METAMORPHOSES OF INSECTS 31 



of life, but merely a particular stage in the process of 

 development. The condition of the young may be 

 well advanced before this event, or the reverse, birth 

 may occur at an early period of development, and 

 causes for the difference are readily discovered. Thus 

 the apparent total discrepancy between the meta- 

 morphoses of insects such as the locust or grasshopper, 

 and the bee or fly. The two insects first mentioned 

 have become highly developed before birth, the bee and 

 fly have emerged into the world from the egg ere 

 metamorphoses have far progressed. The terms larva 

 stage and pupa stage are therefore somewhat arbitrary, 

 since larvae at their birth from the egg are in many 

 stages of youthful development. 



The metamorphoses of insects depend then first on 

 the fact that the young quit the egg at a more or less 

 immature stage of development. The external forces 

 act upon them in their preparatory state, and are 

 different from those which affect the mature form. 

 Consequently it need cause us no surprise to find that 

 larvae and pupae undergo changes which have refer- 

 ence to their immediate wants, rather than to the 

 condition which they will ultimately assume. 



As to the second part of our subject : the ap- 

 parent separation of the development of insects into 

 distinct stages. There is this remarkable point to 

 be observed, that whereas the alterations in many 

 animals go on so ceaselessly and so slowly that we fail 

 to perceive them, in insects the changes appear to be 

 excessively sudden. This does not apply to Orthoptera 

 and others which undergo incomplete metamorphoses, 

 whose development from birth to mature life is gradual 



