more especially the crustaceans, are partial to carrion. If, therefore, the observer desires to study the ways in which the various creatures secure and devour their food, he should introduce into his aquaria live marine worms and other small animals, and also small pieces of fish or flesh. We will now pass on to the more serious undertaking of the construction and management of a permanent salt-water aquarium. The first point to decide is, perhaps, the size of the proposed vessel, and this will in many cases be determined partly by a consideration of the space at one’s disposal, and of the apartment it is intended to occupy. If it is to be placed in a drawing-room or other ordinary apartment of a dwelling-house, preference should be given to a window facing the north in order to avoid the direct rays of the sun, but perhaps no situation is more suitable than a cool conservatory in the shady part of a garden; and in either case a strong table or other support should be provided, of a form and size adapted to those of the aquarium to be constructed. Various materials may be used in the construction of such an indoor aquarium, and we shall deal with two or three different types, so that the reader may make his selection according to his fancy, or to his mechanical ability, if he intends that it shall be of his own construction. We will begin with an aquarium constructed entirely of a mixture of cement and fine sand, this being the most inexpensive and certainly the easiest to make; and although it may not be regarded as the most ornamental--but opinions will differ on this point--yet it has the decided advantage of being the nearest approach to the natural rock pool. Though somewhat heavy and cumbersome, even when empty, the amount of material used in its construction may be varied according to the taste and convenience of the maker. Further, this form of aquarium is one that will readily admit of structural alterations at any future period. It may be deepened at any time; lateral additions or extensions may be made, or a portion may at any time be shut off for the purpose of isolating certain of the animals procured. [Illustration: FIG. 34.--SECTION OF AN AQUARIUM CONSTRUCTED WITH A MIXTURE OF CEMENT AND SAND]