund.” Professor Ray Lan- 
kester pointed out some timeago that O. Schmidt’s Parthenope 
serrata was of the same genus as Ct. pardalis, and this too 
has been figured by Schmidt? with a muscular cesophagus similar 
to Claparéde’s. If low powers are used the real nature of the 
lower lip might easily be mistaken, and I think it quite pro- 
bable that on re-examination the ‘ proboscis” of Parthenope 
serrata would be found to be an organ corresponding to that 
of the genus Ctenodrilus. 

I refer to Zeppelin’s and Kennel’s papers for further details 
on the subject of the lower lip. Whether the organ is used as 
a means of taking in food I have not been able to observe, but it 
probably is. At any rate, it plays an important part in the act 
of locomotion, as I had the opportunity of mentioning before. 

The Vascular System.—We have a dorsal and a ventral 
blood-vessel in Ctenodrilus parvulus, just as in the other 
species, and a communication between the two in front. The 
dorsal vessel (fig. 1, d.v.) divides into two branches in the first 
segment, which, uniting again below the cesophagus, forms the 
ventral vessel (v.v.). The vessels are not readily visible in the 
living animal, except the dorsal, which contains a_ peculiar 
organ known as the ‘‘ rathselhafte” organ (fig. 1, en.), also as 
“corps cardiaque” among French authors. Due to this organ 
the dorsal vessel is comparatively conspicuous. It is likewise 
found in the other species of Ctenodrilus, but neither Kennel 
nor Zeppelin give a satisfactory answer as to its origin or func- 
tion. I shall say some more about it presently. 

The dorsal vessel takes its origin at the anterior portion of 
the stomach, where it is attached to the wall of that part of the 


1 Claparéde, ‘ Beobachtungen tiber Anatomie und Entwicklungsgeschichte 
wirbelloser Thiere d. Kiiste von Normandie,’ Leipzig, 1863. 
2 O. Schmidt, ‘Zur Kenntniss d. Turbellaria rhabdocoela und einiger 


anderer Wiirmer d. Mittelmeers Sitzungsberichte d. Kais. Akademie, Wien., 
vol. xxiii, 1857. 


098 ROBERT SCHARFF. 


alimentary canal. It begins here with a wide mouth, its dia- 
meter decreasing rapidly as it reaches the first segment. The 
above-mentioned enigmatic organ takes up a central position 
in the vessel. It, too, attenuates towards the anterior part of 
the animal and disappears in the head segment. A little more 
light has quite recently been thrown on the function of a 
similar hitherto problematical structure by Horst.1 He looks 
upon it as a gland in connection with a blood-sinus of the ali- 
mentary canal, the latter being a continuation of the short 
dorsal vessel. The blood circulating in this sinus is supposed 
to pass through the glandular organ into the dorsal vessel. As 
there does not appear to be a sinus in the wall of the alimentary 
canal of Ctenodrilus we may regard the so-called enigmatic 
organ as aremnant from some more ancient type, where the 
organ was of more use in connection with the blood system, 
and that it has in time undergone retrograde development. 

Segmentation and Segmental Organs.—The outer 
segmentation corresponds to the inner as in other Cheetopods. 
This, however, is not the case throughout, and the alimen- 
tary canal especially shows numerous constrictions quite 
independent of those of the body. There are from seven 
to ten segments in Ctenodrilus parvulus, one of the dis- 
tinctions between it and the closely related Ct. pardalis and 
monostylos. 

The dissepiments are loose and easily moved forward and 
backward with the alimentary canal. Between the septa are 
seen a number of small nucleated cells, which float about the 
body cavity. Zeppelin is of the opinion that they serve as 
stores for nutritive material in those individuals which are 
still unable to provide food for themselves. As these cells 
appear to be more numerous in specimens that are just under- 
going division, this view is probably the correct one. 

The small segmental organs are not always clearly discernible. 
In no case are they distinct enough to admit of their true 
structure or parts being well recognised. Like Ct. pardalis 


1 Horst, “ Ueber ein rathselhaftes Organ bei den Chloraemiden,” ‘ Zoologi- 
scher, Anzeiger,’ Januar, 1885. 


ON CTENODRILUS PARVULUS. 599 


and monostylos there is here only one pair of them. The 
segmental organs lie in the head segment, one on each side of 
the cesophagus. They are in form of two minute coiled tubes. 
I could only see the ciliated canal and the internal opening; 
an external opening described by Kennel was not visible, but 
it undoubtedly exists. 

No segmental organs are found in the other segments. We 
do not meet with this very peculiar condition in any other 
fully grown Annelid. The larval form of Polygordius, on the 
other hand, exhibits in the so-called “‘ Kopfnieren ” a condition 
not unlike that of Ctenodrilus. Hence we may compare the latter 
in this respect with the Polygordius larva. Kennel! even goes 
further by saying that “in Ctenodrilus the excretory organ of lar- 
va] Annelids has remained as the permanent organ of excretion.” 

The Nervous System.—The nervous system agrees in 
position and structure with that of the other two species of 
Ctenodrilus. It lies in its entire length in the epidermis, and 
consists of a cerebral ganglion sending two commissures towards 
the ventral surface, where they unite to form the nerve-cord. 

A similar condition of the nervous system obtains in a few 
other Annelids mentioned by Semper,? as well as in the 
Gephyrea, Priapulus and Halicryptus.® 

The parts are too small to allow of a more minute examina- 
tion of the structure of the nervoussystem. Asin Halicryptus 
and Priapulus epithelial and ganglionic cells seem to merge into 
one another, and near the cerebral ganglion, for instance, it is 
difficult to say where the former end and the latter begin. The 
epithelium apparently becomes several layered near the nerve- 
cord, as well as close to the cerebral ganglion. Peripheral 
nerves were not to be seen. 


1 Kennel, loc. cit., p. 392. 

2 Semper, “ Die Verwandtschaftsbeziehungen d. gegliederten Thiere,” ‘ Ar- 
beiten aus. d. Zool. Institut, Wiirzburg,’ vol. iii, According to this author 
the following species have the nervous system lying in the ectoderm either 
wholly or partially :—Terebella sp. of Heligoland, Terebella zostericola, 
Hyalinecia tubicola, Maldane sp. 

3 Scharff, “On the Skin and Nervous System of Priapulus and Halicryp- 
tus,” ‘ Quart. Journ. Micr. Soc.,’ vol. xxv, 1885. 

VOL, XXVII, PART 4,—NEW SER, yal 


600 ROBERT SCHARFF. 


The only sensory organs are two small ciliated pits, one on 
each side of the cerebral ganglion. They are not very con- 
spicuous, and may quite easily be overlooked. At any rate 
they are very much smaller than those indicated in Claparéde’s! 
figure of Ct. pardalis. 

Fissiparous Reproduction.—It has been mentioned 
that no traces of reproductive organs could be discovered, but 
many of the animals kept were either young ones or were just 
undergoing division. A lengthy report of the division of 
Ctenodrilus pardalis has been published by Kennel.? The 
general plan of the division in Ct. parvulus is the same as that 
inCt. pardalis. The want of sufficient material prevented me 
from investigating the histological changes going on during the 
act of fissiparous reproduction. Hence I will merely state the 
general characters as far as I made them out, and which agree 
with those reported by Kennel as occurring in Ct. pardalis. 
At the same time it will not be out of place to give a short sum- 
mary of the division in Ct. monostylos in comparison with 
that of the two other forms. A few diagrammatic drawings 
(figs. 3 and 4) will help to make the statements clearer. 

We find a peculiar, but at any rate primitive, condition with 
regard to the division of Ct. pardalis andparvulus. The 
great characteristic of these two Annelids is that almost every 
segment becomes a zooid which rapidly develops into the multi- 
segmented form. Thisis brought about in the following manner: 
—A bud appears between two segments, and, in distinction to 
Naids and kindred forms, the buds are produced in the same 
order as new segments are, viz. from before backward (fig. 3, 0). 
In Naids the production of buds takes place in a similar way to 
that of the tapeworm, a condition which has been termed 
“ strobilation.”” Hence Semper’s® “ proglottidentheorie,” which 
he thought was applicable to all Annelids, does not hold good 
in the case of Ctenodrilus. 

In order to make the terms “ strobilation” and ‘“ segmenta- 

1 Clapareéde, loc. cit., pl. xv, fig. 28 
2 Kennel, loc. cit., p. 395. 
3 Semper, loc. cit., p. 290. 


ON OTENODRILUS PARVULUS. 601 


tion” clearer I will quote the following formula from Kennel. 
Supposing we call the oldest segment 1, the second oldest 2, 
and the youngest w, we obtain: 


Strobilation,],2,0—-l,a—-2... 4,3,2. 
Segmentation, 1,2,3,4 ..... #-%2#-1,z. 


Previous to the act of division the animal generally remains 
in a curved position, the posterior segments exhibiting inde- 
pendent motions which were not before noticed. 

The appearance of buds is the next feature, preceding 
division. The first bud makes its appearance dorsally imme- 
diately behind the third segment, the second behind the fourth, 
and soon. In Ct. parvulus we never find more than three 
or four buds (in Ct. pardalis there may be six or more), 
The first three segments never show any indication of budding, 
nor do the last two or three. 

An accumulation of pigment appears in the buds as soon as 
they show themselves. The red colour of the stomach at the 
same time becomes materially darker. The part between two 
segments is now very much constricted, and the bud grows 
rapidly forward, so as to assume the shape of the head segment. 
The previously red portion of the alimentary canal appears 
almost black just before division, except at the constrictions, 
where it takes the colour of the intestine. 

Zooids have the peculiarity, as long as they remain united, 
never to develop new dissepiments. Only after the division, 
after the breaking up, as it were, of the animal do new seg- 
ments appear. In the true Naids, on the other hand, a differen- 
tiation of the budding zones goes on to such a degree that 
when division occurs each zooid may already be regarded as a 
fully-developed animal. 

The first zooid in Ctenodrilus needs only to regenerate the 
anus, and the last zooid the head. As soon as division has 
actually taken place the zooids very soon develop into the 
adult condition. The alimentary canal is closed at those parts 
where it was ruptured by the constrictions, and a new mouth 
and anus are formed in the two or three middle zooids. The 


602 ROBERT SCHARFF. 


animals I had under observation all completed the act of fisssi- 
parous reproduction within forty-eight hours. 

Comparing the division of Ct. monostylos (fig. 4, a—c) . 
with that of the two forms I just described, the most striking 
difference lies in the fact that there is no appearance of buds. 
In Ct. monostylos we have merely a breaking up of the 
animal into two almost equal parts, each of which may again 
break up into two or more parts. The regeneration only takes 
place after the division has been completed. 

Summing up the result of Zeppelin’s researches on the 
division of Ct. monostylos into a few words, we should have 
the following : 

In the fully-grown normal individuals a constriction takes 
place about the middle of the body, which gradually becomes 
deeper and deeper. At the same time the intestine becomes 
rounded off in the two parts, and ultimately the mother animal 
breaks up into two daughter animals of about the same size, 
one of which bears the head along with some segments, the 
other the anus, also with a few body segments. The regenera- 
tion always begins after division has taken place. 

Both daughter animals are capable of subdivision into parts, 
all of which contain a portion of the original animal’s intestine. 
Those parts are either— 

(1) Parts which have neither head nor anus, consist only of 
one to three segments, and are incapable of division ; or 

(2) Parts without head or anus, possessing more than three 
segments, which may divide again. 

The daughter animal which contains the primary head has 
been noticed to constrict off a part provided with the secondary 
anus. Whether a corresponding constriction also takes place 
in the other daughter animal has not been observed. 

This constitutes the main difference in the mode of fissiparous 
reproduction of Ct. monostylos, on the one hand, and 
Ct. pardalis and parvulus on the other. 


ON CTENODRILUS PARVULUS. 603 


EXPLANATION OF PLATE XL, 


Illustrating Dr. Robert Scharff’s paper on “ Ctenodrilus 
parvulus,” nov. spec. 


