8 MINNOWS GAMBUSIA AFFINIS AND CYPEINODON VAEIEGATUS. 



throughout the season in a perfectly normal way.'* A female kept 

 imder close observation produced five broods after she had been 

 separated from aU other fish. To determine if fish that were sepa- 

 rated from males in the spring would continue to produce young 

 the following season without again coming in contact with males, a 

 number of females were kept in aquaria through the winter. In 

 the followmg spring large eggs, of yellowish appearance, were pro- 

 duced instead of young. Other females that had been with males 

 during the entire smnmer were separated from them late in the fall 

 and also carried through the winter. This lot, too, produced eggs 

 instead of young. In each case the eggs appeared when young 

 would normally have been produced. These experiments show 

 that this fish is able to carry the sperms throughout the breeding 

 season, but indicate that it can not carry them through the winter. 



Ova in various stages of development are present in the ovary at 

 one time. When one brood is bom the eggs of the next set are 

 already well developed, being about 1 mm. in diameter, and several 

 smaller eggs are also present. When the fertilization of the different 

 sets of eggs occm-s is not known. With regard to Phalloceros caudo- 

 macukbtus and Onesterodon decemmaculatus, two viviparous forms 

 belongmg in the same family with Gambusia affinis (the family 

 Poeciliidse), Philippi (1908, p. 22) fomid that the sexual product of the 

 male consists of numerous milk-wliite bodies which stick fast to the 

 first available object. Microscopic examination showed that these 

 bodies consist of closely crowded spermatozoa. The whole mass is 

 held together by a sticky substance, which probably causes the sperm 

 bodies to fasten themselves to the genital papillae of the females. He 

 found also that these bodies were quickly dissolved when they came 

 mider the influence of the ovarian fluid, and the individual sperma- 

 tozoa were set free. Withm the folds of the lining of the oviduct 

 the sperms were fomid in great numbers, even after the birth of 

 young. It is probable that the sperms are retained there throughout 

 the breeding season and that the eggs are fertilized as soon as they are 

 sufficiently mature. 



The fact that the female is capable of producing yomig throughout 

 the breedmg season without coming in contact with the male leads 

 one to look with suspicion upon the many notices of "hybrids'^ 

 produced by crossing species of viviparous fishes. In order to obtain 

 true hybrids of Gambusia affinis with another species, if such cross- 

 breeding will occur at all, it would be necessary to begin the exj^eri- 



a "Zolotnisky (1901, p. 65) observed that a female of P. caudomaculatus which had been separated from 

 males after the appearance of a brooi of young pro luced another within six wee;:s and a third brood four 

 weeks after this. This occurrel although copulation subsequent to the first parturition had not taken 

 place. Fhilippi also isolated females at, or slightly before, parturition. In every instance the females 

 became pregnant for a second time, and one specimen produced a third brood 46 days after the appearance 

 of the second. Poey noted these facts many years ago." (Henn, 1916, p. 102.) 



