356 THE HISTORY OF CREATION. 



That even the origin of man must be explained by this 

 general organic process of transmutation, and that it is 

 simply as weU as naturally explained by it, has, I believe, 

 been sufficiently proved in my last chapter but one. I 

 cannot, however, avoid here once more directing atten- 

 tion to the inseparable connection between this so-called 

 "theory of apes," or "pithecoid theory," and the whole 

 Theory of Descent. If the latter is the greatest inductive 

 law of biology, then it of necessity follows that the former 

 is its most important deductive law. They stand and fall 

 together. As all depends upon a right understanding of 

 this proposition, which in my opinion is very important, 

 and which I have therefore several times brought before 

 the reader, I may be allowed to explain it here by an 

 example. 



In aU mammals known to us the centre of the nervous 

 system is the spinal marrow and the brain, and the centre 

 of the vascular system is a quadrupal heart, consisting of 

 two principal chambers and two ante-chambers. From this 

 we draw the general inductive conclusion that all mammals, 

 without exception, those extinct, together with all those 

 living species as yet unknown to us, as weU as the species 

 which we have examined, possess a like organization, a like 

 heart, brain, and spinal marrow. Now if, as still happens 

 every year, there be discovered in any part of the earth a 

 new species of mammal, a new species of marsupial, or a 

 new species of deer, or a new species of ape, every zoologist 

 knows with certainty at once, without having examined its 

 inner structure, that this species must possess a quadruple 

 heart, a brain and spiaal marrow, like all other mammals. 

 Not a single naturalist would ever think of supposing that 



