[Ill.u.s.tration: FIG. 111.--Slide case, showing method of labeling case and of numbering and labeling slides (original).]

In mounting minute Acarids or mites it has been found best to kill the insects in hot water, which causes them to expand their legs, so that when mounted these appendages can readily be studied. If mounted living, the legs are almost invariably curled up under the body and can not be seen. This method may also be used in the case of other minute insects.

Some insects, such as minute Diptera, are injured by the use of hot water, and for these dipping in hot spirits is recommended.

In the mounting of Aphides the same difficulty is avoided in a measure by Mr. G. B. Buckton, author of "A Monograph of the British Aphides," by first placing a few dots of balsam on the gla.s.s slide, to which the insect is transferred by means of a moistened camel's-hair brush. The efforts of the insect to escape will cause it to spread out its legs in a natural position and a cover gla.s.s may then be placed in position and a drop of the balsam placed at the side, when, by capillarity, it will fill the s.p.a.ce between the slide and cover gla.s.s and the limbs will be found to have remained extended. If three or four drops of the balsam are put on the gla.s.s the wings may also be brought down and caught to them so that they will remain expanded in shape for examination.

_Preparing and Mounting the Wings of Lepidoptera._--The student of Lepidoptera will frequently find it necessary in the study of the venation of wings to bleach them or denude them of their scales in some way. Various methods of bleaching and mounting the wings of these insects have been given, and a few of them may be briefly outlined.

The simplest and quickest, but perhaps the least satisfactory, method is to remove the scales with a camel's-hair brush. This will answer for the larger forms and where a very careful examination is not required. For more careful examination and study the wings are first bleached by the action of some caustic solution and then mounted in balsam for permanent preservation. Chambers's method for Tineina, Tortricina, Pyralidina, and the smaller moths generally, is as follows: The wing is placed on a microscopic slide in from 3 to 4 drops of a strong solution of potash, the amount varying according to the size of the wing. A cover of gla.s.s is then placed in position on the wing as in ordinary mounting.

The quant.i.ty of liquid should be sufficient to fill the s.p.a.ce beneath, but not sufficient to float the cover gla.s.s. The mount is then placed over an alcohol flame, removing it at the first sign of ebullition, when the wing will be found denuded, if it be a fresh specimen. An old specimen, or a larger wing, will require somewhat more prolonged boiling. The fluid is drawn off by tilting the gla.s.s or with bibulous paper, and the potash removed by washing with a few drops of water. The cover gla.s.s is then removed and the wing mounted either on the same slide in balsam or floated to another slide, or at once accurately sketched with the camera lucida. Permanent mounting, however, is always to be recommended.

The Dimmock method of bleaching the wings of Lepidoptera, given in Psyche, Vol. I, pp. 97-99, is as follows: He uses for bleaching a modification of the chlorine bleaching process commonly employed in cotton bleacheries, the material for which is sold by druggists as chlorate of lime. The wings are first soaked in pure alcohol to dissolve out the oily matter, which will act as a repellant to the aqueous chlorine solution. The chlorate of lime is dissolved in 10 parts of water and filtered. The wings are transferred to a small quant.i.ty of this solution and in an hour or two are thoroughly bleached, the veins, however, retaining a light brown color. If the bleaching does not commence readily in the chlorine solution the action may be hastened by previously dipping them in dilute hydrochloric acid. When sufficiently decolorized the wings should be washed in dilute hydrochloric acid to remove the deposit of calcic carbonate, which forms by the union of the calcic hydrate solution with the carbonic dioxide of the air. The wings are then thoroughly washed in pure water and may be gummed to cards or mounted on gla.s.s slides in Canada balsam, first washing them in alcohol and chloroform to remove the moisture. If either of the solutions known as _eau de labaraque_ and _eau de javelle_ are used in place of the bleaching powder, no deposit is left on the wings and the washing with acid is obviated. This process does not dissolve or remove the scales, but merely renders them transparent, so that they do not interfere with the study of the venation.

Prof. C. H. Fernald (_American Monthly Microscopical Journal_, I, p.

