snakes get killed long before a natural decline sets in; to say that not one in a thousand dies of old age would probably be no exaggeration; but if they were as safe from enemies and accidents as some less prolific and more highly-organized animals, so that many would reach the natural term of life, and death came slowly, we can imagine that in such a heat-loving creature the failure of the vital powers would simulate the sensations caused by a falling temperature, and cause the old or sick serpent, even in midsummer, to creep instinctively away to the ancient refuge, where many a long life-killing frost had been safely tided over in the past. The huanaco has never been a hybernating animal; but we must assume that, like the crotalus of the north, he had formed a habit of congregating with his fellows at certain seasons at the same spot; further, that these were seasons of suffering to the animal--the suffering, or discomfort and danger, having in the first place given rise to the habit. Assuming again that the habit had existed so long as to become, like that of the reptile, a fixed, immutable instinct, a hereditary knowledge, so that the young huanacos, untaught by the adults, would go alone and unerringly to the meeting-place from any distance, it is but an easy step to the belief, that after the conditions had changed, and the refuges were no longer needed, this instinctive knowledge would still exist in them, and that they would take the old road when stimulated by the pain of a wound; or the miserable sensations experienced in disease or during the decay of the life-energy, when the senses grow dim, and the breath fails, and the blood is thin and cold. I presume that most persons who have observed animals a great deal have met with cases in which the animal has acted automatically, or instinctively, when the stimulus has been a false one. I will relate one such case, observed by myself, and which strikes me as being apposite to the question I am considering. It must be premised that this is an instance of an acquired habit; but this does not affect my argument, since I have all along assumed that the huanaco--a highly sagacious species in the highest class of vertebrates--first acquired a habit from experience of seeking a remembered refuge, and that such habit was the parent, as it were, or the first clay model, of the perfect and indestructible instinct that was to be.