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Studies from the Morphologi 


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http://www.archive.org/details/cu31924024759510 


STUDIES 


FROM THE “AH 


MORPHOLOGICAL LABORATORY 


IN THE 


UNIVERSITY OF CAMBRIDGE. 


EDITED BY 


ADAM SEDGWICK, M.A., E.RS. 


FELLOW AND LECTURER OF TRINITY COLLEGE, CAMBRIDGE. 


Vol. V. 


London: 
Cc. J. CLAY AND SONS, 
CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, 
AVE MARIA LANE. 


1892 
$ 


CONTENTS. 


PAGE 
18. F, Harmer. On the embryology of the Ectoprocta. Plates I. 


and II. 1 


2A. E. SHretey. On the existence of communications between the 


Body-cavity and the Vascular System . i : . : a AT 
3F. G. Heatucote. On some points of the Anatomy of Polyxenus 
lagurus. Plate III. . ‘ d j ; ; ‘ ’ . 27 
5S. F. Harmer. Notes on the Anatomy of Dinophilus. Plates IV. 
and V. i ; ; ‘ : : : ; 37 
4C, Warzpurton. The Spinning Apparatus of Geometric Spiders. 
Plate VI. ‘ é ‘ ‘ ? : i ‘ - 62 
4A, E. Sarptey. On Phymosoma Varians. Plates VII.—X. . . 7 
2W. Bareson. On the Perceptions and Modes of Feeding of 
Fishes . : : ; ' : ‘ : i ‘ - + 100 
28. F. Harmer. On the Origin of the Embryos in the Ovicells of 
Cyclostomatous Polyzoa . ; 5 ; ‘ . ; . 102 
2A, E, SHIPLEY. On a new species of Phymosoma y : . 103 
28. F, Harmer. Land Planarians at Cambridge . : : . 104 
20. WarBurton. Notes on a collection of Spiders with a list of 
species taken in the neighbourhood of Cambridge .  . 105 


1 Reprinted from the Archives de Zoologie Expérimentale et Générale, Sér. 2, 
Tome v. 

2 Reprinted from the Proceedings of the Cambridge Philosophical Society, 
Vol. v1. 

3 From the Quarterly Journal of Microscopical Science, Vol. 30. 

4 Tbid. Vol. 31. 

5 From the Journal of the Marine Biological Association, New Series, Vol. I. 


iv CONTENTS. 


PAGE 


18. F. Harmer. On the British Species of Crisia. Plate XI. . 


1A,E. Sarptey. On a new species of Phymosoma with a synopsis 
of the genus and some account of its geographical distribution. 


Plate XII. 


1§. J. Hickson. The Medusz of Millepora Murrayi and the gono- 
phores of Allopora and Distichopora. Plates XIII. and XIV. 


20, Warsurton. Supplementary list of ia taken in the 
neighbourhood of Cambridge 


3A, E. Suiptey. On Onchesoma Steenstrupii. Plate XV. 


3A, Sepewick. Notes on the development of Elasmobranchs. Plate 
XVI. 


1 From the Quarterly Journal of Microscopical Science, Vol. 32. 


2 From the Proceedings of the Cambridge Philosophical Society, Vol. VIL. 


3 From the Quarterly Journal of Microscopical Science, Vol. 33. 


109 


165 


181 


214 
217 


234 


ON THE EMBRYOLOGY OF THE ECTOPROCTA 
BY 


SIDNEY F. HARMER, M.A, BSc, 
Fellow of King’s College, 


With Plates I. and II. 


THE opportunity of investigating the development of Alcyoni- 
dium was due to the kindness of Prof. H. de Lacaze-Duthiers, who 
permitted me to make use of the Zoological Laboratory at Roscoff 
during the summer of 1883. I desire to express my best thanks 
for the hospitality so courteously extended to me on that occasion, 
and to mention my agreeable recollections of the uniform kind-. 

“ness with which I was treated, during my stay at Roscoff, by 
Prof. de Lacaze-Duthiers himself and by all the members of his 
staff. 

Alcyonidium polyoum is extremely abundant on the Fucus 
serratus which grows on the rocks exposed at low water in the 
Riviere de Penzé, near Roscoff; its embryos were obtained in 
abundance during the months of July and August. 

The species was first described by Hassall (7), under the name 
of Sarcochitum polyoum, but is included by Hincks (8) in the 
genus Alcyonidium. The form which occurs in the Riviére de 
Penzé has been identified by Joliet (9) as S. polyoum, and I 
can depend on the accuracy of the statement made to me by 
M. Charles Marty, of the Zoological Laboratory at Roscoff, that 
my own specimens belong to the species described by Joliet from 
the same locality. I mention this fact, since the description given 
by Hassall and Hincks is in need of a few corrections, if their 

1 


2 SIDNEY F, HARMER. 


species is really identical with that which is found near Roscoff,— 
of which, however, I am not entirely convinced. 

My own specimens do not show the large papille mentioned 
by Hincks from which the polypides are said to issue. This, 
however, may possibly be due to contraction induced by the 
reagents in which they were preserved. The septa between the 
zoccia are clearly seen from the surface of the colony, whilst the 
embryos are invariably aggregated into spherical clusters, each 
contained in the tentacle-sheath of an individual whose alimentary 
canal has atrophied, instead of being “scattered singly throughout 
the polypidom,” as in Hassall’s description. In spite of the fact 
that in these respects the Roscoff species does not conform to the 
diagnosis given by Hincks for A. polyowm, it does not appear to 
me desirable to give a new specific name to the Roscoff form until 
the correctness of Hassall’s original diagnosis has been verified. 

I have observed individuals with twenty tentacles, the number 
given by Hassall, although in my own specimens twenty-one 
tentacles are more commonly present. It should be noticed that 
these numbers are considerably higher than those which characte- 
rize most species of Alcyonidiwm. 

Most of my observations on the development were made on 
sections of portions of the entire colony which had been preserved 
with corrosive sublimate. The best staining was obtained by 
using picrocarmine and washing successively with very dilute 
solutions of picric acid in water and various strengths of alcohol. 
By this method the nuclei were stained red and the yolk- 
spherules yellow. Hematoxylin followed by eosin and borax- 
carmine followed by hematoxylin were also used for differentiating 
the yolk-spherules from the nuclei. 

The eggs, several of which develop simultaneously in the same 
zocecinm, are large and possess numerous yolk-spherules (similar 
to those figured in the embryos) distributed uniformly throughout 
their protoplasm. During the segmentation and early develop- 
ment of the embryo, these yolk-spherules are met with indifferently 
in all the cells, and do not in the slightest degree preponderate in 
the hypoblastic elements. The segmentation (which is preceded 
by the formation of polar bodies) is of the remarkable type which 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 3 


appears to be characteristic of all the Ctenostomata and Cheilosto- 
mata, as described by Repiachoff (14), Barrois (1,2) and others. 
The segmentation-cavity was first distinguished in embryos com- 
posed of sixteen cells, which are disposed in four longitudinal 
rows of four each, two rows belonging to the oral half of the embryo, 
and two to its aboral half. At the 48-cell stage, the aboral half is 
composed of thirty-two cells, and the oral half of twelve cells, whilst 
four cells are internal. In the aboral region, the arrangement is as 
follows : 

(1) two longitudinal rows, of four cells each, disposed sym- 
metrically, right and left of the median plane, and occupying the 
centre of the aboral surface, 

(2) a ring of eight cells completely surrounding the central 
group of cells, and in its turn surrounded by 

(3) a peripheral ring of sixteen cells, which are, as Barrois has 
shown, the commencement of the ciliated ring. 

The oral half consists of a central group of four large cells, 
surrounded by twelve peripheral cells. 

The segmentation-cavity is at this stage fairly large, but is 
partially filled by four cells which are situated immediately above 
the central oral cells, and which have probably been derived from 
these latter. The four cells lying in the segmentation-cavity are 
the commencement of the hypoblast. 

At a somewhat later stage I have observed the existence of a 
wide depression, the blastopore, situated in the middle of the oral 
surface and continuous with a somewhat irregular cavity surrounded 
by several large hypoblast cells. 

At a subsequent stage, when the segmentation-cavity is 
partially filled by a large mass of cells (probably representing 
hypoblast plus mesoblast), the blastopore appears to have closed, 
whilst still later the segmentation-cavity is completely obliterated 
by the internal cell-mass, and the various organs of the larva are 
commencing to make their appearance. 

In the first stage selected for figuring (Pl. I, fig. 1, a median 
longitudinal section through a young embryo) most of these organs 
are already partially established. The yolk-spherules are still to 
be found in all the tissues of the embryo. Two of the large cells 


1—2 


4 SIDNEY F. HARMER. 


which compose the ciliated ring (¢.7.) are to be seen at opposite 
ends of the section. The front part of the oral surface (within the 
area of the ciliated ring) is in the form of a depression, the 
“pyriform organ” of Barrois. This structure is developed as a 
cup-like involution of the epiblast, and there is no reason for 
believing that in Alcyonidium it makes its appearance in the 
interior of the embryo and subsequently fuses with the skin, as is 
stated by Barrois to be the case in Lepralia (2, p. 24). Not far 
behind the middle of the ventral surface is the aperture of the 
large sucker (s.) or “internal sac” of Barrois; this structure, like 
the pyriform organ, is developed as an invagination of epiblast, its 
aperture being much wider in earlier stages than in the embryo 
figured. 

The alimentary canal consists of stomach (st.) and cesophagus 
(ws.). The stomach is lined by an extremely indefinite epithelium 
and has probably been developed by the hollowing out of the solid. 
hypoblast-mass of earlier stages. The cesophagus (perhaps deve- 
loped as a stomodzum) has a very fine lumen which can be traced 
as far as the stomach. The mouth (m.) is large and is far more 
conspicuous at this than at any of the later stages. 

There is some slight reason for believing that the region 
immediately behind the aperture of the sucker (internal sac) 
represents, potentially, the anal region (vide fig. 1). If this is 
really the case, it is obvious that the embryo is entoproctous, and 
that the part of the body between the posterior end of the sucker 
and the ciliated ring represents the anal cone. 

Figs. 2 and 3 are drawn from median longitudinal sections, the 
latter illustrating the structure of an embryo almost ready to be 
hatched, whilst the former explains the condition of the various 
organs in the period intermediate between the stages represented 
in fig. 1 and fig. 3 respectively. In fig. 2 the alimentary canal is 
seen to have acquired its maximum development. The lumen of 
the stomach (st.) is very conspicuous, although the epithelium 
which bounds it is by no means distinct, at this or at any other 
stage. This epithelium may consist of a mass of yolk-spherules 


1 The distinctness of the anal region has unfortunately been exaggerated in the 
figuie, 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 5 


embedded in a small quantity of protoplasm, with a few nuclei at 
intervals, or it may have the form of a very thin protoplasmic 
layer, in which nuclei are sparingly developed; but it is in any 
case extremely unlike an ordinary secreting epithelium, and this 
taken in conjunction with the facts (1) that the lumen of the 
stomach becomes progressively smaller as development proceeds, 
and (2) that there is probably, in the later stages, no communica- 
tion between the stomach and the exterior, leads me to the belief 
that in Alcyonidium the alimentary canal is a rudimentary 
structure. A reference to fig. 3 will show that food could hardly, 
by any possibility, pass through the cesophagus at this stage of the 
development. Owing to the large supply of food-yolk in the eggs, 
to the fact that development proceeds within the body-wall of the 
adult, to the extremely short free larval life and to the degenera- 
tion of many of the embryonic organs during the metamorphosis, 
the alimentary canal is no longer required in its functional form. 

The mouth (m.) is unmistakeable in fig. 2; the cesophagus, 
whose walls contain large numbers of yolk-spheres, has, however, 
no obvious lumen except near its junction with the stomach; the 
supposed anal region is now provided with a few cilia. The 
sucker is loaded with less yolk than in the preceding stages, 
although a few spheres still remain in its walls. A deep groove 
(m.c.), running round the aboral region of the embryo, has 
appeared on the dorsal side of the ciliated ring, with which it 
is concentric. This groove is already distinguishable in fig. 1, and 
is the structure which has been described by Barrois and others as 
the mantle-cavity. Its function is probably to render possible the 
revolution of the ciliated ring into the interior of the vestibule 
which is formed on the ventral side of the larva during the process 
of fixation. 

The changes which subsequently take place in the alimentary 
canal, sucker and mantle-cavity may be understood by referring to 
fig. 3. The cesophagus is, at this stage, somewhat ditiicult to 
distinguish at the middle part of its course, whilst the stomach has 
thicker walls and a less conspicuous cavity than before. 

The sucker has a very small lumen, and is further characterized 
by the almost complete absence of yolk from its long, columnar 


6 SIDNEY F. HARMER. 


cells. It extends into the lateral regions of the embryo, where it 
passes further forwards than in the middle line; its anterior 
border is thus markedly concave, as figured by Barrois (1) in many 
genera of Cheilostomata and Ctenostomata. The mantle-cavity is 
lined by a very high epithelium. 

The function of the pyriform organ is by no means clear. 
Repiachoff (15) states that in Tendra a mass of cells is segmented 
off from the embryonic hypoblast in front of the mouth, and sup- 
poses that this mass represents the hypoblastic vesicle described 
by Hatschek in the embryos and stolons of Pedicellina. It ap- 
pears to me probable, however, that the region which corresponds 
in Alcyonidium to that including Repiachoft’s supposed hypoblastic 
vesicle in Yendra is occupied by a mass of nervous tissue which 
constitutes the brain of the larva. In spite of this, it is still 
possible to compare this region with the “dorsal organ” of 
the Entoprocta, since there are reasons (cf. 5 and 6) for doubting 
the existence of hypoblastic elements in the “dorsal organ” 
and for regarding it, on the contrary, as an important nerve- 
centre. 

Fig. 4, which illustrates the structure of the region in question 
in Alcyonidium, is a transverse section through the anterior part of 
an embryo of about the same age as that represented in fig. 3, the 
ciliated ring (¢r.) and mantle-cavity (m.c.) having precisely the 
same arrangement as in that figure. In the middle of the ventral 
surface is seen the cup-shaped depression which constitutes the 
pyriform organ; at the sides of the latter, as far as the ciliated 
ring, the epiblast is thick, with finely granular protoplasm and few 
yolk-spheres. 

As in the preceding figures, there is no definite body-cavity, 
although certain irregular spaces occur at intervals in the 
mesoblastic structures. The middle of the section is occupied by 
a large development of fine fibrils, bounded laterally by masses of 
nucleated protoplasm without yolk-spheres, and these masses 
appear to be continuous with the dorsal epiblast at the two sides of 
the middle line. I shall provisionally assume that the structures 
just described are of nervous nature, and that they represent the 
brain of the embryonic Alcyonidiun. 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 7 


The pyriform organ has at first sight the appearance of a 
mucous gland, owing to the presence in it of large spaces filled 
with a transparent substance, which does not readily take up 
staiping materials. A more careful examination seems, however, 
to show that the organ is composed of a series of cells closely 
packed together at their outer ends, and prolonged internally into 
fine processes between which occur other cells filled with vacuole- 
like spaces. The nuclei of the latter cells are situated, for the 
most part, at their inner ends. It is important to notice that 
there is no sharp line between the pyriform organ and the central 
mass of nerve-fibres, which can in fact be traced into the cells 
of the pyriform organ. It seems to me probable, from the facts 
just described, that the principal function of the organ in question 
is a sensory one. The larva ordinarily swims with its pyriform 
organ directed forwards, and it is possible that this structure may 
be of use in estimating the character of the substance on which 
the animal desires to fix itself. The intimate connection of the 
pyriform organ with the central nervous system, together with the 
ciliation of the organ as a whole, is in favour of the view that the 
structure in question is of nervous rather than of glandular nature : 
I am unable to say whether all the cells of the pyriform organ are 
ciliated’. 

The supposed brain of the embryo of Alcyonidiwm consists then 
of a mass of nerve-fibres partially surrounded by ganglion-cells (as 
I identify the masses of nucleated protoplasm seen at the sides of 
the fibrous mass in fig. 4). The ganglion-cells are connected with 
the dorsal epiblast, except near the middle line, where a wedge- 
shaped mass of tissue characterized by the abundance of yolk- 
spheres intercalates itself into the nervous system. The fibrous 
mass of the ganglion sends off a pair of strong nerves (one of which 
is shown on the right side of fig. 4, nv.), which can be traced, in 


1 The pyriform organ has certain obvious resemblances with the structure de- 
scribed by Kleinenberg (Zeits. f. wiss. Zool., T. xutv, 1886, p. 61) in the larva of 
Lopadorhynchus as the Kopfschild, although as the latter belongs to the preoral 
region it is probably not to be regarded as the homologue of the former. The 
Kopfschild is said to be composed of vacuolated cells, which, although not them- 
selves of nervous nature, are in the most intimate connection with the nervous sys- 
tem; the organ is moreover in relation with a ciliated sense-organ. 


8 SIDNEY F. HARMER. 


the sections, as far as the ciliated ring. These two nerves 
probably regulate the action of the cilia of the latter, and appear 
further to give off fibrils to the thick ventral epiblast at the sides 
of the pyriform organ. 

In fig. 3 may be seen the supposed nervous structures of 
an old embryo in longitudinal section, the brain being connected 
with the dorsal epiblast, as in fig. 4. 

In fig. 1, the region of the future brain is indicated by 
br. It is difficult to assert that any nervous structures are at 
present developed, but it may be noticed that the dorsal epiblast 
is very much thickened above the pyriform organ. This character 
is still obvious in embryos of the age of fig. 2, where it can usually 
be seen (and often more distinctly than in fig. 2) that the dorsal 
thickening of epiblast is so intimately connected with the ganglion- 
cells of the brain that it can hardly be doubted that these cells 
have been derived from the dorsal thickening itself. The origin 
of the nerve-fibres is more difficult to ascertain. It is possible 
that they may be developed from the dorsal side, and subsequently 
enter into relation with the pyriform organ and other parts of 
the ventral surface—or that they are developed partly from the 
dorsal and partly from the ventral surface. Such sections as 
figs. 3 and 4 seem to show that the nerve-fibres are not entirely 
derived from the ventral surface, and it appears to me probable, 
on the whole, that the greater part of the nervous system is 
developed from the dorsal epiblast. 

If it can be admitted that even a portion of the “brain” 
has this origin, it then follows that we have in the larve of 
the Ectoprocta, as in those of the Entoprocta, a development of 
nervous tissue. from the dorsal side of the ciliated ring, in the 
anterior part of the embryo. The region just described as “brain” 
in Alcyonidium will thus be the homologue of the “dorsal organ” — 
the supposed endodermic vesicle—of the Entoprocta. It would be 
interesting, in this connection, to know whether the pigment-spots 
described by Nitsche (11) and others in the larva of Bugula are in 
any way connected with this ‘dorsal organ’, as is the case with the 
eyes of the larva of Zorosoma. ; 

The above conclusions do not altogether agree with the 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 9 


statements of previous observers, to which we must now devote 
our attention. 

It is practically certain that the separation of a mass of 
endoderm-cells from the alimentary canal does not take place, 
in Alcyonidiwm, in the region of the pyriform organ, as described 
by Repiachoff (15) in Tendra. The cesophagus is sharply dis- 
tinguished, except in the earlier stages, from the tissues im- 
mediately in front of it by the large number of yolk-spheres 
present in its walls (vide figs. 2 and 3), and it is hardly to be 
supposed that the fibrillar tissue in front of the cesophagus 
could in any case be derived from the latter. I feel myself 
obliged to doubt the accuracy of Repiachoff’s statements on 
this part of the development of Tendra, although it will be 
noticed that in other respects the description I have given 
agrees very closely with that of Repiachoff. 

Vigelius (16) has published certain figures of sections of 
Bugula-embryos which suggest the possibility of the occurrence, 
in that genus, of a nervous system similar to that of Alcyonidiwm. 
Tn fig. 49 of Pl. XXVII Vigelius shows a layer of fibrils running 
round the pyriform organ in exactly the same position as the 
nerve nv. in my own fig. 4. Vigelius does not, however, in his 
description call any attention to the existence of these supposed 
nerve-fibrils. Again in fig. 14 of Pl. XXVI, Vigelius shows that 
the structure of the “calotte” of the larva is almost identical with 
that represented in the dorsal region of fig. 4 of the present 
paper ;—ie. that an internal proliferation of epiblast cells on 
each side of the middle line apparently takes place in this 
part of the larva. These cells may perhaps correspond with 
the structure identified as the brain in Alcyonadium, and the 
similarity between this genus and Bugula is rendered still more 
striking by the existence, in the latter (as is shown by the ' 
figure of Vigelius), of a central region which does not take 
part in the proliferation, and which projects as a wedge-like 
mass into the supposed nervous tissue (cf my own fig. 4). 
Vigelius does not, however, show that there is any connection 
between the cells proliferated off by the “calotte” and the fibres 
round the pyriform organ. 


10 ' SIDNEY F. HARMER. 


It is believed by many writers that there is no fundamental 
difference between the larve of the Ectoprocta and those of the 
Entoprocta, and that the latter belong to the true Trochospheral 
type. This view is now adopted by Barrois (4), who admits 
that the alimentary canal, the oral and aboral surfaces and 
the ciliated ring are of essentially similar construction in the two 
groups of larve, and that the internal sac of the larva of 
the Ectoprocta is the homologue of part of the vestibule of 
the larva of the Hntoprocta*, I am in complete accord with 
this view, but would myself push the agreement between the 
two types of larvae somewhat further, in endeavouring to esta- 
blish the homology of a part of the embryo of Alcyonidium with 
the “dorsal organ” of the Entoprocta. 

Although it is true that in my paper on Loxosoma (5) I 
suggested that the pyriform organ itself might be the homologue 
of the brain of the Hntoprocta, Lankester, in his article Polyzoa in 
the Encyclopedia Britannica (10), has somewhat misrepresented 
the view then expressed by me. 

In Lankester’s fig. 20 (from Balfour, after Barrois), m? is 
the pyriform organ, whilst st. (said to be considered by me as 
the cephalic ganglion) is the sucker or internal sac, the larva 
being turned with its dorsal surface downwards. 

By reference to one of Repiachoff’s figures? of Tendra, one 
of the Chetlostomata, it will be seen that the structure of the 
embryo of this genus is, as has been already explained, extremely 
similar to that of the larval Alcyonidiwm. The pyriform organ 
(a.), the alimentary canal (0., g.) and the internal sac (v.) correspond 
with those of Alcyonidium. The dorsal thickening of epiblast, y., 
which I formerly supposed to represent the cement-gland of the 


+ 1 The work just quoted was published simultaneously with my paper On the 
Life-History of Pedicellina (6), and some of the figures in the latter would not 
have been required had the memoir of Barrois appeared at an earlier date. It will 
be hardly necessary to consider in detail Barrois’ criticisms of my previous results, 
since certain modifications of the views formerly held by me (especially with regard 
to the nature of the metamorphosis) which I have explained in my paper referred 
to, bring me into moderately complete agreement with Barrois on the more impor- 
tant points on which he does me the honour of noticing my results. 
2 Reproduced in Pl. XX, fig. 22 of my paper on Loxosoma. 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 11 


Entoprocta, is more probably the equivalent of the dorsal thicken- 
ing of epiblast connected with the formation of the brain in 
Alcyonidium. The cells e., identified by Repiachoff as hypoblastic 
in nature, are perhaps part of the brain-tissue itself. 

In fig. 24 (Cyphonautes) of the plate just referred to, I 
reproduced one of Repiachoff’s figures which was in some respects 
wrongly interpreted, owing to my previous inability to read Repia- 
choff’s description. I now find that the structure z. c. is merely 
the anterior part of the ciliated band, that #. is the pyriform 
organ and that e. is the supposed endoderm-bud. This latter 
structure is not said by Repiachoff to give rise to the first poly- 
pide, as I formerly supposed. 

It has recently been proved by Ostronmoff (12) that the organ 
shown in Repiachoft’s figure just in front of the rectum (“lorgane 
énigmatique de Schneider”) is in reality the sucker or internal sac, 
by which fixation is effected. The structure of Cyphonautes is 
hence more similar to that of other Hctoproct-larve than was 
formerly imagined to be the case. 

It is difficult to assert at present that the cement-gland of the 
Entoprocta is represented in the L£ctoprocta. Further investi- 
gations are needed to show whether the calotte of the latter 
is to be regarded as the homologue of the cement-gland, of 
the dorsal organ or of any other structure possessed by the larvee 
of the H’ntoprocta. . 

The alimentary canal of the larve of the Ectoprocta appears to 
be functional in Cyphonautes alone (ie. the larva of Membranipcra). 
It has, however, been shown to be present, more or less well de- 
veloped, in Tendra (Repiachoff, 15), some Cyclostomata (Ostroumoff, 
13), whilst I believe it to occur in Flustrella. Barrois (4) has more- 
over suggested that the mouth is really shown as the depression ce 
in Pl. VIL, fig. 13 and elsewhere in his large memoir (1), so that. 
there is a considerable amount of evidence in favour of the view 
that the Zctoproct-larvee were formerly provided with a distinct 
alimentary canal. Even in those cases where a digestive tube 
with a complete ventral curvature does not exist, the hypoblast is 
formed in the embryo as in other Polyzoa with a better developed 
alimentary canal, but afterwards assumes the form of a mass of 


12 SIDNEY F. HARMER. 


cells filling up most of the interior of the embryo. This has been 
shown, for instance, by Barrois (4) and Ostroumoff (13) for Cyclo- 
stomata, by Vigelius (16) for Bugula and by Repiachoff (15) for 
Bowerbankia. . 

The discovery of a well developed (though probably not func- 
tional) alimentary canal in the larve of the Ctenostomata (Alcyo- 
nidium) and of the Cyclostomuta (as shown by Ostroumoff) relieves 
us from the necessity of supposing that Cyphonautes is really an 
archaic larva :—an assumption which is very difficult to reconcile 
with current views as to the highly specialized character of the 
‘Cheilostomata. 

Cyphonautes may perhaps be regarded as a much modified 
type of larva in which the alimentary canal has been preserved in 
a functional form (owing perhaps to a longer larval life than in 
other Polyzoa ?), whilst the oral face has become transformed into 
an atrium in which are situated the pyriform organ and the 
internal sac. 

It is at present hardly possible to affirm that the characters of 
the Alcyonidiwm-larva are retained throughout the group of the 
Ctenostomata, since the accounts given by Barrois (1, 3 and 4) and 
Repiachoff (15) of the larvee of this division of the Polyzoa are by 
no means concordant. : 

Barrois (3) has stated that the Ctenostomata (in which group it 
may be assumed that he does not include Alcyonidium) are 
characterized by the absence of the internal sac. Repiachoff (15) 
has, however, given a description, with figures, of the development 
of Bowerbankia which may perhaps tend to show that this structure 
is not really absent in the larva of this genus. Repiachoff’s 
description and figures are extremely difficult to understand 
thoroughly, but if we accept his statements, the larva of Bower- 
bankia is very different from that of other Ctenostomata. A 
comparison of Repiachoff’s paper (and especially of the series 
of sections of the larva figured on Pl. IV) with my own pre- 
parations of Alcyonidiwm leads me to suspect that Repiachoft’s 
identifications of the surfaces of his larvae were not accurate. 

A further investigation of the larva of Bowerbankia is needed 
to clear up its structure. I will at present merely point out that 


ON THE EMBRYOLOGY OF THE ECTOPROCTA, 13 


a great part of the difficulty in the comparison between Repia- 
choff’s larva and that of Alcyonidium would be removed if it could 
be shown (as I suspect will be the case) 

(1) That Repiachoff’s mantle-cavity (ct. in the figures) is 
really the internal sac or sucker. 

(2) That the ‘dorsal: ciliated furrow’ of the Bowerbankia larva 
is the pyriform organ. 

In conclusion I may allude to Repiachoff’s statement (15) that 
the brown body of the recently fixed larva is ciliated. It is 
probably not very rash to assume that these cilia really belong to 
the external surface of the larva involuted to the interior during 
the process of fixation. 


List of memoirs referred to: 


1. Barrois, J.; Recherches sur l’Embryologie des Bryozoaires; Lille, 


1877. 

2, —— Mém. sur la Métamorphose des Bryozoaires ; Ann. des 
Sci. Nat. (Zool.), 6° Sér., T. rx, 1879—1880, No. 7. 

3. —— Embryogénie des Bryozoaires; Journ, de ]’Anat. et de la 


Physiol., T. xvi11, 1882, p. 124. 


4, —— Mém. sur la Métamorphose de quelques Bryozoaires ; 
Ann. des Sci. Nat. (Zoot.), 7° Sér., T. 1, 1886, No. 1. 


5. Harmer, 8. F.; On the Structure and Development of Loxosoma; 
Quart. Journ. Micr. Sci., Vol. xxv, 1885, p. 261. 


6. —— On the Life-history of Pedicellina; Quart. Journ. Micr. 
Sci., Vol. xxvu1, 1887, p. 239. 


7. Hassall, A. H.; Description of two new genera of Irish 
Zoophytes ; Ann. and Mag. of Nat. Hist., Vol. vi, 1841, p. 
484, : 


8. Hincks, T.; A History of the British Marine Polyzoa (two 
vols.) ; London, 1880. 


9. Joliet, L.; Cont. & Vhist. nat. des Bryozoaires des Cotes de 
France ; Arch. de Zool. Exp. et Gén., T. v1, 1877, p. 292. 


1+ 


10. 


11. 


13. 


14. 


15. 


16. 


SIDNEY F. HARMER. 


Lankester, E. R.; Article ‘Polyzoa’; Encycl. Britannica, 9th 
Ed., Vol. xx, 1885, p. 440. 


Nitsche, H.; Beitrige zur Kenntniss d. Bryozoen—I. Beobacli- 
tungen tiber die Entwicklungsges. ein. chilostomen Bryo- 
zoen; Zeits. f. wiss. Zool., Bd. xx, 1870, p. 1. 


Ostroumoff, A.; Note sur la métamorph. du Cyphonautes; Zool. 
Anzeiger, viul. Jahrg., 1885, p. 219. 


—— Zur Entwicklungsges. d. cyclostomen Seebryozoen ; Mitt, 
a. d. zoo]. Stat. zu Neapel; Bd. vir, 1887, p. 177. 


Repiachoff, W.; Ueb. d. ersten embryonalen Entwicklungsvor- 
ginge bei Tendra Zostericola; Zeits. f. wiss. Zool., Bu. 
xxx Suppl., 1878, p. 411. 


—— On the Morphology of the Polyzoa (Russian); Proc. New 
Russian Soc. Naturalists, Vol. v1, Odessa, 1880. 


Vigelius, W. J.; Zur Ontogenie d. marinen Bryozoen; Mitt. a. 
d. zoo]. Stat. zu Neapel, Bd. v1, 1886, p. 499. 


EXPLANATION OF THE PLATES, 


(Figs. 1—3 were drawn with ;}, oil immersion of Zeiss, 1 oc.—-Fig. 


4 was more highly magnified.) 


General reference letters. 


br. brain ; 

ar, ciliated ring ; 

m. mouth; 

m.c. mantle-cavity ; 

nv. nerve ; 

es. cesophagus ; 

p.o. pyriform organ ; 

s. internal sac or sucker ; 
st. stomach, 


-In all the figures the yolk-spheres are lightly shaded. 


ON THE EMBRYOLOGY OF THE ECTOPROCTA. 15 


PLATE I. 


Median longitudinal section of a young embryo. 


1 
Fig. 2. Median longitudinal section of an older embryo. 


PLATE II. 


Fig. 3. Median longitudinal section of an embryo almost ready to 
be hatched. 


Fig. 4. Transverse section of an embryo of the age of fig. 3 (more 
highly magnified), passing through the region of the brain and pyriform 
organ. 


. The manuscript of the above paper was received by Prof. de Lacaze-Duthiers in 
the beginning of August, 1887. Since that time I have had an opportunity of 
becoming acquainted with two memoirs by Dr Ostroumoff on the Polyzoa of the 
Gulf of Sebastopol. I regret that it was not possible for me, during the correction 
of my proofs, to take into consideration the results arrived at by this observer. 


ON THE EXISTENCE OF COMMUNICATIONS 
BETWEEN THE BODY-CAVITY AND THE 
VASCULAR SYSTEM 


BY 


ARTHUR E. SHIPLEY, M.A. 
Fellow of Christ’s College, Cambridge. 


In the General Considerations which follow Mr Sedgwick’s 
recent paper upon the development of Peripatus Capensis, he sums 
up the characteristics of the coelom in the following terms: (i) the 
coelom does not communicate with the vascular system; (ii) it 
communicates with the exterior through nephridial pores ; (iii) its 
lining gives rise to the generative products; (iv) it developes either 
as one or more diverticula from the primitive enteron, or as a 
space or spaces in the unsegmented or segmented mesoblastic 
bands (in the latter case called mesoblastic somites). Later on 
he calls attention to the fact that “there are certain animals to 
which the above general considerations as to the distinctness of 
the coelom and the vascular system do not apply.” The animals 
here referred to are the Hirudinea and the Nemertea. In a, later 
paper Sedgwick suggests the possibility that the nephridial 
funnels of Leeches might possibly open into a closed vesicle which 
lies in, but does not open into the vascular system. That some 
such structure may have been overlooked is rendered more 
probable when one recalls the number of able observers who failed 
to observe similar structures in Peripatus, and the fact that so 
careful a worker as Oscar Schultze overlooked the comparatively 
large nephridial funnels, when working at the excretory system of 
Clepsine. 

Last term I devoted some time to the examination of these 
points. The forms I investigated were Clepsine, and to some 


2 


18 ARTHUR E. SHIPLEY. 


extent Pontobdella amongst the Rhyncobdellidae, and amongst 
the Gnathobdellidae, Hirudo and Nephelis, and I may as well say 
at once that my researches on these forms confirm the results 
which Bourne published in the year 1884 in his exhaustive paper, 
“ Contributions to the Anatomy of the Hirudinea’.” 

The points to which I particularly directed my observation fall 
under three heads. 

Firstly: Do the internal funnels really open, or end blindly, 
and in what spaces do tbeir internal ends lie ? For instance, are 
there any such sacs as Sedgwick has described enclosing the 
funnels of the nephridia of Peripatus? 

Secondly: the communication between the true blood spaces 
and the sinuses, the nature of the fluid found in these spaces, and 
the circulation of the blood. 

Thirdly: the embryological origin of the sinuses. With re- 
gard to this last I have been unable to make any investigation, 
but a certain amount of information on this subject is found in the 
writings of Nusbaum, Whitmann, and others. 

With regard firstly to the nephridial funnels of Clepsine, I can 
fully confirm Bourne’s statements. The funnel is usually com- 
posed of two cells, but in some cases I have seen three nuclei 
indicating the presence of three cells in the funnel ; these surround 
a lumen; on one side this lumen is continuous with the sinus, and 
on the other hand with a sac. The lumen of the funnel is lined 
with long cilia. Bourne’s figure of this structure is rather dia- 
grammiatic; the lumen of the funnel is occluded ; but he definitely 
states that it opens, and in some of my preparations the coagulated 
mass of fluid in the sinus is joined to a similar coagulum in the 
sac mentioned above, by a strand of. coagulated matter which in 
all respects resembles blood. The sac is usually full of coagulated 
fluid with small corpuscles scattered in it. In one nephridium 
there were two funnels, each opening into the sac; and again, 
I once saw a bunch of three or four funnels connected with the 
single sac of a nephridium. 


The internal end of the nephridium of Hirudo does not open, 


? Quarterly Journal of Microscopical Science, Vol. xxtv. p. 419. 


EXISTENCE BETWEEN BODY-CAVITY AND VASCULAR SYSTEM. 19 


but is surmounted by a number of cells, each with a depression. 
The fact that it does not open is regarded by Bourne as due to 
degeneration. This swollen end lies in a space which contains red 
blood, and there is no sac full of coagulated blood and corpuscles 
as in Clepsine. 

Nephelis, however, is provided with nephridial funnels which 
do open on the one hand into the space in which their internal 
ends are situated, and on the other into a sac similar to that 
found in Clepsine, which contains both coagulum and corpuscles. 

With regard to the spaces in which the funnels lie, there seems 
to me to be no doubt that Bourne’s description is correct. In 
Clepsine, the funnels lie in pairs, in the ventral sinus, with the 
ventral vessel and nerve cord between them. No trace of any 
special sac, such as is found in Peripatus, is present. 

In Nephelis the funnels open into a special enlargement of the 
botryoidal tissue, but there is no reason to regard this as anything 
more than a development of the coelomic spaces, as Bourne has 
done. 

Again, in Hirudo, where the funnels do not open, the blind 
internal end lies in a perinephrostomial sinus, which again possesses’ 
no characteristics which would justify the assumption that it is 
fundamentally different from other coelomic spaces. 

Before passing on to consider the means of communication of 
the vascular and coelomic spaces, I wish to insert a few remarks 
upon the sacs which are present on the nephridia, which have 
internal open funnels, and in which numerous corpuscles from the 
blood are found. These corpuscles seem to be degenerating, and 
in some cases they appear rather more granular than the normal 
corpuscles in the blood. 

It has occurred to me that we have to do here with a pheno- 
menon similar to that which Durham’ has described in Asterias 
rubens. The amoeboid corpuscles, after devouring some substance 
which it is to the advantage of the organism to excrete, instead of 
working their own way to the exterior, are taken up by the open 


1H. E. Durham, “The Emigration of Amoeboid Corpuscles in the Starfish.” 
Proc. Roy. Soc. Vol. 48, p. 327. : ; : 
2—2 


20 ARTHUR E. SHIPLEY, 


funnel of the nephridium, and in the sac they disintegrate and are 
eventually thrown out from the body. In Asteroideae, where there 
are no nephridia, the corpuscles work their way out through the 
body-wall. . 

We owe our knowledge of the paths by means of which the 
fluid passes from the blood vessels into the coelom chiefly to 
Lankester and Bourne. Besides the direct communications which 
exist in the Rhyncobdellidae, there is the communication by means 
of the botryoidal tissue which is seen at its best in the Gnatho- 
bdellidae. A fragment of the brown tissue of a Leech shews at 
once the connection of the lumen of the botryoidal tissue with 
that of the thin walled vessels. And my sections through Clepsine 
and Hirudo shew in numerous places the large openings by means 
of which the botryoidal tissue is put into communication with the 
sinuses, sometimes a continuous coagulum being found, lying half 
in one and half in the other system of spaces. 

The same kind of blood is found in both the true vessels and 
the sinuses, except that, as Bourne points out, certain large 
corpuscles which occur in the sinuses of Clepsine and Pontobdella 
are not found in the blood vessels, being, as he suggests, too large 
to pass through the communicating channels. 

The contraction of the dorsal vessel in its sinus can be seen 
without difficulty, and I have often watched the ventral vessel 
contract, sending the blood from before backward, whilst the 
current in the sinus surrounding the vessel flowed in the reverse 
direction. The fluid and corpuscles in both vessels and sinuses 
being apparently identical. 

The foregoing facts fully corroborate Bourne’s statements that 
the nephridia open into the sinuses, which in their turn are in 
communication with the blood vessels, and which contain the 
same fluid as the vascular system. With regard to the embryo- 
logical nature of these spaces we are largely indebted to the 
researches of Nusbaum’ He describes in Clepsine the meso- 
blastic bands dividing into 33 somites. Each of these somites 
acquires a cavity which gradually increases in size. The walls of 


1 Archives Slaves de Biologie, Vol. 1, pp. 320 and 539. 


EXISTENCE BETWEEN BODY-CAVITY AND VASCULAR SYSTEM. 21 


this cavity on the upper side, towards thé endoderm, become only 
one cell thick, they form the splanchnopleure. The opposite wall, 
the somatopleure, that next the ectoderm, is however several cells 
thick. 

The anterior wall of each somite fuses with the posterior wall 
of the preceding somite, and thus septa, comparable to those of the 
higher worms, are formed, and persist for a short time in embryonic 
life. Soon, however, the somites fuse with one another, and their 
cavities become continuous. Then the walls of the two lateral 
cavities which are thus formed, and at first are only in the ventral 
face of the embryo, commence to grow round the endoderm. Part 
of the tissue forming the septa persists as the dorso-ventral muscles. 
The spaces on each side, growing dorsally and ventrally, fuse, and, 
by the arrangement of the dorso-ventral muscles two longitudinal 
septa are formed which divide the common space into a dorsal, 
ventral, and two lateral sinuses. These are the blood sinuses, 
which by the development of the connective tissue and muscles 
become relatively much smaller in the adult than in the embryo. 

Nusbaum further describes and figures the development of the 
dorsal and ventral vessel, both of which apparently arise as a solid 
cord of cells, proliferated from the splanchnic layer of the meso- 
derm, in the middle dorsal and ventral line. They subsequently 
acquire a lumen, and, separating off, lie in their respective sinuses. 

The same author, in describing the development of the nephridia, 
points out that in the young embryo.they appear in every somite, 
even in those which form the posterior sucker, where they subse- 

- quently abort. 

Thus with regard to the origin of the space and the opening 
into it of the nephridia, the sinuses of the Hirudinea are truly 
coelomic, the embryological researches of Nusbaum confirming in 
a most striking way the predictions of Bourne. 

If we turn to the third characteristic of a coelom, that “its 
lining gives rise to the generative products,” the evidence is not 
quite so satisfactory. The origin of the reproductive cells is 
probably an example of “ precocious segregation.” The sexual cells 
arise from the mesoblasts—the segment cells of Whitmann—which, 
arising posteriorly, multiply and pass forward till a heap of them 


22 ARTHUR E. SHIPLEY. 


is formed laterally in each somite. One pair of these form the 
ovary and seven pairs become testes, According to Nusbaum the 
tunica of the generative glands is formed at the expense of the 
mesoderm. This doubtless buds off corpuscles, just as it does into 
the sinus, and thus forms the colourless corpuscles which Bourne 
found in the fluid surrounding the true ovary. Nusbaum traces 
the oviduct and vas deferens back to nephridia. 

I have attempted so far to shew firstly that there is no doubt 
that the old statements with regard to the blood system of Leeches 
being in communication with the sinus system is true, and secondly 
that the sinus system is coelomic in nature. So that with regard 
to the group Hirudinea, the vascular system is undoubtedly in 
communication with the coelom. 

Let us now turn to the Nemertines, the second group of 
animals mentioned by Sedgwick as forming an exception to the 
rule that the blood system is independent of the coelom. 

The nephridial system of these animals is not so definite in its 
arrangement as amongst the Hirudinea. Oudemans* has examined 
it in a great number of forms, and I have to some extent been 
able to confirm his observations. In his summary at the end of 
his paper he states, “the nephridial system of the Nemertea 
consists of one or more canals, directly communicating, or not, with 
the vascular system, provided, or not, with cilia, and communicating 
with the exterior by means of excretory ducts.” 

But when we come to consider the nature of these spaces 
which contain blood, and in which the internal end of the 
nephridium is sometimes situated, we shall see that they differ 
considerably in their fundamental origin from the sinus system 
of the Hirudinea. 

In his valuable work on the embryology of Lineus obscurus, 
Hubrecht? points out that the blood vascular system together 
with the proboscidian cavity represents the last remnants of the 
archicoel or segmentation cavity. Hubrecht has proposed the 


1 A. C. Oudemans, “ The Circulatory and Nephridial Apparatus of the Ne- 
mertea.” Q. J. M. S. 1£85, Supplement. s 
2 A. A, W. Hubrecht, “ Contributions to the Embryology of Nemertea.”’ 
Quarterly Journal of Microscopical Science, Vol. xxv1. p. 417. : ; 


EXISTENCE BETWEEN BODY-CAVITY AND VASCULAR SYSTEM. 23 


name archi-coelom for this system of spaces, and in which, as is 
stated above, the inner ends of the nephridia sometimes lie. 

I have already drawn attention’ in a previous paper to the 
fact that the cavity of the heart in the embryo Lamprey is 
continuous with the segmentation cavity. In my account of 
the development of the heart the following passage occurs : 
“From the fact...that the mesublast behind the heart has not 
split into somatic and splanchnic layers, and not united ventrally, 
it will be seen that the cavity of the heart communicates posteriorly 
with the space between the ventral yolk cells (hypoblast) and the 
epidermis. Such a space would be equivalent to the segmentation 
cavity.” Such a space exists, and becomes for a time crowded 
with blood corpuscles budded off from the free edges of the 
mesoblast, which occupies its dorso-lateral angles. These sub- 
sequently become enclosed in a secondary cavity formed by the 
down-growth and fusion of the mesoblastic laminae, and so come 
to lie in the heart and subintestinal veins. 

When I wrote the above I was not aware that Biitschli? had 
conjectured that the cavity of the vascular system of Vertebrates 
was derived from the segmentation cavity. What he conceived 
from theoretical grounds I was able to see in the developing Lam- 
prey. I think we are therefore justified in applying to the vascular 
system of Vertebrates the term archi-coelom, which. Hubrecht has 
suggested for the blood-containing spaces in the Nemertea. 

The system of spaces then of Nemertea which contain blood, 
and in which the inner ends of the nephridia sometimes lie, are 
not coelomic in their nature, but archicoelomic; and as the cavity- 
sheath of the proboscis has a similar origin, we are driven to the 
conclusion that there is no coelom in these animals, and therefore 
there can be no communication between the coelom and the vas- 
cular systems in this group, such as has been demonstrated for the 
Hirudinea. 

The Gephyrea form another group of animals in which, like 


1 «On some points in the Development of Petromyzon fluviatilis.” Q. J. M.S. 
Vol. xxvit. p. 325. 

2 “Ueber eine Hypothese beziiglich der phylogenetischen Herleitung des. 
Blutgefiissapparates eines Theils der Metazoen.” Morph. Jahrbuch, Vol. 8, 1883. 


24 ARTHUR E, SHIPLEY. 


the Hirudinea, there is direct communication between the coelom 
and the blood vessels. 

The body-cavity of Sipunculus is developed as a split in the 
mesoblastic bands; the cells lining it give rise to the generative 
products; and the nephridia open at their internal ends into it. 

The blood vascular system arises late. Hatschek’ describes its 
first origin during the metamorphosis of the larva, lying on the 
dorsal side of the alimentary canal. Although his description is 
not very detailed, there is nothing to shew that we have here to 
do with anything more than a normal blood vessel. 

In the adult the main longitudinal vessel lies well surrounded 
by connective tissue, and between two of the longitudinal vessels ; 
it contains usually only blood corpuscles, which are exactly like 
those found freely in the body-cavity; but in individuals which 
are sexually ripe, spermatozoa and ova are often found in it. The 
openings, by means of which the cavity of this vessel communi- 
cates with the coelom, can be seen if the vessel be dissected out 
and exposed under a microscope; and further, Vogt and Yung? 
state that it is easy to inject the former from the latter. 

Another group which stands far apart from both the Hirudinea 
and the Gephyrea, and in which communications exist between 
the vascular system and the coelom, or at any rate with part of 
it, is the Echinodermata. Here, according to the observations of 
Hamann and Koehler, in Spatangids at least the blood system 
is in communication with the water vascular system, embryo- 
logically a part of the coelom and developed from an outgrowth 
of the body-cavity. And according to the French school of 
naturalists who have worked at this group, and amongst whom 
Perrier is the most prominent, this connection may be extended 
to the whole group of the Echinodermata. 

Finally, in the class Vertebrata we again find the body-cavity, 
which is admittedly coelomic in nature, in communication with 
the vascular system, which is to some extent at any rate archi- 
coelomic. The means of communication is through the lymphatic 


1B. Hatschek, “ Ueber Entwicklung von Sipunculus nudus.” Arbeiten aus 
dem Zoologischen Institut. Wien, Bd. v. p. 33. : 


* Vogt and Yung, ‘‘ Lehrbuch. der praktischen vergleichenden Anatomie.” 


EXISTENCE BETWEEN BODY-CAVITY AND VASCULAR SYSTEM. 25 


system. This opens on the one hand into the body-cavity by 
means of open stomata, and on the other by means of the thoracic 
duct into the venous system. 

That fluids can pass from the body-cavity into the blood system 
by means of the lymphatic system has been shewn both by 
Recklingshausen and by Ludwig. The former found that milk 
put upon the peritoneal surface of the central tendon of the 
diaphragm—where numerous stomata exist—shewed little eddies 
caused by the milk globules passing through the stomata and 
entering the lymphatics. Ludwig’s experiment is even more conclu- 
sive. He took a dead rabbit, and removed its viscera, and placed it so 
that the peritoneal surface of the diaphragm was exposed. He then 
poured into this a solution of Prussian blue, and, after imitating 
the respiratory movements for a few minutes, he obtained the lym- 
phatics filled with a blue injection, shewing a beautiful plexus. 

A more direct communication between the blood system and 
part of the body-cavity has been described in one Vertebrate. 
Weldon! has described and figured the structure of the head 
kidney in Bdellostoma Forsteri. He finds running through the 
substance of this organ a number of fine tubules, lined with 
columnar cells and anastomosing with one another. These tubules 
open on the one hand into the pericardium and on the other into 
a central duct. In this duct lies a clot which is exactly similar 
to the blood clots found in the surrounding blood vessels. Further, 
in some cases capillaries were seen to enter this duct. There 
seems to be no reason to doubt that in this animal we have a part 
of the vascular system in communication with a part of the body- 
cavity through the tubules of the head kidney. 

That there is a very primitive connection between these 
systems, is further supported by the remarkable observations of 
Seeliger’, and Van Beneden and Julin* in the development of the 
heart of Clavellina. 

1 “Qn the Head Kidney of Bdellostoma,” by W. F.R. Weldon. @. J. M.S. 
Vol. 24, 1884. 

2 “Die Entwicklungsgeschichte der Socialen Ascidien,” Oswald Seeliger. 
Tenaische Zeitsch. fir Naturwissenschaft, 1885. 


3 «Recherches sur la Morphologie des Tuniciers,” Van Beneden and Julin. 
Gand, 1886. 


3 


26 ARTHUR E. SHIPLEY. 


These authors describe and figure in all stages the development 
of the heart and the pericardium of this Ascidian from an out- 
growth of the ventral wall of that part of the endoderm which 
forms the pharynx, close to the end of the endostyle. This hollow 
diverticulum becomes separated from the endoderm and lies as 
a closed vesicle outside it. One half of the vesicle then in- 
vaginates, so that a two-walled vesicle results, there being a space 
left between the outer and inner wall. This space becomes the 
cavity of the pericardium, whose wall is formed of the outer layer 
of the double vesicle ; this cavity is derived from the cavity of the 
endoderm. 

The inner wall of the vesicle forms the wall of the heart, and 
the cavity of the heart is continuous with the primitive body- 
cavity. The longitudinal opening from the heart into the body- 
cavity persists for some time, until the free swimming larval stage; 
eventually it closes in the middle but still leaves an anterior and 
posterior opening through which the blood enters the heart from 
the body-cavity and leaves it again each time that organ contracts. 

In Kleinenberg’s’ remarkable paper on the larva of Lopado- 
rhyncus, he states that the segmentation cavity becomes the coelom 
in this and in many other Annelids. The coelom is therefore in 
these animals archi-coelic in nature, and we have seen that in some 
Vertebrates the vascular system is of this nature. In the Nemertea 
the spaces which may be perhaps considered to be both body- 
cavity and vascular cavity are also archi-coelic. This group of 
animals would therefore seem to have retained the most primitive 
of all cavities—the segmentation cavity—as the only system of 
spaces between the endoderm and ectoderm: whilst the primitive 
segmentation cavity has differentiated in the higher animals, on 
the one hand into body-cavity—Annelids, and on the other in 
the cavities of the vascular system—Vertebrates. 


» “Die Entstehung des Annelids aus der Larve von Lopadorhyncus.” CKleinen- 
berg, Zeit. f. wis. Zoologie, Bd. 44, 1886. 


POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 27 


On Some Points of the Anatomy of Polyxenus 
lagurus. 


By 
F. G. Heathcote, M.A., 


Fellow of the Cambridge Philosophical Society. 


With Plate III. 


Tue following does not profess to be a complete account of 
the anatomy of this interesting little Myriapod. In working 
out the development of Julus terrestris, certain questions 
occurred which led me to investigate the adult anatomy of 
some other forms, amongst them of Polyxenus, and I con- 
sidered that the following notes might be of interest to other 
observers. I found it very difficult to obtain material, and 
had it not been for the kindness of Dr. St. Remy, who was 
also working at Myriapods, and who took great trouble to 
procure a supply of Polyxenus for me, I must have delayed 
the publication of these notes for a considerable time. This 
form has been investigated by several naturalists, especially by 
Fabre and Bode (2, 1).1_ I have also availed myself of the 
excellent work of Latzel (4). 


External Features. 


In comparing the body of Polyxenus with that of Julus, the 
most striking peculiarity in Polyxenus is the composition of 
the individual segments. Each body-ring, as described by 
Bode, consists of a dorsal plate, two lateral plates, and two 


1 The figures refer to the list of literature at the end of the paper. 
3 


28 F. G. HEATHCOTE, 


ventral plates. The anterior parts of the two ventral plates 
are fused so as to form a triangular point. A section through 
the fused part is shown in fig. 1. These plates are the “ lames 
pedigéres”’ of Brandt. Ina former paper on Julus (5) I called 
attention to the fact that the differences between the body-form 
of the early stages and the body-form of the adult were essentially 
due to a diminution of the ventral region and an increase of the 
dorsal to such an extent that the dorsal plate came to form a 
complete ring round the body. I also pointed out that the 
larval condition showed a great resemblance to the earliest 
fossil forms of Myriapoda. Now Polyxenus, in its anatomy, 
resembles the larval rather than the adult Julus. If we com- 
pare a section through one of the segments of Polyxenus with 
a section through a larval Julus, such as is shown in fig. 34 of 
my former (5) paper; and again, with a section through a 
segment of a nearly adult Julus, such as is shown in fig. 2. of 
the same paper, the resemblance to the larval Julus and the 
difference from the adult shown in the well-developed sternal 
region, the widely separated bases of the legs, and the less 
developed dorsal region, is sufficiently striking to render it 
worth while to compare the features of its general anatomy 
with the results obtained by the investigation of the develop- 
ment of Julus. 

Of the appendages, the pair that seems to différ most from 
those of other Chilognaths is that of the second post-oral 
segment, the deutomale; these have been described by Bode 
and Latzel (1. c.). The most noticeable feature about them is 
the possession of two palps on either side, the one short and 
broad, the other long and slender. The four-lobed plate of 
the adult Julus is of course without any vestige of similar 
structures, but the larval form possesses two short, broad pro- 
jections on either side, which seem to me to be rudiments ot 
structures similar to those of Polyxenus. 

The sense-organs described by Bode, and supposed by him 
to be olfactory, may be mentioned here, as their microscopic 
structure has never been investigated. Each of these organs 
consists of a spine inserted into a structure formed by the 


POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 29 


external cuticle and the hypodermic matrix. At the point of 
insertion of the spine the chitin and matrix are considerably 
thickened. At the external surface the chitin is raised up 
round the spine so as to form a rim or ridge (fig. 4) surround- 
ing a semicircular cup of considerable depth. The hole, for 
the spine to pass through is at the bottom of the cup, and on 
the internal surface the chitin round this hole projects in- 
ternally so as to form a short wide tube corresponding to the 
semicircular depression on the external side (fig. 4, ¢.). The 
spine itself is long and rather stout, thicker in the middle than 
at either end. It is provided with a rim (fig. 4) which fits the 
perforation at the bottom of the semicircular depression, while 
the part below the rim projects internally within the tube and 
ends in a depression, into which a nerve-cell fits. The whole 
internal part of the organ (i.e. the tube and part of the spine) 
is embedded in a mass of hypodermic matrix cells, which serve 
for the renewal of the organ at the moults. On account of 
the manner in which this organ is adapted to convey move- 
ments to the sense-cell, and is rather fitted to convey actual 
pressure than delicate vibrations, I hold it to be a tactile organ 
rather than an olfactory one. 

With regard to the external generative organs, they have 
already been described by several authors, but there is one 
point on which a little uncertainty exists. Fabre describes the 
male external generative organs as very long, and lying against 
the abdomen when not in use. Latzel says that they are 
similar to those of the female, with the exception that they 
have a round opening and not a slit-like one. I can confirm 
his account, having had the good fortune to obtain several 
males among the small number of Polyxenus at my disposal. 
Sections through the male and female external generative 
organs are shown in figs. 2 and 3. The dilation of the oviduct 
into which the external opening passes is shown more markedly 
than the corresponding dilation of the vas deferens; but I am 
inclined to believe this is due to differences in preserving. I 
have noticed that the small, very fine hairs present in both 
sexes round the external generative openings, are more 


30 F. G. HEATHCOTE. 


numerous in the male, but this may possibly be due to 
individual differences. I have not had a sufficient quantity 
of males to make certain. 


The Malpighian Tubes. 


Bode succeeded in dissecting out the Malpighian tubes, but 
their minute structure has never been described, and as they 
show a variation from the ordinary form of these organs which 
is not found in any other Myriapod, it is worth while to give a 
short account of them, 

Each tube—there are a pair of them—leaves the junction of 
the rectum and mid-gut as a stout tube with a definite lumen. 
The lumen is surrounded by a ring of denser tissue which 
has a faintly striated appearance. Each tube passes backwards 
along the rectum to the terminal dilation of the latter where it 
becomes greatly thickened, and is doubled upon itself so as to 
form a great spherical knot, the greater part of which lies in 
the semicircular chitinous elevations which are placed at 
either side of the anus. From this coil each tube passes off 
greatly reduced in size so as to have the form of a thin tube 
(figs. 8, 9, 6, r. malp. t.) like any other Malpighian tube. 
These two thin returning portions pass forward and end 
blindly about the middle of the body. From the anterior end 
of the rectum, where the Malpighian tubes originate, the whole 
of these structures, together with the rectum, is enveloped in 
a membrane (figs 6, 8, 9) which passes backwards and becomes 
fused with the mass of cells forming the hypodermis. This 
membrane is perfectly definite on the external surface of the 
Malpighian tubes, but I have been quite unable to find any 
trace of it between the tubes and the rectum. I am con- 
vinced that it envelopes the tubes and the rectum together. 
Where the small returning portions of the Malpighian tubes 
pass beyond the origin of the tubes and the enveloping mem- 
brane, at the anterior end of the rectum, they pierce the 
membrane, and passing forward lie close to the mid-gut just 
like other Malpighian tubes. 

The salivary glands, which are long and tubular, open on 


° 


POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 3] 


the internal surface of the deutomale in the same position as 
those of Julus and other Chilognaths. I have not thought it 
necessary to give a figure. 


The Nerve-cord. 


The nerve-cord shows a greater resemblance to that of the 
larval Julus and also of Chilopods than does the nerve-cord of 
any other Chilognath with which I am acquainted. Between 
the ganglia the fibrous part of the ventral nervous system is 
divided into two distinct cords as shown in figs. 5, 6, and 12. 


The Internal Generative Organs. 


In both male and female the generative organ has the form 
of a long tube, which communicates with the exterior by two 
short oviducts or vasa deferentia. The female organ (fig. 6) 
consists of a long tube, formed of a single layer of cellular 
membrane, and containing the spongy connective tissue (or 
stroma) within which the ova are produced. Some of the 
cells of this tissue become oya, while others, indistinguishable 
at an early stage, form the follicles which surround the ova. 

At its anterior end the ovary becomes constricted, as shown 
in fig. 5. Its walls increase in thickness, and are composed of 
two layers, an external and an internal, the latter consisting of 
larger cells. Just at the point of division into the two ovi- 
ducts two large receptacula seminis communicate. They are 
composed of a single layer of cells (fig. 5, rec. sem.), and con- 
tain spermatozoa, as shown in the figure. 

The male generative organ also consists of a tube, the 
testis, which divides anteriorly into two vasa deferentia. The 
walls of the testis are formed by a single layer of cells, and 
within it is a mass of spongy connective tissue from the cells 
of which the sperm-cells and the follicles arise. The sper- 
matozoa originate by a sperm morula (fig. 7), and the morula 
is surrounded by a follicle which may perhaps serve to secrete 
the covering of the spermatophores which are formed inside 
the follicles. The spermatozoa are long and thread-like, re- 
sembling those of Lithobius and Scolopendra. 


32 F. G. HEATHCOTE. 


The Heart. 


The heart has been described by Bode, who saw the dorsal 
vessel dividing into three branches in the head, and also found 
an artery in the middle of each segment. The dorsal vessel is 
suspended from the dorsal hypodermis by suspensory muscles, 
and muscle-fibres connecting it with the fat bodies are attached 
to its ventral surface. These muscles form a sort of inter- 
rupted pericardium like that in Julus. 

In each segment of the body there are two pairs of ostia 
occupying the same position as those in Julus, but there is 
only one pair of arteries in the middle of each segment. The 
heart is composed of three coats, an intima or structureless 
internal lining, a muscular coat, and a cellular external cover- 
ing. The layers are not so well marked as in Julus; perhaps 
this is owing to the small size of the animal. The muscular 
valvular apparatus of the ostia is the same as that found in 
Julus (5). The circulation is connected, as in Julus, with the 
spaces in the fat-bodies. These spaces are often crowded with 
blood-corpuscles. There is no definite blood-space round the 
nerve-cord as in Julus. 


The Eyes. 


“The shape of the lens is peculiar, and more resembles that 
of Scutigera (see Grenacher’s paper, 3) than that of any other 
Myriapod with which I am acquainted. Its external surface 
is highly convex, while the internal is flat. The cells of the 
hypodermis are continued round the circumference of the lens 
so as to form a kind of diaphragm. A section through the 
edge of the lens shows this (fig. 13, 4. c.). The crystalline 
cones are arranged in groups, so that a transverse section 
through the retinal depression gives the appearance shown in 
fig. 14, B. TI have been unable to find any intrusive connective- 
cells, but this may be due to want of material. The pigment 
is thickest at the base of the retina, and also at the commence- 
ment of the rods (fig. 13, pot., inner pgt.). 


POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 83 


General Conclusions. 


The principal interest of Polyxenus lies in the likeness of 
some of the features of its anatomy to the anatomy of the 
Chilopods. While it agrees with the Chilognatha in the 
position of its generative organs and the duplication of some 
of its segments (the first four segments are provided with only 
one pair of appendages, the next four have two pairs, and the 
last one pair—Latzel and Bode), and in the fact that it is a 
vegetable-feeding animal, in connection with which fact its 
salivary glands are long and tubular, like those of other Chi- 
lognaths ; it nevertheless resembles the Chilopods in the form 
of its spermatozoa, which are long and filiform, and are con- 
tained in spermatophores; in the general structure of the 
segments, having the legs wide apart, with a ventral region 
between them ; and in the differentiation of the ventral nerve- 
cord. The single artery given off in each segment seems at 
first sight to afford a resemblance to the Chilopod circulatory 
organ, but I believe this resemblance to be superficial. In its 
essential characters the heart resembles that of the Chilognaths, 
and remembering that the Chilognath heart is formed by the 
confluence of spaces in the tissues of the body, the formation 
of the arteries is not a deep-seated character. 

Characters peculiar to itself are the peculiar form of the 
second pair of mouth appendages, and the absence of stink- 
glands and the substitution for them of numerous spines as a 
means of defence. 

In a former paper (5) I advanced certain views about the 
phylogeny of Myriapods, and came to these conclusions :— 
First, that Myriapods were descended from some Peripatus- 
like ancestor; secondly, that the Chilopods and Chilognaths 
branched off from some common ancestor, not differing much 
from the fossil Archipolipoda. Now the characters in which 
Polyxenus resembles the Chilopods are characters common to 
the larval Julus, and to the Archipolipoda (5). With regard 
to the absence of stink-glands, and the substitution of spines 
arranged in tufts over the body, I found in Julus that the 


34 F. G. HEATHOCOTE. 


stink-glands were formed comparatively late in the develop- 
ment as invaginations of the dorsal plate, and I came to the 
conclusion that they were not very deep-seated characters. If 
this is so it is not difficult to understand that they may never have 
been developed in Polyxenus, but that the spines may have been a 
sufficient protection. It is worth noting that the Archipolipoda 
had spines, and not stink-glands. From all these points in the 
anatomy of Polyxenus I am inclined to regard it, not as a 
recently formed link between the Chilopods and Chilognaths, but 
as an animal which has preserved certain traces in its anatomy 
of its descent from a common ancestor of the two classes, 
such ancestor being related to the Archipolipoda. I consider 
it as confirming my view that the Myriapoda are descended 
from a Peripatus-like form, and as opposing their descent from 
Thysanura. I am fully aware that insomuch as I investigated 
Polyxenus with a definite idea, I have probably taken a one- 
sided view of the points I worked at; but I hope that my 
work will induce others to investigate this animal more fully, 
and thus increase our knowledge of the various questions 
suggested by Myriapod anatomy and development. 

My work was entirely carried on in the Cambridge Morpho- 
logical Laboratory. : 


LITERATURE. 


1. J. Bopz.—* Polyxenus lagurus,” ‘Zeitschr. fiir die gesammten 
Naturwissenschaften,’ 1877. 


9, Fasre.—“ Anatomie des organes reproducteures des Myriapodes,” ‘ Ann. . 
des Sci. Nat.,’ 4 sér., 1855. 

3. H. Grenacaer.— Ueber die Augen einiger Myriapoden,” ‘ Archiv fir 
mik. Anat.,’ 18. 

4. Latzet.—‘ Die Myriapoden der oesterreichisch-ungarischen Monarchie,’ 
Wien, 1880. ; 

5. F. G. Heatacots.—‘ The Post-embryonic Development of Julus ter- 
restris, Phil. Trans. Roy. Soc.,’ 1888. 


POINTS OF THE ANATOMY OF POLYXENUS LAGURUS. 35 


DESCRIPTION OF PLATE III, 


Illustrating Mr. F. G. Heathcote’s paper “On Some Points 
of the Anatomy of Polyxenus lagurus.” 


Fie 1.—Part of a transverse section through the middle of the body, 
showing the ventral plate. The bases of the legs are separated and the 
ventral plate—that is, the fused anterior part of the two “lames pedigéres ” 
of Brandt—occupies the space between them. 

Fie. 2.—Part of a transverse section through the body, showing the female 
external generative appendage. dil, ovid. Dilation of the oviduct. 
ext. gen. org. External generative organ. 

Fic. 3.—Section through the male generative appendage. dil. vas. def. 
' Dilation of the vas deferens. 

Fic. 4.—Section through the sense organ. zt. cut. External cuticle. 
hyp. Hypodermis. ¢. Tube. gaz. Ganglion-cell. hyp. c. mass. Hypodermic 
cell mass. 

Fie. 5.—A transverse section through the fourth segment of a female, to 
show the ovary, receptacula seminis, and the general arrangement of the 
organs. The figure is semi-diagrammatic; the outline of the body, the gut, 
ovary, receptacula, and nerve-cord being from an actual section; while the 
heart, muscles, and fat-body are diagrammatic. gy... The ganglionic part 
of the nerve-cord. /. ~.c. The fibrous part. vec. sem. Receptaculum seminis, 
spmzoa. Spermatozoa in the receptacula. ovidct. Oviduct. 

Fic. 6.—Part of a transverse section through the posterior part of the body 
of a female, to show the Malpighian tubes and the ovary. 4g. . c. Ganglionic 
part of nerve-cord. 7. #.c. Fibrous part. fol. ov. Follicle round ovum. ov. 
Ovum. w.ov. Wall of ovary. 7. Malp.¢. Returning part of the Malpighian 
tubes. Malp. ¢. Malpighian tubes. 

Fic. 7.—Part of a section through the testis of a male, showing a follicle 
containing a sperm morula. f. Follicle. sp. mor. Sperm morula, 

Fic. 8.—Part of a longitudinal section through the posterior end, to show 
the Malpighian tubes. a. d. Anal dilatation. 0. . Outer wall of the gut. 
malp.t. Malpighian tube. /. madp. ¢. Lumen of Malpighian tube. memd. 
Membrane. 

Fig. 9.—Section through gut and Malpighian tubes. malp. ¢. Malpighian 
tube. +. malp. t. Reduplicated part of Malpighian tube. mem. Membrane. 

4 


36 F. G. HEATHCOTE. 


Fic. 10.—Longitudinal section through a segment of the heart. ar¢. 
Artery. ost. Osteum. 

Fie. 11.—Transverse section through heart. ewt. cut. External cuticle. 
ext. w. ht. External wall of heart. z#¢. Internal lining of heart. m. w. ht. 
Muscular wall of heart. mzsc. Muscle-fibres from the heart to the fat- 
bodies, forming a sort of pericardium. susp. musc. Suspensory muscle of the 
heart. 

Fie. 12.—Section through the nerve-cord. gze. Ganglionic part. fue. 
Fibrous part. 

Fic. 13.—Section through region of eye, showing two eye-spots and the 
lens of another. r.c. Retinal cells. duner pgt. Pigment round the base of 
the crystalline cones. 7. Lens. 4. c. Cells of the hypodermis. pgt. Pigment 
around the base of the retinal cells. 

Fie. 14.—Section through the region of the eyes, showing one spot cut 
horizontally and one longitudinally. 4. An eye-spot cut longitudinally. 2B. 
An eye-spot cut transversely. 7. Lens. gt. Pigment. c. Crystalline cones. 


Notes on the Anatomy of Dinophilus. 
By 


Sidney F. Harmer, M.A., B.Sc., 
Fellow and Lecturer of King’s College, Cambridge. 


With Plates 1V and V. 


Tue anatomy of Dinophilus, a genus established by Oscar Schmidt 
in 1848, has formed the subject of several memoirs, amongst which 
attention must be specially called to the recent papers of Korschelt 
(6), Repiachoff (12), and Weldon (13). A complete account of the 
synonymy of the genus was given by v. Graff* in 1882, whilst 
Korschelt (7) has, within the last year or two, published a review of 
the facts known with regard to the anatomy of the various species 
of Dinophilus. Full references to the literature of the subject will 
be found in v. Graff’s monograph (loc. cit.) as well as in the memoirs 
of Weldon (13) and Korschelt (6 and 7). In view of the recent 
appearance of the above-mentioned papers, it is unnecessary for me 
either to give a complete list of references or to attempt any histori- 
cal account of our knowledge of the genus. 

The animal which forms the subject of the present paper was 
found at Plymoutht, and has been described as a new species, under 
the name Dinophilus teniatus, at a meeting of the Cambridge 
Philosophical Society. 

D. teniatus was found, in very great numbers, in rock-pools far 
above low-water mark, during the latter end of March and the first, 
half of April. It was unfortunately necessary to interrupt the 
observations on April 18th, a day or two before which time it was 
noticed that the-eggs which were being produced by the females 
were rapidly developing. On returning to Plymouth on June 26th 
no trace of the animal was discovered. Other observers, as Hallez 
(4) and Weldon (13) have recorded the fact that the species of 
Dinophilus which they have respectively described are only to be 


found during the spring. 


* y, Graff, L., Monographie der Turbellarien. I. Rhabdoccelida. Leipzig, 1882. p. 1. 

+ The study of the anatomy of Dinophilus was greatly facilitated by the excellence of 
the arrangements of the Laboratory of the Marine Biological Association, to the Director 
of which, Mr. G. C. Bourne, 1 desire to express my best thanks for the courtesy with which 
I have been treated during my visits to Plymouth. 

t Proc. Camb. Philosoph. Soc., vol. vi, 1889. 


38 NOTES ON THE ANATOMY OF DINOPHILUS. 


It will not be superfluous to call attention to the fact that the 
bright orange colour which is so conspicuous a feature of D. tenia- 
tus (as of certain other species of Dinophilus) cannot easily be re- 
garded as a protective colouration. The rock-pools inhabited by 
this species of Dinophilus contain numerous bright green Algzw, and 
there is not the slightest difficulty in detecting with the naked eye 
individuals of D. teniatus, whether crawling on this green back- 
ground or on the mud or rocks which occur at the bottom of the 
tide-pool. 

With regard to the habits of the animal, it may be noted that, 
so far as I am aware, it never performs those gyrations round a 
centre formed by the attachment of the tail toa foreign body, which 
have been described as of frequent occurrence in D. metameroides, 
for instance (4). The animal crawls (no doubt by means of its 
cilia) with considerable rapidity, but it is able to swim freely in the 
water; the latter method of progression appears to be specially 
characteristic of young individuals. 

Specific Characters.— Dinophilus teniatus is characterised as follows: 
Head with two circlets of preoral cilia. Body composed of five 
segments and a tail. Segments sharply marked off from one 
another in young individuals, each encircled by two rings of cilia, 
incomplete ventrally, where they are interrupted by the uniform 
ciliation of the ventral surface. Anus placed dorsally to the base 
of the conical unsegmented tail, surrounded by a ring of cilia, in- 
complete ventrally. Skin containing large numbers of transparent 
glandular bodies. Sexes not dimorphic. Maximum length, in either 
sex, about 2mm. Colour bright orange, usually brighter in the 
male than in the female. Testes in the male extending nearly the 
whole length of the body, on the ventral and lateral sides of the 
alimentary canal; spermatozoa very long and undulating. Vesicula 
seminalis formed by the modification of the fifth nephridum on each 
side, opening into a median copulatory organ, whose external aper- 
ture is ventral and slightly posterior to the anus. Ovaries in the 
female four-lobed. Nephridia ten in number (five pairs), the fifth 
pair modified as a vesicula seminalis in the male. Ventral nervous 
system segmented. 

As characters recognisable in living specimens, and which are 
sufficient to distinguish this species from all others at present known 
may be mentioned the following: 

(1) The existence of five body-segments (in addition to the tail), 
each encircled dorsally and laterally by two rings of cilia; the seg- 
mentation being sharply marked in immature individuals. 

(2) The four-lobed condition of the ovaries in the female, 

(3) The existence, in the male, of a median penis and of lateral 


NOTES ON THE ANATOMY OF DINOPHILUS. 39 


vesicule seminales (in which respect, however, D. vorticoides may 
possibly be found to agree with D. txniatus). 

The characters above given appear to be amply sufficient to 
justify the formation of a new species. The species which most 
resembles D. teniatus is probably D. gigas, Weldon, which, however, 
differs from it in such important features as the number of the seg- 
ments, the arrangement of the ciliated rings, the general character 
of the reproductive organs, and more particularly the absence of a 
copulatory organ in the male sex. 

External Features—The form of the body is shown in Pl. IV, 
fig. 1, which represents a rather young individual (the distinctness 
of the cilia having been somewhat exaggerated). Inanold animal, 
distended with ripe generative products, the external segmentation 
is not nearly so conspicuous as in the specimen figured. The 
arrangement of the cilia is often difficult to make out in living 
Specimens, but may be very easily observed after treatment with 
hot corrosive sublimate, and before the extraction of the orange 
pigment by means of alcohol. In specimens thus treated, the cilia 
appear as white bands running over an orange background; when 
seen from the dorsal surface, the two rings of each segment together 
give rise to the impression that the middle region of the segment is 
encircled by a broad band; this appearance has suggested the 
specific name teniatus. 

The ciliation of the head is best studied in a sublimate specimen, 
seen from the anterior pole (fig. 8). The general surface of the 
head is not ciliated, the cilia occurring, on the contrary, as two de- 
finite preoral rings, between which are situated the eyes, near the 
dorsal surface. The anterior ring is more or less triangular, the 
apex of the triangle being directed dorsally. 

In looking at the animal from above, it is seen that the posterior 
cephalic ring passes dorsally across the equator of each of the eyes 
(fig. 1). This ring, unlike all the other ciliated rings of the animal, 
is composed of several circlets of cilia. Of these, the first consists of 
long cilia directed forwards, and the third or last of somewhat 
shorter, backwardly-directed cilia. Between the two circlets occurs 
an intermediate series of very minute cilia (figs. 1,15). It follows 
from this description that in structure, as in position, the second 
cephalic ring resembles the preoral ciliated band of a Trochosphere 
larva. No ciliated pits were observed. The head bears long, stiff 
sense-hairs arranged in two groups, situated within the area circum- 
scribed by the anterior ciliated ring (fig. 1). Similar sense-hairs 
occur on various parts of the body and tail. 

The study of longitudinal sections, in which, however, the cilia were 
not very well preserved, appeared to show that the second preoral 


40 NOTES ON THE ANATOMY OF DINOPHILUCS. 


ring becomes much broader in approaching the ventral surface, and 
that it becomes indistinguishable from an investment of cilia which 
clothes the ventral surface of the head and which passes continuously . 
into the ciliated lining of the cesophagus (cf. fig.3). The examina- 
tion of the ciliation of the ventral surface of the head is always 
difficult in fresh specimens, but at the time when these were acces- 
sible to me, I believed that I could convince myself that the anterior 
circlet of the second preoral ring passed completely round the head, 
as shown in fig. 15. The most satisfactory way, it appears to me, 
of reconciling the apparent discrepancy between fig. 3 and fig. 15, 
is to assume that, whilst the anterior circlet of the second preoral ring 
does really pass continuously round the ventral surface of the head, 
the middleand posterior circlets become, ventrally,anextensive ciliated 
area which is continuous with the ciliated lining of the cesophagus. 

The arrangement of the five pairs of ciliated rings which occur on 
the body and of the perianal ring is sufficiently explained by fig. 1. 
All these rings are interrupted by the cilia which cover, in a uniform 
sheet, the entire ventral surface of the body and of the tail. 

Alimentary Canal—The mouth occurs on the ventral surface, at the 
limit between the head and the first segment of the body. The 
aperture of the cesophagus is guarded by two lip-like structures, an 
outer and an inner. Of these, the former constitutes the outer wall 
of a triangular space (fig. 15) which includes in front the aperture 
into the cesophagus, and behind the end of the tongue-like structure 
formed by the muscular appendage of the cesophagus. The arrange- 
ment of this organ is well seen in the longitudinal section figured (fig. 
3), where it will be noticed that the end of the muscular appendage 
(which is covered by a modified, probably hardened epidermis) pro- 
jects into the space enclosed by the outer lip. A similar arrangement 
is figured by Repiachoff (No. 12, pl. iv, fig. 1) in D. gyroctliatus, whilst 
the disposition of the organ appears, from Weldon’s description (18), 
to be somewhat different in D. gigas. 

In front of the tongue-like structure is seen the aperture into the 
cesophagus (fig.15). This aperture is subtriangular, and is bounded 
by the two richly ciliated inner lips. 

The course of the alimentary canal is shown in fig. 3. The 
cesophagus ascends obliquely towards the dorsal surface, the lateral 
walls of its first part being thickened (v. fig. 10), and passing con- 
tinuously into the inner lips. The posterior section of the oesophagus 
lies very near the dorsal skin, and is lined by cells which have a 
more glandular appearance, and which bear longer cilia than those 
which line the anterior two thirds of the cesophagus. The posterior 
division corresponds to the proventriculus (‘‘ Vormagen’”’) described 
by Korschelt in D. apatris. 


NOTES ON THE ANATOMY OF DINOPHILUS. 41 


As in other species of Dinophilus, salivary glands open into the 
anterior division of the esophagus. 

The stomach (which, during life, is of a rich orange colour) is 
ciliated throughout: it ends cecally on the dorsal side of the com- 
mencement of the intestine, as in D. gigas. 

The intestine, like the rest of the alimentary canal, is ciliated. 
It opens into the stomach by a narrow aperture situated on the ven- 
tral side of the latter. 

As will be seen by reference to fig. 1, the esophagus and its 
muscular appendage belong to the first segment of the body, the 
stomach occupying the second, third, and fourth segments, whilst the 
intestine is found in the fifth and posterior part of the fourth segment. 

Nervous System.— Although Korschelt (6) and Repiachoff (12) suc- 
ceeded in finding the brain of D. gyrvciliatus, our knowledge of the 
nervous system of Dinophilus is in the main due to Weldon (13), 
who has not only described the brain, but has shown that this struc- 
ture is connected with ventral cords, whose arrangement resembles 
that found in Protodrilus (v. Hatschek, No. 5).. 

The nervous system of D. teniatus exhibits a feature which has 
not hitherto been described in any species of Dinophilus. The 
ventral cords are distinctly segmented, the number of ganglionic 
enlargements—five—corresponding with that of the segments of the 
body. 

The ventral cords (figs. 8,10 and 11) are situated outside the 
basement-membrane of the skin, and lie, widely separated from one 
another, immediately on the median side of the longitudinal muscles 
(as in D. gigas). The cords seem to be provided with an external 
investment of ganglion-cells along their whole length. The gan- 
glionic swellings (fig. 3) appear to be shifted backwards, relatively 
to the segment to which they respectively belong, so that the middle 
of the segment on the dorsal side (as indicated by the ciliated rings) 
is in front of the corresponding ganglion. 

In transverse section (fig. 10) it may be seen that each pair of 
ganglia is connected by a transverse commissure. I could not 
satisfy myself of the existence of ganglion-cells in connection with 
this commissure, although, as the whole ventral nervous system lies 
in the ectoderm, it is possible that some of the nuclei which are 
adjacent to the commissures may really belong to ganglion-cells, and 
not to the epithelial portion of the skin. No transverse commissures 
were discovered other than those which pass between the ganglia. 

The brain is very large, and fills up nearly the whole of the preoral 
lobe (figs. 3, 9). It consists internally of fibres, and externally of 
numerous ganglion-cells arranged in groups. The structure of the 
brain is very complicated ; its surface appears lobulated, owing to 


42 NOTES ON THE ANATOMY OF DINOPHILUS. 


the arrangement of the ganglion-cells. A similar arrangement is 
figured by Repiachoff (12, pl. ii, fig. 10). 

The brain gives off a pair of strong cesophageal commissures (fig. 
9), which pass round the sides of the mouth to become connected 
with the ventral cords, as has been described by Weldon in D. gigas. 
The brain itself is, for the most part, separated from the skin by the 
basement-membrane of the latter. The cesophageal commissures 
at first lie inside the basement-membrane, but perforate the latter 
shortly before they become continuous with the ventral cords. 

On the ventral side, in front and on the median side of the origin 
of the cesophageal commissures, the brain becomes continuous with 
the ectoderm at two points, one on each side of the middle line (cf. 
fig. 6). It is probable that the tactile organs of the head itself 
receive their nerve-supply from this region of the brain, which, how- 
ever, sends off at the same point an cesophageal nerve (figs. 6, 9, 
and 10) which may be traced, on each side of the cesophagus, as far 
as the end of the latter; these nerves were not observed to occur in 
the proventriculus. The cesophageal nerve supplies the wall of the 
cesophagus itself, and gives off a branch which can be traced as far 
as the surface of the muscular appendage. 

The eyes, which are of a bright red colour, lie on the dorsal 
surface of the brain, immediately below the basement-membrane 
of the skin (fig. 9). Hach consists of a double pigmented sac, 
filled with a clear substance, which no doubt functions ag a lens. 
In surface view (fig. 1) the cavity of the eye is not seen, but it is 
shown in the horizontal -section, fig. 7. Remembering that the plane 
of the section, fig. 9, is at right angles to that of the section, fig. 7, 
the difference between the two eyes in the former is readily accounted 
for by the obliquity of the section. 

The ventral part of the head is provided with a pair of small 
sacs, each of which has an extremely fine lumen opening to the 
exterior at one side of the anterior portion of the mouth (fig. 9). 
These bodies are presumably sense-organs, since they are supplied 
by the above-mentioned cesophageal nerves. Similar organs are 
described by Repiachoff (12, pl. iv, figs. 1, 8, y) in D. gyrociliatus, 
in which species it must be noticed that they occur in addition to 
lateral, cephalic, ciliated pits. 

Body-cavity—The body-cavity is represented partly by irregular 
spaces in the loose connective tissue, as described by Weldon in 
D. gigas, and by Repiachoff in D. gyrociliatus, partly by more definite 
spaces, which seem to be specially connected with the internal ends 
of the nephridia. In males which are sexually mature, by far the 
greater part of the space between the alimentary canal and the skin 
is taken up by the very largely developed generative organs (v. 


NOTES ON THE ANATOMY OF DINOPHILUS. 43 


fig. 13). The further relations of the body-cavity may be con- 
veniently considered in connection with the excretory and repro- 
ductive systems. 

Nephridia—Like D. gyrociliatus, as figured by Ed. Meyer (11, and 
as described, on Meyer’s authority, in Lang’s Polycladen, p. 678), 
D. tzniatus possesses five pairs of nephridia, whose arrangement is 
in some respects différent from that of the same organs in D. gyro- 
ciliatus. It may be at once noted that the occurrence, in two species 
so distinct as D. gyrociliatus and D. teniatus, of five pairs of 
nephridia, raises the question whether the body may not possibly 
consist of five metameres throughout the genus Dinophilus, in spite 
of variations in the number of the ciliated rings. Thus, according 
to Korschelt (6), Repiachoff (12)* and Meyer (11), D. gyrociliatus is 
characterised by the possession of seven post-oral ciliated rings (one 
of which is perianal), in spite of which fact there only five pairs of 
nephridia. It may, however, be noted that Korschelt figures (pl. 
xxii, fig. 43) a recently hatched (female) individual, in which the 
body consists of six segments, sharply marked off from one another, 
in addition to the tail. 

In the female D. tzniatus the five pairs of nephridia are all alike, 
whilst in the male the fifth pair is modified as a part of the genera- 
tive apparatus. The fifth nephridia of the female occur in the fifth 
segment of the body, on the ventral side of the intestine (behind the 
ceecal end of the stomach). The fourth nephridium has exactly the 
same position with regard to the stomach as the fourth nephridium 
of the male; it lies behind the posterior ovarian lobe. The third 
nephridium is situated between the two lobes of the ovary, whilst the 
second and first nephridia are in the same position asin the male sex. 

The following, more detailed description refers entirely to the male, 
in which the nephridia can be more easily investigated than in the 
female. The general arrangement of the system may be understood 
from fig. 15, which illustrates the anatomy of a male D. teniatus as 
seen from the ventral surface under a compressorium. The figure of 
course represents the combined results of a long series of observa- 
tions, but it must be premised that the opacity of the animal was 
sufficient to prevent any complete elucidation of the structure of the 
nephridia. 

The first four pairs of nephridia may be considered together. 
Each nephridium opens to the exterior on the ventral side of the 
body, and probably not far from the longitudinal nerve-cords. The 
observation of the exact point where the nephridium pierces the skin 


* Repiachoff is strongly of opinion that there is no specific difference between Korschelt’s 
D. apatris aud the earlier described D. gyrociliatus. 


44, NOTES ON THE ANATOMY OF DINOPHILUS. 


was extremely difficult, but it may be taken as probable that the ex- 
ternal aperture, in each case, is at a level between the two rings of 
cilia possessed by the segment to which a given nephridium belongs. 
The inner end of the first nephridium is very slightly behind the 
principal (second) preoral ring of cilia; this nepbridium opens to 
the exterior on the first body-segment, and may be regarded as the 
equivalent of the head-kidney of a Trochosphere larva. The second 
nephridium commences at the anterior end of the stomach, runs at 
first dorsal to the testis, then bending round to open to the exterior 
on the ventral surface of the second segment. The third nephridium 
lies at the level of the middle segment, and, like the second, has its 
excretory portion situated on the dorsal surface of the testis, its duct 
curving round to open ventrally on the third segment. The fourth 
nephridium lies, in the fourth segment, on the ventral surface of the 
stomach, its internal end occurring close to the aperture from the 
stomach into the intestine. Its duct, unlike the ducts of the second 
and third nephridia, runs entirely ventral to the testis. 

The internal end of each of the above nephridia lies in a perfectly 
definite space, which contains an orange fluid and which is probably 
merely a specialised portion of the general body-cavity. It is almost 
certainly the case that the spaces which surround the internal ends 
of the nephridia are continuous with one another, as shown on the 
right side of fig. 15. In the case of the first three nephridia, the 
space in question lies on either side of the alimentary canal, and in 
living specimens was usually most readily distinguishable in the re- 
gion of the third nephridium, as a distinct cavity, apparently with- 
out proper walls, between the stomach and the membrane of the 
testis. In transverse sections it could usually be seen that this part 
of the body-cavity extended to the ventral side of the stomach (v. fig. 
13), whilst in the region of the fourth nephridia, the median portion 
of the cavity was, in most specimens, observed to pass down ven- 
trally as far as the skin, thus dividing the testis, in this region, into 
two symmetrical, right and left lobes. In the median space thus 
formed are situated the internal ends of the fourth nephridia. 

The remainder of the general body-cavity consists of a meshwork 
of spaces, filling up the intervals between the various organs and 
the skin. These spaces are, like those described by Weldon in 
D. gigas, devoid of an epithelial lining. Many of the cells which 
bound there lacune are large, branching connective-tissue cells, 
which contain an orange pigment. The pigmented cells are usually 
more numerous in the male than in the female, their pigment in the 
female being often markedly paler in colour than in the male, whilst 
(in the female) their tint tends to be yellow rather than orange, 
The difference in the colouration of the two sexes, above alluded to 


NOTES ON THE ANATOMY OF. DINOPHILUS. 45 


in the description of the specific characters, is dependent on the con- 
dition of the connective-tissue cells. 

Each nephridium (of the first four pairs)'consists of three por- 
tions: (i) the ciliated appendage ; (ii) the excretory portion; (iii) 
the duct. The entire nephridium is almost certainly composed of a 
small number of perforated cells, although no nuclei were discovered : 
it forms a moderately short tube, without convolutions, the curvature 
of the tube, as actually observed, doubtless depending to some extent 
on the position of the animal in the compressorium. Thus the dif- 
ferences between the nephridia of the two sides in fig. 15* probably 
imply nothing more than that the direction of the compression was 
not the same in‘all the observations made. 

The excretory portion of the nephridium is of a distinct greenish- 
yellow or orange colour, the walls of this portion of the tube contain- 
ing numerous colourless vacuoles, and granules of various sizes. 
One or two of the granules are very frequently large and deep orange 
in colour. The excretory portion is pear-shaped, the narrow end 
shading off insensibly, by gradual loss of the vacuoles and granules, 
into the duct. The first nephridia seem to be usually provided with 
two swollen portions, whose walls contain excretory granules and 
vacuoles, instead of with one only, as in the case of the remaining 
excretory organs. The nephridium is often suspended in a cord of 
the above-mentioned pigmented connective-tissue cells. 

The internal end of the nephridium is composed of a triangular, 
ciliated appendage, the apex of which is inserted into the excretory 
portion of the tube. This insertion, in the case of the second, third, 
and fourth nephridia, takes place at some little distance from the 
proximal end of the excretory portion. The appendage is ciliated, 
the cilia together giving the appearance of a pointed flame-like 
structure which projects obliquely into the excretory portion of the 
organ. In certain conditions of the nephridium the ciliated appen- 
dage has exactly the appearance of a flame-cell, although as the 
animal dies and the cilia become more sluggish in their movements, 
the flame-like appearance is lost. I am inclined to believe, as the 
result of along series of observations, that the appendage is pro- 
vided with a number of cilia, which, working together, produce the 
optical illusion of a vibratile flame. This is almost certainly true of 
the portion of the tube described above as the duct, this region being 
undoubtedly lined by cilia, which, under certain conditions, give rise 
to a very flame-like effect. 

In spite of having devoted a large amount of time to the observa- 
tion of the ciliated appendages, I am unable to say whether or not 


* The form of each nephridium representing the result of one or more actual observa- 
tions, made at different times. 


46 NOTES ON THE ANATOMY OF DINOPHILUS. 


these structures open into the portion of the body-cavity which un- 
doubtedly surrounds them. In some cases the appendage appeared 
distinctly bifid (fig. 15), whilst in others it had a fimbriated appear- 
ance, and seemed to be composed of a large number of minute, elon- 
gated, pear-shaped bodies, each attached by its narrow end to the 
point where the appendage as a whole passed into the excretory por- 
tion of the tube. These minute bodies vibrated individually (i. e. 
not in connection with their neighbours) in the body-cavity space in 
which they were situated. These observations do not appear to 
favour the view that the ciliated appendage contains a single vibra- 
tile flame, nor indeed to render it easy to suppose that the appendage 
opens into the body-cavity. 

At the same time, it must be noted that the ciliated appendages 
of the first nephridia are somewhat larger than those of the other 
nephridia, and that several observations were made which seemed to 
show that the appendage did really open into the body-cavity. In one 
of these cases I believed that I could see the individual cilia of the 
appendage projecting into the body-cavity. It is not impossible that 
the anterior nephridia have attained a somewhat higher degree of 
differentiation than the remainder. 

The proximal end of the excretory portion, into which the cilia of 
the appendage project, as above described, does not seem to be 
ciliated, whilst the lumen of this region of the nephridium appears 
to be often in the condition of a series of isolated vacuoles rather 
than of a single passage continuous with the cavity of the rest of the 
organ. Cilia make their appearance towards the end of the pig- 
mented portion, and can be followed uninterruptedly, from that 
point, as far as the external aperture. The “duct” has extremely 
delicate, colourless walls, and, as just stated, is richly ciliated in- 
ternally. 

Generative Organs—a. Male.—The testes consist at first (as is 
shown by the examination of young individuals) of minute, paired, 
linear cords of cells (fig. 11), lying on the ventral side of the stomach 
in the general connective-tissue of the body.* It appeared probable 
that the testicular cells were simply differentiated connective-tissue 
cells. Owing to an injury to the tail end of the individual from 
which fig. 11 was drawn, it could not be ascertained whether or not 
a penis was already developed. 

At a slightly later stage the cords of cells which constitute the 
young testes are found to have become slightly expanded in a lateral 


* Tt is not impossible that this and the next stage described may really be young con- 
ditions of the female generative organs, and that, for instance, the structure described as 
the penis may be the unpaired oviduct. I believe, however, that I am right in identifying 
the animals in question as young males. 


NOTES ON THE ANATOMY OF DINOPHILUS. 47 


direction, so as to form a pair of narrow, horizontally placed plates 
of cells, still separate from one another. The penis is already 
developed as a hollow mass of cells attached in its definitive position 
by a narrow stalk to the ventral ectoderm of the body. There is 
no connection between the testes and penis, nor could any vesicule 
seminales be identified with certainty in the sections on which the 
observation of this stage was made. As development proceeds, the 
lateral extension of the testes goes on increasing, and the two origi- 
nally separate rudiments fuse from place to place across the middle 
line. The testis now consists of a solid plate, composed of a few 
layers of cells, extending along the ventral side of the stomach, and 
still showing obvious traces of its double origin. The testis next 
extends laterally round the stomach, still composed of a solid mass of 
cells. In the final condition, some of these sperm mother-cells are 
found in groups in various parts of the testis, whilst ripe and half- 
' ripe spermatozoa are found moving about freely in the indefinite 
cavity which is by this time excavated in the interior of the organ. 
The testis is separated from the body-cavity by a distinct mem- 
brane. 

Although, in the adult condition, the testis is constantly continuous 
across the middle line in its anterior and posterior regions, it is 
usually divided into two lateral halves, in the region of the aperture 
from the stomach into the intestine, by a median extension of the 
body-cavity, which, as already explained, contains the internal ends 
of the fourth nephridia. The testis, in its most fully developed form, 
extends from the region of the muscular appendage of the cesophagus 
nearly as far as the anus, as shown in fig. 15. 

Unripe spermatozoa are found, attached together in sperm-morule, 
in the cavity of the testis. The fully developed spermatozoon (fig. 
4) is an extremely long, actively moving, undulating fibre. It hence 
closely resembles in form the spermatozoon of D. vorticotdes as de- 
scribed by van Beneden (1) and Mereschkowsky (10), excepting that 
Mereschkowsky describes and figures a swollen head in the sperma- 
tozoon of D. vorticoides. I believe that no such structure occurs in 
D. teniatus, although at the time when fresh material was accessible 
to me I was not familiar with Mereschkowsky’s paper. 

Although ripe spermatozoa may be found in any part of the adult 
testis, they are always present at its posterior end, if they have any- 
where reached their mature condition. As has been already ex- 
plained, the testes are fused together across the middle line in the 
region of the fifth body-segment, and the ripe spermatozoa which 
accumulate in this part of the organ are taken into the interior of a 
pair of vesiculz seminales (v. fig. 15). In their most fully deve- 
loped condition these structures are much larger than in the figure 


48 NOTES ON THE ANATOMY OF DINOPHILUS. 


just alluded to (cf. fig. 8), and occupy a large proportion of the cavity 
of the fifth segment. 

The connection between the testis and the vesicule seminales is 
by no means easy to discover in sections, but can be best made out 
by careful compression of the living animal. Under these condi- 
tions, it may be observed that the anterior end of the vesicula semi- 
nalis is quite closed, and that the communication with the testis is 
effected by the agency of a ciliated funnel, which passes forwards 
from the posterior end of the vesicula, and somewhat from its ventral 
surface, to open into the posterior median region of the testis (fig. 
15). This region is reduced to a narrow space between the two 
vesicula seminales (and therefore ventral to the intestine) during 
the condition of full distension of these structures by spermatozoa. 

The funnel and the adjoining part of the inner wall of the vesicula 
are ciliated, but I believe that cilia do not occur in all parts of the 
latter. The vesicule seminales never contain unripe spermatozoa, 
although mature, actively moving spermatozoa are to be found in 
the cavity of very young and small vesicule, even when no such 
spermatozoa could be seen in the testis itself. This implies that 
the spermatozoa tend to make their way to the posterior part of 
the testis as soon as they become ripe. 

It is perhaps worth while to mention that the above account of the 
communication between the testis and the vesicula seminalis has 
been confirmed, in its general features, by the study of sections. 

The fully developed vesicule seminales are regularly ovoid in form, 
with their principal axes parallel to the main axis of the body of the 
animal. The posterior pole of each vesicula passes into a very obvious 
duct, which opens laterally into the sheath of the copulatory organ. 

The generative pore is a median structure, situated on the ventral 
side of the base of the tail, a little posterior to the level of the anus 
(figs. 3, 15). The pore opens into a vestibule, into which projects 
the extremity of the penis. This organ is embedded anteriorly in a 
solid glandular mass of cells, and consists of two parts. The first 
of these is composed of very distinct cells, of a glandular appear- 
ance, and staining very deeply with carmine or hematoxylin. These 
cells radiate in a single layer from the internal cavity of the organ, 
The second part of the penis projects into the generative vestibule, 
and consists of a series of narrow, spike-like rods (in which nuclei 
could be distinguished), which, lying side by side, form a truncated 
cone, open at its extremity, and continuous with the cavity of the 
penis. 

A copulatory organ of the same general character as that above 
described is well known to occur in the dwarf males of D. gyroctliatus 
(Korschelt, Repiachoff, &c.), whilst from a figure (plate viii, fig. 7) 


NOTES ON THE ANATOMY OF DINOPHILUS. 49 


given by M‘Intosh (9) of D. vorticoides it appears probable that the 
entire male generative apparatus of this latter species closely re- 
sembles that of D. teniatus. 

So far as I am aware, copulation has not hitherto been actually 
proved to take place in any species of Dinophilus.* The proof that 
such a process takes place in D. teniatus is very readily obtained 
by merely placing a considerable number of individuals of both sexes 
in a small quantity of sea-water, as in a watch-glass. Under these 
circumstances, it is noticed, even a very short time after the animals 
have been placed together, that here and there a male is attached, 
by means of its penis, to the body of a female. In these cases, the 
terminal, conical portion of the penis is protruded through the gene- 
rative pore, and is passed into the skin of the female; spermatozoa 
are then seen to have passed from the vesicule seminales, through 
the skin of the female, and to be accumulating themselves into a 
mass immediately beneath the perforation made by the penis. 

There seems to be no localisation of the spot at which spermatozoa 
can be introduced into the female. The penis can obviously be 
inserted into the skin at any point, as is shown by the fact that, in 
the cases actually observed, the point selected was sometimes in the 
region of the neck, in other cases far back in the body of the female, 
and in other cases near the middle of the body. 

The act of copulation has no relation to the maturity of the ova 
of the female, nor is it prevented by the fact that the female has 
already received an ample supply of spermatozoa by a preceding 
operation. It was extremely difficult to discover any female, in which 
ovaries were recognisably developed, which did not contain large 
numbers of spermatozoa in its body-cavity. These were observed in 
almost any part of the body of the animal, their position being pro- 
bably partly dependent on the manner in which fertilization had been 
previously effected. The spermatozoa show, however, a great tendency 
to accumulate into a large compact mass, situated in a space on the 
ventral side of the stomach (v. fig. 14, and description of the female 
generative organs). In some cases it was observed that the female 
was receiving spermatozoa simultaneously from two males; in others 
that while, for instance, fertilization was being effected near the 
posterior end of the body, a great mass of spermatozoa (obviously 
obtained on a previous occasion) was visible at the anterior end of 
the body. In many cases the females were enormously distended with 
spermatozoa, which could hardly have been all received at one time. 

The common occurrence of great numbers of spermatozoa in the 
body of the supposed female might suggest that D. teniatus was 
hermaphrodite. Sucha supposition is rendered sufficiently improbable 

* Korschelt (6) has probably seen something of this process in D. gyrociliatus. 


50 NOTES ON THE ANATOMY OF DINOPHILUS. 


by the following considerations: (i) That no other species of Dino- 
philus is known to be hermaphrodite ; (ii) that the process of ferti- 
lization was frequently observed in D. taniatus; (iii) that the 
spermatozoa so constantly seen in the female of the same species 
were, without exception, ripe and actively moving, no trace of sperm- 
morule or unripe spermatozoa being discernible. Such stages in 
the development of the spermatozoa were never missed in any adult 
male individual. 

It will be noticed that the above-described process of copulation 
in D. txniatus exactly resembles the processes which have been de- 
scribed by Lang (8, p. 281) in certain Polyclada (Anonymus, &c.). 

The morphology of the vesiculza seminales is one of the most 
interesting features of D. teniatus, since there is reason to believe 
that these structures are the modified fifth nephridia of the male. 
The reasons for this conclusion are two: 

(i) Five pairs of ordinary nephridia occur in the female D. 
teniatus (as in the female D. gyrociliatus), whilst the most careful 
examination, often repeated, of the males of the same animal failed 
to show any trace, in that sex, of the existence of a fifth pair of un- 
differentiated nephridia. 

(ii) The consideration of young stages of the vesicule seminales. 

Fig. 5 represents the earliest of these stages which was observed. 
The vesicule seminales were in their definitive position in the fifth 
body-segment, and their identification as vesicule was rendered 
sufficiently certain by the fact that they contained ripe spermatozoa. 
The vesicule were arranged in an obliquely transverse position, their 
outer portions ending blindly at a level between the two ciliated 
rings of the fifth segment, their inner ends opening into the cavity 
of the testis. A part of the vesicula immediately succeeding the 
internal aperture was lined with long cilia ; the next part of the tube 
contained a small mass of spermatozoa. The penis was well deve- 
loped, and obscure indications of a duct leading from the vesicula to 
the penis were observed ; the existence of this duct was not, how- 
ever, completely proved. The resemblance of the young vesicula 
seminalis to an ordinary nephridium was manifested, not only in its 
shape and position, but still more conspicuously by the fact that its 
walls contained an orange pigment, exactly resembling that so com- 
monly found in the walls of the excretory tubes. 

Stages intermediate between that represented in fig. 5 and the 
mature form of the vesicula seminalis were frequently observed. 
The final form is acquired by the gradual distension of the originally 
subcylindrical tube by spermatozoa, this distension being accom- 
panied by an alteration in the direction of its axis, the result of 
which processes is that the end which, in the young vesicula, is 


NOTES ON THE ANATOMY OF DINOPHILUS. 51 


external, is situated, in the adult condition, in front, the whole organ 
having now acquired an antero-posterior direction. The funnel, 
during the above changes, will naturally come to be situated near 
the posterior end of the organ. 

There seems, therefore, fair reason to assume that the young 
vesicula seminalis shown in fig. 5 is morphologically the fifth 
nephridium ; it must be especially noted that the funnel of the vesi- 
cula is in a position corresponding with that of the ciliated appendage 
of an ordinary nephridium, and that the original external aperture 
of the modified nephridium was probably (in the phylogenetic history 
of the organ) at the opposite end of the tube, which ultimately be- 
comes the blind anterior end of the vesicula. The relations of the 
outer end of the young vesicula to the ciliated rings of the fifth seg- 
ment further support this conclusion. The connection of the vesicula 
seminalis with the penis would, in this case, have to be regarded as 
having been acquired secondarily. Should the above account of the 
vesicule seminales of D. t#niatus be confirmed, the structure and 
mode of origin of these organs might be held to have an important 
bearing on the question of the phylogeny of the differentiated 
Cheetopod nephridium. The structure of the first four nephridia in 
the male D. tzniatus, or of all five nephridia in the female, is obvi- 
ously comparable with that of the head-kidney of a Cheetopod larva. 
In this connection the figures given by Ed. Meyer (11) of the larval . 
excretory organs of Nereis (Taf. xxvii, figs. 2,3) and of Polymnia 
(Taf. xxvii, fig. 11) may be especially alluded to. The possibility 
of the conversion of the internal end of a head-kidney-like nephridium 
into a ciliated funnel, and of the entire nephridium into a vesicula 
seminalis, is a fact (if it be a fact) of some morphological interest. 

Whilst the excretory nephridia of the male D. tzniatus open into 
a space which has been described above asa part of the body-cavity, 
the vesicule seminales open into the cavity of the testis. In 
certain other Archiannelids (Protodrilus, Polygordius), the space 
which is partially lined by generative cells is certainly part of the 
body-cavity. From the analogy of these forms, it may perhaps be 
concluded that, in Dinophilus, the hardly differentiated space which 
occurs in the interior of the ripe testis is also a part of the body- 
cavity. In this case we could assume that whilst the excretory 
nephridia open into the general body-cavity, the vesiculze seminales 
of D. teniatus have acquired an opening into a special generative 
division of the cavity. Attention may be called to the similarity 
between the young generative organs shown in fig. 11 and the 
mesoblastic bands of a Cheetopod larva, and also to the similarity 
between the subsequent history of the testis of D. teniatus and of 
the body-cavity of the developing Chetopod. Although I make 


52 NUTES ON THE ANATOMY OF DINOPHILUS. 


this suggestion with all reserve, it is perhaps possible* that in the 
connective-tissue lacunze of the body of Dinophilus we have the 
representative of the so-called “ primary body-cavity,’’ whilst in the 
fully developed male (fig. 13) the “ secondary body-cavity” is 
represented by the cavity of the testis, with which the funnels of 
the vesicule seminales are connected. 

p. Female.—The generative organs in the female Dz. teniatus 
differ considerably from those of other known species of the genus, 
in the fact that the ovaries are four-lobed. The general arrange- 
ment of the ovaries will be understood by referring to fig. 2, where 
it will be seen that the ovaries, like the testes, are paired bodies, 
but that each half is subdivided into two lobes. Hach lobe consists 
partly of small primordial ova and (ina moderately mature condition) 
partly of larger eggs which have already acquired the orange colour 
which characterises the ripe eggs. The ovaries are covered by a 
cellular investment, which is readily seen in fresh specimens to be 
continuous from lobe to lobe on each side of the body. The ovaries, 
as in D. gigas, are found on the ventral side of the stomach. No 
ducts could be discovered in the living animal. Spermatozoa, 
received during the process of copulation, occurred in almost every 
individual in which the ovaries were at this stage or more highly 
developed. In specimens in which the ova had become still further 
developed, the eggs were no longer confined to the four ovaries. 
As many as fourteen large spherical eggs of a distinct orange 
colour may, in such cases, occur on the ventral side of the stomach 
or intestine, and the two ovarian lobes of each side are then usually 
pushed apart from one another by the occurrence of ripe eggs 
between them. 

Fig. 14 represents a transverse section through the region between 
the anterior and posterior ovaries of a female with numerous and 
fully developed ova. On the ventral side of the stomach is a large 
space, containing a great mass of ripe spermatozoa, which appears 
to have no proper wall on its dorsal side at least, being in this 
region merely roofed in by the stomach. Laterally its walls are 
formed by the cellular investment of the ovaries, this investment 
passing across the middle line of the body on the ventral side of 
the space. In a section which passed through one of the ovaries 
on each side, the ovarian lobes would simply take the place of the 
ripe eggs shown in fig. 14. The cellular investment of the ovaries 
already noticed in fig. 2 would be seen to surround each lobe com- 
pletely, and to be further continuous across the middle line on the 
ventral side of the interovarian space, exactly as in fig. 14. 

Fig. 12 represents a longitudinal section through the two ovaries 

* As has previously been suggested, for other animals, by the Hertwigs. 


NOTES ON THE ANATOMY OF DINOPHILUS. 53 


of the same side ata much earlier stage of development, at a period, 
indeed, when the entire ovary is composed of a mass of small, uni- 
form, primordial ova. The relations of the investment of the ovaries 
are further explained by this figure, in which it is seen that the 
space between the anterior and posterior lobes is, as in the later 
stage, devoid of any epithelium on its dorsal side. Ventrally, the 
space is floored by a single layer of cells, separated from the skin 
by loose connective tissue; the space itself contains (as was occa- 
sionally observed in older stages) a few free cells of unknown 
function. 

In the absence of any developmental evidence it is not easy to 
say what is the nature of the interovarian cavity. From the analogy 
of the male, as well as from a consideration of the general arrange- 
ment of the ovaries, it would appear that the ovaries are primitively 
paired bodies, and not merely lateral thickenings of a median cavity. 
The interovarian cavity would thus be a specialised portion of the 
general body-cavity, which conclusion would be supported by the 
absence of any proper wall, the space being bounded partly by the 
investment of the ovaries and partly by the wall of the stomach. 
The conclusion is further strengthened by distinct evidence obtained 
from sections, that the internal ends of the fourth nephridia project 
into the space. 

In most females observed in section there was found to be a mass 
of spermatozoa atthe sides of the stomach and dorsal to the ovaries, 
these masses of spermatozoa usually passing continuously into the 
large central mass which is nearly always present in the inter- 
ovarian cavity. The spaces in which these lateral masses of sper- 
matozoa lie appear to be parts of the general body-cavity, which is 
hence continuous with the interovarian cavity at those points where 
the spermatozoa enter the latter. This continuity does not neces- 
sarily prove that the ventral space is really part of the body-cavity, 
as, from the method in which the spermatozoa are introduced into 
the female, they must probably often have to make their way 
through various obstructions in order to reach the ventral space. 

The layer of cells connecting the two ovaries (figs. 12 and 14) 
across the middle ventral line of the body may thus be provisionally 
interpreted as resulting from the median fusion of two originally 
separate organs, and this process probably takes place at an early 
stage of development, as in the case of the testes of the male. 

The interovarian cavity extends along the middle line of the 
body throughout the whole of the region of the stomach, and there- 
fore occurs, not only between the ovaries themselves, but also behind 
and in front of the ovaries, which are lateral thickenings of the 
walls of the cavity, projecting into it. In consequence of this pro- 


54 NOTES ON THE ANATOMY OF DINOPHILUS. 


jection, the posterior part of the cavity in fig. 12 is separated (in 
the particular section in question) from that part which occurs 
between the anterior and posterior lobes; the posterior part of the 
cavity is of course continuous with the anterior part. It will be 
noticed from fig. 12 that the posterior part of the interovarian 
cavity has an epithelial wall on its dorsal side as well as on its 
ventral side, and the same is true of the anterior end of the cavity 
(not involved by the section shown in fig. 12), The complete con- 
version of the interovarian cavity into a tube which runs backwards 
below the intestine takes place at the level of the posterior ovarian 
lobes, and appears to be due to the fusion across the middle 
line of the investments of the ovaries of opposite sides. The 
tube thus formed runs backwards, becoming much smaller as it 
approaches the end of the body. In one specimen examined, the 
tube was distinguishable almost as far back as the anus, although 
very minute in the hinder part of its course. 

In fig. 14, the eggs which are cut by the section are still outside 
the interovarian cavity. Most of the large eggs in this individual 
possessed two nuclei, as shown in one of those figured. They were 
further provided with a somewhat shrivelled membrane, which is 
probably the vitelline membrane. In the fresh condition, the only 
case noticed in which the vitelline membrane was acquired before 
the eggs reached the exterior was in a dead female, most of the 
tissues of which were beginning to break up into fragments. 

In other sections of the series from which fig. 14 is taken, eggs 
are found in the interovarian space. The posterior, tubular con- 
tinuation of this space may probably be regarded as an oviduct, 
although the process of egg-laying was not directly observed. It 
does not appear to me probable that the eggs are liberated by the 
death of the female, as Weldon (18) supposes to be the casein D. gigas. 

In D. vorticoides (van Beneden, No. 1) and in the species described 
by Korschelt (6) as D. apatris (probably identical with D. gyrociliatus), 
the eggs are known to pass to the exterior by means of a minute 
pore situated on the ventral side of the animal, at the base of the 
tail. This pore is said not to be recognisable except when the eggs 
are being laid; the eggs completely lose their shape in passing 
through the aperture, but regain their spherical form on arriving in 
the water. 

In Protodrilus, an animal to which Dinophilus is probably allied, 
the eggs are said by Uljanin and Repiachoff (v. Repiachoff, No. 12, 
p. 29) to escape from the body in the same way as in the above-men- 
tioned species of Dinophilus. According to the observations of Uljanin, 
quoted and confirmed by Repiachoff, the ripe eggs of Protodrilus 
move about freely in the meshes of the network of connective tissue 


NOTES ON THE ANATOMY OF DINOPHILUS. 55 


which fills the general body-cavity, passing from segment to segment 
through apertures which remain between the interlacing muscle-fibres 
constituting the dissepiments, and finally escape from the body on 
the ventral side of the last segment. 

The above description shows that in Protodrilus the eggs fall 
into the general body-cavity, whilst the same is true of D. gyrociliatus, 
where the body-cavity opens to the exterior by means of a ventral 
pore situated near the base of the tail. The fact thatin D. teniatus 
the interovarian cavity has been above shown to be continued 
ventrally almost as far as the anus, taken in conjunction with the 
admitted difficulty of discovering the actual generative pore except 
when eggs are being laid, is distinctly in favour of the view that 
the eggs of D. teniatus are laid in the same manner as that which 
has been already described in other species of Dinophilus. The 
analogy of D. gyrociliatus, in which the eggs undoubtedly fall into 
the general body-cavity, further suggests that the interovarian cavity, 
into which the ova fall in D. teniatus, and which is continuous with 
a passage which leads towards the exterior, is similarly a part of the 
general body-cavity. 

On the Affinities of Dinophilus.—It has been repeatedly pointed out, 
by Metschnikoff, Lang, Repiachoff, and Korschelt, that Dinophilus 
has affinities with the Annelids, and more particularly with the 
Archiannelids. Weldon (13) expresses himself even more definitely 
in favour of the Archiannelid relationships of this form, supporting 
‘his conclusions by referring to the muscular cesophageal organ, to 
the cihated ventral surface, associated with lateral nerve-cords, and 
to the character of the excretory organs, as described by Meyer. 

The similarities between Dinophilus and theadmitted Archiannelids 
are so numerous and so striking that it can hardly be doubted that 
the above conclusion is amply justified by the facts. It may, how- 
ever, be worth while to call attention to the special resemblances 
shown by D. tzniatus to admitted Archiannelids, and to one or two 
considerations which are suggested by the study of this animal. 

1. External ciliation.—The existence of two rings of cilia on each 
segment, a feature which appears to be so characteristic of D. 
tzniatus, is common to this species and to Protodrilus Leuckartit 
(Hatschek, No. 5). In the latter animal each segment is provided 
with two rings, interrupted, as in Dinophilus, by the uniform cilia 
which cover the ventral surface (ventral groove in Protodrilus). Two 
preoral rings of cilia exist in Protodrilus, which, however, differs 
from Dinophilus in possessing an elongated “‘ postoral region of the 
head ”? (containing the muscular appendage of the cesophagus, and 
hence probably identical with the first body-segment of Dinophilus) 
which bears five rings of cilia. 


56 NOTES ON THE ANATOMY OF DINOPHILUS. 


2. Nervous system.—In Protodrilus, as in Dinophilus, ventral 
nerve-cords run along the sides of the ciliated ventral region of the 
body. In both cases, these cords are connected with the brain by 
cesophageal commissures running round the sides of the mouth. 
Further, the cesophageal commissures in Protodrilus acquire a relation 
to the longitudinal muscles which is precisely similar to that which 
obtains, not only in the same region, but throughout the body, in 
Dinophilus. Protodrilus is well known to possess an almost con- 
tinuous layer of longitudinal muscles, which are separated by small 
interspaces into two ventral and two dorsal groups. In the region 
of the head (v. Hatschek) the four groups of muscles become widely 
separated ; by referring to Hatschek’s fig. 14 (Taf. ii), representing 
a section passing through the region of the mouth, it will be seen 
that the ventral longitudinal muscles, in their relative size and in 
their relations to the cesophageal commissures, are exactly similar to 
the longitudinal muscles of Dinophilus. Still further forwards in 
Protodrilus, the dorsal muscles (which do not seem to be represented 
in Dinophilus) disappear altogether. 

The ventral nervous system of Protodrilus is not known to be 
segmented, and Hatschek describes only one transverse commissure 
between the two cords, occurring at the junction of the “head” 
and body. 

The researches of Foettinger (2) have shown that Histriobdella is 
to be regarded as an Archiannelid. Foettinger re-names this animal 
Histriodrilus, in order to mark its removal from the group of the 
Leeches to that of the Archiannelids. 

In one respect, the nervous system of Histriodrilus shows a closer 
resemblance to that of Dinophilus teniatus than is manifested by 
that of any other Archiannelid. The ventral nervous system has 
been shown by Foettinger to be definitely segmented, in correspond- 
ence with the external segmentation indicated by metameric con- 
strictions of the skin. Histriodrilus possesses about eight ventral 
ganglia, which, however, differ from those of Dinophilus in being con- 
tinuous across the middle ventral line. Inthe intersegmental regions 
alone, the ventral nervous system consists of separated ventro-lateral 
cords. Paired cesophageal nerves, similar to those of Dinophilus, 
are described and figured by Foettinger (pl. xxv, figs. 10, 11). 

3. Exeretory and generative orguns.—The nephridia of D. teniatus 
closely resemble those of Protodrilus, as described by Hatschek. 
According to this observer, each nephridium of Protodrilus commences 
with a small funnel, opening into the body-cavity, and bearing 
internally a single, very long cilium. The difficulty of the investi- 
gation of nephridia of this type makes it possible that the difference 
between the funnel in Protodrilus and the ciliated appendage in 


NOTES ON THE ANATOMY OF DINOPHILUS. 57 


Dinophilus is really less considerable than would appear from a com- 
parison of Hatschek’s figures with my own. 

In many of its features Polygordius differs from Dinophilus far 
more than does Protodrilus. This is sufficiently obvious by such 
characters of Polygordius as the fusion of the ventral nerve-cords, 
the absence of a muscular cesophageal appendage, the form of the 
nephridia, the greater development of the longitudinal muscles, &c. 
(cf. Fraipont, No. 8). All these facts justify us in concluding that 
Polygordius is less closely related to Dinophilus than is Protodrilus. 

Histriodrilus (Histriobdella), on the contrary, is probably more 
closely related to Dinophilus than is Protodrilus. The similarity in 
the nervous systems of the two genera has been already alluded to, 
and the same general resemblances characterise the excretory and 
generative systems. 

The arrangement of the excretory system in Histriodrilus is said 
to differ in the two sexes. The nephridia are somewhat S-shaped, 
intracellular tubes (unfortunately not figured by Foettinger in much 
detail) ; it is stated that five (or perhaps six) pairs are found in the 
male, and four pairs in the female ; their relations to the segments 
are,shown by means of woodcuts on p. 469 of Foettinger’s Memoir. 
The second nephridium was observed on two occasions to end in- 
ternally in a ciliated ampulla. 

In the existence of structures connected with the generative 
apparatus, and which may possibly be regarded as modified nephridia, 
Histriodrilus again shows evidences of affinity to Dinophilus. 

In the female Histriodrilus there are two ovaries, which are more 
or less fused posteriorly (as in D. gigas). These ovaries are situated, 
as in Dinophilus, on the ventral side of the alimentary canal. The 
ripe ova fall into the body-cavity, whence they are taken up by 
the ciliated funnels of a pair of tubes which open to the exterior 
laterally. These funnels (woodcut, p. 481 of Foettinger’s paper) are 
large, and open into the body-cavity on the ventral side of the 
ovaries. The tubes into which the funnels lead possess a dilatation, 
containing spermatozoa which have been presumably derived from 
a male individual. The resemblance of these structures to the 
vesicule seminales of the male D. t#niatus (in which evidence has 
been brought forward above to show that the vesicula is a modified 
nephridium) suggests that they too are possibly modified nephridia. 

The male generative organs of Histriodrilus appear to be very 
complicated, and their structure and functions were not thoroughly 
understood by Foettinger. The testes are placed on the ventral side 
of the alimentary canal, and are more or less paired in front, whilst 
‘they are fused posteriorly. At the posterior end of the generative 
segment are a pair of vesicles containing spermatozoa (Foettinger, 


58 NOTES ON THE ANATOMY OF DINOPHILUS. 


pl. xxix, fig. 3), and obviously comparable with the vesiculee seminales 
of Dinophilus. As in the latter animal, the vesicles open by ducts 
into a median organ, supposed by Foettinger to be copulatory, and 
of very complicated structure. No “communication between the 
vesicles and the body-cavity or testis is described. Anteriorly the 
generative segment has a pair of lateral eversible penes. The exist- 
ence of three separate copulatory organs in Histriodrilus recalls the 
condition met with in some Polyclads (Anonymus, Thysanozoon), where 
more than a single penis is found. 

The above facts, together with other well-known and striking 
resemblances between Dinophilus on the one hand and Protodrilus, 
Polygordius, or Histriodrilus on the other, make it in the highest 
degree probable that Dinophilus is a true Archiannelid, as has been 
insisted on by so many of the more recent writers on the subject. 
In the number of segments, in the segmentation of the ventral 
nervous system, and in the arrangement of the muscular system, of 
the nephridia, and of the generative organs, Dinophilus more nearly 
approaches Histriodrilus than any of the remaining Archiannelids. 
On the other hand, in the character of the muscular appendage of 
the oesophagus, in the wide separation of the ventral nerve-cords, 
and in the method adopted by the female for laying its eggs, Dino- 
philus most closely resembles Protodrilus. Although Dinophilus 
seems so clearly an Archiannelid, it is nevertheless possible to hold 
with Korschelt, Weldon, and others that it gives evidence of having 
been derived from Platyhelminth-like ancestors. 

Weldon (13) has called special attention to the significance of the 
muscular cesophageal appendage as a representative of the pharynx 
of a Planarian. The median position of the generative pore, and 
the method of fertilization adopted by the male Dinophilus tzniatus, 
further support the view of the Platyhelminth origin of the Archian- 
nelids. The median penis of D. teniatus and D. gyrociliatus is 
strictly comparable with the same structure in a Planarian, although 
it is probably a highly significant fact (if this is really the case) that 
this organ has entered into relations with a pair of modified nephridia 
which receive the spermatozoa from the testes. 

