Page:Hardwicke's Science-Gossip - Volume 1.pdf/246
SIMPLE OBJECTS.—VII.
Dermestes and Pencil-tail.
During the last few days of February and first fortnight in March may be obtained, under the bark of aged elm trees, two objects which deserve a place in a microscopic cabinet, though, so far as I have ascertained from dealers, they are not commonly mounted.
The first is the larva of a beetle—some sort of Dermestes. It is of a light brown colour, and covered with fine hairs, similar to those figured in the "Micrographic Dictionary" as from Dermestes Lardarius, but differing from the pictures of that. object in Carpenter's "Microscope and its Revelations," and Hogg's work on the same subject. I imagine this is because the specimens figured there have been damaged in the preparation, perhaps intentionally, with a view to show the structure.
Being certain that many possessors of microscopes have never seen the creature in its living state, I venture to recommend such persons as take a pleasure in preparing objects for themselves to make a search for it.
A low power, say ten diameters, is needed, and opaque illumination. The Dermestes then looks most formidable. It is covered with hairs of several sorts, those of the halbut shape being the most numerous, arranged close to the body, and pointing from the sides to the centre of the back in the anterior segments of the body, but grouped in small bundles, each containing an infinite number of hairs with longer shafts than the others, and looking like tiny sheaves of corn in the hinder segments. These latter can be erected and spread out like fans, giving the creature somewhat of the porcupine appearance.
There is also a bunch of long delicate hairs occupying the place of a tail, and the little fellow protests against interference by switching this article sideways in a ludicrous manner, if touched.
A preserved specimen can never give the full beauty of the living animal; but partial success may be gained by the following plan of mounting:—
I procured a wooden slide, 3in, by 1in., and in. thick, having a hole cut in the centre about in. in diameter. Having fastened to this a piece of clean thin glass, I placed the insect in the cell thus formed, and covered it up with another piece of thin glass. By this means I can view both sides of the creature without trouble, and also by illuminating from above and below the stage simultaneously, obtain certain advantages.
The other creature which is worthy of a search is obtained in similar situations. I have generally found it, however, in rotten bark that is covered with lichens and moss, while the Dermestes prefers a more sheltered situation in the crevices between the dead bark and the living wood.[1]
Its popular name is "Pencil-tail" (Polyrenus lagurus[2]), so called from two silvery tufts of delicate hairs which spring out of the hindmost segment. These myriapods are often very numerous, and a piece of the bark, having a colony of them upon it, is a wonderfully beautiful sight under the microscope.
They are grey, and their backs are covered by transverse bands of curiously-shaped objects intermediate between scales and hairs, of a leaden hue. The sides and head are ornamented with bunches of a similar character.
To see these animals endeavouring to escape into the dark crevices of the bark when the light is condensed upon them by means of the large bull's-eye, cannot fail to excite surprise.