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Full text of "The Pterobranchia of the Siboga-expedition with an account of other species"

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RESULTATS DES EXPLORATIONS 
ZOOLOGIQUES, BOTANIQUES, QCEANOGRAPHIQUES ET GEOLOGIQUES 

ENTBEPKISE3 AUX 
DTDES KEBRLANDAISES OEIENTALES ea 1899 — 1900, 

a bord du SIBOO-^ 

sous LE COMMANDEMENT DE 

Q. r. TYDEMAN 

PUBLIES PAR 

Chef de rexpedition. 



•I. 

»1II. 

IV. 

V. 

«V1. 

vir. 

«VIII. 

IX. 

X. 

*XI. 

OXII. 

•XIII. 

XIV. 

XV. 

»XVI. 

XVII. 

XVIII. 

XIX. 

XX. 

XXI. 

XXII. 

XXIII. 

XXIV 1. 

XXIV2. 

•XXA'. 

XXVI. 

*XXVI««. 

xxvii. 

XXVIII. 

XXIX. 

XXX. 

XXXI. 

XXXII. 

XXXIU. 

•XXXIV. 

XXXV. 

XXXVI. 

XXXVII. 

XXXVIII. 

XXXIX. 

XL. 

XLI. 

XLII. 

•XLIII. 

•XLIV. 

•XLV. 

XLVI. 

• XLVII. 

• XLVIlI 

XLIX'. 

\LIX2. 

L. 

LI. 

• Lll. 
LIII. 
LIV. 

LV. 

• LVI. 
LVII. 

LVIII. 
LIX. 

• LX. 
• LXI. 
LXII. 

LXIII. 

LXIV. 

LXV. 

LXVI. 



Introductioa et description de {'expedition, Mm Weber. 

Le bateau et son equiponient scientifique, tt. F. T yd em an. 

Resultats hydrographiques, G. F. Tydenian. 

Foraminifera. 

Radiolaria, M. Hartniunn. 

Porifera, F. E. Schuize, G. C. J. Vcsmaer et 

Hydropolypi, Ch. Julin. . [J. H. Vernho u t '). 

Stylasteriiia, S. J. Hick son et M'lo H. M. FiU gland. 

Siphouophora, M'lcs Lens et van llienisdijk. 

Hydroraedusae, O. Maas. 

Scyphomedusae, 0. Maas. 

Ctenophora, M"e F. Moser. 

Gorgonidae, Alcyonidae, J. Versluys'). 

Pennatulidae, S. J. Hicksou. 

Actiniaria, P. Mc Murrich. 

Madreporaria, A. Alcock ') et L. Uiide rlcin. 

Autipatharia, P. N. van K a nip en. 

Tarbellaria, L. von Graff et 11. R. von Stunmier. 

Cestodes, J. W. Speugel. 

Nematodes, H. F. Nierstrasz. 

Chaetognatha, G. H. Fowler. 

Nemertini, A. A. W. Kubrccht. 

Myzostomidae, R. R. von Stammer. 

Polychaeta errantia, R. Horst. 

Polychaeta sedeutaria, M. Caullcry et F. Mesnil. 

Gephyrea, C Ph. Sluiter. 

Enteropneusta, J. W. Spengel. 

FtcrobraiR'hia, S. F. Harmer. 

iJrachiopoda, J. F. van Bern m el en. 

Polyzoa, S. F. Harraer. 

Copepoda, A. Scott. 

Ostracoda, G. W. Miillcr. 

Cirrhipedia, P. P. C. Hoek. 

Isopoda, H. J. Hansen. 

Amphipoda, Ch. Perez. 

Caprellidae, P. Mayer. 

Stomatopoda, H. J. Hansen. 

Cumacca, W. T. Caiman. 

Schizopoda, H. J. Hansen. 

Scrgestidae, H. J. Hansen. 

Pecapoda, J. G. de Man. 

Pantopoda, J. C. C. Lorn a u. 

Halobatidac, J. Th. Oudenians. 

Crinoidea, L. Doderlein et C. Vancy. 

Echinoidea, J. C. H. de Meijere. 

Holothurioidea, C. Ph. Sluiter. 

Ophiuroidca, R. Kohler. 

Asteroidea, L. Doderlein. 

Solenogiistres, H. F. Nierstrasz. 

Chitonidac, H. F. Nierstrasz. 

Prosobranchia, M. M. Se hep man. 

Prosobranchia parasitica, H. F. Nierstrasz. 

Opisthobrancbia, R. Uergb. 

Heteropoda, J. J. Tesch. 

Pteropoda, J. J. Tesch. 

Lamellibrauchiata. P. Pelsencer et Ph. Dautzcnberg. 

Scaphopoda, MI'o M. Boisscvain. 

Cephalopoda, L. J o u b i n. 

Tunicata, C. Ph. Sluiter '). 

Pisces, Max Weber. 

Cetocea, Max Weber. 

Liste des algues, Mm« A. Wober. 

Halimeda, MUe E. S. Barton. (.Vtme E. S. Gepp). 

Corallinaceoe, M"'» A. Weber et M. Foslic. 

Codiaceae, A. ct M™* E. S. Gopp. 

Dinoflagcllata. Coccosphacridae, J. P. Lotey. 

Diatomaceae, J. P. Lotsy. 

Deposita marina, 0. B. Boggild. 

Resultats gfologiqucs, A. Wichmann. 



Siboga-Expeditie 



THE PTEROBfiANCHIA OF THE SIBOGA-EIPEDITION 

WITH AN ACCOUNT ON OTHER SPECIES 



BY 



SIDNEY F. HARMER, Sc.d., f.r.s. 

Cambridge 
With 14 plates and 2 text-figures 



Monographic XXVI ^zV of: 

UITKOMSTEN OP Z00L06ISGH, 
BOTANISGH, 0GEAN06RAPHISGH EN GEOLOGISGH GEBIED 

verzameld in Nederlands'ch Oost- Indie 1899 — 1900 

aan boord H. M. Siboga oiider commando van 
Luitenant ter zee 1= kl. G. F. TYDEMAN 



UITGEGEVEN nOOR 



Dr. MAX WEBER 

Prof, in Amsterdam, Leider dcr Kxpeditie 



(met medewerking van do Maatscliappij ter hevonluring van liel Natiiurkundig 
onderzoek der Nederlandsche Kolonien) 



BOEKHANDEL EN DRUKKERIJ 
E. J. BKIJLL 

LEIDEN 



Public Juillet 1905 



Les numeros avec un ast^rique out di}k paru; ceux marques i) seulement en ^artie. 



Voor de uitgave van de resultaten der Siboga-Expeditie hebben 
bijdragen beschikbaar gesteld: 

De Maatschappij ter bevordering van het Natiiurkunclig Ondcrzoek der Nederlandschc 
Kolonien. 

Het Ministerie van Kolonien. 

Het Ministerie van Binnenlandsche Zaken. 

Het Koninklijk Zoologisch Genootschap >Natura Artis Magistra" te Amsterdam. 

De >Oostersche Handel en Reederij" te Amsterdam. 

De Heer B. H de Wa.\l Oud-Consul-Generaal der Nederlanden te Kaapstad. 



SIBOGA-EXPEDITIE. 



Siboga-Expeditie 



UITKOMSTEN 



o? 




WISH 




Li 11 



ill lllulll L J 



1111 



^AT nv 



ffl Ctlilffl 



VERZAMELD IN 

NEDERLANDSCH OOST-INDIE 1899— 1900 

A A N B O O R D H. M. S I B O G A UNDER COMMANDO VAN 

Luitenant ter zee V kl. 0. F. TYDEMAN 

UITGEGEVEN DOOR 

Dr. MAXWEBER 

Pi'of. in AiusteiUan^ I, cider dcr Kxpcdilic 



(met medewerking van de Maatschappij ter bevordering van het Natuurkundig 
onderzoek der Nederlandsche Kolonien) 



ho1':kiiandel en drukkicrij 



\ookhi-:f.s 



PI J. BRILL 

I.EIDF.N 



r> 






Siboga-Expeditie 

XXVI bis 



THE PTEROBRANCHIA OF THE SIBOGA-EXPEDITION 



WITH AN ACCOUNT OF OTHER SPECIES 



RY 



SIDNEY F. HARMER, sc.d., f.r.s. 
/ • » 

Fellow of King's College, Cambridge, and Superintendent of the University Museum of Zoology 



With 14 plates and 2 text-figures 



LATE E. J. BKTLL 

PUBLISHERS AND I'RIN'IEKS 

I.EYUKN — 1905 







CONTENTS. 



I. Introduction and Historical i 

II. Specimens examined 3 

III. Diagnoses of species of Cephalodlscus 4 

IV. Coenoecium 8 

V. External characters of the zooids 17 

\'I. Methods and General anatomy 21 

VII. Proboscis 26 

VIII. Collar (including the arms and the operculum) 30 

IX. Metasome, body or trunk 47 

X. Stalk 50 

XI. Alimentary canal 53 

XII. Muscular system (i(y 

XIII. Nervous system 71 

XIV. Vascular system 74 

XV. Reproductive organs Si 

XVI. Budding 91 

XVII. Development 102 

XVIII. Affinities 112 

XIX. Rhabdopleura 125 

XX. Summary of the principal results 128 

XXI. Bibliography 130 

XXII. Explanation of Plates 1 — XIV 133 



THE PTEROBRANCHIA OF THE SIBOGA-EXPEDITION 

WITH AN ACCOUNT OF OTHER SPECIES 



BV 



SIDNEY F. HARMER, Sc. D., F. R. S. 

Fellow of King's College, Cambridge, and Superintendent of tlie University Museum of Zoology. 



With 14 plates and 2 text-figures. 



I. INTRODUCTION and HISTORICAL. 

Among the organisms obtained during the voyage of H. M.S. "Challenger" in 1873 — 1876, 
one of the most striking novelties was the animal described by M'Intosh (82) as Cephalodiscus 
dodecalopJiJis. It was trawled at Station 311, in the Straits of Magellan, at a depth of 245 
fathoms, from a bottom consisting of blue mud. The gelatinous tube, or coenoecium, contained 
large numbers of female individuals, and many free eggs ; but no trace of a male was to be 
found. The affinities of the organism were entirely problematical. It was at first thought that it 
might be a Compound Ascidian, while it was sent to Professor W. C. M'Intosh for examination 
on the supposition that it was perhaps related to the Annelids. M'Intosh, with Ali.max and 
Busk, arrived at the conclusion that its nearest affinities were with Rhabdopleura^ a result which 
has been amply confirmed by the subsequent work which has done on the two genera. 

Cephalodiscus was introduced to science at the meeting of the British Association in 1882, 
although the Report of that meeting containing the original description (M'Intosh, 83) did not 
appear until the following year, and was thus preceded by the fuller "Preliminary Note", published 
by Professor M'Intosh in the "xA.nnals and Magazine of Natural History" (82). There was at 
this time a general consensus of opinion that R/iaddoplenra belonged to the Polyzoa, although 
constituting an aberrant type ; and there was at first no reason for suspecting that this genus 
and Cephalodiscus had affinities in a widely different direction. The preliminary notes gave an 
account of the coenoecium and of its contents, the "polypides", the free ova and the buds. 

SlBOGA-liXPEDITIE WWl'is. I 



The general structure of the polypides ur zooids was, in many respects, accurately described, 
particularly so far as concerned the external characters, the alimentary canal and the ovaries. 
The selection of the specific name, dodecalophus, in allusion to the existence of six pairs of 
tentaculiferous arms, proves to have been fortunate, since the examination of the "Siboga" 
material shews that the number of the arms is an important specific character. The description 
of the remarkable pigmented oviducts as eyes is a mistake which is a natural one to have 
made, in consequence of the eye-like appearance presented by these bodies in an external view 
of the zooid. 

The article "Polyzoa" written by Professor E. Ray L.vnkestf.r for the "Encyclopaedia 
Britannica" (85) contains the first figures which were published of Ceplialodiscus, these being 
taken from original drawings supplied by Professor M'Intosii. The position of Rhaddopieiira 
and Ccplialodlscus as a Section of the Polyzoa is here definitely formulated. 

M'Intosh published his "Challenger Report" in 18S7, and at the end of that Report 
appeared an ^Appendix in which I was able to demonstrate the close affinity of Cephalodisciis 
to Balanoglossus '). This view was disputed by Ehlers in 1 890 (p. 1 64), while in the same 
year L.\ng provisionally accepted it in a paper (90) written to shew that the differences between 
Cephalodiscus and Balanoglossus were in the main due to the fact that Cephalodiscus has taken 
on a sessile and tubicolous form of life, resulting in the forward migration of the anus and in 
other departures from the arrangement of the organs found in Enteropneusta. 

At the close of his great Monograph on the Enteropneusta of the Gulf of Naples, 
Si'ENGEL (93, p. 753), as the result or his own inve.stigation, expresses his concurrence with the 
view that Cephalodiscus is related to Balanoglossus. 

In 1896 — 1899 appeared a series of papers by Masterman, who in .several important 
respects extended our knowledge of the structure of Cephalodiscus. Masterman was the first 
to describe the vascular system and the details of the budding processes, while he added 
considerably to what was known of the nervous system. I shall have occasion to discuss 
Masterman's results in the later jjortions of this Report. 1 ventured to criticize some of them 
in a note published in 1897, '■'' which year Spexgel (97) also published a few* remarks on 
the same subject. 

In 1899 appeared a paper by Cole on the terminal sw^ellings of the tentaculiferous arms 
of Cephalodiscus. These, which had been regarded by Masterman as compound eyes, were 
described by Cole as having a structure similar to that of the rhabdite-cells of Planarians. 

In 1903 MasternL'VN published a further paper on Cephalodiscus, dealing with the structure 
of the "central complex", or region of the jiroboscis-stalk and adjacent parts. 

The whole of the literature mentioned so far was based on the examination of the 
original "Challenger" material; that is to say, on female specimens of C. dodccalophus. 

In 1903 Andkrsson announced the discovery, by the Swedish Antarctic Expedition, of 
specimens of Cephalodiscus, in four dredgings taken in the neighbourhood of the b'alkland Islands. 
The depths ranged from 80 to 235 M. In ihe absence of a fuller account of the discovery, it 

l) I here ii>i" ihis n:um: in it-i .iltler ^en-it' :>^ including all the species of Enteropneusta, now arranged in a series of genera 
l)y Spe.\gel (01). 



may be presumed that the species is probably C. dodccalophus. Nothing is said about males, but 
Andersson was the first to describe the free larvae, which are ciliated planula-like organisms. 

In the same year (1903) I published a note announcing the fact that I had in my hands 
Cephalodiscus from Oriental Seas; and in the following year (04, p. 26) I mentioned the 
peculiarities of the remarkable male zooids found in one of these colonies. 

In addition to the papers noticed above frecjuent references to Cephalodiscus have 
appeared in other places. Some of these are discussed in the later parts of this Report; but special 
mention must be made here of the work of Fowler (92, 1,2), who was the first to demonstrate 
that Rhabdoplatra, like Cephalodiscus^ conforms to the Balanoglossus-type of structure. 



II. SPECIMENS EXAMINED. 
The material on which this Report is based consists of the following specimens: 

(I) A fragment of the original female colony of C. dodecalophus, dredged by the „Challenger" 
in the Straits of Magellan at a depth of 245 fathoms (;= 448 M.). 

(II). C. gracilis n. sp. 

"Siboga". Stat. 89. Pulu Kaniungan ketjil, reef. [E. coast of Borneo], i Ex., §. 

(III). C. siboga e n. sp. 

"Siboga". Stat. 204. Between islands of Wowoni and Buton; Northern entrance of Buton 
Strait, 75 — 94 Metres. Sand with dead shells. [Off S. E. point of Celebes], i Ex., cT '• 

(IV). C. levinseni n. sp. 

A specimen received from the Copenhagen Museum. Obtained in Long. i28°2o'E. Lat. 32° 10' N. 
[Oft" W. coast of Japan, at the S. end of the Corea Strait], 100 fathoms {- 183 M.j. i Ex., 9- 

(V). RJiabdoplciira sp. 

"Siboga"". Stat. 204. Between islands of Wowoni and Buton, 75 — 94 Metres, i Ex. [This 
specimen, found during the correction of the proof-sheets, will be described in Section XIX]. 

The specimen which I propose to call C. gracilis was found during the examination 
of a colony of Tubucellaria sp. -), one of the Polyzoa which had been entrusted to me for 
description. It consists of a small number of delicate, almost colourless tubes (coenoecium), whose 
association with the Tubucellaria is probably accidental. The tubes have a prostrate habit, and 
are supported along the greater part of their length by the calcareous branches of the Polyzoon. 
Their appearance, as .seen with the naked eye (PI. I, fig. i) is very different from that of any 



1) -V fragment of coenoecium, without zooids, has more lecenily been found by Professor Weber in material from Stat. 204. 
It may be part of the male colony described in this Report. 

2) The species is probably T. fusiformis D'Orb. 



of the other species. They are far less conspicuous, and mi^jht easily be passed over by any 
one who was not acquainted with the genus. It is jjrobable that this species will hereafter be 
found on other marine objects collected during the Expedition. The tubes contain large numbers 
of the zooids, in a good state of preservation, together with buds and embryos. All the zooids 
are female. It is specially noteworthy that this specimen was collected between tide-marks, 
Ccphalodiscus having previously been regarded as an abyssal animal. 

C. sibogac n. sp., (PI. I, fig. 2) is also repre.sented by a single specimen, which was 
growing on a small rock. It is a more conspicuous object than the last species; and it had 
been placed in a bottle by itself and sent to me as a Polyzoon. Although the zooids are 
unfortunately not well preserved, their state was sufficiently good to enable me to make out some 
interesting facts with regard to the males, and in particular to demonstrate the occurrence, in 
Ccphalodiscus^ of an extraordinary sexual dimorphism. The male individuals (PI. Yll, figs. 72 — 76) 
are entirely unlike the females found in other species, being without tentacles and po.ssessing 
only a vestigial alimentary canal. They are accompanied by neuter individuals (PI. I, fig. 3), 
which, except in possessing no reproductive organs, have the typical Cep/ialodiscus-?,truct\xv&. 
These neuters probably perform the functions of digestion and nutrition for the entire colony. 
Xo females are present, and the possibility is not excluded that C. sibogae is the male form 
of C. gracilis. 

C. levinseni n. sp. This species (PI. 1, fig. 10), the property of the Copenhagen Museum, 
was most generously placed in my hantls for description by P)r. G. .M. R. Levinsen. (Jn first 
finding Cep/iaiodiscus among the "Siboga" material, I wrote to Dr. Levinsen, to enquire whether 
he was working at a specimen belonging to this genus which, as I had been informed a year 
or two previously, was in his possession. It appeared to me not improbable that it might belong 
to the same species as one of the "Siboga" forms. With the utmost generosity, for which I 
desire here to express my most cordial acknowledgment. Dr. Levtnsex replied by sending me the 
specimen, and asking me to investigate it with the other material in my hands. It is in many 
respects a very remarkable species, differing in the clearest way from all the others. The zooids 
are all female, and numerous embryos are present. 

Tlie British Museum have recently received other specimens of Ccphalodiscus, of which 
descriptions will doubtle.ss be published in due course. 



III. DIAGNOSES OF SPECIES OF CEPHALODISCUS. 

The most useful specific characters of ilie genus Ccphalodiscus appear to me to be 
afforded by the coenoecium, the proportions of the body and stalk of the zooids, the number 
of tentaculiferous arms, and the pre.sence or absence of vesicle-bearing end-bulbs on the arms. 
The species which have come under my notice can readily be discriminated In- these features, 
Init in the short diagnoses which follow 1 liave made some use of other characters, such as 
the profusion with which buds are produced. Since the diagnosis depends, in each case, upon 



a single colony, too much stress cannot be laid upon the buds, the number of which may 
depend on the season of the year or on the condition of sexual maturity of the zooids. 

The descriptions of C. dodecalophus which have previously been published were drawn 
up in the absence of all information relating to other species of the genus; and until this 
information was forthcoming it was of course impossible to decide which of the characters were 
of specific rather than of generic value. It may, however, be remarked that the specific name 
given by M'Intosh proves to have been well chosen ; since, as I believe, the number of arms 
is a character of specific value. 

The systematic position which Cephalodiscus and Rhahdoplejwa appear to occupy is 
indicated by the following classification. 

HEMICHORDATA ■). 

Bateson (Quart. J. Micr. Sci. XXV, Suppl., 1885, p. iit). 

Order i. ENTEROPNEUSTA Gegenbaur. 

Order 2. PTEROBRANGHIA Lankester. 

(Quart. J. Micr. Sci. XVII, 1877, p. 448). 

= ASPIDOPHORA Allman. 
(J. Linn. Soc. Zool. XIV, 1879, pp. 490 n., 586). 

= BRACHYSCOLECIDA BRANCHIATA Ehlers (90, p. 173). 
= CEPHALODISCIDA + RHABDOPLEURIDA Fowler (92, 2). 

Earn. I. Cephalodiscidae. 

= Enteropneusta Monobranchiata Schimkewitsch (93, p. 238). 

Cephalodiscus M'Intosh (82). 

Earn. 2. Rhabdopleuridae. 

Rhabdopleura Allman. 
(Quart. J. ViXcx. Sci., IX, 1869, p. 57; Rep. Brit. Ass. (1868) 1869, p. 311). 

? Order 3. PHORONIDEA. 
Phoronis Str. Wright. 



i) Numerous other names, such as Pharyngopneusta, Archicoelomata, Trimetamera, Archichorda, Diplochorda, Protochordata, 
Adelochordata, "Urchordaten", "Axobranches", "Vermidiens", "Procoides", Branchiotrema, Hydrotrema, have been used as the equivalent 
of Hemichordata, or of this group in addition to others, or of its subdivisions. These terms ai'e for the most part dealt with historically 
l>y DE Selys I.ongchamps (04, pp. 102 f.). Reference may also be made to Delage .md HliROUAKD (97, 98) .ind to Willey (99). 



Fam. Cephalodiscidae. 

Cephalodiscus Mliuosh. 

Zooids secreting a gelatinous coenoecium formed of numerous lamellae. C o e n o e c i u m 
with a continuous cavity or with a separate cavity for each zooid, each orifice produced into 
one or more peristomial processes. Zooids consisting of proboscis, collar, and metasome. 
Proboscis greatly flattened in an antero-posterior direction, its anterior wall mainly composed 
of a high, glandular epidermis, and provided with a curved, transverse pigment-band, with 
dorsal concavity. Body-cavity of proboscis single, opening to the exterior by two symmetrically 
disposed proboscis-pores, which lie on either side of a median pericardium. Collar with an 
anterior free edge, the dorsal part of which is split up to form 4 — 6 pairs of tentaculiferous 
arms, between the bases of which is the central nervous system ; while the ventral i)art forms 
a simple lower lip, operculum, or post-oral lamella. Body-cavity of collar paired, with complete 
dorsal mesenter\-, which supports a pharyngeal outgrowth ("notochord") passing forwards along 
the septum between the proboscis-cavity and the collar-cavities. These open to the exterior by 
a pair of collar-canals, immediately behind which is a jKiir of gill-slits situated in the septum 
between the collar-cavities and the metasomatic cavities. Metasome, body or trunk 
elongated at right angles to the antero-posterior axis of the zooid, containing the gonads and 
nearly the whole of the alimentary canal. Anus and generative apertures situated dorsally on 
the metasome, which is produced ventrally into a muscular stalk, from the distal end of which 
originate buds. Body-cavity of metasome paired, with complete or incomplete dorsal and ventral 
mesenteries. Sexes dimorphic. 

It will be seen that the generic diagnosis, as above given, includes all the most important 
features which have previous!)- been described in C. dodecaiop/uis. The specific characters are 
in fact subordinated to the striking assemblage of anatomical peculiarities which have already 
been recognized in the type-species. The curiously reduced males of C. si/n[<;'ae have not, 
however, been shewn to possess proboscis-pores, gill-slits or operculum, while the arms are 
reduced to a single pair, and bear no tentacles. 

C. dodecalopJms M'Intosh. (PI. 11, fig. 21. PI. I\', fig. 42, etc.). 

C. dodecalophus .M'liUosh (82, 83, 87J, Lankester (85), Lang (90), Spengel (93, pp- 721, 753). 
Masterman (97, 98, 03), Cole (99). 

Straits of Magellan. "Challenger" Collection. 448 M. 

Female colony. 

Coenoecium large, reaching a length of at least 225 mm., its cavity continuous, opening 
at intervals by irregularly arranged orifices, whicli may bear two or more long peristomial 
processes. Metasome ovoid '), giving off the stalk from its anterior surface. Stalk thick, .short 



i) The material was, in all the species, preserved without special precautions being taken to obtain the zooids in an extended 
condition. There is clear evidence, in most cases, that the greater number are in a highly contracted state, and it is this condition to 
which the diagnoses refer. 



(not so long as the rest of the zooid in the contracted condition), and commonly directed 
towards the mouth, producing buds in small numbers from its free extremity. Tentaculiferous 
arms six pairs, terminating in end-bulbs, which bear numerous vesicles in their epidermis. » 

C. levinseni n. sp. (PI. I, figs. lo, 6, 5. PI. II. figs. 11 — 13. PL III, figs. 23, 24. 

PI. IV, figs. 33, 34, etc.). 

Sea between Japan and Corea. 183 M. (Copenhagen Museum). 

Female colon)'. 

Coenoecium large, subcylindrical, and slightly branched, reaching a length of at least 
1^2 mm.: consistins" of a number of distinct zooecia, the cavities of which do not communicate 
with one another. Orifices borne at the ends of distinct tubular peristomes, which radiate in all 
directions, at an angle greater than a right angle, from the ])rincipal axis of the branch; each 
being produced on its abaxial side into a single, short, blunt process which is rarely branched. 
Metasome elongated and cylindrical, giving off the stalk from its anterior surface. Stalk thick, 
about as long as the rest of the zooid, usually directed aborally in the adults, producing buds 
in .small numbers. Proboscis-stalk very long, giving ri.se to a great mobility of the proboscis, 
which usually forms a mantle-like investment passing partially round the bases of the arms, and 
is commonly found in an inverted or otherwise displaced position. Tentaculiferous arms six pairs, 
without definite end-bulbs or vesicles. 

I have great pleasure in dedicating this species to Dr. G. M. R. Levinsen, as some slight 
acknowledgment of the kindness with which he placed the specimen in my hands for description. 

C. gracilis n. sp. (PL I, figs, i, 4, 7. PL II, figs. 15, 16. PL III, fig. 22. PL IV, fig. 37, etc.). 
"Siboga" Expedition. Stat. 89. E. coast of Borneo, reef. 

Female colony. 

Coenoecium very small and delicate, with continuous cavity, creeping over other objects, 
several times branched, and fimbriated at its extremities by long peristomial filaments borne 
on the margins of the funnel-shaped orifices. Metasome an elongated ovoid, giving off the stalk 
from its anterior surface. Stalk thin, much longer than the rest of the zooid, usually directed 
aborally, and producing buds in great profusion. Tentaculiferous arms five pairs. Small end-bulbs, 
bearing visicles, present in the first two arms of the bud, and occasionally in the third arms; 
apparently absent in some of the adult specimens. 

C. sibogae n. sp. (PL I, figs. 2, 3. PL II, figs. 17, 18. PL IV, figs. 38, 40. PL VII, 

figs. 72 — 76, etc.). 

"Siboga" Expedition. Stat. 204. S. E. of Celebes. 75—94 W- 

Male colony. 

Coenoecium consisting of a dense basal portion which forms a continuous encrustation 



8 

over the substratum, and uf stiti", erect and slightly branched tubes, the foreign inclusions of which 
are more numerous than in the other species. Cavity of erect branches continuous, originating 
from the irregular cavity of the basal encrustation, into which the zooids can be retracted. 
Orifices widely infundibuliform, with a tendency to assume an alternate arrangement on two 
opposite sides of the branch, produced into a few moderately long peristomial filaments. Zooids 
dimorphic, consisting of neuters and males. 

Neuter i n d i \- i d u a 1 s with an elongated metasome, the stalk originating nearly from its 
aboral end; gonads absent, or represented by mere vestiges, or perhaps occasionally developed 
into functional testes. Tentaculiferous arms four pairs, apparently without end-bulbs and vesicles. 
All parts of the epidermis are densely pigmented. 

Male individuals with conical body, which passes continuously into the stalk; 
alimentary canal vestigial; testes two, occupying most of the metasome and part of the stalk, 
and opening in the same position as the ovaries in the other species. Arms reduced to a single 
pair, without tentacles, their epidermis being crowded with large, highly refracting vesicles. 
Epidermis highly pigmented. 

In both kinds of individuals the stalk is e.xcessively long and slender, and apparently 
produces buds in great profusion. 



IV. COEXOECIUM. 



It has been pointed out above that excellent specific characters are afforded by the 
coenoecium, which, however, has a well marked generic character. It is in all cases provided 
with a number of definite orifices, which in the species investigated, are usually bordered by 
one or more peristomial processes; and it is entirely composed of a series of superposed lamellae 
of more or less pronounced orange colour and of gelatinous consistency, as described by 
M'Intosii (87, p. 5) in the type-species. Many of the lamellae include various foreign bodies, 
such as Foraminifera, Sponge-spicules, particles of mud and so on, to an extent varying with 
the species. These lamellae closely resemble tlie rings which compose the tubes of Rhabdopleiira. 
A careful examination of the free portions (^peristomes") of the tubes in that genus (PI. II, 
fig. 19) shews that the rings are not unbroken, but that each is interrupted by an oblique 
suture. The suture is easily seen when it is on that side of the ring which faces the observer (a), 
less easil)- when it is necessary to focus through the tube in order to see it (<$), and may be 
difficult to distinguish when it lies on either edge of the tube [c). I believe, however, that the 
.suture is a typical feature of the tube-ring; and that it indicates that the zooid, in constructing 
a new ring, begins at a definite jioinl and works round the entire peripherj' of the tube until 
it returns to its starting pcjint. It may be presumed thai tlie pari of the new ring £rst secreted 
has by this time somewhat hardened, so thai the junction of llie first- and last-formed part of 
the tube is indicated by the suture. This point escaped the notice of S.\rs (72, p. 3), who 
.supposed the rings of the peristome to be uninterrupted, while he figures the sutures (PI. I, 



fig. 9) in the rings which constitute the creeping portion of the tubes. L.\xkester (84, p. 626) 
also emphasises this supposed difference between the peristomial rings and those of the attached 
parts of the tubes. The sutures of the peristomial rings are, however, clearly described and 
figured by Schepotieff (04, p. 6, PI. I, fig. 3). 

There can be little doubt that the tube-rings of Rhabdopleura are successively constructed 
by the proboscis or buccal shield, as stated by L.\nkester (pp. 624, 626). It may fairly be 
assumed, with M'Intosh (87, p. 6) that the coenoecium of Cephalodisats is formed by the same 
organ, the greatly developed glandular epidermis of whose anterior side appears well fitted 
for this task. 

C. levinseni. (PI. II, figs. 11 — 13. PI. IX, figs. 108 — i 10). 

The coenoecium of this species is characterised by the following features : — (I) by its 
definite law of growth; (II) by the existence of a distinct and separate tubular cavity for each 
of the zooids; and (III) by the prolongation of this tube into a well marked free portion or 
peristome, the orifice of which has a characteristic oblique form. These features are illustrated 
by PI. I, fig. 10 and PI. II, figs. 11 — 13. 

Fig. I 2 represents the details of the peristome A of Fig. 1 1 . The tube has an accurately 
cj'lindrical cavity and is lined by a certain number of longitudinally disposed lamellae, which 
are not shewn in this figure, although some of them are represented in fig. 13. The wall of 
the tube is specially thickened on the side which passes into the projecting lip of the orifice. 
This thickened side forms a sort of mid-rib, which clearly serves as a supporting structure. The 
lamellae of which the peristome is composed closely resemble the tube-rings of Rhabdopleura^ 
as is well seen when they are e.xamined in optical section {e.g.^ left hand side of fig. 13). The 
ring then appears evenly convex distally, and concave proximally where it overlaps the next 
lamella. In the greater part of the peristome, the lamellae are very oblique, sloping proximally 
from the abaxial side, or side of the mid-rib. In the more proximal jjart of the peristome, they 
are broad, indicating a rapid period of growth ; while more distally they become more crowded 
and irregular (fig. 12). They probably never form complete rings, but the majority of those 
which are not merely concerned in the construction of the mid-rib form half rings, starting from 
the mid-rib, passing across the whole of one of the lateral surfaces of the tube, and ending in 
a point on the axial side. This structure is illustrated by the lamella a in fig. 12. The deposition 
of these lamellae may be alternate, so that if a forms part of what may be termed, for descriptive 
purposes, the "right" wall of the peristome, b will form part of the "left" wall, the two lamellae 
overlapping at the mid-rib. Distally this arrangement is by no means constant ; but in the proximal 
region of rapid growth the lamellae may alternate cpiite regularly for a considerable distance. 
When the peristome is examined from the axial side, the interdigitating pointed ends of the 
half rings are often conspicuously seen. 

A elance at fior. 12 will shew that the lamellae which constitute the mid-rib are far 
more numerous than those which form the rest of the tube; and it will further be .seen that 
this disparity is due to the fact that many of the lamellae are concerned exclu.sively in building 

Sn;OGA-EXPEDlTIE XXVI ///.f. 2 



lO 



up the mib-rib. These are especially numerous in the distal part of the peristome; and the 
constant elongation of the mid-rib produced in this way thus results in the acquirement of 
more and more obliquity in the disposition of the tube-lamellae as growth proceeds. 

The structures which have so far been described may be distinguished as the "jjrimary 
lamellae". Cephalodisciis differs from Rhahdopletira in laying down additional series of "secondary 
lamellae", both on the inside and on the outside of the primary lamellae. On the inner side, 
these have a longitudinal arrangement (fig. 13), and their formation can be accounted for by 
the supposition that the zooid lines its tube by additional lamellae secreted by its proboscis. 
The external secondary lamellae may appear as a series of longitudinal layers running down 
the outside of the peristome (figs. 12, 13), or as a series of layers bridging over the interval 
between two diverging peristomes. Fig. 1 3 shews two young peristomes, of which that on the 
left is viewed laterally, while that on the right is seen from the abaxial side. Examining the 
angle between the two peristomes, it will be noticed that growth took place for .some distance 
without the formation of any bridging lamellae; and this arrangement can be made out in most 
cases. After a time, however, intermediate lamellae are depo.sited; and some of these appear 
to be derived from each of the two neighbouring peristomes. On the extreme left side of the 
figure, some of the external secondary lamellae are seen as prolongations of the primary lamellae; 
but many of them are certainly independent formations. It is probable that the extraordinary 
length of the neck-region of the zooid, and the great mobility of the proboscis, in this species, 
are correlated with the length of the peristomes, the animal having the power of stretching its 
proboscis a certain distance down the outer side of its tulie, during the deposition of these 
e.xternal lamellae. 

The laminated structure of the coenoecium is further illustrated by figs. 108 — i 10 (PI. IX), 
representing sections transverse to the principal axis of the entire colony. Fig. 109 shews parts 
of seven zooecia '), most of which are cut more or less transversely; although c and e are cut 
longitudinally, c through the wall of its peristome. In '(a'-^. \ 10, which .shews the details of jjart 
of the same section, b points to one of the jn-imary lamellae of the zooecium c\ and it will 
be noticed that the primary lamellae arc covered both internally and externally by secondary 
lamellae, some of the e.xternal ones being clearlv contributed b\ the jjeristome c. The primary 
lamellae {pr. I.) of the zooecium d are also distinguishable. The zooecia d and / are separated 
from one another by a single series of jjrimary lamellae {pr. /'.), indicating that the zooids do 
not each secrete a complete wall of their own, but economise material by making what use 
thev can of the tubes of their neighbours in constructing their own zooecia. 

Fig. 108 is a section of the basal region of another peristome, with an extensive 
development of both internal and external .secondary lamellae. The two primary lamellae marked 
/;'. /. are cut along nearly their whole length ; and their sutural junction on the axial side is 
indicated in the lower part of the figure. 

I'oreign inclusions are not ver\' numerous in the coenoecium of this species, but they 
are by no means absent, as is indicated by figs. 12, 13. 



1) I use the term "zooecium"' without implying any homology with the structure known by the same name in Polyzoa. The 
term is ctymologically applicable to Cephaloiiisciis^ while its use in the Polyzoa may be defended merely on grounds of convenience. 



1 1 

The mode of growth of the coenoecium in C levinseni is not at first sight apparent. 
The zooecia contain adult zooids, buds and developing embryos, any of which might conceivably 
play their part in the increase of the coenoecium or in the formation of new zooecia. I have 
no actual evidence that the embryos take any such part, but it is by no means impossible that 
they ma)' add a few lining lamellae to the proximal end of the tube, where they mostly occur. 
The analogy of other fixed colonial animals suggests, however, that the embryos become free- 
swimming and thus have the function of originating new colonies. I cannot find any indication 
of bifurcation of the cavities of the coenoecium, or of the formation of diverticula which might 
give rise to new zooecia. The explanation which appears to me most likely is that the buds 
when liberated from the parent stalks make their way out of the orifices of the zooecia and 
crawl along the outer surface of the coenoecium until they find a suitable spot, where they 
settle down and commence to manufacture their own zooecia. The crawling movement would 
presumably be effected by means of the anterior surface of the proboscis, a mode of locomotion 
observed by S.\rs (72, pp. 9, 1 2) in the living Rhabdopletwa. The proximal part of the entire 
coenoecium is considerably thicker than the distal part, and it consists of a larger number of 
zooecia. The increase in thickness can be accounted for by supposing that buds have commenced 
their tube-forming activity on some part of the external surface of the coenoecium. The sup- 
position is also in accordance with the fact that the proximal parts of the zooecia are constituted 
partly by primary lamellae which are buried deeply within the coenoecium. 

In one or two parts of the colony, forming either the tip of the main a.xis, or a lateral 
branch growing out from the axis, there are regions which are clearly young. This is indicated 
by the paler colour of the gelatinous substance, and by the thinness of the walls of the zooecia, 
which are here composed of primary lamellae only. The zooecia although less numerous than 
in the more proximal parts are already obeying the same law of growth. They contain young 
zooids (PL I, fig. 5), of the form described on p. 18, which are already engaged in budding, 
whilst their ovaries contain only immature eggs. In the more proximal parts of the colony, on 
the contrary, there is but little budding activity, while ripe eggs are produced by the ovaries, 
and most of the zooecia contain eggs and embryos The bearing of these facts appears to me 
to be as follows. In the proximal part of the colony but few buds are produced, and accordingly 
the coenoecium increases in diameter comparatively little, the zooids expending most of their 
energies in the production of eggs, which develop into larvae destined to found new colonies. 
Nearer the growing tips there is a budding zone; the buds on escaping from the zooecia 
coming to rest near the bases of the existing peristomes, thus prolonging the coenoecium and 
increasing its diameter. If the outflow of buds is sufficiently great at any point remote from the 
apex of the coenoecium, a branch is formed. It must, however, be pointed out that I have 
searched in vain for positive evidence as to the initial stages in the growth of a new zooecium. 

C. gracilis. (PI. II, figs. 14—16. PI. V, figs. 54, 55). 

The slender coenoecium of this species, and its prostrate habit, are features which are 
in marked contrast with those of the robust and erect species which has just been considered. 



The coenoecium consists of a delicate tube, bifurcating from time to time, and enclosing a 
cavity which is continuous throughout. The orifices, which appear to be confined to the ends 
of the branches '), are funnel-shaped openings, with irregular margins, and they are produced 
into a varying number of fine gelatinous "spines" or peristomial filaments. Similar filaments 
occur in the more pro.ximal ]»arls of the tube, where orifices appear to have been occluded 
by the deposition of gelatinous lamellae. Thus at a in fig. 1 5 three embryos are contained 
in a diverticulum of the main cavity which is completely closed distally, while the remains 
of filaments probably indicate that this was once one of the functional orifices of the coenoe- 
cium, when growth had not e.xtended much beyond this point. Some parts of the tube 
are completely empty, while others contain numerous embryos, as well as zooids (adult and 
immature blastozooids), which are often so closely packed that it is difficult to trace the limits 
of the individuals. It is probable that the zooids, like those of C. dodecalophus^ can wander at 
will through the cavity of the coenoecium. Hut the long, RJiabdoplenra-\\\i&, stalk of this species 
probably enables the zooid to reach an orifice while the base of its stalk is still deep in the 
recesses of the coenoecium. 

The foreign inclusions in the je]l\- are small and inconspicuous, but they include a 
considerable number of Diatoms and sponge-spicules. Many Diatoms are visible on the free 
surface of the coenoecium, and some of these are probably, from time to time, included in 
the jelly, in ])laces where the deposition of fresh lamellae is taking place. It may be noted 
that the inclusions commonly rest immediately on an older lamella, and are covered by the 
next lamella. 

The structure of the coenoecium resembles that found in C. levitiseni^ though its law 
of growth is much le.ss definite than in that species. A consideration of fig. 16 will probably 
give a correct idea of its mode of growth. The figure shews two orifices («, b) and three 
peristomial filaments {c, d, e). These filaments correspond with the ''mid-ribs" of C. levitiseni^ 
but are much more developed than in that species. They project far beyond the orifices as 
cylindrical structures composed in the main of a series of overlapping conical primary lamellae, 
the shape of which is not complicated by taking part in the formation of a tubular zooecium. 
A few secondary lamellae, forming a transparent sheath to the process, occur in the more 
pro.ximal part. 

The tubular cavity of the coenoecium is being prolonged along these processes b)- the 
development of oblique primary lamellae (shewn in the lower part of fig. 1 6), similar to those 
of C. hvinseni except in the fact that they take no share in the formation of the mid-rib, 
which precedes their formation. As the tube of the coenoecium becomes prolonged along the 
process, the mid-rib remains as a supporting rod passing along one wall of the tube. The 
lamellae composing this rod usually become darker in colour with advancing age ; and as they 
have taken no part in the formation of the lateral walls of the coenoecium, the cylindrical 
supporting rod is sharply marked off from the rest of the coenoecium. 



i) Orifices arc present in fig. 15 at the points marked by arrows. It is probable that others are really present as well; but 
all the more proximal ones appear to have been closed. 



At /, in fig. 1 6, there is the edge of a lamella which is so prominent as to suggest 
that it was for a time the edge of an orifice (the lamellae between f and b have not been 
indicated in the figure). There can be no doubt that this was the case ; and it will readil\- be 
seen that at this time the orifice was produced into the principal filamentous process r, which 
soon gave off the lateral branch d\ while a third process e was formed at the opposite side 
of the orifice. With the increase in the length of the coenoecial tube the process e has been 
left unconnected with any orifice. The principal growth has taken place along c, which has 
doubtless increased meanwhile by the addition of new cones to its ape.\. The terminal orifice 
«, with its process c, now has a close resemblance to a peristome of C. levinseni. It consists 
almost entirely of primary lamellae, namely those of the mid-rib, and those of the rest of the 
tube. Secondary lamellae are at present but slightly developed. 

Should further additions be made to the orifice b it is highly probable that they would 
take place along the process d, and a bifurcation of the coenoecium would thereby result. 
Fig. 1 5 shews that a considerable number of peristomial filaments may be developed in con- 
nexion with a single orifice. 

Fig. 54 represents a longitudinal .section through an orifice, with several peristomial 
filaments, of C. gracilis \ while fig. 55 represents part of a transverse section through the 
coenoecium, more highly magnified. The figures both shew a considerable development of 
secondary lamellae on the inner side of the primary lamellae. 

C. sibogae. (PI. II, figs. 17, 18. PI. IX, figs. 102, 103). 

It must be remembered that the colony here described under this name contains male 
and neuter individuals, no females being present. It is thus necessary to consider the possibility 
that it may be the male form of C. gracilis. 

The neuter zooids of C. sibogae are perfectly characteristic Cephalodiscus individuals 
except for the absence of functional reproductive organs. It can hardly be doubted that they 
take an important share in the secretion of the coenoecium, though I see no reason why the 
extraordinary male individuals should not contribute to its growth. But even taking account of 
this possibility, there seems no obvious reason why the characters of the coenoecium should 
differ to any great extent in the two sexes of the same species. The fact that there are definite 
differences in the coenoecia of the forms here described under the names of C. gracilis and 
C. sibogae is one of my principal reasons for regarding them as belonging to distinct species. 

The coenoecium of C. sibogae consists of two very different parts: — (I) a denser 
portion which forms a continuous expansion over the rock on which it grows; (II) a series of 
upstanding tubes, fringed with numerous peristomial filaments, and arising from the basal 
encrustation (PI. I, fig. 2). 

The cavity of the coenoecium is continuous, that of the erect tubes passing into those 
of the basal encrustation. It is a remarkable feature of this colony that the zooids are nearly 
all retracted into the latter, so that the erect tubes are for the most part completely 
without zooids. 



14 

The stalks of the zooids of C. sibo^ae are excessively long and slender (as in C. gracilis). 
It seems to me by no means impossible that they may be sufficiently extensible to permit of 
the protrusion of the tentacles from the orifices while the bases of the stalks still remain in 
the basal encrustation. However this may be, it cannot be doubted that the densely massed 
zooids found in the basal jiart of this colony possessed during life the power of entering the 
erect tubes. 

The tubes may be simple, bifurcated, or somewhat more branched. In one case which 
I have noticed, the tube trifurcated near its ba.se, and two of these branches bifurcated a 
little later, making five branches in all. The branches have a certain straightness, which is 
in contrast with the sinuous and decumbent branches of C. gracilis., and is correlated with a 
firmer consistency of the jell\'. Their colour is definitely orange (in spirit), those of C. gracilis 
having so little of the orange colour as to a])pear almost colourless. While the basal encrustation 
is for the most part free from foreign inclusions, all parts of the erect tubes take up an 
enormous number of particles of detritus or mud (which may possibly be faecal), as well as 
bodies such as the shells of Foraminifera and sponge-spicules. 

The orifices are typically wide funnels which ]:)roject from the walls of the tube, and have 
a tendency to assume an alternate arrangement. The peristomial filaments are stiffer and sliorler 
than in C. gracilis. The lamellae whicli constitute the greater part of the tube are readily seen 
without .staining. The upper half of l*"ig. i 7 shews that they are convex distally and that they 
are of small size, a feature which may be regarded as correlated with the small size of the 
proboscis in this species. They are in fact not large enough to form even one half of the 
transverse circumference of the tube. 

In C. gracilis (Fig. 16) on the contrary, the lamination is more difficult to make out 
without staining. The lamellae are not specially convex distally, and their arrangement recalls 
that found in C. levinseni, a tendency towards an oblicpie arrangement being noticeable, while 
the lamellae in many cases .stretch across the whole of one of the lateral surfaces of the tube. 

The mode of growth of the coenoecium of C sidos'ac resembles that found in C. (gracilis. 
The lower part of fig. 17 shews a funnel-shaped expansion, which was formerly the terminal 
orifice of the tube, its lower lip being still indicated by a prominent line a. This orifice was 
|jrovided with the three peristomial processes d, c, and d, of which d lies in the wall which is 
furthest from the observer. W ith the prolongation of the wall of the tube by the deposition of 
fresh lamellae, the funnel-shaped orifice became narrowed, jiart of it remaining as an orifice c, 
in relation with the process <5, the rest of it extending as a separate orifice along the process d. 
The process c thus became removed from any connexion with an orifice, and so ceased to 
grow. The process d, which in the lower part of the figure lies in the deeper wall of the tube, 
and in the upper part becomes nearly lateral, constitutes the principal skeleton of the tube, and 
is continued beyond its terminal orifice i as the process n. When the tube had reached a 
certain distance, a new peristomial process iji) was formed, which has become the support of 
the orifice /, most of which is concealed by the base of the process. The line g indicates the 
margin of the terminal orifice at a previous stage, although a considerable part of this funnel 
has now been closed by the onward growth of the tube, jjart of it persisting as the orifice /. 



'5 

The end of the tube is a widely open funnel {i), of which /c is the lower lip, and /, 
//I and u are the peristomial filaments. 

The filaments have a structure similar to that found in C. gracilis^ consisting of a series 
of overlapping cones, with an occasional, very delicate, secondary lamella on their outer side. 
Some of the cones contain large numbers of minute granules, which are indicated in the upper 
part of the principal process n. Similar granules may occur in smaller numbers in the lateral 
lamellae. 

It need hardly be pointed out that when the peristomial filaments become included in 
the wall of the tube, they retain the structure which they have at their first formation. The 
series of primary cones may thus be traced throughout the supporting sheletal bars which result 
from the modification of the peristomial filaments. 

Secondary lamellae are not much developed in the erect tubes of C. sibogae, though a 
certain number occur on the outer side of the wall, and are probably in many cases responsible 
for taking up the foreign inclusions which form so conspicuous a feature of the species. The 
basal parts of the tubes may be lined by several layers of internal secondary lamellae. 

The basal encrustation is a continuous film, with a smooth glistening surface, free from 
foreign inclusions. It moulds itself over all the irregularities of the stone on which the specimen 
is growing, and it is traversed by a continuous set of irregular cavities which contain the deeply 
pigmented zooids. The layer in actual contact with the stone is quite thin. A section of a part 
of the basal encrustation is shewn in fig. 102, and a part of the same figure, more highly 
magnified, to illustrate the details of the lamination, in fig. 103. The tube a is cut longitudinally, 
and shews on either side a well marked series of primary cones (</, e), of which the series d 
has given off a lateral branch, /, which has the same structure. In the interval between f and 
the upper part of rt' a few secondary lamellae can be recognized, while a certain number of 
similar lamellae line the cavities of the tubes. It should be noted, however, that some of the 
lamellae to the left of d are really primary lamellae cut tangentially. 

It cannot be denied that the coenoecium of C. sibogae resembles that of C. gracilis in 
some respects; but the differences between the two specimens seem to be sufficient to indicate 
that they belong to distinct species, even making full allowance for the fact that thev are of 
different sexes. 

C. dodecalophtis. (PI. II, figs. 20, 21). 

The general characters of the coenoecium are well illustrated by M'Intosh (87, text-fig. 
on p. 4, PI. I, PI. VII, fig. i). Although offering an obvious generic similarity to that of 
C. levinseni^ the coenoecium of C. dodecalophus differs from it in several noteworthy points. 
In.stead of having a separate cavit\- for each zooid, it resembles that of C. gracilis and C. sibogae 
in containing an irregular, continuous, axial cavity, some parts of which may be empty, while 
others are crowded with zooids and eggs. The cavity communicates with the exterior by rounded 
orifices which are not borne by prominent peristomes (fig. 21). C. dodecalophtis is characterised 



i6 

by developinj^ numerous bridi^es uf jelly not only between adjacent branches, but between 
neighbourintr elevations on the surface of a single branch. Although the orifices are sometimes 
mere holes in a flat surface (<5), they are more often sunk in deep recesses (c) formed by the 
outgrowth or union of gelatinous lobes. The distinction between primary and secondary lamellae 
is at first sight not apparent, though a closer examination reveals traces of it. M'Intosh states 
(p. 5) that "all the spines are hollow", but in this there can be no doubt that he was mistaken. 
The spines in reality have a structure similar to that of C. gracilis^ each of them being 
supported by an a.xis of denser jelly, which has a deeper orange colour than the more superficial 
parts. These axes, which appear to be hollow in certain modes of illumination, are shewn by 
their arrangement to be supporting ribs. One of them, broken at its tip, is seen at a in fig. 2 1 . 
It forms a support for the film of jelly between itself and the main branch, and it is continuous 
at its base with the irregularly arranged development of the same stifter jelly which occurs in 
the main branch. It is characteristic of these supporting pillars that they do not reach the 
end of the lobe or spine which they support. The axis usually extends through about two-thirds 
of the spine or lobe, and then ends abru|)tly in a sharply marked rounded termination. This is 
not indicated in fig. 21, in \\hl;:h, however, the spine d is supported by an axis which extends 
nearly to the tip of its shorter branch, while the longer, more delicate branch of the same 
spine contains no axial support. 

An examination of one of the larger spines (fig. 20) of the colony .shews that the axis 
consists internally of a series of overlapping cones, which corre.spond with the primary lamellae 
of C. levinseni, but are more pointed than in that species. The darker axis is, however, 
completed by a series of thin secondary lamellae; while the rest of the lobe is, for the most 
part, constituted by very numerous secondary lamellae whose paler colour distinguishes them 
sharply from the central axis. Those terminal parts of the lamellae or spines which are not 
supported by an axis are composed entirely of pale secondary lamellae. 

Many of the long spines are clo.sely related to an orifice. Thus the spines d and e 
of fig. 2 1 are peristomial filaments of the orifice which is .seen to their left. As was the case 
in C. gracilis, man)- of the spines which do not at first sight apjjear to belong to an orifice 
may have been so related at an earlier period of growth, and ma)- have lost that connexion 
by the subsequent deposit of secondary lamellae. 

The process shewn in fig. 20 has given off a broad triangular lobe on its right side. 
The axis of this is constituted by characteristic conical primary lamellae, which, however, have 
not acquired the deeper colour seen in the larger axes. 

The mode of growth of the coenoecium of C. dodccaloplius is not quite apparent. 
There is no indication that the secreting part of the proboscis has the extraordinary mobility 
characteristic of C. levinseni. The stalk is moreover very thick and short, which would at first 
sight appear to forbid the assumption that tlie proboscis can be protruded far beyond the 
orifices of the coenoecium. It must, however, be remembered that the stalk of C. dodccaloplius 
possesses a great development of longitudinal muscles, aiul iluu its epidermis and basement- 
membrane are usually very much wrinkled (PI. XIII, fig. 1 69J. This indicates contractility; 
and it may fairly be suggested that the stalk is capable of great elongation, so that it might 



be possible for the zooid to keep the tip of its stalk, with its series of buds, in the shelter 
of the coenoecium, and to crawl on the anterior surface of its proboscis as far as is necessary 
to enable it to add gelatinous lamellae to the spines and other processes of the coenoecium. 
A considerable number of Foraminifera and other foreign inclusions occur in various 
parts of the coenoecium of this species. 



V. EXTERNAL CHARACTERS OF THE ZOOIDS. 

Omitting for the present the males of C. sibogae which must be treated apart (see 
Sect. XV), all the species of the genus shew the typical Cephalodisais character, differing from 
one another only in the relative size and in the shape of the several parts. The zooid consists 
of the three fundamental regions (I) the buccal shield, with part of its supporting neck, together 
homologous with the proboscis of Balanoglossus ; (II) the collar, produced dorsally into 4 — 6 
pairs of tentaculiferous arms, and ventrally into the lower lip or operculum; and (III) the 
metasome or body, continued into the stalk, which produces buds from its distal extremity. 

Masterman (97, I, p. 290 f.) speaks of the three primary regions as "protomere", 
"mesomere" and "metamere", and of their cavities (98, 2, p. 516) as "protocoele", " mesocoeles" 
and "metacoeles" respectively. Willey (99, 2, p. 314) has pointed out that the use of the term 
"metamere" in this special sense is inadmissible, and replaces it by "opisthomere". I shall for 
the most part refer to the three regions as "proboscis", "collar" and "metasome" respectively, 
the last a term which is used by several authors in describing Phoronis. 

C. dodecalophus (cf. PI. I\^ fig. 42). The general appearance of the zooid is well known 
from the admirable figure given by M'Intosh (87, PI. 11). The proboscis forms an antero- 
posteriorly ') flattened disc, which in a front view usually overlaps the whole of the collar 
except the distal parts of the tentaculiferous arms or plumes, also concealing the mouth and 
the external apertures of the gill-slits and collar-canals. Its ventral half bears a conspicuous 
narrow band of reddish pigment, which forms a curved line, with dorsal concavity, extending 
transversely across the organ -). The body is ovoid and relatively short, the stalk originating 
from its antero-ventral surface, some way from its aboral end. The short and extremely muscular 
stalk is u.sually directed transversely to one side, or towards the mouth. Its epidermis is thrown 
into numerous, deep, transverse wrinkles, doubtless caused by the contraction of the muscles 
(see PI. XIII, fig. 169). It seems obvious from this fact that the stalk of the "Challenger" 
specimens is in a highly contracted condition. It may reasonably be inferred that during life 
it is capable of a much greater amount of elongation, and it may be presumed that it then 
frequently places itself in a position parallel to the long axis of the body, with its distal 
end directed away from the mouth. This position is sometimes actually observed (M'Ixtosh 
87, PI. Ill, fig. i); it is the position in which the other species are commonly found; and it 



1) The sense in which I use terms descriptive of the surfaces and of the principal planes is indicated on p. 23. 

2) This curved band of pigment has been erroneously represented as the mouth in a certain text-book. 
SIBOGA-KXl'KUniE XXVI i/>. 3 



i8 



is moreover the position in which stalk and body lie in immature buds. C. dodecalophus has 
six pairs of tentaculiferous arms, each of which ends in a swollen bulb containing remarkable 
refringent vesicles. 

C. kvinseni. (PI. I, figs. 5, 6. PI. Ill, figs. 23, 24). 

In their old condition, the zooids of this species are characterised by having an extremely 
elongated, cylindrical form (PI. I, fig. 6; PI. II, (x'^. 11 ; PI. I\', fig. 33), the apparent length, 
however, being commonly greater than the real length, in consequence of the fact that the 
somewhat coiled distal end of the stalk, sometimes bearing a bud, together with several large 
embryos, usually form a mass having the same diameter as the body, and so closely applied 
to its posterior end that the limit between this mass and the body is not at once made out. 
The elongated masses seen in the cavities of the coenoeciuni in fig. i i thus consist, in most 
cases, of zooid -I- stalk + bud (if any) -|- embryos. The extreme elongation of the old zooids is, 
however, seen in the sagittal section shewn in fig. 33; from which it will be noticed that the 
arms pack themselves away, during retraction, so as to form a continuation of the cylindrical 
form of the rest of the zooid. 

In old individuals the stalk is always directed away fnun the mouth, and is usually 
spirally coiled, the coiling being accompanied by some twisting round the longitudinal axis of 
the stalk, as is indicated by the direction of the muscle-fibres (fig. 6) In younger blastozooids 
(fig. 5), the proportions of the body tend to approach those of C. dodecaloplnis. Their stalk 
originates relatively much nearer the oral end of the body, so that the bend of the alimentary 
canal lies in a caecum of the body-wall which ]jrojects a considerable distance beyond the origin 
of the stalk. As moreover the stalk is commonly carried in such a way that it lies asymmetrically 
on one side of the body, pointing forwards, and with its distal end sometimes overlapped by 
the proboscis, these young individuals have a resemblance to the adult C. dodecalophus which 
is not shared by the adults of their own species. 

Buds are not produced in great profusion, although it may be suspected that in a more 
actively growing colony, they would be more numerous. The old individuals, in which the 
production of eggs is energetically taking jilace, usually have no buds at all. The specimen, 
with young ovaries, shewn in fig. 6 has a single bud; and buds are certainly mort; numerous 
in the two or three regions where the coenoeciuni has an immature character, at or near the 
tips of its branches. These regions contain relatively young blastozooids, which have not yet 
acquired the elongated cylindrical form of the adults. 

One of the most singular and characteristic features of C. kvinseni is the form of its 
proboscis. This is not only relatively large, but it has an extraordinary amount of mobility, a 
peculiarity correlated with the unusually long neck, or proboscis-stalk, of this species. It commonly 
(during retraction) forms a sort of mantle, wrapping round a considerable part of the mass of 
arms and tentacles, as .shewn in fig. 6. A glance at this figure will reveal the singular fact 
that as compared with other species, the pigment-line is upside down; and fig. 1 1 also shews 
various cases in which the position of the pigment-band is not what one would expect it to be. 



19 

Fig. 33, which is a sagittal section through the body and collar, shews no trace of the connexion 
of the two parts of the proboscis which are seen respectively anteriorly and posteriorly, with 
the rest of the animal. 

