CADDIS-FLIES. 71 



gists, and led them to describe the cases as actual shells. 

 The case constructed by the New Zealand insect is about 

 f$ inch in diameter. The whorls are rather flattened,, 

 and the inner portion of the spiral is smooth, and com- 

 posed of extremely minute sand grains ; further out the 

 sand grains become coarser, and near the orifice of the 

 case they are much larger, and give that portion of the 

 structure a somewhat irregular appearance. 



The enclosed larva is very elongate, curved and specially adapted for 

 inhabiting a spiral tube. Its length when full grown is about f g inch. The 

 head is rather large, oval, light reddish-brown. The prothorax is also- 

 reddish-brown, horny, and highly polished. The meso- and meta-thorax 

 are dull green tinged with reddish-brown, and clothed with a few isolated 

 bristles, the sides of the latter segment being furnished with hair-bearing 

 tubercles. The abdomen is bright green and very shining. The first 

 abdominal segment is furnished with an extremely large dorsal hump. 

 The anterior legs are very short, the intermediate and posterior pair of 

 moderate length. There are no visible respiratory filaments. The seg- 

 ments of the abdomen are very cylindrical. The terminal segment has 

 two rather feeble claws. 



These larvae are found in the streams throughout the 

 entire year. In mid-winter they are very abundant, but 

 so minute are the cases that it requires a very close 

 scrutiny to discover them. They are often secreted in 

 the depressions on some of the larger stones in the bed of 

 the stream, and in these situations we may sometimes- 

 find clusters of fifty or a hundred cases. As the season 

 advances the cases become larger, and in warm weather 

 the larvae are very active, pulling their cases after them 

 in all directions. On the approach of any moving object 

 they may be observed detaching themselves from the 

 stones with great celerity, and drifting down-stream like 

 so many small pebbles. These tactics would no doubt 

 preserve them from many enemies, but nevertheless large 

 numbers of the larvae are devoured by trout, as we find 

 their heliciform cases very numerous in the stomachs of 

 fish taken in streams, where the insects are abundant. 

 The mature larva fixes its case very firmly to a large 

 stone in the bed of the stream, generally selecting for 

 this purpose a depression in the rock or stone. When 

 finally anchored, the larva, after having closed the orifices 

 of the case, changes into a pupa inside. 



The pupa has the head small, pale brown, with the eyes prominent and 

 yellowish-brown. The thorax is dull green. The wings are elongate, bright 

 green, and curved upwards towards their extremities. The abdomen is 

 elongate, pale green, with nine visible segments, curved upwards towards 

 the tip ; there is a slender black line on each side. The antenna? and legs 

 are also curved in the same way as the wings and abdomen, so that the 

 whole insect fits perfectly into its heliciform case. 



