CHAPTER I. 



COMMUNITY LIFE IN THE ANIMAL KINGDOM. 



1. A General Survey of the Forms of Animal Com- 

 munities. 



THE multiplicity of bodily shapes apparent in ani- 

 mals is not more remarkable than the variety 

 found in their biological relations. The majority of 

 animals, lower as well as higher, live singly, and only 

 temporarily join other individuals of the same species 

 for breeding purposes ; no lasting psychic tie unites 

 them with others of their species. Other animals live 

 in pairs during the breeding season, and remain united 

 until the young are old enough to shift for themselves ; 

 this is the case with most birds and mammals. If the 

 offspring continue to remain with their parents, fam- 

 ilies develop into herds, embracing the members of 

 different, allied families. Thus, v. g., wild oxen and 

 horses, the chamois, antelopes and many apes are 

 gregarious animals. While real gregariousness is 

 based on family ties in a wider sense and is mostly 

 permanent, other animals flock together to form troops 

 or hordes to undertake journeys in common, e. g., our 

 migratory birds in autumn, the Scandinavian lem- 

 mings, etc. Insects, too, gather into similar temporary 

 masses of individuals of the same or closely allied 

 species, assuming the form of migrating swarms. 

 Migrating locusts are known to everybody; but also 



