252 DISCOVERY REPORTS 



to the right and left sides of the pharynx to the base of the collar pores . The roof of the gill 

 opening occurs immediately behind the collar pores and the right and left pharyngeal 

 blood vessels on reaching the gill region come to an end abruptly. Though it could 

 not be demonstrated in my material, it seems probable that the pharyngeal blood vessels 

 break up into smaller branches which pass into the vacuolated cells of the gill region 

 where the blood is oxygenated. 



From the ventral posterior side of the heart is given off the ventral blood vessel, which 

 at the base of the notochord divides into two lateral branches which pass along the 

 dorsal wall of the collar cavities into the arms. In the arms these vessels are seen as 

 deeply stained wavy lines running between the basement membrane and the coelomic 

 epithelium. On the ventral side of the arms similar vessels occur which are directly con- 

 nected with the median dorsal vessel. PI. XXXVII, figs. 3 and 4 are transverse sections 

 of the heart showing the cavity of the pericardium and heart. The pericardial cavity is not 

 stained at all, whereas the space inside the heart is deeply stained. The wall of the heart 

 is very thick and glomeruli occur on it. The section passes through the lower region of 

 the heart and so the heart and pericardium appear only on the ventral side of the noto- 

 chord. Dorsal to the notochord in the median septum between the right and left collar 

 cavities runs the dorsal vessel already described. On the ventral posterior side of the 

 heart there opens into it a very large vessel, the ventral blood vessel, which runs on the 

 ventral side of the notochord. This dilates into a large space before it opens into the 

 heart (PI. XXXVII, fig. i,vv). The dilated part has thick walls with glomeruli occurring 

 on them. It is not certain whether the walls of the vessel are muscular. It follows the 

 curve of the notochord and ends abruptly on the roof of the pharynx. The vessel which 

 occurs in the median septum between the pharynx and the rectum is very probably a 

 continuation of this vessel. 



It has not been possible to work out the complete course of the circulation since the 

 vessels are indistinct in parts of the body. But from the evidence it seems possible that 

 the dorsal vessel conveys blood from the heart to the gills, arms and proboscis and that 

 the ventral vessel collects blood and returns it to the heart. 



In the stolon there are two vessels, the dorsal and ventral, but I have not been able to 

 discover the connections of these vessels with the vessels of the body. Considering the 

 specific differences in the relation of the stolon to the trunk, the connection of these 

 blood vessels may not be the same in all species. In C. hodgsoni the stolon originates 

 from the mid-ventral side of the body, in C. densiis from the posterior extremity, and 

 in C.fumosiis near the mouth in the pharyngeal region (PI. XXXVI, fig. i). How far the 

 position of the stolon would affect the connection of the stalk vessels with the vessels 

 of the body is difficult to estimate. 



NERVOUS SYSTEM 



Detailed accounts of the nervous system of Cephalodisciis were given by Masterman 

 and later by Harmer. Mastennan (1898 b, p. 342) recognizes (i) the main ganglion on 

 the dorsal wall of the proboscis and collar; (2) an anterior pre-oral nerve over the tip 



