SOCIAL BACKBONED ANIMALS 



129 



procuring prey, and certainly gives an opportunity for co-opera- 

 tion to the benefit of the community. On the other hand, living 

 in shoals must tend very greatly to increase mortality among 

 ill-defended species, which thus are bound to attract the notice 

 of their foes. The well-being of the individual is here, as 

 generally, subordinated to the interests of the species, the matter 

 apparently being determined by the exigencies of spawning. 



Though some of the AMPHIBIANS and REPTILES may be more 

 or less gregarious, but little of interest is known about them in 



Fig. 1102. Part of a Shoal of Herrings (Clupea harengus] 



the present connection, so that we may pass on to the more 

 intelligent animals included in the two highest vertebrate classes, 

 i.e. Birds and Mammals. A comparatively large and complex 

 brain is here associated with sagacity that may make itself 

 manifest in social developments. 



SOCIAL BIRDS (AvEs). Many Birds are eminently social in 

 their habits, and migrant forms may be associated in vast 

 numbers when making their long journeys (see p. 61). But we 

 have yet much to learn regarding the way in which the living 

 together of numerous individuals results in division of labour, or 

 in concerted action. Of two closely related birds the one may 



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