368 Darwin, and after Darwin, 
and assumed all the normal proportions (though 
not yet the size) of the adult creature. The organ, 
therefore, is one of the very latest to appear in the 
ontogeny of R. radiata; and, moreover, it does not 
attain its full development (i.e. not merely growth, but 
Fic. 118.—aza radiata, repiesenting the life size of the youngest in- 
dividual in which muscle fibres have been found developing into electric 
cells. 
transforming of muscular fibres into electrical ele- 
ments) till the fish attains maturity. Read in the 
light of embryology, these facts prove, (1) that the 
electric organ of . radiata must be one of the very 
