12 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



example is afforded by the electrical organ to which I 

 have already referred. The stages of growth in the 

 developing Skate are so slow in time, that its tissues are 

 eminently suitable for such enquiries. 



To take the case of the electrical organ, biologists have 

 endeavoured to answer this question — through what stages 

 of form did the tissue pass before the present electrical 

 organ was evolved ? 



The answer to this, in the case of the Skate, is obtained 

 by the study, first, of the electrical organs in different 

 species of Skate, secondly, of the electrical organs in one 

 species at different stages of its own growth. Both 

 investigations reveal the fact that as far as form is 

 concerned, the early condition is that of a series of muscle 

 fibres, and that these dwindle down to form the plate 

 whilst the nerves to the muscle remain, and by sending 

 out branches in repeated subdivision form the dense 

 nervous net work.* Species are found in which the 

 different plates of the organ present a curious transitional 

 condition between a muscle fibre and an electrical organ 

 plate. Such are the plates of the Eaia radiata; histological 

 specimens show that the structure is still there but quite 

 modified in form. Recent microscopic investigations by 

 Engelmann under polarised light seem to show that such 

 parts of the muscle as act in a special way on the 

 light (doubly refracting), these parts occurring in bands 

 along the muscle fibre, gradually decrease in amount, 

 whilst the adjacent singly refracting substance remains.! 

 With all this, what is the change in function ? It remains 

 at present unknown ; all that I know is that in such an 

 imperfect organ, composed of half muscle and half 



* Ewart. The electric organ of Raia radiata. Phil. Trans., Vol. CLXXIX, 

 p. 539. 



t Engelmann. Pfiugers archiv., Vol. LVII, p. 149. (1894). 



