Chap. V. OSTEOLOGJAL DIFFERENCES. 171 



on the beak and round the eyes, and with Barbs that round 

 the eyes, goes on increasing with age. This augmentation 

 of character with advancing age, and more especially the 

 difference between the males and females in the above- 

 mentioned several respects, are remarkable facts, for there 

 is no sensible difference at any age between the two sexes 

 in the aboriginal rock-pigeon ; and not often any strongly 

 marked difference throughout the family of the Colunibidce. 33 



Osteological Characters. 



In the skeletons of the various breeds there is much varia- 

 bility ; and though certain differences occur frequently, and 

 others rarely, in certain breeds, yet none can be said to be 

 absolutely characteristic of any breed. Considering that 

 strongly-marked domestic races have been formed chiefly by 

 man's selection, we ought not to expect to find great and 

 constant differences in the skeleton ; for fanciers neither see, 

 nor do they care for, modifications of structure in the internal 

 framework. Nor ought we to expect changes in the skeletons 

 from changed habits of life ; as every facility is given to the 

 most distinct breeds to follow the same habits, and the much 

 modified races are never allowed to wander abroad and 

 procure their own food in various ways. Moreover, I find, 

 on comparing the skeletons of Columba livia, cenas, palumbus, 

 and turtur, which are ranked by all systematists in two or 

 three distinct though allied genera, that the differences are 

 extremely slight, certainly less than between the skeletons 

 of some of the most distinct domestic breeds. How far the 

 skeleton of the wild rock-pigeon is constant L have had no 

 means of judging, as I have examined only two. 



Skull. — The individual bones, especially those at the base, do not 

 differ in shape. But the whole skull, in its proportions, outline, 

 and relative direction of the bones, differs greatly in some of the 

 breeds, as may be seen by comparing the figures of (a) the wild 



35 Prof. A. Newton (' Proc. Zoolog. family ef the Treronidse the sexes often 



Soc.,' 1865, p. 716) l'emarks that he ditf'er considerably in colour. See 



knows no species which present any also on sexual differences in the Coluin- 



remarkable sexual distinction ; but Mr. bida?, Gould, 'Handbook to the Birds 



Wallace informs me, that in the sub- of Australia,' vol. ii. pp. 109-149. 



