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QUARTERLY JOURNAL

MICROSCOPICAL SCIENCE.

EDITED BY

Hae A uANKES TER, M.A. bb.D., ERS.

HONORARY FELLOW OF EXETER COLLEGE, OXFORD; CORRESPONDENT OF THE INSTITUTE OF FRANCR
AND OF THE IMPERIAL ACADEMY OF SCIENCES OF ST. PETERSBURG, AND OF THE ACADEMY
OF SCIENCKS OF PHILADELPHIA; FORKIGN MEMBER OF THE ROYAL SOCIETY OF
SCIENCES OF GOTTINGEN AND OF THE ROYAL BOHEMIAN SOCIETY OF SCIENCES,
AND OF THE ACADEMY OF THE LINCEI OF ROME, AND OF TILK AMERICAN
ACADEMY OF ARTS AND SCIENCES OF BOSTON ASSOCIATE OF THE
ROYAL ACADEMY OF BELGIU)D HONORARY MEMBER OF THE
NEW YORK ACADEMY OF SCIENCES, AND OF THE
CAMBRIDGE PHILOSOPHICAL SOCIETY, AND OF
TUE ROYAL PHYSICAL SOCIETY OF EDIN-
BURGH ; HONORARY MEMBER OF THE
BIOLOGICAL SOCIETY OF PARIS;
FOREIGN ASSOCIATE OF THK NATIONAL ACADEMY OF SCIENCES, U.S., AND MEMBER OF
THE AMERICAN PHILOSOPHICAL SOCIETY 3
DIRKCTOKR OF THE NATURAL HISTORY DEPARTMENTS OF THE BRITISH MUSKUM ; LATE FULLERTAN
PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN;
LATE LINACRE PROFESSOR OF COMPARATIVE ANATOMY AND FELLOW OF MERTON COLLEGE, OXFORD.

WITH THE CO-OPERATION OF

ADAM SEDGWICK, M.A., F.R.S.,

FELLOW AND TUTOR OF TRINITY COLLEGE, CAMBRIDGE 5

W. F. R. WELDON, M.A., F.RB.S.,

TON COLLKGK, OXFORD:

LINACRE PROFESSOR OF COMPARATIVE ANATOMY AND FELLOW OF ME
LATE FELLOW OF ST. JOUN’S COLLEGR, CAMBRIDG

AND

SYDNEY J. HICKSON, M.A.,- BIRZS.,

BEYER PROFESSOR OF ZOOLOGY IN THE OWENS COLLEGE, MANCHESTER,

VOLUME 48.—New Sentes.
With Aithographic Plates and Engrabings on ood.

Kp
peer’

OND: OUNE:
J. & A. CHURCHILL, 7, GREAT MARLBOROUGH STREET.
1905.

CON TERN Is:

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.,
Director of the Plymouth Laboratory of the Marine Biological
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
Biology i in the University of Otago, New Zealand. (With Plates
Th) s ‘ 5 : ‘

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.,
Acting Professor of Pathology, Medical College, Caleutta. (With
Plate 25) F ; :

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
Plates 2933)

Notes on the Anatomy of Gazelletta. By G. Herserr Fow ter,
BA. PhD, Rees, Flas: 4

CONTENTS OF No. 192, N.S., FEBRUARY, 1904.

MEMOIRS :
On the Maiotie Phase (Reduction Divisions) in Animals and Plants.
By J. Bretuanp Farmer, D.Sc., F.R.S., and J. EK. S. Moors,
A.R.C.S., F.L.S. (With Plates 34—41) :
On the Structure and Development of the Somatic and Heterotype
Chromosomes of Tradescantia Virginica. By J.B. Farmer,
F.R.S., and Dororuy Smove. (With Plates 42 and’43)

On the Behaviour of the Nucleolus in the Spermatogenesis of Peri-
planeta Americana. By J. E. S. Moors, A.R.C.S., F.L.S., and
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
Waaner, M.A., Instructor in Zoology, University of Wisconsin

TitLe, INDEX, AND CONTENTS,

PAGE

359

367

489

559

New Series, No. 189 (Vol. 48, Part 1). Price 10s.

JULY, 1904.
THE

QUARTERLY JOURNAL

MICROSCOPICAL SCIENCE.

EDITED BY

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

HONORARY FELLOW OF EXETER COLLEGE, OXFORD; CORRESPONDENT OF THE INSTITUTE OF FRANCK
AND OF THE IMPERIAL ACADEMY OF SCIENCES OF ST. PETERSBURG, AND OF THE ACADEMY
OF SCIENCKS OF PHILADELPHIA; FOREIGN MEMBER OF THE ROYAL SOCIETY OF
SCIENCES OF GOTTINGEN AND OF THE ROYAL BONEMIAN SOCIETY OF SCIENCES,
AND OF THE ACADEMY OF THE LINCEI OF ROME, AND OF THR AMERICAN
ACADEMY OF ARTS AND SCIENCES OF BOSTON} ASSOCIATE OF THE
ROYAL ACADEMY OF BELGIUM; HONORARY MEMBER OF THE
NEW YORK ACADEMY OF SCIENCES, AND OF THE
CAMBRIDGE PHILOSOPHICAL SOCIETY, AND OF
THE ROYAL PHYSICAL SOCIETY OF EDIN-
BURGH ; HONORARY MEMBER OF THE
BIOLOGICAL SOCIETY OF PARIS;
FOREIGN ASSOCIATE OF THE NATIONAL ACADEMY OF SCIENCES, U-S., AND MEMBER OF
THE AMERICAN PHILOSOPHICAL SOCIETY 5
DIRECTOR OF THE NATURAL HISTORY DEPARTMENTS OF THE BRITISH MUSEUM, LATE FULLERIAN
PROFESSOR OF PHYSIOLOGY IN THE ROYAT INSTITUTION OF GREAT BRITAIN;
LATE LINACRE PROFESSOR OF COMPARATIVE ANATOMY AND FELLOW OF MERTON COLLEGE, OXFORD.

WITH THE CO-OPERATION OF

ADAM SEDGWICK, M.A. F.BS.,

FELLOW AND TUTOR OF TRINITY COLLEGE, CAMBRIDGE 5

W. F. R. WELDON, M.A., F.B.S.,

LINACKE PROFESSOR OF COMPARATIVE ANATOMY AND FELLOW OF MERTON COLLEGK, OXFORD;
LATE FELLOW OF ST. JOUN’S COLLEGE, CAMBRIDGE 3

AND

SYDNEY J. HICKSON, M.A., F.R.S.,

BEYER PROFESSOR OF ZOOLUGY IN THE OWENS COLLEGE, MANCHESTER.

WITH LITHOGRAPHIC PLATES AND ENGRAVINGS ON WOOD.

ON. DON’:
& A. CHURCHILL, 7 GREAT MARLBOROUGH STREET.

1904.

Adlard and Son,] [London and Dorking.

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.

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.

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

\ { 7 Lilly

ita tet A 202
i"

i =

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,

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

CONS

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.

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

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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Houssay, F.—‘‘ Recherches sur l’opercule et les glandes du pied des
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Jerrries, Gwyn.—‘ British Conchology,’ vol. iii, pp. 286—3386, London,
1865.

JuEnine, H. von.—‘ Zu. Morph. der Niere des Sog. Moll.” ‘ Zeit. fiir
wiss. Zool.,’ Bd. xxix, p. 5883—614, 1877.

Lacaze Dututers.—“ Mémoir sur le systeme nerveux de |’ Haliotide,”
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Lacaze DurHters.—‘ Otocystes ou capsules auditives des Mollusques
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Lacaze Dututers.—‘ De l’epipodium chez quelques Gastéropodes,”
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Moore and Ranpies.—‘“ A New Interpretation of the Gastric Organs of
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Ixx, 1902, pp. 2831—237.

PeLseNEER, P.—‘‘Sur la valeur morphologique de l’epidodium des
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. PrtsENEER, P.—‘‘ Sur l’epipodium des Mollusques,” 3me note, ‘ Bull
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ANATOMY AND AFFINITIES OF THE TROCHIDA. 75

36. PrtsenrER, P.—“ Recherches Morphologiques et Phylogénetiques sur
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37. Perrier, Remy.—‘‘ Recherches sur l’anatomie et l’histologie du rein des
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1889.

38. Ropert, A.—“ Le Troque (Trochus turbinatus, Born.),” § Zoologie
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39. SpenceL.— Die Geruchsorgane und das Nervensystem der Mollusken,”
‘Zeit. fiir wiss. Zool.,’ Bd. xxxv, 1881.

40. TureLe.— Beitrage zur Kenntniss der Mollusken. i, Ueber das Epipo-
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41. TH1eLe.— Beitrage zur Kenntniss der Mollusken. iii, Ueber Haut-
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42. 'TroscuEt, H.—‘ Das Gebiss der Schnecken,’ Berlin, 1856—1863.

43. TRrvon.—‘ Manual of Conchology,’ vol. xi, Trochide.

44, Wrecmann.—“ Contribution & Vhistoire naturelle des Haliotides,”
‘Archiv. de Zool. expér.,’ 2e sér., t. ii, 1884.

45. Woopwarp, M. F.—“ The Anatomy of Pleurotomaria Beyrichii,”
‘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.

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

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. <A section through two of
these is shown in fig. 21 (Pl. 9). ‘They are almost entirely
- cuticular structures (cal.), the epithelial cells only protruding
for a very short distance into them. The internal, lightly
staining layer of the cuticle found in this region of the body,
though curved slightly outwards, is little if at all thickened.
The tubercle is chiefly formed, therefore, by a great thickening
of the outer or deeply staining layer of the cuticle. The
character of this layer seems also to be slightly altered, for in
methyl-blue-eosin preparations it takes on a deep reddish or
purple tint rather than blue, and often exhibits a character-
istic radial structure due to a number of deeply staining,
radiating bars (fig. 21).

The appearance of these tubercles at once brings to mind
those upon which stand the tubes of the gland-cells already

THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. 97

described. In the present case, however, no external openings
can be demonstrated, unless the radial lines already men-
tioned really represent pores. Nevertheless an examination
of a large number both of the gland papille and of the
callosities produces a conviction that the latter are in reality
essentially the same structures as the former, either in a more
highly developed or in a regenerate state.

The cells lying immediately beneath the tubercle on the
right-hand side of the section figured (fig. 21) are somewhat
difficult of interpretation. It is possible that the long process
(p) immediately beneath the cuticle is homologous with the
internal portion of the tube of the gland-cells (figs. 22 and
23), and that the nucleus (n’) is the nucleus of a gland-
cell with which this tube communicates. I have not, how-
ever, found other sections which appear to confirm this
view.

Although gland-cells are by no means uncommon in the
general body epithelium, by far the largest development of
such cells takes place in the dorsal and ventral cirri of the
parapodia. Fig. 25 (Pl. 10), was drawn from one of the cirri
from the regenerated tail end of a living worm, where the
transparency of the tissue allowed the gland-cells to be seen.
Fig. 24 (Pl. 10) represents a section through a cirrus from
about the eighteenth segment of the body. From the latter
figure it will be seen that a cirrus is crowded with a number of
flask-shaped cells, the long necks of which open to the exterior
through papille elevated above the surface of the cirrus. (In
fig. 25 the long necks of the cells are not shown, the fact that
they were not visible in the fresh tissue being probably due
to their great transparency. In fig. 24 the actual continuity
between any one cell and the external opening does not
appear, but this is quite easily demonstrated in a series of
sections.)

The gland-cells in the cirri appear under at least three
forms, which are illustrated in figs. 26, 27, 28, and 29
(Pl. 10). The figures have been drawn from transverse sec-
tions of cirri preserved in Hermann’s fluid and stained with

98 E. J. ALLEN.

methyl-blue-eosin. Cells of each of the three types possess
long necks opening at the exterior as above described.

Type A.—F ig. 26 represents a section of a type of gland-
cell which occurs in cirri from all parts of the body. In
those on the anterior segments, from 1 to 13, it is the only kind
found. Inthe cirri of the segments behind the thirteenth cells
of this character are not numerous and general, but some-
times occur towards the distal end of the cirrus (cf. fig. 24,
the very dark cells). These cells stain very deeply, the pro-
toplasm being crowded with granules, which take on an in-
tense blue colour. There are also present a number of short
rods and particles of different shapes, which are even more
deeply stained than the granules. The nucleus stains red
with the eosin. It contains one large mass of deeply staining
chromatin (nucleolus) surrounded by a clear space. This
space is bounded by a membrane, and attached to this mem-
brane is a hemispherical cap of deeply staining substance
half enclosing the nucleus. A section through this cap gives
the crescent-shaped figure shown in fig. 26 (Pl. 10). The
relation of the cap to the nucleolus reminds one of the
relation of the yolk nucleus of the ovum to the germinal
vesicle (cf. fig. 61). The remainder of the nucleus—that is to
say, the space between the nuclear membrane and the nucleolar
membrane and cap—is filled with a large number of small
granules, stained red with the eosin, but not taking on by
any means such an intense colour as the nucleolus and the
nucleolar cap.

Type B.—Figs. 27 and 28 represent sections through the
type of gland-cells which occupy the greater part of the
bodies of the cirri on all the segments from the fourteenth
backwards. The change from cirri packed with cells of
Type A in segment 15 to those containing almost entirely
cells of ype B in segment 14 is very marked.

Cells of this type have a ground-substance with a homo-
geneous appearance—or showing in preserved material at
most a faint indication of a network—which stains pale blue.
In this ground substance are a number of rods (sections of

THE ANATOMY OF PQ@CILOCHATUS, CLAPAREDE. 99

the rods appear circular) which stain a deeper blue than the
ground substance of their cell, but do not take on by any
means the intense blue colour of the granules in cells of
Type A. The nuclei of cells of Type B resemble those of
Type A in general structure. The nucleolus is, however,
somewhat smaller, and all the structures take on a much less
intense stain. A noteworthy feature in the sections of these
cells is that the cell-substance outside the nucleus contains
patches of fine red granules exactly resembling the red
eranules seen in the nucleus itself. These patches occur
more especially in immediate contact with the nucleus, and
their whole appearance seems to suggest very strongly that
the granules are being manufactured in the nucleus and
passed out into the surrounding substance.

For a valuable summary of our knowledge of the part
played by the nucleus in secretion, and a very extensive list
of the papers dealing with this subject, reference may be
made to a recent paper by Launoy (1903).

Type C.—In cells of the third type (fig. 29), which also
occur in the cirri of segments from 14 backwards, the ground
substance stains pale blue, shows a reticular structure in pre-
parations preserved in Hermann’s fluid, and contains a few
deeply staining rods. The nucleus stains deeply and diffusely,
but is shrunken and irregular in shape. Cells of this type
are apparently those in which the process of the formation of
the secretory product is complete and the nucleus no longer
active. If this be so they are in reality a later stage in the
condition of cells of Type B.

If fragments of the living worm are strongly irritated, a
large mass of clear, transparent mucus is secreted, which is
in all probability discharged from the gland-cells of the cirri
above described.

For a summarised account of epithelial gland-cells of
various kinds found in other Polychztes reference may be
made to Hisig’s monograph on the Capitellide (Hisig, 1887).

100 Bows, ALLEN:

Palps.

The external appearance of the palps (Pl. 7, fig. 1) has
already been described (p. 86). A section of the palp shows
it to be a hollow tube having a large central cavity, through
which the blood-vessel of the palp runs (PI. 10, fig. 30, p. bv.).
The walls of the tube are composed of two layers of cells, a
thick outer layer of large epithelial cells (ep.) lined internally
by a thin sheet of mesoderm cells. The nuclei of both the
epidermic and mesodermic cells have a very characteristic
appearance, since each possesses a single, large, deeply staining
nucleolus. Occasionally a nucleus is seen with two such
nucleoli of equal size, which may indicate division. The
walls of the blood-vessel which runs along the length of the
palp are thick, and contain nuclei similar to those of the
mesodermic cells. From the pulsation of the vessel in the
living worm these walls are known to be muscular.

The cavity of the palp communicates with the general body-
cavity of the first segment of the worm by means of a tube
formed by a continuation into the body-cavity of the meso-
derm-cells lining the cavity of the palp (fig. 30, plp.v.). This
tube, just after it leaves the palp, is surrounded by a strong
band of annular muscle-fibres, by the contraction of which
the cavity of the palp can be completely cut off from the body-
cavity of the first segment. It is clear that the palps, which
are capable of very great extension, are elongated by the
pressure of fluid from the body-cavity into their cavity.
When once the palps are filled, the contraction of the annular
muscle-fibres just described will enable them to continue
extended without the necessity of the body pressure being
maintained. (For an account of the muscular septa which
come into play when the fluid is pressed forward see p. 123.)

At the outer side of the palp, between the base of the palp
and the palp-ganglion, lies a small diverticle (p/p. div.) of the
palp cavity, which appears to run forwards and then end
blindly. The meaning of this structure I have not fully
understood.

THE ANA'LOMY OF P@CILOCHATUS, CLAPAREDE. 101

Cheeta.

An account has already been given, in describing the ex-
ternal features, of the different types of bristles which Poecilo-
cheetus possesses (see Pl. 9, figs. 13—19). ‘lhe shafts of these
bristles almost all show longitudinal striation, together with
transverse markings at irregular intervals. The longitudinal
striations are shown in sections to be due to the fact that the
bristle is built up of a large number of longitudinal tubes
lying side by side. This is especially marked in the stout
hooks of the neuropodium, which occur in segments 2 and 3,
and in the hooks of the notopodium in the terminal segments.
All cheetze with stout shafts also show the structure well.

This type of minute structure in the bristles of Cheetopods
has recently been described in detail by Schepotieff (1903),
to whose paper reference should be made for further details.

Nervous System.

Brain.—Practically the whole of the head of the worm is
occupied by the substance of the brain. This substance con-
sists of a ventral! mass of nervous felt-work (punctated sub-
stance) covered externally by a mass of ganglion-cells.

The arrangement of the parts can be best explained by
reference to the diagrammatic figure of a section of the brain
given in the text (Fig. 1).

This figure represents a thick sagittal (longitudinal-vertical)
section through the brain cut a little on one side of the middle
line, and has been constructed from an examination of several
series of thin sections. The large circumcesophageal commis-
sures, which put the brain in communication with the ventral
nerve-cord of the worm, can be traced from the particular mass
of punctated substance which occupies the centre of the brain

1 In the description of the brain the terms anterior, posterior, dorsal and
ventral are used on the assumption that the worm has the proboscis slightly
everted as in the sagittal section fig. 42 (Pl. 11). In the position of repose,
what is here called the anterior surface, becomes more ventral in position.

102 B23. ALLEN:

(m. b.), it being probably here that the fibres of the commis-
sures from the two sides cross each other. From this region
the fibres pass first forwards and downwards and then turn
outwards, after which, in sagittal sections, they form a circular
patch of transversly cut fibres (comm.), which can be easily
followed through the brain substance. Arising from the
same central mass of punctated substance (m. b.), but at a
level external to that at which the fibres of the commissures
leave it, a bundle of fibres can be traced, which passes
forwards and downwards into the epithelium in front of the
brain, from whence it can be easily followed as a well-marked

ant.gang.
cells ee

'
nt. loomm ap.

Fic. 1.—Diagrammatie sagittal section through one side of the brain
of Pecilochetus. ant. gang. cells, anterior ganglion cells; x. ¢.,
nerve to median tentacle ; comm., cesophageal commissure; 2. p. 1,
anterior root of nerve to palp-ganglion; z. p. 2, posterior ditto ;
nz. p. G., nerve to palp-ganglion ; post. gang. cells, posterior ganglion-
cells; m. d., central mass of fibres from which cesophageal com-
missures and tentacle nerve arise; z.%.g., nerve to nuchal
ganglion.
nerve (n. ¢.) to the median tentacle, which lies just in front of
the mouth (cf. Pl. 11, fig. 42). The bundle of fibres just
described exists on each side of the brain, and two nerves, one
from each side, can be followed with perfect certainty from
the centre of the brain to the single median tentacle.
From about the middle of the ventral surface of the brain
on each side a bundle of fibres arises (7. p. 1) which passes
backwards. This bundle of fibres is subsequently joined by

a second bundle (n.p.2), which leaves the brain at its

THE ANATOMY OF PQCILOCHETUS, CLAPAREDE, 108

posterior end. The two bundles unite to form a stout nerve,
which runs outwards to a large ganglion, situated at the base
of the palp, the palp-ganglion (cf. Pl. 10, fig. 30). The nerve
of the palp-ganglion thus has a double origin in the brain.

From the posterior end of the brain, fibres also pass back-
wards and enter the nuchal organ, where they mingle with
the felt-work of fibres of a large ganglion which lies in the
base of that organ—the nuchal ganglion (fig. 42). The
fibres passing from the brain to the nuchal organ are not
easy to demonstrate, as they do not form definite nerve-
bundles, but rather two thin sheets, one from each half of
the brain, the individual fibres of which pass between or below
the epithelial cells lying at the junction of the nuchal organ
and brain.

The ganglion-cells of the brain form an almost continuous
cap covering the punctated substance. It is, however, pos-
sible to distinguish in each half of the brain an anterior group
of cells (Text-fig. 1, ant. gang. cells), the fibres from which
unite in a bundle, which is directed downwards and back-
wards into the mass of punctated substance lying below that
region (m. b.), where the cesophageal commissures take origin.
The farther fate of this bundle of fibres could not be ascer-
tained, but a comparison with transverse sections appears to
suggest that it may cross with its fellow and then give rise to
the anterior root of the palp-ganglion nerve (n. p. 1) of the
opposite side.

A number of very large ganglion-cells (post gang. cells),
situated at the posterior end of the brain, which send their
processes into the general mass of the central felt-work, are
also conspicuous. hese cells, however, do not appear to
constitute a definite group, but grade off into the general
mass of ganglion-cells.

The Palp-ganglia.—The two palp-ganglia are situated at
some distance from the brain. They are ganglia of considerable
size, and contain large ganglion-cells, as well asa nervous felt-
work. They lie one on each side of the body at the base of
the palp and external to that structure (PI. 10, fig. 30). Hach

104 i? G2CA GLEN.

ganglion receives the fibres of the palp-ganglion nerve (the
origin of which in the brain has already been described), and
gives off a bundle of nerve-fibres, which immediately enters
the palp.

The Nuchal Ganglion.—The nuchal ganglion les in the
base of the nuchal organ, and consists of a considerable mass of
nervous felt-work surrounded by a number of ganglion-cells,
some of them of large size. Bundles of nerve-fibres pass from
it into the different branches of the organ, and these doubt-
less supply the external ciliated grooves which run along
those branches (cf. p. 112), though individual fibres have
not actually been traced so far.

The Relation of the Different Parts of the Brain
to one another.—The arrangement of the brain and the
ganglia connected with it in Poecilochetus is of some theo-
retical interest when considered in connection with that of
other Polychetes. Our recent knowledge of the structure of
the Polychzete enchaphalon is largely based on the careful work
of Racovitza (1896). This author distinguishes three regions,
to which he gives equal morphological importance—the fore-
brain (Cerveau antérieur), with which the palp-ganglia are
connected; the mid-brain (Cerveau moyen) with the anten-
nary and optic ganglia; and the hind brain (Cerveau posté-
rieur) withthe nuchal ganglia. The relations of the parts in
Pecilochetus are noteworthy in that the palp-gangla and
the nuchal ganglion are not fused in the mass of the brain, as in
the forms described by Racovitza, but are separated distinctly
from it. The eyes being simple, there is no development of
optic ganglia, and the antennary ganglia are also not obvious.
With regard to the divisions of the brain itself, the facts
point to the presence of the first two at any rate of Raco-
vitza’s three regions, though the matter is by no means clear.
The anterior ganglion-cells (Text-fig. 1, ant. gang. cells),
with their bundle of fibres, which, as has been stated, very
possibly form the first root of the palp-ganglion nerve, would
represent the fore-brain of Racovitza, whilst the fact that the
nerves to the tentacle (n. t.) and the cesophageal commissures

THE ANATOMY OF PHCILOCHATUS, CLAPAREDE. 105

all spring from the same point in the centre of the brain
(m. b.) would seem to point to this region as the mid-brain of
that author. With regard to the hind brain, there is more
difficulty. Judging from Racovitza’s figures of Hurythee
borealis and Euphrosyne Audonini, it would seem that
what I have termed the nuchal ganglion of Peecilochetus is
homologous with what he calls the hind brain in those species.
But in Pecilochetus this structure is separated sharply
from the brain itself, being only connected with it by nerve-
fibres. These fibres leave the brain at its posterior end, but
there is no region in the brain itself which can be clearly
marked off as a hind brain. The large posterior ganglion-
cells to which reference has been made (Text-fig. 1, post.
gang. cells) might at first sight be regarded as an indication
of such a structure, but against this view it can be urged that
they give off their processes to the region of the mid-brain,
from which the commissures and tentacle nerves take origin.

The relations found in Peecilochetus seem to indicate
that it would be more correct to term what Racovitza calls
the hind brain in Eurythce and Huprosyne the nuchal
ganglia. The nuchal ganglion of Pwecilochetus is clearly
comparable to the palp-gaglion, and not to any division
of the brain itself.

Ventral Nerve Cord—tThe ventral nerve-cord lies en-
tirely in the epidermis (Pl. 10, fig. 32). The ganglia of the
different segments are not very sharply marked off from each
other, ganglion-cells being scattered somewhat irregularly
along the whole length of the cord. Definite ganglia are, how-
ever, indicated in each segment by a considerable increase in
the number of ganglion-cells, by the presence of masses of
nervous felt-work (punctated substance) as well as by the
roots of the lateral nerves.

Two giant fibres (fig. 82 g. f.) run along the cord. In pre-
served specimens these fibres vary in diameter in different
regions, but are generally of very large size. The connection
of these fibres with ganglion-cells has not been traced.

Stomatogastric System—What seems to be a well-

voL. 48, pART 1.—NeEW SERIES, 8

106 kK. J. ALLEN.

developed stomatogastric nervous system, comprising a
ganglion and a large bundle of nerve-fibres on the pharynx,
is found in Pecilochetus, but my preparations have not
sufficed to discover the complete details of its arrangement.

Lateral Sense-organs.

The position and external appearance of the lateral sense-
organs are described on pp. 87—92 (figs. 1, 2, 7, etc.). In
segments 1—6, as well as in the segments at the tail end of
the body, it will be remembered that these organs have the
form of pear-shaped papillz protruding beyond the surface
of the parapodium between the cirri, whilst in the remaining
segments they lie in the parapodium with only a slightly
raised rim protruding beyond the general body surface.

The histological structure is best studied in detail in
organs of the latter type, as, for example, in those at about
segment 20, and the most instructive general view is seen
in horizontal sections of the body. Such a section is shown
in fig. 84 (Pl. 10), which passes through the middle of a lateral
organ. Externally the organ appears as a cup-shaped de-
pression or crater surrounded by a raised circular rim. From
the floor of the depression there springs a mass of stiff hairs,
which, when the organ is not much contracted, extend far
beyond the raised margin of the rim.

The external rim itself is composed of clear, trans-
parent, epithelial cells, often showing vacuoles of some size
(Pl. 10, fig. 34, ep. 7.) ‘These cells, as well as the face of the
depression (hair-bearing area) are covered externally by a
continuation of the ordinary body cuticle (cwu.), which,
excepting at the points of attachment of the muscle-fibres
to be described in the next paragraph, shows no marked
variation in thickness in the region of the lateral organs.

Internal Muscular System.—Immediately within the
epithelial ridge the hair-bearing area is surrounded on its
dorsal, its anterior and its posterior sides by bands of muscle-
fibre (m.f.), which extend from the cuticle to the internal

THE ANATOMY OF PQHCILOCHATUS, CLAPAREDE. 107

apex of the organ, where they pass into the large muscles
attached to that apex (fig. 34, musc.) The arrangement of
these muscle-bands will be seen on comparing the three
figures representing respectively a horizontal section (fig. 34),
a section in the longitudinal-vertical plane of the animal, and
therefore parallel to the hair-bearing surface of the organ
(fig. 38), and a transverse section through the anterior row
of muscle-bands (fig. 35). From figs. 34 and 38 especially it
will be seen that along the anterior margin of the hair-
bearing area a single row only of muscle-bands exists, that
along the dorsal margin there are several rows, whilst on the
posterior side there are two rows with a narrow strip of the
hair-bearing area between them. On the ventral border there
are no muscle-bands at all. The ends of the muscle-bands in
contact with the cuticle broaden considerably, so that the
surface of contact between the bands and the cuticle is greatly
enlarged (figs. 34 and 35), the cuticle itself being at the
same time very much thickened (fig. 35). The course of the
fibres from the margin of the hair-bearing area to the apex
of the organ is easily demonstrated in a series of horizontal
sections such as fig. 34.

In fig. 35, which represents a transverse section through
the anterior line of muscle-bands, it will be noticed that
between the bands a row of rather large, oval nuclei exists.
It is not clear to exactly what cells these nuclei belong.
hey may be the nuclei of the muscle-bands, in which case
each band would be morphologically a single cell, or they
may belong to a series of ganglion-cells of a similar type
to the large ganglion-cells shown in figs. 36 and 387 (see
below).

Fig. 37 is drawn from a transverse section at the level of
the posterior rows of muscle-bands.

In addition to the bands already described a number of
single muscle-fibres pass from the apex of the organ to the
cuticle in the region posterior to the raised rim of the hair-
bearing area; these are also indicated in fig. 34. All these
muscle-bands and fibres stain deeply in sections.

108 BT ALEN:

By means of the muscular system just described, assisted by
the larger muscles (musc.) attached to the apex of the organ,
not only can the whole organ be withdrawn to a certain extent
within the body, but the hair-bearing area and its rim can be
at the same time still further withdrawn, until the external
appearance of the organ is little more than that of a pore with
a number of hairs protruding through it.

The hair-bearing cellsare represented in figs. 34.and 36.
The exact outlines of the individual cells are not marked out
in any of the preparations, and the meaning of the appearances
shown is therefore not quite clear. The great resemblance
between these appearances and those shown by the ciliated
cells of the nuchal groove (PI. 11, figs. 40 and 41) and of the
intestinal epithelium (Pl. 11, fig. 44) gives, however, an
important clue to their interpretation.

Immediately under the external layer of cuticle is an un-
stained space or layer of unstained protoplasm,’ through
which the inner ends of the sensory hairs can be seen to pass
just as in the ciliated cells of the nuchal organ (cf. p. 114)
and of the cesophagus (p. 117).

Then follows a layer of deeply staining short rods (figs. 34
and 36 s.7.), which is succeeded by a layer of faintly staining
long rods (J.7.), just as in the ciliated cells. The only
difference exhibited in the two cases up to this point is that
the hairs, in their course through the clear space between the
cuticle and the line of short rods, stain somewhat deeply
immediately below the cuticle, red in methyl-blue-eosin
preparations like the short rods themselves, producing the
appearance of a secondary layer of short rods (fig. 36, s.r. 2),
which, however, is very much less marked than the main
layer. This layer occupies a similar position to the layer of
“bulbi” of ciliated cells, which are further referred to on
p- 118:

The short rods, as in the ciliated cells, stain bright red in

1 Tt is possible that the size of this space may be exaggerated by contraction

of the protoplasm of the cells caused by the reagents employed. In that case
the layer of short rods would lie closer to the cuticle.

THE ANATOMY OF P@CILOCHMTUS, CLAPAREDE. 109

methyl-blue-eosin preparations, the long rods blue. The
diameter of the latter appears to be somewhat greater than
the diameter of the hairs where these pass through the
cuticle.

In the horizontal section shown in fig. 34, at a level
immediately inside the ends of the long rods, three large oval
nuclei (v./.) are seen, and in neighbouring sections other
nuclei appear in a corresponding position. These I take to be
_ the nuclei of the hair-bearing cells, the interpretation being
based on their similarity in situation to those of the ciliated
cells of the esophagus and nuchal organ already referred to
(cf. p. 114 and p. 117). The possibility must, however, be
borne in mind that these nuclei may really belong to the
posterior row of muscle-bands, and their position in fig. 34
lends some support to this view. In this case they would
resemble the nuclei shown in fig. 35 lying between the
anterior muscle-bands. Should further investigation show
this to be the case, the nuclei of the hair-bearing cells must be
sought elsewhere.

Ganglion.—The remaining structure to be described in
connection with the lateral sense-organ is the ganglion. The
ganglion-cells may be conveniently divided into two groups—
a group of large cells, which occupy the anterior dorsal
portion of the organ, in front of and above the hair-bearing
cells, and a group composed of a large number of small cells,
which constitute the posterior portion of the organ.

The large ganglion-celis are represented in figs. 36 and 37
(transverse sections). They are large, uni-polar cells, with
their processes generally directed towards the cuticle.
Whether these processes eventually reach the cuticle or
whether they come into contact with the hair-bearing cells I
have been unable to determine with certainty. ‘The nuclei of
these ganglion-cells are very large, and either spherical or
oval in shape. ‘he contents of the cell-bodies stain deeply.

The small ganglion-cells (fig. 54, g. 1.0.) do not for the
most part show definite cell-outlines in the preparations, but
appear rather as a mass of more or less closely packed nuclei,

110 EL. GALLEN,

with an intermediate substance, much of which is clearly made
up of a feltwork of fine fibres. The whole structure exactly
esembles what is found in parts of the brain and the ventral
nerve-cord. In many sections fine fibres can be clearly seen
passing from this ganglionic mass to the hair-bearing cells
(fig. 34). The exact relations of these fibres to the latter
cells could not be determined.

The Protruding Lateral Organs of the Anterior
Segments.—Fig. 39 (P]. 10) shows a section through one of
the protruding organs of the anterior segments, the external
views of which are seen in figs. 2, 3,4, and 5 (Pl. 7). The
structure is essentially the same as that of the organs already
described, but the various parts are packed more closely
together, so that the details are less easily made out. No
further description is, however, necessary.

Connection with the Central Nervous System.—
The ganglion of each lateral organ receives a bundle of fibres
from a nerve which passes up the body-wall from the ganglion
of the ventral nerve-cord. ‘The course of this nerve can be
easily followed in sections, its fibres lying immediately
beneath the cells of the epidermis, between these cells and the
muscular layers of the body-wall. After giving off the branch
to the ganglion of the lateral organ the nerve continues its
course in a dorsal direction, and has been definitely traced as
far as the notopodial cirrus.

Muscles.—The muscles attached to the apex of the lateral
organs are described on p. 125.

Historical.—the first detailed description of the structure
of the lateral sense-organs of Polychetes was given by Hisig
(1879 and 1887), who studied them in the Capitellids. ‘There
are some differences of importance between Hisig’s account
of the minute structure of the organs in Capitellids and the
description of what is found in Pocilochetus set forth in
the present paper. In Capitellids Kisig describes a layer of
rods immediately under the chitin, and this is followed by an
irregularly arranged layer of spindle-shaped bodies. ‘lhe
layer of rods would seem to correspond with the long rods in

THE ANATOMY OF PG@CILOCHATUS, CLAPAREDE. 111

the organs of Pecilochetus, whilst the deeply staining
layer of short rods either does not exist in the Capitellids or
was not rendered evident by the methods employed. The
spindles of Eisig I am inclined to regard as the nuclei of the
hair-bearing cells, being led to this view by a comparison of
the structure of the hair-bearing cells with the ciliated cells of
the nuchal grooves and of the cesophagus in Peecilochetus.
On the other hand, they may represent bipolar ganglion-cells.

Ashworth (1902) has recently written on the structure of the
lateral sense-organs in Scalibregma inflatum. He de-
scribes and figures the sensory hairs, the layer of short, deeply
staining rods, and the long rods, all of which have apparently
the same relations as in Pecilochetus. Ashworth, how-
ever, interprets the long rods as hair-bearing cells and the
deeply staining short rods as their nuclei. With this inter-
pretation I am unable to agree, both from the appearance of
the structures themselves in my preparations as well as from
a comparison with the known structure of ciliated cells (cf.
p- 118).

Ashworth also describes and figures large unipolar and
bipolar ganglion-cells similar to those found in Peecilo-
chetus, and states that the processes of these cells can be
traced into continuity with the internal ends of the rods which
carry the sense-hairs. Ihave been unable to make out with
certainty such a connection in Peecilochetus, though the
appearances presented are in no way opposed to its ex-
istence.

Further studies on the lateral sense-organs in the different
groups of Polychetes, made with the aid of more special
methods for determining the course of the nervous fibres, are
necessary before their structure can be fully understood.

Nuchal Organ.

One of the most characteristic features of the genus Peci-
lochxtus is the great development of the nuchal organ,
which, as already stated, consists of a broad, basal portion
springing from the dorsal surface of the posterior end of the

112 E. J. ALLEN.

head, and of three long, tentacle-like processes extending
backwards from it (fig. 7, nuch.). Of these three processes,
the middle one is the longest, and may run at least as far
backwards as segment 6, the lateral ones ending about seg-
ment 4 (fig. 1). The lateral processes have occasionally been
observed with a secondary branch. The whole organ is
covered with a number of sensory hairs, and each process
possesses two lateral ciliated grooves, which run along the
whole of its length and extend on to the basal portion (PI. 11,
figs. 42 and 47, nuch.).

Claparéde (in Ehlers, 1874) and Levinsen (1883) have both
described the three processes, but have failed to recognise
their true nature as nuchal organs. These two authors have,
however, shown clearly that the organ in question develops
as an outgrowth from the posterior cephalic region. Such
enlarged nuchal organs are by no means unknown amongst
Polychetes, though none have yet been described having
dimensions comparable with those of Pceecilochetus. The
nuchal organs of Virchowia clavata figured by Viguier
(1886) may be referred to, as well as those of Amblyo-
syllis spectabilis and Autolytus longiferiens, figured
by Malaquin (1893). Gravier (1896) describes the nuchal
organ of Notophyllum, which takes the form of two lappets
extending from the posterior end of the prostomium to the
middle of the third segment. Racovitza (1896) shows that the
earuncle of the Amphinomide is an enlarged nuchal organ.

In the living Peecilochetus the nuchal organ has a
brown or brownish-green colour. Sections show that this
colour is due to granules deposited in the epidermie cells,
and also to a number of spherical bodies scattered through
the tissue, which possess a single, deeply staining nucleus,
and are filled with dark granules (Pl. 11, fig. 40).

The base of the nuchal organ is occupied by the nuchal
ganglion (fig. 42, auch. gang.), which has already been
described (p. 104). The central axis of each of the pro-
cesses of the organ is formed by a tube lined with mesoderm-
cells, the tube being in direct communication with the general

THE ANATOMY OF PHCILOCHETUS, CLAPAREDE. 1138

body-cavity of the first segment of the worm. ‘lhe space
between this central canal and the epidermis is filled with an
irregular mass of cells, forming a loose tissue, in which may
be seen many of the spherical bodies filled with granules
mentioned in the last paragraph. Figs. 40 and 41 (Pl. 11),
representing respectively a transverse section through one of
the ciated grooves and an enlarged section of a portion of
the epithelium of a groove, show the minute structure of the
tissue of the nuchal organ. The epidermis, excepting in the
ciliated grooves themselves, consists of low epithelial cells
crowded with dark-coloured granules, the granules being in
many places congregated into masses of considerable size.
The epithelial cells are covered externally by a layer of
cuticle resembling the general body cuticle. No gland-cells,
such as have been described in other parts of the body, have
been observed in the nuchal organ.

The ciliated epithelial cells of the grooves are very large
and much elongated, the protoplasm of the bodies of the cells
is filled with dark granules similar to those found elsewhere
in the organ, and the large oval nuclei lie near the bases of
the cells, their long axes being parallel to the long axes of
the cells. The structure of the external or ciliated ends of
the cells presents features of interest, and can be seen from
figs. 40 and 41. The cuticle (cu. g.) covering the cells under-
goes a very considerable external thickening. In sections
stained with methyl-blue-eosin the basal portion only of this
cuticle stains a deep blue, carrying on the line of the general
cuticle of the nuchal organ; the external thickened portion
remains clear and unstained (cw. g.), and in favourable places
is seen to be traversed by a series of faint lines running at
right angles to its surface. Since these lines are much more
widely separated than the cilia, they would seem not to be due
to the cilia passing through the cuticle. Racovitza (1896)
has described a very similar thickening of the cuticle in the
earuncle of Huphrosyne Audouini. In the case of that
worm, however, the thickening does not extend over the
areas of cuticle lying just above the ciliated cells.

114 HK. J. ALLEN.

Immediately inside the cuticle is a narrow zone, which in
sections appears clear, but across which the cilia can be seen
to pass. ‘his zone may, to some extent at least, be due to
shrinkage of the bodies of the cells during preservation and
their consequent withdrawal from the cuticle. It is followed by
what, in transverse sections, appears as a deeply staining line
(stained red in methyl-blue-eosin preparations). ‘This line, on
examination with high powers, resolves itself into a layer of
deeply staining shortrods (fig.41,57.), one rod apparently corre-
sponding with each cilium. Within this layer of deeply staining
rods the internal ends of the cilia can be followed for a consider-
able distance as faintly staining rods (blue in methyl-blue-
eosin preparations), the diameters of which appear somewhat
greater than the diameters of the cilia outside the body (fig.
41, /.7.). In the portion of the cell occupied by these rods
the protoplasm of the cell appears clear, and not granular as
it does throughout the general body of the cell. These rela-
tions will be seen to correspond with those found in the
ciliated cells of the wall of the cesophagus (p. 117, et seq.,
where the work of previous authors is discussed, Pl. 11, fig. 44)
and in the hair-bearing cells of the lateral organs (p. 1068,
Pl. 10, figs. 34, 36, 39).

Iu the nuchal organ of Pcecilochetus, I have failed to
identify nerve-cells, other than the ganglion-cells already
described in the basal portion of the organ. It is quite
possible, however, that some of the cells of the intermediate
tissue are really such nerve-cells.

For a full historical account of the nuchal organ in Poly-
cheeta, as well as for an excellent description of the detailed
histological structure of that organ in a number of different
types, reference should be made to the paper by Racovitza
(1896) already several times mentioned.

Hyes.

As previously stated, Pcecilochztus possesses four eyes,
one pair on the dorsal surface of the prostomium, and a

THE ANATOMY OF P@CILOCHETUS, CLAPAREDE. 115

larger pair on the ventral surface. All four eyes have prac-
tically the same structure, and are of a very simple type.
Fig. 33 (Pl. 10) represents a section through one of the ventral
eyes cut in the longitudinal vertical plane. The eye consists
of a single large optic cell with one nucleus. ‘he proto-
plasm of the swollen, rounded end of the cell is slightly
modified, being more transparent than that found in the rest
of the cell, and showing indications of a radial structure.
This end of the cell is surrounded by a large cup-shaped mass
of black pigment, made up of numerous spherical drops of
black substance. <A nucleus can often be detected at the
outer margin of this mass of pigment, but I have been unable
to satisfy myself as to whether more than one nucleus belongs
to each ; that is to say, whether the pigment cup is unicellular,
or whether it consists of several cells.

Such simple eyes are now weli known amongst the Platy-
helminths, tor instance, in Planaria torva, and also in
certain Polychztes, as, for example, Spio fuliginosus and
Polyophthalmus pictus. A full account of the literature
of the subject, together with a wealth of new observations,
will be found in the series of papers ‘‘ Untersuchungen iiber
die Organe der Lichtempfindung bei niederen Thieren,”’ by
Richard Hesse (see especially Hesse, 1897 and 1899).

Alimentary Canal.

The Divisions of the Alimentary Canal.—tThe ex-
ternal features of the mouth are seen in fig. 8 (Pl. 8), and
have already been described (see p. 88). ‘The animal
possesses a short proboscis with thick walls, which in pre-
served specimens is always almost if not entirely withdrawn
into the mouth. Fig. 42 (Pl. 11) represents a section through
these parts. ‘lhe external folds surrounding the mouth are
seen, as well as the median tentacle (m. tent.), which has its
point of insertion close to the anterior edge of the mouth,
into which its basal portion can be withdrawn.

The portion of the alimentary canal extending from the

116 By oc ALLEN.

mouth to the posterior septum of the eighth segment may be
conveniently divided into two parts corresponding to what
are known in other Polycheetes as cesophagus and pharynx
(or gizzard). ‘lhere is, however, no definite line of demarca-
tion between these two parts. ‘The cesophagus is lined by
elongated, ciliated epithelial cells, outside which is a thin
layer of annular muscles followed by a thin layer of longi-
tudinal ones. Proceeding further backwards the epithelial
layer becomes narrower, the cells being considerably less
elongated, whilst, on the other hand, the muscular layers,
especially the layer of annular muscles, become much more
strongly developed (cf. figs. 42 and 48 with fig. 43). It
is this muscular portion which may be termed the pharynx
(ph.) In its hinder part the epithelium is thrown into folds
or villi, and at the pomt where the septum of segment 8 is
attached to the alimentary canal one large fold, forming a
kind of valve (fig. 43, v.) seems to constitute a definite line of
demarcation between the pharynx and the intestine. As is
explained on p. 128, the septa in this region of the body are
pushed very much backwards; the junction of the pharynx
and intestine, although really at the posterior end of the eighth
segment, may lie as far back as the level of the twelfth
parapodia. From the posterior septum of segment 8 to the
posterior septum of segment 13, the intestine continues as a
comparatively straight tube, not differing much in structure
from the pharynx, excepting that the muscular layers are
rapidly reduced until they almost entirely disappear (figs. 43
and 50). In segments 14 and 15 the intestine is con-
siderably dilated, but narrows again as it passes through
each septum. In the segments from 16 backwards, this
enlargement of the intestine in each segment becomes very
great, so that the dilated intestine occupies a large part of
the body-cavity (figs. ] and 58). In the living worm these
intestinal pouches are constantly expanding and contracting,
the movements of the intestine constituting, in the posterior
region of the body, the principal mode of circulation of the
blood.

THE ANATOMY OF P@CILOCHARTUS, CLAPARRDE., 117

Ciliated Groove of the Alimentary Canal.—tl'ans-
verse sections show the existence of a deep, longitudinal
ciliated groove running along the mid-ventral line of the
alimentary canal throughout its entire length. A similar
groove has been described in many Polycheetes, and is homo-
logous with the secondary intestine (“nebendarm”) of the
Capitellids (Hisig, 1887).

The Epithelium of the Alimentary Canal.—The
epithelium of the alimentary canal, though differing much in
appearance in its different parts, consists essentially of cells
of two kinds, (1) columnar epithelial cells, and (2) goblet-
shaped gland-cells lying between the columnar cells and
opening by more or less narrow necks into the lumen of the
canal.

The columnar epithelial cells of the cesophagus (PI. 11, fig.
44) are narrow and elongated, with large, oval nuclei, the
long axes of which lie parallel to the long axes of the cells.
The cells themselves are strongly ciliated and show a
characteristic structure, similar to that which exists in other
ciliated cells of the worm (compare the groove of the nuchal
organ, p. 114, the lateral sense-organs, p. 108, and the epi-
thelium of the genital funnels, p. 155). The appearance pre-
sented by the ciliated borders is seen in fig. 44. The surface
of each cell is covered by a thin cuticle (cw.) continuous with
the cuticle of the external body surface. Immediately within
this cuticle is a clear space through which the inner ends of
the cilia are seen to pass. ‘This clear space, which may in
part at any rate be due to contraction of the contents of the
cells during the preservation of the tissue, is bounded inter-
nally by a layer of deeply staining short rods (s.7.), which
appear to be in reality slightly thickened, deeply staining
portions of the individual cilia. In sections these rods le in
a straight line which runs parallel to the cuticle. Beyond
this deeply staining layer of rods the ends of the cilia (J. 7.)
can still be traced for some little distance into the protoplasm
of the cell-body, which is at first clear excepting for the
striation due to these inner ends of the cilia, and subsequently

118 KE. J. ALLEN.

becomes granular, many of the granules being of a character-
istic yellowish-brown colour. The cilia cannot be traced as
far as the nuclei of the cells. Insections of material fixed in
Hermann’s fluid and stained with a mixture of methyl-blue-
eosin (fig. 44), the cuticle stains deep blue, the cilia faintly
blue, the layer of short rods bright red, the cell protoplasm
bluish, whilst the nuclei are clear, with chromatin granules
and network stained deep red.

The structure of the ciliated cells above described, as well
as those of the nuchal groove (p. 114) and the hair-bearing
cells of the lateral sense-organs (p. 108), agrees with that found
by Engelmann (1880) in the ciliated cells from the intestine
and gills of Cyclas cornea and Anodonta, and in the
ciliated cells from the nose of the frog. Engelmann clearly
describes the short rods under the name of “ Fussstiicke,”
and also the internal prolongations of the cilia within the
cells, which he was, however, able to trace much further into
the body of the cell than I have succeeded in doing. He also
found between the short rods and the cilia proper a certain
differentiation of the substance of the bases of the cilia, which
he calls the “bulbus.” These ‘‘bulbi” would appear to cor-
respond to the secondary layer of short rods described in the
present paper at the bases of the sensory hairs of the lateral
sense-organs (p. 108, Pl. 10, figs. 34, 36, 39).

Englemann states that Eimer was the first to describe
correctly the relations of the short rods (Fussstiicke) to the
cilia, and he gives several other references to previous papers
dealing with the subject.

More recently Greenwood (1892) has shown a very similar
structure in the ciliated cells of the intestine of Lumbricus,
though in the latter worm, to judge by the figures, the layer
of short, deeply staining rods is less marked. Greenwood,
however, states (p. 245) “the cilia occasionally bear tiny
varicosities before they pass into the body of the cell.
Under a sufficiently high power these are distinguishable as
belonging each to a ciliary thread, and they recall Heiden-
hain’s description of similar thickenings, which may be seen

THE ANATOMY OF P@CILOCHETUS, CLAPAREDE. 119

under suitable conditions at the base of the intestinal rods of
the dog.”

The similarity in structure of the ciliated cells of, say, the
cesophagus and nuchal organ of Peecilochetus to that of
the cells of the intestinal mucous membrane of vertebrates
furnished with a “ striated border,” as described by Heiden-
hain (1888), is very striking, especially if his fig. vi is com-
pared with my figs. 44 or 41, and seems strongly to support
the suggestion contained in Greenwood’s paper, that the cells
of the vertebrate intestine may be modified ciliated cells.

Galvagni (1903) has just published a description with
figures showing a similar structure in the ciliated cells of the
alimentary canal of Ctenodrilus to that found in Peecilo-
chetus.!

In concluding the discussion on these ciliated cells it seems
worth while to draw attention to the possibility that the
“short rods” described in this paper (‘ Fussstiicke ” of
Engelmann) are homologous with the middle-piece (‘ Mittel-
stiick ”’) so well known in spermatozoa. ‘The staining re-
actions of the two structures are similar, and they occupy
similar positions in relation to the cilium and flagellum
respectively.

The goblet-shaped gland-cells in the epithelium of the
cesophagus present themselves in at least three forms. In
preparations preserved and stained by my usual method these
cells show the following features (see Pl. 11, fig. 44) :—(1)
Goblet-shaped cells crowded with granules which stain bright
red, the bright red granules filling both the body of the eell
and the long neck to where it opens into the lumen of the
cesophagus; the intermediate substance of the cell remains
unstained; the chromatin of the nucleus stains red; the
nuclear membrane and the body of the nucleus are clear and
unstained (fig. 44, gl. 1).

(2) Goblet-shaped cells containing granules, which are less

1 Since the above was written an important paper on the epithelium of the
intestine of Polychetes has been published by Brasil (1904) in which the
structures here described are fully dealt with,

120 Bs. ALGEN:

numerous than those in cells of the previous type and stain
blue instead of red (fig. 44, gl. 2).

(3) Cells still of the same general shape, but less swollen,
without granules, but filled with a homogeneous substance
staining faintly blue and showing at most slight indications
of a network such as is usually produced by the action of
preserving fluids ; the nuclei of these cells stain more deeply
and more diffusely than those of the previous types, their
ground substance taking on a faint blue tint, whilst the
chromatin is red or purple (fig. 44, gl. 3).

Cells of the first and second kinds are clearly actively
secreting cells, whilst those of the third kind seem to be cells
of the second which have completely discharged their secre-
tion and are in a resting condition, in all probability waiting
to commence the secretory process upon suitable stimulation.
In some specimens nearly all the gland-cells in the ceso-
phagus are in the condition last described.

As will be seen by comparing the two sets of figures and
the two descriptions, the gland-cells of the cesophagus show
many points of resemblance with the gland-cells of the skin
and of the parapodial cirri.

The structure of the epithelium of the pharynx and of the
anterior portion of the intestine is essentially the same as that
which has been described for the cesophagus ; the cells, how-
ever, become gradually less elongated in shape, and the
number of gland-cells diminishes.

At about segment 16 or 17 the type of intestinal epithelium
which persists through the greater part of the body of the
worm is established. This epithelium is found in two
markedly different conditions, which appear to depend upon
whether the intestine is filled with food and digestion is
actively going on, or whether food is absent from it. These
two conditions are illustrated in figs. 45 and 46 (PI. 11).

Fig. 45 shows the state of things which is found when food
is present and digestion is actively proceeding. ‘I'he epithelial
cells (ep.) are large and swollen, whilst the gland-cells have
shrivelled till little more than the nucleus is visible (gl.).

THE ANATOMY OF PRHCILOCHATUS, CLAPAREDE. 121

The shape of the epithelial cells may differ considerably from
that of those found in the anterior part of the alimentary
canal already described. In those shown in fig. 45 the cell-
body is short and broad, but more elongated cells are also
common. ‘The cells are filled with large granules, which
have a dark brown colour in preparations preserved with
osmic acid mixtures. The granules are crowded together at
that surface of the cell which immediately borders the lumen
of the intestine, and are more scattered throughout the rest
of the cell protoplasm. These cells have not, in my prepara-
tions, the appearance of being ciliated. heir surface is,
however, covered with a faintly staining substance, which
might possibly represent broken-down cilia, but is more
probably a layer of the food-contents of the intestine, which
is being absorbed by the cells. In the same sections the
cilia are often sufficiently well-marked on the cells of the
intestinal groove. The nucleus is situated near the base of
the cell. In the condition now being described (fig, 45) it is
large in size and stains deeply (diffuse blue with red granules
in methyl-blue-eosin preparations). It consists of an outer
membrane filled with granules, and possesses a single nucle-
olus. ‘This nucleolus is surrounded by a clear space, the
space being bordered by a membrane which carries on its
outer side a deeply staining, hemispherical cap. The nucleus
thus resembles very closely the nuclei of the parapodial gland-
cells already described (cf. fig. 26 and p. 98). Nuclei
showing clearly all the points mentioned are not, however,
met with very frequently in the preparations. ‘he bases of
these cells lie close to the blood-sinus which completely
surrounds the intestine (fig. 45, 7.bl.s.).

If one may be permitted to hazard a guess at the physio-
logical processes which are going on in these cells, merely
from a study of their appearance and the arrangement of
their parts, it may be suggested that the cells at their free
ends are absorbing from the cavity of the intestine food
material already partly digested by the action of the secretion
from the gland-cells. A portion, at least, of this material

VoL. 48, PART 1.—NEW SERIES. 9

12? Ee as AGEN:

appears in the cells in the form of the yellowish-brown
granules, which are thickly congregated at the surface of
absorption. ‘The nucleus is obviously in a very active state,
and its position at the base of the cell, at the point of contact
of the cell with the intestinal blood-sinus, seems, if we accept
the view advocated by Korschelt that the nucleus is generally
to be found where the chief function of the cell is in active
progress, to suggest that the food substance there undergoes
transformation and is passed through the cell-wall into the
blood.

The second condition in which the epithelial cells of the
intestine are found (when the intestine does not contain food)
is illustrated in fig. 46. The gland-cells (gl.), which in the
former state were shrivelled and inert, are now large and
active. They are pear-shaped, filled with granules (which in
methyl-blue-eosin preparations stain bright red), and their
necks extend quite to the surface of the epithelial layer.
The nuclei are clear and transparent, with deeply staining
chromatin, the greater part of which is concentrated im a
single large nucleolus.

The columnar cells (ep.), on the other hand, contain no
granules ; their protoplasm stains faintly and diffusely (blue
in methyl-blue-eosin preparations), and shows only an indefi-
nite reticulation probably due to the action of the reagents.
The nuclei are much smaller than in the active epithelial cells
previously described (cf. figs. 45 and 46), the chromatin
eranules stain less deeply (red), and the whole nucleus is
diffusely tinted (blue). It would seem, therefore, that whilst
the gland-cells are now active the columnar cells are inert.

The epithelium in only two other parts of the alimen-
tary canal calls for mention, namely, that in the ventral
ciliated groove and that in the terminal segments of the
body.

The cells of the ciliated groove are elongated and distinctly
ciliated, though they do not show the layer of deeply staining
short rods, which was found in the ciliated cells of the

cesophagus.

THE ANATOMY OF PHCILOCHATUS, CLAPAREDE. 123

The epithelium of the intestine in the posterior region of
the body (rectum) differs only from that already described
for the intestine in the fact that all the cells are ciliated, the
cilia being very long. The action of these cilia can be clearly
seen in the living worm.

Body-cavity.

The well-marked segmentation of the body seen externally
is equally distinct internally, each segment being separated
from that which follows it by a transverse septum. ‘The
septa, the first of which lies between the first and second
segments, appear to divide the body-cavity into a number of
separate compartments, between which no communication
can be shown to exist. ‘hese compartments are not, how-
ever, of equal size, for in the region occupied by the muscular
pharynx the septa, instead of lying in a vertical plane cor-
responding to that of the external segmentation of the body,
are pushed backwards for a considerable distance. This
pushing backwards of the septa, which is shown in the sagittal
section represented in fig. 47 (Pl. 11) and in the horizontal
section fig. 43, commences with the septum at the posterior
end of segment 5, reaches a maximum in segment 8, and
is still obvious in segment 12. The posterior septa of
seements 8, 9, 10, and 11 all extend back to the region,
which external segmentation indicates as segment 12, and
that of seement 12 is pushed back into 13. ‘The septa of
segment 8 to 11 join the alimentary canal immediately behind
the point where the pharynx passes into the intestine (fig.
43, v.). These septa are also noteworthy from the fact that
the muscle-fibres, which are present to a considerable extent
in the septa of most of the segments of the body, are here
developed to a very remarkable extent, so that septa 8 to
11 have become highly muscular organs. ‘This muscular
character of the septa, combined with the manner in which
they are pushed backwards, seems to suggest that they are
concerned with the protrusion of the anterior portion of the
alimentary canal in the form of a proboscis, and probably

124. BE. tn ALE:

also with the extension of the palps. I have only once seen
a protrusion of the proboscis, and it did not then extend
much beyond the front of the head. The structures just
described, however, appear to suggest the possibility of a
much greater protrusion.

In living specimens of Pcecilochztus an indication of
the backward extension of the septa of seements 5 to 12
can be seen in the backward course of the lateral blood-
vessels, which run in the septa (fig. 1 and p. 126).

In the segments from the thirteenth backwards, the internal
and external segmentation correspond.

Each of the septa dividing the body-cavity consists of a
double layer of ccelomic epithelial cells with a layer, more or
less strongly developed, of muscle-fibres between. The
epithelium is extended over the main body muscles, and over
the other organs of the body. On most organs, however,
the cells are seldom much developed, their presence being
often only indicated by occasional nuclei.

Extensions of the body-cavity into the interior of the
nuchal organ and of the palps are mentioned in the para-
graphs dealing with those structures,

Musculature.

The muscles of the body-wall, as is usual in the
Polychztes, are arranged in two layers, a layer of annular
muscles and a layer of longitudinal. Of these two layers,
however, the annular is very feebly developed in Peecilo-
chetus, whilst the longitudinal is well developed. The
principal muscles in each segment are massed into four
bundles, two dorsal lying on either side of the dorsal blood-
vessel and two ventral on either side of the nerve-cord. ‘The
slight development of the annular muscles would appear to
be connected with the more or less sedentary habits of the
worm. The annular muscles attain their greatest develop-
ment in worms which burrow constantly and rapidly in the
soil (e.g. Nephthys, Aricia).

THE ANATOMY OF P@ICILOCHAITUS, CLAPAREDE. 125

Bands of oblique muscles run from the outer dorsal edge of
the ventral nerve-cord on each side, pass over the longitu-
dinal ventral muscle-bands, and are inserted in the lateral
walls of the body between the parapodia.

External Muscles of the Lateral Organs and
Muscles of the Chetal Sacs.—Four large bands of
muscle are inserted at the apex of each lateral organ (PI. 10,
figs. 34 and 37, musc.), viz. (1) a band which runs down-
wards and inwards to the inner end of the neuropodial
cheetal sac, which is clearly one of the two bands used to
protrude the chet; (2) a similar band running upwards
and inwards to the base of the notopodial cheetal sac; (3) a
broad band of muscle which runs from the lateral organ
downwards, passes behind the cheetal sac and is inserted in
the ventral body-wall below the base of the neuropodial
cirrus, and (4) a similar band running upwards and inserted
in the dorsal body-wall above the base of the notopodial
cirrus. Lying in contact with the muscle-fibres of bands 3
and 4 are a number of fibres, which run direct from the
dorsal to the ventral body-wall. ‘These pass close to the apex
of the lateral organ, to which they are joined by connective
tissue, but they have no free ends inserted in that apex.

In addition to the muscle-bands described above, (1) and
(2), running from the apex of the lateral organs to the
inner ends of the two cheetal sacs, a second band runs from
the inner end of each sac, passes in the one case downwards
and outwards and in the other upwards and outwards and is
inserted in the body-wall. Thus each sac has two strong
muscles from its apex to the body-wall, one above and one
below, by the contraction of which it and its chet are
protruded.

Blood System.

The anatomy of the vascular system constitutes one of
the most striking and interesting features of Poecilo-
chetus. The bright scarlet of the blood gives to the
anterior portion of the body its characteristic colour, and the

126 B.. Js ALLEN.

alternate filling and emptying of the larger vessels produces
an appearance of rapid colour-change. A further change of
colour is seen also, which is due to changes in the chemical
character of the blood. Ifa worm be allowed to remain for
some time in a vessel containing only a small quantity of sea-
water, the bright scarlet of the blood changes to a dull purple-
red, but the original colour immediately reappears on the
addition of a new supply of water, as it does under similar
circumstances in Magelona (cf. Benham, 1896). The red
colour therefore would seem to be due to the presence in the
blood of one of the respiratory pigments.

The general arrangements of the principal vessels is
illustrated in fig. 1, which has been constructed from obser-
vations on the living worm, corrected and extended by the
examination of sections. lor the purposes of description
the body of the worm must be divided into three regions, an
anterior region consisting of segments 1 to 11, an inter-
mediate region, comprising the four segments 12, 13, 14, and
15, and a posterior region from segment 16 to the end of the
body.

Anterior Re gion.—Between the alimentary canal and
the dorsal body-wall there is in the anterior region a large,
muscular, dorsal vessel of cylindrical shape capable of very
considerable expansion, waves of expansion and contraction
passing along it from behind forwards.

