The success and extent of such development clearly depend on the relation of two series of activities in the individual which may in the most general way be described as the capacity for varied reaction and the capacity for communication. The process going on in the satisfactorily developing gregarious animal is the moulding of the varied reactions of the individual into functions beneficial to him only indirectly through the welfare of the new unit—the herd. This moulding process is a consequence of the power of intercommunication amongst the individual constituents of the new unit. Intercommunication is thus seen to be of cardinal importance to the gregarious, just as was the nervous system to the multicellular.
Moreover, in a given gregarious species the existence of a highly developed power of reaction in the individual with a proportionately less developed capacity for communication will mean that the species is not deriving the advantages it might from the possession of gregariousness, while the full advantages of the type will be attained only when the two sets