The Origin of the Electric Organs in Astroscopus GuUatus. 155 



caudad and close to the muscle, about halfway between its origin and 

 insertion (plates n and in, R. su., 0. su.}. In the figures the electric 

 area is stippled. 



The number of electroblasts do not increase after once being formed. 

 Each electroblast is the product of a single cell and each electroplax is 

 the product of a single electroblast, so that the amount of electric tissue 

 to be contributed by the various muscles has already been determined. 

 It was most unfortunate that no embryo could be obtained represent- 

 ing a stage between that of the 20 mm. embryo and of the 33 mm. em- 

 bryo, as it is between these two stages that the actual separation of the 

 organs from the muscles takes place. The position of the electric 

 organs in the 20 mm. stage, however, goes a long way toward explain- 

 ing the real process, so that we are safe in drawing pretty definite con- 

 clusions without the intermediate stage. 



Except that the nerves branch much more profusely in all of the 

 muscles, no change has been noted in any but that branch of the ocu- 

 lomotor nerve which goes to the rectus superior. As noted above, the 

 main branch of the oculomotor goes to the rectus superior in two divi- 

 sions. The larger of these two divisions enters the muscle somewhat 

 posterior to the smaller one, and is seen to have enlarged to nearly 

 twice its original diameter. The small branch goes to all parts of the 

 muscle, but the large one goes to the middle of the muscle, where it 

 divides into many parts, all but one of which are seen to approach the 

 electric organ of this muscle and stop. There is a considerable space 

 between the muscle and the electric tissue, and the axones of the nerves 

 must cross this space to enter the electric organ. Although the mate- 

 rial was not favorably fixed for the study of nerves, a few fibers could 

 be traced across the intervening space and into the electric organ. 

 Unfortunately, the nerve-endings could not be seen in any of my 

 material and I have had to pass over this point until more material can 

 be obtained. The last division of this branch, which does not approach 

 the electric organ, passes directly through the rectus superior muscle 

 and can be traced ventrally and mesad until it approaches the electric 

 organ of the rectus internus muscle. It was impossible to trace any of 

 the fibers of this branch into the electric organ, but the nerve itself 

 could be traced until it touched the electric tissue, so that there can be 

 no doubt that the axones do pass in and that with better material they 

 could be seen to be distributed among the electroplaxes of this organ as 

 well as that of the rectus superior. This is the first indication that the 

 nerve which innervates the rectus superior muscle is to innervate the 

 electric organs also, but it is not yet clear that it is the only nerve which 

 will do so, although it is clear that the electric organ of the rectus 

 superior is not the only one to be innervated by it. Later it sends 

 branches to all four of the electric organs. 