172, 1880), mounts the wings of Lepidoptera in glycerin, after having first cleared them by the Dimmock process. After bleaching and washing, the wings are dried by holding the slides over an alcohol flame, and a drop of glycerin is then applied and a cover gla.s.s put on at once. By holding the slide again over the flame until ebullition takes place the glycerin will replace the air under the wings and no injury to the structure of the wings will result, even if, in refractory cases, the wing is boiled for some little time. The mount in this method must be sealed with some microscopic cement, as asphalt or Brunswick black.

A method of mounting wings of small Lepidoptera for studying venation, which I have found very convenient, is thus described by Mr. Howard in _Insect Life_, Vol. I, p. 151:

"Some years ago we used the following method for studying the venation of the wings of small Lepidoptera. We have told it since to many friends, but believe it has not been published. It is in some respects preferable to the so-called 'Dimmock process,' and particularly as a time-saver. It is also in this respect preferable to denudation with a brush. The wing is removed and mounted upon a slide in Canada balsam, which should be preferably rather thick. The slide is then held over the flame of an alcohol lamp until the balsam spreads well over the wing.

Just as it is about to enter the veins, however, the slide is placed upon ice, or, if in the winter time, outside the window for a few moments. This thickens the balsam immediately and prevents it from entering the veins, which remain permanently filled with air and appear black with transmitted light. With a little practice one soon becomes expert enough to remove the slide and cool it at just the right time, when the scales will have been rendered nearly transparent by the balsam, while the veins remain filled with air. We have done this satisfactorily not only with Tortricidae and Tineidae, but with Noctuids of the size of _Aletia_ and _Leucania_. The mounts are permanent, and we have some which have remained unchanged since 1880. Prof. Riley had for some years before this been in the habit of mounting wings in balsam, in which of course the scales cleared after a time."

Prof. John B. Smith recommends a modification of the Dimmock process of bleaching the wings of Lepidoptera, publishing it in Insect Life, Vol.

I, pp. 291, 292, as follows:

"By the Dimmock process the wings are first acted upon by a saturated solution of the chloride of lime, chlorine being, of course, the bleaching agent. Afterward they are washed in water to which hydrochloric acid has been added, to get rid of the slight deposit of lime. The process is a slow one for thickly scaled, dark-colored insects, and it occurred to me to try a mixture of the chloride and acid, liberating the chlorine gas. The method was absolutely successful, the wings decolorizing immediately and being ready for the slide within two minutes. In fact, very delicate wings can scarcely be taken out quick enough, and need very little acid. The advantage is the rapidity of work and the certainty of retaining the wings entire, the chloride of lime sometimes destroying the membrane in part before the bleaching is complete. The disadvantage is the vile smell of the chlorine gas when liberated by the combination of the two liquids. For quick work this must be endured, and the beauty and completeness of the result are also advantages to counterbalance the discomfort to the senses."

For further special directions for mounting, for microscopic purposes, different insects and the different parts of insects, representing both the external chitinous covering and the internal anatomy, the student is referred to special works.

PRESERVATION OF ALCOHOLIC SPECIMENS.

APPARATUS AND METHODS.--The collections of most value, especially to our various agricultural colleges and experiment stations will be largely of a biologic and economic character, and the interest attaching to a knowledge of the life history of insects will induce many collectors to build up independent biologic collections. Very much of this biological material will be alcoholic, and though many immature states of insects may be preserved by dry processes, still the bulk must needs be kept in liquid. This material may, when not abundant, be kept with the general systematic collection, but experience has shown that it is better to make a separate biological collection, and this is recommended especially for State inst.i.tutions where the collections may be expected to attain some considerable proportions. In the case of such collections it is very desirable to adopt some method of securing the vials in such a manner that they can easily be transferred from one place to another and fastened in the boxes or drawers employed for pinned insects. For directions in this regard I reproduce from an article on the subject in _Insect Life_, Vol. II, pp. 345, 346, which was republished, with slight changes, from my annual report for 1886 as Honorary Curator.[7]

[7] Annual Report of the Smithsonian Inst.i.tution for 1886, Part II, Report of the National Museum, pp. 182-186. Washington, 1890.