These curious phenomena are due to the great length of the neck (figs. 23, 24, 139), 
which can be twisted into almost any position, either by being simply bent out of the median 
plane, or by being not only bent but also twisted round its own longitudinal axis. In buds and 
young blastozooids, and in some of the old zooids, the position of the proboscis is normal; that 
is to say, as in other species of Ccphalodisctis. A case of this kind is represented in fig. 34. 
The neck here appears short and thick, though indications are not wanting, in the folding of 
the dorsal epidermis, that a considerable amount of contraction has taken place. It is not difficult 
to imagine that the basal, cylindrical portion of the proboscis in fig. 34 could, during life, be 
considerably elongated, and the discoidal portion rotated round an angle of 180° so as to bring 
the pigmented line to the dorsal side and the real dorsal portion of the disc to the ventral 
side. This is what has taken place in PL IX, fig. 10 1 and in PI. XI, fig. 139. If the rotation 
be not so complete, — for instance, if it extend only to 90°, — the pigment-line assumes a 
more or less longitudinal position, as in several of the zooids seen in fig. 11. In the reconstructed 
individual .shewn in figs. 23, 24 the elongated neck extends straight forwards, the discoidal 
portion looking in the same direction. This individual exhibits another phenomenon which is of 
common occurrence in this species, though something of the same kind may also take place in 
C. dodecalophus. By special contractions of the strong muscles which extend from the septum 
dividing the first from the second body-cavities, part of the glandular anterior epidermis of the 
proboscis may be deeply infolded. Sections of the proboscis of individuals in which this has 
taken place are sometimes difficult to interpret. 

In the individual shewn in fig. 33 the neck is simply bent to one side, so as to have 
a direction at right angles to the median plane. The lateral portions of the mantle-like proboscis, 
with the ends of the pigment-band, have thus in this sagittal section a relation which they 
should normally have in a transverse section. 

The arrangement of the body-cavity of the proboscis materially helps in the interpretation 
of sections of this species. Here, as in all other cases, the body-cavity extends to the extreme 
dorsal end of the organ (figs. 34, 42, etc.), where it is spacious; while it invariably di.sappears 
before the pigment-band is reached. The ventral lobe of the proboscis consists of a double 
layer of epidermis, the layer next the mouth being very thin, but the two layers are in close 
contact with one another without being separated by any part of the first body-cavity. 

It should further be noted that the mobility of the neck in C. levinseni begins in front 
of the notochord and of the septum between the first and second body-cavities. Thus in the 
sagittal section, fig. 33, in which the anterior part of the neck is bent entirely out of the median 
plane, the symmetrical position of the central nervous system [c. n. .y.),. of the notochord {nch.) 
and of the pericardium {per.) has been in no way affected. 

There are six pairs of arms in C. levinseni, as in C. dodecalophus; but I have not 
observed any indication of vesicle-bearing end-bulbs in the adults or at any stage in the growth 
of the buds. 



20 

C. gracilis. (PI. I, figs. 4, 7. PI. Ill, fig. 22). 

This species differs from the two preceding in the Rhabdoplcura-\\\i& slenderness of its 
stalk and in the profusion with which it produces buds (fig. 4). The stallc is, moreover, nearly 
always carried in what may be regarded as its primitive position, forming a continuation of the 
principal axis of the body. 

big. 7 shews a side view of a zooid of this species, with ratlu^r unusually shurl stalk, 
and only a single bud. Pig. 4 represents a mass of buds and young blastozooids, of a kind 
commonly found in the cavity of the coenoecium of this species. 

C. gracilis normally possesses five pairs of arms. End-bulbs, bearing refringent vesicles, 
are present in the first pair of arms at least, and sometimes in the second and third pairs, in 
the buds (figs. 30, 32). They may persist in the adult, but they appear to be sometimes absent. 

C. sibogae. (PI. I, fig. 3. PI. VII, figs. 72 — 76). 

My examination of this species has been interfered with by the failure of the spirit to 
penetrate satisfactorily into the deep lying cavities of the basal coenoecium containing the zooids. 
But in spite of this drawback, some of the main facts appear to be beyond dispute. 

The colony is remarkable for an extraordinary dimorjihism of the zooids. The coenoecium 
contains (I) neuter individuals, of the normal Cephalodiscns type, but usually without reproductive 
organs (which are, however, indicated in their young condition, while they are still immature 
buds); (II) male individuals, of an entirely peculiar character. 

(I) Neuters. 

These resemble the female individuals of C. gracilis in many respects, notably in the 
slenderness of the .stalk. One of them is shewn in '[\<g. 3, in which, however, only a portion 
of the excessively long stalk is present. They appear to differ from the zooids of C. gracilis 
in the following respects, in addition of course to the sexual difference : 

[a) The probo.scis is smaller, in C. sibogae. 

(J)) There are four pairs of arms, in which I have not observed vesicle-bearing end-bulbs, 
(f) The greater part of the zooid is extremely dark in colour (almost black), in old individuals, 
owing to the pre.sence of an unusually large (juantily of pigment in the epidermis. 

[d) The body is more elongated ; and in old zooids may be extremely elongated. 

[e) The stalk originates nearer the aboral end of the body. It is extremely long (many times 
the length of the body) and is indeed so long that I have not succeeded is disentangling 
the masses of stalks sufficiently well to trace the full length of an individual stalk. 

(/) The operculum is larger, although this can only be seen satisfactorily in sections. 

(II) Males. 

I reserve a fuller account of these extraordinary individuals for a later part of this 
Report (Sect. XV). The full grown male (figs. 75, 76) possesses a typical proboscis, with the 
usual pigment-band. The collar is not produced into an operculum and bears only a single 



21 



pair of arms, which are without tentacles. In young males, the epidermis of the arms, except 
for a short region at the base, is entirely filled with refringent vesicles (PI. IX, fig. 99), 
similar to those which occur in the terminal bulbs of the arms of C. dodccalophus and of the 
young C. gracilis. These vesicles appear to have been used u]) in some of the old males. The 
epidermis of the male, as in the case of the neuter, generally contains a great quantity of 
pigment. The body is large, and is almost entirely filled by a pair of enormous testes. The 
alimentary canal is vestigial. 



VI. METHODS AND GENERAL ANATOMY. 

In this Section I give a short description introductory to the Sections dealing with the 
special anatomy of the regions and organs. 

My study of the structure of Cephalodiscus has been greatly facilitated by the use of 
solid reconstructions made from series of sections. The method which has been of most service 
is the one which was introduced by my friend Professor J. Graham Kerr (01, p. 5) and 
improved in some particulars by the late Mr. J. S. Budgett (02, p. 318). The principle of the 
method consists in drawing the sections on plates of finely ground glass, of uniform and suitable 
thickness, and immersing the superposed plates in a liquid having the refractive inde.x of the 
glass. The liquid employed was a mixture of fennel-oil and cedar-wood-oil, as recommended by 
Budgett ; and the proportions of the mixture which I have found it convenient to use are 
two parts of unthickened fennel-oil to one part of cedar-wood-oil. In this way a transparent 
reconstruction is obtained, in which different organs are brought out if they have previously 
been coloured with ordinary water-colour paints. Opaque colours, such as vermilion, can be 
used where it is desired to see only the outer form of an organ ; and transparent colours in 
cases in which it is necessary to see internal details. Figs. 22 — 24 are in the main from 
reconstructions prepared in this way. 

Kerr's method can be most strongly recommended for many purposes; but finding that 
in some complicated cases, a more tangible amount of solidity was required in a reconstruction, 
I turned my attention to a form of modelling clay known as "plasticine". This clay has the 
advantage of not drying up, and of thus retaining its softness for any length of time. Thin 
plates of the plasticine can readily be prepared by pressing the substance on a smooth surface 
(such as a piece of paper), and removing the irregularities from the upper side of the plate 
by means of the back of a scalpel. The sections are drawn with a camera lucida on thin 
paper, and their outlines cut out with .scissors. The paper pattern is pressed on the plasticine 
plate, which is then cut to the shape of the section with the point of a mounted needle. 

The plates are superposed (removing the paper from the lower plate just before adding 
a new one), taking care to smooth off the edges and to fill up irregularities after the addition 
of each plate. The completed reconstruction, if carefully made, is a faithful reproduction of 
the original. The method does not differ in principle from the wax-plate method which has 
previously been used; but among its advantages are its great cheapness, and the ease with 



which the plasticine plates can be prepared. A more striking advantage is that the llexibility 
of the material makes it posible to rearrange the position of the parts of the completed 
restoration. One of the great difiiciilties in dealing with Ccphalodiscus is that such organs as 
the arms, the operculum, and the proboscis may overlap one another in such a way as to 
make it impossible to obtain a view suitable for drawing, or in which all the parts can be 
seen with the necessary clearness. A reconstruction prepared as above indicated overcomes 
many of these difficulties. The ventral lobe of the proboscis can be turned forwards so as to 
expose the operculum, the operculum can be turned down so as to shew the mouth, and the 
arms can be untwisted or straightened out : — and all this without putting any of these parts 
into a position which cannot be assumed during the life of the animal. Thus fig. 25 is a 
reconstruction made from the originals which are shewn in hgs. 43 — 53, but it will be seen 
that the positions of the operculum and of the ventral lobe of the proboscis were modified 
after the completion of the model. The proboscis was also slightly rearranged in fig. 22, in 
order to shew the complete outline of the operculum. 

A further advantage of the plasticine method is that a reconstruction made from oblique 
sections can be cut in a new plane, so as, for instance, to obtain a median sagittal section. 

In studying the general anatomy of Cephalodisctis^ one cannot but be struck with the 
constancy of the morphological type throughout the genus. The number of tentaculiferous arms 
indeed appears to depend on the species, but in other respects the organs already known to 
e.xist in C. dodecalopJnis are found, with practically no variation, in all the species — a fact 
which speaks for the high specialization of the genus. Differences in degree of development 
are, however, well marked; and indeed the species of Cepha iodise us have well defined characters 
of their own. But any one of the species would serve as well as any other to give a good 
idea of the essential generic characters. 

The most fundamental fact in the structure of CcpJiaiodiscus is the division of the body 
into the three regions, proboscis, collar and metasome; the i)roboscis containing an unpaired 
body-cavity, and each of the other two divisions containing its own paired body-cavities. 

The disposition of the three regions is, however, ijy no means simple, since each of 
them is specially developed in relation with .some plane or axis which does not correspond with 
the morphological principal axis of llie animal. Hut an initial difficulty in describing the facts 
is that it is not agreed what is the correct orientation of the Pterobranchia as compared with 
the Enteropneusta. Ccphaiodisais differs from Balanoglossus in the approximation of the anus 
to the mouth, and in the e.xtension of the alimentary canal into a ^/-shaped loop. It can hardly 
be contested that the region characterised by the central nervous s\stem and the apertures of 
the oviducts is dorsal ; and it appears to be natural to regard the alimentary canal as extending 
into an enormous ventral exten.sion of the body, as in Phoro7iis. If this be the correct orientation, 
the morphological po.sterior end of the animal is indicated approximate!)- by the anus. 

This is not the view which is adopted by M.vsterm.vn (98, 2, p. 513), who considers 
that "the pedicle is morphologically the hind end of the body", and that the study of the buds 
favours this interpretation. It ajtpears to me on the contrary tliat the disposition of the alimentary 
canal in immature buds indicates that the stalk is a ventral appendage. 



23 



The text-figure i is based on the sagittal section of an advanced bud of C. dodecalophns 



shewn in PI. XIII, fig. i8i. 
The proboscis, the collar and 
at least half the alimentar)- 
canal in this specimen have 
a position which closely cor- 
responds with the relations of 
these parts in Balanoglossus. 
The principal morphological 
axis may be regarded as the 
line of intersection of what is 
marked as the "frontal" plane 
with the sagittal plane of the 
figure itself. It will then be seen 
that in this figure the pharynx 
(//;.) passes in an antero- 
posterior direction, giving off 
the notochord [nc/i.) forwards 
from its dorsal side, and passing 
posteriorly into the oesophagus 
{pes.) and stomach {stom.). This 
organ has a conspicuous dorsal 
caecum [stotn. d. c), while a 
smaller lobe extends a short 
distance forwards on the ventral 
side of the oesophagus. The 
dorsal line of the metasome is 
shortened, so that the intestine 
(/;«/.), which opens from the 
second stomach {stoiii."), passes 
dorsally and a trifle forwards, 
to open at the anus {an.) 
which has been shifted into a 
somewhat dorsal position. 



Stonidc.^ 




nch. 
Anterior 



bto?n: 



Ventral 



Fig. I. — C. dodecalophns. Median sagittal section of an advanced bud (after PI. XIII, 
fig. l8i), to illustrate the terminology used in this Report. The anterior, 
posterior, dorsal and ventral surfaces and the transverse and frontal 
planes are indicated: — /., proboscis; c, collar; /«(■/., metasome; i, 2 and 3, their 
respective body-cavities; b.c.^h.., the part of the metasoniatic cavity included in the 
loop of the alimentary canal; /'., ventral lobe of proboscis; p.l>., its pigment-band: 
/tv., pericardium; »/., mouth; rich., notochord; //(., pharynx; oes.., oesophagus; 
stom..^ stomach; stoin.d.c..^ dorsal caecum of stomach; stotH.'^.^ second stomach; 
/«/., intestine; r., rectum; ««.. anus; c.n.s..^ central nervous system; 0/., operculum 
or lower lip; ov..^ ovary; sl.^ stalk. 



Comparing the text-figure with the sagittal section of the adult (PI. IV, fig. 42), in the 
same species, it will be seen that the alimentary canal in its definitive arrangement has its 
ventral flexure more strongly marked than in the bud. The morphologically dorsal surface of 
the pharynx now faces, for the most part, posteriorly, and its ventral surface anteriorly, althougn 
the part which immediately succeeds the mouth has its dorsal wall in its original morphological 
position. The pharynx is in fact | -shaped, a right-angled bend having been developed owing 
to the ventral flexure of the alimentary canal. 



24 

The differences between what 1 regard as ilie more primitive condition sliewn by the 
bud and the adult arrangement are in reality very sHght, and can easily be accounted for by 
dift'erential growth. The outlines of the text-figure are taken from a camera lucida drawing, 
the scale of which is indicated. Comparing this witli fig. 42 it will be seen that while the 
diameter of the stalk of the bud, at its base, slightly exceeds 150 y.., that of the adult stalk, 
in the same relative position, is less than 200 a., in spite of the thickening which it has no 
doubt experienced as the result of the contraction of its longitudinal muscles. There is thus but 
little increase in the thickness of the stalk of the adult, as compared with that of the bud, 
the principal increase in .size of which has been due to an elongation of the metasome along 
an axis which is indicated in the bud by a line passing through the middle of the pharynx, 
oesophagus and part ot the second .stomach. This has resulted in the separation of the base 
of the stalk from the mouth, and in the outgrowth of the caecum of the metasomatic wall 
containing the bend of the alimentary canal. With this growth has been associated a ventral 
flexure of the jjIuu), nx just behind the mouth ; a strongly developed dorsal groove which is 
present in this region remaining to mark the point at which flexure took place as the dorsal 
diverticulum (fig. 42, div.) of the pharynx. It thus follows that while there is hardly any 
distortion of the primitive symmetry in front of the line indicating the transverse plane in the 
text-figure, and comparatively little on the dorsal side of the horizontal line indicating the 
frontal plane, the principal modification of the axes of the adult i^ody is due to alterations in 
the lower left quadrant of the text-figure. The pharyngeal limb of the alimentary canal has to 
a large e.xtent lost its antero-posterior direction, and has assumed a ])osition nearlv parallel to 
that of the intestinal limb. 

The correctness of this orientation is confirmed by the consideration of the mesenteries 
of the metasome. The dorsal mesentery is confined to the region between the two limbs of 
the alimentary canal, while the ventral mesentery extends into the stalk, carrying with it what 
may for the present be termed a loop of the ventral vessel. Indications of the anterior {a. v.) 
and posterior {p. r.) limbs of this vascular loop are .seen in fig. 42. 

A turlher confirmation of the orientation lure adopted is afforded by a consideration 
of horizontal sections on the dorsal side of the line indicating the frontal plane in the text- 
figure. A .section in this ]>lane of a young bud was figured by me (87, p. 39) some years 
ago, and demonstrates the Balanoglossu.s-like structure of the animal. But even in the adult 
zooid, horizontal sections in the same region still shew the coelomic cavities in a Balanogflossus- 
like arrangement, as is evident from figs. 154, 155 (PI. XII), which though not actually fully 
grown, do not differ from the adult condition in this respect. A transverse section of a young 
Ccp/ia Iodise Hs is thus one which pas.ses along the line so marked in the text-figure. It is 
convenient to describe a corresponding section which passes through tlie long axis of the adult 
as "transverse", although it is obvious from what has been said that it will not cut all the 
organs of the metasome in a strictly transverse plane. 

Adopting this view, it may be said that the proboscis is flattened in an antero-posterior 
direction to form the great buccal disc. The collar forms a ring which would be transverse 
were it not for the fact that its dorsal region is much more developed than its ventral region. 



The apparent obliquity of the body-cavities in young buds (PI. XIII, fig. 174) becomes 
intelligible if it is assumed that the antero-posterior axis cuts the first and second body-cavities 
at right angles. 

The dorsal region of the collar is distinguished by the development of the central 
nervous system (fig. 42, c. n. s.) which also extends on to the adjacent parts of the proboscis; 
and of the paired tentaculiferous arms on either side of the middle line. Ventrally the collar 
gives rise to the enormous lower lip or operculum (PI. Ill, fig. 25, oJ>.), a structure which 
must be of great importance in feeding, and in regulating the action of the gill-slits and collar- 
canals. The collar-cavities, as seen in a nearly sagittal section (fig. 42) are much larger dorsally 
than ventrally, since they have to give origin to the cavities of the arms. A section which 
cuts the whole of the main part of one of the collar-cavities thus has the form seen in PI. IV, 
fig. 36 or PL XII, fig. 151. 

The long axis of the metasome is at right angles to the antero-posterior axis. In 
describing the parts of the metasome and stalk I shall consider the stalk as lying in the 
position in which it occurs in buds and in the adults of most of the species ; that is, in the 
position shewn in PI. I, figs. 4, 6, 7. The pharyngeal side of the metasome, or that from 
which the stalk originates, is the "anterior" side; while the rectal side is the "posterior" side. 
The most "ventral" part of the body is, for descriptive purposes, the end of the hernia-like 
projection containing the bend of the alimentary canal, although morphologically it more nearly 
corresponds with the base of the stalk. 

The mouth (fig. 25, /u.) is an orifice to which the food is conducted through a passage 
formed, on each side of the proboscis-stalk, by the posterior wall of the ventral half of the 
proboscis and the anterior wall of the collar, constituted by the arm-base {a. 6.) and the 
operculum or lower lip {op.). It leads into a pharynx (fig. 42, ///.) from which a single pair 
of gill-slits open to the exterior, laterally, but somewhat on the anterior surface of the body. 
The external orifice of the gill-slit (fig. 25, g. s. r.) is immediately ventral, or morphologically 
posterior, to that of the collar-canal {c.c.e.) of the same .side of the body; and both orifices 
lie so close to the base of the operculum that it is only in favourable specimens that they 
can be seen from the outside without being viewed through the ventral lobe of the proboscis, 
or through the operculum, or through both these structures. 

The pharynx passes into the oesophagus (fig. 42, oes.) and these two parts together form 
the commencement of the anterior limb of the t'-shaped canal. The opening of the oesophagus 
into the stomach {stoui.) is usually borne on a large papilla which projects into the lumen of 
the stomach between the dorsal and ventral caeca of the stomach seen in the figure on p. 23. 
The second stomach (fig. 42, stout.-) opens from the anterior side of the stomach, in the 
immediate neighbourhood of the base of the stalk [sL). It passes round the ventral border 
of the stomach, where it becomes continuous with the intestine {itit.); this passes, in close 
contact with the posterior wall of the stomach, into the rectum (r.) the anterior wall of which 
is exposed to the body-cavity. The anus (fig. 22, an.) is a transverse slit on the dorsal and 
posterior side of the metasome. 

A great part of the interval between the pharynx and the rectum is occupied (in female 

SIBOGA-EXPEnniE XXVI ^/V. 4 



26 

specimens) by a pair of large ovaries (fig. 22, oz-. r., oz'. /.), each of which leads by a pigmented 
oviduct (oz'tif.) to its external orifice, situated on the dorsal surface of the metasome, not far 
behind the end of the central nervous system. Between the pharyn.x and the rectum, in the 
middle line of the body, and consequently between the two ovaries lies the dorsal vessel (a', v.), 
w'hich is the largest blood-space of the animal. 

The above are the more conspicuous anatomical features of the zooid, and further 
details may be left for the Sections dealing with the several organs. 



VII. PROBOSCIS. 



The general characters of the proboscis or protomere, in the several species, have 
already been described (p. i 7) ; and in particular attention has been called to the extraordinary 
proboscis of C. /evmsetii. The proboscis of that species is of remarkable mobility, owing to 
the presence of an unusually long neck or proboscis-stalk. The neck may be stretched out 
in the direction of the principal axis of the body (figs. 23, 24), carrying the discoidal part of 
the proboscis or "buccal disc" into an endless variety of positions. In fig. 24, the disc has the 
form of a somewhat complicated umbrella; hut it may assume almost any position, and is very 
commonly turned upside down, so that its dorsal edge looks ventrally, and its ventral edge 
dorsally (figs. loi, 139). Iiy the rotalicjn of the neck round its longitudinal axis. These 
remarkable attitudes of the proboscis may make it a matter of some difficulty to interpret the 
sections of the anterior end of the animal ; and the complication is often further increased by 
the retraction of the thick anterior wall of the disc into a strong fold (figs. 23, 24, 139), a 
habit which may also be noticed in some specimens of C. dodccalopJius. The sagittal section, 
fig. 34, is one of the cases in which the proboscis has its normal position; but the e.xtensible 
character of the neck is even here indicated by its thickness and Ijy llic folds in its walls. 

In spite of these peculiarities of C. levinseni the proboscis has the same essential 
characters in all the species, not excepting the male individuals of C. sibogae. It may be 
remarked that the term "buccal disc", which has usually been employed in describing this part 
of the animal, is not exactly synonymous with "jiroboscis". The latter is a morphological term, 
indicating its relation to the similar organ in Balanoglossus. The "buccal disc", however, may 
include dorsally a part of the collar (fig. 42) although in C. levinseni it consists of the anterior 
end of the proboscis, the posterior end of which, with jjart of the collar, constitutes the neck 
or proboscis-stalk. 

The relations of the collar to the proboscis will be described below% in the Section dealing 
with the collar. The proboscis itself invariably terminates in front in the enormous buccal disc, 
which is flattened in an antero-posterior direction. The anterior wail of the disc is composed 
])rincipally of much elongated gland-cells, which give this wall of the proboscis a great thickness. 
As has been pointed out abcn-e (p. 9) there can be little doubt that the gland-cells have the 
function of secreting the gelatinous coenoecium. At the base of the gland-cells may be seen, in 



27 

the thickest part of the proboscis, a transparent layer (fig. 42) which I regard, with Mastermax 
(87, 2, pp. 342, 343), as nervous. 

The unpaired proboscis-cavity (fig. 42, b. c.') extends to the dorsal end of the buccal disc, 
the epidermis passing round this edge as a fairly thick layer. A similar arrangement is seen 
in the lateral edges of the dorsal half of the proboscis (figs, iii, 152). But ventrally to the 
insertion of the proboscis-stalk, the anterior and posterior walls of the proboscis rapidly come 
into contact, by the disappearance of the body-cavity in this region. The greater part of the 
ventral lobe of the proboscis is accordingly formed of two layers of epidermis in close apposition 
(fig. 42), the anterior wall consisting of a thicker epithelium, and the posterior wall of a very 
thin layer which passes into the ventral epithelium of the proboscis-stalk, and so to the upper lip. 

In the region where the two epithelia of the proboscis are apposed, is invariably found 
a characteristic line of pigment (figs. 3 — 7, p. b.), which has a brilliant red colour in the spirit- 
specimens. This line forms a crescent, extending transversely across the ventral lobe, from edge 
to edge, and with its concavity directed dorsally. The pigment can readily be seen in sections 
(fig. 42), and it is clearly very resistent to the action of reagents. The pigment-line occurs very 
early in the young buds, in which the enormous development of the buccal disc is one of the 
most characteristic features (figs. 4, 9), and it is found in the males of C. sibogae (PI. VII, 
figs. 72, 75, 76). 

In a well preserved specimen of C. dodecalophus (PI. XII, fig. 151), the pigment-line is 
related to a special modification of the epidermis on its dorsal side. The cells immediately 
adjoining the pigment are large protoplasmic cells, which have stained (with haematoxylin) less 
intensely than other parts of the proboscis. These are followed by a group of numerous minute 
nuclei in an area which is practically unstained. The deeply staining gland-cells of the anterior 
epidermis then follow, at first sparingly and, near the bend of the ventral lobe, associated with 
a considerable number of the minute nuclei already noticed. These become fewer in passing 
dorsally, and the part of the anterior epidermis which is uniformly tinted in the figure is 
constituted, up to about the reference-line b. c' ., almost entirely by the greatly elongated, densely 
staining gland-cells Avhich e.xtend from the nervous layer to the free surface of the epidermis. 
There are no gland-cells on the ventral side of the pigment-band. 

It is difficult to decide what may be the physiological significence of the pigment-band 
and of its related cells. M'Intosh (87, pp. 27, 34) suggests that the pigmented oviducts may 
be phosphorescent organs. No difference in colour can be noticed between the pigment in the 
pigment-band of the proboscis and that of the oviducts, in the sections shewn in figs. 149 — 151, 
and it is possible that there may be some relation between the functions of the two parts. 
So far as the proboscis is concerned, it is conceivable that the function might be that of 
vision, although the nerve-supply seems inadequate on that hypothesis, and it must further be 
remembered that C. dodecalophtis is an abyssal form. But it seems ver)- improbable that the 
oviducts, which have no distinct nerve-layer, can be used as visual organs. In the case of the 
proboscis, the function of the pigment, whatever it may be, is probablj- associated with a 
sensory function of some kind, as appears to be indicated by the presence of the numerous 
cells wdth small nuclei which occur in the region of the bend of the proboscis in fig. 151. The 



28 

sensory function claimed for the anterior epidermis of the ventral lobe may be connected with 
the deposition of the jrelatinous layers which constitute the coenoecium. The lobe is obviously 
very mobile, as is indicated by the varying positions which it occupies in the preserved zooids. 
Since, however, neither the musculature of the proboscis nor the anterior body-cavity extends 
into it, its movements would seem to depend on protoplasmic contractions of the epidermis. 

It is not improbable that the nerve-layer shewn at the base of the thicker parts of 
the anterior epidermis may extend as a thinner stratum into the ventral lobe, though I have 
not definitely proved that this is the case. 

The ventral extremity of the anterior body-cavity extends, below the base of the 
notochord, as far as the upper lip (figs. 37, 42, 183; ?/./.), which occurs immediately in front 
of the pharyngeal diverticulum (t/iv.), from which the notochord originates (fig. 181). The 
relations of this ventral part of the proboscis-cavity to the upper lip and to the notochord 
suggest those of Balanoglossus, in which the corresponding part of the coelom gives rise to 
the median part of the "nuchal skeleton" or "proboscis-skeleton", and in certain species to the 
structure described by Spexgel (93, p. 175: 03, p. 280) as the "blumenkohlahnliches Organ", 
a structure to which Willev has given the name of "racemose organ" (99, 2, pp. 229, 260). 

In certain positions of the proboscis (figs. 43 — 46) the ventral epidermis of that organ, 
in front of the mouth, forms the roof of the passage which encircles the proboscis-stalk, and 
conveys the food from the arms to the mouth. In passing from the mouth outwards this food- 
channel gradually ascends the proboscis-stalk, and becomes the deep groove (figs. 151 — 147, 
f.c.r.\ fig. 155, f.c.r., f.c.l.) which is bounded in front by the posterior epidermis of the 
proboscis, and behind by the thicker epidermis of the anterior side of the arm-base. The thin 
posterior and ventral epidermis of the proboscis thus has an important part to play in helping 
to define the cavity in which the food must pass from the arms to the mouth. The dorsal 
epidermis of the proboscis immediately in front of the end of the collar contains a strong 
nerve-layer (figs. 35, 37, 42) which is a direct continuation of the central nervous system. 

The more important structures directly connected with the proboscis-cavity, or contained 
in it, are the notochord, the pericardium, the proboscis-pores, the glomerulus, and the muscles. 
Of these the notochord may conveniently be treated in Section XI dealing with the alimentary 
canal, while the muscles are described in Section XII. 

Pericardium and proboscis-pores. 

The pericardium was first figured by M.^sterm.vn (97, 2, figs. 2, 3, 14, etc.) who described 
it, however, as a blood-cavity. This .account was criticized by me in a note (97) in which I 
contended that the pericardium (= "heart- vesicle") has the same relations as in Balanoglossus; 
and M.\STERM.\N has more recently (99, 2; 03, p. 719) accepted this view. 

The pericardium of CcpJialodiscns closely resembles that of Balanoglossus. It may readily 
be found, in all the species, in contact with the dorsal wall of the proboscis, immediately in 
front of the tij) of the notochord, and between the ends of the anterior dorsal horns of the 
collar-cavity. It appears to form a completely closed vesicle (PI. XI, fig. 138; PI. XIII, fig. 181) 
the posterior wall of which is invaginated into the lumen of the organ to form a space which, 



on the analogy of Balanoglossus, must be regarded as a blood-space (fig. i8i, pcr.s.) It will 
be seen from longitudinal sections (PI. IV, fig. 33) that the pericardium more or less overlaps 
the tip of the notochord, which, in sections in other planes, may accordingly he completely 
encircled by the pericardium (PI. XI 1, fig. 160). 

The proboscis-pores, which are invariably two in number, liave a constant relation to 
the pericardium (PI. X, fig. 112; PI. XI, figs. 137, 138; p.p.). The pore is in reality a tube 
of appreciable length; and in consequence of this fact Spexgel (93, p. 470) prefers to term 
it the "Eichelpforte" (in Balanoglossus). In Cepkalodiscies (figs. 112, 138) the epithelium of 
the tube which is situated nearer the middle line closely invests the wall of the pericardium. 
The outer part of the epithelium is intimately related to the anterior dorsal horn of the collar- 
cavity {p. c.~ a.). 

In sagittal sections (PI. XII, figs. 147, 14.8, p.p. r.\ fig. 150, /././.) it is seen that 
the direction of the tube is not vertical to the surface, but that it has an oblique course, the 
internal opening being dorsal to the external opening. The latter is situated close to the base 
of the first arm (PI. XII, fig. 158), and slightly on its median side. The proboscis-pores 
traverse a part of the central nervous system, which is thus divided into an anterior and a 
posterior portion in any sagittal section passing through a proboscis-pore (figs. 42, 151). 

Masterman (03, p. 7 I 7) has described the proboscis-pores as opening into the outer ends 
of a transverse, crescentic furrow of the epidermis which he terms the "ectodermal pit". It is 
easy to find specimens of Cephalodiscus shewing appearances which resemble Masterman's 
figures. Thus an "ectodermal pit" is obvious in PI. XII, fig. 149; but I find that in this 
particular case, the proboscis-pore does not open into the continuation of the pit or furrow, 
but distinctly in front of it. In other cases (PI. V, fig. 45), the relations are reversed, and a 
similar furrow is seen in front of the region where the proboscis-pore opens to the exterior. 
Rememberino- the extremely muscular character of the proboscis and collar I am inclined to 
think that these furrows are not constant structures, but are merely the result of crumpling of 
the skin caused by contraction. 

Glomerulus. 

I have previou.sly stated (97, p. 345) that there appears to be some indication of a 
structure corresponding with the proboscis-gland or glomerulus of Balanoglossus ; and M.asterman 
has recently (03, p. 720) described the organ in detail. I have nothing to add to M.\sterm.\n's 
account, and I have indeed not obtained any preparations which shew its relations so clearly 
as are indicated in his figures. Although I think it is probable, as Masterman states, that it 
contains blood-spaces by means of which the pericardial sinus (PI. XI, fig. 138, per. s.) com- 
municates with other parts of the vascular system, I cannot obtain any certain evidence on 
this point. 

The glomerulus {gl.) is shewn in PI. IV, fig. 42 (C. dodccaloplms), PI. VIII, fig. 93 
{C. sibogae, neuter) and PI. X, figs. 113, 114 (C. levinseni)\ and its wall is doubtless to be 
regarded as a derivative of the epithelium of the anterior body-cavity. 



VIII. COLLAR (including the arms and the operculum). 

This division of the animal is not oiil)- one of the most characteristic and important 
parts of Ccp/ialodisciis, but it is also the most difficult to understand thoroughly. The relations 
of its several parts, and particularly of the arms to the operculum, have not previously been 
adequately described. 

It will be remembered that in Balanoglossus the anterior margin of the collar forms a 
projecting fold encircling the base of the proboscis-stalk. The ventral half of this fold may be 
regarded as constituting a lower lip, while the dorsal part is connected, in the middle line, with 
the anterior neuropore. In CepJialodiscus the neuropore is not represented, and the collar forms 
no projection in the median dorsal line above the base of the proboscis. Except for this interval, 
the whole of the anterior margin of the collar forms a strongly-developed fold, split up dorsally 
to form the arms, and ventrally constituting the operculum. It is necessary to insist on this last 
point because the base of the operculum is so narrow, and the flap itself is .so commonly 
directed away from the proboscis, that the operculum might be taken to be a derivative of the 
posterior edge of the collar, as indeed I at one time (87, p. 43) supposed it to be. Its real 
relations can be most easily seen in C. Icvinscni (PI. IV, figs. 34 — 36), in which the median 
ventral part of the collar-cavity is so long that it is at once apparent that the operculum is 
developed from its anterior margin. Unless this be recognized, it is impossible to form a clear 
conception of the relations of the arms to the operculum. 

Fig. 25 (PI. Ill) represents part of a plasticine reconstruction of C. gracilis, made from 
the series of obliquely sagittal sections some of which are shewn in PI. \', figs. 43 — 53. 

The ventral lobe of the proboscis of the reconstruction has, however, been turned 
dorsally, and the operculum itself has been folded in the opposite direction, in order to expose 
the mouth (w ). The bases of the live arms characteristic of this species are shewn, the first 
and second arms [R. 1, R. 2) having become free from the anterior collar-fold, while the third, 
fourth and fifth arms (/?. 3 — 5) are not \et free, but are indicated by their food-grooves turned 
towards the mouth, and h\ their angular dorsal or external surfaces. The right lateral lobe 
of the operculum {op.) is here shewn in section, exposing the corresponding part of the 
collar-cavity. 

The arm-bases form a gentle curve which is convex towards the mouth. The effect of 
this arrangement is that while the food-groove of the first arm faces almost dorsally, those of 
the second, third and fourth arms face anteriorly, and that of the fifth arm nearly ventrally. 
In passing away from the middle line, the fifth arm (in this specimen) rapidly becomes twisted 
round its own longitudinal axis, so that in the reconstruction fig. 22 (taken from the same 
specimen, but shewing more external portions of the arms and the whole of the right side of 
the operculum) its food-groove faces directly backwards, or towards the anus. The whole 
arrangement of the parts round the mouth shews that the proboscis and the anterior fold of 
the collar together form a highly efficient apparatus for conducting food to tlie moutli. The 
Diatoms and other minute structures which are actually found in tlic alimentary canal are 



31 

doubtless collected by ciliary currents induced in the first instance by the tentacles. It may fairly 
be assumed that the food passes along the grooves situated on the morphologically ventral or 
internal sides of the arms down to the arm-bases, where they enter a passage limited in front 
by the posterior wall of the proboscis and behind by the anterior collar-edge, which consists 
more dorsally of the common base of the arms, and more ventrally of the opercular flap. The 
operculum passes dorsally into the base of the last of the series of arms, to which it is related 
in such a way that the food-groove of that arm becomes continuous with the internal layer of 
epidermis of the collar-edge. 

It will be noticed that in the reconstruction the food-grooves are represented as dying 
away before they actually reach the mouth. Masterm\n (98, 2, p. 507) has given an elaborate 
account of the passage of these grooves, through the mouth, into the pharyngeal part of the 
alimentary canal; and his results are discussed below, in dealing with the mouth. Although the 
inner epidermis of the collar-fold is often a good deal wrinkled, I cannot agree with M..\stkrm.\n 
that the food-grooves of the arms are continued as such into the mouth. Such sections as those 
represented in PI. V, figs. 43, 45; PI. VI, figs. 65, 66 and PI. XII, figs. 145 — 147 shew that 
the arm-base has a perfectly smooth surface in regions where, according to Masterman, grooves 
should be present. The food-channel limited by the proboscis and operculum is an arrangement 
so effective that it is hardly necessary to suppose that each food-groove must be continued 
independently to the mouth. 

The lateral part of the operculum projects a considerable distance beyond the point 
where the fifth arm joins it. This is indicated, not quite successfully, in fig. 22, and is also 
apparent in fig. 25, in which the edge of the collar-fold is quite complete just ventrally to the 
base of the fifth arm, while the lateral part of the operculum is cut by the (sagittal) section in 
such a way as to expose its cavity. The same facts will be obvious from an inspection of the 
sections, PI. V, figs. 50 — 53. 

This lateral projection of the operculum is so situated as to overhang the e.xternal 
openings of the collar-canal (Fig. 25, c. c. e.) and gill-slit {g: s. r.). I think it cannot be doubted 
that the opercular lobe in question is functionally correlated with those apertures, and that it 
serves to separate the food-current passing to the mouth from the |jresumably e.xhalant current 
passing out of the gill-slit at least. The current through the collar-pore is probably sometimes 
inwardly and sometimes outwardly directed. The proper play of the tentacles and arms, and 
of the operculum itself, must depend on their being kept in a proper condition of turgidity. 
In the Enteropneusta there is actual evidence (Spengel, 93, p. 475 ; cf also Ritter, 02) of 
the importance of a turgid condition of the collar-cavity. Now the collar-canal itself appears 
to have no sphincter muscles, and it seems to me probable that the lateral lobe of the operculum 
is important as one of the means of closing the external orifice of the collar-canal during certain 
conditions of the activity of that organ. Any e.Kcess of water which enters the pharynx is 
probably evacuated by the gill-slits ; and as I suggested on a former occasion (87, p. 44) it is 
not impossible that this might have been the primitive function of the gill-slits of Chordata. 

The structure of the collar may be further elucidated by a consideration of the actual 
sections on which the reconstructions, figs. 22, 25 (PI. Ill), are based. The obliquely sagittal 



sections drawn (PI. V, figs. 43 — 53) begin with one which passes nearly medianly through the 
phar)-n.\ (tig. 43) and end with a section (fig. 53) through a plane in which all the five arms 
have separated fi-oni the arm-base. Two points must be noticed in interpreting these sections : — 

(I) the intestine appears to open into the middle of the posterior side of the stomach (figs. 43, 44). 
I find no trace of this arrangement (which has not been shewn in fig. 22) in other specimens 
of C. gracilis^ and I have no doubt that it is due to an artificial rupture or to an abnormality : — 

(II) Owing to a strong lateral curvature of the body (which has not been brought out in fig. 22), 
the end of the metasome connected with the stalk becomes separated, in the sections, from 
the anterior end. 

Fig. 43 represents a section, which passes somewhat to the left of the ]jroboscis-stalk. 
The proboscis (/.) is thus completely separated from the collar. The operculum (<?/.) in this 
individual is directed forwards, and has the appearance of a lower lip. The dorsal part of the 
collar is produced in front into the left arm-base, with whicli the third (/,. 3) and fourth [L. 4) 
arms are connected '). The collar-cavity [b. c.~) extends as a wide space into the arm-ba.se, and 
is separated by an oblique septum from the third body-cavity {d. c:'). On the front side of the 
collar-cavity is the oral muscle (07'. in.), a strong band of longitudinal muscle-fibres on the 
inner side of the anterior bodx-wall. The collar-cavity is interrupted by the mouth {in.), on the 
ventral side of which is the part of the cavity which e.xtends into the operculum. 

Fig. 44 represents a section which passes nearly through the middle of the proboscis- 
stalk. The fu-st and second left arms are now continuous with the arm-base. The septum 
between the first and second body-cavities ■) contains the notochord {iich.), starting from the 
anterior side of the median dorsal diverticulum {div!) of the pharynx, which extends completely 
up to the dorsal body- wall. The posterior wall of the dorsal part of the cavity contains part 
of the central nervous sy.stem [c. n. .$■.). In other respects the collar in this section resembles 
what was described in the previous section, except that it is now continuous with the proboscis. 

In \\o, 45, the middle line has been passed, so the collar-cavity is that of the right 
side. The right edge of the mouth has just been passed, and a strong oral muscle [or. in.), 
corresponding with the similar left muscle shewn in hg. 43. is seen to extend from the septum 
■/a round the edge of the mouth to the anterior wall of tiie arm-base^ The septum '/_• has a 
crenulated appearance, and from it radiate numerous mu.scle-fibres which pass through d. f.' 
to the anterior wall of the proboscis. The internal opening of the right proboscis-pore {p-p-) 
is seen, and the whole extent of the central nervous system (r. n. s.). 

In lig. 46, the right edge of the proboscis-stalk is cut, and the collar-cavity (/'. c.-) is 
continuous from the arm-base {a. d.), dorsally, round the right side of the mouth, to the 
operculum, ventrally. The operculum is clearly a derivative of the anterior edge of the collar, 
while the collar-canal [c. c.) occupies a ventro-lateral recess of the second body-cavity, immediately 
in front of the gill-slit. As the pharynx no longer reaches the dorsal body-wall, the second 
and third body-cavities are separated by a thin septum (s. 7,1). 



1) It will of course be noticed ihal the arms shewn in the reconstructions, figs. 22, 25, are those of the right side. 

2) It will be convenient to indicate this as "septum '/j", and that between the second and third cavities as "septum '/a''- 



In fig. 47, the right arms (those shewn in the reconstructions figs. 22, 25) are becoming 
apparent. While the preceding section (fig. 46) has no trace of food-grooves, the present 
section shews the commencement of the grooves (/?. i, R. 2) of the first two arms of the 
right side. 

The structure of the remaining sections (figs. 48 — 53) will be clear with the aid of the 
reconstructions, figs. 22 and 25. It will be noticed that the food-grooves 2 — 5 successively 
make their appearance; and it is clear that as these sections are transverse to the grooves, 
the fact that the latter are not traceable to the mouth indicates that they die away in 
approaching that aperture. It will be seen that each of the arms passes directly outwards for 
some little distance from its base, as is implied by the fact that near the middle line of the 
animal the arms are cut transversely. This position corresponds closely with that in which the 
arms are developed in the bud (cf. fig. 32); and although the arms are of course able to 
place themselves in a great variet)- of attitudes, they happen to be in what may be regarded 
as their normal position on the right side of this individual. After passing outwards for some 
distance, they for the most part turn dorsally, as shewn for R. i in figs. 52, 53, and for R. i 
and R. 2 in fig. 22. They may at the same time be twisted about their own longitudinal axis, 
as indicated for R. 5 in figs. 25 and 22. 

Tracing the arms from the outer side towards the mouth it will be seen that the food- 
grooves fade away as they pass into a tunnel-like space bounded by the anterior wall of the 
arm-base, the operculum and the posterior wall of the proboscis. This tunnel curves round the 
proboscis-stalk until it leads to the mouth. 

The figures further demonstrate the existence of the lateral lobe of the operculum, 
which projects a considerable distance externally to the point where the arms become free. 
Fig. 51 shews the level at which this lateral lobe begins to be free. It is indeed still connected 
with the base of the fifth arm, but its cavity is disconnected from that of the arm, since the 
section merely cuts the marginal epidermis of the part of the operculum which immediately 
adjoins the arm. In the more external sections (figs. 52 and 53) the operculum is tjuite separate 
from the arms. One further point may be noticed in this series of .sections. The collar-canal 
{c. c.) is seen to be a short tube which opens into the collar-cavity at the end situated nearer 
the middle line of the collar, and to the exterior at its more external end. By the time the 
external opening is reached, the collar-cavity itself has disappeared ; or, in other words, the 
collar-canal occupies a lateral recess of the collar-cavity. 

The number of arms, in this as in other species of CepJialodiscns, appears to be in the 
main constant for each species. It is sometimes, however, no easy task to count the arms in 
sections which are not favourably orientated, while results based on entire preparations are 
uncertain. In one series of sections of C. gracilis, I have convinced myself of the existence 
of six arms on one side, instead of the normal 'tw-f.-, while in one case of C. dodeca lop hits, I 
have only been able to count five arms on one side. It would almost be expected that some 
variation would occur in these respects. The variation might well make its appearance in the 
bud, bv the g-reater or smaller amount of subdivision of the free dorsal edge of the collar. 

SIBOGA-EXfEDITIE XXVI ^/V. 5 



34 
C. dodccalophus. 

The complicated arrangement of the arms in this species can be explained by comparison 
with C. gracilis. I defer considering the account which Mastkrman (^98, 2, p. 52 ij has given 
of this subject until 1 have described the arms cjf C". levinseni. 

The fundamental arrangement ui the arms of Ceplialodiscus is most easily seen in the 
buds, and is shewn in Masterman's figs. 25, 24 and 27 (I'l. 11) of the paper just referred to, 
or in m\- own figures (PI, III, figs. 32, 30 ; I'l. 1, hg. 4) of the buds of C. gracilis. The arms 
are developed as a simple linear series of outgrowths, at the sides of the central nervous system, 
from the dorsal extremity of the collar. The most anterior arm is developed first, and the others 
in regular order from before backwartls. This arrangement is but little disturbed in the adult 
C. gracilis (figs. 52, 53). 

Figs. 151 — 141 (PI. XII) represent every second section of a series of C dodecalophus^ 
and readily admit of comparison with figs. 43 — 53 of C. gracilis. The plane of the sections 
may be described as obliquely sagittal, the first section (fig. 151, which is more highly magnified 
than the others) passing through practically the middle line of the proboscis, at the front end 
of the central nervous system, and through the extreme outer edge of the collar-canal on the 
ventral side. As both sides of the nietasome arc, however, cut there was ])robably some rotation 
of the anterior part of the body in the neck-region. 

Fig. 151 shews the external opening of the left proboscis-pore (/././.), the anterior 
dorsal horn of the left collar-cavity {l).cra}j, the tip of the notochord {nc/i.), and the dorsal 
collar-mesenter}-, connecting the notochord with the central nervous system. The collar-cavity 
[d. c.- r.) is cut along nearly its entire length, the section passing to the right of the mouth. 
At the ventral end of the cavity is seen the outer edge of the collar-canal (/•. c. e.). which lies 
in a recess of this region of the collar-cavitv. Immediately behind the collar-pore is the strong 
nerv-e-tract or lateral nerve (/. n.) passing from the central nervous system (c. ». s.) to the stalk. 

The succeeding figures represent sections l\ing further to the right than the one which 
has just been described. Fig. 150 has nearly reached the superficial groove which separates 
the collar from the metasome. The lateral nerve is seen passing from the central nervous 
system, behind the collar-cavit\-, to reach the ventral surface. The extreme lip of the notochord 
[rich.) is cut by this section; immediately in front of it being the ])ericardium [per.), the internal 
opening of the left proboscis-pore (/. /. /.) and the anterior end of the left collar-cavity {d.c.'a.). 

V\g. 149 shews the last of the connexion between the collar and the metasome. The 
position of the collar-pore in the preceding sections is now overhung by a lateral lobe of the 
operculum {pp. r.), developed as in C. gracilis, its morphologically external wall being cut 
tangentially in this section. 

In Uy;. 148, the lateral lobe of the operculum is cut so as to expose most of its cavity, 
which is separated 1)\- a ridge of the basement-membrane (cf. fig. 153, fi. ///.) from the rest of 
the collar-cavity. The inner edge of the right proboscis-pore yp.P- r.) is cut tangentially. - 

In fig. 147, the lateral lobe of the operculum is separated from the arm-base (rt'.(^.), which 
is the more dorsal ])art of the collar-edge. The external opening of the right proboscis-pore is 



35 

seen, immediately dorsally to the base of the first arm (7v'. ij. The dorsal horn of the right 
collar-cavity {6. cr a.) projects into the first body-cavit)-, the septum '/.■ in lli'^ region affording 
origin to radiating muscles which traverse d. c} to reach the anterior wall of the proboscis. 

Fig. 146 cuts the animal at a level where the collar is just losing its connexion with 
the proboscis. The first arm [R. i) is becoming more distinct, and the food-groove of R. 2 is 
obvious The second and third arms are indicated dorsally by small triangular ridges. It should 
be specially noticed that there is no trace of the food-grooves of the arms 3 — 5 ; and the direct 
continuity of the food-grooves with the mouth, described by Masterman, appears thereby negatived. 

In the succeeding sections (figs. 145 — 141) the arms become progressively more distinct, 
their food-grooves appearing as the series of sections is traced outwards, and their angular 
dorsal surfaces becoming increasingly prominent. The lateral lobe of the operculum comes to 
an end in fig. 142, and in the last section shewn (fig. 141) it is no longer seen, while the 
arms have become completely separated from one another. It will further be noticed that the 
complete separation of the arms from one another is preceded b\- the ingrowth of a ridge of 
basement-membrane, so that the cavities of the arms become individually distinct before their 
epidermic walls are completed. 

C. levins eni. 

The arms of this species are six in number on each side, and their general arrangement 
resembles that found in C. dodecalophus. Their structure may be illu.strated by means of the 
series of frontal sections shewn in PI. X, figs. 11 1 — 118. The histological preservation of the 
specimens not being very good, the nerve-layer is not shewn e.xcept in the region of the central 
nervous system and of the .strong commissural or "lateral" nerves to the stalk. But there is 
no reason to suppose that it differs essentially from that of C. dodecalophus. 

Fig. 1 1 2 pa.sses through both proboscis-pores {p.p.). as well as through the pericardium 
{per.) and the anterior horns of the collar-cavities (d. cr a.). The first three arms of the right 
side [R. I — 3) have not yet separated from the arm-base; while on the left side, the arms were 
lying in such a position that five of them are cut separately. 

Fig. 113, immediately behind the proboscis-pores, .shews both the first arms originating 
from the anterior dorsal extremities of the collar. The six arms of the left side are seen, L. i 
and L. 2 being connected with one another by their epidermis, although the section passes 
dorsally to the level at which their body-cavities become continuous. On the right side is seen 
the common base of the first three arms, posterior to the region where their cavities become 
separate. The tip of the notochord {nc/i.), encircled by the posterior end of the pericardium (/^r.), 
occurs immediately below the central nervous system {c. n. .v.). The proboscis-stalk is separating 
from the buccal disc. 

Fig. I 1 4 — 1 1 7 are sufficiently explained by the lettering, but it will be noticed that in 
passing backwards, the arms first become connected by their e]>idermis and that the complete 
union of their cavities is preceded, as in C. dodecalophus, by the appearance of a ridge of 
basement-membrane which may be cut in such a way as to form a complete septum across the 



3^' 

collar-cavity of this region. The septum has, however, a free internal edge (cf PI. XI, lig. 140), 
so that the arm-cavities become successively continuous with the general collar-cavity. 

The plane of the sections is not well suited to demonstrate the relation between the 
arms and the operculum: Imi it is sufficiently obvious that the base of the operculum is cut 
immediately after the disappearance of the sixth arm on either side (figs. 118, 119), and that 
in fact it is the last arm on each side which becomes continuous with the operculum. It will 
be remembered that the operculum is an exceedingly mobile organ, which can place itself in 
a great variety of positions. In this particular specimen the left side of the operculum is in the 
main standing at right angles to the ])roboscis-stalk, but with some forward direction. On the 
right side, the ^percuhun is directed backwards over tlie region of the collar-pore and gill-slit. 
It thus results that in tracing the scries backwards, the oi)erculum appears first on the left .side 
(figs. 116 — 118); it is later cut tangentially on the same side (figs. 119 — 121), although the 
sections are complicated by the presence of several folds in the organ ; while on the right side 
(figs. 118 — 123) the sections of the operculum have a simple character, owing to the fact that 
it is hansfinor ventrallv and backwards from the moLith. 

The beginning of the right half of the o])erculum is indicated in fig. 118 by a ridge 
of basement-membrane {b. w.) which jirojects into the right collar-cavity. This ridge resembles 
those which form the commencements of the arm-cavities, and like them has a free internal 
edge. The separation of the oj)erculum from the rest of the collar is seen, on the left side, in 
fig. 119 by projections of the basement-membrane (d. iii.) developed from both the dorsal and 
the ventral sides of the collar-cavity. The basement-membrane which lines the operculum is 
quite thin, which is in marked contrast with the condition found in the main part of the collar- 
cavity and in the arm-bases (figs. 119 — 122). It may be presumed that the basement-membrane 
has a supporting value, and that its great development in the arm-bases is connected with the 
fact that these parts are relatively stiff compared with ihc! mobile operculum. 

The later sections figured (figs. 120 — 124) shew the collar-cavities passing at the sides 
of the niduth and finally uniting on the ventral side of that aperture (fig. 122). The collar- 
canals (figs. 121, 122) are situated in the ventral end of that ])art of the collar-cavity which 
is continued into the arm-base. 

The left series of arms shewn in figs, i 13 — i i 7 has an extremely characteristic arrangement, 
which can also be made out on the right .side, although these arms are lying in a position 
which is not quite so favourable for demonstrating their real relations. 

It will be seen from fig. 113 that while the arms A. i and L. 2 have their food-grooves 
facing the proboscis, L. 3 faces directly outwards, and L. 4 — 6 face away from the proboscis. 
A similar arrangement has been described by M.\sterm.\n (97, 2, p. 346, PI. XXVI, figs. 32 — 36; 
98, 2, ]). 521, PI. IV, fig. 68) in C. dodccalopliiis, the diagrammatic figures shewing three of 
the arms facing the proboscis and the other three witii tiieir backs to the proboscis. Now while 
the account given in the earlier account is perfectly correct, in the second paper referred to 
Masterman inverts the numbering, and moreover describes a process of rotation of the arms 
which is .supposed to l)ring them into the position shewn in his figure. No mention is made of 
the discrepancy between the two accounts, and I am unable to explain why Masterman 



37 

discarded his first and correct description for one which does not agree with the facts. The 
point is really one of importance; as without a proper understanding of the order of the arms 
it is impossible to grasp the manner in which the food must pass to the mouth ; and moreover, 
the possibility of comparing the collar-region of Cephalodisciis with that of other animals clearly 
depends on an accurate knowledge of its structure. As I cannot accept Masterman's account, 
it follows that I do not agree with his theoretical conclusions on the subject. 

As no two individuals of Cephalodisciis have their arms in identically the .same position, 
it is clear that the arms can be moved at the will of the animal into an indefinite number of 
positions. I do not therefore assert that Masterman's second diagram represents an impossible 
arrangement, though I do not think it would be easy to find it. But the whole significance of 
a diagram of this kind depends on shewing the relations of the arms to one another at their 
bases, where the arrangement is invariable, except so far as it may be slightly modified by 
muscular contractions. Any such diagram of the bases of the arms must accordingly shew the 
first arm in the position of Masterman's sixth (98, 2); and, vice versa, the sixth in the 
position of his first. It is perfectly certain that the arm which I call the first originates from 
the front end of the dorsal part of the collar, in the immediate neighbourhood of the proboscis- 
pores, and with its food-groove facing the flattened part of the proboscis. This is shewn, for 
C. leviitseni^ in figs. iJ2, 113 and for C. dodecalophiis, in figs. 148 — 143. It may thus be 
stated that in both these species the arms are arranged, as seen in frontal sections, as a 
series of F-like structures, their dorsal angles radiating to a common point, and their food- 
grooves being disposed round the periphery of a circle. The difficulty of getting sections which 
shew this arrangement quite diagrammatically depends on the facts (1) that the arms may be 
directed in any direction — forwards, backwards, outwards or inwards — as soon as they have 
become free, and this movement may be associated with rotation round their longitudinal axes; 
(II) that the arm-bases are not all in a single plane. The first difficulty is most easily overcome 
by examining sections of C. levinseni, in which the arms are very commonly arranged parallel 
with one another in a bundle which is directed straight forwards. The second difficulty cannot 
be so easily surmounted. The arm-bases of each side in reality follow a spiral line, commencing 
close to the proboscis-pore, and passing outwards and then dorsally, the end of the spiral 
reaching the posterior end of the central nervous system. In C. gracilis (fig. 25) the arm-bases 
follow a comparatively simple line, although even in this species no two individuals have 
their arms in the same position. The arrangement in C. levinseni can be understood by 
imagining the number of arms in C. gracilis increased by one, and by supposing the last 
arm of the series to be carried a considerable distance inwards, or towards the middle line of 
the animal. 

I have attempted to shew, in a diagrammatic figure (PI. XII, fig. 158), a po.sterior view 
of the arm-bases of the left side of C. levinseni, based on the frontal sections which have 
already been described. A similar dorsal view of the arm-bases and of the operculum is given 
in fig. 160; while fig. 159 is what I believe to be a fair diagrammatic representation of the 
free edge of the collar. In this last figure, in which the proboscis-stalk is supposed to have 
been cut through, and the anterior end removed, it has been necessary to exaggerate the size 



38 

of the operculum, in order to shew its relations to the food-grooves n{ the arms. It must be 
realized that the food-groove of the sixth arm passes towards the axis of the projected spiral, 
at a deeper level than that shewn in the figure. The free edge of the operculum (which is 
continuous with tlie sixth arm) is thus represented as starting too near the dorsal middle line. 
It will further be apparent from the actual frontal sections that the cavities of all the arms 
pass into the general collar-cavit)- which is situated at a lower level than (in reality, jjosterior 
to) the portion of bod\-wall which is formed by the continuous dorsal surfaces of the arms in 
the diagram. 

Although fig. 159 is thus not an exact representation of the collar of C. levinseni, it 
is, 1 believe, correct as a diagram. The ]iossible relations of the arrangement here shewn with 
the lophophore of PJioronis will be considered later. 

C. sibogae. 

In the neuters of this species the relations of the collar resemble those already described 
in the other species. There are, however, only four pairs of arms (PI. \'III, fig. 93; I'l. IX, 
fifj- 97)1 while the operculum (PI. IV, fig. 40 ; PI. \'II, fig. 78; «?/.) is very large. The collar 
is moreover provided with specially strong muscles, the relatively high development of the 
muscular system being marked in both the collar and the metasome of this species. 

The peculiar features of the male will be considered in Section X\'. The remarkable 
arms (PI. VII, figs. 72 — 76, 79; PI. IX, figs. 95, 96, 99) are only two in number. They are 
circular in section (fig. 79) except close to their base, where a vestige of a food-groove persists, 
leading by means of a food-channel (fig. 79, /". r. r., y. r. /.) to the mouth, which is .shewn in 
fig. 95. The male has no operculum. 

v. n d - 1) u 1 b s. 

Each arm in C. dodecalophus terminates, as is well known, in a globular end-bulb, which 
pos.sesses remarkable refringent vesicles. The.se structures were described by M'Intosh (87, |). 11) 
as glandular in nature. Masterm.\n (97, 2, p. 344) .suggested that they are compound eyes, 
a view which he sub-setjuently discarded (03, p. 725). Cole (99) regards them as rhabdite- 
jiroducing organs. 

I have myself no evidence which decides the function of the end-bulbs, although I refer 
to the subject again in describing the males of C. sibogae (Sect. XV), in which refringent vesicles 
are present in extraordinary numbers along the whole course of the arms. The bulbs are 
conspicuous structures in the buds of C. gracilis, where they seem to be in\'ariabl\- present at 
the ends of the arms of the first two pairs, while they may also occur on the third arms. I 
have no evidence llial ihey are tountl on the tourih am! tilth arms, while it seems jjrobable 
that the vesicles may completely disappear from all the arms of .some of the adult specimens, in 
this species. I have not found di.stinct entl-bulbs or refringent vesicles either in liie neuter 
individuals of C. sibogae or in C. levinseni. 



39 



o 



Some further information with regard to the arms of Cephalodiscus is given in describing 
the muscular system (Sect. XII), while the tentacles are alluded to under the heading of the 
vascular system (Sect. XIV). 

The collar c a v i t )' and its contents. 

The collar-cavity consists of a pair of coelomic .sacs which transversely encircle the oral 
region of the animal. The dorsal mesentery persists throughout, while the ventral mesentery is 
only represented in that region which lies posteriorly to the origin of the operculum (PI. IX, 
fig. 107; PI. X, figs. 123, 124, v.mes.'). In front of this region the right and left cavities 
become continuous by the disappearance of the mesentery (fig. 122), a result which probably 
allows the operculum to behave as a single organ; — which it could hardly do if it were 
subdivided by a median septum. 

