184 BULLETIN OF THE BUREAU OF FISHERIES. 



in all the ovarian follicles. Without assuming the presence of an aperture in the fol- 

 licular walls, it would be difficult to understand how the spermatozoa could come in con- 

 tact with the ova. 



I can not agree with Ryder (1785), however, that "the ovary itself seems to have 

 no exterior investment, so that the follicles lie directly within the abdominal cavity, 

 the young fishes upon the completion of their development rupture them and escape 

 into the latter, and from thence through the abdominal pore into the outer world." <» 

 The ovary, as stated above, is a tubular organ which opens directly into the urogenital 

 sinus. When distended with advanced embryos, the exterior walls of the ovary are 

 very tenuous. The young fishes do not, however, break out into the abdominal cavity, 

 but pass out of the ovary directly through its opening into the urogenital sinus, thence 

 to the exterior. There is no aperture leading directly from the abdominal cavity to the 

 exterior. Furthermore, examination of the ovary of a female immediately after she 

 has given birth to a brood of young shows the walls of the ovary intact. No ruptured 

 ovarian follicles communicate with the coelom. When the exterior walls of the ovary 

 are dissected'off , the ruptured ovarian follicles are found in place in a somewhat shrunken 

 condition. 



It may not be amiss at this point to call attention to an error which appears in the 

 recent paper by Seal (191 1) referred to above. "The ova of a full-sized Gambusia are," 

 he says, "when fully developed, about an eighth of an inch in diameter, transparent 

 and nonadhesive. Each one is held, apparently, by a thread of membrane to a central 

 nucleus, the character of which could only be determined by microscopic observation. 

 The young fish can be seen fully formed, their eyes moving as they turn around in the 



egg." * 



That the author quoted above has mistaken the ovarian follicle for the egg is obvious. 

 The embryo is developed at the surface of the egg, which has no investment of its own 

 save the vitelline membrane. When the yolk has been absorbed by the embryo there 

 remains no trace of the egg. The young fish is then inclosed in the ovarian follicle which 

 is suspended to the central rachis by the structure referred to in the above quotation 

 as "a thread of membrane holding the egg to a central nucleus." 



In the paper quoted above (p. 93), Seal describes the extrusion of the young as 

 follows: "They are expelled one at a time and the ejection of each fish is so rapid that 

 they appear as though shot out with some force. This, however, might be due to the 

 bursting of the follicle and the uncoiling of the fish as it is released from restraint. 

 * * * The follicles are undoubtedly ruptured at the moment of extrusion, whether 

 inside or out I have never succeeded in obsen,'ing, but it appears the more probable 

 that it is inside." 



In view of the fact that the ruptured ovarian follicles are found in place in the 

 ovary after the young fishes are extruded, it is obvious that the rupturing of the follicle 

 occurs not only within the body of the parent but within the ovary. The j'oung fish 

 is, doubtless, uncoiled as soon as it leaves the follicle. This uncoiling could, therefore, 

 add little to the force with which the young fish is extruded. The rapid escape of the 



o Ryder, John A.: On the development of viviparous osseous fishes. Proceedings of the U. S. National Museum, vol. vm, 

 p. 148. 



b Seal, William P.: Breeding habits of the viviparous fishes Gambusia holbrookti and Helcrandria formosa. Proceedings of 

 the Biological Society of Washington, vol. xxiv, p. 93, 1911. 