Korschelt (6) and others have drawn attention to the remarkable 
fact that, whilst the female of one species of Dinophilus differs com- 
paratively little from that of any other species, there are very great 
differences between the males of the various species. In D. gyro- 
ciliatus (including D. apatris) (and possibly in D. metameroides, in 
which the male is not known) there is very striking sexual dimor- 
phism, the female being many times larger than the male. In 
D. vorticoides, D. gigas, and D. teniatus, on the contrary, the males 

_do not differ appreciably in size from the females. Whilst in D. gigas 


NOTES ON THE ANATOMY OF DINOPHILUS. 59 


the male is,said to have neither penis nor vesicule seminales, these 
structures are found in D. teniatus, which is probably closely allied 
to D. gigas. 

I have no observations which explain the disappearance of D. 
tentatus during the summer. It is, however, important to notice 
that the eggs develop immediately after being laid. Small indi- 
viduals were of common occurrence during the early part of April, 
although I did not succeed in finding the segmenting eggs till April 
16th ; the termination of my visit to Plymouth occurring a day or 
two after that date, I have no observations worth recording on the 
development. The eggs may be easily obtained by looking through 
mud drawn by means of a siphon from the bottom of a rock-pool 
which is inhabited by D. teniatus. The general course of the deve- 
lopment is apparently similar to that which has been described by 
Korschelt in D. gyrociliatus (D. apatris) ; the embryo, as in this 
species, acquiring most of its adult characters while still enclosed in 
its vitelline membrane. The absence of any metamorphosis in Dino- 
philus appears to me a noteworthy fact. It is perhaps a legitimate 
inference, from the facts known with regard to Dinophilus, that a 
Trochosphere stage is not to be expected in the ontogeny of this 
animal, since in the persistence of the preoral ring of cilia, and pro- 
bably of the head-kidneys, and in the general characters of the ali- 
mentary canal, the adult Dinophilus may be considered to remain in 
a condition which is practically that of a Trochosphere. 


Postscript.—I owe to the kindness of Dr. Norman the opportunity 
of referring to the description which has been given by G.N. R. 
Levinsen of Dinophilus caudatus, published in a paper which had 
previously been inaccessible to me (Bidrag til Kundskab om Grénlands 
Turbellarienfauna, Vidensk. Meddel. fra den naturh. Foren. i Kjében- 
havn, 1879—1880). 

D. caudatus is identified by Levinsen with the Planaria caudata 
of Fabricius (Fauna Groenlandica, 1780) and of O. F. Miiller (Zool. 
Danica), and, in the words of Fabricius, “ Habitat stupenda multitu- 
dine in confervis, et ulvis littoralibus, sepe illas tegens.” 

It resembles the species above described as D. teniatus in the 
division of the body into segments by deep constrictions of the skin, 
in the form of the testes, and in the existence of a penis and of 
vesicule seminales, but is stated to be so well known that detailed 
description is unnecessary ; it is, moreover, unfortunate that Levinsen 
has published no figure of the species described by him. 

It appears to me quite possible that “ D. taniatus”’ is identical 
with D. caudatus, but as the evidence on this poimt is quite incon- 
clusive, I do not propose to withdraw, for the present at least, the 


60 NOTES ON THE ANATOMY OF DINOPHILUS. 


specific name, which has already been published in the Proceedings 
of the Cambridge Philosophical Society (vol. vi). According to 
Levinsen, D. caudatus is the species which has been described by 
other writers as D. vorticoides ; its colour is stated to be red, whilst 
no mention is made of the existence of four-lobed ovaries or of 
segmental ciliated rings. 


REFERENCES, 


1. van BENEDEN, P. J.—Notice sur un nouveau Némertien de la cdte d’Ostende. Bull. 
de l’Acad. Royale de Belgique, Tome xviii, lre Partie, 1851, p. 15 [Dinophilus 
vorticoides |. : 

2. Forrtinaer, A.—Recherches sur Vorganisation de Histriobdella homari, P. J. van 
Beneden, rapportée aux Archiannélides. Archives de Biologie, Tome v, 1884, p. 435. 

3. Frarpont, J.—Le Genre Polygordius. Fauna und Flora des Golfes von Neapel, xiv 
Monographie, 1887. 

4, HatiEz, P.—Contributions 4 0 Histoire Naturelle des Turbellariés. Lille, 1879, p. 155 
[Dinophilus metameroides]. 

5. HatscHex, B.—Protodrilus Leuckartii. Eine neue Gattung der Archianneliden. 
Arbeiten a. d. Zool. Inst. d. Universitat Wien, Tom. iii, 1880, p. 79. 

6. Korscuent, E.—Uber Bau und Entwicklung des Dinophilus apatris. Zeits. f. wiss. 
Zool., Bd. xxxvii, 1882, p. 315 (and p. 702). 

7. Korscnext, E.— Die Gattung Dinophilus u. der bei ihr auftretende Geschlechtsdimor- 
phismus. (Spengel’s] Zoologische Jahrbiicher, Zeits. f. Syst., Geog., u. Biol. der 
Thiere, Bd. ii, 1887, p. 955. 

8. Lane, A.— Die Polycladen. Fauna und Flora des Golfes von Neapel, xi Monographie, 
1884, p. 678, &e. [Dinophilus gyrociliatus]. 

9. M‘Intosu, W. C.—The Marine Invertebrates and Fishes of St. Andrews. Edinburgh 
and London, 1875, p. 108, and pl. viii, figs. 7—10 [ Dinophilus vorticoides]. 

10. MeRnEscuxowsxy, C.— Ueber einige Turbellarien des Weissen Meeres. Arch. f. Naturg., 
xlv Jahrg., i Bd., 1879, p. 51 [Dinophilus vorticoides]. 

11. Meyer, Ep.—Studien iiber den Kérperbau der Anneliden. Mitt. a. d. Zool. Stat. zu 
Neapel, Ba. vii, 1886-87, p. 592 [Laf. xxvii, figs. 9, 10, Dinophilus gyrociliatus]. 

12. Repracnorr, W.—On the Anatomy and Developmental History of Dinophilus gyro- 
ciliatus, O. Schmidt. Odessa, 1886 [in Russian]. 

13. WELDoN, W. F.R.— On Dinophilus gigas. Quart. Journ. Mie. Sci., vol. xxvii, 1887, p.109, 
and Studies-Morph. Lab. Univ. Cambridge, vol. ii, 1886, p. 258. 


DESCRIPTION OF PLATES IV anp V. 


Illustrating Mr. S. F. Harmer’s paper, “ Notes on the Anatomy of 
Dinophilus.” 


N.B.—All the figures refer to Dinophilus tzniatus, 


Fie. 1.—Dorsal view of a young individual; the mouth, which is ventral, is represented 
as being visible through the semitransparent tissues of the head. 
» Fra. 2.—Ventral view of an adult female, somewhat compressed. 

Fie. 3.—Longitudinal section of an adult male 
of the organs are shown as they appear in a m 
canal, testis, penis, and generative pore. 


(combined from several sections). Most 
edian section; ¢.e. the brain, alimentary 
The eye, ventral ganglia (the distinctness of 


NOTES ON THE ANATOMY OF DINOPHILUS 61 


which is slightly exaggerated), and vesicula seminalis, being laterally placed, would not 
appear in a strictly median section. The two ciliated rings of each of the five segments 
of the body are indicated by one of the brackets to which the numbers 1, 2, 3, 4, 5 refer. 

Fie. 4.—Spermatozoon. 

Fie. 5.—Ventral view of part of the posterior end of a young male, as seen in a com- 
pressorium. The vesicula seminalis is still very young and nephridium-like, opening at its 
internal end into the cavity of the testis. The existence of the structure marked “duct ?” 
was not established with certainty. 

Fie. 6.—Longitudinal section of head, almost median, showing one of the esophageal 
nerves. 

Fie. 7.—Horizontal section of eye. 


Fie. 8.—View, seen from the front, of the surface of the head of an individual killed 
with hot corrosive sublimate. 


Fia. 9.—Transverse section through the head, passing through the origin of one of the 
cesophageal commissures. 

Fre. 10.—Transverse section through the region of the first postoral pair of ganglia. 

Fia. 11.—Transverse section through the middle region of the body of a young individual 
(probably a male). 

Fie. 12.—Longitudinal vertical section, not median, passing through the two ovaries of 
one side of the body, of a young female. 

Fie. 13.—Transverse section through the middle region of the body of an adult male. 

Fig. 14.—Transverse section through the region of the interval between the anterior 
and posterior ovaries of an adult female. 

Fig. 15.—Ventral view of an adult male, as seen under strong compression in a com- 
pressorium. The figure represents the results of a long series of observations. The 
vesicula seminales have been drawn at a rather young stage of development; at their 
period of maximum development they would appear very much swollen, and would extend 
forwards as far as the posterior end of the stomach. The double ciliated rings of the five 
segments are indicated, as in fig. 3, by the numbers 1, 2, 3, 4,5. The testis is not shown 
on the left side of the figure. 


The Spinning Apparatus of Geometric Spiders. 
By 


Cecil Warburton, B.A., 
Christ’s College, Cambridge. 


With Plate VI. 


Tue familiar circular snare constructed by the “ geometric ” 
spiders has always been an object of interest to naturalists, but 
it is remarkable how little has been known until lately of the 
highly complicated organs which compose the spinning apparatus 
of these animals. 

Thanks mainly to the labours of Blackwell,! Emerton,’ 
Bertkau,? and lastly Apstein, a tolerably complete knowledge 
has now been obtained of the structure and general arrange- 
meut of these organs. 

Apstein’s excellent paper,* recently published, contributes 
much that is new and valuable, and fairly represents our 
present knowledge of the subject. Recent researches, however, 
have led me to dissent from some of that author’s conclusions 
as regards the functions of the various spinning glands, con- 
clusions based upon evidence for the most part too indirect to 
be entirely satisfactory. 

Before discussing this matter, some description of the 


1 «Qn the Mammale of Spiders in Spinning,” ‘Trans. Linnean Soc, 
London,’ 1839, vol. xviii, pt. ii. 

2 «The Structure and Habits of Spiders,’ Boston, Cassino & Co., 1883. 

3 Cribellum und Calamistrum,” ‘Archiv fir Naturgeschichte,’ 1882, 
p. 316. 

4 « Bau und Function der Spinnendrusen der Araneida,” ‘Archiy fiir Natur- 
geschichte,’ 1889, p. 29. 


SPINNING APPARATUS OF GEOMETRIO SPIDERS. 63 


morphology of the organs in question will be necessary. The 
large garden spider, Epeira diademata, is taken as the most 
convenient type of the family, but the following remarks apply 
in the main to all its orb-weaving congeners. 


External Spinning Organs. 


These occupy a small round area on the under surface of the 
abdomen towards the posterior end, where, when at rest, they 
. present a bluntly conical protuberance (figs. 1 and 2, sp.). If 
this area be examined under a low power, it is seen to be 
occupied mainly by four conical spinnerets, their bases form- 
ing a quadrilateral, and their apices meeting in the centre of 
the area (fig. 8). The narrow space which intervenes between 
the bases of the anterior (or inferior) spinnerets (a) is filled by 
a small tongue-like process (¢). The wider gap separating the 
posterior (or superior) spinnerets (p) is occupied by a terminal 
projection of the abdomen (z) containing the anus. Each of 
these spinnerets is two-jointed, and furnished at its extremity 
with a multitude of hair-like tubes containing the ducts of the 
spinning glands. 

They are possessed of a wonderful mobility, and can be 
widely separated, or energetically rubbed upon each other with 
a rotary motion at the will of the animal. Their separation 
discloses a third and smaller pair of spinnerets consisting of 
one joint only, and having their apices directed backwards and 
inwards, so as to lie immediately beneath the apices of the 
posterior spinnerets (fig. 10, #). 

These again present a large number of glandular orifices. 
They will be referred to hereafter as the intermediate spinnerets. 
Thus we have, in all, three pairs of spinnerets capable of a great 
variety of movement, and bearing at their extremities, as will 
be presently seen, about 600 spinning tubes. 


Internal Spinning Organs. 
Apstein has shown that there are, in this group of spiders, 
five distinct kinds of glands, to which he assigns the names 
Ampullaceal, Aggregate, Tubuliform, Piriform, and 


64 OECIL WARBURTON. 


Acinate. The first three kinds are few in number and of large 
size, extending throughout the greater part of the abdomen. 
The piriform and acinate glands are minute and numerous, 
and are closely grouped together immediately above the 
spinnerets. 

Their exact arrangement is important and may be summarised 
as follows: 

There are two pairs of Ampullaceal glands (fig. 3) debouch- 
ing on the anterior and intermediate spinnerets re- 
spectively on the inner side. 

There are three pairs of Aggregate glands, their three 
outlets on each side being situate upon the inner surface of 
the posterior spinneret. 

There are three pairs of Tubuliform glands, two opening 
on the inner side of the posterior spinnerets, and one upon the 
outer surface of the intermediate spinnerets. 

The above glands are comparatively large, and their ducts 
terminate in distinct tubular prominences. 

There are about 200 Piriform glands, all connected with the 
anterior spinnerets, where their ducts terminate in hair-like 
tubes. 

Finally, there are about 400 Aciniform glands, each 
posterior and each intermediate spinneret bearing the hair-like 
terminations of about a hundred ducts. 

Or thus, tabulating for one side only: 


GLANDS. 


Ant, SPINNERET. 


INTERMEDIATE. 


PostTERIOR. 


Ampullaceal . 


1 on inner side 


1 on inner side 


Aggregate i a 3 on inner side. 
Tubuliform . wai 1 on outer side 2 on inner side, 
Piriform . | About 100 ‘al 
Aciniform About 100 About 100. 


The question naturally arises as to the different functions 


SPINNING APPARATUS OF GEOMETRIO SPIDERS. 65 


performed by glands apparently so distinct. Apstein attempts 
its solution by reasoning which is mainly indirect and, in my 
opinion, misleading. It occurred to me that the problem might 
be attacked in a more direct manner, and with this view the 
experiments to be now described were performed. 

A spider of this group usually trails a line from its spin- 
nerets while walking. With a little dexterity it can be quickly 
seized, and imprisoned in such a manner that the spinnerets 
from which the line is proceeding can be microscopically 
examined. 

This may be best effected by means of a piece of wood about 
the size and shape of a microscope slide, with a narrow band of 
cloth attached by its end to one extremity. The cloth band 
is then held in front of the crawling animal, which may, with 
a little practice, be thus trapped between the cloth and the 
wood, so that the band passes beneath the cephalothorax, 
leaving the abdomen free for examination with the lately 
emitted line still attached. 

The fourth pair of legs must be kept from interfering with 
the experiment by pins suitably adjusted. The spinnerets will 
now be in their quiescent position, and the precise origin of the 
threads therefore invisible. If, however, it be gently drawn 
forwards, i.e. towards the animal’s head, certain facts with 
regard to it become at once clear. As, however, the phe- 
nomena differ at different times, we must take the various cases 
in succession. 

In the simplest case (fig. 9) one of the anterior spinnerets will 
be pulled forward with the thread, which will be easily seen to 
consist of a single line emanating from one large tube. 

More frequently (fig. 10) the line will be double issuing 
from similarly situated tubes on the inner sides of the two an- 
terior spinnerets. This is probably the most usual case, and I 
have drawn out from a spider many yards of such a double line 
of silk, its origin being all the time plainly visible. 

It is important to note that there is no adherence between 
the two lines, which remain perfectly distinct throughout their 
whole parallel course. 


66 CECIL WARBURTON. 


The spider will probably tire of having its silk thus drawn 
out—a process which it can only influence indirectly. Were 
its hind legs free it would seize the thread and break it. It 
sometimes contrives to do this by a rapid movement of its spin- 
nerets, but occasionally it decides to strengthen the thread 
instead. The spinnerets are accordingly actively rubbed to- 
gether, and a little flocculent mass of silk appears upon the 
line, which is thereafter seen to consist of four strands, two of 
finer calibre having made their appearance between the former 
lines (fig. 11). To see their origin the anterior spinnerets must 
be kept forward by a gentle strain on the thread, and the pos- 
terior spinnerets thrust aside with a needle. The new lines 
may then be traced to the intermediate spinnerets, and proceed 
from large spinning tubes on the inner side. Again, the four 
lines remain distinct and non-adherent. 

Should the spider still resolve on strengthening the line a 
further rubbing together of the spinnerets occurs, and presently 
a large number of strands are seen to proceed from the nume- 
rous hair-like tubes on the anterior spinnerets (fig. 12). The 
four previous lines are still distinguishable by their greater 
thickness. 

If after drawing out several inches of this compound line it 
be slightly slacked, a puff of air separates the strands, showing 
that, though contiguous, they are not adherent. 

Lastly, upon rare occasions, the whole battery of tubes seems 
to be brought into play, the posterior spinnerets contributing 
their quota to the strengthening of the line. Thus the “ trail- 
ing line,” as I have called it, will be found at any moment 
to be constituted as indicated in one of the- cases above 
described. 

It appears, therefore, that such a line usually consists of 
either two or four non-adherent threads emanating from what 
Apstein has shown to be the origin of the Ampullaceal 
glands, and that it may on occasion be strengthened by con- 
tributions from the Piriform and Acinate glands opening 
upon the anterior and posterior spinnerets respectively. 

It was next attempted to apply the same direct method to 


SPINNING APPARATUS OF GEOMETRIC SPIDERS. 67 


the observation of the animal when employed naturally in its 
various spinning operations. Here the difficulties experienced 
were considerable, but some results were obtained by the aid of 
a simple contrivance, consisting of a pair of compasses with the 
points fixed some two inches apart, and between them a narrow 
strip of cloth stretched. 

A flat piece of wood was held behind the spider while at 
work, and between this and the strip of cloth the creature 
was suddenly trapped, the points of the compasses, which pro- 
jected the eighth of an inch beyond the cloth, being buried in 
the wood on either side. 

Flies were now placed in the various webs, and the spiders 
seized in the act of binding them up in the usual manner. The 
fly is held and rotated by means of the jaws, palps, and ante- 
rior legs, while the fourth pair of legs draw up from the spin- 
ners the bands of silk which are to enclose it. These silken 
bands were found to be constituted as shown in figs. 12 or 13. 
There seems no doubt, therefore, that the Aciniform 
and Piriform glands are mainly used in performing this 
operation. 

The structure of the geometric snare was next investigated. 

This is a familiar object, and may be said to consist of— 

(1) a sort of frame or scaffolding, to which are attached 
the distal ends of 

(2) the radial lines ; 

(8) the spiral line, extending from the periphery to near 
the centre. 

(1) The thread of the framework was generally found to be 
composed as exhibited in fig. 11. When necessary the spider 
strengthened the line by repeating the journey, and laying it 
down a second time. 

(2) The same line, or that of fig. 10, was also employed in 
constructing the radii of the snare. 

Thus the framework and radii of the geometric web are 
supplied by the Ampullaceal glands. 

(3) The spiral line requires a more detailed description. 

A low power shows it to consist of bead-like viscid globules 


68 CECIL WARBURTON. 


strung upon a thread with remarkable regularity, as shown in 
fig. 14d. 

It was until a few years ago supposed that these globules 
were separately deposited by the spider, whereas a uniform 
coating of viscid matter is given to the thread in the first in- 
stance, and its subsequent subdivision into globules is an 
entirely physical phenomenon. Boys! well describes the spider’s 
action as follows: 

“ The spider draws these webs slowly, and at the same time 
pours upon them a liquid, and, still further to obtain the effect 
of launching a liquid cylinder into space, he pulls it out like 
the string of a bow, and lets it go with a jerk.” 

That this separation into globules is really a secondary 
phenomenon I have shown by taking upon a slide a portion of 
such a spiral immediately upon its completion. It readily 
stains with hematoxylin, and on microscopic examination 
shows the various stages indicated in fig. 14. 

We have thus separately to consider the ground-line (Grund- 
faden, Apstein) and the viscid matter with which it is en- 
veloped. 

Apstein imagines the ground-line to be furnished by the 
Aciniform glands, and to be many-stranded. 

I have not yet succeeded in tracing it with certainty to its 
origin, but have established the following facts with regard 
to it: 

In the first place, it is not many-stranded, but double 
only. 

When engaged upon this line the creature is so absorbed as 
to allow of pretty close examination with a hand-lens. I have 
at such times noticed that the posterior spinnerets are partly 
open, and that the line is, at first, distinctly double, fusing, by 
virtue of its viscid envelope, where grasped by the leg which 
draws it forth. Moreover, on staining and teasing the spiral 
line, the ground thread readily shows its double nature (fig. 
15), but no amount of teasing breaks it up into further strands, 
as would surely be the case if such existed, for their separate 


» © Quartz Fibres,” by C. V. Boys, F.R.S., ‘ Nature,’ July 11, 1889. 


SPINNING APPARATUS OF GEOMETRIC SPIDERS. 69 


existence as threads implies a degree of dryness inconsistent 
with complete fusion. 

As far as I have been able to trace these lines they have 
appeared to emanate from the intermediate spinnerets. They 
are much more elastic, however, than the radial lines, and can 
therefore hardly proceed from the Ampullaceal orifices. 

The only other paired orifices on the intermediate spinnerets 
are those of the Tubuliform glands. Now, an important 
function of these glands is undoubtedly, as Apstein remarks, 
the spinning of the egg cocoon, for they are always distended 
with yellow fluid in the female just before the deposition of 
ova, and comparatively inconspicuous after, while the cocoon 
consists of yellow silk. 

If, however, they also furnish the ground-threads, this would 
help to explain their presence in the male spider, which has not 
hitherto been very easy to understand. 

The objections to this view are, first, that cocoon silk is not 
especially elastic, and secondly, that I have not been able to 
find threads in the cocoon of the precise diameter of the ground- 
threads. 

In spiders of the species under consideration the following 
thread-diameters were found to be fairly uniform: 


Cocoon line 2 . ‘ ; j : 006 mm. 
Anterior Ampullaceal . ‘ i : : 003_—=C««,, 
Ground-line of spiral . - 2 j ‘ 0025 ,, 
Intermediate Ampullaceal . : ‘ : ‘0016 ,, 


The imperfect view I obtained of the origin of the ground- 
thread led me to think that though it proceeded from the inter- 
mediate organs, it had some subsequent relation to the posterior 
spinnerets. 

It is possible, therefore, that Apstein is correct in supposing 
that the Aggregate glands, which debouch on the inner side 
of the posterior spinnerets, deposit the viscid matter above 
described. 

The arguments hitherto adduced in support of this view are, 
first, the convenient arrangement of the Aggregate orifices for 
such a purpose, and secondly, the presence of these glands in 


70 CEOIL WARBURTON. 


such spiders—and such only—on whose threads the viscid 
matter has been observed. On dissecting out the various 
glands from a spider, isolating them on slides, and crushing 
them, I found that the contents of the Aggregate glands 
retained their viscidity the longest. Evidence was also sought 
from histological changes in the glands themselves before and 
after web-spinning, and though a much larger series of obser- 
vations would be necessary to afford trustworthy results, 
alterations similar to those known to occur in active serous 
glands seemed to be taking place (figs. 19 and 20). 

This would show that the Aggregate glands are used in 
spinning the web, in which case they must furnish the viscid 
matter, all the other structures being accounted for. 

The unsafe nature of such indirect evidence is, however, 
freely admitted, but it may be pointed out that the certainty 
which now exists with regard to some of the glands gives 
greater probability of the true function being allotted to the 
remainder. 

One other web structure remains to be briefly discussed. 
Foundation lines are attached to surrounding objects, and 
ordinary non-viscid lines are glued to one another by little 
patches of silk which we may call attachment discs (Haft- 
scheibe, Apstein). The spider rubs its anterior spinnerets 
against a surface, emitting silk from the Piriform glands, and 
upon walking away a line is drawn out from the spinnerets. 

I have been best able to study these structures in a small 
bottle in which a spider was obliging enough to deposit its 
eggs, fixing the cocoon in its place by a multitude of cross 
threads fixed to the sides of the bottle at their ends, and to one 
another where they intercrossed. Their appearance is given in 
figs. 16—18. It was this structure which led to the belief in 
the highly compound nature of the spider’s line. 


SPINNING APPARATUS OF GEOMETRIC SPIDERS. 71 


Summary. 


1, Facts newly established.—A spider’s line does not 
consist of many strands fused or woven together, but ordinarily 
of two or four distinct threads. 

The framework and the radii of circular snares are supplied 
by the Ampullaceal glands. 

The Acinate and Piriform glands are those mainly em- 
ployed in binding up captured prey. 

The “trailing line” consists primarily of Ampullaceal 
threads, sometimes strengthened by contributions from the 
Acinate and Piriform glands. 

The ground-line of the spiral is double only, and the two 
strands are bound together merely by the viscid matter which 
envelops them. 

2. Corroborative of Apstein.—The “attachment discs” 
are furnished by the Piriform glands. 

The Tubuliform glands supply the silk for the egg-cocoon. 

The viscid matter of the spiral is probably the product of the 
Aggregate glands. 

Finally, the origin of the spiral ground-line is uncertain, 
but it may proceed from the Tubuliform orifices on the inter- 
mediate spinnerets, 


72 CECIL WARBURTON. 


EXPLANATION OF PLATE VI, 


Illustrating Mr. Cecil Warburton’s paper on “ The Spinning 
Apparatus of Geometric Spiders.” 


Fig. 1.—Profile of Epeira diademata, sp. spinnerets. 

Fic. 2.—Ventral aspect of the same species. 

Fic. 8.—Ampullaceal gland. 

Fic. 4.—Agegregate gland. 

Fig. 5.—Tubuliform gland. 

Fie. 6.—Piriform gland. 

Fic. 7.—Acinate gland. 

Fig. 8.—External spinning organs at rest. a. Anterior, p. Posterior 
spinnerets. ¢. Anterior tongue-like fold. z. Terminal fold of abdomen. 


Figs. 9—13 show the composition of the “trailing-line” under various 
circumstances. 7. Intermediate spinnerets. 


Fie. 14.—Stages in the formation of the viscid globules. @. Shows the 
final arrangement. 


Fic. 15.—Teased spiral line, showing that the “ ground-line’’ is double. 
Fie. 16.— Attachment disc” (Haftscheibe, Apstein). 
Fic. 17.—The same, more in profile. 


Fic. 18.—Attachment disc, gluing together irregular strands which held 
an egg-cocoon in position. 


Fie. 19.—Section (somewhat diagrammatic) of aggregate gland at rest. 


Tic. 20.—Ditto of aggregate gland when the spider had just constructed 
its web. (The right half only of Figs. 19 and 20 is shaded.) 


ON PHYMOSOMA VARIANS. 


BY 


ARTHUR E. SHIPLEY, M.A, 


Fellow and Lecturer of Christ’s College, Cambridge, and Demonstrator 
of Comparative Anatomy in the University. 


With Plates, VII.—X. 


THE material which forms the basis of the following paper 
was collected and preserved by Mr W. F. R. Weldon, of 
St John’s College, Cambridge, during a visit to the Bahamas. 
On his return to England Mr Weldon commenced to work at 
Phymosoma, and made many microscopic sections and drawings. 
When, however, he received the appointment which he now 
holds at Plymouth he handed the whole material, -together 
with his drawings, to me, with a request that I would complete 
the work thus interrupted. This statement will serve to show 
how much I am indebted to Mr Weldon, both for material 
and for many of the drawings; but I have further to express 
my indebtedness to him for many suggestions and much help 
in completing the work he was unfortunately obliged to lay 
aside. 

The observations here. recorded were made on a species of 
Phymosoma (Ph. varians, Selenka) collected in the Bahama 
Islands. 

This species was sufficiently common in the island of New 
Providence; but it occurred still more abundantly in the 
lagoon of the Bemini atoll. The specimens were obtained by 
breaking up soft masses of coral rock with a hammer. Pieces 


9 


74 ARTHUR E, SHIPLEY. 


of rock which were completely covered at low water contained 
many more specimens than those which were left dry by the 
tide. 

The species seems to be capable of much variation ; and the 
descriptions hitherto published are incomplete in one or two 
important points. A detailed account of the external cha- 
racters may therefore be not altogether useless. 


EXTERNAL CHARACTERS AND ECTODERM. 


The length of fully extended specimens averages 50 mm., 
varying, however, from about 40 mm. to 55 mm. The greatest 
diameter of the trunk is from 4 mm. to 5 mm.; that of the 
introvert about 2mm. The introvert is at least equal in length 
_to the rest of the body. 

The head (figs. 1 and 5) bears a crown of about eighteen 
tentacles, arranged in the form of a horseshoe, with the open 
ends directed backwards ; the whole structure lying far back 
on the dorsal region of the head (fig. 1). The ends of the 
tentacular horseshoe are connected with the lower lip; which 
is a thick vascular crescent enclosing considerably more than 
three-fourths of the circumference of the head (figs. 2 and 6). 
The mouth is a narrow crescentiform slit, extending between 
the dorsal margin of the lower lip and the convex surface of 
the crown of tentacles. These relations of tentacular crown, 
mouth, and lower lip are shown in the diagram (figs. 1 and 32). 
It will be seen that in this species the condition of the head 
presents a marked resemblance to that which obtains in 
Phoronis. 

The tentacles themselves are short and simple, the surface 
directed towards the outer (convex) side of the lophophor 
being grooved, and the groove is ciliated; the opposite surface 
is covered with a deep brown pigmented epithelium (fig. 5). 

The space included within the concavity of the lophophor 
(the representative of the praoral lobe) is covered with a 
wrinkled, pigmented skin. In its centre lies a deep depression, 
similar to that of Sipunculus, at the base of which lies the 


ON PHYMOSOMA VARIANS. 75 


brain; while a sense- pit opens on to it on each side" (figs. 1 
and 7). 

The introvert is dividable into several regions. Immediately 
behind the head follows a narrow, perfectly smooth region, 
extending for about 2 mm. At the posterior edge of this 
region is attached a small but very extensile collar, its 
anterior margin peing free (figs. 1 and 4). Behind the 
attachment of the collar the introvert swells slightly, and 
there follows a region about 6 mm. in length, which bears 
about twenty rows of hooks. Then follows a region of variable 
length, bearing papille; and lastly a second region of hooks, 
which in our specimens bore from forty to between fifty and 
sixty rings. Among the hooks of the posterior region are 
many papillee ; and these in passing backwards get more and 
more conspicuous, at the expense of the rings of hooks. 
These papilla also exhibit traces of a tendency to form rings 
round the base of the proboscis. The characters of the hooks 
have been well described by Selenka and by Keterstein?: it 
will be sufficient here to refer to the description given by these 
authors, and to the diawing (fig. 21). 

The papille on the introvert have the form shown in fig. 15; 
they are hemispherical or hemielliptical, being often higher 
than broad, each having a central opening surrounded by 
three or four plates of chitin, which often fuse into a single 
piece ; and surrounding this central piece are numerous small 
rounded plates covering at least the upper half of each papilla. 

The papille on the trunk (figs. 11, 14, and 16) have a some- 
what different appearance, being larger and flatter, and having 
no marked central plate. They are also surrounded by a much 
pigmented ring. These trunk papille agree with the de- 
scription given by Selenka, who, however, seems to have over- 
looked the difference between the papilla in the two regions of 
the body. The papillw are large and conspicuous at the two 
extremities of the trunk, where they are present on all sides; 


1 Of. Spengel, ‘Die Sipunculiden,” ‘Reisen im Archipel der Philippinen,’ 
Bd. iv. 1883. 
2 Selenka, loc. cit., Keferstein, ‘Zeit, fiir Wiss. Zool.’ Bd. xv. 1865, 


9—2 


76 ARTHUR E. SHIPLEY. 


in the middle of the body they are, however, almost entirely 
confined to the dorsal surface. These papillae are shown in 
fig. 11. 

The colour varies in different specimens. The ground 
colour is always yellowish-brown, with a peculiar iridescence, 
noticed by other observers: on this are patches of a black or 
deep brown pigment, which are generally so arranged as to 
form a few irregular rings in the middle of the introvert and 
smaller patches on the anterior dorsal part of the trunk. 
Individuals are, however, found in which the pigment is only 
very slightly developed; while in others the whole dorsal 
surface of the body is thickly mottled with dark patches. 

The body wall is everywhere covered by an ectodermal 
epithelium, one cell thick. The characters of the cells pre- 
senting marked differences in different regions. 

The ectoderm covering the lower lip and* the outer 
grooved surface of the tentacles is columnar and covered with 
short thickly set cilia (figs. 4 and 8). 

The preeoral lobe, together with the inner surface of the 
tentacles, is covered by a layer of cubical cells, the outer half 
of each cell in this region being loaded with granules of a dark 
brown pigment (figs. 4, 7, and 8). These cells are not ciliated. 

The epithelium covering the collar is formed of short 
cubical cells, which appear to become more flattened when this 
organ is extended (fig. 4), 

On the remainder of the introvert the ectoderm secretes, 

except in the region of the hooks and papilla, a clear homoge- 
neous cuticle 0-02 mm. thick. 
Each hook is secreted by a raised papilla, which projects 
into the cavity of the hook. The cells covering the papilla 
being large and cubical, provided with conspicuous spherical 
nuclei (fig. 21). 

Behind each hook is a small organ, apparently sensory, 
which will be described below. 

The ectoderm of the trunk consists of lamellar, dome-shaped 
cells, secreting a thick cuticle almost 04mm. in thickness 
(fig. 13). The outer surface of this cuticle is rough and 


ON PHYMOSOMA VARIANS. 77 


granular ; and it absorbs staining fluids with a certain readi- 
ness, while the main body remains in all the preparations 
quite unstained. The cuticular substance appears in the 
greater part of the body to be arranged in wavy columns, 
running more or less regularly at right angles to the surface 
of the body, and resting each on a single ectoderm cell (fig. 
10). Each column exhibits a further tendency to a laminated 
structure, the layers composing it lying concentrically to the 
body of the animal. 

A result of the peculiar shape of the ectoderm cells in the 
trunk-region is the formation beneath them of a series of small 
cavities, containing a coagulum. By a kind of lifting up of 
several cells from the adjacent muscles, these cavities commu- 
nicate with one another and so attain a considerable size (fig. 
10). They communicate with the cavities, to be presently 
described, which lie between the two layers of the papille 
(fig. 16). 

The function of these channels is in all probability con- 
nected with the circulation of the nutrient fluids; but I have 
not succeeded in tracing a connection between these and any 
other of the cavities of the body. The analogy between these 
spaces and the dermal spaces of Sipunculus need hardly be 
pointed out. A surface view of the skin shows that the 
cuticle is broken up into a series of fusiform areas (fig. 11). 
These areas roughly correspond with the skin-papille, the 
lines limiting them being formed by thickened portions of 
cuticle. When the animal is in an expanded condition the 
areas become thicker and shorter. 

The papille of the introvert and trunk are entirely ecto- 
dermal. Their external appearance has already been de- 
scribed; the arrangement seen in section is shown in figs. 14 
and 16. 

The cuticle seems, in the region round the base of each 
papilla, to contain irregular spaces, as if its inner and outer 
surfaces had been pulled apart, an appearance which may, of 
course, be due to the action of the knife used in cutting sec- 
tions. On the papilla itself, the plates seen in surface views 


78 ARTHUR E. SHIPLEY. 


are visible as local thickenings of the cuticle, and are often 
loaded with a bright yellow-brown pigment. 

The body of the papilla has the form of a double cup, as if 
it had been formed by the invagination of a spherical out- 
growth of the general ectoderm. The outer layer of the cup 
is composed of flattened cells, which are continuous with those 
of the general ectoderm at the base of the papilla, and with 
those of the inner cup at its apex. The inner layer of the cup 
consists of large cells, loaded with granules of a bright yellow 
substance, so that the remains of their protoplasm are seen as 
slender strings of stained material, separating masses of the 
yellow formed material. This inner cup contains a small 
cavity, which communicates with the exterior by the pore at 
the apex of the papillae. Between the two cups is a cavity, 
continuous with the subepidermal system of spaces above 
mentioned. : 

In the absence of a detailed knowledge of the habits of the 
living Phymosoma it would be rash to assign any function to 
these very curious organs, but it seems not improbable that 
the secretion they produce may assist in softening the coral 
rock in which the animals form long tubular passages. 


GENERAL ANATOMY, 


The arrangement of the internal organs is shown in fig. 3 
which represents a Phymosoma cut open longitudinally and 
the body wall turned back to expose the viscera. The intro- 
vert is invaginated to almost its full extent, the true anterior 
end of the body being at the point where the sense-pits lie. 

The longitudinal and circular muscles of the skin have been 
omitted for the sake of clearness ; a detailed description of them 
is given below. 

The retractors of the introvert are four in number. They 
fuse round the first half of the cesophagus forming a muscular 
tube, and then separate into a dorsal and a ventral pair. The 
former are much the shorter pair; between them lies the 
dorsal blood-vessel, whilst the ventral pair have at their base 
the generative ridge and between them the nerve-cord. The 


ON PHYMOSOMA VARIANS. 79 


spindle muscle supporting the alimentary canal is shown 
running up the axis of the intestinal coil. The cesophagus is 
' anteriorly surrounded by the retractor muscles, but the poste- 
rior half is free and ends in the coiled intestine. The number 
of coils varies, usually there are about fifteen. The intestine 
forms a thicker tube than the cesophagus, it ends in the 
rectum which passes straight to the anus in the dorsal middle 
line. ; 

_ The only part of the vascular system visible is the crumpled 
dorsal vessel. 

The brain is indicated through the walls of the introvert, 
and close behind it, at the sides, two black spots, the sense- 
pits, are visible; the ventral nerve-cord is seen running down 
the body. 

The nephridia or brown tubes are conspicuous objects, vary- 
ing very much in size and shape in different individuals. 
Their external opening is at the anterior end and a little in 
-front of the level of the anus. The opening is followed by a 
short neck which opens into the swollen portion or bladder 
which passes into the true secreting portion. The anterior 
half of the nephridia is attached to the body wall by muscle- 
fibres, the posterior is free (fig. 18). 

The generative ridge runs across the body at the base of the 
ventral retractors (fig. 22). It is sometimes V-shaped, the 
ridges slanting backward in the middle ventral line. 


THE MuscULAR SYSTEM. 


The muscular system is composed throughout of fusiform 
fibres with simple pointed ends. Each fibre consists of an 
outer contractile and an inner granular portion, the outer por- 
tion being longitudinally striated. The elongated oval nucleus 
lies entirely within the inner layer, the nucleus and the con- 
tractile layer being easily stained, while the inner substance 
does not absorb staining fluids (figs. 13 and 21). 

The fibres of the retractor muscles are much larger than 
those of the body wall, their diameter being at least twice as 


great. 


80 ARTHUR E. SHIPLEY. 


The fibres of the general body wall are arranged in an 
external circular and an internal longitudinal layer, separated 
by an exceedingly delicate layer of oblique fibres. This latter 
can only be seen in surface views, as, owing to its extreme 
thinness, it is difficult to detect in sections. 

The circular muscles commence behind the collar fold, 
where they form a series of rings round the introvert, one . 
lying beneath each ring of hooks (fig. 1). Posteriorly to the 
hook-bearing region the circular fibres form a continuous 
sheath, which extends to the posterior end of the animal 
(fig, 22). 

The longitudinal fibres form a complete sheath round 
the introvert, commencing anteriorly just behind the attach- 
ment of the collar. At the posterior extremity of the intro- 
vert these fibres separate into longitudinal bundles, generally 
about twenty-two in number, which run parallel with one ~ 
another down the trunk. In passing backward these bundles 
gradually fuse with one another, and so become fewer and 
larger, till near the “tail” they form a series of projecting 
ridges, giving to a section of the body-cavity in this region a 
characteristic star-shaped appearance (fig. 13). .At the poste- 
rior extremity of the body the bundles finally unite. The 
longitudinal bands occasionally give off side branches, which 
pass into the adjacent bands (fig. 22). 

The retractor muscles of the proboscis arise by a common 
origin from a kind of dissepiment, stretching across the body 
at the level of the origin of the mantle fold, and just behind the 
skeletal tissue of the collar (fig. 9). Almost immediately after 
their origin they split into two bands, which pass backwards, 
one on each side of the cesophagus, for about half its length. 
Each lateral band then again divides into two branches, a 
shorter dorsal and a longer ventral branch, which run to the 
body wall, where they fuse with the adjacent bands of longitu- 
dinal fibres. The ventral bands, being longer than the dorsal, 
are attached to the body wall behind these, lying one on each 
side of the nerve-cord, and being connected by the generative 
ridge. The posterior ends of the retractor muscles are fan- 


ON PHYMOSOMA VARIANS. 8] 


shaped and split up into bundles of fibres, which pass into the 
adjacent longitudinal bundles. 

A special muscle accompanies the nervous system on each 
side (fig. 29), and is described in connection with the nerve- 
cord. Its purpose is probably to regulate the movements of 
this important organ during the eversion or retraction of the 
introvert. 

The spindle-muscle and the intrinsic muscles of the ali- 
mentary canal are described with the digestive organs, and 
the intrinsic muscles of nephridia with the account of these 
organs. 

Except along the generative ridge, the body wall is lined by 
a layer of flat epithelial cells, which is never ciliated, in this 
respect differing from that of Sipunculus. 


THE SKELETAL TISSUE. 


A curious form of tissue is found in the collar and the ten- 
tacular crown of Phymosoma. As it seems to subserve the 
purpose of supporting and stiffening the collar and tentacles, 
and as a support for the insertion of the retractor muscles, I 
propose to call it the skeletal tissue. 

The cells composing this tissue are large rounded cells, which 
lie close to one another, but are not so crowded as to become 
hexagonal. The cell nucleus is large, and both it and the proto- 
plasm of the cell stain deeply. Running across the cell, usually 
in a radial direction, are a small number of wavy lines. 

This tissue forms a ring lying in the substance of the collar, 
which it seems to stiffen. The horseshoe-shaped blood-space 
lies internal to this tissue, which is thicker at some parts, 
and thus serves to break up the blood-space as indicated in 
figs. 4 and 6. It also sends extensions into the tentacles, a 
group of these skeletal cells being formed on both sides of the 
tentacular nerve in each section of the tentacle (fig. 17). 

From the position of this skeletal ring in the collar it will be 

readily understood that it is just in front of the invaginable 
introvert, and consequently it affords a valuable hold for the 


82 ARTHUR E. SHIPLEY. 


insertion of the retractor muscles which are attached to this 
part of the body. 


THe ALIMENTARY CANAL. 


The digestive tube may be divided into three parts: (1) the 
cesophagus, which extends from the mouth to the beginning of 
the coiled intestine; (2) the intestine which forms a close, 
fairly regular coil with from ten to sixteen turns ; in its coiled 
state it is almost 10 mm. long; (3) the rectum, which is a 
straight tube passing from the anterior end of the coil to the 
anus. 

In spirit specimens the whole of the alimentary canal is 
white in colour, and is usually full of fine sand. A spindle- 
muscle serves to support and keep in position the coiled 
intestine and rectum. This muscle arises from the extreme 
posterior end of the body wall, and passes forward along the 
axis of the coiled intestine and then parallel with the rectum, 
to be inserted into the body wall a little in front of the anus 
(fig. 3). It gives off during its course numerous fibres, which 
are inserted into the walls of the intestine and rectum. In 
addition to the spindle-muscle the intestine is held in position 
by a thin muscle, which arises from the ventral surface of the 
body and is inserted into the anterior end of the coil. 

The position of the mouth has been described above. It is 
a crescentiform slit, lying between the lip and the convex side 
of the tentacular crown (tig. 6). It is lined with a continua- 
tion of the columnar ciliated cells which cover the inside of the 
lip and the ciliated grooves of the tentacles. The walls of the 
cesophagus are produced inwards into a series of from six to 
eight ridges, which reduce the lumen of the cesophagus to a 
star-shaped tube. The grooves between these ridges are 
continuous with the grooves on the outside of the tentacles 
(fig. 9). The whole is beset with short thick-set cilia. 
Surrounding the cesophagus are a few muscle-fibres arranged 
circularly. For about half its length this first part of the 
alimentary canal lies between the retractor muscles, which in 
this region of the body have been reduced to two bundles of 


ON PHYMOSOMA VARIANS. 83 


fibres by the fusion of the anterior and posterior muscles of 
the left and right side respectively. These lateral bundles 
have fused with the cesophagus, a small amount of gelatinous 
connective tissue containing branched cells being found be- 
tween them and the circular muscles of the cesophagus. The 
dorsal blood-vessel lies between the lateral muscles in a 
groove, closely applied to the dorsal side of the cesophagus 
and extending back almost to the beginning of the intestinal 
coil. 

Owing to the presence of very fine sand in the intestine and 
the delicacy of the tube which make it impossible to satis- 
factorily wash the sand out, I had considerable difficulty in 
studying the histology of this part. The intestine is lined 
throughout by a layer of columnar epithelial cells, one cell 
thick. The nuclei of these cells are situated near the base. 
Outside this layer is a thin membrane in which muscle-fibres 
are sparsely scattered. I do not think the intestine is uni- 
formly ciliated, but patches of cilia occur here and there. 
The arrangement of these ciliated patches I failed to make out. 
There is no groove with long cilia running the whole length of 
the animal, such as has been described by Keferstein in 
Sipunculus. 

The lumen of the rectum is almost occluded by the presence 
of numerous folds projecting into it. These folds are covered 
with a number of columnar cells some of which are ciliated, 
but the majority are crowded with large vacuoles containing 
minute granules; these are devoid of cilia. The rectum has no 
ceca opening into it, such as are found in Sipunculus. 

The external cuticle is folded into the anus for a little way, 
and the circular muscle-fibres of the body wall are thickened 
around the anus in this region, forming a very efficient 
sphincter. A number of radially arranged fibres also pass out 
all round the anus; these fibres are derived from the longi- 
tudinal muscles. Their action is obviously antagonistic to that 
of the sphincter. 


84 ARTHUR E. SHIPLEY. 


THE VASCULAR SYSTEM. 


There are two varieties of blood-corpuscle found in Phymo- 
soma. The larger kind exist in great numbers in the body- 
cavity, together with the ripe generative products (fig. 30). 
They are oval, about ‘02 mm. long and two-thirds as broad ; 
their protoplasm is very clear and transparent, but the nucleus 
stains well and they have a very definite outline. The coelomic 
fluid, in which these corpuscles float, bathes all the internal 
organs of the animal, and when the contraction of the poste- 
rior circular muscles forces the fluid forward it would serve to 
evert the introvert, which is withdrawn again by the retractor 
muscles. 

The second variety of blood-corpuscle is much smaller than 
the first, being about half as long and as broad; the proto- 
plasm is not so transparent and stains more readily. These 
corpuscles are contained in a close space which is usually called 
the vascular system. This space may best be described as 
consisting of three parts, all communicating with one another. 
The first of these is a horseshoe-shaped space (figs. 2 and 7) 
at the base of the tentacles. From this space there runs up 
into each tentacle a series of three vessels which anastomose 
freely with each other and communicate at the tip. As a rule 
sections of the tentacles show one vessel near the inner pig- 
mented surface of the tentacle, just external to the tentacular 
nerve and two near the outer surface, one each side of the 
ciliated groove (fig. 17). The free ends of this horseshoe- 
shaped space at the base of the tentacles, near the dorsal 
middle line, are continuous with the ends of another horseshoe- 
shaped space which lies in the collar. This forms the second 
of the above-mentioned spaces. As the diagram (fig. 2) shows, 
it is very irregular in form, breaking up and anastomosing 
into a number of spaces. This communicates only with the 
inner smaller horseshoe, between the two is the crescentiform 
space in which the mouth opens. The third space—usually 
termed the dorsal blood-vessel—is a very extensile sac running 
along the dorsal middle line of the cesophagus between the 


ON PHYMOSOMA VARIANS. 85 


right and left retractor muscles (figs. 2, 3, and 9). It usually 
extends about } cm. behind the head, and it ends blindly behind. 
Anteriorly it opens in the middle ventral line into the smaller 
or tentacular horseshoe, and at the point of junction is a large 
sinus which surrounds about three quarters of the brain—in 
fact, all those parts which are not in contact with the epidermis 
(figs. 2, 4, and 8). The nervous matter is thus in close contact 
with the blood, being separated only by a thin layer of con- 
nective tissue, and the endothelium of the blood-space (fig. 27). 

The walls of this third part or dorsal vessel are muscular, 
and in some specimens are much contracted and crumpled. 
This vessel appears to serve as a reservoir for the corpusculated. 
fluid, and when it contracts and the fluid is forced forward, it 
would serve to evert the lip and extend the tentacles. The 
whole of this space is lined by flat epithelium. I have never 
seen cilia on the walls, and it is entirely closed. 


Tue NEPHRIDIA. 


The nephridia or the renal organs are in the form of a 
single pair of “brown tubes,” as in other Sipunculide. They 
lie on either side of the middle ventral line at some little dis- 
tance from the nerve-cord. Their anterior extremities, near 
which are the external openings, being a little anterior to the 
level uf the anus (fig. 3). 

Each nephridium is about 1 cm. long, the length in preserved 
specimens varying according to the space of contraction of its 
rouscular coat; by means of this muscular layer the whole 
organ has the power of shortening and dilating, and also of 
throwing itself into a number of curious curves. 

At the anterior extremity is a dilated bladder, the diameter 
of which is from four to five times that of the posterior cellular 
portion of the organ. The internal opening is situated at the 
anterior extremity of the bladder and is provided dorsally with 
a prominent ciliated lip’ (fig. 18). The external orifice is just 

1 The existence of this opening is doubted by Selenka, ‘Die Sipunculiden,’ 
but it is sufficiently obvious in all the specimens. It was demonstrated in 
another species of Phymosoma by Dr Spengel. 


86 ARTHUR E. SHIPLEY. 


behind the internal, and opens also into the bladder. The 
opening to the exterior is surrounded by a thickened ring of 
connective tissue with muscle-fibres intermingling, the latter 
forming a sphincter. The walls of the passage are folded and 
lined with cubical epithelial cells. The communication between 
the internal opening and the bladder is effected by means of a 
short passage, the epithelium of which is ciliated. The walls 
of the bladder itself are formed of a single layer of cubical 
cells, a middle coat of irregularly arranged muscle-fibres, and 
an external investment of peritoneum. The relations of the 
bladder and its openings will be evident from the diagram, fig. 
18. The walls of the bladder are very elastic, they contain 
many muscular fibres, and are lined with cubical epithelial 
cells. 

The tubular portion of the kidney is a backward prolonga- 
tion of the bladder, and is attached from the anterior half of 
its course to the body wall by a mesentery, its posterior half 
being free. The tube possesses anteriorly a simple lumen, ~ 
which is broken up posteriorly by a number of septa, producing 
an appearance which reminds one of that presented by the 
interior of a frog’s lung, the transition between the two regions 
is very gradual. 

The epithelium lining the tubular portion of the kidney 
is generally one cell thick; it is produced internally into a 
series of long papille, which are separated from one another 
by a series of depressions (see figs. 19 and 20). 

The cells forming the papilla are extremely long, and are 
loaded with fine, yellowish granules. In specimens killed 
during the functional activity of the organ these papilla-cells 
are furnished at their inner extremities with a series of large 
thin-walled vesicles, which appear to be thrown off from time 
to time into the lumen of the kidney (fig. 20). 

The granules, with which the kidney-cells are loaded, appear 
to decrease in number as the vesicles are approached ; and it 
seems possible that the excretory products of the nephridial 
cells are stored up in the vesicles before being thrown, together 
with the vesicles themselves, into the nephridial tube. The 


ON PHYMOSOMA VARIANS. 87 


whole process is very similar to what takes place in a mammary 
gland during the excretion of milk. Théel mentions that the 
excretory organs of Phascolion emitted yellow vesicles which 
resembled drops of oil when the living animal was disturbed’. 

Between the papillae lie aseries of hemispherical depressions 
lined by a flattened epithelium, the cells of which are usually 
loaded at their base with the yellow granules above men- 
tioned. These cells seem to develop into the high columnar 
cells described above. 

The muscle-fibres form an irregular network outside the 
nephridial cells, lying chiefly at the bases of the papille. The 
hemispherical depressions seem to pass through the meshes of 
the muscular coat, and to lie in direct contact with the perito- 
neal investment of the organ (figs. 19 and 20), forming a series 
of projections visible on the external surface. 

The peritoneal epithelium which surrounds the kidney is dis- 
tinguishable from the nephridial cells by the greater ease with 
which it absorbs staining fluids, and by the absence of secretion 
granules. In the region of the hemispherical depressions 
the peritoneal cells frequently form thick masses several cells 
deep. 

It is difficult to avoid the conclusion that the excretion pro- 
ducts are passed through the peritoneal cells to the cells of the 
hemispherical cups, and thence to the cells of the papille, 
the internal opening of the nepbridium having relation chiefly 
to its function as a generative duct. 

The relative amount of the secreting epithelium to the 
cubical epithelium lining the bladder varies greatly; in one 
specimen even the area between the external opening and inner 
end of the internal opening was lined with the former cells, thus 
reducing the bladder to a very smal] structure. 

The lumen of the nephridium contains nothing but the 
vesicles above described, together with ripe ova or spermatozoa. 
It is remarkable that the coelomic corpuscles appear never to 
pass through the internal opening of the organ. 


1 Théel, “ Recherches sur le Phascolion strombi,” ‘Kongl. Svenska Vetenskaps- 
Akademiens Handlingar,’ Bandet 14, No. 2. 


88 ARTHUR E. SHIPLEY. 


Tue NERVOUS SYSTEM AND SENSE-ORGANS. 


The brain is a bilobed organ, continuous by its anterior 
face with the ectoderm of the invaginated preoral lobe, and 
surrounded elsewhere by a process of the lophophoral blood- 
vessel, from which it is separated, not only by the endothelium 
ofthe vessel, but also by a connective-tissue capsule (see figs. 
2, 4, 8, and 27). The groove between the two lobes is deepest 
and widest on the anterior surface, where the substance of the 
brain is continuous with that of the praoral ectoderm. 

In the brain, as in the ventral nerve-cord, the ganglion-cells 
are aggregated in the side nearest the skin; they are on the 
dorsal side of the animal in the brain, on the ventral in the 
nervous system. 

As the figs. 24, 25, and 26 show, there is a cap of ganglion- 
cells covering the anterior, dorsal, and posterior surfaces of the 
brain. The ventral surface is not invaded by the ganglion- 
cells; but here the fibrous tissue, which makes up the rest of 
the brain, comes in contact with the thin connective capsule. 
It is this region of the brain which projects into the blood- 
sinus. . 

The majority of the ganglion-cells are small, with deeply 
stained nuclei, occupying about one half of the cell; they are 
either unipolar or bipolar. At the postero-dorsal angle of the 
brain, however, a certain number of giant ganglion-cells are 
found (fig. 27). These cells have a diameter of ‘02 mm., at 
least four times that of the smaller cells; their nuclei are rela- 
tively smaller, and they are unipolar. I was unable to trace 
what becomes of the fibres given off from these giant-cells. 
No such giant-cells occur in any other part of the nervous 
system. 

A pair of sense-organs, usually described as eyes, lie em- 
bedded in the substance of the brain. 

Each of these sense-organs has the form of a long tube bent 
upon itself, so that one limb is nearly at right angles to the 
other. The outer limb, the lumen of which is narrow, opens on 
to the surface of the preoral lobe (figs. 1 and 25), the opening 


ON PHYMOSOMA VARIANS. 89 


hes at the dorsal lateral angle of the brain, just dorsal to where 
the circumcesophageal nerve-commissure leaves the brain; the 
lumen of the inner limb dilates into a vesicular swelling in the 
substance of the brain (fig. 23); the whole tube has, therefore, 
nearly the shape of a retort, and lies entirely in the lateral 
part of the brain. The wall of the tube is everywhere formed 
by a layer of clear, nucleated cells. In the outer limb these 
cells form a fairly regular columnar epithelium one cell thick, 
which becomes less regular as the inner limb is approached. 
The cells bounding the inner limb are arranged irregularly, and 
they appear to send out processes from their peripheral extremi- 
ties, which may be supposed to communicate with the pro- 
cesses of adjacent nerve-cells. The cells of the inner limb also 
secrete a deep black pigment, which lies in that portion of each 
cell which is turned towards the lumen of the tube. A clear 
coagulum sometimes lies in the cavity of this sense-pit. These 
organs are visible as two black spots at the level of the brain 
in the dissected animal (fig. 3). 

No trace exists in this genus of the curious finger-like pro- 
cesses which project from the brain of Sipunculus into the 
body-cavity. 

Three pairs of nerves are given off from the brain: (1) 
dorsally, a small pair supplying the skin of the preoral lobe— 
these lie nearest to the middle line (fig. 26); (2) ventrally, a 
nerve on each side, going to the corresponding area of the 
lophophor, and supplying a branch to each tentacle (fig. 24); 
(3) and posteriorly on each side arises a nerve which passes 
round the cesophagus, and joins its fellow of the opposite 
side to form the ventral cord (fig. 24). The lophophoral 
nerve arises between the point of origin of the nerve of the 
preoral lobe and the exit of the circumcsophageal commis- 
sures. 

The ventral cord itself shows no trace either of a division 
snto two halves, or of a segregation of its nerve-cells into 
ganglia. It runs along the ventral surface of the body as a 
perfectly uniform filament, terminating posteriorly without 
glionic swelling such as that found in Sipunculus. 

10 


any gan 


90 ARTHUR E. SHIPLEY. 


The fibres are on the dorsal, the cells on the ventral side of 
the cord. 

Along each side of the nerve-cord runs a longitudinal band 
of muscle-fibres, the cord and its pair of muscles being together 
enclosed in a special peritoneal sheath. The space between 
the sheath and the cord is filled with a peculiar connective 
tissue (fig. 29), which has been regarded by some observers as 
clotted blood, the cord being said to lie in a blood-vessel. My 
preparations afford no evidence in support of this view; and I 
am strongly of opinion that the substance lying between the 
nerve-cord and its peritoneal investment is, as above stated, 
connective tissue. 

By contraction of the muscles within the peritoneal sheath 
the nerve-cord may become crumpled, so that while the sheath 
is perfectly straight the cord within it presents the appearance 
shown in fig. 28. 

The nerve-sheath is attached to the ventral body wall by a 
series of mesenteric cords, each of which contains, not only a 
prolongation of peritoneal epithelium, but also a central axis 
of connective tissue (figs. 28 and 29). 

The peripheral nerves form, as in Sipunculus, a series . 
of rings encircling the body, and lying between the circular and 
the longitudinal muscles. In the region of the introvert a 
nerve-ring lies beneath each ring of hooks, at the base of the 
circular muscle which supports them (figs. 1 and 2). 

Each nerve-ring is connected with the ventral cord by a 
single short nerve, which runs from one to the other in the 
middle ventral line. 

The lopbophoral nerve runs along the base of the tentacles, 
one on each side of the lophophore. Each gives off a series of 
small nerves, one of which passes up the axis of each tentacle, 
lying immediately beneath the ciliated groove (figs. 2, 5, 
and 17). 

In addition to the sense-pits on the brain there are a number 
of ectodermal structures on the introvert, which are probably 
sensory in function, and may well be described here. These 
bodies are arranged in circles parallel to the rows of hooks 


ON PHYMOSOMA VARIANS. 91 


running round the introvert (fig. 21). One of these organs 
is shown in fig. 12; the ectoderm-cells have multiplied and 
increased in size, forming a small “heap ; some of these cells 
have then formed stiff processes, which project beyond the 
level of the skin. These processes are gathered up into a small 
brush by a chitinous ring which surrounds the base. 

The hooks (fig. 21) are very closely packed in a series of 
ridges formed by the circular muscle-fibres of the introvert. 
The point is directed backward, while the row of sense-organs 
lies immediately behind them, embedded in the muscular 
cushion. 


THE GENERATIVE ORGANS. 


Phymosoma varians is diccious; in no case are ova and 
spermatozoa found in the body of the same individual. 

The ovaries are formed by a fold of the peritoneal epi- 
thelium, elsewhere flat, which occurs at the base of the 
insertion of the long ventral pair of retractor muscles. This 
genital ridge extends beyond the inner edge of the muscle 
attachment across the ventral middle line lying between the 
nerve-cord and the skin; it does not extend beyond the outer 
or dorsal end of the muscle. The ridge is not quite con- 
tinuous, but it is interrupted from time to time; its free 
border is also irregular, and this gives it a puckered or frilled 
appearance (fig. 22). 

In transverse section—parallel to the long axis of the 
Phymosoma—the ovary is seen to be much thicker at its free 
border than at its base; the latter indeed is formed of but two 
layers of cells, thus giving the appearance of a simple fold of 
endothelium. These layers, however, thicken towards the free 
edge. Nearly all the cells have become ova, and are held 
together by a very scanty matrix. The organ is solid, and 
the ova dehisce from it into the body-cavity. 

In the ovary the ova increase in size towards the thickened 
free edge, where the oldest are. Tlrose found free in the body- 
cavity also differ somewhat in size, and undoubtedly grow 
whilst suspended in the perivisceral fluid; but there is a very 

10—2 


‘ 


92 ARTHUR E, SHIPLEY. 


marked difference in size between the largest ovarian ovum 
and the smallest floating one—a difference I am quite unable 
to account for. 

The floating ova are oval in shape, the largest about 1 mm, 
long, with a thick zona radiata, in which the radial markings 
can only be detected with very high powers (fig. 30). This 
membrane stains deeply except its outermost layer, which does 
not absorb any staining fluid. The protoplasm is very granular, 
and stains well. The nucleus is very large, and sometimes 
reaches almost from one side of the cell to the other; it does 
not stain at all. No micropyle was to be seen. 

