ARACHNIDA 



103 



of rolling up into a ball when surprised. Its protective resem- 

 blance is good. Its locomotion is by crawling or running. 



Some of the marine Arthrostraca are parasitic on crabs and in 

 the mouths of fishes. 



CLASS H. ARACH'NIDA 



Arachnids are arthropods with the head and thorax generally 

 fused into a cephalothorax, bearing six pairs of appendages. 

 The first and second pairs are for biting. Then follow four 

 pairs of walking legs. There are no antennae, the eyes are simple, 

 and the abdomen is apodal. 1 



The abdomen varies much. It is 

 short in the spiders, long in the 

 scorpions, or is fused with the 

 thorax, forming a stout body in 

 the mites. 



They are usually oviparous. How- 

 ever, some scorpions and some mites 

 are viviparous. They are generally 

 terrestrial, but some live in the 

 water. There is no well-marked 

 metamorphosis. 



Order I. Scorpion'ida. Scorpions 

 (Fig. 76) are arachnids with long 

 slender bodies ending in a poison 

 fang. The head and thorax are 

 fused and bear several pairs of 

 jointed appendages. The abdomen 

 consists of a broad anterior and a 

 narrower posterior portion. There 

 are several pairs of eyes. 



Respiration is by means of four pairs of lung-sacs opening 

 on ventral side of abdomen from the third to sixth segments. 



Food. They are carnivorous, feeding upon spiders and in- 

 sects, which they seize with their pincers and sting to death. 



Multiplication. They are viviparous. The mother cares 

 for the young with great solicitude, carrying them about at- 

 tached to her body. 



1 See Glossary. 



Fig. 76. Carolina scor- 

 pion (Bu'thus carolinia'nus). 



