812 



CLASS V. ARACHNIDA. 



O OO o animals, easily recognized by their stalked 

 000 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 LipJiistius there are 

 seven of these dorsally and they here have a 

 segmental value. 



The chelicerae are two- jointed, the end- joint 

 being a rather sickle-shaped claw which bears 

 near its point the orifice of the duct of the 

 poison gland (Fig. 527). It is this claw that 

 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 seminalis, and spiders have 

 been observed to first 

 deposit their semen on 

 part of a web and then 

 to suck it into this 

 vesicula seminalis 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- 



VOIITX thp ^mall malp FIG. 531. Diagram of palpal organ. 1 tarsus; 2 



J ul jie - bulb ; 3 vesicula seminalis ; 4 opening of vesicula 



TVi o OT rrV f 1 orra Vi Q iro coTron seminalis ; 5 conductor ; 6 haematodocha : 7 alveolus ; 



1 ne eignt legs nave Seven penultimate joint of the pedipalp. After Warburton. 



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oooo 



O O 



o o 

 000 



i 



lG. 530. Arrange- 

 ment of the eyes 

 in different spiders 

 (after Lebert). a 

 Araneus (Epeira); 

 b Tegenaria ; c 

 Dolomedes ; d Salt- 

 icus. 



