64 AMERICAN FISHERIES SOCIETY. 



example, in the case of the stickleback. With the shad this 

 method would not answer. Nor could the ova of salmon be suc- 

 cessfully hatched out by such treatment. What I have said on 

 this point shows, I think, that there is a great difference in the 

 power of resistance to adverse conditions manifested by differ- 

 ent species of eggs under similar conditions. In the case of the 

 silver gar, for instance, I had at last only three eggs with which 

 to work out the later stages of development, and, although I had 

 them under the microscope fully twenty successive times, each 

 time brushing off the accumulations of filth which would lodge 

 among the filaments covering the egg membrane, yet during all 

 these manipulations the normal development of the embryos 

 remained unimpaired. 



I will call your attention to the viviparous types. The one 

 which I have worked out most fully is the genvxs Gainbusia. The 

 parent fishes were from \)i inches \.o \}i inches in length, and 

 are found along the Chesapeake bay and its smaller southern 

 tributaries. This is a fresh-water, or at least anadromous viva- 

 parous species, spawning in July and August. The ovary is 

 lodged in the body cavity, and the vessels pass backward to it, 

 like the subdivided stem in a bunch of grapes to the single ber- 

 ries, each one of the follicles in which the single eggs grow re- 

 ceives a twig from the main vessel and is covered with a net- 

 work of vessels, which branch off from the main twig which 

 enters it, and just at the point where the vessel enters the sin- 

 gle follicle, there is a large round opening which answers to the 

 micropyle of the ordinary fish ^^^ laid directly in the water. The 

 Q^^ of Gambusia is, however, without a true o.^^ membrane, the 

 thin vascular follicle takes its place. The little fish develops 

 within the follicle, in which fertilization also takes place, the 

 spermatozoa finding their way to the e,^^ through the round 

 pore in the follicle spoken of, the male conveying his milt into 

 the ovary by means of an actual copulation with the female by 

 means of his prolonged anal fin. The development goes on until 

 the fish becomes active and the yolk-sac is aborbed. The young 

 fish then ruptures the follicle in which it is imprisoned, and slips 

 out through the abdominal pore, perfectly capable of taking care 



