HISTOLOGY 



tm. s.- 



terurus, whose electroplaxes are placed in the skin and are consequently 

 in doubt as to their origin. 



We shall briefly describe the electroplax as found in three genera 



of teleost fishes, Gymnotus, Mormyrus, and Astroscopus, making some 



-__>_-'_. comparisons and 



afterward discuss- 

 ing briefly the pe- 

 culiar electric organ 

 of Malapterurus. 



The electric tis- 

 sue of Gymnotus, 

 which is an eel- 

 shaped fish inhab- 

 iting some fresh 

 waters of South 

 America, consists 

 of a number of 

 rows of electro- 

 plaxes placed verti- 

 cally and face for- 

 ward, to form 

 several masses of 

 tissue on the sides 

 of the rear part of 

 the body. 



This tissue oc- 

 cupies the place 

 ordinarily filled by 

 muscle, and this, 

 together with the 

 fact that the elec- 

 troplaxes are placed 

 in a myotome ar- 

 rangement, forms 

 fairly good evidence that the tissue is derived from muscle rudiments. 

 When we add to this that we know the electric tissues to be modified 

 muscle in the elasmobranchs where it occurs, we have a strong con- 

 firmation of its relationship. 



Each electroplax is placed with its electric surface, on which the nerve 

 supply ends, facing directly to the rear, and the other side or nutritive 

 surface facing forward. Both in front of and behind the plate is a layer 

 of the electric connective tissue or jelly, the one in front being somewhat 

 the thinner. 



el. s. 



el. c. t. 



FIG. 109. Portion of an electroplax from Gymnotus, the " electric 

 eel." el.s., electric surface; nu.s., nutritive surface; el.c.t., elec- 

 tric connective tissue. Papillae on both surfaces. (After BAL- 

 LOWITZ.) 



