The ( ellular Basis [63 



there were constantly 48 chromosomes in the spermatogonia of 

 a white man, thus indicating the presence of an AT pair of 

 chromosomes in the male and an XX pair in the female. 



The most recent work on the number of chromosomes in man 

 is by Hoy and Muller, who have kindly permitted mc to refer to 

 their work in advance of its publication. In cells of the kidney 

 tubules of an adult male there arc clearly 47 chromosomes, the 

 number observed by Winiwarter in the spermatogonia. Amidst 

 these conflicting results it is not possible at present to say how 

 many chromosomes are present in man, and of course it is un- 

 certain whether in this case sex is determined by the chromo- 

 somes. 



Sex a Mendelian Character- — Correlations between chromo- 

 somes and sex have been observed in more than one hundred 

 species of animals belonging to widely different phyla. In a few 

 classes of animals, particularly Lepidoptera and birds, the evi- 

 dence while not entirely convincing seems to point to the fact 

 that two types of ova are produced and but one type of sperma- 

 tozoa ; but the general principle that sex is determined by the 

 chance union of male-producing or female-producing gametes is 

 not changed by such cases. 



Sex, therefore, appears to be inherited, that is, its factors or 

 determiners are present in the germ cells ; it is a Mendelian 

 character in which the female is usually homozygous for sex 

 while the male is heterozygous. Consequently in the formation 

 of the gametes every egg cell received one sex determiner, while 

 only one-half of the spermatozoa receive such a determiner, the 

 other half of them being without it. If then an egg is fertilized 

 by a sperm with one of these determiners a female is produced, 

 if by a sperm without the sex determiner a male results. This 

 is graphically illustrated in Fig. 57 in which X represents the 

 sex-determiner, which is duplex in the female and simplex in the 

 male, and the chance unions of male and female germ cells yields 

 females (AA r ) and males (XO) in equal numbers. Of course 

 there is no such thing as a "sex-producing" chromosome, sex being 



