METHOD OF HATCHING. 195 



the eggs of the Phryganidse are hatched, they take the 

 form of a little soft grub, resembling a maggot in appear- 

 ance, with a hard horny head, and with six feet upon the 

 future thorax. This is the larva form, and as the skin is 

 very tender and soft, and susceptible of injury, it proceeds, 

 by means of a kind of gluten it possesses, to form for itself 

 a dwelling, and attaches itself to small fragments of stick, 

 sand, stone, and shells, until it has constructed a small, 

 rough, hard tubular case, within which it can shroud itself 

 completely. One end of the case is left entirely open, and 

 from this the animal at times, when it desires to shift its 

 position, protrudes its head and feet, and travels along, 

 drawing the case after it ; the other end is in many species 

 partially closed, leaving only a round air-hole, whicli 

 fulfils a curious purpose in insect economy. It is in the 

 power of the larva to raise itself to the surface of the 

 water by secreting within the tail end of the case a small 

 portion of air sufficient to buoy up the weight of itself and 

 its habitation, and by means of this it may often be seen 

 hanging, as it were, from the surface of the water, appa- 

 rently basking with its tail upwards; but at the least 

 alarm or the slightest touch the air-bubble is expelled 

 through the round hole alluded to, and the creature drops 

 at once to the bottom. When it is about to change into 

 the pupa form, the larva closes up the tube, and thus in a 

 sort of cocoon becomes a pupa, the wing-cases, &c., being 

 developed, as in the Ephemerae, but rather more perfectly. 

 When about to change into the imago, some of the species 

 tear open the closed-up entrance and crawl to the bank of 

 the river, and there abandon their case, and become the 

 imago. Some of the smaller species, however, by the 

 power above mentioned, rise to the surface, and take wing 

 from their cases, using them as a sort of raft. These cases 

 are beautifully smooth and polished on the inside, and 

 well adapted to the creature's habits. The rest of its 



