CHAP, v Social Life of Animals 71 



animals, we find some precise illustrations of such integrated colonies, 

 especially in the Siphonophora of which the Portuguese Man-of-War 

 (Physalia) is a good example. There is no doubt that these 

 beautiful organisms are colonies of individuals, which in structure 

 are all referable to a " medusoid " or jellyfish-like type. But the 

 division of labour is so harmonious, and the compacting or 

 organisation of the colony is so thorough, that the whole moves and 

 lives as a single organism. 



E. Perrier in his work entitled Les Colonies Animales (Paris, 

 1882), shows how organic association may lead from one grade of 

 organisation and individuality to another, and explains very clearly 

 how sedentary and passive life tends to develop mere aggregates, 

 while free and active life tends to integrate the colony. With this 

 may be compared A. Lang's interesting study on the influence of 

 sedentary life and its connection with asexual reproduction Das 

 Einfluss des Festsitzen (Jena, 1889). Haeckel, in his Generelle 

 Morphologic (2 vols., Berlin, 1866), was one of the first to shed a 

 strong clear light on the difficult subject of organic individuality, 

 its grades and its progressive complexity. To Spencer, Principles 

 of Biology (2 vols., London, 1863-67), we owe in this connection 

 the elucidation of the transition from aggregates to integrates, and 

 of the lines of differentiation, i.e. the progressive complication of 

 structure which is associated with division of labour. 



3. Gregarious Life and Combined Action. Most 

 mammals are in some degree gregarious. The solitary 

 kinds are in a distinct minority. The isolated are ex- 

 posed to attack, the associated are saved by the wisdom 

 of their wisest members and by that strength which union 

 gives. Many hoofed animals, such as deer, antelopes, 

 goats, and elephants, live in herds, which are not mere 

 crowds, but organised bands, with definite conventions and 

 with a power of combined resistance which often enables 

 them to withstand the attacks of carnivores. Marmots and 

 prairie-dogs, whose " cities " may cover vast areas, live peace- 

 nil and prosperous lives. Monkeys furnish many illustra- 

 tions of successful gregarious life. As individuals most of 

 them are comparatively defenceless, and usually avoid com- 

 ing to close quarters with their adversaries ; yet in a body 

 they are formidable, and often help one another out of 

 scrapes. Brehm tells how he encountered a troop of baboons 

 which defied his dogs and retreated in good order up the 



