INTKODUCTION. 21 



pupa is seldom wholly quiescent, and is generally active. 

 The pupa possesses well-marked foreshadowiugs of the 

 imago's true wings, in the form of small lobes or pro- 

 cesses on its back; and in some an organ which the larva 

 possessed — as for instance, the curious prehensile mask 

 of the different members of the Dragon-fly family 

 ( Libellulidcv ) — is discarded by the perfect insect. Ento- 

 mologists, therefore, in accordance with this partial and 

 incomplete metamorphosis, have given to those insects 

 which exhibit it the name of " Hemimetabolous."* 

 Again, there are insects in which the larvae differ very 

 little, indeed, from the perfect insects, where there is no 

 metamorphosis properly so called. The perfect imago 

 is often as wingless as the creeping larva, and the latter 

 differs from the former stage, either in point of size, in 

 the number of joints in the antennae, and in the im- 

 mature state of the reproductive organs. Sometimes 

 the adult is rendered not quite so like the larva by the 

 addition of a pair of wings, in which case the thorax 

 and the abdominal segments are more distinctly divided 

 than in insects whose imago is wingless. This kind of 

 metamorphosis obtains (1) in Lice ( Anoplura), Bird- 

 lice (Mallophaga), and Spring-tails (Thysanura), where 

 the imago is wingless, and (2) in some of the Ortlioptera 

 and Hemiptera where the adult is endowed with wings. 

 From the almost entire absence of metamorphosis in 

 such cases, the insects are called " Ametabolous."-|- 



The metamorphosis of insects is no doubt a very 

 striking and remarkable phenomenon in their history, 



• From 1)111 {7]i.u<7v "half") and fieTa(3oXf], 

 t From d not, and fxe-afioXri, 



