Although the crustacean family counts its varieties by thousands, and contains members of all sizes, from minute animalculæ to gigantic American crabs and lobsters, and ranges from the simplest to the most complex forms, yet the edible varieties are not at all numerous. The largest of these are the lobster (_Astacus marinus_) and the crab (_Cancer pagurus_); and river and sea cray-fish may also be seen in considerable quantities in London shell-fish shops; and as for common shrimps (_Crangon vulgaris_) and prawns (_Palæmon serratis_), they are eaten in myriads. The violet or marching crab of the West Indies, and the robber crab common to the islands of the Pacific, are also esteemed as great delicacies of the table, but are unknown in this country except by reputation. Leaving old and grave people to study the animal economy of the larger crustacea, the juveniles may with advantage take a peep at the periwinkles, the whelks, or other mollusca. These are found in immense profusion on the little stones between high and low water mark, and on almost every rock on the British coast. Although to the common observer the oyster seems but a repulsive mass of blubber, and the periwinkle a creature of the lowest possible organisation, nothing can be further from the reality. There is throughout this class of animals a wonderful adaptibility of means to ends. The turbinated shell of the periwinkle, with its finely-closed door, gives no token of the powers bestowed upon the animal, both as provision for locomotion (this class of travellers wherever they go carry their house along with them) and for reaping the tender rock-grass upon which they feed. They have eyes in their horns, and their sense of vision is quick. Their curiously-constructed foot enables them to progress in any direction they please, and their wonderful tongue either acts as a screw or a saw. In fact, simple as the organisation of these animals appears to be, it is not less curious in its own way than the structure of other beings which are thought to be more complicated. In good truth, the common periwinkle (_Littorina vulgaris_) is both worth studying and eating, vulgar as some people may think it. Immense quantities of all the edible molluscs are annually collected by women and children in order to supply the large inland cities. Great sacks full of periwinkles, whelks, etc., are sent on by railway to Manchester, Glasgow, London, etc.; whilst on portions of the Scottish sea-coast the larger kinds are assiduously collected by the fishermen’s wives and prepared as bait for the long hand-lines which are used in capturing the codfish or other Gadidæ. As an evidence of how abundant the sea-harvest is, I may mention that from a spot so far north as Orkney hundreds of bags of periwinkles are weekly sent to London by the Aberdeen steamer.