Fic. 1.—View of Ctenodrilus parvulus (highly magnified, somewhat 
diagrammatic). mo. Mouth. a. Anus. s.0. Segmental organ. d. v. 
Dorsal vessel, v.v. Ventral vessel. @. Cisophagus. st, Stomach. 47. 
Bristles. ez. Enigmatic organ. iz¢. Intestine. 


Fie. 2.—One of the bristles of Ct. parvulus (highly magnified). 


Fic. 8.—Fissiparous reproduction of Ct. parvulus (Ct. pardalis is 
quite similar ; see text). a. First stage. 4. Second stage. c. Third stage. 


Fic. 4.—Fissiparous reproduction of Ct. monostylos. a. First stage. 
6. Second stage. c. Third stage. (Copied from Zeppelin.) 


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71 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 605 


The Relation of the Nemertea to the 
Vertebrata. 


By 


A. A. W. Hubrecht, 
Professor in Utrecht. 


With Plate XLII.! 


In venturing at the close of my Report on the Nemertea, 
collected by H.M.S. “Challenger,” to leave the region of 
demonstrated facts and actual observations, and to enter upon 
that of speculation and suggestion, I gladly availed myself of 
the permission for so doing granted to me by the editor, Mr. 
John Murray. I thought it necessary to ask for that permis- 
sion, because general speculations on the ancestry of the 
Chordata hardly appeared to me to fit into the framework of 
those Reports. My desire in this case to deviate from a rule 
which I held to be salutary, was due to the fact that of late 
these speculations have been conducted along very varying 
channels, an entirely new one having only very lately been 
opened by Bateson’s important series of papers on Balano- 
glossus. An attempt to give more depth to one of these 
channels, and thus to lead into it the attention of a greater 
number of my fellow-workers, especially commended itself to 
me, since it was my conviction that the lines laid down by 
myself in former publications derived considerable support 
from the “ Challenger ” material, and were thus entitled to a 
renewed and full consideration. 


1 Published by permission of the editor of the ‘Zoology of the Challenger 
Expedition,’ Mr. John Murray, F.R.S.. 


606 A, A. W. HUBRECHT. 


I would formulate the proposition, to the further develop- 
ment of which this memoir is to be devoted, as follows: 

More than any other class of invertebrate animals, 
the Nemertea have preserved in their organisation 
traces of such features as must have been character- 
istic of those animal forms, by which a transition 
has been gradually brought about from the archi- 
celous Diploblastic (Celenterate) type to those 
enterocelous Triploblastica, that have afterwards 
developed into the Chordata (Urochorda, Hemi- 
chorda, Cephalochorda, and Vertebrata). 

It will be seen that this statement excludes the idea of any 
direct ancestral relations between Nemertea and Chordata. 
If any such relation were proposed, it might with good reason 
be asked—considering the very extensive variation which is 
met with amongst Nemertea—which species or which genus 
was more particularly pointed to. The question in itself con- 
demns the proposition which leads to it. 

It will, moreover, be seen that this statement accepts the. 
outcome of Bateson’s researches and speculations, in so far as 
the points of agreement between Balanoglossus and Am- 
phioxus are fully recognised. A provisional link between 
these two, and an arrangement of Balanoglossus as amongst 
the Chordata, appears to be quite as justifiable as the elevation 
of the Urochorda to their new dignity in zoological classifi- 
cation. 

There is, however, a great difference between looking at 
Balanoglossus as a low type amongst the Chordata (in 
which I fully agree with Bateson) and rejecting the signifi- 
cance of the Nemertean type as one of transition in the way 
above indicated. 

There is no doubt that the Nemertea represent a more primi- 
tive phase than the Enteropneusta (Hemichorda). They have 
no gill-slits ; but their nervous system shows certain unexpected 
analogies with that of the higher Chordata of more intrinsic 
value than those that obtain between Balanoglossus and 
the Chordata in general. Also for the important question, 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 607 


which is so vital in any consideration of the ancestry of the 
Vertebrates, viz. the origin of metameric segmentation, it 
appears to me that the Nemertea offer points very worthy of 
consideration. The question of the proboscis and its sheath, 
as comparable to hypophysis and notochord was fully treated 
by me in another paper,! and will here only be very briefly 
touched upon. In my opinion, this comparison is all the more 
forced upon us, now that in other respects (nervous system, &c.) 
new evidence of genetic relationship is here brought forward. 

The first point I wish to consider is that of metameric seg- 
mentation. It has been specially treated of late years by 
various authors of renown, with whom I do not wish to enter 
at this moment into any lengthy controversy, but will briefly 
state what may be gathered for the theory in general, from 
a careful consideration of the incipient metamery of the 
Nemertea. 

If we start from a more or less radiate ancestor of the 
earliest diploblastic type, in which neither a radial nor a serial 
repetition of organs or organ systems has yet come about, and 
which may indifferently be considered to resemble either a 
more flattened Trichoplax or a more spherical gastrula, we 
may assume that in the course of the development of other 
internal organs (towards the formation of which the secondary 
accumulation of cells between the two primary layers often so 
largely contributes) the radial symmetry may either be further 
accentuated or may be replaced by a tendency towards bilateral 
symmetry. In the latter case we are inclined to ascribe the 
first impulse towards this bilateral symmetry to a preference, 
which slowly establishes itself in the animal mechanism, for 
moving in one direction rather than in any other, i.e. for 
generally stretching forward, when moving about, one particular 
portion of the body. 

One impulse of this sort will suffice to lead us to understand, 
or rather to deduce, a very considerable number of conse- 
quences, which cannot fail to make their appearance under the 


1 “On the Ancestral Forms of the Chordata,” ‘ Quart. Journ. Micr, Sci.,’ 
vol, xxiii, 1883. 


608 A. A. W. HUBRECHT. 


influence of natural selection acting upon the organisms that 
have inherited this tendency in different degrees. Thus we 
may understand the narrowing and lengthening of an animal 
that moves in one direction in preference to any other; and 
similarly the development in the nervous system of a centrali- 
sation not far away from the anterior extremity. 

All this has already been stated by Balfour in clearer terms 
in his ‘ Comparative Embryology’ (vol. ii, pp. 808, 311), where 
he describes the gradual steps by which a radiate medusa-like 
animal may have passed into a bilateral worm-like form, with 
two longitudinal nerve-stems, which are regarded by Balfour 
as the stretched nerve-ring of the Medusa. 

I fully endorse these views ; only, with respect to the nervous 
system, I hold it to be safer to leave out of comparison the 
already specialised nerve-ring of the Medusa, and rather to go 
back to the Coelenterate nervous system as primitive as that of 
the Actinia, where the plexus, both of the epiblast and the 
hypoblast, with an increase in density in the region of the 
mouth and the tentacles, may be said to be the fair representa- 
tive of one of the lowest starting points. In this the plexiform 
arrangement predominates. 

Now we find in all the lower invertebrates various though 
distinct nerve tracts that are being specialised in this plexiform 
nerve-tissue according to the modes of motion of the animal, 
and according to the general shape of the body. 

Thus in the Meduse, which move about in the water by 
annular contractions of the lower portion of the bell-shaped 
body, one of the nerve-rings already alluded to was demon- 
strated by the Hertwigs to innervate the musculature by which 
this is brought about. 

In the Ctenophora the nerve system is less satisfactorily 
known, but still Lang! does not hesitate to bring them into 
genetic relationship with the Polyclada. Among the latter, 
Gunda, with its two longitudinal lateral stems, may be looked 
upon as an extreme term in this series. 


1 A. Lang, ‘Monographie der Polycladen,’ Leipzig, 1884. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 609 


Another series may indeed be supposed to have derived 
longitudinal stems from a ring which became extended to form 
lateral cords, as the animal passed from the radial to the 
bilateral symmetry, in the way suggested by Balfour. Still, 
even in this case, a nerve-plexus may be expected to be coex- 
istent with or to have preceded the nerve-ring. The longitu- 
dinal stems originating from the anterior thickenings of the 
plexus that innervate the sense organs and the tip of the head 
(specially sensitive in connection with the forwardly directed 
movements of the body), would all the more probably be pre- 
served and increase in development, as during this forward 
movement they form a right and a left centre for the reception 
of outward stimuli. In the same way those of the radially 
arranged stems of the Polyclada that are parallel to the longi- 
tudinal body-axis, and mark out right and left, are more 
strongly developed than the others, presumably on account of 
their importance in connection with the well-directed move- 
ments of the body in response to external agents. 

In the ancestral Mollusca I think we may assume with 
great probability the presence of four longitudinal stems 
—two latero-dorsal and two latero-ventral ones; in the ances- 
tral forms of Annelids and Arthropods two, which have gra- 
dually coalesced ventrally, as was first suggested by Gegenbaur. 
Again, in Nematodes differently situated longitudinal stems in 
what was originally a uniform plexus are preserved ; whereas 
in ancestral Nemertea two lateral longitudinal trunks in the 
plexus were undoubtedly characteristic features. 

That one medio-dorsal stem in this plexus, in which all the 
impressions made by outward agencies on both halves of the 
body might be concentrated, and from whence the correspond- 
ing movements might be regulated, will more fully answer the 
purpose than two lateral stems, however they may be united 
by an intervening plexus, is a priori probable, and would 
explain the first impulse towards the formation of such a 
longitudinal concentration in the uniform plexus. 

And when once such a dorso-median stem is present, in 
addition to two lateral ones, a struggle for supremacy, presided 


610 A. A. W. HUBRECHT. 


over by natural selection, may lead to a diminution of the 
lateral stems, and to an increase of the dorso-median one. 

This, in my opinion, as will be more fully developed below, 
was the case in the ancestors of the Chordata, traces of this 
struggle and of the competing structural elements being duly 
preserved. 

If we suppose the bilateral symmetry to be established in 
one of the lower representatives of the Metazoa, and the type 
to goon increasing in length in the course of generations, 
then this increase indeed exposes it to very different and per- 
haps more numerous dangers and enemies than would 
threaten it were the same bulk concentrated in a spherical or . 
radial circumference. And if, even in the latter case, injuries 
to the individual might prove fatal were it not provided with 
strong powers of regeneration (cf. Star-fishes, Ophiurids, 
Crinoids, &c.), still it needs no comment that, when bilateral 
symmetry and increase in length so considerably enlarges the 
surface which is open to attacks, and so enormously facilitates 
the rupture of the individual, or the severing of parts by rapa- 
cious enemies preying upon it, similar regenerative powers 
are none the less required to insure the persistence of the 
type. 

These dangers, continually threatening the exist- 
ence of the individuals, and thus injurious to the 
species, counteracted as they are by regenerative pro- 
cesses (power of reproduction of lost parts), I hold to be 
at the base of all those cases of metamery in the 
animal kingdom which do not fall under the head of 
strobilation, the latter being comparatively rare with respect 
to the former. Incipient metamery, once established by this 
cause, may further differentiate in the most diverse directions 
(heteronomous segmentation, &c.), even after the absolute 
cessation of the causes that in the first instance have 
provoked it. 

The explanation has, moreover, the advantage of being 
applicable to radial as well as to serial metamery. 

These propositions must now be more fully developed. The 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 611 


power of reproduction of lost parts comes, without doubt, under 
the general laws of formation and growth. We find it even 
in the lowest Protozoa. If the material which heredity has 
accumulated, either in such a unicellular being or in the egg 
of a Metazoon, and out of which the elements of the different 
organ systems will gradually develop, is hereditarily so disposed 
that a compensation for the loss of important parts is facili- 
tated, this will, of course, constitute an advantage. Such a 
compensation may, e.g. be obtained where the generative 
products are developed in very many separate centra, and not 
in one closed sac. Injury to the latter will, ceteris paribus, 
be more fatal than an equivalent injury destroying one or more 
of the former. The same holds good for diffused instead of 
concentrated nervous centra, for the case of liver saccules to 
the intestine, instead of one compact liver, for numerous aper- 
tures and deferent ducts to the nephridial system instead of 
one, &c. And all! this is still more evident when we have 
before us a long, bilaterally symmetrical animal, which is easily 
snapped in two. In this case it must be of pre-eminent impor- 
tance, that the remaining halves, which may in their turn be 
severed by the same cause into smaller parts, should possess 
sufficient power of reproduction to repair the damage. Now, it 
cannot be doubted that an equal distribution of the important 
components of the organism (nervous centra, generative organs, 
nephridia, intestinal appendages, &c.) throughout the whole 
length of the animal meets this requirement. Any severed 
portion will then be provided with these more important parts, 
and will be more or less adapted for a separate and individual 
existence. 

