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THE AMEBIC AN NATURALIST [Vol. XLIV 



Chromosomes and Sex. 

 In recent years two converging lines of evidence have 

 led the most sanguine of ns to hope that before long we 

 shall know, in part, at least, the answer to the outstanding 

 riddle of the ages, the determination of sex. These two 

 lines of research are the experimental study of sex in- 

 heritance, and the microscopic study of the germ cells. 

 Both have led to the conclusion that sex is not, as has 

 been so often supposed, determined by the external con- 

 ditions to which the parents, or the eggs, or embryos are 

 subjected, but that there exists an automatic process in 

 the egg and sperm by which equality of the two sexes is 

 attained. 



Before I bring this evidence forward, I must stop for 

 a moment to point out how the idea that sex is deter- 

 mined by external conditions arose, for this view is by no 

 means defunct. In fact it is a widely current belief at 

 the present time. One might, in fact, appear to justify 

 himself in holding such a view, not only by quoting the 

 names of those who have advocated it or still maintain 

 it, but even by referring to a considerable number of ex- 

 periments that have been claimed to be in favor of such 

 an interpretation. 



Landois stated in 18(57 that he could produce male or 

 female butterflies at will by regulating the amount of 

 food of the caterpillars. Similar statements were made 

 later by others; but the futility of the experiments be- 

 came manifest when it was found that the character of 

 the sexual organs is already determined when the cater- 

 pillar hatches from the egg. 



It has been claimed that the sex of the frog could be 

 determined by the quantity of food, or by the kind of 

 food supplied to the tadpole. More extensive work has 

 disproven completelv this statement also. 



Statistical studies, especially those of Diising, are 

 often cited to show that in man, and in some of the 

 domesticated animals, the nourishment of the parents 

 affects the sex of the offspring. But here again other 

 statisticians have found evidence of the opposite results. 



