With cattle susceptibility to the attacks of flies is correlated with colour, as is the liability to be poisoned by certain plants; so that even colour would be thus subjected to the action of natural selection.

Some observers are convinced that a damp climate affects the growth of the hair, and that with the hair the horns are correlated.

Mountain breeds always differ from lowland breeds; and a mountainous country would probably affect the hind limbs from exercising them more, and possibly even the form of the pelvis; and then by the law of homologous variation, the front limbs and the head would probably be affected.

The shape, also, of the pelvis might affect by pressure the shape of certain parts of the young in the womb.