A SOMATIC MITATION IN DHOSOPHILA MKLANOGASTER 157 



non-curvi'd daughters and w' v f sons, unhappily (Miough the off- 

 spring obtained in this cross (C 2702; p. 150) proved that the mosaic, 

 who died by accident shortly afterwards, had not fertilized any of 

 these control females. 



It is very unlikely indeed that the possibility here mentioned 

 has actually been reali/A'd. Not only are, when binocular is used, 

 mistakes as to the virginity of the females after some training so 

 rare as to be practically excluded. But also the result of the crosses 

 speak against it. Thus, the striking I : 1 ratio between bl pr cu and 

 Sk cu individuals in C 2702 demonstrates that the possibly non-vir- 

 gin female must have been fertilized by a 67v cu male, like the mosaic, 

 though bl pr cu males were in the stock bottle equally numerous. 

 Moreover, the ratio between the non-singed^ and the singed' grandsons 

 speaks against the validity of this explanation, since they indicate 

 that the number of eggs previously fertilized and laid by the supposed 

 non-virgin female must have been practically equal to the total num- 

 ber of eggs later fertilized by the mosaic. Such a coincidence is 

 very unlikely indeed. 



Thus, the author does not doubt that all tlie females used in 

 the test were virgin, but it must be granted, that the early death of the 

 mosaic caused a gap in the genetic demonstration of this fact. 



It might be thought that the apparent inconsistency between the 

 result obtained by the test of the mosaic and the one derived from 

 the study of gynandromorphs might be due to the special conditions 

 present in the latter. It was thinkable that in the sex-mosaics anläge 

 for the formation of both female and male gonads may l)e present 

 in the early embryonic stages, but that one of the two is suppressed 

 in the course of the later development, leaving the other to form both 

 gonads. However, this explanation seems not very likely, since we 

 know from Bridges' studies of triploid intersexes (1921) that one 

 testis and one ovary may in Drosophila he present at the same time 

 in the adult individual. 



It is known that in some insects the germ cells of the ovary or 

 testis arise from a single cell (see Morgan and Bridges, 1919), but 

 that in other insects the gonads develope from a group of cells. In 

 the latter case it would be possible for some of the germ cells to 

 have arisen from one of the first two segmentation nuclei and some 

 from the other. It should in this connection be recalled that several 

 bilateral gynandromorphs are known, for instance in Lepidoptera, 

 in which both testes and ovaries were present. 



