INSECTS. 489 



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

 all, heavier than the water, the creature easily drags 

 it along behind, thus keeping its abdomen always shel- 

 tered. It adheres stoutly to the inside of its dwelling by 

 means of a pair of articulated caudal appendages, generally 

 assisted by three tubercles on the first abdominal segment. 

 Before the change 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 readily passes. 

 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, or creep about plants with the other 

 four ; frequently rising to the surface of the water, they 

 there undergo their final change, using their deserted 

 skin as a sort of raft, from which to rise into the air ; 

 others climb to the surface of aquatic plants for the same 

 purpose. 



The perfect insect (Phryganea grandis) has four wings, 

 with branched nervures, the anterior pair of which, clothed 

 with hairs, are more frequently used than the posterior. 

 The organs of the mouth, except the palpi, are rudimen- 

 tary, and apparently quite unfit for use. The head is 

 furnished with a pair of large eyes, and with three ocelli ; 

 the antennae are generally very long. Some species 

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

 posed to belong to the Lepidopterous order; in point of fact, 

 these insects may be considered to form a connecting link 

 between the Neuroptera and the Lepidoptera. The females 

 have been seen to descend to the depth of a foot or more 

 in water, to deposit their eggs. 



Many species of these insects are found in Britain. The 

 larvae are well known to anglers, under the names of Cad- 

 dis-worms and Straw-worms. They are said to be excellent 

 baits. 



Butterflies and Moths belong to the highest order of the 

 suctorial insects, Lepidoptera, and pass through a complete 

 metamorphosis. The female Butterfly deposits her eggs 



