3. Leaving aside the pre-Darwinian writers, like Toussenel, Fee, and many others, several works containing many striking instances of mutual aid--chiefly, however, illustrating animal intelligence were issued previously to that date. I may mention those of Houzeau, Les facultes etales des animaux, 2 vols., Brussels, 1872; L. Buchner's Aus dem Geistesleben der Thiere, 2nd ed. in 1877; and Maximilian Perty's Ueber das Seelenleben der Thiere, Leipzig, 1876. Espinas published his most remarkable work, Les Societes animales, in 1877, and in that work he pointed out the importance of animal societies, and their bearing upon the preservation of species, and entered upon a most valuable discussion of the origin of societies. In fact, Espinas's book contains all that has been written since upon mutual aid, and many good things besides. If I nevertheless make a special mention of Kessler's address, it is because he raised mutual aid to the height of a law much more important in evolution than the law of mutual struggle. The same ideas were developed next year (in April 1881) by J. Lanessan in a lecture published in 1882 under this title: La lutte pour l'existence et l'association pour la lutte. G. Romanes's capital work, Animal Intelligence, was issued in 1882, and followed next year by the Mental Evolution in Animals. About the same time (1883), Buchner published another work, Liebe und Liebes-Leben in der Thierwelt, a second edition of which was issued in 1885. The idea, as seen, was in the air. 4. Memoirs (Trudy) of the St. Petersburg Society of Naturalists, vol. xi. 1880. 5. George J. Romanes's Animal Intelligence, 1st ed. p. 233. 6. Pierre Huber's Les fourmis indigees, Geneve, 1861; Forel's Recherches sur les fourmis de la Suisse, Zurich, 1874, and J.T. Moggridge's Harvesting Ants and Trapdoor Spiders, London, 1873 and 1874, ought to be in the hands of every boy and girl. See also: Blanchard's Metamorphoses des Insectes, Paris, 1868; J.H. Fabre's Souvenirs entomologiques, Paris, 1886; Ebrard's Etudes des moeurs des fourmis, Geneve, 1864; Sir John Lubbock's Ants, Bees, and Wasps, and so on. 7. Forel's Recherches, pp. 244, 275, 278. Huber's description of the process is admirable. It also contains a hint as to the possible origin of the instinct (popular edition, pp. 158, 160). See Appendix II. 8. The agriculture of the ants is so wonderful that for a long time it has been doubted. The fact is now so well proved by Mr. Moggridge, Dr. Lincecum, Mr. MacCook, Col. Sykes, and Dr. Jerdon, that no doubt is possible. See an excellent summary of evidence in Mr. Romanes's work. See also Die Pilzgaerten einiger Sud-Amerikanischen Ameisen, by Alf. Moeller, in Schimper's Botan. Mitth. aus den Tropen, vi. 1893.