662 



ZOOLOGY 



SECT. 



The organs of respiration are lamelliform gills attached to the 

 abdominal appendages. 



This order includes the King-crabs (Limulus, Figs. 548 and 

 549). 



ORDER 9. EURYPTERIDA. 



Arachnida with a relatively small cephalothorax, followed by 

 twelve free segments and a terminal, elongated, narrow telson. 

 There are a pair of pre-oral leg-like or chelate appendages and 

 four more leg-like appendages on the cephalothorax, the last 

 expanded to form swimming paddles. A broad operculum is 

 situated immediately behind the cephalothorax. There are pairs 

 of lamellate appendages on certain of the anterior free segments. 

 The exoskeleton is characteristically sculptured. 



This order includes only a number of extinct (Paleozoic) forms 

 of large size (Fig. 550). 



3. GENERAL ORGANISATION. 



The external form in the Scorpionida has already been suffi- 

 ciently described. Most nearly related to that order in this 

 respect are the Pseudoscorpionida or Book-scorpions and their 

 allies. In these (Fig. 540) there is an unsegmented cephalo- 

 thorax, or the carapace is crossed by 

 two transverse grooves which may indi- 

 cate segmental divisions. There is a 

 broad abdomen consisting of eleven, or 

 more rarely ten, segments ; the post- 

 abdomen is not represented, nor the 

 caudal sting. The chelicerse are small ; 

 the pedipalpi are large, and resemble 

 those of the Scorpions in their chelate 

 form. Spinning glands are present. 



The Pedipalpi, or Scorpion-spiders 

 (Fig. 541), are intermediate in some of 

 their external features between the 

 Scorpions and the Spiders. The abdomen 

 is broad and marked out into a series 

 of eleven or twelve distinct segments ; 

 in one of the genera of the order there 

 is a short post-abdomen formed of the last three segments, with 

 an elongated, many-jointed anal filament. The chelicerse end 

 in simple claws ; they are probably provided with poison-glands ; 

 the pedipalps are very long, either claw-like or chelate ; the 

 first pair of legs are very long and slender, their terminal part 

 made up like antennae of numerous short joints. There are eight 

 eyes on the carapace, two larger central, and six smaller marginal. 

 The Solpugida (Fig. 542) have 3 at least superficially, the 



FIG. 540. Chelifer bravaisii. 



26, second to sixth pairs of 

 appendages. (From Lang's 

 Comparative, Anatomy.) 



