THE PHYLOGENY OF THE SOUL. 171 



fishes, from which all the gnathostornata descend, the 

 more pronounced division of the five cerebral vesicles 

 sets in. 



IV. Fourth stage — the amphibia. These earliest 

 land-animals, making their first appearance in the 

 Carboniferous period, represent the commencement 

 of the characteristic structure of the tetrapod and a 

 corresponding development of the fish-brain : it 

 advances still further in their Permian successors, 

 the reptiles, the earliest representatives of which, the 

 tocosaiuia, are the common ancestors of all the 

 amniota (reptiles and birds on one side, mammals on 

 the other). 



V.-VIII. Fifth to the eighth stages — the mammals. 

 I have exhaustively treated, and illustrated with a 

 number of plates, in my Anthropogeny, the evolu- 

 tion of our nervous system and the correlative ques- 

 tion of the development of the soul. I have now, 

 therefore, merely to refer the reader to that work. It 

 only remains for me to add a few remarks on the last 

 and most interesting class of facts pertaining to this 

 — to the evolution of the soul and its organs within 

 the limits of the class mammalia. In doing so, I 

 must remind the reader that the monophyletic origin 

 of this class — that is, the descent of all the mammals 

 from one common ancestral form (of the Triassic 

 period) — is now fully established. 



The most important consequence of the mono- 

 phyletic origin of the mammals is the necessity of 

 deriving the human soul from a long evolutionary 

 series of other mammal-souls. A deep anatomical 

 and physiological gulf separated the brain structure 

 and the dependent psychic activity of the higher 

 mammals from those of the lower : this gulf, however, 



