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CONTENTS OF No. 189, N.S., JULY, 1904.
MEMOIRS:
On the Branchial Vessels of Sternaspis. By Epwry S. Goopricu,
M.A., Fellow of Merton College, Oxford. (With Plates 1 and 2)
The Middle Har and Columella of Birds. By Grorrrey Smiru,
New College, Oxford ; F ; :
Notes on Rhabdopleura Neanane Allman. By G. Herpert
Fow ter, B.A., Ph.D., F.Z.8., F.L.S. (With Plate 3) .
Some Observations on the Awatomy and Affinities of the Trochide.
By W. B. Ranpuzs, B.Se.(Lond.) (From the Zoological Labora-
tory, Royal College of Science, London. (With Plates“4—6)
The Anatomy of Peecilochetus, Claparéde. By E. J. Attn, D.Sc.,
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Association. (With Plates 712 and one Figure in the Text) .
Notes on Sporozoa. By H. M. Woopcock, B.Se.(Lond.). I. On
Klossiella muris gen. et spec. nov., Smith and Johnson, 1902
CONTENTS OF No. 190, N.S., SEPTEMBER, 1904.
MEMOIRS :
The Structure and Classification of the Arachnida. By H. Ray
Lankester, M.A., LL.D., F.R.S., Director of the Natural His-
tory Departments of the British Museum
On some New Species of the Genus Phreodrilus. By W. Braxtanp
Benuam, D.Se.(Lond.), M.A.(Oxon.), F.Z.S., Professor of
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On a New Species of the Gane Haplotaxie: with some Remarks
on the Genital Ducts in the Oligocheta. By W. Braxtanp
Benuam, D.Sc.(Lond.), M.A.(Oxon.), F.Z.S., Professor of Biology
inthe University of Otago, New Zealand. (With Plates‘16—18)
The Gstrous Cycle in the Common Ferret. By Francis H. A.
Marsnatt, D.Sc. (With Plates 19—21)
Two New Forms of Choniostomatide: Copepoda Baraeitie on
Crustacea Malacostraca and Ostracoda. By H. J. Hansen,
D.Sc., F.M.L.S., Copenhagen. (With Plate 22)
PAGER
165
271
lv CONTENTS.
CONTENTS OF No. 191, N.S., NOVEMBER, 1904.
MEMOIRS:
On the Existence of an Anterior Rudimentary Gill in Astacus
fluviatilis, Fabr. By Marcrry Moserry. (With Plates 23
and 24) . : t ; :
On the Development of Flagellated Organisms (Trypanosomes)
from the Spleen Protozdie Parasites of Cachexial Fevers and
Kala-Azar. By Lronarp Rocers, M.D., M.R.C.P., I.M.S.,
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The Epithelial Islets of the Pancreas in Teleostei. By Joun
Rennie, D.Sc., F.R.M.S., Assistant in Zoology, Aberdeen
University. (With Plates 26—28)
Observations on the Maturation and Fertilisation of the Ege of
the Axolotl By J. W. Jenxrysoy, M.A., Assistant to the
Linacre Professor of Comparative Anatomy, Oxford. (With
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Notes on the Anatomy of Gazelletta. By G. Herserr Fow ter,
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On the Maiotie Phase (Reduction Divisions) in Animals and Plants.
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F.R.S., and Dororuy Smove. (With Plates 42 and’43)
On the Behaviour of the Nucleolus in the Spermatogenesis of Peri-
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L. E. Rozryson, A.R.C.S., from the Biological Laboratory,
Royal College of Science, London. (With Plates’44 and'45)
On some Movements and Reactions of Hydra. By Gzrorer
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TitLe, INDEX, AND CONTENTS,
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CONTENTS OF No. 189.—New Series.
MEMOIRS:
PAGE
On the Branchial Vessels of Sternaspis. By Epwin 8. Goopricu,
M.A., Fellow of Merton College, Oxford. (With Plates ] and 2) . a
The Middle Ear and Columella of Birds. By Grorrrey Suiru, B.A.,
New College, Oxford. : ; : : : 2 : eet
Notes on Rhabdopleura Normani, Allman. By G. Herpert Fow rer,
B.A., Pb.D.,-¥.Z.8:; ¥.L.8.. “with Plates); ; : é es
Some Observations on the Anatomy and Affinities of the Trochide.
By W. B. Ranpiuzs, B.Se.(Lond.). (From the Zoological Laboratory,
Royal College of Science, London.) (With Plates 4—6) : i ae
The Anatomy of Peecilochetus, Claparéede. By E. J. Atumn, D.Sc.,
Director of the Plymouth Laboratory of the Marine Biological
Association. (With Plates 7—12 and one Figure in the Text) as
Notes on Sporozoa. By H. M. Woopcock, B.Sc.(Lond.). I. On
Klossiella muris gen. et spec. nov., Smith and Johnson, 1902 . 158
AUG 18 1904
ON THE BRANGHIAL VESSELS OF STERNASPIS.
On the Branchial Vessels of Sternaspis.
By
Edwin 8. Goodrich, M.A.,
lellow of Merton College, Oxford.
With Plates 1 and 2.
Some years ago, when studying the interesting worm
Sternaspis thalassemoides, Otto, at the Zoological Station
at Naples, for the purpose of describing the structure of its
excretory and reproductive organs (2), [ examined the very
remarkable and beautiful vascular apparatus which supplies
the gill filaments at the hind end of the body. Finding that
the branchial organs of Sternaspis did not appear to agree in
the details of their organisation with any of the descriptions
hitherto given, I determined to work out their minute ana-
tomy. But owing to their very small size, to the presence of
a tough cuticle, and to an external layer of sandy particles, it
is very difficult indeed to make out the exact relation of the
various blood-vessels to the gill filaments, either by dissection
or by serial sections. It is, therefore, only after repeated
failures, that it is at last possible for me to present what is, I
believe, a correct account of their structure.
Max Miller mentioned the dorsal branchial vessels of
Sternaspis in 1852, and some years later Claparéde figured
them and briefly described them. Hach blood-vessel, accord-
ing to Claparéde, is ‘faccolé a4 un axe solide, élastique et
eylindrique .... . de consistance cartilagineuse,” which is
said to be surrounded by a “série d’anneaux musculaires”’ (2).
The first detailed account of the blood-supply of the gills is
given in Vejdovsky’s great memoir (5). He describes two
bundles of “ branchial arteries” springing from the dorsal
vou. 48, pAkT 1 —-NEW SERIES. if
2 EDWIN S. GOODRICH.
vessel, and running to the perforated plates on either side of
the anus, through which they reach the gill filaments. The
“artery”? passes up the filament to the tip, where it turns
round to return to the base, and issues as a minute ventral
“vein.” These veins are collected together on each side into
a large lateral branch of the median ventral vessel running
above the nerve-cord. The dorsal ‘arteries’? are dis-
tinguished by the possession of a peculiar “ axis,” formed of
an outer sheath of ring-shaped cells with regularly arranged
nuclei, surrounding an internal “ knorpelartiger elastischer
Strang welcher ..... aus den Zellen zusammengesetzt
erscheint.” The cells of this inner strand are said to corre-
spond to those of the outer sheath, and to have a row of
nuclei. Both blood-vessel and axis are described as sur-
rounded by a common sheath of peritoneal epithelium. The
dorsal vessel is supposed to pump the blood forwards, the
circulation being from the veims to the branchial filaments,
and from these through the arteries to the dorsal vessel. The
ill filament itself Vejdovsky describes as having an outer
layer of epidermis, below which are muscles ; a median longi-
tudinal septum runs down the filament separating two
cavities, lied by epithelium, in which are the artery and vein.
Shortly after the appearance of this work Rietsch published
an elaborate account of the vascular system of Sternaspis (4).
I have been able to confirm most of his excellent description.
Curiously enough neither this author nor Vejdovsky seem to
mention the interesting horizontal septum, formed of a
double layer of coelomic epithelium pierced here and there
with holes (fig. 1, hs), which stretches across the posterior
region of the ccelom from the genital ducts to the rectum.
This septum supports the lateral segmental branches of the
ventral vessel, and incompletely separates the body-cavity
into an upper chamber containing the intestine and gonads,
and a ventral chamber in which project the inner ends of the
cheetee placed round the ventral shield, and the nerve-cord.
Rietsch’s account of the branchial apparatus is less satis-
factory than that of Vejdovsky. According to the former,
ON THE BRANCHIAL VESSELS OF STERNASPIS. 3
the branchial vessels ‘“‘se composent d’un axe conjonctif et
@un vaisseau paralléles et enveloppés dans une gaine com-
mune.’ Further, “axe se compose d’une serie d’anneaux
enveloppant un cylindre fibreux. le dernier est constitué
par des fibres longitudinales munies de noyaux allongés ”
(4). On the whole Rietsch’s interpretation of the structure
of these vessels is very much the same as Vejdovsky’s; but
he believes the ‘‘axis” to be continuous behind with the
epidermis, of which it is considered to be a prolongation.
ce
He is not clear as to the exact relation of the dorsal and
ventral branchial vessels to the filaments. Rietsch, indeed,
is not certain that the ventral vessels enter the gills at all,
and believes that they may only supply the body-wall,
pointing out that they are fewer in number than the dorsal
“arteries.” He denies the contractility of the main dorsal
vessel, and suggests that the blood may be propelled by the
lengthening and shortening of the axis supporting the
“ arteries.’ The gill filament is said by him to contain only
one vessel, and the cavity not to be lined by peritoneum.
In answer to Rietsch, who criticised his work, Vejdovsky
published a second more detailed, but scarcely more correct,
account of these complicated organs (6). Here the branchial
“veins” are accurately described and figured; the “axis”
of the branchial ‘
einer hyalinen, bindegewebigen Substanz .... an dessen
‘arteries’? is said to consist “aus
Wandung in zierlicher Anordnung vielfach verastelte Zellen
gelagert sind,” surrounded by contractile “ Halbringen ”
covered with an outer hyaline sheath of cells with large
nuclei situated in a row.
As already mentioned, according to my own observations,
the structure of the branchial apparatus differs considerably
from that described by these authors.
The slender outer gill filaments, as is well known, are
capable of independent movement, and may be quickly
retracted into a closely coiled spiral (see 4, 5, and 38, fig. 16;
also Pl. 1, fig. 8). Two small blood-vessels run along each
filament, and join at the extreme tip (fig. 2). These vessels
4 EDWIN §. GOODRICH.
have contractile muscular walls (fig. 4). When the filament 1s
fully expanded the vessels are swollen with blood, and in
optical section appear to fill almost the entire cavity of the
gill, being separated from each other by a narrow longitudinal
septum (figs. 2 and 3, s). At other times the vessels may
become emptied ; their walls then contract, so that the lumen
is almost or entirely obliterated. ‘This is the case, as a rule,
in preserved specimens ; and such gill] filaments, when cut in
cross-section, present the appearance described by Vejdovsky
and Rietsch, of possessing two large coelomic cavities separated
by a strong longitudinal septum. It will be understood,
however, that this apparent septum is formed by the collapsed
walls of the blood-vessels, and is therefore at right angles to
the true septum separating the vessels in a distended
condition. Fig. 4 shows these vessels in a half-contracted
state. As for the lining of the cavities on either side, it
appears to be continuous with the celomic epithelium of the
body-cavity, although the cells are often very irregularly
disposed.
Now, when we come to examine the blood-vessels supplied to
the base of the gills, we find that there are not two, but
three running to each filament. The main dorsal vessel
situated on the intestine (fig. 1, dv) gives off behind a short
thick branch, which soon divides into two hmbs. From tlie
right and the left limb come off in regular alternate succes-
sion two rows of offshoots, the dorsal branchial vessels (figs.
1, 7, 8, and 14), These generally expand into two marked
swellings, then narrow down to straight vessels running to
the branchial perforated plates. It is this region of the
“artery”? which is said to be supported by an
“ axis,” and it is just this region which has been strangely
branchial
misunderstood by previous observers.
For the sake of clearness in description we may subdivide
the dorsal branchial vessel into three regions: the first is
generally marked off asa conspicuous swelling, it is the
portion nearest the dorsal vessel; the third is the much longer
and narrower region supported by the “ axis,” and reaching
ON THE BRANCHIAL VESSEL§ OF STERNASPIS. ES)
to the branchial plate, from which the gills arise; and the
second region is the intermediate part, generally swollen, and
differing in structure from the other two.
Taking the third region first (figs. 1, 12, 13 and 14), we
find that it contains a slender blood-vessel with thin walls (figs.
12, 13 and 14, ev). This isthe branchial artery of Vejdovsky
aud Rietsch, which we may call the communicating vessel,
for reasons which will appear later. Its walls are formed,
like those of any other small blood-vessel, of a single layer of
granular cells with ordinary rounded nuclei irregularly dis-
tributed. The communicating vessel is capable of consider-
able distension; but in section it generally appears much
folded, and with a very contracted lumen (fig. 5, cv).
The so-called “axis,” along one side of which this
vessel is closely applied, is in reality a second blood-
vessel with specialised contractile walls. It is in
fact the most important blood-vessel in the whole branchial
circulation. This highly contractile vessel, which may be
called the dorsal branchial vessel, has its walls formed
of a regular series of ring-shaped cells, with their large oval
nuclei situated in a row on the surface opposite to that to
which the communicating vessel is attached (figs.5 and 13, 7).
These nuclei have been well figured by Vejdovsky (6). Inside
the dorsal branchial vessel runs a peculiar rod of tissue, to
which alone the name “ axis”’ should be applied.
This axial rod consists not of longitudinal fibres, as
described by Rietsch, but rather of cartilage-like cells, as
mentioned by Vejdovsky in his first memoir (5). As will be
understood on comparing figs. 12 and 13, it is formed of a
shightly irregular row of cells, with a thick hyaline common
wall turned towards the cavity of the blood-vessel (fig. 15, oa).
The cells are attached to the wall of the vessel, on the same
side as the communicating vessel lying outside, by means of
obliquely placed stalk-like bases. In the living tissue the
cells of the axis are seen to present a peculiar vacuolated
appearance, with a few highly refractive granules (fig. 12).
Lying on the surface of the axis are occasionally seen smal]
6 EDWIN S. GOODRICH.
branching cells, which do not appear to form an essential
part of the rod, but rather to be amceboid blood-ceils creeping
over it, such as are found elsewhere in the blood-vessels
(figs. 12 and 16). I can find no common peritoneal sheath
enclosing the dorsal branchial and the communicating vessels.
The dorsal branchial vessel is capable of undergoing great
expansion and contraction. The ring-cells of which it is
formed consist of an outer more protoplasmic coat and an
inner lining of homogeneous refractive substance. When the
vessel is expanded the inner coat appears quite thin; on the
contrary, as the lumen contracts the lining becomes corre-
spondingly thickened and folded. In transverse section it
then acquires a striated appearance, and is seen to be inter-
rupted along the line where the axis is attached (figs. 5 and
10, ci). The thick, contracted, inner lining forms the “ Hal-
bringen”’ of Vejdovsky, and the “bague chitineuse” of
Rietsch. It is difficult to determine whether during con-
traction the function of the inner lining is purely passive.
The real agency by means of which the powerful contraction
is brought about seems to reside in the superficial network of
protoplasmic threads in the outer layer (fig. 6). ‘his remark-
able meshwork, which stretches across uninterruptedly in the
living tissue from cell to cell, can be seen to undergo
changes, the threads becoming slenderer, and the intervening
spaces larger as the vessel expands.
Pecuhar as the histological structure of the wall of the
dorsal branchial vessel appears to be, it may yet be compared to
that of the small blood-vessels in Oligochzetes so well described
by Bergh (1). Here also we have small contractile vessels
formed of rows of ring-like cells, the walls of which consist
of an inner lining and an outer active protoplasmic net-
work. But in the case of Sternaspis the structure is much
more highly specialised.!
Since this was written, Lang has published lis important work, ‘ Beitrage
zu einer Trophocceltheorie’ (‘ Jen. Zeit.,’ 1903). The dorsal branchial vessel
appears to correspond in structure to his figs. 10 and 18, pl.2. The axial rod
probably develops as a longitudinal fold and ingrowth of the walls of the vessel.
ON 'THE BRANCHIAL VESSELS OF STERNASPIS. fi
The contractile dorsal branchial vessel and its contained
inner axis form a most eflicient apparatus for propelling the
blood forcibly from one end of the vessel to the other as
waves of contraction pass down it. When fully contracted
the lumen is entirely obliterated by the closing of the wall on
to the axial rod (figs. 10 and 15).
Passing down to the base of the gill filament we find that
the two vessels, the dorsal branchial and the communicating
vessel, pass directly into the filament through the pore in the
branchial plate, but that the axial rod reaches only to the level
of the pore, where it disappears, merging into the septum
which separates the two gill vessels.
Following the vessels upwards and forwards towards the
intestine, it is seen that at the beginning of what has been
termed above the second region the axial rod suddenly
diminishes to a thin thread, which runs along the wall of the
dorsal branchial vessel and then gradually expands again into
a second short axial rod similar to that in the posterior third
region (figs. 14 and 15). This short axial piece again thins
out to adelicate strand with a nucleus here and there, which is
continued forwards into the expanded first region of the vessel
attached to its inner surface (figs. 9and 14). Near the place
where the branchial vessel opens by a slightly narrowed neck
into the large limb of the dorsal vessel the fine axial strand
swells again into a large plug of vacuolated tissue. The plug
lies loose in the vessel, kept in place by its posterior attach-
ment, and acts as a valve (figs. 7 and 14).
At the point where the first joins the second region of the
branchial vessel the communicating vessel opens into it by
an aperture protected by a thin flap acting as a valve, so as to
prevent blood passing back into the communicating vessel
when the other contracts.
We have seen, then, that two vessels from the dorsal system
pass to the base of each gill filament.
Now, the fine ventral branchial vessels, veins of Vejdovsky,
also run to the base of the gill filaments. These delicate
capillaries pass in near the skin between the dorsal branches,
8 EDWIN 8S. GOODRICH.
and may subdivide so that one minute vessel goes to each
filament. Since only two vessels are found in each gill
filament, and three can be traced to its base, it becomes an
interesting matter to determine what becomes of the third.
This is the point which I found so difficult to settle.
Whilst it is comparatively easy to follow the dorsal
branchial vessel and its accompanying communicating vessel
to the base of a gill filament, it is very difficult indeed to trace
the course of the ventral capillary vessel. ‘hese blood-
vessels are too minute to inject or to follow for certain by dis-
section. Sections taken through the regions where the
vessels pass through the branchial plate show that as a
matter of fact the communicating vessel joins the ventral
branchial vessel quite near the body-wall to form a single
vessel entering the gill. Figs. 10 and 11 show this com-
munication clearly, whilst the relation of the three sets of
vessels to the gills is represented diagrammatically in fig. 8.
The reason for this peculiar arrangement is not far to seek.
Supposing there existed only a dorsal “ artery ” and a ventral
“vein,” as described by previous authors, it is obvious that
on the retraction of the gill filaments the whole circulation of
the blood would be almost entirely stopped. By means of
the communicating vessel the blood has insuch a case
an alternative path open to it leading from the
main ventral to the main dorsal vessel. A somewhat
similar by-path for the blood is present at the base of the re-
tractile gills of the Urodele amphibians, and serves no doubt
the same purpose.
Concerning the circulation of the blood in the living Ster-
naspis, I feel by no means certain that the direction of the
flow is from the ventral vessel to the dorsal vessel through the
branchial filaments, as held by Vejdovsky and Rietsch. The
disposition of the valves and certain contractions in freshly
dissected specimens lead me to believe that the blood is pro-
pelled along the contractile dorsal branchial vessels from
before backwards. However, this is a subject which requires
further study.
ON THE BRANCHIAL VESSELS OF STERNASPIS. 9
List or REFERENCES.
1. Bercu, R. 8.—“ Beitr. z. vergl. Histologie,’ II, ‘Anat. Hefte,’ vol. xiv,
1900.
2. CLaPAREDE.— Annélides Chetopodes du Golfe de Naple.”
3. Goopricu, HK. S.—‘‘ Notes on the Anatomy of Sternaspis,” ‘Quart. Journ.
Mier. Sci.,’ vol. xl, 1897.
4. Rietscu, M.—“ Etude sur le Sternaspis scutata,” ‘Ann. Sci. Nat.,’
Ge sér., Zool., vol. xiii, 1882.
5. Vespovsky, F.—‘ Unters. tiber die Anatomie, ete., von Sternaspis,”’
‘Denkschr. d. Wien. Akad. Math.-Naturw. Cl.,’ vol. xliii, 1882.
6. Vespovsky, F.—“ Bemerk. z. neueren u. iilteren Literatur tiber Ster-
naspis scutata,” ‘Litz. d. k. Bohm. Gesellsch. d. Wissenshaften ,
1882,
EXPLANATION OF PLATES 1 & 2,
Illustrating Mr. Edwin 8. Goodrich’s paper, “ On the
Branchial Vessels of Sternaspis.”
List of Rererence LErrers.
av, Axial rod. aac. Cell of axial rod. 4/y. Blood-vessel. dre. Branching
cell resting on axial rod. ¢. Ceelomic canal. ecbw. Cut body-wall. ei. Inner
coat. co. Outer coat. cov. Cut wall of ovisac. c/¢. Connecting strands of
tissue. cv. Communicating vessel. dév. Dorsal branchial vessel. dv. Main
dorsal vessel. ep. Epidermis. gf. Gill filament. 4s. Horizontal septum.
zt. Intestine. /db. Limb of dorsal vessel. /uddv. Lumen of dorsal branchial
vessel. 2. Nucleus of ring-shaped cell. za. Nucleus of axial rod-cell.
ac. Nerve-cord. ze¢. Protoplasmice contractile network. oa. Outer hyaline
layer of axial rod. oc. Outer layer of cuticle. ovd. Oviduct. p. Point at
which the communicating vessel joins the dorsal branchial vessel. 7, Rectum.
s. Septum. sd. Supporting band of tissue. séc. Stalk of the axial rod-cell.
th. Restraining thread of valvular plug. vv. Ventral branchial vessel. of.
Valvular fold. vp. Valvular plug. vv. Main ventral vessel.
PLATE i
Fie. 1.—Enlarged view of a dissection of the hinder region of a female
Sternaspis, seen from above. Portions of the ovisac, of the rectum, and of
vou. 48, part 1.—NEW SERIES, 2
10 EDWIN S. GOODRICH.
the intestine have been left, but pushed aside to expose the horizontal septum
and ventral vessel.
Fie. 2.—Tip of an expanded branchial filament, enlarged. Fresh.
Fic. 3.—Optical section of an expanded gill filament, enlarged. Fresh.
Fic. 4.—'l'ransverse section of a gill filament in which the blood-vessels are
partialiy contracted. Cam. Z. D, oc. 3.
Fic. 5.—Transverse section of the posterior region of a dorsal branchial
vessel, in a semi-contracted condition. Cam. Z. D, oc. 3.
Fie. 6.—Enlarged view of the outer surface of an expanded anterior portion
of a dorsal branchial vessel, showing the continuous contractile network.
Fresh.
Fic. 7.—Enlarged view of the anterior origin of some of the dorsal branchial
vessels. Fresh.
Fic. 8.—Diagrammatic figure of the branchial circulation. One gill fila-
ment is expanded and the other contracted.
PLATE 2.
Fic. 9.—Enularged view of the region where the communicating vessel opens
into the dorsal branchial vessel, in optical section. Fresh.
Fie. 10.—Section through two dorsal branchial vessels (contracted) and
the accompanying communicating vessels, showing the opening of the latter
into the ventral branchial vessels. Cam. 51; oil imm., oe. 3.
Fie. 11.—Section through the same, taken a little farther forward, where
the ventral branchial vessels have separated off. Cam, 1; oil imm., oe. 3.
Fic. 12.—Optical section through the dorsal branchial vessel and its axial
rod, enlarged. Fresh.
Fie. 13.—Slightly diagrammatic view of the same structures.
Fie. 14.—Eularged view of the anterior half of three dorsal branchial
vessels. Fresh.
Fig. 15.—Enlarged optical section of the region marked with an asterisk in
fig. 14.
Fie. 16.—Enlarged view of two amceboid cells in a blood-vessel.
THE MIDDLE EAR AND COLUMELLA OF BIRDS. 11
The Middle Ear and Columella of Birds.
By
Geofirey Smith, B.A.,
New College, Oxford.
Ir may seem a supererogatory task to add to the pile of
literature which deals with the ear-bone homologies a straight-
forward account of those anatomical and embryological facts
which may be ascertained by the examination of such familiar
types as the fowl and pigeon; but after a painstaking research
into the literature of the Sauropsidan middle ear I have
unwillingly concluded that such a course was desirable.
Although this literature is voluminous there is no single
description of any Sauropsidan type which from a modern
standpoint can be considered at all complete; that is to say,
there is no account which describes in any one type—
1. The development and transformation of the auditory
ossicles from the earliest procartilage stage up-
wards;
2. The relations of the seventh nerve and chorda tympani
to the ossicles at different stages of development.
The words in italics are emphasised because a large part
of the work on this subject fails to be conclusive owing to the
lack of sufficiently early stages of development, and this most
unfortunately is the case in the recent descriptions of
Sphenodon by Howes (14) and Schauinsland (12). Kingsley
(13) gives one isolated procartilage stage in a Lacertilian ;
1 GEOFFREY SMITH.
which serves to prove, at any rate, that these early stages are
absolutely necessary for the interpretation of the later.
The following essay will be divided into three parts :—(1)
anatomical, in which certain new details are described, and
an adequate account of the disposition of the chorda tympani
is given for the first time ; (2) embryological, in which special
attention is paid to the derivation and homology of the stapes
or proximal portion of the columella (an homology which
constitutes the crux of the Sauropsidan middle ear); and
finally (3) a summary with some general conclusions.
I am much indebted to Mr. Jenkinson, Lecturer in Em-
bryology in the University Museum, for his advice and a
great deal of material.
1, ANATOMY.
The Columella (Fig. 1)—Anatomically the columella of
birds is composed of two pieces, an inner ossified piece, the
stapes, apposed to the fenestra ovalis, and an outer cartila-
ginous piece, the extra-columella, united to the stapes proxi-
mally, and attached distally to the tympanic membrane.
There is no real joint between the stapes and extra-columella,
but great flexibility exists between the two, owing to the
phability of the cartilaginous neck which unites them. The
extra-columella may be described as consisting of three
pieces, supra-, extra-, and infra-stapedial, all perfectly
continuous. ‘I'he disposition of these parts is shown in
fig. 1, which represents the left columella of Gallus, viewed
from within the tympanum.
The columella is supplied with a single muscle, the tensor
tympani, which is attached to the infra-stapedial, and
to the edge of the tympanic membrane, between the infra-
and extra-stapedial cartilages. The muscle passes out of the
ear by a large foramen close to the stylo-mastoid foramen,
curls round on to the back of the skull, and is broadly
attached to the basi-occipital bone in a shallow groove which
slopes nearly to the occipital condyle.
THE MIDDLE EAR AND COLUMELILA OF BIRDS. 18
The extra-columella is supplied with one ligament in all
birds, Platner’s ligament, which stretches across the cavity
of the middle ear to the posterior face of the quadrate bone
(Plt., Figs. 1 and 3). In Gallus there are present two
other ligaments attached to the extra- and infra-stapedials
which are in part concentrations of the fibrous constituents
of the tympanic membrane ; I can only find these erroneously
described by Parker (8) as being attached to the quadrate.
In reality they pass beneath the quadrate, are continued
beyond the region of the tympanic membrane into the lining
of the Eustachian tube, and are finally attached to the walls
of the bony Eustachian groove near the point where it
debouches into the mouth (Fig. 2). This is a peculiar dis-
position, not found in other birds that I have examined.
The Seventh Nerve.—tThis nerve has three branches,
which are, counting in order from the root of the nerve
outwards, the sphenopalatine, the chorda tympani, and the
main branch of the seventh. In Gallus the sphenopalatine
and the chorda tympani come off together from the geniculate
ganglion and do not take up any intimate relation to the middle
ear. The chorda tympani, after its origin from the seventh
nerve, runs a little way with it in the Fallopian tube, then
enters a bony canal of its own and so gains the posterior face
of the quadrate. The cross in Fig. 3 shows the approximate
point at which the chorda tympani comes off the seventh nerve
in the fowl. After giving off the chorda the main branch of
the seventh crosses the stapes externally and dorsally to it in
the cancellated bone, and then leaves the skull by the stylo-
mastoid foramen.
In other birds, e.g. Columba, the chorda has a quite
different disposition (ig. 3). It leaves the seventh nerve by
a special foramen in the Fallopian tube just before the seventh
nerve makes its exit from the skull by the stylo-mastoid
foramen ; it then traverses a small piece of cancellated bone
and enters the cavity of the middle ear quite superficially,
viz. between the extra-columella and the tympanic membrane.
It now crosses the extra-columella, keeping this same relation
My
\ { 7 Lilly
ita tet A 202
i"
i =
a
tnt lig
Fic. 1.—Left columella of Gallus from inside tympanic cavity. pit.
Platner’s ligament. eat. Extra-stapedial. eat. lig. Uxtra-stapedial ligament.
inf. Infra-stapedial. inf. lig. Infra-stapedial ligament. sawp. Supra-stapedial.
slap. Siapes. musc. ‘Tensor tympani.
tymp
ewst op
Fig. 2.—Right ear of Gallus. External ear is cut away, and the quadrate
and bony roof of the lower tympanic recess are removed. ¢ymp. Tympanum.
ewt. Wxternal ear lining. eatra coll. Extra-columellar. ew. lig. Extra-stape-
dial ligament. iz/f. dig. Infra-stapedial ligament. muse. Tensor tympani.
car. Carotid. cai. éan. Bony carotid canal. vit. Seventh nerve, ewst. Bony
Eustachian groove. eust. op. Opening of groove into mouth,
4
THE MIDDLE EAR AND COLUMELLA OF BIRDS. 15
to the tympanic membrane, namely lying just internal to it
and external to the extra-columella, save that at the point
where it crosses the neck which unites the supra- and extra-
stapedials it pierces the cartilage superficially.
2s eactr as tap
Fic. 3.—Right ear of Columba. Upper half of tympanic membrane
deflected to show the structures upon its other side. stap. Stapes. supra
stap. Supra-stapedial. eatra stap. Extra-stapedial. p/¢. Platner’s ligament.
vir. Seventh nerve. ch. Chorda tympani. Xx Point at which chorda tympani
comes off in Gallus. ¢ym. Tympanum. gz. Quadrate. For this drawing 1
am much indebted to Mr. Darbishire.
Having traversed the extra-columella, the chorda joins
Platner’s ligament and crosses the tympanic cavity in com-
pany with it, so gaining the posterior face of the quadrate.
This course of the chorda tympani has been confirmed by
means of serial sections in a late embryo of the starling.
The essential difference between the relations of the chorda
16 GEOFFREY SMITH.
tympani in Gallus and in Columba may be seen in the follow-
ing diagram.
I. Columella of Columba; LI, of Gallas, from without. /p. Foot plug.
stap. Stapes. Pit. Platner’s ligament. vit. Seventh nerve. ch. Chorda
tympani. sapra, extra, and infra. Stapedial cartilages.
In these two relations of the chorda tympani to the columella
we see a striking convergence towards the two conditions in
Lacertilia described by Versluys (10). In Lacertilia the
chorda tympani may come off the seventh nerve behind the
columella, and then run forwards, across, and external or
dorsal to the extra-columella, or else it may come off anteriorly
to the columella altogether (e.g. Gecko and those forms
which have no processus internus to the extra-columella).
There can be little doubt that the backward origin is primi-
tive, since Sphenodon shows it, and that the forward origin
in the fowl is secondary, as first suggested by Hasse (2), who
supposed that its forward origin had to do with the peculiar
development of the quadrate articulation in that bird.
2. Empryonoay.
The middle ear cavity is formed from the first gill slit (5).
The earliest stage which is instructive for the purpose in
hand is the five-day-old chick. As yet no chondrification has
taken place, but the hyoid arch and the auditory capsule are
recognisably shown by the thicker aggregation of connective-
THE MIDDLE EAR AND COLUMELLA OF BIRDS. 14
tissue corpuscles in those regions (Fig. 4). The proliferation
of tissue to form the hyoid arch takes place from below
upwards ; this is shown in the figures where the more ventral
portion of the arch (hy.) is thicker than the more dorsal
(stap.), the two portions passing into one another more or
Vil gn
9 marry at aay
o #9 Oe ag 8o86
cron fese meee AN ge
GET Dre)
Pate SL
JUG VEIN
°
:
TAA
50° o
ANTERIOR
CM
CONS
Be
pte Behe 2.8 8
Sugg ee itasat is
iss
Fic, 4.—Longitudinal (slightly horizontal) section through hyoid region
of five-day chick.
less suddenly at the constriction, marked cons., fig. 4. The
seventh nerve crosses the hyoid arch just dorsal to the con-
striction. The hyoid and auditory capsule proliferations are
completely separate, being divided by a space where the
connective-tissue corpuscles are much more thinly scattered,
It is seen in fig, 4 that the dorsal or proximal portion of the
18 - GEOFFREY SMITH.-
hyoid (stap.) has approached quite near to the auditory
capsule, while the latter shows no sign of sending an out-
growth to meet it.
JUG VEIN
JUG VEIN
CONS
HY
2
cae
ae
Poa pie
Fic. 5.—Longitudinal section through six-day chick.
In the six-day-chick the top of the hyoid has fused with
the auditory capsule, both being still in the pro-cartilaginous
condition. This is shown in Figs. 5 and 6. Fig. 5 shows the
seventh nerve crossing the hyoid above the consiriction in
THE MIDDLE EAR AND COLUMELLA OF BIRDS. 19
sensibly the same position as in the five-day-chick. It is
quite clear from Figures 4 and 5 that no considerable out-
growth from the auditory capsule can have taken place to
complete the continuity of hyoid and auditory capsule. There
is no evidence of such an outgrowth, and even if it occurs
between the stages Figs. 4 and 5, the outgrowth can only
AUD CAPS
D005 6°
©9009
ef
Fie. 6.—Ditto; a more median section to show continuity of stapes with
auditory capsule.
Letters used in Figs. 4, 5, and 6:
1. E. Internal ear. aup. caps. Auditory capsule. sap. Stapes. cons.
Constriction in hyoid arch. uy. Hyoid arch. om. Cavity of middle ear.
JuG. VEIN, Jugular vein. vil gn. Geniculate ganglion. vit. Seventh nerve.
Figs. 4, 5, and 6 drawn with camera under Zeiss 4, Aa.
occupy a very small part of the space subsequently occupied
by the stapes, unless we imagine it bodily thrusting the
hyoid arch before it, a process which is not easy to imagine
in ill-defined pro-cartilaginous structures, and for which there
is not the least shadow of evidence.
During the sixth and seventh days of incubation chondrifi-
cation sets in. In the seven-day chick auditory capsule and
hyoid are both perfectly chondrified and perfectly continuous
20 GEOFFREY SMITH.
with one another, the constriction observable in the five-
and six-day chicks having, moreover, disappeared.
In the eight-day chick the stapes is divided off from the
auditory capsule, and the extra-columella is severed from the
extreme distal end of the hyoid arch. This extreme end of
the hyoid arch, which takes no part in the formation of the
extra-columella is excessively small, only running through
a few sections. My series of sections at this stage show the
continuity and homogeneity of the stapes and all parts of the
columella, the ossification of the stapes not occurring until a
later period.
I. Five-day chick. II. Six-day. JI. Seven-day. 1V. Hight-day. All
viewed from without. aud. caps. Auditory capsule. vit. Seventh nerve.
ch. Chorda tympani. cons. Constriction. 47. Branchial blastema. extra
coll. Extra collumella. hy. Hyoid.
It should be plain from this account that the chondrified
stages in the seven- and eight-day chicks, with the descrip-
tion of which previous authors have been content, really tell
us little by themselves; but the previous history of the hyoid
arch in the pro-cartilage condition shows (1) that the whole
of the extra-columella and part, at least, of the stapes are
formed from it; (2) that the derivation of the foot-plug of
the stapes, and perhaps the extreme distal part of the
stapedial rod may be either from hyoid or from auditory
capsule, but from which of the two it is impossible to assert,
since the two elements are already inextricably fused before
chondrification occurs ; without leaving any visible boundary
between them, It would be safe to say that certain cells in
THE MIDDLE EAR AND COLUMELLA OF BIRDS. P|
the foot-plug are derived from the hyoid arch and certain
cells from the auditory capsule. The important fact, how-
ever, clearly expressed in Figs. 4and 5 is that the dorsal part
of the hyoid arch, i. e. the part lying between the seventh nerve
and the auditory capsule (stap. in Figs. 4, 5, and 6), gives
rise to part, at least, of the stapes. The meaning of the
constriction in the five- and six-day chicks must remain
doubtful; it corresponds in position to a division between
hyomandibular and keratohyal, and to the later division
between stapes and extra-columella.
The following diagrammatic reconstructions will make the
foregoing observations clear.
3. CONCLUSION.
The value of the embryological evidence here presented is
partly positive, partly negative.
Positively, it may be stated that in the chick the contribu-
tion of the auditory capsule to the columella is exceedingly
small, probably confined to the foot-plug of the stapes; at
any rate the main part of the stapes and the whole of the
columella is formed from the hyoid arch. Negatively, it
proves the futility of basing arguments upon this question on
isolated stages, or on cartilaginous stages which have not
been traced back to their earliest procartilaginous forerunners.
Taking this into consideration the supposed derivation of the
stapes of Sauropsida from the auditory capsule (9), and the
possible interpretation of Sphenodon in this manner (12 and
14) becomes exceeding doubtful; m birds, at any rate, as we
have seen, the condition confirms the opiniou arrived at on
theoretical grounds by Gaupp (11), that the stapes of Saurop-
sida corresponds to the stapes of Mammalia, and to the hyo-
mandibular of fishes. Mammalia and Sauropsida have this
much in common, that they have both converted the hyomandi-
bular or dorsal portion of the hyoid arch into the stapes ;
but subsequently they have gone on different lines in evolu-
tion, the Sauropsida making use of the more ventral part of
2S GEOFFREY SMITH.
the hyoid to complete their chain of ossicles (extra-columella),
while the Mammalia have pressed into this service the con-
stituents of the arch in front—namely, the quadrate and
articular (incus and malleus).
(Since this article was in type Versluys (15) has published
a most thorough account of the development of the Lacertilian
columella. Iam happy to see that his results are in complete
accord with my own).
a
LITERATURE.
1. Puatner, F.—‘ Bemerkungen iiber das Quadrat-bein und die Pauken-
hohle der Vogel,’ 1839.
2. Hassz, C.—“ Zur Morphologie des Labyrinths der Vogel,” ‘ Anatom.
Studien,’ Bd. i, 1873.
3. Parker, W. K.—*‘ On the Structure and Development of the Skull of
the Common Fowl,” ‘ Phil. Trans. Roy. Soc. Lond.,’ vol. clix, pt. ii, 1869.
4. Huxtey, 'T. H.—* On the Representatives of the Malleus and Incus of
the Mammalia in the other Vertebrata,” ‘ Proc. Zool. Soc. Lond.,’ 1869.
5. Motpennaver, W.— Die Entwicklung des mittleren und des ausseren
Ohres,” ‘Morph. Jahrb.,’ Bd. iii, 1877.
6. Maeninn, L.— Recherches sur l’anatomie comparée de la corde du
tympan des ojseaux,” ‘Comptes Rendus de l’Académie des Sciences,’ t. ci,
1885.
7. Gapvow, H.—‘ Phil. Trans.,’ 1888, vol. clxxix.
8. Gapvow und Sevenka.—* Vogel,” ‘ Bronn’s Klassen und Ordnungen,’
Bd. vi, Abt. 4, 1891.
9. Horrmann, C. K.—* Reptilien,” ‘ Bronn’s Klassen und Ordnungen,’
Bd. vi, Abt. 3, 1891.
10. Verstuys.—* Die mittlere und aursere Olrsphare der Laccartilia und
Rhyncocephalia,” ‘Zool. Jahrb.,’ Bd. xii, Heft. 2.
11. Gaurp, E.—“ Ontogenese und Phylogenese des schalleitenden Appa-
rates bei den Wirbelthieren,” ‘Anat. Hefte,’ 2te Abt., 1898.
(See this paper for discussion of whole question and complete list of
literature.)
12. Scuauinstanp, H.—* Weitere Beitrige zur Entwicklungsgeschichle
der Hatteria,” ‘Arch. Mikr. Anat.,’ lvi, 1900.
13. Kinestpy.—‘ The Ossicula Auditus of Vertebrates,” ‘Tuft’s College
Reports,’ 1900.
14. Howns, G. B., and Swinnerton, H. H.—‘ Developement of the
Skeleton of the Tuatara,” ‘Trans. Zool. Soc. Lond.,’ vol. xvi, pt. 1, 1901.
15. Verstuys, J.—‘ Entwicklung der Columella auris bei den Lacer-
tilien,” ‘Zool. Jahrb.,’ Bd. xix, Heft 1.
NOTES ON RHABDOPLEURA NORMANI, ALLMAN. 23
Notes on Rhabdopleura Normani, Allman.
By
G. Herbert Fowler, B.A., Ph,D., F.Z.S8., F.L.S.
(With Plate 3.)
THESE notes, written mainly some years ago, did not seem
worthy of publication by themselves. But my friend Mr.
Harmer lately called my attention to some remarkable state-
ments made by Messrs. Conte and Vaney! which seem to
justify the publication of the present paper, despite the small
quantity and imperfect preservation of my materials.
These gentlemen state that the peduncle is inserted “en
un point d’ot divergent le corps proprement dit, l’épistome
et les deux bras.” This point, on the ventral surface, is the
mouth; but, as a matter of fact, the peduncle is inserted
considerably behind it (compare Professor Lankester’s figures
from living material”). I can neither confirm nor deny the
statement that the ‘fibres musculaires de ce pédoncle se
prolongent dans les bras et dans V’épistome,”’ but I do not
think it probable that they really extend so far; the longi-
tudinal muscles of the peduncle are for the retraction of the
animal as a whole in its tube; the graceful movements of arms
and epistome, shown so beautifully in Professor Lankester’s
figures, demand an intrinsic musculature, parts of which I
have already recorded? It is stated that I “denied” the
existence of the testis figured and described by Lankester,
1 A. Conte and C. Vaney, ‘Comptes rendus Acad. Sci. Paris,’ exxxv, pp.
63, 748.
2 K. R. Lankester, ‘ Quart. Journ. Mier. Sci.,’ xxiv, pl. 38.
3G. H. Fowler, ‘Festschrift zum 7Oten Gebiirtstage, Rudolf Leuckarts,
Leipzig, 1893, 4to.
24 G. HERBERT FOWLER.
whereas the original runs that “I have been unable to meet
with any generative organs,” my specimens not being sexu-
ally ripe. The account which the French authors have
furnished leads one to await their figures of the generative
organs with interest.
To say of the ccelom that “les sub-divisions indiquées par
Fowler n’existent pas” is rather sweeping, in the face of the
camera drawings which I furnished in my last paper on the
subject; but as our authors go on to say that they have
vainly sought the excretory canals and collar-pores, one
begins to suspect that either the preservation of the material
or the technique of the microtomist was imperfect. When
we further learn, of the structure which I regarded as a
probable homologue of the “notochord” of Balanoglossus
and Cephalodiscus, that “cette prétendue chorde n’était
autre chose que Vextrémité antérieure du pedoncle,” one can
only regret that these gentlemen have not already figured
the way in which the latter post-oral and ventral structure
gets across, or behind, or beside the mouth, so as to become
continuous with the pre-oral “ notochord.”
I regret that I cannot draw the septa between the body-
cavities more clearly than I have already done, but at least
I hope that fig. 19 may convince Messrs. Conte and Vaney
of the existence of the collar-canals and pores. This figure
has been drawn with a camera lucida from five successive
sections; the uppermost exhibiting the external opening,
the next two the collar-canal, the last two the internal open-
ing; the cell-structure is sufficiently well preserved to allow
one to see that the cells are long and columnar in the canal,
with the nuclei near the base of the cell; but, as the histology
as a whole is not good, I prefer to represent the sections as
“coupes histologiques schématiques” rather than to draw
guesses at cell outlines, which are moreover wholly unim-
portant in this connection.
I. Tue Sratk or THE ADULT.
In a series of transverse sections the first appearance of
NOTES ON RHABDOPLEURA NORMANI, ALLMAN. 25
the insertion of the stalk is indicated by a thin crescentic
plate of longitudinal muscle-fibres, which seem to form part
of the somatic mesoderm of the body on the ventral surface.
They are first recognisable some little distance above
(anterior to) the bend of the alimentary canal. At the level
of the intestinal flexure the muscle-plate has become some-
what thicker (fig. 1).
When clear of the body of the polyp, the soft part of the
stalk (“gymnocaulus” of Lankester) shows the relations re-
presented diagrammatically in fig. 2. It is presumably
covered entirely by ectoderm; this ectoderm is certainly
thick and glandular on the upper side, that turned towards
the polyp. Beneath this lies the longitudinal muscle as two
J-shaped bands separated from one another by a septum,
which bisects the cavity of the stalk. At the ventral border
of this septum the ectoderm is thickened into a triangle, the
cells of which are not pigmented, as is the rest of the ecto-
derm, and stain very faintly; they have very much the
appearance of a superficial nerve (figs. 2, 3, a). Abutting on
this triangle a fine canal is excavated in the substance of the
mesentery, recognisable in many sections and several speci-
mens, but not in all; it may perhaps be an artificial
structure (fie. 2, b). In the central part of the stalk another
cavity is always visible, generally completely filled with a
eranular mass, but in the section figured this mass_ had
shrunk away from the walls, which are thus rendered more
conspicuous (figs. 2, 3, end ?).
At the junction of the soft stalk with the body the rela-
tions are extremely difficult to determine, owing to the
obliquity of the structures concerned and to a rotation of the
stalk. The coelom is comparatively broad at the point of
insertion, and I beheve that I can trace the paired cavities of
the stalk into the ccelom, and the central cavity of the
mesentery into continuity with the endoderm. In palliation
of this uncertainty, I have drawn the outline of a human red
blood-corpuscle on the same scale (fig. 2, 7.¢c.), from which it
may be gathered readily that the difficulty of study of such
VoL. 48, PART 1.—NEW SERIES. 3
26 G. HERBERT FOWLER.
minute objects in imperfectly preserved and limited material
is considerable.
At the transformation of soft stalk (gymnocaulus) into
hard stalk (pectocaulus) the high ectoderm spreads round
three-quarters of the circumference, and presumably secretes
the dark brown caulotheca, or stalk-pipe (fig. 5). Still
further posteriorly the caulotheca invests the pectocaulus
completely, the muscles disappear, and the soft tissues now
consist of a central core, apparently continuous with the
central (? endodermal) core of the g@ymnocaulus, and sur-
rounded by a membrane; it is certainiy flanked, and
probably entirely surrounded, by pigmented ectoderm-cells.
As figs. 1 to 4 are all drawn in the same position as
regards the polyp, it will be noticed that there is a rotation
of the stalk through about 90°; the mesentery, which
originally lay in the oro-anal plane of the polyp, finally
comes to lie right and left as regards the polyp-axis,
although dorso-ventral as regards the colony. This may be
accidental (as Mr. Harmer suggests), but is at any rate
not unusual.
Il. Tae Anatomy or A Bop.
The specimen which I select for description was apparently
at a stage intermediate between Nos. 6 and 7 of Professor
Lankester’s fig. 3, pl. 39, in that the lophophoral arms were
longer than in No. 6, but had not yet begun to develop
filaments. It has been drawn as fig. 18 of this paper. The
proboscis or epistome is large, the collar region small and only
slightly larger than the trunk, the trunk indistinguishable
externally from the gymnocaulus. At this stage, therefore,
the long axis of the body is a continuation of that of the
eymnocaulus—a condition unlike that of the adult (cf.
Lankester, op. cit., pl. 37, fig. 1).
As to the lophophoral arms and upper part of the proboscis,
there is nothing of special developmental interest to say ; the
arms simply grow out from the collar region, and contain
off-sets of the collar body-cavity from the beginning.
NOTES ON RHABDOPLEURA NORMANT, ALLMAN, 27
Figs. 5 to 14 are from a continuous series of successive
sections, all of which are drawn; it is therefore possible to
follow the anatomy minutely. The sections are slightly
oblique. Starting with fig. 8, there seems to be a_ well-
marked stomodzeum, which, owing to the obliquity of the sec-
tions, appears erroneously to open on the right side only. This
stomodeeum is sharply separated from the upper (rectal) part
of the alimentary canal by a stout membrane; the canal
itself at this level appeared to be a vacuolated mass, in which
no epithelial-cell outlines were recognised. All three sub-
divisions of the ccelom were represented in this section—a
small part of the proboscis-cavity (be.'), the left collar-
cavity (be.*), and the trunk-cavity, apparently divided into
two parts by the alimentary canal dorsally and ventrally
(be.*). On the animal’s right side the section passed nearly
along the septum between the collar- and trunk-cavities.
In the section above this (fig. 7) the collar-cavity of the
right side appeared, and the trunk-cavity of that side had
almost vanished. The next section upwards (fig. 6) was un-
fortunately folded between proboscis and ccelom, so that not
more than has been drawn could be recognised; it was
obvious, however, that the stomodzeal groove of the previous
section had been folded off as a rod, which contained (I think)
acavity. In the highest section figured (fig. 5) the alimentary
canal was no longer met with; the rod of the previous
section was in the position of the notochord.
Passing downwards from fig. 8, the next section (also
folded at the attachment of the proboscis) showed a thick
muscle-band on the outer wall of the right-hand half of the
trunk body-cavity, other structures remaining much as before
(fig.9). In fig. 10 the stomodzum had entered the alimentary
canal (@), and the lower lip had been reached. In fig. 11
the right trunk body-cavity had increased considerably in
size, and the attachment of the proboscis had been passed.
The left collar-cavity had all but disappeared in fig. 12; the
left trunk-cavity showed its longitudinal muscle, and a septum
separated the two trunk-cavities ventrally. In fig. 13 the
28 G. HERBERT FOWLER.
alimentary canal began to diminish, the mesentery to elon-
eate; and in fig. 14 the alimentary canal appeared to be
represented by the central core of the mesentery of the
eymnocaulus, the two trunk-cavities becoming the paired
cavities of the stalk.
I have endeavoured to express my interpretation of these
sections by an imaginary longitudinal section in fig. 15. If my
views are correct, two things follow—that the notochord
in the bud is of ectodermal origin, and that the
eymnocaulus contains all three embryonic layers,
the proliferation and growth of which give rise to equivalent
structures in the adult.
As regards the notochord, I have long suspected that it
was a stomodeeal structure in Balanoglossus and Cephalo-
discus, and there can be little hesitation in assigning it to
the ectoderm in buds of Rhabdopleura on the strength
of these sections. Figs. 7, 8, and 9 show an epithelial in-
vagination below the proboscis-stalk, which, from the cha-
racter of the cells, is fairly certainly ectodermal, and is
continuous with the so-called notochord; the alimentary
canal, on the other hand, appears, so far as I can see, to be
syncytial and vacuolated rather than epithehal ; this is shut off
by a basement membrane from the stomodeum at the plane
of these sections, and is presumably the future endoderm.
As regards the structure of the adult gymnocaulus, I have
no personal doubt of the view given above, that the contents
of the central cavity in the septum are continuous with the
alimentary canal of the adult, and give rise to the ali-
mentary canal of the bud; they are presumably of endo-
dermal origin. Similarly the paired cavities of the gym-
nocaulus are traceable fairly unmistakably into the trunk-
cavities of the bud, less certainly into those of the adult.
At the same time, the structures in question are so minute
that these views have only the value of a personal conviction,
and require confirmation from other sources.
These notes and drawings of the structure of the stalk and
bud, such as they are, were made before the publication of
NOTES ON RHABDOPLNURA NORMANI, ALLMAN. 29
Dr. Masterman’s paper! on the budding of Cephalodiscus, but
IT am unable to bring the two sets of observations into
accord. There is no doubt that Masterman’s picture of the
stalk in Cephalodiscus is correct in exhibiting two cavities
bounded by a thickish membrane (as in his pl. i, fig. 18),
whatever may be the correct interpretation of these struc-
tures. There is equally no doubt that my fig. 2 is also
correct (interpretations excepted) in showing the ccelom of
the stalk divided completely by a septum. But Masterman
interprets the cavities in Cephalodiscus as “ blood-” sinuses,
whereas my specimens lead me to believe that the central
core of the Rhabdopleura septum is continuous with the lning
of the alimentary canal. Unfortunately buds smaller than
that described in detail above proved to be too minute to
allow of definite conclusions being drawn,? and the prelimi-
nary remarks of MM. Conte and Vaney are too brief and
vague to settle the matter (op. cit., p. 749).
Cephalodiscus and Rhabdopleura agree in the precocious
formation of the epistome, in the continuity of the stallk-
ccelom with that of the bud, and in the presence of a nerve-
like stripe of ectoderm on the stalk.
EXPLANATION OF PLATE 38,
{lustrating Dr. G. Herbert Fowler’s “ Notes on Rhabdo-
pleura Normani, Allman.”
Nore,—As in my previous paper (op. cit. supra), the trunk-ceelom has been
drawn all round the alimentary canal on the authority of Prof. Lankester’s
observations on living specimens, although in my shrunken specimens it is
1 A. 'T. Masterman, ‘Trans. Roy. Soc. Edin.,’ xxxix, p. 507.
2 At the same time, the structures are large enough to allow of accurate
determination in material specially preserved; mine had been roughly pre-
served (apparently merely in strong alcohol), for the sake of the Lophophelia
on which it grew; as it was “Challenger” material, thirty years’ preservation
has not improved it.
30 C. HERBERT FOWLER.
only visible here and there; this has necessitated a slight re-adjustment of the
comparative thicknesses of the body-layers in the figures. ‘The ectoderm has
in many figures been drawn thicker than it actually appears. In my depig-
mented specimens it is invisible over a large part of the body and stalk. With
the exception of fig. 15, all outlines have been drawn with the Abbé camera
lucida. Fig. 15 is based on a plotting of the actual section-drawings on
scaled paper, free-hand curves being drawn through the points thus obtained ;
the horizontal scale is therefore nearly correct, the vertical scale arbitrary,
but estimated roughly on the thickness of the sections.
REFERENCE LETTERS.
a. Streak of unpigmented ectoderm in the gymnocaulus (? nervous). ad.
Alimentary canal. asc. Ascending half of the alimentary canal. 4. Space in
ihe mesentery (2 blood-vessel or artificial). dc'. Ceelom of the proboscis or
epistome. de®. Coelom of the collar region. 4c. Colom of the trunk or body
region. caul. Caulotheca, or stalk-pipe. ¢.c. Collar-canal. d. mes. Dorsal
mesentery. desc. Descending half of the alimentary canal. ect. Ectoderm.
end. Kudoderm of the adult. exd. 7. Core of the mesentery, probably endo-
dermal. mes. Mesentery or septum of the gymnocaulus. mase. Longitudinal
retractor muscle. 2. Dorsal thickening of ectoderm (? nerve-plate). xch.
Stomodeeal diverticulum (so-called notochord). @. Gisophagus. pr. Pro-
boscis. 7. c. Outline of a human red blood-corpuscle, for scale. s. Septum
between the body-cavities of the proboscis and collar. s¢, Stomodeum.
tub. Tubarium, v. mes. Ventral mesentery.
PLATE 3.
Fies. 1—4 relate to the stalk of the adult.
Fig. 1.—Section of the posterior end of the adult, at the point of flexure
of the intestine, showing the continuation of the longitudinal muscle of
the stalk on to the body. x 480.
Fig. 2.—The gymnocaulus, below the body of the animal. x 820.
Fig. 3.—The gymnocaulus, at the commencement of the pectocaulus.
x 820.
Tig. 4.—The pectocaulus. x 820.
Fias, 5—14 are successive sections of the bud drawn as fig. 18. The plane
of section is somewhat oblique and the epistome twisted. Xx 520.
Fig. 5.—Below the attachment of the lophophoral arms.
Fig. 6.—Through the highest point of the alimentary canal, dorsally.
No anus was visible.
Fig. 7.—The stomodaum, open on the right side.
NOTES ON RHABDOPLEURA NORMANI, ALLMAN. 31
Fig. 9.—The right longitudinal muscle of the stalk appears.
Fig. 10.—The esophagus separated from the stomodeum by the lower
lip.
Fig. 11.—Below the proboscis-stalk.
Fig. 12.—The left longitudinal muscle of the stalk appears.
Fig. 14.—The gymnocaulus.
Fic. 15.—Diagrammatic reconstruction of the foregoing sections as a longi-
tudinal section beginning just below the insertion of the lophophoral arms, the
outline of the trunk body-cavity, which of course is not cut in a median dorso-
ventral section, being marked by dashes. ‘The numbered arrows indicate the
corresponding figures of the transverse sections.
Fries. 16, 17, 18.—Buds at the end of a terminal branch, a short length of
pectocaulus intervening between the successive figures. Of these fig. 16 is the
crowing end of the branch, and fig. 18 the oldest bud drawn. xX 140. The
lowest bud in Fig. 16 is viewed from the right side, and gives a good idea of
the way in which the lophophoral arms spring from the end of the body
proper, and the proboscis stands out on the ventral side.
Fic. 19.—Successive sections of the collar-pore and canal of the right side
of an adult animal. x about 520.
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ANATOMY AND AFFINITIES OF THE TROCHIDA. 393
Some Observations on the Anatomy and
Affinities of the Trochide.
By
W. B. Randles, B.Sc.(Lond.
(From the Zoological Laboratory, Royal College of Science, London.)
With Plates 4, 5, and 6.
THe results embodied in this paper are the outcome of a
series of observations on the anatomy of various species of
Trochus. It was my original intention, acting on the sug-
gestion of the late Martin F’. Woodward, to confine my atten-
tion mainly to one species, viz. 'rochus magus, and
study that as a type form. Iwas unaware at that time of the
existence of a memoir on T'rochus, published in the ‘ Zoologie
Descriptive’ (38), in which a very adequate account of the
anatomy of 'rochus turbinatus (Born) is given by
A. Robert. As this article gives a sufficiently detailed account
of the anatomy of a fairly typical form, it will be unnecessary
for me to give more than a general résumé of the main
points of the anatomy, but rather to amplify any features that
have not been fully described, and to point out any differences
that may exist in the organisation of the various species
which I have been able to examine, noting whether these
differences are sufficient to justify the existence of the
numerous sub-genera into which the genus Trochus has been
divided upon conchological grounds.
All the species which I have so far examined are British,
34 W. B. RANDLES.
the greater part of them having been obtained from Plymouth
during the months of July and August, 1901.
For specimens of Trochus exasperatus and ‘Il’. Mon-
tacuti I am indebted to Mr. H. R. Sykes, and of T. magus
to Mr. EK. W. Holt.
I wish here to express my best thanks to the Committee of
the Royal Society for a grant which enabled me to carry on my
researches at Plymouth, also to the British Association and
Zoological Society for the use of their tables at the Marine
Biological Laboratory during July and August, 1901.
The various species of the genus 'rochus of which there
are a considerable number, have been grouped into numerous
sub-genera. These sub-divisions have been founded upon
conchological differences without regard to the anatomical
organisation of the animal. It is highly probable that if
anatomical characteristics are taken into account the number
of sub-genera can be considerably reduced.
The following species of ‘'rochus are those which I have
examined :
1. 'T. magus (Linn.).
2. T. cimerarius (himn:).
T. umbilicatus (Montagu).
T. tumidus (Montagu).
T. lineatus (Da Costa).
. 214zyphinus (Linn.).
T. granulatus (Born).
T. striatus (Linn.).
T. exasperatus (Pennant).
10. T. Montagui (Gray).
These species are, according to Forbes and Hanley (17),
grouped into two sub-genera, viz. 1—5 under the sub-genus
Gibbula and 6—10 under the sub-genus Trochus.
If we follow the classification given either by Gwyn
Jeffries (24) or Tyron (48), we must group the above species
into three subgeneric divisions, viz. 1—4 under the sub-
genus Gibbula (Leach), 5 under the sub-genus Mono-
donta (Lamarck), or Trochocochlea (Klein), and 6—10
© co MD OB wo
eS
ANATOMY AND AFFINITIES OF THE TROCHIDA. 35
under the sub-genus Calliostoma (Swainson), or Zizyphi-
nus (Leach). According to the latter system we have the
species Trochus lineatus included in a separate sub-genus,
Trochocochlea (Klein), which species is the only British
representative of the sub-genus, though there are numerous
exotic species belonging to it. This separation of T. linea-
tus from the sub-genus Gibbula, in which it is placed by
Forbes and Hanley, is based upon conchological grounds
which to my mind do not seem to be of sufficient importance
to justify it, though my own observations are based upon the
exainination of a single species, T. lineatus.
The characters of the three sub-genera Gibbula, Trocho-
cochlea, and Calliostoma are given by Jeffries (24) as
follows:
1. Gibbula (Leach).—Shell low spired and umbilicate.
Examples: 'T. magus (PI. 4, fig. 1).
T. cinerarius (fig. 2).
2. Trochocochlea (Klein).—Spire moderately raised, base
shghtly umbilicate in the adult and perforated in the young,
pillar lip furnished with a strong tubercular tooth.
Example: T. lineatus (fig. 3).
2. Calliostoma (Swainson).—Spire pyramidal, base im-
perforate, pillar lip notched or angulated at the lower part.
Example: T. zizyphinus (fig. 4).
Apparently the only difference in the characters of the sub-
genera T'rochocochlea and Gibbula is in the height of the
shell, the absence of an umbilcus, and the presence of a tooth
on the pillar lp. But these characteristics are not necessarily
confined to the sub-genus Trochocochlea, for species of
Gibbula may occasionally be imperforate or high spired
(T. cinerarius, fig. 3). As Gwyn Jeffries remarks (24,
vol. ii, p. 294), “The shells are usually low spired and deeply
umbilicate, but varieties of T. tumidus, T. umbilicatus,
and Tl’. cinerarius have the spire raised. Again, T. lineatus
is the only representative of Klein’s genus Trochocochlea,
in which the spire is raised, the base imperforate, and the
pillar lip furnished with a blunt tubercle or notch ; the last
36 W. B. RANDILES.
two characters are common, however, to several species of
Gibbula and the typical section Zizyphinus, which last
has a pyramidal spire. It is also not generally known, but
not less the fact, that young shells of 'T. lineatus (the type
of Trochocochlea) are always deeply umbilicate.”
We see, then, that the conchological differences between the
two sub-genera are very meagre and valueless for diagnosis ;
and when we come to compare their anatomical structure, we
find they are so nearly identical that it seems quite unneces-
sary for the separate sub-genus to be retained.
The species 6—9, however, fall into a group quite distinct
from that of Gibbula, and exhibit anatomical differences
that warrant their separation into a sub-genus, viz. Cal-
liostoma. Here, however, although T. zizyphinus and
T. granulatus are very different in many respects from any
species of Gibbula, some of the smaller species of Callio-
stoma, viz. T. striatus, and T. exasperatus, present
points of startling similarity in the raduia and some external
features to T. magus and other species of Gibbula. ‘They,
however, in possessing pyramidal shells, and in the presence
of an accessory structure in connection with the female genital
organs (a structure common to all the British species of Cal-
liostoma which I have examined), undoubtedly belong to
this latter sub-genus.
Kxternal Characters.—The head is moderately large,
and is bent downwards into a cylindrical snout, on the under-
surface of which is situated the mouth. There are present
on either side of the head three appendages, the outermost of
these, the ocular peduncles (figs. 5, 6, 7, oc. p.) are short,
laterally flattened structures, presenting in cross-section a
somewhat oval contour. Near the apices of these the eyes
are situated. Internal to the ocular peduncles are placed
the cephalic tentacles, highly muscular organs, capable of
great extension and covered externally with fine cilia (fig. 7,
GH.)
An interesting condition is seen in the larval forms of
T'rochus (vide Robert, 38, fig. 508, x)— the cephalic tentacles
ANATOMY AND AFFINITIES OF THE TROCHIDA. 37
are branched at their extremities, thus presenting an appear-
ance similar to that described by Woodward in the cephalic
tentacles of Pleurotomaria (45, pl. 15, fig. 1). In none
of the adult specimens of Trochus examined have I noticed
an indication of this branching, even as an abnormality, though
one specimen of T’. zizy phinus exhibited a most peculiar and
interesting abnormality, in that on the right ocular peduncle
three eyes were present in place of the usual one. The left
eye was perfectly normal.?
The third pair of appendages present on the head of the
Trochide are the cephalic lappets (figs. 5, 6, 7, ¢./.) These
structures are very variable in size: in those species belonging
to the sub-genus Gibbula they are large and conspicuous,
their free margins being fringed and ciliated; whilst in
T. zizyphinus and other species belonging to the sub-genus
Calliostoma they are extremely small and sometimes entirely
absent. In connection with the ocular peduncles there is a
most remarkable little organ existing in many of the species
of Trochus, viz. a small pointed appendix situated underneath
and behind the right ocular peduncle (fig. 5, a. oc. p.) In
T. cinerarius (Pelseneer, 86, pp. 46,47) and T. umbilicatus
it is comparatively large, and can easily be found. It is
present in ‘Il’. magus and 'l’. lineatus, though much smaller
than in the preceding species, and is noticeable only as a
small protuberance on the ocular peduncle. Clarke (11,
p. 313) has described a similar appendix in 'T. tumidus asa
penis, though in the three specimens of this species which I
examined I was unable to find any trace of the structure. In
the sub-genus Calliostoma it 1s variable in its appearance
or non-appearance: TT’. zizyphinus and T. granulatus
are entirely without it, while in T. striatus and T. ex-
asperatus, though small, it is usually present. It is not
confined to the Trochidee, but is present in other genera, Viz.
Crepidula, Capulus, and Calyptrea, being especially
well developed in the last genus. It has been regarded by
several observers as being of the nature of a penis, but in
1 Vide ‘ Nature,’ No. 1693, vol. Ixv, p. 535, April 10th, 1902.
38 W. B. RANDLES.
Trochus at any rate it has undoubtedly nothing whatever to
do with the genitalia; at least it is not of the nature of a
penis, because when present it is found in both male and
female. Besides, it is a solid organ and exhibits no trace of
canal or groove which might serve for the transmission of
sperms, and were it of this nature we should expect to find it
in all species, and not, as is actually the case, present in some
and absent in others. Those species in which it occurs are
mainly littoral forms, and there appears to be some correlation
between its presence and the existence of a certain asymmetry
that occurs in the epipodial lobes of these.
The foot is a large muscular organ, capable of great
extension; it is beset on its lateral surfaces with numerous
papilla, giving it a rugose appearance. ‘The anterior margin
presents in some species, T. granulatus, ete. (fig. 6), a
large tranverse groove separating the sole from the upper
part of the foot. A similar groove occurs in Pleurotomaria
and many other Gasteropods; it 1s evidently of importance,
though its function is somewhat enigmatical. In the Trochide
it is present only in those species belonging to the sub-genus
Calliostoma, and is not represented in any of the Gibbule
which I have had the opportunity of examining. When
present this groove leads into a large tubular pedal gland
(fio. 6, p. gl.), which extends some distance into the anterior
portion of the foot; the gland is composed of large deeply
staining cells, containing granular protoplasm and rather
small nuclei. The canal of the gland is lined with ciliated
epithelium. Houssay has described a similar, though shghtly
more complex gland in Trivia Huropea (28, pp. 272—275,
pl. xiv, fig. 2), in which a large transverse groove is present
on the anterior margin of the foot, which leads into a longi-
tudinal ciliated canal surrounded by cells of the pedal gland.
In cross-section the pedal gland presents a similar appearance
to that of Chenopus as figured by Houssay (28, pl. xin,
fig. 4, pp. 278—281).
Though theze is no definite pedal gland in any of the
species of the sub-genus Gibbula, such a structure is not
ANATOMY AND AFFINITIES OF THE TROCHIDA. 39
entirely unrepresented, but takes the form of a number of
large unicellular gland-cells on the under surface of the
foot, aggregated more especially round its anterior margin.
Although Pleurotomaria has the transverse groove on
the anterior margin of the foot very well developed, there
is no longitudinal canal or pedal gland connected with it, such
as exists in I. zizyphinus, ete , butit is more than probable
that the groove contains numerous gland-cells.
On the dorsal surface of the foot there is invariably present
a specialised area running from the opercular lobe to the
posterior extremity. ‘he exact appearance of this differs
somewhat in the different species. In 'l. granulatus (fig. 8)
and 'T’. zizyphinus it is well defined and V-shaped, bounded
by two iateral converging furrows. A shallow median furrow,
together with the two lateral furrows, arise from under the
free border of the opercular lobe and run down the dorsal
surface of the foot for a short distance ; the median furrow
then terminates, and numerous transverse grooves make their
appearance and are continued to the end of the foot, the
posterior grooves being deeper than those more anterior,
These grooves are not continued right across the foot from
side to side, but are bounded by the two converging lateral
furrows. In addition to these deep transverse grooves there
are numerous smaller branching furrows which run in a
transverse direction across the dorsal surface of the foot from
side to side ; these are not interrupted by the lateral furrows.
In the remaining species there is a slight difference in the
arrangement of this specialised portion of the foot. The
lateral furrows are only continued for a short distance beyond
the opercular lobe and do not limit the transverse furrows to
a markedly V-shaped area.
