ABSTRACT
The particular instinct which causes the members of social species to attach themselves to their own kind, or in the absence of these, to other animals, is wanting in the solitary species. Most of the lower animals lead a solitary life. If we disregard certain phenomena shortly to be mentioned, solitary animals never seek out other individuals. Speaking generally they exist, each one for itself, in extreme isolation, even when external conditions throw them together in no matter how great a number. Only at breeding time can we say that exceptions occur, in that the male and female then come together during the one sexual act, only to separate again immediately afterwards. In those species, however, where the fertilization of the eggs takes place without copulation there is not even an attempt on the part of male and female to come together.
