CHAPTER III 

 INSECTS AND THEIR NEAR RELATIVES 



THE Branch Arthropoda includes, besides insects, sev- 

 eral related groups which are usually considered with the 

 insects and which should be familiar to the student of 

 insects for the purposes of comparison if for no other 

 reason. 



19. Crustacea. The Crustacea are forms which are 

 usually aquatic, breathe by means of true gills as do the 

 fishes, and have at least five pairs of jointed legs, the 

 anterior or front pair, in most common forms, bearing 

 pincer-like claws and being used as weapons rather than 

 as feet. Their bodies are made up of only two main parts 

 as the head and the thorax are grown together and form 

 what is known as a cephalothorax. 



Our best known Crustaceans are the crayfish, or "craw- 

 fish," the lobster, crabs, shrimps and the terrestrial form 

 called sow-bug or pill-bug. Their economic importance is 

 not great. Sow-bugs injure greenhouse crops at times and 

 in the Southern States the crayfish is injurious to agri- 

 culture in the marshy districts. These injuries are coun- 

 terbalanced by the importance of the class as food for man. 

 Lobsters and crabs are highly prized in America while 

 crayfish and shrimps are also used for food and many forms 

 are important as food for fishes. 



20. Myriapoda. Myriapoda are the Arthropods with 

 the greatest number of feet. They are commonly called 



19 



