L. DONCASTER 19 



in subsequent generations. Sterility is not much more frequent in 

 all-female fiiniilics than in normal families. 



2. In counts of mitotic figures in ovaries of more than fifty females 

 descended from unisexual families, 55 chromosomes were found in every 

 case (with one exception in family '12.25 ; see No. 5 below). About 

 twenty of these figures wore so good that doubt about the number is 

 hardly possible, and in several the number 55 is absolutely certain. The 

 number 55 was also counted in oogonia of one wild female, but in three 

 other wild females and in four pedigree individuals not descended from 

 the all-female producing stock there were clearly 56. 



3. Males, whether of the stock in which the female has 55 or 56, 

 always have 56 spermatogonial and 28 secondary spermatocyte chromo- 

 somes. In some cases, more commonly in the stock in which the female 

 has 56 oogonial chromosomes than in that in which it has 55, two 

 chromosomes in the secondary spermatocytes are in contact, but it is 

 almost certain that there are never really 27. A single figure with 

 27 in the first spermatocyte was found, but many others in the same 

 testis had 28. 



4. Both equatorial plates of the second polar mitosis in eggs of 

 females which have 56 oogonial chromosomes, have 28. Eggs of females 

 with 55 in the oogonia have 28 chromosomes in one polar equatorial 

 plate, 27 in the other. In some families it is equally common to find 

 27 in the inner or the outer plate, and some of these are known to be 

 bisexual families. In two, however, there is a considerable excess of 

 eggs with 27 in the inner plate, and these are known to be families 

 with excess of females. In one family, in which females are in excess, 

 a majority of the figures counted show 28 in the inner plate. It is 

 suggested that the excess of females in this family is due to mortality 

 of the males. The facts as a whole make it clear that eggs which 

 eliminate the 28th chromosome become females, those which retain it, 

 males; Abraxas thus shows a condition which is the converse'of that 

 described in most other insects. 



5. In the previous paper it was recorded that one female of family 

 '12.25 had 56 chromosomes (only one figure can be counted). Other 

 females of the same brood have clearly 55. In the same brood there 

 was failure of sex-limited transmission of the grossuhmata character 

 in two cases, in such a way that the grossuhmata mother transmitted 

 this character to two of her daughters (out of a total of 16), instead of, 

 as normally happens, only to her sons. It is suggested that this may 



2—2 