Corresponding with each of the body segments from the
third to the eleventh, a lateral vessel is given off on each
side from the dorsal vessel, and runs outwards and downwards
in the posterior septum of the segment. Owing to the fact
already described that the posterior septa of segments 5
to 11 are pushed backwards, the origins of the lateral vessels
in these segments, running, as the vessels do during the first
part of their course, actually in the septum, are also carried
backwards, the vessels being in consequence much elongated
and running forwards (PI. 7, fig. 1). In this way the lateral
vessels belonging to segment 7 arise from the dorsal vessel at
about the plane of the junction of the ninth and tenth para-

THE ANATOMY OF P@CILOCHBTUS, CLAPAREDE. 127

podia, whilst the lateral vessels of segments 8, 9, 10 and 11
arise close together about the level of the twelfth parapodia.
On reaching the base of the parapodium of the segment to
which it belongs, the lateral blood-vessel in each case leaves
the septum and sends a loop forwards into the parapodium,
the loop returning upon itself and joining the septum again in
the neighbourhood of the internal opening of the nephridium.
The vessel here divides into two branches. One of these
branches passes downwards and inwards and opens directly
into the large longitudinal ventral blood-vessel, the other
passes through the septum close to the tube of the
nephridium, and in the segment behind divides up into a
number of blind, finger-shaped processes, which spread out in
the body-cavity of that segment. Under favourable circum-
stances these finger-shaped processes can be seen in the
living worm, alternately expanding and contracting as they
fill with the bright red blood and empty themselves again.
On one occasion, in a worm the body-wall of which had burst
on compression, I was fortunate enough to see one of these
clusters of finger-shaped vessels lying outside the body and
to satisfy myself that each process visible ended blindly.
The vessels when filled with blood are very conspicuous, and
easily followed in sections (PI. 11, figs. 48 and 49), and in
spite of repeated attempts I have never been able to find that
this cluster of vessels has any communication with the rest
of the blood system, excepting through the branch of the
lateral vessel of the segment in front, which accompanies the
nephridial tube through the septum dividing the two segments.
Fig. 51 (Pl. 12), drawn from a longitudinal vertical section,
shows clearly the branch of the lateral vessel (b. lat. v.)
passing back through the septum into the segment behind and
there breaking up into finger-shaped processes (f. p.). Fig. 49
(Pl. 11) represents a transverse section through the finger-
shaped processes (f. p.), and shows the great enlargement of the
blood-vessel which can take place at the point where the pro-
cesses are given off. Fig. 48 (PI. 11) shows well the latter part
of the course of the lateral vessels (dat. v.) to the ventral vessel.

128 E. J. ALLEN.

Shortly after leaving the dorsal vessel, each lateral vessel
gives off a branch, which breaks up upon the wall of the
cesophagus and pharynx, uniting with and helping to form a
rich network of blood-vessels, which extends over the
surface of these organs (Pl. 7, fig. 1). This network also
gives rise to vessels which start from the under surface of
the cesophagus and pharynx and pass directly downwards to
the ventral vessel (fig. 48, it. v.) Blood can thus pass
either directly from the dorsal to the ventral vessel through
the laterals, or indirectly after passing through the network
on the walls of the alimentary canal.

At its anterior end, immediately behind the brain, the
dorsal vessel bifurcates (Pl. 7, fig. 1), sending a large vessel to
each of the palps. These large vessels pass along the axes of
the palps (PI. 10, fig. 30), and in the living worm are subject to
rhythmical pulsations, which keep the blood within them con-
stantly in motion. ‘lhe palps appear to be one of the principal
organs of respiration of the worm (see p. 86).

Immediately after entering the palp the large blood-vessel
gives off a branch, which passes downwards and backwards
through the first and second segments. It sends one secondary
branch to the cesophageal network and another through the
posterior septum of the second segment to form a cluster of
blind, finger-shaped vessels in the third segment, and then, pass-
ing below the cesophagus, joins with its fellow of the opposite
side to form the anterior end of the ventral vessel. ‘These
structures can best be understood from an examination of fig. 1.

As only one blood-vessel passes along the axis of each palp,
it would seem that the pulsations of the vessel itself must take
place in such a manner as alternately to drive blood in and
then out of the vessel, but owing to the readiness with which
the palps are thrown off on the slightest irritation, direct
observations on the point are not easy to make.

The Middle Region.—The modification of the vascular
system in segments 12, 15, 14 and 15, the middle region of
the body, is of special and peculiar interest.

In each of these segments the dorsal vessel is itself much

THE ANATOMY OF P@CILOCHETUS, CLAPAREDE. 129

enlarged, forming on either side large lateral pouches, which
are alternately inflated with blood and emptied (PI. 7, fig. 1;
Pl. 11, figs. 43 and 47, p.dv.).. When fully inflated the pouches
occupy almost the whole of the body-cavity, and the wave of
expansion and contraction, passing from segment to segment
from behind forward, is a striking phenomenon.

The forward movement of the blood from one segment to
the next in front is regulated by a series of valves situated in
the dorsal vessel between each successive pair of pouches, as
well as immediately anterior to the first pair and posterior to
the last. ‘There are thus five valves altogether. These valves,
two of which are shown in sagittal section in fig. 50 (Pl. 11),
consist of somewhat stout membranes composed of spindle-
shaped cells, attached ventrally to the wall of the blood-vessel,
but with a free dorsal edge, which pressed from in front
comes into contact with the wall of the vessel and prevents
the blood from passing backwards. In fig. 50 the anterior
valve (vl. seg. 14) is open, whilst the posterior valve (vd. seg. 15)
is closed. It is clear that contraction of the walls of the
blood-vessel and its lateral pouches will force the blood
forwards, whilst the valves will prevent any blood from going
in the opposite direction.

It must be pointed out that the lateral pouches of the
dorsal vessel in segments 12, 15, 14 and 15 are not swollen
lateral vessels, such as are described by Benham (1896) in
Magelona, for in sections the true lateral vessels, similar in
their general relations to those of the anterior segments, and
like them giving rise to a cluster of finger-shaped processes
in the segment behind, are easily seen aud followed. ‘These
lateral vessels arise from the dorsal vessel in each case behind
the lateral pouches, at the point where the dorsal vessel
passes through the posterior septum of the segment, and they
run throughout the greater part of their course in this septum.

The Posterior Region.—In the posterior region of the
body, from segment 16 backwards, the arrangement of the
vascular system undergoes a great change. The dorsal vessel
can no longer be distinguished as a separate organ, but the

130 B25; ADEN:

dorsal vessel and the network of blood-vessels which sur-
rounded the cesophagus and pharynx, have as it were run
together to form one large sinus, which completely surrounds
the intestine (figs. 45 and 59, ¢. bl. s.). The circulation of
the blood is now brought about, not by the contraction of a
blood-vessel with highly muscular walls, but by the contrac-
tion and expansion of the segmental pouches of the intestine.

The intestinal sinus communicates with the ventral vessel
by short, vertical branches, and it also gives off in each
seginent, from the region of the narrowed portion of the
intestine behind the intestinal pouches, the lateral blood-
vessels. Hach lateral blood-vessel runs in the posterior
septum of the segment, at first upwards and outwards, then
outwards and downwards, to the base of the gills on the
notopodium. It enters the first gill filament, to the tip of
which it runs; it there turns sharply on itself and comes
back again to the base of the gill, thus forming a single,
simple loop, which occupies the whole of the interior of the
gill filaments (PI. 10, fig. 31). After having formed a similar
loop in all the other gill filaments the blood-vessel again runs
in the posterior septum of the segment, its course being
inwards and downwards to the ventral vessel, which it joins.
During this latter part of its course the vessel sends back a
branch along the tube of the nephridium into the segment
behind, which appears to supply not only the nephridium,
but also the genital organs, which lie along the tube of the
nephridium (Pl. 12, figs. 52 and 60, b. lat. v.). There is, how-
ever, no obvious formation of a cluster of blind, finger-
shaped processes such as was met with in the anterior seg-
meuts of the worm.

One point of interest in connection with the lateral vessels
remains to be noticed. In describing the course of the
lateral vessels of the anterior segments, it was stated that
each vessel, before sending back its branch to the finger-
shaped processes in the segment behind, ran forwards and
formed a simple loop at the base of the parapodium. It will
be remembered that the parapodia of these anterior segments

THE ANATOMY OF P@CILOCHEHTUS, CLAPAREDE. 131

have no gills, but the loop just mentioned would seem to
represent in a rudimentary way the loops of the lateral vessels
which supply the gill filaments in the posterior gill-bearing
segments.

The Structure of the Walls of the Blood-vessels.—
The different layers of the walls of the blood-vessels attain
their greatest development in the dorsal vessel. This vessel
is lined internally by an epithelial layer consisting of flattened
cells, the general height of which is less than the diameter of
their nuclei, so that the portion of the cell in the immediate
neighbourhood of a nucleus often appears to protrude into the
blood-space. ‘lhe bodies of the cells generally remain clear
and unstained.

Proceeding outwards from this epithelial layer, one finds
a layer of longitudinal muscle-fibres, which is followed by
several layers of annular muscles, this part of the wall being
especially developed in the dorsal vessel. The whole vessel is
covered externally by a layer of coelomic epithelial cells,
which form the lining of the body-cavity. Like that of the
cells lining the vessel internally, the protoplasm of these
external cells remains clear and unstained (PI. 11, fig. 50).

The differences met with in the structure of the walls of
the other blood-vessels of the body are due to the reduction
of the various layers, more especially of the muscular layers.
In the ventral vessel, as well as in the lateral pouches of the
dorsal vessel, the epithelial layers are well developed, but the
muscular layers, though still obvious, are greatly reduced. In
the lateral vessels and their various branches, especially when
extended with blood, ouly a thin membrane in which an
occasional nucleus is seen can generally be recognised. It 1s
probable, however, that both epithelial layers are present,
whilst the muscular layer has almost, if not entirely, dis-
appeared,

In the external wall of the intestinal blood-sinus the two
epithelial layers can be made out, with a layer of muscle-
fibres between them. Internally the bases of the intestinal
epithelial cells appear to be separated from the blood-space by

132 PAREN,

a thin layer of very flat cells, but the existence of this layer is
not easy to demonstrate satisfactorily. Strands of tissue
cross the blood-space at intervals, having the appearance of
prolongations of the epithelial-lining-cells.

It should be noted that in the walls of the intestinal
pouches no muscle-fibres can be demonstrated excepting
those in the outer wall of the blood-sinus, and the con-
tractions of the pouches would seem to be brought about by
these muscles (figs. 45 and 46).

The Blood.—The blood of Poecilochetus is a bright
scarlet coloured, homogeneous fluid without corpuscles of any
kind. Very occasionally in sections an isolated cell, having a
similar appearance to the cells of the epithelial lining of the
blood-vessels, is seen in the blood-space. Such cells are
probably only celis of this epithelium which have become
detached.

The change of colour of the blood caused by want of oxygen
has already been described (see p. 126).

Nephridia and Nephromixia.

In small living examples of Poecilochetus viewed from
the ventral surface the nephridial organs can be seen as short
ereenish-brown tubes, one pair in each segment, commencing
at the level of the anterior septum, running first backwards
and then turning outwards and forwards, and ending on the
antero-ventral face of the parapodium. By examining the
more transparent segments near the tail end of the worm with
a moderately high power it can be further seen that anteriorly
the nephridium opens in a large ciliated funnel, and that the
whole length of the tube from the anterior internal opening
to the external opening at the base of the parapodium is
strongly ciliated.

The details of the structure of these organs can be made
out with some clearness in series of sections of specimens
preserved in Hermann’s fluid, more especially in longitudinal
vertical (sagittal) and in horizontal sections of the worm.

Adopting the nomenclature of Goodrich (1900, p. 742), it

THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. — 188

may be stated that both nephridia and nephromixia are found
in Pecilochetus. Nephridia, opening by nephridiostomes
into the next segment in front, are found in the anterior
segments (4 to 16), whilst compound organs (nephronnxia),
consisting of nephridia with large genital funnels (gono-
stomes) attached to the nephridiostomes, are found in the
genital segments from segment 17 backwards.

In the two anterior body segments (1 and 2) no trace of a
nephridium has been detected. In segment 5 the nephridio-
stomes of the organs of the following segment are well
developed, and they, as well as the organs to which they
belong, have the structure about to be described, which is
typical of that in all the segments from 4 to 16. he
nephridial tubes in each of these segments are simple and
J-shaped (cf. fig. 58), running from the anterior septum of
the segment straight backwards, then turning outwards and
forwards to the external opening on the parapodium, as
already described. The cells lining the tubes are low,
elongated, ciliated cells, which contain large numbers of
excretory granules. he lips of the nephridiostomes, which
lie close to the posterior septum of the seement next in front,
form a structure of considerable size, with a small ciliated
aperture which puts the lumen of the nephridial canal into
communication with the body-cavity of the latter segment.
Fig. 55 (Pl. 12) represents a transverse section through a
nephridiostome of one of these segments, and fig. 54 a
sagittal section. The lips (/p.nst.) form masses of swollen
cells filled with vacuoles and granules. These masses of cells
are attached to the posterior septum of the segment along a
somewhat narrow border, and protrude for some little distance
into the cavity of the segment (cf. fig. 47). The nephridio-
stome itself (nst.) lies near the lateral wall of the body, but
the swollen masses of cells forming its lips run inwards almost
to the median line of the body. This inward extension of the
lips is seen in the transverse section (fig. 55), and is also well
shown in horizontal sections. Externally the lips are covered
by a layer of ccelomic epithelium (fig. 54).

134 Bio. ALN

Fig. 57 (Pl. 12) shows the appearance presented by cells of
the nephridial lip under a high power, the figure bemg drawn
from a section of material preserved in Hermann’s fluid and
stained with methyl-blue-eosin solution. ‘The cells are much
swollen and vacuolated, and contain, in addition to the nuclei
(n.), large numbers of granules of various sizes, which stam
bright red in the preparations. he protoplasmic ground
substance of the cells stains blne, but the cells, bemg highly
vacuolated, this blue-staininge substance is not uniformly
distributed through them. The red granules are often
surrounded by a spherical mass of blue-staiming protoplasm,
in the case of the smaller granules two or three being found
within each sphere. The appearances suggest that the red
granules are first formed within the blue spherical masses,
that they gradually increase im size within these masses,
whilst the latter subsequently become swollen and break
down, giving rise to the vacuolated appearance of the general
cell protoplasm with free red granules floating in it.

In the segments from 17 backwards the structure and
general shape of the nephridia themselves (fig. 58) remain
practically the same as in the anterior segments, excepting
for the fact that a large ciliated genital funnel is added to
the nephridiostome. The arrangement of this genital funnel
will be gathered from the sagittal section shown in fig. 52
(Pl. 12). The upper portion of the funnel is formed by a
great development of the cells of the coelomic epithelium
covering the face of the septum, which are much increased
in size and richly ciliated (lp. gst. d.). These ciliated cells
cover a large part of the anterior face of the posterior
septum. The lower portion of the genital funnel (/p. gst. v.) is
composed of ciliated cells attached to the lower lip of the
nephridiostome, which form a membrane hanging freely in
the cavity of the segment, and with the upper lip constituting
a funnel-shaped structure surrounding the nephridiostome.
This genital funnel (gonostome) is composed of cells of quite
different structure to those of the nephridium, and the line
of demarcation between the nephridiostome and gonostome

THE ANATOMY OF PRRCILOGHETUS, CLAPAREDE. = 135

is well marked. Fig. 56 shows the appearance of these cells.
Their protoplasm is clear, staining only feebly, and contains
no granules such as are found in the nephridial epithelium.
The cilia are long and their bases extend into the cell-body as
deeply staining rods.

The funnels as well as the nephridiostomes and upper portions
of the nephridial tubes are often filled with the genital products.

From the description above given it will be seen that in
these genital seements we have to do with a compound organ,
consisting of a nephridium and a genital funnel combined,
which Goodrich, to whose very valuable papers we are
indebted for much of our recent knowledge of similar struc-
tures amongst polycheetes, has termed nephromixia.

Genital Products.

The genital products in Poecilochetus are first found in
the seventeenth segment, and occur in every segment behind
that, with the exception of the segments at the extreme end
of the body.

Ova.—The gonads lie along the inner and upper sides of
the nephridial tubes (Pl. 12, figs. 58 (horizontal), 59 (trans-
verse) and 60). As the ova increase in size they separate off
from the gonads and pass upwards into the general body-

cavity, where the process of maturation continues (fig. 59).

In their earliest recognisable stages (fig. 60) the developing
ova appear simply as a number of enlarged nuclei, lying in a
mass of cell substance in which no definite cell outlines are
shown in the preparations. As the nucleus and cell-body
enlarge, the individual ova become clearly marked out by a
definite cell membrane, although for a time they continue to
adhere together. The nucleus develops one large, deeply
staining nucleolus and a number of smaller granules of chro-
matin (fig. 61). A well-developed yolk nucleus, horse-shoe
shaped in section, forms a cap over about one half of the
nucleus. This yolk nucleus consists of deeply staining
granules (fig. 60 and 61, yk. 7.) which in methyl-blue-eosin

136 T(J ARLEN.

preparations stain blue, in contrast to the nucleolus and
chromatin granules, which stain red. It disappears as the
ege continues to mature, when the whole of the protoplasmic
contents of the egg becomes crowded with yolk granules,
which stain blue in the preparations (figs. 62, 63 and 64).
The ripe eggs are lenticular in shape, the long diameter
being about double the short. Around the line of greatest
circumference there is a single row of vesicles, seen clearly in
the optical section of a fresh egge represented in fig. 64.
‘hese vesicles are pear-shaped and open on the exterior surface
of the egg by means of fine tubes passing through the thick
egg membrane. In fresh eggs the vesicles look more clear
and transparent than the general egg substance; in sections
a small, shrunken mass of slightly staining substance appears
in the centre of each (figs. 62 and 63). The function of
these vesicles is unknown, though their appearance suggests
that they may contain a fluid which is at some stage secreted
on to the surface of theegg. ‘That the vesicles are intimately
connected with the egg membrane is shown by the fact that
when the protoplasmic contents of the egg shrink, as they do
when the egg is allowed to remain soaking for some time in
sea water, the vesicles completely retain their position around
the circumference of the egg membrane, their bases being
connected by threads of protoplasm with the shrunken mass
of the cell contents. This is shown in fig. 65, drawn from a
fresh egg which had remained for some hours in sea-water.
Vesicles similar to those just referred to were described and
fieured by Claparéde (1868) in Nerine cirratulus, in which
form one circle of them is found round the equator, just as in
the eggs of Pecilochetus. In Nerine auriseta, on the
other hand, Claparéde found three irregular rows of similar
vesicles arranged round the greatest circumference of the
elliptical eggs. In neither case, however, does Claparéde
describe the fine tubes which place the vesicles in communica-
tion with the exterior. The following observation, which he
records concerning the eggs of Nerine auriseta, is of
interest :—‘“ L’action d’une faibles solution de carminate

THE ANATOMY OF P@OILOCHETUS, CLAPARRDE. 187

@ammoniaque les modifie d’une maniére remarquable. Hlles
se colorent assez rapidement en rouge intense, tandis que le
vitellus ne se teint qu’en rouge pale, et que le chorion reste
parfaitement incolore.” This observation appears to me to
agree better with the suggestion made above that the vesicles
may contain a secretory product than with the view set forth
by Claparéde:—“Je ne puis m’empécher de supposer que
ces vésicules (ou peut-étre mieux ces sphéres protoplasmiques)
jouent un role important dans la formation du blastoderme ”
(Claparéde, 1868, p. 333).

The egg membrane of the ripe egg of Poecilochetus is
very thick and stains deeply (blue in methyl-blue-eosin prepara-
tions). Its surface is ornamented by raised lines, which form
an irregular pattern upon it (fig. 66, froma fresh egg). These
’ lines or ridges are clearly visible in sections (figs. 62 and 63).

The germinal vesicle is large, its diameter being little less
than the smaller diameter of the egg. It contains one large
nucleolus, which is. composed of a larger and a smaller
spherical portion (cf. fig. 64, from a fresh ege, and fig. 63,
from a section). Fig. 62 shows a condition of the nucleolus
which is very often seen in preserved material. It here con-
sists of a very deeply staining portion, which takes the form
of a cap resting upon a more or less spherical, transparent
vacuole. Such a form of the nucleolus is not uncommon in
the eggs of other animals (for literature see Korschelt and
Heider, 1902). When the nucleolus is in the state just
described, a number of other deeply staining granules are
present in the germinal vesicle.

Nothing has been ascertained as to the history of the eggs
after they leave the body of the worm.

The Spermatozoa—The place of origin of the male
germinal cells is less restricted than that of the female.
They sometimes arise, like the ova, from the ccelomic epithe-
hum which surrounds the nephridial tube, but may also be
derived from ccelomic epithelium in other parts of the
segment, more especially from that of the anterior septum.
In ripe males the body-cavity in the genital segments is filled

vou. 48, PART 1.—NEW SERIES. 10

138 fi). J. ALLEN;

with a mass of sperm-cells in various stages of development
and of spermatozoa.

The spermatozoa (fig. 53) have pear-shaped heads, rounded
in front, and with straight posterior ends, to which the
flagella are attached. A deeply staining portion at the
posterior end of the head (mp.) probably represents the
“ middle-piece.”

Tue Dtvistons or THE Bopy.

Now that a description has been given both of the external
characters and of the internal anatomy of Peecilochetus,
we are in a position to discuss more fully the question of the
regions into which the body of the worm can properly be
divided. These are (1) the prostomium, or head; (2) an
anterior region, from the first segment to the eleventh; (3)
an intermediate region, comprising segments 12, 15, 14, 15
and 16; (4) a genital region commencing at segment 17 and
continuing backwards until it passes gradually into (5) the
terminal region, or tail segments, and (6) the pygidinm.

1. The prostomium, or head, has already been de-
scribed. ‘To it must be reckoned the median tentacle, the
palps, the nuchal organ and two pairs of eyes.

2. The anterior region (segments 1 to 11) is character-
ised by the straight, muscular, cylindrical dorsal vessel; by
the straight and muscular cesophagus and pharynx; by the
presence, excepting in segments | and 2, of nephridia with
nephridiostomes, but without genital funnels; by the absence
of gonads; by the backward extension of the septa separating
the body segments (segments 7 to 11), and consequent great
elongation of the lateral blood-vessels which run in these
septa; by the great development of the blind, finger-shaped
vessels given off from each lateral vessel into the segment
behind; by the peculiar modification of the parapodial cirri
(seoments 7 to 11); by the absence of hairy bristles; and by
the pear-shaped lateral sense-organs protruding from the
surface of the body.

THE ANATOMY OF P@CILOCHETUS, CLAPAREDE. 139

It will be noted that the hindermost segments of this
region (7 to 11) have several characters which distinguish
them from those in front. These are the backward extension
of the septa, the presence of spiny bristles, which are absent
in segments | to 6 (excepting for one bristle in each parapo-
dium of segment 2), and the peculiar modification of the
parapodial cirri, which character in P. fulgoris and in the
larve from Norway and Normandy is, according to Claparéde,
confined exclusively to these segments, as it is also in the
pelagic larve of Peecilochztus found at Plymouth.

3. The intermediate region (segments 12 to 16) is
chiefly noteworthy from the presence of the large, contractile,
lateral pouches of the dorsal vessel, which are found in its
first four segments. The nephridia are still without genital
funnels, and no gonads are developed. In the adult P.
serpens the modified parapodial cirri of segments 7 to 11
extend back to segments 12 and 13; but this is not the case
in P. fulgoris nor in any known larve of Pecilochetus.
In the latter the cirri of all the segments in this region have
the conical form found in the genital region, and this is true
also for the cirri of segments 14, 15 and 16 of P. serpens.

In segments 12,13, 14 and 15 the segmental enlargements
of the alimentary canal commence to appear, becoming more
pronounced in each sneceeding segment, whilst in seement
16 these enlargements are fully developed and the intestine
is completely surrounded by a blood-sinus, the dorsal vessel
ceasing to exist.

The hairy bristles of the genital segments are absent in
this region (12—16), and the lateral organs still protrude
from the body surface as in the anterior region.

4, The genital region, from segment 17 to within about
thirty segments of the end of the body of a full-grown worm,
is characterised by the presence of gonads and well-developed
genital funnels; by the large intestinal pouches and intestinal
blood-sinus; by the presence of large numbers of well-
developed hairy bristles (figs. 14 and 16) and of flattened,
membranous, spined bristles (fig. 17), which commence sud-

140 BJs) ALGENS

denly in segment 17; by the comparatively small size and
conical shape of the parapodial cirri; by the change in the
character of the lateral sense-organs, which no longer pro-
trude beyond the body-wall; and by the presence (com-
mencing on the twenty-first segment) of gill filaments on the
posterior faces of the parapodia.

5. The terminal region, or tail segments, may be said to
commence about the thirtieth from the end of the body,
though the line of demarcation is not very definite. The
segments are at first characterised by the presence of stout
bristles with brush-like ends (fig. 18), instead of large hairy
bristles ; by the change in the character of the lateral organs ;
and in the last sixteen or seventeen segments, by the modifi-
tion of the notopodial bristles into large curved hooks lying
on the dorsal surface of the body (fig. 6).

6. The pygidium is characterised by the lobes surrounding
the anus and by the two pairs of anal cirri.

PARASITES.

In the body-cavity of almost every adult specimen of Pceci-
lochzetus examined there occurred one or more examples of
a parasitic Trematode. These were always encysted, and
were readily recognised by the two large suckers.

SysteMArTIc Posrrion.
The Family Disomide, Mesnil.

Mesnil (1897) formed the family Disomidee for the recep-
tion of the two genera Disoma and Peecilocheetus.

The genus Disoma was founded by Oersted (1844), who
described and figured one species, Disoma multisetosum.
This species was again found by Mébius (1873), who gives
further details of its anatomy and some figures.

Michaelsen (1897) was the first to obtain complete speci-
mens of the worm, and he shows that the tail end of a
specimen described and figured by Levinsen (1883) under

THE ANATOMY OF PCILOCHATUS, CLAPAKEDE. = 141

the name Trochocheta Sarsi almost certainly belongs to
Oersted’s species, Disoma multisetosum.

Mesnil (1897), from an examination of the type specimens,
confirms the specific identity of Michaelsen’s specimens with
those of Oersted. He gives some further details, with figures,
of the structure of the worm, and expresses the opinion
that Thaumastoma singulare, described by Webster and
Benedict (1884, p. 757), from the American coast, is the
same species.

Claparéde (1868, p. 357) discussed the relations of Disoma
with Polydora and with Chetopterus, being inclined to
place it near to the latter.

Levinsen (1883, p. 106) pointed out that the two genera,
Disoma and Peecilochetus, were closely related to each
other, and emphasised their resemblance to the Spionide.

Adopting Levinsen’s view of the relation of the two forms,
“sans avoir pourtant une conviction bien ferme,” Mesnil
(1897) placed both in his family Disomidz, which he
characterises as follows :

Prostomium very simple, with two long tentacular palps
analogous to those of the Spionids. Parapodia biramous, at
any rate in the anterior region, always with simple bristles.
Bristles of various kinds, especially large spiny bristles, hairy
bristles, and large lancet-shaped bristles. Stout hooks (soies
aciculaire) in the neuropodia of segments 2, 3, and even 4.
Never two regions of the body clearly marked off. Ventral
and dorsal cirri elongate or fimbriate.

Mesnil considers this family as intermediate between the
Spionidz and Cheetopteride, being somewhat nearer to the
latter. He also points out that in certain characters the two
genera show some affinities with the Aphroditide and Amphi-
nomide, and that this is particularly true of Peecilochetus
on account of the median tentacle and the large spiny bristles.
The two long palps and the tendency of the first segment to
enclose the prostomium also point in the same direction.

My own observations on Peecilochetus and a study of
the different descriptions of Disoma lead me to agree with

142 Boe (uN:

Levinsen and Mesnil in regarding the two genera as nearly
related, and Mesnil’s foundation of the family Disomide
appears justified.

I am inclined, however, to consider this family as more
closely allied to the Spionide than to any other Polychete
family, as was maintained by Claparéde and Levinsen. In
addition to the presence of the large palps this view is
supported by the line of vesicles surrounding the eggs, a
striking character which appears to be found only amongst
the Spionide. The median tentacle of Poecilochetus in all
probability represents the fusion of two lateral tentacles, and
may be homologous to the two lateral processes at the front
end of the head in such forms as Nerine (Scolelepis)
vulgaris. ‘The great development of the nuchal organ might
be held to mark Poecilochetus off from the Spionidze and
to bring it nearer to the Amphinomide, where, according to
Racovitza, the caruncle is a very large nuchal organ. This
argument, however, can have little weight, as the nuchal
organ varies greatly in its development in closely allied forms
within other families (e.g. Syllide, Phyllodocide), and the
organ is present in the form of ciliated grooves at the posterior
end of the head of Polydora, as I have been able to demon-

strate on sections.

Tur Species oF PaciLocHaATUS.

The chief points in which Claparéde’s description of
P. fulgoris (Claparéde in Ehlers, 1874) differs from the
description given in the present paper of the Peecilochetus
found at Plymouth are as follows :

1. The large palps of the Plymouth species are not
described in P. fulgoris. This, however, is not surprising,
and is certainly due to the imperfection of the specimens, it
being exceedingly difficult to prevent the worm from throw-
ing these palps off.

2. The nuchal organ, though indicated by Claparéde both
in his figure and text, appears much less developed in

THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. 143

P. fulgoris. Here, again, imperfect preservation may
account for the difference.

3. The tubercles (openings of epithelial glands), which
cover both the dorsal and ventral surfaces of Poecilochetus
fulgoris, are scarcely represented on the dorsal surface of
Plymouth specimens, though moderately common on the
ventral.

4, Only one pair (dorsal or posterior) of eyes 1s described
by Claparéde, the ventral (anterior) pair not having been
observed.

5. Claparéde describes the buccal segment as having a
single cirrus on each side. he rudimentary dorsal cirrus was
either not present or was overlooked.

6. The long dorsal cirrus of segment 5 1s not described or
figured by Claparéde. The cirri of the seventh to the eleventh
seginents differ in shape from the others, beimg flask shaped
with long, stiff necks in Claparéde’s specimen, whilst in the
Plymouth specimens this character 1s constant for segments
from the seventh to the thirteenth. As, however, all larvae
seen at Plymouth agree with P. fulgoris in this respect, the
difference may be due to the fact that Claparéde’s specimens
were not adult.

7. The second, the third, and the fourth segments of the
“Lightning ” specimens have short, stout spines in the
neuropodium ; in the Plymouth specimens such spines are
confined to the second and third segments.

The differences expressed under the headings (3), (6) and
(7) appear to render it necessary to regard the Plymouth
specimens, at least provisionally, as belonging to a new
species for which I propose the name Pecilochetus
serpens.

DEFINITIONS.
Family Disomide, Mesnil.

Polycheeta having a simple prostomium without tentacles or
with one median tentacle, aud with four simple eyes. A pair

144. Bg; CALLEN.

of large palps capable of great elongation. Mouth ventral
with a short proboscis. Parapodia of the first seoment
greatly developed and directed forwards, provided with long
cheetee which meet in front of the head. Parapodia with well-
developed dorsal and ventral cirri. Cheetz simple, and either
smooth or bearing hairs or spines. Neuropodia of the second
and third (and even fourth) segments, with three or four
short, stout bristles or hooks. Notopodial chete of the
terminal segments modified into stout, strong hooks or spikes
situated on the dorsal surface of the body. Distinct posterior
(genital) region of the body commencing at the seventeenth
segment. Segments from about the twentieth backwards
having three or four filamentous gills.

Genus Disoma, Oersted.

Polycheta having the general characters of the family
Disomidee. Prostomium without tentacles. Both neuropodial
and notopodial cirri well developed in the first segment.
Notopodial cirri from the third to the sixteenth segments
having the form of elongated, crenated plates, running trans-
versely on the dorsal surface. Notopodial and neuropodial
cirri from segment 17 backwards conical. Gulls on either
side of the mid-ventral line commencing at the twentieth
segment. Notopodial bristles of the most posterior segments
stout spines arranged in star-like clusters on the dorsal
surface of the body.

One species only known—

Disoma multisetosum, Oersted.
Synonyms: Trochocheta Sarsi, Levensen.
Thaumastoma singulare, Webster and Bene-
dict.

Genus Pecilochetus, Clapareéde.

Polychwta having the general characters of the family
Disomide. Prostomium with one anterior median tentacle.
Nuchal organ in the form of three lobes or tentacle-like

THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. 145

processes arising from the posterior end of the prostomium.
Neuropodial cirrus of the first segment well-developed, noto-
podial cirrus rudimentary. Neuropodial and notopodial cirri
from the seventh to the eleventh (or to the thirteenth)
segments flask-shaped, with long, stiff necks. Gulls on the
parapodia from segment 21 backwards. Chete from the
seventeenth segment backwards mostly with long hairs;
those of the notopodium in the most posterior segments stout
hooks, forming transverse rows on the dorsal surface of the
body. Anus dorsal, with two long and two short cirri.
Dorsal blood-vessel with large, lateral pouches in segments
13" t4and ‘ht.

T'wo species (provisionally)—

Pecilochetus fulgoris, Claparéde. Anterior dorsal
surface of the body richly provided with tubercles. Para-
podial cirri of segments 7 to 11 different from those on the
rest of the body, being flask-shaped, with long, stiff necks.
Second, third and fourth segments with short, stout spines
in the neuropodium. Nuchal organ moderately developed (°?).

Pecilochetus serpens, n. sp. Anterior dorsal surface
smooth, with few tubercles. Parapodial cirri of segments 7
to 13 (in the adult) different from those on the rest of the
body, being flask-shaped, with long, stiff necks. Second and
third segments only with short, stout spines in the neuro-
podium. Nuchal organ greatly developed, forming three long
tentacle-like processes.

LITERATURE.

1843. OzRstTep.—‘ Aun. dan. conspectus. -I. Maricole,’ 1843, p. 41.

1844. Orrstep.— Zur Classification der Annulaten,” ‘Wiegm. Arch. f.
Naturgesch,’ p. 107.

1863. CrararEDE.—‘ Beobachtungen tber Anatomie und Entwicklungs-
geschichte wirbellosen Thiere an der Kiiste von Normandie angestellt,’
Leipzig.

1868. CLaparEDE, Ep.— Les Annélides Chétopodes du Golfe de Naples,”
Geneve.

146

1878.

1892.

1893.

1894.

1896.

1897.

M. J. ALLMN.

Mosivs, K.—*“ Die Expedition zur Untersuchung der Ostsee,” ‘Comm.
zur Untersuchung der deutschen Meere,’ i, p. 108.

. Huters, h.—* Beitrage zur Kenutniss der Verticalverbreitung der

Borstenwiirmer im Meere,” ‘ Zeitsch. wiss. Zoologie,’ vol. xxv.

. Eiste, H.— Die Seitenorgane und becherformigen Organen der

Capitelliden,” ‘ Mitth. Zool. Stat. Neapel.,’ Bd. i, p. 278.

. Encevmann. T. W.— Zur Anatomie und Physiologie der Flimmer-

zellen,” Pfliiger’s § Archiv,’ vol. xxii.

33. Levinsen, G. M. R.—‘Systematisk-geografisk Oversigt over de

Nordiske Annulata, Gephyrea, Chetognathi og Balanoglossi,
Kjobenhavn.’

. VieurerR.—* Etude sur ies animaux inférieurs de la baie d’Alger. II.

Recherches sur les Annélides pélagiques,” ‘ Arch. Zool. Exp. et Gen.,’
Ser. 2, vol. iv.

. Este, H.—“ Monographie der Capiteliiden des Golfes von Neapel,”

‘Fauna und Flora des Golfes von Neapel.’

. Heipennarn, R.—* Beitrage zur Histologie und Physiologie der

Diinndarmschleimhaut,” Pfliiger’s ‘ Archiv,’ vol. xlili, Suppl. Heft.
Greenwoop, M.—“‘On Retractile Cilia in the Intestine of Lumbricus
terrestris,’ ‘Journal of Physiology,’ vol. xiii.

Mataaquin, A.—“ Recherches sur les Syllidiens,” ‘Mem. Soe. Sci. et
Art. Lille.’

M’Intosu, W. C.—* A Contribution to our Knowledge of the Annelida,”
‘Quart. Journ. Mier. Sci.,’ vol. xxxvi.

Benuam, W. B.—“The Blood of Magelona,” ‘Quart. Journ. Mier.
Sci.,’ vol. xxxix.

Gravier, C.—“ Recherches sur les Phiyllodociens,” ‘ Bull. Sci. France
et Belg.,’ vol. xxix.

Racovitza, HE. G.—‘* Le Lobe Céphalique et Encephale des Anneé-
lides Polychétes,” ‘Arch. Zool. Exp. et Gen.,’ Ser. 3, vol. iv.

Hesse, R.— Untersuchungen tiber die Organe der Lichtempfindung
bei niederen Thieren. II. Die Augen der Plathelminthen, inson-
derheit der tricladen Turbellarien,’ ‘ Zeitschr. wissensch. Zool.,’
vol. Ixii.

Mesnit, F.—* Etudes de Morphologie externe chez les Annélides,”
‘Bull. Sci. France et Belg.,’ vol. xxx.

Micuartsen, W.—“ Die Polycheten Fauna der deutschen Mcere,”
‘Wissen. Meeresuutersuch’ i.

THE ANATOMY OF P@CILOCHATUS, CLAPAREDE. 147

1899. Hesse, R.—‘* Untersuchungen tiber die Organe der Lichtempfindung
bei niederen Thieren. V. Die Augen der polychaten Anneliden,”
‘Zeitschr. wissensch. Zool.,’ vol. Ixv.

1900. Goopricu, HW. 8.—“‘On the Nephridia of Polycheta,” part ii, ‘Quart.
Journ. Micr. Sci.,’ vol. xliii.

1901. Asnwortn, J. H.—‘*The Anatomy of Scalibregma inflatum,
Rathke,” ‘Quart. Journ, Mier. Sci.,’ vol. xlv.

1902. Korscuett anp Hemer.— Lehrbuch der vergleichenden Entwick-
lungsgeschichte der wirbellosen ‘Thiere,” ‘ Allgemeiner Theil.’

1902. Mann, G.—‘ Physiological Histology, Methods and Theory,’ Oxford,
Clarendon Press.

1903. Gatvaent, I.—** Histologie des Genus Ctenodrilus, Clap.,” ‘Arbeit.
Zool. Lust. Wien.,’ vol. xv., part 47.

1903. Scuerotizrr, A.—‘‘ Untersuchungen tiber den feineren Bau der Borsten
einiger Cheetopoden und Brachiopoden,” ‘Zeitschr. wiss. Zool.,’
vol. Ixxiv.

1903. Launoy, L.— Contribution & l’Etude des Phénoménes Nucléaires de
la Sécretion (Cellules & venin, Cellules & evzyme),” ‘Aun, Sci. Nat.
Zool.,’ vol. xviii.

1904.—Brasi, lb.—‘ Contribution a la Conaissanee de |’Appareil digestif
des Annélides Polyehetes. L’épithelium intestinal de la Pectinaire,”
‘Archiv. Zool. Expér. et Gen.,’ ser. 4, t. ii, 1904, p. 91.

EXPLANATION OF PLATES 7—12,

Illustrating Dr. EK. J. Allen’s paper on “The Anatomy of
Pecilochxtus, Claparéde.”

List oF Rererence Lerrers.

b. lat. v. Branch of lateral blood-vessel passing into the next following
segment. dr. Brain. ¢. Cilia. cal, Callosities on cuticle. com. Cisopha-
geal commissure. cz. Cuticle. cw.g. Thickened cuticular layer of nuchal
groove. dors. v. Dorsal blood-vessel. ep. Epithelium. ep. +r. Epithelial
rim of lateral organ. /.p. Finger-shaped processes into which the back-
wardly directed branch of the lateral vessel breaks up. g. Masses of proto-
plasm in which granules are formed in the lip of the nephridiostome.
gang. plp. Palp-ganglion, g.¢. 0. Ganglion-cells of lateral sense-organ.
g.f. Giant-fibres. gl. Gland-cell. gl. 1, gl. 2, gl. 3. Three types of goblet-

148 B.. J; ALDEN.

shaped gland-cells of the cesophagus. gst. Gonostome. 7. d/. s. Intestinal
blood-sinus. ¢zées¢. Intestine. iz¢. v. Blood-vessel from walls of ali-
mentary canal to ventral vessel. /a¢. v. Lateral blood-vessel. 7. 0. Lateral
sense-organ. J/p.gst.d. Dorsal lip of gonostome. /p. gst. v. Ventral lip
of gonostome. Jp. vst. Lip of nephridiostome. 7.7. Long rods of lateral
sense-organ, nuchal organ, and epithelium of cesophagus. m. 6. Mid-brain.
m.f. Muscle-fibres. m.p. Middle-piece of spermatozoon. m. tent. Median
tentacle. mh. Mouth. muse. Muscle. 2. Nucleus; x.’ see page 97. mh.
Supposed nuclei of hair-bearing cells. 2. p. 1, 2. p. 2. First and second roots
of nerve of palp-ganglion. zp. Nephridial tube. xr. c. Neuropodial cirrus.
ust. Nephridiostome. x¢.c. Notopodial cirrus. xuch. Nuchal organ. ue. gan.
Nuchal ganglion. @s. (isophagus. yp. Process from callosity, see page 97.
p. bv. Palp blood-vessel. p. dv. Lateral pouch of dorsal blood-vessel. pA.
Pharynx. plp. Palp. plp. div. Diverticle of palp. pip. v. Palp-valve. sep.
Sepium dividing body segments. 4. Sensory hairs of lateral sense-organs.
sr. Short rods of lateral organs, nuchal organ, and epithelium of cesophagus.
sr. 2. Secondary layer of short rods in lateral organs. v. Point where pharynx
joins intestine. vew?. v. Ventral blood-vessel. ol. seg. 14. Valve in dorsal
blood-vessel between segments 14 and 15 (open). ol. seg. 15. Valve in dorsal
blood-vessel between segments 15 and 16 (closed). yk. x. Yolk nucleus.

All sections and the majority of the other figures were drawn with the
camera lucida.

PLATE 7.

Vic. 1.—Anterior segments of Pacilochetus serpens. ‘The vascular
system is somewhat diagrammatic, having been reconstructed from sections.
X ca 25.

lie, 2.—Parapodium 3, left side. x 66.

Fic. 3.—Parapodium 5, left side. x 66.

Vic. 4.—Parapodium 7, left side. x 66.

Fic. 5.—Parapodium 13, left side. x 66.

PLATE 8.

Vic. 6.—Terminal segments, dorsal view. x ca 50.
Fic. 7.—Head end, dorsal view. xX ca 50.
Fie. §8.—Head end, ventral view. xX ca 50.

PLATE 9.
Fic. 9.—Parapodium 14, left side. x 66.
Fic. 10.—Parapodium 18, left side. x 66.

THE ANATOMY OF PQRCILOCHZTUS, CLAPAREDE. 149

Fig. 11.—Parapodium 30, left side. x 66.

Fic. 12.—Pecilochetus serpens in burrow constructed in sand
between two glass plates. Natural size.

Fie. 13.—Smooth bristle from parapodium 7. x 380.

Fie. 14.—Large, stiff, hairy bristle from parapodium 380. x 380.

Fig. 15.—Spined bristle from parapodium 10. x 380.

Fie. 16.—Small, flexible, hairy bristle from parapodium 30. x 3880.

Fic. 17.—Membranous spined bristle from parapodium 20. x 380.

Fic. 18.—Bristle with hairy terminal brush from twentieth parapodium
from end. x 380.

Fie. 19.—Stout hooks of the notopodium from the dorsal surface of the
seventh segment from the end. x 100.

Fic. 20.—Transverse section of epithelium from the anterior dorsal surface.
x 1180.

Fic. 21.—Transverse section of epithelium from the ventral surface, just
behind the mouth. x 1180.

PLATE 10.

Fie. 22.—Unicellular epithelial gland from anterior portion of body.
x 1180.

Fic. 23.—Section of gland-cells and tubercle from posterior end of body.
x 1180.

Fic. 24.—Section of parapodial cirrus (about segment 20). x 220.

Fig. 25.—Cirrus from near tail of living worm.

Fies. 26—29.—Gland-cells from parapodial cirri. x 1180.

Fie. 30.—Transverse section through the base of the palps and palp-
ganglia. x 185.

Fic. 31.—Transverse section of a gill filament. x 400.

Fic. 32.—Transverse section of the ventral nerve-cord. x 220.

Fic. 33 —Sagittal section through a ventral eye. x 640.

Fie. 34.— Horizontal section through a lateral sense-organ of the genital
region. X 600.

Fic. 35.—Transverse section through a lateral sense-organ of the genital
region passing through the anterior row of muscle-bands, x 690.

Fre. 36.—Transverse section through a lateral sense-organ of the genital
region passing through the hair-bearing cells. x 690.

Fic. 87.—Transverse section through a lateral sense-organ of the genital
region passing through the posterior row of muscle-bands. x 690.

150 BS VAIN

Fic. 88.—Section through the extremity of a lateral sense-organ of the
genital region in the longitudinal vertical (sagittal) plane of the body. x 375.

Fie. 89.—Section through a lateral sense-organ of the anterior region,
x 690.

PDRATE.

Fic. 40.—Section through a ciliated groove of the nuchal organ, x 640.

Fic. 41.—Enlarged view of ciliated cells of the nuchal organ. x 1180.

Vie. 42.—Savittal section through the mouth and median tentacle. x 66.

Fie. 43.—Horizontal section through segments 8 to 14. x 42.

Fic. 44.—Transverse section through ciliated epithelium of the cesophagus.
x 690.

Fie. 45.—Transverse section through epithel’um of the intestine, when the
latter is filled with food and digestion is actively going on. x 690.

Fig. 46.—Transverse seetion through epithelium of the intestine, when
digestion is not active. Xx 690.

Fie. 47.—Sagittal section through the first sixteen segments, x 42.

Fic. 48.—Transverse section through anterior region, showing junction of
the lateral vessels with the ventral vessel. x 42.

Fic. 49.—Transverse section through anterior region, showing cluster of
finger-shaped processes uniting to the branch of the lateral blood-vessel.
x 42.

Fig. 50.—Sagittal section through the dorsal blood-vessel in segments 14
and 15, showing the valves. x 132.

PLATE 12.

Fre. 51.—Sagittal section through two segments of the anterior region,
showing the branch of the lateral vessel going into the segment behind and
breaking up into finger-shaped processes. X 88.

Fic. 52.—Sagittal section of a nephridium and genital funnel of a male
genital segment. x 212.

Fie. 53.—Spermatozoa. x 1770.

Fie. 54.—Sagittal section through the nephridiostome of an anterior
segment. X 424.

Fie. 55.—Transverse section through the lip of the nephridiostome of an
anterior segment. X 424.

Fig. 56,—Ciliated epithelium of the dorsal lip of a genital funnel x 11SO0.

THE ANATOMY OF I'ECILOCHAMTUS, CLAPAREDE. 151

Fre. 57.—Knularged portion of the lip of a nephridiostome. The dark black

dots stain red, the grey shading blue in methyl-blue-eosin preparations.
x 1180.

Fia. 58.—Horizontal section through three genital segments, showing the
relation of the ovary to the nephridium. x 66.

Fria. 59.—Transverse section through a genital segment. x 66.

Fre. 60.—Section through a nephridial tube, showing the development. of the
ova. X 380.

Fies. 61—63.—Sections of ova in different stages of maturation. x 380.
Fre. 64.—Optical section of living mature ovum, xX 212,

Fie. 65.—Optical section of living mature ovum after remaining some hours
in sea-water. xX 212.

Fia. 66.—Surface view of living mature ovum. xX 212.

NOTES ON SPOROZOA. 153

Notes on Sporozoa.

By
H. M. Woodcock, B.Sc.(Lond.).

I, On Klossiella muris gen. et spec. nov., Smith and
Johnson, 1902.

Smith and Johnson (1) recently described a new Coccidian
parasitic in the kidneys of the mouse (Mus musculus).
The seat of the infection is the renal epithelium of the
convoluted tubules of the cortex and of the visceral layer of
Bowman’s capsules. ‘The enormously hypertrophied parasite-
containing cells swell out into and completely occlude the
lumen of the tubule, causing entire disorganisation of the
affected tissue.

The diagnostic characters on which the new genus is based
are as follows. ‘The sporogonic cycle is characterised by the
development of twelve to fourteen spherical spores, each
about 16 by 13m, and containing thirty to thirty-four
banana-shaped sporozoites. Another phase of the life-history
was also met with. This is taken by Smith and Johnson to
represent either schizogony or the formation of microgameto-
cytes, but actually which of the two is left an open question.
As a matter of fact, the authors’ figures leave no doubt that
the stage which they have described as sporogonic is nothing
more nor less than merogony or schizogony, while the other
part of the cycle is, in all probability, the commencement of
gametocyte formation. As this new Coccidian presents
certain very interesting features, I have thought it worth
while to give a re-interpretation of Smith and Johnson’s

voL. 48, parr 1.—NEW SERIES, 11

154 H. M. WOODCOCK.

clear and careful drawings, the real significance of which
will be readily manifest on comparing them with the figures
of another Coccidian, Caryotropha mesnilii, lately des-
cribed by Siedlecki (2) from a Polychete, Polymnia
nebulosa, where it inhabits the testis. The name Klos-
siella muris may quite well be retained, at any rate until
the parasite is re-discovered and the number of its genuine
spores and sporozoites determined, since, notwithstanding
the resemblance between the schizogonic phase in the two
forms, the very different habitat, and important distinctions
in the manner of formation of the microgametocytes already
preclude us from uniting the two genera together.

The drawings in Fig. A are reproduced from Smith and
Johnson’s figures, and those in Fig. B are copied from
Siedlecki’s paper. All are drawn the same size as the
originals.! I will first give, as it were, a revised account of
what is known of the life-history of Klossiella muris, and
then proceed to justify my interpretation of the same, finally
contrasting the genus with one or two other Coccidia. The
authors’ designations of the various stages are enclosed in
square brackets.

In Fig. A (1) we have one of the smallest trophozoites
[sporonts] seen. Such a young form, commencing to
grow, is from 8 to 11m in diameter, and lies in a
vacuole (v.) in the host-cell. Its membrane, so far as it
has one, is very delicate, and practically only a limit
to the cell. Each individual contains from ten to twenty
plastin granules (pl. g.). ‘‘N.” is the nucleus of the host-
cell, and “n” that of the parasite. In the next figure, A (2),
the trophozoite has become considerably larger (even allow-
ing for the difference in magnification), and is now almost
full-grown; it is, in fact, a schizont beginning merogony
[mother-sporoblast]. Such an adult trophozoite or schizont

1 A comparison of Smith and Johnson’s different figures would have been
greatly facilitated if they had been drawn to the same, or multiples of the

same, magnification; while Siedleéki does nat give the magnification of his at
all.

NOTES ON SPOROZOA, is

may attain a diameter of as much as 40 n. In the one before
us the nucleus has already divided up into several, each
possessing one to four karyosomes (k.), with usually a
certain amount of granular chromatin besides. Around each
of these daughter-nuclei the cytoplasm segregates itself, and
thus the parasite becomes (superficially) divided up into a

number of uninuclear portions (Fig. 3). These buds next com-
mence to grow out at the periphery (Fig. 4), forming daughter-
schizonts, or, as Siedlecki terms them, “ schizontocytes”’ (sz.c.)
[daughter-sporoblasts]. The host-cell is by this time greatly
hypertrophied, and consists for the most part of a very
delicate, attenuated layer of protoplasm, enclosing the huge
vacuole in which the Klossiella lies; on one side (at h. c.)
it is rather thicker, and this portion contains the nucleus,
also much altered and hyperchromatosed. The schizontocytes

156 H. M. WOODCOCK.

are at length cut off, and become separate inside the remains
of the cell. According to Smith and Johnson, the central
part of the cytoplasm of the mother-schizont may be entirely
used up (“ resorbed ”) by the daughter ones, as in Fig. A (6),
or some may be left over as a residual body [restiform body].
In Fig. A (6) the contents of each separate schizontocyte
[spore] have further divided up into a great number of
merozoites (m. z.) [sporozoites], all arranged in one direction,
and constituting, indeed, a typical merogonic “ barillet.”
The homogeneous-looking masses are simply deeply stained
daughter-schizonts, too opaque to show the merozoites inside.
It will be observed that the only “membrane” holding the
products resulting from one parasite together is the com-
pletely atrophied host-cell. Fig. A (5 b) shows a single
barillet of merozoites liberated from a fresh kidney; the
cluster is attached to a small secondary residual body (r. b.).
Our authors state that the membrane surrounding the mero-
zoites [i.e. the spore-membrane] is usually rounded, but of
no definite shape and quite structureless, and in optical
section appears only as a sharp line; moreover, it is easily
ruptured on pressure, setting free the enclosed merozoites.
In short, it doubtless represents, in its turn, the remains of
the schizontocyte, nearly all of which has been used up to
form the cluster. At (a) in the same figure are seen two
free, unstained merozoites [sporozoites], each about 7m by
3m and containing several little vacuoles, one of which is
often more prominent than the rest.

Such is the so-called sporogony of this Coccidian. With
regard to the other phase of the life-history (Smith and
Johnson’s two figures of which I have not thought it neces-
sary to reproduce) a few words will suffice at present, since it
in no way affects the question of the sporogony of the phase
above described. ‘he authors term this the “ glomerular ”’
stage of the parasite, since it is found in the epithelium of
Bowman’s capsules, whereas the other form principally occurs
in the convoluted tubules. As the glomerular form was only
found in kidneys already infected with Klossiella, we can,

NOTES ON SPOROZOA, 157

I think, agree with Smith and Johnson that the two are in
some way related.

The chief difference between them is that in the former
there is no “ budding ” nor anything analogous to the forma-
tion of schizontocytes. As the young parasites grow the (at
first single) nucleus divides successively to form a great many,
evenly distributed throughout the cytoplasm. The latter
then segments up around these daughter-nuclei, and there
result numerous “‘ falciform bodies,” which are, however, not
nearly so sickle-shaped as the merozoites, but more of an
elongated lozenge form. Each of them is about 7m by 2n,
and possesses a rather small nucleus, centrally situated. ‘The
further history of these bodies was not followed; the authors
suggest that the process may represent either schizogony or
microgametocyte-formation, saying that the position is a
favourable one for the development of either phase, but they
do not decide between the two hypotheses, though perhaps,
on the whole, rather inclined to support the latter. Nothing
in the nature of macrogametocyte-formation was noticed.

I propose now to summarise my reasons, most of which will
be, I think, already evident, for considering that the more
fully-described part of the life-cycle of Klossiella is, in
reality, only the schizogonous phase—serving for auto-repro-
duction, and not the sporogonic phase—producing resistant
spores capable of transmitting the species to a fresh host.
The spore-forming cyst, or oocyst, in the Coccidia is the result
of fertilisation of a macrogamete by a microgamete, and may
be looked uponas the final stage of the life-history undergone
in the host. Representing, as it does, the termination of
growth, the large macrogametocyte up to the time of matura-
tion is contained within an atrophied host-cell, from whose
shrunken and shrivelled remains it is set free prior to fertili-
sation. After conjugation (indeed in some cases before, e. g.
in Coccidium proprium and C. faurei) a cyst-membrane
is rapidly secreted round the oocyte (now the sporont), which
becomes thick and tough and affords protection to the
developing contents. Obviously, no further increase in size

158 H. M. WOODCOCK.

is possible. Moreover the sporont is typically extra-cellular
during the whole course of sporogony. Compare this with
what we find in Klossiella. In Fig. A (1) we have a young
form possessing, at most, a very delicate membrane, and lying
in a vacuole in a host-cell that as yet shows hardly any effects
of the parasitic invasion. Again, this young ‘‘sporont”
grows from 10 to as much as 40! Further, in the nuclei
and nuclear division in a Coccidian sporont—in fact, while
the sporogonic cycle lasts—there is no sign of karyosomes.
When, as in C. proprium, these are retained in the ripe
gametes and are thus present in the oocyte, they are in-
variably left behind in the residual cytoplasm of the latter
and take no part in spore-formation ; and even their retention
up to this stage is unusual. The presence of karyosomatic
nuclei is, in short, essentially a mark of schizogony, be it
male, female, or indifferent in type; and it is a feature in the
multiplicative stages before us (Fig. A 2,3, 4). Wewill leave
out of account the markedly peripheral origin of the ‘‘ buds,”
—although peripheral budding is characteristic of endogenous
reproduction,—since in polysporous types (Klossia, etc.)
there is a tendency to a similar mode of origin of the sporo-
blasts, with the formation of a central “reliquat kystal.”
Let us pass on to the “spores” themselves. There is now no
doubt about the occurrence of polyzoic spores; Cyclospora
itself and the re-investigated Hucoccidium (“ Bene-
denia”) octopianum are instances of it,—so it is quite
possible that, in these cases, there may also be a more or less
“barillet”-like arrangement of the sporozoites, such as is
often met with in merozoites.

Here, however, the resemblance between the bodies seen in
Fig. A (6) and spores ceases. Besides the very important facts
that they are not enclosed in a definite oocyst and are still
within the host-cell (the former of which, at any rate, would
be without analogy in the order), there is another reason why
these bodies cannot be regarded as representing true spores.
This is their varying and indefinite shape—or rather their
shapelessness,—together with the extremely delicate nature

NOTES ON SPOROZOA. 159

of the envelope enclosing each cluster of germs. A Coccidian
sporocyst is always quite definite in form and fairly tough
and resistant, and generally consists of two valves which
separate under the action of the new host’s digestive juices
(sometimes, this can be effected artificially) to liberate the
sporozoites. Nothing of the kind is mentioned in Smith and
Johnson’s account; the authors simply state that the mem-
brane is very delicate, and easily ruptured on pressure. As
I have above suggested, it much more probably represents
(together with a small amount of residual material) the
remains of a daughter-schizont, most of which has gone to
form the merozoites. Between these and sporozoites, in the
fresh condition, there is little difference, so that I need only
add that if my interpretation is correct, the germs in Fig.
A (5b) belong to the former category and not to the latter.!

Of course the novel, and at that time unexampled variation
which distinguishes schizogony in Klossiella from the usual
method, might, to a certain extent, mislead the authors in
interpreting their observations. Apart from this, however,
the above-mentioned very characteristic facts relative to the
general course of development of a Coccidian parasite and its
relation to the host-cell ought to have rendered them
suspicious in accepting the observed stages as constituting
sporogony. As it happened Siedlecki (I. c.) very soon after-
wards described a similar modification of merogony in
Caryotropha. The resemblance between the process in the
two genera is most striking, and I have above used this
author’s terminology in interpreting the phase as it occurs in
Klossiella.

In Fig. B are reproduced some figures of Caryotropha
for comparison with those in Fig. 4. In (1) the host-cell (a
spermatogonium) and two of its neighbours are greatly
hypertrophied and have fused into a single mass containing

1 Unfortunately it is impossible to tell from fig. 6 (the stained preparation)
whether the germs have a karyosome in the nucleus or not, which would have
conclusively settled the question.

160 H. M. WOODCOCK.

the schizont. ‘The cytoplasm of the parasite is left clear ; its
large karyosomatic nucleus is seen at (n), while at (N) we
have the enlarged spermatogonial nuclei of the altered cells.
“Sp. g.” represent normal spermatogonia around. The para-
site, though not full grown, is, of course, relatively much

older than the young Klossiella schizont of Fig. A (1).
The next stage of Caryotropha depicted, seen in Fig. B
(2), shows a condition intermediate between Figs. A (4) and
(6). The mother individual has divided up into daughter
schizonts or schizontocytes, ten or more in number, which are
separate, but have not yet commenced to form merozoites.
From Siedlecki’s account it is evident that these daughter-
individuals have arisen in a manner perfectly analogous to
their origin in Klossiella. He says that each of the nuclei
resulting from the division of the original nucleus of the
parasite pushes out at the surface of the body (surrounded,

NOTES ON SPOROZOA. 161

doubtless, by a “bud” of cytoplasm), and between them
deep grooves extend inwards, so that at length the whole
schizont becomes cut up into several portions—the schizonto-
cytes. He does not add whether any residual cytoplasm may
be left over unused or not. A small point distinguishing the
schizogony in this genus is the unusually minute size of the
karyosomes, which are present in the daughter-nuclei only as
one or two granules. 1 think the last doubt will be removed
by a comparison of Figs. B (3) and A (6), especially if we
regard each of the clusters in the latter as showing up like
it does in Fig. 5 (b). In both cases all the ‘ barillets”’ are
enclosed by the partly or entirely atrophied cell or cell-mass,
and by that alone. The only slight difference is that in those
of Caryotropha the remains of the daughter-schizonts seem
to have more completely broken down than they have in
Klossiella, leaving no distinct enclosing membrane. It is,
however, most likely that in older clusters of the latter genus
the delicate investment around each also naturally breaks
down, as, indeed, it must do if the essential object of schizo-
gony, namely auto-infection, is to be attained.

The marked correspondence between the schizogonic
process in the two forms does not appear to be maintained
in microgametocyte-formation. In Caryotropha this re-
sembles schizogony to a surprising extent, and serves to
emphasize the complete homology of the two kinds of repro-
ductive germ. Briefly stated, a number of microgametocytes
of the second order (strictly comparable to schizontocytes)
are intercalated between the original microgametocyte (of the
first order) and the ultimate male gametes. The micro-
gametes themselves arise from these daughter-microgameto-
cytes exactly as if they originated in the usual manner from
the microgametocyte of the first order, as, e. g. in Coccidium.
Until ripe and ready for liberation they are all contained
within the atrophied host-cell, just as are the clusters of
merozoites. So far as can be gathered from Smith and
Johnson’s account nothing of the kind occurs in Klossiella;
but this form, on the other hand, would appear to possess a

162 H. M. WOODCOCK.

differentiation in another direction which is not met with in
Caryotropha. In the latter there is no sign of an early
differentiation of sexuality. The merozoites (representing
the end term of schizogony), which grow into microgameto-
cytes of the first order or macrogametocytes, respectively,
are in no way different from the indifferent ones which become
ordinary schizonts ; that is to say, there is no male or female
schizogony accompanied by the formation of male or female
merozoites such as we find in certain cases (Adelea, Cyclo-
spora). Nowin Klossiella the “ glomerular” form men-
tioned above almost certainly represents either male or female
schizogony, leading to gametocyte-formation, and this view
is supported by the authors’ remark that the phase was only
found in kidneys already strongly infected with the other
stage, 1.e. when merogony, we may assume, had almost run its
potential course. In the absence of any further knowledge of
the parasite it is impossible to say with certainty which sex
the lozenge-shaped bodies above described represent; whether,
in other words, they will grow into micro- or macrogameto-
cytes. Smith and Johnson are inclined to think they may
become the former, and suggest that they give rise to the
actual gametes only when attached (“accolés ”) to a female
element ; they did not, however, observe this process taking
place. Their shape somewhat recalls that of the male mero-
zoites of A. mesnili as figured by Perez (3). Whether, if
we accept these as male elements, the female merozoites
(becoming macrogametocytes) are similar to the indifferent
ones (as in A. mesnili, again), and whether they are formed
in the same complicated manner, or by simple schizogony,
are facts which have still to be ascertained. In any case the
rediscovery of Klossiella muris, and the working out of
its complete life-history, would probably furnish some very
interesting and important additions to our knowledge of the
Coccidia.

NOTES ON SPOROZOA. 163

REFERENCES.

1, Situ, T., and Jonnson, H. P.—‘‘On a Coccidium (Klossiella muris,
gen. et sp. nov.), Parasitic in the Renal Epithelium of the Mouse,”
‘J. Exptl. Medicine, Baltimore,’ vi, pp, 1—21, pls. 1—4 (1902).

2. StepLecK1, M.—‘‘ Cycle évolutif delaCaryotropha mesnilii, coccidie
nouvelle des Polymnies: note préliminaire,” ‘Bull. Ac. Cracovie,’
1902, pp. 561—568, 5 text-figs.

3. Perez, C.—“ Le cycle évolutif de PAdelea mesnili,” ‘Arch. f. Pro-
tistenk,’ ii, pp. 1—12, pl., 1 and 4 text-figs. (1908).

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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.

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

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

> 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

Lip

~ eam

9 Io
| ee

f
())
«

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

—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. <A very remarkable feature in Limulus, first de-
scribed by Owen, is the close accompaniment of the proso-
matic nerve centres and nerves by arteries, so close indeed
that the great ganglion mass and its outrunning nerves are
actually sunk in or invested by arteries. ‘he connection is
not so intimate in Scorpio, but is nevertheless a very close
one, closer than we find in any other Arthropods in which
the arterial system is well developed, e.g. the Myriapoda
and some of the arthrostracous Crustacea. It seems that
there is a primitive tendency in the Arthropoda for the
arteries to accompany the nerve-cords, and a “supra-spinal ”
artery—that is to say, an artery in close relation to the
ventral nerve-cords—has been described in several cases.
On the other hand, in many Arthropods, especially those
which possess trachex, the arteries do not have along course,
but soon open into wide blood-sinuses. Scorpio certainly

voL. 48, PART 2,—NEW SERIES. 14

198

E. RAY LANKESTER.

Fic. 29. Fie. 30.

