GENERAL LIFE HISTORY 37 



on dung except where other species are providing the 

 necessary dissolving juice. 



When the common maggots or gentles have ceased 

 feeding, they burrow into the ground or crawl away, 

 often to a considerable distance, apparently seeking a 

 secluded, a more wholesomely clean, and a dryer spot. 

 During this migrating time, they are palatable food 

 for many birds, which would not eat them in their 

 former food-loaded or unsecured state. Indeed, it is 

 doubtful whether either a vulture or a raven could eat 

 a fly-blown carcase without danger of myiasic punish- 

 ment. The skin of the larva whilst growing is trans- 

 parent, but, when about to pupate, it thickens and 

 becomes an opaque creamy white. 



The most marvellous part of the metamorphosis of 

 the blue-bottle is concealed, when the gentle becomes 

 the pupa ; according to Reaumur the embryonic fly 

 develops most curiously inside the puparium by a 

 procedure not exactly like the change from the cater- 

 pillar to the chrysalid in the case of the butterfly. 

 After a pause of a day or two, the front segments of the 

 fully fed maggot contract, so that the body assumes a 

 barrel-like shape ; the skin then hardens, and turning 

 a reddish brown it becomes a much contracted shell 

 or case called the puparium. However, the long 

 slender maggot has done something more than merely 

 shrink and shape itself conformably to the case; it has 

 withdrawn its embryonic head, so small as to be hardly 

 distinguishable microscopically, together with its 

 embryonic legs, wings and thorax into its embryonic 

 abdomen ! As the development proceeds, and the 

 embryonic members of the future perfect insect acquire 



