The elasmobranch fishes (1934) The elasmobranch fishes . elasmobranchfish03dani Year: 1934 114 THE ELASMOBRANCH PISHES The electric discs (ds.), although directed more at right angles to their con- nective tissue septa, have otherwise the same general relations as the fibers of the muscle. Like them they are smaller and less regular at the tip and base of the cone. They are, however, much larger than the muscle fibers. As individual units they are more or less quadrangular in shape, their walls being formed of connec- tive tissue. A glance will show that there are a great number in a single o
The elasmobranch fishes (1934) The elasmobranch fishes . elasmobranchfish03dani Year: 1934 114 THE ELASMOBRANCH PISHES The electric discs (ds.), although directed more at right angles to their con- nective tissue septa, have otherwise the same general relations as the fibers of the muscle. Like them they are smaller and less regular at the tip and base of the cone. They are, however, much larger than the muscle fibers. As individual units they are more or less quadrangular in shape, their walls being formed of connec- tive tissue. A glance will show that there are a great number in a single organ. It has been estimated that as many as 20,000 discs are present in an adidt Rata hatis. One of the most interesting things about the electric organ is the fact that, whether it be in Raja or in Torpedo, it is formed as a series of metamorphosed muscle fibers. The organ as described by Ewart in Raia hatis first appears when the emlu-yo is about an inch long. Here it is confined to the tail and only those muscle fibers are af- fected Mhich belong to the lateral bundles, as described for Lamna (fig. 101). These fibers undergo complete change of form and assume an entirely secondary func- tional role. A group of such fibers (fig. 116a) shows the beginning stages in this metamorphosis. The anterior fibers, near their attachment to the nn'oseptum, are beginning to enlarge into club-shaped structures {), while the posterior fiber (inf.) is still of the mus- cle type. By further growth and difi^erentiation each incipient electric club comes to assume the form of a cone, in the enlarged end of which in time a con- cavity forms. A nerve entering this concavity breaks up into many branches {n., fig. 116b). At this stage, striation characteristic of the muscle fiber has decreased on the cups, but striations are still present on the body of the cone. In a later stage (fig. 116c) the organ has acquired essentially the adult char- acteristics. In this stage it is seen that the disc (
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