The testis occupies in the male a position similar to that of 
the ovary in the female. The mother-cells of the spermatozoa 
separate from the testis before or whilst dividing. Whilst 
floating in the perivisceral fluid the nuclei of these cells com- 
menced to divide, and the whole floats about as a multi- 
nucleated mass of protoplasm. The stages which most com- 
monly occurred were those with eight or sixteen nuclei 
(fig. 8). The males were much rarer than the females, and 
none of them contained ripe spermatozoa. 


SUMMARY. 


The following is a brief summary of the more important 
points described in detail in the body of the paper. 

(1) The head of Phymosoma is surrounded by a stiffened 
vascular horseshoe-shaped lip, the dorsal ends of which are 
continuous with the ends of a hippocrepian lophophor. The 
lophophor bears a crown of about eighteen tentacles—the 
number is always even. In the hollow of the lophophor lies 
the brain, which is continuous with the ectoderm of the 
preoral lobe. The inner surface of the tentacles and the 
ectoderm above the brain is crowded with dark brown pigment- 
gianules, and the ectoderm of the preoral lobe is curiously 
wrinkled. Between the hippocrepian lophophor and_ the 
vascular lip is the crescentiform opening of the mouth. 

(2) At some little distance behind the lip is a thin but very 


ON PHYMOSOMA VARIANS. 93 


extensile collar, which may be so extended as to entirely cover 
the head. 

(3) The ectoderm consists of a single layer of cells. This 
secretes outside a cuticle of varying thickness. The ecto- 
dermal cells are vaulted, so that spaces are left in which a 
nutrient fluid might circulate between the circular muscles 
and the ectoderm. The ectoderm of the lower lip and of the 
outside of the tentacles is ciliated. 

(4) The skin-glands are of two kinds; each is formed by 
the modification of ectoderm-cells, which results in the pushing 
in of certain of the cells to form a double cup. The inner 
layer of cells thus produced develops a number of granules, 
which are extruded through a median aperture. In one kind 
of skin-gland, those of the introvert, this aperture is sur- 
rounded by a chitinous ring, which is absent on those of the 
trunk. 

(5) Rows of hooks set very closely together are found 

‘in the introvert; these are each secreted by a small multi- 
cellular papilla. 

(6) A skeletal tissue is present in the lip and tentacles. 
This seems to stiffen these structures, and to form a firm hold 
for the attachment of the retractor muscles of the introvert. 

(7) The nephridia or brown tubes consist of two parts, the 
bladder and the secreting part. The former opens both to the 
exterior and to the body-cavity, the latter opening being 
shaped like a flattened funnel and ciliated. The secreting 
part opens only into the bladder. Its walls are lined with a 
columnar epithelium, the cells composing which are crowded 
with granules. From time to time a vesicle or bubble crowded 
with these granules is formed at the free end of the cell, and 
ultimately breaks off into the lumen of the uephridium, and so 
passes out of the body. The only other structures found in 
the cavity of these organs besides these vesicles, were the 
ripening generative cells. 

(8) The vascular system consists of a horseshoe-shaped 
plexus in the lower lip, a similar plexus in the lophophor 
which gives off branches into each tentacle, and a reservoir 


94 ARTHUR E. SHIPLEY. 


lying dorsal to the cesophagus, This communicates with the 
lophophoral sinus in the dorsal middle line. Just at this point 
is a blood-sinus which surrounds all those parts of the brain 
which are not continuous with the ectoderm. This system of 
blood-vessels is closed. It contains numerous small oval 
corpuscles. In addition to these the ccelomic fluid contains a 
number of much larger corpuscles, as well as ova and sperm 
morule, The ccelom is lined by a flat epithelium which is not 
ciliated. 

(9) The brain is a bilobed mass, partly connected with the 
ectoderm of the preoral lobe and partly surrounded by a 
blood-sinus. The relative position of the ganglion-cells and 
fibrous tissue is described above. There are a number of 
giant ganglion-cells arranged in the lateral and posterior 
parts of the brain. 

(10) The brain gives off three pairs of nerves: (1) the first 
pair pass to supply the pigmented tissue of the prxoral lobe; 
(2) the second pair run along the base of the lophophor, and 
send a branch into each tentacle; (3) the third pair pass 
round the cesophagus, and unite to form the ventral nerve- 
cord. This is supported by a strand of muscle in each side, 
and by numerous connective-tissue strands which pass to the 
body wall. It has no trace of a double structure, and no seg- 
mentally arranged nerve-ganglia. It gives off from time to 
time a median nerve, which soon splits, and each half runs 
round the body, these fuse together again in the dorsal 
middle line, thus forming a nerve-ring. 

(11) The-sense-organs consist of two pigmented pits in the 
brain, and of certain structures in the introvert. The former 
pits open on to the preoral lobe, and then pass into the brain at 
each side. Each pit is bent on itself, and expands slightly at 
its inner end. The cells lining the pit are crowded with black 
pigment. ‘The sense-organs on the introvert lie in rows close 
behind the rows of hooks. Each consists of a number of ecto- 
dermal cells produced outwards into a stiff process. These 
processes are gathered up into a little brush by a chitinous 
ring which surrounds their base. 


ON PHYMOSOMA VARIANS. 95 


(12) The animals are diwcious. The generative organs 
are in the form of ridges at the base of the ventral retractors. 
The flat coelomic epithelium is here modified to give rise to 
ova in the females and the sperm morule in the males. 


CONCLUSIONS. 


I do not propose to consider at any length the theoretical 
conclusions which might be drawn from the facts above indi- 
eated until I have worked out in detail other forms of the 
Gephyrea, which I hope to do in the immediate future. I 
should, however, like to say something in favour of maintain- 
ing the genus Phoronis in its old position—that is, as a form 
closely allied to the more normal Gephyrea inermia. 

This relationship is most easily seen by comparing a view of 
the head of Phymosoma as seen from above with a view of 
Phoronis (figs. 31 and 32). In both genera the mouth is sur- 
rounded by a pair of vascular horseshoe-shaped ridges, one of 
which is dorsal and the other ventral : the sole point of difference 
lies in the fact that while in the one case the tentacles of the 
lophophor extend along both the ventral and the dorsal horse- 
shoe, they are in the other case confined to the dorsal limb. 

Again, the preoral lobe of Phoronis bears two large 
sensory pits, one on each side of the middle line; these are 
obviously comparable to the similar pits which open into the 
area in the concavity of the Gephyrean lophophor which I 
have spoken of as the preoral lobe. Further, the nervous 
system of Phymosoma, like that of Phoronis, is permanently 
connected with the epidermis. 

I do not enlarge upon the resemblances in the position of 
the anus, and the lengthening of the ventral surface at the 
expense of the dorsal, or on the presence of two nephridia, as 
these points have been already emphasized by Lankester. 
But I would direct attention to two structures hitherto, I 
believe, undescribed in the Gephyrea, which in my opinion 
have homologues in Phoronis. 

The first of these is the skeletal tissue; this, as the descrip- 


96 ARTHUR E. SHIPLEY. 


tion above shows, agrees in position and function with the 
mesoblastic skeletal tissue which supports the tentacles of 
Phoronis as described by Caldwell. The second structure I 
wish to refer to is the thin membranous fold which I have 
above termed the collar. This seems to me to correspond 
very closely with the calyx or web which surrounds the base » 
of the head in Phoronis. 

The absence in the unarmed Gephyrea of mesenteric parti- 
tions in the post-oral body-cavity, similar to those which exist 
in Phoronis, may be accounted for by the twisting of the 
intestinal loop in the more normal genera. The radial 
muscles which extend from the visceral loop to the body wall 
are, in all probability, the remains of an ancestrally continuous 
mesentery. 

It will be remembered that in Phoronis the body-cavity is 
divided into an anterior and a posterior division by a trans- 
verse septum passing from the body wall to the cesophagus, at 
the level of the nerve-ring. The former division includes the 
cavity of the preoral lobe and tentacles, the latter the rest of 
the body-cavity. I am disposed to think that a similar dispo- 
sition of parts obtains in Phymosoma. The organ which is 
usually regarded as forming the blood-vessels in the Gephyrea 
occupies precisely the same position as the anterior body- 
cavity in Phoronis; it has, however, acquired a reservoir— 
the dorsal vessel—into which the fluid may pass when the 
head is retracted. As this involution is impossible in Pho- 
ronis no such reservoir has been developed. If this homo- 
logy holds, there is nothing in the Gephyrea homologous with 
the true blood system of Phoronis. In connection with this 
it is perhaps worth noticing that the so-called vascular system 
in the Gephyrea gives off no vessels or capillaries, but simply 
consists of a number of intercommunicating spaces. 


ON PHYMOSOMA VARIANS. 97 


DESCRIPTION OF PLATES VII, VIII, IX, and X;,' 


Illustrating Mr Arthur E. Shipleys paper 
“On Phymosoma varians.’ 


PLATE VIL 


Fic. 1.—A semi-diagrammatic view of the anterior end of Phymosoma 
varians. The introvert is everted and the tentacular crown expanded. 
The collar is not extended and lies at the base of the head. Only two rows 
__ of hooks are shown. 

Fig. 2.—A semi-diagrammatic view of the closed vascular system and 
nervous system, showing their relation to the alimentary canal. The 
vascular system shows the three parts, the lophophoral, the lower lip, and 
the dorsal blood-vessel. The latter communicates with the lophophoral in _ 
the middle line, and just at this point the sinus round the brain is given 
off. The brain is relatively too small. The three main nerves are shown, 
and the circular nerves which run in the skin. The cesophagus is cut o!t 
abruptly in front in order to display the vascular ring. 

Fia. 3.—View of a Ph. varians which has been opened along the. 
median dorsal line. The introvert is retracted, the true anterior end of 
the body being where the eye-spots lie. Here and there patches of skin 
are seen which bear papille. 

PLATE VIII. 

Fic. 4.—A median longitudinal section through the head. The intro- 
vert is retracted, and the collar expanded until it encloses the whole head. 
The section is not quite in the middle line, or the lip on the dorsal surface 
would not be shown, cf. Fig. 6. The brain is cut through that part which 
is continuous with the ectoderm. 

Fic. 5.—A transverse section through the tentacles: the introvert is 
retracted. The tentacles show the ciliated groove on the outer surface, 
the pigmented epithelium in the inner, and the vascular spaces and 
tentacular nerves. 

Fic. 6.—A transverse section through the base of the lophophor and 
lower lip, just where the two fuse dorsally : the introvert is retracted. The 
skeletal tissue is shown in the lip, which is ciliated all round. 

Fie. 7.—An oblique transverse section through the base of the lopho- 
phor, showing the blood-space ; and in the centre some of the wrinkled 
pigmented tissue of the preoral lobe. The introvert is everted. 


1 Tam indebted to Mr Weldon for the following ner :—Nos. 1, 7, 10, 12, 
14, 15, 16, 20, 21, 23, and 27, 


98 ARTHUR E. SHIPLEY. 


Fic. 8.—A transverse section through the head in the region of the 
brain. The introvert is everted. This specimen had its body wall pushed 
upwards inside the lower lip in the ventral side into a kind of hernia, this 
accounts for the swelling containing blood-corpuscles and sperm-morule. 
The brain is shown in its sinus, also the depressions in the tissue of 
preoral lobe leading to the sensory pits. 

Fie. 9.—A transverse section through the cesophagus. The dorsal and 
ventral retractor of each side have fused into a common lateral muscle, 
which almost fills up the body-cavity. The lumen of the csophagus 
is occluded by ciliated ridges. 

Fig. 10.—A section through the ectoderm and cuticle. Below the 
ectoderm some fibres of the circular muscle may be seen. The ectoderm 
is vaulted leaving spaces which sometimes contain a coagulable fluid. The 
cuticle is traversed by numerous perpendicular lines, and the outer part 
only stains. 

Fig. 11.—A surface view of the skin, showing the longitudinal and 
circular muscle-fibres, the skin papille, and the ridges formed by thicken- 
ings of the cuticle. 

Fic. 12.—A section of one of the sense organs on the.introvert, at the 
base of the ring of hooks. 

Fig. 18.—A transverse section through the posterior end of the 
animal, The longitudinal muscles have fused together and reduced the 
lumen of the body-cavity to a star-shaped mass. The skin papille 
are very numerous in this region, and the cuticle unusually thick. 


PLATE IX. 


Fig. 14.—Section taken through one of the skin papille of the trunk. 
It shows the opening to the exterior, and the small cavity in the cup 
composed of enormous cells crowded with spherules. 

Fic. 15.—Surface view of the papille and hooks in the introvert. The 
chitinous plates round the orifice of these papille are shown. 

Fic. 16.—An oblique section through a trunk papilla, This section 
shows the space between the two layers of the cup in communication with 
the sub-ectodermal spaces of the skin. 

Fie. 17.—Transverse section of a tentacle. At the base of the ciliated 
groove the tentacular nerve lies. Three blood-spaces are seen, and between 
them certain skeletal cells. The inner epithelium is crowded with pigment 
grains. : 

Fie. 18.—A diagram showing the anatomy of the nephridium. The 
posterior blind diverticulum is the secreting part, the anterior thin-walled 
part is the bladder. The arrangement of the internal and external openings 
may also be seen. 

Fic. 19.—An oblique section through the secreting part of the nephri- 
dium, under a low power. This shows the peritoneal epithelium, then a 


s 


ON PHYMOSOMA VARIANS. 99 


dark layer of muscle-fibres and internally the secreting epithelium. The 
breaking up of the lumen into numerous side chambers is also shown in 
this figure. 

Fie. 20.—A portion of the same under a high power. The secreting 
epithelium is seen crowded with granules ; at their free edges these cells 
form vesicles, which break off and fall into the lumen. 

Fig. 21.—A section through parts of several of the hooks on the 
introvert. The multicellular papilla which secrete the hooks are shown. 
One of these sense organs at the base of the hooks is also shown cut 
tangentially. : 

Fig. 22.—A view of the base of the two ventral retractor muscles, 
showing the generative organ. The ventral nerve-cord lies between the 
muscles and dorsal to the generative ridge. The circular and longitudinal 
muscles are also shown, and the outline of the papilla. 


PLATE X. 


Fig. 23.—A section through the antero-dorsal corner of the brain, to 
show the blind end of the sense-pit. The cells lining the inner end of the 
pit are crowded with pigment. A few cells of the ectoderm of the preoral 
lobe are seen, and part of the blood sinus in which the brain lies. 

Fic. 24.—An oblique section through the lateral part of the brain, 
showing the origin of the circumcesophageal commissure and of the 
lophophoral nerve. This figure and the three succeeding ones show 
the arrangement of the ganglion-cells, the giant cells, and nerve-fibres. 

Fig. 25.—A section through the brain, transverse to its long axis, and 
nearer to the middle line than the preceding figure. It shows the fusion 
of the brain with the ectoderm of the przoral lobe, and the commencement 
of the preoral lobe nerve. 

Fig. 26.—A section in a place parallel to the preceding, but still 
nearer to the median line, it shows the origin of the proral lobe nerve. 

Fic. 27.—A horizontal section through the posterior part of the brain 
at right angles to the preceding. This shows the histology of the giant- 
cells and their relative size. 

Fic. 28.—A longitudinal median section of the ventral nerve-cord, 
showing the arrangement of the ganglion-cells and fibres, and the mesen- 
teries which attach the cord to the ventral body wall. 

Fic. 29.—A transverse section of the nerve-cord, showing a mesentery 
from the ventral body wall, the arrangement of ganglion-cells and nerve- 
fibres, the connective-tissue sheath, and the lateral muscles which run 
along each side of the nerve-cord. 

Fre. 30.—An ovum and some of the ccelomic corpuscles. The ovum 
shows the granular protoplasm, the large nucleus, and the zona radiata. 

Fig. 31.—A diagrammatic view of the head of Phoronis, seen from in 
front. 

Fic. 32.--A similar view of Phymosoma. 


ON THE PERCEPTIONS AND MODES OF 
FEEDING OF FISHES. 


BY 


W. BATESON, M.A. 
St John’s College. 


In the course of observations made at Plymouth and elsewhere 
it appeared that the majority of Fishes are diurnal in their habits 
and seek their food by sight, but that a minority are almost 
entirely nocturnal and hunt by scent. To the latter class belong 
Protopterus, Skates and Rays, the Rough Dogfish, Sterlet, Eel, 
Conger, Rocklings, Loaches, Soles, &. These creatures remain 
buried or hidden by day but career about at night in search of 
food, returning to their own places at dawn. If while they are 
thus lying hid, food or even the juice of food-substances is put 
into the water, they come out after an interval and search vaguely, 
without regard to the direction whence the scent proceeds. Some 
of the animals (Rocklings, Sterlet) have special tactile organs in 
the shape of barbels or filamentous fins with which they investi- 
gate their neighbourhood, while others (Conger and Eels) feel 
about with their noses. None of the fishes which hunt by scent 
seem able to recognise food by the sense of sight, even though it 
be hanging freely before their eyes. 

The mode of feeding of the Sole is peculiar. When searching 
for food its skin is more or less covered with sand, which renders 
it inconspicuous when moving on the bottom. This sand adheres 
* to mucus which is probably exuded when the smell of food is 
perceived. The Sole seeks its food exclusively on the bottom, 
creeping about and feeling for it with the lower side of its face. 
If a worm is lowered by a thread until it actually touches the 


MODES OF FEEDING OF FISHES. 101 


upper side of the head of a Sole, the animal is still unable to find 
it but continues to feel for it on the sand. There is however no 
reason to suppose that the sight of these fishes is deficient. A 
Rockling at Plymouth had already learnt to come out to be fed if 
any one came near the tank, though it still did not recognise a 
worm swimming in the water. Particulars were given of the 
various irideal mechanisms which occur among fishes. 

This investigation was undertaken at the instance of the Marine 
Biological Association as a preliminary step towards improving the 
supply of bait. The experience gained suggests that a bait for 
the south coast, where Conger and Skate are chiefly caught, could 
be made by extracting the flavour of Squid or Pilchard and com- 
pounding it with a suitable ground-substance. Though few practical 
experiments were made, it was found that an ethereal extract of 


Nereis or Herring, for example, greatly attracted some of these 
fishes. 


ON THE ORIGIN OF THE EMBRYOS IN 
THE OVICELLS OF CYCLOSTOMATOUS 
POLYZOA. 


BY 


S. F. HARMER, M.A. 
King’s College. 


THE species investigated belonged to the genus Crisia, in which, 
as in other forms of Cyclostomata, the mature ovicells contain a large 
number of embryos. These embryos are imbedded in the meshes 
of a nucleated protoplasmic reticulum, which also contains a mass 
of indifferent cells, produced into finger-shaped processes, the free 
ends of which are from time to time constricted off as embryos. 
The embryos have, at this stage, a structure identical with that of 
the youngest embryos described by previous authors. After de- 
veloping various organs, they escape as free larve through the 
tubular aperture of the ovicell. The budding organ from which 
the embryos are formed makes its appearance at an early stage in 
the development of the ovicell. Evidence was brought forward to 
show that it must be regarded as an embryo, produced from an 
ovum. The supposed ovum is found in very young ovicells, im- 
bedded in a compact follicle, and appears to give rise, by a remark- 
able process of development, to the budding organ above described. 
The embryos are thus produced by the repeated fission of a primary 
embryo developed in the ordinary way from an egg. 


ON A NEW SPECIES OF PHYMOSOMA. 


BY 


ARTHUR E. SHIPLEY, M.A. 
Christ’s College. 


DuRING a visit to the Bahama Islands, Mr Weldon was fortu- 
nate enough to find three specimens of a large brown Phymosoma, 
whilst investigating the Fauna of the Bimini lagoon. He came to 
the conclusion that these specimens belonged to no: described 
species of Phymosoma, and was good enough to hand them over 
to me for description. I propose to call this species Phymosoma 
Weldoniw. - 

The length of the three specimens varied between 3°5 cm. 
and 3 cm.; their bodies are plump and slightly curved. The 
ground colour of the preserved specimens is light yellow, but this 
is modified over the surface of the body by dark brown papille. 
In all three specimens the introvert is retracted, and in this condi- 
tion is about lcm. long. The papillee are of two kinds, flat, brown, 
rectangular, low elevations on the skin of the trunk, and conical, 
elevated protuberances of a light colour on the introvert. 

No hooks or traces of hooks were found on the introvert. 

At the base of the introvert, just behind the head, is a well- 
developed collar, such as I have described in detail in Phymosoma 
varians. 

The mouth is surrounded by a vascular lip, which at the dorsal 
middle line is continuous with the base of the lophophor. The 
latter is in the shape of a double horseshoe, and is composed of 
from 70 to 80 tentacles. 

There is nothing to call for remark in the arrangement of the 
internal organs, with the exception of the fact that there are only 
two retractor muscles. Such an arrangement is only met with 
elsewhere in Ph. Riippellii from the Red Sea. The absence of 
hooks and of any traces of them is striking, but it occurs in five 
other species out of a total of 28 described. — 

Habitat; the Bahama Islands, Bimini lagoon. 


LAND-PLANARIANS AT CAMBRIDGE. 


BY 


S. F. HARMER, M.A. 


A Lanp-PLANARIAN (Rhynchodesmus terrestris O. F. Miiller) 
was first described as a native of England by Rev. L. Jenyns 
(Observations in Natural History, London 1846), who discovered 
it in abundance in the woods of Bottisham Hall, near Cam- 
bridge. In the present instance, a search (made by kind per- 
mission of R. B. Jenyns, Esq.) in the same locality resulted in 
the discovery of a few specimens; and it was ascertained subse- 
quently that R. terrestris is by no means uncommon in Cambridge 
(King’s College, Botanic Gardens). It may readily be found 
hy examining the damp lower surface of logs of wood which have 
been lying for some time on the ground. Since the first discovery 
of the animal in England, it seems to have been very seldom 
found: but from its wide distribution in Europe generally and 
in England, and from the fact that it is not very likely to be 
found unless it is specially looked for, it is probable that this 
animal is much commoner than is usually supposed. Several egg- 
capsules of R. terrestris were discovered on May 15, on examining 
fragments of rotten wood among which some upevimens of the 
animal had been kept for a week. 


NOTES ON A COLLECTION OF SPIDERS,. WITH 
A LIST OF SPECIES TAKEN IN THE 
NEIGHBOURHOOD OF CAMBRIDGE. 


BY 


C. WARBURTON, 
Christ’s College. 


ALL attempts to preserve spiders in the dry state have hitherto 
proved ineffectual. 

When put up in alcohol, the specimens must either be mounted 
in some way, and certain specific characteristics concealed, or 
allowed to lie loosely in tubes, and to present a distorted and 
unsightly appearance. 

For the purposes of exhibition, the former alternative seems 
preferable, especially if care be taken to minimise as far as possible 
its disadvantages. 

A simple but effective method of mounting specimens is here 
described, as likely to prove useful to collectors in this and 
other groups, where no satisfactory dry method of preservation is 
available. 

A specimen tube is filled about one-third full of plaster of 
Paris powder. Water is added, and the tube corked and shaken, 
and then laid lengthwise upon a horizontal surface. When the 
plaster is set, the block is slipped out, smoothed if necessary, and 
the specimen mounted upon its flat surface with strong gum or 
“liquid glue ”—a substance not dissolved by alcohol. 

When replaced, the block of course fits its mould, and cannot 
crush the specimen, as the width of its flat surface is nearly the 
diameter of the tube. It moreover affords a white back-ground 
which is not liable to much discolouration. It is often convenient 
to mount male and female of a species in the same tube. 

‘The tubes are then labelled and exposed on tiers of shelves, 
inclined at a small angle to the perpendicular. 

Thus arranged, the specimens bear some resemblance to the 
living species they typify, and present as sightly an appearance 
as the difficulties of the case will admit. 

11 


106 C. WARBURTON, 


List of Spiders taken in the neighbourhood of Cambridge. 


DYSDERIDA, 
DyspERA 
Cambridgii, Thor.,—occasional, on Castle Hill, Gogmagog hills, etc. 
HARPActEs . 
Hombergii, Scop., not rare, at the bottom of Clare wall, and in the court 
of Christ’s College. 
Oonors 
pulcher, Temp., rare, on Gogmagog hills, 


DRASSIDA., 
MIcaRIa 
pulicaria, Sund., frequent, on Castle Hill, Gogmagog hills, ete, 
ProsTHESIMA 
Petiverii, Scop., rare, Fleam Dyke. 
nigrita, Fabr., rare, Fleam Dyke, 
Drassus 
lapidicolens, Walck., common, 
pubescens, Thor., very rare. 
CLUBIONA 
pallidula, Clk., frequent, in ivy leaves. 
terrestris, Westr., occasional. 
lutescens, Westr., in the fens, 
holosericea, De Geer, occasional, in curled leaves, 
brevipes, Bl., rare. ; 
comta, C. L. Koch, occasional, in trees. 
subtilis, L, Koch, rare, Wicken Fen. 
AGROECA 
brunnea, BI., frequent, in grass. 
HEcAERGE 
maculata, Bl., occasional. 


DICTYNIDA., 
Dictyna 
arundinacea, Linn., frequent, on shrubs. 
uncinata, Westr., occasional. 
AMAUROBIUS 


fenestralis, Stroem, rare, in dry grass, vegetable débris, etc. 
similis, Bl., frequent, in out-houses. 
ferox, Walck., frequent. 


AGELENIDA. 
TEGENARIA 
Guyonii, Guérin, not rare, in buildings. 
Derhamii, Scop., common, in buildings. 
campestris, C, L. Koch, frequent, under ledges of walls. 
AGELENA . 
labyrinthica, Clk., common, on banks, 
Hawgnia 
elegans, Bl., occasional in Wicken Fen. 
TEXTRIX 
denticulata, Oliv., rare, enclosure of University Bathing Sheds. 


NOTES ON A COLLECTION OF SPIDERS. 107 


THERIDIIDA. 
THERIDION 
formosum, Clk., rare, Botanical Gardens. 
tepidariorum, C. L. Koch, in hot-houses. 
pictum, Hahn., frequent, on holly bushes. 
sisyphium, Clk., very common, on holly, ete. 
denticulatum, Walck., occasional, on shrubs, etc. 
varians, Hahn., common, in boathouses, etc. 
pulchellum, Walck., rare, on trees. 
bimaculatum, Linn., frequent, in grass. 
pallens, Bl., not rare, on trees, shrubs, etc. 
NeEstIcus : 
cellulanus, Clk., occasional in damp places, e.g. tanks in Christ’s College 
gardens. 
PHYLLONETHIS 
lineata, Clk., very common; everywhere. 
StratTopa 
bipunctata, Linn., not rare, in out-houses. 
NERIENE 
longipalpis, Sund., common, on railings, ete. 
dentipalpis, Wid., occasional. 
rufipes, Sund., taken at the University Bathing Sheds. 
rubens, Bl., frequent, in grass. 
isabellina, C. L. Koch, rare. 
fusca, Bl., occasional, 
livida, Bl., occasional. 
WaLcKENSERA 
Hardii, Bl., very rare; one example taken in the ‘‘ Backs.” 
antica, Wid., rare, Wicken Fen, 
PacHYGNaTHA 
Clerckii, Sund., frequent, in damp grass. 
Degeerii, Sund., frequent, in grass. 
Linyruta 
nebulosa, Sund., in Christ’s College garden. 
zebrina, Menge, occasional. 
leprosa, Ohl., frequent. 
tenebricola, Wid., common, in grass. 
socialis, Sund., frequent, on trees. 
dorsalis, Wid., occasional, in plantations. 
bicolor, Bl., frequent, in grass. 
bucculenta, Clk., common on Castle Hill, ete. 
montana, Clk., frequent, on Clare wall. 
triangularis, Clk., common, on bushes. 


EPEIRID. F 

MetTA 
segmentata, Clk., everywhere. 

TEYRAGNATHA 
extensa, Linn., frequent, on Clare wall, etc. 

CycLosa : ‘ 
conica, Pall., rare, in wood on the Gogmagog hills. 

ZILLA. 
x-notata, Clk., everywhere. 
atrica, C. L. Koch, frequent. 


Ererra 
cucurbitina, Clk., frequent, on trees, bushes, etc. 


108 C. WARBURTON, NOTES ON A COLLECTION OF SPIDERS. 


diademata, Bl., common. 

sealaris, Walck., rare, in woods. 

arbustorum, C. L. Koch, rare, in woods. 

cornuta, Clk., frequent, in nettles, etc. 

patagiata, Clk., rare, in woods. 

sclopetaria, Clk., not rare, on Clare College wall. 
umbratica, Clk., not rare, at University Bathing Sheds, etc. 


THOMISIDA. 

Xysticus 
cristatus, Clk., common, 
viaticus, C. L. Koch, occasional, on Castle Hill. 
pini, Hahn., rare. 
lanio, C. L. Koch, frequent in wood on the Gogmagogs. 
ulmi, Hahn., rare. 
erraticus, BL, rare. 

OxyYpTILa 
atomaria, Panz., Wicken Fen. 

PuILopRomus 
aureolus, Clk., common, in fir trees, etc. 


THANATUS 
hirsutus, Camb. (or striatus, C. L. Koch), frequent in Wicken Fen. 


TIBELLUS 
oblongus, Walck., common in grass, Castle Hill, etc. 


LYCOSIDA. 
OcYALE 
mirabilis, Clk., occasional, Fleam Dyke, etc. 
Prrata 
piraticus, Clk., conimon, near water. 
TRocHosa 
ruricola, De Geer, frequent. 
terricola, Thor., occasional. 
TARENTULA 
pulverentula, Clk., common. 
audrenivora, Walck., frequent. 


Lycosa 
amentata, Clk., very common. 
lugubris, Walck., very common but local. 
Farrenii, Cambr., rare, in Wicken Fen. 
pullata, Clk., frequent. 
riparia, C. L. Koch, occasional. 
nigriceps, Thor., common. 
monticola, C. L. Koch, occasional. 


SALTICIDA. 
EPipLeEMUM 
scenicum, Clk., frequent, on sunny walls. 
HELIOPHANUS 
cupreus, Walck., rare. 
Evorarys 
frontalis, Walck., frequent in grass, Castle Hill, etc. 


ATTUS 
pubescens, Fabr., rare, on walls. — 


tudies. ML, Vol.V.Pl.1 


Dufour. se 


ren del ALCYONIDIUM POLYOUM 


| 


Studies M LVolWj 


auonnien, el ALCYONIDIUM POLYOUM 


ventraw plate. 


leg <a 
( 


Studies M.L.Vol.V, Pl. IIL, 


2 


Fig, 3. Fig. 4. Spine 


S a 
\ a 


a) tee tl 
, ae ovid. 
\ CG 


F Huth, Lith® Edin? 


\ if 
Oa Seen( 
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Wid Ye: 


second. preeoral rng frrst precoral ring 
1 


brat —— f ! 


TLUSE uloer Gis Get 


outer lip eae 


—~ C230 ha us 

} ae 

= raventriendus | 
5 ae 

ledly = cantly S52 ‘4 


ganglion cam ei) 


\ 


\ ty | 


testis ~~ 
ganglion ANE t 


san 


f 4 
4 ( 
ies. 
ik 
a 
ene, 


2 anal Fang, 


iy 

: 4 . . 
Fug, le vesieula seminales ae | bei Ay \ intestine [ 

aS Say, re 4 % ee an , | i 3 conneclw 
“9 € 5 1 Hy, L ©) urequtas 

( / i] 

) ee ay --- mouth oe \ > \; ; y ode 

/ ( ; = bole trade organ. ganglion ) pi - sy) : i/ | 


\ 


WA 
lendlar ™mass | y | : Wk. ss, cans 
Sturrournciing the pens ; af penis. 
Geer jee ma | 
~ Caul lq. ot 
¢ | 


AY _Nesvcula semunalus 
O- 
testis 


oe 


s 


ai 
S 


- 

a 

s 

gt 

=| 
i 
: 
~~ 


ane! rong ye —— 


ala of tawl ee = 


<a 


Studies M.L.Vol.V, Pl. IV. 


_ &S0 hageal nerve 


a et rs c P 

ee crcl of cesphagus (oy ailicdedl ee in 
v © second ciliated rug 
uy 


— muscular organ. : 
ie ~< eye 


Fy 


Sa livery ee 


Wa 


SS mouth 


Fig. q. ee 


ive lissue, unth ) 
lar lacunae ji 


Fug 10. 


ilonaael 


\ 
oe muscles 


} oe \ 
Ibes is nerve 


Fig. Wl. 


ae 


Ne lealis 


; body - Cl uly 


\ : 
U nte TOvarLan cavily 


‘ spermato es ; 
fig. 13. ke 14. 


Studies M.L. Vol.V, Pl.V. 


,| 
\\ wlll 
Hoiiny 


mt 
cl) mec i 


praeorad TULGS..- 


aperture of esophagus ee 


is 
2 
3 
4 
ao. ephriaucin § 
5 [vesicuda seminacis) 


_.. glandular mass SUPT OUTUMLY 
He penis. 


S.F. Harmer del. F. Huth, Lith® Edin® 


Studies M.L.Vol.V, Pl. V1. 


F.Huth, Lith* Edin* 


Lower lip ~ 


Orifice of Introvert 


Dorsal 
vessel ~ 


Dorsal 
muscle - 


Ventral _ 
muscle 


Skeleton - 


: enhonos* 


Generative _- 
ridge ~ 


Ventral __ 
Nerve Cord — 


Were Ounces 


\4 Stupies.M.L Vot.V. PLAIN. 


“then Nay 


aeoral nerves 
“Brain 


- Lophophor 


Sa speotitial 


OS) 
=-SéENS? OPJaAn 
hy g 


Nerve 


Oesophagus Dorse! blood 
vessel] 


Introvert 


~~ Yen, Nerve Cord 


ores | 
hg ro) 


Oesophagus Dorsed bl.ves. 


--Tentacles 


Nerve Cord 


Oesaphagus 


Fig 4 


Bi 
sy Tentacle 


Pigmenied skin of 
: praeoral lobe 
7) 


BI. sinus at‘ 
Base of Lophophat 


Stupies. M.L.VotV. PL.VII. 


_ Colom 


_--- SVEN marida 


; : 
ine of Lophophor 


© - B/ ves. 


He 
Space of 
praeoral lobe 


Val 5 Ibe 
_- Cuticle Fic 8 


Chifinows ring 
WMLTHOWS FING 


Epidermis (j 


Cuticle 


Papilla 


~- Cuticle 


Epiderimis 


fips 


Lith.&Imp. Camb, Sci. Inst.Co, 


Opening of papilla 


Cells with 
granules 


ie 
iets 
aps eS Se 
ae 
Bo ame 


-dkeletal ells 


Tnt. opening 


Vent Retractors 


Stupies.M.L.VotV. PLA. 


>Glandular cells 


“)----Peritoneal cells 


--Muscles 


Muscles 


Glandular 
cells 


Lith &Imp. Camb. Sci. Inst.Co. 


IMMA S 


to praecorallobe 


i) 
i 
f 
Blood. sinus 


hig 28), 


64 
1 


, 


Oesoph 


nerve 


‘ BN Fig 2 A 


he 


te ee 
Mesentery es ive 
XN . 


Ope 


STUpIEs. MOL VOL.V PX. 


See 
ae Oe oe 
<a mie Sy aeee 


Blood sinus 


Lith.£Imp. Camb, Sci. Inst.Co. 


ON THE BRITISH SPECIES OF ORISIA. 109 


On the British Species of Crisia. 
By 
Sidmey F. Harmer, M.A., B.Sc., 
Fellow and Lecturer of King’s College, Cambridge. 


With Plate XI. 


Tuis paper will be followed by a further memoir, which will 
treat of the development of the ovicells and of the embryos in 
Crisia. I have already published a preliminary note! on this 
subject, and I hope to be able to complete the preparation of 
the more detailed paper without much delay. 

It has often been pointed out that the subdivision of the 
Cyclostomatous Polyzoa into genera and species is attended 
with peculiar difficulties. The character of the zocecia remains 
remarkably constant throughout this group, the systematic 
study of which is not facilitated by the presence of subsidiary 
structures, such as the opercula, avicularia, and vibracula, 
which in the Cheilostomata form so valuable a means of 
distinguishing the species. 

The task of finding satisfactory specific characters within the 
limits of the genus Crisia is not less difficult than in other 
genera of Cyclostomata, as is seen clearly enough by 
examining the numerous works which have already been 
devoted to this genus. Smitt, for instance, in his critical 
analysis of the Scandinavian forms, has asserted that the 
delicate C. geniculata is connected by a continuous series of 
intermediate forms with the coarse form which he calls C. denti- 
culata, and which he regards as the extreme point which has 

1 ¢ Proc. Cambridge Philosoph. Soc.,’ vol. vii, part 2, 1890, p. 48. 

VOL, V, PART I, 12 


110 SIDNEY F. HARMER. 


been reached in the evolution of the genus. In his later works 
he consistently refers to the latter “species” as Crisia 
eburnea, forma denticulata, and is of opinion that the 
“ species ’’ recognised by other authors are, for the most part, 
merely partially fixed points in acontinuous series. Most other ~ 
writers, on the contrary, regard these forms as so many distinct 
species. 

In many of the characters used for distinguishing the several 
species of Crisia from one another—such as the mode of 
branching, the number of zocecia in an internode and their 
individual shape, the position of the ovicells, &c.—each species 
may vary within wide limits about a certain average. The 
most satisfactory specific characters appear to me to be fur- 
nished by the ovicells; and in this respect I am only confirming 
the results previously arrived at by Waters! for other Cyclo- 
stomata. Indeed, I believe that in many cases the species 
cannot be certainly identified unless ovicells are present. 
Unfortunately, in the great majority of works referring to 
Crisia, the information given with regard to these structures 
is of the most unsatisfactory character. Many writers, for 
instance, have mentioned the existence of ‘“ pear-shaped” 
ovicells in certain species; but this character is of generic 
much more than of specific importance, and the same remark 
might be made with regard to many of the other characters 
which have been ascribed to the different species. 

The importance of the form of the aperture of the ovicell, 
as a specific character, has almost entirely escaped the notice 
of previous writers.? Busk® has merely stated that the existence 
of a tubular aperture on the ovicell is a generic character of 
Crisia. 


1 “Qvicells of Cyclostomatous Bryozoa,” ‘Linn. Soc. Journ. Zool.,’ 
vol. xx, p. 275, and in other places. 

? Waters has, however, called attention to the importance of this character 
in several works. See ‘Quart. Journ. Geol. Soc.,’ vol. xl (Nov., 1884), 
p. 676. 

3“ Report on the Polyzoa,”? Second Part, ‘‘Challenger” Rep., Zool.,’ 
vol. xvii, part 50, p. 2. 


ON THE BRITISH SPECIES OF CRISIA. 111 


A comparison of the ovicells (and especially of their aper- 
tures) of various forms of Crisia has led me to the conclusion 
that the British fauna includes more species of that genus than 
are usually recognised. Although the constant occurrence of 
a particular form of ovicell might possibly be explained by the 
assumption of a definite correlation between the variations of 
the zocecia and of the ovicells (the ovicell being regarded as a 
modified zocecium), I do not think that this would give a suffi- 
cient explanation of the facts. I find, indeed, that the essential 
characters of the ovicells are extremely constant, in spite of 
the occurrence of variations of no inconsiderable mpagmiiudet in 
other parts of the colony. 

The following specific diagnoses, which are necessitated by 
the results which I have arrived at, have been drawn up 
on the model of those given by Hincks in his well-known 
‘ History of the British Marine Polyzoa.’ New lists of synonyms 
appear to me to be also necessary, in spite of the recent appear- 
ance of Miss Jelly’s admirable catalogue, to which I must 
express my great indebtedness. My lists do not profess to be 
more than a selection of those works in which particular 
species have been described or figured in sufficient detail to 
make their identification fairly probable. In many cases I have 
been obliged to give up the attempt to identify the species to 
which the description refers. 


C. denticulata, Lamarck. Plate XI, figs. 1—3. 


Zoarium large, erect, of rather straggling habit; the 
average height of well-grown colonies about one inch; the 
branches well separated from one another, and with very 
little tendency to curve inwards. Internodes broad and 
flattened, but usually with a slight convexity running longi- 
tudinally along their anterior face, frequently with a double 
curve of such a character that if the lower part of the 
internode is convex towards the right side (e.g.) the upper 


1 B.C. Jelly, ‘A Synonymic Catalogue of the Recent Marine Bryozoa,’ 
London, 1889. 


112 SIDNEY F. HARMER. 


part is convex towards the left side; in most cases with an 
odd number of zoccia, the dominant number of which 
appears to be 11. Branches arising fairly high in the inter- 
node, usually from the 8rd, 4th, or 5th zocecium of either side ; 
nearly always given off in perfectly regular alternation on 
opposite sides of the axis. Hach internode with an odd number 
of zocecia is normally provided with a single branch, while the 
even-numbered internodes are, with rare exceptions, branch- 
less. Joints of the zoarium and of the rootlets nearly always 
jet-black, except in the youngest parts of the colony. Basis 
rami situated very low down on the zoecium, and appearing as 
if wedged in between the zocecium which bears it and the next 
zocecium below it on the same side. Zocecia entirely adnate 
with the exception of a short portion, of variable length, which 
bears the aperture, and which is bent forwards; a pointed pro- 
jection sometimes occurring at the outer and upper angle of 
the aperture. Ovicell large, always high in the internode, 
usually near the end of a branch, and, like the zoocia, more 
thickly covered with pores than in the other British species ; 
its aperture inconspicuous, not borne on a prominent tube. 
Rootlets usually with black joints, which occur at more fre- 
quent intervals than in C. ramosa. (See also measurements 
on p. 159.) 


C. luxata— 
(1) Fremine.— Hist, of Brit. Animals,’ Edinburgh, 1828, p. 540. 
(2) Covcu.—‘ Cornish Fauna,’ part iii, Truro, 1844, p. 99, pl. xviii, fig. 3. 
C. denticulata— 
(8) H. Mitwz-Epwarps.— Mém. sur les Crisies,” ‘Aun. Sci. Nat.,’ 
2e sér., ‘ Zool.,’ tome ix, 1838, pl. vii, fig. 1. 
(4) Jonnston.—‘ Brit. Zoophytes,’ 2nd ed., London, 1847, p. 284, pl. 1, 


figs. 5, 6. 
(5) Carus.—‘ Prodromus Faune Mediterranew,’ vol. ii, Stuttgart, 1889, 
p. 39. 


C. denticulata (pars).— 
(6) Busx.—‘Cat. Marine Polyzoa Brit. Museum,’ part 3, 1875, pl. iv, 
figs. 1—4. 
(7) Hivcxs.—‘ Hist. Brit. Marine Polyzoa,’ London, 1880, p. 422, 
pl. lvi, figs. 7, 7a. 


ON THE BRITISH SPEOIES OF ORISIA. 1138 


C. eburnea, Linn. Plate XI, fig. 6. 


Zoarium forming dense tufts, usually attached by a single 
stem, the base of which does not, in most cases, develop many 
rootlets ; the average height of well-grown colonies from } to 
inch ; the branches characteristically curved inwards. Inter- 
nodes usually short, somewhat flattened; in most cases with 
an odd number of zowcia, the dominant numbers being 5 and 
7. Branches generally arising from the lowest zocecium in 
an internode, sometimes higher up; one branch is normally 
developed from each odd-numbered internode, even-numbered 
internodes being ordinarily branchless. On the main stem 
or the principal branches, the branches come off in regular 
alternation on opposite sides: nearer the growing-points, they 
are arranged in compound helicoid cymes, of the formula!— 


(2+ 7,) + 
=(4+7,) + 
=(a@+n) + 
&e. 


Joints yellow, or colourless near the growing-points, some- 
times becoming dark brown in the older parts of the colony. 
Basis rami short, not wedged in between two zomwcia. Zoccia 
almost entirely adnate, the upper portion, which bears the 
aperture, free, bent forwards nearly at right angles to the lower 
part; frequently a conspicuous pointed process on the outer 
side of the aperture. Ovicell large, curved inwards, usually 
replacing the second, or, less often, the third zocecium of an 
internode; its aperture conspicuous, elongated from side to 
side, borne on a very distinct tube, which is wider at its base 
than atitssummit. Rootlets usually developed in very small 
numbers. (See also measurements on p. 159.) 


C. eburnea.— 
(4) Jonwston.—P. 283, pl. 1, figs. 3, 4. 


(5) Carus.—P. 38. 


1 This method of representing the branching is explained on p. 146. In 
the above formula z would usually be 5, less often 7 or higher numbers. 


114 SIDNEY F. HARMER. 


(8) Suirt.—“ Om Hafs-Bryozoernas utveckling och fettkroppar,” 
‘Ofvers. af K. Vet.-Akad. Forhandl.,’ 1865, No.1, p. 9, pl. i, 
figs. 15—18, 


C. eburnea (pars).— 
(9) Surrr.— Krit. forteckn. dfver Skandinaviens Hafs-Bryozoer,” I, 
*Ofvers. af K. Vet.-Akad. Férhandl.,? 1865, No. 2, pl. xvi, figs. 
10, 11, 183—19. 
(6) Busx.—PI. ii, figs. 1, 2; pl. v, figs. 1, 2. 
(7) Hincxs.—P. 420, fig. 21 (p. 416). 
C. eburnea, forma eburnea.— 
(10) Suirr.—‘ Bryozoa marina in regionibus arcticis,” ‘ Ofvers. af K. 
Vet.-Akad. Férhandl.,’ 1867, No. 6, pp. 444, 461. 
(11) Suirr.— Recensio Syst. Bryozoorum Novaja Semlja,” ibid., 1878, 
No. 3, p. 12. 
(12) Surtz.—‘‘ Recensio Bry. e mari arctico,” ibid., 1878, No. 7, p. 23. 
(18) FreEse.—‘ Beschr. Ostsee Bryozoen,” ‘Arch. f. Naturg.,’ 54, 
Jabrg., Bd. i, 1888, p. 31, pl. ii, fig. 18. 


C. aculeata, Hassall. Pl. XI, fig. 4. 


Zoarium of very delicate habit, resembling that of the next 
species, from which it may be distinguished by its much 
slenderer appearance; the average height of well-grown 
colonies from 4 to } inch, the branches with very little ten- 
dency to curve inwards. Internodes usually short, often 
consisting of five or seven zocecia; but much longer internodes, 
with more numerous zocecia, may occur, especially at the ends 
of the branches. Branches usually arising from the lst or 
2nd zocecium of either side of an internode, but sometimes 
(especially in the case of internodes near the ends of the 
branches) higher up: an internode (especially a peripheral one) 
may bear two or more branches. In nearly all colonies, in 
addition to the ordinary branches, some of the internodes bear 
long, jointed spines, which are curved inwards over the anterior 
side of the branch ; these spines are most often developed from 
the lower zocecia of an internode, or at the apices of the 
terminal internodes. Joints yellow, or colourless near the 
growing-points. Basis rami usually short, not wedged in 
between two zoccia. Zocecia with a conspicuous, free, tubular 
portion, bearing the aperture; this portion is curved forwards, 


ON THE BRITISH SPECIES OF CRISIA. 115 


but not as in the last species; it is usually lost in the zocecia of 
-the lower parts of the colony. Aperture circular, with no pro- 
jection on its outer side. Ovicell small, fairly high in the 
internode, prominent near its upper end, and falling away very 
suddenly to the aperture, which lies on the surface of the 
zocecium next above the ovicell on the same side of the 
internode; this zocecium curves round the back of the ovicell, 
and always acquires acharacteristic relation to the aperture of the 
latter ; this aperture is inconspicuous, and is never borne on 
a distinct tube. Rootlets resembling those of C. ramosa. 
(See also measurements on p. 159.) 


C. aculeata— 

(14) Hassarn.— Cat. of Irish Zoophytes,” ‘Ann.and Mag. Nat. Hist.,’ 
vol. vi, 1841, p. 170, pl. vii, figs. 3, 4. 

(15) Supp. to ‘ Cat.,’ ibid., vol. vii, 1841, p. 366. 

(4) Jonnston.—P. 285. 

(16) Surrr.— Bidr. till kaon, om Hafs-Bryozoernas utveckling,” 
‘Upsala Univ. Arsskrift,’ 1868, p. 3. 

Smitt agrees with van Beneden (20) in stating that the ovicells are 
completely closed. 


(17) Jourer.—* Cont, & Phist. Bryozoaires, Cotes de France,” ‘ Arch. 
Zool. Exp. et Gén.,’ vol. vi, 1877, p. 286. 


C. eburnea, var. aculeata.— 
(6) Busx.—P. 4. 
(7) Hincxs.—P. 421, pl. lvi, figs. 5, 6. 
(18) Juntien.— Liste des Bry. rec. & Etretat,” ‘Bull. Soc. Zool. 
France,’ t. vi, 1881, p. 14. 
(19) Vive.—‘ Rep. on Recent Marine Polyzoa,” ‘Brit. Association Re- 
port,’ Aberdeen Meeting, 1885, p. 588. 


C. eburnea— 
(3) Mitnz-Epwarps.—Pl. vi, fig. 2. 
?(20) P. J. van BuneDEN.—“ Rech. sur Anat... .. Bryozoaires 
_... Ostende,” ‘Nouv. Mém. de l’Acad. de Bruxelles,’ t. xviii, 
1845, pl. ili, figs. 12—16. 
Van Beneden states that the ovicells are closed on all sides; and 
this statement is more likely to have been made of C. aculeata (in 
which the aperture of the ovicell is very inconspicuous) than of C. 
eburnea. The specimens figured are by no means unlike C. aculeata, 
but they have no spines. 


116 SIDNEY F. HARMER. 


? C. eburnea (pars).— 
(9) Surrt.—Pl. xvi, figs. 12a, 124. 

On p. 135 of Smitt’s paper it is explained that these figures repre- 
sent young ovicells (of C. eburnea), without tubular apertures. 
It may, however, be remarked that an ovicell, with the contents shown 
in fig. 124, would probably have had a well-developed tubular aper- 
ture if it had really belonged to C. eburnea; and, further, that there 
is evidence (see above, No. 16) that Smitt has worked at the ovicells 
of C. aculeata. Ibid., table of formule, Nos. 2,3 (see explanation 
of the formula), and probably some of the later formule. 


P C. denticulata (pars).— 
(6) Busx.—PI. iii, figs. 1—6. 
Notice the spine in fig. 6. In the other figures, the character of 
the branching and of the basal internodes, and the small number of the 
pores appear to me to prove that this plate does not refer to C. 
denticulata, and that it probably refers to C. aculeata. 


C. ramosa,n. sp. Pl. XI, figs. 10, 11. 


Zoarium erect, often of rather straggling habit; the 
average height of well-grown colonies about 2 inch; the 
branches (in well-grown specimens) arranged in fan-shaped 
systems, owing to the large number of branches given off by 
the terminal internodes, and with little or no tendency to curve 
inwards. Internodes often much flattened, of very variable 
length ; often very long, and consisting of numerous zocecia ; in 
this case often with a well-marked double curve, as in 
C. denticulata (and, to a less extent, in other species 
Branches developed in greater numbers than in any of the 
other British species ; even in the lower parts of the colony the 
internodes commonly bear two branches, while the terminal 
internodes, and especially those which bear ovicells, may give 
rise to as many as four or five branches, which do not neces- 
sarily come off alternately on opposite sides of the stem. The 
lowest branch of an internode very commonly comes off from 
the second zocecium of one side; if the lowest branch arises 
from the first zocecium of the internode, the next branch is 
usually given off by the third zoccium of the opposite side. 
Joints yellow, or colourless near the growing-points, never 
black. Basis rami long, usually reaching the aperture of the 


ON THE BRITISH SPECIES OF ORISIA. 117 


zocecium next below it on the same side, unless it is borne by 
the lowest zocecium of an internode. Zoccia usually with a 
long, free, tubular portion bearing the aperture ; this portion is 
distinctly curved forwards, but is usually lost in the older parts 
of the colony; in other cases this tubular portion is not 
developed to more than avery slight extent. Aperture circular, 
without any pointed projection on its outer side. Ovicell 
very large, and more regularly pear-shaped than in any of the 
other species; usually a little higher in the internode than in 
C. aculeata, but in some cases it may occupy as low a position 
as that of the fourth member of the internode; it is perhaps 
most commonly in the position of the 6th—8th member ; its 
aperture circular, borne on a long and very conspicuous 
funnel-shaped tube, which is considerably wider at its summit 
than at its base. Rootlets often developed in considerable 
numbers, sometimes attaining a great length (nearly an inch), 
and composed, for the most part, of long segments, separated by 
yellow or colourless joints. (See also measurements on p. 159.) 

(The following list includes references to several forms of 
Crisia which, as explained below, I do not believe to be 
identical with C. ramosa.) 


? C. cribraria.— 
(21) Srimpson.— Synopsis of the Marine Invertebrata of Grand Manan 
[Bay of Fundy],” ‘Smithsonian Conts. to Knowledge,’ vol. vi, 
1854. 

This species may be identical with C. ramosa, in which case my 
own specific name will have to be given up. The zoccia are described 
as being “so crowded as to form often two or three longitudinal rows, 
in which they are usually opposite” (p. 18). I do not see how such 
a statement could be made of C. ramosa. The figures given (pl. i, 
figs. 8a—c), although not unlike that species, are not drawn with 
sufficient care to enable a satisfactory conclusion to be arrived at. 

? C. arctica — 
(22) M. Sans.—“ Geol. og Zool. Jagtt. anst. p. en Reise Trondhjems 
Stift.,” Christiania, 1863. 

The zoarium of this form is said to reach the height of 30 mm. ; 
the branches and the zoccia are straight, or nearly straight; the inter- 
node possesses, on each side, two to three, often eight to twelve, rarely 
twenty to twenty-one zocecia. The species is said to resemble C. 


118 


SIDNEY F. HARMER. 


denticulata and C. cribraria. It differs, according to Sars’ 
description, from my own specimens in the following respects. 

The zocecia are fused with one another along their whole length, so 
that the upper part, with the aperture, is not free. The outer and 
upper angle of the young zoccia may bear a small knob (never observed 
in C. ramosa). The joints are usually uncoloured, but sometimes 
brown-grey in the older branches (usually yellowin C. ramosa). The 
ovicells are always in the axils of the branches, and they are not 
described as having an aperture (which can hardly be overlooked in 
C. ramosa). ; 

On the whole, Sars’ description suggests a form like C. denticu- 
lata or C. elongata, M.-Edw. It is, perhaps, the form figured by 
Smitt (9) in pl. xvi, fig. 20. The “ basis rami’ in this figure is unlike 
anything I have ever seen in C. denticulata, although resembling 
that of C. ramosa. 


C. eburnea (pars).— 


PC. 


2 C. 


2 C. 


(2) Coucu.—P. 99. 

Some of the larger specimens mentioned by Couch probably belonged 
to this species: the ovicells are “somewhat urn-shaped with narrow 
tubular necks, which are not placed in the centre.” This description 
probably refers to C. ramosa, although the “young specimens” in 
which the branches “all arch inwards” doubtless belonged to C. 
eburnea. The magnified figure (pl. xviii, fig. 2), which is not good, 
may be identified as C. aculeata by the presence of a spine; and 
the figure next to it (natural size) is probably either that species or 
C. ramosa. 

eburnea (pars).— 
(9) Suirr.—Pl. xvi, fig. 9, and p. 185 (fig. 6). (These figs. may refer 
to C. aculeata.) 


eburnea, var.— 

(6) Busx.—PI. v, figs. 5—10. 

denticulata (pars).— 

(6) Busx.—PI. ii, figs. 8, 4. 

(9) Smrrt.—‘ Table of Formule,’ Nos. 14—17, and probably some of 
the earlier numbers (e.g. 12 and 13), which are said to belong 
either to C. eburnea or to be transitional from this form to 
C. denticulata. It is hardly possible that a form with so many 
branches arising from the same internode as in No. 17, for in- 
stance, was really C. denticulata. 

(28) Surrr.— Floridan Bryozoa,” Part 1, ‘Kongl. Svenska Vet.-Akad. 
Handl.,’ B. x, No. 11, 1872, pl. i, figs. 1—5. 

I do not feel certain that the form described in (28) is really iden- 
tical with C. ramosa, although it can hardly be regarded as C. 


ON THE BRITISH SPECIES OF CRISIA. 119 


denticulata. The form of the zoccia is very similar to that found 
in C. ramosa; but, on the contrary, the ovicells do not agree with 
those of the latter. If the left side of fig. 5 represents a young 
ovicell (probably somewhat broken), the ovicells are even less like 
those of C. ramosa in their early than in their fully developed con- 
dition. Is this form possibly identical with the one described by 
Stimpson (21) under the name of C. cribraria? 
(7) Hinoxs.—P. 423. 

The statement that the ovicells of C. denticulata have “a 
tubular orifice at the top’’ was possibly made after an examination of 
C. ramosa; especially as, on the same page of Hincks’s work, occurs 
C. deuticulata, var. a (to which pl. Ivi, fig. 9, presumably 
belongs) ; and there can be little doubt that this is really C. ramosa. 


C. denticulata, var. tenuis.— 
(24) VicELt1us.—“ Cat. of the Polyzoa... Willem Barents,” ‘Nied. Arch. 
f. Zool. Supplementb.,’ i, 1881-2. 

This form is said to correspond closely with Hincks’s unnamed variety 
just referred to. It is, however, impossible to accept tenuis as a 
specific name, since the name C. tenuis had been applied by Mac- 
Gillivray to an Australian species before the appearance of the paper 
by Vigelius (see F. McCoy, “Prodromus of the Zool. of Victoria,” 

‘Decade’ iv, pl. xxxix, Melbourne, 1879. 


? C. fistulosa— 
(6) Busk (non Heller).—P. 5, pl. vi a, figs. 1, 2. 

Even if this form is identical with the species under consideration 
it is better to drop Busk’s name, since the specific name fistulosa 
was originally applied by Heller to a form which is clearly not the one 
described by Busk (see Waters, No. 25). 

Through the kindness of Mr. R. Kirkpatrick I have been enabled to 
refer, at the British Museum, to a specimen of the form described by 
Busk ; and I have also to thank Mr. Kirkpatrick for having subsequently 
given me further information on the same subject. The specimen in 
question is labelled “C. f istulosa, Hell., locality unknown. Lesina?” 
I am informed by Mr. Kirkpatrick that the label is in Mr. Busk’s hand- 
writing, with the possible exception of the last word; and that the 
specimen is probably really from the Mediterranean. 


The specimen in the British Museum is even more like my own 
species than is obvious from Busk’s description, which, in Mr. Kirk- 
patrick’s opinion, was probably taken from that specimen. As many as 
five branches may come off from the same internode, and some of them 
higher than the sixth zocecium, which, according to Busk, is their upper 
limit. The ovicells, of which only two could be satisfactorily 
examined, agree fairly well with those of the Plymouth form. Their 


120 SIDNEY F. HARMER. 


diameter is about ‘45 mm. Mr. Kirkpatrick further informs me that 
the distance from aperture to aperture is ‘4 mm., and that the total 
length of the zocecium is about °7 mm. Although these numbers are 
distinctly smaller than the average measurements of corresponding 
structures in C. ramosa, I am inclined to believe that my own 
specimens belong to the same species as the one in the British Museum. 
Waters (25), in ‘Ann. and Mag. Nat. Hist.,’ 5 ser., vol. iii, 1879, 
p. 269, pl. xxiii, fig. 4 (“‘Bryozoa of the Bay of Naples”), identifies 
C. fistulosa, Busk, with what he calls C. elongata, var. angustata. 
I cannot, however, believe that C. ramosa is identical with the form 
described by Waters. Although the number of zocecia in the internode 
in C. ramosa may be large, this species could hardly be characterised 
as having fourteen to twenty-six zoccia in the internode; nor does 
the description, “‘ brauches arising usually from the fifth to eighth 
“ gocecium of a branch, and at about the same distance a fresh branch 
grows on the other side,” correspond with the branching of C. ramosa. 
As Mr. Kirkpatrick has pointed out to me, Waters’ statement that 
the zoccia are ‘04 mm, apart was no doubt due to an oversight. 
For further remarks on C. fistulosa, Busk, see Vine (19), p. 589. 


The characters of the ovicell are so constant in my specimens 
that, taken in conjunction with other facts, I cannot resist the 
conclusion that this form deserves recognition as a species. 
Although it is obviously alluded to in some of the works just 
quoted, I cannot identify it with certainty with any form which 
has hitherto received a specific name ; and I therefore suggest 
for it the name C. ramosa, in allusion to the large number 
of the branches given off by a single internode. 

C. ramosa has been found in large numbers at Plymouth, 
where it is certainly the commonest of all the forms of Crisia. 

While the identification of fully developed colonies of Crisia 
—in those cases at least where ovicells are present—cannot often 
be a matter of doubt, it may be extremely difficult to identify 
the species to which a small fragment of a colony or a young 
zoarium belongs. The greatest difficulty is found, in these 
cases, in distinguishing C. eburnea from C. aculeata, or 
the latter species from C. ramosa. The characters of the 
several species can be best brought out by a careful comparison, 
under a series of distinct heads, of their more obvious external 


features. 


ON THE BRITISH SPECIES OF GRISIA. 121 


Habit of Zoarium at Different Seasons; Regeneration. 


