THE PHYLA ARTHROPODA AND ONYCHOPHORA 



Fig. 15.13. The blue crab, Callmecles safndus. A and B, ven- 

 tral and lateral views of zoaea larva. C, dorsal view of the 

 .succeeding megalops stage. D, adult male, dorsal view. 

 Note the shrimp-like proportions of the zoaea and the relative 

 enlargement of the cephalothorax in the megalops. {A, B, 

 and C\ reproduced from E. P. Churchill, 1942, Chesapeake 

 Biological Laboratory Publication No. 49, printed bv per- 

 mission; D, reproduced from M. J. Rathbun, 1896, Prnceedmas 

 of the VS. National Museum, vol. 18.) 



and three pairs of legs borne upon the thorax; and the spiracles, which are 

 the external openings of the system of air tubes, or tracheae, which distribute 

 air to the tissues. Representatives of the order Orthoptera, which includes 

 such generalized insect types as the locusts and grasshoppers (Fig. 15.14), will 

 be described to illustrate the typical structural and functixmal aspects of the 

 insects. We shall then consider certain fundamental phenomena in the 

 metamorphosis and life cycles of insects and discuss briefly representatives of 

 selected orders. 



The Locust: Habitat and Activities. Locusts, often referred to as 

 "grasshoppers," are universally distributed on all continents, in climates where 

 in.sect life in open fields is abundant. They crawl upon the grass and other 

 similar vegetation, leap into the air by means of their large posterior legs, 

 and may actually fly if the wings are well developed. Their shrilling as they 

 rest upon the ground, and the clacking of their wings in flight, are familiar 



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