CADDIS-FLIES. 87 



The length of the larva when full grown is a little less than J inch. The 

 head and prothorax are very horny, narrow, and pale brown in colour. The 

 rest of the insect is dull green, and very soft. The segments of the abdomen 

 gradually decrease in size towards the posterior extremity. The terminal 

 appendages are slender, and are each furnished with a pair of strong hooks. 

 The anterior legs are very stout, the tibia and tarsus being modified into 

 two prehensile claws, which are employed by the larva in capturing its prey. 

 I have been unable to detect any traces of external gills in this larva. 



Unlike most of the caddis-fly larvae, this insect does 

 not live in any kind of case, but swims about the streams 

 entirely unprotected, during the whole of its larval life. 

 When full grown, however, it constructs a compact, oval 

 •cocoon of rather small stones, which is firmly affixed to 

 the surface of a boulder in the bed of the stream. These 

 ■cocoons are very hard so long as they remain intact, but 

 when once they are injured in any way they immediately 

 •collapse. Inside the stone cocoon the larva invests itself 

 in an oval, semi-transparent envelope, somewhat resem- 

 bling in appearance thin horn or gelatine. Through this 

 inner cocoon the enclosed insect may be readily seen, and 

 may at once be identified by means of its long, narrow 

 head, which is curved downwards and laid upon the 

 breast of the insect. The creature remains in this 

 transition state for many days, during which time it 

 frequently turns itself round inside the gelatine cocoon. 

 Finally, however, it is transformed into a light green 

 pupa of extreme delicacy. In fact, this pupa is so fragile 

 and soft that it is seldom possible to extract it from the 

 inner cocoon without inflicting the most serious injuries. 

 As the enclosed insect develops, the gelatine cocoon 

 becomes more and more opaque ; thus the final stages 

 of the pupa are not clearly discernible. The mature pupa 

 emerges through an opening in one end of the inner 

 cocoon, but practically leaves no visible sign of its 

 means of exit from the outer stone cocoon. When 

 free the pupa always swims about in the water for 

 several hours before it gives rise to the winged fly. 



The perfect insect is fairly common in the vicinity of 

 streams, and may sometimes be taken at light. 



During the late spring and early summer I have 

 observed that large numbers of the stone cocoons, con- 

 structed by the larvae of this species and its allies, are 

 invariably left high and dry on the boulders situated at 

 the edges of rivers. This circumstance is due to the 

 shrinkage in the volume of water, which nearly always 

 takes place at that season, leading of course to the 

 destruction of very large numbers of the living pupae, 