A very slight acquaintance with the British forms of Crisia 
enables one to distinguish at a glance, in most cases, the 
species to which a given specimen belongs. C. denticulata 
is characterised by the coarseness of its general habit; by the 
regular dichotomous appearance of the branching, as seen by 
the naked eye; and by the fact that the branches diverge from 
one another to such an extent that they are separated from one 
another by considerable interspaces at their ends. In C. 
eburnea the branches are inflected towards the axis of the 
colony, and are so closely massed together that it is impossible 
to study the exact character of the branching without first dis- 
entangling the branches. On flattening the specimen out ona 
slide the cymose character of the branching is at once appa- 
rent. C. aculeata possesses a characteristic delicacy of habit 
(“of a slenderer habit than C. eburnea, which the species 
closely resembles ’’') ; and it may be compared, in external 
form, to a C. eburnea which has become of much laxer and 
slenderer habit than usual, and in which comparatively few 
branches have been developed. The branches are much 
straighter than in C. eburnea. C. ramosa is extremely 
similar, in general appearance, to C. aculeata, but is of dis- 
tinctly coarser habit ; the branches are very straight, and the 
number of the branches to which the internodes near the grow- 
ing-points give rise results, in actively growing colonies, in the 
formation of fan-like systems of branches. The long tubular 
apertures of the zoccia (if developed) give a characteristic 
appearance to the species, which cannot, however, in all cases 
be distinguished by the naked eye from C. aculeata. 

The above remarks apply especially to colonies in their fully 
developed condition; but the appearance of any species de- 
pends largely on the time of year at which it was found. 
Many of the specimens of C. eburnea found in the early 
spring are provided with numerous ovicells, the ultimate fate 
of which seems to have hitherto attracted no attention, although 

1 Johnston, G., ‘ A Hist. of the British Zoophytes,’ ed. 2, p, 286. 


122 SIDNEY F. HARMER. 


there can be no doubt that these structures disappear after the 
end of the breeding season. I have looked in vain for any signs 
of the absorption of the ovicells in Crisia; and the following 
facts probably imply that they are simply thrown off from the 
colony after the liberation of the embryos which have been pro- 
duced in them. 

The typical spring form of C. eburnea possesses a con- 
spicuous main stem, which forms an obvious central axis, from 
which the rest of the colony comes off as a series of branches, 
developed in regular alternation on opposite sides, and decreas- 
ing in size fairly regularly from the base to the summit of the 
colony. The main stem consists of perhaps eleven or twelve 
internodes, each of which normally gives rise to a branch; 
and the branches themselves are usually provided with a 
profusion of ovicells, many of which are still in process of 
development, and most of which are near the ends of the 
branches. 

In a colony of the same species found in May most of the 
ovicells were at some distance from the ends of the branches, 
owing to the development of several (7—8) zocecia above the 
ovicells; and the branches which bore ovicells had, in most 
cases, completely finished their growth: very few ovicells, and 
these of a weakly appearance, were being developed. Most of 
the branches ended in slender internodes, in which growth was 
no longer taking place, as was shown by the fact that no grow- 
ing-points were left. The exhaustion of the colony was further 
shown by the fact that some of the terminal internodes con- 
sisted of no more than two or three zoccia, with no growing- 
points. 

In the summer (August) large and highly branched colonies 
with active growing-points are found, but they are nor- 
mally without any trace of ovicells. In many of these cases 
it may be noticed that the main stem has been broken, and is © 
merely represented by its basal portion. The rest of the colony 
will, in this case, probably consist of a small number of large 
branches given off from the remains of the stem or of its 
lateral branches, and in many cases the sharp contrast between 


ON THE BRITISH SPECIES OF ORISIA. 128 


the clean white appearance of these highly branched parts of 
the colony and the dirty-brown appearance of the stump of the 
main stem, covered as itis by foreign growths of various kinds, 
will give rise to the suspicion that the former have been de- 
veloped at a later period than the latter, and that the latter 
are the remains of colonies which developed ovicells at an 
earlier period of the year. 

Smitt! has called attention to the fact that the free tubular 
portion of the zocecium of C. geniculata is sometimes rela- 
tively transparent, and that it is separated by a sharp line from 
the basal, more highly calcified part, and he suggests that this 
transparent portion has in these cases been regenerated. He 
further points out? that in Aetea argillacea (=Aetea 
truncata, forma abyssicola elongata’) this process of re- 
generation seems to be periodic, since a zocecium consisting of 
portions of three different ages was in one case observed by him ; 
and that in Farrella fusca (=Vesicularia fusca‘) the 
zocecium may attain twice its normal length by the occurrence 
of this regenerative process.’ Milne-Edwards® had previously 
pointed out that the zocecia were able to form rootlets at an 
advanced period of their existence. 

There can be little doubt that Smitt’s suggestion is a correct 
one. InC. eburnea the older parts of the colony are fre- 
quently covered with an encrusting red seaweed, the presence 
of which has no doubt been responsible for the “rose-red” 
colour which has been mentioned by Johnston’ and others as a 
feature which sometimes characterises the species. In certain 
specimens found in April the basal parts of the colonies were 
completely covered by this encrusting growth, while in various 


1 « Ofvers. af K. Vet.-Akad. Férhandl.,’ 1865, No. 2, p. 128. 

2 Om Hafs-Bryozoernas utveckling och fettkroppar,” ‘ Ofvers.,’ &c., 1865, 
No. 1, pp. 29, 30. 

3 « Ofvers.,’ &c., 1867, No. 5, p. 280. 

4 ¢Ofvers.,’ &c., 1866, pp. 502, 505. 

5 Ibid., pl. xiii, fig. 39, and explanation of figure. 

6 «Ann. Sci. Nat.,? 2¢ sér., “Zool.,” tom. ix, 1838, p. 196. 

7 ‘British Zoophytes,’ ed. 2, p. 284. 


124 SIDNEY F. HARMER. 


parts perfectly white growing points or new apertures were 
making their appearance. Similar phenomena of regeneration 
have been repeatedly observed in all the species which I have 
examined. Thus the first glance at an ordinary colony of C. 
ramosa will suffice to show that the tubular ends, so charac- 
teristic of the young zocecia, are absent in the lower parts of the 
colony, where they have been either broken off or absorbed. The 
zocecia which are in this condition are closed by an obliquely 
placed diaphragm, as described in Crisia and other Cyclo- 
stomata by Waters,! Pergens,* and others. On staining a 
specimen of C. ramosa without decalcification, it is at once 
obvious that these diaphragms are used for the closure of 
zocecia which contain brown bodies but no functional polypides. 
They are placed at the point where the zoccium normally 
becomes free from the internode, and the free portion becomes 
gradually broken away or absorbed down to the point where 
the diaphragm is situated. In the younger parts of the colony, 
where the zoccia possess free tubular ends, no diaphragms are 
present, and functional polypides or obvious buds, together 
with the brown bodies formed by the death of the last poly- 
pides, are found in nearly all the zoocia. 

The individual life of the zoecium has not, however, neces- 
sarily come to an end with the formation of one of these 
diaphragms, as may be easily proved by the examination of 
suitable spring colonies which have been stained with borax 
carmine without decalcification. Whilst zowcia in which no 
regeneration is taking place are closed by a diaphragm and 
appear perfectly unstained, the red colour of the regenerating 
parts is obvious at the first glance. The first indication of the 
renewed activity of a zocecium is given by the fact that some 
of the cells below the diaphragm have acquired the power of 


1 A. W. Waters, “Closure of the Cyclostomatous Bryozoa,” ‘Linn. Soc. 
Journ. Zool.,’ vol. xvii, 1884, p. 400; “Fossil Cyclostomatous Bryozoa from 
Australia,” ‘Quart. Journ. Geol. Soc.,’ vol. x1, 1884, p. 675. 

2? Kd. Pergens, “ Revision des Bryozoaires du Crétacé figurés par d’Orbigny,” 
le partie, “ Cyclostomata,” ‘Bull. de la Soc. Belge de Géol.,’ &., tome iii, 
1889, p. 317. 


ON THE BRITISH SPROIES OF ORISIA. 125 


taking up colouring matters; slightly later a young polypide 
bud is seen below the diaphragm, which is then absorbed, the 
zocecium growing out (in C. ramosa) into a long tubular 
portion, at the end of which is the aperture.) In C. ramosa 
the free portions of regenerated zocecia are sometimes con- 
siderably longer than the normal length of the tubular portion. 
In one case the regenerated portion, which was completely free 
from the branch, was ‘69 mm. long. 

It is well known that new stems are given off from various 
parts of the rootlets.2. These*rootlets are usually developed 
from the backs or sides of the zovecia, especially of those near 
the base of the colony. But in cases where regeneration is 
actively taking place the tip of a branch may grow out into a 
rootlet, or a rootlet may take the place formerly occupied by a 
zocecium, usually one of the terminal zocecia of an internode in 
this case.? The rootlet thus formed may grow for a considerable 
distance, and finally produce a new stem as a lateral branch; 
or the new stem may be the actual prolongation of the rootlet, 
which, after a longer or shorter course, assumes the characters 
of astem. In other cases a new growing-point is formed 
from an old joint at the point where a lateral branch or an axial 
internode has previously been lost; or it may be formed from 
the apex of an internode in which the fracture has taken place 
across the middle of the internode, instead of at an axial joint. 
The result of this is that it is very common to observe an old 
brown stem from which start new internodes (lateral or axial), 
which are shown, by reason of the perfectly white appearance 
of their ectocyst, to have been formed at a much later period 
than the brown part of the stem. In one or two cases a 
growing-point had started from the proximal side of a broken 
joint, and had then given rise to a stem which grew in a direc- 
tion directly opposite to that of the internode from which it 
was developed. These cases are somewhat analogous to the 


1 This is the process which was observed by Smitt in C. geniculata. 

2 Cf, Smitt, “Krit. Fért.,” i, ‘ Ofvers.,’ &c., 1865, p. 122. 

3 These statements refer, for the most part, to C. eburnea and to C. 
ramosa. 

VOL, V, PART II. 13 


126 SIDNEY F. HARMER. 


one described by Smitt,! in which a “basis rami” had given 
rise to a normal branch, and also to a growing-point directed 
straight downwards from its base, which was formed by the 
proximal end of the “ basis rami,” from which it was separated 
by a joint. 

Although regenerated lateral branches may start from the 
old lateral joints, it is not uncommon to find that they are 
given off from near the end of the old internode, instead of in 
their normal position lower down ; this is due to the fact that 
the aperture of an old zocecium has become a growing-point. 

In colonies in which the process of regeneration is com- 
mencing, it is frequently noticed that the young growing- 
points are appreciably smaller than the normal ones. These 
small growing-points naturally give rise to slender zoccia and 
branches, which, however, as they grow longer, acquire fresh 
strength, and soon regain their normal diameter. The regene- 
rated parts of a colony are, consequently, often joined to the 
older parts by slender bases, in which, moreover, the basal 
internodes may consist of an unusually small number of zocecia. 
In both these respects they resemble colonies which are deve- 
loped directly from the larva, or from a growing-point which 
starts from the rootlet of an old colony. 

It is important to notice that, so far as my observations go, 
the regenerated parts of a colony always retain the same specific 
characters as the older parts. I have looked in vain for any 
indications which might have been given by regenerating 
colonies that the forms of Crisia described above as distinct 
species might be merely different phases of the same species. 

The general life-cycle of C. eburnea may probably be sum- 
marised as follows:—The breeding season is at its height in 
April and May; and at about this period it is not difficult to 
find young individuals which consist of a single zocecium 
attached by a disc-like base, and which have resulted from the 
metamorphosis of a free larva; small colonies are soon formed 
by these primary zoccia. At first, rootlets may be altogether 
absent, and in many colonies they are developed very sparingly ; 

1 Loe. cit., p. 125. 


ON HE BRITISH SPECIES OF ORISIA. 127 


but when formed, some of them give rise to fresh stems, which 
are the starting-points of new colonies. Or, again, some of the 
specimens found in the summer have resulted from colonies 
which developed ovicells in the earlier part of the year, and 
which, after losing these structures, again burst out into 
renewed growth ; in some cases leaving a single ovicell on the 
colony as some indication of their past history. Inthe spring, 
ovicells, when present at all, are found in large numbers, and 
those well-developed colonies which do not possess them at 
this period are probably in most cases of the male sex. Thus, 
in order to find spermatozoa in April, it was generally quite 
sufficient to select any colony in which there were no ovicells, 
while spermatozoa were not discovered in any of the cases in 
which ovicells were present. 

In the early spring the discoloured stumps of colonies which 
grew during the preceding year are found; from various parts 
of these, new growing-points are developed, and give rise to the 
colonies found at aslightly later period. The production of the 
enormous number of embryos then developed seems to exhaust 
the energy of the colony, whose growth practically ceases for a 
time, many of the branches being thrown off. After a period 
of rest, growth recommences with great vigour, and by the 
middle of the summer large and highly branched colonies are 
again found, although now, as a rule, with no ovicells. 


Number of Zoocia in the Internode, Mode of Branching, &c. 


Most of the previous accounts of Crisia merely mention the 
limits between which the number of zocecia in the internode 
may vary in the several species. Thus Hincks!' says of 
C. eburnea, “ 3—9 cells in an internode ;” while Johnston? is 
a little more explicit, stating that “there are from two to 
five, sometimes seven, and very rarely even nine, cells in each 
internodial space ” in the same species. It appears to me that 
it is quite impossible to define accurately the several species 


1 © British Marine Polyzoa,’ p. 421. 
2 «British Zoophytes,’ ed. 2, p. 284. 


128 SIDNEY F. HARMER. 


without paying careful attention both to the number of zocecia 
in the individual internodes and to the character of the 
branching. Smitt! is the only writer who has done this in a 
thoroughly satisfactory manner, and it will be convenient to 
make use of a modification of a graphic method of repre- 
senting the characters of the colony which he was the first to 
introduce.? 

In this method the limits of each internode are indicated by 
brackets, in which is a number denoting the number of zocecia 
in the internode; 7 indicates a branch, the position of which 
is further shown by means of a number : thus ,7, e. g., indicates 
a branch given off from the first (lowest) zoccium of an 
internode on the left side, while 7, indicates a branch given 
off from the second zoccium on the right side of the inter- 
node; finally # indicates the growing-point, and Ov. an ovicell. 
A key to the method may be obtained by referring to fig. 6, 
the formula of which is included on the formula on p. 154, as 
explained on that page. 

Thus many of the characteristic features of C.denticulata 
(figs. 2, 8) may be represented by the formula— 


(8)+9+y7)+(10) + 9+72)+(9 i Ge Aiea ty) +(18+75)+(9+57)+(8+2) 
=(138+ 57) +(10)+(7+72)+(4+2) 


=(5+4.2) 


=(114+-;7)+(8+0v.+5+7,+2) 


Loe 
Tian 


(11 +r,)-+ (10) +(11-+4r) + (8) + (2) 
Lo+ Ov.+2+ 7+2) 


=(3+2) 
=(10)+(9 = +(5+0v.+5+2) 


=(9+ Ov.+6+7,4+2) 
=(8+2) 


1 « Ofvers. af-K. Vet.-Akad. Férhandl.’? 1865, p. 115. 
2 Loc. cit., p. 139. 


ON THE BRITISH SPECIES OF ORISTA. 129 


—representing the axis of a branch given off by the main stem 
of a colony, together with all the ramifications of two of its 
secondary branches. 

It will be noticed that nearly every internode develops a 
single branch, and that the branches come off in regular 
alternation on opposite sides of consecutive internodes of 
every axis. Although the number of zoccia in the internode is 
very variable, eleven may be regarded as the number most cha- 
racteristic of the species. 

The above formula further shows that every branch-bearing 
internode whose development is complete possesses an odd 
number of zocecia, while in completely developed internodes 
which bear no branch the number is even. Although this rule 
is not quite absolute, it is difficult to find any exception to the 
striking rule that a branchless internode has an even number 
of zocecia; or, conversely, that an internode with an even 
number (whether this number is large or small) of zocecia 
bears no branch. It may be pointed out that even if the 
branches have been broken off, their previous presence can be 
ascertained by the existence of the basal articulation from 
which they formerly sprang. 

It may further be noted that a lateral branch is, with very 
rare exceptions, produced on the side of the basal zocecium of 
the internode (PI. XT, fig. 2). 

The regular alternation of the zoccia of the axis of any 
branch is not disturbed by the development of an axial joint; 
and the last zocecium of the internode below the joint nearly 
always projects beyond the penultimate zocecium (which 
belongs to the other side) in the form of a free tube (fig. 2). 
Since the branch-bearing internode has an odd number of 
zocecia, and since the branch is developed on the side of the 
basal zocecium, it follows that the last zoceicum, which is 
produced into a free tube, will also be on the same side as 
the branch. A moment’s consideration will show that the 
basal zoecium, the branch, and the terminal (“ produced ”’) 
zocecium, in any internode, will normally be on the opposite 
side to that on which these structures are situated, both in 


130 SIDNEY F. HARMER. 


the internode below it and in the internode above it on the 
stem. 

But if an even-numbered internode is developed (fig. 2), 
its last zocecium will of course be on the same side of the stem 
as the last zoccium of the preceding internode; and conse- 
quently the basal zocecium and the branch of the internode 
above it will be on the same side as its own basal zowcium, 
and on the opposite side to the branch next below it ; or, illus- 
trating this by a formula, we shall, as a rule, find cases like 
(138+7,) +(8) + (7+,7), as shown in fig. 2. 

Thus, stating the same fact in another way, an even- 
numbered and branchless internode may be intercalated in the 
stem without disturbing the alternate origin of the branches 
on opposite sides. The same is true of those cases where two 
even-numbered internodes occur consecutively on the same 
axis. 

The more closely one investigates unusual methods of 
branching in this species, the more obvious does it become 
that the growth of the colony is regulated by some well-defined 
law, which finds one of its expressions in the preceding rule. 

Thus it will be seen, by reference to figs. 2, 4,6, and 11, 
that the basal zocecium of a lateral branch is on the abaxial 
side of the latter in all the four species referred to; and 
further, that the branch given off by the basal internode of an 
axis is also on the abaxial side. This is obvious enough for 
C. denticulata, from the formula on p. 146, where it will 
be noticed that, in the one case in which the basal internode 
has an even number of zocecia, the second internode develops 
the first branch, and that that branch (and of course the basal 
zocecium) is on the abaxial side. 

On two occasions abnormal branching of the type (9 + 3r) + 
(13) + (11 +47) was noticed. Here an odd-numbered branch- 
less internode occurs; but such cases seem to be rare. Since 
the number of zocecia in the branchless internode is odd, it 
follows that the basal zocecium, and consequently the branch, 
of the third internode will be on the same side as in the first 
internode. 


ON THE BRITISH SPECIES OF ORISIA. 1381 


In another case the formula (15 + 7,) + (9) + (10) + (9+75) 
was obtained, and it is obvious that this is a further illustration 
of the same principle. 

In an axis, part of the formula of which was (13 + 7;) + 
(14 + or +7,) + (11 + 47), one of the internodes had two 
branches, the first developed on the side of the basal zocecium, 
and the second on the opposite side. Since the number of 
zocecia in this internode was even, the regular alternation of 
the branches was not disturbed. Cases of this kind appear to 
be extremely rare. 

Another abnormal case, from a young colony, had the 
formula— 

+(5+72)+ 
=(7) + (6+72)+ (8) +(6)+(2+2) 

Here it is obvious that the whole of the lateral branch shown 
is very abnormal; the first branch is developed by the second 
internode, which has an even number of zoccia; and it is on 
the same side as the basal zocecium of the first internode, and 
on the opposite side to that of its own internode. Here it must 
be supposed that the tendency to produce the first branch on 
the abaxial side has prevailed over the tendency to produce a 
branch on the side of the basal zoccium of an internode. 

In one case observed, in which the base of an old colony was 
regenerating fresh branches, two small growing-points were 
seen to have been formed, almost exactly opposite one another, 
from thesame internode. If this growth had proceeded some- 
what further, it might not have been obvious that the abnormal 
character of the branching was due to the occurrence of regene- 
rative processes, in which the regularity which characterises the 
normal branching does not seem to be so marked. 

Some of these remarkable relations are obvious enough in 
the figures given by previous authors, none of whom seem, 
however, to have been struck with the general rule illustrated 
by these cases. Thus Milne-Edwards,' in pl. vii, fig. 1 6 
(C. denticulata), shows a portion of a colony in which two 

1 ¢ Ann, Sci. Nat.,’ 2e sér., “ Zool.,” tome ix. 


182 SIDNEY F. HARMER. 


internodes have an odd number of zoccia, and in which, 
further, the branch and the basal zocecium are, in each inter- 
node, on the same side. The third internode which is com- 
pletely figured has 10 zocecia, and possesses no branch. It must, 
however, be pointed out that in his fig. 1 a (C. denticulata, 
under slight magnification) Milne-Edwards represents most of 
the internodes as having an even number of zoccia; but it 
may probably be assumed that in this figure, which gives an 
excellent representation of the general appearance of the species, 
sufficient attention has not been paid to the details of the 
arrangement of the zoecia. Again, Busk! figures, in the same 
species, two complete internodes, one of which has thirteen zocecia 
and a branch, and the next has twelve zocecia and no branch. 

The relations above described are perhaps capable of being, 
to some extent, explained in the following manner. In the 
species of Crisia which I have examined, and, I have very 
little doubt, throughout the genus, the base of an internode, 
whether axial or lateral, is simply the basal part of the lowest 
zocecium of that internode, that part having been separated by 
the development of the joint from its upper or distal part. 
This will be intelligible on referring to Pl. XT, fig. 1, repre- 
senting an axial internode in which only two zocwcia are 
completely separated from the growing-point. The lowest 
zoceclum of the internode is seen to be divided into two parts 
by the horny joint ; and the lower of these two parts forms the 
articulation to which the younger internode is attached. In 
examining the formation of the joint (whether axial or lateral) 
in stained specimens it is at once obvious that the alimentary 
canal of the youngest zocecium of the internode at first extends, 
through the tubular joint, into this lower portion ; confirming 
the statement made above with regard to the morphology of 
the base of the internode. 2 

It is thus clear that the occurrence of an axial joint in 
no ways disturbs the alternation of the zoccia (see any of 
the figures). The last zocecium of the older internode would 

1 «Cat. of Mar. Pol, in Brit, Museum,’ Part IIT, “Cyclostomata,” pl. iv, 
fig. 2. 


ON THE BRITISH SPECIES OF ORISIA. 138 


overlap, and be fused with the next zocecium higher up on the 
same side if it were not for the development of the joint ; which 
is, however, formed in such a position across a zocecium as to 
leave the preceding zocecium in the characteristic “ produced ” 
condition which has already been described. In the ordinary 
type of branching, where successive internodes produce branches 
in regular alternation on opposite sides, the number of zocecia 
must be odd if the branch is to be produced on the side of the 
basal zocecium in each internode. The formation of a new 
axial internode practically amounts to the transverse division 
of a zocecium, while the formation of a branch may be ex- 
pressed as due to the longitudinal division of a zocecium (at 
the growing-point). Suppose that the right side of an axis 
bears a branch (as in the lowest internode shown in fig. 2). 
The tendency of the growing-point to produce new branches 
alternately on opposite sides would normally result in the pro- 
duction of a branch from the left side of the next youngest 
internode; but if a lateral branch has not been produced 
by the time that a new axial joint is to be formed, that axial 
joint would be, as a matter of fact, normally developed from a 
zocecium of the left side, as at the base of the third internode 
in fig. 2; and this implies the existence of an even number 
of zocecia in the second internode. The production of an even- 
numbered internode may thus be regarded as due to the alter- 
nate predominance of the two sides of the growing-point. The 
development of a lateral branch on the right side (e.g.) has 
apparently the effect of leaving the left side of the growing-point 
with an excess of vigour; so that when a new internode is 
formed—whether by the transverse division of a zoccium to 
form an axial joint, or by its longitudinal division to form a 
lateral branch—it is the left side (in this particular case) of the 
growing-point by which this division is effected. Division in 
the transverse direction results in the formation of an even- 
numbered internode, while the production of a lateral branch 
on the left side of the next succeeding internode restores the 
function of producing another axial joint to the right side of 
the growing-point. 


134 SIDNEY F. HARMER. 


That there are exceptions to this rule has been shown above 
by the description of odd-numbered branchless internodes ; but 
it must be remembered that these cases are rare. 

From what has already been said of the laws which regulate 
the growth of Crisia, it is obvious that a representation of a 
colony can easily be reconstructed from a formula of the cha- 
racter introduced by Smitt; and no further justification is 
required for the use of such formule. ; 

In some specimens of C. denticulata the average number 
of zocecia in an internode may be higher than in the one de- 
scribed ; and the numbers 13, 15, 17, and even 19 are by no 
meansuncommon. It may often be noticed that, although inter- 
nodes consisting of any given number of zoccia do not seem 
to be arranged in any definite order in the colony, an indivi- 
dual colony may be characterised by the frequent occurrence of 
internodes with that number of zoccia. Thus if the dominant 
number, in any particular case, be 11—and this seems to me 
the most common case—variations in the number of zocecia in 
the internodes of that colony will apparently take place about 
the number 11 as a mean; so that, although internodes of 9 or 
13 zocecia are common, there may be none of so many as 15 
zoecia. But if the colony have many internodes of 15 zoccia, 
for instance, then it will probably be found that some of the 
other internodes have 17 or 19. 

If the growth of the branch be complete, so that no more 
axial joints are to be formed, the terminal internodes, and 
especially those which have produced ovicells, may have a 
larger number of zoccia than the internodes of the rest of 
the colony; and the number of zoccia formed before the 
growing-point exhausts its activity does not appear to be 
regulated by the laws which govern those internodes which 
are not terminal. But even the terminal internodes normally 
produce no more than a single branch (cf. C. aculeata and 
C. ramosa), the cases mentioned on p. 149 being the only 
ones in which two branches were noted to come off from the 
same internode. 

The articulations of the lateral branches of this species are 


ON THE BRITISH SPECIES OF ORISIA. 135 


alone sufficient to distinguish C. denticulata from the other 
British forms. They are situated at a very low level on the 
zocecia which bear them, and each “basis rami” (Smitt) 
appears to he wedged in between two consecutive zoccia (fig. 
3), instead of being, as in other species, distinctly apposed to 
the outer side of one zoccium (figs. 4,6, 11). The branches 
usually originate from z;,! z,, or z;; less commonly from 2, 
or from 2,. 

The joints, both of the zoarium and of the rootlets, of this 
species are in nearly all cases of a jet-black colour, as recog- 
nised by most of the previous writers.? The young joints are, 
as in other species, uncoloured; but the black colour is in 
almost all cases very speedily acquired. Smitt and Busk do 
not mention this as a specific character, no doubt because they 
have given wider limits to the species than are accepted by 
most writers. 

The ovicell® in all species replaces an ordinary zocecium, 
and in this particular species it is usually borne on a lateral 
branch, and in most cases is situated at some distance above a 
joint. In the instances given in the formula on p. 146 the ovi- 
cell replaces the 4th, the 6th, or the 10th zocecium of an in- 
ternode. I have never seen it lower than 4th nor higher 
than 13th. It is usually very near the end of a branch, and 
this feature is well shown in pl. iv, figs. 2 and 4, of Busk’s 
British Museum Catalogue (Part III). In one of my cases, 
however, thirteen zocecia occurred above the ovicell, and eleven 
below it, and very rarely a joint may be developed above it. 
If the ovicell- bearing internode develops a branch, that branch 
is very seldom given off from a position higher than the 
zocecium which corresponds to the ovicell on the opposite side 
of the branch. 


1 Le. from the third zoccium of either right or left side: the side from 
which a branch comes off has no significance unless considered in relation to 


other characters. am 
2 Cf, Fleming, J., ‘Hist. Brit. An.’ p. 540; Johnston, A., ‘ British 


Zoophytes,’ 2nd ed., p. 284; Hincks, T., ‘ Brit. Mar. Polyzoa,’ p. 423; &e. 
3 See also p. 169. 


136 SIDNEY F. HARMER,. 


The calcareous matter of the ectocyst is considerably thicker 
in C. denticulata than in any of the other British species. 


C.eburnea. Fig. 6. 

Although this species is not likely to be mistaken for C. 
denticulata, I believe that it is more nearly allied to that 
species than are any of the other British forms. This is shown 
by the flatness of the internodes, by the fact that each inter- 
node has normally one branch, and by the characters of the 
apertures of the zoccia. 

The branching may be illustrated by the formula!— 


Bt +r) + (+72) + 7 +r) + 7 +72) +7 +17) + (2) 
(5+) +(7 +27) + (b+) +(7 +7) + (5 +7) + (7 +17) +2) 


=(5+47)+ 
=(5+7,)+ 
=(5+,7)+ | 
| Rte rar ere Te 
=(5+yr)+ 
=(5+n)+ 
=(54+yr)+ 


| ago. +10+7,+7.+2) 
=(1+ 0v.4+-9+,r+2) 
=(4+e 


=) '=8+r+2). 


=(+2) 
—vrepresenting the partial formula of a branch of a colony found 
in April, in which ovicells were very numerous. The ovicell- 
bearing internode on the right side of the formula is the one 
which has been represented in Pl. XI, fig. 6. 

The tendency of the branches of this species to arrange 
themselves as unilateral sympodes is here most marked ; and 
the formation of these helicoid cymes—again borrowing a 
botanical term—is one of the most characteristic features of 
C.eburnea. This was recognised by Johnston,’ who says of 
this species, ‘“ Polypidom much branched, the primary divisions 
alternate, spreading ; the secondary from one side only.” It 
will further be noticed that in parts of a colony in which this 


1 See explanation of this graphic method given on p. 146. 
2 «Brit. Zoophytes,’ ed. 2, p. 284. 


ON THE BRITISH SPECIES OF ORISIA. 137 


method of branching is well developed, the internodes compos- 
ing the sympode are usually made up of five zoccia, and that, 
although the branching may, in other parts of the colony, take 
place from 2, (or rarely from z, or z,), well-developed helicoid 
cymes are invariably composed of internodes in which the 
branching takes place from 2). 

These helicoid cymes do not, however, agree with the method 
of branching defined under that term in text-books of botany, 
in that the main axes of the parts of the sympode are by no 
means suppressed. This is obvious enough from the formula, 
in which the first internode on the left side forms the basal 
member of a helicoid cyme developed on the left side of the 
branch; but it is, at the same time, the basal member of a 
long axis, which develops new cymes alternately on opposite 
sides; and the same is true of the other constituents of the 
sympodes. Thus each of the branches indicated in the formula, 
with the exception of those which are quite near to the grow- 
ing-points, is again the basal member of a helicoid cyme ; and 
these cymes are consequently given off alternately on opposite 
sides, not only by the internodes of the main stem, but 
also by the internodes of its branches of the second, third, 
and other orders. The number of members of which these 
helicoid cymes are composed decreases fairly regularly in a 
centrifugal direction. 

Each internode is typically provided with one branch, and 
at the same time is composed of an odd number of zoecia, 
just asin C. denticulata. It is not uncommon, however, to 
find branchless internodes, whose position in the colony may 
be illustrated by the formula— 


(6 + 1) + (6) + (6 + ")3 


and, just as in C. denticulata, these branchless internodes 
nearly always consist of an even number of zoccia, most 
commonly of four or six, less often of two or eight. Ex- 
ceptions to this rule are somewhat less rare than in C. den- 
ticulata, which this species so closely resembles in its method 
_of branching. The exceptions are more common at the base 


138 SIDNEY F, HARMER. 


of the colony than elsewhere. The branch is developed on the 
same side as the basal zocecium of an internode, and the last 
zocecium is usually somewhat produced. In very rare cases, 
of which the specimen represented in fig. 6 is an example, two 
branches may be developed from the same internode. 

The articulations which bear the lateral branches are rela- 
tively short ; even when the branch is developed from 2, or z, 
the “basis rami” is never wedged in between two zocecia, as 
in the last species; and the joint which bears the branch is 
nearer to the aperture of the zocecium which has developed 
it than in C. denticulata. 

The number of zocecia is typically five or seven, the former 
number being especially characteristic of the members of a 
helicoid cyme. As in C, denticulata, the definiteness with 
which the colony grows is frequently indicated by the regular 
repetition of the same forms of internode in a branch. Thus 
the greater part of the main axis of the branch whose formula 
is given on p. 154 is composed of internodes of the type (7+7,) ; 
in the main axis of the branch given off by the second internode 
of that atem, (5 +7) alternates regularly with (7+ ,7) until 
the end of the axis is nearly reached; while in the next line 
but one will be seen the formula of a branch composed of units 
of the type (5+7,). Theregular repetition of internodes of the 
type (5 +7) in the formation of most of the helicoid cymes is 
a further illustration of the same thing. In many other cases, 
however, no such regularity of arrangement was noticed. In 
a colony found at Plymouth in August, the dominant number 
of zocecia was seven, although internodes with five zocecia were 
not uncommon. But, in correlation with this increase in the 
normal number of zocecia, it was found that several internodes 
of nine zocecia occurred, and two of eleven. 

In the terminal internodes the number of zocwcia may be 
larger ; in one case observed it was as high as twenty, no 
growing-point being left. 

The ovicell most commonly replaces the second zocecium of 
a lateral branch (fig. 6), and is consequently the basal member 
of its own (axial) side; in other cases, however, the ovicell may 


ON THE BRITISH SPECIES OF ORISIA. 139 


replace the third zocecium above a joint (and it is then abaxial), 
but it is very rarely found higher in the internode. A branch 
is never given off by an ovicell. 

As the age of the ovicell increases, fresh zocecia continue to 
be added above it up to a certain point. The old ovicell seems 
to be always surmounted by a considerable number of zoccia; 
in the specimen shown in fig. 6 there are, in addition to two 
incompletely formed zocecia—the last that this branch would 
have produced—ten zocecia above the ovicell. It must be noted 
that in this and other similar cases all zoccia which are 
further from the joint than the ovicell are described as being 
above the latter. The second zocecium of the right side in 
fig. 6 may not, at first sight, appear to be in this position, 
although an examination of the lower end of the ovicell at once 
shows its real place in the series. 

A joint is seldom developed above the ovicell, and the growing- 
point usually completely exhausts its power of developing fresh 
zocecia after a certain period. 

The joints of this species are pale-coloured, or more usually 
yellow. In old parts of the colony the joints may become very 
dark, or almost black; this is especially true of those parts 
which form the starting-point for the regeneration of fresh 
branches. The joints are probably never so dark as they are 
normally in C. denticulata. 

Smitt, in his valuable paper on Crisia,’ gives a series of 
formule illustrative of the branching, &c., of the forms of this 
genus, and many of these formule illustrate in a most instructive 
manner the tendency of some at least of the species of Crisia 
to develop even-numbered internodes without branches. In his 
explanation to No. 8 of this series Smitt expressly points out 
that, in Nos. 4—8, shorter branchless internodes may alternate 
with longer internodes which have developed branches. It isa 
noteworthy fact that the greater number of the branchless 
internodes shown in these formule have an even number of 
zocecia, and that the number is odd in most of those internodes 
which have developed branches. This fact seems, however, to 

1 “ Krit. Forteckn.,” I, ‘ Ofvers. af K. Vet.-Akad. Forhandl.,’ 1865, 


140 SIDNEY F, HARMER. ~ 


have escaped Smitt’s attention. It must further be pointed 
out that some of the exceptions to the rule which has been so 
much insisted on above are probably due to the fact that some 
of the formule refer to C. aculeata, as is admitted by Smitt 
in two of the cases. 

A very interesting abnormality of C. eburnea is figured in 
Pl. XI, fig. 5. The internode in question was the penultimate 
internode of a branch of a thoroughly characteristic colony, in 
which no other abnormalities were detected. In addition to 
bearing two lateral branches in a very unusual position, at its © 
upper end, this internode distinguished itself by producing 
three zocecia arranged in a row along the middle of its front 
surface, giving it, when seen from this side, an appearance very 
much like an Entalophora, for instance. The back of this 
internode appeared normal, and it was not obvious that any of 
the three growing-points borne by the internode was constructed 
in such a manner that it would have reproduced the abnormality 
in the next following internodes. 


C.aculeata. Fig. 4. 


-T believe this form, which is in many respects intermediate 
between C. eburnea and C. ramosa, and which was originally 
distinguished as a species by Hassall,! to be a perfectly good 
species. Nearly all recent authors have regarded it as a variety 
of C. eburnea; this view is taken, for instance, by Hincks,? 
Busk,? Smitt,4 &c. Even Johnston,* although inserting it as 
a distinct species, adds that he cannot persuade himself that it 
is more than a variety of C. eburnea. 

My belief in the specific distinctness of C. aculeata rests 
mainly on the characters of the ovicell; since a particular form 
of ovicell (shown in fig. 4) is invariably found on colonies of 


1 Hassall, A. H., ‘Ann. and Mag. of Nat. Hist.,’ vol. vi, 1841, p. 170. 
2 «Brit. Mar. Polyzoa,’ p. 421. 

3 «Cat. of Marine Polyzoa in Brit. Museum,’ part iii, p. 4. 

4 Loc. cit. 

5 ‘British Zoophytes,’ ed. 2, p. 285. 


ON THE BRITISH SPECIES OF ORISIA. 141 


the aculeata type, and never occurs in any other type of 
colony. 

The method of branching and the number of zocecia in an 
internode are far less constant than in the last two species. 
Some of the characters of C. aculeata may, however, be 
illustrated by a formula, using the letter s to indicate the 
position of a spine, in addition to the symbols which have been 
employed in other cases. 


Rootlet 


| 
(1) + (4) + (3) + (4+) + (9-4 yr+5, +175) + (747) + (51) + (7417) t (7417) +2) 


=(5+ Ov.+10+5,+7,+57)+(2) 
=(8+,8)+(54+.7)+ (00+ +37)+(1+2) 


=(3+ +2) 
=(2) 
=(5+7,+ Ov.+2) 
{eee 


(+2) 


=(640v.+5+ 547,42) 


=(1+2) 
=(6+)7+2) 


'=@-+2) 


The formula represents the whole of a main stem, given off 
from a rootlet, together with the whole of one of its lateral 
branches and a portion of another. In several important respects 
this formula differs from those which have been given of the pre- 
ceding species. Itis by no means uncommon to find completely 
formed internodes which have an even number of zocecia; and 
these even-numbered internodes do not conform to the denti- 
culata or eburnea type by being usually without branches. 
In some cases, indeed, an even-numbered internode has no 
branch ; in other cases it has two branches, one on each side; 
in others again it may have one branch, or it may have a spine, 
which, as has often been pointed out, is a structure which may 
be regarded as a suppressed branch: like the true branches, 
the spine has horny joints at intervals, and is attached to the 


VOL. V, PART II. 14 


142 SIDNEY F. HARMER. 


zocecium by means of a basal piece which is quite similar to 
that of a normal branch. 

The spines shown in fig. 4 have been artificially bent back- 
wards; in their normal position they curve over the front of 
the branches. 

The number of spines developed on a colony is extremely 
variable ; in a few cases spines are altogether absent, and the 
species could then hardly be distinguished with certainty from 
C. ramosa, were it not for the presence of the characteristic 
ovicells. Although, in one or two cases observed, an internode 
had developed spines on all or nearly all its zocecia, it is not usual 
to find more than one or two spines on a single internode, 
while a large proportion of the internodes of a colony do not 
develop any of these structures. The spines most commonly 
occur on the lower zoccia of an internode, and are commonly 
in the position— 

(@ + 4 + 12) 
or (2 + 8, + 8 + 75); 


being found on the abaxial side if the internode is, as is often 
the case, the basal member of a branch. 

The spines may, however, be developed in other positions ; 
thus it often happens that the last structure developed at the 
apex of a branch, before the growing-point ceases to grow, 
is a spine,! which is situated on the axial side of the last 
zocecium, and is consequently in the position of the terminal 
zocecium of the branch to the right of the ovicell in fig. 4. 

In the specimens (most of them from Plymouth or Roscoff) 
which have come under my notice the presence of asingle spine 
on a colony has been quite sufficient to enable the species to be 
identified with certainty as C. aculeata. It is perfectly true 
that the lower parts of the zoarium may have an eburnea- 
like appearance ; but the colony, if well grown, seems always 
to acquire the aculeata form of the zowcia and internodes 
towards the ends of the branches. 

I have in no case found an ovicell of the type shown in fig. 6 


1 Cf. C. acuminata, Busk, ‘ “Challenger” Rep.,’ part 50, pl. iii, fig. 1. 


ON THE BRITISH SPECIES OF ORISIA. 143 


(C. eburnea) on a colony which, from the presence of spines 
or from other characters, was found to belong to C. aculeata. 
I cannot admit that there is sufficient evidence to show 
that this form is merely a variety of C. eburnea. Both 
in the form of its zowcia and in its method of branching 
it is totally unlike this form, although it is sometimes with 
difficulty distinguished from C. ramosa. 

The branches of C. aculeata are usually slightly incurved, 
but not nearly to the same extent as in C, eburnea; and it 
does not possess the well-developed helicoid cymes of the 
latter species. Many of the internodes bear two branches, 
usually on opposite sides, but more rarely on the same side. 
In well-developed colonies the terminal internodes, and espe- 
cially those which possess ovicells, are commonly provided 
with two branches. 

The number of zocecia in an internode is extremely variable ; 
it is usually small in the lower internodes of a stem, such 
numbers as 1, 2,8, and 4 being common in this position. The 
next parts of the stem, and the basal parts of the lateral 
branches given off by it often assume an eburnea-like appear- 
ance, the internodes consisting of 5 or 7 zocecia. At the ends 
of well-developed branches the number usually becomes 
higher ; a terminal internode with 22 zocecia has been observed, 
although this number is higher than is usually the case. 
When the terminal internodes have many zocecia they usually 
bear two branches; but if the number of zoccia is still larger 
the number of branches may increase to as many as five. 

The position of the branches is another very variable 
feature. In the lower parts of a colony the branching takes 
place commonly from z,; while higher up, although some of 
the branches still come off from z,, others are given off quite as 
commonly from z,, and in many of these cases the zocecilum 
below the branch, and on the same side, bears a spine. 
Branching may, however, take place from the higher zoecia of 
an internode, as from z, or 2,; and when several branches 
come off from the same internode, those which are last 
formed have a very high position in the internode. The 


144 SIDNEY F. HARMER. 


most striking case observed illustrating this point had the 
formula— 
7+ 0.+ 11. +7+ % + 7% + or + to + 2). 

It cannot fail to be remarked that the character of the 
branching is much more variable in this species than in 
C. eburnea. 

The joints are usually yellow; the articulations which bear 
the branches are usually short, and are then very similar to 
those of C. eburnea; in some cases, however, they acquire 
the form characteristic of C. ramosa. 

Near the ends of the branches, where most of the zoccia 
have polypides, the ends of the zocecia are, in most cases, long 
free tubes, and are thus strikingly different from those of 
C. eburnea. The free portions of the zoccia are either 
gradually bent forwards from the point where they leave the 
branch, or they may be bent forwards at a distinct angle from 
this point. The curvature of the zoccia is, in either case, 
different from that of C. eburnea. The zoccia are dis- 
tinctly longer and more “loosely aggregated” than in that 
species; and the branches are usually of slenderer habit (as 
recognised by Johnston!). 

The ovicell is nearly always higher in the internode than in 
C. eburnea. In the average of a considerable number of 
observed cases the ovicell was in the position of the 5th—6th 
member of the internode above the joint, and thus replaced 
2, or ,2. In one case the ovicell replaced the 8th zowcium, 
and in another it was the 3rd unit of the internode; in no 
case was it found lower. 

The stem is not usually jointed above the ovicell ; and fig. 4 
is, consequently, a somewhat exceptional case. As in the pre- 
ceding species, the ovicell is normally borne by a terminal 
internode; and a considerable number of zoccia may be added 
above the ovicell. 


1 «Brit. Zoophytes,’ ed. 2, p. 286. 


ON THE BRITISH SPECIES OF CRISIA. 145 


C. ramosa,n.sp. Fig. 11. 
Some of the characteristics of this species are well exhibited 
by the formula!— 


(7-+Ayr+rs) + (11+ 97) + (10 +7,+57) + (5+75+2) 
=(12 ++ 7+7,)+ 
—2+e+n)+ | 
=(5+00.4+7 +r tyrtrstert+2) 
=(5+.r+2) 
=(2) 


=(8+.r+7,+2) 
=(94+ 00.47 4+rotytret rte) 


=(2) 
=(3+2) 
=(9+.7r+7,+2) 


=(1+2) 
: =(4+.r+2) 
=(10+7,+2) | 
=(2) 


=(1+2) 

The branching is seen to be very similar to that of C. acu- 
leata, but the tendency, already manifested by that species, to 
develop more than one branch from an internode, is here 
carried much further, so that a considerable proportion of the 
internodes have two branches each, while the terminal inter- 
nodes, if the colony is well grown, will be found to have at 
least two each. 

The rule relating to odd- and even-numbered internodes, so 
characteristic of C. denticulata and of C. eburnea, here 
breaks down altogether, as, indeed, was the case to a consider- 
able extent in C. aculeata. Odd-numbered internodes are 
not much commoner than even-numbered ones, and either kind 
may produce one or more branches, or be altogether branchless. 
The first branch of an internode is, however—as in other 
species—nearly always developed on the side of the basal 
zocecium, and the last zocecium of an internode is very often 


1 It is obvious that, in the case of the ovicell-bearing internodes, some of 
the branches are given off above the ovicells. For the purposes of the 
formula, however, the ovicell is counted as an ordinary member of the inter- 
node. A branch is probably never developed from the ovicell itself. 


146 SIDNEY F. HARMER. 


situated on the side on which the last branch is developed, 
thus causing the position of the basal zocecium of the next 
internode, and consequently of the first branch of that inter- 
node, to be on the opposite side. 

Just as C. eburnea is, on the whole, characterised by 
branching from z,, so this species may be said to branch nor- 
mally from 2, or to produce branches on the type (1'n+n+27), 
where n usually represents z, or 2,. 

The extent to which this must be taken as a general rule 
may be understood by the following analysis of the complete 


formula of a well-developed colony : 
Number of Cases. 


(1) Internodes with one branch, originating from z, . 24 
(2) Branches arranged on the type (r,+,4r) . ‘i 5 
(3) 9 are sy (Ty +5r) OF (73457) - 5 
(4) ” ” ” (r7,+;7) . 1 
(5) ”? ” ” (T2457) . 5 
(6) ” ” ” (7, +2") . . . 1 
(7) ” ” a” (r3+47) ~ . . . 2 
(8) One branch only, originating from z, ‘ : 2 
(9) ” ” ” 23 8 
(10) ” ” ” 2, . 3 % % 7 
(11) ss is i 5 5 : A . 8 


Total number of internodes which had developed branches 63 
Only eight of the completely developed internodes were 
branchless. Thus in this particular colony, in which no ovi- 
cells were present, and in which no internode possessed more 
than two branches— 
30 p. c. of the branching internodes bore two branches ; 


38 p.c. i 5 s, one branch, originating from z,. 
32 p. c. 43 7 os 3 53 from other 
zocecia. 
100 p. c. 


Or, adding together Nos. 1 to 4, the cases in which the branches 
come off from z,, or in which the second branch is two zocecia 
higher than the first, we find that these cases amount to 55:5 
per cent. of the total number of branching internodes, and this 
may be taken as a case which does not exaggerate this feature 
of the branching. 


ON THE BRITISH SPECIES OF ORISIA. 147 


Since some of the internodes which bore branches were 
immature, and had not had time to develop more than one 
branch, the figures would have been slightly different if the 
growth of the colony had been complete. 

The symmetrical character of the branching noticed in other 
species is also found in C. ramosa. Thus the branches 
originating from an internode whose formula was (14+,7 +7) 
developed altogether five internodes from which new branches 
were given off; in two of these cases the branch was borne by 
23, in two more by 2;, and in the last case by z,; and other cases 
of the same kind may easily be found. 

The symmetry of the branching comes out with special 
clearness in the case of some abnormalities, of which the 
formula given on p. 145 is anexample. Two consecutive inter- 
nodes of the main stem represented in the formula give off 
internodes whose formule are identical. One of these gives off, 
on its right side, a lateral branch consisting of a single long 
internode bearing an ovicell, and the other gives off a precisely 
similar branch on its left side. Both of these ovicells have the 
same deformity, having developed a constriction at a particular 
point near their upper end ; and it will further be noticed that 
the symmetry extends, to some extent, to the branches given 
off by the internodes which bear these ovicells. 

Fig. 12 represents an abnormal ovicell or zocecium of a type 
found in more than one colony. The growing-point appears to 
have started with the intention of developing an ovicell, and 
then to have altered its original purpose, and to have developed 
the incipient ovicell into an abnormal zowcium. This alteration 
of purpose may have been due to the failure of the young 
ovicell to develop the egg! which is normally found in the 
immature ovicell. 

The point which immediately concerns us at present is that 
each of two consecutive internodes of the same stem of this 
particular colony developed lateral branches, one on each side 
of the stem, and that each of these lateral branches bore an 
ovicell of this peculiar “suppressed” form. The same colony 

1 «Proc, Cambridge Philosoph. Soc.,’ vol. vii, p. 48. 


148 SIDNEY F. HARMER. 


possessed two more of these suppressed ovicells, two ovicells 
showing other abnormalities, and several normal ovicells. 

In another colony a normal ovicell, with a “ suppressed ”’ 
ovicell on a lateral branch on each side of it, was noticed. 

In another case (fig. 13) a single internode bore no less than 
four ovicells, and the colony to which this belonged possessed, 
in different parts, four internodes, in each of which two ovicells 
had been developed. It may be noted that the occurrence of 
two ovicells, side by side, in the same internode, is described 
by d’Orbigny! in C. patagonica, apparently as a normal 
feature of the species. 

These cases, and the general remarks which have been made 
with regard to the branching of various species of Crisia, 
show that the growth of the colony is even more definite in its 
character than would appear from a superficial examination, 
and that in each particular species the tendency to vary is sub- 
ordinated to certain principles of growth, which give rise to the 
special symmetry which characterises the species. 

The number of zocecia which compose an internode is even 
more variable in C. ramosa than in any of the other species. 
Generally speaking, the number is smaller near the base of the 
colony, and larger near its periphery, although this rule is by 
no means absolute. The length of the internode depends 
mainly on the number of zoccia it possesses. The longest 
which was measured was a terminal internode in which growth 
had ceased, and which consisted of 28 units, of which the 10th 
was an ovicell; its total length being slightly more than 7 
millimetres. These long internodes usually show a well-marked 
double curve, like a much elongated S, just as was remarked 
in C. denticulata; and they commonly bear 3, 4, or even 5 
branches. 

The appearance of the internodes depends greatly on the 
condition of the zocecia. Near the ends of the branches the 
zocecia generally have very long tubular mouths, and, for the 
most part, contain a functional polypide. This is especially 


1 D’Orbigny, A., ‘ Voyage dans l’Amérique méridionale,’ tome v, 4¢ partie, 
1839 and 1846, p. 7, pl. i, fig, 1, 


ON THE BRITISH SPEOIES OF ORISIA. 149 


true of actively growing colonies found early in the year: ata 
later period, when growth is less energetic, the apertures may be 
much less prolonged, and in many cases they are not more 
prominent than in some specimens of C. denticulata, even 
in the case of those zocecia which are not closed by a diaphragm. 
Lower in the stem the tubular mouths are, in most cases, lost ; 
the zocecium is closed by an oblique diaphragm, and no poly- 
pide is present. The internode is then a flattened structure, 
in which the apertures of the zoccia project even less than in 
C. denticulata. 

In an interesting abnormality found in August, two promi- 
nent tubular apertures occurred, side by side; the extra 
zocecium being in the position which would normally have been 
occupied by a basis rami. 

Busk1! has made rather a point of the fact thatin C. conferta 
the free tubular portion of the zocecium is not a mere produc- 
tion of the peristome, but presents “ the same puncturation as 
is seen on the rest of the cell.” This is certainly the case in 
C. ramosa and in C. aculeata, and to a less extent in C. 
denticulata. C. eburnea is, in fact, the only species I have 
examined in which the tubular portion is usually merely a thin 
prolongation of the peristome. 

The average position of the ovicell is somewhat higher than 
in C. aculeata; but that it varies greatly in position is ob- 
vious from the formula— 

(440.419 +r tortor tre) + 

=(138+ 00.494 r+r3tertrs)+ 
It has never been noted to be lower than 4th in the internode ; 
but it is seldom so low as this. The branch may be jointed 
above the ovicell, although most commonly the ovicell is borne 
by a terminal internode, which usually possesses at least two 
branches. When several branches are developed, two of them 
are usually developed not far above the ovicell, one on each 
side of the internode, whilst the other branches are developed 
from the lower parts of the internode. This is the case in 

1 ‘Catalogue .... Brit. Museum,’ part iti, p. 7. 


150 SIDNEY F. HARMER. 


fig. 11, and in both the above-cited formule in which the ovi- 
cell replaces z, and z, respectively. 

The joints of this species are yellow, or more rarely brown. 
They are never black. Rootlets are very freely developed from 
the base of the stem, and they may attain a great length. 
They usually originate rather low on the zocecia and from their 
lateral edges. As in other species, they become very firmly 
attached to stones and other objects, and form creeping stolons, 
from which (as well as from rootlets which are not attached in 
this way) fresh stems may originate. The colonies do not so 
often consist of a single main stem as in C. eburnea, It is 
frequently remarked that the longest and most branched parts 
of the colony are lateral branches, and not parts of the main 
stems. 

Ovicells—In C. ramosa (figs. 10, 11) the ovicells are consi- 
derably larger than in any of the other species (see figures, all of 
which are drawn to the same scale, and table of measurements 
on p. 159). They are regularly pear-shaped, their main axis 
being straight; they are much inflated above, their curvature 
diminishing gradually in all directions from their most pro- 
minent portion. The aperture is in the form of a distinct 
funnel-shaped tube, which is considerably smaller at its base 
than at its mouth; and the mouth of the funnel, the actual 
aperture of the ovicell, is more or less circular. In the shape 
of the aperture this species differs from all the other British 
forms. 

The tubular aperture is of course not present in incompletely 
developed ovicells: an account of the development of the ovi- 
cells will be given in a forthcoming paper. It must also be 
noted that the aperture is liable to be broken away in old ovi- 
cells, and that in many cases, where the ovicells or their con- 
tents are not normally developed, the tube itself is not formed. 
In normal and completely developed ovicells the shape of the 
aperture is, however, a perfectly characteristic and constant 
feature. 

C. aculeata (fig. 4), which in some other respects is so 
similar to C. ramosa, has a much smaller ovicell than that 


ON THE BRITISH SPECIES OF ORISIA. 151 


species (compare fig. 4 with fig.11).1_ Its shape is very charac- 
teristic, its most prominent portion being considerably nearer 
its distal end than in C. ramosa. From this point the ovicell 
slopes off very suddenly towards its aperture, and more gradu- 
ally towards its base, although this latter slope is steeper than 
in C.ramosa. The aperture is not borne on a distinct tube, 
but it lies in a characteristic position on the zocecium next 
above the ovicell, on the same side of the internode. This 
zocecium curves forwards round the back of the ovicell, the 
aperture of which is situated on it at the point where it makes 
its appearance above the ovicell. 

In C. eburnea (fig. 6) the ovicell is large—considerably 
larger than in C. aculeata. Since the base of the internode 
which bears it is distinctly curved inwards, the ovicell itself 
has the same curvature at its base, as is best seen when the 
ovicell is looked at from the side. The ovicell is well inflated, 
and slopes away more gradually from its most prominent point 
than in C.aculeata. The aperture is quite characteristic ; 
it is borne on a tube-like structure, distinctly broader at its 
base than at its free end, and instead of being circular, as in 
C. ramosa, it is transversely elongated, its lower border being 
often slightly convex towards the centre of the aperture. 

In C. denticulata (fig. 3) the ovicell is fairly large, and 
usually becomes level with the flat surface of the internode 
near its base, the distal portion of the ovicell being very pro- 
minent. The aperture is not situated on a well-developed 
tube ; it is not, however, on the surface of a zocecium, as in 
C. aculeata, but is situated between two zoccia, and it is 
very nearly sessile on the top of the ovicell, as was the case in 
C. aculeata. 

In all four species the aperture is connected with the top of 
the ovicell at the point where the latter joins the front surface 
of the internode. 

The importance of the form of the aperture appears to have 


1 Tt must, however, be pointed out that the ovicell of C. ramosa may be 
smaller, and that of C. aculeata larger, than in the particular specimens 


figured. 


152 SIDNEY F. HARMER. 


been almost completely overlooked by all previous writers on 
Crisia. The aperture is often said to be absent, as indeed it 
may be in injured or abnormal ovicells. As will be seen from 
a later communication, a normal ovicell is, according to my 
observations, never without an aperture from the time when 
the ovicell is first developed at the growing-point to the time 
when embryos are ready to escape from the ovicell. The cal- 
careous aperture is, however, throughout the development 
closed by a thin cuticular membrane, and the presence of this 
membrane sometimes makes it difficult to see the aperture in 
those cases in which this structure is not borne on a distinct 
tube. 

On breaking open an ovicell (fig. 10) it will be noticed that 
the aperture leads into a space partially separated from the 
rest of the ovicell by a valve-like structure of calcareous 
nature. This valve has very definite relations to the structures 
found in the interior of the ovicell, as will be described in my 
subsequent paper. It springs from the posterior wall of the 
ovicell, and passes obliquely forwards, being also attached to 
the lateral walls of the ovicell in such a way as to leave a more 
or less oval opening connecting the main cavity of the ovicell 
with the aperture of the latter. The valve is most developed 
at the back of the ovicell, and gradually dies away laterally as 
it passes to the front wall of the ovicell, where it no longer 
forms a distinct ridge. 

This valve is developed in all the four species which are 
specially discussed in this paper, but it appears to be less well 
developed in C. eburnea than in the other species. 


Note on C. cornuta, Linn., and C. geniculata, M.-Edw. 


Until quite recently I had devoted no particular attention 
to these forms, the specific identity of which appeared to be 
perfectly established by such statements as those of Smitt,! to 
the effect that they may both occur as branches of the same 
stem. But, having recently found some ovicells of C. geni- 
culata, I cannot help believing that the two forms are speci- 

1 « Ofvers.,’ &c., 1865, No. 2, p. 128. 


ON THE BRITISH SPECIES OF ORISIA. 153 


fically distinct, and a more careful examination of C. cornuta 
has convinced me that Smitt’s statement may be explained 
in such a way that it is unnecessary to follow him in his con- 
clusion. 

Even if the two forms are not really distinct, it appears to 
me worth while to call attention to what would then be an in- 
teresting case of a definite variation of the ovicells correlated 
with the presence or absence of spines on the zocecia. 

C. geniculata consists typically of a series of internodes, 
each of which is composed of a single zocecium ; from opposite 
sides of this zocecium arise a pair of branches which are not quite 
at the same level. An excellent figure of this form is given in 
Busk’s ‘ British Museum Catalogue’ (part 3), pl. i, fig. 2. On 
comparing this figure with fig. 7 on the same plate (representing 
C. cornuta), it will be seenthat C. cornutaexactly resembles 
C. geniculata as far as those zocecia which bear two branches 
are concerned; but that, as Busk points out (p. 3), one of the 
branches is usually replaced by a jointed spine. 

It is obvious that spines will be absent in C. cornuta if 
two branches are developed from each zoccium. Further, the 
spines are very readily broken off, and a close examination is 
then sometimes necessary to discover the small basis with which 
the spine articulates. From one or other of these causes I have 
several times observed branchesof normal coloniesof C. cornuta 
having a close resemblance to C. geniculata; and this may 
be the explanation of Smitt’s statement referred to above. 

In every case in which I have observed the ovicells—although 
I must add that I have not obtained many ovicells of C. geni- 
culata—lI have noticed the following characteristic differences 
between the two forms; a reference to Busk’s figs. 2 and 10 
(l. c., pl. i) shows that the forms examined by Busk were 
similar to those which I have myself found. Busk’s fig. 4 (C. 
geniculata) does not, however, quite agree with the specimens 
which I have examined. 

The ovicell of C. cornuta (fig. 9) is the basal and only 
member of its own internode; it bears a lateral brauch on each 
side, these branches originating at not exactly the same level. 


154 SIDNEY F. HARMER. 


After the branches have been given off, the ovicell becomes 
perfectly free, and is in this part considerably inflated. The 
tubular aperture arises near the back of the ovicell, and is 
usually bent somewhat backwards from its point of origin ; so 
that, in looking at the branch from its “front” surface, the 
base of the tubular aperture is nearer to the observer than its 
distal end. 

In C. geniculata, on the contrary, a common arrangement 
is as follows: —The basal member of the internode is an ordinary 
zoccium (figs. 7 and 8), which gives rise to the ovicell as the 
second member of the internode. Immediately above the 
ovicell is another zocecium, which gives off a lateral branch . 
near the level of the upper end of the ovicell. The basal 
zocecium itself gives off a branch on the opposite side to the 
ovicell. The internode may thus be represented as— 


¢ +0v.+1) 
ir r, (counting the ovicell as the basal member of its own side). 


The ovicell itself is distinctly smaller than in C. cornuta, and 
is not much inflated at its upper end. Its tubular aperture is 
most distinctly bent forwards from its base, sometimes at a 
very sharp angle, and the actual aperture is smaller than in C. 
cornuta. Moreover, the ovicell is aot free, asin the latter 
species ; the upper zocecium of the internode being closely 
attached to its back along the greater part of its course. This 
zocecium ultimately becomes free from the ovicell, and curves 
forwards above the upper end of the latter. 

In other cases the ovicell may be the third member of the 
internode, each of the two zocecia below it giving off a branch ; 
and two zocecia, each bearing a branch, may occur above the 
ovicell. The commonest arrangement seems to be either that 
given in the above formula, or the occurrence of three branch- 
bearing zocecia, one of which is below the ovicell and the other 
two above it (cf. Busk’s fig. 2). The ovicellis, in any case, not 
the lowest member of the internode, and one or two zoecia 
are always attached to its back. 

