[SNAKE-INCUBATION.]
The Zoological Gardens of London, always attractive, now and then acquire even additional interest by the arrival of some new inmate, or the occurrence of some rare event among those already established there. Last year the Prince of Wales's Indian collection of animals, the year before the snake-eating snake, drew extra crowds; and of late the anaconda from Brazil has rendered herself popular by bringing forth a family of snakelings; though, owing to the effects of her long journey and close imprisonment, her young ones were dead. A few years ago the largest snake in the Gardens was an African python, that deposited above one hundred eggs in a nest of moss which had been supplied to her; and as some writers about snakes had told us that the python incubates her eggs, and that only this kind exhibits any such maternal instinct, she also drew crowds of the curious.
The pythoness whose proceedings we are about to relate, having deposited her eggs, arranged them in a level mass and then coiled herself around and over them; sometimes they could be just discovered between her coils, and sometimes she covered them entirely. Heat combined with moisture are essential to the development of snakes' eggs; and in the choice of a spot in which to deposit them, the maternal instinct of the animal in a state of freedom is evident. It is generally among decaying vegetation where heat is generated, or in some moist soft herbage where the sun's rays can penetrate. To regulate the temperature in a close cage and keep the moss precisely in a condition to suit snake requirements, was by no means easy, and our pythoness seemed far from satisfied. The fact, however, was established beyond doubt, that she was hatching her eggs by the warmth of her own body.
But a most untoward disaster happened one night in the overflowing of the tank among her eggs, completely saturating them; and it was not surprising therefore, that no young pythons appeared. The enormous reptile remained coiled around and over her addled eggs for above seven weeks, after which they were taken from her. She had, and with good reason, been exceedingly irritable and even savage during this time of trial, as it was mid-winter, the season when under other circumstances she, like her companions, would have been half torpid. But her maternal affection was undeniable, and this alone was worth witnessing; since some authors would have had us believe that snakes (and particularly non-venomous ones) manifest entire indifference regarding their eggs and young. The python's eggs being, as usual, in one long string, the keeper had no little trouble in getting them from under her.
Being aquatic in their habits, and on that account requiring much water, anacondas are difficult to keep in captivity. The one lately arrived among us was no sooner released from its travelling box than it took to the tank with which its cage is furnished, and remained in it for hours and even days together. But not there, poor thing, can its swimming powers be displayed, since in close coils it completely fills it. Notwithstanding these drawbacks of London life, the Gardens can now boast of three of these valuable snakes; one of which has been a resident since 1869; while those in Paris have not survived any length of time.
One still more remarkable characteristic of the anaconda is that, like the sea-snakes (Hydrophidæ), but unlike the python, it produces its young alive. We have long been accustomed to think that only vipers produce live young—and hence their name—and that all the non-venomous snakes lay eggs. But snakes, so far as those in captivity are concerned, are continually doing what is not expected of them. Zoological Gardens afford valuable opportunities to students for acquiring knowledge of the form, size, habits, &c. of animals, and an occasional insight into their modes of life unattainable otherwise. This is especially the case regarding the Ophidians; creatures which in their native haunts are so retiring, inaccessible, and mostly nocturnal, that less has been known of them than of almost any other tribe of creatures. Regarding the subject in question, several very important zoological facts have recently been established at the Gardens, and we may add, to the surprise of the naturalist world in England. In 1862 (the same year in which the pythoness laid her hundred eggs), the then but slightly known non-venomous English snake Coronella lævis gave birth to a family of six live young ones in a cage in London; and several other harmless snakes in the London ophidarium have also afforded cause for surprise, not only in producing live young, but in manifesting a very decided care for them. Some New-world species have been examples of this; as, for instance, the 'garter-snake,' the 'chicken-snake,' and the 'yellow boa' of Jamaica (Chilobothrus inornatus), the latter on several occasions, and sometimes depositing eggs at the same time, but the eggs proving bad.
Mr Philip Henry Gosse, when in Jamaica nearly thirty years ago, gave much careful attention to the habits of this 'yellow boa,' a snake which sometimes attains eight or ten feet in length and is extremely active. He records a great deal of highly interesting matter concerning the chilobothrus; and, as a careful and conscientious observer, his testimony is of much value. That this snake when at liberty lays eggs, was well known, nests with eggs in them being often found. In one case a 'yellow boa' was seen issuing from a narrow passage in a bank, which when dug into was found to lead to a cavity lined with leaves and soft trash, and containing eggs. This hole had been excavated, because the dry crumbled earth was discharged at the entrance, where it lay in a heap. The passage was only just large enough to admit the snake, and the soft rubbish within must have been carried there. We cannot positively assert that the snake constructed this skilful hiding-place for herself, but if she did, she must have forced out the earth as the burrowing snakes do, or by the muscular undulations of her body; and she must have conveyed the leaves there in her mouth. Snakes do, we know, sometimes make nests by coiling themselves round and round to form a hollow. Under either circumstance maternal instinct is undeniable; and if chilobothrus merely discovered and appropriated the nest of some other creature, her intelligence is still worth recording.
We knew an instance where a snake in captivity exhibited restlessness and uneasiness, crawling about the cage as if in search of something. Those who had the care of it suspected she was with eggs, and placed some sand in the cage. This appeared to satisfy her, and the eggs were deposited. Mr Gosse had a Jamaica boa in the same condition. For a long time it manifested discomfort and restlessness, being savage and in every way objectionable, till at length it produced a family of young ones. Knowing it was the habit of this snake to incubate its eggs, Mr Gosse was greatly surprised at the event; and the startling question occurred to him, that when circumstances are unfavourable for the deposition of eggs, could a snake retain them until the young are hatched?
Mr Gosse's surmises have been entirely confirmed both by similar occurrences at the Zoological Gardens and by other writers, who in the subsequent interval have also given careful attention to the habits of Ophidians, and have produced valuable scientific works on the subject. It is now an ascertained fact that not chilobothrus only but several other oviparous species may at pleasure be rendered viviparous by retarding the deposition of their eggs when circumstances are unfavourable for them! In fact we find that we must almost discard those old distinctions of oviparous, viviparous, and ovoviviparous; which German authors tell us are not founded on any other ground than a greater or less development of the fetus in the egg at the time of laying; or on the nature of the exterior covering of the egg; which is thicker and leathery in those which take some time in hatching, and slighter and membranous in those which are hatched either before or on deposition.