These transverse furrows run right across the foot to the
epipodial lobes and frequently branch. In Trochus magus
(fig. 9) this condition is well exhibited ; at the posterior
extremity of the foot a clearly defined median groove is
present; in T. cinerarius this median groove is continued
from the opercular lobe to the extreme tip cf the foot.
AO W. B. RANDLES.
Similarly modified areas occur on the dorsal surface of the
foot of Pleurotomaria (45, p. 219), and Haliotis (44, pp.
335, 336). This specialised area is undoubtedly glandular in
nature, as, when microscopically examined in section, numerous
goblet-cells are seen to exist. ‘lhe epithelium covering the
folds of the grooves consists of large cylindrical, ciliated cells
with granular contents and large rod-shaped nuclei. Inter-
spersed between the ciliated cells are mucous-discharging
ooblet-cells. Underneath this specialised area of the foot
the various blood-sinuses are particularly large and numerous.
No definite function has as yet been assigned to this organ,
though it is without doubt in part a mucous gland; and
Weemann (44) has observed in living specimens of Haliotis
the secretion of a mucous thread from this area. On the
antero-dorsal surface of the foot is situated the opercular lobe
(figs. 8, 9, op. L.), which is bean shaped, having its posterior
margin free.
The ciliation which is so marked on the cephalic tentacles
is continued over the great part of the foot, the cilia on the
margin of the foot being especially long (fig. 7).
The epipodium is well developed in the Trochide,
though more conspicuously so in the members of the sub-
genus Gibbula than in those of the Calliostome. It
originates close to the ocular peduncle (figs. 5, 6, ep.c.) and
extends to the posterior limit of the foot, attaining its
maximum development in the region of the neck, where it
enlarges into a cervical lobe (ep. ¢c.) In the species of
Gibbula the cervical lobes are asymmetrical, the right
being larger than the left and having its free margin entire,
while the margin of the left lobe is digitate and covered with
sensory papile. This fringing of the left cervical lobe is
very conspicuous in T. lineatus (fig. 7, ep. ¢.), also
in T. cinerarius and TT. umbilicatus, whereas in
T. magus, though the right and left lobes are asymmetrical
as regards actual size, the fringing of the left is by no means
so obvious as in the preceding species, in some specimens
scarcely any trace of unevenness in marginal outline being
ANATOMY AND AFFINITIES OF THE 'TROCHIDA., 4]
apparent. On the other hand, in those species belonging
to the sub-genus Calliostoma the right and left cervical
lobes of the epipodium are perfectly symmetrical, their
margins being entire and free from pectinations. According
to Pelseneer (36, p. 46) the lobes during life are rolled up
on themselves, forming channels leading into the mantle-
cavity, and serving to convey water into and out of it.
The epipodium is furnished on either side with three or
more tentacles, which can be extended to a considerable
length. They are highly muscular, and present a great.
similarity in structure to the cephalic tentacles, and, like these,
are covered externally by numerous fine cilia (fig. 7, ep. t.).
The number of these tentacles is very constant in the two
sub-genera; in Gibbula there are always three on each
side, whilst in Calliostoma either four or five are present,
but always more than three. At the base of these tentacles
are situated some small appendices, the epipodial papille
(fig. 7, ep. p.), which either vary slightly in shape and
occasionally in number in the different species, or may be
entirely absent, as in T’. zizyphinus and Tl. granulatus.
In T. cinerarius they are club-shaped structures; in
T. magus they show a tendency to branch, whereas in
T. lineatus they are wart-like projections at the base of
the tentacles. They are undoubtedly sensory in function,
probably tactile, and are innervated by the nerve going to
the epipodial tentacle. In section they exhibit a slight
concave depression at the apex, the epithelium lining this
concavity consisting of elongated cells occasionally pigmented.
These structures have been regarded as accessory eyes,
but it is extremely doubtful if they are other than tactile
organs. In addition to the papille at the base of each
epipodial tentacle there is a similar organ under each
cervical epipodium, totally unaccompanied by any sensory
tentacle. hese anterior papille exhibit exactly the same
structure as those previously mentioned, and though there is
usually one present on either side, two or even three may be
present on one side (generally the left) and one on the other.
vot. 48, PART 1.—Ne&W SERIES. 4.
A2 W. B. RANDLES.
It is of considerable interest to note that in T. zizyphinus
and T. granulatus the entire absence of sensory papille
at the base of the epipodial tentacles and under the cervical
lobes of the epipodium is correlated with the perfect
symmetry of the cervical lobes and the absence of an
appendix on the right ocular peduncle. In the following
species:—T. striatus and T. exasperatus,—which are
included in the sub-genus Calliostoma,—the cervical lobes
are symmetrical, but sensory papille are present under these
lobes and also at the base of the tentacles, and, in addition,
the appendix at the base of the right ocular tentacle occurs.
Moreover the specialised glandular area on the dorsal surface
of the foot more nearly resembles the condition seen in
T. magus than the V-shaped area in T. granulatus.
The operculum is a circular, multispiral, chitinons disc
with a central nucleus; the whorls overlap each other and are
marked in a radial direction by numerous striz indicating
lines of growth. It differs slightly in the two sub-genera,
both in colour and also in the number of whorls com-
posing it. In Gibbula it is dark brown, and the whorls,
which are fewer in number than in Calliostoma, range
from six and a half to seven in adult specimens of T. magus
(fig. 10), to ten or twelve whorls in T. umbilicatus and
T. lineatus. The lines of growth are very distinct, and
on the under side of the operculum a bean-shaped scar
(fig. 10, m. ims.), situated eccentrically, marks the area of
attachment of the operculum to the columella muscle and
opercular lobe of the foot. In Calliostoma the operculum
is of a light yellow colour, the volutions are more numerous,
ranging from thirteen to fourteen in T. striatus,
T. exasperatus, and T. granulatus to as many as
fifteen or sixteen in T. zizyphinis (fig. 11). In this
latter species the lines of growth are very close together, and
are more distinct on the outer half of the whorl. The area of
the muscle attachment is more or less triangular in shape.
The Pallial Complex.—The mantle is thin walled,
with the free edge slightly thickened and occasionally plicated,
ANATOMY AND AFFINITIES OF THE TROCHIDA. 48
Very small and inconspicuous papillae occur on the margin.
The mantle completely encircles the body, but the posterior
portion (fig. 40, m. a.) is very small, its margin being thin.
This part of the mantle is closely attached to the columella
muscle.
The mantle-cavity is large, and is divided by the gill-
septum into two chambers, a large right chamber, into which
the excretory and anal orifices open, and a much smaller left
(dorsal) one, which encloses the lamelle of the left side of the
gill.
The gill (figs. 39—43,9.), is characteristically bipecti-
nate, the gill-axis or septum bearing on either side a series of
triangular gill-plates or lamelle. This septum is attached to
the mantle-wall along two lines of insertion, on the left side
the attachment is near the junction between the mantle and
left body-wall, whilst the other line of insertion of the gill-
septum is near the mid-line of the roof of the pallial chamber.
The gill, and consequently the septum, extends to the posterior
extremity of the mantle-cavity, thus dividing it into the two
chambers previously mentioned. The afferent and efferent
blood-vessels of the gill are situated on the dorsal and ventral
sides respectively of the gill-septum.
The anterior extremity of the gill is free, and is supported
by a rod-like structure of cartilaginous consistency.
The gill-lamelle are not equally well developed on both
sides of the septum, those on the inner (left) side are much
smaller than those on the outer (right).
The microscopic structure of the gill and gill-lamellx of
Trochusis so essentially similar to that of Pleurotomaria
that it will suffice to refer to Woodward’s paper on that genus
(45, pp. 223—226) fora detailed account.
The hypobranchial gland occupies the customary
position between the rectum and afferent border of the gill.
Various degrees of differentation are presented in the different
species. In T. cinerarius and IT’. umbilicatus the gland
is comparatively small, in T. magus (fig. 41, m.g.) it is much
better developed, and the glandular tissue covers the trans-
44, W. B. RANDLES.
verse pallial vein (¢. p. v.), extending up to, and a little way
beyond the orifice of the left kidney ; a moderately sized
mucous gland is present in T. (Monodonta) monodon
(Bernard, 2, p. 324). In T. zizyphinus (fig. 45) the hypo-
branchial gland is lozenge shaped, and the mucus-secreting
cells are thickly distributed over the transverse pallial vein
and the vessels uniting with it. Out of the species examined
the hypobranchial gland is largest in ’. lineatus, where it
extends from the transverse pallial vein to within a short
distance of the thickened edge of the mantle.
Tn all the species the main portion of the mucous gland is
situated on the left side of the rectum, but there is present a
small lobe on the right side. This right lobe is also larger in
T. lineatus than others of the species examined.
The presence of a right lobe is of great interest when con-
sidering the asymmetrical condition of the pallial complex of
Trochus. We have, again, the case of an organ situated on
the right side of the body, which has, owing to the effects
of dextral torsion, become very much reduced, and following
in the wake of the right gill, which in Trochus has been
completely suppressed. ‘That this is so is evidenced by com-
paring it with Pleurotomaria (45, p. 228), in which a large
hypobranchial gland consisting of both right and left lobes
situated on either side of the rectum is present. Here the
right lobe, like the right gill, is smaller than the correspond-
ing structure on the left side, thus foreshadowing the ultimate
reduction and suppression which occurs in the Azygo-
branchiate Diotocardia.
Béla Haller (19, p. 28, note) regards the reduced right lobe
of the mucous gland of Trochus as the remains of the right
gill which has atrophied; but when we consider that in
Pleurotomaria there is present, co-existing with a func-
tional right gill, a well-developed right lobe of the mucous
gland to which the reduced right lobe in Trochus is un-
doubtedly homologous, the fallacy of Haller’s supposition
becomes apparent.
The excretory organs of Trochus have been very
ANATOMY AND AFFINITIES OF THE TROCHIDA. 45
adequately described by Perrier (37, pp. 118—131) in his
admirable memoir on the kidneys of Prosobranchs. There
are two kidneys present in this genus, though one only, the
right, functions as a true depuratory organ. The left
kidney, or papillary sac (figs. 39, 43 and 49), is an oval
body situated on the left side of the rectum at the posterior
end of the mantle-cavity, where it abuts on the pericardium.
It communicates with the exterior by a slit-like aperture
(i. k. a.) at its anterior end. The walls of the papillary sac are
thick, and when opened are seen to be covered with numerous —
filiform papille, which in section are found to be made up of
a thick layer of connective tissue traversed by a central or
axial cavity which functions as a blood-space. The con-
nective tissue is covered externally by a layer of small,
ciliated, epitbelial cells. This kidney is placed in communi-
cation with the pericardium by means of a long reno-peri-
cardial canal (figs. 34, 48, r..p.c.) which runs longitudinally
but somewhat obliquely from the anterior angle of the
pericardium along the floor of the papillary sac. The aper-
ture in the pericardium is large and very easily discernible,
and is situated on the left side of the rectum.
The aperture leading into the kidney is much smaller and
is ciliated (fig. 34,7.’p.c.). This figure, which represents a
longitudinal section through the left reno-pericardial canal
of T. magus, is somewhat diagrammatic, and has been re-
constructed from serial sections, the entire passage of the
canal from the pericardium to the kidney occupying some
fifteen sections, each having a thickness of 10m.
The right kidney (figs. 39, 40, etc., 7. k.) is seen without
dissection as a narrow band of tissue extending between the
pericardium and the stomach and liver. It is differently
coloured in the various species, being most generally of a
yellowish-green colour, though in T. zizyphinus it assumes
a rose-pink tint; and in this case the excretory granules
present in the constituent cells have the same colour when
living tissue is examined, though in material which has been
preserved in alcohol they always present a greenish appearance.
46 W. B. RANDLES.
The right kidney is much larger than it appears to be
from a superficial examination ; it extends ventrally under-
neath the pericardium, and approaches very closely to the left
kidney, though there is no trace of communication between
the two. There are slight differences in extent of this kidney
in the various species, and it is most highly developed in
T. zizyphinus (fig. 49) and its allies. Here the kidney can
be divided into a large posterior lobe (p.7. k.), present in all
species, and a smaller anterior lobe (a.7.k.) lying underneath
‘the cesophagus, and extending almost as far as the transverse
pallial vein ; this anterior lobe is very feebly represented in
T. magus, and almost, if not entirely, absent in T. lineatus.
In Turbo, Haliotis, and Pleurotomaria the anterior
lobe is very large, and forms quite a conspicuous feature of
the right kidney.
T. zizyphinus, in possessing a moderately well-developed
anterior lobe, approximates in this respect very closely to
Pleurotomaria. ‘lhe posterior lobe (p.7.k.) is by far the
largest and most important part of the kidney of Trochus,
and can be divided into two portions, the dorsal portion, con-
sisting entirely of glandular tissue, extending up between the
pericardium and the stomach, and the ventral portion, which
is lined by a thin membranous wall, forming a kind of urinary
chamber (k.c.) into which the excreted products of the gland
are collected. This urinary chamber is continued on as a
thin-walled ureter (w) lying on the right side of the mantle-
cavity to the right of the rectum, and opening to the exterior
by an aperture situated close to the aperture of the left
kidney.
In all the species of the sub-genus Gibbula (figs. 89—41)
the external aperture of the right kidney is bounded by
tumid lips, the borders of which are fringed. This swollen
expansion of the terminal portion of the ureter is very con-
spicuous in females, more especially so during the breeding
season. Numerous mucus-secreting cells are present in this
enlarged portion.
In T. zizyphinus (figs. 42, 49) and other members of the
ANATOMY AND AFFINITIES OF THE TROCHIDA. 47
sub-genus Calliostoma the terminal portion of the ureter
becomes very much enlarged, forming what Perrier terms an
ampulla (amp.). This enlargement is present only in the
female, and the lumen of the ureter is here very small,
becoming almost obliterated by the relatively enormous thick-
ness of the walls (fig. 49). The external aperture of the
ureter is placed at the termination of this thickening. The
walls of the ampulla contain numerous mucus cells, which
swell up enormously when they come in contact with water. A
similar enlargement of the ureter has been described by Wood-
ward as occurring in the female of Pleurotomaria Beyri-
chii. It is undoubtedly an accessory to the female genital
organs, and from its very glandular nature it seems probable
that it is concerned in the secretion of the albuminous material
in which the eggs are enveloped prior to their discharge.
Though this structure is by no means so highly developed in
the members of the sub-genus Gibbula, it is undoubtedly
represented by the tumid and fringed lips at the anterior
extremity of the ureter.
The presence of an anterior lobe to the right kidney and
the accessory genital organ in the female of certain species of
Trochus undoubtedly proves the very close affinities of the
Trochide to Pleurotomaria, in which identically the same
structures are present. Also the presence of these two
structures in certain species and their almost entire absence
in others serve very well as a basis upon which we can
definitely separate the species enumerated into the two well-
marked sub-genera Calliostoma and Gibbula.
Until quite recently no connection had been traced between
the right kidney and the pericardium, and it was thought
that the right reno-pericardial canal had been lost. Pelseneer,
however, in 1898 (86, p. 53), described a right reno-peri-
cardial canal in Trochus cinerarius. My own researches
confirm this observation, as I have been able to demonstrate,
both by dissection in T’. lineatus (fig. 48, 7. p. c.) and by the
examination of serial sections in 'l’, magus (fig. 35, r. p.c.),
that such a communication does exist. The right reno-
48 W. B. RANDLES.
pericardial canal does not open directly into the kidney, but
into the genital duct at the point where it debouches into the
urinary chamber. In some of the females that were obtained
during the breeding season ova were found inside the peri-
cardium, thus demonstrating the existence of a direct com-
munication between the pericardium and either the gemital
duct or the urinary chamber. Fleure (16) las recently
described the existence of a right reno-pericardial pore in
Haliotis, and mentions the fact that ova were frequently
found in the pericardium, having been introduced into that
chamber via the reno-pericardial channel.
The structure of the glandular portion of the right kidney
has been described by Perrier (87) as consisting of a sac
divided by numerous trabecule, these being lined with glan-
dular cells. Haller (21) and Pelseneer (86, p. 53) regard it
rather as a gland composed of a number of acini, the cavities
of the acini uniting into principal branches, which lead into
the urinary chamber. This, according to my observations,
appears to be the true interpretation of the structure of this
kidney. ‘Ihe excretory cells (fig. 37) are pear-shaped bodies
with very Jarge nuclei and very granular protoplasm, in
which are embedded large round granules of a greenish
colour, evidently products of excretion. The ciliated cells
(fig. 37) lining the main passages of the acini and the trinary
chamber are much smaller than the true excretory cells, the
protoplasm is not so granular, and they rarely if ever con-
tain any excretory granules.
Genital Organs.—The genital gland (figs. 39, 40, g. g.) is
in both sexes situated external to the liver, and extends up
to the termination of the spire of the visceral mass. A
difference of colour in this gland is almost the only character
by means of which the male can be distinguished from the
female.
In T. lineatus the male gonad is pink, while that of the
female is green in colour. In both sexes the gemtal products
are discharged through a genital duct (figs. 35, 36, g. d.) into
the urinary chamber of the right kidney. ‘This duct was first
ANATOMY AND AFFINITIES OF THE TROCHIDA., 49
correctly described by Pelseneer (86, p. 54), who found that
it opened into the right reno-pericardial canal. The genital
duct, or rather that portion which is common to the right
reno-pericardial canal and the genital duct, opens into the
right kidney on a small papilla (fig. 36, g.d.). From the
cavity of the right kidney the genital products are discharged
into the mantle-cavity through the ureter. In the male the
ureter is quite unmodified, but in the female the terminal
portion is enlarged, either as a thick-walled ampulla, as in
members of the sub-genus Calliostoma (figs. 43, 49, amp.),
or as a rosette-shaped enlargement in the members of the
sub-genus Gibbula (figs. 39—42).
The Alimentary Canal.—The mouth, situated on the
ventral surface of the snout, leads into a_ thick-walled,
muscular, buccal cavity, on the antero-lateral walls of which
are placed two chitinous jaws (figs. 12, 13). These jaws are
moderately well developed in both T. zizyphinus (fig. 12)
and T. granulatus; each jaw being made up of two
portions—a large outer plate-lke part and an inner smaller
structure, the free margin of which is irregular, and fringed
with chitinous projections. In‘. magus (fig. 13) and the re-
maining species of Trochus examined the jaws are com-
paratively small and insignificant, consisting of very thin
membranous structures composed of chitinous tesseree, which
are more or less restricted to the free margins; there is no
indication of the small inner plate that occurs in Tl’. zizy-
phinus.
A section through the jaw and its associated parts reveals
the fact that each rod-like chitinous tessera is secreted by a
single cell (fig. 14). On the outer margin of the jaw there is
a thin limiting membrane (0. m.) covering the exposed
faces of the tessere (¢. s.); the tessere are long rod-like
bodies closely applied to each other; they present a finely
striated appearance, the striae being arranged in a longi-
tudinal direction. Immediately underlying these and attached
to their basal ends are the formative cells (f. c.), each
tessera being connected to an individual cell. These cells are
50 W. B. RANDLES,.
elongated bodies, whose protoplasm is finely granular, the
granules being arranged in longitudinal striz; each cell
encloses a large oval nucleus.
The formative cells rest upon a clear, thin, structureless
basement membrane (b. m.), which is in turn succeeded by a
layer of muscle-fibres (m. f.) with elongated nuclei.
In many of the exotic Trochide (e. g. T. niloticus, etc.)
jaws are entirely absent.
Closely attached to the body-wall by radiating muscle-
fibres is the buccal mass (figs. 39, 40, 44) ; this is a very
muscular structure, and is supported by the large odontophore
(od.), consisting of two pairs of odontophoral cartilages ; the
larger and anterior pair serve mainly for the support of the
radula, while the smaller basal and posterior pair present
concave surfaces upon which the anterior cartilages articulate,
and also serve as fixed points for the attachment of the
majority of the protractor and retractor muscles of the
odontophore.
The radula is extremely long, and is ensheathed in a
radula-sac (7. s.), which, after emerging from between the
anterior pair of odontophoral cartilages, becomes involved in
the general torsion of the body, and, though situated ventral
to the crop anteriorly, is twisted over the right side, so that
the posterior portion eventually comes to he on the dorsal
surface of the crop.
The terminal portion of the radula-sac is bifid in T.
lineatus (fig. 40, rv. s.), T. magus (fig. 39, vr. s.), and all
other species belonging to the sub-genus Gibbula. In
T. granulatus and T. zizyphinus there is no trace what-
ever of this bifurcation.
The radula of Trochus is typically rhipidoglossate.
Troschel (42) has figured and described the radule of
numerous species of the Trochide.
Amongst the species enumerated in this paper very little
difference in radula structure occurs. We can, however,
distinguish between two fairly distinct types, represented by
T. granulatus and T. zizyphinus on the one hand and
ANATOMY AND AFFINIITES OF THE TROCHIDS. 51
T. magus and the remaining species on the other. In the
former (figs. 20, 21) the radula is characterised by the
extremely large size of the first or admedian marginal tooth,
also by the serrated edges of the cusps of both the central
and lateral teeth. In the latter the cusps of the central and
lateral teeth are devoid of serrations, but the lateral teeth are
notched on their distal margins, and the central tooth has
notches on both sides of the basal portion of the cusp (figs.
15, 18, 19, 28, 29). The first marginal tooth of these species
is also of considerable size, but not so large relatively as in
T. granulatus or T. zizyphinus. In T. lineatus (fig. 19),
on the contrary, the first marginal tooth differs in no way
from the succeeding ones.
In each transverse row of teeth of the radula of Trochus
the following clearly defined regions can be distinguished.
An unpaired median or rachidian tooth, bordered on either
side by five lateral teeth, succeeding which is an indefinite
number of marginal teeth or uncini. We can represent
the dentition of the radula by a formula as follows :
optiily Wee 3B) cee
The marginal teeth vary considerably in shape and size,
those nearer the central tooth being stouter and shorter than
those more remote. The majority of the marginal teeth or
uncini are hooked (figs. 16, 17, 22—24). he teeth situated
some distance from the centre become slender and elongate
(figs. 24, 25). In T. zizyphinus and T. granulatus
these distal teeth are characterised by the deep serrations
on the margins. In teeth still more remote these serra-
tions (fig. 26) become still deeper, and give a brush-like
appearance to the teeth, though they cannot be compared
to the brush-teeth of Pleurotomaria (45, p. 250, figs.
46—52).
At the extreme distal end of the marginal teeth some nine
or ten specialised teeth are situated. These are flattened, and
present neither serrations nor notches on the margins. They
52 W. B. RANDLES.
are spread out in a fan-like manner, and constitute the
flabelliform teeth (fig. 27).
It will be seen on examination of figs. 28 and 29 that the
radulee of T. striatus and I’. exasperatus approximate
more nearly to the Gibbula than to the Calliostoma type,
in that the cusps of the central and lateral teeth are unserrated,
but bear on their distal margins very distinct notches, such as
are present in T’. magus.
It is almost impossible to compare the radula of Trochus
with that of Pleurotomaria, as in the latter we find no
trace of the clearly marked regions which the radula of
Trochus presents. The radula of Pleurotomaria is also
obviously specialised in the possession of such extremely
modified structures as the brush and lamellate teeth. A
peculiar feature of the Pleurotomarian radula is the presence
of a series of accessory basal plates, situated underneath, and
alternating with the bases of the uncinate teeth (Woodward,
45, p. 252, fig. 52). A similar series of basal plates is present
in the radula of Trochus, occupying a _ corresponding
position, viz. at the base of the uncinate or marginal teeth.
The salivary glands are slightly different in the two
sub-genera Gibbula and Calliostoma, In the former they
are small rod-like bodies (figs. 39, 40, sl. g.) lying on the
dorso-lateral surfaces of the anterior portion of the crop, and
opening into the buccal mass slightly in front of the cerebral
commissure. In T. zizyphinus (fig. 44, sl. g.) and other
species of Calliostoma the salivary glands are larger and
racemose. The duct opens into the buccal cavity immediately
over the anterior end of the odontophore.
The Crop.—The anterior portion of the alimentary canal is
enlarged to form the crop (fig. 39, cv.) ; upon the dorsal
surface a rod-like area can be distinguished, which curves
over from the mid-line towards the left side, eventually
becoming ventral in position.
Communicating with the crop are two lateral diverticula,
viz. the right and left cesophageal pouches, the former being
the larger.
ANATOMY AND AFFINITIES OF THE TROCHIDA. Do
Evidence of torsion having affected the alimentary canal is
furnished by the displaced condition of the posterior portion of
the radula-sac (vide p. 50) and by the rotation of the right
cesophageal pouch to the left side, and vice versa (388,
p. 392). Torsion of the crop and its associated structures has
been described by Woodward (45, p. 236) in Pleuro-
tomaria, andin Turbo and other genera by Amadrut (1)
Just beyond the point at which the radula-sac crosses over
the dorsal surface of the crop this latter becomes much
smaller and thicker walled, and may be regarded as the ceso-
phagus (figs. 40, 45, w.); it passes backwards and ulti-
mately opens into the posterior portion of the stomach.
The stomach (figs. 39, 40, 45, st.) is situated underneath
and behind the right kidney, and is a large sac divided into
an oesophageal or posterior and an intestinal or anterior
chamber. From the posterior region of the stomach there
arises a large spiral cecum (sp.c.), a structure character-
istic of the majority of the Diotocardia.
There is a slight difference in the shape of the stomachs in
the members of the sub-genus Gibbula and those of the
sub-genus Calliostoma. In the latter this organ is more or
less U-shaped, and the spiral caecum arises at the bend of the
U, near the confluence of the cesophageal and intestinal cham-
bers; the intestine leads directly out of the latter, and
does not coil on itself in the manner in which it loops in
T. lineatus (fig. 45) and other species of the sub-genus
Gibbula.
In Calliostoma the spiral czecum consists of many turns,
and the apex of the spire can be distinctly recognised on the
outer surface of the visceral mass. In Gibbula, on the
contrary, the spiral cecum consists of few turns, and the
apex of the spire is deeply buried in the substance of the
liver, only the basal coil being visible on the exterior.
When the interior of the stomach is examined (fig. 45) two
conspicuous folds, arising in the vicinity of the cesophageal
aperture, are plainly visible. ‘These folds are continued up to
and throughout the whole length of the spiral caecum, en-
54 W. B. RANDLES.
closing between them a cecal groove (cx.g). Within this
groove, and situated in close proximity to the aperture of the
cesophagus, the larger of the two bile-ducts opens (b.d). It
may be regarded as a point of considerable interest that in all
Gasteropods in which a spiral czecum is present, and also in
many of the Cephalopoda in which a cecal diverticulum
of the stomach exists, whether spiral or otherwise, there is
always this relationship between the aperture of the bile-duct
and the folds, or rather, the czcal groove bounded by the
folds leading into the spiral cecum or stomachic diverti-
culum. This correlation of structure exists in such archaic
forms as Pleurotomaria, Nautilus, and Spirula (Moore,
30), and is undoubtedly indicative of the homology of the
spiral ceecum of the Gasteropods and the cecal diverticulum
of the Cephalopod stomach.
The stomach of Trochus is lined witha thin membrane of
a chitinous nature (fig. 46, cwt.). This cuticle is a product of
secretion of the epithelium (g. ep.) of which the wall of the
stomach is mainly constituted; this epithelial layer is com-
posed of very elongate columnar cells with large nuclei. The
upper portion of these cells, viz. that part immediately
underlying the cuticle, presents a finely striated appearance.
Between this striated border and the nucleus the protoplasm
of the cells is very granular, owing to the presence of numer-
ous small bodies of a greenish colour; these are probably of
the nature of enterochlorophyll, and comparable to the
granules of enterochlorophyll described by McMunn as
present in the epithelial cells lining the stomach of
Patella!
Subjacent to the gastric epithelium is a thin layer of
muscle-fibres with elongate nuclei, and this layer is further
surrounded by a loose connective tissue, many of the cells of
which contain large granules analogous to those found in the
excretory cells of the right kidney. These (fig. 46) are the
1 ©, A. MacMunn, “On the Gastric Gland of Mollusca and Decapod
Crustacea; its Structure and Function” (‘ Phil. Trans. Roy. Sce. Lond.,’
vol. excili, B. 11, 1900).
ANATOMY AND AFFINITIES OF THE TROCHIDA. 55
plasmatic cells of Brock (9), and appear to be of common
occurrence in the connective tissue of Gasteropods.
The intestine either leads directly out of the anterior or
intestinal chamber of the stomach without becoming folded
upon itself as in T. zizyphinus, or it recurves and crosses
over the stomach as in T. lineatus (figs. 40, 45, at.) ;
becoming folded upon itself several times, it then runs
forward to about the level of the terminal portion of the
radula sac, where, bending on itself to form a y-shaped loop,
it retraces its course towards the posterior end of the body,
and on reaching the level of the pericardium curves dorsally
and horizontally, entering the pericardium and penetrating
the ventricle. After emerging from the pericardium it again
curves, and entering the mantle-cavity runs along the roof of
that structure towards the anterior end of the body, debouch-
ing into the mantle-cavity by the anus, which is situated near
the middle line. The terminal portion of the rectum (r.) is
enveloped by the hypobranchial gland (im. g.)..
The Vascular System.—The heart (figs. 39, 47) is
enclosed within a large pericardium, which is situated at the
distal end of the mantle-cavity, abuts on the left kidney,
and is bounded on its posterior border by the right kidney and
stomach. The ventricle (v.) is traversed by the rectum and
is very muscular. It is situated nearly transversely, passing
from right to left of the body ; on the left side the ventricle
is enlarged into a bulbous structure, the aortic bulb, from
which arise two large arteries, the posterior and anterior
aortee. Communicating with the ventricle are two thin-walled
auricles; of these the left (J. aw.) is the larger, and is
situated in the anterior portion of the pericardium; the
right auricle (7. au.) is situated in the posterior region of the
pericardium, and, though of smaller calibre than the left, is
much longer. The walls of both right and left auricles are
very thin, and are produced into numerous fringe-like
processes which, when examined microscopically, are seen to
be clothed with numerous large epithelial cells (fig. 838), each
containing a large round nucleus and protoplasm having
56 W. B. RANDLES.
a granular appearance. These cells are manifestly glandular,
and present a very striking resemblance to the excretory cells
of the right kidney; they constitute the so-called peri-
cardial gland, and according to Grobben! and Perrier (87,
p. 127), the products of excretion are conveyed out of the
pericardium to the exterior through the left reno-pericardiat
canal and papillary sac.
The posterior aorta (figs. 39, 47, p. ao.) arises from the
aortic bulb, crosses over the right kidney and stomach, giving
off branches to the latter; it then curves under this organ,
follows the inside of the visceral spire to its apex, and dis-
tributes branches to both liver and gonad.
The anterior aorta (a.qao.), which also arises from the
aortic bulb, is situated on the left side of the body between
the body-wall and the ascending portion of the intestine. It
follows the course of the intestine for a considerable distance,
furnishing it with several branches, crosses to the right,
passing over the crop, and penetrates between the crop
and radula-sac ; 1t supplies the buccal mass with vessels,
and then recurves to form a sinus situated above the ventral
nerve-cords ; from this the blood penetrates into the lacunee of
the foot.
The venous system is chiefly lacunar, sinuses being con-
spicuous in the foot, especially in the glandular portion on
the dorsal surface. ‘The blood returning from the posterior
region of the visceral mass traverses the right kidney by
numerous sinuses; these are collected into a large vessel, the
efferent renal vein (fig. 48, e.7.v.), which passes into the
mantle-cavity, where it unites with a vessel bringing blood
from the sinuses of the anterior portion of the body; the vein
formed by the union of these vessels crosses over the rectum,
and, emerging from between the apertures of the right and
left kidneys, traverses the mantle from right to left as the
transverse pallial vein (figs. 39—438, t. p. v.) ; 1t receives
fo) ) +)
1 Grobben, C., ‘Die Pericardialdrtise der Lamellibranchiaten (ein Beit-
rag zur Kentniss der Anatomie dieser Molluskenclasse),” ‘ Arb. zool. Inst.
Wien.,’ Bd. vii, 1888.
ANATOMY AND AFFINITIES OF THE TROCHIDA. 57
vessels bringing blood from the lacunee of the anterior por-
tion of the mantle and the perirectal sinus. This vein then
runs along the branchial support, distributing blood to the
lamellee of the gill, constituting in fact the afferent
branchial vein. Part of the blood conveyed by the trans-
verse pallial vein is distributed directly to the left kidney by
two sinuses (fig. 42) arising from that vein as it crosses over
the rectum and emerges between the renal apertures. These
sinuses follow the right and left borders of the papillary sac,
and communicate with the lacune of that organ. The blood,
after passing through the lacune of the papillary sac, is col-
lected into a small vessel which communicates directly with
the left auricle. After aération, the venous blood distributed
to the gill is collected into a large efferent branchial vein
(figs. 39—43, e.b. v.), which runs along the base of the gill
and conveys the arterialised blood to the left auricle.
The right auricle also communicates with the lacune of
the papillary sac, receiving some of the venous blood passing
through that organ. In consequence of the suppression of
the right gill there is no functional efferent branchial vessel
communicating with the right auricle, though it is possible
that a very small vessel which runs on the mantle-wall under-
neath the rectum and communicates with the right auricle
may, according to Thiele (41), represent a vestige of the right
efferent branchial vein.
Nervous System.—The nervous system of the Trochide
presents no differences of importance in any of the species so
far examined. Suchformsas T.striatus, Tl. tumidus, etc.,
being far too small for satisfactory results to be obtained by
dissection, were embedded in paraffin wax and cut into serial
sections, and from an examination of these sections the main
features of their anatomy were subsequently made out, the
nervous system being reconstructed by the method of build-
ing up in wax.
The distribution of nerve-cells is of particular interest. In
Pleurotomaria there isa very general distribution of nerve-
cells throughout a greater part of the nervous system (Wood-
vou. 48, PART 1.—NEW SERIES. 5
58 WwW. B. RANDLES.
ward, 45, p. 240), cccasionally on the nerves themselves
as well as on the commissures and connectives. In this genus
there is scarcely any aggregation of nerve-cells into ganglia,
the only indication of definite nerve-centres being the points
of origin of the various characteristic nerves.
In Trochus, however, the nervous system is more highly
developed, there being definite ganglia in which a concen-
tration of nerve-cells has taken place, and moreover, though
nerve-cells may occasionally occur on the various connec-
tives, they are practically absent along the commissures,
and are thus much more restricted with regard to their
localisation and distribution than is the case in Pleuroto-
maria.
The cerebral ganglia (figs. 30, 40, 44, cb. g.) are situated
on the sides of the anterior portion of the buccal mass, and
are united with each other by a long cerebral commissure
(cb. c.). Nerves are given off from these centres to the snout,
the cephalic lappets, the tentacles, and the eyes, the branches
innervating these two latter structures being quite distinct,
and not, as occurs in Pleurotomaria, arismg from a common
root. From the ventral portion of the cerebral ganglia a
rather broad band is given off, from which two important
nerves arise; one of these, at first comparatively large, but
eventually becoming thin and delicate, passes laterally and
ventrally under the buccal mass, uniting with its fellow of
the other side, and forming the labial commissure (figs. 50,
44, 1. c.). The other nerve which arises from the enlarged
portion of the labial commissure is the buccal or stomato-
gastric nerve (figs. 30, 44). It curves upwards over the
odontophore and penetrates between this structure and the
dorsally situated cesophagus, where it enlarges into the
buccal ganglion (b.g.). The buccal commissure which unites
the ganglia of either side is as well supphed with nerve-
cells as the ganglia themselves, and it is only by the shght
enlargement of the commissure into two masses that we can
speak of definite buccal ganglia. Several nerves are given
off both from the ganglionic enlargements and the commissure ;
ANATOMY AND AFFINITIES OF THE TROCHIDA. 59
these are distributed to the crop, salivary glands, and the
odontophore.
This peculiar method of origin of the stomatogastric nerves _
in Trochus, in arising from the same root as the labial
commissure, finds its parallel not only in Pleurotomaria
(Woodward, 45, p. 242), but also in Patella and Chiton
(Pelseneer, 36, p.48). The extreme fineness of the connectives
uniting the buccal ganglia to the cerebrals, and the fact that
they are only indirectly connected with the latter, arising in
reality in common with the labial commissure, is in all
probability the reason which led Béla Haller (19, p. 26,
pl. i, fig. 3) to overlook the true point of origin of these
nerves, and to suppose that they originated from the sub-
cesophageal mass.
From the posterior border of each cerebral ganglion two
long connectives, the cerebro-pedal (cb. p.), and the cerebro-
pleural (cb. pl.) arise, the latter being the larger of the two.
These cords pass backwards over the odontophore and
penetrate the floor of the body-cavity, where they unite with
the large ganglionic mass, representing the pleural and pedal
ganglia.
The pleural ganglia (pl. g.) in Trochus are perfectly distinct
structures, and are situated at the anterior extremity of the
ventral or pedal nerve-cords (figs. 30, 40, pl. g.) as two pro-
jectine horns immediately in front of the anterior commissure
which unites the pedal cords. ‘he close approximation of
the pleural and pedal ganglia is undoubtedly a specialised
condition, and is in all probability due to the shortening of the
pleuro-pedal connective, which in 'l'rochus has become almost
entirely obliterated, the basal portion of the pleural being
fused to the anterior portion of the large ventral pedal nerve-
cords. Such a condition, though unusual in Prosobranchiate
Gasteropods, is not unique, being met with in Cyclophorus
and also in Ampullaria.
From the pleural ganglia are given off right and left pallial
nerves (figs. 50, 59, pa.n., pa. v’.). These branch shortly
after entering the mantle, the anterior nerves being distributed
60 W. B. RANDLES.
to the anterior thickened margin of the mantle, where they
eventually unite with one another, forming a circumpallial
anastomosis (Pelseneer, 36, p. 50). ‘The posterior branch
of the pallial nerve is distributed to the posterior portion of
the mantle which ensheathes the columella muscle. In
addition to the pallial nerve a collumella nerve is given off
from the pleural ganglion.
Visceral Commissure.—The right or supra-intestinal
branch (fig. 80, sp. int.) of the visceral loop arises from the
right pleural ganglion slightly in front of the pallial nerve of
this side. It passes upwards over the odontophore and
through a fold in the dorsal wall of the crop to the left side
of the body, where it penetrates the body-wall. Here it gives
origin to two nerves, one going to the large branchial
ganglion (bn. g.) which is situated at the base of the gill, the
other nerve (d.) running to and anastomosing with the left
pallial nerve, thus presenting a condition of dialyneury on
the left side of the body. At the point of origin of these two
nerves there is a slight enlargement and concentration of
nerve-cells, and we can consequently look upon this centre as
representing the supra-intestinal ganglion, though it is by no
means so large or so clearly defined as delineated by Pelseneer
(86, pl. xvii, fig. 148). The branchial ganglion innervates
both the gill and the osphradium. ‘The supra-intestinal
branch of the visceral commissure then continues its course
along the left side of the mantle-cavity, situated in the angle
between the body-wall and the gill, it runs parallel to the
latter structure until it reaches the level of the papillary sac,
where it crosses the body from left to right, passing above
the cesophagus and intestine, and terminating in the abdominal
ganglion (ab. g.) which is situated under the epithelium of
the floor of the mantle-cavity.
The subintestinal branch (fig. 30, swb. int.) of the visceral
loop arises from the left pleural ganglion by a trank common
to both this nerve and the left pallial nerve; it then passes
underneath the cesophagus and radula-sac, and continues its
course on the right side of the body between the cesophagus
ANATOMY AND AFFINITIES OF THE TROCHIDA. 61
and the columella muscle until it reaches the aforementioned
abdominal ganglion. There is no trace of a subintestinal
ganglion, and neither by the method of dissection nor by the
examination of serial sections have I been able to make out
any trace of an anastomosis between the subintestinal nerve
and the right pallial nerve, though sucha connection has been
indicated by Bouvier (8, p. 171, fig. D).
The common origin of the subintestinal branch of the
visceral commissure with the left pallial nerve does not
appear to have any special morphological significance, as in
one specimen of I’. cinerarius, the nervous system of which
was modelled in wax from serial sections, exactly the reverse
condition obtained, the supra-intestinal nerve and the right
pallial nerve having a common origin from the pleural
ganglion, the subintestinal branch arising in front of the
left pallial nerve.
The abdominal ganglion (ab. g.) gives origin to three im-
portant nerves. One arising anteriorly is distributed to the
rectum, a median large branch, the visceral nerve (v.7.),
runs along the inside of the visceral spire and innervates the
stomach, liver, and genital gland, while the third nerve is dis-
tributed to the right kidney and heart.
The visceral loop in Trochus is typically streptoneurous.
The ventral or pedal nerve-cords (figs. 30, 40,
pd.c.) are paired structures running in the muscular mass of
the foot throughout its entire length. On their outer lateral
surfaces they are superficially divided into halves by a longi-
tudinal groove (fig. 40). At the anterior end of the foot
these cords approximate one another closely, and are united
by a thick anterior pedal commissure. As they proceed
through the muscle of the foot they diverge shghtly, being
furthest apart at their middle portion, and begin to converge
again as the posterior end of the foot is reached.
In addition to the thick anterior pedal commissure there
are numerous thin transverse commissures joining the pedal
cords together, and giving to them their characteristic
scalariform appearance. Ganglion-cells are distributed evenly
62 W. B. RANDLES.
on the periphery of the pedal cords throughout their whole
length, but are not concentrated into any particular place
which might be termed a pedal ganglion. There is an entire
absence of nerve-cells on the transverse commissures.
Numerous nerves are given off from the pedal cords ; trom
their external lateral surfaces nerves are distributed to the
epipodia and lateral portions of the foot, while on the ventral
surface large nerves originate, and are distributed to the
ventral portion of the foot.
With respect to the composition of these ventral or pedal
nerve-cords of T'rochus and the Diotocardia generally,
there is a considerable amount of diversity of opinion, and
this has led to a somewhat lengthy discussion between the
supporters of two theories that exist at present.
One of the views held concerning the composition of the
pedal nerve-cords is to the effect that they are of a double
nature, consisting of both pleural and pedal elements ; while
the other view regards the nerve-cords as being purely
pedal.
The chief exponent of the former view is Lacaze Duthiers,
who bases his opinion upon anatomical grounds and relation-
ship of parts. During his investigation on the nervous
system of Haliotis (26, p. 272) he came to this conclusion,
and at the same time promulgated the theory that the
epipodium was a pallial structure. Later on he extended his
observations to the Trochide (27), and found the same
condition existing in the pedal cords of this family. In the
longitudinal cords of both Haliotis and Trochus, and also
as has recently been demonstrated in Pleurotomaria, there
is on the outer surface an external groove running along them
to their extremities, and dividing them superficially into an
upper and lower half. Moreover in certain of the Trochide
there is astill further distinction in the fact that the upper half
is white in colour, while the lower part is yellow. Lacaze
Duthiers regards the upper portion of the cords as pleural in
nature and the lower part as pedal. The nerves given off to
the epipodium are, according to this view, conceived as
ANATOMY AND AFFINITIES OF THE TROCHIDA. 65
arising wholly from that portion of the ventral nerve-cord
which is situated above the longitudinal groove, and are
therefore pleural, while the nerves distributed to the foot arise
from the lower half of the cord, and hence are exclusively
pedal; the epipodium being consequently a pallial structure.
Spengel (39, pp. 343, 344), Haller (19, pp. 3, 22), Thiele
(40), and Pelseneer (81—35) deny this double nature of
the pedal cords, and can see no apparent trace of any morpho-
logical separation into halves. ‘hey base their opinion on
histological grounds, and find from the examination of
sections that, though a conspicuous longitudinal groove is
present on the outer side of each cord, there is uno trace
of histological differentiation between the halves of the
cords separated by the groove, and moreover, that micro-
scopical examination with the highest powers fails to reveal
the presence of any connective tissue separating them. Lacaze
Duthiers (29) agrees with Spengel as to the entire absence
of any connective tissue sheath between the halves of the
cords, but he asserts that this does not indicate the ab-
sence of any separation, that the separation is not necessarily
a histological one, and that there is most decidedly a
physiological differentiation of the nerve-cords ; he cites in
confirmation of his view the fact that in the majority of
Gasteropods (Patella, for example) the auditory nerve, which
runs from the cerebral ganglion to the otocyst, is indis-
tinguishably fused with the cerebro-pleural connective, and
that there is no connective-tissue sheath separating the
auditory nerve from the connective. There is, however, a
physiological separation between the two nerves.
‘his view is held by other investigators. Wegmann (44)
considers that the epipodium of Haliotis is a pallial
structure, and that the nerve innervating it is pleural in
origin, as it arises from that portion of the pleuro-pedal (?) or
ventral nerve-cord situated above the longitudinal groove.
He has found that during dissection the pleuro-pedal cord is
apt to break, the rupture occasionally taking place in such
a manner as to separate the pleural from the pedal half
J
64. W. B. RANDLES.
moreover, the epipodial nerve has come away intact with the
pleural portion of the cord, while those nerves distributed
to the foot have remained on the pedal half.
Boutan also supports the theory of the double nature of the
pedal cord from his investigations on the anatomy of Fis-
surella (8) and Parmophorous (4). In the latter genus he
distinguishes three kinds of nerves given off from the ventral
nerve-cord: (1) from the lower surface, nerves which go
exclusively to the foot; (2) laterally, nerves distributed to the
collarette, i. e. the epipodium or inferior mantle ; (3) between
these latter, nerves which go directly to the mantle; thus both
pedal and pleural nerves are given off from the lower and
upper halves respectively of the ventral nerve-cord.
Bouvier and Fischer (8) also regard these nerve-cords as
consisting of pleural and pedal halves and the epipodium as
a pallial structure; they, however, consider that many of the
nerves given off from these cords contain fibres from both
pleural and pedal halves, that these nerves in fact consist of
mixed fibres.
If, however, the ventral nerve-cords are purely pedal, as
Spengel and others maintain, it is obvious that the epipodium,
being innervated from a pedal centre, must be regarded as an
outgrowth of the foot, having no connection whatever with
the mantle.
Arguments in favonr of this view are based upon histo-
logical investigations. Haller (20) finds that in Turbo nerve-
fibres pass from the upper to the lower portion of the ventral
nerve-cord. Again, Woodward (45) finds the same condition
obtaining in Pleurotomaria. Pelseneer, who has always
maintained that the epipodium is a pedal structure, and that
the ventral nerve-cords are entirely pedal, has recently
(36, p. 49) shown that the epipodial nerves receive fibres
from both upper and lower halves of the nerve-cords. From
the examivation of numerous serial sections, both transverse
and longitudinal, of various species of Trochus I have been
able to confirm this observation of Pelseneer’s, and find that
the nerves going to the epipodium have a double origin
ANATOMY AND AFFINITIES OF THE TROCHIDA. 65
(fig. 31), receiving fibres from both upper and lower halves of
the cords. This would necessarily indicate that the epipodial
nerve is constituted in part, at any rate, of pedal fibres; and
if we consider with Lacaze-Duthiers, Bouvier, etc., that the
upper part of the ventral nerve-cord is pleural in nature, then
the epipodium has a mixed innervation, its nerve being com-
posed of both pleural and pedal fibres. But the examination
of other sections has revealed that this mixing of fibres is not
confined exclusively to the epipodial nerves. ‘The transverse
commissures between the pedal cords are themselves com-
posed of fibres from both halves of the cord (fig. 32). These
commissures apparently connect only the lower halves of the
cords, and it is only in sections that we can see that they
originate from the upper as well as the lower halves of the
cords. Again, fibres from the top portion of the cord may be
distributed to definitely pedal nerves. Woodward has
described such a condition as occurring in the large latero-
ventral pedal nerves of Pleurotomaria, in which fibres are
received from both upper and lower portions of the cord,
these often forming a conspicuous double root to the nerves.
The transverse commissures connecting the pedal cords of
Pleurotomaria are, as in Trochus, composed of nerve-
fibres from both halves of the cords.
A conclusive proof of the purely pedal nature of the ventral
nerve-cords is in my opinion furnished by the transverse
section (fig. 33) of the foot of Trochus. Here we have
a large nerve given off from the ventral surface of the
pedal cord and distributed to the sole of the foot; this
receives fibres chiefly from the lower half, but in addition it
has a bundle of fibres running to it from the very top portion
of the ventral nerve-cord, and these fibres are partially
separated from the lower half of the cord by a mass of
ganglion-cells. We have thus a nerve supplying only the
foot, consisting of fibres from both portions of the cord,
and unless we regard the ventral cords as being purely
pedal in composition we have the anomalous condition
of an undoubtedly pedal nerve consisting of both pedal and
66 W. B. RANDLES.,
pleural fibres. It seems much more rational to regard
these structures as entirely pedal, and consequently the
whole of the ventral nerve-cords as purely pedal in com-
position; in this case the epipodium must be looked upon
as an outgrowth of the foot, supplied by pedal nerves,
and we can only regard as pleural centres or ganglia the
two ganglionated horns which le dorsal to the pedal
centres, and from which are given off the visceral com-
missures and the pallial nerves. In Pleurotomaria the
pleural centres are not so well defined as in ‘’rochus; the
visceral loop arises from the cerebro-pleural connective, no
definite concentration of nerve-cells into gangha having
occurred. Here we must look upon that part of the
connective between the cerebral centre and the pedal cords
from which the visceral loop and pallial nerves are given off
as alone representing the pleural centres, no pleura! elements
whatever entering into the composition of the ventral nerve-
cords.
In T'rochus the more definite concentration of nerve-cells
into a pleural ganglion, and the shortening of the pleuro-
pedal connective, causing the close proximity of the pleural
to the pedal centre, constitute the main differences between
the nervous system of this genus and that of Pleurotomaria,
The Sense Organs.—The eye consists of a pigmented
optic cup communicating with the exterior by means of a
small circular aperture in the cornea. Filling the imterior of
this cup is a large spherical vitreous body, the crystalline
lens.
The histology of the eye has been investigated by Hilger
(22).
The otocysts (fig. 30, ot.) are large sac-like bodies lying
on the upper surface of the anterior extremity of the pedal
nerve-cords. Theauditory nerve (of.7.) passes from the otocyst
over the upper surface of the pedal ganglion and runs to the
cerebro-pleural connective, which it accompanies to the cerebral
ganglion. At the point where the otocyst nerve communicates
with the auditory sac a small diverticulum of the sac enters,
ANATOMY AND AFFINITIES OF THE TROCHID”. 67
and runs some little distance into the nerve. ‘This diver-
ticulum, though destitute of specialised sensory cells, con-
tains several of the numerous otoconia that are present in
the auditory sac.
Lacaze Duthiers, in his memoir on the otocysts of Molluses
(27), has described a somewhat similar condition in Patella.
The osphradium (figs. 41—45, os.) is a small patch of
specialised sensory epithelium of a yellowish colour situated
under the branchial ganglion, and extending for a short
distance along that portion of the gill-base which lies free
in the mantle-cavity. Bernard (2, pp. 167—173) has given
a detailed account of the histological structure of the osphra-
dium.
Other sense-organs are the cephalic and epipodial tentacles,
which are undoubtedly tactile. ‘The epipodial papille have
probably a similar function.
Sensory cells occur in the buccal cavity of Trochus,
similar to those described by Haller (19, pl. vi, fig. 28) as
occurring in the buccal cavity of Fissurella, and may be
gustatory im function.
In addition a peculiar series of sensory organs, first men-
tioned by Thiele (41), is found occurring in the mantle-cavity
on the right side, in the angle between the mantle and body-
wall.
Conclusions.—lIt will be seen from the foregoing account
that the various species of ‘'rochus examined present very
few anatomical differences; it 1s, however, possible to dis-
tinguish between two slightly diverse types of organisation,
the characters of which are sufficient to constitute different
sub-genera. Retaining the existing nomenclature, we have
the one sub-genus Calliostoma, in which the shell is pyra-
midal, and into which the following species can be placed :—
T. zizyphinus, T. granulatus, T. striatus, T. exaspe-
‘atus, and I’. Montagui. In another sub-genus, Gibbula,
we can include the remaining forms, viz. T. magus, T. cine-
rarius, T. umbilicatus, T. tumidus, and IT. lineatus.
The sub-genus rochocochlea, in which this latter species
68 W. B. RANDLES.
has previously been placed by conchologists, cannot be retained,
as the internal organisation of this species, and also that of
T. turbinatus (Born), as described by Robert (38), another
species previously included in the sub-section Trochoco-
chlea, is almost identical with the anatomical structure of
T. magus or other species of Gibbula.
As I was unable to obtain any specimens of species belong-
ing to the so-called sub-genus Margarita (Leach), I cannot
say whether sufficient anatomical differences occur to warrant
the existence of this separate sub-genus.
So far, then, anatomical investigations have revealed such
striking similarity of structure as to necessitate the reduction
of sub-genera amongst British Trochide, and it is highly pro-
bable that an anatomical examination of exotic species will
still further considerably reduce the very numerous sub-
genera into which these have been classified.
Although both T. zizyphinus and I. granulatus differ
in many ways from T. magus and other species of Gibbula,
yet the smaller species, I’. striatus and T. exasperatus,
though they have been included in the sub-genus Callios-
toma, agree in some respects more closely with T. magus and
its allies than with T. zizyphinus. ‘his is chiefly in respect
to their external characters; both of these small forms possess
epipodial papille and an appendix on the right ocular
peduncle, while these structures are absent in T. zizyphinus.
Moreover the glandular structure on the dorsal surface of
the foot more nearly resembles that seen in T, magus. In
respect to the structure of the radula of these species, the
condition is an approximation to the Gibbula rather than the
Calliostoma type. On the other hand, the presence of a
transverse notch on the anterior margin of the foot, and also
the enlargement of the terminal portion of the ureter into an
ampulla, together with the arrangement of the alimentary
canal and spiral cecum, tend to show their relationship with
T. zizyphinus and TT’. granulatus, and as their shell is
pyramidal in shape, it seems necessary to include them in
the sub-genus Calliostoma.
ANATOMY AND AFFINITIES OF THE TROCHID. 69
The remarkable resemblance of the internal organisation of
the Trochide, more especially of the species of Calliostoma,
to that of Pleurotomaria is of considerable interest as exem-
plifying the very close relationship which exists between these
genera. There is very great similarity existing between the
digestive, excretory, circulatory, and nervous systems of these
two types. Undoubtedly the nervous system of the Trochidex
is much more specialised than that of Plenrotomaria; there
is a greater tendency to the concentration of nerve-cells into
definite ganglia, and the close approximation of the pleural
ganglia to the pedal ganglia is without doubt a speciali-
sation, the most usual condition in Gasteropods being the
approximation of the pleurals to the cerebrals. The sup-
pression of the right gill in the Trochidee is of little importance
when we consider that in Pleurotomaria the right gill begins
to show a tendency towards suppression, since it is smaller
in size than the left gill. That one gill has been entirely
suppressed in Trochus, but that it undoubtedly existed in
some ancestral form, is shown by the presence of a vestigial
right afferent branchial vein which communicates with the
right auricle.
The relationship of the two kidneys in the Diotocardia and
the homology of the single kidney of the Monotocardia with
either one or other of these has led to considerable discussion,
many zoologists maintaining that the single Monotocardian
kidney is the homologue of the left kidney or papillary sac of the
Diotocardia, while others seek to homologise the Monoto-
cardian kidney with the right one of the Diotocardia. The
former view is the more generally accepted, and is based on
the relative positions of the kidney and its aperture with
respect to the rectum, receiving additional support from
the presence in the Diotocardia (Trochus) of a reno-peri-
cardial canal placing the left kidney in communication with
the pericardium, and the supposed absence of a similar
structure between the right kidney and the pericardium.
Further, von Erlanger’s researches on the embryology of
Paludina (13) tend to give support to this view. He
70 W. B. RANDLES.
asserts that in addition to the functional kidney which is
situated to the right of the anus before torsion there 1s
present a rudiment of the actual right kidney lying to the
left of the anus before torsion.
This observation, however, as Woodward remarks (45, p.
260), loses its value when we consider that this so-called
rudiment of a right kidney is only apparent as a slight out-
growth of the pericardium which quickly loses its identity
without ever showing any indication of the character of a
true kidney.
On the other hand, Perrier (87) seeks to homologise the
single kidney of the Monotocardia with both kidneys
of the Diotocardia, comparing the true excretory portion
with the right kidney and the nephridial gland with the
left kidney or papillary sac. ‘Thus he considers that the two
distinct kidneys of the Diotocardia have been united to form
the single excretory organ of the Monotocardia.
Woodward also supports this view, and, mentioning that
through suppression of the right gill the two kidneys of
the azygobranchiate Diotocardia approach each other very
closely, he suggests that in early Monotocardia a connection
between these two kidneys was formed, thus enabling the
excretory products of the right kidney to pass through the
left kidney and so to the exterior, while the right kidney-
duct, serving for the transmission of the genital products,
would eventually become completely separated from the
kidney and function entirely as a genital duct, the glandular
portion of the papillary sac then degenerating and remaining
only as the nephridial or renal gland of the Monotocardia.
Haller (21) also maintained the view that the kidney of
the Monotocardia was the homologue of the right kidney of
the Diotocardia, and in Turbo described the presence of a
connection between the right and left kidneys (21, figs. 26,
28). This observation is, however, erroneous. In Ampul-
laria Bouvier (7) has described the presence of two kidneys
which are in communication with one another, one of them
corresponding to the right and the other to the left kidney
ANATOMY AND AFFINITIES OF THE TROCHIDA. 71
of Trochus, and having similar functions and relationships.
Burne (10) has recently shown that a reno-pericardial canal
is present in Ampullaria.
One of the chief objections to regarding the Monotocardian
kidney as homologous to the right kidney of the Diotocardia
was the supposed absence of any communication between
this kidney and the pericardium. This objection has, how-
ever, been removed, for Pelseneer (86) has shown that a right
reno-pericardial canal does exist in Trochus. I have been
able to confirm his observation.
In Fissurella, though this is undoubtedly a specialised
form, the only reno-pericardial canal present is between the
right kidney and the pericardium, and this right kidney is
larger and of more functional importance than the left. Again,
in Patella there are reno-pericardial canals between the
pericardium and both kidneys, though with regard to this
genus there has been considerable diversity of opinion, some
observers maintaining the presence of a right reno-pericardial
canal only, others a left; while v. Krlanger (14) demes the
existence of any canal whatever.
Cunningham (12) was the first to deseribe the presence of
two canals, and lately Goodrich (18) has confirmed this
observation by means of the examination of serial sections,
and still more recently I have been sufficiently fortunate to
obtain exactly the same results as Goodrich, also by means of
serial sections through the pericardium and kidneys.
In Haliotis the left kidney is relatively very small, and,
according to Perrier (87), Wegmann (44), and vy. Hrlanger
(14), it is this kidney alone which communicates with the
pericardium. In a recent paper on the kidneys of Haliotis
Fleure (16) finds that a reno-pericardial canal exists between
the meht kidney and the pericardium, but denies the existence
of a left reno-pericardial canal.
With regard to Pleurotomaria, Woodward (45) has
described a left reno-pericardial canal only. I have examined
his preparations of the kidneys and pericardium, and failed
to find any communication between the right kidney and
72 W. B. RANDLES.
the pericardium, though the pericardium at the point where
a canal might possibly have existed was torn, rendering
accurate observation impossible.
We see, therefore, that in the majority, if not all, of the
Diotocardia a communication exists not only between the
left kidney and the pericardium, but also between the right
kidney and that structure, while in some cases only the right
canal persists. This is undoubtedly a point very much in
favour of regarding the right kidney of the Diotocardia as
giving rise in part, if not wholly, to the single kidney of the
Monotocardia.
When we come to consider the total difference in function
between the right kidney and the left or papillary sac of such
forms as Trochus, Haliotis, and Pleurotomaria, it
seems much more rational to suppose the kidney of the
Monotocardia to have been derived principally from the right
kidney of the Diotocardia, for the function of these organs is
the same in the two groups—since they are the true excretory
organs, whereas the left kidney or papillary sac of Trochus
and its allies has an entirely different function. It is more of
the nature of a lymphatic gland, waste products being
removed from the blood traversing it by a process of phago-
cytosis (Pelseneer, 35).
The nephridial gland of the Monotocardia possesses similar
functions, and so, from a physiological point of view, can
more easily be homologised with the papillary sac of
Trochus.
Von Erlanger (14), in maintaining the homology of the
Monotocardian kidney to the left kidney of the Diotocardia,
seeks to homologise the nephridial gland of the former with
the right kidney of the latter, but as this necessitates a com-
plete inversion of the functions of these organs, it to my
mind seems much more difficult of conception than to accept
Perrier’s view.
ANATOMY AND AFFINITIES OF THE TROCHIDA. 73
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74, W. B. RANDLES.
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ANATOMY AND AFFINITIES OF THE TROCHIDA. 75
36. PrtsenrER, P.—“ Recherches Morphologiques et Phylogénetiques sur
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42. 'TroscuEt, H.—‘ Das Gebiss der Schnecken,’ Berlin, 1856—1863.
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‘Quart. Journ. Mier. Sei.,’ vol. 44, 1901.
EXPLANATION OF PLATES 4—6,
Illustrating Mr. W. B. Randles’ paper on “Some Observations
on the Anatomy and Affinities of the Trochide.”’
REFERENCE LETTERS.
a.ao. Anterior aorta. a. dr. Afferent branchial vessel. a. oc. p. Appendix
of ocular peduncle. a.7.4. Anterior lobe of right kidney. ad.g. Abdomina
ganglion. amp. Ampulla (enlarged portion of ureter in T. zizyphinus). 4.d
Bile-duct. &.g. Buccal ganglion. 4. m. Basement membrane. dz. g. Branchial
ganglion. c¢. J. Cephalic lappets. c. ¢. Cephalic tentacle. cae. g. Ceca
groove. cb. c. Cerebral commissure. cb. g. Cerebral ganglion. cd. p.
Cerebro-pedal connective. cb.p/. Cerebro-pleural connective. c/.m. Columella
muscle, er, Crop. d, Dialyneury (left). e.d.v. Efferent branchial vesse
76 W. B. RANDLES.
e.7.v. Hfferent renal vein of right kidney. ep. Epipodium. ep. ec. Cervical
lobe of epipodium. ep. . Epipodial nerve. ep. p. Epipodial papilla. ep. ¢.
Epipodial tentacles. £ Foot. f. ¢. Formative (chitogenous) cells of tessere.
g. Gill. g.a. Genital aperture. g.d. Genital duct. yg. g. Genital gland.
int. Intestine. j. Jaw. &.c. Kidney chamber (right). 7. Liver. 7. aw.
Left auricle. 7. ¢. Labial commissure. /. & Left kidney (papillary sac).
l.k.a. Left renal aperture. m. Mouth. m./. Muscle-fibres. m.g. Mucous
(hypobranchial) gland. wm. ius. Muscle insertion. ma. Mantle. ma. ec.
Mantle-cavity. o. m. Outer limiting membrane of jaw. 0. x. Optic nerve.
oc.p. Ocular peduncle. od. Odontophore. @. Gisophagus. op./. Opercular
lobe. os. Osphradium. of. Otocyst. of. 2. Octocyst nerve. ovd. Oviduct.
p.ao. Posterior aorta. p. gi. Pedal gland. p. 2. Pedal nerve. p. r. &.
Posterior lobe of right kidney. pa. a. Pallial nerve (right). pa. 2.’ Pallial
nerve (left). pce. Pericardium. pd.c. Pedal cords. pl.g Pleural ganglion.
pl. p. Pleuro-pedal connective. 7. Rectum. 7. aw. Right auricle. 7. 4.
Right kidney. 7. hk. a. Right kidney aperture. 7. p. c. Reno-pericardial
canal (right). 7.’ p. ec, Reno-pericardial canal (left). 7. s. Radula-sac.
sb. int. Subintestinal nerve, s/. g. Salivary gland. sp. c. Spiral cecum.
sp.iné. Supra-intestinal nerve. sf. Stomach. ¢. 2, Tentacular nerve. ¢. p. v.
Transverse pallial vein. ¢s. Tesseree of jaw. uw. Ureter. am. Umbilicus.
v. Ventricle. v. a. Visceral nerve.
PLATE 4,
Fig. 1.—Shell of Trochus magus.
Fie. 2.—Shell of T. umbilicatus.
Fig. 3.—Shell of T. lineatus.
Fie. 4.—Shell of T. zizyphinus.
Fie. 5.—Head of T. umbilicatus, viewed from the right side. x 5.
Fic. 6.—Head and foot of T. granulatus, viewed from the left side. ‘The
anterior part of the foot is represented in section to exhibit the pedal gland.
x 24.
Fie. 7.—Trochus lineatus, viewed from the ventral surface. x 23.
Fie. 8.—Foot of T. granulatus, seen from the dorsal surface. x 3.
Fic. 9.—Dorsal surface of the foot of I. magus. x 2.
Fie. 10.—Operculum of T. magus. x 3%.
Fig. 11.—Operculum of T. zizyphinus. x 4.
Fig. 12.—Jaws of TI. zizyphinus. x 12.
Fic. 13.—Jaws of T. magus. xX 25.
Fic. 14.—Transverse section of the jaw of T. zizyphinus. x 250,
ANATOMY AND AFFINITIES OF THE TROCHIDA. 77
lic. 15.—Radula of T. magus; portion of a single transverse row of
teeth. x 75.
Fiés. 16 anp 17.—Radula of T. magus; marginal teeth. x 75.
Fie. 18.—Radula of T. tumidus; portion of a transverse row of teeth.
x 200,
PLATE 5.
Fie. 19.—Radula of Trochus lineatus; portion of a transverse row of
teeth. x 75.
Fie. 20.—Radula of T. zizyphinus; part of a transverse row of teeth.
x 75.
Fig. 21.—Radula of T. granulatus; part of a transverse row of teeth.
x 7d.
Vies. 22—24.—Marginal teeth of T. zizyphinus. x 75.
Fic. 25.—Marginal tooth of T. granulatus. x 75.
Vie. 26.—Marginal tooth of T. zizyphinus. x 75.
Fic. 27.—Flabelliform teeth of T. zizyphinus. x 75.
Vic. 28.—Radula of T. striatus; part of a transverse row of teeth.
x 250.
Vie. 29.—Radula of T. exasperatus; part of a transverse row of teeth.
X 250.
Fie. 30.— Diagram of the nervous system of T. cinerarius, viewed from
above.
Fie. 31.—Transverse section through the anterior portion of the ventral
(pedal) nerve-cord of T. cinerarius (right side). x 75.
Fig. 32.—Transverse section through the middle region of the pedal nerve-
cords of T. umbilicatus, passing through the anterior epipodial nerve. x75.
Fig. 33.—Transverse section through the anterior region of the pedal nerve-
cords of Trochus. xX 75.
Vie. 34.—Longitudinal section through the papillary sac and left reno-
pericardial canal of T. magus (semi-diagrammatic). x 12.
Fie. 35.—Section (oblique) through the pericardium and kidneys of
T. magus, showing the right reno-pericardial pore and the genital duct.
x 15.
Fic. 36.—Section (oblique) through the pericardium and kidneys of
T. magus, showing the genital duct (oviduct) opening on a small papilla into
the ureter (or right kidney-chamber). x 15.
Vic. 37.—Section through the right kidney of T. magus. x 400.
Fic. 38.—Section through part of the left auricle of T. magus, passing
through the pericardial gland. x 350.
78 W. B. RANDLES.
PLATE 6.
Fic. 39.—General dissection of T. magus from above. The mantle has
been cut along the middle line up to the pericardium, each half being reflected ;
the floor of the mantle-cavity and dorsal surface of the head have been removed
to show the arrangement of the viscera. X 33.
Fic. 40.—General dissection of T. lineatus from the right side. The
mantle has been cut on the right side, close to the body-wall, and reflected to
the left. The body-wall has been removed from the right side of the head and
body. x 3.
Fic. 41.—Pallial complex of T. magus. The mantle has been cut along
the right and left sides and removed from the body; the pericardium, heart,
and part of the right kidney being removed with it. x 2.
Fie. 42.—Pallial complex of T. lineatus, removed from tle body as above.
xX 2.
Fie. 43.—Pallial complex of T. zizyphinus. x 3.
Fic. 44.—Side view of the buccal mass of ‘I. zizyphinus, showing the
salivary gland, cerebral ganglia, buccal nerves, and labial commissures. X 3.
Fic. 45.—Stomach of T. lineatus opened to show internal structure.
x 5.
Vie, 46.—Section through the stomach of T. lineatus. x 350.
Fic. 47.—Heart of 'T. magus, seen from above. The roof of the peri-
cardium has been removed. X 4.
Fie. 48.—Pericardial cavity of T. magus; the heart and rectum have been
removed together with the roof of the pericardium. ‘The apertures of the two
reno-pericardial canals are seen on thie left side, and the large efferent renal
vein on the floor of the pericardial cavity. x 5.
Fic. 49.—Dissection of the right kidney of T. zizyphinus, showing the
anterior and posterior lobes, the ampullary enlargement of the ureter, also the
opening of the oviduct into the ureter (semi-diagrammatic). x 3.
THE ANATOMY OF P@&CILOCHATUS, CLAPAREDE. 79
The Anatomy of Pecilochetus, Claparede.
E. J.
By
Allen, D.Sc.,
Director of the Plymouth Laboratory of the Marine Biological Association.
With Plates 7—12 and one Figure in the Text.
Historical.
Occurrence at Plymouth
Habits
Methods .
External Characters
Internal Anatomy and Histolony
Epithelium and Cuticle
Kpithelial Gland-cells
Palps
Cheetee
Nervous System
Lateral Sense-organs
Nuchal Organ .
Hyes . :
Alimentary Canal.
Body-cavity
Musculature
Blood System .
