SPIDERS, invertebrates of the order Aran ea., class Arachnida. The English name spider, spinder, spinner, spinster, the spinning one —comes from the functions for which these creatures have been chiefly distinguished. They are cosmopolitan in distribution; are found in Greenland and swarm in the tropics. They show great and striking differences in form and in general habits. The spinning habit also differs widely; as one may see, by comparing the round web of a garden-spider, with the .snare of the speckled tubeweaver (Agalena neevia), made in hedges, fence-rows, roadsides and angles of out buildings. These typical differences in habit are commonly united with variations in structure and, therefore, have been made the basis of scientific classification by the eminent Swedish arachnologist, Dr. T. Thorell, following sub stantially M. Latraille. In no classification can these functional variations be disregarded; but for the use of the general public such an ar rangement is most satisfactory and is here adopted. Spiders may be roughly divided into two great groups : (1) Sedentary; (2) wander ing. Sedentary spiders live on or in woven habitations and take their prey by means of snares upon or near which they habitually stay. They thus have the distinction, almost unique among lower animals, of resembling man in pro curing a livelihood by use of manufactured im plements. The wandering spiders wholly or in large part hunt their prey afield. These groups may be thus subdivided: I. Sedentary Orbweavers (Orbitelaria), which make open webs circular or partly circular in form, composed of radii issuing from a centre and crossed with spirals armed with viscid beads .for the capture of in sects; these orbwebs are usually vertical, but some are horizontal. (2) Lineweavers or Net weavers (Retitelariee), whose snares are mazes of crossed lines in the midst of which they hang back downward; our common houte and barn cobwebs made in corners or rooms are mostly the product of lineweavers. (3) Tubeweavers (Tubitelaria), which live in silken tubes spun in divers situations sometimes with a sheeted snare outspreading from the mouth, as the com mon speckled tubeweaver that nests in hedges, borders and grass. (4) Tunnelweavers (Ter ritelaria), making tubular nests, usually silk lined, often with extensions above ground ; the trap-door spider (Cteniza californica) is our best-known type.
II. Wandering Citigrades (Citigradee), many of which, as the lycosids, burrow in the ground. (6) Laterigrades (La tcrigrada), which live upon plants and among rocks, getting their name from their rapid side wise movements. (7) Saltigrades • (Salti
grada), jumping-spiders, vivacious creatures, with large, bright eyes, living on plants and walls, etc., over which they move by frequent jumps and among which they make tubular nests of thick white silk.
This arrangement Professor Thorell subse quently modified, dividing the order Aranea into two suborders, Tetrapneumones, containing (1) the Territelaria ; (2) the Dipneumones, em bracing all other tribes. M. Eugene Simon, a distinguished French araneologist, retains the two suborders, which he names (1) Araneer therapbosa, composed of three families, of which the tarantula and trap-door spider are types; and (2) Aremea vent (38 families), con taining all other spiders, divided into two great groups or sections, Cribellater and Ecribellatee.
The early entomologists in cluded spiders among insects and in popular thought they are still so ranked; but they are widely separated therefrom. The most notice able differences are: spiders have eight legs; insects, six; spiders have the head united to the thorax, insects separated therefrom by a neck; spiders have simple eyes, insects have compound. The spider's body is divided into two parts, cephalo-thorax and abdomen, united by a straight pedicle or stem. Two mandibles or jaws are attached to the face, each having a hollow fang folded up within a groove when at rest like a pocket-knife's blade within its handle. A small opening in the fang cates through a minute duct with a pear-shaped poison-sac, in the upper part of the mandible and head. The poison, as in the case of snakes, js forced out when the spider strikes its victims. On either side of the mandibles is a six-jointed palp, shaped like the legs, which, besides other uses, serves to hold and turn the prey when swathing it or feeding upon it. The eight legs are attached to the cephalo-thorax, are seven jointed, covered with spines, bristles and hairs, the tarsal joint ending in a foot •having two or three claws constructed for grasping and handling delicate threads. The second main part of the spider's body is the abdomen, which while generally ovate greatly varies in form; being globular, subtriangular, cylindrical; some times flat, sometimes convex above. The ventral surface is flat or slightly converse. The integu ment is commonly soft, but sometimes leathery; in many species it is hairy; in others nearly tons may be seen hung up thereto in silken swathments, like scalps upon a savage's wig wam.