Fic. 29.—Diagram of the arterial system of A, Scorpio, and B,
Limulus. The Roman numerals indicate the body somites and the
two figures are adjusted for comparison. ce, cerebral arteries ; sp,
supra-spinal or medullary artery ; ¢, caudal artery; /, lateral anasto-
motic artery of Limulus. The Roman numerals indicate the body
somites, and the two figures are adjusted for comparison. ce,
cerebral arteries ; sp, supra-spinal or medullary artery; c, caudal
artery; /, lateral anastomotic artery of Limulus. The figure B also
shows the peculiar neural investiture formed by the cerebral arteries
in Limulus and the derivation from this of the arteries to the
limbs, III, IV, VI, whereas in Scorpio the latter have a separate
origin from the anterior aorta. (Krom Lankester, “Limulus an
Arachnid.’’)

Fie. 30.—View from below of a Scorpion (B. occitanus) opened
and dissected so as to show the pericardium with its muscles, the
lateral arteries, and the tergo-sternal muscles. PRO, prosoma;
dpm, dorso-plastral muscle; art, lateral artery; ¢sm', tergo-sternal
muscle (labelled do in Fig. 31) of the second (pectiniferous) meso-
somatic somite: this is the most anterior pair of the series of six—
none are present in the genital somite; ¢sm*, tergo-sternal muscle
of the fifth mesosomatic somite; ¢sm®, tergo-sternal muscle of the
enlarged first mesosomatic somite; Per, pericardium; VY PIZ! to
VPM’, the series of seven pairs of veno-pericardiac muscles (labelled
po in Fig. 31). There is some reason to admit the existence
of another more anterior pair of these muscles in Scorpio; this
would make the number exactly correspond with the number in
Limulus. (After Lankester, ‘Trans. Zool. Soc.,’ vol. xi, 1883.)

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 199

comes nearer to Limulus in the high development of its
arterial system, and the intimate relation of the anterior
aorta and its branches to the nerve centres and great nerves,
than does any other Arthropod.

An arrangement of great functional importance in regard
to the venous system must now be described, which was
shown in 1883 by Lankester to be common to Limulus and
Scorpio. This arrangement has not hitherto been detected
in any other class than the Arachnida, and if it should
ultimately prove to be peculiar to that group, would have

; ad, md, py" pv- py? pvt pws pve
Geman Is 2 : if py?

= ——— 7
(Gi ee |:
UNS, Aad Jee
H 2 : > —— ; 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

EWM
ST ANE

iS
Se

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.

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

\ 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. <A single specimen was
found in the harbour of Copenhagen in the eighteenth century,
having presumably been carried over by a ship to which it

clung.

A species of Limulus is found in the Buntersandstein of
the Vosges; L. Walchi is abundant in the Oolitic lithographic
slates of Bavaria.

The genera Belinurus, Aglaspis, Prestwichia, Hemiaspis,
and Bunodes consist of small forms which occur in Paleozoic
rocks. In none of them are the appendages known, but in
the form of the two carapaces and the presence of free
somites they are distinctly intermediate between Limulus and
the Trilobite. The young form of Limulus itself (Fig. 40) is
also similar to a Trilobite so far as its segmentation and
trilobation are concerned. The laterai eyes of Limulus
appear to be identical in structure and position with those of
certain Trilobite.

Order 2. Gigantostraca (Figs.46, 47).—Free-swimming forms,
with the appendages of the sixth or fifth and sixth pairs
flattened or lengthened to act as oars; segments of meso-
soma and metasoma (= opisthosoma) twelve in number.

Appendages of anterior pair very large and chelate.
Sub-order Pterygotomorpha, Pterygotide (Ptery-
gotus).

VOL. 48, PART 2,—NEW SERIES. 16

230 HK. RAY LANKESTER.

Appendages of anterior pair minute and chelate.

Stylonuride (Stylo-
nurus),

Kurypteride (Huryp-
terus, Slimonia).

Sub-order Eurypteromorpha

—_

2 NS Sh 4 Ny
Ne a, SOT
uN soar)
6 \— wantuteniap — of

Fie. 46.—Eurypterus Fischeri, Eichwald. Silurian of
Rootzikil. Restoration after Schmidt half the size of nature. The
dorsal aspect is presented, showing the prosomatic shield, with paired
compound eyes, and the prosomatic appendages II to VI. The small
first pair of appendages is concealed from view by the carapace.
1 to 12 are the somites of the opisthosoma; 18, the post-anal
spine. (From Zittel’s ‘Text-book of Paleontology.’ Macmillans,
New York, 1896.)

Remarks.—The Gigantostraca are frequently spoken of
as “the Hurypterines.” Not more than thirty species are

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 2381

known. They became extinct in Paleozoic times, and are
chiefly found in the Upper Silurian, though extending up-
wards as far as the Carboniferous. They may be regarded
as “macrourous” Xiphosura; that is to say, Xiphosura in
which the nomomeristic number of eighteen well-developed
somites is present, and the posterior ones form a long tail-like
region of the body. There still appears to be some doubt

a NS,

=
=
——

Fic. 47.—Pterygotus osiliensis, Schmidt. Silurian of
Rootzikil. Restoration of the ventral surface, one third the natural
size, after Schmidt. a, camerostome or epistoma; m, chilariam or
metasternite of the prosoma (so-called metastoma); oc, the com-
pound eyes; 1 to 8, segments of the sixth prosomatic appendage ;
I’ to V’, first five opisthosomatic somites; 7’, sixth opisthoso-
matic somite. Observe the powerful gnathobases of the sixth pair
of prosomatic limbs and the median plates behind m. The dotted
line on somite I indicates the position of the genital operculum,
which was probably provided with branchial lamelle. (From Zittel’s
‘ Paleontclogy.’)

whether in the sub-order Kurypteromorpha the first pair of
prosomatic appendages (Fig. 46) is atrophied, or whether, if
present, it has the form of a pair of tactile palps or of minute

22 E. RAY LANKESTER.

chele. Though there are indications of lamelliform respiratory
appendages on mesomatic somites following that bearing the
genital operculum, we cannot be said to have any proper
knowledge as to such appendages, and further evidence
with regard to them is much to be desired. (For literature
see Zittel, 22*.)

Grade b (of the Euarachnida). HMBoLOBRANCHIA
(Aéropneustea).

In primitive forms the respiratory lamellze of the append-
ages of the third, fourth, fifth, and sixth, or of the first and
second mesosomatic somites are sunk beneath the surface of
the body, and become adapted to breathe atmospheric oxygen,
forming the leaves of the so-called lung-books. In specialised
forms these pulmonary sacs are wholly or partly replaced by
tracheal tubes. The appendages of the mesosoma generally
suppressed; in the more primitive forms one or two pairs
may be retained as organs subservient to reproduction or
silk-spinning. Mouth situated more forwards than in Delo-
branchia, no share in mastication being taken by the basal
segments of the fifth and sixth pairs of prosomatic append-
ages. Lateral eyes, when present, represented by separate
ocelli.

The pregenital somite, after appearing in the embryo,
either is obliterated (Scorpio, Galeodes, Opileo, and others)
or is retained as a reduced narrow region of the body, the
“‘ waist,’ between prosoma and mesosoma. It is represented
by a full-sized tergal plate in the pseudo-Scorpiones.

Section a. Pectinifera.—The primitive distinction be-
tween the mesosoma and the metasoma retained, the latter
consisting of six somites and the former of six somites in the
adult, each of which is furnished during growth with a pair
of appendages. Including the pregenital somite (fig. 16),
which is suppressed in the adult, there are thirteen somites
behind the prosoma. ‘The appendages of the first and second
mesosomatic somites persisting as the genital operculum and

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 233

pectones respectively, those of the third, fourth, fifth, and
sixth somites (? in Paleophonus) sinking below the surface
during growth in connection with the formation of the four
pairs of pulmonary sacs (see Fig. 17). Lateral eyes mono-
stichous.

Fre. 48. Fig. 49.

Fie. 48.—Dorsal view of a restoration of Paleophonus
nuncius, Thorell, the Silurian Scorpion from Gothland. (Re-
stored after Thorell’s indications by Mr. R. I. Pocock.)

Fic. 49.—Ventral view of a restoration of Palzophonus
Hunteri, Pocock, the Silurian Scorpion from Lesmahago, Scot-
land. Restored by Mr. R. I. Pocock. The meeting of the coxe of
all the prosomatic limbs in front of the pentagonal sternum; the
space for a genital operculum; the pair of pectens, and the
absence of any evidence of pulmonary stigmata are noticeable in
this specimen. (See Pocock,‘ Quart. Journ. Mier. Sci.,’ 1901.)

Order i. Scorpionidea.—Prosoma covered by a single dorsal
shield, bearing typically median and lateral eyes ; its sternal
elements reduced to a single plate lodged between or behind

234 KE. RAY LANKESTER.

the basal segments of the fifth and sixth pairs of appendages.
Appendages of first pair tri-segmented, chelate ; of second
pair chelate, with their basal segments subserving mastica-
tion ; of third, fourth, fifth, and sixth pairs similar in form
and function, except that in recent and Carboniferous forms
the basal segments of the third and fourth are provided with
sterno-coxal (maxillary) lobes, those of the fourth pair meet-
ing in the middle line and underlying the mouth. The five
posterior somites of the metasoma constricted to form a
“tail,” the post-anal sclerite persisting as a weapon of offence,
and provided with a pair of poison glands (see Figs. 8, 10, 12,
18, 14, 15, 21, 22).

Sub-order Apoxypoda.—The third, fourth, fifth, and sixth
pairs of appendages short, stout, tapering, the segments
about as wide as long, except the apical, which is distally
slender, pointed, slightly curved, and without distinct movable
claws. .

Family Paleophonide, Paleeophonus (Figs. 48 and 49).

Sub-order Dionychopoda.—The third, fourth, fifth, and
sixth pairs of appendages slender, not evenly tapering, the
seoments longer than wide; the apical segment short, distally
truncate, and provided with a pair of movable claws. Basal
segments of the fifth and sixth pairs of appendages abutting
against the sternum of the prosoma (see Fig. 10 and Figs. 51,
52, and 53).

Family—Pandinide (Pandinus, Opisthophthalmus,

Urodacus).
re Vejovide (Vejovis, LIurus, Euscorpius,

Broteas).
ie Bothriuride (Bothriurus, Cercophonius).
= Buthide (Buthus, Centrurus).
» *Cyclophthalmide (Cycloph-

thalmus)
% “4 Carboniferous.
om Hoscorpiude (Hoscorpius,
Centromachus)

Remarks onthe Order Scorpionidea.—The scorpion
is one of the great animals of ancient lore and tradition. It

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 235

and the crab are the only two invertebrates which had
impressed the minds of early men sufficiently to be raised to
the dignity of astronomical representation. It is all the more
remarkable that the scorpion proves to be the oldest animal
form of high elaboration which has persisted to the present
day. In the Upper Silurian two specimens of a scorpion
have been found (Figs. 48, 49), one in Gothland and one in
Scotland, which would be recognised at once as true scorpions

Fie, 50.—Comparison of the sixth prososomatic limb of a recent
Scorpion (B), of Paleophonus (C), and of Limulus (A), showing
their agreement in the number of segments; in the existence of a
movable spine, Sp, at the distal border of fifth segment; in the
correspondence of the two claws at the free end of the limb of
Scorpio with two spines similarly placed in Limulus; and, lastly, in
the correspondence of the three talon-like spines carried on the
distal margin of segment six of recent Scorpions with the four larger
but similarly situated spines on the leg of Limulus; s, groove
dividing the ankylosed segments 4 and 5 of the Limulus leg into two.
(After Pocock, ‘ Quart. Journ. Micr. Sci.,’ 1901.)

by a child or a savage. The Silurian scorpion, Palwo-
phonus, differs, so far as obvious points are concerned, from

236 E. RAY LANKESTER.

a modern scorpion only in the thickness of its legs, and in
their terminating in strong spike-like joints, instead of being
slight, and provided with a pair of terminal claws. The legs
of the modern scorpion (Fig. 10: Fig. 51) are those of a
terrestrial Arthropod, such as a beetle; whilst those of the
Silurian scorpion are the legs of an aquatic Arthropod, such as
a crab or lobster. It is probable that the Silurian scorpion
was an aquatic animal, and that its respiratory lamelle were
still projecting from the surface of the body to serve as
branchiz. No trace of “ stigmata,” the orifices of the lung-
chambers of modern scorpions, can be found in the Scottish

Fic. 51.—Drawing from life of the desert Scorpion, Buthus
australis, Lin., from Biskra, N. Africa. (Krom Lankester, ‘Journ.
Linn. Soe. Zool.,’ vol. xvi, 1881.)

specimen of Paleophonus, which presents the ventral surface
of the animal to view. On the other hand, no trace of respira-
tory appendages, excepting the pectens, can be detected in
the specimen (see Fig. 49).

Fossil scorpions of the modern type are found in the Coal
Measures. At the present day scorpions of various genera
are found in all the warm regions of the world. In Europe
they occur as far north as Bavaria and the south of France
The largest species measure nine inches from the front of the

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 237

head to the end of the sting, and occur in tropical India and
Africa. Between 200 and 300 species are known. The
scorpions use their large chele for seizing prey and for fight-
ing with one another. They never use the sting when (as
frequently happens) they attack another scorpion, because,
as was ascertained by A. G. Bourne (24), the poison exuded
by the sting has no injurious effect on another scorpion nor
on the scorpion itself. The stories of a scorpion stinging
itself to death when placed ina circle of burning coals are
due to erroneous observation. When placed in such a
position the scorpion faints and becomes inert. It is found
(Bourne, 24) that some species of scorpion faint at a tempera-
ture of 40° Cent. They recover on being removed to cooler
conditions. A scorpion, having seized its prey (usually a
large insect, or small reptile or mammal) with the large
chele, brings its tail over its head, and deliberately punctures
the struggling victim twice with its sting (Fig. 52). The
poison of the sting is similar to snake poison (Calmette), and
rapidly paralyses animals which are not immune to it. It is
probably only sickly adults or young children of the human
race who can be actually killed by a scorpion’s sting. When
the scorpion has paralysed its prey in this way the two short
cheliceree are brought into play (Fig. 53). By the crushing
action of their pincers, and an alternate backward and for-
ward movement, they bring the soft blood-holding tissues of
the victim close to the minute pin-hole aperture which is the
scorpion’s mouth. ‘The muscles acting on the bulb-like
pharynx now set upa pumping action (see Huxley [26]) ; and
the juices—but no solid matter, excepting such as is reduced
to powder—are sucked into the scorpion’s alimentary canal.
A scorpion appears to prefer for its food ancther scorpion,
and will suck out the juices of an individual as large as itself.
When this has taken place the gorged scorpion becomes dis-
tended and tense in the mesosomatic region. It is certain
that the absorbed juices do not occupy the alimentary canal
alone, but pass also into its cecal off-sets, which are the
ducts of the gastric glands (see Fig. 53).

238 E. RAY LANKESTER.

All Arachnida, including Limulus, feed by suctorial action
in essentially the same way as Scorpio.

Scorpions of various species have been observed to make a
hissing noise when disturbed, or even when not disturbed.
The sound is produced by stridulating organs developed on
the basal joints of the limbs, which differ in position and
character in different genera (see Pocock [27]). Scorpions
copulate with the ventral surfaces in contact. ‘The eggs are
fertilised, practically in the ovary, and develop in situ. The

Fic. 53.

Fic. 52.—Drawing from life of the Italian Scorpion Euscorpius
italicus, Herbst, hoiding a blue-bottle fly with its left chela and care-
fully piercing it between head and thorax with its sting. ‘Two insertions
of the sting are effected, and the fly is instantly paralysed by the poison
so introduced into its body. (From Lankester, ‘Journ. Linn. Soe.’)

Fic. 53.—The same Scorpion carrying the now paralysed fly held in
its chelicere, the chele liberated for attack and defence. Drawn from
life, (From Lankester, ‘ Journ. Linn. Soc.’)

young are born fully formed, and are carried by the mother
on her back. As many as thirty have been counted in a
brood. For information as to the embryology of scorpions
the reader is referred to the works named in the bibliography
on p. 265. Scorpions do not possess spinning organs, nor form
either snares or nests so far as is known; but some species

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 289

inhabiting sandy deserts form extensive burrows. ‘The fifth
pair of prosomatic appendages is used by these scorpions
when burrowing to kick back the sand as the burrow is
excavated by the great chele.

References to works dealing with the taxonomy and geo-
graphical distribution of scorpions are given at the end of
this article (28).

Section (. Epectinata.—The primitive distinction be-
tween the mesosoma and the metasoma wholly or almost
wholly obliterated, the two regions uniting to form an
opisthosoma, which never consists of more than twelve somites
and never bears appendages or breathing organs behind the
fourth somite. The breathing organs of the opisthosoma,
when present, represented by two pairs of stigmata, opening
either upon the first and second (Pedipalpi) or the second
and third somites (Solifugz, pseudo-Scorpiones), or by a
single pair upon the third (? second) somite (Opiliones) of the
opisthosoma, there being rarely an additional stigma on the
fourth (some Solifuge). The appendages of the second
somite of the opisthosoma absent, rarely minute and bud-like
(some Amblypygi), never pectiniform. A pregenital somite
is often present either in a reduced condition forming a
waist (Pedipalpi, Aranez, Palpigradi) or as a full-sized
tergal plate (pseudo-Scorpiones) ; in some it is entirely atro-
phied (Solifugee, Holosomata, and Rhynchostomi). Lateral
eyes, when present, diplostichous.

Remarks.—The epectinate Arachnids do not stand so
close to the aquatic ancestors of the Embolobranchia as do the
pectiniterous scorpions. At the same time we are not justified
in supposing that the scorpions stand in any way as an inter-
mediate grade between any of the existing Epectinata and
the Delobranchia. It is probable that the Pedipalpi, Araneae,
and Podogona have been separately evolved as distinct lines
of descent from the ancient aquatic Arachnida. The Holoso-
mata and Rhynchostomi are probably offshoots from the
stem of the Arane, and it is not unlikely (in view of the
structure of the prosomatic somites of the Tartarides) that

240 E. RAY LANKESTER.

the Solifuge are connected in origin with the Pedipalpz.
The appearance of tracheze in place of lung-sacs cannot be
regarded as a starting-point for a new line of descent com-
prising all the tracheate forms; tracheze seem to have de-
veloped independently in different lines of descent. On the
whole, the Epectinata are highly specialised and degenerate
forms, though there are few, if any, animals which surpass
the spiders in rapidity of movement, deadliness of attack, and
constructive instincts.

Order 2. Pepipalpi (Figs. 54 to 59).—Appendages of first
pair biseemented, without poison gland; of second pair
prehensile, their basal segments underlying the proboscis,
and furnished with sterno-coxal (maxillary) process, the
apical segment tipped with a single movable or immovable
claw; appendages of third pair different from the remainder,
tactile in function, with at least the apical segment many-
jointed and clawless. The ventral surface of the prosoma
bears prosternal, metasternal, and usually mesosternal chitin
plates (Fig. 55). A narrow pregenital somite is present
between opisthosoma and prosoma (Figs. 55, 57). Opistho-
soma consisting of eleven somites, almost wholly without
visible appendages. Intromittent organ of male beneath the
genital operculum (= sternum of the first somite of opistho-
soma).

Note.—tThe possibility of another interpretation of the
anterior somites of the mesosoma and the pregenital somite
must be borne in mind. Possibly, though not probably, the
somites carrying the two lung-sacs correspond to the first two
lung-bearing somites of Scorpio, and it is the genital opening
which has shifted. ‘Che same caution apples in the case of
the Araneee. Hxcalation of one or of two anterior mesoso-
matic somites, besides the pregenital somite, would then
have to be supposed to have occurred also.

Sub-order a. Uropygi.—Prosoma longer than wide, its
sternal area very narrow, furnished with a large prosternal
and metasternal plate, and often with a small mesosternal
sclerite. Appendages of second pair with their basal segments

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA, 241

united in the middle line and incapable of lateral movement ;
appendages of third pair with only the apical segment many-
jointed. Opisthosoma without trace of appendages ; its pos-
terior somites narrowed to form a movable tail for the support
of the post-anal sclerite, which has no poison glands.

Tribe 1. Urotricha.—Dorsal area of prosoma covered with

Fie. 54.—Thelyphonus, one of the Pedipalpi. A, ventral view;
I, chelicera (detached); II, chele; III, palpiform limb; LV to VI, the
walking legs ; sée, sterno-coxal process (gnathobase) of the chele ; sd},
anterior sternal plate of the prosoma; sé*, posterior sternal plate of the
prosoma; pregex, position of the pre-genital somite (not seen); Z, Z,
position of the two pulmonary sacs of the right side; 1 to 11, somites
of the opisthosoma (mesosoma plus metasoma) ; msg, stigmata of the
tergo-sternal muscles; az, anus. B, dorsal view of the opisthosoma of
the same; pregen, the pre-genital somite; p, the tergal stigmata of the
tergo-sternal muscles ; paf, post-anal segmented filament corresponding
to the post-anal spine of Limulus. (From Lankester, ‘ Quart. Journ,
Micr. Sci.,’ N.S., vol. xxi, 1881.)

a single shield (? two in Geralinura), bearing median and
lateral eyes. Post-anal sclerite modified as a long, many-

242 E. RAY LANKESTER.

jointed feeler. Appendages of second pair folding in a
horizontal plane, complete chelate, the claw immovably united
to the sixth segment. Respiratory organs present in the
form of pulmonary sacs.

Family Thelyphonide (Thely phonus [Fig. 54], Hypoc-
tonus, *Geralinura).

Tribe 2. Tartarides.—Small degenerate forms, with the
dorsal area of the prosoma furnished with two shields, a
larger in front covering the anterior four somites, and a
smaller behind covering the fifth and sixth somites; the
latter generally subdivided into a right and left portion ;

RIG. Do- Fic. 56.

Fic. 55.—Thelyphonus sp. Ventral view of the anterior portion
of the body to show the three prososomatic sternal plates a, 4, c, and
the rudimentary sternal element of the pra-genital somite ; opistho 1,
first somite of the opisthosoma. (From a drawing made by Mr. Pickard-
Cambridge, under the directien of Mr. R. I. Pocock.)

Fic. 56.—Thelyphonus assamensis ¢. Ventral surface of the
anterior region of the opisthosoma, the first somite being pushed up-
wards and forwards so as to expose the subjacent structures. opisthol,
first somite of the opisthosoma; opistho 2, second do.; g, genital
aperture; J, edges of the lamelle of the lung-books; m, stigmata of
tergo-sternal muscles. (Original drawing by Mr. Pocock.)

rarely there is a pair of narrow sclerites interposed between
the anterior and posterior shields. Eyes evanescent or absent.
Appendages of second pair folding in a vertical plane, not
chelate, the claw long and movable. Post-anal sclerite short
and undivided. No distinct respiratory stigmata behind the
sterna of the first and second somites of the opisthosoma.

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 243

Family Hubbardiide (Schizomus, Hubbardia) (Figs.
57 to 59).

Sub-order b. Amblypygi.—Prosoma wider than long, covered
above by a single shield bearing median and lateral eyes,
which have diplostichous ommatea. Sternal area broad, with
prosternal, two mesosternal, and metasternal plates, the pro-
sternum projecting forwards beneath the coxee of the second
pair of appendages. Appendages of second pair folding in a
horizontal plane; their basal segments freely movable; claw

Fie. 57.

ostecce pregen
1 opisth=~

Fic. 57.—Schizomus crassicaudatus, one of the Tartarid Pedi-
palpi. Ventral view of a female with the appendages cut short near
the base. a@, prosternum of prosoma; J, metasternum of prosoma;
pregen, the pre-genital somite; 1 opis¢h, first somite of the opistho-
soma; 11 opisth, eleventh somite of the opisthosoma; pa, post-anal
lobe of the female (compare the jointed filament in Thelyphonus,
Fig. 54). (Original drawing by Mr. Pickard-Cambridge, directed by
Mr. Pocock).

Fie.58.—Schizomus crassicaudatus,a Tartarid Pedipalp. Dorsal
view of amale with the appendages cut short. I to VI, the prosomatic
appendages ; a, anterior plate, and 4, posterior plate of the prosomatic
carapace ; pregen, tergum of the pregenital somite; 11, the eleventh
somite of the opisthosoma; pa, post-anal lobe of the male—a conical
body with narrow basal stalk. (Original as above.)

free or fused ; basal segments of fourth and fifth pairs widely
separated by the sternal area; appendages of third pair with
all the segments except the proximal three, forming a many-

244, BE. RAY LANKESTER.

jointed flagellum. Opisthosoma without post-anal sclerite
and posterior caudal elongation, with frequently a pair of
small lobate appendages on the sternum of the third somite.
Respiratory organs as in Urotricha.

Dns BE VeVi eb 11 pa

Fic. 59.—Schizomus crassicaudatus, one of the Pedipalpi.
Lateral view of a male. II to VI, the prosomatic appendages, the
first being concealed (see Fig. 58); 5, the fifth, and 11, the eleventh
tergites of the opisthosoma; pa, the conical post-anal lobe. (Ori-
ginal as above.)

Family—Phrynichide (Phrynichus, Damon).
Admetide (Admetus Heterophrynus).
s, Charontide (Charon, Sarax).
(Family ?) *Geraphrynus.

Remarks.—The Pedipalpi are confined to the tropics and
warmer temperate regions of both hemispheres. Fossil
forms occur in the Carboniferous. The small forms known
as Schizomus and Hubbardia are of special interest from
a morphological point of view. ‘he Pedipalpi have no poison
glands. (Reference to literature, 29.)

Order 3. Aranee (Figs. 60 to 64).—Prosoma covered with
a single shield and typically furnished with median and
lateral eyes of diplostichous structure, as in the Amblypygi.
Its sternal surface wide, continuously chitinised, but with

prosternal and metasternal elements generally distinguishable
at the anterior and posterior ends respectively of the large
mesosternum. Prosternum underlying the proboscis. Ap-
pendages of first pair have two segments, as in Pedipalpi,
but are furnished with poison gland, and are retroverts.
Appendages of second pair not underlying the mouth, but
freely movable, and except in primitive forms furnished with
a maxillary lobe; the rest of the limb like the legs, tipped

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 240

with a single claw, and quite unmodified (except in Q).
Remaining pairs of appendages similar in form and function,
each tipped with two or three claws. Opisthosoma, when
segmented, showing the same number of somites as in the
Pedipalpi; usually unsegmented, the preegenital somite con-
stricted to form the waist; the appendages of its third and
fourth somites retained as spinning mammille. Respiratory

nas asesnER
)
Spawn area LF
eT ll

Fic. 60.—Liphistius desultor, Schiddte, one of the Aranee
Mesothele. Dorsal view. I to VI, the prosomatic appendages ;
4, 5, 6, the fourth, fifth, and sixth tergites of the opisthosoma.
Between the bases of the sixth pair of limbs and behind the proso-
matic carapace is seen the tergite of the small pregenital somite.
(Original by Pickard-Cambridge and Pocock.)

organs (see Fig. 63, stg), as in the Amblypygi, or with the
posterior pair, rarely the anterior pair as well, replaced by
voL. 48, PART 2.—NEW SERIES. ivi

246 E. RAY LANKESTER.

tracheal tubes. Intromittent organ of male in the apical
segment of the second prosomatic appendage.

Sub-order a. Mesothele (see Figs. 60—62).—Opisthosoma
distinctly segmented, furnished with eleven tergal plates, as
in the Amblypygi; the ventral surface of the first and second
somites with large sternal plates, covering the genital aperture

Fig. 62.

Libr

— val yx. een 5

rim M0 LVev VE;
Prosoma : het ape: i
pregen1l1 2 3 4 11

AU 102 sen -+ = Orig

Fie. 61.—Liphistius desultor. Ventral view with the
prosomatic appendages cut short excepting the chelicere (1) whose
sharp retroverts are seen. Between the bases of the prosomatic
limbs an anterior and a posterior sternal plate (black) are seen. 1,
the sternum of the first opisthosomatic or genital somite covering
the genital aperture and the first pair of lung-sacs. In front of it
the narrow waist is formed by the soft sternal area of the pre-
genital somite; 2, the sternite of the second opisthosomatic somite
covering the posterior pair of lung-sacs; 3 and 4, the spinning
appendages (limbs) of the opisthosoma; a, inner, 4, outer ramus of
the appendage; 11, sternite of the eleventh somite of the opistho-
soma: in front of it other rudimentary sternites; az, anus.
(Original as above.)

Fig. 62.—Liphistius desultor. Lateral view. I to VI,
appendages of the prosoma cut off at the base; 0, ocuiar tubercle ;
preegen, the pregenital somite; 1 and 2, sternites of the first and
second opisthosomatic somites; 3 and 4, appendages of the third
and fourth opisthosomatic somites, which are the spinning organs,
and in this genus occupy their primitive position instead of migrating
to the anal region as in other spiders; 5, tergite of the fifth opistho-
somatic somite; 11, eleventh opisthosomatic somite; az, anus.
(Original.)

and the two pairs of pulmonary sacs, the sternal plates from
the sixth to the eleventh somites represented by integumeutal

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 247

ridges, weakly chitinised in the middle. The two pairs of
spinning appendages retain their primitive position in the
middle of the lower surface of the opisthosoma far in advance
of the anus on the third and fourth somites, each appendage
consisting of a stout, many-jointed outer branch and a
slender, unsegmented inner branch. Prosoma as in the
Mygalomorphe, except that the mesosternal area is long and
narrow.
Family Liphistide (Liphistius, * Arthrolycosa).

Sub-order b. Opisthothele (see Fig. 63).—Opisthosoma
without trace of separate terga and sterna, the segmentation
merely represented posteriorly by slight integumental folds
and the sterna of the first and second somites by the oper-
cular plates of the pulmonary sacs. The spinning append-
ages migrate to the posterior end of the opisthosoma and
take up a position close to the anus; the inner branches of
the anterior pair either atrophy or are represented homo-
genetically by a plate, the cribellum, or by an undivided
membranous lobe, the colulus.

Tribe 1. Mygalomorphe.—The plane of the articulation
of the appendages of the first pair to the prosoma (the
retrovert) vertical, the basal segment projecting straight
forwards at its proximal end, the distal segment or fang
closing backwards in a direction subparallel to the long axis
of the body. ‘Two pairs of pulmonary sacs.

Families: Theraphoside (Avicularia, Poecilotheria).
Barychelide (Barychelus, Plagiobothrus). Dipluride
(Diplura, Macrothele). Ctenizide (Cteniza, Neme-
sia). Atypide (Atypus, Calommata).

Tribe 2. Arachnomorphe.—The plane of the articulation
of the appendages of the first pair to the prosoma horizontal,
the basal segment projecting vertically downwards, at least
at its proximal end, the distal segment or fang closing
inwards nearly or quite at right angles to the long axis of
the body. The posterior pulmonary sacs (except in Hypo-
chilus) replaced by tracheal tubes; the anterior and pos-
terior pairs replaced by tracheal tubes in the Caponiide.

248 E. RAY LANKESTER.

Principal families: Hypochilide (Hypochilus). Dys-
deride (Dysdera, Segestria). Caponiide (Caponia,
Nops). Filistatide (Filistata). Uloboride (Uloborus,
Dinopis). Argiapide (Nephila, Gasteracantha). Phol-
cide (Pholcus, Artema). Agelenide (Tegenaria). Lyco-
side (Lycosa). Clubionide (Clubiona, Olios, Sparas-

=<
~ a
VN

Fic. 63.—Ventral view of a male mygalomorphous Spider. I to
VI, the six pairs of prosomatic appendages; a, copulatory apparatus
of the second appendage; 4, process of the fifth joint of the third
appendage; M, mouth; pro, prosternite of the prosoma; mes, meso-
sternite of the prosoma: observe the contact of the coxe of the sixth
pair of limbs behind it; compare Liphistius (Fig. 61) where this
does not occur; ség, lung aperture; gz, genital aperture; a, anus
with a pair of backwardly migrated spinning appendages on each
side of it; compare the position of these appendages in Liphistius
(Fig. 61). (From Lankester, “‘ Limulus an Arachnid.’’)

sus). Gnaphoside (Gnaphosa, Hemiclea). Thomiside
(Thomisus). Attide (Salticus). Urocteide (Uroctea).
Hresidee (Hresus).

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 249

Remarks on the Aranew.—The spiders are the most
numerous and diversified group of the Arachnida; about
2000 species are known. No noteworthy fossil spiders are
known; the best preserved are in amber of Oligocene age.
Protolycosa and Arthrolycosa occur in the Carboni-
ferous. Morphologically the spiders are remarkable for the
concentration and specialisation of their structure, which is
accompanied with high physiological efficiency. The larger

Fic. 64.—Liphistius desultor. Under side of the uplifted
genital or first opisthosomatic somite of the female; g, genital
aperture; p, pitted plate, probably a gland for the secretion of
adhesive material for the eggs; ¢, the edges of the lamelle of the
lung-books of the first pair. (Original drawing by Pocock.)

species of Bird’s-nest Spiders (Avicularia), the opisthosoma
of which is as large as a bantam’s egg, undoubtedly attack
young birds, and M‘Cook gives an account of the capture in
its web by an ordinary house spider of a small mouse. The
“yretrovert ” or bent-back first pair of appendages is provided
with a poison gland opening on the fang or terminal segment.
Spiders form at least two kinds of construction—snares for
the capture of prey and nests for the preservation of the
young. The latter are only formed by the female, which is a
larger and more powerful animal than the male. Like the
scorpions the spiders have a special tendency to cannibalism,
and accordingly the male, in approaching the female for the
purpose of fertilising her, is lable to be fallen upon and
sucked dry by the object of his attentions. The sperm is
removed by the male from the genital aperture into a special
receptacle on the terminal segment of the second prosomatic
appendage. Thus held out at some distance from the body,

250 E. RAY LANKESTER.

it is cautiously advanced by the male spider to the genital
aperture of the female.

For an account of the courtship and dancing of spiders, of
their webs and floating lines, the reader is referred to the

Hoes SD 4
|

' pre-12 3 4 5 6 78910
T ILWLIVV V1 gen Opisthosoma
Prosoma

Fic, 65.—Keenenia mirabilis, Grassi, one of the Palpigradi.
A, ventral view of prosoma and of anterior region of opisthosoma
with the appendages cut off near the base; @ and 4, prosternites ;
c, mesosternite; and d, metasternite of the prosoma; /, ventral
surface of the pragenital somite; g, sternite of the genital somite
(first opisthosomatic somite). B, dorsal view. I to VI, prosomatic
appendages; 1 opisth, genital somite (first opisthosomatic somite).
C, lateral view. Ito VI, prosomatic appendages; a, 4, c, the three
tergal plates of the prosoma; pregen, the pregenital somite; 1 to
10, the ten somites of the opisthosoma. D, chelicera. (Original
drawing by Pocock and Pickard-Cambridge, after Hansen and
Sorensen.)

works of M‘Cook (80) and the Peckhams (81), whilst an
excellent account of the nests of trap-door spiders is given by

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 251

Mogegridge (32). References to systematic works will also
be found at the end of this article (83).

Order 4. Palpigradi = Microthelyphonida (see Fig. 65).—Pro-
soma covered above by three plates, a larger representing
the dorsal elements of the first four somites, and two smaller
representing the dorsal elements of the fifth and sixth.

Its ventral surface provided with one prosternal, two meso-
sternal, and one metasternal plate. Appendages of first pair
consisting of three segments, completely chelate, without
poison gland; of second pair slender, leg-like, tipped with
three claws, the basal segment without sterno-coxal process,
taking no share in mastication, and widely separated from its
fellow of the opposite side; third, fourth, fifth, and sixth
appendages similar in form to the second and to each other.

Proboscis free, not supported from below by either the
prosternum or the basal segments of the appendages of the
second pair.

Opisthosoma consisting of only ten somites, which have no
tergal and sternal elements, the praegenital somite contracted
to form a “waist,” as in the Pedipalpi; the last three
narrowed to form a caudal support for the many-jointed
flagelliform telson, as in the Urotricha. Respiratory organs
atrophied.

Family Koenentidee (Kcenenia).

Remarks.—An extremely remarkable minute form ori-
ginally described by Grassi (84) from Sicily, and since
further described by Hansen (85). Recently the genus has
been found in Texas, U.S.A. Only one genus of the order is
known.

Order 5. Solifugee = Mycetophore (see Figs. 66—69).—Dorsal
area of prosoma covered with three distinct plates, two
smaller representing the terga of the fifth and sixth somites,
and a larger representing those of the anterior four somites,
although the reduced terga of the third and fourth are trace-
able behind the larger plate. The latter bears a pair of
median eyes and obsolete lateral eyes on each side. Sternal
elements of prosoma almost entirely absent, traces of a

DAS BE, RAY LANKESTER.

prosternum and metasternum alone remaining. Rostrum
free, not supported by either the prosternum or the basal
segments of the appendages. Appendages of first pair large,
chelate, bisegmented, articulated to the sides of the head-
shield; appendages of second pair simple, pediform, with
protrusible (? suctorial) organ, and no claws at the tip; their
basal segments united in the middle line and furnished with
sterno-coxal process. Remaining pairs of appendages with

‘me
Mt

OIL /
\ - WF we

Fic. 66.—Galeodes, sp., one of the Solifugse. Ventral view to
show legs and somites. Ito VI, the six leg-bearing somites of the
prosoma; opisth 1, first or genital somite of the opisthosoma; ge,
site of the genital aperture; s¢, thoracic tracheal aperture; /,
anterior tracheal aperture of the opisthosoma in somite 2 of the
opisthosoma ; /3, tracheal aperture in somite 3 of the opisthosoma ;
a, anus. (From Lankester, ‘‘ Limulus an Arachnid.”’)

their basal segments immovably fixed to the sternal surface,
similar in form, the posterior three pairs furnished with two
claws supported on long stalks; the basal segments of the

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 253

sixth pair bearing five pairs of tactile sensory organs or
malleoli. The pregenital somite is suppressed. Opisthosoma
composed of ten somites. Respiratory organs tracheal, open-

es (hy/c Fie. 68.

opisth : ad

’
an

Fie. 67.—Galeodes, sp., one of the Solifuge. Ventral view
with the appendages cut off at the base. I to VI, prosomatic
appendages; s, prosomatic stigma or aperture of the tracheal
system; 1, first opisthosomatic sternite covering the genital
aperture g; 2, second opisthosomatic sternite covering the second
pair of tracheal apertures spl; sp2, the third pair of tracheal
apertures; 10, the tenth opisthosomatic somite; az, the anal
aperture. (Original by Pickard-Cambridge and Pocock.)

Fie, 68.—Galeodes, sp., one of the Solifuge. Dorsal view. 1
to VI, bases of the prosomatic appendages; 0, eyes; 4, lateral
recion of the cephalic plate to which the first pair of appendages are
articulated ; 4, cephalic plate with median eye ; c, dorsal element of
somites bearing third and fourth pairs of appendages; d, second
plate of the prosoma with fifth pair of appendages; e, third or
hindermost plate of the prosoma beneath which the sixth pair of legs
is articulated; 1, 2, 9, 10, first, second, ninth, and tenth somites of
the opisthosoma; gz, anus. (Original.)

ing upon the ventral surface of the second and third, and
sometimes also of the fourth somite of the opisthosoma. A

254, EH. RAY LANKESTER.

supplementary pair of tracheze opening behind the basal
segment of the fourth appendage of the prosoma.

Intromittent organ of male lodged on the dorsal side of
the first pair of prosomatic appendages.

Families : Hexisopodide (Hexisopus). Solpugide (Sol-
puga, Rhagodes). Galeodide (Galeodes).

Remarks.—These most strange-looking Arachnids occur
in warmer temperate, and tropical regions of Asia, Africa,
and America. Their anatomy has not been studied as yet
by means of freshly killed material, and is imperfectly known,
though the presence of the coxal glands was determined by
Macleod in 1884. The proportionately enormous chelez

1 e @ e-b oO

s' 8721 ViVeivini < I
Opisthosoma Prosoma

Fic. 69.—Galeodes, sp., one of the Solifuge. Ito VI, the six
prosomatic limbs cut short; 0, the eyes; 4, ¢, demarcated arex of
the cephalic or first prosomatic plate corresponding respectively to
appendages I, IT, III and to appendage IV (see Fig. 68); d, second
plate of the prosoma-carrying appendage V; ¢, third plate of the
prosoma-carrying appendage VI. The pregenital somite is absent.
1, first somite of the opisthosoma; 2, second do.; 8, prosomatic
tracheal aperture between legs IV and V; S'and 8", opisthosomatic
tracheal apertures; 10, tenth opisthosomatic somite; aw, anus.
(Original.)

(cheliceree) of the first pair of appendages are not provided
with poison glands; their bite is not venomous.

Galeodes has been made the means of a comparison
between the structure of the Arachnida and Hexapod insects
by Haeckel and other writers, and it was at one time
suggested that there was a genetic affinity between the two
groups—through Galeodes, or extinct forms similar to it.
The segmentation of the prosoma and the form of the
appendages bear a homoplastic similarity to the head, pro-,
meso-, and meta-thorax of a Hexapod with mandibles, maxil-
lary palps, and three pairs of walking legs; whilst the

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 255

opisthosoma agrees in form and number of somites with the
abdomen of a Hexapod, and the tracheal stigmata present
certain agreements in the two cases. (Reference to literature,
36.)

Order 6. Pseudoscorpiones = Chelonethi, also called Cherne-
tidia (see Figs. 70—72).—Prosoma covered by a single dorsal
shield, at most furnished with one or two diplostichous

Fie. 70. Gaasale

pre-gen .. Aw

whe
Opistho

Fic. 70.—Garypus litoralis, one of the Pseudoscorpiones.
Ventral view. I to VI, prosomatic appendages; 0, sterno-coxal
process of the basal segment of the second appendage; 1, sternite
of the genital or first opisthosomatic somite; the pregenital somite,
though represented by a tergum, has no separate sternal plate; 2
and 3, sternites of the second and third somites of the opisthosoma,
each showing a tracheal stigma; 10 and 11, sternites of the tenth
and eleventh somites of the opisthosoma; az, anus. (Original by
Pocock and Pickard-Cambridge.)

Fie. 71—Garypus litoralis, one of the Pseudoscorpiones.
Dorsal view. I to VI, the prosomatic appendages; 0, eyes; pregen,
pregenital somite; 1 tergite of the genital or first opisthosomatic
somite; 10, tergite of the tenth somite of the opisthosoma; 11,
the evanescent eleventh somite of the opisthosoma; az, anus.
(Original.)

lateral eyes; sternal elements obliterated or almost obli-
terated. Appendages of the first pair bisegmented com-
pletely chelate, furnished with peculiar organs, the serrula

256 BE. RAY LANKESTER.

and the lamina. Appendages of second pair very large and
completely chelate, their basal segments meeting in the
middle line, as in the Uropygi, and provided in front with
membranous lip-like processes underlying the proboscis.
Appendages of the third, fourth, fifth, and sixth pairs similar
in form and function, tipped with two claws, their basal
segments in contact in the median ventral line. The pre-
genital somite wide, not constricted, with large tergal plate,
but with its sternal plate small or inconspicuous. Opistho-
soma composed, at least in many cases, of eleven somites,
the eleventh somite very small, often hidden within the
tenth. Respiratory organs in the form of tracheal tubes
opening by a pair of stigmata in the second and third somites
of the opisthosoma. Intromittent organ of male beneath
sternum of the first somite of the opisthosoma.

Sub-order a. Panctenodactylii—Dorsal plate of prosoma
(carapace) narrowed in front; the appendages of the first
pair small, much narrower, taken together, than the posterior
border of the carapace. Serrula on movable digit of appen-
dages of first pair fixed throughout its length, and broader
at its proximal than at its distal end; the immovable digit
with an external process.

Family Cheliferide (Chelifer (Figs. 66, 67, 68), Chiri-
dium).
3 Garypide (Garypus).

Sub-order b. Hemictenodactyli.—Dorsal plate of prosoma
scarcely narrowed in front; the appendages of the first pair
large, not much narrower, taken together, than the posterior
border of the carapace. The serrula or the movable digit
free at its distal end, narrowed at the base; no external
lamina on the immovable digit.

Family Obisiide (Obisium, Pseudobisium).
» Chthoniide (Chthonius, Tridenchthonius).

Remarks.—The book-scorpions—so called because they
were, in old times, found not unfrequently in hbraries—are
found in rotten wood and under stones. The similarity of
the form of their appendages to those of the scorpions

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 257

suggests that they are a degenerate group derived from the
latter, but the large-size of the pregenital somite in them

0 =6pregenl 23

Tiuuiivvvil $i
12 3 10
Prosoma Opisthosoma
Fic. 72.—Garypus litoralis, one of the Pseudoscorpiones.
Lateral view. I to VI, basal segments of the sixth prosomatic
appendages; 0, eyes ; pregen, tergite of the pragenital somite; 1,
genital or first opisthosomatic somite; 2, 3, 10, the second, third,
and tenth somites of the opisthosoma; 11, the minute eleventh
somite; az, the anus. (Original.)

would indicate a connection with forms preceding the scor-
pions. (Reference to literature, 37.)
Order 7. Podogona = Meridogastra (see Figs. 73 to 76).—

Fie. 74.

Cc an

Fic. 73.—Cryptostemma Karschii, one of the Podogona.
Dorsal view of male, enlarged five times linear. III to VI, the
third, fourth, fifth, and sixth appendages of the prosoma; a, movable
(hinged) sclerite (so-called hood) overhanging the first pair of
appendages; 4, fused terga of the prosoma followed by the opis-
thosoma of four somites; az, anus; HE, extremity of the fifth
appendage of the male modified to subserve copulation. (Original
drawing by Pocock and Pickard-Cambridge.)

Fic. 74.—Cryptostemma Karschii. Anterior aspect of the
prosoma with the “hood” removed. I to IV, first to fourth
appendages of the prosoma; a, basal segment of the second pair of
appendages meeting its fellow in the middle line (see Fig. 75).
(Original drawing by Pocock and Pickard-Cambridge.)

Dorsal area of prosoma furnished with two shields, a larger
behind representing, probably, the tergal elements of the

258 E. RAY LANKESTER.

somites, and a smaller in front, which is freely articulated to
the former and folds over the appendages of the first pair.
Ventral area without distinct sternal plates. Appendages of
first pair bi-segmented, completely chelate. Appendages
of second pair with their basal segments uniting in the
middle line below the mouth, weakly chelate at apex.
Appendages of third, fourth, fifth, and sixth pairs similar
in form; their basal segments in contact in the middle line

amen een w wee} CIL .

Fic. 75.—Cryptostemma Karschii, one of the Podogona.
Ventral view. Ito VI, the six pairs of appendages of the prosoma,
the last three cut short ; 1, 2, 3, 4, the four somites of the opistho-
soma; a, hood overhanging the first pair of appendages ; J, position
of the genital orifice; ¢, part of third appendage; d, fourth segment
of second appendage. Observe that the basal segment of append-
age III does not meet its fellow in the middle line. (Original
drawing by Pocock and Pickard-Cambridge.)

Fic. 76.—Cryptostemma Karschii. Extremity of the fifth
pair of appendages of the female for comparison with that of the
male E in Fig. 73.

aud immovably welded, except those of the third pair, which
have been pushed aside so that the bases of the second and
fourth pairs are in contact with each other. A movable
membranous joint between the prosoma and the opisthosoma,
the generative aperture opening upon the ventral side of the
membrane. Praegenital somite suppressed, the opisthosoma
consisting of only four visible somites, in addition to a
tubular ring round the anal orifice. Respiratory organs

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 259

unknown. Intromittent organ of male placed at the distal
end of the appendage of the fifth pair.

Family Cryptostemmide (Cryptostemma) (*Polio-
c hera), Carboniferous.

Remarks on the Podogona.—The name given to this
small but remarkable group has reference to the position of
the male intromittent organ (Fig. 73, 5). They are small
degenerate animals with a relatively firm integument. Not
more than four species and twice that number of specimens
are known. They have been found in West Africa and
South America. A fact of special interest in regard to them
is that the genus Poliochera, from the Coal Measures,
appears to be a member of the same group. The name
Cryptostemma, given to the first-known genus of the order,
described by Guérin-Ménéville, refers to the supposed con-
cealment of the eyes by the movable cephalic sclerite.
(Reference to literature, 38.)

Order 8. Opiliones.\—Carapace of prosoma consisting of a
short posterior and a large anterior plate, which bears a pair
of median or one or two pairs of lateral eyes. Sternal
elements consisting of an anterior prosternal sclerite or
labium and a posterior metasternal sclerite. Appendages of
first pair large, three-jointed, and chelate; of second pair
either simple and palpiform or raptorial and subchelate ; of
remaining pairs similar in form and ambulatory in function ;
the basal segments of the second, third, and sometimes of the
fourth pairs of appendages furnished with sterno-coxal
(maxillary) lobe. Opisthosoma confluent throughout its width
with the prosoma, consisting sometimes of as many as ten
segments, the generative aperture lying far forwards between
the basal segments of the sixth or fifth and sixth prosomatic
appendages. Pregenital somite suppressed. Respiratory
organs, tracheal, a single pair of spiracles opening upon the
sternum immediately behind the basal segments of the ap-
pendages of the sixth pair; supplementary spiracles some-
times present upon the fifth segment of the legs. Both

1 Mr. Pocock has furnished me with the above account of the Opiliones
to take the place of that which appeared in the Encyclopadia.—E. R. L.

260 _E. RAY LANKESTER.

male and female furnished with a large protrusible copulatory
organ lying within the generative orifice.

Sub-order a. Cyphophthalmi (= Anepignathi).—First
sternal plate of the opisthosoma small, not covering the
genital aperture, which in the adult forms a gaping orifice.
Opisthosoma presenting ten tergal and nine sternal plates.
Carapace narrowed anteriorly and produced forwards so as
to overlap considerably the basal segment of the appendages

Fic. 77.—Stylocellus sumatranus, one of the Opiliones;
after ‘Thorell: NMularged. A, dorsal view; I to VI, the six pro-
somatic appendages. B, ventral view of the prosoma and of the first
somite of the opisthosoma, with the appendages I to VI cut off at
the base; a, tracheal stigma; ma, maxillary process of the cox of
the third pair of appendages; g, genital aperture. OC, ventral
surface of the prosoma and opisthosoma; a, tracheal stigma; b, last
somite. D, lateral view of the first and second pair of appendages.
KE, lateral view of the whole body and two first appendages, showing
the fusion of the dorsal elements of the prosoma into a single plate,
and of those of the opisthosoma into an imperfectly segmented plate
continuous with that of the prosoma.

of the first pair; basal segments of appendages of second
pair meeting in the middle line above the camarostome.
Remaining appendages stout, having one claw; their basal

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 261

seoments immovably fused. Sternum of prosoma almost
obliterated.

Family Sironide (Siro, Pettalus, Stylocellus).

Sub-order b. Mecostethi.—Generative aperture covered
by the first sternal plate of the opisthosoma. ‘This region
with nine tergal and eight sternal plates. Carapace not
produced on each side of the appendages of the first pair.
Appendages of second pair raptorial, stout, usually spined, their
basal segments not meeting above the camarostome. Coxa of
appendages of third pair furnished with immovable maxillary
lobe ; coxee of remaining pairs immovable. Metasternal plate
long. only its posterior extremity overlapped to a small
extent by the sternal plate forming the genital operculum.

Tribe a. Laniatores.—With two claws upon the append-
ages of the fifth and sixth pairs.

Principal families : Cosmetides (Cosmetus).
Gonyleptidee (Gonyleptis).
Assamiidee (Assamia).
Phalangodide (Phalangodes).
Oncopodide (Oncopus).

Tribe 3. Insidiatores.—With a single bidentate claw
upon the appendages of the fifth and sixth pairs.

Principal families: Adzide (Adzum, Larifuga).
Triznobunide (Triznobunus).
Triznonychide (Triznonyx, Acumon-
tia).

Sub-order c. Plagiostethi.—Differing from the Mecoste-
thi principally in the fact that the sternal area of the first
segment of the opisthosoma is prolonged forwards so as to
cover almost entirely the metasternal plate of the prosoma,
from which the cox of the appendages diverge radially, and
in that the appendages of the second pair are weak and
unspined.

Tribe a. Hupagosterni.—Metasternum of prosoma longi-
tudinal, immovably wedged between the cox; prosternum
narrow and lengitudinal. -No distinct maxillary lobe on the
coxa of the fourth appendage. nie

vou. 48, PART 2.—NEW SERIES. 18

262 E. RAY LANKESTER.

Principal families : Nemastomide (Nemastoma).
Trogulide (Trogulus).

Tribe 8. Apagosterni.—Metasternum of prosoma short,
transverse, not immovably wedged between the cox; pro-
sternum large, quadrate. A distinct maxillary lobe on the
coxa of the fourth appendage.

Families: Ischyropsalide (Ischyropsalis).
Phalangiide (Phalangium).

Nearly related to the Opiliones are the genera from the
Carboniferous strata constituting the group Anthracomarti.
These genera, of which the best known are Hophrynus and
Anthracomartus, seem to have differed from the existing
Opiliones in retaining a movable joint between the prosoma
and opisthosoma, and in the presence of movable lateral
plates upon the terga of the opisthosoma.

Remarks on the Opiliones. —These include the harvest-
men, sometimes also called Daddy-long-legs, with round un-
divided bodies and very long, easily detached legs. The
intromittent organs of the male are remarkable for their
complexity and elaboration. ‘The confluence of the regions
of the body and the dislocation of apertures from their
typical position are results of degeneration. ‘lhe Opiliones
seem to lead on from the spiders to the mites. (Reference to
literature, 39.)

Order 9. Rhynchostomi = Acari (see Fig. 78).—Degenerate
Arachnids resembling the Opiliones in many structural points,
but chiefly distinguishable from them by the following
features:—The basal segments of the appendages of the
second pair are united in the middle line behind the mouth ;
those of the third, fourth, fifth, and sixth pairs are widely
separated and not provided with sterno-coxal (maxillary)
lobes, and take no share in mastication; the respiratory
stigmata, when present, usually belong to the prosoma, and
the primitive segmentation of the opisthosoma has entirely
or almost entirely disappeared.

Sub-order a. Notostigmata.—Opisthosoma consisting of
ten segments defined by integumented grooves, the anterior

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 268

four of these furnished with a single pair of dorsally-placed
spiracles or tracheal stigmata.

Family Opilioacaride (Opilioacarus).

Sub-order b. Cryptostigmata. — Integument hard,

Fic. 78.—Holothyrus nitidissimus, one of the Acari; after
Thorell. Enlarged ten times linear. A, lateral view with
appendages III to VI removed; 1, plate covering the whole dorsal
area, representing the fused tergal sclerites of the prosoma and
opisthosoma; 2, similarly formed ventral plate; 3, tracheal stigma.
B, dorsal view of the same animal; II to VI, second to sixth pairs
of appendages. The first pair of appendages, both in this and in
C, are retracted. C, ventral view of the same; II to VI as in B;
a, genital orifice; 4, anus; c, united basal segments of the second
pair of appendages; d, basal segment of the sixth prosomatic
appendage of the right side. The rest of the appendage, as also of
appendages III, IV, and V, has been cut away. (Original drawing
by Pocock and Pickard-Cambridge.)

strengthened by a continuously chitinised dorsal and ventral
sclerite. ‘Trachez typically opening by stigmata situated in
the articular sockets (acetabula) of the third, fourth, fifth
and sixth pairs of appendages.
Family Oribatide (Oribata, Nothrus, Hoplophora).
Sub-orderc. Metastigmata.—Integument mostly like that

264 E. RAY LANKESTER.

of the Cryptostigmata. Trachez opening by a pair of stigmata
situated above and behind the base of the fourth or fifth or
sixth pair of appendages.
Families: Gamaside (Gamasus, Pteroptus).
Argaside (Argas, Ornithodoros).
Ixodide (Ixodes, Rhipicephalus).

Sub-order d. Prostigmata.—Integument soft, strength-
ened by special sclerites, those on the ventral surface of the
prosoma apparently representing the basal segments of the
legs imbedded in the skin. Trachex, except in the aquatic
species in which they are atrophied, opening by a pair of
stigmata situated close to or above the base of the appendages
of the first pair (chelicerz).

Families : Trombidide (Trombidium, Tetranychus).

Hydrachnide (Hydrachna, Atax).
Halacaride (Halacarus, Leptognathus).
Bdellide (Bdella, Hupodes).

Sub-order e. Astigmata.—Degenerate, mostly parasitic
forms approaching the Prostigmata in the development of
integumental sclerites and the softness of the skin, but with
the respiratory system absent.

Families: ‘l'yroglyphide (T'yroglyphus, Rhizoglyphus).
Sarcoptide (Sarcoptes, Analges).

Sub-order f. Vermiformia.—Degenerate atracheate para-
sitic forms with the body produced posteriorly into an annu-
lated caudal prolongation, and with the third, fourth, fifth,
and sixth pairs of appendages short and only three-jointed.

Family Demodicide (Demodex).

Sub-order g. ‘'etrapoda.—Degenerate atracheate gall-
mites, in which the body is produced posteriorly and annulated,
as in Demodex, but in which the appendages of the third
and fourth pairs are long and normally segmented, and those
of the fifth and sixth pairs entirely absent.

Family Eriophyide (Kriophyes, Phyllocoptes).

Remarks on the Rhynchostomi.—'The Acari include
a number of forms which are of importance and special
interest on account of their parasitic habits. ‘The ticks

STRUCTURE AND CLASSIFICATION OF THE ARACHNIDA. 260

(Ixodes) are not only injurious as blood-suckers, but are now
credited with carrying the germs of Texan cattle fever, just
as mosquitoes carry those of malaria. ‘he itch insect
(Sarcoptes scabiei) is a well-known human parasite, so
minute that it was not discovered until the end of the eigh-
teenth century, and “ the itch” was treated medicinally as a
rash. ‘lhe female burrows in the epidermis much as the female
trapdoor spider burrows in turf, in order to make a nest in
which to rear her young. The male does not burrow, but
wanders freely on the surface of the skin. Demodex folli-
culorumis also a common parasite of the sebaceous glands of
the skin of the face in man, and is frequent in the skin of the
dog. Many Acari are parasitic on marine and fresh-water
molluscs, and others are found on the feathers of birds and the
hairs of mammals. Others have a special faculty of consuming
dry, powdery vegetable and animal refuse, and are liable to mul-
tiply in manufactured products of this nature, such as mouldy
cheese. A species of Acarus is recorded as infesting a store
of powdered strychnine, and feeding on that drug, so poison-
ous to larger organisms. (Reference to literature, 40.)

AUTHORITIES CITED BY NUMBERS IN THE TEXT.

1. Srraus-DuRKHEIM (as reported by MM. Riester and Sanson in an
appendix to the sixth volume of the French translation of Meckel’s
‘Anatomy,’ 1829).

2. LANKESTER.—‘ Limulus an Arachnid,” ‘Quart. Journ. Mier. Sci.,’ vol.
KORE NES Soule

8. LANKESTER.—“ On the Skeletotrophic Tissues of Limulus, Scorpio, and

Mygale,” ‘Quart. Journ. Micr. Sci.,’ vol. xxiv, N.S., 1884.

. LANKESTER.—‘ Trans. Zool. Soe.,’ vol. xi, 1883.

5. LaNKEsTER and Bourne.—‘‘ Eyes of Limulus and Scorpio,” ‘ Quart.
Journ. Mier. Sci.,’ vol. xxiii, N.S., Jan., 1883.

6. Mitne-Epwarps, A.—‘ Recherches sur l’anatomie des Limules,”’ ‘ Ann.
Sci. Nat.,’ 5th series, “ Zoologie,” vol. xvii, 1873.

7. OwEN, Ricuarp.—“ Anatomy of the King-crab,” ‘Trans. Linn, Soc,
Lond.,’ vol. xxviii, 1872.

266 E. RAY LANKESTER.

8. KisuinovyE.—“ Development of Limulus longispina,” ‘Journal of
the Science College of Japan,’ vol. v, 1892.

9. BraveR.—“ Development of Scorpion,” ‘ Zeitschrift fiir wiss. Zoologie,’

vol. lix, 1895.

10. Hansen.—‘ Organs and Characters in Different Orders of Arachnida,”
‘ Entomul. Meddel.,’ vol. iv, pp. 137—149.

11. Warase.—“ On the Morphology of the Compound Eyes of Arthropods,”
‘Studies from the Biolog. Lab. Johns Hopkins University,’ vol. iv,
pp. 287—3384.

12. Nuwrort, Georce.—* Nervous and Circulatory Systems in Myriapoda
aud Macrourous Arachnids,” ‘ Phil. Trans. Roy. Soc.,’ 1848.

13. LankestER.—‘ Coxal Glands of Limulus, Scorpio, and Mygale,” ‘ Quart.
Journ. Mier. Sci.,’ vol. xxiv, N.S., 1884.

13a. Parren and Hazen.—“ Development of the Coxal Glands of Limulus,”
‘Journ. of Morphology,’ vol. xvi, 1900.

133. Bernarp.—‘‘Coxal Glands of Scorpio,” ‘Ann. and Mag. Nat. Hist.,’
vol. xii, 1893, p. 55.

14, Bennam.— Testis of Limulus,” ‘Trans. Linn. Soc.,’ 1882.

15. LankesTER.—‘‘ Mobility of the Spermatozoa of Limulus,” ‘Quart.
Journ. Micr. Sci.,’ vol. xviii, N.S., 1878.

16. Korscuetr and Hziper.—‘ Entwickelungsgeschichte,’ Jena, 1892.
Ibique citata.

17. Laurm.—“ The Embryology of a Scorpion,” ‘ Quart. Journ. Mier. Sci.,’
vol. xxxi, N.S., 1890; and “ On Development of Scorpio fulvipes,”
ibid., vol. xxxil, 1891.

18. LANKESTER.—(Homoplasy and Homogeny.) ‘‘On the Use of the Term
Homology in Modern Zoology,” ‘Ann. and Mag. Nat. Hist.,’ 1870.

19. LanKESTER.—‘‘ Degeneration: a Chapter in Darwinism,” 1878, reprinted
in the ‘ Advancement of Science,’ Macmillan, 1890.

20. LankestER.—‘“‘ Limulus an Arachnid,” ‘Quart. Journ. Mier. Sci.,’
vol. xxi, N.S.

21. Cuaus.—‘ Degeneration of the Acari and Classification of Arthropoda,’
‘Anzeiger d. k. k. Akad. Wissen. Wien,’ 1885; see also ‘Ann. and
Mag. Nat. Hist.’ (5), vol. xvii, 1886, p. 364, and vol. xix, p. 225.

22. Linpstrém, G.—“ Researches on the Visual Organs of the Trilobites,”
‘“K. Svenska Vet. Akad. Handl.,’ xxxiv, No. 8, pp. 1—86, pls. i—vi,
1901.

22*, ZirreL.—American edition of his ‘ Paleontology’ (the Macmillan Co.,
New York), where ample references to the literature of Trilobite and
Eurypterini will be found; also references to literature of fossil scor-
pions and spiders.

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.— “<The Embryology of Limulus,”
‘Journ. Morphology,’ vols. vii and viii. Kisnrnouyr.— Development
of Araneina,” ‘Journ. Coll. Sei. Univ. of Japan,’ vol. iv, 1890.
Locy.—“ Development of Agelena,” ‘Bull. Mus. Harvard,’ vol. xii,
1885. Mertscunikorr.—‘ Embryologie d. Scorpion,” ‘Zeit. wiss.
Zool.,’ vol. xxi, 1871; idem, “ Embryol. Chelifer,’ ibid. ScnImMKE-
witscu.— Développement des Araignées,’”’ ‘Archives d. Biologie,’
vol. vi, 1887.

