200 THE AMERICAN NATURALIST [Vol. XLIV 



direction that they had previously assumed has increased 

 until they now run back and forth at right angles to the 

 axis of the electroplax and consequently in the same re- 

 lation to their former course. This gives the striated 

 appearance which might be taken for the degenerated 

 remains of the real muscle striation that the developing 

 electroplax formerly possessed. 



We thus can see that, while the electroplax of Raja and 

 of Torpedo were formed from single muscle cells, in the 

 first case by a widening of the negative or electric end and 

 in the second instance by a widening of the positive or 

 nutritive end, the electroplax of Gymnarchus is formed by 

 the association of several myoblasts into a single syncy- 

 tium and the widening of the middle part of this struc- 

 ture into the electroplax. 



The other anatomical features of Gymnarchus which 

 have caused it to be classed with the Mormyridce demand 

 that a comparison of this organ be made with the appar- 

 ently widely different organ found in the various mor- 

 myrus groups. That found in Mormyrus Oxyrynchus 

 will serve as a type and its general plan has been well 

 shown by OgnefT and Schlichter. Here it is evident that 

 a number of consecutive and entire myotomes have been 

 converted into electroplaxes and that the middle layer of 

 each electroplax is composed of unaltered and clearly 

 striated myofibril bundles. The large number of these 

 fibril bundles and their distribution indicate that the 

 whole electroplax is a syncytium composed of all or most 

 of the cells which would otherwise have gone to make 

 up the single myotome. In this we find an agreement 

 with the electroplax of Gymnarchus which is also formed 

 from several cells. In the one case all the cells in the 

 myotome have been used; in the latter only those lying 

 in eight particular localities. 



Further homology is seen in the disposition of the 

 probably superfluous myofibrils. In both forms they are 

 relegated to a middle position in the electroplax while 

 the apparently more important cytoplasm forms layers 

 on the anterior and posterior surfaces of the structure. 

 Also, in both, the now useless myofibril bundles are 



