442 



INVERTEBRATE MORPROLOQY. 



abdomen. The seven anterior segments (the praeabdomen) 

 of the abdomen are broader and thicker than the remaining 

 five segments (the postabdomen), the last one of which ter- 

 minates in a curved stout spine which bears at its extremity 

 the openings of two ducts leading from a pair of glands lying 

 in the twelfth abdominal segment and secreting a poisonous 

 fluid. 



The chelicersB (cA) are small chelate appendages situated 

 in front of the mouth, while the pedipalps (^"pe) are long and 



provided with atrong chelae, their 

 basal joints and those of the two 

 succeeding appendages surround- 

 ing the mouth and serving as jaws. 

 The four pairs of appendages be- 

 hind the pedipalps are all similar 

 in form, being six-jointed walking- 

 limbs. Upon the abdomen modi- 

 fied appendages are also found, 

 the second abdominal segment 

 bearing a pair, each member of 

 which consists of a single joint 

 whose posterior edge is beset with 

 a number of processes which give 

 it the appearance of a comb, 

 whence the name pectines iff) 

 applied to these appendages. In 

 front of the pectines lies the geni- 

 tal opening, protected by a small 

 genital operculum {op) which may 

 possibly represent another pair of 

 appendages belonging to the first 

 abdominal segment. 



Upon the ventral surfaces of 

 third, fourth, fifth, and sixth abdominal segments elongated 

 pores are to be found which are stigmata (sf"') leading into 

 the respiratory cavities containing the lung-books, of which 

 there are in all four pairs in this group. No trachese occur. 

 The intestine is quite straight in the Scorpions and lacks 

 csecal outgrowths excepting the two Malpighian tubules sit- 



FiG. 301. — Scorpion (after Owen), 

 c/j = cbelicerse. 

 O'p = genital operculum. 

 pe = pedipalp. 

 pi = pecten. 

 si'-* = stigmata. 



