232 



SYSTEMATIC ZOOLOGY. 



These forms live in the sea, feeding on worms, etc., found 

 in the sea-bottom, coming to the shore in spring and early 

 summer to lay their eggs. The horseshoe crabs are without 

 any economic importance, as they are useless as food, but 

 they are extremely interesting to the naturalist, as they 

 are the last remnants of forms which were once abundant 

 in the seas of past times. 



SUBCLASS II. ARACHNIDA. 



With few exceptions, the Arachnids are terrestrial 

 forms. They breathe by internal lungs or by tracheae, 

 and they lack compound eyes. There are several orders 

 of Arachnids, but only a few of them need be mentioned 

 here, as some are inconspicuous, while others occur only 

 in the warmer regions of the globe. 



ORDER I. SCORPIONIDA. 



The scorpions have a single pair of jaws (mandibles) 

 and a pair of large pincers, much like those of lobster or 



FIG. 60. Under surface of scorpion (Buthus} showing the combs and outlines 



of the lung-sacs. 



crab. The long abdomen is distinctly jointed, the seven 

 basal joints being much larger than the terminal five. 

 The abdomen ends in a very efficient poison-sting. On the 



