Says Rymer Jones, ‘Reptiles do not sit (sic) upon their eggs, hence the latter have only a membranous envelope. In many of the reptiles which lay eggs, especially the Colubri (colubrine snakes), the young one is already formed and considerably advanced in the egg at the moment when the mother lays it; and it is the same with those species which may at pleasure be rendered viviparous by retarding their laying.’[129] The latter words are traced to Cuvier, and prove that this most remarkable power has long been recognised.
In the first few words of the above, Jones spoke of reptiles generally from toads to turtles; with the latter, soft eggs would certainly fare badly did they attempt to incubate them. Still the term ‘reptiles’ is misleading, because, as is now well known, some snakes do incubate, and some lizards are suspected of doing the same. Even our common ring snake has been found coiled upon her eggs.
Serpents are allied to birds in producing young from eggs, but in reptiles the eggs differ from those of birds in undergoing a sort of incubation from the very first; so that at whatever period a snake’s egg is examined, whether it has been laid or not, the embryo will be found more or less advanced. Sometimes in an egg just deposited, a perfectly formed fœtus will be found. ‘Serpents are always oviparous,’ says Schlegel; ‘and it is a mistake to suppose that all venomous snakes produce live young, and all non-venomous kinds lay eggs. Neither has the diversity of generation any relation to the organization of the animal itself. Coronella lævis produces living young, but other coronellas lay eggs. In 1862, when very little was known of the Coronella lævis, Mr. Frank Buckland had one in a cage in London, which to the surprise of most persons produced live young ones. This may have been solely owing to her captivity and her retention of eggs till hatched. Some boas lay eggs, others are viviparous. In the latter case the young are enclosed in a thin membrane, which they tear or break at the moment of birth. In those that are a long while hatching, the tunic is of a thick, coriaceous texture, not easily ruptured. Thus, to sum up with one other authority, Der Hœven: ‘In many serpents and lizards the development begins in the body of the parent before the egg is laid, and in some the membrane of the egg is broken by the young one before birth.’
This latter condition has been considered viperine, but even in a viper the young have been produced in a membrane. This was the case with Vipera nasicornis at the London Zoological Gardens, on Sunday, November 6th, 1881, that gave birth to forty-six viperlings. Some of them had no vestige of membrane clinging about them; others had, but burst it immediately and began to crawl; while yet others did not burst their ‘shell’ at all,—if indeed so filmy and thin a membrane could be called a shell,—but died within it. When the membrane burst, it was seen to collapse and shrivel up into nothing, as children’s air balls do when they are torn; but the texture of these balls is strong in comparison with the extreme tenuity of the viperine egg tunic. Yet it was strong enough to contain a young one, as in the case of those unbroken. There is no means of ascertaining the precise length of time this viper had been in captivity; but as her young ones had all such fully-developed fangs, and the precocity to strike and kill a mouse as soon as born, this was probably another case of postponed deposition. On a previous occasion, September 1875, a family of young vipers born at the Ophidarium were ‘some quite clean and others with the remains of the egg covering about them.’ The quotation from my notebook refers to the Daboia of India, ‘Russell’s viper’ (Vipera elegans). Still these may be exceptional and possibly abnormal cases, but are examples worth noting, and another proof of the many exceptions to what we are accustomed to believe invariable rules.
White, in his History of Selborne, mentions the capture of a viper in which he found fifteen young, the shortest being seven inches. They were active, spiteful, and menacing, and yet ‘had no manner of fangs that we could find, even with the help of our glasses.’
Mr. Frank Buckland tells of a man who cut open a string of snake’s eggs, and the young, thus prematurely introduced into the world, ‘showed fight.’
Of historical ophidians which have figured in many pages, first comes chronologically the Paris python, that in 1841 laid fifteen eggs and incubated them. She has already been alluded to in chap. iv., but claims further mention presently.
A python in the Amsterdam collection next hatched twenty-two eggs.
In 1862 a python at the London Gardens laid above a hundred eggs,—‘more than a bushel,’ according to the keeper,—and settled herself to hatch them. Much interest attaches itself to this lady’s history; but first to complete our list chronologically, the following harmless species in the London collection have within the last ten years produced live young, being examples of that ‘diversity of generation’ of which Schlegel speaks.
August 1872, the ‘seven-banded snake’ (Trop. leberis) had five young and some eggs at the same time.