284 THE LIFE OF AN INSECT. 



of these fine emperor moths in a box in which he 

 had put a cocoon of this kind ; but in which he 

 could not discover the slightest appearance of any 

 insect having escaped from it, until he slit it lon- 

 gitudinally, and then found it to be empty ! 



Mr. Rennie mentions an instance, perhaps not 

 so ingenious, but equally curious, with this history 

 of the proceedings of the emperor moth, in a little 

 insect, also a moth, which also dwells upon the 

 willow. It spins an elastic shroud for its pupa, of 

 the singular shape of a boat with the keel upper- 

 most. Its first step is to spin two walls of whitish 

 silk of the required form ; and when these are 

 completed, it draws them forcibly together with 

 elastic threads, so placed as to retain them closely 

 shut. The passage of the moth out of this cocoon 

 might have struck Rosel with still greater surprise 

 than he had felt at witnessing that of the emperor 

 moth ; for in that cocoon there was at least no 

 apparent difficulty to prevent the egress of the 

 insect, as the opening existed in it at one end, 

 whereas in this there is no opening at all. The 

 insect escapes at the joining of the sides, the 

 threads giving way in a particular spot ; and the 

 sides, though originally requiring force to draw 



