CLASSIFICATION OF INSECTS. 



55 



are shown greatly enlarged in Fig. 24 ; they fre- 

 quently occur in aquaria in which aquatic plants are 

 growing. The sow-bugs (Fig. 25) are also Crustacea. 

 They live about water-soaked wood ; w 7 ith these only 

 one pair of antennas arc well developed. 



Class ARACHNIDA (A-rach'ni-da). 



The Arachnids (A-racli nids]. 



To this class belong the spiders, scorpions, har- 

 vestmen, mites, and certain other less common forms. 

 These animals differ from the other classes of the 

 branch Arthropoda in having no antennae. They 

 have four pairs- of legs fitted for walking, and many 

 of them have very large maxillary palpi, which re- 

 semble legs. The head and thorax are closely 

 united, forming a region which is called the cepJi- 

 alotJiorax (cepJi~a-lo-t]w'ra.v). These characteristics are 

 easily seen in 

 spiders (Fig. 

 26). 



The most 

 common rep- 

 resentatives of 

 the class Arach- 

 nida are the 

 spiders. These 

 are extremely 



interesting ani- FIG. 26. A spider, 



mals on ac- 

 count of the high development of their instinc- 

 tive powers. An account of the habits of some of 

 the common species is given in the chapter on Road- 

 side Life. 



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