182 ROUND THE YEAR 



through the proboscis ; the nerve-cord and dorsal 

 vessel become shortened ; the silk-glands practically 

 disappear ; the reproductive organs enlarge ; the new 

 appendages acquire their motive and sensory appa- 

 ratus ; the voluminous fat-body of the larva is used 

 up. No food can at present be taken into the body, 

 but the pupa breathes all the time, and perishes if its 

 supply of air is cut off. 



At last the organs of the Butterfly have attained 

 the last degree of perfection ; the pupal skin cracks 

 along the back of the thorax, and the winged imago 

 emerges. At first its wings are damp and crumpled, 

 but they speedily expand and stiffen, and in no long 

 time the Butterfly is ready to range the fields, seek its 

 mate, and provide for new generations. 



Not all the larvae bring their life-history to a 

 prosperous end. There are some, in particular years 

 a large proportion, which are attacked by a deadly 

 enemy, an Ichneumon fly (Microgaster glomeratus), 

 which pierces the skin, and lays its eggs in the living 

 body. The eggs hatch, and the larvae which issue 

 from them devour their host alive. The victim has 

 not strength enough to assume the pupal stage. It 

 creeps up some adjacent object, as if with the in- 

 tention of casting its larval skin, but remains 

 immovable, and unchanged. The parasites now 

 devour all the viscera, creep out from the empty skin, 

 and keeping together, spin each its own little cocoon 

 of yellow silk. A cluster of such cocoons may often 

 be seen hard by the empty larval skin, and. people 

 have been known to take them for the eggs of the 

 Cabbage White and destroy them. The fully de- 



