Formalin is very cheap and readily obtained, but it is much less suitable than spirit for most Crustacea, as it tends to make them stiff and fragile, and small forms containing much lime, such as Cumacea, may become decalcified. For Crustacea collected by the tow-net, however, formalin gives good results. A few drops of strong formalin, added to the water into which the tow-net has been washed, kills the animals in a few minutes. After they have sunk to the bottom, the liquid may be poured off and replaced by formalin diluted with sea-water (for marine plankton), or by a mixture of formalin and spirit. The most suitable strength of formalin varies with different organisms, but 5 per cent. (_i.e._, 1 part of commercial formalin to 19 parts of water) is perhaps most generally useful. Crabs, Prawns, and the like, if put alive into strong spirit, may throw off some of their limbs, or else become so rigid that these break on the slightest manipulation. This may often be avoided by killing the animals in weak spirit (30 per cent. or less) before preserving in strong spirit. Marine species may also be killed by placing them in fresh water, care being taken not to allow them to remain in it longer than is necessary, as it causes distortion of the membranous appendages. The larger Crabs, Lobsters, and the like, may be preserved dry, although in this state they are unsuitable for examination of the more delicate appendages. The carapace should be detached, and the soft parts cleaned away as far as possible, a bent wire being used, if necessary, to remove the flesh from the legs. The specimens should be dried in the shade, to preserve as much as possible of the natural colour. With specimens intended for permanent preservation in spirit, the use of corks should be avoided, as they discolour the spirit, and ultimately the specimens. Small specimens are most conveniently kept in glass tubes closed with a piece of clean elder-pith (not cotton-wool), and placed, upside down, in a bottle of spirit. Labels to be placed inside the tubes are best written with Indian ink, and allowed to dry before immersion in the spirit. II. NOTES ON BOOKS The literature of Carcinology is bewildering in its extent, and is for the most part scattered through the volumes of scientific periodicals and the publications of learned societies in most of the languages of Europe. A guide to the current literature is provided by the _Zoological Record_, the latest volume of which, relating to the year 1909, enumerates no fewer than 337 papers dealing wholly or in part with this group of animals. The following short list of books in the English language may be of some help to the beginner. Most of them give references to the literature which will provide the necessary guidance towards a further study of the subject. GENERAL WORK _Huxley, T. H._ The Crayfish: an Introduction to the Study of Zoology. International Science Series, vol. xxviii. London, 1880.