IV, 



FlG. 1 19. Electric organ of the Skate. The left-hand drawing (I) represents the 

 entire organ (natural size) of a fuli-grown /?. radiata. This is a small snate, which 

 rarely exceeds 50 centms. in length ; but in the large R. balis^ the organ may 

 exceed two feet in length. The other drawings represent single muscle-fibres in suc- 

 cessive stages of transition. In the first of the series (II) the motor plate, and the nerves 

 connected with it, have already been considerably enlarged. In the other three specimens, 

 the fibre becomes more and more club-like, and eventually cup-like. These changes 

 of shape are expressive of great changes of structure, as may be seen in the last 

 of the series (V), where the shallow cup is seen in partial section. The electric 

 plate lines the concavity of the cup, and is richly supplied with nerves (only a few of 

 which are represented in the last drawing) : the thick walls of the cup are composed of 

 muscular fibres, the striation of which is distinctly visible. 



* B b 



