CHORDATA 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, 
