8 THE CABBAGE-WHITE BUTTERFLY 

 of form. The Cabbage- White (Pieris brassicae) 

 will serve as example. 



Those who have witnessed the metamor- 

 phoses of this or other lepidopterous insects, 

 must have been struck by the seemingly 

 perfect knowledge manifested by this creature, 

 not only that an event is due, but that it is 

 necessary to make preparations beforehand. 

 Thus we observe the larva when full fed, leave 

 its food-plant and start off over the ground 

 with evidently a determined purpose, which 

 is, in fact, to discover a suitable place for 

 pupation. Should there be a wall in the 

 neighbourhood the caterpillar, though possess- 

 ing no physical sight, is sure to find it and 

 climb to the first ledge or coping, a place 

 exactly suited to its requirements. After 

 determining the right spot the larva spins a 

 pad of silk which affords a good holding for 

 the anal claspers (last pair of legs) for the 

 time being ; but later on it will be seen that 

 this act was an absolutely necessary precau- 

 tion. In the meanwhile, it rests quietly whilst 

 certain changes are in process within. After 

 some days in this positio i, a final touch to the 

 arrangements is added. Raising its head and 

 anterior segments, the caterpillar stretches 

 backwards and with extreme adroitness weaves 

 a silk cord, composed of several strands, trans- 



