ii2 THE PSYCHICAL KINSHIP 



true of the vertebrates. Fishes, amphibians, 

 reptiles, birds, and mammals, all have in their 

 brains the same primary parts, the same five 

 fundamental divisions, as are found in the brain 

 of man. Hence, whatever may be thought about 

 the mental states of invertebrates, we have the 

 right, in the case of the vertebrate orders of life, 

 to infer, from the general similarity of their 

 nervous system to our own, that they have a 

 corresponding similarity to ourselves in mental 

 constitution and experience. 



3. The evolution of mind is suggested b)' the 

 existence in the animal world of all grades of 

 intelligence, from almost mindless forms to forms 

 even exceeding in some respects the mental 

 attainments of men. The jelly-fish and the 

 philosopher are not mental aliens. They are 

 linked to each other by a continuous gradation of 

 intermediate intelligences. The existence of these 

 grades of mental development suggest psychical 

 evolution and kinship, just as the existence of like 

 grades of structural development suggest physical 

 evolution. 



4. In the mental life of animals the same 

 factors of evolution exist as those by means of 

 which organic structures have been brought into 

 existence, and it is reasonable to suppose that the 

 operation of these factors have produced in the 

 mental world results analogous to those produced 

 by the operation of the same factors among organic 

 structures. 



Men and other animals vary in their natures 



