CASTLE : THE HEREDITY OF SEX. 191 



sexual gametes, and the appropriate subject for investigation is the law 

 or laws of its inheritance, rather tlian 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 spermatozoon also bears sex is manifest in the 

 case of animals lilce 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, iu addition to the general ground of the 

 equivalency of egg and spermatozoon, for supposing that sex is a char- 

 acter possessed by every egg and spermatozoon. 



In the following pages I liave 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. 



III. Principles of Heredity Applicable to Sex. 



1. Mendel's Law. 



Perhaps the greatest discovery ever made in the study of heredity is 

 what is commonly known as Mendel's Law. Eateson 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 Mendolian 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 sejrrerration. 



(a) The Principle of Dnniiiance. When there unite in fertilization 

 two gametes, one of wdiich 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 tlie two characters. This char- 

 acter may be called the dominant one. The other character becomes 

 latent, or r-ecessive, and is first seen in the next genei'ation of offspring. 

 For example, when white mice are crossed with wild gray mice, all the 

 offspring ai-e gra}', that character being dominant, white recessive. 

 White mice are never obtained in the first hybrid generation, but upon 

 breeding of the primary hybrids inter se, both white and gray offspring 

 are obtained approximately in the ratio, 1 : 3. 