C. geniculata is a slenderer and more delicate form than 


ON THE BRITISH SPECIES OF ORISIA. 155 


C. cornuta, its zoecia being distinctly longer and thinner than 
in that species; and spines seem to be never developed. As 
already remarked, however, parts of the colonies of C. cornuta 
may be devoid of spines. 


Breeding Period and Occurrence of Species. 


The specimens from which the following statements are made 
have been received at various periods from February to the end 
of August. I have to offer my best thanks to those who have 
most kindly assisted me by supplying me with material; and 
especially to the staff of the Marine Biological Association, 
Prof. H. de Lacaze-Duthiers, and Mr. J. Sinel. 

The dominant species at Plymouth is certainly C. ramosa; 
although, strangely enough, I have not been able to obtain this 
form from any other place, except from a bottle found in the 
Morphological Laboratory at Cambridge. The contents of 
this bottle came either from the Channel Islands or from Arran ! 

At Plymouth, C. ramosa is found commonly at depths from 
4, to 80 fathoms. It is particularly fond of growing on stones, 
but is found on other objects—e. g. glass bottles, shells, red 
seaweeds, Cellaria, and sponges. When it grows in the last 
position it appears to be in danger of being killed by the sponge, 
which grows over its branches. The Crisia is, however, gene- 
rally able to keep pace with the growth of the sponge, so that 
only the basal parts of itscolonies are killed, or at least prevented 
from having functional polypides by the sponge. The speci- 
mens growing at 4—6 fathoms were usually much more luxu- 
riantly branched than the few specimens which I received 
from 20—80 fathoms; and ovicells were obtained only from 
those growing under the first set of conditions. 

C. eburnea is also common at Plymouth, but is almost 
always found on red seaweeds or on Sertularia. The restric- 
tion of various species of Crisia to particular seaweeds, &c., 
has been often noted by previous observers. 

Winther! has stated that, in the Danish forms of this species, 


1 G. Winther, “ Fortegnelse over de i Danmark hidtil fundne Hav-Bryozoer,” 
‘Naturh. Tidsskrift’ (Kjpbenhavn), 3 Raekke, vol. xi, 1877-8, p. 7. 


156 SIDNEY F. HARMER. 


the effects of the brackish water of the Baltic can be easily ob- 
served by comparing colonies found in different localities. 
Those which are nearest to the Baltic are said to have inter- 
nodes consisting typically of three zoccia; in those most 
exposed to the North Sea the internodes have seven zoccia ; 
and in colonies from intermediate localities they have five 
zocecia. I have not been able to observe any definite correla- 
tion between the character of the colony and the conditions 
under which it was growing. 

C. aculeata is less common at Plymouth than either of the 
preceding species; it was found on stones, red seaweeds, and 
sponges, usually from 4—5 fathoms. 

C. cornuta was fairly common, mostly on red seaweeds ; 
while C. denticulata was seldom found at Plymouth. 

By the kindness of Prof. de Lacaze-Duthiers [ received a 
large supply of Crisia from Roscoff in June. The species 
most common at Roscoff appear to be C. aculeata, C. denti- 
culata, and C. cornuta. C. geniculata was less common, 
and only a few fragments of C. eburnea were found. 

From Mr. J. Sinel I have received numerous specimens of 
C. denticulata and C. cornuta found at Jersey ; and a smaller 
supply of C. eburnea, C. geniculata,and C.aculeata, The 
Jersey specimens of C, denticulata were found between tide- 
marks, while Smitt? states that C. denticulata is pre-eminently 
a deep-water form. It is, however, probable that Smitt’s speci- 
mens did not really belong to this species. 

I have also obtained specimens of several species from 
Guernsey and the Scilly Islands. 

Smitt’s valuable contributions to our knowledge of the Poly- 
zoa have been devoted, so far as they concern the genus Crisia, 
to showing that the “ species” which have been distinguished 
in this genus are in reality ‘‘ forms” of a single species. 

In one of his later papers? Smitt remarks, speaking of the 
forms of Crisia discovered in the expedition to which his paper 

1 ¢Ofvers.,’ &c., 1865, No. 2, p. 138, 


2 Recensio syst. .... Bryozoorum .... Novaja Semlja, &.,” 
‘ Ofversigt. af-K. Vet.-Akad. Férhandlingar,’ 1878, No, 3, p. 12. 


ON THE BRITISH SPECIES OF ORISIA. 157 


refers, that he has united all these forms in a single species ; 
and adds, “ Auctores vero si sequi volumus, unamquamque fere 
coloniam speciem distinctam habebimus.” 

Although not in the least denying the difficulty of finding 
satisfactory specific characters other than those derived from 
the ovicells, the result of my investigation has been to con- 
vince me that Smitt has gone too far in denying the specific 
value of certain of the forms of Crisia. My results may 
possibly have to be explained by a suggestion which Smitt 
himself throws out, to the effect that although the series repre- 
sented by the various forms of Crisia living in different locali- 
ties is one in which practically none of the stages in the evolu- 
tion of the species have been lost, “vivit multis in locis altera 
vel altera forma tam constans, ut species bene distincta facile 
censeatur.”! Unfortunately, all the localities from which I 
have been able to obtain Crisia are comparatively close to one 
another ; but I have found no essential differences between the 
forms of the same species from different localities. 

Until it can be shown that any two or more of these forms 
can be developed as branches from the same stem, or as stems 
from the same rootlet, or at least that they can be produced as 
descendants of the same form, it appears to me that it will be 
impossible to deny to them the rank of species. 

C. eburnea begins to breed at Plymouth as early as 
February; ovicells are present in great numbers during 
March, April, and May. Towards the end of the latter month 
they disappear, and are not normally present on colonies 
found in the summer. March and April appear to be the 
months when ovicells are most common. 

C. ramosa commences to breed (at Plymouth) in April; a 
few of the colonies found at this period have young ovicells. 
In May young ovicells are very common ; and the breeding 
period continues from this time until August at any rate. 
Immature ovicells may be found even at this time, but they 
are then becoming uncommon. The breeding season is pro- 
bably at its height in May and June. 

1 © Ofvers.,’ &c., 1867, No. 6, p. 461. 


VOL. V, PART II. 15 


158 SIDNEY F. HARMER. 


C. aculeata.—A large proportion of the specimens found 
at Roscoff in June possessed numerous ovicells. At Plymouth 
ovicells were also found in April and May. The breeding 
season is probably much the same as in the last species. 

C. denticulata.—The only specimens obtained in which 
ovicells were common were found in Guernsey and Jersey in 
the summer (June to August), which may probably be regarded 
as the period at which the breeding season is at its height. 

C. cornuta.—The ovicells appear to be commonest in 
April and May. 

C. geniculata.—The only specimens in which I have found 
ovicells were obtained in the summer (June to August). I 
have not found this species at Plymouth. 


159 


ON THE BRITISH SPEOIES OF ORISIA. 


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160 SIDNEY F. HARMER. 


In A,B, and C of the above table the length of the internode 
is measured from joint to joint, or from joint to apex of 
branch if the internode is a terminal one. The “average 
length ”’ of the zocecia is obtained by multiplying the length of 
the internode by two, and dividing by the total number of 
zocecia. It is obvious that this does not give the total length 
of the zocecium, since the zocecia overlap one another; but an 
approximation to the distance from mouth to mouth of the 
zocecia is obtained. This gives a more accurate average than 
any single measurement of this distance would give, since the 
distance is variable in connection with the extent to which the 
tubular apertures of the zocecia are developed, and with other 
circumstances. For the purposes of this calculation an ovicell 
is counted as an ordinary zocecium. If the length of the inter- 
node of five zocecia shown in fig. 6 (C. eburnea) be compared 
with that of a corresponding number of units, beginning at the 
the base, of the ovicell-bearing internode in the same figure, it 
will be seen that the presence of the ovicell does not affect the 
result so much as would be expected at first sight, and the 
error due to counting the ovicell as a zocecium is further 
lessened by the fact that this structure is nearly always borne 
on an internode which consists of many zoccia. 

In D the length is measured from any point of an aperture 
to the corresponding point of the aperture of the next zocecium 
on the same side of the internode, and in making this measure- 
ment two zocecia whose tubular mouths were about equally 
developed were always chosen. 

E gives the total length of zocecia with well-developed tubular 
apertures from the point where their cavity disappears at their 
proximal end to the furthest point of their apertures, the measure- 
ments being made from transparent (Canada balsam) speci- 
mens. 

G is measured immediately above the aperture of a zocecium. 

H gives the length of the base with which a lateral branch 
articulates. 

I, The length of the ovicell is estimated by drawing an 
imaginary line joining the point where the zocecium next 


ON THE BRITISH SPECIES OF ORISIA. 161 


below the ovicell on the same side becomes free from the 
internode (if any tubular aperture is developed), with the corre- 
sponding point on the zocecium next above that zocecium on the 
other side of the internode. The “length” of the ovicell is 
the distance of the middle point of the line drawn as above to 
the uppermost point of the ovicell, exclusive of its tubular 
aperture, if any. 

This measurement, on the whole, gives the most constant 
results. The relation of the zocecia below the ovicell to the 
ovicell itself is very variable, and it is impossible to take one of 
these zocecia as a fixed point, a more definite result being 
obtained by taking two as described above. In C. eburnea, 
if the ovicell is the second member of an internode the 
imaginary line is drawn from the base of the tubular aperture 
of the first member of the internode in a direction parallel to 
that connecting the apertures of the upper pairs of zoccia in 
the internode (a method which usually gives more satisfactory 
results than might be supposed from fig. 6). 

The numbers given in the table do not profess to give the 
total limits within which a given part may vary, but the limits 
given will probably be found to include nearly all the variations 
which are observed in the ordinary forms of colonies. 

In cases where it seemed to me possible to define the normal 
size of any part, I have put this down as the “ average” size. 

An examination of this table shows that C. eburnea, 
C. aculeata, and C. ramosa form an almost continuous 
series, as Smitt indeed has stated. C. denticulata can hardly 
be confused with any of the other forms, amongst which 
C. eburnea is the one that resembles it the most. 

It will be seen that in every single measurement given 
C. ramosa is the largest of the four species, although in the 
size of the entire colony C. denticulata surpasses it. In 
many of the measurements, however, the upper limit of 
C. aculeata overlaps the lower limit of C. ramosa. As 
these are the two species which most closely resemble one 
another, and which are probably very closely allied to one 
another, it seems to me that it is not possible, in all cases, to 


162 SIDNEY F. HARMER. 


distinguish between a colony of C. aculeata without spines 
and a small variety of C. ramosa unless ovicells are present. 

C. ramosa further appears to me to be much the most 
variable of all the species I have examined, while C. eburnea, 
and, next to this, C. denticulata, are the least variable. The 
greater variability of C. ramosa comes out perfectly clearly by 
subtracting the minimum from the maximum measurements 
given in the table, and comparing together the results thus 
obtained for the different species. If this be done for D—J, it 
will be found that, in every case except F (in which the limits 
are the same for C. ramosa and C. denticulata), the greater 
variability of C. ramosa comes out, and usually with striking 
distinctness. 

It will be noticed that the largest variations are in the length 
of the zoccia, and, correlated with this, in the size of the 
ovicells. But though the ovicells are thus by no means exempt 
from variation, their principal specific character (the shape of 
their aperture) is retained throughout without material alte- 
ration. 

The fact that a colony of C. eburnea, on which some 
unusually small ovicells were present, has been taken into 
account in the table, makes these structures appear much 
more variable than they are in normal cases. 


ON THE BRITISH SPEOIES OF ORISIA. 163 


EXPLANATION OF PLATE XI, 


Illustrating Mr. Sidney F. Harmer’s paper “On the British 
Species of Crisia.” 


(All the figures were drawn with a camera lucida under a Zeiss a objective, 
and were subsequently reduced 24% diameters.) 


Fie. 1.—C. denticulata—Young internode, with growing-point, seen 
from the back (Canada balsam preparation). 


Fie. 2.—C. denticulata.—lIllustrating the relations of an even-numbered 
internode (pp. 129, 130). 


Fie. 3.—C. denticulata.—Ovicell (p. 151, &c.). 
Fie. 4.—C. aculeata.—Ovicell (p. 150, &c.). 
Fie. 5.—C. eburnea.—Abnormality (p. 140). 


Fic. 6.—C. eburnea.—Ovicell (p. 151, &c.). The internode which bears 
the ovicell has two branches, an unusual arrangement. 


Fic. 7.—C. geniculata.—Internode with ovicell ; back view (p. 154). 


Fic. 8.—C. geniculata.—Another ovicell, seen from the front (p. 154). 
Greatest diameter of ovicell = ‘208 mm. 


Fic. 9.—C. cornuta.—Ovicell (p. 153). 

Fre. 10.—C. ramosa.—Ovicell broken open to show the valve (p. 152). 
Fig. 11.—C. ramosa.—Branch with ovicell (pp. 145, 150, &.). 

Fic. 12.—C. ramosa.— Suppressed” ovicell (p. 147). 


Fie. 13.—C. ramosa.—Internode which has abnormally developed four 
ovicells (p. 148). 


Studies M.L. Vol.V. Pl. XI. 


F. Huth, Lith? Edin® 


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ON A NEW SPECIES OF PHYMOSOMA. 165 


On a New Species of Phymosoma, with a Sy- 
nopsis of the Genus and some Account of 
its Geographical Distribution. 


By 
Arthur E, Shipley, M.A., F.L.S., 


Fellow and Lecturer of Christ’s College, Cambridge, and Demonstrator of 
Comparative Anatomy in the University. 


With Plate XII. 


Durine a visit to the Bahama Islands in 1887, Professor 
Weldon made an excursion to the neighbouring island of 
Bimini. Whilst investigating the fauna of the lagoon in that 
island he came across a few specimens of what appeared to him 
to be a new species of Phymosoma. One or two of these he 
dissected on the spot; the remaining three he brought to 
England, and was good enough to give them to me for descrip- 
tion at the time when he handed over to me his specimens of 
Phymosoma varians which form the subject of a previous 
memoir. 

T have divided this paper into the following sections: 

(i) A general description of the new species. 
(ii) A detailed description of those organs which differ 
markedly from the similar organs in Ph. varians. 

(iii) A synopsis of the genus. 

(iv) A short account of the geographical distribution of the 
genus. 


VOL. V, PART II. 16 


166 ARTHUR E. SHIPLEY. 


Part I. 
Genus Phymosoma. 
Phymosoma Weldonii, n. sp. 


The length of the body is 3°5 cm. in the largest specimen, 
3°25 cm. in the second, and 3 cm. in the smallest. The greatest 
width is 1 cm. At the base of the introvert, which was in each 
specimen retracted, the width is 2mm. The body has a plump 
appearance and is slightly curved (fig. 1). 

The ground colour of the preserved specimens is light buff, 
which is modified by the presence of dark brown papille ; 
these are so numerous as to give the animal as a whole a dark 
brown colour. The papille are of two kinds (figs. 2 and 38). 

No hooks or traces of hooks can be detected on the introvert. 

The mouth is surrounded by a vascular lower lip, which in 
the dorsal middle line is continuous with the outer limbs of the 
lophophore. The latter structure is in the shape of a double 
horseshoe, the outer semicircle of tentacles corresponding to 
the lophophore of Ph. varians. In the ventral middle line 
this outer limb is bent dorsalwards, and thus the second horse- 
shoe is produced (fig.5). The lophophore bears a great number 
of long tentacles, seventy or eighty (figs. 5 and 8). 

Behind the head is a well-developed collar, pigmented on the 
anterior surface (fig. 5). 

The alimentary canal is tightly coiled, the number of twists 
being twelve or thirteen (fig. 4). It is supported by a well- 
developed spindle-muscle, which passes up the axis of the coil, 
and is attached at one end to the longitudinal muscles of the 
body-wall in the neighbourhood of the anus, and at the other 
to the posterior end of the body-wall. The anus is situated 
at the line of junction of the two kinds of papille. 

The longitudinal muscles are arranged in ten or twelve 
bundles in the anterior half of the body ; in the middle of the 
body there are about twice that number, as each bundle splits 
into two. These fuse together again at the posterior end of 
the body. At the base of the introvert the usual inversion of 


ON A NEW SPECIES OF PHYMOSOMA. 167 


layers occurs, the longitudinal muscles fusing into a continuous 
sheath, the circular muscles becoming broken up into bundles. 

The retractor muscles are two in number, a right and a left ; 
they arise about the level of the junction of the anterior two 
thirds with the posterior third of the body. They embrace the 
cesophagus, forming a semicircular band of muscle-fibres which 
are wanting only in the dorsal middle line where the heart lies. 

The heart is provided with very numerous cxcal diverticula 
(figs. 4 and 7). 

The external aperture of the kidneys lies on a level a little 
behind that of the anus. 

Habitat: the lagoon, Bimini Island, the Bahamas. 


Part IT. 
The Papille. 

The papille of the skin are of two kinds, those on the body 
and those on the introvert. In the middle of the trunk the 
papille have an oblong outline, and are arranged in very 
regular rings (figs. 1 and 3) ; near the posterior end of the body, 
and also at the base of the introvert, the papille are so crowded 
together as to lose their rectangular outline. These papille 
are of a dark brown colour, and in those regions where they are 
crowded together the buff colour of the rest of the skin is 
completely obliterated. The trunk papille form only low 
elevations above the general level of the skin; each has a 
central pore, surrounded by a number of brown horny plates, 
which are modifications of the cuticle. These plates show a 
faintly laminated structure; they are represented in section in 
figs. 11 and 12. 

Between these brown plates are placed a number of deeply 
pigmented granules of a dark brown, almost black colour. 
These give the dark brown colour to the papille (figs. 9 and 12). 
Neither the plates nor the pigment granules show any trace of 
being connected with any special cells ; they seem to be modifi- 
cations of the cuticle. The papille, like those of Ph. varians, 
are formed by the ectoderm-cells rising up afid invaginating to 
form a double cup. The outer wall of the cup is formed by 


168 ARTHUR EH. SHIPLEY. 


ectodermal cells which have kept their ordinary character, and 
the inner wall is composed of a few cells of enormous size, 
which all but obliterate the cavity of the cup. These cells are 
wedge-shaped, and their broader ends are crowded with small 
spherical concretions, which do not dissolve in alcohol, 
chloroform, or benzine. Towards their outer, narrower ends 
these cells become free from these concretions and stain 
uniformly, or else they contain from two to five or six large 
star-shaped aggregations of crystals (fig. 9), Nothing like 
these were seen in the papille of Ph. varians. 

The papille on the introvert stand out much farther from 
the level of the skin than those of the trunk (fig. 2). They are 
conical in shape, with a narrow basis. At their apex is a pore, 
and microscopic sections show that this is surrounded by a 
number of minute horny plates similar to those in the papille 
of the trunk, though much smaller, and not visible like the 
latter on the surface view. No crystals were found in 
the papille of the introvert, but the large wedge-shaped cells 
were in other respects similar to those described in the trunk 
papille. 

The Head. 

The head is represented diagrammatically in fig. 5. Part 
of the outer limb of the double horseshoe-shaped lophophore, 
involving eight or ten tentacles, has been cut out in order to 
show the pigmented region in the hollow of the original lopho- 
phore, and to display more clearly the arrangement of the 
tentacles. The thin transparent collar is extended over the 
head, a condition in which it is usually found when the intro- 
vert is retracted. The crescentiform mouth is shown sur- 
rounded by the lower lip, and at the base of the pigmented re- 
gion on the dorsal side lies the brain, directly continuous at 
each side with the epidermis. 

The tentacles are very numerous, seventy to ninety. Like 
those of Phymosoma varians, they are roughly triangular 
in section. One side, that directed towards the mouth, is 
grooved, and the groove is lined with cilia; the grooves of the 
various tentacles tend to fuse together near their lower ends, 


ON A NEW SPECIES OF PHYMOSOMA. 169 


and are directly continuous with the ciliated grooves on the 
wall of the cesophagus (fig. 8). A nerve runs along the base of 
the groove, and on each side of the nerve is a blood-vessel ; the 
third blood-vessel occupies the angle opposite the side bearing 
the groove: all these three vessels anastomose occasionally, and 
communicate below with a large blood-sinus at their base. 

In the diagram the plane of the tentacular crown is too flat ; 
instead of being at right angles to the long axis of the body it 
should be raised up, and in a manner overhanging the mouth: 
in other respects the figure represents the disposition of the 
parts, although rather diagrammatically. 

The sides of the tentacles which are directed away from the 
mouth are deeply pigmented, and the pigment is continued 
into a hollow at their base (figs. 5 and 8). This hollow lies 
partly between the two horseshoes of the tentacles, and is 
therefore itself horseshoe-shaped ; at its dorsal end the depres- 
sion becomes deeper, and lodges the brain. 

The most important difference between the tentacles of Ph. 
Weldonii and Ph. varians lies in the absence of the rows of 
those skeletal cells which formed so interesting a feature of 
the latter species. Their place is occupied by a well-developed 
fibrous connective tissue, which passes down into the base of the 
lophophore, and is then continuous with the connective tissue 
which surrounds the cesophagus, and which serves as a point 
of attachment to the retractor muscles. The lower lip is also 
devoid of any skeletal structures; it is, however, very vascular ; 
its inner surface is ciliated, the cilia being continued down the 
cesophagus ; its outer surface is pigmented. 

The area between the lower lip and the collar, as well as 
the inner surface of the latter, is also pigmented, although it 
has not been possible to represent this in the diagram. This 
continuous lining of pigment ceases at the edge of the collar ; 
its outer surface is not pigmented. The collar is represented 
in fig. 5 completely expanded, and covering in the head ; it is 
usually found in this condition when the introvert is retracted. 
It would be interesting to know whether it is ever expanded 
in this way when the head is extended during life. I have 


170 ARTHUR E. SHIPLEY. 


never seen it in this condition in those specimens of the un- 
armed Gephyrea which I have been able to examine alive. 
The absence of hooks on the introvert is a marked feature of 
this species of Phymosoma. Only five other species of the 
genus are devoid of these characteristic chitinous structures, 


The Vascular System. 


The vascular system of the unarmed Gephyrea consists of a 
closed space which has no capillaries in connection with it. 
The system is distributed in the various parts of the head, and 
its chief function would seem to be that of distending the ten- 
tacles and lower lip. In the tentacular blood-vessels the blood 
is separated from the surrounding water by a thin layer of 
tissue, and it is very probable that it becomes aérated during 
its passage through these organs. Its function as a carrier of 
oxygen cannot be of very great importance, since the system 
is entirely confined to one small part of the body. Probably 
those organs outside the head are dependent for their aération 
on the corpuscles in the perivisceral fluid, though it is not easy 
to see where these can get their supply of oxygen and elimi- 
nate their waste matter. 

The large vessel which lies on the dorsal surface of the 
cesophagus, and which is usually known as the heart, acts as a 
reservoir into which the blood retires when the tentacles are 
retracted (figs. 4 and 7). In Ph. varians, where there were 
few tentacles, the heart was a straight blind sac about ‘5 cm. 
long, extending along the dorsal side of the cesophagus ; but in 
Ph. Weldonii the number of tentacles is much greater, and 
the reservoir is correspondingly increased. The heart is much 
longer, being continued along the dorsal side of the cesophagus 
for a centimetre or two, and thus becoming involved in the 
twisting of the alimentary canal (fig. 4). Its capacity is also 
much increased by numerous small diverticula, which project 
as finger-like processes, and give the heart a very characteristic 
appearance. The walls of the heart and its diverticula are 
thin, with few muscle-fibres in its substance. Similar diver- 
ticula occur in the species Ph, antillarum, Ph. pelma, and 


ON A NEW SPECIES OF PHYMOSOMA. 171 


Ph. asser; and Ph. nigrescens has smaller diverticula of the 
same kind. 

The corpuscles contained in this closed system are of two 
kinds—large clear cells with a well-developed outline, a well- 
stained nucleus which lies at one side of the cell, and apparently 
no cell-contents ; the other corpuscles are smaller, with a proto- 
plasmic body which stains well, and a nucleus in the centre. 

In addition to the fluid of this closed system of spaces, the 
general fluid of the body-cavity contains corpuscles and the ova 
or sperm morule. 


The Brain. 


The nervous system has the same arrangement of nerve- 
fibres and ganglion-cells as that which I described in Ph. 
varians. The brain occupies the same relative position, 
situated at the dorsal side of the lophophore at the base of aslight 
depression. This depression is much smaller than the similar one 
in Ph. varians; its area being encroached upon by the bend- 
ing back of the tentacular crown to form the inner horseshoe, 
the space is thus rendered rather slit-like and slightly curved 
(figs. 5and 8). The depression is lined by a curiously crumpled 
and deeply pigmented epidermis, with which the brain is in 
direct continuity in two places. The shape of the brain is 
different from that of the other species, and this difference 
corresponds with the alteration in shape of the pigmented area 
in which it lies. It is bilobed, but the grooves between the 
lobes are very slight. Each lobe of the brain is smaller in 
transverse section than those of Ph. varians; on the other 
hand, their long axis is much longer, so that each lobe is slimmer 
and more elongated. The narrow outer end of the lobe bifur- 
cates into two stout nerves, one of which passes round on each 
side in the connective tissue surrounding the walls of the 
esophagus, and fuses with the similar one of the other side to 
form the ventral nerve-cord. The other passes up into the 
lophophore in the middle dorsal line, and then turns outwards 
and runs along the base of the tentacles, giving off a branch to 
each. ‘There is a second lophophoral pair of nerves of small 


172 ARTHUR 3B. SHIPLEY. 


size, which run into the outer end of the crown of tentacles 
where it fuses with the dorsal ends of the lower lip. I could 
not make out very satisfactorily whether these nerves supply 
branches to the tentacles of this region, but I am inclined to 
think that they do. 

A pair of very minute nerves leave the brain close to the 
middle line ; these run to the pigmented tissue of the depres- 
sion at the bottom of which the brain lies. At about the point 
of the greatest circumference of each lobe the ganglion-cells 
of the brain are in continuity with this pigmented epithelium, 
and at one spot this epithelium is involuted into the substance 
of the brain, its cells become enlarged and crowded with pig- 
ment granules of dense black. The lumen of the involution is 
practically occluded; these pigmented involutions form the 
eyes. 

The ganglion-cells form a cap which wraps round the fibres 
except for about a quarter of the circumference, where they 
come to the surface; this fibrous portion is ventral and posterior 
in position. The whole brain is half surrounded by the large 
blood-sinus into which the dorsal vessel opens anteriorly, and 
which gives off the vessels to the tentacles. 

The arrangement of the fibres and ganglion-cells in the 
ventral cord is the same as that of Ph. varians (fig. 10). 

The remaining organs of Ph. Weldonii resemble those of 
Ph. varians so closely as to render any detailed account 
superfluous. The nephridia are two in number (figs. 4 and 7). 
The relationship of their external and ciliated internal open- 
ings is shown in fig. 11. The outer wall of the nephridium is, 
as this figure shows, continuous with the body-wall, but this is 
for a short distance only. The organ soon becomes free, and 
stretches back to the end of the body, and then in its most 
extended condition may be bent back again. 

In its histological details the structure of the nephridium is 
similar to that which I described in my former paper. The 
inner surface is broken up into a series of crypts which are 
lined by large glandular cells. Outside these is a meshwork 
of muscle-fibres which I have endeavoured to depict in fig. 6, 


ON A NEW SPECIES OF PHYMOSOMA. 173 


and covering these again is the layer of flat peritoneal epi- 
thelium. 

The very curious mode by which the glandular cells of the 
nephridium in Ph. varians excrete their waste products, by 
casting off vesicles into the lumen of the organ, is repeated in 
this species. These vesicles contain granules. Their method 
of formation and of breaking off from the free end of the 
secreting cell is paralleled by the secreting cells which line the 
mammary glands of Mammalia, or by the cells which give 
rise to the secretion of the liver in Astacus. 

The generative organs consist of a band of modified peri- 
toneal epithelium which lies at the base of the retractor 
muscles. The generative products split off into the peritoneal 
cavity. 


Parr III. 
A Synopsis of the Genus Phymosoma. 


In the admirable systematic monograph! on the Sipunculide, 
in which Prof. Selenka, with the assistance of Dr. de Man and 
Dr. Biilow, published the results of their work on the Gephyrea 
collected by Prof. Semper in the Philippine Archipelago, a 
synoptical table of the genus Phymosoma, which included at 
that time eighteen species, is published. Since 1883, the year 
of the publication of the above-mentioned work, nine new 
species have been added to the genns. Eight of these are due 
to the energy of Dr. Sluiter,? who has done so much to increase 
our knowledge of the marine fauna of the Malay Archipelago. 
The ninth was found by Prof. Weldon in the Bahamas. It will 
thus be seen that since the publication of Selenka’s synopsis 
the number of described species of Phy mos oma has increased 
by half the original. I have, therefore, prepared the fol- 
lowing table, which is largely founded on Selenka’s, but 
which includes those new species of the genus which have been 


described since the publication of his monograph. 

1 In a note in my previous paper on Ph. varians this work was inad- 
vertently attributed to Prof. Spengel. 

2 ¢ Beitrage zu der Kenntniss der Gephyreén aus dem Malayischen Archipel,’ 
von Dr. C. Ph. Sluiter. 


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yuosead sxyooyy 


176 ARTHUR E. SHIPLEY. 


Part IV. 
Geographical Distribution. 


The genus Phy mosoma contains considerably more species 
than any other genus of the unarmed Gephyreans with the 
exception of Phascolosoma. Including the new species 
described by Sluiter, and by Selenka in his report upon the 
Gephyreacollected by the “ Challenger,” the former genus com- 
prises twenty-seven species, the latter twenty-five. Next to 
these comes Aspidosiphon with seventeen, and Sipunculus 
with sixteen. 

Of the twenty-seven speciesof Phymosomawhich have been 
described, seventeen are found in the Malay Archipelago ; of 
these seventeen, thirteen have been found there alone, whilst 
four have a wider distribution. Three species are found in the 
West Indies, of which two are found nowhere else ; five species 
in the Red Sea, of which two are peculiar ; and four species in 
the Mauritius, all of which occur elsewhere. 

It will thus be seen that the Malay Archipelago is the 
headquarters of the genus, nearly two thirds of the number of 
species composing the genus being found there, and nearly 
one half of the whole number being confined to that region. 
This is very possibly partly due to the fact that this region of the 
world is much visited by collectors, and its shore fauna is pro- 
bably better known than that of any other considerable area 
within the tropics. On the other hand, the great predominance 
of the species in these seas is undoubtedly striking. 

The following four species have a somewhat remarkable 
distribution : 

(i) Ph. japonicum.—This extends along the Japanese 
coast, and is again met with in the Fiji Islands and off the 
coast of Australia. It was one of the two species brought 
home by the “Challenger,” and was found by that expedition at 
Port Jackson. It thus has a considerable north and south dis- 
tribution. On the other side of the Pacific we find another 
species,— 


ON A NEW SPEOIES OF PHYMOSOMA. 177 


(ii) Ph. Agassizii, which, while it occurs as far north as 
the former species, reaches very much farther south. This 
species stretches from Vancouver’s Island down the west coast 
of America as far as Puntarenas in the Straits of Magellan, 
and has been found at the intermediate points of San Francisco 
and Panama. The third species, with a somewhat unusual 
distribution, is— 

(in) Ph. Lovénii, which is found only in the Bergen 
Fiord. This is still further removed from the equator than the 
southernmost point reached by Ph. Agassizii, but it must be 
remembered that the Gulf Stream keeps the water on the 
west coast of Norway comparatively warm. Finally, we find 
one species, 

(iv) Ph. granulatum, inhabiting the Mediterranean, and 
stretching out into the Atlantic as far as the Azores. 

If we except the four species whose geographical distribu- 
tion is described above, the whole genus is confined, with the 
exception of Ph. antillarum, which extends to Puntarenas, 
between the tropics, or only ventures just beyond them. 

The species just mentioned has a somewhat curious distri- 
bution; it occurs all round the West Indian Islands, as well as 
at Surinam and Puerto Cabello; it then crosses over the 
Isthmus of Panama, and is found along the coast of Chili and 
Puntarenas. Another West Indian species, Ph. pectinatum, 
is found on the west coast of America, and turns up again at 
Mauritius, but has not been described from anywhere else. 
Finally, Ph. pacificum has a wide range, stretching from the 
Red Sea by the Mauritius and India to the Malay Archipelago, 
and thence to the Philippines and the Fiji Islands; and Ph. 
scolops has a very similar range, occurring in the Red Sea, at 
Singapore, at the Philippines, and also off the Mozambique 
coast. ; 

With regard to the bathymetrical distribution of the members 
of this genus there is little to say ; they all live in shallow water, 
and the greatest depth which I have seen mentioned in con- 
nection with them is fifty fathoms. _ 

It is not possible to arrive at any very satisfactory results 


178 ARTHUR E. SHIPLEY. 


from the scanty material at our disposal, with reference to the 
geographical distribution of this Gephyrean. Nevertheless, so 
little has been done with regard to the distribution of the 
lower marine invertebrates, that it seemed to me to be worth 
while to put together what is known about the occurrence in 
space of the genus I have been lately working at. The most 
striking deductions from the facts before us are—(i) the import- 
ance of the Malay Archipelago as the headquarters of the 
genus, but this is possibly more apparent than real; (ii) the 
restriction, with few exceptions, of the genus to tropical seas ; 
and (iii) their preference for shallow waters. The last two 
generalisations are obviously connected with the fact that the 
animals only flourish in comparatively warm water. 

In conclusion, attention may be drawn to the association of 
these animals with coral islands. This may be accidental, and 
due to conditions of temperature only ; but, on the other hand, 
several species make their homes in tubular holes burrowed 
out in the soft coral rock. 


Tue MorrHotocicaL LaBoratory ; 
CampBriper, July, 1890. 


ON A NEW SPECIES OF PHYMOSOMA. 179 


DESCRIPTION OF PLATE XII, 


Illustrating Mr. Arthur E. Shipley’s paper ‘On a New Species 
of Phymosoma, with a Synopsis of the Genus, and some 
Account of its Geographical Distribution.” 


Fic. 1.—A view of Phymosoma Weldonii, enlarged 3 diameters. The 
introvert with its conical papille is slightly protruded. 


Fie, 2.—A conical papilla from the introvert, seen from the side and from 
above. 


Fie. 3.—Some of the depressed oblong papille from the trunk, enlarged to 
show the pore and the cuticular plates. 


Fic. 4.—A view of the animal cut open just to the right of the middle 
ventral line. The introvert is retracted. The ventral nerve-cord is seen 
running up the introvert and back close to the cut edge; the right and 
left retractor muscles and the two kidneys lie on each side of the coiled intes- 
tine. The kidneys are much elongated, and show irregular swellings. The 
heart with its diverticula is seen in places. The longitudinal muscles of the 
body-wall are not indicated. Enlarged 24 diameters. 

Fic. 5.—A diagrammatic view of the head of Phymosoma Weldonii. 
The collar is completely expanded, and surrounds the head. Part of the outer 
limb of the lophophore involving about ten teutacles has been removed in order 
to show the pigmented area within tie lophophore, and the inner circlet of ten- 
tacles. The lower lip surrounds the mouth, and at its dorsal end fuses with 
the end of the lophophore. The dorsal side of the tentacles, which are fully 
expanded, is pigmented. The lophophore is represented too flat; it should 
be oblique and overhanging the mouth. 

Fie. 6.—A_ surface view of a piece of the wall of the kidney, showing the 
glandular areas—crypts—separated from one another by muscle-fibres. 

Fic. 7.—An enlarged view of the end of the coiled intestine, with the heart 
partially dissected out. The spindle muscle running up the axis of the coil is 
shown near its termination by the anus. The anterior ends of the kidneys are 
seen right and left. 

Fic. 8.—A transverse section through the base of the lophophore, showing 
the lower lip, the mouth, some isolated tentacles, the fused bases of others, 
and their blood-vessels and nerves. The fusion of the dorsal ends of the 
lower lip and of the lophophore, and the distribution of the pigmented and 
ciliated epithelia are seen. 

Fig. 9.—A transverse section through a trunk papilla. This shows some 
circular muscle-fibres, the ectodermic epithelium passing into the gigantic 


180 ARTHUR E. SHIPLEY. 


excretory cells. Some of the latter contain crystals, others Jarge granules. 
Only that part of the cuticle which is modified to form the horny plates is 
shown. Between the plates and round the pore are pigment granules. 


Fig. 10.—A transverse section through the skin of the introvert and the 
ventral nerve-cord. The introvert is retracted so that the outer surface is 
concave, the inner convex. The section shows the conical papille, the thick 
cuticle with pigment granules, the single layer of ectoderm-cells, the continuous 
layer of circular and longitudinal wuscles, the latter broken only for the 
insertion of the mesentery supporting the ventral nerve-cord; and the peri- 
toneal epithelium. The nerve-cord shows the dorsal disposition of the nerve- 
fibres and the ventral ganglion-cells. Some of the secondary nerves are cut 
as they leave the cord and traverse the mesentery. 


_ Fic. 11.—A transverse section through both the external and internal 
openings of the nephridium. ‘The structure of the skin is shown, and four of 
the circular nerves arising from the ventral nerve-cord are seen. The outer 
wall of the nephridium is fused with the integument, but becomes free 
posteriorly. The section does not show the whole of either opening, as they 
do not lie wholly in one plane. 


Fic. 12.—A section through the integument. 


Mr. Wilson, of the Cambridge Scientific Instrument Company, has drawn 
Figs. 1 and 5, and Figs. 4 and 7 are drawn from sketches made by Prof. 
Weldon in Bimini. 


jeer 


Fig. 2 
yee 


SIDE VIEW. UPPER VIEW. 


Introvert 


UPPER VIEW. 


Fig. 1 
: fig. 6. 


Werscudar 
network. 


Introvert 


Srdestine 


Shipley del 


Studies M.L. Vol.V. Pl. XU. 


Nerve cora.. 


Nephavadiar, 


Vascular 
= diverted une 


__.-- Position of 
Head 


Mh. .-- Retractcr. 


Positiom of - 
Bram. 


R ----/ndesttiie, 


Nerve 


: Blood-vessels 


\ _ Ten tacles. 


f ei (e eee Ver. nerve cord. 


; 
_- Werves. 


F. Huth, Lith? Edin® 


THE MEDUSZ OF MILLEPORA MURRAYI 
AND THE GONOPHORES OF ALLOPORA 
AND DISTICHOPORA 


BY 


SYDNEY J. HICKSON, M.A., DSc. &., 
Fellow of Downing College, Cambridge. 


With Plates XIII and XIV. 


I. THe Mepus# or MILLEPORA MURRAYI. 


In 1884, Quelch (11), while examining the structure of the 
hard parts of a new species of Millepora (M. murrayi), dis- 
covered a number of small cavities which he supposed to be 
the receptacles of the ova or embryos like the ampulle of the 
Stylasteride. 

Professor Haddon has recently placed in my bands some 
excellently preserved specimens of a species of Millepora 
that he collected on the reefs of one of the islands in Torres 
Straits. This species seems to be closely allied to Quelch’s 
Millepora murrayi, but the identification is a matter of 
some difficulty, as the pieces at my disposal are small. 

On making a series of sections through a portion of a decal- 
cified branch I discovered a number of medusiform structures, 
each bearing a large saucer-shaped spermarium. They are 
situated immediately beneath the surface, and covered by an 
operculum of modified ectoderm cells. 

Sections made by von Koch’s method of grinding hard and 
soft parts together in solid Canada balsam show further that 

6 


182 SYDNEY J. HICKSON. 


these meduse exactly fit into the ampullar cavities of the 
skeleton, and form the only explanation of their presence. 
The eggs of this species are, as in Millepora plicata (6), 
very small and contain no yolk, and I have seen no embryos 
and no parasites that could cause or fit into these cavities, 
Quelch’s ampulle, then, are the cavities that contain male 
medusz. 

The Structure of the Meduse.—The meduse may be 
found in all stages of development in the different parts of the 
same branch. They are very irregularly distributed, and it is 
difficult at present for me to give any hints to guide natural- 
ists in the search for them. They are never found, so far as 
my experience goes, close to the free extremities of the 
branches. In my specimens they were found in greatest 
abundance at a distance of three-quarters of an inch to one 
inch from the free extremity, but a few specimens were found 
quite close to the attached base of the colony. Some branches 
appear to be devoid of them. 

All the stages of development may be found with care and 
patience, but the stage represented in fig. 10 is the most fre- 
quent in my preparations. 

A central MANUBRIUM (Jfan.) hangs in the sub-umbrella 
cavity bearing the large spermarium (Sperm.). It is composed 
of irregular endodermal cells, and contains a considerable cavity 
continuous with the cavity of the subjacent ccenosarcal canals, 

The SPERMARIUM appears to be double in section, but is 
really saucer-shaped. It contains a large number of spherical 
spermoblasts lying in a homogeneous fluid (?). It is covered by 
a very thin coat of flattened ectoderm cells continuous with the 
inner ectodermic lining of the umbrella. 

The UMBRELLA is composed of three layers: a median layer 
of solid endoderm continuous with the endoderm of the manu- 
brium, and an inner and outer sheath of ectoderm continuous 
with one another at the free rim of the umbrella. 

The inner sheath of ectoderm is, as mentioned above, con- 
tinuous at its proximal side with the thin coat of ectoderm 
covering the spermarium. The outer sheath is continuous 


THE MEDUSH OF MILLEPORA MURRAYI. 183 


with a sheath of ectoderm (Gon.) lining the cavity of the 
ampulla; and this again is continuous with the superficial 
ectoderm of the colony. , 

At the margin of the umbrella both ectoderm and endoderm 
are thicker than they are elsewhere, and the medusa presents 
in consequence a thickened rim at its free border. There are 
no radial or ring canals. In meduse at this stage no cavity 
is apparent between the outer wall of the umbrella and the 
ectoderm lining the ampulla. 

Above the codonostome (ie. mouth of the umbrella) there 
is an operculum (op.) of flattened ectoderm cells continuous 
with the superficial ectoderm and the ectoderm lining the 
cavity of the ampulla, which completely closes the gonangium. 

Different Forms of the Medusa—The spermarium 
varies immensely in size.- Sometimes it is simply a thickened 
ring round the manubrium, sometimes it nearly fills the cavity 
of the umbrella. In consequence perhaps of this variation in 
the size of the spermarium, the appearance of the manubrium 
varies. In fig. 10 the manubrium is a large well-developed 
structure with a considerable lumen. In fig. 9, which repre- 
sents a younger stage, there is no manubrium at all apparent, 
but the spermarium simply rests on an irregular mass of vacuo- 
lated endoderm cells. Many intermediate conditions between 
these two extremes may be observed. Further, the condition 
of the endoderm of the manubrium presents many variations. 
In some cases the cell outlines are well marked, and the nuclei 
regular in position and spherical in shape. In other cases the 
endoderm is a loose vacuolated tissue in which no cell outlines 
can be distinguished, and the nuclei are irregular in shape and 
scattered through the spongy substance of the tissue. 

It is not my purpose to offer in this place any explanation 
of these appearances. I wish merely to call attention to them 
before passing on to other matters. 

Development of the Medusa. The medusa of Millepora 
is a transformed zooid. It is not a zooid specially modified 
from its first appearance to bear the spermarium, but an 
ordinary zooid of the colony changed into a medusa after the 

6—2 


184 SYDNEY J. HICKSON. 


migration of spermospheres into its ectoderm, and subsequent 
development there. 

The evidence that supports this statement rests upon a 
number of observed facts, that for convenience’ sake may be 
arranged under the following heads: 

1. The various stages in the transformation of the zooids 
into meduse that can be observed in sections of the decalcified 
corallum. 

2. The absence of any structure that can be compared to 
the ectodermic invagination, called the entocodon or glocken- 
kern, that characterises the early stages in the development of 
the medusa of the Hydroidea. 

3. The position of the meduse in the colony. 

4, The presence of large nematocysts in the superficial 
ectoderm above the younger forms of meduse. 

1. The most important of these, and the only one upon 
which much stress can be laid, is the first. The others afford 
the necessary confirmation. 

The earliest recognisable forms of the sperm mother-cells 
are found in the canals in the immediate neighbourhood of the 
zooids (Sperm. S,., fig. 1). They migrate from this position 
into the ectoderm of the zooids, where they collect together to 
form a spermarium. 

That the sperm mother-cells do actually migrate from the 
germinal epithelium into the zooids seems to me to admit of 
no doubt. The youngest stages of the germ-cells are never 
found in any part of the zooids, and the youngest stages of the 
zooids never bear either germ-cells or spermoblasts. These two 
observations prove, firstly, that the germ-cells do not arise 
in fully developed zooids ; and secondly, that new zooids or 
medusz are not formed at the localities in the canals where the 
germ-cells arise. They must, therefore, move from the position 
where they are first developed to the position they occupy in 
the zooid. * 

In a few cases I have seen two or three spermospheres 
(Sperm. 8,., fig. 1), or aggregations of spermospheres, lying 
separately in the ectoderm of the zooids, but in the majority 


THE MEDUSA OF MILLEPORA MURRAYI. 185 


of cases there is but a single cluster or aggregation (figs. 2, 3, 
and 4). The largest and most fully developed of these lie at 
the apex of the zooids (figs. 5, 6, and 7). 

The conclusions from these facts seem to be that the germ- 
cells developing in the canals until they reach the stage corre- 
sponding to the sperm-morula or spermosphere migrate towards 
the zooids, fusing into aggregations as they do so. Having 
reached the zooids they take up a position between the ecto- 
derm and endoderm of their apices, and continue there the 
later stages of their development. 

The spermospheres are most frequently found in the dacty- 
lozooids, but in a few cases I have found them in gastrozooids 
(fig. 3). They have probably no preference for either the one 
form or the other; but they are found more frequently in the 
dactylozooids, partly because these forms are more numerous, 
and partly because the gastrozooids are usually more remote 
from the larger ccenosarcal canals. 

The spermarium having been formed at the apex of the 
zooid certain noticeable changes take place. In the first place 
by a thickening of the ectoderm the pore becomes narrowed 
(figs. 5, 6, and 7). The tentacles become flattened out, and 
the nematocysts disappear. The spermarium sinks into a cup- 
shaped receptacle on the summit of the zooid, and the endo- 
derm of the edge of the cup grows out, pushing before it the 
ectoderm. 

These changes are represented in the two figs. 6 and 7 In 
the next stage the cup-shaped receptacle of the spermarium 
has grown out into a bell-shaped structure (fig. 8). The sper- 
marium is much larger in size, and the pore is completely 
closed by ectoderm. In the later stages (figs. 9, 10, and 11) 
the following changes may be noted. The operculum is formed, 
shutting off all access from the cavity of the gonangium to the 
exterior. The walls of the bell-shaped outgrowth become con- 
siderably attenuated, and lie close against the ectodermic wall 
of the ampulla. The manubrium is formed probably by a 
regeneration of the endodermic tissue and its growth into the 
centre of the spermarium. 


186 SYDNEY J. HICKSON. 


In the last stage I have observed the medusa is completely 
separated from the canal system, and lies freely within the 
cavity of the ampulla. The walls of the umbrella, except at 
the margin, are extremely thin. The manubrial endoderm 
contains a closed cavity (fig. 11). This stage is probably the 
last that occurs before the embryo escapes from the corallum. 
There are no nematocysts developed on the thickened margin 
of the umbrella, there are no sensory bodies, thére is no velum, 
and no mouth. 

2. In the development of the meduse of Millepora that 
has just been described there is no structure formed at any 
time that can be compared with the inner fold of ectoderm or 
“ glockenkern” that forms the walls of the sub-umbrella cavity 
of the medusa of the Hydroidea. Had such a structure been 
found, there might have been some ground for supposing that 
this medusa is a bud that grows out of the degenerated tissues 
of a zooid. The medusz of Millepora are, however, certainly 
not formed by budding from the zooid in the sense that the 
meduse of such a form as Corymorpha are budded from the 
hydranth. 

3. The diagrammatic figures that are frequently given of 
zooids of Millepora, representing a centrally placed gastro- 
zooid in a complete circle of dactylozooids, is perfectly correct 
for some species of Millepora and the younger branches of 
others. 

In M. murrayi the zooids are scattered over the older 
parts of the corallum in an irregular manner. The circular 
systems can be made out, but over and above the zooids in 
their regular circles there are both gastrozooids and dactylo- 
zooids scattered irregularly within and between the circles 
(cf. Quelch [11], p. 192). 

The medusz occur both in the regular circles and irregu- 
larly between them, as may be seen by reference to Woodcut 1. 
When a piece of Millepora is decalcified and cleared in oil of 
cloves or turpentine, and examined with a low power of the 
microscope, the arrangement of the zooids, meduse, and cceno- 
sarcal canals can be very readily observed. The figure I have 


THE MEDUSZ OF MILLEPORA MURRAYI. 187 


given was drawn, by the help of the camera, from such a pre- 
paration. The larger canals to which I have referred above 
form a wide-meshed network immediately below the surface. 
Each mesh is an irregular polygonal figure embracing the 


| OC FAHO# | 


Woopcur 1. Diagram of the arrangement of the zooids and meduse of 
Millepora murrayi. G. Gastrozooids. D. Dactylozooids. M. Me- 
dus. The larger canals are represented by irregular black lines. 


whole of one circular system of zooids. The meduse are 
always found either upon or quite close to these large canals, 
and thus they are sometimes without the circles, and some- 
times in a position corresponding to that of a dactylozooid of 
the regular circle. 

The position of the medusz in the colony cannot be used as 
an argument against my statement of their origin; in fact, 
whatever bearing it may have is in its favour. 

4, When a decalcified specimen of Millepora is examined 
from above, a cluster of large nematocysts may be seen at the 
mouths of the gastropores and dactylopores. They may also 
be seen in sections (figs. 1, 2, 6, 7, Nemat.). When the medusa 
is formed and the pore closed by the operculum these large 
nematocysts can be of little or no service, so they are shot 
and no new ones take their place. In the figures of the 
sections through the older medusez (9, 10, 11) the reader will 
notice that none of these large nematocysts are to be seen. 
Where the operculum is not completely formed (fig. 8), 
although the zooid has to all appearance changed into a 
medusa, one or two of these large nematocysts remain. 


188 SYDNEY J. HICKSON. 


II. Tut Mate GonopHoRES OF ALLOPORA AND 
DISTICHOPORA. 


1. Distichopora.—The male gonophores of Distichopora 
may be seen in clusters on the branches of the male stocks. 
They are small whitish bodies lying in the ampulle of the 
ccenosteum, and covered by a very thin semi-transparent wall 
of lime and ccenosarcal canals. 

An examination of a series of sections through one of these 
branches shows that the male gonophores are found only in 
these superficial clusters (fig. 12). They are never found 
deeply seated in the ccenosteum, nor in other places than 
those indicated by external appearances. 

One, two, or even three gonophores, in different stages of 
development, springing from a diverticulum of the ccenosarcal 
canal system, may occupy each ampulla. 

A ripe male gonophore (fig. 14,) is a spherical, oval, or 
pear-shaped body, with an endodermal cell-mass, representing 
the trophodise on the side turned towards the axis, and a 
short conical or tubular seminal duct on the side turned 
towards the periphery. The sheath of the gonophore seems 
to be a simple layer of flattened ectoderm; but I am per- 
suaded, after the examination of a great many sections and 
the study of the development, that two layers are represented, 
the inner or endodermal layer being extremely attenuated 
and devoid of nuclei. 

When a very young bud is examined with a high power 
(figs. 13,, 14,, 15), the rudiment of the spermarium may be 
seen to be a homogeneous mass of protoplasm, containing a 
number of large spherical nuclei. It occupies a position 
apparently between the ectoderm and endoderm of the bud. 
As the spermarium increases in size the endoderm becomes 
cup-shaped in the bud, and the margins of the cup are pro- 
duced into a very thin sheath between the ectoderm and the 
spermarium (fig, 16). At the peripheral pole of buds that 
are about half-way developed there is a thickening of the two 
sheaths of the gonophores, cell outlines are well marked, and 


THE GONOPHORES OF DISTICHOPORA AND ALLOPORA. 189 


the cells are nucleated (figs. 14 and 16). In this way the first 
rudiment of the seminal duct is formed. The two layers are 
from their first appearance quite distinct from one another, 
and there is never any indication that the two cell layers 
are formed by a splitting of the ectoderm. Just before the 
spermarium becomes mature the ectoderm, and subsequently 
the endoderm, are folded to form a: conical cap, and this 
subsequently pushes through the superficial covering of the 
gonangium to form the seminal duct to the exterior (fig. 18). 

Meanwhile, changes have taken place in the endoderm at 
the base, ie. on the axial side of the bud. In the early 
stages of the bud there is a wide lumen in the endoderm, 
the cells are cubical in shape, and their outlines well marked; 
in the later stages the lumen becomes obliterated, the cells lose 
their distinct outline, and the endoderm degenerates into an 
irregular mass of tissue, with scattered nuclei (figs. 13, 14, 
15, 16). 

2. In Allopora (fig. 19) the male gonophores are scattered 
irregularly in the corallum, and lie at such a distance from the 
surface that there is no trace of their existence externally. I 
have been able to find them only in the old thick branches. I 
cannot say for certain whether Allopora is hermaphrodite or 
dicecious. The specimens at my disposal consisted of a number 
of fragments in a bottle, and I found on the smaller and younger 
branches numerous female gonophores, and on the thicker and 
older branches numerous male gonophores; but I have not 
found both sexes on the same branches. I have no information 
whether the older and younger branches in the bottle are frag- 
ments of the same colony. If Allopora is not dicecious, then it 
is probably protogynous, like Millepora, the female sexual cells 
being formed first in the younger parts of the colony, and the 
male sexual cells later in the older parts. 

The male gonophores of Allopora resemble those of Dis- 
tichopora in every detail of structure except one, and that 
is that the endoderm of the base is produced into the 
substance of the spermarium as a club-shaped spadix or 
manubrium (fig. 20, Spa.) 


190 SYDNEY J. HICKSON. 


The spermarium is covered by a double sheath of very thin 
ectoderm and endoderm, and the seminal duct is produced in 
the same way that it is in Distichopora. When the sper- 
marium is ripe the seminal duct perforates the superjacent 
structures, and serves as the duct for the spermatozoa to 
escape to the exterior. As the gonophores of Allopora are 
situated much more deeply than they are in Distichopora, 
the seminal ducts are considerably longer. 

As a rule, only one gonophore is seen in each ampulla of 
Allopora, but occasionally two (fig. 19, gonophore 2), and 
very rarely three, in different stages of development may be 
seen. 

Lastly, it must be observed that the fully developed male 
gonophores of Allopora are much larger than those of Dis- 
tichopora. 

From a large number of measurements I have obtained the 
following average measurements : 

Longest diameter of male gonophores of Allopora . 0°38 mm. 
5 55 5 Distichopora 0°19 ,, 

The male gonophores of a few species of Stylasteride have 
been described by Moseley (10). 

In Sporadopora dichotoma the specimens were all males. 
“They are ovoid bodies with the long axes directed at right 
angles to the surface of the coral. Sometimes only one such 
body is present in an ampulla; sometimes two or three. The 
outer extremities of the gonophores are sometimes drawn 
out into a short tail-like prolongation.” This structure pro- 
bably corresponds with the seminal duct of Allopora and 
Distichopora. “There is a cylindrical spadix in the centre. 
The bases of the gonophores are continuous with large canals 
of the ccenosarcal meshwork, the endoderm of the 5 ee being 
continuous with that of these canals.” 

In Pliobothrus symmetricus the male gonophores are 
sacs containing a number of small ovoid bodies, which contain 
spermatozoa, or sperm-cells, in various stages of development. 
The exact structure of these smaller bodies and their relations 
to the endoderm were not determined. 


THE GONOPHORES OF DISTICHOPORA AND ALLOPORA. 191 


Only male specimens of Stylaster densicaulis were ob- 
tained. Each male ampulla contains two or three ovoid gono- 
phores, which are attached to large offsets of the ccenosarcal 
meshwork at one end of their longer axes. They have an 
internal spadix, and in finer structure seem to differ very 
little from the male gonophores of Sporadopora. 

Moseley also describes the male gonophores of Allopora 
profunda, and remarks that they are very similar to those of 
Sporadopora. He does not figure the seminal duct of this 
genus. 

Only one male specimen of Astylus subviridis was exa- 
mined by Moseley. “The male gonophores appear as large 
rounded lobulated masses resting within the ampullar sacs, 
and springing from stout offsets of the ccenosarcal meshwork, 
which pass into the sacs to reach them...... The sac as 
it enlarges becomes gradually pedicellate, and, when mature, 
is attached to the central mass by a narrow pedicle of some 
length. The walls of the pedicle are continuous with the 
ectodermal wall of the sac, which wall contains well-developed 
nuclei in its substance. Within the sac of the lobule a second 
sac, composed of a finer membrane, encloses the mature or 
developing generative elements. The wall of this inner sac 
is not prolonged into the cavity of the pedicle, but, passing 
across its commencement, shuts off the main cavity of the 
lobule from this latter..... No rounded spadix, such as that 
occurring in Allopora, is present in the interior of the lobules.” 
These gonophores seem, from the figures and the description 
given, to be very similar to those of Distichopora. 

It is not at all probable that Moseley overlooked the spadix, 
for in his figure there are represented no fewer than seven 
gonophores; and he remarks that his material was in a good 
state of preservation. The “inner sac” of the gonophore that 
he mentions and figures is most probably the same as the 
inner endodermic lining that I have described in both 
Allopora and Distichopora. It would be certainly very re- 
markable if this membrane is not attached to the endoderm 
of the pedicle in Astylus, but this point can only be deter- 


192 SYDNEY J. HICKSON. 


mined with accuracy by the examination of a continuous 
series of sections. 

The male gonophores of Cryptohelia pudica seem to be 
similar to those of Astylus. 


III. Tuer FEMALE GoNOPHORES OF DISTICHOPORA. 


The position of the female gonophores of Distichopora can 
be readily seen on the female stocks by the prominent swell- 
ings on the surface of the corallum. They are usually situated 
on only one side of the thicker branches, but occasionally 
there may be found in addition a small cluster on the opposite 
side. 

A section through one of these clusters shows the eggs and 
embryos in many stages of development, from the minute im- 
mature yolkless eggs in the ccenosarcal canals to well-advanced 
planulee (fig. 21). 

The mature ova (fig. 23, ovum) are 0°3 to 0-4 mm. in diameter, 
and contain a large number of spherical yolk-globules. The 
large germinal vesicle is situated close to the peripheral border 
of the egg, and is surrounded by a number of yolk-globules 
much smaller in size than those of the other part of the 
egg. The egg rests in the cup-shaped trophodise (cf. Allo- 
pora, Hickson, 7), and is covered by a thin coat of ectoderm 
and endoderm. The trophodisc is similar to that of the female 
gonophores of Allopora, but not so complicated in its foldings. 
In transverse section it exhibits twelve pouches at its margin 
(fig. 24). In vertical section it is simple (fig. 23); the inner 
and outer pliets that I have described in Allopora are not found 
in this genus. 

When fertilisation has taken place the germinal vesicle loses 
its sharp outline, and remarkable changes occur in the shape 
and arrangement of the yolk-globules. My observations are 
not yet complete of the early stages of the development, but I 
hope to be able to publish shortly a separate memoir, giving 
a full account of the development of this form up to the stage 
when the larva escapes from the ampulla, 


THE GONOPHORES OF DISTICHOPORA AND ALLOPORA. 193 


During the early stages of development the trophodisc 
rapidly atrophies, and by the time a layer of columnar epi- 
blast-cells has formed round the embryo no recognisable trace 
of it can be seen (figs. 22 and 25). 

In the meantime young eggs are migrating from the sub- 
jacent canals to the base of the ampulla, and in many cases 
before the larva has escaped a new egg, borne by a new 
trophodisc, occupies a considerable space in the same ampulla 
(fig. 25), 

The young eggs (fig. 22, ov.) are frequently seen quite 
deeply situated in the canal system; those that are nearer 
to the ampulle are larger in size and ameeboid in shape. 
As soon as they reach the ampulla they show very minute 
yolk-granules, which increase in size with the growth of the 
egg and the development of the trophodisc. 

The female gonophores of a few species of Stylasteride have 
already been figured and described by Moseley (10). 

In Pliobothrus symmetricus “the gonophores are con- 
tained in ampulle which are often sunk deep in the ccenosteum. 
.... The ova are solitary, one only being developed in each 
growing ampulla. Each ovum is developed within the cup of 
a cup-shaped spadix,” le. trophodisc. “As the ovum advances 
in development and increases in size the spadix enlarges with it. 
Subsequently, however, in later stages, the spadix appears not 
to increase further, and when in relation with a nearly fully 
developed planula appears proportionately small.” 

In Errina labiata “the female gonophores are closely 
similar in structure to those of Pliobothrus symmetricus; 
but there is this great difference, that whilst in Pliobothrus 
the ampulle and their contained ova and planulz remain until 
maturity immersed in the ccenosteum beneath its surface, in 
Errina the ampulle project more and more above the surface 
as development proceeds. 

“The spadix in Errina labiata is at first cup-shaped, the 
walls of the cup being composed of a very thick layer of endo- 
derm. The cavity of the cup is directed towards the surface of 
the coral, and within it rests the single large ovum with its 


194 SYDNEY J. HICKSON. 


distinct germinal vesicle and spot. Each ampulla contains 
invariably only one spadix and ovum.” 

Moseley gives a detailed account of the female gonophore 
of Cryptohelia pudica. In a late stage the trophodisc 
is “complicated at its margin by subdivision of its lobes, 
which form a network over one half of the surface of the 
ovum, terminating in a fringe of numerous tentacula-like 
lobes.” 

