Henn: South American Pceciliid Fishes. 105 



The ova are quite large, yellowish in appearance, and spherical, 

 measuring on an average 1.5 mm. in diameter. In this list I have 

 counted as ova those which show no differentiation. When develop- 

 ment begins the optic vesicles early become pigmented, and are the 

 first major indication of the initiation of development. Examination 

 with a binocular microscope is sufficient to distinguish a small embryo 

 from an undifferentiated egg. 



It will be seen that the same females often contain both large and 

 small embryos and undifferentiated ova. The latter are often quite 

 small and the birth of the young which they are to produce will be 

 postponed considerably after the birth of the larger ones. Specimens 

 of Diphyacantha chocoensis, which externally seemed pregnant and 

 had evidently just been delivered of one brood, judging from the 

 collapsed ovaries, still contained a few small embryos and ova. Similar 

 conditions were found in specimens of Pseudopcecilia fria. These 

 observations are to be correlated with the observations of Philippi, 

 who noted successive births from a single mating. In other specimens 

 it is common to find a few embryos considerably behind in development, 

 when compared with the average. These probably are the result of 

 later fertilization. The period in which delivery takes place is also 

 variable, since in the same locality specimens are found with the con- 

 tents of the ovary ranging in different examples all the way from small 

 ova to embryos nearly ready for birth. Usually, when taken during 

 the breeding season, all of the mature females from a given locality are 

 pregnant. Occasionally, however, fully mature individuals contain 

 neither ova nor embryos. 



The presence in the ovary at the same time of both ova and embryos 

 in one or two different stages of development seems to have previously 

 been noticed by only one observer. E. G. Boulenger (1912, p. 906) 

 remarked these facts in Lebistes reticulatus, but there is no indication 

 that his observations were based on actual dissection of the ovary. 

 He says, " As breeding goes on all through the year, at least in cap- 

 tivity, the female is in an almost permanently pregnant condition, and 

 within a fortnight of having brought forth a brood (such a period re- 

 presenting the duration of the gestation, at a temperature of over 70°) 

 once more brings a generation into the world. It should be borne in 

 mind, however, that a single impregnation is sufficient for the fertiliza- 

 tion of several broods, the embryos of the second and third generation 

 being already in an advanced condition when the first young are born." 



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