‘Snakes are either oviparous or viviparous,’ is what we are accustomed to read, followed by the explanation that the former are those which lay eggs, and the latter those which produce their young alive. To these two chief distinctions, the more recent one of ovoviviparous has been added, to describe some intermediate cases where the egg is ruptured in parturition, so that again a fully-formed young one is born. For broad distinctions the three terms do well enough, though many exceptions exist. The grand distinction of ‘_viper_’ as applied to those snakes which produce live young, was adopted when snakes were first observed and described by classic writers. ‘Vipers alone are viviparous,’ wrote Aristotle. ‘Sometimes the little vipers eat through their mother and come forth. The viper brings forth one at a time in one day, but she brings forth more than twenty little vipers. Other serpents produce their eggs externally, and these eggs are connected with each other like the necklaces of women. But when they bring forth, they deposit their eggs in the earth, _and there incubate them_. These eggs they disclose the following year.’ We do not quote the above as all fact, but rather to show how very much there has been to _unlearn_ since Aristotle was accepted as an authority. The shadow of truth and the mention of a possible fact as an invariable rule are dangerous mistakes, for, as we have already shown, where a snake is concerned, one can rarely feel safe in asserting anything as positive. It is not impossible that, owing to disease or accident, some gravid viper may have been so wounded as to enable her young to make their début through her ruptured side. Such an occurrence has been seen in our own time. Aristotle or his authority may even have witnessed such an accident, and recorded it under the supposition that it was normal. In whatever way the error may have originated, it is only one out of many that are propagated even to the present day by the uninformed. At the moment of writing, we read in one of our first-class ‘dailies,’ alluding to a brood of young vipers lately born at the Zoological Gardens: ‘The young viper comes into the world in the shape of an egg, and its first business is to push through the filmy membrane which envelops it in its imprisoned form.’ This is contrary to our accepted ideas, though partially true in this instance. The word viper is generally supposed to be derived from the Latin _vipera_, a contraction of _vivipara_, to produce alive. The above words therefore are inapplicable as a rule. So far as was known in Aristotle’s time, only certain venomous species common in the countries with which classic writers were best acquainted did produce live young, and they were mostly what are still known as ‘vipers,’ a term restricted to these and explained as being derived from such signification.