Chap. V. SUMMARY OF DIFFERENCES. 179 



each other merely in colour ; for particular colours when once 

 acquired are not liable to continued improvement or augmen- 

 tation. Some characters become attached, from quite unknown 

 causes, more strongly to the male than to the female sex ; so 

 that we have, in certain races, a tendency towards the appearance 

 of secondary sexual characters, 41 of which the aboriginal rock- 

 pigeon displays not a trace. 



41 This term was used by John not directly connected with the act of 

 Hunter for such dhferences in structure reproduction, as the tail of the peacock, 

 between the males and females, as are the horns of deer, &c. 



N 2 