Nephridia and Mephroniaig
Genital Products .
The Divisions of the Body
Parasites . :
Systematic Position.
The Species of Brreivehatns
Definitions
Literature
Explanation of Plates
ConreENTS.
PAGE
80
81
83
84
8h
93
94
100
101
101
106
112
115
115
123
124
126
132
135
138
140
140
142
144
145
147
80 Be AGLEN:
HISTORICAL.
CLAPAREDE, in his ‘ Beobachtungen iiber Anatomie und
Entwicklungsgeschichte wirbelloser Thiere an der Kiiste
von Normandie Angestellt,’ published in 1863, describes and
figures (pp. 77—80, Taf. vi, figs. 1—11) several stages in the
development of an annelid larva, which he was unable at the
time to assign to any known genus. This larva was very
common in the plankton at St. Vaast, and the same, ora very
similar one, had previously been found (in 1855) by Claparéde
on the coast of Norway. He surmised that the larva must
belong tc some common worm at that time still undescribed.
No further advance seems to have been made in the know-
ledge of this form until the appearance in 1874 of a report by
Claparéde on the annelids collected by the ‘ Lightning ”
Expedition. This report is contained in Khler’s paper,
“ Beitrage zur Kenntniss der Verticalverbreitung der Bor-
stenwiirmer in Meere” (Ehlers, 1874). Amongst the material
collected by the “ Lightning,” Claparéde found a number of
fragments of a worm, which he considered must be the adult
form of the larva he had previously described. He states
that the species is represented in the “ Lightning” material
“par un fragment dans les préparations Nr. 15 et Nr. 24, et par
tous les fragments inclus dans la préparation Nr. 22.” The
localities from which these specimens were obtained are not
mentioned. In the same paper Ehlers refers to two fragments
of the worm described by Claparéde, which he found amongst
the material dredged by the “ P > According to the
table given (loc. cit., p. 25), these were dredged on July
21st, 1869, at 48° 51’ N., 11°7’ W. (11° 9’ W.) in 725 fathoms,
on a bottom of muddy sand.
From the fragments at his disposal Claparéde was able to
give a fair account of the general external features of the
worm, and to convince himself that it was the adult form of
the larva which he had previously described, or at any rate
closely allied to the adult of that larva. He gives to the
worm the name Pcecilochatus fulgoris, both the generic
orcupine.’
THE ANATOMY OF PG@CILOCHATUS, CLAPAREDE. 81
and the specific name being new. He was still unable to
include it in any known family, and thought it not improbable
that a special family would have to be made to receive it.
Figures are given (loc. cit., T'af.i, fig. 1, a, B, c, and p) of the
head end from the dorsal and ventral surfaces, of several
cheetw, of a parapodium, and of the external opening of one
of the epithelial glands, the latter being described as “ petits
tubercules granuleux.”
Levinsen (1883, p. 106) gives some further details of the
structure of late larval stages of Poecilochetus from obser-
vations upon specimens which had been taken by the ‘ Hauch”’
Expedition in the Skager Rack. He also discusses the rela-
tions of Pecilochetus with Disoma multisetosum,
Oersted, and points out that the two genera are closely allied.
He places both genera in the family Spionide.
McIntosh (1894) furnishes some notes, accompanied by
four figures, on the larva described by Claparéde. He con-
siders that the first notice of this larva is due to Maximillian
Miller (1852), but reference to Miiller’s paper has not con-
vinced me that the tail end of a larva which he figures is
really the same as Claparéde’s larva.
McIntosh makes no mention of Claparéde’s discovery of the
adult Poecilochetus, nor of Levinsen’s discussion of the
subject. He states that the larva occurs in considerable
numbers in the bottom-nets at St. Andrews from July to
October. McIntosh gives a figure of an advanced larval
stage, showing the two palps well developed.
Mesnil (1897), in his monograph on the Spionide, discusses
the position of Pcecilochetus in relation to that family.
He proposes to place it with Disoma in a new family, the
Disomide (see further, p. 140).
OccuRRENCE At PLyMouTH.
The larva of Peecilochetus has been constantly and
regularly taken for many years in the plankton collected at
Plymouth during the summer months, though I believe no
82 E. J. ALLEN.
record of the fact has ever been published. The larva is
probably frequent in plankton taken all round our coasts, and
its appearance will be well known to workers, as it renders
itself conspicuous by its rapid, wriggling motion and by the
row of pigment spots (large branching chromatophores)
between the parapodial cirri along each side of the body.
On April 10th, 1902, the Laboratory fisherman brought in
two specimens of a worm which he recognised as unfamiliar.
These specimens he had obtained when digging on a patch of
sand exposed at low spring tide immediately south of the
coastguard station at Mount Batten, on the eastern side of
Plymouth Sound. The worm has proved to be the adult
Peecilochetus, which forms the subject of the present
paper. ;
Since that time I have always been able to obtain a few
specimens whenever the tide has allowed of digging on this
particular patch of sand. Unfortunately the sand is only
uncovered at the lowest spring tides, and it is only on com-
paratively few days during the year that the worm can be
obtained. During the hour, or hour and a half, that the sand
may be uncovered at any tide from six to eight head ends of
the worm have been collected. As the animals break very
readily when disturbed, complete specimens are difficult to
procure, and only two such have as yet been obtained. ‘The
local area of distribution of Pcevilochetus is very restricted.
‘he portion of shore where it is known to live consists of
patches of sand covered with zostera, with intermediate
patches of a somewhat different texture on which no zostera
grows. ‘lhe worm appears to live only in these intermediate
patches, and never in the zostera beds. It has never yet been
obtained from any other locality in the Plymouth district.
I propose tor the species of Pcecilochetus found at
Plymouth and described in this’ paper, the name
Pecilochetus serpens, the specific name being selected
to indicate the rapid, wriggling movement both of the larva
and of the adult worm when swimming.
THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. 83
Hasirts.
Peecilochetus serpens constructs U-shaped tubes in
fine sand. These tubes are lined with a stiff layer of fine
particles of mud or clay held together with mucus. The
worm in its tube is shown in fig. 12 (Pl. 9). This
drawing, of natural size, was made from a tube which had
been constructed by a worm in a glass cell formed of two
glass plates lying about ;4; inch apart and partially filled with
sand. ‘I'he process of burrowing was carefully watched, and
the animal remained under observation in its tube for some
hours. The burrowing was accomplished with the head end
of the worm, more particularly with the forwardly directed
parapodial cirri of the first segment and the long bristles
belonging to it. During the process the anterior part of the
body was constantly waved to and fro in a transverse
direction. The burrowing movement was persisted in until
the complete U-shaped tube had been formed.
When at rest the animal lies in its tube either with the
two long palps extended in front, the ends being often pro-
truded for some distance beyond the opening of the tube, or
with the palps lying in a number of loose coils immediately
in front of the head. A constant current of water, drawing
small particles with it, is kept up through the tube by means
of an undulatory movement of the body and of a fan-like
movement of the parapodia and bristles. ‘The movement of
the numerous feather-like bristles in the posterior part of the
body (Pl. 9, fig. 10) plays an important part in the production
of the current that enters the tube at the end towards
which the head of the worm is directed, and passes back-
wards over the body. If the animal reverses its position
in the tube, which frequently happened in the specimen
under observation, the direction of the current is immediately
reversed.
As the worm possesses no jaws, it seems probable that its
food consists entirely of fine organic particles and of small
organisms carried in the current which it sets up. This is
84. fe ALLEN.
confirmed by the appearance presented by food-masses in the
intestine, as seen in sections of preserved material, which
generally show skeletons of diatoms, etc.
When removed from its tube and irritated, Poecilochetus
often swims with a rapid, serpentine motion, which recalls
the motion of the larva.
Specimens were easily kept alive for some weeks in the
Laboratory when provided with sand in which to construct
their tubes, and worms which through injury had lost the
posterior part of their bodies generally regenerated new tail
ends of characteristic structure.
Peecilochetus appears to breed practically the whole
year round. Specimens were taken in February, April,
May, June, August and December, and on all occasions some
were found to contain almost or quite mature eggs or
spermatozoa. ‘lhe mode in which the eggs are laid has not
been determined. The larva of Poecilochetus is remarkable
for the late stage of development to which it retains the
pelagic habit.
Mernops.
As careful a study as possible was made of the living worm.
For further examination specimens were preserved by the
methods to be described. ‘Che worms were anesthetised by
the gradual addition of alcohol to the sea-water in which they
were living. ‘They were then placed on a glass plate and
killed by dropping on to them a small quantity of the pre-
serving fluid to be employed, the worms being kept straight
and extended with camel’s-hair brushes until contraction had
ceased. ‘They were then transferred to a large quantity of
the fixing fluid and allowed to harden.
The most successful fixation was obtained with Hermann’s
fluid, in which the specimens were allowed to remain from
five to twelve or fourteen hours. The shorter time gave
rather better results for the epithelial structures, especially
the nuchal organ and lateral sense-organs, whilst the longer
time was rather better for internal parts.
THE ANATOMY OF PQICILOCHATUS, CLAPAREDE. 85
Good results were also obtained by the use of corrosive
sublimate-acetic mixture (3 : 1) for three or four hours, the
specimens being then rapidly rinsed in water and at once
transferred to 70 per cent. alcohol, to which tincture of iodine
was added.
Staining was for the most part done with Gustav Mann’s
methyl-blue-eosin mixture (Mann, 1902), sections being
allowed to remain in the mixture overnight, rinsed with
water, and differentiated in absolute alcohol. This method
gave very excellent results with both Hermann and corrosive
sublimate preservation. ‘he formula for the stain is—
1 per cent. Methyl blue. : . 80 Cie.
Lert calle. bg Mosin ; ; ; x, jp henele:
Water : : . : aut OO 0.e;
Heidenhain’s iron-hematoxylin was also employed, but,
excepting for some few special points, I do not consider the
resulting preparations nearly so good as those obtained by
the simpler methyl-blue-eosin method.
Embedding was done in paraffin. ‘Transverse, horizontal
and. sagittal sections, 44 and 5, in thickness, were cut with
the Jung microtome, and fixed to the slide with distilled
water to which a trace of albumen had been added.
I take this opportunity of acknowledging my very great
indebtedness to Mrs. Sexton for the drawings which she has
made, with remarkable skill and accuracy, of the external
features of the animal, as well as of some of the sections.
EXTERNAL CHARACTERS.
The body of Poecilochetus serpens is long and slender,
narrowing posteriorly. A specimen about 55 mm. long, when
alive and extended, was from 1°5 to 1:7 mm. broad (not
including the parapodial cirri) in the anterior region, and
consisted altogether of about 110 segments. ‘The body is
divided into a number of regions, which will be described in
detail subsequently (see p. 138).
The colour of the anterior segments (I—15) varies from
86 E. J. ALLEN.
bright scarlet to deep purple-red according to the degree of
aération of the blood, which, showing through the transparent
body-walls, gives its own colour to this region (see p. 126).
The parapodia and their cirri are here almost colourless.
The posterior part of the body is black or dark green and
white, the dark colour being due to pigment in the cells of
the intestine; the white, which is specially marked in ripe
males, to the genital products.
The head is small and hemispherical, as can be seen from
the dorsal view (Pl. 7, fig. 1, and Pl. 8, fig. 7) and from the
ventral view (Pl. 8, fig. 8). It is provided with four eyes,
two small dorsal and two larger ventral. A short median
tentacle has its origin on the ventral side of the head, being
placed so far back that when the proboscis is completely with-
drawn into the body, the base of the tentacle also comes to lie
actually within the mouth (PI. 8, fig. 8). The tentacle, which
is covered with minute papille (the external openings of
epithelial glands), extends for a short distance beyond the
anterior margin of the head (figs. 1 and 7). As will be
shown later, the single median tentacle represents two lateral
tentacles fused together, for it receives two nerves, one from
either side of the brain.
The very large palps (plp.) arise between the head proper
and the parapodia of the first segment. ‘hese palps are
capable of great extension (cf. Pl. 9, fig. 12), and may attain
a length equal to at least half the length of the body. Their
general appearance can be seen from figs. 1 and 7. They are
horse-shoe shaped in transverse section, are richly supplied
with papille, and a crenated membrane runs along each
margin of the flattened side. A single large blood-vessel,
along which in the living worm a constant succession of
strong pulsations is seen to pass, extends through nearly the
whole length of each palp.
In describing the habits of the worm it was stated (p. 83)
that when the worm is in its tube the palps may either lie
straight in front of the head, being often protruded out of the
mouth of the tube, or they may be formed into a number of
THE ANATOMY OF P(RCILOCHETUS, CLAPAREDE. 87
oose coils lying immediately in front of the head. They
clearly serve, amongst other functions, as important organs
of respiration.
From the posterior dorsal region of the head three long
tentacle-like processes arise, a long median process, which
falls back on the dorsal surface of the body, and two lateral
processes, the three being united into one broad base, which
is attached to the head. ‘These three processes constitute the
nuchal organ (fig. 1 and fig. 7, nwch.), the very great develop-
ment of which is one of the most striking features of the
genus Peecilochetus. Occasionally a specimen is seen in
which one or other of the three processes has further divided,
or rather given off a well-developed lateral branch. The
nuchal organ is generally of a brownish colour in the living
worm.
The first segment, or prostomium, is greatly developed, and
its parapodia and cheete are directed forwards. Hach para-
podium consists of a neuropodium and a notopodium com-
pletely united together, and carries a neuropodial and a
notopodial cirrus, the former being large, flask-shaped and
directed forwards, whilst the latter in this first segment is
small and rudimentary, showing merely as a smal] pro-
jection on the dorsal surface of the parapodium (Pl. 8,
fig. 7).
There are two bundles of simple, long, smooth chete,
which extend for a considerable distance in front of the head.
The notopodial chetz are about twice the length of the
neuropodial, and both sets curve inwards, the longest ones
often crossing their fellows of the opposite side.
The parapodia and their cirri are covered with small
papille, at the ends of which are the external openings of
mucus glands. Between the neuropodial and notopodial
cirrus lies a well-developed lateral sense-organ, similar in
structure to those found on all the anterior segments of the
body. ‘These organs have the appearance of small, pro-
jecting, pear-shaped lobes, with the narrowest portion at the
point of attachment to the parapodium. A number of sensory
88 EB. . ALLEN:
hairs can be seen projecting from a cup-like depression at the
outer extremity of the lobe.
The mouth (fig. 8) lies on the ventral surface of the first
segment. It is bordered posteriorly and laterally by large
cushions or lips, which are distinetly ridged, whilst anteriorly
it is limited by the base of the median tentacle, of which a
portion may actually lie within the mouth, when the proboscis
is completely retracted.
The proboscis is seldom protruded ; indeed, I have only seen
it thus on one occasion. It was then short and broad, almost
spherical in shape, and appeared to carry the median tentacle
on the base of its anterior wall.
The second segment is only a little less developed than the
first, and the parapodia with their cirri still tend to be
directed forwards. The neuropodial cirrus is similar in shape
to that of the first segment, but is slightly smaller. The
notopodial cirrus, unlike that of the first segment, is well
developed, being of about the same size as the neuropodial.
Between the two cirri is a well-developed lateral sense-organ,
like that on the first segment.
The notopodial chet spring from a chetal sac situated
immediately at the base and in front of the notopodial cirrus,
which may itself be said to form the posterior lip of the sac,
The anterior lip of the cheetal sac is broad and short. The
majority of the notopodial chatz are long, slender, and un-
jointed, having the form of simple, smooth hairs. At least one
bristle, however, on each side in this second segment belongs
to another type, being provided with rows of short spines,
the type being the same as that found in segments 7 to 16
(cf. Pl. 3, fig. 15). The neuropodial cheete (fig. 9) consist of
three (or sometimes four, the fourth being rudimentary) !
short, stout, slightly curved hooks, which arise immediately
in front of the neuropodial cirrus. In addition to these hooks
a few very fine, hair-like bristles oceur, which are best
demonstrated in sections.
1 In sections the rudimentary fourth hook can always be seen, though it
seldom pierces the skin,
THE ANATOMY OF PHCILOCHATUS, CLAPARRDE. 59
The third segment resembles the second, excepting that the
cirri are slightly smaller and more conical in shape, and there
is not quite such a tendency for them to be directed forwards.
The neuropodial cheetee consist of three well-developed and one
rudimentary stout hooks and a few fine hairs, all as in seg-
ment 2 (PI. 7, fig. 2). The notopodial cheetz are all smooth
hairs, no spiny bristles like those in segment 2 being present.
In the fourth segment the cirri are not quite so large as in
the third, and are usually directed outwards or slightly back-
wards. The cheete of the neuropodium are no longer stout
hooks, but form a bundle of straight, smooth bristles, similar
to those of the notopodium. There are no spiny bristles.
The fifth segment (figs. 1, 5, and 7) differs from its
neighbours in the fact that the neuropodial cirri are short,
whilst the notopodial cirri are long and slender, being the
longest cirri, with the exception of those on the first segment,
which are found on the whole body of the worm (fig. 3).
These two long cirri are also often carried in a somewhat
different position from those on other parts of the body,
being arched over the back of the worm.
The sixth segment closely resembles the fourth (fig. 1), the
cirri being generally directed backwards. The cheete from
the third to the sixth segment are all smooth hairs, amongst
which no spiny bristles are found.
Segments 1 to 6 may be considered as constituting the
first sub-division of the anterior region of the body. With
segment 7 a change takes place, which is expressed hoth
in the external and internal structure of the worm. Ex-
ternally—that is to say, regarded from the point of view of
the structure of the parapodia only—the second sub-division of
the body would seem to comprise the segments from the seventh
to the thirteenth, but, as will be shown later (p. 139), this does
not quite agree with the division indicated by the internal
anatomy, which points rather to segments 7 to 11 only being
classed together.
The peculiarity of the parapodia of segments 7 to 18 (figs.
4 and 5) lies in the form and structure of the notopodial and
vou. 48, part 1,—NEW SERIES. 7
90 ES) 3s CALLEN,
neuropodial cirri. ‘hese cirri are flask shaped, but the basal
part of each cirrus or body of the flask becomes swollen and
almost spherical, whilst the neck is thin, elongated and
nearly cylindrical, with a slight enlargement at the distal
end. The whole cirrus, including the neck, is very rigid,
being much less flexible than the cirri of the other segments,
and only moves from its base at the point of attachment to
the body of the worm. The stiff movement of the cirri gives
a characteristic appearance to this region of the body in the
living worm, The chete in these segments are of two kinds,
smooth, slender hairs (Pl. 9, fig. 13), which show longi-
tudinal striation under a high power, and spiny bristles
(Pl. 7, figs. 4 and 5; Pl. 9, fig. 15), the number of the latter
being few in each bundle.
Lateral sense-organs in the form of pear-shaped papille
are still found between the cirri, but the bases of the papille,
where they are attached to the parapodium, are broader than
in the more anterior segments.
In segments 14, 15 and 16 (Pl. 9, fig. 9) the parapodia
have a structure more nearly resembling that found in the
fourth and sixth segments. he cirri are shorter and stouter,
nearly conical in shape, and are without the long stiff necks
found in the segments immediately in front. The chaste
remain of two kinds, as in the latter segments, and the lateral
sense-organ still protrudes from the surface of the para-
podium. .
With segment 17 there is again a change, but the structure
then found continues in its essential features, with the
exception of the addition of gill filaments commencing at
segment 21, until about thirty segments from the end of the
body.
Both the notopodial and neuropodial cirri, conical in shape,
are now much smaller in size (figs. 1, 10, and 11), and vary
considerably and somewhat irregularly in the extent to which
they are developed from segment to segment.
There is, on the other hand, a very remarkable development
of the chetz. In both notopodium and neuropodium the
THE ANATOMY OF P&CILOCHATUS, CLAPAREDE. 91
smooth, slender cheete of the anterior segments are replaced
by large, hairy, feather-like bristles (Pl. 7, fig. 3; Pl. 9, figs.
10, 14, and 16), the most dorsal and most ventral in each
segment having long, fairly stiff shafts, with lateral hairs of
moderate length (fig. 14), whilst the imner ones (ventral
bundle of notopodium and dorsal bundle of neuropodium) are
more slender and flexible, but have very much longer hairs
(fig. 16). These bristles give to the region of the body now
under consideration a kind of woolly appearance.
The spiny bristles of the anterior segments also undergo a
special modification in this region. ‘The stoutness of their
shafts becomes very greatly reduced, the spines themselves
become much elongated, show a slight thickening near the
tip, and are connected with the shaft along almost their
entire length by a thin, transparent membrane, which is
practically invisible in fresh material, but becomes quite
obvious after staining (Pl. 9, fig. 17). By this arrangement
the surface of the bristle becomes very greatly extended.
The hairy, feather-like bristles, together with the modified
spiny bristles just described spread out in each parapodium
into a large fan, the movements of which are mainly respon-
sible for the current of water which the worm Stu han Ly
draws through its U-shaped tube (see p. 83).
In this region the lateral sense-organ no longer has the
form of a papilla protruding from the face of the parapodium,
but is seen as a slight depression from the centre of which a
bundle of sensory hairs arises. The depression is surrounded
by acircular rim, which rises slightly above the general face of
the parapodial surface.
Gills —The gill filaments commence on segment 21, and
are found on the succeeding segments to quite near the end
of the body. They are at first short and small in size (PI. 7,
fig. 1), but soon become longer and larger. When fully
developed they consist of long filaments, as long as or longer
than the cirri of the parapodia (PI. 9, fig. 11), which appear
bright red in the living worm from the colour of the blood
which is inthem. Two pairs of such filaments occur upon
92 E. J.: ALLEN.
each parapodium, one pair being attached to the posterior
face of the neuropodium and one pair to the posterior face of
the notopodium.
The terminal segments (Pl. 8, fig. 6) show certain special
features. The general shape of the body is here flattened,
and the dorsal surface is somewhat concave. ‘The neuropodial
and notopodial cirri are of about the normal shape, but the
neuropodial is double the size of the notopodial, and the latter
assumes a more dorsal position than usual. The more dorsal
of the notopodial cheetee are transformed into strong hooks
(figs. 6 and 19), which form a transverse row on either side of
the dorsal surface of the segment. Five or six such hooks
are generally found on each notopodium. The curve of the
hook is directed backwards, and those nearest the middle line
are the stoutest as well as the most strongly curved. ‘These
hooks are found on the last sixteen or seventeen segments
(in full-grown specimens), and obviously serve the purpose of
enabling the worm to hold itself firmly in the tube.
The remaining cheete of the notopodium and those of the
neuropodium in these segments are mostly either of the
ordinary smooth or spiny kinds, the latter being often
rudimentary. ‘here is also found in the terminal region of
the body a special kind of bristle not met with elsewhere
(Pl. 9, fig. 18). This consists of a stout, smooth shaft,
showing longitudinal striations, and ending in a blunt tooth
directed slightly outwards. From the base of this tooth there
arises a hairy terminal portion of the bristle, which forms a
kind of flexible brush attached to the end of the stiff shaft.
Bristles of this character are a modified form of the ordinary
stout, hairy bristles, which, as the end of the body is
approached, at first lose the hairs along the greater part of
the length of the shaft, retaining them only at the ends. The
type of bristle with the hairy flexible end (fig. 18) becomes
established at about the thirtieth sezment from the end of the
body (in full-grown specimens), and occurs in the segments
from this point to about the ninth or tenth from the end.
In the terminal segments the lateral sense-organs have
THE ANATOMY OF P@CILOCHEATUS, CLAPAREDE. 93
again the form of pear-shaped papille protruding from the
surfaces of the parapodia between the cirri.
The pygidium is well developed; the anus is somewhat
dorsal, and is surrounded by five large lobes (PI. 8, fig. 6).
There are two pairs of anal cirri, both situated below the
anus, the more dorsal pair being long and slender, the more
ventral pair short.
The anus and the terminal portion of the intestine are
strongly ciliated, and all the cirri in the hindermost region of
the body, as well as the dorsal and ventral surfaces of the
body itself, are very richly provided with papille, at the
extremities of which lie the external openings of epithelial
glands.
No description of the general aspect of the living Peecilo-
chetus is complete without reference to the remarkable
system of blood-vessels, which is visible through the tran-
parent body-wall (Fig. 1). A detailed account of this vascular
system will be found in the special section on p. 126.
InrernaL Anatomy anp Histronoey.
, Hpithelium and Cuticle.
The character of the epithelium differs in different parts of
the body. The cells composing it may be either almost
cubical, with spherical nuclei (Pl. 9, fig. 20), or they may
be elongated in a direction either perpendicular (Pl. 9,
fig. 21) or parallel to the body surface (Pl. 10, fig. 23). The
elongated cells have oval nuclei, the long axes of which are
parallel to the long axes of the cells.
Over the greater part of the body the epithelial cells are
arranged in a single layer, but in isolated places, more
especially on the ventro-lateral surfaces to be presently
described, two layers can be recognised. The cuticle, which
lies external to the epithelial cells, varies in thickness in
different parts of the body.
Mells nearly cubical in shape are found on the dorsal
94. ESA CALLE.
surface of the anterior segments (Pl. 9, fig. 20). In
preparations stained with methyl-blue-eosin the cuticle is
coloured blue, a thin outer layer being distinguishable by its
very dark colour from the main body of cuticular substance,
which is stained uniformly of a much lighter shade. ‘he
protoplasm of the epithelial cells is very distinctly granular in
preparations preserved in Hermann’s fluid, and the divisions
between the individual cells are often strongly marked. Hach
cell contains a spherical nucleus with a well-marked nuclear
membrane. Within the nucleus is one large mass of deeply
staining chromatin and a few small, scattered particles of the
same substance. The nucleus as a whole has an exceptionally
clear and transparent appearance in preparations preserved in
Hermann’s fluid. The internal ends of the cells appear to be
in immediate contact with the muscular layers of the body-
wall. Towards the tail end of the animal the epithelium of
the dorsal surface becomes more flattened, the individual cells
are less clearly marked, and the nuclei are transversely oval
(Pl. 10} fig. 23).
On the ventro-lateral surfaces of the body the epithelial
cells are generally more elongated ina direction perpendicular
to the body surface (PI. 9, fig. 21; Pl. 10, fig. 22), and have
oval nuclei in which the chromatin is present in the form of a
number of deeply staining particles connected by a network,
no one particle standing out so prominently as the large
single mass of chromatin in the nuclei of the cubical cells of
the dorsal surface. In certain spots the elongation of the
cells is very great, and some of the cells have migrated
inwards, so that an internal layer of nuclei can be recognised
(fig. 21). In this way a pad or cushion of cells is produced,
and this cushion forms the point of insertion of certain muscle-
bands.
Epithelial Gland-cells.
Gland-cells opening externally by means of short, chitinous
tubes which project beyond the general surface of the body
THE ANATOMY OF P@ICILOCHATUS, CLAPAREDE. 95
are abundant in places. In their simplest form these consist
of individual cells lying amongst the cells of the epithe-
lium. One such cell is illustrated in fig. 22 (Pl. 10). It
is pear shaped, with granular protoplasm staining much
more deeply than that of the surrounding cells, and with an
oval nucleus, the long axis of which lies parallel to the body
surface. ‘I'he protoplasm at the mouth of the cell is inserted
in a depression on the internal face of the chitin. The
chitinous tube, which places the interior of the cell in com-
munication with the external water, forms a conical projection
on the body surface, and can also be seen to project internally
for a short distance into the protoplasm of the neck of the
cell.
Such simple gland-cells are not, however, very numerous.
The more usual arrangement is for several cells to be asso-
ciated together and to open externally through one tube.
Glands of this type are especially numerous in the epithelium
towards the tail end of the animal, where the tubes are
situated upon raised chitinous papille, which form a character-
istic feature in external views of the animal. ‘These papillee
and tubes are figured by Claparéde (in Ehlers, 1874), and
their great abundance on the dorsal surface of the anterior
segments in the specimens examined by him constitutes one
marked difference between his Pcecilochetus fulgoris,
obtained from deep water, and the specimens found at
Plymouth near low-tide mark on the shore.
A section through such a gland opening on the dorsal
surface near the tail end of one of the Plymouth specimens is
shown in fig. 25 (PI. 10). The epithelium here consists of
flattened cells, with large, oval nuclei. The cuticle is com-
paratively thin, except in the neighbourhood of the opening
of the gland. It is there greatly thickened and pushed out-
wards, forming a tubercle with a stout chitinous covering
hollowed out internally, the internal hollow being filled with
the protoplasm of the ends of the gland-cells. Through the
centre of the tubercle runs the chitinous tube, which places
the gland-cells in communication with the exterior, the tube
96 E. J. ALLEN.
projecting to an equal extent externally beyond the surface
of the papilla and internally into the protoplasm of the gland-
cells.
On account of the flattened nature of the epithelium, the
eland-cells, which are easily distinguished by their more deeply
staining protoplasm, do not lie immediately beneath the
tubercle, but are drawn considerably to one side. The nucleus
of each gland-cell lies near its proximal end. It is much
smaller than the nuclei of the ordinary epithelial cells sur-
rounding it, spherical rather than oval in shape, contains a
large quantity of chromatin in the form of a considerable
number of large, deeply staining granules of about equal size,
and is thus very readily distinguished from the nuclei of the
epithelium. Usually three or four such nuclei can be dis-
tinguished lying close together in the neighbourhood of the
base of each of the chitinous tubercles. In the figure (fig.
23) only one such nucleus is shown; but three were dis-
tinguished in the sections, two lying one over the other, in
the section from which the figure was made, and one in the
following section.
Scattered over the ventral surface of the cuticle, especially
in the anterior segments of the body, a number of rounded
tubercles or callosities are found.
7
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CONTENTS OF No. 190.—New Series.
MEMOIRS:
PAGE
The Structure and Classification of the Arachnida. By E. Ray
LanxesTER, M.A., LL.D., F.R.S., Director of the Natural History
Departments of the British Museum. ‘ : : : . Ah
On some New-Species of the Genus Phreodrilus. By W. BraxtanD
Benuam, D.Sc.(Lond.), M.A.(Oxon.), F.Z.S., Professor of Biology
in the University of Otago, New Zealand. (With Plates 13—15) . 271
On a New Species of the Genus Haplotaxis; with some Remarks on
the Genital Ducts in the Oligocheta. By W. Buaxtanp Benya,
D.Sc.(Lond.), M.A.(Oxon.), F.Z.S., Professor of Biology in the
University of Otago, New Zealand. (With Plates‘16—18) . . 299
The Qstrous Cycle in the Common Ferret. By Francis H. A.
MarsHatt, D.Sc. (With Plates 19—21) . ; . ye. 3
Two New Forms of Choniostomatide: Copepoda Parasitic on Crus-
tacea Malacostraca and Ostrocoda. By H. J. Hansern, D.Sc.,
F.M.L.S., Copenhagen. (With Plate 22) . = : ; . 347
SEP 15 1904
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 165
The Structure and Classification of the
Arachnida.
By
E. Ray Lankester, M.A., LL.D., F.R.S.,
Director of the Natural History Departments of the British Museum.
(Reprinted by kind permission of the proprietors from the tenth edition of
the ‘ Encyclopedia Britannica.’)
ARACHNIDA is the name given in 1815 by Lamarck (Greek
apaxvn, a spider) to a class which he instituted for the recep-
tion of the spiders, scorpions, and mites previously classified
by Linneus in the order Aptera of his great group Insecta.
Lamarck at the same time founded the class Crustacea for
the lobsters, crabs, and water-fleas, also until then included
in the order Aptera of Linnezus. Lamarck included the
Thysanura and the Myriapoda in his class Arachnida. The
Insecta of Linnzeus was a group exactly equivalent to the
Arthropoda founded a hundred years later by Siebold and
Stannius. It was thus reduced by Lamarck in area, and
made to comprise only the six-legged, wing-bearing “ In-
secta.”” For these Lamarck proposed the name Hexapoda;
but that name has been little used, and they have retained
to this day the title of the much larger Linnean group, viz.
Insecta. The position of the Arachnida in the great sub-
phylum Arthropoda, according to recent anatomical and
embryological researches, is explained in another article
(ArtHRopopA). ‘he Arachnida form a distinct class or line
of descent in the grade Kuarthropoda, diverging (perhaps in
common at the start with the Crustacea) from primitive
Huarthropods, which gave rise also to the separate lines of
von. 48, PART 2.—NEW SERIES. 12
166 BE. RAY LANKESTER.
descent known as the classes Diplopoda, Crustacea, Chilo-
poda, and Hexapoda.
Fig. 1.—Entosternum, entosternite or plastron of Limulus
polyphemus, Linn. Dorsal surface. ZAP, left anterior process ;
RAP, right anterior process ; PAN, pharyngeal notch; AZAR, anterior
lateral rod or tendon; PLR, posterior lateral rod or tendon; PLP,
posterior lateral process. Natural size. (From Lankester, ‘Q. J.
Mier. Sci.,’ N.S., vol. xxiv, 1884.)
SS ie i | | /--zar
I
PMP.
Fic. 2.—Ventral surface of the entosternum of Limulus poly-
phemus, Linn. Letters as in Fig. 1 with the addition of WF,
neural fossa protecting the aggregated ganglia of the central
nervous system; PVP, left posterior ventral process; PIP, pos-
terior median process. Natural size. (From Lankester.)
Limulus an Arachnid.—Modern views as to the classifi-
cation and affinities of the Arachnida have been determined
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 167
by the demonstration that Limulus and the extinct Eury-
pterines (Pterygotus, etc.) are Arachnida; that is to say, are
identical in the structure and relation of so many important
parts with Scorpio, whilst differing in those respects from
other Arthropoda that it is impossible to suppose that the
identity is due to homoplasy or convergence, and the con-
Hirer:
Fic. 3.—Entosternum of Scorpion (Palamnceus indus, De
Geer); dorsal surface. asp, paired anterior process of the sub-
neural arch; sp, sub-neural arch; ap, anterior lateral process (same
as RAP and LAP in Fig. 1); mp, lateral median process (same as
ALR and PLR of Fig. 1); pp, posterior process (same as PLP in
Fig. 1); pf, posterior flap or diaphragm of Newport; m! and m°,
perforations of the diaphragm for the passage of muscles; D&, the
paired dorsal ridges; GC, gastric canal or foramen; AC, arterial
canal or foramen. Magnified five times linear. (After Lankester,
loc. cit.)
Fic. 4.—Ventral surface of the same entosternum as that drawn
in Fig. 3. Letters as in Fig. 3 with the addition of NC, neural
canal or foramen. (After Lankester, loc. cit.)
clusion must be accepted that the resemblances arise from
close genetic relationship. he view that Limulus, the king-
crab, is an Arachnid was maintained as long ago as 1829 by
Straus-Durkheim (1), on the ground of its possession of an
internal cartilaginous sternum—also possessed by the Arach-
nida (see Figs. 1—6),—and of the similarity of the disposition
of the six leg-like appendages around the mouth in the two
168 E. RAY LANKESTER.
cases (see Figs. 45 and 63). The evidence of the exact
equivalence of the segmentation and appendages of Limulus
and Scorpio, and of a number of remarkable points of agree-
ment in their structure, was furnished by Lankester in an
article published in 1881 (‘ Limulus an Arachnid,” ‘ Quart.
Journ. Micr. Sci.,’ vol. xxi, N.S.), and in a series of subse-
quent memoirs, in which the structure of the entosternum, of
the coxal glands, of the eyes, of the veno-pericardiac muscles,
Fie. 6.
Fic. 5.—Entosternum of one of the mygalomorphous spiders ;
ventral surface. PA.N., pharyngeal notch. The three pairs of rod-
like tendons correspond to the two similar pairs in Limulus, and
the posterior median process with its repetition of triangular seg-
ments closely resembles the same process in Limulus. Magnified
five times linear. (From Lankester, loc. cit.)
Fic. 6.—Dorsal surface of the same entosternum as that drawn in
Fig. 5. PA.N., pharyngeal notch. (After Lankester, loc. cit.)
of the respiratory lamelle, and of other parts, was for the
first time described, and in which the new facts discovered
were shown uniformly to support the hypothesis that Limulus
isan Arachnid. A list of these memoirs is given at the close
of this article (2, 8, 4, 5, and 18). The Eurypterines (Gigan-
tostraca) were included in the identification, although at
that time they were supposed to possess only five pairs of
anterior or prosomatic appendages. They have now been
shown to possess six pairs (Fig. 47), as do Limulus and
Scorpio.
The various comparisons previously made between the
le he er ee -
Py eel ee
Fic. 7.—Diagram of the dorsal surface of Limulus poly-
phemus. oc, lateral compound eyes; oc’, central monomeniscous
eyes; PA, post-anal spine; I to VI, the six appendage-bearing
somites of the prosoma; VII, probably to be considered as the
tergum of the genital somite; VII to XII, the six somites of the
mesosoma; XIII to XVIII, the six somites of the metasoma, of
which the first (marked XIII at the side and 7 on the tergum) is
provided with a lateral spine, and is separated by ridges from the
more completely fused five hinder somites lettered 8 to 12.
[This is a new figure replacing the Fig. 7 given in the ‘ Encyclo-
pedia. It is at present a matter for further investigation as to
whether the pregenital somite is merely represented by the piece
marked X at the hinder border of the prosoma, or whether the area
marked VII is the tergum of the pregenital somite, and that marked
VIII the tergum of the genital somite. The disposition of the
muscles and of the entopopliyses should, when carefully studied, be
sufficient to settle this point —EK. R. L.]
170 FE. RAY LANKESTER.
structure of Limulus and the EKurypterines
on the one hand, and that of a typical
Arachnid, such as Scorpio, on the other,
had been vitiated by erroneous notions as
to the origin of the nerves supplying the
anterior appendages of Limulus (which
were finally removed by Alphonse Milne-
Edwards in his beautiful memoir [6] on
the structure of that animal), and secondly
by the erroneous identification of the double
Fig. 9.
Vie. 8.—Diagram of the dorsal surface of a Scorpion to compare
with Fig. 7. Letters and Roman numerals as in Fig. 7, excepting
that VIL is here certainly the tergum of the first somite of the
mesosoma—the genital somite—and is not a survival of the embry-
onic pregenital somite. (From Lankester, loc. cit.) The anus (not
seen) is on the sternal surface.
Fie. 9.—Ventral view of the posterior carapace or meso-meta-
somatic (opisthosomatic) fusion of Limulus polyphemus. The
soft integument and limbs of the mesosoma have been removed as
well as all the viscera and muscles, so that the inner surface of thie
terga of these somites with their entopopliyses are seen. The un-
segmented dense chitinous, sternal plate of the metasoma (XIII to
XVIII) is not removed. Letters as in Fig. 7. (After Lankester,
loc. cit.)
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 171
sternal plates of Limulus, called “chilaria”’ by Owen, with
a pair of appendages (7). Once the identity of the chilaria
with the pentagonal sternal
Fie. 10. plate of the scorpion is
a
> ge recognised — an __identifica-
tion first insisted on by Lan-
kester—the whole series of
segments and appendages in
the two animals, Limulus and
Scorpio, are seen to corres-
pond most closely, segment
for segment, with one an-
other (see Figs. 7 and 8).
Eres il:
Fic. 10.—Ventral view of a Scorpion, Palamneus indus, De
Geer, to show the arrangement of the coxe of the limbs, the sternal
elements, genital plate and pectens. M, mouth behind the oval
median camerostome; I, the chelicere; IJ, the chele ; III to VI,
the four pairs of walking legs; VIIgo, the genital somite or first
somite of the mesosoma with the genital operculum (a fused
pair of limbs); VIIIp, the pectiniferous somite; [Xs¢g to XIIség,
the four pulmonary somites; met, the pentagonal metasternite of
the prosoma behind all the coxe; x, the sternum of the pectinifer-
ous somite; y, the broad first somite of the metasoma.
Fie. 11.—Third leg of Limulus polyphemus, showing the
division of the fourth segment of the leg by a groove § into two,
thus giving seven segments to the leg as in Scorpion. (From a
drawing by Mr. Pocock.)
The structure of the prosomatic appendages or legs is also
seen to present many significant points of agreement (see
72 E. BAY LANKESTER.
Figures), but a curious discrepancy existed in the six-jointed
structure of the limb in Limulus, which differed from the
seven-jointed limb of Scorpio by the defect of one joint.
Mr. R. I. Pocock, of the British Museum, has lately observed
that in Limulus a marking exists on the fourth joint, which
apparently indicates a previous division of this segment into
two, and thus establishes the agreement of Limulus and
Scorpio in this small feature of the number of segments in
the legs (see Fig. 11).
It is not desirable to occupy the limited space of this
article by a full description of the limbs and segments of
Limulus and Scorpio. The reader is referred to the complete
series of figures here given, with their explanatory legends
(Figs. 12—15). Certain matters, however, require comment
and explanation to render the comparison intelligible.t The
tergites, or chitinised dorsal halves of the body rings are
fused to form a “ prosomatic carapace,” or carapace of the
prosoma, in both Limulus and Scorpio (see Figs. 7 and 8).
This region corresponds in both cases to six somites, as
indicated by the presence of six pairs of limbs. On the
surface of the carapace there are in both animals a pair of
central eyes with simple lens and a pair of lateral eye-tracts,
which in Limulus consist of closely aggregated simple eyes,
forming a “ compound ” eye, whilst in Scorpio they present
1 The discussion of the segmentation or metamerism of the Arachnida in
this article should be read after a perusal of the article ARTHROPODA by the
same author (‘Q. Journ. Mier. Sci.,’ vol. xlvii, n.s. p. 528).
Fic. 12.—The prosomatic appendages of Limulus polyphemus
(right) and Scorpio (left), Palamnewus indus compared. The
corresponding appendages are marked with the same Roman numeral.
The Arabic numerals indicate the segments of the legs. co#, coxa
or basal segment of the leg; s¢c, the sterno-coxal process or jaw-
like upgrowth of the coxa; epe, the articulated movable outgrowth of
the coxa, called the epicoxite (present only in III of the Scorpion
and III, [V, and V of Limulus) ; ez!, the exopodite of the sixth
limb of Limulus; a, 4, c, d, movable processes on the same leg (see
for some suggestions on the morphology of this leg, Pocock in
‘Quart. Journ. Mier. Sci.,’ March, 1901; see also Fig. 50 0n p. 235
and explanation). (From Lankester, loc. cit.)
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 173
Mies IP.
174 E. RAY LANKESTER.
several separate small eyes. ‘The microscopic structure of
the central and the lateral eyes has been shown by Lankester
and Bourne (5) to differ; but the lateral eyes of Scorpio were
shown by them to be similar in structure to the lateral eyes
of Limulus, and the central eyes of Scorpio to be identical in
structure with the central eyes of Limulus (see pp. 182, 183).
Following the prosoma is a region consisting of six seg-
ments (Figs. 14 and 15), each carrying a pair of plate-like
appendages in both Limulus and Scorpio. This region is
called the mesosoma. ‘The tergites of this region and those
Fic. 13.—Diagrams of the metasternite sé, with genital operculum
op, and the first lamelligerous pair of appendages ga, with uniting
sternal element sé of Scorpio (left) and Limulus (right). (From
Lankester, loc. cit.)
of the following region, the metasoma, are fused to form a
second or posterior carapace in Limulus, whilst remaining
‘free in Scorpio. The first pair of foliaceous appendages in
each animal is the genital operculum ; beneath it are found
the openings of the genital ducts. The second pair of meso-
somatic appendages in Scorpio are known as the “ pectens.”
Mach consists of an axis, bearing numerous blunt tooth-like
processes arranged in a series. ‘This is represented in
Limulus by the first gill-bearing appendage. The leaves
(some 150 in number) of the gill-book (see figure) correspond
to the tooth-like processes of the pectens of Scorpio. The
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 175
next four pairs of appendages (completing the mesosomatic
series of six) consist, in both Scorpio and Limulus, of a base
carrying each 130 to 150 blood-holding, leaf-like plates, lying
on one another like the leaves of a book. Their minute
structure is closely similar in the two cases; the leaf-like
plates receive blood from the great sternal sinus, and serve
Fic. 14.—The first three pairs of mesosomatic appendages of
Scorpio and Limulus compared. VII, the genital operculum; VIII,
the pectens of Scorpio and the first branchial plate of Limulus; IX,
the first pair of !ung-books of Scorpio and the second branchial plate
of Limulus ; gp, genital pore; eps¢, epistimatic sclerite ; s/y, stigma
or orifice of the hollow tendons of the branchial plates of Limulus.
(After Lankester, loc. cit.)
as respiratory organs. The difference between the gill-books
of Limulus and the lung-books of Scorpio depends on the
fact that the latter are adapted to aérial respiration, while
the former serve for aquatic respiration. The appendage
carrying the gill-book stands out on the surface of the body
in Limulus, and has other portions developed besides the
gill-book and its base; it is fused with its fellow of the
176 E. RAY LANKESTER.
opposite side. On the other hand, in Scorpio the gill-book-
bearing appendage has sunk below the surface, forming a
recess or chamber for itself, which communicates with the
exterior by an oval or circular ‘‘stigma”’ (Fig. 10, stg.). That
this in-sinking has taken place, and that the lung-books or
in-sunken gill-books of Scorpio really represent appendages
(that is to say, limbs or parapodia),is proved by their develop-
Fic. 15.—The remaining three pairs of mesosomatic appendages
of Scorpio and Limulus. Letters as in Fig. 14. 7180 indicates
that there are 130 lamelle in the Scorpion’s lung-book, whilst 7150
indicates that 150 similar lamelle are counted in the gill of Limulus.
(After Lankester, loc. cit.)
mental history (see Figs. 17 and 18). They appear at first as
outstanding processes on the surface of the body.
The exact mode in which the in-sinking of superficial out-
standing limbs, carrying gill-lamelle, has historically taken
place has been a matter of much speculation. It was to be
hoped that the specimen of the Silurian scorpion (Paleo-
phonus) from Scotland, showing the ventral surface of the
mesosoma (Fig. 49), would throw light on this matter; but
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 177
the specimen, recently carefully studied by the writer and
Mr. Pocock, reveals neither gill-bearing limbs nor stigmata.
The probability appears to be against an actual introversion
of the appendage and its lamella, as was at one time
suggested by Lankester. It is probable that such an in-
sinking as is shown in the accompanying diagram has taken
Fic. 16.—Diagram to show the way in which an outgrowing gill-
process bearing blood-holding lamelle may give rise, if the sternal
body-wall sinks inwards, to a lung-chamber with air-holding lamelle.
Tis the embryonic condition ; ds, blood sinus; L is the condition of
outgrowth with g/, gill lamelle ; A is the condition of in-sinking of
the sternal surface and consequent enclosure of the lamelligerous
surface of the appendage in a chamber with narrow orifice—the
pulmonary air-holding chamber; p/, pulmonary lamelle; 4s, blood
sinus. (After Kingsley.)
place (Fig. 16); but we are yet in need of evidence as to the
exact equivalence of margins, axis, etc., obtaining between
the lung-book of Scorpio and the gill-book of Limulus.
Zoologists are familiar with many instances (fishes, crus-
taceans) in which the protective walls of a water-breathing
organ or gill apparatus become converted into an air-breath-
178 E. RAY LANKESTER.
ing organ or lung, but there is no other case known of the
conversion of gill processes themselves into air-breathing
plates.
The identification of the lung-books of Scorpio with the
gill-books of Limulus is practically settled by the existence
~ VIIPrG
go
7 Vai
_Km
Ix
- abpt
PrGabp = ~abp>
abp?- ~abp
aby ~abpi
abp*..
abp*
abps
abpt
Fic. 17.—Embryo of Scorpion, ventral view showing somites and
appendages. sge, frontal groove ; sa, rudiment of lateral eyes ; 0d/,
camerostome (upper lip); so, sense-organ of Patten; PrGapé,
rudiment of the appendage of the pregenital somite which dis-
appears ; abp*, rudiment of the right half of the genital operculum;
abp®, rudiment of the right pecten; abp* to abp’, rudiments of the
four appendages which carry the pulmonary lamelle; I to VI,
rudiments of the six limbs of the prosoma; VIIPrG, the evanescent
pregenital somite; VIII, the first mesosomatic somite or genital
somite; IX, the second mesosomatic somite or pectiniferous somite ;
X to XIII, the four pulmoniferous somites; XIV, the first meta-
somatic somite. (After Brauer, ‘ Zeitsch. wiss. Zool.,’ vol. lix,
1895.
te 18.—Portion of a similar embryo at a later stage of growth.
The pregenital somite, VIIPrG, is still present, but has lost its
rudimentary appendages ; go, the genital operculum, left half; Km,
the left pecten; abp* to abp’7, the rudimentary appendages of the
lung-sacs. (After Brauer, loc. cit.)
of the pectens in Scorpio (Fig. 14, VIII) on the second meso-
somatic somite. There is no doubt that these are parapodial
or limb appendages, carrying numerous imbricated secondary
processes, and therefore comparable in essential structure to
the leaf-bearing plates of the second mesosomatic somite of
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 179
Limulus. They have remained unenclosed and projecting on
the surface of the body, as once were the appendages of the
four following somites. But they have lost their respiratory
function. In non-aquatic life such an unprotected organ
cannot subserve respiration. The ‘pectens” have become
more firmly chitinised and probably somewhat altered in
shape as compared with their condition in the aquatic
ancestral scorpions. Their present function in scorpions is
not ascertained. They are not specially sensitive under
ordinary conditions, and may be touched or even pinched
without causing any discomfort to the scorpion. It is pro-
bable that they acquire special sensibility at the breeding
season, and serve as “guides” in copulation. The shape of
the legs and the absence of paired terminal claws in the
Silurian Palzeophonus (see Figs. 48 and 49) as compared with
living scorpions (see Fig. 10) show that the early scorpions
were aquatic, and we may hope some day, in better preserved
specimens than the two as yet discovered, to find the re-
spiratory organs of those creatures in the condition of pro-
jecting appendages serving aquatic respiration somewhat as
in Limulus, though not necessarily repeating the exact form
of the broad plates of Limulus.
It is important to note that the series of lamellz of the lung-
book and the gill-book correspond exactly in structure, the
narrow, flat blood-space in the lamelle being interrupted by
pillar-like junctions of the two surfaces in both cases (see
Lankester [4]), and the free surfaces of the adjacent lamella
being covered with a very delicate chitinous cuticle which is
drawn out into delicate hairs and processes. The elongated
axis which opens at the stigma in Scorpio, and which can be
cleared of soft surrounding tissues and coagulated blood so
as to present the appearance of a limb axis carrying the book-
like leaves of the lung, is not really, as it would seem to be at
first sight, the limb axis. That is necessarily a blood-holding
structure, and is obliterated and fused with soft tissues of the
sternal region, so that the lamellae cannot be detached and
presented as standing out from it. The apparent axis or
180 E. RAY LANKESTER,
basal support of the scorpion’s lung-books shown in the
figures is a false or secondary axis, and merely a part of the
infolded surface which forms the air-chamber. The macera-
tion of the soft parts of a scorpion preserved in weak spirit
and the cleaning of the chitinised ingrown cuticle give rise to
the false appearance of a limb axis carrying the lamelle. The
Hie 20:
Fie. 19. of
SS
Lip
~ eam
9 Io
| ee
U
f
())
«
S
a mets
Fic. 19.—Section through an early embryo of Limulus longi-
spina, showing seven transverse divisions in the region of the un-
segmented anterior carapace. The seventh, VII, is anterior to the
genital operculum, op, and is the cavity of the pregenital somite,
which is more or less completely suppressed in subsequent develop-
ment, possibly indicated by the great entopophyses of the proso-
matic carapace. (After Kishinouye, ‘Jour. Sci. Coll. Japan,’ vol. v,
1892.)
Fie 20.—View of the ventral surface of the mid-line of the pro-
somatic region of Limulus polyphemus. The coxe of the five
pairs of limbs following the cheliceree were arranged in a series on
each side between the mouth, M, and the metasternites, mets. sf,
the subfrontal median sclerite; Ch, the cheliceree; cam, the camero-
stome or upper lip; M, the mouth; pmst, the promesosternal
sclerite or chitinous plate, unpaired ; mets, the right and left meta-
sternites (corresponding to the similarly placed pentagonal sternite
of Scorpio. Natural size. (After Lankester.)
margins of the lamelle of the scorpion’s lung-book which are
lowermost in the figures (Fig. 15) and appear to be free are
really those which are attached to the blood-holding axis.
The true free ends are those nearest the stigma.
Passing on now from the mesosoma we come in Scorpio to
the metasoma of six segments, the first of which is broad,
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 181
whilst the rest are cylindrical. The last is perforated by the
anus, and carries the post-anal spine or sting. The somites
of the metasoma carry no parapodia. In Limulus the meta-
soma is practically suppressed. In the allied extinct Hury-
pterines it is well developed, and resembles that of Scorpio.
In the embryo Limulus (Fig. 42) the six somites of the meso-
soma are not fused: to form a carapace at an early stage, and
they are followed by three separately marked metasomatic
somites ; the other three somites of the metasoma have dis-
appeared in Limulus, but are represented by the unsegmented
preanal region. It is probable that we have in the meta-
Fie. 21.—Development of the lateral eyes of a Scorpion. 4,
epidermic cell-layer; mes, mesoblastic connective tissue; 2, nerves;
II, ILI, 1V, V, depressions of the epidermis in each of which a
cuticular lens will be formed. (From Korschelt and Heider, after
Laurie.)
soma of Limulus a case of the disappearance of once clearly
demarcated somites. It would be possible to suppose, on the
other hand, that new somites are only beginning to make
their appearance here. ‘The balance of various considerations
is against the latter hypothesis. Following the metasoma in
Limulus, we have as in Scorpio the post-anal spine—in this
case not a sting, but a powerful and important organ of loco-
motion, serving to turn the animal over when it has fallen
upon its back. The nature of the post-anal spine has been
strangely misinterpreted by some writers. Owen (7) main-
tained that it represented a number of coalesced somites,
regardless of its post-anal position and mode of development !
The agreement of the grouping of the somites, of the form of
voL. 48, PART 2.—NEW SERIES, 138
182 E. RAY LANKESTER.
the parapodia (appendages, limbs) in each region, of the posi-
tion of the genital aperture and operculum, of the position
and character of the eyes, and of the powerful post-anal spines
not seen in other Arthropods, is very convincing as to the
affinity of Limulus and Scorpio. Perhaps the most important
general agreement of Scorpio compared with Limulus and the
Eurypterines is the division of the body into the three regions
(or tagmata)—prosoma, mesosoma, and metasoma,—each con-
sisting of six segments, the prosoma having leg-like appen-
lens
Fic. 22.—Section through the lateral eye of Euscorpius
italicus. J/ezs, cuticular lens; zerv.c, retinal cells (nerve-end
cells) ; rhabd, rhabdomes ; xerv.f, nerve-fibres of the optic nerve ;
int, intermediate cells (lying between the bases of the retinal cells).
(After Lankester and Bourne, from Parker and Haswell’s ‘ Text-
book of Zoology,’ Macmillan and Co.)
dages, the mesosoma having foliaceous appendages, and the
metasoma being destitute of appendages.
In 1893, some years after the identification of the somites
of Limulus with those of Scorpio, thus indicated, had been
published, zoologists were startled by the discovery by a
Japanese zoologist, Mr. Kishinouye (8), of a seventh proso-
matic somite in the embryo of Limulus longispina. This
was seen in longitudinal sections, as shown in Fig. 19. The
simple identification of somite with somite in Limulus and
Scorpio seemed to be threatened by this discovery. But in
1896 Dr. August Brauer, of Marburg (9), discovered in the
STRUCLURE AND CLASSIFICATION OF THE ARACHNIDA. 183
embryo of Scorpio a seventh prosomatic somite (see VIIPrG,
Figs. 17 and 18), or, if we please so to term it, a pregenital
somite, hitherto unrecognised. In the case of Scorpio this
segment is indicated in the embryo by the presence of a pair
of rudimentary appendages, carried by a well-marked somite.
As in Limulus, so in Scorpio, this unexpected somite and its
—— a
— SS
MN.
mes.
asl iee
"Le \
Fic. 23.—Section through a portion of the lateral eye of Limulus,
showing three ommatidia, A, B, and C. Ayp, the epidermie cell-
layer (so- called hypodermis), ‘the cells of which increase in volume
below each lens, /, and become nerve-end cells or retinula cells, ee
in A the letters rh point to a rhabdomere secreted by the cell 7¢;
the peculiar central spherical cell; 2, nerve-fibres ; mes, astounds
skeletal tissue; ch, chitinous cuticle. (From Korschell and Heider,
after Watase.)
B C
mes.
appendages disappear in the course of development. In fact,
more or less complete * excalation ”’ of the somite takes place.
Owing to its position itis convenient to term the somite which
is excalated in Limulus and Scorpio “the preegenital somite.”
It appears not improbable that the sternal plates wedged in
between the last pair of legs in both Scorpio and Limulus,
viz. the pentagonal sternite of Scorpio (Fig. 10) and the
gh in
184 BE. RAY LANKESTER.
chilaria of Limulus (see Figs. 13 and 20), may in part repre-
sent in the adult the sternum of the excalated pragenital
somite. This has not been demonstrated by an actual following
out of the development, but the position of these pieces, and
the fact that they are (in Limulus) supplied by an independent
C
—Q
-p 0 a © =
© oto HN
L092 5 Soy a
Qo-as aeg S ga e 20° 0-89 95 GOK
Fie. 24.—Diagrams of the development and adult structure of
one of the paired central eyes of a Scorpion. A, early condition
before the lens is deposited, showing the folding of the epidermic
cell-layer into three; B, diagram showing the nature of this infold-
ing; C, section through the fully formed eye; 4, epidermic cell-
layer; 7, the retinal portion of the same which, owing to the infold-
ing, lies between g/, the corneagen or lens-forming portion, and pr,
the post-retinal or capsular portion or fold; /, cuticular lens ;
g, line separating lens from the lens-forming or corneagen cells of
the epidermis; 2, nerve-fibres; 7/, rhabdomeres. (From Korschelt
and Heider.) How the inversion of the nerve-end cells and their
connection with the nerve-fibres is to be reconciled with the con-
dition found in the adult, or with that of the monostichous eye, has
not hitherto been explained.
segmental nerve, favours the view that they may comprise
the sternal area of the vanished pregenital somite. This
interpretation, however, of the “ metasternites” of Limulus
and Scorpio is opposed by the co-existence in Thelyphonus
(Figs. 55, 57, and 58) of a similar metasternite with a complete
pregenital somite. Hansen (10) has recognised that the
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 185
“pragenital somite” persists in a rudimentary condition,
forming a “ waist ” to the series of somites in the Pedipalpi
and Aranee. ‘I'he present writer is of opinion that it will be
ANH
\X\
IN SUG
(VIF Sas
& SPER nf.
;
Fic. 25.—Section through one of the central eyes of a young
Limulus. L, cuticular or corneous lens; Ay, epidermic cell-layer ;
corn., its corneagen portion immediately underlying the lens; red.,
retinula cells; 2f, nerve-fibres ; coz. ¢iss., connective tissue (meso-
blastic skeletal tissue). (After Lankester and Bourne, ‘Q. J. Micr.
Sci.,’ 1883.)
found most convenient to treat this evanescent somite as some-
thing special, and not to attempt to reckon it to either the
prosoma or the mesosoma. These will then remain as typically
composed each of six appendage-bearing somites—the prosoma
186 BE. RAY LANKESTER.
comprising in addition the ocular prosthomere.! When the
preegenital somite or traces of it are present it should not be
called “ the seventh prosomatic ” or ihe “ first mesosomatic,”
but simply the “ pregenital somite.” The first segment of
the mesosoma of Scorpio and Limulus thus remains the first
segment, and can be identified as such throughout the Eu-
arachnida, carrying as it always does the genital apertures.
But it is necessary to remember, in the light of recent dis-
coveries, that the sixth prosomatic pair of appendages is car-
ried on the seventh somite of the whole series, there being
two prosthomeres or somites in front of the mouth, the first
carrying the eyes, the second the chelicere; also that the
first mesosomatic or genital somite is not the seventh or even
the eighth of the whole series of somites which have been
historically present, but is the ninth, owing to the presence or
to the excalation of a pregenital somite. It seems that con-
fusion and trouble will be best avoided by abstaining from
the introduction of the non-evident somites, the ocular and
the przgenital, into the numerical nomenclature of the com-
ponent somites of the three great body regions. We shall
therefore, ignoring the ocular somite, speak of the first, second,
third, fourth, fifth, and sixth leg-bearing somites of the pro-
soma, and indicate the appendages by the Roman numerals,
I, Il, II, 1V, V, VI, and whilst ignoring the pregenital
somite we shall speak of the first, second, third, etc., somite
of the mesosoma or opisthosoma (united mesosoma and meta-
soma), and indicate them by the Arabic numerals.
There are a number of other important points of structure
besides those referring to the somites and appendages in
which Limulus agrees with Scorpio or other Arachnida, and
differs from other Arthropoda. The chief of these are as
follows:
1. The Composition of the Head (that is to say, of the
anterior part of the prosoma), with especial reference to
the Region in Front of the Mouth.—lIt appears (see
1 See the article ARTHROPODA for the use of the term ‘ prosthomere.”
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 187
ArtHropopa) that there is embryological evidence of the
existence of two somites in Arachnida which were originally
post-oral, but have become preoral by adaptational shifting
of the oral aperture. These forwardly slipped somites are
called “ prosthomeres.” The first of these has, in Arachnids
Fig. 26.—A, diagram of aretinula of the central eye of aScorpion
consisting of five retina cells (ve¢.), with adherent branched pigment
cells (pig.); B, rhabdom of the same, consisting of five confluent
rhabdomeres ; C, transverse section of the rhabdom of a retinula of
the Scorpion’s central eye, showing its five constituent rhabdomeres
as rays of a star; D, transverse section of a retinula of the lateral
eye of Limulus, showing ten retinula cells, ve¢., each bearing a rhab-
domere, rhab, (After Lankester.)
as in other Arthropods, its pair of appendages represented by
the eyes. ‘The second has for its pair of appendages the
small pair of limbs which in all] living Arachnids is either
chelate or retrovert (as in spiders), and is known as the cheli-
cere. It is possible, as maintained by some writers (Patten
and others), that the lobes of the cerebral nervous mass in
Arachnids indicate a larger number of prosthomeres as having
188 rex _. #, RAY LANKESTER.
fused in this region, but there isno embryological evidence
at present which justifies us in assuming the existence in
Arachnids of more than two prosthomeres. The position of
the chelicerz: of Limulus, and of the ganglionic nerve-masses
from which they receive their nerve-supply, is closely similar
to that of the same structures in Scorpio. The cerebral mass
is in Limulus more easily separated by dissection as a median
lobe distinct from the laterally placed ganglia of the cheli-
ceral somite than is the case in Scorpio, but the relations are
practically the same in the two forms. Formerly it was
supposed that in Limulus both the chelicerze and the next
following pair of appendages were prosthomerous, as in
Crustacea ; but the dissections of Alphonse Milne-Edwards (6)
demonstrated the true limitations of the cerebrum, whilst
embryological researches have done as much for Scorpio.
Limulus thus agrees with Scorpio and differs from the
Crustacea, in which there are three prosthomeres—one ocular
and two carrying palpiform appendages. It is true that in
the lower Crustacea (Apus, etc.) we have evidence of the
gradual movement forward of the nerve-ganglia belonging to
these palpiform appendages. But although in such lower
Crustacea the nerve-ganglia of the third prosthomere have
not fused with the anterior nerve-mass, there is no question
as to the preoral position of the two appendage-bearing
somites in addition to the ocular prosthomere. ‘he Crus-
tacea have, in fact, three prosthomeres in the head and the
Arachnida only two, and Limulus agrees with the Arachnida
in this respect, and differs from the Crustacea. The central
nervous systems of Limulus and of Scorpio present closer
agreement in structure than can be found when a crustacean is
compared with either. ‘lhe wide divarication of the lateral
cords in the prosoma and their connection by transverse com-
missures, together with the “attraction” of ganglia to the
prosomatic ganglion group which properly belong to hinder
seoments, are very nearly identical in the two animals. ‘I'he
form and disposition of the ganglion cells are also peculiar
and closely similar in the two. (See Patten [42] for import-
ia3
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 189
ant observations on the neuromeres, etc., of Limulus and
Scorpio. )
2. The Minute Structure of the Central Hyesand
of the Lateral Kyes.—Limulus agrees with Scorpio not
only in having a pair of central eyes and also lateral eyes,
but in the microscopic structure of those organs, which differs
in the central and lateral eyes respectively. The central eyes
are “simple eyes,”—that is to say, have a single lens, and are
hence called “‘monomeniscous.” ‘The lateral eyes are in
Limulus “ compound eyes,’”’—that is to say, consist of many
lenses placed close together; beneath each lens is a complex
of protoplasmic cells, in which the optic nerve terminates.
Kach such unit is termed an ‘‘ommatidium.” ‘The lateral
eyes of Scorpio consist of groups of separate small lenses,
each with its ommatidium, but they do not form a continuous
compound eye asin Limulus. The ommatidium (soft struc-
ture beneath the lens-unit of a compound eye) is very simple
in both Scorpio and Limulus. It consists of a single layer of
cells, continuous with those which secrete the general chitin-
ous covering of the prosoma. ‘The cells of the ommatidium
are a good deal larger than the neighbouring common cells
of the epidermis. They secrete the knob-like lens (Fig. 22) ;
but they also receive the nerve-fibres of the optic nerve.
They are at the same time both optic nerve-end cells, that is
to say, retina cells, and corneagen cells, or secretors of the
chitinous lens-like cornea. In Limulus (Fig. 23) each ommati-
dium has a peculiar ganglion cell developed in a central
position, whilst the ommatidium of the lateral eyelets of
Scorpio shows small intermediate cells between the larger
nerve-end cells. ‘The structure of the lateral eye of Limulus
was first described by Grenacher, and further and more
accurately by Lankester and Bourne (8), and by Watase;
that of Scorpio by Lankester and Bourne, who showed that
the statements of von Graber were erroneous, and that the
lateral eyes of Scorpio have a single-cell-layered or “ mono-
stichous” ommatidium lke that of Limulus. Watase has
shown in a very convincing way how, by deepening the pit-
190 E. RAY LANKESTER,
like set of cells beneath a simple lens, the more complex
ommatidia of the compound eyes of Crustacea and Hexapoda
may be derived from such a condition as that presented in
the lateral eyes of Limulus and Scorpio. (For details the
reader is referred to Watase [11], and to Lankester and
Bourne [5].) The structure of the central eyes of Scorpio and
spiders, and also of Limulus, differs essentially from that of
the lateral eyes in having two layers of cells (hence called
diplostichous) beneath the lens, separated from one another
by a membrane (Figs. 24 and 25). The upper layer is the
corneagen, and secretes the lens ; the lower is the retinal layer.
The mass of soft cell-structures beneath a large lens of a
central eye is called an “ommatcum.” It shows in Scorpio
and Limulus a tendency to segregate into minor groups or
“ommatidia.’”’ It is found that in embryological growth the
retinal layer of the central eyes forms as a separate pouch,
which is pushed in laterally beneath the corneagen layer from
the epidermic cell layer. Hence it is in origin double, and
consists of a true retinal layer and a post-retinal layer
(Fig. 24, B), though these are not separated by a membrane.
Accordingly the diplostichous ommatceum or soft tissue of the
Arachnid’s central eye should strictly be called ‘‘ triplosti-
chous,”’ since the deep layer is itself doubled or folded. The
retinal cells of both the lateral and central eyes of Limulus
and Scorpio produce cuticular structures on their sides ; each
such piece is a rhabdomere, and a number (five or ten)
uniting forma rhabdom (Fig. 26). In the specialised omma-
tidia of the compound eyes of Crustacea and Hexapods the
rhabdom is an important structure.' It is a very significant
fact that the lateral and central eyes of Limulus and Scorpio
not only agree each with each in regard to their monostichous
and diplostichous structure, but also in the formation in both
classes of eyes of rhabdomeres and rhabdoms in which the
component pieces are five or a multiple of five (Fig. 26).
Whilst each unit of the lateral eye of Limulus has a rhabdom
1 See Fig. 11 in the article ARTHROPODA,
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 191
of ten! pieces forming a star-like chitinous centre in section,
each lateral eye of Scorpio has several rhabdoms of five or
less rhabdomeres, indicating that the Limulus lateral eye-
unit is more specialised than the detached lateral eyelet of
Scorpio, so as to present a coincidence of one lens with one
rhabdom. Numerous rhabdomeres (grouped as rhabdoms in
Limulus) are found in the retinal layer of the central eyes
also. ;
Whilst Limulus agrees thus closely with Scorpio in regard
to the eyes, it is to be noted that no Crustacean has
structures corresponding to the peculiar diplostichous central
eyes, though these occur again (with differences in detail) in
Hexapoda. Possibly, however, an investigation of the
development of the median eyes of some Crustacea (Apus,
Palzemon) may prove them to be diplostichous in origin.
3. The So-called “Coxal Glands.”’—In 1882 (‘ Proc.
Roy. Soc.,’ No. 221) Lankester described under the name
“coxal glands” a pair of brilliantly white oviform bodies
lying in the scorpion’s prosoma immediately above the coxe
of the fifth and sixth pairs of legs (Fig. 27). These bodies
had been erroneously supposed by Newport (12) and other
observers to be glandular outgrowths of the alimentary canal.
They are really excretory glands, and communicate with the
exterior by a very minute aperture on the posterior face of
the coxa of the fifth limb on each side. When examined
with the microscope, by means of the usual section method,
they are seen to consist of a labyrinthine tube lined with
peculiar cells, each cell having a deep vertically striated
border on the surface farthest from the lumen, as is seen in
the cells of some renal organs. The coils and branches of
the tube are packed by connective tissue and blood-spaces.