The formation of a new mouth and of new brain-lobes in a 
fragment of this description remains, of course, quite as won- 
derful and inexplicable as before, but still we cannot fail to see 
that such an arrangement as here indicated must somehow be 
beneficial to the species, and that we need not stop short with 
Bateson,’ when he says that “the repetition of various struc- 


1 Bateson, “ The Ancestry of the Chordata,” ‘ Quart. Journ. Micr. Sci.,’ 
vol. xxvi, pp. 545, 546, 1886, 


612 A. A. W. HUBRECHT. 


tures is one of the chief factors in the composition of animal 
forms: #) =. 431k The reason for their appearance is as yet 
unknown, and the laws that control and modify them are 
utterly obscure.” Obscurity is not exchanged for broad day- 
light, but something is gained whev we can see that a growth 
of the principal organ-systems in separate and more or less 
independent batches, which in an elongated and bilaterally 
symmetrical animal insensibly passes into the phenomenon of 
incipient metamery, may be of the highest value for the per- 
sistence of the species. 

Now this is actually the way in which we find the important 
organ-systems distributed in the lower Nemertea. And out of 
this more irregular distribution a gradual metamery, in some 
incipient, in others more complete, is seen to evolve within the 
boundaries of the class. Even the nephridial system, in the 
primitive forms provided with only one opening to the exterior, 
participates in this tendency towards metamery, and acquires 
a greater number of apertures, serially arranged in pairs, 
thereby also tending towards a diminution of damage when 
artificial division into two takes place in the nephridial region. 
The metamery, the regular and serial repetition of parts, is 
thus seen to be of great importance in aiding towards repair 
after damage to a lengthened bilateral form, in the same way 
as the radial repetition of parts facilitates repair in the Echino- 
dermata. In both cases the destruction is only partial, the 
other homonodynamic portions temporarily ministering, thanks 
to their more independent relation to the injured region. 

When the faculty of repair of damage, occasioned by the 
severing of the animal into two or more portions, has in the 
course of generations become more and more complete, it can 
be readily understood that it becomes at the same time a defen- 
sive instead of being only a curative process. An animal that 
at the approach of danger can separate in two or more parts, 
each of them capable of reproducing an entire new animal, 
evades this danger very effectively by doing so; whereas 
another that is attacked in the same way and does not possess 
this faculty, is laid hold of, shaken about, and wholly or partly 


RELATION OF THE NEMBRTEA TO THE VERTEBRATA. 613 


swallowed. Soin the Nemertea there is indeed a very strong 
faculty of spontaneous division combined with the faculty of 
repair;! and anybody who has observed a fresh and living 
Cerebratulus, with its extremely delicate sense of touch, 
commence to rupture into two, in preference at the spot where 
it was grasped with the forceps, cannot fail to see in this a 
defensive action. 

This mode of self-defence may in quite another respect be 
useful to the species, because at the same time it serves for 
propagation. Thus we see that the passage of this defensive 
process to that of reproduction by fission is so gradual, that it 
would be impossible to decide in every case what name should 
properly be applied to it. It cannot well be denied that in all 
probability ours is only a special case, in which the power of 
reproducing the species by a process of fission, reaching down 
as far as the unicellular ancestors, has come to be regulated 
by other motor forces than growth, and—if it may not be called 
voluntary fission—still may be regarded as sudden and spon- 
taneous fission, brought about by external influences, of a 
threatening nature to the further existence of the specimen. 
This regulation is no doubt a consequence of selection. Schi- 
zogony having once been established, it must have been further 
beneficial to the species, on the grounds that were developed 
above, that the internal organs should be present in multiple 
numbers, and this having once come about it is easy to under- 
stand that a regular, rigorously metamerous arrangement of 
this multiple material, still more fully answers the same pur- 
pose, and is gradually evolved under the influence of selection. 

Thus we may be said to be able to follow the appearance of 
metamery in a bilateral animal, along all the gradual steps by 
which it is evolved, and many of these steps have remained 
fixed and permanent in different Nemertean genera. 


1 Both M‘Intosh and Barrois have observed and described very peculiar 
cases of repair in Nemertea, where the head, brain, side-organs, &c., were 
reproduced on a headless trunk-piece. These experiments are well worthy of 
careful repetition. It may be that only those fragments in which a portion of 
the cesophagus was retained were capable of repair of the head. 


614 A. A. W. HUBRECHT. 


The last system that will participate in this metamery is the 
muscular system, and a rash conclusion—such as is not rare 
in these days of ontogenetic fetichism—might lead to the 
rejection of the views concerning metamery here developed, 
on the consideration that it is exactly the metamery of the 
muscular system which appears first of all in the ontogenetic 
development of Vertebrates. I will not circumstantially refute 
this argument, but will only remark that in Polygordius 
and other Chetopods, which are representatives of a group of 
animals in which segmentation reaches such a very high degree 
of perfection, the longitudinal muscular layer of the body-wall 
is as yet continuous in the adult, and not divided into meta- 
meric sections, as it is in certain Arthropods and in Vertebrates. 
Now let us consider contractions of the inner muscular layer 
of the Nemertea, the only layer that is common to all of them, 
from Carinella to Cerebratulus and from Cephalothrix 
to Pelagonemertes. This layer also corresponds with the 
longitudinal muscular layer just alluded to of other lower 
worms, such as Polygordius, and, as was noticed in our 
paragraph on the muscular system, its contraction is some- 
times very distinct in favorable sections. 

We then see the contraction marked out as so many suc- 
cessive blocks of contracted, thickened fibres, separated by 
intervening parts of non-contracted fibrous tissue. The 
sections demonstrate that the phenomenon persists through- 
out the whole breadth of the animal, i.e. that successive 
rings of contractile tissue alternate with intervening rings 
in which no contraction is observed. This phenomenon is 
thus in a certain degree comparable to an arrangement in 
distinct myomeres. 

It is not unimportant that it was especially noticed in the 
fundamental muscular layer, and it may at the same time be 
remarked that it appears, from what I have as yet been able 
to observe myself, that the number of these rings in a given 
length of the animal is the same, or a multiple of the number 
of intestinal cca and transverse nerve-tracts in the plexus; 
in other words, that the incipient metamery of the internal 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 615 


organs is in a definite relation to these phenomena—which 
might also deserve the name of incipient metamery—in the 
muscular layers. 

For the present the fact is, however, not yet definitely demon- 
strated that these successive blocks are indeed present as such 
in the living animal. The possibility is still open that they may 
be waves of contraction which have been fixed at the moment 
of the immersion of the animal in the preserving fluid. For 
this reason I will not lay any undue weight on this observation. 

The ideas concerning the origin of metamery here expressed, 
and advocated for several years in my university lectures, differ 
from those of Lang (loc. cit.) and Sedgwick,! in so far as 
they do not recognise the primary importance of the so-called 
ceelomic sacs—the paired archenteric diverticula of Amphioxus 
—for the solution of this question. 

The question of the Vertebrate ccelome, so full of obscurities 
and difficulties, is purposely left out of consideration here, where 
the relation to archicelous ancestral forms is discussed, and 
where an attempt is made to show that it is indeed probable 
that the impulse towards the establishment of metamery is due 
to forces for which the archenteron was not the only, nor per- 
haps the most important part of the organism to act upon. 

Still more different are they from those advocated by Perrier? 
and Cattaneo,> who have adhered to and extended the idea 
already held by others, but by them most actively defended, 
“that the metamery of Arthropods, Vertebrates, and a great 
many Vermes, has originated out of the multiplication by 
transverse fission of very simple primitive worms which 
were not metamerous. The products of this transverse 
fission remaining connected together have then formed a 
chain of individuals, or a linear colony; later on the unity 
of the chain has become more definitely established, the 
single individuals at the same time becoming different both in 

' A, Sedgwick, “On the Origin of Metameric Segmentation,’ ‘ Quart. 
Journ. Micr. Sci.,’ vol. xxiv, p. 43, 1884. 

? i. Perrier, ‘Les colonies animales,’ Paris, 1881. 


3G. Cattaneo, ‘Le colonie lineari e la morfologia dei Molluscli,’ Milano, 
1883. 


VOL, XXVI1, PART 4,——NEW SER. UU 


616 A. A. W. HUBRECHT. 


form and in function, and the foremost individual thus becom- 
ing the head of the series. Each segment (metamere) thus 
represents a reduced individual; a metameric (segmented) 
animal is the result of the more or less complete fusion of 
single individuals into an individual of higher order.”’ 

Emery, from whose paper! I have translated the foregoing 
sentence, has very successfully combated these propositions. 
This author, however, adheres to Lang’s views in ascribing to 
the archenteric pouches, the “ gemmation” as Emery calls it 
(loc. cit., p. 18) of the intestine, the most important and 
initial significance for the first origin of metamery, “the sex- 
ual glands and excretory canals being in relation to the 
intestinal diverticula,” and following the lead. I have above 
explained why I cannot adhere to this argumentation, which 
brings the ccelome and the sacculated intestine too strongly 
into the foreground, and why I rather suppose incipient 
metamery to have been antecedent to either of these (e.g. 
Carinella). On the other hand, many views contained in 
Emery’s important paper coincide with my own. ‘Thus he 
writes (loc. cit. p. 11), speaking of that interesting marine 
Triclade, Gunda segmentata: 

“The metamery of Gunda is thus manifestly the conse- 
quence not of the ‘symbiotic’ fusion of a colony of equivalent 
‘parts’ (meridi), but of the ‘autobiotic’ differentiation and 
perfectioning of one ‘part’ (meride);” and further on (p. 15): 
—‘“ When I consider the facility with which certain worms 
break into one or more pieces even spontaneously, it appears 
to me that this capacity for rupture may well have been the 
origin of the reproductive purpose of transverse scission in 
similar elongated organisms. The rupture, in the first instance 
accidental, could have contributed to the more rapid multipli- 
cation of the organism, being followed by the regeneration of 
the parts that were deficient in the separate fragments. This 
process of rupture might further have been so perfected that 
the spot best adapted for rupture, with a view to the best con- 
dition of the fragments, was prepared in advance. In the 

" C. Emery, ‘ Colonie lineare e metameria,’ Napoli, 1883. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 617 


more perfect evolutional phases of the process, which are at 
the same time those that have till now been more carefully 
investigated, the new head is formed anteriorly to the rupture, 
or at least its essential parts are pre-established.” 

My own views emphasize the presence of a peculiar process 
ef development of the internal organs, running parallel to this 
predisposition for rupture in a particular spot—the spot which 
will correspond to the outwardly visible demarcation between 
the future segments. They thus go one step further—and, in 
my opinion, a very essential step—in the attempt to explain 
the origin of metamery in the lower Platyelminthes, these 
bilateral descendants of radiate Coelenterata, and at the same 
time predecessors of both Chordata and Appendiculata.’ 

