214 EMBRYOLOGY OF THE LOWER VERTEBRATES oh. 





waiggmp^ 



■^^g^^-sS TSSBBSgaa ^ 



s.l clI. 



==w being now still thicker and 

 the whole fibre having 

 assumed the shape of a 

 mace. In the expanded head 

 portion of the mace the cross 

 striation is becoming closer, 

 while in the slender handle the 

 striation is becoming blurred 

 and in the portion next the 

 head is almost disappearing. 

 The end -plate forms a very 

 definite layer of uniform thick- 

 ness covering the truncated an- 

 terior end of the mace. It is 

 crowded with large nuclei and 

 to it pass nerve- fibres which 

 show a regular dichotomous 

 branching. In the fibre shown 

 in Fig. 118, D, taken from the 

 same 10 cm. embryo, the head 

 of the mace is still more ex- 

 panded as compared with the 

 stem. The main portion of the 

 head, in which the muscle 

 striation had become closer, now 

 forms a thick plate bent into a 



Fig. 118. — Development of the electric organ of Raia batis. (After Ewart, 1888.) 



A and B from an embryo slightly over V cm. in length ; C and D from an embryo about 10 cm. in 

 length; E, from a specimen about 67 cm. in length, a.l, alveolar layer ; e.l, electric layer; el, 

 electrolemma ; n.f, nerve-fibres ; s,l, striated layer ; t, vestigial remains of muscle-fibre. 



