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