618 



ZOOLOGY 



SECT. 



: 

 ; 



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, apparently, 

 to assume the character of swimming paddles. Certain of the 

 more anterior of the free segments bear paired lamelliform 

 appendages which probably carried the branchia? as in the 



Xiphosura. The exo- 

 skeleton is in many 

 cases elaborately 

 sculptured. 



A cartilaginous in- 

 ternal endosternite 

 of the same nature 

 as that which has 

 been described as oc 

 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 mos 

 Spiders, in the Sol 

 pugida and Phalan 

 gida, in some Acarid^ 

 and the Xiphosura 

 In the Solpugida anc 

 Phalangida they oc 

 cur on the bases o 

 the last pair of legs 

 in the Araneida anc 

 Xiphosura, as in th 

 Scorpion, they are 

 found on the bases 

 of the fifth pair c 

 appendages. 



Alimentary system. The oesophagus (Fig. 513, CBS.) of th 

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

 The mcscntcron (mesent.) gives off in the cephalothorax five pain 

 of narrow diverticula (cose.) which enter the bases of the pedipalp* 

 and legs ; in the abdomen it also gives off a number of caeca, which 

 branch and come in close relation with a mass of cells commonly 

 termed liver (hep.), though not known to have the function of that 



a&d 



teLs 



FIG. 511. Ventral view of Limulus. 1 6, appendages of 

 cephalothorax ; abd. abdomen ; ceph. cephalothorax ; operc. 

 operculum, behind which are seen the series of abdominal 

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



