ELECTRIC TISSUES OF ELASMOBRANCHS 



109 



nut. 



series of concentric cones that may be called the electrotomes. The rela- 

 tions of these electrotomes to the myotomes are further explained in the 

 next section on the development of the electric organs in the embryo 

 skate. 



The electroplax, which is the structure that produces the electricity, 

 is a large, disk- 

 shaped syncytium 

 that lies within the 

 compartment with d. 1. 

 its width agreeing elnur 

 with the width of 

 the cavity. It does 

 not occupy the en- 

 tire length of the 

 cavity, however, 

 but leaves an an- 

 terior and a pos- 

 terior space. These 

 spaces are usually 

 of considerable size 

 and, as has been 

 indicated before, 

 are filled with the 

 electric connective 

 tissue whose in- 

 dividual cells are 

 branching forms, 

 as seen in Figure 

 105. These cells 

 secrete the jelly- 

 substance of the 

 tissue. 



The spaces vary 

 much in different 

 skates, the anterior 

 being many times 

 larger than the posterior in a Raja ocellata, while in Raja lavis the 

 exact opposite is true. It is in the electric connective tissue of the an- 

 terior space that the nerves supplying the electroplax ramify. These 

 nerves, which consist of several medullated fibers, when well within the 

 compartment, lose their medullary sheaths and the fibers begin to divide 

 and sub-divide as they approach the anterior surface of the electroplax 

 on which their ramifications terminate in a large number of end-plates. 



FlG. 105. Portion of an electroplax of Raja lavis. el.c.t., electric 

 connective tissue before the electroplax; el.n.e., electric nerve 

 ending; el. I., electric layer; el.nu., electric nucleus; $lr., striated 

 region of electroplax; nut. I., nutritive layer. The mass of stri- 

 ated material in the large central papilla is cut off optically from 

 the striated layer by the irregularity of the papilla. 



