Spider

Collier's New Encyclopedia (1921)

in zoology, the popular name of any individual of Huxley's Araneina. The species are very numerous and universally distributed, the largest being found in the tropics. The abdomen is BIRD SPIDER without; distinct divisions, and is gen erally soft and tumid; the legs are eight in number, seven-jointed, the last joint armed with two hooks usually toothed like a comb. The distal joint of the falces is folded down on the next, like the blade of a pocket knife on the handle, and the duct of a poison gland in the cephalothorax opens at the summit of the terminal joint. There are two or four pulmonary sacs and a tracheal system; eyes generally eight in number; no auditory organs have been discovered. Their most characteristic organ is the arachnidium, the apparatus by which fine silky threads in the majority of the species utilized for spinning a web-are produced. In Epeira diadema, the common garden spider, more tha than 1,000 glands, with separate excretory ducts, secrete the viscid material of the web. These ducts ultimately enter the six prominent arachnidial mammillæ, projecting from the hinder end of the ab- ORB SPIDER domen, and having their terminal faces beset with minute arachnidial papillæ, by which the secretion of the gland is poured out. By means of these silky threads, spiders form their dwellings and construct ingenious nets for the capture of their prey; these threads serve also as a safeguard against falling, and as a means of support from one elevated object to another, being thrown out as a sort of flying bridge. The webs are in high repute pute for stanching blood; the threads are employed for the cross lines in astronomical telescopes, and have been made into textile fabrics as articles of curiosity. Spiders are essentially predaceous. The fate of the victim is always the same the claw joints of the falces are buried in the body, inflicting a poisonous wound, and the juices are then sucked out by the muscular apparatus appended to the esophagus of the spider. The bite of none of the species is dangerous to man. (See TARANTULA.) They are extremely pugnacious, and in their combats often sustain the loss of a limb, which, like the Crustaceans, they have the power of reproducing. The eggs are numerous, and usually enveloped in a cocoon or egg case; the young undergo no metamorphosis.