596 EEPOET — 1882. 



6. Preliminanj Note on Ceplialodiscns, a new form allied to Prof. Alhnan's 

 Rhabdopleura — dredged in H.M.S. ' Challenger.' ' By Professor 

 McIntosh, F.B.S. 



This peculiar form was dredged at Station 311 (in the Strait of Magellan), and 

 at first sight resembles a somewhat massive sea-weed, to which the ccenceciuin is 

 allied in consistence, while the whole surface is hispid with long spinous processes 

 of the same tissue. This ccenacium is secreted hy the minute inhabitants, which, 

 though quite free, are closely allied in structure to Rhabdopleura, an opinion inde- 

 pendently arrived at by Professors Allman and Busk, who kindly requested the 

 author (who had latelj' received the specimens from Mr. Murraj', Director of 

 the Challenger Commission) to continue the description. 



The ccenacium consists of thickish, semi-transparent, irregularly moulded 

 branches, ranging from about 3 mm. to upwards of 5 mm. in diameter, and form- 

 ing arborescent tufts, which apparently have been fi:x;ed to submarine bodies, such 

 as stones, sponges, &c., both by the ends and sides. The whole is permeated by 

 irregular canals and cavities, which open on the surface, often near the bases of the 

 spines. In these cavities are found the free polypides, often in groups, and nume- 

 rous large ova. 



Each adult has a somewhat bean-shaped body, with a pedicle posteriorly- 

 continuous with the ventral surface, the whole measuring about 2 mm. The an- 

 terior end is rounded : indeed often very prominent from the contained ova, two of 

 which are conspicuous. Tlie ventral surface of this region bears two very large 

 eyes. The body is bulbous posteriorly. In front of the mouth a great buccal disc 

 overlaps the neighbouring parts, and is probably the chief agent in secreting the 

 coencecium . In front of it are twelve' long and richly pinnate, branchial, or tentacular 

 organs, which arise from a base devoid of a web, and each of which has a peculiarly 

 enlarged tip. Behind the nioutli is a broad apron-like membranous lamella. The 

 body-wall is formed of a thin hypodermic and an elastic layer, bounded by longi- 

 tudinal fibres internally. The pedicle has the same dermal coverings as the body, 

 and internally consists of strong longitudinal muscular fibres, continued from the 

 ventral surface anteriorly. 



The mouth opens above the buccal shield, at the upper margin of the mem- 

 branous lamella, and leads into a simple alimentary canal, which bends forward at 

 the posterior end of the body, and proceeds along the dorsum, to terniinate in the 

 anus on the prominent anterior end of the body. The food which enters the month 

 must pass between the great flattened shield, on the one haud, and the membranous 

 post-oral lamella, on the other. 



Immediately above the eyes are the two greatly developed ova, and towards 

 the middle of the body several smaller ova. These seem to arise from a spot nearly 

 identical with the ' remarkable organ ' in Pedicellina, and to be homologous with a 

 double organ of similar nature in the embryo of Loxosoma. When discharged 

 these ova are attached to the wall of the cavities of the coencecium by a process or 

 pedicle of the hyaline investment. Their size is remarkable. 



In addition to the foregoing mode of propagation, very active budding takes 

 place at the tip of the pedicle of the adult, the buds being found in all stages, from 

 a minute rounded or clavate process up to a fairly formed specimen. Even in the 

 earlier stages the buccal shield is conspicuous. The branchial or tentacular plumes 

 first appear as globular papillre on the dorsum of the shield. Two or three buds 

 occur on many specimens. This new form will open up interesting comparisons 

 with Doliolum and others having buds on processes. 



The occurrence of these large ova anteriorly, and the numerous buds on the tip 

 of the pedicle posteriorly, bears out Professor Allman's objection to Oscar Schmidt's 

 view that the apparent buds in Loxosoma are really eggs detached from the ovary ^ 

 and developed on the body of the parent. 



' Published by permission of the Lords Commissioners of the Treasury. Published 

 in rxtenso in Annals of Nat. Hist., November 1882. 

 ^ Hence the name of the species — dodecalophns. 



