Manchester Memoirs, Vol. Ixii. (191 7), No. 2 21 



This hypothesis of sex Was developed; to account for the 

 phenomena observed in the sex determination of Abraxus grossu- 

 lariata and in Neuroterus lenticularis. 



In Neuroterus lenticularis after spermatogenesis there would 

 be two kinds of sperms formed, one kind possessing the male 

 determinant $ the second lacking it 0. Thus after fertilisation 

 there will be two types of zygote, one male-producing, <J ? 

 the other female-producing, $0. At maturation the $ ? type wili 

 expel the female determinant and develop into a male, while |the 

 other, which undergoes no maturation, will produce a female. 



Male prod, female. 



6 ? 



Reductive Division 



Egg 6" 



Males. 



Spermotozoa Spermatozoa 



6 



Female prod, female. 



? 



No reduction. 

 Egg? 



Sexual females. 



Egg- 



? 



The female determinant is transmitted to all the eggs of the 

 sexual females of the Summer generation, because the element 

 remains in the pronucleus of the egg Tat maturation. 



This suggestion of Doncaster, though explaining many phe- 

 nomena, is highly speculative, as he admits, and must L , I think, 

 be treated with due reserve. 



The foregoing theories have all had their origin in the 

 assumption that sex determinatijon is a qualitative phenomenon, 

 and that the eggs and spermatozoa carry a factor or determinant, 

 which causes the production of either male or female. 



Another theory propounded by Wilson and lately assumed 

 by Castle presumes that sex production is brought about by a 

 quantitative action of the germ cells. In an earlier part of the 

 paper it was stated that in many animals the chromosome 

 number in the male was found to be less than in the female, 

 thus in Protenor the X element is single in the male, double in 

 the female. 



According to Wilson and Castle the determinants are not 

 male or female respectively, but the female is quantitatively 

 greater in some substance, probably a form of nuclear matter, 

 than the male; thus " femaleness is due to maleness plus some- 



