1883. } Zoölogy. 085 
considerable development of their electric organ in length com- 
pared with the small size of its transverse diameter; whereas in 
the electric rays that live in sea water, which isa good conductor, 
the electric organ has a greater transverse development, conse- 
quently the electromotor powers of the electric organs of the 
electric eel and Malapterurus on the one side, and of the electric 
ray on the other, were to one another inversely as the conducti- 
bility of the surrounding media. The measurements of Hum- 
boldt and of Sachs of growing electric eels had shown that in 
their growth the electric organ increased proportionally more in 
length than in transverse diameter, which is a teleological adapta- 
tion to the badly-conducting fresh water. Now the above-men- 
tioned note of Professor Babuchin contained the communication 
that in growing electric rays the electric organ increased propor- 
tionately much more in breadth than in height; this is likewise 
in conformity with the adaptation to the sea water, which is a 
good conductor, 
