It will be remembered that our test of instinctive as distinguished from truly intelligent action is simply whether all individuals of a species perform similar adaptive movements under the stimulus supplied by similar and habitual circumstances, or whether they manifest individual and peculiar adaptive movements to meet the exigencies of novel and peculiar circumstances. The importance of this distinction may be rendered manifest by the following illustrations. [Illustration: Fig. 8.] We have already seen that the ants which Sir John Lubbock observed display many and complex instincts, which together might seem to justify us in anticipating that animals which present such wonderful instincts must also present sufficient general intelligence to meet simple though novel exigencies by such simple adaptations as the unfamiliar circumstances require. Yet experiments which he made in this connection seem to show that such is not the case, but that these ants, with all their wealth of instinctive endowments, are utterly destitute of intelligent resources; they have abundance of common and detailed knowledge (supposing the adaptations to be made consciously) how to act under certain complex though familiar circumstances, but appear quite unable to originate any adaptive action to obviate even the simplest conceivable difficulty, if this is of a kind which they have not been previously accustomed to meet. Thus, on a horizontal rod B supported in a saucer of water S, and therefore inaccessible to the ants from beneath, he placed some larvæ A. On the nest N he then placed a block of wood C D, constructed so that the portion D should touch the larvæ at A. When the ants had made a number of journeys over C D A and back again, he raised the block C D so that there was an interval 3/10 of an inch between the end of the block D and the larvæ at A. The ants kept on coming, and tried hard to reach down from D to A, which was only just out of their reach. . . . After a while they all gave up their efforts and went away, losing their prize in spite of most earnest efforts, because it did not occur to them to drop 3/10 of an inch. At the moment when the separation was made there were fifteen ants on the larvæ. These could, of course, have returned if one had stood still and allowed the others to get on its back. This, however, did not occur to them; nor did they think of letting themselves drop from the bottom of the paper (P) on to the nest. Two or three, indeed, fell down, I have no doubt by accident; but the remainder wandered about, until at length most of them got into the water.