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QUARTERLY JOURNAL

OP

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-OPEBATION 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.,

Fellow and Assistant- Lecturer of Trinity College, Cambridge.

VOLUME XXV. — New Seeies.
l^itbograpljit plates anb (Kngrabings on SJloob.

LONDON:

J & A. CHURCHILL, 11, NEW BURLINGTON STREET.

1885.

0 ->b c (J \ rh -&1

CONTENTS.

CONTENTS OF No. XCVII, N.S., JANUARY, 1885.

MEMOIRS :

PAGE

The Significance of Kupffer’s Vesicle, with Remarks on other Ques-
tions of Vertebrate Morphology. By J. T. Cunningham, B.A.,
Fellow of University College, Oxford, Superintendent of the
Scottish Marine Station. (With Plate I) . .1

Blastopore, Mesoderm and Metameric Segmentation. By W. H.
Caldwell, M.A., Fellow of Caius College, and Balfour Student
in the University of Cambridge. (With Plate II) . . 15

On the Origin of the Hypoblast in Pelagic Teleostean Ova. By
George Brook, F.L.S. (With Plate III) . . .29

On the Presence of Eyes in the Shells of Certain Chitonidae, and
on the Structure of these Organs. By H. N. Moseley, F.R.S.,
Linacre Professor of Human and Comparative Anatomy in the
University of Oxford. (With Plates IV, V, and VI) . . 37

Archerina Boltoni, nov. gen. et sp., a Chlorophyllogenous Pro-
tozoon, allied to Vampyrella, Cienk. By E. Ray Lankester,

M.A., F.R.S., Jodrell Professor of Zoology in University College,
London. (With Plate VII) . . . . .61

On the Apex of the Root in Osmunda and Todea. By F. O.
Bowes, M.A., Lecturer on Botany at the Normal School of
Science, South Kensington. (From the Jodrell Laboratory,

Royal Gardens, Kew.) (With Plates VIII and IX) . .75

Correction of an Error as to the Morphology of Welwitschia
Mirabilis. By F. O. Bower, M.A., Lecturer on Botany
at the Normal School of Science, South Kensington . . 105

E. Van Beneden’s Researches on the Maturation and Fecundation of
the Ovum. By J. T. Cunningham, Fellow of University College,
Oxford, Superintendent of the Scottish Marine Station. (With
Plate X) . . . . . . . .107

IV

CONTENTS.

PAGE

On the Suprarenal Bodies of Vertebrata. By W. F. R. Weldon,

B.A., Fellow of St. John’s College, Cambridge, Lecturer on
Invertebrate Morphology in the University. (With Plate XI

and XII) 137

On the Life-History of Certain British Hetercecismal Uredines.

(The Ranunculi iEcidia and Puccinia Schoeleriana.) By
Charles B. Plowright . ..... 151

On the Occurrence of Chitin as a Constituent of the Cartilages of
Limulus and Sepia. By W. D. Halliburton, M.D., B.Sc.,
Sharpey Physiological Scholar, University College, London. (From
the Physiological Laboratory, University College, London) . 173

CONTENTS OF No. XCVIII, N.S., APRIL, 1885.

MEMOIRS :

The Urinary Organs of the Amphipoda. By W. Baldwin Spencer,

B.A., Scholar of Exeter College, Oxford. (With Plate XIII) . 183
The Skin and Nervous System of Priapulus and Halicryptus. By
Robert Scharff, Ph.D. (With Plate XI Y) . . . 193

The Eye and Optic Tract of Insects. By Sydney J. Hickson,

B.A. Cantab., D.Sc. Lond., Scholar of Downing College, Cam-
bridge, and Assistant to the Linacre Professor of Comparative
Anatomy at Oxford. (With Plates XY, XVI and XVII) . 215
A Peculiar Sense Organ in Scutigera coleoptrata, one of the
Myriapoda. By F. G. Heathcote, B.A., Trinity College, Cam-
bridge. (With Plate XVHI) ..... 253
The Structure and Development of Loxosoma. By Sidney F.
Harmer, B.A., B.Sc., King’s College, Cambridge, Demonstrator
of Comparative Anatomy in the University. (With Plates

XIX, XX and XXI) 261

A New Hypothesis as to the Relationship of the Lung-book of
Scorpio to the Gill-book of Limulus. By E. Ray Lankester,

M.A., LL.D., F.R.S., Jodrell Professor of Zoology in University
College, London ....... 339

CONTENTS.

v

CONTENTS OP No. XCIX, N.S., JULY, 1885.

MEMOIRS

PAGE

On Spermatogenesis in the Rat. By Herbert H. Brown, Uni-
versity College, London. (With Plates XXII and XXIII) . 343
A Simplified View of the Histology of the Striped Muscle- Fibre.

By B. Melland, B.Sc., Platt Physiological Scholar in the Owens
College, Manchester. (With Plate XXIV) . . . 371

On the Development of a Freshwater Macrurous Crustacean, Atye-
phira compress a, De Haan. By Chiyomatsu Ishikawa,
of the University of Tokio, Japan. (With Plates XXV, XXVI,

XXVII, XXVIII) 391

On the Supposed Communication of the Vascular System with
the Exterior in Pleurobranchus. By Alfred Gibbs Bourne,

D.Sc. Lond., F.L.S., Assistant Professor of Zoology and Compa-
rative Anatomy in University College, London. (With Plate

XXIX) . . . . • . . . .429

Observations on the Nervous System of Apus. By Paul Pel-
seneer, B.Sc. (With Plate XXX) .... 433
Note on the Chemical Composition of the Zoocytium of Ophry-
dium versatile. By W. D. Halliburton, M.D., B.Sc. Lond.,
Sharpey Physiological Scholar, University College, London . 445
The Development of Peripatus capensis. By Adam Sedgwick,

M.A., Fellow of Trinity College, Cambridge. (With Plates
XXXI and XXXII) 449

CONTENTS OF No. C, N.S., OCTOBER, 1885.

MEMOIRS:

On the Chromatology of the Blood of Some Invertebrates. By C.

A. Mac Munn, M.A., M.D. (With Plates XXXIII and XXIV) 469
The Cephalic Appendages of the Gymnosomatous Pteropoda, and
especially of Clione. Bv Paul Pelseneer, D.Sc., of Brussels.

(With Plate XXXV) ' 491

VI

CONTENTS.

Evidence in favour of the View that the Coxal Gland of Limulus
and of other Arachnida is a Modified Nephridium. By G.
Glflland, M.A., B.Sc. (With Plate XXXVI) .

Notes on the Embryology of Limulus. By J. S. Kingsley, D.Sc.,
Malden, Mass. U.S.A. (With Plates XXXVII, XXXVIII, and

XXXIX)

The Anatomy of the Madreporaria. By G. Herbert Fowler,
B.A., Keeble College, Berkeley Fellow of the Owens College,
Manchester. (With Plates XL, XLI, and XLII)

SUPPLEMENT, 1885.

MEMOIRS :

The Circulatory and Nephridial Apparatus of the Nemertea. By
A. C. Oudemans, Conservator at the Zoological Museum of
the University of Utrecht. (With Plates I, II, and III)

The Later Stages in the Development ofBalanoglossus Kowa-
levskii, with a Suggestion as to the Affinities of the Ente-
ropneusta. By W. Bateson, B.A., Scholar of St. John’s College,
Cambridge. (With Plates IV, V, VI, VII, VIII, and IX)

Some Notes on the Early Development of the Rana temporaria.
By W. Baldwin Spencer, B.A., Scholar of Exeter College,
Oxford. (With Plate X) ....

Notes on Echinoderm Morphology, No. IX. On the Vascular
System of the Urchins. By P. Herbert Carpentek, D.Sc.,
Assistant Master at Eton College ....

PAGE

511

521

577

1

81

123

139

The Significance of Kupffer’s Vesicle, with
Remarks on other Questions of Vertebrate
Morphology.

By

J. T. Cunningham, B.A.,

Fellow of University College Oxford, Superintendent of the Scottish Marine

Station.

With Plate I.

Some time ago I undertook the systematic study of the deve-
lopment of Teleosteans, because it seemed one of the more
obscure departments of Vertebrate embryology. I was led to
devote much attention to the herring, for of marine Teleosteans
none offers more facilities to the embryologist.

The researches on which the following discussion is based
have been carried on since the beginning of last August. My
first acquaintance with herrings* eggs was made long before
that time, namely in August, 1883, when I accompanied some
members of the Scottish Fishery Board on an expedition to
study the herring question in the Moray Firth. In the
spring of the present year also, I obtained and artificially
fertilized herring ova at the mouth of the Firth of Forth.
But on neither of these occasions had I sufficient opportunities
to make a study of the subject at all complete. In August of
the present year I stayed about five weeks at the village of
North Sunderland, on the Northumbrian coast, and there I
was able to keep numbers of herring embryos in a healthy
condition from fertilization up to the time of hatching and for
ten days after. During the period of their development I

VOL. XXV. NEW SER.

A

2

J. T. CUNNINGHAM.

carefully examined as many successive stages in the living
condition as time would allow, and preserved specimens at
frequent intervals. These preserved examples I have since
studied by means of section-cutting in the laboratory of the
Scottish Marine Station.

My embryos were preserved by two methods. Some were
placed fresh in a saturated solution of corrosive sublimate,
others in weak solutions of chromic acid, generally about
£ per cent. In either case spirit was substituted after a
short time for the fixing solution. Neither of these methods
is perfectly satisfactory ; the corrosive sublimate leaves the
embryos in too soft a condition, so that it is difficult to extract
them from the vitelline envelope and put them through the
processes of staining and embedding, without breaking them.
On the other hand, when sections are successfully cut they are
found to be satisfactorily stained and to show well the relations
of the layers. The embryos treated with chromic acid are very
hard and easy to manipulate, with the exception that the yolk
in cutting often breaks the other parts ; but these embryos are
very refractory towards staining fluids, and the colouring of
the sections is never as differential as one would wish. Never-
theless, although my sections are not quite perfect in all
respects I have been able to make out a good deal as to the
development of the various organs. The following account
refers chiefly to the origin of the intestine, but I hope to clear
up some other points later. It is scarcely necessary to add
that my sections were cut with the microtome of Jung, by
means of the method perfected by Giesbrecht.

It is well known that the rate of development in herrings’
ova depends largely on temperature. I shall not here discuss
the various experimental data of this part of the subject, but
merely state the temperature to which my specimens were
exposed, and the period at which the chief stages were reached.
The first eggs I obtained were fertilized at 4.30 a.m., August
14th ; the temperature of the surface of the sea at the time
was 133° C. ; the temperature of the water where the eggs
were kept varied from 11-5° C. to 145° C. These eggs began

SIGNIFICANCE OF EUPFFEE’s VESICLE.

3

to hatch out on August 21st, the eighth day, and continued
hatching on the following day. I next obtained eggs at 4 a.m.,
on August 26th ; the temperature was about the same as before,
and hatching took place on the eighth day.

As will be seen from fig. 1, Kupffer’s vesicle is seen on the
third day in the herring, by which time the eyes have appeared
and the two ends of the embryo almost meet at the ventral
pole of the yolk.

Historical. — Kupffer’s vesicle was originally discovered
and described by Kupffer1 in 1868, in the embryos of Gaster-
osteus aculeatus, Gobius minutus, and Gobius niger.
He named it “ the allantois” without considering very carefully
whether its relations corresponded to those of the allantois in
the Amniota. In subsequent papers he has come to the con-
clusion that the vesicle is closely connected with the formation
of the urinary ducts. Balfour in his * Comparative Embry-
ology,’ states that Kupffer’s vesicle is the representative ol
the post-anal vesicle in Elasmobranchs, without discussing the
reasons which led him to this view. Kingsley and Conn2 in
1883 described the origin of Kupffer’s vesicle in Ctenolabrus.
Their figures and descriptions are scanty, and refer only to
optical sections. It is stated to arise from a number of small
granules which fuse together ; it is probable that these granules
are small spaces between the periblast and hypoblast, and it
makes no difference to my account of the vesicle whether it
arises as a single space or from a number.

In a very recent paper by A. Agassiz and C. C. Whitman,3
the following remarks are made concerning Kupffer’s vesicle :
“ Although we have been able to trace the entire history of
Kupffer’s vesicle in several species of ova, its significance
remains as complete a puzzle as ever. Kingsley and Conn
were the first to give an accurate account of the origin of this
vesicle,4 but they give us no information in regard to its

1 * Arch. f. mik. Anat.,’ Bd. iv.

2 ‘Memoirs of Boston Soc. of Nat. Hist.’

3 ‘Proc. Amer. Acad, of Arts and Sciences,’ vol. xx, Aug., 1884.

4 This remark is not altogether impartial — the vesicle is not correctly

4

J. T. CUNNINGHAM.

subsequent history, and almost no details of its origin and
growth. As they have stated the vesicle arises by the fusion
or confluence of a cluster of granules. Those granules are
at first few in number (2 — 4) more or less angular, quite dark,
and not more than '002 mm. in diameter. In general appear-
ance they are not distinguishable from the scattered granules
seen in other parts of the ovum. In Ctenolabrus they appear
soon after the embryonic rim passes the equator. They
increase in number, grow larger, coalesce by degrees, and
finally blend into a single bubble-like vesicle in the course of
five hours. This vesicle, -01 mm. in diameter or more, more
than doubles its diameter in the next hour and a half, and
steadily expanding attains its maximum dimensions at the time
the blastopore closes. During all this time it lies beneath the
chorda and the entodermic stratum and has no sort of relation
with any tubular structure whatever. As the alimentary
canal is not yet in existence it is difficult to see how this
vesicle can be the homologue of a dilatation which arises in
and has no sort of existence outside of the post-anal gut.
Ventrally and laterally it is bounded by periblastic material,
but it has no cellular envelope in the strict sense of the
words.”

The authors then go on to describe the final history of the
vesicle. Their description is not quite clear, but the meaning
seems to be that the hypoblast above the vesicle is hollowed
out to form a longitudinal furrow which deepens until a closed
canal, the lumen of the gut, is formed, the depression in the
periblast disappearing in the process. The authors think it
probable that there exists from this time onward a lumen in
the portion of the gut thus formed.

Agassiz and Whitman give no figures of the vesicle nor do
they state if they confirmed their results by the examination of
sections. Their paper has for its chief object to announce the
important discovery that the nuclei of the periblast are origi-

described when it is said to originate from globules, and Kingsley and Conn
do not even point out its relation to the germinal layers.

SIGNIFICANCE OF KUPFFER’s VESICLE.

5

nally derived by karvokinetic division from the nuclei of the
cells at the edge of the blastoderm. Thus another supposed
case of autogenous origin of nuclei falls to the ground.

I have given the exact relations of the vesicle at the time of
its full development in the herring, as shown by a series of
sections, in fig. 3. Figs. 2 and 4 show the relations of the
layers behind and in front of the vesicle. It will be seen that
at the period when the vesicle exists, the hypoblast is not dis-
tinctly differentiated from the mesoblast, and is not columnar.
There is no distinct separation between the notochord and
hypoblast, but the mesoblast is very sharply marked off from the
notochord on each side. The two layers of the epiblast are
distinctly seen, and the lower one is continuous with the
neurochord. In the latter there is no central cavity; this
appears later as seen in the subsequent figures. Both in front
of the vesicle and behind it the hypoblast and periblast are in
contact. The mesoblast does not extend far to the sides of the
embryo ; over the lateral and ventral parts of the yolk the
periblast and epiblast are in contact.

The ventral wall of the gut in Elasmobranchs is formed by
the differentiation of cells round the yolk-nuclei ; in Amphi-
bians by the differentiation of the superficial layer of the yolk-
cells. There is little doubt that the floor of the gut in the
herring is formed in an exactly similar way. As is shown by
fig. 5, from an embryo sixtv-four hours old, no periblast, or
scarcely any, exists below the floor of the intestine, which is in
this region complete : it is certain that no periblast nuclei are
present here though they are seen beneath the lateral meso-
blast and up to the side of the intestine. The same thing is
shown by fig. 6, which is a transverse section passing through
the otocvsts. We may conclude, then, that this portion of the
periblast has been used up to supply the cells of the floor of
the gut. In the stage represented, figs. 5, 6, and 7, the intes-
tine was not formed in the most anterior region of the body,
and here, in front of the notochord, the neurochord comes into
contact with the hypoblast of which there is a thin layer
between the neural tissue and the periblast. This is shown in

6

J. T. CUNNINGHAM.

the diagram fig. 8, and is referred to in a subsequent part of
this paper.

In the stage represented in figs. 5, 6, and 7, the canal of the
neurochord has appeared. In the posterior part of the embryo
it is deep within the cord ; in the anterior part it opens out above
into a flat cavity covered only by a thin layer of epiblast. I
was not able to satisfy myself whether this layer was only one
cell deep, but it seemed to be so both above the neurochord
and over the otocvsts : it seems as if the lower layer went to
form the neurochord and the wall of the auditory vesicle.

The explanation of Kupflfer’s vesicle in which my reflection
on the subject has resulted is a very simple one.

In the Elasmobranch the invagination of the hypoblast
which takes place at the posterior end of the blastoderm forms
a tubular cavity open to the exterior by the blastopore. The
dorsal wall of this cavity is formed by columnar hypoblast ;
its floor is occupied by the superficial layer of the yolk con-
taining yolk-nuclei, that is by the periblast. This cavity n
the Elasmobranch becomes shut off from the exterior by the
closing of the medullary groove over the blastopore. In this
way the cavity comes to be continuous posteriorly with the
canal of the neurochord, a neurenteric canal being constituted
which subsequently disappears. The history of this stage n
the Amphibian is precisely similar, with the exception that in
the Amphibian the segmentation is complete, and the yolk
is wholly composed of large nucleated cells instead of con-
taining nuclei only near its surface. The cavity of invagina-
tion of which I am speaking never obliterates, it becomes later
the lumen of the intestine. The intestine is formed simply by
the differentiation of the walls of the cavity. The dorsal wall
of hypoblast is hollowed out longitudinally and its lateral parts
approach one another; the floor of the alimentary canal
is formed by cells differentiated round the nuclei of the
periblast.

Kupflfer’s vesicle in the Teleostean is the homologue of the
cavity of invagination in the Elasmobranch and Amphibians :
it is the rudiment of the primitive gastrula-cavity, of that part

SIGNIFICANCE OF KUPFFEK’s VESICLE.

7

of it which is not represented by the body cavity. In the
Teleostean it is never open to the exterior, but this need not
surprise us since the cavity of the otocvst, or of the crystal-
line lens, or of the neurochord, is never open to the exterior
in the Teleostean ; it is very doubtful also whether the neuren-
teric canal ever contains a lumen in Teleosteans. The intestine
of the herring is, I believe, formed in exactly the same way as
the intestine of the Elasmobranch or Amphibian from the
gastrula-cavitv ; fig. 5 shows that the floor of the intestine has
been formed from the periblast.

It is of importance as favouring my view that in many
Teleosteans Kupffer’s vesicle is visible at a much earlier stage
than the one in which I have seen it in the herring. In
Ofasterosteus aculeatus as described in Kupffer’s paper
of 1868, it is present when the blastoderm has got little beyond
the equator of the yolk. The same is the case, as has been
seen from the description of Agassiz and Whitman, in Cteno-
labrus and probably in many other cases. This brings the
period of the existence of the vesicle very closely into agree-
ment with that of the existence of the gastrula cavity in
Elasmobranchs. I am unable to say whether there is a neuren-
teric canal or anything representing it in the herring, which
comes into relation with Kupffer’s vesicle. On my view
one would expect such a relation, but I must test this in the
future.

I do not know whether to rejoice or regret that only in
copying out this paper for the press I have found that a paper
appeared in 1880, by M. Henneguy,1 which advocates very
much the same view as I now put forward. I have not yet
referred to the paper and therefore do not know if M. Henneguy
cut any sections. I found a few words which I had missed in
the paper by Kingsley and Conn, stating that Henneguy
believed he had found traces in the perch of an opening of
invagination leading to the vesicle, and homologized the cavity
with the primitive intestine in Cyclostomi and Batrachia, and
the opening with the anus of Rusconi. Agassiz and Whitman
1 ‘ Annals and Mag. Nat. Hist.,’ ser. v, vol. vi.

8

J. T. CUNNINGHAM.

simply say that the interpretations of Kupffer and Henneguy
are still more unsatisfactory than Balfour’s and need not he
considered. I hope I have shown in this paper that the view
advocated by Henneguy and myself is the one which gives the
true morphological meaning of Kupffer’s vesicle, and places it
on the same basis as the cavity of the canal of the neurochord
and of the otocyst in the Teleostean.

I have arrived at this view quite independently, and flattered
myself I was the first exponent of it. I find M. Henneguy has
anticipated me by four years. I hope my support of the view
will help to gain it the acceptance which so great an authority
as Agassiz has denied it.

There is one more question to be considered. Has the vesicle
any physiological importance in the process of actual develop-
ment? I think not; the intestine is formed in the anterior
part of the body without the aid of such a cavity, and I think
it is a true rudimentary structure which has persisted in spite
of the modifications in the development of the Teleostean
ovum, by reason of the strong tendency to perpetuate itself of
a structure so fundamental in the primitive stages of evolution
as the gastrula-cavitv.

Remarks on General Vertebrate Morphology.

Ever since I became acquainted with the theory which
regards the Vertebrate as a worm turned on its back I have
been more and more convinced of its fundamental truth. Of
this theory Dohrn has been for years the most brilliant and
most profound exponent and investigator, and although he has
had, and may have again, occasionally to retrace his steps, he
has won for us a point of vantage from which we may look
back with clear view on the historical evolution of the Verte-
brate organization. Mr. Sedgwick and his school have not
embraced this theory ; yet one point in Mr. Sedgwick’s paper
published in this Journal, January, 1884, will, in my opinion,
do a very great deal towards completing the Dohrnian hypo-
thesis. The point I refer to is the stress laid on the fact that

SIGNIFICANCE OF KUPFFER’s VESICLE.

9

the primitive ancestor of the Vertebrates had a central nervous
system which had not separated from the epiblast in which it
was developed. As Mr. Sedgwick points out, the nervous system
in the living Vertebrates is continuous with the epiblast, and in
this respect the Vertebrate is on a par with the Ccelenterate
and the Echinoderm. It follows, then, that the limiting surface
of the neural canal in Vertebrates is part of the original surface
of the body. Now, there is one fact in the organization of a
worm which requires to be taken most seriously into account
in forming an idea of its transformation into a Vertebrate.
This fact is the perioesophageal nerve-collar. We may sup-
pose— we must suppose — that, although in the worm -like
ancestor of the Vertebrate the nerve-cords were continuous
with the epiblast, these cords diverged to enclose the mouth,
and met again in front of it just as they do in a modern
annelid. In the Vertebrate, then, we must find a rudiment of
the original mouth within the neural canal. I believe I
have hit upon this rudiment : it is the infundibulum of the
brain. The infundibulum is a deep depression in the floor of
the neural canal which comes into the closest relation with the
hypoblast. I am not referring in the faintest way to the
hypophysis or pituitary body, which seems, according to recent
researches, to be derived from the epiblast of the actual mouth.
But the infundibulum in a Vertebrate embryo is, I believe,
actually in contact with the hypoblast in front of the notochord.
Elsewhere, along the back of the embryo, the neurochord is
separated from the hypoblast by the notochord; the notochord
ceases at the infundibulum. I fully accept all that Mr.
Sedgwick says about tbe elongated blastopore along the Verte-
brate back, and I would point out that Mr. Sedgwick’s view
makes the back of the Vertebrate homologous with the ventral
face of the worm, just as does the Dohrnian hypothesis. But
according to Mr. Sedgwick, a supraoral portion of the nervous
system in the worm has disappeared in the Vertebrate (and in
Balanoglossus) ; and the present mouth and anus in the Verte-
brate are not secondary new structures but the primitive ones.
This I strenuously oppose. If we look at certain Teleostean

10

J. T. CUNNINGHAM.

Fishes, such as the eel or the blennies, on Mr. Sedgwick’s
view we should have a blastopore extending round nine tenths
of the longest circumference of the body, which seems to me
a reductio ad absurdum of embryology. Indeed, if, as
some writers do, we consider the closing of the blastoderm
over the ventral pole of the yolk as part of the original blasto-
pore, we have the complete circle, and the blastopore extends
all round the plane of symmetry. The anterior limit of the
primitively elongated dorsal blastopore is the infundibulum
which remains to indicate the position of the original mouth.
In the preceding number of this Journal Miss Alice Johnson
speaks of a deep pit at the anterior end of the primitive groove
in the newt at which epiblast and hypoblast are fused, and she
believes this pit to correspond in position with the future
mouth. Anyone who has studied Vertebrate embryos knows
how very late the actual mouth is in appearing ; it appears
long after the visceral clefts are wide open and the heart
beating vigorously. I am convinced that the pit observed by
Miss Johnson is the commencement of the infundibulum,
although I cannot speak from actually having traced the origin
of that structure in the newt.

All former attempts to find the original mouth ended in
placing its external opening on the actual dorsal surface, instead
of on the floor of the anterior cerebral vesicle. Dohrn, before
he wrote his ‘ Ursprung der Mirbelthiere ’ in 1875, had
imagined that the primitive oesophagus was represented by the
pituitary body and pineal gland. In the essay I have men-
tioned, he abandons this theory for one which made the fourth
ventricle in the medulla oblongata the rudiment of the
original mouth. In his address at the British Association
Meeting in 1881, Sir Richard Owen revived the first hypothesis
of Dohrn, and stated it as an original discovery. Dohrn has
recently proved that the hypophysis represents a pair of gill
clefts. If this be true, the connection of the hypophysis with
the infundibulum explains itself on my view, because a pair of
gill clefts might have opened into the mouth.

Similarly with regard to the primitive anus I cannot accept

SIGNIFICANCE OF KUPFFER’s VESICLE.

11

Sedgwick’s idea that the present anus is the same structure,
nor do I aceept the proof brought forward by Miss Johnson
on the point as far as regards the newt. The blastopore is
indeed the primitive anus, hut it does not coincide with the
actual anus ; the primitive anus was closed by the same process
as that which removed the hollow neurochord from the surface of
the body, and is represented by the neurenteric canal, which,
in spite of Miss Johnson’s failure to find it in the newt, is, I
believe, never altogether unrepresented in Arertebrate embryos.
Miss Johnson’s researches on the primitive groove in the newt
are extremely valuable as proving that there is originally a
fusion of the three layers along the whole line of the primitive
elongated blastopore.

The notochord was discovered long ago to originate in
many Vertebrates in close relation to the hypoblast, and it was
immediately concluded by morphologists that the notochord
was evolved from the wall of the intestine. Some have
pointed to the typhlosole in the earth-worm as the homologue
of the notochord ; notwithstanding that the typhlosole is a
pushing in and the notochord a growth outwards. The typh-
losole is represented beyond a doubt by the spiral valve in
Elasmobranchs and other fishes, and has never given rise to
anything outside of the intestine. Now, the notochord in the
course of evolution never could have arisen from the intestine,
for this reason : the dorsal aorta of Vertebrates is homologous
with the subintestinal vein of an Annelid, the blood in both
flows the same way, and the two have the same relations to the
intestine. Therefore, if the notochord had been evolved from
the wall of the intestine the aorta would in the Vertebrate have
been on the dorsal side of the notochord, not, as it actually is,
on its ventral side. A glance at fig. 2 of the Plate illustrating
this paper will show that one might as easily suppose that in
the herring the notochord was developed from the neurochord
as from the hypoblast. I am not going to sustain that the
neurochord gave origin to the notochord, because I think it
unlikely that a nervous structure would have given rise to a
skeletal one. I believe the notochord to be really mesoblastic,

12

J. T. CUNNINGHAM.

and that the reason why it has such close relations with both
neurochord and hypoblast is that its development in the indi-
vidual has been thrown so far back, takes place so early, that
the fusion between the three layers due to the influence of the
primitive elongated blastopore has scarcely disappeared before
the central part of the mesoblast is converted into the noto-
chord. "We have got back then to the old idea of the homo-
logy of the notochord and the three giant fibres beneath the
nerve-cord in the earth-worm.

The Origin of the Vertebrate Eye. — Prof. Balfour1
has pointed out that the eyes of Vertebrates like those of Crus-
tacea develop as part of the thickening of epiblast which gives
rise to the nervous system. Prof. Lankester2 has inferred from
the relations of the cerebral eye in Ascidians, that the ancestral
Vertebrate was transparent and had eyes on the floor of the
brain cavity. But Sedgwick’s revelation enables us to go a step
further in tracing the evolution of the Vertebrate eye. In the
ancestor of the Vertebrate before the neural canal had begun
to form, two eyes existed somewhat in front and at the sides of
the mouth actually in the region of the central nervous system.
There is no impossible assumption in this; the eyes of Coelen-
terates in the present day are in contact with the superficial
nervous system, and probably eyes in nearly all cases existed
in the same relation before the nervous system was separated
from the epiblast. These eyes in the ancestral Vertebrate
were open cups like those of a modern Patella, Haliotis, &c.
When the nervous system formed a canal it covered over these
eyes, which were then open to the neural canal, to the cavity
of the anterior cerebral vesicle in the floor of which was the
original mouth. The animal was probably at this time trans-
parent, and light reached the simple eyes both through the
roof of the cerebral vesicle and the sides of the head. Now, as
the walls of the cerebral vesicle increased in thickness, and
perhaps became more opaque than the rest of the body, the

1 ‘Report of Brit. Ass. Meeting,’ 1880, “ Address to Department of Anat.
and Pkys.,” Sec. D.

“Degeneration,” ‘Nature,’ Series 1880.

SIGNIFICANCE OF KUPFFER’s VESICLE.

13

eyes would be affected in greater proportion by the light
passing through the side of the head. For this reason the eye
cups would deepen and begin to grow out from the cerebral
vesicle in order (as already pointed out by Lankester) to
get nearer to the lateral surface of the head. They would
ultimately come into contact with the epiblast at this surface.
The part of the epiblast with which the optic cups came
into contact has remained transparent while the rest of the
body has become opaque. The reason why the crystalline
lens is now formed as an invagination is easily explained.
The epiblast at this region became thickened in order to
act as a lens. The lens was ultimately perfected by being
converted into the biconvex shape and removed from the body
surface. The separation of the retina from the crystalline
lens is also comprehensible, for it was an improvement of the
optical apparatus at every step.

I do not intend here to discuss the rationale of the origin
of the new mouth, of the visceral clefts, or of the actual anus.
Although I believe these to be new structures I am not satis-
fied as to their explanation. Sedgwick regards visceral clefts
as serially homologous with segmental organs, but I have not
considered the subject sufficiently at present to have a definite
opinion. I will conclude with a few words as to segmentation.
Sedgwick’s interesting theory does not at all explain the
peculiarity of the growth of segmental animals, namely by the
formation of new segments between the last and the end of the
body. But this mode of growth is another difficulty in the
way of his view of the blastopore. For he supposes the planes
of segmentation to be originally perpendicular to the direction
of the blastopore, and yet if the actual Vertebrate anus is the
end of the blastopore, the planes of segmentation in the Verte-
brate tail are parallel to the direction of the blastopore.

14

J. T. CUNNINGHAM.

EXPLANATION OF PLATE I.

Illustrating Mr. J. T. Cunningham’s memoir on “ The Signifi-
cance of Kupffer’s Vesicle, with remarks on other Questions
of Vertebrate Morphology.”

Letters or Reference.

Bl. Blastopore. Bp. Epiblast. Gc. Gastrula-cavity. My. Hypoblast.
In. Infundibulum. Ev. Kupffer’s vesicle. Me. Mesenteron. Mes. Meso-
blast. Ne. Neurochord. Ot. Otocyst. No. Notochord. Be. Periblast.
Tk. Yolk.

Pig. 1. — Embryo of herring fifty-four hours after fertilization. Obj. A oc.
3, Zeiss.

Fig. 2. — Section of a herring’s embryo at stage represented (fig. 1). All
the sections were cut perpendicular to both ends of the embryo. The figure
gives a section of the posterior part of the embryo taken near the extremity.

Fig. 3. — More anterior section of the same series, passing through Kupffer’s
vesicle.

Fig. 4. — Section a little more anterior of the same series.

Fig. 5. — From a herring’s embryo, sixty-three and a half hours after fertili-
zation, about the region where Kupffer’s vesicle was at the previous stage.
Fig. 6. — Section passing through otocysts, same stage as fig. 5.

Fig. 7. — Herring embryo sixty-two and a half hours after fertilization.
Fig. 8. — Diagram of a section through the plane of symmetry of a herring
embryo at the stage of Kupffer’s vesicle.

Fig. 9. — Diagram of a section through the plane of symmetry of a frog
embryo at the stage corresponding to that of the Teleostean in fig. 8.

N.B. — All the sections were drawn with the same lenses, the outlines by
means of Abbe’s camera lucida. The scale of y^tli mm. is given in the
plate.

Fu,L

J T. Cunningham del

Jiuyr. Joicrnf/M.. XX7 KS. I.

Y Huth.Liiii1 EdinT

BLASTOPORE, MESODERM AND METAMERIO SEGMENTATION. 15

Blastopore, Mesoderm and Metameric
Segmentation.

By

W. II. Caldwell, M.A.,

fellow of Caius College, and Balfour Student in the University of Cambridge.

With Plate II.

A year ago my observations on the development of certain
forms of invertebrate animals suggested an explanation of the
behaviour of the blastopore, and led me to consider the various
speculations concerning the middle germinal layer put forward
in recent years. The theory which I thus deduced embraces the
question of metameric segmentation. On my voyage to Australia
I wrote the present paper. Meanwhile my friend Mr. Sedgwick,
to whom I had written some of my conclusions, was preparing
a contribution to the same subject. Since then Mr. Sedgwick's
paper1 has appeared, and I find not only that my conclusions as
to the meaning of segmentation are fundamentally different,
but also that he leaves the larger question of mesoderm un-
touched. The origin of mesoderm in Phoronis was the starting-
point of my inquiry. I shall first describe the facts in this
animal, and I would point out that my discoveries are due
entirely to the facilities for investigating minute embryos
afforded by my method of obtaining automatic series of sections.
I failed to observe the details which are contained in the present
paper in my original sections from which a preliminary account
(‘ Proc. Roy. Soc. 5 1882) was composed.

1 ‘ Quart. Journ. Mic. Sci.,’ 1884, “ Origin of Metameric Segmentation.”

16

W. H. CALDWELL.

Development of Phoronis.

The details of the segmentation of the ovum are not required
in this paper. A planula slightly oval in form is the final term
of the process. The long axis of this planula coincides with
the future long axis of the gastrula. One half of the cells are
large (endoblast), the other half are small (ectoblast).

Gastrulation.

The gastrula is formed by invagination. The first sign of
this is the flattening of the endoblast-half of the oval planula.
The sides begin to grow over the endoblast, and this takes place
in such a way that the saucer-shaped structure is deepened
towards the future anterior end (PI. II, fig. 1). The anterior
end also grows rapidly over the endoblast, thus early indicating
the future prseoral lobe. The bilateral symmetry is thus
clearly marked. Posteriorly the sides fold over so as to meet in
the middle line (PI. II, fig. 9). The cavity of the archenteron
is now sufficiently large to form lips to the blastopore. Quite
posteriorly the lips completely fuse, so that during the gastru-
lation the extreme posterior portion of the archeuteric cavity is
obliterated (PI. II, fig. 10). It is represented by a fused solid
mass of cells (r). The lips of the blastopore continue to
approach the middle line, and as they touch fuse with each
other. This fusing proceeds from behind forwards. The
blastopore has in this way become divided into two parts
exactly comparable to the parts long known in some vertebrates
(PI. II, fig. 2). I shall speak therefore of the posterior portion
as the primitive streak, and the groove along the line of closure
as the primitive groove. The invagination has now produced
a gastrula with an opening situated in the anterior portion of
the blastopore into a large archenteric cavity (PI. I, fig. 11). I
shall now use the terms dorsal and ventral as defined by the
non-blastoporic and the blastoporic regions respectively. The
ventral surface now begins to grow very much more rapidly
than the dorsal. The growth results in the posterior point of
the primitive streak becoming terminal. The exact behaviour of

BLASTOPORE, MESODERM AND METAMERIO SEGMENTATION. 17

the cells of the middle of the primitive streak is as follows.
About the middle of the primitive streak the ectoblastic
elements divide very rapidly, and very soon the primitive
groove disappears in this region (cf. PL II, figs. 2 — 6) . Coinci-
dently with this a space appears between ecto- and endoblast
(PL II, fig. 18, v ). Consider the fate of a single one of the
cells of the primitive streak. This cell is destined to give rise
by division to both ecto- and endoblast. The ectoblastic por-
tion increases more rapidly than the endoblastic, and soon the
latter is no longer in contact with the former, i.e. a space has
arisen in the median ventral line. This space extends both
anteriorly and posteriorly. The primitive groove now only
remains as a pit at the posterior end of the embryo (fig. 4, y).
The anterior opening of the blastopore remains open and
becomes the mouth of the future Phoronis, the posterior pit
is destined to undergo some very remarkable changes which
will be described below. During these changes the original
solid mass of cells — the posterior portion of the primitive
streak — remains unaltered as a cord connecting the archenteron
with the ectoderm.

The Separation of the Mesoblast.

Previous Observations. — Kowalewsky originally de-
scribed the mesoblast as originating in Phoronis by delamination
from the ectoderm (vide Plate II, fig. 13). This mistake
arose from the ectoderm cells being darker at their base.
Recently Metschnikoff and Foettinger have attempted to solve
the problem of mesoderm formation. While they have both
recognised Kowalewsky's error, they have fallen into other
mistakes. Metschnikoff describes some mesoblastic cells already
present in the blastula stage ; he figures four of them in his fig.
30. In each cell Metschnikoff has drawn a nucleus. I have fre-
quently observed this appearance of cells. It is caused, how-
ever, by the amoeboid processes of the endoderm cells growing
into the segmentation cavity. This is easily proved by making
real sections. Another possible explanation of Metschnikoff's
account may lie in the presence of certain peculiar bodies in

VOL. XXV. NEW BER.

B

18

W. H. CALDWELL.

the early gastrula stages. In the endoderm cells little spherical
masses of apparently the same material as the body of the cells
themselves are frequently found. Each little mass in hardened
embryos is separated off by a clear space. I have traced these
bodies from their birthplace into the body cavity. They
never possess a nucleus, and they disappear at a very early age.
Their significance remains unknown to me unless they be
merely an excess supply of nutriment analogous to food yolk.
Foettinger has arrived at somewhat extraordinary results. He
says, “ J’ai non seulement constate l’existence des premiers
elements-mesodermiques k des stades plus jeunes que celui
signale par Metschnikoff, mais encore je crois pouvoir reculer
leur premiere apparition jusqu’a l’oeuf en voie de segmenta-
tion.” The bodies referred to the mesoblast are, I believe,
either due to the reagents used in preparing the embryos, or
are the bodies referred to above. I have observed them fre-
quently, but it is certain that they have nothing to do with
the true mesoblast, whose origin I shall now describe.

Before the lips of the blastopore meet there is no meso-
blast (fig. 1). When the closing of the blastopore has already
extended sufficiently far forwards to shut off a small archen-
teric cavity, two pouchings of the endoderm occur on either
side of the blastopore (fig. 8, ad). Each pouch is longi-
tudinally extended in the direction of the long axis of the
body, and is deeper towards its anterior end. The endoderm
cells covering the region of the pouch now undergo some
division (fig. 8), and a mass of cells is budded off on either
side (me'). These cells as they are formed arrange them-
selves into a sac enclosing a cavity (fig. 17, ad). These cavities,
however, never communicate with the cavity of the gut.
The pouch of the endoderm is soon obliterated, and the
cells return to the size of the other endoderm cells. The
hind part of each pouch lies about opposite to the most anterior
point where the lips of the blastopore have closed. On
either side of the primitive streak a few mesoblast cells are
budded off from the cells forming the primitive streak (fig.
18, me"). Behind the primitive groove becomes deeper, and

BLASTOPORE, MESODERM AND METAMERIC SEGMENTATION. 19

this deepening continues after the middle part is obliterated
(figs. 4, 6, 11, and 12). The deepening of the groove soon
forms a very definite pit (g). This pit, when by the growth
of the ventral surface it has become nearly terminal, grows
into two pouches which project into the cavity between the
skin and gut on either side of the solid cord of cells, which
is the persistent hind part of the original primitive sheath
(fig. 13 and fig. 14, pd). These pouches are derived from
cells homologous with those which have already given rise
to mesoblast. The continuity of this posterior pair of pits
with the anterior is kept up by the few cells (me") budded
off in the middle of the primitive streak. The same growth
which opened up the space between ectoblast and endoblast
has separated the anterior and posterior mesoderm. The fact
that in Phoronis the two ends of each mesodermic pouch are
actually connected by an intermediate cord of cells depends on
this formation of a primitive streak along the whole line of
closure of the blastopore.

Nephridia.

The posterior pair of mesodermic diverticula open in the
middle line to the exterior. The closure of this opening pro-
ceeds in such a way that each pouch remains open to the
exterior by a smallbore on either side of the middle line. I
believe — though this fact is not established so certainly as those
above concerning the mesoderm — that each pore persists as
the opening of the nephridium of its own side. The nephridia
appear coincidently with the final narrowing of the mesodermic
pores, but I have yet no sections showing the cells in the
neighbourhood of the pores taking on the form of the intra-
cellularly perforate excretory cells. The formation of these
excretory cells, which lie in a blood space of the splanchno-
pleure and not in the body cavity, I have independently traced
from the mesodermic cells of the posterior pouches.

20

W. H. CALDWELL.

Anus.

Meanwhile the remnant of the primitive streak, the posterior
solid cord of cells, opens up, and forms a canal leading from
the archenteron to the exterior (fig. 15). The alimentary
canal is now complete, mouth and anus having been derived
from the blastopore (fig. 7, m and a).

Hypothesis.

With the help of the various morphological laws implied
by such terms as precocious segregation, superlarvation, abbre-
viation, &c., it is possible to solve almost any morphological
problem in several ways — all equally probable. The speculations
which follow, I am induced to add to those already existing,
not from any belief in their absolute value, but because they
go in the direction of simplification. The theory which I am
about to state reduces the various origins of the mouth and
anus to one type. The same hypothesis gives an explanation
of the various modes of origin of the mesoderm, and leads to a
view of the meaning of metameric segmentation which, so far
as I know, has not been hitherto suggested.

Given a gastrsea already become bilaterally symmetrical by
the elongation of the blastopore and the differentiation of
anterior inhalent and posterior exhalent currents, and in which
the main development of organs takes place around the mouth,
so that the mesoderm thus resulting comes to lie in develop-
ment as two masses of cells on either side of the body.1

I propose to show that the elongation of a long axis of the
body is a possible cause of —

I. The obliteration of the relation of blastopore to mouth
and anus.

II. The masking of the original mode of mesodermic forma-
tion.

III. Metameric segmentation.

1 Whether the mesoderm originally arose as diverticula or not does not
concern the present speculation.

BLASTOPORE, MESODERM AND METAMERIO SEGMENTATION. 21

I. The Obliteration of the Relation of Blastopore
to Mouth and Anus.

Previous Observations. — Since the time of the Gastraea
Theory many writers have occupied themselves with the blas-
topore. Lankester (This Journal, 1877), in accordance with his
planular theory, came to the conclusion that the coincidence of
mouth and anus with the blastopore was only a developmental
convenience. He says (loc. cit.), “ Regarding, as I do, the blas-
topore as an orifice of a secondary nature, existing solely in rela-
tion to the invagination process, and originating after mouth
and anus had made their appearance in the progress of animal
evolution, I seek to explain its occasional relation to the mouth
and to the anus as cases of adaptation.” Balfour, after enu-
merating the different fates of the blastopore in the animal
kingdom, says, “ It is clearly out of the question to explain all
these differences as having connection with the characters of
ancestral forms. Many of them can only be accounted for as
secondary adaptations for the convenience of development.”
The number of groups in which a slit-like blastopore has been
described is very considerable (vide Balfour, vol ii, p. 282).
Lankester was the first to suggest that a slit-like blastopore
which might close at either end would, if taken as the ancestral
type, account for the various fates of the blastopore in mol-
luscs. Hatschek, in his paper on Teredo, has suggested the
possibility of phylogenetically deriving the anus which arises
in this animal ; secondarily, as an ectodermic invagination from
part of a slit-like blastopore. But he bases this view on the fact
that the anus corresponds in position with the hind wall of the
gastrula mouth. Metschnikoff, in combating Hatschek’s views
on the early expression of bilateral symmetry, has denied the
ancestral character of the slit-like blastopore. He says, “ Kann
man dem geschlitzten grossen Blastopor keine palingenetische
Bedeutung zuschreiben und muss ihn als eine embryonale
Anpassungs-erscheinung ansehen.” Sedgwick (loc. cit., p. 27)
concludes that “ the mouth and anus of the Triploblastica are

22

W. H. CALDWELL.

derived from the primitive mouth.” I fail to see how his theory
on p. 34 explains the behaviour of the blastopore. In the first
place his conception of the blastopore is different from that used
in the present paper. Page 35 be writes, “ Consequently the only
course open is that the mouth should be formed as a secondary
perforation entirely independent of the blastopore.” Sedg-
wick’s theory is contained in the following passages (p. 34) :
“ My view is that in those animals in which it does not give
rise to the mouth and anus, it functioned as the larval mouth
while the animal was developing, and persisted until parts of
the embryo were developed between it and the position of the
mouth and anus of the adult, which parts had arisen in the
phylogenetic history in the adult after the primitive mouth had
completely divided into the mouth and anus. These parts
never had been traversed by the original slit-like mouth,
because they had appeared at a stage in evolution subsequent
to the stage in which the mouth and anus were one. It cannot
therefore be a matter of surprise if the blastopore does not
elongate and bisect these latter structures, which never had in
the history of the animal been perforated by the blastopore.”
I ask, how have the cells which are to form mouth and
anus anything to do with blastopore ? My hypothesis is as
follows.1

The behaviour of the blastopore in Phoronis is obviously due
to the attainment of a terminal anus. Suppose the long axis
of the body to increase still more rapidly while the posterior
part of the blastopore still remains terminal. Suppose in the
early stages of development the importance of a complete
alimentary canal is not equal to the importance of the body
form, then the tendency of the endoblast to divide into anterior
and posterior portions attached to anterior and posterior parts
of the blastopore respectively might be consummated. The
behaviour of the cells in the middle of the primitive streak of
Phoronis, which resulted in the opening of a space between
endoderm and ectoderm, would tend to begin at an earlier stage.

1 Delamination need not be discussed, since the existing hypotheses (vide
Balfour, * Embryology,’ vol. ii) are sufficient to bring the case uuder my theory.

BLASTOPORE, MESODERM AND METAMERTC SEGMENTATION. 23

What would be the structure of a planula when this influence
has reached back to the preinvaginated stages ?

The ectoderm cells would grow in from either side, and en-
croach on the solid mass of endoblast until this (i. e. endoblast)
would be completely divided into anterior and posterior masses.
The endoblast may be divided in this way into any number of
separate portions (cf. below metameric segmentations). Let
invagination now take place ; each mass of endoblast will be
invaginated. The invaginated endoblast will grow according
as it has been divided into endoderm or mesoderm ; such
division may have taken place in a great many ways (vide
mesoderm below) ; when the anterior endoblastic mass is the
larger we have a so-called oral blastopore, e. g. Pilidium,
Phascolosoma, and Phoronis, according to previous observers ;
when the posterior is the larger we have an anal blastopore,
e. g. Paludina, Serpula, and Echinodermata. Let the invagi-
nation of the different endoblastic masses cease to be syn-
chronous, and the primitive relations will become still more
marked. The extreme cases are described as stomodoea and
proctodosa. The difference between Sedgwick’s view and my
own consists in the fact that I suppose that portions of the blas-
topore actually exist beyond the “ parts which, in the phy-
logenetic history in the adult, had arisen after the primitive
mouth had completely divided into the mouth and anus.”

II. The Masking of the Original Mode of the Origin
of Mesodermic Formation.

In Phoronis the original pair of diverticula are almost divided
into two pairs. The anterior pair produce only a small proportion
of the future mesodermic structures. Argiope is an instance of
the anterior mesoderm being large. No posterior mesoblast has
yet been described in this form. The mesenchyme of the praeoral
lobe of the Hertwigs is the same anterior mesodermic diverticula
reduced in the opposite direction. In Phoronis the anterior meso-
derm would be described as of endoblastic origin, the middle as
originating at the lips of the blastopore, while the posterior
pouches would be assigned to the ectoblast. But the connec-

24

W. H. CALDWELL.

tion between these three methods, though obvious in Phoronis,
has not been explained in the same way in the rest of the
Triploblastica. The six diagrams (fig. 19) represent six dif-
ferent modes of formation ; they may all coexist in the same
animal. Thus, in Phoronis we find those represented in the
diagram by 3, 4, and 6, and in the Chick and other Verte-
brates 4 and 6.

III. Metameric Segmentation.

In Phoronis the elongation of the blastopore produces two
pairs of masses of mesoblast, each of which might be re-
garded as constituting a “ mesodermic somite but in Phoronis
the first long axis developed is not to be the long axis of the
adult. The long axis of an adult Phoronis is exactly at right
angles to that of the larva. The further slight extension of
the larval long axis is thus able to proceed pari passu with
the growth of the posterior pair of mesodermic pouches. In
Chsetopoda, Arthropoda, and Vertebrata the long axes of adult
and larva are identical. The elongation of the body in these
forms takes place before the mesoderm grows. The same
cause which separated the mesoderm in Phoronis operates
during a much longer developmental period. The mesoderm
cannot keep pace with the ectoderm. It must therefore be
left to afterwards complete its growth. The various positions
in which it may remain give rise to the vai’ious origins of the
mesoderm. Take Amphioxus, where the mesoderm has remained
entirely in the endoblast. Here we have a regular elongation
of the body taking place when the mesodermic cells are still
undifferentiated. The mesodermic diverticula are regularly
drawn out, and as regularly they leave small portions of the
whole in front. Hatschek has described a shallow groove
connecting the separated diverticula on each side, which is
explained by the present hypothesis. I take it to be of the
same nature as the connecting strand of mesoderm in Phoronis.
Echiurus (Hatschek) is a form where the greater part of the
mesoderm remains near the posterior pole of the long axis as in
Phoronis. As the long axis grows the mesoblast has to be left

BLASTOPORE, MESODERM AND METAMERIC SEGMENTATION. 25

in formative masses, which afterwards grow to line the body
cavity (in Echiurus, however, the mesoderm much more nearly
keeps pace with the ectoderm than in Amphioxus). Thus, I
consider that in Chsetopoda, Arthropoda, and Yertebrata the
mesoderm will tend to be left in regular pairs of masses, while
the elongation of the body is taking place ; I seek to explain
the whole of the facts of metameric segmentation as arising
from the necessities of development.

In Phoronis the external openings of the nephridia are parts
of the blastopore. The same considerations w'hich have been
applied to the mouth and anus, mesoderm and metameric
segmentation bear on the question of the origin of nephridia.
The nephridial portions of the mesoderm may remain in
various positions, in other words, the nephridia may in accord-
ance with my hypothesis arise as single or as serial ectoblastic
or endoblastic pairs of pouches with or without connecting
longitudinal canals or cords.

Instances of most of these possible modes of origin have
been described in the different groups of animals. The bearing
of the above facts and hypotheses on the nervous system, gill-
slits, notochord, and other organs, will be obvious to anyone
who has followed me so far. I hope to be excused from
entering into completer discussion of my hypothesis by reason
of the want of books of reference in my present situation out
of the world.

Summary.

Facts in the development of Phoronis —

1. The blastopore gives rise to both mouth and anus.

2. The mesoderm arises in an anterior pair of endoblastic
modified diverticula, and in a posterior pair of ectoblastic
diverticula connected by a few mesodermic cells derived from
the middle of a primitive streak.

3. The nephridial openings to the exterior are parts of the
blastopore.

Preliminary interpretation suggested by these facts of the
development of Phoronis —

26

W. H. CALDWELL.

1. A gastrsea with slit-like mouth and a pair of lateral
diverticula giving rise to mesoderm was the ancestor of
Phoronis.

2. The rapid growth of ectoderm in the median ventral line
nearly succeeded in destroying the continuity of the primitive
streak.

3. The necessity of an early attainment of a terminal position
by the anus caused the ectoderm to grow more rapidly than
the endoblast, and resulted in a division of the mesoderm into
anterior and posterior parts.

4. The nephridia, which might have remained either wholly
or in part with the anterior, have attached themselves entirely
to the posterior mesoderm.

Extension of this interpretation to the other Triploblastica —

1. Phoronis is the first step towards a complete division of
the blastopore. The inducing cause of such division is the
elongation of the body, while the endoblast is still in an
embryonic condition.

2. The division of blastopore caused the division of meso-
derm.

3. The division of mesoderm results in —

i. The masking of the original mode of mesoderm forma-
tion.

ii. Metameric segmentation.

In Camp, Burnett River,

Queensland \ July 27, 1884.

BLASTOPORE, MESODERM AND METAMERIC SEGMENTATION. 27

EXPLANATION OF PLATE II,

Illustrating Mr. W. H. Caldwell’s paper on “ Blastopore, Meso-
derm and Metameric Segmentation.”

List of Reference Letters.

Blastopore, bl. Mouth, ra. Anus, a. Primitive streak, p. s. Primitive
groove, p. g. Posterior pit, g. Posterior solid cord, r. Anterior mesodermic
diverticulum, a. d. Posterior mesodermic diverticulum, p. d. Mesoderm, me.
Prseoral lobe, p. 1. Arckenteron, ar. External opening of nepkridium, n.
Body cavity (coelom), c. Splanclmopleuric vascular space, v. Nutritive (?)
body, x.

All the figures, both of whole embryos and of sections, were drawn by
means of Zeiss’s two-prism camera, from permanent preparations in Canada
balsam. The embryos were treated as follows : — Mixture of two volumes
corrosive sublimate 4- one vol. glacial acetic acid for 1 second, water 15
seconds, alcohol, 50 per cent., 5 minutes, alcohol 70 per cent.

Pigs. 1 — 7. Zeiss’s oc. 2, obj. D. Pigs. 8 — 18. Zeiss’s oc. 2, obj. l-12th
homog. imm. All the embryos belong to the species of Phoronis, living in
the harbour of Naples in dense colonies without sand adhering to their tubes,
except that of which Fig. 13 is a section. This is an Australian Phoronis,
discovered in Port Jackson by Mr. Haswell, of Sydney University. The
sections drawn are taken from complete series. Each section is '005 mm.
thick. I have series ’0025 mm. thick. These, though necessary for observa-
tion purposes, are not so convenient for drawing.

Figs. 1 — 4. — Pour embryos, showing mode of closure of the blastopore.

Fig. 1. Blastopore, bl., before meeting of lips.

Pig. 2. Blastopore fused posteriorly : open part=mouth, m. ; closed part=
primitive streak and groove, p. g.

Fig. 3. Primitive groove, p.g.; disappearing prseoral lobe, p. 1.

Fig. 4. Primitive groove enlarging into pit, g., posteriorly; prseoral
lobe, p. 1.

Figs. 5 and 6. — Two embryos viewed from the left side. Prseoral lobe,
p. 1. ; primitive groove, p. g. ; mouth, m. ; posterior pit, g.

Fig. 7. — Older embryo with complete alimentary canal. Mouth, m. ; anus,
a. ; external opening of nephridium, n.

Figs. 8 — 10. — Three sections in a nearly transverse plane of an embryo in
a stage between that of Fig. 1 and that of Fig. 2.

28

W. H. CALDWELL.

Fig. 8. In front of mouth. Anterior mesodermic diverticula, a. d. ; anterior
mesodermic cell, me. ; archenteron, ar.

Fig. 9. Through the fusing lips of the blastopore. Primitive streak, p. s. ;
archenteron, ar.

Fig 10. Through the posterior part of the primitive streak. Primitive
groove, p. g. ; posterior solid cord of cells, r.

Fig. 11. — Median section, longitudinal vertical, through a slightly older
embryo than Figs. 8, 9, and 10. Pneoral lobe, p. 1. ; anterior mesoderm, me . ;
mouth, m. ; archenteron, ar. ; posterior pit, g ; posterior solid cord of cells,
r ; Nutritive (?) body, x ; body cavity, c.

Fig. 12. — Embryo slightly older than Fig. 4. Median longitudinal vertical
section. Prseoral lobe, p. 1. ; anterior mesoderm, m!. ; body cavity, c. ; vascu-
lar space, v. ; middle mesoderm, m". ; posterior mesoderm, m'". ; archen-
teron, ar. ; posterior pit, g ; Mouth, m.

Fig. 13. — Embryo, Australian species, nearly same stage as Fig. 12.
Longitudinal horizontal section. Archenteron, ar. ; anterior mesoderm, me! ;
posterior mesodermic diverticula, p. d. ; posterior pit, g.

Fig. 14. — Nearly same section as Fig. 13. Vascular space, v. ; posterior
pit, g ; archenteron, ar. ; anterior mesoderm, me". ; posterior diverticula,
p. d. ; posterior mesoderm, me'".

Fig. 15. — Embryo, same stage as Fig. 12. Longitudinal horizontal section.
Reopening of posterior cord of cells to form rectum and anus, a. ; anterior
mesoderm, me' . ; archenteron, ar.

Fig. 16. — Embryo, same stage as Fig. 12. Transverse section through
posterior diverticula, p. d. ; posterior mesoderm me'" . ; archenteron, ar.

Figs. 17 and 18. — Embryos about the stage of Fig. 3. Two transverse
sections. Anterior diverticula, a. d. ; body cavity, c. ; vascular space, v. ;
primitive streak, p. s. ; primitive groove, p. g. ; middle mesoderm, me" . ; arch-
enteron, ar. ; nutritive (?) body, x.

Fig. 19. — Six diagrams, illustrating the typical modes of mesoderm forma-
tion, e. g.

1. Peripatus, cf. Hertwig’s “ Ccelom-theorie,” PI. ii, fig. of insect embryo.

2. Amphioxus.

3. Nemertine larva of Desor (?), Phoronis (posterior).

4. Pristiurus, Phoronis (anterior).

5. Lopadorhynchus (Kleinenberg).

6. Primitive streak region, many Vertebrates and Phoronis.

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ORIGIN OF HYPOBLAST IN PELAGIC TELEOSTEAN OVA. 29

On the Origin of the Hypoblast in Pelagic
Teleostean Ova.

By

George Brook., F.L.8.

With Plate HI.

In a paper which I brought before the recent meeting of
the American Association for the Advancement of Science,
held in Philadelphia, attention was called to certain points of
difference in the development of pelagic and non-pelagic
teleostean ova. After the meeting I had an opportunity of
seeing a paper then just published by Agassiz and Whitman (1),
and when in Cambridge Dr. Whitman very kindly showed me
his beautiful series of drawings on this subject. The conclu-
sions arrived at by Dr. Whitman are so completely at variance
with my own on some points, that it appears necessary for me
to give a detailed account of my observations with carefully
made drawings from actual sections of the egg. I may here
add that whereas in very small pelagic ova I have found an
optical section of the living egg to give fairly reliable details
of the process of segmentation, invagination, &c., I have found
that in larger eggs this method is not to be relied on at all,
and that a clear interpretation of the process of invagination
can only be obtained from actual sections made from eggs
taken at frequent intervals.

The form which I have studied most, and from which most
of my sections were prepared, is Trachinus vipera, a general
account of the development of which will be found in ‘ Linn.

30

GEORGE BROOK.

Soc. Journ. Zool./ vol. xviii, pp. 273 — 290, and unless other-
wise specified, my remarks must be considered to refer to this
species.

It will he well to divide the question under consideration
into two branches.

1st. The origin of the periblast (Agassiz and Whitman) =
parablast (Klein); Dotterhaut (CEllacher) ; Rindenschicht (His) ;
membrane intermediaire (van Bambeke) ; yelk-hypoblast
(Ryder) ; and intermediary layer of American authors.

2nd. The part played by the periblast in the process of
invagination.

It has usually been considered by authors that whatever
might be the ultimate relationship between the blastodisc and
the periblast, one thing was clear at least, that they originated
independently of each other. Hoffmann (2) asserts that he has
actually seen the first cleavage process take place, and that
the first “ spindle ” divides equatorially, dividing the egg into
two parts, the germinal disc and the food yolk with a thin
layer of protoplasm separating the yolk from the germinal
disc, and that this thin protoplasmic layer becomes the peri-
blast. Agassiz and Whitman, however, assert that the first
cleavage process is meridional, and that the periblast is after-
wards formed from the marginal cells of the segmenting disc,
which, when once separated, never again unite with it. I
cannot say from actual observation in which direction the first
cleavage is made, but in Trachinus the periblast arises inde-
pendently of the germinal disc. As the thin protoplasmic
layer settles down to the lower pole of the egg, the majority of
it is included in the first two cells of the blastodisc. As if
not to waste any material the remainder collects around this
disc, and is afterwards developed into the periblast. I have
sometimes observed as early as the two-cell stage, when seen
in optical section, a thin granular layer of protoplasm under
the blastodisc ; and in later stages I have sections showing
a lower lens-shaped mass of cells (the lentille of van Beneden)
differing altogether in structure from those above, and which
possibly forms a central portion of the periblast, but this is

ORIGIN OP HYPOBLAST IN PELAGIC TELEOSTEAN OYA. 31

not clear, and the lower margin of the blastodisc becomes
quite flat again before the marginal periblast is pushed under
it. The gradual development of the periblast (there called the
intermediary layer) in Trachinus has been shown in my
paper already referred to, and it is not necessary to repeat it
again here. About the time free cells are formed in it, a
section has the appearance shown in fig. 1. The epidermal
layer of the epiblast is already differentiated, and there is no
segmentation cavity; nor, so far as I can make out, does the
periblast extend quite under the disc. As early as the sixteen-
cell stage I have noticed that the central cells of the disc do
not lie on the yolk, so that there is a shallow cavity between
the disc and the yolk in its central area ; but this becomes
filled up as segmentation goes on, and does not represent the
true segmentation cavity in which the hypoblast is formed.
As to whether the nuclei in the periblast arise by true free
cell-formation or are derived from a subdivision of the lower
part of the first cleavage spindle I cannot say, but in Tra-
chinus, at least, there appears to be no doubt that they do
not come from the margin of the germinal disc, as Whitman
asserts is the case in Ctenolabrus. If, as Hoffmann asserts,
the first cleavage spindle formed of the male and female pro-
nuclei really does divide at right angles to the axis of the egg
so as to form at the outset two layers, his archiblast and para-
blast (non Klein), it would appear more probable that the
nuclei found later should be the result of the subdivision of
the original nucleus of the layer than that they should arise
independently. In Trachinus and Motella the ring of peri-
blast gradually becomes more granular before cells appear, the
granules cluster together in groups, and it has certainly
appeared to me sometimes as if free cell-formation really did
take place. Nothing short of a careful investigation of this
stage in a large number of different forms may be expected to
settle this question definitely.

Next as to the origin of the hypoblast, Hoffmann and Messrs.
Agassiz and Whitman, though differing in their ideas as to the
origin of the periblast, are all equally confident that this layer

32

GEORGE BROOK.

takes no part in the formation of the hypoblast. Hoffmann
asserts that the invaginate layer of the ring and embryonic
shield is split off from the archiblast as a primary ento-
derm, and that this afterwards is differentiated into the meso-
derm (several cells deep) and the secondary entoderm
(only one cell deep). Henneguy4 also states that in the
trout the invagination is caused by an infolding of the
segmented disc upon itself, and that, as the invagination pro-
gresses, the lower invaginated portion remains quite separate
from the original upper portion, and that indeed he can demon-
strate a space between them. On the other hand, van
Bambeke (11), Klein (8), Kupffer (7), and van Beneden (3),
agree that the hypoblast is derived from the periblast, while
Balfour (10), Ryder (6), Kingsley and Conn (9), and others,
admit that the periblast plays a more or less important part in
the structure of hypoblastic tissues. Haeckel (5) failed to
recognise the periblast altogether, and his diagrams of the
invagination of the hypoblast can scarcely be true for any
Teleostean. The eggs studied by Haeckel were pelagic and
supposed to belong to a species of Motella; but I think there
must be some mistake here, as I have studied the development of
Motella mustela and can confidently assert that the whole
process of development is different from that given by Haeckel.
With a view to studying the process of invagination in
Trachinus, I have preserved eggs at half-hourly intervals from
a little before the appearance of the blastodermic rim until
this was quite well-defined all round the disc, a period of deve-
lopment occupying four hours at a temperature of about
62° Fahrenheit. The eggs were prepared by the picrosul-
phuric acid method and stained with cochineal. It is on
sections made from these eggs that my conclusions are based.
Figure 2 represents a section of one of the earlier of these
stages, in which the periblast is seen to be collected around
the margin of the disc and to have pushed itself some little
way underneath ; but there does not yet appear to be a layer
of periblast on the floor of the segmentation cavity. The
epidermic layer of the epiblast is, however, well differen-

ORIGIN OP HYPOBLAST IN PELAGIC TELEOSTEAN OVA. 33

tiated and has grown down over the periblast, as is shown
in the figure. An hour and a half afterwards (fig. 3) the
periblast is seen to have pushed its way completely across
the floor of the segmentation cavity, and now contains quite
a number of free nuclei and cells. The blastodisc in spread-
ing over the yolk has thinned out somewhat, but there is still
no sign of invagination. Half-an-hour later (fig. 4), the cells
in the periblast have accumulated under the rim of the blas-
todisc ; on the left hand of the figure these cells are seen to
be quite round and arranged in a row ready to take their
places alongside the lowest layer of the blastodisc. The right
hand of the same figure shows an abnormal form of the peri-
blast in which the cells, nuclei, and surrounding protoplasm
have been withdrawn into a pocket in the yolk, possibly caused
by shrinking in the hardening process. The epidermic layer
is still seen to reach some way over this mass of periblast.
Half-an-hour later still (fig. 5), the periblast again covers the
floor of the segmentation cavity more thickly, and free nuclei
are to be observed rising from the yolk to help in building up
this layer. The first row of hypoblastic cells are now seen
attached to the lowest layer of the disc, but are recognised by
their round clear outline. A little later again (fig. 6) two
rows of hypoblast cells are seen in their proper place, and the
living egg in this stage shows a clearly defined ring with the
beginning of the prominence to form the embryonic shield.
The outline of the original blastodisc is well marked off, and
the new cells are sufficiently different in shape to mark off
where one layer begins and the other ends. The epidermic
layer is still seen in its original position and has taken no part
in the process. The new layer is now formed rapidly, and
nuclei and free cells are seen crowding up from the yolk to
help in this work. Fig. 7 represents a little later stage in the
embryo of Motella mustela seen in optical section where
much the same process has been at work. Here, however, the
resulting cells of the new layer are so much larger and clearer
in outline than is usual in Teleosteans that the line of demar-
cation between the old and new layers is quite distinct from

VOL. XXV. NEW SEK.

c

34

GEORGE BROOK.

one end to the other. Free nuclei are also seen both in the
yolk and on the floor of the segmentation cavity. Although
earlier phases of the hypoblast were not observed in Motella,
it seems impossible that such large and well-defined cells could
be the result of invagination from the cells of the archiblast,
when the cells of the latter are scarcely distinguishable under
a magnifying power of 100 diameters. When, however, we
have the data arrived at from a study of Trachinus to work
upon, there is no difficulty in accounting for their origin.

If, now, my figures, which are carefully copied from actual
sections (excepting figure 7), be compared with those of
van Bambeke, Klein, and van Beneden, it will be seen that
our observations agree very closely. Indeed, van Beneden’s
fig. 9 (loc. cit.), which also represents a pelagic egg, shows the
identical process at work which I have described for Tra-
chinus. The question then arises, is the hypoblast formed
by a true process of invagination ? It is quite true that
the rim grows from the margin inwards because the cells
from the periblast commence at the margin close to the over-
lapping epidermic layer and are filled up from within. Is not
something more than this meant by invagination ? I take it
that invagination in the true sense means an ingrowth or an
infolding of a layer already existing, the archiblast. If this
be so, there is no true invagination in such pelagic ova as those
here described, and the hypoblast is not derived from the
archiblast at all, but from the periblast and the yolk by a
process of segregation.

List of Papers referred to.

1. Agassiz and Whitman. — “Ou the Development of Some Pelagic

Fish Eggs,” ‘ Proc. Amer. Acad, of Arts and Sciences,’ vol. xx,
1884.

2. C. K. Hoffmann. — “ Zur Ontogenie der Knochenfische,” ‘ Natuurk.

verb. d. Koninkl. Akad. Amsterdam,’ vol. xxi, 1881.

3. E. van Beneden. — “ A Contribution to the History of the Embryonic

Development of Teleosteaus,” ‘ Quarterly Journ. of Microsc. Sci.,’
vol. xviii, N.S., 1878.

ORIGIN OF HYPOBLAST IM PELAGIC TELEOSTEAN OYA. 35

4. L. E. Henneguy, “ Premiers phenomenes du developpement des pois-

sons osseux,” ‘ Bull. Soc. Phil, de Paris,’ 1880 ; also second notice,
‘ Comptes Rendus,’ xcv, pp. 1297 — 1299, 1882.

5. E. Haeckel. — “ Die Gastrula und die Eifurchung der Thiere,” ‘Jena

Zeitschr.,’ vol. ix, 1875.

6. J. A. Ryder. — “ A Contribution to the Embryography of Osseous

Fishes (Development of the Cod),” ‘ Report of Amer. Commissioner
of Fish and Fisheries for 1882,’ published Washington, 1884.

7. Kupffer. — “ Entwickelung des Herings im Ei,” ‘Jahresb. d. Comm.

z. wiss. Unters. d. Deutsche Meere in Kiel for Years 1874-76.’

8. Klein. — “ Observations on Early Development of the Common Trout,”

‘ Quart. Journ. Micros. Science,’ vol. xvi, N.S., 1876.

9. Kingsley and Conn. — “ Some Observations on the Embryology of

Teleosts,” ‘ Mem. Boston Soc. Nat. Hist.,’ vol. iii, 1883.

10. F. M. Balfour. — ‘Comparative Embryology,’ vol. ii, London, 1881.

11. Van Bambeke. — “Recherches sur l’embryologie des poissons osseux,”

‘Acad. Roy. de Belgique,’ vol. xl, 1876.

36

GEORGE BROOK.

EXPLANATION OF PLATE III,

Illustrating Mr. Brook’s paper “ On the Origin of the Hypo-
blast in Pelagic Teleostean Ova.”

y. Yolk. U. Blastodisc (archiblast). ep. Epidermic layer of the epiblast.
p. Periblast, s. c. Segmentation cavity, v. Vacuoles in the yolk. r. Thickened
rim of the blastoderm. rv Part of thickened rim included in the embryonic
shield, c. Nuclei and cells in the yolk. ev Nuclei and cells loose on floor of
segmentation cavity. c2. Nuclei and cells in periblast (margin). c3. Nuclei
and cells in periblast (centre).

Pig. 1. — Transverse section of the blastodisc of Trachinus vipera taken
at 7 a.m., and about twenty hours earlier than Fig. 2. X 70.

Fig. 2. — Section of Trachinus egg, shortly before commencement of hypo-
blast. x 120.

Fig. 3. — Section of egg, one and a half hours later than Fig. 2. X 130.

Fig. 4. — Section of egg, one and a half hours later than Fig. 3. x 130.

Fig. 5. — Section of egg, half an hour later than Fig. 4. X 130.

Fig. 6. — Section of egg, half an hour later than Fig. 5. X 130.

Fig. 7. — Optical section of a living egg of Motella mustela, showing
segregation of hypoblast well advanced, x 100.

Mocr fiou#*nftX&.m,ES$%/. Ill

Fig. 4.

Fig. 3.

G Brook del

F Huth, LiVhr Edm*

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITOXID^. 37

On the Presence of Eyes in the Shells of Certain
Chitonidse, and on the Structure of these
Organs.

By

II. W. Moseley, F.R.S.,

Linacre Professor of Human and Comparative Anatomy in the University

of Oxford.

With Plates IV, V, and VI.

Introduction.

On examining a specimen of Schizochiton incisus pre-
served in spirit amongst a number of other animals dredged
bv Captain W. Chimmo, R.N., in the Sulu Sea, in H.M.S.
“Nassau” in 1871, and presented by him to the Anatomical
Department of the Oxford University Museum, I was astonished
to remark on the shells certain highly refracting rounded
bodies, arranged in rows symmetrically; they struck me at
once as resembling eyes, and further examination proved that
such is, in fact, their nature. On searching for eyes on the
shells of other Chitonidse I found them present in many other
genera, differing, however, in each genus more or less in struc-
ture and arrangement. I published a preliminary summary
of what I had been able to determine concerning these eyes
in the ‘ Annals and Magazine of Natural History* for August,
1884. In the present paper I enter further into details, and
have the advantage of elucidating my results by means of
figures.

38

PROFESSOR H. N. MOSELEY.

Literature of the Subject.

It is remarkable that the eyes of the Chitonidae should have
hitherto escaped notice. The main reason why they have done
so is probably the fact that they do not occur, as far as I have
been able to ascertain, on any common European representa-
tives of the group such as have been ordinarily chosen for
research by morphologists. Further, they are as a rule not
easily seen in dried specimens of the shells, such as are mostly
under observation in museums. It is not until these are
wetted with spirit that the eyes become conspicuous. Again,
Schizochiton, in which they are largest and most evident, is a
rarity in museums. A molluscan shell is, moreover, almost
the last place in which the naturalist would expect to find
eyes, and the Chitonidae have hitherto in text-books always
had the absence of eyes assigned to them as one of the charac-
teristics of their group.

Middendorf1 named the two distinct layers, of which the
shells of Chitonidae consist, the tegmentum and articulamentum;
and Dr. W. B. Carpenter examined the shells of Chitons by
means of sections, and observed the perforate structure of the
tegmentum in Chiton, writing as follows : “ In Chiton the
external layer, which seems to be of a delicate fibrous texture
but which is of extreme density, is perforated by large canals
which pass down obliquely into its substance, without pene-
trating, however, as far as the middle layer. (Dr. Carpenter
has kindly lent me his original sections of Chiton shells, and
from what I now know I am able to recognise parts of pig-
mented eye-capsules in one labelled Chiton spiniger .)”2 The
late Dr. Gray wrote, in his paper on the “Structure of Chitons
“The greater number of species have a part of the valve which is
not covered by the mantle, but exposed. This exposed part con-
sists of a perfectly distinct external coat, peculiar, I believe,

1 “ Beitrage zu einer Malacozoologia Rossica,” ‘Mem. de l’Acad. de St.
Petersbourgh Sc. Nat./ Ser. iv, t. vi, 1849.

2 ‘ Cyclopaedia of Anatomy and Physiology,’ article “ Shell,” p. 565,

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.®. 39

to the shells of this family. The outer coat of these valves is
separated from the lower or normal portion by a small space
filled by a cellular calcareous deposit, which is easily seen in
a section of the valves/'1 In 1869 Dr. W. Marshall2 made a
great advance in our knowledge. He found that the tegmentum
of Chitons was perforated by a series of fine vertical canals,
which open at the surface in a series of cup-shaped apertures,
and that these vertical canals open into a series of horizontal
canals running in the space between the apposed surfaces of
the tegmentum and articulamentum, and that these canals
opened on the under surface of each shell. He further found
that the larger vertical canals, before reaching the surface,
became enlarged and gave off each a crown of smaller canals
also terminating at the surface in cup shaped apertures, and
that the canals and apertures, small and large, are distributed
evenly over the outer surface of the shell. He decalcified the
shells, and found in the canal system ramifications of soft
tissue, which he recognised as offsets of the mantle and con-
sidered homologous with those of Balanidse and Brachiopods.
He erroneously regarded the soft tissue ramifications as
tubular and respiratory in function. In 188$ Van Bemmelen,
following up his researches, examined the structure of the soft
tissues contained in the shell of Chiton marginatus, and
discovered that the tegmentum is entirely filled with papilli-
form bodies which terminate the branches of the network and
occupy the surface perforations described by Marshall. He
figures and describes the structure of these papillae and their
relations to the tegmentum, and propounds certain theories as to
their homologies which will be referred to in the sequel. At
the time at which I wrote my preliminary account of my dis-
covery of eyes in the shells of the Chitonidae I was not aware
of the existence of Dr. Marshall’s and Mr. Van Bemmelen’s
memoirs, and thought that the papillae in the tegmentum were
also new to science. I much regret that I should have inad-

1 J. E. Gray, “ On the Structure of Chitons,” ‘ Phil. Trans.,’ 1848.

2 W. Marshall, ‘‘Note sur l’histoire Naturelle des Chitons,” ‘Archives
Neerlandaises des Sciences exactes et nat.,’ t. iv, 1869.

40

PROFESSOR H. N. MOSELEY.

vertently ignored the claims of these authors to priority in this
matter. 3 am much indebted to Dr. Marshall for having
kindly drawn my attention to the two papers. My study of
the structure of the shells in numerous genera of the Chitonidse
in connection with my investigation of the structure of the
eyes has, however, I believe, thrown much new light on the
nature and homologies of the papilliform organs.

Methods.

My observations have been principally made on vertical and
horizontal sections of decalcified shells. In my investigations
on the structure of coral, I have had much experience in the
decalcification of tissues for the purpose of histological exami-
nation. I have tried many methods of slow decalcification
recommended, with the result of finding that for all purposes,
including the decalcification of the shells of Mollusca, a com-
paratively rapid decalcification with nitric acid yields the best
results. I place the fragments to be softened, which have
previously been hardened in strong alcohol, in a vessel holding
several ounces of distilled water, and add concentrated nitric
acid drop by drop till a brisk ebullition commences, making
a three or four per cent, solution. If the decalcification is not
completed in twelve hours, I transfer the object into fresh
distilled water and add acid as before. I obtain better results
by this method than any other.

Structure of the Shells and their Contained Soft
Tissue Ramifications.

The tegmenta of the shells of nearly all, if not all, Chito-
nidse are perforated at the surface by circular apertures or
pores of two sizes, arranged in more or less definite patterns
with regard to one another, and sometimes with regard to the
eyes also. As the arrangement of these pores must in future
become of systematic importance it is convenient to adopt
some terms for them, and I shall call them megalopores and
micropores. The pores are constantly thus of two sizes, the

PRESENCE OF EYES TN SHELLS OF CERTAIN CHITONIDA3. 41

difference between the two in size being considerable, and
there being no pores of intermediate size between the two.
The mouth of each megalopore leads into a cylindrical
chamber hollowed out in the thickness of the tegmentum, per-
pendicular to its surface and more or less dilated in accord-
ance with the form of the papilliform body contained within
it. This cylindrical chamber is continued below into a wide
canal, which in its course towards the plane of junction of the
tegmentum with the articulamentum is curved towards the
girdle margin of the tegmentum (PI. VI, fig. 6, pp). On
reaching the plane of junction it joins a plexus of wide main
canals which ramify horizontally in this plane, parallel with
the surface of the tegmentum.

From the sides of the megalopore chambers are given off
fine canals, which perforate the tegmentum in a direction ver-
tical to its surface, and join the bases of the micropore cavities.
In some species a considerable proportion of the micropore
canals are also given off direct from the main vertical branches
of the horizontal plexus, as in Corephium aculeatum (see
PI. Y, fig. 8). Those springing from the megalopores may be
given off from each macropore chamber at the same, or nearly
the same, height all round, or at very various heights (see PI.
IV, fig. 10, bb).

The tegmentum when decalcified persists as a homogeneous
apparently horny substance, which in some species shows a
finely fibrous structure (PI. VI, fig. 4), but in others appears
almost structureless. This substance, which is in the recent
state of the shell impregnated with the lime salts, is termed by
Middendorf the stroma, and by Marshall, Reincke and Van
Bemmelen the cuticula. It retains in the decalcified condi-
tion both the form and dimensions of the tegmentum itself,
and thus in sections of the decalcified shell the disposition of
the contained soft structures with regard to the hard parts is
clearly displayed.

The plexus of horizontal main canals is occupied in the
horny shell by a corresponding ramification of strings of soft
tissue, which are offsets of the mantle substance. These

42

PROFESSOR H. N. MOSELEY.

offsets enter the canal plexus by two sets of openings ; firstly,
at the margins of the tegmenta, which adjoin the borders of the
girdle by a series of fine apertures in the shell substance,
which occupy narrow band-like areas intervening between the
tegmenta and upper surfaces of the articulamenta at their lines
of junction with one another. These bands are sieve-like in
appearance, being perforated all over, and lie just beneath the
external margin of the tegmenta. Secondly, offsets of the
mantle tissue enter the canal plexus at the incisurae, and by
means of fine pore-like apertures on the under surfaces of the
shells. These pores may be irregularly scattered, as, e. g. in
the case of the anterior and posterior shells of Corephium
aculeatum, or they may be concentrated along the so-called
sutural lines of the shells which spring from the marginal
notches or incisurae. The sutural lines where present in the
anterior and posterior shells radiate from the apices (or
mucrones) of the shells to the marginal notches. There are
six such radiating sutural lines in the anterior shell of Schi-
zochiton, and six corresponding notches (see PI. IY, fig. 5.)
On each median shell there are a single pair of lateral sutural
lines, and a corresponding single pair of notches. The sutural
lines are marked on the under surfaces of the shells by a series
of small slit-like apertures, directed transversely to the lengths
of the lines, and when the shell is removed from its bed corre-
sponding minute transverse processes of the mantle are seen
projecting along corresponding lines on its surface, and torn
across. Processes of the mantle tissues also enter the shell
canals at the bottom of each marginal notch, and from the
notch longitudinal canals run in the shell substance along the
sutural lines above the series of slit-like apertures.

The strings of soft tissue forming the horizontal plexus show
a finely fibrous structure, and contain numerous nuclei and
fine granular matter. They are not canals as believed by
Marshall. They contain nerve-fibres within them, as is
certain from the fact that some of them expand into retinas of
typical structure in the eyes. I have been unable to trace the
nerves supplying the soft tissue ramifications of the tegmenta

PRESENCE OE EYES IN SHELLS OF CERTAIN CHITONIDjE. 43

directly to their source, but it is probable that they proceed
from the parietal (branchial) nerves. When sections cut
vertically through the decalcified tegmentum, so as to include
the adjacent articulamentum and girdle, the whole shell and
its attachments in situ are examined, I find abundance of
fibrous structures passing from the girdle tissues directly to
join the plexus of tissue in the tegmentum. These series of
fibres are definitely arranged and readily stained, are of deep
origin, and cannot be regarded as mere processes of the mantle.
I have, however, been unable to trace them to any definite
source amongst the muscular tissues. Similar fibres enter the
tegmenta on their under sides abundantly along their sutural
lines. I believe that nerves must accompany these fibres or
form part of them. Haller describes a series of mantle nerves
as given off from the branchio-visceral cords between every
two gills. Each nerve turns outwards towards the mantle
border. He was unable to determine whether it also gives
off fibres which proceed inwards, and supply the body wall
beneath the shells.1 The nerve-fibres are not to be distin-
guished in the main stems of the ramifications from the tissue
with which they are bound up, but within the eye capsules
the optic nerves break up into bundles of fine fibres which
supply the retina and must be nervous in nature.

Megalsesthetes and Micrsesthetes.

Erom the ramifications of soft tissue are given off branches
to each of the megalopore canals ; these follow the curved
course of the latter and expand within the megalopores into
the “ papilliform bodies” of Van Bemmelen, to which I shall
apply the name megalsesthetes, believing that they are peculiar
organs of touch and are at all events peculiar to Chitonidse and
essentially different in structure and origin to the spines borne by
the girdle in that group. They require a special designation.
In some species the strands passing to the megalopores pass

1 B. Haller, “ Die Organisation der Chitonen der Adria,” ‘ Arbeiten aus
dem Zool. Inst, der Universitat Wien,’ T. iv, 3 Heft, 1882, S. 10.

44

PKOFESSOR H. N. MOSELEY.

directly without branching as separate strings from the plane
of ramification to the megalsesthetes. This is the case in
Acanthopleura spiniger (PL VI, fig. 6) ; in other forms
larger primary branches arise from the ramifications, and, taking
a course vertical to the surface, give off the strands leaving the
megalaesthetes on secondary and tertiary branches (PI. VI,
fig. 8). The mode of ramification is probably dependent on the
thickness of the tegmentum. The macraesthetes where fully deve-
loped, as, for example, in Acanthopleura spiniger, are more
or less fusiform bodies which occupy the cavities of the mega-
lopores. Externally at the mouths of the pores they terminate
in obconical or somewhat dice-box shaped plugs of transparent
highly refracting tissue, which are extremely conspicuous when
the decalcified tegmentum is viewed from the outer surface
under the microscope. Internally their bodies are directly
continuous with their respective strands of soft tissue (PI. VI,
fig. 6, a, p). The bodies of the megalaesthetes are composed
of a number of cylindrical strands of tissue held closely
together so as to form a bundle which, on transverse section,
shows the component strands cut across without indication of
any definite concentric arrangement, Some of the strands show
a transverse situation, whilst others are not striated. They bear
nuclei at intervals. I have not been able to examine these
structures in living specimens, or such as have been specially
prepared for histological examination, and therefore am uncer-
tain as to the details. Van Bemmelen (1. c., fig. 11) has figured
a megalsesthete of Chiton marginatus, giving histological
details of the body of the organ, which are, I feel sure, more
correct than mine.

The terminal knobs, however, of all the megalaesthetes which
I have examined, except, perhaps, in Chitonellus, show a more
complicated structure than van Bemmelen represents in C.
magnificus. All the terminal knobs terminate in a flat disc.
This disc shows, on careful focussing, a series of concentric rings
(PI. V, fig. 8, a), as if composed of a series of concentric layers or
inverted cones fitted one within the other. Further, the neck of
the inverted cone or dice-box forming the knob shows a series

PRESENCE OP EYES IN SHELLS OF CERTAIN CHITONID^E. 45

of transverse ring lines (PI. VI, fig. 6, a) as if composed of a
series of superposed discs. Towards the base of the knob
these lines instead of being simply transverse become bent
towards the body of the megalaesthete as if the knob were there
composed of a series of cup-like layers. Between these trans-
verse lines the tissue of the knob is dotted with very fine
granules. The knobs of the megalaesthetes appear to be capable
of protrusion from the mouths of their pores and retraction, as
many were found protruded in spirit specimens^ To the organs
contained within the micropores I shall give the name micraes-
thetes. Van Bemmelen’s figure, above referred to, shows four
micraesthetes as given off from the summit of the body of a
megalsesthete of Chiton marginatus.

In PI. VI, fig. 6, are shown similar micraesthetes supplied by
small strands given off from the megalaesthetes in Acantho-
pleura spiniger. The micraesthetes are small, knob-like
bodies, exactly corresponding in structure to the knobs of the
macraesthetes. They are similarly obconical in form, and
exhibit exactly similar concentric and transverse ring-marks
(PI. V, fig. 8, b), and are obviously homologous organs. They
are the terminations of fine strands of tissue, which in
Acanthopleura spiniger and the genus Chiton appear to
be given off only from the sides of the megalaesthetes and from
the optic nerves, but in Corephium aculeatum (PI. V,
fig. 8, b ) spring independently directly from the large vertical
branches of the main network.

General Position and External Appearance of
the Eyes.

The eyes in the Chitonidae are entirely restricted to the
outer surfaces of the shells on their exposed areas — the surfaces
of the tegmenta. They never occur on the laminae of insertion,
the articulameta, nor on the girdle or zone of the mantle which
is occupied, as is well known, by various calcareous structures,
some of which have been carefully investigated by Beincke.1

1 “Beitrage zur Bildungsgeschichte der Stacheln, &c., im Mantel rande
der Chitonen,” ‘ Zeitsch. fur wiss. Zool.,’ Bd. xviii, S. 305.

46

PROFESSOR H. N. MOSELEY.

On the intermediate or middle shells the eyes are confined
to the arese laterales or to the lines of demarcation between
the areae laterales and the area ventralis, which latter is usually
entirely devoid of them. The eyes, which are mostly circular
in outline as seen on the shell surfaces, measure about T.3 of an
inch in diameter, in Schizochiton incisus of an inch, in
Acanthopleura spiniger and in Corephium aculeatum,
in which they are oval in outline, -,-L- of an inch by about
In Enoplochiton they are smaller still, and only with
difficulty seen at all. The eyes appear when viewed by
reflected light with a simple lens or low power of the compound
microscope as highly refracting convex circular spots, looking
as if made of glass or crystal (see PL IV, figs. 1, 2, 3, 4).
The highly refracting spot, the cornea, is set off by a surrounding
narrow zone of dark pigment, which is the margin of the pig-
mented eye capsule which forms an iris-like structure round
the lens, and which is seen through the superficial shell
substance (PI. IV, fig. 3). Through the centre of each cornea
is seen a smaller circular area, somewhat darker than the
aperture of the pupil, but showing a brilliant spot of totally
reflected light due to the lens.

Structure of the Eyes.

The eyes are evidently to be regarded as having arisen as
modifications of megalaesthetes. They are connected with the
same network of soft tissues as terminal organs of its ramifica-
tions in the same manner, and have points of resemblance to
them which are convincing as to the homogeny of the two.
The soft structures of each eye lie in a more or less pear-
shaped chamber, excavated in the substance of the tegmentum.
The stalk of the pear, which forms the canal for the passage of
the optic nerve, is directed always towards the free margin of
the tegmentum whence the nerve reaches it. In Acantho-
pleura the eye chambers and the neural canals continued from
them follow in direction the same course as the megalopores
and their canals, and join the main canal ramifications in

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONIDCE. 47

exactly the same manner (PI. VI, fig. 6). One side the
bulb of the pear, more or less near its extremity, is closely
applied to the outer surface of the tegmentum (Pl. YI,
figs. 4, 5), and here its wall is pierced by a circular aperture,
the pupil-like opening. This opening is covered by the cornea,
the periphery of which extends to a considerable distance
beyond its margin all round (PI. YI, fig. 6,/).

The cornea is a concavo-convex, watchglass-shaped lamina.
It is calcareous in structure, being continuous all round its
margin with the superficial calcareous layer of the tegmentum.
It resists the action of strong boiling caustic alkalies, but col-
lapses at once when treated with acid. In sections of the
uudecalcified tegmentum it shows itself to be formed of a
series of concentric lamellae of transparent hard substance.
Probably a continuation of the cuticular substance of the teg-
mentum is present in its substance, but I have been unable to
demonstrate the existence of such by means of acids.

The pear-shaped cavity of the eye in the tegmentum is lined
by a dark brown pigmented membrane, of a stiff and apparently
somewhat chitinous texture, which forms the eye capsule.
This capsular membrane exactly follows the shape of the eye
cavity, except near the surface of the tegmentum, where its
margin curves inwards beneath the cornea, forming a sort of
iris and bounding the circular pupil, which, as before men-
tioned, is of less diameter than the cornea. The aperture of
the pupil is occupied by the front surface of the lens. The
lens is perfectly transparent and hyaline and strongly biconvex,
it is filled in behind the iris aperture. It is composed of soft
tissue and dissolves in strong acetic acid gradually and com-
pletely, showing a fibrous distinct structure in the process.
In Acanthopleura spiniger the lens is a little flatter in
front than behind (PI. YI, fig. 6, g). There is a space between
the front surface of the lens and the cornea.

The optic nerve at some distance from the eye, where
arising from the general ramification, is a compact strand
completely identical in structure in Acanthopleura, with
the strands proceeding to the megalsesthetes. In Onithochiton

48

PROFESSOR H. N. MOSELEY.

the optic nerves are distinguished from the strands supplying
the megalaesthetes by being slightly pigmented for a consider-
able extent of their course. A large proportion of the eyes in
Ornithochiton are supplied by nerves which are given off from
the soft tissue strands entering the shell along the sutural lines,
but many eyes are also certainly supplied by pigmented strands,
which can be traced only to the free margins of the tegmenta
adjoining the girdle. In those shells in which only single rows
of eyes are present coincident with the sutural lines, the eyes
seem to be all supplied by strands passing from the sutural
line and specially ramifying in order to reach them. Within
the pigmented tubular prolongation of the eye capsule the
numerous fine fibres composing the optic nerve become sepa-
rated from one another and loose. Immediately beneath the
retina the fibres become still more widely separated, forming an
expansion of fibres. The retina is formed on the type of that
of Helix, and not, as might have been expected, on that of the
dorsal eyes of Onchidium or the eyes of Pecten. The fibres
of the optic nerve do not pass in front of the layer of rods to
be distributed to them from in front, but are directed to the
rods directly from behind. The retina presents a single layer
of short but extremely well-defined rods (PI. VI, figs. 6, 7),
the extremities of which are directed towards the light.
The rods, when viewed from the surface of the layer they com-
pose, are seen to be hexagonal or pentagonal in outline, and
each contains a nucleus. They form a layer which is concave
towards the lens, there being a space between the hind surface
of the lens and the concave face of the layer.

The rods closely resemble in appearance those figured by
Semper as occurring in Onchidium. Immediately beneath the
rod layer is a stratum or several layers of nuclei amongst the
ramifications of the nerve-fibres. The structure of the retina^
as described, has only been made out in specimens ofAcantho-
pleura spiniger, which alone of the material available were
in a condition of preservation sufficient to permit it. Similar
expansions of the optic nerve have been seen, however, to occur
in many other forms.

PRESENCE OE EYES IN SHELLS OF CERTAIN CHITONIILE. 49

The only pigment present in the eyes examined is that by
which the eye capsules are rendered opaque. No pigment seen
in connection with the rods or in connection with the nervous
elements. Possibly the absence of such pigment is due to the
imperfect preservation of the material.

Not all the fibres of the strand entering the eye cavity
proceed to the retina. A large number of peripherally placed
fibres pass outside the retina all round, and, passing through
apertures in the iris at its outer margin, end at the surface of
the shell all round the area occupied by the corneae. They
terminate in micraesthetes exactly corresponding in structure
to the other micraesthetes present and identical with them in
structure.

They apparently form a sensitive zone round each eye, and
their strands arise from the optic nerve just as do those of many
of the other micraeesthetes from the megalaesthetes (see PI. YI,
fig. 6, b' b' ; fig. 4, b ; PI. Y, fig. 8, b' b'). On their way to the
surface these strands, given off by the optic nerves to the
micraesthetes, traverse a series of slit-like perforations of the
ris, which are conspicuous, and at first very puzzling features
in the iris structure when the eyes are viewed in the decal-
cified tegmentum from its external surface by transmitted
light (PI. VI, fig. 5, b b).

In the eyes of some forms when thus viewed, an open fold
or gutter leading from the bulb superficially along the stalk
of the pear is seen, curiously recalling the choroid fissure
(PI. VI, fig. 5). The occurrence of double eyes, combinations
of two eyes fixed closely side by side with a common nerve
stalk, is not an uncommon mode of growth.

Growth of the Tegmentum, Eyes and ^Esthetes.

The tegmenta increase in growth by additions formed at
their margins where they adjoin the girdle regions of the
mantles. The additions are probably made by the mantle
tissues which immediately abut on the tegmental margins.
At the basal margins of the tegmenta of all forms in which

VOL. XXV. NEW SER,

D

50

PROFESSOR H. N. MOSELEY.

eyes occur in any numbers, the eyes may be seen in all stages
of formation. The eyes are formed in the position which they
always occupy when complete, namely, with the stalk of the
pear-shaped pigmented capsule containing the optic nerve
turned towards the margin of the tegmentum adjoining the
girdle, and the bulb of the eye directed towards the shell apex.
The first trace of a developing eye is a semilunar fold of pig-
mented eye-capsule. This increases till it becomes horse-shoe
shape with the pupil margin well defined. Next the lens
appears, and the cornea and traces of the nervous elements, and
the nerve capsule gradually becomes longer, and finally the
narrow canal into which it contracts is added. At each suc-
cessive stage it appears like a segment of a complete eye, the
tail so to speak of which has been cut off transversely, less and
less shortly.

The megalsesthetes are similarly formed as the tegmenta
increase in growth at their free margins. By preparations so
made as to show the junction of the margin of a tegmentum
with the girdle, the megalsesthetes may be seen in all stages of
formation in a similar manner to the eyes. There is no indi-
cation of any enclosure of the spines borne by the girdle within
the substance of the tegmentum in course of its formation, and
there are no traces of any bodies resembling the megalsesthetes
or micresthetes in the girdle tissues ; none such ever occur
beyond the actual margins of the tegmenta.

Presence or Absence of Eyes in Various Genera of
Chitonidse, differences in the arrangement of
the Eyes when present, &c.

In some genera of Chitonidse eyes are entirely absent. This
is the case with the genus Chiton, which has, as shown by
Marshall and van Bemmelen, the usual megalopores and micro-
pores, megalsesthetes and micrsesthetes, but in no species of
which I have been able to detect any trace of eyes. Van
Bemmelen investigated Chiton marginatus, and I especi-
ally by decalcification only C. magnificus and C. marmo-

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.®. 51

rat us ; but the eyes in the shells of the Chitonidse may, by
a little practice, be readily detected by examining the dried
shells directly with a hand lens ; and I have examined rapidly
in this way all the likely looking specimens in the extensive
collection in the British Museum, and that at Montreal, and
feel pretty certain that no eyes will be found in the genus
Chiton, as now distinguished there. In Molpalia, Maugina,
Lorica, and Ischnochiton, there are apparently no eyes as far
as a cursory examination has yielded evidence to me. In
Chitonellus there are certainly no eyes.

The arrangement and the forms of the eyes vary conside-
rably in different genera, and these characteristics will pro-
bably prove of considerable value in the classification of the
Chitonidae, which has hitherto proved so difficult a problem.

The genus Scliizochiton is distinguished by having the
mantle deeply notched posteriorly, in correspondence with a
deep median notch in the hinder border of the posterior shell
(PI. IY, fig. 1, c ). In Schizochiton incisus the eyes are
restricted to single rows traversing the sutural lines. There
are six rows of eyes on the anterior shell, corresponding with
the number of marginal notches ; two on each of the middle
shells, and six on the posterior shell — twenty-four rows alto-
gether, with an average of about fifteen eyes in each, or in all
360 eyes (see PI. IV, figs. 1, 2, 3, 4, 5). In the single specimen
carefully examined all the rows except one have the eyes ar-
ranged in a single straight row at regular intervals, but at the
base of one row there are as an exception two eyes side by side.
There are also in one or two places a very few irregularly scat-
tered eyes on the arese laterales, showing that the condition
here existing has probably been derived from an ancestral one in
which the eyes were not concentrated into lines, but more widely
diffused on the shell surface. In one row again, one eye is
missing from the spot on which it ought to occur (PI. IV, fig.
2). The rows of eyes are placed on raised ridges on the shell
surface, formed by the development of tubercles on the promi-
nent ridges with which the surfaces of the tegmenta are
ornamented. The eyes in Schizochiton are the largest I have

52

PROFESSOR H. N. MOSELEY.

found in any of the Chitonidse, measuring ,4~th of an inch in
diameter. When seen under the microscope, either by re-
flected light or by transmitted light in thin ground sections of
the tegmentum, they are extremely brilliant and conspicuous.

In Acanthopleura spiniger (see PI. VI, figs. 1, 2, 3,
6) the eyes are irregularly scattered around the bases of the
tubercles with which the surface of the tegmentum is covered,
and are confined, in the specimens I have examined, to the
region of the margins of the tegmenta adjoining the girdle.
The eyes of this species seem to be liable to be broken or to
flake off” in consequence of the decay of the surface laminae of
the tegmentum. Hence those remaining on old specimens are
probably those most recently formed by the mantle at the
margin of the tegmentum. The process of the formation of
eyes pari passu with the growth of the shell has been already
described. In some specimens apparently, according to the
existing systematic rules to be referred to the species
Acanthopleura spiniger, I have been able to find no eyes
at all. It will be necessai’y to examine a series of specimens of
various ages to discover whether the eyes are originally more
widely extended over the shell surface in the young or always
marginal, and thus of late appearance in the life of each in-
dividual in this species.

In Acanthopleura spiniger there are large, prominent
rounded tubercles on the shell surface ; possibly they act as
fenders to preserve the eyes which lie around their bases from
attrition. The micropores and megalopores are borne on iso-
lated, ovoid prominences of the tegmentary surface ; each
prominence bears a single megalopore on its summit, sur-
rounded by a zone of micropores (PI. VI, fig. 3).

In Acanthopleura piceus (PI. VI, figs. 8 and 9) there
are somewhat similar tubercles to those occurring in A. spini-
ger, but they show a tendency to form ridges. The eyes are,
as in A. spiniger, marginal in position, but more numerous.

In a large Corephium aculeatum, the tegmenta of which
were densely covered by a green alga, which perforates and
penetrates the shell substance, immense numbers of eyes were

PRESENCE OF EYES IN SHELLS OF CERTAIN OHITONIDJL 53

found when the alga was scrubbed off, and at the most recently
formed margins of the tegmenta not yet encroached upon by
the plant (PL VI, figs. 10, 11, 12).

The eyes are very small and their cornese are oval in outline,
the long axes of the ovals being directed vertically in the direction
to the heights of the shells. The eye-capsules reach to only a
small depth in the thickness of the tegmenta. The megalo-
pores and micropores are disposed in vertical parallel lines with
great regularity, the megalopores occurring at regular inter-
vels in the lines of micropores (PI. VI, fig. 11). A consider-
able proportion of the micrsesthetes are borne on strands inde-
pendent of the megalaesthetes. The tegmentary surface is
covered with rows of tubercles, so disposed as to form regular
series radiating from the apex of each shell, and also corre-
sponding with one another in position horizontally. The eyes
are never placed on the tubercles, but lie on the flat surface of
the tegmentum between them, and it is possibly because of the
existence of the tubercles all over the tegmentary surface that
the eyes do not get entirely obliterated in the older regions of
the shell.

The eyes are present in enormous numbers. I estimate
roughly the numbers present on the anterior shell alone at 3000,
counting only the younger ones, which are in good condition,
near the free margins of the tegmentum, and not the older
more or less destroyed by the boring of the shell by algae and
animals on the rest of the areae. On the remaining shells, at a
moderate estimate, reckoning as before only the eyes in toler-
able condition, there must be at least 8500 eyes.

InEnoplochiton niger the eyes are excessively minute,
and would not have been recognised at all as such had not the
larger eyes in other forms been previously studied. They are
here also confined to the margins of the tegmenta (PI. IV,
figs. 6, 7, 8, 9).

The cornea is slightly oval, as in Corephium aculeatum,
and as in that species the megalopores and micropores are dis-
posed in vertical lines.

In Tonicia marmorata the eyes have the peculiarity of

54

PROFESSOR H. N. MOSELEY.

being sunk in little pit-like depressions of the shell surface
(PI. V, figs. 1, 2, 3). This no doubt is a contrivance for
preventing them from being worn off, and the result is that
they are all retained complete up to the apices of the shells in
large old specimens. They are arranged in single straight rows,
radiating from the apices on the anterior and posterior shells,
disposed with considerable symmetry. There are thirty-four
such radial lines on the anterior shell in one specimen contain-
ing about eighteen eyes each. On each lateral area of the in-
termediate shells there are from two to four similar rows of
eyes, with a few additional eyes also grouped irregularly. In
some forms placed in the genus Tonicia, in the British Museum
collection, there are no eyes present. It probably will be found
that these should be placed in a separate genus.

I have been unable to obtain any specimen of any species of
Tonicia preserved in spirits for examination of the soft tissues
of the eyes. The pores are arranged in vertical rows, as in
Corephium.

In Ornithochiton the eyes are not sunk so deeply in pits
as in Tonicia, but are disposed somewhat as in that genus,
though the rows are not so regular (PI. V, figs. 4, 5, 6, 7) ; the
pores, megalaesthetes and micraesthetes are arranged as in
Tonicia. The numerous eyes on the terminal shells are dis-
posed in the radial rows at tolerably regular intervals, so as to
form transverse rows also parallel with the tegmental mai’gins.
Amongst these transverse rows some occur at intervals which
are characterised by the eyes composing them being much
smaller than the average size.

In Chitonellus there are no eyes, and the aesthetes are
apparently in a primitive condition of development. They are,
as elsewhere, confined to the tegmenta, and in these areas so
small in this genus, are not numerous. I have not had any very
well preserved material to work on, but there appear to be
both micraesthetes and megalaesthetes present. These terminate
in the typical obconical knobs, but their bodies appear to be
almost undeveloped. They bear no resemblance to the cal-
careous spines of the girdle.

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONIDJl. 55

General Remarks.

I regard the megalaesthetes and micraesthetes as probably
organs of touch which may to some extent take the place of
the tentacles which are absent in the Chitonidae. I base my
conjecture as to their having a sensitive function on the fact
that the megalaesthetes are in certain genera of the Chitonidae
converted into undoubted organs of special sense, viz. eyes.
It is important that experiments should be made on living
Chitons to determine whether the aesthetes are protrusible and
are used as organs of touch, and also as to the sensitiveness to
light of the eyes. I have searched in vain for any traces of
eyes like those of the Chitonidae in the shells of Patella and
allied genera. I am inclined to believe that the megalaesthetes
and micraesthetes are not, as van Bemmelen concludes, homo-
logous with the spines of the girdle or rather with the funicles
by which these spines are supported.1 The structure of the
megalaesthetes seems to me to be quite peculiar and distinct.
The funicles of the girdle spines never give off a series of
small offsets like the micraesthetes. The eyes are obviously
homologous with the megalaesthetes, yet in none of the
Chitonidae is there a trace of an eye or part of an eye in the
girdle region beyond the margin of the tegmentum. In the small
plates of shell developed on the girdle in the Chitonidae and
other genera, there are never any megalopores or microspores,
or any traces of megalesthetes or micresthetes.

The structure of the girdle contrasts most markedly with
that of the tegmentum, and there is an absolutely sharp line
of demarcation between the two at the place where they are
in contact. This is well to be seen in Onithochiton. In the
shell are seen the megalaesthetes and micraesthetes arranged
with exact regularity and the eyes extending up to the very
margin where some of both are seen, as yet only half formed,
whilst in contact with these half-formed growths is the
marginal line of the girdle devoid of micraesthetes and mega-

1 Van Bemmelen, 1. c., p. 91, 95. A. W. Hubrecht, “ Morphology of the
Amphineura,” ‘ Quart. Journ. Micro. Sci.,’ vol. xxii, 1882, p. 214.

56

PROFESSOR H. N. MOSELEY.

laesthetes and eves, but covered by large spines irregularly
disposed. Moreover, the peculiar mode of formation of the
aesthetes and eyes at the margin only of the tegmentum is
evidence against the homology. Were the megalaesthetes
homologous with the funicles of the spines, it would be probable
that in the growth of the tegmentum funicle-like organs contained
in the margin of the girdle would become encroached upon by
the tegmentum and included within it to become aesthetes, but
such is not the case. Eyes being absent in the Solenogastres,
I would suggest that the aesthetes are organs developed origi-
nally in connection with the shells in the Chitonidae, still little
differentiated in Chitonellus, and not homologous with the
spine-bearing funicles at all, which are of more ancient origin ,
occurring in Proneomenia. As a comparatively late modifica-
tion, some of the megalaesthetes have been modified into eyes
in certain genera, whilst in Chiton and other forms, the more
primitive condition in which they all remain as organs of
touch has been retained.

The forms of the Chitonidae which bear well-developed eyes
appear to be mostly non-European. It is therefore not easy
to obtain specimens properly prepared for examining the minute
structure of the retina in a satisfactory manner, but my
father-in-law, Dr. Gwyn Jeffreys, has pointed out to me that
Costa1 figures what are evidently eyes on one of the inter-
mediate shells of a very small species of Chiton, called by him
C. rubicundus (Ornithochiton ?), which species is common
in Sicily. The eyes are figured as mere black dots and referred
to as fine punctuations, but are evidently eyes. Possibly some
interesting results might be got by examining them in the fresh
condition.

In conclusion, I would express my best thanks to Dr.
Gunther for giving me every facility in making use of the fine
series of Chitonidae in the British Museum, and allowing me
to dissect some duplicate specimens preserved in spirits. Also
to Professor Westwood, who supplied me with others out of
the Hope collection, and to Mr. W. H. Dali, who showed me
1 “ Fauna di Napoli,” ‘ Animali Molli Chitone,’ taf. iii, fig. 1, e.

PRESENCE OP EYES IN SHELLS OF CERTAIN CHITONHLE. 57

the Smithsonian collection at Washington and gave me some
specimens from the Pacific coast.

Dr. Woodward kindly went over the fossil Chitons with me,
but we could not detect any traces of eyes in them.

DESCRIPTION OF PLATES IV, V, & VI,

Illustrating Professor H. N. Moseley’s paper “ On the Presence
of Eyes in the Shells of Certain Chitonidse and on the
Structure of these Organs.”

N.B. — All the drawings, with the exception of fig. 2, PI. IV, figs. 4, 5,
and 6, PI. V, and fig. 8, PI. VI, drawn by the author, are made from the
actual shells by a professional artist, Mr. W. H. Hill.

PLATE IV.

Fig. 1. — View of a specimen of Schizochiton incisus, preserved in
spirits, and with the outline of the margin of the mantle somewhat distorted
in consequence, a. Anterior shell, with six rows of eyes. b. Posterior shell,
with six rows of eyes. c. Anal notch in the posterior shell, d. One of the
middle shells, with two rows of eyes. e. Another of the middle shells, which
bears as an abnormality three rows of eyes, two on one side and one on the
other.

Fig. 2. — One of the rows of eyes of a middle shell of Schizochiton
incisus much further enlarged.

Fig. 3. — A single eye from the same specimen as the above, still more
highly magnified, b. Calcareous cornea, g. Lens, bordered by the apertures
of the iris seen through the cornea, c. Pigmented eye-capsule, seen partly
through the superficial layers of the general shell substance.

Fig. 4. — The anterior shell of Schizochiton incisus, outer view; one
half indicated in outline only. On the finished half three rows of eyes are
seen borne on raised ridges of the shell.

Fig. 5. — The same shell ; inner view, a a a. Incisurse marginalis. b b.
The sutural lines of pores for the passage of nerves, continued from the
incisurae.

Fig. 6. — Part of a specimen of Enoplochiton niger, viewed from
the side. Only a part of one of the middle shells and of the girdle is

58

PEOFESSOB H. N. MOSELEY.

shaded. A lower part of the lateral face of one of the middle shells is covered
by minute eye specks, b b. Calcareous plates of the girdle.

Fig. 7- — Outline of the entire specimen of Enoplochiton incisus of
life size, viewed from the side. a. Area included by a dotted line, showing
the situation of the part magnified in Fig. 6.

Fig. 5. — A small portion of the surface marked a in Fig. 6, more highly
magnified, d. Eyes. a. Megalopores. c. Area, still more highly magnified
in Fig. 9.

Fig. 9. — Area marked c in Fig. 8, further enlarged, a. Megalopores.
b. Micropores.

Fig. 10. — Schematic representation of the form and arrangement of the
organs of touch in the shell of Chiton magnificus, as seen after decalci-
fication, in a section vertical to the shell surface, a. Megalaesthetes. b. Mi-
craesthetes. d. Stem of a megalaesthetes. e e. Main soft tissue strands.

PLA.TE Y.

Fig. 1. — Anterior shell of Tonicia elegans; external view, showing
the arrangement of the eyes in radiating lines.

Fig. 2. — Enlarged view of two rows of eyes from the above, only partially
shaded. The eyes are sunk in a series of slight depressions, forming a partial
groove on the surface of the shell.

Fig. 3. — Portion of the surface of the same, still more enlarged, a. Mega-
lopores. b. Micropores.

Fig. 4. — Lateral view of one of the middle cells of a species of Onitho.
chiton. The tegmentum has a series of eyes upon it, which commences as a
single row superiorly and broadens out into a scattered group inferiorly.
t. Tegmentum, a. Articulamentum. b. Incisurae marginalis.

Fig. 5. — Part of the surface of the same, bearing the scattered eyes much
enlarged, a. Macropores, d. Eye. c. Area, shown still more enlarged in
Fig. 6.

Fig. 6. — a. Megalopore. b. Micropore.

Fig. 7- — Anterior shell of the same species of Onithochiton partially
shaded, showing the more or less regular radial rows of eyes.

Fig. 8. — Schematic representation Lof the tactile organs and an eye of
Corephium aculeatum, as seen in a section vertical to the surface in
decalcified specimens, excepting that the calcareous cornea is here retained.
a. Free end of a megalaesthete, projecting at the shell surface, b. Micraesthete.
b' b'. Micraesthetes supplied by offsets of the optic nerve, which perforate
the iris to reach the surface, d. Base of megalaesthete. e. Main nerve
branch, k. Pigmented eye-capsule and cavity of eye-capsule, n. Optic
nerve, h. Iris. /. Calcareous cornea.

PRESENCE OF EYES IN SHELLS OF CERTAIN CHITONID.E. 59

PLATE VI.

Fig. 1. — Sketch of a lateral view of a specimen of Acanthopleura
spiniger. x. Small area on the side of the tegmentum of one of the middle
shells, which is shown more highly magnified in Fig. 2.

Fig. 2.— The area indicated in the foregoing figure enlarged 65 diameters.
a a. Prominent rounded tubercles on the shell surface, b b. Pore-hillocks,
each with a megalopore visible at its summit, d d. Eyes.

Fig. 3. — Three of the pore-hillocks of Acanthopleura spiniger shown
in the preceding figure more highly magnified, a. Megalopore. b. Micro -
pore.

Fig. 4. — View of the surface layer of the soft tissues of a decalcified middle
shell of a species of Acanthopleura from China, viewed by transmitted light,
showing the grouping of the micrsesthetes and megalsesthetes in relation with
an eye. The cuticula of the tegmentum is seen to be finely fibrous, n. Chan-
nel, containing the optic nerve. 1. Lens of the eye. ch. Pigmented eye-
capsule, forming an iris-like border around the lens. b. Tips of micrsesthetes,
which pierce the iris and terminate at the free surface of the shell around the
margin of the cornea, a a a. Macrsesthetes in chambers, hollowed out in
the tissue and continued in the direction of the margin of the shell which
adjoins the girdle into nerve canals.

Fig. 5. — A single eye of Schizochiton decalcified. 1. Lens. ch. Pigmented
eye-capsule, continued inwards to form an iris, b b. Slit-like apertures in
the iris, giving passage to the branches given off by the optic nerve to the
ocular micrsesthetes. s. Cleft in the outer wall of the channel for the optic
nerve.

Fig. 6. — Schemalic representation of the structure of the soft and some
of the hard parts in the tegmentum of a shell of Acanthopleura spiniger,
as seen in a section vertical to the surface and with the margin of the shell
bordering on the girdle lying in the direction of the left side of the drawing.
f. Calcareous cornea. h. Iris. g. Lens. k. Pigmented capsule of eye.
n. Optic nerve, r. Rods of retina, n! . Branches of the optic nerve, per-
forating the capsule wall and terminating in b' b' b'. Ocular micrsesthetes.
p p. Nerves to macrsesthetes. m. Body of macrsesthete cut across, o e. Fusi-
form body of macrsesthete entire, a. Obconical termination of macrsesthete.
e. Nerve given off by macrsesthete to micrsesthete b" .

Fig. 7. — Rods of the retina of Acanthopleura spiniger, viewed from
above in a horizontal section of the eye.

Fig. 8. — Sketch of a specimen of Acanthopleura piceus, viewed from
the side, of natural size. x. Area on the side of the tegmentum of one of the
middle shells, which is seen highly magnified in Fig. 9.

Fig. 9. — The area indicated in Fig. 8, enlarged 26 diameters. The lateral

60

PROFESSOR H. N. MOSELEY.

margin of the shell is indented at intervals ; it overhangs the girdle part of
which is shown beneath it. a a a. Tubercles on the shell surface, dd. Eyes.

Fig. 10. — View of the anterior shell of a specimen of Corephium
aculeatum, enlarged 2 diameters, showing the regular rows of tubercles.
a. Articulamentum. t. Tegmentum.

Fig. 11. — A portion of the surface of the tegmentum of the same shell
near its articulamental margin, enlarged 17 diameters, a a. Tubercles form-
ing rows, d d. Eyes. x. Small area, more highly magnified in Fig. 12.

Iig. 12. — Small area on the surface of the tegmentum of the anterior
shell of Corephium aculeatum, enlarged 185 diameters, d. Oval eye.
a a a. Megalopores. b b b. Micropores.

W H Hfll 4 H H 1LM.

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«

ARCHERINA BOLTONI.

61

Archerina Boltoni, nov. gen. et sp., a Chloro-
phyllogenous Protozoon, allied to Vampy-
rella, Cienk.

By

E. Ray Lankester, M.A., F.R.S.,

Jodrell Professor of Zoology in University College, London.

With Plate VII.

During the months of June and July, 1884, 1 received from
Mr. Thomas Bolton, of Birmingham, several gatherings from
ponds in his neighbourhood which contained an abundance of
a minute, green-coloured, Heliozoon-like organism, to which
he directed my attention. Careful study of the material for-
warded to me by Mr. Bolton established the fact that the
little Protozoon was hitherto undescribed, and that it presented
many features of considerable interest.

The discovery of this form is due to Mr. Bolton, to whom
English naturalists are deeply indebted for constant supplies
of the most interesting and important of our known freshwater
micro-fauna, as well as for the discovery of such novelties as
the Bhizopod, Lithamoeba discus, the Chsetopod, Haplo-
branchus cestuarinus, several new Naidinse, and not a few
Rotifera.

I propose to place the organism thus brought to light in a
new genus, which I dedicate to my friend and former colleague,
Mr. William Archer, of Dublin (the discoverer of so many
Heliozoa), as “ Archerina and as a specific name I asso-
ciate with this interesting form that of its discoverer. It will
thus stand as Archerina Boltoni.

62

PROFESSOR E. RAT LANKESTEE.

Occurrence. — Archerina occurs in great numbers in pond-
water associated with Desmids and other minute chlorophyll-
bearing algae. Its spherical chlorophyll-corpuscles may at
first be mistaken for those of such microscopic plants ; but a
little attention is sufficient to enable one to detect around
many of the bright-green spheres or groups of spheres a halo
of radiant protoplasm, frequently in the form of very long and
stiff filaments. Once recognised, it is not difficult to distin-
guish Archerina in its various phases of growth and multipli-
cation from its associates.

Structure and Life-history. — 1. Actinophryd-form,fig. 7.
— The abundance in which Archerina occurs in the material
sent to me by Mr. Bolton has enabled me to trace it in several
phases of growth. The most convenient of these to commence
with is that represented in PI. VII, figs. 7 and 13. We have
here a spherical body xoVof^ of an inch in diameter, consisting
of a sharply outlined mass of refringent protoplasm, from the
surface of which radiate a number of very delicate but stiff
filaments, some of them four times as long as the diameter of
the sphere and tapering from the base towards the extremity.
There are in such a specimen about fifty of these filamentous
“ pseudopodia, ” more or less. The base of each filament is
relatively broad, and appears to join without penetrating the
surface of the sphere. In such specimens I could detect no
membrane or pellicle on the surface of the sphere or its pseudo-
podia. The pseudopodia are motionless, and did not exhibit
any streaming of granules such as is seen in Actinosphserium.
Within the spherical body is usually one lai’ge spherical
vacuole (fig. 7), but sometimes there are more, and they may
be of various sizes (figs. 8 to 12). Sometimes the whole of
the protoplasm of the spherical body appears of a bright green
colour (fig. 8), but on causing the organism to roll over one
finds that the green colour is limited to two masses, which may
be united on one face of the sphere though separated more
deeply.

Usually the green colour, in the particular phase of
Archerina now under description, appears in the form of two

ARCHERINA BOLTONI.

63

oval masses lodged in the protoplasm of the sphere, as shown
in figs. 7, 10, 11, and 13.

Rarely the green colour is seen to be confined to a single
spherical corpuscle (fig. 12) of half the diameter of the whole
sphere.

The green colouring matter is chlorophyll, identical in tint
with that of the Desmids, Closterium, and Pediastrum, which
abound side by side with Archerina. The chlorophyll in
Archerina is confined to a definite “ chlorophyll-corpuscle,” a
dense portion of the constituent protoplasm of the spherical
body; in fig. 12 this chlorophyll-corpuscle is in a quiescent
condition; in figs 7, 8, 9, 10, 11, 13 it is in process of
multiplication by division.

No other structural elements can be detected in Archerina
in this phase of its growth either before or after the use of
re-agents. It consists simply of a sphere of dense protoplasm
with radiating pseudopodia, one or more large vacuoles, and a
single or bifid chlorophyll-corpuscle. No nucleus can be
detected in Archerina. The examination for a nucleus was
carefully made. The chlorophyll of the chlorophyll-corpuscle
was extracted by alcohol, and the Archerinse were then stained
with borax-carmine ; others after similar extraction were
stained with Kleinenberg’s hsematoxylin, others with picro-
carmine, and some with anilin blue (aqueous solution). In
none of these cases could any nucleus or nucleus-like structure
be detected, excepting the chlorophyll-corpuscle itself, which
(as is usual with chlorophyll-corpuscles) after the discharge of
the chlorophyll exhibited a marked superiority over the sur-
rounding protoplasm in taking up the staining agent in each
of the above instances.

The chlorophyll-corpuscle of Archerina, like those of Spon-
gilla and Hydra (and like those of higher plants), appears to
consist of modified protoplasm resembling that of a cell-
nucleus. In this particular instance it appears that the
chlorophyll-corpuscle is actually taking the place of
a nucleus. As will be seen directly, the life and growth of
the Archerina centres round its chlorophyll-corpuscle. The

64

PROFESSOR E. RAY LAXKESTER.

division of the chlorophyll-corpuscle precedes and is invariably
followed^ sooner or later, by the division of the protoplasm of
the whole organism.

At the same time it does not appear that there is any ground
for regarding the green-coloured corpuscles of Archerina as
ordinary cell-nuclei (or rather, one should say, Protozoon cell-
nuclei) coloured green by chlorophyll. They have none of the
distinctive characters of cell-nuclei as distinguished from
chlorophyll-corpuscles. They do not exhibit any differentia-
tion of chromatin substauce into fibrillae or loops at the period
of division, and moreover they appear as a rule to divide not
into two but into four.

I am not sure that the complete division into two does not
occur in the large individuals such as are drawn in figs. 7 and
13 ; but it is quite certain that in some of these large forms
(figs. 14 and 15), and in all the smaller phases of Archerina
(figs. 20, 21, 22, 24), the dividing chlorophyll-corpuscle forms
a tetrad. It is possible that the curious form presented by the
chlorophyll-corpuscles in figs. 7 to 13 — when there is an
appearance of two oval bodies which are joined by a superficial
shell of green-coloured substance on one hemisphere of the
organism — may be only preliminary to the breaking up of the
chlorophyll-corpuscle into four, and may not really indicate, as
it seems to do, a division into two.

There are reasons for regarding these larger forms as excep-
tional, inasmuch as they appear to have emerged but recently
from the encysted condition (figs. 1, 2, 3, 4, 5, 6). When the
Archerina has once fairly started on an active vegetative
growth (as in the groups of smaller individuals) there is no
doubt that the division of the chlorophyll-corpuscle usually
and characteristically proceeds by the simultaneous fission
of the corpuscle into four segments (fig. 25), and
consequently produces groups of four daughter corpuscles (fig.
21).

In respect of this peculiar quadri-sectional division, the
chlorophyll-corpuscle of the vegetating Archerina very closely
resembles that of Hydra viridis, as may be seen by a

ARCHERINA BOLTONI.

65

comparison of fig. 25 of the present Plate II with fig. 17 a of
PL XX, Yol. XXII (1882) of this Journal.

The chlorophyll-corpuscle of Archerina has accordingly an
interesting relation to the question which has been raised by
Brandt, as to the parasitic nature of the chlorophyll-corpuscles
of Hydra viridis. If the theory is entertained that the latter
are independent green algae which inhabit the endoderm cells of
Hydra as parasites, then it would seem necessary to take a
similar view with regard to the chlorophyll-corpuscle of Arche-
rina. The Archerina would itself be a very simple non-
nucleate G-ymnomyxon similar to Vampvrella, which would be
supposed to be always inhabited and dominated in its movements
of growth and division by the green algal parasite. With regard
to such a conception, it may be justly observed that on equally
valid grounds the nuclei of other Protozoa — and, indeed, of all
animal and vegetable cells — might be regarded as colourless
parasites inhabiting non-nucleated corpuscles of protoplasm.
On the other hand, it would be urged that no independent
organisms resembling the nuclei of cells are known, and that
in the absence of any direct evidence of their intrusion from
external sources into the protoplasm of cells, as well as in view
of the phenomena of their division and their relation to the
protoplasm, it is a gratuitous assumption that they have a
history differing essentially from that of other products of the
modification of cell-substance. In the same way we urge, in
reference to the tetra-schistic chlorophyll-corpuscles of both
Archerina and Hydra viridis, that they do not resemble
any known unicellular green alga, either in structure or in mode
of growth, and that there is no reason for attributing to them
a fanciful origin and history differing essentially from that of
other coloured corpuscles and such products of the modification
of cell-substance.

2. Encysted Form (figs. 1 to 6). — In the earlier gatherings
sent to me by Mr. Bolton, which contained only a few of the
vegetating growths of Archerina, and these only in the condition
of small colonies, with four or eight chlorophyll-corpuscles,
I found many specimens of large encysted Archerinse. These

VOL. XXV. NEW SER. E

66

PROFESSOR E. RAY LANKESTER.

also were again obtained from a tube which contained at first
abundant colonies, such as that drawn in PI. VII, fig. 24.
After a week’s interval the colonies were found to have broken
up into single individuals (that is, individuals containing each
but one chlorophyll- corpuscle), and a week later many were
found to have increased greatly in size, and to have become
enclosed in a cyst. The cyst appears to consist of a resisting
membrane, which is produced on the surface of the protoplasm,
and actually extends for some distance along the filamentous
pseudopodia. As the deposit increases in amount the pseudo-
podia are withdrawn, and finally there results a spherical cyst
provided with numerous truncated processes on its surface,
resembling the short spines of a horse-chestnut fruit. In
such cysts the protoplasm and its chlorophyll body may be
observed in various conditions. I have most frequently found
the protoplasm shrunken, so as to be completely detached
internally from the cyst-membrane (figs. 2 and 3). At the
same time, in such specimens there was no appearance of any
differentiated chlorophyll-corpuscle, but the whole of the pro-
toplasm was uniformly coloured green. Occasionally I have
seen the whole contained mass in a state of granular dis-
integration (fig. 1). On the other hand, the cysts sometimes
show (figs. 4, 6) a disposition of the protoplasm with vacuole
and two chlorophyll-coloured masses not dissimilar to that of
the un-encysted Actinophryd form (fig. 7).

I am not able to state what is the exact position of the
encysted condition in the life-history of Archerina.

I do not know whether the Actinophrvd-forms, such as
figs. 7 and 12, are just about to be encysted, or whether they
have just escaped from the encysted condition. The latter
seems to me to be the more probable.

3. Vegetative Condition — Tetraschistic Colonies (figs. 20,21,
22.) — Alongside of the Actinophrvd-forms of Archerina occur
very numerous specimens in which the protoplasm is no longer so
definitely disposed in the form of a central sphere and clean-
cut radiating filaments, but is irregular in shape with occasional
lobose projections, whilst groups of radiating filaments are

ARCHERINA B0LT0N1.

67

given off here and there from the mass. In these specimens
the most striking feature is the entirely altered appearance of
the chlorophyll-corpuscles. They may he present to the number
of four, arranged as in fig. 15, and clearly resulting from the
tetraschistic division of one parent chlorophyll-corpuscle. Or
they may have proceeded further in the process of fission, each
one of four having itself divided into four, giving thus a group
of sixteen, such as is shown in fig. 21. These may retain a
eery definite and symmetrical arrangement, or the colony may
have become broken and distorted so as to give such irregular
grouping as is shown in fig. 20. That there is at one stage or
other a possible division into two only on the part of the
chlorophyll- corpuscle of Archerina, is shown by the existence
of such a group as that drawn in fig. 22, where we have a
colony consisting of four groups of eight corpuscles. A
curiously irregular fission is shown in fig. 23.

The two corpuscles with abundant protoplasm shown in
fig. 19, are very possibly only a detached “half” of a tetra-
schistic group.

It is to be noted with regard to the form of the chlorophyll-
corpuscles in these groups, that they contrast with the oval and
irregularly flattened out green bodies of the Actinophryd-phase.
They are nearly always spherical, rarely ovoid. Occasionally, as
in fig. 20, each contains a refringent granule, but they are
usually homogeneous in appearance. The chlorophyll is con-
fined to a uniform peripheral layer or crust of the corpuscle.

The spherical form of the corpuscles is apparently connected
with their active state of growth and division, the breaking up
of one parent corpuscle into four daughter corpuscles pro-
ceeding rapidly, and not being delayed in the incomplete state
of fission seen in the Actinophryd-phase. The protoplasm is
more abundant relatively in these groups than in the Actino-
phryd-phase, and is often observed in the act of ingesting solid
food particles such as Bacteria (seen in fig. 20, i, and fig. 24, *).
That the multiplication of the corpuscles and the associated
growth of the protoplasm is very active, seems to be proved by
the occurrence of such extensive growths of the organism as

68

PROFESSOR E. RAT LANKESTER.

that drawn in fig. 24. This is by no means the largest colony
which I observed, and in this specimen the chlorophyll-cor-
puscles were all in an active state of tetraschistic division. I
decolourized this colony by the introduction of alcohol between
the glass slide and cover, whilst under observation, and,
subsequently stained the organism by picro-carmine intro-
duced in the same way. All the larger chlorophyll-corpuscles
then exhibited the structure shown in fig. 25. Whilst the
smaller corpuscles (which presumably had only recently been
formed by tetraschistic division) exhibited the structure shown
in fig. 26. The shaded parts in these two figures correspond
to a decided but not very strong staining effected by the
picro-carmine.

The size of the chlorophyll-corpuscles in these vegetative
groups varies. They are never so large as in the Actinophryd
phase, but may attain a diameter of go'opth of an inch, and
may be, in such exceedingly active specimens as fig. 24, as low
as T6-oooth of an inch.

It appears that there is no constant size which the chloro-
phyll-corpuscle must attain before division, but that this
varies in different specimens according to the individual activity
of the vegetative process in each group. Apparently, where
the protoplasm is abundant and is taking much nourishment,
the chlorophyll-corpuscles multiply rapidly and enter upon the
fission-process at an earlier period of growth — that is to say,
when they have attained a less diameter — than is the case
where the protoplasm is less abundant. It would almost seem
as though, receding from the Actinophryd-phase, the chloro-
phyll-corpuscles divide successively at earlier and earlier stages
of their growth, until a maximum of associated corpuscles and
a minimum of their individual size is attained. It seems not
improbable that this excessive growth and subdivision of the
chlorophyll-corpuscles is favoured by abundant nutrition. A
time arrives when the conditions for nutrition are less favour-
able. The individual chlorophyll-corpuscles then grow instead
of dividing and each becomes detached, together with some of
the protoplasm, from association with its neighbours. Such a

ARCHERINA BOLTONI.

69

growth as fig. 24 would break up into several hundred indi-
viduals. Each of these then would slowly attain to the size
and form of the Actinophryd-phase (fig. 7), the chlorophyll-
corpuscle partially dividing and spreading itself out as seen in
figs. 7, 8, 9, 10, 11.

Probably such individuals now pass on — if conditions adverse
to nutrition are continued — into the encysted condition, from
which they will emerge on the return of conditions favorable
to nutrition.

This life-history is hypothetical. It is, however, favoured
by the fact that specimens of vegetative growths such as fig.
24, when kept in the moist-chamber for two weeks, first of all
broke down into individual units consisting of a single
chlorophyll-corpuscle and some protoplasm, and that later
many were observed of a large size in the Actinophryd-phase,
whilst later still on the same slide numerous encysted indi-
viduals were found which were not previously detected. A
similar observation was made with regard to the contents of
a glass tube kept on the table of my laboratory screened from
the direct sunlight.

4. Skeleton-colonies. — A very curious characteristic of the
colonies of Archerina is represented in fig. 18. In exploring a
slide containing specimens in the early tetraschistic phase
(such as figs. 20 and 22), one comes across groups of ghost-like
outlines corresponding to chlorophyll-corpuscles, and their
radiant filamentous pseudopodia, entirely devoid of any sub-
stance. They are merely outlines, as though sketched with a
pencil, very delicate and inconspicuous. Here and there in
such a ghost-like group one finds a solid chlorophyll-corpuscle
and attendant protoplasm.

These strange outline “simulacra” of Archerina-colonies are
undoubtedly skeletal products of the solid protoplasm, which
after producing them has withdrawn from them and moved
into another position. They appear to indicate that the pro-
toplasm is at this phase of the life-history of Archerina capable
of producing a pellicle on its surface, comparable to the cyst
which is produced when encystation takes place ; but instead

70

PROFESSOR E. RAT LANKESTER.

of being retained as a covering for a definite period, the
secreted material is soon abandoned by the organism, and thus
these ghostly sketches of the Archerina are left empty and
useless. They may be compared to the numerous cellulose -
chambers secreted and rapidly abandoned by the protoplasm of
Archer’s Chlamydomyxa. They are remarkable inasmuch as
they show that the whole surface of the protoplasm of Arche-
rina can secrete a skeletal product. Not only the delicate
layer of protoplasm which invests each chlorophyll-corpuscle,
but also the filamentous pseudopodia as far as their delicate
extremities secrete this skeletal investment. The secretion
of a skeletal investment by filamentous pseudopodia is unusual.
It is known to occur in such oceanic Thalamophora as Glo-
bigerina, where the investment is calcareous, and in some
Radiolaria (Tripylsea) where it is siliceous (hollow spicules).

A membranous investment secreted by pseudopodia is, I
believe, hitherto unobserved. The Heliozoa are known to
obtain a certain stiffness and permanence for their filamentous
pseudopodia by the secretion of an axial horny filament.
Here we seem to have evidence of a capacity for strengthening
and stiffening the radiant pseudopodia, by the development of
an external skeletal tube of a similarly horny (membranous)
nature.

As to how the living matter recedes from the investment
which it has formed so as to leave these empty cases, I have no
suggestion to offer. And I am not able to assert, although it
seems to be unlikely, that the removal of the living matter
from within these ghostly skeletons may not be due to the
death and decomposition of the living matter. In any case,
these skeletal residues of Archerina-colonies are amongst the
most interesting and characteristic of the features presented by
this organism.

5. Physiological Observations. — The protoplasm of Archerina
in all the phases here recorded was extremely sluggish. I did
not detect any streaming movement in it in any case, nor any
change of form which could be followed with the eye. In the
Actinophryd-phase I failed to observe any evidence of the

AEOHEEINA BOLTONI.