A sagittal section of C. dodecalophus (PI. IV, fig. 42) shews a considerable extent of 
collar-cavity on the dorsal side of the body, and a very small portion on the ventral side. The 
operculum is short in the middle ventral line, and a section in this region accordingly shews 
the minimum amount of collar-cavity which it is possible to see. A median sagittal section 
should theoretically include the dorsal mesentery of the collar; but that membrane is extremely 
thin, and moreover it seldoms lies completely in one plane (cf. PI. XI, fig. 137). Fig. 42 thus 
shews one of the collar-cavities, instead of the mesentery, on the dorsal side. 

While the posterior boundary of the collar-cavity lies in a plane which is nearly transverse 
to the first part of the alimentary canal, the anterior boundary has a more complicated course. 
In the position which has been assumed by the individual shewn in fig. 42, the dorsal part of 
the collar-cavity is elongated in a direction which makes rather more than a right angle with 
the posterior wall. In other individuals, in which the neck is more sharply bent (as in figs. 150, 
151), the dorsal part of the collar-cavity may lie almost in the same straight line with the 
transverse part. The dorsal part of the collar-cavity, with which the arms are connected, is 
however, so arranged as to overlie the proboscis-cavity on its dorsal side. A frontal section of the 
buccal disc thus shews three cavities (PI. XII, fig. 152); the two collar-cavities {b.c.^ separated 
by their dorsal mesentery [mes."), and the unpaired proboscis-cavity, which occupies the anterior 
part of the section. Along the .septum Vi thus constituted runs the notochord {nc/i.) supported 
medianly by the dorsal mesentery- of the collar, and laterall\- by the two halves of the septum '/;. 

M.\STERM.\N (03, p. 717) has stated that there is a difference between Cephalodisnis and 
Balanoglossus in the relations of the notochord, which "lies in its primitive position in the 
"collar, and is in no way produced into the pre-oral cavity. It is a backward ventral e.xtension 
"of the buccal shield which makes the subneural gland [= notochord] lie in front of the mouth, — 
"not, as in Balanoglossus, a forward median extension of the subneural gland into the 
"pre-oral cavity". I confess that I am unable to appreciate this distinction. The notochord in 
Balanoglossus may indeed project further into the anterior body-cavity than in Cephalodiscus^ 
but I can see no morphological difference of importance between the condition shewn in the 
figure on p. 23 and that which obtains in Balanoglossus. It is no doubt true that the notochord 
is in relation with the two halves of the collar-cavity along practically its whole length 



40 

(cf. PI. XI, fig. i,iS), hill thti relations which it evciUualK- acquires with the anterior body-cavity 
and the pericardium (PI. XI 11, tig. iSi) do not differ essential!)- from those found in the 
Hnteropneusta. This is indeed admitted by Masterman in a later part of his paper (p. 722). 

Sagittal sections of C. levinseni (PI. IV, figs. 34 — 36) and C. gracilis il'l. \\\ fig. 37; 
I'l. \', figs. 43 — 51) shew an essentially similar condition; but in lioili these species the ventral 
jjart of the collar-cavity is better developed than in C. dodccalop/ius, although in all three cases 
the operculum is lower in the middle line than it is more laterally. 

The relations of the dorsal collar-region are best illustrated by means of sections transverse 
to the loner axis of the zooid. The series of sections of C. levinseni shewn in PI. X are from 
an individual whose proboscis-stalk was turned more dorsally than in PI. I\', fig. 34, so that 
their direction, as compared with that figure would be represented by a line joining the posterior 
end of the central nervous system to the tip of the operculum. 

P'ig. 117, through the base of the nolochord, thus cuts the posterior part of the 
proboscis-stalk in such a way as to shew n(; ])art of the proboscis-cavity (cf. fig. 33). The 
collar-cavities occupy the whole of the proboscis-stalk, extending laterally into the arms and 
.separated medianly by their dorsal mesentery, at the ventral end of which lies the notochord. 

In fig. 115, which is further forward, two portions of the proboscis-cavity ((5. r.') appear 
on the ventral side of the collar-cavities, one of than in a detached ])ortion of the proboscis- 
stalk, due to a fold, doubtless caused by muscular contraction. 

In fig. 1 14, this fold has opened into the main part of b. c.', and the notochord is now 
supported by three membranes, in the way that has been described above. In fig. 113, the 
ventral body-wall of the proboscis-stalk is about to become continuous with the buccal disc. 
The section cuts the tip of the notochord, the hmien of which is here considerably dilated. 
The notochord has moved up the collar-mesentery, so as jjractically to reach the central nervous 
system, as described by Mastermax (03), and it is overlapped by the posterior end of the 
pericardium {J>er.), which separates the two collar-cavities from one another so that they are no 
longer divided by a sim])le mesentery (see also PI. XI, fig. 138). The collar-cavities now rapidlv 
diminish in passing forwards. Immediately in front ot the ba.ses of the first arms (fig. 112) the\- 
are left as a pair of small cavities, the anterior dorsal horns of the collar-cavity {S.cJ'a.), distant 
from one another, and separated from the pericardium by the proboscis-pores {p.p.), just in 
front of which the collar-cavities terminate. 

The whole of this region of the collar-cavity is lined by a strong basement-membrane, 
which in addition to the .stiffening function which it doubtless possesses gives origin to muscles 
that traverse the proboscis-cavity. It seems to me probable that the anterior horns of the 
collar-cavities may be functionally related with the proboscis-pores, closing them by the contraction 
of the muscles which originate from them, aided, it may be, by a dilatation of the anterior 
horns of the collar-cavities by the forcing ol tluid into them trnm the rest of the cavitv. It is, 
however, clear that the horns are most important structures in |)rolonging the origin of the 
-system of muscles (PI. XI 1, figs. 147 — 149) which radiate through the proboscis-cavity. 

The relations of the anterior horns of the collar-cavities described in C. levinseni are also 
found in the other sjjecies, and have already been described, in C. dodecalopJnis, by Mastermax (03). 



41 

Tracing the sections of C. levinseni ventrally it will be seen that the collar-cavities become 
separated from one another by the diverticulum of the pharynx (PI. X, fig. ii8) and begin 
to pass round the alimentary canal to the ventral side. The dorsal projection of the metasome 
(wf/.) containing the oviducts appears behind the collar-region, and the two collar-cavities become 
more and more separated from one another dorsally by the third body-cavities (figs. ii8 — 
124, b.c?"). The operculum originates ventro-laterally from the collar (figs. 118 — 122), as has 
already been described; and the direct continuations of the dorsal parts of the collar-cavities, 
specially connected, as has been shewn above, wn'th the arm-bases, terminate ventrally in the 
regions containing the collar-canals (fig. 122, c.c). The more anterior portions of the cavities 
(cf. PI. XII, fig. 151) are, however, continued round the ventral side of the alimentary canal, 
where they become completely confluent (fig. 122). As soon as the base of the operculum has 
been passed, a ventral collar-mesentery makes its appearance (fig. 123). The collar-cavities may 
be seen, in several sections further, on the ventral side of the third body-cavities (fig. 124), 
the reason for which will at once be apparent from an inspection of the sagittal section (PI. IV, 
fig. 34). The ventral mesentery persists to the posterior end of the collar-region (PI. IX, fig. 107). 

The relations of the collar-cavities in C. dodecalophtis differ in no important respects 
from those above described. This will be clear from an inspection of figs. 151 — 146 (see p. 34); 
but attention may specially be called to fig. 151, which shews that the collar-canal occupies 
the ventral end of the part of the cavity which encircles the alimentary canal, and is a direct 
continuation of the cavity of the arm-base. 

The same arrangement is shewn, for C. gracilis^ in the series of obliquely sagittal sections, 
PI. V, figs. 43 — 51, and in the frontal sections, PI. VI, figs. 63 — 68; and, for neuter individuals 
of C. sibogae, in PL XIII, figs. 182—185 (young), PI. VIII, fig. 93 and PI. VII, figs. 77, 78. 

C o 1 1 a r - p o r e s or C o 1 1 a r - c a n a 1 s. 

There are no organs in Cephalodiscus which have given me more trouble than the 
collar-canals, and this in consequence of the difficulty of forming a reasonable theory as to their 
mode of action. The general facts are perfectly clear. Each collar-pore or collar-canal is an 
ovoid body which lies with its long axis more or less transverse to that of the body (PI. XI, 
fig. 131, c. c). On the median side, the canal opens by a large aperture into the collar-cavity. 
On the outer side it opens by an even larger aperture {c.c.c.) to the exterior. It follows from 
this disposition of the organ that both apertures may be cut in a single section which passes 
either in a transverse plane (fig. 131) or in a frontal plane (PI. X, fig. 121); and that a section 
which passes transversely to the long axis of the organ must have a more or less sagittal 
direction (PI. XI, fig. 140J. But with varying states of contraction of the collar, these relations 
may be somewhat distorted. 

The collar-canal lies at the ventral end of that section of the collar-cavity which is 
directly continuous with the arm-base (PI. XII, fig. 151 ; PI. \\ figs. 46 — 49; PI. XI, fig. 140). 
Its ventral wall is in immediate contact with the dorsal wall of the gill-slit (figs. 46, 131, 140), 
but it rests partly on the septum which divides the collar-cavity from the trunk-cavity (figs. 49, 
140, 155). This wall is composed of a high epithelium with munerous nuclei, implying narrow, 

SIBOGA-EXPEDITIE XXVI Wj. t) 



42 

closely packed cells, and it l:)ears long cilia or flagella (fig. 140). In either a transverse or a 
sagittal section this high epithelium has a characteristic crescentic form. 

The dorsal wall of the canal is formed of a much thinner epithelium (figs. 131, 140; 
PI. \', figs. 46 — 50). It may either be convex towards the lumen of the canal, and therefore 
more or less parallel to the ventral wall (figs. 49, 131), or it may be flat (I'l. Xlll, U^r. 185), 
or it may be concave towards the lumen (figs. 101, 140). The latter condition gives the largest 
size to the cavity, and the collar-canal may be said to be dilated when it is in this condition. 
It appears obvious that the dorsal thin wall is capable of a considerable amount of movement, 
and it may be j^resumed that this mobility is of physiological importance. 

It is further obvious that the longitudinal muscles of the trunk end in the immediate 
neighbourhood of the collar-canal (fig. 140, 77, 93); that a specially strong band of collar-muscles 
originates in much the same position (figs. 131, 77, 93, or. »i.)-^ and that the anterior fle.xible 
wall of the canal is in the closest connexion with a tissue (figs. 131, 140, 121, i2 2,,i-.) which 
appears to consist of a series of radiating lamellae. 

The above facts can easily be verified in any female or neuter zooid (C. siSogae), although 
in the males of C. sibogae the collar-canals are so small that the details of their structure have 
not been made out. 

It follows from the observations of Spencel (93, p. 475) that the collar-canals of Balano- 
glossus are of special importance in taking water from the outside into the collar-cavities, and 
so maintaining the collar as a whole in a proper state of turgidity. I think it cannot be doubted 
that the same is true of CcpJialodiscus. The whole mechanism of the collar appears to depend 
on the proper maintenance of this condition. The movements of the arms and of the operculum 
are alike dependent on it. The arms in particular are provided with strong longitudinal muscles, 
by wliich the)- can be contracted ; but for their elongation and for that of the tentacles, one 
must look to the fluid pressure of the contents of the collar-cavities. The mechanism is j^robablv 
identical with that of the tube-feet of an Kchinoderm, and the resemblance is made all the 
more striking by the fact that most jjarts of the collar-coelom are traversed by short fibres 
which connect the opposite walls (PI. X, fig. 122) as in the case of the ambulacral canals of 
a Crinoid, for instance. When it is remembered that MacBride (96, p. 39O) has given reasons 
for regarding the hydrocoel system of an Echinoderm as actually homologous with the left 
collar-cavity of Balanoglossus the similarity between these cavities in Cephalodisctis and the 
ambulacral vessels of an Echinoderm becomes all the more noteworthy. 

A strong contracticjn of the longitudinal muscles of the arms must have the effect of 
forcing their fluid into other parts of the collar; and as there are no spaces which appear to 
have the function of reservoirs, I think it follows that fluid must leave the collar b\ way of 
the collar-pores. During the e.xtension of the arms, on the contrary, fluid must be supposed to 
be taken in by the collar-pores, which thus act now as exhalant and now as inhalant apertures. 
How are these varying currents controlled? The strong flagella of the ventral epithelium of 
the collar-canals are no doubt of special importance in the process; but the mode of ending of 
some of the strongest muscles of the body in the immediate vicinit\- of the jjores is .significant, 
and it appears to me that it may imply something in the nature of a pumping action. 



43 

A mechanism of this sort would require some power of closinj^ either one or both of the 
apertures of each canal, as occasion requires. The condition in which the canals are left in 
preserved specimens is, however, usually one in which both external and internal apertures are 
widely open. 

The consideration of these questions must be preceded by a more careful study of the 
collar-canals themselves. 

The external aperture of a collar-canal (c.c.e.) is seen in PI. Ill, fig. 25, which is drawn 
from a plasticine reconstruction of the sections belonging to the sagittal series shewn in PI. V. 
The external part of the opercular flap is cut away on the right side, and immediately below 
this part the collar-pore appears as a projection of the body-wall in the form of half of a 
shallow cup. Below the collar-pore is seen the aperture of the corresponding gill-slit {g: s. r.). 
Figs. 50 — 46 shew consecutive .sagittal sections of this collar-canal. It appears from these sections 
that the external aperture of the canal is everywhere overhung by the base of the operculum, 
and the arrangement suggests that this structure when reflected towards the stalk of the animal, 
might be used for closing the collar-pore. There is also clear evidence of a tissue passing from 
the thin dorsal wall of the collar-canal to the base of the epidermis of the oral side of the 
operculum. If this tissue were muscular the collar-canal would appear to be provided with a 
dilating mechanism. 

But in most other ca.ses I have not been able to demonstrate any connexion between 
these supposed dilator fibres, which I will term the "problematical tissue" of the collar-canals, 
and the oral epidermis of the operculum. 

Two sets of muscles are, however, intimately associated with the collar-canals. The first 
of these are the great antero-ventral muscles of the body, continuous ventrally with those of 
the stalk. These muscles (PL X, figs. 125, ws.) divide into two masses when they reach the 
level of the ventral border of the collar (fig. 124), the fibres becoming fewer in number; and 
they diverge outwards as they cro.ss the gill-slits on their anterior side (fig. 123), finally 
disappearing when they reach the trunco-collar ') septum in the neighbourhood of the inner 
openings of the collar-canals. These antero-ventral horns of the third body-cavities {d. c\ a.) are 
.seen in longitudinal section in PI. IV, fig. 41 (C dodecalophus) and in PI. IV, fig. 36 (C levinseni). 
They are essentially alike in all the species which I have examined. 

The second set of muscles are the strong oral muscles [or. m.) which traverse the collar 
in a longitudinal direction. The.se muscles (PI. IV, fig. 41 ; PI. V, fig. 45; PI. VIII, fig. 93) 
originate from the trunco-collar septum close to the insertion of the muscles contained in the 
anterior horns of the third body-cavity, and pass dorsally round the sides of the mouth, ending 
in .septum '/, opposite the point of origin of the radiating muscles which pass freely through the 
cavity of the proboscis. 

Since the ventral wall of the collar-canal is firmly attached to the septum with which 
these two sets of muscles are connected, it would appear that contraction of the muscles must 
have some effect on the collar-canal. This organ has a perfectly characteristic relation to the 



l) I borrow this expression from DE Selys Longchami's (04). 



44 

u^ill-slit, on the dorsal side of which it rests. I'l. XI, lig. 131 will shew, however, that the 
contact between the two organs only concerns the middle of the ventral wall of the collar-canal, 
the inner part of the wall resting on that portion of the trunco-collar septum in which the 
muscles of the metasome end, while the outer part is confluent with the external part of the 
septum. This relation is further illustrated by PI. XII, figs. 156, 155. If a tracing be made of 
fig. 155 and if it be superposed on fig. 156, it will i^e seen that the long a.\is of the collar- 
canal crosses the gill-slit at right angles; and the consideration of the figures which have been 
referred to thus suggests the idea that the wall of the gill-slit in fact forms a fulcrum on which 
the collar-canal moves. If this conclusion be correct, it would appear that the contraction of the 
muscles passing from the stalk to the inner and anterior wall of the collar-canal must depress 
that end of the organ, and elevate its outer end. But the contraction of the longitudinal muscles 
of the trunk presumably increases the fluid ])ressure of the contents of the third body-cavity. 
This increase would probably react mainl\- on the outer end of the collar-canal, partly because 
the area of the septum exposed to the pressure is here greater than at the internal end, and 
partly becau.se the anterior horns of the third body-cavity are for the most part filled with 
muscle. The pressure-effect would thus act in the same direction as the direct eftect of the 
contraction, and the projecting ventral lip of the external aperture of the collar-canal would 
move in a dorsal direction. A collar-canal in this condition is seen in PI. Ill, fig. 24, the 
external opening being here nearly closed, instead of having the wideh- open condition shewn 
in PI. XI, fig. 131. 

\\ hen the collar-canal has assumed the ])osition indicated in fig. 24, it seems natural 
to suppose that the contraction of the strong oral muscle which traverses the collar-cavity will 
restore the collar-canal to its fi)rmer position by elevating the inner end of the organ, since 
the origin of those fibres is immediately adjacent to the insertion of the metasomatic muscles. 

I am inclined to believe that the external opening of the collar-canal can be closed, 
partl\- by the contraction of the mu.sculature of the metasome, and partly by the movements 
of the operculum. Even when the free edge of that organ is directed forwards, the operculum 
might still be effective in helping to close the collar-i)ore, as is indicated by fig. 24, where a 
sharp bend of the operculum is almo.st in contact with the ventral lip of the collar-])ore. If the 
collar-pores were closed, the arms, tentacles and other parts of the collar would presumably be 
in full working order, since their body-cavities would form a closed system, and contraction of 
any ot the muscles would be capable of producing an effect on the fluid pressure of the collar- 
coelom. .Should any sudden retraction of the arms be required this could be effected by the 
contraction of their longitudinal muscles, the fluid meanwhile escaping through the widely open 
collar-pores. 

The "problematical tissue" (.r.) of the collar-pores offers more serious difficulties. It is 
in the first place necessary to decide whether the tissue is muscular or is a modification of 
the basement-membrane, of skeletal or elastic properties. The evidence of stains seems to be 
unequivocal on this point. The tissue stains like the muscles. The clearest evidence is afforded 
by sjjecimens stained with liacmaloxylin and Orange G\ and in these, while the basement- 
membrane has taken up the liacmaloxylin colour, the problematical tissue, like the muscles of 



45 

the stalk and other parts, is brilliantly orange in colour. Although I think that the evidence 
of the stains must be relied on, there are two facts which make it difficult to interpret the 
tissue as muscular in nature. These are (a) the form of the elements of which the tissue is 
composed, and (A) the mode of connexion of the ti.ssue with adjacent parts. 

With regard to [a] it must be pointed out that the tissue appears to be composed of 
oval lamellae, and not of typical muscle-fibres. A sagittal section (fig. 140) or a frontal section 
(figs. 120, 121) will give the impression of muscle-fibres cut longitudinally. It is obvious that if 
a linear organ appears as a line in sections cut in two planes at right angles to one another, 
a section in a plane at right angles to both the others will shew it as a point. I have been 
unable to obtain any sections in which the elements of the problematical tissue appear as a 
series of points; and, on the contrary, a transverse section (fig. 131) gives the impression that 
the organ is composed of a series of oval lamellae. These stain in precisely the same way 
as the typical muscle-fibres of the body, and a certain number of nuclei can usually be made 
out along their free coelomic borders. This form of the elements of the tissue precludes the 
possibility that the problematical tissue consists of a mass of solenocytes ; and Mr E. S. Goodrich, 
who was kind enough to look at one of my preparations, expressed the opinion that the tissue 
cannot be explained in that way. 

With regard to (<^), it may be noticed that the elements of the tissue are not so obviously 
provided with an origin and an insertion as would be expected on the hypothesis that they 
are muscular. This will be seen in such cases as fig. 140 where the lamellae have a free 
coelomic border, a condition which is also seen in figs. 120, 121, 131. 

If the tissue really consists of dilator fibres, a function which is suggested by the specially 
wide lumen of the collar-canal seen in fig. 140, it would be expected that the ends of the 
fibres would originate from the walls of the collar-cavity. In view of the strong development 
of the tissue in question it is clear that its muscular nature cannot be regarded as proved 
unless a sufficient origin can be detected. 

In view of these considerations, and of the fact that figs. 47 — 49 seem to shew that 
the elements of the problematical tissue are connected with the inner wall of the oral side of 
the operculum, I have endeavoured to find evidence that the origin of the fibres has been torn 
away from the body- wall, owing to imperfect preservation. Such a view is, on a priori grounds, 
not improbable, as the elements appear to be very powerful, and might have undergone 
contraction, during the death of the zooids, sufficient to tear them away from their origin. 
Fig. 1 3 1 certainly indicates that the coelomic epithelium of the dorsal side of the collar-cavity 
has been torn away from its basement-membrane; but even in this case, I cannot satisfy myself 
that the oval lamellae can have originated from that wall of the cavity. The probability that 
the relations of the tissue, in the preserved material, are not essentially different from those 
found during life is increased by the considerations (a) that rupture of the connexions of the 
tissue might be expected to occur, in some cases at least, at the end which is inserted into 
the delicate dorsal wall of the collar-canal; and no such rupture is observed; {b) that the 
undoubted muscles of the animal are seldom found to be torn away, at either end, from the 
basement-membrane to which they are severally related. 



46 

I am thus led to the coiulusioii tlial the proljlematical tissue must be inter[jreted as it 
stands, without the aid of any hypothesis to the effect that rujnure has taken place; and it 
remains to consider further the evidence afforded by the sections. Sagittal sections (fig. 140) 
shew that the lamellae stand more or less at right angles to the wall of the collar-canal ; 
or, in other words, that they radiate from its lunu;n. Frontal sections (fig. 121) shew that 
they originate from the lateral body-wall ot the collar, an arrangement which is also seen in 
transverse sections (fig. 131) or in the reconstruction shewn in fig. 24. Although it would not 
be difficult to imagine that the lamellae had been torn away from the basement-membrane 
covering the pharyn.x in figs. 120, 121, the fact that the oral muscle {or.m.) of the collar 
intervenes between the pharynx and the problematical tissue makes it impossible to suppose 
that this tissue was connected with tlie i)haryngeal wall along the whole of what appears as 
its free border in figs. 1 20, 121. 

The relations of the problematical tissue can thus be expressed by saying that each of 
the lamellae of which it is composed is connected, along about half of its circumference (see 
fig. 131) with the thin dorsal wall of the collar-canal and with the external body-wall of the 
collar, and that the remainder of its circumference is freely exposed to the collar-coelom. It is 
difficult to see the purpose of this arrangement ; but I am inclined to think that the tissue must 
be interpreted as muscular; that the principal mode of contraction of the lamellae is along the 
line between the body-wall and the dorsal wall of the collar-canal ; and that the effect of the 
contraction is to dilate the lumen of the canal and its aperture into the body-cavity. 

It is now necessary to return to figs. 47 — 49, in which fibres can be traced from the 
dorsal wall of the collar-canal to the oral epidermis of the ojjerculum. These figures refer to 
C. gracilis, and although the arrangement at first sight seems to differ from that which has 
been examined in C. dodccaloplms and C. levitiseni, 1 think that the difference is more apparent 
than real. Thus in other specimens of C. gracilis I have obtained evidence that the problematical 
tissue is composed of lamellae connecting the wall of the collar-canal with the external body- 
wall, an arrangement which is not precluded by hgs. 47 — 49. Moreover, in the other species, 
there is evidence that certain fibres pass from the wall of the collar-canal to the oral wall of 
the operculum. This is shewn, in C. dodecalophus, in fig. 151, where in addition to the main 
mass of the problematical tissue (.r.) a few delicate fibres, similar to the shorter fibres which 
traverse the collar-cavities in such numbers, pass from the wall oi the collar-canal or even from 
the problematical tissue, to the oral wall of the operculum. A similar arrangement is seen, in 
neuter individuals of C. sidogae, in figs. 77, 78; and it is thus probable that the dilatation of 
the collar-canal may be partly effected by the contraction of these fibres. 

I feel that 1 am far from having understood the mechanism of the collar-canals in 
Ceplialodiscus, but their structural arrangements .seem to me to indicate clearK' that muscular 
action is an im])ortant factor in their mode ot acting. The thin dorsal ejjithclium of the canals, 
and its varying position, suggest that the movements of this part are of im]H)rtance, and it is not 
improbable that it may to some extent have a simple valvular action, controlled by the fluid 
pressure of the contents of the collar-cavity. 

I have not noticed an)- differences of importance between the different species oi Cephalodiscus 



47 

with regard to the structure of their collar-canals. The main relations of these organs seem to 
be quite invariable. The problematical tissue is more highly developed in C. levinseni than in 
C. dodecalopJuts. It is strongly developed in the neuter individuals of C. sibogae, in correlation 
with the muscular nature of the animal generally; and it is less conspicuous in C. gracilis. 



IX. METASOME\ BODY or TRUNK. 

This region, which is characterized by including the third body-cavities, differs in proportions 
in the different species, though there can be little doubt that the examination of contracted 
preserved specimens does not give a complete idea of its shape when the strong antero-ventral 
muscles are relaxed. The body is relatively short in C. dodecalophus^ while the opposite extreme 
is reached in old individuals of C. levinseni^ in which the form is elongated and cylindrical. 
C. gracilis and C. sibogae are intermediate between the other two species, in this respect. 

The metasome contains the whole of the alimentary canal, with the exception of the 
anterior part of the pharynx, and it also includes the reproductive organs. Its junction with the 
collar is not well marked externally on its anterior side, although it is sharply marked internally 
b\- the septum between the second and third body-cavities, while the gill-slits open along the 
line of junction. 

The alimentary canal and reproductive organs will be described below, and the present 
Section deals principally with the third body-cavity. The main part of this cavity is a well 
marked space, which is not obscured by connective tissue or muscles passing across it, as is the 
case in the other coelomic spaces. It is subdivided by a median dorsal and ventral mesentery, 
both of which are typically complete except for the fact that the ventral mesentery breaks 
down in the middle of the stalk. This region is, however, traversed, on its anterior and posterior 
sides by ridges (PL XI, figs. 132, 133) which indicate remains of the mesentery. The cavity' 
of the stalk is usually filled by connective tissue, which ends sharply at the point where the 
stalk joins the body (PI. IV, fig. 42). As the part of the ventral mesentery inside the body is 
attached along its whole length to the surface of this mass of connective tissue, there is no 
open communication between the two halves of the third body-cavity. The cavity is lined by a 
peritoneum, which invests the surface of the ovaries and the whole of the alimentary canal, but 
it does not pass into the region where the anterior wall of the intestine is in contact with the 
posterior surface of the stomach. Included in the principal bend of the alimentary canal, in the 
region of the second stomach there is, however, a small part of the body-cavity, which opens 
widely, on either side, into the main body-cavity. This can always be seen in sagittal sections, 
and it is marked b.c'^b. in PI. IV, figs. 33, 34, 37, I'i. 4^- It is indicated by M'Intosii (87) 
in his fig. 3 on PI. Ill, and is alluded to as a "peculiar fold" in the wall of the alimentary 
canal [t.cit., pp. 17, 41 note). The individual drawn in fig. 42 shews the arrangement described 



I) The stalk is of course to be regarded as part of the metasome, but it may conveniently be considered in a separate Section. 



48 

by M'Intosh cjuite clearl\- in some of ihc more lulcral seclit^ns. The suggestion naturally occurs 
that this arrangement may have some bearing on the manner in which the alimentary canal is 
dirterentiated in the bud; a question which is considered in Section X\"l. 

The opening of this part of the cavity int(j the general metasomatic cavities is shewn 
in PI. XI, fig. 130 and in PI. V, fig. 53. It is possible that the space is of functional importance 
in allowing the second stomach to alter its diameter more freely than would be the case if its 
movements were restricted by a close union of its wall with tliat of the principal stomach. 
As this region of the mctasome is, moreover, probably exposed to considerable alterations in 
shape or position, by the contraction of the antero-ventral musculature, it is possible that the 
part of the body-cavity in cjuestion may have some importance in permitting a certain amount 
of sliding motion of the two liml)s of the alimentary canal over one another, at the bend, thus 
allowing the second stomach to adapt itself to alterations in the position or direction of the stalk. 

The peritoneal investment (//.), which is further considered below, is often so loosely 
applied to the alimentary canal that a considerable space occurs between it and the digestive 
e])ithelium (figs. 43, 51 — 53). This is clearly to some e.xtent the result of defective preservation, 
but I believe that the investment is in reality a somewhat loose one, in certain places at least, 
and that a splanchnic blood-sinus normally occurs below the peritoneum. 

The ventral part of the anterior wall of the third body-cavities is specially concerned 
with th(> principal muscles, those which extend between se])tum ■/;, and the tip of the stalk. 
A ventral horn {d. r.'' a.) extends, in the females, and in the neuter individuals of C. sibogae, 
along the anterior border of the gill-slits (figs. 68, 77, 123, 156) as far as the region of the 
collar-canals. These parts of the third bod\-cavity have already been discussed in the preceding 
Section, and arc further described in Section XII, dealing with the musculature. 

Mesenteries. 

The mesenteries require sejjarate treatment for the difterent species. In C. dodecaloplius 
and C. levinseiii the dorsal and ventral mesenteries are both complete, except in the axial region 
of the stalk, where the ventral mesentery breaks down in all the species. 

In C. dodecalophus (PI. XII, figs. 152 — 157) the dorsal mesentery {mes'f) extends between 
the dorsal body-wall, the pli.n \ nx, the rectum and the dorsal caecum of the stomach; another 
detached portion of it bisecting the small cavity (PI. IV, fig. 42, d.c.^'d.) seen in sagittal sections 
at the bend of the alimentar\- canal. The dorsal mesentery includes the well developed dorsal 
vessel. I-'rom the dorsal mesentery are given off the lateral mesenteries, which carry blood- 
vessels to the ovaries (PI. XII, figs. 152 — 157, ov.v.). 

The lateral or ovarian mesenteries {oz'. m.) extend from the dorsal body-wall and the 
dorsal mesentery to the oviducts, terminating with a free edge ventrally slightly below the 
point where the oviduct joins the ovary (PI. XII, figs. 149 — 156). Il is thus only the extreme 
dor.sal end of the ovary which is su[)ported liy the lateral mesenter\ . In the region where the 
oviduct opens to the exterior the lateral mesentery joins the dorsal body-wall (figs. 150 — 152). 

The ventral mesentery {v. /nes.'^) follows the convex side of the loop of the alimentary 
canal. The rectum and intestine are so closely pressed against the posterior body-w^all that the 



49 

mesentery cannot always be detected in this region (figs. 152 — 157). In some cases, however, 
the posterior limb of the alimentary canal is seen to be suspended by an extremely short 
mesentery, the coelom thus intervening between the canal and the body-wall. In favourable 
specimens (fig. 157) the anterior part of the ventral mesentery is seen to include a small blood- 
vessel {a. z''.), which occurs at the junction of the mesentery with the body-wall. This vessel is 
the direct continuation of the anterior vessel (fig. 133, a. v.) of the stalk. 

The mesenteries of the third body-cavity of C. levinseni agree in all respects with those 
of C. dodecalopJnis^ as may be seen from the frontal sections shewn in figs. 1 20 — 1 30. The 
dorsal and lateral mesenteries are shewn in figs. 119 — 123. In figs. 124, 125, the lateral 
mesenteries have come to an end, while the dorsal mesentery continues uninterruptedly until 
the .stomach is reached. Fig. 130 shews the detached part of the dorsal mesentery which occurs 
at the bend of the alimentary canal. The extreme anterior end of the ventral mesentery, with 
its blood-ve.ssel, is seen in fig. 1 24, between the pharynx and the ventral part of the collar. 
The ventral mesentery can be seen, on the anterior and posterior sides of the alimentary canal, 
in the remaining sections figured (figs. 125 — 130). 

In C. gracilis, perhaps in correlation with its smaller size, the mesenteries are less 
complete than in the two species so far considered. The dorsal mesentery is complete only at 
its extreme dorsal end (PI. VI, fig. 67), while in sections nearer the stalk (figs. 68 — 70) it is 
represented merely by the dorsal vessel. The lateral mesenteries are similarly represented by the 
vessels to the ovaries (fig. 68). The ventral mesentery can be distinguished on the pharyngeal 
side (fig. 6g) for a short distance beyond the collar-region, but it soon disappears completely 
(fig. 70), except so far as it is represented by the blood-vessel, which in favourable specimens 
can be seen on the inner side of the body-wall. The rectum is usually in such close contact 
with the posterior body-wall that no definite mesentery is formed on this side. A portion of the 
ventral mesentery persists near the base of the stalk, where it carries the posterior stalk-vessel 
to the bend of the alimentary canal (fig. 71). I have not detected any portion of the dorsal 
mesentery on the concave side of the bend, in the part of the body-cavity marked b.c?l>. in 
fig. 37; but I am not prepared to .say that it does not exist in that region. 

It may be noted that the ventral mesentery is incomplete even in the buds of C. gracilis 
(PI. V, fig. 56) whereas in C. dodecalophus the observations of Masterm.\n (98, 2, figs. 52 — 58, etc.) 
shew that it is complete at a corresponding stage. 

In the neuter individuals of C. sibogac the dorsal mesentery is incomplete (PI. VIII, 
figs. 90, 91). The lateral mesenteries are not present, in con.sequence of the absence of gonads. 
The ventral mesentery is distinguishable, on the pharyngeal side, in the region of the gill-slits 
(fig. 92). In the males of the same species there are remains of the dorsal and lateral mesenteries 
(figs. 86, 87) and of the ventral mesentery (fig. 89). 

The body-wall of the metasome is in most parts thin and without any specially noteworthy 
characters. The muscular layer is almost confined to the anterior surface (see .Section XII). 
The epidermis may be pigmented, especially in C. sibogae, which is characterized by the presence, 
in practically all parts of the adult animal, of an unusually large amount of very dark pigment. 

SIBOGA-EXPEDITIE XXVI i/>. 7 



50 

The dorsal epidermis in all the species consists, near the middle line, of a specially high columnar 
epithelium ( v.) which is very conspicuous in C. gracilis (PI. Y, figs. 45 — 52) and in the neuter 
individuals of C. sidogac (PI. IV, fig. 39). In the latter case, the organ is obviously ciliated, 
and appears to have a nerve-layer at its base. It is perhaps to be regarded as a sense-organ. 



X. STALK 



The stalk of Cephalodiscns is the muscular aboral part of the metasome. It consists of an 
epidermis, separated by a well marked basement-meml)rane from a strong mass of longitudinal 
muscles. The space surrounded by these muscles may be regarded as morphologically part of 
the third body-cavities, but it is usually filled by connective tissue to such an extent as to leave 
no definite cavity. The ventral mesentery is, in most cases, indicated by parts which enclose 
the two longitudinal vessels, but the mesentery does not appear to persist as a complete septum 
in the adults of any of the species. It has been pointed out by M'Intosh (87, pp. 20, 23) that 
the truncated base of the stalk is proljabK' used as a sucker. It would be difficult to understand 
the mode of action of the powerful muscles of the stalk if the animal were not able to attach 
the base of that organ to the wall of its coenoecium. 

The origin of the stalk from the body differs in the different species. In the buds it is 
invariably a direct prolongation of the rest of the metasome, as shewn for C. dodccalophus by 
Masterman (98, 2, Pis. II, III) or in my own figures of the same species (PI. XllI, fig. 181) 
or of C. gracilis (PI. I, \\>^. 4: PI. Ill, fig. 32). In the adults of C. sibogae (PI. I, fig. 3) this 
relation is but slightly modified, although even here the stalk originates .somewhat on the anterior 
or pharyngeal side of the body. In the other species, the origin of the stalk is usually shifted 
towards the mouth, so that the ventral end of the body projects beyond it, on its posterior 
side, as a caecum containing the loop of the alimentary canal. But in one specimen of C. gracilis, 
I have observed a connexion of the stalk with the body precisely like that shewn, for C. sibogae, 
in fig. 3. The consideration of this case suggests that the appearance of the posterior caecum 
of the body is caused, to some extent at least, by the contraction of the longitudinal muscles 
which run from the stalk ])rincipally along the anterior side of the body, and that in the relaxed 
condition of these muscles the stalk would appear as an almost direct continuation of the 
body itself. 

In C. dodecaloplms the stalk is usually found directed towards the mouth, as in the well 
known figure given by M'Intosh (87, PI. II), although the first figure on the next plate of .the 
same author shews that it can be directed away from the mouth. In young individuals of 
C. levinseni (PI. I, fig. 5) the stalk is usually in the position which is most commonly found 
in C. dodecaloplms, lying beneath the edge of the proboscis, as in the specimen figured, or 
externally to that structure. In old individuals of the same species, I have invariably found it 
directed away from the mouth (fig. 6), usually describing a short si)iral round the bud or 
embryos fountl in the proximal part of the zooecium. In C. gracilis and C. sibogae, I have 



51 

al\va)s found the stalk directed a\va\- from the mouth, except in cases where the metasome or 
the stalk itself is bent towards the mouth (cf Pi. IV, fig. 40). 

The structure of the stalk of C dodecalophus has been described by M'Intosh (87, p. 20, 
PL IV, fig. 5, etc.) and by Masterman (98, 2, p. 513, Pi. I, fig. 18). Masterman adds to the 
general description given by M'Intosh the account of three definite nerve-tracts on the "ventral" 
side of the stalk, and of a "dorsal" and "ventral" blood-vessel running along- the remains of 
the mesentery found on opposite sides of the stalk. Each of the nerve-tracts is said to have 
a fine lumen. 

I can confirm the accuracy of Masterman's account, e.xcept that I have not found a 
lumen in any of the nerve-tracts, and that I prefer to use the terms "anterior" and "posterior" 
instead of "ventral" and "dorsal" respectively. 

The stalks in the "Challenger" material are very strongly contracted, as is indicated 
by the folding of the epidermis and of its basement-membrane as seen in longitudinal sections 
(PI. XIII, fig. 169). These folds are responsible for the irregularities in the outline of the 
transverse sections. PI. XI, fig. 133 shews the three nerve-tracts («./.) described by Masterman. 
These appear to be continuous with a general nerve-ple.xus lying at the base of the entire 
ectoderm of the stalk. The basement-membrane, internal to the nerve-layer, is deeply stained 
with haematoxylin, although its thickness appears greater than it really is in consequence of 
the e.xtensive folding which has been alluded to. The membrane is prolonged inwards in the 
two median lines to support the anterior limb [a. v.) and the posterior limb {/>. v.) of the loop of 
the ventral vessel which descends into the stalk. These prolongations of the membrane represent 
remains of the ventral mesentery, which is complete in the young buds (cf. Masterman, 98, 2, 
p. 515), but cannot be recognized as a complete partition in the adult stalk. The remainder 
of the body-wall is constituted by a powerful development of longitudinal muscles, and the 
interval left free from muscles is entirely filled by an extensive development of connective tissue. 
The body-cavity of the stalk is thus virtual in the adult zooid. 

The stalk of C. levinseni (PI. XI, fig. 132) differs in certain respects from that of C. 
dodecaloplucs. It is more regular in outline, and its nerve-layer forms a single projection, triangular 
in transverse section, towards the interior of the stalk. The layer of longitudinal muscles is 
arranged very definitely, as a pair of oval groups of fibres, open towards the middle line. 1 he 
connective tissue filling the cavity of the stalk is not so much developed as in C. dodecalophus. 
The two parts of the vascular loop are present as in that species, but the basement-membrane 
is not so thick. 

The mode of origin') of the stalk from the body is explained by figs. 125 — 128. In the 
sections nearer the mouth (PI. X, fig. 125), the muscular layer is relatively thin, and surrounds 
the anterior third of the section, being divided into two halves by the ventral mesentery. In 
PI. XI, fig. 126, the ventral mesentery has become incomplete, ending in a connective tissue 
layer which separates the internal tissue of the .stalk from the general body-cavity. A small 
triangular space, doubtless part of the body-cavity, intervenes between the part of the mesentery 



I) The other species agree, in essential respects, with C. levinseni.^ so far as the mode of origin of the stalk is concerned. 



5 2 

which is attached to the oesophagus and the part which bears the anterior limb of the vascular 
loop of the stalk. In fig. 127 the epidermis is raised up into a projection, inside which the 
musculature of the body-wall is taking on the arrangement characteristic of the stalk. The 
ventral mesentery passes from the stomach to the limiting la\er of the connective tissue of the 
stalk, with which it is specially connected on the left side of the figure. The triangular space 
of fig. 126 is no longer distinguishai^le from tiie other spaces in the feebly developed connective 
tissue of the stalk. The muscles, in this and in other sections, have a .tendency to arrange 
themselves in conuli, the apices of which project towards the centre of the stalk. 

Fig. 128 cuts the stalk immediately before it separates completely from the body; and it 
thus shews the posterior limb (p. r'.) of the stalk-vessel at the point where it enters the body. 
The anterior limb [a. c.) of the same vessel is still indicated by a thickening of this part of the 
mesentery, big. 132, which has already been described, is a section, somewhat more highly 
magnified, of the stalk of the same individual, through a part which has become completely 
separated from the body-wall. 

It may be noted here that the stalk of Rhabdopleiira has a .structure essentially cor- 
responding with that of Cephalodisciis. This follows from the recent accounts given by Schepotikff 
(04, p. 10) and Fowlkr (04, p. 24). The stalk of Rhabdopleura, is, however divided In- a 
complete median mesentery. According to Fowler's descrijition and figure (PI. Ill, fig. 2) a 
nerve-tract, triangular in transverse .section, is found on the "ventral" side of the stalk, e.xactly 
as in C. levinseni. In the immediate neigbourhood of this is a space {b), regarded by Fowler 
as perhaps artificial; while ne.xt to this, and almost in the middle of the mesentery, is another 
space marked by Fowler end?. This cavity is "continuous with the lining of the alimentary 
canal" (p. 29), and Fowler rejects the view that it is a blood-vessel, suggesting that it is an 
endodermic structure, which is concerned in the fnrmatinn of the alimentarv canal of the buds. 
This view is further alluded to in Section X\ 1, but in the mean time 1 may point out that 
the two cavities described by Fowler in the stalk-mesentery of Rhabdoplc7ii-a have precisely 
the same arrangement as the two parts of the vascular loop which extends into the stalk of 
Cepha lodiscus . 

The stalk of C. gracilis (fig. 134), differs from that of cither of the species which have 
already been described. The epidermis of the anterior side forms a large ridge projecting towards 
the centre. This is usually bi.sected by a vertical line of ])ignient, on cither side of which is a 
layer of nerve-fibrils. The ridge is relatively more prominent than in C. Icvinseiii, and may be 
parallel-sided in transverse section. The muscular layer is reflected rountl this ridge; and while 
it thus has fundamentally the same arrangement as in C. kvinsetii, the shape of the muscular 
mass is somewhat different. Connective ti.ssue is hardly developed in the stalk, which thus 
contains a definite cavity. The vessels of the stalk, instead of appearing as minute slits in the 
remnants of the mesentery, are commonly very conspicuous in transverse section, and appear 
as large cavities with a delicate wall. In some cases (fig. 134) they are obviously anterior and 
posterior in position, but they often lie side l)y side in the body-cavilv of the .stalk (fig. 135), 
although it can be ascertained, in some of these cases, that one of the vessels is closely 
related to the nerve-ridge of the anterior side of the stalk, while the other is suspended by an 



53 

inconspicuous mesentery from the posterior wall. It has been possible in this species, as in C. 
dodecalophus^ to trace the vascular loop from the bend of the alimentary canal (PI. Ill, fig. 22) 
down the posterior side of the stalk, while the anterior vessel of the stalk is continuous with 
the vessel in the ventral mesentery of the body. The .stalk-vessels in this species have been 
observed to contain a distinct coagulum, confirming the view that they are really parts of the 
vascular system. 

The stalk of C. sibogae (fig. 136) resembles that of C. gracilis. The muscular layer is 
composed of specially strong fibres, and the amount of connective tissue is small. The nerve- 
tract of the anterior side forms a prominent ridge. Remains of the mesentery can sometimes 
he distinguished on the anterior and posterior walls of the stalk, but the state of preservation 
is often too unsatisfactory to allow of the certain identification of the stalk-vessels. 

A considerable number of stalks of C. sibogae end proximally in a single basal disc, 
one of which is shewn in vertical section in PI. VIII, fig. 94. The individuals thus connected 
have presumably arisen by budding from a single parent zooid. A similar arrangement is found 
in C. gracilis and is described below, in connexion with the buds (Section XVI). 



XI. ALIMENTARY CANAL. 

The alimentary canal of all the species of Cephalodiscus is constructed on essentially 
similar lines. Its general features may most easily be studied in sagittal sections (PI. IV). 

If the orientation which is adopted in this Report be correct, the whole of the outer 
outline of the 6''-shaped tube may be described as ventral, and the whole of the inner outline 
as dorsal. 

The size of the lumen of the several parts of the canal differs greatly in different 
individuals, the differences being due partly to age, and partly to the condition of mu.scular 
contraction of the body. One of the parts which shews the greatest variety of form is the 
mouth, the appearance of which is closely correlated with the attitude assumed by the proboscis. 

In C. dodecaloplms (fig. 42) the mouth (;«.) is indicated by a rather sudden thickening 
of the epithelium on both its dorsal and ventral sides, giving rise to distinct upper and lower 
lips. The upper Ifp («. /.) is continuous with the thin ventral epidermis of the proboscis-stalk, 
and it is in close relation with the posterior ventral horn of the anterior body-cavity. The lower 
lip passes into the inner epidermic layer of the operculum, a recess [pp. rec.) being left between 
that organ and the lip when the operculum occupies the position shewn in fig. 42. This recess 
may be a conspicuous feature of sections through the oral region of some the species. 

Immediately behind the upper lip is a conspicuous dorsal diverticulum (div.) of the 
pharynx [ph.). This diverticulum comes into close contact with the posterior end of the central 
nervous system {c. 71. s), and it forms a part of the division between the second and third body- 
cavities. From its anterior side originates the notochord («r//.), a tubular organ which probably 



54 

in all cases opens inlu the pharyngeal diverlicuhim, allhoiij^h llie actual connexion can only be 
demonstrated in a certain proportion of cases (fig. 42: PI. XIII, fig. 181). The pharynx (///.) 
is a large organ, the walls of which are usually a good deal folded, a condition probably due 
not t)nlv to the contraction of its own longitudinal muscles but also to that of the anterior 
longitudinal muscles of the body. The phar\nx passes into the oesophagus (oes.), which is well 
marked off from the pharynx, and opens into the middle of the anterior side of the large 
stomach (s/o///.), the walls of which are much folded. Near the junction of the stalk with the 
body, the stomach opens into a portion which may be called the second stomach {stom.'-), since 
the histology of its walls indicates that it has an important digestive function. The second 
stomach bends round the ventral wall of the stomach, from wliich it is separated by a ])art of 
the third body-cavity (^. r.'M). On the termination of this part of the coelom it passes int(j the 
intestine, which is closely apposed to the posterior wall of the stomach. The junction between 
the second stomach and the intestine may be conspicuously indicated by a fold in the wall, as 
shewn by M'Intosh (87) in his I'l. Ill, fig. 3. This fold is well marked in some of the more 
lateral sections of the series from which fig. 42 is taken, but it does not appear in the section 

figured. M'Intosh remarks (p. 17) that "this peculiar fold probably indicates a tendency to 

"the formation of a second or pyloric stomach, as in Phoronis, and is therefore of considerable 
" morphological significance". 

The dilated rectum (r.) is also partly attached to the stomach, on leaving which its 
dor.sal surface is exposed to the third l^ody-cavity. It opens to the exterior by the transversely 
elono-ated anus, which is not shewn in the figure. The walls of the intestine and rectum are 
thin and probably do not secrete digestive fluids. The size of the lumen of the rectum varies 
"■reatlv in different individuals. 

In C. levinseni (figs. 33, 34) the alimentary canal as a whole shares in the elongation 
of the l)ody as compared with C. dodecalopkus\ but the same parts may be recognized. The 
dorsal diverticulum of the pharynx comes into less extensive contact with the central nervous 
system. In old individuals (fig. 33) the stomach may be greatly elongated, while the intestine 
{int.) may pass continuously into ihe rectum (r.) without shewing the dilatation which usually 
marks the beginning of the latter. This dilatation may, however, be as well marked in C. 
levinseni as in the other species, as is apparent fr(;ni fig. 34 and from PI. I, fig. 6. It may be 
encjuired whether the difference between fig. 33 and fig. 34 is one of age or whether, on the 
contrary, it is not merely a difference in the state of muscular contraction. I regard the latter 
as the more probable explanation, particularly when the much greater antero-posterior diameter 
of fig. 34 is taken into account. If this be the case, the elongation of the body would appear 
to have the result of straightening out the rectum, the lobe which overlaps the stomach in 
fisf. i4 beine in fact the result of the contracted condition of the zooid. The elont^ation of 
fig. 33, as compared with fig. 34, has afi'ected all parts ot the alimentary canal to a greater 
or less extent. The oesophagus {pes^ is much drawn out, antl the antero-ventral caecum of the 
stomach seen in fig. 34 has been obliterated in fig. 33. I have observed two or three neuter 
individuals of C. sibogac shewing the same excessive elongation that is noticeable in i\'-^. 33; 
and it appears natural to regard these as the extended condition of the animal. It is probable 



55 

that the extension is effected by the attachment of the suctorial base of the stalk to the wall 
of the coenoecium, the animal then crawling on its buccal disc away from its fixed end. 

The second stomach of C. levinseni (figs. 33, 34, stonir) is more ^'^shaped than in 
C. dodecalopJms. But a comparison of these figures with fig. 42 (C. dodecalopJuis) will shew 
that there is no essential difference, in this respect, between the two species; and it is not 
impossible that a less contracted specimen of C. dodecalophus might have its second stomach 
more in the position which appears to be characteristic of C. levinseni. In the latter the second 
stomach forms a considerable portion of the bend of the fZ-shaped tube, being about equally 
developed on both sides of the actual bend. Examination of entire specimens (fig. 6) shews 
that the folds of the second stomach are arranged in a spiral line, and it might indeed be 
said that they constitute a spiral valve. The two limbs of the alimentary canal are, as usual, 
separated from one another by a part of the third body-cavity (<5. ^.'(5.), subdivided by a median 
partition (PI. XI, fig. 130, ines?~) which must be regarded as part of the dorsal mesentery. The 
cavity of the rectum is usually large, and commonly contains a large mass of faeces, in which 
the remains of Diatoms may be distinguished. In several of the specimens (as in the one shewn 
in fig. 34) a quantity of these faeces is passing out of the anus, which accordingly appears 
widely open. 

The alimentary canal of C. gracilis is shewn in fig. 37. The second stomach leaves 
the stomach at the end of its main axis, as in C. levinseni, and forms a wide cavity which 
extends on both sides of the bend of the alimentary canal. The third body-cavity passes, as 
usual, between the two limbs of the second stomach, but the space shewn in fig. 37 between 
the stomach and the intestine is not lined by peritoneum and is probably an artefact. 

My examination of the alimentary canal of C. sibogae (neuter forms) has been complicated 
by the unsatisfactory state of preservation of the material. Sections of the mass of zooids still 
contained in the basal coenoecium were not satisfactory; and it was very difficult to isolate 
zooids in an uninjured condition. My results indicate, however, a great elongation of the 
alimentary canal in the adult and uncontracted zooids. In fully extended specimens (fig. 38) 
the second stomach appears to pass off from the extreme ventral end of the elongated stomach, 
and the form of the entire canal is thus more simply ^/-shaped than in any of the other species. 
Fig. 40, taken from an entire specimen, shews a condition which is jjrobably due to contraction 
of the body, the bend of the canal being reflected towards the anterior side of the stomach 
In the uncontracted condition of this specimen it is probable that the position of the second 
stomach would have been as in fig. 38. 

The structure of the mouth and pharynx of Cephalodisctis require a somewhat detailed 
description, which may be preceded by one or two remarks on that of the remaining parts of 
the alimentary canal, and on the nature of the food. 

The structure of the oesophagus resembles that of the pharynx, of which it is indeed 
merely a division. But it is always to be recognised, in suitable preparations, and hence deserves 
a special name. It is probal)ly a sort of ante-chamber to the stomach, through which food 
pas.ses by definite swallowing actions when a sufficient quantity has accumulated in the pharynx. 



56 

Its walls are usually thinner at each of its lateral edjj^es than elsewhere (PI. XI, hg. 126), 
indicating the power of dilating and contracting in a definite way. Its posterior aperture commonly 
projects into the stomach in the manner shewn in figs. 34, 42 (I'l. IV'j. 

The stomach has high, glandular walls which are almost certainly pigmented. The 
epithelium is usuallv not well preserved. The shape of the cavity is complicated by numerous 
folds, which in entire zooids, both of C. dodecalophus and of C. levinseni, are seen to be arranged 
principally in the frontal direction. This may indicate that they arc partly due to the general 
contraction of the body-musculature. 

The second stomach, which opens from the main organ, has an ejjithelium which 
appears to be glandular, and is considerably higher than that of the succeeding part of the 
canal. It may be presumed that digestion is continued in this part. 

The intestine may be considered to Isegin at the point where the coelom which 
extends between the two limbs of the f '^shaped loop of the alimentary canal ends (figs. 34, 37). 
Its relatively thin walls pass continuously into the higher epithelium of the second stomach on 
the one hand and into those of the rectum on the other hand. The rectum is merely a 
part of the intestine, with which it is perfectly continuous, but the name may conveniently be 
employed for the last jjart of the alimentary canal, the dorsal wall of which is exposed to the 
third bodv-cavity. The size and shape of the rectum differ according to the state of contraction 
and the development of other organs. Thus in fig. 42 the small lumen seen in the rectum 
appears to be due to the specially large size of the ovary. 

The food of Cephalodiscus seems to consist principally of microscopic organisms. The 
cell-walls of Diatoms are found in various parts of the alimentary canal, with other detritus, 
among which Sponge-spicules can often be recognised. But in addition to the smaller particles, 
larger organisms are occasionally found. Thus a considerable jjart of the intestine and rectum 
of the individual of C. levinseni shewn in fig. 33 is occupied b\- an organism which seems to 
be a Copepod in a partially digested condition. I have found a similar case in a specimen of 
C. dodecalophus, while the individual of this species shewn in figs. 152 — 155 has in its stomach 
what appears to be a Polychaet, some of the long cirri of which are imbedded in the digestive 
epithelium. 1 am inclined to regard this as a case ol parasitism. 

Mouth, Pharynx and Xotochord. 

The stud\- of the commencement of the alimentary canal is of special importance in 
conne.xion with various physiological problems, and specially in the consideration of the probable 
mode of feeding. As in the case of several other parts of the animal, it is by no means easy 
to distinguish between temporary folds due to contraction and grooves or ridges which are 
permanent, and of morphological or physiological importance; while the varying positions assumed 
by the proboscis-stalk, the arms and the operculum introduce further difficulties in interpreting 
the structure of the mouth. 



57 

In the account which Masterman (98, 2, p. 507) has given of the mouth and pharynx, 
the food-orrooves of the arms are said to be continuous with certain gfrooves on the inner side 
of the wall of the pharynx. The grooves unite, two by two, so as to form a system of three 
lateral "oral grooves" which enter the mouth on each side (figs, i, 2) '. These proceed posteriorly 
and dorsally and finally form a large median dorsal hyperpharyngeal groove (figs. 4 — 9). The 
gill-slits are indicated as two ventro-lateral channels even in sections immediately behind the 
mouth (figs. 2, 3), while further back their walls are seen to be continuous dorsally with the 
"pleurochords", and to be formed of the same sort of tissue (fig. 8). The alimentary portion 
of the phar)'nx commences as a median ventral groove (fig. 4) between the two gill-pouches, 
and soon forms a large section of the pharynx lying ventrally to these structures (figs. 5 — 9). 
Figs. 90 — 92 shew that the dorsal diverticulum of the pharynx has 4 grooves, two dorsal and 
two ventral (or, as I prefer to call them, posterior and anterior, respectively), the section of 
the lumen being hence quadrangular. The four grooves are directly continuous with the lumen 
of the notochord (Masterman's "subneural gland"). The two "dorsal" grooves pass down the 
dorsal wall of the pharynx and are traceable as far as the commencement of the oesophagus, 
being situated on the median side of the pleurochordal outgrowths, in the region of those 
organs (figs. 93 — 99). The "ventral" grooves of the pharyngeal diverticulum pass down the 
sides of the mouth (fig. 93, v.g.)., ventrally to which they unite, in course of time, to form the 
large median alimentary part of the pharynx. This again can be traced to the beginning of the 
oesophagus ; and the lumen of the posterior end of the pharynx is thus triradiate in section 
(two dorsal grooves and one ventral groove). By the median union of the two "ventral" grooves 
of the pharyngeal diverticulum a " peri-pharyngeal band" is constituted. This, if I understand 
Mastermax correctly, is joined by the oral grooves on the anterior side of the pharyngeal 
diverticulum. 

Masterman recognises that the grrooves which he has described are too small to allow 
the supposition that the water-currents carrjang the food pass along them, and he has suggested 
that they direct the flow of a secretion of mucus by which the food-particles are entangled 
and are thus prevented from being washed out through the gill-slits. Here I think he is right, 
although he guards himself from expressing any very definite opinion as to the direction of the 
flow of mucus. The notochord is, however, regarded as a mucus-.secreting organ, while the 
pleurochords serve partly as a channel through which any excess of water which has passed to 
the posterior end of the pharynx travels forwards in order to issue at the gill-slits. This view 
is illustrated by Masterman's diagrammatic fig. 100. 

It is obvious from a consideration of the sagittal sections figured in Plate \\ that the 
relations of the mouth depend greatly on the position which the anterior end of the animal, and 
in particular the proboscis, happens to occup)-. Thus in C. levinseni, the pharyngeal diverticulum 
in fig. 33 has its opening directed towards the anterior side of the animal, while in fig. 34 it 
is directed ventrally. In the one case, a series of sections transverse to the long axis of the 



i) These references relate to the figures given in Plates I and V of Masterman's paper. Figs, i — 9 arc from a transverse 
series of the whole animal, passing therefore transversely through the beginning of the alimentary canal, and longitudinally through the 
main part of the pharynx. Figs. 90 — 99 are transverse to the long axis of the animal, and are therefore what I term "frontal". 
SIliOGA-lCXPEDlTIE XXVI to. S 



individual would have cut the upper lip before any part (jf the diverticulum was reached, and 
in the other, the first part to appear in the sections would have been the caecal end of the 
diverticulum (as in Masterman's figs. 90 — 92). The arrangement of the oral or pharyngeal 
grooves seen in the sections would thus have been very different in the two cases. Figs. 37 
and 43, of C. gracilis, illustrate the same point. On the other hand it is clear that in the case 
of an organ whose wails are so crumpled as is the pharynx in fig. 42, considerable care is 
necessary to distinguish the permanent folds from those which have no definite significance. 

In describing my own observations I begin with the consideration of a frontal series of 
sections of a comparatively young blastozooid of C. dodecaloplnis, in which the structure appears 
to be but little complicated by secondary folding. The first section figured (PI. XII, fig. 152) is 
dorsal to the mouth, and passes through the e.xternal aperture of the right oviduct, the dorsal 
diverticulum of the pharynx (div^ and the notochord (itch.). All the body-cavities are visible, 
the third cavity being .subdivided on each side by the ovarian mesentery {ov. )u.). On the left 
side, the section passes through the arm-base, just dorsally to the beginning of the operculum. 
( )n the right side, the lateral lobe of the operculum {op.}'.) is cut in the main parallel to its 
flat surfaces; and the tentacles of the third and fourth arms are visible. The donsal diverticulum 
of the pharyn.K is circular in section, its cavity being markedly triradiate. One of the grooves 
of the cavity is median and posterior, though shewing indications of being composed of 
Masterman's two "dorsal grooves", the other two are jjaired and on the anterior side. Each of 
the three ridges which separate the grooves from one another is marked by a deeply stained 
patch of cells which appear to be glandular. In more dorsally situated sections the glandular 
area is continuous round the anterior side of the diverticulum; while more ventrally, patches 
which stain in the same way and seem to be unicellular glands, appear here and there on the 
lower lip, at the sides of the mouth, and even in the oral epidermis of the operculum. 

