These facts cannot be ascribed to “instinct,” seeing that tram-cars could not have been objects of previous experience to the ancestors of the ants; and therefore the degree of receptual intelligence, or “practical inference,” which was displayed is highly remarkable. Clearly, the insects must have appreciated the nature of these repeated catastrophes, and correctly reasoned out the only way by which they could be avoided. As this is an important branch of my subject, I will add a few more illustrations drawn from vertebrated animals, beginning with some from the writings of Leroy, who had more opportunity than most men of studying the habits of animals in a state of nature.[41] He says of the wolf:—“When he scents a flock within its fold, memory recalls to him the impression of the shepherd and his dog, and balances that of the immediate neighbourhood of the sheep; he measures the height of the fence, compares it with his own strength, takes into account the additional difficulty of jumping it when burdened with his prey, and thence concludes the uselessness of the attempt. Yet he will seize one of a flock scattered over a field, under the very eyes of the shepherd, especially if there be a wood near enough to offer him a hope of shelter. He will resist the most tempting morsel when accompanied by this alarming accessory [the smell of man]; and even when it is divested of it, he is long in overcoming his suspicions. In this case the wolf can only have an abstract idea of danger—the precise nature of the trap laid for him being unknown.... Several nights are hardly sufficient to give him confidence. Though the cause of his suspicions may no longer exist, it is reproduced by memory, and the suspicion is unremoved. The idea of man is connected with that of an unknown danger, and makes him distrustful of the fairest appearances.”[42] Leroy also well observes:—“Animals, like ourselves, are _forced_ to make abstractions. A dog which has lost his master runs towards a group of men, by virtue of a general abstract idea, which represents to him the qualities possessed in common with these men by his master. He then experiences in succession several less general, but still abstract ideas of sensation, until he meets the particular sensation which he seeks.”[43]