71

ingestion of food particles, but in the later vegetative growth I
often saw Bacteria and Bacilli in course of ingestion (figs. 20,
24, i ).

No contractile vacuole was observed in any phase.

In the Actinophryd-phase only was a vacuole (and that a
non-contractile one) observed. The protoplasm in the Actino-
phryd-phase is free from granules, homogeneous and refrin-
gent. In the vegetative stage it has a finely-flaky appearance.

The pseudopodia were not altered in form by the action of
dilute acids or of alcohol.

Numerous observations were made as to the presence of
amyloid substance in connection with the chlorophyll-cor-
puscles. In small colonies I usually failed to obtain any violet
coloration after removal of the chlorophyll by alcohol and
subsequent addition of iodine solution. But in larger colonies
I obtained decided violet staining of the protoplasm imme-
diately surrounding the chlorophyll-corpuscles, for instance, in
such colonies as that represented in fig. 24.

6. Affinities of Archerina. — Archerina is clearly one of the
non-nucleate Gymnomyxa (Homogenea or Monera), and is, in
so far as regards the various forms which its protoplasm may
assume, not far removed from Cienkowski’s Vampyrella. It
is, however, definitely characterised and distinguished by its
nucleus-like chlorophyll-corpuscle. No other Protozoon is
known the form of which is thus dominated by a chlorophyll-
corpuscle, nor is there any form with a chlorophyll-bearing
nucleus which might be compared with it. In regard to
nutrition it clearly gives evidence of both plant-like assimila-
tion of carbon through the agency of its chlorophyll-corpuscles
and of the usual ingestive voracity of the naked Protozoa.

In respect of its abundant colony-formation, Archerina re-
minds one of Microgromia socialise but it differs widely
from that organism in having a chlorophyll-corpuscle in place
of a nucleus, and in forming a complete membranous envelope
extending over the pseudopodia instead of (as in Microgromia)
a sac-like case with a mouth or orifice for exit.

I shall not be surprised if some naturalists maintain that

72

PROFESSOR E. RAY LANKESTER.

Archerina is a duplex organism consisting of a Moner-like
animal Protozoon, and a simple green alga, living together in
constant association, or “Symbiosis.” But in my judgment
there is no direct evidence, nor are there any grounds of
analogy, for entertaining such a view as to the nature of this
organism.

EXPLANATION OF PLATE VII,

Illustrating Prof. Ray Lankester's memoir on “ Archerina
Boltoni,” nov. gen. et sp.

Fig. 1. — Cyst of Archerina Boltoni, in optical section, a. Cyst wall.
b. Granular contents, coloured green by chlorophyll. Nat. size = y^ooth of
an inch in diameter.

Fig. 2. — Another cyst, similarly viewed, a. Cyst wall. b. Protoplasm
withdrawn from the cyst wall, and uniformly coloured by chlorophyll, c. Long
tubular processes of the cyst.

Fig. 3. — Surface view of a similar cyst.

Fig. 4. — Optical section of another encysted Archerina, in which the colour-
less protoplasm d is distinguishable from the two chlorophyll bodies b b.
Other letters as in Fig. 2.

Fig. 5. — Optical section of another cyst, showing uniformly short processes
of the cyst wall, and green-coloured contents entirely free from the cyst
wall. Letters as in Fig. 2.

Fig. 6. — A deeper focussing of the specimen drawn in Fig. 4, showing the
constricted vacuole e within the protoplasm. Other letters as before.

Fig. 7. — Actinophryd-phase of Archerina Boltoni. Diameter of the
sphere 2 oVgth of an inch, b b. Chlorophyll bodies, e. Vacuole.

Figs. 8 — 12. — Central spheres of different specimens similar to Fig. 7, the
radiating pseudopodia being omitted. They show various dispositions of the
chlorophyll and of the vacuoles.

Fig. 13. — Similar specimen to Fig. 7, showing two large chlorophyll bodies
and a small vacuole.

Fig. 14. — Similar specimen in a stage of tetraschistic division. The radiant
protoplasm is omitted, and the pyramid of four incipient segmentation spheres
is seen from one face.

Fig. 15. — Four segmentation spheres resulting from a complete tetraschistic
fission of the chlorophyll-ooloured body of an Actinophryd-phase of Archerina.

AROBERINA BOLTONI.

73

The uncoloured protoplasm is relatively small in amount and is not seen,
owing probably to its forming in part a thin coating to the chlorophyll-cor-
puscles, and being in part accumulated between and beneath those bodies.

Fig. 16. — Archerina of same size as Fig. 7, but with irregularly-shaped
chlorophyll-corpuscle, and with protoplasm gathered partly into an amoeboid
lobe and partly into one long filament.

Fig. 17. — A specimen of same size, showing few but large filamentous
pseudopodia, and with a chlorophyll-corpuscle sharply cleft into two.

Fig. 18. — Skeletal or “ghost” colony of Archerina. The spheres and
filaments marked h are merely empty cases of great tenuity. Four chlorophyll-
corpuscles are present and lobose protoplasm g. Diameter of each sphere =
4^ooth of an inch.

Fig. 19. — Colony consisting of two spherical chlorophyll-corpuscles sur-
rounded by radiant and, g, lobose protoplasm.

Fig. 20. — Irregularly-grouped chlorophyll-corpuscles and protoplasm, re-
sulting from tetraschistic division of an originally single chlorophyll-corpuscle,
such as that seen in Fig. 12 or 16. The abundant amoeboid protoplasm g is
actively ingesting a bacillus-filament i.

Fig. 21. — Tetraschistic colony of Archerina consisting of four groups of
four chlorophyll-corpuscles, each invested with radiating filamentous proto-
plasm. The regular symmetrical grouping of the products of division is
striking, though not unusual in this organism.

Fig. 22. — A similarly symmetrical colony, consisting of four groups of eight
chlorophyll-corpuscles.

Fig 23. — Small colony, in which the division of the chlorophyll-coloured
spheres has not proceeded symmetrically, the product being one large and
three small spheres. This is a very exceptional condition.

Fig. 24. — Large vegetative growth of Archerina, consisting of some hun-
dreds of chlorophyll-corpuscles and amoeboid protoplasm, g, giving off fila-
mentous radiant pseudopodia at many points. Bacilli, ii, are being ingested
by a portion of the protoplasm. The chlorophyll-corpuscles are arranged
more or less obviously in groups of eight or sixteen, the arrangement resulting
from their method of multiplication. They are of two sizes, the larger measuring
g^jth of an inch in diameter, the smaller ones, k, less. The larger are seen
in many places to be in course of breaking up to form the smaller by tetra-
scbistic division.

Fig. 25. — One of the larger chlorophyll-corpuscles of the specimen drawn
in Fig. 24, after removal of the chlorophyll by alcohol and subsequent staining
with picro-carmine. The fission lines of tetraschistic division are seen.

Fig. 26. — One of the smaller chlorophyll-corpuscles of the same specimen
similarly treated.

.

E Ray Lanleesier id

Y Ku*h, Lift' F-dtn*

APEX OF THE ROOT IN OSMUNDA AND TODEA.

75

On the Apex of the Root in Osmunda and
Todea.

By

F. O. Bower, IB. A.,

Lecturer on Botany at the Normal School of Science, South Kensington.
(From the Jodrell Laboratory, Royal Gardens, Kew.)

With Plates VIII and IX.

Introduction.

The years 1845 and 1877 will always be memorable in the
history of the study of apical meristems. In the former year
Naegeli published in his work, cDie neuern Algensysteme,’ his
investigations on the mode of growth of certain Algae, notably
ofDictyota dichotoma, and introduced the term apical
cell (Scheitelzelle) to distinguish that cell from which seg-
ments are cut off in regular order and succession, these
segments giving rise, by further growth and division, to all the
mature tissues of the organ. In 1877 Sachs produced the first
of that series of memoirs1 which drew together and systema-
tised the immense volume of independent results obtained by
various investigators of meristems during the previous thirty
years. It is true that Hofmeister ( ‘ Lehre von der Pflanzen-
zelle/ 1867, p. 125, &c.) had attempted to draw from a com-
parison of various meristematic tissues, some general conclu-
sions as to the relations of cell divisions to growth, but these

1 1. “Ueber die Anordnung der Zellen in jiingsten Pfianzentheilen,” ‘ Verb,
der Phys. Med. Gesellscli. in Wurzburg, ’ Bd. xi, 1877.

2. ‘Arbeiten des Bot. Inst, in Wurzburg, ’ Bd. ii, Heft i.

3. ‘ Arbeiten des Bot. Inst, in Wurzburg, ’ Bd. ii, Heft ii.

4. ‘ Yoriesungen iiber Pflanzenphysiologie,’ pp. 523 — 55 7.

76

F. 0. BOWER.

were subjected to severe criticisms by Sachs at the opening of
the second memoir of the above-mentioned series (1. c., p. 48).
Thus, practically, the ground was clear for the latter author.
How well he drew together and systematised the whole sub-
ject of the structure of meristems will be already familiar to
most botanists. It may be safely stated that no work has given
a greater stimulus to the study of meristematic tissues than
this of Professor Sachs.

One of the most important points brought forward by Sachs
is that the arrangement of the walls in such organs as grow
with a single apical cell may be shown to fall under a similar
system of construction to that of similar organs in which no
apical cell can be distinguished. He has formulated this in
the proposition that the apical cell “ is merely a gap in the
system of construction of the punctum vegetationis, that
is, the apical cell is that point in the embryonic tissue in which
as yet no anti- or periclinal walls, nor any radial longitudinal
walls have been formed” (f Vorlesungen/ p.555). This view
of the matter affords a bridge connecting those types which
grow with a single apical cell with those having a small-celled
primary meristem, and as a necessary result draws closer atten-
tion to those which may be regarded as transitional types
between the structure which is, roughly speaking, characteristic
of the lower forms, where an apical cell is present, and that
more typical of the higher plants, viz. with a small-celled me-
ristem. Such intermediate types had already been described
in various examples, both of roots and stems, in which the
whole tissue of the organ, instead of being referable in its
origin to a single apical cell, is derived from two or more
initial cells. As examples may be cited the roots of the
Marattiaceae, first investigated by Russow (‘Yergl. Unters./
pp. 107 — 109), but subsequently, and apparently with more
exactitude, by Schwendener (‘ Sitz. d. k. Preuss. Akad. d.
Wiss./ 1882, p. 183). According to the latter author, there
are in this case four oblong initial cells in juxtaposition ; with
the exception of the sides in contact with the other initial
cells, segments are cut off from all the sides of these cells ;

APEX OF THE ROOT IX OSMUNDA AND TODEA.

77

those cut off below (i. e. from the end next the body of the
root) take part in the formation of the body of the root, those
above act as calyptrogen.

A group of initial cells, having apparently very similar
characters to the above, but without the formation of a calyp-
trogen, has recently been described by Bruchmann (ref., ‘ Bot.
Centrbl.,’ 1884, No. 46), in the stem of Selaginella spinu-
losa, though it had already been noted by Sadebeck (‘ Schenk’s.
Handbuch.,’ Bd. i, p. 244). In Selaginella Wallichii
Strasburger found that two wedge-shaped initial cells occupy
the summit of the stem.1 Finally, Strasburger, in his recently
published ‘ Botanische Practicum,’ gives a drawing (1. c.,
fig. 93) of the apex of the stem of Lycopodium selago, in
which three cells (marked i) are distinguished as initial cells.
Two of these are again represented as seen in longitudinal
section in his fig. 94. A useful summary of different varieties of
such meristems is to be found in Haberlandt’s ‘ Physiologische
Pflanzenanatomie,’ pp. 44 — 52. In a note on p. 59 of this work
the question of the mode of transition from growth with one
apical cell to that with two or more initial cells is discussed,
but owing to the want of necessary observations on the subject
it is only treated theoretically. As yet we have no direct evi-
dence as to the manner of transition, though, as Haberlandt
points out (p. 60), the transition must have taken place. It is
the object of this article to add to the information at present
at our disposal.

In a memoir ‘ On the Comparative Morphology of the Leaf
in the Vascular Cryptogams and Gymnosperms,’ communi-
cated to the Royal Society, I have pointed out that in various
characters of the leaf the Osmundaceae occupy a posi-
tion intermediate between the leptosporangiate Ferns and the
Marattiaceae. The idea suggested itself that the Osmun-

1 When it is remembered that Treub found a single wedge-shaped apical
cell of variable form in the stem of Selaginella Martensii, it will be
clear that in this genus variations of structure of the apical meristem of the
stem are to be found which are very similar to those described below in
the Osmundaceee.

78

P. 0. BOWER.

dacete might also be a transitional type in respect of the
structure of the meristem in the root. The result justified mv
expectations, and the observations to be detailed below will
afford material help towards the solution of the problem as to
the mode of transition from growth with one apical cell to that
with a group of two or more initial cells.

Osmunda regalis. — Transverse sections.

In describing the manner in which the arrangement of the
primary meristem of the root of Osmunda regalis differs
from that generally accepted as characteristic of the roots of
Ferns,1 the results obtained from transverse sections will be
detailed first. As the irregularities are in some cases very
great, and as there is not uniformity of structure in the meri-
stem of different roots of this species, even when taken from
the same plant, it is obvious that, in order to attain a clear
idea of the irregularities, the study of transverse sections is
more likely to lead to safe conclusions than that oflongitudinal
sections. Anyone who has made preparations from the roots
of those Ferns which have an almost diagrammatic regularity of
arrangement of the meristem, will, I think, allow that the study
of transverse sections of these is more easy and secure than
that of longitudinal sections. But if there be no definite regu-
larity of arrangement of the meristem the difficulties presented
by the study of longitudinal sections are very greatly increased,
since it is in this case so much less easy to determine whether
any given section be accurately longitudinal, and almost im-
possible to be sure whether it be accurately median. In ob-

1 Naegeli and Leitgeb, ‘ Beitrage z. wiss. Bot.,” Leipzig, 1868. It may
here be stated that I have made sections from the apices of roots of Cyathea
insignio, Eat., Gleichenia circinatn, Sw., Gleichenia flabellata,
R. Br., and Aneimia phyllitidis, Sw., and have found in all of these
that the structure of the meristem corresponds in its chief points to that
described by Naegeli and Cramer for the Polypodiaceae. It is clear that the
prevalence of this type of meristem among the leptosporangiate Ferns makes
the abnormality of structure in the Osmundaceae still more interesting than it
would otherwise have been.

APEX OF THE HOOT OF OSMUNDA AND TODEA. 79

serving transverse sections of roots of irregular meristematic
structure care must be taken to distinguish sections passing
through the root cap, immediately above the actual initial
cells, from those passing through the initial cells themselves.
It is well known that investigators have at times fallen into
error on this point. In all cases I have mounted all the
transverse sections cut from one root on the slide together,
and have not drawn conclusions from any one section till it
has been compared with the other sections of the series,
and its actual position in the original root been thereby
defined. Though the grosser errors have, I think, been ex-
cluded by due care on this and other points, still the difficul-
ties arising from want of uniformity of meristemic structure
make absolute certainty in the interpretation of sections, and
especially of longitudinal sections, almost impossible. Errors
of detail, both of observation and interpretation, may have
crept in, but still the description which follows will amply show
that the structure of the meristem of the roots in Osmunda
and Todea may differ essentially from the type described by
Naegeli and Leitgeb (1. c.).

Among the many roots of Osmunda regalis which have
been investigated, some few show a similarity in the arrange-
ment of the meristem to the type well known for Equisetum
and the Polvpodiacese. These will be first described. The
most regular which has been observed is that represented in
fig. 1 ; unfortunately, this section was not cut exactly in a
transverse plane, and hence, as regards their form, the seg-
mental cells are not so regular as they would otherwise have
appeared ; still it is clear that there is in this case a three-
sided apical cell, from the three sides of which segments i — iv
have been cut off in regular order. It is worthy of note that
this was one of the thinnest of all the roots from which sections
were cut; it measured -fifths of an inch in transverse
diameter at the level of the section : the question as to the
relation of bulk of the root to the arrangement of the apical
meristem will be discussed more at length below.

Three examples of one four-sided apical cell have been

80

F. 0. BOWER.

observed, two of which are represented in figs. 2 and 3. In
the former the square group of cells figured ocupied a central
position, while the succession of segments was regular. In
fig. 3 the succession of segments is as regular as in the former
case, till the segment iv is reached ; then it appeared that
a second segment (v) had been cut off from the same side
of the apical cell as segment iv. The appearance of the
walls as shown in the figure might suggest a possible interpre-
tation of the meristem as being derived from four initial cells,
as described by Schwendener in the roots of the Marattiacese;
a careful examination of the section precludes this idea. It is
further to be observed that the section represented in fig. 3,
passed through the apical cell with its segments, while it also
included a segment (already divided into four cells by walls
disposed crosswise, and here shown by dotted lines) which goes
to form part of the root-cap : this may be observed by focussing
deeply into the section. Such sections, when used with proper
precautions, are of great value, as preventing the possibility of
mistaking cells below the apical cell, or group of initial cells,
for the apical or initial cells themselves.

Occasionally intermediate examples are found between the
type with a single well-marked apical cell, and more complex
arrangements. In the sections represented in figs. 4 and 5,
neither the position of that cell which is probably the single
apical cell, nor the arrangement of the tissue round it, give
evidence of the growth having been strictly according to rule.
Thus in the case represented in fig. 4, the three-sided cell
marked (x) does not hold a central position in the section, and
it is of relatively small size : here the appearance of the tissue,
and the arrangement of the surrounding cells, suggest rather
that the four-sided cell marked (x) has performed the function
of an initial cell. Another example of irregularity is shown
in fig. 5, b. The cells marked (x) hold a central position, and
appear to be sister cells ; the surrounding tissue does not point
to any definite regularity of succession of segments cut off
from them.

Of all the modes of arrangement of the cells of the apical

APEX OF THE ROOT IN OSMUNDA AND TODEA.

81

meristem found in Osmunda regalis, that which is perhaps
the most interesting from a theoretical point of view, is that
represented with varying clearness in the figs. 6, 7, and 8.
In each of these figures it may be seen that the whole tissue
is referable in its origin to three initial cells, which are marked
(x), while the three walls separating these cells from one
another meet at a central point. These three walls are drawn
in heavier lines, and may be traced for some distance from the
central point; they may be called the principal walls (p in
the figures, Cf. Hauptwande, Naegeli andLeitgeb). In each
case the portion of tissue derived from one of these initial cells
is enclosed between two of these principal walls, and thus the
whole meristem may be regarded as consisting of three wedge-
shaped masses. Taking now those masses singly into consi-
deration, it will be clearly seen that in fig. 6 each is divided
into two unequal parts by walls marked (s), which do not
proceed to the centre, but on passing towards it curve
gradually out of the radial plane, and insert themselves at
right angles on the principal walls : these may be called the
sextant-walls (Cf. Sextandenwande, Naegeli and Leitgeb.)
A similar arrangement, but less clearly marked, may be seen
in such examples as those represented in figs. 7 and 8. In each
case the error of regarding sections below the real initial cell
or cells as including the initial cells, has been carefully
avoided ; that the fig. 8 actually represents the apical group,
and not apart of the tissue below it, is proved by the fact that
the section includes division walls characteristic of the root
cap, one of which is represented by the dotted line ; this comes
into view only on focussing deeply into the section : the cell
walls drawn in this figure as continuous lines are those seen on
observing the section from the side more remote from the
root cap.

For comparison with this arrangement of the initial cells and
their derivatives I have quoted, as figs. 9 and 10, two of the
drawings of Naegeli and Leitgeb, which appeared in their well-
known work, ‘ Entstehung und Wachsthum der Wurzeln,5 as
Taf. xii, fig. 8, and Taf. xiv, fig. 5. These represent optical

VOL. XXV. NEW SER.

F

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transverse sections of the roots, in the former case of Equi-
setum hiemale, in the latter of Pteris hastata, at points
immediately below the apical cell. The correspondence of
arrangement of the cells in these sections with that of the apical
meristem of Osmunda, as seen in figs. 6 — 8, is undeniable,
though certain irregularities, which are less common in Equi-
setum and Pteris, are frequent in Osmunda. Thus it will
be observed that the sextant walls in the former usually curve
all in the same direction, and are homodr omous, according
to the terminology of Naegeli and Leitgeb (1. c., p. 105) ; they
accordingly insert themselves successively on the three prin-
cipal walls. This is not the rule in Osmunda (figs. 6 and 7),
but a similar irregularity is to be observed in the fig. 9, of
Equisetum, in which two of the sextant walls are inserted on
opposite sides of one of the principal walls. This hetero-
dromous arrangement (Naegeli and Leitgeb, 1. c., p. 105) of
the sextant walls, which appears to be the exception in Equi-
setum, is not unfrequent in Osmunda. The further con-
sideration of this interesting point must be deferred for the
present.

Before leaving the study of transverse sections it may be
observed that they show that the divisions of the segments
which go to form the root-cap appear to be so arranged that,
whatever the form or number of the initial cells, each successive
addition to the root-cap consists of a group of four cells. This
is illustrated in figs. 3 and 7, in which the group of four cells
may be recognised, though derived from initial cells of very
different types. A similar result was obtained by Naegeli and
Leitgeb, in their observations on Equisetum and the
Polypodiacese.

Lastly, I may state that no clear case of four initial cells,
such as have been described by Schwendener for the Marat-
tiacese (1. c.), has been observed by me in any of my prepara-
tions from the root of Osmunda regalis.

APEX OP THE ROOT IN OSMUNDA AND TODEA.

83

Longitudinal Sections.

In organs having a single apical cell, from which segments
of definite form are cut off in regular succession, the position
and appearance of the apical cell itself, and of its segments
when seen in longitudinal section, may be used as a test
whether the longitudinal sections of the apex be accurately
median or not ; but where there is no rigid regularity of form
of the apical cell, or where there may be more than one initial
cell present, the difficulty of judging whether a section be
median or not is greatly increased. I have shown by means of
transverse sections that the latter is the case in Osmunda;
that where a single apical cell is present it is not always of
uniform shape ; and, further, that the number of initial cells
may be as high as three. Moreover, it' is not asserted that the
varieties which may occur are by any means exhausted by the
foregoing description. This being the case it is necessary to
approach the study of longitudinal sections with great caution,
and to subject the results to strict criticism. It is impossible
to expect that there will be uniformity in the arrangement of
the cells, as seen in longitudinal section, and the observations
about to be detailed show that uniformity does not exist. As
in the case of transverse sections, so also in observing longitu-
dinal sections all the approximately median sections cut from
one root were mounted and examined, usually on both sides,
before conclusions were drawn. But beyond the mere diffi-
culty of ascertaining the structure of the varieties of this irregu-
lar meristem, there remains that of suggesting to which of the
types of structure seen in transverse section any given one
seen in longitudinal section most nearly corresponds. I do
not profess to any near degree of certainty on this point,
and where an opinion is put forward it must be understood
that it is advanced only in a tentative manner.

In the majority of cases cells of a pyramidal form have been
found occupying an approximately central position in median
sections; but in no single instance has an apical cell been
observed having that regularity of form, and of arrangement

84

F. 0. BOWER.

I

of its segments, together with the nearly central position
which are so characteristic of the roots described by Naegeli
and Leitgeb. Taking as the first examples (figs. 11, 12) two
of those which approach most nearly to that type, the pyra-
midal apical cells (x) can be readily recognised in each case ;
but a comparison with the figures of Naegeli and Leitgeb
shows certain points of difference. In the first place there is
a difference in the form of the cell itself; it is in Osmund a
proportionately narrower and deeper, that is, more elongated in
a longitudinal direction, and consequently the principal walls
by which it is bounded laterally are less inclined to the longi-
tudinal axis. Secondly, the arrangement of the cells surrounding
the pyramidal cell does not show any definite regularity, and
it is thus difficult to ascertain their genetic connections. This
irregularity is found not only in the tissue adjoining the sides
of the pyramidal cell, but also in those which have been derived
from its base, and will go to form tissues of the root-cap.
Comparing these figures with Naegeli’s, though the similarity
is obvious in its main points, the regularity of detail so charac-
teristic of the plants he described is absent even in these,
which are the most regular examples of the apex of the root
of Osmunda which I have observed.

A further point to be noted in figs. 11 and 12, but which is
much more prominent in figs. 13 and 14, is that in point of
size the wedge-shaped cell is smaller in comparison with the
adjoining cells, than is the case in other Ferns; whereas in
NaegelFs figures the area of the apical cell exceeds that of any
of the surrounding cells, in Osmunda it is as a rule smaller
than they. It may be observed not unfrequently that one
cell of a group, obviously of sister cells, takes the lead in point
of size, the form of such a cell being usually a truncated
pyramid, as shown in fig. ]5 (x). I think it probable that in
such cells we may trace an ascendancy in more than mere
size; in fact they may have, in part at least, the function of
initial cells. This would appear to be more clearly the case in
fig. 13. In the apex represented in fig. 14, the pyramidal cell
is clearly seen ; here, though there is no marked ascendancy of

APEX OF THE BOOT OF OSMUNDIA AND TODEA.

85

the neighbouring cells in point of size, still if the genetically
connected groups of cells, enclosed between the darker marked
anticlinal walls, be taken into consideration as products of
successive segments, it is clear that the function of the apical
cell is comparatively in abeyance, while the formation of new
tissue is conducted with unusual activity by the cells derived
from recent segments. Pyramidal cells, other than the apical
cell, which appear at points removed from the organic centre
(figs. 13 and 14, marked o ), do not seem to have any func-
tional importance different from that of the cells immediately
surrounding them.

From the example shown in fig. 13 to that in fig. 16 the
transition is easy. In the former case there are two rather
irregular pyramidal cells of unequal size (x, x.), in the latter
there are two such cells, of regular form and equal size, which
overlap one another as seen in this section ; there is in the
latter case a greater regularity in the subdivision of the seg-
ments than is usually to be found in the roots of Osmund a.

Lastly, the less common, but very interesting arrangement
shown in figs. 17 and 18 must be mentioned. Here no pyra-
midal cell is to be found; the median longitudinal section
shows two cells (x, x.) of truncated pyramidal form, from which
segments are cut off, (1) from the base, to form tissues of the
root-cap; (2) from the sides, and, (3) as shown in fig. 17, from
the truncated apex also. In this case the correspondence with
SchwendeneFs description of the apical group in the root of the
Marattiacese is very apparent.

It has been demonstrated repeatedly by various authors that
in the cases of Equisetum and many Ferns there is a certain
order of succession and regularity of position of those walls by
which the segments are divided up into smaller cells. A com-
parison of the drawings above quoted, with those of Naegeli
and Leitgeb, will suffice to show that no such regularity is
found in Osmunda, even where a pyramidal cell is present;
the continuity of the procambial tissue may be traced up to a
point close to the apical cell or group of cells, those cells
which are about to form tracheides being easily recognised at

86

F. 0. BOWER.

very early stages (figs. 11, 16, 17, tr .) ; but the outer limit of
the procambial cylinder does not appear to correspond to any
definitely recurring wall in the young segments, as is the case
in the roots investigated by Naegeli. The same may be said
with respect to the limits of the cortex and epidermis ; the
latter tissue, which can readily be recognised in the older part
of the root, and can be traced as entering below the layers of
the root-cap, loses its identity at a considerable distance from
the actual organic axis of the meristem. This fact is illus-
trated in the figs. 11 and 18; in neither of these examples can
a clear distinction be drawn between those cells which will
develop as tissue of the root-cap and those which will form
epidermis, or cortex.

It remains to suggest which of the several types of arrange-
ment seen in longitudinal section correspond to the several
types above described as being seen in transverse sections, but
it must be understood that what follows is only put forward in
a tentative manner. The observation of thick transverse sec-
tions appears to show that where there is a three-sided apical
cell, it is of pyramidal form; whether the same is the case with
four-sided apical cells is uncertain. On the other hand, where
the number of initial cells is three (or possibly in some cases
four), transverse sections lead to the conclusion that they are of
the truncated pyramidal form. Thus it is probable that where
a pyramidal cell is seen in longitudinal section, it is a cell of a
three-sided or four-sided pyramidal form. Probably, also, the
pyramidal cells marked (o) in figs. 13 and 14 correspond to
such cells as those marked also (o) in the transverse sections
fig. 5, b, and fig. 4. Further, on the grounds above mentioned,
it seems probable that arrangements such as those in figs. 17
and 18 correspond to such meristems as those represented in
transverse section in figs. 4 and 7.

A question of considerable importance is whether in the
individual root a transition may occur at any time from one
of these types of meristematic structure to another. That a
number of roots of a given species or individual differ in
meristematic structure from one another is no argument

APEX OF THE ROOT OF OSMUNDiA AND TODEA. 87

against an approximately uniform structure of the individual
root throughout its development. It is impossible to decide
the question with absolute certainty, but some collateral
evidence may be gathered from the study of the origin and
early development of lateral roots; if there be uniformity in
the first divisions of the rhizogenic cells, while there is irre-
gularity of structure in the older roots, a transition of struc-
ture must necessarily have occurred. With the object of
ascertaining this point, the origin of lateral roots has been
investigated, and certain well-marked examples of the arrange-
ment of the early divisions of the rhizogenic cell are shown in
figs. 19 to 22. As is the case in other Ferns, the lateral root
of Osmunda originates from a single initial cell, which
belongs to the endodermis, and is situated opposite one of the
groups of Xylem. Fig. 19 shows how this rhizogenic cell has
divided by walls inclined to one another, so that from the very
first there is a pyramidal apical cell in this young root. Fig.
20 shows a similar pyramidal cell, but in this case the young
root was further advanced, and its apex had penetrated to the
outer limit of the cortex of the main root. On the other hand,
in the young lateral roots represented in figs. 21 and 22 there
are no pyramidal cells to be seen, the young roots in these
cases appear to show an arrangement of initial cells (x, x)
similar to that in figs. 17 and 18. Thus, in the very first
stages of development differences of meristematic arrangement
may appear, which are quite as great as those between the
most extreme types of structure described above for the apex of
the more mature root. This observation, it is true, affords little
more than negative evidence ; we may conclude from it that
since as great varieties of meristematic structure are to be
found in the roots at their first stages of development as those
seen in more mature roots, it is therefore unnecessary to
assume a transition of meristematic structure from one type
to another in the individual root, in order to explain the
differences of structure in the mature root. We have, how-
ever, no evidence which precludes the idea that such a transi-
tion may actually take place ; all the evidence being taken

88

F. O. BOWER.

into consideration, it seems probable, though not proved, that
there is variation in meristematic structure, within certain
limits, in the individual root during its development just as in
Selaginella Martensii, as demonstrated by Treub, the
form of the apical cell is liable in the individual stem to
certain variations of form.

The study of the anomalous structure of the meristem of
the root of Osmund a affords us information as to another
question, which has an important bearing upon views as to the
connection between external form and internal cellular struc-
ture. The question is this — whether any constant relation is
to be found between the bulk of the individual root and the
type of structure of its meristem ? In order to answer this
question for the roots of Osmunda regalis the sections
from which the drawings were made were measured, so as
to express in y^L-g-ths of an inch the transverse diameter of
each root at the level of the apical cell or apical group. The
result of the measurement is attached to each figure. Though
this method of measurement is open to objection, in that it
does not take account of the actual curve of surface of the
apex of the root, still the results thus obtained give at least
an approximate measure of the bulk of the roots. Further,
as median longitudinal sections do not show any considerable
variation of the actual curve of surface, this may be at least
provisionally neglected. A comparison of these measurements,
and of the meristematic structure of the apices in question,
will show clearly that there is no strict and constant relation
between them. Thus, of the three observed examples of a
four-sided cell, one was oQths of an inch in diameter, another
Y^l^ths, and a third T^-0-ths. Conversely, figs. 3, 4, 5, 7, 8,
11, 16, and 18 are all from roots giving within narrow limits
the same measurement. On the other hand, it is worthy of
note that fig. 1 represents almost the smallest, and fig. 14 the
most bulky of the roots investigated. Thus, my observations
do not bear out in detail the idea which suggests itself from a
comparison of the roots of the Polypodi acese with those of

APEX OF THE ROOT OF OSMUNDIA AND TODEA. 89

the Marattiacise, but rather show the great irregularity of
the roots of Osmunda.1

Todea barbara.

For comparison with Osmunda regalis the roots of
Todea barbara were investigated with the following results :
Of a number of apices from which transverse sections were cut
not one showed a clearly-marked single apical cell. Some,
however, showed somewhat irregular arrangements, such as
that seen in fig. 23, in which case it appears uncertain whether
the meristem is referable to three or four initial cells. In a
majority of the roots observed it is clearly referable to four
initial cells (fig. 24), separated from one another by the four
principal walls ( p ).2 The meristem in this case appears closely
similar to that described by Schwendener in the Marattiacese.
Longitudinal sections, however, do not show so close a cor-
respondence to the structure described by him in this group.
Pyramidal cells are not unfrequently to be found, as in fig. 25 }
where two (x) are to be seen in a similar relative position to
those in the root of Osmunda represented in fig. 16. In
other examples, however, the initial cells have the form of
truncated pyramids, as in fig. 26, segments being cut off from
the truncated apex, as well as from the sides and base. This
arrangement probably corresponds to that shown in transverse
section in fig. 24.

The origin of the lateral roots was also observed in this
plant. As before, in Osmunda, the root originates from a
single cell of the endodermis, situated opposite one of the
groups of xylem. A few irregular divisions may also be traced
in adjoining cells of the cortex, but I was unable to ascertain
whether these cells take any active part in the formation of the
root-cap. Occasionally the divisions of the rhizogenic cell are
somewhat irregular, as in fig. 27, but usually the divisions are
symmetrical, as in figs. 28, 29. These two figures, however,

1 This subject will be more fully discussed below.

3 I see no objection to using this term again here, though there are four of
them.

90

F. 0. BOWER.

show that from the very first the initial cells of the young root
are subject to a certain variation of form, being in some cases
pyramidal, in others truncated. Thus, in this respect again,
Todea barbara resembles Osmuuda regalis.

Angiopteris evecta.

In the first place it may be stated that the comparatively
few preparations of the apex of the root of Angiopteris
which I have made, confirm the results of Schwendener’s in-
vestigation. It would be interesting to know, as the result of
a careful and detailed study, whether, under any circumstances,
wedge-shaped initial cells, similar to those occasionally seen in
Todea barbara, are to be found in Angiopteris. The
descriptions of Russow1 and of Holle2 may have had some foun-
dation in irregularities of this sort. In view of the incon-
stancy of form of the initial cells in Osmunda and Todea it
would be rash to assert that pyramidal initial cells never occur
in the Marattiacese, though cells of truncated pyramidal
form appear to be typical in the roots of these plants.

Since the origin of the lateral roots of the Marattiacese
has not hitherto been described, and as the material for this
work was at hand, I have made some observations on this point.
The lateral root of Angiopteris evecta takes its origin,
as in other Ferns, from a single cell of the endodermis, situated
opposite one of the numerous xylem groups (fig. 30). This
rhizogenic cell enlarges, and divides repeatedly by walls per-
pendicular to the outer surface of the main root into a number
of oblong cells, of which four lying at the centre of the group
assume the properties of initial cells. In those cases which
I have had under observation the walls of segmentation of the
rhizogenic cell are not inclined to one another, and the initial
cells are not pyramidal, but always oblong. The mode of
further subdivision of the cells thus produced, and the position
of the initial cells with their segments are clearly seen in fig. 31,
taken from a more advanced lateral root than fig. 30. Fig. 32

1 ‘ Yergl. Unters.,’ pp. 107 — 109.

2 ‘ Bot. Zeit.,’ 1875, p. 301.

APEX or THE ROOT OF OSMTJNDIA AND TODEA. 91

again shows the group of four initial cells, as seen in a trans-
verse section through a young lateral root of about the same
age as that in fig. 31. It is thus shown that the meristem of
the lateral root of Angiopteris evecta assumes its definite
character from the very first, and the four initial cells make
themselves at once apparent. It is thus impossible to obtain
evidence as to the origin of the mode of growth with a group
of initial cells from the mode of their origin in the individual
lateral root, since the character of the meristem is defined from
the very first.

It is worthy of note that cells of the cortex lying around
and outside the rhizogenic cell also undergo occasional and
irregular division, but do not appear to play an important part.
Other cells of the endodermis and cells of the pericambium
also divide freely (fig. 30).

General Consideration of the Results.

The foregoing description of the structure of the meristem
of the roots in Osmunda and Todea shows, in the first place,
that there is no such strict uniformity in these plants as is
found in the roots of Equisetum and the Polypodiaceae,
on the one hand, and, according to Schwendener, in the
Marattiacese on the other. Secondly, the structure of the
meristem, as above described in the Osmundacese, fluctuates
in its characters between those two well-marked types, and
affords numerous intermediate examples between them.1 In
order that those intermediate examples may be duly appre-
ciated, it will be necessary to enter briefly upon the considera-
tion of those two typical systems of construction between which
the Osmundacese oscillate. The first, that typical of the
Polypodiaceae, is shown diagrammatically in fig. 33, which is
quoted from Sachs (f Arbeiten/ Bd. ii, Taf. iv, fig. 12). Here
the periclinal walls in the body of the root constitute an inter-

1 It may be objected that the roots observed may have been in a resting
state, and so the apical cell may have been segmented as described by Sachs

Arbeiten,’ Bd. ii, p. 90). This, however, was not the case, as at least the
large majority of the roots were in a state of active growth.

92

F. 0. BOWER.

rupted series of confocal paraboloidal surfaces, their common
focus being situated in the apical cell itself. The periclinal
walls in the root-cap, in accordance with Sach’s demonstration,
constitute a series of similar curves, which are, however, not
confocal, but are coaxial. Since the anticlinal walls cut the
periclinals at right angles, those in the body of the root, which
cut the confocal curves, present a concave surface to the axis
of growth, while those in the root-cap, cutting the coaxial
curves, present a convex surface (compare Sachs, 1. c., Taf. iv,
fig. 11).

In the second type, according to the description given by
Schwendener, the arrangement differs from the above type in
certain important points, and a diagram may be drawn to show
the scheme of construction as in fig. 34. In this type of
structure there are in the first place walls in two radial planes,
which cut one another at right angles, and their line of inter-
section is the organic axis of the root. The periclinal walls
are none of them confocal, neither those which lie in the body
of the root, nor even those in the procambial cylinder ; they
are, however, all coaxial, and their common axis is the line of
intersection of the radial walls, that is the organic axis. It
will be obvious that the periclinals are necessarily not confocal
in those organs where the apical cell (or the group of initial
cells) has the form of an inverted truncated pyramid, and gives
off segments from the truncated apex of the pyramid (the
lower end), which take part in the formation of the body of
the organ.1 The apparently transverse walls by which succes-

1 In Sachs’s ‘ Vorlesungen,’ p. 556, the following passage is to be found
immediately succeeding an allusion to the apex of the root in the Marattiaceae :
“ Dagegen ist hervorzuheben, dass Scheitelzellen iiberhaupt nur dann im herge-
brachten Sinne moglich sind, wenn die Peri- und Antiklinen confokale Cur-
venschaaren darstellen oder kurz bei confokal gebauten Yegetationspunkten.
Ist der Vegetationspunkt dagegen mit facherformig verlaufenden Antiklinen
durchzogen, ist die Volumenzunahme gegeu den Scbeitel bin am grossten, wie
oben bei fig. 288 gezeigt wurde, dann konnte man unter Umstanden wohl
auch noch in erweitertem Sinne Scheitelzellen annehmen, allein die Schrift-
steller haben in diesen Fallen iiberhaupt nicht von Sheitelzellen geredet, und so
konnen auch wir davon absehen.” In the scheme here constructed for the

APEX OF THE ROOT IN OSMUNDA AND TODEA.

93

sive segments are cut off from the lower ends of the truncated
pyramidal initial cells, form part of successive periclinal curves.
The number of periclinal curves may thus increase to a high
figure ; there is, however, no corresponding increase in the
number of layers of cells in the mature root beyond a certain
point ; thus some at least of these periclinal curves must stop
short, as would naturally be the case if the structure of the
root were of the fan-like type, but maintained its cylindrical
form. A second necessary consequence of the coaxial system
of construction is that it would be impossible to trace the pro-
cambial cylinder with a smooth outer surface up to the apical
group, or in other words, that the pericambium could not be
so traced as a continuous layer of cells, but would be composed
of parts of successive layers. The same may or may not be
the case for the epidermis, according as it is derived from
portions of the lateral segments, cut off by an epidermal wall
(as in the type described by Naegeli), or has a common origin
with the root- cap from the cap-segments. Schwendener does
not speak definitely on this point, but my own observations on
Angiopteris indicate that the latter is the case. If it be so,
then the epidermis must originate in a manner similar to that
pseudo-epidermis described by Strasburger (‘ Conif and Gnet./
Taf. xxiv, fig. 26) in Taxus baccata; it would originate
from portions of successive layers of the meristem, not from
one acropetally continuous layer. It is to be further noted
in connection with the scheme represented in fig. 34, that the
focus of each successive periclinal, by which segments are cut
off from the initial cells to form the body of the root, lies at
the time of segmentation at a point below the group
of initial cells. In the former type, however (fig. 33), it
will be readily seen that the focus or centre of construction
lies in the apical cell itself (Sachs, l. c.).1 Thus in passing

root of the second type above described, we have a case of four initial o
apical cells, giving rise to all the tissues of the organ, while the resulting
tissues are arranged on a coaxial or fan-like system.

1 It will be interesting to observe in this connection that Sachs has drawn
attention to the fact that in Fucus the centre of construction lies outside

94

F. 0. BOWER.

from the first to the second type of construction, there is a
sinking or lowering of the centre of construction; this is still
more apparent if we pass on to those roots in which the
stratified structure (Sadebeck) is more pronounced. In these
types the centre of construction is situated at a still lower
point; since the anticlinals cut the periclinal curves at right
angles, it follows that where the centre of construction is more
depressed, the sides of the apical cell or of the initial cells will
be less inclined to one another, and more nearly parallel than
is the case where the focus lies at a higher point, for instance
in the apical cell itself. The figures of Schwendener clearly
demonstrate that this is actually the case in the Marat-
tiaceae, in which the initial cells appear almost oblong in
longitudinal section. Lastly, it is clear that in our second
type the initial cells may be represented to the mind as being
gaps in the system of construction in just the same sense as the
idea is applied by Sachs to the single apical cell.

Having now defined the two extreme types of construction,
it remains to compare with them the structure of the apical
meristem of the root in the Osmundaceae, and especially in
Osmunda regalis. The form of the apical or initial cells
may fii’st be taken into consideration. In some cases a single
pyramidal apical cell has been found, as in fig. 1, but longitu-
dinal sections always show (figs. 11, 12, 19) that even where
the segmentation is most regular the cell has a narrower
and deeper form than in the roots investigated by Naegeli and
Leitgeb, that is, the lateral walls are less inclined to one another.
This points to a depression of the centre of construction, though
so long as the single apical cell maintains the pointed pyramidal
form that point must be within the apical cell. In connection
with these examples, which conform more nearly to the first type
of construction, those must be mentioned in which two pyra-
midal cells are seen (fig. 16) which correspond not improbably
to an arrangement like that in fig. 13, but cut in a plane oblique

the initial cells, and, indeed, outside the tissue of the plant altogether. This is
exactly the reverse of what is found in the Marattiaceous type of root-
structure.

APEX 0 E THE BOOT IN OSMUNDA AND TODEA. 95

to the radial wall (x). Next may be taken the cell of the form
shown in fig. 20. This is evidently a transition to the form of
the truncated pyramid, the wall adjoining Segment I being
deflected, so as to form at its lower part an oblique ending to
the whole cell. Lastly, those examples may be cited in which
the initial cells have their lower ends (the apices of the pyra-
mids) decidedly truncated, as in figs. 17, 18, 21, 22. These
figures, drawn from longitudinal sections, show a form of the
initial cells and arrangement of the segments which conforms
closely to the Marattiaceous type. Thus, as regards the form
of the initial cells and the arrangement of the segments,
Osmund a provides various intermediate stages between the
two types of construction above described, and the transition
may be connected, as above pointed out, with a lowering of
the centre of construction. Intermediate forms, though
with less gradual transitions, have been observed also in Todea
barbara, where both pointed and truncated initial cells have
been found.

In respect of the arrangement of the initial cells (where
more than one is present), as seen in the transverse section,
Osmund a again shows intermediate characters between the
two types. From the three-sided cell, seen in fig. 1, we may
pass on to those arrangements with three initial cells seen in
figs. 6 — 8. As I have pointed out above, these correspond
closely to the arrangement seen in transverse sections of roots
of the first type of construction at a point immediately below
the apical cell. I would not suggest that the transition from the
meristem with a single three-sided pyramidal apical cell to this
with three initial cells could occur in the individual root, and
I have no evidence that it does ; but, regarding the matter
from a phylogenetic point of view, we may well conclude that
in these examples we see the result of an upward continuation
of the principal walls in radial planes, so as to divide the apical
cell into three parts ; in fact, this may be recognised as an in-
stance of filling up the gap in construction, accompanied, it
must be remembered, by a depression of the centre of construc-
tion. It is hardly necessary to state that this meristematic

96

F. 0. BOWER.

structure with three initial cells is closely related to that with
four. If we remember that a four-sided apical cell has been
observed in Osmunda, and, according to Holle Bot. Ztg./
1875, p. 301), also in Marattia cicutsefolia, a change similar
to that above suggested in the case of the meristem with a
three-sided cell, would in the case of a four-sided cell produce
a structure corresponding to that observed by Schwendener in
the Marattiacese, and by myself in Todea barbara. Here,
instead of three radial walls meeting at a central point, there
would be four such walls. Observation shows, however, that
where this is the case the four walls do not meet exactly at
one point, but slight irregularities are usually found. It is
well known that in the roots of the type investigated by
Naegeli and Leitgeb, the cap-segments divide by radial walls
disposed crosswise into four cells ; a similar arrangement has
been shown to be the result of divisions in the root-cap of
Osmunda (figs. 5, 7), even where the initial cells are of very
different character. It can hardly be a matter of surprise that
this incongruity between the radial walls of the root cap and
those of the body of the root is removed in that type of struc-
ture which appears to be the more permanent. In the Marat-
tiaceous type the first formed radial walls, both in the root-
cap and in the body of the root, are assimilated to one regular
and uniform system, viz. two planes cutting one another at
right angles. The incongruity of the radial walls in those
examples of Osmunda in which there are three initial cells
may be regarded as characteristic of a transitional structure,
and it is not perpetuated in the more constant Marattiaceous
type.

Before passing on to other points, a comparison is to be
drawn between those roots of Osmunda with three initial
cells and the structure of the apex of the stem of Lycopo-
dium Selago, as shown by Strasburger (‘ Das Botanische
Practicum,’ figs. 93 and 94). Here there are also three initial
cells disposed in a manner similar to that observed in the
figures of Osmunda. Thus there are at least two examples
now known of a type of grouping of initial cells, which is

APEX OF THE ROOT IN OSMUNDA AND TODEA.

97

omitted by Haberlaudt in his ‘ Physiologische Pflauzen-
Anatomie’ (p. 45). This type might be intercalated between
that in the stem of Selaginella Wallichii and that of the
roots of the Marattiaceae.

It has already been pointed out in connection with the
Marattiaceous type of structure of the root that a necessary
consequence of a coaxial but not confocal system of periclinal
curves is that some of them at least must stop short if the root
is to maintain its cylindrical form. A careful observation of
median longitudinal sections of both Osmund a and Todea
shows that a more or less abrupt termination of periclinal
curves in a posterior direction, such as may be readily observed
in root-caps, is to be found in these roots, not only in the root-
cap but also in the tissues of the body of the root. Fig. 35,
a and b, show examples from the cortex of Osmunda and
Todea. In the former case, taken from the same root as
appears in fig. 14, the arrangement of the cells strongly
suggests that characteristic of the root-cap, that is a coaxial
arrangement, no less than four periclinal curves terminating
abruptly in a posterior direction within a comparatively short
distance. In fig. b only one of the periclinal curves termi-
nates within the short space represented. If further evidence
be wanted, it may be found by referring to fig. 14, and observing
that the anticlinals present a distinctly convex surface to the
organic axis of the organ.

It was shown that a second necessary consequence of the
coaxial arrangement is that the pericambium at the limit of
the procambial cylinder would not be traceable as a continuous
1 aver up to the initial group. Observations of both Osmunda
and Todea show that this is actually the case ; the pericam-
bium originates, like the pseudo-epidermis of Tax us, from por-
tions of successive layers of cells. It may here be again stated
that it has not been possible to trace the epidermis as a con-
tinuous layer up to the initial group, nor have I been able
to connect the origin of the epidermis with any wall, which
appears in a definite position in each successive segment, as
can be done in the type described by Naegeli and Leitgeb.

VOL. XXV. NEW SKR.

G

98

F. 0. BOWER.

It lias now been amply shown that the structure of the
meristem in the roots of the Osmundaceae possesses characters
intermediate between the two types of construction above
described, and that these characters are not constant even in
roots from a single plant. The question remains whether
there is variation in the individual root from time to time.
Beyond some few cases of irregular structure, I have no evi-
dence of any change of character of the meristem in the
individual root; moreover, the observations on the origin ot
lateral roots show that in both Osmunda and Todea dif-
ferences in the mode of segmentation of the rhizogenic cells
may be found, which are quite as great as those observed in
mature roots. Thus it is possible that the differences of struc-
ture observed in different roots may have had their origin in
differences of the very first segmentation of the rhizogenic
cells. I have, on the other hand, no reason for thinking that,
within limits, variation of structure may not occur in the in-
dividual root.

It cannot escape observation that those roots in which the
coaxial type of structure is most prominent the roots them-
selves are habitually more bulky than those in which the type
of structure is confocal. Are these characters dependent one
upon another? My observations lead me, as above stated,
to the conclusion that as regards the roots of the species
Osmunda regalis, differences of bulk of the roots cannot be
correlated with corresponding differences of meristematic struc-
ture. Still, if we consider such a series of forms as P ter is,
Osmunda, Todea, and Angiopteris, it certainly would
appear that with an increase of bulk of the root there is also
an advance in complexity of the meristematic structure, and a
transition from the confocal to the coaxial type. Thus, a cor-
relation which does not apply in detail for the individual species
appears to hold for the roots of the above series of genera.
As far as may be judged from observations at hand a similar
progression may be traced roughly, but not in detail, for the
meristem of the stem in different species of S elaginella.1

1 Strasburger, ‘Bot. Zeitg.,’ 1873, p. 79, &c. ; Sadebeck, ‘ Handbucb der

APEX OF THE BOOT IN OSMUNDA AND TODEA.

99

Sadebeck recognises among the investigated species two types
of meristematic structure, the first, represented by S. serpens,
S. Martensii, S. hortensis, S. viticulosa, has a wedge-
shaped apical cell, the latter, represented by S. arborescens,
S. Pervillei (= S. Vogelii, Baker), S. spinulosa, S. Lyalii
(= S. laevigata. Baker), has a stratified character. Speaking
generally, the members of the former series are trailing species,
while those of the latter series of species are more robust. S.
Wallichii, investigated by Strasburger, is also one of the
more robust species, and has two wedge-shaped initial cells.
Thus it appears that a greater complexity of meristematic
structure is found also in the species of this genus to accom-
pany a more robust and bulky character. But here again the
correlation is not very close, though it is clearly recognisable,
though this is not the case in the roots of the species O. regalis.
On the ground of the above observations a general conclusion
may be based which applies, at least for the plants above
quoted, viz. that though greater bulk of the organ cannot be
correlated with increased complexity of the meristem in the
members of plants of the same species (Osmunda regalis),
still that correlation can be traced in different species of the
same genus (stem of species of Selaginella), and is clearly
marked in the members of plants from different genera (roots
of the series Pteris, Osmunda, Todea, and Angiopteris).

That the Marattiaceous type of structure of the apex of the
root is an advance towards those types found among the higher
vascular plants is recognised by every recent writer on the
subject. It is interesting to note, however, that the approach
is rather towards that structure which is found to be charac-
teristic of the Gvmnosperms, than to that of other vascular
plants, or even other vascular Cryptogams, such as the Lvco-
podinse. The coaxial mode of construction, which is dominant
in the Marattiaceous type, is clearly represented also in the
roots of the Gymnosperms, while the confocal type is more
characteristic of the roots of Lycopodium and Isoetes.

Botanik’ (Schenk), tom. i, p. 244, &c. ; Treub, ‘ Recherckes,’ &c.; Bruchmann
(ref.), ‘Bot. Centrbl.,’ 1884, No. 46.

100

P. 0. BOWER.

Lastly, this peculiarity of structure of the roots is a cha-
racter, among many others, which points out the Osmun-
daceae as a family of Ferns having a close affinity with the
Marattiaceae. I have elsewhere shown1 that, in the develop-
ment of the leaf, and especially of the apex of the leaf, and in
the conformation of the base of the leaf, the Osmundaceae
approach the Marattiaceae; also that Todea is in certain
character’s nearer to them than Osmund a. The observa-
tions above detailed bear out this conclusion, and though such
details should not be pressed too nearly home, still it should
be noted that while no clear example of four initial cells was
observed in Osmunda regalis, that structure appeared to
be most frequent in Todea barbara. Again, the recent
observations of Goebel (“ Verleichende Entwickelungsge-
schichte,” ‘ Schenks' Handbuch,’ Bd. iii, pp. 387 — 388) leave it
still in doubt whether Osmunda be a Leptosporangiate Fern
or not.2 Thus in a number of characters, perhaps not very

1 ‘On the Comparative Morphology of the Leaf in the Vascular Crypto-
gams and Gymnosperms,’ communicated to the Royal Society.

2 My observations on the Sporangia of Osmunda, as far as they go, confirm
those of Goebel ; but better material was at hand for the investigation of the
development of the sporangium in Todea barbara. Here the essential
parts of the sporangium originate apparently from a single cell, which is, how-
ever, deeply sunk in the tissue of the young pinnule, but is exposed at the outer
surface. It has a square base, that is the cell is not conical ; divisions appear
in it by walls perpendicular to the outer surface. When observed in surface
view from the outside it is seen that four cells result from this division, three
of them surrounding one central cell. This arrangement is not unlike that
in the young sporangium of the Leptosporangiate Ferns ; the chief differ-
ence is that up to this point the sporangium does not project far beyond the
general surface of the leaf. Subsequently a periclinal wall separates a super-
ficial cell from the archespore. The form of the archespore is a matter of
some interest. Here, as in the case of the apical cell of the root, there is
not exact uniformity ; it is sometimes conical, sometimes rectangular. This
variation depends upon the varying inclination of the three anticlinal walls,
one to another ; in some cases they are nearly parallel, and the result is that
the archespore in these examples has a square base ; in other cases they are
inclined, and may meet one another below ; the result is then a conical arche-
spore. This appears to be the case also in Osmunda, judging from Goebel’s
figures (1. c., figs. 103a and b), and is no doubt to be connected with the

APEX OF THE BOOT IN OS1HJNDA AND TODEA. 101

significant when considered individually, the Osmundacese
are distinguished from the mass of the Leptosporangiate Ferns,
and show themselves to be the nearest of all other groups of
Ferns to the Marattiaceae.

DESCRIPTION OF PLATES VIII & IX,

Illustrating Mr. F. O. Bower’s memoir “ On the Apex of the
Root in Osmunda and Todea.”

All the figures, excepting Figs. 9, 10, 15, and the diagrams. Figs. 33 and
34, were drawn with camera lucida, under objective c, Zeiss, ocular 4 ; but
the drawings have been reduced by the lithographer to two thirds their original
size ; the magnifying power is thus two thirds of 325, that is about x 216.
In all cases the results have been controlled by observation under higher
powers, viz. Zeiss’s objectives d d, and, when necessary, f. The numbers
attached to some of the figures show the diameter of the root at the level of
the initial cells, measured in y^oths of an inch. The apical cell, or initial
cells, are marked (x).

Osmunda regalis. — Figs. 1 — 8 and 11 — 22.

Fig. 1. — Slightly oblique transverse section, showing a three-sided apical
cell with regular segments.

Fig. 2. — Four-sided apical cell, as seen in transverse section, with three
segments.

Fig. 3. — Four-sided apical cell, with regular segments i — iv; but segment
v is cut off from the same side as iv. The dotted lines indicate the walls of

fact that the sporangium is here more deeply seated in its early stages than
in most other Ferns. That this is an intermediate form between that of the
truly Leptosporangiate Ferns and that of the Harattiacea is obvious. In
Angiopteris, Goebel has demonstrated an archespore with a square base (cf.
‘ Systematik,’ p. 284, fig. 208), and such a form is only to be expected where
the insertion of the sporangium is proportionately broad and the curvature of
the outer surface slight.

Further details, together with figures, will be published later.

102

F. 0. BOWER.

division in the root-cap. The section being a thick one, these walls could be
seen by focussing deeply into the section.

Fig. 4. — Three-sided apical cell, segments less regular, and the apical cell
itself is of comparatively small size. The square cell marked (x) may be
assuming the function of an initial cell.

Fig. 5. — a. Section through the root-cap. b. Section from the same root
immediately below a. b shows an irregular arrangement of the meristem,
with apparently two initial cells (x).

Fig. 6. — Three initial cells, separated by principal walls, p.p. Sextant
walls marked s. s.

Fig. 7. — A similar section immediately below the root-cap. By focussing
deeply the wall represented by the dotted line appears ; this is a division in
the root-cap.

Fig. 8. — A similar section, but less regular.

Fig. 9. — Quoted from Naegeli and Leitgeb, Taf. xiv, fig. 5. A transverse
section of the apex of the root of Pteris hastata, s. to., as seen by focus-
sing below the apical cell. p.p. = the principal walls, s.s. the sextant
walls, which are in this case homodromous.

Fig. 10. — Quoted from Naegeli and Leitgeb, Taf. xii, fig. 8. Transverse
section of the apex of a root of Equisetum hiemale, immediately below
the apical cell. The sextant walls are here heterodromous.

Fig. 11. — Median longitudinal section, with pyramidal apical cell. tr. =
cells developing as tracheides.

Fig. 12. — A similar section.

Fig. 13. — An irregular meristem : apparently two pyramidal initial cells of
very unequal size.

Fig. 14. — Very irregular meristem, with a pyramidal apical cell (x). Seg-
ments undergoing repeated periclinal division. Note the curvature of the
anticlinal or principal walls.

Fig. 15. — (x 370.) The products of the development of one segment,
showing how one cell (x) takes the lead ; the arrow shows the direction of the
organic axis.

Fig. 16. — Section showing two pyramidal initial cells of equal size.

Fig. 17. — Two oblong initial cells ; segments are cut off by periclinal walls
from the lower end of them, as well as from the upper end and sides.

Fig. 18. — Two similar initial cells with segments.

Fig. 19.— A group of cells, derived by division from one rhizogenic cell of
the endodermis. (x) The pyramidal initial cell of this very young lateral
root.

Fig. 20. — Apical meristem from a young lateral root, which has extended
to the outer surface of the cortex of the main root.

Fig. 21. — Young lateral root, with two oblong initial cells, xy. — the
xylem of the main root. p. = pericambium.

Fig. 22. — A similar preparation of a young lateral root.

APEX OF THE ROOT IN OSMUNDA AND TODEA. 103

Todea barbara. — Figs. 23 — 29.

Fig. 23. — Transverse section, showing an irregular arrangement of the
meristem.

Fig. 24.— A well-marked meristem in transverse section, showing four
regular initial cells.

Fig. 25. — Longitudinal section, showing two pyramidal initial cells.

Fig. 26. — Lougitudinal section, with two oblong initial cells.

Fig. 27. — Group of cells, derived by irregular division from one rhizogenic
cell of the endodermis.

Fig. 28. — The same, but the division in this case is regular ; two almost
square initial cells.

Fig. 29. — Apical group, from a rather older lateral root, showing two
pyramidal initial cells.

Angiopteris evecta. — Figs. 30 — 32.

Fig. 30. — Transverse section of a main root, showing the mode of origin
of a lateral root from one cell of the endodermis ( e . e.), also the xylem of the
main root, and divisions in the pericambium ( p .) and cortex ( c .). In the cells
derived by division from the rhizogenic cell, two (x) may be recognised as the
initial cells.

Fig. 31. — Group of cells of the lateral root, derived from a single rhizo-
genic cell : the oblong initial cells marked (x).

Fig. 32. — A section transverse to the axis of a very young lateral root, still
embedded in the cortex of the main root. It shows the four initial cells (x)
as described by Schwendener.

Fig. 33. — Scheme of construction of the apex of a root with a three-sided
pyramidal apical cell, quoted from Sachs’s * Arbeiten,’ Bd. ii, Taf. iv, fig. 12.

Fig. 34. — Scheme of construction of a root of the Marattiaceous type.

Fig. 35. — a. A small portion of the young cortex of the same root of
Osmunda regaiis as is represented in Fig. 14. B. A small portion of the
young cortex of Todea barbara. The arrows point towards the apex of
the roots.

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MORPHOLOGY OF WELWITSCHIA MIEABILIS.

105

Correction of an Error as to the Morphology of
Welwitschia Mirabilis.

By

F. O. Bower.

At the conclusion of the second article on Welwitschia
mirabilis communicated by me to this Journal (vol. xxi,
New Series, 1881, p. 571), a postscript was appended, which
suggested a possible explanation of the discrepancy between
my observations of the process of development of this remark-
able plant, and those of M. Naudin, who communicated an
account of the germination of the same plant to the ‘ Gar-
dener's Chronicle/ August 13th, 1881. The origin of the dis-
crepancy was, however, soon after explained by a second letter
from M. Naudin, published in the ‘Gardener’s Chronicle/
January 7th, 1882, which began as follows : “ I find that by an
accident, the seedling which I took to be that of Welwit-
schia, having sown the seed as such, and which I described in
your columns (1881, vol. xvi, p. 217), is really not a Wel-
witschia at all; all my Welwitschias (true) died, &c.”

I had intended that this matter dealt with in my postscript
should have died a natural death, and I should not have again
returned to it, had it not been that in the reference to my
article above quoted, which appears in the ‘ Botanischer
Jahresbericht/ for 1881, Erste Abtheilung, Heft ii, p. 459,
altogether undue prominence is given to the subject, by intro-
ducing it thus : “ Das wichtigste in morphologischer Hinsicht
bringt ein Postscriptum whereas, when the facts are known,
this is the least important part of the whole article.

Since there has been this misunderstanding, it may be well
here to state briefly what the actual succession of members is

106

F. 0. BOWER.

in the seedling of Wei witschia. In all the specimens which
I have examined, the following succession of members has been
observed : (1) two cotyledons, which are present in the mature
embryo ; (2) two plumular leaves decussating with the coty-
ledons, and capable of unlimited basal intercalary growth ; (3)
two structures, which appear between the plumular leaves, and
which I regard as buds in the axils of the cotyledons ; these
together form at least the great bulk of the crown ; (4) the
apical cone of the main axis, which remains rudimentary, and
bears no further appendicular organs. In all the plants at
Kew which have lived long enough, the cotyledons, after their
expansion during the early stages of germination, remain for a
considerable time persistent, without further increase in size
beyond a limit attained at an early period. Later they dry up,
and wither, leaving behind them dried tatters of tissue, like
those represented in ‘ Quart. Journ. Micr. Sci./ 1881, pi. iii,
fig. 10. There are now living in Kew three plants of the
original set sown in August, 1880. Each of them has lost its
cotyledons in this way, but retains the ragged remnants of
them. The plumular leaves of these plants have grown to a
very considerable size, but are subject to progressive dis-
organisation of their tips, so that their present length (about
3 to 6 inches) does not represent the whole extent of their
previous growth. The two lobes of the crown (axillary buds)
have also grown to a considerable size, and have assumed the
appearance represented in ‘Quart. Journ. Micr. Sci.,’ 1881,
pi. xxxii, fig. 3.

Since all the plants germinated at Kew have developed in
the same way, and since the plant described by M. Naudin was
not aWelwitschia at all, the suggestion as to an alternative
mode of development is now entirely unnecessary, and may be
withdrawn. Such a suggestion would never have been made,
had not the observations communicated to the ‘ Gardener’s
Chronicle ’ been contributed by a botanist of such standing as
M. Naudin. It may be now concluded that there is but one
type of development of Welwitschia mirabilis, and that
the type described by me from the plants grown at Kew.

MATURATION AND FECUNDATION OF THE OVUM. 107

E. Van Beneden’s Researches on the Maturation
and Fecundation of the Ovum.1

By

J. T. Cunningham.

Fellow of University College, Oxford ; Superintendent of the Scottish Marine

Station.

With Plate X.

A great many elaborate researches have been made in
recent years into the series of phenomena in ova and sperma-
tozoa which precede and accompany fecundation. By the
synthesis of these it has been found that the series of phenomena
is in almost all cases essentially the same ; the more accurate
the research, the more similar have the phenomena appeared in
different animals. With regard to the ovum, the formation of
polar globules is the most constant and most conspicuous
event of its history previous to fecundation. Some years ago
it was firmly established that there is a very great similarity
between the changes which the germinal vesicle undergoes in
the formation of polar globules, and the process of karyokinesis
in cell-division.

At an earlier period it had been held that the germinal vesicle
disappeared, and no connection had been surmised between that
structure and the polar globules. These globules were regarded
as unimportant drops of viscid substance expressed from the
vitellus. In 1875 Biitschli'3 first described a spindle in an
unfertilized ovum. It was observed in the egg of Cucullanus

1 ‘Arch, de Biologic,’ 1883.

5 ‘ Z. f. w. Z.,’ vol. xxv.

108

J. T. CUNNINGHAM.

elegans, and he was unable to prove that it gave rise to a polar
globule, but he believed that the spindle and the extruded
globule were identical, and that the spindle arose from the
germinal spot. Biitschli's observations initiated a series of
researches which threw a great deal of light on the history of
the germinal vesicle. The most complete and trustworthy
investigations were those of Fol and O. Hertwig ; they
declared that the polar globules were formed by a process
identical with that of cell division and were equivalent to cells.
Balfour, who never formed hasty conclusions, fully accepted
this doctrine. Another result obtained by O. Hertwig was
that the two pronuclei in the ovum, the male and female, united
to form a single nucleus, before the commencement of the
first segmentation.

The elaborate investigations of Van Beneden into the history
of the ovum in Ascaris megalocephala have led to results
which are in direct contradiction to the prevalent conception.
He has satisfied himself (1) that the processes which accom-
pany the formation of polar globules are fundamentally
different from the processes of normal karyokinesis, that there-
fore the formation of polar globules is not a case of cell
division; (2) that the two pronuclei do not unite together to form
a single resting nucleus : what really takes place is that each
pronucleus behaves as a nucleus about to divide, and that the
chromatic V shaped loops and achromatic fibrils formed in each
contribute to form a single karyokinetic figure. In these two
points then Van Beneden is in opposition to those authors who
have hitherto been regarded as most authoritative. He has
made a complete study of the subject with what seems to be
eminently favorable material, and gives a detailed account of
several steps which have before been left in some obscurity.
It is therefore important as well as extremely interesting to
examine his figures and descriptions and to enquire, firstly, if
his conclusions are well founded, and, secondly, what relation
his results bear to our knowledge of the life-history of the cell
and of reproduction.

Material. — Ascaris megalocephala is a Nematode of

MATURATION AND FECUNDATION OF THE OVUM. 109

considerable size (average 25 cm. in length), found in large
numbers in the intestines of horses. It can easily be obtained,
especially in winter (at Liege), in the living condition in any
numbers required. The preparation of its ova is effected with
great ease : its spermatozoa are large, non-motile, and conspi-
cuous; lastly, from a single female a large number of ova in
each successive stage can be obtained, from those still in the
ovary to those which have begun to segment. In order to
expose the sexual organs all that is needed is to slit the animal
longitudinally with scissors. The maturation and fecundation
of the ovum take place during its slow passage down the oviduct
and uterus, the latter of which contains large numbers of
spermatozoa. A given stage of development occurs at a
certain position in the sexual tube, so that by taking a small
portion of the tube thousands of eggs are obtained all in the
same stage. The uterus is fifteen to twenty cm. in length, and
the ova come into contact with the spermatozoa at its upper
end. With regard to the penetration of the male element
the author remarks, ‘ II est facile de demontrer en cinque
minutes, non pas seulement a des histologistes experimentes,
mais au dernier des profanes, la penetration du zoosperme.

Methods. — 1. By examining the eggs fresh, either in
Kronecker’s artificial serum (distilled water 100, NaCl 6,
HNaO '06j or in the liquid of the body of the Ascaris, all the
phases of the penetration of the spermatozoon can be made
out : in the oldest ova the various membranes, the two polar
globules, and the pronuclei can be seen, but the details of the
changes cannot be made out in fresh eggs.

2. One of the methods which gave the best permanent pre-
parations was to kill the ova with nitric acid 3 per cent.,
leave them in this for one hour, then wash with water, place
one or two hours in alcohol 33 per cent., then transfer to
alcohol 70 per cent. For younger ova it is necessary to open
the uterus and prepare the ova on the slide ; for the ova at the
inferior end of the uterus this is not necessary. For staining
after the use of nitric acid, borax carmine, fuchsine, and
methyl green gave the best results.

110

J. T. CU^INGHAM.

3. Fix with alcohol 33 per cent, only, transfer to 70 per
cent., stain with picrocarmine or borax carmine, mount in
glycerine or balsam.

4. Osmic acid, picrocarmine ; mount in picrocarminated
glycerine. This method does not serve for eggs with complete
envelopes.

5. Glacial acetic acid may be used for fixing, but is not
recommended.

6. For the oldest eggs the author found at the end of his
researches that the only method was to place living females in
weak alcohol. The older eggs with thick membranes go on
developing for a certain time, till, after some months, the
alcohol kills them, and then fine preparations, showing the
pronuclei and the early stages of segmentation, are obtained
by staining with picrocarmine and mounting in glycerine.

1. First Period of the Maturation of the
Ovum.

This stage includes the development of the ovum in the
ovary and its changes in its passage down the oviduct, until,
arrived at the upper part of the uterus, it is ready to receive
the spermatozoon. The author has given a great deal of
attention and considerable space in his memoir to the struc-
ture of the ovum, on account of the interest attached to the
question — Can the position of the embryo be recognised in the
ovum even before segmentation ? Some indication has been
given by recent researches of Van Beneden himself and others
that this question may be answered in the affirmative ; that in
the ovum of a bilateral animal a right and left side can be
found corresponding to the right and left side of the embryo,
and similarly an anterior and posterior end. The author found
two years previously that in the ovum of Corella paral-
lelogramma, a simple Ascidian, from the first phases of
segmentation, the median plane of the embryo, its anterior
and posterior ends were fixed. Facts of a similar kind have

MATURATION AND FECUNDATION OF THE OVUM. Ill

been made known by Rabl, 1 Hatschek, 2 Roux, 3 and
Rauber.4

The eggs at the lower end of the oviduct, in the condition
in which they receive the spermatozoon, take, when liberated
on a slide in an indifferent liquid, the form of an ovoid. There
is little difference between the length of the longer axis of the
ovoid and the shorter. In the ovum a morphological axis can
be distinguished with dissimilar poles ; this axis coincides with
one of the shorter axes of the ovoid. At one of its poles there
is a slight projection of the substance of the ovum; this pro-
jection is limited by a circular outline, and it is to the centre
of the projection that the spermatozoon attaches itself. This
pole of the axis may therefore be named the pole of impreg-
nation, while the opposite end is called the neutral pole.
In order to see well the structure of the ovum it must be
examined a little before it has reached the lower end of the
oviduct. The slightly projecting portion may be called the
polar disc. The portion of the vitellus beneath the disc is
more sombre than the rest, and is called the central medulla.
This is enveloped, interiorly, by a layer of the vitellus, a little
more transparent, which reaches the surface of the ovum in a
zone all round the polar disc, distinguished as the parapolar
region. This second layer of the vitellus is the intermediate
layer. Finally enveloping the intermediate layer in its lower
portion is a cortical layer of vitellus, the most transparent of
all, which extends to the surface of the ovum from the neutral
pole to the limit of the parapolar region. This limit between
the cortical layer and the parapolar region, is the parapolar
circle. The germinal vesicle lies in the intermediate layer
close to the inner surface of the cortical layer.

When the ovum leaves the rhachis of the ovary it has the
form of a mallet ; the extremity of the handle of the mallet is

1 ‘ Jena. Zeit.,’ Bd. x.

2 ‘ Arb. Zool. Inst., Wien,’ Bd. iii.

3 ‘ Zeit. der bestimmung der hauptrichtungen des Freschembryos,’ Leipzig
1883.

* ‘Zool. Anz.,’ 1883, No. 147.

112

J. T. CUNNINGHAM.

the region at which the polar disc is formed. Nearly the
whole of the handle of the mallet is occupied by the interme-
diate layer, and its surface is the parapolar region. The ovum
assumes the ovoid form by the gradual shortening of the
handle of the mallet and the consequent decrease in extent of
the parapolar region.

When the polar disc first appears it has some affinity for
carmine : it exhibits a striation perpendicular to its surface,
and contains none of the deuteroplasmic elements. After a time
in the polar disc two layers can be distinguished : the super-
ficial is not stained by picrocarmine. This achromophilous
layer collects towards the centi’e of the disc, and there the
chromophilous layer thins out, and finally disappears. Mean-
time the vitelline membrane forms as an extremely thin layer
all over the ovum, including the polar disc, but not over the
achromophilous layer in its centre. This mass remains bare,
occupying an aperture in the vitelline membrane — the micro-
pyle, from which it usually projects slightly. This projecting
mass of clear protoplasm van Beneden calls the plug of im-
pregnation.

The vitellus contains deuteroplasmic elements of three kinds,
which can be distinguished after treatment with osmic acid
and picrocarmine. They are (1) hyaline spheres, (2) homo-
geneous droplets, and (3) refringent corpuscles.

The hyaline spheres are definite in outline, and slightly
tinged with the carmine ; they show no structure ; within them
are usually smaller spheres like vacuoles.

The homogeneous droplets are of indefinite outline and
irregular shape, and are probably spaces in the protoplasm of
the vitellus, filled with fluid or semifluid substance.

The refringent corpuscles are definite in outline, somewhat
angular in shape, and highly refractive. They are often
arranged in series, and contribute to give the vitellus a radiate
striation, the series converging towards the centre of the
ovum.

The protoplasm forms a continuous thin external layer round
the vitellus, and fills up the spaces between the formed elements.

MATURATION AND FECUNDATION OF THE OVUM. 113

Examined with T‘T homogeneous immersion of Zeiss it is seen
to be finely punctated, and the points are united by slender
threads. The protoplasm is in fact, as has been discovered by
many histologists in animal cells, made up of a reticulum of
moniliform threads. There must be an interfibrillar substance
filling up the meshes of the reticulum.

Nothing is said upon the question whether the ovum is
attached to the rhachis by the end of the tail of the mallet, or
by some other point. This is a question of some importance,
because in some animals, e.g. Lamellibranchs, the micropyle
is formed by the pedicle of attachment of the ovum.

Vitelline Membrane. — In the ova, already detached,
taken from the lower part of the ovary, there is no vitelline
membrane, so that in this animal the formation of the micro-
pyle is not due to the presence of a pedicle of attachment.
Meissner1 has stated that in the nematode egg studied by him,
the micropyle was formed in the way indicated, while other
authors have denied the existence of any membrane before the
entrance of the spermatozoon. In Ascaris megalocephala,
although it is usually impossible to detach a membrane before
the entrance of the male element, it is certain that the external
layer of the vitellus has before that period become differentiated
and resistant. Ova, when ready to receive the spermatozoon,
do not flatten out in all directions as they do at an earlier stage,
but the vitellus escapes at the pole of impregnation. Imme-
diately after a spermatozoon has attached itself to the plug of
impregnation a membrane is present which becomes separated
from the parapolar region and the polar disc during preparation.
In unfertilized females a membrane is formed round the ovum.
It may be concluded then that the vitelline membrane is not
formed in consequence of fecundation.

The Germinal Vesicle, whose position in the ovum has
already been indicated, appears in the fresh state as a clear
space in the vitellus containing a dark spot, the germinal spot
or nucleolus.

In ova treated with osmic acid and picro-carmine (see fig. 1,P1.

1 ‘ Z. f. w. Z..’ Bd. v, 1853.

VOL. XXV. NEW SER.

H

114

J. T. CUNNINGHAM.

X), the germinal vesicle is very conspicuous ; it is coloured uni-
formly pink, is of spheroidal form, and apparently homogeneous.
The germinal spot is a brilliant deeply-stained spherical glo-
bule, with a regular contour. It is situated near the periphery
of the vesicle, and is surrounded by a spherical mass of sub-
stance distinct from the rest of the vesicle. This envelope of
the germinal spot is more deeply stained than the rest of the
vesicle, and remains distinct throughout the changes of the
latter. It is named by van Beneden the prothyalosoma, the
rest of the vesicle being called the accessory portion. Nearly
always in the accessory portion there are one or two formations
similar to the prothyalosoma, each containing a “pseudo-
nucleolus j” these disappear during the changes which the
vesicle undergoes.

The prothyalosoma projects slightly beyond the general
surface of the germinal vesicle. Round the vesicle there is a
distinct membrane : the layer within this occasionally shows
minute granulations. In preparations obtained by treatment
with nitric acid and borax-carmine the germinal spot appears
not as a single body but as a group of small globules. The
author believes that the germinal spot is always composed of
two discs in close apposition, each disc consisting of four
globules. The globules are connected by a substance with less
affinity for staining substances than the globules themselves.

In ova perfectly ripe for fertilization treated with alcohol
and borax carmine, the nucleolus appears as a group of numerous
globules in which no definite arrangement is seen. The acces-
sory portion presents a punctated appearance, and the small
granules to which this is due are arranged in rows resembling
moniliform threads of protoplasm. These rows of granules are
chiefly derived from the transformation of the membrane.
Similar rows of granules connected by very fine threads are
also to be seen in the prothyalosoma.

In ova which are perfectly ripe, whether treated with nitric
acid or alcohol, the spherical shape of the vesicle is deformed
bv the intrusion of a homogeneous droplet on each side so that
the vesicle appears in optical section in the form of a T.

MATURATION AND FECUNDATION OF THE OVUM. 115

The result then of the author’s study of the germinal vesicle
before fecundation is as follows.

Before the ovum is quite mature, that is to say, some little
time before it has reached the upper part of the uterus, the
vesicle is spherical and bounded by a thin achromatic mem-
brane. As maturation progresses traces of a spindle of achro-
matic fibrils are observed in the neighbourhood of the germinal
spot; the fibrils are situated in the prothyalosoma, and are
continuous with the chromatic discs of the spot. Nothing is
to be seen resembling the convoluted chromatic filaments which
appear in nuclei about to divide. The action of picro-carmine
shows that chromatin is diffused to a slight extent throughout
the vesicle. The pseudo-nucleoli behave towards staining
fluids somewhat otherwise than the germinal spot. The
germinal spot is in contact with the interior of the membrane
of the vesicle. The accessory portion is composed of a denser
substance next to the membrane and an internal more fluid part.
Towards the time of the entrance of the spermatozoon some of
the fluid contents passes out from the vesicle, and it therefore
loses its rotundity and becomes smaller. Gradually both the
membrane and the cortical layer of the accessory portion resolve
themselves into delicate moniliform threads similar to those of
the protoplasm of the vitellus. A similar change takes place in
the substance of the prothyalosoma, but a little later. The vesi-
cle is altered in shape by the intrusion of vitelline elements, and
appears T shaped. This is the whole extent of the changes
which take place before the entrance of the spermatozoon (see
fig. 2, PL X. Into the ovum represented a spermatozoon has
already penetrated; but the condition of the germinal vesicle
shown may be reached before the contact of^the male element).

The author gives some details concerning the ova of unfer-
tilized females, but he says nothing about the formation of polar
globules in such ova which is the most interesting point.

Spermatozoa in the Uterus. — Spermatozoa are found
in numbers in all parts of the uterine epithelium ; but they
occur in greatest abundance in the upper extremity of the tube
where the ova first meet with them. Since the uterus is dis-

116

J. T. CUNNINGHAM.

tended with ova, the spermatozoa would be carried down by the
descent of these if they were not protected in the deep furrows
and depressions of the uterine epithelium. A large number in
excess of those which effect an entrance into ova are carried
down mechanically, but as these unattached spermatazoa
diminish in number towards the lower end of the uterus, they
probably pass up again along the epithelium by means of their
amoeboid movements.

Structure of Spermatozoon. — The ripe spermatozoon
consists of two parts :

(1) A head of hemispherical shape enclosing a nucleus com-
posed of chromatin only. Round the nucleus is a perinuclear
layer finely punctated and with no distinct boundary, and
external to this is a cortical layer composed of a reticulum of
moniliform threads.

(2) A tail which may have one of various shapes. The tail
is enveloped by a membrane which ends in a free border where
the head and tail join, the head being destitute of membrane.
The substance of the tail is iu the young state entirely proto-
plasmic, but in older spermatozoa contains a refringent body of
larger or smaller size ; a layer of protoplasm persists between
the membrane and the refringent body.

The structure of the protoplasm of the head is easily seen,
and the author takes occasion to point out that, according to
researches of his own, the fibril of a striated muscular fibre
has a structure similar to that of the moniliform fibrils of this
protoplasm. He thinks it probable that such a structure is
common to all protoplasm.

The spermatozoa when first introduced into the female
organs are spherical in shape and completely destitute of
refringent body. One half of the sphere is covered by a layer
of substance in the form of a cup which is more homogeneous
than the rest of the sphere. This cup grows out into the form
of a papilla, and increasing in size gives rise to the tail. The
first stage of its growth gives the spermatozoon a pyriform
shape; then by farther elongation of the tail the whole appears
like a bell suspended by a string ; this is the campanuliform

MATURATION AND FECUNDATION OF THE OVUM. 117

stage. The interior of the tail is formed by a prolongation of
the cortical layer of the protoplasm of the head ; in this internal
protoplasm at the campanuiiform stage the refringent body
begins to develop ; it is at first linear. At the lower end of
the refringent body is a plate of homogeneous substance still
more refringent, called the limiting plate. Finally, by the
increase in thickness of the refringent body the shape of the
spermatozoon becomes conoid. It is at this stage that the
membrane becomes distinctly visible. The head of the sper-
matozoon can throw out amoeboid processes. The head
uncovered by membrane corresponds to the plug of impregna-
tion in the ovum, while the external protoplasm of the tail
corresponds to the cortical layer of the vitellus. The sperma-
tozoon can effect fertilization either at the pyriform, campanu-
iiform, or conoid stage (see Plate X, fig. 3).

II. — Penetration of the Spermatozoon or
Copulation of the Sexual Elements.

The penetration of a spermatozoon into the vitellus does not
in itself, as is now well known, constitute fecundation. In
many ova, as in the present case, a great many processes take
place after the entrance of the spermatozoon, before the for-
mation of the segmentation nucleus. In other cases the
period between the two events is shorter, the polar globules
being ejected before the spermatozoon enters. Van Beneden,
therefore, distinguishes the two events as copulation of the
sexual elements, and actual fecundation.

Notwithstanding the attention which has been paid to the
phenomena of fecundation recently, these researches of Van
Beneden are the first which have traced the history of the
spermatozoon in a Nematode ovum. Biitschli1 and Auerbach1
were the last investigators who concerned themselves with the
reproduction of Nematodes, and they obtained no information
as to the fate of the spermatozoon after its contact with the
ovum. So recently as 1883, A. Schneider,1 who specially

1 For the earlier literature, vide Balfour, ‘Comp. Emb.,’ vol. i.

118

J. T. CUNNINGHAM.

studied Ascaris megalocephala, denies the existence of a
male pronucleus; he states that the spermatozoon is entirely
absorbed by the vitellus, and that the two pronuclei are formed
by the division of the germinal vesicle.

In the immense majority of cases only one spermatozoon
penetrates into the vitellus. Having examined preparations
which Prof. Van Beneden kindly sent me, I am convinced of
the perfect accuracy of what he says on this point.

In the earliest stages a spermatozoon is seen fixed by its
head to the plug of impregnation ; in the next stage half
immersed in the vitellus, in the next completely immersed.
Thei’e is no uncertainty as to the identification of the sperma-
tozoon ; its size enables it to be seen with a low power, its
refringent body distinguishes it from all the elements of the
vitellus. Before entering an ovum a spermatozoon fixes car-
mine only in its nucleus, the moment it attaches itself to the
plug of impregnation all its protoplasm is affected by the
staining solution. Thus it is possible, without the evidence
afforded by focussing, to distinguish immediately between a
spermatozoon simply attached accidentally to the surface of the
ovum and one actually in the interior of the vitellus.

In one or two instances two spermatozoa were seen within the
vitellus ; but the question whether both of them form male pro-
nuclei which unite with the female pronucleus was not decided.

The author points out that it has not yet been proved for all
animals that fertilization is effected normally by a single sper-
matozoon. In Echinoderms, Fol and Hertwig have shown
that only a single spermatozoon enters the ovum. In Ascaris
megalocephala and Petromyzon,1 according to Calberla, the
micropyle is closed by the spermatozoon itself. Kupffer and
Benecke,2 on the other hand, describe the entrance of several
spermatozoa into the ovum of Petromyzon ; and there are
numerous published researches to support either side of the
controversy. But it has never been proved in the ovum of
any animal that the formation of more than one male pronucleus

1 Calberla, ‘ Z. f. w. Z.,5 Bd. xxx.

1 ‘ Vorgang der Befruchtung im Ei von Petromyzon,’ Konigsberg, 1878.

MATURATION AND FECUNDATION OF THE OVUM. 119

is a normal occurrence. Fol has shown that in Asterias two
male pronuclei are sometimes formed, and give rise to ab-
normal segmentation and abnormal larvae.

In prepared eggs of Ascaris megalocephala, in which a
spermatozoon is attached to the plug of impregnation, a space
is often seen between the vitelline membrane and the vitellus
in the region round the micropvle. This lifting of the mem-
brane never occurs at later stages, or at other parts of the
vitellus. The author discusses very fully the literature on the
subject of micropyles, pointing out that in very few cases has
it been proved that the micropyle, when it exists, forms the
exclusive means of entrance for the spermatozoon. For the
bibliography of this subject the reader may refer to Van
Beneden’s work, and to Balfour, ‘ Comp. Embryology/ vol. i.
Van Beneden is inclined to believe that every ovum has a
morphological axis, at one end of which a single spermatozoon
enters ; but he does not maintain that this has yet been
proved.

After the spermatozoon has fixed itself to the plug of im-
pregnation (the two elements uniting by their homologous
poles), the latter descends towards the interior of the vitellus,
taking the spermatozoon with it. The head of the spermatozoon
executes amoeboid movements, which aid its penetration. When
the head has passed the micropyle, the membrane covering
the tail unites with the vitelline membrane so as to close the
aperture ; and the complete membrane is called the oosper-
matic envelope. As the spermatozoon advances into the in-
terior of the vitellus the membrane follows it, so that when it
is entirely immersed there is a very slight prominence to show
where it entered. After the spermatozoon has entered, its
protoplasm becomes less granular ; its nucleus is less refrin-
gent and less deeply stained. Apparently some of the chro-
matin of the nucleus diffuses through the protoplasm of the
head.

After the spermatozoon is completely immersed it is impos-
sible to distinguish either plug of impregnation or polar disc.
The penetration of the spermatozoon is effected, at least in part.

120

J. T. CUNNINGHAM.

by the contraction of the protoplasm of the plug of impregna-
tion, the fibrils of -which run into the interior of the egg.

III. — Formation of Polar Globules.

Here again the author gives a critical review of the litera-
ture, of which the chief points are : that polar globules are
formed in vegetable ova; that in Toxopneustes lividus
they are formed before the ovum leaves the ovary ; that, ac-
cording to Calberla, they are formed in Petromyzon, at the
metamorphosis of the Ammocoetes; that in Ascidians the
germinal vesicle disappears in the ovary, and polar globules
have not been found in their ova ; and lastly, that in Verte-
brata true polar globules have never been discovered. .

The view that the polar globules are cells is supported by
the division of the first globule which was observed by
O. Hertwig, and still more by the discovery of Trinchese1 and
Blochmann2 that in this division the phases of karyokinesis are
again exhibited.

The stage which previous researches left most obscure was
the transformation of the germinal vesicle into the so-called
directive spindle. Trinchese and Blochmann state that the
equatorial plate is derived from the nucleolus of the ovum.
Trinchese considers the achromatic spindle as the vesicle trans-
formed, while Blochmann gives no opinion on the point. In
Vertebrata, except by Hoffmann in Teleosteans, nothing re-
sembling a directive spindle has ever been found.

Formation of first Polar Globule. — The structure
from which the first polar globule is formed and which is itself
derived from the germinal vesicle, Van Beneden calls the
Ypsiliform figure, because it resembles a Greek upsilon Y.

The figure consists of three branches, each composed of
achromatic fibrils, and of a number of chromatic globules at
the point of union of the three branches, together with certain
other elements all achromatic. The figure, as its name implies,

1 ‘Acad, dei Lincei,’ t. 7.

5 ‘ Z. f. w. Z.,’ Bd. xxxvi.

MATURATION AND FECUNDATION OF THE OVUM. 121

is bilaterally symmetrical : two of its branches which meet at
an obtuse angle are similar to one another, the third is dis-
similar. The plane of symmetry passes through the axis of
this third branch.

At the outer pole of each of the similar branches is a large
group of granules. The form of the whole group is somewhat
hemispherical, the flat base being towards the branch. From
the hemisphere pass outwards a few diverging radii of monili-
form protoplasm, part of the protoplasmic reticulum of the
ovum. The fibrils of each branch arise from the base of
the hemispherical group of granules ; some of these fibrils are
regular in thickness, some present varicosities, some are moni-
liform. Two or three fibrils in each branch are conspicuous by
their greater thickness, they lie near the axis of the branch and
are inserted into the chromatic globules. The other fibrils are
curved, and change direction when they reach a clear spherical
body, in the centre of which the chromatic globules are placed.
The axial fibrils penetrate the spherical body. The fibrils which
are near the vertical branch of the Y meet in acute angles and in-
terlace, and in this way the vertical branch is formed. The ver-
tical branch is not columnar but flattened in a plane perpendi-
cular to the line uniting the two poles of the similar branches.
Another illustration which the author employs to facilitate the
conception of the figure is that of the toy known as cup-and-ball.
The stem of the cup is formed by the vertical branch of the Y,
the ball is the clear spherical body containing the chromatic
globules, while at opposite points the cup runs out into two
poles : it must be remembered that the stem of the cup is flat,
not round. The limits of the clear spherical body become less
distinct as development advances. Usually in optical section
there are two groups of chromatic globules, one on either side
of the plane of symmetry ; each group shows two globules but
really contains four. Outside the figure in each of the angles
between the vertical branch and the superior branches is a
mass of deuteroplasmic vitelline substance limited externally
by a convex surface (see fig. 4, PI. X).

122

J. T. CUNNINGHAM.

Relation of the Ypsiliform figure to the Germinal

V esicle.

A comparison between figs. 2 and 4 shows what this relation
is. The clear spherical body is the prothyalosoma, the
chromatic globules are the germinal spot or nucleolus. The
spheroidal masses at the sides of the figure are the vitelline
elements seen at an earlier stage to push before them the walls
of the germinal vesicle. The axial fibrils of the similar
branches are formed in the substance of the prothyalosoma
partly. The remaining portions of the figure arise from the
transformation of the accessory portion of the germinal vesicle,
and especially from its membrane.

In this connection the author points out that it is doubtful
whether nuclear membranes and nucleoli are always homolo-
gous. He regards chromatin as a kind of fluid which is
absorbed by the more solid achromatic substance. An achro-
matic membrane is not equivalent to a chromatic one, and
while in the ovum all the chromatin or nearly all is contained
in the germinal spot, in an ordinary cell it is diffused through
various parts of the nucleus. Hence he believes the germinal
corpuscle is not homologous with the nucleolus of a cell.
The polar stars of the figure appear early in the transformation
of the vesicle, at first close to the prothyalosoma from which
they afterwards separate. The author regards them as centres
of attraction. The pseudonucleoli probably go to form
achromatic fibrils. The prothyalosoma is at first covered by
achromatic fibrils above, but these separate and it is then
exposed.

Formation of Polar Globule from Ypsiliform
Figure.

The figure passes gradually to the periphery of the ovum ;
there is reason to believe that it reaches the surface at the pole
opposite to that at which the micropyle existed, as in one case
the spermatozoon was still attached to the oospermatic mem-

MATURATION AND FECUNDATION OF THE OYUM. 123

brane when the figure had reached the surface at the opposite
pole.

The two poles of the similar branches both reach the
surface of the vitellus. The angle between these branches
now becomes more and more obtuse, until the prothyalosoma
reaches the surface of the ovum.

The groups of achromatic granules at the poles of the similar
branches become, by the fusion of the granules, homogeneous
discs. A similar fusion takes place among both the axial and
peripheral achromatic fibrils of the figure ; at the same time
the whole figure becomes smaller. By this time the sperma-
tozoon has passed to the centre of the ovum, and fibrils are
seen going from it to reach by a curved course the vertical
branch of the Y. The vitellus has now lost all appearance of
formed elements except its protoplasmic reticulum, and is very
transparent ; but after this commences a formation of granules
round the spermatozoon, which gradually extends throughout
the vitellus till the whole is granular and somewhat opaque, and
the protoplasmic reticulum is obscured.

The next change in the ypsiliform figure is that its vertical
branch becomes superficial, still remaining at right angles to
the line connecting the poles of the similar branches; and then
a new branch is formed opposite to the original vertical
branch, so that a cross is formed at the surface of the vitellus
with the prothyalosoma in its centre. The two last-formed
branches of the cross undergo a longitudinal cleavage which
seems to play an important part in the liberation of the polar
globule.

After this all the branches of the cross disappear, and
nothing remains but a finely granular disc where the cross
existed, surrounded by the granular vitellus. The periphery of
the disc is distinctly defined, and in its centre are the prothya-
losoma and its contained chromatic elements unchanged.
Later even the limits of the disc become obscure. The prot-
hyalosoma is somewhat reduced in size.

The polar globule is formed by division of the prothyalosoma
and its contained globules in a plane tangential to the surface

124

J. T. CUNNINGHAM.

of the vitellus (see fig. 5, PI. X). It is evident from what has
been said that this plane is one which at an earlier stage would
have passed through the axis of the spindle formed by the similar
branches of the T. On this point Van Beneden insists strongly,
that the plane of division as observed by him passes through the
axis of the spindle, and not, as described by other observers,
through the equator. Each of the chromatic discs divides into
two, one half going into the polar globule ; thus the chromatic
part of the latter also consists of two discs. In the polar
globule there is very little, if anything else, besides half the
prothyalosoma.

During the formation of the polar globule a thick layer of
homogeneous substance is thrown off from the vitellus and
lines the oospermatic membrane ; this is the first perivitelline
envelope. The polar globule remains attached to the internal
surface of this envelope.

The half of the prothyalosoma which remains within the
vitellus is called the deuthyalosoma (i. e. deuterohyalosomaj ; it
contains of course two chromatic discs, or two groups of chro-
matic globules.

Changes in the Spermatozoon during this Period.
— The tail gradually becomes smaller, and its refringent body
diminishes and finally disappears. In one female the refrin-
gent body was observed first to have separated from the
spermatozoon, and at last to have escaped from the vitellus
altogether and to lie between it and the perivitelline envelope.
This, however, is exceptional ; the refringent body seems
usually to be absorbed by the vitellus. Ultimately the sper-
matozoon in the centre of the ovum consists of a chromatic
globule round which is a clear perinuclear layer, itself sur-
rounded by a layer of granular or reticulated protoplasm.

Formation of the Second Polar Globule. — Imme-
diately after the expulsion of the first polar globule appears in
the vitellus a second complicated figure, whose developmeut
culminates in the formation of the second polar globule. The
elements which enter into the composition of this figure are :

(1) The deuterohyalosoma and its two chromatic discs.

MATURATION AND FECUNDATION OF THE OVUM. 125

(2) The surrounding protoplasm, which has become scarcely
distinguishable from the vitellus.

Each of the chromatic discs gives off a filament, formed,
during the division of the disc, at the expulsion of the first
polar globule. Similar filaments appear at the internal ends
of the discs. The two discs next divide up into smaller
chromatic globules and the filaments become more numerous —
in what way is not clear. Thus a spindle is formed. The
deuterohyalosoma increases in size.

The spindle is directed radially, one of its poles being deep
the other superficial. At each of these two poles, outside the
deuterohyalosoma, appears a star, consisting of a group of
achromatic granules surrounded by radiating moniliform
threads. These stars may be — at least in part — formed from
the substance of the achromatic fibrils of the first figure, but
the continuity cannot be traced. The rays of the stars directed
towards the deuterohyalosoma elongate and meet, while the re-
mainder disappear to a great extent. Thus a figure in the form
of a lozenge is produced, one of whose diagonals is occupied by
the spindle within the deuterohyalosoma (see fig. 6, PI. X).

One half of the lozenge now gradually disappears, and thus
a figure is formed similar to the ypsiliform figure of the earlier
period. The deep pole of the axial spindle now approaches
the surface of the vitellus, and the division of the deuterohyalo-
soma takes place in a plane passing through the axis of the
spindle, not in the equatorial plane.

The second pseudokaryokinetic figure, as Van Beneden calls
it, is, in its later stages, complicated. An examination of the
Plate XVIII bis, and of the text referring to it, shows that
the division of the deuterohyalosoma into two parts — one of
which is to form the second polar globule, the other the female
pronucleus — that this division takes place long before the
second polar globule is expelled from the vitellus. Before the
change in the position of the spindle occurs, the spindle and
the deuterohyalosoma are divided axially by a median plate,
which moves through an angle so as to become superficial, and
thus the globule is expelled (see figs. 7 and 8, PI. X).

126

J. T. CUNNINGHAM.

As before; each half of the deuterohyalosoma contains two
plates of chromatin, each composed of four globules.

Even before the second polar globule is expelled, the female
pronucleus has, in place of a distinct membrane, a periphery
of punctations. At the time of the expulsion the achromatic
fibrils outside the divided deuterohyalosoma disappear. The
author believes that the second polar globule is the exact
equivalent of the female pronucleus, and that the membrane
round it is an achromatic nuclear membrane.

Changes in the Vitellus during the Formation of
the Second Polar Globule. — The external layer of the
vitellus becomes first clear and reticulated in structure, and
then becomes separated from the vitellus to form the second
perivitelline envelope. After its separation the vitellus con-
tracts, and a perivitelline space is produced. In ova prepared
with alcohol the second envelope becomes fluid and cannot be
distinguished from the perivitelline space. The second polar
globule remains attached to the surface of the vitellus. At
the period of the expulsion of the second globule, as at that of
the first, two concentric circles appear on the surface of the
vitellus round the polar body. The outer one divides the
vitellus into two parts, one of which contains the female
pronucleus, the other the spermatozoon.

No important change occurs in the spermatozoon during
this period; often a radial striation of the vitellus is visible
round the male element.

Formation of the Pronuclei. — The expulsion of polar
globules is quite independent of the presence of the spermato-
zoon. In the rabbit the first polar globule is formed while
the ovum is still in the ovary, and the membrane formed after
this, known as the vitelline membrane, is to be regarded as
the homologue of the first perivitelline envelope in Ascaris.
These processes take place in the rabbit even when spermatozoa
are prevented from reaching the uterus. The influence of the
spermatozoon on the ovum begins with the conjugation of the
pronuclei.

In the living female the ova do not develop further than

MATURATION AND FECUNDATION OF THE OVUM. 127

the formation of the pronuclei : the later stages were studied
in eggs which had continued to develop after the females were
placed in alcohol.

The female pronucleus at first contains two chromatic
discs, which are, as has been seen, probably derived directly
from the two discs of the germinal spot. After each division
the chromatic discs regain their size. Each disc is really
made up of four smaller globules united by a substance com-
posed of moniliform threads. The acromatic membrane of the
pronucleus is also composed of very delicate moniliform threads,
and still more minute fibrils unite the membrane to the
chromatic elements. The changes which the pronucleus under-
goes are exactly similar to those of a cell nucleus about to
divide. The chromatin in the discs diffuses along the achro-
matic fibrils, and ultimately is found in fibrils at the surface of
the pronucleus, the central part being almost empty except
for scattered threads. The pronucleus is usually divided by
a partition into two parts. The male pronucleus is formed
from the chromatic elements in the centre of the spermato-
zoon and the perinuclear layer : the chromatic layer outside this
is thrown off. A membrane appears round the perinuclear
layer and then the same changes take place as in the female
pronucleus (see fig. 9, PI. X).

The female pronucleus approaches the male : the chromatin
in each comes to form a single thick sinuous fibril which
breaks up into two V-shaped loops. The four loops arrange
themselves as a star, on each side of which are achromatic
fibrils forming a karyokinetic spindle. At each pole of the
spindle appears a star derived from the vitellus. The loops at
the equator now divide longitudinally, and the closed ends of
the two groups so produced diverge from one another. As the
groups diverge achromatic fibrils appear connecting them :
these are produced from the loops as they divide, and are not
parts of the original spindle as has been supposed by other
authors. Hence Flemming’s notion that the chromatic loops
travel along the achromatic fibrils to the poles. As was
described in cells by Pfitzner the chromatic loops have a moni-

128

J. T. CUNNINGHAM.

liform structure. The divergence of the chromatic groups is
due to the contraction of the achromatic fibrils towards the
polar stars. These stars take no part in the edification of the
daughter nuclei which are formed by the gradual diffusion of
the chromatin through the achromatic substance. No convo-
lution stage occurs in the reconstruction. The mature daughter
nuclei have the same structure as the mature pronuclei (see
figs. 11, 12, 13, PL X).

Flemming observed a longitudinal division of the chromatic
loops in cells but could not prove that this division was con-
cerned in the division of the equatorial plate formed by the
loops. Van Beneden has proved that the latter phenomenon
is due to the former. It has struck me that here lies the
solution of the controversy between Strasburger and Flemming
pointed out in a previous essay.1 The division of chromatic
elements in the equatorial plane, affirmed by Strasburger and
denied by Flemming, is probably the same thing as the longi-
tudinal division of the chromatic loops described by the latter.

The division of the vitellus into two blastomeres is not due
to a complete constriction. A furrow appears on the outside
of the vitellus, but division is completed by a cell-plate” such
as that described by Strasburger in plants. This cell-plate is
a homogeneous layer formed from the intermediate achromatic
fibrils and in its centre a limiting surface appears which
separates the two blastomeres. The rest of the intermediate
fibrils are assimilated by the vitellus.

The first two blastomeres divide in exactly the same way.
Only four chromatic loops are present at the equator of each
spindle.

Theory of Fecundation. — Of the four chromatic loops
in the first segmentation-spindle two are male and two female.
Similarly every cell formed from the two first blastomeres,
and each of these blastomeres themselves, is hermaphrodite.
Therefore ovarian cells destined to become ova are originally
hermaphrodite, and likewise the cells of the testis destined to
become spermatozoa. But an ovarian cell in becoming an
1 This Journal, 1882.

MATURATION AND FECUNDATION OF THE OVUM. 129

ovum throws off certain parts of its nucleus. It is very
plausible to suppose that the part of the nucleus thus eliminated
is the male part, and the ovum after the expulsion of polar
globules thus differs essentially from an ordinary cell. Van
Beneden therefore calls the ovum containing a female pro-
nucleus a gonocyte.

In the development of spermatozoa also, some part is thrown
off — the cytophore or blastophore, described in very many dif-
ferent animals. In Ascaris megalocephala a spermatogo-
nium divides into two cells — the spermatogemmse ; each of
which divides into four cells — the spermatocytes, which be-
come spermatozoa. Between the four spermatocytes is the
cytophore, composed of four parts, one derived from each
spermatocyte. Each part of the cytophore contains an ele-
ment which takes up carmine, but whether it is derived from
the nucleus of the spermatocyte Van Beneden does not know.
In a subsequent memoir,1 of which I have only been able to
see an abstract, Van Beneden and Julin have discovered a
globule thrown off by the spermatogonium of Ascaris mega-
locephala before the cytophor is formed. They believe this
globule to be expelled from the nucleus in the same way as
described by Van Beneden in the ovum, and to be equivalent
to a polar globule ; the cytophore is not formed by a process
equivalent to cell division. Yan Beneden then concludes that
the spermatozoon has lost the female part of its nucleus, and
is a male gonocyte. The two gonocvtes unite to form a
complete hermaphrodite cell.

With regard to the opposition between himself and previous
investigators, Yan Beneden points out that the discrepancies
cannot be due to his methods or interpretation, because in the
segmentation of the ovum his results confirm and extend those
of earlier researches. If he recognised normal karyokinesis
in the one case he was able to do so in the other if it existed.

1 ‘ Bull. Acad. Roy. Belg.,’ vii, 1884, p. 312.

VOL. XXV. NEW SER.

I

130

J. T. CUNNINGHAM.

Critical Remarks on Van Beneden’s and other
Researches .

In spite of the conclusion arrived at by O. Hertwig and Fol,
that the polar globules were formed by a process equivalent to
cell-division, we find on examining their works that in some
animals certain stages of the process as described by them do
not agree with the corresponding stages of karyokinesis. In
karyokinesis it has been clearly shown that the whole nucleus
is transformed into the achromatic spindle and its chromatic
loops. If we study plate ii of Fol’s elaborate memoir1 we
find that in Aster ias glacial is only a portion of the ger-
minal vesicle or spot is employed in the formation of the
“ Amphiaster de rebut ; ” the figure is represented as originating
entirely on the outside of the germinal vesicle. It is evident
from that plate that a large portion of the germinal vesicle and
spot is left to disappear in the vitellus. On the other hand,
if we examine plate viii of the same work we find that in
Pterotrachea the germinal vesicle and spot are entirely trans-
formed into the spindle of the amphiaster and its equatorial
plate. The results of Fol on other animals are not very
decisive on this point (see figs. 15, 16, PI. X).

If we turn now to O. Hertwig we find that his account of
the phenomena in Hirudinea2 supports the direct transfor-
mation view. On the other hand, his account of the same
phenomena in Asteracanthion (pis. vi and viii of his paper in
‘ Morph. Jahrb./ Bd. iv) agree with the results of Fol on
Asterias glacialis with the following difference: — He found
that a certain portion of the germinal spot passed into the
centre of a star, which was forming in a portion of vitelline
protoplasm projecting into the interior of the germinal
vesicle (see figs. 14, 18, PI. X). It is possible also
that part of the substance of the germinal vesicle goes
to form the spindle, but Hertwig is not very decisive on
this point. It seems, then, that in Echinoderms the germinal
vesicle and spot are not directly but only partially transformed
’ * Commencement de l’henogenie,’ Geneva, 1879.

‘Morph. Jahrb.,’ Bd. iii.

MATURATION AND FECUNDATION OF THE OVUM. 131

into the “ Amphiaster de rebut/’ or “ directive spindle.” The
formation of the directive spindle from the germinal vesicle is
not fully described in the works previous to Van Beneden’s.
On this point Yan Beneden is very clear and decided, and so
far his account agrees with the descriptions of karyokinesis.
But in his description of the structure of the figure produced
and the formation of a polar globule from it, he is directly at
variance with previous writers, and the process he describes is
quite different from karyokinetic division. Fol and Hertwig
describe and figure these later stages as identical, except in
very minor points such as the length of the chromatic ele-
ments, with the division of cell nuclei, and they give the same
account for very different animals ; e. g. Echinoderms, Mol-
luscs, Leeches. It follows, then, either that O. Hertwig and
others were mistaken, or that Yan Beneden is wrong, or that
the processes in Ascaris megalocephala are fundamentally
different from those in other animals. Van Beneden himself
mentions two very recent publications which support the
theory of the cellular nature of polar globules. One is by
Trinchese,1 the other by Blochmann,2 and they have shown
that the division of the first polar globule after its expulsion
which had been observed by O. Hertwig, again exhibits the
phases of karyokinesis. It will naturally be expected that
ultimately the process of formation of polar globules will be
proved to be essentially the same in all animals, but future
researches must decide on this point. As is well known, a
directive spindle has been sought in vain in the ova of Verte-
brates, and the expelled elements in these are not globular in
form. Hoffmann3 alone has described an Amphiaster de rebut
in Teleostean ova, but has not traced its history.

Several papers have appeared subsequently to Yan Beneden’s
memoir, on the subject of fecundation, &c. P. Hallez,4 in
March, 1884, published a note of researches on Ascaris

1 ‘Mem. Acad. Lincei,’ tom. 7.

2 ‘ Z. f. w. Z.,’ Bd. xxxvi.

3 ‘ Natuurk. Verh. Koninkl. Acad. Deel./ xxi.

4 ‘ Comptes rendus/ No. 11, tom. 96, 1881.

132

J. T. CUNNINGHAM.

megalocephala. The results he gives would have been
interesting ten years ago, but at the present time they are
scarcely deserving of serious attention. The formation of
“ the ” polar globule is mentioned but not described. The
male pronucleus is said to be a spindle with rods at its equator.
The female pronucleus is described as a magnificent star.
There is no micropyle. His account of the development of
spermatozoa is astonishing ; the young spermatozoa he calls
deutospermatoblasts ; these congregate in pairs, and when they
separate each gives out a corpuscle de rebut resembling a polar
globule. The rest of the development takes place within the
female organs. M. Hallez has been original enough to
mistake the refringent body for the spermatozoon itself. The
nucleus is always, he says, outside the body of the sper-
matozoon.

A general essay on fertilization is given by A. Sabatier.1
He finds that three kinds of globules are expelled from the
ovum, precocious globules, “ globules tardifs,” and true polar
globules. These eliminated parts are the male element; in the
spermatozoa it is the central part of the original cell which is
eliminated. Sabatier sought to prove that in the partheno-
genetic ova of Aphides polar globules were not formed, but was
not quite successful. He refers on this point to Weissmann’s
account of parthenogenesis in Daphnoidea.

Another paper on the subject which treats of A scar is
megalocephala, is by Prof. Moritz Nussbaum,2 of Bonn.
In some points he confirms Van Beneden, in others is at
variance with him. His figures and descriptions of the direc-
tive spindle are very different from Van Beneden’s and far less
complete. He confirms Van Beneden’s results as to the
presence of four chromatic loops in the first segmentation
spindle. His conclusion with regard to the theory of fecunda-
tion is that it consists in the union of two homologous cells.

Biitschli,3 in discussing the essential meaning of fecundation,

1 * Revue des Sciences Naturelles,’ iii, 1884, p. 362.

2 * Arch. f. Alik. Anat..,’ vol. xxiii.

3 ‘ Biol. Ceiitralbl.,’ iv, 1884.

MATURATION AND FECUNDATION OF THE OVUM. 133

starts with the process of sexual multiplication in the colonial
Volvocineae. He does not agree with the theory which regards
polar globules as the eliminated male element, pointing out that
in the lower Algae there is no such elimination in the sexual
conjugation. In this connection I am led to refer to the most
suggestive remarks on the origin of sexual reproduction in a
paper by P. Geddes1 on the cell-theory. Geddes regards the
original life of a cell as a cycle passing from the encysted
stage to the ciliated, then to the amoeboid and then to the
plasmodial. In the last stage the amoebae unite and the union
results in increased activity of the cells which is shown by
their greater power of motion and especially in their more rapid
multiplication. From this plasmodial union, exemplified in
Myxomvcetes, he derives the sexual union of a male and female
cell. He points out that a multiple union exists according to
Gabriel in Actinosphaeria, according to Gruber in Gregarines,
and results in reproduction. That the nucleus is not indis-
pensable in conjugation results he thinks from the demonstra-
tion by Gruber2 3 that in the young Actinophrys a nucleus is
really absent and develops independently in adult life; and
even if the essence of reproduction lies in the union of nuclei
rather than in that of the protoplasm, we must suppose on the
evolution theory a primitive stage in which nuclei had not yet
been developed. All this, however, although giving a common
me aning to phenomena at first sight isolated, does not explain
why the nucleus when it does exist plays such a conspicuous
part in fecundation and exhibits such a universal and striking
process as the formation of polar globules. We require yet a
series of patient and skilful researches like these of Van
Beneden into the phenomena in question in all living forms,
to give us accurate and more extensive data from which to
generalise. It is not ten years since Biitschli first discovered
the directive spindle, and ten years more will probably throw

1 “ A Restatement of the Cell-theory,” ‘ Proc. Roy. Soc. Edinb.,’ vol. xii,

1883-4.

3 * Zool. Anzeiger,’ No. 118, 1882.

134

J. T. CUNNINGHAM.

further light on the inner meaning of reproduction, the most
mysterious and most distinctive phenomenon of life.

EXPLANATION OF PLATE X,

Illustrating Mr. Cunningham's report on “Van Beneden’s
Researches on the Maturation and Fecundation of the
Ovum.”

List of reference letters.

a. p. Accessory portion of germinal vesicle, c. z. Cortical layer of vitellus.
dth. Deuterhyalosoma. h. d. Homogeneous droplets of vitellus. h. s. Hya-
line spheres of vitellus. p. d. Polar disc. p. g. First polar globule, p. g'.
Second polar globule. p. i. Plug of impregnation, pth. Prothyalosoma.

r. sp. Refringent body of spermatozoon, r. g. Refringent granules of vitellus.

s. n. Secondary nucleus of germinal vesicle, sp. Spermatozoon.

Fig. 1. — Ovum before the entrance of the spermatozoon. Osmic acid,
picro-carmine. Obj. 8, Hartnack. (V. B., PI. X, fig. 5.)

Fig. 2. — Deformation of the germinal vesicle at the time of the penetra-
tion of spermatozoon. Alcohol, borax-carmine. Obj. 8, Hartnack. (V. B.,
PI. XIY, fig. 10.)

Fig. 3. — Spermatozoon in the uterus, conoid stage. Obj. 8, Hartnack.
(V. B„ PI. XI, fig. 14.)

Fig. 4. — Ypsiliform figure. Nitric acid, borax-carmine. Obj. ^th, Zeiss.
(V. B., PI. XV, fig. 3.)

Fig. 5. — Expulsion of first polar globule. Nitric acid, borax-carmine.
Obj. j^th, Zeiss. (V. B., PI. XVI, fig. 17.)

Fig. 6. — Second pseudokaryokinetic figure. Nitric acid. Obj. ^th, Zeiss.
(V. B., PI. XVII, fig. 12.)

Fig. 7. — Later stage of same. Alcohol. (V. B., PI. XVIII bis, fig. 1.)
Fig. 8. — Formation of second polar globule. Alcohol. (V. B., PI. XVIII
bis, fig. 3.)

Pig. 9. — The two pronuclei. Alcohol, borax-carmine. Obj. -j^-th, Zeiss.
(V.B., PI. XIX bis, fig. 9.)

Fig. 10. — Longitudinal division of chromatic loops in first segmentation.
Alcohol, borax-carmine. Obj. d, Zeiss. (V. B., PI. XIX bis, fig. 25.)

MATURATION AND FECUNDATION OF THE OVUM. 135

Fig. 11. — Same stage, showing achromatic part of the nuclear structure.
Same method. (V. B., PI. XIX ter, fig. 3.)

Fig. 12. — Later stage. (V. B., PI. XIX ter, fig. 10.)

Fig. 13.— Edification of the daughter nuclei. (V. B., PI. XIX ter , fig. 13.)

Fig. 14. — Ovum of Nephelis three quarters of an hour after deposition.
Formation of first polar globule. Acetic acid, 1 per cent, glycerine. Zeiss,
f, oc. 2. (0. Hertwig, ‘ Morph. Jahrb.,’ Bd. iii, PI. ii, fig. 3.)

Fig. 15. — Formation of “Amphiaster de rebut” in ovum of Asterias
glacialis. No. Germinal vesicle, no. Germinal spot. Ar1. Amphiaster de
rebut. V. Vitellus. Picric acid, glycerine. 400 diam. (Fol, ‘ Comm, de
l’Henogenie,’ PI. ii, fig. 3.)

Fig. 16. — Formation of “Amphiaster de rebut” iu ovum of Pterotrachea.
Acetic acid, glycerine with alcohol. 400 diam. F. Central. F'. Peripheral
fibrils of forming spindle, f. External rays of polar sun. a. Centre of polar
sun. Nov. Envelope of germinal vesicle. V. Vitellus. (Fol, ibidem, PI. vii,
fig. 14.)

Fig. 17- — Formation of first polar globule in Pterotrachea. Acetic acid,
glycerine, at. Aster interne. Cr1. Corpuscle de rebut. Fc. Chromatin granules.
Ar'. Chromatin left in ovum. Eo. Envelope. (Fol, ibidem, PI. viii, fig. 5.)

Fig. 18. — Origin of directive spindle in ovum of Asteracanthion. Osmic
acid, picro-carmine. Thirty minutes after deposition. (O. Hertwig, ‘ Morph.
Jahrb.,’ Bd. iv, PI. viii, fig. 1.)

Fig. 19. — Ovum of Asteracanthion, forty-five minutes after deposition.
Acetic acid. (Ditto, ditto, fig. 3.)

Fig. 20. — Ovum of Mytilus, immediately after deposition, a. Directive
spindle, b. Residue of germinal vesicle. (Ditto, ditto, PL x, fig. 2.)

Fig. 21. — Ovum of Ascaris megalocephala. Second directive spindle.
K. Refringent body of spermatozoon. Sp. K. Head of spermatozoon. IRK.
First polar globule. II. Rs. Second directive spindle. I. First. II. Second
vitelline envelope. (Nussbaum, ‘Arch. f. Mik. Anat.,’ Bd. xxiii, PI. x,
fig. 34.)

Figs. 22 and 23. — Two spermatogemmae, each composed of four spermato-
cytes and showing the cytophore in the centre in four pieces. Osmic acid,
picro-carmine. (V. B., PI. XIX ter, figs. 19 and 20.)

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ON THE SUPRARENAL BODIES OF YERTEBRATA. 137

On the Suprarenal Bodies of Vertebrata.

By

W. F. R. Weldon, B.A..

Fellow of St. John’s College, Cambridge; Lecturer on Invertebrate
Morphology in the University.

With Plates XI and XII.

The suprarenal bodies of Vertebrates are, as is well known,
made up of two sets of elements, sharply distinguished from
one another, both by their adult structure, and by their mode
of origin in the embryo. The substance which from its posi-
tion in the mammalian suprarenal is known as “ medullary ” is
now almost universally admitted to consist of metamorphosed
nerve-cells, which arise from one or more of the ganglia of
the sympathetic system. As to the origin of the remainder,
however, the so-called “ cortical ” substance, little is certainly
known. In Elasmobranchs, Balfour1 describes the homologue
of this substance as “ making its appearance . . . as a rod-like
aggregate of mesoblast cells, rather more closely packed than
their neighbours, between the two kidneys near their hinder
ends ; ” but he leaves it an open question, whether these cells
arise from the general indifferent mesoblast surrounding them,
or whether they are derived from any of the adjacent organs
of the embryo.

These observations of Balfour were followed, in 1882, by two
1 “ Elasmobranch Fishes,” p. 246.

138

W. F. R. WELDON.

important papers by Braun1 and Mitsukuri,2 the one dealing
with the development of the suprarenals in lizards, the other
in mammals.

In lizards, Braun describes the cortical substance as arising
“ as a thickening in the walls of the vena cava inferior.” In
the earliest stage figured by him, a large mass of cortical
blastema is already established, as seen in PI. 1, fig. 4 of his
paper. In this figure, as in all the others given by Dr.
Braun, it is noticeable, as he himself says, that “ the flattened,
nucleated endothelium (of the blood-vessel) is easily to be
distinguished ” from the adjacent tissue, and that it shows no
sign of proliferation. It is therefore difficult to conclude from
this account that the suprarenals arise as appendages of the
blood-vessels themselves, Braun’s observations throwing little
more light upon the real origin of the cortical substance than
did the earlier ones of Balfour.

In the same way Mitsukuri, treating of mammals, finds the
first rudiment of the cortical substance in a little knot of
isolated mesoblast cells “ on each side of and ventral to the
aorta, on the inner side of the Wolffian bodies, and dorsal to
the mesentery.”

Gottschau, in a later paper3 has described in mammals
phenomena nearly in accordance with those observed in lizards
by Braun, — emphasising more than Mitsukuri the connection
between the cortical substance and the adjacent blood-vessels.

From none of these observations can we learn anything of
the mode of origin of the blastema described, each author
taking up its history at a point when the cells composing it
have already lost any connection which they may primitively
have possessed with another embryonic organ. Janosik4 has
attempted to trace the earlier history in mammals, and has

1 “ Bau u. Entwick. d. Nebennieren bei Reptilien,” Semper’s * Arbeiten,’
Bd. v.

2 “ On the Development of the Suprarenal Bodies in Mammalia,” ‘ Quart.
Journ. Mic. Sci.,’ 1882.

3 ‘ Archiv. fur Anat. u. Phys.,’ 1883.

4 ‘Archiv fiirMikr. Anat.,’ 1883.

ON THE SUPRARENAL BODIES OF VERTEBRATA. 139

been led to believe that the blastema of Gottschau, Mitsu-
kuri, and others arises as a series of (segmental?) outgrowths
from the peritoneum, in the angle between it and the root of the
mesentery and the peritoneum. As, however, very few figures
are given with this paper it is not easy to form an idea of the
exact nature of the events described.

This state of things led me to believe that it might be
worth while to examine carefully embryos younger than those
used by any previous observers, and so to trace the earlier
history of the cortical blastema. This I have been able to do,
during the summer of the present year, in the chick, in
Lacerta muralis, and in Pristiurus. As my observations
are most complete in the case of Lacerta, I begin with an
account of the development in that type. In order fully to
understand the development of the suprarenal body, it will be
necessary to follow the development of the glomeruli of the
mesonephros, which has been described by Braun (loc. cit.)
After the formation of the segmental vesicles and Wolffian
duct each segmental vesicle gives off from its outer margin a
solid column of cells, which joins the Wolffian duct, and soon
acquires the (/) shape characteristic of the young segmental
tubes in so many Vertebrates. After this cord of cells has
united with the Wolffian duct, the lumen of the segmental
vesicle extends into it, and it takes on all the characters of
a segmental tubule. After this has happened, one wall of the
persisting segmental vesicle becomes pushed in by a plexus of
blood-vessels, and forms a glomerulus.

But while the wall of the glomerulus is being thus invagi-
nated, a proliferation of the cells composing it occurs at the
side opposite to the point of attachment of the segmental tube,
that is, on the inner margin of the glomerulus.

In fig. 1, 1 have attempted to represent the condition of things
in one of the anterior glomeruli of an embryo with about
twenty protovertebrse. The section passes nearly through the
centre of the glomerulus, which is seen to be only partially
invaginated ; and I may here call attention to the manner in
which, in lizards at least, the invagination seems to take place

140

W. F. B. WELDON.

before the entrance of the blood-vessels, none of which are
to be seen in the section figured. The epithelium is much
more columnar than at a later stage, and is regularly one cell
thick on the outer side, while on the side undergoing invagina-
tion it is more or less regularly composed of two layers of cells ;
but at every point except one the whole glomerulus is bounded
by cells of a definitely epithelioid character, having no pro-
cesses, and showing no indication whatever of any tendency to
proliferation. At the inner margin, however, the case is
different; here the limiting cells are irregular in shape, and
can in no way be separated, by any sharp line of demarcation,
from the cells forming the /^-shaped mass (s. r. b.), which is
seen to be attached to the inner wall of the glomerulus. This
mass gives rise both to the connecting tubules between testis
and epididymis and to the cortical substance of the suprarenals.
At present it is seen to extend for a short distance dorsal-
wards, between the segmental tubule ( s . t.) and the vena cava
(v. c.), and then to bend rather sharply ventralwards towards
the generative ridge, the anterior end of which ( TV. r .) is seen
in the section. As a contrast to the continuity between the
cell mass in question and the cells bounding the cavity of the
glomerulus I would especially call attention to the distinctness
of the line of demarcation between it and the endothelium of
the vena cava, at the point where the two are in contact — a
distinctness which, persisting, as we shall see it to do, through
all stages of the development of the suprarenal blastema, ren-
ders it extremely difficult to believe that the endothelium is in
a state of proliferation, or that there is any real connection
between it and the suprarenal blastema.

The small blood-vessel ( b . v.) which is seen in the figure
is also perfectly sharply separated from the adjacent tissues.

The section represented in fig. 2,» from an embryo about
4‘5 mm. long, with twenty-four protovertebrse, shows a further
advance in the development of the suprarenal blastema and its
associated glomerulus. The section, which passes through the
entrance of a segmental tube into the glomerulus, shows the
completion of the invagination, and the entrance of blood-

ON THE SUPRARENAL BODIES OP VERTEBRATA. 141

vessels (diagrammetrically indicated by shading). The epithe-
lium of the glomerulus is everywhere, except on its inner side,
formed of a single layer of cells, which are much flatter than
in the preceding stage, but on the inner side the cells pass,
as before, without any definite line of demarcation, into the
suprarenal blastema, which is still composed of a compact mass
of polygonal cells, without any distinction being visible between
the part which is going to form suprarenal body and that
which is going to form a seminiferous tubule. In this section
the distinction between the endothelial cells of the various
blood-vessels and the tissues surrounding them is even better
marked than in the one last described.

The appearances which I have attempted to describe are seen
first in the more anterior, then in the hinder glomeruli of all
that region of the mesonephros which is coextensive with the
generative ridge, and in one or two glomeruli in front of it.

The blastema which I have described grows, in the suc-
ceeding stages, in two directions : dorsalwards between the
cardinal vein (or vena cava) and the tubules of the mesone-
phros, and ventralwards into the prominence of the Wolffian
ridge. In such a section as that shown in fig. 3, for example,
which is taken from the posterior part of the mesonephros of
an embryo of 8 mm., two distinct regions may now be distin-
guished, a region (s. r. b.) dorsal to the point of origin from
the glomerulus, the cells composing which will go to form the
suprarenal, and a region ( s . str .) going from the glomerulus
ventralwards into the generative ridge, which is the rudiment
of the testicular network. No histological difference can as
yet be detected between the one region and the other, the
whole blastema being composed of a mass of polygonal cells
with rounded nuclei, the characters of which are everywhere
identical.

In an embryo of 10 mm. (figs. 4 and 5), a slight dis-
tinction between the two parts is for the first time apparent,
though the histological characters of adult suprarenal cells are
not acquired for some time. Of the two sections figured, that
shown in fig. 4 is taken in front of the Wolffian ridge; in it,

142

W. F. E. WELDON.

therefore, the blastema attached to the glomerulus gives rise
only to suprarenal tissue. For this figure, I have purposely
chosen a section in which the contact between the suprarenal
rudiment and endothelium of the vena cava was as close and
as extensive as possible, in order to show the distinctness
which, in spite of their close apposition, exists between the two
structures, and to contrast once more this distinctness of the
vena cava endothelium with the irregular way in which the
cells of the glomerulus wall are merged in the blastema.
This section is also interesting from another point of view.
One of the arguments used by Dr. Braun, in order to disprove
the existence of any real connection between the rudiment of
the testicular network and that of the suprarenal, is that the
segmental rudiments of the former structures are well developed
before the appearance of any suprarenal tissue at all. Dr.
Braun believes that the whole of the outgrowth from each
glomei’ulus becomes converted into a seminiferous tubule.
But if this be so, what can be the function of such an outgrowth
in front of the testicular region ?

In fig. 5 is seen a section through the beginning of the
generative ridge : the suprarenal and seminiferous rudiments
are still continuous, but the one is a little more deeply stained,
and its component cells are a little smaller than the other. As
before, the endothelium of the surrounding blood-vessels forms
a distinct layer over the blastema, the cells of which are quite
sharply defined and clearly recognisable.

The upward growth of the suprarenal rudiment, already
well marked in fig. 5, is still better seen in fig. 6, from the
middle of the trunk of an embryo of 13 mm. — almost the
oldest in which a connection between suprarenal and semi-
niferous tubules can be seen. In an embryo of 18 mm.
(fig. 7), the separation has already taken place, and the
suprarenal is cut off by blood-vessels from all adjacent struc-
tures, though it remains now, as always before, perfectly
distinct from the endothelium of the vessels themselves.
This stage is only very slightly younger than the youngest
figured by Braun, as fig. 4, PI. I. of his paper shows ; the

ON THE SUPRARENAL BODIES OF YERTEBRATA. 143

chief difference between his figure and mine being that he has,
having overlooked the earlier stages, been led to an erroneous
form of opinion as to the mode of origin of the tissue which
he figures. From this point onwards, however, his observa-
tions as to the histological differentiation of the cortical
substance, and the entrance into it of the medullary ganglion
cells are so complete that it is needless to attempt to add
anything to his description.

In Pristiurus, as in other forms, the early history of the
suprarenals has only been traced from a point at which a meso-
blastic rudiment, distinct from all other organs, already existed.
This is the stage at which Balfour, in the passage already
quoted, begins his account of their development. I propose,
therefore, to trace the history of this blastema in Pristiurus,
which is the only Elasmobranch in which I have observed it.

In figs. 9 and 10 are shown two consecutive sections through
a Pristiurus embryo 8 mm. in length, at a stage corresponding
to Balfour’s Stage I — the stage immediately preceding that
in which he begins the history. Both these sections pass
through the opening into the body cavity of the same seg-
mental tube, which is seen to give off, just after the narrowing
of its funnel-shaped opening into the body cavity, a small
process (s. r .) , which projects towards the root of the mesenterv.
In fig. 9, which passes through the middle of this process, it
is seen to have a very considerable lumen. In fig. 10 it is
cut tangentially, and the lumen is therefore not apparent.

In figs. 11 and 12, from a slightly older embryo, this diver-
ticulum of the segmental tubule is seen to have obtained a
considerable size, and to project quite to the middle line over
the root of the mesentery. It is not seen in the figure to be
joined by a similar structure from the opposite side, because
the section copied was so oblique that the right hand side was
intervertebral. In the next following section, however (fig. 13),
the wall of the outgrowth of the other side is cut.

In an embryo of between 9 and 10 mm. the outgrowth has
become solid, and lies just over the root of the mesenterv, as
shown in fig. 14 ; further, at this stage the outgrowths have

144

W. F. R. WELDON.

so coalesced with those in front and behind that an interverte-
bral section, such as that shown in fig. 15, still passes through
them.

One feature of the sections of this age, which I do not
understand completely, is the shifting of the position, with
regard to the segmental funnel, of the point of attachment of
the suprarenal outgrowth ; while in the preceding stage (see
fig. 12) the outgrowth was external to the primitive ova, open-
ing distinctly into the segmental funnel, it is now attached to
the peritoneal epithelium at the root of the mesentery internal
to the primitive ova. While I am unable to account for
this apparent change of position, I see no reason for doubt-
ing the identity of the structure I have called s. v. in figs. 14
and 15 with that similarly named in the preceding figures.

In the next stage, finally, which is a young embryo of
Balfour’s Stage IV, we find (fig. 16) the unpaired rod of meso-
blast described by him lying at the root of the mesentery,
but still attached segmentally (see the left hand side of the
figure) to the segmental funnel.

I have unfortunately no stage intermediate between this
and the stage last described, but it seems obvious that the
unpaired blastema existing at this stage must be produced by
the fusion of the paired outgrowths of the earlier stages.

An important point with regard to this blastema in Pris-
tiurus, which has apparently been overlooked by Balfour, is
that it extends throughout the whole length of the mesonephros.

It is well known that in an adult Elasmobranch there are
two sets of suprarenal bodies : one a series of paired, more or
less regularly segmental bodies, attached to the dorsal wall of
the cardinal vein on each side in the mesonephric region, and
the other one unpaired, median body, lying between the two
halves of the metanephros.

Balfour was of opinion that the bodies of the anterior set,
though they show in the adult a division into cortical and
nervous positions as distinct as that which exists in the supra-
renals of higher Vertebrates, were yet derived entirely from
sympathetic ganglia. The presence, in the anterior end of the

ON THE SUPRARENAL BODIES OF VERTEBRATA.

145

body, of a blastema such as I have described seems to throw
doubt on the correctness of such a view ; though I have un-
fortunately been unable, owing to want of material, to prove
by examination of later stages the share which this blastema
takes in the formation of the paired anterior suprarenals.

In the chick, as might perhaps have been expected, from the
highly-modified development of the whole kidney, the mode
of origin of the suprarenal blastema differs in many important
points from that which has been described for the dogfish and
for the lizard.

Before the fourth day of incubation there is no trace of any
suprarenal rudiment whatever. By about the end of this day,
however, certain large cells, the rudiments of the cortical sub-
stance, make their appearance in the indifferent mesoblast at
the inner side of the mesonephros. The exact mode of origin
of these cells I have been unable to determine. At their first
appearance they lie, singly or in groups of two t)r three, in the
mesoblast between the aorta and the kidney, being distin-
guished from the surrounding cells by their rounded, un-
branched form, their larger size, and the clearness of their
protoplasm. During the end of the fourth day, aud the early
part of the fifth, they increase in number, either by division or
by addition from the surrounding mesoblast, till in an embryo
of about the middle of the fifth day of incubation, they form
groups of a considerable size, which present in section the
appearances seen in fig. 17. The cells seen in this section,
though they are more numerous than at the time of their first
appearance, have not appreciably changed their relations to the
surrounding parts. They are seen to lie surrounded entirely
by branched mesoblast cells without any connection, either
with the epithelium of the adjacent glomeruli, or with the walls
of any blood-vessels. In this isolated condition the suprarenal
cells remain during the fifth and sixth days, travelling, how-
ever, gradually towards the mesonephric glomeruli, and at the
same time increasing in number, and tending to arrange them-
selves in irregular branched columns, having in section an
elliptical outline. During the seventh day they attach them-

VOL, XXV. — NEW SEK.

K

146

W. F. R. WELDON.

selves to the epithelium of the glomeruli, so as to appear as in
fig. 18. In this figure the epithelium of the glomerulus is seen
to be distinct from the suprarenal for a short distance ; but in
a part of the section I was unable, after a tolerably careful
examination, to convince myself of the existence of any distinct
layer of epithelial cells separating the cavity of the glomerulus
from the adjacent blastema.

Such a section as that shown in fig. 18 may be seen in almost
any glomerulus in the region of the suprarenal during the
seventh day. On the eighth day the appearance of the blas-
tema changes. While still retaining its connection with the
glomeruli (fig. 19) it has increased considerably in size, and its
component cells have acquired most of the histological charac-
ters which they present in the adult. The individual cells are
large, polygonal, and distinctly marked off one from the other ;
their protoplasm, which does not stain very readily with car-
mine or hsematoxylin, is clear or very finely granular, and their
nuclei are clear, oval, or elliptical, with well-defined contours
and a number of coarse granules in their interior. The most
characteristic feature in the blastema of this age is, however,
the definite arrangement of the cells into columns, giving them,
more than at any earlier stage, the appearance of the cortical
substance of an adult suprarenal.

