12 ANIMAL BIOLOGY 



development of the wings which first appear as small folds 

 on the posterior margins of the second and third segments 

 of the thorax. The wings become larger with successive 

 molts and acquire a joint, or articulation, at the base 

 which renders them freely moveable. Forms such as the 

 grasshopper and its allies in which the newly hatched 

 young resembles the adult and passes into the latter by 

 gradual stages are said to undergo an incomplete meta- 

 morphosis. Insects with a complete metamorphosis pass 

 through stages marked by abrupt and extensive changes. 

 In these forms the larva passes into a usually quiescent 

 pupa from which finally emerges the imago or aduh 

 insect. 



The description of a grasshopper previously given will 

 apply to a large number of the more typical kinds. There 

 are several hundred different species of grasshoppers, 

 and they occur in almost all countries of the tropical 

 and temperate regions of the earth. We commonly find 

 considerable differences between the grasshoppers of 

 different countries, and any one country usually contains 

 several species. Grasshoppers are very common in mead- 

 ows and grain fields. The Carolina locust, or roadside 

 grasshopper, frequents roadsides and other bare patches 

 of ground where it is difficult to detect on account of the 

 similarity of its color to that of the soil. Many other 

 species are protectively colored when in their natural 

 surroundings. Certain species of grasshoppers are mi- 

 gratory and some of the most destructive forms belong to 

 this group. In some of the migratory species the air sacs 

 connected with the tracheae are well developed and when 

 inflated with air serve to buoy the insects up during long 

 flights. These forms fly in swarms which sometimes 

 consist of incredible numbers. In 1889 a swarm which 

 passed over the Red Sea was over 2000 square miles in 