In the next section but one (not figured) the base of the notochord is cut longitudinally 
(cf. PI. IV, fig. 42), its lumen being traceable into the outer part of the anterior ridge of the 
pharyngeal diverticulum. 

In fig. 153 (two sections later) the left lateral lobe of the operculum {op. I.) is cut 
horizontally, a fold (/.) of its bod\-wall marking off the .section of the collar-cavity whirli 
contains the collar-canal from the more externally j^laced operculum itself. The section passes 
just ventrally to the base of the notochord, which is of course not seen. The pharyngeal 
diverticulum has much the same structure as in the former figure, except for the fact that the 
dorsal walls of a pair of lateral outgrowths of its cavity are involved by the section. The 
posterior ends of these walls are composed of a tissue which stains but slightly, and they 
constitute the beginning of what Masterman (97, 2, p. 353, note) has described as the "pleuro- 
chords". I make use of this term for descriptive purposes without in any way accepting the 
homology indicated by Masterman in using it. 

Somewhat further ventrally (fig. 154) the lateral outgrowths open into the median part 
of the diverticulum, the pleurochordal tissue in their walls being sharpl\- marked. The three 
grooves seen in the lumen of the median part are present as before. 

^'i&- 155 cuts the donsal edge of the mouth; and the left anterior groove is seen to 



59 

open immediately behind an epithelial ridge (e. r.) which is visible in the former figures projecting 
from the anterior side of the arm-base into the space between the proboscis and the collar. 
The furrow on the median side of the ridge also opens into the mouth in the next section but 
one. A similar arrangement is indicated on the right side, except that the posterior groove is 
bifurcated at its internal end : the section being here at a slightly more dorsal level, the grooves 
do not appear to open into the mouth. The posterior median groove of the diverticulum is 
dying away, and the pleurochordal outgrowths are becoming larger. 

Fig. 156 cuts the mouth {tii.) and both the gill-slits {g.s.), the walls of the latter being 
mainly composed of pleurochordal tissue; while fig. 157 shews that the pleurochordal tissue is 
continued, in the walls of a pair of postero-lateral grooves of the pharynx, beyond the internal 
openings of the gill-slits. There can be no question that, in this specimen, the posterior groove 
of fig. 152 dies away between figs. 155 and 156, merging gradually into the surface of the 
convex epithelium of the posterior wall of the pharynx; and that it cannot be traced beyond 
the pleurochords, as indicated in Masterman's figs. 93 — 99. The median part of the operculum 
in this individual is hanging ventrally from the mouth as an apron-like flap covering part of 
the anterior surface of the body. 

Comparing these sections with the sagittal section, PI. IV, fig. 42, it appears that the 
two grooves on each side of the middle line, opening into the mouth in fig. 155, pass horizontally 
on one of the ventro-lateral sides of the upper lip to the ventral end of the anterior wall of 
the pharyngeal diverticulum ; and that they here meet the two vertical anterior grooves of that 
cavity. They are clearly the structures which Masterman (98, 2, p. 507) describes as the "oral 
grooves". These are seen passing along the sides of the mouth in figs. 2 — 5 given by that 
author, while fig. 6 cuts the anterior wall of the pharyngeal diverticulum (as is shewn by the 
position of the notochord), the oral grooves opening into that structure on either side of the 
median ridge, which is also shewn in my own fig. 152. Masterman's vfig. 7 accordingly passes 
through the middle of the pharyngeal diverticulum. 

The oral grooves are well seen in a plasticine reconstruction (fig. 24) which I made 
from a series of more or less transverse sections through an individual of C. levinsetii\ and in 
this case three oral grooves are distinctly indicated on each side. 

Although I am thus able to confirm this part of Masterman's results I do not find 
complete regularity in the arrangement of the oral grooves, which are not always symmetrical 
on either side of the -middle line (fig. 155). A transverse section across the upper lip of C. 
dodecalophus shews a consijicuous median ridge projecting into the mouth. This is derived in 
front from the ventral wall of the proboscis, and further back from the collar, as will be obvious 
by reference to fig. 42. On either side of the median ridge, there may be only a single lateral 
ridge, so that two principal grooves pass along each side of the lip, as shewn in fig. 155. 
The bifurcation of the lateral ridge may give rise to three grooves on one side. In fig. 24 
(C. levinseni) there may be two ridges on each side, in addition to the median ridge which 
projects from the proboscis-stalk; and three pairs of oral grooves are thus constituted. 

Even when I have found three oral grooves, on each side, I have not succeeded in 



6o 

shewiiiij: the continuity which Masterman describes between each one of them and two of the 
arms. On the contrary, the arm-j^rooves, in man)' favourably orientated specimens, die away in 
approaching the mouth, and tht- inner surface of the arm-base becomes smoothly convex in 
places where grooves ought to occur on Mastermax's hypothesis. This is seen, for instance, 
in figs. 143—147 a'l- XII), figs. 66, 65 (PI. VI) and figs. 47—45 (PI. V). 

In order to obtain as much certainty as possible with regard to the relations of the 
oral grooves, I made plasticine reconstructions of two individuals of C. gracilis, namely those 
from which fig. 25 and figs. 62 — 70 were respectively drawn. 1 failed in these to find any 
evidence of continuity between the oral grooves and the food-grooves of the arms. 

It may further be remarked that it is improbable, on a priori grounds, that a system of 
small grooves could be effective in all the parts where they have been described by Master.man, 
who has himself (98, 2, p. 509) seen the difficulty of supposing that they could direct the flow of water. 

I come next to the pair of "ventral grooves" described by Masterman (98, 2), and 
marked v.g. in his fig. 93. These grooves, which are supposed to start as the "ventral" or 
anterior grooves of the pharyngeal diverticulum, jjass down the sides of the mouth, just inside 
the oral aperture, and can then be recognised "by the fact lliat they are situated exactly internal 
"to the line of junction of the mesentery between collar- and trunk-cavities, with the gut wall". 
They are thus shewn in M.\sterman's fig. 93, though not on the left side of fig. 16 of his 
earlier paper (97, 2), to which a reference is expressly given. In this latter figure, the left 
groove lies entirely in the region of the collar-cavity. 

The series of sections from which figs. 152 — 157 are taken shews the "ventral" grooves 
in an unmistakeable form in the pharyngeal diverticulum (figs. 152, 153); but on pa.ssing to 
the mouth they communicate with the oral grooves (figs. 154, 155), and no trace can be seen 
of them in fig. 156, which passes through the mouth. I am satisfied that the grooves are really 
absent in this section, but the discrepancy between Masterman's results and my own is ncjt 
hard to explain. The parts of the "ventral grooves" which Masterman shews at the sides of 
the moutli appear to me to be outside the mouth, and to belong to the recess (PI. I\', 
figs. 34, 42, op.rec), external to the oral a]jerture, which is formed by the base of the operculum. 
The recess may altogether disappear when the operculum is straightened out and its free edge 
is directed ventrally, as in figs. 156, 157, but it becomes conspicuous in certain other positions 
of the operculum. 

Figs. 119 — 123 (PI. X) are frontal sections of C. levinseni which shew what I think 
there can be no doubt are the parts of Masterman's "ventral grooves" that are supposed to 
e.xtend along the sides of the mouth. In fig. 123, the groove on the right side is continuous 
with a part of the basement-membrane extending, from the anterior horn of the third body- 
cavity (d.c.^a.), between the collar-cavity {/>.c.') and what may be an oral vascular sinus {or.s.). 
On the left side, the wall of the groove projects into the collar-cavity. These are so much like 
the relations shewn by Masterman in fig. 16 of his earlier memoir (97, 2) that there can be no 
reasonable doubt that the grooves are the ones allu^i^d to by him. lint a further consideration 
of figs. 119 — 123 and of the other sections belonging to the same series shews that the two 
"ventral grooves" represent the junction of the base of the operculum with the mouth, and that 



6i 

in this position of the operculum there is an epidermic recess {op. rcc.) which opens into the 
pharynx by the mouth («/.). I am thus inclined to believe that the mouth in fig. 93 of 
Masterman's later memoir (98, 2) is the aperture immediately internal to the "ventral grooves". 

The epidermic recess which I describe is not in any way continuous with the ventral 
groove of the pharynx, but it comes to an end, as it began, on the outer side of the mouth, 
ceasing to be visible in the sections immediately after the mouth is passed. This indeed might 
be anticipated from the sagittal sections shewn in Plate IV. 

The extra-oral "ventral grooves" are seen, in C. gracilis^ in the sections shewn in 
figs. 66, 6; (PI. \T). In the case of this individual I have made a plasticine reconstruction from 
the actual sections ; and there can be no question, from the examination of this reconstruction, 
that the grooves are merely the junction of the operculum with the rest of. the body, and that 
they have no relation to any grooves of the pharjnx itself. 

In fig. 3 of Masterman's memoir a depression on each side of the ventral wall of the 
pharynx, immediately adjacent to the mouth, is identified as the beginning of a gill-slit. I do 
not understand how the gill-slit is supposed to occur in this position. An inspection of figs. 
152 — 157 (PI. XII) will shew that the first indication of the gill-slit appears in connexion with 
the dorsal side of the pharynx, as indeed Masterman has himself pointed out, in insisting on 
the close connexion between pleurochords and gill-slits. In fig. 153 the dorsal ends of the 
pleurochords are seen as vacuolated tracts of the lateral pharyngeal epithelium, and distinctly 
on its dorsal or posterior side. The exact point at which these will open into the diverticulum 
is indicated in this section by a pair of minute depressions of the epithelium which are somewhat 
nearer the posterior than the anterior wall of the cavity. In fig. 154 the pleurochordal grooves 
are well established, while on the right side of fig. 155 the anterior end of the groove is 
recognisable as the dorsal wall of the gill-slit. In fig. 156 both gill-slits are completely formed, 
while in fig. 157 the vacuolated tissue of the pleurochords extends along the sides of the 
pharynx, beyond the points where the gill-slits have been given off. The tissue gradually fades 
away in passing along the sides of the pharynx, and it disappears completely some time before 
the oesophagus is reached. 

With the exception of the point I have indicated with regard to the origin of the gill-slits, 
all this is completely in accordance with Masterman's accounts of the pleurochords (97, 2, 98, 2). 

The close relation between the gill-slits and the dorso-lateral or pleurochordal grooves 
of the pharynx is shewn in the reconstruction of C. levmseiii drawn in fig. 24 (PI. III). The 
cavity of the pharynx is exposed by the removal of its anterior or ventral half, the whole of 
the upper lip and of the pharyngeal diverticulum being left. In the lower part of the figure is 
seen the posterior or dorsal wall of the pharynx, with a strongly convex surface, on either side 
of which are the two pleurochordal grooves. These become much deeper in passing forwards 
and they finally pass into the sides of the pharyngeal diverticulum, from which tlie tubes leading 
to the gill-pores open. In the dorsal view of the same specimen (fig. 23) the wall of the left 
gill-slit is seen curving outwards from the region of the diverticulum to open by its external 
aperture. The same relations are illustrated by figs. i2i — 123 (PI. X). In fig. ^23, the dorsal 
wall of the pharynx is convex towards the lumen of that organ, and on either side of it is one 



of the durso-lateral pleurochordal grooves, continuous on the one hand with the gill-slit, and on 
the other hand extending towards the pharyngeal diverticulum (figs. 122, 121). Fig. 129 (PI. XI), 
of the same species, illustrates the same point. Figs. 45 — 47 (PI. V), of C. gracilis, further 
.shew that the gill-slits curve from the region of the pharyngeal diverticulum in an antero-ventral 
direction to their external apertures. 

The gill-slits of the neuter individuals of C. sibogae are essentially similar to those of 
the other species, but they are associated with an unusually strong development of pleurochordal 
tissue in the more posterior („ventral") part of the pharynx. 

The probable mode of action of tbe arrangements which have just been described may 
now be considered. I am (juite inclined to accept M.\sterman's view that an essential part of 
the feeding mechanism of Ccp/iaiodiscns is afforded by a secretion of mucus which entangles 
the ortranisms brought by the ciliary currents of the tentacles, and prevents them from being 
carried out through the gill-slits. It may be presumed that a current of considerable force passes 
through these apertures; and the need for some entangling mechanism seems probable. I am 
disposed to think tliat the mucus required by this hypothesis is secreted by the glandular 
patches shewn in figs. 152 — 154 (PI. XII) in the walls of the dorsal jjharyngeal diverticulum, and 
by unicellular glands in the walls of the mouth and on the base of the operculum. M.\sterm.\n 
ascribes the secretion to the notochord, which he terms the "subneural gland"; but it must be 
noted that whereas the structures which I regard as mucus-glands shew a strong affinity for 
haematoxylin, the notochord on the contrary takes ii|i staining matter to a slight e.xtent. 

If this be the case, the anterior grooves seen in the pharyngeal diverticulum (figs. 152, 
153) may be supposed to convey the mucus towards the mouth. Here it probably passes along 
the oral grooves to the great food-channels limited b)- the po.sterior wall of the proboscis and 
the anterior wall of the collar. There are not wanting indications that arrangements exist which 
might be capable of directing the mucus for a short distance along paths e.Kternal to the mouth, 
perhaps during a temporary cessation of the ciliary current of the tentacles. Figs. 152 — 155 
shew a perfectly definite epithelial ridge {e.r.) which is continuous with the ridge dividing the 
two principal oral grooves on each .side, and can be traced for some distance along each side 
of the proboscis-stalk. It is ])rol)abU: that this ridge corresponds with the division of the arms 
of its side into two groups of three. Traced in a dorsal direction, the ridge becomes a groove 
at exacdy the level where the arm-base meets the operculum. This transformation is effected 
by the appearance of another epithelial ridge on the median side of the first one, a process 
which has already been effected in fig. 152 on the right side, where e. r. is the ridge that is 
continuous with those seen in figs. 153 — 155. The higher ridge immediately in front of it passes 
some distance along the proboscis-stalk, dying away at the level of the proboscis-pores. 

It appears to me probable that the effect of this arrangement is as follows. The mucus 
leaving the mouth by the outer oral grooves seen in fig. 155 probably passes along the oral 
surface of the operculum and scjon comes into the region of the j)osteriorly directed food-grooves 
of arms 4 — 6. Immediately on the dorsal side of fig. 152 the ridge c.r. becomes continuous 
wMth the ventral side of the arm-base, which is traversed in an antero-posterior direction ])y the 



63 



groove marked -A*. 4 — 6 in rtg. [52. This groove, which is of course open ventrally, may be 
no more than a temporary fold of the arm-base, but it indicates the path which the food- 
particles must take in passing from arms 4 — 6 along the ventral side of the arm-base to the 
food-passage which is bounded in front b\' the posterior wall of the proboscis. It thus appears 
that mucus passing along the anterior face of the operculum in figs. 155 — 152 would be brought 
into relation with the food-grooves of the posterior set of arms. The mucus leaving the mouth 
by the more median oral groove in fig. 155 would for the most part remain on the same 
side of the epithelial ridge c. r. (figs. 154 — 152), while the additional ridge seen between e.r. 
and the proboscis on the right side of fig. 152 would keep the mucus from passing further 
along the dorsal wall of the proboscis; and would, on the contrary, direct it to the region of 
the food-grooves of the first three arms. 

The mucus which passes down the posterior wall of the pharyngeal diverticulum, whether 
in one or two grooves, might spread itself out on the dorsal wall of the phar)-n.x, where it 
would be well placed to entangle food when the pharyngeal diverticulum had the position seen 

in figs. 33, 37 (PI- 1^0- 

Some at least of the food, entangled in the mucous secretion, is probably caught by the 
operculum and passes to the bottom of the opercular recess {op. rec.) indicated in figs. 34, 42. 
Here I imagine it to accumulate and from time to time to be taken into the pharynx by a 
definite swallowing action, due probably to the intrinsic muscles of the operculum (cf. PI. IX, 
fig. 107). It then probably passes down the more median parts of the pharynx, along the deeply 
staining and almost certainly ciliated cells which constitute both its anterior and posterior wall. 
I think that Masterman is probably right in suggesting that the relation of the gill-slits to the 
pleurochordal grooves is to be explained by supposing that the exce.ss of water which passes 
to the oesophageal end of the pharynx travels forwards along the grooves to issue by the gill- 
slits. The relation of the grooves to the pharyngeal diverticulum further suggests that this return 
current of water, entering the diverticulum from behind, would also have the effect of carrj'ing 
tlie mucus forwards along the grooves of the upper lip to the point where it meets the inrush 
of water caused by the ciliary action of the tentacles. Finally it appears to me possible, from. 
a consideration of such preparations as figs. 123 — 125 (PI. X) that the lumen of the pharynx 
is not necessarily widely open during the whole process of feeding. It seems possible that the 
anterior and posterior walls of the pharynx may be apposed to one another in such a way as 
to close the cavity. This might happen during the accumulation of food in the opercular recess, 
the water meanwhile passing directly to the exterior b)- the gill-slits. 

As actual evidence of the existence of mucus in connexion with the feeding process it 
may be remarked that M'Intosh (87, p. 16) in describing the structure of the pharynx states 
that in some preparations a film occurs on the surface of the epithelium which "is evidently 
due to mucus". I have observed appearances in sections of C. dodecalophus which point in the 
same direction, the film in question occurring not only along the free ends of the epithelial cells 
of the pharyngeal diverticulum, but also along those of the cells of the anterior and posterior 
walls of the pharynx, throughout the whole length of that organ, and even on those parts of 
the operculum and proboscis which are near the entrance to the alimentary canal. 



64 

The pharyngeal epithelium of Ceplialodiscus closely resembles in structure the epidermis 
of the oral side of the operculum, with which it is continuous through the nmuth. It is composed, 
for the most part, of deeply staining cells, with numerous nuclei in man\- layers. These probably 
indicate a columnar epithelium composed of very long and narrow cells. Clear evidence of 
ciliation is noticed in various preparations, and it is probable that the whole of the epithelium 
which has this character is ciliated. The remainder of the pharyngeal epithelium consists of the 
dorso-lateral regions which Masterman has termed the "pleurochords", and of the walls of the 
ti-ill-slits with which these are continuous. The epithelium is here vacuolated, and takes up staining 
materials with much less readiness than the other part, the nuclei being much less numerous. 

The differentiation of the pleurochords is of course well marked in C. dodecalophus^ and 
it is also particularly evident in the neuters of C. sibogae. In this case the distinction between 
the deeply staining epithelium of most of the pharynx and the slightly stained pleurochords is 
very marked. The species seems to be further remarkable for possessing an unusually distinct 
hypopharyngeal groove (PI. VIII, figs. 90—92). It is difficult to speak w'ith certainty as to the 
reality of a distinction, in this respect, between the species, as the condition of the pharynx 
differs so w'idelv, in different individuals of the same species, in different degrees of contraction. 
Thus C. dodecalophtis may have a very well marked median ventral groove, while in fig. 157, 
for instance, nothing of the kind is visible. In C. lcvi)iscni the ]jharynx is usually found flattened 
in an antero-posterior direction. 

N o t och o r d. 

I use this term as indicating the homology of this organ with the structure in Balano- 
glossus called by that name by Bai-eson (84, p. 228; 86, pp. 550, 562) and compared by iiim 
with the notochord of Chordata. Whether the latter homology holds good is an open question, 
but I think there can be no doui)t that the "notochord" of Cephalodiscus is the homologue of 
the "notochord" of Balanogflossus. The organ has been termed the "Eicheldarm" bv Spengel 
(in Balanoglossus), the "stomochord" by Willev (99, 1, p. 234; 99, 2, p. 224) and the "sub- 
neural gland" by Mastermax (97, 2, p. 351). 

The notochord of Cephalodiscus is a tubular ') structure which ]M-(jbably always opens 
into the anterior wall of the dorsal diverticulum of ihc pharynx (fig. i on p. 23), although the 
opening is not as a rule easy to demonstrate. The organ lies in septum ' .,, on the dorsal .side 
of that ])art of the anterior body-cavil\- which lies in the- pn^boscis-stalk (PI. I\', figs. 33, 34, 
42; PI. XIII, fig. 181 ; PI. X, figs. 113 — 117) and on the ventral side of the two collar-cavities. 
The dorsal mesentery of the collar supports the notochord along its whole length ; and, as is 
well shewn in Masterman's figures (03, PI. XXXII, figs, i, 2), the length of the mesentery 
becomes less as it passes forwards, so that at its ape.x the notochord almost reaches the central 
nervous sy.stem. At its anterior end the notochord is intimately connected with the pericardium 
(PI. IV, fig. 33; PI. XIII, fig. 181 ; PI. XI, fig. 138) to which its relations are the same as 
those found in Balanoglossus. The resemblance to this animal is further increased by the presence 
of a glomerulus (see p. 29) on the ventral side of the notochord. 



l) SCHEPOTIEIF (04, p. 15) denies the tubular chaiacler. 



Mastermax (97, 2, p. 351) states that the cells of the notochord of C. dodecalophus are 
ciliated internally, and that it may contain in its lumen a rod of mucus. In a later memoir 
(03, p. 718) he describes a vacuolated or "chordoid" appearance at the anterior end of the 
organ. I have observed a stained appearance in the lumen of the notochord in this .species 
which may indicate the presence of mucus, but I feel e.\tremely doubtful with regard to the 
existence of cilia, and I am not convinced that there is sufficient justification for speaking of a 
chordoid modification of the tip of the organ. 

The large relative size of the notochord in the buds of C. dodecalophus (PI. XIII, fig. 
173) — a fact already noticed by M'Intosh (87, p. 28) is of considerable interest as indicating 
the morphological importance of this structure. It is further noteworthy that the organ is specially 
large in the buds of Rhabdopleura^ as appears from the observations of Fowler (04, PL III, 
fig. 15). In the adult condition it retains its greatest relative size in C. levinseni (figs. 33, 23, 
24, 113) where its tubular nature is specially obvious. In the more delicate C. gracilis (figs. 
44, 64) and C. sibogae (PI. VIII, fig. 93) the notochord is small; and in unfavourably orientated 
sections it is not always easy to demonstrate its existence. There is no doubt, however, of its 
presence in all the species which I have investigated, and it may be detected even in the males 
of C. sibogae (PI. VIII, figs. 82, 83). 

The homology of the notochord of Cephalodiscus with that of the Enteropneusta was 
at one time denied by Masterman (97, 2, p. 35 1; 97, 3), who has, however, more recently 
(99, 2, p. 362) admitted that it corresponds with the "vermiform process" of certain Entero- 
pneusta. WiLLEY (99, I, p. 237) had shortly before maintained the same view. 

It appears to me that it is unnecessary to suppose that the notochord of Cephalodiscus 
corresponds merely with the vermiform process. It is true that on a former occasion (97, p. 343) 
I pointed out, in answer to Masterman's statement that the notochord of Cephalodiscus 
differs histologically from that of "every other notochord yet described", that it did not differ 
histologically from the anterior part of the notochord of Schizocardium and Glandiceps known, 
frf)m Spengel's description, as the vermiform process. But I also called attention to the small 
size of Cephalodiscus^ a fact which might be expected to be correlated with some simplification 
of the organs as compared with those of the Enteropneusta. The relation of the notochord of 
Cephalodisctis to the pericardium and to the proboscis-pores appears to me to lend no sujjport 
to the view of Willey and Masterman that the organ corresponds with the vermiform process 
alone. The process in question, as figured by Spengel (93, PL XII, fig. 2 and PL XX, fig. i), 
lies entirel)- in front of the region of the pericardium and of the proboscis-pores, while the 
notochord of Cephalodiscus extends no further forward than this region. As moreover, the base 
of the notochord agrees, in its relation to the upper lip and to the ventral part of the anterior 
body-cavity, with the base of the "Eicheldarm" in the Enteropneusta, it seems to me reasonable 
to .suppose that the notochord of Cephalodiscus corre.sponds with the entire "Eicheldarm", and 
not with the narrow anterior portion of it whose occurrence is limited to a small proportion 
of the species of Enteropneusta. 



SIHOG.\-EXPEDITIE XXVI to. 



66 



Xll. MUSCULAR SYSTEM. 

The strong development of the muscles in Cephalodiscus indicates a great amount of 
contractility. The .system consists almost entirely of longitudinal fibres, which pass from the 
stalk to the proboscis, interrupted b\- tlie two transverse septa of the body-cavity. The more 
important muscles of the metasome pass along the anterior surface of the body-wall, in correlation 
with the origin of the stalk from this surface. The strongest muscles of the collar pass right 
and left of the mouth, while those of the proboscis diverge from septum '4 and after traversing 
the anterior body-cavity are mainly inserted into its anterior wall. The muscular fibres probably 
originate and are inserted into some part of the basement-membrane which lines the body-cavity, 
important groups of the muscles ending in the transverse septa. 

The muscles of the stalk have already been described (p. 51). Tracing these forwards, 
it will be found that at the junction of the stalk and body (PI. XI, figs. 132, 128, 127, 126) 
the closed circle, or rather double crescent, of the stalk-muscles opens out on its posterior side, 
and the two ends of the series of muscles become reflected on to the anterior wall of the body. 
The muscle-fibres are still invested by an amount of connective tissue varying with the species, 
and the ventral mesentery of the metasome fades away in this mass of connective tissue. In 
passing into the body the muscular layer soon spreads along the adjacent parts of the bod\-- 
wall (PI. X, fig. 125; PI. XII, fig. 157), thereby distributing the stress exerted by the contraction 
of the stalk-muscles. Most of the fibres pass in the direction of the mouth, along the anterior 
wall of the body. Some of them, however, pass in the opposite direction (figs. 51, 52) along 
the wall of the caecal prolongation of the metasome which contains the loop of the alimentary 
canal. Immediately on the dorsal .side of the attachment of the stalk (fig. 126) the muscular 
layer is thick, and is not much broader than the diameter of the stalk. In passing dorsally 
(fig. 125) the layer broadens out so as to extend along at least a third of the circumference 
of the frontal section. The layer becomes considerably weaker as it approaches the collar, 
no doubt owing to the fact that some of the fibres successively insert themselves into the 
basement-membrane of the body-wall of the metasome. In C. dodecalophns in particular it is 
very obvious that the basement-membrane which lines the third body-cavity is specially thick 
in the region of this muscular layer. 

When the dwindled remains of the muscles have arrived near the gill-slits (PI. VI, fig. 69; 
PI. XII, fig. 157) most of the fibres are left on the part of the body-wall which is anterior to 
the position of the external gill-pores, though a few of them pass behind these apertures. With 
the commencement of the collar-region (which in frontal sections is first seen on the ventral 
side of the mouth) the two coelomic sacs cease to constitute a median mesentery, and become 
widely separated from one another {^x'g. 124). They are then found as two triangular cavities, 
nearly filled with longitudinal muscle-fibres, and occupying a position immediately anterior to 
the gill-slits (figs. 68, 123, 156, d.c:''a.). We are in fact dealing with two antero-ventral horns 
of the third body-cavity which extend forwards into the collar-region, in much the same way 
that the dorsal perihaemal cavities extend into the collar in Balanoglossus. The ventral horns 



pass forwards as far as the region of the collar-canals (PI. IV, fig. 41 ; PI. VIII, fig. 93), and 
the last of the body-muscles are inserted into the septa which divide the ventral horns from the 
collar-cavity. I think there can be little doubt that none of the fibres traverse the septum ; and 
indeed it may be stated that the longitudinal muscles in each of the segments of Cephalodiscus 
are restricted to that segment, just as the longitudinal muscles of A.mphipxus or of a Fish are 
divided into myomeres by the mjotomes or mj'ocommata. 

From the anterior border of septum -/;(, in the immediate neighbourhood of the termination 
of the metasomatic muscles, originate the principal longitudinal muscles of the collar. These 
consist of a pair of strong bundles of fibres, the oral muscles (PI. VIII, fig. 93; PI. X, figs. 
122 — 117, 01'. III.), which start from the region of the collar-canals, traversing the collar-cavity 
on either side of the mouth, and ending, to some extent at least, in septum '/31 opposite the 
origin of the radiating muscles which pass through the cavity of the proboscis. I point out 
below that these muscles are joined by fibres which have a different origin. 

The arms themselves have a pair of longitudinal muscles, running along the basement- 
membrane of their morphologically inner side ; that is to say, along the side of the arm-grooves ; 
and a pair of weaker longitudinal muscles extending along their outer side (PI. XII, fig. 141). 

The principal muscles of the proboscis form two strong groups of fibres which diverge 
from the thick membrane which forms septum '/j, and are inserted largely into the basement- 
membrane of the anterior wall of the proboscis (PI. XII, figs. 147 — 153, PI. XI, figs. 137 — 139). 
These have already been described by M'Intosh (87) and Masterman (97, 2), both of whom 
have suggested that they enable the proboscis to be used as a sucker. 

It will thus be seen that there is a functional continuity between the stalk-muscles and 
the longitudinal muscles of the anterior end of the animal. The contraction of this svstem will 
not only shorten the stalk (as is indicated by the numerous transverse wrinkles into which its 
wall is commonly thrown), but will also shorten the body, the collar as a w^hole, and its arms 
individually, and will retract the anterior body-wall of the proboscis. This general contraction 
is presumably associated with an attachment of the sucker-like base of the stalk to the wall 
of the coenoecium. The contractions are no doubt of importance, not only in the movements 
of the entire animal, but also of its separate parts. The movement of the proboscis, for instance, 
whether in crawling or in tube-building, must be largely controlled by the muscles which traverse 
its body-cavity. 

The first two segments of Cephalodiscus probably have a mechanism similar to that 
of the tube-feet of an Echinoderm, contraction being effected by longitudinal muscles, and 
expansion by fluid pressure of its contents. It is impossible to avoid being struck by the fact 
that two of the principal sets of longitudinal muscles, namely those of the metasome and those 
of the collar, terminate in close connexion with the collar-canals. The probable action of these 
muscles on the collar-canals has been considered in describing those organs (p. 43). 

The remainder of the muscles of Cephalodiscus appear to be associated with the coelomic 
epithelium, either of the body-wall or of the alimentary canal. The proboscis of C. dodecalophus 
is provided with a well developed layer of muscular fibres on its posterior wall (Fig. 151), the 
direction of which appears to differ according to the part of the proboscis which is e.xamined. 



68 

Some of these fibres may be seen to leave the posterior wall from place to place, and to pass 
across the body-cavity to the anterior wall, where they are inserted into the basement-membrane. 
It appears to me that these muscles really form part of the system of radiating muscles which 
have already been noticed. The system originates from sejjtum '/j, and while some of the 
fibres pass directly across the body-cavity to the opposite wall, others apply themselves closely 
to the posterior wall, along which they run for a certain distance, the fibres detaching themselves 
one by one and crossing the body-cavity to reach the anterior wall. The muscles under 
consideration accordingly radiate in all directions from the proboscis-stalk. Thus in a sagittal 
section of the probo.scis pas.sing at some distance from the median plane, the fibres near the 
middle of the posterior wall might be expected to be cut transversely, while they should become 
more and more oblique in approaching the two ends of the section. This appears to me to 
correspond with observed facts. I do not think that the anterior wall of the proboscis has any 
musculature independent of the fibres which reach it horn the posterior wall. 

The study of the buds (cf. PI. XIII, figs. 176, 179, 181) seems to indicate that the 
morphologically anterior end of the probo.scis is somewhere near the middle of the thick glandular 
epidermis of what I have termed the anterior side. If this he the case, the flattening of the organ 
is in an antero-po.sterior direction, and the radiating muscles may be described, in morphological 
terms, as a system of longitudinal muscles originating in the posterior half of the proboscis, 
and inserted into its anterior wall. 

The collar is traversed, in most of its pans, by numerous fine fibrils, running as a rule 
perpendicularly across the body-cavity from one epithelium to the other. Each fibril is obviously 
nucleated at about the middle of its course (fig. 151). These fibrils are abundant in the operculum 
and along the whole length of the arms, e.xcept in the swollen tips which are characteristic of 
C. dodecalopkus. It appears to me probable that they are contractile, and that the}- are responsible 
for most of the local alterations of fluid pressure which are so ini])ortant for the effective working 
of the entire collar-.system. 

In addition to these fibrils, the collar contains numerous more definite muscle-fibres which 
form part of its body-wall. The principal group is constituted by the strong oral muscles. These 
have been partially described above, in discussing the functions they appear to perform in the 
movements of the collar-canals and in continuing the line of action of the body-musculature as 
far as the base of the proboscis. They are mentioned by M.\.sri.RM.\N (97, 2, p. 353, PI. XXV, 
fig- 'S) who states that in the mesodermic sheath of the pleurochords originate strong muscular 
bands which are inserted into septum '/- opposite the origin of the radiating muscles of the 
probo.scis. This, I think, is only part of the truth, the real facts being that the muscular band 
in question (on each side) is constituted by factors derived from various parts of the coelomic 
wall; and that while some of the fibres orisfinate from the basement-membrane coveringf the 
mouth or pharynx, others start from septum -/:, and others again from the body-wall. Moreover 
it appears to me that the fibres which originate from the wall of the alimentary canal do not 
start from the pleurochords, but from a part of the basemenl-nu-mbrane which covers the ordinary 
epithelium lining the mouth and the commencement of the pharynx. 

r^'to- 93 (^""l- \TH) is a more or le.ss .sagittal section ])assing through one side of a neuter 



69 

zooid of C. sibogae, and it shews the greater part of the course of one of these muscles. The 
metasomatic musculature (/;/^-.) is cut tangentially, and is seen to pass into the septum between 
the second and third body-cavities ^). From the anterior side of this septum, in the immediate 
neighbourhood of the gill-slit [g. s.) and of the collar-canal [c. c.) starts the oral muscle (or. m.), 
which passes through the collar-cavity as far as septum Vs, i'lto which some of its fibres appear 
to be inserted. The muscle receives, however, an important contribution of fibres from the oral 
side of the lower lip or operculum. 

Fig. 107 (PI. IX) is a part of a transverse section of C. levinseni which is favourably 
orientated for the study of part of the origin of the oral muscle. The section passes through 
the ventral side of the collar and metasome in such a way as to expose the surface of the 
basement-membrane [p. in.) belonging to the oral epidermis of the operculum, which is directed 
towards the proboscis. The section will be understood by referring to fig. 123, the bilobed 
portion of basement-membrane marked d. m. being that of the anterior wall of the epidermic 
recess at the base of the operculum. The muscle-fibres start from the ventral collar-mesentery 
and pass in a transverse direction across the wall of this recess, and in the same direction 
across the wall of the mouth (at the level ;;/.), below the end of the recess. It may be noted, 
however, that the transverse fibres and the oblique fibres which are found on the anterior wall 
of septum -/.; are parts of a continuous layer. In suitably stained frontal sections similar to 
PI. XII, fig. 156, the constituents of the oral muscle may be seen, cut transversely, in the 
angle of the collar-cavity on each side of the mouth, some in contact with the wall of the 
anterior horn of the thii'd body-cavity and some in contact with the epithelium lining the mouth 
or with that of the oral surface of the operculum. Here they are continuous with the layer 
(not shewn in figs. 153 — 156) which occurs along the whole of the base of the epidermis of 
both surfaces of the operculum, and they are in fact merely a specialised part of this layer. 
Traced towards the dorsal surface (Figs. 154, 153) the oral muscle becomes more definite. In 
fig. 151, it is seen in sagittal section receiving fibres from the oral wall of the operculum, 
while in adjacent sections of the same specimen it receives other contributions from the basement- 
membrane covering the anterior wall of the mouth or of the commencement of the pharyn.x "). 

The constitution of the oral muscle is thus complicated. It may be regarded as the 
principal muscular pillar of the proboscis, but its base is spread over a wide area, and some 
of its fibres probably act as an oral sphincter. The transverse cour.se of the fibres on the ventral 
part of the operculum is doubtless of considerable functional importance if, as seems not 
improbable, particles of- food pass into the opercular recess below the mouth before they are 
swallowed. The transverse course of the muscles here situated probably enables the opercular 
recess to empty itself by a sort of gulping action into the mouth. 

It is difficult to arrive at complete certainty with regard to the course of the muscle- 
fibres in the operculum. In some parts, the fibres may be cut transversely in a sagittal section, 
while in others their course is more oblique. In the projecting lateral lobe of the operculum 



1) It would haidly be possible from this section to prove that the septum dividcil the muscles of the two cavities; but the 
evidence of other specimens seems to me clear on this point. 

2) It is not easy to say where the mouth ends and the pharynx begins. 



70 

the fibres of the oral surface run parallel to the free edge (fig. 148), while those of the outer 
wall cross them at right angles. The e.xplanation of the course of the opercular muscles seems 
to me, however, much the same as that given for the proboscis; namely that the muscles are 
really a system of fibres which radiate out from the centre of the collar, the course of the 
fibres being differently modified on the two surfaces. 

Thus the fibres of the oral side of the operculum sweep round the free border of the 
lateral lobe in a direction parallel to its free edge (fig. 148), while those of the aboral surface 
pass transversely outwards along the same region (fig. 149), and thus cross the other fibres 
at right angles. The extreme mobility of the operculum, of which there is excellent evidence in 
the varying positions assumed by this organ in preserved specimens, is doubtless due to the 
complicated course of the fibres of the musculature of its body-wall. 

In accordance with wliat has already been said in a previous Section (p. 30) with regard 
to the morphologA' of the collar, both the operculum and the arms may be considered to be 
modifications of the free anterior edge of that region. The musculature of the arms is thus 
probably to be regarded as longitudinal. I am inclined to think that that of the operculum has 
really the same morphological direction, and that the actual course is the result of modifications 
of a longitudinal layer radiating out into what is i>ractically a funnel-shaped edge formed by 
the arm-bases and the operculum. It is indeed not easy to explain the circularly disposed muscles 
seen in fig. 107 as longitudinal, since they appear to be in the line of the transverse circumference 
of the collar; but it must specially be noted that they seem to form j)art of the system of fibres 
seen on septum "/;(. The main parts of the oral muscles again appear tc; have a circular or 
transverse direction, but their longitudinal character is perhaps indicated by the fact that some 
of their fibres pass from septum 'l-^ through the collar-cavit)- to septum '/o. In spite of these 
difficulties of interpretation, I am inclined to take the view, although with a good deal of 
hesitation, that the system of collar-muscles of Cephalodiscus is morphologically longitudinal. 
Some of the fibres can hardly be explained in an\- other wa\-, and moreover I have been unable 
to obtain evidence that more than one layer is present at an\- point. It may thus possibly be 
the case that the entire somatic muscular system of Cephalodisctis is longitudinal. 

In the arm-bases, there is a considerable development of muscular fibres in connexion 
with both the anterior and the posterior wall, although all the fibres are probably morphologically 
loneitudinal. There is clear evidence that numerous fibres run across the coelom from one wall 
to the other, as represented in figs. 147 — 149. These fibres have definitely the character of 
muscle-fibres, as judged by their staining properties, and they appear to differ histologically 
from the delicate nucleated filaments which cross the cavity of the operculum. At the origin 
of the arms, the fibres have a complicated course, and there is a good deal of crossing of the 
fibres which traverse the collar-cavity in ditferent directions. 

The arms them.selves (fig. 141, 5, 6) are provided with a strong layer of longitudinal 
muscular fibres, on each side of the middle line, runing along the whole of the antrrior, grooved 
surface, and with a similar, but somewhat weaker, Ia\'er on each side ot their dorsal surface, 
continuous with the muscles of the dorsal or posterior wall ot the arm-bases. 



71 

The entire wall of the pharynx and oesophagus, so far as it is exposed to the bod)-- 
cavities, whether of the collar or of the trunk, possesses a single layer of fibres. I have never 
observed the slightest indication of any crossing of fibres, although the muscular system can be 
seen with great clearness in sections stained with iron-haematoxylin, particularly where parts of 
the wall of the alimentary canal are cut tangentially, as in fig. 151. It need hardly be pointed 
out that where sacculations of the wall occur, the direction of the fibres may appear to change ; 
but their real course seems to me to be exclusively longitudinal. The pleurochords of Masterman 
are in no way different from other parts of the pharyngeal epithelium, so far as the muscular 
layer is concerned. But when the region of a gill-slit is reached, the fibres take a sphincter-like 
course round the posterior or external wall of the tube leading to the external gill-pore. These 
sphincter-like fibres are a direct continuation of the longitudinal fibres on the part of the pharynx 
which is nearer the stomach, and of the longitudinal muscles of the body-wall of the trunk. 
On the anterior or median border of the gill-slit, the fibres contained in the anterior horn of 
the third body-cavity (fig. 156, d.cJ'a.) no doubt assist in the closure of the gill-pore. 

I have not noticed any differences of importance between the muscular systems of 
different species of Cephalodiscus, except so far as has already been pointed out in describing 
the stalk. The neuter individuals of C. sibogae are, however, provided with muscles which seem 
to be specially strong in proportion to the size of the animal. 



XIII. NERVOUS SYSTEM. 

In 1 88 7 I was able to shew that the nervous system of Cephalodisctis conformed to 
the type found in Balanoglossus. Since then, more detailed accounts have been given by 
Masterman (97, 2 ; 98, 2 ; 03), many of whose results I am able to confirm. 

Masterman (97, 2, p. 342) recognises the following parts of the nervous system of 
Cephalodiscus : (I) the central nervous system; (II) its backward continuation as the lateral 
nerves, which are prolonged down the body as (III) a pair of lateral nerves similar to those 
of Phoronis\ (IV) a post-oral ring given off from (II) at the posterior edge of the collar, and 
becoming lost ventrally in the operculum, over which it forms a nerve-layer, (V) a broad tract 
lying beneath the thickened anterior ectoderm of the proboscis, and connected with the central 
nervous system round the "apex" or dorsal margin of that structure, (VI) a "pre-oral nerve" 
passing ventrally along the posterior wall of the proboscis and originating from the anterior 
part of the central nervous system by a root on each side; (VII) "several nerve-fibres" which 
run down the anterior surface of the metasome, some of them being continued into the nerves 
of the stalk; (VIII) the nerves to the arms. 

In a later account (98, 2, p. 513) Masterman substitutes for (VII) "a broad nervous 
tract", which passes down the ventral line of the body into the stalk, while he states that the 
lateral nerves (III) also extend into the stalk. 

There can be no question of the nervous nature of the parts numbered (I), (II), (VII), 



and (,\'I1I) ill iHe above list. (V) is, I think, almost equally certain; and, as Masterman states, 
it lies at the base of the tjlandular epithelium of the proboscis (PI. 1\', figs. 36, 42). I have 
not been able to trace it with complete certainty round the dorsal or lateral margins of the 
proboscis, although figs. 151 — 146 (PI. XII) appear to indicate that this is really its mode 
of conne.\ion with the central nervous system. I ihiiik that .Masterman is right in describing 
the operculum as being supplied with a nerve-layer, although I have not indicated it in most 
of my figures, and I am not certain of its communications with other parts of the nervous 
system. But it may be remarked that Ccplialodisciis resembles Balanoglossus in possessing a 
general nerve-ple.xus in its epidermis, and that it is only the thicker parts of that ple.xus which 
can be recogni.sed as definite nerve-tracts. It might be going too far to say that the plexus is 
universal in CepJialodisais^ but it is certainly present in many of the thicker parts of the 
epidermis, while its existence is further indicated by the fact that the nerve-tracts commonly 
fade away gradually at their edges. 

The following account of the nervous system, which is based on m\- own observations, 
besides giving a general account of the whole system, refers specially to the parts described 
by Masterman and numbered (HI), (\^I) and (VII) in the above list. 

The nervous system of Cephalodiscus is ver)- strongly developed, and I emphasize this 
fact because it has recently been asserted b)- dk Selys Longchamps (04, p. i 1 3) that it is 
"peu developpe" or even Tudimentaire". Tliis is very far from lieing the case, the central 
nervous system in particular consisting of a large mass of nerve-tissue. It has been pointed 
out by Morgan (94, p. 72) that in retaining its central nervous system in the outer epidermis, 
Cephalodiscus must be regarded as more archaic than its relation Balanoglossus. 

The central nervous system has essentially the same characters in all the species, even 
the curiously reduced male individuals of C. sibogae forming no exception to this statement. 
It gives rise to a great thickening of the epidermis in the dorsal region of the collar, extending 
thence on to the posterior part of the: proboscis. It is shewn in more or less sagittal sections in 
ri. 1\', figs. 42, 41 (C. dodecalopJms), figs. 34 — 36 (C. levitisenij, fig. 37 fC. gracilis), PI. VTII, 
fig. 93 (C sibogae, neuter) and PI. VII, fig. 79 [C. sibogae, male); while I'l. X, figs. 112 — 118, 
referring to C. levinseni, illustrate its relations as seen in fiH)ntal sections. The greater part of 
the nervous mass consists of a conspicuous layer of fibrillar material, resting on the basement- 
membrane; while ganglion-cells may be clearly distinguished, in certain parts of the organ, 
among the bases of the epithelial ectoderm-cells. Thus in the original of fig. 42, some half dozen 
ganglion cells occupy the epidermic swelling which in the figure appears to project into the 
mass of fibrils near the posterior end of the brain. 

In his latest paper on Cephalodiscus (03, p. 717) Masikkman describes what he terms 
the "ectodermal pit", a crescentic groove running transversely across the region of the central 
nervous sy.stem, and representing the line of division between the proboscis and the collar. 
Tlu; proboscis-pores are said to open at the outer ends of the crescent. I have on various 
occasions noticed transverse grooves corresponding to the "ectodermal pit", but I think that 
Masterman is wrong in describing it as a definite structure. It appears to me to be the result 
of the varying positions of the anterior end of the body and of the varying states of contraction 



7o 

of the muscles. In other words, the "ectodermal pit" is simply a temporary crumple of the 
skin, without any constant relation to the proboscis-pores. Thus fig. 42 shews no definite trace 
of the structure, while in figs. 149, 150 (PI. XII) it appears to be well developed. But in 
fig. 151, from the same series, the outer end of the groove is seen opposite the notochord 
(nc/i.), while the proboscis-pore (/./. /.) opens at some distance in front of the groove; and 
the same relations are already indicated in fig. 150. 

The proboscis-pores (PI. X, fig. 112'; PI. XI, figs. 137, 138; PI. XII, fig. 158; /./.) traverse 
the central nervous system at a level which is indicated by the position of the pericardium and 
the anterior dorsal horns of the collar-cavity. I have not certainly found them in the males of 
C. sibogac, but their number and position are, e.xcept for this doubtful case, invariable. 

The strong nerves to the arms are direct lateral continuations of the central nervous 
system. They are seen in the sagittal sections represented in figs. 149 — 141 (PI. XII), and in 
the frontal sections shewn in figs. 113 — 118 (PI. X). The arm-nerve lies at the base of the 
dorsal epidermis, which is often triangular in transverse section (figs. 141, 142). 

The nerve-layer at the base of the glandular epithelium of the proboscis is shewni in 
PI. IV, figs. 36, 42, and elsewhere. 

The part of the central nervous system which extends on to the dorsal side of the 
proboscis is connected with nerve-tracts running in a ventral direction along the posterior wall 
of that organ. In C. dodecalophus I have been able to recognise two lateral tracts and a median 
tract (PI. XII, figs. 152 — 155) which appear to correspond with Masterman's "pre-oral nerves". 

The central nervous system as seen in a median sagittal section (PI. IV, figs. 34, 42) 
comes to an abrupt termination posteriorly at a point which corresponds with the hind edge of 
the collar. On either side of the middle line it passes into the strong "lateral nerves" described 
by Masterman (97, 2, p. 342; 98, 2, p. 513), with whom I do not, however, altogether agree 
as to their further course, since I have been unable to recognise the independence of the two 
nerves which in the diagram given by Masterman in his later paper (98, PI. V, fig. 85) are 
supposed to run, on each side of the body, from the posterior end of the nervous system to 
the stalk. According to my own results, there is on each side a single lateral nerve, which is an 
extremely conspicuous structure passing from the central nervous system in the lateral ectoderm. 

In the first part of its course the lateral nerve is in contact with the basement-membrane 
belonging both to the collar-cavity and to the metasomatic cavity. This is .seen in PI. XII, 
fig. 150 (/.«.); while in fig. 151, a section of the same individual .slightly nearer the middle 
line, the lateral nerve is separated by parts of the pharj-nx and body-cavity from the central 
nervous system, still retaining its position adjacent to both the second and the third body-cavity. 

F"ig. 152 is a frontal section which passes somewhat ventrally to the central nervous system, 
and therefore cuts the lateral nerves near their origin. The sub.sequent sections (figs. 153 — 155) 
shew that the nerves pass behind the collar-canals, with which they are in contact. On reaching 
the level of the gill-slits (fig. 156), behind which they lie, they are found to have lost all 

SIBOGA-EXriCDITIK. XXVI /'/V. lO 



74 

connexion with the collar and to have passed entirely into the metasome. It is thus hardly 
correct to speak of them as passing in the posterior part of the collar along the whole of their 
course to the ventral surface. Mastermax considers that these nerves extend along the body- 
laterally, and he definitely compares them with the lateral nevvcs oi P/ioroms. This is presumably 
illustrated by fig. 17 of his paper published in 1897 {-)■ ^h' "^'^^'i observations indicate that the 
lateral nerves pass ventrally into the strong nerve-plexus which is seen on the anterior side of 
the body in sagittal sections (PI. W. fig. 42 and PI. XIII, fig. 181). Masterman's figure, to 
which I have just alluded, shews the nerves correctly, but sections taken nearer the stalk would 
probabl) have indicated that the paired nerves pass into an unpaired anterior nerve-tract. In 
favourable specimens this course- can be distinctly made out, although it is not always ea.sy to 
demonstrate it in specimens in which the epidermis is much stretched, and it is accordingly not 
shewn in all my figures passing through the region in cjuestion. Figs. 119 — 124 (PI. X) shew 
the lateral nerves, in frontal sections of C. /evinsejii. They differ in no essential respect from 
the corresponding structures in C. dodecalopJms. Mg. 124, immediately ventral to the region 
of the gill-slits, shews the ventral i)ody-musculature along a considerable part of the anterior 
surface. The lateral nerves have reached the posterior ijorders of the muscular areas. In the 
next section figured (fig. 125) the nerve-layer is not so conspicuous as to be demonstrative, 
and it is accordingly not represented in the drawing. Put in similar sections of C. dodccalophus 
it may be seen that tiic lateral nerves, after accjuiring the position shewn in fig. 124, spread 
out rapidly over the whole of the area of the antero-ventral musculature and become continuous 
with the .strong stalk-nerves shewn in U'-^. 133. The sagittal sections (fig. 181) demonstrate the 
existence of a large nerve-plexus along the anterior side of the body from a region not far 
behind the gill-slits to the stalk. 

The function of the lateral nerves is thus to place the musculature of the metasome in 
direct communication with the centra! nervous sy.stem, a conclusion which is in accordance with 
the great development of these nerve-tracts. 

C. gracilis and C. sibogae are less favourable for the examination of the nervous system 
than the other two species, in consecjuence of their less robust structure. The main features of 
the nervous system, as above described, can, however, be recogni.sed in the.se species, and I 
am not able to point out any differences of importance. 

It is a point of special interest that the reduced male individuals of C. sibogae (figs. 79, 
8t — 84) have a well developed central nervous system, indicating that they must be regarded as 
more than mere reproductive appendages of the colony. The development of the nervous system 
is perhajjs principally correlated with the functions of the proboscis and of the pair of arms. 



XI\'. VASCUL.XR .SYSTEM. 

The credit of discovering this system in CcpJialodisais belongs to Masterm.vx, who in 
his first account (97, 2, p. 350), described the following parts: — (I) a large cavit) beneath 



/o 



the central nervous system, which he has more recently admitted (99, 2, pp. 359, 361) not to be 
a blood-space, but to have the peculiar relation to the vascular system possessed b)- the peri- 
cardium of Balanoglossus, as described by Spengel; (II) a vessel proceeding backwards from 
the pericardium in the dorsal mesentery of the collar, bifurcating at the anterior border of the 
dorsal diverticulum of the pharynx, and reuniting behind that cavity to form (III) a vessel lying 
in the mesentery between the pharynx and the rectum, connected with (IV) a system of sinuses 
round the stomach; (V) vessels to the ovaries; (VI) a ventral vessel, passing down the anterior 
side of the body and stalk; and (VII) a vessel on the dorsal side of the body-cavity of each 
arm, giving off a branch to each tentacle. In a later paper (98, 2, p. 512, figs. 12, 13) Masterman 
gives figures shewing that the ovaries are supplied from the dorsal blood-vessel, and in the same 
memoir (p. 513) he describes a "dorsal" and "ventral" vessel in the stalk, which he .states to 
be "direct continuations of the similar vessels in the trunk". 

Still more recently (03, p. 719), Masterman gives a more elaborate account of the 
vascular system of the "central complex", or region between the buccal shield and the mouth. 
The general result of this paper is to indicate an almost complete resemblance between Balano- 
glossus and Cephalodisais in the details of the vascular system of the proboscis-stalk. The blood- 
sinus which runs in the dorsal collar-mesentery communicates with the "heart", which is related 
to the pericardium in the same way as in Balanoglossus. Glomeruli are described, both on 
the anterior wall of the pericardium and on the "ventral blood-sinus" which lies beneath the 
notochord. There is a blood-sinus coming from the dorsal wall of the proboscis to the anterior 
glomerulus; and vessels passing from the arms are said to enter the dorsal sinus at the level 
of the posterior end of the pericardium. The ventral sinus extends backwards as far as the 
base of the notochord, where it divides into two vessels which pass round the mouth. 

I have no wish to dispute the accuracy of most of Mastermax's statements with regard 
to the vascular system, although on one or two points I cannot agree with him. But I must 
admit that I have not been able to satisfy myself of the existence of all the vessels which 
he describes. 

The question really turns on the interpretation which should be given to certain spaces 
in Cephalodiscus which may be vascular and on the other hand may be merely artefacts. There 
is of course no trace of colour in the blood of the preserved specimens, nor are any corpuscles 
to be seen. Certain evidence of the presence of a coagulum inside the "ve.ssels" can only rarely 
be obtained. There are, however, in Cephalodiscus^ numerous spaces between the limiting mem- 
branes of adjacent coelomic spaces, or between the membrane and the ectoderm or endoderm; 
and these spaces may be vascular in nature. But when one remembers the fact that the material 
which is at present forthcoming was not preserved by refined histological methods, and further 
that there is evidence of great contraction in certain parts of the animal, 1 think it is well to 
be cautious in assuming that all the spaces in question are vascular. 

I am none the less inclined to think that most of Masterman's account is substantially 
accurate. I cannot ag^ree with his statement referred to above that the "dorsal" and "ventral" 
vessels of the stalk are "direct continuations" of the "similar vessels in the trunk". This appears 



76 

to me correct for the "ventral" or anterior vessel; but a moments consideration will shew that 
it would be impossible for the median "dorsal" vessel of the stalk to be a direct continuation 
of the dorsal vessel of the bod)- unless it could traverse, or pass to one side of, the second 
stomach and intestine. Xor can I agree with the statement that each tentacle has a vessel on 
the dorsal side of its coelomic cavity. It is easy to find appearances similar to those shewn 
by M.-vsTERMAN (97, 2, Plate XXVI, fig. 27). With certain methods of staining the crescentic 
area seen in the transverse section appears to be hollow. But in other cases it seems to be 
clear that the crescentic appearance is simply due to a thickening of the basement- membrane 
lining the coelomic cavity; and I believe that Masterman's tentacle-vessels are in fact merely 
skeletal thickenings of that membrane. 

My own results on the "vascular system" of Cephalodiscus may be considered under two 
heads: — (i) those spaces whose vascular nature is practically certain, and (2) those with 
regard to which some caution in interpretation seems to be desirable. 

(1) Under the heading of spaces the vascular nature of which is practically certain, 1 
include the vessel which lies in the dorsal mesentery of the metasome, adjacent to the wall 
of the pharynx: the vessels given off from this to the reproductive organs; the two ve.ssels of 
the stalk, and their continuaticjiis in the body; and lastly the "heart", or pericardial sinus, 
which is invaginated into the posterior wall of the pericardium. .All these parts have been 
described by Masterman in one or other of his accounts. Under the heading (2) of spaces 
with regard to whose? interpretation as vessels it is well to e.xercise some caution I include 
practically all the other "vessels" described by M.vstermax. 

Dorsal vessel. 

This name may be employed for the vessel which is contained in the dorsal mesentery 
of the metasome. Evidence of its existence can be obtained in most specimens of Cephalodiscus. 
In those in which the vessel has been jireserved in a dilated condition it forms an extremely 
conspicuous organ, and it is in fact far the largest vessel in the animal. 

The dorsal vessel {d.v}j is shewn in the combined .sagittal .section of C. gracilis (PI. 1\', 
fig- 37). '■! the actual sagittal sections (PI. V, figs. 43 — 46) and in the frontal sections (PI. VI, 
figs. 67 — 70) of the same species, i'l. Ill, fig. 22, reconstructed from the series of sagittal 
sections by the ground glass method, shews this vessel as a large cylindrical space which starts 
irom the anterior caecal projection of the stomach, and then pas.ses in an obliquely dorsal 
direction in such a way as to lie, in the whole of its course, parallel to the dorsal wall of the 
pharynx. The vessel is also conspicuous in the sagittal section (fig. 33) of C. levinseni, where 
it has the same relations. It is .shewn in transverse section (PI. XII, figs. 152—157) in C. 
dodecalophus, and lastly it is clearly seen in both neuter (PI. \'11I, figs. 90, 91) and male 
individuals (figs. 86 — 88) of C. sibogac. The vessel in question is particularly clear in the male 
individual represented in figs. 86 — 88, and in this case, as 1 have also observed in the neuter 
of the same species, it contains an obvious coaguluni. Tiie walls of the vessel are usually very 
thin, although in C. Icvinsc7ti (fig. 33) it appears to be fairly thick. I have not been able to 
demonstrate any system of muscles connected with its wall, allliough 1 am not sure that the\- 



/ / 

are absent. It is not improbable, however, that it functions as a reservoir of blood derived 
from the walls of the stomach. The movement of the blood in the vessel mieht well be effected 
by the pressure of the coelomic fluid induced by contractions of the body-wall. 

There can thus be no question that the dorsal vessel is an important structure in 
Cephalodiscus. Examining its ventral end (figs. 33, 37) it is found to end abruptly on the 
surface of the dorsal caecum of the stomach. In most cases I cannot certainly demonstrate 
any vessels entering it from the stomach; but the evidence of the bud shewn in PI. V, figs. 
57, 58 is in favour of the view that it receives its blood from a system of sinuses lying 
between the gastric epithelium and the limiting membrane of the body-cavity. 

Vessels of the gonads. 

Near its dorsal end, the dorsal mesentery gives off a pair of lateral mesenteries (figs. 
120 — 123, ov. III.) which are inserted into the entire length of the oviducts in the female, and 
into the dorsal part of the internal walls of the ovaries. Each lateral mesentery carries a 
conspicuous vessel (PI. XII, fig. 151 ; PI. V, fig. 45, ov.v.) which passes to the wall of the 
ovary, somewhat ventrally to the internal end of its pigmented duct. The large amount of yolk 
deposited in the eggs of Cephalodiscus implies an abundant nutriment supplied to the ovaries-, 
and I think it may thus fairly be inferred that the blood passes from the wall of the stomach 
in a dorsal direction to supply the ovaries. In the male C. sibogae, a similar arrangement 
obtains. The dorsal vessel (PI. VHI, figs. 87, 86) extends from the dorsal surface of the bend 
of the vestigial alimentary canal to the dorsal ends of the testes, which are supplied by large 
vessels passing along paths which may be regarded as lateral mesenteries homologous with 
those of the ovaries. The vestigial character of the alimentary canal in the male offers, however, 
some difficulty as to the source of the nutritive fluid contained in the vessel. This question 
will be considered under the heading of the male C. sibogae (p. 88). 

