_Glycerine_ may be advantageously used for the preservation of various insects. These should first be cleaned with alcohol to get rid of all extraneous matter, and then, after soaking in glycerine, be mounted with it like other objects. This liquid may also be used for the Entomostraca, which offer a wide field for study. They are to be found abundantly in ponds of stagnant water, &c. Some insects, such as May-flies, &c., are, however, often preserved by immersion in a solution of one part of chloride of calcium in three or four parts of water; but this has not been recommended amongst the “preservative liquids,” as the colour, which is often an attractive quality of this class of objects, is thereby destroyed. We have now noticed the treatment which must be applied to those objects which are to be preserved in liquids and cells. We may here state that all slides of this kind should be examined at short intervals, as they will be found now and then to require another coating of varnish round the edge of the thin glass cover to prevent all danger of leakage. The use of the air-pump, in the first instance (as before recommended), and this precaution as to the varnish, will render the slides less liable to leakage and air-bubbles, which so very frequently render them almost worthless. CHAPTER V. SECTIONS AND HOW TO CUT THEM, WITH SOME REMARKS ON DISSECTION. Many objects are almost worthless to the microscopist until the extraneous matter is removed from them; and this is frequently difficult in the extreme to perform satisfactorily. As an instance, certain Foraminifera may be mentioned in which the cells are placed one upon another, consequently the object must be reduced to a certain degree of _thinness_ before a single uniform layer of these cells can be obtained to show something of the internal arrangements. Most animal and vegetable forms require an examination of the separate parts before much can be known about them. The mass must be divided into separate portions, each part intended to be preserved being cleaned from the useless matter with which it is surrounded. It will frequently be found necessary to make thin sections, which from a very tender substance is no easy matter; and much patience will be necessary to attain anything like proficiency.