SEX AND SEXUAL CHARACTERS 



By J. T. CUNNINGHAM, M.A. 



In his paper on the Determination of Sex in the July number 

 of this Journal, Mr. Doncaster has given an account of recent 

 researches and speculations from the Mendelian point of view ; 

 but there are other lines of research equally (perhaps even more) 

 important to which he has not referred. To him and to others 

 who are absorbed in Mendelian investigations, a Mendelian 

 hypothesis which agrees with the results of certain experiments 

 in cross-breeding seems to have the validity of a complete 

 explanation ; whereas a little consideration will show that there 

 are many other facts which cannot be brought within the 

 Mendelian formula — some because they are inconsistent with 

 it, others because they are altogether beyond its scope. 



According to the Mendelian view, sex is a property of the 

 gametes — that is to say, each gamete bears one sex only ; it has 

 the property of developing either into a female or into a male, 

 but not into both. Thus an ovum may be either male or female, 

 and similarly a spermatozoon may carry either sex. The latest 

 Mendelian theory of sex, the exposition of which is the main 

 object of Mr. Doncaster's paper, and is also explained and 

 illustrated in Bateson's Mendel's Principles of Heredity, 1909, is 

 that male individuals in certain animals are homozygous with 

 regard to sex, being of the constitution S3 and producing 

 only male-bearing spermatozoa, while female individuals are 

 heterozygous, being of the constitution ? & and producing 

 male-bearing and female-bearing ova in equal numbers. Thus 

 at fertilisation the ovum may be male or female, but the sperm 

 is always male ; and when the ovum is female it develops 

 into a female animal, "femaleness" being always dominant. 

 This hypothesis seems to explain satisfactorily the curious 

 heredity of certain characters in Lepidoptera and some birds ; 

 but when it is stated that confirmatory evidence of its truth 

 is afforded by the effects of castration in Vertebrates, while the 

 most important recent discovery concerning those effects is not 

 mentioned, the statement requires careful examination. 



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