the Development of Anableps Gronovii. 443 



mittent organ in the males of some Mammals is remem- 

 bered, as of the Agouti, where spines, projecting in different 

 directions, offer far more serious mechanical opposition, we 

 can readily believe that a structure like that of the anal fin 

 of Anableps may be readily introduced into the genital tube 

 of the female. Still, in the ordinary position of the two 

 sexes it could not be thus used unless bent forwards. 



EXPLANATION OF THE FIGURES. 



Fig. I. Primitive ova, each consisting of a single nucleated cell. 



Figs. II. and III. Ova somewhat enlarged, around which a transparent 

 space is formed in the stroma of the ovary. 



Fig. IV. A more advanced egg, in which the transparent space has 

 become much enlarged. The vitelline membrane is distinctly visible, and 

 the nucleus contains granules or nucleoli of different sizes. On the left 

 of this figure is an earlier ovum, in which the transparent space is just 

 forming. 



Figs. V. and VI. Two foetuses with yelk-bags attached. On compar- 

 ing the two figures, which are of the size of nature, it will be seen that 

 foetus and yelk-bag both grow simultaneously. 



Fig. VII. A more advanced and nearly mature foetus, in which the 

 yelk-bag has been absorbed, and only a linear fissure or umbilicus re- 

 mains ; this is closed by a thin, scaleless membrane, and extends from the 

 space between the pectoral fins in front to that between the ventrals 

 behind. The foetus has acquired a length nearly one fourth of that of the 

 adult Anableps. 



Fig. VIII. A portion of the yelk-bag, highly magnified, showing the 

 papillae filled with granules, which cover its surface. 



Fig. IX. The anal fin. The genital portion is shorter than the fin 

 rays and membrane. In older specimens, however, the former becomes 

 proportionally longer, and the latter become so much diminished in size as 

 to be scarcely traceable.* 



* For complete and accurate descriptions and figures of other details relating 

 to structure and development, reference may be made to the Hist. Nut. des 

 Poissons, by Cuvier and Valenciennes, tome xviii. p. 245. 