_Vials, Stoppers and Holders._--The vials in use to preserve such specimens as must be left in alcohol or other liquids are straight gla.s.s tubes of varying diameters and lengths, with round bottom and smooth even mouth. The stoppers in use are of rubber, which, when tightly put into the vial, the air being nearly all expelled, keep the contents of the vial intact and safe for years.

Various forms of bottles are used in museums for the preservation of minute alcoholic material. I have tried the flattened and the square and have studied various other forms of these vials; but I am satisfied that those just described, which are in use by Dr. Hagen in the Cambridge Museum, are, all things considered, the most convenient and economical.

A more difficult problem to solve was a convenient and satisfactory method of holding these vials and of fastening them into drawers or cases held at all angles, from perpendicular to horizontal. Most alcoholic collections are simply kept standing, either in tubes with broad bases or in tubes held in wooden or other receptacles; but for a biologic collection of insects something that could be used in connection with the pinned specimens and that could be easily removed, as above set forth, was desirable. After trying many different contrivances I finally prepared a block, with Mr. Hawley's a.s.sistance, which answers every purpose of simplicity, neatness, security, and convenience. It is, so far as I know, unique, and will be of advantage for the same purpose to other museums. It has been in use now for the past six years, and has been of great help and satisfaction in the arrangement and preservation of the alcoholic specimens, surpa.s.sing all other methods for ease of handling and cla.s.sifying.

The blocks are oblong, one-fourth of an inch thick, the ends (_c c_, Fig. 112) beveled, the sides either beveled or straight, the latter preferable. They vary in length and breadth according to the different sizes of the vials, and are painted white. Upon the upper side of these blocks are fastened two curved clamps of music wire (_b b_), forming about two-thirds of a complete circle. The fastening to the block is simple and secure. A bit of the wire of proper length is first doubled and then by a special contrivance the two ends are bent around a mandrel so as to form an insertion point or loop. A brad awl is used to make a slot in the block, into which this loop is forced (_e_, Fig. 112, 5), a drop of warm water being first put into the slot to soften the wood, which swells and closes so firmly around the wire that considerable force is required to pull it out. Four pointed wire nails (_d d d d_), set into the bottom so as to project about one-fourth inch, serve to hold the block to the cork bottom of the case or drawer in which it is to be placed. The method of use is simple and readily seen from the accompanying figures, which represent the block from all sides.

The advantages of this system are the ease and security with which the block can be placed in or removed from a box; the ease with which a vial can be slipped into or removed from the wire clamps; the security with which it is held, and the fact that practically no part of the contents of the vial is obscured by the holder--the whole being visible from above.

The beveled ends of the block may be used for labeling, or pieces of clean cardboard cut so as to project somewhat on all sides may be used for this purpose, and will be held secure by the pins between the block and the cork of the drawers.

[Ill.u.s.tration: FIG. 112.--Vial holder; 1, block, with vial, beveled on all sides; 2, do., beveled only on ends; 3, block, end view; 5, do., section; 4, 6, do., side views; _a_, block; _b_, spring-wire clamps; _c_, beveled ends of block; _d_, pointed wire nails; _e_, point of insertion of clamp. (Lettering on all figures corresponds.)]

The use of rubber stoppers in this country was first inst.i.tuted by Dr.

H. A. Hagen in connection with the Cambridge biological collection, and he has made some very careful records to determine the durability of such stoppers. From an examination of some seven thousand vials with rubber stoppers, two-thirds of which had been in use for from ten to twelve years, he comes to the conclusion that less than one in a thousand gives out every year after twelve years' use, and in the first six years probably only one out of two thousand. Stoppers of large size keep much longer than those of small size. American rubber stoppers are all made of vulcanized India rubber and have the disadvantage of forming small crystals of sulphur about the stopper, which become loosened and attach themselves to the specimens. It is supposed that pure rubber-stoppers used for chemical purposes would not present this disadvantage, which may be obviated, however, or very much reduced, if the stoppers are washed or soaked, preferably in hot water, for an hour or two at least.

