200 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES 



mal that has gone in for specialization in a big way. The insects 

 are a subdivision of the Arthropods, animals that have jointed legs 

 and jointed bodies, and as such show definite repetition of similar 

 parts, or metamerism, a phenomenon previously noted in the Annelids. 

 As a group they have become differentiated to such an extent from 

 their not so distant relatives that, like the man on the flying tra- 

 peze, they ''fly through the air with the greatest of ease." In no 

 other group except the birds has this ability been so exploited. In 

 addition some forms, such as the bees, ants, and wasps, show an 

 astonishingly complex social life. 



As a successful group insects show numerous adaptations, not only 

 in structure but in life habits. They are not only active but often 

 so inconspicuous as to pass unnoticed by their enemies. Insects are 

 characterized by a rapidly growing larval period associated with an 

 abundance of food. The protected pupa is characterized by internal 

 changes fitting the organism for the active reproductive life of an 

 adult. They deserve our careful consideration as a type for study. 



The Insect Body Plan 



Adult insects are readily identified because the body is made up of 

 three parts, an anterior head, a mid region or thorax, and a posterior 

 region, the abdomen. The body may be further subdivided into 



Wright Pierce 



The large vagrant grasshopper {Schistocerca vaga Scudder) normal size. A typical 

 insect. Give all the distinguishing marks of an insect as shown in this photograph. 



