(ECO LOG Y. 



2OI 



existence therefore has become dependent upon these ; the 

 single individual can continue to live only while a part 

 of a whole. Thus also division of labor leads to greater 

 centralization ; the more polymorphic an animal colony 

 B 4 



FlG. 106. Praya diphyes. (After Gegenbaur.) A, the entire animal; />, a single group 

 of individuals greatly magnified (Eudoxia). i, protective scale; 2, nutritive polyp; 3, 

 nettle-threads ; 4, sexual bell. 



becomes, the more unified it is, the more it gives the im- 

 pression of being a single animal instead of an aggregation 

 of single animals. 



State Formation. In case of state formation the re- 

 ciprocal dependence of the animals is much less, since 

 here there exists no organic connection, only a voluntary 

 communal cohabitation. As in the case of colony build- 

 ing asexual reproduction is of importance, so here the 

 sexual plays a prominent role. Under the influence of the 

 sexual impulse, many animals, even some of the lowest 

 organisms, flock together, either permanently or periodi- 

 cally; sea-urchins, sea-cucumbers, many fishes, collect near 

 the coast at the time of egg-laying. The sexual impulse 