Sense Organs. BrertKau.—‘Sinnesorgane der Spinnen,” ‘Arch. f. mikros.
Anat.,’ vol. xxvii, p. 589, 1886. Graper.— Unicorneale Trachcaten
Auge,” ‘Arch. f. mikr. Anat.,’ vol. xvii, 1879. GRENACHER.—
*Gehororgane der Arthropoden, Gottingen, 1879. KisH1novyE.—
“Lateral Eyes of Spiders,” ‘Zool. Anz.,’ vol. xiv, p. 381, 1891.
Purceti.—< Phalangiden Augen,” ‘ Zool. Anzeiger,’ vol. xv, p. 461.

General works on Arachnida. BLAancHarp.—“ Les Arachnides,” in
‘L’organisation du régne animal.’ Gauspert.—‘ Recherches sur les
Arachnides,” ‘Ann. Sci. Nat.’ (7), vol. xiii, 1892. Kocu, C.—‘ Die
Arachniden,’ 16 vols., Niirnberg, 1831—1848. Kocn, KryseRtine,
and SOrENsEN.—‘ Die Arachniden Australiens,’ Niirnberg, 1871-90.
Pococxk.-—‘ Arachnida of British India,’ London, 1900; idem, ‘‘On
African Arachnida,” in ‘Proc. Zool. Soc.’ and ‘Ann. and Mag. Nat.
Hist.,’ 1897—1900. Stmon.—‘ Les Arachnides de la France,’ 7 vols.,
Paris, 1874-81. THoreti.—* Arachnida from the Oriental Region,”
‘Ann. Mus. Genova,’ 1877-99.

VoL. 48, PART 2.—NEW SERIES, 19

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 271

On some New Species of the Genus
Phreodrilus.

W. Blaxiand Benham, D.Sc.(Lond.), W.A.(Oxon.), F.Z.S.
(Professor of Biology in the University of Otago, New Zealand.)

With Plates 13—15.

Amonest the Oligocheta obtained by Messrs. Lucas and
Hodgson in their recent biological survey of the New
Zealand lakes, which they were generous enough to hand
over to me for identification,! I find two new species of
Phreodrilus; and a third species I owe to the kindness of
my friend, Mr. Smith, of Ashburton, from whom Mr. Beddard
received the type species of the genus.

The characters of the genus, founded by Beddard in 1891,
for this New Zealand worm, and hitherto represented there
by the single species P.subterranens, have recently
received an extended interpretation by Dr. Michaelsen (5),
so as to include the four species of South American worms
originally placed by Beddard (3) in a distinct genus,
Hesperodrilus; this enlargement of the genus has been
rendered necessary by the discovery of a fresh-water worm
in Kerguelen which in certain respects bridges over the
anatomical gap between the two genera as formulated by
Beddard, just as it serves as a stepping-stone in the geo-
graphical distribution of the genus as now extended.

It is true that in the type species, as well as in a second
species here to be described, there is a peculiarity about the

1 An account of this collection will be found in P. Z. S., 1903.

oH? W. BLAXLAND BENHAM.

male efferent apparatus that does not exist in the South
American nor in the Kerguelen species, and one is tempted
to regard the existence of this “ atrial sac” as diagnostic of
the genus as originally formulated, but the intermixture
presented by other characters is so involved that it seems
better to adopt Michaelsen’s view and place them all in the
single genus Phreodrilus.

The new species described in the present contribution are
(a) P. lacustris, (b) P. beddardi, and (c) P. mauiensis,

PHREODRILUS LACUSTRIS, N. sp.

A small thin worm, usually much coiled in its preserved
state. One individual when stretched measured 20 mm., with
a diameter of + mm., or even less. This individual consists
of seventy-five segments.

The prostomium is prolobic, short, and conical (PI. 13,
fiz. 1). Segments I to VILare very short and distinctly biannu-
late; the following segments are longer, and the annulation
less evident. A “lateral line” is very well marked in the
stained entire individual.

Cheetee—The dorsal bristles are solitary, very delicate,
and simply capilliform; they are not very long, measuring
0-1 mm., and project for a distance equal to about one quarter
to one third the height of body, and are scarcely as long as
half a segment. They commence on the third segment, as
seems to be the typical arrangement in the genus. Here and
there I noted a couple of dorsal cheete, but the second is
quite short. The ventral bristles are in couples, and the two
differ in size and in the character of the free end, though
the differences may readily escape observation. Both are
sigmoid, with a nodal swelling and the free end sharply
curved (fig. 2) ; but whereas in one bristle of each couple (a)
this end is a simple hook, in the other (b) there is a minute
tooth on the convex curvature of this hook-like tip; in some
cases the tooth is absent and a mere difference in the refrin-
gency of this margin suggests a tooth. The chete of this

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 273

second form (b) appear to be rather shorter than the former.
In several segments, however, towards the hinder part of the
worm, both the chet have a tooth. There seem to be no
“yeserve ” chete. Of the two forms, the simpler (a) is the
more ventral of the two, while occasionally in the posterior
half of the worm one of the chete may be absent.
These ventral chetz measure 0°075 mm. in _ length;
they are smaller than in P. kerguelenensis. In the
character of the chete this species resembles the South
American species (“ Hesperodrilus”), rather than the
Kerguelen or New Zealand species. The ventral cheete are
absent in Segments XII and XIII; in the latter they
are replaced, however, by special copulatory _ bristles
(fig. 3), to which reference is made below.

The clitellum encircles the posterior part of Segment XII
and the whole of Segment XIII; its margins in sexually
mature individuals are well defined; anteriorly it ceases
at about the level of the male genital pores (Pl. 13, fig. 4).
In whole specimens, viewed by transmitted light, this
region appears blackish, and the epidermis is at least twice
the thickness of that layer in the neighbouring regions.

The male pores are on the twelfth segment, close to its
hinder margin, in line with the ventral cheete.

The oviducal pores are immediately behind them on the
boundary between the Segments XII and XIII.

The spermathecal pores are in Segment XIII, in front
of the line of ventral cheete.

Thus, the three pores are unusually close together: and
the body of the preserved worm is nearly always abruptly
bent at the thirteenth segment.

Internal Anatomy.

The alimentary canal presents no noteworthy features; the
buccal region is very short; and the pharynx occupies part of
Segment IT and the whole of Segment III. Its roof is pouched,
and the musculature is but feeble. It is remarkable that in

274 W. BLAXLAND BENHAM.

the species recently described by Dr. Michaelsen (5, p. 189),
P. kerguelenensis, there is a “schlundkopf”. similar to
that in Enchytreids; this is certainly not the case in
P. lacustris. The cesophagus, immediately behind the
pharynx, is dilated, but short, as the Septum III/IV is
thrust back by the pharynx nearly to the level of IV/V.
The cesophagus passes back into the ninth segment (or tenth,
in one case), being constricted at each septum and moderately
distended segmentally. Its epithelial cells are, as usual, tall
and ciliated.

In the ninth (or tenth) segment the gut suddenly changes
its character ; the epithelium becomes flatter, and its diameter
greatly increases so as nearly to fill the ccelom; it is here
filled with dirt, and is constricted, though not deeply, by the
septa.

I have but few notes on the vascular system, owing to
the imperfect manner in which the vessels can be traced by
sections alone. But in entire specimens, viewed by trans-
mitted light, the following facts were recorded :

There are undulating commissural vessels putting the
dorsal and ventral trunks into communication in Segments
V, VI, VU, VIII, but I could not detect any enlarged hearts
nor a blood-gland, either in mounted individuals or in sections.

Excretory System.—In several species of Phreo-
drilus there appears to be only one pair of pregenital
nephridia, but these extend through several segments, as
Beddard pointed out (4) in his account of P. (Hespero-
drilus) albus, and as Michaelsen finds in P. kerguelen-
ensis; but in P. subterraneus, the only species hitherto
described from New Zealand, Beddard (2) apparently did
not note any nephridia anteriorly to the fourteenth segment.
In the present species I observed in two series of longitudinal
sections a nephridium in Segment VII and another in Segment
X, but I was unable to trace any connection between these,
or to see either funnel or pore. The extreme tenuity of the
species renders the tracing of so delicate a tube as a neph-
ridium very difficult.

SOMW NEW SPECIES OF THE GENUS PHREODRILUS. 275

In P. albus the single nephridium in each side extends
from Segment V (in which the funnel lies) to Segment X, its
pore, however, being in Segment VI. In P. niger it
extends from VII to IX, and in P. kerguelenensis from
VII to X. It is probable, therefore, that in this new species
—P. lacustris—the pregenital nephridium has the same
disposition as in the last-named species.

Reproductive System.—Of the fairly numerous indi-
viduals obtained, only three turned out to be sexually mature.
One of these was mounted entire, a second was cut into
longitudinal sections, and the third was dissected notwith-
standing its small size; it was bisected in the region of the
reproductive organs, and the latter were partially isolated by
removal, under a dissecting lens, of the gut and part of the
body-wall, so that the true form and disposition of the
spermiducal gland could be studied. In this way a check on
the longitudinal sections was obtained, and a very necessary
check in the case of an organ, serial sectious of which had to
be studied under very high powers.

The single pair of testes hes in Segment XI, attached to
the anterior wall. Beddard, in his account of P. subter-
raneus, emphasises the point that in that species the testes
extend through or below the septum into the preceding
segment. However that may be, it is not the case in
P. lacustris, nor, as Michaelsen insists, in P. kerguelen-
ensis. Anexplanation of the condition described by Bed-
dard seems to be that the septa in this part of the body are
very imperfect, as is evidenced by the presence of sperm-
morulz and bunches of developing sperms in several of the
segments preceding the eleventh. I find, in one case, that
Segments VIII and IX are filled with sperms ; in other cases
the coelom of Segments X, XI, and XII is similarly occupied,
while in a third individual even Segment VII contains a
few of these developing sperms. ‘There are no sperm-sacs ;
the sperm-masses are free in the ccelom inSegments VII to
XII; while I did not find any in the post-clitellar segments
It is interesting to recall that also in P. kerguelenensis

276 W. BLAXLAND BENHAM.

the Segments VII to XI are occupied by sperm-masses, and
none are recorded posteriorly ; whereas in the South American
species Beddard finds the “sperm-sacs” extending back-
wards to Segment XX in P. albus, or even to the twenty-
sixth segment in P. niger, and makes no mention of pre-
clitellar sacs; but in P. branchiatus he states that no
special sperm-sacs exist, but Segments VII to IX are filled
with developing sperms. Thus a second possible generic
difference is seen to be negatived.

The efferent apparatus (fig. 5) is perhaps the most interest-
ing anatomical feature in the worm of this genus, as Beddard
has emphasised in his memoir (2). The funnel of the sperm-
duct is a circular, flattened disc, carried on septum XI/XII,
but not projecting freely into the segment, as is most
commonly the case, for its margin is surrounded by a circle
of non-ciliated cells which are continuous with the septum.
It is true that the septum here bulges forwards (in sections),
carrying the funnel a little distance into the cavity of the
segment, but the funnel itself is morphologically flush with
the anterior surface of the septum. ‘I'he cilia covering the
funnel are quite short, though in examining the entire indi-
vidual I at first mistook a bunch of sperms for long cilia,
and in sections a similar mistake may readily be made. The
sperm-duct passes away from the centre of this flat funnel,
and after a few convolutions in a dorso-ventral direction
immediately behind the septum, passes backwards towards
the hinder wall of Segment XII; it here enters a conical
organ, which is a sac (p.s.) enclosing a protrusible penis.
At the point of entry the sperm-duct is joined by a great
spermiducal gland (gl.), which is cylindrical and somewhat
coiled, or perhaps one should say undulating. The spermiducal
gland occupies the whole of Segment XII, and even pushes
backwards the posterior septum of this segment. It diminishes
in diameter before its junction with the sperm-duct, and this
narrow region may be termed the neck (7).

The gland has a structure similar to that described by
Beddard for P. albus, and to the “appendix of the vas

SOME NEW SPECIES OF 'TH"! GENUS PHREODRILUS. 277

deferens” in P. subterraneus, which, as Michaelsen has
recently pointed out, is nothing else than a spermiducal gland
or “‘prostate” of some authors. The wall of the gland is
formed of large rounded cells (seen superficially in fig. 6
and in transverse section at A, fig. 7), with finely granular
cytoplasm, outside which is a layer of flat peritoneal nuclei
(c. e.), but | am unable to detect any muscular coat.

At its proximal extremity, i.e. the neck, the glandular
cells gradually cease (fig. 7), and the epithelium becomes
quite low and the nuclei flattened; and both cytoplasm and
nuclei are much more deeply stained (in borax carmine) than
in the rest of the gland. It is into this neck that the sperm-
duct enters (fig. 6).

The common duct, or atrium as it may be conveniently
termed, now perforates a cylindrical penis, which when at
rest lies enclosed in a penial sac (figs. 5,6). he orifice of
the atrium (op.) is subterminal.

This penis—which in one specimen was partly protruded
through the male pore (figs. 4, 6)

consists of the following
tissues :—An internal epithelium, a muscular coat, and an
external epithelium. The lumen is small, and the internal
epithelium secretes a cuticle, and is not ciliated. The cells
are low, with large round nuclei; the muscles (mp.) are
both circularly and longitudinally arranged (perhaps in reality
they are oblique), and outside is the more cubical epithelium,
with larger oval nuclei. This epithelium is continuous at
the base of the penis with the lining of the penial sac (fig. 7).
These latter cells are, when viewed superficially (fig. 6, e.),
more or less hexagonal in form, and arranged in circular rows
with some regularity. ‘lhe lining of this sac extends up to
the epidermis, and round the pore there is an abrupt change
in the character of the cells (fig. 7). Outside them is a layer
of circular muscles, but I cannot detect any peritoneal cells
covering them. The longitudinal muscles of the body-wall
are connected with the base and side of the apparatus, and they
appear to pass round the penial sac to form part at least, if
not the whole, of its muscular coat, which dies out before the

278 W. BLAXLAND BENHAM.

external pore is reached. Protrusion of the penis appears to
be effected by the contraction of these muscles,

In comparing this apparatus with that of other species it
will be recognised that it closely agrees with that of
P. niger, in which the gland occupies the whole segment
and pushes back the hind septum. It is much larger than
that of P. albus, which is only half a segment long; while
the organ in P. kerguelenensis differs from all these in
that the sperm-duct apparently enters the spermiducal gland
some little distance from the free end; further, this species is
without a penis; at any rate, Michaelsen neither describes nor
figures any such a'termination to the atrium. But the South
American species are provided with a protrusible organ, and
agree in this matter precisely with P. lacustris.

The ovary lies in Segment XII, alongside of and partially
embraced by the coils of the spermiducal gland ; the oviduct
has the normal structure. In one specimen I noted ova in
Segments XV and XVI, but did not detect any ovisacs.

The spermatheca (figs. 8, 9, 10) is an elongated organ,
and, as in P. albus and others, is differentiated into three
regions, though they are not so sharply marked as in that
species. ‘The external pore in Segment XIII, on the ventral
surface, leads into a narrow duct (a) with a muscular coat; it
is only slightly dilated at the entrance—in contrast with
P. kerguelenensis and others,—and soon narrows; the
muscular coat is longitudinal, and I did not detect any
circular fibres in the first part of the duct, which takes a
vertical direction obliquely backwards towards the hinder
septum ; it then bends abruptly upon itself, and here circular
muscles appear and the longitudinal muscle-fibres pass
onwards beyond the bend, to be inserted in the body-wall (see
fig. 10, lm.). This second region of the muscular duct (a’.),
after a short course parallel to its former course, bends back-
wards and downwards towards the lower part of the septum
(XIII, XIV), and passes through the septum and becomes the
second region (b.)—the muscular coat is here absent, the
epithelium becomes lower and appears to be glandular, as the

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 279

cytoplasm is very granular and takes the stain deeply ; in the
entire isolated specimen the cells are vesicular in form, but in
sections (fig. 9,b.) they appear quite low. This glandular
region passes directly backwards below the gut, and gradually
opens out to form the ampulla (c.), the epithelium of which is
flat; this ampulla occupies Segments XIV and XV, being
slightly constricted by the septum, and is filled with ripe
spermatozoa ; there is no spermatophore.

The absence of a distinctly dilated sac at the external end of
the duct, opening to the exterior, is in contrast to the
arrangement in other species. Lying close to and behind the
aperture of this spermatheca is a peculiarly modified chetal
sac, containing two copulatory chete (figs. 3, 9). This organ
is ovoid, or subglobular; its wall is formed of long cells,
containing very fine granules; these cells are arranged with
their longer axes directed obliquely to the lumen, with the
nuclei at their bases.

The “copulatory chetze’? are more delicate than the
normal ventral chet, and the free end is sharply curved and
more hook-like.

In the entire individual the area of skin surrounding the
spermathecal pore and the copulatory chet is depressed, so
that the two organs appear to open together (fig. 3), but
longitudinal sections show their true relation as above
described (fig. 9). Only in P. kerguelenensis has such an
apparatus been hitherto described ; and Michaelsen’s account
differs in two points from the above ; firstly, he finds only one
cheta in each organ; secondly, the latter opens in common
with the spermatheca. The form of the bristle in his fig. 1
is similar to that of P. lacustris. It is noteworthy that
Beddard expressly states that there are no copulatory chete
in the South American species; otherwise one might have
been tempted to lay stress on this feature as of generic
importance and associated with the absence of a muscular
atrial sac.

Localities.—This species was obtained from Lakes
Wakatipu (Hauls 20, 23, 25) and Manapouri (Haul 1),

280 W. BLAXLAND BENHAM.

both in the South Island of New Zealand. ‘The hauls were
made in depths from 150 to 1000 feet, but I have no
information as to whether the worms came from the bottom,
though this is probably the case.

PHREODRILUS MAUIENSIS, Nn. sp.

Obtained from Lake Taupo, in the North Island. One
individual, unfortuuately immature, belongs to this genus,
but its characters are just sufficient to define the species. It
is evidently distinct from P. lacustris and from P. subter-
raneus.

he length is 18 mm., its breadth 4 mm.; it contains seventy
segments, and is thus twice as stout as P. lacustris, but
not nearly as large as P. subterraneus,

The prostomium is large and rounded.

The dorsal cheetz, commencing in Segment ITT, are capilli-
form and usually solitary, though frequently a shorter one
accompanies the larger.

The ventral cheete are in couples, of two kinds (PI. 14, fig.
11), a is simply hooked terminally, while b has a distinct but
small tooth on its upper convex curvature. This cheta is also
much larger than the former. ‘lhe tooth is much more evident
than in P. lacustris, and the chat are altogether of larger
size, being 0°135 mm. in length.

Of internal organs, the testes are present in Segment XI,
and small ovaries in the twelfth, in which segment there is
also the early rudiment of a sperm-duct; at least, so I
interpret a longitudinal cord of cells lying in this segment.

The vascular system presents a feature not observed in
P. lacustris, viz. a large “heart”? in Segment X, and a
somewhat convoluted, or at least lobulated, organ in XI,
which appears to be of the same nature as the “ blood-
gland” described by Beddard in Segments XII, XIII of
P. subterraneus. This specimen was stained and mounted,
and I have not studied it by means of sections.

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 281

PHREODRILUS BEDDARDI, n. sp.

While working on the previous species I was naturally
led to institute comparisons with the male efferent apparatus
in P. subterraneus. I was puzzled to account for the
creat differences that exist between the complicated arrange-
ment as described and figured by Beddard and the much
simpler condition of the organ in P. lacustris.

In P. subterraneus Beddard (1, 2) describes the apparatus
essentially as follows! :—'he vas deferens, after a few simple
convolutions, unites with a “blind diverticulum” of glandu-
lar structure, and the common duct thus formed is very
much convoluted—at first a narrow tube agreeing in struc-
ture with the vas deferens, it later becomes much wider and
different in structure; this tube opens externally without
any penis. But this highly convoluted common duct is en-
closed in a peculiar muscular sac—the “atrial sac,”’—the wall
of which is over a considerable distance separated from the
wall of the contained tube, but towards the external pore
becomes adherent to the latter. In the closed space thus
formed Beddard finds loose “ripe spermatozoa,’ together
with “free nuclei,” which have, according to him, no relation
to the “‘ sperms.”

Both the vas deferens and the “blind diverticulum ” per-
forate the wall of the atrial sac near its upper end. The
lower extremity of the atrial sac, where its wall adheres
to the duct within, is bent upon the previous region, and
perforates the body-wall without giving rise to any penial
structure.

The arrangement in the species (P. lacustris) that I was
studying at the time agrees closely with the male apparatus
of certain South American and Falkland Island worms de-
scribed by Beddard under the generic title Hesperodrilus;
and with some of the species, P. albus and P. niger, my
species presents several other points of agreement (as noted
in the above account). While thus engaged I received Dr.

1 I do not quote his own words,

282 W. BLAXLAND BENHAM.

Michaelsen’s recent memoir, above referred to, on Phreodri-
lus kerguelenensis, in which he brings forward evidence
in favour of uniting the genus Hesperodrilus with Phreo-
drilus; but, curiously enough, the type species, P. subter-
raneus, presented apparently so totally different a male
apparatus that it seemed to be of great importance to re-
examine this form.

I had, as I thought, a specimen of P. subterraneus, col-
lected by Mr. W. W. Smith, who had furnished Beddard
with his material. My specimen was labelled “P. subter-
raneus” by Mr. Smith, who is a keen observer of Oligo-
chetes. I therefore proceeded to examine the male apparatus,
but the result of my investigation differs, in certain points,
so greatly from Beddard’s account of P. subterraneus that
I am compelled to employ a new name for the worm. As I
was for the moment interested only in the male apparatus,
on the assumption that the worm was identical with Bed-
dard’s species, I made but a cursory examination of the
individual, in order to add any facts that the mature speci-
men might present, supplementary to those recorded by
Beddard for his immature individuals.

I propose for this new species the specific name, P. bed-
dardi, in reference, I need hardly say, to my friend, who has
done so much to elucidate the Oligochetal fauna of New
Zealand.

My specimen measures 40 mm. by 1°25 mm. It is thus
rather shorter than P. subterraneus, specimens of which,
he says, “ measure about 2 inches.”

I counted seventy-eight segments.

The dorsal cheetz visible, as Beddard noted, to the naked
eye are, like the ventral chet, carried on slight promi-
nences; and the muscles of each bundle are relatively of
great size, as they spread out so as to extend almost the entire
length of a segment (PI. 14, fig. 14). The dorsal cheeteze com-
mence in Segment III; they are absent from Segment IT, as
in most other species of this genus. Beddard makes no
reference to this absence in P. subterraneus, though in a

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 283

later paper describing species of Hesperodrilus this ab-
sence is noted. It seems likely that a re-examination of the
species will show that it agrees with the rest on this point.

As a rule a single cheta alone projects, but its base is
supported by a couple of minute bristles within the follicle ;
and here and there I note that one of these smaller cheetz
are elongated, and though not attaining the length of the
normal one, yet project some distance alongside of it.

The ventral cheetz agree precisely with the account given
by Mr. Beddard ; there is no trace of a “tooth” on the con-
vex side, such as exists in most of the other species of this
genus, and in this respect the worm agrees with P. kergue-
lenensis. In the anterior segments the cheeta are pointed,
but posteriorly this point is in many cases worn down, so that
the bristle terminates bluntly. The length of the ventral
cheetz is 0°3 mm.

The clit ellum (fig. 12) is fully developed, and is confined
to Segment XIII, with a sharply marked margin anteriorly
and posteriorly, but when viewed under a lens the body-wall
of Segments XI and XII also appear opaque ; when bisected,
however, and the cut wall examined, the epidermis in Seg-
ment XIII is seen to be very much thicker than that of the
neighbouring segments.

The male pore, situated close to the hinder margin of
Segment XII, is carried on a slightly everted papilla, in line
with the ventral cheetz, which are absent in this segment
(fig. 13). In the foot-note on page 290 of his memoir Beddard
records that in a mature specimen “one of the segments in
the neighbourhood of the thirteenth was furnished with a pair
of tubular processes.”’ This I take to be the penial sac
referred to below.

The spermathecal pore is, under the lens, a very noticeable
vertical slit with distinct cuticulated margin, situated near
the anterior edge of Segment XIII, in line with the dorsal
cheetze (here absent), as Beddard stated to be the case in
P. subterraneus, Though the dorsal chetz are absent,
the chetigerous sac persists (fig. 12, d’). The figure, 13 of

284 W. BLAXLAND BENHAM.

Beddard’s memoir, illustrating the external anatomy accom-
panying the description of P. subterraneus is misleading,
for, althongh he rightly states in his text that the pore is
in Segment XIII, it is unfortunately figured in Segment
AN:

In external features, then, this new species agrees with
Beddard’s account of his species.

So far as the internal anatomy is concerned, my further
notes deal only with the reproductive organs, to which my
attention was more specially directed.

There is no sperm-sac, but the Segments VIII, IX, X, XI
are filled with developing spermatozoa.

The spermatheca (fig. 144) extends through Segments
XIII to XVIII, as in P. kerguelenensis and P. albus.

The slit-like aperture leads into the broader end of a large
pyriform sac with very thick muscular wall; near the hinder
end of the segment the neck of the sac passes gradually
into a narrow duct, also with muscular wall and tall epithelial
lining; this duct (a.) passes backwards through Segments
XIV, XV, XVI, lying either above or below the gut,
undulating slightly, and then opens into a much dilated,
thin-walled sac (c.), the “ampulla” of Michaelsen, which les
in Segments XVII, XVIII, the septum between which nips
the ampulla which is filled with ripe sperms. There is no sign
of any spermatophore, the absence of which seems to charac-
terise the genus.

We do not know the fully developed spermatheca of
P. subterraneus, but that of the present species differs
from that of P. lacustris in the absence of the glandular
region of the duct and in the extraordinary thickness of the
muscular coat near the pore (fig. 15), in which both longi-
tudinal and circular fibres take a share.

The Male Hfferent Apparatus.—For the purpose
of studying this, I had bisected the worm in the neighbour-
hood of the reproductive organs; from one side of the body
I dissected away the male apparatus; the other side, with
apparatus uninjured, was cut into a series of transverse

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 285

sections. In the former I first studied the apparatus while
still in situ in its half of the body as an opaque object; it
was then gently removed from its attachment to the body-
wall near the pore, and later cleared in glycerine, in which it
was possible to turn it over and examine first one side, then
the other. Finally, it was stained and mounted in balsam.
But, as is known to students of the Oligocheta, the glycerine
preparation is of greater value in tracing out ducts, etc.,
than the balsam preparation.

The entire apparatus is shown in fig. 16, which represents
a combination of views of the two sides, obtained by the
above methods of study. It is strikingly different from, and
altogether simpler than that of. P. subterraneus.

The flat circular funnel rests against Septum XI/XIT; the
sperm-duct, after passing through the septum, winds to and
fro in rather a complicated course in between two of the
limbs of a blind glandular diverticulum, or spermiducal
oland, which is curved in the form of an S, and its free end
lies close behind the Septum XI/XII.

The sperm-duct joins the opposite extremity of the gland,
also near the anterior wall of the Segment XII.

Thus far there is a fairly close agreement with Beddard’s
figure and description; but it is in regard to the contents of the
muscular sac that the present species differs from his species.

This “atrial sac’’—as Beddard terms it—is bound to the
ventral body-wall by numerous muscle-fibres (mw.), which
radiate from the body-wall and encircle the sac ; it contains
a tube, or “atrium,” resulting from the union of the gland
and the duct; but this atrium differs from that in Beddard’s
species in the following points :—(a) It is of practically uniform
diameter throughout its course; (b) it is relatively short,
(c) and is only slightly convoluted; while, finally (d), it
terminates in a distinct penis, which projects into a “ penial
sac”’ or sheath, which in turn communicates with the exterior
at the male pore.

There is in the present species no trace of the much convo-
luted, narrow continuation of the sperm-duct within the atrial

voL. 48, PART 2.—NEW SERIES, 20

286 W. BLAXLAND BENHAM.

sac, such as is seenin Beddard’s fig. 7, in which the wider and
shaded portion there shown seems to correspond with the
“ uniform tube,” or atrium, just described. The atrium, how-
ever, in the present species is not absolutely uniform either
in diameter or in structure, for at the point where it receives
the sperm-duct and the gland it is for a very short distance
somewhat narrower than it becomes lower down, and also
varies somewhat in diameter along its course. Moreover, the
upper coiled portion has the same structure as the sperm-duct;
the lower differs in structure. The absence of a distinct penis
in P. subterraneus may possibly be accounted for by the
fact that the individuals which formed the material for
Beddard’s memoir were immature; but, as I shall point out
below, there appears to be a small indication of this organ.

The histological structure of the male efferent apparatus
of the present species agrees in general with the account
given by Beddard.

The spermiducal funnel is a flat, circular disc, perforated
centrally for the exit to the vas deferens. The cells form-
ing this disc are cubical, and bear quite short cilia; this fact,
again, is clear enough in the dissected and isolated apparatus,
but in sections it is not quite easy to distinguish between the
cilia and the spermatozoa accumulated around the funnel. The
spermiducal gland, i.e. Beddard’s diverticulum or “ appendix
of the sperm-duct,” consists (fig. 19, gl.) of an epithelium
surrounding a fairly large lumen, and covered externally by
peritoneum. Between the two layers of cells is a thin coat of
circularly disposed muscle-fibres, which are readily seen in
the glycerine preparation, but are more difficult to recognise
in sections owing to the thinness of the layer. The epi-
thelial cells are tall, granular, with a vacuolated cytoplasm,—
the minute granules being arranged in a network,—and
possess large circular nuclei near their bases.

The spermiducal gland enters the atrial sac at its apex
(figs. 16, 18). Close to this point the circular muscular coat
becomes thicker. The gland then diminishes in diameter,
(fig. 19, ».), the cells become more distinctly columnar,

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 287

longer, and narrower, and the lumen is considerably reduced
in size, while the cytoplasm loses its vacuolar character as
the granules became arranged more compactly.

A comparison of my fig. 19 agrees closely with the figure
12 of Beddard’s memoir.

The spermiducal gland, after entering the muscular sac,
becomes much narrowed to form the neck; this decrease
in size continues, and the change in the character of the
epithelium is more marked three sections lower down (fig.
21), at the level of the entrance of the vas deferens. The
epithelium (at m) has become quite low, and the distinctness
of the cell outlines has disappeared. The cytoplasm becomes
deeply stained, and the nuclei, hitherto circular in outline,
both in the sperm-duct (s.d.) and in the spermiducal gland
(gl.), and only moderately deeply stained, now become oval
or elliptical, and are quite darkly stained in borax carmine;
they are also much more closely arranged than before. This
narrowed neck of the spermiducal gland (cf. P. lacustris,
and Beddard’s figure of P. albus) is of very short extent,
occurring only in six or seven consecutive transverse sections
of the apparatus.

It is into this short narrow neck of the gland that the
sperm-duct opens. ‘The structure of this sperm-duct calls for
no particular description, as it agrees with the usual account,
except that in comparison with the larger Oligochetes the
number of nuclei seen in a transverse section is very small,
usually only three or four (fig. 20), they take the stain only
very feebly ; the cytoplasm is faintly granular; and the cells
are of course ciliated.

Passing now to the “atrial sac”? and its contained tube—
the common duct of gland and vas deferens,—which is con-
veniently termed the “atrium.”?, <A transverse section of

1 Tn his account of P. subterraneus Beddard uses the term “atrium ”
to indicate only the wide, non-ciliated portion of the tube within the muscular
sac—the portion shaded in his fig. 7,—while the narrow, much convoluted
(white) canal, which is ciliated internally, into which the “ diverticulum ”
(spermiducal gland) opens, he speaks of as a continuation of the vas deferens.

288 W. BLAXLAND BENHAM.

this region over a great part of its extent exhibits the
following features (see fig. 22, which is the sixth section
below that drawn in fig. 21):

The wall of the sac consists of a thick coat of circular
muscles, covered externally by a flattened ccelomic epithe-
lium, which forms a distinctly recognisable membrane with
flattened nuclei.

A considerable space is enclosed by this sac, in which le
the sections of the atrium—one, two, or three, according
to the region involved. Passing across this space are
numerous muscle-fibres (7. m.), the direction of which is for
the most part radial. These fibres appear to be developed
as processes, or at any rate as fibrous refringent modifica-
tions of the cytoplasm of certain cells (m.c.) which are
attached to the inner surface of the wall of the sac. The
nucleus of such a cell is oval, and takes the stain well; the
body is only very faintly stained.

Some of these muscle-cells are seen in figs. 22, 25, especially
well at m.c. The general form of the cell is usually spindle
shaped, one extremity of which lies against the wall of the sac
while the other:is ‘frayed out” into fibres, which pass
across the space to be inserted into the wall of the contained
atrium ; others pass from one part of the wall to another ;
others, again, appear to pass from one coil (or section) of
the atrium to another.

In some sections, less favourable than this, where portions

The term “atrium ” is usually, and it seems to me most conveniently, em-
ployed to indicate the tube resulting from the union of the spermiducal gland
(“ prostate ’’) and the sperm-duct, as I attempted to point out in 1890. This
is the sense in which Beddard himself uses the term in his Monograph in
reference to Tubifex and others. The terminology of this region, in spite of
Beddard’s own articles on it, still requires a revision. Neither Beddard nor
Michaelsen, in their monographs, appear to be quite consistent in the terms
employed. The fact that the upper part of the atrium in Phreodrilus
beddardi and P. subterraneus is ciliated is quite in agreement with the
condition in Tubifex, of which Beddard writes in his monograph, p. 105,
‘the elongated atrium has its proximal part ciliated; its distal part not
ciliated ; the latter forms a protrusible penis.”

Bb: ee Ae ere

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 289

of the fibres are cut across without either terminal being
involved, the appearance may suggest bundles of sperma-
tozoa, especially as the cut ends—facing the microscope—
have a greater refringency than the more horizontal portions,
and suggest “heads” (fig. 23 1m’.).

It is possible that these delicate fibres, radiating in groups
in every direction across the cavity of the sac, may have been
mistaken for sperms; yet I hesitate to assume that an error of
this kind would be made by so accurate and experienced
an observer as my friend Mr. Beddard. I merely suggest
this explanation of the mystery, for he himself admits it is
a mystery that surrounds their presence in this completely
closed sac; the more so as it appears to me that the relative
size of “head” to “ tail” indicated in his figures is not that
usual to the sperms of Oligocheeta.

The atrium itself exhibits two regions, distinguishable by
the character of the epithelium, though not otherwise. ‘I'he
upper region (fig. 22 at.) closely resembles the sperm-duct,
and corresponds with the narrow white tube in Beddard’s
species ; the lower region is cuticulated, and otherwise con-
trasts with the sperm-duct, and resembles the shaded portion
(‘‘ atrium”) of Beddard’s figure 7.

The epithelium of the upper region is finely granular ; no cell
outlines are visible, and the round nuclei—more deeply staining
than in the case of the vas deferens—are few and regularly
spaced. The lumen is fairly large, and shows most distinctly
cilia. It might be suggested that these are in reality sperma-
tozoa passing down the canal; but against this interpretation
are the facts, firstly, that many of them are arranged verti-
cally to the surface of the cells, from which they can be seen
arising, and secondly, the failure to discover any heads,
which would of course appear as fairly deeply stained points;
but nothing of the sort occurs.

There appears to be no circular muscle-fibres round the
atrium ; for in such sections as cut it longitudinally or nearly
so I cannot detect any cut ends of fibres, but outside the
epithelium is a layer of muscle-fibres, with which the radiat-

290 W. BLAXLAND BENHAM.

ing fibres previously described are continuous; these fibres
take an obliquely longitudinal course.

The atrium has the above structure for only a moiety,
though the greater moiety, of its course; further downwards,
towards the exterior, its. epithelium gradually changes in
character (fig. 23). The cells are lower, the nuclei oval and
more closely placed; there are no cell boundaries recognis-
able, but the extent of the cell is indicated by the undulations
of the cuticle. The cilia are now absent, and the cytoplasm
secretes a distinct cuticle, which is vertically striated—a fact
which is more evident when this cuticle is cut rather obliquely,
as in the lower half of the figure.

Further, as the duct enlarges the lumen is consequently
wider than before. ‘This widened portion terminates some
little distance before the external aperture is reached, and
forms a short though evident projection into the terminal
region of the atrial sac; this projection—or “ penis,” as it
may be termed—is more readily seen in the preparation of
the entire apparatus in glycerine than in transverse sections ;
but, being aware of its presence, one may distinguish it even
in transverse sections.

The structure of this penis is best understood by the study
of the isolated apparatus (fig. 17). The atrium, now a very
narrow tube, perforates a short truncated cone, whose end
projects into a more capacious chamber, which may be termed
the “penial sac”; at the end of the cone is the aperture of
the atrium itself (0. p.). The wall of the atrial sac is seen to
be continuous with the base of the penial sac.

This figure may be compared with Beddard’s figure 30,
which represents a longitudinal section at a point “some
distance from the external orifice of the atrium,’ where
“the muscular and peritoneal coats become widely separated
from the epithelial layer. At this point the lumen of the
atrium becomes suddenly contracted.” I think that these
sudden changes in character of lumen and relation of the
coats of the organ in P. subterraneus represent a small—
possibly vestigial, or equally possibly a nascent—penis.

a een:

=
\

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 291

Turning now to the sections through this region. The
figures 24, 25, 26 are nearly consecutive, and pass through
the atrium where it traverses the penis.

The first figure is nearly longitudinal, as it cuts the atrium
at a curve; on the right side of the figure, at y, the atrial
epithelium appears to be invaginated into the cavity of the
tube. As a matter of fact, the lining of the tube is here
thrown into longitudinal folds, so that the lumen is more or
less reduced. The next section (fig. 25) is the fourth from
the preceding, and cuts the atrium nearly transversely. The
atrial sac is much reduced in size, and the atrial wall itself
is folded (at y). The following section (fig. 26) involves the
very tip of the short penis, cutting it through rather obliquely.
The penis in this individual is less prominent than in the
individual dissected (compare fig. 26 with fig. 17), for in it
the penial sac was protruded and the penis partially so.
The section figured at fig. 26 is taken just where the atrial
epithelium is being reflected so as to approach (and on the
right side has reached) the inner wall of the atrial sac.
In the centre of the section the aperture of the penis is
shown.

The epithelium of the atrium is continuous at the pore
with that covering the cervical penis, and thus with the
lining of the penial sac, and this epithelium retains practi-
cally its previous character, but the cytoplasm appears to be
vertically striated, especially at the outer (basal) surface,
where minute vacuoles as of some secretion can be seen,
while the cuticle is thicker than before (fig. 27).

There is here no circular coat of muscle, but to the wall is
attached a number of retractor muscle-fibres (as in figs. 17,
28), and outside is a layer of flat peritoneal nuclei.

The epithelium of this penial sac passes up to the lip of
the external pore, and is here continuous of course with the
epidermis ; but there is a sudden change (fig. 28), no transi-
tion being apparent, the epidermal cells having flattened
oval nuclei, which are much smaller and take the stain very

292 W. BLAXLAND BENHAM.

much more powerfully than the nuclei of the internal
epithelium.'

A comparison of the apparatus in P. beddardi with that
described by Beddard for P. subterraneus shows a close
general agreement, both macroscopically and microscopically,
and, apart from a possible error in interpreting the radia-
ting muscles within the atrial sac, the most striking difference
is the absence in this new species of the long, much convo-
luted, and very narrow portion of the atrium and the
presence of a more pronounced penis. In both of these
- points P. beddardi forms an interesting intermediate stage
between the simple conditions of P. albus and the more
elaborate arrangement of P. subterraneus, with P.
kerguelenensis as in some respects a link with the former.

The most characteristic thing about two of our New Zealand
species is the presence of a muscular sac enclosing the
atrium (7. e. the common duct of vas deferens and spermi-
ducal gland), which is more or less coiled so as to be stowed
away within it. No trace of this sac exists in P. kerguelen-
ensis, but the spermiducal gland is shorter and the “atrium ”’
is much longer than in the South American species, and is
moreover glandular, as is the atrium of our New Zealand
forms. The absence of a penis in the Kerguelen species
forbids us placing it asa direct link. But if we start with
P. albus, we find the vas deferens opening into the short,
narrow, and apparently non-glandular neck of a small spermi-
ducal gland. (The gland is much larger and coiled in
P. niger andin P. lacustris, where it occupies the whole
length of its segment). The common duct thus formed
perforates a protrusible penis, contained within a compara-
tively capacious penial sac. The next stage, apart from the
penis, is P. kerguelenensis, in which the common duct
(atrium) is longer and glandular. Then comes an entirely
new structure, and we have the stage in which the muscular
wall becomes separated from the glandular epithelium, so as

1 Unfortunately the lithographer has made the nuclei of the epidermic cells
next the pore round instead of flat.

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 293

to form a muscular “ atrial sac.” In P. beddardi the atrium
is much larger than in the previous species, and is coiled,
and terminates in a small penis. And finally, in P. subter-
raneus the atrium becomes drawn out to an extraordinary
length, and is differentiated into a long narrow, and a short
glandular region, while the penis is quite small.

Mr. Beddard, in his memoir on P. subterraneus, has
called attention to the peculiarity and unique character of
this atrial sac, and has compared it with certain other
structures, and the inclusion of Hesperodrilus in the
genus renders it easier to make comparisons with the closely
allied family, the Tubificide.

In Tubifex itself there is a comparatively simple pro-
trusible penis, surrounded by a muscular wall, forming a sac
in which it lies. This is quite comparable to the arrange-
ment in P. lacustris. But in other genera, such as Lim-
nodrilus, the muscular investment extends much further up
the wall ofthe apparatus ; the penis is much more powerfully
developed it is true, but we do not know to what extent it can
be protruded. From its general structure one is inclined to
think that the extent is limited. This muscular sheath, which
in some species (constituting the genus “Camptodrilus” of
Hisen) is formed of spirally arranged fibres, surrounds a con-
siderable length of the “atrium,” narrowed of course as com-
pared with the saccular region higher up the tube. It seems
to me that the atrial sac of Phreodrilus beddardi is a step
further than this, in which the whole atrium has become
surrounded by muscle.

It appears that protrusion in this case is effected by the
compression of the fluid within the sac by the contraction of
the muscle in the wall, which is aided by the contraction of
the fan-shaped muscle (m.w.) above described. This muscle
is probably homologous with those surrounding the penial
sac of P. lacustris, themselves in continuity with the
longitudinal muscles of the body-wall, and acting as “ pro-
trusors.’ In P. beddardi the penial sac itself is provided
with longitudinal muscles alone, which appear to act as

294 W. BLAXLAND BENHAM.

retractors (¢. m.), and perhaps the spiral muscles covering
the atrium derived from the radiating fibres (r.m.) which
connect it with the wall of the atrial sac serve to retract the
penis.

Dunedin, April 11, 1903.

LITERATURE.

1. Bepparp, F. E.—* Abstract of some Investigations into the Structure of
the Oligocheta,” ‘Ann. Mag. Nat. Hist.,’ 1891, p. 88; Phreodrilus,
p. 92

2. Bepparp, F. H.—“ Anatomical Description of Two New Genera of
Aquatic Oligocheta,” ‘Trans. Roy. Soc. Edinb.,’ xxxvi, p. 273.

8. Bepparp, F. E.—* Pre]. Notice of South American Tubificids, etc.,”
‘Ann. Mag. Nat, Hist.,’ 1894 (6), xili, p. 205.

4. Bepparp, F. E.—“‘Naiden, Tubificiden, und Terricolen,” ‘ Hamburg.
Maghal. Sammelreise,’ 1896.

. Micnartsen, W.— “Die Oligochet. d. Deutsch. Tiefsee Exped.,” ‘Wissensch.

Ergebn., etc.,’ 1902, p. 183.

EXPLANATION OF PLATES 13—15,

Illustrating Mr. W. Blaxland Benham’s paper “On some
New Species of the Genus Phreodrilus.”

Letters HMPLOYED IN THE FIGURES.

a. Muscular duct of spermatheca. aé, Atrium, either its wall or cavity.
ats. Atrial sac, either its wall or cavity. 6. Glandular portion of duct of
spermatheca. c. Ampulla of spermatheca. c. e. Celomic epithelium, or its
nuclei. ¢.m. Circular muscle, whether of body-wall or atrial sac. cp. Sac
with copulatory chete. cp. ch. Copulatory chete. d. Dorsal chete.
e. Epithelium of penial sac, ete. ep. Hpidermis. £ Funnel of sperm-duct.
g!. Spermiducal gland. /g. Longitudinal muscles of body-wall. dm. Longi-
tudinal muscles of other organs. m. Muscle. m’‘. Cut ends of* muscle-fibres.
m.c. Body of muscle-cell. mp. Muscles of penis. mw. Fan-shaped muscle
passing from atrial sac to body-wall. x. Neck of spermiducal gland. op.
Orifice of penis. yp. Penis. p.s. Penial sac, either its cavity or wall.

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 295

r.m, Radiating muscle-fibres traversing the cavity of the atrialsac. s, Septum.
s.d. Sperm-duct. spéh. Aperture of spermatheca. ¢.m. Retractor muscles of
penial sac. v. Ventral chete. ., Point of union of sperm-duct and spermi-
ducal gland. y. Folding of atrial epithelium at the penis. z. Transverse
fold of the epithelium of the penial sac. @ Male pore. 2 Orifice of oviduct.

Figs. 1 to 10 illustrate the anatomy of Phreodrilus lacustris, n. sp.
Fig.'11 refers to P. mauiensis, n. sp.
Figs. 12 to 28 refer to P. beddardi, n. sp.

Fic. 1.—Side view of anterior extremity of P. lacustris. x 40, camera.
Note the conical form of prostomium, the absence of dorsal chet on Seg-
ment II and the annulation of the segments.

Fic. 2.—The two ventral chet of a bundle. x 640. (a) The simple
form; (4) the toothed one.

Fie. 8.—The spermathecal pore and copulatory cheta of Sezment XIII, as
seen in a transparent specimen,

Fig. 4.—Ventral view of Segments X to XIV, to show the clitellum and
genital pores; the former is shaded. On the right side of the figure the
penis (p.) is represented as being protruded from the male pore(¢@). ‘The
ventral chetz are absent in XIJ, XIII, but in latter are replaced by copulatory
chetz (cp.). Q oviducal pore. spth Spermathecal pore.

Fic. 5.—View of the entire male efferent apparatus, constructed from
sketches of the opaque and transparent preparations of the isolated organ.
The apex of the spermiducal gland (g/.) is slightly shifted from its true
position near the septum, so as to exhibit more clearly the course of the
sperm-duct (s.d.); the union of the two is indicated at z. The wall of the
penial sac (p. s.) is represented as being transparent, allowing the penis (p.)
to be seen ; the sac is still attached to the body-wall at the male aperture.

Fig. 6.—A somewhat diagrammatic representation of the penial sac, etc.,
founded on the study of the organ mounted in glycerine. In the upper part
of the sac the circular coat of muscles (m.) is in focus; in the middle of the
sac the bases of the epithelial cells (e.) are shown; while lower down the wall
is in optical section, so that the cavity (ps.) is in view, as well as the external
epithelium of the penis itself. The terminal region of the penis is seen in
optical median section, which brings into view the lumen of the distal part of
the atrium, which opens near the tip of the penis at o. p.

Fie. 7.—A median longitudinal section along the penis and its sac, drawn
as carefully as possible under Leitz, oil immersion, j4;. The spermiducal
gland (g/.) is seen to change its character as it narrows to form the neck (z.),
into which the sperm-duct opens (see fig. 5). This neck is continued through

the penis, and corresponds to the atrium of some other species. The longi-

296 W. BLAXLAND BENHAM.

tudinal muscles (/g.) of the body-wall pass upwards so as to form the coat of
the penial sac. In the upper part of the figure, at a, the spermiducal gland
has been cut transversely in a wider region.

Fic. 8.—The spermatheca in situ. sph. Its orifice. a. Its muscular duct.
6. Glandular region of the duct. c.Ampulla. cp. Organ with copulatory chete.

Fie. 9.—The duct of the spermatheca and the copulatory organ, seen in
longitudinal sections. The details of structure are only partly filled in. The
copulatory organ (cp.), with its cheete, is seen to open by a pore distinct from
that of the spermatheca. a. The proximal portion of the muscular duct. a’.
The recurved portion of the same. 4. The point at which a. passes into a’,

Fic. 10.—The point 4. of the preceding figure, as seen in the entire mounted
specimen, under an oil immersion, 34. The region a. is seen in optical section,
a'. in surface view. The longitudinal muscles (/m.) surrounding a. pass away
to the body-wall. The circular coat (em.) around a’. ceases at hf.

Fic. 1].—The ventral couple of chete of P. mauiensis. x 500.

Fie. 12.—View of the right side of the genital region of P. beddardi.
d. Dorsal bristle. dd’. The chetaless dorsal cheetal-follicie on Segment XIII.
v. Ventral chet. G Male pore. 2 Female pore. sph. Spermathecal pore.

Fic. 13.—Side view of ventral region of the left side of part of Segments
XI, XII, showing the everted penial sac (p. s.). v. Ventral chete of
Segment XI.

Fic. 14.—Optical section of the ventral portion of a segment, showing the
ventral couple of chet, with their greatly developed muscles (m.).

Fig. 144.—The spermatheca in situ, seen from the side. sp¢d. Spermathecal
pore. a. Muscular duct. ce. Ampulla.

Fic. 15.—A transverse section through the muscular duct of the sperma-
theca, a short distance from the pore. It is provided with both circular and
longitudinal muscles, the former of considerable thickness; in the latter the
round nuclei of muscle-cells (?) are seen between the cut fibres and the peri-
toneum (¢.é.).

Fic. 16.—The male efferent apparatus; the figure is constructed from
sketches of the isolated organ as seen as an opaque object and ina glycerine
preparation. ‘The atrial sac is represented as transparent so as to exhibit the
atrium within, and the penial sac also allows the contained penis to be seen.
A fan-shaped bundle of muscle (m. w.), springing from the body-wall, enwraps
the atrial sac, giving rise to its circular coat of muscles.

Fic. 17.—The penial sac and penis in optical section, as seen when isolated
in a glycerine preparation. The lower end of the atrium (qé.) is seen in the
atrial sac (aés.), to the inner surface of which it is connected by radiating
muscle-fibres (7. m.); it is also accompanied by longitudinal fibres. The penis,
in comparison with the preceding species (fig. 5), is seen to be of much

SOME NEW SPECIES OF THE GENUS PHREODRILUS. 297

smaller size, and the orifice is terminal (it is represented too large in the
figure).

[N.B.—Figs. 18—28, representing transverse sections of the efferent
apparatus, are drawn, under Leitz, oil immersion, ;, as carefully as possible ;
they are not camera drawings, and consequently they are not all quite of the
same relative size. ]

Fte. 18.—Cuts through the spermiducal gland at its entrance into the atrial
sac; note the circular muscle at one end of the figure.

Fie. 19.—The section immediately following the preceding. It cuts the
eland twice; one section (g/.) is outside the atrial sac, the other (z.) is now
within the sac. Thereis a marked difference in the character of the cytoplasm
in the two cases and the size of the lumen.

Fic. 20.—Transverse sections of the sperm-duct.

Fic. 21.—Section involving the entrance of the sperm-duct (s.d.) into the
neck (z.) of the spermiducal gland within the atrial sac (a¢s.). The section
is the third below that shown at fig. 19. The epithelium of the neck is
formed of low cells, deeply staining, and apparently ciliated.

Fic, 22.—A transverse section through the upper part of the atrial sac (the
sixth section below fig. 21) at nearly its widest region; it shows the atrium
(at.) cut through thrice, owing to its coiling. The epithelium closely resembles
that of the sperm-duct, and, like it, is ciliated. m.c. Muscle-cells attached to
the inner surface of the wall of the sac, and produced into radiating muscle-
fibres (7. m.) passing to the atrium, which they enwrap ina spiral direction,
so that the fibres in places are cut transversely (as at 7. m’.). The wall of the
sac is formed of circular muscles (c. m.), which appear to be connected with
the muscles (mw.) from the body-wall.

Fie. 23.—A section through the atrial sac some distance lower down. The
diameter of the sac has diminished. The epithelium of the atrium has altered
its character; it no longer bears cilia, and is covered internally by a striated
cuticle. The radiating muscle-fibres are cut obliquely on the right, presenting
the appearance of short filaments and refringent dots. The parent muscle-
cells (m. c.) form almost a complete lining to the sac.

Fic. 24.—The twenty-eighth section below that figured at fig. 22. It
cuts the atrium longitudinally at a bend near its lower extremity, just before
it passes into the penial sac (cf. fig. 17). On the right (y.) the epithelium is
infolded. The circular muscles of the atrial sac are now seen cut across,

Fic. 25.—The fourth section from fig. 24. The epithelium is seen to be
much folded (y.).

Fic. 26.—The section following that drawn at fig. 25 passes obliquely
through the tip of the penis, the aperture of which (op.) is seen to occupy the

298 i W. BLAXLAND BENHAM.

position of y. in fig. 25. On this side of the section the lining of the penial
sac is involved (p.s.); on the left side the cavity of the atrial sac is still seen

[N.B.—The cytoplasmic details are not indicated in figs, 25, 26, 28.]

Fic. 27.—The third section below the last is a transverse section of the
penial sac. The epithelium is totally different from that of the atrium; its
cytoplasm is striated, and small vesicles are seen in it, especially near its base.

Fic. 28.—A longitudinal section through the penial sac involving the male
pore (cf. fig. 17). The fold (z.) in the epithelium is evidently connected with
the non-protrusion of the penial papilla.

ON A NEW SPEOIES OF THE GENUS HAPLOTAXIS. 299

On a New Species of the Genus Haplotaxis; with
some Remarks on the Genital Ducts in the
Oligocheta.

eof, By |
W. Blaxland Benham, D.Sc.(Lond.), M.A.(Oxon.), F.Z.S.
(Professor of Biology in the University of Otago, New Zoaland.)

With Plates 16—18,

Amonest the material collected by Mr. Keith Lucas during
his biological survey of the New Zealand lakes I find two
small worms belonging to the genus Haplotaxis, of
Hoffmeister (= Phreoryctes, auctorum), which differ from
the two species already known—H. gordioides, from Hurope
and America, and H. smithi, from New Zealand—in being
provided with only a single pair of ovaries and oviducts. For
this new species, therefore, I propose the name Haplotaxis
heterogyne. Justification for placing the worms in this
genus, hitherto characterised by the possession of two pairs
of female organs, will be found below.

The worm is further remarkable and of general morpho-
logical interest on account of the very close structural
resemblance, I may almost say identity, of the sperm-ducts
with the nephridia. This matter also is reserved for dis-
cussion till the characters of the new species have been

described.
HAPLOTAXIS HETEROGYNE, 0. sp.

_ Of the two individuals one is sexually mature, the other has
only the rudiments of the genital organs. .The former was

300 W. BLAXLAND BENHAM,

studied at first entire, stained in alum-cochineal, and mounted
in Canada balsam ; it was then cut into a series of transverse
sections. The anterior end of the other was cut longitudinally ;
a portion from the middle of the body was cut transversely,
and other portions of the worm were studied in glycerine.

The prostomium, as usual in this genus, is remarkably
long and narrow, but does not exhibit any annulation. The
sensory cells form a thick layer over its whole extent. The
Segments I and IT are short, and the subsequent ones become
progressively larger; the body is much dilated in the region
occupied by the sexual products (Pl. 16, fig.1). Hach segment
is surrounded by a ring of more deeply stained nuclei at about
the level of the chete, probably a ring of sensory cells; and
a lateral line is evident in transverse section.

The cheetee are four in number in each segment (fig. 15).
The single dorsal cheeta is only about one third to one half
the length of the single ventral one, which is very much
stouter than the former; both are, however, alike in form
—the basal region is straight, the freely projecting portion
is curved so as to be sickle shaped with a simple point. In
the mid-body the dorsal cheeta is about 0°09 mm., the ventral
0°15 mm. in length. The dorsal cheetz are present through-
out the worm.

The clitellum covers Segments XI to XIII and part of
XIV ; it surrounds the body, but is better developed laterally
than either ventrally or dorsally, indeed, it appears in trans-
verse section as thinner dorsally than elsewhere.

I was unable to detect any of the genital pores on the entire
worm; but from a study of sections I believe that the two
pairs of male pores in Segments XI and XII lie just in front
of the ventral chete. There is a single pair of oviducal
pores in Segment XIII; each pore is external to the line of
ventral chet, and lies below a slightly overhanging pro-
jection of the lateral margin of the ventral surface. In the
possession of a single pair of female gonads and ducts this
species differs from the other two known species, H. gor-
dioides, and H. smithi; hence the specific name hetero-

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 301

gyne. The two pairs of spermathecz open at the anterior
margins of Segments VIII and IX.

Internal Anatomy.

Alimentary System.—The buccal region is noticeably
long, extending through the three anterior segments of the
body; there is no pharynx, but the buccal tube opens into a
gizzard in Segment LV (fig. 1, gq). This organ is very different
structurally from a pharynx, for which it may easily be
mistaken unless the worm be studied by means of sections.

It is a cylindrical organ, lined by a thick cuticle (fig. 2) ;
the wall is for the greater part of its extent muscular; the
muscle is equally developed on all sides, and consists in the
main of a thick circular coat, outside which is a layer of
longitudinal fibres, together with others intermingled with
the outer lamellee of the circular coat. A distinct ccelomic
epithelium surrounds the whole. From its dorsal and lateral
walls a few muscle-slips pass to the body-wall.

In the posterior third of the organ the muscular coat
diminishes gradually, and the epithelial cells exhibit more or
less numerous goblet-cells, the contained secretion of which is
not stained by hemalum; these goblet-cells open by distinct
holes through the cuticle.

Such a structure more nearly resembles a gizzard than a
“pharynx ;” there is no ‘dorsal muscular pad,” such as
occurs in HEnchytreids, nor is there any “ dorsal ciliated
pouch,” such as is met with in many earthworms as well as
most aquatic Oligochztes. The presence of a gizzard inaso-
called “ limicoline” member of the order breaks down one
more of the barriers which were formerly supposed to separate
the aquatic from the terrestrial Oligochetes; and it is
remarkable that both Haplotaxis gordioides and H.
heterogyne, purely aquatic worms, should possess a gizzard,
whilst the majority of aquatic species of terrestrial genera
lose the gizzard.!

' In looking up the literature of the subject, after writing out’ my notes, I

VOL. 48, PART 2.—NEW SERIES. ra

302 W. BLAXLAND BENHAM.

The cesophagus is quite a narrow tube, lined by ciliated
epithelium, which is somewhat folded ; it passes backwards,
below the sperm-sacs, as far as Segment XII, where it is
slightly dilated, and the ventral wall thrown into folds,
which are more vascular than elsewhere.

As to the vascular system, the dorsal and ventral vessels
are connected by a pair of undulating “ commissural vessels ”
in every segment, as in the other two species of the genus.

Nephridia.—The first nephridium occurs in Segment X,
with a funnel in the preceding segment; none are present in
the following three segments, in which the genital ducts lie,
but in Segment XIV and in each of the subsequent segments
there is a pair of excretory organs, and these are larger
than those in the tenth segment.

In the immature individual likewise no nephridia are to
be seen in the Segments XI, XII, XIII.

In H. gordioides Forbes (4) finds rudimentary nephridia
in all the genital segments of a quite immature individual in
which no trace of genital organs are yet present.

The disposition and structure of the nephridium is illus-
trated in figs. 3—8. The nephridial funnel of the post-ovarian
organ, at least, has the usual form, with one lip a good deal
higher than the other (fig. 9); the canal, after piercing the
septum, perforates a row of vesicular cells, which form a
loose loop. The cytoplasm of these cells exhibits (when
studied under a ;4, homogeneous immersion lens) a faint
network, but immediately around the canal this network
is replaced by more closely granulated protoplasm, which
forms a distinct but narrow “ wall” to the canal (fig. 8).

These cells do not correspond with the vesicular “peritoneal
cells” that surround the nephridium in certain earthworms,
or which occur, for instance, in Psammoryctes, as figured
by Vejdovsky.
find that Michaelsen (5) has already described this gizzard in H. gordioides
in much the same terms as I have above used. In this paper he corrects
several errors and misconceptions in the description of the various “ species ”

of Haplotaxis, and shows that the European and American species are
identical.

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 303

I failed to detect any cilia in the lumen of the nephridial
canal.

I have not endeavoured to trace out the course of the lumen
in detail, but I note that for the greater part of its course its
wall is quite simple, 7. e. is formed by the faintly granular
protoplasm of the perforated cells; but at the apex of the
loop there is a differentiation of this protoplasm to form a
more distinct, apparently striated, boundary to the lumen

> 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,
: * ( \dors.<vent. dors. >vent..dors.<vent.| alike alike
Male pores . .| XI, XII ON, IN XI, KIL | XI, KELL | 2pairs ony)
Female pores. .| XII/XIIJ, | X1LLI, XIV XIII XII/X111 | XL /X11T |
XILI/X1V
Spermathece . lioeeg 7,8 8,9 8,9 8
Sperm-sacs Median Median Median | Paired; | Paired;
testes free} testes
enclosed
Ovisacs Median Median Median Median ?

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 311

NeEPHRIDIA AND GENITAL Ducts.

From the point of view of general morphology, this new
species of Haplotaxis is of considerable interest owing to
the remarkable structural similarity that exists between the
sperm-duct and the nephridium. The genus belongs to that
section of the Oligocheta which in former days were termed
“ Timicoline” or Microdrili (mihi), in which excretory
segmental organs are in the mature worm absent from the
segments containing the genital ducts. This distinction is no
longer of so much importance now-a-days, since Vejdovsky (15)
has shown that in several families, viz. the Chetovastride,
Naididz, Enchytreeidee, Tubificide, and Lumbriculidee, these
nephridia are present in the genital segments of the immature
worm, but disappear by degeneration before the genital ducts
make their appearance; and Forbes (4) states that in H.
emissarius (=H. gordioides) the anterior nephridia in
Segments X to XV are small and rudimentary. Now the
questions that naturally arise in connection with Haplotaxis
heterogyne are: (1) Do nephridia exist in the immature
worm in Segments X, XI? If so, then (2) have they disap-
peared in these segments and been replaced by the sperm-
ducts, which have assumed the structure of nephridia? Or,
on the other hand (3) have the nephridia persisted in these
two segments and been converted functionally into the
sperm-ducts ? As we have no knowledge of the develop-
mental history of any species of Haplotaxis, we cannot give
a direct or certain answer to either of these questions, but
the striking similarity between the two categories of organs
presented by this species make it scarcely probable that the
sperm-ducts have assumed the structure of nephridia, and
renders it much more probable that the nephridia have been
converted into sperm-ducts, the mimute anatomy of which is
so absolutely unlike that presented by these organs in other
Oligochetes. The small degree of structural difference
between the two organs in the present worm may be due to
the difference in function. If this third question be answered

312 W. BLAXLAND BENHAM.

in the affirmative; if, that is to say, the nephridia in this
worm do act in these two segments as sperm-ducts, then the
question as to the homology of these ducts with nephridia in
the class is to some degree reopened.!

I limit myself to the sperm-ducts, for there is no resem-
blance between the oviduct and the nephridium, and there
need be no debate as to the homology between these. For
it does not necessarily follow that if the sperm-duct be
shown to be homologous with the nephridium, the oviduct
would also be homologous ; in point of fact, Vejdovsky (loc.
cit., p. 158) expressly states that “there is not a complete
homology between the oviducts and the sperm-ducts.” And
further, it is worthy of note that Birger (10), in a recent
paper on the development of Clepsine, finds considerable
difference in the mode of development of the male and
female organs in the Hirudinea. He shows that in the
case of the female organs the entire apparatus, both gonads
and ducts, is derived from a V-shaped “ anlage” ; whereas
only the terminal portion of the male duct is derived from
a corresponding V-shaped “anlage” in its segment, while the
testes, vasa efferentia and v. deferentia develop from quite
independent groups of cells, which are not represented in
the female system. We may therefore, without prejudice to
the larger question, confine ourselves for the moment to the
sperm-duct.