I have already said that the blastema during the eighth day
remains attached to the glomeruli ; such appearances as those
seen at x in fig. 19, which are very frequent, tempt one
strongly to believe that at tbis time the number of the cells
composing it may be added to by proliferation from the glome-
rulus epithelium ; but I have not been able to satisfy myself
that this is the case.

From this time the changes in the cortical blastema, so far
as I have followed them, do not differ in any important parti-
culars from those described by Braun in Lacerta muralis.

A noticeable feature throughout the whole of the early
history of the organ under consideration in the chick, is the
very distinct separation between the cortical blastema and the
blood-vessels, the original blastema-cells being at a great

ON THE SUPRARENAL BODIES OF VERTEBRATA. 147

distance from any vessel, and the later tissue only approaching
one when it has so greatly increased in size as to have pushed
all the intervening mesoblast, so to speak, on one side. There
is no possibility of believing, in this case at least, that the
walls of the blood-vessels have the slightest share in the pro-
duction of the cortical blastema.

The great difference between the results of the investigations
of previous observers and those which have just been described,
is sufficiently obvious. If, however, the accuracy of my
observations be admitted, we have a much more rational expla-
nation of the phylogeny of the suprarenals than is possible if
we adopt the view of Braun, and others ; — an explanation which
receives support, both from the anatomical relations of the
adult organs, and with those of the corresponding organs in
Myxinoids and Teleosteans.

In Bdellostoma, I have already1 attempted to show that
the head kidney has become modified so as to form an organ
functionally analogous to the suprarenals ; while in Teleos-
teans, a most remarkable series of modifications, affecting
every region of the kidney, has been described by Balfour and
Emery ; a series which seems to me to supply every stage
needful to complete our conception of the passage from such a
form as Bdellostoma to that of a higher vertebrate. Balfour
showed2 that the head kidney of many adult Teleosteans con-
sisted, not of renal tissue, but of a mass of parenchymatous
“ lymphatic ” material, richly supplied with vessels, whose
function, whatever it might be, was certainly not that of a
normal kidney. He afterwards found the same kind of modi-
fication to exist in the head kidney of the Teleosteoid
Ganoids.3

Though the observations of Balfour left it highly probable
that the “ lymphatic ” tissue described by him was really a
result of the transformation of part of the embryonic kidney,

1 This Journal, April, 1884.

! This Journal, 1882.

J “On the Structure and Development of Lepidosteus,” ‘Phil. Trans.,’
1882.

148

W. F. R. WELDON.

he did not investigate the details of its development. This
was afterwards done by Emery,1 with the following re-
sults : —

In those Teleostei which he has studied, Professbr Emery
finds that at an early stage the kidney consists entirely of a
single pronephric funnel, opening into the pericardium, and
connected with the segmental duct, which already opens to the
exterior. Behind this funnel, the segmental duct is surrounded
by a blastema, derived from the intermediate cell mass, which
afterwards arranges itself more or less completely into a series
of solid cords, attaching themselves to the duct (see fig. 20).
These develop a lumen, and become normal segmental tubules,
but it is, if I may be allowed the expression, a matter of
chance, how much of the blastema becomes so transformed
into kidney tubules, and how much is left as the “ lym-
phatic ” tissue of Balfour, this “ lymphatic ” tissue remain-
ing either in the pronephros only, or in both pro- and meso-
nephros.

We have here, as it seems to me, an explanation of the
reason why the suprarenals, while arising from the pronephros
in Mvxinoids, are mesonephric in origin in the higher Verte-
brates. The same causes which led to the degeneration of the
original renal pronephros (causes among which the specialisa-
tion of the pericardium, and the development of the air-bladder
and lungs may have played a considerable part) — the same causes
which led to the establishment of the mesonephros as the chief
seat of renal secretion may, and indeed must, have rendered
advantageous the suppression of any glandular organ in the
pronephric region; and thus, when, in consequence of the change
of function of the Wolffian duct more and more of the meso-
nephros became useless as a kidney, it is easy to understand
how some of its component parts underwent in their turn the
same change of function as had been undergone by the
anterior part of the renal organ at an earlier stage in its
evolution, stages in the completion of this process remaining

1 ‘Atti dell’ Academia dei Lincei.,’ 1882.

ON THE SUPRARENAL BODIES OF VERTEBRATA. 149

both in the commencing modification of the Teleostean meso-
nephros on the one hand, and on the other in the suprarenal
of Amphibia, with its own “ portal ” circulation, and its close
connection with the renal tissue.

150

W. F. E. WELDON.

EXPLANATION OF PLATES XI & XII,

Illustrating Mr. W. F. R. Weldon's Paper “On the Supra-
renal Bodies of Vertebrata/’

Complete List of Reference Letters.

At. Alimentary canal. Ao. Aorta. Bv. Blood-vessel, gl. Glomerulus.
g.ep. Glomerulus epithelium, pe.ep. Peritoneal epithelium. Mes. Mesentery.
v. c. Vena cava. s. t. Segmental tubule, s. str. Testicular tubule, s. r. b.
Suprarenal blastema. W. r. Wolffian ridge.

The figures were in all cases drawn by the aid of a Zeiss’s camera lucida.

Fig. 1. — Transverse section through a glomerulus of an embryo ofLacerta
muralis with twenty-one protovertebree.

Fig. 2. — Similar section through an embryo with twenty-three protover-
tebrae.

Fig. 3. — Similar section through an embryo 8 mm. long.

Fig. 4. — Similar section from an embryo 10 mm. long.

Fig. 5. — Similar section from an embryo of 11 mm.

Fig. 6. — Similar section from an embryo of 13 mm.

Fig. 7. — Similar section from an embryo of 18 mm.

Fig. 8. — Transforming blastema of teleostean kidney, copied from Emery.
Figs. 9 and 10. — Two consecutive sections through an embryo of Pris-
tiurus melanostomus of 8 mm.

Figs. 11 — 13. — Consecutive sections from an embryo of Pristiurus of 8^ mm.'
Figs. 14 and 15. — From an embryo of Pristiurus of 10 mm.

Fig. 16. — From an embryo of Pristiurus slightly older than that figured in
figs. 14 and 15.

Fig. 17. — From a five-day chick.

Fig. 18. — From a seven-day chick.

Fig. 19. — From a nine-day chick.

/Irr. <%H*rn~Vct.m:.. W - "ft XI

peep.

\Z •? -

> ■'

10.

- : . . • ■ JST

Mes.

14.

W'.O.

s. t\

Mes.

\

W.D.

17.

CERTAIN BRITISH HETERCECISMAL UREDINES.

151

On the Life-History of certain British Heterce-
cismal Uredines. (The Ranunculi iEcidia
and Puccinia Schceleriana.)

By

Charles B. Plowright.

In the following communication, the life-histories of five
species of Uredines which during the past three years have
been investigated are detailed, together with an enumeration of
the experimental cultures performed in connexion therewith,
by which it will be seen that the conclusions have not been
hurriedly arrived at. It may be thought that many of these
cultures are needless repetitions, but I have found myself com-
pelled to differ in certain points with the eminent Continental
botanists who have made this subject their special study, and
to whom, indeed, we owe all the information we at present
have concerning it. It will be seen that these differences are
mainly connected with the host plants upon which the various
Uredines in question occur. It is hoped that my eminent
confreres will recognise the fact that my investigations have
not been made in any spirit of captious criticism, but rather
with the object of verifying and amplifying the discoveries
they have already made. Hence when any statement of theirs
has been found to accord with my own results, this particular
culture has not been repeated many times. For example,
with Uromyces dactylidis twenty-seven experiments were
made altogether, but of these only five were confirmatory of
Schroter’s statement as to its iEcidium occurring upon Ranun-
culus bulbosus, for the simple reason that Schroter’s
statement on this point is correct, and it would have been a

152

CHARLES B. PLOWRIGHT.

mere waste of time to have proved what is already known to
be true. The other twenty cultures were made upon other
host plants, and were mostly repetitions made over and over
again before I felt myself justified in differing from him.

Experiments 1 to 100 were made in 1882.

„ 101 „ 244 „ „ 1883.

„ 245 „ 426 „ „ 1884.

The Ranunculi iEcidia.

History of the Subject. — The various members of the
Ranunculus family are peculiarly liable, as Schroter1 has
pointed out, to be affected with the secidiospores of various
Uredines. In fact in this country no less than eleven species
have iEcidia occurring more or less frequently upon them,
whereas only four species have either teleutospores or uredo-
spores affecting them. The secidial host plants belonging to
the Ranunculacese in this country are Clematis vitalba, L. ;
Thalictrum alpinum, L. ; flavum, L. ; Anemone

nemorosa, L.; ranunculoides, L. ; Ranunculus acris,
L. ; repens, L. ; bulbosus, L. ; ficaria, L. ; Caltha
palustris, L., and Aquilegia vulgaris, L. ; while teleu-
tospores and uredospores only occur on Thalictrum flavum,
L. ; Anemone nemorosa, L. ; Ranunculus ficaria, L. ;
and Caltha palustris, L.

The author above quoted has shown that many of these
iEcidia are heteroecismal. He pointed out that those writers
who, like Fuckel2 and Cooke,3 have affiliated the very common
HScidium upon R. ficaria with the Uromyces, which also occurs
upon this plant, were wrong in so doing; that these two fungi
are distinct species, having separate and altogether unlike life-
histories, and that their occurrence upon the same host plant is
a mere accidental circumstance. He further showed that the
iEcidium in question is really connected with a Uromyces which

1 Schroter, * Cohn’s Beitrage zur Biologie der Pflanzen,’ vol. iii, Heft 1,
p. 59.

2 Fuckel, ‘ Symbol. Mycol.,’ p. 64.

s Cooke, ‘Uromyces in Grevillea,’ vol. vii, p. 136.

CERTAIN BRITISH HETERCECISMAL UREDINES.

153

affects the various Pose. This he did by a series of artificial
cultures. He was led to try these experiments from his
previously obtained knowledge of the life-history of Uromyces
dactylidis, which he found had its uredo and teleutospores
upon Dactylis glomerata while its secidiospores occur upon
Ranunculus bulbosus. The results obtained by Schroter
were (1) that Uromyces dactylidis, Otth, is produced
from a Uredo upon Dactylis possessing capitate paraphyses
having its iEcidiaupon Ranunculus bulbosus and repens.
(2) That the Uredo without paraphyses and its Uromyces upon
Poa nemoralis are connected with the iEcidium upon R.
ficaria. Winter, in his latest work,1 following Schroter, thus
gives the relationships of these species.

Uromyces dactylidis, Otth.
ibcidiospores on. Teleutospores on.

Ranunculus acris, L. Arrhenatherum elatius, M.and K.

„ polyanthemos, L. Poa nemoralis, L.

„ repens, L. Dactylis glomerata, L.

„ bulbosus, L. Festuca elatior, L.

Uromyces poa Rabh.

iEcidiospores on. Teleutospores on.

Ranunculus ficaria, L. Poa nemoralis, L.

„ pratensis, L.

Cornu2 has, however, still more recently shown that Ranun-
culus repens is the host plant of the iEcidium of Puc-
cinia arundinacea, D. C. He further considers that
P. graminis, Pers., occurs upon Phragmitis communis
not unfrequently, when it is characterised amongst other things
by forming long black lines on the stem.

Rostrup3 regards the JScidium on Ranunculus repens as
being due to Uromyces poae, Rbh.

1 Winter, * Rabenhorst’s Kryptogamen Flora,’ vol. i, p. 162.

3 Cornu, ‘Comptes Rendus,’ 26 Juin, 1882.

3 I regret having mislaid the communication which Mr. Rostrup sent me.
It was a list of Danish fungi, in which the aecidiospores of Uromyces poae
were given as occurring upon Ranunculus ficaria and repens.

154

CHARLES B. PLOWRIGHT.

Personal Investigations. — The above being the state of
our information concerning the affinities of the Ranunculi
iEcidia, the following series of experimental cultures have
oeen made in the hope of definitely clearing up the matter.
These were commenced in 1882 and continued through
1883 and 84.

Contradictory as the above views appear to be in many
points, yet it will be seen that they are none the less in the
main correct.

In order to render this communication the more lucid at the
expense of increasing its length to some extent, each species
will be treated separately, and have appended to it a tabular
statement of the cultures made respecting it.

Uromyces pose, Rbh. — This Uromyces occurs in England
very abundantly upon Poa trivialis, L., and P. pratensis, L.
I have not met with it upon any other species of Poa nor upon
any other grass. Of course it may occur upon other grasses,
but I have never found it, nor have I been able to produce it
upon any other. As Schroter has shown, its iEcidium is very
abundant from February to May upon Ranunculus ficaria.
But not only is R. ficaria its host, but also R. repens.
This latter fact was suggested to me before I knew of Rostrup’s
views from the profusion with which the above-named Poae
were attacked by the Uromyces in localities in which R.
ficaria did not occur, and in which R. repens did. A series
of seven experiments were made, however, by placing the
spores of iEcidium Ranunculi repentis upon Dactylis
glomerata (Expts. 29, 30, 119, 122, 131, 153, 154) before
Schroter and Winter’s statement that it is connected with
Uromyces dactylidis was definitely rejected. The material
employed in these experiments was not collected from a single
locality ; on the contrary, specimens were procured from several
places near King’s Lynn, and even from Shrewsbury, kindly
sent to me by Mr. W. Phillips, F.L.S. Moreover, the iEcidium
upon R. repens gave rise to no Uredo upon P. nemoralis
(143) nor upon P. annua (155). Conversely the germinating
spores of Uromyces dactylidis in five cultures upon

CERTAIN BRITISH HETERCECISMAL UREDINES.

155

R. repens gave no result (118, 249, 254, 270, 290) ; we may
therefore conclude that Uromyces dactylidis is not con-
nected with the iEcidium upon R. repens.

On the other hand, the iEcidium on R. repens was found
to produce the Uredo and Uromyces uponPoa trivialis (190,
322, 333). But here another difficulty confronted me, inas-
much as no less than in seven other cultures with the spores
of the iEcidium on R. repens applied to P. trivialis and
P. pratensis did I fail to obtain any result (120, 146, 147,
155, 191, 336, 370). It is all very well to say that one
positive result is of more value than an indefinite number of
negative results, but succeeding only in three out of ten cultures
requires some satisfactory explanation. Those who have per-
formed cultures with the Uredines know well enough how easy
it is to fail from a variety of causes. I have failed more than
once in infected wheat plants with Uredo linearis in which
no question of specific identity is concerned. It is further-
more very easy to fail with cultures in which secidiospores are
employed as the infecting material, because, in the first place,
the secidial cup is full of spores, but only the few mature ones
at its orifice will germinate at all ; and in the second place,
because even these ripe spores very rapidly lose their germi-
native power. Still these facts were well enough known to
me, at any rate in my later cultures when I had also gained
some knowledge of the minutiae required for successfully
manipulating with these bodies. As will be seen later, the
explanation simply is that upon Ranunculus repens
another iEcidium occurs (that of P. Magnusiana) which so
closely resembles it in appearance, and in the form, size, and
colour of its spores, that I am quite unable to tell the one from
the other. I do not say that this cannot be done by others
more skilled in the differentiation of uredine spore forms, but
up to the present I have been unable to do so.

The iEcidium on R. ficaria gave no result on P. nemoralis
(133, 296), nor upon Dactylis glomerata (297), but upon
P. trivialis (295) it gave rise to the Uredo of Uromyces
Poae.

156

CHARLES

B. PLOWRIGHT.

No. of

Infecting Material.

Plant Infected.

Date of

£xpt.

Infection.

let Result.

190.

JScidium Ranunculi

Poa trivialis

19 June.

10 July.

repentis

322.

J)

99

99 99

25 Apr.

14 May.

333.

99

99

99 99

9 May

20 May.

295.

99

Ranunculi

99 99

9 Apr.

10 May.

ficari®

29.

99

Ranunculi

Dactylis glome-

13 May

—

repentis

rata

30.

99

99

99 19

13 May

—

119.

99

99

99 99

28 Apr.

—

122.

99

99

99 99

28 Apr.

—

131.

99

99

99 99

2 May

—

153.

99

99

99 99

31 May

—

154.

99

99

99 99

31 May

—

143.

99

99

Poa nemoralis

21 May

—

155.

99

99

„ trivialis and

1 June

—

annua

118. Uromyces dactylidis

Ranunculus re-

28 Apr.

—

pens

249.

99

99

99 99

2 Feb.

—

254.

99

99

99 99

8 Feb.

—

270.

99

99

99 99

5 Mar.

—

290.

99

99

99 19

7 Apr.

—

120.

iEcidium Ranunculi

Poa pratensis

28 Apr.

—

repentis

146.

99

))

99 99

21 May

—

147.

99

99

99 99

26 May

—

191.

■ 99

99

„ trivialis

16 June

—

336.

99

99

91 99

9 May

—

370.

99

99

99 99

21 May

—

133.

99

Ranunculi

„ nemoralis

2 May

—

ficarise

296.

99

99

99 99

9 Apr.

—

297.

99

99

Dactylis glome-

9 Apr.

—

rata

Puccinia Magnusian a. — There are certainly two Pucciniae
which occur in this country upon one common reed (Phrag-
mitis communis, Trin.),the one characterised by its teleuto-
spores being born upon very long pedicels and its brown uredo-

CERTAIN BRITISH HETERCECISMAL UREDINES.

157

spores not being mixed with paraphyses. This is P. phrag-
mitis, Schum = (P. arundinacea, D. C.). The other, P.
M a gnu si an a, Korn, has its teleutospores with much shorter
pedicels, and they often form long black lines running down
the sheaths and stems of the affected plant. Its uredospores,
moreover, are deep orange in colour, and always, as far as I
know, mixed with paraphyses. This species has in this country
hitherto generally been regarded as a variety of Puccini a
graminis, Pers.

In a previous paper1 I have shown that P. phragmitis has
its secidiospores upon Kumex conglomeratus, crispus,
obtusifolius, hy drolapathum, and Rheum officinale
(Expts. 140, 178, 179, 180, 181, 182, 183, 334), and conversely
that the secidiospores of iEc. rumicis thus produced, when
placed upon Phragmitis, gave rise to the brown Uredo of
P. phragmitis without paraphyses (148, 166, 172, 188, 189,
208, 209). This being the case, it occurred to me, after
reading Cornu’s 2 communication that it was just possible he
might have confounded these two Puccinise, and that P. Mag-
nusiana might have its iEcidium upon Ranunculus repens.
This possibility was to me the more probable, because I had
in 1882 fallen into a similar error, and I had then operated in
the same manner as M. Cornu appears to have done, namely,
by placing leaves and stems of the Phragmites upon the plant
to be infected. Since 1882 all my cultures with these Puccinise
have been made by germinating the teleutospores in a watch-
glass, having previously separated them from the reed, and
examining them microscopically to insure against error from
the commingling of the spores of the two species. Now, it
happened that after reading M. Cornu’s paper I found, in the
autumn of 1883, a long, straight ditch full of reeds upon
which at both ends, for about twenty yards, the Phragmites
were completely blackened by P. Magnusiana. This ditch
was about a quarter of a mile in length, and the reeds which

1 Plowright, “ On the Life-History of the Dock -dEcidium,” ‘ Proc. Royal
Soc.,’ No. 228, 1883, pp. 47 — 49.

2 Cornu, ‘ Comptes Rendus,’ 26 June, 1882.

158

CHARLES B. PLOWRIGHT.

grew in the intervening part were quite free from the Puccinia.
Neither did I observe anywhere in it a single pustule of P.
phragmitis. In the spring of 1884 I from time to time
visited this ditch and carefully examined the Pumices and
Ranunculi growing on its banks, for I felt certain, from the
localised profusion with which P. Magnusiana occun’ed, that
I should meet with its iEcidium at both ends, but not in the
central part. This surmise was found to be correct, and to
confirm the conclusion I had already, from a series of ex-
perimental cultures, arrived at. At both ends of the ditch
I found the Rumices free from iEcidia, but the plants of
Ranunculus repens abundantly affected with iEcidia,
while in the middle neither one or other of these plants
had any iEcidium upon them. Germinating spores of P. Mag-
nusiana were placed upon Ranunculus repens with the
uniform result of giving rise to the iEcidium (315, 335, 358).
It is obvious that if Ranunculus repens is the host plant to
two specifically distinct iEcidia, the possibility of other Ranun-
culi also being hosts of one or other of them must be considered.
P. Magnusiana was, therefore, applied to R. acris (360)>
R. ficaria (361), R. auricomus (359), but without any
result. When, however, R. bulbosus was infected it always
developed the iEcidium (393, 394, 395, 396, 397), hence P.
Magnusiana has its iEcidium upon both R. repens and R.
bulbosus. Conversely, the secidiospores of P. Magnusiana
which had been artificially produced upon R. re pens (369)
and R. bulbosus (422), were placed on Phragmitis, where in
due time they gave rise to the orange Uredo with paraphyses.
To make more sure, a part of the same spores from R. repens,
which, when placed on Phragmitis (369) gave origin to the
Uredo of P. Magnusiana, were applied to Poa trivialis
(370), but they gave rise to no Uredo ; and in like manner a
part of the spores from the iEcidium R. bulbosus (423) were
placed upon Dactylis glomerata, but they gave rise to no
Uredo. The two iEcidia on R. repens were most carefully
examined side by side, but no difference could be detected by
me. As these two iEcidia occur in a state of nature, however,

CERTAIN BRITISH HETERCECISMAL UREDINES.

159

that of Uromyces pose occurs rather earlier in the year than
that of P. Magnusiana.

Puccinia phragmitis gave rise to no iEcidium on Ranun-
culus repens (137, 138), nor on R. ficaria (142), although
the teleutospores were in active germination when employed.

But the subject is not even yet fully exhausted. The emi-
nent Danish botanist, Mr. P. Nielsen, in 1879,1 found that the
iEcidium onRumex acetosa was developed from P. phrag-
mitis, and Winter 2 gives his adherence to this view. Now,
Mr. Nielsen is a most careful and expert experimenter with
the Urediues. I therefore performed the following experi-
ment. A quantity of P. phragmitis was placed in water in
a watch-glass, when it was found, by microscopical examination,
that the spores were in active germination ; one half was
placed on a plant of Rumex acetosa (347), and the other
half upon one of R. obtusifolius (346). The infected plants
were both treated alike, but while in nine days the R. obtusi-
folius became affected with iEcidium rumicus, the R.
acetosa remains to this date (Oct. 31st) free. This method
of experimenting in duplicate is a very valuable one, and I
have frequently employed it inasmuch as it lessens the possi-
bility of error. P. phragmitis was also applied to R. acetosa
(177), but without result, as was also the case when P. Mag-
nusiana was employed (139, 179, 206, 323). Of course,
these are only negative results, but it is at least remarkable
that I should have had no difficulty in producing iEc. rumicis
on the other Rumices, but always have failed with R. acetosa.
It happens, however, that upon Phragmitis Professor Oude-
mans3 has recorded the occurrence in Holland of P. straminis ;
and in the early part of the year 1882 Mr. Bloome sent me,
from near Worthing, a Puccinia on reed, which I regarded at

1 Rostrup, * Heteroeciske Uredineer,’ p. 10 ; ‘ Observations nouvelles sur
les Uredinees a generations alternantes,’ p. 3 ; ‘ Aftryk. af Oversigt over
d. K. D. Yidensk. Selsk.,’ Fordhandl, 1884.

2 Winter, ‘ Rabenhorst’s Kryptogamen Flora,’ 1881, p. 222.

3 Oudemans, ‘ Bijdrage over niew ontdekte Champignons voor de Flora van
Nederland,’ 1871, p. 22.

160

CHARLES B. PLOWRIGHT.

that time as being either P. straminis or P. sessilis, but,
unfortunately, the specimen was not preserved by me. This
being the case, it is possible that the Puccinia which Oudemans
and myself have seen on reed may be a third species connected
with the iEcidium on Rumex acetosa; and as it is of such an
inconspicuous appearance, may have accidentally crept into Mr.
Nielsen’s cultures. This, of course, is a mere conjecture upon
my part, which can only be confirmed by direct observations.
Lastly, with regard to the belief that P. Magnusiana is
only a form ofP. graminis occurring upon reed, a duplicated
experiment was performed in which P. Magnusiana, taken
from the black lines on the stem, was placed upon Berberis
vulgaris (362) and Ranunculus repens (358) ; on the
former it gave no result, on the latter in ten days its iEcidium.

No. of Infecting Material. Plant Infected. Date of

Esrpt.

315.

Puccinia

Magnusiana

Infection.

Ranunculus re- 24 Apr.

1st Result.

10 May.

335.

39

99

99

pens

„ 9 May

2 June.

358.

33

99

99

„ 18 May

28 May.

393.

33

99

93

bulbosus 7 June

15 July.

394.

9 9

99

99

„ 7 June

15 July.

395.

99

39

39

* „ 7 June

15 July.

396.

99

99

99

„ 7 June

15 July.

397.

33

99

39

„ 7 June

15 July.

34.

33

99

Rumex conglom- 18 May

—

70.

33

99

99

eratus

„ 15 June

81.

39

99

39

„ 15 June

—

167.

93

33

99

„ 5 June

—

72.

33

99

99

obtusifolius 15 June

—

169.

99

39

99

„ 5 June

—

168.

93

99

99

crispus 5 June

—

171.

93

99

99

kydrola- 7 June

—

205.

99

99

99

patkum

„ 28 June

_

184.

99

99

Rlieu

in officinale 12 June

—

187.

99

99

99

„ 13 June

—

CERTAIN BRITISH HETERCECISMAL UREDINES.

161

Expt.

Infection.

1st Result.

f 422.*

.zEcidium

Ranunculi

Phragmitis com-

1 July

20 July.

■s

bu

Ibosi

munis

[423 *

n

it

Dactylis glomerat

a 1 July

—

( 369 *

Ranunculi re-

Phragmitis com-

21 May

9 June.

■s

pe

ntis

munis

[370*

)>

It

Poa trivialis

21 May

—

* Prom Puc

cinia Magnusiana.

140.

Puccinia phragmitis

Rumex crispus

16 May

27 May.

178.

II

„ conglomeratus 8 June

22 June.

179.

It

„ obtusifoliu

s 8 June

19 June.

180.

II

II II

8 June

19 June.

181.

II

ti

„ hydrola-

8 June

19 June

pathum

334.

„

It

II 19

9 May

1 June.

182.

it

ii

R.heum officinale

8 June

19 June.

183.

it

11

II It

8 June

19 June.

148.

iEcidium Rumicis

Phragmitis com-

27 May

4 June.

munis

166.

it

it

a a

3 June

12 June.

172.

„

II

a a

7 June

—

188.

„

ti

a a

16 June

10 July.

189.

it

tt

a a

16 June

10 July.

208.

n

II

a a

2 July

20 July.

209.

it

II

a it

2 July

30 July.

137.

Puccini

i phragmitis

Ranunculus re-

18 May

—

pens

138.

It

II

a a

18 May

—

142.

It

it

„ ficaria

20 May

—

[346.

it

II

Rumex obtusifo-

16 May

25 May.

lius

[347.

it

II

„ acetosa

16 May

—

177.

it

„

II II

8 June

—

139.

a

Magnusiana

II II

17 May

—

179.

a

II

II II

5 June

—

206.

it

II

II II

28 June

—

323.

it

II

II II

26 April

—

360.

it

II

Ranunculus acris

18 May

—

361.

li

II

„ ficaria

18 May

—

359.

a

II

„ auricomus

18 May

—

362.

it

It

Berberis vulgaris

18 May

—

vox.

xxv. —

-NEW SEK.

L

162

CHARLES B. PLOWRIGHT.

Uromyces dactylidis, Ottb. — In 1861 Ottli1 described
this Uromyces as occurring upon Dactylis glomerata
accompanied by its uredospores. He describes the latter, but
makes no allusion to their being associated with paraphyses,
while upon the contrary, in another part of the same commu-
nication,2 he describes an Epitea on Dactylis with “ colourless,
clavate, rather short epiphyses/5 In 1873 Schroter discovered
that U. dactylidis has its aecidiospores upon Ranunculus
bulbosus. In 1878 he states3 that the secidiospores occur
not only on R. bulbosus, but also upon R. repens, L. ;
R. acris, L. ; R. polyanthemos, L. Winter,4 more recently,
while giving the same secidial host plants, states that the
Uromyces occurs not only upon Dactylis glomerata, but also
upon PoanemoralisjL.; Festucaelatior, L., and A vena
elatior, L.

Both these last-named authors consider the uredospores of
the Dactylidis to be characterised by the possession of capitate
paraphyses. Near King’s Lynn Uromyces dactylidis
occurs in one locality sufficiently near for me to obtain
material for experiment and also to watch its growth as it
occurs naturally.

Seven attempts made to produce the Uromyces upon Dactylis
from the spores of the iEcidium in R. repens uniformly failed
(29, 30, 119, 122, 131, 153, 154), and conversely, five attempts
to produce the iEcidia upon R. repens from the teleutospores
of the Uromyces also failed (118, 244, 254, 270, 290). The
aecidiospores applied to Poa nemoralis (143) also pro-
duced no effect. But when the germinating teleutospores of
this Uromyces were placed upon R. bulbosus they invariably
gave rise to the iEcidia (248, 269). In order to see whether
this fungus had its iEcidia upon any other of the commoner
species of Ranunculus duplicated experiments were performed
on R. acris (250, 271), R. ficaria (251, 255, 272), and

1 Of tli, in ‘ Mittheilungen der Naturf. Gesselscliaft,’ Berne, 18G1, p. 85.

2 Ottli, loc. cit., p. 81 .

3 Schroter, in * Cohn’s Beitrage,’ Band iii, pp. 58, 59.

* Winter, ‘ Rabenkorst’s Kryptogamen Flora,’ 1881, p. 162.

CERTAIN BRITISH HETERCECISMAL UREDINES.

] 63

R. auricomus (252, 273), but with no result. Hence it
appears that Uromycesdactylidis has its secid iospores upon
R. bulbosus only, and nut upon R. repens or acris.

Spores from the iEcidia on R. bulbosus were placed upon
Dactylis glomerata (279, 289, 298), where they in all cases
gave rise to a Uredo followed by the Uromyces dactylidis.
iEcidiospores of this iEcidium placed upon Poa pratensis (299)
and P. amma (300) gave no result. These last two cultures
were duplicated with expt. 298.

In no case, however, in which the Uredo was produced upon
Dactylis could I find the least trace of any paraphyses, nor
could any be found upon the Dactylis uredo, as it occurs
naturally here. The question, therefore, presents itself, Have
Dr. Schroter and myself the same fungus in view ? It is very
unlikely that there should be two Uromyces upon Dactylis
both having their iEcidia upon R. repens. Personally, I
rather incline to the belief, and it is only a belief which subse-
quent observation must confirm or disprove, that these
paraphyses are found in certain conditions of the Uredo and
not in others; that in other words, their value as a specific
character is not of vital importance. But what these condi-
tions are which favour the development of paraphyses, I am
unable, at present at any rate, to say. Just as I was unable to
discover any difference externally between the two iEcidia
upon R. repens, so am I unable to point out any anatomical
differences between the two iEcidia on R. bulbosus,
namely, that of Uromyces dactylidis and Puccinia
Magnusiana. Physiologically, however, they are distinct
enough.

164

CHARLES B. PLOWRIGHT.

No. of Infected Material. Plant Infected. ' Bate of

Expt.

Infection.

1st Result.

248.

Uromyc

es dactylidis

Ranunculus

bulbosus

s 2 Feb.

6 Mar.

269.

39

99

99

99

5 Mar.

26 Mar.

279.

AEcidium

Ranunculi

Dactylis glomerata

17 Mar.

25 Apr.

bulbosi

289.

99

99

99

99

7 Apr.

20 Apr.

298.

„

99

99

99

9 Apr.

20 May.

29.

99

Ranunculi repentis „

99

13 May

—

30.

99

99

99

99

13 May

—

119.

99

99

99

99

28 Apr.

—

122.

99

99

99

99

28 Apr.

—

131.

99

99

99

99

2 May

—

153.

99

99

99

93

31 May

—

154.

99

99

99

99

31 May

—

118.

Uromyces dactylidis

Ranunculus

i repens

28 Apr,

—

249.

99

99

99

99

2 Feb.

—

254.

99

99

99

99

8 Feb.

—

270.

• 9

99

99

99

5 Mar.

—

290.

99

99

99

99

7 Apr.

—

143.

iEcidium

Ranunculi re-

Poa nemoralis

2 May

—

pentis

250.

U rotny (

:es dactylidis

Ranunculu

s acris

2 Feb.

—

271.

99

39

))

»)

5 Mar.

—

251.

99

99

99

ficaria

2 Feb.

—

255.

„

99

99

99

8 Feb.

—

272.

99

99

99

99

5 Mar.

—

252.

99

99

„ auricomu

s 2 Feb.

—

273.

99

99

99

99

5 Mar.

—

299.

iEcidium

i Ranunculi

Poa pratensis

9 Apr.

—

bulbosi

300.

99

99

„ trivial

is

9 Apr.

—

Puccinia perplexans, n. sp. — In the spring of this year
I found in two places near King’s Lynn upon Alopecurus
pratensis, L., Avena elatior, L., and upon some blades of
grass which I believe belonged to one of the Poae, the exact
species of which I was unable to determine, an abundant golden
yellow Uredo, the spores of which were freely mixed with well-
developed capitate paraphyses. Naturally the conclusion was
arrived at that here was the Uredo with paraphyses, which
Winter and Schroter have associated Uromyces dactylidis.
The localities were from time to time revisited, but instead of

CERTAIN BRITISH HETERCECISMAL URED1NES. 165

finding the teleutospores of this paraphysed Uredo to be a
Uromyces they were found to be those of a Puccinia. Further
search was rewarded by gathering the last year’s teleutospores
sparingly upon the Poa, but abundantly upon the other two
grasses. These Puccinia spores germinated well, and were used
in the following experiments. In both localities above referred
to numerous plants of Ranunculus acris were found in
close proximity to the grasses affected with the iEcidium.
The germinating teleutospores from the last year’s Puccinia
from the Poa (?) Avena elatior and Alopecurus were applied
to R. acris (373, 381, 382, 383, 388, 389), and in every
instance the iEcidium was produced. Here, then, was quite
an unexpected discovery, that instead of the iEcidium on
R. acris being connected with a Uromyces at all, it was
connected with a Puccinia. Conversely the aecidiospores in
question were placed upon Alopecurus (401, 402, 404) and
Avena elatior (405), with the result of giving rise to a Uredo,
followed in due course by the Puccinia. This Uredo, however,
strange to say, was never once accompanied by any paraphvses
at all. This puzzled me very much, for the paraphysed Uredo
as it occurred naturally was always accompanied by the
Puccinia, but by culture the result was invariably as above
stated. The possibility of this Puccinia giving rise to a para-
physed Uredo upon some other graminacious host suggested
itself. The secidiospores from Ranunculus acris were,
therefore, applied to Poa trivialis (364), P. nemoralis
(367), P. pratensis (365, 366), P. compressa (?) (378),
Dactylis glomerata (379), Lolium perenne (377, 403),
upon all of which paraphysed uredospores are known to occur,
but in every case without any result.

Ranunculus acris was infected with the germinating
teleutospores of Uromyces dactvlidis (250, 271) but with
no success, as was also the case when P.Magnusiana (360) was
employed. Puccinia perplexans bears a strong anatomical
resemblance to P. rubigo-vera, the most obvious difference
being that the last-named species has its teleutospores sur-
rounded by a bed of dark brown paraphyses. In point of fact

166

CHARLES B. PLOWRIGHT.

I have previously mistaken these two Puccinia the one for the
other. P. perplexans upon Lvcopsis arvensis (311, 312,
326), Symphytum officinale (314, 329, 330), Borago
officinale (327), and Pulmonaria officinale (328) gave
no result. The same was the case when Ribes grossularia
(371) and Lonicera pericly menum (313, 317) were infected
with it.

Puccinia perplexans may be thus described —

I. iEcidiospores = iEcidium Ranunculi acridis. —
Spores, 20 to 25 ju. in diameter, rather more orange in colour
than those of the other Ranunculi ^Ecidia, otherwise not
distinguishable.

II. Uredospores. — Sori rubrotund elliptical, but mostly
linear. On both surfaces of the leaves, especially on the upper,
scattered but sometimes confluent, soon naked golden yellow.
Spores, globose, oval or ovate, orange, finely echinulate 20 to
25 jx. wide by 30 to 35 /x. long. With or without capitate
paraphyses.

III. Teleutospores. — Sori small, almost black, punctiform,
linear, or elliptico-elongate, covered by the epidermis, often
clustered and confluent. Spores very irregular in form and
size. Clavate, oblong, or subfusiform on very short pedicels,
apex sometimes thickened, sometimes not ; upper cell rounded,
truncate, or attenuated, often obliquely ; lower cell generally
somewhat cuneiform, central constriction slight or absent.
Epispore pale clear brown, often apparently coarsely granular,
40 to 60 fx. long by 10 to 12 fx. wide.

I. On Ranunculus acris. II. and III. On Alopecurus
pratensis, Avena elatior and Poa sp. ? Near King’s
Lynn. May and June, 1884.

CERTAIN BRITISH HETERCECISMAL UREDINES. 167

No. of
Expt.

Infecting Material.

Plant Infected.

Date of

Infection. 1st Result.

373. Puccinia perplexans

Ranunculus acris

23 May

9 June.

381.

JJ

tt

it tt

29 May

9 June.

382.

it

tt

a it

29 May

9 June.

383.

ft

tt

a a

29 May

12 June.

388.

it

it

a a

31 May

9 June.

389.

ff

a

it tt

31 May

9 June.

401. iEcidium

Ranunculi

acridis

Alopecurus pra-
tensuni

13 June

27 June.

402.

ft

tt

tt a

13 June

28 June.

404.

it

it

a a

16 June

30 June.

405.

tt

it

Abena elatior

1 July

20 July.

364.

it

it

Poa trivialis

19 May

—

367.

it

it

„ nemoralis

19 May

—

365.

a

it

„ pratensis

19 May

—

366.

ft

it

it a

19 May

—

378.

tt

it

„ compressa (?)

28 May

379.

a

it

Dactylis glomerata

28 May

—

377.

a

))

Lolium perenne

28 May

—

403.

it

„

it a

13 June

—

250.

Uromyces dactylis

Ranunculus acris

2 Feb.

—

871.

>*

a

it it

5 Mar.

—

360.

Puccinia Magnusiana

it tt

18 May

—

811.

it

perplexans

Lycopsis arvensis

23 Apr.

—

312.

a

it

it it

23 Apr.

—

326.

tt

a

a a

5 May

—

314.

a

a

Symphytum offici-
nale

23 Apr.

—

329.

a

tt

a a

5 May

—

330.

a

a

a a

5 May

—

327.

a

a

Borrago officinalis

5 May

—

328.

a

a

Pulmonaria offici-
nalis

5 May

—

371.

a

a

Ribes grossularia

23 May

—

313.

tt

a

Lonicera pericly-
menum

23 Apr.

—

372.

tt

tt

a it

23 May

—

Puccinia Schoeleriana, n. sp.

For many years past I have found on "North Wootton
Heath, near King’s Lynn, an iEcidium on S enecio Jacobsea,

168

CHARLES B. PLOWRIGHT.

L. This iEcidium is far from common in Great Britain, but
in the spring of 1882 I met with it again at Skegness, Lin-
colnshire. It has been hitherto regarded either as a spore
form of Puccinia compositarum, Mart., or of P. Sene-
cionis, Desm. In neither of the above localities was the
iEcidium accompanied by any Uredo or teleutospores upon
the same host plant. The North Wootton Station has been
examined with this point in view repeatedly, and at all seasons
of the year. Growing in company with the Senecio, both in
Norfolk and Lincolnshire, was, amongst other plants, Car ex
arenaria, L. In 1882 I noticed upon this Carex a Puccinia
occurred on those plants which grew in the vicinity of the
iEcidium-affected Seneciones, but not elsewhere. A series of
experimental cultures were consequently undertaken, 1883-4,
with the object of elucidation of the life-history of the Puc-
cinia in question. There are, as is already known, several
■well-marked species of Puccinia which occur upon various
carices, of these P. carices. Sebum.; P. limosae, Mag.;
P. sylvaticae, Schrot., and P. dioica Mag., have had their
life-histories worked out; whereas P. microsora, Korn;
P. caricicola, Fcke.; and P. vulpina, Schrot. have not. The
only species with which the Puccinia on P. arenaria can be
compared is P. dioica, Mag. I therefore sent specimens of
my plant to Dr. Magnus, -who at once pointed out the difference
between the teleutospores of the two Puccinia. In P. d i o i c a the
summits of the teleutospores are not only much more thickened,
but also generally prolonged upwards into a conical point.
The uredospores of P. dioica, too, are described by Dr.
Magnus1 as being similar to those of P. caricis, Schum.
Further, Rostrup2 has, to say the least, pointed out the strong
presumptive evidence that exists that Puccinia dioica has
its secidiospores upon Carduus palustris, L.; arvensis, L.,
and lanceolatus, L. It occurred to me that as Puccinia
caricis, Schum., is our commonest carex infesting Puccinia
in this country, C. Schoeleriana might only be a variety

1 Winter, ‘ Rabenhorst’s Kryptogamen Flora,’ 1881, vol. i, p. 182.

2 llostrup, loc. cit., p. 17 and p. v.

CERTAIN BRITISH HETERCECISHAL UREDINES.

169

of it occurring upon C. arenaria. The following duplicated
cultures were therefore made.

a. A quantity of P. Schoeleriana was germinated in water
in a watch-glass. This was divided into two parts, one of which
was applied to a young plant of Senecio J acobaea (260), and
the other to a plant of Urtica dioica (261). The Senecio
became affected with the iEcidium, but the Urtica did not.

b. Conversely, a quantity of P. caricis was germinated in
water in a watch-glass, and divided into two parts, one of
which was placed on a plant of Urtica dioica (258), and the
other upon a Senecio (259). The Urtica became affected
with the iEcidium, the Senecio did not. The spores of
JEcidium Jacobsese applied to Carex arenaria gave rise
to theUredo (199, 888, 389). The teleutospores of Puccinia
Schoeleriana in seven separate cultures in every instance
produced the iEcidium upon Senecio Jacobaea (260, 285,
291, 292, 293, 294, 447).

The Puccinia in question it is proposed to call Schoeleriana
after Schoeler,1 the Danish schoolmaster, who lived at the
beginning of the present century in the village of Hammel,
near Aarhuus, where he, by careful observation of what hap-
pened in nature, came to the conclusion that the yellow fungus
on barberry has some connection with the rust on oats. He
began these investigations in 1807, and continued them for
some years.

In 1816 Schoeler applied the “yellow dust” of the barberry
fungus to some healthy rye plants, which were still moist with
dew, and found the latter had, in the course of some few days,
become badly affected with rust; “while at the same time not
one rusty plant could be found anywhere else in the whole rye
field.” Schoeler was also aware of the fact that rye became
affected with rust without the intervention of the barberry.

1 Shoeler, “ Berberissens Skudelige Indflydelse pa Sseden,” ‘ Landaekom-
miske Tideuder,’ 1818, part viii, p. 289*

170

CHARLES B. PLOWRIGHT.

Puccinia Scliceleriana, n. sp.

I. iEcidiospores (iEcidium Jacobseae, Grev., ‘ Flor.
Edin./ p. 445), iEcidia in circular clusters, mostly upon the
under surface of the radical leaves ; cups with reflexed torn
white edges ; spermogonia upon the corresponding upper sur-
face of the affected leaves ; spores rounded, yellow, finely
echinulate ; I5fi to 20/j. in diameter.

II. Uredospores upon yellow discoloured spots ; sori elon-
gate or rubrotund, surrounded by the ruptured epidermis ;
generally hypophyllous spores, subglobose or ovate, yellowish
brown, rough; 25/ul to 30/ul long by 14/x to 20/u wide.

III. Teleutospores — Sori erumpent, oblong or elongate, large,
prominent, almost black ; hypophyllous naked, surrounded by
the ruptured epidermis ; spores on long, firm pedicels, slightly
constricted ; upper cell subglobose, ovate, or attenuated up-
wards ; apex much thickened, rounded, or pointed ; lower cell
cuneiform, often paler than the upper; rich brown, smooth ;
60yu to 80/j. long by 15 /u. to 20/t wide.

No. of

Infecting 1

Material.

Plant Infected.

Date of

Expt.

Infection.

1st

Result

199.

iEcidium

J acobaeae

Carex arenaria

21 June

15

July.

388.

99

99

99

99

31 May

12

June.

389.

99

99

99

99

31 May

20

June.

C 258.

Puccinia

caricis

Urtica

dioica

16 Feb.

11

Mar.

L 259.

99

99

Senecio

J acobaeae

16 Feb.

—

( 200.

99

Schceleriana

99

99

17 Feb.

15

Mar.

t 261.

))

99

Urtica

dioica

17 Feb.

—

285.

99

99

Senecio

Jacobaeae

6 Apr.

30

Apr.

291.

99

99

99

99

6 Apr.

30

Apr.

292.

99

99

99

99

6 Apr.

30

Apr.

293.

19

99

99

99

6 Apr.

30

Apr.

294.

99

99

99

99

6 Apr.

30

Apr.

447.

99

99

99

99

15 Sept.

26

Sept.

Conclusions. — From the experimental cultures above
it appears —

1. That Ranunculus repens is the host plant upon which
both Uromyces poae and Puccinia Magnusiana have
their secidiospores.

CERTAIN BRITISH HETERCECISMAL UREDINES.

171

2. That these two iEcidia are not to be distinguished from
each other anatomically.

3. That Ranunculus bulbosus is the host plant upon
which bothUromyces dactylidis and Puccinia Magnu-
siana have their secidiospores, which in like manner are
anatomically indistinguishable.

4. That Uromyces pose has its secidiospores upon Ranun-
culus ficaria and R. repens.

5. That Uromyces dactylidis in this district has its Uredo
without capitate paraphyses.

6. That the iEcidium upon Ranunculus acris belongs to
the life cycle of Puccinia perplexans, a Puccinia the
teleutospores of which occur upon Alopecurus pratensis,
Avena elatior, and Poa sp. (?), bearing a close resemblance
to those of P. rubigo-vera, but wanting the dark paraphyses
of the latter species.

7. That the uredospores of P. perplexans are sometimes
mixed with capitate paraphyses and sometimes without
them.

8. That Puccinia phragmitis has its secidiospores upon
Rumex hydrolapathum, R. obtusifolius, L. ; R. cris-
pus, L.j R. conglomeratus, Mur., and Rheum officinale.

9. That P. Magnusiana has its secidiospores upon Ranun-
culus repens and R. bulbosus.

10. That the iEcidium upon Rumex acetosa is neither
connected with P. Magnusiana nor with P. phragmitis.

11. That the iEcidium on Senecio J acobsea belongs to the
cycle of a Carex inhabiting Puccinia — P. Schoeleriana.

172

CHARLES B. PLOWRIGHT.

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CHITIN IN THE CARTILAGES OF LIMULUS AND SEPIA. 173

On the Occurrence of Chitin as a Constituent
of the Cartilages of Limulus and Sepia.

By

W, D. Halliburton, K.D., B.Sc.,

Sharpey Physiological Scholar, University College, London.

(From the Physiological Laboratory, University College, London.)

The question of the chemical composition of the cartilage
that occurs in various invertebrate animals does not seem to
have been the object of previous research.1 In an article
by Professor Lankester on “ The Skeleto-trophic tissues of
Limulus,” which appeared recently in this Journal,2 he states
that Professor Schafer having, at his request, chemically
examined the ento-sternite of that animal, had found that
chitin was probably present in that organ. Professor Lankester
subsequently placed a larger supply of this tissue in my hands
for the purpose of determining the presence of chitin; in
addition I have, at Professor Lankester’s suggestion, submitted
to a similar examination the cartilage found in the head of the
cuttle-fish (Sepia).

These cartilages are in appearance similar to that found in
vertebrate animals ; but chemically they are different, as they
contain chitin in addition to a chondrin-like body.

We may consider the subject under the following heads:

a. Composition of the Cartilage of Sepia.

b. Composition of the Entosternite of Limulus.

c. Existence of Chitin in the Liver of Limulus.

1 In his paper recently published on the subject of cartilage, Krukenberg
makes no reference to the cartilage of the two animals I have examined.
Krukenberg, “ Die chemischer Bestandtheile des ^norpels,’’ ‘ Zeitschrift fur
Biologie,’ xx Band, 3 Heft, Miinchen und Leipsig, 1884.

2 ‘ Quarterly Journal of Microsc. Science,’ Jan., 1884.

174

W. D. HALLIBURTON.

A. — Composition of the Head Cartilage of Sepia.
The specimens from which the cartilage was taken had been
preserved for some time in spirit. After having been soaked
in water for twenty-four hours to remove the spirit, it was
divided into small pieces, and various portions were treated in
the following ways :

1. — Some was boiled with distilled water in a sealed tube for many hours.

Apparently no change took place in the cartilage. After this time the
water was poured off, and tested as follows :

a. It did not gelatinise on cooling.

b. It contained no evidence of proteids.

c. Acetic acid gave no precipitate. This showed that no mucin had dissolved

in the water.

d. Solution of tannin, acetic acid, and ferrocyanide of potassium, lead ace-

tate, and mercuric chloride, all gave small amounts of precipitate.

2. — Hydrochloric acid was added to another portion. In a few hours in the

cold, the cartilage was completely dissolved ; on adding water to this
solution, a small amount was reprecipitated.

3. — Acetic acid was added to a third portion. The cartilage swelled up some-

what, but underwent no further change.

4. — To a fourth portion Baryta water was added. The cartilage became dis-

solved to some extent ; and on adding acetic acid to the solution, a
precipitate was obtained.

5. — Sulphuric acid was added to another portion. The cartilage turned of a

brownish hue, but did not dissolve until the application of a small
amount of heat, when a dark brown solution was formed. On dilut-
ing this, and heating it for half an hour in boiling water, it was found
to possess the property of reducing copper salts.

6. — To a sixth and last portion, strong solution of caustic potash was added.

The cartilage became in the course of a few hours disintegrated, and
to some extent dissolved ; but there was a considerable amount of
residue which was not lessened by boiling. The solution was found to
contain no sulphur.

The conclusions to be drawn from these reactions are as
follows :

1. Elastinis absent, because the cartilage is wholly soluble
in cold concentrated hydrochloric acid.

2. Keratin is absent, because the part soluble in potash
contains no sulphur ; and because acetic acid does not dissolve
anything from the cartilage.

CHITIN IN THE CARTILAGES OF LIMULUS AND SEPIA. 175

3. Mucin is present, as is shown by acetic acid causing a
precipitate when added to the solution in Baryta water.

4. Gelatin, if present at all, is present in very minute
quantity, as is shown by tannin producing a precipitate in the
watery solution; but not present in quantity sufficient to cause
gelatinisation.

5. The basis of the cartilage is a substance soluble in
alkalies. Chondrin is now regarded1 by many as merely a
mixture of mucin and gelatin ; it would seem that this is what
we have here ; the tests for both these bodies can be obtained ;
that the gelatinous element is, however, present to a slight
extent only is shown by the fact that gelatinisation does not
take place ; or this latter fact may be due to the coexistence of
chitin mixed with it.

6. That in addition to this chondrin-like body, the cartilage
contains a body insoluble even in boiling alkalies. This
residue after boiling with potash will presently be shown to
consist of chitin.

7. Little can be concluded from the fact that a sugar-like
body reducing copper salts can be obtained by boiling with
dilute sulphuric acid, since chondrin, mucin, and chitin all
behave in this way.

We have next to consider the composition of the residue left
after boiling with solution of potash.

A large quantity of the cartilage was taken, potash added ;
the residue, a colourless amorphous body, collected, and washed
thoroughly by decantation with distilled water. It was divided
into two parts, which were treated in the following way :

1. One part was dissolved by adding hydrochloric acid to it;
a clear solution was formed. This solution gave the following
tests :

a. On adding water it was reprecipitated.

b. Another portion was treated in a water-bath for about an
hour. The colour of the solution became brown. On evapo-
rating to dryness crystals of a brownish hue were formed ;

1 Mowckowitz, “Zur Histochemie des Bindegewebes,” * Verkandl. d. Na-
lurkist. Med. Vereins zu Heidelberg,’ Vol. i, Part 5.

176

W. D. HALLIBURTON.

portions of these were allowed to crystallise on a glass slide,
and then examined with the microscope ; they were found to pre-
sent the following appearances : — The crystals were single, and
also in clusters and star-shaped masses. They varied in size
considerably ; the average length was '07 to -08 mm., and the
breadth varied from ‘01 to ‘001 mm.

At first sight the star-shaped clusters reminded one of leucin
or tyrosin, but closer investigation showed that they were not
composed of these materials. They had a slightly brownish
tinge, and the crystals were oblique rhombic columns. Some
of these were so thin that they lay flat on the slide as rhombic
plates ; the angles of these rhombs were measured by means of
a goniometer stage attached to the microscope. The acute
angle was found to be very acute, being on the average 39° 25',
the obtuse angle being therefore 140° 35'.

They did not polarise light.

They were readily soluble in water, soluble with difficulty in
alcohol. From the alcoholic solution they could be recrystallised.
The crystals so obtained were slenderer, and had lost their
brownish tint.

2. The other part was dissolved by adding hydric sulphate.
This solution was diluted and boiled for half an hour; it was
then found to have the power of reducing copper salts.

We have now data amply sufficient for the identification of
this body. It is, in fact, chitin.

It will be here convenient to enumerate the properties of
chitin as at present known, and afterwards to point out the
resemblances between it and the body obtained from the cartilage
of Sepia.

The Properties of Chitin are as follows: — It is a white
amorphous body, insoluble in water, in weak acids, and in
boiling concentrated alkalies ; soluble in strong acids. When
dissolved in sulphuric acid it yields a body which reduces
copper salts. This was supposed by Berthelot to be a ferment-
able sugar,1 but the researches of Ledderhose2 have shown

1 Berthelot, ‘ Comptes Rendues,’ xlvii, 227.

2 Ledderhose, “ Ueber Chitin, und seine Spaltungsproaukte,” ‘ Zeitschrift

CH1TIN IN THE CARTILAGES OF LIMULUS AND SEPIA. 177

that this is really a nitrogenous body — glycosamine — having
the formula, C6Hl3N05.

When dissolved in hydrochloric acid the solution of chitin
is colourless, and chitin can be precipitated from this solution
unchanged by the addition of water. When1 the solution is
boiled it becomes black in consequence of a decomposition,
which is completed in about an hour. On evaporation impure
hydrochlorate of glycosamine is obtained, and is purified by
recrvstallising repeatedly. This body is easily soluble in water,
soluble with difficulty in alcohol, and reduces alkaline solutions
of cupric and silver salts.

Professor Gamgee kindly sent to Professor Lankester
some crystals of this salt, which he had prepared from
lobsters. I also prepared some from the exoskeletons of
cockroaches.

The naked-eye examination of these crystals showed them to
belong to the monoclinic system.2

The angles were, however, not perfect; the crystals were
consequently redissolved in water, and allowed to recrystallise
therefrom on a glass slide. They were then submitted to
microscopical examination.

In the case of the salt prepared from cockroaches the follow-
ing are the results obtained : in the impure state they have a
light-brownish tinge, which they lose alter recrystallisation.
Their form is that of flat parallelograms, as in the case of the
crystals prepared from Sepia, and these are sometimes in clus-
ters. Measurement of the acute angle of the parallelogram
gave on the average 39° 25'.

The crystals had no action on polarized light.

In the case of the salt prepared by Professor Gamgee from
lobsters, redissolved in water, and allowed to recrystallise on a

fur Physiol. Chem.,’ vol. ii (1878), p. 213, and “ Ueber Glykosamin,” ibid.,
vol. iv (1880), p. 139.

1 Gamgee, ‘ Physiological Chemistry,’ p. 301.

2 The crystals which I had the opportunity of examining were about half
an inch long ; Professor Gamgee states that with plenty of material he can
obtain crystals several inches in length, and of proportionate width.

VOL. XXV. NEW SER.

M

178

W. D. HALLIBURTON.

slide, the following were the results obtained : they were
colourless,1 and their form was that of flat rhombic columns
radiating from various centres ; measurement of the acute
angles of some of the more perfect of these gave as an average
39° 25'.

The crystals had no action on polarized light.

Having thus seen the properties of the substance obtained
from the cartilage of Sepia, and that generally known as chitin
occurring in the exoskeleton of insects, Crustacea, and other
invertebrates, we can proceed to compare them; and can do so
most readily by means of the following table :

Substance prepared from
Cartilage of Sepia.

Substance prepared from
Chitin.

Condition.

Action of water . . .

Action of weak acids .
Action of boiling alkalies
Action of hydrochloric
acid (in the cold)
Action of sulphuric acid

Prolonged action of hot
hydrochloric acid

Amorphous, white.

Insoluble.

Insoluble.

Insoluble.

Soluble : reprecipitated
by adding water.

Soluble : the solution
reducing cupric salts

The solution becomes
brown, and a crystal-
line substance can be
obtained from it.

Amorphous, white.

Insoluble.

Insoluble.

Insoluble.

Soluble : reprecipitated
by adding water.

Soluble : the solution
reducing cupric salts

The solution becomes
brown, and a crystal-
line substance (hydro-
chlorate of glycosa-
mine) can be obtained
from it.

That the crystalline substance obtained from the cartilage of
Sepia is really hydrochlorate of glycosamine is seen by study-
ing its properties, under the following heads :

Its crystalline form ; including the measurement of its
angles ; the very acute angle is quite characteristic.

1 In more impure crystals sent by Professor Gamgee, the same light-brown
tinge was noticed, as in those prepared by me from cockroaches.

CfllTIN IN THE CARTILAGES OF LIMULUS AND SEPIA.

179

Its action upon polarized light.

Its ready solubility in water.

Its slight solubility in alcohol.

Comparing the properties of the crystals under these four
heads, we find them to be similar in every respect ; the irre-
sistible conclusion is, therefore, that the crystalline substance
obtained from the cartilage of Sepia is hydrochlorate of glyco-
samine, and that the cartilage of Sepia contains chitin.

The question now remains, how much chitin does this car-
tilage contain ? the method I have adopted in the quantitative
analysis has been the following :

A known weight of cartilage is taken, and potash added to
it ; the residue is washed, collected on a dried and weighed
filter ; it is then dried at 100° C., and weighed ; the increase in
weight gives the weight of the precipitate in the dry form,
from this the amount of ash is deducted, and from the
remainder the percentage can be calculated.

The average of two such quantitative experiments gives the
percentage of chitin in the cartilage of Sepia as T22.

B. — Composition of the Entosternite of Limulus.

What has been said for the cartilage of Sepia may be
repeated in very good measure for the cartilaginous Entoster-
nite of the king-crab. The method of analysis was the same,
and the results are as follows :

The greater part of the ground substance is composed of a
chondrin-like body, giving the tests for mucin, and to some
extent also those for gelatin (viz. precipitation by tannin, lead
acetate, mercuric chloride, ferrocyanide of potassium, and acetic
acid) ; but not sufficient gelatin is present to cause gelatiniza-
tion to occur in cooling the hot watery solution.

Keratin and elastin are absent.

Chitin is present : this is shown by —

1. There is a residue insoluble in boiling alkalies, soluble in
cold concentrated hydrochloric acid ; the addition of water
reprecipitating it from its solution.

180

W. D. HALLIBURTON.

2. By boiling it with sulphuric acid a body which reduces
cupric salts is formed.

3. By boiling it with hydrochloric acid, crystals of hydro-
chlorate of glycosamine are obtained.

The percentage of chitin present (the average of three
analyses) is T01.

It should be here mentioned that I performed some control
experiments with the cartilage of two vertebrate animals, viz.
the cat and rabbit, taking the rib cartilages in each instance ;
but in neither was there any residue after boiling with con-
centrated caustic potash.

The cartilage, then, of the two invertebrate animals I have
examined differs in a very important way from that of verte-
brates ; namely, in containing chitin in its composition.

C. — The Existence of Chitin in the Liver of
. Limulus.

The following analysis is merely a qualitative one, and shows
conclusively, that chitin is present in the liver of Limulus,
though whether actually in the liver-cells, or in the connective
tissue of that organ, which is very abundant, I am unable to
say. It seems more probable that the latter is the correct
view.

The livers of four king-crabs, which had just been killed,
were digested with a large amount of caustic potash for three
or four days. After this time most of the constituents of the
liver were dissolved, hut there was a considerable amount of
insoluble residue. This was filtered off. The filtrate was
brown, and perfectly clear ; the residue was also of a brown
colour, thick, muddy, and partially flocculent. The residue
was collected, washed with water, and again digested with
potash of the same strength; it was thus obtained of a lighter
colour; by repeating the process, almost colourless flocculi
were obtained. It (the residue) was then washed w'ith distilled
water and found to be insoluble in boiling water, and also in
concentrated boiling potash. It was soluble in concentrated

CHITIN IN THE CAETILAGES OF LIMULUS AND SEPIA. 181

hydrochloric acid in the cold, from which solution it was
reprecipitated by the addition of water in the form of white,
colourless flocculi.

It was also soluble in concentrated sulphuric acid ; this was
diluted and boiled, and then was found to possess the property
of reducing cupric salts.

These preliminary tests clearly pointed to the body being
chitin ; its solubilities and insolubilities are of themselves
almost characteristic of this substance.

The indication was rendered a certainty by boiling the
colourless solution in hydrochloric acid ; in about half an hour
it became dark brown, owing to the formation in it of the
hydrochlorate of glycosamine as in the previous cases.

Till now the generally received opinion has been that chitin
occurs solely in epiblastic structures; Ewald and Kuhne1 found a
body resembling it in the nervous system of Crustacea, but
this also is epiblastic. In the nervous system of these animals,
it seems to replace what Kuhne calls neuro-keratin, a horny
substance occurring in the nerve-fibres of vertebrate animals.
But it is clearly not confined to the epiblast ; for in three
instances chitin has been now shown to occur in mesoblastic
structures, viz. in the cartilage of the cuttlefish and king-crab,
and in the liver'2 of the latter animal.

1 Ewald u. Kuhne, “ Ueber einem neuen Bestandtheile d. Nervensystem ”
‘ Heidelberg Verhandlungen,’ 1877.

2 If the chitin, present in the liver, is in the liver-cells, not in the connec-
tive tissue as above supposed, we have an instance of chitin occurring in
hypoblast.

The Urinary Organs of the Amphipoda.

By

W. Baldwin Spencer, B.A.,

Scholar of Exeter College, Oxford.

With Plate XIII.

Within the group Arthropoda very various structures are
met with subserving the function of excretory organs.

The most primitive are undoubtedly nephridia as yet known
only to exist in one member — Peripatus, whilst the most
generally occurring are the Malpighian tubes whose presence is
highly characteristic of and possibly confined to the Tracheata ;
indeed, this is usually considered a not unimportant point of
difference between the latter and the Crustacea.

Notwithstanding this it is known that in certain Crustaceans
there do exist small but well-defined appendages opening into
the posterior part of the alimentary canal, though whether into
the mid or hind gut is a disputed point.

In English text-books, with, so far as I am aware, but one
exception, their existence is either passed over in silence or
merely mentioned, whilst nothing definite is stated with regard
to their nature and function.

The one exception is the work of Messrs. Bate and West-
wood on 1 Sessile-eyed Crustacea.’ Here their presence is
fully recognised and a somewhat detailed description is given,
though the power of cutting continuous sections enables us
now to study their structure and relations more accurately
than it was then found possible to do.

VOL. XXV. NEW SER.

N

184

W. BALDWIN SPENCER.

At the suggestion of Professor Moseley, to whom I am
indebted for advice and the material necessary for the work, I
have investigated these organs in two or three typical forms,
and have, moreover, attempted in the following article to give
a short summary of what appears to be known concerning their
existence and nature in the various specimens in which they
are found.

Within the Crustacea they are apparently confined to the
Edriophthalmata, whilst even amongst these their range is
limited as they are not known to exist in the Isopoda. I have
cut continuous transverse sections through the marine from
Idothea, the fresh-water Asellus, and the terrestrial Oniscus,
but in none of these are there present any appendages opening
into the hinder part of the alimentary canal. In the Amphi-
poda and in Caprella, on the other hand, there is no difficulty
in demonstrating their existence.

Of English authors, Huxley,1 whilst treating of the Edrioph-
thalmata, merely says, “ Occasionally there are one or two caeca
which open into the posterior part of the intestine and appear
to be urinary organs analogous to the Malpighian caeca of
insects.”

Gegenbaur2, speaking of the appendages of the hind gut in
Arthropoda, says, “ In the Crustacea we sometimes meet with
caecal organs on the hind gut, as, for example, in the larvae of
the Copepoda, but we cannot safely form any opinion as to their
significance,” whilst he makes no mention of the organs in
Amphipoda.

Balfour,3 also in his summary of arthropodan development,
says, “ The derivation of the Malpighian bodies from the proc-
todaeum is common to most Tracheata. Such diverticula of the
proctodaeum are not found in Crustacea.” These particular
appendages, as well as the manner of their development, are
unnoticed by him.

Various foreign investigators have dealt with the subject in

1 * Anatomy of Invertebrated Animals,’ p. 364.

2 ‘ Elements of Comparative Anatomy,’ English translation, p. 276.

3 * Comp. Embryology,’ vol. i, p. 452.

URINARY ORGANS OF THE AMPHIPODA.

185

considerable detail, and their works will be referred to in the
descriptions which follow.

The presence of these tubes in Gammarus was described by
Sars, who, judging apparently from their position only, came to
the conclusion that they were outgrowths of the hind gut, and
analogous to the Malpighian tubes of insects. In both young
and old specimens of Gammarus their existence may be demon-
strated either by simple dissection or best by cutting continuous
sections through the whole animal. Even in very young Gam-
mari, which have just left the brood pouch of their mother, they
form prominent objects. Thus, in one of 2 mm. length they arise
in the third segment from the posterior end and pass forwards,
lying dorsad of the alimentary canal through four segments,
growing to a slightly greater length in the adult.

To observe their structure and position with regard to the
other organs, the best method, as before said, is to cut sections
through the whole body. Fig. 3 represents one near the
posterior end cut somewhat obliquely, so that only the actual
opening of one of the tubes into the alimentary canal is seen.
It will be observed that the epithelium lining both tubes and
canal is similar and continuous, and that the former arise quite
separately from each other on the dorsal surface.

Below the canal the four liver tubes are seen cut in section,
and below these again the nerve cord with ganglion cells on its
ventral, and fibres on its dorsal side.

A more anterior section shows that the two tubes lie closely
side by side, each surrounded, as are the liver crnca, by a definite
membrane, whilst the alimentary canal is supported by a well-
marked mesentery which in this part divides the body cavity
into two halves, a dorsal and a ventral.

If a fresh specimen be taken the two tubes are seen to have
their walls composed of long cells rounded internally (i. e. the
end of each cell projects slightly into the lumen of the tube),
whilst externally they are roughly hexagonal in shape. When
stained they show large nuclei lying always on their outer side.

The tubes pass forward, retaining the same position, until
having traversed five segments they end blindly.

186

W. BALDWIN SPENCER.

The only change in their position is produced by the deve-
lopment of reproductive products which lie between the tubes
and the alimentary canal, and from which, though in very close
contact, the former may be seen to be separated by a distinct
membrane. Fig. 5 shows diagrammatically the relative positions
of the organs of Gammarus pulex.

These organs in the Gammaridse are treated of in considerable
detail by Nebeski1 in his account of the Amphipoda, and he
describes them as being present in very varying stages of deve-
lopment in different members. In Melita a single and very
rudimentary one is present. Corophiiden and Mcera each
possess a pair of small ones, whilst in Gammarus and Cyrto-
phium the pair are much better developed. In Orchestia not
only were the tubes still more prominent, but he found within
them what he states are excretory products in the form of con-
cretionary bodies, each of which takes its rise within an epi-
thelium cell of the tube, and, gradually growing, pushes the
cell substance aside and comes to lie within the lumen. These
bodies, which appear from his description to exactly resemble
in form others which I have found in the closely allied Tali-
trus locust a, Nebeski states consists of calcium carbonate.

Gamroth2 has described the presence of the tubes in the Ca-
prellidae,and states that though their intimate structure and phy-
siological import is unknown to him, yet he has found granular
concretions in them, and regards them as excretory organs.
When transverse sections of the hinder part of Caprella are
cut their existence is very easily recognised, as they form very
prominent pouches lying one on either side of the walls of the
alimentary canal communicating with the latter by somewhat
constricted openings. Nothing apparently enters these sacs
(for such they are in form in Caprellidse rather than tubes) from
the gut, as in sections in which the latter is full of food the
sacs themselves are quite empty. Their walls consist of elon-
gate nucleated cells, just as in Gammarus and Talitrus.

1 4 Beitrag zur Kentniss der Ampliipoden der Adria,’ Zoo). Institute, Wien
Band iii, 1881.

2 ‘ Zeitscbr. f. Wiss. Zool.,’ Bd. xxxi, p. 115.

URINARY ORGANS OP THE AMPHIPODA.

187

Mayer1 has also described them in the Caprellidae, where he
states that they are well developed in Caprella, and absent, or
only very feebly developed, in Protella, Proto, and Podalirius,
but when present he has never found in them characteristic
concretions, and is very decided in asserting that throughout
the Amphipoda these diverticula, whatever may be their func-
tion and whether they contain excretionary products or not,
belong morphologically to the mid and not to the hind gut, and
that hence they cannot be considered as analogous to the
Malpighian tubes of insecta. He states that there is always
present a sharp break in the epithelium where the mid and
hind gut meet, and that the chitin lining of the latter is not
continued into the tubes whose epithelium resembles that of
the mid, and not that of the hind gut.

I have lately carefully investigated the nature of these tubes
in numerous specimens of Talitrus locusta, where they may
without any difficulty be discerned by carefully removing from
the animal the whole of the alimentary canal, and after laying
this out upon a slide gently separating the two tubes from the
side of the hind gut close to which they lie though clearly dis-
tinguishable by their whitish colour.

Fig. 1 represents part of the alimentary canal of Talitrus
which has been removed from the body with the tail segment
still attached, though the liver tubes when in the body would
lie in the contrary direction. The figure is drawn to scale,
and shows the relative length of the parts.

When compared with fig. 5 of Gammarus a point of con-
siderable difference between the two is seen at once, the tubes
in Talitrus opening at a considerable distance from the anus
and running backwards instead of forwards, as in the former,
to end blindly in the last segment. They are, indeed, very
similar to the Malpighian tubes of insects, more especially
resembling those of such a form as Julus, where only one pair
is present.

Fig. 2 represents a transverse section through the hind gut
of Talitrus in which the two tubes are seen lying some distance
1 ‘ Die Caprelliden des Golfes von Neapel,’ p. 147-

188

W. BALDWIN SPENCER.

apart from each other, not closely applied upon the dorsal
surface of the alimentary canal as in Gammarus, whilst also
their openings into the gut are lateral and not dorsal. The
definite shape of the hind gut may be noticed in passing, as
also the fact that it possesses a distinct cuticular lining beset
throughout the greater part of its course with little processes,
though towards the anterior end these disappear, and the cuti-
cular lining itself becomes very thin indeed.

With regard to the tubes their walls are cellular in nature
just as in Gammarus, and by focussing under a high power
each cell may be seen to have its inner end which faces into
the lumen of the tube rounded, whilst its outer end is roughly
hexagonal in outline. The most interesting fact, however, is
that, in certain specimens, as in the one figured, these tubes
were found to contain very definite concretions. If a great
number of animals be examined there will be found perhaps
one or two of a light greenish colour, and through the cuticle
of which may be seen, on either side posteriorly, a white streak
indicating the position of these tubules. In a specimen of this
description concretions will most likely be found filling the
whole cavity of the tube.

The concretions are of various sizes and arranged as in the
figure, smaller ones being placed between each larger one, the
latter, apparently consisting of several of the former united
together in some manner. In no case could any sign of a
concretion be observed either within or between the cells of
the tubes themselves.

In one or two instances they have been met with in an
animal of a dark reddish-brown colour, differing in tint from
the usual greenish brown, though in this case the concretions
were only small ones and did not exist in the proximal, but
only in the distal half of the tube.

Though as yet I have not been able to obtain definite proof,
still, judging from the condition of the cuticle in the two kinds
of specimens in which only these concretions have been found
(the first mentioned especially being clearly distinguishable
from the normal Talitrus), it may not appear unjustifiable to

URINARY ORGANS OF THE AMPHIPODA.

189

suggest that these concretions have something to do with the
process of “ casting the skin/' and that the first mentioned
were animals in which this had just taken place, whilst the
second were those in which preparation for it was being made.

The concretions are, of course, extremely minute, and have
only been obtained from a few specimens, so that it is not
easy to determine exactly their nature. Distilled water does
not dissolve them, nor is there any uric acid present, but I have
been able to clearly detect phosphoric acid, and hence they
seem to differ from those found by Nebeski in Orchestia
cavimana, where he states that they consist of carbonate of
lime.

It has not been possible to observe what becomes of the
concretions, but in one of the specimens mounted a few of
them, whether accidentally or not I cannot say, have passed
out into the alimentary canal by means of the mouth of the
tube, showing, at all events, that it is perfectly possible for
them to do so.

At first sight it might appear as if these tubes were homo-
logous with the Malpighian tubes of Tracheata, and until their
development has been worked out and compared with that of
the latter, it is impossible to settle the question definitely. In
all specimens they arise from the point of junction of the mid
and hind guts, but on close inspection and by means of sections,
it can be demonstrated clearly, in at all events certain cases,
that they belong really to the mid gut

Thus fig. 4 represents a longitudinal vertical section through
the hinder part of the alimentary canal of Gammarus pulex.
One of the tubes is seen arising on the dorsal surface, but its
lining epithelium is clearly continuous directly with that of
the mid gut, whilst there is seen to be a distinct break
(fig. 4, x ) where the latter ceases and the hind gut begins.

These organs, which have such a strangely limited distri-
bution amongst Crustacea are certainly, as is proved by their
products, excretionary, and are very probably also urinary in
function, but the knowledge which we at present possess of
their point of origin from the alimentary canal prevents us

190

W. BALDWIN SPENCER.

from regarding them as strictly homologous with the Mal-
pighian tubes of Tracheata.

EXPLANATION OF PLATE XIII.

Illustrating Mr. W. B. Spencer's paper on “ The Urinary
Organs of Amphipoda.”

List of Letters employed.

An. Anus. Cr. Concretions in urinary tubes. Cr1. Concretions which
have passed from the tubes out into the hind gut. G. Genital organs. H.
Heart. H. g. Hind gut. L. Liver tubes. Lo. Opening of liver tubes into
mid gut. M. g. Mid gut. Mes. Mesenteries supporting and surrounding the
various organs. M. Ig. Longitudinal muscular fibres of hind gut. M. tr.
Transverse muscular fibres of hind gut. Muse. Ordinary muscles of the body.
N. Nerve cord. R. Rectum. Sg. Last segment of the body removed

with the gut. Ur. Urinary tubes. Ur1. Distal part of urinary tube,

which is always bent forward. Ur. o. Opening of urinary tubes into gut.
X. Point at which hind gut ends and mid gut begins. Y. Anterior termina-
tion of mid gut.

Pig. 1. — Part of alimentary canal of Talitrus locusta, removed from
the body with the tail segment still attached. Only the mid and hind guts are
present and the liver tubes, only one of which is shaded, the rest being only
drawn in outline are turned forwards. The two urinary tubes are seen arising
from the posterior end of the mid gut ; they have been pulled away from the
side of the hind gut, close to which they lie naturally ; the constantly bent
distal part lies normally in the last segment. Large and small concretions are
seen filling up the tubes, some having passed out into the gut.

Pig. 2. — Transverse section through hinder part of body of Talitrus
locusta. The hind gut has a distinct cuticular lining beset with small points.
Both urinary tubes are seen in section, each enclosed by a supporting mesen-
tery, as is also the gut. Below the latter the nerve cord is seen in section.

Fig. 3. — Transverse section through hinder part of Gammarus pulex.
The plane of the section is oblique, so that the opening of only one urinary
organ into the mid gut is seen ; the cells of the other one are also cut through,

URINARY ORGANS OF THE AMPHIPODA.

191

though no lumen is seen. In oonsequence of the obliquity of the section the
liver tubes also are only cut through on one side.

Fig. 4. — Longitudinal vertical section through part of the alimentary canal
of Gammarus pulex. The opening of one of the urinary tubes is seen,
and the continuity between the epithelium of the latter and that of the mid
gut. At the point X is seen the clear termination of the mid gut, and com-
mencement of the hind gut. The muscular fibres of the hind gut are seen in
section.

FiG. 5. — A diagrammatic representation of the internal organisation of
Gammarus, showing the relative position of the urinary tubes.

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PRIAPULUS AND HALICRYPTUS.

193

On the Skin and Nervous System of Priapulus
and Halicryptns.

By

Robert §eharff, Ph.D.

With Plate XIV.

During the past year I have had the opportunity of re-
investigating the anatomy and histology of Priapulus cau-
datus and Halicryptus spinulosusfrom specimens supplied
by the liberality of my esteemed teacher Professor Biitschli,
by whose help and advice I have greatly profited, and to whom
my most cordial thanks are due.

I first intended to give a full account of the anatomy of
these two interesting forms, but the results I obtained agree
in general with those published by Ehlers in his valuable
paper “ Ueber die Gattung Priapulus.” Histologically, how-
ever, he left a good deal to do for later observers, and although
Horst as well as Saenger have extended our knowledge con-
siderably in that respect, a description of the nervous system
and skin, dealing especially with its peculiar dermal organs,
probably of a sensory nature, may be of interest.

The Skin.

According to Ehlers1 we have to distinguish two layers in

1 E. Ehlers, “ Ueber die Gattung Priapulus,” ‘ Zeitschrift fiir wissensckaft-
liche Zoologie,’ vol. xi, p. 223 ; ditto, “ Ueber Halicryptus,” loc. cit., vol. xi,
p. 404.

194

ROBERT SCHARFF.

the skin of Priapulus caudatus and Halicryptus spinu-
losus, viz. a cuticula and a subcuticular layer or hypodermis.

To these two layers I have to add another extremely thin
one consisting of connective tissue (fig. 8, d.). It does not
reach half the thickness of the cuticula in the proboscis, while
in the body or trunk it is still thinner, and could only be
clearly demonstrated in a few places.

In Sipunculus nudus this cutis is well developed, and is
the seat of secreting glands and accumulations of pigment.

The Cuticula.

The cuticula covers the whole body, varying in thickness in
the different parts. At the oral aperture it turns in, coating
the interior of the oesophagus. On the body, especially at the
posterior portion of that of Halicryptus, the cuticula reaches a
considerable thickness.

It is composed of two parts (figs. 1, 2, 3), an external thin
homogeneous layer ( ce .) and an internal thicker one (ci.) also
lighter in colour, which is distinctly stratified. In cutting
sections for the microscope it often happens that the whole of
the cuticula or some of the outer layers split off, and thus
show undoubtedly that it is made up of distinct strata. Reti-
cular markings are seen on the surface of the cuticula on the
proboscis. They are generally in shape of polygonal figures
and correspond to the cells of the hypodermis below, which
have the same form in a surface view, and from which the
cuticula has been secreted.

According to Horst1 the cuticula of the so closely-allied
Priapulus bicaudatus appears to possess a honey-combed
structure, which is produced by two systems of vertical lamellae
crossing one another, dividing it into a series of prisms. The
same writer agrees with Ehlers as to the cuticula of Priapulus
being insoluble, while that of Sipunculus nudus has by
Andreae2 been shown to be soluble in boiling caustic potash.

1 Horst, “ Anatom ie von Priapulus bicaudatus,” ‘ Niederl. Archiv f.
Zoologie/ Supplement to vol. i, p. 16.

2 Andreae, “Beitrage zur Anatomie und Histologie des Sipunculus
nudus,” ‘ Zeitschr. f. wiss. Zoologie,’ vol. xxxvi, p. 207.

PRIAPULUS AND HALTCRYPTUS.

195

Ehlers designates the cuticula of Priapulus as “ chitin
some investigators, on the other hand, like Graber,1 seem to
suppose that its identity with the chitin of the Arthropoda is
as yet very doubtful.

The Hypodermis.

The hypodermis in its various modifications forms the sub-
stratum to the cuticula. It consists generally of a thin layer
of about the same thickness as the cuticula. Looking at the
hypodermis from above it appears as a layer of polygonal cells
corresponding to the markings found on the cuticula. A cross
section reveals the shape of the cells, which contain only a
small quantity of protoplasm, and a comparatively large nucleus
(figs. 1, 2, 3, h .) . They send out numerous processes on the
inner surface, by means of which the cells seem to communi-
cate with one another.

On the proboscis we find longitudinal rows of little spikes or
cones projecting from the skin, which will be described later
on under the head of sensory organs. Their interior is stocked
with hypodermic cells, which have been drawn out in shape of
very long threads. In the small papillae on the body of Pria-
pulus a similar elongation of the cells takes place, while in
those of Halicryptus they are still further modified into three
different groups, showing an important diversity of form (figs.
3 a, 3 b).

Round about the anus the hypodermis of Priapulus cau-
datus undergoes a curious modification (fig. 4) in distinction
to Priapulus bicaudatus and Halicryptus, where this does
not occur. The cells become very much elongated, but at the
same time they expand also in width so as to form a compact
mass (fig. 10), and their protoplasmic contents increase, filling
up the whole of the cells.

Ehlers describes these cells “ as a heap of glandular bodies
lying under the subcuticula,” and Graber2 says “ Bei geeigneter

1 Graber, “Ueber die Haut einiger Sternwurmer,” ‘ Bericlite d. Kais. Ak.
d. Wiss.,5 vol. lxvii, p. 61.

3 Graber, loc. cit., p. 64.

196

ROBERT SCHARFF.

Behandlung kann man fiber die Natur dieser Korper nicht
lange im Zweifel sein. Es sind, um es kurz zu sagen, raum-
lich differencirte Tkeile einer am Stammesende machtig ent-
wickelten Cutis.”

As I shall attempt to show further on, it is extremely
probable that we have here to deal with secretory organs.

The hypodermis as well as the cuticula are also found on the
peculiar respiratory appendage of Priapulus (fig. 11, resp.) the
so-called “ Schwanzanhang the two layers, however, become
very thin.

It now remains to consider the modifications of the hypo-
dermis on the ventral surface of the body where the nerve-
cord runs. An interesting transformation of hypodermic into
ganglionic cells may be seen here, their nuclei swelling up
and the rest of the cells becoming considerably attenuated.
A look at fig. 6 and 7, however, will help to elucidate this
better than a long explanation.

Horst1 describes the hypodermis of Priapulus bicau-
datus “as a thin layer, the thickness of which in the trunk
only amounts to 0'003 mm.” “ It is composed of small
branching cells with pretty large nuclei and only little proto-
plasm. The cellular bodies are connected with one another
by numerous slender processes, and thus they assume a reti-
culated appearance.”

The Cutis.

As already mentioned the existence of a cutis is extremely
difficult to demonstrate, at any rate in the body. In the pro-
boscis it becomes more evident, and consists of a very thin
layer of fibrous connective tissue (fig. 8, d.). It is especially
well seen where the longitudinal muscles are attached to the
body wall, the hypodermis bending somewhat towards the
interior, and the cutis attaching itself to the muscle.

This cutis corresponds as regards position to Keferstein’s2
“ gestrichelten Haut,” which he found underlying the hypo-

1 Loc. cit., p. 17.

3 Keferstein, ‘ Untersuchungen iiber niedere. Seethiere,’ p. 41.

PRIAPULUS AND HALICRYPTUS.

197

dermis in Phascolosoma puntarenae and antillarum. A far
greater development of the cutis is to be found in Sipunculus,
which, according to Andreae,1 consists mainly of areolar tissue,
and in which secreting glands and pigment cells appear to be
embedded.

Sensory and Secretory organs of the Skin.

In the contemplation of the sensory and secretory organs
we shall have to consider Priapulus caudatus and Hali-
cryptus spinulosus separately, there being some difference
between the two with regard to these organs. I shall first
mention the general disposition of these organs on the body,
and then give a description of their form, histological struc-
ture, and probable function, finishing up with a few remarks
as to their relation to similar organs in other animals.

On the proboscis of both of them the small dermal projec-
tions or “ spikes ” are arranged in numerous longitudinal rows
which are more regular in Priapulus than Halicryptus. On
the body or trunk on the other hand there are no longitudinal
but only circular rows of spikes. The spikes are here so dis-
posed as to occupy a median position on each annular muscle,
and thus we get a series of parallel rings of them. In Hali-
cryptus the spikes are similarly disposed to the end of the
body, two larger spikes standing on each side of the anus (see
Sanger,2 pi. x, fig. 6). In Priapulus irregular masses of
papillae are scattered about at the posterior end of the body
(the ordinary spikes being here absent) with the exception of
the immediate surroundings of the nerve-cord on the ventral
surface (fig. 4, p.). Little spikes also occur on the respiratory
appendage.

1 Loc. cit., p. 208.

2 Saenger, “ On Halicryptus spinulosus and Priapulus caudatus,”
‘Transactions of the 2nd Congress of Russian Naturalists in Moscow, 1869.’
(Written in Russian.)

198

EOBEET SCHAEFF.

Priapulus caudatus.

On the proboscis the spikes are in form of small truncated
cones, just visible by the naked eye. It has been mentioned
before that the hypodermic cells which constitute the interior
of these cones undergo a transformation, becoming very much
elongated (fig. 1, h.), and converge somewhat towards the
centre of the base. The cuticula forms the outer layer of the
cone, and leaves a circular opening at the top. Through this
opening a number of small delicate hairs are seen to project,
piercing a thin membrane ( m .) which covers the distal ends of
the cells. The outer darker layer (fig. 1, ce.) of the cuticula
does not quite reach the apex of the cone, but only extends
about half way up and surrounds it as a sort of a sheath.

Various circumstances have led me to believe that the upper
part can be retracted into this sheath, although I never
examined the animal in the living state. Sometimes I met
with sections in which the upper part was actually partly
retracted into the lower sheathed portion. Horst’s “ Rippen-
muskeln,” which run longitudinally underneath the rows of
cones in the proboscis, probably serve to draw in this upper
part. Underneath every spike on the proboscis there is a
hollow space (fig. 1, sp.) in communication with the body
cavity, which has also been described of Priapulus bicau-
datus (Horst).1 I presume that the space which is to be
found beneath every cone can be rapidly filled with blood,
communicating freely with the general body cavity, and in this
way the retracted cone may be pushed out. This view is further
favoured by the great advantage such a mechanism would
have as a protection for these slender structures.

Willemoes-Suhm,2 who observed living specimens of Pria-
pulus, tells us that they are in the habit of burying themselves
into the sand by rapidly pushing out the proboscis, and with

1 Horst, loc. cit., p. 20.

s Willemoes-Suhm, “Biologische Beobachtungen iiber niedere.Meeresthiere,”

‘ Zeitschr. f. wiss. Zoologie,’ vol. xxi, p. 386.

PRIAPULUS AND HALICRYPTUS.

199

the same swiftness drawing it in again. Unless the little
spikes were retractile I think they would be damaged in this
process. In support of this view I may also mention a case
where similar organs occur which have been observed in the
act of being drawn in. I am alluding to the careful researches
of Eisig1 on the cup-shaped organs of the Capitellidse. He
says, “ Die Basis des im iibrigen soliden Sinneshiigels ist mit
einer kleinen Hohlung versehen, welche zunachst von den
Wandungen des Hiigels, sodann aber von denjenigen des
Hautmuskelschlauchs begrenzt, direct in die Perivisceralhohle
iibergeht. An die Hiigel inseriren sich mehrere Muskeln,
deren einer der Retractor, den freien Hiigel mehr oder weniger
tief einzustiilpen vermag. Es ist der Druck des Blutstroms,
der sowie den Russel und die Tentakel, auch das eingezogene
Haarfeld wieder zur Ausstiilpung bringt.”

The two special sets of muscles in the proboscis which have
been mentioned above and which also occur in Halicryptus
run underneath the rows of spikes, one on each side, and join
the longitudinal muscles of the body wall in the trunk (fig.
11, r. m.).

Horst supposes that the above-mentioned hollow spaces are
not without importance in the act of respiration. I have just
stated my own view on this subject, and need not recur to it
again.

As regards the innervation of these organs I have not come
to any definite results, although both osmic acid and chloride
of gold were used. In some cases, indeed, I saw something
like nerve-fibres at the base of a spike, but I was not able to
positively prove that what I saw were really such.

Saenger is quite determinate in his assertion that rings of
nerves surround the body, one in every segment, similar to
those discovered in Si pun cuius nudus. In pi. x, fig. 16,
he has a drawing representing a lateral nerve going off from
the nerve-cord, but as in his diagram the latter is separate
from the hypodermis instead of lying inside it as a modifi-

1 Eisig, “ Die Seitenorgane und beckeriormigen Organe der Capitelliden,”
‘ Mitth. aus d. Zool. Station Neapel,’ vol. i, p. 280.

VOL. XXV. NEW SER.

O

200

ROBERT SCHARFF.

cation of hypodermic cells, I do not attach much importance
to this. Hence I must still regard the view that these dermal
spikes are supplied with special nerves as doubtful. A further
examination to clear this is much needed.

Ehlers,1 who was the first to describe the little cones on the
proboscis, saw quite correctly that the hypodermic layer was
continued into their interior, but he believed that they were
hollow and that the hollow cavities might possibly communicate
with the perivisceral space. Graber,2 on the other hand, mis-
took the hypodermis for a part of the circular muscles of the
proboscis, and describes the spikes as being filled up with their
prolongations. In their description of Priapulus bicau-
datus Daniellsen and Koren3 agree with Ehlers in looking
upon the spikes as hollow outgrowths invested with an internal
lining of epithelium. I will give the following passage in their
own words : — “ In the hollow of every spike, at the base, is
seen an almost round, comparatively large gland (figs. 4, e. ; 5, e.)
composed of connective tissue, covered internally with round
cells (figs. 4, /. ; 5 ,/.), and from the arcuate portion of these
issues the excretory canal (fig. 4, g .) which, passing up through
the hollow of the spike (figs. 4, h. ; 5, g.), disembogues exactly
where the epithelial integument of the latter terminates (figs.
4, i. ; 5, h.). The gland contained a viscid, granulous, pellucid
substance, which we observed once or twice in the aperture at
the free extremity of the spikes.”

There is no doubt that these authors have seen Horst's
“ Integumentalhohlen ” with their containing blood-corpuscles,
which are the glands they mention. Neither Horst nor
myself have seen anything of an excretory canal.

Although Saenger’s figures leave very much to desire, his
investigations seem to have been made with great care, and it
is unfortunate that his works, being written in Russian, are
practically inaccessible. He states on p. 212 of the work cited
before, that the interior of the spikes contains hypodermic

1 Ehlers, loc. cit., p. 221.

2 Graber, loc. cit., p. 62.

3 Daniellsen and Koren, ‘ Den Norske Nordbavs Expedition,’ p. 11.

PEIAPULUS AND HALICRYPTUS.

201

cells, and he even observed the slender hairs projecting from
the apex of the tubes which I described. This latter fact
escaped the notice of all other observers.

Horst’s1 statements differ from my own in some respects,
in so far as he holds that the interior of the spikes consists
of irregularly branching cells of the hypodermis. The cells
are said to converge towards their base and to have a fibrous
structure, which gives them the appearance of radiating from
the cutis lying underneath (see also his pi. ii, figs. 1, 2, 4, s.).

The spikes of the body, of which we have seen that they are
arranged in parallel rings round the body, are comparatively
few in number. On account of the great contraction of the
circular and longitudinal muscles of the body, these minute
organs almost disappear within their folds or become so con-
torted that they are of no avail for the study of their
histological details. They can only be profitably studied with
good immersion systems, but on account of the above-mentioned
disadvantages I was only able to obtain one or two of them
which were at all satisfactory. Their structure, although on
the main points agreeing with the spikes on the proboscis,
shows a few points of difference, and it seems to have reached
a higher state of development. The whole organ has the form
of a conical or somewhat cylindrical elevation. The cuticula
(fig. 2, c.) is thick and slightly sunk in at the apex of the cone,
leaving an aperture at the centre. The outer hypodermic
cells become again elongated just as in the proboscis, but now
we come to the main difference. The cells in the axis of the
cone are enlarged at their upper part and assume a club-shaped
form, their bases becoming apparently resolved into a net-
work of fibres (fig. 2, c. c.). Perhaps the whole organ may be
constructed on a similar plan to those of Halicryptus, which
will be described below. Each of these central cells bears a
short stiff hair ending freely into the surrounding medium, and
as far as I could ascertain without the intervention of a special
membrane as was the case in the proboscis. This, however, is
nevertheless very probably present, and may have only been
• Horst, loc. cit., p. 18.

202

ROBERT SCHARFF.

destroyed in cutting tlie section or by the action of the
alcohol.

Ehlers1 does not give us much information as to the spikes
on the body proper, and merely states that they are small
cylindrical elevations truncated at their upper extremity.
“ Their height is 0143 mm. and their diameter 0111 mm., and
in their interior, chiefly at the base, lies the substance of the
subcuticular layer.” The only other observer in whose writings
I can find anything about these spikes is Horst.2 He makes
mention of the fact that the hypodermic cells form a continuous
layer on the internal surface of the cuticle. The central part
is said to contain a network of nucleated fibres.

We now come to the consideration of those dermal organs
about which there prevails a good deal of difference of opinion
among the various writers. I am alluding to the papillose
clusters of dermal processes at the posterior part of the body
(fig. 4, p.) Even with a strong lens nothing but pretty con-
siderable thickenings of the nature of warts can be made out.
On examining the cuticle separately, however, groups of eleva-
tions can easily be seen, in the centre of which a pore is to
be found (fig. 9). The cuticle here appears to sink into small
funnel-shaped pits. In reality, however, these pits are a
number of extremely minute tubes, only visible under very
high power. In a surface view their real nature might quite
easily be mistaken, and it is probably this reason which induced
Ehlers to describe them as pits. The general arrangement as
seen by a low power is shown in Ehlers’ monograph on the
genus Priapulus (pi. xxi, fig. 18) (see also my diagram, fig. 4).
The main structure of the warts on which the small tubules
stand is made up of modified hypodermic cells. These are
elongated and filled with granulated contents (fig. 10). The
cells differ considerably from those of any other part of the
body in being packed closely together and in being of a much
greater width. Figure 5 is an attempt to make these state-
ments clearer by showing one of these organs in a longitudinal

1 Ehlers, loc. cit., p. 225.

3 Horst, loc. cit., p. 18.

PEI AP PLUS AND HALICRYPTOS.

203

section. At the apex of the tubules I noticed a little pit ( p .)
into which opens a very delicate canal (o.) from a flask-shaped
portion (f.) below, which communicates again with several
large cells (/*.).

These details do not appear in objects coloured with carmine,
and I therefore tried one of the aniline dyes, viz. methyl
violet, which has been successfully used for a similar purpose
by Spengel1 in order to demonstrate the excretory ducts of
glandular organs in the skin of Echiurus Pallasii. The
aniline dyes are said to have the property of staining secretions
very markedly. If this be the case I think I am quite justified
in regarding these organs as organs of secretion, the cells
forming the warts having been stained of a deep blue together
with the flask-shaped portion (fig. 5 ,f.) and the duct, while the
other hypodermic cells only assumed a very slight bluish tinge.
Other investigators maintain, on the contrary, that aniline dyes
cannot be trusted and that their action is very fickle. Never-
theless another circumstance besides the aniline method seems
to give the above-stated view an additional support. In the
spirit specimens the immediate surroundings of the warts were
thickly covered with a yellowish sticky material, which had to
be brushed off in order to allow of a more accurate scrutiny.

The supposition that these organs might be of a secretory
nature has only been put forward by Ehlers, while Saenger
maintains that there are no pores at all. Graber2 believes that
the investigations of Ehlers are in want of improvement, and
scorns at the idea of the existence of pores. These “ secretory
organs ” — if I may venture to call them such — do not exist in
either PriapulusbicaudatusorHalicryptusspinulosus.
Horst as well as Daniellsen and Koren do not mention anything
about them with regard to the former and I have not found
them in the latter.

1 Spengel, “Beitrage zur Kenntniss der Gephyreen,” ‘ Zeitschr. f. wiss.
Zoologie,’ vol. xxxiv, p. 46'L

2 Graber. loc. cit., p. G3.

204

ROBERT SCHARFF.

Halicryptus spinulosus.

As far as I have been able to ascertain, the spikes on the
proboscis agree with those of Priapulus. The cuticula,
however, surrounding the spikes, differs somewhat in not form-
ing a sheath round them, but a crest of little lancet-shaped
blades. Figure 1 1 represents a somewhat diagrammatic view of
their general arrangement.

At the line of junction between the proboscis and the body
proper (fig. 11,/.) the spikes become curiously modified. They
are not always so regularly formed as I have indicated them
on the diagram, aud generally there are three circular rows of
them surrounding the proboscis. Occasionally we find some
that do not exhibit those two prongs at the apex j in fact, there
may be a number of transitory stages between the ordinary
form of the proboscis and this peculiarly modified form.

According to Saenger we find at the apex of the subcuticular
elevation a large transparent cell containing a quantity of
yellowish droplets looking like fat. He observed the animal
in the living state, and noticed that under ordinary circum-
stances these little prongs are never withdrawn into the
interior. They form the boundary up to which the invagina-
tion of the proboscis takes place, and probably act as a kind of
support. By means of these prongs the worm keeps his
position even when the anterior part is drawn in, and they
may also be advantageous in locomotion. I have not been
able to investigate their histological structure.

The most interesting of the dermal organs of Halicryptus
are those of the body proper. They are almost twice as long
as the ordinary spikes of the proboscis (fig. 3 a, and fig. 11,
sp. /.). We can distinguish two parts, a lower and an upper.
The former rests on a broad base tapering somewhat towards
the apex, while the latter consists of a slender portion resem-
bling in external appearance the sting of a bee. The hypodermic
cells filling up the interior of the lower portion are modified
into three different sets, one being replaced by another as we

PRIAPULUS AND HALICRYPTUS.

205

approach the axis of the structure. This is best understood by
examining a longitudinal section such as fig. 3 a. The hypo-
dermic cells forming the circumference of the spike elongate
just as we have seen it before in Priapulus. Internally to
these we now find large pear-shaped cells (figs. 3 a, 3 b ,p. c.),
containing a protoplasmic network and nucleus, and tapering
above into a fine filament which suddenly swells up again into
a club-shaped portion. This set of cells again surrounds
another set (figs. 3 a, 3 b, i. c .), which I have not been able to
trace clearly, but which are probably filamentous in shape
from base to apex and end in long hairs. The latter (/. h .)
occupy the hollow interior of the sting. A membrane (fig. 3
a, m.) through which the hairs project stretches across the
opening from the lower into the upper part of the organ. A
cross-section a little lower down (fig. 3 b) stained with chloride
of gold, exhibits internally a cluster of small dark-stained cells
( i . c.) surrounded by larger lighter ones ( p . c.), the latter repre-
senting the upper parts of the pear-shaped cells (I may
mention that in sections stained with carmine according to
Grenadier’s prescription I have likewise obtained very instruc-
tive views of the minute structure of these organs). The
cuticle encircling the two groups of cells in this part is made
up of an internal and an external dense part, staining darker
than the rest, which lies between. Further down towards the
base it assumes its ordinary composition again, the internal
dark portion being wanting. Fig. 3 represents a cross-section
through the sting, showing the hairs originating from the
central group of cells and surrounded by the cuticular wall.

Having considered the anatomical and histological details of
all these sensory organs, it now remains, after having made a
few remarks on similar organs in other animals, to show their
relation to these.

In Sipunculus nudus, which has recently been reinves-
tigated by Andreae,1 structures composed of modified hypo-
dermic cells have been discovered, the bases of which are in
connection with nerves (pi. xii, fig. 9). No sensory hairs
1 Andreae, loc. cit., p. 219.

206

ROBERT SOHARFF.

were observed, which may be due to their having been destroyed
through the action of the alcohol.

Keferstein1 makes mention of similar organs in Phasco-
losoma, but he seems as yet doubtful whether he should call
them “ sensory organs,” not having been able to find any
connection with nerves. Soon after, however, he published
another paper2 in which he calls them organs of touch
(Tastorgane), and proves that they are supplied by special
nerves.

One of the more recent writers is Teuscher,3 who, in his
description of the skin of Phascolosoma, mentions utricular
bodies in connection with two or three nerves-fibres. “ Their
interior contains, in a finely granulated mass, a number of
larger grains which seem partly attached to threads hanging
down from the apical part.” This passage reminds me very
much of the elongated hypodermic cells which I have so often
described, and it seems to me not at all unlikely that the
above-mentioned long threads are nothing but similar cells
with their conspicuous nuclei. GreefF,4 who made the
Gephyrea armata his special study, gives us much valu-
able information as to the occurrence of organs of touch
(Tastpapillen), which, however, lie in a layer of connective
tissue beneath the epithelial or hypodermic layer. They are
either arranged in rings round the body, or they may be spread
all over. The nervous connection was traced all the way from
the nerve-cord to these papillae.

I have already had the opportunity in another place of
referring to Eisig’s researches “ liber die Seitenorgane der
Capitelliden.”5 He describes sensory organs having the form of
buds, and others sunk down into cup-shaped invaginations of

1 Keferstein, “ Uutersuchungeu liber niedere Seethiere,” ‘ Zeitsclir. f. wiss.
Zoologie,’ vol. xii, pp. 41, 42.

2 Keferstein, “Beitrage zur Anatomie und systematischen Kenntniss der
Sipunculiden,” ‘ Zeitsclir. f. wiss. Zoologie,’ vol. xv, p. 405.

3 Teuscher, “Notiz liber Sipunculus und Phascolosoma,” ‘Jeuaische
Zeitschrift,’ vol. viii, p. 495.

4 Greeff, “ Die Echiuren,” ‘ Nova Acta Akad.,’ vol. xli, p. 44.

5 Eisig, loc. cit., p. 280.

PRIAPULUS AND HALICRYPTUS.

207

the skin, both of them having sensory hairs. He has estab-
lished experimentally that the apparently different structures
are one and the same thing, the latter' being simply an invagi-
nation of the first kind.

The most noteworthy analogy to the sensory organs of
Priapulus and Halicryptus, however, is to be found among the
lower Vertebrates, such as fishes and larval Amphibians. In
order to show how closely the organs of which the so-called
lateral line in fishes is composed of agrees with those I have
described, I will give a few extracts from some of the more
important works on this subject.

Leydig1 was the first to prove the nervous nature of these
organs, which were generally believed to excrete mucus, and
showed that they were sensory organs peculiar to fishes. A
few years later he wrote an excellent and well-known treatise2
on sensory organs in general, and attributed to those found in
the lateral line of fishes the function of a sixth sense unrepre-
sented in the higher Vertebrates.

M. Schultze, as well as F. E. Schulze, have extended the
knowledge about these organs very considerably. It was the
latter who first discovered the peculiar protuberant structures
in the skin of young fishes, and indicated that they were peri-
pheral sense organs corresponding to those of the lateral line
found in adult fishes. Shortly after he published another
paper3 in which he describes their histological structure : —
“From the epithelial cells, of which these organs are chiefly
made up and which stand in connection with nerves, I saw a
number of delicate stiff hairs projecting into the water similar
to those found on the Crista acustica, only much shorter.”
Moreover, he describes “ a slender tube, rising from the margin
of this structure, open at the end and obliquely truncated.”

1 Leydig, “ Ueber die Schleimkanale der Kuochenfische,” ‘ Muller’s
Archiv,’ 1850.

2 Leydig, “ Ueber Organe eines sechsten Sinnes,” ‘ Nova Acta Leop. Carol./
vol. xxxiv.

3 F. E. Schulze, “ Ueber die Sinnesorgane der Seitenlinie bei Fischen und
Amphibien,” ‘ Archiv f. mikrosc. Anatomie,’ vol. vi, p. 63.

208

ROBERT SCHARFF.

The latter evidently acts as a sort of protection to the fine
hairs, and is analogous to those of Priapulus and Halicryptus.

Langerhans1 and also Solger2 give further details as to their
composition. The latter says : “ Two parts may be readily dis-
tinguished in longitudinal sections — firstly, an outer integu-
ment, and secondly, an inner nucleus. The former is con-
structed of several layers of long cylindrical cells. These
mantle-cells surround the second inner part which form a
group of club or pear-shaped cells (Kolben oder birnformig
gestalteten Zellen) (see Langerhans, pi. xxxi, figs. 10, 11, 12).
The latter correspond to Bugnion’ s3 “ cellules pyriformes ”
and to the pear-shaped cells in Halicryptus. Bugnion’s
“ cellules-a-batonnet ” would then be analogous to an internal
group of cells I described (see also Bugnion, pi. xiii, figs.
1, 3, 6). Moreover, Merkel,3 in his very detailed description
of the sensory organs of Vertebrates, points out that the set of
cells surrounding the hair-cells secretes a sieve-like “ mem-
brana limitans/’ through the meshes of which the hairs project
into the surrounding medium. A similar limiting membrane
was described above with regard to Priapulus and Halicryptus
(fig. 1 and fig. 3 a, m.). This furnishes us with an additional
point of similarity between the sensory organs of these two
Gephyreans and the corresponding structures of the lower
Yertebrata.

The Nervotjs System.

The results I obtained as regards the nervous system agree
in general with those of Horst. It is composed of a ventral

1 Langerhans, “ Ueber die Haut der Larve von Salamandra maculosa,”
* Archiv f. Mikrosc. Anatomie,3 vol. ix.

2 B. Solger, “ Zur Kenntniss der Seitenorgane der Knochenfische,” ‘ Cen-
tralblatt d. medic. Wiss.,’ 1877, p. 818.

3 E. Bugnion, “ Sur les organes sensitifs,” * Bulletin de la Societe Vaudoise
des Sc. nat.,’ vol. xii, p. 268. (Dissertation inaugurale.)

4 Merkel, ‘Ueber die Endigungen der sensiblen Nerven in d. Haut d.
Wirbelthiere,3 Rostock, 1880.

FRIAPDLUS AND HALICRYPTUS.

209

cord and an oesophageal ring. Both in Priapulus and Hali-
cryptus the nervous system lies entirely in the ectoderm — a
condition which is of rare occurrence, but which has, as far as
I know, been likewise noticed in a few Annelids — for example,
Hesione and Ovenia.

Ou the body proper the position of the cord is well-marked
externally by a shallow groove running along the ventral surface,
whose two sides are slightly raised, while two of the spike-
bearing ribs indicate its continuation on the proboscis. The
nerve- cord is not continued into the tail appendage (Schwanz-
anhang), but ends at the posterior part of the body in a con-
siderable swelling. Anteriorly it divides into two branches
which surround the oesophagus. Its position is here again
indicated externally by a very deep groove (fig. 8, g.).

Although it appears in cross-sections as if swellings existed
in the cord at regular intervals, I believe this to be merely
due to the powerful contractions of the annular muscles,
allowing the cord to bulge out slightly in the intervening
spaces. In the oesophageal ring, however, a real thickening,
already observed by Saenger, exists dorsally. As regards the
size of the nerve-cord in the ring as compared with that in the
body, the diameter in the former is about two to three times
as great.

All previous observers state that the nervous system lies
immediately under the hypodermis, between it and the annular
muscles. In reality, however, it is placed within the hypo-
dermis-, the ganglionic cells being simply modified hypodermic
cells and the fibrils their processes. As the hypodermis
approaches the cord its cells become elongated just as we have
seen before in the case of the spikes, and ultimately they swell
up, becoming modified into ganglionic cells (figs. 6, 7, 8).
Internally the cells of the hypodermis send out numerous
processes. These are well seen in the long cells close to the
large mass of nerve-fibres in the body (fig. 6, h.p.). The dorsal
part of the cord is wholly taken up by the nerve-fibres (figs.
6, 7, S,/.), and on each side ventrally we find a cluster of
ganglionic cells (fig. 6, g. c.). A similar arrangement has been

210

BOBEET SCHABEF.

observed in Priapulus bicaudatus and Hamingia,1 also in
Sternaspis,2 which, however, has now been removed from the
Gephvrea. In Echiurus the cellular part of the nervous
system is also arranged in form of two peripheral rows of cells.

Immediately above the two masses of nerve-cells on each
side of the cord the space seems filled up with connective
tissue (fig. 6, h. p.) which would correspond to the great deve-
lopment of the same in Priapulus bicaudatus (see Horst,
fig. 15). Whether this is really connective tissue or whether
the branches of the hypodermic cells assume a structure
simulating connective tissue, I have not been able to settle.
In the peripheral part of the central mass of nerve-fibres a few
cells may be seen scattered here and there (figs. 6, 7, n.c) In
the proboscis two longitudinal muscles appear on each side of
the cord externally to the annular muscles (fig. 7, m.). The
result is that the cord becomes compressed laterally and the
two clusters of cells become fused into one (fig. 7, g. c .)

A section through the nerve riug is shown in fig. 8. The
ring, as we have seen before, is situated at the base of a
groove ( g ), surrounding the mouth. The retractor muscles of
the proboscis are attached to the ring, while it is itself again
closely united to the skin by muscular tissue. The greater
part of the nerve ring is taken up by fibres (f.) and ordinary
cells ( g . c.), and the latter send their processes into the fibrous
portion. A few larger cells lie above the fibrous part inter-
nally (fig. 8, g,g.)

The considerable swelling at the posterior end of the ventral
nerve-cord has been very ably described by Horst with regard to
Priapulus bicaudatus. I can only confirm his statements
in the most essential points. His figure 14 is a very good
representation of a cross section. The hypodermic cells send
their branches to the interior from the peripheral part, while
the central portion is taken up by smaller ganglionic cells,
which are surrounded by larger ones. Such is the arrange-

1 Daniellsen and Koren, loc. cit., p. 30.

2 Sluiter, “ Ueber eineu indischea Sternaspis,” ‘Naturkundig Tijdschrift
vor Nederl. Indie,’ vol. xli, p. 274.

PR1APULUS AND HALICRYPTUS.

211

ment in the posterior part of the ganglion. A little more
towards the anterior end nerve-fibres make their appearance in
the centre between the small cells and gradually displace the
cellular part, until they occupy the position which I have
described in dealing with the arrangement in the body proper.

In his anatomy of Halicryptus, Saenger describes lateral
nerves going off from the main trunk and surrounding the
body in a similar way as in Sipunculus nudus. The median
fibrous mass, he says, remains without a change at the points
where the branches originate, and does not send any fibres
into them. In spite of my endeavours to find these lateral
nerves, I have not been able to identify them. Horst did not
find them either. On the other hand, Daniellsen and Koren1
mention that the central nervous cord sent off numerous
branches to the skin and muscles.

In Echiurus Pallasii2 the cellular portion runs along the
whole of the cord in its peripheral part. A canal situated
immediately under the dorsal median line is mentioned in
GreefFs3 description of Echiurus, who supposes it to be a
remainder of the invagination from the Ectoderm. According
to Andreae4 the arrangement in Sipunculus nudus is rather
different. The cord also lies internally to the muscular system,
and consists of a sheath of connective tissue forming an
external neurilemma. The nervous elements are surrounded
by a similar internal sheath, and between the two lies a finely-
granulated mass with small nuclei but without cells.

It will be seen by the above description that I have not
been able to trace any peripheral nerves coming off from the
nerve-cord. It would be rash to assert on the strength of
this that they do not exist, and a further examination of fresh
specimens is needed to clear up these doubts. At the same
time I think it quite possible that the whole of the hypodermis
acts as a kind of nervous layer. On the other hand, the well-
1 Daniellsen and Koren, loc. cit., p. 17.
s Spengel, loc. cit., pp.484 — 86 .

3 Greeff, loc. cit., p. 85.

4 Loc. cit., p. 249.

212

ROBERT SCHARFF.

developed sensory organs, as well as the organisation of the
nerve-cord, seem to lead to a different conclusion, and I hope
these points may soon be definitely settled.

EXPLANATION OF PLATE XIV,

Illustrating Mr. Robert Scharffs paper “Oa the Skin and
Nervous System of Priapulus and Halicryptus.”

Fig. 1. Priapulus. — Longitudinal section of a spike on the proboscis.
h. Hypodermis. ci. Inner layer of cuticula. ce. Outer layer of cuticula.
m. Limiting membrane, sp. Hollow space underneath spike in communica-
tion with body cavity.

Fig. 2. Priapulus. — Longitudinal section of a spike on the body proper.
h. Hypodermis. ci. Inner, ce. outer layer of cuticula. c. c. Club-shaped
cells of the hypodermis bearing short hairs.

Fig. 3 a. Halicryptus. — Longitudinal section of a spike on the body
proper, h. Hypodermis. ce. Outer, ci. inner layer of cuticula. e. c. Ex-
ternal modified hypodermic cells, p. c. Pear-shaped cells. i. c. Internal
modified hypodermic cells, m. Limiting membrane. 1. h. Long hairs project-
ing through membrane.

Fig. 3 b. — Cross section below the limiting membrane. Letters same as
above.

Fig. 3 c. — Cross section of the upper portion of spike, showing it to be a
tube containing hairs which seem to radiate outward.

Fig. 4. Priapulus. — Posterior part of the body. A ventral view, showing
nerve-cord (».), papillae ( p .), also the tail-appendage ( t .).

Fig. 5. Priapulus. — Diagrammatic longitudinal section of part of a pa-
pilla. c. Cuticle, h. Hypodermic cells, greatly elongated and ending above
in a flask-shaped portion (y.) with an opening (o.).

Fig. 6. Priapulus. — Cross section of nerve-cord in the body. c. Cuti-
cula. h. Hypodermis. a. m. Annular muscles, f. Fibrous nerve-mass. g. c.
Ganglionic cells, h. p. Processes of hypodermic cells, n. c. Scattered cells.

Fig. 7. Priapulus. — Cross section of nerve-cord in the proboscis, c.
Cuticula. h. Hypodermis. f. Mass of nerve-fibres, g. c. Ganglionic cells.
m. External longitudinal muscles of the proboscis, g. c. Ganglionic cells.

PRIAPULUS AND HALICRYPTUS. 213

Fig. 8. Priapulus. — Cross section of oesophageal ring. h. Hypodermis.
g. Groove surrounding oral aperture, d. Cutis, f. Mass of nerve-fibres.
g. c. Ganglionic cells, g. g. Larger ganglionic cells, r. m. Retractor muscles
of the proboscis.

Fig. 9. Priapulus. — Surface view of a cluster of papillae at posterior end
of body.

Fig. 10. Priapulus. — Cross section of a papilla, showing the cells filled
with granulated contents.

Fig. 11. Halicryptus. — Strip of skin from the junction between proboscis
and body, exhibiting three different kinds of spikes, sp. p. Spike of proboscis.
sp. t. Spike of body. j. Line of junction between proboscis and body proper,
with the peculiar forked spikes, r. m. External longitudinal muscles of pro-
boscis. 1. m. Internal longitudinal muscles, c. m. Circular muscles, sp.
Hollow space underneath every spike in communication with perivisceral
cavity.

Fig. 12. — General view of Priapulus caudatus, three times natural

size.

Scharff 3d

FHulh,LithT Edir*

THE EYE AND OPTIC TRACT OF INSECTS.

215

The Eye and Optic Tract of Insects.

By

Sydney J. Hickson, B.A. Cantab.. D.Sc. Conti.,

Scholar of Downing College, Cambridge, and Assistant to the
Linacre Professor of Comparative Anatomy at Oxford.

With Plates XV, XVI and XVII.

The structure of the eyes of the Arthropoda has been a
favourite subject with morphologists for many years, and many
beautiful monographs have been published detailing the results
of the careful observations that have been made upon this
subject. Until the last few years the observations stopped
short at the basilar membrane, and the tract lying between the
percipient elements and the brain remained unknown. Of late
years, however, several papers have appeared dealing with the
optic tract and its relations to the eye proper, or ommateum
(Lankester and Bourne), and as some of these have attempted
to throw doubts upon what were formerly considered to be
well-founded homologies, I have gathered together in this
memoir some of the most interesting results of the researches
I have been carrying on for the last two or three years with
the hope of being able thereby to throw some light upon these
obscure or disputed points. In order to make my memoir
more complete I have carefully revised the structure of the
ommateum itself in Musca vomitoria, and I shall here
give a detailed account of it based upon my own observations
before I proceed to describe the nervous elements which connect
it with the brain.

The descriptions which have been published of the ommateum
of insects in general and Musca in particular, are now so

VOL. XXV. NEW SER.

P

216

SYDNEY J. HICKSON.

numerous that to attempt to refer to previous authors in the
course of my description would only tend to hamper and
obscure it. Consequently, I shall leave all reference to previous
authorities to a separate section at the end of the paper, when
I shall attempt to discuss the various disputed points and clear
up the inconsistencies between my own descriptions and those
of other observers.

§ 1. The Eye and Optic Tract of Musca vomitoria.

The eyes of the blow-fly are large brown protruding struc-
tures situated upon the anterior surface of the head. Exter-
nally they are protected by the chitinous cornese which are
broken up into a large number of biconvex facets. The number
of these facets varies in the individual. Muller (17) gives
4000 for Musca domestica. In a vertical section through
the middle of an eye of a blow-fly which had emerged from
its pupa twenty-four hours, I was able to count 62 (PI. XY,
fig. 2). In some I could count as many as 80, and in some
only 40. The external convexity of the facet is usually formed
of a greater arc of a sphere than the internal, so that between
each facet there may be seen, internally only, a small flat surface.
This is invariably covered with a dense pigment. This differ-
ence between the external and internal convexity of the corneal
facets gives a plano-convex appearance to sections that do not
pass through their centres (v. PI. XV, fig. 3, c).

Internally to the cornea is situated the so-called pseudocone,
which is ensheathed by two or three nucleated pigment-cells
(fig. 3 ,pg.x).

The pseudocone consists of four cells, each of which consists
of a clear transparent external portion and a smaller proto-
plasmic portion containing the nucleus situated internally
(n.p. c). The clear transparent portion of each pseudocone-cell
contains in the living eye a watery or perhaps slightly albu-
minous fluid, for in specimens preserved in spirit all that can be
seen of this portion of the cell is a band of protoplasmic
substance stretching from the nucleus to the cornea, and
staining deeply with hsematoxylon. Between each element of

THE EYE AND OPTIC TRACT OF INSECTS.

217

the ommateum or ommatidium as I shall call it, adopting the
term introduced by Carriere (3) there is situated in the region
of the base of the pseudocone, a large pigment-cell (figs. 3 and
10, pg..^). Each of these pigment- cells consists of a central
rounded portion containing a large spherical nucleus and two
or more delicate processes which pass externally {ex.) to the
flat portions of the internal surface of the cornea, and internally
{in.) to accompany the retinulse towards the basilar membrane.

The rhabdom of Musca consists of a bundle of six long
delicate chitinous rods, more or less firmly united together
(fig. 3, rh.). The rhabdomeres or elements of the rhabdom
are more clearly distinguished from one another in the outer
part of their course (fig. 4) than they are in the inner part of it
(fig. 5.) The rhabdom is surrounded by the retinulse. These
are six in number, and in the outer region of their course are
free from one another (fig. 4, r.), but in the inner region are
fused into a sheath.

Each retinula element possesses a nucleus just behind the
nuclei of the pseudocone (fig. 3, nr.) and some of them possess
an additional nucleus in the middle of their course (fig. 3, nrv).
Thus we find a ring of six retinular nuclei around the central
rhabdom, just behind the pseudocone and two or three nuclei
somewhat more irregular in position about half way down.

When quite fresh the retinulse are of a deep carmine colour,
but this soon fades away under the influence of the light, and the
retinulse are left with a yellowish-brown colour. Between the
ommatidia internally there are found pigment-cells (figs. 3,
pg.3), each of which stands on the basilar membrane and sends
a fine process outwards towards the internal process of the
external pigment-cell {pg.2)> The pigment-cells are filled with
bright carmine-coloured granules which change to a deep brown
colour when treated with alcohol.

The basilar membrane of Musca is very thin and perforated
for the passage of tracheal diverticula and the optic nerve-
fibrils.

Between the ommatidia are situated long tubular thin-walled
air- sacs, which may be traced into connection with the nume-

218

SYDNEY J. HICKSON.

rous branching trachese -which traverse the nervous network
just behind the basilar membrane. These tracheal vesicles are
easily seen in fresh-teased specimens of the eye of Musca, but
they are not easy to see in thin sections through hardened
specimens, as their wails are very thin, unpigmented, and
stained with difficulty.

Turning now to the anatomy and histology of the optic tract.
Between the brain and the basilar membrane of the eye we are
able to distinguish three distinct ganglionic swellings. The
first one of these (fig. 1, op.) is separated from the cerebral by
a narrow constriction, which, as Berger (2) has pointed out, is
the homologue of the optic nerve of the other Arthropoda. I
shall call it in this paper the opticon.

The second ganglionic swelling is separated from the opticon
by a tract of fine nerve-fibrils, which partially decussate, and
a few scattered nerve-cells ; and I shall call it the epi-opticon
(fig. 1, e. op.).

The third ganglionic swelling is much flatter in shape than
the others, is separated from them by a bundle of long optic
nerve-fibrils, which cross one another ; and I shall call this the
peri-opticon (fig. 1, p. op.).

The three optic ganglia, together with the cerebral ganglia,
are surrounded by a sheath of very densely-packed nerve-cells
(fig. 1, n. c. s.), the “ Punktsubstanz” of Leydig. I have
examined this sheath very carefully in numerous types, and I
find it to consist of densely-packed cells, each composed of a
very large nucleus surrounded by a very delicate envelope of
cell-protoplasm. The individual cells are connected with one
another by protoplasmic connectives, and in some places fine
nerve-fibrils anastomose between the cells, and are probably
connected with them by fine anastomosing branches.

In the silkworm moth (PI. XV, fig. 15) the protoplasmic
sheath surrounding each nucleus is thicker than it is in Musca
and most other Arthropods, so that the cellular nature of this
sheath is in this case very clearly seen.

In the brain of the developing bee the cells are not so
densely packed as they are in adult animals, so that in well-

THE EYE AND OPTIC TRACT OF INSECTS.

219

stained specimens it is easy to distinguish the cell-protoplasm
and the anastomosing branches (PI. XV, fig. 6).

I have spoken of these cells as nerve-cells because it is
necessary to distinguish them from ganglion-cells, which are
more isolated in position, and possess a considerable quantity
of cell-protoplasm. I shall refer to this point again in
Section 3.

The opticon itself consists of a very fine granular matrix,
traversed throughout by a fine meshwork of minute fibrillse,
similar to the minute network of primitive fibrillse described
by Gerlach in the mammalian brain and spinal cord. This
description of the minute structure of the opticon applies
equally to the epi-opticon and principal ganglia of the body.
As this tissue is very commonly met with in the animal
kingdom, and has not, as far as I am aware, yet received any
separate name, I propose to call it a neurospongium. In
many insects the neurospongium of the opticon is traversed by
fibrils, and in some cases it contains a few scattered nerve- or
even ganglion-cells.

The epi-opticon is connected with the peri-opticon by a
bundle of decussating nerve-fibrils, and as these fibrils approach
the peri-opticon they are connected with a number of scattered
nerve-cells (fig. 2, n. c.), and at the decussation two or three
larger nerve-cells may be seen in each section (fig. 2, ys.)

The peri-opticon of Musca is composed of a number of
cylindrical masses of neurospongium arranged side by side, which
I shall refer to as the elements of the peri-opticon (fig. 2, p. op.),
and between them a single nerve-cell is very frequently seen.

As this ganglion has been recently subjected to considerable
investigation I have taken considerable pains to study it
thoroughly. In addition to numerous sections of hardened
specimens, made both transversely and horizontally, I have
succeeded in isolating the peri-opticons of fresh flies, and
teasing them carefully with needles, both before and after
staining in gold and other reagents, and the following account
is based on these investigations.

The nerve-fibrils coming from the epi-opticon divide into two

220

SYDNEY J. HICKSON.

ov three main fibrillae on entering the cylindrical elements of
the peri-opticon (PL XYI, figs. 16 and 17, A/), and these
fibrillae again subdivide and form the ultimate fibrillar mesh-
work of the neurospongium.

Each little cylindrical mass of the peri-opticon is not entirely
separated from its neighbours, but is connected with them,
either directly by fine fibrillae, or indirectly by the intermedia-
tion of nerve-cells (figs. 16 and 17, n.c.). I have observed also
that some fibrils do not break up to form any neui’ospongium,
but pass straight through without undergoing anv subdivision

(fig- 16,/.).

Sometimes the structure of the elements of the peri-opticon
is complicated by the deposition of pigment. This deposition
of pigment may take the form either of small cylindrical rods
or of a fluted hollow cylinder, or of a smooth hollow cylinder
(figs. 8, a, b, c, and 9). The presence of pigment in this region
is, however, very variable. The figs. 8 and 9 were drawn from
a permanent preparation I have in my possession now, all the
varieties ( a,b,c ) being found in one eye, whilst the other eye
has no pigment at all in this region.

The number of the elements of the peri-opticon does not seem
to bear any relation to the number of ommatidia; in some of
my preparations they seem to be of about the same number;
in others they are considerably less, and in one of my sections
I could only count half as many.

Externally a number of fibrils leave the elements of the
peri-opticon, and at once form a complicated anastomosis with
the numerous nerve-cells found in this region, which in its turn
furnishes the fibrils which pass through the basilar membrane
to supply the retinulae.

In this “terminal anastomosis” are found a number of
branching tracheae — distinguished by their spirally-marked
walls — which run more or less parallel with the basilar mem-
brane (fig. 2, t.). They spring from two main tracheal trunks
(T.t.), situated at the sides of the head behind the eyes. The
tracheae of the terminal optic anastomosis supply the tracheal
vesicles which are found between the ommatidia.

THE E7E AND OPTIC TRACT OF INSECTS.

221

In Musca vomitoria only a few tracheae with spirally-
marked walls are found behind the peri-opticon, and these
arise from separate tracheal trunks situated at the sides of the
optic tract.

§ 2. The Minute Anatomy of the Optic Tract
of various Insects compared.

When the brain and optic tract of a very young Periplaneta
is examined, it is found that the optic nerve separating the
cerebral ganglion from the opticon is much longer in propor-
tion than it is in the adult blow-flv. The opticon is a well-
marked ganglion, and the epi-opticon is small, though distinct.

From the epi-opticon, however, the optic fibres pass straight
to the ommateum without passing through any intermediate
neurospongium. In fact, the peri-opticon described above in
Musca does not exist in the young Periplaneta (fig. 18). The
optic fibres leaving the epi-opticon do not decussate, but as they
approach the basilar membrane they break up into numerous
branches which undergo a loose anastomosis. In this anasto-
mosis a few large nerve-cells may be seen (fig. 18, n. c.). In
the adult Periplaneta the opticon is very large and separated
from the cerebral ganglion by a very considerable optic nerve.
The fibres connecting the opticon and the epi-opticon decus-
sate (fig. 19, d.f.). The epi-opticon is a smaller hemispherical
well-marked ganglion, and the fibres which pass from it to the
ommateum partially decussate (Nf.). My figure (19) is taken
from a preparation of the head of an adult male cockroach with
fully-developed wings, so that I am inclined to think that in
this genus the optic fibres never completely decussate in this
region. The number of fibrils passing from the epi-opticon
to the ommateum is relatively much larger than in the young,
and the nerve-cells in the meshes of the anastomosis are more
numerous. The anastomosis is, perhaps, rather denser and
more complicated than it is in the young, but I cannot find
anything comparable to the loopings of Nepa to be described
immediately, nor anything that could be described as a neuro-
spongiura.

222

SYDNEY J. HICKSON.

In Nepa the optic fibres leave the epi-opticon, and without
decussating, at once form a very complicated anastomosis in
which there are a number of small nerve-cells. Before entering
the ommateum the anastomosis passes through the pores of a
membrane situated a little distance behind the basilar mem-
brane. A similar perforated membane in this position has
been described by Berger (2) and Ciaccio (4) in Musca, but I
have not been able to detect it. In that part of the anasto-
mosis which corresponds in position with the peri-opticon of
Musca, some of the principal fibrils have the appearance of
broadening or flattening out, and when they are examined with
a high power these flattened portions are seen to be made up
of a number of minute fibrillse. Between the principal fibrils
run ordinary anastomosing branches, transverse connecting
fibrils and fibrils which seem to turn round and run back again
to the epi-opticon, and which have a looped appearance in the
sections. These iooped fibrils are also found in the optic tract
of the developing bee.

In Musca, as I have described above, the optic fibrils on
leaving the epi-opticon decussate and then break up into small
cylindrical masses of neurospongium, which together form
what I have called the peri-opticon.

In Agrion bifurcatum (figs. 20, 21), one of our common
English dragon-flies, the opticon is small compared with the
enormously large epi-opticon (fig. 20, e. op.) the fibrils passing
between the two do not decussate, but after undergoing a
considerable anastomosis with one another pass straight across.
The decussation of the fibrils between the epi-opticon and the
peri-opticon is complete (fig. 20, nf.). The peri-opticon is
composed (figs. 20, 21, p. op.) of a number of long, slender
cylindrical elements, each composed of a delicate neuro-
spongium. Between the elements there are a few connecting
fibrillse, and a number of nerve-cells. The terminal anasto-
mosis is much more complicated here than in Musca, and takes
up very much more room, so that the peri-opticon is, compara-
tively speaking, situated some distance behind the basilar
membrane (fig. 20, ta.).

THE EYE AND OPTIC TRACT OF INSECTS.

223

The terminal anastomosis of Agrion may be conveniently
divided into four regions. First, the region (1) lying nearest
to the peri-opticon in which the nerve-cells are numerous, and
the fibrils leaving the peri-opticon form a complicated plexus,
the region (2), next to this, in which the fibrils have collected
into bundles separated by spaces occupied by very thin-
walled tracheae in which there are no spiral markings, and lymph
spaces; next, the region (3), in which the fibrils form a final
plexus, and in which there are again a considerable number of
nerve-cells, and, lastly, the region (4), in which the fibrils are
again collected into bundles, separated by spaces containing
tracheae, which perforate the basement membrane to supply
the retinulae.

In Noctua, Sphinx, and Acherontia, the three genera of
Lepidoptera I have examined, the peri-opticon is composed
of the usual cylindrical elements, but they are much longer,
thinner, and more tightly packed than usual, so that the whole
ganglion has a much more compact and spherical appearance
than it has in any of the genera we have hitherto considered.

The peri-opticon is closely connected with the epi-opticon
by a thick nerve tract in which the nerve-fibrils completely
decussate, but neither in this region nor in the epi-opticon nor
in the peri-opticon is there any trace of tracheal vessels per-
forating the tissues.

The terminal anastomosis of the Lepidoptera is most extraor-
dinarily complex, and the four regions described above in Agrion
can be readily distinguished (conf. Leydig, Taf. x, fig. 2). In
region 2, the large thin- walled, but still spirally-marked tracheae
may be readily seen branching between the nerve-fibril bundles.

The terminal anastomosis of the Lepidoptera is usually very
deeply pigmented. In the bee and the wasp, the only two
members of the order Hymenoptera I have examined, the
peri-opticon is very similar to that of the Lepidoptera, the
elements being long, delicate, and very close to one another.
The terminal anastomosis is not so complicated, nor is it
usually so densely pigmented. No spirally-marked trachea} pene-
trate the optic tract at any part of its course in Hymenoptera.

224

•SYDNEY J. HICKSON.

In Aeschna grandis, one of the Libellulidse, owing to the
very large size of the eyes, the peri-opticon can be easily seen, on
making a simple dissection, to be a large flat ganglion under-
lying the basilar membrane. On making a fine section through
it it will be seen to differ from that of the forms hitherto
described, in that it can no longer be divided into a number of
cylindrical elements well marked off from one another, and
easily separated by teasing (fig. 7, p. op.). In other words,
the elements of which the peri-opticon is composed in Musca
are here fused into a single mass of neurospongium, which
differs from the neurospongium of the epi-opticon and opticon
itself only in the fact that it contains a number of irregular
spaces (s.), which correspond, perhaps, with the spaces between
the elements in Musca.

The nerve-cells ( n . c.), which in the forms hitherto de-
scribed are situated between the elements of the peri-opticon,
are here found to be scattered irregularly through its sub-
stance.

The terminal anastomosis of Aeschna is not so clearly divi-
sible into four regions as it is in Agrion, but still the fibrils, on
leaving the peri-opticon, may be seen to form a loose plexus
with the numerous nerve-cells found in this region (fig. 7, 1),
then to collect together into a number of bundles separated
from one another by considerable spaces, (2) then to form a
second plexus (3) before finally breaking up into the individual
bundles (4) which run through the basilar membrane to supply
the retinulse.

In Eristalis lupinus the opticon and epi-opticon are very
similar to those of Musca, but the peri-opticon and the neigh-
bouring parts present some interesting features (fig. 23). The
nerve-fibrils leaving the epi-opticon completely decussate, and
run a very long course before entering the peri-opticon. In
the middle of the decussation there may be usually found one
or more large nerve-cells, and a few others close up to the
peri-opticon (fig. 23, n.c.). The peri-opticon is in Eristalis a
continuous ganglion, and cannot be said to be composed of
numerous separate elements.

THE EYE AND OPTIC TRACT OF INSECTS.

225

In longitudinal sections ( v . fig. 23) through the peri-opticon
there is certainly an appearance somewhat similar to that of
Musca ( v . fig. 2, p. op.), but this is not due in Eristalis to its
being composed of a number of cylindrical elements, but to
the fact that it is perforated by bundles of thin-walled tracheal
vessels (v. fig. 23, t. v.), which seem in such a section to divide
it into elements. "When a section is examined which is made in
a plane at right angles to the direction of these vessels it is seen
that the peri-opticon forms a continuous ganglion (PI. XVII, fig.
24, p. op.), and that these vessels run through it in bundles ( t . v.)
situated at fairly even distances from one another. In fact
we have in Eristalis a further stage in the complexity of the
ganglion than we have in Aeschna, for the elements which in
the latter have only partially fused together are in this form
completely fused. In Eristalis, however, a system of tracheal
vessels perforates this structure, a system which seems to be
absent in Aeschna and the other forms we have so far
considered.

In the silkworm moth (Bombyx), however, there is a solid
homogeneous peri-opticon devoid of tracheal vessels.