This view of the origin of metamery also affords an explana- 
tion for the very different degrees in which we find metamery 
or segmentation expressed in the different divisions of the 
animal kingdom. The incipient metamery which we have 
traced (and which we have pictured to ourselves as arising 
through natural selection amongst those forms, which, while 
developing in length, find metamery to be a protective pecu- 
liarity) immediately creates, by the fact of its existence, new 
and variable material for selection, again to be acted upon. 
And whilst metamery develops in one direction in one line of 
descendants, the other line brings to the foreground a different 
set of advantageous combinations, each of them again the 
stock of new and varied forms. In other words, metamery 
once established in its most primitive form, and intimately 
connected with spontaneous fission under the influence of ex- 
ternal agents, has been of very great moment in the bringing 


1 Gegenbaur, in his ‘Grundriss der Vergleichenden Anatomie’ (1878), hints 
at similar explanations to those advocated by Emery and myself, when he says 
(p. 64):—“ Die Metamerie . . . lasst Zustinde des Beginnes und der 
nicht ausgefiihrten Beendigung mannichfach erkennen . . . . In dem 
Maasse als ein Metamer die Abhingigkeit vom Gesammntorganismus durch die 
Ausbildung seiner eigenen Organe aufgicbt emancipirt er sich vom Ganzen 
und gewinnt die Befabigung freier Existenz.” Further on he speaks of inci- 
pient metamery as “eine stellenweise, fiir den Organismus praktisch werdende 
Ausbildung ” of the different organ systems. 


618 A. A. W. HUBRECHT, 


about of new and endless variations of animal life. And it is 
irrational, when we have before us, say one of the lowest 
Vertebrata, in which nobody will deny the presence of distinct 
metameric segmentation, to conclude that this metamery must 
necessarily be in many respects reduced, and that in the an- 
cestral forms it must have been far more complete, must have 
stretched forwards along the whole of the head, must have 
been more forcibly expressed than it is now—in all the cephalic 
nerves, in the nephridia, the gill-slit, &c. ;—all this on the pre- 
sumption of the existence of an ancestor so completely and 
exemplarily segmental as to throw no light on the origin of 
segmentation and metamery, unless by the aid of Perrier’s and 
Cattaneo’s exaggerations. Such conclusions must, however, 
necessarily be made by those who follow Dohrn’s and Semper’s 
lead concerning the phylogeny of the Chordata. 

Bateson, in taking Balanoglossus as his starting-point, 
finds the acknowledged points of resemblance in the meta- 
merous gill-slits, &c., and adds to them important data con- 
cerning the metamerous ccelomic diverticula. Still, for a 
general view on the origin of metamery, Balanoglossus 
offers no points that we do not find more strongly represented 
and more forcibly expressed in the Nemertea. It certainly 
deserves mention that long before Bateson drew renewed 
attention to the numerous points of agreement between 
Balanoglossus and the Chordata, M‘Intosh! had done the 
same for Balanoglossus and the Nemertea, a separate para- 
graph of his monograph being devoted to the discussion of 
these homologies. 

Sedgwick (loc. cit.) holds the unsegmented worms to be 
wholly ‘ negligeable quantities,” at any rate superfluous links 
in the chain that connects the Chordata with the antecedent 
Diploblastic stages. In my idea both these authors, valuable 
as certain of their suggestions are, have not been thoroughly 
aware of the necessity that, in all discussions on the origin of 
metameric segmentation, we must attempt to grasp at data 


1 W. M‘Intosh, ‘A Monograph of British Annelids,’ ‘A, Nemerteans,” 
Ray Society Publications, 1878, 1874. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 619 


that give a clue to the possible action of natural selection in 
the gradual evolution of metamery. This clue appears to me 
to be far more distinctly contained in the views here advocated 
than in the other hypotheses. 

It may further be remarked, now that we have once more 
alluded to Bateson’s phylogeny of the Chordata, that even 
this naturalist does not feel justified in wholly rejecting 
the Nemertea from the Vertebrate pedigree. Whilst in the 
text of his article (loc. cit. p. 566) he does seem to prefer 
this negative alternative ; still, in the subjoined diagram of the 
general relationships of Urochorda, Hemichorda, Cephalo- 
chorda, and Vertebrata, the Nemertea are introduced—with a 
point of interrogation, however—as a side branch lower down 
on the common parent stock. Now, this being concordant 
with my own views of the Chordate phylogeny,—the point of 
interrogation excepted,—it is necessary to inquire why there 
is this discrepancy between Bateson’s speculations in the body 
of his treatise and the hypothetical pedigree at the end of it. 
It appears to me that this is due to his hesitation (loc. cit. 
p. 555) in accepting the views hitherto entertained and advo- 
cated by myself as to the phylogenetic connection between the 
Nemertean and the Vertebrate nervous system. For this hesi- 
tation Bateson has good reasons, and while I appreciate the 
soundness of them, I hope in the remainder of this chapter to 
remove the reluctance of him and others to accept the phylo- 
genetic significance of the Nemertea, thanks to new light that 
may be thrown on the evolution of the central nervous system 
of the Chordata by the observations recorded by me on the 
nervous system of the “‘ Challenger ” Nemertea. 

It is to these speculations on the nervous system that we 
now have to turn our attention. 

As will be seen from the terminology introduced in the 
paragraph on the nervous system in my Report on the “Chal- 
lenger’ Nemertea, and as it is now time more fully to develop, 
I am inclined to attach considerable morphological importance 
to the arrangement of the different constituent parts of the 
nervous system in the Nemertea. In former publications I 


620 A. A. W. HUBRECHT. 


have repeatedly insisted on the significance of certain points in 
the anatomy of the Nemertea, when considering the general 
question of the relationship of the Chordata to their unknown 
invertebrate ancestors, and I have insisted not only on the 
possibility of the homology between the Nemertean proboscis 
and the hypophysis cerebri of the Vertebrates, but I have, 
even earlier still, attempted to show that the nerve-system of 
these two groups might be considered in a common light, as 
was first indicated by Harting in his ‘ Leerboek van de Grond- 
beginselen der Dierkunde,’ of the year 1874. Further reference 
to the hypothesis here alluded to is found in Balfour’s Mono- 
graph on the Elasmobranch Fishes (pp. 170—172), in my own 
publications'—, and in Balfour’s ‘Comparative Embryology ”” 
(vol. ii, p. 258). Iwill not here enter upon this hypothesis 
more fully, but will briefly state that it attempted to consider 
the central nervous system of the Vertebrates as a possible 
median coalescence of two nerve-trunks, that were lateral in 
the primitive ancestors of the Vertebrates, in the same way as 
the coalesced ventral nerve-cord (Bauchmark) of Annelids and 
Arthropods may be considered with Gegenbaur as having 
arisen out of a double lateral trunk, which in certain, still 
more highly differentiated, forms have fused ventro-medially. 
A strong argument against the first-mentioned hypothesis 
is the fact that the spinal cord ontogenetically always makes its 
appearance as a median unpaired plate or thickening, a very 
faint trace of a possible double origin of this plate being 
hitherto only observable in one species of Amphibia, Triton 
teniatus; whereas in all other Vertebrates); Amphioxus 


1 «Zur Anatomie und Physiologie des Nervensystems der Nemertinen,” 
‘ Verhandel. van de Koninkl. Akad. van Wetenschappen,’ Amsterdam, 1880, 
vol. xx. ‘The Peripheral Nervous System of the Palso- and the Schizo- 
nemertea, one of the layers of the body-wall,” ‘ Quart. Journ. Micr. Sci.,’ vol. 
xx, 1880. 

* It may here be remarked that Balfour has omitted to mention that 
Harting was the first to bring forward this hypothesis ; it is well to be reminded 
of this when Beard, Bateson, and others similarly ignore this claim to priority 
of my venerated predecessor, 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 621 


and the Cyclostomata not excepted, the unpaired origin is most 
evident. The bilateral symmetry of the full-grown brain and 
spinal cord is a much later feature, and can hardly be regarded 
as the expression of a primary coalescence of two separate 
halves to form a median whole. 

I am the more inclined to abandon this hypothesis because 
I will attempt to show that we can establish phylogenetic com- 
parisons between the Chordate and the Nemertean nervous 
system ona much more simple basis; comparisons which at 
the same time cover a far more extensive ground than did 
those of Harting, Balfour, and myself, which I have just 
alluded to. 

- Since in the nervous plexus of all the Nemertea a median 
longitudinal tract, sometimes of comparatively large size, has 
now been detected, since even in the Hoplonemertea, where 
the plexus has disappeared, the same medio-dorsal nerve-tract 
has in most cases been preserved, and, finally, since from this 
dorso-median stem metameric and paired nerve-tracks may be 
seen to emerge in Palzonemertea and Schizonemertea, we 
must inquire in how far the direct comparison of this medio- 
dorsal nerve-stem with a primitive spinal cord may be said to 
hold good. 

In order to do this we must first consider the relation of 
this stem, to which we have given the name of medullary nerve 
or medulla, to the rest of the nervous system, more especially 
the brain-lobes.! Ina former publication,? where the medullary 
nerve was for the first time noticed and described as the pro- 
boscidian-sheath-nerve, I traced its origin to the dorsal com- 
missure between the two lateral halves of the brain (loc. cit., 
pl. i, fig. 1). Thanks to certain very favorable specimens in 
the Challenger collection, I have now been able to add new 
data to this statement. Sections through the brain of Cere- 
bratulus macroren, Cerebratulus corrugatus, and 


1 Tn the course of these considerations a certain amount of repetition of 
facts already noticed in the paragraph on the nervous system cannot well be 
avoided. 

? Verhand. Kon. Akad. v. Wetensch., Amsterdam, vol. xx, 1880. 


622 A. A. W. HUBRECHT. 


Cerebratulus angusticeps (‘Zool. Challenger, Exp.,’ 
Part 54, pl. xii, figs. 1, 7,8; pl. xiii, fig. 1) show that the 
condition of things is indeed less simple than this original 
statement would imply,—that the medullary nerve is not an 
eminently fibrous cord springing at right angles from the 
eminently fibrous upper brain-commissure, but that the nerve- 
tissue constituting the foremost and uppermost portions of the 
upper brain-lobes spreads out over a far more considerable 
surface than the fibrous tract which is known as the dorsal 
commissure. This expansion of nerve-tissue, in which the 
cellular elements are no less conspicuous than the fibrous, is 
posteriorly directly continuous with the plexus above described, 
laterally with the brain-lobes, anteriorly with the cephalic 
nerves springing from these lobes. It attains its fullest deve- 
lopment just before and behind the region where a transverse 
bundle of fibres uniting the fibrous core of the lateral brain- 
lobes forms the well-known dorsal brain-commissure. ‘This 
commissure is a transverse fibrous tract forming part of a more 
extensive nerve-plate. To this expansion of nerve-tissue the 
presence of nerve-cells gives a more primitive, at any rate a 
less specialised, character. These nerve-cells and nerve-fibres 
are directly continuous with those of the medullary nerve and 
(backwards) with those of the nerve-plexus, of which this 
nerve is only the median longitudinal thickening. ‘There is 
even more reason to look upon the fibres of this medullary 
nerve as a tract of the general fibrous stroma not necessarily 
connected with the fibres of the brain-commissure. In other 
cases a more direct continuity between the commissural and 
the medullary nerve-fibres was, however, observed. 

In order clearly to understand the relative importance of 
the different parts of the nervous system here noticed, the 
primitive Paleonemertea offer the best starting-point. 

Thus in Carinella we find the brain-lobes not yet separated 
into distinct upper and lower lobes, nor do we find a posterior 
lobe (side-organ). The brain is a double lateral and anterior 
thickening in the nerve-plexus, situated like it and like the 
lateral nerve-stems outside the muscular body-wall in the 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 623 


deeper strata of the integument. The only difference between 
the medio-dorsal medullary nerve in this species and the lateral 
nerves with their anterior enlargements (the brain-lobes) is its 
position and its greater tenuity (Pl. XLII, fig. 1), which, 
however, does not prevent its being very clearly observable in 
every transverse section. Its connection with the brain-com- 
missure was already described and figured by me (loc. cit., p. 25, 
pl. iii, fig. 81). It must, however, be remarked that in these 
most primitive Paleeonemertea the anterior dorsal brain-com- 
missure is less significant than in the Schizonemertea, and 
hardly anything else than the foremost of those numerous 
transverse metameric tracts in the plexus (dvr, Pl. XLII, fig. 1) 
which connect the lateral stems with the medullary nerve 
(dorsally) and with each other (ventrally). 

