606 ZOOLOGY SECT.. 



where they are united laterally for a longer or shorter distance. 

 The posterior, narrower part of the abdomen, known as the post- 

 abdomen, consists of five segments, each enclosed 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 lobe which over- 

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

 three-jointed appendage the chelicera (Fig. 496. chel.) which is 

 terminated by a chela. Behind these are the very\a,rgepincer~Glaws 

 or 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 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- 

 cerse, the pedipalpi, and the four pairs of walking legs belong 

 to the cephalothorax. The first segment of the prse-abdomen 

 (Fig. 496) has a narrow sternum, on which there is placed a soft 

 rounded median lobe divided by a cleft ; this is termed the genital 

 operculum (pp.) ; at its base is the opening of the genital duct. To 

 the sternum of the second segment of the prse-abdomen are attached 

 a pair of remarkable appendages of a comb-like shape ihepectincs 

 (ped.) each consisting of a stem, along the posterior margin of 

 which is a row of narrow processes, some- 

 what like the teeth of a comb ; the function 

 of these appendages is doubtful, but is prob- 

 ably sensory. The remainder of the seg- 

 ments of the prse-abdomen, and all those of 

 the post-abdomen, are devoid of appendages. 

 The sterna of the third, fourth, fifth, and 

 sixth segments of the praa-abdomen, which 



PIO. 497.-Endosternite ^ ^^ br ad ' beai> 6ach a P air f obli qU6 



of scorpion. (After slits the stigmata (stig.) leading into the 



Lankester.) y V. *V & 



pulmonary sacs. 



In the interior of the cephalothorax, over 



the nervous system, is a cartilaginous plate the endosternite 

 (Fig. 497) which serves to give attachment to muscles, and is 

 comparable to the cephalic apodeme of Apus (p. 491). 



