oil and water is proverbial. Fortunately, both water and xylol, the highly volatile oil used to dissolve the balsam, are miscible with alcohol. Thus alcohol can be used as an intermediate step between the two. In preparing a specimen for slide-mounting, the water in the tissues is wholly replaced by alcohol. During the process any air which may be trapped in the body cavities is, incidentally, dissolved. Then the alcohol is replaced by xylol and the xylol by a solution of balsam in xylol. When the oil evaporates, the solid resin remains, filling and covering the specimen completely and permanently. In taking a specimen through the slide-mounting men in each bath for about an hour. Change the liquid on the specimen or the specimen in the liquid, as you prefer; but in either case, drain the creature thoroughly at each change. A bit of absorbent paper grasped with forceps is convenient for mopping up the last drop in the bottom of a vial. If you are using a capsule, press one end of it against a blotter. It will drain at once. When lowering a capsule into a bath, hold it vertically, so that the air may escape at the top as the liquid rises from the bottom. One bath can be employed to process many specimens, if you are careful to avoid unnecessary dilution. Once used, however, the fluid should never be returned Fig. 12. Series of dehydrating baths for the preparation of spiders and soft bodled insects. The specimen, pinned to a chip of balsa wood, floats up-side-down in the dish. processes, the sequence of operations will be as follows: 1. Catch your specimen and kill it by dropping into hot water. This extends the appendages. Specimens killed in alcohol, although otherwise suitable, are likely to be difficult to arrange on a slide because the contracted position in which they are fixed. Prick the abdomen with a fine needle to admit fluids more readily. 2. Dehydrate the specimen by "stepping up" through a graduated series of alcohols. For most eggs and adult insects or spiders, however small, 50%, 70%, and 95% or full strength will be enough. For extremely minute or delicate immature forms, baths of 60% and 80% may be included. Leave the speci- to the stock bottle. Keep it in a special bottle marked "used." The 95% alcohol is the most critical step of the de-hydration, and should be renewed frequently. Save the old alcohol to feed the spirit lamp for the caterpillar oven. 3. From 95% alcohol, transfer the specimen to carbol-xylene. This serves two purposes. The phenol, which has a great affinity for water, will remove the last traces of moisture from the specimen. The xylol replaces the alcohol and dissolves the natural fats and oils of the body, making it transparent. This is called "clearing." If clearing fails to occur after a few hours, you may reasonably suppose that the carbohic acid is exhausted, and the solution should be changed. Carbol xylene turns brown with prolonged