86 



ZOOLOGY 



Determina- 

 tion of 

 sexual 

 characters 

 through 

 secretions 



apterous. In a kind of bee (Melissodes) the females 

 have the face black, but in the males a large part of the 

 face (the clypeus) is yellow. A specimen was collected 

 in Texas, which had the clypeus half yellow and half 

 black, the division between the colors perfectly sharp 

 and definite. In other cases the sexual characters are 

 variously combined, forming a sort of mosaic. 



Various explanations have been given for these 

 strange phenomena, but as Morgan has recently (1914) 

 shown, it is almost certain that they are due to accidents 

 in cell division at an early stage of growth. If at some 

 early division, after fertilization, the sex chromosome 

 fails to enter a particular cell, the tissue developing from 

 that cell will appear as if the chromosomes in question 

 had been absent from the start. Thus the determina- 

 tion of sex at fertilization is only determination in this 

 sense, that it provides the machinery for the develop- 

 ment of sex. If that machinery goes wrong, the ex- 

 pected results do not follow. 



8. Among the vertebrates, especially, secondary sex- 

 ual characters are determined by certain secretions 

 which act upon the various parts of the body. In such 

 animals the gynandromorphic phenomena could not 

 occur. The development of the characters does not 

 depend on the chromosomes in the tissue cells, but on 

 the special activities of certain localized cells connected 

 with the sexual organs. ' Consequently, as is well 

 known, the removal of the sexual organs or their in- 

 jury by disease results in profound changes, affecting 

 different structures. It is not especially surprising that 

 when the sexual organs of certain male animals are re- 

 moved, special male characters, such as horns, fail to 

 develop. We are more astonished, however, to find 

 that in various birds the removal or degeneration of the 