These important metameric nerve-pairs are most distinctly 
observed in Carinella. Here, as in the Schizonemertea, the 
medullary nerve is also continued forwards in front of the brain 
thickenings. This continuation sometimes shows a short bend 
just on the level of the commissure, so that both the medullary 
nerve and its anterior continuation may be seen in one section. 
Posteriorly the medullary nerve can be followed down to the 
hindmost extremity of the body. In Eupolia and the Schizo- 
nemertea the arrangement remains the same, the metamery of 
the transverse stems is perhaps more clearly expressed, the 
whole plexus and the longitudinal stems are no longer in the 
integument, but between the muscular layers. Still, the whole 
of the nervous system also answers to the general type as 
represented in the diagrammatic fig. 1 on Pl. XLII. 

We have now seen enough of it to understand that a comparison 
with the central apparatus of the Vertebrate nervous system 
cannot indeed be called a strained comparison. On the con- 
trary, the comparison is much less artificial than was the one 
which Balfour was inclined to adopt, and which, as noted 
above, rendered necessary the acceptance of the phylogenetic 
development of the Vertebrate medulla of a double cord. 

And so I do not hesitate to proclaim the medullary nerve of 
the Nemertea to be a very important link in the phylogenetic 


624 A. A. W. HUBRECHT. 


chain, of which the Vertebrate spinal cord is the outcome. 
Like the Nemertean medulla, the Vertebrate spinal cord is 
median, unpaired, and composed of nerve-cells and nerve- 
fibres; like the Nemertean medulla, it is a thickening in a ner- 
vous plexus, originally wholly epiblastic, of which, among 
Vertebrates, the Amphibian embryos offer such a striking 
example. This instructive and suggestive case was known to 
Remak and Stricker (as the “* Nervenschicht” of the frog em- 
bryo), it was more carefully studied and elaborately described 
by Goette (his “Grundschicht” of the epiblast, in his ‘Entwicke- 
lungsgeschichte der Unke’), and it has been again recently 
brought into the foreground by Baldwin Spencer, in his latest 
paper on the subject.1 The latter author compares the Am- 
phibian plexus with that of Paleonemertea and Schizone- 
mertea (loc. cit., p. 134), as had already been done before 
him by my friend Professor Ray Lankester, with whose sug- 
gestion I at that time (1880) did not yet venture fully to 
associate myself. 

The numerous data that have since been accumulated for a 
direct comparison of Nemertea with lower Vertebrates appear, 
however, now to fully justify that comparison which was first 
expressed in a footnote to a former paper of mine.? There can 
hardly be any doubt as to the existence, consequent upon 
natural selection, of a constant tendency in the different 
component parts of living organisms towards simplification 
and increased efficiency (Roux’s ‘Kampf der Theile im Or- 
ganismus’). This fact enables us to understand the gradual 
supremacy of the median cord in the Nemertean plexus over 
the two lateral ones. It seems as if it were mathematically 
demonstrable that for the delicate adjustment of the impressions 
from the exterior to the co-ordinated movements thereby occa- 
sioned, one longitudinal central stem in bilateral, lengthened 
animals would be more efficacious than two lateral ones. And 
if we ask if, at the final stage of this struggle for supremacy 

1 Baldwin Spencer, “Some notes on the early Development of Rana tem- 


poraria,” ‘Quart. Journ. Mier. Sci.,’ vol. xxv; Suppl., p. 123, 1885. 
2 ‘Quart. Journ. Micr. Sci.,’ vol. xx, 1880, p. 438. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 625 


between three longitudinal stems, any remnants of the lateral 
cords are yet detectable in the Vertebrate embryos, perhaps 
even in the adults, I am inclined to answer in the affirmative. 
Here I must be allowed to insert a reference to the three 
figures on Pl. XLII, which will facilitate the exposition of the 
further consequences of the hypothesis I am here developing 
Fig. 1 represents the chief points in the nervous system of the 
Nemertea. The brain-lobes are simple lateral swellings of the 
longitudinal stems, as in Carinella; plexus, medulla, and 
transverse stems, together with brain-lobes and lateral stems, 
may be considered as forming part of the integument (ef. 
Carinina). A double innervation of the respiratory portion 
of the intestine is indicated; one due to visceral branches 
(vi. sy) springing from the plexus (or from its transverse 
tracts), the other to the more specialised nerve (v), which has 
above been indicated as the Nemertean vagus nerve. The 
plexus and its innumerable radial fibres, both sensory and 
motor, are not indicated in this figure, nor are the nerve-stems 
which, when present, pass from the lateral stems directly to 
the integument. 

This figure must now be compared with the two others. Of 
these, Pl. XLII, fig. 2, diagrammatically represents the chief 
points that may be considered as characteristic of the nervous 
system of a lower Vertebrate, in which the dorsal and ventral 
roots of the spinal nerves (dr and vr) are as yet separate nerve- 
tracts, in which the sympathetic nerve system is as yet only 
represented by visceral branches given off by these dorsal roots 
(vz. sy), and in which the polymerous character of a primitive 
vagus (Vag) is established. 

Pl. XLII, fig. 3, stands for Amphioxus, as far as we know 
its nervous system, more particularly through the researches of 
Rohon and others. It differs from the foregoing by the 
absence of a distinct brain swelling and of a polymerous vagus. 
A number of spinal nerves are considered as homologous with 
the vagus of Vertebrates by Rohon. The commissural con- 
nections between the successive spinal nerves form a plexus, 
which is peripherally even much more elaborate, according to 


626 A. A. W. HUBRECHT. 


Rohon’s figures. This plexus does not reveal the presence of 
any distinct lateral longitudinal nerve, nor any ganglia of 
spinal or cephalic nerves. The latter (cn) may be said to be 
three in number. Visceral branches (v7. sy) are given off by 
the dorsal nerves (d7). The ventral ones, springing from the 
lower edge of the medulla, are here represented as shorter 
stems (vr). 

The opposite half of the system, seen in transparent per- 
spective, as given in the two other figures, is purposely omitted 
here, because of the asymmetry of Amphioxus in this 
respect. 

Now a glance at these figures will convince us that the 
situation of the Nemertean medullary nerve in its plexus, and 
with its set of transverse nerves, is directly comparable to the 
Vertebrate medulla and spinal nerves. The nerve-plexus 
filling up the intervening spaces in Nemertea is present as a 
transitory structure in Amphibian embryos. 

The ulterior appearance of an anterior enlargement forming 
the Vertebrate brain; the higher complication attained by the 
brain and spinal cord when its mass increases, but not its 
dorsal expansion, by the appearance of medullary ridges ; and 
the formation of a neural canal by infolding of the neural 
plate, all these are important developmental facts which do not 
in any way weaken the grounds for comparison of the two 
structures. They may be looked upon as adaptations to the 
much more considerable efficiency and concentration that is 
gradually attained by the central nervous system as we ascend 
higher in the scale of the animal kingdom. 

The fact that the neural ridge in so many Vertebrata 
precedes the appearance of the spinal nerves, and is inserted 
along the top of the folds that bend together to form the 
neural tube, may be thus interpreted, that during the phylo- 
genetic process of infolding the transverse nerve-tracts (dorsal 
spinal roots) remain attached in the same way to the medio- 
dorsal collecting trunk as they did in the ancestral forms, and 
are dragged upwards by the infolding process. The ventral 
roots must be phylogenetically linked to the plexus as well; 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 627 


inasmuch as the musculature originally lies inwards of the 
nervous plexus, their deeper situation is not surprising. 

In the points hitherto enumerated there is entire coinci- 
dence between Amphioxus and the other Vertebrata, as far 
as their comparability with the Nemertean diagram goes. 
Another point of coincidence is the way in which the foremost 
position of the intestinal canal and adjacent blood-vessels are 
innervated by visceral nerve-stems, indicated in all the three 
diagrams by vw. sy. 

The claims to validity of the comparison here made between 
the spinal nerves of the Chordata and the transverse stems 
of the Nemertea should again be insisted on, now that the 
researches of Rohon,' Freud,” Schneider, Ransom, and d’Arcy 
Thompson? have established for the lower Chordata (Cephalo- 
chorda and Cyclostomata) that the typical chordate spinal 
nerve is not originally provided with a double root, but that 
this double root appears to have arisen by the coalescence of 
what were primitively in the groups just mentioned separate 
and alternating dorsal and ventral nerve-tracts. With these 
so much simpler spinal nerves the transverse nerve-stems of 
the Nemertea undoubtedly offer points of comparison. These 
Nemertean nerves specially differ from the Vertebrate spinal 
nerves in two respects: (1) they give off nerve-fibres in differ- 
ent directions, which are probably motor as well as sensory 
and visceral, according to the different organ systems they 


1V. Rohov, “Untersuchungen itiber Amphioxus lanceolatus,’’ 
* Denkschr. d. k. Akad. d. Wiss. Wien,’ Bd. xlv. 

2 §. Freud, “ Ueber Spinalganglién und Riickenmark des Petromyzon 
(‘Sitzungsb. math.-nat. cl. k, Akad. Wiss. Wien,’ Bd. Ixxviii, Abth. 3, 1878). 
This author says (p. 154) :—‘“‘ Ich kann wenigstens von den letzten Wurzeln 
des Caudalmarks sagen dass ihre Selbstandigkeit so gross ist, dass man von 
vorderen und hinteren Spinalnerven, anstatt von vorderen und_hinteren 
Wurzeln reden konute ”; and Wiedersheim in the 2nd edition of his ‘ Lehr- 
buch der Vergleichenden Anatomie’ (p. 321) :—* Vieles spricht dafiir dass die 
Vorfahren der heutigen Wirbelthiere getrennte dorsale und ventrale Ner- 
venwurzeln besessen haben miissen.” 

3 W. R. Ransom and d’Arcy W. Thompson, “ On the Spinal and Viscera 
Nerves of Cyclostomata,” ‘ Zool. Anzeiger,’ No. 227, July, 1886. 


628 A. A. W. HUBRECHT. 


terminate in; and (2) they go round ventrally, each of them 
forming a loop all round the body. As to the first point of 
difference just alluded to, it is the expression of a low and 
primitive degree of differentiation, and when a step forwards 
is made differentiation of labour will tend to develop certain 
tracts more particularly containing sensory and visceral nerve- 
fibres, which are more especially directed towards the epithelia 
(the primitive dorsal or posterior roots), and others more 
particularly containing motor nerve-fibres, and more especially 
directed inwards towards the muscles (the primitive ventral or 
anterior roots), because the musculature, as was already men- 
tioned, is originally situated internally to the nervous system. 

For the present we can only hold it to be established that 
the fibres of these three categories are blended in the Nemer- 
tean plexus, without being able to determine in how far the 
specialisation therein observed, of the appearance of transverse 
metameric nerves, may at the same time be accompanied by a 
commencement of differentiation, such as has just been alluded 
to. We may, in other words, not yet assume that among 
these metameric stems there is already a tendency to an 
alternation between such as have sensory and visceral and 
such as have motor predispositions. 

Only in a few cases may we be justified in saying that 
certain nerve-tracts belonging to the Nemertean peripheral 
system are more especially sensory or visceral, and these no 
doubt offer important analogies in their situation and connec- 
tions to similar nerve-tracts of the Vertebrata 

The second point of difference, viz. the continuity in the 
ventral median line of the transverse tracts of the Nemertea, 
is no doubt a consequence (a) of their origin, in a perfectly 
continuous plexus, (4) of the cylindrical arrangement of the 
muscular layers, which in most cases are uninterrupted both 
in the dorsal and in the ventral median line. It is all the 
more important to notice that, more especially in the primitive 
Carinellide, the tendency is very marked towards a scission of 
this muscular body-wall into a right and a left half. 

This longitudinal scission is no doubt the first expression of 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 629 


the phenomenon which shows us the musculature of the right 
and left half of the body, developing quite independently in 
the Chordata. It is easy intelligible how, as this phenomenon 
gradually becomes more and more marked, no more ventral 
connecting fibres across the non-muscular region were required 
for the innervation of the musculature of the right and left 
half of the body. 

