ELECTRIC TISSUES, TELEOSTS 



II? 



The posterior surface is evaginated into a large number of short, 

 medium thick papillae, while the anterior face is drawn out into very 

 many very thick projections, so thick and so closely set that their sides 

 touch, for the most part. Each papilla system may roughly be said to 

 be as thick as the solid middle layer. 



Figure 109 shows a small part of a section taken transversely to the 

 electroplax. The cytoplasm is seen to be a delicate reticular substance 

 slightly denser, perhaps, toward the anterior surface and especially around 

 the edges of the spaces which separate the 

 anterior papillae. 



The edges of the section show that over 

 the entire surface of the electroplax there is a 

 continuous series of short rod-like structures 

 pointing at right angles from the electrolemma 

 into the cytoplasm. Those on the posterior 

 surface are the heaviest, and may represent 

 the " stabchen " or little rods first described 

 by Ballowitz in the torpedo. 



The nuclei are not numerous when one 

 considers the large mass of cytoplasm that 

 they must care for. They are found near 

 the edge and usually out in the papillae, more 

 in the posterior than the anterior. 



The nerve fibers approach the electroplax FlG II0 ._ Endsof 

 in the posterior jelly layer as medullated from the electric surface of 

 fibers, which divide and send non-medullated 

 branches to the ends of the posterior or elec- 

 tric papillae. Here the nerve forms its motor 

 endings, consisting of a thick, heavy plexus 

 that embraces the upper part of the papilla lying in an intimate contact 

 with its cytoplasm. Figure no shows a surface view of the ends of 

 two of the papillae with their relations to the nerve supply. 



Comparing this organ with the electroplax of Raja, which we hold to 

 be the most rudimentary and complete electroplax, it can be seen that 

 it is highly differentiated. The striation is absent, which shows special- 

 ization, and the points of contact with the ends of the nerve fibers are 

 multiple, which seems to argue for a multicellular origin for the electro- 

 plax. 



The electric tissue of Mormyrus, as described by Schlichter, shows 

 some striking similarities to that of Gymnotus, as well as some wide 

 differences. As in the electric eel (it is not an eel, but another kind of 

 elongate fish) the tissue is a modified portion of the posterior, lateral, 

 body musculature and is also composed of upright plates or electroplaxes 



the electroplax of Gymnotus. 

 Nerve fibers ending in delicate 

 mesh-shaped nerve-endings on 

 the papillae. (After BALLO- 

 WITZ.) 



