276 THE LIFE OF AN INSECT. 



certain sharp points, which are all directed towards 

 the tail of the insert ; these sharp points are called 

 by entomologists adminicula. They are of infinite 

 consequence to the insect. Who has not himself 

 performed, or been the subject of, the trick of 

 causing a grain of barley to creep up the sleeve ? 

 The manner in which it is gradually pushed up is 

 strikingly similar to that in which the pupa of the 

 cossus is forced upwards and out of its wooden 

 gallery. It will be readily supposed that, in con- 

 sequence of the peculiar direction assumed by the 

 tooth-like processes in question, it will be very 

 difficult to push the pupa backwards, as the points 

 would catch in any obstacle and arrest its progress 

 in that direction ; but they offer no resistance to 

 its moving in a forward direction. The manner 

 in which the insect proceeds, then, is as follows : 

 Being capable of slightly shortening and lengthen- 

 ing the lower part of its body, which is the part 

 thus provided with hooks, it begins to push back- 

 wards, but the hooks catch in the sides of the wood, 

 and thus prevent it from moving back, and it is, 

 consequently, actually driven forwards ; and so it 

 continues to thrust itself gradually forwards in this 

 simple manner, just as a boy with his hands tied 