A similar pair of coxal glands, lobate instead of ovoid in
shape, was described by Lankester in Mygale, and it was
also shown by him that the structures in Limulus ealled
1 Though ten is the prevailing number of retinula cells and rhabdomeres
in the laterai eye of Limulus, Watase states that they may be as few as nine
and as many as eighteen.
192 KE. RAY LANKESTER,
“ brick-red glands” by Packard have the same structure
and position as the coxal glands of Scorpio and Mygale. In
Limulus these organs consist each of four horizontal lobes
lying on the coxal margin of the second, third, fourth, and
fifth prosomatic limbs, the four lobes being connected to one
another by a transverse piece or stem (Fig. 28). Maicro-
lies, Qy/e
Fig. 27.—Diagram showing the position of the coxal glands of a
Scorpion, Buthus australis, Lin., in relation to the legs, dia-
phragm (entosternal flap), and the gastric ceca. 1 to 6, the bases
of the six prosomatic limbs; A, prosomatic gastric gland (sometimes
called salivary) ; B, coxal gland; C, diaphragm of Newport = fibrous
flap of the entosternum; D, mesosomatic gastric cxca (so-called
liver) ; E, alimentary canal. (From Lankester, ‘Q. J. Micr. Sci.,’
vol. xxiv, N.S., p. 152.)
Fic. 28.—The right coxal gland of Limulus polyphemus,
Latr. a? to a®, posterior borders of the chitinous bases of the
coxx of the second, third, fourth, and fifth prosomatic limbs; 4,
longitudinal lobe or stolon of the coxal gland; ¢, its four transverse
lobes or outgrowths corresponding to the four coxe. (From
Lankester, loc. cit., after Packard.)
scopically their structure is the same in essentials as that of
the coxal glands of Scorpio (13). Coxal glands have since
been recognised and described in other Arachnida. It has
lately (1900) been shown that the coxal gland of Limulus is
provided with a very delicate thin-walled coiled duct which
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 193
opens, even in the adult condition, by a minute pore on the
coxa of the fifth leg (Patten and Hazen [18a]). Previously to
this, Lankester’s pupil Gulland had shown (1885) that in the
embryo the coxal gland is a comparatively simple tube,
which opens to the exterior in this position, and by its other
extremity into a ccelomic space. Similar observations were
made by Laurie (17) in Lankester’s laboratory (1890) with
regard to the early condition of the coxal gland of Scorpio,
and by Bertkau (41) as to that of the spider Atypus. H. M.
Bernard (138) showed that the opening remains in the adult
scorpion. In all the embryonic or permanent opening is on
the coxa of the fifth pair of prosomatic limbs. Thus an
organ newly discovered in Scorpio was found to have its
counterpart in Limulus.
The name “coxal gland” needs to be carefully distin-
guished from “crural gland,” with which it is apt to be
confused. The crural glands, which occur in many terres-
trial Arthropods, are epidermal in origin and totally distinct
from the coxal glands. The coxal glands of the Arachnida
are structures of the same nature as the green glands of the
higher Crustacea and the so-called “shell glands” of the
Entomostraca. The latter open at the base of the fifth pair
of limbs of the Crustacean, just as the coxal glands open on
the coxal joint of the fifth pair of limbs of the Arachnid.
Both belong to the category of “ccelomoducts,” namely,
tubular or funnel-like portions of the coelom opening to the
exterior in pairs in each somite (potentially), and usually
persisting in only a few somites as either ‘uroccels”’ (renal
organs) or “ gonoceels” (genital tubes). In Peripatus they
occur in every somite of the body. They have till recently
been very generally identified with the nephridia of Cheetopod
worms, but there is good reason for considering the true
nephridia (typified by the nephridia of the earthworm) as a
distinct class of organs (see Lankester in vol. ii, chap. iii, of
‘A Treatise on Zoology,’ 1900). The genital ducts of
Arthropoda are like the green glands, shell glands, and
coxal glands, to be regarded as ccelomoducts (gonoccels).
194 BE. RAY LANKESTER.
The coxal glands do not establish any special connection
between Limulus and Scorpio, since they also occur in the
same somite in the lower Crustacea, but it is to be noted that
the coxal glands of Limulus are in minute structure and
probably in function more like those of Arachnids than those
of Crustacea.
4, The Entosternites and their Minute Structure.
—Straus-Durkheim (1) was the first to insist on the affinity
between Limulus and the Arachnids, indicated by the
presence of a free suspended entosternum or plastron or
entosternite in both. We have figured here (Figs. 1—6) the
entosternites of Limulus, Scorpio, and Mygale. Lankester
some years ago made a special study of the histology (38) of
these entosternites for the purpose of comparison, and also
ascertained the relations of the very numerous muscles which
are inserted into them (4). The entosternites are cartila-
ginous in texture, but they have neither the chemical
character nor the microscopic structure of the hyaline
cartilage of Vertebrates. ‘They yield chitin in place of
chondrin or gelatine—as does also the cartilage of the
Cephalopod’s endoskeleton. In microscopic structure they
all present the closest agreement with one another. We find
a firm, homogeneous, or sparsely fibrillated matrix in which
are embedded nucleated cells (corpuscles of protoplasm)
arranged in rows of three, six, or eight parallel with the
adjacent lines of fibrillation.
A minute entosternite having the above-described struc-
ture is found in the Crustacean Apus between the bases of
the mandibles, and also in the Decapoda in a similar position,
but in no Crustacean does it attain to any size or importance.
On the other hand, the entosternite of the Arachnida is a
very large and important feature in the structure of the
prosoma, and must play an important part in the economy of
these organisms. In Limulus (Figs. 1 and 2) it has as many
as twenty-five pairs of muscles attached to it, coming to it
from the bases of the surrounding limbs and from the dorsal
carapace and from the pharynx. It consists of an oblong
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 195
plate two inches in length and one in breadth, with a pair of
tendinous outgrowths standing out from it at right angles on
each side. It “ floats ” between the prosomatic nerve centres
and the alimentary canal. In each somite of the mesosoma
is asmall, free entosternite having a similar position, but
below or ventrad of the nerve-cords, and having a smaller
number of muscles attached to it. The entosternite was
probably in origin part of the fibrous connective tissue lying
close to the integument of the sternal surface—giving
attachment to muscles corresponding more or less to those at
present attached to it. It became isolated and detached,
why or with what advantage to the organism it is difficult to
say, and at that period of Arachnidan development the great
ventral nerve-cords occupied a more lateral position than
they do at present. We know that such a lateral position
of the nerve-cords preceded the median position in both
Arthropoda and Cheetopoda. Subsequently to the floating
off of the entosternite the approximation of the nerve-cords
took place in the prosoma, and thus they were able to take
up a position below the entosternite. In the mesosoma the
approximation had occurred before the entosternites were
formed.
In the scorpion (Figs. 3 and 4) the entosternite has tough
membrane-like outgrowths which connect it with the body-
wall, both dorsally and ventrally forming an oblique dia-
phragm, cutting off the cavity of the prosoma from that of
the mesosoma. It was described by Newport as “the dia-
phragm.” Only the central and horizontal parts of this
structure correspond precisely to the entosternite of Limulus:
the right and left anterior processes (marked ap in Figs. 8
and 4,and RAP, LAP, in Figs. 1 and 2) correspond in the
two animals, and the median lateral process Imp of the
scorpion represents the tendinous outgrowths ALR, PLR of
Limulus. The scorpion’s entosternite gives rise to out-
growths, besides the great posterior flaps, pf, which form the
diaphragm, unrepresented in Limulus. These are a ventral
arch forming a neural canal through which the great nerve-
196 E. RAY LANKESTER.
cords pass (Figs. 3 and 4, snp), and further a dorsal gastric
canal and arterial canal which transmit the alimentary
tract and the dorsal artery respectively (Figs. 3 and 4, GC,
DR).
In Limulus small entosternites are found in each somite of
the appendage-bearing mesosoma, and we find in Scorpio, in
the only somite of the mesosoma which has a well-developed
pair of appendages, that of the pectens, a small entosternite
with ten pairs of muscles inserted into it. The supra-pectinal
entosternite lies ventrad of the nerve-cords.
In Mygale (Figs. 5 and 6) the form of the entosternite is
more like that of Limulus than is that of Scorpio. The
anterior notch Ph.N.is similar to that in Limulus, and the
pairs of upstanding tendons correspond to the similar pairs
in Limulus, whilst the imbricate triangular pieces of the
posterior median region resemble the similarly placed struc-
tures of Limulus in a striking manner.
It must be confessed that we are singularly ignorant as to
the functional significance of these remarkable organs—the
entosternites. Their movement in an upward or downward
direction in Limulus and Mygale must exert a pumping
action on the blood contained in the dorsal arteries and the
ventral veins respectively. In Scorpio the completion of the
horizontal plate by oblique flaps, so as to form an actual
diaphragm shutting off the cavity of the prosoma from the
rest of the body, possibly gives to the organs contained in
the anterior chamber a physiological advantage in respect of
the supply of arterial blood and its separation from the
venous blood of the mesosoma. Possibly the movement of
the diaphragm may determine the passage of air into or out
of the lung-sacs. Muscular fibres connected with the suc-
torial pharynx are in Limulus inserted into the entosternite,
and the activity of the two organs may be correlated.
5. The Blood and the Blood-vascular System.—
The blood fluids of Limulus and Scorpio are very similar.
Not only are the blood-corpuscles of Limulus more like in
form and granulation to those of Scorpio than to those of
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 197
any Crustacean, but the fluid is in both animals strongly
impregnated with the blue-coloured respiratory proteid
hemocyanin. This body occurs also in the blood of Crus-
tacea and of Molluscs, but its abundance in both Limulus
and Scorpio is very marked, and gives to the freshly shed
blood a strong indigo-blue tint.
The great dorsal contractile vessel or “heart”? of Limulus
is closely similar to that of Scorpio; its ostia or incurrent
orifices are placed in the same somites as those of Scorpio,
but there is one additional posterior pair. The origin of the
paired arteries from the heart differs in Limulus from the
arrangement obtaining in Scorpio, in that a pair of lateral
commissural arteries exist in Limulus (as described by
Alphonse Milne-Edwards [6]) leading to a suppression of
the more primitive direct connection of the four pairs of
posterior lateral arteries, and of the great median posterior
arteries with the heart itself (Fig. 29). The arterial system
is very completely developed in both Limulus and Scorpio,
branching repeatedly until minute arterioles are formed, not
to be distinguished from true capillaries; these open into
irregular swollen vessels which are the veins or venous
sinuses. —— ; x 2 i ; . lv
ee crt Pe dvs a dvs 7 a
stig’
Fic. 31.—Diagram of a lateral view of a longitudinal section of a
Scorpion. d, chelicera; ch, chela; cam, camerostome; m, mouth ;
ent, entosternum ; p, pecten ; sézg', first pulmonary aperture; stig‘,
fourth pulmonary aperture ; dam, muscle from carapace to a preoral
entosclerite ; ad, muscle from carapace to entosternum; md, muscle
from tergite of genital somite to eutosternum (same as dpm in Fig.
30); dv' to dv®, dorso-ventral muscles (same as the series labelled
tsm in Fig. 30); po' to po’, the seven veno-pericardiac muscles of
the right side (labelled VPM in Fig.30). (After Beck, ‘ Trans.
Zool. Soc.,’ vol. xi, 1883.)
considerable weight as a proof of the close genetic affinity of
Limulus and Scorpio.
The great pericardial sinus is strongly developed in both
animals. Its walls are fibrous and complete, and it holds a
considerable volume of blood when the heart itself is con-
tracted. Opening in pairs in each somite, right and left
into the pericardial sinus are large veins, which bring the
blood respectively from the gill-books and the lung-books to
that chamber, whence it passes by the ostia into the heart.
The blood is brought to the respiratory organs in both cases
by a great venous-collecting sinus having a ventral median
position, In both animals the wall of the pericardial
200 E. RAY LANKESTER.
sinus is connected by vertical muscular bands to
the wall of the ventral venous sinus (its lateral ex-
pansions around the lung-books in Scorpio) in each somite
through which the pericardium passes. There are seven
pairs of these veno-pericardiac vertical muscles in
Scorpio, and eight in Limulus (see Figs. 830—32). It is
obvious that the contraction of these muscles must cause a
depression of the floor of the pericardium and a rising of the
roof of the ventral blood-sinus, and a consequent increase of
Per
a
EWM
ST ANE
iS
Se
WN
|
Fic. 32.—Diagram of a lateral view of a longitudinal section of
Limulus. Sze, suctorial pharynx; a/, alimentary canal; PA,
pharynx ; 1, mouth; Zs/, entosternum ; VS, ventral venous sinus ;
chi, chilaria ; go, genital operculum ; 471 to dr°, branchial append-
ages; met, wnsegmented metasoma; extap*, fourth dorsal entapo-
physis of left side ; sm, tergo-sternal muscles, six pairs as in Scorpio
(labelled dv in Fig. 31); VPM! to VPM, the eight pairs of veno-
pericardiac muscles (labelled pv in Fig. 81). V Pd" is probably
represented in Scorpio, though not marked in Figs. 30 and 31.
(After Benham, ‘ Trans. Zool. Soc.,’ vol. xi, 1883.)
volume and flow of blood to each. Whether the pericardium
and the ventral sinus are made to expand simultaneously or
all the movement is made by one only of the surfaces con-
cerned must depend on conditions of tension. In any case
it is clear that we have in these muscles an apparatus for
causing the blood to flow differentially in increased volume
into either the pericardium, through the veins leading from
the respiratory organs, or from the body generally into the
great sinuses which bring the blood to the respiratory
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 201
organs. These muscles act so as to pump the blood through
the respiratory organs.
It is not surprising that with so highly developed an
arterial system Limulus and Scorpio should have a highly
developed mechanism for determining the flow of blood to
the respiratory organs. That this is, so to speak, a need of
animals with localised respiratory organs is seen by the
existence of provisions serving a similar purpose in other
animals, e. g. the branchial hearts of the Cephalopoda.
The veno-pericardiac muscles of Scorpio were seen and
figured by Newport but not described by him. Those of
Limulus were described and figured by Alphonse Milne-
Edwards, but he called them merely ‘transparent lga-
ments,’ and did not discover their muscular structure.
They are figured and their importance for the first time
recognised in the memoir ov the muscular and_ skeletal
systems of Limulus and Scorpio by Lankester, Beck, and
Bourne (4).
6. Alimentary Canal and Gastric Glands.—The
alimentary canal in Scorpio, as in Limulus, is provided with
a powerful suctorial pharynx, in the working of which
extrinsic muscles take a part. The mouth is relatively
smaller in Scorpio than in Limulus—in fact, is minute, as it
is in all the terrestrial Arachnida which suck the juices of
either animals or plants. In both the alimentary canal takes
a straight course from the pharynx (which bends under it
downwards and backwards towards the mouth in Limulus)
to the anus, and is a simple, narrow, cylindrical tube (Fig.
33). The only point in which the gut of Limulus resembles
that of Scorpio rather than that of any of the Crustacea is
in possessing more than a single pair of ducts or lateral
outgrowths connected with ramified gastric glands or gastric
ceca. Limulus has two pairs of these, Scorpio as many as
six pairs. The Crustacea never have more than one pair.
The minute microscopic structure of the gastric glands in the
two animals is practically identical. The functions of these
gastric diverticula have never been carefully investigated.
202 E. RAY. LANKESTER.
It is very probable that in Scorpio they do not serve merely
to secrete a digestive fluid (shown in other Arthropoda to
resemble the pancreatic fluid), but that they also become
Vic. 33.—The alimentary canal and gastric glands of a Scorpion
(A) and of Limulus (B). ps, muscular suctorial enlargement of the
pharynx; sa/, prosomatic pair of gastric ceca in Scorpio, called
salivary glands by some writers; c' and c?, the anterior two pairs of
gastric ceca and ducts of the mesosomatic region; c’, c*, and c’,
ceca and ducts of Scorpio not represented in Limulus; J/, the
Malpighian or renal cecal diverticula of Scorpio; pro, the procto-
dzum or portion of gut leading to anus, and formed embryologically
by an inversion of the epiblast at that orifice. (From Lankester,
“ Limulus an Arachnid.”)
distended by the juices of the prey sucked in by the scorpion
—as certainly must occur in the case of the simple un-
branched gastric ceca of the spiders.
The most important difference which exists between the
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 208
structure of Limulus and that of Scorpio is found in the
hinder region of the alimentary canal. Scorpio is here
provided with a single or double pair of renal excretory
tubes, which have been identified by earlier authors with
the Malpighian tubes of the Hexapod and Myriapod insects.
Limulus is devoid of any such tubes. We shall revert to this
subject below.
7. Ovaries and Spermaries; Gonocels and Gono-
ducts.—The scorpion is remarkable for having the special-
ised portion of ccelom, from the walls of which egg-cells or
sperm-cells are developed according to sex, in the form of
a simple but extensive network. It is not a pair of simple
tubes, nor of dendriform tubes, but a closed network. The
same fact is true of Limulus, as was shown by Owen (7) in
regard to the ovary, and by Benham (14) in regard to the
testis. This is a very definite and remarkable agreement,
since such a reticular gonoccel is not found in Crustacea
(except in the male Apus). Moreover there is a significant
agreement in the character of the spermatozoa of Limulus
and Scorpio. ‘The Crustacea are—with the exception of the
Cirrhipedia—remarkable for having stiff, motionless sperma-
tozoids. In Limulus Lankester found (15) the spermatozoa
to possess active flagelliform “tails,” and to resemble very
closely those of Scorpio, which, as are those of most terrestrial
Arthropoda, are actively motile. This is a microscopic point
of agreement, but is none the less significant.
In regard to the important structures concerned with the
fertilisation of the egg, Limulus and Scorpio differ entirely
from one another. The eggs of Limulus are fertilised in the
sea after they have been laid. Scorpio, being a terrestrial
animal, fertilises by copulation. The male possesses ela-
borate copulatory structures of a chitinous nature, and the
eggs are fertilised in the female withont even quitting the
place where they are formed on the wall of the reticular
gonoceel. The female scorpion is viviparous, and the young
are produced in a highly developed condition as fully formed
scorpions,
20-4 i. RAY LANKESTER.
Differences between Limulus and Scorpio.—We
have now passed in review the principal structural features
in which Limulus agrees with Scorpio and differs from other
Arthropoda. ‘There remains for consideration the one im-
portant structural difference between the two animals.
Limulus agrees with the majority of the Crustacea in
being destitute of renal excretory ceca or tubes opening
into the hinder part of the gut. Scorpio, on the other
hand, in common with all air-breathing Arthropoda except
Peripatus, possesses these tubules, which are often called
Malpighian tubes. A great deal has been made of this
difference by some writers. It has been considered by them
as proving that Limulus, in spite of all its special agreements
with Scorpio (which, however, have scarcely been appreciated
by the writers in question), really belongs to the Crustacean
line of descent; whilst Scorpio, by possessing Malpighian
tubes, is declared to be unmistakably tied together with the
other Arachnida to the tracheate Arthropods, the Hexapods,
Diplopods, and Chilopods, which all possess Malpighian
tubes.
It must be pointed out that the presence or absence of
such renal excretory tubes opening into the intestine appears
to be a question of adaptation to the changed physiological
conditions of respiration, and not of morphological signifi-
cance, since a pair of renal excretory tubes of this nature is
found in certain Amphipod Crustacea (Talorchestia, etc.)
which have abandoned a purely aquatic life. This view has
been accepted and supported by Professors Korschelt and
Heider (16). An important fact in its favour was discovered
by Laurie (17), who investigated the embryology of two
species of Scorpio under Lankester’s direction. It appears
that the Malpighian tubes of Scorpio are developed from the
mesenteron, viz. that portion of the gut which is formed by
the hypoblast ; whereas in Hexapod insects the similar cecal
tubes are developed from the proctodeum or inpushed
portion of the gut, which is formed from epiblast. In fact,
it is not possible to maintain that the renal excretory tubes
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 205
of the gut are of one common origin in the Arthropoda.
They have appeared independently in connection with a
change in the excretion of nitrogenous waste in Arachnids,
Crustacea, and the other classes of Arthropoda when aérial,
as opposed to aquatic respiration has been established—and
they have been formed in some cases from the mesenteron,
in other cases from the proctodeum. Their appearance in
the air-breathing Arachnids does not separate those forms
from the water-breathing Arachnids, which are devoid of
them, any more than does their appearance in certain Amphi-
poda separate those Crustaceans from the other members of
the class.
Further, it is pointed out by Korschelt and Heider that
the hinder portion of the gut frequently acts in Arthropoda
as an organ of nitrogenous excretion in the absence of any
special excretory tubules, and that the production of such
ceca from its surface in separate lines of descent does not
involve any elaborate or unlikely process of growth. In
other words, the Malpighian tubes of the terrestrial Arach-
nida are homoplastic with those of Hexapoda and
Myriapoda, and not homogenetic with them. We are
compelled to take a similar view of the agreement between
the tracheal air-tubes of Arachnida and other tracheate
Arthropods. They are homoplasts (see 18) one of another,
and do not owe their existence in the various classes
compared to a common inheritance of an ancestral tracheal
system.
Conclusions arising from the Close Affinity of
Limulus and Scorpio.—When we consider the relation-
ships of the various classes of Arthropoda, having accepted
and established the fact of the close genetic affinity of Limulus
and Scorpio, we are led to important conclusions. In such a
consideration we have to make use not only of the fact just
mentioned, but of three important generalisations, which
serve, as it were, as implements for the proper estimation of
the relationships of any series of organic forms. First of all
there is the generalisation that the relationships of the various
206 BE. RAY LANKESTER.
forms of animals (or of plants) to one another is that of the
ultimate twigs of a much-branching genealogical tree.
Secondly, identity of structure in two organisms does not
necessarily indicate that the identical structure has been
inherited from an ancestor common to the two organisms
compared (homogeny), but may be due to independent de-
velopment of a like structure in two different lines of descent
(homoplasy). Thirdly, those members of a group which,
whilst exhibiting undoubted structural characters indicative
of their proper assignment to that group, yet are simpler than
and inferior in elaboration of their organisation to other
members of the group, are not necessarily representatives of
the earlier and primitive phases in the development of the
group, but are very often examples of retrogressive change
or degeneration. ‘The second and third implements of analy-
sis above cited are of the nature of cautions or checks.
Agreements are not necessarily due to common inherit-
ance; simplicity is not necessarily primitive and ancestral.
On the other hand, we must not rashly set down agree-
ments as due to “ homoplasy”’ or “convergence of develop-
ment” if we find two or three or more concurrent agreements.
he probability is against agreement being due to homoplasy
when the agreement involves a number of really separate
(not correlated) coincidences. Whilst the chances are in
favour of some one homoplastic coincidence or structural
agreement occurring between some member or other of a
large group a, and some member or other of a large group J,
the matter is very different when by such an initial coinci-
dence the two members have been particularised. The chances
against these two selected members exhibiting another really
independent homoplastic agreement are enormous; let us
say 10,000 to 1. The chances against yet another coincidence
are a hundred million to one, and against yet one more
‘‘eoincidence” they are the square of a hundred million to
one. Homoplasy can only be assumed where the coincidence
is of a simple nature, and is such as may be reasonably
supposed to have arisen by the action of like selective
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 207
conditions upon like material in two separate lines of de-
scent.!
So, too, degeneration is not to be lightly assumed as the
explanation of a simplicity of structure. There is a very
definite criterion of the simplicity due to degeneration, which
can in most cases be applied. Degenerative simplicity is
never uniformly distributed over all the structures of the
organism. It affects many or nearly all the structures of the
body, but leaves some—it may be only one—at a high level
of elaboration and complexity. Ancestral simplicity is more
uniform, and does not co-exist with specialisation and elabora-
tion of a single organ. Further, degeneration cannot be
inferred safely by the examination of an isolated case:
usually we obtain a series of forms indicating the steps of a
change in structure ; and what we have to decide is whether
the movement has been from the simple to the more complex,
or from the more complex to the simple. ‘lhe feathers of a
peacock afford a convenient example of primitive and degene-
rative simplicity. The highest point of elaboration in colour,
pattern, and form is shown by the great eye-painted tail
feathers. From these we can pass by gradual transitions in
two directions, viz. either to the simple lateral tail feathers,
with a few rami only, developed only on one side of the
shaft and of uniform metallic coloration—or to the simple
contour feathers of small size, with the usual symmetrical
series of numerous rami right and left of the shaft and no
remarkable colouring. The one-sided specialisation and the
peculiar metallic colouring of the lateral tail feathers mark
them as the extreme terms of a degenerative series ; whilst
1 A great deal of superfluous hypothesis has lately been put forward in the
name of ‘the principle of convergence of characters ” by a certain school of
paleontologists. The horse is supposed by these writers to have originated
by separate lines of descent in the Old World and the New, from five-toed
ancestors! And the important consequences following from the demonstration
of the identity in structure of Limulus and Scorpio are evaded by arbitrary
and even fantastic invocations of a mysterious transcendental force which
brings about “convergence” irrespective of heredity and selection. Mor-
phology becomes a farce when such assumptions are made.
208 E. RAY LANKESTER.
the symmetry, likeness of constituent parts inter se, and
absence of specialised pigment, as well as the fact that they
differ little from any average feather of birds in general,
mark the contour feather as primitively simple, and as the
starting-point from which the highly elaborated eye-painted
tail feather has gradually evolved.
Applying these principles to the consideration of the
Arachnida, we arrive at the conclusion that the smaller and
simpler Arachnids are not the more primitive, but that the
Acari or mites are, in fact, a degenerate group. This was
maintained by Lankester in 1878 (19), again in 1881 (20) ; it
was subsequently announced as a novelty by Claus in 1885
(21). Though the aquatic members of a class of animals are
in some instances derived from terrestrial forms, the usual
transition is from an aquatic ancestry to more recent land-
living forms. ‘There is no doubt, from a consideration of
the facts of structure, that the aquatic water-breathing
Arachnids, represented in the past by the Hurypterines and
to-day by the sole survivor Limulus, have preceded the
terrestrial air-breathing forms of that group. Hence we see
at once that the better-known Arachnida form a series
leading from Limulus-like aquatic creatures through scorpions,
spiders, and harvestmen to the degenerate Acari or mites.
The spiders ave specialised and reduced in apparent com-
plexity, as compared with the scorpions, but they cannot be
regarded as degenerate, since the concentration of structure
which occurs in them results in greater efficiency and power
than are exhibited by the scorpion. The determination of
the relative degree of perfection of organisation attained by
two animals compared is difficult when we introduce, as seems
inevitable, the question of efficiency and power, and do not
confine the question to the perfection of morphological de-
velopment. We have no measure of the degree of power
manifested by various animals, though it would be possible
to arrive at some conclusions as to how that “ power” should
be estimated. It is not possible here to discuss that matter
further. We must be content to point out that it seems that
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 209
the spiders, the Pedipalps, and other large Arachnids have
not been derived from the scorpions directly, but have
independently developed from aquatic ancestors, and from
one of these independent groups—probably through the
harvestmen from the spiders—the Acari have finally re-
sulted.
Leaving that question for consideration in connection with
the systematic statement of the characters of the various
groups of Arachnida which follows below, it is well now to
consider the following question, viz. seeing that Limulus and
Scorpio are such highly developed and specialised forms, and
that they seem to constitute, as it were, the first and second
steps in the series of recognised Arachnida, what do we
know, or what are we led to suppose with regard to the more
primitive Arachnida from which the Eurypterines and Limu-
lus and Scorpio have sprung? Do we know, in the recent or
fossil condition, any such primitive Arachnids? Such a
question is not only legitimate, but prompted by the analogy
of at least one other great class of Arthropods. The great
Arthropod class, the Crustacea, presents to the zoologist at
the present day an immense range of forms, comprising the
primitive Phyllopods, the minute Copepods, the parasitic
Cirrhipedes and the powerful crabs and lobsters, and the
highly elaborated sand-hoppers and slaters. It has been
insisted, by those who accepted Lankester’s original doctrine
of the direct or genetic affinity of the Cheetopoda and Arthro-
poda, that Apus and Branchipus really come very near to the
ancestral forms which connected those two great branches of
Appendiculate (Parapodiate) animals. On the other hand,
the land crabs are at an immense distance from these simple
forms. ‘he record of the Crustacean family tree is, in fact,
a fairly complete one—the lower primitive members of the
group are still represented by living forms in great abundance.
In the case of the Arachnida, if we have to start their genea-
logical history with Limulus and Scorpio, we are much in the
same position as we should be in dealing with the Crustacea
were the whole of the Kutomostraca and the whole of the
210 E. RAY LANKESTER.
Arthrostaca wiped out of existence and record. There is no
possibility of doubt that the series of forms corresponding in
the Arachnidan line of descent to the forms distinguished in
the Crustacean line of descent as the lower grade—the
Entomostraca—have ceased to exist; and not only so, but
have left little evidence in the form of fossils as to their former
existence and nature. It must, however, be admitted as
probable that we should find some evidence, in ancient rocks
or in the deep sea, of the early more primitive Arachnids.
And it must be remembered that such forms must be expected
to exhibit, when found, differences from Limulus and Scorpio
as great as those which separate Apus and Cancer. The
existing Arachnida, like the higher Crustacea, are ‘ nomo-
meristic,’—that is to say, have a fixed typical number of
somites to the body. Further, they are like the higher
Crustacea, “‘somatotagmic,’—that is to say, they have this
limited set of somites grouped in three (or more) “ tagmata,”
or regions of a fixed number of similarly modified somites—
each tagma differing in the modification of its fixed number
of somites from that characterising a neighbouring “‘ tagma.”
The most primitive among the lower Crustacea, on the other
hand, for example the Phyllopoda, have not a fixed number
of somites; some genera—even allied species—have more,
some less, within wide limits; they are ‘‘ anomomeristic.”
They also, as is generally the case with anomomeristic
animals, do not exhibit any conformity to a fixed plan of
“tagmatism,” or division of the somites of the body into
regions sharply marked off from one another; the head or
prosomatic tagma is followed by a trunk consisting of somites
which either graduate in character as we pass along the
series, or exhibit a large variety in different genera, families,
and orders of grouping of the somites.. They are anomotagmic
as well as anomomeristic.
When it is admitted, as seems to be reasonable, that the
primitive Arachnida would, like the primitive Crustacea, be
anomomeristic and anomotagmic, we shall not demand of
claimants for the rank of primitive Arachnids agreement with
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 211
Limulus and Scorpio in respect of the exact number of their
somites and the exact grouping of those somites; and when
we see how diverse are the modifications of the branches of
the appendages, both in Arachnida and in other classes of
Arthropoda (q. v.), we shall not over-estimate a difference in
the form of this or that appendage exhibited by the claimant
as compared with the higher Arachnids. With those con-
siderations in mind, the claim of the extinct group of the
Trilobites to be considered as representatives of the lower and
more primitive steps in the Arachnidan genealogy must, it
seems, receive a favourable judgment. They differ from the
Crustacea in that they have only a single pair of preoral
appendages, the second pair being definitely developed as
mandibles. This fact renders their association with the
Crustacea impossible, if classification is to be the expression
of genetic affinity inferred from structural coincidence. On
the contrary, this particular point is one in which they agree
with the higher. Arachnida. But little is known of the
structure of these extinct animals; we are therefore compelled
to deal with such special points of resemblance and difference
as their remains still exhibit. They had lateral eyes,! which
resemble no known eyes so closely as the lateral eyes of
Limulus. The general formand structure of their prosomatic
carapace are in many striking features identical with that of
Limulus. ‘The trilobation of the head and body—due to the
expansion and flattening of the sides or “pleura” of the
tegumentary skeleton—is so closely repeated in the young of
Limulus that the latter has been called “the Trilobite stage”
of Limulus (Fig. 42 compared with Fig.41). No Crustacean
exhibits this Trilobite form. But most important of the
evidences presented by the Trilobites of affinity with Limulus,
and therefore with the Arachnida, is the tendency, less
marked in some, strongly carried out in others, to form a
1 A pair of round tubercles on the labrum (camerostome or hypostoma) of
several species of Trilobites has been described and held to be a pair of eyes
quite recently (22). Sense-organs in a similar position were discovered in
Limulus by Patten (42) in 1894.
212 E. RAY LANKESTER.
pygidial or telsonic shield—a fusion of the posterior somites
of the body, which is precisely identical in character with
the metasomatic carapace of Limulus. When to this is
added the fact that a post-anal spine is developed to a large
size in some T'rilobites (Fig. 38), like that of Limulus and
Scorpio, and that lateral spines on the pleura of the somites
are frequent as in Limulus, and that neither metasomatic
fusion of somites nor post-anal spine, nor lateral pleural
spines are found in any Crustacean, nor all three together in
any Arthropod besides the Trilobites and Limulus, the claim
of the Trilobites to be considered as representing one order of
a lower grade of Arachnida, comparable to the grade Ento-
mostraca of the Crustacea, seems to be established.
The fact that the single pair of preoral appendages of
Trilobites, known only as yet in one genus, is in that particu-
lar case a pair of uniramose antenne, does not render the
association of T'rilobites and Arachnidsimprobable. Although
the preoral pair of appendages in the higher Arachnida is
usually chelate, it is not always so; in spiders it is not so;
nor in many Acari. ‘The biramose structure of the post-oral
limbs, demonstrated by Beecher in the Trilobite Triarthrus,
is no more inconsistent with its claim to be a primitive
Arachnid than is the foliaceous modification of the limbs in
Phyllopods inconsistent with their relationship to the Arthros-
tracous Crustaceans such as Gammarus and Oniscus.
Thus, then, it seems that we have in the Trilobites the
representatives of the lower phases of the Arachnidan pedi-
gree. The simple anomomeristic Trilobite, with its equi-
formal somites and equiformal appendages, is one term of
the series which ends in the even more simple but degenerate
Acari. Between the two and at the highest point of the are,
so far as morphological differentiation is concerned, stands
the scorpion; near to it in the T'rilobite’s direction (that is on
the ascending side) are Limulus and the Hurypterines—with
a long gap, due to obliteration of the record, separating them
from the Trilobite. On the other side—tending downwards
from the scorpion towards the Acari—are the Pedipalpi, the
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 2138
spiders, the book-scorpions, the harvestmen, and the water-
mites.
The strange Nobody-Crabs or Pycnogonids occupy a place
on the ascending half of the are below the Eurypterines and
Limulus. They are strangely modified and degenerate, but
seem to be (as explained in the systematic review) the
remnant of an Arachnidan group holding the same relation
to the scorpions which the Lemodipoda hold to the Pod-
ophthalmate Crustacea.
We have now to offer a classification of the Arachnida, and
to pass in review the larger groups, with a brief statement of
their structural characteristics.
In the bibliography at the close of this article (referred to
by leaded Arabic numerals in brackets throughout these
pages) the titles of works are given which contain detailed
information as to the genera and species of each order or sub-
order, their geographical distribution, and their habits and
economy so far as they have been ascertained. The limits of
space do not permit of a fuller treatment of those matters
here.
TABULAR CLASSIFICATION! OF THE ARACHNIDA.
Crass ARACHNIDA.
Grade A. ANOMOMERISTICA.
Sub-class TRILOBITZ.
Orders. Not satisfactorily determined.
1 The writer is indebted to Mr. R. I. Pocock, assistant in the Natural
History departments of the British Museum, for valuable assistance in the
preparation of this article and for the classification and definition of the
groups of Hu-arachnida here given. The general scheme and some of the
details have been brought by the writer into agreement with the views
maintained in this article. Mr. Pocock accepts those views in all essential
points, and has, as a special student of the Arachnida, given to them valuable
expansion and confirmation.
vol. 48, PART 2,—NEW SERIES. 15
214 KH. RAY LANKESTER.
Grade B. NOMOMERISTICA.
Sub-class I. PANTOPODA.
Order 1. Nymphonomorpha.
,, 2. Ascorhynchomorpha.
,, 3 Pycnogonomorpha.
Sub-class II. EVARACHNIDA.
Grade a. Dernoprancuia, Lankester (vel Hypro-
PNEUSTEA, Pocock).
Order 1. Xiphosura.
5, 2 Gigantostraca.
Grade b. EmponoprancutA, Lankester (vel A&éRO-
PNEUSTEA, Pocock).
Section a. Pectinifera.
Order 1. Scorpionidea.
Sub-order a. Apoxypoda.
x b. Dionychopoda.
Section B. Epectinata.
Order 2. Pedipalpi.
Sub-order a. Uropygi.
Tribe 1. Urotricha.
» 2. Tartarides.
Sub-order b. Amblypyegi.
Order 3, Aranez.
Sub-order a. Mesothele.
oe b. Opisthothelee.
Tribe 1. Mygalomorphe.
» 2. Arachnomorphe.
Order 4. Palpigradi (= Microthelyphonida).
Order 5. Solifugee (= Mycetophore).
Order 6. Pseudoscorpiones (=Chelonethi).
Sub-order a. Panctenodactyl.
3 b. Hemictenodactyli.
Order 7. Podogona (= Meridogastra).
Order 8. Opiliones.
Sub-order a. Cyphophthalmi.
b. Mecostethi.
ce. Plagiostethi.
3)
2)
STRUCTURE AND CLASSIFICATION OF THE ARAUHNIDA. 215
Order 9. Rhynchostomi (= Acari).
Sub-order a. Notostigmata.
b. Cryptostigmata.
c. Metastigmata.
d. Prostigmata.
e. Astigmata.
jf. Vermiformia.
g. Tetrapoda.
Crass ARACHNIDA.—Enuarthropoda having two pros-
thomeres (somites which have passed from a post-oral to a
preoral position), the appendages of the first represented by
eyes, of the second by solitary rami which are rarely antenni-
form, more usually chelate. A tendency is exhibited to the
formation of a metasomatic as well as a prosomatic carapace
by fusion of the tergal surfaces of the somites. Intermediate
somites forming a mesosoma occur, but tend to fuse super-
ficially with the metasomatic carapace or to become co-
ordinated with the somites of the metasoma, whether fused
or distinct to form one region—the opisthosoma (abdomen of
authors). In the most highly developed forms the two
anterior divisions (tagmata) of the body, prosoma and meso-
soma, each exhibit six pairs of limbs, pediform and _plate-
like respectively, whilst the metasoma consists of six limbless
somites and a post-anal spine. The genital apertures are
placed in the first somite following the prosoma, excepting
where a pregenital somite, usually suppressed, is retained.
Little is known of the form of the appendages in the lowest
archaic Arachnida, but the tendency of those of the prosomatic
somites has been (as in the Crustacea) to pass from a general-
ised biramose or multiramose form to that of uniramose
antenne, chele, and walking legs.
The Arachnida are divisible into two grades of structure—
according to the fixity or non-fixity of the number of somites
building up the body.
Grade A (of the Arachnida) ANOMOME-
RISTICA.—Extinct archaic Arachnida in which (as in the
Entomostracous Crustacea) the number of well-developed
216 E. RAY LANKESTER.
somites may be more or less than eighteen, and may be
grouped only as head (prosoma) and trunk, or may be further
differentiated. A telsonic tergal shield of greater or less
size is always present, which may be imperfectly divided into
well-marked but immovable tergites indicating incompletely
Si
i
Mm
l
iy
\ j
Fic. 34.—Restoration of Triasthrus Becki, Green, as deter-
mined by Mr. Beecher from specimens obtained from the Utica Slates
(Ordovician), New York. A, dorsal; B, ventral surface. In the
latter the single pair of antenne springing up from each side of the
camerostome or hypostome or upper lip-lobe are seen. Four pairs
of appendages besides these are seen to belong to the cephalic
All the appendages are pediform and biramose; all have
tergum.
a prominent gnathobase, and in all the exopodite carries a comb-like
series of secondary processes. (After Beecher, from Zittel.)
differentiated somites. The single pair of palpiform appen-
dages in front of the mouth has been found in one instance to
be antenniform, whilst the numerous post-oral appendages in
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 217
the same genus were biramose. The position of the genital
apertures is not known. Compound lateral eyes present ;
median eyes wanting. The body and head have the two
pleural regions of each somite flattened and expanded on
either side of the true gut-holding body-axis. Hence the
name of the sub-class signifying trilobed, a condition realised
also in the Xiphosurous Arachnids. The members of this
eroup, whilst resembling the lower Crustacea (since all lower
eroups of aphylum tend to resemble one another), differ from
them essentially in that the head exhibits only one prostho-
mere (in addition to the eye-bearing prosthomere) with palpi-
Fic. 35.—Triarthrus Becki, Green. a, Restored thoracic
limbs in transverse section of the animal: J, section across a pos-
terior somite; c, section across one of the sub-terminal somites.
(After Beecher.)
form appendages (as in all Arachnida) instead of two. The
Anomomeristic Arachnida form a single sub-class, of which
only imperfect fossil remains are known.
Sub-class (of the Anomomeristica) TRILOBITA.—The single
sub-class 'rilobite constitutes the grade Anomomeristica. It
has been variously divided into orders by a number of writers.
The greater or less evolution and specialisation of the meta-
somatic carapace appears to be the most important basis for
classification—but this has not been made use of in the latest
attempts at drawing up a system of the Trilobites. The form
of the middle and lateral regions of the prosomatic shield has
been used, and an excessive importance attached to the
218 BK; RAY LANKESTER.
demarcation of certain areas in that structure. Sutures are
stated to mark off some of these pieces, but in the proper
sense of that term, as applied to the skeletal structures of the
Vertebrata, no sutures exist in the chitinous cuticle of Arthro-
poda. That any partial fusion of originally distinct chitinous
plates takes place in the cephalic shield of Trilobites, com-
parable to the partial fusion of bony pieces by suture in
Vertebrata, is a suggestion contrary to fact.
The Trilobites are known only as fossils, mostly Silurian and
pre-Silurian ; a few are found in Carboniferous and Permian
strata. As many as two thousand species are known. Genera
Fie. 836.—Triarthrus Becki, Green. Dorsal view of second
thoracic leg with and without sete. ez, inner ramus; ev, outer
ramus. (After Beecher.)
Fic. 37.—Deiphon Forbesii, Barr. One of the Cheiruride.
Silurian, Bohemia. (From Zittel’s ‘ Paleontology.)
with small metasomatic carapace, consisting of three to six
fused segments distinctly marked though not separated by soft
membrane, are Harpes, Paradoxides, and Triarthrus (Fig. 34).
In Calymene, Homalonotus, and Phacops (Fig. 38) from six
to sixteen segments are clearly marked by ridges and grooves
in the metasomatic tagma, whilst in Ilenus (Fig. 39) the
shield so formed is large, but no somites are marked out on
its surface. In this genus ten free somites (mesosoma) occur
between the prosomatic and metasomatic carapaces. Asaphus
and Megalaspis (Fig. 39) are similarly constituted. In Agnos-
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 219
tus (Fig. 40) the anterior and posterior carapaces constitute
almost the entire body, the two carapaces being connected
by a mid-region of only two free somites. It has been held
that the forms with a small number of somites marked in the
posterior carapace, and numerous free somites between the
anterior and posterior carapace, must be considered as anterior
to those in which a great number of posterior somites are
Ric. 35. Fie. 39.
Fic. 38.—Dalmanites (Phacops) limulurus, Green. One of
the Phacopide, from the Silurian, New York. (Krom Zittel.)
Vic. 39.—Megalaspis extenuatus. One of the Asaphide
allied to Ilenus, from the Ordovician of Hast Gothland, Sweden.
(From Zittel.)
traceable in the metasomatic carapace, and that those in which
the traces of distinct somites in the posterior or metasomatic
carapace are most completely absent must be regarded as
derived from those in which somites are well marked in the
posterior carapace and similar in appearance to the free
somites. The genus Agnostus, which belongs to the last
category, occurs abundantly in Cambrian strata, and is one
of the earliest forms known. This would lead to the supposi-
220 E. RAY LANKESTER.
tion that the great development of metasomatic carapace is
a primitive and not a late character, were it not for the fact
that Paradoxides and Atops, with an inconspicuous telsonic
carapace and numerous free somites, are also Cambrian in
age, the latter, indeed, anterior in horizon to Agnostus.
On the other hand, it may well be doubted whether the
pygidial or posterior carapace is primarily due to a fusion of
the tergites of somites which were previously movable and
well developed. The posterior carapace of the Trilobites and
of Limulus is probably enough in origin a telsonic carapace—
that is to say, is the tergum of the last segment of the body
Fic. 40.—Four stages in the development of the trilobite
Agnostus nudus. A, youngest stage with no mesosomatic
somites. B and C, stages with two mesosomatic somites between
the prosomatic and telsonic carapaces; D, adult condition, still with
only two free mesosomatic somites. (From Korschelt and Heider.)
which carries the anus. From the front of this region new
segments are produced in the first instance, and are added
during growth to the existing series. ‘his telson may en-
large, it may possibly even become internally and sternally
developed as partially separate somites, and the tergum may
remain without trace of somite formation, or, as appears to
be the case in Limulus, the telson gives rise to a few well-
marked somites (mesosoma and two others), and then en-
larges without further trace of segmentation, whilst the
chitinous integument which develops in increasing thickness
on the terga as growth advances welds together the unseg-
mented telson and the somites in front of it, which were
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 221
previously marked by separate tergal thickenings. It must
always be remembered that we are liable (especially in the
case of fossilised integuments) to attach an unwarranted
interpretation to the mere discontinuity or continuity of the
thickened plates of chitinous cuticle on the back of an Arthro-
pod. ‘These plates may fuse, and yet the somites to which
they belong may remain distinct, and each have its pair of
Fie. 41.—Five stages in the development of the trilobite Sao
hirsuta. A, youngest stage; B, older stage with distinct pygidial
carapace; C, stage with two free mesosomatic somites between the
prosomatic and telsonic carapaces; D, stage with seven free inter-
mediate somites; KH, stage with twelve free somites; the telsonic
carapace has not increased in size; a, lateral eye; g, so-called facial
“suture” (not really a suture); p, telsonic carapace. (From
Korschelt and Heider, after Barrande.)
appendages well developed. On the other hand, an unusually
large tergal plate, whether terminal or in the series, is not
always due to fusion of the dorsal plates of once-separated
somites, but is often a case of growth and enlargement of a
single somite without formation of any trace of a new somite.
For the literature of Trilobites see 22*.
Grade B (ofthe Arachnida). NOMOMERISTICA.
—Arachnida in which, excluding from consideration the eye-
bearing prosthomere, the somites are primarily (that is to say,
222 K. RAY LANKESTER,
in the common ancestor of the grade) grouped in three
regions of six—(a) the “ prosoma”’ with palpiform appendages,
(b) the “ mesosoma” with plate-like appendages, and (c) the
‘“‘metasoma” with suppressed appendages. A somite placed
between the prosoma and mesosoma—the pre-genital somite
—appears to have belonged originally to the prosomatic
series (which with its ocular prosthomere and palpiform
limbs [Pantopoda] would thus consist of eight somites), but
to have been gradually reduced. In living Arachnids, ex-
cepting the Pantopoda, it is either fused (with loss of its
appendages) with the prosoma (Limulus,! Scorpio), after
embryonic appearance, or is retained as a rudimentary,
Fie. 42.—So-called “trilobite stage” of Limulus polyphemus.
A, dorsal, B, ventral view. (From Korschelt and Heider, after
Leuckart.)
separate, detached somite in front of the mesosoma, or dis-
appears altogether (excalation). The atrophy and total dis-
appearance of ancestrally well-marked somites frequently
take place (as in all Arthropoda) at the posterior extremity
of the body, whilst excalation of somites may occur at the
constricted areas which often separate adjacent “ regions,”
though there are very few instances in which it has been
recognised. Concentration of the organ-systems by fusion of
neighbouring regions (prosoma, mesosoma, metasoma), pre-
1 Mr. Pocock suggests that the area marked vii in the outline figure of the
dorsal view of Limulus (Fig. 7) may belong to the tergum of the suppressed
pregenital somite. A small area on the prosomatic carapace (marked * in fig.
7) is also considered by Mr. Pocock as possibly belonging to the pre-genital
somite, and this latter suggestion is what commends itself to the present writer.
Embryological evidence must settle exactly what has become of the pre-genital
somite,—E. R. L.
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 223
viously distinct, has frequently occurred, together with
obliteration of the muscular and chitinous structures indica-
tive of distinct somites. This concentration and obliteration
of somites, often occompanied by dislocation of important
seomental structures (such as appendages and nerve-ganglia),
may lead to highly-developed specialisation (individuation,
H. Spencer), as in the Araneze and Opiliones ; and, on the other
hand, may terminate in simplification and degeneration, as in
the Acari.
The most important general change which has affected the
structure of the nomomeristic Arachnida in the course of
their historic development is the transition from an aquatic
to a terrestrial life. This has been accompanied by the con-
version of the lamelliform gill-plates into lamelliform lung-
plates, and later the development from the lung-chambers,
and at independent sites, of trachez or air-tubes (by adapta-
tion of the vasifactive tissue of the blood-vessels) similar to
those independently developed in Peripatus, Diplopoda,
Hexapoda, and Chilopoda. Probably trachez have developed
independently by the same process in several groups of
tracheate Arachnids. The nomomeristic Arachnids comprise
two sub-classes—one a very small degenerate offshoot from
early ancestors, the other the great bulk of the class.
Sub-class I (of the Nomomeristica). PANTOPODA.—Nomo-
meristic Arachnids in which the somites corresponding to
mesosoma and metasoma have entirely aborted. ‘The seventh
leg-bearing somite (the pre-genital rudimentary somite of
Kuarachnida) is present, and has its leg-like appendages
fully developed. Monomeniscous eyes with a double (really
triple) cell layer formed by invagination, as in the Huarach-
nida, are present. The Pantopoda stand in the same relation
to Limulus and Scorpio that Cyamus holds to the thoracos-
tracous Crustacea. The reduction of the organism to seven
leg-bearing somites, of which the first pair, as in so many
Euarachnida, are chelate, is a form of degeneration connected
with a peculiar quasi-parasitic habit resembling that of the
Crustacean Leemodipoda. The genital pores are situate at
224 KE. RAY LANKESYTER,
the base of the seventh pair of limbs, and may be repeated on
the fourth, fifth, and sixth. In all known Pantopoda the
size of the body is quite minute as compared with that of the
limbs: the alimentary canal sends a lone czcum into each
lee (cf. the Aranez), and the genital products are developed
in gonoceels also placed in the legs.
The Pantopoda are divided into three orders, the characters
of which are dependent on variation in the presence of the
full number of legs.
Order 1 (of the Pantopoda). Nymphonomorpha, Pocock (nov.)
(Fig. 43).—In primitive forms belonging to the family Nym-
Fre. 43.—One of the Nymphonomorphous Pantopoda, Nymphon
hispidum, showing the seven pairs of appendages 1 to 7; ad, the
rudimentary opisthosoma; s, the mouth-bearing proboscis. (From
Parker and Haswell’s ‘ Text-book of Zoology, after Hoek.)
phonide the full complement of appendages is retained—the
first (mandibular), the second (palpiform), and the third (ovi-
gerous) pairs being well developed in both sexes. In certain
derivative forms constituting the family Pallenide, however,
the appendages of the second pair are either rudimentary or
atrophied altogether.
Two families: 1. Nymphonide (genus Nymphon), and
2. Pallenide (genus Pallene).
Order 2. Ascorhynchomorpha, Pocock (nov.).—Appendages
of the second and third pairs retained and developed, as in
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 225
the more primitive types of Nymphonomorpha; but those of
the first pair are either rudimentary, as in the Ascorhynchide,
or atrophied, as in the Colossendeide. In the latter a further
specialisation is shown in the fusion of the body segments.
Two families: 1. Ascorhynchide (genera Ascorhynchus
and Ammothea) ; 2. Colossendeide (genera Colossendeis
and Discoarachne).
Order 3. Pycnogonomorpha, Pocock (nov.).—Derivative
forms in which the reduction in number of the anterior
appendages is carried farther than in the other orders,
reaching its extreme in the Pycnogonide, where the first and
second pairs are absent in both sexes, and the third pair also
are absent in the female. Inthe Hannoniide, however, which
resemble the Pycnogonide in the absence of the third pair in
the female, and of the second pair in both sexes, the first
pair are retained in both sexes.
Two families: 1. Hannoniide (genus Hannonia); 2.
Pycnogonide (genera Pycnogonum and Phoxichilus).
Remarks.—The Pantopoda are not known in the fossil
condition. They are entirely marine, and are not uncommon
in the coralline zone of the sea-coast. The species are few,
not more than fifty (23). Some large species of peculiar
genera are taken at great depths. Their movements are
extremely sluggish. They are especially remarkable for the
small size of the body and the extension of viscera into the
legs. Their structure is eminently that of degenerate forms.
Many frequent growths of coralline Algz and Hydroid polyps,
upon the juices of which they feed, and in some cases a species
of gall is produced in Hydroids by the penetration of the
larval Pantopoda into the tissues of the polyp.
Sub-class II (of the Nomomeristic Arachnida). EUARACH-
NIDA.—These start from highly developed and specialised
aquatic branchiferous forms, exhibiting prosoma with six
pediform pairs of appendages, an intermediate pregenital
somite, a mesosoma of six somites bearing lamelliform pairs
of appendages, and a metasoma of six somites devoid of
appendages, and the last provided with a post-anal spine.
226 E. RAY LANKESTER. ,
Median eyes are present, which are monomeniscous, with dis-
tinct retinal and corneagenous cell layers, and placed centrally
on the prosoma. Lateral eyes also may be present, arranged
in lateral groups, and having a single or double cell layer
beneath the lens. The first pair of limbs is often chelate or
prehensile, rarely antenniform ; whilst the second, third, and
fourth may also be chelate, or may be simple palps or walking
legs.
An internal skeletal plate, the so-called “ entosternite ”’ of
fibro-cartilaginous tissue, to which many muscles are attached,
is placed between the nerve-cords and the alimentary tract in
the prosoma of the larger forms (Limulus, Scorpio, Mygale).
In the same and other leading forms a pair of much-coiled
glandular tubes, the coxal glands (ccelomoccels in origin), is
found with a duct opening on the coxa of the fifth pair of
appendages of the prosoma. The vascular system is highly
developed (in the non-degenerate forms); large arterial
branches closely accompany or envelop the chief nerves;
capillaries are well developed. ‘The blood-corpuscles are large
amoebiform cells, and the blood-plasma is coloured blue by
heemocyanin.
The alimentary canal is uncoiled and cylindrical, and gives
rise laterally to large gastric glands, which are more than a
single pair in number (two to six pairs), and may assume the
form of simple ceca. ‘lhe mouth is minute, and the pharynx
is always suctorial, never gizzard-like. The gonadial tubes
(gonoccels or gonadial ccelom) are originally reticular and
paired, though they may be reduced to a simpler condition.
They open on the first somite of the mesosoma. In the
numerous degenerate forms simplification occurs by oblitera-
tion of the demarcations of somites and the fusion of body-
regions, together with a gradual suppression of the lamelli-
ferous respiratory organs and the substitution for them of
tracheee, which, in their turn, in the smaller and most reduced
members of the group, may also disappear.
The Euarachnida are divided into two grades with refer-
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 227
ence to the condition of the respiratory organs as adapted to
aquatic or terrestrial life.
Grade a (of the Huarachnida). Dr&LoBRANCHIA
(H ydropneustea).
Mesosomatic segments furnished with large plate-like
appendages, the first pair acting as the genital operculum,
Fie. 44.—Dorsal view of Limulus polyphemus, Lim. One
fourth the Natural size, linear. (From Parker and Haswell, ‘ Text-
book of Zoology,’ after Leuckart.)
the remaining pairs being provided with branchial Jamelle
fitted for breathing oxygen dissclved in water. The pre-
genital somite partially or wholly obliterated in the adult.
The mouth lying far back, so that the basal segments of all
the prosomatic appendages, excepting those of the first pair,
228 E. RAY LANKESYTER.
are capable of acting as masticatory organs. Lateral eyes
consisting of a densely packed group of eye-units (‘ com-
pound ” eyes).
Order 1. Xiphosura._—-The pregenital somite fuses in the
| TAGs
Fie. 45.—Ventral view of Limulus polyphemus, Lim. S&S
Subfrontal sclerite; Cam, camarostome; MM, mouth; Pmst, prome-
sosternum; chz, chilaria; op, genital operculum or first pair of
appendages of the mesosoma; Br.app, second to the sixth pair of
appendages of the mesosoma bearing the branchial lamine.
embryo with the prosoma and disappears (see Fig. 19). Not
free-swimming, none of the prosomatic appendages modified
to act as paddles; segments of the mesosoma and metasoma
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 229
(=opisthosoma) not more than ten in number, distinct or
coalesced.
Family—Limulide (Limulus).
Belinuride (Belinurus, Aglaspis, Prest-
wichia),
is Hemiaspidee (Hemiaspis, Bunodes).
Remarks.—The Xiphosura are marine in habit, frequenting
the shore. They are represented at the present day by the
single genus Limulus (Figs. 44 and 45; also Figs. 7, 9, 11, to
15 and 20), which occurs on the America coast of the Atlantic
Ocean, but not on its eastern coasts, and on the Asiatic coast
of the Pacific. The Atlantic species (L. polyphemus) is
common on the coasts of the United States, and is known as
the king-crab or horseshoe crab.
23,
24.
25.
26.
27,
28.
29.
30,
31.
32.
33.
34.
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 267
Horx.—“ Report on the Pyenogonida,” ‘ Challenger Expedition Reports,’
1881. Mernert.—“ Pyenogonida of the Danish Ingolf Expedition,”
vol. ili, 1899. Morgan.— Embryology and Phylogeny of the Pycno-
gonids,” ‘ Biol. Lab, Baltimore,’ vol. v, 1891.
Bourne, A. G.—* The Reputed Suicide of the Scorpion,” ‘ Proc. Roy,
Soc.,’ vol. xlii, pp. 17—22.
LANKEsTER.—“ Notes on some Habits of Scorpions,” ‘Journ. Linn. Soc.
Zool.,’ vol. xvi, p. 455, 1882.
Huxtey.— Pharynx of Scorpion,” ‘Quart. Journ. Mier. Sci.,
(old series), 1860, p. 250.
Pococx.—“ How and why Scorpions hiss,” ‘ Natural Science,’ vol. ix,
1896. Cf. idem, ‘Stridulating Organs of Spiders,’ ‘Ann, and Mag.
Nat. Hist.’ (6), xvi, pp. 230—233.
KRrarpPELIn.—‘ Das Thierreich (Scorpiones et Pedipalpi),’ Berlin, 1899.
Peters.—‘ Hine neue Kintheilung der Skorpione,” ‘ Mon. Akad. Wiss.
Berlin, 1861. Pococx.—‘ Classification of Scorpions,” ‘Ann. and
Mag. Nat. Hist.’ (6), xii, 1893. THorett and Linpstrém.—“ On a
Silurian Scorpion,” ‘ Kéng!. Svens. Vet. Akad. Handl.,’ xxi, No. 9,
1885.
Campripee, O. P.—‘ A New Family (Tartarides) and Genus of Thely-
phonidea,”’ ‘ Ann. and Mag. Nat. Hist.’ (4), x, 1872, p. 418. Coox.—
** Hubbardia, a New Genus of Pedipalpi,” ‘ Proc. Entom. Soc. Washing-
ton,’ vol. iv, 1899. Kragrvetin.—‘ Das Thierreich,’ Berlin, 1899.
THORELL.—“ Tartarides, etc.,”’ ‘Ann. Mus. Genova,’ vol. xxvii, 1889.
> vol. vill
McCoox.—‘ American Spiders and their Spinning Work,’ 3 vols., Phila-
delphia, 1889-938.
Peckuam.— On Sexual Selection in Spiders,” ‘ Occasional Papers Nat.
Hist, Soc. Wisconsin,’ vol. i, pp. 1—1138, 1889.
MoceripcE.—‘ Harvesting Ants and Trap-door Spiders,’ 1873.
BertKau.—‘ Arch. f. Naturgesch.,’ vol. xviii, pp. 316—362; idem,
same journal, 1875, p. 235, and 1878, p. 351. Camprincs, O. P.—
“* Araneidea,” ‘in ‘ Biologia Centr. Americana,’ vols. i and ii, London,
1899. KerysERLING.—‘Spinnen Amerikas,’ Nirnberg, 1880-92.
Pococx.—‘ Liphistius and the Classification of Spiders,” ‘Ann. and
Mag. Nat. Hist.’ (6), x, 1892. Smron.—‘ Hist. nat. des Araignées,’
vols. i and ii, 1892, 1897. Wacner.— L’industrie des Araneina,”’
‘Mém. Acad. St. Pétersbourg; idem, “ La mue des Araignées, *‘ Ann.
Sci. Nat.,’ vol. vi.
Grasst.— Intorno ad un nuovo Aracnide artrogastro (Ke nenia mira-
bilis), ete.,” ‘ Boll, Soc. Ent. Ital.,’ vol. xviii, 1886,
268
EK, RAY LANKESTER.
‘85. Hansen and Sérensen.—‘‘ The Order Palpigradi, Thorell-(K enenia),
36.
37.
38.
39.
40.
and its Relationships with other Arachnida,” ‘Ent. Tidskr.,’ vol. xviii,
pp. 288—240, 1898. Krarprtiy.—‘ Das Thierreich,’ Berlin, 1901.
Brernarp.—‘‘ Compar. Morphol. of the Galeodide,”’ ‘Trans. Linn. Soe.
Zool.,’ vol. vi, 1896, ibique citata. Durour.— Galeodes,” ‘Mém.
prés. Acad. Sci. Paris,’ vol. xvii, 1862. Kranprtin.—‘ Das Thier-
reich,’ Berlin, 1901. Pocock.— Taxonomy of Solifuge,” ‘Ann. and
Mag. Nat. Hist.,’ vol. xx.
Batzan.—‘' Voyage au Venezuela (Pseudoscorpiones),” ‘Ann. Soc.
Entom. France,’ 1891, pp. 497—522.
GuERiIn-MENEVILLE.—‘ Rev. Zool.,’ 1838, p. 11. Karscu.—‘ Ueber
Cryptostemma Guer,”’ ‘ Berliner Entom. Zeitschrift,’ xxxviil, pp, 25—
32, 1892. ‘THorELL.—“ On an apparently New Arachnid belonging
to the Family Cryptostemmide, Westw.” ‘Bihang Svenska Vet.
Akad. Handligar,’ vol. xvii, No. 9, 1892.
SérexsEN.—“ Opiliones laniatores,” ‘Nat. Tidskr.’ (3), vol. xiv,
1884. THoRELL.—“ Opilioni,”’ ‘Ann. Mus. Genova,’ vol. viii, 1876.
Bervese.—‘ Acari, ete., in italia reperta,’ Padova, 1892. CaNnESTRINI.—
*Acarofauna Italiana,’ Padova, 1885. Canestrinr and KraMER.—
“‘Demodicide and Sarcoptide,” in ‘Das Thierreich,’ Berlin, 1899.
Micnart.—‘ British Oribatide,’ Ray Soc.; idem, ‘‘Oribatide,” in
‘Das 'Thierreich,’ Berlin, 1898; idem, ‘Progress and Present State
of Knowledge of Acari,” ‘Journ. Roy. Mier. Soc.,’ 1894. Natepa.—
**Piytoptide,” ‘Das Thierreich,’ Berlin, 1898. Trovrssart.—
“Classification des Acariens,” ‘Rev. Sci. Nat. de l’Quest,’ p. 289,
1892. Wacner.— Embryonal Entwick. von Ixodes,’ St. Petersburg,
1893.
41. BertKau.—* Coxaldriisen der Arachniden,” ‘Sitzb. Niederl. Gesellsch.,’
1885.
42. Parren.— Brain and Sense Organs of Limulus,” ‘Quart. Journ. Mier.
Sci.,’ vol. xxxv, 1894; see also his “Origin of Vertebrates from
Arachnids,” ibid., vol. xxxi.
AUTHORITIES NOT CITED BY NUMBERS IN THE TEXT,
Lung Books. BerTEaux.—“ Le poumon des Arachnides,” ‘ La Cellule,’
vol. v, 1891. Jawarowski.— Die Entwick. d. sogenn. Lunge bei
den Arachniden,” ‘ Zeitsch. wiss. Zool.,’ vol. lviii, 1894. Macteop.—
“ Recherches sur la structure et la signification de |’appareil respira-
toire des Arachnides,” ‘Arch. Biologie,’ vol. v, 1884. ScHnEIpER.
—‘‘Mélanges Arachnologiques,” in ‘Tablettes zoologiques,’ vol. ii,
STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 269
p. 135, 1892. Srmmons.—‘‘ Development of Lung in Spiders,”
‘Amer. Journ. Science,’ vol. xlviii, 1894.
‘Coxal Glands. Brrrkav.— Ueber die Coxaldriisen der Arachniden,”
‘Sitzb. d. Niederl. Gesellseh.,’ 1885. Loman.— Altes und neues
iiber das Nephridium (die Coxaldriise) der Arachniden,” ‘ Bijd. tot. de
Dierkunde,’ vol. xiv, 1887. Macirop.—‘‘ Glande coxale chez les
Galeodes,” ‘ Bull. Acad. Belg.’ (3), vol. viii, 1884. Prtsenrer.—“‘On
the Coxal Glands of Mygale,” ‘Proc. Zool. Soc.,’? 1885. ‘TowER —
“The External Opening of the Brick-red Glands of Limulus,” ‘ Zool.
Anzeiger,’ vol. xviii, p. 471, 1895.
Entosternite. ScuminKewrtscu.—< Bau und Entwick. des Endosternites
der Arachniden,” ‘Zool. Jahrb., Anat. Abtheil.,? vol. vili, 1894.
Pococx.—“ The Arachnidan Entosternite.” ‘Quart. Journ. Microsc.
Sci.,’ vol. 46 (1902), p. 225.
Embryology. Ba.rour.— Development of the Araneina,” ‘ Quart. Journ.
Mier. Sci.,’ vol. xx,1880. Kinesury.— “ in the
(fig. 13, a), comparable to the wall of the “ ampulla’
nephridium of Lumbricus.
After leaving the funnel the nephridial loop mounts up
alongside the gut, and nearly reaches the dorsal body-wall.
The nephridial canal passes to the body-wall a short dis-
tance in front of the ventral cheeta (figs. 5, 6, 7), passing
amongst the cheetal muscles to the cheetal gap in the longitu-
dinal muscle of the body-wall. Here the structure of the
nephridial cells suddenly changes ; the cytoplasm is now very
highly granular, the cells, or rather syncytium, becoming
much more deeply stained than elsewhere; there is no trace
of the cytoplasmic network which is observable in the greater
part of the nephridium; the nuclei, too, are rather different
(figs. 10, 11). This very granular region may, for conveni-
ence, be termed the “duct;” but although I traced the
nephridial canal thus far, I was unable to detect any perfo-
ration of the more superficial granular cells. They pass
through the muscular wall into the epidermis, where they
spread out slightly; but I could detect no pore.
This “ duct” is readily distinguished from the surrounding
epidermis by its affinity for the stain, the epidermal cells
appear homogeneous, and spaces exist between the bases of
many of the cells. The “duct,” however, passes right
through the epidermis to the surface.
The nephridium in Segment X appears to be in a state of
degeneration; it is relatively smaller than the following
ones, and the loop only reaches upward as far as the lateral
line, though the diameter of the body is here greater than it
is more posteriorly (figs. 12 and 13).
304 W. BLAXLAND BENHAM.
The nephridial funnel, lying in Segment IX, is situated
immediately in front of the root of the first testis, as shown
in the figure of the longitudinal section of this region of the
immature individual (fig. 14). The funnel is smaller than
that of the post-ovarian nephridium.
I was unable to trace this first nephridium to the body-
wall; it was easy enough to follow it upwards to a point
close to the body-wall near the lateral line, some little way in
front of the chet, but there it seems to cease.
It is interesting to find that Forbes was equally unable to
find a pore in the case of the first nephridium in “ Phreo-
ryctes emissarius.”
Reproductive System.—There are two pairs of testes
attached to the anterior wall of Segments X, XI respectively,
and on the posterior wall of each of these segments is a pair
of spermiducal funnels of a simple plate-like form.
The course of the sperm-duct from funnel to the body-wall
is shown in figs. 16—24.
Hach of the four sperm-ducts leaves its funnel close to the
lower or ventral margin (fig. 32), as described by Beddard
(1) for H. smithi; it then passes through the septum, and
afterwards behind the funnel and ontside the following testis ;
it soon becomes slightly undulating, and reaches to the level
of the lateral line; then, bending down, it reaches the body-
wall at a point about midway between the margin of the
segment and the ventral cheta (figs. 24, 29).
I have been quite unable, however, to detect any external
opening in either of the four ducts, and, indeed, only in the
case of the left duct of the anterior pair was I able to trace
it actually to the body-wall and into continuity with the
epidermis (fig. 29).
Owing to the slight obliquity of the sections and to the
displacement due to the previous compression in mounting
the specimen, the duct of one side is cut transversely, and
that of the other side longitudinally in at any rate part of
its course (fig. 28), and in this figure both the upward and
downward part of the canal are involved. The duct has
almost all the appearance of a nephridium, and its general
ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 305
disposition in the body is similar to that of the more
posteriorly placed excretory organs (cf. figs. 3 and 7 with
figs. 16—24). Section across it does not show a definite
epithelium, but the lumen appears to traverse a single row of
cells. ‘hese cells, or rather syncytium, for I cannot detect
any boundary to the component cells, are not vacuolated as
are the uephridial cells, nor is the protoplasm immediately
bounding the lumen of the duct specially granular to form so
distinct a ‘ wall” as in the case of the nephridium. Indeed,
when first examining the sections I mistook the duct for a
nephridium, but a more careful examination of consecutive
sections, drawn with a camera, shows quite without any doubt
that this tube, if it be a nephridium, at any rate acts as a
sperm-duct. In the right duct a group of deeply stained
spermatozoa can be seen entering the tube (fig. 32), which,
as stated above, starts from the ventral edge of the funnel.
