102 Annals of the Carnegie Museum. 



were placed in normal salt solution, where they sank to the bottom. 

 After eighteen hours the majority were unchanged; one had released 

 a wisp of sperm, which remained about the otherwise unchanged mass, 

 some showed softening, but very few had broken up. The following 

 day the great majority were still unchanged, although somewhat 

 swollen, and on the fourth day they still remained unchanged. 



A number of these sperm-bodies were placed in a dish in which the 

 ovary and genital tract of a freshly killed female had been crushed. 

 Within a very short time (six minutes) after coming under the influence 

 of the ovarian fluid these bodies had dissolved and the individual 

 spermatozoa were set free. 



A receptaciilum seminis is formed by numerous unsymmetrical folds 

 in the lining of the oviduct. Within these folds the spermatozoa are 

 found in incredible numbers, and they remain here even after the birth 

 of the young. 



Subsequent Fertilization from a Single Mating. 



Zolotnisky (1901, p. 65) observed that a female of P. caiidomacidatus , 

 which had been separated from males after the appearance of a brood 

 of young, produced another within six weeks, and a third brood four 

 weeks after this. This occurred, although copulation subsequent to 

 the first parturition had not taken place. Philippi 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 

 forty-six days after the appearance of the second. Poey noted these 

 facts many years ago. 



Many notices of " hybrids " among the viviparous species have 

 appeared in the literature of fish-fanciers. These presumable hybrids 

 have certainly arisen through the ability of bringing forth young with- 

 out fertilization between broods. A female of one species, for ex- 

 ample, which has borne young is placed with a male of another species. 

 After some weeks young appear, which are taken for hybrids, but are 

 in reality a product of the first mating. Actual hybrids can be ob- 

 tained only by carefully rearing young fishes until discrimination of 

 the sexes is possible. After this they must be kept rigidly separated, 

 and the first mating of the young female must be made with a male of 

 a diff'erent species. Unless this method has been practised, accounts 

 of " hybrids " among these fishes are worthless. 



