THE PHYLOGENY OF THE SOUL. 169 



vertebrates ; it is always the same in the early 

 embryonic sketch of the organism, and it is always 

 the chief feature of the different kinds of psychic 

 organ which evolve from it in time. Only one single 

 group of invertebrates has a similar structure : the 

 rare marine tuuicata, the copelata, ascidia, and 

 thalidiae. These animals have other important 

 peculiarities of structure (especially in the chorda 

 and the gut) which show a striking divergence from 

 the other invertebrates and resemblance to the verte- 

 brates. The inference we draw is that both these 

 groups, the vertebrates and the tunicates, have arisen 

 from a common ancestral group of the verm alia, the 

 proehordonia. 1 Still, there is a great difference 

 between the two classes in the fact that the body 

 of the tunicate does not articulate, or form members, 

 and has a very simple organisation (most of them 

 subsequently attach themselves to the bottom of the 

 sea and degenerate). The vertebrate, on the other 

 hand, is characterised by an early development of 

 internal members, and the formation of pro- vertebrae 

 (verteb ratio). This prepares the way for the much 

 higher development of their organism, which finally 

 attains perfection in man. This is easily seen in the 

 finer structure of his spinal cord, and in the develop- 

 ment of a number of segmental pairs of nerves, the 

 spinal nerves, which proceed to the various parts of 

 the body. 



The long ancestral history of our " vertebrate- 

 soul " commences with the formation of the most 

 rudimentary spinal cord in the earliest acrania ; 

 slowly and gradually, through a period of many 



1 See chaps, xvi. and xvii. of my Anthropoyeny. 



