46 MENTAL EVOLUTION IN ANIMALS. 



deal. But here we have to remember that besides size or 

 mass, there must certainly be a no less important factor to be 

 taken into account — that, namely, of structure or complexity. 

 Now we really know so little about the relations of intelli- 

 gence to neural structure, that I do not think we are justified 

 in forming any very strong conclusions a priori concerning the 

 relation of intelligence to mere size or mass of brain. Know- 

 ing in a general way that mass plus structure of brain is 

 necessary for intelligence, we do not know how far the 

 second of these two factors may be increased at the expense 

 of the first. And, as a mere matter of complexity, or of 

 multum in parvo, I am not sure that even the brain of an 

 ant deserves to be considered more wonderful than the ovum 

 of a human being. Lastly, in this connection it may be as 

 well to observe that there is as good evidence to show the 

 importance of cerebral structure as a factor in determining 

 the level of mental development, as there is to show the 

 importance of cerebral mass. Throughout the vertebrated 

 series of animals the convolutions of the brain — which are 

 the coarser expressions of more refined complexities of 

 cerebral structure — furnish a wonderfully good general indi- 

 cation of the level of intelligence attained; while in the 

 case of ants Dujardin says that the degree of intelligence 

 exhibited stands in an inverse proportion to the amount of 

 cortical substance, or in direct proportion to the amount of the 

 peduncular bodies and tubercles. In view of these con- 

 siderations, therefore, I do not feel that the supposed diffi- 

 culty, which I have thought it desirable to mention, is one of 

 any real solidity. 



