THE FACTORS WHICH DETERMINE SEX 635 



been shown by Guyer,i who has investigated the matter for 

 the chicken and guinea-fowl.^ (See footnote^, p. 657.) 



The manner in which the spermatozoon with the accessory 

 chromosome (or chromosomes) produces a female is stiU an 

 open question. It is often supposed that the accessories are 

 themselves the carriers of those hereditary characters which 

 distinguish the female sex, but it may be that the result is due 

 simply to the greater amount of chromatin carried into the egg 

 in the process of fertihsation. " The result," as Morgan remarks, 

 " is similar to that of the bee, in the sense that the fertihsed egg 

 contains more chromosomes than the unfertihsed, and produces 

 in consequence the female.^ In the absence of aU knowledge as 

 to how the greater quantity of chromatin produces a female, one 

 is tempted to assume that the result is reached through assimi- 

 lative changes that take place in the early cells, and there is some 

 evidence in favour of the view that one of the main functions of 

 the chromatin is to carry on the assimilative processes in the cells." 

 Morgan has shown further that in Phylloxera, in which all 

 the fertilised ova become females, the " male " spermatozoa 

 are rudimentary.* 



The theory that there are two kinds of sexually differentiated 

 ova has also been advanced. In support of this contention it 

 has been pointed out that in Hydatina senta, Phylloxera, and 

 Dinofhilus apatris, there are two sizes of eggs, and that in each 

 case the large eggs produce females and the small ones males. 

 It is not clear, however, whether the size determines the sex, 

 or the sex controls the size, but Beard says : "As the size of 

 the egg will naturally be attained during the oogenesis, it would 

 seem to follow, that here the destination of the oogonium must 



' Guyer, "The Spermatogenesis of the Domestic Chicken," Anal. Anz., 

 vol. xxxiv., 1909 ; "Guinea-fowl," Anat. Am., vol. xxxiv., 1909. 



' So also in the Nematode Heterakis and probably also in Ascaris (see 

 Boveri and Gulick, Arch. f. Zellforsch, vol. iv., 1909). 



' It is said that in the process of spermatogenesis in the drone one of the 

 maturation divisions is suppressed, a fact which suggests that only half the 

 normal number of chromosomes is present in the cells (Meves, Arch. f. Mikr. 

 Anat., vol. Ixx., 1907). 



* Morgan, "The Production of two Kinds of Spermatozoa in PhyU 

 loxerus," &o., Proc. Soc. Exp. Biol, and Med., vol. v., 1908 ; " Sex De- 

 termination and Parthenogenesis in Phylloxera and Aphids," Science, 

 vol. xxix., 1909. 



