CORRELATED VARIATION. I37 



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 tlieir 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. 

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

 I Geoffroy St. Hilaire has forcibly remarked that certain mal- 

 'conformations 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 com- 

 plete whiteness and blue eyes with deafness, or between 

 the tortoise-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 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 

 difference between the outer and inner flowers in some 

 compositous and umbelliferous plants. Everyone is 

 familiar with the difference between the ray and central 

 florets of, for instance, the daisy, and this difference is 

 often accompanied with the partial or complete abortion of 

 the reproductive organs. But in some of these plants the 

 seeds also differ in shape and sculpture. These differences 

 have sometimes been attributed to the pressure of the in- 

 volucra on the florets, or to their mutual pressure, and the 

 shape of the seeds in the ray florets of some composite 