From these descriptions of Moseley and my own it seems 
probable that the female gonophores of the various genera 
of Stylasteride are very similar in general structure to one 
another. Moseley does not describe nor figure an inner en- 
dodermal membrane covering the egg, but in other respects 
his descriptions of the female gonophores of the three genera, 
Errina, Pliobothrus, and Cryptohelia, agree with mine of Allo- 
pora and Distichopora. The chief point of variation among 
the different genera is probably the lobulation or branching of 
the margins of the cup-shaped trophodisc. 

I prefer to retain the word trophodisc that I introduced in a 
former paper to the word spadix used by Moseley for the cup- 
shaped receptacle of the ovum. This structure cannot be con- 
sidered to be strictly homologous with the spadix or manubrium 
of the adelocodonic gonophore of the Hydromeduse. It seems 
to me to be more probable that it is homologous with the 
umbrella. 


IV. THe GoNOPHORES OF THE HYDROCORALLINE AND 
HyYDROMEDUSZ COMPARED. 


In the absence of a knowledge of the minute anatomy of 
- the gonophores of the Hydrocoralline, the true position of 
this group in the classification of the Hydrozoa has not yet 
been very satisfactorily made out. 

The peculiar characteristics of the group, namely, the dimor- 
phism of the polyps and the extensive skeleton of carbonate of 
lime, have not been considered by naturalists to be of sufficient 


THE GONOPHORES OF THE HYDROCORALLINA. 195 


importance by themselves to justify the separation of the Hydro- 
corallinz from the Hydromeduse. 

Lankester (9) places them in a separate order of the sub- 
class Hydromeduse. 

In the classification used at Cambridge Balfour placed 
Millepora and the Stylasteride in the sub-order Hydroidea 
of the order Hydromeduse. 

Claus, in his ‘Grundzuge der Zoologie’ makes the Hydro- 
corallinz the first sub-order of the order Hydromedusz. 

In Jackson’s edition of Rolleston’s ‘Forms of Animal Life’ 
(8) the order Hydroidea is divided into the three sub-orders 
(1) Tubulariz, (2) Hydrocoralline, and (3) Campanularie. 

The opinion I have come to, based upon Moseley’s researches 
and my own, is that the Hydrocoralline should be placed in 
an order apart from the Tubularie and Campanularie (ie. 
Hydroidea of Balfour and Jackson). 

The classification of the Hydrocoralline with the Hydroidea 
was perfectly justified by the state of knowledge at the time. 
Both dimorphism and skeletal structures are, comparatively 
speaking, uncertain features for the purposes of classification, 
and the character and structure of the polyps and their con- 
necting canal systems show undoubted affinities with many 
forms of Tubulariz. ; 

Unless, then, the organs that bear the sexual products can 
be shown to differ very widely from those of the Hydroidea, 
and present characteristics peculiarly their own, the Hydro- 
coralline must remain in the position that is assigned to them 
by some authorities in the order Hydroidea. 

These considerations demand a careful and exhaustive com- 
parison of the typical gonophores of the Tubulariz, and of those 
Hydrocorallines that are at present known to us. 

To aid in the discussion of the homologies I have given on 
p. 390 diagrammatic figures representing the structure of 
(Woodcut 2) a phanerocodonic medusa, (3) a medusa of Mille- 
pora, (4) an adelocodonic medusa, (5) the male gonophore of 
Allopora, (6) the male gonophore of Distichopora, (7) the 
female gonophore of Distichopora. 


196 SYDNEY J. HICKSON. 


Figs. 2 and 4 are copied from Allman with this modifica- 
tion, that both endodermal tissue and endodermal cavity are 


od 


Cox 
Soo 


E 


Woopvcuts 2—7. The structures of the different gonophores compared, 
Diagrammatic sections of—2. A phanerocodonic gonophore. 3. The 
Medusa of Millepora. 4. An adelocodonic gonophore. 5. Male gono- 
phore of Allopora. 6. Male gonophore of Distichopora. 7. Female 
gonophore of Distichopora. A. Manubrium. B. Gonad. C. Endoderm. 
D. Ectoderm. E. Umbrella. 


represented in black. The diagrams are modified in this way, 
because no important morphological distinctions can be drawn 
between endodermal structures possessing a cavity and those 
that do not. For example, no one would think of drawing a 
fine morphological distinction between the dactylozooids of 
Millepora and those of Allopora because in the case of the 


THE GONOPHORES OF THE HYDROCORALLINE. 197 


former there is a lumen and in the case of the latter the endo- 
derm is solid. 

In comparing the structure of the phanerocodonic medusa 
and the medusa of Millepora a very general similarity may be 
observed. 

In both there is a centrally placed manubrium (A). 

In both the generative elements (B) are developed between 
the ectoderm and endoderm of the manubrium. 

In both there is a contractile bell umbrella, from the ceutre 
of whose concavity the manubrium is suspended; in both this 
umbrella is composed of a centrally placed sheath of endoderm 
covered by a sheath of ectoderm on both sides; and in both 
the gonophore lies in a gonangial cavity of ectoderm, which, 
before the medusa is set free, is continuous with the ectoderm 
of the outer wall of the umbrella. 

The principal points in which these two forms differ from 
one another are these : 

The manubrium of 2 possesses a mouth. 

The manubrium of 3 does not. 

There is a system of canals (longitudinal and ring) in the 
umbrella of 2. 

There are no canals in the umbrella of 3. 

There are tentacles and sensory epithelium at the margin of 
the umbrella in 2. 

There are no tentacles or sensory epithelium at the margin 
of the umbrella of 3. 

There is a velum in 2, 

There is no velum in 3. 

Too much stress should not be laid upon any of these points 
of difference, for it is quite possible that tentacles, eyes, or 
auditory organs, a velum and a system of gastro-vascular canals, 
may be subsequently developed in the medusa of Millepora after 
it is set free. 

It is of importance to note, however, that these organs are 
not developed while the medusa is still attached to the parent 
stock, as they are in the typical phanerocodonic medusa of the 
Tubulariz. 

7 


198 SYDNEY J. HICKSON. 


Comparing the medusa of Millepora with the adelocodonic 
gonophore (fig. 4) of Hydromeduse, the following points of 
difference may be observed : 

There is a codonostome in the former, there is none in the 
latter. 

In the former the endoderm extends almost to the margin 
of the umbrella, in the latter the endoderm is reduced to a 
shallow cup surrounding the base of the manubrium. 

In other respects the two gonophores are practically similar. 

Comparing the adelocodonic gonophore (fig. 4) with the male 
gonophore of Allopora (fig. 5), two points of difference may. be 
observed. In the first place the endoderm completely surrounds 
the gonad in the latter, excepting at a small aperture at the 
distal pole, where it forms the inner wall of a narrow seminal 
duct. Secondly, there is no layer of ectoderm between this 
endoderm and the gonad in Distichopora. In the adelocodonic 
gonophore there are two layers of ectoderm between the gonad 
and wall of the gonangium. 

The male gonophore of Distichopora (fig. 6) resembles that 
of Allopora (fig. 5) in all respects except one, namely, that in 
the former there is no manubrium. 

The female gonophores of the two genera of Stylasteride 
resemble the male gonophores in most respects, but in the 
former there is a more complicated plieting of the base to form 
a nourishing disc (trophodisc), and no structure corresponding 
to a manubrium can be observed. 

Do these gonophores of the Hydrocoralline represent stages 
in the degeneration, or do they represent stages in the evolu-- 
tion of the free medusiform gonophore ? 

It would be more satisfactory, perhaps, to leave these 
questions to be answered at a time when we are better ac- 
quainted with the minute anatomy of the gonophores of 
other species of Millepora and the other genera of the Sty- 
lasteridee. 

The very convincing proofs that have been brought forward 
by Balfour, Weismann, and others, showing that the gonophores 
of the Hydroidea, however simple in structure, represent stages 


THE GONOPHORES OF THE HYDROCORALLINZA. 199 


in the degeneration of meduse, may lead to the conclusion that 
these gonophores of the Hydrocorallines are also degenerate 
meduse ; and it is necessary to issue a warning that this is 
probably not the case. 

That the medusa of Millepora is not degenerate but primi- 
tive in its simplicity must be apparent. 

In the course of its development there is no abbreviation nor 
any trace of organs that were at one time functional and have 
since become rudimentary. Moreover, it cannot be considered 
at all probable that a free-swimming medusa, bearing immature 
spermatozoa, would have lost its mouth, tentacles, sensory organs, 
endoderm canals, and velum; or, if it is a degenerate medusa, 
that the development of these organs would be postponed until 
after its escape. ; 

The only view that seems to me to be at all tenable is the 
one that considers the medusa of Millepora to be primitive in 
its simplicity. 

As regards the male gonophores of Allopora and Disticho- 
pora, there is without doubt a close similarity in appearance 
between certain stages in the development of the male gono- 
phores of both these genera and the younger stages of the 
meduse of such forms as Pennaria and other Tubularians (cf. 
this paper, Pl. XIV, and Weismann (12), pl. xvii. fig. 3); and 
the manubrium of Allopora is undoubtedly closely similar in 
general appearance to the manubrium of the adelocodonic 
gonophore of many of the Tubularie. In fact, the gono- 
phores of some of the Hydroidea, such as Clava (Allman) and 
Corydendrium (Weismann), are much less like adelocodonic 
medusee, even when they reach their full development, than 
are these gonophores of Allopora and Distichopora. 

If it could be shown that the inner membrane covering the 
spermarium is derived from the ectoderm and is not endodermic 
as I have described it, and that structures corresponding to the 
“glockenkern” do occur in the development of these gonophores, 
then my principal objections to the view that they are degene- 
rate medus would fall to the ground. A very careful examina- 
tion of my sections of gonophores in all stages of development 


7—2 


200 SYDNEY J. HICKSON. 


convinces me that there is in these forms no true “glockenkern,” 
and that the two membranes covering the gonad are truly homo- 
logous with the two membranes covering the ova, namely, an outer 
ectodermic membrane and an inner endodermic membrane. 

The manubrium of the gonophore of Allopora is, I believe, 
strictly homologous with the manubrium of the medusa of 
Millepora; that is to say, it is a subsequent endodermal in- 
growth into the spermarium developed for the purpose of 
affording increased nourishment to the rapidly increasing sper- 
moblasts. 

These gonophores, then, do not represent, in my opinion, 
stages in the degeneration of meduse. The Stylasteride never 
possessed free-swimming meduse, I believe, although their 
gonophores may indicate to us some of the stages that the 
meduse of Hydroidea passed through in the course of their 
phylogeny. 

Before entering into a discussion of the meaning of the 
gonophores of the Hydrocorallines, it is necessary to consider 
briefly the principal views that have been put forward con- 
cerning the primitive or ancestral form of the Hydrozoan. Is 
it probable from the evidence at our command that the ances- 
tral form was a fixed colonial hydroid, or was it like a scyphis- 
toma larva (Hydra tuba); or, lastly, was it a floating Hydra or 
actinula ? 

Balfour says, “ A condition like that of Hydra, in which the 
ovum directly gives rise to a form like its parent, is no doubt 
the primitive one, though it is not so certain that Hydra 
itself is a primitive form. The relation of Hydra to the 
Tubulariz and Campanulariz may best be conceived by sup- 
posing that in Hydra most ordinary buds did not become 
detached, so that a compound Hydra became formed; but 
that at certain periods particular buds retained their primi- 
tive capacity of becoming detached, and subsequently developed 
generative organs, while the ordinary buds lost their generative 
function.” 

Weismann’s view is similar to that of Balfour. He says, 
“Die niedrigste d. h. einfachste Form der heute lebenden 


THE GONOPHORES OF THE HYDROCORALLINA. 201 


Hydroiden ist wohl Hydra; es scheint mir wenigstens fiir 
jetzt kein Grund vorzuliegen, sie fiir eine riickgebildete Form, 
wohl aber manche Griinde sie fiir eine sehr alte Form zu 
halten, wie oben schon genauer begriindet wurde, und wie es 
auch so von den meisten Forschern angenommen wird ” (12). 

Both of these authors considered that the primitive type of 
Hydrozoan was a simple sessile form more or less similar to 
our modern Hydra, and that the medusa originated by the 
modification of individuals bearing the sexual cells that were 
budded from, and set free from, the primitive simple sessile 
Hydra. 

Lankester says, “The particular form which the proximate 
ancestor of the Hydrozoa took is most nearly exhibited at 
the present day in Lucernaria, and in the scyphistoma larva 
(Hydra tuba) of Discomeduse. It was a hemispherical cup- 
like polype with tentacles in multiples of four, with four lobes 
to the wide enteric chamber. This polype, after passing a 
portion of its life fixed by the aboral pole, loosened itself and 
swam freely by the contractions of the circular muscular fibres 
of the hypostome (sub-umbrella), and developed its ovaria and 
spermaria on the inner walls of the enteric chamber. This 
ancestor possessed, like its descendants, a very marked power 
of multiplication, either by buds or by detached fragments of 
its body. Accordingly it acquired definitely the character of 
multiplying by bud formation during the earlier period of its 
life; each of the buds so formed completed in the course of 
time its growth into a free-swimming person. We must sup- 
pose that the peculiarities of the two phases of development 
became more and more distinctly developed, the earlier budding 
phase exhibiting a more elongated form and simple enteric 
cavity (Hydra form), which subsequently became changed in 
the course of ontogeny into the umbrella or disc-like form, with 
the coalesced enteric walls and radial and circular surviving 
spaces (medusa form). And now the ancestry took two distinct 
lines, which have given rise respectively to the two great groups 
into which the Hydrozoa are divided—the Scyphomeduse and 
the Hydromeduse.” 


202 SYDNEY J. HICKSON. 


Another view has been put forward by Brooks (3), who, from 
a consideration of the developments of the Trachomedusx and 
Narcomeduse, comes to the conclusion that the ancestral form 
was a simple solitary floating or swimming Hydra. 

It does not seem to me to be at all clear that Claus pre- 
viously expressed the same view in the ‘Grundziige der Zoologie, 
for although he says that Hydra is certainly not a primitive 
form, that the medusa is a higher form than the polype, and 
that intermediate forms between the medusa and polype are 
represented by the actinula of Tubularia and Tetrapteron 
volitans, he does not commit himself to the view that the 
ancestral Hydrozoan was a free-swimming Hydra-like larva. 

Bohm (2), on the other hand, expresses his views very clearly : 
“Eine der nichsten Nachkommen der uralten Gastraea muss 
als die Stammform der Zoophyten, cine nicht weit von ihr 
entfernte als die der Hydromedusen angesehen werden. Bei 
der hypothetischen Construction der letzteren hat man zwischen 
drei Moglichkeiten zu wahlen. 

“ Entweder war diese schon entschieden polypoid, ihre niich- 
sten Nachkommen waren Polypen, und die Medusen haben sich 
erst: spater aus diesen entwickelt. 

“Oder sie war ganz medusoid, die Medusen die primiren 
die Polypen die secundaéren Nachkommen. 

“Oder schliesslich es war eine intermediiire zwischen Poly- 
pen und Medusen stehende Form, und Polypen wie Medusen 
haben sich von ihr aus nach zwei verschiedenen Richtungen 
hin entwickelt. 

“Die letztere Annahme scheint mir manche Griinde fiir sich 
zu haben. Denn der lange Weg vom wenig differenzirten 
festsitzenden Polypen bis zur hochausgebildeten freischwim- 
menden Meduse wird wesentlich abgekiirzt durch die Annahme 
einer Mittelform.” 

Notwithstanding the arguments of these authors, it is not 
easy to believe that the free-swimming actinula represents 
an ancestral type of Hydromedusan. The parasitic or semi- 
_ parasitic habits of the actinula of most of the Narcomeduse 
suggest that it is an extremely modified form, and it seems to 


THE GONOPHORES OF THE HYDROCORALLINE. 203 


me to be extremely hazardous on the part of Brooks to base 
his phylogenetic considerations upon such a weak and slender . 
foundation. The views of the earlier writers that the sessile 
form is the more primitive, that in those cases in which the 
medusa develops directly from the egg the trophosome has 
disappeared from the developmental cycle, seem to be more 
probable. 

It is not necessary to enter further into the discussion of 
these extreme speculative questions. 

I have referred to them not in the hope of adding anything 
new, nor of throwing light upon them, but in order that I may 
place clearly before the reader the position I take with regard 
to them. 

It seems to me to be more satisfactory to regard the sessile 
trophosome rather than the free-swimming actinula as the 
primitive type, and the medusa as a structure produced ori- 
ginally by a polypoid colony for the nourishment and distri- 
bution of the gonads. 

Having thus stated my opinion as to the original form of 
Hydroid, it is necessary to go further and express an opinion 
as to the mode in which medusz originated. 

The views of Weismann and Balfour on this question are as 
nearly as possible identical. They supposed that the medusa 
originated by certain buds bearing the primitive sexual cells, 
retaining their primitive capacity of being detached from the 
parent, and that such buds became modified for a free-swimming 
existence. According to these views the medusa is homologous 
with a polype, it is simply a modified trophosome, or that 
trophosomes and gonophores are both modifications of some 
common type. 

Huxley’s original view that the gonophore is a peculiar 
sexual organ has in recent years been subject to a storm of 
criticism, and there are very few naturalists of the present day 
who would defend. the position he took. “A medusoid, though 
it feeds and maintains itself, is in a morphological sense simply 
the detached generative organ of the hydrosoma on which it is 
developed.” 


204 SYDNEY J. HICKSON. 


The gonophores of the Hydrocorallinz do not seem at first 
sight to throw much light upon these questions. If we arbi- 
trarily assume that they are degenerate meduse comparable 
to the adelocodonic gonophores of the Tubularize and Cam- 
panulariz, we cannot expect to find in them any evidence to 
support either the one view or the other. But there is no 
reason to suppose that they are degenerate medusiform gono- 
phores. Neither in Millepora, nor in Allopora and Distichopora, 
are there any features in development that suggest rudimentary 
structures of meduse. 

If they are not degenerate structures, then, but gonophores 
of a primitive type, how can we reconcile the medusa of Mille- 
pora, which is a metamorphosed polype, with the gonophores 
‘of Allopora and Distichopora, which show no trace of polypoid 
er medusoid structure ? 

The explanation I would samuel is briefly as follows: 
When the ova or sperm-mother cells reach a certain size and 
are too large to move freely in the canal system, they set up a 
local stimulus or irritation, which causes a cup-shaped folding 
of the adjacent canal or polype wall. This cup-shaped fold 
being of advantage to the sexual cells during their maturation, 
by affording increased facilities for nourishment and by in- 
creasing the size of the cavity by solution of its walls, has 
been modified into a definite form in each species by natural 
selection, When the sexual cells arrive at their maturity the 
nourishment afforded by these cells is no longer necessary, and 
consequently the stalk of connection with the canals becomes 
constricted until the gonophore is set free in the cavity of the 
ampulla. In the ancestral form of the Millepora a ready access 
to the exterior was opened to the separated gonophore by way 
of the dactylopore, and thus the detached gonophore was able 
to escape and lead a free-swimming existence. 

It is reasonable to suppose that all the cells of the colony of 
a Millepora are capable of a certain amount of contractility, 
and that the slight power of contractile movement that the 
original free gonophore possessed being of advantage to the 
species—by enabling the gonophore to keep afloat longer and 


THE GONOPHORES OF THE HYDROCORALLINA. 205 


thus spread the sexual products farther—was increased by 
natural selection. Similarly the rim of the gonophore cup 
was produced until it assumed the size and shape of a medusa. 

The whole of this hypothesis of the origin of the medusx 
_ Tests upon the supposition that the sexual cells when they 
reach a certain size set up a local irritation or stimulus, causing 
a cup-shaped growth of the ccenosarc in its immediate neigh- 
bourhood. 

Is it reasonable to suppose, in ith first ae that the gonads 
when they reach a certain size do produce a local stimulus or 
irritation? In young immature stocks there is no trace of 
ampulla or other receptacles in the ccenosteum of sufficient 
capacity for the mature gonads. Nor are there found in stocks 
that are bearing but few sexual organs any empty cavities in 
the ccenosteum. It is almost certain, then, that the gonads, 
when they reach a certain size, cause a stimulus to certain cells 
to secrete an acid (?) which dissolves the lime of the ccenosteum 
and causes an ampulla to be formed. There can be no doubt, 
then, that the sexual cells do cause one kind of stimulus to the 
tissues. 

But is a local irritation or stimulus likely to cause any such 
modification as circumferential folding of the canals in its 
neighbourhood ? 

The only direction in which we can look for an answer to 
this question is to the effects caused by the irritation of foreign 
substances and parasites. The Hydrocorallines, like most of 
the corals, are subject to the attacks of many kinds of parasites. 
Worms, molluscs, barnacles, and other forms may be seen in 
every specimen that is examined. 

When the colony is attacked by such a form as Tetraclita, 
for example, the coenosarc at the immediate spot on which the 
parasites settles is killed, but this does not cause an atrophy of 
the surrounding canal system. On the contrary, a pronounced 
hypertrophy of the canal system immediately surrounding the 
parasite takes place, and in time it grows round and over the 
parasite until it is almost buried in its substance. An exami- 
nation of other forms of coral will show similar examples of 


206 SYDNEY J. HICKSON. 


parasites and other foreign bodies covered by an hypertrophied 
growth of the ccenosare. 

The formation of the corbula of Aglaophenia may be 
accounted for by a similar explanation. The stimulus of 
the growing blastostyles causes, not only an increased acti- _ 
vity in the growth of the lateral branchlets, but a growth in 
such a manner as to enclose the blastostyles in a cup. 

Similarly the various kinds of animal galls found in Hy- 
droids and Alcyonarians are probably caused by a circum- 
ferential hypertrophy of the tissues surrounding the parasitic 
pycnogonid, crab, or mollusc. 

From this evidence, then, it does seem probable that a local 
stimulus or local irritation of the ccenosarc of these forms 
causes a growth of the tissues which gradually folds over 
the seat of the irritation. 

If this is the case, then, the production of a very rudi- 
mentary and imperfect umbrella-shaped structure is a phy- 
siological result of the stimulus caused by the growth of the 
sexual cells, and the medusa is simply a modification, produced 
by natural selection, of such a structure. 

If this view is a reasonable one, we get over the principal 
difficulty in accepting the view that the ancestral Hydrozoan 
was a colonial Hydra form. 

One of the chief features of the higher Protozoa and of 
the Coelenterata is the power they possess of forming large 
colonial organizations by asexual reproduction. And it is 
reasonable to suppose that when the primitive Hydrozoan 
became differentiated off from its colonial Protozoan ancestry it 
retained the power of forming colonies by fission or gemmation. 

It has seemed to me improbable that Hydra can be closely 
related to the ancestral type, because it does not possess this 
power. 

If this view of the origin of meduse is correct, there is 
no difficulty in believing that the ancestral form was a colonial 
trophosome, and that meduse of different kinds may have 


originated quite independently of one another from the 
Hydroid stocks, 


THE GONOPHORES OF THE HYDROCORALLIN As, 207 


The original position of the gonads was thé centre of the 
concavity of the umbrella. As they became larger and larger 
in phylogeny a conical growth of the endoderm, with respiratory 
and nutritive functions, penetrated them, and became the manu- 
brium. All of these stages may be seen repeated in the onto- 
geny of the medusa of Millepora. When a mouth was formed 
at the end of the manubrium the gonads were in some forms 
(anthomedusz) restricted to the sides of that organ; but in 
other forms (leptomeduse) they were shifted to a more con- 
venient place in the radial canals. According to my view, 
then, the manubrium of the male gonophore of Allopora does 
not prove that it is a degenerate medusa, but, rather, that it is 
one stage further than Distichopora on the road that all meduse 
have travelled in the early history of their phylogeny ; that is to 
say, a stage with a larger spermarium, and a special process of 
endoderm for its more perfect nourishment and respiration. 

Another question arises in connection with the gonophores 
of the Hydrocoralline that at one time would have been con- 
sidered one of vital importance. 

In the description given above of the development of the 
medusa of Millepora, I have shown that it is formed by a 
metamorphosis of a dactylozooid. This would support the 
view, then, that the medusa is a modified trophosome. 

In the description of the development of the gonophores of 
Allopora and Distichopora I do not mention the zooids at all. 
The gonophores are not developed in these genera (figs. 12, 19) 
in connection with either the gastrozooids or dactylozooids, they 
arise quite independently from the ccenosarcal canals. They 
have no particular relation to the systems in which the zooids 
are arranged, and there is every reason to suppose that they are 
quite independent of them. Further, these gonophores are not, 
according to my view, degenerate meduse. They must, there- 
fore, be special organs of the colony bearing the gonads. 

To those naturalists who believe that there is a sharp dis- 
tinction to be drawn between the idea of the “individual” 
and the “organ” in the animal kingdom, these apparently 
contradictory cases must be very puzzling. In the one case 


208 SYDNEY J. HICKSON. 


they would say the gonophore is an “individual;” in the 
other, it is an “organ.” 

I am not inclined, however, to believe that it is possible 
to draw a sharp distinction between these two ideas. They 
are relative ideas, as Claus (5) maintains, just as “cell” 
and “tissue,” “individual” and “colony,” must be. 

The stimulus of the sexual cells of a certain size would 
produce the same effect if they were formed in the ccenosarcal 
canals or the zooids; but natural selection has stepped in 
in the case of the Hydrocorallines, so that in the case of 
Millepora the gonads do not produce this effect until they 
reach the zooids, and, in the case of the Stylasteride, not 
until they reach certain parts of the canal system. 

The two kinds of gonophores are, then, to my ideas really 
homologous, although in the one case they have reached such a 
stage of development as to justify us in considering them 
“individuals,” while in the other case they cannot be con- 
sidered more than sexual “ organs.” 


General Conclusions. 


1. In Millepora murrayi (sp. ?) the male gonads are 
borne by medusze which escape from the ampulle in which 
they are developed before the spermatozoa are matured. 

2. The ova of this species are, like the ova of Millepora 
plicata, extremely small and alecithal. They move in an 
amceboid manner in the ccenosarcal canals, and do not ulti- 
mately rest in gonophores, nor in any specialized portion of 
the system. 

3. The meduse of Millepora murrayi have no radial 
nor ring canals in the endoderm of the umbrella, no velum, 
no sensory organs, and no mouth. 

4. The medusze are formed by a metamorphosis of an 
ordinary zooid; in the majority of cases dactylozooids, but 
in others gastrozooids. 

5. The sperm-cells originate in the ectoderm of the cceno- 


‘THE MEDUS OF MILLEPORA MURRAYI. 209 


sare and wander into the ectoderm of the zooids, where they 
fuse into aggregations to form a spermarium. 

6. The young spermarium is formed at the distal extremity 
of the dactylozooid, and when it has reached a certain size 
it causes a retrograde metamorphosis of the tissues. The 
tentacles flatten out and disappear, and the zooid loses all 
its characteristic features. 

7. A cup-shaped outgrowth next appears which forms the 
umbrella of the medusa, and subsequently a conical growth 
of the endoderm penetrates into the substance of the sper- 
marium and forms the manubrium. 

8. The male gonophores of Distichopora occur in groups of 
two or three in each ampulla in different stages of develop- 
ment. The gonad is supported by a small cup-shaped tropho- 
disc, and enclosed in a double sac of ectoderm and endoderm. 
At the distal pole of the ripe gonophore there is a short 
seminal duct. 

9. The male gonophore of Allopora differs from that of 
Distichopora, in the fact that it is provided with a club-shaped 
endodermal manubrium or spadix. 

10. The female gonophore of Distichopora resembles that 
of Allopora described in a previous paper; but the folds of the 
trophodisc are not so complicated. 

11. The gonophores of the Hydrocorallinz are not degene- 
rate medusa. 


210 


1, 
2. 
3. 


4. 


5. 


12, 


SYDNEY J. HICKSON. 


BIBLIOGRAPHY. 


F. M. Batrour.— Comparative Embryology,’ 1880. 

R. Boum.— Helgolander Leptomeduse,” ‘Jen. Zeits.,’ xii. 1878. 

W. K. Brooxs.—“The Life History of the Hydromeduse:” a discussion 
of the origin of Medusz and the significance of Metagenesis, ‘Mem. 
Bost. Soc. Nat. Hist.,’ vol. iii. No. 12, 1886. 

Craus.— Ueber Halistemma tergestinum,” &c., ‘Arbeiten des Zool. 
Instit. zu Wien,’ tom. i. 1878. 

C. Craus.—* Zur Beurtheilung des Organismus der Siphonophoren 
und deren phylogenetischer Ableitung,” ‘ Arbeiten Zool. Instit. zu 
Wien,’ viii. Heft 2, p. 159; translated in the ‘Annals and Magazine 
of Natural History,’ vi. 21, pp. 185—198. 

8. J. Hicxson.—‘ The Sexual Cells and the Early Stages in the 
Development of Millepora plicata,” ‘Phil. Trans., vol. clxxix. 
1888, B., pp. 193—204. 

8. J. Hickson.—“On the Maturation of the Ovum and the Early 
Stages in the Development of Allopora,” ‘Quart. Journ. Micr. Sci.,’ 
vol, xxix. p. 579. 

W. H. Jacxson.—‘ Rolleston’s Forms of Animal Life,’ 2nd edition, 
1888. 

E. Ray Lanxester.—Article “ Hydrozoa,” ‘Encyclopedia Britann.,’ 
9th edition. 

H. N. Mosetzy.—* Report on Certain Hydroid, Alcyonarian, and 
Madreporarian Corals,” ‘“ Challenger” Reports,’ vol. ii. 1881. 

J. J. QuetcH.—“ On the Presence of Ampulle in Millepora mur- 
rayi,” ‘Nature, vol. xxx. 1884, p. 539; and in ‘“ Challenger” 
Reports,’ vol. xvi. “Reef Corals.” 

A. Wuismann.—‘Die Entstehung der Sexualzellen bei den Hydro- 
medusen,’ Jena, 1883. 


THE MEDUSZ OF MILLEPORA MURRAYI. 211 


DESCRIPTION OF PLATES XIII & XIV. 


Illustrating Mr Sydney J. Hickson’s paper “The Meduse of 


Millepora murrayi and the Gonophores of Allopora 
and Distichopora.” 


Cale. The calcareous skeleton or ccenosteum. Cen. The ccenosarcal 
canals. In the superficial regions the canals are crowded with. zooxan- 
thelle. ct. Ectoderm, coloured red. nd. Endoderm, coloured blue. 
Gon. The ectodermal lining of the ampulla forming the wall of the 
gonangium. Man. Manubrium of the medusa. Wemat. Large nema- 
tocysts guarding the dactylopores. op. Operculum of modified ectoderm 
cells covering the pore of the ampulla, Sperm. Spermarium. Sperm. S, 
Spermospheres or aggregations of spermospheres in the ectoderm of the 
zooids, Sperm. 8, Young spermospheres in the ectoderm of the canals. 
Tent. Retracted tentacles. Umb. Umbrella of the medusa, consisting of a 
solid endoderm covered on both sides by ectoderm. 


PLATE XIII. 
Millepora murrayi. 


Fie. 1.—Section through a retracted dactylozooid of Millepora mur- 
rayi, showing a number of spermospheres (Sperm. S,.) in the ectoderm of 
the coenosare, and in the ectoderm (Sperm. S,.) at the base of the dactylo- 
zooid. 


Fic. 2.—Section through a retracted dactylozooid, showing a single 
small aggregation of spermospheres (Sperm. S,.) in the ectoderm at the 
base of the dactylozooid. 


Fia. 3.—Section through a retracted gastrozooid, showing an aggrega- 
tion of spermospheres in the ectoderm. The gastrozooids may be readily 
distinguished from the dactylozooids by the presence of a mouth and by 
the large endoderm cells, the peripheral portions of which are filled with 
mucus. Just below the gastrozooids may be seen a plate of vacuolated 
ectoderm cells in section, which forms the last tabula of the gastropore. 

Fra. 4.—Section through a dactylozooid, showing a large aggregation of 
spermospheres on its side in a condition very similar to that I have de- 
scribed in Millepora plicata (6). The spermospheres have caused a very 
considerable depression in the dactylozooid, and are partially covered by 
the surrounding parts. 

Fra. 5.—An aggregation of spermospheres at the peripheral extremity 
of a dactylozooid. The tentacles (tent.) are visible. 


212 SYDNEY J. HICKSON. 


Fie. 6.—An aggregation of spermospheres (Sperm. S,.) at the peripheral 
extremity of a dactylozooid, sunk in a cup-shaped receptacle. At Umb. may 
be seen the first trace of the formation of the umbrella by the growth of 
the endoderm. The position of the tentacles is still indicated by the rows 
of small nematocysts. 


Fra. 7.—Section through another dactylozooid, showing a still further 
growth of the folds forming the umbrella. All trace of the tentacles has 
disappeared. 


Fia. 8.—Section through a young medusa of Millepora. The form of 
the dactylozooid is completely lost. The endoderm of the umbrella is 
solid, and much thicker than it is in later stages. The opening of the 
dactylopore can still be traced, although it is blocked with the thickened 
ectoderm cells. The pore is guarded by nematocysts (Vemat.). 


Fia. 9.—Section through another medusa. The umbrella is not com- 
pletely developed, but the endoderm is much thinner than it is in Fig. 8. 
The spermarium is much larger, but there is no trace of a manubrium. 
The dactylopore is completely closed by an operculum (op.) formed by 
flattened strap-shaped ectoderm cells. 


Fia. 10.—Section through another medusa, with a well-developed 
manubrium (man.), containing a cavity continuous with a large canal. 
The umbrella walls are much thinner than they are in the specimens 
drawn in Figs. 8 and 9, except at the margin. 

Fic. 11.—Section through a medusa that lies freely in the gonangium. 
It is not connected organically with the colony at any point. It is probably 
ready to escape. The umbrella (Umb.) is extremely thin, except at the 
margins. There is a small cavity in the endoderm, but there is no mouth. 
There are no tentacles, velum, nor sensory bodies on the margin of the 
umbrella. Between the codonostome and the superficial ectoderm there is 
a layer of mucus. 


PLATE XIV. 


Fic. 12.—Transverse section through a decalcified branch of Disti- 
chopora, showing the male gonophores lying in the ampulle. One, two, 
or three gonophores occur in each ampulla. At the edges of the branch 
are situated the rows of dactylozooids (Dact. Z.) and gastrozooids (Gast. Z.). 

Fie, 13.—Section through an ampulla of Distichopora, containing two 
young male gonophores. Each of these is supported by its own trophodise 
containing a large lumen. 

Fie. 14.—Section through an ampulla of Distichopora, containing three 
male gonophores in different stages of development. The largest of these 
(1) contains ripe spermatozoa, and shows on its distal pole a conical cap of 


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THE MEDUSH OF MILLEPORA MURRAYI. 213 


cells, the undeveloped seminal duct. The trophodise (troph.) is reduced to- 
an irregular mass of endoderm cells. 

Fig. 15.—Section through a very young male gonophore of Distichopora. 
The young spermarium (sperm.) lies apparently between the ectoderm and 
endoderm of the bud, but the endoderm is cup-shaped, and the margins of 
the cup project between the ectoderm and the proximal hemisphere of the: 
spermarium. 

Fie. 16.—Section through an older male gonophore of Distichopora, 
showing the spermarium covered by the two membranes, a thin nucleated 
ectoderm and a thinner non-nucleated endoderm, which is continuous with 
the endoderm of the trophodisc. 

Fic. 17.—Section through the earliest stage I have found of the forma- 
tion of the seminal duct. The ectodermic and endodermic elements are: 
from the very first quite distinct from one another. 

Fie. 18.—Section through a seminal duct of a ripe male gonophore, 
open to the exterior. 

Fic. 19.—Section through a portion of a decalcified branch of Allopora, 
showing three male gonophores lying in their ampullew. As a rule, only one 
gonophore is found in each ampulla; but one case is figured (gonophore 2) 
in which a large gonophore and a very young bud occur in the same 

_ampulla. 

Fic. 20.—Section through a nearly ripe male gonophore of Allopora, 
showing the club-shaped endodermal spadix, and the two membranes (Ect. 
and £nd.) surrounding the spermarium. 

Fig. 21.—Section through a portion of a decalcified branch of a female 
stock of Distichopora, showing a number of ova and planule in various 
stages of development lying in their ampulle. 

Fig. 22.—A portion of the same as Fig. 21, more highly magnified. 
The ampulle are occupied by planule. Below the ampulle there may be 
seen in the endoderm of the canals some very young eggs, containing no- 
yolk-granules and showing blunt amceboid processes. 

Fig. 23.—An ovum of Distichopora that is nearly mature, as seen in 
section. The germinal vesicle (Germ. Ves.) lies near the superficial side of 
the egg, and is surrounded by small yolk-granules. The trophodise is 
simple, in vertical section, and contains a pronounced lumen. 

Fic. 24.—Transverse section through an ovum and trophodise of Disti- 
chopora in the plane represented by the line wz’ in Fig. 23, showing the 
twelve pouches of its margin. 

Fig. 25.—Section through an ampulla of Distichopora, containing a 
planula, and below it a young ovum in a young trophodise. 


SUPPLEMENTARY LIST OF SPIDERS TAKEN 
IN THE NEIGHBOURHOOD OF CAMBRIDGE. 


BY 


C. WARBURTON, B.A., 
Christ’s College. 


In Part I. Vol. v. of these Studies a list was given of some 
hundred species of local Araneze. To these must now be added 
the following, some of which have been taken since the former 
publication, while others are inserted on the authority of the 
Rev. O. Pickard-Cambridge, who has kindly furnished a list of 
Spiders sent to him some years ago by the late Mr Farren. 

Unfortunately Mr Farren did not record the exact locality 
nor the frequency of his captures, but he is known to have 
carefully searched Wicken Fen, which is probably the habitat 
of most of his species. 


DYSDERIDAE. 
DysDERA 
crocota, C. L. Koch, rare, Castle Hill. 


SEGESTRIA 
senoculata, Linn. 


DRASSIDAE. 


Dnrassvs : 
troglodytes, C. L. Koch, rare, Wicken Fen. 
plackwallii, Thor. 

CLUBIONA . : 
corticalis, Walck., rare, University bathing enclosure. 
reclusa, Cambr. 

ANYPHAENA 
accentuata, Walck. 


PHRUROLITHUS 
festivus, C. L. Koch, Fleam Dyke. 


DICTYNIDAE. 
Dicryna 
latens, Fabr. 


MR WARBURTON, ON SPIDERS NEAR CAMBRIDGE. 


AGELENIDAE. 
Haunia 
nava, Bl., rare, Wicken Fen. 


Letra 
humilis, Bl. 


‘THERIDIIDAE. 


THERIDION 
simile, C. L. Koch. 
tinctum, Walck., common, on shrubs and bushes. 
rufolineatum, Luc. 
NERIENE 
cornuta, Bl., rare, in the ‘Backs.’ 
nigra, Bl., rare, Turf Fen, Chatteris. 
fuscipalpis, C. L. Koch. In the bathing enclosure. 
apicata, Bl, 
bicolor, Bl. Castle Hill. 
bituberculata, Wid. 
‘WALCKENAERA 
bifrons, Bl. 
unicornis, Bl. 
cristata, Bl., rare, Christ’s Coll. Garden. 
PacHYGNATHA 
listeri, Sund. 
Evryopis 
blackwallii, Cambr. 
Linyeaia 
nigrina, Westr. 
setosa, Cambr., Wicken Fen. 
clathrata, Sund.,, Wicken Fen. 
circumspecta, Bl. rare. 


EPEIRIDAE. 


EPEIRA 
acalypha, Walck. 
solers, Walck. 
quadrata, Clrk., occasional, Fens. 


ERRATA. 


In the previous list, Amaurobius fenestralis should have been recorded as rare 
instead of common, and the habitat of Theridion varians as being ‘ boathouses 


and out-buildings” rather than “ bushes.” 


On Onchnesoma Steenstrupii. 
By 
Arthur E. Shipley, Mi.Ae, F.L.S., 


Fellow and Lecturer of Christ’s College, Cambridge, and Demonstrator of 
Comparative Anatomy in the University. 


With Plate XV. 


————— 


Tuer genus Onchnesoma was established in the year 1877 by 
Koren and Danielssen,' its name being derived from 8yyvn =a 
pear,and c@ua =body. The genus is characterised as follows: 

“ The body small, pear-shaped. The proboscis long. The 
anal aperture a little in front of the base of the proboscis. 
No tentacles; no vascular system. One retractor.” 

The genus consisted of two species: O. Steenstrupii, 
which the authors regard as synonymous with Sipunculus 
pyriformis of Danielssen? and Phascolosoma pusillum 
of Sars ;?and O. Sarsii, synonymous with the Phascolosoma 
levissimum of Sars. These two species, with their charac- 
teristics, are mentioned in Selenka’s monograph of the Sipun- 
culide. In 1881 a third species, O. glaciale, was described 
by the Norwegian authors* from amongst the material col- 
lected by the Norwegian North Atlantic Expedition, so that 


1 * Contribution to the Natural History of the Norwegian Gephyrea,’’ by 
J. Koren and D, C. Danielssen, ‘Fauna Littoralis Norvegie,’ Bergen, 1877. 

2 Danielssen, ‘ Videnskabsselskabet Forhandlinger i. Christiania,’ Aaret, 
1859. 

3 Sars, ‘ Videnskabsselskabet Forhandlinger i. Christiania,’ Aaret, 1868. 

4 ©The Norwegian North Atlantic Expedition, 1876—1878, Gephyrea,’ by 
D. C. Danielssen and Johan Koren, Christiania, 1881. 


VOL, V, PART Il. 8 


218 ARTHUR E. SHIPLEY. 


the genus at present comprises three species, all found on the 
north-west coast of the Scandinavian peninsula. 

The species differ considerably in size. O. Steenstrupii, 
whose body measures but 3 mm. in length, is the smallest 
Gephyrean hitherto described, and, corresponding with its 
minute size, the structure of the body is very much simplified. 
O. Sarsii attains a body length of 8 mm., whilst the body of 
O. glaciale is 85 mm. long. I have hitherto been unable to 
obtain specimens of the two last-mentioned species; but, 
thanks to the kindness of Professor E. Ray Lankester and 
Canon Norman, I have been enabled to investigate the struc- 
ture of the smallest species, of the minute anatomy of which 
the following is an account. 


Tur Externat APPEARANCE. 


In the better preserved specimens the body was about 3 mm. 
long, pointed behind, and in front passing abruptly into the 
introvert (figs. 1 and 2); some, however, which were not well 
preserved, and which did not appear to be normal, had a longer 
and more slender body, which passed gradually into the intro- 
vert. The length of the latter structure varied in accordance 
with the amount of its protrusion : it was, when fully extended, 
almost invariably coiled up, and consequenily difficult to 
measure, but in no specimen was it 34 mm. long, the length 
described by Koren and Danielssen. 

The skin is of a French grey, almost greenish colour, and 
is divided into small areas by numerous crinkles, which at 
the posterior end of the body cross one another almost at 
right angles; in some cases such folds of the skin occurred 
at more or less regular intervals round the proboscis, giving 
it a superficial appearance of being segmented (fig. 1). 

The introvert is covered with papillz, which, according to 
Koren and Danielssen, are disposed in regular rows. The 
nature of these organs, which correspond with the papille of 
the larger Sipunculids, will be described below; they open to 
the exterior, but the opening is not always situated on an emi- 
nence, but may be found anywhere on the wrinkled surface -of 


ON ONCHNESOMA STBENSTRUPII. 219 


the body. The skin of the introvert, when extended, is traxs- 
parent, so that the oesophagus and nervous system may be seen 
through it. 

There is a marked thickening of the skin where the introvert 
joins the body ; the anus is situated a little anterior to this. 
The external opening of the kidney is a little behind, just to 
the side of the ventral nerve-cord. 


THE Srructure oF THE SKIN. 


The layers which compose the skin of Onchnesoma have 
been described by the Norwegian writers ; there are, however, 
one or two details which may be added to their account. As 
in the skin of other Sipunculids, we meet with six layers. 
The state of preservation of my specimens did not allow the 
epidermal cells to be made out. But this outermost layer of 
cells probably forms part of the deeply stained external layer 
seen in fig. 6. 

In section this layer appears ridged, the ridges corresponding 
with the wrinkles on the surface of the animal. It is obscured 
by a number of granules, which stain very deeply with hema- 
toxylin; these granules are apparently produced by certain 
structures which correspond with the epidermal glands of 
other forms. Between the darkly stained external layer 
and the circular muscles is a thick gelatinous connective- 
tissue layer, or cutis, in which hardly any trace of cells 
could be detected. At the base of this the skin glands are 
situated. 

The state of the preservation of my material did not allow 
me to see this point very clearly, but I have no doubt that the 
epidermal glands are composed of specialised epidermal cells. 
Each gland is of a spherical shape; from the outer edge of this a 
duct with sharply defined outline leads through the cutis to 
the surface of the body. Within the glands lie numerous darkly 
stained granules, similar to those which cover the outside of 
the body; and there is little doubt that the latter have their 
origin in these structures, and pass out with the mucus which 


220 ARTHUR E. SHIPLEY. 


has in some cases been seen to exude from the pores of the 
glands. 

The external circular layer of muscles is well developed in 
the introvert, and in the anterior half of the body; but about 
the middle of the body it fades away, so that the posterior end 
is provided only with longitudinal muscles (fig. 7). The cir- 
cular muscles are arranged in bundles, but the longitudinal 
are in a continuous sheet. 

Both the cutis and the external and internal layers of 
muscles take part in the thickening of the skin which exists 
at the junction of the proboscis and the body. 

The body-wall is lined by an endothelium, which extends over 
the internal organs. In the living specimens, according to 
Koren and Danielssen, it can be distinctly seen that this endo- 
thelium is ciliated, and that the cilia, by their action, keep 
the perivisceral fluid in motion. 


Tur GENERAL ANATOMY. 


If a longitudinal incision be made in the body-wall of 
Onchnesoma, and the sides reflected, the arrangement of the 
internal organs and their relation to one another become at 
once evident without further dissecting. These relations are 
clearly shown in fig. 3, which I have borrowed from Koren 
and Danielssen’s ‘Fauna Littoralis Norvegie.’ It will be 
seen that the esophagus is very long and loosely coiled, in 
order to allow for the extension of the introvert. The intestine, 
whose diameter is larger than the cesophagus or rectum, is 
also much coiled. The anus is situated rather too far forward 
to the right of the ventral nerve-cord. 

There is only a single retractor muscle, which has its origin 
at the extreme posterior end of the body, where the skin is 
thickened and produced into a blunt point (fig. 7). The other 
end of this muscle is inserted into the wall of the oesophagus 
immediately below the brain. The muscle-fibres which com- 
pose this retractor muscle are bigger than those of the mus- 
cular sheaths in the skin. They are fusiform, with a rather 
flattened transverse section and a faint longitudinal striation. 


ON ONCHNESOMA STEENSTRUPIL. 221 


There is no closed vascular system such as exists in the 
larger Sipunculids. The perivisceral fluid which bathes the 
internal organs is crowded with nucleated corpuscles and gene- 
rative cells. 

The single kidney varies in position; in some of my speci- 
mens it was situated to the left of the ventral nerve-cord, in 
others to the right. Both its internal and external openings 
are too small to be made out except by section. The ventral 
nerve-cord may be seen as a very fine strand running just 
inside the skin (fig. 8). 


Tur Heap. 


The head of Onchnesoma is of a remarkably simplified 
nature compared with that of the larger Gephyrea, but 
whether the simplification is primitive or the result of dege- 
neration is not an easy matter to decide. The hooks which 
are so common in the group, arranged in rings round the 
proboscis, are entirely absent in this genus. This is a point 
of some interest taken in connection with the absence of 
several other structures which are usually met with in the 
group, but too much stress must not be laid on it, as with one 
exception, S. australis, the whole genus Sipunculus is 
devoid of these structures, and in other genera several species 
are without hooks ; they are also apt to drop off as the animal 
grows old. 

A more important feature is the entire absence of any ten- 
tacles. There is no trace whatever of the lophophoral ring of 
tentacles such as occurs in Phymosoma, and the crumpled 
pigmented tissue which occupied the hollow of the horseshoe 
is also entirely absent. The place of these structures, in the 
dorsal side of the mouth, is occupied by a slight elevation or 
blunt process which contains the brain. This process has a 
slight resemblance to a Doge’s cap, but it is really nothing 
more than an extension of the body-wall on the dorsal side of 
the thickened lip which surrounds the mouth. The skin 
covering this process is not pigmented, but the whole of it is 
uniformly ciliated, the cilia being continuous with those which 


222 ARTHUR E. SHIPLEY. 


line the cesophagus. The cilia also cover the ventral lip. 
The lobe is more or less solid (fig. 12), and contains the brain, 
the rest of the space being filled up with connective tissue. The 
brain gives off a median nerve (figs. 10 and 11), which passes 
into the lobe, and is distributed, I believe, to the epidermal 
cells, so that doubtless the lobe has a tactile and sensory 
function. 

Just beneath the brain, on the dorsal surface of the ceso- 
phagus, the retractor muscle is inserted ; it wraps round about 
two thirds of the circumference of that tube (fig. 12). 

Corresponding with the absence of the tentacular crown 
there is a total absence of any vascular system, a peculiarity 
which Onchnesoma shares with Petalostoma and Tylosoma. 
There can be no doubt that in those forms which possess ten- 
tacles they have both a tactile and sensory function, and that 
they serve, by the currents their cilia give rise to, to bring 
food to the mouth. It is also believed that they have a respi- 
ratory function ; and though this is probably the case, it must 
not be overlooked that the above-mentioned genera manage 
to respire without tentacles. Where the exchange of gases 
takes place is not so easy to state. The skin of Onchnesoma is 
relatively to the size of the animal at least as thick as that of 
the larger Sipunculids, and is covered by a thick cuticle. It 
has occurred to me that the coelomic fiuid may possibly obtain 
the oxygen it requires from the water which passes through 
the intestine of the animal. The coiled nature of this tube 
exposes a very considerable area to the fluid in the celom, and 
the extreme thinness and delicacy of its walls would favour a 
ready exchange of gas. If such a function were exercised by 
the alimentary canal, it would possibly explain the thinness of 
the digestive walls, which in other respects seems ill adapted 
to a diet of sand. ; 

In Onchnesoma there is only one kind of corpuscle in 
the coelomic fluid; this is spherical or nearly so, with 
granular protoplasm and a well-defined nucleus (figs. 7 
and 8). The celomic fluid must be kept in very constant 
motion, both by the ciliated cells of the peritoneal epithe- 


ON ONOHNESOMA STEENSTROUPII. 228 


lium, and by the alternate protrusion and retraction of the 
introvert. 

In the two species of Phymosoma which I have described ! 
there is a very extensile fold of skin or collar which surrounds 
the base of the head, and which, when the introvert is re- 
tracted, usually completely encloses the head. The function 
of this collar is perhaps to shield and protect the delicate 
ciliated tentacles and lips from contact with the indurated 
surface of the introvert, provided as it often is with horny 
hooks. No such collar is found in Onchnesoma. 


Tut Nervous System. 


The brain is an elongated mass situated dorsal to the mouth, 
at the base of the median dorsal ciliated lobe (fig. 11). It 
shows no trace of being bilobed. Like that of Phymosoma, 
the brain of Onchnesoma consists of a cap of ganglion-cells 
which cover in a fibrous portion on all sides except that 
nearest the cesophagus, the ventral (fig. 12). There are no 
giant ganglion-cells tobe seen. The nerve-cells are all of one 
size, with nuclei which stain deeply. On the dorsal surface 
the brain is continuous with the epidermis ; but in this region, 
just at the base of the median dorsal process, the epidermal 
cells are not in any way modified. The pigment which accu- 
mulates in similarly placed cells in other Sipunculids is 
absent. There are also no eyes. 

The brain gives off three nerves; a median nerve to the 
median dorsal lobe, and one on each side, which pass round 
the cesophagus and fuse together to form the ventral nerve- 
cord (figs. 9,10, and 11). The median nerve is doubtless the 
equivalent of the pair of nerves which supply the pigmented 
pre-oral lobe in Phymosoma. The median lobe is probably 
sensory and tactile, and is therefore supplied with a stout 
nerve. The second pair of nerves in Phymosoma, which supply 

1 On Phymosoma varians,” ‘Quart. Journ. Mier. Sci.,’ April, 1890. 


“Qn a New Species of Phymosoma, with a Synopsis of the Genus,” ‘ Quart. 
Journ, Mier. Sci.,’ March, 1891. 


224 ARTHUR E, SHIPLEY. 


the tentacular lophophore, is naturally not represented in 
Onchnesoma, as the tentacles are absent. 

At the sides the brain is continued into two nerves which 
pass round the mouth embedded in the tissue, just where the 
retractor muscle is attached to the cesophagus (fig. 9); they 
fuse together on the ventral surface, and form the ventral 
nerve-cord, which shows no sign of its double origin (fig. 8). 
The portion of this cord which lies in the introvert is oval in 
cross section ; that which lies in the body is round. In Phy- 
mosoma and in Sipunculus the ventral nerve-cord is supported 
by numerous strands of muscle continuous with the skin, 
which permitted the introvert to be extended or withdrawn 
without any strain being placed on the cord; but in Onch- 
nesoma the cord is closely attached to the skin, and in the 
region of the introvert is almost embedded in the muscular 
layer. 

As is the case in other Sipunculids, the ganglion-cells are 
arranged on the ventral surface, the fibres on the dorsal. The 
nerve-cord gives off numerous branches into the body-wall, 
whose course I was not able to follow; but Koren and 
Danielssen have traced them into a fine ganglionated network 
amongst the muscles, &c. 

The nerve-cord extends to the posterior end of the body. 


Toe NEPHRIDIUM. 


There is only a single nephridium in Onchnesoma, and its 
position is not very constant ; it may lie either to the right or 
to the left of the nerve-cord, but its external orifice is always 
a little below the ring-like thickening which marks the 
junction of the proboscis and the body. 

In its main features the nephridium resembles the same 
organ in Phymosoma varians, with the exception that there 
is no distinction between glandular and non-glandular regions, 
The external orifice leads straight into the lumen of the gland, 
which is as arule somewhat pear-shaped. The internal opening 
is close to the external ; it has a flattened, funnel-shaped border, 
and is ciliated, : 


ON ONCHNESOMA STEENSTRUPII. 225 


The walls of the nephridium are lined throughout, with the 
exception of the small area between the external and internal 
opening, with glandular cells of a considerable size; with the 
exception of the ova they are the largest cells in the body 
(fig. 4). The lumen of the kidney in Onchnesoma is not split 
up into a series of crypts communicating with a central cavity, 
as was the case in Phymosoma ; and the cells do not get rid of 
the product of their secretion by breaking off a bubble from 
their free end. Each of the large columnar cells has a very 
definite outline ; their protoplasm is very clear and does not 
stain well, but scattered through it are a great number of 
granules which stain deeply. These concretions differ in size ; 
they are always spherical, and the larger ones have a double 
contour. These latter are often found in the lumen of the 
nephridium, having doubtless passed out of the glandular cells, 
and being on their way out of the body. 

I have never seen ova or spermatozoa in the lumen of the 
kidney, though I have no doubt that they leave the body 
through this channel. 

The muscular layer is not so well developed in the nephridium 
of Onchnesoma as in that of some other Sipunculids, and the 
size of the kidney was more constant. Covering the outside of 
the organ is a layer of peritoneal epithelium. 

With regard to the number of nephridia, two is undoubtedly 
the normal number in the Sipunculids; the genera Phasco- 
lion, Tylosoma, and Onchnesoma being singular in having but 
one. There are, however, exceptions to this rule: thus Phas- 
colosoma squamatum has but one, and Aspidosiphon 
tortus also retains but one; and in both these cases it is the 
left that persists. Some species of Phascolion, on the other 
hand, retain the kidney of the right side only ; and in Onchne- 
soma sometimes the left and sometimes the right persists, but 
never both together. 


Tue ALIMENTARY CANAL. 


The cilia which cover the dome-shaped dorsal process of the 
head and the lower lip are continued without break into the 


226 ARTHUR E. SHIPLEY. 


alimentary canal (fig. 12). When the introvert is extended, 
the first part of the digestive tube or the oesophagus forms a 
straight tube with smooth walls; when, however, the introvert 
is retracted, the walls of the esophagus are thrown into a 
number of circular folds with intervening depressions. The 
cells lining this part of the alimentary canal are cubical, and 
thickly beset with cilia. 

Throughout the intestine the lining epithelium is surrounded 
by a layer of connective tissue, which is in its turn covered by 
the peritoneal epithelium ; the connective tissue varies in thick- 
ness in different parts of the tube, but it is especially thick on 
the dorsal surface of the anterior end of the esophagus: it is 
just here that the single retractor muscle is inserted. 

The cesophagus passes into the descending intestine, whose 
walls are lined by large glandular cells: these have, when the 
intestine is comparatively empty, a columnar shape ; but if the 
intestine is full of food its walls are stretched, and the liuing 
cells become cubical, or even depressed. Owing to the small 
size of the animal it is not possible to wash the food out of 
the alimentary canal, and the nature of the food rendered it 
very difficult to cut satisfactory sections of the walls of the 
alimentary canal. These were in most cases torn ; hence I have 
not been able to settle quite definitely whether the cells lining 
the descending intestine are ciliated or not, but I am inclined 
to think they are. 

The ascending intestine is certainly lined with ciliated cells. 
It is distinguished by the possession of a longitudinal groove, 
which is lined by cells bearing especially long and large cilia. 
A similar groove is described by Mr. E. A. Andrews in Sipun- 
culus Gouldii.! He states that “in it a current of liquid 
passes from the action of cilia, and possibly also of the radiat- 
ing fibres, towards the anus during life.” The absence of this 
groove is the only thing which distinguishes the short rectum 
from the descending intestine. 

1 «Notes on the Anatomy of Sipunculus Gouldii, Pourtalés,” E. A. 


Andrews, ‘Studies from the Biological Laboratory,’ Johns Hopkins Uni- 
versity, Oct., 1890. 


ON ONOCHNESOMA STEENSTRUPII. 227 


The whole alimentary canal is attached to the body-wall by 
a few fibrous strands, but there appears to be no spindle muscle 
running up the axis of the spirally coiled intestine. 

The food of Onchnesoma, judging by the contents of the 
intestine, consists of vegetable débris ; mixed with this is a con- 
siderable amount of sand and a number of spicules, whose 
precise nature I was not able to make out. 

The enormous amount of sand and mud which passes through 
the body of the Sipunculids shows that these animals must 
take a considerable share in the reducing action to which the 
mineral substances at the bottom of the sea are subjected. 
Mr. J. Y. Buchanan has recently published an interesting 
paper “ On the Occurrence of Sulphur in Marine Muds,”? in 
which he has drawn attention to the fact that most silicates 
are to some extent soluble when pulverised under water, and 
the sand is to some extent crusted in passing through 
the body of most mud-eating animals, and this solubility 
is increased by the sulphates in the sea water which passes 
through the intestine of the animals. The sulphates are 
reduced by the organic products of the body to sulphides, and 
these unite with the iron or manganese of the silicates, and 
leave the body as sulphides of iron or manganese. These sul- 
phides are then oxidised by the oxygen which exists in sea 
water, and form the red clays and chocolate muds which cover 
a considerable extent of the bottom of the sea. Thus the con- 
stitution of the mud at the bottom of the sea is to a very large 
extent artificial, and the Sipunculids play a considerable réle 
in bringing this about. 

These processes must be mainly effected by Holothurians, 
Echinids, Polychztes, and Sipunculids ; and to arrive at some 
sort of an estimate of the amount of sand taken into the body 
of the latter animals, I recently weighed five specimens, 
chosen at random, of S. nudus from Naples, and then weighed 
the sand in their intestines. The average weight of their body 

1 “Qn the Occurrence of Sulphur in Marine Muds and Nodules, and its 
Bearing on their Mode of Formation,” J. Y. Buchanan, ‘ Proc. of the Royal 
Soc, of Edinburgh,’ Dec., 1890, 


228 ARTHUR E. SHIPLEY. 


was 19:08 grms., that of the sand 10:03 grms. In two of 
them the sand weighed more than one half the total weight, 
the body being in one case 24°4 grms. and the sand 13°72, and 
in the other 15:05 grms. and 9:45. The contents of the 
intestine consisted of blackish sand with a few Foraminifera 
mixed with it. In spite of the considerable amount of sand 
which these figures show to be contained in the intestine, the 
wall of this tube in all the Sipunculids with which I am 
acquainted is excessively thin, and apparently but poorly 
adapted to retain the sharp and jagged pieces of sand which lie 
within it. A similar tenuity of the wall of the alimentary 
canal also occurs in Echinids and Holothurians. Although 
this wall is so thin I have never found a Sipunculid with its 
intestine ruptured, so that in spite of appearances it seems to 
serve its purpose well. 

I have mentioned above that I am of opinion that the 
respiration of Onchnesoma is carried on through the walls of 
the intestine. The seat of the process of respiration is still a 
debatable point in the anatomy of the unarmed Gephyrea. 
Of the two recent authors who have written on the anatomy 
of Sipunculus, Mr. Andrews! is convinced that the tentacles 
act as branchie, whilst Mr. Ward? is of opinion that they do 
not. In Onchnesoma, at any rate, there cannot be any 
question as to the respiratory action of the tentacles, as the 
latter are entirely absent. In other Sipunculids the tentacles 
may to a slight extent serve as the organs of respiration, but 
the closed vascular system which supplies them with blood is 
of such a very limited extent that it would ouly suffice for a 
small portion of the body ; on the other hand, it seems to me 
quite possible that the brain, which is almost entirely sur- 
rounded by this system, may obtain its oxygen from it. 

