The Butterfly Book. W. J. Holland
may be preserved by simply putting them into tubes containing alcohol, or they may be placed in vials containing dilute glycerine or a solution of common salt. The vials should be kept tightly corked and should be marked by a label written with a lead-pencil and placed within the bottle, upon which the name of the species and the date of collection should be noted, or a reference made to the collector's note-book. Unless the eggs of insects are preserved in fluid they are apt in many cases to dry up and become distorted, because, on account of their small size, it is impossible to void them of their contents. The larvæ escaping from eggs often void the shell very neatly, leaving, however, a large orifice. Such remnants of shells may be preserved, as they often are useful in showing some of the details of marking; but great vigilance in securing them should be exercised, for almost all the larvæ of butterflies have the curious habit of whetting their appetites for future repasts by turning around and either wholly or partially devouring the shell of the egg which they have quitted. Eggs are most neatly mounted in the form of microscopic slides in glycerine jelly contained in cells of appropriate depth and diameter. It is best, if possible, to mount several specimens upon the same slide, showing the side of the egg as well as the end. A cabinet filled with the eggs of butterflies thus mounted is valuable and curious.
The Preservation of Chrysalids.—Chrysalids may be deprived of their vitality by simply immersing them in alcohol, or they may be killed by means of chloroform, and they may then be fastened upon pins like the imago, and arranged appropriately in the collection with the species. Some chrysalids, however, lose their color when killed in this way, and it is occasionally well to void them of their contents by making an opening and carefully removing the parts that are contained within, replacing with some material which will prevent the chrysalis from shrinking and shriveling. This method of preserving need, however, be resorted to only in exceptional cases. When a butterfly has escaped from its chrysalis it frequently leaves the entire shell behind, with the parts somewhat sundered, yet, nevertheless, furnishing a clear idea of the structure of the chrysalis. If no other specimen of the chrysalis can be obtained than these voided shells they should be preserved.
The Preservation of Caterpillars.—The caterpillars of butterflies when they first emerge from the egg, and before they make the first moult, are, for the most part, extremely small, and are best preserved as microscopic objects in cells filled with glycerine. After each successive moult the larva increases rapidly in size. These various stages in the development of the caterpillar should all be noted and preserved, and it is customary to put up these collections in vials filled with alcohol or a solution of formaline (which latter, by the by, is preferable to alcohol), or to inflate them. The method of inflation secures the best specimens.
In inflating larvæ the first step is carefully to remove the contents of the larval skin. This may be done by making an incision with a stout pin or a needle at the anal extremity, and then, between the folds of a soft towel or cloth, pressing out the contents of the abdominal cavity. The pressure should be first applied near the point where the pellicle has been punctured, and should then be carried forward until the region of the head is reached. Care must be exercised to apply only enough pressure to expel the contents of the skin without disturbing the tissues which lie nearest to the epidermis, in which the pigments are located, and not to remove the hairs which are attached to the body. Pressure sufficient to bruise the skin should never be applied. A little practice soon imparts the required dexterity. The contents of the larval skin having been removed, the next step is to inflate and dry the empty skin. A compact statement of the method of performing this operation is contained in Hornaday's "Taxidermy and Zoölogical Collecting," from the pen of the writer, and I herewith reproduce it:
Plate V.
"The simplest method of inflating the skins of larvæ after the contents have been withdrawn is to insert a straw or grass stem of appropriate thickness into the opening through which the contents have been removed, and then by the breath to inflate the specimen, while holding over the chimney of an Argand lamp, the flame of which must be regulated so as not to scorch or singe it. Care must be taken in the act of inflating not to unduly distend the larval skin, thus producing a distortion, and also to dry it thoroughly. Unless the latter precaution is observed a subsequent shrinking and disfigurement will take place. The process of inflating in the manner just described is somewhat laborious, and while some of the finest specimens which the writer has ever seen were prepared in this primitive manner, various expedients for lessening the labor involved have been devised, some of which are to be highly commended.
"A comparatively inexpensive arrangement for inflating larvæ is a modification of that described in the 'Entomologische Nachrichten' (1879, vol. v, p. 7), devised by Mr. Fritz A. Wachtel (Fig. 61). It consists of a foot-bellows such as is used by chemists in the laboratory, or, better still, of a small cylinder such as is used for holding gas in operating the oxyhydrogen lamp of a sciopticon. In the latter case the compressed air should not have a pressure exceeding twenty pounds to the square inch, and the cock regulating the flow from the cylinder should be capable of very fine adjustment. By means of a rubber tube the air is conveyed from the cylinder to a couple of flasks, one of which contains concentrated sulphuric acid, and the other is intended for the reception of any overflow of the hydrated sulphuric acid which may occur. The object of passing the air through sulphuric acid is to rob it, so far as possible, of its moisture. It is then conveyed into a flask, which is heated upon a sand-bath, and thence by a piece of flexible tubing to a tip mounted on a joint allowing vertical and horizontal motion and secured by a standard to the working-table. The flow of air through the tip is regulated by a cock. Upon the tip is fastened a small rubber tube, into the free extremity of which is inserted a fine-pointed glass tube. This is provided with an armature consisting of two steel springs fastened upon opposite sides, and their ends bent at right angles in such a way as to hold the larval skin firmly to the extremity of the tube. The skin having been adjusted upon the fine point of the tube, the bellows is put into operation, and the skin is inflated. A drying apparatus is provided in several ways. A copper plate mounted upon four legs, and heated by an alcohol-lamp placed below, has been advocated by some. A better arrangement, used by the writer, consists of a small oven heated by the flame of an alcohol-lamp or by jets of natural gas, and provided with circular openings of various sizes, into which the larval skin is introduced (Fig. 63).
"A less commendable method of preserving larvæ is to place them in alcohol. The larvæ should be tied up in sacks of light gauze netting, and a label of tough paper, with the date and locality of capture, and the name, if known, written with a lead-pencil, should be attached to each such little sack. Do not use ink on labels to be immersed, but a hard lead-pencil. Alcoholic specimens are liable to become shriveled and discolored, and are not nearly as valuable as well-inflated and dried skins.
"When the skins have been inflated they may be mounted readily by being placed upon wires wrapped with green silk, or upon annealed aluminium wire. The wires are bent and twisted together