not need to be very various in pattern: but far from this, they vary in appearance as much as the shell. Not only is there a different pattern for every different order of the class, but a different pattern for every genus; nay, there are even distinctions between the tongues of different species in the same genus. Consequently some authorities on shell-fish prefer to classify them by their tongues, a classification which for the most part holds good. So characteristic is the tongue of the Gasteropod, that when new animals have turned up which were difficult to classify by means of the structure of the body, they have been finally recognised as Molluscs, somewhat related to the snails, by the tongue. This file-like tongue-ribbon of the snails is often called the Odontophore or Tooth-Carrier; sometimes the part which actually bears the teeth receives the name of the radula. The snail and its relative, the slugs, belong to the Pulmonate (_i.e._ air-breathing) division of the Gasteropoda. The sea-slugs, in which, like the land slugs, the shell is absent or reduced, are relatives of the land snails. Some of those found on our own shores are handsome creatures, brilliantly coloured. Both groups fall under the division Euthyneura, while the majority of the marine univalves belong to the division Streptoneura (_i.e._ Gasteropods with twisted nerves). The Gasteropods, in the course of the evolution of their shell, have had the body thrown crooked by the burden of carrying it; the Streptoneura are the forms in which this crookedness is most pronounced; in the Euthyneura it is less so. There are degrees of crookedness even among the Streptoneura; and the limpet is less crooked than the periwinkle (see Table, p. 30). The older classifications of the Gasteropoda were largely founded on the characters of the shell; but these, though in the main they hold good, have required some modifications in recent times. Conchology, the study of shells, was at one time the hobby of many collectors whose knowledge of the animals possessing the shells was not of a very extensive kind; and consequently the very name of conchology is often enough to ruffle the feelings of the zoologist of the present day. Yet many interesting problems of variation may be studied from shells alone, by those whose circumstances forbid them to study the living animal. Nor is there any branch of zoology which is more useful to the teacher who wishes to catch the eye and the attention of the beginner in the study of natural history, especially if the beginner is young, as beginners ought to be. Therefore we must by no means undervalue the past labours of conchologists, or the valuable collections which their industry has brought together and set in order for the benefit of the world.