72 McCLUNG. 



look elsewhere for an explanation of the various phenomena in- 

 volved in the problem. I shall therefore venture to advance a 

 theory which has been suggested to me by a careful study of the 

 structure in various species in the hope that an early elimination 

 of the improbable factors of the question will bring us closer to 

 the true explanation. 



In offering a theory to account for the function of the acces- 

 sory chromosome, I do so with considerable reluctance, for I 

 realize how little real general knowledge we have of this struc- 

 ture. It seems to me, however, that something is necessary to 

 concentrate the interest of spermatologists upon the fundamental 

 character of this most suggestive chromatin element, and I know 

 no better way of aiding in this than by publishing the working 

 hypothesis with which I have attacked the problem. 



This has led me into the field of theories concerning sex and 

 its determination, but I have tried to avoid any more extensive 

 discussion than is necessary to outline, in a preliminary way, the 

 opinion I hold concerning the meaning of the accessory chromo- 

 some. Even with this reservation I have nevertheless been 

 obliged to go further afield than I should desire with our present 

 knowledge as a guide. I can only hope that my excursions may 

 accomplish a measure of the purpose for which they were under- 

 taken. 



Briefly stated, then, my conception of the function exercised by 

 the accessory chromosome is that it is the bearer of those quali- 

 ties which pertain to the male organism, primary among which 

 is the faculty of producing sex cells that have the form of sper- 

 matozoa. I have been led to this belief by the favorable re- 

 sponse which the element makes to the theoretical requirements 

 conceivably inherent in any structure which might function as a 

 sex determinant. 



These requirements, I should consider, are that : (<?) The element 

 should be chromosomic in character and subject to the laws 

 governing the action of such structures, (b] Since it is to deter- 

 mine whether the germ cells are to grow into the passive, yolk- 

 laden ova or into the minute motile spermatozoa, it should be 

 present in all the forming cells until they are definitely estab- 

 lished in the cycle of their development, (c] As the sexes exist 



