324 



INTRODUCTION TO ZOOLOGY 



Within the closed case, in a few days' time, the larva casts 

 its skin piecemeal, and the soft white pupa is exposed ; on it 

 can be seen the antennae, quite free from 

 the body, and the legs and folded wings of 

 the imago (Fig. 243). This pupa is peculiar 

 in possessing several organs not found in 

 the imago. There are respiratory hairs on 

 the abdominal segments, and the head bears 

 great toothed mandibles which cross over 

 the face (Fig. 244). The presence of the 

 mandibles is specially interesting, since the 

 imago possesses as a rule no 

 trace of them. They are of 

 distinct use to the pupa, for it 

 is with them that it breaks 

 down the covering at the end FlG - 24 4. 

 of the case, when it is ready 

 to emerge ; these mandibles are 

 shed with the pupal skin. from in 



The pupa retains the power 

 of movement in its abdomen, and thus is able to keep up the 

 current of water which is necessary for respiration. 

 Emergence After two or three weeks, the pupa breaks down 

 of the the end of the case, and still enveloped in the 

 Imago, pupal skin it swims, back downwards, to the 

 surface of the water, and climbs out into the air by means 

 of some projecting weed, or other object (Plate III., P). 

 When at a height of a few inches above the water it stops and 

 rests, then its skin swells and splits, and the new Caddis-fly 

 quickly emerges and flies away : the complete empty pupal 

 skin remaining like a pupal ghost behind. 



The imago is at first rather pallid and greenish, but it 

 darkens in colour in a few days ; the antennae are thin and 

 tapering, and longer than the body ; the legs also are long, 

 but the body is nevertheless usually held rather low down 

 against any support, the drooping wings often hiding the 



Pictet.) 



This is the history of the life lived by most caddises, 

 though a few species differ in some details of their habits. 

 There are certain small caddises which do not actually leave 

 the water before the imago emerges, but merely float to the 



