INTRODUCTION. 
21 
pupa is seldom wholly quiescent, and is generally active. 
The pupa possesses well-marked foreshadowings 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 
(LibellulidcG )—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 larvse 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 Orthoptera 
and Hemiptera where the adult is endowed with wings. 
From the almost entire absence of metamorphosis in 
such cases, the insects are called “ Ametabolous.”y 
The metamorphosis of insects is no doubt a very 
striking and remarkable phenomenon in their history, 
* From >)/u (yfucrv il half”) and fiera(3o\{j, 
t From d not, and fisra€o\r . 
