Chap. XXVIII. CONCLUDING REMARKS. 417 



tion with, one another, as the length, of the wing and 

 tail feathers — the number of the primary wing-feathers, as 

 well as the number and breadth of the ribs, in correlation 

 with the size and form of the body — the number of the 

 scutellae with the size of the feet — the length of the tongue 

 with the length of the beak — the size of the nostrils and 

 eyelids and the form of lower jaw in correlation with the 

 development of wattle — the nakedness of the young with the 

 future colour of the plumage — the size of the feet with that 

 of the beak, and other such points. Lastly, as our birds are 

 supposed to be confined in an aviary, they would use their 

 wings and legs but little, and certain parts of the skeleton, 

 such as the sternum, scapulae and feet, would in consequence 

 become slightly reduced in size. 



As in our assumed case many birds have to be indiscrimi- 

 uately killed every year, the chances are against any new 

 variety surviving long enough to breed. And as the varia- 

 tions which arise are of an extremely diversified nature, the 

 chances are very great against two birds pairing which have 

 varied in the same manner; nevertheless, a varying bird 

 even when not thus paired would occasionally transmit its 

 character to its young ; and these would not only be exposed 

 to the same conditions which first caused the variation in 

 question to appear, but would in addition inherit from their 

 modified parent a tendency again to vary in the same manner. 

 So that, if the conditions decidedly tended to induce some 

 particular variation, all the birds might in the course of time 

 become similarly modified. But a far commoner result would 

 be, that one bird would vary in one way and another bird in 

 another way ; one would be born with a beak a little longer, 

 and another with a shorter beak; one would gain some black 

 feathers, another some white or red feathers. And as these 

 birds would be continually intercrossing, the final result would 

 be a body of individuals differing from each other in many 

 ways, but only slightly; yet more than did the original rock- 

 pigeons. But there would not be the least tendency towards 

 the formation of several distinct breeds. 



If two separate lots of pigeons were treated in the manner 

 just described, one in England and the other in a tropical 



