Directions for Collecting and Preserving Insects Part 8

In mounting minute insects a few precautions are necessary. The beginner usually uses too much glue or sh.e.l.lac, and the result is that the mounted specimens are more or less covered with the fluid, so as to render them unfit for examination. If, on the other hand, too little of the glue is used, the specimens are not securely fastened to the paper point, and are liable to be jolted off by the slightest jar. Before mounting specimens the legs and antennae must be brought into the proper position by means of a brush or with a dissecting needle, so that they may easily be seen. A supply of paper points should always be at hand, and after selecting one of the proper size for the specimen, with an acute tip for a very small specimen and with a more obtuse point for a larger one, a small quant.i.ty of glue is applied to the tip by means of a pointed stick, such as a toothpick, the amount varying with the size of the specimen. The tip of a moistened brush may be used to transfer the specimen to the point, or one will soon become dextrous enough to do this without the aid of the brush. The specimens are then allowed to dry in a horizontally placed box. If the drying box is placed in a vertical position the specimens, especially long-bodied ones, are liable to topple over before the glue has become firm.

[Ill.u.s.tration: FIG. 101.--Cecidomyiid mounted on pith (original).]

Delicate flies and Microlepidoptera, which it will not do to fasten with mucilage, may first be mounted on the fine pins described above and these thrust into oblong or triangular bits of pith or cork, which are mounted on larger pins as shown in Figures 101 and 102. This affords a very satisfactory method of mounting, particularly as the different s.e.xes may be brought together on the same bit of pith, or the adult and puparium in Diptera, as shown at Figure 101. Strips of stout cardboard with the pins run through the narrow edge may also be used. The method of mounting minute Hymenoptera and Diptera and other insects on a bent wire, mentioned above, is ill.u.s.trated at Figure 94. This method has not proved so satisfactory, as the wires are apt to become loose on the pin.

[Ill.u.s.tration: FIG. 102.--Microlepidoptera mounted on pith (original).]

[Ill.u.s.tration: FIG. 103.--Method of mounting duplicates (original).]

_Mounting Duplicates._--If the collector finds more specimens of a rare species than he cares to have in his collection, the excess may be mounted as duplicates. If the species happens to be of a large size the specimens are pinned in the ordinary way, but if small enough to be gummed, there is a most convenient method of rapidly mounting the specimens so that they may be sent through the mail with much less risk of getting broken or knocked off than if glued on paper points, and will also take up very little room in the duplicate boxes. It consists in gluing the specimens in a transverse row on a strip of white card paper with one of the glues soluble in water, care being taken that between the individual specimens some s.p.a.ce be left, and further that the heads and antennae do not project beyond the edge of the paper. The width of the paper strip must be somewhat greater than the length of the specimen, so that below the latter there is sufficient room for inserting a pin through the paper. After the glue has become dry the row of specimens is cut with scissors into several smaller rows of convenient size, so that on each of these rows there are two or three or more specimens, according to the size of the species. A locality label is pushed high up on a No. 3 or No. 4 pin, and one of the mounted rows of specimens is then pinned and pushed up near the locality label; a second row is then pinned and pushed near the first row, and the same process continued with the third row and so on. A single pin will thus bear five or six rows, and in giving away or sending away specimens the lowest row is taken from the pin and repinned for mailing. The accompanying figure (Fig. 103) ill.u.s.trates the mounting of a moderate-sized species in rows of two specimens each. This method of mounting duplicates may be adopted not only for Coleoptera, but also for Heteroptera, h.o.m.optera (excepting Aphididae and allied families), smaller Orthoptera, and Hymenoptera. It is, however, impracticable for Lepidoptera, Diptera, and most Neuroptera.

