The _antennæ_ also are often mounted on separate slides, as being better suited for higher powers and more minute examination than when connected with the insect. These two projecting organs, issuing from the head, are jointed, and moveable at will. They differ very much in form amongst the various species, and are well worth the attention of the microscopist. They are usually mounted with the head attached, and perhaps they are more interesting when thus seen. Some few are very opaque, to prepare which the following method has been advised:--
Bleach the antennæ by soaking in the following solution for a day or two:--
Hydrochloric acid, 10 drops. Chlorate of potash, ½ drachm. Water, 1 oz.
This will render them transparent. Wash well, dry, and mount in Canada balsam. Instead of the above, a weak solution of chloride of lime may be used, by which means the nerves will be well shown. Many, however, are rendered transparent enough by simply soaking in turpentine for a longer or shorter time. Where the antennæ, however, are “plumose,” or feather-like, extreme care is required in mounting, though the difficulty is not so great as some seem to think. If they are first dried with gentle pressure, and then subjected to the action of the air-pump in a small quantity of turpentine until the air is thoroughly expelled, they can be easily finished upon the slide, especially when balsam and chloroform are used.
Insects supply us with another series of beautiful objects, viz., the _feet_.[D] These are sometimes simply dried and mounted without any medium, as before mentioned; but most of them are rendered much more fit for examination by using balsam in their preservation, as it greatly increases their transparency. The smaller kinds may be dried with gentle pressure betwixt blotting-paper, and then immersed for some days in turpentine, without requiring the treatment with liquor potassæ. This immersion will render them beautifully transparent, when they may be mounted in balsam in the usual manner.
[D] See Mr. Hepworth’s interesting articles on the fly’s foot in the second and third volumes of the _Microscopic Journal_.
It is, however, sometimes found difficult to fix the feet when _expanded_, in which state the interest of the object is greatly increased. Mr. Ralph recommends the following mode:--“First wash the feet, while the insect is yet alive, with spirits of wine; then holding it by a pair of forceps close to the edge of a clean piece of glass, the insect will lay hold of the upper surface by its foot, then suddenly drop another small piece of glass over it, so as to retain the foot expanded, and cut it off with a pair of scissors, tie up and soak to get rid of air.” Mr. Hepworth says that he never found any difficulty in expanding the foot on a drop of water or well-wetted slide, and laying a thin glass cover over it, tying with thread, drying, and immersing in turpentine.