x PHYLUM ARTHROPODA 255 



of which in the living animal is habitually carried over the 

 back (Fig. 151), constituting the "tail," at the end of which 

 the sting is placed. The cara- 

 pace bears a pair of large eyes 

 about its middle, and several 

 pairs of smaller eyes on the 

 antero-lateral margin. The an- 

 terior, broader part of the ab- 

 domen, which is termed the 

 pr a- abdomen, consists of seven 

 segments, each of which is pro- 

 tected by firm, chitinous, dorsal, 

 and ventral plates, or terga and 

 sterna. The tergum and sternum 

 of each segment are separated 

 from one another laterally by 

 intervals of soft skin, except in 

 the seventh, where they are 

 united laterally for a longer or 

 shorter distance. The posterior, 

 narrower part of the abdomen, 

 known as the post-abdomen, con- 

 sists of five segments, each en- FIG. i 5 i.-Euscorpio. (From Cuvier's 



Animal Kingdom.} 



closed in a complete investing 



ring of hard chitinous matter. Articulating with the last 

 segment of the post-abdomen is a terminal appendage, the 

 caudal spine or sting, swollen at the base and acutely pointed 

 at the apex, where open 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 



