CHAPTER VII. 



THE JOINTED ANIMALS, concluded. 



THE SEA-SPIDERS, KING-CRABS, AND* CRUSTACEANS, 

 Classes Pantopoda, Gigantostraca, and Crustacea. 



THE animals belonging to the first of the three classes named above present 

 such a marked general resemblance to the true spiders, that they have been 

 included in the same class. On the other hand, from their marine mode of life, 

 some writers have come to the conclusion that their affinities are rather with 

 the Crustaceans. As a matter of fact, it appears impossible to affiliate them with 

 either of these groups, and the general opinion is that they are entitled to form 

 a class by themselves. In all these creatures the adult is provided with four 

 pairs of well-developed legs, composed of a large and varying number of segments, 



and each tipped with a single 

 claw. These limbs, which are 

 often exceedingly long and 

 slender, radiate from the sides of 

 the cephalothorax, which is pro- 

 duced into stalks for their support. 

 In front of these limbs, and 

 attached to the headpiece, are 

 sometimes three additional pairs of 

 appendages. Hence the full com- 

 plement of limbs is seven, and not 

 FEMALE OF SLENDER SEA-3PIDER, WITH EGGS (much enlarged). S1X pairs as in the true spiders. 



The first pair of appendages, form- 

 ing the mandibles, are short and often pincer-like ; the second pair, or palpi, being 

 also short; while the third pair, which are only developed in the females, are 

 shorter than the true legs, and, from their function, are termed the egg -bear ing 

 legs. In some cases, however, these three pairs of appendages have entirely 

 disappeared, as in the shore-spider (Pycnogonum littorale). Projecting forwards 

 from the front end of the body is a long rigid beak, or proboscis, at the 

 tip of which the mouth is situated. This beak is not formed by the fusion 

 of limbs, like that of the ticks, but results from the great development of the 

 area immediately around the mouth. The cephalothorax is divided into four 

 distinct segments, of which the first, or head, supports the first four pairs of 

 appendages, and has on its summit a pair of eyes, while the rest bear the three 

 posterior pairs of limbs. Attached to the last of these segments, and projecting 



