ABSTRACT
An association is formed by environmental factors causing a number of animals, whether of the same or of different species, to gather together in one place ; the mere presence of other animals does not keep the individual at the place in question ; it is, therefore, some factor in the environment which acts as the binding force. The aggregations of protozoa and small crustaceans which, under certain conditions, people in countless multitudes both fresh and salt water, are instances of associations ; so also are the collections of plant lice where the bond is merely a suitable feeding ground and not a social instinct. The gathering of birds and beasts of prey round the fallen body of a large wild animal in the tropics is an association, not a society ; as also are the gatherings of many species round a watering place in dry districts.
