CHROMOSOMES AND SEX-DETERMINATION 401 



The evidence just given seems to prove beyond the possibihty 

 of reasonable doubt that all zygotes in the all-female families 

 are female, and that these families do not arise by the death 

 of male zygotes. The problem then presents itself whether 

 all eggs of these families before fertilization contain twenty- 

 seven instead of twenty-eight chromosomes. In the letter to 

 ' Nature ' referred to I announced that I found evidence that 

 this was not so, and further work has contirmed this conclusion. 

 In 1914 I preserved eggs from four pairings, of which the 

 eggs subsequently laid yielded only females. The data with 

 regard to these families are as follows, excluding the eggs 

 preserved for microscopic examination : 



It will be noticed that in families 14.9 and 14.28 over two- 

 thirds of the eggs kept for rearing were reared to imagines 

 (or in 14.28, thirty-six imagines and nine pupae). The eggs 

 of these same families preserved for microscopic examination 

 gave the following chromosome counts in the equatorial plates 

 of the second maturation division. 



14.9. In the inner spindle 27, in the outer 28 — four cases 

 recorded as ' good '. 

 In the inner spindle 27, in the outer 28 — two cases recorded 

 as ' probable '. 



trace of it in the manuscript unless it be the following, which I find on 

 a page of note-paper along with the manuscript: '.Summaries to 1916 

 show that all-female families are not due to mortality, due to " lethal" or 

 other causes, of male. -Apart from such cases as 14.16, and 14.18 (37 and 

 58 females from 47 and 63 eggs),* the fact that in all-female families in 

 which over 50 per cent, of the eggs are reared to imagmes there are twice 

 as many females per cent, of eggs (64-6 per cent.) as compared with per- 

 centage of females in bisexual families (32-3 per cent.) proves this.' 



See table given on previous page, 1914.16 and 1914.18. 



