CHROMOSOMES, HEREDITY AND SEX. 
507 
have 28, it can hardly be doubted that eggs with 27 give rise 
to females, those with 28 to males. This case is thus exactly 
the converse of the typical examples of au accessory 
chromosome in the male, as seen in the Hemiptera, Orthoptera, 
etc. It is remarkable that in this case the male has one 
chromosome more than the female, although in forms in which 
the spermatozoa are dimorpliic the male has one less. The 
bearing of this fact on theories of sex-determination will be 
referred to ngain later. 
Finally, mention must be made of the conditions found in 
the Hyrnenoptera. In this order parthenogenesis is common, 
but differs from that of most parthenogentic animals in the 
existence of two polar divisions. Most commonly unfertilised 
eggs of Hyrnenoptera give rise to males; when females are 
produced parthenogenetically there is evidence that no 
reduction occurs, either because one or both polar divisions 
are suppressed,^ or because both are equational. No case is 
known in which males are produced from eggs which are 
certainly fertilised, and in all which have been examined the 
male has half the number of chromosomes found in the female. 
The male has a haploid set, the female a diploid. Corre- 
spondingly, in all cases examined,^ one maturation division of 
the spermatocytes is suppressed, so that the spermatocytes 
contain the same (haploid) number as the spermatogonia.’^ 
Nachtsheim (46) brings these phenomena into line with the 
facts known about sex-chromosomes by the suggestion that 
^ L. Doncaster, “ G-ametogenesis of the Gall-fly Neiiroterns lenti- 
cular is,” ‘Proc. Roy. Soc,,’ b, Ixxxiii, 1911, p. 476. It should be noted 
that in N e n r o t e r n s, as in Morgan’s case of P h y 1 1 o x e r a, it is predeter- 
mined which eggs shall undergo reduction and become males, and which 
eggs shall suppress the maturation divisions and become females, since 
all the eggs laid by any one female l)ehave in the same way. 
^ E. g. in the bee, F. Meves, ‘ Arch mikr. Anat.,’ Ixx, 1907, p. 414; H. 
Nachtsheim, ‘ Arch. f. Zellforsch.,’ xi, 1913, p. 169; in Neiiroterns, L. 
Doncaster, ‘ Proc. Roy. Soc.,’ b, Ixxxii, 1910, p. 88. Several other forms 
give concordant results. 
Armbriister, L., ‘ Arch. f. Zellforsch.,’ xi, 1913, p. 242, interprets his 
observations on Osmia differently ; his figures and discussion are not 
convincing. 
