PHYLUM ARTHROPODA 



255 



segment of the post-abdomen, immediately in front of the 

 sting. 



The aperture of the mouth, which is very small, is at the 

 anterior end of the cephalothorax on its ventral aspect ; a 

 lobe which overhangs it in front is the labrum. On each 



chel 



FIG. 141. Scorpion. Ventral surface of the cephalothorax and prae-abdomen. 

 chel. chelicerae ; op. operculum ; pect. pectines ; ped. pedipalpi ; stig. stigmata. 

 (After Cuvier.) 



side of the mouth is a three-jointed appendage the chelicera 

 (Fig. 141, chel.) which is terminated by a chela. Behind 

 these are the very large pincer-claws, w pedipalpi (ped.), each 

 composed of six podomeres and terminating in powerful 

 chelae. The basal joint of each pedipalp has a process 

 which bites against the corresponding process of the other 