The process by which the transverse nerve-tract, with radial 
- nerve-fibres leaving it at short intervals, both centripetally 
and centrifugally, gradually assumed the form of a nerve-stem 
with a dorsal and a ventral branch, such as we find in the 
spinal nerves, must have gone on pari passu with those 
numerous other changes which we cannot as yet fully trace, 
but which must have occurred when (1) the muscular meta- 
mery became gradually established, (2) the dorso-median me- 
dullary tract became so preponderant that an increase in mass, 
with economy of bulk, was only to be obtained by a process 
of folding-in already discussed above, and (3) the attachment 
of the spinal nerves (transverse tracts) to the medulla was 
modified in consequence of this process. 

None of these phenomena, however, offer anything that is 
in any way inconsistent with, or opposed to, the general theory 
here developed. 

We have now sufficiently insisted on the chief point of 
comparison here proposed, viz. that between the Nemertean 
medullary nerve and its metameric transverse nerve-cords and 
the Vertebrate cerebro-spinal axis and spinal nerves. 

If Amphioxus were the only Vertebrate known, we should, 
recognising the phylogenetic importance of the plexiform 
arrangement still met with in the adult of that species, admit 
that, as far as we know at present, the primary lateral nerves 
with their anterior swellings of the Vermian ancestors had 
disappeared in the same measure as the dorso-median spinal 
cord had come more and more into the foreground. 

But our consideration of other Vertebrates leads us to the 
conclusion that, when once the general homology between the 
two nervous systems is admitted, there may perhaps be secondary 


630 A. A. W. HUBRECHT. 


points in regard to which the comparison can be further ex- 
tended. And it must be recognised that, if we should also 
succeed in rendering more or less probable a comparison in 
secondary details, this might again be favorably interpreted 
for the primary and more important part of the hypothesis. 

The search after these secondary points of agreement was 
instituted by me when the question above alluded to presented 
itself, viz. if any remnant could be traced of the central ner- 
vous system of Nemertea-like ancestors, i.e. of the brain-lobes 
and lateral stems, in those Vertebrate descendants in which 
the medio-dorsal tract had become so preponderant as to give 
rise to the unpaired medulla and brain. 

It is clear that if it shall be possible to trace any such rem- 
nants, and to render their homology with the Nemertean central 
nervous system probable, they will have to be sought for— 
(a) in the head, as lateral more or less independent nerve- 
centra, innervating sense-organs of the integument, and passing 
posteriorly into parallel longitudinal stems; or (8) in the trunk, 
as longitudinal nerve-stems, in which the central character 
should be somewhat less marked than in the anterior swelling, 
but in which the original significance as parts of the central 
system should still be indicated either by histological or by 
embryological features. 

To these latter conditions nothing can answer in the Verte- 
brate nervous system excepting the so-called ramus lateralis 
vagi. It is present in all Vertebrates above Amphioxus, 
long and important in the aquatic Ichthyopsida, gradually 
disappearing when the aquatic medium is exchanged for an 
air-breathing existence, and finally only retained in the higher 
Vertebrates as the inconspicuous ramus auricularis vagi. 

Its course is indeed strictly lateral, and has always been a 
puzzle to anatomists. Stannius! characterises the existence 
and the course of this sensory nerve along the trunk down to 
the tail as “ one of the most interesting facts of anatomy.” 

None the less startling is its development. Whilst Balfour 
attempted in this respect to bring it on one line with the other 

‘ «Das peripherische Nervensystem der Fische,’ p. 108. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 631 


parts of the peripheral nervous system, the corresponding re- 
sults of Semper, Goette, van Wijhe, and Hoffmann are all in 
the contrary direction. They have seen the nervus lateralis 
appear as an independent product of the epiblast, 
arising in loco along its whole length, its formation often 
even preceding that of the spinal nerves. These results have 
again been fully confirmed and definitely established by the 
latest investigator of the problem, Beard,! who also gives a 
detailed description and figures of the connection between the 
nervus lateralis and the vagus ganglion, both of them so much 
more massive and conspicuous in early embryonic stages than 
later on. 

And now that we are attempting to find out whether there 
is a possibility of comparing the lateral nerve-stems of lower 
worms with the nervus lateralis of Vertebrata, we are naturally 
led to consider, in the second place, the question whether the 
anterior swellings of these lateral stems (the paired brain-lobes 
of the worm) may have their morphological equivalents, their 
remnants, in the set of anterior nervous swellings that are 
found in the head on a level with the nervus lateralis, and 
longitudinally connected with it; viz. the variable set of 
ganglia of the cephalic nerves. 

As to the origin of these ganglia of the cranial nerves I have 
no observations of my own, and must rely on the data of other 
observers. 

It is suggestive to give the opinion of the three latest in- 
vestigators of the development of these organs in different 
groups of Vertebrates in their own words. 

Professor A. Froriep,? who studied Mammalian embryos, 
writes (loc. cit., p. 35):—“The ganglia (of facialis, glosso- 
pharyngeus, and vagus) enter into a peculiar, very intimate 
connection with the epiderm ;” further (p. 40), “these gangli- 
onic connections with the epiderm must probably be regarded 

1 «The System of Branchial Sense-Organs, &c., in Ichthyopsida,” ‘ Quart. 


Journ. Mier. Sci.,? November, 1885, p. 95. 
2 «Ueber Anlagen von Sinnesorganen am Facialis, &.,” ‘ Archiv f. Anat. u. 


Phys.,’ 1885, Anat. Abth. 
VOL. XXVII, PART 4,.—NEW SER, xx 


632 A. A. W. HUBRECHT. 


as rudiments of organs which have phylogenetically disappeared, 
and which are only now retained in the ontogenetic develop- 
ment ;” then (p. 43) “ for the Gasserian ganglion there is no 
indication of a connection with the epiderm;” and, lastly 
(p. 52), “it appears to be hardly any longer possible to look 
upon these nerve-ganglia (Nervenknoten) as simply homologous 
with spinal ganglia.” 

Baldwin Spencer! writes (loc. cit., p. 129) concerning 
Rana temporaria: “Along certain lines the cells of the 
nervous layer proliferate, and it is by this proliferation that 
the rudiments of the cranial nerves are laid down;” further 
(p. 180), ‘the development of the ganglia at the level of the 
lateral line, and the fact of their long connection with the epi- 
blast at this point,.... . is of great interest in connection 
with certain points in the development of the Elasmobranch 
nerves.” 

Concerning the developmental phenomena of the trunk- 
region at this period, the spinal nerves are stated to be not 
yet visible, ‘though the nervous sheath is clearly developed 
and in this the lateral line.” 

The author next mentions observations made by him on Dr. 
Beard’s sections of Elasmobranch embryos, and goes on to say 
(loc. cit., p. 131): 

“The Gasserian ganglion is, at all events in part, formed 
directly from the epiblast..... the same development 
takes place in the case of the ganglion of the third and 
seventh nerve—in that of the ciliary ganglion the develop- 
ment is particularly clear—..... The ganglia arise 
along a level of the lateral line continued on the 
head.” 

He next says: “‘ The curious origin of the ganglia of the 
cranial nerves points strongly to the conclusion that ..... 
their present condition and nature must..... be regarded 
as a secondary and certainly not primitive condition. 

“Tn passing, I may just notice that on this supposition an 


1 «Early Development of Rana temporaria,” ‘Quart. Journ. Mier, 
Sci,,’ Suppl., 1885. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 633 


explanation is offered as to the origin and meaning of the 
two curious branches which unite respectively the ganglia of 
the fifth and seventh and fifth and third cranial nerves ; they 
may be regarded as persistent parts of the lateral nerve . 

in the head.” 

In the third place extracts will be given from Beard’s more 
extensive paper.! He writes (p. 97) as an introductory state- 
ment: “ At present we are acquainted with no Invertebrate 
nervous system which is built upon the same plan as that of 
Vertebrates,” and then passes to the results of his investiga- 
tions, chiefly carried out on embryos of Torpedo and a 
few other Elasmobranchs. I make the following selections 
(p TOL): 

“At the point of fusion” (of the cephalic nerve with the 
epiblast) “a local thickening of epiblast has previously taken 
place. After the fusion has taken place a proliferation of some 
of the cells composing the thickening ensues. The proliferated 
cells form a mass of actively dividing elements still connected 
with the skin. ... . This mass of cells is the rudiment of the 
ganglion of the dorsal root.” 

On p. 110 he adds: “ Along with the separation of the 
(vagus) ganglion from the skin the sensory thickening begins 
to grow backwards along the lateral surface of the trunk. 
This thickening is the rudiment of the so-called lateral line. 
BU A gar eee: The so-called lateral nerve is formed from the deeper 
portion of the sensory thickening...... That there is no 
actual growth backwards of the nerve is obvious enough.” 

Recapitulating, we must acknowledge that the mode of origin 
of the ganglia of the cephalic nerves, as described by these 
authors, is certainly a peculiar one—a mode of development 
sui generis. One of Beard’s accompanying diagrammatic 
figures, reproduced in Wiedersheim’s second edition (1886) of 
the ‘Lehrbuch der Vergleichenden Anatomie’ as woodcut 
No. 265, moreover, shows how the position of the cephalic 
ganglion, developing as an ectodermal proliferation, is in this 

1 “Branchial Sense-Organs in Ichthyopsida,” ‘Quart. Journ. Micr. Sci.,’ 
November, 1885, No. CI, 


634 A. A. W. HUBREOHT. 


early stage eminently lateral, a conclusion corroborated by 
the figures of his actual sections. This primitive position is, 
of course, gradualiy lost, and could never be predicted from 
a study of these ganglia and their position and significance in 
the adult animal. Yet it is not without significance when seen 
in the light of the suggestion here brought forward. And that 
the interpretation of the phenomena in question as given by 
these authors is not universally accepted, thus leaving room 
for new suggestions, is proved by the following citation from 
Ransom’s and d’Arcy Thompson’s latest article,! running as 
follows :—‘‘ Although the lamprey presents a_ well-marked 
lateralis nerve it has not also a regular lateral line, for the 
sense-organs of the skin are scattered and without segmental 
arrangement. The sense-organs do not, therefore, appear to 
be in direct relation with the spinal ganglia, and the view of 
the close connection between them (Spencer, Beard, Froriep) 
does not receive support...... It seems more natural to 
consider the lateralis as a relic of the extensive and irregu- 
lar commissure system connecting the posterior roots of 
Amphioxus.” 

Passing from a consideration of the embryonic ganglia to 
their connection in the adults, I must mention the connection 
of the ramus lateralis vagi with cephalic nerves anterior to 
the vagus. I will not here give a description of the numerous 
varieties presented by this nervous connection, but merely 
refer to the arrangement in Vertebrates so low as the lam- 
preys. We there find, according to Johannes Miller, the 
ramus lateralis originating from the seventh as well as from 
the tenth pair of cephalic nerves, and if we compare the very 
satisfactory figure which was only lately? given by Ahlborn 
of this arrangement, we must recognise that this nervous con- 
nection is importaut, and has more the aspect of a direct for- 
ward continuation of the nervus lateralis than of a sensory 


1 «On the Spinal and Visceral Nerves of Cyclostomata,” ‘ Zool. Anzeiger,’ 
No. 227, July, 1886. 
2 ¢ Zeitschr. f. wiss. Zool.,’ Bd. xl, pl. xviii. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 635 


branch from the facialis, establishing a connection between it 
and the vagus. 

Ahlborn mentions the existence of a similar connecting 
stem reaching further forward still, and connecting the trige- 
minus and facialis. How these connections vary in the different 
adult Vertebrata will not be discussed here. 

