308 THE EVOLUTION OF THE METAZOA 



The second type of development of the complex individuals 

 was similar to the one we have just described in connection 

 with the evolution of plants. As in the case of plants we 

 find now in the Flagellata an inclination to develop colonies. 

 In the true colonies the products of division of the maternal 

 cell remain only mechanically attached to each other (coenobia, 

 colonies s.str.). This had finally led to the formation of 

 cormi when certain cytoplasmatic connections developed 

 between the members of the same colony. In this way 

 the coordination, and finally the differentiation of partners 

 became possible. This is how I imagine the evolution of 

 Spongiae which begun characteristically from an already more 

 highly developed and therefore more specialized group of 

 Flagellata. I am supported in this suggestion by important 

 factual arguments. These species of Flagellata were charac- 

 terized by a cytoplasmatic collar w^hich had developed around 

 the basis of the flagellum (Choanoflagellata, Craspedomon- 

 adida). During this development the ability has not been lost 

 either to abolish the collar form or even to assume an entirely 

 amoeboid form and type of movement. Even if there were 

 no species of Proterospongia (two such species have actually 

 been described in the meantime) it would still be very probable 

 for reasons that cannot be discussed here that the Spongiae 

 had evolved from some originally freely-living cormi of 

 Choanoflagellata after the latter had adopted the sessile way 

 of life. Nothing can be changed in this connection by the 

 fact that examples can occasionally be found among the Eumeta- 

 zoa whose cells have a collar formation. The organization of 

 Spongiae is in fact entirely different from that of alltheEumeta- 

 zoa. Neither can this situation be changed by the fact that 

 a sexual phase with an oogeny can also be found in Spongiae 

 as well as in the Eumetazoa because we know that the same 

 sexual conditions had also evolved in various plant groups. 

 These are properties that had been inherited from the pro- 

 tistic ancestors of all the polycellular forms, in spite of the 

 fact that we have here several lines of evolution. It may be 