Vessels of the stalk. 

These vessels occur in the position already described by Masterman, on what he terms 
the "ventral" and "dorsal" sides of the stalk respectively. In view of the orientation adopted 
in this Report, according to which the entire stalk is a ventral appendage of the body, I 
prefer to call the vessels respectively "anterior" and "posterior", and to regard them as two 
limbs of a loop-like ventral vessel which extends into the stalk. The continuity of the two 
vessels at the basal end of the stalk has not however, been demonstrated with certainty. 

The vessels are seen in transverse section, in C. dodecalophus (PI. XI, fig. 133), as 
small dilatations of the two ridges of basement-membrane which alone represent the ventral 
mesentery of the stalk. It may be supposed that primitively the ventral mesentery extended as 
a complete partition down the stalk. With the filling up of its cavity which this organ has 
for the most part undergone by the development of the longitudinal muscles and their investing 
connective tissue, the ventral mesentery has persisted as a distinct structure at the anterior 
and posterior sides only. 

The condition of the stalk-vcsscls is probably not cjuite sim])lc at the basal e.xtremity 



-8 

of the stalk. It is complicated by the development of the buds, which, as Masterman has 
shewn (98, 2, p. 515) receive branches from one of tlic stalk-vessels. There is some evidence 
in C. sibogac that the two vessels communicate b\- means of a plexus at the basal end of the 
stalk ; but whether the connexion is usually of this nature, or whether, as some sections seem 
to indicate, the two vessels form a simple loop at the base of the stalk, it is probable that 
they may be regarded as respectively afferent and efferent in function. 

The anterior vessel passes from the stalk along the anterior part of the ventral mesenterj- 
of the body (figs. 29, 126, 125, a.v.^a.v))^ where it lies close to the body-wall; and in suitable 
specimens it can be distinctly traced as far as septum '/.■• The posterior vessel, on entering the 
body, passes in the ventral mesentery as far as the wall of the alimentary canal. In C. gracilis 
(PI. VI, fig. 71, PI. \', fig. 53, and the reconstruction I'l. HI, ^•g. 22) it ends on the surface 
of the second stomach as a distinct dilatation, the structure of which cannot clearly be made 
out, although in one specimen the dilatation has been observed to receive muscle-fibres from 
the longitudinal layer of the anterior wall of the metasome. The ending of the posterior stalk- 
vessel on the second stomach is also somewhat dilated in C. dodecalopJms (PI. XIII, fig. 169). 

The clearest proof that the structures here described as vessels are really of that nature 
is obtained from C. gracilis. The stalk-vessels are here unusually large (figs. 28, 29, 134, 135); 
and although they are commonly displaced so as to take u]) a lateral po-sition, a careful 
examination of the stalk usually serves to shew that they are connected respectively with its 
anterior and posterior walls. The connexion is, however, far less obvious than in C. dodecalophus 
and C. Icvitiseni, since remains of the ventral mesentery connecting the vessels with the body- 
wall are not easily discovered. The vessels are large, thin-walled cavities lying internally to the 
muscular layer, in the sparse connective tissue which occupies the central part of the stalk in 
this species. 

The stalk-vessels of C. gracilis are sometimes very conspicuous in entire preparations of 
young buds. They are shewn in PI. Ill, figs. 28, 29; and in this sijecimen it could be proved 
that the posterior vessel becomes attached to the wall of the alimentary canal of the bud, while 
the anterior vessel passes along the inner side of the median line of the anterior wall ol the body. 

Attention may here be called to the account which has recently been given by Fowler 
(04, ]). 23) of the structure of Rliabdopleura. The resemblance between the stalk, as described 
by Fowler, and the stalk of Cephalodiscus is practically complete, both as regards mode of 
origin and minute structure. Fowler's fig. 2 might stand for the stalk of C. Icvinscni almost as 
well as for that of Rhabdopletira, the completeness of the mesentery and the difference in size 
e.Kcepted. It shews a triangular ventral or anterior thickening of the epidermis which has "very 
much the appearance of a .superficial nerve". The longitudinal muscles are related to those of 
the body exactly as in Cephalodiscjis. The cavity of the stalk is divided by a median mesentery, 
in which run two canals. The one next the nerve [b) was not found in all specimens, Init the 
one {end}) which occurs at the middle of iIk- mesentery is always present and is "generally 
completely filled with a granular mass". 

1 think there can be no doubt that these two cavities are the homologues of what 
M.vsterm.w has described as the stalk-vessels of Cephalodiscus^ and indeed Fowler admits that 



79 

homology. He is apparently induced to reject Masterman's interpretation by finding that the 
central or posterior tube of the stalk is "continuous with the lining of the alimentary canal". 
The proof of this last statement is not given by Fowler, and 1 think it more probable that the 
relation of the posterior tube to the alimentary canal is of the kind indicated in figs. 22 and 
71 for C. gracilis. Fowler supposes that the central tube is endodermic, and I imagine that 
his view of the budding is that it behaves in somewhat the same way as the epicardium of a 
Tunicate. But there is no evidence that this is the case, and the account given by Masterman 
(98, 2) of the budding of Cephalodiscus is distinctly opposed to Fowler's view. There can be 
little doubt that the same interpretation of the structures in question applies to the two genera; 
and it appears to me probable that in both cases the .stalk is provided with an anterior and 
a posterior limb of a loop-like ventral vessel, the posterior limb terminating on the wall of the 
alimentary canal. 

Pericardial sinus or heart. 

The pericardium and pericardial sinus form a conspicuous feature of all specimens that 
are sufficiently well preserved. The pericardium [per.) has precisely the same relations as those 
of the same organ in Balanoglossus (the "Herzblase") as described by Spengel (93, p. 505). 
It is well shewn in Masterman's most recent paper (03, figs, i — 8), and is illustrated by 
PI. XIII, figs. 181, 182, 173; PI. XI, fig. 138, PI. IV, figs. 33, 37 of the present Report. 
It is in contact with the tip of the notochord (fig. 33) and lies immediately beneath the central 
nervous system. The proboscis-pores open into the anterior body-cavity between its lateral walls 
and the dorsal horns of the collar-cavity (figs. 112, 137, 138). The posterior wall of the 
pericardium is invaginated, the space thus formed (heart) having the same relation to the 
pericardium that is found in the Tunicata (cf Ritter, 02, i). Spengel (93, pp. 506, 625) has 
given reasons for believing that in Balanoglossus the pericardium, although not in itself a 
va.scular space, may be regarded as functionally a part of the vascular system, since the blood 
in the heart is propelled by the rhythmical contractions of the pericardium — contractions 
which are well known to occur in Tornaria. The identity of the relations of the pericardium 
to other organs in Enteropneusta and Cephalodiscus makes it highly probable that what is true 
of the former is also true of the latter. 

The pericardium in Cephalodiscus is developed at a very early stage in the buds, and 
is further considered in Section X\T. 

I come now to those parts of the vascular system which I regard as less certainly 
proved to exist. Among the.se are the "vessels" described by M.\sterman in the immediate 
neighbourhood of the pericardium and notochord. I do not feel myself in a position either to 
a.ssert or to deny the existence of these vessels, though I regard it as highly probable, on a 
priori grounds, that they do exist. 1 have indicated above (p. 74) the general nature of 
Masterman's results with regard to these particular vessels. 

Althoujjh I have devoted a considerable amount of attention to the region in which 
the dorsal vessel terminates in front, I have found but little evidence which appears to me 



8o 

demonstrative. In many cases I can obtain no proof that the vessel in question supplies any 
organs other than the gonads. In the sections of C. levinseni shewn in I'l. X, however, there 
is evidence that the vessel is prolonged as far as the dorsal side of the dorsal diverticulum 
of the ]jharynx at least (fig. 119). In several sections through the collar-region I find spaces 
similar to the triangular space at the dorsal root of the collar-mesentery in figs. 114, 115, or 
in other positions between the central nervous system and the limiting membrane of the collar. 
Some of these spaces have very much the appearance of being artefacts (and indeed I have 
not represented them in all the figures), but it is not impossible that they may be normal 
structures. In Masterman's original account oi the vascular system (97, 2, figs. 7, 8) the main 
vessel of the collar is represented as occupying the entire height of the mesentery, and in fact 
as being a space between the two collar-cavities, whose limiting membranes do not actually meet 
at any point. In most cases I can obtain no certain evidence that the collar- mesentery has 
this double character. 

In several of the sections of C. levinseni I find evidence of the existence of a finer 
membrane internally to the principal limiting membrane of the collar (figs. 116 — 118). The 
latter is thick and is in immediate contact with the epidermis, by which it has presumably 
been secreted. The inner mcmlirane is much thinner, and there seems reason to believe that 
it constitutes that part of the limiting membrane ("Grenzmembran" in Spengel's sense) which 
is derived from the coelomic epithelium. It is by no means impossible that the spaces between 
these two layers of the limiting membrane are vascular in character. 

The ]jeritoneum is often not in contact with tlie outer surface of the epithelium of the 
alimentary canal. Some of the spaces thus constituted are almost certainly due to defective 
preservation, but I regard it as highly j^robable that splanchnic sinuses do occur, externally to 
the alimentary epithelium. Perhaps the most constant of these spaces is a large oral sinus (?) 
which I find jjassing from the sides to the ventral aspect of the mouth in C. levinseni (PI. X, 
figs. 121 — 124, oi\ s.). 

Although I fully admit the unsatisfactory nature of the evidence with regard to the 
peripheral vessels of CepJialodiscus^ it may be worth while to attemjjt to torm some idea of 
the probable nature of the circulation in this animal. 

The cardinal fact with which it appears to me justifiable to start is the large size of 
the main dorsal vessel which connects the stomach with the reproductive organs. It is highly 
probable that this is a nutritive arrangement, in which case it may be inferred that the blood 
is collected from sinuses which lie on the surface of the stomach (as appears to be indicated 
by PI. \', figs. 57, 58) and that it then jjasses forwards through the dorsal vessel to suppl\' 
the ovaries. I have no evidence with regard to the efferent vessels of the ovaries; but it is 
conceivable that these might pass to tiie skin along the oviducts. 

If Masterman is correct in his account of the vessels of the "central complex'", it is 
probable that that porlicjii of the blood which dcjes not enter the ovaries continues its course 
along the dorsal side of the alimentary canal and is carried 1)\- the sinus in the dorsal collar 
mesentery, as far as the heart. Here the circulation is ])resumably reinforced by the contractions 



of the pericardium, whicli would projjel tlie blood through the glomeruli and along Masterman's 
ventral sinus (which is said to underlie the notochord) to the front border of the mouth, 
travelling round the sides of the mouth through the two vessels described in that position by 
Masterman. These may be continuous with the oral sinus of which I have obtained some 
evidence in C. levinseni. The course of the blood, as thus suggested, would be in agreement 
with the course which has been described by Spengel in Balanoglossus. 

The anterior ventral vessel of the body and stalk can be traced as far as the septum 
between the second and third body-cavities, or in one case (C levinseni, PI. X, fig. 124) even 
into the incomplete ventral mesentery of the collar. It appears to me probable that this ventral 
vessel in .some way receives a part at least of the blood coming from the collar, and conveys it 
to the stalk by the vessel running on the anterior side of this structure. After having traversed 
the entire length of the stalk, it may be supposed that the blood returns by the posterior stalk- 
vessel to the wall of the second stomach where, in C. gracilis at least (figs. 22, 71) it appears to 
end in a dilated structure which is probably muscular. This may have the function of propelling 
the blood through the sinuses of the stomach and so of enablino- it to reach the oriein of the 
dorsal vessel. It is, however, possible that it acts in exactly the opposite direction, and that 
the posterior vessel is the afferent vessel of the stalk. 

If there be anything in this entirely tentative scheme of the circulation it may be noted 
that the force of the beat of the pericardium would appear to be largely of importance in 
driving the blood through the stalk. In the long-stalked forms (C gracilis and C. sidogae) there 
must be a considerable amount of resistance to be overcome in this region ; and it may further 
be remembered that the stalk requires an efficient nutritive arrangement, not only to supply its 
strongly developed muscles, but also for the growth of the buds which are produced so profusely 
from the basal end of the stalk in these species. 



XV. REPRODUCTIVE ORGANS. 

The zooids of C. dodecalophus appear to be without exception female. As all the previous 
literature of the genus refers to this species, it follows that the male organs have not hitherto 
been described, although I have alluded to the males of C. sidogae in \'ol. VII of "The 
Cambridge Natural Hi.story" (04, p. 26). The only previous accounts of the male organs of 
the Pterobranchia refer to Rhabdopletira, and are represented by Lankester's observation 
(84, p. 633) that a single testis occurs on the right ^) side of the intestine, opening to the 
exterior near the anus, its blind end in some cases projecting beyond the part of the body- 
wall which contains the loop of the alimentary canal; and by the remarkable statements of 
CoNTE and Vaney (02, i), to which I shall refer later. 

The material at present under con.sideration consists of female colonies of C. dodecalophus^ 
C. levinsefii and C. gracilis and a male colony of C. sidogae. 



1) Lankester's fig. 7 (PI. \I.) shews the testis on the left side, as indicated in the explanation of the Plates (p. 645). The 
figure is perhaps reversed. 

SIBOGA-EXrEDlTIE XXVI ^/V. " 



82 

Female or<jans. 

In the three species represented by female colonies it is probably not too much to say 
that all the adult zooids without exception possess a pair of ovaries. These make their 
appearance at an early stage in the budding, so that it is really only the very young buds 
ill which gonads cannot be detected. 

The ovaries are a pair of organs, symmetrically disposed on either side of the middle 
line, and they occur in the dorsal ])art of the third ])()d\-cavity, between the anus and the 
pharyn.\. The major part of the organ is composed of an ovoid mass containing the eggs. In 
adult specimens it is usual to find that in addition to a number of immature eggs the ovary- 
contains a single egg in which a large tjuantity of yolk has made its appearance. The ripe 
ovarian egg thus reaches a large size (as much as 380 ij.. in length in C. gracilis)^ and in an 
individual which contains a ripe egg there is commonly some asymmetry of the two ovaries, 
one of which may be much smaller than the other owing to the fact that it contains no ripe 
egg. In favourable specimens, there is an indication of a central cavity in the ovary; and 
the organ appears to be a hollow sac, the lining epithelium of which gives rise to the eggs. 
The ripe egg occupies the ventral part of tlie ovary (fig. 42), while the remains of the 
germinal epithelium are at the base of the oviduct. 

The oviducts are one of the most characteristic features of Ccphalodiscus. Their wall 
contains a pigment which is not dissolved by spirit, and the oviducts are thus so readily 
seen through the thin body-wall that they were originally described as eyes. The oviduct is a 
tubular prolongation of the cavity of the ovary. The external apertures are situated on the 
dorsal swelling of the metasomc which immediately .succeeds the central nervous system. 

The frontal sections of C. Icvinseni represented on Plate X will serve to explain the 
relations of the ovaries and their external apertures. On reaching the posterior end of the 
collar (fig. I 1 8) the dorsal projection of the metasome first makes its appearance as a 
longitudinal ridge of body-wall attached to the dorsal side of the collar. The two collar-cavities 
are here separated from one another by the dorsal diverticulum of the pharynx (div.), and 
between this and the central nervous system is seen the extreme tip of the right third hoch- 
cavity [p. cj^). The longitudinal ridge of body-wall separates from one another the entrances to 
two deep recesses lined by the epidermis of the metasome, and bounded in front liy the part 
of the collar-wall which contains the lateral nerve-tract passing from the central nervous system 
to the stalk. This is shewn, on the left side, in fig. 119, while in fig. 120 it will be seen that 
the same oviduct opens into the posterior .side of this recess. On the right side of fig. i 20 the 
recess is already passed, and the oviduct is no longer connected with the body-wall. The part of 
the body which contains the oviducts is marked by a conspicuous dorsal furrow (figs. 119 — 122). 
Each oviduct is supported by a lateral or ovarian mesentery, which reaches the body-wall 
dorsally (figs. 119, 120), while more ventrally it leaves the body-wall and passes along the 
dorsal mesentery of the metasome to the dorsal vessel. In the region of the external opening 
of the oviduct the ovarian me.sentery passes from llie Ixuly-wall, near the middle line, to the 
oviduct in such a way as to appear to cut off a posterior section of the third body-cavity 
(figs. 119, 120); but in later sections in which the oviduct has relincjuished its connexion with 



83 

the bod)--\vall, this division is in free communication with the remainder of the cavity round the 
posterior wall of the oviduct (figs. 121, 122). At the ventral ends of the oviducts, the mesenteries 
of these organs originate from near the middle of the median mesentery (fig. 122). The ovarian 
mesenteries are continued as far as at the extreme dorsal ends of the ovaries (fig. 123), which 
along the greater part of their course are not supported by mesenteries (figs. 124, 125). In zooids 
in which ripe eggs are not being produced, the ovary and oviduct lie in the same straight line. 
This is seen in fig. 33, in which the right ovary is shewn, on the far side of the large dorsal 
vessel. The wall of the epidermic recess into which the oviduct opens is seen as an ovoid ma.ss 
of cells which carries the pigmented oviduct to some little distance from the level of the median 
part of the dorsal body-wall. In zooids containing ripe eggs, the dorsal part of the ovary may 
be considerably bent, as shewn in fig. 139 (PI. XI). 

The relations of the ovaries and oviducts of C. dodecalophus are essentially similar to 
those found in C. levinseni. Fig. 42 shews an old ovary, bent in the way just referred to in 
the other species. The ovarian mesenteries are shewn, in frontal sections, in figs. 152 — 156, 
while fig. 157 demonstrates the absence of the mesenteries in the more ventral parts of the 
ovaries. Fig. 1 5 i illustrates the position of the mesenteries as seen in an obliquely longitudinal 
section, which passes mostly through the right side of the animal, but also shews some of the 
organs of the left side. The edge of the right oviduct {pvd. r.) is just cut, while the right 
ovarian mesentery [pv. m. r.) carries a distinct blood-vessel which joins the right ovary in one 
of the neighbouring sections. The left ovarian mesentery {ov. m. I.) is cut near its dorsal end, 
where it forms a bridge passing from the body-wall to the median mesentery, and thus isolates 
a section of the third body-cavity. The external openings of the oviducts in C. dodecalophus 
are situated in epidermic recesses, as in C. levmseni. 

In C. gracilis I do not find any epidermic recesses connected with the external apertures 
of the oviducts. These apertures are situated very close together (PI. VI, fig. 61) on a part 
of the dorsal swelling of the meta.some which is very prominent in some specimens (PI. Ill, 
fig. 22). The pigmented oviduct extends completely up to the level of the epidermis (figs. 
45 — 51) and opens on the convex surface of the dorsal swelling. The relations of the ovarian 
mesenteries are essentially the same as those of the other species, with the exception of the 
fact that the median dorsal mesentery of the body is incomplete in C. gracilis, and the ovarian 
mesenteries join the part of it which persists, namely that which is attached to the pharynx. 
The mesentery here carries a large and very conspicuous vascular space (figs. 45, 68) and it 
is easy to demonstrate that this gives off a conspicuous blood-vessel which runs in the ovarian 
mesentery to the dorsal part of the ovary. Evidence to this effect is not wanting in the other 
species, but I have seen it most conclusively in C. gracilis. One important function of the 
ovarian mesentery is thus to carry the nutritive blood-vessel of the organ. That vessel having 
found its w'ay to the ovary there is no further use for the mesentery, which accordingly 
disappears in the ventral part of the ovar\-. 

It is not easy to account for the universal occurrence of the pigment of the oviducts. 
I have, in Section VII (p. 27), called attention to the suggestion of M'Intosh that this substance 
may have something to do with phosphorescence; and I have mentioned the resemblance which 



^^4 

appears to exist between the narrow piu-ment-line of the proboscis and the oviducts in the 
constitution of the pigment. It is not impossible that the pigment (jf the oviducts has an 
excretory function, with which its resistance to sokition by s|jirit is quite in accordance. Fig. 46 
(C. gracilis) gives some evidence that the pigment can be discharged to the exterior from 
the aperture of the oviduct ; but it is cjuite possible, in the absence of further evidence, that 
this appearance is unnatural. 

C. sibogae. 

The most interesting outcome of my work, on the "Siboga" material is the discovery 
ol the males of CepJialodiscus. It is of course impossible to say how far the facts ob.served in 
C. sibogae will be found to apply to other species; but in view of the very small amount of 
anatomical differences, in other respects, between species which are at first sight extremely 
unlike one another, I suspect that what is true of C. sibogae will be found, with modifications, 
to be of general application in the genus. 

The ordinary zooids of C. sibogae are usually completely sterile or neuter individuals 
(PL 1, fig. 3), though in immature blastozooids (PI. XIII, fig. 184) the reproductive organs 
may be represented by a pair of minute vestiges {g^, similar in position to the ovaries of the 
other species. I am inrlined to regard the neuters as modified males rather than as modified 
females, since 1 have found at least one case in wliich functional testes appear to be present 
in a specimen which otherwise resembles a neuter. 

In the tangled masses of zooids which occur in the basal jelly of the colon)- are found 
considerable numbers of individuals of an entirely different appearance (PI. \'II, figs. 72 — 76); 
and these are the males. While shewing the general CepJialodiscus structure in an unmistakeable 
way, the males have vcr)- remarkable jjeculiarities of their own, the most striking of which is 
the complete want of any arrangements for taking food. This is indicated by the absence of 
tentacles and of the operculum, and by the vestigial character of the alimentary canal. 

A full-grown male, drawn to the same scale as the neuter individual, fig. 3, is represented 
in fig. 75, from which it will be seen that there is not much difference in size between the 
males and the neuters. This individual was cut into frontal sections, some of which are .shewn 
in figs. 80 — 89 (PI. Mil). The proboscis (/.) is rather small, but it has the same relations 
as in normal CepJialodiscus zooids, and even possesses the characteristic line of red pigment 
across its ventral lobe. The collar is produced into a single pair of arms (7?. a. and L. a.), 
which possess no trace of tentacles. The epidermis of these curious arms of the male is, except 
for a short region at the base, almost entirely con.stituted by enormous numbers of refringent 
vesicles (PI. IX, fig. 99), similar to those which occur in the terminal knobs of the arms of 
the female C. dodecalopJius or in those of some of the arms of C. gracilis. I'he arms seem to 
be subject to great variation in length. In the individual shewn in h'g. 75 they are relativel\- 
short, but in other cases they ma) be at least twice as long. The refringent vesicles make their 
appearance at a young stage, and there is some evidence that they may become used up in 
some of the older males. In other cases, however, they are still present in undiminished numbers 
in individuals in which the testes are fully developed. 



85 

The single pair of arms of the male C. sibogae agree in position with the first pair of 
arms of an ordinary Cephalodiscus\ or, in other words, they are developed from the anterior 
end of the dorsal side of the collar (figs. 72, 74). 

The metasome is much the largest part of the adult male, and it is almost entirely filled 
by a pair of large testes, one of which is usually longer than the other. The body passes 
gradually into a long, slender stalk, although I have not been successful in obtaining specimens 
in which this is complete. It will be noticed that the stalk is attached to the extreme end of the 
body, and does not originate from its anterior side as in the female zooids of other species. 

The young male (fig. 72) differs from an ordinary Cephalodiscus bud in no striking 
character e.xcept that of the arms. The proboscis is of great size, as is usual in buds, and its 
buccal disc overhangs the whole of the collar and metasome. The dorsal part of the collar 
[c. 11. s.) is indicated by an obvious swelling, separated from the body by a constriction. From 
the anterior region of this swelling originate the two characteristic arms, with their epidermis 
crowded with refringent vesicles (not shewn in the figure). The left arm has been broken off in 
this individual, but its torn base {L. a.) is clearly visible. The metasome is constituted by the 
slightly swollen portion which immediately succeeds the collar, and it passes without any line 
of demarcation into the stalk. 

Other young males, which differ in no essential respect from the above, are shewn in 
fifaS. 73, 74. In some cases, indications of the alimentary canal, the collar-pores and the gonads 
can be seen through the body-wall. In fig. 73 the right testis (/. r.) has reached a moderate 
size, while the left testis, partially concealed by the right arm, is smaller. The left arm of this 
individual is bifurcated at the tip. 

It will be noticed that the principal difference between the young and the adult male 
is in the proportions of the metasome, which increases, concurrently wath the development of 
the testes, to a large size, the other regions remaining stationary in their growth. 

A second adult male, in which the body-wall has been accidentally torn, is shewn in 
PI. VII, fig. 76 and PI. IX, figs. 95, 96. The testes are elongated bodies which, as in several 
other cases observed, shew constrictions or lobulations at intervals. The posterior end of the 
left testis (/. /.) has been broken. The ventral lobe of the proboscis is turned dorsally, the 
pigment-line being thus seen through its posterior epidermis. This position is favourable for 
the examination of the mouth (fig. 95, w.), a more or less triangular aperture which appears 
to lead into the vestigial alimentary canal indicated in the figures. Close to the anterior wall 
of the pharyngeal portion of the alimentary canal are a pair of collar-canals {c. c). I have not 
found gill-slits in any of the males, and in view of the absence of the tentacles, it is hardly to 
be expected that they are present ; but the material is not sufficiently well preserved to enable 
me to be certain of their absence. The rectal limb of the alimentary canal is indicated in 
fig^- 95 1 96 by a slender cylindrical mass of cells (r.) which is seen near the left testis. 

The posterior view of the same individual (fig. 96) shews the distinct collar-swelling 
indicating the position of the central nervous system {c. n. s.). Immediately posterior to this, 
the metasome rises into a dorsal swelling, as in an ordinary female zooid; and on the anterior 
part of this swelling, close behind the end of the collar, I believe that I have been able to 



86 

make out the two generative pores (^. p^. Posteriorly to the iiyier edge of the left testis is seen 
the vestigial rectum (r.), and between this and the central nervous system is a conspicuous 
blood-space (fl'.f.). The strand connecting this blood-space with the rectum may be a contracted 
part of the vessel. 

Fio-. 79 is a more or less sagittal section of an (jld male, in which how-ever the proximal 
end of the body was bent round in such a way as to be cut transversely, thus exposing both 
the testes. Althou>Th the state of preservation is not all that could be desired, there can be 
no doubt of the existence of the three body-cavities characteristic of Ccphalodisais, of a central 
nervous system, and of a collar canal. 

¥\<y^. 80 — 89 are sections nearly transverse to the long axis of the old male shewn in 
fitr. 7^. FitJf. 80, through the proboscis and the two arms, indicates that each of the latter 
has a distinct central cavity. This cavity, which is continuous with that of the collar, is limited 
b)- a definite basement-membrane, which in some of the imperfecdy preserved male individuals 
is exposed by the loss, by maceration, of the vesicle-containing epidermis. The membrane 
probably has a supporting function, as in the arms of a normal zooid. The epidermic vesicles, 
in this specimen, have a degenerated appearance, and are not well stained. The cavity of the 
left arm {L. a.) shews distinct evidence of lodgitudinal muscles at the distal end, where it is 
cut tangentially, and of fibres passing transversely across the cavity in the rest of its extent. 

Fig. 81, through the anterior ])art of the central nervous system {c.n.s.}, shews the cavity 
of the left arm opening into the dorsal horn of the collar-cavity, here lined by a very definite 
epithelium; a similar space occurring on the right side of the section. The space between the 
two dorsal horns, and underlying the central nervous system, is the pericardium ; it contains a 
considerable number of nuclei, the exact arrangement of which is uncertain. The next (more 
dorsal) section shews some indication of the external part of the left proboscis-pore, though not 
with sufficient clearness to justify me in asserting that proboscis-pores exist in the male. 

In the next section more ventrally (fig. 82) the pericardium no longer appears, and the two 
collar-cavities are separated by a dorsal mesentery, at the ventral end of w'hich an excessively 
minute notochord is indicated. 

In fig. 83 the notochord is still visible, the right arm opens into the collar-cavity, and 
the pigment-band of the proboscis has come into view. The i^roboscis is extremely muscular, 
the muscles on the left side of its cavity being cut transversely. 

Fig. 84 cuts the mouth (/;/.) and the left collar-canal (^. ^.), behind which are the lateral 
nerve and the left testis (A). 

Fig. 85 shews the right collar-canal, with the corresponding lateral nerve, and the pharynx 
(///.) supported bj- a dorsal mesentery which carries a minute blood-space. This mesentery gives 
off a branch to the left testis, while on the right side is seen the corresponding generative 
pore (/./.). 

Three sections further (fig. 86) the alimentary canal has become very small. l)oth testes 
are now seen, with the conspicuous dorsal vessel (d. v.), containing a coagulum and giving oft 
vessels to the testes. These travel along paths whicli may be regarded as lateral mesenteries, 
similar to the lateral or ovarian mesenteries found in the female CcpJialodiscus. 



87 

In fig. 87, the alimentary canal is represented by an excessively small structure, in which 
a lumen can barely be detected. As this immediately precedes the appearance of the recurrent 
or rectal limb of the canal, it appears to correspond with the stomach or the second stomach 
of the female. The v^estigial character of the alimentary canal is thus distinctly indicated, and 
it can hardly be rash to assert that no digestion takes place in the male zooid. The dorsal 
vessel has reached its maximum size in this section, and the ves.sels to the testis are distinct. 
The ventral mesentery is probably complete on the side of the alimentary canal opposite the 
dorsal vessel. 

Two sections later (fig. 88) the recurrent limb of the alimentary canal is seen as a 
cylindrical body with an obvious lumen. This meets the body-wall at one point, which probably 
represents the anus, although I have not observed any indication of an actual perforation. The 
rectal limb of the alimentary canal was obviously lying in a nearly frontal plane ; and it will 
be noticed that in the individual shewn in figs. 95, 96, the rectum travels but a short distance 
in the direction of the anterior end of the animal. The donsal vessel in fig. 88 is continued as 
a lobe which lies to the left of the rectum, the right testicular vessel being also visible. In the 
next section the dorsal vessel has completely disappeared, without apparently giving off any 
branch in this direction. 

The proximal part of the male is of fairly uniform structure (fig. 89). The body-cavity 
remains spacious, and there are distinct indications of a median mesentery. At the two extremities 
of this mesentery are an anterior and a posterior vessel {a.v.,fi.v.) which, in the particular male 
figured were more distinct near the stalk than nearer the other end of the metasome. The 
anterior side of the body-wall has a layer of longitudinal muscles (wx.) which correspond with 
those of an ordinary female Cephalodisciis. 

There can be no reasonable doubt that the two vessels shewn in fig. 89 are continued 
into the two stalk-vessels which I believe to be typical of Cephalodiscus. It will be noticed that 
the relations of these vessels in the greater part of the testicular region of the animal is like 
those of the vessels in the stalk of an ordinary zooid ; that is to say, each vessel is closely 
apposed to the inner side of the body-wall. The anterior vessel is indeed found in this ])Osition 
in the body of the female zooid, but it will be remembered that the posterior vessel, on entering 
the body, in the female, becomes attached to the second stomach (fig. 22). Taking these facts 
into account, and considering further the po.sition of the bend of the alimentary canal, it appears 
that the greater part of the "body" of the male is really a dilated part of the stalk; or in 
other words that the testes have grown far beyond the limits of the body, as that term is 
understood in the female, and have extended into the cavity of the stalk. 

This fact may have some bearing on the remarkable statements made by Conte and 
Vaney (02, I, p. 64) with regard to the testis of Rhabdopleura. That organ was described by 
Lankester (84, p. 633, PI. XL, fig. 7) as an asymmetrical body, situated on the right side, 
and opening near the anus. It has in fact much the same position as one of the gonads of a 
female Cephalodisms, except that in some cases it appears to form a hernia-like projection of 
the body-wall in which its blind end lies. Lankester points out that the young testis is possibly 
represented by the "cellular body" described by Sars (72, p. 5, PI. II, fig. 15, r) in the same animal. 



88 

Lankester's acct)unt is confirmed by Conte and \'anev, but the testis is said to be "une 
diftcrentiation de I'extremite anterieure du pedoncule", the axial part of which gives rise to the 
testis. It is not quite clear what is the precise meaning of this passage, taken in conjunction 
with the statement that Lankester's account is correct; nor do I profess to understand the 
short description given by the same observers of the ovary of Rhabdoplejira. But what is said 
of the testis mav perhaps indicate tluit this organ is developed at the anterior end of the 
metasome (as in C. sibogae) before that part shews any differentiation into body and sialk. 

It is hardly necessary for me to criticize Conte and Vaney's account of the general 
morphology of Rliabdopletira, and I ma\- merely refer to the remarks made by Fowler (04) 
on the subject. But I think there can be no reasonable doubt that Rhabdopleiira is really 
related to Cephalodiscus, and the denial by Conte and \'aney of the presence in Rhabdopletira 
of such organs as the collar- pores or of subdivisions of the body cavity are directly controverted 
bj- the careful work of Fowler (92, i , 2 ; 04) and Schepotieff (04), as well as by the few 
observations I have been able to make on the same subject. 

In the case of the zooid of C. sibogae shewn in fig. 3, there is some evidence of the 
existence of a single, posteriorly situated testis ' similar to the organ described by Lankester 
in Rhabdoplaira; while in the specimen to wiiicli the abnormal arm shewn in fig. 98 belongs 
there appear to be two testes situated in the third body-cavity, in tlie position of the ovaries 
of a female Cephalodisctis. I do not feel (juite confident of the accuracy of these observations, 
but it does not seem to me impossible that one of the individuals which is normally neuter mav 
exceptionally develop a testis. If this is really the case, it appears to imply that the vestigial 
gonads of the neuter are to be regarded as testes, and the neuters themselves as males with 
suppressed gonads. But this conclusion rests on too slight a basis to be worth much. I need 
hardly say that I have no evidence that anything like protogynous hermaphroditism occin-s in 
CepJialodisacs, as is believed b}- Conte and Vaney to be the case in Rliabdopleui-a. 

Two questions relating to the physiology of the male will at once occur to anv one 
conversant with the facts; — namely (I) the mode of nutrition, and (II) the function (jf the 
curious vesicles of the epidermis of the arms. 

(Ij Nutrition of the male. 

It has just been shewn that the alimentary canal of the male is a vestigial structure. 
There is no trace of a glandidar stomach ; and moreover the arms are not provided with 
tentacles, and there is no recognisable operculum. V^e.stiges of food-grooves can, however, be 
distinguished in section at the bases of the arms, which in other parts are circular in section. 

The male has on the contrary a well developed vascular .system; and it a])pcars to me 
that this is the direction in which one must look for the solution of the question indicated. The 
males are probablv nourished bv the neuter individuals, throuLrh the medium of the vascvilar 
system, in a manner analogous to that in which the nutriment absorbed by one set of individuals 
in Dolioluin is said to be transferred through the vascular system of the asexual form to an 
entirely different set of individuals. 



I) This is not shewn in the figure, which represents an anterior view. 



89 

I have unfortunately been unable to trace the stalks of the males into continuity with 
those of the neuters. But it is a striking feature of this species that there occur, here and there 
in the colony, discoidal masses of tissue from which originate a number of stalks (PI. Mil, 
fig. 94). Somewhat similar masses occur in C. gracilis, in which it is not difficult to ascertain 
that the mass in which a number of stalks unite represents the budding region of an old stalk, 
as may be seen by referring to the group of buds shewn in PI. I, fig. 4. 

It may thus be inferred, with a reasonable degree of probability, that the union of a 
number of stalks in a common di.sc (fig. 94) implies that all the individuals represented by these 
stalks are the blastozooids produced by a single budding individual. I am not in a position to 
shew that some of these stalks belong to males and others to neuters, but I regard it as in 
the highest degree probable that this is the case, and that the nutrition of the male takes 
place by means of the union of its vessels with those of a neuter individual (or individuals) 
though the common stalk-base. 

The state of preservation of the material is not suitable for the detailed examination of 
the vessels of the stalk ; but I have convinced myself of the existence of both anterior and 
posterior stalk-vessels, as in other species of Cephalodiscus. There is also evidence that a vascular 
continuity between the stalks of different individuals does exist in the .stalk-bases. In one case 
it appeared that the posterior vessel of a stalk passes into the interior of the stalk-base, and 
travels, in the middle of the cavity of that structure, far enough to underlie the base of the 
next stalk. The appearances suggest the exist of a vascular plexus in this position, and there 
is some evidence that the ve.ssels of other stalks communicate with this plexus. The anterior 
vessel of the stalk first alluded to can be traced as far as the basement-membrane of the basal 
ectoderm of the common disc, although its exact mode of termination is uncertain. 

The principal difficulty in this view of the nutrition of the male zooids is the large size 
of the dorsal vessel (PI. VIII, figs. 86, 87). It has been argued above that this vessel, in the 
female Cephalodisctis, is a nutritive structure which conveys the products of digestion to the 
ovaries. The vessel in question is certainly not less developed in the male than in the female, 
and yet it starts from a stomach-region which is so vestigial that no stomach can be discriminated 
from the rest of the alimentary canal. A further difficulty is that I have been unable to discover 
any vessels from which the dorsal vessel could derive its blood. 

It is not inconceivable that the alimentary canal, though vestigial as a digestive organ, 
might be capable of taking in some nutritive secretion discharged by the neuter individuals into 
the cavities of the coenoecium. The mouth of the male is sufficiently well developed to make 
this possible. But any hypothesis of this kind could hardly be accepted without more definite 
evidence in its favour; and it seems more reasonable to look elsewhere for an explanation of 
the large size of the dorsal vessel. 

The explanation which appears to me most probable is that this receives its blood from 
the posterior vessel of the stalk and of the proximal jiart of the body, and that its large size 
adapts it for acting as a reservoir of blood. I have not been able to demonstrate any continuity 
between the two vessels in question ; and indeed the posterior .stalk-vessel in passing forwards 

SinoGA-EXPEDITIF. XXVt/'/V. 12 



90 

becomes more and more obscure, and cannot certainly be recognised in the region of tlie 
intestinal loop of the gut. I do not think that this forbids the assumption I have just indicated. 
The thin-walled vessels of Cephalodiscns are very difficult to distinguish in their empty condition, 
and the failure to find a vessel in a particular case is no proof that it does not exist. It will 
be remembered that, in the female Cep/ialodiscus, the posterior stalk-vessel ends in the wall of 
the second stomach, and I have suggested above that its ijlood, after passing through the 
sinuses of the alimentary canal, finally makes its way to the donsal vessel. With the practical 
disappearance, in the male, of the first and second stomachs, the posterior stalk-vessel might 
still retain its function of supplying the dorsal vessel. On a priori grounds therefore it appears 
to me probable that there is an indirect cominunication between these two vessels. 

(II) The function of the epidermic vesicles of the arms of the male. 

I think there can be little doubt that these structures are homolog-ous with the vesicles 
which occur in the end-bulbs of the arms of the females of certain species, and especially of 
C. dodecalophus. I have not found them in C. Icvinseni, but they are well developed in the 
anterior pairs of arms in the buds of C. gracilis, and sometimes at least they persist in the 
adults of that species. 

I have in one or two cases noticed appearances (PI. IX, fig. 98) for which I cannot 
quite account, in C. sibogae. An ordinary tentacle-bearing arm has been found, in a partially 
teased preparation, with its di.stal end prolonged into an elongated, vesicle-bearing portion without 
tentacles, similar to the entire arm of a male. I think there is little doubt that this is a correct 
observation, though in view of the tangled condition of the zooids the possibility is not quite 
excluded that the arm of a male has adhered to that of a neuter by defective preservation. 
There is, however, practically no doubt that the arm shewn in fig. 98 is in continuity with an 
individual which bears tentaculiferous arms and has the general characters of a neuter. But it 
also appears that the metasome of this individual contains, in the position occupied by the 
ovaries of an ordinary Cephalodiscus, a pair of small testes, which seem to be functional organs. 
I therefore regard this case as one of correlated variation, in which a zooid has not only the 
male character of possessing testes l)ut also the associated character of developing numerous 
vesicles on one of its arms. I cannot, unfortunately, decide whether the abnormal arm belongs 
to the first pair, though this is by no means impossible. It must further be pointed out that 
there is some difficulty in disentangling a complete zooid from. the ma.ss of somewhat badly 
preserved individuals found in the basal encrustation of the coenoecium ; and it is thus not 
impo.ssible that all the neuters may have one or more of their arms prolonged into vesicle- 
bearing portions. The evidence is, however, distinctly opposed to any such view; and fig. 98 
thus appears to represent an abnormality. 

It the vesicles of the male arms represent those of the end-bulbs of the arms of C. 
dodecalophus, it is probable that their function cannot be one whicii is exclusively correlated 
with the other peculiarities of the male. This makes it less probable that the vesicles have the 
nature of reserve-supplies of nutritive material, developed precociousl\ in the young l)ud for the 
nutrition of the future testes. Some support might be given to this view by the fact that some 



91 

of the old males seem to have lost most of their vesicles; although, on the other hand, others 
shew no trace of this tendency. 

Masterman (97, 2, p. 344) suggested that the end-bulbs of C. dodecalophus had the 
nature of compound eyes, a function which their position makes not improbable; although he 
subsequently abandoned that hypothesis (03, p. 725). Colf, (99) on the other hand believes that 
the vesicles are comparable with the rhabdites of Turbellaria. Although I have not examined 
the structures with the aid of the histological methods recommended by Cole, the suggestion 
of this observer seems to me not improbable. If this were the case it would follow that the 
male individuals of C. sibogae are not only the individuals which produce the spermatozoa, but 
that they have a subsidiary function, analogous to that of the dactylozooids of Hydrozoa, of 
producing weapons for the defence of the colony. It may be presumed that the zooids of both 
kinds can be protruded more or less from the orifices of the coenoecium. It is not difficult to 
imagine that the long arms of the immature and adult males, waving about in the water among 
the plumes of the neuter zooids, might be valuable weapons of defence, on the assumption that 
Cole's view that the end-bulbs of C. dodecalophus are rhabdite-batteries is the correct one. 

It seems to me not impossible that the remarkable "Harchen" of the epidermis of 
Phoronis gracilis^ of which a description has recently been given by de Selys Longchamps 
(03, p. 28, figs. 22 — 26), may be comparable with the epidermic vesicles of Cep/ialodiscus. 



XVI. BUDDING. 



The details of this process have been described b)- Mastermax (98, 2), some of whose 
more important results may be summarised as follows. — 

The buds are formed on either side of the middle line of the parent stalk, from the 
proximal, sucker-like extremity of that structure. A new bud may develop from the stalk of a 
young individual which has not yet become free. The tissues of the bud are derived entirely 
from ectoderm and mesoderm, the endoderm taking no part in the process. The coelomic cavities 
are formed from that of the parent stalk, and in the youngest stage observed are represented 
by a single pair of cavities, completely subdivided by a median mesentery, and continuous with 
the cavity of the stalk of the adult. The mesentery contains a vessel which is given off by the 
anterior stalk-vessel. The vessel contained in the bud assumes a dorsal position distally, where 
it dilates to form the '■'subneural sinus". The proboscis early becomes conspicuous, its undivided 
body-cavity being the distal extremity of the coelom of the young bud, although it is not 
explained exactly how the unpaired anterior body-cavity is related to the paired coelom of the 
more proximal part of the bud. It must be supposed from the account given, and particularly 
from a consideration of Masterman's figures 29 and 30 that the median mesentery ends abruptly 
before reaching the distal end, which is accordingly undivided. The alimentary canal early makes 
its appearance as an ectodermic invagination, the orifice of which persists as the mouth. At 
about the stage when the first pair of arms begins to be indicated externally, the enteric sac 



92 

meets the body-wall at two circular lines of contact, thus dividin<,'^ the coelom into the: unpaired 
proboscis-cavity and the two pairs of cavities characteristic of the adult. The external division 
of the bud into the three regions has meanwhile been ]jrogressing. The future metasome is 
directly continuous with the young stalk, and its body-cavities are hence prolongations of those 
ot the parent stalk. The intestinal limb of the alimentary canal develops as a dorsal diverticulum 
of the originally simple enteric sac, and fig. 39 of the original memoir shews it passing from 
its origin freely through the body-cavity, the coelomic epithelium dipping down between it and 
the stomach. The intestine grows dorsally till it meets the body-wall, when it opens to the 
exterior by the anus, which is from the first in its definitive position. The pharyngeal region 
gives rise to evaginations which form liic notochord and the gill-slits. The ovaries are developed 
from the wall of the coelom ; but the oviducts, like the collar-pores, are ectodermic invaginations. 
The arms are of course formed as donsal outgrowths of the collar. 

Fowler (04), in describing the budding of Rhabdopleura^ states that most of the alimentary 
canal is probably derived from a thin-walled tube present in the mesentery of the parent-stalk, 
and he supposes that this tube is of endodermic origin. The commencement of the alimentary 
canal is, however, believed to be formed from ectoderm, and it is from this stomodaeal portion 
that he believes the notochord to origfinate. 

The analogy of the Tunicata shews that there is no a priori improbability in Fowlkr's 
account of the origin of the alimentary canal; antl the supposed endodermic tube of the stalk 
could be regarded as an epicardium-Iike formation. I'rom such observations as 1 have been able 
to make on the budding, I am, however, inclined t<j think that Mastkrmax is right in deriving 
the entire alimentary canal of the bud from ectoderm, a process which is believed by the majority 
of investigators to take place in the budding of the Ectoproct Polyzoa. I have, moreover, given 
reasons above (p. 78) for believing that the "endodermic" tube in the stalk of Rhabdoplejira 
is the posterior stalk-vessel. Fowler has not, as a matter of fact, brought forward evidence 
shewing that this structure gives rise to an)- part oi the alimentary canal of the bud; and, on 
the analogy of Cephalodiscus, I consider it probable that the entire alimentary canal of Rhabdo- 
pleura is derived from a single "Anlage". If this be the case, 1''owler's contention that the 
notochord of Rhabdopleura is morphologically ectodermic loses most of its force, since it might 
be argued on similar grounds that the entire alimentary canal of Cep ha Iodise us is to be regarded 
as a stomodaeum. 

It may be noted that Mastkr.max's account of the origin of the coelomic cavities of the 
bud is similar to that which has been given by Scmultz (03, i) of the origin of the cavities 
in regenerating specimens of Phoronis, in which both the preseptal and the postseptal cavities 
are derived from the general body-cavity. 

There appears to be a marked contrast between C. dodecalophus and C. levinscni on 
the one hand, and C. gracilis and C. sibogac on the other hantl, in respect of the extent to 
which the blastozooids remain connected with one another. It may, however, be remarked of 
C. levinseni that the colony a])pears to have been killed at a season when budding was not 
taking place with special activity. 

C. gracilis and C. sibogae on the contrary shew a distinct tendency to the production 



93 

of small colonies of individuals, connected by the basal disc from which the whole series of buds 
has been developed. A characteristic group of young individuals of C. gracilis is represented 
in fig. 4, but the mass in this case consists of the products of two budding individuals, which 
are represented respectively by the letters A and B. A. i — 4 are deeply pigmented bodies, 
probably representing degenerated stalks, A. i being the main stalk. The bodies of the zooids 
had presumably been lost before or at the commencement of the degeneration of the stalks. 
The only healthy zooid belonging to this group is the young bud ^.5. The second group {^B) 
consists of a budding disc prolonged into the structure B. i, which is clearly the base of an 
old stalk whose zooid has degenerated. B.-i is a pigmented body, probably a stalk whose 
degeneration took place some considerable time before the specimen was killed. B. 3 has also 
lost its zooid, but its degeneration has not advanced far. .5. 4 is a healthy bud which is seen from 
behind. The limit between its collar and its metasome is distinct, while the collar is produced 
into five arms on the right side and three on the left. The first arms of both sides already bear 
tentacles, and each ends in a swollen knob filled with refringent vesicles, as in C. dodecalophus. 
The base of the third right arm of this bud is concealed b\- the second and fourth arms, beneath 
which the distal part of the arm can be detected. .6". 5 is a somewhat younger bud, seen from in front. 
B. 6 is still younger, and is seen from the side. The collar and the metasome are already clearly 
marked off from one another, and a single pair of arms, represented by their vesicle-bearing 
knobs, are developed, although they are not well shewn in the figure. jS*. 7 is a very young bud, 
in which the proboscis is already marked off from the more proximal part. All these structures, 
B.2 — B.-j^ are derivatives of the disc (</.) which constitutes the base oi B.\. 

Groups of this kind occur in considerable numbers throughout the coenoecium. In at least 
one case evidence was obtained tending to shew that degeneration of a zooid begins by the 
throwing off of the proboscis and collar, leaving the metasome, with the alimentary canal, attached 
to the stalk. The number of structures which can be interpreted in no other way than as the 
basal ends of degenerated stalks seems to shew (I) that degeneration of the zooids is of frequent 
occurrence, and (II) that it is usually not succeeded by any regeneration of the lost parts. 

One of the youngest buds observed is shewn at the base of the stalk in PI. I, fig. 7 
(C gracilis) and more highly magnified in PI. Ill, fig. 26. The distal end of the bud is swollen 
into an ovoid form and is easily recognisable as the future proboscis. The anterior body-cavity, 
lined by a distinct epithelium, can clearly be seen in optical section. The swollen region 
which intervenes between the proboscis and the base of the old stalk probably represents the 
collar + metasome. 

Fig. 27 is a rather older bud of the same species, somewhat less magnified than 
fig. 26, and is attached to the basal disc of a zooid which has not degenerated. The proboscis 
has assumed its adult character, being already flattened in an antero-posterior direction, and it 
is convex anteriorly and concave posteriori)-. The collar, which could not be distinguished from 
the metasome in the earlier stage, is now well marked, and is growing out dorsally into the first 
pair of arms. Both probo.scis and collar have well marked cavities, but it cannot definitely be 
ascertained whether these cavities are continuous with one another or not. 

Fig. 8 is a po.sterior view of an older bud, considerably less magnified, and corresponding 



94 

in the degree of its development with //. 6 in fig. 4. The proboscis has acquired its pigment- 
line, while the two arms of the first pair are short bodies, each ending in a knob containing 
refringent vesicles. The collar is marked off dorsally from the metasome by a slight groove. 
It may be noted that the male individuals of C. sibogae remain at this stage of development 
in respect of their arms and of the absence of any demarcation between body and stalk. 

Fig. 30 is an anterior view of an older bud, more highly magnified. The proboscis is 
somewhat torn on the right side of the figure, and the first arm nf the same side has been 
lost. The other first arm is a good deal longer than in fig. 8, and a second pair, also with 
vesicles, has been developed behind it. The mouth and a small alimentary canal are seen through 
the more or less transparent wall of the proboscis, while it may specially be noted that the lower 
lip or operculum [pp^ is continuous with the second arms, which are for the moment those which 
are most posteriorly situated. Ovaries are already present, but are not represented in the figure. 

Fig. 9 is a similar view of a somewhat older bud, in which some indication of the 
development of new arms may be observed. In fig. 32 four pairs of arms are ]>resent, five of 
which shew young tentacles. No vesicles can be found at the tip of the first arm of the left 
side, but a few are present in the corresponding right arm and in the second ant! third left 
arms. Their condition in the second left arm seems to shew that they are in process of being 
lost. This is probably a normal feature in this species, since it is practically certain that no 
vesicles are present in any of the arms of some of the adult individuals, although I have been 
able to recognise them at the tips of the first two pairs of arms in one or two adult zooids. 

Most of the adult organs are already developed in fig. 32. The intestinal limb of the 
alimentary canal is seen in the foreground, while the mouth (;«.) can be made out by deeper 
focussing. On the right side of this is seen the triangular lateral lobe of the operculum [pp. r.). 
The two ovaries are visible, somewhat overlapped b\- the rectum. The body is still a direct 
prolongation of the stalk, aiul it ma)- specially be noted that the arms are developed in such 
a position that their food-grooves at first face the posterior side of the jiroboscis. The posterior 
limb of the vascular loop of the stalk is seen attached to the bend of the alimentary canal. 

Fig. 31 is a similar bud, seen oblicjuely from the left side. The alimentary canal has 
acquired its adult arrangement, and the left gill-slit (^4''. .f. c.) and collar-pore (c. c. c.) are shewn 
in the figure, which further indicates the course of the food-grooves of the first three left arms 
on their way towards the mouth. 

The bud B. 4 in fig. 4 possesses the full number (5) of arms on the right side, the 
fifth arm having the form of a nearly spherical swelling which is partly concealed by the base 
of the fourth arm. This specimen, like fig. 32, shews clearly that the arms are donsal outgrowths 
of the collar-region. 

F"ig. 29 illustrates the fact thai the stalk-vessels are well developed in the ])ud, a fact 
which is no doubt of great physiological importance in connexion with the sujjply of nutriment. 
The posterif)r limb of the vascular loop is, as usual, attached to the bend of the alimentary 
canal, while the anterior limb fades away in the anterior part ot the body-wall of the metasome. 
Pig. 28 shews the two parts of the stalk-vessel of the same Inul at a point a good deal nearer 
the base of the stalk. 



95 

I have been vinable to obtain any confirmation of the account given by Masterman of 
the changes in the position of the arms during the development of the bud. I have already 
discussed this question (p. 36), and I will merely repeat in this place that I believe that the 
complicated rotation of the arms described by that author does not occur, and that the hypothesis 
suggested to explain it is accordingly unnecessary. 

In examining sections of buds of various ages, in C. dodecalophiis and C. gracilis^ I have 
come to certain conclusions which do not agree with those of M.\sterman (cf. p. 91). There 
can be no question that the structure described by him as the "subneural sinus", in the later 
stages at least, is the pericardium. Masterman has more recendy (99, 2) admitted that the 
space which he at first described, in the adult, as the subneural sinus is in reality a pericardium, 
similar to that of Balanoglossus, although in his latest paper (03, p. 725) he states that it is 
evident that in his account of the budding "the origin of the pericardial sac must have been 
overlooked". From this I understand Masterman to mean that while he would admit that the 
"subneural sinus" shewn in figs. 60 and 81 of his paper (98, 2) on the budding is the pericar- 
dium, he would probably maintain that the "subneural sinus" shewn in earlier stages such as 
figs. 36, },'] and 39 was really a vascular space. I am inclined to think, on the contrary, that 
the "subneural sinus" shewn by Masterman in figs. 37 and 39 at least is the same structure 
as that of the later stages (figs. 80, 8 1 ). In all these cases the organ is represented as having 
no proper wall of its own, but as being a blastocoelic space between the ectoderm and the 
coelomic epithelium. This does not agree with my own results, and in further criticism of 
Masterman's fig. 39 I must point out that I have reason to believe, from my study of the 
same species, that the proboscis-cavity is not really continuous with the paired body-cavities at 
a stage so late as this, nor does the intestine pass freely through the body-cavity from its point 
of origin in any of the young specimens which I have had under observation. 

The buds of C. dodecalopJms make their appearance, as pointed out by Masterman, on 
either side of the middle line of the sucker-like base of the stalk, and on its anterior surface. 
F'&- 7i of C. gracilis^ would at first sight seem to imply that the buds of this species are 
developed on the posterior side of the sucker. It must, however, be remembered that in the 
long-stalked species of Cephalodisats^ rotation of parts of the stalk round its own longitudinal 
axis are commonly observed, as may be seen by an examination of the course of the longitudinal 
muscles in entire preparations, or of the anterior nerve-tract in sections transverse td the long 
axis of the stalk. There is evidence of twisting in the stalk of fig. 7, and I think that the bud 
which faces posteriorly in the preserved specimen is really situated on the anterior side of the 
sucker. It is certainly a lateral bud, and a still younger bud is indicated by deeper focussing 
in the same specimen. 

In its earliest recognisable condition (PI. XIII, fig. 164, b)) the bud of C. dodecaloplms 
is a spherical vesicle lying in the thickness of the parent ectoderm, and formed as an outwardly 
directed bay of the basement-membrane. The interior of the parent-stalk is occupied by muscles 
and connective tissue which are developed to such an extent that no definite coelomic space 
remains, although the condition of the stalk throughout the development of the bud shews that 
the whole of the tissue internal to the basement-membrane of the epidermis must be regarded 



96 

as filliiij^f the third l>ody-cavil\- of this region. The \')ung bud is occupied by a derivative of 
this packing' tissue-, and although the cells in question may perhaps at first constitute a solid 
mass, they have arranged themselves as an epithelium surrounding a central cavity at the 
earliest stages recognisetl as young buds. The central cavity is in communication with the virtual 
cavity of the parent stalk ; and although this communication is interrupted in the particular 
section figured (fig. 1 64), it is clearly seen in other sections of the same bud, and it is visible 
in the older bud {d') shewn in the .same figure. The butl thus originates as a diverticulum of 
the third body-cavity, which shortly gives rise to a corresponding projection of the ectoderm. 
At its first appearance, as shewn in transverse sections, the diverticulum appears to be undivided. 

.\t a slightly later stage (fig. 162), as stated by Masterman (98, 2, p. 515), the cavity 
of the bud is divided by a prolongation of the anterior mesentery of the parent stalk. The 
parent mesentery carries a blood-vessel {a. v.), and although I have not been able to demonstrate 
the entry of a branch of this vessel into the bud 1 liave little doubt that Masterman is right 
in stating that this is the fact. I cannot, however, agree with him that the three divisions of 
the coelom remain continuous with one another up to the late stages shewn in his figs. 37 and 
39. On the contrary, I find that in stages in which the ectoderm of the bud forms merely a 
hemispherical outgrowth of the parent stalk (figs. 161 — 163) a terminal coelomic vesicle ((5.^-') 
is sharply marked oft", and occupies the distal end of the bud. 

Figs. 161 — 163 cut the parent stalk transversely to its long axis, and the bud is 
accordingly cut in a frontal direction. The three figures represent consecutive sections, fig. 161 
being the one which passes nearest the base of the parent stalk. The lateral origin of the bud 
is clearly shewn by these figures. The pro.ximal part is divided by a median mesentery, the 
right and left divisions of the coelom communicating freely with the parent stalk. The distal 
end of the bud in fig. 161 is occupied by a spherical vesicle, with a well marked coelomic 
epithelium. In the next section (fig. 162) the vesicle is divided from the paired coelom of the 
right side of the figure by a minute oval vesicle {/>er.}), which contains several nuclei. In tiie 
next section (fig. 163) the left paired cavity has almost disappeared, while the distal end of 
the bud is occupied by a cavity whose wall is not certainly constituted b)' an epithelium. I am 
unable to decide whether this cavity is continuous with the terminal cavity of fig. 162 or whether 
it is to be regarded as a vacuolated condition of the terminal ectoderm : but I am inclined to 
adopt the latter hypothesis. It is in any case quite clear that in the young bud of C. gracilis 
shewn in PI. Ill, fig. 26, the end of the bud is occupied by a single ovoid epithelial vesicle. 

.Although I cannot identify the parts of the young bud shewn in figs. 161 — 163 with 
certainty, it appears to me highly probable, from a comparison with later stages, that the vesicle 
marked b. r.' is really the coelomic sac of the anterior body-cavity, that the paired cavities 
represent the third body-cavities and probably the collar-cavities as well, and that the minute 
structure per.', is the pericardium. There is no clear evidence tt) shew how these structures 
have originated '), though I consider it probable thai the)' have been formed by the tlivision 
(if the single coelomic .sac seen in the younger l)ud in lig. 1O4. It is not impossible that the 



I) In regenerating specimens of Balanoglossus, DawyijOFF (02) tinds that the pericardium is derived from the proboscis-cavity, 
and the latter from the perihaemal spaces; the amputation having been made through the collar. 



97 

pericardium and the anterior body-cavity are the members of an anterior pair of coelomic spaces, 
and that they have been segmented off respectively from the distal ends of the right and left 
cavities of the proximal part of the bud. The view that the pericardium is the fellow to the 
anterior body-cavity has been suggested for Balanoglossus by Bourne (89, p. 66) and Spengel 
(93, pp. 682, 689) but it may be remarked that the strictly median position of the pericardium 
in the later stages of Cephalodiscus and the fact that both proboscis-pores open into the atiterior 
body-cavity are not in favour of this view. Some of the later stages {e.g. figs. 177 and 179 -f 180) 
might suggest that the pericardium represents an independent somite. 

Whatever view is taken of figs. 161 — 163 there can be no reasonable doubt that they 
indicate a segmentation of the coelom beginning at a very early stage in the budding, and that 
Masterman (98, 2, p. 516) is mistaken in supposing that the coelom remains undivided until 
after the alimentary canal has become obvious. 

