Common objects of the microscope

by J. G. Wood

Fig. [11], in the centre of the Plate, shows one of the most curious examples of insect structure, the proboscis or trunk of the common bluebottle-fly. The maxillary palpi covered with bristles are seen projecting at each side, and upon the centre are three lancet-like appendages, two small and one large, which are used for perforating various substances on which the insect feeds. The great double disc at the end is composed of the lower lip greatly developed, and is filled with a most complex arrangement of sucking-tubes, in order to enable it to fulfil its proper functions. The numerous tubes which radiate towards the circumference are strengthened by a vast number of partial rings of strong filamentary substance, like that which we have already seen in the breathing-tube of the silkworm. Some of these partial rings are seen on Fig. [12], a little above. The mode in which the horny matter composing the rings is arranged upon the tubes is most wonderful, and requires a tolerably high power to show it. The fine hairs upon the proboscis itself afford most admirable practice for the young microscopist. They should, when properly lighted and focused, be quite black and sharp. Any errors of manipulation will cause them to be “fuzzy.”

Fig. [5] shows the tongue of the common cricket, a most elegantly formed organ, having a number of radiating bands covered with zigzag lines, due to the triangular plates of strengthening substance with which they are furnished, instead of the rings. A portion more highly magnified is shown at Fig. [6], exhibiting the manner in which the branches are arranged.

The legs of insects now claim our attention.

Fig. [9], Plate VII., shows the “pro-leg” of a caterpillar. The pro-legs are situated on the hinder parts of the caterpillar, and, being set in pairs, take a wonderfully firm hold of a branch or twig by pressure toward each other. Around the pro-legs are arranged a series of sharp hooks, set with their points inwards, for greater power in holding. Fig. [10] represents one of the hooks more magnified.

Fig. [15] is the lower portion of the many-jointed legs of the long-legged spider (Phalángium), the whole structure looking very like the antenna of the cricket. Fig. [17] is the leg of the glow-worm, showing the single claw with which it is armed. Fig. [26] shows the foot of the flea, furnished with two simple claws. Fig. [16] is the foot of the Trombídium, a genus of parasitic creatures, to which the well-known harvest-bug belongs. Fig. [26], Plate VI., shows the leg of the green Aphis of the geranium, exhibiting the double claw, and the pad or cushion, which probably serves the same purpose as the pads found upon the feet of many other insects. Fig. [8] is the lower portion of the leg of the ant, showing the two claws and the curious pad in the centre, by means of which the insect is able to walk upon slippery surfaces. The Típula has a foot also furnished with a single pad (see Plate VI. Fig. [30]). This organ is seen under a very high power to be covered with long hair-like appendages, each having a little disc at the end, and probably secreting some glutinous fluid which will enable the creature to hold on to perpendicular and smooth surfaces. Many of my readers will doubtless have noticed the common fly, towards the end of autumn, walking stiffly upon the walls, and evidently detaching each foot with great difficulty, age and infirmity having made the insect unable to lift its feet with the requisite force.

Fig. [21] is the foot of one of the ichneumon-flies (Ophíon), the hairy fringe being apparently for the purpose of enabling it to hold firmly to the caterpillar in which it is depositing its eggs, and which wriggles so violently under the infliction that it would soon throw its tormentor had not some special means been provided for the purpose of enabling the latter to keep its hold. Fig. [20] is a beautiful example of a padded foot, taken from the little red parasitic creature so plentifully found upon the dor or dung beetle (Geotrúpes), and of which the afflicted insect is said to rid itself by lying on its back near an ant’s nest, and waiting until the ants carry off its tormentors.

Fig. [18] is the foot of the common yellow dung-fly (plentiful in pasture lands), having two claws and two pads; and Fig. [19] shows the three pads and two claws found in the foot of the hornet-fly (Ásilus).

Few microscopic objects call forth such general and deserved admiration as the fore-foot of the male water-beetle (Dytiscus), when properly prepared and mounted, for which see Fig. [13].

On examining this preparation under the microscope, it is seen that three of the joints are greatly expanded, and that the whole of their under surface is covered profusely with certain wonderful projections, which are known to act as suckers. One of them is exceedingly large, and occupies a very considerable space, its hairs radiating like the rays of the heraldic sun. Another is also large, but scarcely half the diameter of the former, and the remainder are small, and mounted on the extremities of delicate foot-stalks, looking something like wide-mouthed trumpets. In the specimen from which the drawing was taken the smaller suckers are well shown, as they protrude from the margin of the foot.

One of the larger suckers is seen more magnified on Fig. [14].