THE CYPRINODONTS. 73 
abdomen and the permanent ventral walls coalesce from the pectorals back- 
ward, and to some extent from the vent forward, closing the fissure, separat- 
ing the body cavity from the pouch, which shrinks, shrivels up, and is 
absorbed or otherwise destroyed. Traces of the cleft remain for a time; 
finally these are covered by scales and obliterated. 
The entire fissure represents the umbilicus. Apparently the disappear- 
ance of the sac precedes the extrusion and independent life of the young 
fish but a short time, during which the substance of the pouch itself and the 
liquid contents of the ovarian cavity furnish subsistence. 
Valenciennes (1846) says the sac enters the abdomen and that the size 
and number of the foetuses occasion the permanent separation of the ven- 
tral fins. In Wyman’s work (1857) both of these points are correctly treated. 
Valenciennes describes the rows of papilla as vascular striw, in which he is 
nearer the truth than Wyman is. Fertilization takes place, so far as the 
action of the spermatozoon is concerned, as in viviparous Cyprinodonts in 
general. Wyman’s idea, that the spermatozoon “ must act simply by its pres- 
ence on the surface of the egg-sac or by an endosmosis of its fluid contents 
through the membranes by which the ovum is invested,” is incorrect. Val- 
enciennes described the sexual organs and decided from the scales and their 
arrangement on the male organ that it was not intromittent, but, “s'il y a 
un accouplement nécessaire A la fécondation des ceufs dans l'intérieur de la 
femelle, il ne peut se faire que par une simple juxtaposition de l’extrémité 
de la verge du mile dans la fente allongée et vulviforme des sacs ovariens de 
la femelle.” His conjecture is in part borne out by the facts of the anatomy 
of the organs, which also discloses a great deal he has overlooked. The 
structure of the anal of the male, after its modification, is such as to allow 
a very limited motion downward, but provides much greater freedom of 
movement sideways. The purpose of this lateral reach is evident at once on 
comparison of a number of specimens of both sexes. Copulation is effected 
by the male, at the side of the female, bending the anal to one side so as 
to bring the extremity of the organ into the opening to the ovaries of the 
female. In the posterior half of the adult male organ a bend is made to 
either the right or the left as may be (Plate VII. Fig. 2, 3). Of seventeen 
males, the bend is to the right on eleven, to the left on six. Further than 
this, there is a small fleshy tubercle at the side of the seventh or the sixth 
anal ray, at the beginning of the outer half of its length, When this prom- 
inence is on the left side the organ bends to the right, or if on the right side 
to 