Passing from the Hexapoda I will describe briefly the optic
tract of Carcinus moenas as a type of Crustacean. A lon-
gitudinal section through the ophthalmic peduncle reveals the
same three optic ganglia I have described in insects ; the
opticon (fig. 14, op.) is situated at the end of the optic nerve
(o. n.), and this is connected by nerve-fibrils, which do not
appear to decussate with the epi-opticon (fig. 14, e. op.), and
this again by nerve-fibrils ( N.f .), which completely decussate
with the peri-opticon (p. op.).

The peri-opticon in Crustacea (Carcinus, Astacus, Homarus,
Squilla) is a solid ganglion, similar to the epi-opticon, and
cannot be separated into elements. The terminal anastomosis
(fig. 14, ta.) is more complicated than it is in most insects
(ta.), but the four regions I previously described may be
recognised (1, 2, 3, 4).

I shall not continue here my description of the optic tract of
Crustacea, as I hope soon to be able to collect my observations

226

SYDNEY J. HICKSON.

upon this group into a separate paper ; but I have said
sufficient to show the relation that exists between the peri-
opticon and terminal anastomosis of Crustacea and the homo-
logous structures of the Hexapoda.

Before leaving this part of my subject I must refer to some
observations I have made upon the development of these
structures in the bee.

In a young bee, some time before it emerges from the cell,
the fibrils passing from the epi-opticon to the peri-opticon do
not cross one another (fig. 6, Nf.), but the decussation takes
place at a later stage in a manner I have been unable to follow.
I imagine, however, that is due to a shifting of the position of
the fibrils at their origin from the epi-opticon, in a manner
somewhat similar to that which occurs in Vertebrata when the
roots of the posterior spinal nerve shift from the neural crest
to a lateral position.

At first the fibrils pass straight from the epi-opticon to the
eye, but an anastomosis soon takes place, and the limits of the
peri-opticon are indicated by two rows of nerve-cells, by the
presence of well-marked transverse and looped anastomosing
fibrillae, and by a thickening of many of the original fibrils
(fig. 6). As development proceeds the thickened fibrils split
up into masses of neurospongium, joined together by the trans-
verse anastomosing fibrillae, and each of these forms one of the
elements of which the peri-opticon of the adult is composed.
Before the bee is fully developed these elements stand some
little distance apart from one another, as they do in Musca,
but the spaces between them are gradually filled up by the
development of new elements and the growth of those already
formed.

To recapitulate, then, I have shown that in the young Peri-
planeta the optic nerve-fibrils which leave the peri-opticon pass
without decussating to the ommateum; in the adult Periplaneta
there is a partial decussation ; and that in Nepa there is no
decussation, but the anastomosis is complicated by the presence
of looped and transverse anastomoses. In Musca the fibrils are
split up into little cylindrical blocks of neurospongium, which

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227

I have called the elements of the peri-opticon ; in bees, wasps,
and many Lepidoptera the elements of the peri-opticon are
long, slender, and close-set ; in Aeschna they have partially
fused with one another ; and in Bombyx, Eristalis, and the
Crustacea they have completely fused to form a complete and
continuous ganglion, similar in every way to the opticon and
epi-opticon.

§ 3. Further Remarks upon the Histology of the
Optic Tract.

In the optic tract of insects we can distinguish the following
nervous structures : nerve-fibrils and fibrillse, neurospougium,
nerve-cells, and occasionally ganglion-cells. The nerve-fibrils
are found in the regions between the opticon and epi-opticon,
between the epi-opticon and the peri-opticon, and in the
terminal anastomosis. They must be considered to be naked
axis cylinders, are devoid of any medullary sheath, and fre-
quently break up to anastomose freely with their neighbours.
In the vicinity of the main ganglia they break up into a number
of minute fibrillse, which, anastomosing together, form a dense
plexus or meshwork, which forms the main part of the ganglia,
and which I have called a neurospongium. This connection be-
tween nerve-fibrils, fibrillse, and neurospongium maybe well seen
in the epi-opticon of the young bee (PI. XVII, fig. 25, e. op.).
Each nerve-fibril seems to be composed of a number of very fine
fibrillse closely cemented together, and to be capable of splitting
up into its component parts, where an intimate anastomosis is
requisite or necessary. The different stages of the complexity
of this anastomosis have been seen in the peri-opticon of the
various insects I have described above. Thus, in Blatta the
fibrils split up into finer fibrils in this region, which anastomose
with one another, but the most ultimate division of each fibril
seems never to occur. In Nepa the anastomosis is still more
complicated, and in some cases the nerve-fibrils seem to split
up into their ultimate fibrillse. In Musca finally the sub-
division of the fibrils is complete, and a true neurospongium is
formed by the anastomosing fibrillse.

228

SYDNEY J. HICKSON.

In many cases it is difficult to make out, even after the most
careful histological treatment, the reticulum of fibrillse of the
neurospongium of adult animals. In the adult Aeschna
grand is, however, the nature of the neurospongium of the
epi-opticon can be readily seen with high powers (fig. 22).
The younger the animal, too, the coarser is the neurospongium ;
thus in the very young Periplaneta or bee, the fibrillae may be
very readily seen (Pis. XV, XVII, figs. 6 and 25).

Nerve-cells are so very commonly met with in the central
ganglia and elsewhere, and are very frequently crowded toge-
ther, forming a kind of sheath embracing the other parts of
the ganglia, that they must play a not unimportant part
in the physiological processes of these parts. They were
recognised as cells by Leydig (13), and described by him
as such, but owing to the introduction of his term “Punkt-
substanz ” for the nerve-cell sheath, their true nature seems
to have been over-looked or misunderstood by some of his
successors.

It is true that in such forms as Musca, and many other adult
insects, the cellular nature of the “ Punktsubstanz ” is not
easy to make out, and it seems at first sight to be composed
of numerous nuclei closely packed together. In the young
bee, however, each nucleus can be seen to be encased in a
delicate sheath of clear protoplasm which is drawn out into a
number of fine processes which communicate with similar pro-
cesses of other cells or with the nerve-fibrils. In the silkworm
moth, the true cell-protoplasm is comparatively large (PI. XV,
fig. 15) in the adult, and as it stains well in borax-carmine
and hsematoxylon it can be readily seen.

Ganglion-cells differ from nerve-cells only in the relative
amount of cell-protoplasm to nucleus. They are not usually
found in the optic tract of insects, although they are present
occasionally in some. The best ganglion-cells I have seen are
in the brain of Periplaneta (PI. XVII, fig. 23) and in such the
cell-protoplasm is very considerable, and stains well. I have
found in this region apolar, bipolar, and tripolar ganglion-
cells (a, b,c.).

THE EYE AND OPTIC TRACT OF INSECTS.

229

§ 4. The Comparative Anatomy of the Ommateum
of the various orders of insects is, thanks to valuable mono-
graphs of Max Schultze (18), and Grenacher (7), so well
known that it would be superfluous for me to go over the
ground again. I have made careful series of sections through
the eyes of many of the genera described by Grenacber, and
I have been able to assure myself in almost every particular
of the accuracy of his observations.

The question of the relation of the so-called pseudocone of
certain insects to the well-known crystalline cone of others,
is, however, one to which I have devoted some attention, and
the result of my observations may not be devoid of interest.

The term “ pseudocone ” was given by Grenacher to the
structure corresponding to the crystalline cones of the majority
of insects and Crustacea, which is found in the following
genera of the Diptera, Tabanus, Sarcophaga, Hsematotopa,
Syrphus, Musca, and I can add as a result of my own
researches, Eristalis. The pseudocone, according to Grenacher,
differs from the “ eucone ” and “acone” in possessing the
following characteristics which I quote verbatim from his work
(p. 88). “Wahrend beim Acone Augen die vier hinter der
Facette gelegenen und sie abscheidenden Zellen zeitlebens
als solche unverandert persistiren ; beim euconen aber ausser
der Facette noch den aus ebensoviel Segmenten, als Zellen
vorhanden sind, bestehenden Krystallkegel aussondern (und
zwar erscheint jedes Segment urspriinglich im Innern der
zugehorigen Zelle) : scheiden die vier Krystallzelleu beim

pseudoconen Auge eine weiche, halb oder ganz fliissige Substanz
aus, die, zusammengehalten durch trichterformig gestaltete
Haupt (tp.) pigmentzellen, functionell dem Krystallkegel zuver-
gleichen ist.

“ Sie ist aber vor den Zellen gelegen, durch deren Thatig-
keit sie entstanden ist, zwischen denselben und der Facette;
die Kerne jener Zellen, die man als Semper’sche bezeichnet,
liegen demnach nicht, wie bei den andern zussamengetzten
Augen, der Facette stark genahert, sondern in einem oft
recht erheblichen Abstand von ihr abgeriickt.”

230

SYDNEY J. HICKSON.

According to this view then, the pseudocone is a space filled
with a fluid or semi-fluid substance situated between the cornea
and the “ Semper’s nuclei.”

In Musca this space is seen to be traversed by four very
delicate clear bands passing from the innermost regions of
the pseudocone to the facet. (Grenacher, p. 90, figs. 63,
64, Ps. C.).

There can be no doubt now, I think, that these bands do not
exist as such in the living eye, but that their appearance is due
to the action of reagents. I have found them in a similar
position in Eristalis, and I am led to believe that they
represent the shrivelled remains of the external part of the
cone-cells.

This portion of the cone-cell I believe to be filled in the
living condition with a fluid or semifluid substance which
performs the same function as the crystalline cone of the
“ eucone eyes/’ but that it is partially or wholly dissolved by
reagents and only the cell walls, and perhaps part of the proto-
plasmic cell substance are left in the form of four bands
passing through the space formerly occupied by the pseudocone.
The inner part of the cone-cells containing four nuclei
(‘ Semper’s nuclei ’ Grenacher) are seen at the base of the
pseudocone in close contact with the end of the rhabdom.
The development of the crystalline cone has been carefully
investigated by Claparede (5), and he shows that it is developed
in four pieces in the primitive cone-cells (Krystallzellen) on
the inner side of the nuclei, that each part increases in size
until it forms with the three others the crystalline cone by
apposition. In the adult condition the crystalline cone is with
difficulty divisible into its four constituent parts, and the nuclei
of the cone-cells remain as the “ Semper’s nuclei ” of the adult.
From my own researches upon the developing bee and cock-
roach. I believe this to be a very fair statement of what
occurs. The structure of the adult crystalline cone may be
very well studied in Aeschna grandis (figs. 12 and 13) in
which the “ Semper’s nuclei ” are seen to be large, well marked,
and usually situated in the four corners of the quadrangular

THE EYE AND OPTIC TRACT OF INSECTS.

231

protoplasmic mass, just behind the facet. It is not easy, either
in the adult or developing condition, to see the outlines of the
four cells composing this protoplasmic mass, but I have no
doubt that if it were properly stained by nitrate of silver they
could be easily demonstrated. Even in the adult the four
portions of the cone are never completely fused, but delicate
bands of protoplasm staining well in borax carmine remain
between them throughout life.

If this description of the pseudocone and eucone eye is
accurate, and I believe it so to be, the difference between the
two, although fundamental, is not so excentric as it was
formerly thought to be. The difference between them, I
believe, lies in the fact that in the former the refracting body
formed by the cone-cell lies behind the nuclei, and in the latter
in front of it. In the acone eye, as Grenacher explains, the
four primitive cone-cells remain, and no refracting body is
developed in them at all.

The pigment of the ommateum of insects is usually very
copious, and is supplied by cells whose protoplasm is drawn
out into long processes, which sheath the ommatidia. Of
these pigment-cells three series may be very generally recog-
nised, although additional series are sometimes present, e. g.
Lepidoptera. The three series are : 1. A series of pigment-
cells, which ensheath the cone (fig. 3) and prevent extraneous
rays of light from escaping ; these may be called the “ cone
pigment-cells. ”

2. A series of pigment-cells situated in the outer region of
the rhabdoms, which have long processes passing between the
retinulse and elsewhere, which may be called the external
pigment-cells (fig. 2).

3. A series of pigment-cells usually resting upon the basilar
membrane (fig. 3), whose processes pass externally between the
retinulse, and internally, in some cases, through the basilar
membrane to the terminal auastomosis, and may be called the
internal pigment-cells.

These three series of pigment-cells are very constant through
the Hexapoda.

VOL. XXV. NEW SER, q

232

SYDNEY J. HICKSON.

The basilar membrane is in all cases perforated by two sets of
apertures, which are best seen in Agrion (PI. XVII, fig. 28, b.m.) ;
the larger apertures are for the passage of the tracheal vesicles,
the smaller for the nerve-fibrils passing to the retinulae.

The thickness of the basilar membrane varies considerably.
In Agrion, Aeschna, and the Libellulidse generally it is thick,
but in the Diptera, Hymenoptera, and others very thin.

§ 5. The Distribution of Tracheae to the Optic
Tract and Ommateum.

The tracheae of the insect may be divided under four heads :

(1) large tracheal trunks lying in the various parts of the body ;

(2) smaller tracheal vessels ramifying through the various
viscera, with spiral markings on their walls; (3) very thin-
walled vessels devoid of spiral markings, ramifying in the
various tissues and organs of the body, and in some cases anas-
tomosing with one another ; and finally, (4) tracheal vesicles,
first recognised by Strauss-Durckheim (20), as closed sacs or
dilatations of the tracheal vessels. Speaking of them he says,
p. 319, “Dans les vesicules tracheenes qui ne se rencontrent
que chez un certain nombre d’insectes, le fil spiral n'existe
point, et elles sont reduites a la tunique exterieure ; car
l’interieure ne s’y laisse aucunement apercevoir.,!

The extent to which spirally-marked tracheae are present in
the nerve-ganglia seems to vary enormously, as may readily be
seen by examining sections through the brain and optic tract
of various insects, or consulting the figures which have been
published by Leydig (12) and others.

Taking the tracheae of what I have called the terminal anas-
tomosis alone, we find that in Eristalis the spirally-marked
tracheae in this region are very large and very numerous ; in
fact they form a very dense network just behind the basilar
membrane. In Musca they are also very numerous, but the
network of them is not nearly so dense as it is in Eristalis.
They are present in this region in Blatta and Dytiscus (Leydig),
and in the Lepidoptera (Sphinx, Acherontia, Noctua), although

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233

in this order the walls are very thin and the spiral markings
indistinct. Iu Apis, Aeschna, Nepa, Agrion, &c., spirally-
marked tracheae are absent in this region. Again, in that
region of the optic tract situated just behind the peri-opticon
we find very few tracheae in Musca, and in some individual
examples I have found none at all, but in Eristalis they are very
numerous (PI. XVI, fig. 23), and even decussate with the optic
nerve-fibrils. But although the spirally-marked tracheae may
be absent in many parts of the optic tract there is very good
evidence for believing that in all cases it is copiously supplied
with thin-walled tracheal vessels. Thus, in Aeschna and
Agrion the region marked 2 in the terminal anastomosis is
undoubtedly occupied by thin-walled tracheal vessels, and in
the former genus the spaces (PI. XV, fig. 7,s.) found in the
peri-opticon are probably occupied by such vessels.

The difficulty of differentiating these vessels in hardened and
stained sections is remarkable. Thus, the tracheal vessels
found in the ommateum of Musca (fig. 2, t. v.; fig. 3, t.v.) are
quite invisible in many of my sections, although when the
fresh eye is examined they are most conspicuous. It is true
that in one series I have, that was stained in a remarkably
good haematoxylon fluid [vide infra), I was able to see them
fairly well, and it was in this series that I was able to trace
their connection with the tracheae behind the basilar membrane
[vide fig. 3, T. tv.) ; but, as a rule, they cannot be seen in
hardened sections. I have turned my attention, however, more
particularly to the distribution of the tracheae in this region in
Eristalis and Musca.

In both these forms two large tracheal trunks (Ttv Tt2)
are to be found at the sides of the optic tract lying in the
groove between the epi-opticon and peri-opticon. The larger
of these is external, the smaller internal. The larger one sends
off special tracheae to the terminal anastomosis, and does not
send any branches into the peri opticon or behind it. The
smaller of them sends tracheae into the optic tract behind the
peri-opticon, never in front of it.

The tracheae of the terminal anastomosis send off thin-walled

234

SYDNEY J. HICKSON.

vessels devoid of spiral markings, which perforate the basilar
membrane to end in the inter-ommatidial tracheal vesicles
(fig. 3, t.v.). These vesicles are at the base broad, but taper to
a point externally, and end in the region of the external
pigment-cells.

In addition to these the tracheae of the terminal anastomosis
send off other thin- walled vessels, which perforate the peri-
opticon and communicate with similar offshoots from the
tracheae situated behind it.

These cannot be seen very distinctly in Musca, but in
Eristalis they are gathered together in bundles as they perforate
the peri-opticon, and are easily distinguished by their com-
paratively thick walls (PI. XVI, fig. 23).

§ 6. Historical and Critical.

The history of the research into the anatomy and develop-
ment of the Arthropod eye practically dates from the publica-
tion of Johannes Muller’s work ‘ Zur vergleichenden Physio-
logic des Gesichtssinnes ’ in 1826 (17). From that time to
the publication of Grenacher’s (7) great work ‘ Unter-
suchungen fiber das Sehorgan der Arthropoden ’ in 1879, the
study was carried on by numerous investigators both in England
and abroad, and much light was thrown upon the numerous
branches of the subject.

It is not my purpose to enter here into the various points
that have formed subjects for animated discussion in times
gone by, nor is it my purpose to give any detailed account of
researches previous to 1879, for all such information has been
skilfully brought together and digested in the learned ‘ His-
torischkritische Uebersicht ’ of Dr. Grenacher’s work. Since
then, however, certain papers have been published describing
certain structures in the eye and optic tract of insects, which
cannot be allowed to pass by without some criticism.

The eye of the blow-fly was described by Grenadier (7, p. 90)
in considerable detail, and the description I have given above
differs from his only in a few minor points. He says, for
instance, that the corneal facets are plano-convex, but they

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THE EYE AND OPTIC TRACT OF INSECTS.

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are in reality biconvex, the plano-convex appearance being seen
only when the sections are cut not quite perpendicularly, or do
not pass quite through the centre of the facets. Carriere (3)
figures the facets of Musca plano-convex. Lowne (15),
whilst figuring them biconvex as I have done, places them
amongst what he calls the “ kistoid cornese.” The “ ‘ kistoid
cornea * consists of a chitinous (?) articular membrane folded
on itself so as to resemble a piece of honeycomb, the openings
of the hexagonal cells being turned inwards.” “ The cavity
of the corneal cell is occupied by the oil-like lens.” I have
never yet been able to find anything that would answer to this
description. I have never found anything like “ an oil-like
lens,” nor can the cornea be truly compared with a honeycomb.
Each facet in Musca is formed of chitin, the outer layers of
which are the hardest and do not stain, whilst the inner ones
are softer and frequently take up a considerable amount of
haematoxylon or borax carmine staining. I have not made a
special study of the development of the cornea, but since the
publication of Mr. Lowne’s paper, I have re-examined many
of my preparations of adult and immature eyes. As a result
of this, I must express a very strong opinion that the facets are
not developed from “ four original cells,” but from a con-
tinuous sheath of protoplasmic substance which underlies the
whole surface of the cornea, and which remains as a living
protoplasmic lamina until the eye is fully developed and then
shrivels up. That the so-called “ Semper’s nuclei ” have
nothing whatever to do with the formation of the facets,
I should think has been amply proved by the researches of
Claparede (5), Max Schultz (IS), and Grenacher (7).

My description of the ommatidia given above is almost
identical with that of Grenacher’s ; the only point in which I
am inclined to differ from him is in his description of the nuclei
of the retinulae.

He says : “ Von den Kernen der Retinula liegen sechs im
vordern Drittel, wo sie (an geharteten Augen) buckelartige
Auftreibungen verursachen, der siebente findet sich immer im
hintern Drittel und gehort wohl zum Centralstabschen.”

236

SYDNEY J. HICKSON.

Carriere (3) says that only five nuclei lie in the uppermost
end of the retinulse. My own researches lead me to believe
that six nuclei are found in the uppermost part which belong
to the six retinulse, and that the one or two nuclei which are
found about half way down are additional nuclei belonging to
one or two of these six retinulse. In other words, 1 believe
that some of the retinulse possess two nuclei, and my opinion
upon this point is supported by the investigation of the
same structures in other Insects and Crustacea, and by
the researches of Claparede and Weissman upon their de-
velopment. I cannot see anything morphologically monstrous
in supposing that the retinula cells possess more than one
nucleus.

The inter-ommatidial tracheal vesicles have been known to
exist for some time. They were mentioned by Swammerdam,
who said : “ Es ist wunderbar, wie und in was fur einer grosseu
Menge die Luftrohren .... hinaufklimmen,” by Serres, by
Will, and by Leydig (11, 12). Grenacher (7) figures a
portion of one of them in Tabanus bovinus (Taf. vii,
fig. 60), and they are mentioned by Lowne. By some autho-
rities they have been supposed to perform the function of a
tapetum owing to their brilliant glittering appearance in the
living eye, but the sheath of pigment-cells surrounding the
ommatidia, and between them and the tracheal vesicles, mili-
tates against this view ; and they must be regarded, I think,
simply as vessels for the aeration of the ommateal tissues.
They were also known to Ciaccio (4), whose description of the
distribution of the tracheae to the optic tract in the Diptera is
exceedingly accurate. Berger (2) also mentions the tracheal
diverticula, but does not figure them.

The function of the retinulse has been a subject which has
been very largely discussed by the older writers, but the balance
of opinion has always been in favour of considering the
retinulse to be the true nerve-end cells. This was most cer-
tainly the opinion of Muller (17), but although this was
combatted by Gottsche (6), and by Wagner (21), who thought
he could trace the nerve-fibrils through the retinulse to the

THE EYE AND OPTIC TRACT OF INSECTS.

237

crystalline cones, in 1864 Leydig was able to express a very
strong opinion that the retinulse (Nervenfasern) are the nerve-
end cells and “ dass man die Analoga nicht in den gewohn-
lichen Nervenprimitivfasern der Wirbelthiere suchen darf,
sondern einzig und allein in den Bacillis und Conis der Retina
hoherer Thiere.”

The same opinion was expressed in 1868 by Max Schultz
(18), who at the close of his exceedingly careful and valuable
work on the compound eyes of Crustacea and Insects, says
that it is a proved fact that the retinulse (Sehstaben) are the
end-organs of the optic nerves.

In 1879 Dr. G-renacher, after a prolonged and laborious
re-investigation of the whole subject, came to the same con-
clusion, and for the first time introduced the term “ retinulse ”
for the structures which are now almost universally known by
that name.

After the subject had thus been thoroughly investigated and
re-investigated by such celebrated naturalists, and the results
of such investigations had led to conclusions which in all
important respects were identical, it might have been thought
that the matter was definitely settled. However, a short paper
was published last year in the ‘ Proc. Roy. Soc./ by Mr. Lowne
(15), in which a view was put forward that the retinulse are not
the nerve-end cells at all, but that the true retina is situated
behind the basilar membrane. Lowne’s retina is situated in
Musca in a position identical with my peri-opticon, and I have
no doubt that he has mistaken the elements of this ganglion
for cells, just as Carriere (3) did, and supposed that they
corresponded with the retinal cells of other animals. But this
view is perfectly untenable, for not only does anatomy teach
us that the optic nerve-fibrils end in the retinulse, but morpho-
logy teaches us that they are homologous with the nerve-end
cells of the eyes of other animals, and the few physiological
experiments that have been made also show that they are
eminently adapted for light-perceiving purposes.

If anything further were required to prove that the retinulse
are homologous with visual nerve-end cells of other animals, it

238

SYDNEY J. HICKSON.

is the fact that Ley dig (11) discovered that they are possessed
of a true retina purple. As this substance is not known to
occur anywhere in the animal body but in the visual nerve-
end cells, and as the retinulae of Arthropods possess this
substance and Lowne’s bacillar layer does not, the retinulae
must be the nerve-end cells of the Arthropod eye.

This being the case, the terms “Dioptron,” and “ Neuron,”
“ Retina/’ and “ Great rods,” introduced by Lowne, must be
rejected, and the nomenclature used which has been introduced
by Grenacher (7), and Lankester and Bourne (15).

The first important paper upon the optic tract of Arthro-
poda was by Emile Berger (2), who described and figured this
region in the larva of Libellula, in Musca, Dytiscus Apis,
Pieris, Squilla, Astacus, &c.

He was the first to describe the true position of the optic
nerve, namely, between the opticon and the cerebrum ; and
he also figured, fairly accurately, the epi-opticon and the optic
nerve-fibrils decussating between this and the peri-opticon.
The rest of the optic tract he divided as follows. The optic
nerve-fibrils, after they have decussated, enter a ganglion -cell
layer, this is followed by a molecular layer (Marksubstanz),
which is situated immediately behind a nuclear layer (Korner-
schicht), which is separated from the basement membrane of
the ommateum by a “ nerve-bundle sheath.” These various
layers, however, are not so constant as he supposed, nor are
they in all cases just as he described. The ganglion-cell layer is
not always present, and sometimes it is only represented by a
few scattered cells as in Eristalis, nor can any distinction be
drawn between the cells situated in this region and the region
situated in front of the peri-opticon. In both cases the cells
are nerve-cells and not ganglion-cells, according to the distinc-
tion I have drawn between the two ; that is, in neither region
are cells found containing a considerable quantity of true cell-
protoplasm.

The molecular layer of Berger corresponds with my peri-
opticon. He does not seem to have noticed that it is composed
of a number of elements, but his idea that it corresponded in

THE EYE AND OPTIC TRACT OF INSECTS.

239

structure with the substance of the epi-opticon and opticon
shows that he was able to appreciate its histological nature as
far as possible, and he did not fall into the error of supposing,
as some subsequent observers have done, that it contained
bacillar or cubical cell-elements. The nuclear layer and the
“ nerve-bundle ” sheath of Berger together make up what I
have termed above the “ terminal anastomosis.”

Previous to the publication of Berger’s paper, the optic tract
of Insects had been briefly described and names given to the
various regions. Thus Weissmann (21) called the opticon and
epi-opticon the “ bulbus,” the region where the optic fibrils
decussate the “ Stiel,” and the peri-opticon the “Augen-
scheibe.” Leydig (2) described the three ganglia in
Formica as the “ kleiner Kern des Sehlappens,” “ grosser
Kern d. S.,” and “ dritter Kern, d. S,” and in Dytiscus as the
“erster,” “zweiter,” und “dritter” nuclei. Ciaccio (4) describes
the following layers of the retina : 1. A “membrana limitans”
posterior. 2. The layer of optic nerve- fibrils. 3. The layer
of nerve-cells. 4. The “ membrana limitans ” anterior. 5.
The layer of rods. In fact, Ciaccio anticipated Berger’s idea,
that the retina of insects contains a number of nerve-layers as
the Vertebrate retina does, but was unable to give it the
minute histological analysis it deserved.

Since Berger’s paper appeared Carriere (3) has described the
peri-opticon as a layer of “ long, palisade-shaped cells, the
number of which corresponds with that of the eye units.
Every one of these palisade-cells possesses an oblong nucleus
at its foremost somewhat broader end.” My researches show
that this description is quite inaccurate. The elements of the
peri-opticon are not cells, and the large oval nucleus situated
in each element which Carriere figures does not exist. Nerve-
cells, when they exist in the region of the peri-opticon in
Musca, lie between the elements, and not in them, as my
figures show.

In a young Sarcophaga carnaria Carriere found “ a
refracting chitinous or cuticular tube, which lies in the midst
of the ‘ palisade-cell,’ ” and he finds in Musca vomitoria

240

SYDNEY J. HICKSON.

that each palisade-cell has a cylindrical axis, which he says
may be such a chitinous tube.

I have examined my sections of Musca, both transverse and
longitudinal, very carefully, but can find no evidence of the
existence of any such tube, and I have also, by a process of
maceration described below, satisfied myself that no chitinous
structures of this kind are present in the optic tract behind.

The tubes of Sarcophaga may possibly be tracheal tubes
similar to those I have described in the peri-opticon of Eris-
talis, and the appearance which Carriere describes (but does
not figure) in Musca may be due to the curious effects which
the pigment often pi’oduces ( v . figs. 8 and 9).

The recent paper by Lowne upon the retina of insects I
have referred to above and criticised elsewhere (8). My
description of the optic tract of insects is quite different from
his, as is my opinion of the function of the various parts.

§ 7. Some general Considerations upon the Eye and
Optic Tract of Insects.

The layer composed of the retinulse and rhabdoms cannot, as
Ciaccio (4), Berger (2), and others have shown, be considered
to be the equivalent of the retina of other animals. It is only
part of the retina, namely, that part of it which bears the
nerve-end cells, and corresponds, functionally at any rate, to
the layer of rods and cones of the Vertebrate eye. In Verte-
brates and in those Invertebrates with large, highly-organised
eyes, such as Cephalopods and such genera as Pecten and
Spondylus among Lamellibranchs, and Alciope among the
Polychgeta, the retina contains, in addition to the rods and
cones, several layers of nerve-cells, ganglion-cells, neurospon-
gium, &c., which are very different in order and arrangement
for different groups of animals, but very constant in the
individual genera and species.

In Arthropoda we also find behind the basilar membrane of
the ommateum similar complicated nervous strata, which in
all probability perform the same function.

THE EYE AND OPTIC TRACT OF INSECTS.

241

We cannot, however, trace the same layers of nerve-cells,
ganglion-cells, &c., layer for layer, in Arthropoda, that we
find in the retina of Yertebrata, any more than we can trace
them in Cephalopods, in Alciope, or in Pecten. All that we
can say is that there is present in all animals with highly-
organised eyes certain complicated nervous structures situated
between the nerve-end cells and the brain which are probably
for the purpose of elaborating and combining the sensations
received by the nerve-end cells.

How much, then, of the optic tract of insects should be
considered to belong to the retina ? It seems to me that to
be consistent we should consider all the nerve structure lying
between the crystalline cone-layer and the true optic nerve to
be analogous with the retina of other animals.

According to my view, in fact, the retina of insects consists
of the retinulse, peri-opticon, epi-opticon, opticon, and all the
intermediate nerve-tracts.

Both Ciaccio (4) and Berger (2) considered the retina proper
to end at the region of the decussating fibres ( N.f .). If this is
the case the decussating nerve-fibrils should represent the optic
nerve, which they do not, as Berger himself has shown.

The true optic nerve lies between the opticon and the
cerebral ganglion, and it is this which is so enormously
elongated in the podophthalmatous Arthropoda.

It may seem strange at first to have to consider those
structures in the eyes of Arthropods, which have hitherto
been somewhat loosely described as “ optic ganglia,” to be
really part of the gigantic retina ; but if the nervous layers of
the retina are really for the purpose of combining and elabo-
rating the impressions received by the nerve-end cells, as I
suppose they must be, it is only natural to find them larger
and more complicated in the Arthropod eye than in the
Vertebrate eye.

In the Vertebrate eye the nerve-end cells are, comparatively
speaking, extremely small and very closely packed, and con-
sequently the nervous effort of translating the sensations of
the nerve-end cells into a picture is very much less than it is in

242

SYDNEY J. HICKSON.

the Arthropods, where the nerve-end cells are comparatively
very large and widely separated from one another.

In the human eye, for example, the distance between the
centres of two adjacent cones is only mm., but in Musca
the distance between adjacent ommatidia is ^4^- mm. In
fact the picture, as received by the nerve-end cells of the
Vertebrate eye, is much more complete in itself than it can
possibly be in any Arthropod eye, and consequently the latter
possesses a much more elaborate and complete translating
apparatus in their retina than the former possesses.

If this view be a sound one it is necessary to give up the
term “ optic ganglion,” as applied to terminal ganglionic
swellings in the optic tract of animals, such as the so-called
optic ganglia of Cephalopods and of Arthropods, and consider
them all as forming part of the true retina.

The observations I have made concerning the comparative
anatomy and development of the peri-opticon may possibly
possess an interest outside the bounds of comparative ophthal-
mology.

In considering the origin of the nervous system of animals
we are able to see fairly clearly the origin of nerve-fibres and
ganglion-cells. Thus Balfour (1) said : “ From embryology
we learn that the ganglion-cells of the central part of the
nervous system are originally derived from the simple un-
differentiated epithelial cells of the surface of the body “ that
ganglion-cells have been evolved from simple epithelial cells
of the epidermis and that “ the primitive nerves were out-
growths of the original ganglion-cells but the evolution of
the central ganglia has not hitherto been investigated.

It is, I think, evident, from both embryological and phylo-
genetic considerations, that the formation of the central ganglia
was subsequent to that of the ganglion-cells and nerve-fibres,
and that they must have originated from either one or both
of these elements.

The characteristic feature of a ganglion is the very fine
reticulum of nerve fibrillse which forms what I have called a
neurospongium, with which are associated a number of larger

THE EYE AND OPTIO TRACT OF INSECTS.

243

nerve-fibrils, and a number of nerve- and ganglion-cells. The
evidence I have brought forward by my researches upon the
phylogeny and development of the peri-opticon of insects leads
me to suppose that the neurospongium is formed by a breaking
up of the nerve-fibrils into a number of ultimate fibrillse which,
anastomosing with one another, form the neurospongium.
I have not been able to turn my attention to the develop-
ment of the central ganglia in other animals, so I am unable
to say definitely that this is the case universally throughout
the animal kingdom, but it is very probable that it is so, and
that we have in the various forms of peri-opticon an indication
of the manner in which central ganglia were primarily evolved
from the primitive nerve-fibres and ganglion-cells which pre-
ceded them.

§ 8. Methods.

As a short description of some of the methods I have employed
in studying the eyes and optic tract of Arthropods may be
useful to those engaged in similar researches, I propose in
this section to mention a few of those that I have found most
useful and have given the best results. For making sections
through the eye of Musca vomitoria I have found it best to
dissect away the posterior wall of the cranium of the fresh insect
and then to expose it to the fumes of 1 per cent, osmic acid
solution for forty minutes, then to wash in 60 per cent, spirit
for a few minutes, and finally, to harden in absolute alcohol.
Crania thus prepared may be cut into fine sections by the
automatic microtome, and stained in hsematoxylin or borax
carmine. With most insects, however, I have found it impos-
sible to use this microtome owing to the hardness of the chitin
of the cranium and of the mouth appendages. In such cases I
have used a Jung’s microtome with the razor set so as to give
a long sweep at each stroke, and the sections carefully removed
from the razor, and mounted one by one.

I have tried various methods for depigmenting the eyes such
as bleaching powder, nitric acid, chlorine, &c., but the best is
that of exposing the sections when cut to the action of nitrous

244

SYDNEY J. HICKSON.

fumes. This is done in the following manner. The sections
are fixed in position on the slide by Meyer’s albumin and
glycerine solution, and when the paraffin has been removed by
turpentine and the turpentine driven off by absolute alcohol,
the slide is inverted over a capsule containing 90 per cent, spirit,
to which a few drops of strong nitric acid have been added.
Copious nitrous fumes are given off and the pigment dissolves.
The action can be stopped at any moment by washing with
neutral spirit and when the washing is complete the sections
can be stained in haematoxylon or any other solution.

For teasing the best solution is chloral hydrate. I leave the
eye or optic tract in a 5 per cent, solution of chloral hydrate for
twenty-four hours, and then tease with needles and mount in gly-
cerine. In some cases I have made very satisfactory preparations
by fixing the teased tissues to the slide with albumin and gly-
cerine solution and then washing with spirit and staining in the
ordinary way, or staining after depigmenting with nitrous fumes.

I have tried various kinds of haematoxylon stains, but the
solution which gives the best results, and is in every way the
most satisfactory, is one which 1 have made by following
Mitchell’s (16) instructions, with a few additional precautions.
I will describe here the mode in which I now make haema-
toxylon stain.

Take 56 grammes of the logwood extract and thoroughly
pound it in a mortar. Then place it on a filter, and pour
about a litre and a half of ordinary tap water through it. The
filtrate may be thrown away and the residue allowed to dry.
In the meantime prepare a solution of alum as follows : — Take
25 grammes of alum, and after they have been thoroughly
pounded in a mortar pour them into 250 cc. of distilled water.
To this solution add strong potash until a precipitate is formed,
which will not dissolve upon stirring and standing.

Pour the alum solution thus made on to the haematoxylon
residue, and allow them to macerate together for three or four
days in a warm room. Then filter the haematoxylon solution
into a bottle provided with a closely-fitting stopper, and add
to it 10 cc. of pure glycerine and 100 cc. of 90 per cent, spirit.

THE EYE AND OPTIC TRACT OE INSECTS.

245

(The residue need not be thrown away, for it can be macerated
again with alum solution for a week or more, and a good strong
stain obtained as before.) When the solution is thus made it
should be well shaken, and allowed to stand for some weeks
before being used. This solution of hsematoxylon improves
considerably with age. The oldest I have was made about
twelve months ago, and is by far the best.

The hsematoxylon stain produced by this recipe possesses
several advantages over others. In most cases it differentiates
the tissues admirably ; nuclei stain deeply, cell protoplasm
faintly ; it seems to last a long time without showing signs
of fading, and, as it penetrates well, it is very useful for staining
in bulk.

§ 9. Summary.

In this memoir, then, I have described in detail the eye and
optic tract of Musca vomitoria. The pseudo-cones I have
found to be composed of four cells with their nuclei situated
internally, each one containing a large watery or albuminous
vacuole, which serves the same purpose, and is morphologically
homologous with the crystalline cone of the “eucone” eyes.
There are six retinulse cells, each possessing a nucleus situated
in that part of it which lies immediately behind the pseudo-
cones, and in some cases an additional nucleus, situated about
half way down. I have figured for the first time the inter-
ommatidial tracheal vesicles which have been previously ob-
served by several investigators. In tl^e optic tract I have
described three ganglia — the opticon, epi-opticon, and peri-
opticon. The last of these is composed of a number of small
cylindrical elements of a tissue composed of a sponge work of
nerve-fibrillse, which I have called a “ neurospongium.” The
opticon and the epi-opticon are present in all insects and in
most of the higher Crustacea. The peri-opticon appears
comparatively late in development, but is never found even in
the adults of Periplaneta and Nepa.

The peri-opticon, when present, is usually composed of a
number of cylindrical elements, which partially fuse in Aeschua

246

SYDNEY J. HICKSON.

and completely in Eristalis, Bombyx, and the Crustacea. In
Eristalis the peri-opticon is traversed by a number of delicate
tracheal vessels.

The terminal optic anastomosis of Nepa is more complicated
than it is in Periplaneta, and seems to be an intermediate
stage between the simple anastomosis and the true peri-opticon
of Musca.

A similar series of intermediate stages between the simple
anastomosis and a true peri-opticon has been traced in the
development of these parts in the Bee.

The development and comparative anatomy of the peri-
opticon of insects is interesting, as it may indicate the mode in
which central ganglia were first formed from primitive nerve-
fibrils and cells.

My researches seem to me to corroborate the opinion of the
majority of previous investigators, that the retinulse are the
true nerve-end cells.

My researches were carried on entirely in the morphological
laboratory at Oxford, and I have to thank Professor Moseley
for much valuable help and advice, and to Professor Lankester
for many valuable suggestions.

§ 10. Bibliography.

The following list does not pretend to be a complete biblio-
graphy of the subject, but it contains the most important of
the works I have consulted in preparing this memoir. For
further information T must refer to Grenadier (7).

1. Balfour, F. M.— “ Address to the Department of Anatomy and Physio-

logy,” ‘ British Assoc. Report,’ 1880.

2. Berger, E. — ‘ Untersuchungen iiber den Bau des Gehirns undder Retina

der Arthropoden,’ Institut. Wien, i, Heft 2, 1873.

3. Carriere, J. — “ On the Eyes of some Invertebrata,” * Quart. Journ.

Micr. Sci.,’ vol. xxiii, p. 673.

4. Ciaccio, M. G. V. — “De l’oeil des Dipteres,” ‘Journ. de Zoologie,’ v, p.

312, from the ‘ Rendiconto Acad. Scienze Instituto di Bologna,’

1875-6, p. 99.

THE EYE AND OPTIC TRACT OF INSECTS. 247

5. Claparede, Ed. — “ Zur Morphologie der Zusammengesetzten Augen bei

den Arthropoden,” 1 Zeit. f. wiss. Zoologie,’ x, p. 191.

5a. Dietl, M. J. — “ Die Organisation des Arthropodengehirns,” ‘ Zeit. f.
wiss. Zoolog.,’ xxvii, p. 488.

6. Gottsche. — “Beitrag zur Anatomie und Physiologie des Auges der

Krebse und Fliegen,” ‘ Archiv fiir Anat. und Pliys.,’ 1855.

7. Grenacher, H. — ‘Untersuchungen viber das Sehorgan der Arthropoden,’

Gottingen, 1879.

8. Hickson, S. J. — "The Retina of Insects,” ‘Nature,’ vol. xxxi, pp. 341

and 433.

9. Krieger. — “ Ueber das Centralnervensystems des Flusskrebses,” ‘ Zeit. f.

wiss. Zool.,’ xxxiii, p. 527.

10. Lankester, E. Ray, and Bourne, A. G. — “ The Minute Structure of

the Lateral Eyes of Scorpio and of Limulus,” vol. xxiii, p. 177.

11. Leydig, F. — ‘ Das Auge der Gliederthiere,’ Tiibingen, 1864.

12. Leydig, F. — ‘Tafeln zur vergleichenden Anatomie,’ Tubingen, 1864.

13. Leydig, F. — ‘Handbuch der vergleichenden Anatomie,’ Tubingen, 1864.

14. Lowne, B. T. — “ On the Simple and Compound Eyes of Insects,” ‘ Phil.

Trans.,’ 1878, p. 582.

15. Lowne, B. T. — “ On the Compound Yision and the Morphology of the

Eye in Insects,” ‘ Trans. Linn. Soc.,’ ii, pt. 11.

16. Mitchell, C. E. — “ A New Staining Fluid for Microscopic Sections,”

* The Science Monthly,’ March, 1884.

17. Muller, J. — ‘ Zur vergleichenden Physiologie des Gesichtssinnes,’ 1826.

18. Schultze, Max. — ‘ Untersuchungen iiber die zusammengesetzten Augen

der Krebsen und Insecten,’ Bonn, 1868.

19. Stecker, A. — “Ueber die Ruck-bildung von Sehorganen bei den Arachni-

den,’ ‘ Morph. Jahrb.,’ 1878.

20. Straus-Durckheiji, H. — ‘ L’Anatomie comparee des animaux articules,’

Paris, 1828.

21. Wagner, R. — “ Einige Bemerkungen iiber d. Bau d. zusammeng.

Augen,” * Arcbiv f. Natiirgesch.,’ 1835.

22. Weissaian, A. — “Die Nachembryonale Entwickelung der Musciden,’

‘ Zeit. f. wiss. Zool.,’ xiv, p. 280.

VOL. XXV. NEW SER.

A

248

SYDNEY J. HICKSON.

DESCRIPTION OF PLATES XV, XVI, & XVII,

Illustrating Dr. Hickson’s Memoir on “ The Eye and Optic
Tract of Insects.”

Reference Letters throughout.

b. m. Basilar membrane. c. Cornea. ce. Cerebrum, co. Commissure.

c. c. Crystalline cone. e. op. Epiopticon. n. Nucleus. Nf. Optic nerve-
fibrils between the epiopticon and periopticon. n. c. Nerve-cell. n. c. s.
Nerve-cell sheath, oe. (Esophagus. om. Ommateum. o. n. Optic nerve.
op. Opticon. pc. Pseudocone. p. op. Periopticon. pg.v pg.2 , pg.3. Pigment-
cells. r. Retinulse. Rh. Rhabdom. rh. Rhabdomere. Tt.v Large tracheal
trunk in the head. Tt.2. Smaller tracheal trunk. T. Tracheae with spirally-
marked walls, t. v. Thin-walled tracheal vessels and vesicles.

Fig. 1. — Diagrammatic vertical section through the head of Mu sea
vomitoria, showing the relative positions of the cerebral and optic ganglia.
ce. Cerebral ganglion, co. Commissure between the cerebral ganglia, o. n.
Optic nerve, op. Opticon. e. op. Epiopticon. p. op. Periopticon. t. a. Ter-
minal anastomosis, om. Ommateum. n. c. s. Nerve-cell sheath, oe. (Eso-
phagus.

Fig. 2. — Vertical section through the eye and optic tract of Musca
vomitoria. In the greater part of the ommateum the pigment-cells have
been omitted to prevent confusion, but the pigment-cells are drawn in the
centre of the figure at pg.v pg.v pg.v In a similar manner the tracheal
vesicles between the ommatidia are only inserted in two instances, t. v. Tt.x.
The large tracheal trunk which sends the branches to the terminal auastomo-
sis, t. a., to supply the tracheal vesicles of the ommateum. Tt.2. The smaller
tracheal trunk which supplies branches to the optic tract behind the peri-
opticon.

Fig. 3. — Ommatidium of Musca, semi-diagrammatic, c. Cornea, pc.
Pseudocone. pg.v Pigmented cells surrounding the pseudocone. pg-2. Ad-
ditional pigment-cells. pg.3. Basal pigment-cells, n. pc. Nuclei of pseudo-
cone. r. Retinulse. n. r. Nucleus of retinulse. Rh. Rhabdom. b. m. Basilar
membrane. T. Trachea, tv. Tracheal vesicle, t. a. Terminal anastomosis
sending fibres to the retinulse.

Fig. 4. — Transverse section through the retinulse and rhabdom in their
outer region, showing the six retinulse (r.) free from one another, and the
rhabdom composed of six rhabdomeres fused together (rh.). The processes
of the pigment-cells and their relation to the retinulse are shown at pg.2, and
the relative size and position of the tracheal vesicle in this region is shown
at t. v.

THE EYE AND OPTIC TEACT OF INSECTS.

249

Fig. 5. — Transverse section of the same in the inner region, i.e. near the
basilar membrane. The six retinulae become fused into a tube ensheathing
the rhabdom. The tracheal vesicle, t. v., is very much larger proportionately.

Fig. 6. — Section through the periopticon of a young bee. e. op. epiopticon.
Nf. Nerve-fibrils not decussating in this region at this stage, p. op. Peri-
opticon indicated by a row of nerve-cells in front and behind, and by a
thickening of the longitudinal fibrils, and by the characteristic looping trans-
verse anastomoses, t. a. Terminal anastomosis, n. c. s. Nerve-cell sheath.

Fig. 7. — A small portion of the periopticon and terminal anastomosis of
Aeschna grandis. Nf. The optic-nerve fibrils beyond their decussation.
p. op. The periopticon, the elements of which are incompletely fused, t. a. The
terminal anastomosis, showing four not very well-marked regions, 1, 2, 3, 4.
pg.A. Pigment-cells and their branches, situated behind the basilar membrane.
6. m. Basilar membrane, r. The retinulse. The pigment-cells and their
branches are omitted in the lower part of the figure. s. Spaces in the
periopticon.

Fig. 8. — Transverse section through three elements of the periopticon of a
blow-fly, showing the pigmentation of the outer region which is occasionally
present. At a, the pigmentation has taken the form of five pillars ; at (3
and y, the form of a hollow cylinder. All of these varieties were found in
one specimen.

Fig. 9. — Longitudinal section of the same, showing that this irregular
pigmentation sometimes gives the appearance of small rods in the periopticon.

Fig. 10. — One of the outer pigment-cells, n. Nucleus, in. Internal pro-
cess. ex. External process.

Fig. 11. — Transverse section through a portion of the ommateum of
Aeschna grandis in the region of the retinulse and rhabdoms. r. Re-
tinulae. Rh. Rhabdoms. pg.2. Branches of the outer pigment-cells, t. v.
Tracheal vessels of the ommateum.

Fig. 12.— Transverse sections through a portion of the ommateum of
Aeschna grandis, showing the relations of Semper’s nuclei, s. n. They
are usually four in number [a. a.), but occasionally five are to be seen (b.), and
usually regular in position (a. a.), but sometimes irregular (c.).

Fig. 13. — Two crystalline cones ( c . c .) of Aeschna grandis, showing
the position of Semper’s nuclei (S. n.) and the investing pigment-cells, pg.x.

Fig. 14. — Longitudinal section through the ophthalmic peduncle of
Carcinus moenas. o. n. Optic nerve, op. Opticon. e. op. Epiopticon.
Nf. Decussating fibrils between the epiopticon and periopticon. p. op. Peri-
opticon, a solid ganglion like the epiopticon. t. a. Terminal anastomosis
very extensive and complicated, but capable of being separated into four
regions, 1, 2, 3, 4. om. Ommateum.

Fig. 15. — A small piece of the nerve-cell sheath of the brain of Bombyx
mori (imago), showing the nuclei and cell protoplasm, in this form very con-

250

SYDNEY J. HIOKSON.

siderable, of the cells. Between the cells may be seen the nerve-fibrils anas-
tomosing with one another and with the cell processes.

Fig. 16. — Four elements of the periopticon ofMusca vomitoria, showing
their connection with the optic fibrils {Nf.) internally, and with the nerve plexus
and nerve-cells (». c.) of the terminal anastomosis externally. Some of the
optic fibrils {/.) run right through without breaking up into a neurospongium.

Fig. 17. — One of the elements of the periopticon ofMusca vomitoria
more highly magnified, showing the course of the nerve-fibrils through the neuro-
spongium, and the relation of the fibrils of the neurospongium to the nerve-cells.

Fig. 18. — Section through the eye of a very young Periplaneta. e. op. Epi-
opticon. n c. s. Nerve-cell sheath. Nf. Optic nerve-fibrils, leaving the
epiopticon without decussating, n. c. Nerve-cells in the terminal loose anas-
tomosis. b. m. Basilar membrane, r. Retinulse. c. c. Crystalline cone. c.
Cornea incompletely faceted in the middle, unfaceted at the periphery.
pg.2. Pigment-cells between the ommatidia.

Fig. 19. — Section through the eye of a full-grown male Periplaneta. op.
Opticon. e. op. Epiopticon. Nf. Optic nerve-fibrils, partially decussating in
the adult, n. c. Nerve-cells in the terminal anastomosis, which is here much
denser and more complicated than it is in the young cockroach, b. m. Basi-
lar membrane, r. Retinulse.

Fig. 20. — Section of the eye and optic tract of Agrion bifurcatum,
showing the general arrangement of the parts, o. n. Optic nerve, op. Opti-
con. e. op. Epiopticon. n. c. s. Nerve cell sheath. Nf. Optic nerve-fibrils
t the point of their decussation, p. op. Periopticon. t. a. Terminal anasto-
mosis. b. m. Basilar membranes, om. Ommateum.

Fig. 21. — Periopticon and terminal anastomosis of Agrion bifurcatum
more highly magnified than Fig. 20, showing the character of the elements of
the periopticon, p. op., and the structure of the terminal anastomosis. La. 1.
The first layer of the terminal anastomosis, consisting of a plexus of fibrils
and nerve-cells, n. c. 2. The second layer, in which the fibrils are collected
together in bundles. 3. The final optic plexus and nerve-cells. 4. The layer
in which the optic fibrils are collected in bundles to be distributed to the
retinulse (r.).

Fig. 22. — The eye of an adult Nepa cineraria, e. op. The epiopticon.
Nf. The optic nerve-fibrils, going to form the terminal anastomosis, p. m.
Perforated membrane through which this anastomosis passes. II. Loopings or
recurrent anastomoses of the nerve-fibrils, om. Ommatidia covered with the
branches of the pigment-cells. In the centre of the ommateum three omma-
tidia are figured without their accompanying pigment, in order to show the
retinulse (/.) and the crystalline cone ( c . c.).

Ftg. 23. — Section through the epiopticon, periopticon, and terminal anas-
tomosis of Eristalis lupinus. e. op. Epiopticon. Nf. Nerve-fibrils
decussating between the epiopticon and the periopticon. p. op. The periopticon

THE EYE AND OPTIC TRACT OE INSECTS.

251

here formed of a continuous neurospongium, perforated by numerous thin-
walled tracheal vessels. The tracheal vessels passing through the periopticon
are only represented on the right-hand side of the figure, they pass from the
thick-walled spirally-marked branching tracheae ( T ) behind the periopticon to
similar tracheae situated in front of it. The tracheae passing in front of the
periopticon are supplied by the large tracheal trunk, Tt.v whereas those
passing behind are supplied by the smaller tracheal trunk, Tt.2 Rh. The
rhabdom. r ■ The retinulse. b. m. The basilar membrane. pg.3. The internal
pigment-cells.

Eig. 24. — Transverse section through the periopticon of Eristalis
lupin us, X 600 diam. t. v. The bundles of tracheal vessels perforating
the neurospongium of the periopticon, p. op.

Fig. 25. — A portion of the epiopticon of a young bee, with nerve-fibrils
proceeding from it and the nerve-cells connected with them. The neuro-
spongium of the epiopticon ( e . op.) is composed of a large number of very fine
fibrillae, forming a dense meshwork and combining together in bundles to form
the nerve-fibrils (Nf.) which pass out of it. The nerve-cells (». c.) consist of a
large nucleus surrounded by a delicate investment of cell protoplasm, which
gives off fine branches communicating with the neurospongium and the fibrils.

Fig. 26. — A small portion of the epiopticon of an adult Aeschna
grand is, showing the character of the neurospongium and the relative size
and position of the nerve-cells ( n . c.) and nerve-fibrils {iff.).

Fig. 27. — Ganglion-cells from the brain of an adult male Periplaneta
orientalis. a. A tripolar ganglion-cell. b. A bipolar cell. c. An
apolar cell.

Fig. 28. — Portion of the basilar membrane of the eye of Agrion bifur-
cat um, showing the perforations, the larger ones for the tracheal vessels and
the smaller ones for the terminal optic fibrils, r. Retinulae. t. a. Terminal
anastomosis.

Figs. 29 — 32. — Diagrammatic figures of the four principal varieties of
periopticon met with in the Hexapoda. The nerve-cells are omitted.

Fig. 29. — The condition in Blatta in which the fibrils simply split up and
anastomose.

Fig. 30. — The condition in Nepa and the developing bee, in which the
anastomosis is complicated by fine looped and transverse anastomoses.

Fig. 31. — The condition in Musca in which the fibrils split up into their
ultimate fibrillse and these anastomose to form a true neurospongium.

Fig. 32. — The condition in Crustacese in which the elements of the peri-
opticon have fused to form one single continuous neurospongium.

Fig. 33. — Diagram of the * Acone ’ without any refracting bodies.

Fig. 34. — Diagram of the ‘ Pseudocone,’ with the nucleus internal and the
refracting bodies external.

Fig. 35. — Diagram of the * Eucoue,’ with the nuclei external and the
refracting bodies internal.

PECULIAR SENSE ORGAN 11$, SCUTIGERA COLEOPTRATA. 235

On a Peculiar Sense Organ in Scutigera
coleoptrata, one of the Myriapoda.

By

F. G. Heathcote. B.A.,

Trinity College, Cambridge.

With Plate XVIII.

In the spring of the year I was fortunate enough to get a
fair number of Scutigera in the South of Europe. In making
an examination of their anatomy I found a sense organ which
seemed to me to be of sufficient interest to render a more com-
plete examination desirable. This organ is placed on the
ventral surface of the head at a short distance behind the
mouth and near the base of the mandibles. Its external
appearance under a low power of the microscope (Zeiss's
objective a a) is shown in fig. 1.

General Features.

The organ which was first mentioned by Latzel, consists of
a chitinous sac with a slit-like opening (fig. 1, eo.). The
opening is placed between the base of the mandibles and the
maxillae. The sac has a somewhat complicated form which
will be best understood by reference to four diagrams (see
Plate, pp. a, b, c, d.

The first of these shows a rough outline of the appearance
of the organ from the ventral side ; the second, third, and fourth
being diagrammatic sections through the dotted lines AB, CD,
and EF. B is a transverse section through the anterior portion
of the organ. It shows the main sac communicating with the

254

F. G. HEATHCOTE.

exterior by a narrow neck and two lateral recesses opening into
the neck and placed ventrally to the main sac parallel with the
ventral surface of the head. The section C taken through the
median portion of the organ exhibits similar relations, excepting
that the median dorsal wall of the sac is projected into the
interior in two longitudinal folds which make a partial division
of the sac into three portions, two deep, wide lateral pouches,
and one deep narrow recess between them. This latter I shall
speak of as the median recess. A third section, D , is taken
through the hinder part of the organ. Here the lateral
recesses and the slit-like opening to the exterior are absent
and the two dorsal folds almost completely divide the main
sac in three portions.

It is worthy of note that the effect of the median and lateral
recesses is to produce a freely projecting lip or edge on the
dorsal and ventral aspects of each pouch.

The general shape of the interior of the organ is therefore
posteriorly that of two pouches projecting into the interior of
the head, while between them is a median dorsal recess formed
by the folds above described, which constitute the inner walls
of the pouches where they approach one another. Anteriorly
the division into two pouches is not so perfect, but there are
two deep lateral ventral recesses. The slit-like opening to the
exterior begins at the anterior end and extends about a third
of the length of the whole organ.

The chitinous exoskeleton is continued into and lines the
whole organ. It is not, however, of uniform thickness. In the
median and lateral recesses and on the folds constituting the
lips of the pouches it is smooth, but in the pouches themselves
it is thrown into a number of folds and bears a large number
of chitinous hairs (fig. 2, h .) which project into the lumen of
the pouches. The folds form alternate ridges and depressions,
so that when looked at from the surface through a microscope
the chitinous lining of the pouches has a reticulated appearance
(fig. 8). The hairs, whose length is about that of the diameter
of each pouch, are of peculiar form (fig. 9). Each consists of
a stout elliptical basal portion, the inner end of which is inserted

PECULIAR SENSE ORGAN IN SCUTIGERA COLEOPTRATA. 255

into the chitinous lining of the pouch and indeed projects for
a short distance on the inner side of the latter. The outer end
is prolonged into a long fine hair.

General Features of the Internal Anatomy.

The hypodermic layer of cells or matrix lying beneath the
exoskeleton accompanies the chitin round the lateral recesses,
and at the edge of the folds which form the lateral lips of the
two pouches becomes continuous with a thick layer of sensory
epithelium which lines the greater part of the two pouches
(fig. 2, s. e.). On reaching the dorsal lips of the pouches, which
lips bound laterally the median recess, the epithelium loses its
sensory character and again becomes simple hvpodermis. On
the dorsal part of the median recess the epithelium again
becomes sensory in character. The nerve supply is furnished
by two short thick nerves (fig. 2, N.) which arise from the front
portion of the suboesophageal ganglion. The two nerves enter
the sensory epithelium, one to each pouch, near the posterior
part of the organ, and there breaks up into a number of fibres
which become lost in the epithelium. The form of the organ
as indicated by the division into two pouches (fig. 2, p.) and
the double nerve supply seem to me to show conclusively that
it is double, and that each of the two pouches with its other
parts is to be regarded as constituting a separate sense organ.

Histology.

The histology of the cellular tissues demands a more detailed
account. The cells forming the matrix from which the
exoskeleton is renewed after each moult are large, rather
columnar in their character, and have a well-defined nucleus.
They are closely applied to the chitin and accompany it up to
the end of the lateral recesses (refer to fig. 3, hy .) where the
folds forming the ventral lips of the pouches begin. Here the
chitin is thrown into folds somewhat like those which charac-
terise the surface of the pouches. The hypodermic cells here
lose their regularity of outline and follow the chitin into the

256

F. G. HEATHCOTE.

folds and irregularities into which it is thrown (fig. 3, hy.).
Their nucleus is larger and stains more deeply. At the lateral
ventral lip (fig. 2, Ivl .) the cells are more elongated and more
closely packed together, and gradually take the character of
the sensory epithelium which forms the greater part of the
lining of the pouches. These sensory cells are long and
columnar and at their outer ends are prolonged into a blunt
projection of less diameter than the rest of the cell (fig. 7 , oe .)
and about one third the length of the whole. At the folds
which bound the median recess the cells lose their sensory
character and take the form of the ordinary hypodermic cells.
The mass of sensory cells at the top of the median recess which
are continuous with the hypodermic cells are of a character
distinct from those described as lining the pouches. They are
of irregular elongated shape and resemble ganglion-cells, the
inner end' being sometimes bifurcated (fig. 6, Bi..). The sensory
epithelial layer is of considerable thickness (fig. 2).

I have hitherto spoken of the epithelial layers simply as in-
vesting the chitinous pouches with their hairs, but I will now
consider the means by which the hairs and cells come into
relation. There is no doubt that the terminal parts of the
sense cells project into the depressions (fig. 3) in the chitin,
caused by the folds spoken of above, and that each chitinous
hair is inserted into the chitin immediately outside this pro-
jecting part of a sense cell. I am also inclined to believe,
though, owing to the small amount of material at my command
my evidence on this point is not conclusive, that the bases of
the chitinous hairs, i. e. the part which projects on the inner
side of the chitinous lining, have a small cavity in their basal
parts, into which a threadlike prolongation of the sense cell
projects.

I have invariably found foreign bodies in the median and
lateral recesses, and as the latter are in communication with
the exterior they may possibly be grains of dirt or sand, but
I think that they may be concretions.

PECULIAR SENSE ORGAN IN SCUTIGERA COLEOPTRATA. 257

Conclusions.

The active predatory habits of this Myriapod and its power
of swift locomotion would seem to render well-developed sense
organs a necessity to it ; in fact it has facetted eyes in place
of the simple eye-spots of most Myriapods.

The organ above described must, I think, be included among
the great number of widely dissimilar organs usually classed
together as auditory, and may be compared to the tympanic
organ of insects.

The auditory organs of insects have been investigated prin-
cipally by v. Siebold (‘ Archiv fur Naturg./ 1844), Leydig
(‘Muller’s Arch./ 1855 and 1860), v. Hensen (‘Zeitschr. f.
wiss. Zool./ tom. xvi, 1866), and v. Graber (‘ Deutschr. der K.
Akad. der Wissensch./ Wien., 1875). The tympanic organ of
the Acridiidae consists essentially of a tympanic membrane sup-
ported by a chitinous ring. Places in the tympanic membrane are
thickened, so as to form solid chitinous pieces of peculiar form,
the internal surface of which is covered with indentations in
which the extreme ends of the sensory apparatus end (Fr.
Leydig, ‘ Muller’s Archiv,’ 1855, p. 401). The auditory nerve
spreads out on these chitinous pieces and forms a ganglion,
from which fibres ending in peculiar sense cells are given off.
A trachea lies close to the ganglion internally to it, and not
unfrequently swells to a vesicle.

On comparing the organ of Scutigera with such an organ
there is found to be a great similarity in the general plan.
Each pouch in Scutigera represents the insect tympanum.
In both cases we have a thick nerve breaking up into a number
of sensory elements, which end in depressed spaces in the
chitinous membrane. WTith regard to the chitin hairs which
project through the chitin in Scutigera, I think it will be
worth while to consider Hensen’s investigations on the auditory
rods of insects (Horstrifte, v. Hensen, 1. c.). He makes an
interesting comparison between these structures and the audi-
tory hairs of the crustacean auditory sac, and draws the con-

258

F. G. HEATHCOTE.

elusion that the two structures present a very great morpho-
logical resemblance. If his arguments hold good it seems to
me permissible to compare the hairs of Scutigera to those in
the auditory sac in Crustacea, and also to the auditory rods
(Horstifte) in insects.

There is one point, however, in which the organ of Scutigera
differs greatly from the tympanic organ, viz. in the absence of
a tracheal vesicle. I think it doubtful, however, whether this
tracheal vesicle is an essential part of the insect auditory
organ. The swelling of the tracheal trunk seems not to take
place in all cases (Leydig, 1. c.), and Hensen, in giving
what he considers the most probable hypothesis as to the
action of the tympanic organ, says : “ Die tracheen schwin-
gungen sind ohne Bedeutung.’ Balfour, in his short account
of the auditory organ of terrestrial insects (‘ Comp. Emb./ ii,
423), does not mention the tracheal vesicle.

I have examined this sense organ of Scutigera, both by dis-
section and by means of sections. I found that the tissues
were best preserved by a mixture of corrosive sublimate and
acetic acid. The difficulty of cutting the chitin in sectioning
was overcome by embedding in very hard paraffin.

My investigations were entirely carried on in the Cambridge
Morphological Laboratory.1

1 Since forwarding this paper (November, 1884) to the editor of this
Journal my attention has been drawn to a paper by Dr. Haase in Schneider’s
* Zool. Beitrage,’ 1884, upon “ Schlundgerust und Maxillarorgan von
Scutigera.”

As I am on the point of leaving England on a long voyage it is now too
late for me to make an extensive reference to this work, but I may add that
in my opinion Dr. Haase’s observations do not necessitate any alterations in
the foregoing paper.

PECULIAR SENSE ORGAN IN SCUTIGERA COLEOPTRATA. 259

DESCRIPTION OF PLATE XVIII,

Illustrating Mr. F. G. Heathcote’s Paper “ On a Peculiar Sense
Organ in Scutigera coleoptrata, one of the Myria-
poda.”

Letters used in all the Figures.

m. Mouth, f. Furrow iu chitin. e. o. External opening of sense organ.
o. Sense organ, mxl. 2nd maxilla. N. Nerve, s. e. Sense epithelium.
h. Chitinous hairs, ky. Hypodermis. p. Pouch. Ir. Lateral recess. Mr.
Median recess. Ivl. Lateral ventral lip. Mdl. Median dorsal lip. ch.
Chitin. Bi. Bifurcated end of cell at top of median recess, oe. Outer
end of cell. Ih. Base of chitinous hairs projecting into interior, bp.
Basal part of chitinous hair. fh. Free end of hair.

Fig. 1 was drawn for me by Mr. Chapman ; all other figures were drawn by
myself with the aid of Zeiss’s camera lucida. Fig. 2 is combined from three
sections.

Fig. 1. — Ventral view of head of Scutigera coleoptrata. The sense
organ is seen through the chitin. m. Mouth, f. A furrow in the chitinous
exoskeleton, marking out two irregular areas just in front of the organ, e o.
Opening of organ to the exterior, o. Organ seen through the chitin. oc.
Eye. mxl. 2nd maxilla.

Fig. 2. — Transverse section through the organ, showing the nerve (V.), sense
epithelium ( se.), chitinous hairs ( h .), hypodermis (hy.), median recess {Mr.),
and lateral recesses {br.) ; also the two pouches {p.). (Zeiss’s c c objective.)
Owing to the action of the reagents used the sensory epithelium has shrunk
away from the chitinous lining of the sac. Ivl. Lateral ventral lip. Mdl.
Median dorsal lip.

Fig. 3. — Transverse section through the region of the lateral recess, show-
ing the transition from the hypodermis to the sensory epithelium, hy. Hypo-
dermic cells, se. Sense cells, br. Lateral recess, ch. Chitin. h. Chitin-
ous hairs projecting into the pouch. Ivl. Lateral ventral lip of pouch.
(Zeiss’s f objective.)

Fig. 4. — Transverse section, taken so as to show the hypodermic cells (hy.)
joining the sense cells (se.) in the region of the median recess. (Zeiss’s f
objective.) hy. Hypodermic cells, se. Sense cells, ch. Chitin.

Fig. 5. — Transverse section through the anterior part of the organ, show-
ing the hypodermic cells becoming continuous with the sense cells (se.). The

260

F. G. HEATHCOTE.

section is in front of Fig. 4. (Zeiss’s d objective.) se. Sense epithelium.
ch. Chitinous lining of the organ, hy. Hypodermis.

Fig. 6. — Tailed cell from sense epithelium at top of median recess. Bi.
Bifurcated end. oe. Outer end. (Zeiss’s f objective.)

Fig. 7. — Sense cells from epithelium (se.). oe. Outer end of cell.
(Zeiss’s f objective.)

Fig. 8. — Surface view of chitinous lining of pouch seen from the internal
side, showiug the projecting bases of the chitinous hairs, bh. Base of hair
projecting through the chitin. (Zeiss’s water immersion l objective.)

Fig. 9. — Chitinous hair under high power. (Zeiss’s l water immersion.)
bp. Basal part of hair. Bh. Part of the basal piece which projects through
the chitinous lining of the pouch towards the interior, fh. The hair itself
projecting into the interior of the pouch.

STRUCTURE AND DEVELOPMENT OP LOXOSOMA.

261

On the Structure and Development of
Loxosoma.

By

Sidney F. Harmer, B.A., B.Sc..

King’s College, Cambridge, Demonstrator of Comparative Anatomy
in the University.

With Plates XIX, XX, XXI.

The investigations which form the subject of the present
paper were carried on during an occupation of the Cambridge
University Table at Naples from January to July, 1884. An
account of my main results was communicated to the Montreal
meeting of the British Association in September, 1884, and a
short abstract will appear in the forthcoming report.

Pakt. 1. — Species of Loxosoma found at Naples.

The specific characters of this genus have been found some-
what difficult to establish satisfactorily, and considerable doubt
has on various occasions been thrown on the validity of many
of the characters ascribed to the different species. Although
the number of the tentacles and of the buds is not so constant
as Schmidt (20) has supposed, the majority of the species which
have been described are no doubt perfectly distinct from one
another.

The following have come under my own observation at
Naples :

1. L.Tethyse, Salensky . — Number of tentacles in most cases
twelve, but in many individuals thirteen or fourteen. Buds not

262

SIDNEY F. HARMER.

restricted to two, as supposed by Schmidt ; they are formed
alternately on the two sides of the body, as in L. Kefer-
steinii (10), and a young bud usually occurs at the base of
every nearly mature bud, in addition to a third on the opposite
side, intermediate in age between the two just mentioned.
The stalk in most cases is at least twice as long as the calyx,
and is provided with a well-developed foot-gland with lateral
wing-like expansions. Round the free edge of the calyx, as
seen when the tentacles are retracted, is a definite series of
gland-cells described by Salensky (15). The ectoderm of the
stalk is arranged as eight longitudinal rows of cells (PI. XIX,
fig. 9), and this is not the case in any of the other species
investigated.

Habitat, on the sponge Tethya.

2. L. pes, Schmidt (originally described by Schmidt as L.
singulare). — The tentacles are thick and short, and were ten
in number in all the individuals examined. In no case
observed was either side of the body provided with more than
a single bud. The stalk is usually considerably shorter than
the calyx ; the foot-gland is very large, and the foot is pro-
vided with well-developed alate expansions. The character-
istic gland-cells of L. Tethyse are not present, and the
ectodermic cells of the stalk are arranged irregularly. The
larva (Schmidt, No. 11, Taf. ii, fig. 25) resembles that of L.
Tethyse.

Found in small numbers on Euspongia and Caco-
spongia.

3. L. singulare, Keferstein. — This species was found on
the ventral side of Aphrodite (as described by Barrois), and
of Hermione hystrix. The identification is somewhat
doubtful, Keferstein's individuals possessing ten tentacles,
whereas in the Naples species the number is larger, and in the
very few specimens obtained appeared to be twelve or thirteen.
The stalk, terminating in a slightly expanded disc, as in the
form described by Keferstein (2), is very short and is much less
distinctly marked off from the calyx than in the other species,
the whole animal being somewhat pear-shaped. None of the

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

263

individuals observed possessed more than a single bud, which
was provided with a foot-gland, a structure absent in the adult.
The larva (see Barrois' figure, No. 13) is not unlike that of
L. neapolitanum (Kowalewskv, No. 3, fig. 10).

(There can be little doubt that the species just described is
identical with L. claviforme, Hincks (26), occurring on
Hermione hvstrix. Hincks acknowledges that his dia-
gnosis is very incomplete, owing to the bad preservation of his
material, and it has seemed to me better, therefore, to identify
my species provisionally as L. singulare, until the distinctness
of L. claviforme can be more satisfactorily shown.)

4. L. crassicauda, Salensky, found in large numbers
attached to the floor of a tank in the Zoological Station. The
number of buds is large, two, three or more occurring in most
cases on each side of the body. The number of tentacles is typi-
cally eighteen, but is by no means constant (fig. 1 ; — seventeen
tentacles). The individuals are much larger than those of any
other species discovered ; the stalk is very long, with no regular
arrangement of its ectoderm cells, the foot-gland being absent
or (Schmidt) preserved as a rudiment in the adult ; the termi-
nation of the stalk is cylindrical. Numerous gland-cells occur
at the edge of the calyx, whilst the special development of two
posterior sense organs (fig. 1, jos.) is a noteworthy feature of the
species. The larva is at present unknown.

5. L. Leptoclini, Harmer, new species, not uncommon
at Naples on the compound Ascidian Leptoclinum macu-
losum. I propose for the new form the specific name
Leptoclini ; as far as my observations extend, it is confined
in its occurrence to the genus Leptoclinum, although I
have searched for it on numerous genera of Sponges and
Ascidians. The number of tentacles is perhaps invariably ten
in the adult ; the buds are few, although the occurrence of three
at the same time, as in L. Tethyse, is by no means rare. The
individuals are small, their total length (with the stalk)
averaging about half a millimetre (the measurements having
been made from glycerine preparations). The stalk is at most
about equal in length to the calyx, which has the character-

VOL. XXV. NEW SER.

8

264

SIDNEY P. HARMER.

istic form represented in fig. 2. The foot-gland is well
developed, the termination of the foot is alate, and there is no
definite arrangement of the ectoderm cells of the stalk. At
each side of the calyx occurs a series of gland-cells (fig. 2 ,gc.).
The larva differs considerably in structure from any other
Loxosoma larva at present described. Perhaps the most
characteristic feature of the adult is the presence of a group of
remarkable cells (fig. 5, ac .) at the apex of the vestibule. The
stomach is divided into a median and two lateral portions, as
represented in the figure.

Explanation of the terms Dorsal, Ventral, &c., as applied to
descriptions of Loxosoma.

It will be convenient to define at once the use of such terms
as “ dorsal ” and “ ventral,” “ transverse,” and so on. From
reasons which will appear in the sequel, I am led to support
the view that the ventral line of the body is that between
mouth and anus, in opposition to Caldwell’s theory (34) that
this surface is dorsal in the Polyzoa.

The dorsal region is drawn out into the stalk on which the
calyx or body of the animal is borne, whilst the anus is of
course posterior to the mouth.

A transverse section is one which passes in the plane of
the stalk through the right and left sides, and therefore
parallel to the flat surfaces of the somewhat discoidal calyx,
whilst a horizontal plane is at right angles to the long axis.

Part 2. — Anatomy of the Adult Loxosoma.

The entire animal consists of two parts, the calyx or body,
and the stalk by which it is attached to its resting place. The
two budding regions are situated at about the middle of the
calyx, right and left ; owing to the fact that the buds become
free as soon as they reach maturity, Loxosoma, unlike
almost all other Polyzoa, never forms colonies.

The ventral side of the body is produced into a free fold
enclosing the vestibule on the oral face of the animal. The

STRUCTURE AMD DEVELOPMENT OF LOXOSOMA.

265

tentacles, ciliated on their inner sides, are borne on the oblique
lophophore, and can be extended to the exterior (fig. 1), or,
when the animal is irritated, can be completely sheltered
within the vestibule (fig. 2). In the latter case, the vestibular
aperture is reduced by means of sphincter muscles to a small
circular hole situated on the anterior side (fig. 2, va .) .

The body is covered by a delicate, transparent cuticle,
secreted by an ectoderm composed of a single layer of cells.
The study of these cells is immensely facilitated by the use
of nitrate of silver applied in a manner suggested to me by Dr.
W. H. Ransom, of Nottingham, the essential feature of the pro-
cess consisting in washing the tissues in a solution of a neutral
salt (KN03) which gives no precipitate with nitrate of silver,
the solution having the same specific gravity as sea water [i. e.
about 5 per cent. KN03 in distilled water). By means of
this process a precipitate of silver chloride can be completely
avoided, whilst the tissues suffer practically none of those
changes which are brought about by washing with distilled
water (No. 44). PI. XIX, fig. 3, represents the appearance
of the posterior side of the calyx treated in the above manner,
these preparations being in nearly all instances so successful
that it was possible to draw, by means of a camera lucida,
the outline of every ectodermic cell.

These cells are of the following kinds :

(i) Ordinary epithelial cells, which are large and polygonal,
with a conspicuous nucleus (fig. 7) ; they occur over the whole
of the calyx and stalk, on the outer and part of the inner
surface of the vestibular fold, and on the dorsal and lateral
portions of the tentacles. The inner sides of the latter are
covered with a much higher epithelium, which is composed of
cylindrical cells provided with large active cilia. In most
regions of the ectoderm it is not possible to distinguish any
definite arrangement of the epithelial cells, which, however, on
the stalk of L. Tethyae occur in eight definite longitudinal
rows, of which three are represented in fig. 9.

(ii) Sense Cells. — In fig. 3 are indicated, scattered at
irregular intervals, certain small round areas, which occur

266

SIDNEY F. HARMER.

amongst the purely epithelial cells. These structures, much
less numerous than the latter, are in reality ectoderm cells,
which form the terminations of sensory nerves. Each is a
nucleated cell of small size, bearing one or more fine, stiff,
tactile hairs, projecting into the water (fig. 8).

(iii) Gland Cells. — In certain regions of the body occur
large unicellular glands opening to the exterior, and presenting
a considerable amount of variation in the different species.
Attention was first directed to these structures by Salenskv
(15), who described them in L. crassicauda and L. Tethyae.
In silver nitrate preparations of the former they may be seen
to open between the ordinary epithelial cells by wide aper-
tures (fig. 7, age), whose margins are surrounded by a thick
black line : in most cases they occur in a row parallel to the
edge of the vestibule, and reaching almost to the beginning of
the stalk. The apertures of the gland-cells are situated just
on the anterior side of the edge, in the condition of complete
retraction of the tentacles. In L. crassicauda two very
distinct forms of gland-cells are present (fig. 8) : the one
nearly transparent and filled with large spheroidal vacuoles
(gc.1) ; the other opaque, and composed of a large number of
small granules (gc.2); the nuclei of the gland-cells can be
detected in sections. In L. Leptoclini (fig. 2) the gland-
cells occur only at the sides of the calyx, and differ from those
of L. crassicauda in possessing a large central vacuole sur-
rounded by a thin layer of protoplasm, embedded in which is
the nucleus. Whether the characteristic apical cells of L.
Leptoclini (fig. 2, ac.) belong to the same category as the
gland-cells appears doubtful ; it is, perhaps, more probable
that they belong to the mesoderm, as in section they
appear to be covered externally and internally by a layer
of epithelium. The function of these curious cells has not
been made out ; their position is sufficiently indicated by
fig. 2.

In L. Tethyse the gland-cells are very numerous, and closely
packed together round the ventral end of the vestibule ; they
are composed of a granular material, which stains with great

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 267

difficulty. Salensky describes, in the stalk of L. Tethyae and
in that of L. crassicauda, definite longitudinal rows of gland-
cells, which have altogether escaped my observation.

Large oval granular cells are found in the gelatinous tissue
of the tentacles and other regions of the body of Pedicellina
(fig. 5, ctp), and have been already mentioned by Nitsche (6).
In my preparations I can discover no aperture from these cells
to the exterior, so that it is probable that they are not of the
same nature as the gland-cells of Loxosoma.

Foot-Gland. — This structure is eminently characteristic of
the genus Loxosoma, many species retaining it in the adult
condition ; whilst in others it is present only in the bud. In
the former case, when the long axis of the foot lies in a straight
line with that of the stalk, the “ sole,” by which attachment
takes place, is on the anterior side, the apex of the foot in its
usual position being directed posteriorly.

In L. pes, L. Tethyae, and L. Leptoclini (as well as in
L. Raja and L. cochlear, Schmidt), the foot is provided with
wing-like lateral outgrowths (fig. 2, al.). Barrois (13) from
the presence of these outgrowths, which cannot in reality be held
to be distinctive of any single species, has given the name of
Loxosoma alata to a species discovered by him, and states
that it is identical with L. pes. As there can belittle doubt of
the specific distinctness of L. pes, L. Tethyae, and L. Lepto-
clini, all of which are provided with alate expansions of the
foot, it is obvious that no sufficient diagnosis of L. alata has at
present been given.

The foot-gland has been described by Schmidt (11) as
consisting of a round granular mass situated in the angle of
the foot, and communicating with a duct which traverses the
“ sole ” and opens at the free end of the foot by a small pore ;
the duct is surrounded by four rows of large cells. In L.
neapolitanum, Kowalewsky (3) states that the duct opens
by a series of pores occurring in variable number along the whole
of its course. In L. pes, L. Leptoclini, and L. Tethyae,
my observations confirm neither of these statements ; and it is
worthy of remark that in L. pes I have had occasion to

268

SIDNEY F. HARHER.

examine the same species whose foot-gland has formed the
subject of Schmidt’s description.

The foot-gland appears to me to be composed of two distinct
portions ; — (i) the “ gland,” and (ii) the “ duct ” of Schmidt.
The “ gland” consists of a small number of granular nucleated
cells arranged round a central lumen, as described by Kowal-
ewsky. (See fig. 21, a section passing somewhat obliquely
through the foot, so as to avoid the “ duct.”) This glandular
mass opens at the angle of the foot by a pore which has no
connection with the “duct” (fig. 2). The latter in the three
species I have examined is in reality an open groove (fig. 20),
extending along the whole of the “sole” of the foot, as may
be clearly seen by means of sections or of glycerine prepara-
tions. The rows of cells described by Schmidt along the
“ duct ” are the high ectoderm cells lining the open groove.
In certain conditions, when its edges are closely approximated,
the appearance of a closed duct is produced. The foot-gland
originates as a longitudinal groove on the anterior side of the
base of the bud, which is attached to the adult by that portion
which will ultimately become the free end of the foot. During
the period when I had fresh Loxosoma at my disposal, I
failed to give any special attention to the development of the
“ gland,” but (from glycerine preparations) it appears to me
that the longitudinal groove, soon after its formation, becomes
constricted into two parts (fig. 19) — a longer dorsal and a
shorter ventral portion. The latter forms the “ gland ” after
becoming completely separated from the elongated portion of
the groove, which persists as such in the adult.

Nervous System. — The character of the nervous system of
Loxosoma has always been exceedingly doubtful, although
from the analogy of Pedicellina there could never be any
real question of the existence of a ganglion between mouth
and anus in the former. Such a structure has, however, never
been correctly described, Salensky’s identification being, as I
shall attempt to show, erroneous. As a matter of fact, the
ganglion has been unmistakeablv figured by ^itsche (10),
Schmidt (11), and Salenskv (15), but by all these observers has

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 269

been considered to form a part of the generative apparatus.
According to Nitsche, there exists in the bud, lying trans-
versely across the intestine, on its oral side, a dumb-bell
shaped mass (1. c., Taf. xxv, fig 19, GA ) which Nitsche does
“ not hesitate to identify as the rudiment of the generative
organs.” The same structure may be observed in the adult,
and is represented in (Nitsche’s) Taf. xxv, fig. 5, GA. This
“generative rudiment” has been figured by Schmidt as the
“testes” in L. Raja1 (Taf. i, fig. 1, t), whilst Salensky, in his
fig. 3 of PI. xii, has lettered the same organ gs., without
explaining the meaning of these letters; from the text, how-
ever, it seems obvious that the structure in question is con-
sidered either a portion of the generative system, or some other
form of gland. I have not the slightest doubt that the organ
so consistently described by the above observers as a gonad
is in reality the suboesophageal ganglion. The structure
figured by Nitsche (No. 10, Taf. xxv, fig. 5, N), and con-
sidered by him to be possibly nervous, I believe to have no
existence as a special organ. Schmidt (20) has expressed his
opinion that Salensky’s “ ganglion ” is really the empty vesicula
seminalis, and with this view I entirely concur. Salensky has
pointed out the difficulty of discovering the “ ganglion,”
except in young individuals which have developed no genera-
tive organs : in the adult one may assume that he recognised
the true nature of the vesicula seminalis from the presence of
the spermatozoa. Although Schmidt is right in denying the
nervous nature of this supposed ganglion, his opinion that the
large nerves figured by Salensky are also parts of the generative
apparatus is erroneous; the existence of these nerves cannot be

1 On p. 7 of No. 11, Schmidt says, “ Ich finde hei Loxosoma singulare
oberhalb der Hoden, aber auch zwischen Oesophagus und Enddarm quer
gelagert eine Art von Nervenband oder Doppelganglion, dessen Bedeutung mir
aber desshalb sehr fraglich, weil ich bei den anderen Arten nichts Ent-
sprechendes gesehen.” Schmidt has thus apparently really identified the
ganglion in L. singulare, although, led astray by the belief that the same
organ was a gonad in L. Raja and other species, he has failed to convince
himself of the correctness of his own identification of the organ in L.
singulare.

270

SIDNEY F. HARMER.

doubted, and Salensky’s account of them is quite accurate.
The latter observer has figured sensory hairs on the tentacles
of an advanced bud of L. crassicauda, but has fallen into a
singular error in denying their existence in the adult, as in
this very species the sense hairs are undoubtedly well developed
in the mature animal.

According to my own observations, the nervous system has
the following characters (PI. XIX, fig. 1). The dumb-bell
shaped ganglion ( ga .) lies transversely across the intestine,
immediately on its anterior or oral side (fig. 11). In sections
of L. Tethyse (fig. 16) it is seen that the organ consists
medianly of a fibrous commissural portion in which there are
no ganglion cells, and of two lateral ganglia, in each of which
the cells form a layer round the outer end of the commissure.
In these preparations it is not possible to distinguish the
outlines of the ganglion cells, the number of which is, how-
ever, clearly indicated by the nuclei. There is no doubt that
the central portion of the ganglion is really fibrous, as above
described; and there is no trace whatever of a central duct,
whose presence is required on the hypothesis of the generative
nature of the organ. The ganglion can be easily observed in
any individual of all the species I have examined, and is found
not only in the buds but also in the adults, whether the latter
are provided with generative organs, male or female, or are
sexually immature : — It can be discovered in sections as
readily as in the living animal.

The peripheral nervous system is most easily examined in
the living condition, L. crassicauda, on account of its great
transparency, forming a most favorable species for investiga-
tion. The most conspicuous part of the peripheral nervous
system is formed by a pair of tactile prominences on the
posterior wall of the calyx (already described by Vogt (12) and
Salensky (15) in other species), and by the strong ganglionated
nerves connected with these organs. From each end of the
ganglion passes off a strong nerve which swells into an en-
largement formed of bipolar cells (fig. 1, gas.). From the
end of the latter a nerve passes, without branching, to the

STRUCT QBE AND DEVELOPMENT OP LOXOSOMA. 271

tactile prominence on either side of the posterior wall of the
calyx, situated not far from the level of the ventral surface of
the stomach (fig. 1, ps.). Each of these sense organs, whose
structure is described below, bears a tuft of long stiff hairs.
The tentacles are provided with a rich development of sense-
cells, supplied by nerves (one for each tentacle) connected
with the ganglion. Owing to the somewhat varying number of
the tentacles, the arrangement of their nerves cannot be
absolutely constant, although certain general features can
always be made out. The tentacles belonging to the posterior
half of the lophophore appear to be invariably supplied by two
pairs of nerves running in the posterior vestibular wall. The
more median pair arises directly from the ganglion, each of
the two nerves usually supplying three tentacles in the manner
indicated in the figure. The outer pair arises from the nerves
of the posterior tactile prominences, and usually forks so as to
give rise to two tentacular branches. The origin of the nerves
belonging to the tentacles of the anterior half of the lopho-
phore is less easy to determine; but their arrangement, as
given in fig. 1, is probably not very inaccurate. With the
exception of the two pairs figured, no nerves were with certainty
observed to arise directly from the ganglion,1 although it is
possible that those supplying the dorsal regions of the body
may have this origin. At the base of each tentacle the nerve
swells into a small ganglion (fig. 1, tga.), consisting in most
cases of about four or five bipolar cells. This ganglion gives
off one or two nerve-fibrils, passing directly to as many sense-
cells, and is prolonged into a fine nerve, which passes up the
axis of the tentacle, the rest of whose sense- cells it supplies.
These tactile organs are not very numerous, and they occur
entirely on the outer (unciliated) and lateral portions of the
tentacle. Each bears a fine stiff hair, or more rarely two or
three. A single large hair occurs in the middle of the convex
side of each tentacle near its apex, and when these organs

■ In the adult, there is no trace of a brain or of circumcesophageal com-
missures, even the tentacles of the anterior portion of the lophophore being
undoubtedly supplied with nerves from the subcesophageal ganglion.

272

SIDNEY F. HARMER.

are retracted the hairs radiate towards the centre of the
vestibular orifice, immediately behind which they form a
circlet, so that nothing of an irritant nature can pass through
the aperture without at once coming into contact with one or
more of the tentacular sense hairs.

The calyx, like the tentacles, is well supplied with sense hairs,
which are most numerous in the neighbourhood of its edge ;
they occur (rarely) on the ventral portions of the stalk,
although they are absent nearer its attached end. The con-
nection of the more dorsal sense-cells with the ganglion could
not be made out, in consequence of the opacity of the stomach.
On the right side of fig. 1 is represented a nerve passing down
the stalk, and giving off a branch to a sense-cell. In other
regions of the body sense-cells are supplied from various parts
of the nerves ; none were discovered with certainty on any part
of the inner wall of the vestibule, although the elongated cells
of the epistome and oral end of the oesophagus have doubtless
a sensory function, being probably endowed with the faculty
of taste or smell.

The most reliable means of noticing the distribution of the
sense-cells is in silver-nitrate preparations, fig. 3, for instance,
representing the entire posterior wall of the calyx of L. cras-
si cauda. In addition to the large epithelial cells may be
observed very small cells which are provided with sense hairs
in the living condition. By staining the silver preparations
with picrocarmine (fig. 7), each of the small areas of fig. 3
was seen to be provided with a nucleus, the whole structure
thus forming a small ectoderm cell.

In picrocarmine-silver-nitrate preparations was further
observed the direct continuity between the latter and a nerve
fibril, swelling into a bipolar ganglion-cell, whose deeper process
passed directly into a nerve (see also figs. 1 and 8). This
connection of the sense-cell with the central nervous system
by means of the interposition of a ganglion-cell invariably
occurs, whether the latter is isolated in the gelatinous tissue of
the body, or is a constituent of the ganglion at the base of a
tentacle (fig. 1, tga.). The connection of these cells with the

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 273

ectodermic sense-cells may be seen either in the living animal
or in glycerine preparations in a manner which leaves room for
no doubt as to the actual existence of this arrangement.

It remains now to consider the structure of the two posterior
sense organs of L. crassicauda. In silver preparations
(fig. 4) each is seen to consist merely of an exaggerated sense-
cell, bearing a number of hairs, and provided with a large
nucleus. The sense-cell passes into a nerve continued into a
large number of ganglion-cells, instead of one only, as in other
regions of the body of this species. The increase in the
number of these cells is no doubt correlated with the speciali-
sation of the sense organ. The arrangement in L. pes indi-
cated in fig. 6, forms an intermediate condition between the
two kinds of sense-cells of L. crassicauda. The posterior
sense organs of the latter differ from the sense-cells borne on
other parts of the body in forming distinct papillae, at the
apex of each of which is an enlarged sense-cell. In most
cases (fig. 6) three of the flat epidermic cells are concerned in
the formation of the papilla.

In Pedicellina no special attention was given to the
peripheral nervous system. The ganglion ( ga .) is, however,
shown in fig. 12, a horizontal section ; it consists of a central
fibrous mass and of peripheral ganglion-cells. Instead,
however, of being greatly elongated transversely, as in
Loxosoma, it is oval; at the sides come off several pairs of
nerves.

In a picrocarmine-glycerine preparation of Pedicellina,
each tentacle (fig. 5) is traversed by a fine nerve, which gives off
branches on its outer side, each passing into a bipolar ganglion-
cell connected with an ectodermic sense-cell ; one of the latter
appears to be provided with a sense hair.

In the larva of Pedicellina, Hatschek (14) has called
attention to the existence of tactile hairs on various parts of
the body (Taf. xxix, fig. 26). These have exactly the appear-
ance of the sense hairs of the adult Loxosoma, but their
connection with the nervous system has not been observed. To
the same category probably belong the stiff hairs arranged in a

274

SIDNEY F. HAEMER.

ring round the foot-gland or sucker of the larva of both Pedi-
cellina and Loxosoma. Sensory hairs have hen
described in various species of Ectoprocta; Nitsche (4), for
instance, has figured on the tentacles of Alcyonella fun-
go sa, tactile hairs exactly like those of Loxosoma, and
arranged singly or in groups of two or three. In the former
case each hair, and in the latter each group of hairs, is no
doubt borne on a sense-cell similar to those of Loxosoma.

Sense organs, in external appearance resembling the pair
described above in L. crassicauda, occur in Rhabdo-
pleura1. Lankester has suggested the possible homology
between these organs and the “osphradia” (Spengel’s olfactory
organ) of the Mollusca. Although this homology is not
impossible, the character of the tactile organs of L. crassi-
cauda seems to indicate that the posterior sense organs are
merely specialised sense-cells, exaggerated in size, and I there-
fore regard it as probable that these organs in the Polyzoa
have no homology with the osphradia of Mollusca.

The only portion of the nervous system whose development
I have followed in the bud is the ganglion (in Loxosoma).
Although the share which is taken by the derivatives of the
different germinal layers in the budding processes of this genus
is still obscure, the ganglion may be definitely stated to origi-
nate from ectoderm cells. It is, in fact, developed from
the floor of the vestibular cavity, and this can only be regarded
as ectodermic, whatever may be the origin of the alimentary
canal. In a longitudinal section through a fairly-advanced bud
(fig. 15) it is seen that a narrow slit-like diverticulum of the
vestibule passes behind the epistome. This diverticulum,
which remains in very much the same condition throughout
life (see fig. 11), does not give rise in toto to the ganglion, which
is merely formed by a differentiation of some of its ectodermic
cells. Hatschek (14), in his account of the budding of Pe di-
ce 11 in a, describes the development of the ganglion as a diver-

1 These organs are on the posterior side, and are two in number ; their
position, however, differs somewhat from that of the similar organs of L .
crassicauda.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 27o

ticulum from the vestibule, at a later stage pinched off as a sac
containing a small lumen (Taf. xxx, fig. 40, g). It appears to
me, however, unlikely that Hatschek’s account is perfectly cor-
rect. Fig. 12 is a horizontal section through a Pedicellina.
The ganglion ( ga .) is oval, and consists of a peripheral layer
of cells, enclosing a central fibrous mass, as in Loxosoma.
In order to transform Hatschek’s ganglion rudiment into the
adult condition it would be necessary to atrophy the lumen
and to replace it by a development of nerve-fibres. The latter
would thus be formed from the primitively external surface of
the cells, a conclusion which appears most improbable, since
the position in which nerve-fibres originated phylogenetically
was no doubt the deeper surface of cells which formed part of
the outer ectoderm. This consideration, as well as the history
of the ganglion in Loxosoma, leads me to suspect that the
lumen in Hatschek’s ganglion is in reality the commencement
of the fibrous tissue, which in optical sections might easily be
supposed an empty space. Similarly Nitsche (10) has described
the ganglion of Alcyonella as originating as a diverticulum
from the tentacle sheath. I regard it as probable that the
explanation which I have suggested for Pedicellina will hold
also for A lcyonella.

Salensky has pointed out the similarity between the two
posterior sense organs of L. crassicauda and the similar
organs of Rotifera (vide Mobins, No. 9, Taf. v, fig. 2). These
organs in Brachionus consist of a pair of bunches of fine
hairs, borne laterally on the surface of the body, and each
supplied by a nerve from the brain. Mobius describes, further,
certain bipolar ganglion-cells passing by means of a nerve-
fibril directly to the body-wall, although no tactile hairs are
described in this position.

Alimentary Canal. — The general characters of this system
are already well known, and a reference to the figures accom-
panying this paper will sufficiently explain its anatomy.
Behind the mouth (fig. 11) is a large epistome, the size of
which has hitherto been hardly sufficiently recognised, and in
extent, indeed, is not far inferior to the buccal shield of

276

SIDNEY F. HAEMEE.

Rhabdopleura (its homologue). Its anterior portion, which
forms the posterior boundary of the mouth, is composed of
very long, ciliated, rod-like ectoderm-cells, with much elongated
nuclei (figs. 11 and 18). The posterior wall of the epistome
is formed of large cells, and bounds anteriorly a diverticulum
from the vestibule. At the bottom of this diverticulum is the
ganglion.

The oesophagus communicates with the dorsal and anterior
end of the stomach, as indicated in fig. 2, the passage of the
stomach into the intestine being shown in fig. 1 and fig. 11.
The rectum is separated by a constriction from the intestine ;
in L. cr as si cauda it protrudes into the vestibule as a large
cone-like process (fig. 11), whilst in most other species the
posterior wall of the rectum is closely applied to that of the
vestibule, so that in these cases there is no free rectal cone.

The whole of the alimentary canal in L. crassicauda is
lined by cilia, even the “ liver-cells” of the stomach forming
no exception to this statement. These cells are nucleated
peripherally, whilst more centrally they contain yellow
“ hepatic” spherules, which give their characteristic colour to
this part of the stomach.

In L. Leptoclini the stomach is produced laterally into a
pair of wing-like outgrowths (fig. 2). In some species the
occurrence of a parasite, a holotrichous Infusorian, swimming
about in considerable numbers in the stomach, is very constant ;
three of them are seen in fig. 11 (/).

Connective Tissue and Muscular System. — These structures
are best studied in the living animal or in glycerine prepara-
tions. The whole space between the ectoderm and the ali-
mentary canal is completely filled, either by the gonads and
other organs, or by a gelatinous matrix enclosing connective-
tissue-cells, muscle-cells, &c.

The Entoprocta possess no body-cavity nor any definite
system of spaces representing this structure.1 The gelatinous
matrix is perfectly transparent and hyaline, and, I believe,

1 Paired spaces, shown in fig. 11, usually occur in the epistome of L.
crassicauda.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

277

corresponds completely to the substance existing in the same
position in an ordinary Trochosphere before the appearance
of a definitive body cavity.

The connective-tissue cells of Loxosoma are large and
granular (fig. 10), usually elongated, and giving off processes
anastomosing with those of other cells ; they occur in all parts
of the body — in the axis of the stalk, at the sides of the
stomach, in the tentacles, and so on. In Pedicellina (fig. 5)
these cells are more similar to ordinary stellate connective-
tissue- corpuscles. The muscle-fibres are elongated nucleated
spindle-shaped cells, often branched at their ends ; they are
best developed in the stalk, where they form a longitudinal
layer immediately beneath the epidermis. Special muscular
fibres are connected with the foot (in those cases where the
foot-gland persists), the tentacles, and other parts of the body.
I have nowhere observed with certainty the endings of nerves
in the muscles.

Excretory Organs. — With the details of the structure of these
organs, so important for a correct appreciation of the syste-
matic position of the Entoprocta, we are almost altogether
unacquainted. Schmidt (11) has alluded to the nephridia, but
appears to have considered them as parts of the generative
system. Hatschek (14), who has detected them in both
adults and larvae of Pedicellina, makes the important state-
ment that in the former the nephridia are composed of per-
forated cells, whilst Joliet (24), who has devoted an entire
paper to the treatment of these organs, asserts that their walls
are so delicate that the existence of an excretory function is
doubtful.

The nephridia of Loxosoma are found lying on the ventral
wall of the stomach, one on each side of the oesophagus (see
Joliet’s figure), and situated near the anterior surface of the
body. In examining their structure, best observed in the
living condition, the animal should be looked at from in front.
The proximal portion can be investigated with more ease than
the part which is nearer to the external aperture, since the
organ in the latter position is covered by the oesophagus,

278

SIDNEY F. HARMEK.

through whose thick walls the examination of fine details is a
matter of great difficulty. The proximal part consists of a
small number of cells (fig. 17), which, in opposition to Joliet's
statement, I consider undoubtedly excretory in function. The
number of these cells seems to be invariably about four (L.
crassicauda) ; they are of a distinct yellowish-green tint, the
general appearance of which I have attempted to indicate in
the figure, although on examination with high powers it is
seen that this is entirely due to the presence of numerous
granules which alone are coloured. The distal portion of the
nephridium is a colourless duct, which presumably has no
excretory function. In this portion only two nuclei were
observed, the remainder of the duct being partly concealed by
the oesophagus, although its cilia could be distinctly made out
almost as far as the external opening (fig. 17). It seems to
me certain that the two nephridia open independently, their
apertures occurring in the depression of the vestibular floor
situated behind the epistome ; there can be no doubt that
the nephridia open to the exterior in front of the
ganglion. The proximal portion is invariably curved, the
concave side being internal, and the entire organ is perforated
by a ciliated duct, beginning at its proximal end, and opening
distally into the vestibule. The proximal cell I believe to be a
flame-cell, as represented, although I am not prepared to state
positively that this is really the case. In many individuals,
however, I have felt satisfied that I have detected the single
flagellum of the flame-cell, the difficulty consisting in the dis-
tinction of the movement of a flagellum of this kind from the
appearances produced by the co-ordinated movements of a
series of cilia like those occurring in most parts of the nephri-
dial duct. The proximal portion of the duct, which ends
apparently csecally, is somewhat swollen, whilst the next
portion is constricted ; at the bend of the nephridium, the duct
increases very largely in calibre, the widened portion being
continued slightly beyond the termination of the excretory
cells, and thence narrowing to the aperture. The duct per-
forates the individual cells of the nephridium, the cell limits

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 279

being indicated on the exterior by constrictions, whilst in
glycerine preparations made with osmic acid and picrocarmine
it has been possible to observe the nuclei of the perforated
cells, seen also with less certainty in the living condition.
My observations on the nephridia of Loxosoma are confined
entirely to the adult, but from the analogy of Pedicellina
there can be little doubt that the larva also is provided with an
excretory organ.

Although the nephridium described above differs in a very
marked degree from that of the Brachiopoda, it has the
closest possible similarity to the head-kidney of many Trocho-
spheres (see Hatschek’s papers on Polygordius (17) and
Echiurus (25). The resemblance between the nephridium of
Loxosoma and the head-kidney of the larval Polygordiu
is, however, more striking than could have been anticipated,
since Fraipont (43) has shown that each branch of the head-
kidney of the larval Polygordius ends blindly, and has not
in reality the form of a ciliated funnel opening into the body
cavity. The probability that the excretory organ of the adult
Loxosoma is to be regarded definitely as a head-kidney is,
however, most clearly shown by an inspection of the results of
the researches of Eduard Meyer on the head-kidneys of various
Annelid larv@e. Dr. Meyer was kind enough, during my stay
at Naples, to show me his drawings (at present unpublished)
of these structures, which resemble the nephridia of Loxo-
soma in a more striking manner than does even that of
Polygordius, the similarity being obvious in the number of
the excretory cells, in the relative size of the lumen in different
parts of the organ, in the mode of termination in a flame-cell,
and in other points.

The Trochospheral head-kidney opens to the exterior on
each side in front of the anterior end of the ventral nerve-cord,
as is the case in the Echiurus larva (Hatschek), in the adult
Loxosoma, and (Joliet) in the adult Pedicellina. Al-
though it is by no means impossible that fine apertures may
really exist in the proximal end of the head-kidney of Loxo-
soma, it is probable that the flame-cell termination, situated

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280

SIDNEY F. HARMER.

in the “primary body cavity/5 is morphologically different
from the ciliated funnel which opens into the “ secondary body
cavity’5 in Chaetopoda, Mollusca, and Brachiopoda.
This is the view adopted by Lang (47), who has pointed out
(p. 678) the support afforded to it of Ed. Meyer’s observation
that the ciliated funnel in Polymnia (Ter eb ell a) is in its
first development quite separate from the excretory organ,
with which it secondarily enters into connection. It appears
to me, therefore, that the Polyzoa have remained (in this
respect at any rate) in a far more archaic condition than the
Brachiopoda, which possess a nephridium provided with a
ciliated funnel.

It is probable, as Joliet (24) has already pointed out, that
the “ segmental organ 55 which has been described in some
Ectoprocta is not the homologue of the nephridia of the
Entoprocta.

1 have in no species of Loxosoma succeeded irt discovering
the paired organs described by Salensky (15), and supposed by
him to be renal. They are said to occur at the sides of the
intestine in L. crassicauda, each consisting of a group of
eight stalked cells opening to the exterior by a common duct.

Generative Organs. — The gonads of the Entoprocta are un-
doubtedly “ idiodinic,” to adopt Lankester’s term (No. 38,
p. 682), i.e. they have their own ducts to the exterior, and do
not make use of nephridia for the extrusion of the generative
products. The Entoprocta have usually been described as
hermaphrodite, although some observers, like Kowalewsky (3),
and Vogt (12), have asserted the separation of the sexes.
Although I have examined a very large number of specimens
ofPedicellina and Loxosoma, belonging to various species,
I have in no single case been able to find in the same individual
mature ovaries and testes. One or two of my preparations
perhaps indicate that male and female generative organs can
be developed in the same individual at different seasons ; and
I am inclined to believe that this is what really happens.1 In

1 The fact that buds are developed indifferently on males and females alike
perhaps indicates the correctness of this view.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 281

L. pes the structure of the generative organs is certainly
more complicated than in most of the other species, in which
I have invariably found that mature ovaries and testes are
mutually exclusive. It is easily shown that individuals contain-
ing developing embryos in their vestibule are not provided with
testes in the species of Loxosoma and Pedicellina which I
have examined. In some cases (as in fig. 16) a vesicula seminalis
containing spermatozoa is found, although the testes seem to
be completely absent. This fact, perhaps, indicates that the
male gonads, which must have been originally present, have
atrophied in order to make room for the development of the
ovaries.

L. Tethyse and L. Leptoclini. — The generative organs,
in individuals of either sex, consist of a pair of glands situated
at the sides of the body in the region marked ot. in fig. 2 ;
they lie on the ventral side of the stomach. In the male
(fig. 13) the testes are large bodies, consisting of a capsule
enclosing a mass of sperm mother-cells and mature sperma-
tozoa (with intermediate stages). I have not studied the
details of the spermatogenesis. From each testis runs towards
the middle line a short duct (vd.), opening into the posterior
side of a large oval vesicula seminalis, which in mature males
always contains numbers of elongated filiform spermatozoa,
which execute various movements even before their escape to
the exterior. The aperture of the vesicula into the vestibule
is very difficult to discover, but has apparently been seen by
Yogt, although this observer’s statements have been most
unjustly questioned by Schmidt. It is worthy of note that
the ganglion can easily be observed in all mature males, and
that Schmidt’s identification of this structure as the “ testes ”
is hence undoubtedly erroneous.

In the female the gonads have the same position as in the
male, and open by a single pore into the space between the
epistome and the ganglion (fig. 14). This pore ( p .) leads into
an unpaired oval cavity, from which proceeds on each side a
duct to the ovary. The arrangement in Pedicellina is very
similar, except for the fact that the unpaired portion is pro-

282

SIDNEY F. HARMER.

longed into a passage opening at the end of a projecting papilla.
In this genus, howeAfer, the ovaries are situated between the
ganglion and the intestine, whereas in Loxosoma they are
found between the ganglion and the (Esophagus, as indicated
Lv the position of the unpaired part of the generative duct.
(Compare fig. 12 with fig. 14; notice also fig. 16, a male.)
The ovary in L. Tethyae consists of a small number of cells,
of which only one becomes mature at the same time (fig. 14).
The cell which is becoming an ovum increases in size at the
expense of the neighbouring ovarian cells ; the latter are
absorbed by the egg, or rather appear to fuse with it, so
that the nearly mature ovum contains several nuclei whose
cells are separated from one another only by indistinct
boundaries. These disappear in later stages, and the absorp-
tion of other primordial ova by the developing ovum is then
only indicated by the fact that the latter is polynuclear. At a
still later stage presumably, the nuclei of the nutritive cells
are absorbed, as the mature ovarian ovum contains only a
single nucleus. In addition to this process of the fusion
of several ovarian cells to form a single ovum, another
method by which the latter is nourished takes place in
L. Tethvae. In many of my sections the developing ovum is
seen to be engaged in devouring curious masses marked vt. in
fig. 14, and differing entirely in appearance from the ovarian
cells. The latter stain readily with haematoxylin, whilst
the bodies vt. hardly absorb any of this colouring matter ;
they have in fact precisely the same appearance as the yolk
material diffused through the mature ovum and segmentation
spheres of this species of Loxosoma. There can hence be
very little doubt that the bodies which are thus devoured by
the ovum play the part of a vitellarium. In the ovaries of
L. Tethyse I have seen no structures with any resemblance
to the bodies in question, whilst the gland-cells occurring
round the edge of the calyx (described by Salensky, vide his
figure) behave in exactly the same manner with respect to
colouring matters, and have the same characteristic granular
appearance as the bodies vt. in fig. 14. These vitelline masses

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 283

in the ovum do not seem to be provided with a nucleus,
although there can be little doubt that they are really of
cellular nature, whilst the “ gland-cells ” of L. Tethyae are
usually true nucleated cells. In spite of this difference, I can
see no course open but to suppose that these “ gland-cells ”
lose their nuclei, and are absorbed by the ova in the manner
indicated by the figure. If this is really the case, it is difficult
to believe that the bodies in question really have the nature
of gland-cells, and it is possible that they may belong to the
mesoderm, and have no connection with the exterior.1

Whatever the origin of the vitelline masses observed in the
nearly ripe ovum, it is a fact of some interest that the yolk in
L. Tethyae appears to be prepared in part by cells which have
no connection with the ovary, and that the vitellarium is
probably not a modification of a primordial germinal mass
containing potentially both yolk-gland and ovary. In L.
Leptoclini, the only other species which I have found sexually
mature at Naples in considerable quantities, I have not observed
any processes for the nutrition of the ovum comparable to either
of the methods described inL. Tethyae; and it is a noteworthy
fact that the “ gland-cells ” of this species differ in their
histological character from any cells occurring in the other
species which I have examined.

It is difficult to reconcile some of the statements of Schmidt
with the appearance of my own preparations of the generative
organs of the Entoprocta. I have been unfortunately unable
to study in detail the structure of the generative organs of
L. pes, the form specially investigated by Schmidt (11 and 20),
and I have reason to believe that these generative organs do

1 In position, the “gland cells” of L. Tethyae correspond with the
“apical cells” ( ac ., fig. 2) of L. Leptoclini, except for their greater
lateral extension (nearly as far as the middle of the calyx on each side) in the
former species. It appears to me not improbable that these two sets of
structures are homologous, although I have in L. Leptoclini no evidence
as to their nature. Perhaps in this species the cells, originally playing the
same part as those of L. Tethyae, are at present mere functionless rudi-
ments.

284

SIDNEY F. HARMED .

really differ from those of both L. Tethyae and L. Leptoclini.
In Taf. i, fig. 1 (No. 11), Schmidt has figured the ganglion
of L. Raja as “testes/5 and what are doubtless the testes as
“ ovaries •” so that his statements as to the hermaphrodite
nature of this species, at any rate, are based on a misunder-
standing. As may be concluded from the description of L.
pes, on p. 7, Schmidt seems further to have believed that the
nephridia formed parts of the generative organs. In Taf. ii,
fig. 8, he has represented (L. pes) a duct passing from the
vesicula seminalis to the “ovary55 on each side, this “ovary55
consisting of a large rounded body containing “ ova 55 and sper-
matozoa. From his second paper (No. 20) one may conclude
that Schmidt considers it probable that the spermatozoa cannot
escape to the exterior, their only exit from the vesicula semi-
nalis being through the ducts leading to the “ ovaries.55 I am
convinced that Schmidt’s “ovaries’5 are in reality the testes, and
his “ova55 the sperm mother-cells. By referring to my own
fig. 13 it will he seen that the testes of L. Tethyae have the
same characters as Schmidt5s so-called “ ovaries55 in L. pes. I
must most strongly express my conviction that in no species of
Loxosoma is there any duct passing from the vesicula semi-
nalis to the ovaries, and that where such an arrangement has
been described the duct is really the vas deferens, and the
“ ovary 55 is the testis. Vogt’s account of the passage of a
bundle of spermatozoa from the vesicula seminalis to the exte-
rior is doubtless correct, although Schmidt has questioned its
accuracy. I have not observed the process of fertilisation in
Loxosoma.

What may be the nature of the bodies t and t' in Schmidt’s
Taf. ii, fig. 8 (No. 11), I cannot say, but I am unable to agree
even with his second account of their character (No. 20). In
this paper he states that the dorsal one is a bud rudiment,
which is the same thing as the “ generative rudiment” described
by himself, Nitsche, and others in the bud (that is to say, the
organ which on my view is the ganglion). The “ bud rudi-
ment” described by Schmidt in the adult is thus very different
in nature from the structure identified by him as the same

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 285

organ in the bud ; and it appears to me to have no real con-
nection with the budding processes.

In L. crassicauda, L. Leptoclini and L. Tethyae there
is certainly no such “ Knospenstock” as that described by
Schmidt. In the woodcut fig. 2, on p. 75 of Schmidt's second
paper the generative organs of a male L. pes have probably
been represented ; o is in this case the testis, and the vas
deferens is not indicated. Schmidt’s attempt to elucidate the
nature of the two pairs of bodies described by him respectively
as “ testes” and “ bud-rudiments” can thus hardly be con-
sidered successful, and I am unable myself to throw any fresh
light on the nature of these problematical organs of L. pes.

Part 3. — The Development of Loxosoma.

Our present knowledge of the embryology of Loxosoma
is exceedingly limited, in spite of the statements of Vogt,
Barrois, and others on the subject. That of Pedicellina
has, however, been most accurately worked out by Hatschek
(14), whose account I can confirm in its main features, with
the exception of that part which refers to the development and
the nature of the “ dorsal organ,” his “ Entodermsackchen.”
My study of the development of Loxosoma has been made
almost entirely by means of sections passing through the
embryos in various planes.1 L. Leptoclini differs from
L. Tethyae in possessing two specialised diverticula of the
posterior portion of the vestibule, one on each side of the
intestine, which by its projection as a large longitudinal ridge
(covered of course by ectoderm) into the vestibular cavity,
gives rise to the two diverticula. In these the earlier stages of
development take place, the older embryos, however, escaping
into the main vestibular cavity, and no doubt nourishing them-
selves on food particles brought to the vestibule by the cilia
1 The material was preserved with osmic acid, picric acid, or corrosive
sublimate ; the best staining of the embryos was obtained, after cutting, by
means of Mayer’s method for fixing sections on the slide (39). In this case,
hematoxylin, picrocarmine, or picrocarmine followed by hematoxylin gave
the best results.

286

SIDNEY F. HARHER.-

of the maternal tentacles, as is the case, according to Hatschek,
in Pedicellina. In L. Tethyae there are no specialised
brood pouches, and development takes place in the general
cavity of the vestibule. In L. Leptoclini, however, where
the amount of yolk is very small, the lining of the two brood
pouches at the sides of the intestine consists of an epithelium
of high columnar cells, altogether unlike the flat cells which
line the greater part of the vestibule. During the earlier
processes of development (figs. 25 — 34) the embryo hardly
increases at all in size, if allowance is made for the appearance
of internal cavities (blastocoel, archenteron), by which the cell
layers are forced asunder.

At about the stage of fig. 43, however, the epiblast in certain
regions becomes very thin, and these portions are found closely
applied to the columnar epithelium lining the brood pouches
(fig. 47). The embryo forthwith commences to grow rapidly
(figs. 43 — 45), and although this increase in size may be partly
due to the digestion of food particles taken in by the mouth
(which is already present), it is probable that it is mainly due
to the activity of the columnar cells of the brood pouch.
These may be supposed to secrete a nutrient material through
the thin walls of the embryo into its primary body cavity,
which at this stage is a wide space between epiblast and hypo-
blast. The connection between the thin walls of the embryo
and the epithelium of the brood pouch is often so intimate that
careful observation is necessary to discover the existence of the
former (see fig. 47). It is probable, therefore, that in L. Lepto-
clini the embryos are nourished by a placenta composed of a
layer of glandular cells, modified epidermic elements of the
vestibule, forming a portion of the outer limit of the gela-
tinous substance (of the adult), which serves as a medium for
the diffusion of the various products of metabolism to the
different organs.

In Pedicellina echinata the epithelium lining the brood
pouch is similar to that found in the corresponding position in
L. Leptoclini. It is, however, thrown into numerous folds
(fig. 12), whilst no intimate connection is set up between the

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 287

embryos and the vestibular epithelium. It is hence probably
the case that in Pedicellina the brood pouch can be almost
completely shut off from the rest of the vestibule, nutrient
substances being secreted into it by its glandular epithelium,
which is largely increased in area by the formation of folds.
This is, probably, in the main a consequence of the large
number of the embryos present at the same time, and of the
great increase in size which they experience during their stay
in the brood pouch.

In the whole course of the development of L. Tethyse, the
increase in size of the embryo is small compared with that of
L. Leptoclini and of Pedicellina; so that whereas the
ovum of L. Tethvae is much larger than that of L. Lepto-
clini, this difference in size being still very obvious in
comparing, for instance, fig. 29 with fig. 60, or fig. 38 with
fig. 62 (representing corresponding stages of the two species
magnified to the same extent), the embryo of L. Leptoclini
early equals that of L. Tethyse in size, the free larva of
the former species being considerably larger than that of the
latter.

It is worth noting that the marked growth of the embryos
of L. Leptoclini and of Pedicellina cannot probably be
entirely ascribed to the fact that they devour particles of solid
food, since in L. Tethyse, whose embryo is quite early pro-
vided with a mouth, the increase in size during develop-
ment is comparatively small.

Segmentation, Formation of the Germinal Layers, and Completion
of the Alimentary Canal ; Mesoblast.

L. Leptoclini. — The ovum (fig. 25), on escaping into the
vestibule, segments completely, at first into two (fig. 26), and
then into four (fig. 27). The latter figure was drawn in the
living condition, and shows the vitelline membrane present at
this and some of the later stages. I have not observed polar
bodies, this being probably a result of my almost exclusive use
of the section method. At the next stage represented (fig.
28), the embryo is a solid mass consisting of about eight cells,

288

SIDNEY F. HARMER.

four of which occur iu the section ; whilst in fig. 29 the number
of cells is larger, and a segmentation cavity or blastocoel has
made its appearance. The embryo at this stage is usually
much flattened, partly owing to the pressure of larger embryos
which are found at the same time in the brood pouch. The
number of embryos in each brood pouch is, however, consider-
ably smaller than in Pedicellina, and seldom exceeds about
two or three. In fig. 30 it is seen that a slight depression has
been formed in the centre of the flattened side, representing
the commencement of the archenteron. The cells on the side
of the blastopore are somewhat higher than on the opposite side,
whilst the blastocoel is almost obliterated, owing to the pres-
sure of other embryos. In fig. 31 the blastocoel is larger,
although the invagination has proceeded a stage further. Fig.
32 and fig. 33 represent sections of other embryos slightly
older than fig. 31. In fig. 33 the section has just missed the
blastopore, so that the invagination appears solid, whereas in
most other cases, a central depression is present from the first
in the invaginating mass of cells. Fig. 32 shows the appear-
ance of a large cell in the immediate neighbourhood of the
blastopore ; this is one of the two pole-cells of the mesoblast.

The figures 60 and 61 represent two early stages of L.
Tethyse, drawn with the same magnifying power as those of
L. Leptoclini. In fig. 60 the blastocoel has just made its
appearance. In fig. 61 the invagination has progressed to a
considerable extent, the section passing transversely through
the archenteron and blastopore, and cutting both of the pole-
cells, which even at this early stage are completely shut out
from any share in bounding the archenteron ; they have
already taken up their definitive position between the epiblast
and the hypoblast.

Fig. 34 represents a section of a gastrula ofL. Leptoclini;
the archenteron is wide, the blastocoel apparently obliterated,
and one of the two pole-cells is seen in the neighbourhood of
the blastopore, although the relation of this cell to the two
germinal layers could not be distinctly made out.

The fate of the blastopore is difficult to trace with certainty.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 289

From a comparison, however, of numerous sections of L. Lep-
toclini and L. Tethyse at this and somewhat later stages, I
have come to the conclusion that the blastopore closes in the
position where the anus is subsequently formed, and that the
oesophagus makes its appearance as a stomodseum in front oi
this region.

The mesoblast in Loxosoma originates in great part at
any rate from the pair of pole-cells. In the later stages, as
long as they are present, they are found in the immediate
vicinity of the anus, each giving rise to a forwardly directed
mesoblastic band. It is difficult by means of sections to deter-
mine the period at which the anus originates, but even in the
adult the anus can hardly be discovered except during the
process of defsecation. I am unable to state positively how
much of the alimentary canal is formed as a proctodaeum, but I
regard it as probable that the whole of the “rectum,” as far as
the constriction dividing the posterior limb of the alimentary
canal into two parts (fig. 52), originates in this way; fig. 40,
an, probably indicates the formation of the rectum as a proc-
todseum. Whatever may be the real history of this part of
the embryo, the intestinal end of the hypoblast seems to
remain from the earliest stages in connection with the epi-
blast, marking the spot where the blastopore either closes or
persists as the anus. In front, however, occurs a large funnel-
like epiblastic involution which forms the stomodseum, and
early communicates with the arehenteron. In the embryo
fig. 38 it is probable that the stomodseum extends as far as
the line z, the histological difference between the (supposed)
epiblastic and hypoblastic cells being very conspicuous.

From a consideration of sections of L. Tethyse it appears
probable that some of the mesoblast may originate entirely
independently of the pole-cells from any portion of the embryo,
but in later stages of L. Leptoclini the main production of
mesoblast is probably due to the pole-cells, as indicated by
fig. 40. This is a section passing through one of the meso-
blastic bands formed from a pole-cell. The commencement of
the band is at the side of the anus, as shown by the position of

290

SIDNEY F. HARMEE.

the vestibular invagination ( v .), described later. The band
consists of a series of branched cells, lying in the blastocoel
(“ primary body cavity55 of Hatschek), in which are seen, in
addition, three mesoblast cells, whose origin is uncertain. In
the next stages the mesoblast consists of cells with anastomosing
processes (figs. 41 and 42), scattered irregularly through the
blastocoel, but I have never observed anything corresponding to
a splitting of the mesoblast into splanchnic and somatic layers.
In still later stages the mesoblast occurs mainly at the sides
of the body, the more median regions being occupied by the
alimentary canal, “ dorsal organ,55 and “ vestibular invagina-
tions.55 The mesoblast cells, however, fill up almost all the
interspaces between these structures, so that the mature lava
is practically a solid mass of closely-packed tissues, this fact,
of course, rendering it a difficult undertaking to distinguish
the nature of all its constituent cells.

The disposition of the mesoblastic bands (which at first are
situated near the ventral surface), and their relation to the
pole-cells (which originate at the sides of the blastopore, and
are subsequently found at the sides of the anus), seem to me
to support the view that the blastopore and anus are identical
in position.

The alimentary canal of the embryo is completed at an early
stage, and subsequently undergoes no very striking changes
until the larva becomes free. It consists in advanced embryos
of the following regions, all distinctly marked off from one
another : (i) the oesophagus (fig. 52, ce.) doubtless formed as
a stomodseum; (ii) the stomach and intestine (st. and int .)
passing quite gradually into one another. Dorsally and late-
rally the stomach is lined by low hypoblast cells, ventrally by
cells which are high and columnar, nucleated peripherally, and
containing yellow spherules ; these cells, in fact, are the precise
equivalent of the “ liver-cells55 of the adult; (iii) the rectum
( rec.)} separated from the intestine by a constriction, and pro-
bably formed as a proctodaeum. The anus opens on a well-
marked rectal cone projecting into the vestibule.

The alimentary tract of the larva thus resembles in every

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 291

particular that of the adult, in which can be similarly distin-
guished oesophagus, stomach (with “liver-cells” ventrally),
intestine, and rectum, the various parts having exactly the
same relations to the two limbs of the U-shaped gut in the adult
and in the embryo alike. Both the mouth and the anus open
within the circumference of the ciliated ring ( cr .), with respect
to which the larva is entoproctous, just as is the adult in
relation to the lophophore.

Formation of the Sucker, Dorsal Organ, and Vestibule. — At
the time when the alimentary canal is just completed a series
of most important changes takes place in the constitution of the
embryo, involving the appearance of the sucker (the homologue
of the adult foot-gland), of the “ dorsal organ,” and of the
vestibule. Fig. 37 is an almost median longitudinal section of
an embryo at a a period when the sucker and the “ dorsal
organ” are still in a very early stage of development. The
oesophagus (02.) is cut medianly, the epiblastic invagination
from which it has been formed extending as far as the mark
z. The sucker (5.) is distinctly marked out as a group of
epiblast cells much higher than their neighbours, and already
indicated on the exterior by a slight depression of the surface
of the embryo. The alterations by which the sucker passes
into its permanent form are very unimportant, the most
noticeable change consisting in a deepening of the involution,
and an increase in the number and in the height of the cells
composing the organ. The sucker, which is retractile, serves
for the attachment of the embryo to the walls of the brood
pouch, and this is one of the causes of the fact that it is func-
tional at so early a stage. The foot-gland is no doubt the homo-
logue of the larval sucker, with which it is much more similar
in structure than could be supposed from previous descriptions
of the adult organ. If my description of the latter is correct
the main difference between the embryonic sucker and its
adult representative consists in the elongation of the rounded
depression, constituting the former, to the open elongated
groove of the latter; in the adult, however, an additional
complication has taken place in the separation of the ventral

292

S1DNET F. HARMER.

portion to form the "gland,” the "duct” of the organ
remaining throughout life fundamentally in its embryonic
condition. In fig. 37 the dorsal organ ( br ) is seen, contrary
to the statements of Hatschek on Pedicellina to consist of
a few columnar epiblast cells. The section in question is
only one of a considerable number, giving the same evidence
as to the earliest development of this structure. From its
position there cannot be any doubt that the epiblastic thicken-
ing is correctly identified as the dorsal organ, which neither
in its earliest appearance nor in its ultimate fate shows the
slightest evidence of its supposed function as a bud-producing
organ. At the earliest stage at which it is possible to identify
the dorsal organ with certainty, it invariably consists of a single
layer of cells forming part of the one-layered body wall, and
there can hence be no question as to its epiblastic nature.
One further point may fairly be urged against Hatschek' s view
of the developmeut of his " Entodermsackchen.” According
to Hatschek certain hvpoblastic cells are budded off from the
anterior wall of the mesenteron ; they enter into connection
with an epiblastic thickening, with which they form a budding
organ, the endoderm cells of the bud being derived from the
hypoblastic mass, which has taken origin from the walls of the
mesenteron. My own sections lead me to believe that the
stomodaeum extends inwards a greater distance than was sup-
posed to be the case by Hatschek in Pedicellina (see figs.
37 and 38), and if my view is correct the dorsal organ makes
its appearance opposite a portion of the stomodaeum. This
being the case, judging from Hatschek's description, the first
cells forming the dorsal organ, and occurring between the epi-
blast and the hypoblast, are derived from the epiblastic cells
of the stomodaeum, and this hypothesis refuses to adapt itself
to Hatschek’s own view on the nature of the budding process.
Finally, I must state that I have satisfied myself, by means of
sections, that even in the embryos of Pedicellina the dorsal
organ first appears as a thickening of the epiblast.

In order to prepare the way for the following description
of the further history of the development, I may at once state

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

293

my conviction that in the “dorsal organ ” of the Entoprocta
we may recognise the supr a-oesophageal ganglion or
brain of these animals.

The horizontal1 section fig. 43 cuts the oesophagus (ce.)
and the intestine ( int .) ; the epiblast is somewhat thick, as
this is the region of the ciliated ring. The space between the
alimentary canal and the epiblast has increased in size ; on the
right side is a mass of mesoblast cells growing forward from
the region of the anus, the left wing of the mesoblast not being
seen, owing to a slight obliquity of the section. Between the
oesophagus and the intestine occurs a bilobed, apparently solid,
mass of cells which are derived from the epiblast, and repre-
sent an early stage in the development of the vestibule. Each
of the halves of the bilobed mass in reality corresponds to a
shallow depression of the ventral surface of the embryo in
front of the anus.

Fig. 41 represents a section of a somewhat later stage,
passing in an obliquely longitudinal direction and cutting one
side of the oesophagus (which is considerably elongated trans-
versely), and also a vestibular invagination. Behind the latter
occurs the commencement of one of the paired mesoblastic
bands, which is seen passing forwards and breaking up into an
irregular mass of branching mesoblast-cells. Anteriorly is
cut one of the two lateral halves of the brain, which has
already grown inwards as a pair of wings, one on each side of
the oesophagus. In a horizontal section of a considerably older
stage (fig. 44), each vestibular invagination is composed of
cells, whose nuclei are arranged in several layers. The section
shows anteriorly a portion of the ciliated ring, indicated by the
thickness of the epiblast and the elongation of the nuclei,8

1 This term is used somewhat loosely in the description; in some “hori-
zontal ” sections, for instance, the oesophagus and stomach are cut ; in others
the oesophagus and intestine or rectum.

2 The existence of the nuclei on the outer side of the cells of the ciliated
ring in the figure is due to the fact that a slight fold of the body wall has
been produced by the action of reagents, and has been involved by the
section ; the cells of the ciliated ring are of course part of the external
epiblast.

294

SIDNEY F. HARMER.

characters retained in all subsequent stages ; throughout life it
consists of a single row of cells bearing long cilia.

In a still later stage (fig. 45), the two vestibular cavities ( v .)
have fused in the middle line, and form a transversely extended
groove separating from one another the process of the body
bearing the rectum ( rec .) and the epistome ; the mouth at this,
as at other stages of the embryonic history, is a transversely
elongated funnel, connected on each side with a groove
which runs round the ventral surface of the body, just
within the ciliary ring. This “ oral groove ” is represented
in fig. 40, og.

Only the deeper portions of the vestibule are formed from
the invaginations just described; the peripheral parts originate
from a growth ventralwards of the region of the body bearing
the ciliated ring, which can be either extended to the exterior,
as in swimming, or can be retracted into the interior of the
vestibule, whose aperture is then constricted, as indicated in
fig. 55, va.

We may now take up the further history of the dorsal organ
or brain, which we left in the condition of a thickened area
of the epiblast, composed merely of a single layer of cells.
In fig. 38 the dorsal organ (br.) is seen to have become two
cells thick. Fig. 46 represents a somewhat earlier stage, seen
in horizontal section ; the epiblast, elsewhere very thin, has
proliferated off a bilobed cellular mass, the wings of which
pass as far as the sides of the oesophagus. The number of
cells composing this structure, the brain, increases consi-
derably, and before long it may easily be observed by means of
horizontal sections (figs. 47 and 48) that the cells are arranged
in a single layer round a lumen which opens medianly to the
exterior. It is probable that the brain is at first formed by a
solid ingrowth of cells, in which a cavity subsequently appears,
although it is not impossible that a lumen may be present from
the very commencement, and that owing to its small size it
cannot easily be detected in sections. In either case, the brain
is formed by a process of epiblastic invagination.

Hatschek (14) has already illustrated and described in

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

295

Pedicellina the stage corresponding to fig. 52 of Loxo-
soma; according to the statements of this observer, the
“ Entodermsackchen,” originally a solid cell mass, becomes a
sac enclosing a lumen ; the sac attaches itself to the epiblast,
and its lumen then opens (secondarily) to the exterior. The
latter stage undoubtedly exists in Pedicellina, although, as
explained above, Hatschek's statement that the dorsal organ
contains hypoblastic elements is probably erroneous. The
main difference between the brain of Pedicellina (for such I
consider to be the nature of the dorsal organ in this genus
also) and that of Loxosoma consists, at the present stage,
merely in its greater transverse elongation in the latter genus,
that of the former being represented by an oval sac whose long
axis is directed transversely.

Uljanin (5), it may be noted, states that in examining the
larvae of Pedicellina, he at first erroneously supposed that
the dorsal organ and the sucker were nervous structures. He
says (p. 437) : “ Sieht man eigenthiimliche ganglienformige
Organe, die mit einander durch Commissuren vereinigt sind.
Dieses Organ sieht einer Ganglienkette so ahnlich, dass ich es
auch anfangs fur ein solches gedeutet habe. Eine griindlichere
Untersuchung bewies aber dass eine solche Behauptung
nicht die richtige war . . . . im Innern dieser Organe

konnte ich, trotz aller meiner Bemiihungen, nichts Ganglien-
zellen Aehliches finden.”

In Loxosoma Leptoclini, before very long after the stage
represented in fig. 48, there appears on the deep surface of the
invaginated brain a layer of fibrous tissue (fig. 49 and fig. 52,
fbr.), which resembles the commissural part of the adult
ganglion in staining very slightly even after prolonged treat-
ment with borax carmine, or hsematoxylin. On each side of
the brain is now found a pigment spot or eye, whose mature
form is shown in the free larva, fig. 55, o. The eyes make
their appearance at a time when the brain still possesses a
conspicuous lumen, which soon after their formation atrophies
by the mutual apposition to one another of the two cell layers
forming the walls of the sac ; in the larva which is ready for a

VOL. XXV. — NEW SER. U

296

SIDNEY F. HARHER.

free swimming existence, the brain has the appearance of
fig. 50 and fig. 51, two consecutive sections (horizontal) of the
same embryo. Fig. 51 shows the two eyes (o) which the
neighbouring section (fig. 50) has just missed, although it
passes through the fibrous region of the brain at its thickest
part ( fbr .) On the outer side alone of the fibrous portion is
a mass of ganglion-cells, which in agreement with the mode of
their development are not arranged in a single layer. There
thus exists a well-marked distinction between the development
of the adult ganglion (suboesophageal) and that of the larval
brain. The latter is formed by a process of invagination, the
fibrous layer making its appearance entirely on the deep side
of the ganglion- cells, which are arranged in more than a single
layer ; the former arises by the differentiation of a solid cell
mass from a thickened ectodermic region, the cells which com-
pose the ganglion separating from one another centrally, and
depositing a fibrous layer on their inner sides in such a
manner that the adult organ consists of a fibrous core sur-
rounded by a single layer of cells.

The finer histological details of the structure of the brain
cannot well be made out in paraffin sections, and in the fresh
condition it is even more difficult to investigate the minute
anatomy of the nervous system of the larva. From the
examination of a very large number of sections of embryos of
various ages, I can assert the constancy of the relations to one
another of ganglion cells, fibrous layer and eyes, as described
above. It is especially important to notice that the fibrous
layer is invariably present, and can readily be found in any
series of sections passing through a mature embryo. The
existence of the eyes on the dorsal organ is a very strong
a priori argument for the occurrence of nervous tissue in this
region.

Fig. 54 is an obliquely horizontal section, passing through
oesophagus and intestine, brain, and vestibular invaginations.
On the left the section cuts the lumen of the latter, but on
the right only the cells limiting its blind end. Each of the
two invaginations consists of more than one layer of cells, and

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 297

anteriorly has given off a solid outgrowth which has met one
end of the brain. This union of an outgrowth from each
vestibular invagination with an end of the crescent- shaped
brain is a constant occurrence ; and it may be concluded that
some of the deeper cells of the vestibular invaginations sepa-
rate from the external epiblast to form a pair of suboesophageal
ganglia, united with the brain (and with one another) by
means of a circumcesophageal commissure. It must, however,
be distinctly understood that the suboesophageal ganglion
arises from the deeper cells of an epiblastic thickening, and
not by a direct conversion of the vestibular invaginations into
nervous tissue. The formation of the ganglion in the bud
thus takes place in exactly the same manner as that of its
homologue in the embryo. In stages more advanced than
fig. 54, it is still possible to discover a commissure running
from the brain on each side to a mass of tissue in the post-oral
region, although at no period is it at all easy to observe the
limits of the suboesophageal ganglion, which is closely packed
with mesoblast cells, very difficult to distinguish in section
from ganglion-cells.

