27 



epithelium of the dorsal tubercle, as well as in the tentacles, 

 the peripharygneal 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 inay 

 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 n^ay 

 extend over the whole left side, is undoubtedly a renal 

 organ without a duct. Each vesicle (PI. IV., fig. 11) is 

 apparently a little closed sack formed of modified meso- 

 blast cells which elnninate nitrogenous waste matters from 

 the blood in the neighbouring lacunae 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 

 curiously wavy outline (PL IV., figs. 11, 12, and 13), 

 which gives them a characteristic appearance. The con- 

 tents of these cells seem to differ considerably (PI. IV., 

 fig. 13) in different cases, probably as a result of their 

 functional activity. 



