1088 



SCANDINAVIAN FISHES. 



cm., long after it lias left the egg and in general \ the same and simple enough. One muscle fil)re after 



assumed the external foi-ni of an adult member of the 

 species. The course of the develojjinent is, however. 



another (tig. 306, J, 1 — 5) thickens at one end — where 

 the many terminal tiljrils of the motor nerve are at- 





Fig. 306. Development of the electric elements in the tail of 



lion Skate (Raja balls). Mngnified. After Ew.\rt. 



A: Horizontal section tliruugli a part of the lateral muscle of the tail in an embryo 7 cm. long. The muscle fibres are obliquely extended 

 between the intermuscular septa (s), and their transformation proceeds from in front, the hindmost of tlie 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 tlie expanded enil ; but in the most transformed (clubdike) fibres the nuclei begin to pass towards the thick- 

 ened end. Between the fibres and tlie intermuscular septum lie numerous connective tissue cells, and between these nerve fibrils are 



supplied to the fibres. 



B: Two isolated clubs from a somcwliat ohler embryo. Tlu' thick end is here llattened and at the top (in front) has a layer of surco- 

 plasnia with muscle nuclei (a), under tliis a denser striation (rhalidia). within which the nuclei are beginning to disappear (i), next a layer 

 of sarcoplasma with nuclei and sparser striation (c), and al the bottom tlie 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; /) is destined to form the so-called striated 



layer, c tlic so-called alveolar layer. 



and /'; Two different stages of development approximating to the bilboquet form. Letters as iu B. 



E: A fully developed electric clement, with a part of the stem (./) still persistent and at the posterior end (c) still showing traces of stria- 

 tion; a, b, and t' as in B. f, gelatinous ]t\yer of ccuinective tissue; </, nerve tilirils; ii, nerve fibre: s, septum between two electric elements; 



*', ]iart of the original transverse intermuscular septum. 



