THE INSECTS. 317 



this state, calls it incomplete that is, having all the limbs 

 distinct, but folded upon the breast, the head being fur- 

 nished with a pair of curved mandibles, which appear to 

 have no other purpose than of making a passage through 

 an open-work grating of silk which the larva had formed at 

 the opening of its case previous to assuming the pupa state. 

 " When, therefore, the time arrives for the insect to quit 

 its watery abode and assume the winged state, it is endowed 

 with powers of motion far greater than is possessed by any 

 other incomplete pupa, so that it is enabled, not only in the 

 first place to cut through the grating of silk, but to creep 

 out of its case, and then, rising to the surface, it crawls up 

 some plant, where it throws off its outer skin." 



Kirby and Spence, in the " Introduction to Entomology 

 Habitation of Insects," give a most interesting account 

 of these larvae : 



" The larvae of the various Phryganece, a tribe of four- 

 winged insects, which an ordinary observer would call 

 moths, but which are even of a distinct order (Trtchoptera), 

 not having their wings covered by the scales which adorn 

 the Lepidopterous race. If you are desirous of examining 

 the insects to which I am alluding, you have only to place 

 yourself by the side of a clear and shallow pool of water, 

 and you cannot fail to observe at the bottom little oblong 

 moving masses, resembling pieces of straw, wood, or even 

 stone. These are the larvae in question, well known to 

 fishermen by the title of caddis-worms, and which, if you 

 take them out of the water, you will observe to inhabit 

 cases of a very singular formation. Of the larva itself, 

 which somewhat resembles the caterpillars of many Lepidop- 

 tera, nothing is to be seen but the head and six legs, by 

 means of which it moves itself in the water and drags after 

 it the case, in which the rest of the body is enclosed, and 

 into which on any alarm it wholly retires. 



" The construction of these habitations is very various 

 some elect four or five pieces of the leaves of grass, which 

 they glue together in a shapely polygonal case ; others 

 employ portions of stems of rushes placed side by side, 

 forming an elegant fluted cylinder; some arrange round 



