127 wi/-^ ' ^' 



REPORT ON CEPHALODISCUS DODECALOPHUS. 25 



prominent lens, but whether the latter is a solid body, a cuticular formation, or only 

 fluid in the centre of the mass, is not explained. Mr. Harmer bases one of his arguments 

 for the interpretation he has' given of the " dorsal organ" (brain) on the constant relation 

 to each other of ganglion-cells, a fibrous layer and the eyes, and he seems to have facts 

 in his favour. 



In Rhabdopleura a ciliated tubercle (considered by Lankester and others to be a 

 sense-organ) was discovered by Sars on the dorsal surface at the base of each aiTo of the 

 lophophore. In Loxosoma also Vogt ^ describes a tactile papilla on each side near the 

 arms, and Salensky ' traced nerves from the ganglion to these posterior sense-organs in 

 Loxosoma crassicauda. No such organs, however, can be observed in the preparations 

 of Cephalodiscus, though it is possible the search in the living animal might be more 

 successful. The oral folds of glandular tissue and the parts connected with the gill- 

 fissures are probably highly sensitive and ciliated, but no other sense-organs could be 

 observed. 



Reproductive Organs. 



No differentiation was noticed in regard to the sexes, and no dimorphism of the 

 zoids, as in Professor Ehler's remarkable burrowing form {Hypojjhorella expxinsa^). 

 Nothing is more striking, however, than the profusion of buds and the abundance of 

 ova, apparently one of the chief ends of the species being propagation. The chambers 

 of the ccencecium present many of the large ova, and they are occasionally found amongst 

 the plumes, as in Phoronis, with its swarms of minute eggs ; but such in the former is 

 probably accidental ; and almost every adult bears one or more buds attached near the 

 tip of the pedicle. 



Ovary. — In most specimens a pair of large ova are observed projecting anteriorly 

 (PI. III. fig. 2, ov), so that their pure white colour is recognised through the attenuated 

 integument above and behind the eye-like oviducts, which, as it were, mark the anterior 

 boundary of the ovary. In section it is found that a septum passes from the median 

 wall of the rectum to the opposite wall of the body, thus dividing the body-cavity in 

 that region into two spaces, in which are the ova supported on a pair of lateral 

 mesenteries. As soon as the glandular tissue forming the dorsal wall of the buccal 

 cavity appears, the mesenterial septum just indicated is attached to its basement-layer 

 externally, and also more or less in the median line. The septum disappears on the approach 

 of the stomach, or about the posterior termination of the great buccal disk, and any 

 product remaining towards the end of the latter is generally pushed to one side. As a 



' Sur les Loxosoma dcs Phascolosomes (sep. copy), p. 8, pi. xii. fig. 1. 

 » Ann. <L Sci. Nat. (Zool.), sur. 6, t. v. p. 12 (art 3), pi. xii. figs. 2, 3. 

 ' Abhandl. d. k. Gcsdlsch. d. xciu. GiitUngen, 1876. 

 (ZOOL, CHALL. EXP. — PAIIT LSIl. — 1887.) V'1'1 -i 



