108 



Mr. L. Doncaster. 



[Sept. 21, 



into their constituents, so giving the same number in male and female 

 body-cells, as is observed. In the male Bee a single S determinant would 

 be present in the spermatocytes : this would pass into one spermatid, the 

 other being left with none (O). The latter spermatids are the "male polar 

 bodies " which degenerate. All the spermatozoa thus contain the ^ factor, 

 their presence in the egg causes the ? factor to remain in the polar divisions 

 and the fertilised egg is thus ? and becomes a female. 



This assumption that the presence of a spermatozoon in the egg causes a 

 difference in the maturation process, and leads to the removal of the male 

 instead of the female sex-determinant seems improbable at first siglit, but 

 there are considerations which reduce its improbability on further examina- 

 tion. If both eggs and spermatozoa are commonly of two kinds, the 

 hypothesis of selective fertilisation cannot be avoided, and if there is some 

 definite attraction between a c? -bearing and ? -bearing nucleus, the presence 

 of a -bearing spermatozoon (or male pronucleus) in the egg may attract the 

 ? determinant to the inner end of the maturation spindle, although in an 

 egg with no spermatozoon it would be expelled. Clearly some such attractive 

 force exists, the nature of which is at present unknown, for otherwise in the 

 saw-flies the male pronucleus might conjugate equally often with one of the 

 polar nuclei, which to all ap])earance exactly resemble the egg-nucleus, instead 

 of with the egg-nucleus itself. If it is assumed that, in cases where tlie egg 

 matures before the entrance of the spermatozoon, the sex-determinant 

 remaining in the egg attracts only one of the two kinds of spermatozoa, it 

 does not seem a very im2:>robable extension of the hypothesis that the presence 

 of one kind of spermatozoon in the unmatured egg may cause tlie expulsioji 

 of the corresponding sex-determinant at the maturation division. 



In Wasps and Ants* the spermatogenesis takes place much as in the Bee, 

 except that two apparently similar spermatids are formed by the spermatocyte 

 division, each of which becomes a spermatozoon. Their spermatogenesis thus 

 closely resembles that of Ncuroterus, and the most probable assumption seems 

 to be that tv^o kinds of .spermatozoa are formed, and © respectively, but 

 that only the J* -bearing are functional. They would tlius be exactly com- 

 parable with the Bee, except that the reduction of the useless spermatozoa is 

 not cari'ied so far. Other possibilities are of course not excluded, e.g., that 

 the S determinant divides and passes into l)oth spermatids, or that, as in 

 Nmroterm,i\\wX\o\VA\ and © spermatozoa occur, and therefore that among 

 the offspring of the female wliich founds tlie nest there may bo two kinds of 

 female individuals produced, one of which would contain no S determinant. 

 In ants and wasps the workers an; not sharply separated from the (jueens 

 * Meves and Diiesberg, ' Arch. Mikr. Aiiat.,' vol. 71, 1908, p. 672. 