In the lumen of the left duct I see a bunch of sperms some
distance away from the funnel; these appear both in a
portion of the duct cut transversely (figs. 25, 26) and a
little further along, appear in a longitudinal section at a bend
in the duct (fig. 27), and they can be traced through several
consecutive sections. ‘hese sperms are deeply stained by
the hemalum, and show up perfectly unmistakably.
In this connection it is interesting to recall the fact that
the earlier students of Haplotaxis gordioides believed
that the nephridia of these segments acted as sperm-ducts,
but Mr. Beddard was the first to identify true genital ducts
in the genus in his examination of H. smithi; he describes
(1, p. 391) the duct as “a ciliated tube composed of a single
layer of columnar cells,” and his figure 6 (pl. xxiii) illustrates
this statement.
However this may be in H. smithi, the sperm-duct in
the present species can scarcely be distinguished structurally
from a nephridium, except that the margin of the canal is a
little more distinctly marked in the latter, and the cytoplasm
of the cells is vacuolated, and the canal is more convoluted
than in the sperm-duct, in which, too, cilia can be seen dis-
306 W. BLAXLAND BENHAM.
tinctly in most of the sections. These points of difference
require very high magnification, and are not recognisable
without a homogeneous immersion lens. Butif there isa close
similarity between the excretory and genital ducts, there is an
immense difference between the spermiducal funnel, with its
high ciliated cells forming a conspicuous, broad, thick dise on
the septum (fig. 31 et seq.), and the minute nephridial
funnel just projecting through a septum.
In the Segments XI, XII I find no nephridia
i.e. besides the sperm-ducts,—nor is there any funnel belong-
ing to these tubes other than the flat, wide sperm-funnels.
no tubes,
Even in the immature worms no nephridial funnels exist
alongside the young sperm-funnels (fig. 37).
It is a curious fact that the sperm-ducts, even in a worm
in which ripe sperms fill the sperm-sacs as well as the sper-
mathece, and with large ova in their proper segments,
should be so difficult to trace; Michaelsen, too, was unable to
follow their course in sections of H. gordioides, or to
detect the pores, though it is true his specimens do not appear
to have been as fully mature as is one of my individuals.
There are two median unpaired sperm-sacs, or, more
properly, septal pouches which act as sperm-sacs (figs. 1, 16).
Segment X is filled with loose masses of developing sper-
matozoa in all stages, mostly fully formed; the Septum
X/XI is pushed backwards above the gut, and is also filled
with sperms; the end of this sac is at about the level of the
end of Segment XI. In Segment XI we have a repetition of
this; its hinder wall is also pouched, and reaches to the
middle of the thirteenth segment.
There is only a single pair of ovaries, which are
situated in Segment XII; I sought in vain for a second pair
both in the entire and in sectionised specimens.
A single pair of oviducts corresponding to these ovaries
starts from large, wide, flat funnels in Segment XII (cf. figs.
1, 38). The oviduct (figs. 388—42) is a remarkably wide tube,
of much greater diameter than the sperm-duct. It is at first
directed backwards, and continues in this direction for some
ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 307
distance ; then it curves outwards and downwards towards
the latero-ventral angle of the body-wall, which it penetrates
well within the Segment XIII, to open just anterior and
external to the ventral cheta. The pore is overlapped by a
prominent flap, which seems to be entirely due to the greater
development of the muscular coats of the body-wall in this
segment (fig. 42). The position of this pore so far back in
its segment is a very unusual one; for in nearly all the
“limicoline” Oligocheetes the pore is intersegmental, and even
in the earthworms it is usuaily nearer the margin of the seg-
ment than it is in the present worm.
It should be stated that in the younger individual the testes
and ovaries are quite small, and except for the rather larger
nuclei in the female gonad and a more compact outline of the
organ, there is no difference between the two sexes; yet in
it the oviduct has already the character described for the
adult—a comparatively wide tube (figs. 43, 45) with a wide
funnel-shaped opening into the ccelom; the duct is trace-
able as far as the body-wall, which it reaches near to the
ventral cheete.
There is a striking difference both in dimension and in
structure between the oviduct and sperm-duct, for whereas
the latter has a very narrow lumen, which appears to be a
perforation through a string of cells and is in many respects
like a nephridium, the oviduct is quite a wide tube, sur-
rounded by an epithelium of several cells, or, at any rate,
a multinuclear syncytium, bearing long cilia within (figs.
Ad, 46).
The oviducal funnel does not project much into the seg-
ment, and in the younger individual has an appearance quite
different from that presented by the young sperm-funnels,
which are merely smaller representatives of the adult con-
dition. The oviducal funnel, however, is here but little defined
(fig. 45) ; the duct appears in longitudinal section as if the
septum were pouched backwards to form a tube, which tube
is lined by cells bearing cilia. The lip of the funnel, how-
ever, is ill defined ; its upper margin is distinct enough and
308 W. BLAXLAND BENHAM.
formed of cubical cells, in which I could not detect cilia, but
the lower lip is as yet not prominent; but by the time the
worm is sexually mature the lip of the funnel becomes a
much more prominent structure.
The hinder wall of Segment XII is pouched, and in the
ovisac so formed are some large ova; others lie free in
the segment, and still others are free in Segment XIII under
the sperm-sac ; while in the fourteenth segment still larger
ego's distend the body (fig. 1). The presence of eggs in various
stages of development in Segment XIII led me to expect a
second pair of ovaries here, but I have failed to make them
out. It is true that a small group of cells appears in trans-
verse sections to be attached to the underside of the ovisac;
this I took at first for a second ovary, but following the
sections along, it becaine evident that it was only a group of
small “nutritive” cells adherent to a larger ovum. ‘he
mass is free in the segment, and moreover there is no trace
of a second pair of oviducts nor their funnels in either of
my two specimens.
The funnel of the oviduct (in Segment XII) is so con-
spicuous an object, its nuclei are so deeply stained, and the
funnel is so thick, that I feel sure that I have made no error in
this matter. Moreover, in the longitudinal sections the three
pairs of young gonads and funnels are quite evident, but no
corresponding fourth pair exists.
In Segments XI, XII, and XIII there is a pair of solid
glands connected with the epidermis. In the twelfth seg-
ment the gland opens in the neighbourhood of the ventral
cheta on each side, but in each of the eleventh and
thirteenth segments the two glands open below the nerve-
cord in the median line. Hach gland (fig. 30) consists of
a group of long club-shaped cells, with faintly granular and
vacuolated contents, which are not stained by hemalum.
The gland projects freely into the ccelom, and the necks of
the cells are easily traceable through the epidermis. In
each case the gland is nearly of the same length as the
segment.
ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 309
These “copulatory glands” are comparable to the glands
of several Enchytreeids.!
There are two pairs of globular spermathece (fig. 1) filled
with spermatozoa, communicating with the exterior along
the lateral line. They practically fill the anterior half of
Segments VIII and IX; there is no differentiated duct, but the
epidermis is here invaginated to pass through the muscles
and reach the sac. The short tube thus formed is lined by
cuticle; there are no special muscles around this tube.
Dimensions.—About 20 mm. by $ mm; about sixty
segments. (‘lhe worm was not measured before it was cut
in pieces for sectionising, but the portion cut longitudinally
measures 10 mm., contains twenty-three segments; and the
uncut remains measures 8 mm., contains thirty-one segments;
while the transverse series of sections involves two [?]
segments.)
Locality.—Lake Wakatipu, South Island, New Zealand,
from a depth of 550 feet.
REMARKS.
The new worm which I place in the genus Haplotaxis
differs from the other two species in a number of minor
points, but most noticeably in the possession of a single pair
of ovaries and oviducts. The presence of a second pair of
these organs has hitherto been a character of the genus
which therein differs from all other Oligochetes except the
Lumbriculide. But apart from the absence of the second
pair of female organs, the new worm agrees in all other
points with the generic characters as given by Michaelsen in
his article in the ‘ Tierreich,’ in the more detailed papers
by Beddard, and in his Monograph. The possession of
two pairs of sperm-ducts opening independently is another
character of the genus, which, however, is shared by Pelo-
drilus. The latter genus was founded by Beddard (8) for a
1 Forbes describes a pair of glands, of similar character apparently, in every
segment of the body, and suggests that they are seusory.
310 W. BLAXLAND BENHAM.
worm from New Zealand (P. violaceus), in which the sperm-
ducts present the peculiarity of both opening independently,
but in the same segment. Since this genus is provided with
only a single pair of ovaries, I have kept in view the possi-
bility of this being the case in the new worm, but although I
did not succeed in tracing the second pair of male ducts to the
body-wall, yet there is nothing in the direction of the ducts to
indicate that the first pair passes through an entire segment.
Moreover, a second species of this genus, P. ignatovi, has
recently been described by Dr. Michaelsen (6), in which the
arrangement of the sperm-ducts is similar to that in Haplo-
taxis, so that the general arrangement of the genital ducts
and pores in this species agrees pretty well with that
described in H. heterogyne.
here, for
But the agreement ceases
in all those anatomical characters by which
Pelodrilus is distinguished from Haplotaxis the new
species now under discussion agrees precisely with the latter.
It forms, in fact, with P. ignatovi, a link between the
genera Pelodrilus and Haplotaxis as originally charac-
terised. This is seen in the following tabular summary of’
the characters under discussion, though there are several
other differences between the two genera :
| H. gordi- Hl hj, Hs hetero-| P. igna- | P. viola-
oides. Se gyne. tovi. ceus
Bile { 4 isolated, | 4 couples, | 4 isolated, | 4 isolated,| + couples,
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CONTENTS OF No. 191.—New Series.
MEMOIRS:
On the Existence of an Anterior Rudimentary Gill in Astacus
fluviatilis, Fabr. By Marcery Mosrtry. (With Plates’93 and
“ 94) ; ‘ ‘ : - : 5 : .
On the Development of Flagellated Organisms (Trypanosomes) from
the Spleen Protozdic Parasites of Cachexial Fevers and Kala-Azar.
By Leonarp Rocers, M.D., M.R.C.P..1.M.S., Acting Professor of
Pathology, Medical College, Calcutta. (With Plate 23)
The Epithelial Islets of the Pancreas in Teleostei. By Jonn Runnin,
D.Se., F.R.M.S., Assistant in Zoolugy, Aberdeen University.
(With Plates 86—98) . chal Megha St a ea
Observations on the Maturation and Fertilisation of the Ege of the
Axolotl, By J. W. Jenkinson, M.A., Assistant to the Linacre
Professor of Comparative Anatomy, Oxford. (With Plates 99
—43) .
Notes on the Anatomy of Gazelletta. By G. Herpert Fowter, B.A.,
PED IUZ.5., Palos: : :
PAGE
359
367
379
407
483
ASTACUS FLUVIATILIS. 309
On the Existence of an Anterior Rudimentary
Gill in Astacus fluviatilis, Fabr.
By
Margery Moseley.
With Plates 23 and 24.
Tue theoretical gill formula for the Decapod crustacea is
four on each side of each somite, corresponding to the three
maxillipeds and the five legs—that is, Somites VII to XIV,
counting the ophthalmic somite as No. 1.
Professor Huxley distinguished the four gill plumes
according to their position on the somite. He recognised one
podobranch on the limb, two arthrobranchs on the arthrodial
membrane, and a pleurobranch on the pleuron or side of the
somite between the leg-joint and the tergum.
The complete theoretical gill formula according to Huxley
for one side of the animal would be—
Podo- Arthro- Pleuro-
Somite. branchie. branchiz. branchize. Total.
VII j 1 2 1 4
VIII i 2 1 4
IX 1 2 i 4
xX 1 2 i A.
XI 1 PA 1 4
XII 1 2 1 4.
XIII 1 2 1 4
XIV 1 2 1 4
32
The nearest approach to this is found in certain Peneide,
VoL. 48, PART 3.—NEW SERIES, 26
360 MARGERY MOSELEY.
belonging to the subfamily Aristewina. Alcock’ gives the
following formula for the subgenera Plesiopeneus, Ariste-
omorpha and Aristzopsis of the genus Aristzus and
for the genera Benthesicy mus and Gennadas.
Podo- Arthro- Pleuro-
Somite. branchie. branchie. branchiz. Total.
NEL 0 (ep.) 1 : 0) j i pee
NAULES es 1 (ep.) ih 1 5 +ep.
Lexy. 1 (ep.) 2 1 4+ ep.
x 1 (ep.) 2 1 4+ep.
XI 1 (ep.) 2 1 4+ ep.
Ake 1 (ep.) 2 1 4+ ep.
p40 ane O (ep.) 2 1 3+ ep.
XIV 0 0 1 1
24+°7 ep.
A practically identical formuia is given by Boas* for the
aberrant Penzid Cerataspis longiremis.
The formula given by Professor Huxley for Astacus
fluviatilisis as follows? :—
Podo- Arthro- Pleuro-
Somite. branchie. branchie. branchiz. Total.
VEE, O (ep.) 0 0) ep.
Viti. 1 1 0 2
xX 1] 2 0) 3
x 1 2; 0 3
XI 1 2 OQorr. . 3+0 orr
PG 1 2 r : 3+r
bt] Ca 1 2 = ; 3+r
DCEVE =. @) 0) 1 : 1
18+ep+ 2r or 3r
1 *Deser. Catalogue Indian Deep-Sea Crustacea,’ pp. 35, ete. (1901).
2 ¢ Vidensk. Selsk. Skr. 6 Raekke, naturvid. math. Afd.,’ i (2), p. 43
(1880). Gf also Claus, ‘Arb. Zool. Inst. Wien,’ vi, p. 49 (1885) and
Bounier, ‘ Trav. Stat. Zool. Wimereux,’ vii, p. 38 (1899).
3 Huxley does not enumerate the epipodites accompanying the podobranchs
as is done in the formula quoted above from Alcock.
ASTACUS FLUVIATILIS. 361
He recognised two kinds, the stone-crayfish and the noble-
crayfish, which he called Astacus torrentium (Schrank),
and Astacus nobilis (Huxley). He mentions that A.
torrentium never has more than two rudimentary pleuro-
branchs, whereas he had found three in A. nobilis. The stone-
crayfish A. torrentium was the same as that found in
England, and he left it an open question whether they were
both varieties of A. fluviatilis, or whether they were
specifically different, in which case A. nobilis was the true
A. fluviatilis.
Of A. leptodactylus, and the closely allied forms A.
pachypus and A. angulosus, Professor Huxley says that
«if A. angulosus and A. pachypus are varieties of
A. leptodactylus, I cannot see why Gerstfeldt’s conclusion
that A. nobilis is another variety of the same form need be
questioned on morphological grounds.” Faxon! and Ortmann’
recognise the following European species: Astacus fluvia-
tilis, Fabr.,>A.leptodactylus Esch., A.pallipes Lereb.,*A.
torrentium Schrk., A. pachypus Rthke. and A. colchicus
Kessl., which differ from each other not only in colour and in
the form of the rostrum and limbs, but also in some cases in
the number of rudimentary pleurobranchiz in the -hinder
somites of the gill-bearing region.
Whilst A. fluviatilis, A.leptodactylus, A. pachypus,
and A.colchicus have three rudimentary pleurobranchia,
A. pallipes has only two, the third most anterior rudiment
having been reduced to a minute papilla, and A. torrentium
has two without the least trace of the third.
The crayfishes which are used by students in University
and college classes in this country are supplied by London
agents, as a rule, who make a regular business of importing
1 *Mem. Mus. Comp. Zool.,’ Harvard, x (4), 1885, and ‘ Proc. U. S. Nat.
Mus.,’ xx, pp. 643-694, 1898.
2 * Proc. Amer. Phil. Soc.,’ xli, p. 286, 1902.
3 The A. astacus (Linn.) of Faxon’s later paper. Ortmann employs the
generic name Potamobius in place of Astacus.
* Huxley’s A. torrentium included this and the following species,
362 MARGERY MOSELEY.
the various kinds. The native A. pallipes of the Thames
was for many years used at Oxford, but within the last twenty
years it has become rare in the Thames owing to a disease of
the gills, and finer examples are now supplied by London
dealers. These most frequently consist of French specimens,
écrevissesa puttesrouges, the true Astacus fluviatilis,
Fabr. On examining aspecimen of the true A. fluviatilis in
the Oxford laboratory, I observed a minute rudimentary gill
in a position which appeared to correspond to the arthrodial
membrane of Somite VII (that of the first pair of maxillipeds).
I give a more detailed account of this rudimentary gill
below ; here I wish to point out especially the very curious
fact that this anterior rudimentary gill is not present in
A.torrentium, A. pallipes, or A. leptodactylus, but it
is present on both sides in every specimen of true A.
fluviatilis which I have examined. These amount to about
thirty, varying in size from 34 inches to 44 inches fromthe tip of
the rostrum to the end of the telson. It thus becomes a specific
character of A. fluviatilis, and the fact that it is not present
in the smaller and larger species allied to A. fluviatilis goes
some way towards explaining how it was that it escaped the
observation of Professor Huxley, and that Oxford was for
many years supplied with A. pallipes explains why it was
not found in the Oxford laboratory before.
I have been enabled to examine a number of specimens of
exotic species of Astacidez belonging to the Natural History
Museum, South Kensington, by the kindness of Professor
Lankester, and have not discovered in them the new rudi-
mentary anterior gill. However, ina male specimen of Astacus
dauricus! from Corea, of length 5} centimetres from tip of
rostrum to end of telson, on the right side and in exactly the
same position as the new rudiment in A. fluviatilis there was
a minute papilla, just visible to the naked eye, of length $ milli-
metre. This is the only specimen of A. dauricus which I have
examined, and on the left side, which I looked at first, I could
1 Specimens in the Museum collection are so labelled. More probably,
however, they are A. (Cambaroides) similis, Koelbel, (W. T. C.)
ASTACUS FLUVIATILIS. 363
find nothing, but as this part of the specimen was in a rather
brittle condition I may have broken it away.
The other exotic specimens examined by me were :
Cambarus (rusticus ?) Astacine;
Parastacus pilimanus
Astacoides madagascarensis
Cheraps bicarinatus
Paranephrops planifrons
also Scyllarus latus, Madeira; Panulirus penicilla-
tus, Gulf of Akaba; neither of which had any sign of the
Paragtacin® ;
gill.
DESCRIPTION OF THE RuDIMENTARY PostERIOR ARTHPROBRANCH
ON THE SOMITE OF THE FIRST MAXILLIPED IN ASTACUS
FLUVIATILIS.
In the Jess well developed examples the gill appears as a
small white filament resting on a white bulb or cushion
(fig. 2) from which it depends outwards and downwards. In
the better developed examples there are as many as seven fila-
ments attached to a central stem depending from the cushion
(figs. 1,3, 4, 5, 6,7). The sizes of cushion and gill vary
from 2 mm. to 34 mm. gill and 1} mm. to 3 mm. cushion
in crayfish of length 4} to 44 inches, and 2 mm. gill and
1 mm. to 14 mm. cushion in crayfish of length 34 to 34 inches.
This bulb or cushion at the base of the gill is also present in
the rudimentary pleurobranchiz, but is nothing like so large
in proportion to the filament. Minnte hooked sete are
present on the cushion and sometimes on the stem of the gill
(figs. 4, 5, 6, 7,a). The relative sizes of cushion and gill vary
in different specimens. ‘he position of the gill is shown in
figs. 1 and 2; it is situated on the somite of the first maxilli-
ped. The cushion.is attached to, or rather springs from,
the upper part of the edge of the lamina (fig. 1, k), which
connects the epipodite (fig. 1, g) with the hard ridge (fig. 1, e) ;
the cushion is also firmly attached to the ridge e, so that if
364 MARGERY MOSELEY.
the first maxilliped be torn from the animal the cushion and
gill stay behind. This position corresponds to that assigned
by Claus! to the rudimentary gill on the first maxilliped in
Peneeus, as he objected to the two arthrobranchs of Huxley
being classed together, and considered the posterior one as
having a closer relation to the series of pleurobranchiz. The
epipodite passes posteriorly to the gill and touching it.
The amount of development of this gill, as with most
rudimentary organs, is very variable, but it was fairly equally
developed on the two sides of the animals I have examined
(figs. 5 and 7, also 4 and 6, from same specimens); also
it varies equally in development in males and females. In
the better developed specimens in which there is a central
stem the filaments of the gill are all developed on the outer
side of this stem (figs. 1, 3, 4, 7). The filaments are fre-
quently discoloured with brown patches.
According to Dr. Calman the only other Decapods known
to possess branchiz on the first thoracic somite? are
Stenopus, some Penzide, and certain aberrant Thalassi-
nidz (Jaxea and Naushonia) which possess a minute
arthrobranch on each side of that somite.
In Peneus the gillis less rudimentary than in A. fluvia-
tilis, and rests on a fleshy lobe or cushion in the same position
as that in Astacus, but which stands out straight from the
body of the animal instead of lying flat against it as in A.
fluviatilis. The filaments of the gill, of which there are many
more than in A. fluviatilis, all spring from the cushion in a
fan shape, not from a central stem as in A. fluviatilis.
As before mentioned, this gill is only found in A. fluvia-
tilis, Stenopus, and some Peneide and Thalassinide;
however, in A. dauricus there was the minute papilla on
the right side of the specimen I examined, and there seem to
be traces of the gill in some other of the allied forms which
I examined.
1 « Arb. Zool. Inst. Wien,’ tome 6, p. 46, 1886.
* Apart from the branchial filaments developed on the epipodite of the first
maxilliped in many Parastacine.
ASTACUS FLUVIATILIS. 365
In aspecimen of Nephrops norvegicus, lent me by
the British Museum, in exactly the same position as the
cushion in A. fluviatilis is a partly calcified flap which
hooks over the epipodite of the same somite, and apparently
serves to prevent its coming forward. In Homarus vul-
garis this hook is larger and easier to make out.
A specimen of Cambarus (rusticus?) male, from British
North America, had in the same position a small hard knob ;
one of A. torrentium (male), from Bavaria, had a small hard
cushion in the same position. Another of A. leptodactylus
female, Asia Minor, also had a cushion in the same position.
According to W. Faxon “‘the gills of A. gambelii present
the nearest approach to the primitive type of any living
members of the genus Astacus,” in that the three rudi-
mentary pleurobranchiz are jointed near their base and
possess, the middle pair two short lateral branches, and the
anterior and posterior pairs one short lateral branch, at
the joints. Unless this species proves also to possess
the new rudimentary arthrobranch, its gill formula must,
however, be considered less primitive than that of A.
fluviatilis.
In conclusion, I take the opportunity of thanking Professor
Ray Lankester for kindly helping me to write this paper,
and for enabling me to examine the specimens in the British
Museum, and Dr. Calman for helping me in so doing, and for
important assistance as to the crustacean gill generally.
Oxford, October, 1904.
EXPLANATION OF PLATES 238 & 24,
Illustrating Margery Moseley’s paper, “On the Existence of
an Anterior Rudimentary Gill in Astacus Fluviatilis.”
PLATE 23.
Fic. 1.—Left anterior rudimentary gill in situ from a male, 34 inches
in length (from tip of rostrum to end of telson). Magnified 35 diameters.
366 MARGERY MOSELEY.
A. Cushion to which gill is attached. 3». Stem of gill to which seven filaments
are attached. c. Cut edge of epipodite of first maxilliped. pb. Bulb to which
is attached scaphognathite, which is not shown. £. Strongly calcified ridge,
part of thoracic wall, representing part of fused epimera of anterior thoracic
segments. ¥. Cut edge of thoracic wall, which here turns outwards to join
lining of branchiostegite. @. The part of epipodite not cut off. H. Pivot, part
of thoracic wall, to which is articulated the coxopodite of the third maxilliped.
I. Boss which bears coxopoditic sete, which are not shown. x. Outer edge of
lamina, part of first maxilliped, connecting that limb with hard ridge (£), and
bearing at its upper end cushion to which gill is attached.
PLATE 24.
Fic. 2.—Left anterior rudimentary gill in situ, showing adjoining thoracic
wall and limbs. Magnified 6 diameters. a. Cushion to which gill with single
filament is attached. 4. Calcified ridge as e in Fig. 1. ¢. Cut edge of
thoracic wall. dande. Regions of thoracic wall, Strongly calcified ridge,
to which is attached arthrodial membrane of third maxilliped. g. Scar left by
posterior arthrobranch, cut off. 4. Scar left by podobranch, cut off. ¢. Exo-
podite of third maxilliped. Jj. Boss which bears coxopoditic seta. &. Proto-
podite of mandible. 7. Basipodite and coxopodite of first maxilla at their
region of attachment to body-wall. m. Bulb to which is attached scapho-
gnathite, which is cut off. 2. Exopodite of first maxilliped. 0. Exopodite of
second maxilliped. p. Stump of podobranch, cut off, of second maxilliped.
gq. Stump of arthrobranch, cut off, of second maxilliped. 7. Scar left by
anterior arthrobranch, cut off. s. Scar left by scaphognathite. 7¢. Scar left by
epipodite, cut off, of first maxilliped. «. Endopodite of second maxilliped.
v. Endopodite of third maxilliped. w. Basipodite of third maxilliped.
x. Endopodite of first maxilla.
Figs. 3, 4, 5, and 7 viewed under microscope by transmitted light with
coverglass. (a) Minute hooked sete.
Fic. 3.—Rudimentary gill plume from right side. Magnified 30 diameters.
Fie. 4.—Rudimentary gill plume from left side of male. Magnified 35
diameters.
Fia. 5.—Rudimentary gill plume from left side. Magnified 38 diameters.
Fig. 6.—Rudimentary gill plume from right side of same specimen as
Fig. 4, viewed in drop of spirit without coverglass. Magnified 28 diameters.
Fie. 7.—Rudimentary gill plume from right side of same specimen as
Fig. 5. Magnified 34 diameters.
THE DEVELOPMENT OF FLAGELLATED ORGANISMS. 367
On the Development of Flagellated Organisms
(Trypanosomes) from the Spleen Protozoic
Parasites of Cachexial Fevers and Kala-
Azar.
By
Leonard Rogers, M.D., M.R.C.P., I.M.S.,
Acting Professor of Pathology, Medical College, Calcutta.
(With Plate 25.)
THE small oval parasites, known under the name of
Leishman-Donovan bodies (although they appear to have
been first found by D. D. Cunningham in Dehli boil) were
described last year as occurring in the enlarged spleens of
patients dying of chronic fever with marked cachexia by
Leishman, who considered them to be degenerate trypano-
somes, because he found somewhat similar bodies form with a
large and a small chromatine mass in the spleens of rats
which had died forty-eight hours before of trypanosomiasis
due to the organisms of tsetse fly disease. Donovan, working
in Madras, found similar bodies in blood obtained fresh from
patients suffering from this fever, thus proving that those
seen by Leishman were not degenerate trypanosomes, and
Laveran, after examining Donovan’s specimens, came to the
conclusion that the parasite was a piroplasma. Ross, Nuttall,
and Manson have all dissented from this view, and regard
the organism as probably belonging to a new genus.
Christophers suggests that it is a microsporidium.!
I have elsewhere shown that the parasite is to be found in
1 Professor Ray Lankester, in the ‘ Quarterly Review,’ July, 1904, expresses
the view that Schawdinn’s recently published researches, ‘On the Trypano-
somes of the Blood of the Stone Owl,” render it probable that Leishman’s
corpuscles, as well as those of Delhi sore, are stages in the life-history of
a ‘Trypanosoma.
VoL. 48, PART 3.—NEW SERIES. 27
368 LEONARD ROGERS.
the great majority of cachexial fevers with enlarged spleens
occurring so commonly in Calcutta, and also in still larger
numbers in all cases of active kala-azar, which, as I main-
tained in 1897, is nothing but a severe form of the disease
hitherto known as “ malarial cachexia,” but for which I have
suggested the more appropriate one of ‘cachexial fever”
until further advances in our knowledge of the new parasite
enabled a better one to be decided on. In the course of my
recent investigations I tried various methods of studying the
parasites outside the body, and eventually found one by
which they could be kept alive for some days, during which
they multiplied greatly, and in some instances developed new
forms of considerable interest. The method by means of
which these results have been obtained is an extremely simple
one. The blood obtained by spleen puncture was imme-
diately ejected into small sterile test-tubes containing a little
sodium citrate to prevent the blood from coagulating, and
these were then incubated at varying temperatures, portions
of the culture being removed with a platinum loop from time
to time for examination with the microscope. At blood heat I
found the spleen parasites rapidly underwent degenerative
changes, and after twenty-four hours most of them had disap-
peared and the remainder stained badly. As the presence of
a macro- and a micro-nucleus in the spleen parasites pointed to
their possible relationship with the flagellated class of proto-
zoa, and it is known that trypanosomes live much longer out
of the body at low temperatures than at blood heat, I next
tried incubating the culture tubes in a cold incubator at 27°
C., ice being used, as the laboratory temperature was several
degrees above that point. At this temperature I found that
the parasites lived for some days, retaining fully their stain-
ing properties. Further, in favourable cases, in which a
large number of parasites were present in the blood when
first obtained (which is only the case in about one fifth of
those met with in Calcutta), it was soon evident that they
were undergoing division and increasing very materially in
numbers, for, instead of two or three in a field of an immer-
THE DEVELOPMENT OF FLAGELLATED ORGANISMS. 369
sion lens, as in the original specimens, as many as fifty or
more were sometimes seen in the same area in those from the
cultures. Moreover, divisional forms, which are rare in fresh
spleen blood, appeared in very large numbers in the cultures
after from one to three days, thus allowing the modes of
division to be much more easily studied.
DrvisionAL Forms wirHout DrvELOPMENT.
The divisional forms, which occur in great numbers in
cultures at 27° C., are of two kinds. The first is a simple
subdivision of the small oval parasites into two, both the
macro- and the micro-nucleus first dividing, and then the body
of the cell splitting into two, the cleavage beginning at one
end, so that just before they separate they remain attached
only by the other poles. This mode of division is illus-
trated in line I of the plate, figs. 1 to 4. These forms can be
found in small numbers by long search in films of blood
obtained by spleen puncture when numerous parasites are
present, but they form only a very small proportion of the
total number of organisms seen. On the other hand, in
cultures they are present in very much larger numbers,
several in various stages being often seen in a single field of
the microscope.
The second mode of division is a multiple one, as shown in
line I, figs. 5 to 8. The macro- and micro-nucleus divides
a number of times, as in fig. 6, instead of only once, the
outline of the cell becoming less definite, until eventually the
appearance shown in fig. 7 is reached, in which a number of
very small nuclei arranged in pairs of a small and a large
kind enclosed in a zoogloea-like material is seen. Next these
enlarge gradually, and each pair becomes surrounded by a
faint capsule, which becomes more and more distinct with the
growth of each young form, until the characteristic groups of
the oval bi-nucleated, fully-grown spleen parasites result, as
shown in fig. 8 of line II of the plate, which are not very
rarely seen in good specimens of spleen puncture blood.
370 LEONARD ROGERS.
Fig. 8 of line I shows a nearly full-sized group. All stages
of these multiple divisional forms occur in large numbers in
favourable cultures at 27° C., every stage being sometimes
seen in a single field of the microscope. They are found
most abundantly in a slimy material, which appears in the
tubes after a day or two, and which stains rather like fibrin,
but contains very few red corpuscles. This mode of division
also takes place within the spleen during life, probably
accounting for the greater number of the parasites, and the
different stages can be seen in smears made from the organ
shortly after death. The smallest multiple form is, however,
very rarely seen in films of blood obtained by spleen puncture,
probably because the cells, distended by a number of the larger
forms, are more readily ruptured by the suction action of the
syringe than are those containing the smaller forms. The
formation of these multiple young forms in a zooglcea-like
material derived apparently from the protoplasm of the
dividing parasite itself, and occurring in. culture-tubes in
which the blood-corpuscles have broken down, clearly proves
that the parasites are not growing in the red corpuscles, and
thus renders Laveran’s contention that the parasites are
piroplasma untenable.
At a temperature of 27° C. only the above-described forms
were seen in large numbers. Noye’s blood-agar culture
medium was also tried without success. On next reducing
the temperature of the cold incubator down to about 22° C.
and making further cultures in a new series of cases of
citrated spleen blood, further and more important changes
were soon found.
DEVELOPMENTAL Forms.
The first thing noticed was an enlargement of the small
oval spleen parasites, affecting especially the macro-nucleus
and the protoplasm of the cell, the micro-nucleus remaining
unchanged. ‘Then one day a culture of only twenty-four
hours’ growth, the fully developed flagellated forms shown
THE DEVELOPMENT OF FLAGELLATED ORGANISMS. 371
in figs. 8 to 12 of line XI of the plate, were suddenly en-
countered, together with the intermediate forms shown in
the first seven figures of the same line. Since that time a
number of cultures have been made and further intermediate
forms have been met with, but in these it has taken three or
four days before large flagellated forms were found, and the
fully elongated trypanosoma-like forms of case 37 have not
again been seen so perfectly. What the conditions were
which favoured the full development in so short a time in
that case I cannot say. ‘The case was a more acute one than
is often seen in Calcutta, but a second lot of spleen blood
obtained a few days later failed to develop in the same way,
so there must have been some other factor present. As in
all my other successful cultures the steady development of
the parasites day by day could readily be traced, it will be
best to describe these changes in the order of their develop-
ment. For the purpose of illustrating the progress of the
evolution the forms seen each day in two cases have been
drawn in the plate, each line representing one day’s appear-
ances.
Stage of Development after Twenty-four Hours,
—At the end of one day at 22° C. an examination of the
citrated blocd shows the forms figured in lines III and VIT
of the plate, while lines II and VI show those seen in the
spleen blood of the same cases before incubation. It will be
seen from line III that at the end of one day the organisms
have already increased considerably in size, while the macro-
nucleus is also larger, this being a striking feature. On the
other hand, the micro-nucleus has not altered, but still
remains small and rod shaped. The forms shown in line
VII also show that the macro-nucleus, in addition to being
larger, is beginning to present a granular appearance, while
it does not stain so darkly as in the original spleen parasites.
Further, the protoplasm of the cell is also increasing in
amount and now take ona bluish staining, and has a very
finely granular appearance. These are the only changes met
with as a rule on the first day.
ane LEONARD ROGERS,
Stage of Development after Forty-eight Hours.—
By the end of the second day much more marked changes are
met with, the principal forms of which are shown in lines IV
and VIII of the Plate. In the first place there is a still
further and very marked increase in the size of the organisms
still affecting especially the macronucleus and the protoplasm,
as in figs. 5 and 7 of line IV. Secondly, and of much greater
interest, is the appearance of double forms, such as are not
met with on the first day. These show every degree from
apposition at one point of their circumference of two of the
large oval forms, through closer degrees of contact up to
nearly complete fusion of the two cells. At first I took these
stages for a method of division, but as a further study showed
that the latter developments into elongated and flagellated
forms always takes place in pairs or rarely threes, I have
come to the conclusion that these early double forms are
really a kind of conjugation, such as is known to occur in
other protozoa preparatory to the evolution of new stages
in their life history. In favour of this view there is also the
fact that the pairs of large oval organisms during the second
and third days are found to be in contact with each other in
very varying positions, and to present no regularity in this
feature, as is the case with the small spleen forms undergoing
fission shown in figs. 1 to 4 of line Iof the Plate. Thus, while
fies. 4 and 6 of line LV show contact of the sides of the oval
bodies, figs. 5 and 7 of line V show apposition of the end
of one to the side of the other, and similar variations are
shown in the figures of line VIIT.
In addition to the forms showing mere apposition, others
show more or less complete degrees of fusion of two oval
forms, as in figs. 1, 2, and 8 of line IV, the two macro- and
micronuclei being each distiuctly seen. Further, even on the
second day, forms approximating to the next stage in the
development of the organism may be found—namely, an
elongation of the conjugating forms, as shown in figs. 1, 6,
and 7 of line VIII,—but as a rule these do not appear in any
numbers until the third day.
THE DEVELOPMENT OF FLAGELLATED ORGANISMS. 373
Stages of Development after Seventy-two Hours.
—The third day is characterised by the elongation of the
conjugating pairs of organisms, and the first appearance of
flagellated forms, although sometimes the latter may not be
found until the fourth day. The commonest appearance of
these pyriform bodies is that shown in fig. 1 of line V, in
which the macronuclei are seen in the thick ends of the
organisms, while the micronuclei have passed to the thinner
ends from which the flagella will eventually arise. In Case
58, from which the figures of lines II to V have been drawn,
the culture-tube was unfortunately left out of the cold incu-
bator for half an hour owing to an interruption in my work,
and no further development occurred although the tempera-
ture of the laboratory was only 28° C. at the time ; so sensitive
are the partially-developed forms to arise of the thermometer.
In Case 47 some early flagellated forms were found on the
third day, as shown in figs. 4, 5, and 6 of line IX. In these
only a single flagellum has yet developed although two of the
forms are distinctly double ones, while some which appear to
be single are really double ones lying on one side, for inter-
mediate appearances showing the double nuclei partially
obscuring each other in this manner have been met with.
The remaining forms shown in line IX have all reached the
elongated stage although still without flagella.
Stage of Development after Ninety-six Hours.—
In the figures of line X are shown some of the flagellated
forms found on the fourth day in Case 47, in addition to which
there were much more numerous double pyriform organisms
without flagella, for only a very small percentage of the con-
jugating forms eventually reach the flagellated stage under
the artificial conditions of the cultures, which must be very
far from being as favourable to the development of the
organism as the natural conditions in which it takes place,
whatever they may be. Nevertheless, the elongated flagel-
lated forms have now been found in eight different cases,
including two of kala-azar from Assam. In fig. 3 of line X
the two flagellated bodies have apparently just separated.
374 LEONARD ROGERS.
Very occasionally groups of three instead of two organisms
are found both in the early conjugating stage and in the
later elongated and flagellated forms, as shown in fig. 2 of
line X.
The Trypanosome-like Stage of Development.—
From the forms so far described all that could safely be said
is that flagellated organisms with an elongated body and
micronucleus at the flagellated end have been obtained, but
it could hardly be called a definite trypanosome. However,
the forms shown in line XI of the plate go far to support the
view that the organism is really a trypanosome, these having
been found in a one day culture of Case 37, in which the
conditions must have been in some unknown way much more
favourable to the development of the organism than in the
other cases. ‘he forms shown in figs. 8 to 12 of line XI are
precisely like the flagellated forms described above, except
that they have elongated out to a much greater degree, so as
to very closely resemble trypanosomes in everything except
the absence of an undulating membrane, but this is known to
be absent in very young trypanosomes, so that it would be
expected to be the last feature to be developed in the growth
of the organism from the plasmodial spleen form. The
double forms shown in figs. 8, 10, and 12 of line XI are of
great interest as an indication that these trypanosome-like
forms have also developed in pairs, as in the more pyriform
flagellated forms shown in line X. Further, fig. 9 of line XI
was one of two precisely similar forms lying close together as
if they had just separated, as in fig. 3 of line X. Moreover,
the figs. 2, 3, and 4 of line XI are precisely similar in nature
to the early stages of Cases 47 and 58 already described,
from which they only differ in the greater elongation of 3
and 4, A possible explanation of the more typically try-
panosome-like appearance of the flagellated forms of Case 37
is that as they developed within twenty-four hours, instead
of only after three or four days as in the other cases, they
must have found the blood in which they were growing much
less altered than it is after several days’ incubation in a test-
THE DEVELOPMENT OF FLAGELLATED ORGANISMS. BYE,
tube, and consequently, the conditions being less unnatural,
their development has more nearly approached the typical
form of trypanosomes.
Amceboid Forms.—The small flagellated forms repre-
sented in figs. 1, 5,6, and 7 of line XI are also of great
interest, for they correspond very closely with the forms of
Trypanosoma Brucii described by Rose Bradford and
Plimmer in the ‘ Quarterly Journal of Microscopical Science’
of February, 1902, as “amoeboid” stages, and found by them
in the lungs of animals affected by tsetse fly disease. The
origin of the flagella from the micronuclei is well seen in
figs. 6 and 7 of this series, which I have only found in this
case, although that shown in fig. 5 has been met with in
others as well. As these very delicate organisms do not
appear to form part of the regular cycle of development of
the trypanosome stage from the spleen parasites, it appears
to me to be possible that they may be a portion of the life-
history of the parasite which is well fitted to live in the
circulation, and which might conceivably be carried from one
patient to another by the bites of flies and mosquitoes without
undergoing any development within the insects, just as I
showed in a previous paper the trypanosoma of surra may be
carried from one animal to another by the bites of horse flies
in a purely mechanical manner, an observation which has
since been confirmed both in South America and in the
Philippine Islands. In this connection it is worth while re-
calling the fact that when Indian cattle are inoculated with
the surra trypanosoma they suffer from only a mild chronic
form of the disease, and the trypanosomes are only found in
their blood for a few days after a definite incubation period.
Nevertheless, they every now and then get attacks of fever
for many months afterwards (very like the repeated attacks
in cachexial fever and kala-azar), but trypanosoma can no
longer be found in their blood at such times by ordinary
microscopical examination. Nevertheless, I found that if a
little of their’ blood, taken during one of these periodical
attacks of fever, is inoculated into a susceptible animal they
376 LEONARD ROGERS.
readily contract a fatal form of surra with innumerable
trypanosoma in their blood. It is possible that a small
amoeboid stage of the parasite is the infective agent in such
cases, and that in a similar way the infection of cachexial
fever may be due to some such form carried from one person
to another by the bites of flies and mosquitoes. The fact,
which I pointed out some years ago in the case of kala-azar,
that the infection is very largely a house one and always
extremely localised (the movement of healthy people from an
infected line to a new site half a mile or so away which I
recommended having proved successful in preventing the
spread of the disease), is in favour of such a mode of in-
fection.
It is also worthy of note that the plasmodial form of T.
Brucii described by Rose Bradford and Plimmer very closely
resembles the parasites found in the spleen of these chronic
fevers in man and the small multiple forms in my tubes; so
that in this disease I have now obtained in cultures the
plasmodial, amoeboid, and flagellated forms found by those
authors in a variety of animals after long study of the disease
produced by the T. Brucii; a fact which can leave but little
room for doubt that the human parasite belongs to the
trypanosomes. Successful inoculation experiments are still
wanting to prove this, all the animals I have tested—including
tank fish (which are commonly infected with a sluggish,
much curved, double S-shaped trypanosome) having proved
insusceptible even when injected with cultures containing the
large flagellated form of the parasite ; but further work based
on the knowledge of the true nature of the organism now
available should lead in time to further elucidation of a disease
which is certainly second to none in the frequency and
seriousness of the illness it produces in many parts of India,
and also appears to be widely distributed in other countries.
THE DEVELOPMENT OF FLAGELLATED ORGANISMS, 377
EXPLANATION OF PLATE 25,
Illustrating Mr. Leonard Rogers’ paper ‘On the Develop-
ment of Flagellated Organisms (Trypanosomes) from the
Spleen Protozoic Parasites of Cachexial Fever and Kala-
Azar.”
All the drawings in this plate were made from the actual specimens by the
Medical College artist, Behari Lal Das, as seen under a ;; lens and a No. 4
ocular, the magnification being 925 diameters. ‘The preparations were all
stained with Romanosky’s stain, used by Leishman’s method.
Line I, Figures 1 to 4, show the simple method of division of the spleen
parasites, and 5 to 8 the multiple form of division.
Line II shows the organisms present ina film made from freshly obtained
spleen blood, Figure 8 representing a group of young parasites.
Line III shows the forms found after one day’s incubation of the same
blood, the parasites showing only enlargement.
Line IV shows the same after two days, both single large oval forms and
conjugating ones being represented.
Line V shows the same at the end of three days, both conjugating forms
and elongated pairs being present.
Lines VI to IX show similar development day by day of Case 47, the early
flagellated forms being seen in Figures 4 to 6 of Line IX.
Line X shows the large flagellated pairs, with the flagella arising from the
ends containing the micronuclei.
Line XI shows all stages of the development from a one day culture of
Case 37. Figures 8 to 12 represent the fully developed long trypanosome-
forms with macro- and micro-nucleus, three of which still show the double
form of the typical development. Figures 1, 5, 6, and 7 show the small
flagellated amoeboid forms resembling those found by Rose, Bradford, and
Plimmer in Trypanosoma Brucii.
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EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEIL. 379
The Epithelial Islets of the Pancreas in Teleostei.
By
John Rennie, D.Sc., F.R.MLS.,
Assistant in Zoology, Aberdeen University.
With Plates 26, 27, & 28.
Introductory and Historical.
HE question of the anatomical and functional nature
of the islet-like groups of cells occurring within the pancreas
of vertebrate animals has been studied by a large number of
investigators since attention was first directed to them by
Langerhans in 1869. ‘These inquiries have for the most part
been confined to the higher vertebrates, and summaries of
their results have already been given by other writers
(Laguesse, 1894; Oppel, 1900). Notwithstanding the some-
what extensive literature of the subject, there is so much
disagreement as to the real nature of these bodies that further
inquiry was desirable. Oppel (13) wrote in 1900, “ Was die
Bedeutung der intertubularen Zellhaufen anlangt, so ist
dieselbe, so viel auch daruber geschrieben wurde und so viele
Ansichten auch daruber bestehen, noch nicht ganz erklart.’’
Although much has been written regarding these cell-
The present research has been carried out in several ]aboratories and upon
material obtained from various sources. Cordial thanks are due to Prof,
McIntosh, F.R.S., for the valuable privilege of the use of the Gatty Marine
Laboratory, St. Andrews, and to Professors Heincke and Ehrenbaum, of
Heligoland, not only for the free use of the laboratory there, with its abundant
supply of material, but also for their friendly treatment during my stay in the
institute under their charge. I acknowledge also the assistance of a grant
from the Carnegie Trustees in defraying part of the cost of material and pre-
paration for publication of this research.
380 JOHN RENNIE.
groups, it appears that very little has been done in the
investigation of the lower vertebrates. Indeed, until a short
time ago, there appears to have been some doubt as to their
existence in cold-blooded animals. According to Laguesse
(7), “ Les ilots de Langerhans paraissent constants chez les
Mammiferes et les Oiseaux, leur existence est douteuse chez
les Vertebres inferieurs. . . . Lesauteurs ne les signalent pas
en general chez les Vertebres inferieurs; Lewaschew les a
cherches et ne les a jamais trouves chez les animaux a sang
froid; Harris and Gow ne les ont pas vus chez les Reptiles,
mais pretendent les apercevoir chez la grenouille ; Von Ebner
les y a decrits egalement. Enfin, quelques points des descrip-
tions d’Ogata et de Platner pourraient s’interpreter en faveur
de leur existence.” No reference is made to their possible
occurrence in fishes. Indeed, Harris and Gow, whom
Laguesse quotes, expressly state that in consequence of their
doubt as to the nature of the so-called pancreas in fishes
they did not investigate the group. In the following year,
however, Laguesse recorded the existence of cell-islets in the
pancreas of Crenilabrus; in 1898, Massari (12) described
them in the eel (Anguilla vulgaris); and in 1899 Diamare
(3), in an important paper, established their occurrence in six
different species of Teleostei, as well as in all the other verte-
brate divisions. I shall have occasion later on to refer to the
work and opinions of these writers.
In the investigation of which the present paper is a partial
account attention has been limited to the bony fishes, of which
about twenty-five different species have been studied. In
general these islets are fewer in number and proportionately
larger than in mammals. Owing to the diffuse condition of the
pancreas in most Teleostei, they may, even when minute, be
identified by the unaided eye. They are usually of a pale
colour,and, being somewhat thicker, are seen distinctly against
the more translucent sheet of the surrounding pancreatic
alveoli. Wherever a careful search was made, either macro-
or microscopically, these bodies were found, and hence it may
reasonably be concluded they constitute a common feature of
EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 381
this group. This is all the more probable since they appear
to possess some functional activity.
As a result of pursuing specially the study of the con-
ditions in bony fishes, I have, inter alia, discovered the
existence of a “principal islet” (15). This has enabled me
to offer a fresh suggestion as to the possible phylogenetic
significance of these bodies in higheranimals. Ihave, further,
been able to confirm the opinion of Massari, Diamare, and
others regarding them as ductless glands with internal secre-
tory function, and also to test experimentally the theory that
derangement of the function of these bodies leads to diabetes.
A record of these experiments, which are still in progress,
will appear later.
Names and Systematic Arrangement of the
Species Examined.
Teleostei.
Physostom1:
Cyprinide—Cyprinus carpio.
Physoclysti:
Acanthopteri :
Scombriformes—Zeus faber, Agonus cata-
phractus, Lophius pisca-
torius, Cottus scorpius.
Gobiformes—Cyclopterus lumpus, Callio-
nymus lyra, Cyclogaster
Montagui.
Bleniiformes—Anarrhichas lupus, Zoarces
viviparus, Pholis gunnel-
lus, Chirolophis galerita.
Anacanthini :
Gadide—Gadus virens, G. eglifinus, etc.,
Onos mustela.
Ophidiide—A mmodytes tobianus.
Pleuronectidee — Hippoglossus vulgaris,
Pleuronectes platessa, ete,
382 JOHN RENNIE.
Lophobranchii:
Syngnathus acus, Nerophis equoreus,
Siphonostoma typhle.
General Relations of the Islets.
The following account indicates the general relations and
macroscopic appearance of the bodies observed. In most
instances, particularly in those cases where a “ principal
islet’ is stated to exist, numerous specimens were examined.
Cyprinus carpio.—tThe islets observed in this species
are among the smallest found. The pancreas is diffuse, and
they appear in sections of it in different regions of the body-
cavity. In some instances they lie alongside the zymogenous
tissue, but in most instances they are surrounded by it, and do
not possess a limiting capsule.
Zeus faber.—Here there exists a “ principal islet,’ which,
in specimens of about 25 cm., is as large as 5 mm. in length.
There are also smaller forms in the neighbourhood of the
pyloric ceca which may be dissected out, and also numerous
microscopic ones within the intercecal pancreatic masses.
The principal islet hes within a small mass of zymogenous
tissue, which is attached to the base of the gall-bladder (see
P|. 26, fig. 1). Itand the smaller ones near the czeca were found
ovoid inform. ‘The interceecal examples which are invested
by more compact masses of zymogenous tissue, are rounded,
oval, or irregular in outline. In serial sections they are seen
to vary a good deal in this respect, owing to their being
closely surrounded by the irregularly arranged pancreatic
alveoli. ‘he large forms have a more or less distinct limiting
capsule; such a structure is not present in the smaller ones
within the compact masses of the pancreas.
Agonus cataphractus.—lIn this species, occupying a
position between the gall-bladder and the spleen, within a
small mass of pancreatic tissue, is the principal islet. Annee 45, ser. 9,
pp. 819, 820, 1893.
10. Lancrernays, P.—‘‘Beitrage zur mikroskopischen Anatomie der
Bauchspeicheldrise,” ‘ Inaug. Diss.,’ Berlin, 1869.
11. LewascuEew, S.— Uber eine eigentiimliche Veranderung der Pankreas-
zellen warmblitiger Tiere bei starker Absonderungsthatigkeit der
Driise,” ‘ Arch. f. mikr. Anat.,’ Bd. xxvi, s. 453—485, 1886.
12. Massari.—‘ Sul pancreas di pesci,” ‘ Rend. R. Accad. dei Lincei,’ vol.
vii, Fase. 5, pp. 134—137, 1898.
18. Orret, A.—‘ Lehrbuch der vergleichenden mikroskopischen Anatomie
der Wirheltiere,’ Jena, 1900.
14, Pearce, R. M.—“ The Development of the Islands of Langerhans in the
Human Embryo,” ‘Amer. Journ, Anat.,’ vol. li, No. 4, Oct., 1908,
pp. 445—455. :
15. Renniz, J.—‘‘On the Occurrence of a Principal Islet in the Pancreas of
Teleostei,” ‘Journ. Anat. and Phys.,’ vol. xxxvii, p. 375—378.
16. StarKewitscu, P.—‘‘ Uber Veranderungen des Muskel- und Driisenge-
webes sowie der Herzganglien beim Hungern,” ‘ Arch. f. exper. Path.
u. Pharm.,’ Bd. xxxili, pp. 415—461.
DESCRIPTION OF PLATES 26—28,
Illustrating Dr. John Rennie’s paper on “The Epithelial
Islets of the Pancreas in Teleostei.”’
REFERENCES TO ALL THE FIGURES.
Art. Artery. Cap. Capsule. ca. Capillary. ¢. ¢. Connective tissue. cy. d.
Cystic duct. d. c. Darkly staining cells. g. 6. Gall-bladder. Js. Islet tissue.
Ts.1 and Is, 2. Islets in Lophius referred to intext. Js. 3. Separated portion
of large islet in Ammodytes. Int. Intestine. /. Liver. ¢. c. Lightly staining
cells. me.a. Mesenteric artery. p. Pancreas. p.d. Pancreatic duct. pa. ts.
Pancreatic tissue within islet. po. v. Portal vein. pr. ts. Principal islet.
EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTET. 405
py. ¢. Pyloric ceca. re. Rete mirabile. sm. 2s. Small islet in Ammodytes.
sp. Spleen. sé, Stomach. v. Vein.
PLATE 26.
Dissection of Zeus faber to show relation of principal islet to other organs,
PLATE 27.
Abdominal viscera of Lophius piscatorius, showing general distribution
of the islets. The principal, which is always the largest, is seen directly
anterior to the spleen.
PLATE 28.
Fic. 3.—Principal islet in Syngnathus acus. X about 50 times,
Fic. 4.—Interceeal islet from Zeus faber. x 350. The centre portion
throughout the series stained more darkly than the rest of the islet. Note
the absence of a capsule.
Fic. 5.—Principal islet from Anarrhichas lupus. Here there is a
slight penetration of its tissue by pancreas. The full thickness of the latter
tissue in the proximity of the islet is shown. x 72 times.
Fic. 6.—Islet from Ammodytes tobianus. x 350. This islet shows
well the relation to pancreas wherever the latter is at all massive. Dark and
light cells are well contrasted. Capillaries are extremely abundant, but it
should be noted that in this fish a similar appearance, in this respect, is seen
in other organs, e.g. the liver. Besides the main islet, which in this section
appears in two portions, there is a very small one to the right near a large
vein. A large pancreatic duct is present.
Fic. 7.—Dark and light cells from the section in fig. 6. x 810. The
nuclei (w.) in the light cells appear similiar to those seen by Diamare also, and
described by him as “ contorti.”
Fic. 8.—Pyloric islet from Pleuronectes platessa. x 50. It
shows areas of dark and light cells, and also a considerable amount of penetra-
tion of pancreas.
Fic. 9.—Portion of the principal islet of Pleuronectes, showing
different appearances of the dark and light cells. x 810.
Fic. 10.—Rete mirabile from capsule of Lophius. x 810.
Fic. 11.—Principal islet from Zoarces viviparus. X 72.
Fig. 12.—(a) Dark and (b) light cells from islet in fig. 11. x $10.
Fic. 13.—Portion of islet from Onos mustela. x $10. Showing the
contrast between the two types of cell in this species.
74
baal dbthns
Trgwows Sm nc erro
-
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 407
Observations on the Maturation and Fertilisation
of the Egg of the Axolotl.
By
J. W. Jenkinson, M.A.,
Assistant to the Linacre Professor of Comparative Anatomy, Oxford,
With Plates 29—33.
CoNTENTS.
PAGE
I. InTRODUCTORY i ; ; , . 408
II. Descriptive : ; 5 ; . 412
A. Maturation ; : : : . 412
1. The first polar division . ; ; . 412
2, The second polar division : . 414
3. Further history of the polar fede: : 2) ay
4. The direction of division of the chromosomes . 418
5. The number of the chromosomes . : . 418
B. Fertilization . : ‘ : . 419
1. General outline A : : . 419
2. The entry of the spermatozoon . : . 420
3. Changes in the spermatozoon; development of the
sperm aster; disappearance of the middle piece . 422
4, Formation of the pronuclei; appearance of the defini-
tive centrosome . ‘ ; . 424
5. Union of the pronuclei; the fertilisation spindle . 429
6. Remarks on the work of Fick and Michaelis . 440
11]. HistoricaL AND CRITICAL ; : ’ . 442
A. Maturation ‘ : . 442
1. The structure of the velit apinidles : . 442
2. The reduction of the chromosomes - . 444
Bs oe ‘ ‘ : . 446
. The entrance of the spermatonson : . 446
; The centrosome in fertilization . : . 449
a. The centrosome as an organ of the cell. . 449
i. Intra-nuclear origin of the centrosome . 449
ii. Structure and functions of the centrosome . 450
b. The origin of the cleavage centrosomes . 454
IV. ExpeRIMENTAL 2 ; ; : « 458
VOL. 48, PART 3.—NEW SERIES, 30
4.08 J. W. JENKINSON.
I. Inrropucrory.
ELEVEN years haye elapsed since the appearance of Rudolf
Fick’s memoir on the fertilization of the axolotl; yet, in
spite of the host of authors who have since dealt with this,
the earliest moment of development, his paper still stands
out as one of the completest studies of the behaviour of the
spermatozoon in the egg.
My own investigations were begun with no intention of
controverting Fick’s conclusions, but originated merely in
the wish to demonstrate the process of fertilization to a class
of students. In the result, however, I have found myself
obliged to differ from my predecessor in one important par-
ticular, the origin of the cleavage centrosomes; and if in
other respects I have succeeded in giving a more detailed
description of the facts it must be set down simply to the
modern improvements in our methods of research.
I have also included the phenomena of maturation in the
field of my observations ; but here I have been able to add
but little to what the really admirable work of Carnoy and
Le Brun has taught us of the polar divisions in many other
Amphibia. I have indeed laboured under some difficulty here
for want of sufficient material. Of all the females which I
killed only one was found to have eggs in her oviducts.
Of these only six, in the upper portion of the oviduct, ex-
hibited stages of the first polar spindle; the remainder, a
few in the middle region of the oviduct and a very large
number in the uterus, were about to undergo the second
maturation division. ‘The rest of my material, which is
fairly abundant, comprises eggs killed at various intervals
after laying.
It is only quite recently, however, that I have been able
to secure the most critical stages; I owe this to Professor
Weldon’s kindness in purchasing some fresh axolotls for my
use. This will perhaps explain why my work, begun as long
as three years ago, is only published now.
MATURATION, ETO., OF THE EGG OF THE AXOLOTL. 409
I have preserved the eggs in two mixtures: chromic
(4 per cent.) ninety-five parts, glacial acetic five parts, and
corrosive sublimate, with 5 per cent. to 10 per cent. acetic
acid added. I tried a picro-corrosive mixture but found it
useless.
The aceto-corrosive eges have been stained in borax-
carmine, followed by picro-indigo-carmine, and iron-hema-
toxylin; those preserved in chromic and acetic in gentian-
violet, followed by eosin or orange, and in iron-hematoxylin.
I have often unmounted preparations first stained in carmine
or gentian and re-stained them in iron-hematoxylin.
The cutting of the eggs is a most formidable task, as any
one who is acquainted with what Fick calls ‘die schwierige
Technik der Amphibieneier-Untersuchung ”’ will understand.
Even with the very briefest sojourn in the water-bath the
egos become so brittle that it is impossible to cut them into
continuous ribbons of unbroken sections. They must be cut
on a Jung microtome with the knife oblique, and the block
must be painted before each section is cut with a mixture of
gum mastic and collodion dissolved in ether and absolute
alcohol. The thickness of the sections was always 7°5 wp.
The eggs were oriented by being placed, in a known position,
in a square hole cut in an oblong slip of liver, and cemented
down with albumen, which is then coagulated with alcohol.
The liver, with the egg, can of course be cut in any desired
plane.
I have ventured to add to the descriptive part of this
paper, not only a critique of current theories of fertilization, but
also an account of a few experiments I have made in the hope
of throwing some light on the nature of the physical processes
involved. In making these experiments I have had the
advantage of the counsel and help of my friend Dr. Ramsden,
of Pembroke College; I am under the greatest obligation to
him for the assistance he has so generously afforded me.
I must not conclude this introductory chapter without
attempting to define my attitude to the criticism which the
botanist Alfred Fischer published two cr three years ago
410 J. W. JENKINSON.
on the validity of our conceptions of cell structure and
phenomena.
Fischer has shown that a structure can be given to solu-
tions of proteids by precipitation with the ordinary fixing
reagents, the structure being either granular or reticular, and
from this he argues that much, if not all, of the structure
observed in preparations is artifact and devoid of any
natural existence whatever. Similar views were expressed
about the same time by Hardy.
Doubtless there is much force in the criticism, but at the
same time the thorough-going scepticism which Fischer
would seem to advocate is surely a little exaggerated. For
in the first place such structures as chromosomes, spindle,
asters, centrosome have all been observed in the living cell.
And in the second, when with the same reagent we find
different appearances in successive stages of a process, then
we are bound to assume that these differences are at least the
outward and visible signs of a real series of changes. For
example, I shall have to describe in the sequel the gradual
formation of a system of vacuoles in the centre of the sperm
sphere ; these must be at least an indication of the local
concentration of some watery substance, for on Fischer’s
own showing absorption of water precedes the formation of
vacuoles in the artificial vacuolation of aleuron grains and
such bodies which he produces by means of reagents. Nor
is this all. If the different structures which we are asked to
regard as artifacts form a regular series when placed in
chronological order, is it not a little too much to expect us
to believe that this artificial is merely parallel with, but in no
way gives us a true representation of, that other unknown
real series ?
Without then going so far as to assert, what I suppose no
one would maintain, that our reagents are absolutely infallible,
I should certainly hold that such structures as those just
referred to are faithfully preserved in our preparations.
Fischer himself admits as much when he says “sind solche
schon in der lebenden Zelle zu sehen so ist es zweifellos dass
MATURATION, ETC., OF THE EGG OF THE AXOLOTL, 411
sie auch vom Fixirungsmittel conservirt werden.” Within
this real structure alterations are undoubtedly produced (let
me instance the frequently described microsomal structure of
astral rays and the minute—reticular or alveolar—structure
of cytoplasm) ; these must remain as a permanent source of
difficulty which will always prevent us from deciding where
nature leaves off and art begins. There are other cell struc-
tures again about which we should preserve a frankly open
mind. I should certainly be prepared to admit for example
that the achromatic reticulum of the nucleus was artificial.
Secondly Fischer has criticised the current views of the
nature of the centrosome, aster, and spindle. ‘his criticism
falls into two parts; the first is an attack on the iron-
hematoxylin method as diagnostic of the centrosome and
centriole, the second is a theory of the formation of centro-
somes and asters. The centrosome is regarded as produced
through a precipitation of the albumins of the cell by nucleic
acid, the nucleus opening for the purpose at the poles. ‘The
asters are also looked upon as precipitation products. Fischer
has shown that a radial structure can be artificially made in
two ways. In the first, which he terms “ Fremdstrahlung,”
elder pith cells are injected with solutions of proteid and then
fixed. Asters are found in the cells, bnt only when some
small nodule is present to form a centre for the radiations.
In the second method“ Selbststrahlung”—the rays are
formed in a proteid solution about a crystal of sublimate or
a drop of osmic exuding from a capillary tube. He suggests
that in the living cells asters originate around the centrosome
by one or other of these processes. In the first case the pre-
cipitating reagent is either the nucleic acid of the nucleus or
the fixative employed; in the second it is the centrosome
itself. Further, centrosome, aster, and spindle (formed by
the conjunction of two asters) are looked upon as entirely
passive, mere incidental accompaniments of the activities of
the cell; for the movements of the chromosomes are attributed
by Fischer to the ordinary streaming and growth motions of
the cytoplasm.
412 J. W. JENKINSON.
The first part of this criticism has already been met by
Boveri (1901), and I can do no better than fully endorse his
reply. While admitting fully that many particles besides
the centrosomes will stain in this way, and that many bodies
which have been described as centrosomes, even at the poles
of the spindle, may be the artificial products of “ concen-
trische KEntfiirbung,” he justly points out that two such
bodies lying in a sphere, or one lying excentrically, cannot
be thus accounted for. Moreover the centrosome, if not
actually visible intra vitam, may often be seen in an un-
stained preparation.
The second part contains what I aiseets is a valuable con-
tribution to the theory of the origin of both centrosome aud
aster, of the former through precipitation by nucleic acid, of
the latter by a process of ‘‘Selbststrahlung” about the centro-
some so produced. The conclusion drawn is, however, wholly
unwarrantable, and would never have been adopted if, as
Boveri points out, Fischer had kept the hard facts of
cytology in sight, instead of deliberately ignoring the gradual
cycle of changes which these cell organs undoubtedly pass
through.
IJ. Descriptive.
A. Maturation.
1. Pirst polar division.
(a) Metaphase.—In my earliest stage the spindle is fully
formed, and is at the surface (fig. 1) ; its direction is either
radial or slightly oblique. The spindle is closely surrounded
by yolk-granules and pigment, and consists of wavy,
frequently anastomosing fibrille. The appearance is not
inconsistent with the view that we have here to do with
elongated alveoli. Some of the spindle-fibres are united in
definite bundles, and to some of these bundles the chromo-
somes are attached. Almost all the fibres pass continuously
from one pole to the other, but at the outer end of the spindle
MATURATION, ETC., OF THE EGG OF THY AXxoLoTL. 413
immediately below the surface, there are a few fibres radiat-
ing between the yoke-granules. These ‘‘ mantle”’ fibres are
the only representatives of an aster.
At the outer pole the fibres appear all to converge in a
single dense mass, but at the inner end their behaviour varies
in different preparations. In some cases this end of the
spindle is also unipolar, but in other cases, as in that figured,
the fibres undoubtedly converge to two separate points.
There is no trace of any centrosome at either spindle pole
except the mass formed by the convergence of the fibres.
The chromosomes at this stage have the form of rings,
which by being indented at four places assume the shape of
across. The cross is so placed on the spindle that two arms
—those by which it is attached to the fibres—are parallel to
the spindle-axis, while the remaining two are either in or
parallel to the equatorial plane, and therefore at right angles
to the first two. ‘These equatorial arms, however, do not lie
in the same plane as the two meridional arms, but project
outwards, making an angle with one another. Hach such
cruciform ring is in reality composed of two chromosomes,
the extremities of which can be distinctly seen at the ends of
the equatorial arms of the cross. These extremities are
often twisted over one another, as indicated in the figure.
Though the above description may be taken as appropriate
to a typical chromosome of this stage, many of these bodies
are exceedingly irregular in form, twisted and contorted into
many curious shapes. Such irregularities in the shape of the
chromosomes in the first maturation spindle have been de-
scribed by many authors, notably by Griffin for Thalassema,
as well as by Carnoy and Le Brun for the Amphibia.
The chromosomes do not all lie in the equatorial plane, and
are not confined to the outer surface of the spindle. They are
scattered irregularly through it and at different levels. In
the spindle, therefore, the fibres—or rather the fibre-bundles
—attached to the chromosomes are mingled with those which
pass from pole to pole, and the spindle is ‘‘ mixed” according
to Meves’ (1896, 1898) nomenclature.
414, J. W. JENKINSON.
(b) Telophase (fig. 2).—The next stage I have is a telo-
phase. The spindle consists of wavy bipolar fibres, but no
bundles are to be seen. ‘The chromosomes are united at each
pole into an irregular, thick, annular skein; at the outer end
the surface is raised up into a little flat disc with a homo-
geneous border. Later, this flat disc is constricted off as the
first polar body, and found united only by a narrow stalk to
the egg, and lying in a slight depression at the surface of the
latter (fig. 3).
In the polar body the chromosomes are not yet distinct, as
they will be later; there are also present pigment and yolk-
granules. The stalk is fibrillated, the fibrille thickened to
form “intermediate bodies” (“‘Zwischenkérper” of Flemming).
The stalk contains a few pigment-granules.
In the egg the chromatin skein is resolved into chromo-
somes, which are V-shaped, aggregated by their apices, and
lie in a clear area devoid of yolk-granules.
2. Second polar division.
(a) It is apparently from, or in, this clear area that the
second polar spindle is formed, for a little later the chromo-
somes—which have meanwhile split longitudinally—are seen
lying in an elongated area, which is distinctly fibrillated, and
occupies a tangential position (fig. 4).
In the first polar body the chromosomes have simulta-
neously undergone longitudinal fission.
In one other preparation that I have the second polar
spindle occupies a similar position, but the fibres are much
more evident, and there seems to be a distinction between
them, some being arranged in bundles and attached to chro-
mosomes, others passing continuously from one end of the
spindle to the other.
(b) Metaphase.—In describing the next stage in the
formation of the second polar spindle I must distinguish
between two lots of eggs; one lot was obtained from the
oviduct and uterus, the second comprises freshly-laid ova.
MATURATION, ELC., OF THE EGG OF THE AXOLOTL. 415
To begin with the second, in all these ova the spindle is found
in a radial or nearly radial position (fig. 5). It consists of
outer and inner fibres; the former radiate out amongst yolk-
granules and pigment, and lose themselves in the general
cytoplasm ; the fibres from opposite poles do not cross, but are
diverted into the equatorial plane. They are to be regarded
as astral rays. The inner fibres pass from pole to pole, are
wavy, and frequently meet; certain of them are gathered
together into bundles, and to these bundles the apices of the
chromosomes are attached. Towards the poles the constituent
fibres of the bundles again separate from one another and
mingle with the general fibres of the spindle. If we examine
a transverse section of such a spindle we find a poly-
gonal meshwork thickened at the nodes; in addition, the
fibre-bundles just described are seen occupying each the
centre of a system of triangular areas. The whole appear-
ance—as seen in both longitudinal and transverse section—
is therefore quite consistent with the supposition that we are
here dealing with elongated alveoli (I do not use the word
with the whole of Biitschli’s connotation), the fibres in that
case being merely the optical sections of the inter-alveolar
lamellee.