_Temporary Storage of Specimens._--If the entomologist is prevented from mounting his captures soon after returning from an expedition, or if, on extended collecting trips, time does not offer for this purpose, specimens of almost all orders except the Lepidoptera, Orthoptera, and Neuroptera may be placed in a small, tightly closing pill box, care being taken to keep the larger specimens apart from the small ones. In this way specimens will keep for an indefinite period, provided they are properly packed. In the case of the traveling collector, where the material is to be carried from point to point at great risk of breaking, specimens should be packed very carefully to prevent any shaking or rattling about in the boxes. This may be done by placing a round piece of soft paper on the top of the specimens in the pill box. This paper should be gently pressed down and the empty s.p.a.ce above filled with other layers of paper or with cotton. The packing of specimens between cotton is not recommended, as it is a difficult and tedious task to afterwards free them from the adhering fibers. Layers of soft paper or, yet better, velvet, are preferable.

[Ill.u.s.tration: FIG. 104.--Method of preserving Diurnal Lepidoptera in paper envelopes. (After Kiesenwetter.)]

_Envelopes for Lepidoptera, etc._--On an extended trip, it will be found impracticable to mount and prepare insects requiring c.u.mbersome apparatus for spreading, as Lepidoptera or Neuroptera, and a very excellent plan consists in folding the wings of the insect so that the lower surfaces come together and then placing it in a triangular envelope, as shown in the accompanying ill.u.s.tration. The collector should be provided with a quant.i.ty of paper of the requisite dimensions for making these envelopes, and specimens, as they are taken from the collecting bottle, may be rapidly inclosed in them, labeled, and packed away in a tight wooden (not tin) box containing a supply of naphthaline, the specimens thus occupying the minimum of s.p.a.ce. Specimens secured in this way may be kept without further manipulation indefinitely or until time is found to relax and set them. This is also an excellent method of sending diurnal Lepidoptera and Dragon-flies through the mails and is preferable in some respects to mailing spread specimens.

[Ill.u.s.tration: FIG. 105.--Spreading board for Lepidoptera.]

[Ill.u.s.tration: FIG. 106.--Needle for spreading insects.]

_Directions for Spreading Insects._--"For the proper spreading of insects with broad and flattened wings, such as b.u.t.terflies and moths, a spreading board or stretcher is necessary. One that is simple and answers every purpose is shown at Fig. 105. It may be made of two pieces of thin whitewood or pine board, fastened together by braces at the ends, but left wide enough apart to admit the bodies of the insects to be spread; strips of cork or pith, in which to fasten the pins, may then be tacked or glued below so as to cover the intervening s.p.a.ce. The braces must be deep enough to prevent the pins from touching anything the stretcher may be laid on, and by attaching a ring or loop to one of them the stretcher may be hung against a wall, out of the way. For ordinary-sized specimens I use boards 2 feet long, 3 inches wide, and 1/3 inch thick, with three braces (one in the middle and one at each end) 1 inches deep at the ends, but narrowing from each end to 1 1/6 inches at the middle. This slight rising from the middle is to counteract the tendency of the wings, however well dried, to drop a little after the insect is placed in the cabinet. The wings are held in position by means of strips of paper (Fig. 105) until dry. For stretching the wings and for many other purposes, a handled needle will be found useful. Split off, with the grain, a piece of pine wood 3 or 4 inches long; hold it in the right hand; take a medium-sized needle in the left hand; hold it upright with the point touching a walnut table, or other hard-grained wood, and bring a steady pressure to bear on the pine. The head of the needle will sink to any required distance into the pine, which may then be whittled off, and you have just the thing you want (Fig. 106). To obtain uniformity in the position of the wings, a good rule is to have the inner margins of the front wings as nearly as possible on a straight line. When the specimens are thoroughly stiff and dry, they should be taken from the stretcher and kept for several weeks in the drying box before being permanently placed in the cabinet. The drying box is simply a box of any required dimensions, containing a series of shelves on which to pin the specimens, and without a solid back or front. The back is covered on the inside with fine gauze and on the outside with coa.r.s.er wire, and the door in front consists of a close-fitting frame of the same material, the object being to allow free pa.s.sage of air, but at the same time to keep out dust and prevent the gnawings of mice and other animals. The shelves should be not less than 2 inches deep, and if made in the form of a quadrangular frame, braced with two cross-pieces on which to tack sheet cork, they will serve for the double purpose of drying spread specimens and for the spreading of others, as there are many insects with long legs which are more conveniently spread on such a board, by means of triangular pieces of stiff cardboard braces or 'saddles,' than on the stretcher already described. Two of these braces are fixed on the setting board, by means of stout pins, at sufficient distances apart to receive the body between them. The wings are then spread upon them and kept in place until dry by means of additional braces. In the case of bees, wasps, etc., the pin may be thrust well into the cork or pith so that the wings may be arranged in the proper position and braced and supported by strips of stout cardboard. This method is especially recommended in the case of the Fossorial wasps, the legs of which, if mounted in an ordinary spreading board, can not be properly arranged.

