CHAPTER IX 

 ELECTRIC TISSUES 



IN a very few organisms, certain tissues are able to produce electricity. 

 They are especially developed and constructed to do this, and they pro- 

 duce it specifically, and apart from the electricity generated in small 

 quantities as a by-product in some other tissues. These few animals 

 are all fishes, some teleosts, some elasmobranchs. 



Electric tissue is composed, in the few known cases where it occurs, 

 of a series of plate-like units, each of which may be designated by the 

 name electroplax. Each electroplax. lies in a connective-tissue compart- 

 ment, imbedded in a jelly-like mass of tissue which fills the compartment. 

 The nerve and blood supply come from some side or corner of the com- 

 partment and are distributed through the jelly tissue to the electroplax. 

 These plate-like electroplaxes are arranged in rows or are irregularly 

 massed. All the electroplaxes in a given fish are oriented alike. 



The electroplax may be considered to be a single cell with many 

 nuclei or, in other cases, as a syncytium formed by the union of a number 

 of cells. Some might consider it an organ unit composed of many 

 cells on account of the fact that each nucleus is surrounded by its own 

 portion of unspecialized cytoplasm, but it can probably be considered 

 better as a syncytium in the same sense that a voluntary muscle fiber is 

 so considered. 



The electroplax is composed of three principal layers, a nervous or 

 electric layer forming one surface on which the nerve ends, a middle 

 layer which may be called the striated layer, and a posterior layer whose 

 exact function is not known, but may, perhaps, be a nutritive layer. This 

 layer is really a part of the anterior or electric layer, and is continuous 

 with it around the edge of the middle layer. In fact, the nerve some- 

 times passes through or around the entire electroplax, and turns, to branch 

 out and innervate the posterior layer instead of the anterior (Mormyrus). 

 The apparently different functions of these two similar layers are then 

 reversed. The striated layer is sometimes missing. 



These three layers form the body of the electroplax, and this body is 

 best understood by comparing it to a voluntary muscle fiber which has 

 grown wider and shorter until it is wider than it is long. This process is 

 carried on to different degrees ; only slightly in some rays, more in others, 



105 



