600 



IN VERTEBRA TE M ORPHOL OGY. 



upon the inner surface of which there is on each side a collar- 

 pore. 



The mouth (rri) opens beneath the epistorne into an oesoph- 

 agus, which in the collar region bears a dorsal diverticuluin, 

 the notochord (x), projecting forwards into the epistoine. In 

 this same region there is on each side a branchial slit (sp), 

 structures which are apparently wanting in Bliabdopleitra. 

 Behind the oesophagus opens into a saclike stomach from 



FIG. 273. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH Cephalodiscus 



(after EHLERS from KORSCHELT and HEIDER). 

 a = anus. n = nervous system. 



ex = excretory organ. sp = branchial slit. 



g = ovary. t = tentacles. 



TO = mouth. x = notochord. 



which the intestine, bending upon itself, passes forwards to 

 open (a) upon the dorsal surface of the visceral sac, a short 

 distance behind the collar. 



The collar-pores probably serve as excretory organs, and 

 it has been stated that the epistome-pores open into well- 

 developed tubes (ex) terminating in the epistome cavity in a 

 dilatation ; they also have been regarded as excretory. The 

 reproductive organs (g) are paired sacs, which open on the 

 dorsal surface just in front of the anus. No circulatory system 



