well-known instinct in another class of creatures, which has a strong resemblance to that of the huanaco, as I have interpreted it, and which may even serve to throw a side light on the origin of the huanaco's instinct. I refer to a habit of some ophidians, in temperate and cold countries, of returning annually to hybernate in the saine den.
A typical instance is that of the rattlesnake in the colder parts of North America. On the approach of winter these reptiles go into hiding, and it has been observed that in some districts a very large number of individuals, hundreds, and even thousands, will repair from the surrounding country to the ancestral den. Here the serpents gather in a mass to remain in a wholly or semi-torpid condition until the return of spring brings them out again, to scatter abroad to their usual summer haunts. Clearly in this case the knowledge of the hyberna-ting den is not merely traditional--that is, handed down from generation to generation, through the young each year following the adults, and so forming the habit of repairing at certain seasons to a certain place; for the young serpent soon abandons its parent to lead an independent life; and on the approach of cold weather the hybernating den may be a long distance away, ten or twenty, or even thirty miles from the spot in which it was born. The annual return to the hybernating den is then a fixed unalterable instinct, like the autumnal migration of some birds to a warmer latitude. It is doubtless favourable to the serpents to hybernate in large numbers massed together; and the habit of resorting annually to the same spot once formed,
322 The Naturalist in La Plata.
we can imagine that the individuals--perhaps a single couple in the first place--frequenting some very deep, dry, and well-sheltered cavern, safe from enemies, would have a great advantage over others of their race; that they would be stronger and increase more, and spread during the summer months further and further from the cavern on all sides; and that the further afield they went the more would the instinct be perfected; since all the young serpents that did not have the instinct of returning unerringly to the ancestral refuge, and that, like the outsiders of their race, to put it in that way, merely crept into the first hole they found on the approach of the cold season, would be more liable to destruction. Probably most 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;
The Dying Huanaco. 323
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.