THE ACCESSORY CHROMOSOME. 75 



logically forced to the conclusion that the peculiar chromosome 

 has some bearing upon this arrangement. 



I must here also point out a fact that does not seem to have 

 the recognition it deserves ; viz, that if there is a cross division of 

 the chromosomes in the maturation mitoses there must be two 

 kinds of spermatozoa regardless of the presence of the accessory 

 chromosome. It is thus possible that even in the absence of any 

 specialized element a preponderant maleness would attach to one 

 half the spermatozoa, due to the " qualitative " division of the 

 tetrads. 1 



(</) As I elsewhere suggest, it is most appropriate that the sex 

 determinant should have its locus in the spermatozoa. These 

 elements are most commonly freed from any close relation to the 

 parent organism at maturity, and thus lose the opportunity to 

 receive from it any bias toward the production of an unusual 

 proportion of the one sex or the other as environmental condi- 

 tions might require. It is otherwise with the ova. They are 

 usually retained by the maternal organism in such intimate rela- 

 tion to it that surrounding conditions might easily imprint their 

 demands upon them. Even up to the time of fertilization the 

 female elements are so placed as to react readily to stimuli from 

 the mother. Here they are approached by the wandering male 

 elements from which they may choose if we may use such a 

 term for what is probably chemical attraction either the sper- 

 matozoa containing the accessory chromosome or those from 

 which it is absent. In the female element, therefore, as in the 

 female organism, resides the power to select that which is for the 

 best interest of the species. 



(/) The strength with which sex is established in different 

 species of animals is variable. Moreover it is a fact of common 

 observation that all cell elements vary widely in different animals. 

 We should not be surprised to find, then, that a determinant 

 would exhibit marked varieties of form which might even be 

 carried to the extreme of its entire suppression as a definite 

 element. Incomplete as are the observations upon the behavior 



1 It is suggestive that in all those cases where there appears to be no cross 

 division of the chromosomes in maturation, nothing like the accessory chromosome 

 has been noted. This would seem to be some indication that there might be two 

 types of division. 



