INSECTS. 303 



The family of Phryganeidce, the larvae of which are aquatic, present 

 almost as little resemblance to the imago as those of some metabolous 

 insects. They are long, softish grubs, furnished with six feet, and 

 with a horny head armed with jaws, generally fitted for biting veget- 

 able matters, although some appear to be carnivorous. To protect 

 their soft bodies, which constitute a very favourite food with fishes, 

 these larvse always enclose themselves in cases formed of various mate- 

 rials ; bits of straw and sticks, pebbles, and even small shells, being 

 commonly employed in this manner. The materials of these curious 

 cases are united by means of fine silken threads, spun like those of the 

 caterpillars of the Lepidoptera, from a spinnaret situated on the labium. 

 In increasing the size of its case to suit its growth, the larva is said to 

 add only to the anterior end, cutting off a portion of the opposite ex- 

 tremity. When in motion, the larva pushes its head and the three 

 thoracic segments, which are of a harder consistence than the rest of 

 the body, out of its case ; and as the latter is but little, if at all, 

 heavier than the water, the creature can readily drag it along behind 

 it, thus keeping its abdomen always sheltered. It adheres stoutly to 

 the inside of its dwelling by means of a pair of articulated caudal ap- 

 pendages, generally assisted by three tubercles on the first abdominal 

 segment. 



Before passing to the pupa state, the larva fixes his case to some 

 object in the water, and then closes up the two extremities with a 

 silken grating, through which the water necessary for the respiration 

 of the pupa can easily pass. The pupa is furnished with a large pair 

 of hooked jaws, by means of which, when about to assume the perfect 

 state, it bites through the grating of its prison, and thus sets itself free 

 in the water. In this form the pupae of some species swim freely 

 through the water by means of their long hind legs, also creeping 

 upon the other four limbs ; these frequently rise to the surface of the 

 water, and there undergo their final change, using their deserted skin 

 as a sort of raft, from which to rise into the air, whilst others generally 

 creep up the stems of aquatic plants for the same purpose. 



The perfect insect {Ph/rygcmea grandis, shown in fig. 136, near its 

 la/rva-case), has four wings, with branched nervures, of which the an- 

 terior pair are clothed with hairs ; the 'posterior are folded in repose. 

 The organs of the mouth, except the palpi, are rudimentary, and appa- 

 rently quite unfit for use. The head is furnished with a pair of large 

 eyes, and with three ocelli, and the antennre are generally very long. 

 Some species are so exactly like Moths, that they have often been sup- 

 posed to belong to the Lepidopterous order ; and, in fact, these insects 