In spreading Lepidoptera I have used, in the place of a number of paper strips pinned across the wings, blocks of gla.s.s of various sizes to hold the wings in position. My method of mounting, with a large amount of material on hand to be attended to, consists in pinning a row on the spreading-board and fixing the wings in position with spreading needles, fastening them with a single narrow strip of paper placed next the body.

The entire spreading-board is filled with specimens in this way, a single long strip of paper on either side answering to keep the wings of all the specimens in position. Then, instead of pinning additional strips to hold the wings flat and securely in position, the pieces of gla.s.s referred to are used, placing them on the wings of the insect.

With the use of gla.s.s the spreading-board must always be kept in a horizontal position and must never be disturbed. The advantage of the gla.s.s is that the wings can be seen through it and more truly adjusted.

Spreading-boards may be made as described above, or it may be of advantage, when a good deal of work is to be done, to adopt a somewhat different method. Five or six spreading-boards may be made together, forming a sort of shelf. A number of these shelves may be constructed and the whole combined in a case with a screen cover to exclude insects.

The individual shelves may be arranged with grooves to slide on tongues in the side of the case. A screen-covered case for spreading-boards is always desirable, as the insects are otherwise very liable to be eaten by roaches or other insects. A spreading-case of the form described is shown at Fig. 107.

_A new Apparatus for Spreading Microlepidoptera._--For the spreading of Microlepidoptera my a.s.sistant, Mr. Theo. Pergande, has devised an apparatus, represented in the accompanying ill.u.s.tration, which he finds very convenient. It consists of a small spreading-block represented at _B_ and the support with attachment shown at _A_. The former is made in a long strip of the shape shown in the ill.u.s.tration, having a square groove, _c_, cut in the top. Over this is glued a thin strip of wood, _b_, say 1/8 inch thick, and a narrow slit is sawed in the center of this above, cutting through into the groove _c_. This is then sawed up into pieces of uniform length, say 1 to 2 inches, and the block is completed by the insertion of a rectangular strip of pith or cork into the groove. The Micro is pinned on a short black pin, and the pin is thrust down into the narrow opening made by the saw and is held firmly by the pith or cork. This block is then slid into the groove in the setting-board _A_, which narrows slightly from _e_, and pushed along until firmly secured (_d_). The operator can then rest his hands and arms on either side of the support, and, if necessary, bring a large hand lens over the object by means of a support with ball-and-socket joint shown at _e_. The wings may thus be easily and accurately arranged and fixed in position with pins or strips of paper, as in the ordinary mounting of such insects. Two or three specimens may be mounted on each of these blocks. The construction of the support is indicated in the annexed drawing. One side is attached by clamps, shown enlarged at _f_, which afford means of adjusting the width of the slit in which the small sawed blocks slide and correct the shrinking or swelling which may take place in moist or dry seasons. The advantage of the apparatus is that the operator has the setting block firmly fixed before him and has both hands free to manipulate the wings of the insect in addition to having the lens in a convenient position, the use of which is necessary in the preparation of the very minute forms.

[Ill.u.s.tration: FIG. 107.--Spreading-case (original).]

[Ill.u.s.tration: FIG. 108.--Spreading apparatus for Microlepidoptera (original).]

