SUBMENTAL FILAMENTS: GYMNOTID EEL 691 
COMPARISON WITH KNOWN ELECTRIC TISSUE 
Electric organs are found in certain rays of the Atlantic Ocean 
and southern seas, and in the African Siluroid, Malopterurus 
electricus. The organs of the Rajas show unmodified electric 
tissue while those of the Electrophorus electricus possesses a 
specialized electric tissue. 
In Raja ocellata® the electric tissues occupy two unmodified 
regions of the tail muscle, forming a symmetrical, spindle-shaped 
region on each side. The electric organ is divided into a series 
of minute spindle-shaped compartments whose dividing walls are 
connective tissue, which surround a jelly-like mass of connective 
tissue supporting the electroplaxes. 
The electroplax of Rajaocellata isa large, disce-shaped syncytium 
occupying the entire width of each compartment, not extending 
the whole length of the compartment, but leaving anterior and 
posterior spaces filled with connective tissue. The size of these 
spaces varies with the species. Each electroplax consists of three 
layers, the electric and nutritive which are continuous around the 
edge; the middle or striated which forms a core and is the thickest 
layer. The blood vessels are usually introduced from the nutritive 
side, and branch in the electric connective tissue. The nerve 
supply enters the anterior corner or edge of each compartment, 
lose their medullary sheath, and the fibers begin to divide and 
subdivide as they approach the electric surface on which they 
terminate. The electric surface is flat, and the nutritive surface 
is evaginated into many papillae which contain a portion of the 
striated layer. The nuclei are found in all three layers, forming a 
regular close arrangement in the electric layer; sparingly scattered 
through the striated portion; and irregularly arranged and some- 
what smaller in the nutritive layer. Surrounding each nucleus 
is a mass of granular cytoplasm which connected with the other 
masses form a separate layer. The syncytium is surrounded by 
a delicate cell membrane, the electrolemma. 
The electric tissue of Electrophorus electricus® consists of a 
number of electroplaxes placed vertically and facing forward to 
’Dahlgren and Kepner, Principles of animal histology, pp. 105-122, 1908. 
®‘Dahlgren and Kepner, |. ec. 