The different facts and speculations here brought forward in 
connection with the cephalic ganglia and the nervus lateralis 
vagi may suffice for the present. They may severally be 
brought to bear upon the question of the eventual homology 
of Vertebrate cephalic ganglia and nervus lateralis, on the one 
hand, and Vermian paired brain-lobes and lateral nerve-stems 
on the other. The parts here compared being indicated in 
figs. 1 and 2 of Pl. XLII, with corresponding letters (Ly and 
In), a glance at these figures may further convey a notion of 
the purport of these speculations. 

There is one fact, however, which is not indicated in these 
figures, which is nevertheless of very high importance for the 
views here considered, and which I must therefore develop 
more in detail. 

It is the connection between the successive spinal nerves 
and the ramus lateralis vagi. 

The existence of similar connections between the (eminently 
sensory and cutaneous) dorsal roots and the (similarly sensory 
and cutaneous) lateral nerve is for the first time mentioned 
by Ransom and d’Arcy Thompson for Petromyzon in the 
following passage (loc. cit., p. 422): 

“The dorsal rami of the posterior roots pass up (over the 
lateralis nerve) to the skin of the back, but appear also to 
send fibres into the lateralis. (For this statement we 
at present rely only on sections, but we hope shortly to test it 
by dissections of the large Petromyzon marinus.)” 

It hardly needs comment that if this observation should be 
confirmed the fact would be of the utmost importance for the 
hypothesis under discussion. We should then be permitted to 
consider these metameric connections between the dorsal roots 
and the nervus lateralis of Petromyzon, as the relics of an 


636 A. A. W. HUBRECHT. 


earlier stage, still permanent in the Nemertea, where the 
metamerically consecutive transverse nerve-tracts similarly 
unite the medullary nerve and the lateral stems. 

This connection is, as we know, also brought about in the 
Nemertea by the plexus, in those parts of it which spread out 
between the transverse tracts, and it may here be asked if 
relics of such a plexus between the successive precursors of the 
spinal nerves are perhaps retained, not only in Amphioxus 
(see above, p. 625, and Rohon, loc. cit., fig. 13), but also in 
Osseous Fishes, in the numerous superficial nerves described 
and figured by Stannius,’ or whether we must rather look 
upon this multiplication of lateral nerves (one of which is 
called by Stannius the nervus lateralis trigemini, others, rami 
communicantes of the dorsal branches of spinal nerves, &c.) 
as derivatives from the nervus lateralis vagi.? This question 
can, of course, only be solved by careful anatomical and 
embryological investigations. That the nervus lateralis was 
often (Stannius) observed in the Petromyzontide only along 
a part of the length of the body (Schneider and Born, ac- 
cording to Ahlborn,’ observed it as “bis an das Hinterende 
des Korpers”’?) is not confirmed by modern investigators. 
Ahlborn’s description (loc. cit., p. 304) of the variable 
situation of this nerve in Petromyzon is very suggestive 
in connection with the views here advocated. Ransom and 
d’Arcy Thompson consider that the regularity of the in- 
tegumentary sensory apparatus is not yet established in 
Petromyzon, as may be concluded from the citation given 
above. 

We have now considered the superficial ramifications of 
what I may call the lateral nerve-system, both in lower worms 
and in Vertebrates; we must now turn to the intestinal, to 


1 «Das peripherische Nervensystem der Fische,’ 1849, pls. ii—iv. 

2 It should be remembered that Beard is inclined (loc. cit., p. 139) to look 
upon the superficial longitudinal nerve-fibres, by which the successive epithelial 
modifications along the lateral line are often connected (Solger, Bodenstein), 
as such derivatives (by longitudinal fission in its very early stages) of the 
nervus lateralis. 


3 *Zeitschr. f. wiss. Zool.’ Bd. xl. pp. 303 and 301. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 637 


the visceral branches of this same system, from which other 
and important data may be gathered for further elucidation of 
the hypothesis under consideration. 

We have already seen that in Nemertea the typical innerva- 
tion of the respiratory portion of the intestine is brought 
about—(a) by a pair of nerves directed backwards and spring- 
ing from the anterior lateral swellings (the brain-lobes) of 
the lateral nerve-stems; (0) by numerous visceral branches 
starting from the plexus, directed inwards as branches that 
spread over the wall of blood-lacune and intestine. 

In the Vertebrata, Amphioxus excepted, we also find that 
the innervation of the anterior respiratory portion of the 
intestine and of the circulatory apparatus is obtained from 
two sources, viz. (1) the cephalic nerves, amongst which the 
vagus nerve is in this respect the most important;! (2) the 
visceral branches of the spinal nerves, which are at the basis 
of what is afterwards more highly differentiated and separately 
recognised as the sympathetic nerve-system. 

In Nemertea it is very difficult to determine in the anterior 
part of the intestinal wall which tracts belong to the so-called 
vagus nerve, which to this system of visceral nerve-branches. 

So it is often in Vertebrata, and the blending together 
(in both divisions of the animal kingdom) of two systems, 
each of them again mutually comparable when separately 
considered, is an important point of agreement, and would, 
if no actual homology were at the base of it, be a very puzzling 
coincidence. 

It is in this respect highly suggestive that Born notices, as 
early as 1827, what was afterwards confirmed by Ahlborn 
(Joe. cit.) and others, that in Petromyzon, i.e. one of the 
lowest Vertebrates, the spinal nerves send out connecting 
branches towards the pneumogastric nerves. The existence 


1 Ventrally these nerves (e.g. the n. hypoglossus) are sometimes commis- 
surally united with their representative of the opposite half of the body. It 
must remain an open question whether these commissures are in any way 
comparable either to the Nemertean vagus commissures (cf. p. 83), or to the 
general ventral commissural system of these worms. 


638 A. A. W. HUBRECHT. 


of superficial metameric connections (Ransom and d’Arcy 
Thompson, vide supra) as well as of this set of deeper 
connections between the transverse and the latero-longitu- 
dinal nerve-stems (n. lateralis and nu. pneumogastricus, of 
Petromyzon would thus be a remarkable repetition of the 
similar arrangement in the Nemertea, as it has been here for 
the first time demonstrated. 

The facts as they lie before us do not, however, admit of 
any very circumstantial comparison so far as the nerves in 
particular are concerned, and I purposely refrain from entering 
into any details. Yet it should be remarked : 

(1) That the polymerous root of the Vertebrate vagus nerve 
is very readily explicable if we take the Nemertean arrange- 
ment as a starting-point (Pl. XLII, figs. 1, 2, vag), as is also 
the mixture of sensory and motor elements in this root.! 

(2) That similarly, if the anterior cephalic nerves (e.g. the 
fifth) should prove to be polymerous, this would in no way be 
astonishing nor difficult to bring into harmony with that same 
starting-point. 

(3) That the presence of superficial branches to the integu- 
ment and to the musculature, and of deeper branches to the 
intestinal epithelium in those parts that will contribute to 
form the cephalic nerves, is similarly foreshadowed in the 
Nemertea. 

(4) That the equivalent of the Nemertean vagus nerve will 
have to be sought for in such branches of the Vertebrate vagus 
as more especially innervate the intestinal epithelium,” whereas 


1 Rohon, “‘ Ueber den Ursprung des Nervus vagus bei Selachiern,” ‘ Arbeit. 
Zool. Inst. Wien,’ vol. i, p. 159. 

2 | have good reasons, based upon actual observations made by my pupil, 
Mr. Dobberke, to believe that the ramus intestinalis vagi in adult Hlasmo- 
branchs may be traced centripetally from its region of innervation of the 
foremost portion of the intestinal wall, towards the brain, as a bundle of nerve- 
fibres running parallel to and combined with those for the branchial apparatus, 
but that, nevertheless, this bundle can be separately traced up to the vagus 
ganglion, without any further intimate relation to those branchial branches 
(cf. Beard, loc. cit., p. 110). If this should actually be the case, the 
possibility of a direct comparison between the Nemertean 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 6389 


the innervation of the Vertebrate gill-slits, which marks a later 
phylogenetic stage, in which these perforations of the anterior 
trunk region have appeared, may be as well put to the account 
of more superficial parts of the transverse tracts. 

(5) That the common starting-point of the sensory, lateral, 
and the intestinal portion of the vagus has also attracted the 
attention of former observers. Ransom and d’Arcy Thompson 
write: “In the embryo dog-fish the second or ventral com- 
missure, described by Balfour, &c., as uniting the roots of the 
vagus, ventral to the ganglia, is essentially a sympathetic com- 
missure, whose (visceral) fibres pass on, as described by Balfour, 
to form the intestinal branch of the vagus. In that intestinal 
branch we have an outflow of visceral fibres, quite comparable 
to, e.g. a splanchnic branch of the dorsal sympathetic system. 
The connection between the origin of the lateralis and this 
ventral commissure connecting the vagus roots in the dog-fish, 
and similarly the relation of the lateralis to the loops uniting 
the ganglia of the fifth, seventh, and tenth nerves in Petro- 
my zon, may probably be described as indicating a fusion in this 
region of the two great commissural systems which posteriorly 
are separate, viz. that of the sensory branches (lateralis) and the 
visceral or sympathetic. 

“We agree with Gaskell that the term sympathetic should 
be suffered to fall into disuse, as tending to perpetuate the old 
conception of the primary importance of the longitudinal 
nerve-tract ; whereas the leading fact is the metamerically 
recurring outflow of visceral fibres, which may or may not be 
united together by successive longitudinal commissures.” 

In the Nemertea this anterior ‘‘ fusion of the great com- 
vagus nerve and the Vertebrate ramus intestinalis vagi, of 
course, comes more closely within our reach. It need not be insisted upon 
that if these comparisons prove correct the separate intestinal nerve-systems 
(sympathetic nerve system) of other Invertebrates (Annelids, Arthropods, 
Molluses) cannot be looked upon as homologous with the sympathetic nerve- 
system of the Vertebrates, but would rather be homologous with that portion 
of the intestinal innervation of the latter which comes to the account of their 


cephalic nerves, in so far as these represent derivatives of the Nemertean 
vagus, and are marked » in figs. l and 2 of Pl. XLII. 


640 A. A. W. HUBBECHT. 


missural systems”’ is foreshadowed at the point where brain- 
lobe, lateral stem, and “ vagus nerve ” meet, or rather diverge. 
It has been attempted in figs. 1 and 2 to indicate the points 
here alluded to in a general way, special comparisons being, on 
the grounds that have been stated, purposely avoided. 

If we now turn to Dohrn’s and Semper’s hypothesis we must 
recognise that no such satisfactory general comparisons are 
there possible. Even if we were inclined to accept the “ turn- 
ing over” of Geoffroy St. Hilaire, by which back and belly 
became exchanged, and to admit the brain-piercing cesophagus, 
regarding the Annelid supracesophageal ganglion and the 
ventral nerve-cord as respectively homologous to cerebrum and 
medulla, it must still be conceded that we have not then in 
any way before us a nerve-system offering as many points of 
comparison with the Vertebrate system as does that of the 
Nemertea. 

Concerning the Annelids we have no observations by which 
the cephalic ganglia and the cephalic nerves are so clearly 
foreshadowed, none which would throw light on the origin of 
the vagus, its connection with the nervus lateralis and with the 
anterior cephalic ganglia, none concerning the sympathetic 
system and its blending with the vagus system in the lowest 
Vertebrates, indications of which are even retained in the 
highest. Nor is the ventral nerve-cord of Annelids, with its 
undeniable double character and double origin a match, so 
far as comparison goes, for the Nemertean medullary nerve, 
with its transverse nerves preceding the spinal nerves of 
Amphioxus and the Cyclostomata. 

And if we are then asked to consider the lens of the Verte- 
brate eye as a modified ectodermal branchial invagination, as 
the outer portion of what was once a functional gill-slit,! we 
feel that the ground under our feet is becoming rather uncom- 
fortable, and that it is high time to reconsider whether all 
these ingenious speculations in which the most beautifully 
pliable hypothetical and unknown Annelids play a too conspi- 
cuous part should not be definitely abandoned, and a new 

1 Dohrn, ‘Studien,’ x, p. 459, 1885. 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 641 


departure made by those who are interested in the phylogeny 
of the Chordata. In due time arduous and detailed morpho- 
logical investigations on the Platyelminthes in general, and on 
the Nemertea in particular, may then lead us to more satis- 
factory conclusions than are the fata morgana that are so 
temptingly evoked before our eyes by the ingenious manipula- 
tions of the indefatigable founder of the first and foremost 
Zoological Station, when, following his lead, we find ourselves 
wandering in the barren deserts of that province of phylogeny 
in which he attempts to establish a close connection between 
Chordata and Annelida. 