It is unnecessary to recapitulate in detail all the points of
resemblance and the few points of difference exhibited by
the sperm-duct and the nephridium in the Oligocheta in
general, or to repeat the historical arguments and views of
Claparéde and of Lankester in support of the homology ;
for this has been recently given by Beddard in his account
of the development of Octochztus multiporus (7). It
is sufficient to note that many modern zoologists have
withdrawn their adherence to the theory involving any such
homology, owing to the facts recorded in recent embryolo-
gical memoirs; while the whole subject of ‘nephridium ”

* See postscript, p. 322.

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS., 313

and “ccelomo-ducts” involved in the more recent theory
has been summarised and reviewed by Goodrich (11), and
has been accepted, and the ideas of terminology in con-
connection with this view have been extended, by Lankester
in his ‘Treatise on Zoology’ (part ii, p. 32).

According to this modern view, a sharp distinction,
founded on the different modes of origin, is drawn between
the excretory organs and the genital ducts of the Oligo-
cheta. The former being, according to the observations of
Vejdovsky (16) and of Wilson (17), derived from epiblastic
ingrowths, the latter from mesoblastic outgrowths from the
wall of the cclom. There is still some doubt, however, as
to whether the whole nephridium is epiblastic, for whereas
Vejdovsky and Wilson derive it from a ‘ nephric cord” of
cells which originate from a superficial teloblast, Bergh (9)
insists that the whole organ is developed from the funnel-cell,
which he regards as mesoblastic in origin, and not as having
pushed its way from the surface into the mesoblast. If this
statement of Bergh’s should turn out to be true—and it is a
case of one good observer against two good observers,—it is
clear that a modification will have to be made in the view as
to the sharp distinction between the two categories of organs.
However this may be, it seems clearly and satisfactorily
determined that the genital funnel at any rate is formed
as a proliferation of the ccelomic epithelium covering the
anterior face of the septum to which the nephridial funnel
is attached. Now, Goodrich (12) has shown in a series of
valuable memoirs that in the Polycheta the “ccelomic
funnel” or ‘ccelomostome,” which functions as a genital
funnel, may become grafted on to a nephridium, with or
without the loss of the “solenocytes ” of the latter organ.

It appears to me that in Haplotaxis heterogyne some-
thing of this kind has occurred, for the sperm-funnel is anato-
mically quite different from the nephridial funnel of the neigh-
bouring segments ; while the sperm-duct is pratically in-
distinguishable from a nephridial tube, and it originates
from the funnel at the extreme ventral margin, in the posi-

314 W. BLAXTLAND BENHAM.

tion, that is, in which a nephridial funnel, if it were present,
would le; in other words, the duct does not issue from the
centre of the funnel as in the sperm-ducts of other Oligo-
chetes. And I suggest that in this worm we have such a
composite organ as Goodrich has described in several of the
Polycheetes (e. g. Goniada, Phyllodocids, Syllids), and to
which Lankester gives the name “ nephromixium.”

In connection with the mode of origin of the sperm-duct from
its coelomostome, it 1s rather remarkable how little we really
know ; and if is as well to insist upon this absence of know-
ledge, and to note precisely how far embryologists have traced
(a) the development of the genital funnel, and (b) the deve-
lopment of the duct from this funnel.

Vejdovsky (15) has put on record the general course of the
history for Chetogaster, and in less detail for certain other
genera in which, he says, the same course is followed. The
genital funnel appears as a thickening of the peritoneal cells
on the anterior face of the septum, and the genital duct
grows back from it as a solid cord of cells; this cord reaches
the epidermis and becomes hollowed out to form a tube.

In Chetogaster the nephridium has no funnel; but in
Stylaria lacustris, which he proceeds to describe (p. 129),
he finds that, first of all the nephridium of this segment, VI,
gradually undergoes a retrogressive metamorphosis, breaking
up into cells, which separate till nothing but the nephridial
funnel remains on the anterior face of the Septum V/VI.
This, he says, persists for a long time. His next stage
figured represents the flat, thick, genital funnel in place of
the small nephridial funnel. He does not state in so many
words that the latter goes entirely, and it is possible, in the
light of Bergh’s researches, that it may contribute to the
formation of the genital funnel.

At any rate, there is apparently no doubt, in spite of what
Roule later on suggests, that a nephridium lies at first in
the segment, then disappears; that the genital funnel is
formed from the ccelomic epithelium, and gives rise to the
genital duct.

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. SS

Bergh (8), in 1886, describes in detail the development of
the funnels in Lumbricus, bnt he failed to trace the deve-
lopment of the genital ducts therefrom. The genital funnel
develops as a thickening of the peritoneal cells immediately
above (dorsad of) the nephridial funnel (which of course
does not disappear in this earthworm); the development in-
volves partly the cells forming a covering for the back of the
nephridial funnel and partly the cells forming the anterior face
of the septum itself. The same is true both for oviduct and
sperm-duct, and this very close association of nephridial
funnel and ccelomostome is, it seems to me, likely to be of
interest when the development of the entire nephridial funnel
is fully known.

At present we do not know whether the “ marginal” cells
of the Lumbricid nephridial funnel are ccelomic in origin.
It is quite possible that they are. For the “central cell” is
probably the original funnel-cell, which, according to Vej-
dovsky, divides so as to permit the tubule to communicate
with the coelom. If it should turn out that these peripheral
marginal-cells are coelomic, then the close topographical rela-
tion of genital funnel with the nephridial funnel described and
figured by Bergh will indicate that the whole “ nephridium ”
of earthworms is a “ nephromixium.”

A wholly different history is given by Roule (18), in 1889,
for an Enchytreid. In the earlier stages in the development
of “Knchytreoides marioni” the twelfth segment, in
which at a later period the sperm-ducts will arise, contains
no excretory organs, though these are present in the pre-
ceding segments, IX, X, XI, and in the segments following
it, namely, XIII, X1V, etc. The young sperm-duct, when it
does ultimately make its appearance, is ‘‘en tout semblable
i une trés jeune néphridie, et deplus, il occupe exactement
la place qu’aurait Porgane segmentaire s’il s’était developpé
dans la XIIme anneau.” Its mode of origin is stated to be
quite like that of a nephridium, after this has separated
itself from the nephric cord (which is observable in the pos-
terior, but not in the anterior segments) ; it now consists of

316 W. BLAXLAND BENHAM.

three or four cells more or less fused to form a syncytium ;
and Roule considers it certain that the sperm-duct is nothing
else than the nephridium of this twelfth segment, which is
late in appearing, for its special function is not called into
play till a much later stage than that of the segmental organ.

It will be noted that this is a very different history from
that given by Vejdovsky; and it is well to note that Roule
studied sections through successive stages, whereas it appears
from Vejdovsky’s words that he studied living specimens and
entire preparations only.

Then follows Beddard (7), who dealt with a “ micro-
nephric ” earthworm, Octochetus multiporus, a form in
which the earliest segmental organ is a “ meganephridium,”
which becomes broken up into a number of micro-nephridia
which are without funnels. According to this author the
original funnel of the meganephridium persists in the genital
segments, and becomes converted into the genital funnel in
each case; whilst the genital duct is for the first part of its
course derived from part of the nephridium, which starts to
grow once more, and extends back to form the rest of the
genital duct (p. 578).

If, now, we consider these various statements, and if we
regard, as I believe most zoologists will do, the “Limicoline”
Oligocheetes as ancestral to the ‘ Terricoline,” it seems pro-
bable that, phylogenetically, the history of affairs with regard
to the organ under discussion has been somewhat as follows:

First stage.—The nephridia act as genital ducts, for Stole
(14) finds that in Aeolosoma spermatozoamay escape from all
or any of the segmental organs ; in the genital segments these
are slightly larger than in other segments, though otherwise
similar to them. ‘The funnel of the nephridium is of very
simple structure, and there are no representatives of the
“marginal cells.’ Further, according to Roule, the sperm-
duct is a late-appearing nephridium in one species of
Enchytreeid.

Second stage.—A special ccelomostome becomes devel-
oped, which, added to the nephridium, increases the efficiency

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 317

of the organ as a collector of spermatozoa; we thus have a
“nephromixium” comparable to the arrangement in several
genera of Polychetes. Such is the condition of the sperm-
duct in Haplotaxis heterogyne, as I believe; while in
Octochetus multiporus a short part of the genital duct
is apparently also purely nephridial in origin.

Third stage.—The colomostome gives rise to its own
ccelomo-duct, which may either coexist in the genital sexment
with the nephridium (as in most “ terricoline”’ Oligocheetes),
or the nephridium, owing perhaps in some cases to the small
size of the worm, disappears from the segment during or
before the development of the genital duct (as in “ limicoline”
Oligocheetes and Pontrodrilus).

We have, then, to some extent a parallel series of phe-
nomena analogous to those described with so much care by
Goodrich in the Polycheta, from which it would appear
that the sperm-ducts are not absolutely homologous through-
out the Oligocheta.

BIBLIOGRAPHY.

A, HAPLOTAXIS, ETC.

1. Bepparp, F. E.—‘ Ann. Mag. Nat. Hist.,’ 1888 (ser. 6), vol. i, p. 389.
2. BEpDarRD, F, E.—‘ Trans. Roy. Soc. Edinb.,’ 1889, vol. xxxv, p. 629.

3. Bepparp, F. E.—‘ Trans. Roy. Soc. Edinb.,’ 1890, vol. xxxvi, p. 292
(Pelodrilus violaceus).

4. Forses, S. A.—‘ Bullet. Illinois State Lab. Nat. Hist.,’ vol. iii, p. 107.

5. Micnartsen, W.—‘ Zool. Jahrb. (Syst.),’ 1898, vol. xii, p. 105 (synonymy
of Phreoryctes).

6. Micuartsen, W.—‘ Verh. Naturw. Verein. Hamb.,’ 1903 (P. ignatovi):

B. RemMaRKs ON GENITAL Ducts.
7. Bepparp.—‘ Quart. Journ. Micr. Sci.,’ vol. xxiii, p. 522.
8. Brreu.—‘ Zeit. f. wiss. Zool.,’ vol. xliv, p. 3038.
9. Bercu.—‘ Zeit. f. wiss. Zool.,’ vol. 1, p. 498.
10. Bixczr.—‘ Zeit. f. wiss. Zool.,’ vol. Ixvii, p. 534.
11. GoopRricu.—‘ Quart. Journ. Mier. Sci.,’ vol. xxxvii, p. 477.

VoL. 48, PART 2.—NEW SERIES. 22

318 W. BLAXLAND BENHAM.

12. GoopricH.—‘ Quart. Journ. Mier. Sci.,’ vols. xl, xli, xliii.

18. Rovte.—‘ Ann. Sci. Nat.’ (Zool.), ser. 7, vol. vii.

14. Storc.—‘G. B. Bohm. Gesel.,’? 1889 (abstracted by Beddard, loc. cit.
supra).

15. Vespovsky.— Syst. u. Morph. Oligochet.’

16. Vespovsky.—‘ Entwick. Untersuch.’

17. Witson.—‘ Journ. Morph.,’ vol. iii, p. 419.

EXPLANATION OF PLATES 16—18,

Illustrating Dr. W. Blaxland Benham’s paper, “On a New
Species of the Genus Haplotaxis; with Remarks on the
Genital Ducts of the Oligocheta.”

REFERENCE LETTERS.

br, Cerebral ganglion. 6.#. Body-wall. c.c. Coelomic corpuscles. cc. ep.
Ceelomic epithelium. ¢.m. Circular muscles. cu. Cuticle. @. Dorsal cheta.
d.v. Dorsal blood-vessel. ep. Epidermis or epithelium. g. Gizzard. gl.
Copulatory gland or its external opening. zt. Intestine. 7. Lateral line.
l.m. Longitudinal muscles of body-wall or other organ. m. Muscle-fibres.
m.ch. Muscles of cheta. 2. Nucleus. z.c. Ventral nerve-cord. ze. Ne-
phridium. xe. d. Nephridial duct. ze. o. Position of nephridiopore. 2. /,
Nephridial funnel. o. Ovum. o.d. Oviduct. @. Cisophagus. o0.f. Ovi-
ducal funnel. ov. Ovary. ov.s. Ovisac. jy. Lateral prominence outside
ovipore. s. Septum. s.c. Circle of sensory cells surrounding a segment.
sp. Spermatozoa. sp.d. Sperm-duct. sp.f. Spermiducal funnel. sp. s.
Sperm-sac. spt. Spermatheca or its aperture. ¢. Testis. v. Ventral
cheta. v.v. Ventral blood-vessel. @ Male pore. ¢ Female pore.

PLATE 16.

Fic. 1.—View of the anterior extremity of a mature specimen of Hap lo-
taxis heterogyne stained and mounted in Canada balsam. (Camera,
x 40.) In the anterior segments the circular segmental series of sensory
cells are shown; further back these are indicated in the optical section of the
body-wall. The extreme dilatation of Segments XIII and XIV is partly due
to compression. The small size of the intestine in the genital segments is
shown. o. d. is the funnel of the oviduct.

Fig. 2.—A transverse section across the gizzard. (Camera, x 500.) The

ON A NEW SPECIES OF THE GENUS HAPLOTAXIS. 319

greater part of the wall consists of circular muscles, between which, towards
the external surface, bundles of longitudinal muscles are intercalated.

Fics. 83—7 represent five sections of one of the post-ovarian nephridia, as
seen in transverse sections of the immature individual. These five are selected
out of nineteen sections which involve a single nephridium. (Camera, x 120.)

Fig. 3 shows the nephridial funnel projecting through a septum, and a
small part of the post-septal region of the nephridium.

Fig. 4 is at about the middle of the series, showing the nepbridium at its
greatest height.

Fig. 5 involves the muscles of the ventral cheta; the nephridium is
passing downwards towards the body-wall.

Fig. 6 is a few sections onwards.

Fig. 7 shows the short “‘ duct,” represented by more granular cells (see
fig. 10).

Fic. 8.—An enlarged view of a nephridium in such a section as is repre-
sented in fig. 4. (Camera, x 500; details as seen with Leitz, ~; homog.
imm. lens.) The vacuolated condition of the large nephridial cells, and the
distinct ‘ wall” to the canal are seen.

Fic. 9.—A funnel of a post-ovarian nephridium from a longitudinal section,
which is neither sagittal nor frontal, but which cuts the worm obliquely.
(Camera, X 700.) No details of cell-structure are shown.

Fies. 10, 11.—Two consecutive sections through the ‘‘duct” of the
nephridium., (Camera, x 700; details under 7; hom. imm.) The cytoplasm
of the nephridial cells, or better ‘‘ syncytium,” is no longer vacuolated, but
highly granular.

Fig. 10 is a highly magnified view of fig. 7.

Fig. 11 is the next section. It shows the ‘‘duct” passing into and
through the epidermis, from which it is readily distinguished. I was
unable to trace the canal to a pore.

Fic. 12.—A transverse section through the body of the mature individual,
nvolving the first nephridium in Segment X. (Camera, x 120.)

Fie. 13,—The same nephridium—next section—more highly magnified.
(Camera, x 700.) The cytoplasmic network not indicated. Towards the
upper part of the organ the wall of the canal (a.) is much thicker than else-
where.

Fic. 14.—The funnel of the first nephridium, as seen in a longitudinal section
of the immature individual. It is smaller than that of the post-ovarian
funnel (cf. fig. 9), (Camera, x 700.)

Fic. 15.—A transverse section of the body through the esophageal region
(x 120), showing the relative sizes of the dorsal and ventral chete.

320 W. BLAXLAND BENHAM.

PLATE 1/7.

Fics. 16—24 represent a series of nearly consecutive transverse sections of
the mature specimen through the first pair of sperm-funnels and the second
pair of testes. (Camera, x 120.)

In fig. 16 the entire section, with all the organs involved, is drawn; in the
rest only the ventral half or less is drawn. In fig. 16 the spermatozoa
filling the first sperm-sac and surrounding the gut are shown, but
they are omitted in subsequent figures. The worm having been first
mounted entire and somewhat compressed, the organs have been
slightly displaced, so that the right and left organs are cut through at
different planes in a section. On the right side the course of the
sperm-duct can be followed easily up to fig. 20, where it has reached
its greatest height in the body; it then descends, and the last trace
that I was able to detect (fig. 22) was close to the chetal muscles;
the base of the cheta is cut through here, but the shaft comes into
view and perforates the body-wall nine sections further along. The
body-cavity was here filled with a coagulum, which, being stained in
hemalum, rendered it impossible to trace the sperm-duct further ;
but on the left side the duct was traced right up to the epidermis
(fig. 24) (see also fig. 29),

Figs. 25—27.—Three consecutive sections through part of the left sperm-
duct in the region shown in figs. 20, 21, in order to show the structure of the
duct and the presence of spermatozoa therein. The sperms (sp.) can be traced in
several other sections, even when the duct is close to the body-wall (cf. fig. 29).
(Camera, 3 hom. imm., Leitz; x oc. 3, Leitz.)

Fie. 28.—A section cutting the sperm-duct (of Segment XII) longitudinally
near the upper end of its course, showing the upward and downward limbs of
the duct. (Camera, x 700.)

Fie. 29.—From a transverse section (fig. 24), showing the sperm-duct passing
through the muscles of the body-wall towards the epidermis, which is reached
in the next section (not figured). Spermatozoa are seen in one of the sections
across the duct. (Camera, x 700.)

Fic. 80.—The copulatory gland from Segment XIII, as seen in a transverse
section of the mature worm. (Camera, x 700; details under +5 hom. imm.)

PLATE 18.
Fics. 31—386 show the sperm-funnel and the commencement of its duct:
Camera, x 700; details under 7; hom. imm.)

Fics. 31—384 are four consecutive sections through the first sperm-funnel
on the right side.

ON A NEW SPEOIES OF THE GENUS HAPLOTAXIS. 321

Fig. 31 cuts through the lip of the funnel.

Fig. 32 cuts through the middle of the funnel; it shows the sperm-duc
issuing from the extreme ventral margin, and a few spermatozoa, with
which the segment is filled, are seen entering the mouth of the duct.

Fig. 33 cuts across the sperm-duct as it bends backwards behind the
funnel; a spermatozoa is seen in the duct as a small dot. (This
figure is an enlargement of fig. 16.)

Fig. 34, which is from a section between those drawn in figs. 16 and 17,
involves the lip of the funnel and the root of the second testis, below
which is the sperm-duct.

Fig. 35 is an enlarged view of a section near that represented in fig. 18.
The funnel is no longer present ; the second testis is seen, and the sperm-duct
is cut through below the testes, and again on the right of the figure.

Fig. 36, from a section intervening between those represented in figs. 19 and
20, shows the sperm-duct passing upwards behind the septum. The ciliation
of the duct is shown in this figure.

Fic. 37.—A longitudinal section through the second sperm-funnel and duct
and the ovary of the immature specimen. (Camera, x 700.)

Fies. 388—42 represent a series of successive but not consecutive transverse
sections showing the oviduct. (Camera, x 120.)

In fig. 38 all the organs in the left half of the section are shown; in the
remainder only the organ in question. In this section the oviducal
funnel is cut through at about its widest part, but somewhat obliquely.

Fig. 39 (which represents the fourth section after the previous one) cuts
through the lower part of the funnel, which was torn in the section (cf.
fig. 44). In this figure half of the copulatory gland is seen (ef. fig. 30).

Fig. 40 (the fourth section beyond the previous one) cuts the oviduct
somewhere about the middle of its course.

Fig. 41 represents the eighth section from the last, shows the duct
entering the body-wall, which is here and in the next few sections
much thicker than elsewhere.

Fig. 42 is the third from the preceding; the duct is now close to the
epidermis, In the following section (not figured) the duct opens to the
exterior below the prominence (p.), due to the greater development of
the longitudinal muscles of the body-wall.

Fic, 43.—The oviduct (in longitudinal section) of the immature specimen.
(Camera, X 120.) It shows practically its full length, and it will be noticed
that it reaches back as far as the cheetal muscles.

Fic. 44.—A transverse section of the oviducal funnel (see fig. 39), the wall
of which has been ruptured during manipulation. (Camera, x 700; details
under the 4; hom. imm.)

Fic. 45.—Enlarged view of fig. 43, combined from it and neighbouring

322 W. BLAXLAND BENHAM.

section. The lip of the funnel is only definitely formed on its dorsal border,
where it is seen passing upwards in front of the septum; on this lip I could
detect no cilia, though these are quite evident in the duct itself. The septum
is seen to be somewhat pouched backwards. (Camera, X 700.)

Fic. 46.—A transverse section of the oviduct about mid-way between figs.
40 and 41. (Camera, x 700.)

Postscript.—Since despatching my MS. from New Zealand I have come
across an article by Mr. Beddard in the ‘ Proc. Zool. Soc.’ in 1902, vol. il,
p. $9, which I had unfortunately overlooked. In discussing the female repro-
ductive organs of Eudrilus he introduces some remarks, on p. 95, relative to
“ nephridia ” and “ ccelomo-ducts ” which are in agreement with the views put
forward in the present paper. He is “ not convinced ” that the oviducts and
sperm-ducts are “ccelomo-ducts.” Further, he makes use of Bergh’s account
of the origin of the genital duct from the “ peritoneal” covering of the
nephridial funnel in the same manner as I have done, and indicates the
probability of part of the nephridial funnel being peritoneal in origin. He
concludes (p. 97), “It appears to me that these various considerations show
that it is at least premature to regard the gonad-funnel of the Oligocheta as
essentially different from the nephridial funnels.”

I regret that by this oversight my friend’s views receive no recognition in
the body of my paper.

June 6th, 1903.

(2STROUS CYCLE IN THE COMMON FERRET, 328

The Gsstrous Cycle in the Common Ferret.

By
Francis H. A. Marshall, D.Sc.

With Plates 19—21.

“‘(strus vocatur hoc malum.”—Ptiny.

ContTENTS.

PAGE
1. Introductory : : ; : 3 . 323
2. The Gstrous Cycle . : ; : : . 324
3. Ovulation . . 328
4, Note on the Anatomy of the Gite! Genital Geen . 330
5. The Histology of the Uterus during the Mstrous Cycle . 330
6. Summary and Concluding Remarks . : . 337
7. References to Literature . : ‘ ; . 342
8. Description of the Plates. . : . 344

INTRODUCTORY.

The investigations which form the subject of the present
paper were commenced in the summer of 1901,and were carried
on at the University of Edinburgh in connection with the
Zoological Department. A preliminary account has already
been published, being included in the memoir on ‘ The CHstrous
Cycle and the Formation of the Corpus Luteum in the Sheep ’
(Marshall, 1903).

Through the courtesy of Professor Schafer I was permitted
to make use of the resources of the Physiological Department
for keeping the ferrets used in the research. Both “ polecat

324 FRANCOIS H. A. MARSHALL.

ferrets”’ and white ferrets were employed, and were kept
under constant observation.

The material for the histological part of the work was
generally fixed and preserved in a 10 per cent. solution of
formalin, and afterwards treated in the usual way for section
cutting. Sometimes corrosive sublimate was used instead of
formalin as a fixing agent. The stains ordinarily employed
were a combination of hematoxylin and eosin.

I wish to record my obligations to Professor Ewart and
Professor Schafer for the encouragement and assistance which
they have rendered me in furthering my researches. To Mr.
Heape, also, I must express my indebtedness for valuable
suggestions on a subject which he has made peculiarly his
own. Lastly, I take this further opportunity of thanking
Sir Thomas Gibson Carmichael, Bart., for his great generosity
in providing an endowment.

Tur (strous CyYcLe.

The ferret is monostrous, the female usually coming in
season at the end of March or beginning of April. If per-
mitted to become pregnant at this time a second sexual
season may be entered uponin July, while occasionally ferrets
have been known to breed three times within twelve months
(Carnegie and other authorities, 1901).

I do not know whether the female ferret ever experiences
a second sexual season after failing to become pregnant
during the first cestrus. It is frequently stated by fanciers
that for ferrets to live healthily it is necessary for them to
breed, and that “a doe ferret will sometimes die the first

1 The above statements are based upon information given by ferret breeders
(cf. Carnegie, etc., 1902). In my paper on the “(@strous Cycle in the Sheep”
(1903) I stated that the ferret was moncestrous and had a single sexual season
annually. This conclusion, which is only sometimes correct, I had deduced
from my own observations, having never hada ferret which experienced more
than one oestrous cycle. As stated in the text, I have kept ferrets from
October to the end of March, during which time they showed no signs of
coming “on heat.” A ferret fancier assures me that only very exceptionally
has he known ferrets come in season between August and February.

(ESTROUS CYCLE IN THE COMMON FERRET. 325

time she is refused access to the buck” (Carnegie, etc., 1902).
Several of my ferrets grew unhealthy and died during the
sexual season, and while still “on heat,” and I am disposed
to believe that the mortality was partly due to their being
refused copulation.

The period of cestrus in the absence of the male I have
found to be extremely prolonged. In one individual it
extended for six weeks, at the end of which time the animal
was killed, the uterus being found to be in a condition of
advanced recuperation. In another ferret, however, in which
cestrus was observed in the beginning of June (at the time
when it was procured), the period of ‘ heat”? was completely
over at the end of the first week of July, coition not having
been permitted. Five bitch ferrets which I obtained in the
month of October lived perfectly healthily during an aneestrous
period which extended until the close of the following March,
when they began to show signs of coming “on heat,” and
were subsequently killed during the sexual season.

It appears then, that the ferret, to some extent, showed a
transition between the moncestrous and polycestrous condition,
since in those individuals which experience two breeding
seasons these are restricted to the spring and summer; so
that it must be a matter of some doubt whether the time
between the two “heat” periods should be correctly described
as a dicestrous or an ancestrous interval. But, as already
indicated, this interval is, as a matter of fact, generally, or
perhaps always, occupied partly by gestation.

A number of interesting observations bearing on this
subject have been made by Mr. A. H. Cocks, who has kept
several members of the family Mustelide in activity. A
female otter is described (Cocks, 1881} as coming in season
nearly every month in the absence of the male. Upona male
being introduced, copulation was observed on July 17th, and
a second time on August 12th, or nearly a month later.
Young were born on October 12th, so that pregnancy lasted
apparently for sixty-one days. [From these observations it
may be inferred that the female otter is polycestrous in the

vol. 48, PART 2.—NEW SERIES. 25

326 FRANCIS H. A. MARSHAL.

absence of the male, the duration of the dicestrous cycle being
about a month, there being also a longer ancestrous period.

Bell (1874) describes the otter as having young in March
or April, thus indicating that the wild otter has a single sexual
season about the beginning of the year. The same author
states that the progeny of the stoat are produced in April or
May, while the polecat, of which the ferret is a domesticated
variety, is said to give birth to young in May orJune. These
animals, therefore, are probably moncestrous, or perhaps
dicestrous, while the weasel may perhaps be inferred to be
polycestrous from Bell’s account (1874).

With the pine-marten, in captivity, it appears from Cocks’
description (1900) that the cestrous period may extend to about
a fortnight. A female was noticed to deposit here and there
in her cage little mouthfuls of straw, an indication of her
being in season, this habit having been previously observed
in the case of the otter. A male wasadmitted on January 5th,
shut off on the 16th, readmitted on the 17th, and finally
separated on the 18th. Copulation is supposed to have
occurred probably on the 8th, 10th, and 13th, and possibly
also at other times, but was never actually observed. Young
were produced on April 22nd. Cocks states that it is
hazardous to allow the male and female to run together at
other times than the oestrous period, as it is apt to result in
the death of the female.

The badger is probably moncestrous, with an annual sexual
season, its period of gestation being between four and five
months (Meade-Waldo, 1894). (See postscript at end of
paper.)

I made no observations on the length of the ferret’s gesta-
tion, but this period is generally stated to be about six weeks,
or approximately the same as that observed for the polecat
(Harting, 1891; Cocks, 1891).

External Kvidence of the Pro-cstrum and Mstrus,
—The pro-cestrum with the female ferret appears to extend
for about three weeks, and is characterised by a marked
swelling of the vulva and a sanguineo-mucous flow. With

(ESTROUS CYCLE IN THE COMMON FERRET. 327

two or three individuals I did not observe any external
bleeding, but it may have occurred and escaped my notice,
since it was sometimes impracticable to make regular observa-
tions upon the animals during their prolonged sexual season.
But bleeding into the uterine cavity, as I shall presently
show, regularly occurs at the pro-cestrum, and is accompanied
by a greater or less removal of uterine mucosa. I am in-
clined to think, however, that the discharge so formed is
usually disposed of very gradually.

During the pro-cestrum, as at all other times during the
cycle excepting at the cestrous period, the female will not
permit copulation.

The period of cestrus can be recognised by the behaviour
of the female ferret towards the male. The vulva remains
enlarged, and a slight flow of mucus may continue to be
discharged at the external genital aperture. As before
remarked, the oestrus may last for several weeks, and is
associated throughout with the swelling of the vulva. This
extension, in the absence of pregnancy, of the period of
desire, is perhaps comparable to what occurs in the case of
bears in captivity, for with these animals in the Zoological
Society’s Gardens cestrus is said to last continuously for two
or three months. (Heape, 1900.)

The female ferret, as already described, is moncestrous,
coming in season about the end of March, but presents a
transition to the polycestrous condition in sometimes having
a second (and occasionally a third) cestrous cycle in the
summer months. In showing this tendency towards a con-
centration of sexual seasons the ferret may be regarded as
standing midway between such animals as the dog or cat
which are moncestrous, with, as a rule, two fairly regularly
recurring cestrous cycles, and the otter, which, in captivity
at any rate, is polycestrous, and has a recurrent dicestrous
cycle of a month’s duration. (Cocks, 1881.)

So far as I am aware there is no periodicity of the sexual
season with the male ferret, which is said to be capable of
copulation at any time of the year.

328 FRANCIS H. A. MARSHALL.

OVULATION.

So far as my observations go, ovulation in the case of the
ferret probably takes place at the beginning of the period of
cestrus, but only as a result of coition. If the female is not
allowed to copulate the mature follicles and contained ova
appear to undergo atresia, notwithstanding the continuance
of the cestrus. Asa consequence the female fails to become
pregnant if warded too late in the season. Thus the per-
sistence of the cestrus, which may continue far into the
recuperative period of the uterus, or even beyond it, is asso-
ciated with degenerate follicles in the ovary. ‘These facts
may perhaps afford an explanation of the observations made
by Robinson (1898), who found that, with the ferrets em-
ployed in his investigation, coition very frequently did not
result in pregnancy, although the animals might have copu-
lated more than once during cestrus.

The extension of the period of cestrus under conditions
such as to preclude the possibility of the occurrence of preg-
nancy can only be regarded as one of those “ disharmonies”
in the apparatus of reproduction upon the existence of which
in the animal and human organisation Metchnikoff in his
recent work (1903) has laid so much stress.

A bitch ferret which I artificially inseminated failed to
become pregnant, owing probably to the presence of the
spermatozoa in the uterus without the additional stimulus of
coition failing to induce ovulation; but it may have been in
this case also that the mature Graafian follicles had begun to
degenerate, and that the season for ovulation had passed by.

In failing to ovulate during cestrus except as a result of
coition the ferret resembles the rabbit in some cases at any
rate (Heape, 1897), and the sheep more exceptionally
(Marshall, 1903). ‘The majority of the mammalia in which
the subject has been investigated have been found to ovulate

omvheat.-

spontaneously when
Fig. 9 represents a section through an atretic follicle from

a ferret in which cestrus had lasted for at least three weeks,

(ESTROUS CYCLE IN THE COMMON FERRET. 329

and perhaps longer. The animal had copulated on the day
on which it was killed, but not previously during that cestrus.
The ovum is seen to be much shrunken and obviously
degenerate, while it is no longer surrounded by a discus
proligerus. The membrana granulosa has almost completely
disappeared, but afew cells in an advanced state of degenera-
tion remain scattered in the cavity. There is the beginning
of a loose ingrowth of connective tissue, but this, at the stage
under consideration, is very slight. ‘The connective-tissue
wall of the follicle presents the appearance of being composed
of very irregularly arranged strands, the distinction between
theca externa and theca interna having become obliterated,
while there is no distinct line of separation from the outlying
ovarian stroma.

The Formation of the Corpus Luteum.—I made no
attempt to obtain a series of stages illustrating the develop-
ment of the corpus luteum in the ferret. Such few examples
as I have examined show the usual ingrowth among the
lutein cells of connective tissue from the follicle’s wall; and,
although, taken by themselves, they do not prove that the
lutein cells are derived from the membrana granulosa, they
are, ina general way, confirmatory of the description given
elsewhere of the origin of the corpus luteum in the mouse,
the rabbit, and the sheep, there being distinct evidence of
the interepithelial nature of the ingrowth. I have also
lately obtained sections through a young corpus luteum of a
cat which, at the time of killing, was ‘on heat,” or had been
very shortly before; and these sections show the same point.

Since the publication of my account a paper by Cohn
(1903) describing an experimental investigation on the mode
of formation of the corpus luteum in the rabbit has appeared,
and the result of this investigation has been to further
confirm the view that the lutein cells are formed from the
follicular epithelium. Cohn obtained a series of stages, the
animals being killed at stated intervals after coition.

A similar conclusion has been arrived at by Sandes, who
describes the process of formation of the corpus luteum of

3800 FRANCIS H. A. MARSHALL.

Dasyurus in a paper read before the Linnean Society of
New South Wales and abstracted in ‘ Nature’ (1903). This
author states further that the corpus luteum atreticum is
formed in the same way as the corpus luteum verum, a result
which, so far as I am aware, differs from those of all other
investigators. (See postscript at end of paper.)

Papers bearing on this subject have also lately appeared by
Bihler (1902) and Wallace (1903), who describe the changes
undergone by newly-discharged follicles in various fishes.
Bihler’s descriptions, which refer to Cyclostomes and to
certain Teleosteans, indicate that there is nothing of the
nature of a corpus luteum formed in the cases investigated,
while Wallace shows that with the Teleostean Zoarces and
the Elasmobranch Spinax there is a very distinct hyper-
trophy of the follicular epithelium after rupture, thus con-
firming Giacomini’s account (1896) of the recently discharged
follicles of certain Elasmobranchs.

Nore oN THE ANATOMY OF THE INTERNAL GENITAL ORGANS.

The uterus of the ferret is typically bicornuate, each of the
uterine horns passing forward into a slender Fallopian tube,
which is very much coiled at its anterior end, passing several
times round one side of the ovary. The mouth of the
Fallopian tube encloses the ovary, so that the ova on being
discharged pass into a sac, and consequently are not shed
into the body-cavity. Fig. 8, Pl. 20, represents a transverse
section through the ovary, and shows its attachment to the
wall of the body-cavity, as well as tle sac into which the eggs
are shed and the coiled Fallopian tube. The latter appears
no less than six times in the section.

Tur Histonocy or THE UTERUS DURING THE CisTRous CYCLE.

The changes through which the non-pregnant uterus of the
ferret passes during the cestrous cycle may be conveniently
arranged according to the same method of grouping as that

GSTROUS CYCLE IN THE COMMON FERRET. Bel

employed in describing the similar phenomena occurring in
the monkey (Heape, 1894) and the sheep (Marshall, 1903), as
follows :

1, Period of rest.

2. Period of growth.

3. Period of degeneration.

4. Period of recuperation.

The changes taking place during each of these periods
occur almost simultaneously throughout the whole uterus.
Period 1 represents the ancestrum, while the pro-cestrum
occurs during Periods 2 and 3. (istrus, or the period
of desire, commences at the close of the period of degenera-
tion, and, as already mentioned, may extend until the end of
the recuperation stage, or perhaps even beyond it. Con-
sequently there may be no metcestrum with the ferret, since
the period during which copulation can occur is liable to
persist until the uterus has reached the resting stage.

1. Period of Rest.—The stroma, of which the greater
part of the uterus is formed, is bounded internally by an
epithelium consisting of a single row of cubical cells. There
is no very clear line of demarcation between the protoplasm
of the epithelial cells and the protoplasm of the stroma,
neither are there distinct boundaries between the individual
cells of the stroma. The latter tissue is fairly uniform in
character throughout both the body of the uterus and the
two cornua. It contains numerous glands, bounded by
epithelia similar to that lining the cavity. Blood-vessels of
small size are also present, but are not nearly so abundant as
in the succeeding growth stage. Some of these are shown
in the figure (PI. 19, fig. 1), where the general nature of the
uterine stroma during the resting stage is indicated.

In comparison with the other stages of the cycle, the
uterus at this period may be described as being negatively
characterised.

The general shape of the uterine cavity, as it appears in
transverse section, is shown in fig. 5 (Pl. 20), which, however,
represents a section through an early stage of the growth

332 FRANCIS H. A. MARSHALL.

period. The same shape and the same general relations
between the various layers of tissue are maintained both for
the two horns and for the body of the uterus, transverse
sections of the latter having a diameter only slightly longer
than that of sections cut through one of the horns.

2. Period of Growth.—The beginning of the pro-cestrum
is marked by the growth of the uterine stroma, which goes
on until the cavity is reduced to about half its normal size.
The growth takes place through multiplication of the stroma
nuclei, the increase in number occurring for the most part
regularly throughout the whole tissue, and not being confined
to any particular part. As a result of this process the size
of the uterus, as indicated by the length of the diameter of a
transverse section through the body or one of the horns, is
slightly enlarged, the increased thickness of the walls being
not entirely compensated for by the reduction in the size of
the cavity.

The multiplication of the stroma nuclei occurs, apparently,
by direct division, no mitoses being visible. This appearance
is scarcely due to the method of fixation, since evidence of
mitotic division can be detected among the cells of the
epithelium.

The first indications of growth are followed by an increase
in the size of the blood-vessels. At a slightly later stage
these also multiply in number, apparently by division of one
vessel into two. The increase of the vessels, like that of the
nuclei, occurs fairly equally throughout the stroma. The
blood-vessels in the surrounding muscular tissue also tend to
become enlarged and congested.

Before the close of this period the blood-vessels of the
stroma become still further enlarged and packed with cor-
puscles, while their walls appear stretched, as if preparatory
to the breaking-down process which characterises the com-
mencement of the next period,

The epithelium lining the cavity undergoes no material
change, though cell-division is perhaps somewhat more
frequent. ‘The same may be said of the epithelium of the

(ESTROUS CYCLE IN THE COMMON FERRET. gon

glands, which at the beginning of this period undergo a
marked swelling, accompanied by greater secretory activity.
3. Period of Degeneration.—Fig. 2 (Pl. 19) represents
a portion of a transverse section through the uterus, showing
the commencement of the breaking-down process which
characterises the period of degeneration. Many of the
blood-vessels have their walls still intact, but these are for
the most part much congested. Others have apparently just
given way, and red corpuscles are already scattered in con-
siderable quantities in the mucosa. lLeucocytes are also seen
in the tissue outside the vessels, and these probably were
extravasated at the same time as the red corpuscles.

The breaking-down process, so far as I have observed,
occurs throughout practically the whole of the stoma, and is
not confined to the more superficial portion, as in the case of
the pro-cestrum of the sheep. The walls of the vessels in the
muscular layers, however, do not give way, neither is there
any evidence elsewhere of a breaking-down of vessels.

The single layer of lining epithelium during the earlier
stages of this period undergoes no change. Subsequently,
when nearly all the vessels in the underlying stroma have
ruptured, and corpuscles are lying free in most parts of the
tissue, indications of degeneration are seen both in the
epithelial cells (including those of the glands) and also in
the cells of the stroma.

The degeneration of some of the stroma nuclei is accom-
panied by a tendency on the part of the blood-corpuscles to
become aggregated in the more superficial part of the
mucosa, where the tissue has become looser, the nuclei being
much less densely packed. The process results in the
denudation of some portion of the mucosa, and the pouring
of little streams of corpuscles into the cavity of the uterus.
Meanwhile the glands in the deeper part of the mucosa show
an increased secretory activity.

Fig. 6 (Pl. 20) represents a transverse section through
one horn of a uterus in which denudation has recently
occurred. Most of the blood-corpuscles have tlready been

334 FRANCIS H. A. MARSHALL.

got rid of, or at any rate have passed into the lower part of
the uterine cavity. Pieces of mucosa, accompanied by cor-
puscles and mucus, can, however, still be seen lying free in
the cavity. A portion of the same section, more highly
magnified, is shown in fig. 11 (Pl. 21), where isolated epi-
thelial cells, in a more or less degenerate condition, can be
detected among the denuded fragments. In the mucosa
forming the uterine wall it is seen that considerable tracts of
tissue have been stripped of the lining epithelium, while in
some places portions of the underlying stroma also appear to
have been removed. EHxtravasated corpuscles are still seen
in the mucosa, but not in any considerable quantity. In
some parts of the section there are already indications of
recuperation having set in. |

I am disposed to believe that there is a not inconsiderable
amount of variation in the severity of the pro-cestrous
phenomena of the ferret, and that in the case above described
the denudation of tissue was exceptional. ‘This was the only
example of a ferret killed during the period of degeneration
which showed indications of a definite removal of stroma,
although a comparison between the thickness of the uterine
wall (and, conversely, the size of the uterine cavity) in
animals at the beginning of the recuperation stage and during
the period of rest also points to the conclusion that destruc-
tion is not always confined to the epithelium. In the case of
the sheep I found evidence that the severity of the process
tended to diminish with each successive dicestrous cycle in
the breeding season, so that it is not unlikely that the ferret
is subject to some similar variation, depending possibly upon
age or upon physical condition.

The chief characteristics of the period of degeneration in
the ferret occur in aregular succession almost simultaneously
throughout the whole of the uterus, so that this period is
capable of subdivision into two or more stages, the first of
which is marked by the rupture of the vessels and the ex-
travasation of blood in the stroma. Then further degenera-
tion sets in, and the corpuscles tend to become aggregated

(ESTROUS CYCLE IN THE COMMON FERRET. 335

in the proximity of the surface epithelium; and finally,
bleeding into the cavity takes place. The whole process,
therefore, is very closely comparable to what occurs with
monkeys during the degeneration period of menstruation
(Heape, 1894, 1897). ‘There is, however, no pro-cestrous clot
formed in the ferret’s uterus, the discharge seeming to be
disposed of very gradually.

4, Period of recuperation.—Fig. 7 (Pl. 20) isa drawing
of a part of transverse section under a low magnification,
showing the relatively large cavity and correspondingly
slight thickness of the mucosa during an early stage of the
recuperation period. ‘lhe epithelium is almost entirely re-
formed, but is somewhat attenuated, the individual cells
being less columnar in shape than they are normally. Another
section through one of the horns of the same uterus is
represented in fig. 3 (Pl. 19), which is more highly magnified.
This shows that the nuclei of the epithelium are more
irregularly arranged than during the other stages of the
cycle, while the line of demarcation between epithelium and
stroma is even less evident.

The new epithelium is formed, for the must part at any
rate, either from that covering certain particular tracts which
escaped denudation, or from the epithelium of the glands. I
am not quite certain, however, whether the whole of the new
epithelium arises in this way, for the absence of a separating
line between this layer and the underlying stroma, and the
irregular arrangement of the nuclei, upon which I have
commented above, suggest that parts of the epithelium may
be re-formed from the tissue of the stroma. This is the view
adopted by Mr. Heape (1894, 1897) regarding the manner
of formation of the new epithelium with monkeys during the
recuperative stage of menstruation.

During the earlier stages of recuperation a variable and
frequently a large number of red corpuscles, accompanied by
wandering cells, remain scattered free in the stroma. These
are very numerous in the sections represented in fig. 3

(PL. 19) and fig. 10 (PL. 21). At a subsequent stage of re-

336 FRANCIS H. A. MARSHALL.

cuperation these extravasated corpuscles are no longer seen
in any quantity, while numerous small blood-vessels appear
to have been formed. In the case of the sheep, it has been
shown that the blood which is extravasated during the pro-
cestrum, and which is not discharged into the cavity of the
uterus, forms pigment in the mucosa. On the other hand, I
have never found any trace of pigment formation in the
uterine mucosa of the ferret, while sections of this tissue
from animals with which recuperation had lately commenced
support the view that the corpuscles are gathered up afresh
into the circulatory system by becoming enclosed within the
walls of newly formed blood-vessels. It is a matter of difh-
culty in a case of this sort to make quite sure of the
correctness of one’s interpretation of a series of sections, but
unless this explanation, which is in agreement with Mr.
Heape’s description of what occurs with monkeys, is adopted,
IT am unable to account for the disappearance of the extrava-
sated corpuscles during the later stages of recuperation.

At a subsequent stage of this period the stroma tissue tends
to become more and more dense, and also to increase in
thickness, until the mucosa once more acquires its normal
condition. ‘This process is effected by the multiplication of
the stroma nuclei.

Conclusions.—lt is evident, from the foregoing account,
that the pro-cestrous process in the ferret is homologous with
that of the bitch (Retterer, 1892), the sheep (Marshall, 1902),
and the monkey (Heape, 1894, 1897). In severity it is inter-
mediate between the pro-cestrum of the sheep and that of the
monkey, while it differs from the same process in the bitch
in the somewhat greater denudation of mucosa, at any rate
in particular individuals. The “heat” period with the ferret,
however, is of considerably longer duration than is the case
with the other animals mentioned. Another point of differ-
ence from the sheep exists in the absence of pigment formation
during the ferret’s metoestrum.

The study of the cestrous cycle in the ferret shows very
clearly the erroneousness of the view that the degenerative

(ESTROUS .CYCLE IN THE COMMON FERRET. 337

stage of the pro-cestrum occurs as a consequence of the
absence of a fertilised ovum, for which the uterus was pre-
paring, in the preceding growth stage. For, since copulation
and ovulation can only take place during cestrus, the uterine
denudation occurs prior to the period when fertilisation
becomes possible. This is a point to which I have already
alluded.

The view that the pro-cestrum is an act of preparation,
followed, where this happens to be useless, by a destruction
of the preparation, being untenable, I am led to the conclu-
sion that this process is the result of a “‘ wave of disturbance,”
as Mr. Heape expresses it, which ushers in the period of desire,
and is of the nature of a consequence rather than a purpose.
On the other hand it appears to me not altogether improbable
that the renewal of the mucosa tissue which is consequent
upon the degenerative changes may, in some way, help to
prepare the uterus for the attachment of the ovum. ‘This
view seems to have been entertained by Milnes Marshall
(1893).

There is evidence, however, that the pro-cestrous discharge
may become not only functionless but even injurious, as in
the more severe cases of menstruation in women. ‘his is in
accord with the view of Metchnikoff (1903) that the condition
of the menstrual flow in the human subject at the present
time is essentially a “disharmony” of organisation, and is
probably the result of modifications acquired recently in the
history of the race. Metchnikoff refers also to the existence
of similar disharmonies in the reproductive apparatus of
animals, and especially of animals kept in captivity, and pro-
bably the severity and long duration of the ferret’s ‘ heat”
period would be regarded by this author as a further example
of the occurrence of such disharmonies,

SumMARY AND ConcLupIna REMARKS.

The female ferret is moncestrous, and may have one, two,
or three sexual seasons within a year; but although the

308 FRANCIS H. A. MARSHALL.

cestrous cycle may recur the “heat” periods are usually
restricted to the spring and summer months, the autumn and
winter being occupied by a prolonged aneestrum. Jn showing
this tendency towards a concentration of sexual seasons the
ferret approaches the polycestrous condition, being in fact, in
this respect, intermediate between the dog or cat, which have
two, or occasionally three, fairly regularly recurrent cestrous
cycles, and the otter, which, in captivity at any rate, has
-been shown to be polyestrous with a series of dicestrous
cycles, each of a month’s duration, occasionally interrupted
by a longer ancestrous period.

The pro-cestrum with the ferret may extend for three
weeks, while the cestrus, in the absence of the male, may last
for another six weeks, or even longer.

The changes which occur in the non-pregnant uterus during
the cestrous cycle may be divided according to four periods
as follows:

(1) Period of rest.

(2) Period of growth.

(3) Period of degeneration.

(4) Period of recuperation.

The first period corresponds to the ancestrum during which
the uterus is in the normal state. ‘his is followed by the
growth period during which the uterine cavity becomes
reduced to about half its usual size, while the mucosa is
correspondingly thickened. Meanwhile the blood-vessels
become much congested and subsequently break down, thus
marking the commencement of the period of degeneration.
The blood-corpuscles become scattered in considerable
numbers in the stroma, and eventually in the uterine cavity
also, owing to the removal in many places of the lining epi-
thelium. In one specimen I found evidence also of a pro-
cestrous denudation of the underlying stroma tissue. Cistrus
probably commences towards the close of the period of
degeneration, and continues throughout the recuperation
stage, or perhaps even beyond it. During the latter period
the uterus recovers its normal condition, though the cavity is

CSTROUS CYCLE IN THE COMMON FERRET. 339

at first larger in size than at any other time throughout the
cycle.

The character of the changes described affords further
proof of the homology between the menstrual cycle of the
primates and the cestrous cycle of the lower mammalia, the
processes which occur in the uterus of the ferret during the
cycle being essentially similar to those which take place in the
monkey (Heape, 1894, 1897), the bitch (Retterer, 1892), and
the sheep (Marshall, 1903).

Ovulation occurs probably at the commencement of the
cestrous period, but only as a result of sexual intercourse. An
attempt to induce pregnancy by artificial insemination was a
failure, the mere presence of the sperms in the uterus being
apparently insufficient to produce the stimulus necessary for
ovulation. But while ovulation does not appear to take place
in the absence of coition, the cestrus continues for a consider-
able period after that the time for ovulation has passed by,
so that the persistence of the cestrus is associated with the
presence of atretic follicles in the ovary.

Since coition and ovulation take place after the pro-cestrum,
it is clear that the degeneration stages of the pro-cestrum
cannot be of the nature of an undoing, in consequence of the
absence of a fertilised ovum, of preparations made during the
earlier growth stages.

Fraenkel, however, in a recent paper, (1903) adopts the
view that the phenomena of menstruation, which has been
shown to be homologous with the pro-cestrum, are brought
about by the secretory activity of the corpus luteum.! This
hypothesis, in the light of the facts stated above, appears to

1 According to Fraenkel the corpus luteum is the organ of internal
secretion in the ovary, and controls the nutrition of the uterus, not only
during pregnancy, but throughout the whole cycle, there being, properly
speaking, but one corpus luteum, which renews itself in slightly different
positions, in the case of the human subject at monthly intervals. According
to this somewhat extended view of the nature of the corpus luteum, it would
seem that the secretions of that organ must be regarded as varying from time
to time both in character and quantity, to account for the changes which take
place during the uterine cycle.

340 FRANCIS H. A. MARSHALL.

me to be untenable, while the absence in the ferret’s ovaries
of corpora lutea (or, at any rate, of newly-formed corpora
lutea!) during the period of desire, an absence resulting from
failure to ovulate, precludes the possibility that cestrus in
some way results from an internal secretion of the corpus
luteum.

It is important to note in this connection that Mr. Heape
found (1897) that not one out of forty-two menstruating
females of Semnopithecus entellus had a recently-dis-
charged follicle in either ovary, while one only among seven-
teen individuals of Macacus rhesus, which were menstru-
ating, had a newly-discharged follicle in one ovary. In this
case the monkey was passing through a late stage of
menstruation (the stage of the formation of the menstrual
clot), while the follicle appears to have been one that had
very recently ruptured.

There is, however, a considerable amount of evidence
supporting the view that the pro-cestrum is brought about
by some kind of ovarian secretion. Thus, it is generally
stated that if ovariotomy be performed menstruation ceases,
the small percentage of cases where it has been known to
continue being accounted for on the supposition that some
portion of one of the ovaries was not removed. Moreover,
Glass (Halban, 1901) has shown that in the case of a woman
with whom menstruation had ceased in consequence of
ovariotomy, it was avain induced by the grafting of a new
ovary. Knauer (Halban, 1901) has performed similar opera-
tions on dogs, and similar results were obtained. Halban
(1901) also found that after removing the ovaries of monkeys
menstruation ceased, while it continued after a grafting of
the ovary. Halban’s experiments show further that the
recurrence of menstruation after the latter operation was not
a purely nervous phenomenon, since it took place when the
ovary was grafted in a position different from the normal.
These and similar observations seem to dispose of the view

1 In any case, on Fraenkel’s hypothesis, the occurrence of the pro-cestrum
seems to be entirely dependent upon a previous ovulation.

(ESTROUS CYCLE IN THE COMMON FERRET. 541
that the pro-cestrum occurs as a result of ovulation, or is
brought about by the pressure of the growing Graafian
follicles on the nerve-endings, as supposed by Strassmann
(1896).

There are other considerations pointing to the conclusion
that the pro-cestrum and cestrus are produced by substances
circulating in the blood, though not necessarily secreted by
the ovary. Kehrer states that the milk from a suckling sow
is affected at the ‘ brunst” period, the young, as a conse-
quence, developing unhealthy symptoms; while similar
phenomena have been noted in the case of suckling women
during menstruation (Halban, 1901). Youatt (1835) says
cestrus can be induced in cows by giving them milk obtained
from other cows which are “on heat.”

The statements of Ferré and Bestion (Dixon, 1901) that
injections of ovarian extract may produce genital excitement
have perhaps more direct bearing on this question, but these
observations have not so far been confirmed.

Although I am unable, for the reasons stated above, to
agree with Fraenkel that menstruation is induced by the
secretory activity of the corpus luteum, his experiments,
carried on in collaboration with Cohn (1901, 1903), appear to
me to go a long way towards establishing the view of these
investigators regarding the nature of the connection between
the existence of the corpus luteum and the changes taking
place in the uterus during gestation. The late Gustav Born
had suggested that the corpus luteum was an organ, the
function of which was to secrete into the blood substances
which prepared the uterus for the attachment and growth of
the embryo; and the investigations of Fraenkel and Cohn
were undertaken to test this view, to which they lend support.
The corpora lutea of rabbits were destroyed by a galvano-
caustic needle, when it was found that pregnancy did not
continue unless at least one corpus luteum was allowed to
remain. Thus the occurrence of pregnancy was shown to
depend upon the existence of one or more corpora lutea in
the ovary. .

vot. 48, PART 2.—NEW SERIES, 24

342 FRANCIS H. A. MARSHALL.

It seems possible that the formation of the corpus luteum
marks a change in the character of the ovarian secretion,
which, in the presence of that structure, may have regard
especially to the preparation of the uterus for pregnancy and
the attachment of the ovum, and perhaps even the suppres-
sion, so to speak, of a pro-cestrous or cestrous secretion during
gestation. When, as is sometimes the case with the ferret,
ovulation does not take place during the “ heat” period, the
persistence of the cestrus may possibly be directly correlated
with the absence of the corpora lutea.

But whereas such suggestions in the present state of our
knowledge are of course highly speculative, the results of
recent experiments seem to me to point to the conclusion that
the solutions of some of the problems concerning the cestrous
cycle and the ripening and final rupture of the Graafian
follicles, will be found in the study of the ovary as an organ
of internal secretion.

Postscript.

Since concluding the present paper I have read Sandes’
account of the formation of the corpus luteum in Dasyurus,
of which I had previously only seen an abstract (see p. 330).
It is to be noted that this author, although stating in his
summary of conclusions that “the corpus luteum atreticum
is formed in the same way as the corpus luteum verum,”
says also that “other atresic follicles are reduced to fibrous
tissue or remain cystic.’”? In the body of the paper he
describes the former process as occurring only in atretic
follicles which had become ripe, or nearly so, but in which
the ovum had not been discharged. In the case of the
smaller follicles Sandes describes the follicular epithelium as
frequently degenerating but never hypertrophying.

Two new articles on the gestation of the badger by Mr.
A. H. Cocks have lately been published in the ‘ Zoologist.’
In the last article Mr. Cocks arrives at the remarkable con-
clusion “that the pairing may take place at any time during

(ESTROUS CYCLE IN THE COMMON FERRET. 343

a range of some ten months, and yet that the young are
always born within a season limited to about six weeks;” in
other words, the gestation period of the badger may be
anything between under five and over fifteen months. (See
above, page 326, where Meade-Waldo’s paper is referred to.)

REFERENCES TO LITERATURE.

Bett.—‘ A History of British Quadrupeds,’ 2nd edition, London, 1874.

Biinter.—“ Riickbildung der Eifollikel bei Wirbelthieren,”’ ‘ Morphol. Jahr.,’
vol. xxx, 1902.

CaRNEGIE and other authorities. —‘ Ferrets and Ferreting,’ 3rd _ edition,
London, 1902.

Cocxs.—“ Note on the Breeding of the Otter,” ‘Proc. Z. S.,’ 1881.

Cocxs.—* Habits of the Polecat,” ‘The Zoologist,’ 1891.

Cocxs.—“ Note on the Gestation of the Pine Marten,” ‘ Proc. Z. S.,’ 1900.

Cocks.—‘‘ Tne Gestation of the Badger,” ‘The Zoologist,’ 1903, 1904.

Coun.—* Zur Histologie und Histogenesis des Corpus luteum und des inter-
stitiellen Ovarialgewebes,” ‘Arch. f. Mikr. Anat.,’ vol. Ixii, 1903.

Dixon.—‘“‘ The Ovary as an Organ of Internal Secretion,” ‘The Practitioner,’
vol. Ixvi, 1901.

FrarNxkeL.—“ Die Function des Corpus luteum,” ‘ Arch. f. Gynak.,’ vol. xviii
1903.

FRAENKEL and Conn.—‘ Experimentelle Untersuchungen iiber den Hinfluss
des Corpus luteum auf die Insertion des Hies,” ‘ Anat. Anz.,’ vol. xx,
1901.

Gracominr.—‘ Contributo all’ istologia dell’ ovario dei Selaci,” ‘Ricerca ve
Laboratoria di Anatomia normale della Roy. Universita di Roma,
vol. v, 1896.

Hatsan.—“ Ovarium und Menstruation,” ‘S. B. d. Akad. d. Wissenschaften,’
vol. ex, Wien, 1901.

Hartine.—‘ The Polecat, Mustela putorius,” ‘The Zoologist,’ 1891.

’

Heare.—‘‘ Tue Menstruation of Semnopithecus entellus,” ‘Phil. Trans.
B.,’ vol. elxxxv, 1894.

Hearg.—‘‘ The Menstruation and Ovulation of Macacus rhesus,” ‘Phil.
Trans. B.,’ vol. elxxxviii, 1897.

Heare.—“The Artificial Insemination of Mammals, ete.,” ‘Proc. R. S.,’
vol, xi, 1897,

344 FRANCIS H. A. MARSHALL.

Hrapr.— The Sexual Season of Mammals,” ‘Q. J. M. S.,’ vol. xliv, 1900.

Marsuatt, A. Mrtnes.— Vertebrate Embryology,’ London, 1893.

Marsuatt, F. H. A.—‘‘ The Gistrous Cycle and the Formation of the Corpus
Luteum in the Sheep,” ‘ Phil. Trans. B.,’ vol. exevi, 1903.

Meape-Watpo.—‘ The Badger: its Period of Gestation,” ‘The Zoologist,’
1894.

Metcunikorr.—‘ The Nature of Man’ (Mitchell’s translation), London,
1903.

RetrEerer.—‘ Sur les Modification de la Muqueuse Uterine a Epoque du
Rut,” ‘C. R. de la Société de Biologie,’ vol. iv, 1892.

Roginson.—‘ Observations upon the Development of the Common Ferret,
Mustela ferox,” ‘ Anat. Anz.,’ vol. viii, 1893.

SanpEs.—“ The Corpus Luteum of Dasyurus viverrinus, ete.,” Proc.
Linnean Society of New South Wales (vol. xxviii, 1903); abstract in
‘Nature,’ August 20th, 1903.

STRASSMANN.—*“ Beitrag zur Lehre von der Ovulation, Menstruation, und
Conception,” ‘Arch, f. Gynak ,’ vol. iii, 1896.

Watwace.—* Observations on Ovarian Ova and Follicles in certain Teleostean
and Elasmobranch Fishes,” ‘Q. J. M. 8.,’ vol. xlvii, 1903.

Youvatt.—‘ Cattle,’ London, 1835.

EXPLANATION OF PLATES 19—21,

Illustrating Mr. Francis H. A. Marshall’s paper on “The
(strous Cycle in the Common Ferret.” The figures
were drawn by Mr. J. Taylor, of Edinburgh.

feference Letters.

b.v. Blood-vessel. 4. v.rup. Recently ruptured blood-vessel. cav. Cavity
of uterus (in Fig. 8 cavity of Fallopian tube). ¢.¢. Connective tissue of
stroma. ep. Epithelium. ep.c. Isolated epithelial cell. ep. g/, Epithelium
of gland. ew. 6. Extravasated blood corpuscles. g/. Uterine gland. dew.
Leucocyte. muse. Muscular layers of uterine wall. ov. Ovary.

(ESTROUS CYCLE IN THE COMMON FERRET. 345

PLATE 19.

Fic. 1.—Transverse section showing portion of uterine mucosa. (Period
ini x ea. 300;

Fic. 2.—Transverse section showing portion of uterine mucosa. (Period
III, very early stage.) x ca. 300.

Fic. 3.—Transverse section showing portion of uterine mucosa. (Period
IV.) x ca. 300.

Fig. 4.—Transverse section showing portion of uterine mucosa. (Period
LV, advanced stage.) x ca. 300.

PLATE 20.

Fic. 5.—Transverse section of horn of uterus. (Period II, early stage.)
X ca. 50.

Fic. 6.—Transverse section of horn of uterus. (Period III, advanced
stage.) xX ca. 50.

Fic. 7.—Transverse section of body of uterus. (Period IV. The entire
section is not shown.) XX ca. 50.

Fie. 8.—Transverse section of ovary, showing its attachment to the wall of
the body cavity, and its enclosure by a sac into which the ova are discharged.
x ca. 14. The section passes six times across the coiled Fallopian tube.

PLATE 21.

Fic. 9.—Section through atretic follicle. x ca. 300. The membrana
granulosa has almost completely disappeared, while the ovum is much shrunken
and in a very degenerate condition. Ingrowth from the connective tissue
wall of the follicle has commenced, but has not advanced very far.

Fic. 10.—Transverse section showing portion of uterine mucosa. (Period
IV.) xX ea. 300. Large numbers of blood corpuscles are seen extravasated
in the stroma, while at the same time new (?) blood-vessels are apparently in
process of being formed.

Fig. ]1.—Transverse section showing portions of uterine mucosa, as well

as products of denudation, in the uterine cavity. (Period III, advanced
stage.) x ca. 300.

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TWO NEW FORMS OF CHONIOSTOMATIDA. 347

Two New Forms of Choniostomatide:

Copepoda Parasitic on Crustacea Malacostraca
and Ostrocoda.

H. J. Hansen, D.Sc., F.M.L.S.
(Copenhagen).

With Plate 22.

Duriné a stay—in August, 1902—in the house of my friend,
the Rev. Canon A. M. Norman, I had the good luck to discover,
in his splendid collection, a new parasitic Copepod on a couple
of specimens of a rare Norwegian Amphipod. He asked me
to work out the parasite, which I promised, and the result is
given here.

Since the present writer, six years ago, published the book,
‘The Choniostomatide,’ Copenhagen, 1897 (4to), no species
has been added to this rich and very interesting family of
parasitic Copepoda, though the animals do not seem to be so
rare as probably generally believed. In the preface to the
book named I stated that in the course of 1895-97 I had
found, ‘on the material brought home from the sea near
Iceland and Greenland by the ‘Ingolf’ expedition, several
new forms which cannot be included in the present treatise,”
and since 1897 I have accumulated additional material.
During the study of the species from Canon Norman’s collec-
tion I felt that a paper dealing only with that single form

348 H. J. HANSEN.

would be rather meagre, but for various reasons it was im-
possible for me to work out the whole new material collected
since 1895. Under these circumstances I resolved to embody
here one very interesting form, secured on animals from New
Zealand, and extending in various respects our knowledge of
the family. ‘‘ The Choniostomatide, a family of Copepoda,
parasitic on Crustacea Malacostraca” is the complete title of
my above-mentioned book, but the new form from New
Zealand of the same family lives on a species of Ostracoda,
an order of Crustacea Entomostraca. Besides, nobody has
ever, as far as I know, found any Copepod parasitic on any
species of Ostracoda, while on three forms belonging to this
order G. O. Sars has discovered one, and Th. R. R. Stebbing
a second, and G. W. Miiller a third species of the Cryptonis-
cine (a sub-family of parasitic Isopoda) ; the two first-named
authors have produced full description of the parasites, while
that found by Miller was left undescribed.

