PHYLUM ARTHROPODA 



667 



narrow pointed telson. There are usually five pair of limbs sur- 

 rounding the mouth and, with the exception of the first, toothed 

 at the bases in order to perform the functions of jaws; the last 

 pair are stouter than the others and are . expanded so as, ap- 

 parently, to assume the character of swimming paddles. Certain 

 of the more anterior of the free segments bear paired lamel- 

 liform appendages 

 which probably car- 

 ried the "branchiae, as 

 in the Xiphosura. 

 The exoskeleton is in 

 many cases elabor- 

 ately sculptured. 



A cartilaginous in- 

 ternal endosternite 

 .of the same nature 

 as that which has 

 been described as oc- 



ojberc 



curring in the Scor- 

 pions is found in 

 Limulus and in. cer- 

 tain Spiders, but 

 not in the other 



groups. 



Coxal glands, 



similar to those that 

 have been described 

 in the Scorpion, oc- 

 cur also in most 

 Spiders, in the Sol- 

 pugida and Phalan- 

 gida, in some Acarida, 

 and in the Xiphosura. 

 In the Solpugida and 

 Phalangida they oc- 

 cur on the bases of 

 the last pair of legs : 

 in the Araneida and 

 Xiphosura, as in the 



Scorpion, they are found on the bases of the fifth pair of 

 appendages. 



Alimentary system. The oesophagus (Fig. 551, ces.) of the 

 Spiders is expanded behind into a special sucking stomach (suck. st.). 

 The mesenteron (mesent.) gives off in the cephalothorax a pair 

 of. large diverticula from each of which arise five narrow 

 diverfcicula (ccec.) which enter the bases of the pedipalps and legs ; 

 in the abdomen it is surrounded by a mass of cells commonly 



Fro. 549. Ventral view of Limulus. 16, appendages of 

 cephalothorax ; aid. abdomen ; ceph. cephalothorax ; operc. 

 operculum, behind which are seen the series of abdominal 

 appendages : tels. caudal spine or telson. (After Leuckart.) 