Figs. 175 — 177 represent a later bud, cut nearly sagittally, the parent stalk being however 
cut more or less transversely to its main axis. The coelomic cavities are now separated from one 
another, although the third body-cavities are continuous with those of the parent stalk. This is 
shewn in fig. 175, in which b.cr represents the collar-cavity of one side. It is so closely connected 
with b. c? as to suggest that the two cavities have been developed as the result of the inter- 
ruption of a single cavity by the formation of a transverse septum. The anterior body-cavity 
[b. c?) appears separated from the collar-cavity by a considerable interval, but this is partly 
because the proboscis is cut somewhat tangentially. Two sections further in the series, the walls 
of the first and second cavities are continuous with one another, while in the nearly median 
section shewn in fig. 176, both sets of paired cavities have disappeared, the proboscis being 
occupied by the anterior coelomic sac [b. c?) in front, while at its base is a smaller vesicle {per.) 
which can be recognised with certainty as the pericardium. In fig. 177, on the other side of the 
middle line, four cavities are visible, the pericardium {per.) intervening between the anterior 
body-cavity {b. c.'^) and the collar-cavity {b. c"), and already shewing the ventral ingrowth of its 
wall which will give rise to the heart. The alimentary canal is distinguishable, in this bud, as 
a thick-walled sac opening by the mouth (fig. 176, ;;/.), which is in its definitive position on 
the ventral side of the proboscis. It is uncertain whether the whole of the internal mass in this 
figure belongs to the alimentary canal, or whether the posterior portion of it may be part of 
the wall of the third body-cavity, cut tangentially. A small part of the lumen of the alimentary 
canal is cut in the neighbourhood of the mouth. As regards its external characters it may be 
noted that the proboscis is spherical, shewing hardly any trace of the flattening which is .so 
characteristic of the adult. The boundaries of the collar are slightly indicated externally. 

Fig. 164 is a sagittal section of the terminal sucker of an old stalk, on the anterior side 
of which are two buds. The younger of these {b.^) has already been described. The older one ((5.-), 
situated nearer the sucker, shews the continuity of its third body-cavity with that of the parent, 
while the small ovoid vesicle {b. c.') is almost certainly one of the collar-cavities. In fig. 165, another 
section of the same bud, the anterior body-cavity {b. c.'^) and the third body-cavity {b. c.^) are 
unmistakeable, while it is highly probable that the vesicle marked per. is the pericardium and the 
structure marked b. c.' is the collar-cavity of the opposite side to that which is shewn in fig. 1 64. 

SlBOGA-IiXPEDITIE XXVI W.f. 1 3 



98 

I fully admit that the evidence afforded by the stages which have so far been described 
is anything but convincing with regard to certain points, but in the next stage figured (figs. 
178 — 180) we are on surer ground. The sections are in much the same plane as the preceding 
ones, and are from a bud in which the first pair of arms is beginning to develop. 

In fig. 178 are seen the proboscis and collar with their respective cavities, the collar- 
cavity being prolonged into the developing arm (a./.). A portion of the metasome {met.), with 
its body-cavity, is cut tangentially. 

In fig. 179, the proboscis and collar are cut medianly. The proboscis has not only become 
somewhat flattened, but it shews another of its adult characters in having a ventral lobe composed 
of a fold of ectoderm, with ba.sement-membrane between the two layers, but not containing a 
prolongation of the proboscis-cavity. The pericardium {per.) possesses a thickening on its posterior 
wall which indicates the wall of the future vascular space. The mouth {m.) and part of the 
alimentary canal are well developed, although the posterior outline of the latter is obscurely 
marked off from the epithelium of the third body-cavit\-. The notochord {nch.) is present, beyond 
doubt, as a small diverticulum of the pharynx, reaching the wall of the pericardium. 

In fig. 180, the middle line has been passed, so that the other collar-cavity and first 
arm are cut, while the coelomic sac of the proboscis is cut tangentially. The bud was probably 
not lying with its axis in one plane, since the trunk is cut oblicjuely transversely to its main 
axis. The intestinal limb of the alimentary canal, which meets tlie body-wall in the position of 
the future anus, is connected with the ventral wall of the body by the median mesentery, on 
either side of which are the paired third body-cavities. 

Assuming that the pericardium here described is M.\sterm.\x's "subneural sinus", it will 
be noticed that this specimen lends no support to the statement of that author (98, 2, p. 516, 
figs. 37, 39) that the notochord (= "subneural gland") is at first at some distance from the 
pericardium (= "subneural sinus") and at a later stage .shifts its position so as to meet it. 

I think that there is very little reason to believe that the structure marked sti.g. by 
M.\STERM.\x in fig. 37 has anything to do with the "subneural gland", a structure which I 
describe under the name of notochord. In stages so late as his figs. 37 and 39 I should not 
have expected to see a body-cavity extending continuously from the proboscis to the metasome 
on the ventral side of the pericardium; and for this reason and for others which I have explained 
above I cannot consider the figures in question as anything but diagrams (probably combination- 
figures), representing M.\sterm.\n's views with regard to the structure of the buds. 

The five body-cavities and the pericardium are easily recognisable from the stage represented 
in figs. 178 — 180 onwards, the third body-cavities remaining continuous with those of the parent- 
stalk until the bud is liberated, e.xcept so far as they are obliterated in the stalk of the bud 
by the development of muscles and connective tissue. The early appearance of the pericardium 
as a sliarply marked epithelial sac is certainly one of the most characteristic features of the 
budding of C. dodccalophus. 

The bilateral origin of the buds is well shewn in figs. 169 and 172. 

The parent slalk is turned forwards towards the jjroboscis, and its terminal sucker is cut 



99 

nearly frontally. Fig. 172 cuts the free end of the stalk tangentially, so as to shew a thick 
mass of ectoderm (d.) which is the edge of the sucker. In this mass are seen the third body- 
cavities of two buds (<^.\ d.'-) of different ages, in each case subdivided by a median mesentery. 
The middle line of the actual anterior edge of the sucker corresponds with the interval between 
the two buds, as is seen in sections which cut the parent stalk nearer its central axis. Some 
of these sections demonstrate the continuity between the cavities of the buds seen in fig. 172 
and that of the old stalk. 

Fig. 169 shews the highly crumpled condition of the ectoderm and of the basement- 
membrane, due to the contraction of the muscles of the stalk. Part of the edge of the sucker 
is still seen as two masses of ectoderm in contact with the younger bud (d.^). In both the buds, 
the edge of the mesentery which is further from the parent stalk corresponds with the anterior 
surface of the bud. The older bud (<$.") is cut somewhat obliquely through its stalk, the part 
which is nearer its base being still indicated by the third body-cavities. 

The structure of the younger bud, which is cut in a direction at riorht anales to its lone 
axis, may be studied from before backwards. Fig. 166 shews two cavities, lined by a distinct 
epithelium, of which the smaller, the pericardium (per.), is more dorsally placed. The larger (6. r.') 
is of course the anterior body-cavity. The pericardium is absolutely median, so far as can be 
seen, although it has not been found possible to decide whether it is a median structure or not 
in the younger stages. A section corresponding with fig. 166, though somewhat older, is figured 
by M'Intosh (87, p. 28, PI. V, fig. 3), although the pericardium, which is marked vc, is supposed 
to be part of the collar-cavity. 

Fig. 167 cuts the bud at the level of the collar-cavities and of the mouth (;«.) which is 
overhung by the ventral lobe of the proboscis. In the next section, the alimentary canal appears 
as a single vesicle, while in the next (fig. 168) the centrally placed nuclei {a/.} belong to the 
enteric sac, while the cavities at the sides {6. c:') are the third body-cavities. While the inner 
limit of the epithelium of these cavities is very distinct, the outer outline is much less so, and 
I have not been able to identify with certainty the boundary between the antero-ventral ectoderm 
and the internal tissues of the bud. Some of the thick ventral wall (upper in figures), both of 
this section and of the section of the same bud (S?) shewn in fig. 169 may really belong to 
the coelomic wall, and there are appearances in the sections which suggest that a proliferation 
of cells takes place on the outer side of the coelomic epithelium, in the anterior and antero- 
lateral regions, to give rise to the musculature of the body and stalk. The alimentar}' canal 
has disappeared in fig. 169, although the median mesentery persists as far as the junction 
with the parent stalk, both in this and in the older bud (figs. 169, 172). The mesenter}' seen 
in fig. 169 (younger bud) appears to contain a blood-vessel, while as another indication of a 
probable vascular space may be noticed the interval shewn in figs. 167, 168 between the 
epithelium of the alimentary canal and the coelomic epithelium. 

Fig. 170 is a section transverse to the principal axis of the older bud shewn in fig. 169. 
The alimentary canal is in contact with the posterior body-wall, and the intestine (inf.) is being 
constricted off from the stomach {siom.). In the section (fig. 171) of the same bud next in front 
of fig. I 70 the intestine has been completely constricted off, and it fills up the interval between 



lOO 

the stomach and the posterior epidermis; the two divisions of the aUmentary canal lying in a 
common peritoneal investment, formed exactly as in lit;. 170. The same section shews one of 
the ovaries [ov.) as a minute body continuous with the coelomic epithelium, from which it has 
probably been developed, in accordance with Mastermax's statement (98, 2, ]>. 519) to that effect, 
f^'&s. 173, 174 are drawn to shew the great proportionate size of the notochord (nc/i.) 
in the bud, a fact already commented on by M'Intosii (87, p. 28), and the obliquity of the 
lirst and second body-cavities to the long axis of the. bud. The proboscis with its body-cavity, 
and the pericardium have already acquired their adult relations. This bud still jjossesses a 
single pair of arms. 

.M_\- observations on the tirst development of the alimentary canal in the bud are, so 
far as they go, in favour of Masterman's view (98, 2, p. 515) that the entire alimentary canal 
develops as an ectodermic invagination ; and they are consequently opposed to those of Fowler 
(on RJtabdopleurd)^ according to which part of it is a derivative of an endodermic tube in the 
stalk. From the earliest stage in which 1 can recognise the alimentary canal, this organ appears 
to open definitely to the exterior by the mouth, and 1 have noticed no discontinuity of the 
kind which would be implied by 1"owi,ek's view that while most of the canal is endodermic, 
the anterior part is developed as a stomodaeum. 

W ith regard to the later development of the alimentary canal I cannot, however, agree 
with Masterman, according to whom the intestinal limb cjf the alimentary canal is developed 
as a diverticulum from the ventral and posterior end of the enteric sac. This is said to grow 
in a dorsal direction towards the position of the future anus, and in Masterman's fig. 39 
CPl. Ill) it is represented as traversing the coelom, and being covered throughout by peritoneum. 
In the "transverse" sections shewing the stomach and intestine given in the same paper 
(figs. 54 — 56) these parts are in close contact with one another and appear to be suspended 
in a common peritoneal sac, formed by the inner walls of the two third body-cavities ; and 
except in fig. 55 there is no indication that the peritoneum extends between them. If Masterman's 
account is correct, it must therefore be supposed that the intestinal limb of the alimentar\- 
canal, after passing along the mesentery at a certain distance from the stomach, comes into 
contact with the posterior wall of the stomach as it travels towards the dorsal border of that 
organ. This, as a matter of fact, is precisely the arrangement which is found in the adults of 
all the species, and I was accordingly prepared to find that Masterman's account of the 
formation of the intestinal flexure was correct. But the evidence seems to be opposed to 
M.\sterm.\n's statements. The intestinal limb, at its first origin, is enclosed in a peritoneal 
sac common to it and the stomach (figs. 170, 171 ; 56), and it becomes separated from the 
other limb of the alimentary canal only when it has passed the stomach and has become the 
rectum. In this position the intestinal limb has a peritoneal investment of its own, even in 
comparativel}- xoung Inids; but I can find no evidence in the young stages of any trace of body- 
cavity in the concavity of the bend of the alimentary canal, as represented in Masterman's 
fi.^- 39- i'le arrangement found in the adult must therefore be acquired at a later stage in 
the budding, and I imagine that what takes place is that the splanchnic epithelium of the 



lOI 

coelom (cf. fig. 171) grows in between the stomach and the intestine from either side until the 
two layers come into apposition and form a median mesentery. The stomach and intestine are 
separated, at the principal flexure of the gut, by a section of body-cavity in the advanced bud 
shewn in fig. 181. It is perhaps significant that this is found at the end of that part of the 
alimentary canal which still retains, in this bud, what may be regarded as the primitive antero- 
posterior direction. It is thus not impossible that the intervention of the body-cavity at this 
point only of the fle.Kure has some morphological importance in indicating the region at which 
a dorsal flexure of the alimentary canal was first initiated. 

I have but few observations on the later stages in the budding. In a bud in which 
two pairs of arms have developed their terminal knobs, I find that the ventral mesentery has 
already acquired its adult arrangement in the stalk, where its middle portion has broken down, 
leaving merely the anterior and po.sterior mesenteric ridges which support the corresponding 
stalk-vessels. Figs. 56 — 58 are sections transverse to the long axis of a bud of C. gracilis^ 
and shew (<^) that the ventral mesentery is incomplete in the region of the stomach in the 
buds of this species, as in the adult; {5) that the stomach and intestine are invested in a 
common peritoneum, the intestine only acquiring a coelomic covering on its axial or dorsal 
side when it becomes the rectum ; [c) that the dorsal vessel originates by two lateral roots 
which are formed by folds of the splanchnic mesoderm covering the stomach, which is probably 
surrounded by a system of vascular spaces between its own epithelium and that of the coelom. 
This origin of the dorsal vessel is also indicated in the sagittal section of C. dodecalophus 
shewn in fig. 181. 

Fig. 59 shews a section of an advanced bud of C. gracilis, cut transversely to its 
long axis. The mesenter)^ of the third body-cavities is complete at this level, although it breaks 
down in the middle immediately after the alimentary canal ceases to be visible in the sections. 
The pharynx and stomach run in a horizontal plane, as in fig. 181 ; the next section nearer 
the basal end of the stalk merely cutting the ventral wall of the stomach tangentially, while 
the next section nearer the dorsal surface shews the intestine, which has started from the 
posterior end of the stomach seen in fig. 59. 

The two collar-cavities (b. c\~) are seen at the sides of the mouth (w.) the projecting 
lobes of the body-wall in which they lie being parts of the operculum. Between the operculum 
and the metasome, on the right side, is seen one of the collar-canals {c. c), which appear to be 
formed, as Masterman states (98, 2, p. 518), as derivatives of the ectoderm. The evagination 
(g. s.) of the pharyngeal wall seen on the right side can be identified as one of the gill-slits, 
from its relation to the collar-canal ; and here too I am confirming one of Masterman's results. 
The proboscis in this specimen is not lying symmetrically. 

F'to- 5i of ^- levinseni, is of interest as shewing that the proportions of the body, in 
young individuals of that species, are not unlike those of the adult C. dodecalopluis. 



I02 



XVII. DEVELOPMENT. 



The observations which have hitherto been made on this subject are of the most fragmentary 
nature. The "Challenger" specimens of C. dodccalopJms^ although containing numerous eggs, each 
enclosed in a vitelline membrane and lying freely in the cavity of the coenoecium, were obviously 
obtained at a period shortly before the normal developmental season, and nearly all the eggs 
are unsegmented. M.vsterman's observations (98, 2, p. 513) have already shewn, however, that 
some of the eggs are developing; and I have myself found several embryos. 

The preliminary note ])ublished by Andersson (03) shews that the embryos leave the 
parent colony in the form of ciliated "planulae". In the absence of evidence to the contrary, 
it \\\\x\ be presumed that Andersson's statements refer to C. dodecalopJms, since the larvae were 
obtained from material dredged in the Beagle Channel. The date on which the dredging 
was made was Oct. 30, whereas the "Challenger" material, in which development has hardly 
commenced, was collected on Jan. 11. 

My own observations on the development have been made on C. levinseni and C. 
gracilis^ in both of which the coenoecium contains embryos in various stages of development. 
My examination of this material has been incomplete, partly owing to the difficulties of .staining 
— which are no doubt the result of imperfect preservation — and partly owing to the fact 
that I have not felt myself justified in sacrificing more than a small portion of the unique 
material, in each case, in order to study the development. The following statements with regard 
to this subject may, however, be made : — 

(I) The egg of Cephalodiscus contains a large cjuantity of yolk. 
(II) Segmentation is complete, although the later stages are influenced by the presence of yolk. 

(III) The embryo leaves the colony at a comparatively early stage. This has been definitely 
observed by Andersson, whose results are confirmed — so far as the negative evidence 
is worth anything — by the absence of later stages in the coenoecium of the specimens 
at present under consideration. 

(IV) The structure of the oldest embryos observed makes it probable that development is direct, 
and that there is at no time any transparent, pelagic, larval stage. 

(V) The embryos of the two species observed differ widely from one another in general 

appearance, but agree in essential features. 
(\'I) The body-cavity occurs in a completely segmented form before the time of hatching. 
(\TI) The alimentary canal, in the latest stages observed, has the character of a mass of yolk. 

It is unfortunate that even the oldest embryos do not appear to throw any light on the 
way in which most of the organs of the adult are developed ; and much remains to be done 
in the study of the development of the Pterobranchia. 

AH the develo]jnH-ntal .stages which have been observed are still enclosed in the vitelline 
membrane. C gracilis and C. levinseni have a simple spherical or ovoid vitelline membrane, 
which is not prolonged into the narrow stalk found in C. dodccalopluis. 



(a) Embryos of C. levinseni. 

The oldest embr^-os (PI. XI\\ figs. 198, 199) usually have an ovoid form, their greatest 
length being about 550 u.. The most striking facts which can be made out in the entire embryo 
are : — (I) that the yolk is practically confined, at this stage, to a central mass, which is 
distinctly divided into two regions; (II) that a large area of the ectoderm of one surface of the 
embryo is composed of cells which stain more readily than their neighbours; (III) that a part of 
the ectoderm near this differentiated region contains numerous, highly refractive, rod-like bodies. 

Several frontal sections through an advanced embryo are shewn in PL XIV, figs. 207 — 210. 
It can hardly be doubted, from an inspection of these figures, that the region {vac^ containing 
the refractive bodies is the anterior end of the embryo. The part indicated above by (II) appears 
to be the ventral side, and I shall speak of it as the "ventral thickening" (f. /.). Its general 
shape is shewn in fig. 207, which is a frontal section cutting the whole of this "ventral" region. 
The subsequent sections (figs. 208, 209) shew that the ventral thickening extends round the 
anterior end of the embrj'o towards the dorsal surface, but that it disappears before it reaches 
that surface. 

Figs. 203 — 205, from a transverse series, shew more of the characters of the ventral 
thickening, which contains a large proportion of much elongated cells of a glandular appearance. 
This tissue closely resembles that which composes the anterior, thickened wall of the proboscis 
of the adult. In both cases, the elongated gland-cells constitute the greater part of the epithelium, 
and moreover have exactly similar staining properties. Thus the gland-cells, of the adult proboscis 
and of the embryonic ventral thickening alike, stain intensely with Heidenhaix's haematoxylin 
or with "Orange G". It accordingly appears probable that the ventral thickening of the embr\-o 
is in some way converted into the glandular epidermis of the proboscis of the adult. If this be 
the case, it may perhaps be inferred that the embryo comes to rest, after a short free-swimming 
period, and secretes the commencement of the future coenoecium by means of the gland-cells 
in question. 

The view just indicated with regard to the further history of the ventral thickening 
receives further support from the embryo represented in fig. 200. The part [vac^ containing the 
refractive bodies is much elongated, a condition which appears to be due to the fact that the 
embrj-o is squeezed into a narrow space between a zooid and the wall of its tube. The ventral 
thickening is closely applied to this wall, in a way which suggests that the embryo was crawling 
on it. The resemblance of these parts of the embr^-o to the proboscis of the adult is very 
striking, and it is rendered more significant by the fact that the free dorsal and lateral edge 
of the adult proboscis (PI. I, fig. 5) contains refractive bodies somewhat similar to those of the 
embryo, although not behaving in quite the same way with varying modes of illumination. 

The yolk-containing central mass of these embryos has a highly characteristic form, which 
may be described as umbrella-shaped (figs. 198 — 201). Distinct indications of a central cavity 
may be found in the median part of this mass (figs 198, 199), which is sharply marked off 
from the anterior part by the absence of yolk-globules in the intervening tissue. The whole of 
the rest of the umbrella-shaped central mass is crammed with numerous yolk-globules, which 
have a diameter of about 3 — 4 a. 



I04 

The general structure of the embryo may be ilhistrated by figs. 207 — 210. Fig. 207 
shews practically the whole e.xtent of the ventral thickening {v. f.). It consists of numerous 
o-land-cells, cut transversely, and stained intensely with iron-haemato.\ylin, separated from one 
another by epidermic cells which are practically unstained. Posterior to the ventral thickening 
is a deep median groove which may be traced through a number of .sections until it reaches 
the posterior end of the embryo (fig. 209). It is one of the characteristics of the older embryos 
found within the coenoecium that the epidermis is a good deal folded (fig. 210). It is thus 
not easy to decide whether the invagination shewn in fig. 207 is more than an unimportant 
fold. It does not appear, in the corresponding position, in figs. 205, 206, which may however 
belonor to a younger embryo. But in the embryos of C. gracilis^ a definite invagination 
(fi^s. 1 89, 190, post. p.), which may be termed the "posterior pit", occurs at the posterior 
end. The fold shewn in figs. 207 — 209 may provisionally be referred to under the same name. 

Fio-. 208 still cuts the ventral thickening, and shews on the right side a few of the 
refractive bodies which have already been noticed. The central yolk-mass is dilated in front 
and narrower behind, the posterior portion being surrounded by a space which appears to be 
blastocoelic in nature. The body-cavity consists of the five divisions characteristic of the adult. 
The collar-cavities {d. c.') lie e.xternally to the blastocoelic spaces just mentioned, that of the 
left side being specially sharply marked, although both of them are (juite definitely separated 
from the anterior body-cavity. The posterior body-cavities {d. c.'^) are seen on either side of the 
posterior pit. 

It is not possible to decide from this section whether the proboscis-cavity possesses an 
epithelium or not. A clear .space external to its cavity is due to the fact that the gland-cells 
of the ventral thickening do not extend quite through the thickness of the epidermis. The 
collar-cavities and the metasomatic cavities have indications of nuclei internally to the membrane 
which forms their outer boundary. The left metasomatic cavity contains posteriorly a mass of 
cells which has the appearance of being a definite organ. 

In fig. 209 the ventral thickening is disappearing, and the ectoderm of the anterior end 
has the vacuolated appearance which is characteristic of the region containing the refractive 
bodies. Examined with a higher power, these appear to be rod-like accumulations of pigment- 
like granules. The posterior ]jart of the ectoderm is not vacuolated. The umbrella-like character 
of the yolk-mass is very obvious. The anterior part is separated from the more axially placed 
mass b)- a region in which yolk-spherules are absent, or are present in very small numbers. 
This region is bisected, on the left side (and throughout, in other specimens favourable for the 
examination of this point), by a distinct line which may probably be regarded as part of the 
posterior boundary of the anterior body-cavity. The collar-cavities are distinct, while the posterior 
body-cavities are separated from one another by an obvious mesentery. There are still indications 
of a a blastocoelic space surrounding the yolk, and limited externally by the splanchnic membrane 
of the second and third body-cavities. 

In fig. 210, the yolk-mass is continuous with the epidermis. This may be regarded as, 
in all probability, representing the l)lasto]jore and at tlic same time the future anus. The axial 
part of the )olk contains a cavity. This ajjpears to be the enteric cavity, although neither here 



I05 

nor in any of the other embryos is there the shghtest indication of the differentiation of a 
digestive epithelium. The section passes on the dorsal side of the communication between the 
axial mass and the anterior yolk, which thus appear separate from each other. The intervening 
tissue, which is in the main free from yolk-spherules, shews part of the membrane which has 
already been mentioned. The anterior part of the ectoderm consists of vacuolated cells with 
refractive bodies, while the posterior two thirds is a good deal folded and consists of unvacuolated 
cells which appear to be provided externally with long cilia. The posteriorly directed fold of 
the collar-epidermis on the right side of fig. 210 cannot certainly be differentiated from the 
other folds of the epidermis which are characteristic of the older embryos. But as a precisely 
similar fold appears, a few sections further, on the other side of the embryo, with a similar 
relation to the left collar-cavity, I am inclined to regard it as of some significance. 

Figs. 104 — 106 (PI. IX) are taken from a sagittal series of sections. Fig. 104, which 
belongs to the lateral region of the embryo, shews the two transverse septa between the body- 
cavities. Fig. 105 shews that not only is the posterior limit of the anterior body-cavity prolonged 
into the yolk-mass as a region traversed by a definite line and free from yolk, but that a similar 
yolk-free region corresponds with the division between the second and third body-cavities. This 
is the case on the dorsal side at least. On the ventral side it is not certain that the collar- 
cavity exists. The ventral thickening resembles the anterior epidermic thickening of the adult 
proboscis in the fact that the gland-cells are separated from the basement-membrane by a 
homogeneous layer which in the adult has been interpreted as part of the epidermic nerve-plexus. 
The dorsal posterior part of the epidermis is obviously ciliated in the section from which fig. 105 
was drawn. 

In fig. 106, which is nearly median, the third body-cavity can be recognised both dorsally 
and ventrally to the intestinal region, while the collar-cavity can only be made out dorsally. 
This section shews the edge of an invagination {s. 0.) of the dorsal vacuolated ectoderm of the 
anterior end, which forms a conspicuous organ better seen in the series next to be described. 

Figs. 202 — 206 represent five .sections taken from a transverse series of sections of an 
advanced embryo, stained with haematoxylin and Orange G. Fig. 202, through the anterior 
end, shews the front part of the ventral thickening, the gland-cells of which, like those of the 
adult proboscis of specimens treated in the same manner, are intensely coloured with the orange 
stain. The dorsal vacuolated ectoderm, in which some of the refractive bodies are seen, projects 
inwards in the form of a rounded organ {s. 0.) which has the appearance of a series of large 
vacuoles separated by trabeculae coloured wath haematoxylin. A crescentic section of the anterior 
body-cavity {d. c}) adjoins this organ, while the other space seen in the section is shewn, by 
comparison with other specimens, to be external to the basement-membrane {d.m.) of the epidermis, 
and may be artificial. Part of this space remains at the base of the ventral thickening in fig. 203, 
in which is seen the anterior part of the yolk, in the middle of which is an interval free from 
yolk-spherules and traversed by a distinct line. This is the extreme anterior part of the division 
between the two parts of the yolk shewn in fig. 210. The yolk-spherules are intensely stained 
with Orange G, and the whole mass is surrounded on all sides by the anterior body-cavity, in 

smOGA-EXPEDlTIE XXVI/^;V. I4 



io6 

the somatic wall of which there are some indications of an excessively tliin epithelial lining. 
The dorsal ectoderm, which has taken, in the main, the haematoxylin colour, still shews at its 
base remains of orange-coloured yolk-spherules. It further contains a certain number of vacuolated 
structures, stained with haematoxylin, and similar to those which compose the organ s. o. seen 
in tig. 202. These structures may probably be regarded as gland-cells. The rest of the ectoderm 
consists oi closely packed narrow cells. In fig. 204 the yolk-free region in the middle of fig. 203 
has extended as an elliptic line through the yolk-mass, which is thus divided into a central and 
a peripheral portion. The former surrounds a split-like cavity, which may be regarded as the 
commencement of the future alimentarj^ canal. The ectoderm no longer contains any gland-cells. 
On one side of the section is a narrow space [p. c.) lined b\- an obvious epithelium. This appears 
to be one of the collar-cavities, although the series of sections is not suitable for distinguishing 
between the second and third body-cavities in the more posterior parts of the embryo. It is, 
however, probable that in fig. 205 the ventral mesentery is that of the third body-cavities, 
while the septum between these and the collar-cavities is not visible. I have assured myself that 
in some of the embrj-os adjacent body-cavities may appear continuous as the result of defective 
preservation. It can hardly, be doubted that in the embryo here represented the paired body- 
cavities have a splanchnic lining as well as the more distinct somatic lining, but there is no 
evidence of the existence of a splanchnic layer in the region of the anterior body-cavity. 

The last remains of the anterior yolk-mass are seen in fig. 206, a few sections beyond 
which the posterior yolk-mass becomes connected with the epidermis by the divergence from one 
another of the two laminae of the ventral mesenterw In the more posterior sections a dorsal 
mesenter)- seems to be indicated, in addition to the ventral mesentery. 

The consideration of figs. 203 — 206 shews that in this embryo the anterior body-cavity 
sends a median prolongation backwards, on the dorsal side of the yolk, between the halves of 
the paired cavities. A similar arrangement is shewn in fig. 201, an obliquely longitudinal section, 
in which although the three segments of the body-cavitv are seen with moderate certainty on 
the dorsal side (left of figure), it is not quite certain that the collar-cavity is represented on 
the ventral side. 

((5) Embryos of C. gracilis. 

The oldest embryos of this species have the form represented, in side view, in fig. 188. 
The embrj-o here shewn measures 300 y.. in length, and like all the other embryos, both of this 
species and of C. levinseni, it is still enclosed in the vitelline membrane. Its most conspicuous 
organ is a large invagination of ectoderm (iv. ?«£>.), on what may be regarded as its ventral side. 
At the anterior end is a median organ [s. 0^ characterised by its transparency, while at the 
opposite end is a median depression of the ectoderm [post.py. In the interior of the embr\() is 
a mass ot yolk, which can be seen to be composed of two portions separated by an indentation. 
The refractive liodics characteristic of the anterior end of the embryos of C. levinseni do not 
occur, or at least not in precisely the same form. Thev mav, however, be represented by cells 
containing a brownish pigment which are .scattered irregularly throughout most of the ectoderm, 
though found in somewhat larger numbers near the posterior pit. 



Other embryos have a more spherical form, as for instance that shewn in fig. 187, a 
view from the ventral and anterior sides. The anterior transparent organ {s. 0.) is indicated 
externally by a depression, while the orifice of the ventral invagination is very conspicuous. 

Fig. 189 represents a spherical embryo seen from the ventral side, some of the organs 
being shewn in optical .section. It is probably somewhat older than fig. 187, the aperture of the 
ventral invagination being considerably shorter from before backwards than in that specimen. An 
emargination occurs in the outline at each end of the sagittal plane of the embryo, representing 
respectively the transparent organ [s. 0.) and the posterior pit {post. p.). These emarginations 
are even more conspicuous in the younger stages. 

The most striking difference between these embryos and those of C. levinseni is due to 
the presence of the large ventral invagination in C. gracilis. It seems to me probable that this 
is the representative of the ventral thickening of the embryos of C. levinseni, and that it is to 
be regarded as a ventral flexure, comparable with that of the embrj-os of other animals which 
undergo part of their development within an egg-membrane. It may be supposed that with the 
escape of the embryo from the vitelline membrane, the ventral invagination will flatten itself 
out and the embr)-o will thereby assume a more elongated form. 

Fig. 197 is a sagittal, nearly median section of an advanced embryo of C. gracilis, 
shewing the transparent organ (s. 0), the ventral invagination [v. inv.) and the edge of the 
posterior pit [post. p.). The internal yolk-mass has an emargination dorsally, in which lies a well 
marked coelomic vesicle [d. c.'). It can hardly be doubted that this represents the collar-cavity, 
and accordingly that the undivided space {d. c.'^) in front of it is the anterior body-cavity, while 
the spaces {6. t.^) at the opposite end are the third body-cavities. Both the right and the left 
cavity, with the ventral mesentery, are here seen, in consequence of a slight obliquity of the 
section. The anterior third of the ectoderm, between the two arrows shewn in the figure, is 
vacuolated in this embryo, while the remainder of the ectoderm is composed of narrow, closely 
packed epithelial cells of considerable height. 

Figs. 190, 196, 195 are three horizontal sections of a similar embryo. Fig. 190, which 
shews some histological detail, passes through the dorsal end of the ventral invagination (v. inv) 
the epithelium of which is cut tangentially ; and the lumen of the organ is thus not seen. 
Rather more than half of the ectoderm, at the anterior end, has a vacuolated structure, 
resembling that of the same part in C. levinseni. The rest of the ectoderm is composed of 
narrow, closely packed cells. In all parts of the ectoderm, except in the anterior transparent 
organ, occur the pigmented cells noticed in the entire embryos. There is some indication, in 
this and in other cases, that an accumulation of the pigment occurs on either side of the 
organ i-. 0. There is distinct evidence that rounded masses of the pigment are passed to the 
outer side of the ectoderm, where they are found within the vitelline membrane (fig. 197, ^.r^.), 
an observation easily made both in sections and in entire embryos. It may naturally be suggested 
that this embryonic pigment is of excretory nature; a conclusion which perhaps carries with it 
the consequence that the refractive bodies found in the embryos of C. levinseni, and moreover 
the epidermic pigment of the adult Cephalodisctis, may have the same physiological value. 

The transparent organ {s. 0) has a pear-shaped outline, and consists of a highly vacuolated 



io8 

tissue traversed by excessively fine threads containing a few minute nuclei. The organ is connected 
laterally with a part of what appears to be an epidermic nerve-plexus. This («. /.) is seen on 
tlie right side of fig. 190, but it is seen also on the left side in other sections of the same 
embryo. The intimate connexion of the transparent organ with the embryonic nervous system 
su2feests that the or^jan it.self is a sense-organ : and both in structure and in its relation to 
the nervous system it recalls the "pyriform organ" of the larvae of Ectoproct Polyzoa : — a 
resemblance which need not indicate any affinity of Ccphalodiscus to the Polyzoa '). 

The five coelomic spaces of Cephalodisacs are probably indicated in fig. 190. The 
proboscis-cavity [b. c}) has a somatic epithelium, in its anterior part at least, but 1 find no 
evidence of the existence of a splanchnic layer. The collar-cavity {b. ^.'), on the leit side, has 
a form and position which appear to be very characteristic of this species. It is somewhat 
triangular in section, with its base applied to the ectoderm and its apex projecting into the 
emargination of the yolk. On the right side (which passes through a more ventral region than 
does the left side of the section), the collar-cavity is a small oval vesicle, lying more posteriorly 
than the corresponding left cavity. A similar difference is noticeable in the third body-cavities, 
the section cutting the lumen of the left cavity and the ventral wall of the right cavity. 

Fig. 196 represents a more dorsal region of ilie same embryo. It involves the dorsal 
end of the posterior pit, which in this embryo has the form of a vertical slit, and it shews 
the five body-cavities. The manner in which the paired cavities end ventrally has not been 
ascertained with certainty, but it seems that the trunk-cavities are .separated by a ventral 
mesentery, as in fig. 197. 

Fig. 195 appears at first sight to indicate that the two collar-cavities become continuous 
with one another in the middle dorsal line. The sections are, however, not accurately horizontal, 
and an e.xamination of the neighbouring sections leads to the result that the cavity seen in 
fig- 195 is really the dorsal end of the right collar-cavity. 

Figs. 191 — 194 illustrate the structure of an advanced embryo as seen in transverse 
sections. F"ig. 191 shews the anterior sense-organ (i'. <?.), on either side of which is a mass of 
what seems to be nerve-tissue («. /.). The dorsal two thirds of the ectoderm is composed, as 
is usual in embryos at this stage, of vacuolated cells. In the ne.xt section further back (not 
drawn) the nerve-tissue can be seen underlying the ventral ectoderm, while in later sections 
(figs. 192 — 194) it underlies the greater part of the ectoderm, wherever this layer has assumed 
the form characterised by the absence of conspicuous vacuoles. There is in fact, in this embryo, 
a general epidermic nerve-plexus similar to that of Balanoglossus. There appears to be a 
slight concentration of this plexus at the angle between the wall of the ventral invagination 
and the lateral ectoderm (fig. 192). A ventral nerve is perhaps visible in fig. 193. 

The ventral invagination consists partly of vacuolated cells, intermingled with the narrow 

i) It might be possible to make a detailed comparison between the embryo of C. gracilis and that of one of the Ectoprocta, 
based on the similarity of the internal mass of undifferentiated yolk and on the pyriform organs of the two embryos, and comparing 
the ventral invagination of Ccphalodiscus with the "internal sac" of the Ectoprocta. Believing as I do that the Ectoprocta are related to 
the Entoprocta, and that the larvae of the latter indicate afTinitics with other groups characterised by the possession of a Trochosphere 
larva, I am not at present prepared to admit that the embryology of CcphaloJiscus suggests any affmity between that animal and 
the Polyzoa. 



I09 

epithelial elements characteristic of the rest of the ectoderm, while a certain amount of substance 
which is faintly stained (with borax carmine) may represent the glandular cells of the adult 
proboscis. This substance occurs, in the present instance, mainly near the bases of the ectoderm- 
cells, although in another embryo it occurs in larger quantity throughout the ventral invagination, 
which has lost the vacuolated condition just noticed. 

Some of the cells on the right side of the orifice of the ventral invagination in fig. 192 
project individually to the exterior. By comparison with other sections of the same embryo, it 
appears probable that this is a stage in the evacuation of excretory products. Turning to the 
body-cavities, fig. 192 shews the anterior cavity, with a distinct somatic epithelium, while in 
fig. 193 are seen the second and third cavities. The collar-cavities {S. cr) are separated from 
one another dorsally by a slight median thickening of the ectoderm, perhaps the commencement 
of the central nervous system. In their ventral region they pass round the outer borders of 
the posterior body-cavities, an arrangement which is also indicated in fig. 196. Both pairs of 
coelomic spaces are complete sacs, surrounded on all sides by an epithelium. In fig. 194 the 
collar-cavities have disappeared, while the posterior coelomic sacs seem to be continuous ventrally 
with the yolk. 

It would undoubtedly be possible to obtain fuller information with regard to the early 
development of Cephalodisciis from the material at present at my disposal; but I have refrained 
from sacrificing more than a small quantity of the specimens in order to study this subject. 
It is moreover highly probable that satisfactorily preserved material will soon be forthcoming, 
as is indicated by the short statement that has recently been published by Andersson (03). 
The examination of these heavily yolked eggs and embryos would undoubtedly be facilitated 
by the employment of specimens preserved by suitable histological methods. The history of the 
development, so far as I have been able to follow it, by means of the embryos described above, 
together with the few earlier stages I have examined, may be summarised as follows. 

(Ij The &go is large (300 — 400 a. in greatest length) and is richly provided with yolk. It 
becomes surrounded by a vitelline membrane on passing into the cavity of the coenoe- 
cium, and it remains inside this membrane during the whole of the earlier stages of its 
development. The embryo is probably hatched at the stage represented by figs. 188, 198 — 200 
(cf. Andersson, 03). 
(II) Segmentation is complete. Fig. 186 (C. gracilisj shews the first cleavage, one of the 
blastomeres being apparently preparing for a second division. Masterman (98, 2, p. 514, 
PI. \\ fig. 89) describes an embryo which, according to his statement, is a larva divided 
into two segments by a more or less equatorial furrow. Although I do not wish to dispute 
the accuracy of this statement, there is nothing in Masterman's account to forbid the 
supposition that the figure might represent an &gg divided into two blastomeres. 

I have found one or two late segmentation stages, from which the only conclusions 

I can certainly draw are that the cleavage continues to be complete, and that it gives 

rise to a solid embryo. 

(Ill) The solid embry^o just indicated consists of numerous cells, a large number of which are 

internal. The formation of the inner layer appears to take place by a process of delamination, 



I lO 



the externally placed cells difterentiating themselves off as an ectoderm, while the central 
mass gives rise to the yolk-mass of later embryos, and probably to the coelomic spaces. 
(IV) Immediately after the difterentiation of the ectoderm, the yolk is equally distributed 
throughout the (Miil)rvo. It mnv disappears from the ectoderm, and in the later stages is 
found entirely in the large yolk-mass which occupies the greater part of the cavity. 
(V) The yolk-mass becomes constricted, in front of the middle fC. levinseni) or behind the 
middle (C. gracilis). The anterior part projects backwards over the posterior part as an 
umbrella-shajjed mass of yolk, specially noticeable in C. levinseni. There is practically no 
sign of histological differentiation in the yolk-mass at any stage observed, although a cavity, 
probably the future enteron, appears in the posterior part of the yolk (C. levinseni). 
(VI) The ectoderm undergoes a considerable amount of histological differentiation. 

{a) The antero-dorsal portion becomes highly vacuolated, and at its front c-nd a 
larval sense-organ is formed. In C. gracilis this is a sharply marked pear-shaped organ 
(fig. 190, s.o.)^ which reaches the exterior at the base of a slight depression of the surface, 
while in C. levinseni., the organ is connected with a more definite invagination of the anterior 
ectoderm. It is not impos.sible that this sense-organ may represent the similar organ found 
in Tornaria (cf. Morg.a.n, 94. p. 33, PI. Ill, fig. 19). The anterior vacuolated ectoderm 
in C. levinseni contains numerous refractive bodies, while in C. gracilis nearly the whole 
of the ectoderm contains scattered pigment-ma.sses (fig. 190) which are probably excretor)-, 
since their occurrence between the vitelline membrane and the epidermis indicates that 
they are discharged to the exterior. 

{ti) The anterior half or more of the ventral ectoderm, in C levinseni, is somewhat 
thickened and forms a glandular mass, described above as the "ventral thickening". This 
tissue stains in the .same way as the thickened glandular epidermis of the anterior side of 
the adult proboscis, and it may probably be identified with this part of the adult animal. In 
C. gracilis, the corresponding part of the embryo forms a conspicuous "ventral invagination", 
which is probably due to a flexure ot the emliryo within its vitelline membrane. 

{c) At the posterior end of the embryo is a vertical .slit-like invagination, or 
"posterior pit" in C. gracilis (figs. 188 — 190); while in C. levinseni (figs. 199, 207 — 209) 
there appears to be a longer slit-like groove exending from the posterior end along part 
of the ventral surface of the embryo. 

{d) The remainder of the ectoderm, in both species, consists of much elongated, 
very narrow cells. Distinct evidence that these are ciliated was obtained in some cases 
(fig. 210). In the older embryos of C. levinseni, the ectoderm becomes folded in a 
complicated way. An early stage in this process is shewn in fig. 210, but in older embryos 
the folds acquire a much greater degree of comple.\ity. 
(VII) The body-cavity is represented by five coelomic spaces, corresponding with those of the 
adult. The proboscis-cavity may have distinct indications of a somatic epithelium, but there 
is no proof that a splanchnic layer is present. The second and third cavities, on the 
contrary, are probably sacs with a complete epithelial investment. The origin of the 
coelomic spaces has not been traced. 



1 1 1 



While the embryos described above shew obvious indications of possessing the essential 
structure of Cephalodiscus, the clue to the precise relations between embryo and adult will 
probably be furnished by the study of the later stages, which are not yet forthcoming. The 
consideration of the embryo of C. levinseni shewn in fig. 200 suggests that the ventral thickening 
can be used as a crawling organ, and that it is probably already in a condition to secrete the 
commencement of the coenoecium. The absence of a functional alimentary canal further points 
to a free life of brief duration, and it appears probable that the larva constructs its tube after 
a very short free life, and undergoes an important part of its metamorphosis within its tube. 
The very striking folding of the ectoderm in the old embryos of C. levinsein is perhaps a 
preparation for the stretching of the body-wall necessary to provide accommodation for the 
future alimentary canal, the anal region of which appears to be indicated in fig. 210. 

One of the points which appears to be most problematical in the structure of the 
embryos is the meaning of the anterior umbrella-like ma.ss of yolk. It is conceivable that in 
the rearrangement of the viscera which presumably accompanies the metamorphosis, it might give 
rise to part of the anterior end of the alimentary canal. That conclusion seems to be improbable 
if the part in question is really in front of the collar-cavities (cf. figs. 209, 210). 

Another possibility which must not be left out of account is that the embryo undergoes 
no metamorphosis, but that it may fix and give rise to the adult zooids by budding. A process 
of this kind is characteristic of the great majority of Ectoproct Polyzoa, in which (with rare 
exceptions) the alimentary canal of the free larva is represented by at most a mass of yolk- 
like material, as in Cephalodiscus. Although this possibility can hardly be excluded, it seems to 
me that the embryos of Cephalodiscus possess sufficient indication of the adult organs - — and 
particularly of the body-cavities — to make it probable that the embryo undergoes a meta- 
morphosis into a zooid. 

It is not impossible that the umbrella-like mass of yolk represents in itself the splanchnic 
epithelium of the anterior body-cavity. While the paired cavities, in some of the specimens at 
least, are unmistakeably complete coelomic sacs, I have not been able to convince myself in 
any case that the anterior body-cavity has a splanchnic epithelium distinct from the yolk-mass 
itself. I am in fact inclined to accept this explanation as the most likely one which can at 
present be given. This interpretation is in accordance with the account given by Bateson 
(84, p. 218) of the development of Dolichoglossus kozvalevskii^ a species of Balanoglossus in 
which the development is direct. It appears from Bateson's account that the entire front end 
of the archenteron is separated off as the anterior enterocoel, the walls of which overlap the 
axial enteron in precisely the same manner, though to a less e.xtent, as the anterior yolk 
overlaps the posterior yolk in Cephalodiscus levinseni (cf. Bateson's figs. 35, 40, 27, 28). 
There are indeed differences in detail between the two cases. Thus in Balanoglossus, the 
somatic layer is as thick as, or thicker than, the splanchnic layer, while in Cephalodiscus the 
somatic wall is excessively thin, and at first barely recognisable, while the splanchnic layer is, 
ex hypothesi, constituted by the thick yolk-mass itself. Again, while in Bateson's larva, the 
anterior enterocoel communicates at first with the enteron, in CepJialodiscus the whole complex 
forms a solid mass of yolk without any cavities. 



I I 2 



If it lie permitted to appeal to animals whicii thoui,r]i less nearly related to Cephalodisais 
are still, as it appears to me, possessed of affinities to Balanoglossus, allusion may be made 
to Amphioxus and Echinoderms, in support of the explanation giver) above of the structure 
of the embryo of CepJialodisais. The anterior body-cavit\- of Amphioxus, as described by 
Hatschek, is developed from the anterior end of the original archenteron, and shortly before 
its separation from the mesenteron it forms a cavity projecting backwards beyond the anterior 
end of the mesenteron in much the same manner as that in which the anterior yolk-mass of 
Ccphalodiscns overlaps the remainder of the yolk. A similar arrangement has been described 
in many Echinoderms, as by Ludwh, and MacBride in Astei'ina, by Masterman ^) in Cridrclla, 
and by MacBride ") in Ec/iinus. 

The characteristic relation of the collar-cavities in the embryo of Ccphalodiscns to the 
constricted region of the yolk makes it b\- no means improbable that these cavities are true 
enterocoels, given off from the archenteron in this region; while fig. 194 appears to suggest 
that the third body-cavities have a definite relation to the posterior end of the yolk-mass. It 
is not impossible that the somatic epithelium of the paired body-cavities is first differentiated 
at the surface of the yolk, and that llie splanchnic epithelium gradually spreads round the \olk- 
mass in the manner which might be indicated by the posterior end of fig. .201. Against this 
view mav be set the fact that the paired coelomic spaces, at the earliest stage at which they 
have been recognised, appear to l)e separated from the yolk by a distinct membrane (figs. 208, 
209), even though no epithelial Iming can be detected on the outer side of this membrane. 

The general arrangement of the coelomic spaces in the embryo appears to me to have 
a close resemblance to that .shewn by B.\teson in his well known diagram (84, PI. XXI, 
fig. 40) of the embryo of Dolichoglossiis kowalevskii, with the exception of the fact that the 
archenteron is represented, in Ccplialodisctis^ by a practically solid mass of cells. 



XVIII. AFFINITIES. 

In 1887 I had the opportunity of bringing forward evidence tending to shew that Ccphalo- 
discus must be placed in the same group with Balanoglossus. 1 indicated at the .same time mv 
belief that it might have affinities with PJioronis^ though not with the Polyzoa. It appeared to 
me not improbable that Rhabdopleiira was related to Ccphalodiscns, as had been assumed from 
the first by M'Intosh, Lankester and others; but in view of the want of evidence with regard 
to the structure of Rhabdoplcnra I refrained from expressing a definite opinion on this part 
of the question. 

The subject of the affinities of Ccphalodiscns has aroused a good deal of interest in 
recent years. It may conveniently be considered under several headings, as follows: — namely 
the affinity of Ccphalodiscns to: 



i) Trans. Roy. Soc. Edinburgh, XL, I't. 2, 1902, p. 385 f. 
2) Phil. Trans. Roy. Soc. London (B), CXCV, 1903, p. 296. 



(I) Rhabdopleura. 

(II) Enteropneusta. 

(III) PJwronis. 

(IV) other animals. 

(I) Relations to Rhabdopleura. 

The researches of Fowler (92, 1,2; 04) and of Schepotieff (04) appear to me to 
have demonstrated the correctness of the opinion expressed by the earliest investigators of 
Cephalodiscus (M'Intosh, 87, pp. i, 32) that this animal is most nearly related to Rhabdopleura. 
It is true that Fowler's results have been criticised by MM. Conte and Vaney (02) whose 
conclusions have been published in the form of preliminary communications only. They have 
been replied to by Fowler (04), but in the absence of the full memoir it is difficult to do 
justice to the results of the French authors. The most important of their statements are perhaps 
{a) that the body-cavity of Rhabdopleiira is not subdivided in the way characteristic of Cepha- 
lodiscus; (b) that the testis has the form figured by Lankester (84, PI. XL, fig. 7) and that 
it is formed from "une differentiation de I'extremite anterieure du pedoncule"; while the ovary, 
described for the first time, is formed at the expense of the axial part of the peduncle, "mais 
"a I'extremite opposee a celle 011 se developpe le testiciile"; (<) that collar-canals do not exist; 
[d) that the notochord is merel)- the anterior part of the peduncle ; [e) that Rhabdopleura is 
related to the Entoproct Polyzoa. 

The denial of the existence of the notochord, collar-canals and subdivisions of the body- 
cavity is directly opposed to the results of Fowler, which appear to me to be reliable. I have 
satisfied myself of the existence of the collar-canals at least, although I have had but little 
material suitable for the examination of the structure of Rhabdopleura. Schepotieff (04) with 
a knowledge of the statements of Conte and Vaney has, moreover, confirmed Fowler's results 
in essential particulars, although he considers (p. 16) that the cavity of the two arms is not 
continuous with that of the rest of the collar, and he alludes to the collar-canals (p. 15) as 
"Nephridien". One point in the results of MM. Conte and Vaney is of special interest in 
connexion with Cephalodiscus, namely the account of the gonads and particularly of the testis. 
The statement that that organ is a differentiation of the axial part of the stalk may well have 
some relation to the phenomena which I have described in C. sibogae. I do not profess to 
understand their statements with regard to the ovary. 

If Fowler's results, confirmed by Schepotieff, may be accepted, it seems to me hardly 
possible to doubt that Rhabdopleura is the nearest known ally of Cephalodiscus. The subdivisions 
of the coelom and the corresponding external segmentation, the relations of the arms to the 
collar-region, the structure of the stalk, the phenomena of the budding, the existence of the 
notochord and collar-canals, all these form a cumulative body of evidence ') which appears to 
point conclusively in that direction. 



i) In the copy of his paper which M. Schepotieff has h.ad the kindness to send me, he has added the following MS note 
'Ein Paar dorsalen Poren am Kopfschild warden neulich gefiinden". 

SlHOGA-EXrEDITIE XXVl/'/V. 15 



1 14 

(II) Relations to the Enteropneiista. 

The resemblances of Ccphalodiscus to Balanoglossus have been confirmed by several 
workers who have had the op])ortunity of studying sections of the former animal; and particularly 
by Masterman (96 — 03) and Spengel (93, pp. 721, 753). Lang (90) has accepted the same 
conclusion, and has given reasons for regarding Ccphalodisais as a Balanoglossus-like form 
which has been specially modified in connexion witli its sedentary and tubicolous habits. Ehlers 
(90, ]i. 164) on the contrarj' denied the affinity of Cephalodiscns to Balanoglossus. 

It seems to me hardly necessary to discuss this question further. If any weight is to be 
attached to morphological resemblances it must be concluded that Ccphalodiscus is related to 
Balanoglossus. When account is taken of the differences between the e.\ternal form, the size, 
and the habits of the two types, it is indeed extraordinary that .so many of the anatomical 
peculiarities of Balanoglossus should reappear in Cephalodiscns. As facts confirming the relationship 
of the two forms, but not known at the time of the ])ublication of the "Challenger" Report may 
be mentioned, — the existence of a pericardium, and probably of a glomerulus, in Ccphalodiscus; 
the discovery, by M.\stermax, of a vascular system in the same animal: and the resemblances 
of the embryos of Ccphalodiscus, so far as I have been able to make out their structure, to 
those of Dolichoglossus koivalevskii. 

It cannot, however, be disputed that in spite of the resemblances, Ccphalodiscus differs 
from Balanoglossus in various particulars which are so obvious as not to require mentioning. 
But the general result seems to me clear, namely that Ccphalodiscus and Rhaddopleura, 
constituting the Pterobranchia or y\s[jidophora, must l)e included, with the Enteropneusta, in 
a larger group, for which I acrejjt B.vteson's name Hemichordata. 

(III) Relations to Phoronis. 

Here we are on much more controversial ground. The hypothesis of the affinity of 
Phoronis to the Pterobranchia has been accepted by a certain number of authors, among whom 
I may mention Lankester (85), Masterman (96—00), Schimki^witsch (93), Del.\ge and Hi^rouard 
(97), RouLLv (01, p. 226), and Scmultz (03, i, 2); but it has been rejected by many others. 
Masterman's comparisons of Actinotrocha with Ccphalodiscus and the Enteropneusta have 
unfortunately been vitiated by the mistakes into which he appears to have fallen with regard 
to the structure of Actinotrocha, as shewn 1)\ the concurrent testimony of Ikf.da, (iooDRiCH. 
and DE Selys Longchamps. Schultz (03, i, p. 414: 03, 2, p. 489), while accepting the verdict 
of these authors with regard to the facts, believes nevertheless in the affinity of Phoronis to 
Jialanoglossus, and expresses his conviction that evidence of this relationship is to be found 
more in the .structure of Phoronis than in that of its larva. He bases his conclusions on the 
result of a study of the regenerative processes of Phoronis, whether after the spontaneous loss 
of the tentacular end of the animal or after artificial section ; and on the study of regeneration 
in .Actinotrocha after section, lie liiuls that regenerative processes are capable of giving valuable 
aid in the elucidation of phylogenetic problems. 

Dk Selys Longchamps (04) has just published an important memoir on the structure 
and metamorphosis of Actinotrocha. The full bibliography which he has given, and his careful 



H5 

discussion of the opinions which have been expressed by various writers make it unnecessary 
for me to attempt the same task in all its details. I may therefore limit myself to comments 
on a few of the points which seem to me to need further discussion. 

De Selvs Longchamps concludes that Phoronis is not nearly allied to Cepkalodisais. 
He shews, with Ikeda and Goodrich, that Masterman's proboscis-cavities and collar-cavities in 
Actinotrocha are not distinct spaces, but that the body-cavity is divided into two parts only by 
the oblique septum which has universally been recognised as occurring at the base of the series 
of larval tentacles. He recogni.ses, however, the fact pointed out by Ikeda and confirmed by 
Goodrich (03) and Schultz (03, 2) that at a somewhat late stage in the development of 
Actinotrocha, there originates a coeloniic space which lies just in front of the larval septum 
and sends outgrowths into the permanent tentacles. In his discussion of the cavities of the body 
he does not seem to me to take enough account of the morphological importance of this space, 
the mode of development of which is, however, not quite certain. Goodrich (p. iii) and de 
Selys Longchamps (p. 33) consider that it is formed as a schizocoel, while Schultz (03, 2, 
p. 487, figs. 18, 19) states that in Actinotrocha, regenerating after injury, it arises as two 
anterior diverticula of the post-septal coelomic cavity. But, however it may first originate, authors 
are agreed in stating that it increases in relative size during the further development. At the 
metamorphosis, when a large part of the anterior region of Actinotrocha is thrown off, the 
remains of the praeseptal blastocoelic cavity persists as the vascular ring or rings, while the 
praeseptal coelomic space becomes the lophophoral coelom of the adult, giving rise also 
(Schultz, 03, 2, p. 487) to the cavity of the epistome. 

Schultz, with Fowler (92, 2, p. 297), considers that the praeseptal coelom is to be regarded 
as the homologue of the collar-cavity of the Enteropneusta ; but he is of opinion that this 
Enteropneust feature is only acquired with the assumption of the adult characters, the larva 
having the significance of a Trochosphere, and not shewing any indications of "trimetamery". 
I am inclined to accept the view that the adult lophophoral cavity is a collar-cavity, but I 
think that the view of Schultz with regard to the significance of Actinotrocha requires some 
modification. It may be noted that although this author recognises the second and third body- 
cavities of the Enteropneusta in the adult Phoronis, he does not attempt to shew that there 
is any representative of the anterior body-cavity in that animal. My own view with regard to 
this point is intermediate between that of Masterman and that of Schultz. 

De Selys Longchamps lays stress on the distinction between the haemocoelic nature of 
the large praeseptal cavity of Actinotrocha (which he nevertheless terms the "cavite collaire") 
and the coelomic nature of the metasomatic or postseptal cavity. It can hardly be doubted, 
from the relations of the larval blood-corpuscles, which lie freel)- in the praeseptal cavity and 
at the metamorphosis pass into the blood-vessels, that the cavity itself has intimate relations 
with the vascular system. But in the younger stages of Actinotrocha, the praeseptal cavity is 
continuous with the metasomatic cavity, the septum being differentiated first on the ventral side, 
and being completed dorsally only at a comparatively late stage in larval life. When the septum 
is complete, there is a postseptal coelomic cavity with a coelomic epithelium, ami a praeseptal 
haemocoelic cavity which has no complete epithelial lining. 



I I 6 

It seems to me that if, as nic Ski.vs Loncjciiami'S shews, the two cavities are continuous 
in the earlier stages it is difficult to assume that they differ from one another to quite so great 
an extent as is maintained by that author. Botli cavities ma\ in fact be said to be formed 
from the original blastocoel, the mesoderm cells in one case arranging themselves round the 
cavity so as to give rise to a coelomic epithelium, and in the other case not behaving in this 
manner. It must be remembered that at the metamorphosis of Actinotrocha, a considerable part 
of the anterior region of the body, including the praeoral lobe, is completely lost. The balance 
of evidence appears to be in favour of the view that the adult epistome is not a remnant nf 
the praeoral lobe (cf. de Selys Longchamps, 03, p. 42 and 04, p. 731. If then the anterior region 
of the larva is not destined to give rise to an adult protomere (or proboscis), in consequence 
of the peculiar phenomena which occur at the metamorphosis, it is perhaps possible that it may 
have lost some of the characteristics of the protomere. The metasomatic cavity is admittedly 
indistinguishable from the blastocoel in the younger larvae. If this be conceded, I see no great 
difficulty in supposing that the cavity of the protomere of Actinotrocha remains in the same 
undifferentiated condition. The praeseptal cavity might thus represent not only the vascular 
space which it is shewn to be by actual evidence, but also the region in which the anterior 
body-cavity is potentially present. The [iraeoral lobe of Actinotrocha may thus possibly represent 
the protomere of the Hemichordata. The region in Actinotrocha between the praeoral lobe and 
the larval tentacles may represent the collar, as sujjposed by Masterman, although the definitive 
ioriiiation of its coelom is deferred to a late ])eri()d in ontogeny. De Selys LoNGCiiAMrs (04) 
throughout speaks of this as the "region collaire"; although, as he does not accej)t the homology 
implied by that term, it may be presumed that he uses it for descriptive purposes merely. 

It is thus possible to imagine that in Actinotrocha, the anterior body-cavity never acquires 
its full development, while the collar-cavity develops late; and that the adult Phoronis has lost 
its proboscis, while its collar-region is represented by the praeseptal part of the body, including 
the lophophore and tentacles. 

