memory by repetition, and the impression is liable to become effaced by lapse of time. Sir John Lubbock found it necessary to teach the insects, by a repetition of several lessons, their way to treasure, if that way were long or unusual. With regard to the duration of memory in ants, it does not appear that any direct experiments have been made; but the following observation by Mr. Belt on its apparent duration in the leaf-cutting ant may be here stated: In June, 1859, he found his garden invaded by these ants, and on following up their paths he found their nest about a hundred yards distant. He poured down their burrows a pint of diluted carbolic acid. The marauding parties were at once drawn off from the garden to meet the danger at home, while in the burrows themselves the greatest confusion prevailed. Next day he found the ants busily engaged in bringing up the ant-food from the old burrows and carrying it to newly formed ones a few yards distant. These, however, turned out to be intended only as temporary repositories; for in a few days both old and new burrows were entirely deserted, so that he supposed all the ants to have died. Subsequently, however, he found that they had migrated to a new site, about two hundred yards from the old one, and there established themselves in a new nest. Twelve months later the ants again invaded his garden, and again he treated them to a strong dose of carbolic acid. The ants, as on the previous occasion, were at once withdrawn from his garden, and two days afterward he found "all the survivors at work on one track that led directly to the old nest of the year before, where they were busily employed in making new excavations. . . . It was a wholesale and entire migration." Mr. Belt adds, "I do not doubt that some of the leading minds in this formicarium recollected the nest of the year before, and directed the migration to it." Of course, it is possible that the leaders of the migration may have simply stumbled on the old burrows by accident, and, finding them already prepared as a nest, forthwith proceeded to transfer the food and larvæ; but, as the old and the new burrows were separated from one another by so considerable a distance, this supposition does not seem probable, and the only other one open is that the ants remembered their former home for a period of twelve months. This supposition is rendered the more probable from a somewhat analogous case recorded by Karl Vogt in his "Lectures on Useful and Harmless Animals." For several successive years ants from a certain nest used to go through certain inhabited streets to a chemist's shop six hundred metres distant, in order to obtain access to a vessel filled with sirup. As it can not be supposed that this vessel was found in successive working seasons by as many successive accidents, it can only be concluded that the ants remembered the sirup-store from season to season.
Recognition.—I shall now pass on to consider a class of highly remarkable facts. It has been known since the observations of Huber