ABSTRACT
Polymorphism was frequently mentioned in the preceding lectures but I refrained from discussing it because it keeps recurring in very nearly all the social insects and could not be viewed in proper perspective till their idiosyncracies had been surveyed. It is twenty years since I first discussed this perplexing subject (1907a). In the meantime it has been constantly in my thoughts and I have, of course, consulted all the pertinent works to which I could gain access. At no period have the students of the social insects been so numerous, evinced a keener interest in or been better equipped to deal with the subject. And yet we have made little progress towards the solution of the many problems suggested by the phenomena of polymorphism. It is, in fact, so intricate that although I have set apart two lectures for its discussion I shall be able to present only a small number of its many aspects and difficulties. Perhaps it will conduce to clearness, if I confine this lecture to an account of some of the leading facts and more obvious inferences and in the next delve into the speculations which they have suggested and will no doubt long continue to suggest.
