CORRELATED VARIATION. 129 



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 

 pnrts 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 remarkable 

 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, ac- 

 cording 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 Saint-Hilaire has forcibly remarked that certain 

 maleonformations frequently, and that others rarely, coexist 

 without our being able to assign any reason. What can be 

 more singular than the relation in cats between complete 

 whiteness and blue eyes with deafness, or between the tor- 

 toise-shell color and the female sex ; or in pigeons, between 

 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 color of its 

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

 teeth in the naked Turkish dog, though here no doubt 

 homology comes into play ? With respect to this latter 

 case of correlation, I think it can hardly be accidental that 

 the two orders of mammals which are most abnormal in 

 their dermal covering, viz., cetacea (whales) and edentata 

 (armadilloes, scaly ant-eaters, etc. ), are likewise on the whole 

 the most abnormal in their teeth, but there are so many ex- 

 ceptions 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 

 difference between the outer and inner flowers in some com- 

 positous and umbelliferous plants. Every one is familiar 

 with the difference between the ray and central florets of, 

 for instance, the daisy, and this difference is often accon> 