At the outer pole of the spindle is a slight depression in
the surface of the egg.
At both ends of the spindle the fibres converge to a dense
granular mass, somewhat flattened in the direction of the
spindle-axis, which may perhaps be regarded as a centro-
some; but Iam unable to state anything of its origin, and
later it certainly disappears.
The chromosomes in the spindles are V-shaped, moniliform,
and paired; they lie in the equatorial plane with their apices
pointing inwards; they are not disposed in a regular ring,
but some are nearer to, some further from, the spindle-axis.
We have, therefore, here again a “ mixed”’ spindle in Meves’
sense.
In the other lot of eggs—that taken from the middle of
the oviduct and from the uterus—the spindles are also radial,
416 J. W. JENKINSON.
or nearly so, and do not differ in any respect from those just
described except that the outer end projects slightly from
the surface of the egg (figs. 6a and6b). The chromosomes,
however, are beginning to diverge by their apices, and we
can see in many—though not, I think, in every case—that
these divergent points are still connected by a fine, frequently
twisted thread (the connecting thread, or ‘ Verbindungs-
faden”’). Further, the pairs of chromosomes are not placed
so regularly in the equatorial plane, but many are scattered
over the spindle.
From this one might argue that we are dealing here with
a late prophase of mitosis, and this opinion is certainly
strengthened by the fact that the ova in question were
obtained from the middle part of an oviduct in the upper
portion of which only stages of the first polar division were
found. On the other hand, the commencing divergence of
the chromosomes and the protrusion of the outer end of the
spindle above the surface of the egg inclines me to the belief
—though I cannot express avery positive opimion—that these
spindles are in reality in the condition of the early anaphase.
As a possible explanation of the irregular position of the
chromosomes in the spindle, I may add that it is not unknown
a case 1s described by Boveri (1888), for example, in the
egg of Ascaris—for both chromosomes of a pair to pass to one
pole.
(c) Anaphase (figs. 7 a and 7 b).—In the later anaphase
the daughter chromosomes pass in the ordinary way to the
opposite poles, where their apices converge. Between them
the general fibres of the spindle are clearly apparent; the
fibre-bundles to which the chromosomes were attached can,
however, no longer be distinguished. The external fibres
have the same relations as in the previous stage.
The outer pole of the spindle is occupied by a dense hyaline
mass, which passes together with some of the superficial
pigment of the egg into the small projecting disc which
marks the first appearance of the second polar body.
The second polar body, when fully formed (fig. 8), is a
MATURATION, ETC., OF THE EGG OF THE AXOLOTI.. 417
slightly flattened, rounded mass, though much less flattened
and much smaller than the first polar body. Like the latter
it contains some pigmentand yolk-granules. The narrow stalk
by which it is connected to the egg contains the remains of
the spindle fibres, but I have not observed any thickenings of
these which could be identified as ‘Zwischenkoérper.” The
chromosomes retain for a time the arrangement described in
the last stage.
The second polar body is formed below or near the de-
pression in which the first is lodged. It protrudes a little
above the surface of the egg; the vitelline membrane is
correspondingly pushed out.
3. Further history of the polar bodies.
In the first polar body the V-shaped chromosomes are
united in pairs by their apices. At first they are closely
grouped together, but later they become scattered, and each
pair assumes a cruciform shape (fig. 9). It is now impossible
to decide which of the four arms of the cross belong to which
of the two constituent chromosomes, for all four arms are
equally separated by constrictions from one another at the
point of union. The surface of the chromosomes is produced
at intervals into little tooth-lke projections.
In one case only have I observed the reconstitution of a
nucleus in the first polar body (fig. 10). The chromosomes
are still distinct and still in pairs, but they lie in a circum-
scribed oval area which seems to contain an achromatic
reticulum, staining dissimilarly to the cytoplasm. I ought
to say, perhaps, that there is no doubt that this is a first and
not a second polar body, for a second polar spindle is present
in the same egg. At the same time it is possible that the
cell just described is one of the two products of the division
of the first polar body; its small size is in favour of this
view. Fick saw one case of such division.
The first polar body always contains some pigment and
yolk-granules ; the latter tend to become aggregated into
418 J. W. JENKINSON.
irregular clumps. The polar body is in a slight depression
at the surface of the egg. It persists for some time and may
be found throughout the earlier stages of fertilization.
The second polar body also persists for a considerable time.
Like the first it contains pigment and agglomerated yoke-
granules. In it, however, the nucleus is very frequently
reconstituted. A clear vacuole is formed round the chro-
mosomes (figs. 11 and 12); these send out little processes
towards the wall of this vacuole (fig. 13), which thus forms
the nuclear membrane, and to one another. The chromo-
somes then break up into irregular coarse fragiments (fig. 14);
but I have never observed the formation of a completely
reticular nucleus. These changes in the nucleus of the
second polar body do not necessarily keep pace with the
similar changes in the chromosomes which remain in the egg.
4. The direction of division of the chromosomes.
It is perfectly clear that in the second polar spindle the
chromosomes are divided longitudinally, that is quantitatively
in Weismann’s sense. But in the case of the first maturation
division I have not the material for deciding this point.
The chromosomes are placed on the spindle in the form of
rings, broken into two half-rings at the equator. ‘This arrange-
ment certainly reminds one at first sight very strongly of the
heterotypical spindles of the Salamander, Amphiuma, and
Batrachoseps, in which, according to Flemming, Meves (1896),
McGregor, and Hisen the chromosomes are longitudinally
split. But it will be impossible to determine whether this is
so in the first maturation division of the ova of these
Amphibia until we know accurately the mode of formation of
the chromosomes themselves in the interior of the germinal
vesicle.
5. The number of the chromosomes.
I have not paid a very great deal of attention to this point,
but I believe the number to be fifteen in each of the two polar
MATURATION, ETC., OF THE EGG OF THE AXOLOTL, 419
divisions, and in the first polar body, though sometimes I
have seemed to make sixteen, sometimes only fourteen. In
the fertilization spindle I have counted about thirty chromo-
somes.
This disagrees with the computations of Fick, who counts
eight in the polar divisions, and of Kélliker, who has
given the number in the dividing nuclei of blastomeres as
twelve.
B. Fertilization.
1. General outline of fertilization.
The spermatozoon may enter the egg at any point in the
animal hemisphere. Its entry is accompanied by the forma-
tion at the surface of a deep pit or funnel filled with a plug,
the entrance cone.
The sperm lies at the bottom of this funnel, and a clear
area—the sperm-sphere—rapidly forms round the head and
middle-piece.
The last named disappears; as it disappears the sperm-
sphere assumes a radiate structure, the sperm-aster, and the
centre of this soon becomes occupied by large vacuoles. The
sperm head becomes gradually transformed into an oval
sperm-nucleus which, preceded by its aster, moves into the
interior of the egg and meets with the female pronucleus.
The definitive centrosome is formed in connection with the
sperm nucleus, probably from it. This centrosome divides.
The fertilization spindle is then formed between the two
centrosomes, the male and female pronuclei breaking up
independently into chromosomes in its equator.
I cannot state the time occupied by these processes with
very great certainty. The female axolotl begins depositing
her ova soon after midnight or early in the morning, and
continues laying at short intervals throughout the early part
of the day. It is necessary to watch the animal closely and
remove each batch of eggs as soon as it is laid; but even so
the time of laying can only be ascertained approximately.
420 J. W. JENKINSON.
In this way I have found that the entry of the spermatozoon
and the formation of the spermn-sphere takes about two hours,
the formation of the sperm-aster, the disappearance of the
middle-piece, and formation of the two pronuclei about five
hours. About seven hours after laying the pronuclei have
met, while the definitive centrosome has made its appearance
and divided into two; and about two hours later the fertiliza-
tion spindle is complete. These observations were made in
March, 1901.
Fick makes the whole time much shorter, but he carried
on his work later in the year.
2. The entry of the spermatozoon.
T have not observed the actual entrance of the spermatozoon.
In the earliest stage in my possession the sperm—the tail
of which is taken into the ege with the head—is seen lying
in a clear area of cytoplasm in the midst of the yolk-granules
(fig. 15). This clear area, which I will call the sperm-sphere,
since it corresponds to what has been described under that
name by other authors, lies at the inner end of a deep funnel-
shaped depression of the surface of the egg. The superficial
pigment of the egg is continued down the sides of this de-
pression to the bottom (fig. A). The funnel itself is occupied
by a plug of clear hyaline coagulum, apparently of some
watery substance, which projects slightly at the mouth of the
funnel, and is here surrounded by a circular groove; its
outermost layer is very dense. The whole is covered con-
tinuously by the vitelline membrane. ‘This plug is the
entrance cone (wrongly termed by earlier observers the cone
of attraction), formed on contact of the sperm with the ovum ;
it has been observed in numerous cases.
The substance of the plug is later on invaded by the sur-
rounding pigment and yolk-granules. Its position in the egg
is thus marked by a track of pigment, which may be termed
here, as it has been in other cases, the “ penetration”? path of
the sperm.
MATURATION, E'TC., OF THE EGG OF THE AXOLOTL, 421
At its bottom the entrance-funnel widens out into the
sperm-sphere already alluded to. This is an area of yolk-
free cytoplasm possessing a finely recticular or alveolar
structure—which I must leave an open question—and con-
taining scattered about in it a few pigment granules. The
spermatozoon lies in it in such a manner that the middle-
piece here, as in the salamander and other Urodela, a very
Fic. A.—Outline camera drawing of a section parallel to but not actually
including the egg-axis. The section shows the entrance cone and funnel
and the spermatozoon lying in a clear area at the bottom of the latter, the
sperm-sphere. The superficial pigment of the animal hemisphere is represented,
but the yolk-granules are omitted. ‘The sperm-sphere is dotted.
large, easily distinguishable body, lies nearest the interior of
the ovum, while the head and tail, bent on one another
at this point, are both directed outwards up the entrance-
funnel. It is as though the apical body of the sperm-head
had on entering been caught amidst the yolk-granules, and
the middle-piece then been swept onwards into the interior of
422 J. W. JENKINSON.
the egg. In immediate proximity to the sperm-head are a
few clear vacuoles.
The structure of the axolotl-spermatozoon is well known,
and closely resembles that of the salamander and newt.
The head is very long, and tapers to the apex, the tail is even
longer, and provided with an undulating membrane or fin.
The middle-piece is embedded in the posterior end of the
head, and stains less deeply than the latter with iron-hema-
toxylin, while with gentian-violet and orange, and _ borax-
carmine and picro-indigo-carmine it takes in each case the
plasma stain. This middle-piece is derived in the axolotl—
as Meves (1897) has shown it to be in the salamander—from
one of the two centrosomes of the spermatid.
The sperm may enter at any point in the animal hemi-
sphere, and sometimes even a little way below the equator.
In the Axolotl polyspermy is normally of frequent occur-
rence, and two sperms may even enter by the same funnel.
There is nothing to distinguish the accessory spermatozoa
from that one which copulates with the female pronucleus.
The changes they all go through are similar and _ practically
synchronous, and centrosomes are formed—as we shall see
later on—in connection with them all. There is no fact that
I am aware of to indicate that this process is pathological ; it
must, on the contrary, be compared with the exactly similar
physiological polyspermy observed by Riickert (1899) in
Elasmobranchs and by Oppel and Nicolas in Reptilia. Of
the ultimate fate of these accessory spermatozoa I am not in
a position to say anything.
3. Changes in the spermatozoon; development
of the sperm aster; disappearance of the
middle-piece.
The sperm-head soon begins to shorten and thicken ; at the
same time a few small vacuoles make their appearance in its
substance, which thus comes to have an extremely coarse reti-
cular appearance (fig. 16). This is the first indication of the
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 423
transformation of the sperm-head into the sperm-nucleus. I
believe, however, that the tapering apical extremity of the
sperm-head is not used in this process, but is cast off, and
degenerates in the cytoplasm. At any rate I have noticed
in some of my preparations a chromatic body placed near the
sperm-head, or in the sperm path, sometimes filamentous
and twisted, sometimes rounded and vacuolated, which seems
to be the remnant of this portion of the spermatozoon.
The sperm-head lies a little to one side of the sperm sphere,
sometimes just outside the sphere between the yolk-granules.
The tail makes an angle with it as before, but is completely
severed from it, and there is no trace whatever of the middle-
piece. Instead the centre of the sphere is occupied by a
spherical vacuolated mass in which no pigment granules are
found.
The sphere itself has meanwhile assumed a radial struc-
ture. Arising from the outer surface of the central vacuolated
mass are numerous filamentous processes—as they appear in
sections. ‘These processes radiate in all directions, and are
continued outwards for some distance between the yolk-
granules beyond the limits of the sphere, disappearing finally
into the general cytoplasm of the egg. ‘They constitute the
well-known sperm-aster. ‘These filamentous rays are united
to one another by frequent anastomoses, and the structure
presented by the whole is that of a large number of elongated
chambers, or alveoli, radially arranged ; this interpretation is
borne out by the appearance of a section tangential to the
sphere, which is that of a polygonal meshwork, thickened at
the nodes. The spaces—whether alveoli or not—between the
rays and their anastomoses are filled with a faintly-staining
coagulum. Pigment granules are scattered freely, but not
abundantly throughout the sperm-aster, as in the stage last
described, but are absent from the vacuolated central mass.
I believe, though I cannot positively assert, that this
central mass originates from the dissolution of the middle-
piece ; I have one preparation (fig. 17) in which a small faintly
staining irregular vacuolated body is found near the centre of
VoL, 48, PART 3.—NEW SERIES, 31
424 J. W. JENKINSON.
the sperm-aster, and separated from the sperm-head ; this
body, I think, may be the last remains of the structure in
question, though it is possible that it is the remnant of the
tail.
But whether it dissolves in this fashion, or whether it is
withdrawn into the sperm nucleus—as I suppose is a not
impossible view—of its actual disappearance there cannot be
the shadow of a doubt. Ina stage which is, to judge by the
further shortening and thickening of the sperm-head and by its
increased vacuolation, more advanced than that just under dis-
cussion, no sign of the middle-piece can be seen (fig. 18) ; the
ceutre of the sperm-aster is occupied, as before, merely by a
vacuolated mass. ‘he tail has also now disappeared.
4. Formation of the pronuclei; appearance of
the definitive centrosome.
(a) The female pronucleus.—The chromosomes left in the
egg lie in a small, clear area. At first they converge by
their apices (fig. 8), as in the anaphase, but presently
become arranged in a tangled skein, without, however, losing
their individuality. A little later stili a nuclear membrane
appears, surrounding the chromosomes (fig. 28, a.). These
lie in an achromatic network ; but whether this is derived
from the chromosomes or not I cannot say. It certainly stains
differently, but at the same time the surfaces of the chromo-
somes are everywhere produced into small, tooth-like pro-
cesses, which lends some colour to the view that the achromatic
network is in reality the result of the continued outgrowth
of these.
The chromosomes become broken up into at first coarse
(fig. 28, b. and c.), but ultimately very fine fragments, which
are evenly distributed over the achromatic reticulum; these
small granules seem to lose much of their staining capacity
(fig. 28, d. and e.). It is not possible to speak very
positively, but it seems as though a great deal of the chro-
matin had gone into solution in the nuclear sap. In any case
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 425
the persistent identity of the chromosomes cannot possibly be
maintained for an instant.
The female pronucleus thus reconstituted begins to move
into the interior of the egg; at the same time it enlarges
considerably, and becomes irregularly lobed. It is, as a rule,
closely surrounded by the yolk-granules, but a few vacuoles
may be developed in its immediate proximity (fig. 28, d.) ;
this, however, is not of frequent occurrence. It cannot be
traced to any action of the preserving fluid. True achro-
matic nucleoli appear later on in its interior; these bodies
stain very deeply with the plasma stains, eosin and indigo-
carmine, and also very deeply with iron-hematoxylin. They
may be slightly lobed and vacuolated (fig. 27).
(b) The male pronucleus.—Ultimately the male pronucleus
has precisely the same structure as that just described
for the female, but this structure is arrived at simply by a
continued process of vacuolation. At no time in the trans-
formation of the sperm-head is it possible to detect any
separate chromosomes.
In the stage last described the sperin-head was in the form
of an obtuse cone (fig. 18). The substance of this cone, which
is highly chromatic, now becomes considerably vacuolated.
The vacuoles vary in size; many of them areso close together
that only a thin separating lamella is left. By a continuation
of this process the nucleus comes to assume a typical reticular
structure (figs. 26, b.; 20). ‘lhe coarse, and now achromatic,
reticulum is apparently derived from the remains of the
lamelle, while the chromatin is confined to the large, often
irregular granules at the nodes. Gradually, however, the
reticulum becomes much finer, the chromatin more minutely
divided and less intense in its staining reactions, while true
nucleoli make their appearance (figs. 19, 21). ‘The male pro-
nucleus is now exactly similar in structure to the female.
Like the latter also it is at first rounded but subsequently
irregularly lobed, and undergoes a marked increase of volume.
Though the above seems to be the normal series of changes
which the sperm-head passes through, a slight variation of
426 J. W. JENKINSON.
this process sometimes occurs (figs. 23, 29, 36). The chro-
matin may become crowded together in the centre of the
nucleus, and here form a compact, coarse, deeply staining
reticulum, the surrounding intra-nuclear space being occupied
by an achromatic.substance which is sometimes homogeneous,
sometimes reticular. The male pronucleus may be observed
in this condition even in the fertilisation spindle, in which
case the chromosomes seem to be formed directly from this
chromatic network without the intervention of a typical resting
stage.
(c) Appearance of the definitive centrosome—In the
previous stage the centre of the sperm-aster was occupied
by a vacuolated mass. These vacuoles now swell up
enormously and assume a radiate arrangement about the
centre of the aster (figs. 19, 21, 24). The separating lamellee
between them become so extremely thin and delicate as to be
almost invariably ruptured during the process of fixation or
subsequent passage through the alcohols. Consequently the
centre of the aster seems to be occupied by one great vacuole,
the cavity of which is traversed by irregular broken strands,
the remains of the thin inter-vacuolar lamelle (fig. 50). A
few pigment granules may be seen dotted along these strands,
but they are much more numerous around the periphery of
the large vacuole. ‘They are also to be seen in the outer zone
of the aster.
This latter has still the same structure as before, that is to
say it consists of a system of radiating fibres connected by
numerous anastomoses and continued outwards for some
distance between the yolk-granules. As before the spaces
between these fibres or lamella—whichever they may be—are
occupied by a faintly-stainmg coagulum; the large central
vacuole, or vacuoles, is occupied by a coagulum of precisely
the same nature.
This substance would appear to be of more watery con-
sistency than the rest of the cytoplasm. The formation of the
large vacuoles is in that case to be looked on as a concen-
tration in the centre of the sperm-aster of water withdrawn
MATURATION, KTC., OF THE EGG OF THE AXOLOTL. 427
—probably under the immediate influence of the middle-
piece—from the cytoplasm of the egg. If so, this is a fact of
the very highest physiological importance in the process of
fertilisation. I must however defer the full discussion of it
to another part of this paper.
The sperm-nucleus lies a little to one side—the outer side—
of the sperm-aster; and as soon as the large vacuoles are
formed projects slightly into them. These then appear as a
system of clear spaces partially surrounding the inner side of
the sperm-nucleus and preceding it in its progress into the
interior of the ovum to meet the female pronucleus. The path,
generally termed the “copulation” path, which the sperm-
nucleus now pursues is not as a rule in the same straight
line as its earlier “penetration” path, but makes an angle
with it.
It is during this stage, when the sperm-nucleus is already
coarsely reticular, that the definitive centrosome appears
(figs. 19—21). This is a large rounded body, composed of
a granular substance staining faintly with carmine, and not
very deeply with iron-hematoxylin. Occasionally one or
more intensely-staining granules may be discerned in its
interior. Its diameter is about one-quarter or one-third that
of the sperm-nucleus. It is always surrounded by a cloud of
pigment which may be so dense as to entirely obscure the
centrosome within (fig. 23); this can, however, easily be
demonstrated after depigmentation with the fumes of nitric
acid (fig. 22). It hes in front of the sperm-nucleus, between
it and the system of vacuoles. When the sperm-nucleus
comes to project into the vacuoles the centrosome occupies
approximately the centre of the system.
This body is also found in connection with the accessory
sperm-nuclei, where it has exactly the same character and
behaves im precisely the same manner (figs. 19, 22, 23, 24).
The centrosome very soon divides ina direction which is at
right angles to the “sperm” path (fig. 22). Preliminary to
division it becomes elongated and constricted (figs. 20, 21).
The halves may be at first connected by fibrille. In one case
428 J. W. JENKINSON.
I have observed the two halves united by two curved rods,
the whole having the appearance of an oval ring (fig. 27).
The diverging halves move apart till they are separated by
a distance a little greater than the longer diameter of the
nucleus. The division usually occurs before the pronuclei
have met, but it may be deferred (fig. 27).
With regard to the mode of origin of this centrosome I do
not wish to speak too positively. It may be argued, in view
of the known persistence of this organ from one cell-generation
to the next in cases of ordinary division, that the centrosome
must arise here also from the middle-piece, which, as we know,
is itself merely the enlarged centrosome of the spermatid. In
this case we should have to suppose that the middle-piece,
after being dissolved in an early stage became reprecipitated
in a later. The solution and reprecipitation of a nuclein is
of course no very extraordinary process; it occurs quite
normally in the nucleus in the disappearance and re-formation
of the chromosomes.
Now, however much may be said for such an hypothesis
from a purely theoretical and comparative point of view, it is
hardly supported in the case of the axolotl by any positive
evidence at all, and is, as I believe, directly negatived by the
evidence which I am able to bring forward in favour of a
totally different origin of the centrosome, namely, from the
sperm-nucleus itself.
I have observed in many cases that the membrane of the
sperm-nucleus cannot be detected, or is at least very much
weakened on the side turned towards the centrosome (figs. 22,
23), and in some preparations the centrosome is so closely
apposed to this side of the nucleus that it appears to be
actually emerging from it (figs. 24, 25). The dense cloud of
pigment which, as we have seen, obscures the centrosome,
appears to come into existence simultaneously, for deeply
pigmented processes are observed passing inwards from the
centrosome into the interior of the nucleus. To judge by this
evidence, then, centrosome and pigment are both formed not
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 429
merely in connection with but through the active agency of
the sperm-nucleus.
It cannot indeed be said that the centrosome is, literally, of
intra-nuclear origin, for no formed body at all like it is ever
observable in the interior of the sperm-nucleus. What does
however seem to me probable is this, that this body is pro-
duced through the precipitation of albumins or globulins
present in the cytoplasm by nucleic acid or nucleins emerging
from the nucleus, a view which coincides with that advanced
by Fischer of the formation of the centrosome in general.
The origin of the pigment, on the other hand, is a matter
about which I hardly care to advance any conjectures ; but I
think it is certain that it is too abundant to allow us to
suppose that it has been dragged in by the spermatozoon on
its entrance into the egg ; besides it is absent in the previous
stages.
I cannot conclude this paragraph without alluding to some
preparations I have which may be considered to favour the
reprecipitation hypothesis mentioned first. In these a dense
(fig. 26, a.) granular mass, undeniably like a centrosome, is
found in company with a sperm-nucleus (fig. 26, b.), which is in
an earlier stage of development than that in which the
centrosome usually first makes its appearance; further, the
nuclear membrane is quite intact in these preparations.
Against this interpretation I must urge that the middle-piece
is certainly absent at an earlier stage still, that nucleic acid
may diffuse through without actually bursting the nuclear
membrane, and that there is no reason why the production of
the centrosome by the other method should not have taken
place precociously.
5. Union of the pronuclei. The fertilisation spindle.
Preceded by its centrosome, sphere, and aster, the sperm-
nucleus makes its way into the interior of the egg. The
female pronucleus has meanwhile been moving away from its
position at the animal pole, and sooner or later the two
430 J. W. JENKINSON.
pronuclei meet. Although eventually the fertilisation spindle
will intersect the egg-axis, the separate “copulation ” paths
of the pronuclei frequently converge to a point which is not
actually in this axis, and may be some distance away from it ;
in other cases, however, the sperm-nucleus reaches the axis
before the female pronucleus has joined it. In this latter
case “ penetration” path, “copulation” path, and egg-axis all
lie in one plane, which, since the centrosome divides at right
angles to it, is the plane of the first furrow. This may then
be said to be determined by the point of entry of the sperma-
tozoon. When the point in which the pronuclei meet is
ex-axial, the plane of the first furrow may possibly be
determined by the “copulation” path alone, as Roux has
shown to be the case in the frog.
This variability in the position in which the pronuclei first
meet is obviously partly due to the variability of the point at
which the spermatozoon enters the egg, and consequently of
its “penetration” and “copulation” paths; but also partly
to variations in the path pursued by the female pronucleus,
which does not necessarily descend vertically from the animal
pole towards the centre of the egg, but may diverge from the
ege-axis (figs. B. and C.).
A further result of this is that the female pronucleus may
come in contact with the sperm sphere at any point on its
inner and upper surface.
The end is, however, always the same; the female pro-
nucleus enters the vacuolated substance of the sphere, and
comes to lie close to the sperm-nucleus, with the centrosome
or diverging centrosomes between the two (fig. 29), the line
joining the two pronuclei intersecting that between the two
centrosomes at right angles. The large vacuoles of the
sperm sphere are thus divided into two sets, one adjacent to
each centrosome (fig. 31). These two sets of vacuoles usually
appear in preparations each as a single large vacuole ; this
appearance is artificial and due to the breaking down of the
thin separating lamellee.
Although it seems clear that here, as in many other cases,
Tic. B.—Meridional section showing female pronucleus in the ege-
axis, and two sperm-nuclei with their asters. A the animal pole
Is the second polar body. Camera drawing.
PB.
Fig. C.—Outline camera drawing of a meridional section of an egg,
showing female pronucleus in an ex-axial position and sperm-
nucleus with aster. The polar body is a little to one side of the
animal pole.
4.32 J. W. JENKINSON.
the movements of the two pronuclei are influenced by one
another, I am unable to offer any suggestion as to what the
nature of that influence may be.
For a time the sphere which encloses the two pronuclei and
centrosomes retains its original form, but soon it begins to
elongate in the direction of the (future) spindle axis (figs. 31,
32), that is of the line joining the two centrosomes. Simul-
taneously the external radiations separate into two distinct
terminal or polar groups, each of which centres in a centrosome ;
the middle or equatorial region being now devoid of radia-
tions, and occupied merely by rounded vacuoles (figs. 32, 33).
The whole structure then moves into its definitive position
in the egg-axis if it has not already reached it. This position
is such that the pronuclei and centrosomes all lie in one plane
which cuts the egg-axis at right angles at the distance of about
one quarter of a diameter from the animal pole, the egg-axis
passing midway between the two pronuclei and between the
two centrosomes. Fertilisation spindles are, however, occa-
sionally observed in an ex-axial position. The result of this
is, of course, that the first furrow is not accurately meridional,
a fact of frequent occurrence.
The formation of the fertilisation spindle now begins. The
first sign of this is the outgrowth of fine, nearly parallel
fibres from the centrosomes towards the pronuclei (figs. 31,
32). Here, again, there is reason to believe that these spindle
fibres are in reality the optical sections of inter-alveolar
lamelle ; each has a conical base at its point of attachment
to the centrosome, and also at its opposite end where it
touches the nuclear membrane. The inter-fibrillar spaces
have, therefore, the appearance of extremely elongated elipses.
It is of interest to observe that such spindle fibres may grow
out from the centrosome towards an accessory sperm-nucleus
(fig. 19).
The centrosomes remain for a time united by a narrow,
deeply pigmented cord (fig. 32) ; this sooner or later breaks,
the centrosomes becoming pear-shaped (fig. 31), but soon
assuming the spherical form.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 433
With the formation and elongation of the spindle-fibres the
centrosomes move further apart; at the same time they begin
to enlarge, and continue to do so until they have attained a
very considerable size (fig.33). Pari passu with this enlarge-
ment the vacuoles—the vacuoles of the original sperm-sphere
—gradually disappear. I believe that the two processes are
intimately related, that, in fact, the centrosomes enlarge at
the expense of these vacuoles, and that their growth consists
essentially in an imbibition by them of the watery substance
concentrated at an earlier period in the centre of the sperm-
sphere.
This growth of the centrosomes is accompanied by the
formation not only of the spindle fibres, but also of the polar
asters. Under this heading are comprised all those radia-
tions which pass outwards from the centrosomes, with the
exception of those—the spindle fibres proper—which pass
to the two pronuclei.
The outer ends of these astral radiations are distinguishable
from the first from the spindle-fibres by their coarser struc-
ture; the fibres—or lamelle—are stouter, the inter-fibrillar
spaces—or alveoli—much wider, and seem to be identical
with the earlier radiations of the sperm-sphere, separated, as
we have seen, by the elongation of the latter into two distinct
halves, centring each in a centrosome. The pigment which
surrounded the sperm sphere is found thickly scattered about
these outer rays (figs. 51—34).
The inner ends of the astral rays on the other hand, though
perfectly continuous with the outer, differ greatly from them
in their appearance and in the mode of their formation. In
the fineness of their structure they resemble the spindle-
fibres, and they occupy the space previously taken up by the
large terminal vacuoles (figs. 35, 34). They may, and indeed
must, I believe, be regarded as outgrowths of the centrosomes,
developed at the expense of the contents of the vacuoles which
they replace. ‘The exact nature of such an outgrowth I shall
have occasion to discuss later on; but I may say here that in
describing the process by this term 1 do not mean to imply
434 J. W. JENKINSON.
that they consist entirely of centrosomal substance. On the
contrary, I suspect that we have here to do with the precipi-
tation of the proteids of the cytoplasm by the dissolved
substance of the centrosome, in which case these outgrowths
owe their origin as much to the former as to the latter.
The further metamorphosis of the centrosomes and asters is
as follows :—
As stated above, the inner portion of the aster consists of
thin, closely set rays in immediate contact with the centro-
some. This radiate structure persists for some time, the con-
stituent rays becoming even finer and more closely set (fig.
34). Later, however, in the fully formed spindle (figs. 388—41)
the radiate arrangement is lost, and the mner portion of the
aster becomes a sphere with an exceedingly fine reticular or
alveolar structure. From the surface of this centrosphere
start the outer astral rays; in its centre is placed the
centrosome.
‘This body has also undergone important modifications. In
the earliest stage of the fertilisation spindle the centrosomes
are small, round, sometimes axially compressed bodies (figs.
31, 32); they are not coloured deeply with iron-hematoxylin,
but may contain a larger or smaller number of granules which
do stain intensely with that dye. ‘They then, as we have seen,
enlarge very considerably (fig. 33), while the fibres of the
spindle on the one hand, the inner astral rays on the other
grow out from them (fig. 34). When the metamorphosis of
the inner portion of the aster so formed is completed the
centrosome is once more small (figs. 388—41). It is not easy
to see in material preserved with corrosive and acetic (figs.
38, 39), having a reticular structure distinguishable only with
difficulty from the fine reticulum of the centrosphere itself.
With chromic and acetic (figs. 40, 41), however, the centro-
some stands out from the substance of the centrosphere as a
small, compact, homogeneous body, slightly lobed, and con-
taining a deeply staining particle, the centriole ; occasionally
the centriole (fig. 40), and sometimes the whole centrosome
(fig. 35, a.) is seen to have divided. In this case the daughter
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 435
centrosomes are flattened against one another; the direction
of their division is at right angles to the axis of the spindle.
This division takes place as a rule during the anaphase, but I
have found the centrosome doubled at an earlier stage.
The cycle of changes which this cell-organ passes through
would then appear to be as follows :—At first a small body,
the centrosome begins to swell by absorption of the watery
contents of the adjacent vacuoles; then spindle fibres and
astral rays begin to grow out at its expense in turn; finally,
while the large centrosphere is being formed by the reticular
degeneration of these rays the centrosome once more returns
to its original volume and divides. If we choose, with Boveri,
to look on the centrosphere as simply an enlarged centrosome—
and I think that, with certain reservations, there is much to
be said for this view—then we shall regard the small cor-
puscle found in its centre as a “ reduced” centrosome in his
sense, as coming into being by a condensation of the central
portion of the larger body.
Though I have not made any extended observations on the
behaviour of the centrosomes during segmentation, I may,
perhaps, be allowed to give an account here of what little I
have been able to make out.
In the telophase of the first division two small centrosomes
may be found on the polar side of the nucleus (fig. 35) ; they
are usually extremely hard to detect, mainly, I fancy, because
they lie in a depression of the nuclear membrane. The
centrosphere has, as such, totally disappeared, and with it the
astral rays. Its place is occupied by a large highly vacuolated
area surrounding the nucleus, and resembling exactly the
system of vacuoles formed in connection with the sperm-
nucleus.
In the metaphase of the dividing nuclei of blastomeres a
large centrosphere is present at each spindle pole, and in the
centre of this is a reticular centrosome (I have at my
disposal only material preserved with aceto-corrosive) which
can barely be distinguished from the surrounding reticulum.
These facts seem to me to indicate that the centrosomes of the
436 J. W. JENKINSON.
blastomeres go through precisely the same cycle of changes as
that which I have described above for the cleavage centro-
somes, and that this body, when introduced into or formed
in the ovum, becomes a permanent organ of the embryonic cells.
Before leaving the aster I have to describe certain changes
that take place in its peripheral region.
We have seen that the centrosphere is surrounded by
coarse radiations which pass out between the yoke-granules
into the general cytoplasms, and appear to be identical with
one half of the radiations of the sperm-aster. These radia-
tions do not at first extend into the equatorial region of the
spindle, which is occupied only by a mass of round vacuoles
(figs. 32, 33); but in the fully-formed spindle a complete
mantle of radiations is found wrapping round the spindle
proper and extending as far as the equator (figs. 38, 41).
Here the radiations meet without, as far as I can see, ever
intercrossing with those derived from the opposite pole; on
the contrary the two sets of rays seem to diverge outwards
and to le parallel to one another, one on each side of the
equatorial plane. The rays become closely crowded together
by the expansion of the nuclear spindle (figs. 38, 40, 41), and
are thickly beset with pigment granules.
These equatorial astral rays thus appear to be a completely
new formation, replacing the round vacuoles of an earlier
period ; but whether they are in reality outgrowths of the
previous rays—and in this case we might have to attribute
their formation ultimately to the activity of the centrosome—
or whether they arise merely by the compression of the
round vacuoles, is not easy to determine. The persistence of
the pigment granules leads me to incline to the latter view ;
for I have noticed that in the case of new formations, for
example in the formation of the vacuoles of the sperm-sphere,
the pigment granules are swept aside. On the other view we
should have to suppose that the pigment in question was
pushed outwards from the centrosome by the continued
growth of the rays, and this is favoured by the fact that the
dense pigment which surrounded the centrosome at its first
MATURATION, ETC., OF THE EGG OF THE AXOLOTL, 437
appearance is certainly not found, except for a few sparse
granules, about the fully formed centrospheres. Some of
this original pigment, that between the pronuclei, seems
simply to disappear in situ, but the remainder is probably
carried to the periphery.
We may now return to the consideration of the spindle.
At present we have only described that portion which lies
extra-nuclear—between the centrosome and the pronuclei,
and arises by outgrowth from the former. ‘These polar
portions increase considerably in length before the equatorial
part is formed. The extreme polar ends of the fibres become
merged in the centrospheres.
The equatorial portion is most distinctly intra-nuclear in
origin. The two pronuclei, greatly increased in volume and
elongated in the direction of the spindle axis, are closely
applied to one another. In a stage when the chromosomes
are being formed the nuclear membrane appears indented at
the ends, apparently by the growth of the extra-nuclear
fibres. Soon openings appear in the membrane (fig. 38), and
through these the extra-nuclear fibres and inter-fibrillar spaces
become continuous with a similar set of fibres and spaces,
each with each, which are formed inside the nucleus by a re-
arrangement of the achromatic reticulum. In other words, the
threads of this reticulum, previously irregularly distributed,
became now parallel to the axis of the spindle, and continuous
through the openings in the membrane with the fibres outside.
This is, I think, a fair account of the appearances of
sections ; whether it is a true description of what actually
occurs is another matter. I have indicated briefly above that
the inner rays of the aster and the extra-nuclear spindle
fibres may possibly be regarded as produced by the precipita-
tion of the albumins of the cell by a substance derived from
the centrosome ; in the same way these intra-nuclear fibres
may be regarded as produced by an extension of the process,
that is to say by the precipitation through the same agent of
the albumins of the pronuclei themselves. I shall discuss the
point in greater detail further on.
43 J. W. JENKINSON.
With the completion of this process and the total disap-
pearance of the nuclear membranes, which seem to be used
in the formation of the fibres, the spindle may be said to be
fully established. It consists now of undulating fibres passing
continuously from one pole to the other, and frequently
united by anastomoses (fig. 39). Transverse sections show a
polygonal meshwork thickened at the nodes; we have as good
reason here as in other cases for regarding the fibres as the
optical sections of inter-alveolar lamellae. The spindle
increases in diameter as well as in length.
Very considerable changes have been meanwhile taking
place in the pronuclei also.
In the early fertilization spindle they are round, somewhat
irregular bodies, much increased in volume since their first
formation. They possess a fine achromatic reticulum, chro-
matin in a state of minute subdivision, and true nucleoli or
plasmosomes (figs. 31,52). In this condition they remain
during the early stages, except that they become enlarged
and lengthened in the direction of the spindle axis (fig. 32),
but when the latter is beginning to elongate the chromatin
granules increase both in size and number (fig. 33). The
total quantity of chromatin in the nucleus seems therefore to
be greater than before, as though it had been reprecipitated
from solution.
Of the first steps in the production of the chromosomes I
can say very little (fig. 36). In the earliest stage which I
have irregular moniliform chromatic threads are scattered
through the nucleus; their length is variable, and they
appear to be in process of formation by the linear aggrega-
tion of granules. In this stage the nucleoli are still to be
seen, but later they disappear. The chromosomes certainly
do not arise directly from them.
The chromosomes appear separately in each pronucleus,
while the nuclear membranes are still intact (figs. 34, 38).
Each chromosome is a twisted rod of uniform thickness,
showing very little, if any, traces of the earlier moniliform
structure. The chromosomes lie scattered throughout the
MATURATION, BTC., OF THE EGG OF THE AXOLOTL. 439
pronuclei quite independently of the achromatic reticulum.
This has now assumed a much coarser arrangement than
before; there are very obvious granular thickenings at the
nodes.
With the disappearance of the nuclear membrane and the
completion of the spindle, the chromosomes are thrown on, or
rather in, the equator of the latter in two distinct groups,
derived from the two pronuclei, as may readily be seen in
transverse sections (fig. 37). The Axolotl is therefore one of
those very numerous forms in which no “segmentation
nucleus ” is formed, but the maternal and paternal chromo-
somes preserve their individuality in the fertilisation spindle.
The chromosomes at first project to one side and the other
of the equatorial plane (fig. 39), but soon le wholly im it.
They then split longitudinally (fig. 40). Further they are
not merely placed on the periphery of the spindle, but are
scattered throughout it.
It is at this stage that certain bundles of fibres first become
distinguishable from the general fibres of the spindle (fig. 40).
These bundles—the “Zugfasern” of cytologists—are_attached
by their equatorial ends to the chromosomes ; at their polar
ends the constituent fibres separate and become lost in the
general fibrillo-reticulum. The bundles from the opposite
poles of the spindle are arranged in pairs, a pair for every
pair of chromosomes ; the two bundles of a pair are attached
exactly opposite to one another one to each chromosome, at or
near one end of the latter.
In the anaphase the chromosomes diverge by these ends
(fig. 41), which become hooked when the point of attachment
is not actually terminal. No trace of the bundles can be
seen between the chromosomes, and the whole appearance
most decidedly lends support to the view that the bundles
are the actual agents which pull the chromosomes apart, the
latter being quite passive during the process. At the same
time though the bundles shorten they never, as far as I have
seen, thicken; we have, therefore, here no evidence at all
that the “Zugfasern” contract like muscle-fibres, and that
VOL. 48, PART 3,—NEW SERIES, 32
4.4.0 J. W. JENKINSON.
their behaviour can be explained simply by comparison with
these.
After the separation of the chromosomes the general
spindle-fibres remain behind. An achromatic equatorial plate
(the cell plate) is now clearly visible (fig. 41), though indi-
cations of it may indeed be seen in the metaphase (fig. 40).
This plate consists of a thickening and union of the fibres in
the equatorial plane. Axially, the spindle-fibres are perpen-
dicular to this plate ; outside the axis they make an angle with
it, more peripherally still they curve outwards and lie parallel
with it. Where the fibres meet the plate they are thickened.
It looks as though two opposing sets of alveoli had here met
and fused. What relation, if any, this equatorial plate bears
to the subsequent cytoplasmic division I cannot say.
In the telophase the nucleus becomes once more completely
reticular, and the plasmosomes reappear. Its polar surface is
deeply indented (fig. 35). The division of the centrosome,
the degeneration of the centrosphere, the formation of large
vacuoles round the nucleus have already been described.
6. Remarks on the work of Fick and Michaelis.
The foregoing account differs seriously from that given by
Fick in one important particular, the origin of the definitive
centrosome.
After describing the formation of the sperm-aster about
the middle-piece, and showing that the latter becomes
separated from the sperm-head, swells up and loses the
distinctness of its outline (in all of which I am able to agree
with him entirely), Fick proceeds as follows: “ Die Attrak-
tions-sphire zieht ihre Strahlen ein, ballt sich zusammen zu
einer intensiv roth-gefarbten Kugel oder zu einem Unregel-
missig gestalteten abgerundet eckigen Klumpen, ganz
aihnlich wie die von Boveri bei Ascaris abgebildeten Archo-
plasmaklumpen.”
This, preceding the sperm, divides to form the centrosomes
(though he does not apply this term to them) of the fertilisa-
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 441
tion spindle. The cleavage centrosomes, therefore, are
derived from the middle-piece which is, as Fick surmised and
as we now know, the enlarged centrosome of the spermatid.
As I have tried to show, such a view is untenable; for not
only is there a stage in which the middle-piece has clearly
disappeared, but also we have direct evidence for the
formation of the definitive centrosome de novo from the
sperm-nucleus.
The point is one of considerable theoretical importance.
Up till now the Axolotl has been the only form in which the
persistence of the centrosome from the spermatid to the
fertilisation spindle could be positively asserted ; for though
on the one hand the origin of the middle-piece from the
previous centrosome has been traced in many cases, while on
the other there are numerous observations of the formation of
the fertilisation spindle by division of the sperm-aster, both
processes had been seen in no animal but this.
In several other respects I have been able to go into
greater detail than Fick; the polar spindles, the structure of
the sperm-aster, and notably the formation of the fertilisation
spindle. Fick’s description of the last is mdeed very
deficient.
On the other hand he has described the mode of entry of
the spermatozoon and the entrance-cone and funnel. The
entrance-cone is, according to him, an aggregation of
“ Hiplasma,” and is produced by something in the nature of a
ferment provided by the spermatozoon. It has a dense,
radially striated border.
More recently Michaelis has published a short paper on the
fertilisation of a closely-allied form—the newt.
His observations on the fate of the middle-piece agree
closely with my own. Radiations appear at an early stage,
but “dass dei genannten Strahlungen in irgend einem
Zusammenhang mit der spaéteren Attraktions-sphire stiinden
ist kaum anzunehmen.” Later there comes a stage in which
“vom Mittelstuck ist nichts mehr zu sehen.”
He has failed to find any cleavage centrosome, though it
44? J. W. JENKINSON.
can hardly be doubted from the work of van der Stricht (1892)
and Braus that such exists in segmentation stages.
On another small point I must disagree with Michaelis. He
says there is a segmentation nucleus. I find, on the contrary,
im some preparations of fertilisation spindles of Triton which I
have, that there are two distinct sets of chromosomes. At the
same time we ought to bear in mind Bovert’s (1890) assertion
that in one and the same species of Hchinus there is a
variation in this respect.
III. Historica AND CRITICAL.
A. Maturation.
1. Structure of the polar spindles.
In a series of elaborate and valuable memoirs Carnoy and
Le Brun have described the formation of the polar spindles
and bodies in both Anurous and Urodelous Amphibia. Their
observations are very complete and detailed, but do not differ
in any other important respect from my own.
The first polar spindle is of intra-nuclear origin, arising
from a special portion of the germinal vesicle—the “ plage
fusoriale.” Both first and second polar spindles are described
and figured with inner or bi-polar and outer or mantle fibres.
In many cases, especially in the early stages of their for-
mation, the poles are surrounded by astral radiations. The
authors fail to find any centrosome beyond the somewhat
indefinite body into which the spindle fibres converge. But
that Carnoy regards this body, as I do also, as a physiological
centre, seems to follow from his remark that some substance
comes from the nucleus—“ qui agit sur le réseau et y produit
les mémes irradiations que si ces substances provenaient d’un
centrosome véritable.”
In the Trout, according to Behrens, the maturation spindles
have this same structure. In Amphioxus (Sobotta, 1897)
only the second polar spindle is provided with mantle fibres,
while in the Mouse (Sobotta, 1895) these fibres are absent in
both the first and second.
MATURATION, ETC , OF THE EGG OF THE AXOLOTL. 443
In Invertebrates it is the very general rule for the asters
and centrosomes of the polar spindles to be well developed
(Platyhelmia [Francotte, van der Stricht (1898), von
Klinckowstrom, Gardiner, Henneguy, Goldschmidt, Halkin],
Nemertines [Coe, von Kostanecki (1902)], Mollusca [Hillie,
von Kostanecki (1896), Boveri (1890), Mark, Linville, Griffin,
Garnault], Chatopoda [Foot, Vejdovsky, Korschelt, Griffin],
Arthropoda [Ishikawa], Echinoderms [Matthews], Ascidia
[Castle]) ; but centrosomes are stated to be absent in Ascaris
by Boveri (1887), though this is denied by Carnoy and
others; in Sagitta by the same observer (1890), and by
Brauer (1892) in Branchipus.
Considering the wide-spread occurrence of the centrosome
as an active cell-organ I believe that the ill-defined body
which is undoubtedly present in these cases at the spindle
pole may be looked on as a physiological centre, even though
it contains no corpuscle which will react to the iron-hema-
toxylin stain; and considermg what we now know of the
growth and metamorphosis of the centrosome it ought not to
surprise us that this body should in certain cases not merely
cast off the peripheral portion of its substance, as it admit-
tedly does, but wholly disappear into the aster to which it
gives rise. I shall have to recur to this point later on.
Many authors besides Carnoy have attributed to the first
polar spindle an intra-nuclear origin, either in whole or in
part.
In Ascaris (Boveri [1887]), in Branchipus (Brauer [1892]),
and in Ophryotrocha (Korschelt) the germinal vesicle becomes
directly transformed into the spindle.
In other cases the nuclear membrane disappears under the
influence of the astral rays, and the equatorial portion of the
spindle arises in the interior of the nucleus (Polyclada
[Francotte and van der Stricht (1898)], Cerebratulus [Coe]
and others). Such a double—extra- and intra-nuclear—
origin of the fibres also occurs in the fertilisation spindle. I
have described this above for the Axolotl; it has also been
observed in Polyclada, Cerebratulus, Thalassema, Ophryo-
444, J. W. JENKINSON.
trocha, Rhynchelmis, and Toxopneustes; and in Ascaris,
according to von Hrlanger, but not Boveri (1888).
The slight temporary depression at the surface of the egg
over the polar spindle which I have noticed in the Axolotl has
been seen by others also (Francotte, Griffin, von Kostanecki
[1896], Linville).
2. Reduction of the chromosomes.
It is no part of my programme to enter at any length into
this vexing and perhaps fruitless controversy.
As far as the Amphibian ovum is concerned, however, it is
clear from the careful work of Carnoy that in the second
maturation division the chromosomes are split longitudinally.
What happens to them in the first polar spindle is more
difficult to determine, as this depends, as I have pointed out
above, very largely on the view we take of the manner of their
formation in the first instance.
On this matter there are two conflicting opinions. Accord-
ing to the observations of Born on Triton—and Riickert
(1892) has made similar statements for the Elasmobranchs—
the chromosomes persist in the nucleus throughout the whole
period of growth of the oocyte, although they cease to be
chromatic; at the time of maturation the chromosomes of the
first polar spindle are formed from them, quite independently
of the numerous chromatic nucleoli which are present in the
germinal vesicle and cast out into the cytoplasm when the
nuclear membrane disappears. ‘This view has been adopted by
Miss King in her researches on the maturation of the toad’s
ego.
The other view is that advocated originally by Schulze and
later by Carnoy and Fick (1899). According to Carnoy the
chromosomes of the young oocyte are disintegrated. The
chromatin passes into a state of solution and is continually
being reprecipitated—as nucleoli—and redisintegrated and
dissolved during the long period of growth of the oocyte.
During this period the yolk-granules are deposited in the
MATURATION, ELC., OF THE EGG OF THE AXOLOTL. 445
cytoplasm. The formation of the yolk seems indeed to be
intimately related to the solution of the chromatin, for some
of this dissolved substance passes through the nuclear
membrane and contributes to the nuclein which can_ be
demonstrated in the yolk. It is during these processes of
disintegration that the figures are produced which have beer
mistaken by Born and Riickert for chromosomes.
At the time of maturation the nuclear membrane disappears
and some of the chromatic nucleoli are used in the production
of the chromosomes in a very complicated fashion. According
to Carnoy the resulting division is longitudinal, but I think it
must be conceded that when, as here, there is no spireme stage,
when the chromosomes are formed from round nucleoli, it is
almost idle to attempt to distinguish between a longitudinal
and a transverse division.
It will be convenient to discuss briefly at this poimt two
questions which are raised by the subsequent behaviour of the
pronuclei. The first relates to the theory of the persistent
individuality of the chromosomes.
I have found no evidence in my preparations and very little
in the literature in support of this assumption. Carnoy’s
account of the history of the chromatin is, of course, dia-
metrically opposed to it.
The second question is the formation of a segmentation
nucleus. This has been seen in Hlasmobranchs (Rickert
[1891, 1899]), the Trout (Behrens), Petromyzon, Amphioxus
(Sobotta [1897]), Cerebratulus (Coe), Prosthiostomum,
Thalassema, Toxopneustes, and Ciona (Castle, but not Boveri
[1890]).
In other cases the chromosomes arise from the two pro-
nuclei in two separate groups.
The distinction, however, seems to be worth little; Boveri
(1890) has shown that in Echinus microtuberculatus
both modes may occur, Michaelis has described one mode,
myself the other in Triton, and Sobotta (1895) found in the
Mouse one isolated case of a segmentation nucleus.
4A6 J. W. JENKINSON.
B. Fertilisation.
In the act of fertilisation two distinct processes are involved.
The first is the union of two cells, the bearers of those
hereditary characters which reappear in the offspring sprung
from the union. ‘The second is the restoration to the germ-
cells of their lost power of reproduction by division. That
this is true of the egg-cell is obvious, and is proved to be so
in the case of the spermatozoon, or at least of its nucleus, by
the experimental production of a larva from the fertilisation
of an enucleated fragment of an egg.
It is with the second only of these two processes that I am
here concerned. In it a stimulus is conveyed to the ovum by
the spermatozoon, under the influence of which it divides and
gives rise to a new multicellular organism.
All the recent work on the subject has been devoted to the
discovery of the mechanism by which this is effected. On
the one hand we see in the purely descriptive treatises of the
past few years, a constant effort to ascertain the part played
by the sperm-centrosome in the process, in short to test the
hypothesis, first put forward by Boveri, that the sperm-
centrosome is the active agent in the act of fertilisation. Nor
has experimental proof of the theory been lacking. Boveri
himself showed that a sperm-centrosome will divide in an
enucleated blastomere, which, as Ziegler was able to demon-
strate, may itself divide too. On the other hand the work on
artificial parthenogenesis initiated by Loeb has suggested
that the stimulus so given to the egg may be described in
physical or chemical terms.
It is this theory of Boveri’s that [I propose in particular to
discuss. In doing so it will be convenient to consider separately
the phenomena accompanying the entrance of the spermato-
zoon, and the formation of the cleavage—or fertilisation—
spindle.
1. The entry of the spermatozoon.
The time at which the spermatozoon enters the ovam varies
in different forms.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 447
In Ascaris the entrance takes places while the nucleus of
the primary oocyte is yet intact; the same is true of Nereis
(Wilson), Myzostoma (Wheeler), and some others. In others
again the sperm enters during some stage of the first polar
spindle (Ophryotrocha [Korschelt], Cheetopterus [Mead],
Physa [von Kostanecki], Sagitta [Boveri], and many more) ;
or again the entrance may be deferred until the first polar
body has been extruded and the second polar spindle formed,
as, for example, in Amphioxus (Sobotta), Petromyzon
(Bohm), the Trout (Behrens), the Newt (Michaelis), the
Mouse (Sobotta), and the Axolotl, or even until the second
polar body also has been given off (Toxopneustes [ Wilson,
1895], Echinus [Boveri], Tiara [ Boveri, 1890]).
It is an interesting speculation whether in the cases first
mentioned the formation of both polar bodies, or of the second
only, is dependent on the entrance of the spermatozoon.
Fick has surmised that this is so in the Axolotl, and Mead in
Cheetopterus ; while Boveri makes the same suggestion for the
species of Sagitta investigated by him, though he quotes an
observation of Fol’s on another species that the polar bodies
will form in any case, though much more slowly in an unferti-
lised egg. With this may be compared Hill’s statement that
in Phallusia the formation of the polar bodies is independent
of fecundation.
That an immediate change is wrought in the cytoplasm of
the egg by the entrance of the spermatozoon is proved by an
interesting experiment of Ziegler’s, in which the egg is
divided into two pieces, one containing the egg nucleus, the
other the sperm and centrosome. ‘The latter segments
normally ; the former makes amceboid movements and
attempts at division, while its nucleus repeatedly passes
through the initial stages of division but is each time recon-
stituted.
The place of entrance of the spermatozoon often varies in
the same species ; this can naturally only occur when there is
no micropyle. We have seen such a variation in the Axolotl ;
it is also found in Amphioxus (Sobotta), Diaptomus (Ishikawa),
4.48 J. W. JENKINSON.
Pterotrachea (Boveri), Cerebratulus (Coe), Physa (von
Kostanecki).
The tail of the spermatozoon may be left outside (Toxop-
neustes [Wilson], the Mouse [Sobotta]); but in the great
majority of cases, of which the Axolotl is one, is taken into
the egg (Polyclada [Francotte and van der Stricht], Amphi-
oxus [van der Stricht], Polystomum [Halkin and Gold-
schmidt]). It always degenerates.
An entrance funnel and cone similar to those observed in
the Axolotl have been seen in Myzostoma (Wheeler), Ophryo-
trocha (Korschelt), Toxopneustes (Wilson), Insects (Henking),
Petromyzon (Bohm and Herfort), Unio (Lillie), Allolobo-
phora (Foot), and Rhynchelmis (Vejdovsky).
The most accurate description of the formation of this
structure is that given by the author last named.
According to Vejdovsky there are outside the yolk two
layers, an external alveolar sheet, and a granular plasma
zone. As soon as the first has been pierced by the head of
the sperm, the second is depressed to form the entrance pit or
funnel. While this funnel becomes filled by a granular mass,
derived by Vejdovsky from the ground-substance of the cyto-
plasm, the alveolar sheet covering it is much thickened, pro-
trudes outwards and exhibits a radial striation. This corre-
sponds exactly to the outer dense zone seen by Fick and
myself in the Axolotl. Later the entrance cone breaks up and
disappears.
A very similar entrance cone is described by Miss Foot in
Allolobophora, and by Lillie in Unio; it is termed by the
latter merely the sperm-path.
Miss Foot and Vejdovsky have suggested that the acrosome
is the organ which is actively concerned in the production of
this structure. It is interesting to notice that according to
Meves, the acrosome of the Salamander and Guinea-pig, and
according to von Lenhossék that of the Rat, arises from the
sphere of the spermatid.
The “ Pol-plasma ” observed by both B6hm and Herfort in
Petromyzon is essentially a cone of entrance.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 449
We have seen that in the Axolotl soon after the entrance
of the spermatozoon, the head and middle-piece become sur-
rounded by a clear area devoid of yolk-granules. Such a
sperm-sphere is of wide-spread if not of universal occurrence.
Without stopping now to inquire into its physical significance
I may quote a few of the cases in which it has been seen.
It has been described by Griffin in Thalassema, by Lillie in
Unio, by Castle in Ciona, by Gardiner in Polycheerus, by
Henking in Insects, by both Coe and von Kostanecki in
Cerebratulus, and by Vejdovsky in Rhynchelmis.
Both Coe and von Kostanecki express the opinion that the
yolk-granules are driven away by the formation of the sphere,
while Castle and Vejdovsky hazard the conjecture that the
sphere grows by the addition of material brought to it by
streams of protoplasm moving along the surrounding astral
rays.
In the Axolotl the sperm-sphere becomes subsequently
vacuolated. Such vacuoles have been observed by Vejdovsky
in Rhynchelmis, by Herfort in Petromyzon, and by Oppel and
Nicolas in Reptilia.
2. The centrosome in fertilisation.
(a) The centrosome as an organ of thecell.
(i) Intra-nuclear origin of the centrosome.
In the Axolotl the definitive centrosome is derived from the
male pronucleus, through what I must regard as a precipita-
tion of the egg-cytoplasm by the nucleins of the sperm.
Although no such mode of formation of the cleavage centro-
some has up to the present been described by any author
(except by Carnoy in Ascaris), there are yet several instances
on record of the intra-nuclear origin of this body in germ-cells.
The case which stands nearest to my own observation, is
that of Styelopsis, where Julin has described the emergence
of the centrosome from the nucleus of the spermatid, without,
however, being able to trace it into the fertilisation spindle,
450 J. W. JENKINSON.
In the primary spermatocytes of Ascaris, Brauer (1893) has
observed and figured the appearance and even the division of
the centrosome, with accompanying formation of the spindle,
in the interior of the nucleus.
Hertwig has shown that in the reproductive cycle of
Actinospherium, a centrosome emerges from the nucleus
immediately before the polar divisions of the secondary cysts.
Schaudinn has actually seen intra vitam the centrosome
escaping from the nucleus in the spore of Acanthocystis.
Lastly, in the primary oocyte Riickert (1894) has asserted
a similar origin of the centrosomes in Cyclops, while the same
view has been, though more doubtfully, expressed for other
forms (Cerebratulus [Coe], Thalassema [Griffin], Prosthe-
cereus [von Klinckowstroém], Myzostoma [von Kostanecki],
Asterias [Matthews], Thysanozoon [van der Stricht], Poly-
cheerus [Gardiner], and Cyclas [Stauffacher]); in all these
cases the centrosomes first appear im invaginations of the
membrane of the germinal vesicle.
(11) Structure and functions of the centrosome.
The centrosome is a body which is almost invariably to be
found during the division of the animal cell. There are,
however, some exceptions. It is stated by Boveri (1887,
1890) to be absent from the polar spindles of Ascaris and
Sagitta. Sobotta has made the same statement of the polar
spindles of Amphioxus and the Mouse, Brauer and Behrens
of those of Branchipus and the Trout respectively, and various
authors (Carnoy, Fick, and myself) of the polar spindles of
Amphibia. Further, its existence in the cells of the higher
plants is totally denied by Strasburger and his school.
With regard to all these cases, I venture to make two
suggestions. As far as the plants are concerned, it is only
fair to say that Guignard and many other observers still
adhere to the opposite view. In the second place, no one will
pretend that the pole of a spindle is occupied by a Huclidian
point ; some small particle is undoubtedly there which may be
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 451
physiologically a centrosome, even though it refuses to stain
with iron-hemotoxylin. With respect to its alleged absence
from certain polar spindles, it may be pointed out that in
Ascaris it has been seen by several investigators (Carnoy,
Sala, and Fiirst), and that in any case the broad plate which
here occupies the pole of the intra-nuclear spindle has just
as much title to be regarded as active in the production of
the spindle fibres as has the quite similar pole-plate in the
spindles of Infusoria, Actinospherinm, and other Protozoa.
That the centrosome is not merely passive I hold to be
proved, first, by its division antecedently to the formation of
those structures on which the division of the nucleus and cell
obviously depends; and secondly, by the fact that these
structures (astral rays and spindle fibres) clearly grow out
from the centrosome. Further, I think it possible that the
activity depends, as Biitschh (1894) first suggested, on its
faculty of absorbing the watery substances of the cytoplasm. .
Such absorption will readily account for its growth, and per-
haps also for the remarkable series of periodically recurrent
changes which it passes through.
These changes have been noticed and figured by many
cytologists (Coe, Lillie, Vejdovsky, MacFarland, Sobotta
[Amphioxus], Conklin, van der Stricht [1898], Linville, Gar-
diner, Griffin, and myself) ; but itis to Boveri (1901) that we
owe the clearest description of the details of the process.
In spite of much disagreement, especially with regard to the
nomenclature of the different parts of the structure, all are at
one in regarding as the essential feature of the metamor-
phosis (a) the enlargement of the centrosome at a certain stage
in mitosis, (b) the gradual fusion of the centrosome with the
aster, from which it now becomes indistinguishable, and
together with which it ultimately degenerates, (c) the for-
mation of a new centrosome inside the old; this new centro-
some divides preparatory to the next mitosis, while around its
halves the new asters are formed.
This is essentially Boveri’s account of this cycle of changes
in the fertilization spindle of Kchinus. The centrosome, by
452 J. W. JENKINSON.
which he understands the reticular spherical body from which
the rays of the aster start, grows in the anaphase and gradu-
ally merges with the aster. Meanwhile, by condensation of
the central portion of the old, a new centrosome is formed,
which divides, and is the starting-point for new asters and a
new spindle.
In Ascaris the process is a little different. Here the
centrosome enlarges until the metaphase is reached; it then
begins to diminish, and continues to do so until it divides. It
should be noticed that a centriole is distinctly visible in its
interior throughout. What happens during its diminution
may best be described in Boveri’s own words: “ Natiirlich
mussen gewisse T'eile abgestossen werden ; allein dieser Pro-
zess scheint sich in den meisten Fallen so allmahlich zu
vollziehen dass er kaum bemerkbar ist und die abgestossene
Teile nicht als soleche erkannt werden konnen” (the surface
of the centrosome is rough and ragged at this stage) ; “ diese
Bilder mogen mit der Auflésung peripherer Centroplasmasch-
ichten zusammenhangen.” Again he says: ‘ Das verklemerte
Centrosom ist stets der Mittelpunkt der Radien die sich ihm
unmittelbar anfiigen und die offenbar aus dem abgestossenen
Centroplasma gebildet sind.” Finally he concludes: “ Das
periphere Centroplasma sich von dem centralen gesondert und
ahnlich wie beim Seeigelei der Sphire angeschlossen hat.”
I think it is perfectly clear from this that Boveri regards
the diminution of the centrosome in the anaphase of Ascaris
as parallel to the condensation of a new centrosome in the
interior of the old in Echinus. In that case the only differ-
ence between the two is this: in Hchinus the centrosome
erows by simple enlargement, in Ascaris it grows by giving
off rays which become continuous with the older rays outside.
In both cases the outer portion of the enlarged centrosome
becomes indistinguishable from the aster, and together with it
undergoes a granular or reticular degeneration.
The changes figured by Conklin in Crepidula are closely
similar to those described by Boveri for Hchinus ; the same
may be said of Sobotta’s figures of Amphioxus, Coe’s of
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 4538
Cerebratulus, van der Stricht’s of Thysanozoon (second polar
spindle), and Griffin’s of Thalassema. The cleavage centro-
some of the Axolotl, on the other hand, resembles that of
Ascaris. At first small, it increases in volume, and then gives
off fine rays, which become continuous with the older astral
rays outside. These rays then degenerate to form the centro-
sphere, in the middle of which a “reduced” centrosome (to
use Boveri’s expression) is found. This divides for the next
mitosis, and, like the centrosome of Ascaris, contains a minute
centriole.
Lillie describes in the maturation and fertilisation spindles
of Unio an inner radiate sphere immediately outside the
centrosome, between which and the aster proper is a second or
outer, also radiate sphere. In the anaphase the inner sphere
enlarges, while the centrosome divides, a spindle being formed
between the halves. Then, while the inner sphere disinte-
grates together with the outer sphere and aster, each
centrosome grows to form the inner sphere of the next gene-
ration, one central particle remaiming as the centrosome.
Lillie’s inner sphere is clearly a derivative of the centrosome,
and its whole history shows very clearly that a part—the
outer part—of the centrosome may in the course of its life
assume a radial structure. This, as pomted out above, is
admitted by Boveri, and, I think, follows from my own
observations.
Vejdovsky’s interpretation of the corresponding changes in
Rhynchelmis is very different. The substance of the sphere,
which is cytoplasmic in origin, assumes a radiate arrangement
under the influence of the central body or centriole (he admits
no centrosome). ‘The central portion of this sphere, or centro-
plasm, as Vejdovsky calls it, undergoes degeneration only
once more to assume a radial arrangement about each half of
the dividing centriole. The central body, therefore, under-
goes no increase of size, and exhibits no alteration of struc-
ture. The changes are entirely confined to the surrounding
cytoplasm (centroplasm), and are merely called forth by the
activity of the centriole.
454, J. W. JENKINSON.
I cannot help thinking that a media via may be found
between these two opposite views; for if, as I have suggested
above, the centrosome is capable of sending out radial pro-
cesses which precipitate the cytoplasm, it is quite clear that
the centrosphere must be derived from one as much as from
the other.
(b) The origin of the cleavage centrosomes.
The dominant theory of the origin of the cleavage centro-
somes is undoubtedly that propounded by Boveri on the basis
of observations on the egg of Ascaris. It is this: the egg
lacks the organ of cell division, the centrosome; this ‘is
supplied in the act of fertilisation by the spermatozoon.
How powerful the influence of this conception has been on
the interpretations which subsequent investigators have put
upon their work s patent to anyone who is acquainted with
the hterature of the subject, and is seen in the frequency with
which the identity of the cleavage with the sperm-centro-
somes is asserted on purely & priori grounds when positive
evidence is wanting.
On the other hand, there have been a few who have been
content to leave the origin of these organs undetermined,
while a very few either deny the participation of the sperm-
centres in the formation of the fertilisation spindle altogether,
or at least assert that the ege centres also play a part in the
process.
Lastly, an attempt has been made, in extension of Boveri’s
original hypothesis, to prove the persistence of the centrosome
of the spermatid as the sperm- and consequently as the
cleavage-centre.
These various hypotheses I propose to examine separately.
(i) The participation of the ege centres in the formation
of the cleavage spindle.
While the majority of investigators agree in asserting the
disappearance of the egg centrosomes and asters after the
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 455
formation of the second polar body (Castle [Ciona], Coe and
von. Kostanecki [Cerebratulus], Griffin [Thalassema and
Zirpheea], Foot [Allolobophora], Lillie [Unio], ete.), Wheeler
has stated that in Myzostoma not only do they persist but
alone are concerned in the production of the fertilisation
spindle. ‘I have never been able,” says this author, “to find
any traces of such archoplasm or any centrosome in connec-
tion with the male pronucleus.” This account is, however,
contradicted by von Kostanecki (1898), who, while fully
admitting the prolonged persistence of the egg-centres,
claims to have discovered two centrosomes in proximity to
the sperm-nucleus, and to have seen the formation of the
fertilisation spindle from these. He admits, however, that
the verdict must ultimately be given on “die Analogie mit
dem Befruchtungsvorgang bei anderen Thierspecies.”
While no one except Wheeler has denied to the sperm-
centres some share in fertilisation, Conklin and others have
revived Fol’s almost forgotten ‘ Quadrille des centres.”
Conklin described this in Crepidula, but in a subsequent
paper contradicted his earlier account. His later view is that
the sperm and egg-asters fuse and that then the combination-
aster divides, the cleavage centrosomes arising within the
daughter-asters in a manner which is not further determined.
Blane has made a somewhat similar assertion for the Trout,
but he is contradicted by Behrens; while van der Stricht’s
figures of the “Quadrille” im Amphioxus are shown by
Sobotta to be really taken from polyspermatic ova.
(11) Origin of the cleavage centrosome not determined.
In Arenicola (Child), Allolobophora (Foot), Pleurophyl-
dia (MacFarland), Unio (Lille), Prosthecereus (von
Klinckowstrém), Polystomum (Halkin), Insects (Henking),
and Cerebratulus (Coe), the sperm-asters and centres disap-
pear; the cleavage centrosomes then arise de novo. In
some cases (Cerebratulus, Allolobophora, Unio) they are first
VoL. 48, PART 3.—NEW SERIES. 33
456 J. W. JENKINSON.
seen at the poles of the united pronuclei, and Lille surmises
that one is derived from each. Others (Coe, MacFarland)
conjecture that they must, nevertheless, be considered to
come from the sperm.
(iii) Origin of the cleavage-, from the sperm-centres.
The remaining authors express themselves more posi-
tively, and in some cases the evidence is_ perfectly
good. It is so, for example, in the Axolotl, in Cyclops
(Riickert [1895]), Diaptomus (Ishikawa), Branchipus (Brauer
[1892]), Rhynchelmis (Vejdovsky), Ophryotrocha (Kors-
chelt), Toxopneustes (Wilson), Ciona (both Castle and
Boveri).
