Page:Hardwicke's Science-Gossip - Volume 1.pdf/179

Larva of a Gnat.—In the "Microscopic illustrations" by A. Pritchard is a description of a beautiful transparent larva of a kind of gnat, which is to be found in clear ponds at this time of year, and in some places is very abundant. The drawings by Mr. Pritchard are very nicely drawn, and give a good idea of its appearance. But in addition to his description I find it has two jaws, and feeds on other animals—the blood-worm for one, as I found the head and part of the body of one in its stomach. Speaking of the stomach, there is a curious circumstance I have often noticed. On squeezing the larva from its tail upwards, the stomach is forced, inverted, out of its mouth, and then will be seen to be covered with rows of spines, I suppose to retain its food. The use of the shell-like bodies I cannot make out; but they are pretty objects, and beautifully spotted, hollow, and of a fibrous structure. The larva casts its skin like others, but it requires close looking to find it.—E. T. Scott.

Movements of Endochrome in Diatomaceæ.—During an excursion with the members of the Tyneside Naturalists' Field Club, on Friday, May 26, I made a collection of Diatomaceæ from the bed of the river Blyth, a small river which empties itself into the sea near a town bearing the same name. The stones on the bottom of the river were covered with Fragilaria for an extent of some miles, and intermixed with the Fragilaria there were many beautiful varieties of Cymbella, Cocconema, Pleurosigma, Nitzschia, Comphonema, Surirella, &c. The Cymbella lanceolatum or Cocconema gastroides, I am not quite certain which, they are exactly alike, and the only mode of deciding the species is by seeing the Cocconema on its stipes, Cymbella being a free form. I could not in the gathering made observe the least indication of stipes, and I therefore infer that they are Cymbella lanceolatum. In this I saw what I had never before seen,—a free motion of the endochrome: it was as free as the motions of the granules in the desired Closterium, but not quite so regular. I examined the gathering three hours after making the collection, and saw the motion of the endochrome;—sixteen hours after, and saw it yet move freely, but only in one frustule;—forty hours after, and saw it very slightly in one frustule; ninety-eight hours after, but could not observe the slightest motion in any frustules, although I examined many of them very carefully. I infer that the best time for seeing the motions of endochrome is when the diatoms are newly gathered.—T. P. B.

How are Large Insects Mounted Whole?—Though the text-books explain how to mount the legs, antennæ, or other separate parts of an insect, they do not give the information necessary to enable an amateur to mount an insect whole without air-bubbles. The great object to be achieved is to discover a chemical agent which will unite with the balsam without injuring its clearness, and by which to prepare the insect before placing it on the slide. In the common process of mounting, the slide is prepared, and the insect placed in the balsam, the slide being then warmed, the clean thin glass is allowed to drop gently on the specimen. But here the great difficulty arises, for if the insect be a large one, the body is too thick to allow the glass to lie anything like flat, and even then the limbs generally break off, to the utter destruction of the work. Mr. Jabez Hogg's work on the microscope states that a clergyman at Acton Abbotts has discovered a medium which will attain the required object. The slides sold at the opticians', and mounted on three-inch circles (intended for the magic-lantern, though equally adapted under the large objectives for the microscope) are beautifully clear and perfect. How is the process performed in these cases? What is the medium used? Perhaps some of your correspondents may be able to solve this difficulty. Again: How are young crabs and moderate-sized prawns mounted whole,—shell and all? I have seen some so prepared at Newtwon's, Temple Bar, and as an amateur I should, in common, no doubt, with many others of your numerous correspondents, be glad to attempt the use of the process.—J. H. W.

Microscopic Powers.—The quarter-inch object-glass of my microscope with the low eye-piece has a field of view not larger than the aperture made by an ordinary-sized sewing-needle, No. 5; yet, in that field I have seen eleven circular diatoms from guano, and these in no way crowded, but with spaces between them. Each of these tiny circles possesses markings, apertures, or elevations, of the most minute yet regular character, hexagonal or circular. I have endeavoured to count the number of apertures in the radius of one of the smallest and coarsest of these circles on my slide (Eudicta), and I made up the number to be twenty-five. From this I conclude that, at a rough calculation, there cannot be less than three hundred apertures in the diameter of one of the larger circles (Coscinodiscus), eleven of which, as I have said, scarcely fill a space equal to the aperture of a sewing-needle. This, which any amateur microscopist may verify for himself, with perhaps more wonderful results, affords a practical and ready method of explaining to many the reality of the wonderful fact, that marvellous skill in design and beauty in execution has been displayed on very tiny atoms. And it show the extraordinary perfection and power, even of a moderate-priced modern achromatic microscope. No wonder that the instrument has become popular, and that science is the innocent and profitable subject of "Gossip" indulged in by the "Lovers of Nature."—Lewis G. Mills, LL.B., Armagh.