STATES OF INSECTS. 279 



them into their required position, become so elastic as to 

 close again when the moth has passed between them and 

 made her escape ; the cocoon preserving its usual shape, 

 even when deprived of its inhabitant a . A similar cocoon 

 is constructed by another leaf-rolling caterpillar, that of 

 Tortrix chlorana b . Many similar proofs of contrivance 

 in the construction of silken cocoons might be adduced, 

 but I shall confine myself to one more only — I mean that 

 furnished by the flask-shaped brown one of Saturnia Pa- 

 vom'a, and some other moths. If you examine one of 

 these cocoons, which are common enough in some places 

 on the pear-tree or the willow, you will perceive that it 

 is generally of a solid tissue of layers of silk almost of 

 the texture of parchment; but at the narrow end, or. 

 that which may be compared to the neck of the flask, 

 that it is composed of a series of loosely-attached longi- 

 tudinal threads, converging, like so many bristles, to a 

 blunt point, in the middle of which is a circular opening . 

 It is through this opening that the moth escapes. The 

 silk of its cocoon is of so strong a texture and so closely 

 gummed, that had both ends been similarly closed, its 

 egress would have been impracticable ; it finds, however, 

 no difficulty in forcing its way through the aperture of a 

 sort of reversed funnel, formed of converging threads 

 that readily yield to pressure from within. But an ob- 

 jection will here probably strike you. You will ask, Is 

 not this facility of egress purchased at too d&'ar a rate? 

 Must not a chrysalis in an open cocoon be exposed to 

 the attacks of those ichneumons of which you have said 

 so much, and of numerous other enemies, which will find 



a Bonnet, CEuvr. ii. 229. b De Geer ii. 477. 



c Sepp. iv. t. xi./. 8. 



