CEPHALODISCUS 



597 



line between the mouth and anus is the inter- stomatal middle 

 line. 



In the inter-stomatal region or in its immediate vicinity lie the 

 following parts of the body: (1) the preoral buccal shield with its 

 two pores ; (2), the central nervous system ; (3), the twelve feathered 

 tentacles ; (4), the apertures of the two oviducts ; (5), the postoral 



Fig. 470.— Median section through Cephalodiscus dodecalophus somewhat near the median 

 plane (after Harmer). 2, Nervous system ; 3, anterior paired ccelom (collar calom) ; 5, fold of the 

 anterior trunk region ; 8, paired trunk crelom; 9, pharynx ; 10, oesophagus ; 11, stomach-intestine; 12, 

 hind-gut ; 13, buccal cavity ; 14, pedicle ; 15, ovary ; 16, anus ; 17, oviduct ; 18, buccal shield ; 19, 

 ccelom of the same = proboscidal coeloni ; 20, one of the proboscis pores ; 21, anterior diverticulum 

 (proboscidal diverticulum) of the pharynx. 



lamella; (6), the two postoral pores of the body cavity; (7), the 

 two gill-slits (Figs. 470, 471). 



The buccal shield, which is comparable with the proboscis of the 

 Enteropneusta, is a plate, which projects downwards from the inter- 

 stomatal region immediately in front of the mouth by means of a 

 rather short stalk, in such a way that its free surface, the epithelium 

 of which is enormously thickened, faces ventrally (Fig. 470, 18). 



The central nervous system lies in the hypodermis, almost at 



