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 fetuses with yelk-bags attached. On compar- 
ing the two figures, which are of the size of nature, it will be seen that 
foetus and y elk-bag both grow simultaneously. 
Fig. VII. A more advanced and nearly mature fetus, 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 fetus 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 
papille filled with granules, which cover its surface. 
Fig. I 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 
‘0 structure and development, reference may be made to the Hist. Nat. des 
Poissons, by Cuvier and Valenciennes, tome xviii, p. 245. 
