Chap. V. CORRELATION OF GROWTH. 179 



sacral and caudal vertebraj have been augmented in number ; 

 the sternum has likewise increased in length (but not in the 

 depth of the crest) by "4 of an inch more than would follow 

 from the greater bulk of the body in comparison with that 

 of the rock-pigeon. In Fantails, the length and number of 

 the caudal vertebrae have increased. Hence, during the 

 gradual progress of variation and selection, the internal bony 

 framework and the external shape of the body have been, to 

 a certain extent, modified in a correlated manner. 



Although the wings and tail often vary in length inde- 

 pendently of each other, it is scarcely possible to doubt that 

 they generally tend to become elongated or shortened in 

 correlation. This is well seen in Jacobins, and still more 

 plainly in Eunts, some varieties of which have their ^vings 

 and tail of great length, whilst others have both very short. 

 With Jacobins, the remarkable length of the tail and wing- 

 feathers is not a character which is intentionally selected by 

 fanciers ; but fanciers have been trying for centuries, at leiini 

 since the year 1600, to increase the length of the reversed 

 feathers on the neck, so that the hood may more completely 

 enclose the head ; and it may be suspected that the increased 

 length of "the wing and tail-feathers stand in correlation with 

 the increased length of the neck-feathers. Short-faced Tumblers 

 have short wings in nearly due proportion with the reduced 

 size of their bodies ; but it is remarkable, seeing that the 

 number of the primary wing-feathers is a constant character 

 in most birds, that these Tumblers generally have only nine 

 instead of ten primaries. I have myself observed this in 

 eight birds ; and the Original Columbarian Society ^' reduced 

 the standard for Bald-head Tumblers from ten to nine white 

 flight-feathers, thinking it unfair that a bird which had only 

 nine feathers should be disqualified for a prize because it had 

 not ten white flight-feathers. On the other hand, in Carriers 

 and Eunts, which have large bodies and long wings, eleven 

 primary feathers have occasionally been observed. 



Mr. Tegetmeier has informed me of a curious and inexpli- 

 cable case of correlation, namely, that young pigeons of all 

 breeds which when mature become white, yellow, silver {i.e., 

 extremely pale blue), or dun-coloured, are bom almost naked ; 



3" J. M. Eaton's Treatise, edit. 1858, p. 78. 



x 2 



