216 Secondarij Male Character's in a Flieasant 



In fact the " Presence and Absence " theory, the " Inhibition " 

 theory, and the "Unequal Volume" theory of Dominance and Recessivity 

 are all as relevant to the study of the physiology of sex as they are to 

 the study of the origin of all unit characters. Moreover, sex itself being 

 a unit character, observations on abnormal examples like the present 

 may possibly throw light on the larger problem. 



For instance the fact that in vertebrates the sex gland influences 

 the epithelial or other tissues which develop secondary male characters 

 by means of some internal secretion, probably an enzyme, suggests that 

 genetic factors in the nucleus of the fertilized ovum exercise their long 

 drawn out influence over the development of all unit characters in 

 the zygote in the same way. In both cases three elements are con- 

 cerned : 



(a) Peripheral cells or unit characters. 



(6) Central sex gland or gametic factor. 



(c) Some communicating medium, possibly an enzyme, circulating 

 in the blood rather than any structural continuity between (a) and (6). 



We may even extend Ehrlich's side chain theory of immunity to the 

 field of the development of secondary sex characters. We may conceive 

 of the sex gland as liberating an Hormonic key capable of fitting the 

 peripheral cell lock, but this must be made available and carried to 

 the cell by some intermediate agency, and this intermediate handle 

 or amboceptor may be supplied by one or more of the other ductless 

 glands. 



Just as it is possible by cross fertilization to replace one gametic 

 factor by another and so to substitute one unit character for another 

 in the zygote, so also by the removal of the sex gland in the indi- 

 vidual (and more especially by parasitic castration) it is possible to 

 bring about the replacement of the secondary sex characters normal 

 to one sex by those peculiar to the other. 



