534 EVOLUTION, HEREDITY, EUGENICS 



Miss N. M. Stevens and E. B. Wilson, working independently 

 on insects, and Boveri, working on sea-urchins, found that all of the 

 eggs at maturity have one extra or accessory or so-called " X- 

 chromosome." The sperms are of two types, one-half containing 

 the X-chromosome and the other half lacking it. Wilson clarified 

 matters in 1905, showing that the female has in each of her body cells 

 one more chromosome than the male, her chromosome groups con- 

 taining two X-chromosomes, and those of the male containing but 

 one^ while other chromosomes are distributed identically in the two 



sexes. 



Following some earlier work by others, faulty in technique. Von 

 Wini water demonstrated in 191 2 that in man there are 48 chromo- 

 somes in the female and 47 in the male. Oogenesis results in the 

 appearance of 24 chromosomes in each matured egg (23 plus X); 

 but after spermatogenesis, one-half the sperms have 23 plus X, and 

 the other half have only 23. The egg fertilized by the sperm with 

 the X-chromosome develops into a female, while the other type of 

 sperm without an accessory chromosome produces a male at fertili- 

 zation. Painter has also found the Y-chromosome, and concludes 

 that the male has 46 plus X, plus Y; and the female has 46 plus 2 X. 

 The Y-chromosome has apparently no significance except as the 

 bearer of somatic characters. 



Goldschmidfs Enzyme Theory of Sex Determination. — Gold- 

 schmidt has attempted to reconcile the fact that the gonads pro- 

 duce hormones which apparently under certain circumstances are 

 able to override the influence of the chromosome constitution, 

 producing intersexes or even reversing the sex completely. 



Goldschmidt suggests that the X-chromosome carries the gene 

 (factor) of an enzyme-producing character which determines female- 

 ness, while the Y-chromosome, or possibly the cytoplasm, carries 

 the gene of a male-determining enzyme. In the fertilized egg with 

 two X-chromosomes, the female enzyme is present in double 

 quantity and produces a female. If but one X-chromosome is 

 present, the cytoplasm (or possibly the Y-chromosome) produces an 

 enzyme which " overpowers " the female producer and a male 

 results. Goldschmidt and others have stressed the point that the 

 variability of intersexual types depends on the degree of strength 

 of the two sex-producing factors or enzymes, these varying in speed 

 of action. (See Goldschmidt, R., 1916, Science, n. s., vol. 43, p. 98.) 



