176 CATERPILLAR AND IMAGO OP LEPIDOPTERA. 



leaves, in which they excavate galleries; others envelope 

 themselves in the membrane of the leaf itself, which they roll 

 together and attach by threads, as seen in Fig. 399, repre- 

 senting the nest of the larva of Tortrix viridissima (a small 

 nocturnal Butterfly), which is constructed upon the leaves of 

 the Oak. Many construct cases or sheaths, either fixed or port- 

 able, by agglutinating several substances together, as is done 

 by the larva of the common Clothes'-Moth ; and there are some 

 that live in societies, dwelling together under a tent of silk, 

 which they spin in common, and which serves to defend them 

 from the inclemency of the weather. 



704. The Imago, or perfect Insect, when it throws off its 

 last envelope and comes forth into the air, of which it is hence- 

 forth to be one of the gayest inhabitants, is not altogether 

 perfect, although capable of very soon becoming so. The wings 

 appear at first very slightly developed, and sometimes even 

 hang loosely at the sides ; and it is not until the animal 

 has injected their tracheae with air, by taking several full 

 inspirations and then forcing it into these passages, that they 

 become expanded so as to serve for flight. From that period 

 the body is supported by them, during by far the largest pro- 

 portion of their active state ; the legs being weak and used only 



FIG. 400. TORTOISE-SHELL 

 BUTTERFLY JUST EMERGED 

 FROM THE CHRYSALIS. FIG. 401. DANAIS PLEXIPPA. 



to rest upon, and one pair being sometimes undeveloped 

 (Fig. 401). 



705. The Lepidopterous insects are divided into three 