_Spreading Microlepidoptera._--The mounting of Microlepidoptera is about the most delicate work in entomotaxy, and I can not do better than quote the explicit directions given by Lord Walsingham on the subject.

Returning to camp I put a few drops of liquid ammonia on a small piece of sponge and place it in a tin canister with such of the boxes as do not contain the smallest species, and put these and the remainder away until morning in a cool place. In the morning I prepare for work by getting out a pair of scissors, a pair of forceps, my drying-box containing setting-boards, a sheet of white paper, and some pins.

First, I cut two or three narrow pieces of paper from 3 to 6 lines wide, or rather wider, according to the size of the largest and smallest specimens I have to set. I then double each of these strips and cut it up into braces by a number of oblique cuts. Now I turn out the contents of the canister and damp the sponge with a few drops of fresh ammonia, refilling with boxes containing live insects. Those which have been taken out will be found to be all dead and in a beautifully relaxed condition for setting. Had the smallest specimens been placed in the canister over night there would have been some fear of their drying up, owing to the small amount of moisture in their bodies.

If the weather is very hot there is some danger of killed insects becoming stiff while others are being set, in which case it is better to pin at once into a damp cork box all that have been taken out of the canister, but under ordinary circ.u.mstances I prefer to pin them one by one as I set them.

Taking the lid off a box, and taking the box between the finger and thumb of the right hand, I roll out the insect on the top of the left thumb, supporting it with the top of the forefinger and so manipulating it as to bring the head pointing toward my right hand and the thorax uppermost. Now I take a pin in the right hand and resting the first joint of the middle finger of the right against the projecting point of the middle finger of the left hand to avoid unsteadiness, I pin the insect obliquely through the thickest part of the thorax, so that the head of the pin leans very slightly forward over the head of the insect.

After pa.s.sing the pin far enough through to bring about one-fourth of an inch out below,[6] I pin the insect into the middle of the groove of a setting board so that the edge of the groove will just support the under sides of the wings close up to the body when they are raised upon it.

The board should be chosen of such a size as will permit of the extension of the wings nearly to its outer edge. The position of the pin should still be slanting a little forward. The wings should now be raised into the position in which they are intended to rest, with especial care in doing so not to remove any scales from the surface or cilia of the wings. Each wing should be fastened with a brace long enough to extend across both, the braces being pinned at the thick end, so that the head of the pin slopes away from the point of the brace; this causes the braces to press more firmly down on the wing when fixed.

The insect should be braced thus: The two braces next the body should have the points upwards, the two outer ones pointing downwards and slightly inwards towards the body, and covering the main portion of the wings beyond the middle. Antennae should be carefully laid back above the wings, and braces should lie flat, exercising an even pressure at all points of their surface. The fore wings should slope slightly forwards so that a line drawn from the point of one to the point of the other will just miss the head and palpi. The hind wings should be close up, leaving no intervening s.p.a.ce, but just showing the upper angle of the wing evenly on each side. I can give no more precise directions as to how this desirable result may most simply and speedily be attained; no two people set alike. Speed is an object; for I have often had to set twelve dozen insects before breakfast. A simple process is essential, for a man who is always pinning and moving pins, and rearranging wings and legs, is sure to remove a certain number of scales and spoil the appearance of the insect, besides utterly destroying its value. I raise each of the fore wings with a pin, and fix the pin against the inner margin so as to keep them in position while I apply the braces. Half the battle is really in the pinning. When an insect is pinned through the exact center of the thorax, with the pin properly sloped forward, the body appears to fall naturally into its position on the setting board, and the muscles of the wings being left free are easily directed and secured; but if the pin is not put exactly in the middle it interferes with the play of the wings. Legs must be placed close against the body or they will project and interfere with the set of the wings. Practice, care, and a steady hand will succeed. When all the insects that have been killed are set the contents of the canister will be found again ready, twenty minutes being amply sufficient to expose to the fumes of ammonia. Very bright green or pale pink insects should be killed by some other process, say chloroform, as ammonia will affect their colors.

