SUCTORIAL CRUSTACEA. PYCNOGONIDA. 



279 



as well as from the conformation of the mouth, that their prey 

 must consist of either dead animal matter, or of living animals 

 as defenceless as themselves. 

 The females are distin- 

 guished by the possession 

 of a pair of spurious legs 

 (Fig. 504), placed in front 

 of the rest, and appropriated 

 to the purpose of holding 

 and carrying the eggs. 

 These are collected into 

 globular masses, enveloped 

 with a thin skin or mem- 

 brane,each massbeing firmly 

 adherent to the limb. There 

 are several of these masses 

 in most species of the 

 tribe ; but in Pycnogonuin itself, the eggs form a single broad 

 square membrane laid under the body. The proboscis of these 

 curious animals, which seems to refer them to the group of 

 Suctorial Crustacea, is really the entire head ; and the organs 

 which have been usually described under the name of palpi and 

 mandibles, as appertaining to it, are in reality appendages of the 

 thorax, and must be considered as metamorphosed legs ; so that 

 the Pycnogonidae really have seven pairs of legs, like the Crus- 

 tacea to which they are most nearly allied. 



FIG. 504. NVMPHOV GKOSSTPJSS, and under side 

 of its Beak. 



There now only remains to be considered the third sub-class 

 of the Crustacea ; which consists of but a single Order. 



ORDER XII. XYPHOSURA. 



817. Although this group only contains a single genus, the 

 Limulus, or King-crab, yet the structure of this departs so 

 widely from that of all the Crustacea we have hitherto con- 

 sidered, that it cannot be referred to the same Order, or even 



