CHORDA TA 445 



matter is not as a rule expelled from the body, but is stored 

 up in certain cells in which the renal products continue to ac- 

 cumulate throughout life. In Ciona the renal cells are found 

 close under the epidermis, in the neighbourhood of the opening 

 of the vas deferens; they are of an orange colour, and con- 

 tain granules which give micro-chemical reactions character- 

 istic of uric acids and urates. It is the accumulation of these 

 cells which forms the orange-red ring around the external 

 opening of the vas deferens. The cells have no ducts, but 

 since they are separated from the surrounding water by but a 

 thin layer of epithelium, it has been thought that their excreta 

 may diffuse out. In other genera of simple Ascidians, the 

 renal cells are arranged around a vesicle into which they pour 

 their secretions ; the cavities of these vesicles are closed, and 

 the nitrogenous waste matter does not leave the body. Like 

 the lumen of the genital glands and of the pericardium, the 

 cavities of these vesicles are possibly derived from the coelom. 

 The vesicles are usually of a brown colour, and are found in 

 the loop of the intestine, extending along its wall. 



The Ascidians are hermaphrodite. In Ciona the testes con- 

 sist of numerous follicles branching over the stomach and 

 intestine ; these are whitish in colour, and their presence gives 

 this part of the alimentary canal a peculiar appearance ; the 

 larger of the follicles gradually unite to form a narrow duct, 

 the vas deferens, whose wall is continuous with that of the 

 testis. The vas deferens runs along by the side of the rectum, 

 and ultimately opens into the atrial cavity about an inch in 

 front of the anus. The cells lining the cavity of the follicles 

 of the testis give rise to the spermatozoa. The latter are 

 minute, .with small heads and long tails; they apparently 

 ripen and are discharged from the body at the same time as 

 the ova. 



The ovary is a comparatively compact gland situated in 

 the general perivisceral space, in a loop of the intestine ; the 

 ova are modified cells lining the walls of its cavity. The 

 walls of the ovary are continuous with the oviduct, which 

 runs alongside the vas- deferens and opens into the atrial 

 cavity close behind the pore of the male duct. The oviduct 

 may be distinguished from the vas deferens by its large size, 



