KING-CRABS 



423 



West Pacific. There has been much discussion as to its classi- 

 ficatory position, some authorities including it in the Crustacea 

 and others in the Arachnida. In support of the latter view it 

 has been shown that, allowing for the fact that one is a marine 

 and the other a terrestrial ani- 

 mal, there is a very remarkable 

 agreement between King-Crab 

 and Scorpion. As, however, the 

 matter is by no means settled, 

 it appears better for the present 

 to assign Limulus a class of its 

 own. 



The body of a King-Crab 

 (fig. 262) is divided into two re- 

 gions, a cephalo-thorax covered 

 above by a large horse-shoe- 

 shaped shield, and a similarly 

 protected abdomen to which a 

 long movable spine is attached 



-, f f, . - Fig. 262. — King-Crab {Limulus jy reduced 



behmd. A pair of simple eyes ^, From above = b. from beW. r,Chelicer«; 2-6, legs. 



a t-p situated on the too of the "^^^ mouth is seen in b as a darkly-shaded slit between the 



^ bases of the legs. 



front shield towards the anterior 



end, and farther back there are a pair of large compound eyes, 



placed at a greater distance from each other. 



Upon the under side the appendages can be seen, the first 

 of which are the small chelicer^, provided with pincers and 

 situated in front of the mouth. Then follow five pairs of legs 

 apparently equivalent to the pedipalps and legs of the Scorpion. 

 The first of them are provided with pincers in the female, and 

 the next three pairs are similarly provided in both sexes. The 

 ends of the last pair are curiously modified so as to fit them for 

 digging. The bases of these leg-like appendages are provided 

 with biting projections, which between them almost surround the 

 elongated mouth. The remaining appendages are six plates, 

 obviously formed by the fusion of pairs of appendages and borne 

 by the abdomen. The first of them is equivalent apparently to 

 the operculum of Scorpion (p. 386), and the second to the combs 

 of that animal. All but the first bear numerous gill-folds. 



