72 THE AMERICAN NATURALIST [Vol. XL V 



of different kinds of ducts, glands, copulatory organs, or 

 other accessory sexual apparatus ; and also by structures 

 not essential to reproduction. These last we call the 

 secondary sexual characters. 



It has long been known that in the embryonic develop- 

 ment of the vertebrates some of the accessory organs of 

 the male appear in the female, and conversely some of 

 the accessory organs of the female in the male. This 

 evidence seems to me to point with no uncertain mean- 

 ing to the conclusion that each sex carries the genes of 

 the other. It is however the secondary sexual characters 

 rather than these accessory organs of which I wish to 

 speak now ; for, these often appear to be present in one sex 

 only. Are these characters represented in all eggs and 

 sperm or are they by-products of the sexual condition of 

 the animal 1 Fortunately there is a good deal of experi- 

 mental evidence that bears on this question, but it is also 

 true that the evidence teaches that the matter must be 

 handled with care, and if I seem to speak dogmatically 

 it is for lack of time rather than for want of caution. 



It has been shown by Meisenheimer that removal of 

 the gonads of the caterpillar of Ocneria dispar fails to 

 produce any effect, or very little, on the secondary sex- 

 ual characters of the moth. It would seem, therefore, 

 that these characters are represented in the germ cells in 

 the same way as are other characters, and are not depend- 

 ent for their development on the presence of the gonads. 

 Some mechanism must exist by means of which the genes 

 of these organs are distributed so that two kinds of in- 

 dividuals are produced. It has been suggested by Castle 

 that the secondary sexual characters may be carried by 

 the Y-element in the formulas XX = female, XY = male, 

 but this hypothesis fails to explain the results when the 

 Y-element is absent, as E. B. Wilson has pointed out. It 

 also fails to explain how the male secondary sexual or- 

 gans can appear in the female after castration. 



On the sex formulae that I have suggested it is pos- 

 sible to account for the results, if the genes for these 