[6] This applies to the use of short pins, which should subsequently be connected through strips of pith with longer pins. For some of the larger micros the long pins may be used directly and a different spreading board employed.

Insects should be left on the setting boards a full week to dry; then the braces may be carefully removed and they may be transferred to the store box.

In my own experience I have found that a touch or two of the chloroform brush on the pill-box containing small moths is sufficient to either kill or so asphyxiate them that they can easily be mounted. I have also found that strips of corn pith or even of soft cork, with grooves cut into them, are very handy for the pinning and spreading, and that by means of a small, broad-tipped, and pliable forceps the smallest specimens can be deftly arranged in the groove and kept in place until pinned. In fact, for all persons who have not very great experience and dexterity this method is perhaps more to be recommended than that of holding them between the thumb and fingers. Where chloroform is used either to kill or deaden specimens, it is important that after they are once spread and in the drying box they should be subjected to an additional asphyxiation, as the larger species may revive and are apt to pull away from the holding strips, and thus rub off their scales.

Microlepidoptera, together with Microhymenoptera and Diptera may be conveniently pinned on fine, short pins, and these thrust into an oblong bit of cork or pith. This form of mounting has already been described and is represented in figure 102. The neatest mounting of Microlepidoptera which I have seen is the work of my a.s.sistant, Mr.

Albert Koebele, who mounts these insects on an oblong strip of pith.

This is very light and presents no difficulty in pinning. The strips may be made of considerable length and both s.e.xes may be pinned on the same block (see Fig. 103). Most Lepidoptera present on the under surface an entirely different aspect from that on the upper surface, and, in such cases, it is a good plan to mount a number of specimens obversely.

_Relaxing._--It will frequently be desirable to re-spread insects which have been incorrectly mounted, or to spread specimens which have been collected and stored in papers, or pinned and allowed to dry without being prepared for the cabinet. Such specimens may be relaxed by placing them in a tight tin vessel half filled with moist sand to which a little carbolic acid has been added to prevent molding. Small specimens will be sufficiently relaxed to spread in twenty-four hours. Larger specimens require from two to three days. More rapid relaxing may be caused by the use of steam, and a flat piece of cork with the specimens laid or pinned thereon and floated on the top of hot water in a closed vessel const.i.tutes an excellent relaxing arrangement.

_Inflation of the Larvae of Lepidoptera._--The larvae of Lepidoptera preserved in alcohol are excellent for anatomical and general study, but are not very suitable for use in economic displays. This means of preservation also has the disadvantage of not generally preserving the natural color and appearance of the specimens. These objections may be avoided, however, by the dry method of preserving larvae, viz, by blowing or inflation. The process may be described as follows: The larva may be operated upon alive, but should preferably be first killed by dipping in chloroform or alcohol, or in the cyanide bottle. It is then placed on a piece of blotting paper and the alimentary ca.n.a.l caused to protrude from one-eighth to one-fourth of an inch, by rolling a pencil over the larva from the head to the posterior extremity. The protruding tip is then severed with a sharp knife or pair of dissecting scissors, and the contents of the abdomen are forced out by pa.s.sing a pencil, as before, a number of times over the larva. Great care should be exercised in expressing the fluids not to press the pencil too strongly against the larva or to continue the operation too long, as this will, especially in delicate larvae, remove the pigment from the skin, and the specimen when dried will show discolored spots and be more or less distorted. The larva should be moved from place to place on the blotting paper during the operation, so as not to become soiled by its own juices. A straw, or a gla.s.s tube drawn to a point at the tip, is then inserted in the protruding portion of the alimentary ca.n.a.l. If a straw is used the larva may be fastened to it by thrusting a pin through the wall of the ca.n.a.l and the straw. In the case of the gla.s.s tube the alimentary ca.n.a.l can be caused to adhere by drying for a few minutes and this operation may be hastened and the fastening made more secure by touching the point of union with a drop of glue. The straw or gla.s.s tube is then attached to a small rubber bag, previously inflated with air, the ordinary dentist's or chemist's gas bag answering admirably for this purpose. The larva is now ready for drying, and for this purpose a drying oven is required into which it is thrust and manipulated by turning it from side to side, to keep it in proper shape and dry it uniformly until the moisture has been thoroughly expelled. An apparatus which I have found very convenient for this purpose is represented at Fig. 109. It consists of a tin box with mica or gla.s.s slides, _e_, to allow the larva to be constantly in sight. It has also a hinged top, _b_, which may be kept closed or partly open, or entirely open, as may be necessary, during the operation. The ends of the box are prolonged downward about 5 inches, forming supports for it, _g_. Beneath it is placed an alcohol lamp, _f_, which furnishes the heat. In the end of the box is a circular opening, _d_, for the introduction of the larva, and this may be entirely or partly closed by a sliding door, _a_. It will be found of advantage to line the bottom of the box (inside) with a bra.s.s screen of very fine mesh to distribute and equalize the heat. This apparatus can be very easily made by any tinsmith and will answer every purpose.

