432 



ZOOLOGY 



division of its body into three regions, — the proboscis, collar, 

 and trunk, — and in the arrangement of its coelomic cavities and 

 the possession of proboscis- and collar-pores. Moreover, it is 

 provided with gill-slits, with a diverticulum of the alimentary 



FiQ. 249. — Longitudinal section of an 

 adult Cephalodiscus, supposed to 

 be talcen sufficiently on one side 

 of the middle line to allow of the 

 representation of one of the ovaries, 

 and of one of the proboscis pores. 

 After Harmer. 



canal (notochord) growing into the proboscis stalk, and with 

 a nervous system which closely resembles that of Bcdanoglossus. 

 Cephalodiscus has only been found once. It was dredged 

 in the Straits of Magellan by the " Challenger " from a depth 

 of 245 fathoms. The various " polypides," with their budding 

 pedicles, live inside a coenoecium or tubular case secreted around 

 them, in much the same way as Appendicularia secretes its 

 " house." 



Sub-class III. Khabdopleueida. 



Chaeacteeistics. — Gill-slits and proboscis pore absent. The 

 intestine has a neural flexure. There are two tentacular 

 plumes having the same relation as in the Cephalodiscida. 



