The External Anatomy of Spiders 



series of well-marked segments. The following parts can be 

 recognized in the abdomen of spiders. 



The pedicel. — In all spiders the abdomen is joined to the 

 thorax by a slender stalk, the pedicel, which is usually concealed 

 from above by the convexity of the part immediately following 

 it. In certain spiders, which are ant-like in form, the pedicel 

 of the abdomen is conspicuous; but in many of these a prolonga- 

 tion of the thorax enters into the composition of the pedicel. 

 In the dorsal wall of the pedicel there is a slender, longitudinal 

 sclerite, which is termed 

 the brum of the pedicel; in 

 some genera the lorum is 

 divided by a transverse 



Fig. 127. LORUM OF THE 

 PEDICEL OF P1SAURIXA 



Fig. 128. ARANEA FROXDOSA, 

 SHOWING FOLIUM 



suture (Fig. 127). In some forms there is also a sclerite in the 

 ventral wall, the plagula (plag'u-la). The plagula is well- 

 developed in the Dysderidae. 



The muscle-impressions. — On the dorsal aspect of the abdo- 

 men, there are several pairs of muscle-impressions; these are 

 small, hardened, depressed points, which, like the radial furrows 

 of the thorax, indicate the points of attachment of muscles to 

 the body-wall. There is also near the base of the abdomen 

 a median, unpaired muscle-impression, which is more or less 

 prominent. In some spiders there are muscle impressions on the 

 ventral aspect of the abdomen. 



127 