The dorsal organ of L ox o soma, as is well known, is pro-
vided with a pair of ciliated sacs, one on each side, in the
neighbourhood of the eyes, and opening to the exterior on its
surface. These sacs are provided with active cilia, and extend
inwards so as to lie in close contact with the external surface
of the brain. As far as I am aware, the presence of these two
sacs is the only foundation for the statement in Yol. i of
Balfour’s f Comparative Embryology/ that the dorsal organ of
Loxosoma is double, whereas that of Pedicellina is single.
The brain of Loxosoma is in reality developed from an
unpaired rudiment, and except for the fact that it extends
further laterally than that of Pedicellina, there is no reason
whatever for assuming its double nature. In Pedicellina
the lumen of the brain atrophies, as already described by
Hatschek ; but before this process has taken place, there occurs,
in the same position as in Loxosoma, a deposition of fibrous
tissue, as I have been able to observe from sections. The

298

SIDNEY F. HAR5IER.

brain in Pedicellina, however, is not provided in any known
species with eyes, this being in all probability a retrogression
from a more archaic condition. An unpaired ciliated sac,
described by Hatschek, is connected with the dorsal organ of
Pedicellina.

These ciliated sacs of the Entoproctous larvae are not to be
confused with the primitive cavity of invagination of the brain,
which loses its lumen during the conversion of its indifferent
cells into nervous tissue ; they are mere secondary epiblastic
involutions, either developed for the aeration of the central
nervous system or having the nature of olfactory organs, as
suggested by Hatschek (17) for the similar structures in
Polygordius.

The eyes of the larva of L. Leptoclini consist of crescentic
reddish-brown masses of pigment (fig. 55, o), in whose con-
cavity is imbedded a prominent transparent lens ; the finer
details of the structure were not made out.

Eyes are present in most larvae of Loxosoma hitherto
described, although they appear to be absent in L. pes
(Schmidt, No. 11). The larva of this species differs to a con-
siderable extent from that of L. Leptoclini. In Schmidt’s
figure (Taf. ii, fig. 25) there occurs nothing which can with
certainty be identified as the dorsal organ, whilst the larva is
provided with three pairs of bodies of an entirely proble-
matical1 nature. The larva of L. Tethyae I find, in external
features, to be almost exactly like that of L. pes figured by
Schmidt ; but at present I have not been able to elucidate the
nature of the three pairs of problematical organs. Eyes are
absent in the larva of L. Tethyie, although I have succeeded
in obtaining preparations which demonstrate the existence of
a brain, especially unmistakeable in the stage represented in
fig. 62 ( br .). The dorsal organ of the larva of L. Tethyse is,
however, not nearly so highly developed as that of L. Lepto-
clini. By comparing the development of the latter with that

1 Schmidt, in his second paper (20), suggests that one of these pairs may
constitute the “ Knospenstiicke ” or budding organs of the larva, identical
with the structures described as such (probably erroneously) in the adult.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

299

of certain other Trochospheres (as described below), we obtain
evidence that the history of the brain in L. Leptoclini is
really archaic in its general features, and there hence appears
to be little reason for hesitation in the assumption that the
larvae of both L. Tethyae and L. pes are degenerate forms, in
which the sense organs (eyes) and the brain have suffered
retrogressive modifications. A similar change, though to a
less marked extent, seems to have occurred in the larva of
Pedicellina, which in this respect thus shows itself to be less
primitive than that of L. Leptoclini.

It has been suggested by Hatschek (14) that the dorsal
organ becomes the first hud in Pedicellina, the first pair of
buds in Loxosoma; in order to establish my view of its
nature, it is necessary to examine the history of the metamor-
phosis, to ascertain if the larva makes use of its dorsal
organ as a budding region. This I find definitely to be not
the case in L. Leptoclini, and the hypothesis of the nervous
nature of the dorsal organ remains in consequence unshaken
when the budding processes of the larva are studied.

My method of obtaining free larvae was to place a large
number of L. Leptoclini growing on the Ascidian in a glass
vessel, blackened in every part with the exception of a small
window facing the light. On covering the top of the vessel
with a piece of black paper, the larvae, as they were hatched,
made their way to the only part of the glass whence any light
was proceeding, and in this position they could be easily detected
and captured.

From various causes, and chiefly from the death and conse-
quent putrefaction of the Leptoclinum within a day or two
from its removal from the sea, the number of the larvae which
I succeeded in observing during the process of their metamor-
phosis was very small. In no single case did I observe any
permanent fixation of the larva, but the method of the fixation,
if this really takes place normally, is perhaps not of very great
importance. If, as is probable, the normal resting-place of
the larva is on the surface of the Leptoclinum which bears
the adult individuals, the dying condition of the Ascidian in

300

SIDNEY F. HARMEE.

captivity is sufficient to account for the refusal of the larvae to
attach themselves.

My observations on the metamorphosis of L. Leptoclini
are exceedingly incomplete, but they have been sufficiently
successful to demonstrate that the free larva may produce a
pair of buds (fig. 55, b), although I am unable to say whether
the budding takes place normally during a free life, or as a
general rule only after fixation. In the most successful expe-
riment, four larvae were kept alive and apparently healthy for
four days after the commencement of their free existence.
They had produced buds considerably older than those repre-
sented in fig. 55, although, as in the adult, they were unequally
developed on the two sides of the body. The older one of each
larva was more elongated than those of the figure, and was
somewhat pear shaped, being attached by its narrow end.

At its free end was an elongated slit, the opening into the
vestibule, and these, the oldest larval buds observed, had exactly
the appearance of those normally developed on the adults soon
after the opening into the vestibule is a longitudinal slit on the
anterior side. As I was not aware that I should fail in rearing
larvae a second time to the same age, I neglected to kill any of
the four-day larvae, which twenty-four hours later were found
dead and disorganised. There could not, however, be the
slightest doubt that the two structures described above were
really correctly identified, and the larva of L. Leptoclini
at any rate may be stated to produce a pair of buds in a position
corresponding to that of the budding regions of the adult.
The probability that this would be found to be the case had
already been indicated by Hatschek, who made this suggestion
on the hypothesis that the dorsal organ was the budding
region. In my four-day larvae, however, this structure showed
not the slightest change from its condition at the commence-
ment of the free existence ; the position of the head was still
continually varied for convenience of vision (this region of the
body being exceedingly moveable), and the cilia in connection
with the dorsal organ, like those of the epistome and ciliary
ring, were working vigorously.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 301

Fig. 55 represents a larva after a free existence of about
twenty-four hours ; the animal is seen from the ventral side,
the ciliated ring being completely retracted into the vestibule,
the narrowed opening of which is seen in the centre ( va ). By
careful focussing could be made out the ciliary movements of
the oesophagus and rectum, not indicated in the figure. The
head or dorsal organ with its two eyes is very conspicuous and
has in no way been altered in appearance by the production of
the buds, which are seen as a pair of round projections at the
sides of the dorsal organ, and at a level intermediate between
it and the edge of the retracted vestibule. This position of
the buds having been observed, it at once became obvious what
was the nature of certain cells which had been repeatedly
seen in the more advanced embryos within the brood pouch in
exactly the position of the larval buds. These cells (fig. 57, b)
form a group on each side, consisting of a small number of
large rounded epiblastic cells lying at the sides of the brain,
and between this organ and the ciliated ring. In larvae one
or two days free they are found to be more numerous and form
a considerable projection composed in the main of enlarged
epiblast cells. In fig. 59, a horizontal section of a larva which
had been free two days, one of the buds ( b ) is cut on the left
side. It consists externally of a layer of very high epiblast
cells. On the inner side of these cells occurs a large rounded
mass which seems to contain only a single nucleus. This large
cell in all probability belongs to the epiblast, which I have
observed, from an examination of other larval buds, to give rise
to a mass of cells which projects inwards, and no doubt
eventually forms the lophophore and vestibule, in the same
manner as in the buds developed by the adult. The section
has passed through the eye of the opposite side, together with
a portion of the corresponding half of the brain, and it is easy
to see, from an inspection of this and other series of sections
of larvae at the same or earlier stages, that the dorsal organ
remains quite unaltered during the budding.

In fig. 56 are represented two groups of cells ( hst .), appa-
rently developed from the sides of the stomach. In larvae

302

SIDNEY F. HARMER.

which have just become free occur two very conspicuous lateral
masses of large cells (figs. 50 and 51, hst.) lying between the
epiblast and the stomach, and corresponding to those which
seem to be originating in fig. 56. In larvae which have been
free two days, the lumen of the stomach is almost completely
atrophied (fig. 58, st.), although the oesophagus and intestine
are much less altered. The figure represents the oesophagus at
the point where it passes into the stomach, whose “ liver-cells”
are still recognisable (/.). At the sides of the stomach are two
masses of cells, probably corresponding to those developing
in fig. 56 ; that of the left side is seen to pass to the base of
the bud, whose outer portion is just involved by the section.
In the other sections passing through the same larva, no stomach
lumen could be discovered, but only a mass of cells (repre-
sented in fig. 59), which fill up the whole of the central portions
of the larva, and which pass to the bases of the bud. These
appearances, which are not confined to a single larva, have led
me to form the following hypothesis of the budding processes,
in default of a complete series of actual observations.

One of the earliest formed parts of the bud is the epiblastic
thickening, which occurs long before the embryo is ready to
become free, and during embryonic life consists of a small
number of large granular cells. Almost at the same time are
proliferated off from the sides of the stomach a pair of lateral
wings of hypoblast cells, destined to take part in the budding.
After the commencement of the free life these cells increase in
number by subdivision, new ones being at the same time
formed from the walls of the stomach, which atrophies coinci-
dently with their formation. The stomach is thus completely
lost, and is replaced by a large mass of cells filling up the centre
of the larva. The epiblastic thickening meanwhile has grown
inwards, and the bud forms a projecting rounded lobe of the
body of the larva. The epiblastic portion forms the lopho-
phore and vestibule, the latter originating as a longitudinal
slit, just as in the buds formed on the adult. The central mass
of hypoblast cells is employed mainly as a food material
during the development of the bud, but some of these cells

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

303

apply themselves to the deep end of the lophophore, and give
rise to the stomach of the adult. I have one preparation of a
larval bud, which seems to show this application of a hypoblast
cell to the end of the lophophore.

The origin of the various organs in the buds developed on
the adult has been a subject of much controversy. The bud
commences as an ectodermic thickening, growing inwards to
form the lophophore. It is very difficult to determine satis-
factorily whether the endoderm develops from cells proliferated
from the stomach or from the ectodermic thickening which
occurs at the apex of the bud. According to most observers
the latter is the case. Although at present I have been unable
to satisfy myself on this point, it has seemed to me, on the
whole, probable that in the adult the stomach does give rise to
cells, which apply themselves to the end of the lophophore, and
are destined to form the stomach of the bud. I have been
unable to convince myself of the accuracy of Haddon’s account
(37), according to which the stomach at its earliest appearance
is quite distinct from the lophophore. My own sections lead
me to believe that the stomach is connected with the lopho-
phore, even in its youngest condition, and that the only method
by which it can have an endodermic origin is by the prolifera-
tion of cells from the stomach, and by the application of these
cells to the ectodermic part of the bud. The ectoderm and
endoderm on this hypothesis become indistinguishable, so that
at a later stage the stomach appears to be developed from part
of the ectodermic thickening forming the lophophore.

The most noteworthy features of the history of the larva to
which it is necessary to call attention are (i) the fact that the
dorsal organ takes no part in the budding, and (ii) the atrophy
of the stomach after the commencement of the free larval
existence. The latter fact probably indicates that the larva
never becomes adult, but that it dies after the production of
its buds. Although it is organised on a plan fundamentally
similar to that of the adult there is still a very well-marked
distinction between the anatomy of these two forms, and in the
four days during which I succeeded in keeping some of my

304

SIDNEY F. HARMER.

larvse alive there was not the slighest indication of the loss of
any of the larval characters or of the approximation, in a single
feature, to the adult condition. The (probable) fact that the
larva does not become adult throws some light on the absence
of the brain in the stalked Loxosoma, since we may assume
that this organ has been inherited by the larva from a brain-
possessing ancestor, but has been transmitted to none of the
individuals produced by budding, and whose development
cannot be regarded to any great extent as a recapitulation of
the phylogeny of the Entoprocta.

In experimenting with the larvse of L. Tethyse and Pedi-
cellina I have completely failed to obtain any indications of
the processes of the metamorphosis. This is especially striking,
since on one occasion larvse of the former were kept alive for
as much as eight days after they were hatched ; at the end of
this time they were still free-swimming, and, externally at any
rate, showed no obvious indications of buds.

Part 4. — On the Affinities of the Polyzoa.

The embryology of Dentalium has recently been inves-
tigated in considerable detail by Kowalevsky (36) ; the agree-
ment between this description and my own observations on
Loxosoma is very striking, especially with reference to the
nervous system. The alimentary canal of Kowalevsky’s larva
possesses the characteristic Trochosphere bend, whilst the
mesoblast develops from a pair of pole-cells in the neighbour-
hood of the blastopore. The shell-gland appears dorsally at an
early period (whilst the embryo is still a gastrula), and has
at a certain stage the form of an involuted sac, whose similarity
in Molluscs in general to the foot-gland of Loxosoma has
already been pointed out by Lankester (8). In the anterior
region of the embryo, in the middle of the velar area, originates
a pair of separate epiblastic invaginations, the “sincipital
tubes ” of Kowalevsky. These tubes grow backwards into the
praeoral lobe for a considerable distance, ending blindly one on

STRUCTURE AND DEVELOPMENT OP LOXOSOMA.

305

each side of the oesophagus. Even at a late stage, each pos-
sesses its own opening to the exterior, although early in their
development the two tubes become connected by a median
bridge of subepithelial epiblast cells. Eventually their lumina
disappear, and they are either partially or completely converted
into the nervous tissue of the brain, Kowalevsky inclining to
the latter hypothesis. The manner in which the median com-
missure connecting the two halves of the ganglion is developed
has not been satisfactorily followed. In the young Den ta-
li um the brain is a transversely elongated structure in front
of the oesophagus, consisting of a central fibrous core sur-
rounded by ganglion-cells. The similarity between this
ganglion and the brain of the larva of L. Leptoclini or the
ganglion of the adult Loxosoma, is so striking that I have
reproduced Kowalevsky's fig. 92 in my own fig. 23 for com-
parison with figs. 50 and 51 of the brain of the larva of
L. Leptoclini, and with fig. 16 of the ganglion (sub-
oesophageal) of the adult L. Tethyse. When it is remem-
bered that neither of these organs in Loxosoma has hitherto
received the interpretation suggested in this paper, it will
probably be admitted that the histological characters of the
structure which is undoubtedly the brain of Dentalium,
confirm very strongly the view that the above-mentioned
organs of Loxosoma are similarly nervous in character.

The pedal ganglia of Dentalium develop as paired thicken-
ings of the epiblast at the sides of the foot, not far behind the
oesophagus. They originate quite independently of the cephalic
ganglion, with which a secondary connection is established ;
and this, as Kowalevsky points out, is in all probability cha-
racteristic of the development of the Mollusca in general.1

In both Loxosoma and Dentalium the brain originates
by a process of invagination, the suboesophageal ganglia (pedal)
as paired thickenings of the epiblast, and not, like the brain,
as invaginations, whilst the connection between the two por-

1 In the same way, in Lumbricus trapezoides (Kleinenberg), the
brain and ventral cord originate independently and become secondarily con-
nected (Balfour, * Comp. Emb.,’ vol. ii, p. 336).

306

SIDNEY ¥. BARHER.

tions of the nervous system is secondarily established. The
existence of two cephalic invaginations in Dentalium in no
way impairs the comparison which has just been instituted
between it and Loxosoma, where a single invagination
occurs. Nothing could show this more clearly than the
manner in which the brain develops in some Pteropods
(Hyaleacea), described by Fol; this may be explained by the
quotation of a few lines from Balfour (f Comp. Emb.,’ i,
p. 227) : “ A disc-like area appears in the centre of the velum,
which soon becomes nearly divided into two halves. From
each of these there is formed by invagination a small sack.
The axes of invagination of the two sacks meet at an angle on
the surface. The cavities of the sacks become obliterated ;
the sacks themselves become detached from the surface, fuse
in the middle line, and come to lie astride of the oesophagus.”
This mode of the development of the brain forms a most
instructive transition from Dentalium to Loxosoma. In
Dentalium the two halves of the brain are separate in-
vaginations, extending inwards for a considerable distance
parallel to the long axis of the embryo. In the Pteropods
just described, the axes of invagination are inclined to one
another on the surface, their apertures being situated close
together ; and by supposing the invagination in the latter case
to encroach on the middle line, the two apertures would fuse,
and we should have precisely the same arrangement as that of
Loxosoma represented in fig. 48.

It seems to me that if we once admit the nervous nature of
the parts which I have described as such in Loxosoma, the
identification of the surfaces in the Entoprocta is no longer
a matter of doubt. The dorsal organ, if a ganglion at all,
must be supra-oesophageal, from its position, from the mode of
its development, and from the fact that it is provided with
paired eyes (doubtless true cephalic eyes inherited from an
ancestor common to the Trochosphere group, and not
accessory eyes like those developed on other parts of the body
in many Ectoproctan larvae).

Caldwell (34) has recently suggested a view of the body plan

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 307

of the Polyzoa, based on an investigation of the metamor-
phosis of Actinotrocha; he states that “the dorsal surface
in Polyzoa is indicated as in Phoronis by the line between
mouth and anus/5 and gives the following explanation of his
views on the larvae : “ The larvae of Brachiopoda and Polyzoa I
regard as modified from the Trochosphaere by the earlier
attainment of the relation of the ventral surface which in
Phoronis is only accomplished during the metamorphosis.”
In Actinotrocha, the larva of Phoronis, the surfaces
correspond to those of ordinary Trochospheres, but their
relations become much distorted by the formation (by invagi-
nation) of a large ventral sac between mouth and anus,
subsequently everted as the “ foot,” into which the alimentary
canal passes. The Trochosphere bend of the alimentary
tract is thereby exactly reversed, the “ foot ” becoming the
body in which the gut forms a (J -shaped tube with a dorsal
flexure. Caldwell’s suggestion is that this dorsal flexure of
the alimentary tract has become already acquired during the
larval condition of Polyzoa and Brachiopoda. In the
developmental history of Loxosoma, however, there is not
the slightest trace of the existence of a flexure of the alimen-
tary canal towards the dorsal surface. We have already
compared the larva of Loxosoma with that of Dentalium,
an admitted Trochosphere; we have found that in both
forms the mesoblast develops as two lateral masses near the
surface containing the mouth and the anus. Further, the
comparison already instituted between the dorsal organ of
Loxosoma and the brain of Dentalium, between the sub-
oesophageal ganglion of the former and the pedal ganglia of
the latter, seems to leave no doubt that the dorsal organ of
Loxosoma represents its prseoral lobe, and as such a part of
the dorsal and not of the ventral surface. As an additional
indication of the surfaces, I must insist on the position of the
apertures of the nephridia between mouth and anus, and in
front of the (supposed) suboesophageal ganglion. On Cald-
well’s hypothesis, we must regard the adult ganglion as the
brain, and the curious result follows that the head-kidneys

308

SIDNEY F. HAEMEE.

open dorsally on the praeoral lobe, between the brain and the
mouth !

Lankester (45 and 49) has adopted Caldwell's explanation of
the surfaces of the Polyzoa as the most probable which has
been suggested ; the buccal shield of Rhabdopleura, and
therefore, one may conclude, the large epistome of Loxo-
soma, being considered possibly a representative of the mantle
area.

Lankester's earlier opinion (7 and 8) on the relations of the
surfaces of the Polyzoa is well known, the epistome being
homologised with the foot, and the foot-gland with the shell-
gland of Mollusca. This opinion has of course been re-
nounced in accepting Caldwell's view of the Polyzoa.

Balfour (28) has urged two difficulties against the view of
the homology of the foot-gland (undoubtedly the same organ
in both the adult and the larva of Loxosoma) with the
Molluscan shell-gland. These difficulties are — (i) the ciliation
of the foot- gland of the larva ; (ii) its relation to the velum.
The sucker of the larva of the Entoprocta is not, however,
invariably ciliated ; it is indeed surrounded by a circlet of stiff
hairs, probably tactile like the sense hairs of the adult Loxo-
soma or of the larval Pedicellina; but it seems quite
natural to suppose that special tactile organs would be advan-
tageously localised in the neighbourhood of any apparatus
commonly used for the temporary attachment of its possessor
o foreign objects. The presence of these sensory hairs, quite
similar to those occurring in other regions of the body, need in
itself form no valid objection to Lankester’s (former) view.
The shell-gland of Mollusca is not used for attachment, and
does not require a development of these tactile hairs.

The objection which refers to the position of the velum
appears to me of a more serious nature. The ciliated ring of
Loxosoma has generally been regarded as homologous with
the velum of Trochospheres, and on this supposition the
ciliated furrow running along the inner border of the ring (in
the larva of Loxosoma) and produced by means of the oral
groove into the (Esophagus, corresponds with the similar ciliated

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 309

area which Hatschek (17) finds to be invariably present behind
the velum in Trochospheres.

The shell-gland of Mollusca is commonly situated more
posteriorly than the sucker of Polyzoa; it is not impossible
that if it were once used for purposes of temporary attachment,
it would be most conveniently situated in the centre of the
aboral surface, in order to allow the cilia connected with the
mouth to assume the position most favorable for nutritive
purposes. The shell-gland might thus travel somewhat forward
as a result of its new function, the cilia concerned in nutrition
and locomotion alike becoming confined simultaneously to the
ventral surface.

Hatschek (17) has pointed out that in Polygordius the
ciliary apparatus (velum and oral cilia) does not originate as
a closed ring ; it appears first on the ventral side, and subse-
quently completes itself dorsally. This mode of development
is also characteristic of some Gastropod Trochospheres, as
shown by Bobretsky (48) . Thus in the phylogenetic history
of the Entoprocta, it is possible that when the sucker was
situated more posteriorly, the velar ring was at first completed
on its anterior side ; that as the sucker travelled forwards, it
reached a point where it interrupted the velum dorsally ; and
that finally, when it had arrived at a subcentral position, the
posterior union of the two halves of the velum took place
behind it, thereby increasing the efficiency of the nutritive
cilia, when the animal was fixed. It is worth noting that in
Dentalium, Kowalevsky (loc. cit.) describes the shell-gland
as originating during the gastrula stage, whilst in Loxosoma
the sucker similarly develops exceedingly early, and is func-
tional whilst the brain, for instance, is still quite rudimentary.
Although this early appearance of the sucker in Loxosoma
may be merely due to the fact that it is an important embryonic
organ, the period of its development, as well as its striking
similarity to the young shell-gland of Mollusca, renders
possible the view of its homology with the latter. The
constancy of the occurrence of the shell-gland in larval Mol-
lusca and of the sucker in embryos of Poly zo a (Ento-

310

SIDNEY F. HARMER.

procta and Ectoprocta alike) indicates the probable phylo-
genetic importance of these structures in the two groups.

Both the Molluscan foot and the Polyzoan epistome are
ventral outgrowths of the body situated between mouth and
anus, and with each of these organs is connected a pair of
suboesophageal (pedal) ganglia. The foot in Gastropod
Trochospheres (Bobretzky, No. 48) bears a striking resem-
blance to the epistome of Loxosoma ; it forms a conspicuous
prominence immediately behind the mouth (see fig. 106, vol. i,
of Balfour’s ‘ Comp. Embryology’). It is separated from a
region bearing the anus by a deep transverse groove, which on
the supposition that the epistome represents the foot of Mol-
lusca would correspond with the vestibular invaginations of
the larval Loxosoma or with the median depression behind
the epistome in the adult.

Professor Lankester has kindly furnished me with a proof of
his article “ Polyzoa,” shortly to appear in the ‘ Encyclopaedia
Britannica.’ In considering the phylogeny of the class, Lan-
kester has adopted the view that the Entoprocta do not in
reality exhibit archaic characters, but that they have been
derived from forms like Phoronis with a hippocrepian lopho-
phore, a large coelom, and a dorsal flexure of the gut. There
is, however, really no evidence that the circular Entoproctous
lophophore is a special modification of the horse-shoe-shaped,
and it appears to me more natural to consider it as replacing
the larval ciliated band, which probably represents the similar
structure in Trochospheres. My conclusions with regard to
the surfaces of the larva are diametrically opposed to those of
Lankester, and I must again refer to the characters of the
nervous and excretory systems as indicating the relations of
the Entoprocta to other animals.

On the assumption that Loxosoma is not an archaic form,
it is necessary to show that the complicated ontogeny of the
Ectoprocta has been here replaced by a direct development,
whereby the enigmatical larval organs of these forms have
been lost.

It appears to me, however, that the development of the

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 311

Entoprocta is not in reality direct. The larva, it is true,
possesses many organs which have their homologues in the
adult ; but I have already explained my reasons for believing
that it does not itself become mature, and that the permanent
individuals are produced indirectly by budding. Lankester’s
theory affords no explanation of the occurrence of the dorsal
organ, a structure which is entirely confined to the larva.

Hatschek (17) has exemplified by means of two diagrams
(p. 106) the homologies between a Pedicellina larva and that
of an Annelid; he points out that the only difficulty in the
comparison is the fact that the “ Scheitelplatte” of the former
has never been identified, although he suggests that this
structure may be represented by the sucker. His diagram is,
as I believe, perfectly correct in most of its essential features : —
in the identification of the surfaces, in the relations of the
parts of the alimentary canal, in the position of the ciliated
ring, of the head-kidney, of the subcesophageal ganglion, and
of the pole-cells of the mesoblast. The only characters in the
diagram to which I take exception are (i) the identification of
the sucker instead of the dorsal organ, as the “Scheitelplatte,”
or brain; and (ii) the opening of the nephridium into the body
cavity by a ciliated funnel (which Hatschek supposed to be
also the case in the Polygordius larva).

Leaving entirely out of consideration the ciliated ring, the
sucker or foot-gland, and the epistome, all of them structures
whose homologies are uncertain, the Entoprocta, adult and
larval, remain essentially modified Trochospheres. The
existence of paired nephridia, corresponding to the head-kidney
of Annelid larvae, their inner ends situated in the primary
body cavity, and their external apertures in front of the
suboesophageal ganglion, seems to me of especial importance
in the consideration of this view. The absence of anything
corresponding to a ciliated funnel, opening into a secondary
body cavity, is again of importance. The identity of the gut-
flexure of the Entoprocta with that of Trochospheres has
not been disproved by Caldwell, who has failed to bring
forward a single argument against the ordinarily received view

VOL. XXV. NEW SER.

X

312

SIDNEY F. HARMEK

of the surfaces of the Polyzoa, hut has based his conclusion
entirely on a study of Phoronis. When we add to these
facts the position of the nerve-ganglia and of the pole-cells of
the mesoblast, I consider that it is impossible to resist the
conclusion that Phoronis in no way gives an explanation of
the anatomy of the Polyzoa.

Before passing to a consideration of the larvae of the
Ectoprocta it will be necessary to examine the statements
of Uljanin (5), van Beneden (1), and Barrois (13, 29, and
33), with regard to the metamorphosis of Pe dice 11 in a.
Uljanin’s statements have already been shown by Barrois (13)
to be based on the supposition that adult calyces fallen from
their stalks were larvae which were commencing to undergo
their metamorphosis. Van Beneden's account and those of
Barrois differ in fundamental particulars, and although it is
conceivable that there may really exist a great difference in the
post-larval stages of various species, it is very possible that van
Beneden’s account is incorrect. According to this observer
we have in Pedicellina a metamorphosis of the simplest
kind ; the larva fixes by its sucker, this extremity growing out
into a stalk, and a circlet of tentacles appears on the inner side
of the ciliated ring, which is subsequently atrophied. If this
account is correct (and it is not impossible) the first individual
of the colony is the fixed larva.

Barrois’s account (33) of the post-larval changes (in the
Entoprocta in general) is the following : — (i) The larva fixes
by its oral face ; (ii) the vestibule sinks to the interior, and
becomes divided into several portions : (a) an “ inferior’' por-
tion corresponding to the outer part of the vestibule, that car-
rying the ciliated ring; this gives rise to the foot-gland,
permanent in Loxoso m a, temporary in Pedicellina; ( b ) a
“ superior” portion, the deeper part of the vestibule ; and (c)
a middle portion, forming a mass of globules filling the stalk.
The portion described as b remains attached to the alimentary
tract, which twists round (the details of this process are not
given), so that the concavity of its flexure is ultimately directed
towards the free surface of the fixed larva instead of towards

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 313

the attached oral face, as was previously the case. The ecto-
derm of the free surface (aboral of larva) now becomes
thickened (“ labial thickening’''), and subsequently invaginated
to meet the part of the vestibule connected with the reversed
gut. Into this portion of the vestibule the labial “ invagina-
tion” opens, and forms the outer part of the permanent ves-
tibule. The oral face of the larva thus becomes the aboral side
of the adult, and vice versd, and the foot-gland of the adult
Loxosoma is not homologous with the sucker of its larva.
The sucker and the dorsal organ are both derived from the
two primary layers of the embryo, but are simply larval sense
organs of no morphological importance ; they disappear after
the metamorphosis.

By comparing these somewhat remarkable statements with
figs. 13, 14, and 15 of PI. II of Barrois’s earlier memoir (13),
it has appeared to me possible to suggest an explanation of the
“ metamorphosis,” at least as probable as that of Barrois him-
self. I would suggest (1) that the post-larval changes consist
in a process of budding ; (2) that the surfaces of the adult are
in every way homologous with the similar surfaces of the larva,
so that the foot-gland of the former (Loxosoma) is the
actual homologue of the sucker of the latter ; (3) that the
cf labial thickening” of the fixed larva is the epiblastic thicken-
ing which probably gives rise to the whole of the vestibular
cavity of the first individual formed by budding ; (4) that the
changes of the larval vestibule and alimentary tract described
by Barrois consist in their atrophy, as in Loxosoma, de-
scribed above, after the fixation, the hypoblastic cells of the
alimentary tract probably giving rise to the stomach and
other endodermic (?) tissues of the bud, as would seem to be
the case according to Barrois’s own description; (5) that the
sucker and the dorsal organ, like the other purely larval struc-
tures, atrophy during the budding.

If the post-larval changes are not to be regarded as a meta-
morphosis, but as consisting in the production of a new indi-
vidual, it is conceivable that the larva might just as well fix
itself by its oral as by its aboral face, whereas, if it becomes

314

SIDNEY F. HARMER.

adult, it is almost inconceivable that it should not attach itself
by the end which bears the sucker. On the theory that the
process is a mere metamorphosis, the fact that the larva should
fix by its oral face, and that it should be thereby obliged to
develope a new vestibule, mouth, and anus at its primitively
aboral end, is an occurrence of the most extraordinary nature.
The metamorphosis of a more or less bilaterally a symmetrical
Echinoderm larva to the radiately- arranged adult form is not
a parallel case. The sexually mature Pedicellina has pre-
cisely the same general arrangement of its organs as its larva,
whose most direct way to become adult would consist in the
development of a stalk and budding stolon at the aboral end,
with the possible atrophy of the dorsal organ. The whole life
cycle of the Entoprocta appears to me to consist in a division
of labour, leading to an alternation of generations ; the indi-
viduals produced from the egg having given up the sexual
function, but having retained many of the ancestral features
which favour a free pelagic existence; the individuals produced
by budding having, on the contrary, retained the generative
function, but having acquired a sessile habit. The organisa-
tion remains, however, fundamentally the same in larvae and
adults alike, and both kinds of individuals are capable of the
production of buds, one of the most characteristic features of
the Polyzoa. Barrois’ account probably shows that the larval
Pedicellina produces a single bud instead of two, as in
Loxosoma. PI. II, fig. 14 (loc. cit.), represents a stage some
time after the fixation. In this individual can be distinguished
a disc of attachment, and connected with it a cylindrical body,
at whose apex is a young vestibule with its tentacles. The
proximal portion probably represents part of the larva, which
is fixed by its oral face ; the larval organs have degenerated,
but the bud is already well developed. The nature of this
process is here less obvious than in Loxosoma owing to the
absence of any constriction separating the bud from the larva.

Of all the Ectopr octa, with the details of whose development
we are acquainted, Cyphonautes, the larva of Membrani-
pora, appears most easily comparable to that of the Ento-

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

315

procta. The most important feature of Cyphonautes is the
fact that the alimentary canal is well developed in the larva ;
broadly speaking, it has the same arrangement as that of the
Entoprocta, and is obviously functional during larval life,
as can be concluded from the presence of food particles in the
stomach, as indicated by Repiachoff (27). In the paper just
referred to, Repiachoff has given figures of Cyphonautes,
which I have been able to understand, partially at any rate,
by means of a short description in the ‘ Zool. Anzeiger ’ (22)
(the longer paper is in Russian). It i3 pointed out in this
paper that the “ bud ” described by Hatschek (14) in
Cyphonautes consists of two parts:1 (i) an invagination,
composed of columnar cells opening into the anterior side of the
vestibule at its extreme ventral edge (fig. 24, zc ) ; this portion
is surrounded by a ring of cilia ; (ii) of a mass of cells, cor-
responding to the “ Entodermknospe ” described by Hatschek
in Pedicellina, situated on the dorsal side of the invaginated
part, and apparently (from another figure of RepiachofFs)
giving rise to the first polypide of the colony. It appears to
me not impossible, from this description, that the first part,
the invaginated sac, corresponds to the epiblastic invagination
which forms the dorsal organ of Loxosoma or Pedicellina.
Ey reflecting the anterior portion of the body of an Ento-
proctan larva into the vestibule, as Hatschek has suggested
(although with a different identification of the dorsal organ),
the aperture of the invagination might come to lie within the
area of the latter, and the involuted sac (zc, fig. 24) may thus
possibly represent the dorsal organ, which, instead of develop-
ing to a functional ganglion, remains in its embryonic con-
dition as a mere rudiment. The mass of cells between the sac
zc in Cyphonautes and the sucker on the dorsal side of the
larva, appears from Repiachoff’ s fig. 2 to be concerned in the
larval budding; and it is important to notice that in the figure
it is in intimate connection with the epiblast of the anterior
ventral portion of the vestibule, but not with that forming the

1 See fig. 24, in which are reproduced the essential details of Repiachoff’s
Taf. i, fig. 1.

316

SIDNEY F. HARMER.

outer body wall of the larva, lending support to the view that
the anterior portion of the body is here reflected into the
vestibule. If, therefore, the invaginated sac corresponds to
the brain of Loxosoma, the budding regions in Cypho-
nautes and Loxosoma will also correspond (by imagining
an eversion of part of the vestibule in the former). In pro-
ducing a single bud, however, Cyphonautes probably re-
sembles the larval Pedicellina.

From RepiachofFs account (18) of the development of
Tendra zostericola, one of the Cheilostomata, it may
be seen that the early processes are not unlike those of
Loxosoma. At the morula stage there is a narrow blastocoel,
the cells of the dorsal side being smaller than those of the
ventral side. The latter are now invaginated, forming an
archenteron, which loses its connection with the exterior. The
account of the development may from this point be carried on
from No. 21 in the list of references, aided by figures in the
Russian paper already referred to. The epiblast thickens
ventrally, and is invaginated as the “ Saugnapf ” (shown in a
later stage ( v ) in fig. 22, a reproduction of RepiachofFs PI. ii,
fig. 5). In front of this “sucker/’ which must not be con-
fused with the larval foot-gland, appears a stomodaeum which
meets the archenteron, and the latter gives off anteriorly at
the point of union with the oesophagus, an outgrowth (hypo-
blastic) which segments off as a mass of cells compared to
Hatschek’s “ Entodermknospe.” Just in front of the
oesophagus is an invagination of the epiblast (fig. 22, #), pro-
bably (as I conclude from the figure) corresponding to the
invaginated sac of Cyphonautes; whilst dorsally occurs an
epiblastic thickening ( y ) representing the foot-gland of the
larval Loxosoma.

If this account of RepiachofFs is correct (it is doubted by
Barrois, No. 23), it seems to me that it forms an important
clue to thestructure of Cyphonautes and of other Ectoproctan
larvae. (I am unable to say what view Repiachoff takes of the
subject in his Russian paper.) The explanation which I would
suggest is the following. The curvature of the alimentary

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 317

canal is the same as in Loxosoma, the stomodseum being
homologous in the two cases; Repiachoff’s “sucker” ( v ,
fig. 22) represents the vestibular invaginations of Loxosoma,
as has been pointed out by Barrois (33). The identity in
general relations between these structures in Loxosoma
after their median fusion (fig. 45, v) and the “sucker” of
Repiachoff’s Tendra (fig. 22, v) is in fact very apparent.

The hypoblast cells budded off from the front of the archen-
teron represent, on my view, not Hatschek’s dorsal organ,
but the cells which I believe to be proliferated from the larval
stomach (long after the development of the dorsal organ) and
to enter into the composition of the bud. The cephalic
ganglion of Loxosoma would in this case be represented
by the epiblastic invagination x of fig. 22, the relations of
this to the budding organ being possibly different from that of
the same structure in Cyplionautes, although this does not
absolutely follow from the figure.

Barrois (23), in describing the development of Lepralia
unicornis (Cheilostomata), confirms Repiachoff’s account
of the invagination of the archenteron, and further calls
attention to two lateral mesoblastic bands at the sides of the
blastopore. In a subsequent paper on the metamorphosis of
Ectoprocta (33), Barrois has suggested, as mentioned above,
the homology of his “ internal sac,” Repiachoff’s “ sucker,’’
previously described by Barrois himself (13) as “ stomach,”
with the vestibular invaginations of Entoprocta, although
his identification of other parts appears to me unsatisfactory.
During the metamorphosis, the larva is attached by the
evagination of this “ internal sac,’’ and a complicated process
takes place, resulting in the formation of the first polypide of
the colony. From the organ described in Balfour’s ‘ Text-
Book’ as the “ ciliated disc,” and which one might suppose to
correspond to the foot-gland of Loxosoma (this view is con-
troverted by Barrois) develops an invagination which forms
the polypide. The eversion of the “ internal sac ” during
fixation does not seem to me to preclude the possibility of its
homology with the vestibular invaginations of Loxosoma;

318

SIDNEY F. HARMER.

the bud, as one may assume the young polypide to be (Barrois
takes the view that it is not a budding process), in this case
occupies a position which is by no means unlike that of the
young bud of Cyphonautes and of those of Loxosoma,
that is to say, it occurs on the dorsal side of the ciliated ring.

It is possible that in many Ectoprocta the dorsal organ, and
even the foot-gland, may be completely lost at all stages of
development, as if Barrois is correct in stating that the poly-
pide (possibly only its tentacle sheath and the organs con-
nected with it?) develops from the "ciliated disc,” it is
obvious that the latter cannot entirely correspond with the
sucker of Loxosoma, but must represent in addition part of
the region situated more anteriorly in the latter.

It seems to me that a consequence of the facts known with
regard to the development of Membranipora and Tendra
must be an inquiry as to the validity of the assumption that
the Cheilostomata form the most modified of the groups of
the Marine Polyzoa, a conclusion, I believe, based mainly on
the characters of the aperture of the zocecium or "cell.”

It is now necessary to consider the possible relationships of
the Polyzoa with Phoronis and the Brachiopoda.

Caldwell has stated that " the identity of the Phoronis larva
up to the formation of the nephridia, and before the outgrowth
of the anal region, with the Trochosphsere type of Hatschek
is complete,” and as far as the larval characters go, I am ready
to admit that there is probably a real affinity between Phoronis
and the Polyzoa. From the commencement of the meta-
morphosis of Actinotrocha, however, it seems to me that
every step taken towards the attainment of the adult condition
is a step away from the Polyzoa.

The permanent nephridium of Loxosoma is the head-kidney
which forms a provisional excretory organ in Actinotrocha
and other Trochospheres. Thus the adult Loxosoma, in
the absence of the " secondary body cavity ” and of the
ciliated funnel of the nephridium, and in the retention of the
" primary body cavity ” of the larva, has remained at a grade
which is passed by Phoronis long before the adult condition

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 319

is reached. The larval Phoronis resembles Loxosoma in
the possession of a ventral flexure of the alimentary canal, the
dorsal gut-flexure of the adult being entirely unrepresented in
the Entoprocta. Thus the epistome of Polyzoa is ventral,
and the ganglion developed in its neighbourhood is to be homo-
logised with the pedal ganglion of Molluscs rather than with
the brain of Phoronis.

The vascular system of Phoronis is entirely unrepresented
in the Entoprocta, whilst the asymmetrical generative organs
of the former differ markedly from the simple paired gonads
of the Entoprocta. The four divisions of the alimentary
canal, characteristic, according to Caldwell, of Phoronis and
Brachiopoda alike, are not represented in the Polyzoa,
whilst the nervous system, which in Phoronis consists of a
plexus of fibres and cells lying outside the basement membrane
of the epidermis, and concentrated in certain definite regions,
is in striking contrast with that of Loxosoma. It seems to me,
in fact, that a comparison between the adult Phoronis and
Loxosoma is exceedingly difficult, whereas in many of the
Trochosphere characters of the larvae it is easy to point to
parallels in the two genera.

It is not altogether impossible that the invagination occur-
ring on the ventral side of Actinotrocha, and subsequently
evaginated to form the foot or body of the adult Phoronis, may
be represented by the vestibular invaginations of Loxosoma.
In the Ectoprocta, according to the researches of Barrois,
fixation universally takes place by the evagination of the
“ internal sac” (the homologue of the vestibular invagina-
tions). If instead of losing their stomach at an early period
of development the Ectoproctan larvae retained this organ,
and became adult, it would not be impossible for the gut to
pass into the evaginated “ internal sac,” and thus to reverse its
former curvature, as in the case of Phoronis. I believe that
the question of the relationship of the Polyzoa to the
Brachiopoda can only be satisfactorily resolved by a re-
newed study of the embryology of the latter. Caldwell has
laid special stress on the resemblances between Brachiopoda

320

SIDNEY F. HAEMEE.

and Phoronis, and if any affinity between the two does really
exist, it follows that the Brachiopoda are not totally unre-
lated to the Polyzoa, although the question still remains
whether the latter approach most closely the Trochospheres of
Chsetopoda, Mollusca, Phoronis, or Brachiopoda.
Judging by the descriptions we at present possess, the Bra-
chiopod larva is much further removed from the Trocho-
spheral type than those of any of the other groups we have
considered. If the points in which it differs from the typical
Trochosphere are such as imply a real dissimilarity, and are
not merely secondary larval characters, then it follows that the
similarities between the Brachiopoda and the Polyzoa have
no phylogenetic significance. The character of the lopho-
phore has always formed one of the main reasons for associat-
ing together the Polyzoa and the Brachiopoda, and its
arrangement in the form of a horse-shoe in Argiope (for
instance) and the Phylactolmmata has usually been con-
sidered a proof of tlie affinity of the two groups. If, however,
the Phylactolaemata are not so primitive as the Ento-
procta, the hippocrepian character of their lophophore cannot
be regarded as an archaic feature, but has been secondarily
acquired. It seems to me, however, that a comparison between
the developmental history of the Polyzoa and that of the
Brachiopoda serves to show a considerable difference in the
lophopliores of the two groups. In Argiope ( vide Oehlert
and Deniker’s abstract of Kowalevsky’s Russian paper. No.
40), after the mantle lobes have turned forward and the ten-
tacles have begun to make their appearance, the young
Brachiopod has a striking superficial resemblance to an adult
Loxosoma. But by comparing the latter with its larva, we
find that its lophophore replaces the larval ciliated ring, and
that the head is outside the circlet of tentacles. In Argiope,
however, the mantle lobes are developed entirely behind the
cephalic segment which bears the eyes, and probably repre-
sents the head, so that when they bend forwards after fixation,
the part of the body bearing the eyes remains within the
mantle cavity, a condition entirely different from that of

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 321

Loxosoma. The tentacles of Argiope are formed from the
dorsal lobe of the mantle. The Brachiopod larva is stated not
to possess the head-kidney so characteristic of ordinary Tro-
chospheres.1

Shipley (41) after pointing out the importance of the
absence of the head-kidney in Brachiopoda, has come to the
conclusion that there is no close relationship between these
animals and the Polyzoa, and further that they are not
nearly allied to P boron is. My observations do not warrant
me in criticising Caldwell’s statements on this head, although
it does not appear to me improbable that the similarities
between Brachiopoda and Phoronis may be superficial.
The position of the cephalic segment with the eyes inside the
mantle cavity during the metamorphosis of Argiope, seems,
however, to render Caldwell’s view that the prseoral lobe in
Brachiopoda persists in part as the epistome, as in Pho-
ronis, not impossible.

Brooks’ observations (16) on Lingula probably show that
the larvae of this form are more easily reducible to the
Trochosphere type than those of the hinged Brachiopods.
It appears to me that the curvature of the alimentary canal of
Lingula is the same as that of a Trochosphere, and
consequently directed in the opposite direction to that of
Phoronis. It is hardly necessary to criticise Brooks’ remarks
on the similarity between the larvae of Brachiopoda and
Loxosoma, based, as they are, on what I regard as an entirely
mistaken view (due to Barrois) of the archetype from which
the Polyzoan larvae are derivable.

One of the main difficulties in the comparison between the
Polyzoa and other forms is the great uncertainty of the rela-
tionships of the Polyzoa inter se. Lankester (45) has adopted
the view that Rhabdopleura and the Phylactolaemata are
allied to Phoronis and consequently are more archaic than
the Entoprocta; the main reason for this view is their posses-
sion of a body cavity, a structure certainly not present in the
Entoprocta in the same form. From the researches of
1 This statement probably requires further proof.

322

SIDNEY F. HARMER.

Caldwell on Phoronis, and of Hatschek on Polygordius (17)
and Echiurus (25), it appears possible that the ancestral
Trochosphere-like form was provided with a well-developed
body cavity, a structure represented also in some Molluscan
Trochospheres. If this is the case, we must suppose that in
most Trochospheres the formation of the body cavity has been
postponed till after the commencement of the free existence.
The Polyzoa are in this case probably descended from a
Trochosphere-like organism, in which a postponement of the
formation of the body cavity had become normal. It is possible
that the Entoprocta have never advanced beyond this stage,
whereas the Ectoprocta, in other respects more modified,
have retained the habit of developing a body cavity. That
this is really the interpretation of the body cavity of the
Ectoprocta appears to me, however, in the highest degree
doubtful, and in no known Ectoproctan ontogeny does a
coelom develop in the embryo by an enterocoel formation or
by any means which can be considered a modification of this
process, as in Actinotr ocha.

The larvae of the Ectoprocta are not provided, as far as is
known, with a body cavity, a structure which appears first in
the adult. In all probability the primary individual of the
Ectoproctan colony is developed as a bud on the larva, and the
wide difference in structure obtaining between the adult and
the larva is quite comprehensible on this hypothesis. It
seems to me that the body cavity of the Ectoprocta is a
structure which is developed solely in relation with the adult
condition, and that it is not directly comparable to that of
other animals. The suggestion that the coelom of Ecto-
procta is a space developed between gut and body wall for
the purpose of permitting the retraction of the lophophore
with its tentacles into the cavity of the zooecium appears to me
not unreasonable. In the Gymnolsemata (see Yigelius,
No. 46) the body cavity is a space traversed by irregular
strands of connective tissue, and is as a general rule lined
neither on the side of the gut nor of the body wall by an
epithelial layer (Flustra). In the Phylactolsemata, how-

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 323

ever (Nitsche, 4), it is in many parts lined by a distinct
ciliated epithelium. It is not impossible, however, to regard
this as merely an advance on the condition found in F lustra,
as the result of an increased differentiation of certain cells
situated between body wall and gut, instead of supposing that
it represents an archaic character, which we see in various
stages of degeneration in other Polyzoa. On this hypothesis,
the cilia would have arisen in order to provide a means for the
circulation of the body fluids. Lankester has described a body
cavity in Rhabdopleura, although it is far less pronounced
than in the Oymnolsemata. The question arises, how far
can Rhabdopleura and Cephalodiscus (35 and 49) be
considered archaic forms ? In the characters of the budding
processes, these genera show a very slight amount of complica-
tion, Cephalodiscus being solitary, and producing paired
buds from the end of the stalk, whilst the branching of R h a b d o-
pleura is of a simple nature compared with that of many
Ectoprocta. In certain features these forms are more
modified than the Entoprocta; it is probable that the
arrangement of their tentacles is less primitive than in Loxo-
soma; the existence of a mesoblastic skeleton (vide Lankester)
and the character of the tu barium are again features in advance
of those of the Entoprocta. The occurrence of a pair of
eyes in the adult Cephalodiscus is a fact of considerable
interest; the eyes are borne on an organ which is stated to be
an ovary, and M’Intosh (35) suggests that this will be found to
be the nature of the dorsal organ of the Entoprocta! In
Rhabdopleura no retraction of the tentacles is possible,
and the body cavity can hardly have the origin which has been
suggested for that of the Ectoprocta.

It will be difficult to determine the relation of Rhabdo-
pleura to the other Polyzoa until we are able to learn
something of the embryology of this form.

As a result of the foregoing considerations, it appears to
me that in order to understand correctly the phylogeny of the
Polyzoa, we must derive the group from a Trochosphere-
like organism, and that the Entoprocta have remained

324

SIDNEY F. HARMER.

permanently at a grade hardly higher than that of this
hypothetical ancestor. Loxosoma shows itself the most
primitive genus by the fact that it forms no colonies, by the
greater development of the brain in the larva, and by the
invariable presence of a foot-gland in the buds, if not in the
adult. Rhab do pleu’ra and Cephalodiscus on the one hand,
and the Ectoprocta on the other, have probably branched
olf independently from the Entoproctan stem. In certain
features the Gymnolsemata show themselves more archaic
than the Phylactolsemata; this is perhaps the case with
the “ body cavity,” whilst embryology, as far as we under-
stand the facts, seems certainly in favour of this hypothesis.
The occurrence of statoblasts, as well as the great differentia-
tion of the funiculus, again prove that the Phylactolsem at a
are in some of their characters at least as much modified as
the Gymnolsemata. In the structure of the nervous system,
the former are, however, perhaps more archaic than the latter;
in Alcyonella, Nitsche (4) describes a large sub oesophageal
ganglion sending off nerves to the lophophore, and connected
in front of the (Esophagus by a thin commissure containing,
however, no ganglion cells.

The similarity in many important features between Loxo-
soma and a Molluscan larva has already been pointed out,
and of all organisms with whose ontogeny we are acquainted,
the Mollusca come nearest to the Polyzoa. The com-
parison between the development of the brain and pedal
ganglia in Dentalium and the Hyaleacea, and the same
structures in Loxosoma, may again be called attention to.
The ciliated ring of the Entoprocta is very probably the
velum, and the foot-gland the shell-gland. Allman’s sug-
gestion that the buccal shield of Rhabdopleura (and hence
the epistome of Loxosoma) may represent the mantle area
of Lamellibranchs cannot be accepted, if we are to identify
the dorsal organ as the brain. If it is necessary to look for a
mantle cavity in the Entoprocta, it seems to me that we
may possibly find it in the vestibule. In this case the tentacles
would represent, not gill filaments of Lamellibranchs, but

STRUCTURE AND DEVELOPMENT OF LOXOSOMA.

325

rather the tentacular structures developed at the edges of the
mantle lobes in some of the latter.

The Rotifera, as has frequently been suggested, in many
points of their structure resemble the Polyzoa, and more
especially the Entoprocta: many of these similarities have
already been indicated by the Hertwigs (31). Salensky (15)
has drawn attention to the possible homology of the “ antennae ”
of Rotifers with the posterior sense organs of Loxosoma
crassicauda. Histologically, the resemblances between Ro-
tifera and Entoprocta are striking: in the characters of
their nervous system, muscular fibres, terminations of the
excretory organs, and so on. Perhaps the similarities between
the two groups are less striking than those obtaining between
the Entoprocta and the Trochosphere larvae of Molluscs
and Chaetopods, but the fact remains that the Rotifera and
Polyzoa being alike groups which have persisted in the
Trochosphere stage, must necessarily show a considerable
number of similarities to one another in various features.

The affinity between the Polyzoa and the Brachiopoda
is probably much less close than that between the former and
the Rotifera and the Trochospheres of Mollusca and
Chsetopoda, so that the association of the Polyzoa with
the Brachiopoda as Molluscoidea appears to me un-
natural, although I do not at all deny the possibility of
certain affinities between these two groups. It is, further, not
impossible that Phoronis may (through Actinotrocha) to
a certain extent connect the Polyzoa with the Brachio-
poda, although not in the way that Caldwell supposed.

Summary of Results.

1. Species investigated : Loxosoma crassicauda, L. pes,
L. singul are (?), L. Tethyse, and L. Leptoclini, new
species. The last two alone were studied embryologically.

2. The adult Loxosoma possesses a large suboesophageal
ganglion, dumb-bell-like in shape, hitherto described as some
part of the generative apparatus. The ganglion is developed

326

SIDNEY F. HARMER.

from the ectodermic floor of the vestibule in the bud, and is
connected with a well- developed system of peripheral nerves,
ending in sense-cells bearing tactile hairs, situated on various
parts of the body. The adult has no supraoesophageal
ganglion.

3. The excretory organ (paired) probably begins with a
flame-cell : it is composed of a few large perforated cells,
their walls filled with greenish-yellow granules, and it opens
into the vestibule by an aperture (on each side) between the
ganglion and the oesophagus. The nephridia are completely
homologous with the head-kidneys of Trochosphere larvae.

4. No hermaphrodite individuals were discovered in any
species of Loxosoma or Pedicellina. Previous statements
as to the hermaphroditism of Loxosoma are partly due to
an erroneous interpretation of the ganglion as the testes. It
is by no means improbable, however, that the same individual
develops ovaries and testes at different seasons. Schmidt's
accounts of the generative organs are not correct.

5. In L. Leptoclini and in P. echinata the ova are small,
and the embryo is supplied with nutriment from the glandular
epithelium of the brood-pouch. In L. Tethyse this is not
the case, but the ovum is large, and during maturation
devours various cells which play the part of a vitellarium.

6. After the formation of the gastrula the blastopore pro-
bably remains in the position of the anus, a stomadaeum being
formed anteriorly. The mesoblast arises mainly from two
pole-cells situated at the sides of the blastopore.

7. The ff dorsal organ” is not hypoblastic in origin; it is
formed first as a thickening, and then as an unpaired invagi-
nation of epiblast. The invagination closes, a layer of fibres
is formed on its deep side, and a pair of large eyes with well-
developed lenses appears on the organ. The “ dorsal organ”
is not a budding structure, but is the supra-oesophageal
ganglion.

8. Between mouth and anus is formed a pair of invagina-
tions of epiblast, their cavities soon fusing medianly. These,
the “ vestibular invaginations,” remain permanently open,

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 327

their cavity widening. They form the deeper part of the
vestibule, the suboesophageal ganglia arising as a pair of thick-
enings of their floor. The wings of the crescent-shaped brain
meet the suboesophageal ganglia at the sides of the oesophagus,
thereby establishing a complete circumoesophageal nervous
ring.

9. After the commencement of the free life (L. Leptoclini)
no fixation was observed ; the larva, however, developed a pair
of buds similar to those of the adult. These buds are situated
at the sides of the dorsal organ, but are quite distinct from it;
they are visible as epiblastic thickenings long before the
embryo is ready to be hatched.

10. The stomach, before the larva becomes free, seems to
bud off paired lateral bands of cells (L. Leptoclini). During
the free life these increase in number, and the cells of
the stomach themselves divide up during an atrophy of its
lumen. This, no doubt, indicates the approaching death of
the larva, after the buds have reached maturity. Some of the
hypoblast cells, whose origin has been just described, probably
form the endodermic tissues of the bud.

11. The Entoprocta, larval and adult, are true Trocho-
spheres, possessing a ventral flexure of the alimentary
canal, no true body cavity, and a pair of head-kidneys.

12. The nervous system of Loxosoma develops in almost
exactly the same manner as that of Dental ium, in which the
brain arises by invagination (paired), the pedal ganglia as thick-
enings of the epiblast ; the connection between these two
independently developed parts is secondarily set up as in
Loxosoma.

13. The metamorphosis of the Ectoprocta is to be re-
garded as a process of budding. Cyphonautes and Tendra
probably supply important evidence with regard to the
derivation of the larvae of Ectoprocta from those of
Entoprocta.

14. The Entoprocta, being true Trochospheres, have certain
affinities with Actinotrocha ; there is every evidence that
the direction of the gut-flexure differs from that of the adult

VOL. XXV. NEW SER.

Y

328

SIDNEY F. HARMER.

Phoronis, although it is identical with that of Actino-
trocha. The line between mouth and anus is ventral in
Polvzoa, but dorsal in Phoronis.

15. The affinity of the Polyzoa to the Brachiopoda is
probably more doubtful than to Phoronis, the larvae of the
two groups differing in many important characters ( e.g . the
absence (?) of head-kidneys in the larval Brachiopod).

16. The nearest allies of the Polyzoa (i.e. of the Ento-
procta) are the Trochosphere larvae of Mollusca or
Chaetopoda and the adult Rotifera.

17. The Entoprocta form the most archaic of the groups
of the Polyzoa, their relations to the other forms being,
however, somewhat doubtful.

Note. — Fewkes (42) has recently described a new larva,
belonging to an unknown adult, and regarded by him as being
of great importance in forming a connecting link between
Polyzoa and Annelids. In spite of the assertion of Fewkes
that “ there is no doubt that it is a larval Annelid,” I venture
to believe that it has no importance in the sense ascribed to it
by the American zoologist, and that the animal in question is
simply a very characteristic larval Loxosoma. The relations
of the ciliated ring in Fewkes’ larva are precisely those of the
Entoprocta; there are two eyes, no doubt indicating the
presence of a dorsal organ (whose cilia are described) ; the
anus opens on an anal cone; the stomach has orange granules,
the situation of the mouth not having been observed with com-
plete certainty, although believed to occur just within the
ciliary ring, which can be reflected over the oral face of the
larva.

These features, together with the figures given, leave no
doubt in my mind that the larva described by Fewkes is merely
that of a Loxosoma.

List of Papers referred to.

1. P. J. van Beneden. — “ Rechercbes sur l’Anatomie, la Physiologic et le
Developpement des Bryozoaires (Pedicellina),” * Nouveaux Mem. de
l’Acad. Roy. des Sciences et Belles Lettres de Bruxelles,’ T. xix
1845.

STRUCTURE AND DEVELOPMENT OP LOXOSOMA. 329

2. W. Kefersteih. — “ Untersuchungen iiber niedere Seethiere viii,

“Ueber Loxosoma singulare, gen.et sp. n. * Zeits. f. wiss. Zool.,’
Bd. xii, 1863, S. 131.

3. A. Kowalewsky. — “ Beitrage zur Anatomie und Entwickelungsgeschichte

des Loxosoma Neapolitanum, sp. n.,” ‘Mem. de l’Acad. Imper.
des Sci. de St. Petersbourg,’ viie Ser., T. x, No. 2, 1866.

4. H. Nitsche. — “ Beitrage zur Anatomie und Entwickelungsgeschichte der

Phylactolaemen Siisswasserbryozoen,” * Arch. f. Anat. und Physiol.,
Jahrg., 1868, S. 465.

5. B. Uejanin. — “ Zur Anatomie und Entwickelungsgeschichte der Pedi*

cellina,” * Bull, de la Soc. Imp. des Naturalistes de Moscou,’ T. xlii.
Part i, 1869, p. 425.

6. H. Nitsche. — “ Beitrage zur Kenntniss der Bryozoen II, “ Ueber die

Anatomie von Pedicellina echinata;” ‘ Zeits. f. wiss. Zool.,’ Bd.
xx, 1870, S. 13.

7. E. B. Laxkester. — “ Remarks on the Affinities of Rbabdopleura,”

‘ Quart. Journ. of Mic. Sci.,’ vol. xiv, 1874, p. 77.

8. E. R. Laxkester. — “ Observations on the Development of the Pond-

Snail,” ‘Quart. Journ. of Mic. Sci.,’ vol. xiv, 1874, p. 365.

9. K. Mobitjs. — “ Ein Beitrag zur Anatomie des Brachionus plicatilis.

Mull., eines Raderthieres des Ostsee,” ‘ Zeits. f. wiss. Zool.,’ Bd. xxv,

1875, S. 103.

10. H. Nitsche. — “ Beitrage zur Kenntniss der Bryozoen,” V ; ‘ Zeits. f.

wiss. Zool.,’ Suppl. Bd. xxv, 1875, S. 343.

11. 0. Schmidt. — “Die Gattung Loxosoma,” ‘Arch. f. mik. Anat.,” Bd. xii

1876, S. 1.

12. C. Vogt. — “Sur le Loxosome des Phascolosomes (Loxosoma phas-

colosomatum),” ‘Arch, de Zool. Exp. et Gen.,’ T. v, 1876, p. 305.

13. J. Barrois. — ‘ Recherches sur l’Embryologie des Bryozoaires,’ Lille,

1877,

1 4. B. Hatschek. — “Embryonalentwicklung und Knospung der P e d i c e 11 i n a

echinata,” ‘Zeits. f. wiss. Zool.,’ Bd. xxix, 1877, S. 502.

15. M. Saleh sky. — “Etudes sur les Bryozoaires Entoproctes,” ‘Ann. des

Sci. Nat.,’ 6e Ser., Zool., T. v, 1877, No. 3.

16. W. K. Brooks. — “ The Development of Lingula and the Systematic

Position of the Brachiopoda,” * Chesapeake Zool. Lab., Sci. Results,’
Session 1878, Baltimore, p. 35.

17. B. Hatschek. — “Studien zur Entwicklungsgeschichte der Anneliden,”

* Arb. a. d. Zool. Inst, zu Wien,’ Bd. i, 1878, S. 277.

18. W. Repiachoff. — “Ueber die ersten Entwicklungsvorgange bei Tendra

zostericola,” ‘ Zeits. f. wiss. Zool.,’ Suppl. Bd. xxx, 1878, S. 411.

330

SIDNEY F. HARMER.

19. Brehm’s Thierleben. — Zweite Auflage, Bd. x, Leipzig, 1878, S. 180.

(Die niederen Thiere von Oscar Schmidt.)

20. 0. Schmidt. — “ Bemerkungen zu den Arbeiten iiber Loxosoma,” ‘ Zeits. f.

wiss. Zool.,’ Bd. xxxi, 1878, S. 68.

21. W. Repiachoff. — “Zur Embryologie der Tendra zostericola,” ‘Zool.

Anzeig.,’ ii Jahrg., 1879, No. 20, S. 67.

22. W. Repiachoff. — “ Bemerkungen iiber Cyphonautes.” ‘ Zool. Anzeig.,’

ii Jahrg., 1879, No. 39, S. 517.

23. J. Barrois. — “ Memoire sur la Metamorphose des Bryozoaires,” ‘ Ann.

des Sci. Nat. (Zool.),’ 6e Ser., T. ix, 1879 — 1880, No. 7.

24. L. Joliet. — “ Organe segmentaire des Bryozoaires Endoproctes,” ‘Arch.

de Zool. Exp. et Gen.,’ T. viii, 1879 — 1880, p. 497.

25. B. Hatschek. — “ Ueber Entwicklungsgeschichte von Echiurus,” ‘ Arb.

a. d. Zool. Inst, zu Wien,’ Bd. iii.

26. T. Hincks. — ‘ A History of the British Marine Polvzoa,’ 2 vols., London,

1880.

27. W. Repiachoff. — ? (Russian) Odessa, 1880.

28. F. M. Balfour. — ' A Treatise on Comparative Embryology,’ 2 vols.,

London, 1880 — 1881.

29. J. Barrois. — “Metamorphose de la Pedicelline,” ‘Comptes rendus de

l’Acad. des Sci.,’ T. xcii, 1881, p. 1527.

30. J. Fraipoxt. — “ Recherches sur l’Appareil Excreteur des Trematodes et

des Cestodes,” ‘Archives de Biol.,’ T. ii, 1881, p. 1.

31. O. axd R. Hertwig. — 4 Die Coelomtheorie,’ Jena, 1881.

32. W. J. Yigelius. — “ Catalogue of the Polvzoa collected during the Dutch

North-Polar Cruises of the ‘ Willem Barents,’ ” ‘ Niederland Arch. f.
Zool.,’ Suppl. Bd. i, 1881—1882, 3 Lief.

33. J. Barrois. — “ Embryogenie des Bryozoaires,” ‘ Journ. de l’Anat. et de

la Physiol.,’ T. xviii, 1882, p. 124.

34. W. H. Caldwell. — “Preliminary Note on the Structure, Development,

and Affinities of Phoronis,” ‘ Proc. Roy. Soc.,’ No. 222, 1882, p. 371.

35. W. C. M’Ixtosh. — “Preliminary Note of Cephalodiscus, a New Type

allied to Rhabdopleura,” ‘ Ann. and Mag. of Nat. Hist.,’ 5th Ser.,
vol. x, 1882, p. 337.

36. A. Kowalevsky. — “ Iitude sur l’Embryogenie du Dentale,” ‘ Annales du

Mus. d’Hist. Nat. de Marseille, Zool.,’ T ler, 1882 — 1883, Mem. No. 7.

37. A. C. Haddon. — “ On Budding in Polyzoa,” ‘ Quart. Journ. of Mic. Sci.,’

vol. xxiii, 1883.

38. E. R. Laxkester. — Article “ Mollusca,” ‘ Encyclopaedia Britannica,’ 9th

Ed., vol. xvi, 1883.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 331

39. P. Mayer. — “ Einfache Methode zum Aufkleben mikroskopischer

Schnitte,” ‘ Mitt. a. d. Zool. Stat. zu Neapel,’ Bd. iv, 1883, p. 521.

40. Oehlert and Deniker. — “ Observations sur le Developpement des

Brachiopodes ” (abstract of Kowalevsky’s Russian paper), * Arch. d.
Zool. Exp. et Gen.,’ iie Ser., T. i, p. 57.

41. A. E. Shipley. — “On the Structure and Development of Argiope,”

‘ Mitt. a. d. Zool. Stat. zu Neapel,’ Bd. iv, 1883, S. 495.

42. J. W. Fewkes. — “A New Pelagic Larva,” ‘American Naturalist,’ vol.

xviii, 1884, p. 305.

43. J. Fraipont. — “ Le rein cephalique du Polygordius,” ‘Arch.de Biol.,’

T. v, 1884, p. 103.

44. S. P. Harher. — “ On a Method for the Silver Staining of Marine Ob-

jects,” * Mitt. a. d. Zool. Stat. zu Neapel,’ Bd. v, 1884, S. 445.

45. E. R. Lankester. — “ A Contribution to the Knowledge of Rhabdopleura,”

* Quart Journ. of Mic. Sci.,’ vol. xxiv, 1884, p. 622.

46. W. J. Vigelius. — “ Morphologische Untersuchungen iiber Flustra Mem-

branaceo-truncata Smitt,” * Biolog. Centralblatt,’ Bd. iii, No. 23
S. 705.

47. A. Lang. — “Die Polycladen (Seeplanarien),” ‘Fauna and Flora des

Golfes von Neapel,’ xi Monographic, Leipzig, 18S4, pp. 674 — 679.

48. N. Bobretsky. — “Studieu fiber die embryonale Entwickelung der Gas-

tropoden,” ‘ Arch. f. mik. Anat.,’ Bd. xiii, 1877, S. 95.

49. E. R. Lankester. — Article “ Polyzoa,” ‘ Encyclopaedia Britannica,’ 9th

Ed., vol. xix, 1885.

EXPLANATION OF PLATES XIX— XXI,

Illustrating Mr. S. F. Harmer’s Paper “ On the Structure and
Development of Loxosoma.”

Reference Letters.

ac. Cells at the apex of the vestibule in L. Leptoclini. afg. Aperture
of foot-gland, age. Aperture of gland-cell. at. Lateral expansion of foot.
an. Anus. b. Bud. bl. Blastopore, blc. Blastoccel. br. “ Dorsal organ ”
(= Brain), cd. Ciliated duct of nephridium. cr. Ciliated ring. ct. Con-
nective-tissue cell. ctp. Large cells in tentacles of Pedicellina. cut.
Cuticle, ean. External aperture of nephridium. ebp. Glandular epithelium

332

SIDNEY F. HARHER.

of brood pouch, el. Epithelial cell of ectoderm, em. Embryo, ep. Epiblast.
epst. Epistome. f Foot. fbr. Fibrous part of brain (or “ dorsal organ ”).
fg. Foot-gland, fgd. “ Duct ” of foot-gland, fl. Flagellum of flame-cell.
ga. Ganglion of adult, gac. Ganglion-cell. gas. Ganglion of posterior sense
organ of L. crassicauda. gc, gc1, and gc2. Gland-cell. hst. Hypoblastic
outgrowth of stomach, hyp. Hypoblast. I. Parasitic Infusorian, int. Intes-
tine. 1. “ Liver-cells ” of stomach. 1st. Lateral wing of stomach, m.
Mouth, me. Mantle cavity, rues. Mesoblast. mus. Muscle-cell. n. Nucleus.
nv. Nerve. o. Eye. ee. (Esophagus. cec. (Esophageal commissure, og.
Oral groove, ot. Position of ovary or testis, ov. Ovary, ovd. Oviduct.
p. External aperture of female generative organs, pm. Pole-cell of mesoblast.
ps. Posterior sense organ of L. crassicauda. rec. Rectum, s. Sucker.
sc. Sense-cell. sg. Position of subcesophageal ganglion of embryo, st.
Stomach, std. Stomodseum. t. Tentacle. tes. Testis, tga. Tentacular
ganglion, v. Vestibule, or vestibular invagination of embryo, va. Aperture
of vestibule. vd. Vas deferens. vm. Vitelline membrane, vs. Vesicula
seminalis. vt. Vitelline body in ovum. z. Junction of stomodamm and
mesenteron of embryo.

PLATE XIX.

Fig. 1. — Loxosoma crassicauda. Calyx, seen from the posterior side
(living) to show the nervous system ; the cilia of the tentacles are not repre-
sented. The figure is combined from numerous sketches of the different parts
of the neiwous system, made from living specimens or from glycerine prepara-
tions. The individual represented has neither buds nor generative organs.
st. Stomach, ga. Ganglion. A full explanation of the figure is given in the
text.

Fig. 2. — L. Leptoclini (new species). An entire animal, from the
anterior side.

Fig. 3. — L. crassicauda. The whole of the posterior ectoderm cells of
the calyx, after treatment with silver nitrate, ps. One of the posterior sense
organs.

Fig. 4. — L. crassicauda. A posterior sense organ, after the action of
silver nitrate, osmic acid, and picro- carmine, ps. is the actual sense cell,
situated at the apex of a rounded papilla formed by three ordinary ectoderm
cells. (From a nearly mature bud.)

Fig. 5.— Pedicellina echinata. A portion of a tentacle, from a pre-
paration treated with osmic acid and picro-carmine and mounted in glycerine.
The tentacle is seen in optical section, el. outer ectoderm of the tentacle.

Fig. 6. — Loxosoma pes. A sense cell in connection with two ganglion-
cells. (From a glycerine preparation.)

Fig. 7. — L. crassicauda. A portion of the edge of the calyx (silver
nitrate, osmic acid, and picro-carmine), showing the apertures {age.) of the

STRUCTURE AND DEVELOPMENT OP LOXOSOMA.

333

gland-cells, and two ganglion-cells {gac.) in connection with their respective
sense cells {sc.).

Fig. 8. — L. crassicauda. Part of the edge of the calyx (living) in
optical section.

Fig. 9. — L. Tethyse. A portion of the stalk, from a glycerine prepara-
tion, previously treated with palladium chloride. The upper half of the figure
shows the ectoderm in surface view, the lower half representing an optical
section of one of the rows of cells.

Fig. 10. — L. crassicauda. Connective-tissue cells, from the side of the
stomach. (From a glycerine preparation.)

PLATE XX.

Fig. 11. — L. crassicauda. A median longitudinal section of an entire
individual ; only the ventral end of the stalk is involved by the section, which
passes through the whole of the alimentary canal, through the ganglion (ga.),
and two of the tentacles {(.). At the base of each of the latter, on its outer
side, is seen a small accumulation of nuclei (ectodermic), representing all that
can be made out in the section of the crumpled edge of the vestibular fold,
which during retraction of the tentacles completely encloses the vestibular
cavity. The animal was killed, during extension of the tentacles, by boiling
corrosive sublimate (a saturated solution in sea water).

Fig. 12. — Pedicellina echinata. A horizontal section of a female con-
taining embryos {em.) in the brood pouch, which is lined by a glandular
epithelium {ebp.) thrown into numerous folds. The oesophagus («?.) and
intestine {ini.), the ganglion (ga.) and the ovaries (ov.) with their ducts {ovd.)
are also represented. The figure was combined from two series of sections.

Fig. 13. — Loxosoma Tethyee. A horizontal section through a male
individual, killed with the tentacles extended in boiling sublimate, tes. Testis.
vd. Vas deferens, vs. Vesicula seminalis.

Fig. 14. — L. Tethyse. Horizontal section of a female, with tentacles
retracted (the figure is combined). Ganglion {ga.), ovaries {ov.), and oviducts
{ovd.) are represented. In the left ovary is indicated the process of the
absorption of several of the primordial ova by the developing ovum. In
addition to this mode of nutrition, the ovum on each side is devouring a
vitelline body {vt.).

Fig. 15. — L. Leptoclini. An advanced bud in nearly median longitu-
dinal section. The ganglion {ga.) is still in intimate connection with the
vestibular diverticulum from which it has been formed.

Fig. 16. — L. Tethyae. A horizontal section of an adult, passing through
the ganglion {ga.), the vesicula seminalis {vs.), and the wide mouth {m.),
opening into the vestibule («?.). In this individual the testes appear to have
atrophied,

334

SIDNEY F. HARMER.

Fig. 17. — L. crassicauda. A nephridium, in the living condition, very
highly magnified (Zeiss, Jj, No. 5 eye-piece). The adult from which the
figure is taken was in the same relative position as that represented in Fig. 2,
and the’nephrid ium corresponding to the right side of the figure was drawn ;
the lower end of Fig. 17, containing the flame-cell {fl .) should lie on the
ventral side of the stomach, the upper end ( ean .) opening into the vestibule,
the median plane of the entire animal being situated to the left of the figure.

Fig. 18. — L. crassicauda. Horizontal section of an adult, through the
epistone ( epst .), the mouth (/».), and the bases of some of the tentacles (tf.).
Only the basal portion of the bud ( b .) on the left side has been represented.

Fig. 19. — L. crassicauda. Surface view of the foot-gland of a young
bud, from a glycerine preparation. The constriction of the groove probably
indicates the separation from one another of the “gland ” and the “duct.”
Fig. 20. — L. Leptoclini. Transverse section through the middle region
of the foot of an adult, al. Lateral expansions of the foot (cf. Fig. 2).
fgd. The “ duct ” of the foot-gland, in reality an open groove.

Fig. 21. — L. Leptoclini. Obliquely longitudinal section through the
foot, passing through the “ gland ” ( fg .), but missing the “ duct.”

Fig. 22. — Tendra zostericola, copied from Repiachoff (27), plate ii, fig-
5 (a median longitudinal section of an embryo). Probable explanation of
Repiachoff’s letters : — o. Mouth, v. Vestibular invagination (cf. fig. 39).
g. Stomach, y. Sucker or foot-gland, e. hypoblastic cells taking part in
the formation of the first bud. x. dorsal organ (?)

Fig. 23. — Dentalium. Transverse section of a young individual (copied
from Kowalevsky, No. 36 in the list of references, pi. viii, fig. 92). br. Brain.
oe. oesophagus, me. Mantle cavity. /. Foot.

Fig. 24. — Cyphonautes. An entire larva (slightly modified from Repia-
choff, No. 27, plate i, fig. 1). Probable explanation of the lettering : — a. Vesti-
bule. ce. (Esophagus, y. Sucker, g. Stomach (containing food particles).
r. Rectum, zc. Dorsal organ (?). x. Epiblastic portion of young bud.
e. Hypoblastic portion of the bud.

PLATE XXI.

With the exception of figs. 27 and 55, all the figures represent actual
sections illustrating the embryology of Loxosoma. Figs. 25 — 59 belong to
L. Leptoclini; Figs. 60 — 62 to L. Tethyae. The sections are all drawn
to the same scale, with the exception of Figs. 54, and 56 — 59, which are more
magnified.

L. Leptoclini :

Fig. 25. — Ovarian ovum.

Fig. 26. — Two-cell stage.

STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 335

Fig. 27. — Drawn living, as seen through the walls of the vestibule of the
adult, vm. Vitelline membrane.

Fig. 28. — A section of an embryo consisting of about eight cells.

Fig. 29. — Blastosphere stage, blc. Blastocoel.

Fig. 30. — Commencement of the invagination ; the blastocoel is almost
obliterated.

Fig. 31. — The invagination has progressed to a considerable extent, but
the blastocoel is much larger than in Fig. 30.

Fig. 32. — A slightly older embryo, pm. Pole-cell of the mesoblast.

Fig. 33. — A similar stage, the section having missed the blastopore and the
pole-cells.

Fig. 34. — The invagination is here far advanced, the blastocoel obliterated.
The blastopore appears to be filled up by one of the pole-cells, which really,
however, lies in a somewhat deeper plane of the section.

Fig. 35. — A nearly median longitudinal section of a stage after the forma-
tion of the stomodeeum, whose position in a neighbouring section is indicated
by the line m. The ventral gut flexure is already acquired ; at the posterior
end are two mesoblast cells.

Fig. 36. — Another section of the same embryo, v. is the commencement
of one of the vestibular invaginations ; og. is the oral groove. The cells
which fill up part of the blastocoel belong in part to one of the lateral walls of
the stomach.

Fig. 37. — A more advanced embryo in median longitudinal section, z.
Junction of stomodseum and meseuteron. s. The sucker, br. The epiblastic
thickening forming the dorsal organ or brain.

Fig. 38. — A stage slightly further advanced in development. The brain
(br.) consists of two layers of cells (neither this section nor Fig. 37 has passed
through the intestine).

Fig. 39. — Obliquely longitudinal section of an older embryo, cutting the
oesophagus ( ce .), stomach (st.), sucker («.), brain (br.), and one of the vesti-
bular invaginations (v.).

Fig. 40. — More advanced than Fig. 39. The section passes at some dis-
tance from the middle line, but parallel to the symmetrical plane of the
embryo, og. Oral groove, v. Vestibular invagination, br. One of the
lateral wings of the brain (compare with fig. 46). st. Wall of the stomach.
mes. Mesoblastic band. The blastocoel contains in addition one or two meso-
blast cells which in the section do not appear connected with the mesoblastic
band.

Fig. 41. — A somewhat similar section, passing obliquely in such a manner
as to cut only the more ventral regions of the embryo, and thereby to avoid
the stomach. The blastocoel contains numerous mesoblast cells, mus. is a
muscle-cell, branched at one end.

Fig. 42. — Another section of the same embryo avoiding the brain, vestibule,

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LUNG-BOOK OF SCORPIO AND GILL-BOOK OF LIMULUS. 339

A New Hypothesis as to the Relationship of
the Lung-book of Scorpio to the Gill-book
of Limulus.

By

E. Ray Lankester, M.A., L.L.D., F.R.S.,

Jodrell Professor of Zoology in University College, London.

The view which I advocated in my essay f Limulus an
Arachnid/ as to the mode of conversion of an external lamel-
ligerous appendage into the hollow lamelliginous lung of
Scorpio no longer commends itself to me. A much simpler
and, as it appears to me, a thoroughly satisfactory explanation
of the relationship of the two organs, has occurred tome in the
course of recent investigations, and is supported also by em-
bryological data. In the essay above referred to I suggested
that by the enlargement of the hollow stigmata connected
with the thoraco-branchial muscles of an ancestral Scorpion,
resembling Limulus in having branchigerous appendages on
the mesosoma, and provided with thoraco-branchial muscles,
the branchigerous appendage might come to lie in the pit or
hollow of the tendon of the thoraco-branchial muscle, and
eventually the hollow might enclose it. The conversion of the
insunken appendage into a hollow air-holding sac and the
corresponding conversion of the surrounding pit into a closed
blood-holding space, involved serious difficulties which were
indeed fatal to the hypothesis.

When I found (f Transact. Zool. Soc./ vol. xi, part x, 1884)
that the muscle (veno-pericardiac) attached to the apex of each
lung-sinus in Scorpio had no possible relation to the thoraco-
branchial muscles of Limulus, but was represented in
Limulus by exactly similar veno-pericardiac muscles, I gave

340

PROFESSOR E. RAY LANKESTER.

up my over-strained hypothesis. I trust that the failure of my
previous suggestion will not unduly prejudice those interested
in this subject against that which I now advance.

Since my memoir f Limulus an Arachnid/ Dr. MacLeod,
of Brussels, has published some speculations on this subject, in
which he puts forward an ingenious theory of his own as to
the mode in which the lamelligerous appendage of a Limulus-
like animal might be converted into the lamelligerous lung-
book of an Arachnid. I will not enter into a discussion of Dr.
MacLeod's hypothesis, but will merely point out that inasmuch
as it deals with not the less modified lung-book of Scorpion,
but the more modified lung-book of the Araneina, it is unsatis-
factorily elaborated. The lung-book of Scorpio has a definite
axis carrying the leaf-like lamellae, and corresponding to the
axis of the same animal's pecten. Such an axis is not present
in the Araneine lung-book, and yet must be accounted for as
a primary structure in any theory as to the origin of these
organs.

The hypothesis which I now put forward is perfectly simple,
and leaves, I think, nothing to be desired. In Limulus, as
in Scorpio, there is on each side of the sternal surface a great
blood-sinus in free communication with the lamelligerous
organs. Let us suppose such to have been the case in the
common ancestor of these two animals, and let us suppose that
this ancestor possessed six pairs of mesosomatic appendages, of
which five were lamelligerous and intermediate in form between
the pectens of Scorpion and the recent Limulus appendage.
Now, suppose that in the Scorpion branch of the family the
mesosomatic appendages grew relatively smaller and smaller,
were no longer locomotor organs, but purely respiratory, and
served for aerial rather than aquatic respiration. If we ima-
gine the four hinder pairs of these reduced appendages to have
taken on in the embryonic condition a very common
trick of growth, viz. an inward growth of invagination, so that
they grew into the Scorpion’s body, turning their outside in,
just as a glove may have all its fingers and part of the hand
turned outside in — then we should have without further alte-

LUNG-BOOK OF SCOKPIO AND GILL-BOOK OF LIMULUS. 341

ration the exact condition of the modern Scorpion’s lung-
book. The appendages growing thus inwards by introversion
(instead of outwards, as is normal) would simply be tucked or
pushed into the great blood-sinus, which would constitute
around each in-grown appendage a veinous sac, just as we
actually find in the Scorpion. The most familiar case of
inward growth taking the place of outward growth is in the
development of the Tsenia-head upon the cyst of the hydatid
in such a form as T. solium. The head develops in a per-
fectly normal way, excepting that it is completely introverted,
pushed outside in, and at a certain stage it becomes everted, as
it should have been from the first, bad it retained in growth
its ancestral relations. The cause of the introverted growth of
the Tsenia-head on its cyst is very probably external pressure ;
in fact, the growing mass of tissue takes the direction of least
resistance, and grows into the cyst instead of out from it.
It is not at all improbable that such a condition of external
pressure might in the first instance have induced the inward
growth, during development, of the lung-books of the Scor-
pion. The development of the young Scorpion goes on at the
present day under very remarkable conditions, actually in the
ovary, the egg-cell never moving from its place of origin until
it has grown into the fully-formed Scorpion ; the pressure of
the ovarian tunic upon the surface of the growing embryo must
he considerable, and is at any rate a possible cause of the in-
vagination of the four hindermost pairs of mesosomatic appen-
dages in the first instance. Probably the lamelligerous appen-
dages of the young Scorpions, of a certain stage in the ancestry
of recent Scorpions, were everted and assumed the normal
relations of appendages as external processes of the body-wall
as soon as the young were born. But as the lamelligerous
appendages were only required to act as aerial respiratory
organs it would be no disadvantage, but positively an advan-
tage, that they should remain in the introverted condition; and
this at last has become the permanent condition. This hypo-
thesis accounts for the fact that the four pairs of lung-books
do not ever appear on the surface of the embryo Scorpion as

342

PROFESSOR E. RAY LANKESTER.

up-standing appendages. They are from the first introverted,
and remain so. It also agrees with the disposition of the cuti-
cularised surfaces of the Scorpion’s lung-book, as seen in the
adult. The cuticularised surface remains in the in-pushed as
it is in the out-growing appendage, the surface in contact with
the air. Each bag-like lamella is introverted together with the
axis of the limb ; and one cannot better picture to oneself the
relative conditions of out-growth and in-growth than by fixing
a kid glove by the margin of its opening to the margin of an
opening of the same size on the outside of a box. The coloured
surface of the kid will represent the cuticle, the fingers the
lamellae, the hand the axis. Thus tbe glove will represent a
lamelligerous appendage, standing up on the ventral surface of
an Arthropod, its cavity communicating with the cavity of the
venous sinus of the animal, as the cavity of the glove does with
that of the box.

Now, without removing the glove, push all the fingers from
their tips inwards into the hand, and then the hand into the
box, so as completely to turn the glove outside in. Thus the
glove will represent the appendage when introverted into the
veinous sinus as in the modern Scorpions.

The tips of some of the introverted lamellae of the Scorpion’s
gill-book have aquired laterally, but not in every part, an
attachment to the wall of the veinous sac into which, they have
pushed their way. These attachments and the relation of
blood-space, air-space, and cuticle in the lung-lamellae of
Scorpio are figured in the 'Trans. Zool. Soc.,’ vol. xl, 1885.

On Spermatogenesis in the Rat.

By

Herbert H. Brown,

University College, London.

With Plates XXII and XXIII.

The following paper is the result of an investigation which
I have made during the past year, in the Physiological Labo-
ratory at University College, upon the spermatogenesis of the
Rat, which, owing to the large size of its spermatozoa, and
especially of the “ middle piece,” presents peculiar advantages
for the purpose. Although minor points of difference exist
(in the relative length of the “ middle piece ” of the sper-
matozoon and in the shape of the “ head ”) the process is
apparently in all essential points identical with that which
occurs in other mammals, and hence may be taken as a type
of “ mammalian spermatogenesis.”

Methods of Research. — I have studied the process of
spermatogenesis by means of sections, and by teased prepara-
tions.

(1) Sections prepared by the paraffin-shellac method from
the testis gradually hardened in alcohol, i. e. by being placed
in alcoholic solution of gradually increasing strength. The
sections were prepared from small pieces of the organ, stained
in bulk, by immersion in Kleinenberg’s alcoholic hsematoxylin
solution for about three hours, the excess of stain being removed
by acidulated alcohol, or by prolonged immersion (for a week)
in a very dilute watery solution. From sections stained with

VOL. XXV. NEW SER. Z

344

HERBERT H. BROWN.

hsematoxylin the history of the process and the structure of
the nuclei can be made out.

(2) Sections stained with gold. Small pieces of the fresh
testis were soaked in chloride of gold solution, 1 per cent., for
one hour, after previous immersion in lemon-juice or dilute
formic acid, and exposed to the direct sunlight of midsummer
in distilled water acidulated with acetic acid, until the reduc-
tion of the gold was complete. Then the pieces of tissue were
carefully and gradually dehydrated with alcohol, and sections
prepared by the paraffin-shellac method. These preparations
show in particular the protoplasmic structures and the outlines
of the cells, the nuclei being entirely unstained and appearing
like vacuoles; thus they present a marked contrast to the
haematoxylin-stained sections.

(3) Sections stained with osmic acid, prepared by soaking
small pieces of the fresh testis in osmic acid solution, 1 per
cent., for two days, washing with water, and dehydrating carefully
with alcohol. Then the sections were prepared by the paraffin-
shellac method, and mounted in balsam.

(4) Teased osmic acid preparations. Small pieces of fresh
testis were soaked in osmic acid solution 1 per cent, for two
days, and small pieces of tubules were broken up with needles
in glycerine and water.

From these teased preparations the development of the
spermatozoa themselves can be best studied.

Nomenclature.1 — I shall first describe the different cell-
elements contained in a tubule, and give them the names
which I propose to adopt in this account, and then trace out
what I consider to be the history of the development of the
spermatozoa.

1 The question of nomenclature presents some difficulty, since so many differ-
ent names have been given to the same elements by different observers, which
leads to confusion in the mind of the reader; consequently I have, at the
suggestion of Professor Lankester, avoided the use of such general terms as
“ spermatoblast,” “spermatocyte,” &c., and have substituted simple descrip-
tive expressions, descriptive of the appearance or function of the elements of
the tubule. I may here mention that 1 am much indebted to Professors Schafer
and Lankester for their kindness in offering suggestions and advice.

ON SPERMATOGENESIS IN THE RAT.

345

In a section stained with haematoxylin tubules are seen, cut
more or less transversely, and presenting different appearances
according to the stage of development of their contents.
Since the process of development of spermatozoa is a con-
tinuous one, it would be possible to take any one stage as a
starting-point for description ; but it is, on the whole, more
convenient to start with the stage represented in fig. 1, in
which a crop of spermatozoa is fully formed and ready to leave
the tubule.

A tubule in this stage (fig. 1) consists of four layers of
seminal elements, with a basement membrane formed of
flattened cells, and these four layers correspond to four genera-
tions.

The most external layer immediately within the basement
membrane consists of cells, the nuclei of which are all in the
resting condition.

Of these nuclei there are three kinds represented in fig. 1
corresponding to three classes of cells.

(1) There are large pale nuclei, the diameter of which is
about 18 /a, each containing a distinct round nucleolus, and
being bounded by a definite nuclear membrane (fig. 1, e). In
this stage some of these nuclei are seen resting upon the base-
ment membrane, while others are seen extending between the
cells of the second layer, and here and there one is found
among the cells of the third layer. These nuclei belong to
supporting cells, each of which serves for the support of a
group of spermatozoa during their development. The proto-
plasm of these cells forms a sort of network upon the base-
ment membrane, in the meshes of which the other cells of the
outer laver are contained, while from the inner extremitv of
the nucleus a protoplasmic process extends towards the sper-
matozoa in the lumen of the tube. These cells appear to be
constant among Vertebrata; they have received various names
from different investigators, and have had very different func-
tions assigned to them.

(2) Besides these supporting cells there are a considerable
number of small cells containing oval nuclei, which stain

346

HERBERT H. BROWN.

darkly with hsematoxylin and present the ordinary appearance
of resting nuclei ; they contain an irregular coarse chromatic
network embedded in a stroma which stains less darkly, and
are bounded by a nuclear membrane (fig. 1, b). These I shall
call growing cells.

(3) The other cells in the outer layer, which might easily
be overlooked, are much fewer in number than those last-
mentioned, and their nuclei are larger, somewhat paler, and
more homogeneous in appearance, the chromatic substance
being diffused in a very fine network throughout the nucleus
(fig. 1, a). These appear to me to be the cells from which all
the other elements of the tubule, with the exception of the
supporting cells, are derived, and I shall therefore call them
spore-cells. Probably they are the direct descendants of the
primitive male ova.

The cells of the second layer are large, and contain large
spherical nuclei, which are all in the kinetic condition. At
this stage the nuclei form for the most part a single row, but
here and there a cell is seen containing two nuclei, one being
internal to the other. These correspond to the growing cells
of the outer layer of the preceding generation, which have
now attained a considerable size. They are destined to divide
by karyokinesis into groups of cells which ultimately become
spermatozoa. They are in fact growing cells which have nearly
finished growing.

The third layer (fig. 1, c) is composed of smaller cells, three
or four deep, with spherical nuclei which are pale, containing
only a small amount of chromatin. These cells have been
called spermatoblasts, spermatocytes, &c., but since each cell
is destined to develop into a spermatazoon, I shall call them
simply young spermatozoa, or young spermatozoa
with spherical nuclei.

The fourth layer is composed of spermatozoa which are just
ready to leave the tubule. Between the heads of the sperma-
tozoa and the cells of the third layer, there are numerous
irregular darkly-stained granules1 (fig. 1, x), each granule

1 These bodies are the “ seminal granules ” which have been so often

ON SPERMATOGENESIS IN THE RAT.

347

being surrounded by a small amount of protoplasmic material.
The dark granules are not derived from the destruction of
nuclei, but make their appearance in the protoplasm of the
developing spermatozoa at a certain stage of their develop-
ment, and are cast off, together with a small amount of unaltered
protoplasm, when the development is nearly completed. They
appear to consist of a mixture of albuminous and fatty
material, since in osmic acid preparations their place is taken
by a cluster of minute black granules (fig. 15).

A very different appearance is presented by sections prepared
by the chloride of gold method (figs. 12, 13, 14). A stage of
development corresponding to fig. 1 is represented by fig. 12 ;
in this preparation the nuclei are entirely unstained, and
resemble clear vacuoles, but the protoplasmic structures and
cell-outlines are rendered very conspicuous. The large growing
cells of the second layer are seen to contain large granules —
the “accessory corpuscles” of Henson — which are darkly
stained by the reagent (fig. 12, b"), and in the small cells of
the outer layer similar but smaller bodies are seen. The
young spermatozoa which form the third layer, also each
contain an accessory corpuscle, which at this stage is embedded
in the protoplasm at the inner part of the cell (fig. 12, c).
The fully formed spermatozoa (fig. 12, d) show an obvious
division into three parts, head, body or middle piece, and tail.
The tail is entirely unstained, but the middle piece contains a
spiral filament which is darkly stained, and consequently very
conspicuous. It winds in a close spiral round a slightly tinted
core, which is continuous with the tail of the spermatozoon.

noticed ; they are produced, not by the destruction of nuclei, but from the
protoplasm of the developing spermatozoa, from which they separate off at a
late stage of their development. They are of great interest, since they
appear to represent the polar globules of the ovum, and their separation
possibly means the separation of the female element from the
spermatozoa. They are, I believe, constant in mammalia ; although owing
to the shortness of the middle piece of the spermatozoon in most animals
e.g. the dog, rabbit, man, their separation cannot be made out with such
distinctness as in the case of the rat.

348

HERBERT H. BROWN.

Dr. Heneage Gibbes1 has observed a spiral filament in the
spermatozoa of several animals, e. g. horse, guineapig, and
bull, which presents a somewhat similar appearance to that
which I have just described; he considered this to correspond
to the so-called spiral filament of the newt’s spermatozoon,
which is an undulating filament attached to the spermatozoon
by a fine membrane, which acts as a mesentery ; but it is
difficult to see much resemblance between the spiral filament
which is stained by the gold method, and is confined to the
middle piece of the spermatozoon, and the long undulating
filament of the spermatozoon of the newt. I have not yet
looked for this spiral filament in the middle piece of the
spermatozoa of other animals, but will endeavour to do so
during the present summer.

History of the Process of Spermatogenesis. — Hav-
ing thus briefly described the various elements of the seminal
tubule, I shall proceed to trace out continuously the history
of the origin and development of the spermatozoa.

The process is a continuous one, i. e. a new crop of cells
makes its appearance near the basement membrane as each
successive crop of ripe spermatozoa leaves the tubule ; and in
a section of a single tubule four or five generations of cells at
different stages of their development are contained, so that
the entire process of spermatogenesis occupies a corresponding
number of cycles. An entire cycle is represented by figs. 1 to
10. During this period a crop of spermatozoa leaves the
tubule, their place is taken by a similar crop into which the
young spermatozoa with spherical nuclei of the third layer have
developed, the growing cells of the second layer produce by
their division another generation of young spermatozoa, the
small growing cells of the outer layer increase in size and
become the large cells of the second layer, and a new crop of
young growing cells makes its appearance in the outer layer.
Thus, during a single cycle each of the layers described has
moved forwards one stage, and the entire process of develop-
1 ‘Quart. Journ. Mic. Sci.’

ON SPERMATOGENESIS IN THE RAT.

349

ment from the spore-cell to the fully-formed spermatozoa
would occupy four cycles, during which time four fresh gene-
rations of cells would have been produced ; and so the process
goes on.

The first part of this process, i. e. the origin of the new crop
of growing cells, which makes its appearance in the outer layer,
is the most difficult to make out. These cells are first seen at
the stage of fig. 9, and are produced by the karyokinetic division
of larger cells, which are also found in the outer layer (this
division by karyokinesis is represented in fig. 8, a"). The
parent cells appear to be derived from the spore-cells by a
process of division by budding, and not karyokinesis, but it is
difficult to feel certain about this. The spore-cells apparently
increase in size, and divide by a process of budding, for this
seems to be the explanation of an appearance such as is repre-
sented in fig. 7, a', as if a small outgrowth made its appearance
from one part of the nucleus, increased until the two parts
were about equal in size, and then separated off. Of the two
cells which result from this division one divides by karyokinesis
and produces growing cells, but the other remains in the
resting condition as a spore-cell, destined to repeat the process
in the following cycle, and thus perpetuate the production of
spermatozoa in the tubule.

During the time in which a new crop of small-growing cells
has been produced, the growing cells of the previous generation
have been increasing in size, and now, since the new cells have
appeared between them and the wall of the tubule, come to
form the second layer. The manner in which this growth takes
place will be understood if they are followed through the series
represented by PI. XXII,1 figs. 1 — 10, b, b' , and fig. 1, b". In
fig. 1 these cells are all in the resting condition, and their nuclei
present the ordinary appearance of resting nuclei, but very
soon they begin to pass into the kinetic condition, the nuclear
membrane disappearing and the chromatin becoming converted

1 Figs. 3, 8, 9, and 10 are drawn on a somewhat smaller scale than the
others.

350

HERBERT H. BROWN.

into an irregular skein of filaments (fig. 2, b'). In this con-
dition they increase in size without dividing, and gradually
leave the wall of the tubule, until by the division of the spore-
cells and formation of a new crop of cells between them and
the basement membrane, they come to form the second row
(fig. 8, b '). By the time the stage of fig. 1 is reached the nuclei
of these cells have attained their full size, but the protoplasm
continues to increase in amount. The nuclei are spherical and
large (diam. 10 fi), and present the appearance represented in
the figure (fig. 1, b"). A large granule — the accessory cor-
puscle— which stains darkly with chloride of gold, is embedded
in the protoplasm near the nucleus (fig 12, b"). Even at the
stage of fig. 1 a cell is occasionally seen containing tw’O nuclei,
one being placed internal to the other ; apparently all the cells
when their growth is completed divide into two, though the
nuclei do not as yet show any further karyokinetic changes, so
that at a later stage the cells are arranged in a double row.

Sometimes a nucleus may be seen apparently in the act of
dividing, and cells containing two nuclei become more frequent
(fig. 5, b") ; and now the growing cells having reached their full
development, divide by karvokinesis, the phenomena of which
may be very well observed, and give to a tubule in this stage
a very characteristic appearance (PI. XXII, fig. 6, b'"). The
astral and diastral forms can be readily recognised, and, viewed
in profile, the achromatic filaments may also be seen. (Fig. 6
represents the appearances presented by these cells under a
magnifying power of about 750 diameters.) In chloride of
gold preparations the accessory corpuscle appears to become
broken up during karvokinesis ; perhaps it forms the accessory
corpuscles of the young spermatozoa, and some small granules
wdiich stain slightly with hgematoxvlin and appear to be pro-
duced during karvokinesis may represent this process.

It appears that the cells which result from the karyokinetic
division of a growing cell do not separate from one another
entirely, but remain at first united in groups by a very small
amount of the protoplasm of the mother cell. The outlines
of the cells of which these groups are composed cannot be

ON SPERMATOGENESIS IN THE RAT.

351

made out from sections stained with hsematoxylin, but in
chloride of gold preparations the cell outlines are rendered very
distinct (PI. XXIII, fig. 14, c ). The nuclei are spherical, of a
diameter of 5 n, and are faintly stained by hsematoxylin ; they
possess a nuclear membrane, and a scanty network of chromatin.
Between the nucleus and protoplasm of the cell a clear space
makes its appearance, fitting like a cap over part of the nucleus,
and in the neighbourhood of the clear cap a small chromatic
granule is usually to be seen (PI. XXII, figs. 8, 9, c ).

Stained with chloride of gold, the young spermatozoa presents
an appearance such as is represented in fig. 14. There is a
small accessory corpuscle attached to the nucleus, which
subsequently becomes separated from it by a small vesicle
which seems to be derived from the accessory corpuscle (fig.
14, e).

A few minute fatty granules are seen dotted about in the
protoplasm of these cells, in osmic acid preparations, and the
accessory corpuscles are also to be seen (fig. 15). It is
difficult to make out clearly what is the origin of the clear
space which is seen in haematoxylin preparations between
part of the nucleus and the protoplasm of the cell ; apparently
it corresponds to the small vesicle seen in chloride of gold pre-
parations, attaching the accessory corpuscle to the nucleus,
which may be increased in size by the action of alcohol on the
fresh cell.

The groups of cells are separated from one another for a
short time by bundles of spermatozoa, which extend between
them (fig. 9), but when the spermatozoa have left the sup-
porting cells, it becomes difficult to make out a separation into
groups, and there appears to be a layer of cells, three or four
deep, between the growing cells and the spermatozoa, for now
only the thin protoplasmic strands of the supporting cells
extend inwards between the groups, to the layer of granules in
which the heads of the spermatozoa are now embedded (PI.
XXII, fig. 10). And now the stage of fig. 1 is again reached. In
this stage the young spermatozoa present a different appearance ;
they are apparently free in the tubule, having been set at

352

HERBERT H. BROWN.

liberty by the disintegration of the original groups. The
nucleus now occupies the outer part of eacli cell, i. e. that
directed towards the wall of the tubule, and the outer part of
each nucleus is covered only by the clear cap. At the same
time the chromatin leaves the substance of the nucleus and
accumulates at the nuclear membrane, and chiefly at its outer
part which becomes thickened, while the nuclear membrane in
other parts seems to disappear, so that the nuclei appear to be
breaking up. It is apparently such an appearance as this,
represented by fig. 1, c, which has led Y. Ebner and other
observers who have investigated the spermatogenesis of the
Rat, to the belief that these cells undergo liquefaction, and
produce the liquid portion of the semen, or serve for the
nutrition of the spermatozoa {vide the account of sperma-
togenesis given by Professor Schafer in Quain’s ( Anatomy/
vol. ii, ninth edition), and the granules of chromatic material
which are found between these cells and the spermatozoa, have
been attributed to the disintegration of nuclei. The accessory
corpuscle leaves the nucleus at this time, and becomes em-
bedded in the protoplasm at the inner part of the cell (fig. 12,
c ), where it remains inactive during the development of the
spermatozoon, and is finally cast off with a residual portion of
the protoplasm, when the process of development is nearly
completed.

The young spermatozoa are free in the tubule for a very
short time only, and they now begin to form groups in con-
nection with the supporting cells. The remainder of their
development takes place in these groups and occupies the
fourth and last cycle.

The manner in which the connection between the young
spermatozoa and the supporting cells is brought about is not
very clear; apparently the young spermatozoa congregate
round the processes of the supporting cells which extend
towards the lumen of the tubule, and become embedded in the
protoplasm, without of course any fusion between the sub-
stance of the young spermatozoa and of the supporting cell
taking place ; but the appearances presented by the supporting

ON SPERMATOGENESIS IN THE RAT.

353

cells and young spermatozoa at this stage (fig. 1) are difficult
to explain.

At this stage some supporting cells are seen which contain
a more or less conical nucleus, situated in the outer layer
upon the wall of the tubule, from which a protoplasmic strand
extends inwards through the third layer of cells as far as the
granules among which the heads of the spermatozoa are
embedded ; but the nuclei of other supporting cells appear to
be pushing their way towards the lumen of the tubule ; they
are elongated in a radial direction, and may be seen between
the second and third layers, and even in the middle of the third
layer of cells, but farther inwards than this I have never seen
them. In many cases the nuclei are seen to be connected to
the outer layer by protoplasm, so that probably this is a
migration of the nucleus and not of the entire cell (figs. 1 and
1, a). At the same time some of the young spermatozoa
appear to move in the opposite direction towards the wall of
the tubule, so as to occupy the position in the outer layer
vacated by the supporting nucleus (fig. 1, a). These appear-
ances at first appeared to me to justify the supposition that
the supporting cells which have finished their work, having
served for the support of the crop of spermatozoa which has
just been discharged, are now in their turn being cast off into
the lumen of the tubule, there to undergo disintegration, and
that the cells which are passing outwards towards the wall of
the tubule are destined to become the new supporting cells,
retaining their connection with their brother cells, which
develop into spermatozoa j so that according to this view the
supporting cell and the group of spermatozoa which it sup-
ports would result from the division of a single cell.

But there are numerous objections to such a view as
this :

1. The young spermatozoa at this stage are apparently free,
and not connected together in groups.

2. It is very difficult to believe that, of a group of cells which
are all exactly alike, and are produced by the karyokinetic
division of a single cell, that which happens to be most ex-

354

HERBERT H. BROWN.

ternal should become a supporting cell, while the others all
develop into spermatozoa.

3. This improbability is rendered still more glaring by a
comparison with the corresponding elements in the testes of the
hedgehog and other animals, for in the hedgehog the nuclei of
the supporting cells and of the young spermatozoa are remark-
ably dissimilar.

4. Nuclei of supporting cells cannot be seen in the lumen of
the tubule, or in the semen from the vas deferens or epidy-
dvmis, and the nuclei which have migrated inwards show no
signs of disintegration.

5. In the stage of development immediately succeeding this
(vide fig. 2) nuclei of supporting cells are seen, which are
quite as large as those in the present stage.

On all these grounds, then, it is impossible to adopt this view
of the origin of the connection between the supporting cells
and the spermatozoa. Probably the migration of the nuclei
into the midst of the young spermatozoa has something to do
with bringing about this connection, and having accomplished
this the nuclei return to the outer layer.

The grouping of the young spermatozoa becomes more evi-
dent as soon as the preceding generation of spermatozoa with
the seminal granules has left the tubule (this stage is repre-
sented by fig. 2). Each group contains about ten or twelve
spermatozoa. At this time a curious appearance is presented
by the supporting cells themselves; large globules, which stain
black with osmic acid, are seen in the protoplasm near the
nuclei; these globules are not simply fat-globules, since they
stain very darkly with gentian violet, and in chloride of gold
preparations become quite black from the great affinity which
they have for the metal (vide fig. 13). Iu sections stained
with hcematoxylin vacuoles are seen in the protoplasm of the
supporting cells, each of which contains a spherical body, which
is slightly stained by the reagent; so that they would appear
to consist of a mixture of fatty and albuminoid material. In
many cases these bodies are found indenting the nucleus of the
supporting cell, and sometimes look as though they were

ON SPERMATOGENESIS IN THE RAT.

355

protruded from the nucleus ( vide PI. XXII, fig. 2, e and

11).

I was at first inclined to attribute the appearance of these
bodies to a process of disintegration of the nuclei and proto-
plasm of the supporting cells taking place at this stage. If
this were the case it would be very difficult to understand how
these cells could be so quickly reproduced, for in the next stage
of development (fig. 3) the nuclei of the supporting cells are
fully developed, and present no signs either of growth or of
degeneration, although a few fatty globules may still be seen
in their protoplasm. Prof. Schafer, however, pointed out to
me that the appearance of these globules is probably due to an
increased nutrition of the supporting cells taking place at this
time, when they are about to enter upon a new phase of
activity, and to serve for the support and probably also for the
nutrition of a fresh crop of spermatozoa ; and this appears
to me to be the most probable explanation. Apparently the
same supporting cell serves for the support of several suc-
cessive crops of spermatozoa. I have not, however, been able
to make out in what manner this reproduction takes place, and
can say little about their life-history.

It is much easier to make out the history of the supporting
cells in the Elasmobranch testis, which contains in a single trans-
verse section every stage of development, from the embryonic
condition to the fully- formed spermatozoa. The result of my
own investigations on the testis of the dogfish is in agreement
with the opinion of aSwaeu and Masquelin, that while the
spermatozoa are derived from primitive male ova,
the supporting cells are descended from follicular
cells, corresponding to the cells of the Graafian
follicle in the ovary. It is probable that the same is the
case in the mammal, but in order to make out the origin of
the supporting cells in the mammal it would be necessary to
trace them back to the embryonic condition.

The function of the supporting cells appears to be in great

1 “ £tude sur la spermatogenese,” par A. Svvaen and H. Masquelin, ‘Archives
de Biologie,’ tom. iv, fasc. 3, 1883.

356

HERBERT H. BROWN.

measure mechanical; they serve the purpose of supporting and
keeping in order the complex testicular epithelium, forming a
sort of sustentacular framework like that of the Mullerian
fibres of the retiua. They serve for the support of, and also
probably convey nutritive material to the young spermatozoa
during their development, and when this is completed they
expel them into the lumen of the tubule.

I must now return to the history of the development of the
spermatozoa, at the point at which I left off to describe the
supporting cells. We have at present reached the stage of
fig. 2 in the fourth cycle.

A young spermatozoon at this stage is somewhat conical in
shape, the rounded apex of the cell, which is directed outwards,
being occupied by the nucleus.

The nucleus has become oval and projects from the cell
protoplasm so that its outer hemisphere is covered only by the
clear cap. As the development progresses the nucleus lengthens
out, and projects more and more from the cell, until finally
only its inner extremity remains embedded in the protoplasm.
The projecting part of the nucleus is covered by the clear cap
which increases with it, but when the hooklike form of the
nucleus is established (fig. 6, d) the clear cap is no longer to
be seen.

As the nucleus increases in length it diminishes in thickness,
and becomes more and more intensely stained by hsematoxyliu ;
there is no chromatic network, but the chromatin appears to
be uniformly diffused throughout its substance. Before long
the nucleus begins to curve (fig. 4) and the hooklike shape of
the head of the spermatozoon is established by the time the
stage of fig. 6 is reached.

The remainder of the process is occupied chiefly by the
development of the body and tail of the spermatozoon, and
can be studied much more satisfactorily from teased osmic acid
preparations, from which the series of drawings (figs. 16 — 24)
is taken. Growing spermatozoa at an early stage corresponding
to fig. 14 are represented by fig. 22, a. They are small cells,
elongated in a radial direction and contain a spherical nucleus

ON SPERMATOGENESIS IN THE RAT. 35 7

situated at about the centre of the cell ; the accessory
corpuscle is to be seen in these cells attached to the nucleus
by a minute vesicle, and another small refracting granule is
attached to the nuclear membrane, at the point from which
the development of the body of the spermatozoon is about to
begin. There are also a few minute fatty granules dotted
about in the protoplasm (fig. 15, c). The manner in
which these cells develop into spermatozoa is represented by
fig. 22.

The nuclear membrane over the outer hemisphere of the
nucleus becomes slightly thickened, and at the opposite pole
of the nucleus, where the small granule is attached, a fine
filament makes its appearance in the protoplasm, and extends
from the nucleus to the surface of the cell, where it is pro-
longed by a delicate protoplasmic filament, the rudiment of
the tail of the spermatozoon. At this time the1 accessory
corpuscle breaks away from the nucleus and becomes embedded
in the protoplasm at the inner part of the cell, where it remains
inactive during the remainder of the process, to be finally cast
off with the protoplasmic residue when the development is
nearly completed. The protoplasm of the cell now becomes
collected entirely at the inner part of the nucleus, leaving the
outer hemisphere, upon which is the thickened membrane,
covered only by the clear cap (22, d).

This corresponds to the stage of development represented by
figs. 1 and 12, at which the young spermatozoa appear to be
free in the tubule. The nuclei of the cells are now commencing
to elongate in the radial direction and to take on the oval form,
and a small prominence becomes visible at the outer pole of
the nucleus at the centre of the thickened membrane, the
“ bouton terminal of Renson (fig. 22, e ). It is at this stage
that the grouping in connection with the supporting cells is first
seen. Fig. 16 represents a group of young spermatozoa em-
bedded in the protoplasm of a supporting cell, but the nucleus
of the body cannot be seen, and the protoplasm appears to be

1 I have not been able to make out what the origin of the accessory
corpuscle is. Perhaps it is derived from the nucleus of the growing cell.

358

HERBERT H. BROWN.

broken off short. This, however, is readily explained, when it
is considered that the tubules were broken up with needles, by
which process the inner part of the supporting cell contain-
ing the young spermatozoa becomes broken off from the base
which contains the nucleus, and is found to remain adherent
to the basement membrane.

The manner in which the oval nucleus becomes transformed
into the head of the spermatozoon will be understood from fig.
22. The nucleus increases in length and projects more and
more from the cell, and the thickened part of the nuclear
membrane progresses so as to cover the whole of the pro-
jecting portion. Soon the nucleus begins to curve, the curva-
ture first appearing near the apex, presumably owing to an
increased growth of one side of the thickened membrane. As
development goes on the curvature increases, and the denser
portion involves more and more of the substance of the
nucleus.

The thickening of the nuclear membrane is apparently
due to a condensation of the nuclear substance and its trans-
formation into that of the head of the spermatozoon, which,
beginning at the surface and at the outer pole of the nucleus,
progresses until the whole nucleus is converted into the
spermatozoon head.

During this time the cilium which springs from the inner
extremity of the cell has reached a considerable length, but
very little progress has been made with the development of
the middle piece of the spermatozoon, although the cell
protoplasm has elongated to some extent.

The young spermatozoon is now (fig. 22, l ) pyriform in
shape, the base of the hooklike nucleus being inserted into the
narrow end of the cell, a long cilium springs from the broad
end, and connecting the nucleus to the cilium is a delicate
filament which can only be seen with some difficulty ( vide figs.
17 and 6, c'). The remainder of the process is occupied chiefly
by the development of the middle piece of the spermatozoon
(figs. 18 — 20). The cell protoplasm rapidly elongates and
assumes a club-shaped form, since the upper extremity which

ON SPERMATOGENESIS IN THE RAT.

359

contains the accessory corpuscle and some fatty granules
remains bulged (figs. 18 and 23). The filament which joins
the nucleus to the cilium is more plainly seen in the narrow
part of the cell. This lengthening of the spermatozoon is
accompanied by a corresponding movement of the heads
downwards along the protoplasm of the supporting cell, until
when the spermatozoa have attained their full length their
heads reach the outer layer, in the neighbourhood of the
nucleus, where they remain until the spermatozoa are cast
off into the lumen. A group at this stage is represented
by figure 19. The middle piece of the spermatozoon is now
clearly visible passing through the protoplasm, which is col-
lected chiefly at its upper end near the junction with the tail.
The middle piece is formed out of the protoplasm of the cell,
but not, as might be supposed, from the whole of the protoplasm,
for a residual portion separates off from the spermatozoon,
when its development is nearly completed. This residual part
of the protoplasm, which contains the accessory corpuscle and
one or two clusters of small fatty granules, gradually accumu-
lates in the form of a globule, which separates from the body
of the spermatozoon. At first the globule remains attached to
the upper part of the body by a short pedicle (a group of
spermatozoa at this stage is represented by fig. 20, and columns
of spermatozoa in situ with the globules attached in fig. 15),
but before long it breaks away entirely from the spermatozoon.

In sections stained with haematoxylin small chromatic gra-
nules make their appearance in the columns of spermatozoa
(fig. 9, x), and when the spermatozoa have passed into the
lumen these granules, each of which is contained in a small
amount of protoplasmic material, are found detached from the
columns, and occupying the interval between the heads of the
spermatozoa and the cells of the third layer. These bodies
have been previously described as the seminal granules ; they
are, in fact, the globules which, as we have just seen, separate
from the spermatozoa at a late stage of their development, and
the chromatic granules seem to be formed in part by the clusters
of fatty granules seen in osmic acid preparations (figs. 10 and

VOL. XXV. NEW SER.

A A

360

HERBERT H. BROWN.

1, x). This separation of globules is of considerable interest
from a biological standpoint, for it apparently corresponds to
the separation of polar globules from the ovum, and may re-
represent the elimination of the female element from the
spermatozoa. Apparently the ova and spermatozoa are derived
from similar embryonic cells — the primitive ova, which are
hermaphrodite. In a cell which is destined to develop into
spermatozoa the male element predominates, and increases
until, by the separation of the globules, the spermatozoa
become wholly male, while in the cell which is going to become
an ovum the female element predominates, and by the separa-
tion of the polar globules the cell becomes unisexed and ready
to be fertilised by the addition of a new male element.

In invertebrate animals the separation of the female element
would seem to take place at an earlier period during the pro-
duction of the spermatozoa, and not, as in the present in-
stance, during the development ; and this is probably the
meaning of the blastophoral body, as described by Blomfield
in the case of the earthworm.1 In this animal the young
spermatozoa undergo their development in groups — “ the sperm
polyblasts.” The “ sperm polyblast” is a mulberry-like mass,
which results from the repeated division in geometrical pro-
gression of a single cell — “ the spermatospore,” or male ovum ;
during each division a certain amount of the protoplasm of the
mother cell remains behind, connecting together the daughter
cells; this residual protoplasm accumulates at the centre of the
group of cells, so that when the process is completed the sperm
polyblast is composed of a central protoplasmic body — the
“ sperm blastophore,” which is covered all over by “ sperma-
toblasts,” or young spermatozoa, which remain planted on the
blastophore until their development is completed.

This interpretation of the separation of the globules, and
the comparison with the blastophore of the earthworm, was
suggested to me by Professor Lankester, The blastophore of
the earthworm, though it has much the same function as the

1 “The Development of the Spermatozoa,” part i, “Lumbricus,” by J.
E. Blomfield, B.A., ‘ Quart. Journ. Jlicr. Sci.,’ Jan., 1880.

ON SPERMATOGENESIS IN THE RAT.

361

vertebrate supporting cell, has a different morphological sig-
nificance, the supporting cells being probably derived from
follicular cells which appear not to be represented in the in-
vertebrate testis.

As soon as the separation of the globules has taken place,
or even before this, the spermatozoa begin to travel bodily
towards the lumen of the tube. This movement is apparently
produced by the supporting cells, which convey the sperma-
tozoa inwards to the lumen of the tube, where they finally
become detached. A supporting cell which is thus casting off
its group of spermatozoa, is represented by fig. 21. For a
short time the head of the spermatozoon remains embedded in
a protoplasmic envelope, perhaps derived from the supporting
cell, and a small granule of protoplasmic material, darkly
stained in gold preparations, remains for some time at the
junction of the head with the middle piece (fig. 24, b, c), but
eventually disappears.

A mature spermatozoon, examined fresh, or mounted in gly-
cerine after osmic acid, shows no trace of a division into body
and tail, appearing to be composed of two parts only, the head
and the long tapering body ; but by treatment with chloride
of gold, as before described, the division into middle piece and
tail is rendered very conspicuous.

Fig. 25 represents a spermatozoon from the epidymis, which
is mounted in glycerine after having been treated with chlo-
ride of gold. The middle piece is somewhat swollen and
stained by the reduction of the gold, the staining being chiefly
concentrated in a fine spiral fibre, which winds closely round
this portion. It has a length of about ’07 mm., and presents a
striking contrast to the tail, which is absolutely unstained ;
the length of the tail is about -08 mm. The spiral filament,
as seen in sections mounted in balsam, has been already de-
scribed (fig. 12, d). I have not been able to make out the
manner of its development. It is first seen when the sperma-
tozoa have reached their full length, before they have begun to
travel to the lumen of the tubule (fig. 14) .

362

HERBERT H. BROWN.

Review of the Literature of Mammalian Sperma-
togenesis.

I will uow give a brief account of some of the different
views upon mammalian spermatogenesis which have been put
forward during the last fifteen years, describing chiefly those
which are of most interest for the purpose of comparison.

For this I am to a considerable extent indebted to the
digest of the literature upon the subject which is given by
Renson in the ‘Archives de Biologie^ for 1882, in his paper
upon “ Mammalian Spermatogenesis.”

Yon Ebner, in 1871, gave an account of spermatogenesis,
taken from a study of the testis of the Rat by means of sec-
tions, which has received a good deal of support.

The supporting cells are described under the name of sperma-
toblasts, and are considered to be the parent cells of the
spermatozoa, which are formed endogenously from the proto-
plasm of the spermatoblasts. Von Ebner describes an external
layer, resting upon the wall of the tubule, composed of two
kinds of cells, which differ from one another in the appearance
of their nuclei, some of them having large nuclei which con-
tain a spherical nucleolus, and others containing small granular
nuclei. The cells with the large nuclei are the “ spermato-
blasts.” The protoplasm of each spermatoblast joins that of
its neighbour on each side, to form a sort of protoplasmic
network upon the wall of the tubule, in the interstices of which
are contained the small cells with granular nuclei. On the
inner side the spermatoblast gives off a protoplasmic process,
which extends radially towards the lumen of the tubule. The
inner extremity of this process enlarges and splits up into
digitations, and at the base of each digitation a nucleus de-
velops, being formed out of the protoplasm of the mother cell ;
then the nucleus elongates and becomes the head of a sperma-
tozoon, a filament grows out from the extremity of each digi-
tation and forms the tail, while the protoplasmic digitatiou
itself is converted into the middle piece. During their de-

ON SPERMATOGENESIS IN THE RAT.

363

velopment the heads of the spermatozoa travel downwards
towards the base of the cell, so that they reach the outer layer ;
on the completion of the process they travel back again, and
finally are thrown off into the lumen. The “ round cells,”
which occupy the spaces between the columns of spermatozoa,
according to von Ebner, serve only for the production of the
liquid portion of the semen.

It is obvious that this account is due to an erroneous inter-
pretation of the appearance of columns of spermatozoa, which
is so conspicuous a feature in the testis of the rat ; there
cannot be the least doubt that it is from the “ round cells ”
that the spermatozoa are derived, and that they are not
produced endogenously in the protoplasm of the supporting
cells.

Merkel, in 1871, gives a very different account of the
process to that of von Ebner. He considers that the sperma-
tozoa are derived from the small round cells which, according
to von Ebnor, undergo liquefaction ; these become embedded
in cavities which are hollowed out in the protoplasm of the
supporting cells, thus producing the spermatoblasts of von
Ebner, and in these supporting cells undergo development into
spermatozoa.

Sertoli, in 1874, gives a much fuller account of the process.
He describes fixed, or supporting, and mobile cells, which he
divides into three classes. 1. “ Germinative ” cells, which
are small, and situated in the outer layer between the bases of
the supporting cells. 2. “Seminiferous” cells, which are
larger, and form the second layer, and correspond to the
germinative cells of the preceding generation, which have
increased in size, and become pushed inwards by the formation
of a new layer of germinative cells, between them and the wall
of the tubule. 3. “ Nematoblasts,” which are small cells
produced by the division of the preceding generation of
seminiferous cells, and destined to develop into spermatozoa.
Sertoli gives no account of the mode of production of the ger-
minative cells.

Lavalette St. George, who has published numerous papers

364

HERBERT H. BROWN.

upon spermatogenesis, takes a different view. He considers
that the connection between the spermatozoa and the support-
ing cells is primary, both being derived from the division of a
single cell. These cells are situated in the outer layer between
the germinative cells of Sertoli, which, according to this ob-
server, are follicular, and take no share in the production of
spermatozoa. They divide in a radial direction into two cells,
which do not entirely separate from one another. The external
of the two remains in the resting condition attached to the wall
of the tubule, and is called the spermatogonium, while the
other cell increases in size and its nucleus repeatedly divides,
so that a multinucleated mass is produced — the “ spermato-
gemme this becomes segmented, and each segment develops
into a spermatozoon. The cell at the base, or spermatogonium,
retains its connection with the spermatozoa until their develop-
ment is completed.

Somewhat similar accounts have been given in 1880 hv
Meyer, in the 'Memoirs of the St. Petersburgh Academie/
and by Brissand in the £ Archives de Physiologie.’

Helmann in 1879, and W. Krause in 1881, agree with
Lavalette St. George in considering the supporting cell and
the spermatozoa to be derived from the same parent cell, but
agree with Sertoli that the germinative cells of the outer layer
are the progenitors of the spermatozoa. They consider that
one of the nuclei of the spermatogemme migrates towards the
wall of the tubule, passing between the cells of the second
layer to become embedded in the outer layer upon the basement
membrane, and that this nucleus, retaining its connection with
the spermatogemme and increasing in size, becomes the sup-
porting nucleus, while the spermatogemme develops into a
group of spermatozoa ; so that, according to this view, there
are no follicular cells in the tubules. I myself held for some
time such an opinion as this upon the relation between the
spermatozoa and the supporting cell, and have already ex-
plained at some length why I felt obliged to give it up.

Klein, in the 'Atlas of Histology/ in 1881, gives an account
of the development of spermatozoa in the dog and some other

ON SPERMATOGENESIS IN THE RAT.

365

mammals. He describes the development of spermatozoa
from small cells resulting from the division of the inner seminal
cells ; these daughter-cells are at first free in the tubule, but
gradually form fan-shaped groups, which sink between the
inner seminal cell towards the wall of the tubule.

Klein has not observed the existence of supporting cells, to
which the groups of spermatozoa are attached, and offers no
explanation of this grouping.

Schafer, in the ninth edition of Quain’s f Anatomy,5 in 1882,
gives a short account of the testis of the Rat ; he attributes
to the small cells of the third layer a nutritive function, and
considers that some of the proliferating cells (the large cells of
the second layer) give rise by their division to groups of sper-
matozoa, while others form the small cells, which ultimately
break down and liquefy.

Renson, in the ‘ Archives de Biologie,5 1882, gives a descrip-
tion of mammalian spermatogenesis, taken chiefly from a study
of the process in the Rat, which agrees very closely in most
points with the result of my own investigations.

Renson traces the origin of the spermatozoa to the small
round cells of the outer layer, which he calls after Sertoli,
“ germinative55 cells, and which make their appearance sud-
denly in the outer layer upon the basement membrane, but
he has not been able to discover in what manner this new
layer of cells is produced, and the production of spermatozoa
perpetuated.

The germinative cells increase in size, and become in the
next cycle the “ seminiferous55 cells which form the second
layer. The seminiferous cells divide by karyokynesis into
groups of daughter cells, which he calls “ cysts.” The “ cysts55
disintegrate, and their component cells, the “ nematoblasts,55 are
set free. Soon they contract a connection with the supporting
cells, in which they become embedded in groups. Finally,
when this development is completed, they are thrown off by
the supporting cells into the interior of the tubule. Renson
also describes the appearances presented by the nematoblasts
during their development, as studied by teased preparations

366

HERBERT H. BROWN.

and his account of the process agrees very closely with that
which I have given, but he does not describe the separation of
the globules of residual protoplasmic material which takes
place when the development is nearly completed. He describes
the accessory coi’puscles, both in the seminiferous cells and in
the nematoblasts, and suggests that they may represent the
polar globules of the ovum.

Swaen and Masquelin, in the 'Archives de BiologieJ for
1883, give the results of their investigations upon spermato-
genesis in the Selachians, the Salamander, and the Mammal.
Their account of the process in the mammal was taken from a
study of the testis of the Bull, and agrees in many particulars
with that of Benson. These observers give an acccount of
the manner in which the continual production of succeeding
generations of spermatozoa is kept up in the tubule, which
presents some resemblance in principle to the view of the
process which I have taken, though differing from it in detail.
They call the small cells of the outer layer — the germinative
cells of Sertoli and Benson — while they are in the resting
condition “ inactive male ovules.” These cells passing into the
kinetic condition become the active male ovules, and gradually
leave the wall of the tubule. Before long each cell divides
into two bv karvokinesis in a radial direction : the external of

* i J

the two cells becomes embedded in the outer layer, and passing
into the resting condition, becomes an inactive male ovule,
which repeats the process in the succeeding cycle. The other
cell, which is internal, increases in size, and finally divides by
karvokinesis into a group of cells, the “ spermatogemme.”

The cells of which the spermatogemme is composed are
called spermatocytes, and afterwards, when they have obvi-
ously begun the process of development into spermatozoa,
receive the name of nematoblasts. The nematoblasts become
attached to the supporting cell without being first free in the
tubule, for the inner extremity of a supporting cell which has
discharged its spermatozoa fuses with the intercellular material
of the spermatogemme.

The account which I have given of the origin of the growing

ON SPERMATOGENESIS IN THE RAT.

367

cells of the outer layer from spore cells, which divide in the
first instance by a process of budding, and the subsequent
division of one of the resulting cells by karyokinesis, has not
been confirmed by any previous investigations. It is possible
that I may have been misled by the appearance of division by
budding which is occasionally to be seen in these cells in the
outer layer, and is represented in fig. 7, a! , consequently I have
been much interested in finding a similar method of division by
budding of the nucleus described by Arthur Bolles Lee, in a
recent 1 paper on spermatogenesis in the Appendicularia. This
observer suggests a theory to explain the occurrence of the two
methods of cell division, which is an ingenious one, and cer-
tainly fits in very well with the account of the process which I
have given above.

He suggests that the complex method of division by karyo-
kinesis is intended to serve for the accurate division of the
constituents of the nucleus between the resulting cells, so that
the daughter cells, possessing in an equal degree the properties
of the parent nucleus, exactly resemble one another. On the
other hand the method of division by budding consists of an
elimination of one part of the nucleus from the remainder, so
that the resulting cells will not exactly resemble one another.

I have described above the spore cell as dividing by budding,
and of one of the resulting cells remaining as a spore cell
while the other divides by karyokinesis, so that the result of
the division by budding is to produce two dissimilar cells. On
the other hand, the cell which divides by karyokinesis pro-
duces the growing cells which are all precisely alike, and these
later on dividing again by karyokinesis give origin to the
young spermatozoa which again are all alike.2

1 “ Recherches sur l’ovogenese et spermatogenese chez les Appendicularia,”
par Arthur Bolles Lee, ‘ Recueil Zoologique Suisse,’ vol. i. No. 4.

2 It might be supposed that the mode of separation of the polar globule
from the nucleus of the ovum goes against this theory ; but it appears that,
according to van Beneden, this is not a true process of cell division by karyo-
kinesis (vide a paper on “ E. van Beneden’s Researches on the Maturation
and Fecundation of the Ovum,” by J. T. Cunningham, * Quart. Journ. Micr.

368

HERBERT H. BROWN.

EXPLANATION OF PLATES XXII & XXIII,

Illustrating Mr. Herbert H. Brown’s Paper “ On Spermato-
genesis in the Rat.”

PLATE XXII

Represents sections of tubules from tlie testis of the Rat, stained with
haematoxylin.

Most of the figures in both Plates are drawn under a magnifying power of
750 diameters, but Figs. 3, 8, 9, 10, 14, and 15 on a slightly smaller scale.

Figs. 1 — 10 show consecutive stages in the production of spermatozoa.
a. Spore-cell. o'. Ditto, dividing by fission, a". Cells dividing by karyoki-
nesis to produce the young growing cells, b. Young growing cell in resting
condition, b' . Ditto, in kinetic condition. bn . Growing cell at a later stage
(in the second row), c. Young spermatozoa with spherical nuclei, c1. Young
spermatozoa undergoing development, d. Adult spermatozoa, e. Supporting
cells, x. Seminal granules.

Fig. 11. — Nuclei of supporting cells, showing the large fatty -albuminoid
globules (stage corresponding to Fig. 2).

PLATE XXIII.

Figs. 12 — 14. — Sections prepared with chloride of gold (lettered as
Figs. 1—10).

Fig. 12. Corresponds to Fig. 1.

Fig. 13. Ditto to Fig. 5.

Fig. 14. Ditto to Fig. 9.

Fig. 15. — Section stained with osmic acid. Stage corresponding to Figs.
14 and 9.

Figs. 16 — 20. — Groups of developing spermatozoa from osmic acid prepara-
tions, mounted in glycerine.

Fig. 16. A group of young spermatozoa with oval nuclei.

Fig. 17. Group of young spermatozoa at stage of Fig. 6.

Fig. IS. Young spermatozoa slightly more developed, showing elongation
of the protoplasm.

Sci.,’ January, 1SS5, p. 107). In this paper the theory as to the separation of
the female element from the spermatozoon and the male element from the
ovum is also brought forward.

ON SPERMATOGENESIS IN THE RAT.

369

Fig. 19. Group of young spermatozoa, stage of Fig. 8. (The middle
piece of the spermatozoa has now reached its full length.)

Fig. 20. A group of spermatozoa, showing the separation of the seminal
granules.

Fig. 21. — A supporting cell casting off its spermatozoa.

Figs. 22 — 24. — Osmic acid preparation. Separate spermatozoa.

Fig. 22 ( a — l). A series showing the development of young spermatozoa,
detached from the groups. The gradual transformation of the nucleus
into the spermatozoon head is especially shown.

Fig. 23. A spermatozoon at the stage of Fig. 18.

Fig. 24. Spermatozoa almost fully developed, a. The residual globule is
still attached, b. This is thrown off, but the head of the spermatozoon
is not yet free. c. There is only a small granule remaining at the
junction of the head and middle piece.

Fig. 25. — A spermatozoon from the epidydymis of the Rat, stained with
gold, showing the spiral filament.

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HISTOLOGY OF THE STEIPED MUSCLE-F1BEE.

37]

> A Simplified View of the Histology of the
Striped Muscle-Fibre.

By

B. Yfellaml, B.Sc.,

Platt Physiological Scholar in the Owens College, Manchester.

With Plate XXIV.

Introduction.

Everyone who has considered the subject must admit the
essential identity from a physiological point of view of all those
tissues which possess in a special degree contractility. The
contraction of a white blood-corpuscle or amoeba is essentially
the same phenomenon as the contraction of an involuntary
fibre-cell or a striped muscle-fibre.

When we consider these three contractile tissues from a
histological point of view we are struck by an apparently
essential difference in character between the striped muscle-
fibre and the elements of the other two contractile tissues, and
indeed cells generally. The voluntary muscle-fibre is morpho-
logically a cell like the muscle-fibre cell and the amoeboid
corpuscle. Yet it differs from the latter and from all other
cells in showing a characteristic transverse striation.

According to Klein,1 the protoplasm of the simpler con-
tractile tissues, (1) the amoeboid cell, (2) the ciliated cell, and
(3) the involuntary fibre-cell, agrees, inasmuch as it consists
of two parts — a matrix and an arrangement of fine fibrils,
the intracellular network. The actual arrangement of

1 ‘ Klein, ‘ Atlas of Histology/ diagrams 1 and 4, and fig. 2, pi. xv.

