336 



COLLEGE ZOOLOGY 



adult except for the absence of wings and mature reproductive 

 organs. Such a stage is usually spoken of as a nymph. Orders 

 II to XI of Table XII contain heterometabolous insects. Many 

 of the species belonging to these orders change considerably 

 during their growth period, but they are all more or less active 



FIG. 258. Partial metamorphosis of a grasshopper, Melanoplus femur- 

 rubrum, showing the five nymph stages, and the gradual growth of the wings. 

 (From Packard, after Emerton.) 



throughout their development and are said to undergo direct 

 or incomplete metamorphosis. 



Holometabolous insects, such as the honey-bee (Fig. 247), pass 

 through both a larval and a pupal stage in their development. 

 The majority of insects belong to this type (Table XII, orders 

 XII to XIX). 



c. General Survey of the Orders of Insects 



Classification. Insect classification is based principally on 

 the following characteristics: (i) the presence or absence of 

 wings, and their structure when present, (2) the structure of the 

 mouth-parts, and (3) the character of the metamorphosis. Au- 

 thorities differ with regard to the number of orders that should 

 be recognized, and two rather definite classifications have re- 



