In mounting blood of any kind to show the corpuscles, or, as they are often called, _globules_, which are round or oval discs, it is but necessary to cover the slide on the spot required with a coating as thin as possible and allow it to dry before covering with the thin glass. There is a slight contraction in the globules when dried, but not enough to injure them for the microscope. The shape of these varies in different classes of animals, but the size varies much more, some being many times as large as others.--Some of the _larvæ skins_ are beautiful objects; but, like many sections of animal and other fragile matter, are difficult to extend upon the slide. This difficulty is easily overcome by floating the thin object in clear water, immersing the slide and when the object is evenly spread gently lifting it. Allow it then to dry by slightly raising one end of the slide to aid the drainage, and cover with the thin glass as other objects. The tails and fins of many small fish may be mounted in a similar manner, and are well worth the trouble. A few objects which are best shown by mounting _dry_ may be here mentioned as a slight guide to the beginner, though some of them have been before noticed;--many of the Foraminifera as elsewhere described. Some _crystals_ are soluble in almost any fluid or balsam, and should be mounted _dry_; a few, however, deliquesce or effloresce, which renders them worthless as microscopic objects. The wings of butterflies and gnats, as before noticed, afford many specimens wherewith to supply the cabinet of the young student. A great variety also may be found amongst the ferns; indeed, these alone will afford the student occupation for a long time. On the under-side of the leaves are the reservoirs for the “spores,” which in many instances somewhat resemble green velvet, and are arranged in stripes, round masses, and other forms. The spores are usually covered with a thin skin termed the _indusium_, which is curiously marked in some specimens, often very like pollen-grains. The manner in which these spores with all their accompaniments are arranged, their changes and developments afford almost endless subjects for study; different ferns presenting us with many variations in this respect totally invisible without the aid of the microscope. The hymenophyllums (of which two only belong to England) are particularly interesting, and the structure of the leaves when dried makes them beautiful objects, often requiring no balsam to aid their transparency. Portions of the _fronds_ of ferns should be mounted as opaque objects, after having been dried between blotting paper, when they are not injured by pressure; but care must be taken to gather them at the right time, as they do not show their beauty before they are ripe, and if over-ripe the arrangement of the spores, &c., is altered. The spores may be mounted as separate objects in the same manner as pollen, before-mentioned, and are exquisitely