The following descriptions of the two forms were written
nearly in conformity to those in my earlier monograph.

Spheronella norvegica, n. sp.
Pl. 22, figs. la—lg.

Female.—tThe specimen drawn (fig. 1a) and dissected
measured 1°7 mm. in length, and nearly the same in breadth ;
the two other specimens seen are almost similar in size. The
head is proportionately very small and well-defined from the
trunk.

‘The frontal margin (fig. 1 d) is well developed, adorned with
a row of very short hairs, but the most lateral portion of the
margin, towards the base of the antennule, is naked. The
antennule (a) are long, three-joimted, with the terminal setze
very long; the third joint has, a little before the middle, an
olfactory seta (s), which is a little shorter than the terminal
ones. ‘Theantenne (b) are of moderate length, three-jointed ;
the joints decreasing strongly in length from the first to the

TWO NEW FORMS OF CHONIOSTOMATID. 349

third, which terminates in a seta. (In the specimen dis-
sected the left antennzx had been lost, while the right one is
shown on the left side of the figure.) The mouth is good-
sized, with a broad border. The maxillulee (d) with a well-
developed“ additionalbranch” (d'). Themaxille (e)are large;
the basal joint is robust and long, with a rounded protuber-
ance on the lower side, a little from the base and from the
outer side, but without hairs, excepting the usual row along
the distal margin. ‘The maxillipeds (f) are long; the basal
joint moderately robust without hairs ; the three other joints
are well marked off from each other; the terminal one is
slender, and terminates in a few exceedingly fine, spiniform
processes. The submedian skeleton presents two pairs of
conspicuous chitinous strips; each of these is sinuate, and,
besides, anteriorly bent very sharply in an acute angle, thus
forming an outer short strip turning outwards and backwards;
the subtriangular space between the outer set of these strips,
situated near the posterior admedian angle of the maxilla, is
adorned with very long hairs, and some moderately long
hairs are also found at the posterior margin of the maxille.
Behind the maxillipeds two transverse strips are seen ; rather
near the middle the strips onthe same half of the animal run
together, forming a single strip which bends backwards and
inwards, uniting itself in the middle line with the correspond-
ing one from the other half; the front one of these trans-
verse strips is adorned with some long hairs, and close to the
posterior strip or a little removed from it some similar hairs
are seen. ‘The lateral margin of the head with a fringe of
moderately long hairs. On the dorsal surface, a little behind
the frontal margin, a rather small, oblong, transverse area, set
with numerous very short hairs, is seen about equidistant
from the middle line, and from the base of the antennula.
‘The trunk is on the anterior half, and especially on the an-
terior third, set with a good number of rather conspicuous,
simple, stiff hairs ; on the posterior half these hairs are much
less numerous, shorter, and not easily observed; the trunk-
legs are exceedingly small, but one of each pair was found.

350 H. J. HANSEN.

The genital area (fig. 1) is a little broader than the head (it
is not visible in fig. 1 a, being situated above and in front of
the posterior outline of the body) ; it is a transverse plate
with six rounded angles, but not very regularly shaped ; the
posterior margin of the plate is straight, about as long as the
postero-lateral margin, which is longer than the antero-lateral
one ; the front margin is wanting, the large anterior middle
portion of the area being occupied by membranous skin. The
plate is adorned with a moderate number of short, stiff hairs,
each originating from a conspicuous “‘ foot,” and these hairs
are spread very irregularly. The genital apertures (gy) are
rather curved, and they diverge a little with their anterior
third ; they are placed in the penultimate fourth part of the
plate, and the distance between them at the middle is some-
what shorter than the length of one of them. The caudal
stylets (st) are situated close together, at a good distance in
front of the posterior margin of the plate, a little behind the
genital apertures.

Male.—The single specimen (figs. 1 b, 1 f, and 1 g) measures
°3 mm. in length, and ‘213 mm. in breadth ; it is thus nearly
six times shorter, and between seven and eight times narrower
than the female. Seen from below the head occupies a little
more than one third of the length; its lateral outlines from
the antenne backwards diverge rather feebly, but where the
subglobular trunk begins the lateral margins begin to diverge
strongly. ‘The frontal border has a fringe of fine hairs. The
antennule are rather slender, of moderate length, very dis-
tinctly three-jointed ; the setee on the distal front angle of the
first joint, and especially those at the apex of the third joint
are long. The antenne (b) are rather well developed, nearly
as in the female; the basal joint is much longer than the
second, which is longer than the third, the latter one is short
and terminates in a rather short seta. The border of the
mouth is moderately broad. The maxillule (d) have a well-
developed additional branch (d'). The maxille (e) are
medium sized, the basal joint with a rounded protuberance
on the posterior side. The submedian skeleton has a chitinous

TWO NEW FORMS OF CHONIOSTOMATIDA. Stil

longitudinal strip at the inner base of the maxille, and this
strip is posteriorly scarcely produced into a free process; from
the anterior part of the inner margin of this strip projects
another less developed shorter strip backwards and a little
inwards ; no processes are found between the maxillipeds, but
behind their insertions is seen a narrow, transverse strip,
which, at the middle, is curved a little backwards, and behind
this strip still another very narrow strip, interrupted at the
middle, constitutes the limit between head and thorax. In-
side the postero-interior angle of each maxilla a short trans-
verse row of long hairs is found. ‘The maxillipeds (/) con-
sist of four distinct joints ; the basal joint is rather long and
slender without hairs; the fourth joint has the end obtuse,
and adorned with a few fine spines. The lateral margin of
the head has a row of moderately long hairs, and this row
begins above the insertion of the antennula; the head has
besides a short oblique, transverse, dorsal area with rather
short hairs inside and a little in front of the anterior end of
the insertion of each antennula (fig. 1g), and a short row of
hairs on the dorsal surface rather near the middle line and
somewhat in advance of the thorax. The trunk is everywhere,
with exception of a narrow and badly-defined transverse belt
at the base on the lower surface, clothed with rather long
setiform hairs, which show an interesting structure. From
tiny transverse chitinous knots two or three hairs originate,
and the middle one is much longer than the others; besides,
the knots are arranged in short or moderately long, more
or less regular, transverse, or somewhat oblique rows; the
length of this clothing is about the same on all parts of the
trunk and nearly as long as the diameter of the basal joint of the
maxillipeds. ‘lhe two pairs of trunk-legs are nearly similarly
shaped, both consisting of a single truncate joint; the joint
of the first pair (J!) is somewhat longer than thick, and not
as thick as that of the second pair (/?), which is as long as
thick ; the joint of the first pair terminates in two sete, one
only a little shorter than the basal joint of the maxillipeds,
while the other seta is about three times shorter ; the joint of

302 H. J. HANSEN.

the second pair with two nearly similar sete, but its long
seta is scarcely as long as that on the first pair of legs. The
caudal stylets (st) are rather similar to the second pair of
legs, each terminating in two or three setex, the longest of
which is a little shorter than the corresponding one of the
legs, while the other sete are more than half as long as the
long seta.

Ovisacs.—The ovisacs belonging to two females differed
little in size, while those of a third female differed consider-
ably from each other, but that was to a certain degree due to
the different stage of development of their contents. The
two ovisacs figured (fig. 1c) give the average size of them as
compared with the female (fig. 1a) and the male (fig. 15),
all being drawn with the same degree of enlargement; the
large one of these ovisacs measures nearly ‘7 mm. in diameter.
The ovisacs are generally subglobular, sometimes irregularly
flattened from pressure ; each contains a rather high number
of eggs.

Larva and Post-larval Development.—Unknown.

Habitat.—Among several specimens of Rhachotropis
leucophthalmus, G. O. Sars, secured by Canon A. M.
Norman in Throndhjemsfjord (Norway) from a depth of 250
—500 fathoms, I found two adult females with this parasite.
In one marsupium I found one female, one male and twelve
ovisacs, the latter ones all adhering to each other; in the
other marsupium was one female with six free ovisacs. The
single male was very dirty, and, hoping to get some fine
specimens, I applied myself to Prof. G. O. Sars, who, with
his usual courtesy, lent me his whole material of that rare
Amphipod for inspection. I found only one infested speci-
men, with one female, eight free ovisacs, but no male. (I
succeeded afterwards in cleaning the male rather well with
two brushes, each consisting of one short and fine hair fixed
in a small stick).

Remarks.—The male is large in proportion to the same
sex in most other species of Spheronella, and it is much
larger than one of the eggs; by the shape of the legs and

TWO NEW FORMS OF CHONIOSTOMATIDZ. 353

the length of the seta on these appendages and on the caudal
stylets it differs considerably from all other forms hitherto
known. Furthermore, I have not observed the existence of
two hairy aree in front and two transverse rows of hairs more
backwards on the upper surface of the head in the male of
any other species. ‘The structure of the hairs on the trunk
is rather similar to that met with in Sph. Giardii, H. J. H.
The female is, as usual, less characteristic than the male, but
presents yet some distinguishing features: in most other
species the trunk is almost totally naked; in no other
female I observed two hairy areas on the upper surface of
the head behind the frontal margin, and the distribution of
hairs on the lower surface of the head is rather similar to
that in Sph. intermedia, H. J. H., but differing from most
other species; the shape of the submedian skeleton and of
the transverse strips just in front of the trunk was not ob-
served in any other form.

Spheronellopsis, n. gen.

Female.—The body is more or less ovate. The head is
rather large, well defined from the trunk. The frontal
border is at most feebly developed, while the lateral margins
are wanting. The antennule are small, two-jointed; the
antenne wanting. The mouth of moderate size; its border
is narrow. ‘The maxillule are well developed, with a good-
sized additional branch. ‘The maxille are rather smail,
but normally shaped. ‘I'he maxillipeds consist of only three
joints: the basal one is short, but very thick, inflated ; the
second joint, which certainly is formed by the complete
fusion of two joints, is rather short; the terminal joint is
nearly rudimentary. The trunk has two quite rudimentary
pairs of legs, each consisting of a joint with one terminal
seta. ‘The genital area is well developed, situated on the
posterior surface of the body, nearly as long as broad; the
genital apertures are situated as in Spheronella rather

354 H. J. HANSEN.

near each other and in the posterior part of the area, but
from its anterior (lower) portion a broad, low protuberance
(fig. 2 g, p) is directed downwards, the lower rounded or
rather truncate end of which protrudes freely and conceals
the anterior (lower) margin of the area itself and a small
portion of the skin in advance of that area. The receptacula
seminis (fig. 2 g, 7) are very long, slender, sausage-shaped,
and very curved, situated beneath the middle of the area,
and their entrances, which could not be distinguished with
certainty, must be rather near the genital apertures. ‘The
caudal stylets (fig. 2 g, st) are completely fused with each
other in nearly their whole length.

Male.—Unknown.

Ovisacs.—As in Spheronella, and deposed freely.

Larvaand Post-larval Development.—Unknown.

Habitat.—The upper posterior space between the shells
of Ostracoda, hitherto found only at New Zealand.

Remarks.—Unfortunately only the female and the ovisacs
of one species are known, while the male is unknown. The
female is similar and closely allied to the rich genus
Spheronella, but differs in the following features: the
fusion of the caudal stylets, the genital area being furnished
with a large protuberance, and the sausage-shaped, strongly
curved receptacula seminis. Besides, the habitation of the
parasite on Ostracoda is a most remarkable feature.

Spheronellopsis littoralis, n. sp.
Pl. 22, figs. 2a—2g.

Female.—The largest specimen (fig. 2 b), which scarcely
had begun to deposit ovisacs, measured ‘57 mm. in length to
the end of the projecting mouth and ‘41 mm. in breadth, but
the body was rather depressed; another similarly depressed
female (tig. 2 a), found together with eight ovisacs and with
a much smaller half evacuated female, measured °48 in length

TWO NEW FORMS OF CHONIOSTOMATIDA. 355

and ‘4 mm. in breadth, but in this specimen the mouth turns
essentially downwards. The head is sharply defined from
the thorax, broader than long, without lateral borders. The
antennule (fig. 2 e) are small, two-jointed, the second joint
not well defined, as long as or shorter than the first, with an
olfactory seta (s) nearly longer than the whole antennula,
and besides with two, three, or four acute, somewhat shorter
sete. The maxille (e) have no protuberance or hairs on the
rather slender basal joint; the second joint is thick at the
base. The maxillipeds (f) are rather anomalous; the basal
joint is short, but exceedingly thick, only very little longer
than thick, with the admedian margin concave and the outer
side strongly vaulted; a transverse row of short hairs is seen
on the inner part of the lower side on its proximal half, and
a similar and little longer row at the distal margin near the
articulating membrane. ‘The second joint is rather short,
and not completely regularly shaped; the third joint is
shaped nearly as a short thick claw inserted on the anterior
surface of the second joint near its end. The submedian
skeleton is not very strongly developed, without processes.
Head and thorax without hairs. ‘The genital area (fig. 2 g)
is about half as broad as the base of the head, nearly as long
as broad, with the outline almost circular, but somewhat
emarginate behind; the protuberance (p) mentioned in the
diagnosis of the genus is well chitinised, especially the lateral
parts of its proximal half, but the lateral part of the area
itself is less chitinised, and the portion in the main covering
the muscle of each half, is rather thin-skinned. The pro-
tuberance is distally either rounded or truncate, with the
angles rounded. The genital apertures (g) are long, strongly
curved, their most anterior (lower) portion is nearly parallel,
and the distance between them is here slightly more than
one half of their length, while the distance between their
opposite ends is about two and a half times longer than one
of them. ‘'he whole area is naked. ‘The muscles (m) to the
antero-lateral half of the frame of each aperture are directed
somewhat outwards and essentially forwards, The sausage-

356 H. J. HANSEN.

shaped, strongly sinuate receptacula (r) are situated at the
admedian margin of the muscles; on the figure the two
receptacula are very differently curved; they were drawn in
the position observed, but I believe that the receptaculum on
the left half of the figure is the normal one. The caudal
stylets (st) are fused with each other, together a little
broader than long, more or less incise behind, and from the
end of each half originates a comparatively strong seta which
is from two to almost three times longer than the stylets;
these are inserted on the posterior (upper) margin itself of
the chitinised area.

Male.—Unknown.

Ovisacs.—They differ very considerably in size, and are
subglobular, shortly ovate or somewhat flattened. I have
figured, with the same degree of enlargement, one of the
smallest (fig. 2c) and one of the largest (fig. 2 d) ovisacs
together with the largest of the two females found together
with them ; the greatest dimension of the smallest ovisac is
‘2 mm., of the largest one*27 mm. The eggs are propor-
tionately large, in one of the smallest ovisacs about eight or
nine, in a large one between twenty and thirty.

Larva and Post-larval Development.—Unknown.

Habitat.—Years ago I discovered this species in three
specimens of the Ostrocod Sarsiella hispida, Brady, from
Akaroa Harbour (New Zealand), six fathoms. In two speci-
mens I found only a female without ovisacs, in the third
specimen one rather large female, one very small, half
evacuated female, and eight ovisacs. Between several hun-
dreds of Sarsiella Hanseni, Brady, from Lyttleton
Harbour (New Zealand), one to five fathoms, I found a good
number of Sarsiella hispida, Brady, and two of these
infested, in one specimen a female without ovisacs, in the
other one very small female with nine ovisacs. The parasite,
surrounded by its ovisacs, is placed in the posterior upper
half of the space between the shells, essentially above
the posterior half of the body of the Ostracod; some
of the ovisacs were also found within the hollow pro-

TWO NEW FORMS OF CHONIOSTOMATIDA. 357

tuberances projecting from the upper postero-lateral angles
of the shell in that species of Sarsiella. I looked in vain
for males. It is interesting that while several infested
specimens of S. hispida were discovered, I did not find the
parasite on any specimen of 8S. Hanseni, which was taken
together with the other form, but was much more abundant,
and I have inspected a good number of the latter species.
Prof. G. 8. Brady established both species of Ostracoda on
material from the Copenhagen Museum.

Remarks.—The rich material of both species of Sar-
siella was procured to our Museum in the following way.
I wrote an instruction to H. Suter, Esq., how he should deal
with the bottom material and send it to us preserved in
spirit; in sieved mud received from him I found a good
number of tolerably preserved specimens of these Ostracoda
and of numerous other Crustacea, many of which were new
to science. ‘The above-described parasite must be rather
easy to secure by zoologists living in New Zealand or staying
there during some time. I will exhort these colleagues to
take up the investigation and look for males and stages of
development. I suppose that if my own material had been
somewhat better preserved or still richer I should have been
able to find these tiny animals, which probably were fallen
out before my inspection. My earlier monograph of the
family gives full information on the mode of proceeding
apphed by me in order to find and deal with such minute
forms without damaging them. I am inclined to believe that
several species of Ostracoda inhabiting other places in the
world are infested with hitherto unknown species of Sphero-
nelloides. Our knowledge of parasitic Copepoda is still in
its infancy, and numerous interesting, even startling, dis-
coveries in this field are to be done by zoologists in the
future.

voL. 48, PART 2.—NEW SERIES. 2é

308 H. J. HANSEN.

EXPLANATION OF PLATE 22,

Ilustrating Mr. H. J. Hansen’s paper on “Two New Forms
of Choniostomatide.”

Fic. 1.—Spheronella norvegica, n. sp.

Fic. 1 a—Female, from below. xX 28, 7, leg of the first pair; 7, leg of
the second pair.

Fic. 1 6.—Male, from below. x 28.

Fic. 1 ¢.—Two ovisacs. x 28.

Fic. 1 d.—Head of the female, from below. x 322. a. Antennula.
6. Antenna. c. Mandible. d. Maxillula. d@!. Additional branch of the
maxillula. e. Maxilla. # Maxilliped. s. Olfactory seta on the last joint of
the antennula.

Fic. 1 e—Genital area of the female. x 182. yg. Genital aperture.
m. Muscle to the outer strip of the frame around the aperture. 7. Recepta-
culum seminis indicated with dotted outline, as seen through the skin (the
other receptaculum is omitted). sf. Caudal stylet.

Fie. 1 f—Male, from below. xX 170. 4. Antenna. d. Maxillula. d'.
Additional branch of the maxillula. e. Maxilla. f Maxilliped. 7. Leg of
first pair. /, Leg of second pair. s¢. Caudal stylet.

Fic. 1 g.—Head of the same male, from the side. x 222. The lettering
as in Fig. 1 ft

Fic. 2.—Spheronellopsis littoralis, n. gen., n. sp.

Fic. 2 a.—Female, from below. x 71. g. Genital area.

lic. 2 6.—Large female, with the head directed forward. x 71. Of the
trunk-legs, only those on the right side of the figure are shown.

Fig. 2¢.—Small ovisac. xX 71.

Fic. 2 d.—Large ovisac. xX 71.

Fic. 2 e.—Head of a female, from below. x 240. The lettering has the
same significance as on Fig. | d.

Fic. 2f:—Anterior part of the head of the female represented in Fig. 2 4,
showing the border of the mouth and the maxillule, with their three branches
or setiform processes. X 285.

Fic. 2 7.—Genital area of a female. x 325. g. Genital aperture. m.
Muscle opening that aperture. yp. Anterior (lower) end of the large pro-
tuberance, met with only in this genus. #7. Receptaculum seminis. st.
Caudal stylets fused with each other.

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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.

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. <A
similar body occurs close to the pyloric ceca. Both are
contained within a firm connective-tissue capsule.

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 383

Lophius piscatorius.—In this species the number of
islets which can be seen in a naked-eye examination is rela-
tively large. The pancreas is diffuse, lying for the most part
in the mesenteric area between the intestine anteriorly and
the spleen. When this area is spread out (see Pl. 27, fig.2), the
islets, being opaque, may be easily observed. ‘I'he “ principal”
lies a short distance in front of the spleen, several others are
scattered between the cystic duct and the intestine. About
half-way along this duct, between it and the intestine, there
occurs with great frequency a fairly large islet, and, as
already noted (15), several near the pylorus, amongst which
is the second largest in size in this species. In appearance
they are most frequently quite white, sometimes the minute
vessels on their surface show as fine red streaks, and at
others they are so distended with blood as to give the organ a
dark ruddy hue. This variable appearance doubtless has
some relation to the fact that retia mirabilia are numerous
in and around the organ. ‘The principal islet is in large
specimens frequently of relatively great size. It is flattened,
circular as a rule in outline, and ellipsoid in vertical section.
In one case it measured 14 mm. in diameter, and about 5 mm.
across its thickest part. It not infrequently in adults is as
large as the supra-renal of a rabbit. The islet near the
pylorus I have found 8 mm. in diameter. ‘They are sur-
rounded by a loose capsule of areolar tissue.

Cottus scorpius.—The pancreas in this species is in the
form of narrow bands adhering to the intestine, and
occupying the interceecal spaces. One of these bands lies
near the spleen. Immediately above this organ the principal
islet may be seen with great distinctness even in small
specimens as a pale, somewhat angular mass faintly streaked
with blood-vessels. The portal vein passes close to it, and
the main branches of the cceliaco-mesenteric artery pass
ventralwards a little distance in front. In a specimen 22 cm.
long the islet measured 3 mm. in diameter.

Cyclopterus lumpus.—Here there is a principal islet
situated slightly anterior to the spleen. Its position and

VOL. 48, PART 3,—NEW SERIES. 28

384. JOHN RENNIE.

relations are very similar to those described for Cottus
scorpius. It is very pale and of relatively large size; in
large specimens it is about 1 cm. in length. The amount
of pancreatic tissue around it is very slight.

Callionymus lyra.—Several islets have been observed
in this species, the largest—the principal—lying close to the
portal vein on the right side of the fish where that vessel
enters the liver. As in other cases, it is slightly anterior to
the spleen, and in the same portion of the mesentery. ‘The
others are all in the same region, but lie nearer the intestine ;
they are whitish in appearance and very small.

Anarrhichas lupus.—Besides a principal islet, several
others—never a large number—have been observed in the
anterior region of the abdominal cavity. Hxcept in the case
of the principal, constantly occurring forms or large
examples were not made out. The principal is usually
ovoid in shape; in specimens of about 40 cm. its longest
diameter is 9 mm. It is usually of a pale red colour,
and lies in a thin sheet of pancreas in a portion of the
mesentery well forward under the right lobe of the liver,
and quite close to the mesenteric artery, from which vessel
it is very easily injected.

Pholis gunnellus.—The situation of the principal islet
in this species has already been indicated in my preliminary
note. Further, in sections of the abdominal viscera in this
region may be seen a fair-sized islet close to the intestine
at the pylorus, a common position for these bodies,

Chirolophis galerita.—lIna position very similar to that
of the principal islet in Pholis there is an islet in this
species. Only two examples were examined, and it was
found in both. It is well forward under the right lobe of the
liver, between it and the stomach, near the portal vein. It
was found oval in form, enclosed in a firm capsule, and was
easily separated from the surrounding tissue. In a specimen
15 cm. long it measured 2 mm.

Gadus virens.—lIslets are situated in the intercecal
pancreatic tissue. They do not appear to be very numerous,

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 385

but some are of fairly large size; they are circular, elliptical,
or irregular in outline. They do not possess a special
limiting capsule, but are surrounded by the ordinary con-
nective tissue of the pancreatic alveoli.

Gadus eglefinus.—The islets here occupy the same
position as in the preceding species. Their relations to the
zymogenous elements are also similar.

Cyclogaster Montagui.—Four specimens of this small
species were examined, and in a position corresponding to
that of the principal, an islet was in each case found. It is,
of course, very minute, but may be found on the right side
of the fish slightly anterior to the spleen and near to the
pyloric ceca.

Zoarces viviparus.—In this species the principal islet
occupies a position similar to that in Pholis gunnellus
within the triangular area already referred to, which is
slightly larger than in the related genus; the islet has a
variable position, lying in some cases close to the hepatic
artery and in others lower down in the angle between the
mesenteric artery and the portal vein. There are present, in
some instances at least, one or two smaller islets nearer
the gut and within the area bounded by the vessels already
named.

The pancreas is of the commonest type, viz. diffuse, and is
sometimes greatly obscured by the presence of fatty tissue.
Hence, although the islets are definitely separated from the
zymogenous elements by a firm capsule, they may be more or
less concealed by this tissue, and not so readily observed as
in other instances. They are ovoid or spherical, and in
medium sized adults the larger is about 2 mm. in length.
The capsule is usually pigmented.

Onos mustela.—lIslets exist within the pancreatic tissue
which is found alongside the pyloric ceca. I noted in
particular a large example of elongated irregular outline.
The islets are in close relation to the ordinary pancreatic
tissue, and do not have any special limiting capsule.

Ammodytes tobianus,—The pancreas here is of the

386 JOHN RENNIE.

extended type, stretching the whole length of the intestine in
two narrow bands, a condition which is common in small
slender bodied fishes. A principal islet was not found by
dissection, but on sectioning the entire viscera in the usual
region of its occurrence several fairly large islets of irregular
outline were found (fig. 6).

Hippoglossus vulgaris, Pleuronectes platessa, etc.
—In the Pleuronectidz examined the position of the principal
islet is the same, and they may therefore in this section be
referred to collectively. It is the same as in Zeus, viz.
within a small pancreatic mass attached to the gall-bladder.
In the larger forms, e.g. Hippoglossus, it is very apparent
as an ovoid mass of a ruddy colour. Here the pancreatic
investment is slight. In smaller forms the outline of the
islet is not so apparent, being masked by the surrounding
zymogenous tissue. Smaller islets exist in other parts of the
pancreas; thus in both Hippoglossus and in Pleuronectes
a fairly large one occurs with very great frequency, if not
with absolute regularity, near the origin of the pyloric ceca.

Syngnathus acus, Nerophis equoreus, Syphonos-
toma typhle.—In these Lophobranchs the pancreas consists
mainly of two well-defined bands following the blood-vessels
‘ alongside the gut. On one of these portions where the
portal vein crosses to the liver (the usual position, in fact)
the principal islet occurs as a small, somewhat flattened, ovoid
body, whitish in colour, slightly pigmented, and about 1 mm.
in length in adult specimens. Its position in the three
species is identical; it is found most readily by dissection
from the right side, lying between the mesenteric artery and
the portal vein (fig. 3).

In my previous paper I enumerated certain species in which
a principal islet existed, and in the foregoing statement such
particulars of its position in the several instances are given
as will enable its occurrence to be verified. In the present
paper additional examples are quoted, and it is more than
probable that the list could be extended. For, after the
geueral relations of the body became known, I failed to find

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 387

it in few fresh species, and these were of small size, where it
is liable to be missed when sought for by macroscopic methods.
It will be seen that the position is practically the same in all
cases. It lies a short distance in front of the spleen in the
mesenteric fold between the portal vein and the mesenteric
artery. In a certain number this islet, though still in
a position agreeing generally with the foregoing, has a relation
which enables its situation to be even more exactly stated.
It is in close proximity to the gall-bladder, and has the
appearance of a compact nodule attached to its base or
posterior wall.

In the following species—Agonus cataphractus,
Lophius piscatorius, Pholis gunnellus, Anarrhi-
chas lupus, Zoarces viviparus, Onos mustela,
Ammodytes tobianus, Hippoglossus vulgaris, and
Pleuronectes platessa—I found an islet at the pylorus.

It was always smaller in size than the “

principal.” This is
the one referred to in my preliminary note. Although I can-
not at present say that it is constant, its presence here in so
many different species is of interest and an indication at any
rate that thisisacommon position. In one particular instance,
Lophius piscatorius, I endeavoured to obtain some evidence
on this question of constantly occurring islets. This species is
the one in which I have found the largest number of these
bodies. I examined many hundreds of specimens and I noted—

1, That the “ principal,” the largest islet (see Pi. 27, fig. 2),
was present in every case.

2. That an islet at the pylorus (PI. 27, fig. 2, Js. 1), and the
islet marked “ Is. 2”’ occurred very frequently, although they
were not found in every case.

3. That there seemed to be considerable variation in the
numbers of the others.

These facts are in complete accordance with the suggestion
I have already made. Here constant and varying islets
exist, whose relations may be compared to those of thyroid
and accessory thyroids or spleen and accessory spleens.!

1 Tn this connection it is worthy of note that I found accessory spleens of

388 JOHN RENNIE.

The principal islet, where it exists, is on this view to be
regarded as a distinct organ, the others as supplementary
bodies of similar function. In those cases, viz. certain —
fishes and all higher animais, where it is presumably absent
this organ in the course of phylogeny has disappeared and
the supplementary bodies have increased in numbers and
importance.

Histology.

The material made use of for histological purposes was
fixed immediately after death, in either corrosive sublimate
or Bles’s fluid. After washing (in the case of the sublimate)
and dehydration, the tissue was embedded in paraffin and cut
serially with a Cambridge rocking microtome. ‘The sections
were stained with hematoxylin and eosin and examined under
a Beck microscope possessing a ;4; oil immersion objective
as well as lower powers.

In agreement with the results of other investigators, the
tissue of these islets was found to stain a lighter tint
than the surrounding pancreatic alveoli. Hven when small
they are very noticeable as paler areas in the pancreatic
mass; they are frequently, however, more massive than the
adjacent organ, from which they are definitely separated by
a capsule. They are an epithelial tissue consisting of
very small polyhedral or cylindrical cells well supplied with
blood-capillaries. A common size of cell is about 10 u across
the narrow diameter.

In a number of instances there was noted a difference in
the staining capacity of different areas within the islets.
This feature has been noted by other observers, particularly
Massari (12) and Diamare (38). The latter has interpreted it
as indicating a difference in functional state of different
parts of the islet ; he regards such appearances as the accom-
paniment of different phases of the same kind of cell.

fairly frequent occurrence in Lophius. ‘These appear to be common also in
the skate, where two or three minute examples may be seen in a single fish,

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTET. 389

Although some of the material examined by me might be
interpreted similarly (e.¢.in Zeus faber) in several instances,
of which I give a detailed account, the contrast in size,
form, structure, arrangement, and relation to the capillaries
of the cells of the two regions of the islet, as well as their
different staining capacities, appear to me so marked that
I am not prepared to accept Diamare’s explanation as
satisfactory.

In the descriptions which follow I have not considered it
necessary to detail the appearances in each of the species
already enumerated; I have selected such as together illus-
trate fully the essential structure of these bodies as a whole.

Zeus faber.—In this species, apart from a slightly less
intimate relation of islet and acini in the case of the principal
as compared with the others, the histological structure of
these bodies is similar in every respect. They are fairly
numerous in the interceecal pancreatic masses, where they lie
close to the zymogenous tissue, and are without any special
capsule. Some are of distinctly irregular outline. They
consist of polyhedral cells, smaller than the cells of the
pancreas ; their walls are well defined, and the cytoplasm
exhibits a delicate meshwork of fibrils. The nuclei are
irregularly circular or oval, and show a large nucleolus
which always stained a dark red. Chromatin net-knots were
always observed, as also the nuclear membrane. Apart from
size and the possession of a capsule of areolar tissue which
may send in supporting partitions, the principal islet exhibits
the same structure as the others. The pancreatic acini,
however, in the examples sectioned, did not completely en-
velop the islet.

The differently staining patches already spoken of were
usually observable in preparations of islets from this species.
Examination with high powers showed that this difference is
due mainly, though not altogether, to the staining capacity
of the nuclei in the respective areas. The chromatin is
more abundant in the nuclei which stain more darkly. At
the same time, the cytoplasm of these cells appears to take

390 JOHN RENNIE.

up a deeper tint than the cells of the lighter areas, though
no structural differences were made out in this region of the
cell. Capillaries are only fairly numerous in this type
(fig. 4).

Pholis gunnellus.—The two islets referred to in an
earlier part of this paper possess the same structure, except
that the principal has a very definite capsule not apparent in
the other, and its relation to the pancreas is less intimate.
The structure is similar to that described for Zeus, but the
cells are smaller and more cylindrical. Cell-walls are less
easily seen, but are present. In parts the capillaries run in
nearly parallel rows, and the cells are arranged in bands
between. The cytoplasm shows a delicate network, which, in
contrast to that visible in the neighbouring acini, is very
fine. Differently staining areas, as noted in Zeus, were not
observed.

Anarrhichas lupus.—The principal islet is a large
body with a well-defined capsule which sends in numerous
supporting partitions (fig. 5). It is surrounded by a very
thin band of zymogenous tissue, from which portions pene-
trate within the islet. This feature is not uncommon in the
case of large islets in fishes ; Diamare noted it in some of the
species examined by him, and I have met with several
instances, as willbe seen. ‘The tissue of the islet proper pre-
sented similar features to that seen in Zeus. Light and
dark areas were observable, and they were respectively
traceable through series of sections. In the main the nuclei
of the lightly staining areas were seen to be irregular in
outline, while those of the dark areas were circular or oval.
There was also a difference in size, the former being
larger.

In Onos mustela a large islet of very irregular out-
line was examined. It occurred in a mass of pancreatic
tissue adherent to the intestine at the pylorus. In some
sections it appeared as two separate bodies, but examination
of the series showed a connection. ‘I'his islet had no limiting
capsule, it was invested by the connective tissue of the

EPITHELIAL ISLETS OF THE PANOREAS IN TELEOSTEI. 391

surrounding zymogenous elements, which were here massed
and not spread out in a thin sheet as is more common in
smallfishes. Here, again, darkly and lightly staining patches
of irregular outline were present, whose cells exhibited
differences in arrangement and structure. No cell-walls
were seen in the case of the darkly staining elements ; but,
from the very close arrangement of the nuclei, if walls were
present the cells must have been of an elongated fusiform
type. These cells are arranged in bands between the
capillaries, and one could count half a dozen nuclei on an
average in a row across a band between two capillaries. No
network could be made out in the cytoplasm; the nuclear
details were similar to those already given. These bands
were not so definite in some parts as in others, and the arrange-
ment resembles more the irregular grouping characteristic
of the lighter staining areas of the islet. Although this was
the case, it was noticeable that the nuclei of the irregularly
arranged dark cells were more numerous than those of the
light and also more crowded together. The lightly staining
patches showed a more open appearance owing to the cells
being larger; they were seen to be polyhedral in form. The
nuclei did not differ much from those of the dark areas (fig.
13). In Cyclopterus lumpus the tissue of the principal
islet is in every way similar to that here described. There is,
however, a capsule around the body, outside of which a slight
layer of pancreatic tissue is present.

Lophius piscatorius.—The islets are surrounded by a
capsule of rather open areolar tissue. In those examined I
observed no indication of an arrangement of the cells in
bands as is apparent in many species; the tissue was quite
uniform. Capillaries appeared abundant, and in the con-
nective tissue around the islet as well as within it I noted
the presence of retia mirabilia upon the vessels (fig. 10).
As many as four were seen in a single section; the com-
ponent vessels had distinct walls, and were united by a
surrounding and interlacing connective tissue. The cells of
the islet are of the usual polyhedral type, with cytoplasm

392 JOHN RENNIE.

granular or fibrillate, the nuclei with distinct nucleolus and
chromatin network. Distinctively dark and light areas
were not observed.

Zoarces viviparus.—As may be seen from fig. 11, the
relation between pancreas and principal islet is extremely
slight. This is one of the cases where, were it not from the
known relations as revealed in other species, it would be
difficult to relate the body to its proper category. It is
surrounded by a fairly thick capsule, upon which there is a
deposition of pigment. I sectioned one throughout its whole
length, and found that it was penetrated by no large blood-
vessels, though capillaries were abundant. ‘The greater part
of the space within the capsule is occupied by bands of
darkly staining cells. The parts between these bands, which
wind irregularly, are occupied by cells which stain lightly
and are of different form from the others. The columns of
darkly staining cells are more richly supplied with capillaries
than are the cells occupying the spaces between. The
former are narrow, cylindrical, or fusiform, with very finely
granular contents, and measure about 10 u across the narrow
diameter. The nucleus is oval, and stains very darkly,
being filled with numerous minute chromatin granules. It
frequently almost fills the width of the cell, and is about 9 p.
The cells of the lightly staining areas are irregularly poly-
hedral in form, their cytoplasm shows a network of fibrils
rather than granules, while the nucleus has an irregular
outline and contains fewer chromatin granules than that of
the darkly staining form (fig. 12).

Ammodytes tobianus.—Besides small islets, two fairly
large examples of irregular outline were found in this species.
They were all completely enveloped in pancreatic tissue, and
did not possess a: limiting capsule. ‘The capillaries were
very abundant, so much so that in many parts they were
separated from each other by the width of only a single cell.
In consequence of this arrangement the cells appeared in
columns in certain parts, they stained more darkly than the
rest of the islet, and were of different form (fig. 6). The

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 393

contrast between the two was in fact marked. The darkly
staining cells were columnar, with finely granular cytoplasm ;
nuclei almost uniformly oval with a distinct nucleolus and
granular chromatin. The lighter staining cells were irregu-
larly polygonal, their cytoplasm not so granular, and their
nuclei of very irregular outline. A few of these are given
in fig. 7. A frequent form is that with a deep cleft
between two portions. There are fine fibrils of chromatin
with net-knots and also distinct nucleolus visible. The
contrast here is very different from the appearance in Zeus,
and I do not think can reasonably be attributed to differences
in functional state of the same kind of cell. They appear to
me to constitute two interlacing tissues.

Pleuronectes platessa (figs. 8 and 9).—The principal
islet hes within a small mass of pancreas which is attached to
the gall-bladder. The greater part of this mass, which is that
spoken of by Cole and Johnstone (1) as a “little nodular
swelling,” consists of islet; the zymogenous tissue forms a
small envelope around it. There is a definite capsule, but I
did not see any supporting trabecule. It is usually pene-
trated by zymogenous elements, and where this is so, con-
nective tissue surrounds these and separates them from the
islet tissue. This penetration by pancreatic tissue is a feature
which has already been noted in other instances, and, as in
those cases, it was here traceable as continuous with the same
elements around the capsule. The components of the islet are
very small cells richly supplied with capillaries. The capil-
laries are not equally distributed throughout, but are more
abundant in the inner regions. In these parts the cells
occur in columns or strands having a somewhat sinuous
arrangement ; they evidently in many instances surround and
follow the course of the capillaries. These cells stain darkly.
In the spaces between these winding strands, and also in
other parts of the islet, where, as already indicated, the
capillaries are not so numerous, cells, lightly staining, are
massed. The arrangement is quite different, but besides a
difference in staining capacity and relation to the capillaries,

394 JOHN RENNIE.

certain structural differences were made out with high
powers.

1. The form of the cell. In the darkly staining strands
this was seen to be always more or less columnar, and was
probably due to their position and arrangement between the
capillaries. The cell-walls could not be made out clearly.
The lightly staining cells are irregularly polyhedral, their
walls could usually be traced with distinctness, and they are
evidently larger than the columnar types.

2. The appearance of the cytoplasm. In the columnar
types this appeared diffusely and finely granular. The light
cells showed a fairly open network of fibrils.

3. The nuclei. In the columnar cells these appeared
regularly ovoid or spherical, and smaller than those of the
polyhedral type. These latter were very variable and very
irregular in outline. Both kinds showed nucleoli and net-
knots, the polyhedral cells showing these very clearly.
Regarding those nuclear differences, I do not think they can
be attributed to fixatives, since the irregular forms were found
only among the polyhedral cells.

In Hippoglossus vulgaris the conditions are similar to
those described for Pleuronectes.

In the Gadidz only small islets were examined, and in
these no special features were observed. ‘The cells were all
of one type, and similar to those of the lightly staining areas
of those forms exhibiting two types. The islets were com-
pletely surrounded by pancreatic tissue, and no capsule was
present.

Lophobranchii.—Examples of three different genera of
this group were examined. A principal islet only was found,
and this was sectioned in each case. There is a distinct
limiting capsule, which may be pigmented, of a different
tissue from that supporting the pancreatic acini. These latter
are quite apart from the islet, and in fact are more closely
associated with the mesenteric blood-vessels than with this
body. Capillaries are numerous, but I did not find the cells
arranged in columns around these, nor did I find two types of

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 995

cell. The elements were small, and resembled the lightly
staining or polyhedral forms. They presented in their finer
structure no features of a special nature.

The conditions observed in Anarrhicas, Onos, Cyclo-
pterus, Zoarces, Ammodytes, Pleuronectes, and Hip-
poglossus, it will be noted, are suggestive of a double tissue
within the islet. No such appearance is observable in the other
forms examined. Massari describes a two-fold tissue in
Anguilla, distinguishing the two kinds of cell as ‘ chromato-
phile” and “achromatophile.” Diamare has sought to refute
this view, his interpretation, as already indicated, being that
the differences seen are indications of different functional
states in the two regions, and that there is one tissue only.

It is satisfactory to note that on the point at issue there is
a remarkable agreement even in some matters of minute detail
as to the actual conditions. Diamare’s paper did not reach
me until after my own observations were made, and although
the species examined were not the same, and his methods of
fixation and staining were different and more varied than
mine, all the appearances noted by him are to be seen on my
own preparations. The question is largely a matter of inter-
pretation of results.

The facts are briefly these. Tracts of more or less
columnar or fusiform cells wind through the islets, and
around and between these are slightly larger polyhedral cells
arranged in masses. The columns stain more darkly than the
masses. Diamare speaks of tracts showing intermediate
staining which force the suspicion that they do not represent
two different categories of cells. I myself found islets in
which the contrast in the two types was less marked than in
others, but even here it is deserving of notice that the columns
were always darker than the masses. If a difference of
functional state be indicated by these appearances, we expect
the columns will at some time show the lighter staining
effect, and also that the polyhedral cells will be found in the
darker phase. Such conditions were not found by me.
Diamare, further, makes much of the fact that the one type

396 JOHN RENNIE.

could be seen to be continuous with the other, sometimes a
dark column merged with a light, or dark cells occurred on
one side of a capillary and light ones on the other. I am not
sure that there is much in this, but in any case he does not
appear to have observed the contrast in grouping of the two
sets as noted by me, e. g. in Pleuronectes, nor the relative
distribution of the capillaries of the two regions. In this
species I found the capillaries more abundant in the inner
regions, and here the columnar cells were most noticeable,
while the other type occupied along with the capillaries the
spaces between and also the surrounding areas. In Zoarces
the arrangement suggested by the grouping was that of
columns of cells with an interstitial tissue. It is true that the
columnar arrangement is due probably to the abundance of
the capillaries, whose course the cells follow; but if they are
all one tissue I have been unfortunate, as also has Massari, in
seeing preparations which exhibited the columnar cells in one
phase only, and that different from the rest of the islet.
Diamare himself compares the appearance of an islet in
Motella to the supra-renals of birds, where the cortical and
medullary substances interlace.

I examined some very small islets in Ammodytes and
Pleuronectes where there was only a limited number of cells
visible in a section. They were so small that a difference of
functional state between different parts was scarcely to be
looked for, and yet the two types were apparent (fig. 6, Sm.
is, and Is. 3).

Although I incline to the view that we have here two
distinct tissues, from a consideration of the fact that in many
species this double nature is not evident, I do not think they
are likely to be of independent secreting function. _ The dark
cells appear to stand in a relation intermediate to the
capillaries on the one hand and the lght-cells on the other.
It may be that they regulate the supply to the capillaries of
the substance secreted by the light-cells, or they may effect a
final stage in its elaboration.

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTHI. 397

Relation of the Islets to the Pancreatic Acini.

From the foregoing account it will be seen that in bony
fishes these islets, though undoubtedly existing under con-
ditions similar to those met with in higher animals, also very
commonly occur in distinctly less intimate morphological
relation to the pancreatic alveoli. It will have been noted
that various conditions have been observed, from that where
the tissue of the islet stands in the same relation to the zymo-
genous elements as the separate alveoli of the latter do to
each other (figs. 4 and 6) to cases where a thick investing
capsule exists around a large islet with no alveoli in contact,
and only a very few of these in the surrounding parts, e. g.
Syngnathus (fig. 3). Indeed, my attention in the first
instance was confined to these latter bodies in such fishes as
Pholis gunnellus and Syngnathus acus, where the
ordinary pancreatic tissue is in no more intimate relation to
them than it is to the portal vein or mesenteric artery, along
which vessels it extends as narrow bands. Accordingly I
hesitated to relate these distinctly encapsuled and separate
glands with the pancreatic “islet” of the usual type until I
had found in various species bodies of identical structure in
situations which left no further room for doubt. Amongst
these encapsuled glands there is included the body already
noted as a “ principal islet.” Diamare, without making any
reference to the question of regular occurrence, describes this
body in Orthagoriscus mola, Rhombus levis, and
Lophius piscatorius as a pancreatic islet. Indeed, no
reasonable doubt can be raised as regards the homology of
the principal islet.

A feature observed in the islets in Hippoglossus vul-
garis, Pleuronectes platessa,and Anarrhichas lupus,
viz. the penetration of these by zymogenous elements, had been
previously noted by Diamare in other species. ‘hese elements
may appear continuous with the pancreatic tissue outside, or
as detached alveoli surrounded by the islet. In the latter

398 JOHN RENNIE.

instances, however, they could be seen in serial sections to
be continuous with the same tissue outside (figs. 5 and 8). I
do not consider it a feature of any morphological importance.
In all the cases where the peculiarity was noted the pancreas
is of a very diffuse type, and in the spreading of its alveoli
during development, as is well known, it may invade or
become attached to other organs of independent function. A
common feature is the close envelopment of the leading blood-
vessels throughout the body-cavity by long strands of pan-
creatic tissue, and in several instances (Syngathus, Pleuro-
nectes) such tissue accompanies the vessels within the liver,
ramifying with these throughout the tissue of that organ.

Pancreatic elements penetrating the islets are supported by
connective tissue, which is continuous with such tissue beyond
and around the islet. On account of this Diamare has argued
that the capsule is of the nature of interstitial tissue of the
pancreas, and that here, owing to the larger development of
these islets, it has assumed a capsular form; and he definitely
opposes the interpretation that the tissue enclosed by the
capsule is merely joined to the pancreas, and is not an inherent
portion of it. The capsule, he says, in these cases is a
“secondary ” formation.

The view thus contested is, from evidence already partly
submitted and partly to follow, one that I continue to hold.
In the first instance we may recall the fact just referred to
that a pancreas, intra-hepatic, exists ; and if it can invade the
tissue of an organ undoubtedly distinct and having embry-
onically a separate origin, there is no argument for identity
in the fact that pancreas is found sometimes within another
organ which has its rise from the same embryonic tissue,! and
which we may assume is from the first in closer proximity.
Further, I find the capsule is best developed where, owing to

1 According to Laguesse (9) and, more recently, Pearce (14), they have the
same embryonic origin. ‘This does not affect the present argument, for we
recall such facts as the origin of thymus and thyroid from branchial epithelium,
and (according to 8, Vincent) the medulla of the supra-renal from sympathetic
elements.—J. R.

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTRY, 399

the extremely diffuse condition of the pancreas, interstitial
tissue can scarcely be said to exist, the organ deriving support
from the several other organs to which it is adherent, e. g.
the larger blood-vessels (Lophobranchs). In fact, just in
proportion as the pancreatic tissue has a more or less massive
arrangement, the capsule is more or less indefinite. That is
to say, the capsule tends to disappear where the form of the
zymogenous tissue approaches most nearly the common form
in higher animals. This is well seen in those fishes where the
pyloric czeca have their interspaces filled with pancreas. The
islets observed in such cases had no capsule. Where they
have come to be enclosed within pancreatic elements, the
necessity for a protecting capsule has ceased to exist.

In further support of the view which regards these islets
as independent organs, two other points appear to me worth
stating. In many fishes the peritoneal membrane and blood-
vessels are pigmented, and in such cases so also is the capsule
of these bodies, although I have never seen any pigment laid
down within or upon pancreatic tissue. As examples may be
quoted Pholis gunnellus, Zoarces viviparus. In this
last I have found several islets within pigmented capsules
inasingle fish. The second point has reference to the intra-
hepatic pancreas of certain fishes. If the islets are inherent
portions of the pancreas in such fishes, related directly to its
functions as a digestive gland, and, according to Jarotsky (6),
who conducted an extensive series of experiments on white
mice in dieting and fasting, “they probably supply a sub-
stance or substances representing a chemical stage of
development of a ferment or substances necessary to the
cells producing it,” we would expect to find islets in the
not inconsiderable part of the gland placed inside the liver.
I have looked carefully for islets in this region in both
Syngnathus acus and Pleuronectes platessa, and
have found none.

The view I now bring forward may bestated asfollows:—The
conditions observed in various Teleostei force the conclusion
that here “islet ” and pancreasare distinct organs. In certain

VOL, 48, PART 3.—NEW SERIES, 29

400 JOHN RENNIE.

genera, e.g. Lophius, Pholis, Zoarces, Syngnathus,
the “islet” tissue has no more intimate relation to pancreas
than to other neighbouring organs. Diamare, indeed, points
out that the “islets” are glands of a more primitive type
than the pancreas, which represents an advance in the evolu-
tion of organs. What he fails to appreciate is the fact that
the more highly developed organ, in its most primitive
state, is distinct from the still more primitive internal
secreting gland. The compact pancreas, I consider, is a
further development, in which the association of the two
tissues is strengthened, so that they become virtually one
organ, although there is no evidence but that they are still of
independent function. This association is due to the fact that
they arise from the same embryonic tissue. The results of
Pearce (14) on the development of the islands in the human
embryo are of interest, and their bearing on this point worth
quoting. He does not agree with Laguesse and Renaut that
the islands arise from ‘peculiar cells with rich eosinophilic
protoplasm, comparable to the parietal or oxyntic cells of the
gastric tubules.” He finds that the pancreas develops as
branching glandular processes, which become tubular later.
The islets develop as side branches of these processes, and,
from a careful study of the paper, I consider it clearly
brought out that the island is formed from the “ branching
elandular process” before the remainder of itis trans-
formed into acini. ‘Thus the interesting point seems to
be established that “island” is an earlier formation than
acinus; that is, the phylogenetic order is paralleled in
ontogeny.

Certain observers, investigating the pancreas of mammals,
have concluded that the islets exhibit transitional forms indi-
cating a change of islet tissue into gland lobuli. Lewaschew
(11) claimed that irritation caused the groups to become
more numerous and larger, and that various transitions
became apparent. Statkewitsch (16) asserted that some of
the lobuli of the pancreas underwent such changes during
fasting that they assumed the islet form. On the other hand,

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 401

Diamare has, as the result of similar experiments, failed to
find any appearance which might be taken as representing
transitional forms, and his histological methods and results
seem beyond reproach. Laguesse, who held the opinion that
throughout life there was a repeated transformation of islet
tissue into zymogenous and vice versa, has (according to
Pearce), in deference to Diamare’s work, in large measure
abandoned this view. I have never observed any appear-
ances which might be regarded as transitional, but in any
case the facts already adduced are eutirely opposed to such
interdependence as is here described. It is, indeed, quite
possible that under such unnatural conditions as those of the
experiments of Lewaschew or Statkewitsch the pancreatic
lobuli underwent degeneration, or possibly reverted to the
condition of the cellular “ processes” of Pearce, which,
although distinct in appearance from the islets, might well be
mistaken for transitional forms.

The fact is not without interest that hitherto observers
have failed to find anything like epithelial blood-islets within
the pancreas in elasmobranchs. It is possible, assuming that
they do not exist within this organ, that their function is
carried out by certain of the other ductless glands in these
fishes. In elasmobranchs both interrenal and supra-renal
glands exist, while in teleosts adrenals, regarded as corre-
sponding to the interrenals, are the only forms. May not one
or other of the glands in the former group carry on the
function of the missing “islets” ?

The Function of the Islets.

Amongst the later investigators there appears to be agree-
ment concerning the functional nature of these bodies. They
are regarded as blood-glands with internal secretion. This is
the opinion of Laguesse, who until recently held the some-
what peculiar view that they are alternately ‘“ endocrine
islets” and “ esocrine glands/’ the change being repeated
during life. Other investigators, e. g. Dogiel (2), have held

4.02 JOHN RENNIE.

them to be functionless effete portions of the pancreas, or
embryonic remains. Others, again, regard them as contri-
buting to the production of the pancreas secretion, e. g.
Giannelli ed Giacomini (4) and Jarotsky, already quoted.

The facts as far as observed by me seem to point clearly to
an internal secretory function. These bodies are ductless
glands; they are all well supplied with capillaries, and in
some cases these are very abundant. In some, structures for
regulating the flow of blood through their tissues are present ;
and this, taken in conjunction with the different appearances
met with in the cytoplasm and nuclei, leaves little doubt but
that they are active organs. Whether two types of cell
exist in certain instances or not, the irregularly polyhedral
lightly staining forms occur in all. Reviewing these, it is
noted that the nuclei occurred with regularly spherical or
oval outline, and also very irregular in form. In the latter
the chromatin was not so abundant ; the cytoplasm, too, was
more open and less granular. Such like differences Diamare
also noted and correctly, I think, interpreted as indications of
different functional states. They correspond, according to
Baum (‘ Deutsch. Zeitschr. f. Thiermed. u. vergl. Pathol.’
xii, 1886), with resting and active conditions respectively of
gland-cells.

In a future paper I hope to give an account of certain
experiments with extracts of these “islets,” the results of
which, as far as at present obtained, appear to indicate the
presence in them of substances possessing some physiological
activity.

Conclusions.

The occurrence of epithelial islets of the pancreas is wide-
spread in Teleostei.

In many of these there is an encapsuled islet (“ principal
islet ”), of relatively large size and of constant occurrence,
whose relation to the pancreatic tissue is frequently extremely
slight. In some species it was the only body of this nature
found,

EPITHELIAL ISLETS OF THE PANCREAS IN TELEOSTEI. 403

The smaller islets, which do not appear to be constant in
number (Lophius), it is suggested, probably originated as
‘“‘accessory bodies,” but are now established as definite organs.

These islets are blood-glands which have entered into a
secondary relation with the pancreas. This has been brought
about in Teleostei mainly by the tendency of the diffuse
pancreas to envelop or invade other tissues. In the case of
these so-called islets in the compact pancreas of Teleostei, and
also of higher animals, the closer relation is due to the common
embryonic origin of the two tissues. Here the islets form a
constituent part of the pancreas, although they maintain
their function as an internal secretory gland. The primitive
condition, however, is that seen in Teleostei with diffuse
pancreas, where the islets are both morphologically and
functionally distinct.

No evidence of transitional forms to support the view that
the islets undergo metamorphosis into zymogenous tissue was
found. The reputed changes of zymogenous elements to islet
tissue are possibly degenerative, or regressive to the “ cellular
process ”’ condition of the embryo.

From internal histological evidence, these bodies are pro-
bably functionally active. (Confirmatory of Diamare’s work.)

REFERENCES.
1. Cote and Jonnstone.—“ Pleuronectes,” ‘ L.M.B.C. Memoirs,’ 1901.
2. Dogiet, A. S.—‘ Zur frage tiber die Auslirginge des Pankreas des

Menschen,” ‘ Arch. f. Anat. u. Phys.,’ Anat. Abt. Jahrg., s. 117—122,
1893.
8. Diamare, V.—“ Studii comparativi sulle isole di Langerhans de
pancreas,” ‘Intern. Monatsschr. f. Anat. u. Phys.,’ Bd. xvi, pp. 155—209,
4, GIANNELLI ED Gracomint.— Richerclie istologiche sub tubo digerente
dei Rettili,” ‘R. Accad, d. Fisiocrit. in Siena,’ 1896.

5. Harris and Gow.—“ Note upon one or two Points on the Comparative
Histology of the Pancreas,’ ‘Journ. of Anat. and Phys.,’ vol. xv,
pp. 849—3860.

6. Janorsxy, A. J.—Uber die Veranderungen in der grosse und im Bau der
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u. Phys.,’ Bd. elvi, Heft 3, s. 409—450, 1899.

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7. Lacuesse, E.—“ Structure et développement du pancréas d’apres les
travaux récents,” ‘Journ. de l’Anat. et de la Phys.,’ vol. xxx,
pp. 591—608 and 731—783.

8. Lacurssz, E.—“ Sur le Paneréas du Crénilabre, et particuligrement sur
le pancréas intrahépatique,” ‘ Rev. Biol. du Nord de la France,’ vii,
No. 9, pp. 3483—360, 1895.

9. Lacurssz, E.—‘Sur ja formation des ilots de Langerhans dans le
pancréas,” ‘Compt. rend. de la Soc. biol.,?> 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.

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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.

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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Scuaupinn, F.—‘“ Ueber das Centralkorn der MHeliozoen.,” ‘ Verhandl.
Deutsch. Zool. Gesellsch.,’ 1896.

Scuuize, O.— Untersuchungen wher die Reifrung und Befruchtung des
Amphibieneies,” ‘Z. w. Z.,’ xlv, 1887.

MATURATION, ETC., OF THE EGG OF THE AXOLOTL. 477

Soporra, J.—“Die Befruchtung und Furchung des Hies der Maus,”
‘A.m.A.,’ xlv, 1895.

Soporta, J— Die Reifung und Befruchtung des Kies von Amphioxus
lanceolatus,” * A. m.A.,’ J, 1897.

Sravrracuer, H.— Hibildung und Furchung bei Cyclas cornea,”
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VAN DER Stricut, O.—* Contribution & i’éiude de la Sphere attractive,”
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VAN DER Stricut, O.—“ La maturation et la fécondation de l’ceuf d’A m phi-
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VAN DER Srricut, O.—“ La formation des deux globules polaires et |’appar-
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Vespovsky, F.—‘‘ Entwickelungsgeschichtliche Untersuchungen,” Prag.,
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Vespovsky, F., and Mrizex, A.—* Umbildung der Cytoplasma wahrend
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WueerLer, W. M.—‘‘ The Behaviour of the Centrosomes in the Fertilised Egg
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Wiuson, E. B., and Marruews, A. P.—‘‘ Maturation, Fertilisation, and
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Witson, E. B.—“Archoplasm, Centrosome and Chromatin in the Sea-
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Witson, HE. b.—‘* Atlas of the Fertilisation and Karyokinesis of the Ovum,”
New York, 1895.

Witson, EH. B.—“ The Cell in Development and Inheritance,” New York,
1902.

Wizson, K. B.—‘‘ Experimental Studies in Cytology. I. Artificial parthen-
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‘Arch. f. Ent. mech.,’ vi, 1898.

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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LATE FULLEMTAN

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W. F. R. WELDON, M.A., F.RB.S.,

LINACKR PROFESSOR OF COMPARATIVE ANATOMY
LATE FELLOW OF S8T. JOHN'S COLLEGE, CAMBRTDGK,

AND

SYDNEY J. HICKSON, M.A... E.RS.,

BEYER PROFESSOR OF ZOOLOGY IN THE OWENS COLLEGE, MANCHESTER,

WITH LITHOGRAPHIC PLATES AND ENGRAVINGS ON WOOD.

J. & A. CHURCHILL, 7 GREAT MARLBOROUGH STREET.
1905.

Adlard and Son, | [London and Dorking

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. <A careful re-examination of our own amphibian
material has, however, convinced us that the older interpre-
tation of the origin of the diaschistic (heterotype) chromo-
somes is, in this respect, incorrect. It would seem, indeed,
that amphibia, although possessing gigantic cells, are
peculiarly unfavourable objects for the elucidation of the
prophases of the first maiotic division. But when re-exam-
ined after a knowledge of what occurs in the corresponding
stages among the more favourable materials presented by
many plant and some animal forms, we have been irresistibly
driven to the conclusion that the rings in the amphibia, like
those of the cockroach, are produced by a folding or some
other form of association between two portions of the split
chromatin riband, It is quite easy in the case of axolotl
and triton to discern the longitudinal split in many fully
formed diaschistic (heterotype) loops, and in these forms we
find no essential difference between the particular phases of
the first maiotic division and what occurs in a more obvious
manner among the types we have previously described.

It remains, then, merely to refer briefly to what is known
with respect to this process in the higher vertebrates, such
as the birds, reptiles, and mammals. Of the first two we
have at present little to say ; but with respect to mammals,
we have examined the prophases of the first maiotic division in
the testis both of the mouse and the rat,! with the result that
we have become assured that the evolution of the diaschistic
(heterotype) chromosomes is here the same as in the lower
forms. Quite recently we had the opportunity of examining
the same stages in man; and although it is necessary that the
full results of this investigation shall be published in a
separate memoir, it may be stated that with respect to the
prophases of the first maiotic (heterotype) division, and the
manner in which the diaschistic chromosomes are evolved,

1 Moore, J. KE. S., “Some Points in the Spermatogenesis of Mammalia,”
‘Int. Monat. f. Anat. u. Phys.,’ 1894.

THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 543

our results in the case of the human species are identical
with those obtained among the lower members of the verte-
brate class.

CoNCLUSIONS.

In attempting to form any opinion respecting the conclu-
sions which may naturally emerge from the preceding mass of
details respecting maiosis, or the reduction of the chromosomes,
in animals and plants, it will have become evident, as was
pointed out in the introductory portion of this memoir,
that whatever particular significance we may be inclined to
attach to the process in question, the essential details are in
all respects similar throughout the higher numbers of both
the animal and the vegetable kingdoms.

Or, in other words, it follows that whatever significance may
ultimately be attached to maiosis itself, this process is pro-
bably one of the most fundamental facts with which biologists
will have to reckon. Such being the case, it may not be un-
desirable briefly to review the essential features of reduction
before attempting to draw whatever conclusions may seem
legitimate from the facts that have now been ascertained.

In all multicellular animals and plants, the elements which
from the first division of the ovum onwards gradually build
up the soma or body of such an organism multiply in general
by the process of karyokinesis, and in all cases this somatic
cell division is carried out on an essentially similar plan. In
the better known examples of such division, like the types
described by Flemming, Rabl, Strasburger, and many others,
the obscure chromatic reticulum of the resting nucleus is
transformed into an increasingly definite spirem thread,
which, when fully formed, often presents the appearance of a
single and endlessly coiled filament. It is this thread which
ultimately breaks up into the number of segments that are
destined to constitute the future definitive chromosomes. Yet
although this interpretation could be put upon the appear-
ances observed during the prophases of division in a large
number of animal and vegetable forms, there certainly exist

544 J. BRETLAND FARMER AND J. E. S. MOORE.

other instances from which it is more natural to draw a some-
what different inference. In the cockroach, for example, the
chromosomes of the pre-maiotic mitoses do not originate
through the breaking up of a coiled spirem filament. For
in this example it is usually possible to see the limits of the
individual chromosome even when the nucleus is in a con-
dition indistinguishable from the rest. The primordia (or
“anlagen”) of each future chromatic element first become
discernible in the form of a slight chromatic condensation.
At such a time the linin masses which will be involved in the
future chromosomes appear always to be visibly discrete and
separated from one another. The more or less completely
resting aspect of the cell is produced by the linin framework
of each chromosome possessing an alveolar or reticular struc-
ture in which the chromatin is irregularly distributed. The
evolution of the chromosomes is brought about by the separa-
tion and condensation of each vesicular linin element, and the
chromatin granules become eventually closely packed together
within the axis of each condensing element. A somewhat
similar state of affairs has been observed in the somatic pro-
phases in Drosera and in Tradescantia, and in all these
instances it would seem that it is not strictly accurate to
assume that the chromosomes originate through the breaking
up of a spirem filament; for in none of them is the spirem,
as generally understood, produced in the first instance, and
in Blatta it is never formed at all.

