2 AN INTRODUCTION TO ENTOMOLOGY. 



the typical adult is furnished with six legs ; the segments of the 



body are grouped into three regions, head, 

 ^-^r~ y< thorax, and abdomen, Fig. 2 ; and the 



body is usually furnished with wings. 

 Exceptions to each of these characteristics 

 occur. The more important of these ex- 

 ceptions are discussed in the course of the 

 following chapters. 



Fig. *.-Monobia. jj j HE METAMORPHOSES OF INSECTS. 



Among the marvellous facts revealed by the study of insects, 

 none is more striking than the wonderful transformations which many 

 of these creatures undergo. A large part of this book is devoted to 

 indicating these changes. In this chapter I wish simply to make 

 a few generalizations regarding the metamorphoses of insects, and 

 to define a few terms which are used in describing these changes. 



Complete Metamorphosis. — From the egg of a butterfly there 

 emerges a worm-like creature, known as a caterpillar, which has upon 

 superficial examination very little in common with its parents. This 

 caterpillar eats and grows, and when fully grown changes to an ob- 

 long, apparently lifeless object, the chrysalis. After a time there 

 bursts forth from this chrysalis a butterfly, like that which produced 

 the egg. In a similar way, from the egg laid by a fly upon a piece 

 of meat there hatches, not a fly, but a footless, worm-like maggot. 

 This when fully grown changes to a quiescent object corresponding 

 to the chrysalis of the butterfly. Later from this object there 

 escapes a winged fly like that which laid the egg. Those insects, 

 like the butterflies and flesh-flies, which when they emerge from 

 the egg bear almost no resemblance in form to the adult insect 

 are said to undergo a complete metamorphosis. In other words, the 

 change of form undergone by the insect is a complete one. 



Incomplete Metamorphosis. — There are, however, many insects 

 which after leaving the egg do not undergo such a remarkable change 

 of form as that indicated above. A young grasshopper just out from 

 the egg can be easily recognized as a grasshopper. It is of course 

 much smaller than the adult, and is not furnished with wings. Still 

 the form of the body is essentially the same as that of an adult. 

 After a time rudimentary wings appear; and these increase in 

 size from time to time till the adult state is reached. During 

 this development there is no point at which the insect passes 



