Seal — Breeding Habits of Viviparous Fishes. 95 



August 26-27, found 5 more. 



September 3d to tOth found several more. Also found several 

 young with a pair hatched early in July. 



It is thus positively demonstrated, not only that there can be 

 two or more generations of these species horn in a summer, but 

 also a second generation in less than three months, so that 

 although the fecundity is not so great as with oviparous species 

 there is more rapid reproduction as well as protection both 

 through the egg stage and by reason of the greater development 

 and activity of the young when first hatched, the danger period 

 with the others. This will account for the great numbers of 

 these species where they abound, notwithstanding they are the 

 prey of all the larger species. 



I have repeated these observations several times with both 

 species with the same general results — any difference being in 

 the varying numbers produced, which, however, were a close 

 approximation . 



Notwithstanding that these two species live together appar- 

 ently in perfect harmony there is sexually an apparently rigid 

 racial antipathy. I have succeeded a number of times in 

 hybridizing a male Gambusia with a female Heterandria, but not 

 the reverse, probably because of the very small size of the males 

 of the latter species. The offspring of these crosses had the 

 appearance of Gambusia, none of the conspicuous markings of 

 Heterandria appearing on any of them. They were fertile and 

 reproduced, but the young also bad the appearance of Gambusia. 

 This fact would have caused me to suspect a mistake somewhere 

 in the course of the experiment if I had beard or read of it, 

 but I know that there was no possibility of error because they 

 were isolated in small jars with no change or interference. If 

 it were not for such an antipathy, which appears to be confined 

 to the females, the species would soon be intermixed. 



The attitude of the female Heterandria toward the male Gam- 

 busia was even more hostile and savage than that of females of 

 the same species. She would not only repulse him savagely 

 but at times would follow him biting him viciously until he 

 succeeded in hiding from her. Notwithstanding these vicious 

 rebuffs he would soon be back, following persistently at the left 

 and rear, rushing and retreating all through the hours of day- 

 light at least. 



