1883.] NATURAL SCIENCES OF PHILADELPHIA. 215 



Many animals were placed in a vessel of water, and the following 

 facts were observed : 



1. That not all the animals found the need of coming to the 

 surface to breathe, and that many stayed at the bottom of the 

 vessel. 



2. That the need of air did not seem very strong, as they came 

 slowly to the surface. 



3. That certain individuals remained in the upper portion of 

 the fluid. 



4. That many went only partially out of the water. 



5. That others left the water entirely', but remained in the 

 neighborhood of it. 



These and other facts show that they breathe air and are not 

 water animals. Further on he sa3^s : — 



1. Seven animals wei'e placed in tall champagne-glasses, which 

 were filled with water ; in the middle of the glass was placed a 

 partition, so that the animals could not come to the surface ; the 

 water, however, could freely circulate. The animals lived three 

 daj's, at which time they were taken out. 



2. Three individuals were placed in 45 cu. mm. of well-water, 

 and these lived only eight hours. 



3. Six Ancyli were placed for three days in 25, 30 and 50 

 cu. mm. of river-water ; all remained living and some deposited 

 eggs. 



This last experiment seems to prove that they are not amphib- 

 ious. 



I made essentially the same experiments with the same results, 

 and further found that when the Ancyli were placed in aquaria, 

 in which there was running water, the}' never came to the surface ; 

 if, however, the water was not fresh, they would invariably come 

 to the surface of the water. I think, therefore, that the apparent 

 amphibian habits are due to the fact that the water was not suffi- 

 ciently aerated. Probably the cause of such rapid death in the 

 caTse of the animals that were placed in the well-water, was the 

 presence in it of such a small percentage of air. 



I will first take up the anatomy of both species in general, and 

 describe the differences between them, and then consider the 

 special part, which consists in : — 



1. Formation of the radula. 



2. Observations on the nervous system. 



3. The anatomy of the excretory organ. 



