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 



FIG. 1 18. Raia radiata, representing the liie 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, (i) that the 

 electric organ of R. radiata must be one of the very 



