THE SPIDER 115 



less developed than that of insects. Although they belong 

 to the air-breathing arthropods they arc without wings, antl 

 are therefore confined to the surface of the ground, except in 

 the case of the ballooning species just described. In conse- 



FiG. 116. — The entrance of the vertical tube to the sand-Lycosa. 



quence, the thorax is not a distinct and prominent part of 

 the body, as in insects, but is indistinguishably united mth 

 the head. The abdomen never carries legs as does that of the 

 water arthropods. In this respect the Arachnid a agree \^dth 

 the insects rather than wth the water-inhabiting crustaceans. 

 Although the spiders are the largest group of the Arachnida, 

 there are several other kinds of animals included in this class. 



