CHAPTER LXI 
ASSOCIATION OF ANIMALS—COLONIES 
Having considered the chief sorts of relation which exist 
between animals and plants, we have now to deal with the asso- 
ciation of individual animals, whether of the same or different 
species. In the sections on Food and Defences (volume ii) one 
kind of connection has been treated at considerable length, ze. 
that which links carnivorous (and to some extent omnivorous) 
forms with their prey, and we have seen that the bodily structure 
of both attackers and attacked have been more or less perfectly 
adapted to the exigencies of attack and defence. Another chapter 
of the same story will engage our attention rather later on, when 
Animal Parasites receive consideration, but it will be convenient 
in the meantime to enter into some particulars regarding other 
kinds of relation. 
Animals of the same species may be associated together in 
three chief ways, conveniently described under the headings of 
Colonial Animals, Social Animals, and Courtship and Mating of 
Animals. 
COLONIAL ANIMALS 
CoLoniaL ANIMALCULES (PRoTOzOA).—The minute and lowly 
creatures known as Animalcules are distinguished from animals 
higher in the scale by the fact that they are single cells or units 
of structure, z.e. they are unicellular. They propagate, as a rule, 
by splitting (fission) or budding (gemmation), and in a number 
of species the new individuals which thus come into existence 
remain connected together, forming a colony (fig. 1089). The 
members of such a colony are usually all alike, each of them 
performing all the duties of life for itself, and species for which 
this is true have therefore been described as “ physiologically 
unicellular”. Most of them are fixed, as, for instance, in Epistylis 
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