372

B. MELLAND.

the fibrils differs somewhat in the three cases. In the
white blood-corpuscle they are arranged into a network or
meshwork with polygonal meshes. In the ciliated cell they
also form a network which seems to be in peculiar relation
with the cilia. In the ciliated cell of the Mollusc, according
to Engelmann,1 the fibrils are arranged in a longitudinal
manner as fine varicose filaments running the whole length of
the cell, and in connection with the bases of the cilia. In the
protoplasm of the involuntary fibre-cell the fibrils are arranged
in a central or axial bundle, anastomosing at the poles of the
nucleus with the intranuclear network.

Observations on which I have been engaged for some time
past, and which have been partly worked out in the Physio-
logical Laboratory of Owens College, lead me to the belief
that the striated muscular fibre really agrees fundamentally as
regards histological structure with the other contractile tissue
elements, in containing an intracellular network, differing
from them merely in the greater amount of differentiation, and
more regular arrangement of the network.

I believe, further, that the various conflicting descriptions
given by different observers, and those points on which com-
petent histologists differ more materially, can be explained and
brought into harmony with one another by this view.

I have observed this network in the fibres of Dvtiscus, the
Bee, Crayfish, Lobster, Frog, and Rat prepared by a somewhat
special method of gold staining, the network being the only
part of the fibre stained by the gold.

It may be specially stained also by treating the fibre with
acetic acid and subsequently staining with hsematoxvlin.

It may be demonstrated, though not so completely, in the
living fibre, and in acetic and osmic acid preparations. I have
submitted my drawings and preparations to the examination
of Prof. A. Gamgee and Prof. A. Milues-Marshall.

1 Engelmanu, * Pfliiger’s Archiv,’ xxiii, 1880, and ‘ Quain’s Anat.,’ 9th
edition, vol. ii, fig. 210.

HISTOLOGY OF THE STRIPED MUSCLE- FIBRE.

373

Demonstration of an Intracellular Network in the
striped Muscle-Fibre.

I. The Muscle-Fibre prepared with Gold Chloride.

(a) Dvtiscus marginalis.

Method of Gold Staining. — Decapitate a Dytiscus, open
the thorax, remove a portion of a leg muscle, and place in
I per cent, acetic acid for five to fifteen seconds, then into gold
chloride solution 1 per cent, for forty-five minutes, and leave
in formic acid 25 per cent, for forty-eight hours in the dark.
Tease and mount in glycerine.

If now examined with a magnifying power of about 700
diam. the appearances seen in figs. 1, 2, 3, 12, 13, and 14 will
be seen in certain of the fibres. The method of preparation
has a great tendency to soften the fibre, so that it becomes
much expanded on compression by the cover-slip •, it also has
a great tendency to split the fibre into transverse discs.

Fig. 1 represents a fibre which has retained its natural size
and form. Narrow transverse bands of granular substance,
deeply stained with the reduced gold, are seen crossing the
fibre separated by wider bands of lighter substance. These
deeply stained granular bands correspond in position to
Krause’s “membrane.” The usual separation into light and
dim discs of about equal thickness is lost by this method of
preparation. Traversing the wider unstained discs, and giving
the fibre the appearance of longitudinal striation, are seen fine
longitudinal lines.

In fig. 2 is seen a portion of a fibre which has been more
flattened out by pressure. In it the deeply stained, narrow
granular band is seen to consist of a transverse row of dots.
The lougitudinal lines are seen to represent fine rod-like bodies
traversing the position usually occupied by the dim stripe, and
being continued into the dots at either end. In some fibres a
minute thickening of the rod is apparent midway in the position
of the so-called “ Hensen’s disc” (in the middle of the dim
stripe).

374

B. MELLAND.

This method, as was before stated, has a tendency to split
the fibre into transverse discs. These isolated discs are
found in many parts of the preparation ; they present the
appearances seen in figs. 4 and 5. They are seen plainly in
all cases to consist of two parts — (1) a network of fine lines
highly refracting, stained by the gold, and having thickenings
at the nodes ; and (2) an unstained substance lying in the
interstices of the network.

The appearance of this network differs somewhat with the
degree of compression of the discs. When much compressed
the network appears more open, and the nodal dots less
marked. Towards the outside of the fibre the meshes appear
more oblong, the network extending mostly in a radial direc-
tion. This network evidently corresponds when it is in its
transverse position in the fibre with the deeply-stained, beaded
disc occupying the position of Krause’s “ membrane.” This
is shown in certain fibres in which the discs are not seen
perfectly edgeways but in perspective (fig. 6). The beaded
disc at each membrane of Krause is here seen to consist of
a transverse or horizontal network, united to the discs above
and below by fine thread-like lines. This method of
gold staining, then, brings out a network arranged in a
manner represented diagrammatically in diagrams 1, 2, 3,
and 4.

This network differs chemically from the rest of the fibre,
inasmuch as it resists to a larger extent the action of acetic
acid, and possesses in a greater degree the power of reducing
gold.

It will be shown later, by other methods of preparation, that
this network differs again from the matrix in its physical pro-
perties. The network is isotropous and highly refractile. The
refractive power is somewhat altered bv gold staining, but
certain optical effects are still produced by the refractive action
of the network upon light. These optical effects can be more
definitely seen in isolated portions of the network than in
the whole fibre.

HISTOLOGY OF THE STRIPED MUSCLE-FIBRE.

375

Optical Effects produced by the Network.

Fig. 12 represents a small piece of the network isolated from
the rest of the fibre, consisting of nine or ten rows of dots and
the connecting longitudinal bars. There is a single layer only
of network and dots. This isolated piece seems to be a portion
of sarcolemma stripped off the fibre, along with the portion of
network immediately below the sarcolemma, and attached to it
by each transverse network.

When exactly focussed (fig. 14, l) each dot appears as a dark
granule surrounded by a bright halo. The blending of these
haloes causes a crenated bright transverse band. The effect of
alternating light and dim bands is thus obtained, the bright
band being crossed transversely by a row of dots, the dim band
longitudinally by a series of fine lines.

On altering the focus (raising •0025 millimetre, about), the
refractive effects are to a certain extent transposed (fig. 14, u).
The dots now appear bright, surrounded by a dark border.
By coalescence the appearance of a narrow bright disc is pro-
duced, separated from the dim disc at each side by a dark
crenated line.

Similar refractive effects and transposition on focussing
are seen in the discs isolated by transverse splitting of the
fibre.

Transposition of the Bands.

The effect known as “ transposition ” of the bands has been
noticed by many observers. On raising the objective what was
previously the bright band appears now darker than the dim
band.

This so-called transposition is seen in fibres prepared by the
gold method, better in fibres prepared with osmic acid ; diag. 6,
u represents a fibre at the upper focus. The light band in the
position of Krause’s membrane appears very bright, and is
bordered by a dark line at the junction of the light and dim
bands. On focussing about '0025 mm. lower down (with
Zeiss d obj.) the appearance seen in Lis obtained. The darkest

VOL. XXV. NEW SEE.

B B

376

B. MELLAND.

part of the fibre is now in the centre of what was the bright
band, that is, in the position of Krause’s membrane. Border-
ing on this dark band, and separating it from the dim band, is
a bright zone. The dim band remains much the same as
before, though by contrast with the now dark Krause’s mem-
brane it may appear lighter.

The bright haloes round the nodal dots of the network may
be compared with the similar effects observed whenever any
highly retractile particle, such as a micrococcus or minute
oil-globule, is observed in a medium of lower refracting
index.

In the oil-globule suspended in water similar and very
definite transposition effects are seen on altering the focus. If
focussed low it appears as a dark spot surrounded by a bright
halo or border (l, diag. 7). On raising the objective (about
•0025 mm., Zeis D) the oil-globule appears bright, surrounded
by a dark border.

The effect produced when a row of oil-globules are seen side
by side is at the lower focus (l), a bright band (formed by the
coalesced haloes) with a series of dark dots traversing it. At
the upper focus (u) a narrower bright band, bordered by dark
edges. The beads at the nodes of the transverse network may
be looked upon as refracting and reflecting the light, in the
same way as an oil-globule in water, and as causing the so-
called “ transposition” of the bands seen on altering the
focus.

( b ) Bee. — Insect muscle may be very conveniently obtained
from the thorax or leg of the bumble bee.

Prepared with acetic acid and gold chloride, by the method
already described, it shows a network identical with that
described in Dytiscus.

In order to obtain muscle in as uncontracted a condition as
possible, gold preparations were made from the leg muscles
of a bee, rendered insensible and immovable by chloroform
vapour, in which presumably there was complete relaxation of
the muscle-fibre. These preparations, however, could not be
distinguished from those prepared without chloroform.

HISTOLOGY OF THE STRIPED MUSCLE-FIBRE.

377

As the fibres are rendered soft by the method of preparation
their size and the size of their elements varies with the pres-
sure of the coverslip ; hence measurements are of little or no
value.

Identity of Network with Schafer’s Muscle-rods.

We cannot but be struck by the resemblance of the appear-
ances brought out by gold staining with those described by
Schafer1 in the living fibre as muscle-rods. The two views
differ, however, on two points : (1) Schafer describes in a
transverse section of the fibre a bright ground substance with
a number of minute specks or dots ; no appearance of a net-
work. (2) He considers that there is typically a double
transverse row of dots in the middle of each bright stripe.

Concerning the appearance on transverse section we
must not forget that Schafer’s conclusions were drawn from
the living fibre in optical transverse section. Probably he
saw all that it is possible to see of the transverse network in
the living fibre, namely, the thickenings or dots at the nodal
points, the fine network, seen so plainly in a transverse view
when stained with gold, not being visible in the fresh fibre
examined in this way.

Is there a single or a double row of dots in the middle
of the bright stripe ? In the fresh fibre sometimes a single
sometimes a double row of dots is seen, the two appearances
often alternating with a higher or a lower focus. The same
variation is seen in alcohol and some other preparations.

In the gold preparations, when the fine granular disc or
transverse network is seen perfectly edgeways and in focus, it
appears invariably made up of a single transverse line of
dots.

When the transverse network is not seen perfectly edge-
ways, through not lying in a plane quite at right angles to the
longitudinal axis, but slightly obliquely or in perspective, it

1 ‘ Phil. Trans.,’ xii, 1873, E. A. Schafer “ On the Minute Structure of
the Leg Muscles of the Water-beetle.”

378

B. MELLAND.

may appear as a double row of dots or as a granular or dotted
band crossing the disc transversely.

In a perspective view of the fibre (figs. 3, 6, and 17), not
only the dots (nodal points of the network) at the near side of
the fibre are seen, but at the same time those deeper down or
at the far side. Hence the appearance of two or more rows of
dots crossing the fibre. When by raising the focus the nearer
edge of one of these obliquely-arranged discs is alone focussed
it is seen to consist of a single row of dots.

It was noticed a few moments ago, when speaking of trans-
position of the bands, that at the upper focus (diag. 6, u) the
coalesced bright dots form a bright band bordered at each side
by a dark crenated line. Each dark line is not unlike a row of
dots. Schafer1 seems to have figured muscle at this upper
focus, and hence describes two lines of dots traversing the
light disc where it borders on the dim disc.

(c) Frog. — The fibres from the gastrocnemius of the frog
treated by the same gold method as before yield an unmistake-
able network. The fibi'es when examined are seen to be more
changed by the process than is the case with insect muscle.
They become very much softened and when pressed upon by
the coverslip expand to many times their natural diameter,
and thus often altogether loose their shape. Owing to this
disturbance of the fibre the network usually shows no distinct
differentiation into horizontal or transverse, and longitudinal
portions. Hence there is no transverse striation.

In many places in the preparation isolated portions of fibre
show a network with polygonal meshes as in fig. 7. This net-
work is also seen at the ends of certain fibres which curling up
show a transverse section. The meshes are often, when the
fibre is much expanded by compression, large enough to be
seen with Zeiss A. obj., at other times much smaller, approxi-
mating in size to the meshes of the horizontal networks in
insects’ muscle. The size of the meshes seems to depend
entirely on the degree of compression of the fibre. When the
1 ‘ Quain’s Anat.,’ vol. ii, 9th edition, fig. 119.

HISTOLOGY OF THE STEIPED MUSCLE-FIBEE.

379

meshes are small, distinct thickenings or dots are seen at the
intersections of the fibres composing the network. This net-
work is particularly sharply defined and is plainly seen to be a
true network^ that is, the lines represent linear fibres only. It
is not a honeycomb work. The lines do not represent the
edges of plates of interfibrillar material.

(d) Crustacean. — An exactly similar network can be
brought out in the muscle of the lobster. My friend Mr. C.
F. Marshall has made preparations of lobster muscle with
acetic acid and gold which show this network in a most
beautiful manner. The muscle in this case was left in 15 per
cent, acetic acid for fifteen minutes (a much longer time than
I use), in gold chloride thirty minutes, and in 25 per cent,
formic acid in a warm chamber for three hours exposed to the
light.

This network represents the transversely and longitudinally
arranged network described in insects’ muscle pulled out of
shape. In some of the fibres indeed it is still seen arranged
in the rectangular manner. Fig. 8 represents a portion of a
fibre in which transverse are crossed by longitudinal lines with
dots at the intersections. In this case the ordinary light and
dim transverse striation is obtained by refraction round the
nodal dots.

At first sight the meshes of the irregular network described
in the frog and lobster look too large to correspond in size
with the meshes of the horizontal network in Dytiscus, that is,
with the end view of sarcous elements. But we must not
forget the effect of pressure ; it expands the fibre to about ten
times its normal diameter, and a corresponding increase in the
size of the meshes takes place. Fig. 11 represents a transverse
section of the fibre of the frog cut fresh with the freezing
microtome and stained by the gold method. It has not been
much enlarged by pressure and hence the meshes of the net-
work are small.

Fig. 10 represents a portion of a fibre of the lobster which
has split into fibrils; an uncommon effect in gold preparations.

380

B. MELLAND.

When muscle splits into fibrils the fibres of the transverse net-
work rupture midway between the nodal points ; the longi-
tudinal threads and dots remain often attached to the fibril of
sarcous substance, and cause it to appear transversely striated.

The muscular fibres of the crayfish show exactly the same
network, the precise method of gold staining seems to make
little difference. Isolated portions of network are seen pulled
out of shape, and thus with polyhedral meshes as in fig. 7.
At other points the network is seen still arranged in its typical
manner as in fig. 8.

(e) Rat. — Iu the Rat most of the fibres show the typical
arrangement into transverse and longitudinal portions (fig. 9).
The transverse network is most marked. In certain isolated
portions the dots at each nodal point of the network are seen
surrounded by bright haloes as already described.

Such then is the effect of gold staining on the muscular
fibre. Can this network be demonstrated in any other way ?
Any method which fixes the fibre in that condition in which it
is when living gives rise to appearances closely resembling
those described. Acetic and osmic acids seem to act in this
way.

II. Acetic Acid Preparations.

Muscular fibres from the leg of the bee were placed in dilute
acetic 1 per cent, for from five to fifteen seconds, then into
glycerine and mounted.

On examination they are seen to present a transverse row of
dots at each membrane of Krause and longitudinal connecting
rods. The network, like the sarcolemma, seems to resist the
action of acetic acid more than the matrix or sarcous substance.
If the fibre be stained in hsematoxylin after the action of the
acetic, the network becomes stained to a greater extent than
the matrix, which remains relatively unstained.

The fibre now presents the appearance seen in fig. 15. Thin
granular deeply-stained discs are seen crossing the fibre in the
position of each Krause’s membrane. They are attached to

HISTOLOGY OP THE STRIPED MUSCLE-FIBRE.

381

the sarcolemma at the edges, and appear to divide the fibre into
compartments. If the near edge of one of these discs be
focussed it appears as a transverse row of dots crossing the
fibre, and in many fibres fine longitudinal lines may be seen
joining the dots of two adjacent discs.

In some fibres the appearance of a double row of dots
crossing the fibre in the position of the transverse network is
seen. This is represented in fig. 16. It is noticed in the pre-
parations made with acetic acid, that the double rows of dots
are met with, as a rule, in those fibres which have undergone
least pressure. In fibres expanded by pressure a single row of
transverse dots is alone observed.

Fig. 17 represents a fibre treated with acetic acid and after-
wards stained in watery solution of logwood. At the upper
part of the fibre the thin dotted transverse discs are not seen
edgeways but partially from below. Lower down in the fibre
the discs are seen more nearly edgeways, and appear in pers-
pective view as narrow granular bands. These granular bands
appear crossed longitudinally, and more or less broken up into
short parallel longitudinal segments, by fine bright lines. These
bright lines are caused by refraction from the longitudinal
rods of the network.

Ill, Osmic Acid Preparations.

Preparations made by placing living muscles from the bee in
osmic acid 1 per cent, for ten minutes, and mounting in balsam,
give on examination the appearances figured in fig. 18 and
diag. 6. Thickenings (Engelmann’s “ fixed waves of contrac-
tion'”) are seen on many of the fibres.

In diag. 6, l the fibre is seen crossed at intervals by a
dark well-marked line, Krause “ membrane ” or the horizontal
network. On focussing upwards this line appears as a thin
bright disc, and the appearance u is obtained.

In certain fibres (fig. 18), by careful examination, it can be
seen that this dark line consists of a row of dots, and occa-
sionally fine longitudinal lines may be seen joining them.

A fixed wave of contraction is shown in this figure.

38a

B. MELLAND.

The contracted part of the fibre is widened out transversely
and the distance between the transverse networks diminished.
The series of haloes round the rows of dots extends to the
whole of the now diminished interval between the successive
rows. There is consequently a bright band in the position
usually occupied by the dim band. Traversing this bright
band longitudinally are seen fine lines joining the dots of
adjacent networks. Between this fully contracted and the
relaxed part of the fibre is the portion showing the “ homo-
geneous stage ” of Engelmann. The transverse marking is
here to a large extent lost, and this can be easily understood,
when we consider that at the onset of contraction the trans-
verse network would be probably more or less pulled out of
shape. The individual dots would no longer lie in the same
transverse plane, and hence the haloes would not blend into a
continuous bright transverse disc. This agrees with the fact
mentioned by Schafer,1 that mechanical shifting of the elements
of a fibre causes a disappearance of the transverse striations.

Another point often observed in osmic acid preparations is
a caving in of the sarcolemma between each transverse net-
work, that is opposite the dim stripe. In other preparations
usually the sarcolemma bulges at these points, and appears to
be contracted at its attachment to the transverse network or
Krause’s membrane. This may be explained if it be supposed
that in osmic acid preparations there is a certain amount of
contraction of the matrix or sarcous substance, by exosmosis
for instance. The sarcolemma will follow this decrease in bulk
but will be prevented from doing so at those points where it is
held outwards by the more rigid transverse networks.

IY. The Living Fibre.

The fibres from the leg of Dytiscus, or the bee, mounted
without the addition of any fluid, and examined whilst fresh
or living, give the appearances seen in figs. 19 and 20. Most
of the fibres are seen to present the appearance of alternate
dim and bright bauds, the dim bauds being the thicker. Each
1 ‘ Quaia’s Anat.,’ vol. ii, 9th edition, p. 129.

HISTOLOGY OP THE STRIPED MDSCLE-PIBRE.

383

dim band is traversed by a series of longitudinal lines of a
highly refractile substance. Running across the middle of the
bright band transversely is seen a single row of dots. The
fine dark lines crossing the dim stripe are traceable at either
end into the dots of the bright stripe. In this case, just as in
the acetic acid preparations, there often appears to be a double
row of dots in the centre of the bright stripe. Fibres are seen
side by side, one with a single row, another with a double row
of dots in this position. When a double row is present, the
corresponding dots of the two rows appear to be always joined
longitudinally by fine lines across the middle of the bright
stripe. This is mentioned by Havcraft1 but not by Schafer.

Sometimes again the appearance shown in fig. 20 is observed.
A series of short parallel longitudinal lines is seen in the
position of the transverse network. These lines appear dotted
on careful examination. This appearance is similar to that
described in the acetic acid preparation (fig. 17), and may be
explained in the same way as a perspective view of the net-
work crossed by longitudinal bright lines, caused by refraction
from the longitudinal rods. “ Transposition ” of the bands
may be seen on altering the focus, similar to that already
described. The line of dark dots, with its series of bright
haloes forming the bright disc, becomes now a line of bright
dots bordered by two crenated dark lines. The above obser-
vations on the living fibre were made by means of the gas
chamber. The chitinous integument of the leg of the bee was
slit longitudinally, the muscle scooped out, and quickly teased
on a cover-glass and inverted over the moist gas chamber.
This method may be used for studying the phenomena of con-
traction, by blowing air charged with alcohol vapour into the
chamber, and thus causing the fibre to contract by chemical
stimulus.

On contraction the fibre becomes shorter and thicker, the
transverse rows of dots approach one another and appear
darker, probably by contrast with the now bright “ dim ”
disc. These appearances are similar to those seen in the
1 ‘Quart. Jouru. Micr. Sci.,’ April, 1881, p. 23.

384

B. MELLAND.

“ fixed waves of contraction/’ described in the osmic acid
preparations.

In a preparation of fresh muscle I have seen a fibre undergo
slow rigor mortis, commencing at one end and gradually ex-
tending towards the other. It exactly resembled a very slow
contraction wave passing over the fibre, and the changes
undergone by successive discs, as the contraction affected them,
were similar in appearance to those described in fig. 18, and
could be observed with more deliberation than usual.

The Fibre under Polarised Light. — The effects observed
in the living fibre with crossed Nichols were exactly similar to
those figured and described by Briicke and Schafer Quain’s
Anat./ 9th ed., vol. ii, fig. 125). Briicke’s drawing is almost
identical with diagram 3.

The fibre is chiefly made up of doubly refractile or aniso-
tropous material, but a band of singly refractile or isotropous
material crosses the fibre transversely in the position of each
Krause’s membrane, and this band is seen with a high power
to consist of a row of rhomboidal dots. Fine lines of isotro-
pous material are described running longitudinally across the
anisotropous discs and joining the rhomboidal dots. The
appearance of the muscle-fibre under polarised light leads us
to the belief that the network consists of isotropous, the matrix
or ground substance of anisotropous or doubly refracting
material.

V. Alcohol Preparations.

Alcohol preparations of muscle show, in most cases, a some-
what different character to those prepared by the preceding
methods.

Spirit has a tendency to split the fibre into fibrils and sarcous
elements. After the muscle has been in alcohol it may be
stained with some reagent; Kleinenberger’s hsematoxylin, for
instance, gives excellent results. Alum carmine may also be
used. Mount in Canada balsam.

Absolute alcohol has a somewhat different effect from
ordinary spirit. It sometimes seems to fix the fibre as

HISTOLOGY OF THE STRIPED MUSCLE-FIBRE.

385

appears during life — that is, there is no differentiation into
sarcous elements, but transverse rows of dots, and longitudinal
lines are alone seen, as in the living fibre. Fixed waves of
contraction may also be found.

Fig. 21 represents a portion of a fibre of Dytiscus stained in
hsematoxylin after the action of spirit. It shows an alter-
nation of bright and dim discs, the dim discs stained a deep
purple and made up of a series of sarcous elements side by
side. Across the middle of the bright discs a dotted or
granular transverse line is seen. Fine longitudinal lines, the
longitudinal bars of the network, may occasionally be seen
crossing the bright discs.

This account agrees for the most part with that given by
Klein1 as to the structure of muscle. He, however, figures a
continuous line — the homogeneous Krause’s membrane — in
the middle of the bright stripe, and no longitudinal fibrillation
in the bright disc.

Let us consider the influence of the intracellular network in
producing the appearances known as sarcous elements, and
Cohnheim’s areas, in the muscle-fibre.

The matrix, or substance which lies in the interstices of the
network, is of far greater bulk than the network. It is homo-
geneous throughout ; nevertheless, it may be looked upon as
being partially divided into columns or fibrils by the longi-
tudinal bars of the network, and partially into discs — the con-
tents of muscle compartments — by the transverse networks
By the action of spirit the matrix becomes split into fibrils.
The reagent causes this “ sarcous substance ’’ to shrink (pos-
sibly by abstraction of water), and the homogeneous mass now
separates into fibrils along the lines of greatest weakness — that
is, along the guide lines formed by the longitudinal bars of the
network. These fibrils may again divide transversely at the
horizontal networks, producing sarcous elements (diag. 8).
Thus the appearance of sarcous elements is seen, as described
by Klein,2 to be a post-mortem phenomenon. In conse-

1 ‘ Atlas of Histology,’ p. 77.

2 Loc. cit., p. 76.

386

B. MELLAND.

quence of shrinking the sarcous substance no longer entirely
fills up the skeleton “ muscle caskets,” and the division into
sarcous elements, which was foreshadowed only before by the
bars of the network, becomes evident by the development of
intervening spaces between adjacent elements. The appear-
ance known as Cohnheim’s areas is somewhat differently
described by different observers. For the present we may
follow Klein’s1 description. The prismatic sarcous elements
which lie side by side in the living fibre with no intermediate
substance, shrink through coagulation on dying, and become
separated from one another by a transparent interstitial fluid
substance. In a transverse view there are thus seen small
polygonal areas separated by clear lines, each polygonal area
corresponds to a sarcous element.

Cohnheim’s areas may be described, as the appearances pro-
duced by coagulation and splitting of the matrix along the
guide lines formed by the transverse network ; they represent
an end view of sarcous elements, and are post-mortem phe-
nomena (diag. 9).

Previous Views.

I think it unnecessary to give a historical account of the
different views which have been published with regard to the
structure of the striped muscle-fibre.

An epitome of the historical results may be found in
Schafer’s2 paper on the leg muscles of the water beetle ; or by
the same author in ‘ Quain’s Anat.,’ 9th ed.

Reference has already been made to most of the appearances
described by different observers, and the way in which these
appearances may be explained as caused by the presence of a
highly refracting network.

The relation of this network to Krause’s3 views may be
noticed. Krause’s “ muskel-kastchen” are bounded above and

1 Loc. cit.

2 Loc. cit.

3 “ Ueber den Bau der quergestreiiten Muskel laser,” ‘ Zeitschr. f. rat.
Med.,’ xxiii.

HISTOLOGY OF THE STRIPED MUSCLE- FIBRE.

387

below by Krause’s membrane, and laterally by the boundaries
of Cohnheim’s areas. Briicke1 regards the isotropous lines
which traverse the anisotropous disc as optical sections of
the partitions between muskel-katschen. These partitions
correspond with the longitudinal bars of the network and
with Schafer’s rods. The alternation of bright and dim trans-
verse bands has been looked upon by several observers as an
optical effect, and not due to any anatomical differentiation
here present.

Heppner2 and Strieker look upon the bright band as the
expression of total reflexion, which occurs at the line of de-
marcation between Krause’s membrane and the chief substance
of the fibre.

Bowman suggested that the transverse striping shown by the
fibrillse was caused by their moniliform shape. Hay craft 8 has
recently developed this view, and extended it to the whole
fibre.

Striped muscular fibres are met with in the animal kingdom,
from the Ccelenterata upwards ; there is no reason to suppose
that the cause of the transverse striation is different here from
that in the insect.

I have received the greatest sympathy during this investi-
gation from my friend Mr. C. F. Marshall, with whom I
have verified most of my results. The drawings of the net-
work in the fibres of the Rat and Lobster are from gold pre-
parations by him. Mr. Marshall is at present working on the
histology of the muscle fibre, from the lowest types of the
animal kingdom in which it occurs upwards, and has 'already
obtained interesting results. A study of the comparative
development or phylogeny of this network, and at the same
time of its embryology, may lead to its undoubted recognition
as an ordinary intracellular network.

My thanks are also due to Prof. A. Milnes-Marshall, who

1 ‘Quain’s Anat.,’ p. 127 ; and “Muskelf. im polarisirten Licht,” ‘Wiener
Denkschr.,’ xv.

2 * Strieker’s Handbook ’ (Syd. Socy.), p. 548, vol. iii.

3 ‘Quart. Journ. Micro. Sci.,’ April, 1881.

388

B. MELLAND.

has kindly examined my drawings and specimens, and sug-
gested alterations in the paper, and to Mr. J. Priestly, M.B.

Brief Summary of Results.

The chief results at which I have arrived may be sum-
marised as follows :

There is an intracellular network present in the striped
muscle-fibre of Dytiscus, the Bee, Frog, Lobster, Crayfish,
and Rat, which may be most clearly demonstrated by certain
methods of gold staining. The network alone is stained by
the reduced gold, and, owing to this differentiation, is plainly
visible even with comparatively low powers. This network
may be demonstrated, though not so completely, in the living
fibre, and in acetic and osmic acid preparations.

Crossing the fibre transversely, united to the sarcolemma,
and more or less separating the muscle-fibre into compartments,
are network partitions — the transverse networks.

Running longitudinally down each compartment, and join-
ing the dots at the intersections of the fibres of the transverse
network, are a series of fine rods. The arrangement of this
network will be made evident by reference to diagrams 1, 2,
3, and 4.

This network consists of an isotropous material, and is more
highly retractile than the rest of the muscle substance, which
is anisotropous. This network serves to explain the transverse
striation and other complicated appearances presented by the
muscle-fibre, and brings into harmony many of the conflicting
statements of histologists on this subject.

HISTOLOGY OF THE STRIPED MUSCLE-FIBRE.

389

DESCRIPTION OF PLATE XXIV,

Illustrating Mr. B. Melland’s Paper on “ A Simplified View
of the Histology of the Striped Muscle-Fibre.”

Diag. 1, 2, 3, and 4. — Diagrammatic view of the network in striated muscle.

Diag. 1. Perspective view of the fibre, showing the transverse network a
at each membrane of Krause, and the longitudinal lines.

Diag. 2. Perspective view of a portion of the network, showing : — a. The
transverse networks, with polygonal meshes and dots at the nodes.
b. The longitudinal bars of the network ending in the dots.

Diag. 3. The fibre seen in longitudinal view. The transverse network, «,
appears as a row of dots crossing the fibre (in the position of Krause’s
membrane), c. Minute thickenings on the longitudinal bars of the
network, midway between the transverse networks.

Diag. 4. The fibre seen in transverse section.

Diag. 5 — Network as seen in a longitudinal view of the fibre, showing the
production of alternating bright and dim bands by refraction around the
nodal dots.

Diag. 6. — So-called transposition of the bands, as seen in an osmic acid
preparation of muscle of Bee. u. Appearance at upper focus, l. Appearance
at lower focus.

Diag. 7. — Oil globules in water, showing their refractive effect upon light,
u. At the upper focus, each globule surrounded by a dark border, l. At the
lower focus, each globule surrounded by a bright halo.

Diag. 8. — Production of sarcous elements by contraction of the matrix and
splitting along the guide lines formed by the bars of the network (seen in
spirit preparations).

Diag. 9. — Formation of Conheim’s areas by contraction of the matrix as
above. In this transverse view of the fibre the prismatic sarcous elements
are seen on end, and appear as polygonal areas separated by bright lines.

Fig. 1. — Fibre of Dytiscus, prepared by the gold method. Zeiss, D obj..
No. 5 oc.

Fig. 2. — Dytiscus, gold method, portion of a fibre more compressed than in
Fig. 1.

Fig. 3. — Fibre of Bee, prepared by the gold method ; transverse networks
in perspective.

Figs. 4 and 5. — Dytiscus, gold method, showing isolated discs consisting of
a network.

Fig. 6. — Fibre of Dytiscus, gold method, splitting into discs.

390

B. MELLAND.

Fig. 7. — Lobster fibre, gold chloride ; isolated portion of a fibre, network
pulled out of shape. Exactly similar networks are seen in the Frog and
Crayfish.

Fig. 8. — Frog, gold method; network arranged typically, and showiug
transverse striping.

Fig. 9. — Rat, gold chloride ; longitudinal view of portion of a fibre. (Pre-
paration by C. F. Marshall).

Fig. 10. —Lobster, gold chloride, splitting into fibrils.

Fig. 11. — Frog. Transverse section of the frozen fibre, stained by the
gold method.

FTg. 12. — Dytiscus, gold method ; isolated portion of the network.

Fig. 13. — The same, more highly magnified. (Zeiss, F obj , No. 5 eyepiece.)

Fig. 14. — The same, showing refracting effect of the network, l. Lower
focus, u. Upper focus.

Figs. 15 and 16. — Fibres of Bee, treated with acetic acid, then Kieiuen-
berg’s hsematoxylin.

Fig. 17. — Fibre of Bee, treated with acetic acid, then watery solution of
logwood. The transverse networks seen more or less obliquely.

Fig. 18. — Fibre of Bee, prepared with osmic acid, shows a fixed wave of
contraction.

Fig. 19. — Living fibre of Bee, showing longitudinal view of network
(Jj immersion obj).

Fig. 20. — Living fibre of Bee, transverse networks seen somewhat obliquely.

Fig. 21.— Portion of a fibre of Dytiscus, stained in hsematoxylin after the
action of spirit. Shows sarcous elements.

Where not otherwise stated, the drawings were made from Zeiss, D. obj..
No. 5 occ.

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ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 391

On the Development of a Freshwater Macru-
rous Crustacean, Atyephira compressa,
De Haan.

By

CliiyomatKii Ishikawa,

Of the University of Tokio, Japan.

With Plates XXV, XXVI, XXVII, XXVIII.

The species on which the following observations were made,
is very commonly found in freshwater streams and ponds in
the vicinity of Tokio. Its specific determination has very
kindly been made for me by Dr. Ed. J. Miers, of the British
Museum, through the kind offices of Professor Whitman and
Dr. Paul Mayer. Dr. Miers wrote a valuable paper on it, in
the * Annals and Magazine of Natural History ’ for March,
1882 (pages 193, 194).

My investigations on the development of Atyephira com-
pressa, De Haan, were begun in the spring of the year
1881, under the direction of Professor Whitman, to whose
valuable assistance and instruction I am deeply indebted. By
the spring of the next year I had nearly completed the study
of the development of the ovarian ovum, and on my gradua-
tion in July of that year, wrote a thesis on this subject under
the name of “ On the Ovarian Ovum of Atyephira com-
pressa, De Haan.” In the spring of 1883 I extended my
investigations to the development of the post-ovarian ovum,
under the direction of Professor Mitsukuri, to whose constant

VOL, XXV. — NEW SER.

c c

392

CHIYOMATSU ISHIKAWA.

advice and never-failing encouragement I am very much in-
debted.

To the authorities of the University of Tokio, and especially
to the President, Mr. H. Kato, I am deeply indebted for the
use of the instruments, chemicals, and other things necessary
for pursuing my work.

I must here also express my great obligation to Dr. Faxon,
for sending me ‘ The Memoirs of the Museum of Comparative
Zoology at Harvard College,’ vol. ix, No. 1, which was of
great use to me.

Methods.

For the dissection of the ovary, I have used Zeiss’s Dissecting
Microscope, with a magnifying power of about fifteen diameters.

For examination of fresh specimens :

a. Ovaries were examined in bicarbonate of potash or of
ammonia 2 per cent, strong. Connective tissues were treated
with acetic acid per cent.) and coloured with aniline.

b. Embryos were removed from the yolk mass by means of
needles in the normal salt solution, and exposed to the fumes
of osmic acid ( 05 per cent, strong) for about five minutes.

For the surface view of the ovarian walls, nitrate of silver
was always employed.

For sections embryos were hardened in Kleinenberg’s picro-
sulphuric or Mayer’s picro-nitric acid for about three hours, and
passed through successively weak, strong, and absolute alcohols.
They were then stained in the logwood-solution or borate of
carmine. In the former fluid the yolk-spherules were coloured
magnificently, while in the latter they remained uncoloured.

Books of references are noted throughout this paper by the
use of the Arabic numerals. The denominators in the frac-
tions refer to the list of authors at the end of this paper, and
the numerators indicate the page. There are, however, many
works to which I could not get an access. These are referred
to, as far as possible, by citations found in those books at my
command. Such works ai’e noted in the list by an asterisk.

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA.

393

An interrogation point used in a fraction indicates that the
pages are unknown.

The Ovary.

The female generative organ of Atyephiracompressa
consists of two elongated sacs joined with each other near the
anterior end. They extend in the body cavity parallel to, and
above, the digestive canal, beginning at the middle portion of
the cephalothorax, a little in front of the heart, and reaching
posteriorly as far as the middle of the second abdominal
segment. At about the middle point of its length each of
these sacs sends out a canal laterally, which taking a direct
course downwards, opens on the internal face of the basal
joint of the third thoracic leg. The mouth of this canal is
covered over by a membrane which is slightly raised above the
level of the general surface. There is a transverse slit across
the middle of this membrane, which thus forms a sort of a
valve, and prevents water from getting into the ovary (fig. 1,
o.oc?.). The elongated sacs above mentioned constitute the
essential part of the ovary, while the two lateral ducts serve as
oviducts.

The fully ripened ovary (fig. 2) measures about 4.5 — 6 mm.
in length and 4 mm. in breadth across the point of junction.
These measurements, however, vary according to the size of the
animal, for an animal not larger than 10 mm. in length is
often provided with a small ripe ovary, containing a small
number of eggs.

On the under side of each ovarian tube there is to be seen
a narrow transparent band, sharply distinguished from the dark
green colour of the ripe ova (fig. 2, ger.), running the whole
length of the ovary. Anteriorly it runs nearer to the median
than to the outer side. It meets with its fellow of the opposite
side at the point of junction, whence it takes its course diagon-
ally outwards to the region of the oviduct in a curved line ; here
it turns posteriorly, and taking its course along the outer edge
of the ovarian tube, ends blindly at its hind extremity. These
bands are very well seen when the ovary is acted on by acids

394

CHIXOMATSU ISHIKAWA.

such as chromic, picro-sulphuric, or nitric. They appear dis-
tinctly as white bands on the now orange-red (with chromic)
or reddish-yellow (with picro-sulphuric or nitric) portion. They
represent the formative place of the eggs, and are filled with
young ova that have not yet acquii’ed yolk- elements. I desig-
nate these bands under the name of “ germogen ” inasmuch
as it is in these parts that the primordial ova are found. The
rest of the ovary will be spoken of as “ vitellogen,” where the
vitellus or the yolk-elements are formed.

A section of an ovary (fig. 3) will therefore show two
distinct groups of eggs, one consisting of larger and the other
of smaller eggs. The former (fig. 3, Vit.) fills up nearly the
whole cavity of the ovarian sac, while the latter (fig. 3, ger.)
occupies only a small portion. This latter represents the
white band shown on a surface view (fig. 2 , ger.).

The section represented by the fig. 3 is a transverse one cut
through the posterior portion of the ovary, the smaller group
of eggs occupying the outer side of the tube, and the larger
the inner.

This arrangement seems to be almost universal in the crus-
tacean ovary. The sexual organs of Amphipods have been
studied by Bruzelius, Spence Bate, and de la Yalette St.
George. They have all described these organs as cylindrical
tubes, whose peripheral parts are occupied by young eggs, while
the central portions are filled with much more advanced eggs.
Of the Isopod ovary Leuckart says : “ The ripened eggs always
take the whole inner side of the egg sac; the youngest, on the
contrary, lie on the outer side in its entire length. Only the
outer side is the formative place of the eggs.” Edouard van
Beneden, in speaking of the Amphipods and Isopods together,
expresses his views in the following words (^-f-^) : — “ In all
these animals there must be distinguished throughout the
length of the ovary two very distinct parts ; the one situated
on the external side presents itself under the form of a narrow
band, and filled with young eggs at different stages of
development.”

The Ostracod ovary is stated to be of a similar nature (^).

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA.

395

Among Decapods we find it in Eupagurus, Crangon,
Panulirus, Atyephira, and so on. Mayer’s description of
the ovary of Eupagurus corresponds with that of Atye-
phira in almost every point Pf3). In our common Crangon
(probably C. vulgaris, Fabr.) the white band takes its peri-
pheral position on the anterior half of the ovary, while pos-
teriorly it penetrates into the interior of the ovary, and takes
the axial course. In Panulirus japonicus, Gray, I have
found it taking the axial course through the whole length of
the ovarian tubes.

Structure of the Ovarian Walls. — The wall of the
ovarian tube consists of two sets of layers, the outer aud the
inner, more or less separated from each other. The outer set
is formed of (1) a connective-tissue layer, and (2) a super-
ficial epithelium layer ; the inner consists of (1) a fine struc-
tureless membrane, and (2) a layer of pyramidal epithelial cells.
The outer connective-tissue layer (fig. 4) is formed of a thin
matrix, embedded in which are seen fine, wavy, parallel lines,
seemingly marked out into imperfect fibres, running in no one
definite direction, but, on the whole, lengthwise. The nuclei
of this layer (fig. 4, nc.) are very variable in sizes, measuring
0‘013 — 001 mm. in length, and 0-006 — 001 mm. in breadth.
Their forms are somewhat flat and elliptical. They have very
delicate contour, and are provided generally with nucleoli,
which appear as minute dots. We often recognise in this
tissue the presence of pigment patches, whose form and size
vary exceedingly. The colour of the pigment varies also from
yellow to dark carmine. Clear spaces or lacunae of variable
dimensions are generally to be seen intermixed with nuclei.

This connective tissue can best be studied, as I have already
said, in fresh specimens treated with very dilute acetic acid
(•005 per cent.), and coloured with aniline or carmine, or else
by simply colouring the freshly-taken ovary with Beale’s car-
mine. By the former method the nuclei appear to be a little
larger than they should, being (most probably) swelled up by
the action of acetic acid.

This connective-tissue layer extends all over the ovary and

396

CHIYOMATSU ISH1KAWA.

oviducts, connecting the two ovarian tubes together, and it also
covers over other organs — the heart, the alimentary canal, &c. —
and therefore may not properly be said to belong to the ovary.
A similar layer of the connective tissue is stated to be present
in the ovaries of Isopods and Amphipods.

Below the connective- tissue layer comes a layer of epithe-
lium cells. This layer (fig. 5) consists of cells with irregular
outlines, of about 0‘03 mm. in diameter, provided with an oval
nucleus of about OOl mm. in length. It extends all over the
ovary and oviducts. The cells on the latter are much smaller
than those on the former, although the nuclei are nearly of the
same dimensions (compare figs. 5 and 6). The nuclei are very
difficult to make out, even in silver staining. In fine prepara-
tions, however, they appear to be provided with one or more
very small dots — the nucleoli.

This epithelium is sometimes (perhaps always) followed by
another sheet of a cellular layer, apparently similar to it in
structure, differing, however, from it in its being turned in,
sometimes, though rarely, between the egg follicles. This
cellular layer I am inclined to consider as akin to the ovarian
stroma of other animals.

Between this and the inner set of layers a space (figs. 7 and
8) occurs filled with finely granular fluid, in which clear
nucleated cells ( b c) are to be discerned. This space is not
continuous all around the ovary. It remains always uncoloured,
or only very slightly coloured by various staining fluids, and
appears of a dirty yellow hue. Of the cells floating in it the
nuclei and the nucleoli colour very deeply, while the cell body
always remains uncoloured. They have a very delicate but
definite contour. By these and other peculiarities they are
easily distinguished from all the other cells found in the ovary.
They are sometimes found solitary, when they have a round
or oval form, but often in groups, when they are polygonal.
Sometimes in narrow spaces they arrange themselves in com-
pact rows of square cells. This granular mass evidently
represents blood plasma and the cells blood-corpuscles.

I made many attempts to inject the ovary with some

ON DEVELOPMENT OF ATYEPHtRA COMPEESSA. 397

colouring fluid, and thus to bring out the nature of these
spaces clearly, but unfortunately I have not succeeded in doing
so. Still I think I have enough reason for believing that they
are blood spaces, and nothing else ; for in the first place the
sections of the heart and blood-vessels show us that in their
cavities the same granular mass with similar cells occur. The
granular substance and the cells exhibit no difference what-
ever to those found in the ovary. In the second place, blood
taken out of the body of the animal, and exposed to the fumes of
osmic acid 05 per cent, strong for about five minutes, and coloured
with Ranvier’s picro-carmine, shows the blood-corpuscles
exactly corresponding in shape and size to those found in the
ovary. In the third place, the above-mentioned cells are ex-
tremely variable in form, and have no definite position in the
granular mass. In the fourth place, the ovary of Panulirus
japonic us, Gray, whose blood-vessels have been injected with
a blue injecting mass, shows the presence of blood in similar
places. Finally, fresh specimens show blood-corpuscles in the
corresponding place.

Blood not only gets into these spaces, but enters into the
vitellogen, and fills up the spaces or lacunae between the adjoin-
ing eggs (figs. 3 and 13 bs.), while in the germogen no trace of
them can be detected. These blood spaces are best observed
in the ovary not fully developed.

Of the distribution of the blood vessels in the ovary, I have
not been able to make a satisfactory observation in Atyephira ;
but I have made it out clearly in Panulirus, of which I may
therefore be allowed to write a few notes here.

The ovary of Panulirus j aponicus, injected with the blue
injecting mass, showed me that the sternal artery gives off a
large branch to the right ovarian lobe. It soon divides into
two branches, of which one, running anteriorly for a short
time, sinks deep into the body of the ovary, while the other
runs through the entire posterior lobe. Slightly anterior to
the origin of the sternal artery, a small branch is given off to
the left lobe directly from the lower side of the heart. This
runs posteriorly for a short distance, but soon divides into two

398

CniYOMATSU ISHIKAWA.

branches. Like that to the right lobe, one of these taking the
backward course runs through the entire posterior part, while
the other running anteriorly, soon sinks into the substance of
the ovary.

In front of the heart two other branches are given off, from
the antennal arteries. Each of these soon divides into three
main branches : the anterior, the posterior, and the median or
lateral. The anterior runs along the whole length of the
anterior half of the ovary, the posterior divides into fine
capillaries, and penetrates into the interior of the ovary, while
the lateral unites with its fellow of the opposite side. There
are no large vessels on the lower side of the ovary.

In some specimens, the sternal artery runs over the left lobe
of the ovary, giving off a branch to it, while the right lobe
was supplied with one given off directly from the heart.

The inner set of layers in the ovarian walls consists of (1) a
fine structureless membrane (fig. 10, mb.), and (2) a layer of
pyramidal epithelial cells. This epithelial layer will be spoken
of as the “ internal ” epithelial layer in contradistinction to
the one already described, which will be called the “external.”
The internal epithelial cells exist only over the vitellogen, the
wralls of the germogen being devoid of the epithelium properly
so called. The epithelium cells (figs. 8, 9, and 10, fe.) are in
general somewhat elongated, and are furnished with a finely
granular nucleus, in which a nucleolus can be detected. The
ceils measure about 0'2 mm. in length and 0 08 mm. in
breadth, and the nuclei are about one tenth the size. The
epithelium, together with the structureless membrane, enter
into the ovary and surround the eggs in the vitellogen, form-
ing thus a sort of a follicle (figs. 8, 9, 10, 13, fe.).

The wall of the oviduct shows the same structure as that of
the ovary itself, excepting that the superficial epithelial cells
are, as already stated, decidedly smaller than on the ovary
proper, being only about one third.

It appears thus that the wall of the ovary and oviducts
consists (1) of a connective-tissue layer; (2) of an external
epithelium ; (3) of stroma ; (4) of blood space ; (5) of a struc-

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 399

tureless membrane, on the inner side of which is (6) a layer of
internal epithelial cells.

The Formation of Eggs: — In the white band already-
spoken of (figs. 2 and 3, ger.), we find the youngest eggs. They
appear perfectly clear and transparent, and measure about
OOl mm. in diameter, with roundish nuclei of about 0.008
mm., the size of the nuclei of the inner epithelial layer. A
section of an unripe ovary, whose lobe measures about O’ 14
mm. in cross diameter (fig. 9), shows us that the ovary is
surrounded by a single-layered wall. This wall corresponds to
the external epithelial layer of a ripe ovary. The sac is filled
with a general mass of nucleated cells embedded in protoplasm,
which latter shows a fine granulation in prepared specimens.
The wall of these cells is extremely delicate, but is clearly dis-
tinguishable in fine preparations. Some of these cells probably
arrange themselves around the inner side of the ovarian wall as
the internal epithelial layer, some surround the larger eggs that
have moved to one side of the ovarian tube and become the
follicular (?) epithelium (fig. 9,/ e.), while the others grow into
primordial ova (p. o.). Thus at this stage of the development
of the ovary there is no marked difference to be observed
between the cells that grow into eggs and those that become
the internal epithelial or follicular cells.

In the section of a larger ovary we find the youngest ova all
along the external side of the germogen immediately below the
external epithelial layer. But the interesting stages are repre-
sented in those sections (figs. 10 and 11), cutting through the
oviducts, whose internal epithelial cells ( i . e. od.) are seen to
acquire a more rounded form {p. o.) and pass uninterruptedly
into small eggs. Mayer (pp) affirms that a genetic relation
exists between these two elements. Waldeyer in his “Eier-
stock und Ei” (^5) mentions a similar case in the ovary of
Astacus fluviatilis. Of this last animal Professor Huxley
also says (-f-2) : “ The growth of these cells gives rise to
papillary elevations which project into the cavity of the ovary
and eventually become globular bodies attached by short stalks,
and invested by the structureless membrane as a membrana

400

CHITOMATSTJ ISHIKAWA.

propria. These are the ovisacs. In the mass of cells which
becomes the ovisac, one rapidly increases in size and occupies
the centre of the ovisac, while the others surround it as a
peripheral coat. This central cell is the ovum.” If we con-
ceive a number of such ovisacs to arise in a special part of
the ovary, and joined with one another in a line longitudinal
to the ovary, we shall have a case somewhat similar to that of
Atvephira, from which, however, it differs in the fact that only
one, out of a number of cells that constitute an ovisac, grows
to be an ovum. In Atyephira, as we have already seen, all of
the cells, or the majority of them, no doubt, in the pouch are
destined to become eggs. It will be observed further, that a
complete distinction is here made between the cells which con-
stitute the follicular epithelium, and those which become eggs.

The youngest eggs (figs. 9, 10, and 11 ,p.o.) have their size
equal to those of the epithelial cells. They have a very deli-
cate contour, and their germinal vesicle generally contains one
or two germinal dots. They are quite transparent until they
grow to the size of at least *09 mm. in length. In a little
older eggs, the protoplasm, however, shows a very delicate
tint of blue, while the germinal vesicle appears of a very faint
ochre. There is also present in the ovum one or more
vacuolar spaces (figs. 10, 11, 13 and 14, vac.). They appear in
the ovum of about -035 mm., and their number rapidly in-
creases when the ovum is transferred into the vitellogen. Ed.
van Beneden has observed beautiful amoeboid movements in
very young eggs of Isopods, Amphipods, and some Decapods —
C rang on vulgaris — when they are held in suspension in the
serum of blood or in aqueous humour. My experiments have
failed to detect such a phenomenon in the eggs of Atyephira.

The germinal vesicle is at first uniformly granulated by fine
granules, provided with one or more germinal dots, which latter
can only be distinguished from the granules by their larger
size, and by their being strongly coloured by staining fluids
(figs. 10, 11, and 12). As it grows in size these granules
become coarser, and patches of stellate figures (figs. 13
aud 14) are formed, probably by the union of the granules.

ON DEVELOPMENT OF ATYEPH1RA COMPRESSA. 401

The size of the germinal vesicle is proportionately larger in
young eggs than in the older ones, the growth of the vesicle
being slower than that of the egg. Their proportionate sizes are
to be seen from the following : —

Egg.

Ger. Ves.

•01

mm.

. '007 mm.

•on

33

•009 „

•013

93

•009 „

•014

93

•0095 „

•016

99

. -oi „

•017

99

. -oi „

•018

99

. -oi „

•020

33

CM

r-H

o

•021

99

• -012 „

•024

33

. -013 „

•026

93

. -013 „

Egg.

Ger. Ves.

•028 mm.

•014 mm.

•05 „

•02 „

•052 „

oo

04

o

•068 „

•03 „

•08 „

•035 „

•085 „

•03 „

•09 „

•03 „

•095 „

•035 „

•160 „

•045 „

•350 „

•07 „

It is clear from this that while the germinal vesicle is at
first more than one half, it is only one fifth when the egg
attains the diameter of about ‘35 mm. In Eupagurus, Mayer
mentions a similar case, where he found the germinal vesicle
of 44 jj. in the egg of 72 fi, and soon after the germinal
vesicle of 62 n in the egg of 146 n (I4p ).

The germinal vesicle is provided with one or more germinal
dots, but never more than three. They generally take an
excentric position, and are, in the first stages of their develop-
ment, simply aggregations of the protoplasmic granules in the
germinal vesicle ; which gradually coalesce into a form of con-
siderable dimension (fig. 12). This coalescence takes place
either at a single spot, when only a single dot is formed, but
often at two or three different places, when we have two or
three germinal dots. At this stage of development, which is
represented by the egg of, at the most, *02 mm., they have no
definite boundary, but as they grow in size, the granulations
seemingly fuse together into a roundish mass, having a smooth
edge. At the same time, a number of vacuoles appear in them,
which, however, dwindle away later.

When the eggs grow to the size of at least *10 mm. in

402

CHIYOMATSU ISHIKAWA.

diameter, they pass into the vitellogen, to be charged with
nutritive elements. Here they grow very rapidly, and their
colour gradually becomes altered to a dark green. Nutritive
elements or yolk-spheres grow and multiply rapidly on all
points of the egg, but especially in a region near the peri-
phery. The vacuolar spaces, mentioned above, also increase
very rapidly in number and size, while the protoplasm becomes
thus alveolar in its structure (fig. 14). The protoplasm which
had originally filled the entire body of the ovum, has now
become very scarce; i. e. in proportion to the size of the egg;
and when the egg attains its Tull dimensions, it becomes a
matter of great difficulty, even in nicely prepared sections, to
discern the presence of protoplasm among thickly crowded
vacuoles and yolk-spheres.

This peculiar arrangement of protoplasm suspending the
deutoplasmic elements in its meshes, is also stated to occur
among Vertebrates (4T9).

But how, it may be asked, do the yolk-spheres of the egg
originate ? Do they develop in the protoplasm of the egg or
do they arise from the investing follicular cells ? Lereboullet
(A) regards them as originating in a special kind of cell con-
taining the yolk substance, while Waldeyer (8T5) derives the
yolk-elements from the follicular epithelium cells. Ed. van
Beneden (A) says : “ I have believed, at first, that the nutritive
elements of the vitellus had taken birth in the special cells of
the vitellogen, and that these cells are absorbed by the proto-
plasm of the egg-cell. But I have soon recognised that there
is a considerable error, and that the germs never present the
cellular appearance, if we observe them in the interior of the
sexual utricle or in an indifferent fluid, such as the iodite of
serum or a solution of albumen. At present I am certain that
the nutritive elements of the vitellus always form themselves
in the interior of the protoplasm of the egg-cell, as Mr. de la
Valette St. George has recognised long ago.” In Astacus
fluviatis, according to Professor Huxley (AJ4), “ the proto-
plasm of the cell, as it enlarges, becomes granular and opaque,
assuming a deep brownish-yellow colour, and is thus converted

ON DEVELOPMENT OF AT YE PH IRA COMPRESSA. 403

into the yolk or vitellus.” I believed for a long time that the
nutritive elements were derived from the vacuolar spaces already
mentioned, because in these spaces I have often observed, in
fresh specimens, small refracting spheres which resemble very
much those of the yolk-elements. I have, however, found out
that my so imagined yolk-spheres were nothing but the
particles of water that have, in some way or other, found their
way into these vacuolar spaces; for when I examined the ovary
in the solution of bicarbonate of potash or ammonia (2 per
cent, strong), I have invariably found that the vacuolar spaces
are free from any such thing, and that these elements are only
seen when the ovary is examined under water.

As the egg increases in size the protoplasm becomes coarsely
granular at the periphery. These granules are quite opaque
at first, but become more or less transparent as they grow in
size ; they assume a deep greenish colour and become con-
verted into the yolk-spheres. The yolk-spheres are in general
round and homogeneous, showing no trace of a nuclear struc-
ture. Their size varies much, the smallest being no larger
than yolk-granules, and the largest often measure *003 mm. in
diameter. My observations therefore point out that the yolk-
spheres originate endogenously out of the protoplasm of the

egg-

This agrees with the statements made by Huxley in his
Crayfish (-MpO; and still more with the results obtained by
Professor Whitman in his Clepsine

As the yolk-spheres and the vacuoles are formed the proto-
plasm of the egg becomes reticular in its structure, suspending
these spherules in its meshes. But at two places the proto-
plasm remains in a more or less thick continuous layer. These
are around the germinal vesicle, and at the extreme periphery*
of the egg. The peripheral protoplasm appears to give origin
to a distinct membrane, which I call by the indifferent name of
“ primary egg-membrane.” In the oviduct it receives another
membrane from the lining epithelial cells, which at this time
present a glandular appearance (fig. 15). This outer membrane
will be spoken of as “ secondary egg-membrane.” Between

404

CHIYOMATSU ISHIKAWA.

these two membranes a certain quantity of clear liquid is found,
which coagulates and becomes finely granular in alcohol.

The primary egg-membrane always shows a granular reticu-
lated appearance, with oval or round interstices. These are
caused by the yolk-spheres, on which the membrane closely
adheres at the beginning, and is not to be mistaken for the
cellular markings found in insect ova. The secondary egg-
membrane is perfectly structureless, and is thicker and firmer
than the primary. Both egg-membranes are at first extremely
elastic, as is seen in the exit of an egg through the narrow
opening of the oviduct.

A number of different observers have spoken of the existence
of two membranes on the eggs of Decapods. Rathke (-|) and
Reichenbach (^7) have found them in the eggs of Astacus
fluviatilis, Bobretzky in Palsemon, Erdle in Homarus,
and Dohrn in Scyllarus arctus f2-^1), Palinurus vul-
garis (2T5f), and in Portunus (Vr)-

It remains now for me to consider very shortly the germinal
vesicle and its final fate. The germinal vesicle presents one or
two or rarely three germinal dots in younger eggs ; but in those
eggs which are grown to a considerable size, and which are
found in the vitellogen, are always provided with a single dot.
It is thus distinguished from the ova of Astacus, in which
Lereboullet, Waldeyer (\5), Huxley (^-§-2-), and others have
found many germinal dots, and from that of Eupagurus, where
Mayer has found only a single dot in all the stages of the
development of the egg. It does not grow, as I have already
mentioned, as rapidly as the egg, and when the egg is
quite ripe the germinal vesicle disappears. I have made hun-
dreds of sections of the ripe ovary, and have always found
the ripened eggs devoid of nucleus, while the younger ones
show it very plainly. No nuclear structure can also be seen
in freshly-laid eggs. Mayer speaks of it so explicitly in the
egg of Eupagurus that I will quote his own words here (-i-f-2) : —
“ Nach einiger Zeit, und zwar noch wahrend das Ei im Ova-
rium befindlich, verschwindet — wie dies auch schon Rathke
von Astacus angibt — das Keimblaschen, so dass die frisch

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 405

gelegten Eier positiv kernlos sind.” But how it dwindles
away is a question not yet decided. The germinal vesicle,
which is at first always in the centre, is often found to be
somewhat excentric in position in an egg little advanced, but
never at the periphery. Commonly, however, I have seen the
wall of the vesicle indented and rather indistinct. Whether
this shows the transitional stage from the nucleated cell to a
cytode or not I cannot venture to affirm. All that I can say
is that the germinal vesicle disappears while the egg is still in
the ovary.

To sum up, then —

1. The ovarian egg of Atyephira compressa originates
from the inner lining epithelium of the ovary, and is, at the
beginning, a cell with a nucleus, and one, two, or rarely
three, nucleoli. Later, the deposition of the yolk takes place
endogenously.

2. The protoplasm of the egg collects at two points, the one
around the nucleus and the other at the periphery. The
former spreads out like rays towards the latter, and unites
with it.

3. The germinal vesicle grows less vigorously than the
egg. It disappears speedily when the egg attains a certain
size.

4. The ripened egg is covered by two membranes, the one
formed by the hardening of the peripheral protoplasm of the
egg, while the other is formed by the product of the epithe-
lial cells of the oviduct. Between these two membranes a
certain quantity of a clear transparent liquid is found.

5. The freshly-laid egg is unfurnished with a nucleus, and is
therefore a cytode.

Laying of Eggs. — When the eggs are fully grown, and
ready to be laid, the region of the oviduct appears white by
the reflected light through the carapace. The section of such
an epithelium will show that the lining cells are very much
elongated (fig. 15). If an animal in such a condition is put
into a vessel and watched for a day or two the laying of eggs
can easily be observed. This generally takes place in the early

406

CHIYOMATSU ISHIKAWA.

morning, and is preceded by an exuviation, which usually occurs
during the night. The mode of egg-laying seems to be essen-
tially the same as that described by Lereboullet, although, un-
fortunately, I have not been able to get an access to his original
description, an inconvenience which often happens to a natu-
ralist working here.

The prawn before the egg-laying is seen to be very uneasy
(the uneasiness may, perhaps, be owing to the late exuviation),
continually moving about until it finds a good resting place.
It then bends its body downwards in the form of a fish-hook,
and thus forms a sort of a pouch with its abdomen, the tail of
the animal corresponding to the point of the hook. Into this
pouch the eggs are laid.

During the act of laying the thoracic legs are kept continually
moving, the last pair seemingly assisting to drive the eggs
downwards, while the swimmerets are seen to be in rapid
motion. The abdominal segments from the first to the fifth
are also seen to move rhythmically.

The eggs in coming out of the oviduct become very much
elongated, almost rod-like, and, outside of the body, seem to
take their course along the median line until they reach the
abdomen, where they stick to the swimmerets. As regards
the position of the eggs in relation to the swimmerets, I have
observed that those eggs which come out earlier are received
by the anterior pairs, while the later ones are driven to the pos-
terior by the last pair of thoracic legs. As soon as they leave
the oviduct they become more spherical, until they take their
characteristic ellipsoidal form.

There seem to be various opinions as to the means of the
fixation of the eggs to the hairs of the swimmerets. Accord-
ing to Lereboullet, the soft skin of the abdomen of the mother
crayfish (Astacus fluviatilis) secretes a liquid which gives
origin to both the outer egg-membrane and to the substance
binding the eggs to the swimmerets. Huxley in his Crayfish
says (L0) : "These as they leave the apertures of the oviducts,
are coated with the viscid matter, which is easily drawn out
into a short thread.” For my own part, I can say almost nothing

ON DEVELOPMENT OP ATYEPHIKA COMPRESSA.

407

on this point except that I have not seen any gland other than
those found in the oviducts.

At an early period of development, the inner and the outer
egg- membranes lie so closely together that it is a matter of
great difficulty to separate them. They are both very elastic
and are quite structureless, except that the inner egg-membrane
is marked with the polygonal areas already spoken of. The
newly-laid eggs show no structure like a nucleus in them. I
have often tried by means of sections and otherwise to find out
how the nuclei of the post-ovarian eggs arise, and how the
spermatic elements act upon them, but I have entirely failed, as
I did in the case of the disappearance of the nuclei. All that
I am certain of is that the original nuclei disappear before the
formation of fresh ones capable of segmentation, and that the
egg probably receives the male elements as soon as they come
out of the oviducts, for the reason that I have often observed
a spermatophore attached on the sterna of the female during
the breeding season.

Judging from figs. 14 and 15 represented in Faxon’s
“ Embryological Monographs,” pi. iv, I see that the male
and the female pronuclei were found in the eggs of a Copepod
(Cetochilus septentrionalis) by Grobben. In sections
of freshly-laid eggs I have twice observed an appearance that
may be interpreted as the process of the fusion of these two
elements ; but this I can say only with much caution, for I
have never seen the stages before or after it.

The form of the egg is in general ellipsoidal, measuring
about 0 75 — 0 85 mm. in long axis and 0*45 — 055 mm. in
short axis. Its colour varies much according to the colour
of the mother prawn, but is usually of a yellowish green. The
colour of the animal varies again with the surrounding objects ;
thus when the prawn is caught among the green grass it is
more or less greenish, but when it is caught among the dead
grass, which is usually the case in the late autumn and in
winter, it partakes somewhat of the colour of hay. When,
again, the animal is transferred from its natural habitat to a
white dish, it gradually loses its colour in the course of a few

VOL. XXV. NEW SER.

D D

408

CHIYOMATSU ISHIKAWA.

days, until it becomes nearly colourless. This also seems to be
the case with the eggs ; undergoing similar changes, when
they are subjected to different external conditions. A case of
similar nature is also stated to occur in the eggs of Eupa-
gurus by Dr. P. Mayer where he says (-244) : “Es bestehen

aber in der Intensitat der Farbe individuelle Abweichuugen,
wie dies auch schon vor mir andere Autoren beobachtet und
mit seltener Uebereinstimmung auch stets (ob mit recht?)
auf Yerschiedenheiten in der Farbung des Mutterthieres
zuruckgefuhrt haben.”

Development.

Segmentation: — The newly-laid egg shows no nucleus, as
before remarked, but soon a definite one appears in the centre.
The inner and the outer egg-membranes, which at this early
date lie so closely together, separate after a lapse of ten to
fifteen hours, and a certain quantity of albuminous fluid collects
between them. A similar fluid is stated to occur in the
Orchestia eggs by Ulianin ( Vk1), where, however, the occur-
rence is of a much later date, namely, at such stages where a
fine cuticular skin becomes distinguishable around the embryo.
This fluid becomes coarsely granular when the egg is treated
with such reagents as alcohol, acids, &c. It becomes a cause
of great hindrance for hardening, as has already been pointed
out by Ulianin (4-4J); and in order to avoid this difficulty I
have used the same method described by him, by which means
alone I was enabled to harden the eggs properly. This method
consists in breaking off' the secondary egg-membrane by means
of the points of needles under the dissecting microscope, the
eggs being placed in a watch-glass under water. After the
greater part of the albuminous fluid has escaped out of the
slit thus made, the eggs were brought to the hardening fluid,
which now reaches the embryo easily.

Segmentation begins by a slight notch on one side of the
egg transverse to the long axis (figs. 17 and 18). This notch
gradually elongates both ways, until the egg is divided into

ON DEVELOPMENT OF ATYEPHIEA COMPRESSA.

409

two equal parts (tigs. 19 and 20). After remaining in this
condition for about two or three hours, the segmentation line
becomes narrower, the two halves gradually approaching each
other, and at last the egg is again in a condition not externally
different from that which Ave started (tig. 23). Internally,
however, we see the nuclei clearly separated from each other,
and these are sometimes in the state of division, showing thus
the commencement of the second or the longitudinal furrow.
After resting three to four hours more, the first line becomes
visible again (fig. 24). It soon divides the egg into two equal
halves as before. Immediately after (5 — 12 minutes) the
second line of division makes its appearance at right angles
to the first and divides the egg into four equal parts (fig. 26).
This line generally makes its appearance first on one half
close to the first furrow, and is soon followed by a corre-
sponding line on the other half. They travel in opposite
directions, until they meet with each other on the other side
of the egg. Sometimes, as an exceptional case, two lines of
the second furrow appear simultaneously on the two halves of
the egg close to the first furrow at a distance of 90° from each
other. These divide the egg into four equal parts as before,
but only with this difference, that the four segments do not
lie in the same plane. This irregularity is, however, soon
lost in the next stage, when the division of the egg proceeds
up to eight segments, the second vertical furrow appearing at
the distance of 90° from the first vertical furrow. About two
hours after the egg has been divided into four parts, the
second line becomes narrower, and the four divided parts
again coalesce into two. Some time later, the first transverse
furrow becomes also fainter, and the egg apparently retro-
grades to its first stage before segmentation, with the difference
of having four nuclei instead of one (figs. 2 7 and 28). At
the end of a short period of repose, the nuclei prepare to
divide, and with this the original furrows are again restored
in order of their appearance, soon followed, this time, by the
second set of longitudinal furroAVs dividing the egg into eight
equal parts (figs. 30, 31, 35, 36, and 37).

410

CH] YOMATSU ISHIKAWA.

A similar case of segmentation is stated to occur in the egg
of Lucifer by Brooks

The segmentation to this stage may thus be compared to the
first segmentation period of Mayer (- °-5~2-2-!). After this it
goes on regularly. Each of the eight spheres is now divided
into two by the second set of equatorial furrows, and the egg
therefore consists of sixteen equal spheres (figs. 32 and 38).
In each of these the protoplasm takes the peripheral position
and the deutoplasm the central. The nuclei of the egg can
now be seen on the surface. After a pause a third set of longi-
tudinal furrows appears almost simultaneously, and divides
the egg into thirty-two parts (fig. 33). The central deuto-
plasmic portion of each segment now segments off from the
peripheral protoplasmic and form “ yolk-segments ” (Bal-
four '-j^) of unequal sizes (fig. 39, ysg.), the cells arranged
at the periphery being well marked from these segments.
This seems to be an exception to what is generally seen among
the Decapod eggs, where the apices of the segments, at such an
early stage, are usually fused in the deutoplasmic mass in the
centre of the egg, the mass showing no distinct divisions into
segments. Transverse furrows now divide the egg into sixty-
four parts. New yolk- masses are separated off from the
segments. Longitudinal furrows again divide the egg into
128 parts (fig. 34). After the egg is divided into 256 parts
by new furrows, its shape becomes spherical and the segmenta-
tion unequal.

Now the segments at a small area near one pole of the egg
divide faster than the rest (figs. 41 and 42). This area is
depressed a little, and the egg appears bean-shaped when
viewed from the side. A section of this stage shows a row of
lenticular cells near one pole (fig. 40, b l ), separated from the
yolk-mass, while the nuclei at the rest of the egg- periphery
still occupy their position at the surface of the pyramidal cells.

Each “yolk-segment” (figs. 40, 43, 51, and 53) contains a
number of yolk-spheres and clear vacuoles. The yolk-spheres
are normally oval in shape, but become polygonal in hardened
specimens. The vacuoles are of varying sizes, often very

ON DEVELOPMENT OF ATTEPHIRA COMPRESSA.

411

small, but sometimes so large as to fill up nearly two thirds of
a yolk-segment. Within the yolk-segments are seen a fair
number of nuclei, placed not at the centre, but rather to one
side of them. Each nucleus is furnished with a dark-staining
nucleolus, and a layer of protoplasm prolonged into a reticu-
lum. I have not traced the origin of these nuclear bodies.
It is, however, probable that they are derived from the seg-
mentation nuclei. In one or two of my sections I have
observed them in eggs segmented to 128 parts. Balfour
figures and describes the nuclear bodies in the “ yolk-seg-
ments” of Agelena, which in all particulars correspond with
what I have seen in those of Atyephira. Of the origin of the
nuclear bodies in the “ yolk-segments,” he says ( 4tt*) : “The

nuclei of the yolk-cells are probably derived from the nuclei
of the segmentation rosettes, and it is probable that they take
their origin at the time when the superficial layer of proto-
plasm separates from the yolk-columns below to form the blas-
toderm.”

The depressed area appears white by reflected light.
Starting from this area, the lenticular cells are gradually
formed all over the rest of the surface, by the separation of the
superficial protoplasmic layer from the yolk- segments below.
While this is going on, the cells of the area become a little
thicker (fig. 43) and the depression smaller, and the egg again
assumes the elliptical form. The “ yolk-segments ” are now
of nearly equal size.

Gastrula, &c. — The white area, or “the Keimscheibe,” is
depressed a little, and the egg appears bean-shaped from the
side (figs. 42 and 44). The cells near one point (nearer to one
pole of the egg) of this depression multiply faster than those
in other parts of the surface. These cells gradually sink down
into the yolk and eventually form a cup-shaped cavity whose
mouth is bounded by about twenty cells (figs. 45, 46, and 51,
y. m.). This cavity, or the gastrula, is at first very shallow,
but it soon grows inward and forward, so that it becomes com-
paratively deep (fig. 52, g. m.). While this is going on, an
elevation of the cells takes place on the middle part of the

412

CHIYOMATSU ISH1KAWA.

depression, transverse to the long axis of the egg, and divides it .
into an upper circular (figs. 45 and 46, a.) (containing the
gastrula cavity) and a lower oval one (figs. 45 and 46, b .).
The cells around the blastopore become much elongated, and
appear white by reflected light. The lower oval depression
disappears, while the blastopore and the circular depression
get much smaller (fig. 47). The white area around the blasto-
pore shifts upwards and takes a definite triangular shape (fig.
49, ab). The depression becomes shallow and the blastopore
closes (figs. 50 and 53, g. to.).

Germinal Layers. — With the formation of the gastrula,
we can already distinguish the origin of the germ-layers. The
endodermis formed from the invaginated cells of the gastrula,
while the rest of the blastoderm gives origin to the ectoderm.
The cells of the bottom of the cavity as well as those near the
blastopore gradually elongate, as was already said, and give off,
by continual division, the cells of the mesoderm (fig. 52, ms).
The formation of the mesodermic cells is more vigorous at
the forward edge of the cavity than on the floor, and the con-
sequence is that the opening of the cavity is gradually lessened,
as has been clearly shown by Reichenbach (ff). At the time
of the closure of the gastrula, there is seen a mass of proto-
plasmic elements, aggregated just below the superficial ecto-
derm (fig. 53, w. y.), which is very likely to be compared to
the white yolk-elements of Reichenbach. After the closure of
the blastopore the endoderm cells gradually travel into the
yolk-segments, and their nuclei become indistinguishable from
those of the yolk (fig. 54, h y ). Whether there exists a definite
cell-outline to each of the endoderm cells after they have
removed into the yolk, or whether the cell outliue is lost, I
cannot tell with certainty.

At a region somewhat in front of the late blastopore, a fresh
invagination takes place, which gives rise to the permanent
anus (fig. 62, pd.). The triangular white patch becomes more
definite, and there is formed on each side of it, in front, a
circular elevation (figs. 55 and 56, md.), which later becomes
the mandible. The oval area in front of these becomes circu-

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA.

413

lar and forms the first rudiments of the carapace (figs. 54, 55,
56, cp.). On the side diametrically opposite to this two oval
elevations (figs. 56, 58, 59, oc.) appear. These are at first
somewhat separated from each other, but their interval is
gradually lessened until they become connected together bv an
elevation of the intervening space. These are the first traces
of the cephalic lobes. These gradually travel upwards (or mor-
phologically backwards) as will be seen from figs. 60 and 61,
oc. Immediately behind these the first traces of the first pair
of antennae become visible as oval elevations, and a little
smaller than the cephalic lobes (fig. 60, At. 1). Then the
second pair of antennae (fig. 60, At. 2) is formed, so that the
order of the formation of the parts of the embryo is as
follows : — Abdomen, mandible, cephalic lobes, carapace, the
first pair of antennae, and the second pair of antennae.

After a while the cephalic lobes come closer together, the
first pair of antennae elongates, and a crescent-shaped depression
(fig. 61, lb.) is produced on the median line of the embryo in
the region between the first pair of antennae, which marks out
the labrum. The second pair of antennae, which up to this
time was single, now becomes bilobed (fig. 61, At. 2), and the
abdomen (fig. 61, ab.) takes a more spherical form. A section
at this stage (fig. 62, ab.) shows that the cells of the abdominal
region are much larger than those of other parts. The meso-
dermic cells (fig. 62, ms.) are very much crowded in the tho-
racic region, and a few in the cephalic and abdominal. This
is the nauplius stage of the embryo.

In Palaemonites vulgaris, according to Faxon (S-£J),
“ the parts of the embryo which first appear are the abdomen,
the labrum, and the cephalic discs, and the first three pairs of
appendages.” The rudimentary carapace, which in Atye-
phira compressa appears before the first three pairs of
appendages are formed, here comes into view after the third
pair of maxillipedes is formed (31^8).

Stomodseum and Proctodseum. — Soon after the closure
of the gastrula cavity a fresh invagination of the ectoderm
takes place slightly in front of the late blastopore. This gives

414

OHIYOMATSU ISHIKAWA.

rise to a very narrow tube — the proctodseum. The invagina-
tion deepens as the embryo grows larger, and the cells lining
its wall become columnar. The cells at the blind end of the
proctodseum later become continuous with the peripheral cells
of the yolk-mass (fig. 76), and thus the communication is
made between the proctodseum and the yolk-mass. Slightly
before the stage represented in fig. 61 a crescentic depression
is formed between the cephalic lobes and the first pair of
anteunse, which gives rise to the stomodseum. It is at first a
narrow blind tube like the proctodseum, and is directed upwards
and forwards ; but as it grows it makes a sudden turn back-
wards, and its blind end considerably enlarges, forming a
spacious chamber, the future cardiac division of the stomach.
The communication between this chamber and the yolk-mass
is opened at a much later date than that of the proctodseum,
namely, at a stage slightly before the hatching of the embryo.
It will thus be seen that both of these invaginations arise
after the closure of the gastrula cavity, and independently
of it.

Secondary Mesoderm. — At the stage now described some
of the yolk-segments which lie close below the embryo become
markedly changed. They show a number of small granules
(fig. 62, sms.), which are easily coloured by logwood solution.
These granules are sometimes of considerable size, each having
a clear cellular outline. They gradually come out of the mass
and become transferred to take their position immediately
below the ectoderm (figs. 64 and 65, sms.), mingled with other
mesodermic cells. These are mostly aggregated in the cephalic
region, between the involutions of the ectoderm cells, but are
also found in all places. Their size is very small compared
with other cells, as will be seen in the figure. The time of
their appearance and their position seem to indicate that they
may probably be comparable to the “ Secundare Mesodermele-
mente” of Reichenbach ( -4 9, V -5 2 ) , from which they differ,
however, in size and in general appearance.

Nervous System. — Although my observations on this head
are very imperfect, some of the sections I obtained show struc-

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 415

tures which appear to me of some interest. Up to the valuable
contributions of Reichenbach almost nothing was known on
the origin of the nervous system among the Decapod crus-
taceans.

The result of his investigation is briefly this (x 5.2t~0' 59).
The whole nervous system arises from (1) the median groove,
(2) the lateral strings, and (3) the depressions in the cephalic
lobes. The cells of the lateral strings and the groove give rise
to the ventral cord, while those of the cephalic depressions
become the supra-oesophageal ganglion. Some of my sections
of the nauplius seem to show the similar structure. Thus the
fig. 63, which is the transverse section of an embryo through
the cephalic region, shows the thickening of the ectoderm cells
on both sides of the median line (fig. 63, cd.). In figs. 64
and 65, which represent two consecutive sections passing
through the mouth opening, are shown the structures of the
same nature. In fig. 66, a section cutting through the posterior
part of the mandibles, the ectoderm is quite thick on both sides
of the median line, which possibly corresponds to the lateral
thickening of Reichenbach. Fig. 67, which represents a sec-
tion similar to fig. 66, but of an embryo slightly older than it,
shows two circular masses of cells on each side of the median
line below the ectoderm cells. These appear to be the section
of the two lateral portions of the ventral nerve-cord after its
separation from the superficial ectoderm. But as these are the
only sections by which I can get any knowledge of the origin
of the nervous system, and as I have neither traced the origin
nor the fate of the structures described, I have not written
here anything more than a short description.

The embryo gradually gets larger (fig. 68). New appen-
dages (fig. 68, mx. 1, 2, and mxp. 1) are formed, behind the
mandibles, in regular succession. The two maxillae (fig. 68, mx.
1, 2) are at first single appendages like the mandible ( md .), but
soon become bilobed. The appendages behind the maxillae
are bilobed from the time of their appearance. The appearance
of the maxillae as single-lobed appendages differs a little from
the case ofPalaemonites (3-A?), where they are bilobed from

416

CHIYOMATSU ISHIKAWA.

the start. From the embryo of Panopeus (yg-) it differs in
the fact that the second pair of maxillae of that Crab is bilobed
from the beginning, and is not single as in Atvephira.

At the base of the second pair of antennae is now seen the
first trace of the antennal gland (fig. 68, gg., and fig. 90). The
ectoderm cells group themselves at this spot into a circular
mass, the cells of which are well distinguishable from other
cells by their regular roundish shape.

The superficial ectodermic cells of the cephalic lobes (fig. 68,
oc.) become marked off from the inner layers. The labrum
(fig. 68, lb.) pushes downwards, so as to lie between the second
pair of antennae (fig. 68, At. 2). Beneath the labrum is seen
the oesophagus (fig. 68, as.) as a square opening. New thoracic
segments become visible behind the first pair of maxillipedes.
The abdomen gets larger, and its end becomes bilobed. In the
notch between the two lobes is the anus (fig. 68, an.), bounded
by about thirteen or fourteen cells. Continued from the anus
is seen the latter part of the intestinal canal, lined with
columnar epithelium. No nauplius eye has as yet appeared.

In fig. 69 all the pairs of the maxillipedes (mxp. 1, 2, and 3)
have appeared. Both antennae {At. 1 and 2) have changed
considerably. The cephalic lobes become more definite in out-
line. The cells of the superficial ectoderm, which later become
the crystalline cones, elongate. The abdomen gets still longer;
five succeeding segments behind the third pair of maxillipedes
have appeared, and the future telson is marked off from the
abdomen at the sides. The outline of the carapace is now
seen extending to over the third pair of maxillipedes. The
depression of the antennal gland becomes deeper.

Fine nervous striations now become visible within the
supra-oesophageal cellular mass (fig. 69, sgn.), whence the
branches are given out first to each of the cephalic lobes.
Each of these branches sends out a branchlet near its base to
the median ocellus (oc/.), the nauplius eye, which is now
formed. Behind they i’un downwards and surround the
oesophagus, giving off branches to both antennae.

Traces of the nervous striae are also seen faiutlv on each

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA.

417

side of the median line as far back as to the segment bearing
the first pair of maxillae. These give out short branches to
the mandibles.

At a little later stage than the last, a short spine-like process
(fig. 70, d.s.) becomes visible on the dorsal median line of the
carapace. This is the rudimentary dorsal spine, which so com-
monly occurs in the Crab Zoea. At the posterior end of the
yolk-mass, where it joins the proctodaeum, small vacuoles and
oil drops (figs. 70 and 71, lv.), both of very refractive appear-
ance, appear. I have not clearly followed the development of
these vacuoles and oil drops, but I am inclined to consider them
as the first indication of the liver.

The heart (figs. 70, 71, h .) now appears on the dorsal aspect
of the embryo within the mesodermic cells occupying the
position just outside the place where the liver (?) globules have
appeared. I have not obtained any good section which shows
the origin of the heart, but my observations tend to show that
it is mesodermic in its origin. The pigment of the eye is now
seen for the first time in this stage.

More segments come into view, and at the stage represented
in figs. 72 and 73, the segments posterior to the last pair of
maxillipedes have increased up to ten.

The first pair of antennae {At. 1) now shows a slight con-
striction on its sides, thus marking out the future basal and
the proximal portions.

The second pair of antennae [At. 2) which is as long as the
first pair, shows the future flagellum and the scale, the latter
considerably broader than the former, and beset with a number
of short setae on its upper side. The flagellum is bifurcated
at its tip.

The mandible (figs. 72, 73, md .) shows no definite structure
as yet.

The first and the second pairs of maxillae and the first pair
of maxillipedes (figs. 72 and 73, mac. 1, 2, mocp. 1) have consi-
derably changed. They all show traces of the future lobules on
their inner sides. The exopodite of the first pair of maxillae is
furnished with three short points, while those of the second

418

CHIYOMATSU ISHIKAWA.

pair of maxillae and the first pair of maxillipedes are provided
with two such.

The second and the third pairs of maxillipedes (figs. 72, 73,
mxp. 2, 3) show no marked change except in size. The telson
becomes more definite in outline. It is somewhat notched on
its inner angles. Inside these notches, on the posterior border
of the telson, are seen five rudimentary setae.

The nervous striations have increased very much. Those
going to the cephalic lobes expand into the shape of a fan in
the anterior third of the lobe. The ocular pigments have
also considerably increased. The ocellus has grown larger.

The yolk-segments are now seen to have a radial arrange-
ment with their nuclei on the periphery. These segments fuse
together in the centre.

Within the intestinal canal (fig. 75, in.) are already seen the
concretions of extraneous matter.

A longitudinal section through this stage (fig. 76), shows
that the epithelial cells have been considerably formed at the
periphery of the yolk-mass near the anterior end of the future
hind gut (in fig. 76, just below the heart, h.). Five bundles
of flexor muscles ( f.m .) are also seen in the abdominal region.
Each of these consists of an aggregation of spindle-shaped
cells, with oval nuclei. No striations have yet made their
appearance within the cells.

The yolk- mass, which up to this time has been uniformly oval,
now changes its form. A large space (figs. 77, 78) is formed
in front of the cephalic lobes by the absorption of the yolk
there. On each side of the embryo, about in the line with the
second pair of maxillipedes, a constriction occurs. A similar
constriction takes place on each side of the cephalic lobes.
Thus the yolk-mass shows five lobes, one antero-median, two
lateral, and two posterior. The lateral and the posterior lobes
later differentiate into the liver.

About two days later the embryo presents the following
characters.

The anterior-median lobe of the mesenteron, which is seen
in the last figure as a single lobe, becomes elevated from the

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 419

rest, and shows two lobes plainly. These lobes indicate the
future csecal ends, (fig. 79, ce .) situated above the pyloric
division of the alimentary canal.

The first pair of antennae (fig. 80, At. 1.) becomes two-jointed,
bearing four setae at its extremity. The endopodite has not
yet appeared.

In the second pair of antennae (fig. 80, At. 2), the setae of
the exopodite {At. 2, ex.) have much increased both in size
and number. From the internal branch two long setae become
visible.

The mandible is now a bilobed appendage ; the anterior lobe,
which is larger, shows two rows of about seven teeth. A small
moveable appendage (endopodite?), beset with minute setae on
its border, is seen at the end of this lobe.

Both lobes of the first pair of maxillae (fig. 81) have a number
of setae on the ends. The inner side of the inner lobe shows
about five lobules beset with setae.

The second pair of maxillae (fig. 82) is little smaller than the
first pair, and is furnished with numerous setae on its inner
lobe, which is cut into five lobules.

The first, second, and the third pairs of maxillipedes (fig. 83)
have not undergone much change. They are, however, all
provided with setae on their extremities.

Behind the maxillipedes the first pair of ambulatory legs
(fig. 83, amb. 1) becomes visible as a simple bilobed appendage.

The dorsal spine is lost.

About twenty-four hours afterwards the mandible and the
maxillae (fig. 84, md., mx. 1, 2) have undergone great changes.
The scaphognathite (fig. 84, mx. 2, s. g) of the second pair of
maxillae is seen in rapid motion. The pigment patches now
appear at different parts of the body. Their distribution is
almost similar to the first stage after hatching.

Embryo just hatched (fig. 85). — About twelve hours after
the stage last described the embryo is hatched. It measures
about 3j mm. in length. The carapace is broad, produced
between the eye into a rostrum ( rs .), at the base of which is a
simple median eye {ocl.). The compound eyes (oc.) are large,

420

CHI YOMATSU ISHIKAWA.

supported upon very short stalks. The abdomeu consists of
but six segments, the telson being still united with the last.
The broad triangular fin (fig. 86) is furnished with fourteen
long setae, each of which is finely feathered on both sides,
except the two outermost pairs, which are feathered only on
the inner side. The three inner pairs of the long setae are,
moreover, provided with short spines on both sides. The
spaces between the long setae are furnished with short setae
( iV°)- Within the abdominal segments, from the first to the
fifth, are seen ganglia (fig. 85, n .) of the ventral nerve-cord,
united by double commissures. The first, second, and the
third ganglia are large, and spherical in form, while the two
succeeding ones are small. The anus is seen as a longitudinal
slit on the lower side of the telson.

The first pair of antennae (fig. 85. At. 1) consists of a basal
segment, and a short distal one, which carries four setae, two
of which are the modified sensory organs. The outer two
are of unequal length, the shorter being feathered on both
sides. The proximal segment carries a single, long, large seta
on its distal end.

The second pair of antennae (fig. 85, At. 2) is nearly of the
same length as the first pair. It consists of a short distal
segment, with two proximal branches, the outer of which (the
future flagellum) is large, and furnished with thirteen setae on
its distal margin. The inner branch is slender, and furnished
with two setae of unequal length, the longer of which is
feathered on both sides. The shorter is curved, and bears a
small, bud-like appendage on its inner side near the base.
There is also a short, stout spine at the base of the inner branch
on the distal end of the proximal segment of it.

The green gland (fig. 85, gg., figs. 93 and 94) is situated at
the base of the proximal segment, its opening being perched
on a little eminence on the inner side of the segment.

The labrum (fig. 85, lb.) is large, lying slightly posterior to
the second pair of antennae.

The mandible (fig. 84, md .) consists of two branches, the
anterior of which is furnished with numerous teeth, and the

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 421

posterior branch is divided into two points. A small, single-
jointed appendage, feathered on both sides, is seen on the
proximal end of the anterior branch as in the preceding stage.
This appendage is lost in future stages.

The first pair of maxillae (fig. 87) consists of a long piece
with two lobes, the outer, or basipodite (fig. 87, bp.), bearing
three setae, and the inner, or coxopodite {exp.) with four setae.
On the outer border of it, somewhat proximal to the division
of the lobes, a single-jointed palpus, or endopodite (fig. 87, en.),
with two long feathered setae, is placed.

The second pair of maxillae (fig. 88) is about as long as the
first, but is much the broader. It is divided into an inner and
an outer lobe. The former consists of a large endopodite (en.),
beset with six rather short setae on its inner border ; a small
basipodite (bp.) consisting of two lobes, both of which bear long
setae, and a coxopodite (exp.), also divided into two lobes at its
extremity, bearing setae. The outer branch of the second
pair of maxillae is a large scaphagnathite ( sg .) beset with
setae.

The first pair of maxillipedes (fig. 89) consists of a broad
basal segment, and two terminal ones. The outer branch (ex.)
is considerably longer than the inner, and consists of two
joints, bearing five long setae on its extremity. The inner
branch (en.) is about two thirds the length of the outer. It
consists of four joints, beset with a few setae on its inner
border. The basal segment also bears short setae on its inner
border.

The second and the third pairs of maxillipedes are similar in
structure to the first pair, except that the basal segment of the
second pair of maxillipedes is less broad than that of the first
pair, and that of the third is again less than that of the second,
while the length of the entire appendage increases in the
reverse order.

Thoracic Appendages. — Four pairs of the rudiments of
these appendages (fig. 85, amb. 1 — 4) are already formed, each
presenting two lobes. The first pair is about half as long as
the third pair of maxillipedes. Each of the two branches of the

422

CHIYOMATSU ISHIKAWA.

first and the second pairs and the inner branch of the two last
terminate in two rudimentary spines.

Within the branchiostegite two rudimentary gills are seen
above the first and the second thoracic legs. The anterior is
about three times as large as the posterior, and shows four simple
lobes within it, while the posterior is as yet a simple sac.
Blood-corpuscles are seen in rapid motion inside these gills.

No trace of the abdominal appendages is as yet visible.

Pigments. — Two large blotches of pigments are seen just
behind the eye-stalks. Three smaller ones are also seen above
the branchial chamber on each side of the carapace, and one on
the median line of the abdomen. On the sternal aspect there
is a large patch at the foot of the rostrum just above the
ocellus, and a series of large median pigments are seen on the
posterior part of each of the abdominal segments. On the last
segment three patches are distributed, one above the anal
opening and the two others on the two lobes of the fin.

The Antennal Gland. — The first trace of this gland
(figs. 68 and 90, gg.) becomes visible at the base of the second
pair of antennae at the time when the first pair of maxillipedes
appear in the embryo. The cells which are concerned in the
formation of it are all ectodermic, and are at first about eight
in number (fig. 90). They form a circular group near the
inner side of the antenna. The median part of this is de-
pressed, and forms a shallow cup-shaped cavity with a tolerably
large mouth (fig. 91). The protoplasm of the cells that are
thus depressed show granulations by which the area can be
easily detected in the surface view. The depression becomes
gradually deeper (fig. 92), while its opening gets smaller and
becomes produced outward. The involution goes on still
further. Granular fluid is already formed in the cavity, some-
times before the hatching of the embryo. The canal formed
by the involution becomes twisted round among the meso-
dermic cells, and by the time the embryo is hatched its con-
volutions are about three or four in number (figs. 93 and 94).

Olfactory Setae. — At the stage of the embryo represented
in fig. 79 the first trace of the olfactory setae becomes visible.

ON DEVELOPMENT OP ATYEPHIEA COMPEESSA.

423

The extremity of the first pair of antennae (fig. 80, At. 1, and
fig. 95). is at this time furnished with four setae. At the base
of each of the two inner setae there is a nucleus enclosing a
darkly-staining nucleolus. No definite external distinction
can as yet be made between these and other setae. Gradually,
however, these become distinct from others (fig. 96). Granu-
lations appear on the upper part of the two setae destined to
become the olfactory organ. A constriction occurs at the
base of these setae, where the nerve-fibre, running from the
ganglionic mass, ends in an enlargement. At the time the
embryo is hatched they show the appearance shown in fig. 96.
After some time, when the embryo is about 4 mm. in length,
they become spatula-shaped, their ends present the form of a
prominent papilla (fig. 97).

At each moulting they appear in twos on the distal end of
each segment, in the same manner as the two first were
formed.

The further changes of the embryo correspond in the main
with what has been observed by Faxon on Palaemonites
(3,°.3,-?32.3). After each moulting the embryo gets more of the
characters of the adult. The last pair of abdominal appen-
dages become visible as two oval plates within the caudal fin
soon after the first moulting. The other appendages are regu-
larly formed from behind forward, while the number of the
ambulatory legs becomes complete.

In the embryo measuring 4 mm. (i. e. two moults after the
hatching of the embryo) the caudal fin or telson separates from
the sixth abdominal segment.

Branchiae other than those already mentioned are regularly
formed. A rudiment of the podobranchiae is first seen at the
coxopodite of the second pair of ambulatory legs as a simple
sac, similar to those of the pleurobranchiae. These (podo-
branchiae) next appear almost simultaneously on the other am-
bulatory legs excepting the last, and then successively on the
third, second, and first maxillipedes. Of these only one pair
(i. e. that on the second pair of maxillipedes) develops into
a permanent gill, while five others (those on the third pair of

VOL. XXV. NEW SEK.

E E

424

CHIYOMATSU ISH1KAWA.

maxillipedes, and the first, second, third, and fourth pairs of
ambulatory legs) modify into peculiarly-shaped appendages, the
tips of which are provided with a structure like avicularia
(fig. 98, pdb' .), while the one other (i. e. that on the fourth
pair of maxillipedes) remains as a simple sac.

While these branchiae are being formed a long seta develops
on the coxopodite of each of the ambulatory legs, just in front
of them. These setae are at first comparatively very long.
Their number gradually increases while their size diminishes,
until in the adult prawn we have a dozen setse of moderate
length (fig. 98, cxs.).

List of References.

1. *Ed. van Beneden. — ‘ Recherches sur la Composition et la signification

de l’oeuf,’ 1868.

2. H. Ludwig. — 1 Ueber die Eibildung im Thiereiches,’ Wurzburg, 1874.

3. P. Mayer. — “ Zur Entwicklungsgesehichte der Decapoden,” ‘ Jenaische

Zeitschrift,’ vol. xi, 1877.

4. Waldeyer. — ‘Eierstock und Ei,’ Leipzig, 1870.

5. Huxley. — ‘The Crayfish,’ S.S., 1880.

6. C. 0. Whitman. — “The Embryology of Clepsine,” ‘ Quart. Journ. Micr.

Sci.,’ vol. xviii, N.S., 1878.

7. Balfour. — * Comparative Embryology,’ vol. i.

8. *Lereboullet. — “ Recherches d’embryologie comparee sur le developpe-

ment du Brochet, de la Perche et de l’Ecrevisse,” ‘ Mem. Savans

etrangers,’ xviii, J853 ; II “Embryologie de l’£crevisse.”

9. *Rathke. — Untersuchungen fiber die Bildung und Entwicklung des

Eiusskrebses,’ 1829.

10. Reichenbach. — “ Die Embryonalanlage und erste Entwicklung des

Flusskrebses,” ‘Z. f. w. Z.,’ Bd. xxix, 1877.

11. Dohrn. — “ Untersuchungen fiber den Bau und Entwicklung der Arthro-

poden,” ‘ Z. f. w. Z.,’ Bd. xx, 1870.

12. W. Faxon. — “ Selections from the Embryological Monographs : I. Crus-

tacea,” ‘ Memoirs of the Museum of Corap. Zoology at Harvard

College,’ vol. ix, No. 1, 1882.

13. B. Ulianin. — “ Zur Entwicklungsgesehichte der Amphipoden,” * Z. f.

w. Z.,’ Bd. xxxv.

14. Brooks. — “Lucifer: a Study in Morphology,” ‘Philosophical Transac-

tions,’ 1882.

ON DEVELOPMENT OF ATYEPHIRA COMPEESSA.

425

15. Balfour. — "Notes on the Development of the Araneina,” ‘ Q. J. M. S.,’

vol. xx, N.S.

16. Parker. — “ An Account of Reichenbach’s Researches on the Develop-

ment of the Fresh-water Crayfish,” ‘ Q. J. M. S.,’ vol. xviii, N.S.

17. Faxon. — " On the Development of Palaemonites vulgaris,” ‘Bul-

letin of the Museum of Comparative Zoology at Harvard College,
Cambridge, Mass.,’ vol. v, 1878-1879.

18. Birge. — “Notes on the Development of Panopeus sayi (Smith),”

‘ Studies from the Biological Laboratory, John Hopkins University,’
vol. ii. No. 4, 1883.

EXPLANATION OF PLATES XXV, XXVI, XXVII,
AND XXVIII,

Illustrating Mr. Ishikawa’s Paper “ On the Development of
a Freshwater Macrurous Crustacean, Atyephira com-
pressa, De Haan.”

List of Reference Letters,

amb. Ambulatory leg. an. Anus. At. 1. Antenna. At. 2. Antennule.

b. c. Blood-corpuscles, bl. Blastoderm, b. s. Blood space, bp. Basipodite.

c. d. Cephalic depression. ce. Caecum. cp. Carapace. exp, Coxopodite.
cx. s. Coxopoditic setae, c. t. Connective tissue. d. s. Dorsal spine, e. e.
External epithelium, en. Endopodite. ep. Ectoderm, f. e. Follicular epi-
thelium. f. m. Flexor muscle, ger. Germogen. g. g. Green gland, g. m.
Gastrula mouth, h. Heart, hy. Endoderm. i. e. o. Internal epithelium of
the ovary, i. e. od. Internal epithelium of the oviduct, in. Intestine, lb.
Labrum. Iv. Liver, mb. Structureless membrane. md. Mandible. nix.
Maxilla, mxp. Maxillipede. ms. Mesoderm, n. Nerve, n. c. Nucleus of
the connective tissue, o. od. External orifice of the oviduct, od. Oviduct.
ocl. Simple eye. OC. Compound eye. ol. s. Olfactory setae, ce. (Esophagus.
p.F Palp? pd. Proctodaeum. p.o. Primordial ova. pdb'. Podobranchia
modified, rs. Rostrum, sd. Stomodaeum. sg. Scaphognathite. s.gn. Supra-
cesophageal nerve ganglion. s. ms. Secondary mesoderm, nil. Vitellogen.
vac. Vacuole, w. y. White yolk. y.s. Yolk-spheiule. y. sg. Yolk-segment.

Fig. 1. — Coxopodite of the third ambulatory leg of the female Atyephira,
showing the external orifice of the oviduct. X 12.

426

CHIYOMATSU ISHIKAWA.

Fig. 2. — A fall-grown ovary viewed from ventral side, showing the germinal
hand, x 20.

Fig. 3. — A transverse section of a middle-sized ovary. Drawn with camera
a and 2 (Carl Zeiss).

Fig. 4. — Connective-tissue layer of the ovary, treated with acetic acid.
Camera d d and 4.

Fig. 5. — External epithelium layer of the ovary. Camera e and 2.

Fig. 6. — External epithelium layer of the oviduct. Camera e and 2.

Fig. 7. — A portion of the wall of the vitellogeu viewed from inside, showing
a small capillary branch. Camera d d and 4.

Fig. 8. — A transverse section of the ovary wall, showing the blood space.
Camera d d and 4.

Fig. 9. — A transverse section of a young ovary of about 014 mm. in cross
diameter. Camera D d and 4.

Figs. 10 and 11. — Transverse sections of a larger ovary, passing through
the oviduct. Camera d d and 4.

Fig. 12. — Three young eggs from the germogen, showing the growth of
germinal dots. Camera d d and 2.

Fig. 13. — A section of a young ovum with developing yolk-spherules.
Camera d d and 2.

Fig. 14. — A section of a germinal vesicle, surrounded by a network of
protoplasm. Camera D d and 2.

Fig. 15. — Internal epithelium of the oviduct during the breeding season.
Camera D d and 4.

Fig. 16. — Primary egg-membrane, showing the polygonal markings. Camera
d d and 4.

Figs. 17 — 40. — Magnified 40 diameters.

Figs. 17, 18, and 19. — Eggs dividing into two equal parts.

Fig. 20. — First transverse furrow completed.

Figs. 21, 22, and 23. — First resting stage.

Fig. 24. — First transverse furrow restored.

Fig. 25. — First longitudinal furrow appearing.

Fig. 26. — First longitudinal furrow completed. The egg is divided into
four equal parts.

Figs. 27 and 28. — Second resting stage.

Fig. 29. — First transverse furrow restored.

Fig. 30. — First longitudinal furrow restored.

Fig. 31. — Egg divided into eight equal parts by the second longitudinal
furrow.

Fig. 32. — Egg divided into sixteen equal parts by the second set of
transverse furrows.

Fig. 33. — Egg divided into thirty-two parts by the third set of longitudinal
furrows.

ON DEVELOPMENT OF ATYEPHIRA COMPRESSA. 427

Fig. 34.— Egg divided into sixty-four parts by the third set of transverse
furrows.

Fig. 35. — Egg at the end of the second resting stage, seen by the trans-
mitted light. A weak acetic acid preparation.

Figs. 36 and 37. — Two longitudinal sections of an egg of the same stage
as Fig. 30.

Fig. 38. — A longitudinal section of an egg divided into sixteen equal
parts.

Fig. 39. — A longitudinal section of an egg divided into sixty-four parts.

Fig. 40. — A longitudinal section of an egg divided into 256 parts.

Figs. 41 and 42. — Two views of an egg, showing the germinal disk. Im-
mersed in Kleinenberg’s picro-sulphuric acid for about fifteen minutes. X 65.

Fig. 43. — A longitudinal section of the germ disk of an egg of the same
stage as Figs. 41 and 42. Camera b b and 2.

Fig. 44. — Side view of an egg of the stage slightly later than that repre-
sented by Fig. 42. X 40.

Figs. 45, 46, 47, and 48. — Different stages of the gastrula of the egg.
Front and side views, x 40.

Figs. 49 and 50. — Gastrula cavity nearly closing. X 40.

Fig. 51. — A longitudinal section through the gastrula cavity of an egg at
the same stage as Figs. 45 and 46. Camera b b and 4.

Fig. 52. — A longitudinal section through the gastrula cavity of the stage
represented in Figs. 47 and 48, showing the formation of mesoderm cells.
Camera d d and 2.

Fig. 53. — A longitudinal section through the gastrula cavity at the stage
represented in Figs. 49 and 50, showing the closure of the blastopore.
Camera B b and 4.

Fig. 54. — A longitudinal section through the region where the gastrula
cavity has closed. Camera d d and 2.

Figs. 55 and 56. — Two views of an embryo in which the carapace ( cp .),
mandibles ( md .), and the cephalic lobes (oc.) have appeared. X 40.

Figs. 57, 58, and 59. — Three views of an embryo, slightly more developed
than the last, x 40.

Fig. 60. — Embryo still more developed, seen from embryonic pole. X 40.

Fig. 61. — Nauplius stage of an embryo, viewed from embryonic pole. X 40.

Fig. 62. — A longitudinal section of an embryo represented by Fig. 61.
Camera D D and 2.

Figs. 63, 64, 65, and 66. — Three consecutive transverse sections of the
nauplius, showing the formation of the nervous system. Camera d d and 2.

Fig. 67. — A transverse section of a nauplius, slightly older than the last.
Camera d d and 2.

Fig. 68. — Surface view of an embryo older than Fig. 61. X 150.

428

CHIYOMATSU ISHIKAWA.

Fig. 69. — Embryo older than the last. Simple median eye and nerve
striations are for the first time visible. X 150.

Figs. 70 and 71. — Embryo slightly older than Fig. 69, showing the forma-
tion of liver globules. X 40.

Figs. 72 and 73. — Two stages of an embryo slightly older than that repre-
sented in Figs. 70 and 71. X 150.

Figs. 74 and 75. — Two views of an embryo of the same stage as Fig. 73.

Fig. 76. — A longitudinal section of an embryo of the stage represented by
the Figs. 74 and 75. X 65.

Figs. 77 and 78. — Embryo further developed than the last, showing a
change occurring in the form of the yolk-mass, x 40.

Fig. 79. — Embryo about two days after the last, showing the intestinal
caeca. X 40.

Fig. 80. — Two pairs of antennae of the embryo given by Fig. 79. x 150.

Fig. 81. — First maxilla of the same. X 150.

Fig. 82. — Second maxilla of the same, x 150.

Fig. 83. — Three maxillipedes and the first ambulatory leg of the right side
of the same embryo. X 150.

Fig. 84. — A labrum, a mandible, and maxillae of an embryo about twenty-
four hours older than the one represented by Fig. 79. X 150.

Fig. 85. — Embryo just hatched, from below. X 30.

Fig. 86. — Telson of the same, x 60.

Fig. 87. — First maxilla of the same. Camera d d and 4.

Fig. 88. — Second maxilla of the same. X 150.

Fig. 89. — First maxillipede of the same. x 150.

Fig. 90. — Surface view of an antennal gland of an embryo represented in
Fig. 68. x 400.

Fig. 91. — Antennal gland of an embryo slightly more developed than Fig.
68. X 400.

Fig. 92. — Antennal gland of an embryo of about twelve hours before
hatching. X 400.

Fig. 93. — Antennal gland of an embryo just hatched. X 400.

Fig. 94. — A section of the same. X 400.

Fig. 95. — Extremity of the first antenna of the left side, from an embryo
represented by Fig. 79, showing the olfactory setae, x 400.

Fig. 96. — The same of the right side, from an embryo just hatched. X 400.

Fig. 97. —The same from an embryo 4 mm. in length. X 400.

Fig. 98. — First ambulatory leg of the left side of an adult animal. X 10.

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COMMUNICATION OF VASCULAR SYSTEM.

429

On the Supposed Communication of the Vascular
System with the Exterior in Pleurobranchus.

By

Alfred Gibbs Bourne, D.Sc. Loud.. F.L.S.,

Assistant Professor of Zoology and Comparative Anatomy in University
College, London.

With Plate XXIX.

Lacaze-Duthiers1 has described in Pleurobranchus a
special canal opening on the one hand to the exterior and on
the other to the branchial vein, and in Dentalium, two
orifices leading from the exterior into the two great veins in
the mantle.

These statements have remained hitherto unchallenged. I
have not examined Dentalium in this respect, but in the
case of Pleurobranchus I am in a position to deny the exist-
ence of any such communication.

At the request of Professor Lankester, who had long desired
to re-examine the structure described by Lacaze-Duthiers in
Pleurobranchus, I prepared some specimens of this mollusc
when at Naples in the spring of last year, and I have recently,
at Professor Lankester’s request, completed the examination of
this material in the laboratory of University College.

The orifice described by Lacaze-Duthiers in Pleurobran-
chus may be easily found (PL XXIX, fig. 1, x), but further

1 Lacaze-Duthiers, ‘Ann. Sci. Nat.,’ ser. 4, vol. vi (Dentalium), and
1. c., vol. xi (Pleurobranchus).

430

ALEEED GIBBS BOURNE.

investigation has proved that this orifice leads into a sac which
a complete series of sections have shown to be entirely closed.
Fig. 4 shows the sac as seen when the pericardium is opened
and one wall of the branchial vein removed. It is impossible to
remove the whole of the branchial vein since one wall is closely
adherent to the pericardial wall, with which is also fused one
wall of the sac : the whole forms a very thin membrane (fig. 3, w,
and fig. 5, w). The sac is lined inside by an epithelium.
This does not form an even surface but is very irregular,
dipping down into branched crypts ; the section chosen for
fig. 5 passing through the orifice of the sac does not show
these crypts.

The epithelium is of very different thicknesses in different
regions, every here and there occur patches of a much thickened
epithelium, and at other places the cells become very small
indeed. A large number of the cells, more especially in the
thickened patches, present glandular contents which stain
deeply. I am inclined to think that the greater number of
the cells in the thickened patches, perhaps all of them, are
glandular, but those only show which happen to present con-
tents. The whole surface appears to be ciliated, even the
gland-cells. This may be, however, due to imperfect pre-
servation, that is to say there may be smaller cells between
the glandular cells which are richly ciliated and these may
cause the whole membrane to appear ciliated. The structure
of a portion of a thickened patch is shown in fig. 6, where a is a
cell with glandular contents, m is the refringent margin which
the cells present, p the slight amount of pigment which exists
among the bases of the cells.

It is easy to understand how any injection might have
ruptured the thin membrane dividing the lumen of the sac
from that of the branchial vein, and so how Lacaze-Duthiers
was led to the belief that here was a special communication
between the exterior and the blood-vascular system. There
is, however, no doubt that such does not exist.

What is this sac? Does it represent any structure found
in other members of the group of Ctenidiobranchiate Palliate

COMMUNICATION OP VASCULAR SYSTEM.

431

Opisthobranchs to which Pleurobranchus belongs? Is
it nephridial in nature ? If it were it would be the rudiment
of the second nephridium which persists in so few Gastropods
(e . g . Fissurella, Patella) since there is a nephridium as
well developed in Pleurobranchus as in Aplysia. This
is not likely ; its structure is not nephridial and I am con-
vinced that it has no opening into the pericardium. Professor
Lankester has suggested to me, and the view seems an extremely
probable one, that we have here the homologue of that grape-
shaped gland in Aplysia which has been long known as the
“ poison-gland." The position of the orifice of this gland is
shown in fig. 2, z, and corresponds precisely in position with
that of my sac.

Whether this suggestion as to the homology of the organ
prove correct or not, it is I think quite certain that the special
means of communication between the vascular
system and the exterior, which has always been
stated to exist in Pleurobranchus, has no existence.

432

ALFRED GIBBS BOURNE.

EXPLANATION OP PLATE XXIX,

Illustrating Dr. A. G. Bourne’s Paper “ On the Supposed
Communication of the Vascular System with the Exterior
in Pleurobranchus.”

Fig. 1. — Pleurobranchus testudinarius. Dorsal view of a specimen
from which the mantle-flap and a portion of the dorsal integument have been
removed by cutting along the surface m. per. Pericardium, vent. Ventricle.
aur. Auricle, an. Anus. br. ctenidium (gill), g. External genital organs.
x. Orifice of the glandular sac. re. The orifice of the renal sac lies in this
direction underneath the gill.

Fig. 2.— Aplysia limacina. Similar view. Other letters as in Fig. 1.
x. Orifice of the grape-shaped gland, g. Genital groove, g. p. Genital pore.

Fig. 3. — Diagram of the relation of the glandular sac to the pericardium
and auricle, gl. The glandular sac. x. Its orifice. br. The ctenidium.
br. v. The branchial vein. au. The auricle, v. The ventricle, ao. The aorta.
per. Pericardium, w. The wall separating the lumen of the glandular sac
from that of the auricle' and branchial vein, composed in reality of three layers,
the wall of the sac, the pericardial wall, and the auricular wall, which together
form a single exceedingly thin membrane.

Fig. 4. — The glandular sac, as seen from the lumen of the auricle, x. Its
orifice.

Fig. 5. — Longitudinal section of the sac passing through its orifice x.
ep. Epidermis, c. The neck of the sac. gl. ep. The glandular epithelium
lining its walls, a. Gland-cells, showing deeply-stained contents, c. t. Con-
nective tissue, to. The exceedingly thin wall separating the lumen of the
sac from that part of the auricle.

Fig. 6. — A portion of the glandular epithelial wall of the sac more highly
magnified, a. Gland-cells with contents, b. Other cells, ci. Cilia, m.
Highly refracting margin, p. Pigment, c. t. Connective tissue.

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 433

Observations on the Nervous System of Apus.

By

Paul Pelseneer, B.Sc.

With Plate XXX.

The nervous system of Phvllopods recalls, by its appear-
ance, that of some Chsetopods. The two lateral cords are
rather distant from one another, and the commissures which
join the corresponding ganglia are rather long in the anterior
part. Zoologists agree to recognise that, among the living
Crustacea, the Phyllopods show the most primitive condition
of the nervous system, and that this has remained in a rather
archaic condition. Its study will be, therefore, for the expla-
nation of some morphological facts, more useful than that of
the nervous system of superior Crustacea, which has under-
gone many alterations.

The anterior part of the nervous system of Apus shows,
when dissected, the following external appearance (fig. 1) :
From the upper part of the brain c come the optic nerves
n o, and from the lower part the two abdominal cords
c a. From the latter, and rather far behind the brain,
come, one after the other, the nerves of the two pairs of
antennae (a i and a ii).1 A little further elongated swelling

1 The two pairs of antennae always exist in Apus ; this fact being already
stated by Prof. E. Ray Lankester (this Journal, 1881, p. 316). Claus mentions
the absence of the second pair of antennae as characteristic of the Apusidae
(‘ Grundziige der Zoologie ’). As for me, I always saw the second pair of
antennae, even in large specimens of Apus, measuring 3 5 cent, from the head
to the extremity of the abdomen. The first pair has, in these specimens, a

434

PAUL PELSENEER.

r a is found in each cord ; then come, in succession, the
mandibular and maxillary ganglia, the maxillipedal nerves,
which are observed coming out of the cord like the antennary
nerves, and the ganglion of the first thoracic foot.

Professor Ray Lankester has already pointed out the peculiar
disposition of this nervous system, and when I came, during
the winter of 1884 to 1885, to wrork under his direction, he
urged me to study the subject. I take the opportunity to
thank him here for the courteousness with which he received
me in his laboratory, and for the good advice which he gave
me during the time I spent in London.

In the course of my researches I have tried to elucidate the
different points to which Professor Ray Lankester had drawn
the attention of zoologists ; they are the following :

I. The antennary nerves issue from the abdominal cord
between tbe brain and the elongated swelling. Does this
swelling arise from the fusion of the first and
second ganglia? Or have the ganglia of these two
appendages entirely disappeared, like the maxil-
lipedes’ ganglion, instead of fusing with others?

II. A pair of postoesophageal ganglia (the elon-
gated swellings) exist anteriorly to the mandiblu-
lar ganglia, which are generally considered as the
first ganglia of the abdominal cord.

III. Among superior Crustacea the brain gives birth to the
nerves of the two pairs of antennae. If we consider the nervous
system of Crustacea as finally formed by two more or less
distant lateral cords upon which is found a ganglion for every
appendage, and a special cerebral ganglion-pair in which the
two cords unite in front of the mouth, then the brain of supe-

length of 2'3 mill., the second of 0’9 mill. It is generally difficult to notice
the second pair when one does not know where it is situated. Its position
is not exactly shown by Zaddach (* de Apodis cancriformis anatomia et
historia evolutionis,’ pi. i, fig. 5, b) ; its insertion, in comparison with the first,
is external, not internal.

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 435

rior Crustacea is to be regarded as formed by the fusion of
the ganglia situated before the mandibular ganglion, a fusion
which is connected with the welding of the cephalic segments.
In Apus the optic nerves only are seen coming out
of the brain. There are then good reasons to think
that this brain is a simply primitive brain.1

IV. Since one sees the nerves of the two pairs of antennae
of Apus coming, not out of the brain, but rather far behind
it, out of the abdominal cord, the two pairs of antennae
are metastomial appendages, which, in superior Crus-
tacea, became prostomial in consequence of further displace-
ment.

I shall now examine successively these different questions :

I. The first antennary nerve does not immediately turn for-
ward when it comes out of the cord as it is shown in Zaddach’s
figure (loc. cit., pi. iii, fig. 5, b ). On the contrary, it goes
from forward backwards, showing a curve of a quarter of a
circle, and going finally forward. This disposition is easily
understood when one examines with a small magnification
that part of the nervous system of Apus. One may then
observe (fig. 1) that the fibres composing the first antennary
nerve (a i), after having entered the abdominal cord (c a),
proceed from behind forwards, and then towards the brain
(c). They may be followed very far and teazed away from
the other fibres composing the cord. At the point where the
nerve joins the cord, one remarks upon the internal side of
the latter, between the envelope and the nervous fibres, a large
nerve ganglion-cell (c n) which has no relation with the
first antennary nerve (a i).

The ganglionic cells from which this nerve comes off are
not to be found in the elongated ganglion (r a, fig. 1) but in
the brain. Therefore, if the latter is an archicerebrum, the

1 Professor Ray Lankester calls these brains when formed by the single
pair of primitive cephalic ganglia, archicerebrum, in opposition to the
syncerebrum, or complex brain formed by the union of several pairs of
ganglia (“ Observations and Reflections on the Appendages and on the
Nervous System of Apus cancriformis,” this Journal, 1881).

436

PAUL PELSENEEE.

first antennarv nerve proceeds from the primitive cephalic gan-
glion ; if, on the contrary, the brain comprises the first anten-
nary ganglion it is a svncerebrum. It -will be stated further
on, under No. Ill, that the latter hypothesis is the true one.

The second antennarv nerve, when coming out of the cord,
goes immediately forward. In examining that part of the
nervous system under a low power of the microscope, one
observes the following disposition (fig. 2) : the fibres of the
second antennary nerve go into the abdominal cord (c a) from
in front backwards, towards the elongated swelling (ra), The
latter is situated upon the internal side of the cord and pro-
trudes rather strongly. In the interior of the cord, towards
its external side, one observes another smaller group of nerve-
cells (g a). It is a small ganglion, composed of a few cells,
and there the fibres of the first antennary nerve end.

From the preceding statements it results :

1st. That the elongated ganglionic swelling does not repre-
sent the fused ganglia of the first and of the second antenna.
2nd. That the two pairs of antennary ganglia have not disap-
peared ; they still remain in a very distinct manner. The
second antennary nerve comes indeed from a small ganglion
situated in the cord in an external position to the elongated
swelling ; and we shall see further on that the fibres of the
first antennary nerve come from a special and distinct ganglion,
situated on the posterior part of the brain.

As for the maxillipede nerve, its fibres go to a small ganglion
which is found in the cord a little in front of the first thoracic
foot ganglion. Therefore, as in the case of the two antennae,
the ganglion has not disappeared.

II. The ganglionic elongated swelling (r a) is joined to its
homologue by a double commissure, like all the ganglia of
the ventral cord. According to Zaddach (loc. cit., pi. iii,
fig. 5, e), it seems that the anterior commissure comes out of
the stomatogastric nerve. But, when dissected (fig. 2), both
the stomatogastic nerve (n s) and the commissure (c i) are seen
coming out of the elongated ganglion.

The homologue of the latter exists also among Decapods.

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 437

It is the small ganglion situated between the brain and the
mandibular ganglion, a little before the first postcesophageal
commissure. To that ganglion come, on one side, the fibres of
this commissure; on the other, the fibres of the stomatogastric
nerve. In another Phyllopod, a neighbour of Apus, Limnetis,
I think this ganglion may be seen in the swelling in front of
the mandibular ganglion, a little behind the ganglion of the
second antenna.1

This ganglion has been considered as the first postcesophageal
ganglion of the abdominal cord.2

I think that it cannot be homologized with the ganglia of
the cord. In consequence of the great development of the
stomatogastric nerve, it is easily understood that a ganglion
appears on the point where it joins the ventral cord. We have
not here a segmental ganglion; it is only an adventitious one.
Its lateral position in Apus is a proof of this statement. It
belongs more to the enteric system than to the somatic.

Nevertheless there are, in the abdominal cord, ganglia
situated before the mandibles. They are : the ganglia of the
second pair of antennae, the existence of which we have just
ascertained, and the ganglia that we shall see in the brain,
and from which come the nerves of the first antennae.

III. — It is necessary to study the histological structure of
the brain of Apus, and the disposition of the ganglionic cells,
to show if it is an archicerebrum or a syncerebrum.

The brain of Apus is small and thin, and can be studied
by transparency. But I tried the method of serial sections
after embedding in paraffine, to obtain more exact and precise
results. I used as colouring Kleinenberg's haematoxvlin. I
have made transverse (bilateral vertical) and longitudinal (an-
tero-posterior horizontal) sections. By means of Caldwell's
microtome I obtained complete series of sections. But, the
brain of Apus being very small, I found some difficulty in
obtaining vertical transversal sections, and I have used prin-

1 Grube, “ Bemerkungen fiber die Phyllopoden,” * Archiv fur Naturg.,’
1853.

3 Gegenbaur, ‘ Manuel d’Anatomie comparee,’ p. 352.

438

PAUL PELSENEER.

cipally horizontal longitudinal ones. I have thus been obliged
to use a great many specimens.

The brain of Apus is flattened and its shape quadrangular
(fig. 5). It is situated obliquely in relation to the longitudinal
axis of the body (fig. 3, c), and if one takes account of the dorsal
flexure of the nervous cord in front of the oesophagus,1 the
brain’s superior surface is in fact the ventral (infra-neural), and
the posterior margin out of which come the optic nerves is
the anterior margin.2

The ganglionic cells are accumulated on the ventral surface
of the brain ; among these one can observe two distinct shapes :
first, small cells round or oval, forming a single layer on the
ventral surface (figs. 6 and 7, c s.) and a thicker mass on the
posterior edge of the brain (fig. 5, ap); secondly, large pyriform
cells which are found in certain parts of the brain.

I have drawn, cell by cell, the whole series of transverse
sections, so that I could clearly determine by superposition the
disposition of the ganglionic cells.

On the anterior part of the brain the large cells form a very
thick mass (fig. 4, a) at the beginning of the optic nerves.
That mass extends backward without transition, and assumes a
charactei'istic shape. In a transverse section taken a little
in front of the middle of the brain (fig. 6) the large cells, the
prolongations of which go toward the interior of the brain,
are divided into two symmetrical groups, distinct though joined
(g 1) ; they are the primitive cephalic ganglia.

If one goes on observing the successive transverse sections
from before backwards, the primitive cephalic ganglia will
be seen ending, without any continuation, a little after the
middle of the brain. Towards the edge of the latter, and princi-
pally towards the ventral surface, a second pair of groups of
large pyriform cells will appear (fig. 7, g 2). This group pro-

1 Such a flexure is found in many Crustacea.

2 I shall hereafter speak of the brain of Apus morphologically, not topo-
graphically, i.e. the surface which is superior when the brain is in situ will
be called ventral surface ; the posterior margin, by dissection, will be the
anterior margin, and vice versa.

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 439

ceeds as far as the posterior end of the brain (figs. 4 and
5, g 2).

We have there a true second pair of ganglia held in the
brain. The cells which form it are not small cells of the super-
ficial layer ; they are large pyriform cells attaining some
thickness. These two ganglionic masses do not belong to the
primitive cephalic ganglia, like the mass at the beginning of the
optic nerves ; they are, on the contrary, far from them, and
entirely separated (see fig. 6, g 1, and g 2). They are then
wholly independent of the primitive cephalic ganglia.

What is that second pair of ganglia ?

If one examines a longitudinal section near the ventral
surface of the brain (fig. 8) one can see that the prolongations
of the cells composing these ganglia proceed backward, and
that the nervous fibres which come from them go into the cord
on the side whence come the fibres of the first antennary
nerve. We have, therefore, here the ganglion of this
appendage.

Therefore the brain of Apus is a complex brain, a syncere-
brum formed by the juxtaposition of two pairs of ganglia, the
formative elements of which remain separate. These two
pairs of ganglia are the primitive cephalic ganglia and the
ganglia of the first antennary pair, or first pair of the
abdomin al cord.

This proves obviously that the second pair of ganglionic
masses in the brain is a pair of the abdominal cord, which has
moved into juxtaposition with the primitive cephalic ganglia.
These two groups (g 2, fig. 5) are not joined, as is the case
for the last (g 1) ; they are very far from one another, and
situated on the external edges of the brain, showing the same
disposition as the ganglia of the abdominal cord. A horizontal
section passing through one of the thoracic ganglia (fig. 9) shows
the ganglionic cells situated on the lateral edges, just as is
the case with the second pair of ganglionic masses of the brain.

As for the group of small cells situated on the posterior edge
of the brain (fig. 7, a p), I do not give to it a special morpho-
logical signification. It is only a part of the superficial invest-

VOL. XXV.

NEW SER.

F F

440

PAUL PELSENEEK.

ment which has here a greater thickness. That mass seems to
he common to the brains of all Crustacea, both inferior (Bran-
chi pus) and superior (Astacus), and is also to be found on
the anterior and posterior edges of the abdominal ganglia
(fig. 9, a a and a p).

IV. The second antennary ganglion is situated next the first
postoesophageal commissure (fig. 2). Its position determines
in consequence this appendage as equally postoesophageal.
There cannot remain any doubt about the second antenna ;
it is a metastomial appendage.

Is it the same with the first antenna ?

Yes it is. The point where its nerve comes out of the
abdominal cord evidently shows that the ganglion correspond-
ing to that appendage must originally have been found far behind
the prostomial cephalic ganglia (properly called cerebral
ganglia). If it were not so the nerve, instead of coming out of
the cord, would come out of the posterior part of the brain,
as among other Phvllopods, Branchipus, e. g. Besides, we
have seen that the ganglia from which come the anterior anten-
narv nerves have the structure of the abdominal ganglia, and
therefore that they are ganglia of the abdominal cord. They
were then originally postoesophageal, as well as the ganglia of
the posterior antennae. The corresponding appendages are
thus also metastomial appendages.

We observe, then, that in Apus, in the anterior (praegenital)
part, every pair of appendages, the two pairs of antennae, and
the maxillipedes included, is provided with a pair of ganglia.
Morover, the two pairs of antennae are metastomial, as well as
the following appendages.

We observe, too, that every ganglion has a kind of attraction,
not only upon its homologue of the other cord, but even upon
the preceding and following ganglia situated on the same cord.
We see thus that the ganglia of the anterior antennae run all
along the cord to come into juxtaposition with the primitive
cephalic ganglia ; we observe also that the ganglia of the pos-
terior antennae pass to a place near the elongated ganglia of
the stomato-gastric nerve, and that the maxillipede’s ganglia

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 441

take up a position near those of the first thoracic feet. The
two last pair of emigrated ganglia, reduced to a small size
in consequence of the rudimentary condition of the corre-
sponding appendages, have lost every sign of a commis-
sure (fig. 2).1 The ganglia of the anterior antennae show, in
the brain, nervous fibres which unite them with one another.

The facts we have observed in Apus, in regard to the anten-
narv nerves, do not constitute an isolated case in contradiction
with what is remarked among other animals of the same
class. If one compares the nervous system of Apus with
that of other Crustacea, a great concordance is found on
the contrary.

Let us take a type in every family of the Branchiopodous
Phyllopods. In Limnetis2 the first antennary nerve comes
equally out of the cord, but immediately behind the brain. Its
ganglion is evidently held in the brain, just as in Apus. The
posterior antennae have a distinct pair of ganglia joined by a
postoesophageal commissure.

In Branchipus3 the nerve of the anterior antenna arises
at the posterior part of the brain out of a group of cells distinct
from the primitive cephalic ganglia; the nerves of the posterior
antennae, just as in Limnetis, come out a pair of cellular
groups joined by a postcesophageal commissure.

Among Cladocerous Phyllopods Daphnia4 shows a condition
very like that of Branchipus.

In the Amphipod Phronima,5 the nerves of the second pair
of antennae are also observed coming out of the abdominal
cord, a little behind the brain.

1 The two first postoesophageal commissures belong to the elongated
ganglia of the stomatogastric nerve.

2 Grube, “ Bemerkungen fiber die Phyllopoden,” * Archiv ffir Naturg.,’
1853.

3 Claus, “ Zur Kenntniss des Baues von Branchipus, &c.,” ‘ Abhandl.
der K. Gesellsch. der Wissensch.,’ Gottingen, 1873.

4 Claus, “ Zur Kenntniss der organisation der Daphniden,” c Zeitschr. ffir
wiss. Zool.,’ t. xxvii.

5 Claus, “Der Organismus der Phronimiden,” ‘Arbeiten aus dem Zool.
Inst. Wien,’ t. ii.

442

PAUL PELSENEER.

We observe, then, that from the Crustacea with the most
primitive nervous system to the most superior forms there
are a great many transitions (Apus, Branchipus, Daphnia,
Phronima, Astacus) between the condition in which the
nerves of the two pairs of antennae come out of the cord, and
the condition in which these nerves come out of the brain.

Since then a histological examination shows in Apus,
which among the actual Crustacea has the most primitive
nervous system, that the brain is a syncerebrum, and since
among superior Crustacea the anatomy of the nervous system
shows that the brain is at least as complex as in Apus, it
seems very probable that among living Crustacea there are not
any with an archicerebrum.

The classification of the brains of Crustacea established by
Packard1 has no grounds whatever.

1 ‘ American Naturalist,’ 1882.

OBSERVATIONS ON THE NERVOUS SYSTEM OF APUS. 443

EXPLANATION OF PLATE XXX,

Illustrating Mr. Paul Pelseneer’s Paper on “ Observations on
the Nervous System of Apus.”

Fig.1. — Left half of the anterior part of the nervous system of Apus.
c. Brain. N o. Optic nerve, c a. Abdominal cord, a i. Nerve of the first
antenna, a n. Nerve of the second antenna. ra. Elongated swelling,

c n. Nervous cell.

Fig. 2. — Beginning of the second antennary nerve, c a. Abdominal cord,
All. Nerve of the second antenna, ga. Ganglion of the second antennary
nerve. N s. Stomato-gastric nerve; ra. Elongated swelling (ganglion of the
stomato-gastric nerve), c 1 and c 2. Anterior and posterior commissures
of the elongated swelling.

Fig. 3. — Anterior part of the nervous system of Apus, side view. c. Brain,
o. Bight eye. o i. Median (larval) eye. c a. Abdominal cord. B. Mouth.
T g. Digestive canal, a i. Beginning of the first antennary nerve, a ii. Be-
ginning of the second antennary nerve.

Fig. 4. — Vertical projection of the brain of Apus.1 o. Right optic
nerve, o i. Median (larval) eye. a. Anterior cellular mass, g 1. First right
ganglionic group (primitive cephalic ganglion), g 2. Second right ganglionic
group (ganglion of the first antennary nerve), c a. Abdominal cord.

Fig. 5.— Horizontal projection of the brain of Apus. ap. Posterior mass
of small cells, oi. Nerves of the larval eye. 6 — 6. Line showing the
direction of the section drawn in Fig. 6. 7 — 7. Direction of the section drawn
in Fig. 7. Other letters as for Fig. 4.

Fig. 6. Transverse section of the brain of Apus, passing through the
line 6 — 6, Fig. 5. g1. First ganglionic group (primitive cephalic ganglion),

c s. Superficial lining of small cells.

1 In this projection, and in the following, the thin layer of small cells
forming the superficial coating of the brain has not been drawn (see c s, Figs.
6 and 7).

PAUL PELSENEEP,

AAA

XXX

Eig. 7. — Transversal section of the brain of A pus, passing through the
line f — f. Fig. 5. g 2. Second ganglionic group of the brain (ganglion of
the first antenna), fn. Nervous fibres, joining the two ganglia, c s. As in
Eig. 6.

Fig. 8. Left half of a longitudinal section of the brain of Apus. fnai.
Nervous fibres of the first antennary nerve. Other letters as in Eig. 4.

Fig. 9. — Horizontal section of a ganglion of the abdominal cord, g g.
The groups of ganglionic cells, c 1 and c 2. Anterior and posterior com-
missures. has. Upper anterior nerve, nai. Lower anterior nerve, np.
Posterior nerve, a a. Anterior mass of small cells, a p. Posterior mass of
small cells.

JUor.

Fiq. 7.

Fro 9.

P Pelseweer del

P Huth LW Rdmr

CHEMICAL COMPOSITION OF ZOOCYTIUM.

445

Note on the Chemical Composition of the
Zoocytium of Ophrydium versatile.

By

W. ]). Halliburton, M.I>., B.Sc. bond.,

Sharpey Physiological Scholar, University College, London.

(From the Physiological Laboratory, University College, London.)

Ophrydium versatile is a ciliated Protozoon which grows
iu colonies or social clusters, exuding a common coalescent
mucilaginous investing matrix or Zoocytium.1

Professor Lankester, to whom a large supply was kindly
brought by Mr. Groom from the canal at Hereford, placed a
quantity of this material in my hands with the object of deter-
mining the chemical nature of the jelly.

The lumps of jelly were on the average about an inch in
diameter ; the material was firm, colourless, and perfectly
transparent. On its surface were patches of green due to the
chlorophyll which is present in the animal itself.

The diagnosis of the material of which it was composed
seemed to me to rest between mucin and cellulose ; and it was
found that the latter supposition was the correct one.

The percentage amount of solid matter in the jelly was found
to be *28 of which ’07 consisted of ash, and the remainder
organic matter.

By digesting with warm water, a small amount of proteid
material was extracted, doubtless contained in the protoplasm
of which the animal itself is composed. This was removed by

1 Kent, * Manual of the Infusoria,’ vol. ii, p. 733.

446

W. D. HALLIBURTON.

digesting some hours with weak hydrochloric acid. The ash
was found to contain the bases soda and lime, combined with
chlorides, phosphates, and the merest trace of sulphates.

The basis of the jelly, however, was not nitrogenous ; this
fact, together with its absolute insolubility in lime water,
baryta water, and other weak alkalies, showed that it could not
be mucin.

The material was purified by successively washing it in cold
water, hot water, dilute hydrochloric acid, dilute caustic pot-
ash, alcohol, and ether; it was insoluble in all these reagents,
and the residue much shrunken by the action of the last-
named reagents retained the shape of the original lumps.

It was then found to contain no nitrogen, and that it was cel-
lulose was shown by the following properties that it possessed :

(1) It was insoluble in weak acids and alkalies.

(2) It was soluble in concentrated hydrochloric and sul-
phuric acids in the cold.

(3) The solution in sulphuric acid was diluted with distilled
water and boiled for some hours ; after this time it was con-
verted into a sugar like dextrose which reduced cupric salts,
and was capable of the alcoholic fermentation.

(4) With iodine and sulphuric acid it gave a yellowish-brown
colouration.

(5) It was soluble to a slight extent in an ammoniacal solu-
of cupric sulphate.

This substance then resembles vegetable cellulose in its
general properties, and differs from it in being less easily con-
verted into sugar. In this latter property it resembles tunicin,
the substance of which the test of the Tunicata is composed ;
tunicin, however, is still more difficult to convert into dextrose,
and according to Berthelot1 requires some weeks boiling with
dilute sulphuric acid to effect the change. Moreover, Ber-
thelot says that tunicin gives a pale blue colour with iodine
and sulphuric acid, resembling that given by cholesterin with

1 Berthelot, ‘ Ann. de Chemie et de Phys.,’ s6rie 3, tome lvi, p. 153.

CHEMICAL COMPOSITION OF ZOOCYTIUM.

