SEA-FISHERIES LABORATORY. 437 



lumen of the end sac had broken free. Whatever may be 

 the condition of things in Maia, there is no doubt that in 

 Cancer the walls of the end sac are uniformly only of one 

 cell in thickness. As in Maia, there are cells in the 

 cavity of the end sac, and I agree with Marehal that these 

 are epithelial cells of the end sac which have broken away. 

 There appears to be nothing surprising that certain cells 

 of this single layer of epithelial cells should be gradually 

 nipped off by the activity of the surrounding cells and 

 thus shed into the lumen of the end sac. An examination 

 of serial sections through the end sac reveals cells in 

 every stage of this process of shedding. This explains 

 why certain cells of the end sac epithelium project farther 

 into the lumen than others, as described above. 



Cuenot investigated the excretory organs of Crus- 

 tacea by injecting various colouring matters into the body 

 of the living animal. He has placed these colouring 

 matters into three groups, according to where they were 

 eliminated. 



(1) Fuchsin acid, Bismarck brown, safranin, indigo- 



carmine, etc. 



(2) Methylene green, ammonium carminate, etc. 



(3) Methylene blue. 



After such injections it was found that the cells of 

 the renal tube of the labyrinth and the cells of the bladder 

 have a decidedly alkaline reaction and excrete the 

 substances of the first category. The cells of the end sac, 

 on the other hand, have an acid reaction and eliminate 

 the substances of the second category. 



By the above method of injection Cuenot discovered 

 that in addition to the antennary gland and its connec- 

 tions there are two other kinds of excretory cells, viz. : — 

 The ferment cells of the digestive gland, and the cells 

 in the branchial septum. 



