ARTHROPOD A 



109 



imago state, lives from a few hours to several years, and 

 dies after the process of reproduction. Growth takes 

 place only during larval life;- and all metamorphoses 

 occur then. Among the social tribes, as bees and ants, 

 the majority (called "workers ") do not develop either sex. 



Insects (the six-footed arthropods) comprise about 

 one half of the whole animal kingdom as known, more 

 than two hundred and fifty thousand species having been 

 described. They may be grouped into seven principal 

 orders : 



i. Orthoptera have four wings : the front pair some- 

 what thickened, narrow, and overlapping along the back ; 



FIG. 65. Metamorphosis of a Cricket (Gryllus). 



the hind pair broad, net veined, and folding up like a fan 

 upon the abdomen. The hind legs are usually large, and 

 fitted for leaping, all the species being terrestrial, although 

 some fly as well as leap. The eyes are small, the mouth 

 remarkably developed for cutting and grinding. The lar- 