In Cheetopterus and Thalassema, again, Mead and Griffin
assert most categorically the continued existence of the
sperm-centrosomes, but in Cerebratulus and Physa and in
the Mouse the sperm-centres disappear, and von Kostanecki
and Sobotta are constrained to fall back on a priori con-
siderations in order to establish their identity with the definitive
centrosomes.
In other cases there is less certainty (Polyclada [Francotte],
Petromyzon [Bohm], Amphioxus [Sobotta]), and even in
Ascaris Boveri (1888) was unable to do more than state what
was in his opinion the very great probability of the intro-
duction of the cleavage centres by the spermatozoon. Von
Erlanger has, however, since shown that this was justified
by demonstrating the presence of a centrosome in the
spermatozoon, and its division to form the centres of the
fertilisation spindle.
(iv) The persistence of the centrosome of the spermatid
as the sperm- and cleavage-centre.
It is true that the most recent investigations agree in
tracing the centrosome of the spermatid into the middle-
piece of the spermatozoon. At the same time the sperm-
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 457
centre is first seen in the majority of cases on the inside
of the sperm-nucleus. In this case, its origin from the
middle-piece cannot be said to have been demonstrated.
The rotation of the sperm-head has, however, been observed
in Toxopneustes, the Trout (Behrens), Petromyzon (Herfort),
Sponges (Maas), Ophrytrocha, Branchipus; while the formation
of an aster round the middle-piece is recorded for Polyclada
(Francotte and von Klinckowstrém), Allolobophora, Physa,
Crepidula, Petromyzon, Rhynchelmis, Toxopneustes, Ascaris,
the Axolotl, and the Newt. Miss Foot and Wilson, however,
assert that in Allolobophora and 'Toxopneustes the middle-
piece disappears and stands in no obvious genetic relation
to the cleavage centrosomes.
It is, perhaps, a matter of little moment that the middle-
piece should have been traced to the previous centrosome in
none of these cases except the Axolotl ; what is of importance
is that the formation of an aster about this structure is no
indication whatever of its survival as the cleavage centrosome,
as its fate in the Axolotl and Newt, in Allolobophora and
Toxopneustes clearly shows.
The difficulty of drawing any pesitive conclusion from this
conflicting mass of testimony is obviously very great; for as
Wilson has pointed out, if the sperm-centres disappear there
is no more reason for deriving the cleavage centres from
them than from the egg-centres. The possibility of the
formation of centrosomes afresh in the cytoplasm has also to
be reckoned with (Mead, centrosomes in the oocyte of
Cheetopterus; Wilson [1901] and Morgan, centrosomes in
the parthenogenetic ova of Hchinoderms).
It would be unwise to prophesy too dogmatically until
we have a much fuller knowledge of the exact mode of
formation of the cleavage centres; but it does not seem
impossible that they may arise in other forms, as they do in
the Axolotl, from the sperm-nucleus; and that those sperm-
asters which have so often been observed, and so often
disappear, are the transitory primary radiations which arise
around the middle-piece. By giving up therefore the doctrine
458 J. W. JENKINSON.
of the continued persistence of the centrosome from the
spermatid to the completely fertilised ovum, we may be
taking the first step towards re-establishing on a securer
basis Boveri's original generalisation.
The rehabilitated theory of the prime activity of the
spermatozoon in renewing the ovum’s lost power of cell-
division might then be enunciated as follows :—On contact
with the egg an apparatus—the entrance-cone—is produced
for ensuring the entrance of the sperm; the organ respon-
sible for this is the acrosome. In the interior of the egg
a sperm-sphere appears which imparts (as Ziegler’s experi-
ment has shown) a second stimulus to the cytoplasm; the
organ which is now concerned is the middle-piece. When
the pronuclei have met a spindle, formed directly by the
divided sperm-centrosome, completes the process of nuclear
and cell-division. Since, however, all these three organs
either are, or are derived from centrosomes, the supreme
physiological importance of the centrosome in the act of
fertilisation is vindicated to the full.
IV. EXprerRiIMENTAL.
In this section I propose to give a brief account of some
experiments I have made in the hope of throwing some light
on the nature of the physical processes concerned in the act
of fertilisation, that is to say in the restoration to the ovum
of its lost power of cell-division.
We have seen that not only in the Axolotl, but also in a
large number of other forms the following phenomena have
been observed during fertilisation :—
1. The formation round the spermatozoon of an entrance-
funnel filled with a plug—the entrance-cone—consisting of
some coagulable, apparently watery material.
2. (a) The appearance of a clear area devoid of yolk-
granules round the sperm-head and middle-piece when the
latter has reached the interior of the egg.
(b) The vacuolation of this clear area and simultaneous
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 459
assumption by it of a radial structure, the rays being pro-
longed outside it between the surrounding yolk-granules.
(c) The formation of a spindle between the centrosomes,
accompanied by a great increase in volume of the latter.
In considering these two classes of phenomena I could
hardly refrain from indulging in vague conjectures in expla-
nation of them, and it was with a view to testing these specu-
lations that I undertook the two sets of experiments now to be
described. Asa result, I have been tempted to form certain
conclusions; but I must state most explicitly that the experi-
ments are themselves very far from being thorough or
searching, and that the hypotheses founded on them are
tentative in the very highest degree.
1. It occurred to me that the entrance of the spermatozoon
with the accompanying formation of entrance-cone and funnel
might be due to a local alteration of the surface tension of
the egg. I floated a fairly large drop of acetic acid between
a layer of chloroform and a layer of benzole in a glass vessel.
The drop assumed approximately a spherical shape. In the
same vessel I floated a drop of filtered albumen. When the
drops were made to touch and coalesce the acetic seemed to
spread over the outer surface of the albumen; and this was
very clearly the case when the drop of acetic was much
smaller than the other, the acetic producing a patch of
coagulum on the outer surface of the albumen. I concluded
from this that the surface tension between acetic and the
mixture of chloroform and benzole was less than that be-
tween albumen and the mixture. I then took a large drop
of acetic and a small drop of albumen; in this case, when
the drops coalesced the smaller streamed into the interior of
the larger.
Exactly the same thing occurred when I substituted for the
albumen either a drop of gum or a drop of a semi-solid mixture
of 1 per cent. gelatin and albumen in equal parts. The shape
of the instreaming drop varied, however, in the three experi-
ments. In the case of the albumen the inner end was broader
than the outer, with the gum the drop streamed in as a
460 J. W. JENKINSON.
cylinder, while the gelatin-albumen preserved its spherical
form.
I suggest, therefore, merely of course as a working hypo-
thesis, that the entrance-cone—the plug of apparently watery
substance which fills up the entrance funnel—is in reality the
agent which produces this deep depression at the surface of
the egg, and carries the spermatozoon with it into the interior;
and that it does so in virtue of its greater surface tension.
We should expect then a more watery proteid like albumen
to behave toward a less watery one such as egg-yolk as the
albumen behaves toward the acetic acid; and this is in fact
the case. A small drop of albumen will enter a large drop of
ege-yolk, while conversely a small drop of yolk spreads over
the surface of a large drop of albumen.
The substance with the greater surface tension is of course
derived from the egg itself. It appears only when the sper-
matozoon comes in contact with the egg, and we must
therefore ascribe to the male cell the important function of
withdrawing water from the cytoplasm. It is further pro-
bable that this intense hygroscopic activity may be located in
a particular organ of the spermatozoon, the acrosome; Miss
Foot and Vejdovsky have indeed already suggested that this
is the active agent in the production of the entrance-cone.
In this connection it is of the greatest interest that Meves
should have described the origin of the acrosome in the
salamander and guinea-pig from the sphere of the spermatid,
a body related most intimately to the centrosome; for, as I
believe, and as I hope the experiments next to be described
may show, the activity of the centrosome also depends very
largely on its power of absorbing water from the cell.
2. The second series of experiments starts from the observed
concentration of a watery substance in the centre of the sperm-
sphere.
I began by placing a small crystal of ammonium sulphate
in a drop of filtered albumen on a slide. As the crystal
begins to dissolve a pool or vacuole of its own solution is
formed immediately round it, and outside this there quickly
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 461
develops a system of bright, radiating lines. These lines
appear equally well whether the preparation is covered by a
glass or not. I soon came to the conclusion that the bright
lines were tracts of albumen left between tubular outgrowths
of the vacuole, though it is not very easy to make this out in
this particular experiment. In other cases, however, to be
described in a moment, this can be clearly seen to be so. If
carmine particles are placed in the albumen they may be
observed to stream towards the crystal.
As the crystal continues to dissolve the solution approaches
the saturation point; a thick brown ring or wall of precipi-
tated albumen is then formed round the central vacuole.
Through this, however, the solution passes, and there are
produced outside the wall a number of fine rays of precipi-
tate. This “diffusion aster,” as I will term it to distinguish
it from the other or “ excurrent aster,” is of course identical
with the structure described by Fischer under the title of
“Selbststrahlung.” Both kinds of aster are transitory and
soon dissolve in the albumen.
The experiment may be varied by using instead of the
ammonium sulphate crystal a drop of glycerin, or glycerin
and albumen, or glycerin and sublimate ; or again a small
particle of dried gum, the gum being either used pure or with
the previous admixture of potassium carbonate, picric acid,
or ammonium sulphate. The result is the same except that
when the substance employed is a precipitating reagent the
radiating lines of albumen between the tubular outgrowths
become fixed. With some substances, chromic for example, I
found that only the diffusion aster could be produced.
I found subsequently that very much better results could
be obtained by employing a thin layer of albumen; using
these, beautiful asters can be made with a drop of sublimate,
picric, or ammonium sulphate. Although the layer of albumen
is exceedingly thin, still I believe that even here the out-
growths take place in the thickness of the film; for the drop
spreads before the radial outgrowths are given off from its
periphery, and an upper membrane of precipitate can be
462 J. W. JENKINSON,
lifted off the lower layer which forms the floor of the central
circular area.
I next tried gelatin, principally a solution of about 6 per
cent., and succeeded in producing the excurrent aster with
picric acid, either alone or with the admixture of glycerin
or cane sugar; with chromic acid and glycerin, and with
Flemming’s solution; with albumen mixed with either glycerin
or cane sugar; with a crystal of either ammonium sulphate or
sodium chloride, and with saturated solutions of either sub-
stance; and with a mixture of gumand sublimate. As before the
results are far superior when a thin layer of gelatin is used. The
asters retain their form long enough for the gelatin to set;
they may then be fixed in alcohol and preserved permanently.
Thirdly I experimented with yolk of egg. Ifa small crystal
of ammonium sulphate be immersed in a drop of egg-yolk, it
does not matter how large or thick, a clear area is at once
formed round it, the yolk-granules being driven away. This
can be seen in the drop and is easily verified by the aid of
sections. Soon there appears internally to this clear area a
thick brown wall of precipitate, as in the case of albumen
described above, and inside this a central vacuole as the
crystal finally dissolves away.
If instead of ammonium sulphate a small crystal, the smaller
the better, of salt or sugar be employed no precipitate is
formed, but short radial tubes grow out into the clear zone
from the central vacuole, and not only in a horizontal plane.
It is important to observe that these outgrowths can be pro-
duced as easily in a large drop as in a small, and that in the
former case their formation is quite independént of any con-
tact with the lower surface of the drop next the glass.
If on the other hand a thin film of egg-yolk be employed
the aster is much more fully developed. In egg-yolk I have
made asters with solutions of picric, picric and cane sugar,
cane sugar, glacial acetic, aceto-corrosive, chromic, chromic
and acetic, glycerin and sublimate, glycerm and _ picric,
ammonium sulphate and 90 per cent. alcohol. ‘The best
results are given by glacial acetic and cane sugar.
MATURATION, ETC., OF 'THE EGG OF THE AXOLOTL. 463
As the process takes place much less rapidly here than in
other cases the formation and structure of the aster may be
very readily observed. The drop spreads out in the thickness
of the film; radial processes are then given off from its
circumference, which as they grow out branch repeatedly and
anastomose with one another. In this way tracts of egg-yolk
left in between the excurrent radii may be cut off and isolated
from one another. Where the radi leave the central drop,
and where their branches leave the radu, they are frequently
exceedingly narrow ; in their formation the contained liquid
first pierces a small aperture in the surface (or surface mem-
brane) between itself and the yolk, and then expands on the
outer side. The intervening portions of yolk are naturally
thickened here and often fuse with one another, pieces of the
excurrent radu being thus cut off in their turn. In this way
the whole aster comes to have the appearance of a system of
radially elongated alveol, more or less completely separated
from one another by thin intervening lamelle. When two such
asters are formed close together and simultaneously, a spindle
results with a plane equatorial plate where the opposing radii
meet (fig. D.). The aster is frequently made up of concentric
zones ; this is due to the radi branching, and rebranching at
equal distances from the centre.
Lastly, asters of the same type were made with many of
the above-mentioned reagents in mixtures of gum and gela-
tin and of gum and albumen.
My next efforts were directed towards producing these
outgrowths in the bulk of the colloid, and here I have been
less successful.
The following experiments were tried:—A small drop of
dried gum saturated with potassium carbonate was supported
on a needle-point in a vessel of filtered albumen. Tubular
processes were given off in all directions, but soon turned
down and sank to the bottom. In albumen, however, which
has become highly viscid by desiccation, the tubes which are
given off retain their original direction.
A drop of picric acid was placed in a } per cent. cold solu-
464 J. W. JENKINSON.
tion of gelatin; whether this solution is wholly liquid or
contains solid matter I must leave it to the physicists to
decide, but it seemed to me to be a fluid containmg some
solid in suspension. The picric acid sinks but slowly, and
gives of tubes in the bulk of the fluid.
In a 2 per cent. solution of gelatin set to a jelly, which, as
Hardy me shown, contains liquid and solid side by side,
a NN
iN Ai
FUN
Fie. D.—Photograph of an artificial spindle made with glacial
acetic acid in a film of egg-yolk on a slide. Note the cquatorial
plate.
drops of 1 per cent. chromic and saturated ammonium
sulphate sink partially below the surface; radial tubes are
given off in all directions from the underside of the drops.
Other substances give results; they are not, however, nearly
so good.
This led me to make a few experiments with fluids in
which solid particles are suspended. I have tried albumen
MATURATION, BTC., OF THE EGG OF THE AXOLOTL. 465
beaten up but unfiltered (which of course contains much solid
matter), a mixture in equal parts of 1 per cent. gelatin and
albumen, and filtered albumen mixed with a little yolk of
egg. With the first both picric and metaphosphoric acid
(about 1 per cent.) will give off radial tubes in the bulk of
the liquid; with the second, gum and picric, metaphosphoric
acid and crystals of salt and ammonium sulphate; with the
third, metaphosphoric acid. I did not make a very extended
series of trials.
In none of these cases could I succeed in obtaining such
fine asters as in thin films and on a glass slide; and I always
observed that the tubular outgrowths developed much more
rapidly when they could run along the under side of the
surface of the fluid.
The difficulty of getting the tubes to grow out in the bulk
of the liquid depends no doubt in part on the difference in
specific gravity of the two substances employed, the drop
always sinking to the bottom before it has time to send out
its processes. It is, however, due, I believe, in much larger
measure to the absence of certain very essential physical
conditions.
It will have been noticed that the reagents selected for the
production of these artificial asters are, with the exception of
gum, all crystalloid, and possessed therefore of a far higher
osmotic pressure than the colloidal solutions in which they
are placed. They were indeed chosen for this very reason ;
for I was under the impression that we had here to do simply
with phenomena of osmosis, and that the tubular outgrowths
were merely due to an excess of pressure on the inside. I
believed, in fact, that the behaviour of the ammonium sul-
phate crystal in albumen was strictly comparable to the
behaviour of a crystal of potassium ferrocyanide in a solution
of copper sulphate. In this experiment (for which I am
indebted to Dr. Ramsden) a colloidal membrane of copper
ferrocyanide is rapidly formed round the crystal as it dis-
solves, from which membrane numerous irregular twisted
tubes grow out in all directions.
4.66 J. W. JENKINSON.
This, however, is by no means the case; for in the first
place a drop of distilled water will produce an aster in egg-
yolk or albumen; and further, the asters can be made much
more readily, as already pointed out, on a glass slide and in
a thin film, or at the surface of a lquid, than in the bulk of
a liquid, and in the latter much better when there are solids
present.
It is quite evident then that though a central excess of
osmotic pressure may be to a certain extent responsible for the
production of the aster, surface-tension phenomena of a very
complicated nature have still to be reckoned with. More
than this as to the physical nature of the process it is impos-
sible to say. There seems to be an important difference
between these asters and the well-known “cohesion figures ”
of Tomlinson. No doubt both are capillary phenomena, but
while 'omlinson’s figures are formed at the surface these
orow out beneath it im the thickness of the film. Surface-
tension relations with both air and glass are thus apparently
excluded. My asters also are quite dissimilar to the “strain”
asters produced by Biitschh (1898) in gelatin under the stress
of a contracting air-bubble, and made by Hardy with a small
elobule of mercury rolled on a thin film of albumen. Dr.
Ramsden has pointed out to me that the latter is: nothing
more than the wrinkling of a solid surface membrane, and
can hardly be compared with any radiations formed in the
bulk of a fluid.
It only remains to be considered whether any hypothesis,
however tentative, can be based on these experiments which
shall elucidate the natural asters which we observe in the
living cell.
We have seen that when the spermatozoon reaches the
interior of the ovum a clear yolk-free area is formed round it,
in the centre of which the middle-piece gradually dissolves.
The behaviour of the middle-piece in the egg seems quite
comparable with the behaviour of a small crystal of salt or
other substance in a drop of egg-yolk; here also a clear
yolk-free area is formed round the dissolving particle.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 467
Subsequently the sperm-sphere assumes a radiate struc-
ture. I suggest that this structure is due to the outgrowth
of tubular processes from the central dissolved mass. These
outgrowths, filled with a slight coagulum, constitute the
alveoli or inter-fibrillar spaces; the intervening tracts of the
substance of the sphere the inter-alveolar lamellee or fibres.
In addition to these rays, however, other rays are formed,
passing outwards between the yolk-granules. These external
rays I must regard as originating by a different process ;
I believe that they represent the paths along which water is
being withdrawn from the cytoplasm. Biitschli (1894) has
described such rays round the contractile vacuole of Balan-
tidium and some other Protozoa. The water thus continually
withdrawn from the egg becomes concentrated in the large
vacuoles which we have seen occupying the centre of the sphere.
It is at this moment that the definitive centrosome makes
its appearance. Its probable origin through precipitation of
the albumins of the ege-cell by the nucleic acid or nucleins
of the sperm-nucleus has already been discussed. It has
also been shown that the spindle-fibres appear to grow out
from the centrosomes, and that as the spindle is gradually
developed so the centrosomes gradually enlarge. It seems to
me that the physical interpretation suggested above of the
formation of the sperm-aster is applicable here also, only that
the active hygroscopic particle is now the centrosome instead
of the middle-piece. Accepting this view, we regard the
spindle-fibres and such parts of the astral rays as come into
being at this stage as inter-alveolar lamelle, the alveoh
themselves as outgrowths of the dissolved substance of the
centrosome. The intra-nuclear portion of the spindle arises
by the extension of the tubular outgrowths into the cavity of
the nucleus, the membrane being first dissolved. ‘The fibres
are then formed from tracts of achromatic substance, Just as
outside they are formed from the cytoplasm.
Assuming that the centrosome—and the middle-piece is
also a centrosome—contains nucleic acid or even nuclein we
have in it an agent capable of producing these effects ; meta-
468 J. W. JENKINSON.
phosphoric acid, a characteristic constituent of the nucleins
(Mann) has already been mentioned as one of the reagents
used in the production of the artificial asters; and Berg has
shown that the precipitation granules produced by the action
of nucleic acid and nuclein on clupein, a protamin, are
capable of swelling up with the water they absorb. Further,
since, as is well known, nucleic acid and nuclein precipitate
albumins—in virtue apparently of this same metaphosphoric
acid—we shall, on the hypothesis I am advocating, have to
regard the spindle-fibres as solid or at least as solid as these
proteid precipitates usually are. That the spindle has a con-
siderable amount of rigidity seems to be shown by the fact
observed by Gardiner and Vejdovsky that it does not readily
change its shape even when the egg is deformed or burst.
The spindle-fibres are then primarily lamellee lying between
radial tubes running out from the centrosome and consisting
of a precipitate of the albumins of the cell (or nucleus) by the
nucleins in solution in the tubes; by the anastomosis of
adjacent outgrowths the lamella may become converted into
actual fibres; while the concentric zones of the real asters
are produced, as they are in the artificial, by the branching
of the outgrowths at points equidistant from the centre.
Where two such radial systems meet a spindle is formed, the
chromosomes being pushed into the equator ; 1f the opposed
ends of the radial tubes fuse bi-polar fibres will result, if they
inter-digitate, fibres intercrossing at the equator, if they meet
but do not fuse, an achromatic equatorial plate. ‘This condition
may be easily imitated (Fig. D.). In the anaphase of the
fertilisation spindle of the Axolotl I have described such a
plate ; but there is an earlier stage in which the fibres pass
continuously from pole to pole. I thimk this may be explained
as follows: I have often observed that the outer end of the
artificial tubes are covered only by an extremely thin mem-
brane, apparently because the concentration of the liquid inside
is too low to produce a copious precipitate. Such thin-walled
ends would readily fuse, but as the concentration imcreased at
this point the dissolved proteids would be reprecipitated.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 469
I have also a word to say on the so-called contractile fibres
or “ Zugfasern ” attached to the chromosomes.
In the Axolotl I have seen such fibres, or rather fibre-
bundles, passing to but not beyond the chromosomes; as the
latter diverge the fibre-bundles shorten, though they cannot
be said to thicken. Usually the fibre-bundle is attached to
the end of a chromosome but sometimes at a short distance
from the end. In this case the point of attachment is during
the anaphase invariably nearest the spindle-pole, the chromo-
some thus assuming a hooked form. This all seems to me to
be strongly in favour of the belief that these fibre-bundles
do actually pull the chromosomes apart. There is of course
a large amount of evidence to the same extent from many
other sources. At the same time I believe it to be a wholly
gratuitous error to attribute to such fibres the properties of
pieces of elastic, as so many authors have done, or to assume
with Boveri (1888) that all the laws that hold good for
muscles can also be applied to these.
On the view I have put forward these fibres, produced
by the precipitation of a proteid, are probably in the con-
dition of a highly viscous fluid. When a drop of egg-yolk
falls from a glass rod it draws out a long thread behind it ;
when the drop is detached the thread flows back on to the
rod, And soin the spindle. As the tubes grow out some
of the lamellz, or fibres, become attached to the chromosomes ;
when the chromosomes split the fibres retreat into the
substance of the centrosome, carrying the halves of the
chromosomes with them. The astral rays on the other hand
do not behave in this way, probably because their outer ends
never become severed from the surrounding cytoplasm.
Cases have been described (Iijima, Mark) in which the
astral rays are curved, apparently by streaming movements
in the cell. Such a curvature may easily be imparted to
the artificial radiations by simply tilting the slide. It is
very difficult to believe that these rays are any more elastic
than the spindle-fibres.
Lastly, the living aster and spindle dissolve and disappear
470 J. W. JENKINSON.
in the cytoplasm in exactly the same way as, for example,
the ammonium sulphate aster is resoluble in an excess of
the surrounding albumen.
My theory then of the formation of these structures which
appear in the egg during fertilisation is that they are
produced under the influence of the middle-piece and centro-
some in virtue of a capacity which these bodies possess of
withdrawing water from the cytoplasm,! of swelling up and
dissolving in the water so absorbed, and then giving off
radial outgrowths which precipitate the proteids of the cell
so producing an aster and, by the combined effect of two,
the fertilisation spindle.
I am therefore very closely in accord with those authors
who hke Meves (1896, 1898) see in such facts as the invagina-
tion of the nuclear membrane, the divergence of the centro-
somes and the broadening of the spindle, strong grounds for
holding that spindle-fibres and astral rays are structures
which grow out from the centrosome. The difference between
us is that according to my theory it is not the fibres, but the
inter-fibrillar spaces or alveoli which are the more actively
concerned in the process. Not that I regard all asters as
necessarily formed in this way. It is quite probable that in
many cases asters may be precipitated by the centrosome in
the manner termed “Selbststrahlung” by Fischer. Most
authors of course figure asters of this type, that is, systems
of radiating disconnected straight lines.
On the other hand I stand in absolute opposition to those
who regard rays and fibres as permanent organs of the cell,
and whose whole cytological philosophy is summed up in the
dogma “Omnis radius e radio.” Such theories ignore the
periodic disappearance and re-formation of these structures,
1 Dr. Ramsden has suggested to me that the centrosome may not only be
hygroscopic, but may either itself undergo decomposition or possess a ferment
which would produce such an effect on the cytoplasm. In either case the
result would be an increase in the number of molecules, that is, in the osmotic
pressure. This might be partly responsible for the formation of the aster (see
above ).
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 471
and, when they apply the theory to the explanation of cell-
division, the very obvious fact that in many cases these
“elastic” threads never reach the surface of the cell at all.
Neither can I agree that the centrosome is passive, the mere
“Tnsertionsmittelpunkt ” of contractile fibrille. In spite of
the asserted absence of the centrosome in the higher plants—
and we shall do well to remember that the question is still
sub judice and that much depends on our definition of a
centrosome—and in spite of the difficulties presented by the
facts of multi-polar mitosis, I confess I am one of those who
believe in the centrosome as active—whether permanent or
not is of little moment—and as active because it is hygro-
scopic. This conception of the centrosome as an absorbent
of the water of the cell is of course not new. Bitschli (1894)
suggested that it had this function and showed that in his
artificial foams a radial structure might be induced round a
central hygroscopic particle. But here our paths diverge.
For Biitschli an alveolar structure is appropriate to all
living substance and the aster we see is but the radial
rearrangement of the alveoli that existed before. The
theory has grave objections. In the first place an assump-
tion is made as to the structure of protoplasm, an assumption
which has not yet been vindicated; and in the second no
explanation is offered of the manner in which an aster so
produced could perform its functions.
On the other hand while the theory which I have ventured
to put forward asks for no other preconception of the nature
of lving substance than that it is a colloidal fluid, it does, I
hope, indicate a way in which those structures which we do
really see may not only be formed, but also be capable of
effecting the observed results, as far at least as the division
of the nucleus goes. (The division of the centrosome is
another matter entirely.) This way is by the redistribution
of the watery contents of the cell, and should this lead to a
disturbance of the equilibrium of internal surface-tensions a
way may be opened for the explanation of cell-division as
well. The facts of normal fertilisation might thus be brought
VOL. 48, PART 3,—NEW SERIES. 34
4,72 J. W. JENKINSON.
completely into line with the phenomenon of artificial
parthenogenesis, a phenomenon which, as is well known,
Loeb has attributed to the increased osmotic pressure of the
medium in which the eggs are placed.
But whether this withdrawal of water is or is not the
essential factor in the formation of the wonderful structures
we observe in fertilisation, whether my tentative hypothesis
may usefully serve as a light to lighten the path of other
investigators, or whether it is destined to be cast into the
outer darkness of misguided speculations, I hope that it may
at least show the urgent necessity of supplementing the
descriptive by the experimental study of developmental —
processes ; for until that is done we can make no profitable
progress, hor can our theories claim to be scientific in the
fullest sense of the word.
Oxrorp, March, 1904.
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MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 473
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A74: J. W. JENKINSON.
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1902.
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Herrort, K.—“ Die Reifung und Befruchtung des Hies von Petromyzon
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MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 475
Isuikawa, C.—‘‘Spermatogenesis, Oogenesis, and Fertilisation in Diapto-
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4.76 J. W. JENKINSON.
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MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 477
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478 J. W. JENKINSON.
EXPLANATION OF PLATES 29—33,
Illustrating Mr. J. W. Jenkinson’s paper on “ Observations on
the Maturation and Fertilisation of the Heg of the Axolotl.”
All the figures were drawn with the aid of Zeiss’ camera lucida; comp.
oc. 6, achr. obj. 2mm. magn. 750 x.
Figs. 1—14. Maturation.
Fie. 1.—Metaphase of first polar spindle. At the outer end may be seen
some astral rays. The inner end is bi-polar.
Fre. 2.—Telophase of first polar spindle. The chromosomes have united
into an annular skein. The surface of the egg is raised up into a flat disc ;
the beginning of the first polar body.
Fic. 3.—Formation of the first polar body. This is still united to the
egg by a narrow stalk in which Zwischen-korper are seen. The chromo-
somes are again distinct.
Fic. 4.—The first polar body is completely separated. The chromosomes
in it have divided longitudinally, the chromosomes of each pair being united by
their apices. In the egg the chromosomes have also divided, and lie ina
tangentially elongated striated clear area, the first sign of the second polar
spindle.
Fic. 5.—Metaphase of the second polar spindle from a freshly laid egg
preserved in aceto-corrosive. Note the fibre-bundles attached to the apices
of the chromosomes. ‘The latter are paired and lie in the equator. The
outer spindle pole is slightly depressed.
Fie. 5a.—The same, cut across. The apices of the chromosomes point
towards the spindle axis.
Fic. 6a.—The same, but form an oviducal egg preserved in picro-acetic.
The chromosomes, scattered irregularly over the spindles, are beginning to
diverge by their apices. Note the ‘Zugfasern” and the ‘“ Verbindungs-
faden.” The outer spindle pole projects above the surface.
Vie. 6 6.—The same as the last, but preserved in chromo-acetic.
Fic. 7 a.—Late anaphase of the second polar spindle. There are no
“Zuefasern” to be seen. Note the outer fibres diverging into the equatorial
plane.
Fic. 7 6.—The same as last, but a little later; the first stage in the for-
mation of the second polar body.
MATURATION, EIC., OF THE EGG OF THE AXOLOTL. 479
Fig. 8.—The second polar body completely formed, but not yet quite
constricted off. Note the protrusion of the vitelline membrane. The chromo-
somes in both polar body and egg converge by their apices; in the latter
they lie in a clear area.
Fie. 9.—First polar body, cut equatorially. Notice vacuolated cyto-
plasm, agglomerated yolk-granules, pigment and cruciform jagged chromo-
somes.
Fie. 10.—First polar body with nucleus partially reconstituted. The
chromosomes, though still distinct, lie in an oval area. This, however, may
possibly be one of the products of division of the first polar body (see text).
Fics. 11—14.—Second polar body showing the reconstruction of the
nucleus. Figs. 11, 12 and 14 are cut equatorially. Notice vacuolated cyto-
plasm, pigment and clumps of yolk-granules. In Fig. 11 there are vacuoles
round the chromosomes. In Fig. 12 these vacuoles have united into one
oval nuclear vacuole, the wall of which forms the nuclear membrane; the
chromosomes are still distinct. In Fig. 13 the chromosomes are still distinct,
but are sending out processes to one another and to the wall, while in Fig.
14 they have given rise to a very coarse reticulum.
Figs. 15—41. Fertilisation.
Fig. 15.—The spermatozoon with head, middle-piece and tail lying ina
clear area, slightly pigmented, but devoid of yolk-granules, the sperm-spliere.
The tail (on the left) is pointing towards the sperm-path.
Fic. 16.—A little later. The sperm-head has shortened and thickened ;
the tail is seen to the right. The middle-piece has vanished. Instead, the
centre of the clear area is now occupied by a vacuolated pigment-free mass.
From this start the radiations of the sperm-aster which have meanwhile
been developed.
Fic. 17.—A little earlier than the last. ‘'he central mass is finely radiate,
and in it is a small irregular vacuolated body which may be middle-piece or
perhaps tail, The rest of the sperm-head is in the next section.
Fie. 18.—A little later than Fig. 16. The sperm-head has become shorter
and thicker still; it is obtusely conical. Its vacuolation has increased.
Fic. 19.—An accessory sperm-nucleus with centrosome. ‘The nucleus
contains large plasmosomes staining black with iron-hematoxylin, and
minutely divided granules of chromatin; these stain faintly. There is an
achromatic reticulum, The centrosome lies in front of (right-hand side in
the figure) the nucleus; between it and the nucleus are fine parallel “spindle”
fibres. It is granular. Large vacuoles are developing in the centre of the
sperm-aster.
Vig. 20.—Sperm-nucleus in an earlier stage, coarsely reticular (the section
does not pass through the middle of the nucleus, the full length of which has
480 J. W. JENKINSON.
not therefore been shown). Centrosome about to divide. Note the cloud of
pigment. The sperm-path is on the left side.
Fic. 21.—Centrosome elongated. The rest as in Fig. 19.
Fie, 22.—The daughter centrosomes have moved apart. The (accessory)
sperm-nucleus is coarsely reticular, and the nuclear membrane is hard to see
on the right-hand side. The large size of the yolk-granules is due to the
sperm having entered below the equator. Depigmented preparation; originally
like Fig. 23.
Fie. 23.—In the (accessory) sperm-nucleus the chromatic portion is
crowded into the centre. ‘Towards the cloud of pigment which obscures the
centrosomes the nuclear membrane is very much weakened. This sperm
also has entered below the equator.
Fic, 24.—Origin of the centrosome from the (accessory) sperm-nucleus.
Note the closeness of the centrosome to the nucleus, the absence of a mem-
brane here, and the pigmented processes running up into the nuclear cavity.
Fic. 25.—Exactly as the last, but nucleus and centrosomes are cut con-
secutively. cur consecutive sections; @ is the topmost, d at the bottom of
the series, and the pigment in dis over the centrosome. In tlie nucleus the
chromatin is crowded together centrally.
Fic. 26.—Sperm-nucleus. and centrosome. a. The centrosome, granular.
6. The nucleus, very coarsely reticular, and consequently in an earlier stage
than in Figs. 19—25.
Fic. 27.—Annular dividing centrosome. Division later than usual, the
pronuclei having met.
Fic. 28.—Formation of the female pronucleus. «@. Membrane formed,
but chromosomes still distinct. 4. Chromosomes breaking up. e. Chromatin
coarsely granular; a chromatic reticulum clearly visible. d, e. Chromatin
minutely subdivided, pronucleus enlarged and lobed. In d a few vacuoles
between the pronucleus and the yolk-granules.
Fig. 29.—The pronuclei have met. The male pronucleus is on the left;
in it the chromatin is aggregated centrally. The centrosomes have moved
apart, in a direction at right angles to the line joining the pronuclei. Note
the pigment, and the vacuoles of the sperm-aster.
Fic. 30.—The same as the last, but only one pronucleus is shown. Note
the fine parallel “ spindle” fibres between it and the centrosomes. Note aiso
the enormous central vacuoles of the sperm-aster with the remains of the
separating lamella, and the astral rays passing out between the yolk-granules.
Fic. 3].—Early stage in the formation of the fertilisation spindle. Notice
the fine parallel spindle-fibres between the centrosomes and the pronuclei;
and the large terminal vacuoles of the elongated sperm-sphere. The plasmo-
somes are stained black with iron-heematoxylin.
MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 481
Fic. 32.—Later. The terminal vacuoles are reduced. The pronuclei are
elongated parallel to the spindle axis. A pigmented cord still connects the
centrosomes. Plasmosomes as in the last.
Fic. 33.—Later still. ‘lhe centrosomes are much enlarged, and the terminal
vacuoles have disappeared. From each centrosome pass out a number of fine
‘inner’ astral rays (see text). Note the round vacuoles at the equator.
Fie. 34.—Only one pronucleus is shown ; the chromosomes are forming in
it. The achromatic reticulum is coarse, and bears granular thickenings. The
spindle is mach longer, the centrosomes smaller and reticular (aceto-corrosive
preparation), and the inner astral rays exceedingly fine.
Fic. 35.—Resting nucleus of one of the first two blastomeres; in it are
seen plasmosomes, finely divided chromatic granules, and an achromatic
reticulum. On its polar—the right—side is a depression, and on the same
side two small centrosomes. It lies in a clear, much vacuolated area.
Fic. 35 a.— Division of the centrosomes in the anaphase of the fertilisation-
spindle. The centrosomes are flattened against one another; each is lobed
and contains a centriole. Chromo-acetic preparation.
Fic. 36.—EKarly stage in the formation of the chromosomes by linear aggre-
gation of granules. In the female proneucleus (on the left) a plasmosome is
still visible. In the male pronucleus there is a very coarse granular network
of chromatin crowded together in the centre of the pronucleus. In both
pronuclei the achromatic reticulum is coarse.
Fic. 37.—Transverse section of thie fertilisation spindle in early metaphase
showing two distinct sets of chromosomes.
Fic. 38.—Formation of the equatorial portion of the spindle from the
achromatic reticulum of (one of the) pronuclei. The continuity of the extra-
and intra-nuclear fibres through the openings in the membrane of the upper
pronucleus is readily seen. Centrospheres and centrosomes as in the next
figure. Pronuclei as in Fig. 34,
Fic. 39.—EKarly metaphase. Aceto-corrosive preparation. The inner rays
have undergone reticular degeneration and now form the centrospheres. In
each centrosphere is an ill-defined reticular centrosome. The spindle-fibres
are undulating, united by anastomoses, and pass continuously from pole to
pole. Outside the spindle is a mantle of equatorial astral rays; these are
closely pressed together and pigmented. The chromosomes lie unevenly in
the equatorial plane.
Fic. 40.—Metaphase. Aceto-chromic preparation. The chromosomes
are split, lying in the equator. To each pair of chromosomes is attached a
pair of special fibre-bundles (‘‘ Zugfasern ’’). The centrospheres are reticular
and contain each a homogeneous lobed centrosome ; inside each of these
the centriole has divided.
482 J. W. JENKINSON.
Fic. 41.—Anaphase. Aceto-chromic preparation. Centrospheres and
centrosomes as in the last, except that the centriole is undivided. The fibre-
bundles attached to the ends of the chromosomes are pulling the latter apart ;
where the point of attachment is subterminal the end of the chromosome is
clearly hooked. The equator is occupied by an achromatic plate, and the
peripheral spindle-fibres clearly turn outwards to become parallel with the
plane of the equator.
NOTES ON THE ANATOMY OF GAZELLETTA. 485
Notes on the Anatomy of Gazelletta.
By
G. Herbert Fowler, B.A., Ph.D., F.Z.S8., F.L.S.
In a recent paper I described, as completely as the state of
preservation of the material would permit, the anatomy of
Planktonetta atlantica, Borgert,! a remarkable type of
Pheodarian Radiolarian. Associated with this species were
some specimens of Gazelletta, probably G. fragilis, named
by Dr. Borgert from broken material obtained by the
National.?, I am obliged to him for permission to publish a
short note upon the main points in which it differs from
Planktonetta. As, however, this organism is even more
fragile, and therefore worse preserved than the former, and
as my specimens were fewer in number, the only excuse for
so incomplete an account lies in the structural novelty of the
interesting family (Medusettida) to which it belongs.
It seems probable that my collection included at least two
species. Of five specimens cut for sections, one had a very
thick body-wall, the others only a comparatively thin wall ;
of the loose bodies found in the material, most are of the
thick-walled type. The anatomical relations seem, however,
to be the same in both cases. Fig. 2 is taken from a speci-
men with a thin capsule; Fig. 1 from one with a thick
gelatinous wall; the latter type appears to have a special
membrane lining the interior, of which no trace could be
detected in the former.
For descriptive purposes, and until a special terminology
1 *Quart., Journ. Mier. Sci.,’ xlvii, 133.
2 ¢ Zool. Jahrbiicher (Abth. Syst. u. s. w.),’ xvi, 570.
484. G. HERBERT FOWLER.
is called for, Gazelletta may be divided into the body
(? = central capsule) and head (=‘‘shell-mouth”’ and arms),
the intra-capsular protoplasm and nucleus lying in the body,
the extra-capsular protoplasm and pheodium in the head.
The body is nearly spherical or ovoid. The body-wall stains
deeply in hematoxylin, is soft and elastic, and shrivels very
greatly in preparation for sections. It seems to me to be
homologous with the central capsule rather than with the
shell of Planktonetta, because it is the only recognisable
membrane in the position of a central capsule, and it shows
no sign of being continuous with the shell-mouth, which is
Aboral
Fic. 1.—Specimen with thick body-wall, and with ten arms, most of
which have been broken; all except the most anterior pair
should lie more or less by the side of the body. Drawn from
the ‘‘ posterior ”’ side; the terminal spines of the arms alone
have been drawn. c.c. Body (central capsule?); m. its internal
lining membrane; 0, alleged opening of the shell-mouth ; p. row
of pores.
undoubtedly skeletal. It is continued as a very thin
membrane over the “oral” surface of the intra-capsular
protoplasm, where it is perforated by the suspensory pro-
cesses and by the bundle of communicating tubes, as in
Planktonetta. These processes and tubes are the only
apparent means by which the body is attached to the
remainder of the organism, but I dare not state positively
NOTES ON THE ANA'TOMY OF GAZELLETTA. 485
that the body-wall is not also continuous with the edge of
the diaphragm, a condition which seemed to be probable in
Planktonetta. The attachment being so slight, one naturally
finds numerous separate heads and bodies, but only a few
specimens in which they are still united; the separation takes
place between diaphragm and central capsule. If one has
Oral
Posterior
Fie. 2.—Diagrammatic section of the central portion of a specimen
with thin body-wall, founded on camera drawings. a. Oblique
sections of arms; ¢. c. body-wall (central capsule?) perforated
above by suspensory processes and by the bundle of communica-
ting tubes between extra- and intra-capsular protoplasm; d.
diaphragm; e. p.7. extra-capsular protoplasm free from phzodial
corpuscles, protruding from under the shell; centrally it shows
portions of the tubes by which it communicates with the
interior of the capsule ; in the remainder of the extra-capsular
protoplasm the pheodial corpuscles and portions of the skeletal
meshwork are diagrammatically indicated ; 7. p. 7. intra-capsular
protoplasm containing the large nucleus ; m. skeletal meshwork
between the arms, which apparently serves for the attachment
of the diaphragm; sf. shell.
either body or head alone before one, it is not possible to
infer the existence of the other part. The intra-capsular
486 G. HERBERT FOWLER.
protoplasm is of the same character as in Planktonetta, but
the suspensory processes are fewer and more slender. The
shell-mouth (to use temporarily the same term as in
Planktonetta) has been figured by Dr. Borgert (op. cit.) ;
having only the head before him, he made the natural
mistake of thinking that the larger opening was oral, the
smaller (if it really exist) aboral; but the reverse is the case,
and his figure is drawn from the “oral” aspect. I am not
convinced that the smaller opening has a real existence, but
I incline to think that in life it is occupied by a thin film of
shell, which disappears in the process of cleaning. If
present, it is certainly not the mouth, as will appear shortly.
Fie. 3.—The central ends of two arms projecting out from under the
protoplasm, showing the skeletal meshwork.
“aboral” opening is closed below by a fibrous
diaphragm; the circumference of this is not inserted into
The large
pits of the shell-mouth, as in Planktonetta, but is apparently
attached to, or continuous with, a skeletal meshwork
developed between the aborally directed arms. Into this
diaphragm are inserted the suspensory processes of the intra-
capsular protoplasm, and it is perforated by the communica-
ting tubes.
The shell-mouth is slightly saddle shaped, the lappets of
the saddle lying right and left of the organism, but its rim
is raised a little anteriorly.’
The arms, according to Dr. Borgert, are 8—10 in number,
in my cleaned specimens 10—13. The anterior pair are
1 In Dr. Borgert’s drawing the right side of the structure is lowest in thie
figure; the ‘anterior ” edge is on the right of the figure.
NOTES ON THE ANATOMY OF GAZELLETTA. 487
directed away from the body, more or less in the long axis
of the organism; most, if notall, of the rest lie at the sides of
the body, directed aborally. Between these aboral arms is
developed a skeletal meshwork (Fig. 3),serving for the attach-
ment of the diaphragm, and to some extent protecting the
body ; it is borne on the spines of the arms, and lies between
them and the body. The general relations of the shell-mouth
are obvious in Figs. 1 and 2, and its finer structure has been
adequately figured by Dr. Borgert.
The extra-capsular protoplasm is less voluminous than
in Planktonetta; but is similarly divisible into (a) a highly
vacuolated portion charged with pheodial corpuscles, lying
mainly posteriorly and laterally, but also present anteriorly
and (b) an anterior protoplasmic mass devoid of pheodium.
This mass, which presumably marks the point of ingestion
and egestion of food, does not approach the alleged smaller
opening of the shell, but projects from under the raised
anterior lip of the saddle-shaped shell-mouth. Through
protoplasm and pheodium runs a fine skeletal meshwork, as
in Planktonetta.
As regards the distribution of these two Medusettids, there
can be no doubt that they were, at the date and place of
capture (extending to nearly three weeks), purely confined
to the upper Mesoplankton, with a centre of distribution at
or somewhat below the 100-fathom horizon. They were
captured as shown in the table.
Open nets, towed at the depth indicated for half to one hour, then hauled
to surface :
In 0 hauls out of 25 = 0 percent. at 0 fathoms.
0) i 12s 0) 5 25F ss
Gn. 5 Te ——ab5 PA 500) 5
ee “ T= 27 i C55
rly a Lea s 10@- 5;
Mesoplankton closing net :
In 4 hauls out of 7 = 77 per cent. at 200 to 100 fathoms.
Ss M4 3 = 33 és o50P 150i";
0 = 3= 0 ne 300 ,, 200,
They occurred in no haul which closed at a greater depth than 200 fathoms.
vou. 48, PART 3.—NEW SERIES. 39
488 G. HERBERT FOWLER.
It will have been apparent that the terms of orientation
used in describing Planktonetta, however suitable there, are
really inapplicable to Gazelletta; nevertheless they have
been used in these notes in order to avoid unnecessary mul-
tiplication of temporary terms. Although it would have
been easy to coin pseudo-classicisms for the various parts,
they would not fit the anatomy of the next Medusettid
described, should it differ as much from these two as they
do from one another. What really is the shell-mouth in
Planktonetta, i. e. a ring round the point of ingestion, is in
Gazelletta a shell-cap over the extra-capsular protoplasm ;
the body-shell of Planktonetta is (apparently) not repre-
sented in Gazelletta; and the terms “oral,” “aboral,”’
“anterior,” ‘ posterior,” will probably have to be altered as
our knowledge of the family increases. The fixed point in
both seems to be the bundle of connecting tubes. At present
it appears likely that the intrinsic shell is what I have termed
the shell-mouth; this may cover (Gazelletta) or encircle
(Planktonetta) the point of ingestion; it may also be con-
tinued aborally so as to surround the central capsule (Plank-
tonetta). The float of Planktonetta is doubtless a subsidiary
structure, as it is only attached by the spines and meshwork
to the central shell.
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CONTENTS OF No. 192.—New Series.
MEMOIRS:
PAGE
On the Maiotic Phase (Reduction Divisions) in Animals and Plants.
By J. Brettanp Farmer, D.Sc., F.R.S., and J. E. 8S. Moorg,
A.R.C.S., F.L.8. (With Plates 34—41) ; , : : . 489
On the Structure and Development of the Somatic and Heterotype
Chromosomes of Tradescantia Virginica. By J. B. Farmer,
F.R.S., and Dorotuy Suove. (With Plates 42 and 43) : .- 009
On the Behaviour of the Nucleolus in the Spermatogenesis of Peri-
planeta Americana. By J. EH. S. Moors, A.R.C.S., F.L.S., and
L. E. Rosiyson, A.R.C.S., from the Biological Laboratory, Royal
College of Science, London. (With Plates 44 and 45). : > ae
On some Movements and Reactions of Hydra. By Groner WaGNER,
M.A., Instructor in Zoology, University of Wisconsin . = . 585
Witnu Titte, Contents, aND JNDEX TO VoL. 48.
THE MAIOTIC PHASE IN ANIMALS AND PLAN'S, 489
On the Maiotic Phase (Reduction Divisions) in
Animals and Plants.
By
J. Bretland Farmer, D.Sc., F.R.S.,
AND
J. E. S&S. Moore, A.R.C.8S., F.L.S.
With Plates 34—41.
INTRODUCTION.
‘We think it desirable, in the interests of clearness, to explain
the meaning of the nomenclature that is employed in this
memoir in connection with the “ reduction ” divisions.
We propose to apply the terms Maiosis or Maiotic
phase® to cover the whole series of nuclear changes included
in the two divisions that were designated as Heterotype and
Homotype by Flemming.
Our reason for introducing this terminology is in order to
emphasise the fact that these two mitoses invariably con-
stitute a perfectly definite and recognisable phase, and one
which is normally intercalated in the cellular life-cycle of ail
metazoa and metaphyta in which the sexual union of gametes
takes place.
The actual point in the life-history at which the maiotic
phase may occur is not identical in every organism, and it is
1 This paper contains the evidence on which our preliminary communication
to the Royal Society in May, 1903, was based. Its earlier publication has
been delayed by the pressure of other work.
2 peiworc, reduction ; petwrexéc, that which is reduced.
vou, 48, part 4.—NEW SERIES. 36
4.90 J. BREI'LAND FARMER AND J. HE. S. MOORE.
only the essential details within the phase itself that admit of
complete comparison in the case of some of the more widely
sundered groups—such, for example, as animals and plants
respectively.
On the one hand, in the metazoa the divisions included in
the maiotic phase invariably lead directly to the formation of
the sexual cells. In plants, on the other hand, not only is
the position of the phase far more variable, but it never
culminates, so far as is known, directly in the production of
sexual cells. The latter are only formed after a greater or
less number of intervening (post-maiotic) divisions have been
passed through.
It is evident, then, that we may group the cells that are
produced in the life cycle of an animal or plant into three
categories, viz. Premaiotic, Maiotic, and Post-Maiotic re-
spectively. The convenience of this classification will at once
be obvious. Thus in animals there are (normally) no post-
maiotic divisions, whereas in plants there may be, and often
are, a large number. In a fern, for example, the whole
prothallial generation consists of post-maiotic cells, and it
thus becomes clear that there exists no necessarily direct
relation between the maiotic divisions and the differentiation
of the sexual cells or gametes.
Referring to the terms in common use, viz. “heterotype,”’
“homotype,” and “synapsis,” we employ these as descriptive of
incidents that invariably are present in the maiotic phase.
The word “heterotype”’ is applied to the first mitosis as it was
originally used by Flemming, and the synapsis represents
that series of events which are concerned in causing the tem-
porary union in pairs of pre-maiotic chromosomes, previously
to their transverse separation and distribution, in their
entirety, between two daughter nuclei. We restrict the term
“homotype”’ to signify the second division in the maiotic phase,
instead of extending it, as some writers have done in the case
of plants, to include all post-maiotic mitoses.
Thus the scheme of the cellular life cycle in any animal or
plant may be represented as follows:
THE MAIOTIC PHASE IN ANIMALS AND PLANTS, 491
Pxe-marotic PHASE, Matotic PHAsE. Post-MAtoTic Puase.
Occurs in animals and Occurs in animals and Occurs in plants (game-
plants, and begins with plants. tophyte of the higher
the development of the forms). Normally ab-
fertilised ovum. sent in animals.
We further suggest the desirability of using definite terms
in order to express and describe the diverse aspects pre-
sented by different classes of mitoses in a given animal or
plant ; and since in any cellular life cycle all the pre-maiotic
and post-maiotic, as well as one of the two maiotic, divi-
sions are essentially characterised by the longitudinal
splitting of the mature chromosomes, these might, for
descriptive purposes, be termed Anaschistic mitoses.
Sinilarly, inasmuch as the characteristic feature of the other
of the two maiotic divisions (usually, if not always, the first)
is transverse as regards the mature bivalent chromosomes
this division might be designated as Diaschistic.
As regards the words “heterotype” and “homotype,” they
are not really necessary if our term of maiosis be accepted.
They could more simply be designated as the first and second
maiotic divisions respectively. But inasmuch as they are so
well understood, and so widely adopted, we have continued
to use them in the sense as already defined.
The series of phenomena that for convenience may be in-
cluded under the terms of “ regeneration,” “variation,” and
“heredity” have gradually come to be more clearly apprehended
as resolving themselves into cell-problems. And in reflecting
on the results of modern cytological investigations in this
connection, it is impossible to escape the idea that in some
way or other the nuclear chromosomes of an organism must
be intimately related with the structural characters by which
it is distinguished. The intricate sequence of changes under-
gone by the chromosomes during the phases of a nuclear divi-
sion, coupled with the surprising degree of similarity betrayed
in these respects between the cells of plants on the one hand
and of animals on the other, renders it impossible to avoid the
conclusion that a fundamental significance lies behind the
492 J. BRETLAND FARMER AND J. E. 8. MOORE.
structural features that reappear at each division of the
nucleus.
Again, the regular recurrence of a numerical reduction of
the chromosomes in the maiotic phase, which is intercalated
once in every normal life cycle, emphasises the importance of
these bodies in a still higher degree. But although it
becomes obvious that in the details of maiosis we may reason-
ably expect to find an important clue as to the nature of that
relation which must exist between the chromosomes and the
essential features of ontogeny, opinions are still much divided
on matters of cardinal importance connected with the
process.
As is well known, two conflicting classes of interpretation
have been advanced to account for the phenomena witnessed
during the maiotic divisions. The divergence of opinion is
largely due to the extreme difficulty of disentangling the true
sequence of the events that are proceeding in the intricate
series of changes that constitute the mitoses in question.
The view that may first be briefly summarised is one
which has found much favour, and especially with zoologists.
Weismann long ago insisted on the theoretical necessity of a
reduction division in connection with his views as to the re-
lation of ancestral characters with material primordia. The
investigations of Hacker, Riickert, and others gave a welcome
support to Weismann’s views, and seemed to prove that they
accorded with actual facts. They showed, in the animals in-
vestigated by them, that during the prophase of the hetero-
type mitosis the spireme thread, instead of giving rise to the
full number of chromosomes characteristic of the preceding
cell-nuclei, only formed one half the number of these bodies.
Each chromosome was therefore regarded as bivalent, and as
consisting of two monovalent chromosomes of preceding nuclear
generations. ‘The two individuals constituting a bivalent
chromosome were considered as being attached end to end.
Furthermore, the entire bivalent chromosome suffered longi-
tudinal fission, and the question to be decided hes in the
exact determination of the method by which the daughter
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 493
chromosomes of the heterotype and homotype mitoses respec-
tively are provided for.
Hacker considered that during the heterotype division the
longitudinal halves of each bivalent chromosome were
separated, exactly as happens during an ordinary mitosis. At
the second (homotype) division, however, each chromosome
(which is still bivalent) splits transversely into its mono-
valent individuals, and in this way is provided the mechanism
of reduction postulated by Weismann. Riickert and others
have sounded a less certain note as to the particular mitosis
during which reduction is effected. They admit that it may
occur in the heterotype mitosis. Now, if either of these two
slightly differing views as to the general significance of the
heterotype and homotype mitoses prove to be generally true,
it is clear, in the first place, that the opinion of those who
hold that the chromosomes are to be regarded as permanent
and persistent entities gains a strong, if somewhat indirect,
support. For the significance of the numerical reduction is
clearly related to the restoration of the full number of chromo-
somesat the next succeeding fertilisation. And on the view just
outlined above, reduction involves no loss of individuality, for
it is effected by the migration of half the entire number of
somatic (or pre-maiotic) chromosomes to each of the two
daughter nuclei respectively.
The second view, which has been largely entertained by
botanists and by some zoologists, explained the processes
differently. During the later stages of prophase of the
heterotype mitosis, an appearance strongly suggestive of a
second longitudinal fission of the chromosomes may often be
observed. This was believed to provide for the division of
these bodies in both the heterotype and homotype mitosis.
In each of these, then, the mode of chromosome distribution
would be similar, and it would resemble in all essential
respects the process as it occurs in an ordinary somatic
division. And furthermore every precaution would seem to
have been taken, during the prophase of the heterotype
mitosis, to secure the utmost degree of similarity between the
494, J. BRETLAND FARMER AND J. E. 8S. MOORE.
chromosomes of each of the four nuclei that result from the
two maiotic divisions.
But such an interpretation involves important conclusions,
not only as to the nature of reduction, but also as to the kind
of importance to be attached to the chromosomes themselves.
For if it be really valid, it becomes impossible to consistently
retain a belief in the permanence of the chromosomes from
one life-cycle to another. It is obvious that if their number
is thus periodically reduced to one half, and if the resulting
chromatic elements are distributed to the daughter nuclei
solely after duplication by means of longitudinal fission, the
individual chromosomes that arise during the maiotic phase
could not possibly correspond to any that existed in the
nuclei of the cells previous to the incidence of this phase of
reduction. The only hypothesis consistent with such a
view would demand the previous longitudinal fusion in
pairs of the original chromosomes, a view that has not been
seriously held by any who have maintained the existence of
two longitudinal fissions during the heterotype prophase.
Hence it would follow that during the prophase of the
heterotype mitosis the chromosomes for the next generation
must, so to speak, be formed afresh. ‘That is, they are entirely
reconstituted—out of the original matter perhaps, but with a
complete rearrangement of substance that would preclude any
idea of continuity in their organisation. And this is equiva-
lent to a denial of the permanence of the chromosomes from
one generation to another.
Such a view does not, of course, necessarily involve a
similar denial of the equivalence of the somatic chromosomes,
in which there is no numerical reduction, but it relegates the
whole question to a position of subordinate importance. It is
obvious that such a result must profoundly affect any con-
ceptions as to the nature of the relation that may be supposed
to exist between the chromosomes and the mechanism of
heredity. For if the inherited and other qualities of an
organism are to be associated in any way with the chromo-
somes, and if these structures have no persistent organisation
THE MAIOTIC PHASE IN ANIMALS AND PLAN'S. 495
of their own, the supposed relation can at best be dynamical,
depending on the chromosome substance as a whole
rather than on that of the individual units. No doubt the
connection of the nuclei with the specific organisation of the
cell—or of the cell aggregates—is, in the last resort, almost
certainly of this nature; but the whole problem turns on the
question as to whether the discrete particles (chromo-
somes) are endowed with different activites, or whether
each of them merely acts as a portion of a homogeneous
whole.
Many a priori considerations appear to be opposed to
the latter view, and seem strongly to point to a difference
between the different chromosomes, each of which, by itself
or in combination with others, can produce a definite effect in
directing or influencing the latent activities present in the
nucleus or the cell. ‘he complex series of events during a
normal somatic mitosis whereby an exact longitudinal
division of the chromosome material is effected has often been
commented on, and it is difficult to comprehend why longi-
tudinal fission should be so invariable a rule in normal differ-
entiating body cells, unless there is an individuality possessed
by the chromosomes themselves—an individuality that would
manifest itself in retaining or modifying the specific traits
distinctive of the organism. Again, the remarkable constancy
of numbers, especially in the reproductive tissues, fails to
find any satisfactory explanation.
It is true that some, like O. Hertwig, have regarded
equality of mass as the essential advantage secured by longi-
tudinal fission, but this standpoint, from the point of view of
the facts of ontogeny, seems an unsatisfactory one. ‘The
celerity with which two cells of common parentage may pro-
ceed to differ, in spite of the equivalence of their nuciear
mass at the instant of their genesis, coupled with the rapidity
with which nuclei may grow or diminish in size, are difficult
facts to reckon with when regarded from this, comparatively
speaking, simple standpoint. The results of experiments on
regeneration of embryos and missing portions of older
496 J. BRETLAND FARMER AND J. EK. S. MOORE.
organisms emphasise the importance of constituents,
rather than of the substance regarded as a whole.
Again, the interesting results obtained by Boveri and others
during a study of the effects of polyspermy, and the analysis
of the subsequent behaviour of the supernumerary chromo-
somes in relation to abnormalities, further emphasise the
individual importance of each of these structures, and tend
to show that normal organisation depends, inter alia, ona
normal grouping of chromosomes, and not on the presence
of a mere normal amount of chromosomic substance.
Furthermore, a considerable weight of evidence has accu-
mulated within recent years that renders it difficult to dis-
sociate the facts of heredity from an admission of the
existence of discrete particles that are, individually or collec-
tively, responsible for the appearance of those particular traits
that characterise one organism and separate it from others.
Investigations on the behaviour of hybrids militate strongly
against the assumption that during fertilisation any real
fusion of the parental substances responsible for the expres-
sion of particular features occurs.
To avoid possible misconception, however, we may as well
state expressly that in thus formulating the problem as it
presents itself to our own minds, we are far from supposing
that the “hereditary substance” may not operate cor-
relatively, so as to become responsible for the production of
groups of characters. But admitting that the chromosomes
really possess the sort of importance usually assigned (on
good grounds, as we think) to them, we fail to understand
how a mixture, amounting really to complete fusion, of such
hereditary substances can produce the opserved appearances.
How, for example, could one account for the segregation of
ancestral characters in inter-breeding hybrids, if the indi-
viduality of the original chromosomes becomes really obliter-
ated during each generation? But, on the other hand, as
Weismann long ago pointed out, it is impossible to continue
indefinitely to accumulate the primordia (anlagen) of cha-
racters, as they are doubled at each act of fertilisation,
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 497
within a limited and approximately constant mass of sub-
stance. Hence if we admit that the chromosomes divide
longitudinally (anaschistically) throughout the maiotic, as in
the somatic, cell generations, we are confronted with the
following difficulties :
1. The reduced chromosomes cannot continue to be com-
pounded of the antecedent premaiotic chromosomes and at
the same time preserve their organisation unchanged. They
must each represent a new structure. Why, then, under these
circumstances do they appear strictly as half the number
characteristic of the preceding nuclei? Jor if the equal
division of the mass be the essential feature, there would
seem to be no specific reason for constancy in respect of
number.
2. If chromosomes arise de novo from the substance of the
previous ones that have now lost their identity, the only
result must be a mingling of substance, but no retention
of organisation. But such a mingling cannot be simply
of the nature of a mixture. It is more akin to the produc-
tion of a new chemical combination at each reduction, since
the parental masses of nuclear substance can scarcely be
supposed to be absolutely identical, especially in the case of
hybrids. But it is just in hybrids that we meet perhaps the
strongest evidence in favour of the continued existence of
the primordia as attached to discrete particles retaining their
individuality, for how could the remarkable numerical re-
lationships of dominants and recessives be otherwise main-
tained ?
The difficulties briefly sketched above seem to render
the existence of a double longitudinal fission during the
mitoses in question not only inherently improbable but im-
possible to reconcile with the facts so strongly pointing to
the important influence exerted by the separate chromosomes
in controlling and determinating the organisation of an indi-
vidual plant or animal.
Moreover, such a mode of fission, with the consequences
that accrue from it, would afford no satisfactory explanation
498 J. BRETLAND FARMER AND J. FE. S. MOORE.
of the series of changes that so constantly recur in the
heterotype and homotype mitoses of animals and plants. For
itis not apparent why the mere halving of the numbers
should lead to events so peculiar and characteristic as are
those prevailing during these divisions. It is, therefore,
doubtful whether Hertwig’s suggestion that the intrinsic im-
portance of the two mitoses lies in the consecutive and sudden
reduction of the chromatin to one fourth of its original mass,
can be accepted, seeing that, in some cases at any rate, a lapse
of no inconsiderable time may intervene between the termina-
tion of the heterotype and the onset of the homotype mitosis.
In short, the assumption of a double longitudinal fission as
constituting the essential mode of division not only fails to
explain difficulties arising out of comparative observations, but
it raises others of a serious kind which are opposed to both
observation and theory.
But in spite of the difficulties inherent in it, the view we
have just discussed has been widely adopted as that most in
conformity with the best observations. It appeared to have
rested on a solid foundation, for example, in the special case
of Ascaris, the spermatogenesis of which was carefully worked
out by Brauer. Flemming and, more recently, Meves have
repeatedly insisted on the absence of any appearance that
could be conclusively interpreted in the sense of a transverse
separation of entire chromosomes in the Salamander. We,
ourselves, formerly shared the same opinion. But when one
proceeds to critically examine the evidence on which it is
founded, it becomes clear that, with very few exceptions, there
are lacunee in the descriptions. ‘hese omissions are noted to
refer to identical stages, both in animals and in plants. Hvery-
one may have carefully observed the early stages of prophase,
but one constantly discovers that the description and figures
hurry on tothe later stages, in which the definite chromosomes
can be fully identified. The intermediate steps are missed
out, and this is due to the great difficulty which they present
in the way of satisfactory fixing and subsequent observation
and elucidation.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 499
Thus much of the existing divergence of opinion relates to
the interpretation to be placed on these later stages, although
these cannot really be understood save by the study of an
unbroken series. Naturally the omission was not intentional.
But the later stages seemed to fit so well on to the earlier,
that the necessity for special caution as regards the inter-
vening ones was not apparent.
Speaking broadly, the longitudinal fission of the spireme (or
its representative) has been very generally recognised, but the
phase which has next attracted the largest share of attention
has been that in which the chromosomes are becoming
definitely segregated previously to the assumption by them
of their mature form and their final congregation on the
spindle.
With the hiatus that intervenes between these two phases
we are not now concerned, as it forms the main part of the
observations recorded in the body of this memoir, but we may
briefly glance at some of the interpretations that have been
put on the structure of the heterotype chromosomes themselves.
In the case of salamander and lily, as examples of an
animal and plant respectively, the definite heterotype chromo-
somes exhibit the forms of rings, loops open at one end with
the sides more or less twisted round each other, and finally,
especially in the lily, of rods, lying either parallel or twisted
round each other. ‘These figures were easily referable to, and
were supposed to be derived from, the split spireme thread
by its transverse segmentation, and the more or less intimate
union of the ends of the parallel halves of the transversely
isolated segments with each other. Within the last ten years
an increasingly large number of examples have been dis-
covered in which the two “longitudinal halves” of each
heterotype chromosome were observed to show signs of a
fission, and this has been commonly interpreted as the second
longitudinal fission preparatory to the further division of the
chromosomes in the next succeeding (homotype) mitosis.
In another series of examples, of which Arthropoda
(Riickert, Hacker, and others) and ferns (Calkins) may be
500 J. BRETLAND FARMER AND J. E. 8S. MOORE.
cited as examples, the processes seemed easier to interpret
in another sense. ‘The chromosomes appear as tetrad-like
bodies, which separate as pairs of dyads in the heterotype,
whilst in the homotype mitosis each dyad further divides into
monads, which are thus distributed between the daughter
nuclei at this (second) division.
It has been often maintained that these appearances
indicate a true sorting of somatic chromosomes, i.e. is a
qualitative reduction in Weismann’s sense. The tetrads are
admitted to have arisen as the result of a longitudinal, asso-
ciated with a transverse, fission of the substance of the
chromosome, each of the latter thus being a bivalent (Hicker)
structure, and representing a pair of adherent longitudinally
split somatic chromosomes.
One of the most important memoirs on this subject of
reduction is that by Korschelt! on Ophryotrocha. He
maintained that in the heterotype prophase the full somatic
number of chromosomes appeared, and that these sub-
sequently fused in pairs to form the reduced number. During
the metaphase they again became separated from each other
‘and distributed to the daughter nuclei, and thus the first
(heterotype) mitosis was clearly a qualitative one. Korschelt’s
observations did not fall very well into line with the process
as described for other forms by other investigators, and
Wilson, in his work on the cell, comments on the isolated
nature of the results. But our own observations, extending
over a wide range of forms, of which a brief abstract has
already appeared (1903), as well as the more recent results
obtained by Strasburger (1904), show that Korschelt’s results,
obtained in Ophryotrocha, are susceptible of a much wider
application.
In 1895 a paper was published by H. H. Dixon,? in which
he suggested the existence of a reduction division arising by
the distribution of the equivalents of entire chromosomes, but
1 Korschelt, ‘Ueber Kerntheilung, Eireifung, und Befruchtung bei
Ophryotrocha puerilis,” ‘ Zeitschr. fiir Wiss. Zool.,’ Ix.
2 ¢Proc. Roy. Ir. Acad.,’ ili.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 501
his account failed to carry conviction because it was evident
that he had either misinterpreted the longitudinal fission
(which does actually exist) as due, not to fission, but to the
lateral approximation of distinct parts of the spireme thread,
or else he overlooked the fission altogether, confusing it with
that approximation which really does occur at the later
stage. To judge from his figures, the former alternative
appears to express the real explanation of his results.
Schaffner! in his investigations on Lilium philadelphicum
undoubtedly gave a correct explanation, in all important
respects, of the sequence of events so far as the reduction
divisions of this plant are concerned. His results, however,
did not meet with the reception they merited because
they were overshadowed by statements respecting centro-
somes which were in contradiction with the positive results
of all the most careful work of that time.
Atkinson,* in a paper on the reduction divisions in
Arisema and Trillium published in 1899, stated that
the reduction was qualitative, i. e. essentially consisted in
the transverse division of bivalent chromosomes. But he
suggested that in the former plant the process was accom-
plished during the heterotype, whilst in Trillium it occurred
during the homotype, mitosis. We have had the opportunity,
through the kindness of Professor Atkinson, of examining
some of his slides illustrating each of these plants, and we
are quite in agreement with him as far as Arisema is con-
cerned. With respect to Trillium, however, the material
at our disposal did not enable us to reach a definite conclusion ;
but we are strongly inclined to think that in this plant also
the qualitative division is accomplished during the hetero-
type mitosis, and we are strengthened in this by a study
of the excellent series of figures given by Ernst® in his
memoir dealing with Trillium and Paris. The appear-
ances are essentially similar to those met with in Lilium; and
' « Bot. Gazette,’ vol. xxiii.
2 Tbid., vol. xxviii.
3 Ernst, ‘ Flora,’ Bd. xci.
502 J. BRETLAND FARMER AND J. E. 8S. MOORE.
though Ernst himself decides in favour of a double longi-
tudinal fission, we feel but little doubt that a renewed investi-
gation will show that the chromosomes are really bivalent.
