1088 
SCANDINAVIAN FISHES. 
cm., long after it has left the egg and in general 
assumed the external form of an adult member of the 
species. The course of the development is, however, 
the same and simple enough. One muscle fibre after 
another (fig. 306, A, 1 — 5) thickens at one end- — where 
the many terminal fibrils of the motor nerve are at- 
Fig. 306. Development of the electric elements in the tail of a common Skate (Raja batis). Magnified. After Ewart. 
A: Horizontal section through a part of the lateral muscle of the tail in an embryo 7 cm. long. The muscle fibres are obliquely exteuded 
between the intermuscular septa (s), and their transformation proceeds from in front, the hindmost of the figured fibres (1) being entirely 
unaltered, the others (2 — <5) more and more club-shaped the further forward they lie. In all these fibres the muscle nuclei and the stria- 
tion are still distinct, even at the expanded end; but in the most transformed (club-like) fibres the nuclei begin to pass towards the thick- 
ened end. Between the fibres and the intermuscular septum lie numerous connective tissue cells, and between these nerve fibrils are 
supplied to the fibres. 
B: Two isolated clubs from a somewhat older embryo. The thick end is here flattened and at the top (in front) has a layer of sarco- 
plasrna with muscle nuclei (a), under this a denser striation (rhabdia), within which the nuclei are beginning to disappear (6), next a layer 
of sarcoplasma with nuclei and sparser striation (c), and at the bottom the aborting stem (d). a is the rudiment of the so-called electric 
plate, to which the nerve fibrils (e, with nerve nuclei and connective tissue bodies) are attached; b is destined to form the so-called striated 
layer, c the so-called alveolar layer. 
G and D: Two different stages of development approximating to the bilboquct form. Letters as in B. 
E: A fully developed electric element, with a part of the stem (</) still persistent and at the posterior end (e) still showing traces of stria- 
tion; a, b, and c as in B. f, gelatinous layer of connective tissue; g, nerve fibrils; n, nerve fibre; s, septum between two electric elements; 
s', part of the original transverse intermuscular septum. 
