THE PHYLOGEXY OF THE SOUL. 165 



The soul of the cnidaria is of the utmost impor- 

 tance in comparative and phylogenetic psychology ; 

 for in this numerous group of the ccelenterates 

 the historical evolution of the nerve-soul out of 

 the tissue-soul is repeated before our eyes. To this 

 group belong the innumerable classes of stationary 

 polyps and corals, and of swimming medusae and 

 siphonophora. As the common ancestor of all the 

 cnidaria we can safely assign a very simple polyp, 

 which is substantially the same in structure as the 

 common, still-surviving, fresh-water polyp — the hydra. 

 Yet the hydrae, and the stationary, closely-related 

 hydropolyps, have no nerves or higher sense-organs, 

 although they are extremely sensitive. On the other 

 hand, the free-swimming medusae, which are developed 

 from them — and are still connected with them by 

 alternation of generations — have an independent 

 nervous system and specific sense organs. Here, 

 also, we may directly observe the ontogenetic evolu- 

 tion of the nerve- soul (neuropsyche) out of the tissue- 

 soul (histopsyche), and thus learn its phylogenetic 

 origin. This is the more interesting as such phe- 

 nomena are polyphyletic — that is, they have occurred 

 several times — more than once, at least — quite inde- 

 pendently. As I have shown elsewhere, the hydro- 

 medusae have arisen from the hydropolyps in a different 

 manner from that of the evolution of the scypho- 

 medusae from the scyphopolyps ; the gemmation is 

 terminal in the case of the latter, and lateral with the 

 former. In addition, both groups have characteristic 

 hereditary differences in the more minute structure of 

 their psychic organs. The class of siphonophora is 

 also very interesting to the psychologist. In these 

 pretty, free-swimming organisms, which come from 