It is perhaps a fact of some significance that the cavities of Actinotrocha have a 
characteristic obliquity, the " trunco-collar septum", as de Sei.ys LoxniAMrs calls it, extending 
much fin-ther fi)rwards dorsally than venlrally. The same obliquil\- is visible in the lophophoral 
cavity which is developed late in larval life, since this rests on the anterior face of the main 
septum, a relation which is well shewn by Goodrich (03, fig. 2). A similar obliquity of the 
coelomic cavities to the actual main axis of the animal is obvious in Ccphalodiscus, and is 
shewn for instance in the sagittal section of a bud figured in PI. XIII, '^\g. 174 of this Report. 

It I am right in the explanation I have given in Seel. \ III (p. 30) of the morphology of the 
arms and operculum of CepJialodiscus (cf. PI. Ill, fig. 25; PI. XII, figs. 158 — 160), the entire 
anterior border of the collar of that animal is prolongetl into a free fold, with the exception 
of two lateral regions where there ma)- be an interruption in the fi)ld, and of the mid-dorsal 
region. The ventral half of this fold is constituted by the operculum, and the tlorsal half 
by the tentaculiferous arms. If the lojihophore of Phorottis belongs to a region which is 
morphologically comparable with the collar of the Hemichordata, it ma\- be sugge.sted thai its 
tentacles should be compared not m(n-cl\- with llu; arms of Ccphalodiscns, bul with the whole 



of the anterior edge of the collar in that animal. In other words, the operculum must be taken 
into account, as indeed I formerly suggested (87, p. 46), although in Ccphalodisctis this region 
has not been split up into arms or tentacles. In constructing a diagram to shew the actual 
anatomical relations of the arms and operculum in Cephalodiscus^ I arrived at the result seen 
in hg. 159. This diagram is supposed to represent an individual in which the proboscis was 
directed forwards (as in fig. 23), the proboscis itself having been cut away with the exception 
of the part which is present in the proboscis-stalk. The operculum is further supposed to have 
been stretched so as to pass completely externally to the series of arms, instead of being 
partially concealed by their bases in the way shewn, in a dorsal view, in fig. 158. The free 
anterior edge of the collar thus forms a funnel leading to the mouth, incomplete dorsally, and 
elongated in a transverse direction, the lateral parts being reflected towards the dorsal side. 
This diagram, constructed without any theoretical bias, has considerable resemblances to figures 
of the lophophore of Phoronis, for instance to those given by BENn.\M (89, PI. X, figs. 12, 7). 
It is indeed possible that the interruption, in the mid-dorsal line, of the series of tentacles 
described by Benham and other authors in PJioronis may be related to the fact that the free 
edge of the collar is interrupted in a similar position in Cephalodisctis . It may be noted, in this 
connexion, that Schultz (03, i, p. 405), in describing the regeneration of the lophophore in 
Phoronis^ calls attention to a bifid condition of that structure which he specially compares 
with the two lophophoral arms of Rhabdopleura. 

De Selys Longchamps (04, p. 38) gives a description of the vascular system oi Phoronis 
differing in certain respects from that of most of his predecessors. It appears from his statements, 
confirming an earlier account by Schneider, that both the principal longitudinal vessels of the 
adult are differentiated on the dorsal side of the stomach of the larva, from a space which 
originates between the splanchnic mesoblast and the epithelium of the stomach, and (pp. 89 — 91) 
that they communicate with one another merely through a splanchnic sinus which has the same 
relations. It is perhaps significant, in this connexion, that the largest vessel in Cephalodiscus 
is the dorsal vessel (figs. 22, 33, '^•]\d.v^\ that this vessel appears to originate from the wall of 
the stomach as a space between the splanchnic mesoderm and the digestive epithelium 
(figs- 57, 58); and that the only communication between the dorsal vessel and the po.sterior 
vessel of the stalk seems to be through a splanchnic or gastric sinus similar to that of Phoronis. 

In his account of the muscular system de Selys Longchamps (04, pp. 108, 115) discusses 
the supposed predominance of that of the protocoele or proboscis-cavity in Masterman's group 
Archichorda, and he comes to the conclusion that Phoronis does not shew this predominance. 
I may be permitted to point out that Cephalodiscus shews it no more than does Phoronis. 
The principal musculature of the former is assuredly the great mass of muscles in the stalk 
and on the antero-ventral side of the metasome. This is equally the case in Phorojiis, in which 
(p. 115) "le tronc est la region musculaire par excellence". 

With regard to the nervous system, and leaving on one side the description, which has 
not been confirmed by later authors, given by Masterman (97, i) of the peripheral nervous 
system of Actinotrocha, it may be noted that the nervous system of Phoronis remains in the 
epidermis, externally to the basement-membrane, and that there is evidence (de Selys Longchamps, 



iiS 

04, p. qy) of a general nerve-plexus in ihe epidermis of the entire lophophoral region. Sent ltz 
03, 1, p. 406) finds that in regenerating specimens of Phoronis the central nervous system 
develops on the oral side of a dorsal invagination, which he compares with the medullary plate 
of \'ertebrates and with the dorsal centre found in the collar of Balanoglossus. In his second 
paper (03, 2, p. 477) he confirms this homology, with the modification that he regards the 
invag-inated cranofHon as an adult ortran which replaces the original larval ganglion, stating that 
a process takes place in Actinotrocha, at the time of metamorphosis, identical with what he 
describes in the regenerating Phoronis. 

I formerly called attention (87, p. 46) to the resemblance between the ovarian mesenteries 
of Ccplialodisais and the lateral mesenteries of Phoronis., although suggesting that it was by 
no means certain whether the oviducts could be regarded as the representatives of the nephridia 
of Phoronis. Masterman (98, 2, p. 512) has accepted this homology of the oviducts of Ccpha- 
lodiscus. The consideration of the lateral mesenteries of Phoronis is, however, complicated by 
the difference of opinion which exists as to the interpretation which should be given to the 
mesentery which connects the oesophageal with the intestinal limb of the alimentary canal for 
some distance below the region of the nephridia. It has been maintained that this is a remnant 
of a dorsal mesentery, while it was suggested by Caldwell (82, p. 373) that it is clue to the 
secondar)- connexion of the intestine with the left lateral mesentery, which, nearer the lophophore, 
resembles the corresponding right mesentery in ])assing from the oesophageal limh to the body- 
wall (cf. Caldwell's diagram, p. 383). The question has recently been discussed by de Selvs 
LoNGCHAMPS (03, ]). 1 8), who accepts Caldwell's view, pointing out that in Actinotrocha there 
is no trace of a dorsal mesentery, and (p. 22) that the lateral mesenteries are suspensory bands 
of the nephridia. 

In Cephalodiscus the lateral mesenteries are suspensory mesenteries of the oviducts, but 
one of their principal functions is to carry the ovarian vessels originating from the dorsal 
vessel, which is contained in a dorsal mesentery. At their extreme dorsal end (figs. 149 — 152) 
they are connected with the body-wall of the metasome. They do not, however, originate from 
the pharyngeal limb of the alimentary canal, but from the dorsal mesenterj- and dorsal vessel. 
In view of the absence of the dorsal mesentery in Actinotrocha, iliis difference is perhaps not 
fundamental. The question of their homology in Cephalodiscus and J'horonis appears to me to 
turn on the propriety of regarding the oviducts of the former as comparable with the ne}ihridia 
of the latter. The resemblance in the position of the external a|)enures of the two sets of organs 
is undoubtedly striking, and the organs are definitely compared witii one another in two tliagram- 
matic figures given by Masterman (98, 2, figs. 16, 17). But the homology does not seem to 
me to be definitely established, and on the contrary it must be remembered that the genital 
ducts of Balanoglossus do not resemble nephridia. 

INMntosh (88, p. 5) states that the "hyaline and often .semi-translucent tube" oi Phoronis 
buskii "is finely and concentrically striated, — la\er upon la\er of the hypodermic secretion 
entering into its composition"; and further that it includes "man) minute sponge-spicules, diatoms, 
fragments of silex or accumulations of coarser sand-grains". It may be enquired whether there 
is anv relation between the constitution of the tubes of Phoronis and that of the coenoecium 



119 

of Ccphalodisais\ although if any such relation did exist it could hardly mean more than that 
the faculty of secreting a tube was formerly possessed by the epidermis generally. It may be 
noted that in Balanoglossus a "tenacious tube" is formed by mucus secreted by the epidermis, 
and that the surface of the proboscis and of the collar at least are concerned in the secretion 
of this tube (Morgan, 94, pp. 17, 19). 

In the budding processes of Cephalodiscus the coelomic cavities are almost certainly 
formed by the segmentation of a space derived from the virtual metasomatic cavity of the stalk. 
In Phoronis Schultz (03, i, p. 409; 2, p. 487) states that the cavity of the lophophore, the 
supposed collar-cavity, is an outgrowth of the metasomatic coelom, both in normally developing 
larvae and in adults and larvae which are regenerating after artificial section. 

One of the most striking features in which Cephalodisais differs from Balanoglossus is 
the approximation of the anus to the mouth; and it can hardly be doubted that in Cephalodiscus 
and Phoronis the short line between the mouth and anus represents the dorsal surface. It is 
not impossible that the adult relations found in Cephalodiscus may be the result of ontogenetic 
proces.ses similar to those which occur in the metamorphosing Actinotrocha. It is unfortunate 
that the study of the embryos found in the coenoecium has thrown no light on this point; but 
on the contrary the buds of C. dodecalophtis (PI. XIII, fig. 181) may give some clue to the 
manner in which the flexure of the alimentary canal has arisen. 

In conclusion I may express the opinion that while Phoronis is not closely related to 
the Pterobranchia, its affinities are really in that direction ; and that conclusion I have tentatively 
adopted in my article " Hemichordata" in Vol. VII of the 'Cambridge Natural History' (04). 

(IV) Relations to other animals. 

It would be going too far afield to discuss all the possible relationships oi Cephalodisctis\ 
and for a general consideration of this question I must content myself with referring to the works 
of ScHiMK^wiTSCH (93), M.A.STERMAN (96, 1,2; 98, i) and Delage and HSrouard (97, 98). 

Masterman (96, i) has instituted a group Trimetamera, which includes the Hemichordata, 
the Echinodermata, the Brachiopoda, the Chaetognatha, the unarmed Gephyrea (with Phoronis)^ 
the Polyzoa and possibly the Mollusca, while he assumes that the Chordata diverged from the 
ancestral line which culminated in the Hemichordata. Schimki^witsch (93) had previously expressed 
the same idea with regard to all these groups except the Mollusca, but he did not suggest 
anv name for the assemblag-e. 

If Phoronis be related to Cephalodiscus, the question naturally arises whether the Sipun- 
culoid Gephyrea have affinities in the same direction. I may here refer to a paper by Shipley 
(90), who gives a diagram (fig. 32) of the lophophore of Physcosoma which is strikingly similar 
to my own diagram (PI. XII, fig. 159) of Cephalodiscus. The lophophore oi Physcosoma consists 
of a crescent, placed on the dorsal side of the mouth, with its concavity facing the anus. It 
bears a small number of short tentacles, which are provided, as in Cephalodiscus, with ciliated 
grooves on the sides corresponding with the outer or convex side of the crescent. Its dorsal 
ends are connected with a crescentic lower lip in precisely the same way as that in which the 
arms of Cephalodiscus join the operculum. The so-called "vascular system" is a closed space 



I 20 

surroiindiiii^ the mouth and following the bases of the lophophore and lower lip ; or, in other 
words, having the form of two crescents facing in the same direction and united at their tips. 
This double crescent extends into the lower lip, and sends off branches into the tentacles; and 
Shipley suggests that it may be homologous with the "anterior body-cavity" of Phoronis\ that 
is, with the praeseptal space which perhaps represents the collar-cavit\-. If there is anything in 
this suesrestion, and if the arrangement has an\' rt:Iation to what is fountl in the Hemichordata, 
it is necessary to suppose that the proboscis has been greatly reduced — if it l)c not altogether 
absent — in PJiyscosonia as in PJioronis. 

On the other hand Gerol'Ld ') considers that the transitory metamerism which he has 
observed in the larva ci{ Phascolosoma^ together with other features, "indicate the close relationship 
between the Sipunculids and the Annelids". It appears however, from an earlier part of the 
.same preliminary note that the metamerism consists of a division into four segments, noticed 
in the nerve-cord and in the mesoblastic bands immediately before the metamorphosis. This 
question of metamerism in Sipunculids is clearly one of great importance, but the small number 
of metameres mentioned by Gerould suggests the possibility that the arrangement is not 
fundamentally difterent from that found in the Hemichordata. 

Here, as in the case of the Brachiopoda, which are next considered, it appears to me 
that affinities to the Hemichordata may ])erha]js exist, but that the pre.sent state of our knowledge 
does not juslif\- any positive statement on the subject. 

The affinity of the Brachiopoda to the Hemichordata has been maintained by Masterm.\x 
(98, i); while it was suggested some years earlier by Caldwell (83) that these animals are 
related to Phoronis. In this connexion reference may be made to a recent embryological paper 
by CoNKLix ■), who comes to the conclusion (p. 69) that "the affinities of Phoronis and Brachio- 
poda are well established", and (p. 70) that except for the absence of segmentation in the 
coelom, "there are no important differences between Actinotrocha and the brachiopod larva". 

The account given by Conklix is a confirmation of the general accuracy of the figures 
published by Kowalevskv in 1874. The development of the Brachiopoila, as indicated by these 
two observers, shews certain resemblances to that of the Enteropneusta and of Ccphalodiscus. 
There is, for instance, a conspicuous anterior region of the body-cavity which is developed as 
an unpaired enterocoel from the front of the archenteron. The manlle-fold of the young larva 
forms a more or less equatorial swelling, which gives rise to the a])pearance of a division of 
the entire larva into three segments. Masterman (98, i, p. 288) gives a figure indicating that the 
second of these "segments" (the mantle-fold) is the equivalent of the collar of the Enteropneusta, 
al. hough he explains on the preceding page that the arms as well as the mantle are to be 
regarded as derivatives of this region. From the account which has recently been given by 
Yatsu ') of the development of IJiigu/a, it would, however, appear that the arms develop from 
a region which is in front of that of the mantle-fold ; and it is not easy to assume that both 



i) J. H. Gerould, "The Development of Phascolosoma"^ Arch. Zool. Exp. et G6n. (4) 11, Notes ct Revue, 1904, NO 2, p. xvii. 

2) E. G. CONKLIN, "The Embryology of a Brachiopod, Tcrcbratuliiia septeitlrioiiaUs'^\ Proc. Amer. Phil. Soc. XLI, 1902, p. 41. 

3) N. Vatsi', "On the Development of Lingula anatina'\ Journ. Coll. Sci. Tokyo, XVII, 1901 — 1903, Art. 4. 



I 2'I 

the arms and the mantle belong to the collar. Xow those zoologists who have supported the 
view that the Brachiopoda are related to Phoronis and to other tentaculiferous animals have 
assumed that the lophophores are homologous structures in the several groups. If then the arms 
are to be regarded as the representatives of those of P/iorotiis or Cephalodiscus, it seems to 
follow from the evidence of Lingula that the mantle-fold is not part of the collar; — or, in 
other words, that the structure which in the larvae of certain Brachiopods appears to represent 
the collar is not in reality of that nature. I do not in fact find much in Yatsu's account which 
obviously confirms the view that the Brachiopoda are related to the Hemichordata. 

It must, however, be noted that Blochmann ^), as the result of his careful studies on 
the anatomy ot Brachiopoda, is convinced of the affinity of this group to Phoronis, the Sipun- 
culids and the Polyzoa. The relationship is nearest between Brachiopods and Phoronis, with 
which the Sipunculids are connected; while the affinities to the Polyzoa are more remote. 

I do not feel myself qualified to criticize the view of the Brachiopod affinities of the 
Hemichordata, particularly in the absence of information with regard to many features of 
importance in the later development of the Brachiopoda. But the testimony of such authorities 
as Blochmaxx cannot be ignored; and if this observer is right in maintaining that the 
Brachiopoda are related to Phoronis, it may perhaps follow that they are also related to 
Ceplialodiscns. 

Although it appears to me probable that the Hemichordata are related both to the 
Echinodermata and to the Chordata, I do not propose to discuss these questions at length, 
since their consideration is more easily approached from the side of Balanoglossus than from 
that of Cephalodisctis. Independently of the papers dealing with the resemblances of Tornaria 
to Echinoderm larvae, the affinity between the Enteropneusta and the Echinodermata has been 
maintained by Bury (88, p. 295; 95, p. 125), MacBride (96, p. 395), Masterm.an (98, i, p. 289; 
02, p. 403) and others, and it is recognised as possible by Spengel (93, p. 750). 

The question of the Chordate affinities of the Hemichordata has formed the subject of 
numerous papers. As long ago as 1877 Huxley (77, p. 674) went so far as to institute a group 
Pharyngopneusta for the reception of the Enteropneusta -|- Tunicata, in allusion to the existence 
of gill-slits in both groups. The affinity is rejected by Spengel (93, p. 721), but it is supported 
by Batesox (86), Masterman, MacBride (98, 00), Willey (94; 99, 2, p. 295) and others. 
Kemna (04, pp. 50, 52) considers that Cephalodiscus more nearly resembles the common ancestor 
of the Chordata than does any other living form. Although I do not discuss the views of these 
writers, the important recent work by vax Wijhe (01) on the head of Amphio.\us seems to 
me to call for special remark. 

\'ax WijfiE accepts, though with some modifications, MacBridk's account (98, 00) of the 
development of the coelomic cavities of Amphioxus, according to which the embryo is constructed 
on the Hemichordate type so far as it possesses representatives of the protocoel, the mesocoels 
and the metacoels. 



I) E. Blochmann. — "Cber die Anaiomie und die venvandtschaftlichen Heziehungen der Brachiopoden", Arch. d. Ver. d. 
I'lcunde d. Xatg. Mecklenburg, Jg. 46, 1S92, p. 37. 

SIBOO.^-EXPEnniK XXVI Wx. 16 



1 2 2 



The cavities in tlie head of the adult are very comphcated; imd, if I have understood 
the orijjinal account correctly, they may be described as follows. — 

(I) a system of "Schnauzenhohlen" in contact with the anterior end of the notochord. Of these, 
which 1 may allude to as the praeoral cavities, there are four; two lying respectively along 
the dorsal and ventral sides of the notochord, and the other two having a lateral position. 
(II) the "Stomocoel", composed of right and left halves, which are very unequally developed. 
The ventral mesentery which separates the two cavities lies at the right side of the mouth, 
which is thus, in the adult as in the larva, an organ of the left side. The right stomocoel 
(loc. cit., fig. 23) has a dorso-ventral portion at the side of the true mouth, prolonged 
forwards as a longitudinal lube which lies on the right side of the roof of the buccal 
cavity. V'entrally the stomocoel passes into the right "epipterygial cavity", which lies on the 
ventral .side of the mouth and of the beginning of the pharyn.\, dorsally to the pterj-gial 
or sub-atrial muscles. The left stomocoel is murh more complicated. Its large epipterygial 
portion is separated from the corresponding right cavity by a well developed ventral 
mesentery, the asymmetrical position of which has already been noticed. The "outer lip- 
cavity" is a direct anterior continuation of the left epipterygial cavity, and it occupies the 
outer or ventral portion of the lip, which itself forms the floor of the (praeoral) buccal 
cavity; sending a prolongation into each of the oral cirri. The "inner lip-cavity" occupies 
the whole of the dorsal side of the lip, and is therefore close to the buccal cavitw It is 
said to be in origin a part of the left stomocoel. The " vclicavum", or coelom of the 
velum, is continuous with the left stomocoel in the larva, but in the adult it resembles the 
inner lip-cavity in being completely closed. It is regarded as the left antimere corresponding 
with the dorso-ventral portion of the right stomocoel, altered in position owing to the 
assumption of a transverse position 1)\- the mouth, which in the larva opens on the left 
side. Each epipterygial cavity is continuous with the "pterygocoel ' or "Seitenflossenhohle" 
of its own side, a space which is better known under the name of the m(;tapleural or 
lymph-canal. 
(Ill) the "peribranchial cavity", consisting of the two dorsal spaces at the sides of the hyper- 
pharyngeal groove, the unpaired ventral portion which underlies the endostyle, and the 
coelomic spaces of the pharyngeal bars which connect the dorsal and ventral parts. The 
coelom of the first [jharyngeal bar differs from the similar spaces in the other bars by 
running from the epipterygial cavities to the ventral or endostylar coelom of the pharynx. 

The comparison made by v.w Wijiie with the Knteropneusta gives the following results. 
The dorsal praeoral cavity is not accounted for. The ventral cavity constitutes the whole of the 
anterior body-cavity, since v.\x W'ijiik holds that the left head-cavity of other authors is not 
part (jf the protocoel, but on the contrary is derived from ectoderm. The left "head-cavity" 
gives rise, as is well known, to the " Riiderorgan", or system of ciliated grooves of the buccal 
cavity; and it is regarded as the representative of the .stomodaeum of Craniata, and of the 
dorsal tubercle of Ascidians. - 1 1.\ts(1ikk's groove", which is an anterior prolongation of the 
Riiderorgan, represents the subneural gland of Ascidians and the notochord of Hemichordata. 



1 2' 



The lateral praeoral cavities are derived from the collar-cavities, and are in fact the 
antero-dorsal processes shewn in Hatschek's well known figs. 50 — 52 (81) of an embryo of 
AmphioxLis. The remainder of the collar-cavities is constituted by the right and left stomocoels, 
together with at least three myotomes (p. 68), and the anterior parts of the metapleural canals. 
These had been supposed by MacBride, in his earlier paper (98), to belong entirely to the 
collar, but van Wijiie considers that their innervation shews that they belong for the most 
part to the metasome, only their anterior ends belonging to the collar. The collar thus ends, 
as in Enteropneusta, at the beginning of the branchial region, and the more posteriorly situated 
coelomic spaces belong to the metasome, which by a secondary .segmentation has given rise 
to the remainder of the myotomes. The collar-canals of the Hemichordata are represented in 
Amphio.xus by the first pair of nephridial tubules, which open from the epipterj'gial cavities 
(— parts of the collar-cavities) into the atrium. 

Van Wijhe thus definitely recognises the affinity of the Hemichordata to Amphio.xus. 
The latter is indeed placed, with the Tunicata and the Craniata ("Craniota") in the Chordata; 
while the Enteropneusta and Cephalodisats, constituting the Pharyngotremata, are associated, 
with Rhabdopleura and Phoronis (to which no group-name is assigned) as Prochordata. But 
he carries the comparison even further than has been done by most morphologists, since he 
considers (p. 69) that the protocoel, mesocoels and metacoels can be identified in the embryos 
of Petromyzon, Elasmobranchs and even in the higher Craniata, while (p. 70 n.) a proboscis- 
pore can be recognised in the embryos of Elasmobranchs. 

It appears to me that a critical examination of van Wijhe's views can onl)- be made 
as the result of an independent investigation of Amphioxus; but there are nevertheless one or 
two points on which I should like to comment. The account of the collar-cavities is undoubtedly 
of interest, confirming as it does the general accuracy of MacBride's observations on the 
development of Amphroxus. Fig. 27, 28, and 32, given by van Wijhe, are specially significant 
in shewing the existence, in the adult Amphioxus, of a well marked transverse septum between 
the collar-cavities and those of the metasome. The prolongation of the outer lip-cavity into the 
oral cirri may indicate that the floor of the buccal cavity corresponds with part of the operculum 
in Ccphalodiscus, while somewhat further back the collar-cavity is .subdivided by a ventral 
mesentery (cf. figs. 9 — 18), as in the same animal. The backward extension of this region of 
the collar, on the ventral side of the pharynx, is also suggestive. Thus van Wijhe's fig. 1 5 
represents an arrangement which is similar to what may be seen in sections of Cephalodiscus 
transverse to the long axis of the zooid, in which the meta.somatic cavities occupy the dorsal 
part of the section, while the collar-cavities still appear on the ventral side, subdivided by a 
median mesentery. Taking this into consideration with H.\tschek's figs. 50 — 52 (81) of an embryo, 
there is a remarkable similarity between the collar-cavities of Cephalodiscics and Amphioxus, 
the coelomic sac in both cases having a triangular form when .seen from the side, the dorsal 
j)art being much longer than the ventral part. While in Cephalodiscus the elongated dorsal 
region of the collar-cavitv is connected with the arms, the anterior parts of the same region in 
Amphioxus are cut off to form the lateral praeoral cavities ("Schnauzenhohlen") of van Wijhe. 
The relations of the collar-cavities of the larval Amphioxus to the notochord and to the ventral 



124 

praeoral cavity, as shewn in 1 Iatscukk's tig. 145, suggest that the ventral cavity may currespunJ 
with that part of the anterior body-cavity of Ccplialodiscus which hes in the proboscis-stalk, 
ventrally to the notochord ; and that in fact the proboscis in Ainphioxus is represented only 
by a part of the proboscis-stalk. It would be interesting to know more of the nature of van 
Wijue's dorsal praeoral cavity ("Schnauzenhohle"); and it is conceivable that it might be the 
homologue of the pericardium of the I'.nteropneusta. 

The only group with regard to which it appears necessary to say more is that of the 
Polyzoa. A large number of writers have assumed — and it appears to me on inade(|uate 
grounds — that Phoronis is related to tin- Polvzoa. If /'/loronis be so related, it is not foreign 
to the oljjcct oi this memoir to consider the questic^n in its bearings on Cephalodiscus. 

It may be remembered at the outset that on the occasion of the first discovery of 
RJiabdopleura by Sars and Norman, no doubt was entertained of the correctness of the view that 
this animal was an aberrant Polyzoon. The later discovery of Ceplialodiscus^ and its association 
with RJiabdopleura, naturall\- led to the same view being adopted with regard to the subject 
ot this Report. With the discovery that Cephalodiscus has affinities in the direction of Balano- 
glossus, it appeared reasonable to remove it from the I'olyzoa, since these animals had not been 
shewn to ]jossess any i»f the characters which specially connect Ceplialodiscus with Balanoglossus. 
What holds good tor Cephalodiscus mu.st, I think, also ai)|il\- to Rhabdopletira. 

In again taking up the study of Cephalodiscus I have seen no sufficient reason for 
modifying the views I formerly expre.ssed (87) with regard to this cpiestion. It might indeed be 
maintained that the embryo of C. gracilis with its large internal volk-ma.ss, its conspicuous 
ventral invagination of ectoderm and its "pyritorm organ" was directly comparable with the 
larva ot one ot the marine P^ctoproctous Polyzoa. To this might perhaps be added the fact 
(if it be a fact) that in both groups the alimentary canal of the bud is developed entirely from 
an invagination of the outer layer. 

It remains to be seen whether the later developmental history of Cephalodiscus will lhr(jw 
any further light on this particular <]uestion ; but for my own part I do not anticipate that it 
will tend to strengthen the view that the Pterobranchia are allied to the Polyzoa. In order to 
accept this view it is necessary either to regard the Ectoprocta as the most primitive of the 
Polyzoa, or to take the view — which is adopted by Korschelt and Heider in their well 
known text-book of Embryology — that the Ectoprocta have no close affinity to the Entoprocta. 
It appears to me that this view is untenable, and I may fortify my own opinion by (juoting 
that of Prouho '), the excellence of whose work in both subdivisions entitles him to speak with 
authority, that " Aujourd'hui, aucun des zoologistes iiui etudient les Bryozoaires ne met en doubte 
"le bien fonde des vues de Xitsche" [to the effect that the Entoprocta and the Ectoprocta are 
two groups belonging to the same phylum]. The Entojirocta, on this view, furnish many clues 
to the understanding of the Ectoprocta. In particular, the comjjarative study of the development, 
taking into account such (juestions as the structure of the larvae of Entoprocta, the metamorphosis 
of Pcdicellina, and the structure of Cyphonautcs appears to me to shew that the Polyzoa, as 

l) H. rKciiiio, "Contribution a I'llistoiie des Bryozoaires", .Xrch. Zonl. Exp. et den. (2) .K, 1892, p. 641. 



I 2- 



the term is usually understood, are a monophyletic group, and that the larval forms of the 
Ectoprocta receive a reasonable amount of explanation by comparing them with the larvae of 
Entoprocta. The attempt to explain the facts in the converse direction has, I think, never been 
seriously attempted ; nor can I believe that it would be successful, particularly if the Phylacto- 
laemata were taken as the starting point. It must be remembered that the Phylactolaemata are 
the forms which have most frequently been compared with Phoroiiis. 

Another fact of which sufficient account is not usually taken in comparing Phoronis 
with the Polyzoa is the palaeontological evidence. The Polyzoa are a very ancient group, and 
the earliest known forms do not appear, so far as can be judged from their calcareous skeletons, 
to shew any approach to Phoronis or to Cephalodiscus or to any form which might fairly be 
supposed to have been ancestral to either of these. 

I do not feel myself competent to express any opinion with regard to the view adopted 
by .ScHEPOTiEFF (04, p. 1 7) that Rhabdopleura is related to the Graptolites. 

In conclusion, I may state my opinion that while Rhabdopleura is the nearest living 
ally of Cephalodiscus, the affinity of both these genera to the Enteropneusta has been clearly 
demonstrated. I am inclined to accept the view that they have affinities in the direction of 
Phoronis, the Chordata and the Echinodermata, and to reject the suggestion that they are in 
any way related to the Polyzoa. 



XIX. RHABDOPLEURA. 

While this Report was going through the press Professor Weber sent me a stone from 
Station 204 in the hope that it might bear additional specimens of Cephalodisctts sibogae. No 
such specimens were found, but a microscopical examination of the surface of the stone was 
rewarded by the discovery of a colony of Rhabdopleura. Although the specimen is a mere 
fragment, with its zooids in poor condition, its occurrence in the "Siboga" dredgings is of 
considerable interest in extending the geographical range of Rhabdoplejira, which is indeed 
probably world-wide in its distribution. Originally known from deep water off Shetland and the 
Norwegian coasts, by the labours of Nijrman, Allman and G. O. Sars, and more recently 
described from one of the same districts by Laxkester and Schepotieff, it has since been 
recorded from the coasts of Ireland and Brittany, by Hincks and Jullien respectively; from 
Tristan d'.Acunha in the South Atlantic by Fowler : and from the Azores by Jullien ; while 
its extreme recorded limits are West Greenland ') and .South Australia (Harmer, 04, p. 23). 

Several species of Rhabdopleura have been described, although in the absence of a 
comparative study of the genus it is uncertain how far these are really distinct. The specimens 
from the North Sea, from Greenland and from Tristan d'Acunha are described as R. norma7ii 
Allman (~ R. mirabilis Sars). Those from Ireland and Brittany are known as R. compacta Hincks ; 

l) N'oKMAN, -Ann. Ma^. Xat. Ilist. (7) -XIi, 1903, p. loi n. 



I 26 

while the specimens from the Azores are said to beloiig^ to two species, R. griina/dii Jullien, 
;iii(l R. niaimbialis Jullien. 

A', iioriiiaiii appears to be characterised by the great length of the peristomes, or free 
cylindrical parts of the tube. R. compacta is said to have very short, crowded peristomes. 
R. (^riutaldii has a short peristome, continuing a creeping portion of equal length, which is 
characterised 1)\ the presence of '"deu.x tubes tres fins, convergeant par leur e.xtremite anterieure", 
and running longitudinally along its free wall; while the orifice is somewhat expanded. In 
A", niannbialis the peristome is about twice as long as the attached portion of the zooecium, and 
its tube-rings seem to be very prominent. The species is not, however, very well characterised, 
although it is said to differ from R. griuialdii by the colour of the coenoecium (yellowish instead 
of brown), by the absence of the two "tubes" of that species, and by the fact that the axial cord or 
pectocaulus extends into the attached part of the zooecium, which is not \\\iicA^<i.\x\ R. grimaldii. 
The specimen dredged by the "Siboga" is a perfectly tyjjical Rhabdopletira, its coenoe- 

(iuni consisting of a creeping portion attached to 
llu; stone, and provided with the characteristic, dark 
l)n>wn i>ectocaulus embedded in its lower wall. 

I iiave been able to examine onl\- two 
peristomes which appear to be complete. The 
s])ecimen figured {A) consists of 1 3 rings, the last 
of which seems to have been somewhat distorted 
tluring the preparation of the slide. The rings are 
much more prominent than in A', normani, giving 
the peristome an annulated appearance. As in that 
species the substance of the ring is not completely 
continuous, but is interrupted by a suture (5-.), which 
is visible, however, only in cases in which it happens 
to ()ccu|)y a tavourable position. In the creeping 
ptjrtion of the zooecium (t^), the sutures have the 

I'ig. 2. — A7/a/<//'p/>/cHn7 sp. (Stal. 204). .r/, a complele perislonif. i . • .• • ,• . . i ■ i i i 

. . .. ' . f .u • .• r.i, ■ characteristic zigzag disposition which has been 

originating from part ol the creeping portion of the coe- " , => i 

noecium; /.'. finginent of the creeping portion: 0., orifice; noticed in Other SpecieS of RJiabdopletira . The 

/., pectoc.iulus; j., suture of tiibe-ring; -tf/., septum; ir., . . . •in 

ma«s of detritus (X 80: magnified to the same extent as junctions ot SUCCeSSIVC lamellae HI thlS portion fomi 

the free end of the peristome of R. „orm„„i shewn in rijcres wliich, liowevcr, are iiot SO prominent as 

Pi. II, fig. 19). ■ ^ ' 

those of the peristomes. The cree])ing part is inter- 
rupted by transver.se septa (-i4, scp^)^ as in other species of the genus, and its lower or attached 
wall contains the tubular pectocaulus [p?^. The prejiaration shews one zooid, with recognisable 
tentacles, and indications of several buds '). 




l) The stone on whlcli the KUohilciflcttra was found Wore several tubes which in size and in being composed of a series of 
distinct rings have a curious resemblance to the peristomes of KluthilopUHia. One or two of these structures were in fact mounted under 
the impression that they belonged to that genus. Their wall is, however, much thinner than in Khahiloplciira^ the rings are made up 
of a series of smaller segments, and the tubes arc conical instead of being cylindrical in form. There can be no question that they belong 
to ^lephaiioscyphiis^ and 1 am unable to distinguish them from .S'. miruhUis described by Allman in 1875 (Trans. I.inn. Soc, (2), Zool., 
I, p. 61). Professor Cii. Jui,is, to whom I sent a preparation of the organism, informs me that he agrees with this determination. 



I 27 

My examination of Cephalodiscus has convinced me that the characters of the coenoecium 
form a reliable means of distinguishing the species in that genus. I am accordingly inclined to 
think that the specimen of Rhabdopletira from Station 204 is probably a new species, characterised 
by the small number of tube-rings, by their comparative delicacy and thinness, and by their 
angular projection to the exterior. The specimen is, however, so fragmentary that I do not 
consider myself justified in giving it a specific name. It may be hoped that other specimens 
will hereafter be found among the "Siboga" dredgings which will make it possible to come to 
a more satisfactory conclusion on this point. There is at present no reason for assuming that 
the peristomes found have acquired their full number of rings. 

The following comparison of the "Siboga" specimen with Norwegian specimens of R. 
nonnaui illustrates some of the differences between the two forms ; — 

Rhahdopleura sp. ("Siboga"') 1\ . nonnaui. 

Number of rings of peristome 13 — 15 50 — 60 

Length of peristome '64 — -70 mm. 2-59 — 2'88 mm. 

Diameter of peristome 175 — 210 a. 255 — 270 u.. 

Thickness of wall of peristome, at the middle of a tube-ring. 7"5 — 11 "5 v.. 16 — 24,0.. 

Diameter of pectocaulus 20 — 22 a. 32 a. 

It will be observed that the East Indian form is in all respects smaller than the Norwegian 
form, while the thickness of the wall of its peristome is distinctly less. 

The following synonymy gives references to some of the more important memoirs dealing 
with Rhabdoplciira. Other papers, not mentioned here, are referred to by Fowler (92, 2). 

R. norinani Allman. 

R. normani Allman, (Quart. J. Micr. Sci. IX, 1869, p. 58; Rep. Brit. Ass. (Norwich meeting, 
1868), 1869, p. 311; HiNXKS (80), p. 580, PI. LXXXII, fig.S. I, 2, 4—7; L.VNKESTER (84), 

p. 622, Pis. XXXVII^w— XLI; Fowler (92, i; 92, 2; 04); Norman, Ann. Mag. Nat. Hist. 
(6) XIII, 1894, p. 131; (7) XII, 1903, p. loi n.; CONTE et Vanev (02, r, 2); Schepotieff (04). 
R. mirabilis Sars (72); Quart. J. Micr. Sci. XIV, 1874, p. 23. 

R. compacta Hincks. 

R. compacta Hincks (80), p. 58 1, Pi. LXXII, figs. 8, 8rt, 9; Jullien, Bull. Soc. Zool. France, 
XV, 1890, p. 183. 

R. grivialdii Jullien. 

R. grimaldU Jullien, Bull. Soc. Zool. France, XV, 1890, p. 180; JULLIEN et CaLVET (03), 
p. 23, PI. I, figs. \a, \b. 

R. Dianjibialis Jullien. 

A', manubialis Jullien et Calvet (03), p. 24, PI. I, fig. 2. 



S. mirabilh appears to be identical with Spongkola Jis/u/aris, described by V. E. Schli.zk in 1S77, and it has been demonstrated by 
the observations of S. Lo Bia.sco and P. Mayer (Zool. Anz., XIII, 1890, p. 687; of. also Miii,i.Y, Rep. Brit. Ass. (Cardiff, iSgi), 1S92, 
p. 368) that this is the Scyphistoma form of NausUhoe. Two other species of Stcphanoscyphus are described by Kirki'atrilK (Ann. Maj;. 
Nat. Hist. (6), V, p. 13), one of them from the China Sea. Nausithoe is recorded by Maas in his account of the Scyphomedusae collected 
by the ''Siboga"-Expedition (Monogr. XI, 1903, p. 19). 



12S 



RliabdoplcHi-a /loriiiaui lias already been referred to in this Report on jj. 8 (coenoeciiim), 
on \}\>. 52, 78 (stalk), on pp. 81, 87 (reproductive organs), and on p. 92 (budding). Should the 
genus include more than one species it may, however, be (juestioned whether the form described 
by FowLKK from Tristan d'Acunha is really identical with A', norvtani. 



XX. SrMM.XRV OF THE PRIXCII".\L RESULTS. 

(i). The geographical and bathymetrical range of Ccpltalodiscits are largely extended b\- the 
description of three new species from Oriental waters, one of them (C gracilis) having 
been obtained, at or near low tide mark, on a Coral Reef on the coast of Borneo. The 
second [C. sibogae) is from 75 — 94 metres off the S.E. point of Celebes, while the third 
[C. levinseni) is from about 183 metres at the S. end of the Corea Strait. 

(2). While the specimens of C. gracilis and C. levinseni resemble the "Challenger'" specimens 
of the type-species (C dodecaloplms) in consisting exclusively of female individuals, that of 
C. sibogae is of the male sex. The possibility is not excluded that C sibogae may be the 
male of C. gracilis; but it is concluded that it is real]\- a distinct species. 

(3). The colonv of C sibogae offers a striking case of dimorphic zooids. Certain individuals are 
of the type characteristic of a female Ccphalodiscns except for the absence of gonads. 
These are termed neuters, and they doubtless provide for the nutrition of the colony. 
The remaining individuals are males, and are remarkable for the vestigial nature of the 
apparatus connected with the collection and digestion of food. Their curiously modified 
arms are reduced to a .single pair, which are not ])rovided with tentacles; the operculum 
is absent; and the alimentary canal is in a vestigial condition. The principal organs are 
a pair of large testes, which correspond in the position of their external apertures and in 
their relation to the dorsal ves.sel with the ovaries (jf the females of other species. The 
proboscis is well developed, while the central nervous system, the bodv-cavities, the collar- 
canals and the vascular sy.stem resemble those of an ordinary Ccphalodiscns. Their nutrition 
is probably provided for by vascular connexions with the neuter individuals. 

(4). The characters of the coenoecium are shewn to be of importance in discriminating 
the species. 

(5). The zooids of the several species, while differing from one another to a marked extent 
in form, in tiie number of their tentacular arms, and in the characters of their stalk, are 
strikingly uniform in all essential points ot structure. 

(6). The arms and (Operculum are regarded as modifications of the anterior free edge of the 
collar. The number of arms of the female or neuter zooids ranges from four |jairs in 
C. sibogae to six pairs in C dodecaloplms and C. levinseni \ C gracilis occuiJ\ing an 
intermediate position in possessing five pairs of arms. 



I 29 

(7). The structure of the collar-pores or collar-canals is described, and it is shewn that they 
are closely related with parts of the muscular system ; suggesting that their modus 
operandi is partly due to muscular action. 

(8). The stalk differs widely in proportions in the several species, and is specially long and 
slender in C. gracilis and in C. sibogae. 

(9). The structure of the pharynx is described, and the probable mode of feeding is 
considered. 

(10). The most important constituents of the vascular system are {a) a large dorsal vessel 
applied to the dorsal surface of the pharynx, and sending off vessels to the gonads; 
{b) the anterior and posterior vessels of the stalk. The anterior stalk-vessel is continuous 
with the corresponding vessel of the trunk. The posterior stalk-vessel ends on the wall 
of the second stomach, and is probably in communication with the dorsal vessel through 
a perigastric sinus. 

(11). Some account is given of the early development, which appears to shew some resemblances 
to that of the large-yolked species of Balanoglossus. The five coelomic spaces of the adult 
can be recognised in the embryo. The latest embryos are not old enough to give any 
indication with regard to the mode in which most of the adult characters are acquired. 
The two species investigated (C gracilis and C. levinseni) differ to a striking extent in 
some of their embryonic characters. 

(12). A partial account is given of the budding, in C. gracilis and in C. dodecalophus. The 
position of the parts of the alimentary canal of the bud shews some approach to the 
condition found in Enteropneusta, the pharynx and stomach lying in the morphologically 
antero-posterior line. 

(13). Cephalodiscus shews unmistakeable affinities to RhabdoplciLra and to the Enteropneusta. 
It is probably related to Phoronis; and, through Balanoglossus, to the Echinodermata 
and the Chordata; but it is not nearly related to the Polyzoa. 



[Postscript. — An interesting note by Schepotieff (05) on Rhabdopkiira has appeared just 
as this sheet was about to be printed off. The paper contains important results 
with regard to the body-cavities, proboscis-pores, pleurochordal grooves, pericardium, 
vascular system, muscles, testis and budding, and it appears to me to complete 
the proof of the fundamental resemblance in structure between Rhabdopleura and 
Cephalodisczis. The extra-oral parts of Schepotieff's "Kiemenrinnen" are what I 
describe as the "food-channels" in this Report. The alimentary canal of the bud 
is developed partly from an endodermic "Anlage", and not as I suppose it to be 
developed in Cephalodisctis\. 



SIBOOA-EXPF.DITIF. XXV[ ///.t. I7 



XXI. i;ii;li()GRAPhv. 

03. Andersson, K. a. — Einc Wiedcrentdeckung von Cephalodiscus. Zool. Anz., XXV'I, 1903, p. 368. 

84. Rateson, W. — The Early Stages in the Development of Balanoglossiis. Quart. J. Micr. Sci., XXIV, 
1884, p. 208. 

86. The Ancestry of the Chordata. Quart. J. Micr. Sci., XXVI, 1886, p. 535. 

89. Hkniiam, W. B. — The Anatomy of Phoronis Australis. Quart. J. Micr. Sci., XXX, 1890, p. 125. 

89. Bourne, G. C. — On a Tornaria found in British Seas. J. Mar. Biol. Ass. (N.S.), I, 1889—90, p. 63. 

02. BUDGETT, J. S. — On the Structure of the Larval Polypterus. Trans. Zool. Soc, XVI, 1903, p. 317 
[Methods]. 

88. HlK\, 11. — The Early Stages in the Development o{ Antedoii. Phil. Trans. Roy. Soc, CLXXIX, 
1889, (B), p. 257. 

95. The Metamorphosis of Echinoderms. Quart. J. Micr. Sci., XXXVIII, 1896, p. 45 (p. 125). 

83. Caldwell, W. H. — Preliminary Note on the Structure, Development, and Affinities of Phoronis. 
Proc. Roy. Soc, XXXIV, 1883, p. 371. 

99. Cole, F. J. — On the Discovery and Development of Rhabdite-'cells" in Cephalodiscus dodecalophiis. 
Journ. Linn. Soc, XXVII, 1899 — 1900, p. 256. 

02 (i). CONTE, A. et Vaxev, C. — Contributions a I'etude anatomiquc ilu Rhabdopleiira. Comptes rendus 
Acad. Sci., CXXXV, 1902, p. 63. 

02 (2). Recherches sur le bourgeonnement de Rhabdopleiira. Comptes rendus Acad. Sci., CXXXV, 

1902, p. 748. 

90. CORI, C. J. — Untersuchungen iiber die .\natomie and Histologie der Gattung Phoronis. Zeitschr. f. 

wiss. Zool., LI, 1 89 1, p. 480. 

02. Dawydoff, C. — Uber die Regeneration der Eichel bei den Enteropneusten. Zool. Anz., XXV, 

1902, p. 551. 

97. DelagE, Y. et Herouard, E. — Traite de Zoologie Concrete. V [Phoronis, Pterobranchia, etc.]. 

98. ■ Traite de Zoologie Concrete. VIII [Enteropneusta, etc.]. 

90. liHLERS, E. — Zur Kenntnis der Pedicellineen. Abh. K. Gcsellsch. Gottingen, XXX VI, 1890. 

92 (1). Fowler, G. H. — Note on the Structure o{ Rhabdopleiira. Proc. Roy. Soc, LII, 1893, p. 132. 

92 (2). The Morphology of Rhabdopleiira. Festschr. 70'"' Geburtstage R. Leuckarts, 1892, p. 293. 

02. Article "Hemichorda". Encycl. Britann. 10'" Ed., XXIX, 1902, p. 249. 

04. — Notes on Rhabdopleiira. Quart. J. Micr. Sci., XLVIII, 1905, p. 23. 

03. Goodrich, E. S. — On the Body-Cavities and Nephridia of the Actinotrocha Larva. Quart. J. .Micr. 

Sci., XLVII, 1904, p. 103. 

87. IIarmer, S. F. — Appendi.K to Report on Cephalodiscus. Challenger Reports, Zool., XX, Pt. L.XII, 

1887, p. 39. 

97- O" the Notochord of Cephalodiscus. Zool. Anz., X.\, 1S97, p. 342. 

03. On new localities for Cephalodiscus. Zool. Anz., XXVI, 1903, p. 593. 

04. -— Article "Hemichordata". Cambridge Natural History, VII, 1904, p. 21. 

81. Hatschek, B. — Studien iiber l^ntwicklung des Amphioxus. Arb. Zool. Inst. Wien, IV, 1882, p. i. 

80. Hlvcks, T. — A History of the British Marine Polyzoa, Two Vols., 1880. 

77. IIU.VLEV, T. H. — A Manual of the Anatomy of Invcrtebratcd Animals, 1877, pp. 52, 674, 680. 



13' 

03. JULLIEN, J. et Calvet, L. — Bryozoaires provenant des Campagnes de rHirondelle. Res. Camp. Sci. 

Prince de Monaco, Fasc. XXIII, Bryozoaires, 1903. 

04. Kemna, a. — L'origine de la corde dorsale. Ann. Soc. Roy. Zool. et Malacol. Belgique (Bull, des 

seances), XXXIX, 1904, p. i [sep.]. 

01. Kerr, J. G. — The Development of Lepidosiren. II. Quart. J. Micr. Sci., XLV, 1902, p. 3 [Methods]. 

go. Lang, A. — Zum Verstandniss der Organisation von Cephalodiscus. Jen. Zeitschr. XXV, 1891, p. i. 

84. Lankester, E. R. — a Contribution to the Knowledge of Rhabdopleiira. Quart. J. Micr. Sci., XXIV, 
1884, p. 622. 

85. Article "Polyzoa". Encycl. Britann. 9"' Ed., XIX, 1885, pp. 430, 434. 

03. LONGCHAMPS, M. DE Selys. — Uber Phoronis und Actinotrocha bei Helgoland. Wiss. Meeresuntersuch. 

(N. F)., VI, Abt. Helgoland, Heft i, 1903. 

04. — — Developpement Postembryonnaire et Aflinites des Phoronis. Mem. Classe Sci. Acad. Belgique, 

I [sep. J. 

96. MacBride, E. W. — The Development of Asterina. Quart. J. Micr. Sci., XXXVIII, 1896, p. 339 [p. 395]. 

98. — — The Early Development of Amphioxus. Quart. J. Micr. Sci. XL, 1898, p. 589. 

00. Further Remarks on the Development oi Amphioxus. Quart. J. Micr. Sci., XLIII, 1900, p. 351. 

82. MTntosh, W. C. Preliminary notice of Cephalodiscus, a new Type allied to Prof. Allman's Rhabdo- 
pleiira, dredged in H. M. S. 'Challenger'. Ann. Mag. Nat. Hist. (5) X, 1882, p. 337. 

83. Preliminary Note on Cephalodiscus, a new form allied to Prof. Allman's Rhabdopleiira. Rep. 

Brit. Ass. (Southampton, 1882), 1883, p. 596. 

87. Report on Cephalodiscus dodecalophus. Challenger Reports, Zool., XX, Pt. LXII, 1887. 

88. Report on Phoronis buskii. Challenger Reports, Zool., XXVII, Pt. LXXV, 1S88. 

96 (i). Masterman, a. T. — Preliminary Note on the Structure and Affinities of Phoronis. Proc. Roy. 
Soc. Edinburgh, XXI, 1897, p. 59. 

96 (2). On the Structure of Actinotrocha considered in relation to the suggested Chordate affinities 

of Phoronis. Proc. Roy. Soc. Edinburgh, XXI, 1897, p. 129. 

96 (3)- ■ Preliminary Note on the anatomy of Actinotrocha. Zool. Anz., XIX, 1896, p. 266. 

97 (')• 0» the Diplochorda. I. The Structure of Actinotrocha. Quart. J. Micr. Sci., XL, 1898, p. 281. 

97 (2). On the Diplochorda. II. On the Structure of Cephalodiscus dodecalophus. Quart. J. Micr. Sci., 

XL, 1898, p. 340. 

97 (3). On the 'Notochord' of Cephalodiscus. Zool. Anz., XX, 1897, p. 443. 

98 (i). On the Theory of Archimeric Segmentation and its bearing upon the Phyletic Classification 

of the Coelomata. Proc. Roy. Soc. Edinburgh, XXII, 1900, p. 270. 

98 (2). On the further Anatomy and the Budding Processes of Cephalodiscus dodecalophus. Trans. 

Roy. Soc. Edinburgh, XXXIX, 1900, p. 507. 

99 (i). On the origin of the Vertebrate Notochord and Pharyngeal Clefts. Rep. Brit. Ass. (Bristol, 

1898) 1899, p. 914. 

99 (2) On the "Notochord" of Cephalodiscus. Zool. Anz., XXII, 1899, pp. 359, 361. 

00. On the Diplochorda. III. The Early Development and Anatomy of Phoronis Buskii. Quart. 

J. Micr. Sci., XLIII, 1900, p. 375. 

02. The Early Development of Crihrella oculata. Trans. Roy. Soc. Edinburgh, XL, Pt. II, N" 19, 

1902, p. 373 [p. 403J. 

03. On the Diplochorda. IV. On the Central Complex of Cephalodiscus dodecalophus. Quart. J. 

Micr. Sci., XLVI, 1903, p. 715. 

94. Morgan, T. H. — The Development of Balanoglossus. Journ. Morphol. IX, 1894, p. i. 



I 32 

02 (i)- RlTTER, VV. E. — The Structure and Significance of the Heart of the ICntcropneusta. Zool. Anz., 
XXVI, 1903, p. I. 

02 (2). The Movements of the Enteropneusta and the Mechanism by which they are accomplished. 

Biol. Bull., Ill, 1902, p. 255. 
01. ROULE, L. — Etude sur le Developpemcnt Embryonnairc des Phoronidiens. Ann. Sci. Nat., (8) XI, 

1900 [1901], p. 51. 
72. SarS, G. O. — On some Remarkable Forms of Animal Life from the Great Deeps oft" the Norwegian 

Coast. I. Christiania Univ. Program for the 1st half-year, 1869, p. i. 

04. SciiEPOTlEFF, A. — Zur Organisation von Rhabdopleura. Bergens Museums Aarbog, 1904, N» 2. 

05. Uber Organisation und Knospung von Rhabdopleura. Zool. Anz., XXVUI, 1905, p. 795. [Published 

after nearly all the sheets of this Report had been printed off]. 

93. SCHIMKEWITSCH, W. — Sur les relations genetiques de Metazoaires. Congres Int. Zool. 2" Se.ss. 

(Moscou, 1892), 2" Partie, 1893, p. 215. 

03 (i). ScilULTZ, P2. — Aus dem Gebiele der Regeneration. III. Ub. Regenerationserscheinungen bei Flioronts. 

Zeitschr. i. wiss. Zool., LXXV, 1903, p. 391. 
03 (2). do. IV. tJb. Regenerationserscheinungen bei Actinotrocha. Zeitschr. f wiss. Zool., LXXV, 

1903, p. 473- 
go. Shipley, A. E. — On Phymosonia varians. Quart. J. Micr. Sci., XXXI, 1890, p. i. 

03. Spengel, J. W. — Die Enteropneusten des Golfes von Neapel. Fauna u. Flora d. Golfes v. Neapel, 

18 Monogr. 
n-, Bemerkungen zu A. P. Masterman's Aufsatz "On the 'notochord' o^ Cephalodiscus". Zool. Anz., 

XX, 1897, p. 505- 

01. Die Benennung der Entcropneusten-Gattungen. Zool. Jahrb. Abth. Syst., XV, 1902, p. 209. 

03. Neue Beitrage zur Kenntniss der I'2nteropneusten. I. Ptychodcra flava PIschsch. von Laysan. 

Zool. Jahrb. Abth. Anat. XVIII, 1903, p. 271. 

01. WijHE, J. \V. VAN. — Beitrage zur Anatomic der Kopfregion des Amphioxus. Petrus Camper, Jena, 
Jaarg. I, Afl. 2 [sep.]. 

94. WiLLEV, A. — Amphioxus and the Ancestry of the Vertebrates. Columbia Univ. Biol. Ser. II. 

gg (i). Remarks on some Recent Work on the Protochorda. Quart. J. Micr. Sci., XLII, 1899, p. 223. 

gg (2). Enteropneusta from the South Pacific. WillEY's Zool. Results, 1902, p. 223. 



EXPLANATION OF PLATES I-XIV 



The scale of the figures is indicated on each plate, and is further explained in the legend, 
in each case. The plane of the sections and the nomenclature of the surfaces are described in 
accordance with the text-figure on p. 23; a section transverse to the actual principal axis of the 
zooid being regarded as "frontal", while a "transverse" section is parallel to that plane. The 
terms "right" and "left" are used for descriptive purposes, and do not necessarily corre.spond 
with the actual right and left sides of the original specimens. Certain details are omitted in 
some of the figures : thus the nerve-layer of the epidermis is only shewn when it is unmistakeably 
present; while many of the strands which traverse the collar-cavities are omitted. 



LIST OF REFERENCE-LF.TTl'.RS. 



a. arm. 

n. b. arm-base. 

al. alimentary canal. 
an. anus. 

a. V. anterior vessel of stalk. 
a.'cK anterior vessel of body. 

b. bud. 

b.c} proboscis-cavity. 
b. c? collar-cavity. 

b. c? a. anterior dorsal horn of collar-cavity. 
b. c? metasomatic cavity. 

b. c.^ a. anterior ventral horn of metasomatic cavity. 
b. c.^ b. part of metasomatic cavity in loop of aliment- 
ary canal. 
b. m. basement-membrane. 

b. w. body-wall. 

c. collar. 

c. c. collar-canal. 

c. c. e. external opening of collar-canal. 

c. c. i. internal opening of collar-canal. 

c. n. s. central nervous system. 

d. basal disc of stalk. 

div. dorsal diverticulum of pharynx. 

d. jii.- dorsal mesentery of collar. 

d. m? dorsal mesentery of metasome. 

d. V. dorsal vessel. 

e. embryo. 
ep. epidermis. 

e. r. epithelial ridge. 
exc. e.xcretory granules. 
/. fold of body-wall. 

/. c. food-channel. 

f. c. I. left food-channel. 

f. c. r. right food-ciiannel. 
fil. peristomial filament. 

g. gonad. 

gl. glomerulus. 

g.p. generative pore. 



g. s. gill-slit. 

g. s. c. external opening of gill-slit. 

int. intestine. 

L. I — 6. left arms. 

L. a. left arm. 

l.g. labial or oral groove. 

/. ;/. lateral nerve. 

w. mouth. 

nies.' dorsal mesentery of collar. 

nies.^ dorsal mesentery of metasome. 

met. metasome or trunk. 

in. r. mid-rib of peristome. 

ms. longitudinal muscles of metasome. 

VIS. p. muscles of proboscis. 

ncli. notochord. 

n. t. nerve-tract. 

o. orifice of coenoecium. 

oes. oesophagus. 

op. operculum. 

op. I. left lobe of operculum. 

op. r. right lobe of operculum. 

op. rec. recess at base of operculum. 

or. ni. oral muscle (of collar). 

or. s. oral sinus {?). 

ov. ovary. 

ovd. oviduct. 

ov. I. left ovary. 

ov. m. ovarian mesentery. 

ov. r. right ovary. 

ov. V. ovarian vessel. 

p. proboscis. 

p! its ventral lobe. 

/. b. pigment-band of proboscis. 

per. pericardium. 

per. s. pericardial sinus or heart. 

ph. pharynx. 

pL g. pleurochordal groove. 

post. p. posterior pit of embryo. 



LIST OK REFERENCE-LETTERS. 



p.p. proboscis-pore. 

pr. I. primary lamella of coenoecium. 

prob. St. proboscis-stalk. 

pst. peristome. 

//. peritoneum. 

p. V. posterior vessel of stalk. 

p.v^ its termination on the alimentary canal. 

r. rectum. 

R. I — 6. right arms. 

R. a. right arm. 

rec. recess into which oviduct opens. 

J. '/j septum between proboscis and collar. 

s. -/g septum between collar and metasome. 

sec. I. secondary lamella of coenoecium. 

s. 0. sense-organ of embryo. 

sp. mass of spermatozoa. 

St. stalk. 

stom. stomach. 



stom."^ second stomach. 

t. testis. 

tent, tentacles. 

/. /. left testis. 

/. ;-. right testis. 

/. V. vessel of testis. 

u. I. upper lip. 

vac. vacuolated ectoderm of embryo. 

V. inv. ventral invagination of embryo. 

V. III. vitelline membrane. 

V. ines."^ ventral mesentery of collar. 

V. iiies.^ ventral mesentery of metasome. 

V. t. ventral thickening of embryo. 

X. problematical tissue of collar-canal. 

y. thickening of ectoderm near anus. 

yk. yolk. 

yk. a. its anterior subdivision. 

z. zooid. 



PLATE I. 



Figs. I, 4, 7, S, 9. — Cephalodisais gracilis. 
Figs. 2, 3. — C. sibogae. 
Figs. 5, 6, 10. — C. levinseni. 

Fig. I. C. gracilis, >( l- — The left hand portion of tiie figure shews a portion of the colony, detached 
from the substratum; its transparent coenoecium containing masses of orange-coloured zooids. The 
right hand portion shews another part of the coenoecium, including but few zooids, growing on 
a species of Tubucellaria (probably 7". fiisiformis U"Orb.). 

F'ig. 2. C. sibogae, /. i. — Shewing the erect, orange-coloured tubes of the coenoecium, originating from 
a basal encrustation on a stone. The dark masses seen in the tubes to the left of the figure are 
zooids, most of which are, however, retracted into the basal encrustation, which owes its dark 
colour to the zooids contained therein. The colour of the stone has not been indicated. 

Fig. 3. C. sibogae. — Anterior view of a neuter individual. Of the five arms seen on the right side of the 
drawing, the most posterior belongs to the right side, while the others are the four left arms. 
One of the right arms is marked R. a., but the details cannot be made out in the preparation. 
The only part of the operculum which can be distinctly seen is that marked op. I. 