The facts revealed by the above instances are not without
theoretical importance. They strongly favour the hypothesis
of the persistent identity of the chromosomes from generation
to generation, and it is not impossible that they show more
clearly than the commoner types of cells the manner in which
the chromatic elements become obscured during rest and re-
appear at each succeeding divisional prophase. For example,
when, as usually is the case, the somatic chromosomes
are relatively very long, thin, rod-like structures, if these
persist as vesiculated masses within the resting cell their
existence would not generally be evident owing to the dis-

THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 545

tribution of the chromatin throughout the vesiculated linin.
Indeed, as such cases as those represented in figs. 42-46 will
show that, when the linin masses begin to separate and
contract, and the chromatin collects along the axis of each
originally vesiculate filament, there will result the appearance
of an endless spirem which has generally been described.

However, by whatever method chromatin thread-work
actually originates, it generally does appear later as an intri-
cate coiled mass of chromatic filaments, and these filaments
eventually separate out and contract into the characteristic
number of rod-like somatic chromosomes.

In the somatic (anaschistic) divisions by means of which
the tissues of an adult multicellular organism are gradually
built up this late nuclear spirem sometimes, but by no means
always, shows indications of being longitudinally split before
the somatic chromosomes are definitely separated out. But
at whatever time the longitudinal fission first becomes
actually apparent, it is always to be seen when the chromo-
somes are finally grouped upon the spindle in the so-called
equatorial plane; and this splitting invariably provides the
mechanism by which the halves of the somatic (anaschistic)
chromosomes are distributed in equal numbers among the
daughter nuclei of each succeeding generation of cells.

The sharp distinctions between the innumerable somatic
(anaschistic) divisions which follow one another during the
ontogeny of a multicellular organism and the single hetero-
type (diaschistic) mitosis whereby certain cells of the body
are ultimately fitted for sexual union, is brought about by the
intercalation of a series of definite changes which are
characteristic of the prophase of this particular division. In
their entirety, these added portions of the metamorphosis
constitute what has already been distinguished by us as the
synaptic change, and the whole process of synapsis consists
essentially of the following successive phases :

Whilst at first they are indistinguishable from the resting
or pre-maiotic cells, those which are destined to proceed to the
heterotype mitosis become at first characterised by the closer,

546 J. BRETLAND FARMER AND J. E. S. MOORE.

more chromatic, and often polarised, arrangement of their
nuclear reticulum. In the more readily elucidated examples,
such as Blatta or Osmunda, this polarisation increases and
the chromatin becomes finally arranged in a number of
definite loops. In a large number of instances these loops can
readily be counted, and when this is the case, there are
always found to be half as many loops as there were somatic
chromosomes in the preceding pre-maiotic divisions.

At thesame time, the whole chromatic network contractsaway
from the nuclear membrane, this change producing the First
Contraction figure. As time goes on the loops become not
only increasingly chromatic but also opened out again, until
the apparent polarisation is more or less completely lost and
the nuclei present the well-known coarse spirem figure
within the strands of which double beading or actual longi-
tudinal fission is nearly always more or less apparent. The
coarse spirem figure often constitutes a prolonged phase, but
it is in all cases ultimately succeeded by a short-lived and
easily missed resumption on the part of the split chromatic
thread-work of its earlier polarised arrangement; and this is
followed by a strong Second Contraction and thickening
of the individual loops. Hven before the second contraction
has fully supervened, the longitudinal fission of the thread-
work has in the great majority of cases almost closed up and
disappeared ; and although the exact details of the subse-
quent evolution may, and to some extent do, vary in the
different types, the general statement that each of the indi-
vidual loops in this second contraction figure becomes
directly converted into one of the heterotype chromosomes
sufficiently expresses the really essential parts of the process.

In some cases, as in the cockroach and Osmu nda, the loops,
throughout the whole series of events, remain distinct from
one another, with their free ends open in the region of the
pole field; but during the later stages of their formation
they often break transversely in the curve of the loop as well.
Consequently since the number of unbroken loops is half the
number of pre-maiotic chromosomes, in this stage as well

THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 547

as much later we reach, in the prophase of the hetero-
type mitosis, a condition of things wherein the full number
of the pre-maiotic chromosomes are really separated out,
although disguised by the fact that the pair represented
by a disjointed loop always remain associated. The different
forms which this association may take give rise, as we have
seen, to all sorts of different figures ; thus, in the later stages
of the division we sometimes encounter heterotype chromo-
somes having the appearance of loops twisted upon them-
selves ; or again, we may have a pair of rods open at both
ends, joined at both ends in the form of a ring, or lying over
one another at right angles in the form of a cross. But in
whatever form the heterotype chromosomes appear they are
always obviously to be interpreted as pairs of somatic rods
attached or associated together.

In the succeeding stages of the division, when the chromo-
somes are definitely attached to the spindle, the individual
somatic elements of which each chromosome is composed
become simply separated from one another and pass into the
daughter cells) And in some cases, as in the cockroach,
while this separation is in progress, and the chromosomes
become lengthened out upon the spindle, the original longi-
tudinal split in each is again quite clearly evident. Such
figures explain at once the real meaning of the longitudinal
fission which has frequently been observed in the daughter
elements as they divaricate from one another during the
heterotype diaster.

The second maiotic (or homotype) mitosis follows im-
mediately upon the heterotype (first maiotic) division. In the
cases studied by us it consists clearly in the completion of
that initial longitudinal fission of the spirem that was
accepted (but not finished) during the prophase of the first
of the two maiotic divisions.

Thus the essential peculiarities of the maiotic phase can be
explained as follows: They are due to the coherence in
pairs of pre-maiotic chromosomes and to the inter-
calation of a special form of chromosome-distribu-

548 J. BRETLAND FARMER AND J. E. S. MOORE.

tion during the course of what otherwise would not
differ materially from an ordinary pre-maiotic
mitosis. In the first of the two divisions, a dis-
tribution of entire pre-maiotic chromosomes is
secured, and thus the number of these bodies is
really halved. In the second division, the longi-
tudinal fission begun, but temporarily arrested, in
the preceding prophase takes effect. Consequently
this mitosis as a whole resembles the later stages of an
ordinary one save in the reduced number of the chromosomes.

It is, of course, possible that the succession of these two
series of events might become inverted, and cases have been
described in which the first (heterotype) maiotic division is
said to be anaschistic, while the second one is diaschistic ;
but if fresh investigations should confirm this, it would in no
way detract from the utility of regarding the collection of
events in question as constituting a definite and essential
phase (maiosis) in the cellular hfe history of an organism.

It is obvious from the foregoing description of the events
characteristic of maiosis that in any succeeding cell-genera-
tions we shall encounter only half the number of chromo-
somes that were present before that phase supervened ; and it
can only be after fertilisation, or some other process analogous
to that described by us for the case of apogamous ferns, that
the reduced (post-maiotic) number can again be brought back
to the full pre-maiotic complement. ‘he number of post-
maiotic cell-generations varies. There may be none, as
in the normal cellular cycle of an animal, in which the
differentiation of sexual cells follows immediately upon the
second maiotic (homotype) division. On the other hand, there
may be a considerable number, as for example in ferns, in
which the whole prothallial individual consists of post-
maiotic cells. In animals it is only in certain pathological
growths that an analogous condition appears to obtain.

In plants, however, there is no case known at present in
which the maiotic phase leads directly to the production of
sexual cells, although in Fucus, and also in some of the

THE MAIOTIC PHASE IN ANIMALS AND PLANTS. 549

highest flowering plants, the formation of the ovum (oosphere)
is only separated from it by a single mitosis. In these cases
it appears probable that the small number has been brought
about by a process of shortening the life history, and it is
probably correct to say, for the great majority of plants at
any rate, that the occurrence of a number of post-maiotic
cell-generations is the rule.

The facts of reduction, as set forth in this paper, appear to
afford strong grounds for supposing the chromosomes to be
permanent structures that retain their identity from one
generation to another in the individuals composing a species.
This aspect of the question has already been touched on in the
Introduction, but its importance is so great that a few addi-
tional remarks are called for here.

We have seen that, notwithstanding the impossibility of
recognising the delimitation of a chromosome in the resting
nucleus, the chromatin or nuclein nevertheless does aggregate
in the linin, at the very commencement of prophase, in such
a way that it is difficult to escape the inference that the
reconstitution of the chromosome represents, mutatis
mutandis, the exact converse of the series of changes
witnessed during the preceding telophase. Many other
authors have been driven to a similar conclusion, and we
think that in favourable instances, such as those of Trades-
cantia and Periplaneta, the evidence in support of the view
that would regard the whole process as an unravelling, rather
than as a new construction, is extremely cogent. The close
correspondence between the actual primordia of the chromo-
somes, before the spirem thread is built up, and the vacuo-
lating chromosomes of the telophase can hardly be accidental,
and, moreover, the evidence based on the identity in numbers
cannot be disregarded.

Again, the nature of a reduction which resolves itself into
a sorting of chromosomes rather than that of a mere halving
of chromatic substance is not easy to explain apart from the
existence of a specific individuality that is vested in each one
of the structures in question.

550 J. BRETLAND FARMER AND J. BE. S. MOORE.

And finally, the reappearance during a long series of divi-
sions of chromosomes that can be recognised by some
peculiarity such as that of size, as in the case of Brachy-
stola mentioned by Sutton,! as well as the remarkable
features to be observed during the heterotype mitosis of
Drosera hybrids described by Rosenberg,? appear only to
find a satisfactory explanation on the assumption of persistent
identity.

It will be remembered that Rosenbere found that in
Drosera rotundifolia there were twenty, in D. longi-
folia ten, chromosomes during maiosis. Consequently, in
the hybrid forms there were normally thirty in each somatic
nucleus. When reduction supervened, it might have been
anticipated that fifteen would have been the number pro-
duced. Instead of this, Rosenberg found in every case that
twenty were present. But of the twenty, ten were large
and ten were small; and the inference drawn by him was that
the ten large ones were bivalent, resulting from the union of
pairs derived respectively from D. longifolia and D.
rotundifolia, whilst the ten small ones represented single
chromosomes that originated from the surplus number (ten)
of chromosomes belonging to the rotundifolia parent.

It is, however, equally clear that a change, probably of the
nature of re-arrangement, may at least occasionally occur in
both a plant and an animal. For whilst there is a striking
degree of constancy manifested in the number of the chromo-
somes characteristic of a species, it by no means follows that
closely related species possess closely related numbers, such
as multiples of one another.

The various species of lilies or of Ascaris afford examples
of the truth of this statement. Possibly the alteration in the
number of chromosomes may be correlated with an alteration
of specific characters such as bring about what De Vries has
termed “mutations.” But be this as it may, it is clear that

1 W. S. Sutton, “On the Morphology of the Chromosome group in

Brachystola magna,” ‘ Biol. Bull.,’ iv.
1 Rosenberg, ‘ Ber. Deutsche Bot. Gesellsch.,’ 1904.

THE MALOTIC PHASE IN ANIMALS AND PLANTS. ol

the chromosomes are variable or constant in something the
same way as are the specific characters themselves.

Perhaps we may be permitted to push the matter further.
There is a belief shared by some investigators that a very
close relation, of a casual nature, exists between the
chromosomes, or combinations of chromosomes, and the
specific characters manifested by an organism. At any rate,
such a connection is demonstrably existent between the
nuclei and such characters as is shown, for example, by the
character of the larve resulting from the fertilisation of
enucleated fragments of eggs, by sperms of other species, or
even genera, of Hchinoderms.!

And the remarkable monstrosities, and, still more, the
occasional normal larve, produced after polyspermy find
their most natural explanation in the view that the main
direction of the course of ontogeny is to be attributed to the
chromosomes. The analysis made by Boveri? of the chromo-
some distribution to the blastomeres of eggs which had been
fertilised by two sperms showed strong reasons for concluding
that the peculiarities in the resulting offspring are due to
disturbances in the normal relations of chromosomes in the
cells to which they are distributed. For polyspermy is
usually followed by pluripolar mitoses; and by observing
these and then separating the first-formed blastomeres it
was possible to make a comparative study of the deviations
from the normal form under different conditions of chromo-
some distribution. Thus it is clear that in a tripolar mitosis
there is some chance that two, or at least one, of the three

1 The parthenogenetically produced echinoderm larve are specially inter-
esting in this connection since they only contain half the somatic number of
chromosomes, since they result from the asexual development of a post maiotic
cell (ovum or sperm), This fact proves that the group of chromosomes
present in such a post maiotic cell are sufficient to ensure correct develop-
ment, and, taken with the circumstances detailed in the following paragraph,
lend support to the view that maiosis leads to the separation of the male and
female halves that are temporarily united in the heterotype prophase.

* Boveri, ‘ Ergebnisse w. d. Constitution d. Chromatischen Substanz des
Zellkerns,’ Jena, 1904.

aye J. BRETLAND FARMER AND J. E. S. MOORE.

resulting cells might receive the entire lot of chromosomes
contributed by one of the three gametes that have taken
part in the previous fusion. In such a case a normal
larva might result. On the other hand, with a quadri-
polar mitosis such a sorting would be almost impossible.
Boveri found that the facts accorded well with the hypothesis,
and hence concluded that the normal characters of the
larvee were dependent on the appropriate distribution of the
chromosomes.

The very remarkable results obtained from crossing
hybrids are also found to accord very well with the view
of the chromosomes regarded as persisting individuals,
although, of course, such results could be equally well
accounted for on the supposition that there exist other
physical entities to which the manifestation of specific or
individual characters could be ascribed, provided they could
be shown to persist and to be equally distributed in the same
way as we now know the chromosomes to be. But failing
their demonstration, we may reasonably admit the claims of
the chromosomes to represent the physical machinery to the
operation of which the manifestation of the characters in
question is to be ascribed.

We would, however, reiterate here the reservation made
by us already. We do not look on the chromosomes as
primordia of characters, but as agents, by the influence
of which on the rest of the protoplasm are incepted those
complex physical and chemical changes that culminate in the
production of the individual characters.

‘'oo many cases are now known to conform to the
Mendelian rules when hybrids of the first (and succeeding)
generations are interbred with each other for the results
to be a mere matter of chance; and they point strongly in
the direction of the existence of a structural, rather than a
purely dynamical, combination as responsible for the phe-
nomena in question.

Assuming the causes responsible for the characters or
groups of characters concerned to be resident in the chromo-

THE MALOTIC PHASE IN ANIMALS AND PLANTS. 55S

somes, it is clear that on the basis of the mode of reduction
maintained in this paper the Mendelian proportion of
D+2DR+R ought to follow, where D represents a
character (dominant) and R the correlative character (reces-
sive) derived from each parent respectively. It is further
obvious that such a result can only follow provided the
chromosomes of the one parent combine with those of
the other in such a way that each bivalent chromosome
of the heterotype prophase consists of somatic chromo-
somes derived from each of the two parents respectively.
For if such bivalent chromosomes are formed of pairs
derived from the same parent, then a simple analysis will
show that quite different relations will obtain, and that in
the case of the further hybrid offspring the D and R qualities
will not be present in equivalent proportions. The latter
case would, however, not affect the validity of the views here
advanced of the nature of reduction, but only the parental
origin of the constituents of each bivalent chromosome.!

Of course the simple Mendelian relation will only occur in
cases in which the chromosomes are distributed in the
average manner. Ifsome combinations are more favoured
than others, then the proportions will be correspondingly
disturbed. Similarly with the mosaic hybrids; these might
be due, as has been pointed out by others, to a preponderant
influence of certain chromosomes, or of combinations of each,
in certain parts of the organism. But we would suggest that
it might also be explained in another way. The chromosomes,
as we have been careful to point out, cannot be regarded as
the primordia of characters, but only as the agents that are
competent to produce serial changes in the protoplasm they
can influence. This implies that the substance on which they
work, or which they can “ activate,’ must also be reckoned
with. The recent work on regeneration clearly emphasises the
importance of the cytoplasm, which in this connection may
be compared with raw material,and it is certainly a factor by no
means destitute of significance. Ifthe raw material differs,

1 See footnote on p. 551.
VOL. 48, PART 4.—NEW SERIES. 40

554 J. BRETLAND FARMER AND J. BE. S. MOORE.

then the result cannot be expected to be identical, and in the
interaction of the chromosomes on the one hand, and the
cytoplasm on the other, we may perhaps find a clue to the
explanation of the sudden sports and other variations often
met with in hybrids. For these might seem at first sight to
be antagonistic to any form of explanation primarily applic-
able to the simpler Mendelian cases. But this aspect of the
matter is clearly a matter for experimental investigation, and
we have only introduced it in this place because we think
that the conclusions to be drawn from the behaviour of the
nuclei during the reduction divisions suggest that such ex-
periments would probably be fruitful in results.

We take this opportunity of expressing our sense of Pro-
fessor Ray Lankester’s kindness in discussing with us the
questions of terminology which have arisen in connection with
the subject of this memoir.

EXPLANATION OF PLATES 34—41.

{Hustrating Prof. J. Bretland Farmer’sand Mr. J. E.S. Moore’s
paper “On the Maiotic Phase (Reduction Divisions) in
Animals and Plants.”

The figures 1—38 inclusive refer to the divisions of the spore-mother-cells,
and all except Figs. 20, 21, 37, and 38 refer to the first (heterotype) mitosis.

The Figures 40—87 refer to the somatic, heterotype, and homotype mitoses
of Periplaneta Americana.

Figs. 1—21.—Lilium candidum.

Figs. 22—28.—Osmunda regalis.

Figs. 29, 30.—Psilotum triquetrum.

Figs. 31—38.—Aneura pinguis.

Fig. 89.—Diagrams illustrating various interpretations of the reduction
phenomena.

Figs. 40—52.—Periplaneta Americana, somatic mitosis.

Figs. 53—79.— 5 heterotype mitosis.

Figs. 80—87.— 5 homotype mitosis.

THE MATOTICe PHASE IN ANIMALS AND PLANTS. 5DD

Fie. 1.—Very early stage of prophase of first maiotic (heterotype) mitosis,
first appearance of chromatic fibrils.

Fie. 2.—Slightly later stage, first contraction figure.

Fic. 3.—The opening out of spirem after the first. contraction. The
beginning of longitudinal fission is shown.

Fie. 4.—Slightly later stage, longitudinal fission completed.

Fie. 5.—The divarication of the longitudinal halves of the spirem, The
second contraction figure is just commencing.

Fries. 6,7, 8, 9, 10.—Stages in the second contraction (synapsis). The
longitudinal fission still clear, but the thread as a whcle is contracting and
thickening.

Fre. 11.—Still later stage, showing the loops and parallel arrangement of
the spirem, with indications of the fission now almost obliterated.

Fries. 12, 13.—The chromosomes rapidly forming, indications (clear in one
of fission still apparent.

Fic. 14.—The congregation of the chromosomes just before the formation
of the equatorial plate.

Fie. 15.—The chromosomes on the equatorial plate, illustrating some of
the various shapes commonly present.

Fics. 16, 17.—Diaster (heterotype). ‘The chromosomes show the re-
appearance of the longitudinal fission. The variation depends on the modes
in which they are arranged on the spindle.

Fic. 18.—Late anaphase of diaster (polar view).

Fre. 19.—Telophase of heterotype.

Fic. 20.—Homotype diaster.

Fic. 21.—Homotype telophase.

Fic. 22.—Early spirem of Osmunda.

Fie. 23.—Late spirem, showing the longitudinal fission and the looping
of the spirem.

Fies. 24, 25.—Later stages, the clromosomes definitely isolated.

Fies. 26, 27.—The various forms assumed by the chromosomes during their
later differentiation.

Fre. 28.—The heterotype equatorial plate stage of Osmund a,

Fie. 29.—Psilotum, early stage in development of the heterotype chromo-
somes, after the spirem phase is over.

Fie. 30.—Psilotum, heterotype chromosomes corresponding to those of
Osmunda in fig. 27.

Fie. 31.—Aneura pinguis. Early prophase. In each of the cells shown
a centrosphere is figured.

556 J. BRETLAND FARMER AND J. E. ‘S. MOORE.

Fre. 32.—The spirem thread is split.

Fre. 33.—The chromosomes are delimited, longitudinal fission obvious in
some of them.

Fies. 34, 35.—Chromosomes contracting to their definite form. The
quadripolar achromatic figure visible in Figs. 31—35, especially in Fig. 34.

Fig. 36.—The equatorial plate stage.

Fie. 37.—The homotype mitosis, equatorial plate stage, one spindle in
profile, one in polar, view.

Fic. 38.—Anaphase of the homotype mitoses.

PERIPLANETA.

Fic. 40.—Resting pre-maiotic cell from the testis.

Fies, 41—44.—Early stages in the formation of the pre-maiotic chromo-
somes.

Fies. 45—48.—Still later stages in the formation of the pre-maiotic
chromosomes.

Fies. 49, 50.—Early stages in the formation of the pre-maiotice spindle
figure.

Fic. 51.—Cell in the “ equatorial plate” stage.

Fic. 52.—Cell showing the separation of the daughter chromosomes in an
ordinary pre-maiotic division.

Fic. 53.—Cell in a very early stage of the first maiotic (heterotype) pro-
phase.

Fic. 54.—Cell a little later, showing the polarisation of the chromatin, and
the first contraction of the chromatin from the nuclear wall.

Fic. 55.—A later stage in which both the polarisation and contraction is
more strongly marked.

Fic. 56.—A cell in which the chromatic loops characteristic of the hetero-
type division have become differentiated.

Fic. 57.—A later stage during the differentiation of the loops. In this cell
the contraction of the chromatin has about reached its maximum.

Fre. 58.—Cell in which the loops are beginning to open out again.

Fies. 59, 60.—Stages in this process.

Fras. 61—63.—Still later stages, in which the loops are still further opened
out to form the coarse spirem, and in which the longitudinal fission of the
thread-work is becoming visible.

Fics. 64—66.—Coarse spirem stages,

Fic. 67.—Later stage, in which the thread is again becoming polarised, and
in which the fission is well seen.

THE MAIOTIC PHASE IN ANIMALS AND PLAN'S. aay)

Fic. 68.—A cell in about the same stage as in fig. 67.

Fic. 69.—Cell in still later stage, where the second or ‘‘ synaptic contrac-
tion” is fully formed and the fission of the thread is no longer visible.

Fic. 70.—The same stage, another view.

Fic. 71.—A cell in which the loops are becoming still more thick and
contracted.

Fie. 72.—Cell showing the condition of the loops, at the time of the first
appearance of the heterotype spindle figure.

Fic. 73.—Cell in which the spindle figure has reached a later stage and in
which the loops which now constitute the heterotype chromosomes have
become separated. In one the original split is still, however, clearly visible.

Fie. 74.—Cell showing the manner in which the heterotype chromosomes
may be arranged in the equatorial plate stage.

Fig. 75.—A later view of the same.

Fie. 76.—Still later stage in the heterotype division.

Fie. 77.—Shlightly earlier stage with the heterotype loops spread out on the
spindle, aud their separating halves showing the longitudinal fission as they
divide.

Fic. 78.—Reconstruction of the nuclei after the heterotype division.

Fie. 79.—Later stages in the same.

Fig. §0.—Resting cell after the heterotype division and before the homo-
type.

Figs. $1—83.—Stages in the formation of the homotype chromosomes.

Fig. 84.—First appearance of the homotype spindle figure.

Fic. 85.—Kquatorial plate stage of the homotype division.

Figs. 86, 87.—Later stages of the homotype division.

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CHROMOSOMES OF TRADESCANTIA VIRGINIOA. 509

On the Structure and Development of the
Somatic and Heterotype Chromosomes
of Tradescantia Virginica.

By
J. B. Farmer, F.R.S., and Dorothy Shove.

With Plates 42 and 43.

THE object of this paper is to attempt to elucidate the
series of changes that occur during the evolution of the
chromosomes from the resting nucleus. We have expressly
excluded all matter relating to the formation of the spindle,
the cell wall, and other irrelevant structures from our account.

I. Somatic Mrroszs.

Tradescantia virginica has proved a more suitable
object for cytological study than might have been anticipated
from the known difficulties it presents in the way of good
fixation of the cell contents. This difficulty has been experi-
enced by others as well as by ourselves. ‘Thus Strasburger
has commented upon the tendency of the nuclear contents to
assume a condition during the prophase of the heterotype
mitosis that obscures all the finer details of structure.
We have found that Flemming’s strong solution and
Hermann’s fixative give fair results when allowed to act
for a long time, and the tissues are carefully washed and de-
hydrated afterwards. But on the whole the best material
was yielded after fixing with a mixture of absolute alcohol
and glacial acetic acid in the proportions of 2:1. he fixa-

560 J. B. FARMER AND D,. SHOVE.

tive was allowed to act for 15—20 minutes, and the tissues
were then thoroughly washed with absolute alcohol, and then
embedded as rapidly as possible by the usual methods.

We made a study of the cells of the root, in order to follow
out the changes in the divisions of vegetative tissues. For
this purpose plants were potted, and gently forced till they
provided a plentiful crop of young roots.

While the nucleus is the resting state the chromatin is
fairly evenly distributed throughout its substance, and there
is a large nucleolus, often excentrically situated. The first
signs of approaching mitosis is seen in a tendency on the part
of the chromatin to aggregate into broad band-like areas,
between which are left comparatively clear spaces. The
nucleolus becomes replaced by a number of denser nucleoli
which lie in close juxtaposition to the bands, though they are
not arranged in any very definite order.

The band-like agglomerations of chromatin, when they first
make their appearance, are not distributed throughout the
nucleus, but are commonly visible in one region, whilst they
fade away in another into the homogeneous granular arrange-
ment characteristic of the resting nucleus.

It is important to notice that when a band is cavetalle
examined the chromatin is seen to merely represent a closer
and denser granular aggregation.! It is only at a much later
stage that the spireme, with its single row of granules is
formed. ‘lhe contraction of the bands soon follows, and a
reticulum, as shown in figs. 2 and 2a, is the result. The
separate granules have now disappeared, and the chromatic
reticulum appears merely to be rather irregular in thickness,
and it readily takes the ordinary basic dyes. The next stage
is marked by the more definite appearance of aspireme. ‘I'his
seems to be formed by the gradual breaking down of the
original points of anastomosis, and the consequent restriction
of the chromatin to a linear arrangement.

It is excessively difficult to ascertain whether a continuous

1 Gregoire and Wygaerts (‘ Beihefte z, Bot. Centralbl.” xiv) have observed
similar arrangements in the roots of the plants examined by them.

CHROMOSOMES OF T'RADESCANTIA VIRGINICA. 561

filament is present. In many cases the evidence pointed
strongly in favour of the existence of free ends, but it was
not possible to make out any relation between them and the
number of chromosomes to be ultimately produced. At this
stage it was, however, clear that the arrangement of the
chromatin within the linin filament (or filaments) was of that
intermittent character to which the appearance of alternate
stainable and non-stainable discs is due.

Closely following on this stage the granules or discs of
chromatin can be sometimes made out to be double. We
look on this as an indication of that longitudinal fission of the
thread which only reaches its climax when the isolated
chromosomes are arranged on the equatorial plane of the
spindle—an event that happens long after the stage we are
now describing. The fission is not very easily seen, but it
can hardly be missed if looked for.

During the next phase the spireme undergoes a remarkable
polarisation. Loops are formed in such a way as to make
the “ pole field” (Rabl) strikingly obvious (fig. 8). Within
these loops the signs of longitudinal fission can sometimes be
detected, though usually only with difficulty. The nucleoli
at this stage are easily recognised as scattered through the
region occupied by the polarised spireme thread, and we
think the relation almost irresistably compels one to associate
these bodies with the function of increasing the chromatin
within the linin filament.

The filamentous structure now can with certainty be
recognised as discontinuous (figs. 8—10), and a number of
separate loops are readily distinguished. It is, however, not
easy to determine whether their number is identical with that
of the chromosomes, though this seems sometimes to be the
case. The double arrangement of the chromatic beads in
parallel series (indicating fission) was often observed at this
stage (fig. 11).

The chromosomes now become capable of identification,
and though, as we have said, we do not feel able to speak
positively as to whether they have always been separated,

562 J. B. FARMER AND D. SHOVE.

there can exist no doubt of the fact during this part of the
prophase (figs. 12—14). Careful examination of the free
ends will often indicate that each chromosome is really split,
and this becomes very clear as the equatorial plate stage is
reached (fig. 15).

The diaster is formed in the well-known fashion, by the
separation of the longitudinal halves of the individual
chromosomes and their distribution to the appropriate pole.
During the anaphase irregularities are often encountered.
Some chromosomes often seem to get away from the main
groups, as shown in figs. 17 and 18.

When the number of the chromosomes of these nuclei is
estimated one soon comes to realise that it is not constant.
There can be no doubt whatever on this point, and, as it is
of some interest, we may state we paid special attention to it,
and made a very large series of drawings and countings of
those examples that admitted of a reliable estimate being
arrived at. ‘lhe number varies from about twenty-six to
thirty-three. ‘lhe last was the highest number observed.
As regards the lower numbers, we confined ourselves to those
cases in which the razor had not touched the nuclei, in order
to exclude the possibility of accidental removal of any of the
chromosomes.

As the anaphase and telophase supervene, the chromosomes
pass through the reverse series of changes already observed
during the prophase. The vesiculation, long ago noticed by
van Beneden, and since then confirmed by numerous obser-
vers, is strikingly shown in these Tradescantia nuclei. The
chromosomes become thicker, and finally the chromatin is
seen to be distributed as a cloud of fine granules through the
linin band. At the same time the nucleoli are regenerated,
and it is a significant fact that they always appear in the first
instance in close connection with the chromatic bands, and
they are much more numerous than during the later stages
of telophase. This diminution in number is clearly effected
by fusion or running together of the previously discrete
nucleolar masses. ‘lhe clear area that surrounds each

CHROMOSOMES OF TRADESCANTIA VIRGINICA. 563

nucleolus in fixed preparations indicates a precipitation of
the coagulable constituents which during life probably were
of a fluid or viscous consistence. Hence, when the solidified
matter is thrown down, the light aureole represents the fluid,
non-precipitable remainder. Slowly the bands of linin, which
contain the chromatin, continue to swell up till their apparent
individuality is lost, as the equal spacing of the stainable
substance necessarily obliterates the criteria of boundaries.
But it does not follow that this obliteration extends to the
real morphological, and still less to the physiological, limi-
tations.

Il. Tan Hererotyre Mirosis.

The cells of the sporogenous tissue in the anther, just before
they enter upon the two final (maiotic') mitoses by which the
pollen grains will be formed, are bound together into a compact
tissue. ‘lhe nuclei of the cells are large, but they do not
exhibit that even distribution of chromatin which is often
met with in other cells. ‘lhe nucleus when carefully examined
is seen to contain fibrils of chromatic linin. Sometimes
(fig. 26) these are so arranged as to simulate more granular
arrangement, but closer inspection shows the case to be
otherwise. It is quite certain that during these early stages
of prophase there is no continuous spireme present. ‘lhe
ends of the stainable threads can be clearly recognised. On
the other hand, there is nothing recalling that differentiatiou
into broad chromatic bands which forms so characteristic
a feature of the ordinary somatic prophase. It is not clear
that one is justified in laying too much stress on this
difference. It may depend on accidental circumstances,
such, for example, as the length of time that elapses between
the telophase of one mitosis and the prophase of the next.

Soon the fibrillar structure becomes more dense, and the
separate fibrils cannot with certainty be any longer identified.

* See Farmer and Moore “On the Maiotic Phase (Reduction Divisions) in
Animals and Plants,” ‘Q. J. M.S.,’ 1904.

564 J. B. FARMER AND D. SHOVE.

If they are really present they must increase greatly in
length, or else the coiling of the filaments now proceeding
must be attended by end-to-end fusion (fig. 7).

During the prophase of this mitosis two ‘contraction ”
figures may be recognised ; the first, appearing as the fibrillar
arrangement, seems to give way to a more filamentous
structure. Possibly the two circumstances may be in some
way related, but at any rate after the contraction passes
away the chromatin appears as a much coiled filament, while
there is a clear alternation of stainable and non-stainable
discs, as noted long ago by Strasburger and others. The
stainable (chromatic) discs divide in such a manner as to
bring about the fission of the thread, though the two halves
do not, during prophase, divaricate much from each other.

A second point is easily established with respect to the
filament after the first contraction is over; the coils, into
which it is thrown, become very strongly polarised. Indeed,
the effect is nearly as striking as in the case of animals
(figs. 30—34). The loops thus formed and spread out can
be easily examined, and they are clearly seen to be split
longitudinally. This early longitudinal fission is of some
importance, because it has often been regarded as diagnostic
of the heterotype mitosis, but, as we have already seen it to
be present during the earlier stages of the somatic division,
it is obvious that this criterion, as a means of diagnosis,
breaks down.

The polarisation of the spireme is also common to the
heterotype and the somatic mitoses, but it does not seem
possible to correlate the number of loops of the spireme with
the final number of chromosomes to be produced. ‘The
polarised appearance, during which the spireme folds lie so
regularly arranged within the nuclear wall, is, however, a
transient phase. A second contraction of the thread follows
it, and results in the balling together of the filament to one
end of the nucleus, usually around the nucleolus. Whilst in
this state (figs. 34 and 35) the longitudinal fission can still
be seen, though it is becoming for the most part obliterated

QHROMOSOMES OF TRADESCANTIA VIRGINICA. 565

owing to the re-fusion of the two halves into which the
filament had commenced to split.

A considerable increase in thickness of the thread now
occurs, and as the coils once more loosen the number of
chromosomes that will be ultimately produced can be deter-
mined. The isolated lengths of the filament are partly bent,
each limb showing a tendency to coil round the other, or two
quite separate rods lie in close approximation. There is no
doubt whatever that the paired structures thus lying in juxta-
position have been formed from different lengths of the
spireme, and not by the shortening of the longitudinally-
divided halves of single lengths. The cases in which they
can be recognised as being formed from one loop, the sides of
which have become closely adjacent to each other, coupled
with the fact that the fission can still be recognised in each
limb, sufficiently indicates the mode of origin of the parts of
which the heterotype chromosome are made up, and shows
that each is really a bivalent structure. But when the evi-
dence of number is taken, it is less satisfactory than in most
other cases. There is no doubt but that in this plant the
number of the chromosomes is not constant during the
heterotype division, and it certainly varies between twelve
and sixteen; possibly the common failure of the plant to set
seed may be related to this irregularity.

As the chromosomes advance towards maturity they
separate from each other, and it is possible to observe other
forms in addition to those just described that support the
views here advocated as to their bivalent character. Fig. 39
shows a case, not very uncommon, in which the lowest
chromosome is clearly not composed of parallel sides at all,
but its components are adherent end-to-end, and showing this
by the thin zone where they are attached together. This
figure explains the presence of the long rod-like chromosomes
that are sometimes seen on the spindle; such forms always
ultimately divide across the middle zone (cf. fig. 44).

The majority of the chromosomes assume the form of oval
closed rings, but they become so thickened as they congregate

566 J. B. FARMER AND D. SHOVE.

at the equatorial plane of the spindle that their real form is
not easy to discern. At this period all trace of the longi-
tudinal fission is obliterated—at least we have never been
able to recognise it with certainty, even in the best pre-
parations.

The chromosomes next enter on the stage of the diaster.
The ring-like ones sometimes break across the middle, leaving
two half rings to travel to each pole. Often only one of two
sides breaks at first, and then this frequently becomes almost
straightened out, as though it were being forcibly pulled to
the pole. There are many differences in the exact mode of
division pursued, as might have been anticipated when dealing
with viscous structures, but in principle the result is invari-
ably the same. The chromosome, as representing a continuous
length of the spireme, breaks transversely, and so different
entire segments of the spireme are distributed between the
two daughter nuclei.

Immediately after the separation of the daughter chromo-
somes from each other, they undergo a change which admits
of the reappearance of the longitudinal fission. This was
figured and described by Strasburger’ some years ago, and
we are quite in agreement with his statement of the facts
(see our figs. 45—48). This peculiar occurrence has been
several times observed in various animals, but its significance
was not, until recently, properly appreciated. It is also of
wider occurrence in plants than is often supposed.

A remarkable irregularity, similar to that described by
Juel2 for Hemerocallis, has been found by us? to occur in
Tradescantia. This irregularity consists in the frequent
omission of some of the chromosomes to reach the daughter
nuclei with the rest of their fellows. Consequently they get
left out in the cytoplasm when the two daughter nuclei

1 Strasburger, “ Reductions Theilung,’ etc., ‘ Histologische Beitrage,’ vi,
p. 51.

2 Juel, ‘ Pringsheim’s Jahrb. wiss. Bot.,’ Bd. 92.

3 Prof. Marcus Hartog has also observed the phenomenon in question, and
kindly communicated his results to us,

CHROMOSOMES OF TRADESCANTIA VIRGINICA. 567

become reconstituted. Sometimes they are found in the
equatorial zone, but often they lie near the cell periphery or
even in the cytoplasm, They do not appear, however, to
give rise to small pollen grains, at least as a rule, but perhaps
in most cases they degenerate.

In one example it was clear that the chromatic fragment
thus left in the cytoplasm originated as a detached fragment
of a chromosome.

ITI. Homoryrer Mtrosts.

After the telophase of the heterotype division the nuclei do
not revert to a resting condition. The chromosomes cannot,
however, be identified as separate structures. They swell,
and undergo those regressive changes that if completed would
bring about the resting condition. Here and there signs of
a double or parallel arrangement of chromatin granules sug-
gests a persistence of the longitudinal fission. Then the
mitotic activity is again resumed, the chromatic thread-work
shortens and contracts, and the chromosomes themselves be-
come easily recognised, although it is difficult and generally
impossible to distinguish any signs of longitudinal fission at
this stage. They are thinner and longer structures than
those met with in the prophase of the former division, and
they exhibit curious varicosities over their entire length.
Finally, when they are arranged upon the spindle they adopt
the same form of grouping as that characteristic of somatic
cells. As in the latter the longitudinal fission now becomes
unmistakeable, and the two halves are then separated and
distributed to the two daughter nuclei.

It thus becomes evident that the essential phases in the
heterotype mitosis whereby reduction by a sorting out of entire
chromosomes is effected, are to be regarded as an intercalated
series of events breaking the ordinary rhythmical sequences.
The longitudinal fission begins during the prophase of the
heterotype mitosis, but its natural outcome is postponed
whilst the train of events runs off on a loop-line, the track

568 J. B. FARMER AND D. SHOVE.

being once more rejoined after the true reduction has been
effected. The normal process is again resumed at the spot
where the divergence first occurred, and the longitudinal
fission achieves its logical result in the equatorial plate of
the homotype division.

EXPLANATION OF PLATES 42 & 48,

Illustrating Prof. J. B. Farmer’s and Miss D. Shove’s
paper “On the Structure and Development of the
Somatic and Heterotype Chromosomes of Trades-
cantia Virginica.”

Somatic Divisions.
Fie. 1.—Resting nucleus, chromatin evenly distributed.
Fic. 2.—Nucleus showing definite strands of linin with chromatin granules.
Fre. 3.—Linin strands undergoing contraction.
Fic. 24.—Nucleus showing reticulate structures.

Fic. 34.—Breaking down of reticulum, with shortening and thickening of
the strands.

Fic. 4.—Chromatin granules arranged in single rows in the linin strands,
and strands in form of spireme.

Fis. 5, 6.—The linin strand further contracted.

Fic. 7.—A transition from above stages to the well-marked polarisation
figure.

Fics. 8, 9.—Complete polarisation of loops of spireme strand, each loop
representing a complete chrosome.

Fie. 10.—The loops have lost their polarisation, and are undergoing con-
traction. The nucleolus has lost the greater part of its stainable substance
when this stage is reached.

Fig. 11.—Longitudinal fission clearly marked by the arrangement of
chromatin in two parallel rows of granules.

Fre. 12.—Further contraction, which shows individual chromosomes lying
at periphery of nucleus; longitudinal fission can be seen.

Fre. 13.—The chromosomes are scattered over the largest area they cover
during their life history.

Fie. 13a.—Ditto.
Fres. 14, 15.—Formation of the equatorial plate.
Fic. 16.—Equatorial plate.

CHROMOSOMES OF TRADESCANTIA VIRGINICA. 569

Figs. 17, 18.—Diasters.

Fie. 19.—The swelling up of the chromosomes at the poles, and formation
of the cell plate.

Fries. 20, 21.—Later stage in swelling up of chromosomes, and the forma-
tion of nucleoli.

Fic. 22.—Two daughter nuclei in a resting condition.

Reduction Divisions (Maiotic Phase).

Fie. 23—Resting nucleus of pollen mother cell.

Fries. 24, 25.—Fibrillar arrangement of chromatin; early prophase.

Fre. 26.—Fibrillar arrangement evenly distributed.

Fies. 27—29.—First contraction figure.

Fries. 30—33.—The stages following on the contraction figure and effecting
a polarisation of the spireme. Longitudinal fission to be seen.

Fie. 34.—Commencement of the second (synaptic) contraction.

Fies. 35, 36.—Further stages in the synapsis. The longitudinal fission
clear in Fig. 35.

Fic. 37.—Loosening of the synaptic contraction.

Fics. 38—42.—Stages in the evolution of the chromosomes.

Fies. 43—45.—TIllustrate the common types of chromosomes seen during
the diaster.

Fries. 46—48.—The groups of daughter chromosomes showing the reopening
of the longitudinal fission.

Fics. 49—53.—Various figures showing extra-nuclear chromosomes left
behind at the reconstitution of the daughter nuclei.

Fie. 55.—Nucleus preparing for homotype mitosis.

Fries. 56—58.—Stages in the homotype mitosis. In Fig. 56 one pair of
nuclei are seen in profile, and the other in polar view.

vol. 48, PART 4,—NEW SERIES, 4]

bain — 2)

-
-

SPERMATOGENESIS OF PERIPLANETA AMERICANA, 9571

On the Behaviour of the Nucleolus in the Sper-
matogenesis of Periplaneta Americana.

By
J. E. S. Moore, A.R.C.S8., F.L.S.,
and

L. E. Robinson, A.R.C.S.,
From the Biological Laboratory, Royal College of Science, London.

With Plates 44 and 45.

THE present communication has arisen as a by-product of
the work upon the reduction processes in animals and plants,
upon which the authors have for some time past been
engaged.

Only a few cytologists have paid particular attention to
the nucleolus, although this structure appears to be constantly
present in both the male and female reproductive cells.

The great majority of writers on the subject of spermato-
genesis figure the nucleolus in their drawings, but refrain
from giving any definite account of its behaviour throughout
the whole period of the maturation of the reproductive
cells.

In recent years, however, the behaviour of this body has
arrested the attention of a small band of cytologists on
account of the part it may possibly play in some of the
hitherto unexplained functions of the male reproductive
element.

Henking appears to have been the first investigator to
describe changes in the nucleolus of the reproductive cell in

ay he J. E. S. MOORE AND L. E. ROBINSON.

his work on Pyrrhocoris (‘Z. wiss. Zool.,’ Bd. li, 1890), which
led to its consideration as a modified chromosome, endowed
with special functions, distinct from those of the normal
chromosomes of the cell. Since Henking published this
work, a few investigators have devoted their attention
particularly to this subject, describing the nucleolus as an
“accessory chromosome,’ and attempting to connect its
function with such interesting problems as “ determination
of sex” and “‘ heredity.”

In the male reproductive cell of Periplaneta americana
the nucleolus is conspicuous in almost all phases of the
spermatogenesis, and consequently its actual changes can
be studied without any great difficulty.

(I) The Premaiotic (Somatic) Divisions.—Through-
out the somatic divisions, from the resting phase up to the
complete differentiation of the chromosomes, the nucleolus
is prominent as a large chromatic structure occupying a
position inside the nuclear membrane. In the resting
somatic cells the nuclei are large and oval in shape, and,
on account of the small quantity of chromatin present, pale
(fig. 1). The nucleolus (nc.’) arises as an indefinite cloudy
mass suspended in the linin reticulum. At first it stains
very feebly, but rapidly becoming denser, finally retains the
ordinary chromatin stains very powerfully (fig.2). It always
assumes a more or less spherical shape, and by the time that
the nucleus exhibits the aggregation of chromatin granules
in the angles of the linin reticulum (fig. 2), the nucleolus is
by far the most conspicuous object in the cell.

In its early condition the nucleolus is usually irregular and
ill-defined in outline, often somewhat stellate, the angular
processes merging insensibly into the general linin reticulum.

Its structure at first is not homogeneous, there being fre-
quently enclosed masses which stain more deeply than the
general mass (fig. 1). As the chromatin granules increase in
quantity the nucleolus becomes denser, staining more deeply,
and finally reaching a stage in which it is as chromatic as a
fully-formed chromosome, ‘he outline of the nucleolus loses

SPERMATOGENESIS OF PERIPLANETA AMERICANA. 9573

its indefinite nature and becomes rounded off, and is readily
distinguishable from the knot-like masses of chromatin
usually termed karyosomes, but often described as a form of
nucleoli. These bodies have nothing whatever to do with
the nucleolus which is being described ; they are collections
of chromatic substance which are utilised, finally, in the
formation of the chromosomes. ‘The aggregations of
chromatin rapidly assume the appearance of definite patches
on the periphery of the nucleus (fig. 3), each patch being the
early representative of a chromosome. Almost at the com-
mencement of aggregation of the chromatin, it is seen that
each patch is divided, this division being the line of separa-
tion of the halves of the chromosome on the spindle. When
this stage is reached the linin reticulum begins to break
down, and a considerable amount of linin substance collects
in a mass round the nucleolus (figs. 3 and 4).

Delicate strands of linin continue to extend between the
chromosomes, affording them support, until the appearance
of the spindle. ‘lhe chromosomes become denser and more
sharply defined, and ultimately the extremities of each half
are recurved, giving the divided chromosome the appearance
of a tetrad (figs. 4—6).

As this condition is reached, owing to the size and
density of the chromosomes, the nucleolus often becomes
obscured, but its presence within the nucleus can be verified
in a complete cell by counting the chromatic bodies within
the nucleus. ‘lhe number of chromosomes in the premaiotic
division in P. americana is thirty-two, but at this stage
thirty-three chromatic bodies may be counted within the
nuclear membrane, one of these being the nucleolus.

The archoplasm (fig. 4, a.) at this time is differentiated as
a dense cloudy mass of cytoplasm lying close to the nuclear
membrane. Radiating striations soon appear in the archo-
plasmic mass, and the nuclear membrane, first becoming in-
definite, finally disappears.

The radiating strize now extend over the chromosomes
which become massed together in the nuclear space, and the

574 J. HE. S. MOORE AND L. EH. ROBINSON.

nucleolus now undergoes fragmentation, the fragments being
rapidly passed out towards the cytoplasm (fig. 5, f. ne.’).

The somatic spindle develops rapidly, and during the
separation of the chromosomes on the equator of the spindle
(fig. 6), the fragments of the nucleolus are seen to be under-
going rapid degeneration in the cytoplasin.

At the time of the appearance of a membrane between the
two daughter cells, these fragments have, as a general] rule,
become indistinguishable.

The Second Maiotic (Heterotype) Divisions.—The
nucleolus present in the nucleus of the spermatocyte is
differentiated very soon after the immediately preceding
somatic division, probably at the time of the reconstruction
of the nucleus. It arises de novo, and not from the remains
of the nucleolus present in the previous generation of cells.

The resting condition of the nucleus preceding the hetero-
type division differs markedly from the corresponding stage
in the spermatogonium. This nucleus (fig. 7) is larger and
usually spherical. The karyoplasm is more regular, consisting
of a rather fine reticulum of linin, in which numerous small
karyosomes (k.’) appear.

The nucleolus, a prominent, highly chromatic body (nc.”),
lies in contact with the nuclear membrane, and _ usually
exhibits a bifid condition, which gradually disappears.

A large mass of dense cytoplasm, the archoplasm (a.),
becomes visible, lying close to the nucleus, and the appear-
ance of this structure is the signal for the commencement of
the remarkable series of changes about to take place in the
arrangement of the nuclear contents, in connection with the
phenemenon of reduction.

The whole nucleus becomes more chromatic, the increased
deposition of chromatin granules rendering the linin reti-
culum sharp and distinct (fig. 8). Almost immediately the
nuclear contents become polarised in the direction of an
axis, passing through the archoplasm and the centre of the
nucleus. ‘he linin threads lying in the direction perpen-
dicular to this axis rapidly break down, leaving a number of

SPERMATOGENISIS OF PERIPLANETA AMERICANA. 575

meridional bands of linin which are densely infiltrated with
chromatin granules (fig. 9).

This alteration in the disposition of the chromatin also
affects the nucleolus. This body, being supported in the
linin substance, becomes pulled out, at the time of the
polarisation of the reticulum, into an elongated pear-shape
(fig. 9). The elongated nucleolus at this stage often comes
to lie in contact with one of the chromatic bands, and, as
these bands shorten and thicken in the contraction of the
nuclear contents, the nucleolus often closely simulates the latter
in appearance (fig. 10). Shortly after the appearance of
polarity, the nuclear contents contract away from the nuclear
membrane, which becomes ill-defined, and it is then seen
that the chromatin is arranged in a system of loops, sixteen
in number, whose tapering, free extremities are gathered
together at that portion of the periphery of the nucleus
adjacent to the archoplasm (figs. 10, 11). This constitutes
the first synaptic contraction of the heterotype prophase.

As the loops of chromatin contract the nucleolus also
becomes shorter and thicker, the extremity remote from the
archoplasm assuming the appearance of a dense blot on the
surface of the nucleus (fig. 11). The loops of chromatin now
begin to lengthen out so as to extend over the periphery of
the nuclear space, and this takes place to such an extent
that the appearance of polarity is lost. During this latter
phase the long attenuated “ tail” of the nucleolus is retracted,
and the nucleolus assumes a spherical form, and apparently
lies freely suspended in the nuclear sap among the skein-like
mass of chromatin bands (fig. 12).

It remains quiescent in this condition throughout the
following heterotype prophases, until the chromatic loops
again contract towards the nuclear membrane at the point
adjacent to the archoplasm (fig. 14). The nucleolus then
undergoes fragmentation, giving rise to a number of small,
highly-refractive, chromatic bodies, lying entangled in the
bunch of contracted loops.

The heterotype spindle appears about this time as a

576 J. E. S. MOORE AND L. BE. ROBINSON.

radiating striation, extending out from the archoplasm over
the nuclear contents. ‘The centrosomes rapidly move apart,
and the chromatic loops fall asunder. ‘he free ends of each
of the loops are now seen to have fused together, giving rise
to the typical heterotype ring chromosomes (fig. 15).

The fragments of the nucleolus, which have usually been
imprisoned in the cluster of loops, are now liberated, and, as
the spindle rapidly develops, they pass to the periphery of
the nucleus, and are finally thrown out into the cytoplasm.

‘hese fragments persist for some time, being visible after
the homotype division has taken place as a number of small
spherical masses of chromatic substance in the cytoplasm.
They finally degenerate and undergo absorption (figs. 16—
18).

The Second Maiotic (Homotype) Division.—Imme-
diately after the completion of the heterotype division, the
nuclei of the daughter cells do not enter a complete resting
stage, the formation of the chromosomes proceeding almost
immediately. ‘The chromosomes appear as small angular
masses, united by strands of linin, which are studded with
granules of chromatin (fig. 19). ‘'he chromatin present in
the linin strands gradually disappears as the chromosomes
mature, being used up in this maturation process.

The chromosomes do not all develop at the same rate ; 16
is usual to find perfectly-formed chromosomes in the same
nucleus in company with the rudimentary angular masses
(fig. 20). ‘he homotype chromosomes lke the somatic,
exhibit a dual nature almost from the time of their ditferen-
tiation, and, when mature, are very similar in appearance to
those of the somatic nucleus. ‘l'hey consist of short, curved,
thick rods, the swollen, free extremities of which give rise to
an appearance of tetrads arranged on the periphery of the
nucleus (figs. 20—22). ‘lhe spindle appears at this time (tig.
22), and as the chromosomes pass on to the spindle they
shorten up in such a manner as to completely lose their
original tetrad appearance (fig. 23). ‘They now appear on the
equator of the spindle, in the divided condition, each as a

SPERMATOGENESIS OF PERIPLANETA AMERICANA. 577

pair of rounded masses. As the two parts separate and move
to opposite poles of the spindle, a strand of their substance
remains as a connecting link for some time, giving them the
appearance of a number of dumb-bells (fig. 24).

‘Throughout the homotype prophase no structure resembling
a nucleolus has appeared in the nucleus, but the remains ot
the heterotype nucleolus still persist in the cytoplasm (figs.
19—2d).

‘he reconstructed nuclei of the daughter cells, produced
by the homotype division, present at first a dense, highly-
chromatic appearance. An intermediate body (cf. Flemming)
persists for some time, attached to which are the collapsed
remnants of the spindle, and these finally separate and form
an elliptical or rounded mass of dense cloudy cytoplasm, the
nebankern, a structure which probably takes part in the con-
struction of the cephalic vesicle, and the tail of the sperma-
tozoon (figs, 20—27).

The outer system of the homotype spindle-elements, as
described by one of us in Klasmobranchs, is also often per-
ceptible (fig. 26).

The Spermatid.—tThe nucleus of the daughter cell or
spermatid rapidly loses its dense appearance (fig. 27), the
chromatin gradually breaking down, and, as this proceeds, a
well-defined, spherical, chromatic body becomes visible in the
nucleus. It is smaller in size than either of the previously
described nucleoli, in proportion to the reduced size of the
nucleus in the spermatid.

The nuclear contents, at this stage, consist of a coarse
reticulum of linin (fig. 28), suspended in which are the
rapidly-disappearing, rounded masses of chromatin. At this
stage the chromatic body or nucleolus of the spermatid (n.’”,
figs. 28—31) is seen to lie in contact with the nuclear mem-
brane, forming a very conspicuous object in the nucleus.

The coarse reticulum gradually breaks down into a finer
structure, still supporting afew minute granules of chromatin.
The nucleolus now undergoes fissure (fig. 31), one half remains

578 J. E. S. MOORE AND I. HE. ROBINSON.
in contact with the nuclear membrane, the other passes
inwards to the middle of the nucleus (fig. 32).

The cytoplasm, at this stage, contains a well-marked
nebenkern, but the remnants of the heterotype nucleolus are
by this time so altered as to be invisible.

The portion of the spermatid nucleolus which is still in
contact with the nuclear membrane now passes through, and
is extruded into the cytoplasm, where it appears as a rounded,
highly chromatic mass (fig. 33), and is subsequently lost sight
of in the liquor seminis.

The other portion of the nucleolus remains at the centre of
the nucleus, and undergoes a slow process of degeneration,
staining more and more feebly until it is finally lost sight of.
The extra-nuclear portion of the nucleolus sometimes under-
goes further fragmentation in the cytoplasm (fig. 34), but
such fragments can be readily distinguished from the pale,
degenerated fragments of the heterotype nucleolus, which
may still be visible.

Before this stage is reached the centrosomes have not been
recognised. They probably he in contact with the nuclear
membrane throughout the early phases of the metamorphosis
of the spermatozoon, and, owing to the nature of the nucleus,
this would explain the fact of their invisibility.

The formation of the cephalic vesicle, the axial filament,
aud the tail of the spermatozoon, and the behaviour of the
nebenkern in connection with these processes are not yet
sufficiently elucidated, and will possibly form the subject of a
future communication.

‘he cytoplasm of the spermatid, which is not utilised in the
formation of the spermatozoon, does not collect as a residual
corpuscle in this insect, but undergoes a process of mucoid
degeneration in situ. The extra-nuclear portion of the
nucleolus is not affected by these degenerative changes of its
surroundings, and large numbers of these chromatic bodies,
derived from the different spermatids, may be seen among
clusters of ripe spermatozoa in a ripe tubule of the testis
floating in the liquor seminis.

SPERMATOGENESIS OF PERIPLANETA AMERICANA. 579

The degeneration of the cytoplasm takes place before the
spermatozoa can mature, and these pass through their final
metamorphoses suspended in dense masses in the grumous
liquid derived from the degenerated cytoplasm.

Conclusion.—As will have been seen from the preceding
description, the behaviour of the nucleolus in the different
stages of spermatogenesis of P. americana is distinctly
interesting on account of the wide difference in its behaviour
from that ascribed to similar structures by various authors in
other animals. We find it, in fact, frequently discussed as
an “accessory chromosome,” differing from the ordinary
chromosome both in structure and function.

In the somatic cell the nucleolus does not persist after the
appearance of the spindle, but undergoes fragmentation, and
is thrown out into the cytoplasm, where it undergoes
degeneration. This process occurs in each successive somatic
division, a nucleolus arising, de novo, in each of the daughter
nuclei resulting from such division.

The operations described by Sutton as occurring in
Brachystola (‘Kan. Univ. Quart.,’ vol. ix, No. 2, 1900), and
by Miss Wallace, in Spiders (‘ Anat. Anz.,’ Bd. xviii, Nos. 13
and 14), do not occur in the typical insect we have studied.

The nucleolus of the heterotype cell is not derived from
that of the immediately preceding somatic cell, but arises
anew in the earliest condition of the heterotype stage.

But in such cells essentially the same phenomena are
repeated. ‘he alteration in form of the nucleolus, in this
case, appears to be due solely to the mechanical influences
brought to bear upon an elastic structure enclosed in a
nucleus, the contents of which are in a state of strain.
Immediately this strain is relieved the nucleolus returns to
its original spherical condition. With regard to the bifid
condition of the nucleolus of the heterotype cell in its early
stages, this is probably only an early manifestation of a
tendency to division, such as occurs in the spermatid,
analogous to the futile development of a flagellum in the

580 J. E. S. MOORE AND L. E. ROBINSON.

homotyle cell in Klasmobranchs as already described by one
of us (‘Quart. Journ. Micr. Sci.,’ vol. xlvi).

As was the case in the somatic period, the nucleolus of the
heterotype cell undergoes fragmentation prior to the division
of the cell, and being extruded from the nucleus, undergoes
degeneration in the cytoplasm.

This nucleolus is undoubtedly the homologue of the struc-
ture described by McClung as the “ accessory chromosome ”
(‘ Zool. Bull.,’ vol. 11, 1899); by Montgomery in “ Pentatoma,”
(‘Zool. Jahrb.,’ Bd. xi) ; and by Paulmier, in “ Anasa ‘lristis”
(‘Journ. Morph.,’ supplement to vol. xv, 1899).

Toyama, in his investigations on Bombyx, and other
Lepidoptera (‘ Bull. Coll. Agric., Imp. Univ. Japan,’ vol. ii),
describes the presence of two nucleoli in the heterotype
nucleus, both of which are cast out into the cytoplasm to
undergo degenerative changes. Platrus, in his work on
Lepidoptera (‘ Internat. Monatschr. fiir Anat. med. Physiol.,’
vol. 111), gives nothing very definite in his description of the
nucleolus, but evidently noticed nothing approaching the
behaviour of a chromosome in these structures.

In his researches upon Caloptinin femur rubrum and
Cicada tibicen (‘ Bull. Imus. Comp. Zool., Harvard Univ.,’
vols. xxvii, xxix, 1895, 1896), Wilson describes the reaction to
stains of the different nuclear elements. He found that
under certain conditions the nucleoli stain differently to the
chromosomes. He also noticed that in Cicada the nucleoli
in the heretotype all underwent fission, and were finally
extruded. In the present case material was used which
had been fixed by various methods,—by I'lemming’s uid,
Hemann’s fluid, corrosive acetic, Rabb’s method, and van
Rath. It was stained either by Flemming’s triple method or
Heidenhain’s iron hematoxylin, counterstained with Orange
G, but in all cases the nucleolus was stained in the same
manner as the chromatin.

‘he nucleolus of the spermatid appears to be differentiated
directly from the chromatin of the reconstructed daughter
nucleus immediately after the homotype division, and the most
feasible explanation oi the process which follows is, that it is

SPERMATOGENESIS OF PERIPLANETA AMERICANA. 581

carried out in order to get rid of a portion of the chromatin
in the spermatid.

The extra-nuclear chromatic body has often been figured,
but less frequently described. Hermann describes a chro-
matic structure in the spermatid, which is probably the
homologue of the one under consideration (‘ Arch. f. Mier.
Anat., Bd. xxxiv). One of us, during investigations on
mammalian spermatogenesis, have described the nuclear
origin of the extra-nuclear body in the spermatid of the rat
(Internat. Monatschr. f. Anat. u. Physiol, Bd. xi, 1894).
But until more is known of the behaviour of the nucleolus in
the late phases of both spermatogenesis and oogenesis, in
different types, all attempts to draw theoretical conclusions on
the function of this body, and the part it plays in the
problems referred to in the introductory portion of this
communication, must be of little value.

EXPLANATION OF PLATES 44 & 45,

Iustrating Mr. J. E. 8. Moore’s and Mr. L. E. Robinson’s
paper “On the Behaviour of the Nucleolus in the
Spermatogenesis of Periplaneta americana.”

All the figures were drawn under Zeiss’ 2 mm. Apochromatic Immersion,
1:40 n. a., with No. 18 ocular.

ac.’ =nucleolus of somatic division. zc.’ =nucleolus of heterotype division.
a.=archoplasm. 4.=karyosomes. /f.ne.’, f. nc." = fragments of the nucleolus
in the somatic and hetereotype divisions respectively. xc.'’ = nucleolus of
spermatid. iz. xe.” = intra-nuclear portion of spermatid nucleolus. ex. ze.’”
= extra-nuclear portion of spermatid nucleolus. B. 7, = intermediate body
of Flemming. WV.= Nebenkern.

PLATE 44.

Fic. 1.—Somatic cell in resting condition, showing nucleolus in early state.

Fies. 2—4.—Somatic cells showing differentiation of chromosomes, with
condition of the nucleolus during the somatic prophase.

Fie. 5.—Somatic cell showing development of the spindle and extrusion of
the fragments of the nucleolus.

582 J. E. S. MOORE AND IL. I. ROBINSON.

Fre. 6,—Somatic cell with fully formed spindle. Fragments of the nucleolus
in the cytoplasm.

Figs. 7, 8.—Heterotype cells in early prophase. Nucleolus bifid.

Fic. 9.—Heterotype cell in which polarization has commenced. The
nucleus has undergone extrusion.

Fie. 10.—Heterotype cell in condition of synapsis. Loops contracting in
direction of archoplasm.

Fic. 11.—Heterotype cell in late synaptic phase. Nucleolus reassuming
spherical condition.

Fic. 12.—Heterotype cell in which the loops of chromatin are extruded
out on the periphery of the nucleus, the nucleolus lying free among the loops.

Fie. 13.—Heterotype cell. Later stage than Fig. 12.

Fie. 14.—Heterotype cell. The chromatic loops are contracting to form
the heterotype ring chromosomes.

Fic. 15.—Heterotype cell. Ring chromosomes separating. Spindle de-
veloping. Nucleolar fragments passing out into the cytoplasm. ;

Fic. 16.—Heterotype cell. Chromosomes dividing on the spindle. Nucle-
olar fragments in the cytoplasm.

Fic, 17.—Heterotype cell in stage of diastes.

Fic. 18.—Heterotype cell in stage of late diastes. A cell membrane has
appeared, dividing the cell into two daughter cells.

PLATE 45,

Fics. 19—21.—Homotype cells showing stages of differentiation of the
chromosomes. Fragments of heterotype nucleolus in the cytoplasm.

Fie. 22.—Homotype cell. Chromosomes going on to the spindle.

Fig. 23.—Homotype cell. Spindle with chromosomes on equator.

Fic. 24.—Homotype cell. Stage of diaster with dumb-bell-shaped chromo-
somes.

Fie. 25.—Homotype cell. Late diaster. Daughter cells separated, show-
ing Flemming’s intermediate body. Fragments of heterotype nucleolus in
the cytoplasm.

Fic. 26.—Homotype cell. Later stage than Fig. 25, showing reconstruc-
tion of the nuclei in the daughter cells.

Fic. 27.—Spermatid showing nebenkern. Chromatin breaking down.

Fic. 28.—Spermatid. The nucleolus is differentiated. Some fragments of
heterotype nucleus still visible in the cytoplasm.

Fic. 29.—Spermatid. Later stage than Fig. 28.

SPERMATOGENESIS OF PERIPLANETA AMERICANA. 588

Fic. 30.—Spermatid. Nucleolus lying in contact with nuclear membrane
prior to fission.

