Manchester Memoirs, Vol. Ixii. (191 7), No. 2 19 



paper, however, that the parthenogenetic eggs of the Psychidae 

 have been studied by Dr. Seiler, whose paper is in the press. 



ChalcididcE. — In this group of insects we find examples o? 

 polyembryony. Silvestri studied Litomastix truncatellus; the egg 

 gives rise to a number of cell /clusters, each of which develops 

 into a larvae. A point of interesjt is that each individual which 

 arises from the egg is of the 'same sex. If the original egg 

 was fertilised females are produced, if unfertilised only males 

 appear. iSilvestri was also able to examine the maturation 

 divisions of the ovum, and found that in both the partheno- 

 genetic eggs and the Fertilised ones they were the same. Here 

 then we have an excellent example of sex determination by fer- 

 tilisation. Further, as the maturation divisions of both kinds of 

 eggs are of the normal order, thlq males will arise from eggs 

 having the reduced number of chromosomes, and will therefore 

 be like those of the bee and Hydatina senta. 



Parthenogenesis and "Sex. 



If a summary is made of the preceding cytological facts it 

 will be found that the types of maturation in parthenogeneisfe 

 are two : — 

 (A.) iOne maturation division, which is not reductive, as in the 



Ostracoda. 

 (B.) Two maturation divisions :■ — 



(1) Chromosome reduction as in the Ants, Bees, Wasps, etc. 



(2) No chromosome reduction, both divisions being equational, 



as in Rhodites rosae, etc. 



A third type described by Brauer in x^rtemia we have seen 

 to be probably incorrect. 



Before proceeding to a discussion as to how the cytological 

 study of parthenogenesis affects the problem of sex determina- 

 tion, it will be of advantage to enumerate the more important 

 theories regarding sex. Castle (1903) propounded the theory 

 that the male and female were heterozygous for sex, and that at 

 maturation the male or female elements were eliminated with 

 the polar bodies in the case of the female, and were segregated 

 from one another at spermatogenesis in the male. Selective fertilisation 

 was also assumed to occur, so that only male-producing spermatozoa 

 could fertilise female ova, and only female -producing spermatozoa 

 could conjugate with male ova. The zygote thus produced must 

 of necessity be heterologous and the resulting sex was male or 

 female according as to which was the dominating element. 

 There are many objections to this view, but taking one case, 

 that of the bee, we at once encounter difficulties. As the males 

 are produced from the unfertilised eggs which have undergone 



