THE DETERMINATION OF SEX 637 



It should be said in this connection, too, that in certain species 

 the accessory seems always present, in both spermatozoa as 

 well as in all female cells, but that when this is the case the 

 accessories are distinguished by some kind of qualitative differ- 

 ence not understood, but that gives to two of the spermatozoa 

 of each group of four a different character from the other two. 



If, therefore, it shall appear that all female cells, after extru- 

 sion of the polar bodies, are in possession of this accessory chro- 

 mosome, whatever its peculiar quality, and if, out of each group 

 of four spermatozoa arising from a single spermatocyte, two are 

 in possession and two are destitute of this accessory, then we 

 have in the spermatozoa themselves a very evident fundamental 

 cause of sex determination, and, as the numbers are equal, under 

 the law of chance the sexes should be equal, as in fact they 

 practically are. 



Here in truth would seem to be a fundamental cause of sex 

 determination. Whether it is operative in all forms of life or only 

 in certain species, it is yet too early to even speculate. A fertile 

 field of inquiry is here opened up, and the near future may be 

 expected to afford important additional data on this most 

 difficult subject. 



Summary. There are various circumstances that appear to 

 influence the sex of offspring. These seem, in some cases, to be 

 connected with nutrition, and, in others, with the inherent nature 

 of the germ. The present state of knowledge is insufficient to 

 solve the problem of sex differentiation, but it is safe to say that 

 none of the traditional beliefs are warranted by the known facts. 



ADDITIONAL REFERENCES 



CHANGING SEX IN PLANTS. Tropical Agriculture, 1903, pp. 789-790. 

 CHROMOSOMES IN RELATION TO SEX DETERMINATION IN INSECTS. 



By E. B. Wilson. Science, XXII, 500-502. 

 Do SEEDLESS FRUITS REQUIRE POLLINATION? Experiment Station 



Record, XV, 1080. 



EXPERIMENTAL ZOOLOGY. By T. H. Morgan. Chapters XXIV-XXVII. 

 EXPERIMENTS IN HEREDITY AND SEX DETERMINATION IN MOTHS. 



Report of the British Association for the Advancement of Science, 



1904, p. 594. 



