INTERNAL ANATOMY. 59 



In 1889 WEISS undertook the task of determining ex- 

 perimentally whether Johannes MUller's renal papilla and 

 Lankester's brown funnels really served an excretory 

 function. The method of research consisted in feeding 

 full-grown individuals with various colouring matters held 

 in solution or in suspension in sea-water. For instance, 

 carmine suspended in sea-water would be carried into the 

 digestive canal and then absorbed through the intestinal 

 epithelium into the capillaries surrounding the intestine. 

 It would thus get into the vascular system, and also by 

 some means into some of the lymph spaces, and finally 

 would be excreted by the cells of the renal papillae or by 

 whatever other structure, or set of structures, might 

 possess the renal function. In fact, Weiss found that the 

 so-called renal papillae did actually excrete a quantity of 

 the carmine with which the animals had been fed, and, 

 further, that a similar excretion of carmine occurred at 

 other points of the atrial epithelium. The atrial epi- 

 thelium, as a whole, probably has more or less the power 

 of excreting waste products which have found their way 

 into the vascular and lymphatic systems. 



But above all, Weiss discovered a very active excretion 

 of carmine in certain small tubules which he found lying 

 in the dorsal ccelom applied against the most dorsal por- 

 tion of the double-layered membrane (ligamenturn denti- 

 culatum) which separates the ccelom from the atrial cavity 

 (Fig. 29). There is one of these tubules to each primary 

 gill-cleft of the pharynx. At the top of each tongue-bar 

 Weiss made out an opening of the tubule into the atrial 

 cavity, but he did not succeed in finding any openings into 

 the dorsal coelom. After the operation of feeding with 

 carmine was completed, at the close of a week or fortnight, 

 and time had been allowed for its absorption and subse- 



