CASTLE: THE HEREDITY OF SEX. 191 
sexual gametes, and the appropriate subject for investigation is the law 
or laws of its inheritance, rather than the visionary external causes of 
SeX. 
That sex is borne by the egg is shown clearly by the case of partheno- 
genetic animals, which without the intervention of a male produce young 
of both sexes. That the spermatozo6n also bears sex is manifest in the 
case of animals like the honey-bee, for the egg of the bee, if unfertilized, 
invariably develops into a male, but if fertilized, into a female. We 
have, therefore, specific reasons, in addition to the general ground of the 
equivalency of egg and spermatozoén, for supposing that sex is a char- 
acter possessed by every egg and spermatozoén. 
In the following pages I have attempted to formulate certain of the 
laws of sex-heredity, an attempt which is greatly aided by recent devel- 
opments in our knowledge of heredity in general. 
TL. Principles of Heredity Applicable to Sex. 
1. MeENDEL’s Law. 
Perhaps the greatest discovery ever made in the study of heredity is 
what is commonly known as Mendel’s Law. Bateson and Saunders (: 02) 
in a recent paper suggest that sex may be inherited in accordance with 
that law. In the light of this suggestion certain phenomena of sex. are 
in this paper examined, and found to have their almost perfect parallels 
in recognized Mendelian phenomena. In consequence we get a new 
point of view from which to study the phenomena of sex, and many of 
its long-time mysteries find ready explanation. The basic principles 
of Mendel’s law are two, the principle of dominance and the principle 
of segregation. 
(a) The Principle of Dominance. When there unite in fertilization 
two gametes, one of which bears one of a pair of alternative characters, 
while the other gamete bears the other character, it often happens that 
the zygote formed manifests only one of the two characters. This char- 
acter may be called: the dominant one. The other character becomes 
latent, or recessive, and is first seen in the uext generation of offspring. 
For example, when white mice are crossed with wild gray mice, all the 
offspring are gray, that character being dominant, white recessive. 
White mice are never obtained in the first hybrid generation, but upon 
breeding of the primary hybrids cnter se, both white and gray offspring 
are obtained approximately in the ratio, 1: 3. 
