634 PRACTICAL PROBLEMS 



SECTION IV SEX IN MAMMALS 



Temperature and nutrition seem to be controlling factors in 

 many of the lower forms, and when such is the case it is remark- 

 able that in every instance the production of females seems to 

 accompany the more favorable conditions, and that of males 

 the harder or less favorable. 



Among mammals there is little experimental evidence, but 

 that little points to the same general fact as found among lower 

 animals, though the larger animals are manifestly less directly 

 influenced by surrounding conditions. Girou divided a flock of 

 three hundred ewes into two equal lots, one of which was ex- 

 tremely well fed. This lot was served by two young rams ; the 

 other, scantily fed, by two mature ones. The well-fed lot (served 

 by young rams) produced 60 per cent females, the other lot only 

 40 per cent females. 1 The difference in age of the rams intro- 

 duces a second element, but the facts, if true, are significant. 



This is about all that is known of this phase of the question. 

 Experimental evidence seems to indicate that abundant food, 

 optimum temperatures, and generally favorable conditions tend 

 to the production of females ; but when we come to predict the 

 limits to which the rule will apply we must proceed with great 

 caution, confessing that our exact knowledge is exceedingly 

 limited. 



SECTION V THE " ACCESSORY CHROMOSOME" AND 

 SEX DETERMINATION 2 



Certain inequalities between germ cells in respect to the dis- 

 tribution of chromatin matter have long been known. 3 



1 Geddes and Thomson, The Evolution of Sex, p. 51. 



2 Wilson (1906), "Studies on Chromosomes, \\\" Journal of Experimental 

 Zoology, III, No. i, pp. 1-39. Also the following : Beard, The Determination of 

 Sex; Castle (1903), "The Heredity of Sex," Bulletin of the Museum of Com- 

 parative Zoology, XL, 4; McClung (1902), "The Accessory Chromosome. Sex- 

 Determinant?" Biological Bulletin, III, i, 2; Morgan (1904), "Self-Fertilization 

 Induced by Artificial Means," Journal of Experimental Zoology, I, i ; Studies in 

 Spermatogenesis with Special Reference to the Accessory Chromosome, Publica- 

 tion No. 36, Carnegie Institute, Washington, D.C., September, 1905 ; Wilson, "The 

 Chromosomes in Relation to the Determination of Sex in Insects," Science, XX11, 

 564, October, 1905. 8 Wilson, The Cell, pp. 271-272. 



