The bibliography (appendix E), which has been carried down to the close Of the year 1908, is unfortunately very voluminous and includes many titles Of unimportant works. Like all such compilations, it is necessarily incomplete, and undoubtedly contains positive errors. A serious attempt has been made, however, to reduce these to a minimum, and I shall be glad to receive any additions or corrections. For portions Of the text and many Of the figures I have drawn rather freely on my previously published papers. A few entire chap ters, in fact, such as those on polymorphism, have been reproduced with only slight verbal alterations. Others, like Chapters XVIII and XX, are abridgments Of longer accounts of the fungus-growing and honey ants recently published in the Bulletin Of the American Museum Of Natural History.