XI 



PHYLUM ARTHROPOD A 



639 



the ducts of two poison-glands. The anal opening is situated on 

 the ventral surface of the last 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 over- 

 hangs it in front is the labrum. On each side of the mouth is a 

 three- jointed appendage the chelicera (Fig. 544, chel.) which is 

 terminated by a chela. Behind these are the very large pincer- 

 claws or pedipalpi (ped.), each composed of six podomeres and 

 terminating in a powerful chela. The basal joint of each pedipalp 



chfl 



: 



Fin. 543. Euscorpio. (From 



Cuvier's Animal Kiwjdmn .) 



FIG. 544. Scorpion. Ventral surface of the 

 cephalotliorax and pre-abdoinen. chel. cheli- 

 cerae ; op. operculum ; pect. pectines ; ped. 

 pedipalpi ; stig. stigmata. (From Leuckart 

 and Nitsche's Diagrams.) 



has a process which bites against the corresponding process of the 

 other pedipalp, these processes thus performing the function of 

 jaws. Following upon the pedipalpi are four pairs of walking 

 legs, each composed of seven podomeres, the last of which is 

 provided with curved and pointed horny claws. The basal segments 

 of the first two pairs of walking legs are modified so as to perform 

 to some extent the function of jaws. 



All the six pairs of appendages hitherto described the cheli- 

 ceree, the pedipalpi, and the four pairs of walking legs belong to 

 the cephalothorax. The first segment of the pre-abdomen (Fig. 

 544) has a narrow sternum, on which there is a soft rounded 



