INTRODUCTION 



jOOLogical research of the last decade has led to a sharp 

 separation of two chief divisions of the animal kingdom: 

 the Protozoa and the Metazoa. In the group Protozoa the 

 individual can, from its structure, be referred to the funda- 

 mental type of a cell. These unicellular individuals exist 

 either separately or united in great numbers to form colonies 

 or corms. In the latter case, however, the different indi- 

 viduals remain equivalent to one another in structure and 

 function. In the group Metazoa, or Germ-layer animals, 

 on the contrary, there always results a multicellular or- 

 ganism (cell-community or cell-corm), in which the single 

 cells give up their independence for the good of the com- 

 munity, and accommodate themselves to a division of labour, 

 in consequence of which there is brought about a diversity 

 in the structure and function of the cells of the Metazoan 

 organism. While the development and differentiation of 

 distinct tissues with specific functions result from this poly- 

 morphism of the cells, the entire colony gains a higher 

 functional capacity and a more complete unity. In this 

 way there arises an individual of higher rank or second 

 degree, w^hich we designate as person. These Metazoan in- 

 dividuals also may, through incomplete separation after 

 budding, remain united in colonies, and then there results 

 an individual of the third degree, the stock or corm. By- 

 adaptation of the stock-forming persons to various functions, 

 accompanied with their polymorphous development, a higher 

 functional unity may be reached in this case also. 



As a result of the division of labour which is effected 

 among the cells of the Metazoan organism, it comes about 



K. H. E. 1 B 



