ABSTRACT
With the single exception of the termites, all the groups of really social insects recognized in the preceding lecture, are confined not only to a single order, the Hymenoptera, but also to a single sub-order, the Aculeata. And since these social organisms have undoubtedly arisen from solitary species still represented by more or less closely allied forms in the existing fauna, we are confronted with the problem of the phylogenetic origin of the order Hymenoptera as a whole and of the Aculeata and each of its eleven social types in particular. So much interesting material bearing on this problem has been accumulating during recent years that even for its brief consideration this and the three following lectures will be required. We may perhaps reach nothing more conclusive or satisfactory than has resulted from other similar phylogenetic disquisitions but we shall encounter many singular and suggestive phenomena which, I trust, will lose none of their intrinsic value by being interpreted as representing significant stages in a very long and complicated evolutionary process. I believe, moreover, that such a review as the one I am undertaking is really necessary for the purpose of discriminating between the ancient morphological and behaviouristic characters, which the social insects still retain as a heritage from their solitary ancestors, and those which they have more recently acquired in response to their peculiar communal environment.