[Ill.u.s.tration: FIG. 109.--Drying oven for the inflation of larvae (original).]

The larvae of Microlepidoptera or young larvae may be dried without expressing the body contents, and will keep, to a great extent, their normal shape and appearance. The method consists in placing them on a sand bath, heated by an alcohol lamp. The vapor generated by the heat in the larvae inflates them and keeps the skin taut until the juices are entirely evaporated. They may then be glued at once to cardboard and pinned in the cases.

In the mounting of large inflated larvae I have adopted the plan of supporting them on covered copper wire of a size varying with the size of the larva. A pin is first thrust through a square bit of cork and the wire brought tightly about it and wrapped once or twice, compressing the cork and giving a firm attachment to the pin. The wire is then neatly bent to form a diamond-shaped loop about one-sixth of an inch in length and again twisted loosely to the end--the length of the twisted portion about equalling that of the larva to be mounted. This is then either thrust into the blown skin of the larva through the a.n.a.l opening, the larva being glued to the wire by the posterior extremity, or the larva is glued to the wire by the abdominal legs and venter, thus resting on the wire as on a twig. This style of mounting is ill.u.s.trated in Pl. I.

With a little experience the operator will soon be able to inflate the most delicate larvae and also the very hairy forms, as for instance _Orgyia leucostigma_, without the least injury, so that the natural colors and appearance will be preserved.

Another very good method, and still safer, is to blow with straw, cut the straw square off at the a.n.u.s, and then preserve the thoroughly dried and blown specimen in a gla.s.s tube of about the same length and diameter as the larva. This arrangement in conjunction with the tube holder, which will be described further on, is one of the most satisfactory for the preservation of inflated larvae.

For the biological-display collection, larvae may be blown in various natural positions, to be subsequently fastened on leaf or twig or in burrows which they have occupied. Fastened to artificial foliage in which nature is imitated as much as possible, such blown larvae are quite effective.

_Stuffing Insects._--Large larvae may sometimes be satisfactorily preserved for exhibition purposes by stuffing them with cotton. The method consists simply in making a small slit with the dissecting scissors or a short scalpel between the abdominal prolegs, and removing the body contents. Powdered a.r.s.enic or some other preservative should be put in the body of the larva with the cotton used in stuffing it, and the slit closed by a few st.i.tches, when the larva may be dried and mounted on a twig or leaf. This method of stuffing with cotton is also applicable in the case of certain large-bodied insects which, if mounted and put away without preparation, would be liable to decompose, as, for instance, the larger moths, gra.s.shoppers, etc. A slit can be made in the center of the abdomen or near the a.n.u.s beneath, and the body contents removed and replaced with cotton. Stuffing in this way with cotton is of especial advantage in the case of certain of the large endophytous insects which grease badly. The cut will not be noticed after the insect has dried, or it may be closed by a st.i.tch or two.

_Dry Preservation of Aphides and other soft-bodied Insects._--Difficulty has always been experienced in preserving soft-bodied insects, particularly Aphides, in a condition serviceable for subsequent scientific study. Kept in alcohol or other antiseptic fluid, they almost invariably lose much of their normal appearance, and many of the important characteristics, especially of color, are obscured or lost.