If stoppers are stored for a considerable time and exposed to the air they become very hard and unfit for use, and Dr. Hagen has drawn attention to a method recommended by Professor W. Hemple, of Dresden, Saxony, of preventing them from becoming thus hardened. He says that to keep rubber stoppers or rubber apparatus of any sort elastic, they should be stored in large gla.s.s jars in which an open vessel containing petroleum is placed. This treatment prevents the evaporation of the fluids which are fixed in the rubber in the process of vulcanization. It is better also to keep the light from the jar. To soften stoppers which have already become hardened, they should be brought together in a jar with sulphuret of carbon until they are pliable and afterward kept as recommended above.

In the use of the rubber stopper the novice may find some difficulty in inserting it in a vial filled with alcohol. The compression of the alcohol, or alcohol and air when the vial is not completely filled, forces the stopper out, and this is true whether of rubber or cork. If a fine insect pin is placed beside the cork when this is thrust into the bottle, the air or liquid displaced by the cork will escape along the pin and the latter may then be removed and the cork remains securely in position.

If cork stoppers have been used the vials may be stored in large quant.i.ties together in jars filled with alcohol. This will prevent evaporation of the alcohol from the vials, and the specimens may be preserved indefinitely. This is only desirable in the storage of duplicate specimens and unarranged material and is not recommended as a subst.i.tute for the use of the rubber stopper. With cork stoppers evaporation can be in a measure prevented if the cork is first anointed with the petroleum preparation known as vaseline. This substance is practically unaffected at ordinary temperature and is sparingly soluble in cold alcohol. Experiments with it have shown that at ordinary spring and summer temperatures there is no appreciable loss of alcohol from vials and jars.

My old method of keeping alcoholic specimens, which I abandoned for the method outlined above, was fairly serviceable, inexpensive, and warrants description.

I had special folding boxes constructed resembling in exterior appearance a large insect box. The bottom of the box was solid and was made by gluing together two 1-inch planks.

Holes extending nearly through the lower plank and of various sizes to accommodate vials of different diameters were bored as closely together as the wood justified without splitting or breaking.

The holes were numbered consecutively and the vials when placed in them were numbered to correspond; the box also had its number, and in the notes the vial was referred to by number of box and vial thus, 3/73 (box 3, vial 73). The vial should project one-half to 1 inch above the hole, and should be loose enough to provide for the swelling of the wood in moist weather.

To protect the vials a cover having a depth of about 1 inch was hinged to the back and secured in front by hook-and-eye fastenings.

This method of storing vials is satisfactory enough for private collections, but for larger public collections is not so suitable.

[Ill.u.s.tration: FIG. 113.--The Marx tray for alcoholic specimens (original.)]

A rather convenient and inexpensive method of storing vials is that used by Dr. Marx. In this method the vials are stored in a wooden frame, shown at Fig. 113. The top piece of the tray into which the vials are thrust has a cork center, in which holes corresponding to the size of the vials are made with a gun-wad punch. The outer end of the tray bears a label or labels describing the material in the tray. The vials used by Dr. Marx are of thinner gla.s.s than those which I recommend and flare slightly at the top, as shown in the accompanying ill.u.s.trations. They are made in various sizes to accommodate larger and smaller specimens. A vial thrust into the hole punched in the cork rests on the bottom piece of the tray, the f.l.a.n.g.e or neck preventing it from sliding through.

These trays are arranged on shallow shelves in a case or cabinet, especially constructed for the purpose and a large quant.i.ty of material may be stored by their use in small compa.s.s. The use of the cork center piece in the upper part of the tray is not a necessity, and a wooden piece may be used in which holes are bored with a bit of proper size.

[Ill.u.s.tration: FIG. 114.--Vials used in the Marx tray (original.)]

_Preserving Micro-larvae in Alcohol._--The following is quoted from Packard's "Entomology for Beginners," for which it was translated from the "_Deutsche Ent. Zeitg._," 1887, Heft I:

