ASCIDIA. 63 
epithelium of the dorsal tubercle, as well as in the tentacles, 
the peripharyeneal bands, the endostyle, and neighbouring 
parts. 
As to the function of the neural gland—apart from the 
dorsal tubercle—it is still somewhat mysterious. It may 
be merely to secrete viscid matter which is poured like 
that from the endostyle into the peripharygneal groove, or 
it may possibly be that the function is renal—for the 
removal of nitrogenous waste matters in the neighbour- 
hood of the nervous system. 
RENAL ORGAN. 
A mass of large clear-walled vesicles, which occupies the 
rectal loop and the adjacent walls of the intestine, and may 
extend over the whole left side, is undoubtedly a renal 
organ without a duct. Each vesicle (Pl. IV., fig. 11) is 
apparently a little closed sack formed of modified meso- 
blast cells which eliminate nitrogenous waste matters from 
the blood in the neighbouring lacuns and deposit them 
in the cavity, where they form one or more constantly 
increasing concentrically laminated concretions of a yel- 
lowish or brown colour, sometimes coated with a chalky 
deposit. These concretions (PI. IV., fig. 14) contain uric 
- acid, and in a large Ascidian are very numerous and of 
considerable size. The nitrogenous waste products are 
thus deposited and stored up throughout life in the renal 
vesicles in place of being excreted from the body. 
The cells forming the walls of the renal vesicles have a 
Guciously wavy outlme (Pl. IV., figs. 11, 12, and 13), 
which gives them a characteristic appearance. The con- 
tents of these cells seem to differ considerably (Pl. IV., 
fig. 13) in different cases, probably as a result of their 
functional activity. 