The chief circulating medium in the body of the unarmed 
Gephyrea is undoubtedly the corpusculated coelomic fluid, and 


1 Loc cit., p. 419. 

2 “Onsome Points in the Anatomy of Sipunculus nudus, L.,” Henry B. 
Ward, ‘Bull. of the Museum of Comp. Anat., Harvard College,’ vol. xxi, 
No. 3, May, 1891. 


ON ONOHNESOMA STEENSTRUPII. 229 


in the case of Onchnesoma this forms the only circulating 
fluid. All the organs of the body, the alimentary canal, the 
nerve-cord, the nephridia, the chief muscles, and the genera- 
tive organs, are suspended in this fluid, and bathed by it on all 
sides. The ccelomic fluid is kept in constant movement by 
the protrusion and retraction of the introvert, and by the 
action of the ciliated peritoneal epithelium which lines the 
body-wall and covers the internal organs. Thus the corpus- 
culated ccelomic fluid is continually flowing over and circulating 
around all the organs suspended in it, and there is not much 
doubt that it acts as a carrier of oxygen to them. 

The problem next arises, where does it effect the exchange 
of gas which constitutes respiration? This seems capable of 
two solutions: the celomic fluid takes its oxygen either from 
the corpusculated fluid of the closed vascular space, or through 
the walls of the alimentary canal. I am inclined to think that 
the latter alternative is responsible for the chief supply of 
oxygen to the body. 

The walls of the vascular system are not very thin, and they 
do not present a very large surface to the coelomic fluid; and 
although I think it possible that this fluid acts to a certain 
extent as a carrier of oxygen, more particularly to the brain, 
which, except where it is continuous with the epidermis, is 
surrounded on all sides by it, I still think that the primary 
function of the closed vascular system is to extend the tentacles 
by the contraction of its muscular walls forcing fluid into them, 
and that the primary function of the tentacles is to bring food 
to the mouth by the action of their cilia. For these reasons I 
think it, both on morphological and physiological grounds, in- 
expedient to speak of the tentacles as branchiz. 

The alimentary canal, on the other hand, has very thin 
walls, and owing to its looped and coiled disposition presents 
a very large surface to the celomic fluid. A considerable 
amount of water must be continually passing through the 
alimentary canal, since the food of the animal is brought into 
the esophagus in a current of water set up by the cilia. This 
current is set up by the cilia lining the lips and esophagus, 


230 ARTHUR E. SHIPLEY. 


and is, I believe, maintained as a constant flow by the action 
of the cilia lining the ciliated groove which runs along one 
side of the ascending intestine. This groove is lined by cells 
bearing strong cilia. I have never seen any trace of food in it ; 
and its chief function is, I think, to maintain the current of 
water which passes through the alimentary canal. 

Professor Semper, in his ‘ Animal Life,’ has drawn atten- 
tion to those animals which breathe through their intestine. He 
has described certain foliated processes on the stomach of a 
Holothurian—Stichopus variegatus—which function as 
gills; he also mentions the common loach, Cobitis fossilis, 
which breathes through its stomach, but in this case it 
swallows air from the surface of the water. This air “is de- 
prived of a portion of its oxygen in the intestine.” Certain 
Brazilian fish, of the genera Calichthys, Doras, and Hypo- 
stomus, which also swallow air, have curious processes or folds 
of the lining of the intestine, which have been regarded as 
especially adapted for respiration. The anal respiration, 
which Professor Hartog has described in so many Crustacea 
and insect larve, is but another example of the alimentary 
canal being used as a respiratory organ. These instances are 
sufficient to show that in ascribing a respiratory function to 
the alimentary canal of Sipunculids one is supported by 
numerous analogous cases. 


TuE GENERATIVE ORGANS. 

Onchnesoma, like other Sipunculids, is dicecious. The testes 
are formed by the growth of a small clump of cells lining the 
coelomic cavity in the neighbourhood of the point of origin of 
the single retractor muscle (fig. 7). I have not been able to 
find any ovary, though I suspect that when mature it is to be 
found in the same situation. Numerous ova were found float- 
ing in the celomic fluid of the females; but, as Koren and 
Danielssen have remarked, “ while the ova continue their 
development in the perivisceral cavity, the last vestiges of the 
ovary disappear entirely, so that no trace of it remains.” 

Like the ova, the spermatozoa undergo a considerable de- 


ON ONCHNESOMA STEENSTRUPII. 231 


velopment whilst floating in the coelomic fluid. They leave 
the testis in the condition of the mother-cells of the sperma- 
tozoa ; these segment, and the sperm morula result. The 
spermatozoa keep together in sperm morule till they have 
passed through the nephridium and out of the body. 


ConcLUSIONS. 


Onchnesoma is the smallest Sipunculid with which we are 
acquainted, and its anatomy is to a considerable extent more 
simple than that of other members of the group. 

The head is much simplified; the lip which surrounds the 
mouth bears no tentacles, but is produced dorsally into a blunt 
process covered with cilia. The simplicity of structure is 
shown by the absence of any tentacles, hooks, collar, pig- 
mented skin, and eyes; there is also no vascular system, 
no spindle muscle, and no giant-cells are found in the brain. 
The retractor muscle is single and arises from the extreme 
posterior end of the body, and is, therefore, symmetrical ; the 
nephridium is also single, and may lie to the right or left of 
the body. The brain is not bilobed. 

Until we know something of the development of Onchne- 
soma it would be hazardous to express an opinion as to whether 
the absence of the above-mentioned organs is due to degenera- 
tion, or whether they are primitive. On the one hand, the 
small size of the animal and the presence of one nephridium, 
which occurs on either side of the median line, points to 
degeneration ; whilst, on the other, the structure of the head 
indicates a primitive condition, which might admit of modifi- 
cation in various directions. 

The absence of any closed vascular system, correlated with 
the absence of tentacles, may throw some light upon the vexed 
question of the seat of the respiratory processes in Sipunculids. 
Since there are no tentacles, there is one Sipunculid at least 
which does not breathe by them; and although I think, when 
they are present, some respiration may be carried on by them 
and the closed vascular system, especially in reference to the 


232 ARTHUR E. SHIPLEY. 


brain, I am disposed to think that the main function of the 
tentacles is to create a current, and thus bring food to the 
mouth ; and the chief use of the vascular system is to extend the 
tentacles. 

I am inclined to look for the chief respiratory organ in the 
intestine ; this has very thin and extensive walls, and exposes a 
large surface to the coelomic fluid, which in its turn bathes all 
the organs of the body except the brain. A considerable 
volume of water passes through the alimentary canal, enough 
to supply the oxygen required, and this current is maintained 
by the ciliated cells of the groove in the ascending intestine. 


Tur MorpHotocicaL LABORATORY, 
CamBripce; August, 1891. 


EXPLANATION OF PLATE XV, 


Illustrating Mr. Arthur E. Shipley’s paper on “ Onchne-. 
soma Steenstrupii.” 


Fie. 1—An enlarged view of O. Steenstrupii, with the introvert 
partially retracted. 

Fic. 2.—The same, life size. 

Fic. 3.—A view of the arrangement of the internal organs, shown by opening 
the body-wall along the right side and reflecting the sides. Copied from 
Koren and Danielssen. 

Fic. 4.—Section through a portion of the glandular wall of the nephridium, 
showing the glandular cells and their concretions. 

Fie. 5.—Section through the ascending intestine to show the ciliated 
groove. 

Fie. 6.—Section through the skin, parallel with the long axis of the body, 
showing cutis, epidermal glands and their secretions, circular and longitudinal 
muscle layers, and lining peritoneal cells. 

Fic. 7.—Longitudinal section through the posterior end of the body, 
showing origin of single retractor, and the group of peritoneal cells which 
form the testis. 


ae 
° 
Xe. 


o 


Shipley del 


neph ridin: 


retractor mits cle 


corpuscles a 


om cure. rd 
Cates 


retract! 


SEPT UT UA 


testis. ee 


Studies M.L.Vol.V, Pl. XV. 


rad of wntrovert, 


4) 
—~ 


‘ / { = os 
ee Ze 
go ge 
og aay =é 
— Ohne eo 


.. lateral nerve 


4 
: 
> 


lly, 


VTS 


Og. 
ASO EUS === =~ 
POLI CL, TULEC 


F Huth, lith® Edin™ 


ON ONCHNESOMA STEENSTRUPII. 233 


Fic. 8.—Transverse section through the introvert, showing the layers of 
the skin, the cesophagus, retractor muscle, and ventral nerve-cord. The 
body-cavity contains corpuscles and sperm morule, 

Fig. 9.—Longitudinal lateral section of the extended introvert, showing 
mouth, cesophagus, and thickened ciliated lip, with the circum-cesophageal 
nerve of each side. 

Fic. 10.—A section of the brain, parallel to the preceding (fig. 9), but more 
dorsal. It shows the distribution of the ganglion-cells and fibres in the brain, 
and the three main nerves given off from it ; also the insertion of the retractor 
muscle, and one of the recesses formed by the crumpled nature of the 
cesophagus. 

Fic. 11.—Diagram representing the arrangement of parts in the head, 
which is supposed to be divided medianly. The right half only is shown. 

Fic. 12.—Section through the head and brain. The introvert is retracted. 
The section is not quite in the middle line, and does not show the counection 
of the brain with the epidermis. 


VOL. V, PART II, 9 


Notes on Elasmobranch Development. 
By 


Adam Sedgwick, M.A., F.R.S., 
Fellow and Lecturer of Trinity College, Cambridge. 


With Plate XVI. 
ConTENTs., 
PAGE 
1. On the Formation and Growth of the Embryo and on the Blastopore 234 
2. On the Formation of the Mouth and Gill-clefts é F . 245 


3. Segmentation of the Cephalic Mesoderm and Development of Nerves 247 


1. On the Formation and Growth of the Elas- 
mobranch Embryo. 


My observations on this subject, which were made upon the 
genera Scyllium and Raia, have led me to conclusions which 
differ in some respects from those of previous observers. In 
some of the points with regard to the tail I have been 
anticipated by Schwarz (‘ Zeit. f. wiss. Zool.,’? Bd. xlviii, p. 
191), Kowalevsky, and Kastschenko (‘ Anat. Anzeiger,’ 3) ; 
but as Schwarz’s account—excellent though it is—does not go - 
over the whole ground, and Kastschenko’s is without figures, 
while Kowalevsky’s is inaccessible, being published in Rus- 
sian, I have thought it worth while to treat the matter fully. 

As is well known, the blastoderm attains a certain size before 
any trace of the embryo is visible, spreading by a uniform 
growth at all points of its circumference over the yolk. 
At Balfour’s Stage A, however, the first trace of the embryo 
appears as a slight thickening at one point of the circumfer- 
ence of the blastoderm. This point is usually regarded as the 
hind end of the blastoderm. This is not quite correct, for it 


NOTES ON ELASMOBRANCH DEVELOPMENT. 235 


really becomes the front end of the future embryo. After the 
appearance of the embryonic rim the blastoderm still con- 
tinues to spread over the yolk by a uniform growth of all 
parts of its circumference, but in the centre of the embryonic 
rim a slight indentation appears. This indentation shares in 
the uniform growth of the blastoderm edge, and advances over 
the yolk equally with the rest of the embryonic rim and 
general edge of the blastoderm. As the embryonic rim 
travels away from the point of its first appearance, the surface 
of the blastoderm so formed—that is to say, the surface of the 
part of the blastoderm extending between the point of first 
appearance of the embryonic rim and the embryonic rim at 
any given moment of its growth—is slightly elevated from the 
rest of the blastoderm, and traversed by an inconspicuous 
longitudinal median groove. This raised part of the blasto- 
derm soon becomes marked off by two ridges, which in front, 
i.e. at the point which marks the site of the first appearance 
of the embryonic rim, are continuous with one another, while 
behind they are continuous with the parts of the embryonic 
rim which bound the indentation. These portions of the 
embryonic rim are more markedly swollen than the rest, and 
form the “ tail swellings ”’ of Balfour. This elevated part of 
the blastoderm is the medullary plate, and the shallow groove 
traversing it marks the line of growth of the indentation 
above referred to. These points are all illustrated by my 
fig. 1, which represents the embryo at a stage where the 
indented embryonic rim has grown back a considerable dis- 
tance from the point of its first appearance. Various stages 
in the process may be seen in Balfour’s figures’ of Stages B, 
C, D, and in Schwarz’s figs. 1 and 2. The indentation of the 
embryonic rim is always placed at the hind end of the groove 
which marks the centre of the medullary plate. This groove 
is a transitory structure, and soon disappears ; its importance 
consists in the fact that it indicates the line of growth of the 
indentation of the embryonic rim. (It is conterminous in 

1 ‘Monograph of Development of Elasmobranch Fishes,’ pl. vii; pl. vili 
of the Memorial Edition. 


236 ADAM SEDGWICK. 


extent with the notochord, though the notochord beneath the 
front part of it is not at first developed.) 

It must be clearly understood that the growth of the whole 
edge of the blastoderm has so far been a uniform one. The 
indentation in the embryonic rim advances equally (after its 
first establishment) with the more prominent parts of the 
embryonic rim called the caudal swellings. There is no 
reason to suppose that this advance of the indented part of 
the embryonic rim is due to the fusion of the divergent caudal 
swellings. On the contrary, there is every reason to suppose 
that the indented part of the embryonic rim advances by 
growth of its own substance, just as do the other parts of the 
edge of the blastoderm. 

After a certain time the caudal swellings and the part 
between them begin to grow more rapidly than the adjacent 
portions of the edge of the blastoderm, and come to project 
beyond the latter like a kind of tongue overhanging the yolk 
(fig. 2). This appears to happen at about the time when the 
medullary groove is closing in its anterior part to form the 
medullary canal. 

At the same time the edge of the blastoderm remote from 
the embryo has continued its rapid growth. It is only the 
edge of the blastoderm next the embryo in which the growth is 
retarded. The result of this is that the posterior projecting 
part of the embryo lies in a kind of bay of the edge of the 
blastoderm. Fig. 2 is drawn from an embryo at a stage when 
this bay was but little marked. 

I now wish the reader to concentrate his attention upon the 
projecting tongue which will form the under part of the 
embryo. Its sides, which are part of the edge of the blasto- 
derm, bend ventralwards and towards each other.! It consists 
on its dorsal face of the medullary plate ectoderm, which has 
become folded so as to form the neural canal (in fig. 2 the 
neural canal is established in the front part of the embryo, but 
widely open at the hinder end of this projecting tongue). At 


1 A good figure of this is given by His in the ‘ Zeitschrift f. Anatomie u. 
Entwick. Gesch.,’ 1877, pl. vii, fig. 6. 


NOTES ON ELASMOBRANOH DEVELOPMENT. 237 


its edge, which is part of the general edge of the blastoderm, 
the ectoderm is continuous with the endoderm which forms 
the under side of the tongue. A good idea of the appearance 
of a transverse section through this tongue is given by fig. 
14, pl. x,' of the ‘ Elasmobranch Fishes’ (Mem. Ed.). The 
hinder end of the tongue is of course notched, and the notch 
is continued forwards along the line of the groove above men- 
tioned as occupying the centre of the medullary plate, as a 
slit which actually completely perforates the blastoderm, so as 
to lead into the space between the endoderm of the tongue 
and the yolk. This is shown clearly in fig. 3, and at a later 
stage in fig. 4. Whether this slit is due to a bilobed back- 
ward growth of the notched portion of the embryonic rim, 
the growth at the middle point, i. e. at the bottom of the notch, 
ceasing—in other words, to an emphasising of the notch already 
present—or whether it arises as a secondary perforation of the 
medullary plate and endoderm along the line of the groove 
before mentioned, I am unable to say; but I think it is due to 
the former. 

While these changes have been taking place—and I must 
now refer back to fig. 2—the sides of the projecting tongue 
become bent ventralwards and towards each other until they 
meet or nearly meet in the ventral middle line. Now two 
important structural results, which should be noted and under- 
stood, follow from this bending: (i) the two angles formed by 
the junction of the edge of the blastoderm in the embryonic 
region with the edge of the blastoderm in the non-embry- 
onic region—the angles, one of which is marked a in fig. 2, 
become closely approximated ventrally beneath the embryo ; 
and (ii) a space is enclosed on the ventral side of the embryo, 
which space is lined by endoderm, and opens ventrally to the 
exterior through a slit formed by the contact of the ventrally 
bent edges of the tongue, and dorsally into the neural canal 
by the slit in the medullary plate. This space’ is the hind 

1 Old edition, pl. ix, fig. 12. 

2 A section of the tongue iu this stage in front of the neurenteric slit is 
shown in Schwarz’s fig. 16, 


238 ADAM SEDGWIOK. 


gut, and the two slits which are continuous with one another 
round the hind end of the embryo are portions of the blasto- 
pore. By the timethat the two angles marked a and the edges of 
the embryonic part of the blastoderm have come into contact 
ventrally, the non-embryonic edges of the blastoderm adjacent 
to the embryo have grown backwards over the yolk to form 
the bay mentioned by Balfour. The two sides of this bay, 
which it will be remembered are portions of the edges of the 
blastoderm, come to lie close together on the yolk beneath 
the tail of the embryo. For a little time they remain unfused, 
and the yolk is still freely exposed between them in a linear 
streak.! This slit, which is bounded by the edges of the non- 
embryonic part of the blastoderm of the two sides, is a part of 
the blastopore, and is continuous, passing along the hinder 
side of what will be called the umbilical stalk, with the portion 
of the blastopore leading into the hind gut and extending 
along the ventral side of the tail. This last portion is, as we 
have seen, continuous with a dorsal portion which leads 
through the medullary plate into the medullary canal. 

The last part of the blastopore to be mentioned is the so- 
called yolk-blastopore, described by Balfour in the ‘ Elasmo- 
branch Fishes,’ p. 81 (Mem. Edition, vol. iii, p. 296), and in 
the ‘ Comparative Embryology,’ lst ed., ch. iii, p. 52.2. The 
lips of this portion are continuous with the lips last men- 
tioned as running back on the yolk parallel to one another, 
and ventral to the tail of the embryo. 

To recapitulate : the blastopore of Hlasmobranchii is at the 
present stage—i. e. the stage immediately before closing—an 
elongated narrow slit, slightly dilated in front, where it lies 
on the floor of the medullary canal (fig. 3) and more dilated 
behind (Balfour’s yolk-blastopore, ‘Comparative Embryology,’ 
vol. ii, ch. iii, fig. 30 6). Between these two limits it takes 
the course of a reversed letter S, as shown in the adjoining 
woodcut, where its lips are represented unfused. 

The anterior part, @ 6, perforates the floor of the medullary 


1 Again see Schwarz’s fig. 16, d.o. 
> Mem. Ed., vol. iii, p. 63. 


NOTES ON ELASMOBRANCH DEVELOPMENT. 239 


canal, and is dorsal; this is continuous round the end of the 
tail, 6c, with a ventral part, which extends forwards along the 
ventral side of the tail, c d, as far as the yolk-stalk, along which 
it passes, @ e, to continue backwards along the yolk, ef, as the 
slit-like non-embryonic part of the blastopore, which passes 
behind into the more dilated and posterior part of the so-called 
yolk-blastopore. 


Shortly after this stage the blastopore completely closes, 
excepting one point in its dorsal portion, which persists for 
some time as the neurenteric canal. 

Balfour, asis well known, was the first to compare the primi- 
tive streak of the Amniota to “the linear streak in Elasmo- 
branchii, formed by the coalesced edges of the blastoderm 
which connect the hinder end of the embryo with the still 
open yolk-blastopore” (‘Comparative Embryology,’! 1st ed., 
vol. ii, ch. xi, p. 240); and he also says, in the same place, 
that “the passage at the front end of the primitive streak [the 
neurenteric canal] is the dorsal part of the blastopore, which 
in Elasmobranchii becomes converted into the neurenteric 
canal.” But he never, either in the chapter quoted or in 
his account of the actual development of Hlasmobranchs in 
ch, iii, p. 52, describes the ventral embryonic part of the 
blastopore (woodcut, ¢ d) which connects together the linear 
streak on the yolk, e f, with the dorsal part of the blastopore, a 5.? 
In fact, he says (ch. iii, p. 52), “ It is interesting to notice that, 
owing to the large size of the yolk in Elasmobranchs, the pos- 
terior part of the primitive blastopore becomes encircled by 
the medullary folds and tail swellings, and is so closed long 


1 Mem. Hd., p. 288. 
2 This part of the blastopore is clearly recognised and figured by Schwarz. 


240 ADAM SEDGWICK. 


before the anterior [what I have called posterior] and more 
ventral part, which is represented by the uncovered portion of 
the yolk.” 

T have dwelt at some length upon this point because Balfour’s 
description of the Elasmobranch blastopore has always bothered 
me, in that it does not show the connection between the yolk 
part of the blastopore—the linear streak—with the dorsal 
part ; and also because I wish to present a slight modification 
of the comparison which Balfour made between the primitive 
streak of the Amniota and the linear streak on the Elasmo- 
branch yolk. Balfour does not say that the two structures are 
homologous ; he expressly guards himself from this. Hesays 
(‘Comparative Embryology,’ Ist ed., vol. ii, ch. iii, p. 51), “A 
linear streak [my woodcut, e/'] formed by the coalesced edges of 
the blastoderm is left connecting the embryo with the edge of 
the blastoderm. This streak is probably analogous to (though 
not genetically related with) the primitive streak in the 
Amniota” (the italics are mine). But he undoubtedly does 
compare the primitive streak with this linear part of the yolk- 
blastopore of Elasmobranchs ; and he says (‘Comparative Hm- 
bryology,’ vol. ii, 1st ed., ch. xi, p. 240), “That it (primitive 
streak) is in later stages not continued to the edge of the 
blastoderm, as in Elasmobranchii, is due to its being a rudi- 
mentary organ.” 

The modification which I would propose to suggest in the 
comparison is as follows. The primitive streak of the Am- 
niota is, as is well known, partly involved in the tail fold, and 
tucked under on to the ventral surface of the embryo. It 
thus becomes divided into a dorsal part, at the front end of 
which is the neurenteric canal or its rudiment, and a ventral 
part. The dorsal part is in birds for some time placed in a 
dilated posterior part of the still open medullary groove called 
the sinus rhomboidalis. This part I would compare to 
the dorsal part of the blastopore shown in the same position 
and relations in my figs. 3 and 4. The ventral part, on the 
other hand, I would compare to the part of the blastopore 
which in Elasmobranchs runs along the ventral side of the tail 


NOTES ON ELASMOBRANOH DEVELOPMENT. 241 


io the yolk-stalk (my woodcut, c d); while the linear part 
f the yolk-blastopore in Elasmobranchii (my woodcut, e f) is 
mrepresented or rudimentary in Aves and Amniota gene- 
‘ally—is, in fact, the rudimentary part referred to by Balfour 
n the above quotation from the ‘ Comparative Embryology.’ 

The comparison has the advantage of bringing together the 
syrowing points of the embryos in the two cases. In 
Amniota the primitive streak is the growing point where the 
sells are proliferated, out of which the greater part of the 
2mbryo is formed. In Elasmobranchii the tail swellings 
which form the sides of the dorsal and ventral parts of the 
smbryonic blastopore (my woodcut, @ b ¢ d) are the points 
where the active growth takes place, as a result of which the 
hinder part of the embryo is formed. Indeed, the prominence 
of the tail swelling is due to the mass of mesoderm-cells pro- 
duced by this proliferation at the edge of this part of the 
blastopore. 

The proliferation of mesoderm takes place in a rudimentary 
fashion in Elasmobranchii, at all points of the circumference 
of the blastoderm; which circumference, gradually creeping 
over the yolk and enclosing it, constitutes the lips of the 
widely open blastopore; but the proliferation is very feeble 
except at the notched embryonic rim, the growth of which 
forms, as above described, the tail end of the embryo. 

It is interesting to notice the different manner in which the 
tails of Elasmobranchii and Amniota are formed. There is in 
the former no tail fold as in the latter, but simply a bilateral 
bending round of the posterior tongue-like projection formed 
by the growth backwards of the notched part of the embry- 
onic rim. 

The above account of the Elasmobranch blastopore is not 
given for the first time, although when I did my work—now 
some years ago—I was unaware that a correct account of the 
process had been published by Schwarz in 1889 (‘ Zeit. f. wiss. 
Zool.,’ Bd. xlviii). 

Kastschenko, in the previous year, published an excellent 
paper on Selachian development in the ‘Anatomischer An- 


242 ADAM SEDGWICK. 


zeiger,’ vol. iii, p. 445, in which he calls attention to the fact 
that Kowalevsky, in a paper published in Russian in about 
1870, was the first to describe it correctly. That Kowalevsky’s 
description, if correct, as maintained by Kastschenko, should 
have been overlooked, is of course attributable to the fact of 
its being written in Russian, and not reproduced in any of the 
more commonly known European languages. It seems a great 
pity that an observer of the eminence of Kowalevsky should 
thus secrete his work and render it unavailable to science. 

Kastschenko’s account of the matter is as follows: 

“The closure of the medullary tube presents in the dog- 
fishes interesting peculiarities, which were first discovered and 
correctly described by A. Kowalevsky. .. .. The medullary 
folds are continuous at their hinder ends with the caudal 
lobes, and by means of the latter with the general edge of the 
blastoderm. Each caudal lobe presents a marked knee-shaped 
bend, the point of which is directed backwards. The lateral 
limbs of the paired caudal lobes approach one another on the 
ventral side of the embryo; and when the medullary folds 
fuse on the dorsal surface the adjacent caudal lobes also fuse. 
By the fusion of the former the medullary tube is formed, and 
by the fusion of the latter the neurenteric canal and the hind 
gut. The hind gut, therefore, is the immediate continuation 
of the medullary tube, and the neurenteric canal must be 
regarded as nothing else than a portion of the blastopore. 
Further forwards the hind gut remains for some time open 
ventralwards, but eventually this opening also fuses, the anus 
appearing considerably later in the same place.” 

This account, however, as will be gathered from my descrip- 
tion, does not give the whole gist of the matter. It fails to 
notice the slit-like form of the dorsal part of the blastopore 
which perforates the floor of the medullary canal, and the 
author does not appear to understand, or at any rate fails to 
draw attention to the fact that the ventral opening leading 
into the hind gut is part of the blastopore, and is continuous 
with the slit-like non-embryonic part of the blastopore running 
along the yolk. The only point in which it supplements 


NOTES ON ELASMOBRANOH DEVELOPMENT. 243 


Balfour’s description is in the account given of the formation 
and of the at first open condition of the hind gut. 

I quite agree with Kastschenko’s remarks on the view that 
the embryo is formed by the fusion of two separate halves. It 
must, however, be admitted that the embryo is formed by a 
bilateral growth ; that there are two growing points—one in 
each caudal lobe, which contributes to its development. With 
regard to the growth of the blastoderm, I agree essentially 
with Balfour, but I differ from him as to the growth of the 
embryo. His views are expressed in the following passage 
(‘Comp. Emb., Ist ed., ch. iii, p. 85; Mem. Ed., vol. iii, 
p. 43) :—‘ This rim [the embryonic rim] is a very important 
structure, since it represents the dorsal portion of the lip of 
the blastopore of Amphioxus. The space between it and the 
yolk represents the commencing mesenteron, of which the 
hypoblast on the under side of the lip is the dorsal wall. The 
ventral wall of the mesenteron is at first formed solely of yolk, 
held together by a protoplasmic network with numerous 
nuclei. The cavity under the lip becomes rapidly larger, 
owing to the continuous conversion of lower layer 
cells into columnar hypoblast along an axial line. pass- 
ing from the middle of the embryonic rim towards the centre 
of the blastoderm.”? The italics are mine, and are used to 
bring out the point in which my view is divergent from 
Balfour’s. He regards the embryonic rim, at its first appear- 
ance, as marking the hind end of the future embryo, which is 
formed by a differentiation forwards of the blastoderm, as 
already established. I, on the other hand, regard the same 
point as marking the extreme front end of the future animal, 
and consider that the notched embryonic rim grows over the 
yolk uniformly with the rest of the blastoderm edge. It 
certainly does so extend itself, at any rate until the stage of 
my fig. 1, and of fig. 2 also, allowing for the shoot back of the 
caudal tongue. And it appears to me that this view—which 
is, to a certain extent, in accordance with the view of Roux 
on the growth of the Amphibian embryo (‘ Anat. Anzeiger,’ 
yol. iii, p. 705)—must be looked upon as being nearer the 


24.4, ADAM SEDGWIOK. 


truth than Balfour’s; for if Balfour’s view is correct, the 
embryonic rim being stationary in growth backwards—all the 
differentiation being forward—ought, from the first, to be 
placed in a bay of the edge of the blastoderm. 

According to my view, then, the blastoderm grows uniformly 
over the yolk at all points of its circumference. Indeed, its 
edge is everywhere raised into a marked ridge, which is con- 
tinuous with the embryonic rim. The difference between the 
growth at the embryonic rim and elsewhere consists in the 
fact that, as the former extends over the yolk, a trail of 
columnar epithelial cells is left separated from the yolk by a 
space, whereas elsewhere the raised edge of the blastoderm 
simply slides over the yolk, leaving, as far as one can see, little 
(possibly a few mesoderm-cells) or no trail. 

Further, it is clear, from what I have said above, that the 
notch of the embryonic rim represents the anterior end of the 
blastopore, and that on the view of embryonic growth above 
stated the blastopore does at one time or another perforate the 
whole length of the medullary plate. Posteriorly it does 
actually form for a short time a slit through the medullary 
plate, but anteriorly it keeps closing up as the embryonic rim 
grows backwards, so that it is never present in this region as 
more than a notch. : 

It will be maintained by some that this view of the growth of 
the embryo, and of the relation of the blastopore to the medul- 
lary plate, is incompatible with the objection to the concres- 
cence theory above formulated. Tothisthe reply would be that 
the body of the Elasmobranch embryo is no more formed by 
the fusion of two lateral halves than is the body of the Peri- 
patus embryo, in which nearly the whole of the ventral surface 
is at one time traversed by the long blastopore. 

The phenomenon we are in both these cases dealing with is 
the closure of the blastopore; and to talk about concrescence 
and fusion of two halves is merely obscuring the real question, 
and seeking to explain a process of growth by a phrase which 
has no satisfactory meaning. 

Before leaving this part of my subject I may point out that 


NOTES ON ELASMOBRANCH DEVELOPMENT. 245 


while the anus is formed within the area of the blastopore, and 
is in some Vertebrates actually a persistent part of the blasto- 
pore, in no Vertebrate has the mouth been traced into connec- 
tion with the blastopore. The fact that no such connection 
has been established is not surprising when one remembers 
how early the anterior part of the blastopore closes in Elasmo- 
branchs and Amphibia, and must not be taken as proving that 
the blastopore never extended in front of the present medullary 
plate on to the ventral surface of the head. I shall return to 
this question in the part of this paper which deals with the 
Vertebrate head. : 

It will be seen from the above account that the behaviour of 
the blastopore of Elasmobranchs—in its relation to the anus, 
neurenteri¢ canal, and growing point—resembles very closely 
that of the frog as described in the admirable paper by 
Assheton and Robinson in vol. xxxiiof the ‘ Quarterly Journal 
of Microscopical Science.’ 


2. On the Formation of the Mouth and Gill-clefts 
in Elasmobranchs. 


I have had a number of drawings made of the head of 
embryos of Scyllium canicula to illustrate certain points 
in the formation of the mouth and clefts. Some of the points 
have been known before, and some are, I believe, recorded for 
the first time. 

The mouth makes its first appearance in Stage I as a row of 
dots lying in the middle line between the two mandibular 
arches (fig. 5), and connected by a kind of shallow groove in 
the ectoderm, along which the ectoderm and endoderm are 
fused. These pores soon become connected (fig. 6) to form a 
long slit, which extends from the ventral point of junction of 
the mandibular arches forward along the depression between 
the latter as far as the pocket of ectoderm which is destined to 
give rise to the pituitary body. The first rudiment of the 
mouth actually extends into the rudiment of the pitui- 
tary body. At the front end of the buccal slit the fore-gut, 
the notochord, the ectoderm, and the mesoderm are all con- 


246 . ADAM SEDGWICK. 


tinuous with each other. The mouth soon widens and shortens 
(figs. 8, 10, 12) until it attains its adult form. 

The mandibular arch is at first directed almost from before 
backwards (figs. 5,6, 7), and its anterior end is under the 
mid-brain. 

The hyoid arch is also directed very much backwards, 
though not so much as the mandibular; and its anterior 
(dorsal) end is well in front of the auditory sac (fig. 7). 

The branchial arches are also directed backwards, but the 
inclination is less in the posterior arches than in the anterior 
(fig. 9). 

The question now arises, what is the meaning of this back- 
ward direction of the visceral arches? The only answer that 
I can suggest to this question is that the same cause which 
has produced the flexure of the brain, and of the front end of 
the notochord, has affected the arches. If this is so the cranial 
flexure should really be called cephalic flexure, for it affects 
not merely the brain, but all the organs of the head. 

To account for this flexure we must either suppose that 
there has been a great forward extension of the dorsal anterior 
end of the head, which would carry the dorsal ends of the 
arches forward, and, if the anterior end of the notochord and 
the infundibulum, i.e. the anterior end of the cranial axis, 
remained fixed at the front end of the mouth, would also 
cause the flexure of the brain and anterior part of the noto- 
chord; or that there has been a great shrinking of the ventral 
parts of the head just behind the mouth. If either of these 
views is correct, it necessarily follows that the mouth was 
originally a nearly vertically directed slit looking straight 
forward. It may even have extended on to the dorsal surface. 

The early slit-like form of the mouth is very remarkable, 
and may be regarded as being in favour of the view that the 
mouth is derived from the anterior part of the slit-like blasto- 
pore, though I admit that this does dot constitute a very 
powerful argument. 

The extension forward of the first rudiment of the mouth 
into the pituitary pocket is also very remarkable. 


NOTES ON ELASMOBRANCH DEVELOPMENT. 247 


In Scyllium and Raja the hyobranchial cleft is formed 
before the spiracular cleft. 

It is interesting to notice in this series of heads the manner 
in which the at first straight mandibular arch is bent upon 
itself at the point which will become the point of articulation 
of the upper and lower jaws. The part anterior to the 
angle develops a forward projection and forms the upper 
jaw—the part behind is bent ventralwards and outwards 
and forms the lower jaw. The widening and shortening of 
the mouth seems largely due to this bending of the mandibular 
arch (cf. series of figures of heads in ventral and side view). 

The view that the mouth is derived from the anterior end of 
the blastopore was originally put forward in my paper on “ The 
Origin of Metameric Segmentation” (‘Quart. Journ. Micr. 
Sci.,’ 1884, and these ‘Studies,’ vol. ii). Considering the early 
stage at which the anterior end of the blastopore closes in Verte- 
brates, and the relatively late appearance of the mouth, one 
would not expect to find any direct embryological evidence in 
support of this view. For the argument and indirect evidence 
in favour of it I refer the reader to pp. 73 et seq. of my paper 
above mentioned. To that evidence I now add the long slit- 
like form of the primitive Elasmobranch mouth. 


3. Segmentation of the Mesoderm and Development 
of Nerves. 


v. Wyhe! describes the cranial mesoderm in Scyllium as 
segmenting from behind forwards, and he says that in Stage I 
—and not before—the whole of the cephalic mesoderm is 
broken up into somites, and that all these somites contain a 
cavity except the first. 

Kastschenko? says that the first somite is formed at what 
appears to be the junction of the head and trunk, and that the 
segmentation of the mesoderm extends backwards and forwards 
from this point. Anteriorly it becomes more and more 

1 ‘Ueber die Mesodermsegmente u. d. Entwick. d. Nerven d. Selachier- 


koppes,’ Amsterdam, 1882. 
2 * Anat, Anzeiger,’ vol. ili, p. 462. 


248 ADAM SEDGWIOK. 


indistinct as the front end of the embryo is approached, so 
that the anterior part of the cephalic mesoderm is at no stage 
of development broken up into somites. This unsegmented part 
of the cephalic mesoderm, which corresponds, according to 
Kastschenko, to several somites, is comprised in the second 
somite of Wyhe. The first somite of Wyhe occupies, in 
Kastschenko’s opinion, a special position. Kastschenko’s 
observations were made on the genera Scyllium and 
Pristiurus, but he does not state precisely the ages of the 
embryos to which his observations refer, nor distinguish 
between the genera in describing his observations. As the 
different genera of Elasmobranchs differ, as I hope to show, 
very remarkably in the condition of the mesoderm during 
these early stages, this latter point is one of considerable 
importance. 

It is perfectly obvious to anyone who examines Hlasmo- 
branch development that the work of these two observers 
has been exceptionally thoroughly and carefully done; and if 
the results and views which I have arrived at differ from theirs, 
I would wish my work to be considered alongside of theirs, not 
as contradicting, but as supplementing it, by the future workers 
who succeed in obtaining a fuller and more accurate knowledge 
of the development of the different genera of this interesting 
group. 

Balfour (‘ Elasmobranch Fishes,’ Mem. Ed., p. 802), in de- 
scribing Pristiurus, says that “coincidently with the appear- 
ance of a differentiation into a somatic and splanchnic layer 
the mesoblast plates become partially split by a series of 
transverse lines into protovertebre.’’ This statement I can 
entirely confirm for Pristiurus and Scyllium; its import- 
ance has not been fully appreciated or understood. What it 
means is this, that the body-cavity at the very first 
sign of its appearance (differentiation of mesoderm into 
somatic and splanchnic layers) is segmented. 

Balfour goes on to say, “ In the head, so far as I have yet 
been able to observe, the mesoblastic plates do not at this 
stage (D) become divided into protovertebre.’’ The term head 


NOTES ON ELASMOBRANCH DEVELOPMENT. 249 


here must be regarded as meaning the anterior end of the 
body, for it is not possible in these young embryos to dis- 
tinguish the head from the trunk. I am, however, in entire 
agreement with the statement that there is a stage in which 
there is a considerable tract of mesoderm in front of the first 
formed somite, which is entirely unsegmented, and with no signs 
of differentiation into somatic and splanchnic layers, But in 
Pristiurus this stage is of very short duration, for, according to 
Balfour, even in Stage D there is a cavity in the anterior part 
of the mesoderm. I can entirely confirm Balfour as to the 
presence of this cavity at this early age in Pristiurus ; but it is 
not, as he seems to imply, ever continuons with the general 
body-cavity. It is, indeed, a somite—the second or mandi- 
bular somite of v. Wyhe,—and its appearance is followed by 
the breaking up of the mesoderm between it and the first 
so-called trunk somite into successive and contiguous but 
indistinct somites. I am not able to say in what order these 
somites are formed, whether from behind forwards, as 
Kastschenko maintains, or in the reverse direction. All I can 
say on this subject is that in Pristiurus the mandibular somite 
is formed before those behind it, and that in Scyllium I have 
an embryo a little older than Stage F, but younger consider- 
ably than Stage G, in which the whole of the mesoderm 
in front of the first so-called trunk somite is broken up into 
somites successively traceable in a series of transverse sections. 
The first of these somites (the second of Wyhe) is the most 
distinct and, I expect, the first formed, as in Pristiurus. 

This early segmentation of the anterior part of the meso- 
derm into somites almost exactly like those in the hinder part 
of the body is a morphological point of great interest. It is 
very transitory in the genera mentioned, and disappears before 
any trace of the pharyngeal pouches are formed, except in the 
case of the mandibular somite, and possibly also of the one 
next it. In Stage I, where, according to v. Wyhe, the segmen- 
tation of the anterior part of the mesoderm is complete, I 
cannot find in either Scyllium or Pristiurus or Raja any 
of the somites described by him as the fourth, fifth, and sixth ; 


VOL. V, PART Il. 10 


250 ADAM SEDGWIOK. 


moreover the posterior limits of the third cannot be made out 
in Stage I. 

Dohrn,! however, in his fifteenth study describes a complete - 
mesodermal segmentation as occurring in Torpedo mar- 
morata at a stage in which the mandibular and hyo- 
branchial pouches could be made out. The embryos in ques- 
tion were considerably younger than the embryos in which 
v. Wyhe first observed the segmentation of the cranial meso- 
derm, and Dohrn ascribes them to Stage F; but the above- 
named pouches being present, he was able to compare his 
cephalic myotomes with those of Wyhe. He makes out ten 
myotomes in front of the hyoid pouch, arranged as follows : 


4 myotomes in the place of Wyhe’s first. 


3 . » » second or mandibular. 
3 2 ry) ” hyoid. 
2 or 3 ”» » ° ” fourth. 


He admits that they are very transitory structures, and that 
they have lost their distinctness (by fusion with one another) 
in Stage G, i.e. before the stage at which v. Wyhe first saw 
them. Having a very practical acquaintance with the great 
variation of the mesoderm in embryos of different genera of 
Elasmobranchs I do not venture to impugn the accuracy of 
Dohrn’s observations on a genus which I have not examined ; 
but knowing the extreme difficulty of satisfactorily observing 
these rudimentary cranial somites, even when they are un- 
doubtedly present, I cannot help feeling that it is desirable 
that Dohrn’s statements should receive some confirmation. 
This confirmation is, to a certain extent, supplied by Herr 
Killian’s* recently published work on Torpedo ocellata. 
I say “to a certain extent,” because Killian’s list of somites 
does differ slightly from that of Dohrn. I think that it is 
possible, and I trust that Dr. Dohrn (and Herr Killian) will 
forgive me for making the suggestion, that he has been misled 
by deceptive appearances afforded by the somites at the time 
of their disappearance. I know very well that in looking 


1 <Mittheil. a. d. Zool. Station zu Neapel,’ Bd. ix. 
2 * Anat. Anzeiger,’ Erganzungsheft, 1891, 


NOTES ON ELASMOBRANCH DEVELOPMENT. 251 


through any one series of sections it is very easy to make out 
what appears to be a great number of somites, but on care- 
fully comparing the two sides of the embryo, and on estimating 
the intervals which the somites occupy, it is in my experience 
always found (after Stage F in the head region) that, with the 
exception of the first three head segments and the three poste- 
rior segments, these supposed somites are in embryos, in which 
the rudiments of the spiracle and hyoid cleft are apparent, 
quite irregular, and are either simply spaces in the mesoderm 
or remains of broken-down somites. This result comes out 
still more forcibly if one attempts to confirm one’s observa- 
tions on one embryo by similar observations on another embryo 
of the same size. 

But even if Dohrn is right in his enumeration of the 
anterior somites, it is clear that Torpedo differs much from’ 
Scyllium, Raja, and Pristiurus, whether my account or 
Wyhe’s be taken as correct. For in Torpedo there are four 
somites where in the other genera there is most unquestionably 
one, e.g. the somite of Wyhe.! 

It would appear, then, if the number of primitive cranial 
somites in any given region of the head does really differ 
in closely allied genera in the manner indicated by the diver- 
gent observations of Wyhe, Dohrn, Killian, and myself, that 
the supposed indications of segmentation, which are found in 
the adult and are constant throughout the Vertebrata, can have 
very little value as real tests of the primitive metameric seg- 
mentation—i. e. of the segmentation which obviously persists 
in the trunk region, and which begins with the segmentation 
of the mesoderm, and is moulded upon it in the manner cha- 
racteristic of all metamerically segmented animals. 

We may, I think, even go further, and say that the adult 
arrangements of nerves and branchial arches, &c., character- 
istic of the Vertebrate head, must have arisen subsequently to 

1 T leave out of consideration the supposed somite anterior to the preman- 
dibular somite (first of Wyhe), which has been described by some observers 


in Acanthias, Torpedo, &c. Ihave seen traces of it in Scyllium, but it 
is in that genus merely a diverticulum of the premandibular somite. 


252 ADAM SEDGWIOK. 


the disappearance of the primitive segmentation. This position 
will be still further strengthened if my contention turns out 
to be correct, viz. that in embryonic development the meso- 
dermal cranial segments do largely become indistinguishable 
before the adult landmarks have appeared. 

If my arguments and facts are sound, it follows that any 
attempt to elucidate the adult structure of the head from the 
point of view of its being composed of a series of segments 
comparable to those of the trunk is foredoomed to failure; 
and the result of the whole inquiry shows up most thoroughly 
the weakness of the position of those who hold embryological 
research to be of small importance in comparison with the 
study of adult structure. 

To a student of the multitudinous changes of structure which 
‘an organism passes through in the course of its existence it 
seems strange even now, and in the future will ever seem 
stranger to the philosophical morphologist, that one condition 
of structure only, and that the most complex and inexplicable, 
should have been regarded by anyone as holding the key to 
the solution of even a simple anatomical problem. 

To sum up the matter, v. Wyhe holds that there are nine 
cranial segments which can be traced into the adult. Dohrn 
holds that there is a much greater number of cranial somites, 
some of which can be traced into the adult, and some of which 
disappear. I agree with Dohrn in asserting that the anterior 
mesoderm is completely segmented in Stage F, but maintain, 
in opposition to him, that it is not possible to say how these 
segments are related to adult structures, because they have 
for the most part vanished before any of the adult landmarks 
have appeared. 

The premandibular somite of Balfour (the first somite of 
Wyhe).—There can be no doubt this is not, as Balfour sup- 
posed, separated off from the mandibular. 

Kastschenko says that it develops from what he calls the 
prechordal portion of the gut, which becomes solid when the 
medullary plate is formed, and then subsequently again 
acquires a cavity. I find myself unable to accept this account 


NOTES ON ELASMOBRANCH DEVELOPMENT. 253 


of the origin of the first somite. It is true that at the time 
of the formation of the medullary plate the notochord stops 
some little distance short of the front end of the body, and 
there is a portion of the gut in front of it; but this is only a 
temporary state of affairs, and is due to the fact that the front 
end of the notochord, which is developed from behind for- 
wards, is not yet formed: moreover the solid mass of endo- 
derm referred to by Kastschenko is present at the front end of 
the gut even at this stage. When the notochord has acquired 
its furthest anterior extension in Scyllium, just before 
Stage G, it terminates in a solid mass of cells, which is con- 
tinuous also with the front end of the gut. The notochord 
has hitherto during the whole of its growth been continuous 
in front with the endoderm, and its condition at the period 
referred to is merely a persistence of that continuity. Wyhe’s 
account of the anterior end of the notochord appears to me to 
be quite correct. 

When the notochord has acquired its utmost anterior 
extension there is no portion of the gut in front of it, but 
merely this solid mass of cells, with which both it and the gut, 
and afterwards the ectoderm of the buccal slit and pituitary 
body, are continuous, and which underlies the very front end 
of the medullary tube. If this mass of cells be regarded as 
partly consisting of the anterior end of the notochord still uvn- 
differentiated, it may be said that the notochord reaches in 
Scyllium, at any rate, to the very front end of the neural 
tube; in other words, that Scyllium at this stage is truly 
cephalochordate in the sense that Amphioxus is cephalo- 
chordate. 

The solid mass of cells in which the notochord and gut 
terminate becomes in Scyllium and Pristiurus very early, 
before Stage G, connected with the ventral ectoderm. Wyhe, 
who connects this fusion with the formation of the mouth, 
puts it down as taking place later in Stage H; but I can posi- 
tively assert that in Scyllium and Pristiurus it is present 
before Stage G—before any trace of the cranial flexure has 
appeared, 


254 ADAM SEDGWICK. 


There can be no question that the first or preoral somite 
develops in connection with this solid mass of cells, but 
whether entirely from it, as Wyhe appears to maintain, or 
only partly from it, is difficult to say. In Scyllium there are 
very clear indications that a part of the tissue from which the 
somite develops is derived from a paired ingrowth from the 
ectoderm. In Stage G the cell mass is continued forwards on 
each side in continuity with the ectoderm, and these paired 
tracts present the appearance of ingrowths. 

The mass of cells of which I am speaking presents very 
remarkable differences in its relation to adjacent organs in the 
different genera that I have examined. In Scyllium and 
Pristiurus it is continuous with the ventral ectoderm 
throughout its whole extent from the earliest stage at which 
IT have seen it, i. e. Stage F, or the earliest stage at which the 
ventral ectoderm is folded in. 

In Scyllium it is for the most part not continuous with 
the medullary ectoderm, unless there is such a continuity, of 
which I am not certain, at its very frontend. In Pristiurus 
and Rajait is markedly continuous with the medullary ecto- 
derm throughout its entire extent, while in Raja the dorsal 
lateral outgrowths, which are soon formed from it, are also 
continuous with the medullary ectoderm. Further, Raja 
differs from the other two genera in that this cell-mass is not 
continuous with the ventral ectoderm at all (excepting through 
the endoderm and buccal slits). 

As Wyhe has correctly stated, the first or premandibular 
somite of Balfour is formed by the hollowing out of this mass 
of cells and its lateral prolongations, and Kastschenko seems 
to be justified in placing it in a different category from the 
other somites. It differs from the other somites in two 
respects: (1) in its connection at origin with the ectoderm, 
either of the body-wall or of the neural tube (Raja, Pris- 
tiurus) ; (2) in its continuity with its fellow across the middle 
line. 

Before leaving this cell mass which gives rise to the first 
somite, and which eventually breaks off from the various 


NOTES ON ELASMOBRANCH DEVELOPMENT. 255 


organs with which it is at first continuous, i.e. notochord, 
ectoderm, and gut, I should like to point out a resemblance 
in its early condition to the primitive streak of the Amniota. 
Like the primitive streak, it is a densely packed mass of nuclei 
in continuity with all the layers and organs of the body. 
The ectoderm, endoderm, notochord, and mesoderm, all are 
continuous with it; and as the primitive streak is the 
growing point for the hind end of the embryo, so it appears to 
contribute in a similar manner to the front end. 

The Anterior Somites in Raja—In Raja the segmentation 
of the anterior mesoderm and the prominence of the first two 
somites are not nearly so conspicuous as in the other genera. 
The condition of the anterior mesoderm after its separation 
from the endoderm is quite different from that in Scyllium and 
Pristiurus. It does not assume the condition of an “ epithe- 
lium ” arranged round the cavities or the incipient cavities of 
somites. On the contrary, it at once assumes the form of 
“embryonic connective tissue,” i.e. of a mass of stellate 
cells all connected together by their processes. In other 
words, it at once takes on the form which is only secondarily 
attained by the same mesoderm of the two other genera after 
passing through the epithelial condition. This difference in 
the early structure of the cephalic mesoderm of Raja and 
Scyllium is another proof, if such were needed, that the 
distinction between “ mesenchyme ” and epithelial mesoderm 
to which the Hertwigs have so prominently called attention 
has not the importance which they attribute to it. The cavi- 
ties of the first two somites make their appearance in this 
stellate mesoderm at about Stages G,H. But they are at first 
inconspicuous, having the appearance of blood-vessels, and are 
without the conspicuous epithelial lining. In fact, the cells 
lining them have at first simply the characters of the reticulate 
mesoderm tissue, of which, indeed, they are merely a part. 


256 ADAM SEDGWICK. 


Continuity oF Cextis anp Layers. 


The continuity between the different layers and organs of 
the embryo to which I first called attention in Peripatus is 
found in all Vertebrate embryos that I have examined. In 
fact, there is a network of pale protoplasmic fibres extending 
inwards from the nucleated protoplasm of the various surfaces. 
When this network has nuclei at the nodes, we get the reticu- 
lated tissue, or embryonic mesoderm, or mesenchyme. In 
Scyllium it is at first sparse and without nuclei. In Raja, 
on the other hand, it is very richly developed, and rich in 
nuclei. In Raja, in other words, the protoplasmic connections 
passing between the various organs and layers are very con- 
spicuous and well marked. In Scyllium this tissue is at first 
without nuclei, as I have said. But soon it acquires nuclei and 
becomes denser. Where do the nuclei come from? In my 
opinion they are derived partly from the epithelial walls of 
the somites, partly from the anterior mass of mesoderm in 
which the notochord, gut, &c., ends, and partly from the 
growing tissue of the caudal swellings, and perhaps also from 
the neural crest. 

We now pass on to speak of the neural crest in those 
Elasmobranchs which I have studied. 

The nerve crest was first discovered by Balfour in the trunk 
region of Elasmobranch embryos. Marshall! has observed it in 
the chick, and describes it as occurring in the anterior part of 
the spinal cord region and extending continuously forward 
into the fore-brain. 

Van Wyhe and Kastschenko also both describe the nerve 
crest in the Elasmobranch embryos they examined as reaching 
from the region of the fore-brain continuously backwards. 
The cranial nerves and the posterior roots of the spinal nerves 
grow out from the nerve crest, and the nerve crest persists 
itself in part as the longitudinal commissure. Both Balfour 
and Marshall state that this longitudinal commissure extends 

1 «Quart. Journ. Mier. Sci.,’ vol. xviii. 


NOTES ON ELASMOBRANCH DEVELOPMENT, 257 


back continuously from the root of the glossopharyngeal to 
the spinal cord, connecting together the posterior spinal roots 
and the roots of the vagus and glossopharyngeal. It is not, 
however, developed in front of the glossopharyngeal, the nerve 
crest atrophying between the ninth and seventh, and between 
the seventh and fifth nerves. 

My observations agree with this account except in one 
point, and that relates to the nerve crest. In Scyllium and 
Pristiurus the nerve crest is not a continuous structure, as 
Wyhe and Kastschenko assert (Balfour and Marshall have no 
observations on the cranial part of the nerve crest in Elasmo- 
branchs). It is in three separate pieces. The first of these 
is found in the anterior part of the brain; the fifth nerve and 
presumably the ophthalmicus profundus grow out from it. 
The second is found a little further back, and gives origin to 
the seventh and eighth nerves. The third piece occurs a little 
further back, and reaches from the hind brain continuously 
back the whole length of the spinal cord. The ninth and 
tenth cranial nerves and the posterior roots of all the spinal 
nerves grow out from it. It is this latter part of the nerve 
crest which gives rise to the longitudinal commissure of 
Balfour. 

There are three views as to the origin of the peripheral 
nerves. 

1. According to Hensen’s! view, the rudiments of the nerve- 
fibres are present from the beginning as persistent remains of 
the primitive connections between the incompletely separated 
cells of the segmented ovum. 

2. Balfour? regarded them as cellular outgrowths from the 
central nervous system extending to the periphery. The 
original continuity between the central and peripheral organs, 
which must have existed, has, it was supposed, been lost in 
ontogeny by rupture, and reacquired by means of these out- 
growths. 


1 ¢Virchow’s Archiv,’ vol. xxxi, 1864. _ 
2 * Development of Elasmobranch Fishes,’ Mem. Ed., p. 384, vol, i, 


258 ; ADAM SEDGWICK. 


3. The view of His,! which was previously held by Bidder. 
According to this view the nerve-fibres are the elongated pro- 
cesses of cells. The anterior roots are derived from non-cel- 
lular outgrowths of the spinal cord, consisting of the elongated 
processes of the nerve-cells of the central organ. The fibres 
of the posterior roots, on the other hand, are the elongated 
processes of the ganglion-cells of the ganglion on the posterior 
roots. Processes of these cells grow out to the periphery and 
inwards to the centre. 

Balfour expressed on a priori grounds a strong preference 
for the view of Hensen, but rejected it on the ground that 
there was no evidence for the connection which it demanded. 
Now, however, we know that in many types the segmentation 
of the ovum does not bring about a complete separation of the 
cells of the ovum.’ 

There is no such separation in Peripatus; and in many 
Arthropoda—if not in all—it is known not to take place. It 
does not take place in Elasmobranchs, as I can certify from my 
own observations; but for a summary of the facts and a dis- 
cussion of the whole question I must refer the reader to my 
monograph already quoted.® 

If the segmentation of the ovum does not bring about a 
complete separation of the cells of the germ, as it was formerly 
supposed to do, then the connections required by Hensen’s 
theory exist. 

Turning to the special case before us of the Vertebrata, I have 
in the present paper dwelt upon the fact (see above, p. 256) 
that the cells of the young embryo (subsequent to cleavage) are 
connected by delicate processes, and that these processes are 
often extremely fine, and unite together into networks below 
the epithelial arrangement of the protoplasm which is charac- 
teristic of the surfaces. This network is sometimes of a very 


1 « Anatomischer Anzeiger,’ vol. iii, p. 500. 

* See Self, ‘ Monograph on the Development of Peripatus capensis,” 
in ‘Studies from the Morphological Laboratory of the University of Cam- 
bridge,’ 1889, pp. 47—50, and pp. 130, 131. 

3 Loc. cit., pp. 99—106, 


NOTES ON ELASMOBRANCH DEVELOPMENT. 259 


loose mesh, and its fibres are always delicate; and it is no 
doubt often torn and destroyed by the preserving processes to 
which the embryo has to be subjected. But delicate as it is, 
there can be no doubt of its existence in Vertebrate embryos ; 
and there can be no reasonable doubt that it is derived from 
the processes and strands left between the cells as a result of 
the incomplete cleavage of the ovum. There can be no doubt, 
I say, that the network exists; but that the peripheral nerve- 
fibres and the central nerve-fibres are derived from it has not 
yet been shown. That is the point which now needs investi- 
gation, and I hope myself to treat of it in a future paper. 

Meanwhile I may say that there is in my opinion evidence 
to show that the whole of the nervous connections (by nerve- 
fibres and otherwise), both in the central organ and at the 
periphery, are developments of this pre-existing network, which 
connects together at all times the whole of the cells derived 
from the fertilised ovum. 

I do not dispute for one moment the description given by 
Dohrn! of the structure of particular stages in the development 
of a nerve-fibre ; but in saying that it consists of a row of ecto- 
derm-cells laid on end to end he is, I think, going beyond his 
facts, being led to such an interpretation of the appearances 
not so much by observation of previous stages as by a process 
of reasoning based upon the cell theory of structure, which 
theory implies that the animal body at one stage of its onto- 
geny consisted of cells which are separate from one another 
and only secondarily fuse to form the adult tissues and com- 
binations. 

1 ¢Studien z. Urg. d. Wirbelthierkérpers,’ No. 17. 


260 ADAM SEDGWICK. 


EXPLANATION OF PLATE XVI, 


Illustrating Mr, Sedgwick’s ‘Notes on Elasmobranch 
Development.” 


Fie. 1.—Embryo of Scyllium canicula, 23 mm. in length. The hinder 
end of the embryo is notched. The medullary groove is just beginning. The 
tail swellings of Balfour are well marked. 


Fic. 2.—Embryo of Raja? sp., 4 mm. in length. The medullary groove is 
closed except at the hind end. The notched embryonic part of the edge of 
the blastoderm has grown faster than the rest, and come to project over the 
surface of the yolk. The sides of this projection are already slightly bent 
ventralwards. They will eventually meet and form the ventral part of the 
caudal region of the body. 

Fic. 3.—Raja ? sp. Embryo of Stage E or F, 42—5 mm. in length. The 
medullary canal is still open, but the medullary folds are almost touching 
except behind, where the medullary canal widens out in a wide medullary 
groove, in the floor of which is placed the dorsal part of the blastopore. The 
blastopore is slit-like, but dilated in front; posteriorly it is continued round 
the hind end of the body into the ventral portion. 

Fic. 4.—Raja ? sp. Stage E or F,5—53 mm. in length, a little older than 
Fig. 3. Medullary canal closed except behind, where it widens out and 
encloses the blastopore. The blastopore is slit-like, but the hinder end of 
the dorsal portion is faintly marked. 

Figs. 3 and 4 are somewhat diagrammatic, but they show correctly the 
relations of the medullary groove and dorsal part of the blastopore. I 
hope to publish figures of the sections through them shortly. 

Fic. 5.—Ventral view of head of Scyllium canicula between Stage I 
and K. Total length 7—8 mm. The two first pharyngeal clefts are open. 
The mouth rudiment is present as a longitudinal groove in the ectoderm of 
the buccal depression, which is fused with the endoderm. At intervals there 
are perforations along this groove. The groove reaches into the rudiment of 
the pituitary body. The mandibular arch is present as a backwardly directed 
longitudinal ridge, and bounds the buccal depression externally. 


Fic. 6.—Ventral view of head of Scyllium canicula a little older than 
the preceding. The buccal groove has become a longitudinal slit. 

Fic. 7.—Side view of head of Scyllium canicula a little younger than 
Stage K. Total length about 9mm. JI could nof distinguish any trace of 


NOTES ON ELASMOBRANCH DEVELOPMENT. 261 


the limbs. I do not think the fourth slit is open. The posterior end of the 
mandibular arch is slightly bent ventralwards. 


Fic, 8.—Ventral view of head of same embryo drawn to a slightly smaller 
scale. The anterior part of the buccal slit has become much wider. 


Fic. 9.—Side view of head of Scyllium canicula about Balfour’s 
Stage K. Total length about 11—12 mm. External gills have appeared 
on the first and second branchial arches. The ventral bend of the hind end 
of the mandibular arch is more marked. 


Fic. 10.—Ventral view of the same head drawn to a slightly smaller scale. 
The future angle of the jaw can be distinguished, the mouth being widest at 
that point. The posterior slit-like part of the mouth is still present. 

Fig. 11.—Side view of head of Scyllium canicula about Balfour’s Stage 
L. Total length about 16 mm. The external gills have increased in number, 
and are present on the mandibular arch. The angle of the jaw where the 
lower part of the mandibular arch bends ventralwards is very marked. 

Fic. 12.—Ventral view of same head drawn to asmaller scale. The mouth 
has much widened, and the posterior slit-like part has almost entirely dis- 
appeared. The anterior part of the mandibular arch has a process towards 
the middle line. The hinder end of the body has been tilted upwards so as to 
bring the fronto-nasal process into view. 


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