618 



Comparative Animal Physiology 



huge branches from the tenth cranial nerve arise in large lobes of the medulla. 



The electroplaxes are derived embryologically from electroblasts similar to 

 sarcoblast precursors of muscle.**-^ The elongate multinucleate cell enlarges 

 laterally, nuclei increase around the cell periphery, and the center becomes 

 filled with mucous protein (Fig. 235). One surface is innervated, usually 

 the electronegative surface, and the other is frequently papilliform. The 

 single electroplax resembles a motor end-plate (Fig. 236)^^. 



When an electric fish discharges, each organ fires repetitively, usually 

 3 to 5 spikes, sometimes many more. Each spike is of constant height and 



Papillae 



Nerve 



Electric layer 



Connective tissue 



Fig. 235. Diagram of two electroplaxes. Nerve elements in black, electric layer 

 granular and nucleated. From Ihle, Kampen, et al.^"' 



'*" ' '~)^^^°::T^^^i Muscle striation 



Telogiia 



Teloglial nucleus 



Motor axon 



Fig. 236. Diagram of motor end-plate. Axon termination in black; myelin sheath 

 stops before axon branching; zone of telogiia dotted and teloglial nuclei shown. Muscle 

 striations around end-plate. From Couteaux.'^ 