All these considerations have induced me to give this rapid 
outline sketch of the degree of comparison which I hold to 
exist between Chordate and Nemertean (more especially Palzo- 
nemertean and Schizonemertean) nervous systems, although I 
am perfectly aware that there is a growing tendency among 
those authors at present occupied with questions concerning 
the morphology of the Vertebrate nervous system (Froriep, 
Baldwin Spencer, Beard, Cunningham, Kleinenberg, and many 
others) to accept Semper’s and Dohrn’s views of the Annelidan 
descent of Vertebrates. Wiedersheim, in the new edition of 
his ‘ Vergleichende Anatomie’ (1886), does not even hesitate 
to bring these results in their unripe phase before the more 
extensive public of students, and this generally in acquiescent 
terms. It is curious to see how, e.g. the quéstion of the 
cephalic nerves and their comparison to spinal nerves, that 
of the nerve-roots, the cephalic ganglia and their respective 
connecting trunks, have given occasion to the most diverse 
twisting and retwisting of the facts in order to bring out a 
fixed scheme or diagram, which might then be compared to 
what obtained in Annelids, and in which the highest degree of 
similarity between the respective somites might be obtained, 
thus establishing a preconceived idea of the Vertebrate ancestor 
as a most rigorously segmented animal. The value of these 
speculations has been already tested above, and I may be 
allowed once more to express my conviction that our com- 
parisons between the Chordata and their lower Invertebrate 


64.2 A. A. W. HUBREOHT. 


predecessors may only be looked upon as in any way satisfactory 
so long as they remain on a very broad and general basis, and 
that any very special homology said to be demonstrated ought 
for that very reason to be more especially suspected.} 

For my part I believe that, along the lines above indicated, 
a comparison between Vertebrate and Invertebrate nervous 
systems will in future prove to be more fruitful, but I wish to 
repeat that for the present we can only indicate general points 
of coincidence between the two, and must rigorously refrain 
from making comparisons in detail. 

On the other hand, it is suggestive once more to consider 
what has been recorded in my ‘Challenger Report’ concerning 
the nervous system of Drepanophorus Lankesteri, when 
compared with that of certain Annelids; and we may, I be- 
lieve, safely come to the conclusion which was formulated by 
me seven years ago, but which I now hold to be much more 
solidly established, that we have in the Nemertea an important 
group through which definite glimpses may be obtained at the 
sources from which both Chordata and Appendiculata (Ray 
Lankester) have respectively sprung. The proposition first 
formulated by Gegenbaur, about the phylogenetic origin of 
the ventral nerve-cord and cesophageal ring of the Annelida 
out of ancestors with lateral cords, has obtained new support 
from the arrangement which was met with in the species just 
mentioned. And just as we have before tentatively discussed 
the question, in how far remnants of the lateral cords were 
retained in those descendants in which the median one had 
been raised to the dignity of a medulla spinalis (the Verte- 


1 Bateson (loc. cit., p. 562) seems to take a similar view of the efforts here 
alluded to. He says: ‘“‘No doubt the cranial nerves may, by arbitrary 
divisions and combinations, be shaped into an arrangement which more or less 
simulates that which is supposed by some to have been present in the rest of 
the body, but little is gained by this exercise beyond the production of a false 
symmetry.”—Dohrn himself, whose suggestions have so largely contributed 
to the accumulation of all this conflicting evidence, is now rather in the 
position of Goethe’s Zauberlehrling, and writes (‘Studien,’ x, p. 468, 1885): 
“Auch auf diesem Gebiet (die Frage nach der Bedeutung der Hirnnerven) 
bildet die bisherige vergleichende Anatomie das Bild eines auf stiirmischer 
See steuerlos herumgeschleuderten Schiffes.” 


RELATION OF THE NEMERTEA TO THE VERTEBRATA. 648 


brata), we might now consider whether any remnants of the 
median dorsal cord are retained in those descendants in which 
the lateral cords have differentiated into brain-lobes, cesopha- 
geal ring, and ventral cord (the Annelida). To this question 
I have no definite answer to offer, but I may call attention to 
the significant fact that the beautiful and exemplary investiga- 
tions into the embryonic development of Lopadorhynchus, 
very recently published by Kleinenberg,' have demonstrated 
the existence in the larva of that Annelid of a nerve-stem 
answering to the conditions here required. It is dorso-medially 
situated, it is anteriorly connected with the brain, or rather 
with a transverse nerve-tract (Kleinenberg’s prototrochal nerve- 
ring), which in its turn is connected with the brain,” it appears to 
be connected close to the anus with the ventral cord (the fused 
lateral stems), and though appearing in early larval life, and 
having only a temporary existence, it is regarded by Kleinenberg 
as having considerable physiological importance. If the light 
in which I am inclined to look at it is not deceptive, its 
morphological significance also can hardly be overrated. 

In closing this chapter of general considerations we may 
ouce more bring before our minds the proposition with which 
it was opened. We have here and in the foregoing chapters 
adduced facts and arguments which appear to speak in its 
favour; we will once more rapidly enumerate the common 
characteristics of Nemertea and Cceelenterata, as well as those 
of Nemertea and Chordata. 

The Ccelenterate characteristics that are also found in the 
Nemertea are the following : 

a. The presence of nematocysts in the _ proboscidian 
epithelium. 

b. The elaborate nerve-plexus in the integument, and its 
histological features. 

c. The presence of epiblastic muscle-fibres separate from the 
general body-musculature. 

1 «Zeitschr. f. wiss. Zool.,’ Bd. xliv, Heft. i, ii, October, 1886, p. 107; 
pl. vii, fig. 27a. 

2 For comparison with the Nemertea, cf. Pl. XLII, fig. 1. 


644, A. A. W. HUBRECHT. 


d. The presence and the chemical constitution of a some- 
times very massive intermuscular jelly by which the other 
internal organs are at the same time surrounded. 

e. The mode of development of the mesoblast (at least in 
Lineus obscurus), which is less specialised than in most. 
other Invertebrates. 

f. The absence of any distinct enteroccele. 

The points of resemblance with the Chordata may be thus 
tabulated : 

a. The general features of the nervous system. 

b. The presence of a homologue of the hypophysis cerebri as 
a massive and important organ (the proboscis). 

c. The presence of tissues which may have become converted 
into the notochord (viz. the material of which the proboscidian 
sheath is built up). 

d, The respiratory significance of the anterior portion of the 
alimentary tract. 

At the base of all the speculations contained in this 
chapter lies the conviction, so strongly insisted upon by 
Darwin, that new combinations or organs do not appear by 
the action of natural selection unless others have preceded, 
from which they are gradually derived by a slow change and 
differentiation. 

That a notochord should develop out of the archenteric 
wall because a supporting axis would be beneficial to the 
animal may be a teleological assumption, but it is at the same 
time an evolutional heresy. It would never be fruitful to try 
to connect the different variations o ffered, e.g. by the nervous 
system, throughout the animal kingdom, if similar assump- 
tions were admitted, for there would be then quite as much to 
say for a repeated and independent origin of central nervous 
systems out of indifferent epiblast just as required in each 
special case. These would be steps that might bring us back a 
good way towards the doctrine of independent creations. The 
remembrance of Darwin’s, Huxley’s, and Gegenbaur’s classical 
foundations, and of Balfour’s and Weismann’s brilliant super- 
structures, ought to warn us away from these dangerous regions. 


INDEX TO VOL £XVIL 


NEW 


SERIES. 


Aniline dyes used in staining Bacteria, 
by Hankin, 401 

Antedon rosacea, symbiotic alge 
in, by P. H. Carpenter, 379 

Anthea cereus, chromatology of, 
by MacMunn, 573 


Bacteria, aniline dyes used in stain- 
ing, by Hankin, 401 

Benham on Criodrilus lacuum, 
561 

», studies on Earthworms, No. 

i, 77;..No. TE, 561 

Bourne, G. C., on the anatomy of 
Fungia, 293 


Carpenter, P. H., on symbiotic alge 
in Antedon rosacea, 379 

Chelonia, germinal layers of, by Mit- 
sukuri and Ishikawa, 17 

Chromatology of Anthea cereus, 
by MacMunn, 573 

Criodrilus lacuum, by Benham, 
561 

Criodrilus lacuum, by Orley, 551 

Ctenodrilus parvulus, nov. spec., 
by Robert Scharff, 591 

Cunningham on reproductive elements 
of Myxine, 49 

Bs review of Dohrn’s in- 

quiries into the evolution of organs 
in the Chordata, 265 


Dinophilus gigas, by Weldon, 109 
Dohrn on the evolution of organs in 
the Chordata (review), 265 


Earthworms, studies on, by Benham, 
No. II, 77; No. III, 561 

Kchinoderm morphology, No. X, by 
P. H. Carpenter, 379 

Eyes of Molluscs and Arthropods, 
review of Patten’s memoir on, 285 


Fowler on anatomy of Madreporaria, 1 
Fungia, anatomy of, by Gilbert C. 
Bourne, 293 


Hankin, new methods of using the 
aniline dyes for staining Bacteria, 
401 

Harmer on the life-history of Pedi- 
cellina, 239 

Hartog, liberation of the zoospores in 
the Saprolegniex, 427 

Heape on the development of the 
Mole (Talpa), 123 

Hubrecht on the relations of the 
Nemertea and Vertebrata, 605 


Ishikawa and Mitsukuri on the ger- 
minal layers of Chelonia, 17 


Lacertilia, pineal eye of, by Spencer, 
165 


646 


Lendenfeld on the function of nettle- 
cells, 393 
Liver, nerves of, by Macallum, 439 


Macallum on the uuclei of striated 

muscle-fibre in Necturus, 461 
», onthe termination of nerves 

in the liver, 439 

MacMunn on the chromatology of 
Anthea cereus, 573 

Madreporaria, anatomy of, by G. 
H. Fowler, 1 

Mitsukuri and Ishikawa on the ger- 
minal layers of Chelonia, 17 

Mole, development of the, by Heape, 
123 

Muscle-fibre, nuclei of, in Necturus, 
by Macallum, 461 

Myxine, reproductive elements of, 
by Cunningham, 49 


Nemertea and Vertebrata, relations 
of, by Hubrecht, 605 

Nerves, termination of, in the liver, 
by A. B. Macallum, 439 

Nettle-cells, function of, by Dr. R. 
v. Lendenfeld, 393 


Orley on Criodrilus lacuum, 551 


Patten on the eyes of Molluses and 
Arthropods (review), 285 

Pedicellina, life-history of, by 
Sydney F. Harmer, 239 


INDEX. 


Peripatus, development of, by 
Adam Sedgwick, 461 

Petromyzon, development of, by 
Shipley, 325 

Phytophthora infestans, life- 
history of, by H. Marshall Ward, 
413 

Pineal eye of Lacertilia, by Spencer, 
165 


Saprolegniew, liberation of zoo- 
spores in the, by Hartog, 427 

Scharff on Ctenodrilus parvulus, 
591 

Sedgwick on the development of the 
Cape species of Peripatus, 461 

Shipley on the development of Petro- 
myzon, 325 

Smith, W. Robert, on the ammoniacal 
decomposition of urine, 371 

Spencer on the pineal eye of Lacer- 
tilia, 165 


Talpa, development of, by Heape, 123 


Urine, ammoniacal decomposition of, 


by W. Robert Smith, 371 


Vertebrata and Nemertea, relations 
of, by Hubrecht, 605 


Ward, Marshall, on the life-history of 
Phytophthora infestans, 413 
Weldon on Dinophilus gigas, 109 


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