8 MINNOWS GAMBUSIA AFFINIS AND CYPRINODON VARIEGATUS. 



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

 under close observation produced five broods after she had been 

 separated from all 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 following spring large eggs, of yellowish appearance, were pro- 

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

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

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

 instead of yomig. 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, m diameter, and several 

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

 sets of eggs occurs is not known. With regard to PhaUoceros caudo- 

 ina,culatus and Gnesterodon decemmaculatus, two viviparoas forms 

 belonging in the same family with Gamhusia affinis (the family 

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

 male consists of numerous milk-white 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 jDrobably causes the sperm 

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

 foimd 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 found in great numbers, even after the birth of 

 young. It is probable that the sperms are retained there tln-oughout 

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

 sufficiently mature. 



The fact that the female Ls capable of producmg young throughout 

 the breeding season without conling in contact with the male leads 

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

 produced by crossing speci(>s of viviparous fishes. In order to obtain 

 true hj^brids of Gamhusia affi,nis with another species, if such cross- 

 breedmg will occur at all, it would be necessary to begm the experi- 



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

 males after the apppamnce of a brood of young proluced another \vithin six weeks and a third brood four 

 weeks after this. This occurre 1 although copulation subsequent to the first parturition had not taken 

 place. Philippi also isolated females at, or shghtly before, parturition. In every instance the females 

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

 of the second. Poey noted these facts many years ago." (Ilenn, 1910, p. 102.) 



