CLASS V. ARACHNIDA. 



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Q animals, easily recognized by their stalked 

 abdomen and by the presence of the spin- 

 nerets. The prosoma, often called the cephalo- 

 thorax, bears the eyes, never more than eight, 

 and usually in two transverse rows, each con- 

 sisting of a pair of median eyes with a lateral 

 eye on each side (Figs. 528, 530). Ventrally 

 there is the sternum in two pieces (Fig. 526), 

 the posterior being much the larger and separat- 

 ing the points of origin of the right and left 

 legs. The abdomen is often globular but may 

 be cylindrical or may assume many bizarre 

 shapes. In some cases it is strengthened by 

 sclerites and in the genus Liphistius there are 

 seven of these dorsally and they here have a 

 segmental value. 

 FIG. 530. Arrange- The chelicerae are two-jointed, the end-joint 



ment of the eyes . . 



in different spiders being a rather sickle-shaped claw which bears 



(after Lebert). a . 



Araneus (Epeira); near its pointthc orifice ot the duct or the 

 Doiomedes ; d Salt- poison gland (Fig. 527). It is this claw that 



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poisons the prey of the spider. The pedipalps 

 are of fair size with six joints ; the coxa bears a gnathobase 

 or " maxilla " which projects towards the mouth. In the male 

 the terminal joint appears after the last moult in a very 

 modified condition known as the palpal organ (Figs. 531, 

 533). This contains a vesicula seniinalis, and spiders have 

 been observed to first 

 deposit their semen on 

 part of a web and then 

 to suck it into this 1- 

 vesicula seniinalis and 

 then to deposit it by 

 the palpal organ on or 

 in the female orifice, an 

 operation not unat- 

 tended with danger, as 

 the larger female some- 

 times seizes and de- 



FIG. 531. Diagram of palpal organ. 1 tarsus: 2 

 bulb; 3 vesicula seniinalis: 4 opening of vesicula 

 seminalis ; 5 conductor ; 6 haematodocha : 7 alveolus ; 

 penultimate joint of the pedipalp. After Warburton. 



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