An inspection of Fig. 5, Pl. 34, of his memoir strongly supports
this suspicion.
Montgomery,! in a series of papers of which the most
important appeared last year, describes a state of things for
the amphibia investigated by him which is in complete
accord with the conclusions arrived at by ourselves. We
were unaware of his investigations when our preliminary note
was published, and his paper only came into our hands after-
wards. It is gratifying, however, to find that another in-
vestigator, working quite independently, had arrived at
conclusions precisely similar to those which our own extended
series of researches on critical examples, both of animals and
plants, had led us to adopt as a general interpretation of the
phenomena of reduction. More recently, Williams, in working
out the cytology of the reproductive cells in Dictyota, and
also Gregory, who has investigated the genesis of the spores
of a number of ferns, have each arrived at results that are
concordant with those put forward by us in the paper already
referred to.
In a recent paper by Jules Berghs,? an attempt is made
to sustain the older view for the cases of Allium fistulosum
and Lilium lancifolium. We have ourselves examined
the latter plant, and we are quite unable to concur with
M. Berghs’ conclusions. We readily agree with him that it
is entirely a “question de sériation,” but we cannot
agree with him that it is possible, at any rate except in most
exceptional cases, in one anther lobe to obtain anything
approaching to complete sériation of the stages to be found
in a single loculus. It is indeed just to his assumption of
such a possibility that we attribute M. Berghs’ error of inter-
1 Montgomery, “The Heterotype Mitosis in Amphibia and its General
Significance,” ‘ Biol. Bull.,’ iv, 1903.
2 Berghs, J., “La Formation des Chromosomes Heéterotypiques dans la
Sporogénése Végétale,” ‘La Cellule,’ t. xxi.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 503
pretation. A simple inspection of the figures that accompany
and illustrate his paper suffices to show that the very stages
that we regard as of critical importance are lacking. More-
over, his drawings do not carry conviction. They are either
very schematic, or else they are based on preparations in
which all the finer details of structure have been inadequately
preserved. And finally, in the text, he gives no evidence of
having paid special attention to the admittedly difficult stages
which alone contain the solution of the problem.
As long ago as 1894 Belajeff, in a paper published in
‘Flora,’ on [ris and Larix, maintained that a true reduc-
tion occurred in these plants. But he was led, by the
emphasis laid by him on the figures exhibited during the
later stages of the process, to attribute the real reduction
(qualitative) to the homotype mitosis, just as some of the
Freiburg investigators had done. Strasburger and others
have since shown this position to be untenable, and the con-
viction has slowly grown up that the second (homotype)
mitosis—in plants, at any rate—is certainly associated with a
longitudinal fission, and not with a transverse or qualitative
distribution.
As these lines are being written we have received from
Professor Strasburger! a memoir dealing with reduction
divisions. The results are in substantial agreement with
those contained in our previous communication, and which
are here presented in an amplified form. The case of
Galtonia, as described by Strasburger,” is especially in-
1 Strasburger, E., ‘‘ Ueber Reductions Theilung.,” ‘ Sitz. ber. d. K. Preus.
Akad. d. Wiss.,’ 24 Marz, 1904.
? We note on p. 6 of the separate copy that the author seems perhaps to
have not quite understood onr position,as taken up in the preliminary note read
before the Royal Society. The closed rings (geschlossene schleifen) were
described by us being most common, but our diagrammatic fig. 4, in the note
referred to, shows clearly one bivalent chromosome with both ends free, which
proves we had not overlooked these cases. The regularity of the loops is
much greater in animals than in plants, hence perhaps the emphasis that was
put upon these figures in the note, which had very briefly to indicate the
general results of the investigation as a whole rather than to discuss details.
504 J. BRETLAND FARMER AND J. E. S. MOORE.
teresting, since it puts the facts of reduction for this plant
in a light as diagrammatic as Korschelts’ investigations had
already done for Ophryotrocha.
Perhaps one may venture to suggest that the Arthropoda,
and other forms, in which the transverse division has been
assigned to the homotype mitosis (Hicker and others) are
worth re-examination from the new point of view. It must
be remembered that the location of the transverse plane of
separation in a symmetrical tetrad is not an easy matter ; and
the assertion that, in the heterotype mitosis, it les in the
longitudinal axis of the spindle, can only be maintained pro-
vided it can be shown that the developing chromosome
retains its primary orientation unchanged from the time at
which the transverse and longitudinal planes could be dis-
tinguished. Otherwise some unaltering mark is required to
enable the observer to fix the planes in some other way. The
difficulty of deciding as to the particular plane affected is at
once rendered obvious on reflecting how the remarkable
movements of the chromosomes themselves, just prior to
their congregation on the spindle, may affect their ultimate
orientation.
We have made no pretence, in this brief introduction, of
dealing exhaustively with the immense mass of literature that
has grown up around the problems connected with reduction.
That formed no part of our task. We desired merely to
indicate some of the principal trends of opinion in these
matters, and to point out that it is plainly desirable to ascer-
tain whether or no some reconciliation between the various
conflicting views may not be possible. [or when one reflects
on the widespread occurrence of the phenomena in question,
extending as it does to all the metaphyta and metazoa (if we
exclude certain suggestive cases of parthenogenesis) it is
clear that we are in the face of a fact of fundamental im-
portance, whatever its true significance may ultimately turn
out to be. And furthermore, our own comparative studies of
karyokinesis in plants and animals, extending over many
years, have impressed us with the remarkable similarities
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 505
that characterise the reduction divisions in the representatives
of both kingdoms alike. We are convinced that it is highly
improbable that these obvious similarities mask any funda-
mentally important differences.
The extreme orderliness to be observed in the whole pro-
cess strongly suggests that in both kingdoms the true
sequence and the actual nature of the processes involved
will turn out to be identical. Otherwise the very orderliness
of the process finds no meaning. And if it be true, as we
believe it to be, that we can gauge the importance of phe-
nomena in the organic world by the regularity of their
appearance and procedure, then it would be difficult to dis-
cover any instance that more amply fulfils the required con-
dition than do these complex series of changes involved in an
ordinary nuclear division, as well as the no less remarkable
and constant deviations from it that characterise the hetero-
type mitosis.
The results of our investigations, set forth in the following
pages, have been such as to convince us that so far as
metazoa and metaphyte are concerned, a real similarity
between the process of reduction, as it occurs in animals and
plants, does obtain. |
The reduction is achieved by the association or by the
non-separation of somatic pairs of chromosomes during the
heterotype prophase.
The heterotype mitosis essentially consists in the separa-
tion and distribution between the daughter nuclei of entire
somatic chromosomes, the separate identity of which is
masked by their temporary union previously to the onset
of the diaster, and thus the exact numerical reduction is
accounted for.
The homotype mitosis is associated with the completion of
the longitudinal division of the chromosomes already incepted
during the prophase of the heterotype division.
If (as in many plants) there be post-heterotype cell genera-
tions, the reduced number of chromosomes is retained until
the occurrence of nuclear union at fertilisation.
voL. 48, PART 4,—NEW SERIES. 37
506 J. BRETLAND FARMER AND J. E. S. MOORE.
DETAILED Description oF TyprcAL ExAMPLES oF ANIMALS AND
PLANTS INVESTIGATED.
I, Lilium Candidum.
The development of the spores in different species of lilies
has so often served as the subject of investigation that it
might seem but slightly probable that any fact of material
importance still remained generally unknown. It has already,
however, been remarked that divergent views as to the course
of events during the heterotype and homotype mitoses in
these plants have been advanced, and the matter cannot, there-
fore, be regarded as yet to be conclusively settled. Whilst
the majority of observers hold that a longitudinal division of
the chromosomes obtains in both the homotype and the hetero-
type mitoses, Schaffner! has adduced evidence in support of
a “reducing” (i.e. transverse) division occurring in the
heterotype, whilst Dixon? has considered that this was
achieved during the homotype division.
The principal evidence relied on by those who advocated
the existence of a longitudinal fission in each mitosis has been
the supposed proof of the existence of a double fission during
the late prophase stages in the heterotype. ‘he more recent
work of Grégoire and others appear to show conclusively that
at any rate the homotype mitosis does not, in hlies, effect a
transverse separation of chromosomes, but merely consummates
a longitudinal fission already incepted during the early stages
of the preceding mitosis.
We have also studied the homotype division in lilies
afresh ; and whilst in certain points our views diverge from
those held by most other investigators, we still consider that
the most important features of this mitosis consist essentially
in the separation and subsequent distribution to opposite
poles of equivalent halves of the chromosomes, and that these
equivalent halves had already been marked out and defined
1 «Bot. Gazette,’ Joc. cit.
2 *Proc. Roy. Ir. Acad.,’ iii.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 507
during the earlier stages of the preceding (heterotype)
mitosis.
When one turns to the first maiotic (heterotype) division
itself, the case is widely different, and it is a singular as well
as a somewhat unfortunate circumstance that a genus offering
such special difficulties in the way of correct interpretation of
the sequence of changes should have been so constantly and
often exclusively studied by those who have generalised on
the events that obtain during the course of the mitosis in
question. For even in a single anther the temptation to
regard the series as therein presented as representing a trans-
itional series of phases has misled some writers. It very
seldom happens that any such a complete series that embraces
the critical, but transient, phases can really be so traced ; and,
moreover, some of these important phases are often not easy
to fix satisfactorily, perhaps just on account of their changing
character.
As the result of an examination of a very long series of
preparations, illustrating the processes in a number of species,
we have been irresistibly driven to the conclusion that the
evidence for the existence of a transverse (reducing) division
during the heterotype mitosis is irrefragible, and we think we
are in a position to explain the sources of the more important
differences of opinion expressed by others who have worked
on these plants.
At the conclusion of the last archesporial division of the
sporogenous tissue the nucleus goes into a state of almost
complete rest. The chromatin exists as scattered granules,
though here and there a thread-like arrangement can be seen
(Pl. 34, fig. 1). The great bulk of the staining matter in
the nucleus is, however, concentrated in the nucleolus, of
which there may be one or more in each nucleus. As yet the
archesporial cells are closely coherent, but as they increase
in size intercellular spaces begin to appear at the angles
where several cells meet. About the same time the linin
becomes more chromatic, and in the majority of cases the
general impression is conveyed that this increase in chromatin
508 J. BRETLAND FARMER AND J. FE. S. MOORE.
is connected with changes in the nucleoli. The linin frame-
work becomes more and more clear, but at first it is impossible
to make ont in it anything suggesting a continuous thread.
Rather it appears as a large number of fibrils irregularly
arranged in groups (fig. 1). Attempts were made, though
without decisive results, to ascertain whether the number
of these groups bore any definite relation to the number
of chromosomes. In some cases there appeared to be such
a correspondence. The outline of the individual linin fila-
ments is irregular, and staining droplets of a chromatin-like
substance, possibly of nucleolar origin, are often found
adhering to them. Perhaps this substance may be regarded
as equivalent to the “ basichromatin ” of some authors.’ The
general appearance exhibited by the nucleus at this stage is
that of a sphere containing, besides the more or less numerous
nucleoli, a grumous precipitate which tends to become
agoregated in delicate fibrils.
From these fibrils the linin spireme arises. It appears, in
uninjured nuclei, to form a continuous thread, although it is
difficult, owing to the numerous convolutions of the skein, to be
quite certain of this. It is of course impossible, save from the
continuity of stainable substance, to form any valid judgment
as to the nature of the spireme as to whether it is continuous
or otherwise, and it may be that the appearance of isolated
fibrils in the previous stage is really due to lack of equidistance
in the arrangement of the chromatin. In other words, it
may be that a continuous thread of linin does really exist in
this earlier stage, although we have not been able to identify
it as such, and for the present do not feel disposed to
assume more than the appearance observed seems to warrant.
Perhaps the matter is not one of great importance, for it is
at any rate certain that at the close of the previous di aster
no such continuous filament was present.
But the definite spireme thread can be distinguished very
clearly at an early period in karyokinetic activity, certainly
long before the spore mother-cells dissolve their union with
* Heidenhain, ‘ Ueber Kern and Protoplasma,’ 1893.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 509
each other. It forms a colourless thread, at first infiltrated
with chromatin throughout, but the latter soon collects into
serial beads so as to give rise to the well-known alternation of
stainable (chromatin) and non-staining (linin) discs. The
numerous small nucleoli previously seen have disappeared
and become replaced by one or more relatively large ones.
At first irregularly coiled in the nucleus, the differentiating
spireme next aggregates towards one side, and there
forms what we may designate as ‘the first contraction
figure” (Fig. 2). The thread becomes densely coiled in the
vicinity of the nucleolus, exhibiting a highly characteristic
arrangement. This figure has often been dismissed as the
result of imperfect fixation, but there exists strong evidence
to show that it represents a normal occurrence in the life
history of these cells. Miss Sargant states she has observed
it in the living spore mother-cells of lies, and we have
not unfrequently seen it in the corresponding cells of
Tradescantia, Osmunda, and several Liverworts, as
well as in some animal spermatocytes. It is a style that
persists for some time, but as it passes away the filament
again becomes more loosely coiled and diffused, especially
about the periphery of the nuclear cavity. It is perhaps a
fact of some significance that the nucleus at this stage is
relatively large, the average diameter in the case of pollen-
mother-cells of Lilium candidum being 32, as com-
pared with diameter 29 w reached by the nuclei at the con-
traction-figure stage just described.
A certain degree of polarity is observed to characterise the
spireme thread as a whole at this stage, for the convolutions
are absent from, or at least scarce in, one region of the
nucleus, and this seems to be related to the emergence from
the stage of contraction. ‘The region of comparative freedom
trom convolution is about diametrically opposite to the spot
at which the aggregation previously had occurred.
The longitudinal fission of the thread is now to be seen
(figs. 3,4). At first the beads or discs of chromatin lengthen
out somewhat in the plane of cross-section of the thread ;
510 J. BRETLAND FARMER AND J. E. S. MOORE.
then they are seen to be furrowed and to assume a dumb-bell-
shaped appearance. Finally the halves of each bead separate
from one another and come to lie in two parallel rows at the
edges of the flattened spireme ribbon.
The ribbon itself next splits longitudinally. The fission is
irregular, especially at first, and it merely forms open loops,
closed at either end where the ribbon has not yet split. But
later on it becomes much more complete and the halves
proceed to divaricate (Fig. 5) more or less considerably from
-each other. This fission has been more or less clearly recog-
nised as such by most writers who have investigated lilies, with
the exception of Dixon, who regarded the appearance as due
to an approximation of originally separate filaments. In the
lilies the result of fission is much more marked than in the
majority of other plants studied by us. It is doubtless to
this circumstance that the prevalent misconception as to the
true nature of the succeeding changes is due, and it serves to
emphasise the necessity of comparative study as opposed to
an undue reliance on the results of investigations made on
single types, however promising these may individually seem
to be. Thus a comparison of the processess as they are
manifested in the lily with those corresponding to them in
the Osmunda, Tradescantia, or Aneura, at once throws
light on the actual sequence of events, though the investi-
gation in no case is an easy one. But the evidence is quite
decisive, and indicates re-approximationof theseparated
halves of the ribbon. Thus the split gradnally closes up
again (Figs. 7-11) and may be so nearly obliterated as to
become very difficult to recognise. At the same time the
thread is shortening and thickening, whilst the polarisation
already alluded to may be more easily seen. The thread, in
many of its convolutions, is attached rather securely to the
nuclear wall, whilst the rest becomes aggregated into a some-
what dense tangle towards the centre, where the nucleolus is
now commonly situated. The latter body (there may be one
or more of them present in each nucleus) is vacuolated and
has clearly lost much of its substance. This has been utilised
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. sath
in the development of the chromatin element in the spireme,
as is Shown both by staining reactions, and by its intimate
relation with the spireme during the progress of differentia-
tion and growth of the latter. About this time the nucleus
attains to its largest size, 35 u being an average measurement
of the diameter in Lilium candidum. As the contraction
proceeds, which it does with great rapidity, the original
longitudinal fission ceases to be noticeable and is only visible
in exceptionally favourable cases. But a rearrangement of
the thread, first correctly explained by Schaffner in the case
of L. Philadelphicum, now sets in. Parts of the thread
forming the spireme become pulled into parallel positions.
This is specially well seen in those places where at the bend
of a convolution an attachment to the nuclear periphery has
taken place. Often the nuclear wali is drawn inwards at these
spots. Thus a close and parallel approximation of lengths of
the entire spireme thread is effected, and this parallel
arrangement has been commonly interpreted as representing
the parallel split halves of the spireme thread. Such an
interpretation is, however, shown to be unsound by a careful
study of the stages just described. Sometimes in one or both
sides of the narrow V-shaped figures thus produced the
original fission can still be traced, and this is especially the
case when free ends of the thread can be observed. For at
this time, and possibly earlier, the definitive chromosomes begin
to be recognisable, though often each one is still connected
by strands of linin with those lying next to it. ‘This relic
of the original fission has been recognised by others, but it
has been commonly interpreted as due to the occurrence of a
second longitudinal fission. No such second fission, how-
ever, really takes place at all.
As a consequence of the bending over of the spireme
thread, or rather parts of it which give rise to the chromo-
somes, the segments when isolated very often exhibit the
form of a loop, open at one end, with sides either parallel to
each other or, more commonly, twisted over one another
(Figs. 9, 11). But it by no means follows that all the bivalent
512 J. BRETLAND FARMER AND J. EB. S. MOORE.
chromosomes are formed in this way, and as a matter of fact
they are not. Sometimes two more or less straight rodlets
become approximated with or without interlacing, whilst at
others the ends of the rodlets may unite together so as to
give rise to figures of rings, ellipses, etc. These various figures
(c f. Figs. 11-18) may originate in various ways, and it is
not necessary to discuss them more fully.1. The important
point to bear in mind is this, that the two rods, sides of loops,
or whatever other form the structure as a whole may assume,
represent, not the longitudinal halves of a split thread, but
the approximation of serially distinct regions of the
spiremeas awhole. Thus each heterotype chromosome is
a bivalent structure, and their “reduced” number (i. e.,
half that of the somatic chromosomes) 1s due to the approxima-
tion and more or less intimate, though temporary, union of
the equivalents of pairs of somatic chromosomes.
It will be convenient to speak of the compound (paired)
structures which are thus formed as chromosomes, although
it must be remembered that each is in reality a double or
bivalent body. As they become shorter and thicker, they
become more homogeneous, and all trace of the primary
fission (second fission of other authors) becomes completely
obliterated. ‘I'he nucleus shrinks in size, now measuring
about 30min diameter. The nucleolus, although it has lost
much of its substance, is still recognisable as a large, often
irregularly-shaped body, or it may have fragmented into a
number of smaller pieces. A very characteristic phase then
comes on. ‘lhe chromosomes act as though affected by a
mutual repulsion, and instead of being more or less massed
together towards the centre of the nucleus, they move apart
and le at the periphery of the nucleus, the nuclear wall
becomes thinner, and nucleolar matter escapes from the
nucleus into the cytoplasm. Often, indeed, it seems as if it
were forcibly ejected.
The characteristic cytoplasmic radiations now appear,
* Cf. Farmer and Moore, * On the Essential Similarities existing between
the Heterotype Nuclear Divisions in Animals and Plants,” ‘Anat. Anz.,’ 1895.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 513
starting, as has been observed by ourselves and others, from
many centres. The radiations, however, soon become more
definitely polarised, and the nuclear wall, often at this time
showing irregularities in contour, gradually disappears, and
the chromosomes become grouped in the equatorial plane.
At first they are irregular in their arrangement, but soon
exhibit the well-known definite plate-like arrangement. The
achromatic spindle-fibres are very clearly differentiated
during the movements referred to, and they give the im-
pression of actively driving the chromosomes to their final
equatorial positions. We do not adopt this view of their
nature, as we believe them to represent protoplasm modified
by. the forces at work in the cell rather than actively growing
entities that are spontaneously concerned in producing the
movements in question. Thus we consider that the move-
ment is produced by the same causes that operate so as to
differentiate the spindle. The latter appears then as a passive
manifestation of the real operating agency, rather than an
active director of the movements in question.
Outside the area occnpied by the chromosomes isolated
spindle-fibres, or groups of such, are seen to diverge from the
main polar directions and to end upon deeply staining droplets
of nucleolar origin. This fact, long ago pointed out by one of
us! (1893), is of special interest as bearing on Strasburger’s
view of the connection of the nucleolus with kinoplasm.
The individual (bivalent) chromosomes assume many
different forms on the spindle, as has already been pointed
out by us in a previous paper; but during the metaphase
one general mode of procedure is seen to govern their
division. Hach bivalent chromosome divides so as to
separate monovalent elements, which are then distributed
to the respective poles. The mode of separation varies
in the case of different chromosomes, the difference depend-
ing on the manner in which the latter are arranged with
1 J. B. Farmer, ‘ Annals of Botany,’ vol. vii, 1893; cf. also ‘ Flora,’ 1895.
2 On the Essential Similarities existing between the Heterotype Nuclear
Divisions in Animals and Plants,” ‘ Anat. Anzeiger.,’ 1895.
514 J. BRETLAND FARMER AND J. E. S. MOORE.
reference to the spindle-fibres, i. e. to the forces that effect
their final separation. In the majority of cases a chromo-
some is as a straight or twisted structure, projecting radially
from the equatorial plane. Then each monovalent half is
attached at or near one end to a sheaf of achromatic spindle-
fibres, and the two halves (i. e. the monovalent constituents)
of each chromosome slide over each other and travel towards
the appropriate pole. As soon as this migration commences
the longitudinal fission once more becomes apparent, and the
rod splits open along the greater part or even the whole of
its length, so as to give rise to the V-shaped daughter
chromosomes. Each limb of the V represents the original
half of the spireme thread that was formed during the pro-
phase. Grégoire! was the first to recognise that this V-
shaped form is due to the re-opening of a previously effected
longitudinal fission. But he considered that two longitudinal
fissions occurred during the prophase, and that the appearance
in question was due to the re-opening of the second of these.
Although we cannot accept the interpretation in that form,
since we have shown that the supposed second split really
represents the first (and only) one in a disguised form, it is
obvious that Grégoire was correct in his main contention,
viz., that the production of the V depended on the re-opening
of a previously effected fission. And the interpretation
receives a striking confirmation from certain types of
chromosomes that are occasionally to be observed in the
diaster of lilies. The chromosomes in question assume
the forms of V’s, but each is seen to be completely split
throughout its entire length. Sucha figure is produced when
a heterotype chromosome becomes attached by the middle
instead of by the end, to the spindle-fibres (cf. Figs.
15, 16, 17). The whole daughter chromosome is then bent
over into a y-shaped structure instead of forming a rod-like
bedy. Hence the longitudinal fission, on its re-appearance,
gives rise to the figures of split Y-shaped bodies.
1 V. Grégoire, “ Les Cinéses Polliniques chez les Liliacées,” ‘ La Cellule,’
Levis
THE MALOTIC PHASE IN ANIMALS AND PLANTS. 5D
Although such figures are rare in the lily, they are quite
common in T'radescantia, and also in the salamander, as
was long ago figured and described by Flemming. The same
interpretation, as will be apparent from what follows below,
is also applicable to such cases.
When the daughter chromosomes arrive at their respective
poles the nuclei are reconstituted, and a complete bipartition
of the pollen-mother-cell takes place. It is not necessary to
give details of these processes here, as they are not relevant
to the main object of the paper.
The nuclei do not pass into a state of complete rest, although
it is not practicable to trace with certainty the individual
identity of the chromosomes throughout the whole period in-
tervening between the appearance of the nuclear wall and
the next mitosis. But enough can be seen to leave no doubt
as to the course of events that characterise the second (homo
type) mitosis of the spore-mother-cell.
As the chromosomes for this second (homotype) mitosis
disentangle themselves from the chromatic plexus of the
nucleus, they are found to present some diversity in form, and
this is continued up to the stage of the diaster.
Often they look like sinuous V-like structures with the ends
thicker than the middle. The limbs of the V are long, and
finally break asunder at the bend. ‘The two halves then
separate, but usually show a crook or curvature where they
separate. Finally the respective limbs diverge one towards
each pole. In other examples the chromosomes appear as
longitudinally split V-like bodies. These are to be related
with the similar structures seen as occasional varieties during
the diaster of the preceding heterotype mitosis. Both these
forms have long been familiar to us, and have been observed
by others, but it is clear that they are only special cases of
the general phenomena. But the former and much more
commonly occurring forms have been regarded by some,
e.g. Belajeff,’ as indicating the existence of a transverse
fission during the homotype mitosis, and thus as proving
1 ¢ Blora,’ 1894 (Erganzungsbd).
516 J. BRETLAND FARMER AND J. E. S. MOORE.
that a true reduction division was associated with this par-
ticular karyokinesis. After what has been said it will, how-
ever, be clear that there is no real difference between the
two cases, but that the second (homotype) mitosis results in
the separation of the longitudinal halves of the original
spireme thread that by their partial divergence have already
given rise to the figures of Vand A\ duringthe previous diaster.
Since the preceding account of the liéterotype and homo-
type mitoses in Lilium was written, # paper has appeared
from the pen of Professor Grégoire! in which he contests the
correctness of the interpretation advanced in our preliminary
communications last year. Professor Grégoire has consider-
ably altered the views previously expressed ,by himself as to
the actual sequence of events during the mitoses in question,
and he cites in support of his present position some as yet
unpublished work of his pupil M. Bergh. We think it
desirable to examine the evidence for the views he now seems
to hold in so far as they are set forth in his last paper.
He divides the prophase stage of the heterotype mitosis
into two phases, the first extending from the commencement
of the process and terminating with the formation of the thick
spireme (spiréme épais), the second beginning with this
phase and culminating in the formation of the definitive
chromosomes. After the first differentiation of the chromatic
filaments by the breaking down of the alveolar arrangement
which previously was associated with the distribution of the
chromatin in a reticular-like way throughout the nucleus, the
synaptic contraction sets in. Most of the filaments are indis-
tinguishable, but those that can be identified are thin. In
several places filaments may be seen to run parallel, some-
times twisted (entrelacées) and finally the two thin threads
fuse to form a thick one. Following on this is seen a thick
continuous spireme thread which disengages itself from the
synaptic contraction and spreads through the nucleus. Soon
a “longitudinal fission”’ appears in the thread, but he con-
1 V. Grégoire, “ La Réduction numérique des Chromosomes et Iés Cinéses
de Maturation,” ‘ La Cellule,’ t. xxi. is
.
~
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 517
siders that the split really represents the separation of the
threads that havejust before fused. The longitudinal
fission therefore, strictly speaking, would not exist. The
separated halves of the “thick spireme” contract and give
rise to the two halves of each bivalent chromosome, when,
by the transverse segmentation of the spireme thread, they
can be identified as distinct individuals.
We have tried to state M. Grégoire’s position as fairly as
we can, and if we have correctly apprehended his meaning
we find ourselves wholly unable to agree with him.
It appears to us that two series of events have been con-
fused. There is not only one, but there are two contraction
figures. In the first one, which Professor Grégoire seems to
regard as the synaptic figure, we have been able to trace the
spireme continuously ; and there cannot exist the slightest
doubt but that, as it emerges from this figure, the longitudinal
fission occurs as we have described. It seems to us that
Grégoire (and Berghs) has either omitted to observe the
fission and has only seen the re-fusion of the split thread,
or else he interprets the earlier stage in which the fission is
as yet incomplete in a sense opposite to that in which we,
together with most other observers, regard it. But it is
rather difficult to follow the account given by Grégoire,
inasmuch as he makes no mention of the second contraction
(which we regard as the essential synaptic one) wherein the
lateral approximations of the spireme occur. For we can
hardly suppose that this contraction can have been confused
with the earlier one, and yet apart from some such assump-
tion it is ditficult to reconcile the differences between our
results. Moreover, Grégoire’s account of course excludes
the existence of a longitudinal fission in the approximated
lengths of the now differentiating chromosomes, since he
identifies these lengths with the products of that “ longitu-
dinal fission” (approximation according to him) which occurred
at an earlier period. And yet traces of this fission can be
seen at all the stages under consideration.
M. Grégoire appeals to the figures in M. Berghs’ memoir
518 _ J. BRETLAND FARMER AND J. E. S. MOORE.
in support of his views, but we have already expressed our
reasons for regarding them as inadequate to afford a com-
plete picture of the whole series of changes.
The main points of difference between us are these:
1. M. Grégoire considers that during (?) the “synaptic”
(1st) contraction a lateral approximation of thin spireme
thread occurs, and that this then fuses. Our view is the
reverse of this. —
2. The closed, jointed threads next split asunder, and the
doubled segments of the spireme thus formed give rise to
the definitive chromosomes, with their variously twisted
limbs. We regard the original longitudinal fission as
temporarily closing ; this is followed by an approximation of
the thread into parallel lines, whether this is formed by loop-
ing or otherwise. At this stage the second contraction figure
is intercalated. We find traces of the longitudinal fission to
occur in the collateral threads from the first, whilst Grégoire
does not admit its existence till after the chromosomes are
arranged in the spindle.
M. Grégoire is in agreement with us in regarding each
chromosome as a bivalent structure, and as equivalent to two
somatic chromosomes lying in close juxtaposition or even
partially united; and further, that during the heterotype
mitosis a distribution of entire somatic chromosomes takes
place.
II. Osmunda regalis.
The archesporial cells in the sporangium are characteristic
in their appearance. The cells are large and somewhat
oblong, and the very prominent nucleus is commonly placed
excentrically, being nearer one end of the cell than the other.
The nucleus possesses a well-defined wall, and contains a
nucleolus. The chromatin can certainly, at least in the early
stages, be said to exist in such an arrangement as to suggest
aspireme. Sometimes the granules of chromatin appear to
be scattered irregularly, so as to give the impression that
one is confronted by a foam structure, the granules lying
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 519
in the angles where the walls meet; whilst at other times
these granules can be traced as lines or rows for short dis-
stances within the nuclear cavity. The regular spireme
arrangement is thus the result of a progressive differentiation,
a result encountered in other cases, e. g. in Tradescantia,
and less prominently perhaps in Lilium.
As the spore-mother-cells approach maturity the chromatin
assumes a more regular arrangement, and the linin frame-
work begins to stand out more clearly from the paralinin that
surrounds and encloses it. The thread now forms a thin,
much-convoluted filament which seems to be continuous,
though free from the cross anastomoses present at an earlier
stage. At least no free ends could be with any certainty dis-
covered. The chromatin is now very distinctly arranged in
a single serial row of granules in the lini. Atthis stage the
first contraction figure is to be met with. The coils of the
spireme are densely aggregated at one side of the nucleus,
but some parts of the whole thread remain free from the
general tangle. Gradually the dense mass again becomes
looser, and the thread rapidly shortens and thickens, whilst
at the same time the chromatin granules are seen to
be larger, though whether their increase in size is due to
fusion, or, as seems more probable, to growth, could not be
decided. Here and there signs of the longitudinal fission
become apparent, inasmuch as single granules are replaced by
double ones that le in pairs along limited lengths of the
thread (Fig. 22). The latter is still much convoluted, and its
windings can easily be traced just beneath the nuclear wall.
The longitudinal fission just mentioned does not become
emphasised as in the case of Lilium, and the thread does not
separate so distinctly into two longitudinal halves as in that
genus,
The second (synaptic) contraction figure now sets in. The
thickening thread gradually becomes massed together in the
vicinity of the nucleolus, but distal loops are still easily seen
which extend, and may be attached to, the nuclear wall. In
these looped portions the signs of longitudinal fission are very
520 J. BRETLAND FARMER AND J. E. 8. MOORE.
clear (Fig. 23). The sides of the loops become drawn into
parallel positions as the tangle increases, and at the same
time the nucleolus suffers a considerable loss of substance, as
is evidenced by its vacuolation at this stage.
The sides of the loops just described continue to approxi-
mate more closely together, and thus simulate an appearance
of a longitudinal fission. It is quite clear, however, that this
appearance is illusory, for the real fission can often be traced
in their parallel sides (Fig. 24) even at a much later stage.
Gradually the tangle around the nucleus vanishes, and the
chromatic filament is then observed to have segmented trans-
versely so as to form the definitive chromosomes. The actual
process of transverse separation is somewhat slow, for all
stages can be followed in suitable preparations. The stainable
substance (chromatin) seems gradually to become attenuated
so as to give the impression of a viscous body being pulled
asunder.
It is very clear that much nuclein or chromatin has been
withdrawn from areas of the original filament, for consider-
able tracts of the linin thread can be seen to evince no
affinity for basic aniline dyes, and it often happens that these
unstained lengths can be traced as being in direct continuity
with others in which chromatin is abundantly embedded.
Although the parallel arrangement of the chromosome con-
stituents may be provided for in the way just described,
namely, by the approximation of the sides of an originally
looped structure, this by no means exhausts the variations by
which the same appearance can be produced. Sometimes
long, rod-like forms with a slight bend in the middle are
met with, and at others it seems as if the parallel arrange-
ment of the sides is certainly affected by the approximation
of two portions of the thread (Fig. 25) that have broken
apart from each other. In fact, many different forms are to
be seen, often in the same nucleus. The U-shaped loop is
perhaps the most common, and a simple variation of this is
produced when the sides or limbs of the loop are twisted
round each other; at other times rings or ellipses are en-
THE MAIOTIC PHASE IN ANIMALS AND PLAN'S. 521
countered. These become much more frequent at later stages,
and they clearly owe their origin to the fusion of ends
previously free from each other. Again, the two sides may
be twisted over each other whilst both ends remain discon-
nected.
Meanwhile the spore-mother-cells have become completely
detached from each other by the solution of the middle
lamella, and the excentric position of the nucleus is strongly
marked, A curious appearance is seen in each cell, at this
and earlier stages, in the vicinity of the nucleus. In the
cytoplasm at the narrower end of the spore-mother-cell a
remarkable vacuolar arrangement of the fibrous cytoplasm
is regularly seen as a highly characteristic feature that per-
sists through the greater part of the whole stage of prophase
(fig. 23). It seems to have nothing to do with the spindle
formation that occurs later, and without hazarding any theory
as to its significance, it may perhaps be suggested that it
possibly indicates a withdrawal into the nucleus of substances
previously contained in the extra-nuclear cytoplasm. As
the formation of the definitive chromosomes proceeds, rapid
changes begin to affect the tapetal tissue. ‘The cells com-
posing this nutritive layer have become enlarged, and the
nuclei have multiplied, first, mitotically, and later on by an
abbreviated process more akin to amitosis. The cell walls
ultimately break down, and the cytoplasmic contents, together
with the nuclei, escape into the interspaces between the spore-
mother-cells. ‘The nuclei long retain that curious condition
of prophase so characteristic of the nuclei of many actively
secreting gland-cells. Gradually, however, they undergo dis-
integration in the slimy mass that now fills the interstices
between the separated spore-mother-cells.
Meanwhile the chromatic thread has segmented with the
definitive chromosomes, or if previously in reality discon-
tinuous, it at least now can be certainly so recognised. Many
of these young chromosomes consist at first of U-shaped
loops, with sinuously curved limbs. Sometimes the limbs are
twisted round each other, and the impression is conveyed to
voL. 48, pari 4,—NEW SERIES. 38
522 J. BRETLAND FARMER AND J. BE. &. MOORE.
the observer that this twisting increases and becomes more
prevalent in the following stages. The chromosomes now
shorten rapidly and attain their final shapes, but the original
longitudinal fission can often be traced quite distinctly in the
thick limbs. The remains of the nucleolus may also be still
recognised amongst the chromosomes, and indeed it does not
really disappear until after the chromosomes become arranged
in the equatorial plane of the spindle.
Immediately before the latter event takes place the
chromosomes are, as is so common at this phase, distributed
over the periphery of the nucleus just within the wall. They
are thus in a specially favourable position to enable the
relation of the various forms to one another to be traced.
Speaking generally, the shape assumed depends very much
on the character of the primitive or young chromosome as it
emerges from the synaptic contraction (figs. 26, 27). The
commonest forms are those of X, O, and 8. The last are
easily derived from the U-shaped structure, whilst the figures
O are due to the approximation and fusion of extremities
previously free from one another. The very characteristic X
figures may arise in several ways—either the spireme thread
breaks up transversely into rods, and two of these approxi-
mate and cross, so as to form the shape in question, or they
may have arisen from the §-like chromosomes, by the com-
plete breaking asunder and divergence of the limbs. Finally,
it sometimes happens that the X-like form is produced by
the approximation of two bent rods, thus: )<. A less
commonly met with chromosome possesses the form of a long
rod. This means either that a U-shaped loop has straightened
out or that a piece of the linin, straight ab origine, is
bivalent. Finally, it might arise, though we have no positive
evidence as to this, by the end-to-end attachment of pre-
viously isolated segments of the spireme thread.
But these types very rarely maintain their individual
characters up to the appearance of the spindle, and the great
majority become transformed into X-lke forms (fig. 28). It
may happen that the monovalent constituents of many of the
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. ~ 523
bivalent chromosomes become almost or quite detached
from each other about this stage. But they seem always to
unite again before the completion of the spindle formation.
The fact, however, is of interest, seeing that Korschelt has
described, in the case of Ophryotrocha, an example in
which the somatic number of chromosomes appears at the
heterotype prophase ; these then unite in pairs before they
become finally arranged on the spindle.! The appearances
here described for Osmunda are very plainly visible in
many pleridophytes. Figures 29 and 30 illustrate corre-
sponding phases in Psilotum triquetrum, a lycopodineous
plant. When the chromosomes of Osmunda congregate on
the equatorial plane of the spindle their differences of form
become less marked; as they begin to separate on the com-
mencement of the diaster, it is clearly seen that the division
is a transverse one. Most of the chromosomes are more or
less oval or diamond-shaped, but some retain the form of long
rods that divide transversely across the middle.
The longitudinal fission so often recognisable in other
plants at this stage is often difficult or impossible to distin-
guish, though it may be seen with certainty in some cases.
The diaster is, as a whole, rather irregular. The daughter
chromosomes cling together by one end equatorially, in a
manner recalling that so often met with at the corresponding
stage in Tradescantia. ‘The way in which these rod-like
chromosomes ultimately break asunder suggests a pull rather
than a repulsion as the cause of their final separation,
although the fact that the chromatin leaves the central zone
when the final breaking occurs might perhaps be utilised as
an argument to support the hypothesis of mutual repulsion.
At the close of the diaster the chromosomes can still be
recognised as bands within the nuclear-wall which is formed
before the onset of the next (homotype) mitosis.
The chromosomes as they become isolated and distinct at the
1 Strasburger in his recent paper (“ Uber Reductionsteilung,” ‘Sitzher. d.
R, Pr. Akad. d. Wiss.,’ March 24th, 1904) has described a similar condition
or Galtonia eandicans.
O24 J. BRETLAND FARMER AND J. E. S. MOORE.
commencement of the homotype division form, for the most
part, rod-like bodies directed radially in the equatorial
plane ; often they are very clearly seen to be double at this
stage, and when looked at from the side present the appear-
ance of dyads. Some of the chromosomes are scattered
through the equatorial plane, and are thus not confined to a
peripheral position. As the daughter elements separate from
each other they assume remarkable forms; the general
impression obtained is that of viscous bodies forcibly pulled
asunder. ‘Thus they become very much attenuated and
elongated as they finally separate and travel to the respective
poles of the spindle. On reaching the poles they very rapidly
shorten and thicken as the daughter nuclei pass into the state
of telophase and ultimately of rest.
IL, Aneura pingure:
This species of Liverwort exhibits certain remarkable
peculiarities connected with the formation and division of the
spore-mother-cell that are absent from the corresponding
mitoses of most plants. On the other hand, they are shared
by most, if not by all, of the members of the Jungermannia
series of Hepatice,! although in different degrees. At the
close of the archesporial cell-divisions, as the individual cells
become free from each other by the dissolution of the middle
lamelle, those cells that are destined to give rise to spores
soon become differentiated from those that will ultimately
form the elaters. At first the contour of each is irregularly
spherical, but as they enlarge in size, it 1s seen that each
spore-mother-cell becomes symmetrically bulged out at four
spots, so as to form a quadrilobed cell. ‘The lobes are arranged
tetrahedrally, each diverging from the common centre, and
thus the axis of no two or more of them can le in the same
plane. Hence it follows that it is necessary to exercise care
in interpreting and combining the results of observations made
on sections of sucha structure. Aneurais, however, specially
1 Cf. Farmer, “ Studies in Hepatic,” * Annals of Botany,’ vols. viii and ix,
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 525
favourable for study, inasmuch as, like Fossombronia, the
lobes are not much extended in the radial direction, as is,
for example, the case in Pellia.
The nucleus occupies the centre of the cell, and it is thus
surrounded by, and enclosed in, cytoplasm which is chiefly
ageregated into four masses corresponding with the four
lobes already referred to.
The nucleus contains one or more nucleoli, and at this
stage the spirem thread can be traced as a probably con-
tinuous filament within the nuclear wall.
The early contraction figure already described for the pre-
ceding plants occurs here also, but judging from the relative
infrequency with which it was observed, it appears to repre-
sent a very transient phase.
As the nucleus begins to show signs of approaching mitosis,
the first obvious change is seen in the cytoplasm. In each of
the four lobes a centrosphere is differentiated (figs. 31-85),
and sometimes a central body (centrosome) could be dis-
tinguished in each. The centrospheres when formed appear
to exert (or to represent the foci of) tractive forces acting on
the nucleus, which now changes its form and becomes dis-
tinctly drawn out, so that an angle projects towards each lobe.
Before the formation of the centrospheres the nucleus was
either spherical or even slightly flattened opposite each lobe.
These facts can be made visible both in spore-mother-cells
stained in bulk and mounted in glycerine, although of course
the details can only be followed in sections. When sections
are examined only three lobes at most can be seen at once,
and unless the sections are fairly thick one can only trace
fragments of the whole apparatus, since the axes of the centro-
spheres and spindles lie in four different planes. Aneura
multifida, owing tothe smaller size of its spore-mother-cells,
affords a more favourable object in which to study the process
in the unsectioned cell; and indeed that species, together
with Fossombronia pusilla, is habitually used by us to
demonstrate the quadripolar spindle and centrospheres to
classes of students.
526 J. BRETLAND FARMER AND J. E. S. MOORE.
The spireme thread is much twisted and convoluted within
the nucleus, and it shows longitudinal fission through con-
siderable portions of its length (fig. 32). The fission is, how-
ever, very transitory, and it becomes even more obscured later
on, through the fusion of the split halves.
The spirem now shortens and thickens, but the convolu-
tions are still numerous—more so than the number of chro-
mosomes ultimately to be produced. As the contraction
proceeds, it is easily seen that in many places the loops of
the spirem are adherent to the nuclear wall, and the latter
may even be slightly pulled inwards at these spots. The
chromatic thread rapidly becomes more rich in nuclein, the
nucleolus contributing to this process and itself losing a large
portion of its stainable constituent. The filament is now
seen to break up into its definite chromosomes (figs 33-35),
and in number these are sometimes easily seen to be the
number characteristic for the reduced number, which seems
to be eleven for the species in question. Hach chromosome,
however, is clearly seen, on following its subsequent history,
to be bivalent. For the previous parallel arrangement of the
threads during the looping-over stage is responsible for the
simulation of the duplicate character to be observed in each
chromosome at this period. In the most frequently recurring
forms, the bivalent chromosomes at this stage resemble
double rods, which might easily be mistaken for the shortened
and thickened halves resulting from the previously recorded
longitudinal fission did not the intervening stages preclude
such an explanation. Very often the transverse delimitation
give rise to a bent-V-shaped body, the two limbs of which
represent a continuous length of the original spirem, and
hence clearly betray the bivalent character of the chromo-
some. It may happen, however, that the halves become
entirely separated from each other, and independently of any
bending over of the thread. But nevertheless they come
together so that the reduced number of (bivalent) chromo-
somes is affected. In cases such as that just mentioned the
conjugation of somatic chromosomes during the heterotype
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 597
prophase is placed beyond a doubt. It does not seem to be a
matter of any consequence how the bivalent arrangement is
produced, since there is so much variability in the process,
but the temporary union in pairs of somatic chromosomes is
the really important feature.
The further history of the chromosomes is less easily
followed than in Osmunda, but the same types are repro-
duced here in almost every detail, and they pass on to the
spindle in a precisely similar manner; perhaps, however, the
ring-like figures are rather more frequent in Aneura than
in Osmunda.
The spindle in its earlier stages has already been described
as a quadripolar structure. ‘The individual kinoplasmic
threads can easily be distinguished in good preparations ; but
as the chromosomes begin to assume their definite form,
and before they pass on to the spindle, the quadripolar
arrangement becomes obscured, and usually obliterated. The
sheaves of fibres become shortened, and hence project less
into the lobes, and then the ends fuse in pairs, so that a
bipolar arrangement supervenes. But it sometimes happens
that a sharp bipolar form is not attained, and then at one or
the other end the pole is seen to bifurcate somewhat, in
correspondence with its mode of origin.
When they come to lie on the spindle the chromosomes
are often difficult to analyse. They may form the twisted
figures so frequent in the corresponding stage of a lily, or
they may exhibit the form of closed rings with equatorial
thickenings, or finally they may form X-like structures (figs.
39, 36). And as the period of the diaster approaches they
present the highly characteristic form and arrangement that is
met with in the heterotype mitoses of both plants and animals.
When the diaster is formed it is seen that each bivalent
chromosome is so divided (fig. 36) that transverse halves (i. e.
its monovalent constituents) are distributed to the two
daughter nuclei. Sometimes this can be made out very
clearly when the ring-like forms break asunder at first at one
side. The whole is then straightened out in the direction of
528 J. BRETLAND FARMER AND J. E. S. MOORE.
the spindle, recalling the corresponding figures that are so
much more frequently to be seen in Tradescantia. But
as a general rule the V shape of the daughter chromosome is
not easy to identify. They are swollen and stumpy structures,
and very seldom show the reopening of the fission that is so
conclusively exhibited in Tradescantia and sometimes also
in Lilium.
A wall is formed across the interzonal fibres at the close of
the heterotype mitosis, and the daughter nuclei at once divide
again, the new spindles being formed close together, but
their axes not being in the same plane. ‘The fission of these
(homotype) chromosomes is clearly longitudinal (Fig. 37), and
seems beyond doubt to correspond with the hitherto obliter-
ated primary fission of the spirem thread of the previous
karyokinesis.
The four nuclei are thus distributed to the four lobes of the
original mother-cell (fig. 38), and the respective lobes are
delimited from each other, at the centre of the original cell,
by walls that take up the same position as do soap films when
placed in boxes of corresponding form. Ultimately fresh
walls are formed around the contents of each cell (special
mother-cell) and the spores separate by the solution of the
original walls. But this process need not be described here,
as it is not pertinent to the main objects of this memoir.
IV. Periplaneta Americana.
(a) The pre-maiotic period.
As an illustration of the manner in which the sexual cells
become matured among the metozoa, no individual type
appears to be more suitable, or on the whole more interesting,
than the common cockroach.
In this insect, as in so many other cases, the male gland
consists of numerous small spaces filled with cells in different
stages of development; and as in all cases among the metozoa,
these generative cells have themselves arisen through the
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 529
continued multiplication of the elements which, in the first
instance, constituted the so-called generative blastema of the
embryo.
In the adult male, the cells which are about to become
sexually mature are found to be still multiplying through the
continuation of the same series of pre-maiotic divisions
whereby they have been increased from the segmentation of
the ovum onwards, and as this pre-maiotic multiplication
differs only in certain details from the processes already
described so fully in numerous treatises upon cell division in
general, it will only be necessary here to briefly recount the
successive stages of the process, so that the history may
appear complete and the special peculiarities of the somatic
cell division in the cockroach may be brought into sufficient
prominence.
In the example we have chosen the cells of the pre-maiotic
series which are about to divide, whether they are encoun-
tered within the sexual glands or elsewhere in the tissues of
the body, present the rather characteristic appearance repre-
sented in fig. 40, a very irregular network of chromatin
and linin being grouped within the nuclear membrane round
one or two highly chromatic nucleoli. Among such elements
mitosis is ushered in by the increasingly chromatic appear-
ance of the cells, this being followed by the gradual evolution
of a definite arrangement of the chromatin, and in the
particular type under consideration the latter process is not
by any means without interest from a general point of view.
At first the cells which are preparing for division present
an almost even granulation of the chromatin within their
nuclei, and this in its consistency strongly suggests a foam
structure of the ordinary type; but after atime the “ chro-
matic confusion,” as it were, sorts itself out into obvious
condensations or cloudy areas, and it is apparently unques-
tionable that each of these primitive chromatic clouds is
individually the forerunner of one of the future chromosomes
(figs. 41-44).
The gradual condensation which occurs in each such cloud
530 J. BRETLAND FARMER AND J. HE. S. MOORE.
proceeds, moreover, in such a manner that the chromatic
granules become arranged or grouped in two distinct rows,
or tracts. So that by the time the individual chromosomes have
attained to some sharpness of definition they appear also as
if they had been split longitudinally from end to end. Inthe
cockroach, however, it is obvious that this split has not arisen
from the sundering of a pre-formed riband, but by the
gradual grouping of the chromatin granules into the form of
a short double rod (figs. 46—48).!
It will have been seen that the method of chromosome
formation here depicted presents nothing exactly comparable
to the long spirem thread which is figured in so many of the
existing accounts of pre-maiotic division which have hitherto
appeared.
In all cases which we have examined the number of the rod-
like chromosomes which are eventually produced appears to
be generally thirty-two; that is, by counting the chromosomes
in a large number of cells, and then taking the average of such
counts, the number thirty-two has always been attained. But
it is not intended, nor should it be assumed that there is an
absolute numerical rigidity in all the individual cells; for
many figures have been encountered in which the number
appeared to be more or less than this, by one, two, or even
more, yet in these cases there was no reason to suppose that
the cells under examination had in any way been altered by
manipulation.
When the pre-maiotic mitosis has reached the above stage
the cells which present themselves in groups with the short
double chromosomes just described possess the characteristic
appearance represented in fig. 47; while about the same
time the parts of the karyokinetic figure related to the
centrosomes, as well as these bodies themselves, emerge once
more into prominence.
All the ensuing stages of the pre-maiotic divisions are in
1 Cf. Farmer and Shore, “On the Structure and Development of the
Somatic and Heterotype Chromosomes of Tradescantia Virginica,”
Quart. Journ, Mier. Soe.,’ 1904.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. Dok
perfect accord with what has hitherto been described, the
centrosomes separate to the opposite ends of the cell, where
they lie a short distance within the bounding membrane,
while at the same time the chromosomes, after being bunched
in a confused mass, are gradually drawn into the usual equa-
torial figure (see fig. 51). During this process, however, the
short split rods generally become more curved, and since they
are all attached by the middle of this curvature to the spindle
fibres, they often present the appearance of sharply defined
tetrads, the manner in which this appearance is produced
in the type under consideration being, however, at once
apparent upon comparison (figs. 47-51). It must be admitted
that these tetrad figures occurring in the pre-maiotic divisions
of the cockroach are singularly like those described among
various arthropods by Hicker and others, but always
referred by these authors to the process of reduction, and not
to the pre-maiotic stage at all.
In the later stages of the pre-maiotic divisions the halves of
each of the thirty-two chromosomes gradually separate and
pass away to the poles of the spindle figure, to form the group
of chromosomes belonging to each daughter nucleus, and the
division of the cells becomes complete.
In the cockroach, as in so many other animals, the remains
of the spindle persists for some time as a sort of band connect-
ing the daughter cells together, and this connecting spindle
relic may still be encountered during several subsequent
divisions of the daughter elements; but there are no inter-
mediate bodies produced quite comparable to those origin-
ally described by Flemming in amphibia, and_ seen
subsequently in so many other animal forms.
During pre-maiotic divisions, the conspicuous nucleolus of
the cells breaks up and is formed anew within the daughter
nuclei, the remains of the old nucleoli passing into the cyto-
plasm where they disappear.
The divisions of the pre-maiotic elements of the cockroach
can be followed with the greatest exactitude and ease in the
mature testis of this animal, and for all major details the
532 J. BRETLAND FARMER AND J. EK. S. MOORE.
mode of procedure here pursued is identical with that en-
countered among the cells composing the rest of the animal’s
body ; for although it is by no means so easy to follow out
the whole cycle of events among the cells composing the
ordinary body tissues, a sufficient number of phases of
division have been encountered to show that the number of
the chromosomes is thirty-two and that the characters of the
division of these elements are similar to those of the pre-
maiotic series of the testis.
The number of the ordinary pre-maiotic divisions which
actually occur in the testis and precede the onset of the
reduction process is not easy to ascertain ; it is not less than
six or eight, and it may possibly be as many as ten to
twenty; but whatever the number of these divisions there may
actually be, the process of pre-maiotic multiplication in the
testis, as in the ovary, sooner or later comes to an end, and is
succeeded by the chain of events which results in the
reduction of the number of the chromosomes in each cell by
one half, and the rendering of the resulting elements ready
for sexual conjugation.
(b).The Maiotic Phase.
The onset of this singular metamorphosis, the maiotic
phase, is first apparent by virtue of an alteration in the resting
nuclei which are about to enter upon the change. Such nuclei
become obviously more chromatic than those of the pre-maiotic
cells, whilst the chromatin network, from being loosely
scattered through the nuclear substance, assumes a fine and
very even granular appearance, which often suggests the
existence of a very closely tangled spireme thread. As time
goes on, however, the fine meshwork of chromatin becomes
more and more definitely arranged—polarized, in fact. That
is to say, it presents strands which run round the nucleus in
loops, and these as they develop assume a horseshoe form
with their rather pointed ends open, and all are collected
together at one side so as to form a distinct pole field in the
ordinary sense. It is at this period that the sphere and
THE MAIO'TIC PHASE IN ANIMALS AND PLANTS. 5380
centrosomes can be first discerned in the cytoplasm opposite
the ends of the emerging chromatic loops.
From the time at which these maiotic cells can be first
distinguished they present—unlike the pre-maiotic elements
which have anteceded them—a single, distinct, and relatively
large nucleolus ; and during the onset of the synaptic phase
this body becomes stretched out and lengthened as the
polarization of the nucleus increases, so that eventually it
produces a curious and characteristic appearance represented
in figs. 53-56.
In the succeeding phases the polarisation of the chromatic
loops becomes at first more complete. Or, in other words, the
original chromatic meshwork becomes more and more
definitely drawn out into the broad, horseshoe-like struc-
tures which are represented in figs. 57-58. At the same time
the whole chromatic substance of the nucleus tends to con-
tract away from the nuclear membrane towards the sphere
(archoplasm). It is this first contraction figure which has often
been spoken of as the synaptic contraction, but as a matter
of fact there are in reality two contraction stages, of which the
figures represented in figs. 53-67, only illustrate the first.
When the chromatic loops have acquired the definite
characters delineated in fig. 57, they begin to open out
over the surface of the nucleus, and often become actually
thinner, until figures like those represented in figs. 63-66
are frequently obtained. ‘The process of unravelling, however,
continues still farther than this, until the nucleus presents a
typical course spireme irregularly distributed over its surface,
as 1s shown in fig. 66.
At about this stage im the cockroach it is generally possible
to observe that the nuclear threadwork is becoming longi-
tudinally split, and the appearance which the cells then
present is reproduced in fig. 67, the whole of this phase
of the division reaching its maximum in such elements as
have been represented in figs. 64-67. In all these later
figures the cells present the coarse spirem appearance which
is so well known. However, it is not in this stage that the
Dd4 J. BRETLAND FARMER AND J, E. S. MOORE.
final transverse breaking up of the spirem thread into chromo-
somes actually takes place. In the cockroach it is easy to
demonstrate, positively, that immediately after this period a
second contraction stage ensues.
The coarse spirem thread becomes again polarised, and
this second polarisation is carried to a far greater degree than
in. the first contraction figure, as will be seen on comparing
fig. 57 and fig. 72. ‘The whole threadwork is, in fact,
at last drawn into short thick loops, which usually radiate
from a centre in the manner represented in fig. 69.
Nevertheless, at this period it is usualiy possible to trace the
original longitudinal splitting of the threadwork running
round the limbs of the individual loops. Or, in other words,
the series of figures (67-72) show that the short loops in
fig. 72 are not to be taken as portions of the opened-out
split in the threadwork represented in Fig. 68, but as
divided threads which have become bent round upon them-
selves.
From the stages represented in figs. 56-60 we pass to such
stages as those reproduced in figs. 71-72, in which it can be
seen that the loops arising in the second contraction figure
are directly metamorphosed into the diaschistic (hetero-
type) chromosomes ; but even in this later stage it is often
possible to trace the remains of the original split (the ana-
schistic fission) running round the edges of the diaschistic
(heterotype) loops or rings, as in fig. 73,
From a contemplation of the above facts and figures we
are brought to the conclusion that the diaschistic hetero-
type chromosomes are different in origin and character from
those of ordinary pre-maiotic cells. Each of these loops or rings
does not represent the opening out of a segment of split
thread-work, as Flemming originally conceived, but is in
reality seen to be composed of a portion of the split spirem-
thread which has become bent round upon itself in the form
of a ring or a loop. Moreover, it often happens that the
diaschistic chromosomes, instead of assuming the form of a
loop or ring, appear as a couple of thick rods placed side by
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 535
side, and not attached together ateitherend. Each rod, how-
ever, 1s longitudinally split, and the pair together constitute
a diaschistic (heterotype) chromosome of a characteristic
and familiar type.
Now, as is well known, the number of the heterotype
diaschistic chromosomes is always half that in the preceding
divisions, and in such a diaschistic figure as the above we
have a condition of things which would be exactly attained if
two ordinary somatic chromosomes were to become associated
together.
In many instances, even before the nuclear membrane has
disappeared, we have found that the short, thick loops have
already divided transversely in their curved portion, thus : ©)
and through the existence of such figures we immediately
see how those diaschistic (heterotype) chromosomes having
the form of a pair of actually, or potentially, split rods
have been produced. In the case of the more usually shaped
chromosomes, as division proceeds the separation of the loops
or rings into two halves takes place while the elements are
on the spindle, and is brought about by a similar transverse
breaking of the curved loop. Or the process may be still
further modified in detail in a number of ways which we have
already described in a former paper.'
Whatever the exact method adopted the result is the
same, and it comes to this: that the pre-maiotic number of
chromosomes tends to be formed; that these for a longer or
shorter time remain united in pairs, so that there are ouly
half as many chromatic aggregates in the cell as in the case
of the ordinary pre-maiotic divisions, while during the later
state of the first maiotic or heterotype mitosis the united
chromosomes simply separate from one another and pass
in their entirety into each of the daughter cells.
In the cockroach there are, as a matter of fact, two chief
variations of the manner in which the diaschistic (heterotype)
chromosomes are arranged, and separate from one another on
the spindle, during the later stages of division. In the one
1 Farmer and Moore, loc. cit.
536 J. BRETLAND FARMER AND J. E. S. MOORE.
we have the chromosomes in the form of small rings which
divide in the manner represented in figs. 74, 75; in the
other the ring is open at one side, or is a loop, and being
attached to the spindle in the fashion shown in fig. 77, opens
out in the manner represented. In this latter variation
the final condition of the dividing chromosomes is extremely
interesting ; for the original longitudinal split can be traced
with great clearness, and can actually be watched as it forms
the characteristic longitudinal split of the daughter chromo-
somes of the first maiotic (heterotype) division first described
by Flemming, in the salamander, among animals,and by Stras-
burger, in Tradescantia, among plants. From such figures
in the cockroach it becomes at once obvious that this singular
and well-known split condition of the daughter chromosomes
of the first maiotic (heterotype) division, to which the above
authors long since drew attention without offering any
explanation, is nothing more nor less than the persistence in
these daughter elements of the original longitudinal split of
the synaptic spirem thread.
From the above it will have become obvious that in the
cockroach the first maiotic (heterotype) division differs from
the pre-maiotic divisions which have anteceded it in this;
that here, instead of the chromosomes consisting of thirty-two
split rods or lengths of the spirem thread the halves of
which will be distributed between the daughter cells, we find
that the spirem thread-work tends at first to separate into
only half as many lengths, that eventually the full somatic
number of elements are formed, but these remain associated
together in parts to form the potentially double heterotype
chromosomes ; or, in other words, the first maiotic division is
distinguished from the pre-maiotic divisions by the temporary
union of the pre-maiotic chromosomes in pairs, and by the
simple separation of these elements during the ensuing mitosis.
In this way the cells of the second maiotic generation receive
only half the number of chromosomes which have characterised
the preceding generations. Nevertheless, in the diaschistic
(heterotype) prophase the thread-work is longitudinally split,
THE MALOTIC PHASE IN ANIMALS AND PLANTS. 537
just as it isin the pre maiotic divisions, and it is this splitting
in the segments of the chromosomes which constitutes the
longitudinal fission seen in the daughter elements as they
recede from one another.
In the cockroach after the first maiotic (heterotype) division
has been completed the resulting nuclei pass into a condition
of almost complete rest. That is to say, the nuclei again
return to the state in which there is merely a coarse chromatic
reticulum where it is impossible to trace the daughter
chromosomes any further, and it is consequently only after a
considerable period that the second maiotic (homotype)
division is brought about. In this (the last division of the
series), as in the ordinary pre-maiotic divisions, the sixteen
chromosomes emerge each from definite chromatic condensa-
tions, wherein the chromatin becomes again arranged in
two thick streaks or bands, the chromosomes presenting
the appearance of so many short split rods; and as division
proceeds these pass on to the spindle and divide in the
ordinary pre-maiotic manner.
Thus, although it would seem to be strongly suggested that
the ordinary longitudinal split of the segments in the synaptic
spirem thread constitutes the fission by means of which the
reduced number of chromosomes in the second maiotic mitosis
are ultimately divided, this is not absolutely demonstrated
in the Periplaneta itself.
V. Elasmobranchs.
(a) The pre-maiotic phase.
In view of the remarkable character of the reduction
process as it appears to be carried out in the typical arthropod
example constituted by the cockroach, we have re-examined
the elasmobranch material which had been obtained and
already described by one of us! in 1894; such a re-examina-
1 Moore, J. HE. S., On the Structural Changes in the Reproductive Cells
during the Spermatogenesis of Klasmobranchs,” ‘Quart. Journ. Mier. Sci.,’
vol. 38, new series.
VOL. 48, PART 4.-—NEW SERIES. 39
538 J. BRETLAND FARMER AND J. E. S. MOORE,
tion has made it obvious that although the main features of
the spermatogenesis of these fishes were correctly ascertained,
certain aspects of the maiotic phase were not fully appreciated
at the time.
In many ways the functional male gland of an elasmo-
branch is an admirable object for the study of all the stages
of development in the sexual cells; but it is also true that
as far as the heterotype prophases are concerned, the pheno-
mena in these fishes are somewhat confusing, and are far
more readily interpreted correctly, after a knowledge of what
actually takes place has been obtained in some form like that
of the cockroach.
In the various forms of elasmobranch testis the young
tubules are found crowded with cells which are just rapidly
multiplying through successive pre-maiotic mitoses as they
do in the testis of the cockroach, the chief distinction
between the fish and the insect being that in the former there
is present a much more complete spirem thread than in the
latter ; in fact, we have here pre-maiotic prophases which are
directly comparable with those already fully described by
Flemming and others in several amphibian types.
A long coiled threadwork is ultimately formed which splits
longitudinally and then breaks up into lengths, the resulting
split segments representing the twenty-four somatic chromo-
somes. As the mode of division of these cells has been
fully figured and described by us, it will be unnecessary to
recapitulate the entire sequence here, and we may pass on to
a consideration of the first maiotic prophase itself.
(b) The Maiotic Phase.
As in the cockroach, cells which are about to pass out
of the pre-maiotic cycle and enter upon the synaptic meta-
morphosis present an increase in their chromatin, and a
gradual enlargement, which for a time seems to keep pace
with the nuclear metamorphosis. In torpedo and other ex-
amples of elasmobranch fishes we find that the very fine spirem
THE MALOTIC PHASE IN ANIMALS AND PLAN'S. 539
which at first emerges from the resting nucleus gradually
becomes, as in the cockroach, more and more polarised ; and,
just as in the insect, we have found that the subsequent
metamorphosis consists of a gradual thickening of the in-
dividual threads and an unfolding of the contraction figure
into a coarse spirem which in its fully-developed condition is
evenly distributed over the surface of the nucleus. At about
this period many of the individual threads can be seen to be
longitudinally split, and the cells then remain for a long
period in the same condition, the threadwork merely becom-
ing thicker and more chromatic as time goes on. When
this period has come to an end, as in the cockroach, the
threads become once more polarised, and this contraction
corresponds with the second synaptic figure previously de-
scribed. We have found, moreover, that in the elasmol! ranch
as in the cockroach, these secondary loops are unquestionably
to be regarded as the individual forerunners of the dias-
chistic (heterotype) chromosomes; their sides present an
obvious longitudinal split, and in many cases the loops be-
come twisted upon themselves as they do in plants; in fact,
all the various types of diaschistic (heterotype) chromosomes
are found to which we have already referred.
Now, in the amphibia which had been described before we
had examined the elasmobranchs spermato-genesis the hollow
of the heterotype loop. The aperture in the ring, or the space
between the twisted rods with open ends, had always been
regarded by Flemming, Meves, and others as the opened-out
portions of the original longitudinal split traversing the
spirem thread; but when that which happens in the cock-
roach is borne in mind, it becomes obvious that all the stages
in the insect and the fishes up to this point correspond,
and consequently it became at once suggested to us that
probably these and the subsequent stages among the verte-
brates had been misinterpreted.
A careful review of the ensuing stages among elasmo-
branchs has convinced us that this supposition is correct ; and
that for all practical purposes the later stages in the first maiotic
540 J, BRETLAND FARMER AND J. E. S. MOORE.
(heterotype) division in these fishes are, like the earlier ones,
carried out in the same manner as in the cockroach itself.
There seems to be no room left for doubt that the coarse
spirem contracts again into a polarised figure and that the
loops of this second contraction are converted directly into
the diaschistic heterotype chromosomes.
We have found no figures which in any way militate
against this view of the origin of the heterotype chromosomes
among these fishes; and the apparent reason why the process
has not hitherto been apprehended seems to be that among
elasmobranchs the second contraction-figure, or synapsis,
is much more rapid than in the cockroach. Consequently
one is apt to pass over its existence, from stages corre-
sponding to that represented in fig. 68 to the later stage
given in fig. 73, whereby it might be natural to conclude
that the heterotype loop, or ring, arose from the opening out
of the longitudinal split in the spirem segments. So far,
then, as the origin of the reduced number of heterotype
chromosomes is concerned, we reach, after a renewed study of
the process in elasmobranchs, exactly the same conclusion
as we did in the case of the cockroach; that is, the
synaptic and pre-maiotic prophases in the origin of the repro-
ductive elements in these widely separated animal types are
apparently identical. In both, the reduction of the number of
chromosomes is brought about by a special prophase, wherein
pairs of longitudinally split somatic chromosomes become
temporarily united together, and afterwards merely separate
from one another during the diaschistic (heterotype) division.
In Elasmobranchs the later phases of the first maiotic
mitosis have already been fully described by one of us,! and
at the present time we have nothing to add to the descrip-
tion already published. With respect to the second maiotic
division, however, it is now necessary to append some
correction to the previous description. In this it may be
remembered that the second maiotic or homotype division
was described as having the same characters as the first
' J. E. 8. Moore, loc. cit.
THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 541
maiotic division itself, or as being a second diaschistic
(heterotype) mitosis. This we have found now not to be
the case; for although the details in the second maiotic
division in these fishes are extremely difficult to elucidate,
we have been able, through a careful re-examination, to
determine that the apparent similarity of the phases in this
to the first maiotic series is fictitious, and that in reality
this division has the ordinary pre-maiotic anaschistic
characters as in other animals and plants.
We have now dealt fully with a typical insect, and several
Elasmobranch types, and the intention has been to use
these as illustrations of the manner in which reproductive
elements become matured in widely sundered classes of
animal forms. It has been found that so faras these different
examples are concerned there is a complete parallelism among
them all. It has been shown further that the similarity which
exists between the reduction in insects and Elasmobranchs
also subsists between all these zoological examples and the
various vegetable forms previously described. Throughout
the whole series the process is carried out on an essentially
similar plan. In themselves, and certainly when we bear in
mind what has already been ascertained with respect to a host
of other animal and vegetable forms, the present examples
would be quite sufficient to indicate that there exists through-
out the whole range of living forms a fundamental similarity
in the manner in which the numerical reduction of the
chromosomes is achieved. Still, it will also be apparent that,
especially among the vertebrate class, several amphibia and
mammals have been dealt with by various authors in great
detail, notably salamander, triton, and the rat, and it will also
be apparent that the results attained in relation to these are
not in accord with those put forward with respect to insects and
fishes by ourselves. Especially in the able works of Flemming
and Meves, we find a view taken with respect to the origin of
the diaschistic (heterotype) chromosomes similar to that held
by many botanists with respect to the flowering plants—
542 J. BRETLAND FARMER AND J. E. S. MOORE.
namely, that the loops and rings arise through the opening
out of the longitudinal split in the segments of the spirem
thread. by the neontologist who proposed the new classification. . . . In
FP. A. Bauer, M.A. like manner, Mr. Bather supplies the results of some ten years’
assisted by assiduous studies of fossil crinoids, and the classificatory portions
of the work are, therefore, beyond the general knowledge of
J. W. Grecory, D.Sc., and zoologists, and present us with a distinct advance on existing
i
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A. Lhe heterotype, and homotype mitoses according to Hicker Vom Rath and Riickert.
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