TRACHEA TA 



409 



and Galeodes. They are usually six-jointed, and are frequently 

 clawed, but never chelate. In the male as it grows older the 

 terminal joint of the pedipalps grows larger, and after the 

 final moult it appears as the palpal organ, whose presence may 

 modify the shape of the adjacent joints. The palpal organ 

 varies in different species, 

 but it consists essentially 

 of a hollow sac which com- 

 municates with the exterior 

 by a duct, opening at the 

 tip of the segment. The 

 use of these organs is to 

 deposit the spermatozoa in 

 the receptaculum seminis 

 of the female. 



The four legs are seven- 

 jointed, the terminal joint 

 bearing two or three claws, 

 and in some species a num- 

 ber of short hairs, which 

 aid them in walking up 

 walls and on ceilings. 



The abdomen is sepa- 

 rated from the thorax by 

 a constriction, it is unseg- 

 mented and soft, and is 

 larger in the female than 

 in the male. Near its base 

 on the ventral surface is 

 the unpaired genital open- 

 ing, and on each side of 

 this lies the opening of a 

 pulmonary sac; in some species there are two pairs of 

 these openings, the posterior pair leading in some species 

 {Mygale) into a second pair of pulmonary sacs, in others 

 (Argyroneta) into a tracheal system. 



Near the posterior end of the abdomen are found the 

 spinnerets, these are four or six in number, according to the 

 species. In Upeira diademata, one of our largest spiders, there 



Fig. 2-35. — A Spider ( Cmnbridgea'fasciata, 

 Koch). Adult male. 



1-7. Seven joints of leg. 



