586 CLARENCE E. McCLUNG 



as an 'exclusively male' or exclusively female character is not 

 to be found. The evidence here would indicate that the 'fac- 

 tors' for maleness, are such controls of the developmental proc- 

 esses as will eventuate in a certain degree of differentiation of 

 each cell of the body. The sum of all these, in any somatic 

 region, produces a condition which we call a male character, 

 and the total complex of these constitutes an individual which is 

 a male. In another individual the same series of elements ob- 

 tains, but each cell and each part is slightly different and the 

 sum total of the characters produces an assemblage which we 

 recognize as a female. Should the conditions be varied, even by 

 the internal secretion of the gonad, in some cases, these may be 

 altered to resemblance of the opposite sex. 



However much the entire complex is involved in the produc- 

 tion of characters which are called sexual, it is apparent from 

 the history of the accessory chromosome in the Orthoptera that 

 it is a differential agent. All other things apparently being 

 equal, the presence of one accessory chromosome so shapes the 

 developmental processes that a male results, while if two are 

 involved a female is produced. In some way, not now apparent, 

 the action of this particular one of the chromosomes differs 

 from all the others in producing an effect of which they are not 

 capable — that is, it has a specific action. Apparently it is un- 

 like them in being concerned with the entire body, including 

 the germ cells, which are differentiated into eggs or spermatozoa. 

 A further indication 'of the specific nature of this particular 

 chromosome is afforded by sex-linked characters whose develop- 

 ment is conditioned by exactly the same circumstances of dis- 

 tribution as those which mark the alternatives of maleness or 

 femaleness. The facts relating to the accessory chromosome are 

 the strongest evidence we have in support of chromosome 

 specificity, because the history of this element is so clear, its 

 continuity so unbroken and its relations to certain characters so 

 definite. But any evidence for specificity of one chromosome is, 

 at the same time, support for the general conception of the dif- 

 ferential nature of chromosomes, and for this reason the facts 

 concerning the accessory chromosome have additional value. 



