THE DETERMINATION OF SEX 571 



or induced by external factors ; and in at least one case of 

 sexual reproduction (that of Dinophilus apatris, according to 

 Malsen) the ratio between male and female eggs may thus 

 be somewhat modified. Nevertheless, most of the exact re- 

 searches of recent years strongly indicate, if they do not fully 

 prove, that in dioecious organisms, when once the egg is fertilised 

 its sex is already fixed ; and they show, further, that in some 

 cases even the gametes can be distinguished as male-producing 

 and female-producing (I do not say male or female) before their 

 union. 



Some of these facts have long been known. In the par- 

 thenogenetic reproduction of certain phylloxerans and rotifers 

 there are large and small eggs, which produce respectively 

 females and males. The same is true of the sexual eggs of 

 Dinophilus apatris, and has been asserted of several other 

 cases. More recently, researches by the Marchals, Strasburger 

 and Blakeslee demonstrate that the spores of dioecious mosses 

 and liverworts (Blakeslee finds analogous phenomena in some 

 of the fungi) are already predestined as male-producing and 

 female-producing, probably in equal numbers ; while the work 

 of Correns and Noll indicates that the same is true of the 

 pollen-grains of certain dioecious flowering plants. Apart from 

 this direct evidence, there is a considerable and increasing- 

 body of data — such as the similar sex of double monsters 

 and of multiple embryos derived from the same egg — to show 

 that even when the sex of the germ-cell escapes observation 

 by the eye, it is already determined at the beginning of 

 development. In the famous case of the honey-bee the eggs 

 produce females if fertilised, males if unfertilised, and the 

 same appears to be true, or at least the rule, in the wasps, 

 ants and certain other Hymenoptera. 1 



On the experimental side it has been made known by 

 crossing experiments that the sex-characters are in certain 

 cases transmitted according to a definite law that is independent 

 of external conditions and is at least nearly akin to Mendelian 

 heredity. I need not review a subject that has been so recently 

 and ably discussed by Bateson. 2 It need only be recalled that 



1 The evidence in the case of the bee seems overwhelmingly strong, despite 

 the fact that the Dzierzon theory has been disputed. In the ants and wasps the 

 case is not so clear. 



3 MendePs Principles of Heredity, 1909. 



