156 ORIGIN OF SPECIES 



less completely by natural selection; thus a family of stags 

 once existed with an antler only on one side; and if this 

 had been of any great use to the breed, it might probably 

 have been rendered permanent by selection. 



Homologous parts, as has been remarked by some authors, 

 tend to cohere; this is often seen in monstrous plants: and 

 nothing is more common than the union of homologous 

 parts in normal structures, as in the union of the petals into 

 a tube. Hard parts seem to affect the form of adjoining 

 soft parts; it is believed by some authors that with birds 

 the diversity in the shape of the pelvis causes the remark- 

 able diversity in the shape of their kidneys. Others believe 

 that the shape of the pelvis in the human mother influences 

 by pressure the shape of the head of the child. In snakes, 

 according to Schlegel, the form of the body and the manner 

 of swallowing determine the position and form of several 

 of the most important viscera. 



The nature of the bond is frequently quite obscure. M. 

 Is. Geoffroy St. Hilaire has forcibly remarked, that certain 

 malconformations frequently, and that others rarely, co- 

 exist, without our being able to assign any reason. What 

 can be more singular than the relation in cats between com- 

 plete whiteness and blue eyes with deafness, or between the 

 tortoise-shell colour and the female sex; or in pigeons be- 

 tween their feathered feet and skin betwixt the outer toes, 

 or between the presence of more or less down on the young 

 pigeon when first hatched, with the future colour of its 

 plumage; or, again, the relation between the hair and teeth 

 in the naked Turkish dog, though here no doubt homology 

 comes into play? With respect to this latter case of corre- 

 lation, I think it can hardly be accidental, that the two orders 

 of mammals which are most abnormal in their dermal cov- 

 erings, viz., Cetacea (whales) and Edentata (armadilloes, 

 scaly ant-eaters, &c.), are likewise on the whole the most 

 abnormal in their teeth ; but there are so many exceptions to 

 this rule, as Mr. Mivart has remarked, that it has little 



value. 



I know of no case better adapted to show the importance 

 of the laws of correlation and variation, independently of 

 utility and therefore of natural selection, than that of the 