The balsam mount is also unsatisfactory in many respects, as the body is always more or less distorted and little can be relied upon except the venation and the jointed appendages. A method of preserving soft-bodied insects by means of the sudden application of intense heat was communicated to the _Entomologische Nachrichten_, Vol. IV, page 155, by Herr D. H. R. von Schlechtendal. It is claimed for this method that the Aphides and other soft-bodied insects can be satisfactorily preserved in form and coloring, the success of the method being vouched for by a number of well-known German entomologists, Kaltenbach, Giebel, Taschenberg, Mayr, and Rudow. A condensed translation of the method employed by Schlechtendal is given by J. W. Douglas in the _Entomologists' Monthly Magazine_ for December, 1878, which I quote:

The heat is derived from the flame of a spirit or petroleum lamp. Above this is placed a piece of sheet-tin, and over this the roasting proceeds. A bulging lamp cylinder, laid horizontally, serves as a roasting oven. In this the insect to be dried, when prepared as directed, and stuck on a piece of pith, is to be held over the flame; or the cylinder may be closed at the lower end with a cork, which should extend far inwards, and on this the insect should be fastened; the latter mode being preferable because the heat is more concentrated, and one hand is left free. The mode of procedure varies according to the nature of the objects to be treated. For the cla.s.s of larger objects, such as Hemiptera, Cicadina, and Orthoptera, in their young stages of existence, the heat must not be slight, but a little practice shows the proper temperature required. If the heat be insufficient, a drying up instead of a natural distention ensues. The insect to be roasted is to be pierced by a piece of silver wire on the under side of the thorax, but it is not to be inserted so far as to damage the upper side, and the wire should then be carried through a disk of pith, placed beneath the insect, on which the legs should be set out in the desired position. But with some objects, such, for instance, as a young _Strachia_, the drying proceeds very quickly, so that if distention be not observed then the heat is too great, for the expansion of the air inside will force off the head with a loud report; also, with softer, thicker Pentatomidae care must be taken to begin with a heat only so strong that the internal juices do not boil, for in such case the preparation would be spoiled.

It is of advantage to remove the cylinder from time to time, and test, by means of a lens, if a contraction of the skin has taken place on any part; if so, the roasting is to be continued. The desired hardness may be tested with a bristle or wire. For _Aphides_ the _living Aphis_ is to be put on a piece of white paper, and at the moment when it is in the desired position it is to be held over the flame, and in an instant it will be dead and will retain the att.i.tude. Then put it, still on the paper, into the oven; or, still better, hold it over the heated tin, carefully watching the drying and moving the paper about in order to prevent it getting singed. The roasting is quickly accomplished in either way, but somewhat slower out of the oven especially in the larger kinds, such as Lachnus. If the paper turn brown it is a sure sign that caution is requisite. To pierce these brittle preparations for preservation is hazardous, and it is a better way to mount them with gum on card, placing some examples on their back.

For Cecidomyidae, Agromyzidae, Cynipidae, and other small insects liable to shrink, yet containing but little moisture, such as Poduridae, Pediculidae, Psyllidae, etc., another method is adopted. Over the insect, mounted on a wire, etc., as above directed, a thin chemical reagent gla.s.s or gla.s.s rod, heated strongly at one end, is held, and the heat involved is generally sufficient to bring about the immediate drying and distention, but if the heat be too little the process must be repeated; and, although by this method the danger of burning is not obviated, yet the position of the legs is maintained much better than by the aforesaid roasting.

Larvae of all kinds, up to the size of that of _Astynomus aedilis_, even when they have long been kept in spirits, may be treated successfully by the roasting method; but with these objects care must be taken that the heat is not too strong or else the form will be distorted. For small larvae it is preferable to use a short gla.s.s, in order better to effect their removal without touching the upper part, which becomes covered with steam, and contact with which would cause the destruction of the preparation. Larvae of Coleoptera, which contain much moisture or have a mucous surface, must lie on a bed of paper or pith in order to prevent adhesion and burning, and these may be further avoided if the cylinder be slightly shaken during the process, and the position of the object be thereby changed.

