254 Heredity and Eugenics 



bearers of that which conditions the characteristics of the 

 subsequent generation. Recent cytological studies, how- 

 ever, have demonstrated that the early conception of 

 equality in the distribution of the chromosomes is not 

 entirely true, but that there is a regular and unequal dis- 

 tribution of the chromosomes which occurs in many, if 

 not all animals, producing in some two classes of ova, in 

 other instances two classes of spermatozoa. 



These chromosomal differences in some unknown manner 

 are now generally admitted to be associated with the 

 determination of sex; hence the "accessory chromosomes" 

 which go to make chromosomal differences in the germ 

 cells are regarded by some as sex determinants. That they 

 are sex determinants in the sense in which "determined" 

 has been used is not proven. The results obtained by 

 Morgan in Phylloxera seem crucial and show that the extra 

 chromosomes are an accompaniment of differentiation, and 

 not the cause thereof. At any rate it is definitely proven 

 that the existence of the accessory chromosomes represents 

 a definite difference in the qualities and constitution of the 

 germ cells, and thus gives in gametogenesis germ cells 

 differing from one another by sharp alternative differences. 

 There is no a-priori reason why the same may not be true of 

 attributes and qualities in the germ cell which are not 

 capable of observation by present cytological methods. 



In the last decade the work of many investigators, but 

 especially that of Conklin, Lillie, Morgan, Driesch, and 

 Wilson, has shown that the germ cells are in reality highly 

 complex structurally, possessing a definite organization 

 and polarity, with a distribution of various elaborated sub- 

 stances which are individually more or less necessary to the 

 proper development of particular parts of the future embryo. 



