exposure to light, but this does not seem to impair its efficiency. It is rather viscous, and if you are using a capsule, you may have to open it to let this liquid in. 4. When the specimen is perfectly clear, rinse it in two baths of xylol to remove the phenol. Allow for each the same length of time as was required for the clearing. 5. Clean and polish a slide and cover glass. Use soap and water. Handle the polished glass by the edges only, to avoid finger prints. Beware of dust and lint. Select the cell, glass fragments, or bits of plastic sheeting to support the cover. Be sure that the tools, balsam, and "duco" cement are ready at hand. 6. With pen and india ink, copy the data relative to the specimen onto one of the gummed paper labels, and stick it to the extreme left-hand end of the slide. If there is more information than one label will hold, put another at the right-hand end. 7. Lay the slide in the jig. Place the cover glass supports in position, in the corners of a rectangle or evenly spaced around a circle, just inside the outline marked on the jig. Fasten each with a little clear cement. Place a large drop of balsam in the middle of the slide and spread it with a needle almost to the limits of the outline all around. Allow it to stand for several minutes to become tacky. Remove your speci- men from the xylol and place it over the dot at the center of the jig. Spread out the legs and other ap- pendages by the aid of needles. The tacky balsam will help to hold them in place. If several specimens are to be mounted on the same slide, arrange them in some orderly manner. Then flood each with a small drop of balsam, guiding the flow with a needle so that the air is forced out ahead of the liquid, and no bubbles are formed. Only experience can teach you just how much balsam you will need. Try not to spill or smear it on the glass where not wanted. It is a great nuisance to remove. If you get it on your clothes, you can wash it out with xylol or turpentine. Specimens sometimes come loose and float out of position, even after the cover glass is on. If they are sufficiently tough and rigid, you can prevent this by gluing them to the slide. Instead of the first layer of thick balsam, put a small drop of thin plastic cement on the glass. Dry the surface of the specimen by blotting or blowing. Place the animal upon the drop cement, and arrange the appendages. Then flood with balsam. 8. Pick up the cover-glass with forceps, and touch one edge of it to the slide at a point indicated by the outline on the jig. Lower the other edge slowly, so that as the glass touches the balsam, the air is driven out before it. Press the cover down gently, until it rests on the supports, and secure it in position by means of a bobbypin clamp. If there is not quite enough balsam under the cover to fill the space, apply 9. Check the centering of the cover glass by means of the jig, and set the slide away to dry. This will take a very long time, and during that while the slide should be kept clean, dry, and warm, with a good circulation of air if possible. It must remain in a hori- zontal position, and nothing should be allowed to touch its upper surface. The top shelf of a closet is a pretty good drying spot, if you do not forget what you have there and put a hat on top of the slides by accident. Inspect the slide from time to time, as it dries. On the first day, you will find that the duco cement has turned milk white, but within a week it will have cleared again. As the xylol evaporates, the balsam shrinks, and empty pockets may form at the edges of the cover. If so, fill them with drops of liquid balsam. After about a month, it will be safe to take off the clamp. You may now examine the slide with the microscope, if you are very careful. However, it will be six months to a year before the balsam is dry enough to permit you to put the slide away in a slide box in a vertical position, or to examine it from the back without grave danger of dislodging the cover-glass. It is doubtful if very thick cell-mounts ever become completely solid. When the cover is so firmly cemen- ted to the slide that you cannot shift it by a gentle shove, you may remove unsightly smears of balsam with a cloth moistened in xylol. There is no objection to leaving a neat ring of balsam around the cover. Indeed, it acts as a protection to the fragile edges of the glass. It is possible, though risky, to hasten the drying of balsam by heating the slide carefully over a spirit lamp; but if you are ingenious as well as impatient, you can combine a metal box, an electric lamp and some bits of screen to produce a drying oven which will safely reduce the drying time to a few days. 10. Store your finished slides in a slide box, or boxes, arranged in some convenient order, so that you can always find the one you want without looking through the whole collection. The usual plan is to arrange them taxonomically, that is, according to their scientific classification, in the order given by a book of reference. You may find it easier or more interesting to arrange them ecologically, that is, according to the kind of place in which you found them, all the apple tree insects in one place, and all those that live on oak- trees in another, for instance. Slide mounted specimens are usually viewed by transmitted rather than by reflected light. That is, the light shines through them from below. There are 11