HYDROCAMPA NYMPH^ATA. 99 



whereas after a moult it sometimes makes a new case 

 entirely ; when, therefore, it wants only a new roof or 

 a new floor, it takes it from a suitable plant nearest 

 at hand, cutting the new piece a little larger than its 

 predecessor, and in this way, by changing the top and 

 bottom alternately, it soon brings a small case up to 

 a good size. 



On the 11th of June I noticed a larva looking as if 

 about to moult, and isolated it for observation ; the 

 moult took place on the 13th. After the skin burst at 

 the neck the old head-cover first fell off, and then the 

 (almost colourless) larva began slowly to advance into 

 the water out of its case until nearly exposed ; then it 

 stopped still for about ten minutes, when suddenly the 

 hinder segments were set free with an effort that sent 

 the case adrift, while the larva remained quite naked 

 in the water. I secured the abandoned case, and 

 opening it found the cast flaccid skin — not shrivelled 

 up, but held out at full length by silk threads along 

 the ventral region. 



This larva now proceeded to make itself a case of 

 Alisma plantago, first securing a piece of leaf that was 

 near, and then fastening this under another leaf that 

 floated by. Three hours after it thus hid itself I 

 turned the leaf over, and found the piece by this time 

 fashioned into a suitable oval shape and attached to 

 the oval edge of the leaf, so that on that side there 

 was no need of cutting ; next day the larva was shap- 

 ing the second piece — not merely by cutting a channel, 

 but by eating away a large irregular hole outside its 

 case, still, however, leaving a narrow isthmus uncut, 

 so as to keep itself securely moored for a day or two 

 longer; but at last, when it had to stretch out further 

 and further to continue feeding on the leaf, it made 

 its case tight, cut the mooring, and floated off. 



When the larva is about to pupate it attaches its 

 case at the edge of one side beneath some floating leaf 

 or submerged stem, often (as Mr. Jeffrey found a great 

 number) to the decumbent stems and tough fibrous 



