202 Proceedings of Royal Society of Edinburgh. [sess. 
may be, therefore, stated that the stomach or pyloric sac of the 
Asteridea is a digestive cavity and a renal organ; it has a dual 
function. This is no exception among Invertebrates, for, as Darwin 
states in The Origin of Species (chap, vi.), ‘‘ numerous cases could 
be given among the lower animals of the same organ performing at 
the same time wholly distinct functions,” 
In conclusion, it would be interesting to know whether the out- 
wandering cells in Echinoderms contain uric acid. If so, it would 
be proved that these cells form an additional means of eliminating 
this nitrogenous substance from the system — ^just as the skin in the 
higher animals supplements the kidneys in eliminating excretory 
products. 
