TRACHEATA 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 Thee 
oe 5 _ Fie, 235.—A Spider (Cambridgea fasciata 
the unpaired genital open Koch) Adult male , 
ing, and on each side of 1-7. Seven joits of leg. 
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 Epeira diademata, one of our largest spiders, there 
