256 MANUAL OF ZOOLOGY SECT. x. 



pedipalp, these processes thus performing the function of 

 jaws. Following upon the pedipalpi are four pairs of walk- 

 ing 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 

 chelicerae, the pedipalpi, and the four pairs of walking legs 

 belong to the cephalothorax. The first segment of the 

 prae-abdomen (Fig. 141) has a narrow sternum, on which 

 there is placed a soft rounded median lobe divided by a 

 cleft ; this is termed the genital operculum (op.} at its base 

 is the opening of the genital duct. To the sternum of the 

 second segment of the prae-abdomen are attached a pair of 

 remarkable appendages of a comb-like shape the pectines 

 (pect.} each consisting of a stem, along the posterior margin 

 of which is a row of narrow processes, somewhat like the teeth 

 of a comb ; the function of these appendages is doubtful, 

 but is probably sensory. The remainder of the segments 

 of the prae-abdomen, and all those of the post-abdomen, are 

 devoid of appendages. The sterna of the third, fourth, fifth, 

 and sixth segments of the prae-abdomen, which are very 

 broad, bear each a pair of oblique slits the stigmata 

 (stig.} leading into the organs of respiration. 



All the appendages of the Scorpion are post-oral in posi- 

 tion, and the most anterior the chelicerae are probably 

 best regarded as corresponding to the antennae of the Cray- 

 fish, the equivalent of the Crayfish's antennules and of the 

 antennae of the Cockroach not being present. The pedi- 

 palpi would then be the homologues of the mandibles of the 

 Insect and the Crustacean. 



The organs of respiration in the Scorpions are in the form 

 of pulmonary sacs or book-lungs (Fig. 142, pul.\ the stigmata 