447

the same reagents ; the substance I examined gave a brown
tint, so resembling some varieties of vegetable cellulose.

The proof of the existence of cellulose in the Ophrydium is
interesting as showing that cellulose is not limited among
animals to the Ascidian family ; its coexistence with chloro-
phyll, another vegetable product, in the same animal is also
noteworthy.

THE DEVELOPMENT OF PERIPATUS OAPENSIS.

449

The Development of Peripatus Capensis.

By

Adam Sedgwick., M.A.,

Fellow of Trinity College, Cambridge.

PART I.

With Plates XXXI and XXXII.

Introduction.

The development of Peripatus capensis was first studied
by Moseley,1 *who stopped for a short time at the Cape in
November and December some years ago. His observations
related only to stages which were comparatively late in develop-
ment. Balfour, in 1882, found some younger embryos in speci-
mens collected by Mr. Lloyd Morgan in July and August, and
sent to Professor Huxley, who gave them to Balfour. He had
only time to make a very few observations, of which he left a
short record in the form of four rough drawings and a short note,
and a letter to Professor Kleinenberg, before starting on his last
expedition to Switzerland. His observations were so interest-
ing that they were made the subject of a short communication
to the Royal Society in the autumn of 1882, and they were
slightly extended by the editors of his last work on the
Anatomy of Peripatus capensis,’ and published with that
monograph in the ‘ Quarterly J ournal of Microscopical
Science ’ in the spring of 1883.

The subject seemed so important that the Government
Grant Committee of the Royal Society granted, in the spring of
1883, the sum of £100 to enable me to go to the Cape for the
1 ‘ Phil. Trans.,’ vol. 164.

450

ADAM SEDGWICK.

purpose of obtaining well-preserved embryos, and of studying
the development on fresh specimens.

Accordingly, I went to the Cape in the summer of 1883,
arriving early in July, and remaining till the middle of
August. I obtained a large number of specimens, and brought
back with me over 300 alive. Some of the latter lived at
Cambridge till the following July. The results of my obser-
vations at the Cape and after my return to England have been
to show that the embryos remain thirteen months in the
uterus ; that the fertilised ova pass into the uterus in April,
and the young are born, fully developed, in the May of the
year following. That is to say, the young ova pass into the
uterus one month before last year’s young are born. I was
not prepared for this, and I did not, in 1884, examine my spe-
cimens for the early stages until May, when the young were
being born. The result was that I missed last year the early
stages of development, and had it not been for the kindness of
Mr. "Walter Heape, who went to South Africa last summer, and
who collected and brought back some more live specimens, I
should have been obliged to leave the early stages undescribed.
Thanks to him, however, and to my experience gained last year,
I have this April been able to find several of the younger
stages, and to complete my observations.

Two species ofPeripatus are commonly found at the Cape.
One, the most common, is the well-known Capensis; the
other is a new species, differing from Capensis in having
eighteen pairs of fully-developed legs, in being of a smaller
size, and in other points. This species I propose to call Peri-
patus Balfouri. It will be fully described in the forth-
coming monograph by Moseley and myself on the ‘ Species of
Peripatus.’

Besides the work of Balfour and Moseley on the develop-
ment of Peripatus capensis, some observations on the
development of a West Indian species have been published by
Dr. J. Kennel, of Wurzburg (Semper’s ‘Arbeiten,’ Heft ii,
Bd. 7). I do not propose to enter here into any detailed ex-
amination or criticism of Dr. Kennel’s account of his observa-

THE DEVELOPMENT OP PETtlPATUS CAPENSIS. 451

tions, which relate almost entirely to the early stages. Dr.
Kennel has described his observations at very great length, but
I do not think that his account of them can be regarded as en-
tirely satisfactory. It is quite clear that Dr. Kennel has been
hampered by want of material in the early stages, and by the
great difficulty of the subject, and I therefore defer a detailed
examination of his work to a later paper in the series of which
this forms the first, by which time I hope that he will have been
able to throw some more light upon certain points in the early
development of the West Indian species, which are left some-
what obscure in the first account in Semper’s ‘Arbeiten.’ On
one point, however, there can be no doubt, viz. that the early
stages in the development of the West Indian species are very
different from those of the Cape species. Whether they are
as different as Dr. Kennel makes out I am inclined to ques-
tion, but that, as I have said, is a matter for further elucidation.

Some of the. more important results of my observations on
the development of Peripatus capensis, e. g. the derivation
of the mouth and anus from the blastopore, the fate of the
grooves in the cerebral ganglia, have already, some time ago,
been published in my paper “ On the Origin of Metameric
Segmentation ” (this Journal, 1884).

My observations are nearly completed, and I have already
(May of this year) communicated a preliminary account of
them to the Royal Society. They will be published in full, I
trust, in a series of papers in this Journal.

The present paper is the first of the series, and relates
almost entirely to the segmentation and general development
of the embryo. I have deferred all discussion of the facts
described to a more convenient opportunity in a later paper in
the series.

All the drawings in this paper, with the exception of figs.
23 — 27, have been made by Mr. E. Wilson, of the Cambridge
Scientific Instrument Company. They are very careful and
accurate representations of the specimens, and I cannot suffi-
ciently express my thanks to Mr. Wilson for the great trouble
he has taken with them.

452

ADAM SEDGWICK.

The segmentation stages were all drawn in the laboratory as
I removed them from the uterus, and it is entirely owing to
Mr. Wilson’s kindness that I have been able to obtain a per-
manent and accurate record of tbe various stages of the living
segmenting ovum.

The Generative Organs.

At the outset I must give a short description of the general
arrangement of the generative organs. Their minute struc-
ture I shall describe more fully when I come to their develop-
ment.

Male Organs. — The description given by Moseley1 and by
Balfour2 is correct so far as the general arrangement is con-
cerned, but a slight rectification is necessary in the significance
to be attached to the various parts. The structures called testes
by these authors (Balfour, loc. cit., PI. XX, fig. 43, te .) are ap-
parently merely seminal vesicles, in which the spermatozoa de-
velop and gain maturity. The true testes are the so-called
prostates (Balfour, loc. cit., fig. 43, pr.), the lining cells of
which fall into the cavity of tbe tube, pass into the swollen
seminal vesicle, where they develop into spermatozoa. The
spermatozoa, when ripe or nearly ripe, pass into the vasa
deferentia, at the lower end of which they apparently become
packed together in small masses, which become surrounded by
a structureless coat, and are passed out as small, oval, white
spermatophores.

The male generative organs of Peripatus capensis con-
sist, therefore, of a pair of blind tubes, which are separate in
front, but united behind for a short distance to form a common
terminal portion (Balfour, loc. cit., fig. 43, p), and at the front
end of which are formed the mother-cells of the spermatozoa.
The latter fall into the cavity of the tube, and gradually de-
velop as they pass backwards towards the external orifice, the

1 ‘Phil. Trans.,’ vol. 164.
s This Journal, 1883.

THE DEVELOPMENT OF PEEIPATUS CAPENSIS. 453

main portion of the development taking place in a specially
dilated portion of the generative tube — a portion which may be
called a vesicula seminalis.

I have never seen the extrusion of the common terminal
portion of the system, and I doubt very much whether it ever
is extruded so as to act as a penis.

The Female Organs. — The o.varv, though apparently a single
structure, is in reality paired, and consists of two tubes closely
applied together. The ova are derivatives of the epithelial
lining of these tubes. Each ovarian tube is continued into the
oviduct of its own side. The oviducts are thin-walled, narrow
tubes, each of which is continued behind into a more dilated and
thicker-walled tube — the uterus. The uterus is of consider-
able length and much bent, and unites with its fellow close to
the single external opening, which lies in the middle line of
the ventral surface of the hind end of the body, just in front
of the anus. For figure of female organs, vide Moseley, loc.
cit., pi. 74, fig. 1, and Balfour, PI. XIX, fig. 33.

From the above description it is evident that the organs of
the female, like those of the male, consist of two tubes united
behind near the external opening but ending blindly in front,
where the generative products are produced.

The ovarian parts of the generative tubes are placed between
the fifteenth and sixteenth pairs of legs, and are united to the
floor of the pericardium by a delicate band of transparent
tissue. They, i. e. the ovaries, contain spermatozoa, some of
which project through the ovarian walls into the body-cavity.
This condition has been figured and described by Moseley (loc.
cit., pi. 74, fig. 1).

The ovaries always contain spermatozoa, but in smaller
numbers directly after the eggs have passed into the ovi-
duct than at any other time. This is a very marked feature
of an ovary, say, of the beginning of April, when compared
with an ovary from which the ova have just passed into the
oviducts, say, of the beginning of May, the former being of an
opaque-white colour to the naked eye, while the latter has a
much more transparent appearance.

454

ADAM SEDGWICK.

This fact would seem to imply that fresh spermatozoa pass
each year into the ovaries. This brings me to the question of
the manner in which the male discharges his function. The
vesiculae seminales (testes of Moseley and Balfour) are almost
empty of spermatozoa in the months of February, March, and
April. At the end of April, however, they begin to swell
again and contain spermatozoa, which increase in number as
time goes on, until, in October, they are fully distended with
spermatozoa in all stages of development. There seems to be no
functional intromittent organ, but the male deposits little oval
spermatophores quite casually on any part of the body of the
female, and, for all that I know, of the male also ; e. g. I have
often seen them on the head. How these little packets of
spermatozoa get into the vagina, and then up the uteri,
which are always full of embryos, I cannot conceive. The
spermatozoa exhibit a certain amount of vibratory movement,
and no doubt, once within the vagina, they are set free from
the spermatophor and make their way up the female genera-
tive tube, between the embryos and the uterine walls. Inas-
much as the deposition of spermatophores lasts from June
until January, each female probably has a large number of
spermatophores deposited on her, and some of these are prob-
ably near the generative opening, and are, somehow or another,
transported through it into the vagina.

Fertilisation is apparently effected in the ovary. I have
never seen spermatozoa in any part of the female apparatus
except in the ovaries, and in small numbers in the upper end
of the oviducts at the time when the ova are entering the
latter.

The ripe, and probably fertilised, ova pass into the oviduct
in April, while the uterus is still full of embryos almost ready
for birth. Segmentation and the early stages of development
take place during the passage of the ova down the oviduct.
In May the young of the previous year are born. Into the
uterus, thus emptied, the young ova pass, and establish them-
selves in the positions which they maintain until the following
May, when they are born.

THE DEVELOPMENT OF PERIPATUS CAPENSIS.

455

The passage of the ova down the oviducts and uteri is
effected by the peristaltic contraction of the walls of these
structures. I have never been able to see cilia in the genera-
tive organs, or in any other part of the body of Peripatus
capensis.1

The living ripe ovarian ovum is somewhat elliptical in shape
and of dark colour by transmitted light. The opacity is due
to the presence of granules, which are uniformly distributed
in the protoplasm, but absent altogether from the larger
germinal vesicle.

As I have stated above, I propose to defer my account of the
ovary and ovarian ovum until their development is con-
sidered.

The Fertilised Ovum.

The youngest ovum found in the oviduct is shown on
PI. XXXI, fig. 1. It is of an elongated form — length ’4 mm.
— and is surrounded by a transparent, structureless mem-
brane, which is either a vitelline membrane or derived from
the follicular cells surrounding the young ovarian ovum.
This membrane persists until birth ; it has a dense structure
and allows fluid to pass through it by diffusion. Water
diffuses through it more rapidly than alcohol, and alcohol
more rapidly than turpentine ; so that when an embryo is
removed suddenly from weak alcohol into strong, or from
absolute alcohol into turpentine, the membrane shrinks and
closely invests the embryo ; in fact, in the latter case all the
alcohol diffuses out before any turpentine enters, so that the
membrane completely collapses and squashes the embryo flat.
When, on the other hand, an embryo is removed from strong
alcohol into weak, or into water, the water passes in more
rapidly than the alcohol passes out, so that the membrane is
distended, and the space between it and the embryo much
enlarged. In the normal embryos there always is a space
between the membrane and the ovum, which contains fluid in
1 This remark applies to the nephridia, all parts of which I have carefully
examined in the fresh state without ever seeing a trace of cilia.

VOL. XXV. MEW SER.

G G

456

ADAM SEDGWICK.

which the embrvo floats. The membrane, therefore, has much
the same function as the amnion of the Vertebrata.

The protoplasm of the ovum 1 is differentiated into two parts —
the main mass being of a pale colour with relatively few dark
granules, while at one point it is especially dark in colour. This
small dark patch (fig. 1) is placed at the surface on one of the
long sides of the ovum. I may call it, from its position as
determined by the later development, the dorsal or animal pole
of the ovum. When the ovum is viewed from the side (fig. 1),
it is seen that the surface of the dark patch is pitted inwards,
and that the space so formed contains two small clear bodies,
which I take to be polar bodies. When viewed from the face,
the dark patch presents a central circular transparency more or
less free from the dark granules which are found in such large
numbers in other parts of it. This central clear body I take to
be the first segmentation nucleus. The polar bodies are only
seen during this stage, and I have no observation either on their
origin or fate.

I have figured two other unsegmented ova (figs. 2 and 3)
which differ in certain respects from the above. In one of
these (fig. 2) the dark patch is smaller than in fig. 1, and
without the central transparent area ; in the other (fig. 3) there
were several dark patches, each with its own clear spot. I have
not been able to make out the meaning of these differences,
i.e. whether they are normal stages in the development of the
ovum, and if so, where they come in the developmental series.

Segmentation.

Segmentation is complete. The first furrow is in the trans-
verse plane of the ovum, and divides it into two halves (fig 4),
the dark patch being divided as well as the main mass of the
ovum. The second furrow is at right angles to the first, and
divides each of the first formed segments into two (figs. 5 and 6),
so that the ovum now consists of four segments, each con-
sisting of a lighter-coloured main mass and a small dark patch

1 The following description of the segmenting ova refers, unless otherwise
stated, to fresh living ova seen in transmitted light.

THE DEVELOPMENT OF PEKIPATUS CAPENSIS. 457

which closely adjoins the dark patches of the three other cells
at the animal pole, and which contains a central clear area
(fig. 5).

The two first furrows, therefore, are at right angles to one
another, and in the vertical plane. The next furrow is hori-
zontal, and divides each of the four segments into two unequal
parts ; a small animal part consisting almost if not entirely of
the dark animal part of the cell, and a larger, clearer mass ; so
that the ovum now consists of eight cells, four small cells lying
close together at the animal pole, and consisting almost entirely
of the darkly granular parts of the cells of the previous stage,
and four large, clearer, but more or less granular cells. Each
of the small dark cells contains a central transparent area, which
I take, as before stated, to be the expression of the nucleus.

The four small dark cells give rise to the ectoderm,
and the four larger cells to the endoderm. — The sub-
sequent division of these two kinds of cells proceeds inde-
pendently.

In the next stage I have figured (fig. 7), there are eight dark
cells, each with its central clear area, and an undetermined
number of large endoderm cells.

At the end of segmentation (fig. 8), the ovum consists of a
number of large-branched endoderm cells scattered irregu-
larly within the egg membrane, while the ectoderm cells con-
sist of a mosaic of more or less hexagonal cells closely applied
together and placed close to the membrane on one side at
about the middle of the long axis of the egg.

The egg at this stage presents a very peculiar appearance,
and I would not believe for some time that I was not dealing
with an abnormal or injured ovum. But I found the stage so
often, and so many stages intermediate between it and the
earlier and later stages of development, that I cannot but believe
in its normal existence. I found it also when every precaution
was taken to avoid injuring the ovum ; when I merely opened
the animal and examined the ovum through the transparent
walls of the oviduct without even touching any part of the
female organs.

458

ADAM SEDGWICK.

The endoderm cells at this stage — and I have no doubt this
is the case in other stages, but in this case the fact can be
clearly seen — are branched, and the branches of adjoining cells
in some cases anastomose. One must suppose in fact that the
endoderm cells of this stage are amoeboid and capable of inde-
pendent movement, in order to account for the changes which
now take place.

In fig. 9 I have had drawn an embryo of this stage as an
opaque object, with reflected light. The drawing shows clearly
the mosaic of ectoderm cells, which in this light seem to be
composed of a brilliant white substance with a central dark
area.

The endoderm cells now begin to draw together towards
the centre of the egg, and come to lie directly beneath the
ectoderm mosaic, which rests upon them like a cap. I have
had various stages of this process drawn in figs. 10 — 14.

This change can only be explained as being due to an
active movement of the endoderm cells, which travel from
all parts of the egg towards the centre, where they aggregate
in masses which gradually unite with one another, forming
at first a ring and then uniting further until they form one
more or less spherical solid mass of cells on which the
ectoderm mosaic rests like a cap. Fig. 15 shows a side view
of an embryo at this stage, in which this process of aggre-
gation of the endoderm cells is completed. Fig. 15 is drawn
from a preserved embryo made transparent by turpentine.

The nucleus of the ectoderm cells, which has been con-
spicuous in all these stages by its transparency and freedom
from granulations, presents quite a different appearance in
embryos which have been treated with reagents. In the latter
case instead of a central transparency, we find a central mass
of dark granules, which are much more marked than the
granules of the body of the cell. Further, it should be
pointed out that, in the latter stages, the granulation of the
ectoderm cells is a much less marked feature [vide figures),
and that the boundary between the ectoderm cells becomes
less distinct ( vide especially fig. 13).

THE DEVELOPMENT OF PEEIPATUS CAPENSIS.

459

The ectoderm now grows round the endoderm cells and
entirely surrounds them, excepting at one point. At this
point, which is opposite to that on which the ectoderm cap
was placed, the endoderm cells may be seen for a short time
projecting (figs. 17 and 18).

The embryo has thus acquired a spherical form, and consists
of a solid gastrula, the small uncovered spot of endoderm con-
stituting the blastopore. A cavity next appears in the centre
of the endoderm cells, so as to open to the exterior through
the blastopore (figs. 19 and 21).

We have thus arrived at the stage of a typical gastrula formed
of two layers of cells, which are continuous with one another at
the blastopore and enclose a central cavity. It may be at
once stated that the blastopore, which is on the ventral surface
of the embryo — on the surface opposite to that on which the
ectoderm cap was placed — persists and gives rise to the mouth
and anus1 of the adult, and that the cavity of the gastrula
becomes the mesenteron.

The General Development of the Embryo.

The segmentation, as we have seen, is complete but unequal;
the large cells giving rise to the endoderm, and the small cells
to the ectoderm. The gastrula arises by a modified process of
epibole. The fully-developed gastrula is shown in figs. 19 and
21. The embryo has already become slightly oval, and the
blastopore now begins to elongate in the direction of the long
axis.

Stage A (fig. 22). — An opacity appears at the hind end of th
blastopore. This opacity is the primitive streak. It appears
to be due to the active proliferation of some cells, which cannot

1 These were called in Balfour’s memoir (this Journal, 1888), and perhaps
more correctly, the embryonic mouth and anus, — more correctly because
they come in the adult to lie internally, in consequence of the ingrowth of
ectoderm at the two ends of the alimentary canal to form the stomodaeum and
proctodaeum. They constitute in the adult the openings between the mesen-
teron and the stomodaeum and proctodaeum respectively. It must, however,
be borne in mind that they never become closed.

4G0

ADAM SEDGWICK.

be definitely assigned either to the ectoderm or the endoderm,
at the hind end of the blastopore. This stage, which has
already been described in Balfour’s Memoir on Peripatus
(this Journal, vol. xxiii), is found most commonly at about
the middle of June in England.

The embryo now grows considerably in length (fig. 23), the
blastopore presenting a corresponding elongation, and the meso-
derm, which arises from the proliferation of the undifferentiated
cells of the primitive streak, grows forward as two ventro-
lateral bands, one on each side of the blastopore.

The mesodermal bands next divide by transverse division
from before backwards into somites, which contain a cavity,
part of the future body cavity. The first somite to appear is
the anterior, and then successively backwards.

Stage B (fig. 25). — The blastopore now divides into two
parts (figs. 24 and 25) by the obliteration of its median portion
— into an anterior part which becomes the mouth of the adult,
and a posterior part which is at first placed at some little dis-
tance from the hind end of the embryo and gives rise to the
anus of the adult.

The primitive streak still persists and extends from the hind
end of the blastopore to the hind end of the embryo. It is
now marked by a groove — the primitive groove (fig. 25).

The anterior pair of somites have shifted forward to quite
the anterior end of the body ; they give rise to the mesoderm
and body cavity of the praeoral lobes.

Stage C (figs. 26 and 27). — The hind end of the body now
becomes curved ventrally (figs. 26 and 27). The curve is pro-
duced by the growth of the hind end of the body. As this
growth proceeds the curve becomes more marked, and assumes
a spiral form, that is to say, the hind end of the body is spirally
coiled, the coil being applied to the ventral face of the anterior
part of the body (fig. 28).

Stages B and C are found in July and August at the Cape.

Stage D (figs. 28 and 29) . — The spiral stage is characterised by

THE DEVELOPMENT OF PERIPATUS CAPENSIS.

461

the appearance of the appendages and of the lip-fold which
encloses the jaws in the adult, and of the eyes.

The appendages arise as hollow processes of the body wall,
containing prolongations of the somites. The first to appear
are the antennae, into which the praeoral somites are pro-
longed. The remainder appear from before backwards in
regular order, viz. jaws, oral papillae, legs, 1, 2, . . . 17, and
the rudimentary anal papillae, which are the appendages of
the last, i. e. the twenty-first somite.

The full number of somites and their appendages is not,
however, completed until a later stage, the posterior being the
latest to appear.

The eyes appear in this stage as invaginations of the sides of
the nervous thickenings (the future supracesophageal ganglia)
of the praeoral lobes (fig. 29, e). The invaginations are at first
shallow, but soon become deeper, and in the next stage con-
verted into closed vesicles, the front wall of which (i. e. the wall
next the skin) forms the epithelium outside the so-called lens
of the adult eye, while the internal wall thickens, and remains
continuous with the cerebral ganglion, and gives rise to the
retina. The enclosed vesicle persists, and apparently becomes
filled by the structureless lens of the adult eye, if the struc-
ture described as such be not a mere coagulum produced by
reagents. The eye of Peripatus is therefore a cerebral eye.

The lips. — The end of the spiral stage is also characterised
by the appearance of the buccal fold or fold which encloses the
jaws and buccal cavity, and so constitutes the tumid lips of the
adult. This is a fold of the side walls of the body immediately
outside the jaws, and extending from the praeoral lobe of its side
to just behind the jaw. It is at first most marked in front,
which fact led Moseley to describe it as a backward process of
the praeoral lobe.

The first indication of the lip is shown in fig. 29, just behind
the eye ; it is seen better, however, in the figure of the next
stage (fig. 30, L).

This stage is also characterised by the fact that the anus has
shifted to the hind end of the body (the primitive streak

462

ADAM SEDGWICK.

having apparently disappeared). The prseoral lobes have also
become markedly bilobed as compared with the previous stage

(fig- 26).

Stage E (figs. 30 — 34). — In the next stage (fig. 31), which is
found early in October in England, the spiral straightens out,
and the embryo becomes bent double, the ventral surface of the
hind part of the body being applied to the ventral surface of
the front portion, and the tail end of the embryo being curled
round the front end of the head. The bend occurs at the level
of the eighth somite.

An embryo straightened out and drawn from the side is
shown in fig. 30.

The main features of this stage, in addition to the loss of
the spiral form, are — (1) the increase in the number and size
of the somites and appendages ; (2) the closure of the eye-pits ;
(3) the growth of the lips ; (4) the appearance of a groove in
the thickened ectoderm on the ventral surface of the prseoral
lobes ; (5) the presence of a well-marked dorsal projection at
the level of the anterior bend of the body ; (6) the beginning
of the ectodermal invagination which will form the stomo-
daeum; (7) the appearance of a pit at the apex of the oral
papilla (fig. 33, or. p.) ; and (8) of a perforation on the hinder
part of the ventral swellings at the base of the oral papillae
(fig. 33, o. s.).

"With regard to these points, I may make the following
observations :

1. The antennae have become ringed, and the number of
somites is almost completed. There are ultimately twenty-one
somites; in this specimen twenty could be made out (fig. 32).

2. In the specimen figured (fig. 30) the eye-pits were not
closed ; they remained open in this specimen abnormally late.

3. The lip-fold has grown considerably, and extended on to
the ventral surface behind the jaws (figs. 30, 33, L.).

4. These grooves are shown in fig. 35 (c. g.), which is taken
from a young specimen of the next stage. They are at first
wide and shallow, but, as we shall see, soon become deep and
narrow, and eventually closed.

THE DEVELOPMENT OF PERIPATUS CAPENSIS. 463

5. This projection had already appeared in the spiral stage
(figs. 28, 29), but it first becomes conspicuous in this stage
(fig. 30, d.). It is placed at the level of the eighth somite,
and consists simply of a thickening of the dorsal and lateral
ectoderm.

6. This process is shown in its two first stages in figs. 33 and
34, st. In fig. 33 the posterior margins of the buccal opening
are beginning to grow in beneath the anterior margins ; the
same feature being shown more clearly in fig. 34, st.

7. These pits are caused by an ectodermal invagination
which will give rise to the slime glands.

8. These two perforations (fig. 33, o. s.) are actual perfora-
tions leading through the body wall into the body cavity of the
third somite (somite of the oral papillae) ; they become the ex-
ternal openings of the salivary glands.

Stage F (figs. 35, 36). — The next stage, which is also found
in October in England, is very close to the previous one, and
I have only thought it necessary to figure a ventral view of the
head (figs. 35, 36). Fig. 35 is from a specimen slightly younger
than fig. 36, in fact from a specimen intermediate between this
stage and the previous stage. It has already been referred to
as showing the grooves in the brain ( c . g.), which first appear in
stage E. The main features of interest in this stage relate
to the head and anterior somites.

(1) The lips bave become very conspicuous and folded (fig. 36) ;
they have extended on to the ventral surface, passing inwards
between the jaws and oral papillse, behind the openings of the
salivary glands, which they have completely covered up, and
finally have united with one another in the median ventral line,
so as to form the posterior part of the adult lips.

Fig. 35 is especially interesting as showing an earlier phase
in this growth. In this figure the folds have not yet reached
the middle line, and are still very inconspicuous behind the
salivary openings (o. s.), which are still exposed.

(2) The cerebral grooves (fig. 36) have become much deeper,
and their opening reduced to a narrow slit, ending behind in
the mouth and slightly dilated in front.

464 ADAM SEDGWICK.

(3) The ingrowth of ectoderm into the mouth-opening is
completed in fig. 35. In fig. 36 the mouth-opening has become
reduced to a narrow slit by the approximation of the ventral
swellings at the base of the jaws (cf. figs. 35 and 36,.;. s.).

(4) The praeoral or cerebral lobes, which were distinctly
bilobed and separate in the previous stage (fig. 33) , have now
again become quite continuous across the middle line (cf. figs.
33, 35, 36), a shallow groove only marking the original line of
separation.

Stage G (figs. 37, 38). — The last stage which I have thought it
necessary to figure and describe is found in England in De-
cember (figs. 37, 38). The differences between this and the
previous stage consist mainly in the growth of parts already
present.

The embryo is characterised by its great transparency. The
full number of appendages is present, and the appendages have
acquired more nearly their adult form. They are all ringed,
and the rudiments of claws have appeared on the legs. The
appendages (fig. 37) are antennae, jaws (now completely hidden
by the lips) oral papillae, seventeen pairs of legs, and the small
anal papillae {an. p.).

The skin presents slight projections, shown as white opaque
marks in the figure ; these are the commencement of the
papillae, which cover the skin of the adult. The dorsal pro-
jection is still a conspicuous object {d), though not so con-
spicuous as in the earlier stages.

The integument presents a ringed appearance (fig. 38); the
rings, however, have nothing to do with the segmentation of
the body, being far more numerous than the segments.

The mesenteron is distinctly visible as a wide tube which
behind passes into the narrow rectum ( R ). The rectum is pro-
bably lined by an ingrowth of ectoderm through the anus and
may be looked upon as a proctodaeum.

The salivary glands (s. g .) can be seen through the skin, and
have grown some distance backwards. The same is to be said
of the slime glands {si. g.) which, however, are directed more

THE DEVELOPMENT OP PERIPATUS CAPENSIS.

465

dorsally. The salivary glands are, as I have said in my pre-
liminary paper, the nephridia of the third somite, i. e. the somite
of the oral papillae.

The remaining nephridia are also visible through the skin,
those of the fourth and fifth legs being especially conspicuous
by their greater size.

Fig. 38 represents this embryo in its natural position within
the uterus, a position which is retained until birth.

From January onwards the changes are merely those of
growth. When the young are born, i. e. in May, the antennae
are green, but the rest of the body is either quite white or of a
reddish colour. This red colour differs, however, essentially
from that of the adult, in the fact that it is soluble in spirit.
The just born young vary considerably in size, the average size
in the case of Peripatus capensis being from 10 — 15 mm.
The just born young of Peripatus Balfouri are about half
this size.

EXPLANATION OF PLATES XXXI and XXXII,

Illustrating Mr. Sedgwick’s Paper on “ The Development of
Peripatus Capensis.”

List of Reference Letters.

a. Anterior end. a. Anus. an. p. Anal papillae. At. Antennae, c. g.
Groove in brain, d. Dorsal ectodermal thickening, e. Eye. ec. Ectoderm.
en. Endoderm. F. 1 . . . . fyc. Feet. j. Jaw. j. s. Swellings at base of
jaws. L. Lip. M. Mouth, me. Mesenteron. or. p. Oral papillae, o. s.
Opening of salivary gland, p. s. Praeoral somite. R. Rectum, s. 20. 20th
somite, s. g. Salivary glands, si. g. Slime glands, s.o. 4 and 5. Nephridia
of 4th and 5th legs. st. Ectodermal ingrowths into embryonic mouth.

PLATE XXXI.

All the figures on this Plate, except 15, 17 — 22, are from fresh specimens.
Fig. 1. — Per. Balfouri. Side view of unsegmented ovum, showing polar
bodies and dark patch. Greatest length ‘4 to '48 mm.

466

ADAM SEDGWICK.

Fig. 2. — Per. Balfouri. Unsegmented ovum with dark patch, but with-
out central clear spot.

Pig. 3. — Per. Balfouri. Unsegmented ovum with numerous dark patches,
each with a clear centre.

Pig. 4. — Per. Balfouri. Ovum with two segments from side.

Pig. 5. — Per. Balfouri. Ovum with four segments from animal pole.

Pig. 6. — Per. Balfouri. Side view of ovum with four segments.

Fig. 7. — Per. Balfouri. Ovum with eight dark segments from animal
pole. Greatest length ’4 to '48 mm.

Pig. 8. — Per. capensis. Ovum fully segmented, with mosaic of ecto-
derm cells and scattered branched endoderm cells. Greatest length (of egg-
shell) -56 to ’6 mm.

Fig. 9. — Per. Balfouri. View of ovum from animal pole, as opaque
object.

Pig. 10. — Per. capensis. Aggregation of the endoderm cells beginning.

Pigs. 11 and 12. — Per. Balfouri. Completion of same process.

Pig. 13. — Per. capensis. Illustrates the same point. Length of ecto-
derm patch -32 to ‘4 mm.

Pig. 14. — Per. capensis. Another phase of the same process.

Pig. 15. — Per. capensis. Side view of ovum from preserved specimen.
Cap of ectoderm cells covering half the endodermal mass. Progress of
epibole. Diameter ’240 mm.

Pig. 16. — Per. Balfouri. Stage in which the endoderm cells are
covered by the (/.) latter ectoderm cells. Diameter \32 mm.

Fig. 17. — Per. capensis. Side view of embryo. A few endoderm cells
exposed.

Pig. 18. — Ventral view of same.

Pig. 19. — Per. capensis. Gastrula stage, ventral view. Blastopore
distinctly circumseribed. Size '204 mm. X '240 mm.

Pig. 20. — Side view of same in outline.

Pig. 21. — Per. capensis. Gastrula stage, ventral view. Same stage as
Fig. 19, but embryo slightly more elongated.

Pig. 22. — Per. capensis. Stage A, showing slightly elongated blasto-
pore with primitive streak at hind end. Greatest length *48 mm. a. Denotes
the anterior end.

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THE CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY

THE DEVELOPMENT OF PERIPATUS CAPENSIS. 467

PLATE XXXII.

All the figures on this Plate are of embryos of Peripatus capensis.

Pigs. 23 — 27. — Prom the original drawings by Miss Balfour, a. Denotes
the anterior extremity.

The remainder of the figures on this Plate from drawings by Mr. E. Wilson.

Pig. 23. Stage between A and B. With three somites and elongated
blastopore. Length of embryo ’7 mm., length of blastopore ’45 mm.

Pig. 24. Stage between A and B. With five somites. The blastopore is
closing in its middle portion. Length of embryo '74 mm., of blasto-
pore '46 mm.

Pig. 25. Stage B. The blastopore has completely closed in its middle
portion and given rise to two openings, the embryonic mouth and anus.
The anterior pair of somites have moved to the front end of the body,
and the primitive groove is very marked. Length of embryo 1'32 mm.

Fig. 26. Stage C. Embryo, in which the flexure of the hind end of the
body has begun ; with about thirteen somites. The remains of the
original blastopore are present as the mouth, placed between the second
pair of mesoblastic somites, and the anus, placed on the concavity of
the commencing tail flexure, and still removed from the hind end of
the body. Greatest length when lying on its back 1’12 mm.

Pig. 27. Side view of same embryo.

Pigs. 28 and 29. — Stage D (spiral stage).

Pig. 28. A young embryo of this stage, viewed from the side. With
commencing antennae and dorsal projection (d).

Pig. 29. Bather older embryo of same stage (end of spiral stage), side
view. Eyes ( e ) as pits. Jaws and postoral appendages sprouting.
Budiments of eleven pairs of legs. Length from anterior end of head
to bend ( d ) P6 mm. At. Antennae, d. Dorsal thickening, e. Eye.
j. Jaw. or. p. Oral papilla, p. s. Praeoral somite.

Pigs. 30 — 34. — Stage E.

Pig. 30. Side view of straightened-out embryo. Antennae ringed. Bucca
fold (L) extending round the jaw (j) on to the ventral surface. Sixteen
pairs of legs. Praeoral somite ventrally grooved. Apex of oral papilla
perforated. Length from front end of praeoral lobe to bend ( d ) 1'76 mm.
Eye still as an open pit (it is usually closed at this stage), d. Dorsal
ectodermal thickening, e. Eye. F. 1 .... 8pc. Peet. j. Jaw. L.
Lip. or. p. Oral papilla, p. s. Praeoral somite.

Pig! 31. Embryo of same stage, in natural position in egg membrane.

Pig. 32. Hind end of embryo of same stage, ventral view. a. Anus.
s. 20. 20th somite, s. 19 and 18. Legs of 19th and 18th somites.

463

ADAM SEDGWICK.

Fig. 33. Ventral view of head and segments of jaws and oral papillae of
young embryo of same stage (E). Brain ungrooved. Ectoderm of
sides of mouth beginning to grow inwards (s^.). Oral papillae perforated.
Opening of salivary glands ( o . s.) at base of oral papillae, j. Jaw.
L. Lips (buccal fold). M. Mouth, o. s. Opening of salivary gland.
p. s. praeoral somite, st. Ectodermal ingrowth at sides of posterior
part of mouth to form stomodaeum.

Fig. 34. Same view of slightly older embryo, with sides of mouth quite
infolded (st.) and a new posterior border to the mouth formed. Brain
still ungrooved. References as in Fig. 33.

Fig. 35. — Ventral view of head of embryo intermediate between Stages E
and F. Grooves in brain wide and shallow. The lips have grown considerably
and have extended behind the openings of the salivary glands, but have not
yet joined in the middle line. At. Antennae, c. g. Groove in brain, j. Jaws.
j. s. Swelling at base of jaws. L. Lips. M. Mouth, or.p. Oral papillae
o. s. Opening of salivary glands.

Fig. 36. — Stage F. Groove in brain almost closed ; the opening is slightly
wider anteriorly. Lips complete and folded, salivary opening quite covered by
them. Jaws completely enclosed. Swelliugs at base of jaws closely approxi-
mated so as to reduce the mouth opening to a narrow sb’t. The praeoral lobes
have completely united with one another (cf. Figs. 33 — 35). References as
in Fig. 35.

Figs. 37 and 3S. — Stage G-.

Fig. 37. Side view of embryo of Stage G. Full number of legs and oral
papillae. Length 5 — 6 mm. An. p. Anal papillae. At. Antennae.
d. Dorsal ectodermal thickening. F. 1 — 17. The legs. me. Mesen-
teron. or.p. Oral papillae. R. Rectum, s. g. Salivary glands, s. o.
4 and 5. Segmental orgaus of 4th and 5th legs. si. g. Slime glands.

Fig. 38. Embryo of Stage G, curled up as in the uterus.

On the Chromatology of the Blood of Some
Invertebrates.

By

C. A. Mac >1 linn, M.A., M.D.

With Plates XXXIII and XXXIV.

The following account of a few observations made by me
during the last two years on the blood of some invertebrate
animals may prove of use to others engaged in the same kind
of work, and although the observations are not by any means
complete, I have thought it advisable to publish the results,
with the remark that the present account is merely a pre-
liminary one, and that I hope to follow up the subject more
fully when an opportunity occurs of doing so.

As is well known, the colour of the blood in invertebrate
animals does not as a rule belong to the corpuscles, but to
what in them answers to the liquor sanguinis of Vertebrates,
although there are many exceptions. In some haemoglobin
occurs. Thus, Prof. Lankester has shown1 that in Glycera,
Capitella and Phoronis, and in Solenlegumen, it is found
in special corpuscles ; while in the vascular fluid of others it is
found dissolved, e.g. with certain exceptions in some Chaetopod
Annelids, in some Leeches (Nephelis, Hirudo), in Polia
sanguirubra (a Turbellarian), in the special vascular system of
a marine parasitic Crustacean observed by E. van Beneden,in the
general blood-system of the larva of the midge (C hironomus),
in the general blood-system of the Mollusk PI an or bis, and
in the general blood-system of the Crustaceans Daphnia and

1 “ A Contribution to the Knowledge of Haemoglobin,” ‘ Proc. Roy. Soc.,’
vol. xxi (1872), p. 71, &c.

VOL. XXV. NEW SER.

H H

470

C. A. MAC MUNN.

Cheirocephalus.1 Mr. Sorby has been inclined to doubt the
exact identity in position of the bands of haemoglobin in the
blood of Planorbis with those of vertebrate haemoglobin, but
Prof. Gamgee shows that the bands there occur in the same
position as those of vertebrate haemoglobin — a statement which
I can confirm.2

Haemocyanin. — The blood of many Mollusks and Arthro-
pods is of a blue colour after exposure to the air, and this is
in most cases due to the presence of another pigment — haemo-
cyanin. This pigment has quite an extensive literature of its
own. It is not within the scope of this paper to refer to all
the work that has been done with regard to the latter colour-
ing matter, so I will dismiss the matter in as few words as
possible. In 1816 Ermann had observed the blue colour of the
blood of Helix, which he thought was due to opalescence;3
E. Witting4 observed the feebly bluish blood of Unio pic-
torum, also that of Astacus, but he missed the blue colour
in the latter case. Genth5 observed the blue colour of the
blood of Limulus cyclops in 1852. Rouget in 1859 made
some observations on the blood of Octopus vulgaris (also on
that of Sipunculus oxyurus6). In 1847 Harless and von
Bibra observed the blue colour which the blood of Helix
pomatia acquired on exposure to air and lost on treatment
with CO„ ; they also observed that ammonia removed the blue
colour, which came back on neutralising with hydrochloric
acid.7 They stated that this blood contained copper, but no

1 Lumbricus and Arenicola also contain haemoglobin in their blood.
Also Eunice.

3 ‘Physiological Chemistry,’ vol. i, 1880, pp. 130, 131. Dr. Mays has
obtained haemin crystals from this blood. Cf. Krukeuberg, loc. cit.

3 “ Wahrnehmungen iiber das Blut einiger Mollusken,” ‘Abhandl. d. K.
Akad. d. Wissen. zu Berlin aus den Jahren 1816, 1817 ’ (Berlin, 1819),
S. 199—218.

4 “ Ueber das Blut einiger Crustaceen und Mollusken,” ‘ Journ. f. pract.
Chemie,’ Bd. Ixxiii, 1858, S. 121 — 132.

5 “ Ueber die Asclien bestandtheile des Blutes von Limulus Cyclops
(Fabr.),” ‘Ann. d. Chem. u. Pliarm.,’ Bd. lxxxi, 1852, S. 68 — 73.

6 ‘Journ. d. la Physiol.,’ t. ii, 1859, pp. 660 — 670.

7 ‘Muller’s Archiv,’ 1847, pp. 148—157-

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 471

iron, but Gforup-Besanez found iron also in its ash.1 Harless
made an elementary analysis of the colouring matter, and
found in it — besides copper — carbon, hydrogen, oxygen, and
nitrogen. The same investigators examined the blood of the
Cephalopods Loligo and Eledone; they found copper, but
no iron, and stated that the blue colouration of the blood was
removed by oxygen and restored on its abstraction — an error
which has since been refuted.

In 1857 Haeckel2 made some observations on the blood of
HomolaCuvieri, in which he show ed that the colourless blood
became gradually grey and then black ; he also observed that
the bright blue blood of a lobster became after many hours a
darker violet. P. Bert3 in 1867 found the blood of Sepia
colourless, feebly bluish, especially in the veins of the gills,
and that it acquired a bright blue colour on exposure to air.
This colour (he showed) belongs to the plasma, and is not lost
by boiling. Rabuteau and Papillon4 in 1873 experimented on
the blood of the Octopus. They examined its spectrum, and
arrived at the conclusion that it gives no bands ; they found
that it became blue on exposure to the air, that this colour
was lost on treatment with C02, but on shaking with air again
appeared. They observed the same colour changes in the
blood of Crabs. Jolyet and Regnard 5 showed in 1877 that
on shaking Crabs' blood with air it showed a beautiful blue or
brownish colour according to the manner in which it was
examined ; it gradually loses this colour, becoming reddish
and then feebly yellow, but on treatment with pure oxygen its
original colour is restored. They found two colouring matters6
in Crabs’ blood ; one is blue, and is precipitated by alcohol
with the albumen of the blood ; the other is reddish, and
remains in the alcoholic filtrate.

1 * Lebrbuch d. physiol. Chemie,’ p. 369.

2 Muller’s Archiv,’ 1857, S. 511, Anm. i.

3 * Compt. rend.,’ t. lxv, 1867, pp. 300 — 302.

* * Compt. rend.,’ t. lxxvii, 1873, p. 137.

5 4 Extr. des Archives de Physiologie,’ 2 ser., t. iv, 1877, p. 36, &c.

6 See p. 175, foot note.

472

C. A. MAO MUNN.

In 1878 Fredericq,1 in a paper on the physiology of Octopus
vulgaris, showed that the blue colouring matter of the blood of
this species is combined with a proteid and with copper ; the
proteid is more complex than an ordinary proteid, since it yields
one as a decomposition product. Fredericq found that this blood
lost its colour in vacuo and regained it on treatment with
oxygen ; and he observed its blue colour in the arteries of the
living Octopus. He found that it showed no absorption bands.
The following year Fredericq2 stated that the colouring matter
of the blood of the lobster is identical with that of Octopus;
it behaves in the same manner in vacuo and on treatment with
oxygen; he further showed that the statements of Jolyet and
Regnard with regard to Crabs’ blood also apply to the blood
of the lobster, which is blue with reflected and brownish with
transmitted light. The red pigment also present does not
belong to the albuminous constituents; it contains no copper,
and has nothing to do with the change of colour of the blood,
nor is it constantly present in the blood. The same authority
showed that the blood of Helix and Arion contains a similar
blue colouring matter to that of Octopus, Homarus, and Crabs,
i. e. haemocyanin. Prof. Lankester3 has shown that the blood
of Limulus and Scorpio becomes blue on exposure to air,
and contains hsemocyanin ; and Golch and Laws,4 of Oxford,
have found that in Limulus polyphemus the blood colour-
ing matter was allied to haemocyanin, and contained a proteid
united to copper, like it.

Krukenberg5 has examined the blood ofEledonemoschata,
S epi a officinalis, Homarus vulgaris, Carcinusmaenas,
Eriphia spinifrons, Portunus depurator, Grapsus

1 * Extr. des Bulletins de l’Acad. r. de Belgique,’ 2 ser., t. xlvi, No. 11,
1878, pp. 4—21.

2 ‘Extr. des Bulletins de l’Acad. r. de Belgique,’ 2 ser., t. xlvii, No. 4,
Avril, 1879.

3 ‘Quart. Journ. Micro. Sci.,’ 1878, p. 453, et seq. ; ibid., vol. xxiv, p. 151.

4 ‘ Brit. Assoc. Reports,’ 1884.

5 ‘ Vergleich. physiol. Studien.,’ 1st Reihe, 3 Abtli., 1880, S. 72, &c. The
above account of the literature of hsemocyanin is partly taken from this work.
I am also indebted to Gamgee’s ‘ Physiological Chemistry ’ for a few references.

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 473

marmoratus, Maja verrucosa, Pilumnus villosus,
Squilla mantis, and in all has seen the blood become blue
by shaking with air and oxygen, and the blue colour disappear
more or less with C02. He thinks it probable that a part of
the hsemocyanin or of its uncoloured reduction product becomes
decomposed or insoluble in the blood after some hours’ quiet
standing. In Limnseus stagnalis he found that the blood
after becoming blue on exposure to air was hardly changed in
colour on shaking with C02 ; now, it seems to me that a
current of C02 ought to be conducted into the blood before
one can arrive at a negative conclusion. Krukenberg, however,
thinks that in the blood of Helix pomatia and aspersa, and
of Limnseus stagnalis a body exists which is at least very
nearly related to hsemocyanin. Perhaps he might have gone
further, and concluded that hsemocyanin is present, as Fredericq
has shown for the first species to be the case. Krukenberg
also found great differences in the blood of individual Gastero-
pod Mollusks, which led him to assume that perhaps the
oxygen in such cases is in a firmer combination with the
hsemocyanin than is the case in Crabs and Cephalopods. He
also made the interesting observation that the blood of Crabs
and Cephalopods on treatment with carbonic oxide became
colourless, but regained its blue colour on shaking with air.
This behaviour is different from that of haemoglobin when
similarly treated. It was further found that blood which
had become blue by reception of oxygen if allowed to stand
in a test-tube exposed to the air did not lose its blue colour
from above downwards, but from below upwards, whence he
concludes that the blueing is not due to suspended particles,
but to the presence of a chromogen which becomes blue
by reception of oxygen. With H2S the blue Crabs’ and
Eledone’s blood became a feeble yellow, and lost the property
of again becoming blue with oxygen. He could find no
haemocyanin in the blood of several Mollusks (e. g. Tethys
fimbria, Doris tuberculata, Aplysia depilans, Pleuro-
branchus, &C.1).

1 Krukenberg further shows that (besides Planorbis in which the blood is

474

C. A. MAC MUNN.

In AnodontacygneaC. Schmidt1 found the blood colour-
less. My own observations on the blood of Mollusks and
Arthropods have been scanty, and made to determine whether
absorption bands are present or not. I have examined the
blood of Helix pomatia, Helix aspersa, Paludina vivi-
pera, Limnseus stagnalis, Homarus vulgaris, Cancer
pagurus, Carcinus msenas, and Astacus fluviatilis, but
in none of them could I see any bands.

The blood of Helix aspersa was found to be a bluish-
white colour by daylight, but by gaslight it had a purplish
tinge ; after twenty-four hours’ standing that had disappeared,
and it was then very slightly brownish. Examined in a deep
layer, no bands could be seen ; on treatment with ammonia,
the blue colour persisted and no bands came into view. With
acetic acid the blue colour persisted, and no bands appeared.
After repeated filtering the blue colour remained, hence it
can hardly have been due to particles in suspension. On
treatment with reducing agents the blue colour was lost, and
no bauds appeared.

Blood of Helix pomatia. — The blood assumed a distinct
blue tinge on exposure to the air, and gave no absorption
bands, but absorbed a little of the violet end of the spectrum.
On treatment with ammonia its colour was not so well
marked and it had a faintly reddish tinge, but no bands
could be seen, nor after treatment with acetic acid which did
not remove the colour. On treatment with sulphide of
ammonium the blue colour disappeared and could not be again
brought back by shaking with air, the solution being free
from bands. In some specimens exposed to the air for some
time the fluid had assumed a bronze colour, and with gaslight
a faint violet tint, but no bands were seen.

red) the blood of Apus is intensely red (it contains haemoglobin like that of
its congener Cheirocephalus, as shown by Lankester), of Gammarus violet
(v. Siebold), of Limnadia ruby red (Klunzinger), of Palinurus (Lund and
Schultz) and Astacus (Haeckel) pale red, ofLernanthropus (C. v. Heider)
reddish-yellow.

1 Lehraanu’s ‘ Physiol. Chem.,’ vol. iii, p. 256.

I

CHROMATOLOGY OR BLOOD OF SOME INVERTEBRATES. 475

Blood of Limnaeus stagnalis. — On exposure to air it
assumed a whitish-blue colour, gave no bands, nor after treat-
ment with ammonia, acetic acid, or sulphide of ammonium ;
the last discharged the colour completely, which could not be
restored on shaking with air.

Blood of Paludina vivipara. — The blood of this Mol-
lusk is frequently exuded when the animal is pricked with a
needle or otherwise irritated, and is of a blue colour. It is
quite free from bands. Ammonia slightly diminishes the
colour, but does not remove it ; acetic acid does not remove
it ; with neither reagent nor with sulphide of ammonium could
any distinct bands be obtained.

The blood of Homarus, Cancer, Carcinus, and Astacus1
were also examined with the same negative result as regards
bands, their colouring matters are, I believe, all identical, and
generally agree when present with the description of hsemo-
cyanin given by Fredericq and others referred to above. I need
not therefore enter into further detail as this paper deals only
with the spectroscopic characters of the colouring matters.

The blood of Serpula contortuplicata and Sabella
tubularia (Gosse). — A few preliminary remarks on the
chromatology of the blood of some worms is necessary before
describing the results of my examination of the above. Those
worms which contain haemoglobin in their pseudohaemal system
or perivisceral cavity have already been referred to.

In his paper above referred to Professor Lankester men-
tions the fact that Sipunculus nudus of the Gulf of Naples
contains a pale madder-like colouring matter in its peri-
visceral cavity, which is due to a large number of coloured
corpuscles from ^Vp-th to 4 ^ 0th of an inch in diameter, and
that this colouring matter, also found in other parts of the
worm, is not haemoglobin.

1 Halliburton has shown since the above was written that in the blood
plasma of Homarus a red pigment, soluble iu alcohol, ether, chloroform, &c.,
occurs, which appears to be the same red pigment as that found by me in
other parts of the same animal. See his report on Proteids of Blood, ‘ Brit
Med. Journ.,’ July 25th, 1S85.

476

C. A. MAC MUNN.

Delle Chiaje1 showed that in Sipunculus balanorophus
and echinorhynchus the arterial blood is red, the venous
brown. G. Schwalbe2 found that the body-fluid of Pliasco-
losoma elongatum (a Gephvrean) is a bright rose- or greyish-
red colour, and is cloudy owing to the presence of morphological
elements, and that on standing in the air it gets darker and
darker until it assumes an intense Burgundy-red colour. By
long standing in the air this colour goes into a dirty brown
owing to decomposition, and in drying the whole assumes
a dirty green colour. Krukenberg3 found the blood of Si-
punculus nudus to contain the same colouring matter as
that observed by Schwalbe ; he finds that it is the oxygen of the
air which brings about the colour change, and that the colour is
removed by C02. This colouring matter gives no absorption band
either in the oxidised or reduced condition. Krukenberg calls
this pigment haemery tb rin, and the chromogen belonging to
it haemerythrogen. The colouring matter is decomposed by
H2S. The oxygen in the oxidised blood-pigment seems,
according to Krukenberg, to be more firmly fixed than in oxy-
haemoglobin. Milne-Edwards4 in 1838 discovered that certain
Annelids possessed green blood, his observations being made
onSabella. In Chloronema Edwardsi M. de Quatrefages
found similar blood.

Professor Lankester5 on examining the blood of Sab ell a
ventilabrum and Siphonostoma (sp. ?) with the spectro-
scope discovered the interesting fact that it not only gives
a banded absorption spectrum, but is capable of being oxi-
dised and reduced, and it behaved in such a way with cyanide
of potassium and sulphide of ammonium as to have led him to
conclude that haemoglobin and this colouring matter (which Pro-
fessor Lankester named chlorocruorin) “ have a common base

1 ‘ Memorie sulla st.oria e notomia degli animali senza vetebre del regno di
Napoli,’ t. i, pp. 13 and 127.

2 ‘Arch. f. Mikr. Anat.,’ Bd. v, p. 218, et seq., 1869.

3 Loc. cit., p. 85.

4 ‘ Ann. des Sciences Natur.,’ 1838, 2nd serie, vol. x, p. 190.

5 ‘ Journ. of Anat. and Physiol.,’ 1868, p. Ill; also 1870, p. 119.

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 477

in cvanosulphaem, and perhaps in Stokes’ reduced haematin.”
Now, Krukenberg1 tries to show that this reduction is not such,
hut that chlorocruorin and erythrocruorin are one and the
same substance which is not reduced by sulphide of ammonium.
If Krukenberg had studied Professor Lankester’ s paper he would
have seen that Professor Lankester says that “ on addition
of reducing agents the two bands are changed into one, having
nearly the same position as the darker of the two hut fainter.
On agitation with air the two returned.” The extra-
ordinary mistake of Krukenberg in missing the fact that
what he calls “ Ilelicorubin ” — and takes to himself the credit
of having discovered, although previously discovered by Dr.
Sorby — is capable of existing in the oxidised and reduced
state, is an exact parallel to this.2

His other criticisms on the action of cyanide of potassium
on chlorocruorin are based on a mere comparison of spectrum
maps and are therefore valueless.

Professor Lankester could not obtain derivatives of chloro-
cruorin, owing, as he has stated, to the apparent instability of
this body, which decomposes rapidly.

I have really nothing of importance to add to the descrip-
tion given by Professor Lankester, but I have examined the
aqueous solution of chlorocruorin, its behaviour with some
reagents, and measured its bands in wave lengths. For the
sake of comparison I have mapped these spectra in the accom-
panying Chart I. I have only been able to obtain about a
dozen specimens, so that my examination is not complete, but
I hope to be able to study this subject again.

On slitting up a worm and collecting the green fluid which
exudes on a watch-glass and examining with the microspec-
troscope a dark band is seen before D, and a feeble one
between D and E (sp. 1, Chart I). The brown gills of the

1 Loc. cit. and ‘ Grundziige einer Yerlgleichenden Physiologie der Farb-
stoffe und der Farben,’ 1884.

2 I have shown that this gives the bands of hsemochromogen. Kruken-
berg’s map of it is quite incorrect. See my sketch in ‘ Proc. Roy. Soc.,’ No.
226, 1883. I have lately proposed the name “ enterohsematin ” for this
pigment.

478

C. A. MAC MUNN.

specimens examined by me gave no bands, and did not con-
tain therefore the same pigment which I found in those of
Serpula to be referred to further on.

The green fluid had a reddish tinge with reflected gaslight,
and in most cases was green with transmitted daylight, and
reddish with transmitted gaslight. On dilution with water the
fluid gave two bands : — the first from X 618 to X 593, the second
from X 576 to X 554’5. On then adding ammonium sulphide
I obtained sp. 2, Chart I. As well as I could make out the
first of these bands extended from X 625 to X 596’5 (?), but
this and also the second band were very faint. If now caustic
soda were added to this solution a dark band was seen covering
D, which recalls to mind the band of alkaline hsematin (sp. 3,
Chart I), and this band extended from X 595 to X 576.

If an aqueous solution is treated with caustic soda alone this
appearance is not seen, as the bands become faint and gradually
disappear, but if then ammonium sulphide is added, the same
band covering D appears (sp. 3, Chart I).

If the blood is treated with rectified spirit and caustic
potash and filtered a yellowish solution is obtained free from
bands, but on adding ammonium sulphide a band appears
covering D, as in the case of the aqueous solution (sp. 4,
Chart I).

In some specimens the second band did not occupy the same
position as before in aqueous solutions of the blood ; it some-
times read from X 569 to X 551, and with ammonium sulphide
the band of this reduced chlorocruorin extended from X 623 to
X 593 (see sp. 5 and 6). But on adding caustic soda to this
reduced fluid the band, like that of sp. 3, again appeared.

On treating aqueous solutions with acetic acid the bands
faded away, and the colour of the solution changed to brownish
(gaslight).

I tried the action of rectified spirit acidulated with sulphuric
acid on chlorocruorin, and obtained a faint greenish solution,
which showed a faint shading in the green too indistinct to
map.

On treatment with sulphuric acid a brownish-yellow solution

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 479

was obtained, which, on adding absolute alcohol, showed a hand
in green, bat as it is very doubtful whether this is not due to
the action of the acid on a proteid I have not mapped the
spectrum.

Hence none of the decomposition products of haemoglobin or
haematin could be obtained,1 the pigment, as Prof. Lankester
had already shown, being destroyed by the reagents required
to produce acid haematin and hsematoporphyrin. I digested the
gills of several specimens of Sabella in chloroform, but failed
to obtain a coloured solution ; digestion with rectified spirit and
caustic potash furnished a yellow solution, but in this no
well-marked bands could be detected.

The blood2 of the pseudo-haemal system of Serpula con-
tortuplicata presents some resemblance to that of Sabella,
and I believe it has not been examined until now. There are
slight differences in the blood spectra of some specimens, which
doubtless are due to the pigment being present in different
states of oxidation, and on comparing some of these spectra
with those of the histohaematins and with decomposition pro-
ducts of haemoglobin a striking likeness is apparent.

On putting a Serpula into the compressorium, and
bringing gentle pressure to bear on the upper surface of the
animal, and examining with the microspectroscope, using a
good achromatic substage condenser, a series of spectra are
obtained when the various parts of the animal are moved
under the objective ; what these parts are is seen by looking
down the left-hand tube of the microscope.

In this way we can differentiate the blood-vessels, intestine,
gills, operculum, and other parts, and study the spectrum of
each. A portion of the pseudo-haemal system, with its con-
tained blood of a worm gave sp. 7, Chart I, the band before D is
like that of chlorocruorin, but the first after D and also the

1 At the same time this colouring matter is certainly closely related to
hsematin, as sps. 2 and 8 show. In 8 (from serpula-blood) bands like those of
hsemochromogen are present.

2 I have not given this pigment a name, as I believe it to be a kind of
chlorocruorin.

480

C. A. MAC MUNN.

second are different. In some of the blood-vessels only the
band before D was visible.

An aqueous solution obtained from nine Serpulse was a
reddish-yellow colour by gaslight, yellow by daylight, and this
gave a spectrum like 7. The band before D was from A 620 5
to A 593, the second about A 583'5 to A 572, the third uncer-
tain (about A 551 to A 532). After adding sulphide of ammo-
nium the only band seen with certainty was that before D.
which seemed slightly nearer violet. In rectified spirit ex-
tracts only a faint lutein band was visible in the yellow solution
from about A 501 to A 477.

In a specimen in which the blood appeared a bright carmine-
red colour sp. 8, Chart I, was obtained ; the second band of
this spectrum resembles the first band of haemochromogen, and
is really the same as sp. 2. The principal blood-vessel showed
two round dilatations, and in these I observed sp. 9, Chart I.
The darkness of the second band at once distinguishes the
pigment from chlorocruorin.

In other specimens the same dilated part of the pseudo-
haemal vessels gave sp. 10, Chart I, while in another specimen
the blood showed sp. 11, Chart I.

An aqueous solution of blood obtained from a dozen speci-
mens— whose blood gave the above spectra — was yellow, and
showed the three bands represented in sp. 12, Chart I, and
these gave the following readings : — First band A 618 to A 593,1
second A 582 to A 570‘5, third A 551 to A 529'5 (?). On treat-
ment with sulphide of ammonium the solution became slightly
greener ; no bands could then be seen after D, and that before
it was very faint. Hence it would appear that the two- or three-
banded spectrum denotes the oxidised state.

On digesting the bodies of some Se rpulae in caustic potash
and rectified spirit a yellow solution was obtained, giving no
definable bands, except some feeble shading at the blue end of
green, but on adding sulphide of ammonium the solution
became faintly red, and a band like the first band of

1 I.e., exactly the reading of the first band of oxychlorocruorin.

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 481

haemochromogen was just visible, and perhaps a second
like its second band.

In some Ser pulse whose blood was not red but brown, the
bands before and after D reminded of chlorocruorin (sp. 13, Chart
I). In these, too, the gills were not red, as in the other speci-
mens, and failed to show a band. An aqueous solution of the
blood of these specimens had a reddish tint by gaslight, and
gave three bands, which read as follows : — First X 620’5 to
X 595, second X 583 5 to X 570 5, third X 551 to X 532. On
adding sulphide of ammonium the band before D read X 620'5
to X 598, and a second band was visible after D, which could not
be measured. On adding to this reduced fluid some caustic
soda at first the only change produced was the disappearance
of the faint band after D, but, after standing, sp. 14, Chart I,
appeared, of which the bands read : first X 623 to X 607,
second X 596'5 to X 579. This shows that the blood of these
Ser pulse did not contain the same kind of chlorocruorin as
Sabella, but a pigment very closely related to it, probably
nearer to hsematin than it. I had not enough material
for further study.

In most cases the gills gave sp. 15, Chart I, while in
others the band was slightly nearer violet. On extracting
them with absolute alcohol an orange solution .was obtained,
which strongly absorbed the violet end of the spectrum, and
allowing only the red and beginning of the green to pass in a
deep layer. In a shallow one a shading was seen from about
X 509 to X 467 (?). This solution became blue, and then
colourless with nitric acid, but was not much changed by
hydrochloric acid. Caustic potash developed a more distinct
shading, from X 509 to X 481.

The red opercula gave a band covering D, sp. 16, Chart I;
they vary much in colour, some being very red, while others
are colourless, and in some gills the same band is seen.

The band of sp. 15, Chart I, belonging to the gills, though
resembling that of reduced haemoglobin, has no connection
with it, as I found by extracting the gills with rectified spirit
and caustic potash, and adding sulphide of ammonium, the

482

C. A. MAC MUNN.

result obtained being negative, so far as hsemochromogen is
concerned. The pigment present in them is closely related to,
if not identical with, tetronervthrin, and in the hypoderm of
Cancer pagurus and integument of U raster rubens, where
I have shown tetronerythrin1 to be present, the solid pigment
gives the same kind of band. In some Serpulae I could per-
ceive the bands of the colouring matter of the blood itself in
the gills. The tetronerythrin of the gills and other red parts
is probably of no respiratory use, and I think its action with
reducing agents in other cases goes to show that too much
importance has been attached to its supposed respiratory func-
tions. It is not unlikely that, especially when its likeness to
Kuhne’s chromophanes is taken into consideration, it may be of
use in absorbing certain rays of light concerned in some obscure
photochemical process.

The colouring matter of the perivisceral fluid of
Strongylocentrotus lividus. In 18832 I stated that in
various parts of the body and in the perivisceral fluid of
Echinus (esculentus ?) and sphaera I had detected a colour-
ing matter of a brown colour which gave two bands, one
between D and E covering E, the other between b and F, the
first of which became decidedly darker with ammonium
sulphide. I found that it went into chloroform and alcohol, but
owing to a dearth of material I did not arrive at any very definite
conclusions, except that this pigment is respiratory. Professor
Schafer informed me some time after the publication of these
results that in working at the coagulation of the perivisceral
fluid of an Echinus he had seen the same bands ; and P. Geddes3
had observed the colour changes of a similar pigment. The
latter observer has worked out the morphology of the cor-
puscles of the perivisceral fluid of various Echinoderms4 and

1 ‘Proc. Birm. Philos. Soc.,’ vol. iii, 1883.

• ‘Proc. Birm. Philos. Soc.,’ loc. cit., pp. 380, 381.

3 See Gamgee’s ‘Physiological Chemistry,’ pp. 134, 135.

4 ‘ Proc. Roy. Soc.,’ No. 202, 1880. I have not seen his paper
‘ Archives de Zoologie Experimentale.’

CHROMATOLOGY OF BLOOD OF SOME INVERTEBRATES. 483

has made observations on its coagulation ; he does not, however,
say anything about its spectroscopic characters.

I named this pigment echinochrome and have lately
made several observations on fresh specimens of Stron-
gylocentrotus livid us, which I was able to procure alive
in considerable quantity. On opening a specimen a fluid
of a pale red colour exudes from the perivisceral cavity ; it
sometimes has a violet tinge. In a short time a clot forms ;
this becomes gradually darker in colour and it contracts more
and more, until all its connections with the side of the contain-
ing vessel are broken, and it finally shrinks into a small brown-
red mass. The corpuscles are carried down by this clot and it
is to them, not to the plasma, that the colouring matter
belongs. Geddes1 has shown that the coloui’less, finely granular,
pale corpuscles run together to form plasmodia, and that it is
to their fusion that the clotting is due.

The corpuscles present all degrees of colouration, from a
brilliant lake red, through a pale orange, to colourless. The
red ones are nucleated and of irregular shape, and rapidly
throw out amoeboid processes, so also do the others. The
nucleus is strongly refracting and gives the corpuscle the
appearance of a round hole having been punched in it. The red
corpuscles measure from —gV^-th inch in long diameter x -g-^o 0 th
in short, down to -g-glg-g-th in long x g-gy-g-th in short, while several
measure ^t-g-th in both diameters. The pale ones 0 th
x ^g-g-th down to -g-Q^-gth x -g-gVo^ > tatter are multi-
nucleated.2

The pigment itself in the fresh state showed no distinct
bands but treated with caustic potash in the solid condition the
colour changed to dark purple and showed the bands of sp. 1,
Chart II.

It seems to me that the deepening of colour which echino-
chrome undergoes on exposure to the air must be in part due
to the oxidation of a chromogen, if so we may infer the
existence of such, and name it echinochromogen.

1 Loc. cit.

2 I think the red corpuscles only differ from the white in possessing pigment.

484

C. A. MAC MUNN.

It is not a difficult matter to obtain solutions of this colour-
ing matter for spectroscopic examination, as it is taken up by
a great number of solvents, in which point it differs much
from the blood pigment of most invertebrate animals; and it
resembles in its solubility lutein and tetronerythrin (= Kru-
kenberg’s lipocliromes) ; still its spectroscopic and other cha-
racters show that it is not either one or the other.

Echinochrome can be obtained in solution and isolated by
two methods : (1) The fresh blood-clot can be extracted with
the solvents mentioned below, or (2) the clot may be separated
from the serum by filtering, the pigment dried at the tempera-
ture of the air (as it changes by using heat) and the dried
pigment thus obtained treated by solvents. By the adoption
of the latter method it can be obtained in a purer condition.1

The “ serum ” after separation of the clot is a faint yellow
colour and shows two faint bands in green, but if allowed to
stand some time in contact with the clot it becomes a faint violet
red, and then shows Chart II, sp. 2. Treated with caustic
soda these bands are intensified, but then the fluid is not quite
as coloured as before, but if instead stannous chloride be added
the dark bands of sp. 3, Chart II, appear, the fluid being then
violet-reddish. These bands read from X 54T5 to X 532 and
X 506 to 486'5 ; on agitation with air they are not as distinct
but do not altogether disappear.2 The serum was found to be
faintly acid, or neutral, faintly opalescent on heating, opales-
cent with absolute alcohol, and faintly so with ether.

The brownish-red clot shows after standing in contact with
the “ serum ” sp. 4, Chart II, and with caustic soda sp.
5, II.

An absolute alcohol solution of the fresh clot is a
red colour, allowing red, orange, yellow, and a little green to
pass in a deep layer, while in a thinner layer examined by day-
light sp. 6, Chart II is seen. These bands have the following

1 The filter paper with the dried pigment on it is cut up and put into test-
tubes containing the solvents, and corked up and left in a dark place.

2 Because in the oxidised condition bands of the same kind, but feebler,
are visible.

CHROMATOLOGY OP BLOOD OF SOME INVERTEBRATES. 485

positions : 1st, X 557 to X 545'5,x 2nd, X 524-5 to X 501, 3rd,
X 4945 to X 475. This third band is merged into the second.
On adding sulphide of ammonium two new bands appear of
which the 1st is from X 531 to X 507, and 2nd, X 494-5 to X
475, the colour of this solution being changed to yellow and on
shaking with air remaining the same. With caustic soda
similar hands appeared and the solution became yellow ; the
bands read : first, X 532 to X 509 ; and second, X 494-5 to X
477. On neutralising this solution with acetic acid it became
again faintly red, and the original bands reappeared but were
very faint.

On treatment of an absolute alcohol solution with acetic acid
the colour changed to reddish yellow and sp. 7, Chart II, was
seen. On treating with caustic soda to alkalinity, the same
bands as those seen when an alcohol solution is treated with
that reagent appeared. The spectrum of the original absolute
alcohol solution is that of the neutral pigment, as can be
proved. Peroxide of hydrogen did not affect the bands. Hydro-
chloric acid produced the same effect as acetic acid ; the bands
reading : first, X 545'5 to X 529’5 ; second, X 51 1*5 to X 488.
When the alcohol solution is treated with stannous chloride
the colour changes to yellow, and two very well-marked bands
appear (sp. 8, Chart II). Dark part of first band X 535 to
X 51T5; second, X 496-5 to X 477. Hyposulphite of sodium
changed the colour to yellow but the original bands could
be seen, although faint.

On evaporating the alcohol solution on the water-bath a
brownish- red residue was left, in which were numerous crystals
of chloride of sodium ; on treating with chloroform a fine red
solution was obtained, but a good deal of the residue remained
undissolved, and what did remain of it was more of a pink
colour than its previous colour brown ;2 on filtering the chloro-
form the paper was stained a pale rose colour. On a white
dish this chloroform solution had a violet tinge and gave sp. 9,

1 If the feeble shading at each side of the band is included it reads from
X 560 to X 513.

s Owing to decomposition.

i i

VOL. XXV.

NEW SER.

486

C. A. MAC HUNN.

II ; on evaporation of the chloroform a brown-red residue with
a violet tinge was left. This residue was now only partially
soluble in absolute alcohol, forming a pale reddish-violet solu-
tion, giving, however, the same spectrum as the original abso-
lute alcohol solution, and with caustic soda it gave the same
reaction as before. From the fact, however, that the whole
of the residue was not now soluble in absolute alcohol, it is
quite evident that the pigment was decomposed by evaporating
it down by the aid of heat. I stated above that the residue
left after the evaporation of an alcohol solution was not quite
soluble in chloroform, and what was left after the chloroform
extraction was treated with ether ; this solvent took up a pig-
ment whose absorption spectrum is remarkable for the two
narrow bauds in green, which recall to mind some histohaematin
spectra. This ether solution was reddish, and gave sp. 10,
Chart II ; its bands reading as follows : first band, X 554'5 to
X 547 ; second, X 540 to X 535 (?) ; and third, about X 516 to
484’5 (= darkest part). Although so different in spectrum
from the alcohol solution, yet when the ether was evaporated
and the residue again dissolved in absolute alcohol, a rose-
coloured solution was obtained whose spectrum closely resem-
bled that of the original alcohol solution, and with caustic
soda it changed to yellow, and the bauds already referred to
were seen. Hence the pigment present in the ether could not
have been much changed. After the extraction of the
residue left after the evaporation of the absolute alcohol by
ether and chloroform, some was still left untouched by these
solvents ; on treatment of this residue with nitric acid the
colour was discharged, the acid itself now becoming yellowish.

That the above ethereal solution contained a slightly different
colouring matter from that present in chloroform is proved by
this experiment. An alcohol solution of clot was evaporated
down, the residue extracted with chloroform, the latter eva-
porated down ; it then left a brown amorphous pigment. On
dissolving this in ether I obtained not sp. 10 but sp. 11; but
when the residue from the alcohol solution already ex-
tracted by chloroform was treated with ether, a reddish-

CHROM A.TOLOGY OF BLOOD OF SOME INVERTEBRATES. 487

yellow solution was obtained which did give sp. 10 again,
showing the splitting up of the echinochrome into two pig-
ments.

If a chloroformic solution obtained as above be evaporated
and the residue1 extracted with bisulphide of carbon, a red
solution is obtained which gives sp. 12, Chart II. The residue
is also soluble in benzene, giving similar bands.

If the second of the methods mentioned above for obtaining
echinochrome — namely, filtering off the clot from the “ serum,”
drying on the paper, and extracting with absolute alcohol — be
adopted a pale red solution is obtained, which gives the same
spectrum as the alcohol solution of fresh clot, and the same
spectrum with stannous chloride.

An aqueous solution of dried echinochrome gave no
distinct bands, but on adding stannous chloride the usual
bands appear, which still persist after acidulating with hydro-
chloric acid ; after which they read : first band, X 537 to
X 513; second, X 505 to 484‘5 (?) ; the colour of the solution
being reddish.

An ether solution of the dried clot is reddish -yellow and
gives sp. 13, II ; that this solution contains the same pigment
as the alcohol solution is shown by adding stannous chloride
which develops the bands referred to, measuring in this case :
first band, X 533-5 to X 520; second, X 496-5 to X 477, the
solution having a violet-red tint. On treatment of this with
an ether solution of peroxide of hydrogen the bands produced
by the stannous chloride were not changed.

A chloroform solution of the dried clot is reddish yellow
— and in one degree of dilution violet red — and gives sp. 14,
Chart. II. On treating with stannous chloride the usual
bands are seen : first, from X 540 to X 516 ; second, from X 505
to X 484-5 (?).

A bisulphide of carbon solution of the dried clot is
violet red, and gives sp. 15, Chart II. The bands measure
approximately, first X 566 to X 554"5, while the dark shading
commences at X 537, and its darkest part ends at X 511-5, the
1 Which is of a violet colour.

488

C. A. MAC MUNN.

feeble shading extending to A 484‘5, and with stannous chloride
the result was the same as before.

A benzene solution of the dried clot gives sp. 16, II, and
is similarly changed by stannous chloride ; the bands produced
by this reagent: — measuring first from A 538'5 to A 516, the
second A 505 to A 484'5.

A petroleum ether solution gave a similar spectrum, and
altered in the same manner by stannous chloride.

Glycerine is also a good solvent for fresh echinochrome,
it forms with it a deep red solution in which two bands are
seen, the first from A 560 to A 545’5, sp. 17, II. On treatment
with caustic soda the solution is reddish-yellow, and two bands
(as in other cases) are seen ; the first from A 54T5 to A 516,
and the second A 503 to 484'5 (?). On adding acetic acid to
this solution they disappear, and they can be brought back with
more caustic soda. When a glycerine solution is treated with
acetic acid, the same change as that produced by this reagent
in the case of alcohol solutions takes place (see Chart II, sp. 7).
Hydrochloric, sulphuric, and nitric acid produce the same
effect. Ammonia changes the red colour to orange yellow,
and this solution shows two bands : first, A 537 to A 516 ;
second, A 501 to A 482'5. On treating a glycerine solution
with stannous chloride the solution is reddish yellow and gives
sp. 18, II ; the first band is from A 540 to A 513, the second
from A 503 to A 481 ; they are unaffected by hydrochloric acid.
The above are the most important characters of echinochrome;
the colours of the solutions were observed mostly by gaslight
owing to circumstances over which I had no control.

Although I have now examined a great number of animal
colouring matters, I have not met any which — as regards
spectra and solubility — resembles this one.

It is partially soluble in water and alcohol, soluble in gly-
cerine, ether, chloroform, benzene, bisulphide of carbon, and
petroleum ether. It is certainly capable of existing in two
states of oxidation,1 and is therefore respiratory. It is — when

1 The surmise of Krukenberg that the appearance of the dark bands on

CHROMATOLOGY OP BLOOD OP SOME INVERTEBRATES. 489

its solutions are evaporated — quite amorphous, as in no
instance have I been able to obtain it crystallised.

The spectroscopic study of the blood of Ascidians and some
other Invertebrates I hope to continue shortly, but my obser-
vations in these cases are not sufficiently advanced to allow of
their being published at present.

EXPLANATION OF PLATES XXXIII & XXXIV,

Illustrating Dr. C. A. Mac Munn's Paper “ On the Chroma-
tology of the Blood of some Invertebrates.”

CHART I.

Sp. 1. — Spectrum of Professor Lankester’s oxychlorocruorin, from the
green fresh blood of Sabella.

Sp. 2. — The same with ammonium sulphide, after dilution with water.
(Note the attempt at the first band of hsemochromogen.)

Sp. 3. — The solution treated with caustic soda, after ammonium sulphide;
the band recalls to mind that of alkaline haematin.

Sp. 4. — The blood is treated with rectified spirit and caustic potash, and
then treated with sulphide of ammonium.

Sp. 5. — Aqueous solution of oxychlorocruorin.

Sp. 6. — The same with ammonium sulphide.

Sp. 7. — Spectrum of the blood (while in the living animal) of Serpula
contortuplicata.

Sp. 8. — Spectrum of the bright carmine-coloured blood of another worm.
(Note the bands like those of hsemochromogen.)

Sp. 9. — Ditto of a dilatation of the principal pseudoheemal vessel of a
Serpula.

Sp. 10. — Ditto in another specimen.

Sp. 11. — Spectrum of the blood of another specimen, evidently like that of
oxychlorocruorin.

Sp. 12. — Aqueous solution of blood of a Serpula.

Sp. 13. — Brownish blood of another specimen.

adding reducing agents is caused by precipitation, is sufficiently refuted by
what I have shown in this paper.

490

C. A. MAC MUNN.

Sp. 14. — The same blood in aqueous solution after the addition of sulphide
of ammonium and caustic soda. Compare Sp. 3.

Sp. 15. — Spectrum1 of the gills of some Serpulm.

Sp. 16. — Spectrum of an operculum. In the gills of some Serpulae this
band is seen.

CHART II.

Sp. 1. — The colouring matter of the perivisceral fluid of Strongylocen-
trotus lividus with caustic potash (in the solid state).

Sp. 2. — The “serum” of this fluid, after standing in contact with the clot
for a considerable time.

Sp. 3. — Action of stannous chloride on the same. Reduced echinochrome.

Sp. 4. — Spectrum of the brownish clot (of same fluid).

Sp. 5. — The same treated with caustic soda.

Sp. 6. — Absolute alcohol extract of fresh clot.

Sp. 7. — The same with acetic acid (acid echinochrome).

Sp. 8. — Absolute alcohol extract of fresh clot with stannous chloride.

Sp. 9. — Chloroform extract of residue from the evaporation of an alcohol
solution of echinochrome.

Sp. 10. — What was left untouched by the chloroform went into ether,
giving this spectrum.

Sp. 11. — An absolute alcohol solution was evaporated down, residue dis-
solved in chloroform ; this was evaporated, and the residue dissolved in ether
gave this spectrum, which differs from Sp. 10.

Sp. 12. — Bisulphide of carbon solution of the residue left from the evapora-
tion of a chloroform solution.

Sp. 13. — Dried clot in ether.

Sp. 14. — Dried clot in chloroform.

Sp. 15. — Dried clot in bisulphide of carbon.

Sp. 16. — Dried clot in benzene.

Sp. 17. — Glycerin extract of fresh echinochrome.

Sp. 18. — The same with stannous chloride.

A comparison of these spectra shows how remarkably unstable echino-
chrome is ; it is on this instability that its usefulness as a respiratory substance
depends.

1 This band is rather too dark.

JUcrrJowrnPjk mj.sM. mm

B C D E h F

G

Sp. I .
2.
3.
4

5.

6.

7.

8.

9.

10.

12.

13.

14.

15.

16.

Oxychloro-

cruorin.

The same
-t-NlUKS

M° 2+flaHQ

Aq.sol.+NaHO‘ ■

thenNIUHS

Aqueous solution'
of Oxychlorocruo

■

The sams+Tl H-t H

Blood of Serpula
living animal. ,

Blood of another,
Serpula.

D? from a dilatec
part of hloodves

D°from same pa
a third specirm

D° from same pa
a fourth specim

Aqueous solutio
of Blood of Serp

D° other
Specimens

D° + 11a HO, the
NHtHS.

Gills of Serpul

Operculum of
Serpula.

Mac Muna del

F Huth, LilhT Edtnr

JtmJownM,. mjs&tjniv

B C D Eb F

G

Sp. I.
2.

3.

4.

5.

6.

7.

8.

9.

10.
II.
12 .

13.

14.

15.

16.

17.

18.

Echino chrome
+ RHO. fresh clot.

Echino chrome
in"SeTuml

D° + Stannous
:hloride .

Echinochrome
in Wood clot.

D° + flaHO

D? in absolute
alcohol.

DEwith acetic
acid.

D? with stannous
chloride

Residue fromAkoh
solution in chlorofb

Residue after
chloroform in ether

Residue from
chloroform in eths

D°obtarad as
described rnpapei

Dried dot in
ether.

D° in chloroform.

D? in carbon
bisulphide.

D? in benzene.

Fresh dot in
glycerine.

D°with stannous
chloride.

Mac Munn del

F HutH.IithT £dir*

The Cephalic Appendages of the Gymnosomatous
Pteropoda, and especially of Clione.

By

Paul Pelseneer, D.Sc,,

Brussels.

With Plate XXXV.

Eschricht formerly made known, on the three pairs of
cephaloconi (“ Kopfkegel ”) of Clione borealis, some struc-
tures which he described and represented as real suckers ; at
the same time he drew attention to the analogy of their situa-
tion with that of the suckers of the Cephalopoda.1

This fact was of great importance, since it accorded with the
presence of suckers on the two buccal appendages of another
Gymnosomate, viz. Pneum odermon, and gave great support
to the opinion expressed by R.. Leuckart, that the six conical
appendages of the head of Clione correspond with the arms
of the Cephalopoda.2

From that time the assertion that Clione possesses aceta-
buliferous appendages has been admitted everywhere, and it
is found reproduced in the most valuable and most recent
works.

However, the excessive smallness of the structures which
Eschricht had described as suckers (he attributes to them
0005'" of diameter) permitted one to call in question their
assimilation with the suckers of Pneumodermon and of the

1 Eschricht, * Anatomisclie Untersuchungen iiber Clione borealis,’ p. 9.

2 It. Leuckart, * Ueber die Morpbologie und die Verwaudscbaftsverbalt-
nisse der Wirbellose Thiere.’

492

PAUL PELSENEEE.

Cephalopoda, the more so as Hobboll, who has observed Clione
living, and has often seen their cephaloconi expanded, has
never remarked that these animals fixed themselves by these
appendages,1 while several naturalists have seen Pneumoder-
mon in life, and have noticed that it frequently fixes itself
with the aid of its acetabuliferous appendages.

Therefore, during the sojourn which I made in the winter of
1884-85 at the zoological laboratory of University College
(London), Professor Ray Lankester proposed to me to study
the structure of the cephaloconi of Clione.

Having set to work, I immediately saw that in a large number
of well-known and even very recent works great confusion pre-
vailed on the cephalic appendages of Clione. The reason of
this is specially to be found in the imperfection of the original
figures, which are generally obscure on the subject; and those
which are most often reproduced are just the most defective,2
for they give a very bad idea of the cephalic appendages of
Clione, or are even absolutely incomprehensible on this
point.

Those of Eschricht are small, and also difficult to under-
stand, so that the reproductions which have been made of
them are inexact, and, as Keferstein has remarked, “ all those
processes which have been named tentacles by Eschricht want
a new description/’ 3

"When I had comparatively examined other Gymnosomata,
I remarked that there also a confusion quite as great existed
on the cephalic appendages, the more so since the original
authors do not agree on this question.

In order to dispel the confusion which exists on this sub-
ject, I have thought useful to represent on a rather large
scale, and under different aspects, the cephalic part of some

1 Eschricht, loc. cit., p. 9.

2 For example, the figure of Clione given by Rang (Rang et Souleyet,
‘ Histoire naturelle des Mollusques Pteropodes,’ pi. vii, fig. 9), reproduced by
Keferstein (Bronn’s ‘ Thierreich ’), by Claus (‘ Elementary Text-Book of
Zoology ’), &c.

3 Keferstein, Bronn’s ‘ Thierreich/ Abth. iii, p. G13.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 493

Gymnosomata. I thus have been induced to extend to the
cephalic appendages of the gymnosomatous Pteropoda a work
specially undertaken to make known the structure of the
cepbaloconi of Clione.

This paper is divided into three parts, corresponding to the
different genera which I have studied: Clione, Clionopsis,
and Pneumodermon.

I. Clione.1

Clione (PI. XXXV, figs. 1 — 4) possesses two kinds of
cephalic appendages :

1. Tentacles properly so called.

2. Cepbaloconi or buccal cones.

I shall examine successively these two orders of appen-
dages.

a. Tentacles properly so called.

Clione possesses two pairs of them — an anterior or labial
pair, and a posterior or nuchal pair.

Anterior Pair. — It is situated on a hood, whose two
halves, right and left, may fall back laterally, or be joined to-
gether again on the antero-posterior mesial line, and hide the
buccal opening and the three pairs of buccal cones. These
tentacles are long and retractile. They are not absolutely
anterior, as in the figure of Eschricht, which represents them
as equally distant from the dorsal and ventral faces ; 2 they are
situated nearer the dorsal than to the ventral face, as shown in
Plate XXXV, fig. 2.

Very powerful longitudinal muscles occupy the whole of the
interior part of these appendages; externally, we find a thin
layer of annular muscular fibres. The epithelium is like that
of the other parts of the body ; their cells are cylindrical and
provided with a large nucleus.

Sections which pass towards the free extremity of these ten-
tacles show a rather large number of nervous cells, but I have

1 The species studied is Cl. limacina, Phipps, = Cl. borealis, Pallas.

2 Eschricht, loc. cit., Taf. 2, fig. 10.

494

PAUL PELSENEER.

not seen any special nervous terminations, such as we shall
find on the buccal cones.

Posterior Pair. — It is situated on the dorsal face of the
neck. These tentacles are much shorter than those of the first
pair. Upon the animals preserved in spirit they are always
retracted, so that they are difficult to see, their presence being
then disclosed only by two slight recesses, from which their
extremities are sometimes seen emerging under the form of a
white point.

According to Eschricht, this second pair is oculiferous ; 1 but
this fact has been called in question by several naturalists,
and categorically denied by von Ihering.2

The histological examination which I have made of the
nuchal tentacles of Clione, Clionopsis, and Pneumo-
derm on, allows me to assert that these appendages do present
eyes at their free extremity.

Unfortunately the specimens which have served me in my
researches had not been specially prepared for the study of the
nervous system and of nervous terminations as delicate as the
retinal ones. It follows that I can neither draw nor describe in
a complete manner the structure of the eyes of the Gymnoso-
mata. That is a point which I intend to take up as soon as
possible.

Nevertheless, the profound dissimilitude which I have
observed between the labial and nuchal tentacles, and the
characters of the structure of the latter in the three species
which I have studied, show that the nuchal tentacles are quite
different from those of the first pair, and the presence of a
refracting body shows that the sense of which they are the seat
is that of sight.

At the free extremity of these tentacles, the epithelium
becomes much thinner, so as to make a pellucida or cornea.
Under this membrane we find a spherical lens, of which the
structure is similar to that of the Pulmonata. As I have

1 Eschricht, loc. cit., taf. 3, fig. 29.

1 Von Ihering, ‘ Vergleichende Anatomie der Nervensystem und Phylogenie
der Mollusken,’ p. 240.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEEOPODA. 495

already said, the retinal part is not perfect in any section, but
its position and general form recall to mind those of the retina
of the Gastropoda. In the specimens of Clione the pigment
had disappeared, but in those ofPneumodermon it was pre-
served. Finally, towards the base of the tentacle the nerve
traverses an optic ganglion.

b. Buccal Cones.

They number three pairs, symmetrically situated on the two
sides of the “ lips.” The two dorsal cones are the longest, the
two ventral cones the shortest (fig. 3).

These cones are very extensible, and in the state of expansion
they are much longer than they are generally represented.
They are absolutely conical, as my figures show them, which I
made from specimens1 of the “ Challenger,” preserved with the
extended cones and all the appearances of the living animal.

These cones are brightly coloured during life. They are
inserted on the two sides of the “ lips ” as shown in fig. 4.

They are hollow in their lower half, and their cavity is con-
tinuous with that of the head, which includes the buccal
mass and the penis. Examining these cones with a magni-
fying glass, one sees that they are covered with innumerable
very small tubercles, which have been described by Eschricht
as so many groups of suckers.

Structure of the Buccal Cones.

On any section of a buccal cone of Clione we may easily
distinguish three different regions :

1. A middle, muscular region formed of two parts: a. an
exterior layer with annular fibres (fig. 11, a); b. an interior
layer with longitudinal fibres (fig. 11, a').

2. An internal region formed of glandular cells (fig. 11, b).

3. An external region, or epithelial clothing (fig. 11, c).

1 Mr. John Murray, F.R.S.E., Director of the Challenger publications,
kindly supplied Professor Lankester with these specimens as soon as he heard
that Clione was undergoing investigation in the laboratory of University
College.

496

PAUL PELSENEER.

I shall examine these different parts successively.

1. Muscles of the Buccal Cones. — The muscular cells
are unstriped, elongated, and contain a nucleus of a prismatic
form (fig. 13, b'). The muscular external layer of annular fibres
is much less developed than the internal layer. This latter is
very powerful, which explains the great extensibility of the
cones. The longitudinal fibres are united in distinct groups
(fig. 13, b).

2. Glandular Internal Cells. — A transversal section of
one of the cones shows that their interior is filled with cells
united in groups (fig. 11, b). In the lower half of the cone
the centre of the sections is empty, and the cells are only
found against the longitudinal muscular layer.

A longitudinal section will make this disposition better
understood (fig. 12). The cells in question are united in
elongated groups, having the form of follicles. Each cell
possesses a proper prolongation, which is continued to the
epithelial covering of the cone. Each of these groups possesses
a basement membrane of connective nature, but the different
groups are pressed one against the other without one being
able to see between them any free connective tissue, under
the form of cells or fibres. The spaces which are seen in
several places, on the figure 10 of the plate, proceed from dis-
placements which occur during the preparation of the sections.
Among the groups which have been displaced I have not seen
any traces of connective tissue.

These groups of secreting cells do not constitute a gland,
for nowhere on any section, longitudinal (fig. 16) or transversal
(fig. 17), can a lumen be seen, nor efferent duct. Each cell
is an independent unicellular gland. The contents of these
cells is a slightly granular substance. The nucleus is large
and spherical ; it gives indications of its reticulated structure,
but not clearly enough to make drawings of them showing this
structure.

The cells situated at the interior extremity of the groups
have excessively long prolongations (fig. 16, d) ; the cells
situated near the muscular layer have, on the contrary, much

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 497

shorter ones. When these prolongations arrive at the longitu-
dinal muscular layer their contents change their appearance
and present themselves under the form of a fibroid secretion
(fig. 18, c) which absorbs much haematoxylin. These fibroid
prolongations pass between the groups of longitudinal nmscular
fibres ( d} fig. 13), traverse the layer of circular muscles, and
pass into the reticulum of subepithelial connective tissue ;
afterwards each prolongation penetrates into an epithelial cell,
which it traverses by passing between the membrane and the
cellular contents.

3. Epithelial Investment. — This is the most character-
istic part of the buccal cones of Clione. The epithelial cells
are united in a variable number, so as to form an infinity of
small circular groups on the surface of the cones. It is these
small groups which give to the cones their rugose or wrinkled
aspect.

A transversal or longitudinal section shows that these
groups, pressed one against the other, cover the whole surface
of the cone, and that each group is formed of a little elevation
upon which the epithelial cells are found.

Examining one of these groups with an ordinary magnifying
power (Yerick, obj. 6) we see that the space between the
annular muscular fibres and the epithelial cells is occupied by
a reticulum of connective tissue which unites the two above-
named elements.

The epithelial cells (fig. 13,/) are elongated, nearly cylindrical,
but wider towards their lower part. They are separated from
one another at their higher part, and end at their free extre-
mity in a button-like enlargement.

The cellular contents (A) have nearly the form of the cell.
At the lower part the contents have the form of a club, the
big end of which would be turned towards the bottom ; at
the higher part the contents fill exactly the terminal enlarge-
ment.

This cellular substance is finely granular, but does not com-
prise any nucleus.

The cellular membrane is rather thick and presents, in its

498

PAUL PELSENEER.

thickness, longitudinal striae which are strongly coloured by the
haematoxylin.

Between the cellular substance and the membrane we find
the fibroid secretion ( d ) of the glandular cells which occupy
the interior of the cone.

Each of the epithelial cells so constituted has been taken by
Eschricht for a sucker.

Under each epithelial group, at the surface of the annular
muscular layer, or even between the fibres of the latter, is
found a large sensorial cell (i), which sends a prolongation (&)
across the subepithelial connective tissue. This prolongation
continues between the epithelial cells and terminates freely at
the surface of the cone.

These sensorial cells possess a large refracting nucleus (j),
with a strongly colourable nucleolus.

The prolongation, rather narrow in the connective tissue,
enlarges a little between the epithelial cells and constitutes a
rod in the form of an elongated cone (/), with the base turned
towards the surface. The part of the prolongation, contained
in the connective tissue, presents in some series of sections
strongly coloured, a very special aspect; it appears to be reti-
culated (fig. 14, a). The conical part, situated between the
epithelial cells, presents numerous longitudinal striae. The
rod is terminated by a kind of small horizontal rather thin disc
(fig. 13, m), which is more strongly coloured than the sub-
jacent part. This disc does not bear cilia such as we see upon
the extremity of some sensorial cells. I do not think that in
the specimens I have studied, the sensorial cells have lost their
ciliary covering, for the other parts of the body which bear
cilise have their ciliary investment intact.

At the prolongation of the sensorial cell, towards the base of
the epithelial cells, we find a spherical or ovoid refracting body
(: n ) joined to it, whose membrane seems rather thick, and in
the interior of which we find a corpuscle deeply coloured by
the hsematoxylin.

The complicated structure of these epithelial groups is very
clearly shown by a series of transversal sections of these groups,

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 499

that is to say, by sections made tangentially on the surface of
the cone. Such sections are difficult to obtain exactly, but
when they are in the direction wished for, they are very
instructive.

I represent four of these sections, which I shall describe
successively, passing from the base to the free extremity.

1. Section passing above the annular muscular layer (fig. 19) .
We see the sensorial cell (a) in the middle of the reticulated
connective tissue ( b ), in which we find also fibroid prolonga-
tions (c) of the internal glandular cells.

2. Section passing through the base of the epithelial group
(fig. 20). Here we see the prolongation ( a ) of the sensorial
cell, the continuation of the fibroid prolongations ( c ), and the
surrounding connective tissue (6).

3. Section passing through the extreme base of the epithe-
lial cells (fig. 21). We find the rod (a) at the centre, with the
refracting body ( b ), which is joined to it. All around are the
bases of the central epethelial cells (e), in the interior of which
we see the fibroid secretion ( d ) of the internal glandular cells.
At the external part one sees connective tissue (e).

4. Section passing through the epithelial cells (fig. 22). The
external cells are already separated from their neighbours.
We see in the middle the section of the rod (a), of which we
distinguish the striated structure. In the membrane ( b ) of the
epithelial cells we find some coloured points (c), indicating the
sections of the longitudinal striae in this membrane, which I
have already described.

Summary. — What Eschricht has taken for suckers are
epithelial cells terminated by a button-like enlargement. It
is noticeable that there is no nucleus to be observed in these
cells. Besides, they are penetrated by the secretion of the
glandular cells which occupy the interior part of the cone.
The latter are so numerous (apparently as numerous as the
cells of the epithelial groups) that they doubtless fulfil im-
portant functions. I think that their secretion is spread out-
side of the cone across the button-like extremity of the
epithelial cells, for on some specimens of which the epithelium

500

PAUL PELSENEER.

has remained quite intact this secretion had spread outwardly,
had become coagulated under the influence of the spirit, and
had formed a stratified deposit, which absorbs much colouring
matter on the surface of the cone.

Each group of epithelial cells is provided at its centre with a
sensorial cell with a rod-like prolongation. This fact deter-
mines the buccal cones of Clione as organs of special sensi-
bility. A refracting body is invariably found towards the
central part of the epithelial groups at the base of the cells ;
it is also probably, on account of its situation in contact with
the rod, an integral part of the sensorial apparatus.

With respect to the special nature of these organs, I may
make a remark with reference to the sense of smell in aquatic
animals. Is smelling possible in water, such as exists among
the superior Yertebrata? I do not think so. There must be
a special sense of which Mammalia cannot be conscious ; and a
truly aquatic animal cannot have an idea of the smelling of
aerial animals. This sense must be a peculiar one, interme-
diate to that of smell and that of taste. The buccal cones of
Clione are probably the seat of such a sense.

II. — Clionopsis.1

Clionopsis only possesses one kind of cephalic appendages —
tentacles properly so called.

As with Clione, there are two pairs — a labial pair and a
nuchal pair (fig. 5).

The labial tentacles are less elongated than with Clione.
As in the latter they are inserted more dorsally than ven-
trally. Their structure is that of the corresponding appendages
of Clione.

The nuchal pair has already been described by Troschel.2
Gegenbaur says that it is absent.3 Upon the specimen which

1 The species studied is Clionopsis Krohni, Troschel, — ' Clio, medi-
terranea, Gegenbaur.

2 Troschel, “ Beitrage zur Kenntniss der Pteropoden,” ‘Arch, fur Naturg.,’
1854, p. 229.

3 Gegenbaur, ‘ TJntersuchungen fiber Pteropoden und Heteropoden,’ p. 70,
Taf. iv, fig. 14.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEEOPODA. 501

I have studied the nuchal tentacles were extended and very
easily visible. Their structure is that of the nuchal tentacles
of Clione. The eyes are not situated near the tentacles, as
Troschel says,1 but on their top.

Clionopsis does not possess any other cephalic appendages.
The lips open into a narrow buccal cavity, and do not form a
hood which can fall back, as with Clione.

III. Pneumodermon.2

Pneumodermon is provided with two kinds of cephalic
appendages :

1. Tentacles properly so called, corresponding to those of
Clione and Clionopsis.

2. Two acetabuliferous buccal appendages, characteristic of
the genus (figs. 8, 9).

a. Tentacles properly so called.

Like Clione and Clionopsis, Pneumodermon pos-
sesses two pairs of tentacles, a labial pair and a nuchal pair.

As with the two preceding genera, the labial tentacles are
found situated on the two sides of the mouth, rather dor-
sally.3

The nuchal pair has already been described by Souleyet.4
Gegenbaur asserts that the first pair is the only one which
exists.6 The second pair is, indeed, very difficult to see,
being retracted in the preserved specimens, the recesses which
result from it being imperceptible ; however, this place is less
coloured than the adjacent parts. By making some trans-
versal sections in the anterior part of Pneumodermon, I

1 Troschel, loc. cit., pi. x, fig. 9, o.

The species which I studied are : Pneumodermon mediterraneum,
van Ben., and P. Peronii, Lam.

3 Figure 7 may be applied to Pneumodermon as well as to Clionopsis.
Besides Souleyet (‘ Zoologie du voyage de la Bonite,’ pi. xv, fig. 15) has
already very well represented this aspect of Pneumodermon.

* Loc. cit., vol. ii, p. 256, and pi. xv, fig. 14.

* Gegenbaur, loc. cit., p. 24.

VOL. XXV. NEW SER.

K K

502

PAUL PELSENEER.

have been able to assure myself with certitude that the second
pair of tentacles positively exist in this genus, as with Clione
and Clionopsis. But I have not remarked that they had
the bifid form indicated by Souleyet.1 These tentacles bear at
their free extremity an eye, which has the same structure as
those of the two preceding genera.

b. Acetabuliferous Buccal Appendages.

These appendages are inserted on the internal wall of the
buccal cavity, on the ventral side. Two figures of Souleyet
show this disposition perfectly (loc. cit., pi. 15, figs. 17 and
30) ; fig. 17 has been badly understood by Fischer, who gives
the two groups of suckers for the jaws.2

The acetabuliferous appendages of Pneumodermon have
the form of a flattened cylinder, upon which are inserted the
peduncles of the suckers. These vary in number according to
the species. Pneumodermon Peronii possesses a large
number of them, about thirty on each appendage; P. viola-
ceum, ten to fourteen on each appendage, and P. mediter-
raneum five or six. However, in this last species I have
sometimes found seven suckers, but then one or two were very
small.

In the state of inactivity the suckers have the form of a
very flat porringer. It is in P. mediterraneum that I
saw the largest ; they were one line in diameter.

Structure of the Acetabuliferous Buccal
Appendages.

It does not at all resemble that of the buccal cones of
Clione. The whole of its mass is formed by longitudinal
muscular fibres. Externally we find a uniform epithelium ;
that is to say, it is not provided with sensorial cells like the
epithelium of the cones of Clione. The buccal appendages of
Pneumodermon are not, then, sensorial organs, as some

1 Loc. cit., vol. ii, p. 256.

5 Fischer, ‘ Manuel de Conchyliologie,’ fig. 42, p. 44.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 503

authors say.1 Moreover, there is nothing in these appendages
which recalls to mind the internal glandular mass of the cones
of Clione.

Structure of the Suckers.

The only histological knowledge of these organs which we
formerly possessed proceeds from Gegenbaur’s researches,
who attributes a very simple structure to them.2 But this
knowledge was not very extensive.

During the month of January, 1885, I studied the structure
of these suckers by means of a series of transversal sections.
I had scarcely finished this study when I received the thesis of
Niemiec, “ Recherches morphologiques sur les ventouses dans le
regne animal.’’3 In this work the structure of the suckers of
Pneumodermon is carefully described and represented. My
own observations agreeing almost entirely with those of the
Swiss zoologist, I believe it useless to explain them at length.
Hence I refer to the memoir of Niemiec, limiting myself to
the principal points relative to the structure of the sucker and
to indicating a few points of detail in which I do not entirely
agree with the Swiss zoologist.

The body of the sucker is formed of a layer of large, pris-
matic, muscular cells (figs. 24 and 25), the contents of which
are formed of different separated fasciculi of fibres (a). These
fasciculi have the form of very flat, three-sided prisms, of
which the most acute angle is turned towards the centre of
the cell. In this place we find the nucleus (6), which has a
shape analogous to that presented by the nucleus of the mus-
cular cells of the cones of Clione. All around, towards the
upper side of the disc formed by this layer of prismatic cells,
we find a sphincter formed of not very numerous annular mus-
cular fibres. The upper face of the muscular disc is covered
with a pavimentous epithelium (fig. 23, c) with excessively flat-
tened cells, whose nucleus is consequently excessively flat.

1 Claus, ‘ Handbuch der Zoologie,’ French translation, p. 1056.

2 Gegenbaur, loc. cit., p. 77.

3 ‘ Recueil zoologique suisse,’ t. ii, 1885.

504

PAUL PELSENEEE.

Between this epithelium and the prismatic muscular cells we
see absolutely no connective tissue. On the upper side of
the disc, outside the sphincter, the epithelial lining thickens
very much, which is explained by the fact that it is by this
part that the adherence of the sucker to foreign bodies is
produced.

I have not remarked the constant presence of the cuticular
pads (“bourrelets”) which Niemiec described.1 Perhaps these
parts are specially visible in suckers of large size.

Beneath the epithelial thickening of which I speak, we find,
all around the disc, glandular cells in the form of a flask with
a very narrow neck. The efferent duct of these cells traverses
the epithelial thickening and passes out at the upper face of
the exterior ring of the sucker, that is to say, on the point
where the adherence is produced. The secretion of these cells
probably makes this adherence more perfect.

On the lower face of the sucker the epithelium is less flat-
tened than on the upper face, and it is united to the prismatic
muscular cells by connective tissue.

The peduncle is covered with an epithelium continuous with
that of the upper face of the sucker, and quite analogous to it.
The peduncle itself is formed by the continuation of the longi-
tudinal muscular fibres of the buccal appendage. These fibres
turn to the lower part of the acetabular disc.

According to Niemiec, some fibres of the peduncle go to the
side of the sucker. Such fibres I have not observed. In my
opinion the longitudinal muscular fibres of the peduncle (fig.
23, a) only go to the central part of the disc, and are inserted
on it, between two prismatic muscular cells, by their extremity,
which ends in a point ( b ). A retracting muscle inserted on
the side of the sucker would be far from having a useful
effect. Since it is at this point that the adherence is pro-
duced, the action of such muscles could only tend to combat
it, while the muscles inserted on tbe centre of the sucker, by
removing this point from the body to which the circumference

1 Loc. cit., pi. iii, fig. 2, c.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 505

of the disc adheres, augment the vacuum under this disc, and
consequently the adherence.

Except this point of detail, I quite agree with Niemiec on
the physiological mechanism of the suckers of Pneumo-
dermon. I am specially persuaded that the prismatic mus-
cular cells fulfil an important part during the first moments of
fixation. These cells are especially worthy of the attention
of those who are interested in the comparative study of dif-
ferent forms of muscular tissue.

Cirrifer.

In 1879, G. Pfeifer described by this name a gymnosomatous
Pteropod, which much resembles Pneumodermon, whose
caudal and lateral gills it possesses.1

This Pteropod bears two buccal appendages like Pneumo-
derma, but instead of being provided with suckers these two
appendages are terminated by two small branches bent round
in the form of a sickle. According to the drawing of Pfeffer,
these appendages differ further from those of Pneumodermon,
in that they are not inserted separately on the buccal wall, but
reunite in a common stem before arriving at that wall.

Pfeffer describes two superior or labial tentacles ; it is very
probable that the nuchal tentacles, very small and retracted,
have escaped him, as those of Pneumodermon have escaped
Gegenbaur.

Summary.

The different authors agree but little on the cephalic appen-
dages of the gymnosomatous Pteropoda, and many of them
consider all these appendages as tentacles. In short their
homologies are very obscure.2

We have stated that in the Gymnosomata there exists in a
constant manner two pairs of tentacles properly so called. I

1 ‘ Monatsberichte der Akad. der Wissensch.,’ Berlin, 1879, p. 249, fig. 20.

2 “ The connections between these conformations and the tentacles of the
Gastropoda are not yet very clear,” Gegenbaur, ‘ Grundzuge der Vergleichen-
den Anatomie,’ French translation, p. 481.

506

PAUL PELSENEEB.

do not think it will be rash to identify these appendages with
the two pairs which tbe Gastropoda Euthyneura (Opistho-
branchia and Pulmonata) possess, and which occupy the same
position among these animals as with the Gymnosomata.

In the Thecosomata we find a pair of rudimentary ten-
tacles, for example, in Hvalaea, Cleodora, and Creseis,1
Cuvieria and Spirialis,2 Tiedemannia3 and Cymbulia.4

With several of these animals the tentacles present rudi-
mentary eyes, Creseis for example.5

If they do not present eyes in the adult state they possess
them in some stage of the development, as in Tiedemannia
and Spirialis.6

This pair of tentacles is, in my opinion, equivalent to the
oculiferous nuchal pair of the Gymnosomata. As to the
anterior pair, its disappearance is explained by the displace-
ment of the swimming lobes, which encircle the head and
between which the mouth opens. The development of the fins
in this position has caused the disappearance of the anterior
tentacles.

Besides the two pairs of tentacles properly so called, we
have seen that most of the Gymnsomata possess buccal
appendages; such are Clione, Pneumodermon, Cirrifer.

Without prejudging anything as to the morphological value
of these appendages, I believe that they have the same origin,
however varied their aspect may be in the three genera above
named.

Apparently it seems that with Clione they are inserted
around the mouth, while with Pneumodermon and Cirrifer
they are inserted on the internal wall of the buccal cavity.
But it should be noted that in Clione there exists a hood which
can fall back. This hood covers the buccal cones, and its
opening corresponds to the buccal opening of Clionopsis,

1 Gegenbaur, ‘ Untersuchungen uber Pteropoden,’ p. 8.

2 Souleyet, loc. cit., vol. ii, pp. 199 and 209, pi. xii, fig. 32, and pi. xi, fig. 15.

3 Gegenbaur, loc. cit., p. 60.

4 Gegenbaur, loc. cit., p. 45.

6 Gegenbaur, loc. cit., p. 8, Taf. ii, fig. 1.

« Krohn, ‘ Beitrage zur Entwickelungsgeschichte der Pteropoden/ p. 21.

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 507

Pneumodermon, and Cirrifer (compare figs. 2, 4, and 7)
The “lips" situated between the cones of Clione are not
then equivalent to the lips of the other Gvmnosomata, in
which there is no developed hood like that of Clione.
They would be a differentiation of the internal wall of the
buccal cavity, which is produced behind the buccal appendages.

In this manner we see that with Clione, as with Pneu-
modermon and Cirrifer, the buccal appendages are inserted
on the internal wall of the buccal cavity.

At the same time it must be remembered that this front
portion of the buccal cavity may be regarded as not part of the
true oral cavity, but as only an “ introvert ” like that of pro-
boscidiferous Gastropods.

EXPLANATION OF PLATE XXXV.

Illustrating Dr. Paul Pelseneer’s Paper on “ The Cephalic
Appendages of the Gymnosomatous Pteropoda, and espe-
cially of Clione/’

Fig. 1. — Head of Clione. Dorsal aspect, a. Labial tentacles, b.. Nuchal
tentacles, c. Buccal cones, d. Fins. e. “Lips.” /. Edge of the hood.

Fig. 2. — Head of Clione. Oral view, the hood being nearly closed, a.
Labial tentacles, c. ^Buccal cones. /. Edges of the hood.

Fig. 3. — Head of Clione. Lateral view. a. Labial tentacle, b. Nuchal
tentacle, c . Buccal cones, d. Fin. e. Foot. /. Edge of the hood. g.
Orifice of the penis.

Fig. 4. — Head of Clione. Oral view, the hood being open. a. Labial
tentacles, c. Buccal cones, d. “ Lips.” f. Edge of the hood.

Fig. 5. — Head of Clionopsis. Dorsal aspect.

Fig. 6. — Head of Clionopsis. Lateral view. a. Labial tentacles, b. Nuchal
tentacles, c. Foot. d. Fins. e. Orifice of the penis.

Fig. 7. — Head of Clionopsis. Oral view. a. Labial tentacles, b. Mouth.
e. Lips.

508

PAUL PELSENEEB.

Fig. 8. — Head of Pneumodermon. Dorsal aspect.

Fig. 9. — Head of Pneumodermon. Lateral view. a. Labial tentacles.
b. Nuchal tentacles, c. Acetabuliferous buccal appendages, d. Fins. e. Lips.
f. Foot. g. Orifice of the penis.

Fig. 10. — Head of Creseis. Dorsal aspect. (After Gegenbaur.) a. Mouth.
b. Tentacles with eyes. c. Foot. d. Fins. e. Mantle.

Figs. 11 — 22. — Clione.

Fig. 11. Transverse section of a buccal cone. a. Annular muscular
layer, d. Longitudinal muscular layer, b. Internal glandular cells.
c. Epithelial covering.

Fig. 12. Longitudinal section of a buccal cone. Letters as in Fig. 11.

Fig. 13. An epithelial group of the section Fig. 11, more magnified.
a. Annular muscular layer, b. Longitudinal muscular layer. V . Nu-
cleus. c. Internal glandular cells, d. Their fibroid secretion, e. Re-
ticulated connective tissue, f. Epithelial cells, g. Its button-like
termination, h. Cellular contents, i. Sensorial cell. j. Its nucleus.
k. Its rod-like prolongation. 1. The striated conic part of the rod.
m. The terminal disc of the rod. n. Refracting body.

Fig. 14. — An epithelial group, showing the reticulated aspect of the rod
of the sensorial cell. a. Prolongation of the sensorial cell. b. Striated
part of the rod. c. Refracting body. d. Epithelial cells, e. Fibroid
secretion of the internal glandular cells.

Fig. 15. — An epithelial cell, showing the striae of the membrane.
a. Striae of the cellular membrane, b. Cellular contents, c. Fibroid
secretion.

Fig. 16. — Longitudinal section of a group of glandular cells of the in-
terior of a buccal cone. a. Internal glandular cells, b. Its nucleus.
c. Basement membrane, d. Prolongation of the glandular cell.

Fig. 17. — Transversal section of several groups of internal glandular
cells, a. Glandular cells, b. Nucleus, c. Basement membrane.

Fig. 18. — A glandular cell adjacent to the muscular part of the cone,
showing the passage of the cellular substance to the fibroid secretion.

a. Nucleus, b. Cellular contents, c. Fibroid secretion.

Fig. 19. — Transverse section of an epithelial group, passing a little
above the annular muscular layer, a. Sensorial cell and its nucleus

b. Reticulated connective tissue, c. Fibroid secretion of the internal
glandular cells.

Fig. 20. Ditto, through the base of the group, a. Prolongation of the
sensorial cell. b. Reticulated connective tissue, c. Fibroid secretion
of the internal glandular cells.

Fig. 21. Ditto, through the extreme base of the epithelial cells, a. Pro-
longation of the sensorial cell. b. Refracting body. c. Base of the
central epithelial cells, d. Fibroid secretion, e. Connective tissue.

Paul Pelseneer lei.

mv.

Y. Hxith.Lithr'Ednfc

CEPHALIC APPENDAGES OF GYMNOSOMATOUS PTEROPODA. 509

Fig. 22. Ditto, through the body of the epithelial cells, a. Rod or pro-
longation of the sensorial cell. b. Membrane of the epithelial cells.
c. Striae of this membrane, d. Fibroid secretion.

Figs. 23 — 23. — Pneumodermon.

Fig. 23. Part of a transverse section of a sucker, showing how the
longitudinal muscles of the peduncle are inserted on the muscular disc.
a. Longitudinal muscular fibre of the peduncle, b. Its pointed ex-
tremity. c. Epithelium of the upper face of the sucker, d. Prismatic
cells of the muscular disc.

Fig. 24. Transverse section of a prismatic muscular cell. a. Prism of
muscular fibres, b. Nucleus.

Fig. 25. Longitudinal section of a prismatic muscular cell. a. Nucleus.

COXAL GLAND OF LIMULUS AND OF ARACHNIDA.

511

Evidence in favour of the View that the Coxal
Gland of Limulus and of other Arachnida
is a Modified Nephridium.

By

G. L. Gulland, M.A,, B Sc.

With Plate XXXVI.

The following observations were made by the author whilst
acting as assistant to Professor Lankester in connexion with
a research on the comparative histology of the vascular ,
system and connective tissues of Arthropoda and Mollusca, in
aid of which a grant was made by the Government Grant
Committee of the Royal Society. The specimens of Limulus,
of various sizes, from a quarter of an inch diameter upwards,
were very kindly procured for Professor Lankester by Professor
H. Newell Martin, of Baltimore.

In a transverse section of a young Limulus of the size repre-
sented by fig. 3, a at the level of the 4th or 5th appendage
(such as is represented diagrammatically in fig. 1), the ob-
server’s eye is at once caught by three or four large spaces lined
by a peculiar epithelium, in the connective tissue immediately
external to the entosternite and on the same level with it.
This is the representative of the coxal gland. As we had a
complete series of transverse sections of the prosoma, we pro-
ceeded to reconstruct the gland, by making sketches of the
spaces at frequent intervals, colouring the drawings so as to
ensure the recognition of each space through all its changes,
and from this series of sketches by drawing to a certain scale
we compounded a diagram which is reproduced in fig. 2.

512

G. L. GULLAND.

It must be borne in mind that the tubes though necessarily
drawn on one plane in order to show the relation of the whole,
are really clustered together, so that the true appearance of the
gland, if dissected out, would be more like that shown in fig. 3,
cogl. From this diagram it will be seen that the gland consists
of a tube which, opening posteriorly at a point to be referred to
presently, passes forward towards the anterior end of the body
as a simple tube, is bent upon itself, passes again towards the
posterior end of the body, and on its way gives rise to several
secondary tubes, which in their turn have outgrowths. The
process of budding and division is best seen in the tubes at the
right hand of the diagram where there are several commencing
outgrowths, and one tube is being divided into two by numerous
septa which pass across its lumen.

These tubes are completely closed and are lined by an
epithelium, to be described afterwards, except at one point
where the wall is deficient and the lumen of the tube is con-
tinuous with the connective-tissue spaces which everywhere
surround the gland. (The details of this are shown in figs.
4 to 9, and will be described later on.)

The relations of the gland to surrounding structures approxi-
mate pretty closely to those of the gland in the adult. There
is, of course, no trace of the lobes which correspond to the
coxae of the second, third, fourth, and fifth limbs, but the
anterior end of the gland reaches as far forward as a point
corresponding to the posterior edge of the coxa of the second
limb, while the caecal posterior end reaches to the anterior
edge of the coxa of the fifth limb, as is shown in fig. 3. The
gland as a whole is straight, and lies midway between the
lateral thickening of the entosternite (which has at this stage
the same general form as in the adult) and an imaginary line
dividing the body from the coxae of the limbs. As the centre
of the gland is on a level with the plate of the entosternite the
two lateral ridges of that structure if they were produced as
they are in Mygale would embrace the gland, a relation which,
as M. Pelseneer has shown in a paper recently read before the
Zoological Society, is in Mygale actually present. The

COXAL GLAND OP LIMULUS AND OP ARAOHNIDA. 513

anterior end of the gland passes in front of the main mass of
the entosternite, and is in relation to its anterior cornua.
The blood supply of the gland could not be ascertained with
certainty from the fact that all the specimens had been cut
into to ensure their preservation, but from the presence of
blood-corpuscles we can assert that some of the spaces in the
connective tissue surrounding the gland are blood spaces,
though there is no trace of the central blood-vessel which is
present in the adult.

Communication with the exterior is effected by means of the
primary tube, which, lying ventrally and nearest to the ento-
sternite, curves gradually away from the rest of the gland, and
at the level of the anterior edge of the fifth appendage is
separated from it by a muscle, passes slightly downwards,
turns gradually, ascends close to the main artery of the limb,
passes away from this and runs for a short distance close
beneath the integument, and opens at the bottom of a slit-like
depression at the base of the coxa of the fifth limb on the side
next the fourth appendage and on the dorsal surface. At the
base of this appendage, and of the second, third, and fourth
limbs as well, is a very curious sculpturing which is not present
in the adult, and which can be best understood by reference to
fig. 13. Furrows running in various directions separate that
part of the coxa which lies nearest to the dorsal surface of the
animal into three lobes, which, if looked at from the dorsal
surface, lie one distal and median, and two proximal, right and
left ; the two proximal ones being together about double the
breadth of the distal one. From the apex of the median lobe
another furrow passes obliquely upwards and forwards towards
the distal end of the limb, and soon bifurcates, giving rise to
two right and left lobes less strongly marked than the proximal
ones, the one nearest the fourth appendage being much smaller
and lying more deeply than that on the side of the sixth
appendage. Parallel to the coxa, and on the side of it nearest
the anterior end of the body, a chitinous ridge runs, and it is
at the bottom of the deep furrow between this and the smaller
of the two distal lobes that the duct of the coxal gland opens.

514

G. L. GULLAND.

The difference in sculpturing between the fifth and the second,
third, and fourth limbs consist in the almost entire absence of
the chitinous ridge in the three last, and in the fact that the
distal furrows is in them nearly median in position, and the
two distal lobes therefore more nearly equal in size. In the
interior of the limb the furrows are represented by a thickening
and slight ingrowth of the chitinous cuticle. It is worthy of
note that in the adult the depression which exists at the base
of the coxae of all the limbs is most marked at the base of the
fifth.

For a short distance from the opening the duct is lined by a
continuation inwards of the chitinogenous cells of the integu-
ment, and these have a cuticle (fig. 11) on their internal
surface, the whole being enclosed by a basement membrane, to
which the trabeculae of the connective tissue are attached.
The chitinogenous cells soon pass into the proper epithelium
of the gland, which is identical in structure through the whole
course of the tube. It consists of a continuous layer of proto-
plasm surrounding the lumen, in which in a transverse section
the nuclei are placed somewhat irregularly, and in which the
division into cells, as in the adult, is not evident (figs. 4 to 10).
The cortical part of the protoplasm when highly magnified is
seen to be striated radially in the same way as in the adult
(fig. 10) ; the internal part of the protoplasm is granular, and
in it the nuclei lie. A basement membrane encloses each
tube, and, as in the adult, the intertubular connective tissue is
slightly modified from the ordinary connective tissue, inas-
much as the lacunae are smaller, and the relative amount of
trabecular or skeletal substance therefore greater.

The internal opening of the tube is on a level with the
point where the coxa of the fifth limb is just beginning to
appear in the sections (fig. 1 is at this point). The tube
marked D in figs. 4 to 9 is derived, as seen in fig. 4, from
tube C, and is ventrally placed alongside of, and external to, the
primary tube A. Its ventral wall disappears, and for several
sections its lumen is in free communication with
the spaces in the connective tissue which lie be-

COXAL GLAND OF LIMULUS AND OF AEACHNIDA. 515

tween the gland and the ventral blood-sinus. It is
then closed by a connective-tissue trabecula, and the tube soon
disappears from the sections. The gland epithelium does not
end suddenly, but gradually passes into the typical connective-
tissue cells, the extent to which it passes out into the spaces
varying in different sections (figs. 6, 7, 8). The basement
membrane becomes continuous with the trabeculse of the con-
nective tissue, and on these connective-tissue cells or rather
nuclei are scattered irregularly.

Note on the Foregoing.

By Professor E. Bay Laxkister.

From the preceding observations it is clear that the coxal
gland of Limulus has the essential anatomical features of a
“ nephridium,” such as that of the Chaetopod worms and of
Peripatus, viz. it is, in the young animal, a tube opening to
the exterior by one extremity and to the primitive body cavity
or coelom (the space between the trabeculae of the connective
tissue) by the other ; further, it is a paired organ, occurring on
the right and left sides of the body, and moreover the pair
appear to belong to a single segment, and to be therefore
possibly the single surviving pair of a number of such nephridia,
of which one pair were developed originally in each segment of
the body.

The conversion in Limulus of what is in the young an ex-
ternally-opening tubular gland into a “ ductless gland ” in the
adult, finds a close parallel in the history of the supra-renal
body of Vertebrata as determined by Mr. Weldon (this
Journal, January, 1885). The coxal gland of Limulus, with
its curious brick-red pigment, is probably not only morpho-
logically similar to the modified bit of mesonephros which
forms the supra-renal body of Vertebrates, but also physio-
logically resembles that organ.

516

G. L. GULLAND.

The observations here recorded on the structure and connec-
tions of the immature coxal gland tend to render it probable
that the green glands of Crustacea (antennary coxal gland) are
also to be regarded as a pair of modified nephridia. In figs. 14,
15 are reproduced Grobben's drawings of the antennary glands
of two forms of Crustacea. It seems not improbable that the
so-called “ end-sac ” of these glands is not part of the nephri-
dium, but is developed from the connective-tissue space
(coelom ic space) into which the true tubular nephridium
originally opened. It certainly would be possible to bring
about such a structure by allowing the space into which the
inner end of the young coxal gland of Limulus opens to
enlarge and become vesicular instead of allowing the nephridial
tube to close up.

It is important to note further the possibility that other
structures present in Arthropoda are to be regarded as modified
nephridia.

The demonstration of the extensive changes which the coxal
gland of Limulus undergoes in its development opens our eyes
to the probability of such changes in other cases. It is a
remarkable fact (as has been pointed out by Mr. Kingsley,
who has independently demonstrated the tubular character and
external opening of the coxal gland in the embryonic Limulus)
that the “ shell-gland ” of Entomostraca opens at the base of
the fifth pair of appendages (the second pair of maxillae) in
those animals, and thus corresponds with the coxal gland of
Limulus and of the Arachnida in position. But when once
the notion is admitted that ducts opening at the base of limbs
in the Arthropoda are possibly, and even probably, modified
nephridia, we immediately conceive the hypothesis that the
genital ducts of the Arthropoda are modified nephridia.

It will require careful embryological work to test this
hypothesis. It is supported by the analogy of Vertebrata,
where as close a connection and as direct a continuity of the
gonad with the adventitious duct derived from the renal excre-
tory system is attained in the male sex, as is observed in both
male and female among Arthropods.

COXAL GLAND OF LIMULUS AND OF ARACHNIDA. 517

The view that the genital ducts of the Arthropoda are modi-
fied nephridia is further supported by the consideration that
there is no other plausible suggestion as to their origin and
significance. From this point of view we have to bring into
consideration all animals whose genital ducts are continuous
with the gonads and open to the exterior. Animals are, as I
have elsewhere pointed out (‘Encycl. Brit./ article “Mollusca”),
either Schizodinic or Porodinic, that is, discharge their genital
products by rupture or by permanent pores. The Porodinic
forms are, according to our present knowledge, divisible into
those which are nephrodinic and those which are idiodinic, the
ducts being in the first case “ nephro-gonaducts,” and in the
second case “ idio-gonaducts.” But it seems possible that such
a thing as “ idio-gonaducts” have no real existence. The
gonad itself in Ccelomate animals is essentially a group of cells
forming part of the lining of the coelom or body cavity, and it
seems quite likely that in all cases the duct, even when it is
intimately fused with the gonad, was primitively a nephridium.
If this is universally true we have to reckon nephridia as form-
ing gonaducts by fusion with the gonads in Echinoderms, in
Platyhelminthes, and in Nematoid worms, as well as in Arthro-
poda and Mollusca — cases which at present are regarded as
typical instances of the occurrence of idio-gonaducts.

Possibly the generalisation may not prove to be justified in
all these groups, whilst holding for the Arthropoda and
Mollusca.

The full consideration of the suggestion here made involves
a more definite conception than we at present possess of the
nephridium as a primary organ of the ancestral Coelomate.
How many pairs of nephridia may we assign to that ancestral
animal? Is every tubular structure opening from coelom to
exterior necessarily to be considered as belonging to one cate-
gory— the nephridium? How can pores such as the dorsal
pores of the Earthworm be distinguished from rudimentary
nephridia ? If pores leading from the coelom to the exterior
have an existence independently of nephridia, how are we to
distinguish those pores which are merely “ reduced” nephridia

VOL. XXV. NEW SER.

L L

518

G. L. GULLAND.

from those which are autogenous? If autogenous pores can
exist, is it not possible for the gonad to acquire continuous
membranous connection with such a pore or pores, and so
elaborate for itself an idio-gonaduct, which would have nothing
to do with a nephridium ?

These and similar questions present themselves for solution
and must be answered before we can come to definite conclu-
sions with regard to this unexplored question of the nature and
significance of genital ducts.

Finally, a point of great importance, which I propose to deal
with more fully elsewhere, is the fact that the space in the
connective tissue into which the young nephridium opens
internally is not a blood-space. The blood-system in tbe
larger Arthropoda is, I have recently ascertained, alto-
gether distinct from the general system of lacunse of
the connective tissue. These lacunse form a “lymphatic
system/’ which contains a liquid distinct from the blood; they
represent the coelom or body-cavity, and as such receive the
internal openings of the nephridia.

COXAL GLAND OF LIMULUS AND ARACHNIDA.

519

EXPLANATION OF PLATE XXXVI,

Illustrating Mr. Gulland’s paper on “ Evidence in favour of the
View that the Coxal Gland of Limulus and of other
Arachnida is a Modified Nephridium.”

Fig. 1. — Diagram of a transverse section of Limulus at the level of the
internal opening of the coxal gland, co. gl. Coxal gland. A. Primary tube.
m. Muscle, h.c. Hepatic caeca, ento. Entosternite. int. Intestine. H. Heart.
p.c. Pericardium, n.c. Ventral nerve-cord.

Fig. 2. — Diagram of the coxal gland spread out on a plane surface, ant.
Anterior end. post. Posterior end. du. Duct or external opening, int. op.
Internal opening, sep. Septa in the lumen of the gland.

Fig. 3. — Dorsal view of young Limulus (the original was 12 millimetres in
length from the anterior end to the root of the spine, 19 mm. altogether, and
12 mm. in breadth at the level of the 4th appendage, where it was broadest),
to show the relations of the coxal gland. I — VI. The coxae of the appendages.
co. gl. Coxal gland, ento. Entosternite.

Figs. 4 — 11. — Common references. A. Primary tube of coxal gland.
B. C. D. Secondary tubes, c. gl. e. Epithelium of coxal gland, b. m. Base-
ment membrane, m. Muscle, c. t. c. Connective-tissue corpuscles. T. Tra-
beculae of connective tissue, b. c. Blood-corpuscles.

Fig. 4. — To show the derivation of tube D from C, and the continuity of
the epithelium.

Fig. 5. — Transverse section of the coxal gland, showing the relations of
tubes to one another, the intertubular connective tissue, and to the left
of D, the space into which that tube is about to open.

Fig. 6. — The next section to Fig. 5 ; the partition between D and the
connective tissue is no longer present.

Fig. 7. — The next section but one to Fig. 6, the intervening one being
exceedingly like Fig. 6, was not drawn.

Fig. 8 — The next section to Fig. 7.

Fig. 9. — The next section to Fig 8. The connective-tissue trabecula T,
has closed the opening of D, which becomes smaller in each succeeding
section, and soon disappears.

Fig. 10. — A small portion of the gland epithelium more highly magnified
showing the radial striation of the cortical part.

Fig. 11. — Part of a section of the coxa of the fifth limb, showing the
duct of the coxal gland near its opening, and while it is still lineU with

520

G. L. GULLAND.

chitinogenous cells, ck. c. Chitinogenous cells of the integument.
bm. Basement membranes, du. Lumen of the duct. b. c. Blood-
corpuscles. cu. Cuticle, etc. Connective-tissue corpuscles.

Big. 12. — The second to the sixth limbs of the right side of a young
Limulus magnified, showing the opening of the coxal gland, du, iu its relations
to the fifth and other appendages, and also the sculpturing on the bases of the
coxse. The projecting part of the carapace has been cut away close to the
bases of the coxee. c. c. is the cut edge, and the animal is represented lying
on its back, with the anterior end towards the left hand. The limbs are thus
seen from their dorsal surface, and are numbered II to VI.

Fig. 13. — The base of the coxa of the fifth limb much more highly mag.
nified, viewed as an opaque object under Pillischer, Obj. f, oc. 3, showing the
sculpturing and the position of the opening, du, of the coxal gland, c. r. The
chitinous ridge.

Fig. 14. — Internal termination of the antennary gland of a young Estheria
(Phyllopod), showing the end-sac, e. s., probably a specialised connective-
tissue lacuna, and not part of the nephridium itself. (After Grobben,
‘ Arbeiten Zool. Inst. Wien.,’ vol. iii, 1881.)

Fig. 15. — Antennary gland of Mysis. Ceph. Urinary tubes, eo. External
aperture, hb. Urinary bladder, e. s. End-sac (probably a closed connective-
tissue lacuna, into which the nephridium opens).

eroto-

Fig. Ik.

G.L .Gullan d del.

X£i>

"F Huth.Lrth* r.dinT

NOTES ON THE EMBRYOLOGY OF LIMULUS.

521

Notes on the Embryology of Limulus.

By

J. 8. Kingsley, D.Sc.

Malden, Mass., U.S.A.

With Plates XXXVII, XXXVIII, XXXIX.

Several papers have been published upon the development
of Limulus polyphemus, the titles of which will be found in
the appended bibliography. Since Professor Ray Lankester
has recently strongly advocated the Arachnidan affinities of
Limulus it has seemed especially desirable to study the embry-
ology of this form by means of sections, a method scarcely
touched by Dr. Packard, the most voluminous writer upon this
subject.

I would here return my sincere thanks to my friend George
H. Thompson for his assistance in obtaining material for my
researches.

I have not witnessed the process of oviposition, which, how-
ever, has been described by Dr. Lockwood ('70),1 but with
some of his conclusions I would express dissent. The eggs are
not all laid above high-water mark, for I have found them half
way between tides, and have frequently taken the male and
female coupled together, and buried in the mud below low-
water mark.

All of my attempts at artificial impregnation have been
unsuccessful, for animals kept in confinement, even when

1 I have, in referring to the bibliography, adopted the admirable plan of
Dr. E. L. Mark, by which the reference number gives the reader at once the
approximate date of the article. A bibliography is appended.

522

J. S. KINGSLEY.

caught in copulating, utterly refuse to lay their eggs. I ob-
tained an abundance of good milt, and to all appearances the
eggs were ripe. Again and again was fertilization tried, but
although the eggs were kept for four weeks they showed no
signs of change except those that might be the effect of
decomposition (see infra). A further difficulty was found in
manipulation of the early stages of the eggs obtained from the
natural nests, and many experiments were tried to ascertain
the best method of procedure. For surface views a slight
staining with osmic acid proved best, while for sections har-
dening in successive grades of alcohol proved at least equal to
chromic acid, Merkel's fluid, Perenyi's fluid, or corrosive sub-
limate. The coagulation of the albumen by heat, so advan-
tageous in studying many Arthropods, was here worthless. The
greatest difficulty with the earlier stages was found in the
extremely refractory chorion, which did not separate at all
readily from the egg proper. I had in most cases to cut
it and the egg together, and the results were far from
satisfactory.

The eggs were embedded in paraffin by chloroform, cut in
ribbons, and fastened to the slide by the collodion method.
They were then stained by eosin or haematoxylin. They did
not readily take color, usually requiring ten minutes to stain
with the former dye, which generally works much more quickly.
My best results were with haematoxylin, overstaining, and then
submersing in acid alcohol.

' The eggs and embryos possess great vitality, living in con-
finement with only the slightest care; and, as I write, I have
specimens living which I obtained five months ago : they
have spent the last three in a common saucer, the only atten-
tion being to replace evaporation by ordinary hydrant water.
The density of the water seems to have but little effect upon
them, and I have had them live for several weeks in perfectly
fresh water. This vitality, which is also characteristic of the
adults, has an extremely interesting aspect when we consider
the fact that Gigantostraca have an ancestry extending back
to the Palaeozoic rocks. Professor E. S. Morse has noticed a

NOTES ON THE EMBRYOLOGY OF L1MOLUS.

523

similar correlation between the vitality of the individual and
of the race in the case of the Brachiopods.

The eggs vary considerably in their characters. Some are
spherical, others markedly oval. According to my measure-
ments the average diameter is about two millimetres, varying
between l-75 mm. and 2-2 mm. Some are brown, some are
ashy green, and others yellow or pink. Color seems unim-
portant, as I have had pink embryos hatch, the color persisting
for some time after escape from the membranes. The egg is
enveloped in a thick and dense chorion, which is apparently
made up of layers, about twenty in number, the whole having
a total thickness of about yoVo^ an iQCh- In rupturing
this chorion the line of tear usually goes straight across, and
but rarely can traces of lamination be seen. Usually no traces
of pores are visible, and I have sought in vain for a micropyle.
Occasionally I have seen indistinctly what may be pores, and
it is certain, for reasons which will appear anon, that there is
some way in which water penetrates the chorion.

