126 SEXUAL DIMORPHISM 



a hen in one and a cock in the other. The owner should 

 visit them as often as possible, and use always the same call, 

 at the same time removing the partition so that the two 

 birds can see each other, " the instant this is done they will 

 generally put themselves into the best and most striking 

 attitudes. By doing this on each occasion they will soon 

 learn, every time the owner goes near or speaks to them, to 

 expect to see their mates, and will begin to fill their crops 

 and strut about with delight, unless in the case of a very 

 few sulky birds. If you have one familiar hen it is also a 

 good plan to train her to stand on your hand, and thus show 

 her in front of a pen containing cock birds. This will set 

 them all into fine show, which should of course be accom- 

 panied by the call, and is an excellent way of training 

 Pouters." After this it is of little use to dispute whether 

 selection alone could produce the chief peculiarity of the 

 Pouter. The important fact is that the peculiarity has not 

 been produced by spontaneous variation and selection, but 

 by the excessive stimulation of a certain action associated 

 with pleasurable and essentially sexual excitement. It is 

 scarcely possible to deny that the action of " showing " in 

 the Pouter has influenced not merely the size of the crop, 

 but also the general shape and carriage of the bird, which 

 are considered equally important by the fancier. 



In contrast with these characters we may consider the 

 feathering of the legs, which occurs in the Pouter and in 

 several other fancy breeds of pigeons. No training or 

 other special conditions can be discerned which might have 

 produced this character, which is common to both sexes. 

 This is a spontaneous variation of the typical kind. But it 

 is the expression of a general tendency, a variation in a 

 definite direction. It is an example of the general principle 

 that serially homologous parts tend to resemble or imitate 

 one another, just as offspring resemble their parents. The 



