108 HISTOLOGY 



of structure can probably be demonstrated and their relations understood 

 as well as in any form. The electroplax is not highly specialized, and 

 material is easily obtained all over the world. A complete demonstra- 

 tion is somewhat delicate and difficult, and nitrate of silver preparations 

 are essential to a demonstration of the fundamental points. 



Technic. It is more true of electric tissue than of muscle that chance 

 plays a large part in the winning of good results. Several of the better 

 fixatives should be tried, and the use of dead tissue which has recently 

 died of secondary causes (as bleeding or suffocation or narcotics) should 

 not be neglected. Nitrate of silver used after the rapid method of Golgi 

 is an all-important method in the study of electric tissue, and should be 

 used in the study of each form. It serves to demonstrate much more 

 than the nerve connection of the electroplax. 



LITERATURE 



No really comprehensive survey of the subject has been written other than the shorter 

 accounts in the text-books of zoology and some encyclopaedias. The subject must be 

 read up in the separate articles, some of which are mentioned after the following parts. 



ELECTRIC TISSUE OF ELASMOBRANCH FISHES 



The electric tissues of Raja ocettata consist of two modifie regions of 

 the tail muscle ; a symmetrical spindle-shaped area in each of the mus- 

 cular masses that lie, one on each side of the tail. The spindles begin 

 anteriorly in this ray at about the level of the ventral fins and extend 

 almost to the end of the tail. The electric tissue can be easily distin- 

 guished from the surrounding muscle tissue in the fresh specimen by its 

 jelly-like appearance. 



The organ is divided into minute compartments whose outline is 

 apparent on the outer surfaces as well as on cut surfaces of the spindle. 

 The dividing walls of these compartments are of a white fibrous connec- 

 tive tissue, and the interior of each compartment is filled with a jelly-like 

 connective tissue, the electric connective tissue in which the electroplax 

 lies. From the anterior, inner corner or edge of the compartment, a 

 nerve supply enters to innervate the electroplax. Blood vessels are 

 introduced, usually from the opposite or posterior side, and branch in 

 the electric connective tissue to furnish the electroplax with blood. 



The compartment is wider than it is long, a polyhedral cavity placed 

 with its two large surfaces cephalad and caudad. It will average, in a 

 three-foot ocellata, about 600 to 800 microns in width and 390 to 450 

 microns in length. The myotomes of the tail muscles are continued 

 directly into the electric organ, dividing its mass of electroplaxes into a 