I greatly regret that I have nothing to offer regarding seg-
mentation and the formation of the blastoderm, but my earliest
embryos are already far along in their development. In the
following pages I shall speak but briefly of the external de-
velopment, except when my observations are at variance with
the previously published accounts of Dohrn ('71) and Packard
(J72). In studying the internal development I am unfortunate
in having no predecessor, as I thus have nothing with which to
check my results, and hence there is more chance for error to
creep in. Even more unfortunate is the fact that I have no
knowledge of the formation of the blastoderm wherewith to
settle some features of the later stages which are uncertain.

External Development.

The earliest egg seen was treated with osmic acid, and pre-
sented the appearance shown in fig. 4. Upon the surface is a
longitudinal pyriform depression in the centre of a lighter field.
This lighter area corresponds to the germinal area so frequently

524

J. S. KINGSLEY.

described, in Arthropod embryology, and tbe depression is the
so-called germinal or ventral groove. In reality, at least in
tbe case of Limulus, the lighter area marks the extension of
the mesoblast (the epiblast extending entirely around the egg),
and, in my opinion, the ventral groove is a modified blastopore.
To this I will recur again.

Larval Envelopes. — In this stage sections show that the
epiblast cells have begun the secretion of the first larval enve-
lopes, which Dr. Packard has endeavoured to compare with
the amnion of insects. This comparison is utterly without
foundation, as this is a cuticular not a cellular structure, the
polygonal cell-like markings with which the surface is orna-
mented being due to its mode of origin. Anticipating our
account a little we will trace the history of what I would call
the first larval cuticle throughout its history. In the stage 4,
outside the mesoblastic area, the blastoderm consists of a
single layer of large polygonal epiblast cells (fig. 39) resting
directly upon the yolk. Each cell is covered with a thin
cuticle which refuses to take any stain. This cuticle follows
closely the contour of the surface of the epiblast, extending
down between the various cells, thus giving rise to the poly-
gonal markings which, in the later stages, are confined to the
external surface, and which were so puzzling to Dohrn and
Packard.

At the time of the appearance of. the limbs this cuticle is
nearly as thick as the epiblast, having increased by additions
to the inner surface. The outer still retains its markings,
but the inner is nearly smooth. As yet it is in close contact
with the epiblast, the cells of which are still contributing to
its increase (fig. 45). When the embryo arrives at stage 11
the cuticle separates from the epiblast, and the cells of its
surface have an average diameter of mm. ’0033. Of the
explanation of the ensuing phenomena I am not certain, and
the following is but tentative. It would seem that an osmotic
action begins whereby water is taken in through the chorion
and cuticle, thus creating a pressure which ruptures the

NOTES ON THE EMBRYOLOGY OE LIMULUS.

525

chorion. From the time of this rupture until the assumption
of a free life this larval cuticle functions, as Dr. Packard has
aptly expressed it, as a “vicarious chorion.” As the embryo
develops this cuticular envelope increases in size, always having
a considerable space between it and the embryo (cf. Packard,
’72, pis. iv, v, figs. 19, 24, a). This increase continues until
at last the “ vicarious chorion ” has about twice the original
diameter of the egg. This increase in size is not due to any
growth, but only to elasticity. In the later stages the pseudo-
cells are no longer visible, but long before the final hatching
they have twice their original diameter.

A second cuticle is formed and molted before the embryo
hatches. It makes its appearance at the stage 6, and in
fig. 11 it is represented as lifted up on the extremities of
the limbs. The active movements of the embryo soon tear
this second cuticle off, and in the subsequent stages it is seen
as a delicate membrane wadded up at one side of the chorion.
Dr. Packard (’72, p. 165) describes this molt.

Between 4 and 5 a considerable gap occurs in my material,
and I am not able to say whether here, as in scorpions (Metsch-
nikoff, ’71) and spiders (Balfour, ’80, b ), any metamerism
appears before the appendages or not. In fig. 5 all the
cephalothoracic appendages have appeared, and I have seen
no evidence to support Dohrn’s idea that the first pair appears
later than the others. Occasionally it is invisible in the living
egg, but osmic acid always renders it distinct. An important
fact was pointed out by Packard that at this early stage all
the appendages are post-oral, although long before hatching
the first pair acquires a pre-oral position. These appendages
are at first simple outgrowths from the surface. In the
median line of the embryo can be seen mouth and anus, each
having a slender pyriform outline, the narrow end being in
front. On first seeing this in connection with fig. 4, I was
forcibly reminded of Balfour’s figures of Peripatus (’83, pi. xx,
figs. 34 to 37), and, were the narrower end of the mouth turned
in the opposite direction, the natural inference would be that

526

J. S. KINGSLEY.

the blastopore had closed in the middle, leaving the mouth
and anus at the ends. This, I believe, is the true explana-
tion, allowances being made for the modified form of gastru-
lation ( vide infra). The fact that the narrow extremity of
the oral opening is turned forwards is due to its being in the
act of transference from a position in front of the first pair of
appendages to one behind it. Between the mouth and anus
is apparently a shallow groove. In reality this is produced by
the neurulation, and is internal. Sections show that the
external surface is smooth (fig. 47), and that the blastopore
has entirely disappeared, except as mouth and anus.

The first pair of abdominal appendages (opercula) are par-
tially marked out, and it is to be noticed that these and the
gill-bearing appendages develop in a slightly different manner
from the true limbs, a fact which would not be inferred from
Dr. Packard’s drawings (e. g. ’72, ph iv, fig. 16). In reality
they arise as broad plates, separated from the surrounding
surface by a tucking in of the epiblast behind (cf. ‘ Forma-
tion of Lungs of Scorpion/ Metschnikoff, ’71, p. 225, pi. xvi,
fig. 12). Besides the opercula the abdomen as yet shows no
trace of segmentation or appendages. The limit of the meso-
blast is much more distinct than in the preceding stage. It
extends slightly beyond the limbs, and has an elongate oval
outline slightly narrower in front. Outside the limits of the
mesoblast, on a line between the fourth and fifch pairs of
appendages, are seen the rudiments of the compound eyes.
They are not visible in the living egg, but stain readily and
deeply with osmic acid.

Between this and the stage figured in 6 the changes are
slight. This is slightly earlier than Dr. Packard’s (’72) pi. iv,
fig. 16. The mouth and anus still retain the same outlines
as before, and the neural groove is still conspicuous. The
limbs are now elevated above the surrounding surface and
begin to show traces of flexure. In the abdominal region the
opercula are better developed and the first pair of gill-bearing
appendages have appeared. In this and earlier stages I have
failed to find that segmentation outside the mesoblastic area

NOTES ON THE EMBRYOLOGY OF LIHULUS.

527

described and figured by Dr. Packard as existing outside^the
“ germinal area/’ and am of the opinion that it does not
exist, as usually metameric segmentation does not exhibit
itself in epiblast alone, and the mesoblast has not yet extended
itself so far.

As was noticed by Dr. Packard, between this and the next
stage a second moult takes place, the cuticle being lifted up upon
the feet as shown in fig. 11. Now motion begins, and the
movement of the limbs, at first very slow, tears this second
cuticle, the remains of which can be seen until the time of
hatching inside the “ vicarious chorion.’5

In the next stage necessary to be mentioned (fig. 12) a limu-
loid appearance is visible. The body is elongated and the
abdomen is differentiated, and it and the cephalothorax are dis-
tinctly segmented, six somites being visible in the latter and
eight in the abdomen, the ninth or telson not being separated
from the preceding segment. The cephalothoracic limbs are
jointed and the chelae outlined, while the peculiar whorl of
spines on the sixth pair is already formed. The flabelliform
appendage on the outer side of the coxa of the same pair and
the metastoma are also visible. In the abdomen the oper-
culum and the first branchial appendages are well developed,
and the gills upon it are beginning to be formed. The second
branchial appendage is just appearing.

Fig. 14 corresponds so closely with Dr. Packard’s (’72) fig. 24
that there is no necessity for describing it here. I would, how-
ever, state that his representation of the appendages (a matter
of no great morphological importance) is extremely faulty, and
in 24, a, the eye is much too remote from the margin. At this
stage specimens just killed with alcohol show the posterior
portion of the nervous system very plainly through the integu-
ment, but I have not been able by surface views to show
exactly the innervation of the anterior pair of limbs. This,
however, is to be the less regretted, as my sections settle this
point. I would in passing state that Dr. Packard’s (’80, a) pi.
v, fig. 8, cannot be relied upon as proving that the first pair
are post-oral ; the stage is too late for that demonstration.

528

J. S. KINGSLEY.

Figs. 16 and 17 correspond with Packard’s (’72) figs. 25
and 25, a, reproduced here. They represent the young
Limulus as it leaves the egg. It is 4 mm. long; the cephalo-

thorax has a semicircular outline, and the abdomen, though
smaller, has a similar shape. The dorsal surface of the cepha-
lothorax is without traces of segmentation except in the lines
bounding the cardiac region, where the depression marking the
attachment of the muscles of the limbs are visible. These are
not shown in the adjacent woodcut taken from Dr. Packard’s
paper, which is otherwise good, except that the segmentation of
the abdomen is much less distinct in nature. I may say here
that the segmentation in Limulus nowhere affects the epiblast
and its derivatives, and at no time in the development do we
find the body divided into a series of somites moveable upon
each other like those in the abdomen of a lobster ; the only
joints are those between the cephalothorax and abdomen, and
between the latter and the caudal spine.

Dr. Packard’s figure of the ventral surface at this stage is
very inaccurate. A better illustration will be seen in fig. 17, from
which it will be seen that the appendages are closely similar
to those of the adult female.

A number of individuals which hatched on the same day were
isolated and the first moult after hatching was watched for
with considerable interest. Soon after hatching the young
Limuli bury themselves in the sand as do the adults, and appa-

NOTES ON THE EMBRYOLOGY OF LIMULUS.

529

rently undergo exuviation while thus concealed. The carapax
splits along the frontal margin as in the adult. The first
specimen moulted in exactly five weeks after hatching, while
the others struggled along at intervals of one or two days, the
last one of the lot casting its skin in seventy-two days after
leaving the “ vicarious chorion.” After the moult the animal is
much larger, and the most important change is in the increased
length of the caudal spine, the general appearance being shown
in Packard’s (’72) fig. 27 of plate v. For our purpose it is not
necessary to carry the account of the external changes any
further. Nowhere in the external development are there any
startling metamorphoses, and nowhere, except in the closure of
the blastopore and the post-oral position of the first pair of
appendages, do we find facts which aid us in a discussion of
the affinities or phylogeny of the Xiphosura ; certainly nothing
which would indicate Crustacean relationships.

Internal Development.

The earliest stage of which I possess sections is that of fig. 4,
but from difficulties of manipulation these are not very satis-
factory, though they show some important points. The egg was
cut transversely to the rudimentary blastopore, and one section
is shown in fig. 44. The epiblast, a single cell in thickness, enve-
lops the whole egg. The groove, which I regard as blastopore,
is as deep as the thickness of the epiblast. Beneath this groove
and extending to a short distance either side is the mesoblast,
the limits of which correspond to the lighter area in fig. 4.
This mesoblast arises wholly from the bottom and edges of the
groove, and in the sections a rapid cell-proliferation is visible
here. Beneath these two layers (epiblast and mesoblast) is the
yolk. I believe that not only this groove but the primitive
streak of all tracheates, as suggested by Balfour, is the homo-
logue of the blastopore and that the yolk is wholly hypoblast.
Schimkewitch (’84) comes to the same conclusions from studies
of the spiders. How this modification arose I am not now
ready to discuss, but when we consider the recent researches
of Balfour on Peripatus, Hatschek on Amphioxus, and

530

J. S. KINGSLEY.

Bateson on Balanoglossus, and especially the Hertwigs’ Coe-
lomtheorie and Sedgwick’s essay on metameric segmentation,
and the light they throw on the origin of the mesoblast, I
think we are justified in reversing the course of reasoning and
concluding that, on account of the origin of the mesoblast, the
primitive groove is the homologue of the blastopore.

The hypoblast has recently been recognised in the yolk,
though in a rather vague and indefinite manner. Only one
recent author (Ayres, ’84), so far as I am aware, has had other
views. The indecision has doubtless been caused by the late
appearance of the archenteric, or rather mesenteric lumen.
To this we will recur again ; but now I call attention to the
fact that at the stages of figs. 4 and 5 the yolk is broken up into
true cells, each with its nucleus and cell wall. 1 have yet to
see any “ free yolk-nuclei.” In describing the development
of spiders Balfour (’80h) refers to and figures cells migrating
from the yolk and taking part in the formation of the meso-
blast, and says that the middle part of the dorsal mesoblast
arises largely, if not wholly, in this manner. On the other
hand Patten (’84), treating of the development of the Phry-
ganids, reverses the operation, and claims a migration of meso-
blast into the yolk. My observations do not allow me to
decide which of the two is correct; indeed, I have seen but
very slight indications of any migration, and those would, as I
interpret them, tend to show that part of the mesoblast which
forms the heart may arise in this manner. This view (a
migration of yolk-cells into the mesoblast) does not conflict
with the more recent ideas of the origin of the mesoblast in
triploblastic animals nor with the nature of the yolk as above
expressed, but merely shows that it is archenteric rather than
strictly hypoblastic. Mr. Patten’s views are rather difficult to
reconcile with what we know of the origin of the mesenteric
tissues in other Arthropods. It would seem to me that he
has misinterpreted his facts.

Of the closure of the blastopore or neural groove I have
nothing to say, as I have seen no eggs between figs. 4 and 5.
Still, judging from the appearance of the two, I think the

NOTES ON THE EMBRYOLOGY OF LIMULUS.

531

inference justifiable that here, as in Peripatus capensis,1 it
closes in the middle, the extremities persisting as mouth and
anus.

On a previous page I spoke of the shape of the oral opening,
and said that it was due to the transference of the mouth.
The mouth in fig. 5 is in front of the first pair of appendages,
in the adult behind them. The process of this transference is
interesting. After the disappearance of the primitive groove
behind the mouth a depression gradually extends backwards,
and at the same time at the front the edges rise up and finally
unite to form a close tube, the stomodseum (figs. 40, 41, 42,
43), in almost exactly the same way that the neural canal is
formed in the chick. This seems to me an important point,
for it shows that the functional mouth is not a strictly homo-
logous structure throughout the animal kingdom, but that
in those forms with a stomodeum it has been considerably
modified in position. Unfortunately we do not know if a
similar modification exists in Peripatus. The anus (fig. 46)
is a shallow pit, and at this stage shows no signs of forming a
proctodseum.

From this point on it will prove the easiest and possibly the
best to consider separately each of the tissues or organs without
attempting to describe the embryo at each stage as a whole.

Mesoblast.

In fig. 4 the mesoblast constitutes a broad sheet (fig. 44),
but between this and fig. 5 a considerable gap occurs in my
material. In this latter stage it has become separated into
two broad bands, except at the extremities. It seems probable
that this separation is effected partly by the rapid growth of
the epiblast in the ventral region, and partly by a migratory
movement of the cells. In the region of the mouth it is still

1 Kennel’s (’84) recent researches on two South American species of Peripatus
do not prove Balfour wrong in his interpretation, and until further observa-
tions are published onP. capensis, I think that his observations, certified to
by Moseley and Sedgwick, should be accepted. Nor do I think Kennel has
proved Sedgwick’s ideas “ ungeheurlich,” for Lang on the Planarians and
Wilson on the Alcyonaria come to the same general conclusions.

582

J. S. KINGSLEY.

continuous and not differentiated from the epiblast, although
it has become separated in the anal region (fig. 46). In the
middle region the broad bands on either side extend into the
legs (fig. 47), but no trace of a coelom has yet appeared. On
the neural side of the limbs it is a single cell thick, but in the
region of the appendages it is much thicker. This thicker
portion soon splits into somatoplure and splanchnoplure, and
the resulting coelom extends into the legs (fig. 30). It is to
be noticed that the ccelomic cavities are separate, one being
formed to each segment on each side, and further, that each
metameric cavity forms at first as several parts which afterwards
unite. In the stage of fig. 6 the mesoblast has extended itself
to the edge of the carapax where it thins out, the coelom
not reaching quite so far. ' In a slightly later stage (fig. 34),
but still not far enough advanced to be equal to fig. 11, longi-
tudinal sections show larger coelomic cavities, eight in number,
one for each segment developed.

The mesoblast gradually extends itself upwards on either side
until at the stage of fig. 12 (fig. 21) it meets as a single layer of
cells iu the dorsal region. On the dorso-lateral region it forms
a longitudinal band-like thickening (fig. 21, m ), the earliest
appearance of the extensor muscles and the points of attach-
ment of the muscles of the limbs. At the same time on the
ventral surface of the body, either side of the median line,
portions of the mesoblast grow up into the yolk, dividing it
into segments (fig. 22, mp.). By this segmentation, as shown in
the section just referred to, we have conclusive evidence that
the metastoma (chilaria) is not to be regarded as a morphological
appendage, since both it and the sixth pair of legs arise from
the same segment. This was more than suspected by Professor
Lankester, and is an important point in the series of homo-
logies he has suggested between Limulus and the Scorpions. I
might incidentally mention that embryology affords not the
slightest evidence of the missing abdominal segments needed
to render the correspondence between the two exact.

These septa not only furnish the boundaries between the
segments, but they also give rise to the muscles of the appen-

NOTES ON THE EMBRYOLOGY OF LIMULUS. 533

dages, and eventually join the dorsal mesoblastic bands men-
tioned a few lines above. The septa are not wholly formed
from these ventral ingrowths, but at the same time lateral
inpushings are taking place as shown in fig. 13, the section
being horizontal and passing above the level of the eyes, so
that only a few of the abdominal segments are included. The
result of this is that the yolk in the cephalothorax is broken up
into a central mass and six pairs of lateral lobes, the history of
which will be traced later.

It is not an easy task to trace the history of the coelom past
the point where we left it, though some isolated features are
readily seen. Thus it is seen that the mesoblast does not
split in the dorsal region until after the formation of the heart
as a tubular organ.

Heart.

Soon after the union of the two halves of the mesoblast in
the dorsal region a longitudinal cord several cells in thickness
is formed. How this thickening is produced I cannot say.
In the yolk beneath it the nuclei are very numerous, and the
cells are much smaller than in other parts, and it may be that
some of these migrate into the mesoblastic tissues ; but although
I have examined many sections I have not yet seen any indis-
putable evidence of such migration.

Soon a lumen appears in this cord, and the size increases, at
least to a considerable extent, through the budding of mesoblast
cells into the tube, where they become transformed into blood-
corpuscles. These processes are represented in figs. 31 to 33,
which represent sections from the same individual, 31 being
the most posterior. Two sections back of this is the end of
the lumen. Between 31 and 32 intervenes a distance of 0'025
mm., and between 32 and 33 a distance of 02 mm. From
this it appears that the heart is formed from in front back-
wards, and gradually the walls are reduced to a single cell in
thickness. Not until after this stage is reached does the heart
separate from either of the mesoblastic layers, and from these,
first from the splanchnoplure (fig. 33). This single-celled

VOL. XXV. NEW SER,

M M

534

J. S. KINGSLEY.

condition of the walls is found in all the embryonic stages, and
the heart does not have epithelial and muscular layers until
after hatching. This mode of the formation of the heart is
paralleled in both Crustaceans and Spiders, and hence throws
no light upon the affinities of Limulus.

At about the same time that the dorsal mesoblast begins to
thicken for the heart a similar thickening is noticeable in the
epiblast immediately above it (fig. 31). Reichenbach (! 77)
has noticed a similar thickening in the Decapods. Of the
meaning I am uncertain ; it may be that it is the remains of a
degenerate “ dorsal organ,” but it seems more probable (at
least in the case of Limulus) that it is the early stage of the
median dorsal crest or ridge of the adult. In the latest stages
which I have studied I have found no further change in it.

Segmental Organs (nephridia).

Under this head I would place the brick-red glands first
noticed by Dr. Packard (’75a), and recently described in detail
by Professor Lankester (’84). Concerning their earliest stages
I am yet in doubt. The earliest trace of them which I have
seen was in the shape of two patches of mesoblast, one on
either side in the fifth segment of the body. With growth
they increase in size, forming a well-defined tube, and join the
epiblast by the posterior extremity. This junction takes place
in the posterior coxo-sterual articulation of the fifth pair of
legs, and soon after an opening appears enabling the organ to
communicate with the exterior. I have not been able to
follow exactly the way in which the complicated organ of the
adult is developed from its comparatively simple beginning, as
I have had to rely solely on sections. From these (figs. 23, 26,
27, and 30) and others I have constructed a diagrammatic figure
of the shape of the organ at the time of communication with
the exterior (figs. 9 and 10). From the opening a narrow tube
lined with quadrate epithelial cells goes forward and upwards
(fig. 23) a short distance and then widens out into a spacious
sac, which narrows again before reaching the fourth segment
of the body. The cells of this portion are more columnar, and

NOTES ON THE EMBRYOLOGY OF LIMCTLUS.

535

have the nuclei placed at the ends away from the lumen.
Fiom this point the tube bends back on itself, going back a
short distance, and then turning again enters the fourth
segment, where it turns again and comes back to its first turn,
where it terminates. As to the character of the termination I
am yet in doubt, although I have examined many sections,
both transverse and longitudinal. In some it appears to com-
municate directly with the body cavity, the internal end being
open (fig. 27 ,/«.). I have been unable to detect cilia in any part.
In various parts of the tube the epithelium varies in character
between columnar and quadrate cells. In all the cells the
nuclei are very large, and are placed at times nearer the fore, at
others to the deeper end of the cells. The general character of
the quadrate cells is shown in fig. 28, which closely resembles
Professor Lankester’s delineations of these glands in the adult
Limulus.

I see no reason why these glands in Limulus and the corre-
sponding ones in the Scorpion, together with the so-called
shell-glands of the Crustacea, should not be regarded as seg-
mental organs. Later in this paper I will return to their
discussion, but here I would call attention to the fact that at
least in the later stages the inner end of the gland terminates
csecally as in the various Crustaceans. The closure of its
efferent duct takes place later.

Respiratory Organs.

On a previous page I have described the early stages of the
abdominal appendages. They arise as broad lamellar out-
growths from the lower surface of the abdomen. At first, and
in fact until the appearance of the gill books but two of these
appendages are visible. These correspond to the operculum
and first gill-bearing appendage of the adult. The others arise
in regular sequence until the whole number (five) is reached.
At first each of these appendages is simple, nothing that could
be interpreted as a biramous condition appearing until the
stage of fig. 12. One fact requires mention here : these appen-
dages are from the beginning broad and leaflike, differing in

536

J. S. KINGSLEY.

this respect from the corresponding embryonic limbs of
Arachnids.

The operculum never develops gills, but in the adult bears the
genital openings. In the others the leaflike respiratory organs
first appear at the stage of fig. 14. The method is shown in
figs. 37 and 38, and needs but little description. The leaves of
the gill book arise as outgrowths from the posterior surface of
the appendage, accompanied apparently by an intucking of the
adjacent epiblast. This operation takes place first at the distal
portion of the appendage, and new leaves are added at the base,
the whole series overlapping each other like the shingles on a
roof.

So far as I am aware, Professor Van Beneden was the first
to suggest ('71) the homology between the branchiae of Limulus
and the pulmonary books of the Arachnids. This was further
elaborated by Professor Lankester (’81). At first this resem-
blance seemed as far-fetched to me as it did to Dr. Packard
(’82, p. 290), but subsequent studies seem to me to indicate its
general validity, although I am not ready to follow all of
Professor Lankester’s intermediate steps, nor those of
McLeod (’82).

Of the development of the pulmonary organs in the Arachnids
the literature is extremely scanty, but with Lankester I am
inclined to believe that when more is known of it, it will be
found that the lamellae arise in connection with the temporary
abdominal appendages. On this point Metschnikoff, treating
of the Scorpion, says (’71, p. 225): “ The lungs also arise as
invaginations of the epiblast (Hornblattes), which appear close
under the segmental appendages of the four abdominal seg-
ments (Taf. xvi, fig. 12, pn).1 They appear from the first as
pocket-like sacs, which open by a broad mouth. With the
further development of the lung sacs, which is accompanied
by an atrophy of the abdominal segments [? appendages] (with
the exception of the second pair of the same), they become
more spacious and deeper. Only at the latest embryonic stage
(Taf. xvi, fig. 14 from the ventral, fig. 15 from the dorsal, sur-
1 Reproduced on PI. XXXVII, fig. 15.

NOTES ON THE EMBRYOLOGY OP LIMULUS.

537

face) there grows from the dorsal wall of the lung a blind pro-
jection (Auslaufer), by which the leaf-formation of the interior
of the pulmonary cavity is begun. The external opening is at
this time evidently smaller. The walls of the embryonic lungs
are lined with cylindrical epithelium, which secretes a thin
cuticula. On the outer upper surface of the lung occur here
and there some cell masses, which belong to the middle layer

Bertkau (72, pp. 211, 212), speaking of the increase in size
of the lungs of Lycosa, says : “Mit dem Wachsthum der Spinne
wachst auch der Luftsack und zwar starker als das Stigma, so
das seine Spitze bald weit von demselben entfernt ist. Der
erste Anlage eines Fachers zeigt sich in Auftreibungen
des Bodens des Luftsackes, von diesen die jedesmalig jiingste
dicht neben der nachst alteren entsteht und durch Intussus-
ception neuen Bildungsmaterials wachst.

Both of these accounts, as far as they go, agree with the
development as it occurs in Limulus, and the addition of new
lamellae, as described and figured by Bertkau, is exactly paral-
leled by that occurring in Limulus, both in position and in
manner, if we accept Lankester's views or those given below.

It, however, seems to me hardly necessary to invoke the aid
of “ parabranchial stigmata ” in order to derive the internal or-
gans of the Arachnids from the gills of Limulus. The change
in the needs of the animal owing to its assumption of a terre-
strial in place of an aquatic life would seem to be sufficient to
account for a part. Such a change in habit would necessitate
a protection for the respiratory organs, and this would be best
secured by an outgrowth of the surrounding parts, so that
finally appendages and gills would be enclosed in pits, the open-
ings of which would then grow smaller. The greatest difficulty
with this whole homology, as carried out by Lankester, is that
this opening must become completely closed, and another one
developed, that the side which at first was exposed to water
and then to air should subsequently be bathed with blood,
while the portion which originally contained the vascular fluid
should finally become opened to the air. Although I believe
that there is a genetic relationship between the respiratory

538

J. S. KINGSLEY.

organs in the two groups this physiological change is too great
to be readily accepted until we know more about the develop-
ment of these organs in the Arachnids. Still, the description of
Metschnikolf quoted above is, so far as it goes, not wholly in-
compatible with this view, that the primary stigma formed by
the insinking of the respiratory book is not the functional one
of the adult, since this author notices its decrease in size, while
the mode of origin of the lamellae from the dorsal surface of
the cavity is still more in its favor. Emerton (’72, pi. 2, figs.
11, 13, 15) represents the abdominal appendages of the embryo
Pholcus as broad and like those of Limulus at a corresponding
stage, a fact opposed to their being merely modified ambula-
tory appendages, but in full accord with their homology with
those of Limulus.

On the other hand, the derivation might be much more
direct, and thus avoid the inversions and the functional
changes. As I have mentioned above, the process of formation
of the gill-leaves is largely by a process of outgrowth, but there
is also a slight ingrowth, especially noticeable at the distal
portion of the appendage. This, however, disappears with
growth, but is very noticeable in all my sections. To transform
the gill of Limulus into the lung of Scorpio it is only necessary
that, together with the sinking of the whole organ, as described
above, the inpushings of the integument to form the lamellae
should be exaggerated, and the outgrowths correspondingly
decreased. On Plate XXXVII, figs. 18 to 20, 1 have diagram-
matically illustrated the steps in the process, the gill-leaves
being few in number to secure clearness. In 18 we have the
typical condition found in Limulus, one appendage being shown
half in section and half in perspective. In 19 we have an in-
termediate condition, when, as suggested above, the animal
was leaving the water and seeking a terrestrial life. Here the
gill-bearing appendage ( ga .) is partially sunk in the surround-
ing tissues to secure protection. The same causes would also
tend to produce a similar change in the gill-leaves ( gl .), and
they would also tend to be formed rather as ingrowths than as
protruding processes. This change in structure would be the

NOTES ON THE EMBRYOLOGY OF LIMULUS.

539

more readily effected on account of a change of the medium of
respiration. A gill needs either to project freely into the
water, or to have some means of constantly changing the fluid
which bathes it. An organ for aerial respiration, on the other
hand, is not so restricted in its position, since the air is more
fluid and more elastic, and hence more readily changed.
Another advantage to the animal resulting from the change
is that the oxygen is thus- brought nearer to the tissues
requiring it.

In fig. 20 we have a diagrammatic representation of the pul-
monary sac of the Arachnids. The appendage ( ga .) has now
become sunk in the body and the hole through which it passed
is the stigma (stg.) The gill lamellae have entirely disappeared
and the pulmonary ones (pi.) have taken their place. The
process here described is different from that imagined by
McLeod ('82). It accords more with the development of the
gills in Limulus, and avoids the necessity of union of the gill-
laminae and the expansion of the sternum.

Having derived the lungs of the Scorpion in this manner, but
little needs to be said concerning the origin of the tracheae in
the spiders. Many years ago Leuckart showed that the so-
called lungs of the Arachnids were but modifications of the
peculiar tracheae of the same group. This conclusion holds
good to-day, and I would accept it in an inverted condition:
The tracheae of the Arachnids are but modifications of the pul-
monary organs existing in some of the group. To transform
the lungs into the other type of organ but slight changes are
necessary. A prolongation of one of the sac-like pulmonary
lamellae towards the thorax gives the condition found in
Argyroneta; a slight amount of branching produces the
tracheal system of Zilla, and so on through forms like Thomisus
until the most complicated condition is reached. McLeod’s
observations are interesting in this connection.

The existence of the so-called spiral threads in the tracheae
of some of the Arachnids is to be explained on mechanical
grounds. In some forms nothing of the sort is found and here
the tracheae are flattened tubes. To prevent them from being

540

J. S. KINGSLEY.

completely closed by the pressure of the surrounding viscera
and to enable them to open readily for the inspiration of air on
the relaxation of the pressure some elastic element is needed.
This is supplied at first by scattered chitinous rods or thicken-
ings ; next, these are arranged transversely to the tube, and,
lastly, the rods become united to form the spiral. All of these
stages can be seen in the adult Araneinse. Leydig^s observa-
tions (78, p. 265) on the respiratory apparatus of the Onis-
cidse are suggestive in connection with the origin of tracheae.
They will be referred to again.

Nervous System.

Not until the mesoblast has become divided into the two
bands mentioned above do we find any trace of the nervous
system. Its first appearance is as two longitudinal epiblastic
thickenings (fig. 47), one on either side of the median line.
There is no external neural groove, but in its stead one on the
inner surface of the cord. This of course is a variation from
the normal of but minor importance, and doubtless arises from
the fact that the egg fills its envelope so completely that an
inward bending is impossible. In either band the arrangement
of the cells show that a rapid proliferation is taking place, the
result being a broad band on either side, the inner portions of
which are to form the neural cord. At first, as is shown by
longitudinal sections, this neurulation is continuous, there being
no differentiation into commissures (connectives)1 and ganglia
until a later date.

The separation of the neural cords from the epiblast takes
place at first in front and progresses more and more slowly
posteriorly (fig. 29). The separation of the commissural
portions is effected before that of the ganglionic areas, and in
the latter the cleavage takes place first in the median line
(fig. 25), even while in the lateral areas the epiblast is still

1 I follow Professor Lankester and others in restricting the use of the
term commissure to the cords whcih serve to unite the ganglia of the same
pair, and employing for those which unite the ganglia of a side the term
connective.

NOTES ON THE EMBRYOLOGY OP LIMULUS.

541

adding to the substance of the nervous system. I am not
positive as to the origin of the commissures. From the figure
last cited it would seem that here as in many other Arthropods
they arose as epiblastic ingrowths. This at least is most
reasonable. In the stage of fig. 12 (fig. 29) there are distinctly
eight pairs of postoral ganglia and this number is not exceeded
in embryonic life. Of these six correspond to the six pairs of
ambulatory appendages, one to the operculum and one to the
first pair of respiratory appendages. As will be seen, there is
no ganglion for the metastoma (chilaria), another proof, if
more were necessary, that they are not to be regarded as
morphological equivalents of the limbs.

In the stage of fig. 14 several important features are intro-
duced. Here begins that concentration of the anterior part of
the nervous system which results in the nervous collar of the
adult. I have found it difficult to trace the changes and have
obtained my best results by external views of the whole animal
treated in the following manner : — On removing the embryo
from its envelope I placed it in a watch crystal on the stage of
the microscope and then added some fifty per cent, alcohol.
This, on penetrating the cuticle, first affected appreciably the
protoplasm of the nervous centres rendering it alabaster white,
and thus in most regions readily distinguishable against the
darker background formed by the as yet indifferentiated food
yolk. Soon, however, other parts were affected and their dis-
tinctness was lost. Fig. 14 was drawn from these specimens
so treated, and as a camera was used it is correct in all
respects except possibly the brain and the metastoma. These
parts I was unable to see distinctly, and from my sections I
am inclined to believe them incorrect. This figure shows pos-
teriorly the nerves going from the respective ganglia to the
sixth, fifth, and fourth pairs of legs. In the third and second
pairs of nerves there seems to be a shifting forwards so that
they do not arise exactly opposite to the centres of the ganglia
but rather from their anterior margins. I have shown on a
preceding page the manner of the shifting of the mouth, and
this change in its position, and, consequently, in that of the limbs

542

J. S. KINGSLEY.

accords well with the facts just noted. The anterior appendages
•were thus brought further from their nerve-centres and hence
(if I may use the expression) they exert a tractive force first
on the nerves which supply them and secondarily on the ganglia,
for it is for the evident advantage of the animal to have the
nerve-centres nearer the parts most used.

The foregoing account mentions five postoral and pregenital
ganglia ; the remaining one, the first of the series, has, as far
as I can see, been merged in the cesophageal collar, and the
corresponding pair of nerves (which supply the small first
pair) appear to arise from the outer surface of the collar at
about a level with the posterior margin of the brain. Of the
exact position, however, I am not quite certain.

I have spoken above of the commissures, and while not sure
of their origin, I am confident that the connectives do not
arise as secondary epiblastic invaginations, but merely as dif-
ferentiations of the primary neural ridges. With the speciali-
zation of the ganglia, which is brought about by a more rapid
increase in size, the formation of the fibrous portion of the
nervous system begins. In transverse section this has a
granular appearance with scattered superficial nuclei, which
may play a part in the formation of the neurilemma. The
nerves to the appendages arise as outgrowths from the ganglia
which extend themselves among the mesoblastic tissues (fig.
35). These outgrowths contain but few nuclei at any stage
but are mostly fibrous, and are directly connected with the
corresponding portion of the central nervous system.

One of the most marked peculiarities of the adult Limulus is
the fact that the ventral nervous cord is ensheathed by the
large sternal artery, a fact without parallel except in the
Arachnids. The early stage of this artery is shown in fig. 36.
At all times there is a considerable space between the meso-
blast and the nervous system, and at this time processes begin
to grow out above and below, on either side, from the meso-
blast. These in the section figured partially embrace the
cords at a later stage the two halves unite and form the walls
of the artery.

NOTES ON THE EHBEYOLOGY OF LIMULUS.

543

The description of the development of the brain, of the eyes,
the midgut and its appendages, the genital organs and other
mesoblastic structures, I leave for the second part of this paper
where will he discussed their bearings. Still a few facts may
be of interest here, without the details which will be given
later.

The brain is at first separate from the rest of the nervous
system. It arises as two halves and each lobe is divided in
front as shown in fig. 11, presenting a marked similarity to
that of the spiders. The mesenteron is formed from the
central mass of yolk, the lumen appearing after the first moult
after hatching. The diverticula of the liver arise from the
lateral yolk masses, and the primary lobes of which it is com-
posed are produced by the mesoblastic septa of the cephalo-
thoracic region (fig. 13). After the stage where we left the
oesophagus on a preceding page, it continues to elongate and
joins the midgut soon after the lumen in the latter begins to
appear. It is at all times much longer than the proctodseum.
The outer layer of the cells of the mesenteron feed upon the
central ones, absorbing and assimilating them, thus producing
the lumen.

The Position of Limulus.

Professor Lankester has so recently discussed in an able
manner the relationship of Limulus (’81) that all that I can
add are the few facts gained from embryology. I must admit
that at first I was strongly inclined to regard Limulus as a
Crustacean, but a careful consideration of the subject leads me
to believe in its being much more closely allied to the Spiders,
and its being a representative in the seas of to-day of the
stock from which the Scorpions sprang. On the other hand,
its relationships to the Phyllopods are marked ; in fact, it
takes us back to a time when the distinctions between the
Crustacea and the Arachnida were far less marked than they
are to-day. The day of a belief in “ types ” is past, and yet
some of the terminology once in vogue is convenient ; in this
way we may still call Limulus a synthetic type.

544

J. S. KINGSLEY.

Since writing the earlier part of this paper I have learned
that during the past summer Mr. H. L. Osborn attempted
artificial fertilization of the eggs of Limulus at Beaufort, and
that like myself he came to the conclusion that the operation
was not a success and threw these eggs away. A few, how-
ever, were overlooked, and when found some time afterwards
it was seen that they were really developing, and that the
early changes were very slow. This fact recalled at once my
observations on the eggs which I attempted to fertilize and the
early changes that I witnessed in them, which I thought to be
the indications of decomposition. At first the eggs were
regularly granular, but half an hour after impregnation the
surface inside the chorion became irregular and pitted with
cavities varying greatly in size, each filled with a transparent
fluid, which at the time I interpreted as caused by a migration
of the protoplasm to the surface (fig. 1). These pits in-
creased in size and number especially at one side of the egg,
until they ran together leaving the surface ornamented by a
number of hemispherical globules of yolk which twenty-one
hours after impregnation presented the appearance shown in
fig. 2. After this, though I kept the eggs for several weeks, I
noticed no change except in those which were undoubtedly
spoiled except in one instance. In that egg, twenty-nine hours
after impregnation, a profile view showed two mushroom-shaped
bodies (fig. 3) raised from the rest of the yolk, and suggest-
ing polar globules but not very vividly. The meaning of these
three observations is uncertain. If connected with the deve-
lopment of the egg the second would at once recall the peculiar
segmentation occurring in some spiders. It is not certain
that it was a normal condition, and any conclusions drawn
from it are of no value until it is confirmed.

The first definite fact is the formation of a larval cuticle.
This Dr. Packard regarded as cellular, but as he used no
sections his mistake, as well as that of Dohrn in regard to the
same envelope, is readily explained. Since the publication of
my preliminary note Dr. Packard has re-examined the subject,
and informs me that lie agrees with my account of the nature

NOTES ON THE EMBRYOLOGY OF LIMULUS.

545

of this envelope. This early moulting of a cuticle seems to me
to be of but little importance in ascertaining the relationships
of Limulus, for it is paralleled more or less completely in both
Crustacea and Arachnida. The cases which will at once
suggest themselves are those of Apus, as described by Zaddach
(’41), and Atax, by Claparede (’68). Indeed, it might be well
to adopt the latter author’s term deutovum for all such
envelopes. Other cases, where the correspondence is not so
exact (Asellus, &c.), will readily be recalled; but until a more
definite knowledge is obtained of the exact origin of these
deutova speculation as to their homology and meaning is
useless. Kennel’s speculations (’84) seem poorly founded.

The simultaneous appearance of the six pairs of ambulatory
limbs seems equally unimportant, paralleled as it is with more
or less exactness in either group. It merely indicates a con-
centration of development, and the fact that through abundant
food supply the embryos or its nearer ancestors have not been
compelled to begin free life at an early stage. The closest
resemblance, however, exists in the scorpions and spiders,
where, the first pair of appendages excepted, the corresponding
parts appear. Were Dohrn’s account true nothing more could
be asked, but as I have had abundant material of earlier stages
than any of his I believe that (as he suggests) he overlooked
the first pair. I have not seen the slightest evidence in favour
of his account. There is nothing in the development of
Limulus that even suggests a Nauplius or a Zoea.

The position and early appearance of the compound eyes
suggest some points of interest. Since in the Decapod and
some other Crustacea (Squilla, Branchipus, Tanais, &c.) the
compound eyes are borne on stalks, which are articulated to
the body, some morphologists have adopted the idea that
these pedicles are homodynamous with the true limbs, and a
few have even gone so far as to seek an “ ocular segment ” in
the head of Hexapods. Without entering into a discussion of
the many arguments against this view (which I believe totally
erroneous even in the case of Squilla), I would say that I
regard the eyes of all Arthropods merely as specialised portions

546

J. S. KINGSLEY.

of the epiblast of the head,1 and as having a common phylo-
genetic origin, namely, from an Annelid ancestor.

Such being the case, I regard the dorsal surface of the
cephalothorax of Limulus as but the greatly expanded upper
portion of the head, and believe that the segments indicated by
the six pairs of appendages below are without proper terga.
If we follow Packard and Lankester and recognise the dorsal
surface of the shield as composed of six (or seven) coalesced
terga, then the fact that the eyes are borne on the fifth or
fourth and fifth2 of these segments is difficult of explanation.
This vagueness of expression as to the position of the eyes results
from the fact that the dorsal epiblast of the cephalothorax
never segments or shows any traces of division into somites,
while in different specimens the boundary between the fourth
and fifth mesoblastic somites is not constant in position as
regards the eye, but at times it passes in front of the eye and
at others beneath this organ, so that half of it is in one seg-
ment and half over the other. The ocelli are placed over the
first of these segments. It seems to me that these facts can
be explained only in the way indicated at the beginning of this
paragraph.

A nearly parallel case is found in the carapax of the Decapod
Crustacea. As usually described the carapax of the lobster or
crayfish is regarded as composed of the coalesced terga of the
segments visible below, and the obliquely transverse section
which crosses it (the “ cervical suture ”) is held to indicate the
line of division between head and thorax. In the Brachyura
the homologous suture is usually sought in the depressions
surrounding the cardiac region of the carapax. The true
explanations of these various structures was pointed out by
Dana ('52, pp. 23 — 28) over thirty years ago, and their total
neglect by all subsequent students is a partial excuse for their
mention here. The carapax of the lobster is wholly composed

1 The peculiar lateral eyes of Euphausia are not included.

2 Dr. Packard, in his text (’72, p. 165), speaks of the compound eyes
appearing “ on the third segment of the cephalothorax,” but his figures
(pi. v, figs. 24, 24a) show them in their proper position.

NOTES ON THE EMBRYOLOGY OP LIMULTTS.

547

of the coalesced terga of the second antennal and the mandi-
bular segments, and the “ cervical suture ” indicates merely
the line of their junction. In the crab the homologous suture
is to be sought on the deflexed surface of the carapax below
the lateral margin. The mandibular terga are comparatively
small, and are the epimera of H. Milne Edwards.1 It is need-
less to say that I do not accept the opinions of Young (’80) on
this subject, nor his views of the supra-oesophageal ganglia.

This same view is perfectly applicable to the Arachnida, where
otherwise we should have to regard the eyes as distributed on
different segments in different species and even in the same
species. A further confirmation is found in the fact that in
the Scorpions (nor so far as I am aware in any Arachnid) the
cephalothoracic tergum does not segment, or show any signs of
the metamerism so evident on the ventral surface. This point
seems to me an additional argument in favor of the union of
Limulus with the Scorpions.

The post-oral nature of the first pair of appendages and the
non-appendicular nature of the metastoma needed to render
valid the comparisons of Professor Lankester have been
previously suspected or proved, and my observations are only
confirmative, though in the case of the metastoma conclusive
proof was hitherto lacking.

Unfortunately Metschnikoff’s account of the development
of the mesoblast is very scanty owing to the fact that he did
not employ sections, and so I can only refer to Balfour’s
account of the Arachnida. The process in Limulus and
Agalena is closely similar and in its details considerably
different from that found in Crustacea. In the latter group
the mesoblast does not as a rule become divided into somites,2
nor does the schizoccele extend into the legs at first. In both
Agalena and Limulus it arises as a single broad sheet, which
later divides into two bands which migrate to the region of the
appendages. Then the coelom is formed by splitting and

1 ‘ Hist. Nat. Crust.,’ pi. i, fig. 9, b.

2 It. does so in Mysis (Metschnikoff, teste Balfour) aud in Cyclops (Urba-
nowicz in ’84).

548

J. S. KINGSLEY.

extends into the legs. The mesoblastic processes in both
divide the yolk up into a series of lobes, but these partitions
never reach clear across the body. A similarity is observable
in the late appearance of the lumen of the alimentary tract
cf. Isopods), and apparently in both (certainly in Limulus) the
hepatic organs are formed from the lobes of yolk which extend
between the mesoblastic partitions.

The yolk in Limulus never communicates with the coelom
as it does in many Hexapods and Crustaceans. Apparently the
same is true with spiders.

The heart in Limulus arises by the hollowing out of a solid
rod of mesoblast, its cells becoming transformed into blood-
corpuscles. This is paralleled in spiders and in some Crustacea.
Metschnik off’s account of the origin of the dorsal vessel in the
scorpions is very improbable and needs confirmation before it
can be accepted.

The close resemblances in the segmental organs of the adult
scorpion and of Limulus have been pointed out by Lankester
(’82 and ’84), though in his later paper he does not refer to
their possible homology with the segmental organs of worms,
(suggested by Packard ’75a) as he was unable to find any
ducts. As described above I have found these ducts in the
young, and doubtless the same result will be obtained when
the young of the scorpion is studied by means of sections.
This is the more probable since Bertkau (’84) has found homo-
logous glands in various spiders, which were without external
openings in the adult, but in the young of Atypus the duct
was found to open at the base of the third pair of legs (fifth
pair of appendages.)1 Michael (’83, p. 21) describes similar
glands in the Oribatidae but failed to find their openings.
The exact correspondence of these glands both in position and
in their ducts, and their closely similar histological structure, is
a point of no little importance in the argument for the union

' These glands have long been known in spiders, but had been regarded
generally as belonging to the digestive tract. They were practically discovered
and their true structure first described both in Scorpions and Spiders by
Professor Lankester.

NOTES ON THE EMBRYOLOGY OP LIMULUS.

549

of the Arachnids and Limulus in a common group. It should
be noted, however, that in complication, size, &c., the resem-
blance between the glands of Limulus and those of the spiders
is closer than between those of Limulus and those of the most
limuloid of Arachnids, the scorpions.

Packard (’75a), discovered these organs and suggested their
homology with the segmental organs of worms ; Lankester
(’82, p. 101) said “ Possibly such coxal glands are the modified
and isolated representatives of the complete series of tubular
glands (nephridia) found at the base of each leg in the archaic
Arthropod Peripatus ; ” while Michael (’83) suggests the
homology of the glands in the Oribatidae with those of Scorpio,
Limulus, Crustacea and Worms. Packard, in a later paper
(’83), while failing to see the argument for the close asso-
ciation of the Arachnids and Limulus derived from this
organ, recognises the correspondence between the glands of
Limulus and those of the Crustacea; but instead of making
his comparisons with the “ shell-gland ” he refers only to the
“ green-gland ” of the Decapods, an organ which occupies a
different position in the body. His conclusion that “ The
occurrence of these organs in the Arachnida, as well as in
Crustacea, indicates the independent origin of these two
groups of Arthropoda ” is intelligible only on the supposition
that the word here italicised is a slip of the pen. This simi-
larity of segmental organs in Limulus and the Arachnida
neither loses nor gains in force by a comparison with the shell-
gland of the lower Crustacea. This organ is a coiled tube with
a coecal inner extremity and an efferent duct which opens at
the base of the second maxilla (a position which I shall
show further on is exactly comparable to that where the seg-
mental organs of Limulus and the spider’s empty) but differs
from the glands in the other groups in retaining its external
opening through life. Thus the coxal glands of the one are the
exact homologous of the shell-glands of the other.

In the Crustacea two of the primitive series of segmental
organs are found, one being the shell gland, the other the organ
variously termed antennal gland or green gland. Grobben

VOL, XXV. — NEW SER.

N N

550 J. S. KINGSLEY.

('80, p. 103) says that the antennal and shell glands agree in
structure. Both terminate coecally, and have a long convoluted
duct opening at the base of the corresponding pairs of
appendages.

The homology of the shell gland of the Crustacea with the
segmental organs of the worms has been alluded to by many
observers since Leydig first suggested it. Their similar origin,1
structure, position, and ducts, all seem to point to their
homology. The strongest arguments against it are that the
series contains at the most but two pairs,2 and that no connec-
tion with the body cavity exists. Recent authors (Leydig, '78,
Weissman, 74, and Urbanowicz, ’84) seem to strongly favor
the homology.

The consideration of the evidence presented by the nervous,
digestive, and circulatory systems I leave for another article ;
that by the respiratory system has already been alluded to. It
may be well here to combine the various points of similarity
between Limulus and the Spiders, on the one hand, and the
Crustacea on the other. In this I embody the results gathered
by Professor Lankester in his valuable paper (’81), so often
referred to.

Limulus agrees with the Arachnida and differs from the
Crustacea (1) in having six pairs of primitively post-oral
pediform appendages ; (2) a seventh pair bearing the outlets
of the reproductive organs ; (3) the ninth, tenth, eleventh,
and twelfth, modified for respiratory purposes (the eighth
pair in each shows a readily homologised structure, but dif-
ferent functions) ; (4) in the character and structure of the
upper lip ; (5) in the presence of a metastoma derived from the
sternal portion of the sixth cephalothoracic segment.

1 Reichenbach (’77) claimed that in Astacus the antennal gland was
epiblastic in origin, a mistake which was corrected by Grobben (’79). Though
Jshickawa (’85) repeats the statement for Atyephira.

2 Huet (’82, I have not seen his final paper) describes a series of what he
regards as segmental organs in the thorax of terrestrial Isopods (Oniscidae),
which are arranged one pair in each segment. The caudal glands of Lere-
boullet (’52) would appear to belong to the same series. Some of these have
been found in the aquatic Oniscidae.

NOTES ON THE EMBRYOLOGY OF L1MULUS.

551

The same agreements and differences are seen in (6) the pos-
session of an entostermite with the same shape, position, and his-
tological structure ; (7) in the backward extension of the tergum
of the head, so as to form tlie dorsum of the cephalothorax ;
(8) in the distribution of the eyes ; (9) in the existence of
a blood colored blue by the presence of hsemocyanin (10) in
the branching and anastomosing spermatic duct (Benham, ’83) ;

(11) in the mode of formation of the mesoblast, its segmenta-
tion, and the early extension of the body cavity into the limbs ;

(12) in the mode of formation and structure of the alimentary
canal and its appendages;1 (13) the elongate stomodseum and
the short proctodseum ; (14) in the origin of the sternal artery
and its intimate association with the ventral nervous cord ;
(15) the early closure of the duct of fifth (the only) segmental
organ; (16) the absence of the second segmental organ (an-
tennal gland).

Besides these points there are a number of other points in
which the two agree, and which are but rarely paralleled in the
Crustacea, and then not in groups which anyone would think
of placing near Limulus. Among these may be mentioned the
possession of vibratile spermatozoa (paralleled in the bar-
nacles2), the concentration of the nervous system around the
oesophagus (also in Brachyura), a brain which never supplies
any of the appendages.

This array of similarities is almost conclusive, but we must
turn to the other side of the question, and seek the arguments
against the association of Limulus with the Scorpions. Dr.
Packard is by far the most able advocate of the Crustacean
affinities of Limulus, and in his latest paper (’82), in which he
deals with this subject (confessedly a reply to Lankester’s
“ Limulus an Arachnid”), we find the following summary of
the arguments against placing Limulus in the Arachnidan
phylum. In the quotation I have inserted numerals for con-
venience of reference below : “ At the outset it will be remem-

1 These points will be discussed in the second part of this paper now in
preparation.

2 They also have a slight motion in some other Crustacea.

552

J. S. KINGSLEY.

bered that Limulus differs from the Tracheates, including the
Arachnids, (1) in having no tracheae, (2) no spiracles, and (3)
no Malpighian tubes. It differs from the Arachnids in these
characters, also (4) in having compound eyes, (5) no functional
mandibles or maxillae, (6) the legs not terminating, as generally
the case in Tracheates, in a pair of minute claws, while (7) its
brain does not, as in the Arachnida, supply both eyes and the
first cephalic appendages. On the other hand, Limulus agrees
with the Crustacea (8) in being aquatic (9) and breathing by
external gills attached to several pairs of biramous feet, in
having (10) a simple brain, which, as in some typical Crus-
tacea (Branchiopoda, &c.), does not supply any of the appen-
dages, while the structure of (11) the circulatory, (12) inges-
tive, and (13) reproductive organs agrees with that of the
Crustacea; and, (14) as we have shown in our embryology of
Limulus, .... the development of Limulus is like that of
certain other Crustacea with a condensed metamorphosis, (15)
the possession of an amnion being paralleled by that of Apus.
In all essential points Limulus is a Crustacean, with some fun-
damental features in which it departs from the normal Crusta-
cean type, and with some superficial characters in which it
resembles the Scorpion.”

Of these points numbers 1, 2, and 15 have already been dis-
cussed in this paper, while numbers 5, 6, and 8 are trivial and
of no importance. Since Dr. Packard wrote the above, Mr.
Benham (J83) has shown that the thirteenth of these points is
not true, while the answer to 11 may be found in Professor
Lankester’s paper. In regard to number 12 I would say that
in development, except to a slight extent in some Tetradeca-
pods, Limulus does not agree with the Crustacea, the hypoblast
being solid and a midgut not appearing until after hatching.
The origin of the liver and the structure of its ducts are
greatly different in the two groups. Points 7 and 10 are the
same and deserve more attention. It has been shown by
Balfour and by Schimkewitch that in the spiders the ganglia of
the first pair of appendages are primitively post-oral, and that
with development they acquire a pre-oral position and eveutu-

NOTES ON THE EMBRYOLOGY OF LIMULUS.

553

ally fuse with the “ brain.5’ In Limulus the same process
occurs but stops just short of the fusion of the corresponding
ganglia with the pre-oral ones. For a knowledge of the condi-
tion of the brain in the Scorpions, one must await a detailed
account of the structure. As the case is at present Dr.
Packard distinctly states (580a) that the brain supplies the first
pair of appendages ; while Newport’s figure (’43, pi. xii, fig. 15)
shows the nerves as arising from the side of the brain. Newport
was a very careful worker but the subject needs further study.
On the other hand, in all the Crustacea, not excepting Apus and
Limnetis (Branchiopoda), this coalescence of ganglia has gone
still further than in Limulus or Arachnids, and even in the
earliest stages the first pair of appendages are pre-oral in inner-
vation, while the ganglia of the second pair (Apus excepted)
move forward with growth from a primitively post-oral position
and form an important part of the brain.

Fourth in the series comes the presence of simple lateral
eyes in the Arachnids and compound eyes in the other. I
have not yet studied my sections of the eyes of the young
carefully enough to throw any light on the question. Since
Dr. Packard wrote, Lankester and Bourne have shown (’ 83)
that if a comparison be made of the whole compound eye
of Limulus with the entire lateral group of the Scorpion
the correspondence is very nearly perfect ; and that “ if we
supposed a common ancestor of the Scorpion and King Crab
to have exhibited a lateral ‘ ocular area ’ which possessed
a single feebly developed cuticular lens, then by two slightly
divergent lines of differentiation we can obtain the grouped
eyes of Scorpio on the one hand, and the polymeniscous
eye of Limulus on the other hand.” The same authors
also show that “ the essential agreement of the central eyes
of Limulus with those of Scorpions is obvious.” As to Pro-
fessor Lankester’s well-known accuracy in histological work
no comment is necessary and no confirmation is needed, but I
would say that before his results were published I carefully
studied the eyes of the adult Limulus, and so far as that

554

J. S. KINGSLEY.

animal is concerned I can vouch for the accuracy of his
account.

In regard to the eighth point of Dr. Packard’s paper, it will
at once be recalled that the gills in the Crustacea are formed
on several distinct plans, and an effort to homologise those
for instance, of forms so closely related as the Lobster and
Squilla is not easily carried out. I regard the gills of
Limulus, like those of Apus, as derived from some ancestral
form with expanded and flattened appendages, which exposed a
large surface to the water and hence became largely the seat
of respiration. With a thickening of the cuticle and increase
in size, the necessity for increased respiratory surface led in
Limulus to the formation of outgrowths (gill-lamellae) from
these appendages just as occurs (though not from the same
reason) in the individual to-day. The not very plainly marked
biramous character of the abdominal appendages of Limulus is
an ancestral feature which may have been lost in the Arachnid
stems from the early change which they undergo. Nothing
approaching a biramous condition is found in the six cephalo-
thoracic members of either spiders 1 or horseshoe crabs except
in^tlm sixth pair of the latter, and to homologise the joints of
that member with the protopodite, exopodite, endopodite, and
epipodite of the “ typical ” crustacean limb is a task that I do
not care to undertake. It seems, on the other hand, to be much
more like one of the thoracic feet of Apus.

The condensed metamorphosis mentioned in the fourteenth
point is, I suppose, another method of saying that the develop-
ment is direct, for certainly Limulus shows nothing that could
be regarded in the light of a metamorphosis, and it is just this
lack of any larval forms which renders it so difficult to decide
upon the affinities of the forms in question. Had we any
nauplius or zoea stage the problem would be an easy one to
solve. As it is the development is direct just as it is in Tetra-
decapods, Spiders, and many other forms.

The third of the points is the most difficult to explain. In

1 Croneberg’s observations on Dendryph antes ('80; pi. xvi, fig. It — 16)
need confirmation.

NOTES ON THE EMBRYOLOGY OF LIMULUS.

555

both Hexapods and Arachnids two or more urinary tubules
are developed from the proctodseum (their development in
Arachnida has not been described) ; in Limulus nothing of the
sort is found, nor is anything of the kind certainly known in
the Crustacea. As I shall have again occasion to refer to
these organs I will leave the enumeration of the horns of the
dilemma until then.

The close relationship existing between Limulus and the
Trilobites has often been insisted upon by naturalists since
Lockwood first saw a young horseshoe escape from its egg.
The recent work of Walcott (’81), though I cannot accept his
interpretations in many respects, serves to show that the
resemblance between the two are not so great, or rather the
differences are too great, to warrant a close association of these
forms. This is more apparent from the discovery of the Ohio
specimen described and figured by the same gentleman (’84).
The veteran carcinologist, Henri Milne Edwards (’81), also
fails to recognise these affinities, though he places his objection
on different grounds from those that I hold. I do not care to
enter into a discussion of the problem, but would state that
according to these results and specimens the Trilobites had a
series of non-chelate ambulatory limbs extending to the ex-
tremity of the body. Each limb consisted of a basal joint,
from which arose an endopodite with six cylindrical joints, a
three- jointed setose epipodite (exopodite ?), and outside of
these, just as in the lobster, the branchial organs. These latter
were filamentary and straight or spirally coiled. With such a
different appendicular structure it seems to me that we must
have more than a strained resemblance of dorsal surfaces before
admitting any close resemblance between the two, though it
must be said that there is a certain resemblance between the
four anterior legs of the Trilobite and their relationship to the
mouth (as restored by Walcott, ’81, pi. vi, fig. 1) and the four
posterior cephalothoracic limbs of Limulus.

If we are to accept these resemblances as indicative of a
homology between the two we must conclude that the first two
pairs of appendages of the Trilobites have been lost, to say

556

J. S. KINGSLEY.

nothing of the change in form and function of the abdominal
appendages. It also necessitates a change in the nomenclature
of the regions of the Trilobite body. The head will correspond
to the cephalothorax of Limulus, and the thorax and abdomen
or pygidium together will equal the abdomen of the horseshoe
crab.

The Systematic Position of the Arachnida.

Since 1858, when Leuckart divided the old group Articulata
into Worms and Arthropods, and the latter group into the
equivalents of Branchiates, not a single author, so far as I am
aware, with the exception of Van Beneden and Lankester, has
questioned the close association of the Arachnids with the
Hexapods and Myriapods in a common group called either
Insecta or Tracheata. Entirely independently of Professor
Lankester’s papers (’77 and ’81) I came to somewhat similar
conclusions, which may be stated as follows : — Omitting Peri-
patus, the Arthropods should be divided into three equivalent
groups or classes, one embracing the Crustacea, the second
Limulus and the Arachnids, and the third the Hexapods and
possibly the Myriapods. The last of these for convenience
may be called Insects, the second Acerata (a modification of
the name given by Latreille to the Arachnida alone). The
Crustacea and Acerata are more closely allied to each other
than either to the Insects, and the nearest representatives
to-day of their common ancestor are Limulus and Apus.
Before these two classes diverged the Insects had left the
primitive Arthropod stem.

The points of difference between the Arachnids and the
Insects are many, those between the former group and the
Crustaceans less in number and more readily to be considered
as derivations of a common ancestor. These points and their
hearings I will consider in a rapid manner beginning with the
anterior appendages, the posterior in all of the groups showing
too many variations to afford any decisive results.

First, in the Insects we have antennae which are primitively
pre-oral, and not to be homologised in position or character

NOTES ON THE EMBRYOLOGY OF LIHULUS.

557

with any structures as yet found in Crustacea or Acerata. It
has been shown by several students that in the latter group all
of the appendages are, in the embryo, post-oral both in
position and in nerve supply. The same is true of the second
pair in the Crustacea, and in the adult Phyllopods (which are
admitted by all to be the most primitive of the Crustaceans),
both anterior pairs receive their nerves from the oesophageal
commissure, the corresponding (?) ganglia being distinctly post-
oral in position.1 It would appear possible that in the very
early stages of other Crustacea the same condition may exist,
as in several forms the rudimentary first pair of appendages
has not a distinctly pre-stomial position. The first to suggest
itself is Moina, where, according to Grobben (’79), the first
pair of appendages to appear have a position decidedly posterior
to the stomodeal invagination. This pair Grobben interprets
(and possibly correctly) as the second antennae, but there is
not certainty on this point. In the Nauplius of Palaemon,
according to Bobretzky2 (73), the first pair are on a level with
the labrum, and show distinctly the similarity to the rest of the
post-oral series. In the corresponding or a little earlier stage
of Astacus (Reichenbach, ’77, pi. x, fig. 8) they are some distance
behind the labrum and the oral depression. The same is true
of Eupagurus (Mayer, ’77, pi. xiii, fig. 18) and of Crangon (my
own studies).

The antennae of Insects, on the other hand, always arise
from the procephalic lobes. The possibility that Peripatus is
a but slightly modified descendant of the ancestors of the
Hexapods and Myriapods makes its evidence of some import-
ance in this connection. Balfour, after a careful study of the
anatomy, concludes that in Peripatus (’83, p. 217) “the
antennae are prolongations of the dorso-lateral parts of the
anterior end of the body and his figures show that the eyes
intervene between the antennae and the other appendages.
Kennel, from a study of two other species of the same genus,

1 Pelseneer’s results as to the brain of Apus [’85] require a modification
of this statement.

3 Teste Faxon (’82, pi. xi, fig. 6).

558

J. S. KINGSLEY.

comes to"a similar conclusion, and carries it further, as follows
(’84, p. 200) : — “ Obwohl nun dieses segment [the f praeorale
Abschnitt'] seiner Entstehung nach alien anderen des Korpers
homodynam ist, glaub ich doch es denselben gegeniiberstellen
zu miissen da es sich in ganz anderer Weise umbildet und
niemals Organe erzeugt, wie sie alien anderen Segmenten aus-
nahmlos^eigen sind ; es entstehen in ihm keine Segmental-
organe, keine Driisenbildung, auch keine Extremitaten ; denn
ob die Tentakel fur Gebilde gehalten werden diirfen, welche
den^Extremitaten der Rumpfsegmente homolog sind, ist auch
bei den iibrigen Tracheaten, sofern man die Antennen derselben
als gleichwertige Bildungen durch die ganze Reihe hindurch
auffast, nicht ausgemacht.”

A considerable difficulty arises when we try to homologise
the antennae of Insects with those of Peripatus. In the latter,
as has just been said, these organs receive their nervous supply
from the brain in front of the eyes. In Myriapods, according
to Newport, the case is the same ; but in Hexapods the case
seems to be different ; but careful study is yet needed to settle
this point. In the embryo Hexapod the antennae rise from the
posterior side of the procephalic lobes, and there appears to be
much evidence that they are innervated from a distinct ganglion
from that which supplies the eyes. On the other side, Ayres
(’84 pi. 20, figs. 22 and 23) represents the antennal lobe in
CEcanthus as being in front of the ocular lobe and between it
and the origin of the nerves to the ocelli, a condition which
needs confirmation.

Should this view that the antennae of Peripatus and Hexapods
are not homologous prove true it would throw considerable
doubts upon the comparatively close relationship which has
been supposed that they hold to each other, a relationship
which may be doubted on several other grounds, some of which
will be mentioned later.

In the Spiders but one recent author (Croneberg, '80) has,
so far as I am aware, found what he regards as antennae. He
figures (pi. xvi, figs. 14 — 16) the embryo of Eendryphantes,
showing the upper lip (rostrum) arising as two appendage-like

NOTES ON THE EMBRYOLOGY OF LIMULUS.

559

lobes, in front of the rudimentary chelicerae and between the
procephalic lobes. His figures clearly show however, that on
account of their relations to the nervous system these lobes
cannot be regarded as homodynamous either with the post-oral
appendages, or with the appendages of insects.

Assuming for the moment that the view that the antennae
of Insects are not represented in either the Acerata or the
Crustacea is correct, a comparison of the three groups may
give us some further interesting points. In the following
schedule only the anterior segments are included, and the appen-
dages are called by their usual names, which no one regards as
indicative of homologies extending through the whole Arthro-
podan phylum.

Hexafoda.

Acerata.

Crustacea.

(1) Antennae

. Absent

Absent.

(2) Mandibles

. Chelicerae .

Antennulae.

(3) Maxillae

. Pedipalpi .

Antennae.

(4) Labium

. 1st legs

Mandibles.

(5) 1st pair legs .

. 2nd pair legs

1st maxillae.

(6) 2nd pair legs .

. 3rd pair legs

2nd maxillae.

(7) 3rd pair legs .

. 4th pair legs

1st maxillipeds.

This comparison is a strictly serial oue and starts on the
assumption that the first pairs of primitively post-oral appen-
dages are homologous throughout. That this is true in the
cases of the two last groups is, to my mind, very probable, but
with regard to the Hexapods there is some reason for doubt.
In following it out we are led to some interesting regional
coincidences. It brings the end of the thorax of the Hexapod
and Spiders into exact correspondence. In the case of the
Crustacea a line of demarcation at the same spot is frequently
visible, and one needs but to mention that it corresponds
exactly to the posterior end of the head of the Tetradecapods,
and is well paralleled in Squilla, and in the larva of Palinurus.
In the Entomostraca a division at the same point may be seen
in the larvae as also in the protozoea of Lucifer. These may
all be analogies, and the fact that no such regional distinctions

560

J. S. KINGSLEY.

are found in the most primitive group of Crustacea, the Phyllo-
pods, is against their having much significance.

The comparison also leads to another correspondence in the
Crustacea and Acerata, which goes as far to prove its validity
as did the regional comparison in the case of the Spiders and
Hexapods. In both Crustacea and Arachnids the segmental
organs (shell glands of the former, coxal glands in the latter)
empty at the same point ; at the base of the third pair of
walking legs in the Spiders and Limulus, and at the base of the
second maxillae in the Crustacea, or, in other words, at the base
of the fifth pair of appendages in each. It seems to me that
this persistence of exactly the same segmental duct in these
two groups and the absence of any corresponding organs in the
Hexapods is an argument of no little weight.

If, however, it be shown that a variation or a disappearance
of segments or appendages may take place at the anterior end
of the Arthropod body this comparison will lose part of its
force. That such obsolescence in the adult occasionally occurs
is well known, but the presence of the appendages in the
young readily enable us to check our results. Setting aside
the parasitic forms the best known cases are presented by
certain Copepods, Apus, and the Oniscidse, but the fact that
the normal condition is found in their near relations shows
that tbis fact is of no morphological importance in this con-
nection. In Eurvpterus, according to Lankester, there is a
case of an apparent disappearance of one pair ; but until it is
proved that the Trilobites are related to the Acerata (a point
on which, as mentioned above, Walcott’s observations throw
considerable doubt) the assumption that the cephalic buckler
of these forms is the exact homologue of the cephalothorax of
Limulus is not warranted, and in case it turns out that the
two are different these fossils throw no light on the subject.
Until it is proven that a segment or an appendage may dis-
appear in the anterior end of the adults of a large group of
animals, it is justifiable to assume the exact homology of the
first pair in all three groups, as I have done above. It is
possible that an embryological study of the cement glands,

NOTES ON THE EMBRYOLOGY OF LIMULUS.

561

together with the mandibular glands of Hexapods and the
cheliceral glands of Spiders, may throw some light on this
point.

If, as pointed out by Lankester, the tracheae of the Arachnids
have arisen from the gills of the Limulus,1 then either those of
the Hexapods must have been derived from those of the
Arachnids, or those in the two groups must have arisen inde-
pendently. The latter I believe to be the true case, and with-
out entering into any argument to establish this point, I
would call attention to the fact that in the terrestrial Isopods
(Oniscidae) the gills become permeated with trachea-like air-
tubes. Long ago Lereboullet (’52, pi. vii, figs. 148 and 149)
figured these ramifying tubes, while, to consult a more recent
student, Leydig (’78, p. 265, pi. xi, fig. 32) describes the
mode of their formation. The cells of the blood-spaces of the
gills secrete an internal cuticula, and in the branching cavities
which this contains the air circulates. This forms tracheae,
certainly without any phylogenetic connection with those of
the so-called tracheates, but which present many analogies
with them. It also affords good grounds for the supposition
of Professor Lankester that the trachea, at least in some
groups, have followed the course of pre-existent blood-vessels.

Another fact of some weight in this connection lies in the
position of the tracheal openings. In the Arachnids they

1 Schimkewitsch (84a) denies this, but offers no reasons, but rather seems
to misapprehend the whole argument relative to the relationships of Limulus to
the Arachnids. He says (1. c., p. 67), “ Les poumons memes peuventetre con-
siders comme une modification des trachees en faisceaux des chenilles et des
myriapods. II est tres probable que les ancetres des Arachnides et des autres
Tracheates avaient cette forme des trachees en faisceaux, laquelle a ete trans-
formee cliez les Araignees en poumons. Tout cela me fait croire que les
formes tracheennes et les Tetrapneumones sont plus anciennes que les
Dipneumones.” Further on (p. 84) he says, “ Par leur apparail circulatoire et
leur systeme musculaire, les Arachnides superieures se rapprochent au contraire
des Limulides ; mais cette resemblance peut etre expliquee par l’identite
qu’existe dans la configuration generale du corps de ces deux formes; car les
Limules, d’apres leur evolution (etat Nauplius et etat de Trilobite) et d’apres
la constitution des l’appariel respiratoire, sont des vrais Crustacea prives
d’antennes.”

562

J. S. KINGS LEY.

perforate the ventral plates, as also in the diplopod Myriapods.
In the Hexapods and the chilopodous Myriapods the stigmata
are placed outside these plates. These differences in position
of the external openings may indicate a separate origin in all
these groups, especially when we consider Sedgwick’s specula-
tions (’84) on the origin of tracheae. Again, it should be
noticed that no traces of cephalothoracic stigmata or tracheae
occur in the Spiders.

One objection to the separation of the Hexapods and Arach-
nids, and the closer connection of the latter with the Crustacea,
lies in the fact that biramose appendages are characteristic
of the branchiate and simple of the tracheate Arthropods.
This, however, may be regarded in two lights. In the an-
cestral Arthropod both exopodite and endopodite may have
been present, and both branches may have been retained in the
aquatic and only one in the terrestrial forms, or the ancestor
may have had broad and flattened but unbranched appendages
which have been variously differentiated in different groups.
There are several facts in favor of either of these views,
though the evidence presented by Apus, together with many
other points render the latter the more probable. To mention
one or two of these : Apus is by nearly all morphologists
regarded as the most ancestral type of Crustacea. Its
members (Lankester, ’81a) are broad and flattened plates
bearing typically six internal and two external lobes, but
studying the adult alone no one would ever arive at the idea of
exopodite, endopodite, and epipodite. In the Nauplius stage,
in the second and third appendages, a biramose condition
exists. This is, however, to be regarded as secondary in its
nature, just as is the Nauplius itself. In the maxillae of forms
even as high as Decapods, this lamellar condition persists, and
all attempts to trace the homologies of exopodite and endo-
podite meet with but partial success.

The evidence on the other side is fragmentary. Croneberg
(’80, Pl. xvi, figs. 14 — 16) describes and figures an embryo
Arachnid (Dendryphantes) in which the pedipalpi are distinctly
bifid at the tip. This, however, has never, so far as I am

NOTES ON THE EMBRYOLOGY OF LIMULUS.

563

aware, been seen by any other observer, and needs confirmation.
Among other groups of Tracheates are the peculiar antennae of
the Pauropids, with their basal joints bearing two branches, one
of which in turn is bifid. The investigations of Mr. Wood-Mason
(’79) show that in some of the Thysanura and in the Cock-
roaches some of the appendages exhibit a biramose condition.
While some of his facts and many of his speculations need con-
firmation,1 I think that in some instances (enough for our
purposes) he has proved his points. Probably more extended
studies on the Thysanura will throw important light on the
relationships of the Hexapods to other forms. Patton (’84,
p.596) describes a similar condition in Blatt a germanica:
“ A rather striking variation was found in the first and second
maxillae of Blatta, which were formed respectively of two and
three branches, the second maxillse thus attaining the typical
trichotomous structure of the Crustacean appendages.”

The existence of Malpighian tubes in Spiders and Hexapods
is, without doubt, the greatest obstacle to the arrangement of
the Arthropods here advocated, since they are absent in Limulus
and the typical Crustacea. Their mode of development debars
us from considering them as modified segmental organs, and we
can only say that they are either inherited from an ancestor
common to all Arthropods and have disappeared from some
groups, or we must admit that they have appeared indepen-
dently in two or more branches of the Arthropods. 'Which of
these two alternatives we must take cannot be at present de-
cided, though some facts may throw light upon the subject.
The first thing that we notice is that those groups (Hexa-
pods, Myriapods, and Arachnids) which possess them are ter-
restrial, while the great bulk of the Crustacea are aquatic ; and
this at once suggests that the organs may have an origin from
similar physiological causes without any phylogenetic connec-
tion existing between them. Turning to those Crustacea which
lead a terrestrial life we meet with some striking confirmations
of this hypothesis.

Zenker ('54, pp. 106, 107) describes inlthe young Asellus
1 E.g The structure of the mandible in Machilis.

564

J. S. KINGSLEY.

(a fresh-water form) six glandular spots on either side of the
abdomen, which later unite to form a tube, though he did not
find the place where it opened. Weber (’79, p. 237) mentions
and (’81, pp. 608 — 612) describes and figures tubes emptying
into the hinder intestine in Trichoniscus, and says that they
also occur in other Oniscidae. He also states that he found
depositions of urates, a fact which at once deprives the opinion
of Wrzesniowski (’79, pp. 514, 515) of much of its force. The
investigations of Nebeski (’80, pp. 122 — 127) are the most
interesting. This author describes certain organs arising at
the beginning of the hind gut of certain Amphipods. In the
strictly aquatic genera these glands are small, but in the more
terrestrial Gammarus they become well developed, while in
Orchestia, a form living in the sand above high tide, they are
very long and tubular, and the histology shows that they have
active secretory or excretory functions. In position and origin
they correspond closely with the Malpighian tubes. His series
on pi. ii, fig. 14, is very instructive.

Nebeski’s observations, however, are not conclusive, for he
shows the rudiments of the same organs in Amphipodous
genera which are solely aquatic. Gamroth (’78, pi. x, fig. 14)
figures two globular glands occupying the same position in
Caprella which he regards as urinary, and Haller (’80, p. 384),
studying the same genus, agrees with him. These forms are
all confined to the Tetradecapods, and so far as I am aware, no
similar organs have been found in any other Crustacea. Still
they may be derived from an ancestor common to them and to
all the Trackeates. These ancestral glands may have been
very small, possibly mere glandular surfaces, and changed con-
ditions in life have caused their increased development. A
somewhat parallel case is that noted by Grobben (’80) that the
antennal gland differs in its length and complication in the
salt- and in the fresh-water members of the same genera of
Copepoda.

This of course is but analogy. It seems at present as if
these organs had arisen in the Crustacea independently of their
existence in other Arthropods. If this be the case, their

NOTES ON THE EMBRYOLOGY OF LIMULUS.

565

existence in Hexapods and Myriapods loses some of its force.
If the reverse be true the argument, derived from these organs,
for the maintenance of the group Tracheata has even less
weight.

From these and other facts it seems to me probable that the
ancestral Hexapod left the main Arthropod stem some time
before the separation of the Crustacea and Acerata. The
common ancestor of all three was an elongate animal with
flattened ambulatory appendages, some of which (except pos-
sibly the first) were adapted for the purposes of eating. The
head bore on its dorsal surface scattered sensory (optic)
organs. In most, if not all, the segments of the body were
segmental organs, through which passed the products of the
genital glands, no genital ducts being differentiated. The
reproductive glands were probably ventral in position ; the
nervous system consisted of a single supra-oesophageal gan-
glion, a ventral chain and a supra-intestinal loop (vide Peri-
patus). The alimentary canal traversed the whole length of
the body ; and, contrary to the opinions of the Hertwigs (’81),
it seems probable that circulation was effected by the pulsation
of the dorsal splanchnopleural muscles, the coelom containing
the circulatory fluid, and that this portion was constricted off
to form the heart.

The Hexapods left this stem at a time when the first pair of
originally post-oral appendages were moving towards a pre-oral
position.1 The Spiders and Crustacea continued together until
they had the following characters in common : — One pair of
appendages had a distinctly pre-oral position, and the basal
joints of at least the two succeeding pairs were employed in
the comminution of food. The segmental organs had dis-
appeared from the first, third, fourth, and sixth body segments
and possibly from others. The genital glands became con-
centrated near the middle of the body, and the reproductive
products passed out through the segmental organs in the same
region. The genital glands themselves had assumed a dorsal

1 Hatschek (’77) says that the ganglia of the mandible of the embryo
Bombyx becomes transformed into part of the oesophageal connectives,
von. XXV. NEW SER

o o

566

J. S. KINGSLEY.

position. Most of the post-oral parts were concerned in
respiration.

In the foregoing I have taken no account of Pauropus and
the Myriapods, the facts concerning them being not yet well
enough known. It seems possible that they have no connec-
tion with the Hexapods. The structure and relationship of
the trachea, the ventral position of the genital glands, the
mouth parts, the innervation of the antennae, the existence of
segmental organs in Peripatus and their possible homologues
in the foramina repugnatoria of the Myriapods, all need
to be taken into consideration in this connection.

I do not intend to defend in extenso these points at the
present time; a few explanatory notes may, however, be of
value. The relationship of the oviducts to the exterior in the
Arthropods seems to point to the conclusion that here, as in
many other animals, they are modified segmental organs. The
positions in which these ducts empty would then warrant the
conclusions given above regarding the relationships of the
segmental organs. Several authorities (especially Grobben,
79 and ;81b ) have pointed out that the genital glands of
Arthropods are ventral in origin, and that they later assume a
dorsal position. This author also points out, as an indication
of inferiority, that they permanently retain a ventral position
in Peripatus and Myriapods.

Whether the first pair of appendages in the ancestral
Arthropod played a part in eating is uncertain, though the
facts that it now does so in the Hexapods, Myriapods, and
Peripatus, and that in the other groups it at first has a post-
oral position is in its favor. In Limulus, as in Apus, and in
the Nauplii of various Crustacea, the basal joints of at least
two pairs behind the first are so employed, and in the two
forms first mentioned the series is extended further. In all it
is the basal joint which is so employed, and in the young of
some and the adults of others the distal portion is used for
ambulatory purposes.

Note. — Since this article was sent to the printer several papers have
appeared which have more or less bearing on the subjects here discussed, though

NOTES ON THE EMBRYOLOGY OF LIMULUS.

567

none cause any serious modification of the views here held. Professor Lankester
[’85], entirely independently, has arrived at essentially similar views as to the
homology existing between the lungs of Arachnids and the gills of Limulus.
The causes assigned for the change differ, a matter of no importance in this
connection. Mr. Pelseneer [’85] has shown that the brain of Apus is a
“ syncerebrum,” a fact which modifies some of the statements in the text.
The discovery by Mr. Spencer that the urinary tubules of the Amphipods are
mesenteric [’85] is more important, though I must say that my argument
demands analogies rather than exact homologies.

Dr. Packard [’85] has studied some sections of a stage about equal to my
figure 5, and from them he draws the conclusion that the development of the
brain of Limulus is entirely different from that of Arachnids. He distinctly states
that the stage cut had the first pair of appendages in a post-oral position, but
still he regards the nervous invagination in sections which pass through the
first pair of limbs as the brain. This being the case, his argument falls to the
ground. Contrary to his statements, I would say that the development of the
brain of Limulus is closely like that of the Arachnids, and that Crustaceans
do have procephalic lobes.

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NOTES ON THE EMBRYOLOGY OF LIMULUS.

569

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570

J. S. KINGSLEY.

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’70‘. Packard, Alpheus Spring, jr. — [“The Development of Limulus”]
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NOTES ON THE EMBRYOLOGY OF LIMULUS.

571

’72. Packard, Alpheus Spring, jr. — “The Development of Li m ulus
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’85- Packard, Alpheus Spring. — “On the Embryology of Limulus
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’84. Patten, William. — “ The Development of Phryganids, with a Pre-
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’77. Reichenbach, Heinrich. — “ Die Embryonalanlage und erste Entwick-
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’84. Schimkewitsch, Vladimir. — “ Zur Entwicklungsgeschichte der Ara-
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’84a. Schimkewitsch, Vladimir. — “ £tude sur TAnatomie de l’Epeira,”
‘Ann. Sci. Nat.,’ vi serie, t. xvii, art. No. 1, pp. 94; pis. i — viii
(1884).

’84. Sedgwick, Adam. — “ On the Origin of Metameric Segmentation and
some other Morphological Questions,” ‘ Quart. Journ. Micr. Sci.,’
xxiv, pp. 43 — 82 ; pis. ii and iii (1884).

’85- Spencer, W. Baldwin. — “The Urinary Organs of the Amphipoda,”
* Quart. Journ. Micr. Sci.,’ xxv, pp. 183 — 191, pi. xiii, 1885.

’81. Ulianin, B. — “ Zur Entwicklungsgeschichte der Amphipoden,” ‘ Zeitschr.
wiss. Zool.,’ xxxv, pp. 440—460 ; pi. xxiv (1884).

572

J. S. KINGSLEY.

’84 Urbanowicz, Felix. — “ Zur Eutwicklungsgeschichte der Cyclopoden,”

‘ Zool. Anzeiger,’ vii, pp. 615 — 619 (1884).

’81- Walcott, C. D. — “ The Trilobite : New and Old Evidence relating to
its Organization,” * Bulletin Museum Comp. Zool.,’ viii, pp. 191 — 224 ;
pi. vi (1881).

’84. Walcott, C. D. — “Appendages of the Trilobite,” ‘Science,’ iii, pp.
279—281 (1884).

'79 Weber, Max. — “Ueber Asellus aquaticus Schiodte in I. Teste
Leydig (As. Sieboldii de Rougemont),” ‘ Zool. Anzeiger,’ ii, pp. 233 —
238 (1879).

'81- Weber, Max. — “ Anatomisches fiber Trichonisciden,” ‘Archiv f. mikros.

Anat.,’ xix, pp. 579 — 648 ; pis. xviii — xix (1881).

79- Wood-Mason, James. — “ Morphological Notes bearing on the Origin of
Insects,” * Trans. Entomol. Soc. London,’ pp. 145 — 167 (1879).

’79 Wrzesniowskv, August. — “Vorlaufige Mittheilungen iiber einige
Amphipoden,” 4. “Ueber den Darmcanal und seine Anhange,” ‘Zool.
Anzeiger,’ ii, pp. 511 — 515 (1879).

’80. Young, John. — “On the Head of the Lobster,” ‘Journal Anat. and
Physiol. (London),’ xiv, pp. 348 — 350 ; pi. xviii (1880).

’41- Zaddach, Ernestus Gustavus. — “De Apodis cancriformis, SchaefT.

Anatomie et Historia evolutionis,” pp. 72 ; 4 plates, Bonn® (1841).
’54- Zenker, Wilhelm. — “Ueber Asellus aquaticus,” ‘Archiv fur
Naturgeschichte,’ xxi, i, pp. 103 — 107 ; pi. vi, figs. 3 — 6 (1854).

NOTES ON l’HK EMBRYOLOGY OE LIMULUS.

573

EXPLANATION OF PLATES XXXVII, XXXVIII,
AND XXXIX,

Illustrating Dr. J. S. Kingsley’s Paper on “ The Embryology
of Limulus polyphemus.”

Reference Letters.

a. Anns. ab. Abdomen, ap. Appendage, b. Modified blastopore, be.
Blood-corpuscle, bl. Blastoderm, bs. Blood-sinus, c. Coelom, cm. Com-
missure. cn. Connective, co. Connective tissue, ct. Second larval cuticle.
ex. Cephalothorax. dt. Deutovum. e. Eye. ec. Edge of carapax. ei.
Epiblastic invagination for brain, eo. External opening of segmental organ
ep. Epiblast. f. Flagellum of sixth pair of legs. fn. ? Funnel of segmental
organ. ga. Gill-bearing appendage. gl. Gill-lamellae. gn. Ganglion.
h. Heart, m. Mesoblast. mo. Mouth, mp. Mesoblastic partitions, mt.
Metastoma. mu. Muscle. n. Nerve. nf. Nerve-fibres, ng. Neural
groove, nr. Neural thickening, nu. Nucleus, o. Operculum, oc. Ocelli.
p. Proctodaeum. pub. Abdominal appendage, pc. Procephalic lobes, pi.
Pulmonary lamellae. pn. Pulmonary invagination. sg. Segmental organ.
so. Somatopleur. sp. Splanchnopleur. st. Stomodaeum. stg. Stigma, t.
Telson. x. Problematical organs of Fig. 3. y. Yolk. yg. Yolk-granules.

The Roman numerals, I, n, in, &c., refer to the segments ; the Arabic, 1,
2, 3, &c., to the appendages of the body.

PLATE XXXVII.

Fig. 1.—- Surface view of egg half an hour after attempted artificial im-
pregnation.

Fig. 2. — Same egg twenty-one hours later.

Fig. 3. — Surface view of an egg twenty-nine hours after artificial impreg-
nation, showing two peculiar protuberances on the surface. For detailed
description of Figs. 1 — 3 see p. 544.

Fig. 4. — Early embryo of Limulus. The lighter area ( m ) indicates the
extension of the mesoblast ; the key-hole-shaped centre ( b ) is the modified
blastopore. Osmic acid preparation.

Fig. 5. — Embryo after the appearance of the compound eyes ( e ), tbe six
pairs of cephalothoracic appendages (1 — 6), and the operculum (o). The
blastopore has now divided into the pyriform mouth and anus. The neural
groove (ng) is seen. Osmic acid preparation.

574

J. S. KINGSLEY.

Fig. 6. — “ Germinal disc ” of embryo after the appearance of the eighth
(first gill-bearing) appendage {gav). The distinction between the cephalo-
thoracic and abdominal regions is now distinct. Osmic acid preparation;
camera drawing.

Figs. 7 and 8. — Surface and sectional views of deutovum after separation
from the embryo. X 160.

Fig. 9. — Diagrammatic upper and. Fig. 10, side views of segmental organ,
constructed from sections. I am not certain about the internal termination,
f. Cf. Fig. 27.

Fig. 11. — Embryo at the time of moulting. The second larval cuticle {ci)
viewed obliquely from the front to show the procephalic lobes {pc).

Fig. 12. — Embryo at the time it escapes from the chorion and assumes a
Limuloid appearance. The position of the eye (e), extending across a meso-
blastic partition, is noticeable.

Fig. 13. — Horizontal section of an embryo of the stage shown in Fig. 14,
taken above the level of the eyes, to show the extent of ingrowth of the
mesoblastic partitions {mp). x 14.

Fig. 14. — Under surface at the “trilobite stage,” constructed from camera
drawings. Owing to difficulties of manipulation the brain could not be seen,
and the metastoma may not be correct.

Fig. 15. — Reproduction of Metschnikoff’s figure (’71, PI- xvi, fig. 12). “A
part of the embryo [of Scorpio] to show the first formation of the lung.”
p. ab. Abdominal appendage, pn. Pulmonary sac.

Fig. 16. — Dorsal and, Fig. 17, ventral views of young Limulus at the
escape from the deutovum and beginning of a free life. X 14.

Figs. 18, 19, and 20. — Diagrams illustrating the derivation of the pulmonary
sacs of the Arachnids from the branchiae of Limulus.

Fig. 18. A single gill-appendage with the gill-lamellae, as shown in the
adult Limulus.

Fig. 19. The gill-appendage is partially sunk in the ventral surface, and
the gill-lamellae exhibit a condition shown in Figs. 37 and 38.

Fig. 20. Diagram of pulmonary sac of an Arachnid. The gill-lamellae
are replaced by the pulmonary lamellae ; the pit of invagination has
narrowed above and foims a spiracle.

NOTES ON THE EMBRYOLOGY OF LIMULUS.

575

PLATE XXXVIII.

Fig. 21. — Transverse section through fourth segment of embryo, shown in
Fig. 12. The mesoblast has met above and below. X 64.

Fig. 22. — Longitudinal section through the fourth to the seventh segments
of an embryo in stage shown in Fig. 12. The section passes to one side of
the median line, and shows the metastoma as a portion of the sternum of the
sixth segment. X 76.

Fig. 23. — Longitudinal section of embryo, Fig. 12, showing the opening of
the segmental organ and the vesicular enlargement, x 150.

Fig. 24. — Section through the nervous cord (not yet separated from the
epiblast) behind the eighth ganglion of Fig. 12. x 380.

Fig. 25. — Section through seventh ganglion of Fig. 12. The separation of
the nervous tissue from the epiblast is complete in the middle, though not at
the sides.

Fig. 26. — Section parallel to and outside of Fig. 23, cutting through three
folds of the segmental organ. A thirteenth of a millimetre intervenes between
the two sections.

Fig. 27. — Transverse section of half of fifth segment, showing three
portions of the segmental organ and its internal opening,/®, x 150.

Fig. 28. — Section of middle portion of segmental organ, x 1000.

Fig. 29. — Median sagittal section of embryo. Fig. 15. The section passes
through the edge of the mouth (mo) and shows the epiblastic involution (ei)
which later takes part in the formation of the brain. Though the first pair of
appendages are distinctly preoral (cf. Fig. 12), the first ganglion of the ventral
chain ( gn i) retains a postoral position. Behind the eighth ganglion the
nervous tissue has not separated from the epiblast. X 75.

PLATE XXXIX.

Fig. 30. — Transverse section of third appendage and adjoining region of
Fig. 6 at the first appearance of the coelom, showing it to be a schizocoele.
X 150.

Figs. 31 — 33. — Formation of the heart, Fig. 31 being the most posterior.
A twentieth of a millimetre behind Fig. 31 no lumen occurs in the solid
mesoblast. A thirteenth of a millimetre intervenes between Figs. 31 and 32,
and a fifth of a millimetre between Figs. 32 and 33. The conversion of
mesoblast cells into blood-corpuscles is shown in all three figures. The
thickening of the dorsal epiblast immediately above the heart is noticeable.
X 442.

Fig. 34. — Constructed from three longitudinal sections of Fig. 6, showing
portions of ihe coelom in each segment of the body.

576

J. S. KINGSLEY.

Fig. 35. — Transverse section through the middle of the fourth segment of
Fig. 14, showing the segmental organs and the origin of the nerve to the
fourth pair of appendages, x 75.

Fig. 36. — Section through the metastoma (ep) of Fig. 14, showing the
mesoblastic outgrowths ( co ) to form the artery surrounding the ventral
nervous cord. X 150.

Figs. 37 and 38. — Longitudinal section of abdominal appendages, Fig. 14,
showing the mode of formation of the gill-lamellse, the inpushing being as
marked as the outgrowths. Compare with Fig. 19.

Fig. 39. — Origin of deutovum as a cuticle secreted by the blastoderm.
The section is taken from an egg in the stage represented in Fig. 4. x 300.

Figs. 40 — 43. — Transverse sections of the mouth region of Fig. 6, illustra-
ting the formation of the stomodeum by a closing-in of the epiblast. Fig. 40
is the most posterior. X 200.

Fig. 44. — Transverse section of the germinal area of Fig. 4, showing the
origin of the mesoblast from the elongate “germinal groove” (modified
blastopore).

Fig. 45. — Relative proportions of blastoderm and deutovum at the stage
shown in Fig. 5.

Fig. 46. — Transverse section through anus of Fig. 5. X 175.

Fig. 47. — Transverse section through the fourth pair of appendages of
Fig. 5, showing the extension of the mesoblast and the absence of a coelom at
this stage.

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THE ANATOMY OF THE MADREPORARIA.

57 7

The Anatomy of the Madreporaria : I.

By

G. Herbert Fowler, B.A.,

Keble Coll., Oxon., Berkeley Fellow of the Owens College, Manchester.

With Plates XL, XLI, and XLII.

By the kindness of Professor H. N. Moseley I have been
enabled to study the anatomy of certain Madreporaria obtained
by him during the voyage of H.M.S. “ Challenger/’ As in
lecture-courses and text-books but little information is given
relative to this ancient and interesting group, and the few
papers on the subject are scattered, a short sketch of the more
recent researches is prefixed to my own results. Two forms
only are described in this paper, Flabellutn patagonichum
and Rhodopsammia parallela; others, it is hoped, will
follow shortly. Throughout the text will be reduced as far as
possible.

An acquaintance with the anatomy and development of an
ordinary Actinia is presupposed in the reader, this being the
type by which comparisons are made ; but a list of the more
technical names used to describe the anatomical parts of the
polyp is given, with their synonyms for the use of those
desirous of cousulting the literature of the subject.

578

G. HERBERT FOWLER.

Mouth-disc = Mundscheibe, Peristome.

Body wall = Leibeswaud.

Stomodaeum (oesophagus) = Scblund-, oder Magen-robr.

Coelenteron = Darmhoble, Leibesbohle, Estomac.

Mesenteries (sarcosepta) = Scheidewande, Parietes, Replis
mesenteroides.

Mesenterial filament (craspedon) = Mesenterialfaden, Cordon
pelotonne.

Septa (sclerosepta) = Sternleisten, Cloisons, Lames.

Theca = Mauerblatt, Muraille.

A “ pair ” of mesenteries is constituted by two mesenteries
whose longitudinal muscle-fibres are ranged on their adjacent
faces, (except in the case of the two “ directive pairs,” each of
which is placed at one end of the longer axis of the mouth
oval, and in which the arrangement of the muscles is reversed).
For the chambers (Radial-taschen, Loges,) into which the
coelenteron is periaxially divided by the mesenteries, I am
compelled to coin new names; to those chambers which lie
between a “pair” of mesenteries the term entocoele is applied
(fig. 1, b) ; to those chambers of which one lies between every
two pairs of mesenteries the term exocoele (fig. 1, a). The
septa lying in these two classes of chambers are similarly
called exosepta and entosepta

The classification adopted will be found at the end of the
paper, together with the bibliography.

Recent Researches into the Morphology of the Group.

In 1873 Lacaze Duthiers (1), studying the development of
Astroides calycularis on the coast of Algiers, found that it
agreed in every important point with the development of
Actinia, his observations on which (2) were corroborated and
corrected by the Brothers Hertwig (3). With regard to the
developing skeleton, he recorded two facts of importance :
firstly, as appears in his pi. xiv, fig. 27, that it was formed
outside the polyp; and secondly, that the theca arose
independently of the septa. Owing to various practical
difficulties his investigation was incomplete.

The chief worker in this field has been Georg von Koch,

THE ANATOMY OP THE MADREPORARIA.

579

who, in the course of several investigations, has arrived at the
conclusion that the theca is a secondary structure, derived
from fusion of the peripheral ends of the septa. The evidence
adduced in support of this theory appears to me to be at
present insufficient for complete proof, though from our slight
knowledge of the group it is injudicious to absolutely deny its
truth.

Yon Koch first published this theory in 1879, founding it on
the following observations on Caryophyllia (4). There is no
living tissue on the greater part of the exterior of the corallum,
but at the apex the peripheral edge of the mouth-disc overlaps
the lip of the calyx in such a way that in the highest sections
the septa appeared to stand free in the ccelenteron, in sections
a little lower to have fused peripherally into a theca. The
costae are, according to him, and as will be seen by the figures,
the outermost ends of the septa (PI. XL, a, b).

Further, the mesenteries and chambers between them
appeared to be continued into this external part of the polyp.
These appearances he explained by supposing that as the peri-
pheral ends of the septa approximated and fused they sur-
rounded the mesenteries, dividing them ultimately into a
central and a peripheral part. As a further proof he adduced
the observation that in microscopic sections of the corallum
sutures were visible in the theca at the points where he
supposed the septa to have fused.

I venture to think with Moseley (5) that this explanation is
erroneous ; that the appearances in the first section (PI. XL, a)
are due merely to the fact that in this, as in many corals,
the secretion of calcium carbonate is most active about the
septa, which consequently rise slightly above the level of the
theca, as may be seen in any figure of Caryophyllia ; and
further that, in the second section (PL XL, b), the apparent
continuation of the mesenteries and chambers between them
over the tip of the calyx is not due to their having been cut
into two portions by fusion of the septa, but to more or less
abnormal contraction due to the use of alcohol; in life the
polyp, when fully expanded, undoubtedly stretches over the

580

G. HERBERT FOWLER.

lip, but in these forms, so far as I can ascertain, in natural
contraction it is completely within the calyx. Further, as
appears from his own researches and those of others on
different forms, the whole skeleton, instead of being, as he
describes, free in the coelenteron, is shut off from it by a layer
of endoderm and mesoderm, and as much outside it as the rest
of the corallum ; these layers he himself figures as clothing
another part of the septum, though of this portion no histo-
logical details are given. Yon Heider, in a paper shortly to
be referred to, states that von Koch has overlooked the fact
that the whole of the corallum is covered externally by ecto-
derm and mesoderm ; certainly this form requires more com-
plete investigation. Again, having ground many microscopic
sections of corals I can afford no credence to “ sutures •” in
the process cracks fly through the coral in all directions. But
if evidence of a directly contrary character is needed, the case
of Flabellum may be adduced, in which, according to Moseley
(5), sutures run, not between the fused ends of the septa, i.e.
through the theca, but down the centre of each septum.

Though von Koch gives no detailed description of the anatomy
of Carvophyllia, the following account may be inferred from his
figures and text (4) (6). The polyp is built on the Actinian
type, consisting of mouth-disc, stomodseum, mesenteries ; the
muscles of the latter being arranged as in Actinia. No external
body wall, its place being taken by the theca; inner body wall
of mesoderm and endoderm, lining the coelenteron, aud clothing
the interior of the calyx, both theca, aud septa. Mouth-disc
drawn down in abnormal (?) alcoholic contraction over the
lip of the calyx. Entosepta and exosepta both present. No
mention made of tentacles.

Of Madrepora variabilis he records, in 1880, the fol-
lowing facts (6). Structure Actinian ; in the end-polyps of
the colony six pairs of mesenteries, six entosepta, and six
exosepta ; in the side-polyps also six pairs of mesenteries, but
six entosepta only.

V. Koch has also studied Stylophora digitata in some-
what greater detail (7). The form of the colony resembles

THE ANATOMY OF THE MADREPORARIA.

581

that of Alcyonium digitatum ; the polyps live in small calyces
on the surface of the colony, but the living tissues are not
continued down into its centre, as in Alcyonium ; the lower
part of the cavity formerly inhabited by the polyp being
shut off by a kind of tabula as it grows upwards. Over the
surface of the colony lies the coenosarc, the fleshy rind of the
otherwise calcareous colony, which puts the polyps in commu-
nication with one another, being permeated by canals which
are continuous with their coelentera, and similarly lined
by endoderm. The polyp possesses six pairs of mesenteries,
six larger tentacles, six smaller tentacles, and six entosepta.
There are two distinct types of nematocyst. Longitudinal
muscles occur on the mesenteries, but the smallness of the
latter rendered it impossible to detect whether their arrange-
ment agreed with Actinia or not.

In 1881, Dr. von Heider, of Graz, published a description
of Cladocora astraearia and Cl. cespitosa (8). These
species are also built on the Actinian type ; and Heider
describes for them the same continuation of the mesenteries
and mesenterial spaces that v. Koch mentions as occurring in
Caryophyllia cyathus. I have examined macroscopically
and by sections Cl. cespitosa in a completely retracted state,
and can find no trace of such a condition, an observation which
confirms my belief that this appearance is due to partial contrac-
tion, owing to the use of alcohol. There is no true coenosarc
such as occurs in Stvlophora; just as there is no true coenen-
chyme, the calyces being free outwardly from the rest of the
colony. In luxuriant growth and budding, however, according
to Heider, both skeletons and soft tissues of adjacent polyps
may fuse ; an observation interesting as probably indicating
the history of the formation of the coenosarc and coenenchyme
which characterise many other forms. There is one correction
to be made in his work, which for the sake of future workers
in this field ought to be mentioned here ; namely, that in his
PI. III. he frequently figures as endodermal cells small spherical
bodies with a well-staining nucleus, which are zooxanthellae or
symbiotic unicellular Algse, living free in the coelenteron in

\OE, XXV. NEW SEK.

p p

582

G. HERBERT FOWLER.

such numbers as often to completely obscure the true endo-
derm, with which they of course have no connection. While
accepting v. Koch’s theory as to the origin of the theca from
fusion of the septa, he differs from it in some details, regarding
the “ sutures ” as merely cracks artificially produced in the
corallum. Septa and tentacles both entocoelic and exoccelic;
mesenteries and their muscles arranged as in Actinia; for
further details, which are very thoroughly worked out, his
paper should be consulted. One point of importance deserves
mention ; between the corallum and the structureless meso-
derm-lamella which overlies it immediately and was generally
understood to secrete it, v. Heider detected certain cells, for
the most part scattered, but in some places forming a definite
layer. To these he gave the name calycoblasts, and assigned
the function of coral-secretion ; with great justice, as later
researches proved, though their origin was a matter of doubt
till cleared up by v. Koch.

The latter, in a paper on the development of Astroides
calicularis (9), brought into notice the following facts.
When first fixed, and before the secretion of the skeleton has
commenced, the embryo is plano-convex, and its ectoderm may
be divided into two regions, corresponding to its surfaces, the
plane disc of attachment, or basal ectoderm, and the convex
portion or lateral ectoderm, the centre of which is iuvaginated
as the stomodeeum. The skeleton first appears as sm-all pellets
of calcium carbonate lying between the basal ectoderm
and the foreign body to which the embryo is
attached, and is therefore outside the animal, and conse-
quently the result of secretion by the ectoderm.
As the corallum is always described in text- books as a product
of the mesoderm, this observation cannot be too strongly
insisted upon. These pellets become, first a ring-shaped disc,
then a complete disc lying between the basal ectoderm and the
foreign body to which the embryo is attached. Where septa
are to be formed the three body layers, endoderm, mesoderm-
lamella, and basal ectoderm, rise upwards as a fold into the
ccelenteron ; and as they rise, coral is deposited beneath them

THE ANATOMY OF THE MADREPORARIA.

583

which fuses with the original disc ; the septa are thus also
deposited outside the basal ectoderm. They then begin to
bifurcate at their distal ends. The originally basal ectoderm
to which the secretion of the skeleton is attributable, persists
in the adult as the calycoblasts of v. Heider.

Yon Koch further asserts that the theca results from the
fusion of the bifurcating ends of the septa ; but, though not
venturing to deny this, I would point out that he neither
describes the process nor gives figures to illustrate it ; whereas,
on the other hand, we have the direct evidence of L. Duthiers
to the effect that the theca and septa arise independently of
each other (“ les septa et la muraille ne sont pas unis ”), and
a figure which appears to bear out his statement. It must,
however, be borne in mind that Lacaze Duthiers may have
described as theca what v. Koch terms epitheca, a secretion of
the lower portion of the lateral endoderm of the embryo which
fuses with the periphery of the original basal disc, and ulti-
mately combines also with what he terms the true theca formed
as above mentioned, to become the outer wall of the corallum.
Were this the case, however, the costae could not be, as he
l’egards them, the peripheral ends of the septa. But the
question can only be finally settled by a study of the embryonic
development of widely different forms.

Professor Moseley (10) has published a preliminary note on
Seriatopora and Pocillopora. These forms were originally
classed with the Tabulata, but his account of their anatomy
brings them into close connection with the other Madreporaria
at present described. The polyps of Seriatopora are oval in out-
line, with twelve short tentacles, which in complete retraction
are covered over by the indrawn margins of the disc, a condition
common in Actiniaria, but very rare in Madreporaria. There
are twelve mesenteries, only two of which, the same two in
every polyp, are enormously long and bear mesenterial filaments
and generative organs. The elongation of this pair of mesen-
teries deep into the colony suggests an inevitable comparison
with the Alcyonaria ; and the similarity is strengthened by the
marked orientation of the polyp, for a division into “dorsal”

584

G. HERBERT FOWLER.

and “ventral” halves is clearly distinguishable in both soft
tissues and corallum. Two of the septa are very rudimentary,
and both this fact and the absence of mesenterial filaments on
ten of the mesenteries would seem to indicate a degeneration,
of which I hope to bring forward a second instance in a future
paper. Between the polyps runs a similar canal system to
that already described by v. Koch in Stylophora. The anatomy
of Pocillopora, so far as mentioned, appears to agree in all
respects with that of Seriatopora, and the polyps exhibit the
same marked orientation.

Moseley (11) has also described the macroscopic anatomy
of three other Madreporarian polyps. His observations on
Flabellum are mostly incorporated with my own below, and
need not therefore be recapitulated here; and of Stephano-
phyllia I hope to give a detailed description in a future
paper.

Of Bathyactis, which is planoconvex in shape, the plane
being the basal surface, he records that on decalcification a
lamina of ectoderm and mesoderm separates off from the base.
This fact, together with its shape, suggests that the original
basal ectoderm of the embryo persists in this species through-
out life, in its primitive position, except for such part as grows
up with the skeleton (the calycoblasts).

To sum up the undoubted facts elucidated by these observers :

1. The adult Madreporarian polyp is built distinctly on the
Actinian type, except for the absence of an external body-
wall in some cases (Caryophyllia, Cladocora), which is then
replaced physiologically by the imperforate theca.

2. The corallum is a product of the ectoderm, and deposited
outside the embryo.

3. This ectoderm persists in the adult as the layer of
calycoblasts, to which the continual growth of the corallum
is attributable; thus the skeleton is morphologically ex-
ternal to the polyp throughout life.

4. Between this layer and the cavity of the coelenteron, and
clothing every part of the skeleton, is a layer of mesoderm and
endoderm, forming the internal body wall.

THE ANATOMY OF THE MADREPORARIA.

585

5. Septa, when present, always lie between a pair of mesen-
teries (entosepta), sometimes also in the spaces intermediate
between pairs of mesenteries (exosepta).

6. Tentacles may be exocoelic as well as entocoelic, but
exosepta may be present without corresponding tentacles.

The present classification of the Madreporaria is admittedly
unscientific. I have therefore laid stress on what may perhaps
seem the trivial point of the relations of septa and tentacles
to the mesenterial spaces, as it is probable that, since the
morphological differences of the whole group of Zoantharia
hexacoralla are very slight, such structural variations might
be useful for a new classification; which, if based upon the
relations of polyp to skeleton, will be on a far sounder
foundation than the present one, which rests upon the skeleton
alone.

Flabellum patagonichum (Moseley).

This is an imperforate Madreporarian, belonging to the
family Turbinolidm. As Moseley (11) has given a full descrip-
of the specific characters of the corallum in his “ Challenger ”
Report (to which reference should be made for figures of the
complete calyx), only a few of them will be mentioned here.

i. The corallum is solitary and conical, the apex of the
cone forming a pedicle by which the polyp is attached when
young; in the adult the pedicle becomes obliterated, and the
coral free (vide figs. 2, 3, Pe.). The outline of the mouth of
the calyx is oval (fig. 1). There are four orders of septa, all of
which are entocoelic ; six of the first order, which meet in an
elementary form of columella; six of the second, which are
nearly as long as the primary septa; twelve of the third, and
twenty-four of the fourth order. In some specimens the full
number is not developed. The corallum is about 2 cm. high
in a well-grown specimen; and the longer axis of the calyx
mouth about 2£ cm., the shorter axis 2 cm. in length.

Along the lines which correspond on the exterior surface of
the theca with the attachments of the septa on the interior, are
shallow but distinct grooves running from lip of calyx to tip of

586

G. HERBERT FOWLER.

pedicle, each corresponding exactly in position with a septum.
These do not agree with von Koch's views as to the origin of the
theca from fusion of the septa ; to accord with which costae
should be developed in this position, such as occur in many
forms.

The whole of the exterior surface of the theca shows well-
marked lines of growth (tig. 4), so arranged as to appear to
indicate that the chief centres of activity for the secretion of
coral lie in the septa. Hence the lip of the calyx is slightly
dentate (figs. 3, 4).

While the upper fourth of the external surface of the theca is,
like the whole of the interior of the calyx, glistening, white and
hard, the lower three fourths are soft in texture and brownish.
This latter portion was described by Moseley as a “ light-brown
epitheca.” But on decalcification the brown substance falls off
as soft flakes, which, by means of sections, are found to consist
of dead tissues and algal (?) parasites. There is really no
epitheca present, recognisable as such in the adult.

The columella (fig. 3, col.) is incomplete, the septa not
always meeting regularly along their free edges.

In the retracted condition of the polyp there is no tissue
external to the corallum (figs. 1, 2), nothing corresponding to
the condition described by Heider in Cladocora and by Koch
in Caryophyllia. When expanded, however, the soft tissues
almost certainly stretch outwards and downwards over the
upper fourth of the exterior of the theca, which is thus kept
white and hard, as mentioned above. Were the polyp thus
completely expanded to be plunged into a killing fluid, the
same appearances would ensue as the above-named observers
have described.

ii. Anatomy. — This agrees in all essential details with the
Actmian type, except in the absence of an external body wall,
the whole polyp being enclosed in the corallum (figs. 1, 2).
Moseley mentions that in some specimens tissues external to
the theca were observed round the lip, and figures them (11),
pi. xvi, fig. 10, as consisting of ectoderm and mesoderm, but
had not the means of studying them by sections. None of my

THE ANATOMY OF THE MADREPORARIA.

587

specimens had any trace of such, and from observations on
Desmophvllum, a closely allied form, I imagine that these
tissues were simply due to the expansion of the polyp, and
contained a continuation of the ccelenteron such as was
described by v. Heider in Cladocora. On decalcification the
polyp appears conical, and divided into a series of wedges by
the spaces where the septa had been. At the base of the
polyp, i.e. the apex of the cone, these wedges appear to be
connected together by little bridges of tissue; these latter are
of no morphological importance, being due apparently merely
to the incompleteness of the columella, and their arrangement
varies in different specimens. The polyp consists of a mouth-
disc, bearing tentacles : a stomodseum, which opens into the
ccelenteron, the latter being periaxially divided into exocoeles
and entocoeles by the mesenteries.

The mouth-disc (fig. 2, md) is peripherally fastened to
the extreme edge of the lip of the calyx, and is centrally
invaginated into the typical Anthozoan stomodseum.

On the disc are borne the tentacles, which are simple
hollow evaginations of the entocoeles, i.e. one is placed over
each septum. They are covered by small prominences, each
of which is a “ battery ” of nematocysts. I have not been able
to determine whether they possess an opening at the tip or not.
They vary in size and position according to the order to which
they belong, the primary tentacles being the largest and the
nearest to the mouth. ( Vide Moseley (11), pi. xvi, fig. 12.)

The mouth is oval in outline, and at each end of its long
axis is in most cases a well-marked gonidial groove.

Through the periphery of the mouth-disc protrude the
acontia. I have by a fortunate section been able to satisfy
myself that they are ejected through definite openings, not by
rupture of the disc ; these are therefore directly comparable to
the cinclides of Actiniae.

A mesentery of the first order is drawn in fig. 5 to show
the general trend of the muscles, though they are much more
numerous than there represented. They are best seen by
mounting the mesentery whole in glycerine.

588

G. HERBERT FOWLER.

In the arrangement of the longitudinal muscles on the
inner (entocoelic) faces of the mesentery Flabellum agrees with
Actinia; these are the retractors of the polyp. On the outer
(exoccelic) faces are ranged the protractors, oblique in direc-
tion ; these differ slightly in the species, being confined in FI.
alabastrum to the upper third of the mesentery, while the
longitudinal fibres extend for its whole length. Both sets of
fibres are continued into the tentacles ; the oblique muscles of
the mesentery becoming their external longitudinal coat, the
longitudinal muscles of the mesentery passing into the internal
and approximating circular fibres of the tentacle. This
apparent change of direction will be understood by fig. 5.

The two pairs of “ directive mesenteries ” at the ends of the
longer axis of the mouth appear to possess the same general
direction of the muscle-fibres, though bearing them on reverse
faces; but the oblique protractor muscles (in this case ento-
coelic) are, proportionately to the retractors, somewhat more
strongly developed, implying perhaps that the expansion of the
polyp is their especial function.

There are no perforations through the mesenteries, such as
are described in Actiniae, putting the chambers in communi-
cation.

Both the primary and secondary orders of mesenteries are
attached to the stomodaeum for its whole length ; the tertiaries
are attached to the mouth-disc, but, as the latter passes imper-
ceptibly into the stomodaeum, no importance is to be attached
to this.

What Moseley (11) has termed “the contorted mesenterial
filaments,” a mass of coils lying on the side of the mesenteries,
appear to me after careful investigation to be, in part at least,
organs corresponding to the acontia of Actiniae, namely, long
lamellar offsets of the free edge of the mesentery, with one
edge thickened to correspond to the mesenterial filament, and
charged with very large nematocysts. They protrude in some
instances, as above stated, through definite openings in the
mouth-disc. Their exact origin from, and relation to, the
mesenteries I have not been able to detect owing to the brittle

THE ANATOMY OF THE MADREPORARIA.

589

condition of the specimens, which did not allow of their being
dissected out.

The ova are developed on all three orders of mesenteries ; as
their origin and position does not appear to differ from the
type described by the brothers Hertwig for Actinia, no figures
are given. I have not seen the testes, hence Flabellum may
be regarded as dioecious. The filament is present along the
whole course of the free edge of the mesentery, including that
region in which ova are developed. The latter is mostly below
the part which is characterised by great contortion of the free
edge and by (?) the giving off of acontia.

iii. Histology. — The ectoderm of the mouth-disc (fig. 6)
is characterised by deeply- staining, very numerous nuclei; and
has distinctly the appearance of a secreting layer. It probably
produces a similar secretion to the slime poured forth in
quantities by an irritated Actinia.

This figure (which is a section along the line a, fig. 2) is
taken from a well-grown polyp, and shows traces of the
originally basal ectoderm which secretes the corallum (the
calycoblasts of v. Heider) {ch., fig. 6). In a younger and
actively growing polyp these are much more definitely marked
( ch ., fig. 7). The nuclei lie in a gelatinous-looking matrix,
which stains slightly with borax carmine, but in which no cell
outlines are distinguishable. In the calycoblast layer sur-
rounding the septum, at the same height and in the same
polyp, the nuclei are much rarer {ch., fig. 8).

The characters of the ectoderm alter considerably on the
tentacles; as above mentioned, it is on them raised into
a series of knobs, each of which is a “ battery ” of nemato-
cysts. A transverse section through the wall of a tentacle is
shown in fig. 9, and exhibits the structure of a battery ; the
nematocysts are confined to the peripheral part, and behind
them lie a very large number of nuclei, probably instrumental,
as was first suggested by v. Heider, in the formation of the
cells which replace the ejected nematocysts. On the peripheral
face of the mesoderm-lamella lie longitudinal muscle-fibres

590

a. HERBERT FOWLER.

continuous with the transverse fibres of the mesentery ; on the
central face oblique fibres.

The stomodseal ectoderm is not essentially different from
that of the mouth-disc ; and, though there are well-marked
gonidial grooves (food grooves, Mundwinkelfurchen), they
show no differentiation of ectoderm comparable to that of
Alcyonarians (the “ siphonoglyphe ” of Hickson).

The whole of the coelenteron is lined by endoderm of
cubical or columnar cells ; generally it is only one cell deep,
and in the living animal presumably ciliated throughout. At
the point where it passes into the thickening known as the
mesenterial filament (if that be indeed endodermal in
origin) its characters change, and the number of nuclei
increases enormously, together with the length of the cells.
Its histological appearance entirely bears out what physio-
logical investigation has also shown for the similar filament in
Actiniae, that it is secretory in character, producing a prote-
olytic fluid (fig. 10).

Nematocysts do not occur apparently in the true mesen-
terial filament, but oulv on that portion of it which is con-
tinued on to the contorted lamellae, which I regard, in part at
least, as equivalent to the acontia of Actiniae. Those occurring
on the tentacles are of a different size and shape from those
which characterise the acontial filament, though in the latter
both forms are found. The smaller, occurring on the tentacles,
is '06 mm. x '01 mm. ; the larger, which is only to be found
on the acontial filament, is -1 mm. x '025 mm. The thread
of the latter form is covered with minute barbs, which give it,
when coiled up in the capsule, a granular appearance.

Rhodopsammia Parallela (Semper.)

This form, belonging to the family Eupsammidae, affords a
very good example of a perforate Madreporarian. Budding
sparsely, it forms no coenenchyme, so that the polyp can be
studied easily and without the complications incident to coenen-
chymatous species.

i. Of the Corallum the systematic characters have been

THE ANATOMY OF THE MADHEPORARIA.

591

already described by Semper (12), but certain corrections are
to be made in his account relative to the arrangements of the
septa. Beautiful figures of the colony will be found in his
paper, which contains much valuable and curious information
about the group Madreporaria.

The corallum of a polyp is about 30 cm. in height ; the calyx,
which is as usual oval in outline, measures about 18 mm. in
the longer axis, and 9 — 13 mm. in the shorter. Fresh polyps
may be budded off from the side, or, more rarely, from the
calyx.

The theca has the porous appearance characteristic of the
Perforata, and is marked on the external surface by distinct
spinous costae, or ridges; each of which corresponds exter-
nally to the attachment of a septum on the interior surface of
the theca (fig. 14).

Both exosepta and entosepta occur in this form. Of true,
i.e. entocoelic septa, there are only three orders, with occa-
sional traces of a fourth ; from the sides of each primary and
secondary entoseptum grows out au exoseptum (fig. 14), and
the relations of these two classes to each other are rather
complicated. Such a system as a — a in fig. 22, shows, in a
transverse section taken high up in the polyp, the arrangement
diagrammatised in fig. 19, consisting of five true entosepta
(each of which lies between a pair of mesenteries), and four
exosepta alternating with them. In a lower section (fig. 20),
the two exosepta which grow out from the sides of adjacent
primary and secondary entosepta, fuse over and with the inter-
mediate tertiary septum into one. Lower yet (fig. 21), the two
compound septa thus produced in each system meet over and
with the secondary septum ; so that the columella is due to
the irregular fusion (fig. 15) of twelve primary entosepta,
distinct for their whole length, and twelve other septa thus
elaborately compounded.

ii. Anatomy. — In Rhodopsammia, which, like all the other
forms as yet described, bears a close resemblance to an Actinia,
the mouth-disc, unlike the case in Flabellum, passes into a dis-
tinct external body wall of ectoderm, mesoderm, and endo-

592

G. HERBERT FOWLER.

derm (extending in some specimens very much further down than
is represented in the diagram, fig. 13). Between this and the
theca lies a narrow space, in which run, parallel to the long
axis of the corallum, lamellae of tissue, connected on the one
hand with this external body wall, on tbe other with the tissues
clothing the exterior surface of the theca (figs. 13, 14, 17, M.')
These lamellae correspond externally to the attachments of the
mesenteries on the interior surface of the theca, and are appa-
rently continuous with them over the lip of the calyx (fig. 13).
They thus divide the space between body-wall and theca into a
series of long chambers, corresponding to the exocceles and ento-
coeles, in each of which lies a costa. Between these chambers
and the exocoeles and entocoeles, a system of ramifying canals
permeates the theca, placing the two sets of cavities in com-
munication with one another. The columella is perforated by
a similar system of canals which unites the whole circle of
entocoeles and exocoeles ; there is thus free communication
throughout the whole of the polyp, despite the comparative
preponderance of skeleton over soft tissue. The canals are
composed of endoderm and mesoderm, continuous with the
same layers that clothe all the rest of the skeleton ; and in the
meshes of the network lies the corallum, theca, or columella.

The polyp thus consists of an external body wall, mouth-
disc with tentacles, stomodseum, and mesenteries ; with a
coelenteron divisible into columellar canal-system, exocoeles,
entocoeles, thecal canal-system, and chambers exterior to the
theca, corresponding to, and continuous over the lip with, the
mesenterial chambers.

The body wall and mouth-disc are composed of simple ecto-
derm, endoderm, and mesoderm, agreeing with those of other
Hexactinise.

The outline of the stomodseum is oval as usual, but I have
not observed any trace of gonidial grooves at the ends of the
longer axis.

The tentacles, which are simple evaginations, appear to be
entocoelic only ; they are so invaginated into pockets on each
side of the septum that it is impossible to make out their

THE AN ATOM'S OF THE HADREPORAR1A.

593

exact size and shape. This condition is probably due merely
to alcoholic contraction, and does not imply that involution is
the normal method of tentacular contraction. A similar
invagination had taken place at the bases of the tentacles of
Flabellum. They are covered with nematocysts, which are not
so sharply defined into batteries as was the case in Flabellum.

At a varying depth below the lip of the calyx (but generally
at a lower point than is represented in fig. 13, which is consi-
derably shortened in the longer axis) the external body wall
perishes, owing probably to the various parasites that infest the
external surface of most coral thecae and polyps; notably a
sponge, which in some places eats its way right into the theca.
The cavity marked / in fig. 15 is thus filled with sponge
spicules. Below the point at which the body wall ends, is
visible in some places a thin line of tissue indicated in fig. 15, g,
which may or may not be a part of the polyp. The appearance
of the periphery of the theca in such a section suggests very
strongly that a secondary line of corallum has been deposited
round the circumference to protect the canals from direct
communication with the sea water and against the parasites.
At the top of fig. 15 the semicircular outline of the canals
seems to indicate such a formation.

The mesenteries vary in number, and are, like the entosepta,
generally of three orders. They are divisible into “ pairs ” as
in the other forms described, and possess the same arrangement
of longitudinal retractor muscles on their entocoelic faces, with
the usual difference in the two directive pairs. The trend of
these muscles is roughly indicated in fig. 13 ; but their minute-
ness renders it impossible to recognise the arrangement of the
protractor muscles, though they are just visible in microscopic
sections. There appears to be but little contortion of the free
edge of the mesentery ; and the traces of any organs resembling
acontia are rare. This, however, may be due to deficiency of
material, which has much hampered my investigation of this
form.

Both primary and secondary mesenteries appear to be united
to the stomodseum for its whole length ; those of the third

594

G. BERBERT FOWLER.

order become disconnected very high up, and do not run dee p
down into the colony, the cavities in which they lie disappearing
among the other perforations of the theca.

The number of pairs of mesenteries right and left of the
“ directives ” is not necessarily equal. Complete systems, both
of mesenteries and septa (i, 3, 2, 3, 1, in notation), are
generally found only at the ends of the long axis of the calyx,
i.e. in the neighbourhood of the directives. This has been
noticed in many other corals.

That the almost exact correspondence of costae with septa,
and of the external lamellae (AT in the figures) with the
mesenteries, adds to the probability of the correctness of
v. Koch’s view, is undeniable. But it is to be noted, that no
muscles are to be recognised on the mesoderm plates of these
lamellae, as would probably be the case had they once been part
of the mesenteries ; nor in the highest sections of the decalci-
fied polyp are any cases of decaying tissue visible, where the
growiRg theca is supposed to have cut them.

iii. Histology. — This is of such a simple chai’acter as to
hardly require comment. The ectoderm is composed of simple
columnar cells, the endoderm of similar but more cubical cells.
Calycoblasts are present, but in small numbers in comparison
with Flabellum. Nematocysts are of two forms and sizes, of
which, as in Flabellum, the smaller is the only one occurring
on the tentacles. Of the mesenterial filament, as unusual in
outline, a sketch is given in fig. 16.

In conclusion, I have to acknowledge my obligations to
Professor Moseley for much kind assistance and most of my
material; to Professor Milnes Marshall for valuable advice;
to Mr. John Murray, of the “ Challenger ” office, for several
specimens of Flabellum ; and lastly, to the anonymous donor
of the Berkeley Fellowship, whose generosity has enabled me
to pursue the investigation.

THE ANATOMY OF THE MADREPORARIA.

595

Classification of the Zoantharia (Hexacoralla).

1. Actiniaria (Malacodermata).

i. Hexactinise .

ii. Edwardsiae.

iii. Zoantheae.

iv. Ceriantheae.

2. Madreporaria (Scleroderiuata).

A. Imperforata (Aporosa).

i. Turbinolidae

ii. Oculinidae .

iii. Pocilloporidae

iv. Astreidae

B. Fungida.

i. Fungidae

C. Perforata.

i. Eupsammidae

Actinia.

Flabellum.

Caryophyllia.

Stylophora.

Focillopora.

Seriatopora.

Cladocora.

Bathyactis.

Stephanophyllia.

Rhodopsammia.

Literature of the Group.

1. Lacaze Duthiers. — “ Developpement des Coralliaires,” ‘Arch. Zool.

exp. et gen./ tome ii, 1873.

2. Lacaze Duthiers. — “Developpement des Coralliaires,” ‘Arch. Zool.

exp. et gen.,’ tome i, 1872.

3. 0. u. R. Hertwig. — “Die Actinien.” Jena, 1879.

4. von Koch. — “ Bemerk. ii. d. Skelett d. Korallen,” ‘ Morph. Jahrb.,’

Band v, 1879.

5. Moseley. — “ Remarks on some Corals,” ‘ Proc. Zool. Soc.,’ 1880.

6. v. Koch. — ■“ Notizen ii. Korallen,” ‘ Morph. Jahrb.,’ Bd. vi, 1880.

7. v. Koch. — “ Mitth. ii. Colenteraten,” ‘ Jen. Zeitschr.,’ Bd. xi.

8. v. Heider. — “Die Gattung Cladocora,” ‘Sitz. d. k. Akad. Wiss.,’ 1881.

9. v. Koch. — “ Entwick. d. Kalkskeletes v. Astroides caly cularis,”

‘ Mitth. d. Zool. Sta. Neap.,’ Bd. iii.

10. Moseley. — “ Seriatopora, Pocillopora, &c.,” ‘ Quart. Journ. Micr. Sci.,’

October, 1882.

11. Moseley. — ‘ Rept. Voyage H.M.S. “Challenger,”’ vol. ii.

12. Semper. — “ Generationswechsel bei Steinkorallen,” ‘ Zeitschr. f. wiss.

Zool ,’ Bd. xxii.

v. Koch. — “ Die Morphologische Bedeutung d. Korallenskelets,” * Biol.
Centralblatt.,’ Bd. ii.

v. Koch. — “Mitth. ii. d. Kalkskelet d. Madreporaria,” ‘Morph. Jahrb.,’
Bd. viii.

596

G. HERBERT FOWLER.

DESCRIPTION OF PLATES XL, XLI, and XLII,

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

b. w. Cut edge of internal body-wall. ch. Calycoblast layer. Cal. Ccelen-
teron. C. or Col. Columella. Cos. Costa. D. “ Directive 55 septum and
mesenteries. Ed. Ectoderm. En. Endoderm. En. S. Entoseptum. Ex. S.
Exoseptum. M. or Mes. Mesentery. M'. “Peripheral” part of mesentery.
M. D. Mouth-disc. Me. Mesoderm. Me'. Mesenterial muscles. M. F. Me-
senterial filament, m. long. Longitudinal muscles, m. obi. Oblique muscles.
n. Nematocyst. Pe. Pedicle. S. Septum. St. Stonodseum. Te. Tentacle.
Th. Theca.

Fig. 1. — Section through two quarters of Flabellum, diagrammatic, the right
alf showing the primary and secondary mesenteries attached to the stomo-
dseum, taken along the line b, Fig. 2, the left being lower down in the polyp,
where the mesenteries have all developed filaments, taken along the line c,
Fig. 2. A. Exoccele. B. Entoccele. i, ii, iii. Orders of septa and mesen-
teries. Corallum coloured deep black throughout the figures.

Fig. 2. — Diagrammatic section along the line a , Fig. 1, i. e. in an exocoele,
so that the external face of the mesentery is seen flat, while the mouth-disc
and internal body-wall are cut. The contortions of the free edge of the
mesentery are omitted.

Fig. 3. — View of half of the corallum of Flabellum, showing the relations
of pedicle, theca, and septa, and the incomplete union of the septa marked x,
in Fig. 1 into a columella.

Fig. 4. — Portion of the lip of the calyx of Flabellum, viewed from the
exterior by transmitted light, to show the grooves, i, ii, iii, corresponding to
the septa of those orders, with the lines of growth of the theca curving
upwards at those points.

Fig. 5. — Primary mesentery and base of primary tentacle of Flabellum,
showing the direction of the muscles, contortions of the free edge omitted.

Fig. 6. — Section along the line a. Fig. 2, from a full-grown specimen, with
the layer of calycoblasts between mesoderm and theca.

Fig. 7. — Similar section through the internal body-wall of a younger polyp,
in which the calycoblasts are much better marked.

Fig. 8. — Section through the tissues clothing the septum of a young
Flabellum.

Fig. 9. — Section through the wall of a tentacle, including one complete
“ battery.”

Fig. 10. — Section through a mesenterial filament of Flabellum.

THE ANATOMY OF THE MADREPOKAR1A.

597

Fig. 11. — Transverse section through part of a mesentery, to show the
mesodermal pleatings on which lie the muscles.

Fig. 12. — Transverse section of an acontium of Flabellum.

Fig. a. Transverse diagrammatic section of Caryophyllia (after v. Koch) .
a. Septa, b. Mesenteries.

Fig. b. Similar section through Caryophyllia, in a lower plane than a
(after v. Koch), a. Septa, b'. Central, b". Peripheral parts of the
mesentery, c. Costae, th. Theca.

Fig. 13. — Diagram of a longitudinal section of Rhodopsammia, considerably
shortened in the longer axis ; the right half of the figure taken along the
lines c. c. in Figs. 14 and 15, i. e. in an exoccele ; the left along the lines d. d.
in the same figures, and therefore cutting through a septum and a tentacle.
c. Cut edge of external body-wall. d. Cut edge of tissues clothing theca and
columella. B. Tissue clothing the entoseptum, which is seen projecting from
behind the mesentery. On the left side the inner face of a mesentery (m)
is seen similarly projecting from behind the septum. The costae being in this
form rows of spines, appear as projections in both transverse (Fig. 14) a
longitudinal (Fig. 13) sections.

Fig. 14. — Transverse section of half of the calyx of Rhodopsammia, along
the plane a. Fig. 13 (camera drawing). The numerals 1, 2, 3 are placed in
the entocceles formed by a pair of mesenteries of those orders. Complete
systems, 1, 3, 2, 3, 1, are only found in the region of the directives. The
dashed numerals, 1', 2', 3', are placed in the external chambers which corre-
spond to the entocoeles. ext. b. w. External body-wall. Corallum deep black,
soft tissues in lighter black lines.

Fig. 15. — Similar section along the plane b, Fig. 13. The septa have fused
into the columella, and are numbered 1, 2, 3, according to their orders.
/. Cavity filled with sponge spicules, y. Line of tissue which may belong to
the polyp.

Fig. 16. — Mesenterial filament of Rhodopsammia in transverse section.

Fig. 17. — Fart of Fig. 14, enlarged to show the relations of the three
body-layers. Mesoderm black, corallum grey. c. Thecal canal system in
transverse section. c\ External chambers, corresponding to exocceles and
entocceles, in each of which lies a costa.

Fig. 18. — Part of the thecal canal system of Rhodopsammia, after removal
of the corallum by decalcification.

Figs. 19, 20, and 21.— Diagrams of the relations of a complete system of
septa of Rhodopsammia at different heights. The numerals are placed at the
bases of the entosepta.

Fig. 22. — Calyx of Rhodopsammia, viewed from above. From a specimen
in the British Museum.

Q Q

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INDEX TO

JOURNAL.

VOL. XXV, NEW SERIES.

Amphipoda, urinary organs of, by
Baldwin Spencer, 183

Apus, nervous system of, by Pelseneer,
433

Archerina Boltoni, a Protozoon
allied to Vampyrella, by Lankester,
61

Atyephira compressa, develop-
ment of, by Ishikawa, 391

I

Balanoglossus, development of, by
Bateson, Supplement, 81

Bateson on the development of Bala-
noglossus, Supplement, 81

Blood of Invertebrates, Mac Munn on,
469

Bourne on the supposed communi-
cation of the vascular system of
Pleurobranchus with the exterior,
429

Bower, correction as to Welwitschia,
105

„ on the apex of the root in
Osmunda and Todea, 75

Brook on the hypoblast of Teleosteans,
29

Brown, Herbert H., on spermato-
genesis in the rat, 343

Caldwell on blastopore, mesoderm, and
metameric segmentation, 15

Carpenter on Echinoderm morpho-
logy, Supplement, 139

Chitin in Limulus and Sepia, by Hal-
liburton, 173

Chitonidse, eyes in the shells of, by
Moseley, 37

Clione, cephalic appendages of, 491

Coxal gland of Limulus, a nephri-
dium, by Gulland, 511

Cunningham on the significance of
Kupffer’s vesicle, 1

Ecchinoderm morphology, No. IX,
by Carpenter, Supplement, 139

Eye and optic tract of insects, by
Hickson, 215

Eyes of Chitonidse, by Moseley, 37

Fowler on the anatomy of Madre-
poraria, 577

Gulland on the coxal gland of Limulus,
511

Halicryptus, skin and nervous system
of, by Scharff, 193

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