Page:Hardwicke's Science-Gossip - Volume 1.pdf/81

Spiders' Webs.—When we walk on a bright summer's morning alongside our garden walls, those who have a very quick eyesight, or a common eyeglass, may see the net-like webs of the common garden spider studded with minute drops glittering like dew; but as these do not evaporate when the suna advances, they must be something more substantial. Under the microscope, they will be seen arranged with beautiful regularity on the cross-bars of the web only. They are viscid to the touch; the web, in this way, being delicately lined, to take the smallest insects striking against it. When mounted as objects for the microscope, as they often are, the surprising fact at length grows upon us, that these minute beads of fluid, though kept in dry rooms and cabinets for months, and even years, never dry up, and apparently never change. What makes up these little persistent globules, and how are they arranged so evenly? If a newly-spun web is brought down upon a slip of glass, and made to adhere to it, the viscid drops spread upon the surface, and show a little nucleus or core of gum in the centre of each; it will be seen too, that the viscid fluid surrounds not only the cores but the whole line of the cross-bar, being collected only more copiously on the little cores dotted along it, and which have served as centres of attraction; but for these, the fluid, when poured upon the web, would have run into larger drops and fallen to the ground, or at least have been unequally distributed. The cores adhere but loosely to the web, and may be easily moved with a fine mounted hair; and, in doing so, it will be found that the cross bars, unlike the other lines of the web, are highly elastic. If the fresh viscid drops (still under the microscope) are made to touch blue litmus paper, they instantly sink into and redden it. The common solution of chloride of calcium also reddens the test paper; and it seems not unlikely that to the presence of this, or some other highly deliquescent salt, the undrying nature of the viscid fluid may be due. This spider's web is a complicated structure, and is composed of various materials: the side and radial lines of a fluid, which, like silk, hardens as it leaves the spinneret; the elastic cross bars which never harden, the little cores of transparent gum dotted along them, and the saline and viscid fluid poured over all; and yet, upon close examination of the spinneret, it is comprehensible that the web should be completed at one operation, that is, that no part of it should be gone over twice. A view of the insect at her work might clear up this point, and our fern-cases might, perhaps, be turned to further good accound for this purpose. But the spiders have now gone into winter quarters, and we must wait another summer. Meantime these few facts and queries may show us that there is something yet to learn of this curious and beautiful structure.—S. S., in Gardener's Chronicle.

Lists of Acari.—Can you refer me to complete list Acari?—R. B.

Koch's continuation of Hahn's Arachniden; and Koch's series of Apterous Insects in Henrich Schäffer's continuation of Panzer's German Insects, contain the most complete series of Acari. An excellent summary is given in Walckenaer's Hist. Nat. Ins. Apteres, in the Suits à Buffon, vols. 3 and 4.—J. O. W.

Embryonic Development.—All organs spring from a blastema, which is primarily composed of sarcode, and gradually assume their special features afterwards; but when first perceived they differ only in size from the adult forms. The embryo, in point of fact, is a miniature of the perfect being. In the course of development every animal exhibits very strange phenomena, both as to its entire economy, and in regard to special organs; and this is particularly the case with reference to mammalia. Daily, ay, even hourly, the scene is changed, and this unsettled condition applies not only to essential, but also to merely accessory organs. One might fancy that nature was feeling her way to a conclusion. Here may be seen cavities being gradually partitioned off, divided, as it were, into distinct chambers, or drawn out in the form of canals, which, in their turn, are often refilled with solid matter, and converted into ligaments; in another locality we observe previously solid masses transformed into cavities, membranous folds being rolled out into tubes, isolated portions of tissue drawn together to form a continuous organ, or even a mass hitherto entire, being cut up into several new structures. Not only the form and proportions, but the relations also of the various mechanisms are being momentarily altered. Parts which at first had been closely related separate from each other and become distinct, and organs which had heretofore been distant from each other form ties of close alliance. Those apparatus whose office is a temporary one rapidly increase in size, acquire an enormous volume, and eventually disappear altogether. Others are arrested in their growth at a certain period, and, though all the organs in their neighbourhood continue their development, yet they remain in their primitive condition, and may be detected in the adult, where they testify to a former state of things very different from the existing one. Thus we perceive that the history of embryonic development may be summed up as consisting in incessant transformations and constant activity.—Quatrefages' Metamorphoses, translated by Dr. Lawson.

The Irrationale of Speech.—To the minute philosopher, who holds that things are strange in proportion to their commonness; that the fit attitude for the human mind is that of habitual wonder; and that true science, so far from explaining phenomena, only shows that they are inexplicable, or likely to be so, not merely as to their final, but as to their proximate causes;—to him, I say, few things seem more miraculous than human speech. He has not time to ascend to the higher question of the metaphysics of language; not even to that first question, How did the human race ever make the surprising discovery that objects might be denoted by symbols, by names; and how did they communicate that discovery to each other? Puzzling as that question is, he is stopped short of it in wonder by a puzzle equally great—by the mere physical fact of articulation, which man has in common with the parrot and the daw.—The Irrationale of Speech.

Mounting Polyzoa.—A correspondent desires to be informed of any process by means of which he may be able to mount specimens of the Polyzoa in their expanded state. He has sought the information in various text-books, and tried several methods, alike without success.