"Dr. H. Dewitz mounts the larvae and pupae of Microlepidoptera, and also the early stages of other small insects, in the following way: The insects are put into a bottle with 95 per cent alcohol. Many larvae turn black in alcohol, but boiling them in alcohol in a test tube will bleach them. They may then be finally placed in gla.s.s tubes as small and thin as possible, varying from 0.003 to 0.006 meter in diameter, according to the size of the insects. About 0.07 meter's length of a tube is melted over a spirit lamp, and the tube filled three-quarters full with 95 per cent alcohol, the insects placed within and the contents of the tube heated at the end still open, and then closed by being pulled out with another piece of gla.s.s tubing. After the gla.s.s has been held a few minutes in the hand until it is slightly cooled off, the end closed last is once more held over the lamp so that the points may be melted together, and this end of the gla.s.s may be finished. During the whole time from the closure of the tube until the complete cooling of the gla.s.s it should be held obliquely in the hand, so that the alcohol may not wet the upper end, for if the tube is too full it is difficult to melt it, as the steam quickly expanding breaks through the softened ma.s.s of gla.s.s. The tube may be mounted by boring a hole through a cork stopper of the same diameter as the gla.s.s. The stopper is cut into the shape of a cube, a strong insect pin put through it, and the gla.s.s tube inserted into the hole. It can then be pinned in the insect box or drawer, near the imago, so that the free end of the gla.s.s may touch the bottom, while the other end stands up somewhat; while to keep the tube in place the free end resting on the bottom may be fastened with two strong insect pins. The specimens thus put up can easily be examined with a lens, and if they need to be taken out for closer examination the tube can be opened and closed again after a little practice."

[Ill.u.s.tration: FIG. 115.--Method of preserving minute larvae etc. (After Dewitz.)]

PRESERVATIVE FLUIDS.--The princ.i.p.al liquids in which soft-bodied insects may be successfully preserved are the following:

_Alcohol._--As indicated in the foregoing portions of this work, alcohol is the standard preservative used for soft-bodied specimens, and may be used either full strength or diluted with water. Diluted alcohol should always be first used with larvae, since the pure alcohol shrivels them up. The weak spirits can afterwards be replaced by strong, for permanent preservation.

_Alcohol and White a.r.s.enic._--The method of preserving insects recommended by Laboulbene and quoted in Packard's Entomology for Beginners, consists in plunging the insects in the fresh state into a preservative liquid, consisting of alcohol with an excess of the common white a.r.s.enic of commerce. The larva placed in this mixture absorbs .003 of its own weight, and when removed and pinned is safe from the attacks of museum pests. This liquid is said not to change the colors, blue, green or red of beetles, if they are not immersed for more than twenty-four hours. This treatment is applicable to the orders Coleoptera, Hemiptera, and Orthoptera. If the insect is allowed to stay in this mixture for a considerable time, say three or four weeks, and then removed and dried, it becomes very hard and brittle and can not be used for dissection or study, but makes a good cabinet specimen. The white deposit of a.r.s.enic which will appear on drying can be washed off with alcohol.

_Alcohol and Corrosive Sublimate._--The same author recommends another preparation consisting of alcohol with a variable quant.i.ty of corrosive sublimate added, the strength of the solution varying from 100 parts of alcohol to 1 part of corrosive sublimate for the strongest, to one-tenth of 1 part of sublimate in 100 parts of alcohol for the weakest. The insects are allowed to remain in this mixture not longer than two hours before drying. The last-described preparation is said to preserve the specimens from mold. Both of these solutions are very poisonous and should be used with care.

_Two Liquids to preserve Form and Color._--Professor Packard also quotes the formula of A. E. Verrill for preserving insects in their natural color and form. Two formulas are given; the first consists of 2 pounds of common salt and 4 ounces of niter dissolved in a gallon of water and filtered. The specimens should be prepared for permanent preservation in this solution by being previously immersed in a solution consisting of a quart of the first solution and 2 ounces of a.r.s.enite of potash in a gallon of water. Professor Packard gives also the formula of M. H. Trois for preserving caterpillars, for which it is claimed that the colors of the caterpillars are preserved perfectly, even when exposed to strong light. The formula for this solution is as follows:

Common salt grams 2.35 Alum do. 55 Corrosive sublimate centigrams 18 Boiling water liters 5

Allow the liquid to cool and add 50 grains of carbolic acid, and filter after standing five or six days.

_Glycerin._--Glycerin, either pure or mixed with water or alcohol, is frequently used to preserve the larvae of delicate insects. It preserves the color and form better than alcohol, but particularly in the case of larvae, it causes a softening of the tissues which renders them unfit for study.