18 ('/int/ii,o,soinefi and Sex in Abraxas 



Uii this hypothesis, there should of course be ;is many exceptional 

 lacticolor males as (jrossulariata females, unless, as is possibli', when ^1/ 

 and G separate, M always goes into the polar nucleus. In any case, 

 since only 21 males were reared, the absence of lacticolor males from 

 the family is not surprising'. 



Since only one oogonial figure with 56 was found, and this is not 

 entirely unequivocal, it is obviously impossible to found any important 

 theoretical conclusions on the case, but the fact that the abnormal 

 chromosome number was recorded before the existence of exceptional 

 transmission of the ijros.'i. character was suspected, makes some discu.ssion 

 of the matter justifiable. 



It should be mentioned that two other exceptions occurred in the 

 moths hatched in 1913, for which I can offt'r no explanation. In family 

 '12.40, of which the parents were lacticolor $ and wild tjru.ssulariata </, 

 among 19 gross, males and 14 gross, females, there were one male and 

 one female lacticolor'-. 



Summary. 



1. The families reared in the year 1912-13 in general confirm the 

 conclusions given in the former paper on the inheritance of a tendency 

 to produce all-female amilies in Abraxas grossidariata. About half 

 the females belonging to such families usually have only female off- 

 spring, but the 1912 inatings show that they may sometimes have a 

 few males amctng a very lai'ge excess of females. The tendency to 

 produce only females is thus variable in intensity, and ranges through 

 varying degrees from equality of the sexes to complete absence of males. 

 In families in which males are produced, evidence is given that there is 

 no important difference in the sex-ratio between the offspring of the 

 earlier and later eggs laid by the mother. When there is great excess 

 of females, there appears to be a tendency for this excess to diminish 



' Since this was written, C. B. Bridges has published a hypothesis to account for excep- 

 tions to sex-limited transmission in Drosopliila. (Journ. Exp. Zool. Vol. xv. 1913, p. 587.) 

 He suggests that exceptionally the sex-chromosomes may fail to separate at the maturation 

 division, and both pass into one gamete, so that gametes with two sex-chromosomes, and 

 others with none, would be provided. If a spermatozoon with no MG chromosome 

 fertilized an egg with one, a iirost:idariutu female would result. In this connexion it may 

 be noted that one primary spermatocyte with only 27 chromosomes was found in a male 

 of '12.7, the father of which was brother to the male parent of '12.25. 



2 A female hictirolor could arise from this mating from a spermatozoon lacking the 

 sex-chromosome, according to Bridges' hypothesis mentioned in the footnote above, but it 

 is impossible on this hypothesis to account for a male lavticolor in this case, unless 

 'non-disjunction' occurred simultaneously in the egg. 



