Page:Popular Science Monthly Volume 33.djvu/808

788 designated when it is named. In these animals the head and corselet are confounded into a single mass, at the upper part of which is a kind of dorsal buckler, supporting in front the organs of vision. The eyes are generally eight in number, but are variously grouped, according to the types. Walckenäer, at the beginning of this century, made the disposition of the eyes a criterion of distinction between the genera and species. More recently, some remarkable coincidences having been noticed between the disposition of the eyes and the habits of the species, it became recognized that that feature could be relied upon in an animal wholly a stranger to determine the conditions of its existence and the way it got its living. The eyes do not turn in their socket like man's, for the cornea is only a tegumentary part which remains transparent. This immobility is an imperfection which is amply compensated for by the different orientations of the numerous organs, and their dispersion and grouping in such a manner as to respond to all the visual necessities of the animal. Being silent animals, and never having to answer to a call, spiders are backward in distinguishing sounds. This fact is assured by some features in their conformation. The romances that have been woven about their fondness for music are purely illusory. The disturbances which they experience at the playing of violins and pianos are simply effects of the vibration of their webs. Alarmed by it, they quit their hiding-places and rim about in panic.

Beneath the front of the spider project two thick processes armed with a movable hook—the antennæ forceps—which conceal a poison-gland with a little tube running out to near the point of the hook. All who have seen a spider taking a fly have remarked how it stings its victim so as to kill it before introducing it to its mouth. At the edge of the buccal orifice of those species that live on fluids, exist only a simple tongue and two highly developed palpi behind it.

Spiders are differentiated from insects, which have six legs, by having four pairs of legs (Fig. 1). These members support hooks at their ends, which are working instruments of astonishing perfection. The body and limbs are covered with hair, fine down, and spines. These are the organs of touch, often of exquisite sensitiveness, planted in the skin. Under the microscope the downy hairs, which are hardly visible to the naked eye, appear fringed and bearded like incomparably delicate feathers. When we consider the habitual neatness of their clothing, to which grains of dust would so readily stick, we are satisfied that spiders are far from the hindmost in the care they give to their toilet. Their long, hooked legs perform an office that leaves nothing to be desired. At the extremity of the body may be found mobile articulated