Page:Popular Science Monthly Volume 1.djvu/696

680 cohesion. It is a remarkable fact that the spinnerets are under the prompt control of the spider's will, so that, in dropping from a height by the rapidly-forming line, the descent can be instantaneously stopped at any point. It is equally curious that, in ascending the line, a spider winds up the superfluous cord into a ball, and has a special claw or comb inserted between the others for the purpose.

Some kinds of spiders take to ballooning or migrating from place to place through the air. For this purpose they spin those long, loose and amazingly attenuous threads called gossamer, which exert a buoyant influence by which the animal is enabled to commit itself to atmospheric currents and move from place to place, and by which it gains the partial advantage of wings.

In the construction of webs for the snaring of its prey, the resources of the spider are endless. Dr. Samuelson, from whose admirable monograph our illustrations are taken, says: "With wonderful rapidity and instinct, the spider employs these threads to weave its web, or wanders from place to place, often constructing a perfect net, to entrap its prey, upon accurate geometrical principles, in less than an hour; and, what is most remarkable of all, performing this task in what to us would be total darkness. There are many other curious and mysterious circumstances connected with these webs. The garden-spider, for instance, covers all the concentric filaments of its net, at regular intervals, with glutinous or adhesive globules, presenting under the microscope the appearance of pearls strung upon a thread, and destined to facilitate the capture of its prey."

The work of the geometrical spiders may at almost any time in the proper season be observed in the garden. As the flight of insects is mainly in an horizontal direction, the net is usually fixed in a perpendicular or somewhat oblique position to intercept them. The first thing is to enclose a space with strong lines as a kind of frame, within which the web is to be formed. It is immaterial what is the shape of this enclosed area, as the spider is aware that she can as well inscribe a circle in a triangle as in a square. But these outside lines must be strong, and so they are formed of several threads glued together and attached to various objects of support. Mr. Spence thus describes the subsequent construction: "Having completed the foundations of her snare, she proceeds to fill up the outline. Attaching a thread to one of the main lines, she walks along it, guiding it with one of her hind-feet that it may not touch in any part, and be prematurely glued, and crosses over to the opposite side, where, by applying her spinners, she firmly fixes it. To the middle of this diagonal thread, which is to form the centre of her net, she fixes a second, which, in like manner, she conveys and fastens to another part of the lines encircling the area. Her work now proceeds rapidly. During the preliminary operations she sometimes rests, as though her plan required meditation. But no sooner are the marginal lines of her net firmly stretched, and