THE ACCESSORY CHROMOSOME. 77 



serve the interest of the species. To it come the two forms of 

 spermatozoa from which selection is made in response to envi- 

 ronmental necessities. Adverse conditions demand a preponder- 

 ance of males, unusually favorable circumstances induce an excess 

 of females, while normal environments apportion an approxi- 

 mately equal representation to each of the sexes. 



Those theories regarding sex determination which contain any 

 element of truth within them will be found dependent upon this 

 principle. It is expressed by Geddes and Thompson in these 

 words : " But the general conclusion is tolerably secure that 

 in the determination of the sex, influences inducing katabolism 

 tend to result in production of males, as those favoring anabolism 

 similarly increase the probability of females." The authors just 

 cited clearly recognize that we must consider the sexual elements 

 in the light of their elemental structure and function when the 

 final explanation of sex is sought. They say : " That the final 

 physiological explanation is, and must be, in terms of proto- 

 plasmic metabolism, we must again, however, remind the reader." 



The role that I have suggested for the accessory chromosome 

 in no way changes the ordinary conception of the part played in 

 sex determination by the various observed factors, but it does 

 offer some tangible means by which to correlate these and to 

 fix the nature of their participation. 



The conception of two forms of sexual elements which would 

 be operative in the determination of sex is not new. It has been 

 assumed on purely theoretical grounds that there are two kinds 

 of ova, one of which, in the event of fertilization develops into a 

 male organism while the other under similar conditions gives 

 rise to a female. This theory is dismissed by Geddes and 

 Thompson on the ground that the two forms of ova have never 

 been observed and for the further reason that later influences 

 might possibly change the earlier tendency. 



The latter objection would prove fatal to any theory which 

 located the determination of sex in a structural difference of the 

 germinal elements. I do not consider this position well taken 

 for reasons that I will give later. The more serious objection 

 lies in the fact that, so far as observation has gone, all eggs of a 

 species are practically alike. It is also to be depreciated because 



