49 6 CLAPP. [Vol. V. 



In "A Preliminary Notice of the Development of the Toad- 

 fish," 1 Dr. Ryder gives a figure of the embryo in about the same 

 stage of development as seen in Fig. I. c. The peculiarity in 

 the growth of the blastoderm over the yolk seems to have been 

 overlooked, for the embryo is represented, as in the ordinary 

 teleost, developing at the margin of the blastoderm. 



There is a striking resemblance between the appearance of 

 the blastoderm in Fig. I. c, and Balfour's diagram of the Elasmo- 

 branch type of development, 2 and also great similarity between 

 Fig. I. e and^-, and Figs, i and 2, PL VIII., of Balfour's "Elasmo- 

 branch Fishes." 



The egg of Batrachus is enormous, as compared with that of 

 the pelagic fish egg, being about 5 mm. in diameter, and also 

 larger than the egg of most amphibians, owing to the accumula- 

 tion of food yolk. In this respect there is an approximation to 

 the condition seen in the Elasmobranch egg, and to this must 

 be attributed the peculiarities of the blastopore. 



In comparing Fig. I. e and g, with Balfour's figures of Pris- 

 tiurus, before mentioned, the following points may be noticed: — 



In the case of Pristiurus, at the time when about two-thirds 

 of the yolk has been enveloped by the blastoderm, we find the 

 embryo folded off from the yolk, and connected with it by a 

 narrow umbilical cord, the embryo being still at the edge of 

 the blastoderm, and the tail extending beyond it. 



At a later stage, but before the closure of the blastopore, 

 the circulation of the yolk sack is well established, and a venous 

 trunk occupies the position of the linear streak which marks the 

 line of coalescence behind the embryo. Fig. I. e and g, shows 

 the same form and position of the blastopore in Batrachus as 

 seen in Pristiurus ; but, on examination, it is found that the 

 caudal portion of the embryo is not free from the yolk, at the 

 time of the closure of the blastopore, neither are there any blood- 

 vessels in the yolk sack. 



In Batrachus we find a teleost exhibiting one of the interest- 

 ing features of the Elasmobranch type of development, the clos- 

 ure of the blastopore being evidently delayed, in consequence 

 of the great amount of food yolk, and giving rise to the yolk 

 blastopore, which Balfour describes as " the anterior and ventral 

 portion of the primitive blastopore." 



1 Bull. ofU. S. F. C, 1886. 2 Comp. Em., II. p. 126. 



