CHAPTER LXIll 
ASSOCIATION OF ORGANISMS—SOCIAL BACKBONED 
ANIMALS (VERTEBRATA) 
That many backboned animals are of gregarious habit is too 
well known to require emphasis. Our vocabulary includes many 
words signifying communities of animals, e.g. we speak of a “ shoal ” 
of fishes, a “flock” of birds, a “pack” of wolves, a “herd” of 
antelopes, and so on. The societies of which the existence is 
implied by many such words exhibit a type of communal life 
differing greatly from that described for insects, and one that is 
in some respects less interesting, except in so far as it throws 
light on the problems of sociology, with which all intelligent 
persons are more or less concerned. The complex conditions 
resulting from numerous individuals living together have not 
here led to profound anatomical specialization, as they have in 
the case of such insects as ants. 
SocraL Fisues (Pisces).—That so many Fishes should be 
associated together in shoals would seem to be dependent in many 
instances on the place and manner of spawning. In ordinary 
bony fishes (Teleostei) the eggs are nearly always fertilized 
externally, and it is obvious that this process is facilitated when 
numerous individuals seek the same locality for the purpose. The 
Herring (Clipea harengus), fig. 1102), for example, approaches 
our shores in order to deposit its eggs in shallow water, where 
they adhere to various objects; the Salmon (Sadmo salar) ascends 
rivers for the same purpose; and the Common Eel (Anguilla 
vulgaris) migrates in vast numbers to the deep sea in order to 
spawn. How far the movements of migratory fish involve 
division of labour is not at present known. It is not impossible 
that some of the older individuals may act as “leaders”, though 
this is littke more than a conjecture. 
The gregarious habit of many predaceous fishes, such as 
Sharks, Dog-fishes, and Mackerel, may conduce to success in 
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