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 (18-46) 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 papillae as vascular striae, 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 necessaire a la fecondation des oeufs dans I'interieur de la 

 femelle, il ne pent se faire que par une simple juxtaposition de Fextremite 

 de la verge du male dans la fente allongee 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 efiected 

 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 