Many Aphides and Coccids are covered with a waxy secretion which interferes very materially with their easy examination. Mr. Howard has overcome this difficulty by the following treatment:

"With Aphides and Coccids which are covered with an abundant waxy secretion which can not be readily brushed away, we have adopted the plan of melting the wax. We place the insect on a bit of platinum foil and pa.s.s it once over the flame of the alcohol lamp. The wax melts at a surprisingly low temperature and leaves the insect perfectly clean for study. This method is particularly of use in the removal of the waxy coc.o.o.n of the pupae of male Coccidae, and is quicker and more thorough than the use of any of the chemical wax solvents which we have tried."

(_Insect Life_, I, p. 152.)

_Mounting Specimens for the Microscope._--The study of the minuter forms of insect life, including Parasites, Thysanura, Mallophaga, the newly hatched of most insects, etc., requires the use of the microscope, and some little knowledge of the essentials of preparing and mounting specimens is needed. The subject of mounting the different organs of insects and the preparation for histological study of the soft parts of insects opens up the immense field of microscopy, the use of the innumerable mounting media, the special treatment of the objects to be mounted, staining, section-cutting, and many other like topics, a full description of which is altogether out of place in the present work.

Anyone desiring to become thoroughly versed in the subject should consult some of the larger manuals for the microscopist, of which there are many. For the practical working entomologist, however, a knowledge of all these methods and processes is not essential, and in my long experience I have found that mounting in Canada balsam will answer for almost every purpose. The softer-bodied forms will shrink more or less in this substance, and it is frequently necessary to make studies or drawings of them when freshly mounted; or, if additional specimens are preserved in alcohol, they will supplement the mounted specimens and the material may be worked up at the convenience of the student. The materials for the balsam mounts may be obtained of any dealer in microscopical supplies. They consist of gla.s.s slides, 3 inches by 1 inch, thin cover-gla.s.ses of different dimensions, and the prepared balsam. The balsam is put up very conveniently for use in tin tubes. A sufficient quant.i.ty is pressed out on the center of the gla.s.s slide, which has previously been made thoroughly clean and dry, the insect is removed from the alcohol, and when the excess of liquor has been removed with bibulous paper, it is placed in the balsam, the limbs and antennae being arranged as desired by the use of fine mounting-needles. A cover-gla.s.s, also made thoroughly clean and dry, is then placed over the specimen and pressed gently until the balsam entirely fills the s.p.a.ce between the cover and the gla.s.s slide. The slide should then be properly labeled with a number referring to the notes on the insect, preferably placed on the upper edge of the slide above the cover-gla.s.s, and also a label giving the number of the slide and the number of the slide box. On the opposite end of the slide may be placed the label giving the name of the specimen mounted and the date. If a revolving slide table is employed to center the mounts, the appearance of the slide may be improved by adding a circle of asphalt or Brunswick black. With the balsam mounts, however, this sealing is not necessary. The slide (Fig.

110) should then be placed in a slide case with the mount uppermost, and should be kept in a horizontal position to prevent sliding of the cover-gla.s.s and specimen until the balsam is thoroughly dried. For storing slides I have found very convenient the box shown at Fig. 111.

It is constructed of strong pasteboard and is arranged for holding twenty-six slides. The cover bears numbers from 1 to 26, opposite which the name of each insect mounted, or the label on the slide, may be written. This box when not in use is kept in a pasteboard case, on which may be placed the number of the box. These slide cases may be stored in drawers or on shelves made for the purpose. In mounting specimens taken from alcohol it is advisable to put a drop of oil of cloves upon them, which unites with the balsam and ultimately evaporates. The occurrence of minute air bubbles under the cover-gla.s.s need occasion no uneasiness, for these will disappear on the drying of the balsam.

[Ill.u.s.tration: FIG. 110.--Balsam mount, showing method of labeling, etc.

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