403 



AUACIISIDA. 



Order 3. ARANEIDA * (-SPIDERS). 



AracJinida icith poison glands in the subchelate clielicercs ; with 

 pediform pedipalpi and stalked unsegmented abdomen. They hare 

 four or six spinning mammillae, 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 clielicerse, 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 peculiarly 

 modified in the male and func- 

 tions as a copulatory organ. 

 The mouth is bounded on tho 

 under side by an unpaired 

 plate, forming a sort of lower 

 lip. The four pairs of usually 

 long legs, whose form and size 

 vary according to the manner 

 of life, end with two toothed 



claws, to which a small claw (-7%) and several 

 accessory claws may be added (fig. 394). The 

 -ti-nnaof abdomen in the female is always larger and more 

 swollen than in the male ; at the base (anterior 

 i- part) of its ventral surface is placed the unpaired 

 sexual opening, at the sides of 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 (". A. Walckcnacr. Treviranus. C. J. Sundevall, T. 

 Tina-ell. Menfre, "Koch, Duires. Leltert . etc., compare. E. Claparedc, ," Rechcrches 

 sur revolution des Araiirnecs." Geneve, 1802: E. Claparede. "Etudes sur la 

 circulation du saner cliez les Aranees du crenre Lyrose." Geneve, 18G3 : F. 

 Plateau, " Rechcrchcs sur la structure dc 1'appareil ditrestif et sur les pheno- 

 ruenes de la digestion chcz les Aranees dipneiuuoncs." Bruxcllcs, 1877. 



FIG. : 

 thru 

 side 



Wl.Dytdera r-n/- 



irr i'n.ni thu ventral 

 (ri-Lrnc animal). 



FIG. :w:j. Poison i^limd 

 and terminal joint of 

 chelicera of Mii<i<ile 

 (rc^rne animal). K, 

 claw ; Gd, poison- 

 gland ; B, poison 

 vesicle. 



jJT, basal joint 



palrm 

 (jaw) 



p. iini 



the trachea'; a, 





' ' 



<' iramrniia 1 



