INTRODUCTION. 9? 



menstruum acting on the gum which holds the fibres 

 of the silk together, and the animal is able to force 

 itself through without having recourse to any other 

 means. It is found that the cocoons, from which 

 the silk-worm moth has emerged, can occasionally 

 be unwound in an unbroken thread, but in far the 

 greater number of instances this is impossible. 

 When the caterpillar provides for the egress of the 

 moth, it generally does so by making a circular 

 incision near the one end, leaving only a small 

 portion entire to act as a hinge, and this the moth 

 easily pushes outwards when it desires to escape. 

 But sometimes a much more elaborate contrivance 

 is resorted to, of which a curious example is afforded 

 by the flask-shaped cocoon of the Emperor -moth. 

 This has frequently been so well described, that we 

 cannot expect to make it better understood than by 

 using the words of a previous writer. " 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 com- 

 pared to the neck of the flask, that it is composed 

 of a series of loosely-attached longitudinal 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 



* In Scotland they are most frequently foumjl on heaths 

 and moor-land, the larva subsisting on the heather. 



