154 



NATURAL HISTORY. 



SPIDERS, MITES, AND SCORPIONS. 



To many it may seem strange that the species which is introduced first 

 under this heading is the king-crab, or horseshoe-crab, a form which in all 

 of the text-books is placed among the Crustacea. It appears, however, 

 that is where it really belongs. The arguments for this course are too 

 abstruse for insertion here, as they are based on the facts of structure and 

 development. We may. however, say that the king-crab of to-day appears 

 to be not far different from the form from which the scorpions, and 

 through them the spiders and mites, have descended. Every feature in 

 which the horseshoe seems to resemble the Crustacea can have an entirely 

 different interpretation, and one which seems far more reasonable, and 

 which points to the conclusion indicated above. 



The horseshoe-crab (Limulus) is distributed along our coast from 

 Maine to Florida. None are found on our western shores or on the coasts 



of Europe ; but other species occur on 

 the Asiatic shores and on the east coast 

 of Africa. This distribution seems pecul- 

 iar, but it is paralleled by that of many 

 animals and plants. Why it is so no one 

 has yet been able to say. There is a 

 good deal of learned talk about simi- 

 larity of environment and the like, but 

 the explanation needs to be explained. 



The horseshoe has its body com- 

 posed of three parts, — an anterior por- 

 tion which in outline is much like the 

 foot of a horse, a middle triangular por- 

 tion, and a long caudal spine. Its color 

 is a dirty olive-green. The front portion 

 has a sharp edge, so that the animal can 

 readily force itself through the mud and 

 sand, using its feet and its pointed tail 

 as points of resistance. It burrows along 

 just beneath the surface, hunting for its 

 food, which consists of clams, worms, and 

 the like. Its method of eating is pecul- 

 iar. It has no proper jaws like the 

 msects and crustaceans, but on the basal joints of its legs are numbers of 

 spines which, moving against each other, serve to tear its food into shreds. 



I'm,. 1 '.?. — Horseshoe-crab, or kiug-crab 

 {Limulus). 



