LITERATURE. 



89 



belongs the chief part of the central nervous system (n), which lies on the 

 dorsal side continuous with the ectodermal epithelium, and at its anterior 

 part is continued into the proboscis-region. Connected with the anterior part 

 of the collar-region, on either side of the proboscis, are six biserial pinnate 

 tentacles (t), each with a terminal knob, and into these the collar-cavity is 

 continued. Further back are the pigmented apertures of the paired sac-like 

 genital organs (g). The alimentary canal forms a dorsal loop, and the anus 

 (a) is displaced far forward. The most anterior section of the alimentary canal 

 shows a pair of lateral apertures, 



the so-called gill-slits (sp), and an f 



antero-dorsal diverticulum (x, noto- 

 chord), which lies below the ner- 

 vous system and extends into the 

 proboscis. The body of Cephalo- 

 discus is provided with a stalk, 

 but the individuals are able to 

 move about freely within the com- 

 mon gelatinous coenoecium. The 

 conditions of budding resemble 

 those in Loxosoma. Fowler's 

 more recent researches have re- 

 vealed a considerable agreement 

 between Rhabdopleura and Cephalo- 

 discus Here also the intestinal 

 diverticulum known as the noto- 

 chord is found, as well as a pair 

 of collar-pores, while the branchial 

 clefts and proboscis - pores are not 

 to be recognised. From all that 

 is known, it appears that these 

 genera are nearly related to Balano- 

 glossus, while no connection with 

 Phoronis and the Bryozoa can be 

 proved to exist,* since, as shown 

 by Lang (No. 7), the agreement 

 in structure between these forms 

 can easily be shown to result from 

 similarity in their manner of life. 



Fig. 42.— Diagrammatic median section through 

 Cephalodiscus (after Ehlers, combined from 

 McIntosh and Harmer). a, anus ; ex, excre- 

 tory organ (proboscis-pore) ; g, genital gland ; 

 to, mouth ; n, nervous system ; sp, gill-slit ; 

 t, tentacle ; x, intestinal diverticulum (noto- 

 chord of authors). 



LITERATURE. 



1. Caldwell, W. H. Preliminary note on the structure, develop- 



ment, and affinities of Phoronis. Proc. R. Soe. London. 

 Vol. xxxiv. 1882-1883. 



2. Claus, C. Grundziige der Zoologie (4). 1882. Bd. ii., p. 89. 



4th Ed. 



3. Ehlers, E. Zur Kenntniss der Pedicellineen. Abh. k. Gesellsch. 



Wixsensch. Gottingen. Bd. xxxvi. 1890. 



* [Masterman's researches on Adinotrocha, if confirmed, would show that 

 Phoronis is undoubtedly nearly related to Cephalodiscus and its allies. — Ed.] 



