498 



ABACILNIDA. 



Order 3. ARANEIDA * (SPIDERS). 



Arachnida -with poison glands in the subckelate ckelicerce ; with 

 pediform pedipalpi and stalked unsegmented abdomen. They lave 

 four or six spinning mammittce, and two or four pulmonary sacs. 



The peculiar shape of the true spiders is clue to the swollen and 

 unsegmented abdomen, the base of which is constricted to form the 

 stalk by which it is united to the rest of the body (fig. 392). The 

 large subchelate chelicerse, which project beyond the front of the 

 head, consist of a powerful basal portion grooved on the inner side, 

 and a claw-shaped terminal joint at the point of which the duct of a 

 poison gland opens (fig. 393). At the moment of the bite the secre- 



tion of this gland flows into the wound, and in the 



case of small animals causes an almost instanta- 



neous death. The pedipalpus bears on its broad 



coxal joint, which constitutes a kind of biting- 



blade (fig. 392 A"), a many- 



jointed palp, the terminal re- 



gion of which is peculinrly 



modified in the male and func- 



tions as a copulatory. organ. 



The mouth is bounded on the 



under side by an impaired 



plate, forming a sort of lower 



lip. The four pairs of usually 



long legs, whose form and si/< j 



vaiy according to the manner 



o f \{f e> em \ w [t\i two toothed 



Kt 



B 



G 



FIG. 393. Poisim 

 and tei*minal joint of 

 chelicera of Mt/imlf 

 (regne animal). K, 

 claw ; GJ, poison- 

 gland ; S, poison 

 vesicle. 



FIG. 392.-JD.yw/pm f ,-y. 



/// from the ventral 

 side (regne animal). 



iy,cheiicera ; .z:#,pedi- claws, to which a small claw (Ik) and several 

 palpus; K, basal. joint accessory c i aws mav b e added (fig. 394). The 



(jaw) of pedipalpus; 



p, lungs; , stigma of abdomen in the female is always larger and more 

 lungs; St. posterior u than in the male at the base (anterior 



stigma leading into 



the trachea?; G, geni- part) of its ventral surface is placed the unpaired 



at the sides of which are *- he two 



slit-like apertures of the lung sacs. There is often 

 a second pair of stigmata behind these openings leading either into the 



* Besides the works of C. A. "VValckenaer, Treviranus. C. J. Sundevall, T. 

 Thorell. Menge. Koch, Duges, Lebert, etc., compare, E. Claparede. " Recherches 

 sur revolution des Arai-rnees," Geneve, 1862: E. Clnparede. "Etudes sur la 

 circulation du sang chez le.s Aranees du genre Lyeose." Geneve, lS(io : F. 

 Plateau, '' Recherches sur la structure de 1'appareil digestif et sur les jiheno- 

 menes (le la digestion chez les Aranees dipneumones," Bruxelles, 1877. 



