782 A TEXTBOOK OF PHYSIOLOGY 



developed. It is suggested that, owing to the amputation and dimin- 

 ished nutritive conditions, the indifferent germ cells had developed 

 into male cells. On the other hand, experiments in the breeding of 

 mice have shown that nutritive changes and the age of the parents 

 have made but little difference in the proportion of the sexes. 



That sex in certain cases is largely determined by the conditions 

 of general metabolism is illustrated by the effects which follow castra- 

 tion, by infection with r, parasite, of several varieties of crabs. In 

 all cases the castrated male takes on female characteristics, and 

 even defends the parasite as if he were protecting his eggs. The 

 castrated female shows no sign of altered structure or instinct. It 

 has been suggested, in the case of the .crab, that the parasite alters 

 the composition of the male's blood, which tends to bring about a 

 female condition, which may be followed by the onset of female 

 characteristics, or even the production of female organs from 

 indifferent germ cells. On the other hand it may be an internal 

 secretion effect from the traces of female tissues present in male. 



In support of the view that sex is predetermined in the ovum is 

 the fact that " identical " twins that is to say, twins arising from the 

 same ovum and included in a single chorion are always of the same 

 sex. More conclusive is the fact that, in certain mosses, spores of 

 identical appearances, asexually produced, are predetermined as male- 

 or female-producing elements. In the primitive worm Dinophilus, 

 the large fertilized ova develop into females, the small fertilized ova 

 into males. The same is true for the vine pest Phylloxera, and for 

 the rotifer Hydatina. In certain parthenogenetic invertebrates, such 

 as the Hymenoptera, the unfertilized eggs give rise to males, the 

 fertilized eggs to females. Whether fertile queens or infertile worker 

 bees are developed from female larvae depends on the nature of the 

 food given them. 



As to the influence of the male element, it has recently been shown 

 that certain animals, especially insects and arachnids, produce two 

 forms of spermatozoa. Half the spermatozoa have in their nucleus 

 an odd chromosome, or x chromosome; half have not. In the ova 

 the x chromosome is always present. Union of a spermatozoon con- 

 taining the x chromosome with the ovum produces a female; union 

 of a spermatozoon without the x chromosome produces a male. 



By some, maleness and femaleness are regarded as Mendelian 

 characters, like shortness or tallness. If sex be due to some factor, 

 like the x chromosome, it is possible, on the Mendelian interpretation, 

 that males and females may both be cross-breeds (heterozygous), or 

 that the male alone may be heterozygous, the female recessive, or the 

 female heterozygous and the male recessive. Experiments tending 

 to support the last view have been made upon the currant moth. 



It is asserted that in vertebrates castration suppresses the 

 maleness, but does not induce any expression of female character- 

 istics. On the other hand, the castrated female, while losing her female, 

 characteristics, tends to develop markedly those of the male. Further 

 proof is needed of such a view. 