Fig. 4. C. gracilis. — Group of buds. Two budding systems, marked respectively yi and ^, are intermingled: 
the numbering indicates the approximate relative ages of the inilixiiiuals. The system A consists 
of four degenerated stalks [A. i — ./) and a single bud [A. j), which has two arms (not drawn). 
The system B consists of a basal disc ((/.), belonging to the degenerated stalk B. i : B. 3, j are 
degenerated stalks: B. ^ shews five right arms and three left arms: B. j is seen in anterior view, 
two arms (not shewn) being moderately well developed on its right side : B. 6 has a single pair 
of arms, indicated as spherical knobs: B."] has just difierentiated its proboscis. 

Fig. 5. C. levinseni. — Young zooid. The complicated fold of the anterior surface of the proboscis is 
represented with only partial success. The stalk [st.], which is much like that of C. dodecalophus, 
is overlapped by the proboscis: — a, mass of arms and tentacles. 

Fig. 6. C. levinseni. — Side view of an older zooid. The proboscis is in the reversed position which it 
frequently assumes in this species, as is indicated by the position of the pigment-band (/. b.). 

Fig. 7. C. gracilis. — Side view of adult zooid. 

Fig. 8. C. gracilis. — Posterior view of a young bud with a single pair of arms [a.]. The pigment-band 
of the proboscis is already developed, and is seen through the metasome [met.), while the collar (c) 
is marked off from the metasome by a slight dorsal groove. 

Fig. 9. C. gracilis. — Anterior view of an older bud, from the same budding system as fig. 8. The arms 
are seen through the proboscis. The young posterior arms are seen at the base of the two well 
developed arms on the left of the figure. 

Fig. 10. C. levinseni. — Part of the coenoecium, X i, represented in its natural colour. Some of the elongated 
zooids are visible in the cavities of the zooecia. 

\Figs. I, 2 and 10, draivn by Mr. E. Wilson, are of the natural size. The remaining figures ivere drawn 
ivith Zeiss, A Obj. and have not been reduced]. 



Siboga-Expeililit' XXVl/'is. S. F. Harmer. Pteiobnuichia. 



/ 





N. 



/ 



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PLATE 11. 



Structure of the coenoecium. 

Figs. II — 13. — Cephalodiscus levinseni. 
Figs. 14 — 16. — C. gracilis. 
Figs. 17, 18. — C. sibogae. 
Figs. 20, 21. — C. dodecaloplius. 
Fig. 19. ■ — Rhabdopleiira normani. 

Fi'T. II. C. levinseni. — Part of the coenoecium (GreENOUGH's binocular, a"). The diameter yi!/) = 12 mm.; 
the length of tiie peristome Z>'^=4,2mm.: — ;;., zooids, each contained in a distinct compartment 
("zooecium") of the coenoecium; the varying positions of the pigment-line indicate a considerable 
variety of position in the proboscis; o., orifice; pst., peristome; e., embryos. 

Fig. 12. C. levinseni. — The peristome marked A in fig. 11, to shew the laminated structure of the coe- 
noecium (GreeNOUGII, a'j. For explanation of a, b, see text (p. 9); c, a secondary lamella. 

Fig. 13. C. levinseni. — Two young peristomes (GreenouGH, a''). 

Fig. 14. C. gracilis. — The peristomial filament marked B in fig. 15 (Greenough, a'). 

Fig. 15. C. gracilis. — Portion of a colony, shewing the continuous cavity of the coenoecium (Greenough a") 
— z., masses of zooids, which are so crowded that their limits are not easily seen ; b., bud ; e., embryos 
o., orifices; a., an occluded orifice; fil., peristomial filaments of coenoecium, surrounding orifices 
/), the filament shewn in fig. 14. 

Fig. 16. C. gracilis. — ■ End of another branch, more highly magnified than fig. 15 (Greexough, a'-): — 
a.,b. orifices. (For explanation of c^f, see text, pp. 12, 13). 

Pig. ly. — c. sibogae. — End of a branch of the coenoecium (GreenougH, a^): — c.,f.,i., orifices. (For 
explanation of other letters, see text, pp. 14, 15). 

Fig. 18. C. sibogae. An erect branch of the coenoecium, less highly magnified (GREENOUGH, a"). The position 
of the orifices is indicated by the peristomial filaments (y?/.). The dark patches are foreign inclusions: — 
B., part of the encrusting base of the coenoecium. 

Fig. 19. Rhabdopleiira nonnani. — Free end of a peristome (Zeiss, C). (For explanation of lettering, see 
text, p. 8j. 

Fig. 20. C. dodecaloplius. — Portion of coenoecium (Greenough, a''). 

Fig. 21. C. dodecaloplius. — Portion of coenoecium, less highly magnified (GrkenouGH, a"): — b,c, orifices. 
(For explanation of other letters, see text, p. 16). 

[ The figures on this Plate zvere draxvn as follows : 

GreeNOUGH's binocular, a": — Figs. 11, 15, 18, 21. 

GreeNOUGH's binocular, a-: — Figs. 16, 17. 

GreENOUGH's binocular, a'': — Figs. 12, 13, 14, 20. 

Zeiss, C: — Fig. 19. 
All the figures were afterwards reduced '/j. or two diameters]. 



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PLATK III. 

Figs. 22, 25 — 32. — C. gracilis. Fig?. 23, 24. — C. levinseni. 

Fig. 22. C. gracilis. — View of a reconstruction, made by the ground glass method, with the assistance of 
a plasticine reconstruction, from the specimen shewn in PI. V, figs. 43 — 53. The details of the first 
arm (A'./) are based on the individual shewn in PI. I, fig. 7. The lateral flexure of the specimen 
indicated by figs. 45 — 53 has for the most part been omitted. The left ovary [ov.l.) is mainly 
occupied by a single large ovum. The broad pharynx {ph.) is seen from its narrow edge, the sharp 
bend just before its junction with the oesophagus [oes.) being probably the result of muscular 
contraction, which has also affected the dorsal vessel [d.v.]. The last four arms [R.2 — j) have been 
cut off near their bases, which in tiie case of R.j — 5 pass transversely outwards, while R. ^ is 
rotated round its own longitudinal axis so much that its groove faces posteriorly. 

Fig. 23. C. levinseni. — A reconstruction similarly matlc by the ground glass method; seen from the 
posterior surface and somewhat from the left. The proboscis (p.) is directed forwards, shewing the 
long, narrow proboscis-stalk {prob.st.) characteristic of this species; its morphologically anterior 
epithelium is infolded in a complex manner. There is also some rotation of the proboscis-stalk 
round its principal axis, since the left proboscis-pore [p. p. I.) lies at the edge of the drawing, while 
the right pore [p.p.r.) is also brought to the left of the median plane of the metasome. The right 
arms are already separate from one another, but R.2 turns ventrally from its origin, and is not 
visible in this view. On the left side, the section passes at a more ventral level, so that the common 
arm-base {a.b.) is seen, continuous with the left lobe of the operculum [op.]. The region of the 
central nervous system [c. n. s.) is conve.x, and through it is seen the notochord (nch.). The dorsal 
vessel (d. v.) lies in the dorsal mesentery ((/. ;«.), and the left ovarian vessel {ov. v.) is also seen : — 
r. is a lobe of the rectum; g. s., seen tlirough the left ovary, is the projecting portion of the 
pharyngeal wall leading from its dorsal diverticulum to the external aperture (g. s. e.) of the slit. 

Fig. 24. C. levinseni. — Anterior view, seen somewhat from the right side, of the same reconstruction, the 
details of the upper lip added from a plasticine reconstruction. The arms are omitted, with the 
exception of part of R.2. In addition to the median ventral projection of the proboscis-stalk, the 
upper lip is traversed by two ridges on each side, thus giving rise to three oral grooves on each 
side of the middle line. The greater part of the ventral wall of the mouth is cut away, with the 
exception of a fragment of the lower lip, seen in the foreground, in the middle line. The convex 
dorsal wall of the pharynx (ph.) is exposed, on either side of which is one of the deep pleurochordal 
grooves; the right gill-slit [g.s.), cut near its external aperture, opens nearly vertically into one of 
these, and on its median side is seen the blind end of one of the anterior horns of the metasomatic 
cavity (b.c.'^a.). The right collar-canal has its external opening {c.c.e.) directed dorsally, while 
between this and the internal opening is the problematical tissue {x.) of the collar-canal, attached 
above to a fold of the body-wall of the collar. The free edge of the right lobe of the operculum 
{op.) is directed dorsally, that of the left lobe ventrally. 

Fig. 25. C. gracilis. — Another view of the specimen shewn in fig. 22, from a plasticine reconstruction. 
The thickness of the layers of plasticine having been somewhat too great, the transverse diameter 
is exaggerated. The figure shews that both the operculum and the arms are modifications of the 
anterior free edge of the collar: — g-s.r. right gill-slit; c.c.e. external opening of right collar- 
canal; g.s. I. position of opening of left gill-sIit; b.iv., body-wall of metasome. 

Fig. 26. C. gracilis. — - Base of stalk of fig. 7 (Zeiss, DD): d., basal disc; /., proboscis of bud. 

Fig. 27. C. gracilis. — Base of stalk of a functional zooid, with a young bud (Zeiss, C). The collar of the 
the bud shews indications of the first pair of arms [a.); and both the first {l>.c.^) and second (b.c.-) 
body-cavities are visible. 

Fig. 28. C. gracilis. — Part of stalk of Fig. 29, shewing the two stalk-vessels (ZEISS, C). 

Fig. 29. C. gracilis. — Posterior view of metasome of a bud, at about the stage of fig. 32, shewing the 
posterior vessel ip-i'.) of the stalk ending on the alimentary canal, and the anterior vessel (a. v.) 
prolonged for a short distance along the anterior body-wall (Zeiss, C). 

Fig. 30. C. gracilis. • — Anterior view of a bud (Zeiss, C). The left half of the proboscis is injured, and 
the first arm of the same side has been lost. The mouth (w.) is seen through the proboscis; the 
arms possess terminal vesicles, and the bases of the posterior pair are continuous with the oper- 
culum (op.), the free edge of which is indicated by a circular line partly surrounding the mouth: — 
al., developing alimentary canal. 

Fig. 31. C. gracilis. — Advanced bud, seen from the left side (ZEISS, C), shewing the course of the food- 
grooves of the first three left arms {L. / — .?): — /., edge of proboscis, which covers the greater part 
of the bud; >//., mouth, seen through the proboscis; op. I., left lobe of operculum; c.c.e., external 
aperture of left collar-canal; g.s.e., e.xternal aperture of gill-slit; ph., pharynx -j- oesophagus; 
int., intestinal limb of alimentary canal. 

Fig. 32. C gracilis. — Posterior view of a similar bud (Zeiss, C): c. n. s., position of central nervous 
system; R.i, first right arm, thrown over to the leftside; and, like /,..> and Z..J, possessing terminal 
vesicles; m., mouth, seen through the rectum and pharynx. 

[figs. 22 — 2j -tvere drawn by 'Sir V.. WiLSON. All the figures zvere reduced -/j]. 



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PLATE IV. 



Figs. 33 — 36. • — C. Icinnseni. 
Fig- n- — C. gracilis. 
Figs. 38 — 40. — C. sibogae. 
F'igs. 41, 42. — C. dodecalophus. 

F^isj. 33. C. levinseni. — Sagittal section of an old zooid, reconstructed from several sections. The proboscis 
(/.) is turned at right angles to the left of the specimen, so that its lateral parts are seen on the 
anterior and posterior sides. The first five arms of the left side (Z,. / — 5) are seen. The five 
unnumbered arms belong to the right side. The ovaries of this specimen are very small. The 
right ovary yov.) with its pigmented duct, is represented, partially overlapped by the dorsal vessel 
[d.v.) and the rectum (r.). 

Fig. 34. C. levinseni. — Median sagittal section of another zooid, tlraun from a single section with the 
exception of part of the epithelium of the lower lip. The difference between this figure and fig. ^t, 
is probably due to contraction of the longitudinal muscles. The anus (an.) is widely open, as a 
large mass of faeces is being discharged to the exterior. The course of the notochord {nc/i.) is 
indicated from the adjacent sections. The wall of the intestine is cut somewhat tangentially, so 
that one of its folds subdivides its lumen: the alimentary canal is not cut medianly at its principal 
bend. The proboscis {/>.) has its normal position, but its stalk is greatly contracted, as indicated 
by the folds of its wall. 

Fig. 35. C. levinseni. - — A section to the right of the middle line of the same individual. A lobe [op.) of 
the operculum is seen disconnected from the basal part of the organ. The oral muscle (or. in.) is 
seen both dorsally and vcntrally to the mouth (/«.). 

Fig. 36. C. levinseni. — A still more lateral section of the same individual: — ins, anterior longitudinal 
muscles of metasome, inserted into septum -\^; c. c, edge of collar-canal; g. s., wall of gill-slit ; 
p.p., internal opening of proboscis-pore. 

F'ig. 37. C. gracilis. — Median sagittal section, combined from the sections of a nearly sagittal series. 
The notochord is not well shewn in this individual. 

F'ig. 38. C. sibogae. — Median sagittal section of the alimentary canal of a neuter. The bend of the canal 
is injured, but its arrangement, as indicated by the neighbouring sections, is shewn by dotted lines. 

Fig. 39. C. sibogae. — Part of a sagittal section of a neuter. The strongly marked epidermic thickening (y) 
behind the central nervous system (c. n. s.) is obviously ciliated, and probably has a nerve-layer 
at its base. The muscles are not indicated. Part of the h)-popharyngeal groove is seen, and is 
marked pk. The upper lip is somewhat broken. 

Fig. 40. C. sibogae. — Side view of an entire neuter individual. The anterior part of the zooid is lost, 
but the operculum (op.) is entire. 

Fig. 41. C. dodecalophus. — Combined from three sections of the series to which fig. 42 belongs; to shew 
the relations of the muscles (ms) of the metasome to septum -/,, to the collar-canal {c.c.) which is 
cut tangentially, to the gill-slit (g.s.) and to the origin of the oral muscle (or. in.): — • /■/• internal 
opening of proboscis-pore; l.n. origin of lateral nerve. 

Fig. 42. C. dodecalophus. — Median sagittal section of the same specimen, drawn from a single section. 
The notochord is not cut medianly, but its opening into the pharyngeal diverticulum {div.) is 
seen in the middle of the glandular area in the anterior wall of that cavity. 

[All the figures mere dratvn zuith Zeiss C Obj., and ivere then reduced '/oj. 



Siboga-Expeditie XXVI/<w. S. F. Harmer. Pterobr.inchia. 



/r 




S. F. Harmer del. 



P W. M. Trap inipr. 



PLATE V 



C. gracilis. 

Figs. 43 — 53 (Zeiss, C) are obliquely sagittal sections of the specimen of which reconstructions are shewn 
in PI. Ill, figs. 22, 25. The specimen had a strong lateral fle.xure towards the right, so that 
in figs. 50 — 53, the animal is cut in two separate pieces. It was abnormal in having a com- 
munication between the posterior side of the stomach and the intestine. The series starts with 
fig. 43 which is near the middle line, and proceeds outwards towards the right side of the 
body. Figs. 46 — 50 represent consecutive sections. 

Fi". 43, near the median plane, cuts the mouth (>«.), pharynx (ph.) and oesophagus (oes.) nearly mcdianly. 
The peritoneum (pt.) is loosely attached to the stomach, and does not enter the interval (probably 
in the main artificial) between the stomach and the intestine. The dorsal part of the collar-cavity 
(b. c.-) is that of the left side, with the bases of the last three arms [L. J — j). The stalk, which 
is cut at a bend, shews its anterior nerve-tract («. /.) : — g. s., pleurochordal tissue of dorsal 
diverticulum of pharynx, continuous with the left gill-slit. The ovary {oi>. I.) is that of the left 
side. The operculum [op.) is shorter than in the more lateral sections. 

Fig. 44. — /., end of the fold of the body-wall, which divides the sections shewn in figs. 50 — 53 into two 
parts; ov.r., median edge of right ovary; pi., pleurochordal tissue continuous with right gill-slit. 

Fig. 45 passes just to the right of the mouth. The arms of the left side {L. i — j) extend beyond the 
middle line of the collar to the right side of the animal ; the base of the stalk [st.) is cut, and 
the opening of the second stomach [stoin.-) from the main stomach: — b.cr, right collar-cavity; 
p.p., internal opening of right proboscis-pore; ;-., right wall of rectum; ov.v. branch from dorsal 
vessel to left ovary; g. s., wall of gill-slit. 

Fig. 46. — The ventral half of the body, which is completely separated from the dorsal half by the fold of 
the body-wall ( /") seen in fig. 45, is not represented: — c.c.i., internal opening of right collar-canal; 
g.s.c:, external opening of gill-slit; oiyL, left oviduct, from which a discharge of pigment is 
taking place. 

Fig. 47. — p., proboscis, which has just separated from the collar; K.1,2, food-grooves of first and second 
right arms; x., problematical tissue of collar-canal; /.;/.., lateral nerve, originating from the central 
nervous system [c.n.s.); ovd.r., pigment in epidermis indicating the median edge of the right oviduct. 

Fig. 48. — g-S; outer edge of gill-slit; c.c.e., fold of epidermis into which the collar-canal opens in fig. 49. 

Fig. 49. — C.C.C., external opening of collar-canal; x, problematical tissue of collar-canal, extending to 
base of oral epidermis of operculum. 

— This and figs. 51 — 53 shew both parts of the metasomc, the ventral half giving origin to the 
stalk (st.), and containing the second .stomach. 

— The collar has just separated from the metasome, but a part of its free anterior edge still 
connects the base of the fifth arm (A'. 5) with the operculum (op.): ■ — p.t'.\ edge of termination 
of posterior stalk-vessel on the alimentary canal. 

— The operculum (op.) is no longer continuous with the last arm (R- s). The stalk-vessels are not 
easy to distinguish from one another in the distal part of the stalk, but the zigzag vessel (a.v.t) 
there shewn is probably part of the anterior vessel. 

l-'g- 53- — The part of the body-cavity (b.c.^b.) extending into the loop of the alimentary canal in figs. 

50 — 52 is about to open into the general metasomatic cavity. 
Fig. 54. — Longitudinal section of coenoecium through an orifice (^.): — _/?/., peristomial filament (ZEISS, A). 
Fig- 55- — Transverse section through the coenoecium (ZEISS, C). 
Figs. 56 — 58. Frontal sections of a bud (transverse to its long axis) (ZEISS, F). 
Fig. 56 passes a short distance dorsally to the point where the intestinal limb of the alimentar)- canal (////.) 

opens into the stomach (stoin.). Both parts of the canal are contained in a common peritoneal 

investment (pt.). 
Fig. 57 is taken more dorsally than the last. It shews the origin of the dorsal -; ovarian vessels (ov.v.) 

from a reflection of the peritoneum of the alimentary canal. 
Fig. 58 is the next section on the dorsal side of fig. 57. The two roots of the dorsal vessel (d-v.) have 

united, and the ovarian vessels (ov.v.) are being given oft' from the common trunk. 
]-"ig. 5g. — Frontal section of an older bud (Zeiss, F). The proboscis (p.) lies asymmetrically: ^ — c.c, right 

collar-canal, the emargination on the left side being merely the interval between the operculum 

(op.) and the metasome: g.s., developing right gill-slit. 

[The figures have been reduced '/il- 



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PLATE YI. 



C. gracilis. 

Fig. 60. — Frontal section througli arms and dorsal lobe of proboscis. All the arms appear in the section 
except the fourth left arm. 

pjcr. 61. — A more ventral section of the same specimen, cutting the dorsal edge of the mctasome, with 
the two oviducts {ovd.). The grooves of the ten arms are indicated: — op.r., right lateral lobe 
of operculum. 

FifTs. 62 — 70. — Frontal sections of another individual in which the ventral lobe of the proboscis is turned 
forwards, as in fig. 37. The arrangement of the arms and operculum was made out with the 
aid of a plasticine reconstruction. 

Fig. 62. — Through the proboscis-stalk, in front of the beginning of the collar: — per., pericardium, 
ventrally to which are seen the two principal groups of proboscis-muscles {ms.p). 

Fig. 6j. . — Through the proboscis-stalk, in the region of the proboscis-pores (p.p.), and the tips of the 
anterior horns {b.c.'-a.) of the collar-cavities. 

Fi". 64. — Through the notochord (nch.). The second left arm is directed ventrally from its base (somewhat 
as in the case of R. i in fig. 32), which is thus represented only by a part of the food-groove. 
The arm curves forwards later, so that it is cut near its tip in fig. 63 {L.2). 

Fig. 65. — Through the mouth (iii.) and the pharyngeal diverticulum (div.). The left half {op.) of the 
operculum is directed straight forwards {/. e., away from the stalkj, while the right half is folded 
backwards in a complicated manner, and thus does not appear in the section. The right arms, 
which are beginning to appear, are with the exception of K. i all thrown back along the posterior 
side of the metasome, while the left arms (seen in figs. 63, 64) are for the most part directed 
forwards. The ventral side of the right arm-base {a. b.) shews no trace of food-grooves. 

Fig. 66. — Through the mouth (w.) which opens into the recess {op.rec.) formed by the base of the 
operculum. The part of the right lobe of the operculum marked op', is backwardly directed, 
so that its oral surface faces posteriorly: — the direction of this lobe is probably correlated with 
that of the last arm, which is also thrown backwards; a.b., ventral surface of right arm-base. 
The left collar-canal shews both its external {c.c.e.) and internal (c.c.i.) apertures. The fold of the 
body-wall between this and the left oviduct (ovd.) is of no special significance: — x., problematical 
tissue of right collar-pore; g.s., dorso-lateral grooves of pharynx leading fioni the dorsal diverti- 
culum {div.) to the gill-slits. 

Fig. 67. — Through the ventral wall of the left collar-canal (c.c.) and through the external opening (c.^.^.) 
of the right collar-canal. The opercular recess {op. rec.) is still present. The fold of the body-wall 
seen on the right side between it and the collar-canal appears from the reconstruction to be 
correlated with the throwing back of the arms and of the operculum of this side. 

Fig. 68. — Through both gill-slits {g.s.) and the anterior horns of the metasomatic cavity {li.c.^a.). The 
collar-cavities {b.c."^) are here divided by a ventral mesentery {v.iiies.-). 

Fig. 69. — Through the region of the pleurochords {pL), on the aboral side of the gill-slits: — the muscles 
seen in b.c.^a. in fig. 68 arc continuous with those marked ins. in this figure. 

Fig. 70. — Immediately on the dorsal side of the dorsal lobe of the stomach: — ///. is probably the 
posterior end of the pharynx (its passage into the oesophagus not being very obvious in sections 
cut in this plane). 

Fig. 71. — Belonging to the individual shewn in figs. 60, 61, and cut in a frontal plane on the aboral 
side of the origin of the stalk: — p.v.^ termination of the posterior vessel {p. v.) of the stalk on 
the second stomach {stoin."^). 

[Fig. -jr ivas drazvii ivith Zeiss, DD Obj. — Tlie other figures zvere draivii with Zeiss C, and none of 
the drawings have been reduced]. 



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PLATE VII. 

C. sibogae. 

Figs. 72 — -jd, 79. — Male. 
Figs, f-j, 78. — Neuter. 

Fig. 72. — Young male, posterior view. The left arm has been broken oft', but its base is indicated by 
L. a. The refractive vesicles of which the epidermis of the arms of the male is almost entirely 
composed are not indicated in figs. 72 — yS, but they have the character shewn in PI. IX, fig. 99: — 
c.n.s., position of central nervous system. 

F'g- 73- — Older male, shewing the right testis {t.r.). The left testis is smaller and is seen through the 
right arm [R. a.). The left arm (L.a.) is bifurcated at the tip. The arms are shorter than usual. 
The proboscis (p.) is a good deal folded. 

Fig. 74. — Male, intermediate in age between figs. 72 and -jt,. The collar [c.) is marked off from the 
metasome (met.) by a conspicuous dorsal groove. The left side of the proboscis (p.) is somewhat 
injured. Both arms are incomplete distally. 

F'S- 75- — Old male, seen obliquely from the right side. This specimen was cut into the sections represented 
in PI. VIII, figs. 80 — 89. The right and left testes {t.r.,t.l.) are fully developed, and the metasome 
(met.) forms much the largest part of the animal. The arms (R.a., L.a.) are shorter and thicker 
than in most of the young individuals. 

Fig. j6. ■ — Anterior view of old male, with longer arms. Some of the details of this specimen are further 
illustrated in PI. IX, figs. 95, 96. 

Figs, jj, 78. — Transverse sections of a neuter. 

Fig- 77- — Through both apertures of the right collar-canal, and the external aperture [g.s.e.) of the right 
gill-slit. The muscular system is unusually strong in the neuters of C. sibogae: — ins. muscles of 
metasome, passing to septum ^/^ (s.-l^); from the anterior side of this septum originate the oral 
muscles (or. in.), some of the fibres of which spread over the dorsal side of the mouth. The three 
epithelial ridges seen on the dorsal side of the pharynx pass in the section next in front of this 
one into a triangular upper lip which is of the same size as the three ridges together. The two 
grooves marked in', pass laterally to the exterior, two sections on the ventral side of fig. 77; the 
mouth being thus situated at the level marked nt. The operculum (op.) is directed forwards on 
the right side, and backwards on the left side. 

Fig. 78. — A more posterior section of the same specimen. The gill-slit (g.s.) on the left side shews both 
its internal and external apertures. That on the right side is cut on the posterior or dorsal side 
of its external aperture ; in the next section further back the deeply stained epithelial lobe between 
the two arrows has disappeared, and the vacuolated tissue of the gill-slit has become continuous 
with the extensively developed plcurochordal tissue of the dorso-lateral part of the pharynx. The 
whole of the arms of the right side are indicated (A'. / — ./). 

fig- 79- — Obliquely sagittal section of an old male. The space between the central nervous system (f. //..y.) 
and its basement-membrane is probably an artefact. The collar is cut in a plane which is inter- 
mediate between sagittal and frontal: thus the projection L.a. is the base of the left arm, between 
w^hich and the posterior wall of the proboscis is a groove (f.c.l.) corresponding with the principal 
food-channel of an ordinary Cephalodiscits; f.c.r. is the corresponding groove of the right side, 
and both grooves unite in the mouth, which occurs in a later section: — R.a. appears to be 
part of the right arm; while the arm cut transversely seems to be that of the left side; — c.c, 
right collar-canal; t.r.,t.l., right and left testes. The section does not involve more than half 
the length of the animal, which is bent into a 6'^-form, in accordance with the shape of the 
coenoecial cavity in which it lies. The metasome and the testes are thus at least twice as long 
as the parts shewn. 

\Figs. J 2 — jd zvere drawn with Zeiss A Obj.; 77 — 7p luith C Obj. None of the draivings have been reduced]. 



Sil>(\ira-F.\ft;iiti,' WVl/'/s. S. F. Harmer. Pterohranrliia. 



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PLATE VTTT. 



C. sibogae. 

Figs. 80 — 89. — Male. 

Figs. 90 — 93. — Neuter. 

Fig. 94. — Common stalk-base. 

Figs. 80 — 89. — Frontal sections of the male shewn in I'l. VII, tig. 75. For explanation, see text, p. ^6. 

Fig. 80. — Through dorsal lobe of proboscis (/.). The arms (L.a., R.a.) are somewhat macerated. 

Fig. 81. — Through region of pericardium (7 sections later). 

Fig. 82. — The ne.xt section. 

Fig. 83. — The ne.xt section but one. 

Fig. 84. — Through the mouth (3 sections later). 

Fig. 85. — Two sections later. 

Fig. 86. • — Three sections later. 

Fig. 87. — Three sections later. 

Fig. 88. — Two sections later. 

Fig. 89. — Forty four sections later. 

Figs. 90, 91. ■ — Frontal sections of a neuter. 

Fig. 90. — Through the entire length of the right gill-slit (g. s.) : — //., plcurochordal tissue of groove 
continuous with the left gill-slit and the left pleurochord. 

Fig. 91. — Five sections nearer the stalk, cutting both pleurochords (pL). 

Fig. 92. — Obliquely frontal section of another neuter, cutting the posterior end of the ventral side of 
the collar. The arms of this specimen are shewn in PI. IX, fig. 97. 

F'g- 93- — Obliquely frontal section of the anterior end of a neuter. The left arms have been broken 
off, a torn place in the section marked L.a. indicating part of their base. The section shews the 
strong muscles {ins.) of the metasome inserted into septum "/,, from which starts one of the 
origins of the large oral muscle (or. in.). The wall of the gill-slit [g.s.) is composed of pleurochordal 
tissue. The ventral epithelium of the collar-canal (c.c.) is strongly ciliated. The problematical tissue 
(x.) of the collar-canal has a distinct row of nuclei on its coelomic border, while a band of muscle 
passes from it across the collar-cavity to the basement-membrane of the epidermis. 

Fig. 94. — Common-base of stalks, in vertical section. 

[Fig. g.f. tuns drawn witli ZEISS DD Obj.; 80 — c^j with C Obj. None of the drazvings have been reduced]. 



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PLATE IX. 



Figs. 95 — 99, 102, 103. — C. sibogae. 
Figs. 100, lOi, 104 — 1 10. — C. lei'inseni. 

Fig. 95, 96. C. sibogae. — Two views (Zeiss, C) of the anterior part of the male shewn in I'l. \'II, fig. 76. 
Pig, c)5. — Anterior view. The ventral lobe (/'.) of the proboscis is turned forwards, exposing the mouth 

(w.), on each side of which is seen a collar-canal [c.c). The mouth leads to a vestigial alimentary 

canal, the intestinal limb of which is marked r. R.a. and L.a., right and left arms; t.r.,t.L, 

right and left testes. 
Fig. 96. — Posterior view of the same specimen: — c.n.s., swelling of collar due to the presence of the 

central nervous system; g.p. appears to be one of the generative pores; d.v., dorsal vessel; 

r., intestinal limb of alimentary canal. 
Fi". 97. C. sibogae. — Frontal section of anterior end of the specimen shewn in PL \'I1I, fig. 92, shewing 

the proboscis (/.), and the four pairs of arms (ZEISS, C). 
Fif. 98. C. sibogae. — Abnormal arm of a tentaculiferous individual, the distal end of which is produced 

into a long vesicle-bearing portion, resembling the arm of a male (ZEISS, C). The arm may 

belong to the first pair, but this is uncertain. The individual to which this arm belongs appears 

to have a pair of testes, in the position of the ovaries of a female Ceplialodiscns. The testes, 

though small, seem to be functional. The specimen in other respects resembles a normal neuter: — ■ 

tent., tentacles. 
Ficr. 99. C. sibogae. — Base of arm of a young male, partly in optical section, shewing the characteristic 

epidermic vesicles, which do not occur in the pro.ximal region of the arm (Zeiss, D D). 
Fig. 100. C. levinseni. — Obliquely sagittal section of a young individual (ZEISS, C). The proboscis-stalk 

is strongly contracted and bent, as is indicated by the fold (/.) of its dorsal body-wall: — 

«.', one of the first arms. 
Fie. loi. C. levinseni. — Lateral sagittal section of an old individual with reversed proboscis (ZEISS, C): — 

/.,/., folds of body-wall of proboscis which appear to indicate the region where the rotation 

has been effected. 
Fio'. 102. C. sibogae. — Section of part of the basal encrustation of the coenoecium (Greenougm bino- 
cular, a-.). The letters indicate the corresponding parts in fig. 103. 
Fi<T. 103. C. sibogae. — Part of fig. 102, more highly magnified (ZEISS, A). For explanation of lettering, 

see text, p. 15; ^^ a secondary lamella. 
Figs. 104 — 106. C. levinseni. — Sagittal sections of an embryo (ZEISS, C). 
Fig. 104. — Lateral section, shewing the dorsal vacuolated ectoderm {vac), the ventral thickening {v. t.) 

and the three body-cavities {b. f.'"''). 
?\o. 105. — Nearer the middle line: — the yolk-mass (yk) is divided into three portions. 
Fjcr. 106. - — More median region: — s.o., sense-organ (?), which appears as an invagination of the vacuo- 

lated ectoderm [vac). The two principal divisions of the yolk-mass are less clearly seen here 

than in some of the figures on PI. XIV: (Ui. is probably the future anus: b.c.'- is visible on the 

dorsal side of the yolk-mass. 
Fi". 107. C. levinseni. — Transverse section through the ventral border of the collar and jiart of the 

metasome (Zeiss, D D). The operculum (op.) is directed forwards, and appears emarginate in the 

middle line: — v.ntes."^, ventral mesentery of collar; v.mes.'^. of metasome; s.-j^, trunco-collar 

septum; III., level of mouth; b.in., basement-membrane of oral epidermis of operculum, with muscles. 
Fif'. 108. C. levinseni. — Transverse section of a peristome (Zeiss, A): — w. ;-., mid-rib; pr.l., primary 

lamellae. 
Fi". 109. C. levinseni. — Transverse section through an entire branch of the coenoecium (GreENOUGH 

binocular, a.^). The letters indicate the corresponding parts in fig. no. 
Fig. I 10. C. levinseni. — Part of fig. 109, more highly magnified (ZEISS, A): d, e, f, cavities of zooecia; 

pr.l., primary lamellae. For other letters, see text, p. 10. 

\All the figures have been reduced ^/,]. 



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PLATE X. 



C. levinseni. 

Piers. Ill 125 are from a frontal scries of an adult zooid. The proboscis is in the normal position. 

Fig. III. — Through dorsal lobe of proboscis, which is here strongly infolded (cf. PI. Ill, fig. 24). 

Fig. 112. — Thirty four sections further. Through pericardium {per.), both proboscis-pores (/./.), and 
anterior dorsal horns of the collar-cavities [h.cra.]. The oval line surrounding the figure indicates 
the outline of the lumen of the coenoecial tube. 

Y\a, 113. Six sections further. Through the anterior end of the notochord [nch.), the lumen of which 

is here specially large. The ventral lobe of the proboscis (/>.) is about to separate from the 
proboscis-stalk. 

pjCT. 114. Four sections further. The ventral lobe of the proboscis has just separated from the proboscis-stalk. 

Pio-. 115. — Seven sections further. Slightly dorsal to the mouth, through the transverse part of the 
pigment-band {p.b.) of the proboscis: — prob.st., lobe of proboscis-stalk, cut .separately;/., fold 
of ventral lobe of proboscis. 

Fi". 116. — Four sections further. Through the upper lip, which shews a distinct labial or oral groove 
(/. '^) on each side of its median ridge. The ventral lobe (/.) of the proboscis is folded in a 
complicated manner. The free edge of the left lobe {op. I.) of the operculum has appeared. 

Fig. 117. — Two sections further, still through the upper lip, with its oral grooves {l.g.). The course of 
the food-groove of the fifth right arm {R. 5) round the ventral side of the arm-base is illustrated 
by figs. 115 — 117, and shews the manner in which the grooves of the posteriorly directed arms 
pass towards the mouth. 

Fig. 118. — Three sections further. Through the anterior wall {div.) of the pharyngeal diverticulum, and 
the beginning of the metasome {met.): — b.m. ridge of basement-membrane in right collar-cavity, 
indicating the base of the operculum. 

Fig. 119. — ■ Four sections further. Through the mouth {in.) and pharyngeal diverticulum {div.). The mouth 
opens straight forwards, as in PI. IV, fig. 33. The left half of the operculum {op. I.) is folded, 
and lies principally in the plane of the section. The right lobe {op.r.) has its free edge directed 
towards the stalk, so that this lobe appears in the sections as far as fig. 123. The median part 
of the operculum and the base of both of its lateral lobes is, however, turned away from the 
stalk, so as to constitute the epidermic recess seen in figs. 121 — 123 (cf. I'l. 1\'. fig. 34): — 
b.m., two ridges of basement-membrane indicating the base of the left lobe of the operculum. 

l-'i'T. 120. — Two sections further. The dorsal wall of the pharynx is beginning to be distinctly trilobed. 
This condition, which is more marked in fig. 121, indicates the commencement of the dorso- 
lateral grooves {g.s.) which lead to the gill-slits and pleurochordal grooves. The emargination in 
the dorsal body-wall of the metasome is a short longitudinal groove between the regions of the 
two oviducts, and may have something to do with directing the faeces when they escape from 
the anus. 

Pi,T. 121. Two sections further. Part of the thin dorsal wall of the right collar canal is cut: or.s. is 

possibly a vascular sinus. 

Pi<r. 122. — Three sections further. The mouth (w.) opens into the epidermic recess {op.rec.) constituted 
by the base of the operculum. The median dorsal groove of the pharynx seen in the previous 
sections has died away. 
Fig. 123. — Six sections further; through the ventral end of the mouth and both gill-slits. The rectum (;-.) 

has appeared. 
Fi<'. 124. — Five sections further. The distinction between the ordinary pharyngeal epithelium and the 
pleurochordal tissue is much less marked than in C. dodecalophus. The anterior horns of the third 
body-cavity are opening into the main cavity, of which a lobe divided by the ventral mesentery 
{v.ines.'^) appears between the pharynx and the collar-cavity: — g.s., basement-membrane of 
ventral (posterior) wall of right gill-slit; ov.v., ventral edge of ovarian vessel. 
Y\". 125. — Thirteen sections further. The pleurochordal tissue has almost disappeared. The nerve-layer 
has become very indistinct, and is not represented. 

[ The figures zoere all draion zi'llh ZEISS, C Obj., and reduced -\^. 



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PLATK XI. 



Figs. 126 — 132, 137 — 140. — C. levinseni. 
Fig- 133- — C. dodecalophus. 
Figs. 134, 135. — C. gracilis. 
Fig. 136. — C. sibogae. 

Figs. 126 — 128, 132, 130 are continuations of the series (C. levinseni) siievvn on PI. X. 

Fig. 126. — Twenty two sections further than fig. 125. — Through the oesophagus {oes.) The muscular 
layer is thicker and narrower, indicating the approach of the stalk. The nerve-layer (ti.t.) is more 
definite. [The oesophagus terminates in the si.xth section after fig. 126]. 

F"ig. 127. — Fourteen sections further. Through the beginning of the stalk [st.). 

Fig. 128. — Five sections further. The stalk [st.) is more distinct. 

Fig. 129. C. levinseni. — Frontal section of a young individual, shewing the position of the stalk {st.), 
which is arranged as in Pi. I, fig. 5: — g.s.r., ventral (posterior) wall of right gill-slit; g.s.L, 
left gill-slit; ph., folds of anterior (ventral) wall of pharynx; c.c., ventral wall of left collar-canal. 

Fig. 130. C. levinseni. — Seventeen sections further than fig. 132. Shewing the extension (b.c.^b.) of the 
third body-cavity between the first {stovi.) and second [stoin.-) stomachs. 

Fig. 131. C. levinseni. — Obliquely transverse section of another individual: — f.c.r., right food-channel 
between arm-base [a.b.) and right lobe of operculum [op.r.]. The ventral epithelium and basement- 
membrane {b.ni.) of this part of the collar arc cut tangentially, so that the right collar-cavity 
appears to be divided into two halves. The arrow indicates the course of the food to the mouth. 

Fig. 132. C. levinseni. — Four sections further than fig. 12S. The stalk, which is more liiL^hly magnified 
than that of fig. 128, is now completely separate from the body. 

F'g- ^ZZ- C. dodecalophus. — Section of stalk, transverse to its principal axis. The epidermis is folded; 
the nerve-layer has three principal concentrations, on the anterior side («. /.), but appears to 
extend the whole way round the section. 

Fig. 134. C. gracilis. — Similar section of the stalk of the individual shewn in PL VI, figs. 60, 61, cut 
near its junction with the body. 

Fig. 135. C. gracilis. — Section of another stalk. 

Fig. 136. C. sibogae. — Section of a stalk. 

Figs. 137, 138. C. levinseni. — Two frontal sections of a young individual. 

F'g- 1 37- — Through the dorsal part of the collar-cavities and the proboscis-pores (p.p.), which are seen 
to traverse the central nervous system {c.n.s.). The epidermis of the collar is injured on the 
left side. 

Fig. 138. — Two sections nearer the ventral side, through the pericardium [per.), the internal openings 
of the proboscis-pores {p.p.), the notochord (nch.), and the anterior horns {b.c.^a.) of the collar- 
cavities. 

F'ti- '39- ^- levinseni. — Sagittal section of anterior end of an individual with reversed proboscis: p.b., 
pigment-band of proboscis; b.c.'-a., tip of anterior horn of the collar-cavity of the opposite side; 
/., fold of wall of jjroboscis-stalk indicating the region where most of the twisting has probably 
taken place. 

Fig. 140. C. lei'inseni. — Section through the left side of the individual shewn in PI. IV, figs. 34 — t,6: — 
ph., tangential section of left edge of pharynx; g.s., gill-slit; c.c, collar-canal, in dilated condition. 
The second arm {L.2) is cut along its groove. The fourth and fifth arms appear, in other sections, 
in the positions indicated by L..f, L. j. 

[Figs. /.?_' — Ij6 were draivn tvith ZEISS, DD Obj., the others zcith C Obj. All are reduced ^/j]. 



Sibo^a-Expeditie XXVI/v'f. S. F. Harmer. Piemhrniirliin. 



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PLATE XII. 

Figs. 141 — 157. — C. dodecalophus. Figs. 158 — 160. — C. In'inseni. 

Figs. 141 — 151. C. dodecalophus. — Obliquely sagittal sections, through the right half of the anterior end. 
Ever\- second section is drawn, beginning with fig. 141, which is the most external. Fig. 151 
is more highly magnified than the others. The series illustrates the relation of the arms and of the 
operculum to the rest of the collar, together with the more important parts of the nervous system. 
The muscles, and the filaments traversing the collar-cavity are only partially represented. 

Fig. 141. — Shews the lateral part of the dorsal lobe of the proboscis (/.) and the six arms (/ — 6) of the 
right side. The longitudinal muscles are shewn in 5 and 6 only. 

Fig. 142. — The lateral lobe of the operculum (op.r.) is cut tangentially. Arm / is still distinct, but 2 — j 
have passed into the common arm-base. 

Fig. 143. — The ventral lobe of the proboscis is beginning to appear, with the end of the pigment-band. The 
arm-base is traversed by food-grooves, continuous with those of the arms. Grooves 7 — <5 are passing 
transversely inwards. The collar-cavity in the arm-base is interrupted by projections of the basement- 
membrane which are the first indications of the separation of the arms from the common base. 

Fig. 144. — The first arm has joined the arm-base. The dorsal sides ofthe arms are marked R. i — 6; and the 
grooves / — 6. Grooves ? — 5 are shallower than in the last figure. The coelom ofthe part ofthe arm- 
base corresponding with arms j — 6 has become continuous. A fold ofthe dorsal wall ofthe proboscis 
is cut tangentially, and the nerve-layer is accordingly thicker here than in other parts ofthe section. 

Fig. 145. — Grooves ^, 5 have quite disappeared, the anterior surface ofthe arm-base [a.b.) being here smooth. 

Fig. 146. — The dorsal portion of the collar is beginning to be connected with the proboscis. The tip 
of the right anterior horn of the collar-cavity is seen projecting into the proboscis-cavity. 

Fig. 147. — The first arm (A'. /) is cut at its base, its cavity communicating with the anterior horn of the 
collar-cavity. The two parts of the collar are about to become continuous: — p.p.r., external 
aperture of right proboscis-pore. 

Fig. 148. — A lobe of the operculum (op.r.) which is continuous with the base ofthe sixth arm, projects 
backwards, in the plane of the section, over the collar-pore, which is seen in fig. 151 (c.c.e.). 
The septum on the dorsal side of op. r. is a ridge of basement-membrane, indicating the point 
at which the operculum becomes free from the rest of the collar (cf. figs. 152, 153): — p.p.r., 
right proboscis-pore, cut tangentially; per., pericardium. 

Fig. 149. — Cuts the animal at the level where the collar first joins the body: — ovd., right oviduct, 
with the ovarian vessel [oikv.) and mesentery {ov.ni.)\ ines.^, dorsal mesentery, on the other side 
of which is seen the left ovary [ov. I.) and the left lateral edge of the rectum (r.). 

Fig. 150 shews the origin of the lateral nerve (/.«.) from the central nervous system [c.n.s.): — div., edge 
of the pharyngeal diverticulum; ovd., right oviduct; p. p. I., internal opening of left proboscis-pore; 
b.c.-a., tip of anterior horn of left collar-cavity. 

Fig. 151 cuts the tip of the notochord [ncli.], which is supported by the dorsal mesentery of the collar ;/>./. /., 
external opening of left proboscis-pore; c.fi.s., ganglion-cells of central nervous system; ov.l. and 
ov.r., left and right ovaries, with their respective mesenteries (ov.in.L, ^i;.;«.r.) ;/.«., lateral nerve; 
c.c.e., external aperture of right collar-pore, with its problematical tissue {x.); or.m., oral muscle. 

Figs. 152 — 157. — Frontal sections of a young individual, passing from the dorsal side towards the ventral 
side. The figures illustrate the arrangement of the oral grooves, the dorsal diverticulum of 
the pharynx, the pleurochords, the gill-slits and other organs. 

Fig. 152, near the dorsal extremity ofthe pharyngeal diverticulum (div.), with, its glandular patches, cuts the 
right lateral lobe (op.r.) ofthe operculum tangentially: — ^/., ventral end of glomerulus, attached 
to the anterior side ofthe notochord (nch.); .v., tlorsal end of problematical tissue of right collar- 
pore, attached to the epidermic fold which separates the lateral lobe of the operculum from the 
rest of the collar; g.p., right generative pore; R.^ — 6, groove on the ventral surface of the 
common arm-base leading to the food-grooves of the ^"' — (5"' right arms. The epithelial ridge 
(e.r.) seen in this figure and in figs. 153 — 155 is discussed on p. 62. 

r"'S- '53> through the left lateral lobe (op./.) of the operculum, shews the dorsal ends ofthe pleurochords 
(/>/.); or.m., oral muscle. 

Fig. 154. — The pleurochords (/>/.) open into the diverticulum ofthe pharynx, on either side of its posterior 
groove. The right collar-canal (c.c.r.) lies in a direction which is seen to be at right angles to 
that of the corresponding gill-slit (g.s., fig. 156). 

1' 'R- '55> through the dorsal edge ofthe mouth, shews a labial or oral groove (l.g.) between the base ofthe 
operculum (op. I.) and a ridge (c.r.) which is prolonged dorsally as the epithelial ridge visible in 
figs. 154 — 152. The oral groove communicates with one ofthe anterior grooves ofthe pharyngeal 
diverticulum. The right pleurochordal region is about to open by the gill-slit, the dorsal wall 
(g.s.) of which is cut tangentially; c.c, ventral wall of right collar-canal. 

Fig. 156 shews both gill-slits (g.s.), the ventral wall ofthe left collar-canal (r. c), and the anterior horns of the 
third body-cavity (^.c.'^z.), filled with longitudinal muscles. These structures just extend into fig. 155. 

Fig. 157 shews that the pleurochords (pi.) extend back laterally along the pharynx. The operculum (op.) is 
about to terminate in the middle line, as is indicated by the absence of body-cavity in this region. 

Figs. 1 58 — 160. — Diagrams ofthe proboscis and collar of C. levinseni, based on the specimen illustrated in PI. X. 

Fig. 158. — Diagrammatic posterior view of proboscis (/>.), collar (c.) and dorsal part of metasome (met.); 
p.p., proboscis-pores ; L. i — 6, arms of the left side; op. operculum. 

Fig. 159. — Diagrammatic anterior view of a specimen in which the proboscis-stalk is directed dorsally, and 
the buccal disc has been removed by a cut transverse to the proboscis-stalk. The operculum (op.) 
is supposed to have been stretched so as to pass completely outside the series of arms (cf. fig. 160): 
L.I — 6, food-grooves of the left arms; the body-cavity of the left arm-base is partially divided 
by ingrowths of the basement-membrane, corresponding with the intervals between the arms. 

Fig. 160. — A similar diagrammatic view, with the proboscis in its usual position. 

\Figs. 141 — /50, ij3 — /J7 loere draicn with Zeiss, C Obj., fig. 151 with Zeiss, DD. All the figures were 
reduced '/,1. 



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PLATE XIII. 



BUDDING. 

Figs. i6i — 1 8 1. — C. dodccalophus. 
Figs. 182 — 185. — C. sibogae. 

Ficrs. 161 — 163. C. dodecalophiis. — Consecutive sections through the base of an old stalk, transverse to 
its long axis, with a young bud {b.). 

Fig. 164. — Sagittal section through base of an old stalk, shewing a very young bud (/;.') and the base 
[br) of the bud shewn in fig. 165. 

Fig. 165. — More median sagittal section of b? in fig. 164. 

Ficrs. 166 — 172 are from an obliquely sagittal section of an old stalk, and are all drawn in the same 
relative position. Figs. 169, 172 shew the stalk, with its much wrinkled epidermis, and parts of 
the two buds b.\ b}. The younger bud (1^.') is further shewn in figs. 166 — 168; and the older 
one in figs. 170, 171. 

Figs. 166 — 168 are frontal sections of the bud b} in figs. 169, 172. Fig. 166 is through the proboscis; 
fig. 167 is through the proboscis and collar; and fig. 168 is through the metasome. Fig. 172 
shews the metasomatic cavities passing through the epidermis of the parent-stalk. 

Fig. 169. — Obliquely sagittal section of old stalk, with the two buds {b}, b.-). The section of /?.' is 
between fig. 168 and fig. 172: that of b.^ is between fig. 170 and fig. 172. 

Figs. 170, 171 are frontal sections of the bud /;.- in figs. 169, 172. Fig. 170 is at the bend of the alimentary 
canal; fig. 171 is nearer the dorsal side: — inf., intestinal limb of alimentary canal. 

Fig. 172 is through the edge of the basal sucker (d.) of the stalk, and it follows fig. 169. 

Figs. 173, 174. — Two sagittal sections of a moderately old bud. 

Figs. 175 — 177. — Three sagittal sections of a young bud, with part of the parent stalk. 

P'igs. 178 — 180. — Three obliquely sagittal sections of an older bud, which has just begun to develop its 
first pair of arms. 

Fig. 181. — Median sagittal section of an advanced bud. 

Figs. 182 — 185. C. sibogae. — Obliquely sagittal sections of an advanced neuter bud. 

Fig. 182. — The pleurochordal groove (//.), the histological characters of whose walls are not yet fully 
differentiated, appears to be separated from the rest of the pharyngeal cavity by one of the dorso- 
lateral epithelial ridges seen in PI. VIII, figs. 90—92. In the sections before this one is reached, 
the right gill-slit communicates with the anterior end (g.s.) of this groove. The cells lining the 
pharyngeal diverticulum {dn'.) are much vacuolated: — b.c.'r., right collar-cavity. 

Fig. 183. — Through the other dorsal half of the collar-cavity [b.crl.]: — p.p. internal opening of left 
proboscis-pore. 

Fig. 1 84. — Passing to the left of the mouth, hut shewing the right gonad-rudiment (g.). 

Fig. 185. — Through the external opening of the left gill-slit {g.s.e.) and collar-canal [c.c.e.). The rectum 
(;-.) already contains faeces. The beginning of the wall of the stomach (st.) is cut tangentially. 

[The figures iverc all draiun zvitk ZEISS, DD Obj. and reduced -j^]. 



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PLATE XIV 



I'MHRYOS. 

Figs. 1 86 — 197. — C. gracilis. 
Figs. 198 — 210. — C. lei'inseni. 

Fig. 186. C. gracilis. — Two cell stage, mounted whole. 

Fig. 187. — Ventral view of an advanced embryo. 

Fig. 1S8. — Lateral view of a similar embryo: — b.c^-, position of collar-cavity. 

Fig. 189. — Optical frontal section of a similar embryo from the ventral side. The constrictions at the 

sides of the yolk ()'/•) correspond with those in which the collar-cavities lie in other preparations; 

V. inv., external aperture of the ventral invagination. 
Fig. 190. — Actual frontal section, more highly magnifictl: — v. inv., dorsal wall of ventral invagination, 

cut tangentially (other sections of the same embryo are shewn in figs. 195, 196). 
Fig. 191 — 194. — Transverse sections of a similar embryo. Fig. 191 is through the anterior sense-organ 

{s.o.); fig. 192, through the anterior part of the ventral invagination (v. inv.); fig. 193, through 

the collar-cavities [b.c.-] and the metasomatic cavities (b.c.^); and fig. 194, through the metaso- 

matic cavities (b.c.^). 
Figs. 195, 196. — Horizontal sections of the individual shewn in fig. 190. 
Fig. 195 is through the dorsal region of the embryo: — b.c.''-, collar-cavity. 

Fig. 196 is between fig. 195 and fig. 190: — vac, vacuolated ectoderm, extending as far as the two arrows. 
Fig. 197. — Nearly median sagittal section of a similar embryo. The region of the posterior pit {post. p. 

is, however, cut somewhat frontally, so that both third body-cavities (b.c.''') are visible. The 

somewhat crumpled vitelline membrane [v. ni.) is seen, while between it and the ectoderm are 

what are probably excretory granules [exc). The anterior ectoderm between the two arrows has 

the vacuolated character shewn in fig. 190. 
Figs. 198 — 210. C. levinseni. 
Fig. 198. — Advanced embryo, seen obliquely from the dorsal side. The central yolk-mass (yk) has a 

lumen; the edge of the reflected part of the yolk is not easily seen where it crosses the central 

mass, but is probably correctly represented: — vac, vacuolated ectoderm, which in the embryos 

of this species contains numerous refractive bodies. 
Fig. 199. — Another embryo, probably somewhat older than fig. 198, seen from the side. The embryo was 

found in a peristome, close to its orifice, and may have been about to be liberated. 
Fig. 200. — Advanced embryo of unusual appearance, in which the vacuolated ectoderm {%>ac.) and the 

ventral thickening (v.t.) have together the appearance of the proboscis of the adult. 
Fig. 201. — Obliquely sagittal section of an advanced embryo. The vacuolated ectoderm (i'«c.) is invaginated 

dorsally and in front. It is uncertain whether the collar-cavity is seen on the ventral side, which 

is turned to the right. A space (artificial?), which is also seen in fig. 202, occurs outside the 

basement-membrane yb. m.) at the anterior end. 
Figs. 202 — 206. — Five .sections of a transverse series of a similar embryo. The limits between the second 

and third body-cavities are not obvious in this series. 
Fig. 202. — Through the anterior end. 
Fig. 203. — Through the anterior yolk-mass. 

Fig. 204. — Through the central yolk-mass, which is here encircled by the refiected part of the anterior yolk. 
Fig. 205. • — Through the extreme posterior end of the ventral thickening. 
Fig. 206. — Through the extreme posterior end of the anterior yolk-mass. 
Fig. 207 — 210. — Four sections of a frontal series of an older embryo. 
Fig. 207. — Through the entire area of the ventral thickening {v.t.). 
P'ig. 208. — Near the ventral surface, but cutting the five coelomic spaces. 
Fig. 209. — Through about the middle of the embryo. 
Fig. 210. — Through the dorsal half of the embryo. 



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CONDITIONS GfiNfiRALES DE VENTE. 



i^. L'ouvragc du „Siboga" sc composcra d'une serie de monographies. 

2°. Ces monographies paraitront au fur et a mesure qu'elles seront pretes. 

3°. Le prix de chaque monographic sera different, mais nous avons adopte comme base generate du prix de 
vente: pour une feuille d'impression sans fig. flor. 0.15; pour une feuille avec fig. flor. 0.20 a 0.25 ; 
pour une planche noire flor. 0.25; pour une planche coloriee flor. 0.40 ; pour une photogravure flor. 0.60. 

4°. I) y aura deux modes de souscription : 

a. La souscription a I'ouvrage complet. 

b. La souscription a des monographies separees en nombre restreint. 
Dans ce dernier cas, le prix des monographies sera majore de 25 "/o- 

5°. L'ouvrage sera reuni en volumes avec titres et index. Les souscripteurs a l'ouvragc complet rcccvront 
ces titres et index, au fur et a mesure que chaque volume sera complet. 



J X * Soll&crtption MnnogrnphicK 

a I'ouvr.lKc comflct &cparci.-& 

ic Livr. (Monogr. XLIV) C. Ph. Sluiter. Die Holothurien der Siboga-Expedition. Mit loTafcln. / 6. — / 7.50 

2c Livr. (Monogr. LX) K. S. Barton. The genus Halimeda. With 4 plates , 1.80 „ 2.40 

3^ Livr. (Monogr. I) Max Weber. Introduction et description de I'expcdition. Avcc Liste dcs 

Stations et 2 cartes „ 6.75 „ 9. — 

4<-' Livr. (Monogr. II) G. F. Tydeman. Description of the ship and appliances used for .scientific 

exploration. With 3 plates ami illustrations , 2. — , 2.50 

5"^ Livr. (Monogr. XLVII) H. F. Nierstrasz. The Solenogastres of the Siboga-Exp. With 6 plates. , 3.90 , 4.90 

6'; Livr. (Monogr. XIII) J. Versluys. Die Gorgoniden der Siboga-Expedition. 

I. Die Chrysogorgiidac. Hit 170 Figuren im Text , 3. — , 3.75 

7<^ Livr. (Monogr. XVI «) A. Alcock. Report on the Dccp-Sca Madrcporaria of the Siboga- 
Expedition. With 5 plates , 4.60 „ 5.75 

8c Livr. (Monogr. XXV) C. Ph. Sluiter. Die Sipunculiden und Echiuriden dcr .Siboga-Exp. 

Mit 4 Tafeln und 3 Figuren ini Text ■ „ 3. — , 3.75 

ge Livr. (Monogr. Via) G. C. J. Vosmaer and J. H. Vemhout. The Porifcra of the Siboga- 
Expedition. I. The genus Placospongia. With 5 plates „ 2.40 , 3. — 

IOC Livr. (Monogr. XI) Otto Maas. Die Scyphomeduscn der Siboga-Expedition. Mit 12 Tafeln. „ 7.50 ^ 9.50 

lie Livr. (Monogr. XII) Fanny Moser. Die Ctcnophoren der Siboga-Exi>cdition. Mit 4 Tafeln. „ 2.80 „ 3.50 

I2e Livr. (Monogr. XXXIV) P. Mayer. Die Caprellidae der Siboga-Expedition. Mit 10 Tafeln. , 7.80 , 9.75 

13^- Livr. (Monogr. Ill) G. F. Tydeman. Ilydrographic results of the Siboga-Expedition. With 

24 charts and plans and 3 charts of depths ^ 9. — , 11.25 

14c Livr. (Monogr. XLIII) J. C. H. de Meijere. Die Echinoidca der Siboga-Exp. Mit 23 Tafeln. , 15.— , 18.75 

156 Livr. (Monogr. XLVrt) Rene Koehler. Ophiures de I'Expedition du Siboga. 

ie Partie. Ophiures de Mer profonde. Avec 36 Planches „ 16.50 „ 20.50 

i6c Livr. (Monogr. LII) J. J. Tesch. The Thecosomata and Gymnosomata of the Siboga- 
Expedition. With 6 plates „ 3.75 „ 4.70 

i7<^ Livr. (Monogr. LVIrt) C. Ph. Sluiter. Die Tunicaten der Siboga-E.xpedition. 

I. Abteilung. Die socialen und holosomcn Ascidien. Mit 15 Tafeln „ 6.75 , 9. — 

i8e Livr. (Monogr. LXI) A. Weber— van Bosse and M. Foslie. The Corallinaceae of the Siboga- 
Expedition. With 16 plates and 34 tcxtfigures , 12.50 „ 15.50 

19c Livr. (Monogr. VIII) Sydney J. Hickson and Helen M. England. The Stylastcrina of 

the Siboga Expedition. With 3 plates ^ 1.50 , 1.90 

20c Livr. (Monogr. XLVIII) H. F. Nierstrasz. Die Chitonen der Siboga-Exp. Mit 8 Tafeln. ., 5.— , 6.25 

2iL Livr. (Monogr. XLV^) Rene Koehler. Ophiures de I'Expedition du Siboga. 

2e Partie. Ophiures littoralcs. Avec 18 Planches „ 10.25 „ 12.75 

22e Livr. (Monogr. XX VI<^/jr) Sydney F. Harmer. The Pterobranchia of the Siboga-Expedition, 

with an account of other species. Witii 14 plates and 2 text-figures „ 6.75 , 9. — 



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