hypothesis is formed.' It throws light however on the essentially speculative character of his intellect to find that this admittedly doubtful hypothesis of Pangenesis is the part of the book on which he looks with the greatest affection,--'my beloved child,' as he phrases it. _The Descent of Man_ (1871) ranks next in wide importance to _The Origin of Species_. It is the application in detail of the same principles to the human race. That the application was inevitable was already evident in the earlier book; and it was this that brought upon the _Origin_ the most virulent abuse. Just because it is so inevitable, _The Descent of Man_ has not the unique interest of _The Origin of Species_. Once we are familiar with the view that all the species of animals have been produced by the accumulation of minute variations, there is no surprise in the idea that man and all his powers may have been so produced likewise. Nevertheless, Darwin differs on this point from the man who shares with him the honour of discovering the theory of evolution. Mr. Wallace, while arguing with Darwin that man has been evolved out of some lower form, holds that 'natural selection could only have endowed the savage with a brain a little superior to that of an ape,' and that in the higher human faculties there is evidence of the working of a supernatural power. The position is a strange one. If the whole creation moves harmoniously through all its grades by the action of one law, it will need overwhelming evidence to show that just at the end this law is superseded by another altogether unlike it. Either the supernatural governs the whole of life, or its introduction to explain one stage is gratuitous. After _The Descent of Man_ came _The Expression of the Emotions in Man and Animals_ (1872); and that again was followed by _Insectivorous Plants_ (1875). The former was originally intended merely to form a chapter in the _Descent_; but the materials grew, and the result is one of the most readable of books. The _Insectivorous Plants_ embodies one of the most remarkable of Darwin's discoveries. Its richness is due to the patience and skill with which the facts were accumulated. Sixteen years passed between the time when Darwin first noticed that plants lived on insects and the appearance of the book. In the interval he had done many things; but, whenever he had leisure, he was always adding to his store of facts relating to this class of plants; and, as he justly says, 'a man after a long interval can criticise his own work, almost as well as if it were that of another person.'