403 



Order 3. ARAXEIDA * ^SPIDERS). 



Arachnida with poison glands in the subchelate chelicerce; with 

 pediform pedipalpi and stalked unsegmented abdomen. They have 

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



The peculiar shape of the true spiders is due 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 chelicene, 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 K), a many- 

 jointed palp, the terminal re- 

 gion of which is peculiarly 

 modified in the male and func- 

 tions as a copulatory organ. 

 The mouth is bounded on the 

 under side by an unpaired 



J FIG. 393. Poison gland 



plate, forming a sort of lower and terminal joint of 



lip. The four pairs of usually 

 long legs, whose form and size 

 FIG. 392. Dyidera ery- vary according to the manner 



na from the ventral o f Jif e end with two toothed 



side (regne animal). 



-2y,cheiicera:.o,pedi. claws, to which a small claw (Tk) and several 

 paipus; r, basal joint accessO ry claws may be added (fig. 394). The 



(jaw) of pedipalpus ; * 



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



chelicera of Mygale 

 (rcgne animal). K, 

 claw ; Gd, poison- 

 gland ; S, poison 

 vesicle. 



swollen than in the male ' at the base ( anteriop 



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



tal opening ; Sf, Spin- , . , . , c i i 



uing mammilla. sexual opening, at the sides or which are the 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. Walckenaer, Treviranus, C. J. Sundevall, T. 

 Thorell. Mengc^och, Duges, Lcbert, etc., compare, E. Claparede, _" Eecherchcs 

 sur 1'evolution des Araignees," Geneve, 1802; E. Claparede, "Etudes sur la 

 circulation du sang chez les Aranecs du genre Lycnsc." Geneve, 1863 : F. 

 Plateau, " Peclicrcries sur la structure de 1'appareil digestif et sur les phono- 

 menes de la digestion chez les Aranees dipneumones," Bruxcllcs, 1877. 



