564 



THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



meandering layer is probably the vestige of the cross striations of those 

 voluntary muscle fibres which have been transformed into the plates, 

 since in the embryonic stage of B. batis and the adult stage of B. circu- 

 laris, the layer can be identified with the materials forming the cross 

 stria; of a slightly modified muscle fibre, and the meandering layer of 

 the organ in adult B. batis still possesses those optical properties which 

 characterise striated muscle. The protoplasmic layer on the caudal 

 border of each plate or disc contains many nuclei, and is thrown upon 

 its free surface into a number of projecting processes, upon which 

 extended surface blood capillaries ramify. Every column consists of a 

 series of such compartments, each containing a plate of essentially the 



Transverse septum. 



Medullated fibres of the plexus 



Terminal ramification of 11011- 

 niedullated nerves. 



xus, ^ 



1 Nerv 



I 



ous 

 lamina. 



Nucleated lamina, 

 Striated lamina 



Ah eolated lamina, 



na, , 



t 



The disc. 



Connective tissue. 



Transverse septum. At its junction with the 

 longitudinal septum a nerve is seen in 

 section. 



Fig. 292. — Electrical organ of skate. Diagrammatic view to show the 



structure of a disc. 



same structure. As the fish grows in size, the organs also increase, but 

 the number of compartments and plates is fixed at an early stage of 

 growth, and thus the organ of large specimens affords the most favour- 

 able specimens for the examination of the plates, since the plates are 

 now some distance apart. The nerves which supply the columns and 

 plates arise from the caudal portion of the spinal cord, and appear to 

 come from special nerve cells situated on the dorsal side of those which 

 give rise to the nerve fibres innervating the muscles. An exception to 

 the structure just described occurs in the embryonic condition of B. batis 

 and the adult condition of certain species, e.g. B,. circularis. Here the 

 compartments composing the columns are irregular, since each contains 

 a modified muscle fibre forming a cross striated multinucleated mass. 



