80 INTRODUCTION. 



envelops with external gills or just before 

 their appearance, with the tail more or less 

 developed. 

 Vitellus 1 — 1| millimetres in diameter, black 



above Discoglossus. 



Vitellus 2 millimetres in diameter, brown above. 



Bombinator. 



b. Irregularly disposed iu a thick mucilaginous 



band (formed by fusion in the cloaca of the 

 contents of the two oviducts) ; vitellus dark 

 brown or black, with the lower pole white, 

 1^ — 1\ millimetres in diameter, the embryo 

 leaving the envelops before the appearance 

 of the external gills and tailless. 



Pelodytes, Pelobates. 



c. In regular files in two long 1 mucilaginous 



strings ; vitellus entirely dark brown or 

 black, or with a whitish lower pole, the 

 embryo leaving the envelops before the 

 appearance of the external gills and with a 



rudimentary tail Bnfo. 



Vitellus 1^ — 2 millimetres in diameter; eggs, in 

 each string, in three or four files when floating, 



in two when stretched B. vulgaris. 



Vitellus 1 — \\ millimetres in diameter; eggs in 

 three or four files when floating, in two when 



stretched B. viridis. 



Vitellus 1 — 1^ millimetres in diameter, with 

 whitish lower pole ; eggs in two files when 

 floating, in one when stretched . B. calamita. 



d. In large lumps ; upper pole brown or black, 



lower whitish or yellowish ; the embryo 



leaving the envelops with external gills and 



a well-developed tail. 



1. Envelop, when fully swollen out, measuring 



3 — 4 millimetres in diameter; vitellus 



yellowish white with brown upper pole, 1J 



millimetres in diameter; embryo yellowish. 



Ilij la. 



