144 
LAWS OF VARIATION. 
Chap. V. 
the petals of the corolla into a tube. Hard parts seem 
to affect the form of adjoining soft parts ; it is believed 
by some authors that the diversity in the shape of the 
pelvis in birds causes the remarkable diversity in the 
shape of their kidneys. Others believe that the shape 
of the pelvis in the human mother influences by pres¬ 
sure the shape of the head of the child. In snakes, 
according to Schlegel, the shape of the body and the 
manner of swallowing determine the position of several 
of the most important viscera. 
The nature of the bond of correlation is very fre¬ 
quently quite obscure. M. Is. Geofiroy St. Hilaire has 
forcibly remarked, that certain malconformations very 
frequently, and that others rarely coexist, without our 
being able to assign any reason. What can be more 
singular than the relation between blue eyes and deaf¬ 
ness in cats, and the tortoise-shell colour with the female 
sex; the feathered feet and skin between the outer toes 
in pigeons, and the presence of more or less down on the 
young birds when first hatched, with the future colour of 
their plumage; or, again, the relation between the hair 
and teeth in the naked Turkish dog, though here pro¬ 
bably homology comes into play ? With respect to this 
latter case of correlation, I think it can hardly be acci¬ 
dental, that if we pick out the two orders of mammalia 
which are most abnormal in their dermal covering, viz. 
Cetacea (whales) and Edentata (armadilloes, scaly ant- 
eaters, &c.), that these are likewise the most abnormal 
in their teeth. 
I know of no case better adapted to show the im¬ 
portance of the laws of correlation in modifying im¬ 
portant structures, independently of utility and, there¬ 
fore, of natural selection, than that of the difference 
between the outer and inner flowers in some Compo- 
sitous and Umbelliferous plants. Every one knows the 
