Origin of Electric Tissues of Gymnarchus Niloticus. i8i 



of it also have been permanently left in the main body of the core, usually 

 near its anterior end. These inclusions (fig. 20, plate 7) may or may not 

 include the nuclei. They always contain some of the largest of the granules. 



The nuclei do not show any internal peculiarities which would dis- 

 tinguish them as electric nuclei from some of the other tissue nuclei, par- 

 ticularly from muscle nuclei, which they much resemble. They have a 

 large chromatic content and a particularly large plasmosome which stains 

 deeply. They can be sharply distinguished from some other nuclei, as 

 connective-tissue nuclei for instance, where the more delicate outline and 

 different chromatic pattern is discernible at a glance. 



Each nucleus shows some sign of a surrounding differentiated layer of 

 cytoplasm. This consists of larger granules and a zone in which the 

 hyloplasm seems to be in greater proportion than elsewhere. At dift^erent 

 places in a preparation one may see more or less of a contraction zone 

 around the nuclei. While this may be a physiological condition, it is more 

 probably an artifact due to the fixing or hardening. 



One interesting condition is to be seen in most of the few nuclei which 

 become detached from the outer layer and included with some small portion 

 of the outer cytoplasm in the fibrillar core. These nuclei probably become 

 so placed during a very early stage, and the further they are separated from 

 the layer to which they rightly belong, the larger they grow and the more 

 diffuse their chromatin becomes. The plasmosome diminishes in size and 

 the whole structure looks more like a connective-tissue nucleus, except 

 that it is very much larger. I have seen this same condition in the electro- 

 plax of Raja. 



It was not possible to find a real electrolemma or cell-membrane covering 



this electroplax. A connective-tissue covering, more or less closely applied 



to the surface, was always present, but the fact that this covering possessed 



its own nuclei seems proof that it was a real connective-tissue covering and 



not any product of the activity of the electroplax tissue. At such points, 



as this connective tissue did not actually touch the electroplax, a careful 



examination was made to see if some actual cell-membrane did exist. 



Beyond the fact that the outer edge of the electric layer was sharply defined 



and that its surface was rounded and even as if some membrane was present, 



no real membrane could be demonstrated, either by its refractive properties 



or by its color. 



INNERVATION. 



A general survey of the innervation is desirable, as too little exact topo- 

 graphical work has been done on those fishes in which the electric-motor 

 centers are thinly distributed in character over large areas of the cord, as, 

 for instance, in Gymnotiis, Raja, and the mormyrids. Regions D and E 

 were selected in the 42-day-old embryo as the most favorable parts to study. 

 The work was not as exact as it could be if the investigator had had plenty 

 of live material, especially adult material, on which to use some of the well- 

 known neurological methods. But even in this embryo, which was well 



