214 Secondary Male Characters hi a Pheamnt 



absence of any given factor, or by the unequal volume of any factor 

 on opposite sides of the body, or by the inhibition of one factor by 

 another, or by a third or metabolic factor as suggested by Geoffrey 

 Smith (Proc. Linnean Soc. March 6, 1913) and Doncaster (Brit. 

 Assoc. Birmingham, 1913), which acts as an intermediary between 

 the sex gland and the secondary sex characters, still this bird 

 differs from the normal individual in the fact that a process which 

 normally affects both sides of the body equally, in this case affects 

 them unequally. And yet this does not occur in a sharply defined or 

 clear cut manner. In some parts, as for instance the limbs, the head 

 and neck, this hemilateral limitation of influence is well marked, while 

 along the middle line of the body and in the posterior part of the trunk 

 there is some overlapping, and in the tail the influencing factor is 

 broken up into secondary factors which control individual tail feather 

 areas. 



This latter is I think a point of some importance. It suggests that 

 the segregation of controlling factors (whatever may be their material 

 basis in heredity) does not occur suddenly at one stage only in the 

 development of the organism but that it runs on and accompanies 

 those cell divisions which at different stages regulate the growth of 

 the different organs and tissues of the body. 



Now if the oirtological process be continuous and gradual, may not 

 the segregation of gametic factors in the germ cell be a gradual and 

 continuous process also ? Although we draw an arbitrary line at the 

 stage of fertilization, it is probable that gametic and blastomeric 

 segregation are one and the same process which becomes accelerated 

 at the time of fertilization. 



If this be so, then from what we know of the irregular and 

 asymmetrical cell divisions which lead to overlapping and blurring of 

 unit characters in the zygote, it is reasonable to suppose that those 

 qualitative divisions of the nuclear hereditary material (whatever it be, 

 by which the gametic factors, the precursors of unit characters, are 

 separated out in the germ cells) may also be less sharply defined than 

 we have been led to think. Segregation may not be the cutting 

 asunder of a chromosome or a portion of a chromosome by a sharp 

 division into two distinct portions but the pulling asunder of one 

 portion from another with detached particles adhering to either end. 