Fie. 31.—Spermatid. Nucleolus divided.

Fie. 32.—Spermatid. Nucleolus divided. Halves separating.

Fic. 33.—Spermatid. Nucleolus divided. The extra-nuclear portion has
just been extruded; intra-nuclear portion degenerating within the nucleus.

Fig. 34.—Spermatid. Nucleolus divided. The extra-nuclear portion has
undergone fragmentation in the cytoplasm. The intra-nuclear portion has
become almost invisible.

Fie. 35.—Spermatid. Extra-nuclear chromatic body well defined. The
intra-nuclear portion has vanished.

Fie. 36.—Spermatid. Showing extra-nuclear chromatic body in two
fragments.

oS tae nA™

ee er a, ia

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 585

On Some Movements and Reactions of Hydra.

By
George Wagner, M.A.,
Instructor in Zoology, University of Wisconsin.

Tis study of the movements and reactions of Hydra was
undertaken at the suggestion of Professor H. 8. Jennings,
whose own researches (?97—’02) on the reactions of protozoans
have added new interest to this line of work.

Trembley (1744) described the normal movements of Hydra
in considerable detail. lurther observations on the same
subject were made by Baker (1743), Résel von Rosenhof
(1755), Marshall (82), and Zoja (90). The works of Baker
and von Rosenhof have not been accessible tome. Wilson
(91) made a detailed study of phototaxis in Hydra, while
Pearl (01) investigated its behaviour toward the constant
electric current.

Normal Movements.—Trembley (|. c.) made a thorough
study of the movements of Hydra, and his description of them
is fairly complete. Hydra is usually attached by its foot to
some solid substratum, as a submerged stem or branch, or a
floating leat, less frequently to the surface film. When not
so attached it is helpless, for it has not the power of swimming.
When attached the body is usually moderately expanded,
seldom extremely so. In Hydra viridis the tentacles, also
moderately expanded, extend obliquely outward and forward,
forming the framework otf a sort of funnel with the hypostome
at the bottom. In Hydra fusca, and especially Hydra

vol. 48, PART 4.—NEW SERIES. 42

586 GEORGE WAGNER.

grisea, Where the tentacles have enormous capacity for
expansion, they sometimes hang down in great garlands into
the water, the individual tentacles often so thin that even
under a lens they are barely visible.

Even when undisturbed Hydra contracts at intervals. This
contraction is very sudden and rapid, while the expansion,
which almost immediately follows, is gradual and slow. The
contraction may involve both body and tentacles. It may, on
the other hand, be restricted to either body or tentacles, or
even to a single tentacle. The contraction occurs at much

Fie. la.—Positions occupied by Hydra after successive contractions.
For explanation see adjacent text.
more frequent intervals in Hydra viridis than in the other
forms; Hydra viridis is also in most other respects the
most active form.

On closely observing Hydra viridis for a period of from
three to four hours it was observed that many of these con-
tractions were really not spontaneous, but due to slight
tremors produced by occurrences very easily overlooked.
Such were the slamming of a door in some remote part of the
laboratory, some person walking across the room on the floor
above, and so on. Nevertheless, there remain many coutrac-
tions which are evidently, as Marshall (l.c.) suggests, the
results of internal physiological changes. These may very
properly be termed spontaneous.

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 687

After each contraction Hydra soon expands again, but
toward a different direction from what it previously occupied
—a fact to which my attention was called by Professor
Jennings. Let us suppose that the Hydra was previously
standing with its long axis oblique to the substratum. If
now, for any reason, it contracts, it soon begins to expand
again, at first perpendicularly to the substratum, then the
body flexes more or less in a new direction, so that when
expansion is completed the head and tentacles are directed

into a region different from that which they occupied before.

As illustrated in Fig. la, when a represents the contracted
condition the Hydra may occupy, successively, positions B, A,
CG; A; Dy AG Ey ete:
It may be useful to give here a case from actual] observation.
A Hydra viridis was placed in a small dish under a dis-
secting microscope and left undisturbed for half an hour.

Then its

“spontaneous ” movements were recorded. Pre-

cautions were taken to prevent disturbance of the dish in any

manner. For the sake of brevity in writing the record the
plane of the microscope table was looked upon as a map.
Thus “north” means the side away from the observer,
“east” lies to his right, etc. A movement “upwards”
means a movement toward the surface of the water.

Here is a portion of a record made in this manner.

9.23:

oboe
9.27.
9.28.
“Oo.
9.35.

19.36.

9.38.

Hydra contracted. Expansion to south by west, then
west.

Contraction. Slight expansion to west. Contraction.

Expansion to north. Swaying to west.

Swaying to north-west.

Contraction. Expansion to south-east.

Partial contraction. Rest. Total contraction. HExpan-
sion to west, slightly north.

Contraction. Expansion to east, slightly south, and
strongly upward.

Contraction. Expansion to north-east.

And so forth for three hours.

588 GEORGE WAGNER.

The extended Hydra may also change the direction of its
long axis without a general contraction, by mere flexion of
the expanded body. Sometimes the change from one oblique
position to another is brought about by first swaying to the
vertical, and then to the new oblique position. Quite as often,
however, it occurs through circumnutation around the
attached foot. In this case there appears first a contraction
of the ectoderm on one side near the foot. This contraction
then travels towards the hypostome in slightly spiral form.
The Hydra, in this manner, slowly swings around, the body
curved into a complete loop or even beyond (Fig. 1).

It can be seen that by either of these methods Hydra
extends its body successively in many different directions in

—

Fie. 1—Hydra viridis changing position of body by a spiral
contraction near the foot.

a comparatively short space of time. It is thus enabled to
explore a relatively large space, and so greatly increase the
probability of its chances of capturing prey. Herein lies,
undoubtedly, the biological significance of the behaviour
described.

These intermittent spontaneous contractions and expansions
are much more frequent in Hydra viridis than in the other
species. Marshall (1. c.) is probably correct when he corre-
lates this fact with the shorter tentacles of Hydra viridis.
‘The other species have long thread-lke tentacles often ex-
tended toa length several times that of the body. By swaying
these to and fro they can explore a large territory without any
movement of the body, while in a quiet Hydra viridis the
tentacles have very little spread.

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 589

When one observes Hydra (again especially Hydra viridis)
for a longer time one is impressed with the fact that it can
and does move from place to place with considerable rapidity.
If a quantity of freshly collected Ceratophyllum is put into
an aquarium that is unequally illuminated, the Hydra present
will wander from the Ceratophyllum to the better lighted
wall of the aquarium often within twenty-four hours. As
Hydra cannot swim this involves a rather circuitous journey.
But even without such a directive stimulus its movements are
considerable. For example, a green Hydra was placed in a
glass dish, and this was set over asheet of ruled paper on the
laboratory table. ‘The lines of the paper were so numbered
that the position of the Hydra could, at any time, be charted
ona second piece of ruled paper similarly numbered. The
chart of the journeys of this Hydra is shown in Fig. 2. Al-
though the illumination was not entirely equal from all sides
yet it was not one-sided enough to influence the movements.
At all events the record shows no such effect.

Now, how are these movements brought about? The
method can easily be seen by placing a single Hydra in a
small dish and observing it under a dissecting microscope.
The body, expanded and with expanded tentacles, bends over
to one side. As soon as the tentacles touch the bottom they
attach themselves and contract. (Zykoff [’98] claims that this
attachment of the tentacles is by means of pseudopodia, but
during observations covering many months I have never seen
the formations he figures.) Now one of two things happens :
(1) The foot may loosen its hold on the bottom, and the body
contract. In this manner the animal comes to stand on its
tentacles with the foot pointing upward. The body now bends
over again until the foot attaches itself close to the attached
tentacles. These loosen in their turn, and so the Hydra is
again in its normal position. The successive steps of the
movement are illustrated in Fig. 3. Trembley described the
movement, and illustrated it (1. c. Memoire 1, Pl. 3, figs. 1-9) ;
(2) In the other case the foot is not detached, but glides
along the bottom until it stands close to the tentacles, which

590 GEORGE WAGNER.

now loosen their hold. The result in either case is the same.
By one such manceuvre Hydra sometimes travels a distance
several times its own length when contracted. Hydra is
further able to make slower journeys by gliding about on its
foot without aid from the tentacles. This movement is very

Fig. 2.—Diagram showing movement of a Hydra viridis in
absence of any directive stimulus. The figures represent positions
of the Hydra when observations were made. For further explana-
tion see texf.

slow, and noticeable only on very close observation. Never-
theless, Hydra travels considerable distances by means of it.

It has been stated above that Hydra is often found hanging
from the surface film. A slight touch to such a Hydra will
usually loosen its hold and cause it to fall to the bottom, but
this is not always the case. Trembley (I. c. Mem. 1, p. 77, et

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 591

seq.) studied this phenomenon very carefully, and pointed
out that during such suspension the basal disc of Hydra rests
at the base of a capillary depression of the surface film. 'The
disc, however, is above the surface film and dry. He com-
pares the suspension with that of a pin or similar object when
earefully let down into a vessel of water. These observations
can easily be verified. Scourfield (01), apparently without
knowledge of Trembley’s work, investigated the same sub-
ject, and came to practically the same conclusions as Trembley.
He observed further, however, that there was present on the
disc, in such cases, a gelatinous substance, often extending
beyond the disc in minute strands. He believes that this
substance, as water-repellent, is essential to the process of
suspension. ‘The fact that, in some cases, he found it difficult
to force Hydra to leave the surface film adds weight to the
view. I have myself seen a number of such cases. Bnt
Trembley’s experiment with the pin shows that even without
such a repellent substance the suspension is easily explained.

I have observed in a number of other cases a different
method of suspension. In these a large air-bubble was
attached to the basal disc, and this bubble apparently kept
the Hydra afloat. It was, moreover, far from easy to remove
this bubble or to break it. It seems to be surrounded by a
tough substance, very probably of the same nature as that
observed by Scourfield. Suspension from a longer thread,
such as Scourfield reports, I have never seen.

Reactions tro MecHanicaL STIMULI.

As previously mentioned Hydra viridis contracts and
expands at much more frequent intervals than the other
species observed. All its other movements are also more
promptand decisive. Hydra grisea and Hydra fusea are
very sluggish both in responding to stimuli and in recovering
after their removal. Furthermore, their tentacles expand so
greatly that they form tangled masses that interfere seriously
with the accuracy of results. I have therefore used Hydra

592 GEORGE WAGNER.

viridis almost exclusively in these experiments, and the
descriptions apply entirely to that species. I did, however,
experiment enough with the other forms to find that their
reactions are practically the same.

Variation in Sensitivity.—A great variation in sensi-
tivity to stimulation between different individuals became
immediately apparent in the work on the reactions of Hydra.
Many specimens proved useless for such work, because even
the slight disturbance on the surface of the water caused by
the breathing of the operator as he bent over the microscope
produced immediate and complete contraction. On the other
hand, there were specimens in which an actual wound had
to be produced in the ectoderm before they responded at all.
Between these two extremes all degrees of sensitivity occurred.
The terms “ weak” and “ strong,” as applied in this paper to
stimuli, have, therefore, only a relative meaning. What is
“weak” to one specimen may be exceedingly “strong” to
another.

Non-localised Mechanical stimuli.—If the watch-
glass containing a Hydra is slightly jarred the Hydra con-
tracts. The same result occurs after any disturbance of the
surface of the water. If after one such stimulus the dish
remains undisturbed the Hydra soon expands again.

Now what is the result if the Hydra is subjected to
rhythmically repeated, uniform mechanical stimuli? Such a
succession of stimuli is best applied by tapping the stage of
the microscope with some metal body at intervals of about
one second. After the first tap there occurs complete con-
traction. As the tapping continues this state of contraction
is maintained for several seconds, sometimes even for from
one half to one minute; but sooner or later, in spite of con-
tinuous stimulation, the Hydra slowly expands. When it has
reached its normal state of expansion it remains in that
position as long as the stimulus is not increased, or even when
it is slightly increased. Thus Hydra soon becomes used to a
slight non-localised mechanical stimulus recurring at frequent
intervals, and no longer responds to it. If the increase im

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 598

the force of the taps becomes very marked, or if by the
motion of the water the Hydra is thrown against any solid
surface, contraction recurs.

When in its natural surroundings, whether in stagnant or
running water, Hydra is exposed to just such a rapid suc-
cession of stimuli, due to the constant motion of the water.
If it were not for its power of acclimatisation to such a
succession the Hydra would necessarily be constantly in a
state of contraction. The response on increasing the force
of the blows may have its biological significance as a protec-
tion against being washed away by any sudden increase in
the motion of the water.

If the interval between stimuli is considerably increased so
as to allow the Hydra to expand fully after each contraction,
the tap being given the moment expansion ceases, the result
is a different one. There is, in this case, no change whatever
in the reaction after repeated stimulation. The course of
events after the fiftieth tap is no different from that after the
first; after each stimulation there is a contraction, followed
shortly by re-expansion. Thus we get a different result so
far as acclimatisation to the stimulus is concerned, depending
on whether the stimuli are repeated rapidly or only after a
considerable interval. In the lateral case one stimulation has
evidently no effect on the response to a succeeding one.
Recovery from the acclimatising effect must, therefore, be
very rapid.

Localised Mechanical Stimuli.—In order to apply
localised mechanical stimuli I prepared capillary glass rods,
attached by means of sealing wax to larger glass rods as
handles. With such a rod it was very easy to touch with
any desirable force any part of the Hydra without producing
any movement in the water such as in itself might cause a
contraction.

A Hydra touched with such a rod will, of course, contract,
provided the blow is not too light. This contraction is
usually so sudden that no details of the process can be
observed. In some cases the body does not at once com-

594 GEORGE WAGNER.

pletely contract; instead, it partly contracts, remains at rest
a few seconds, then, without additional stimulation, contracts
further, and so on, repeating the process three or four times
before contraction is complete.

Of variation in sensitivity between individual Hydras I
have already spoken. I attempted to discover whether there
was any such variation between various parts of an individual.
There is one difficulty in the way of such an attempt. Even
after considerable practice it is almost impossible to give two
successive stimuli of exactly the same magnitude. Perhaps
slight differences in sensitivity would be thus obscured ; but
IT am convinced that so large a number of experiments as were
made would eliminate this source of error. I therefore feel
justified in saying that all parts of Hydra are about equally
sensitive. An individual Hydra will give practically the
same response after each of many stimulations of approxi-
mately equal strength. ‘his is true whether the successive
stimuli are applied to the same region of the body or to
different regions of the body, foot, hypostome, or tentacles.

Next the effect of stimuli of different intensities was tested
when applied to the same part of the organism. Of course,
very sensitive specimens completely contract after even an
excessively weak stimulus. But in most cases there is a
variation in the reaction parallel to the variation in the
stimulus. This is not in accord with Marshall, who states
(loe. cit.) that in response to an external stimulus both body
and tentacles always contract.

Remembering that “weak” and “strong” are relative terms
only, the reactions may be perhaps classified as follows :

A. Stimulation of body :

1. Weak: body partly contracts.
2. Medium: body completely contracts.
3. Strong: body and tentacles contract.

B. Stimulation of a tentacle :

1. Weak : tentacle stimulated contracts.
2. Medium: all tentacles contract.
3. Strong: tentacles and body contract.

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 595

Minor deviations are numerous, but all fall readily into the
above scheme. One Hydra, for instance, was stimulated at
the tip of a tentacle while body and tentacles were expand-
ing. The tentacle stimulated contracted sharply, but the
rest of the organism kept on expanding. It was only after
this tentacle, now contracted, was stimulated a number of
times that the whole Hydra contracted. After a short period
of rest it expanded again. ‘The stimulation was repeated in
the same manner as before, and the same result was obtained
step by step. It is a fact worth noting here that in most
Hydras an exact repetition of a stimulus, after an interval of
several minutes, reproduces the same sequence of events as
at first.

In another Hydra I could make the tentacles contract one
by one by means of stimulation at their tips, until all were
contracted. The body in the meanwhile remained expanded,
and contracted only after the last tentacle to contract has
been stimulated a number of times. In other specimens
repeated stimulation of one tentacle first caused the contrac-
tion of this one, then of some other, or several others, until all
were contracted. Finally, the body also contracted. There is
seemingly no constant relation between the tentacle stimulated
and the one immediately succeeding it in contraction. This
latter is sometimes the one standing next to the one stimu-
lated, but by no means always. Quite as frequently it is the
one opposite, or any other one of the circle. There occurred
cases where the body contracted simultaneously with the
last arms to contract; but in no case, where the stimulus was
applied to atentacle, did the body contract and leave some of
the tentacles expanded ; that is, a stimulus applied to one
tentacle did not radiate to the body without also radiating to
all the other tentacles. It did often radiate to these tentacles
without reaching the body. This indicates that there is a
particularly intimate connection for the transmission of
stimuli between the individual tentacles; such connection
would necessarily be through the hypostome. This is, of
course, far from assuming that these parts are more sensitive

596 GEORGE WAGNER.

to external stimuli. I have already stated that this is not the
case as regards mechanical stimuli.

So far I have spoken chiefly of stimulation of the tentacles.
It is also possible by careful slight stimulation on the body to
cause the latter to contract without contraction of the tentacles.
It is not, however, so frequent a result as contraction of the
tentacles without contraction of the body. This is for the
reason, as far as I can make out, that the violent contractions
of a mass, relatively so large as the body, results in a recoil
which is often strong enough to affect the tentacles. Their
contraction in such acase is caused by this secondary stimulus,
without transmission to them of the primary one.

Sometimes the body, after a very slight stimulus, contracts
only partially, and then immediately expands again. At other
times, when it contracts completely, the tentacles will remain
expanded for from twelve to thirty seconds or more and then
suddenly contract.

In Hydra with buds it is possible to stimulate the body of
the parent so as to cause its contraction without contraction
of the bud; or the bud can be stimulated and caused to
contract without contraction of the parent. But here also
the recoil from the contraction of one part interferes with any
fine gradations in the response.

It is to be noticed that in all these results there is no indi-
cation of any orientation movement on the part of the Hydra.
The organism does not move definitely toward or away from
the source of stimulation. No matter where the stimulus is
applied the single response is simply a contraction, partial or
complete. Now, as the foot is attached to the substratum, it
definitely fixes the direction in which contraction will move
the Hydra as a whole. Contraction causes a moving of the
mass of the Hydra towards the foot. The contraction so
fixed, there can of course not be any fixed relation between it
and the place at which the stimulus is applied ; for no matter
where the stimulus acts, the direction of the contraction is
always the same. In hundreds of experiments I have not
seen a single case where Hydra showed any bending either of

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 997

body or of tentacles definitely toward or away from the source
of mechanical stimulation.

Considerable importance attached to this comparatively
simple point. It is at present quite frequently assumed that
all organisms respond to stimuli having hedonic value, by
either moving toward or away from the source of stimulation.
Of sessile organisms it is similarly stated that they expand
toward or contract away from the stimulus. So Professor
Baldwin (’97, pp. 198-9) says: “All organisms behave in
two great and opposite ways towards stimulations; they
approach them, or they recede from them. Creatures which
move as a whole move towards some kinds of stimulations,
and recede from others. Creatures which are fixed in their
habitat expand towards certain stimulations and contract
away from others.” .... “The stimulations which the
organism tends toward are those which heighten its vitality,
which give it pleasure ; and those from which it draws back
are those whose effect upon it is the contrary—the damaging,
the painful ones.”

If we try to apply this statement, as far as it concerns
contraction, to the response of Hydra to a mechanical stimulus,
we find that it goes beyond the facts. Hydra does indeed
contract after such stimulation. But this contraction is not
necessarily a movement away from the stimulus. It is such
if the stimulus is applied to hypostome or tentacles. It is
not such if the stimulus acts near the foot. In this case, in
fact, the body comes as a whole nearer to the source of
stimulation than it was when expanded. ‘This is true also of
a tentacle which contracts when stimulated near its base.
As a whole the tentacle approaches the source of stimulation
rather than moving away from it. It may be objected that
the stimuli given in the laboratory represent artificial con-
ditions, and that in nature the contraction of Hydra probably
draws it away from the painful stimulus. But to make this
objection allowable it must first be shown that harmful
stimuli are more apt to reach the hypostome than the foot.
At present I see no reason for believing that such is the case.

598 GEORGE WAGNER.

It seems to me that Richet, as quoted by Baldwin (I. c., p. 178),
has expressed the probable object of contractions much better
when he says, “ There takes place a series of general move-
ments of flexion, as if the animal wished to make itself
smaller, and to offer less surface to the pain..... 72 iis
is exactly the result we get in Hydra. As it contracts it
becomes more nearly spherical, and so reduces the size of its
exposed surface. It is in this reduction of exposed surface,
and the consequent reduction of the chances of being hit, that
the adaptive value of contraction in Hydra really lies. Perhaps
the closer crowding of cnidoblasts, consequent on such reduc-
tion of surface, also plays a part.

What will happen if a localised mechanical stimulus is
repeated at regular intervals? A Hydra viridis was stimu-
lated so as to contract. Itwas then allowed to expand again, but
the moment expansion was complete the stimulus was repeated,
and so on forseveral hours. Two questions are here of special
interest: first, does repetition of the stimulus cause Hydra to
contract less readily; and second, has such repetition any
effect on the subsequent re-expansion, either as to rapidity or
the occurrence of any orientation movement? Both questions
are answered decidedly in the negative as far as stimulation
at longer intervals is concerned. Here, as with non-localised
stimulation, the response after many stimulations did not
change. The contraction was as rapid and as complete after
the fiftieth stimulation as after the first.

Re-expansion also was not changed in character. As to
the direction of such expansion one might perhaps expect
that in the course of time it would be in a direction away
from the side from which the stimulus was applied. But no
such thing occurred. As after spontaneous contraction, so
here re-expansion was toward a different direction after each
contraction. But this change in direction could not be
referred in any way to the direction from which stimulation
came. ‘I'he re-expansion was as often toward the stimulus as
away from it, and equally often it was at right or oblique
angles to the direction of stimulation. Such repeated stimu-

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 699

lation at longer intervals does not, therefore, cause any change
in the reaction. In other words, we do not here see any
evidence of acclimatisation or memory.

A second method of studying the effects of repeated stimu-
lation varied from the first only in the length of the interval
between stimuli. Instead of allowing the Hydra to expand
after each stimulation the stimulus was applied at intervals of
about one second. ‘There results of course a contraction.
The Hydra remains contracted for from one half to one
minute. ‘Then, in spite of continued stimulation, it slowly
expands, and does not again contract unless, as often happens,
the intensity of the stimulus is accidentally increased. If,
on the other hand, the blows are kept up without any increase
in intensity, one of two things happens:

(1) In many cases the Hydra now acts as if no stimulation
were present ; it entirely ignores the blows of the rod.

(2) In a minority of cases the result is decidedly different.
The Hydra slowly bends its body to one side until its expanded
tentacles touch the glass at some distance from the foot. They
then attach themselves and contract. 'The foot loosens its
hold, and the body of the Hydra contracts. But the body
immediately re-expands and bends over, until the foot touches
the glass close beside the tentacles. The foot now reattached
itself, the tentacles loosen their hold, and the body straightens
out. The Hydra thus again occupies its normal position, but at
some distance from the place where it was subject to stimula-
tion. Its further movements are those of anormal Hydra. As
to the direction towards which Hydra travels in the ‘‘ escape,”
it has again no relation to the direction from which stimu-
lation comes. ‘I'o resort again to the points of the compass
as convenient symbols of direction let us suppose the glass
rod to stimulate the Hydra on the west side. I have seen
such a Hydra escape toward the east. But I have seen others
escape in almost all of the other directions. Some even bent
toward the west, over the rod that stimulated them, and
escaped in that direction. Here again, therefore, we have in
no sense an orientation.

600 GEORGE WAGNER.

Fic. 3.—Common method of travel in Hydra. A. Body bending
toward substratum. B. ‘Tentacles attaching themselves. C. Foot
loosened and body contracted. D. Body re-extended, foot end
beginning to bend over, EH. Foot attaching itself near hypostome.
F, Upright position regained,

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 601

As to the mechanism of this ‘‘escape’”? movement it will
be readily recognised that it is identical with the mechanism
ordinarily employed by Hydra to move from place to place,
as shown in Fig. 3. The important point is that here on
repeated stimulation there is at first a simple contraction,
then comes a period where apparently there is some sort of
acclimatisation to the stimulus which now has apparently no
effect. However, this is only apparently so, for there may
soon follow the third stage in which the Hydra responds to
the stimulus by a movement entirely different and even
directly opposed to the first response by contraction. ‘This
final movement is furthermore one of very considerable com-
plexity.

Jennings (02) has found in Stentor and Vorticella a very
similar modification of reactions due to repetition of stimu-
lation. In Stentor roeselii, in response to continued
stimulation by powdered carmine, there is the following
sequence: bending away from source of stimulation, reversal
of ciliary current, contraction, and finally abandonment of its
tube. In Stentor coeruleus the results are similar. When
continuously stimulated by means of some solid, like powdered
carmine, this form responds at first by bending into a new
position ; on continuance of stimulation it reverses the ciliary
current, and thus repeats its first manceuvre; this is followed
by contraction, and finally by loosening its hold on the sub-
stratum and swimming away.

‘These responses result from stimulation by carmine powder,
which stimulates in part chemically. If a purely mechanical
stimulus be used Stentor coeruleus at first contracts after
a single blow, but subsequently it may require as many as
forty. But eventually this form always loosens its hold on
the substratum and swims away. In particular sensitive
individuals this last movement is resorted to at the first blow
from a glass rod, but this is the exception. Stentor
roeseliil, however, as well as Vorticella and some other
forms, show true acclimatisation, and never break away as
the result of a purely mechanical stimulation.

VOL, 48, PART 4,—NEW SERIES. 43

602 GEORGE WAGNER.

Jennings (Il. c., pp. 49-51) discusses at length the possible
explanation for the failure on part of an organism to react to
a stimulus to which at first it responds very readily. The
three possibilities he mentions are motor fatigue, sensory
fatigue, and a third unknown element. ‘lhe facts concerning
Hydra that bear on this matter fully support Jennings’ con-
tention. Motor fatigue is entirely out of the question, for I
have been able, under proper conditions, to keep Hydra con-
tracting continuously for as long as three hours, at the end of
which time it responded as readily as at the beginning.
Furthermore, we have seen that after long repeated stimula-
tion at such frequent intervals as to bar any possibility of
recovery from fatigue, Hydra finally undertakes the very
complicated ‘‘ escape”? movement. ‘This, in itself, involves a
large amouut of work, and makes explanation by motor fatigue
impossible.

Further, this last-mentioned “escape” movement proves,
with equal force, that the stimulus is still perceived, otherwise
there could be noreaction. ‘This being the case, the explana-
tion by sensory fatigue is clearly inadmissible. ‘here remains
only the third possibility. We may suppose that the stimulus
which causes a contraction at the same time affects the physio-
logical condition of the organism in such a way that the hmen
for that particular character of stimulation israised. If part
of the energy involved in the stimulus comes to act on the
chemical constituents of the organism this may well cause a
change in the character of these constituents. Irritability
must depend largely on the chemical character of these con-
stituents; this, it seems to me, is well shown by the action of
narcotics and anesthetics. ‘lherefore, a chemical change in
body constituents would necessarily involve a change in 17i-
tability, and so a change in the readiness of response to
stimulation. ‘'lhese considerations may very well explain the
lack of response after repeated stimulations.

‘he return of the Hydra to a position of semi-extension,
after a contraction reaction, is apparently simply a return to
the position of rest. Zoja (I. c.) found that Hydra, aneesthe-

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 608

tised by chloroform or ether, always assumed this position of
semi-extension.

There still remains the very involved “ escape”? movement.
It will be useful to compare this with the reactions of Para-
mecium toward stimuli of various kinds as studied by
Jennings. Paramecium responds by stopping its spiral
movement, jerking backwards, swinging toward the aboral
side, and finally moving forward again. If it then comes in
contact with the source of stimulation again it goes through
the whole manceuvre again, until finally its forward movement
carries 1t out of the region of stimulation. As far as is now
known this method of reaction is never varied as a result of
experience. ‘l'hat escape is finally effected depends entirely
upon the element of chance involved. ‘lhe movement, as
such, bears no relation to the source of stimulation ; it bears
a very definite relation to the structure of the Para-
mecium.

‘he mere contraction of Hydra in response to a mechanical
stimulus is a reaction quite parallel to this. It also has no
relation to the direction from which stimulation comes, while
it has a fixed relation to the structure of the Hydra. ‘There
is, however, a difference. If the Paramecium does not suc-
ceed in escaping from the stimulus at the first trial, it may do
so at a second or any subsequent attempt. If the Hydra
does not escape by the first contraction it will not escape by
a subsequent one, for its sessile mode of life precludes the
element of chance involved in the movements of a free
swimming form like Paramecium. Hydra, however, does
not continue to respond indefinitely by contraction, but
resorts, after a short time, to another method not a necessary
consequence of the first, and by this second method accom-
plishes its purpose. ‘his second movement also has no strict
relation to the direction from which the stimulation proceeds.
Nevertheless, it always succeeds in removing the Hydra from
the influence of the stimulus. Having no fixed relation to
the stimulus the idea arises that it may have a definite rela-
tion to some structural feature of the Hydra. But evidence

604. GEORGE WAGNER.

on this point is lacking, Hydra being purely radiate, as far
as is known.

On the whole Hydra, in its manner of reaction toward
mechanical stimuli, is a close paralle] of Stentor and Vorti-
cella. Jennings (02), in his paper on these forms, has dis-
cussed, at some length, the psychological questions involved.
This discussion applies with equal force to the reactions of

Hydra.

RHEOTROPISM.

In order to determine whether Hydra reacted in any definite
way to a current of water a very simple apparatus was con-
structed by taking a glass tube eighteen inches long and
abcut one and a half inches inside diameter. A small hole
was made into one side near the middle for the introduction
of the animals. ‘he tube was placed horizontally, and so
arranged that water flowed into it over a dam made of a
bisected cork, and flowed out at the other end over a similar
obstruction. After a number of Hydra were introduced the
current of water was turned on. It could be increased or
diminished by regulation of the amount of water supplied,
and especially by tilting the tube. In this apparatus I had
Hydra under observation for a number of days, but there
was absolutely no sign of response to the currrent. ‘lhe
current was certainly much stronger than that to which the
Hydra is ordinarily exposed in nature. Yet there was no
travelling either up or down stream, nor any curvature of the
body with or against the current. ‘There is thus no evidence
of rheotropism in Hydra.

Riesting Reaction,

Hydra usually has its foot attached to the substratum,
while body and tentacles, moderately extended, project out

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 605

into the water. In Hydra viridis, as well as in the other
forms, the tentacles frequently attach themselves to the sub-
stratum and assist inmovement. But they remain so attached
only for very brief periods. The foot, on the other hand, is
seldom detached. Loeb (’91) has shown that Cerianthus,

Fre. 4.—Righting reaction of Hydra viridis. A, Hydra placed
in reversed position, tentacles attached to substratum. B. Body
extending, foot end bending over. C. Foot attached, tentacles
ready to loosen. D. Upright position regained.

placed in an unnatural position, will strive successfully even
under difficulties to place itself in such a position that its
long axis is vertical, with head up, and foot attached to the
substratum. In Hydra a simple experiment shows that a
similar righting reaction occurs. A. green Hydra, strongly
contracted, is taken and placed so that it rests on the bottom
of a watchglass on its tentacles, which act like the legs of a

606 GEORGE WAGNER,

stool. The foot of the animal extends straight up into the
water. Almost immediately the body begins to extend.
When about half extended it bends to one side until the foot
touches the glass and attaches itself. Sometimes the tentacles
loosen before the foot is attached and the Hydra simply
tumbles over. But more commonly the entire action is an
active one of orientation, not a passive tumbling over. I
have tried to represent the process in Fig. 4.

We have here, then, a process comparable to that observed
by Loeb in Cerianthus, but not quite so complicated. Ceri-
anthus seeks not only contact for its foot but a vertical posi-
tion. In Hydra thigmotaxis alone is involved, for it can be
easily observed that Hydra, normally, have their long axes
disposed at all possible angles to the force of gravity,

Reactions To CHEMICAL STIMULI.

Non-localised.—To any solution in which Hydra is im-
mersed it responds, if the solution be strong enough to affect
it at all, by a general contraction. Only in rare cases is
another reaction produced; these will be discussed in the
account of the food reactions. When contraction does occur
the body remains contracted for a considerable time, then
slowly begins to extend. But this extension never goes
very far before contraction again occurs. This continues
until the animal perishes, usually in a comparatively short
time.

Localised.—The method of applying localised chemical
stimuli was as follows :—The tip of a capillary glass tube was
pressed into the finely powdered chemical. In this way a
considerable amount of the chemical was forced up into the
tube. If the end of the tube was then placed under water
the water dissolved the chemical slowly, and the solution
gradually diffused from the mouth of thetube. If this mouth
was placed very close to a Hydra the diffusion cloud would

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 607

strike at first a very limited area on the surface of the body.
In other words, the stimuli was distinctly localised. A
number of chemicals were experimented with in this manner
including citric acid, acetic acid, sodium chloride, sodium
carbonate, potassium bichromate, methylene blue, and others.
The action of all was precisely the same. I found, however,
that methyl green was most convenient to handle, on account
of the colour, by means of which the limits of the diffusing
cloud, were easily recognised, and because it gave the most cer-
tain results. I shall describe as a type, therefore, the effects
obtained by the use of this substance. That the results
obtained were due to chemical action, and not to mechanical
agitation is shown by the fact that no effect was produced by
streams of distilled water or of an excessively weak solution
of methyl green used in the same manner.

When a cloud of methyl green is allowed to strike Hydra
a little above the foot, in a few seconds there is a flexion of
the body at the point where the chemical touches it. The
body bends over slowly, and this bending is toward the side
on which the chemical acts. In some cases there is also a
separate bending just below the hypostome, toward the same
side. This latter peculiar movement gives the appearance of
the presence of a neck region. The same movement has
been observed by Pearl (01) under the influence of the
electric current, and it can also be observed as occurring’ in
apparently unstimulated Hydra. As the methyl green spreads
and affects a larger area on the surface of the Hydra complete
contraction results.

If the methyl green is similarly brought near to the middle
of an expanded tentacle the tentacle flexes at this point in
the direction from which the chemical approaches it. Then,
as it enters the denser cloud of stain, it contracts. The
tentacles are decidedly more sensitive to the action of the
chemicals than the rest of the body. Usually the tentacle
flexes before the visible green cloud has reached it, indicating
that the edges of this cloud, containing yet too little stain to
be visibly coloured, are still concentrated enough to produce

608 GEORGE WAGNER.

the reaction. This never is the case when the body is the
part stimulated.

If the tube is placed inside the circle of tentacles, so that
the cloud first reaches the surface of the hypostome, the
tentacles simultaneously sway inward, then contract.

Here we have then a definite orientation reaction toward a
chemical stimulus. It is important that we understand just
how it comes about. If after the application of such a
localised stimulus we carefully remove the methyl green that
has gone into solution by means of a pipette, the Hydra will
soon begin to expand. But now it can be noticed that in the
region affected by the stain there is no expansion, and the
ectoderm in this region is seen to be permanently stained.
Often there is no return of mobility in this region, even after
some hours, the cells in such cases being probably dead. On
account of this local absence of expansion the body, as soonas
it begins to expand, also begins to flex again toward the same
side as it did before under the influence of the stimulus.

The direct result then of such local chemical stimulation is
a contraction of those ectoderm cells that come in direct
contact with the chemical. This local contraction necessarily
causes the body (or tentacle) to flex at the point affected, and
to flex toward the side from which the stimulus acted. But
only injurious chemicals cause this reaction, and by it the
Hydra is carried into a destructive solution. This bending
of the body is, therefore, anything rather than adaptive in
nature. Itis probable that such strongly localised chemical
stimuli of a destructive nature play no part in the normal life
of Hydra. The reaction, therefore, forms no part of the
normal behaviour, but is more or less pathological in character.
It recalls the false tropisms in plants, more especially false
traumatropism. Ciesielski (’72) found that when a root was
severely injured on one side at some point lying within the
growing zone there was produced a curvature at this point,
the curving being toward the side injured. If, on the other
hand, the injury was only slight a curvature also resulted,
but in this case it was away from the side injured. The

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 609

latter result is a true response to stimulus; the former is a
purely mechanical effect, due to the fact that the severely
injured cells ceased growing and the continued growth on
the opposite side forced the root to curve toward the injured
side. The response to a chemical in Hydra is probably a
mechanical result of this kind, except that in place of growth
it is movement that is checked.

Foop REACTIONS.

The process of taking in food as it occurs in Hydra has, as
far as I know, been described in detail only by Hartog (’80),
although Trembley has a long general discussion of it.
Hartog’s note on the subject was unknown to me until after
T had studied the process myself and written out a descrip-
tion that coincides in large part with his.

If a Hydra that has been kept without food for a week or
ten days has a bit of raw meat placed on or very near one of
its tentacles the course of events is about as follows :—The
tentacle first touching the meat fastens itself to it, apparently
by means of some secretion, and then contracts. ‘The other
tentacles begin rather active movements, which, however,
show little correlation. Nevertheless, soon all the tentacles
find their way to the meat, become fastened to it, and
contract. There is, however, so little definiteness in all these
movements that the meat often falls away from the tentacles.
In such cases the Hydra makes no very great effort to find it
again. Vague movements of the tentacles may continue for
some time; sometimes they even strike simultaneously toward
the hypostome, as if clutching for something.

In other cases, however, the food is by the movement of
the tentacles brought to the hypostome. As soon as this is
touched by the meat, sometimes even some seconds before,
the mouth begins to open, and its edges fasten to the meat.
Immediately the tentacles loosen their hold and swing away
from the mouth. They play no further part in the swallowing.
It is usually stated that they push the food into the mouth,

610 GEORGE WAGNER.

but this is not at all the case. The actual process of swallow-
ing depends entirely on the activity of the tissue of the hypo-
stome and body. Occasionally a tentacle remains attached
to a food particle after the mouth has opened, and in some
cases the tentacle is even drawn into the food cavity with the
food. But in all such cases which have come under my
notice it could be seen that the tentacle was passively pulled
along, having by its nematocysts, or in some other way,
become attached to the food, and being unable to release its

hold.

Fre. 5.—Hydra grisea, with partially ingested annelid.
(Camera lucida drawing.)

The food is now slowly drawn into the body cavity, but at
the same time another movement takes place. The hypostome
slowly draws itself upwards over the food particle. This
peculiar action is very well compared by Hartog (I. c.) to the
method in which asnake gets outside its prey, or in which an
automatic stocking might stretch itself onto the foot and leg.
The food once well within the cavity the mouth closes. Now
the body-wall expands for some distance in front of the
particle, while it strongly contracts behind it. And so the
food is forced to the lower portion of the food cavity.

Both cilia and pseudopodia have been observed on the
ectodermal cells of Hydra, and it is commonly stated that it
is the former that are chiefly concerned in the act of swallow-
ing. But it is difficult to see how cilia could have enough
strength to play any part in the swallowing of entire entomo-

ON SOME MOVEMEN''S AND REACTIONS OF HYDRA. 611

straca, annelids, insect larve, and the like, which form the
ordinary food of Hydra. The difficulty increases in such a
case as came to my notice recently, where a Hydra grisea
made an attempt, partially successful, to swallow an annelid
fully fifty times its own bulk (Fig. 5). The extent to which
the tissues of the Hydra were stretched during this perform-
ance is almost beyond belief. Another Hydra from the same
dish attempted the same gastronomic feat on a leech (Clepsine)
certainly five hundred times its own bulk. Needless to say
this one did not succeed. It seems to me we must assign the
leading réle in swallowing to pseudopodia. I hope, however,
to obtain direct evidence on this point from sections before
long.

The food having reached the lower portion of the digestive
tract, rests here until digestion is complete, except for the
fact that it is churned up and down the cavity more or less as
the Hydra expands and contracts. Digestion completed, the
insoluble residue is discarded through the mouth. This
ejection I have seen performed several times, and in every
case the food was forced out by a very sudden squirt that
threw the débris to some distance.

During these experiments it was soon noticed that Hydras
would not always attempt to capture food that was offered.
Hydras taken from a dish in which food was abundant were
commonly quite indifferent to any food offered them, no
matter what its character. The same Hydra were then kept
in a dish of filtered water for a week, thus being deprived of
all food material. At the end of this period they swallowed
very readily any food offered them, the process of ingestion
often being over in less than half a minute. Hydra, there-
fore, does not react to offered food at all times, but only after
a period of abstinence. It is an intermittent, not a constant
feeder. It sounds very simple to say that Hydra will not
feed except when hungry. Nevertheless, a determination of
the fact is not superfluous. The case is different for instance
in Planaria; Pearl (05, p. 668-9) found in these that the
food-seeking reaction was not at all affected by conditions of

612 GEORGE WAGNER.

hunger, although the food taking was. In the protozoans
even food taking (swallowing) is seemingly a continuous
process. One sometimes sees Paramecia with bodies crowded
with food material still steadily taking in more.

The Hydras used in subsequent work were therefore starved
for a period of seven or eight days by keeping them in fil-
tered water. There is a remarkable increase in activity in
such Hydras. Their tentacles are in almost constant and
rather rapid motion, and the body sways to and fro, expands
and contracts, in a very nervous manner. Green Hydras
stand starving very poorly, usually perishing in two or three
days. I therefore used Hydra grisea for this part of the
work. Its larger size gives it another advantage.

Let us now consider what factors in the food enable the
Hydras to recognise it as such. It is evident that any stimu-
lus coming from, say, a piece of meat must be either chemical
or mechanical.

Let us consider the mechanical stimulus first. The result
of experiments directed to this point could be foreseen. In
studying the effect of mechanical stimuli several hundred
Hydras, from many sources, were stimulated by prodding
with glass rods on every part of the body, including hypos-
tome and tentacles, and at all degrees of intensity. In no
case did there result any reaction resembling in any way
the movements concerned in feeding. ‘To make sure, how-
ever, I tested Hydra that had been starved for from seven to
ten days by placing minute bits of filter-paper on the hypos-
tome. ‘This paper had been soaked for several days in water
from exactly the same source as that in which the Hydra
were kept while starving. All possibility of chemical stimu-
lation was thus removed. The result wasas expected. ‘here
was no trace of a food reaction, and the paper soon rolled
away from the animal. A mechanical stimulus alone, then,
cannot call forth a food reaction.

Is the same thing true of a chemical stimulus? To test
this I took Hydras, starved for seven or eight days, and
placed them in small watch-glasses. The water was drawn

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 618
off from them as completely as possible, and filtered beef-tea
made from beef extract was substituted. Of the chemicals in
meat only the soluble ones can stimulate chemically, and
these are well represented in beef extract. Soif the stimulus
producing a food reaction were purely chemical we might
expect such a reaction here.

But there was no trace of it; the Hydras acted exactly as
they did in ordinary water, except when the beef-tea was
made too strong. In that case a Hydra contracted just as it
does in the case of any other chemical in strong solution.
So far as this evidence goes, therefore, a chemical stimulus
alone is no more adequate to produce a food reaction than is
a mechanical one. ‘That this is not absolutely true we shall
see I a moment.

Next, we may consider the effect of a combined stimulus.
Some of the Hydras used in the experiment last mentioned
were returned from the beef-tea to hydrant water. ‘There
were now presented to them minute pieces of filter-paper
previously soaked in beef-tea. The result was very striking.
As soon as the paper touched the tentacles these seized it and
drew it toward the hypostome. As soon as the paper touched
this the mouth opened, and the morsel was engulfed. Here,
as always, no effort was made to turn the object in any way,
so as to make swallowing it easier. ‘I'he way it was pre-
sented was the way it went down. Such a piece of filter-
paper is, however, usually anything but smooth. It has
projecting fibres in many places, and these projections, after
the paper was swallowed, caused the body wall of Hydra to
bulge out in very grotesque fashion. ‘I'he same experiment
was repeated many times, always with the same result.

he food reaction can also be brought about by immersing a
starved Hydra in beet-tea, and then stimulating the hypostome
mechanically witha glassrod. The reaction does not, however,
appear quite as constantly as in the previous experiments.

Thus we see that by properly combining a chemical stimulus
with a mechanical one, the food reaction can be brought
about in Hydra by an object which itself has no food value,

614 GEORGE WAGNER.

Having at hand some Hydras that had been without food
for twelve days I started to repeat the same series of experi-
ments on them. ‘l'o my surprise they all responded with a
typical food reaction when immersed in pure filtered beef-tea.
Shortly after this was poured over them the tentacles began
vigorous movements, which were, however, but little corre-
lated. ‘lhe mouth opened wide, and remained open for a
minute or so, then it closed, and apparently some of the beef-
tea had been taken in, for the body could be seen to be con-
siderably expanded just back of the hypostome. In some
cases this expansion even travelled backward. In fact there
was, in every case, a very typical food reaction.

What is more, the same food reaction was secured by means
of a solution of quinine. In this case, however, the quinine
very strongly affected the entoderm after the mouth was
opened, and the Hydra soon perished with its mouth wide
open. Quinine is a strong poison to most of the lower inver-
tebrates. So much the more remarkable is the fact that it
should be able to call forth a food reaction.

These experiments then give us the evidence that there
may be three factors concerned in the production of a food
reaction. ‘l'hese factors are a state of hunger in the Hydra,
a chemical stimulus, and a mechanical stimulus. ‘lhe first
two must be present to produce the reaction. ‘The third is or
is not necessary, depending upon the intensity of the first
factor—hunger. <A food reaction may thus be brought about
in two ways: first, by the combined action of a chemical and
a physical stimulus, in presence of a moderate degree of
hunger; second, by a chemical stimulus alone, when the
hunger has become intense.

While keeping Hydra under observation for a number of
months it was noticed that ostracods formed no part of their
tood, though these crustacea were fairly numerous in the
aquaria in which the Hydra were kept. Jt was further
noticed that an ostracod could come freely in contact with
Hydra at any time without calling forth any attempt at
capturing it. ‘l’his was the case even when the Hydra had been

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 615

starved for some time. A Cyclops presented to the same
Hydra was captured and swallowed very quickly, as was a
piece of raw beef.

Why does Hydra not capture and swallow ostracods just
as it does others of the smaller crustacea? It seems to me
the answer is not far to seek. Ostracods are enclosed in
hard chitinous shells, which, as far as I have observed, are
never opened more than a little way. ‘The organic fluids
given off by the animal therefore escape very slowly beyond
the confines of the shell. Hence the minute chemical stimulus
given by an ostracod as it comes into contact with the Hydra
is inadequate ; but adequate chemical stimulation is, in all
cases, a prerequisite of the food reaction, and so the ostracod,
giving only a mechanical impulse, is not recognised as food.
lf this theory is correct, then we ought to be able to cause
the Hydra to swallow the ostracod, by bringing to bear a
chemical stimulus while simultaneously presenting the ostra-
cod. ‘l'his is easily done by crushing the ostracod slightly,
so that some of the juices of the body freely flow out. If
such an ostracod is presented to a starved Hydra the rapidity
with which it disappears into the food cavity is little short
of marvellous.

Nematocyst DiscHARGE.

As is well known Hydra, like most ccelenterates, carries in
its ectoderm a great number of cnidoblasts. They are fairly
plentiful over most of the body, but occur most numerously
on the tentacles, where they form small tubercle-like masses.
‘hey seem to serve chiefly for the capture of prey, though
secondarily they may also form a means of protection against
enemies.

There has been considerable controversy as to the nature
of the action of the nematocysts on the organism at which
they are discharged. Various authors (for instance, Schneider,
*90) claim that the usual supposition that the nematocysts

616 GEORGE WAGNER.

penetrate the epidermis of the prey is incorrect. They argue
that the nature of the nematocyst is too fragile to permit of
such a result. The nematocysts, according to their views,
merely adhere to the outside of the captured animal.
Grenacher (’95) is, as far as I know, the only one who has
published a direct observation on this subject, reproducing
from memory a drawing of an observation made many years
previously. It represents a single nematocyst that has pene-
trated the cuticle of a Culex Jarva. Opportunities for such
observations are not so frequent as might be supposed.
Professor Jennings was so fortunate, however, as to procure

Fic. 6.—Insect larva pierced with nematocysts. (Copied from a
drawing by Mrs. Jennings.)

a specimen that settles the point for Hydra very conclusively.
The victim, a fly larva, is thickly covered with Hydra nemato-
cysts, and these can be plainly seen to penetrate the skin, and
project into the interior of the larva (Fig. 6). Not only the
point, but, in some cases, the lateral barbs also have pene-
trated. The specimen was taken from among the tentacles
of a Hydra just as the latter was preparing to swallow it.
The effect of the nematocysts is almost instantaneous para-
lysis or even death of the animal attacked. It seems, more-
over, to be effective on Hydra itself. On one occasion, seeing
a Hydra grisea with its mouth widely open, I quickly
thrust a second Hydra into it. The first one made an attempt
to swallow it, but did not get very far, for the victim began

ON SOME MOVEMEN''S AND REACTIONS OF HYDRA. 617

avery profuse discharge of nematocysts. ‘he first Hydra
reciprocated, and in a very short time both Hydra were
apparently dead.

As far as my observations go the nematocysts are not
always necessary for paralysing prey. Apparently this is
sometimes brought about by some purely fluid discharge from
the tentacles. In larger specimens of Hydra grisea the
discharged nematocysts can easily be seen under the Braus-
Driiner microscope. Yet I have often observed, with such a
microscope, that small crustacea, such as Cyclops, were para-
lysed when approaching too near the tentacles, without any
discharge of nematocysts. At least, very close search, even
with a microscope of higher power, disclosed none. It may
be said that what occurred here is simply the death-feigning
so common in the lower crustacea, but that is not the case.
Death-feiguing lasts only a very short time. In the pheno-
menon under consideration the animal remains motionless for
many minutes, and then, provided the Hydra has been
removed, or, for some reason, does not attempt to swallow its
prey, motion slowly and gradually returns.

The structure of the cnidoblast, and especially the pro-
truding cnidocil, suggest a direct mechanical arrangement for
its discharge. Schulze (’71) suggests such an explanation
for these discharges. He believed that a pressure from
without on the enidocil would directly disturb the mechanical
equilibrium in the cnidoblast, and so cause a discharge.
After the muscular and nervous nature of certain cells in
Hydra was recognised the explanations offered took on a
more physiological character ; according to Chun (’93) there
was involved a long passage of the stimulus through distinct
ganglia and nerve fibres; but al] explanation, as far as I know,
hold to the idea that the cnidocil serves the mechanical
function of a trigger.

Zoja (1. c.) found that he could touch the cnidocils repeatedly
and rudely without getting a discharge of nematocysts, but
he did not draw any conclusions from this fact. R. v.
Lendenfeld (’83), working with actinians, found that the ten-

von. 48, PART 4.—NEW SERIES. AA

618 GEORGE WAGNER.

tacles discharged their nematocysts when touched by a particle
of some digestible substance, but not when sand was allowed
to fallon them. Although he found the same thing true of
an isolated tentacle he expressed the opinion that nematocyst
discharge depended on the will of the animal.

I tried similar experiments with a great many Hydras of
various species, and in no case was I able to secure a dis-
charge of nematocysts by mechanical stimulation alone.
Large specimens of Hydra grisea, in which the nematocysts
could easily be recognised under the Brauns-Driiner micro-
scope, were stimulated by means of a capillary glass rod.
The tip of the rod was moved over the body in all directions,
often with pressure enough to produce a wound. But even
after five or ten minutes of such treatment no discharge of
nematocysts results. There is such a discharge when Hydra
is crushed under a cover glass. This discharge is due,
however, to the direct pressure brought to bear on the enido-
blasts, and has no bearing on the normal reaction, as it is in
no sense a vital phenomenon. It is clear, therefore, that
mechanical stimuli are not adequate for nematocyst discharge.
Ihe cnidocils must, therefore, serve a function different from
that suggested by their common name of “ trigger.”

Chemical stimuli was next resorted to. Various chemicals
were used, such as acetic acid, methylene blue, citric acid, and
methyl green. It was found that all of these, if in solutions
of proper strength, would cause nematocyst discharge. Even
beef tea, when strong enough, had the same effect. The
most certain in action, however, and, on account of its colour,
the easiest to observe, was methyl green. If a small amount
of solid methyl green was applied to a Hydra in the manner
previously described (pp. 603 to 606) there was always a dis-
charge of nematocysts, provided the solution of the stain was
not too dilute when it reached the Hydra. This discharge is
absolutely limited to the area directly touched by the stain.
After the stain had acted a short time the surplus was
removed by a pipette or the Hydra was placed in another
watch-glass. It was then easily seen that the ectoderm cells

ON SOME MOVEMENTS AND REACTIONS OF HYDRA. 619

over the area directly touched by the stain-cloud were stained
green, and that nematocyts were discharged only over the
area so stained,

Similar results are obtained by experimenting with tenta-
cles cut off from the body. A tentacle can thus be cut at
any place without causing any great discharge of nematocysts.
If such a tentacle is then stimulated with methyl green it
will discharge nematocysts profusely, just as it would have
done had it remained attached to the body. The discharge
is restricted absolutely to the region touched by the solution
of the chemical.

The discharge of nematocysts depends then entirely upon
chemical stimulation. The action of the stimulus is probably a
very direct one on the protoplasm of the cnidoblast, for if
there were involved a nervous mechanism of such complexity
as Chun (l.c.) supposes, we could reasonably expect the dis-
charge to reach beyond so strictly limited an area. It is also
obvious that the enidocil can only serve a sensory function,
as was suggested by Schneider (90). The results with
isolated tentacles certainly dispose of v. Lendenfeld’s theory
of the discharge as controlled by the will of the animal.

To my teacher and friend, Professor H. S. Jennings, I am
deeply indebted for constaut aid and encouragement in this
work. It was undertaken at his suggestion and carried out
in his laboratory. ‘lo Professor Reighard I am grateful for
more than ordinary courtesies extended to me while in the
laboratories in his charge.

SUMMARY.

The principal points that I have attempted to bring out
in this paper are:

1. An undisturbed Hydra does not remain motionless, but
contracts at fairly regular intervals. After contraction it
expands in such a way as to occupy a different position from
that previously occupied.

620 GEORGE WAGNER.

2. Hydra has only one form of response to a single
mechanical stimulation, localised or non-localised ; this re-
sponse is by contraction, more or less complete, dependiug
on the intensity of the stimulus. Such contraction is not
necessarily toward or away from the stimulus.

3. A non-localised stimulus, repeated as soon as Hydra has
regained the expanded stage, causes no change in the
response, contraction resulting after each stimulation. The
same thing holds true of a localised stimulus applied in a
similar manner.

4. If a non-localised mechanical stimulus is repeated at
very brief intervals, say one second, acclimatisation is soon
affected, and the Hydra no longer responds.

5. A localised stimulus applied at such brief intervals
brings about at first an apparent acclimatisation. ‘This is
soon followed in many cases by the complicated “ escape ”
movement, the Hydra moving away from the region where
stimulation occurs. This shows that the physiological
condition of the animal has been changed, so that to the
same stimulus under the same external conditions it now
gives a reaction different from that given at first.

6. Hydra shows no orientation movements in response to
stimulation by a current of water.

7. Hydra normally has its foot attached to the sub-stratum.
If the foot is detached the animal performs active movements
directed toward restoring the normal condition. Geotaxis
plays no part in this reaction.

8. Non-localised chemical stimuli cause general contraction.
An exception is found in certain food reactions.

9. A strong localised chemical stimulus causes a bending
of the body or tentacles, as the case may be, toward the side
stimulated. Such bending is caused by the contraction of
the ectoderm cells directly affected by the chemical. The.
result is not adaptive, as it carries the body or tentacles into
the region where it is most injured.

10. Hydra reacts to food only after a period of hunger.

Il. In the presence of a moderate state of hunger it

ON SOME MOVEMENTS AND REACTIONS OF HYDRA, 621

requires a combination of a chemical and a mechanical
stimulus to produce a food reaction. If starvation is extreme
a chemical stimulus alone suffices.

12. A mechanical stimulus will not produce a discharge of
nematocysts ; a chemical stimulus will.

13. The action of the chemical is probably quite direct, not
involving the nervous system. Nematocyst discharge is
restricted absolutely to the area touched directly by the
chemical.

14. The nematocysts can, and do, pierce the epidermis of
the prey at which they are discharged.

15. Hydra seems to be able to paralyse prey without dis-
charging nematocysts.

BIBLIOGRAPHY.

Baker, H.—1748. ‘ Essays on the Natural History of the Polypes,’ London,
1743.

Batpwin, J. Marx.—’97. ‘Mental Development in the Child and the Race:
Methods and Processes,’ New York, 1897 (Second Edition).

Cizsietski, T.—’72. ‘Beitrage zur Biologie der Pflanzen (Cohn),’ Bd. i,
zweites Heft., p. 1.

Cuun, Caru.—’93. “ Die Canarischen Siphonophoren. II. Monophyiden,’’
‘Abhandl. d. Senkenb. Nat. Gesell.,’ 1893.

Grenacuer, H.—’95. ‘Zool. Anzeiger,’ Bd. viii, 1895, p. 310.

Hartoc, M. M.—’80. ‘Quart. Journ. Micr. Sci.’ (N. S.), vol. xx, p. 248,
1880 a. Same volume and page.

Jennines, H. S.—’97. ‘Journal of Physiology,’ vol. xxi, pp. 258—322.
1902. ‘American Journal of Physiology,’ vol. viii, pp. 23—60. [This
paper contains references to most of Jennings’s previous papers. |

v. LenpENFELD, R.—’83. ‘Zeitschr. f. wiss. Zoologie,’ Bd. xxxviii, pp.
355—371.

Lors, J—’91. ‘Untersuchungen zur Physiologischen Morphologie der
Thiere,’ “I. Ueber Heteromorphose,’’ Wirzburg, 1891.

Maxsuatn, W.—’82. ‘Zeitschr. f. wiss. Zoologie,’ Bd. xxxvii, pp. 664—702.

Peart, R.—’01—’03. ‘Quart. Journ. Mier. Sci.’

Rosev v. Rosennor.—175d. ‘Iusektenbelustigungen,’ Theil iii, Niirnberg,

1755.

622 GEORGE WAGNER.

Scuneiper, C. K.—’90. ‘Archiv f. mikr. Anatomie,’ Bd. xxxv, pp. 321—
379.

Scuutze, F. E.—’71. ‘Uber den Ban und die Entwickelung von Cordylo-
phora lacustris,’ Leipzig, Englemann.

Scourrietp, D. J.—’01. ‘Journ. Queckett Microscopical Club’ (Ser. 2),
vol. vill, pp. 187—142.

TremBLey, A.—1744. ‘Mémoires pour servir 4 |’Histoire d’un genre de
Polypes d’eau douce a Bras en form de cornes,’ Paris, 1744. [There
are two editions of this work, one published at Leyden. I had only
the Paris edition at my disposal. ]

Witson, E. B.—’91. ‘Am. Naturalist,’ vol. xxv, pp. 4138 —433.

Zora, R.—’90. ‘Alcune Ricerche Morfologiche e Fisiologiche sull’ Hydra,’
Pavia, 1890. [Abstract in ‘ Archives Italiennes de Biologie,’ tome xv,
pp. 125—128. ]

Zykorr, W.—’98. ‘ Biologisches Centralblatt,’ Bd. xviii, pp. 270—272.

INDEX

TO! Vor F248;

NEW SERIES.

Allen on the anatomy of Pecilochztus,
79

Arachnida, the structure and classifi-
cation of, by Lankester, 165

Astacus fluviatilis, an anterior
rudimentary gill in, by Margery
Moseley, 359

Axolotl, maturation and fertilisation
of the egg of, by Jenkinson, 407

Benham on new species of Haplotaxis
and on the genital ducts of Oligo-
cheeta, 299

Benham on new species of Phreo-
drilus, 271

Birds, ear and columella of, by
Geoffrey Smith, 11

Choniostomatide, new forms of, by
Hansen, 347

Chromosomes of Tradescantia, by
Farmer and Shove, 559

Columella and ear of birds, by
Geoffrey Smith, 11

Copepoda, parasitic, on Crustacea, by
Hansen, 347

Ear and columella of birds, by
Geoffrey Smith, 11

Farmer and Moore on the reduction
divisions of the cell nuclei of
animals and plants, 489

Farmer and Shove on the chromo-
somes of Tradescantia, 559

Ferret, cestrous cycle in the, by
Marshall, 323

Fertilisation of egg of Axolotl, by
Jeukinson, 407

Fowler, notes on Rhabdopleura, 23

Fowler on anatomy of Gazeletta, 483

Gazeletta, anatomy of, by Fowler,
483

Genital ducts of Oligocheta, by
Benham, 299

Gill, an anterior rudimentary, in
Astacus fluviatilis, by Margery
Moseley, 359

Goodrich on the branchial vessels of
Sternaspis, 1

Hansen on Choniostomatide parasitic
on Malacostraca and Ostracoda,
347

Haplotaxis, new
Benham, 299

Hydra, movements and reactions of,
by Wagner, 585

species of, by

624.

Jenkinson on the maturation and
fertilisation of the egg of the
Axolotl, 407

Lankester, E. Ray, on the structure
and classification of the Arachnida,
165

Leishman-Donovan corpuscles, deve-
lopment. of into trypanosomes, by
Rogers, 367

Marshall on the cestrous cycle in the
common ferret, 323

Moore and Farmer on the reduction
divisions of the cell nuclei of
animals and plants, 489

Moore and Robinson on the behaviour
of the nucleolus in the spermato-
genesis of Periplaneta, 571

Moseley, Margery, on the existence
of an anterior rudimentary gill in
Astacus fluviatilis, 359

Nuclei of animal and plant cells,
reduction divisious of, by Farmer
aud Moore, 4$9

Nucleolus in spermatogenesis of
Periplaneta, by Moore and Robin-
son, 571

Oligocheta, genital ducts of, by
Benham, 299
Ostracoda, parasites on, by Hansen,

347

Pancreas of Teleostei, by Rennie, 379

Periplaneta, nucleolus in spermato-
genesis of, by Moore and Robinson,
571

Phreodrilus, new species
Benham, 271

of, by

INDEX.

Pecilochztus, the anatomy of, by
Allen, 79

Randles on the anatomy and affinities
of the Trochide, 33

Rennie on the epithelial islets of the
pancreas of Teleostei, 379

Rhabdopleura, notes on, by Fowler,
23

Robinson and Moore on the behaviour
of the nucleolus in the spermato-
genesis of Periplaneta, 571

Rogers on the development of try-
panosomes from the parasites of
Kala-Azar fever, 367

Shove and Farmer on the chromo-
somes of Tradescantia, 559

Smith, Geoffrey, on the ear and
columella of birds, 1].

Sporozoa, notes on, by Woodcock,
153

Sternaspis, branchial vessels of, by
Goodrich, 1

Teleostei, epithelial islets in pancreas
of, by Rennie, 379

Tradescantia, chromosomes of, by
Farmer and Shove, 559

Trochide, the anatomy of, by Randles,
33

Trypanosomes, development of, from
the parasites of Kala-Azar fever,
by Leonard Rogers, 367

Wagner on the movements and reac-
tions of Hydra, 585

Woodcock, notes on the Sporozoa by
153

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Fig 1.

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Diagrams illustrating three interpretations of the process of reduction in Animals and Plants.
A. Lhe heterotype, and homotype mitoses according to Hicker Vom Rath and Riickert.
B. The heterotype, and homotype mctoses according to te views held by Flemming and. others, and formerly by ourselves.
C. The heterotype, and homotype mitoses according © the views held by us, and embodied in the present paper.

Huth, Lith? London

Quart. Gourn Micr Sci Vol LE NSHL 38

44.

43.

42.

40.

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47,

46.

45,

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52.

ol.

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uart. Journ Mac Sei Yel LE NSA 10

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Huth, Lith London

ERNST MAYR LIBRARY

Date Due

JUN 23 1960
APR 1 3 iva

APR 2 5 2006

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