Returning now to the causes which are supposed to induce variability. Some authors (22/31. Devay 'Mariages Consanguins' pages 97, 125. In conversation I have found two or three naturalists of the same opinion.) believe that close interbreeding gives this tendency, and leads to the production of monstrosities. In the seventeenth chapter some few facts were advanced, showing that monstrosities are, as it appears, occasionally thus induced; and there can be no doubt that close interbreeding causes lessened fertility and a weakened constitution; hence it may lead to variability: but I have not sufficient evidence on this head. On the other hand, close interbreeding, if not carried to an injurious extreme, far from causing variability, tends to fix the character of each breed. It was formerly a common belief, still held by some persons, that the imagination of the mother affects the child in the womb. (22/32. Muller has conclusively argued against this belief, 'Elements of Phys.' English translation volume 2 1842 page 1405.) This view is evidently not applicable to the lower animals, which lay unimpregnated eggs, or to plants. Dr. William Hunter, in the last century, told my father that during many years every woman in a large London Lying-in Hospital was asked before her confinement whether anything had specially affected her mind, and the answer was written down; and it so happened that in no one instance could a coincidence be detected between the woman's answer and any abnormal structure; but when she knew the nature of the structure, she frequently suggested some fresh cause. The belief in the power of the mother's imagination may perhaps have arisen from the children of a second marriage resembling the previous father, as certainly sometimes occurs, in accordance with the facts given in the eleventh chapter. CROSSING AS A CAUSE OF VARIABILITY.