L. DONCASTER 9 



number from the normal. It should be mentioned that in the males 

 of '12.25, almost constantly some of the spermatocytes are binucleate 

 or more rarely have four nuclei, and these give rise to binucleate or 

 quadrinucleate spermatozoa. I have not traced the stage at which this 

 condition arises. 



It would be premature to discuss at this early stage the meaning of 

 the observations described above. It appears probable that all the 

 females of a unisexual family have 55 chromosomes instead of 56. 

 Those which have only female offspring must therefore transmit only 27 

 to each of their offspring, and one chromosome is thus not accounted 

 for. An attempt will be made when the moths hatch to find out 

 whether one chromosome is eliminated at the maturation of the egg, 

 and until that point is decided it is useless to speculate on the relation 

 of the chromosome number to sex-determination. 



There is one point of considerable theoretical importance, however, 

 which should be referred to. A grossulariata female which h{i« only 

 female offspring does not transmit the gross, fixctor to any of them — the 

 mother receives it from her male parent, but does not transmit it to her 

 daughters, and since in this case she has no sons, she does not transmit 

 it at all. In some way, therefore, it is eliminated, perhaps most 

 probably at the maturation of the Qgg. She also receives 28 chromo- 

 somes from her male parent, but transmits only 27 to her offspring; 

 one chromosome must therefore be eliminated. It seems, therefore, 

 highly probable that this chromosome, which is not transmitted by the 

 female whose offspring are all females, may be the determiner or bearer 

 of the grossulariata factor. It is tempting also to suggest that this 

 chromosome is a sex-determiner — that if it is received from the mother 

 and a corresponding one from the father, the zygote becomes a male, 

 and if it is received from the father only, it becomes a female. A diffi- 

 culty arises, however, from the fact that some females at least, whose 

 mothers belonged to unisexual families, have 56 chromosomes, as has 

 been shown in the case of family 12. 25. It is probably best, therefore, 

 to reserve further consideration of this part of the subject until our 

 knowledge of the, facts is more complete. 



Summary. 



1. Families consisting wholly of females have appeared in six 

 successive generations of Abraxas grossulariata ; they may consist of 

 var. lacticolor, of grossulaiiata, or of equal number of each, accoixiing 

 to the constitution of the male parent. 



