THEIR FECUNDITY. 179 



five days, and the female will give birth to twenty 

 thousand young. Hence the assertion of Linnaeus, 

 with regard to M. vomitoria, that three of these flies 

 would devour a dead horse as quickly as a lion would 

 do, astonishing as it may appear, is, perhaps, not 

 overstrained. 



Not only are those flies endowed with rapidity of 

 growth, and extreme fecundity, but, to render those 

 powers available for the purposes for which they are 

 given, there is reason to believe that they possess an 

 instinct which, instead of making them keep, together 

 for companionship, prompts them to scatter widely 

 over the land in search of their fitting food, and con- 

 gregate only at the very place where their services 

 are required. Hence, they are constantly at hand 

 when wanted, and without delay commence the ful- 

 filment of their important task. I am the more 

 tempted to make this remark, from a circumstance 

 mentioned by my friend, Dr. J. L. Drummond. He 

 had procured a number of the maggots of the com- 

 mon blue-bottle fly, and had put them into a glass 

 vessel with a quantity of little pellets of paper, 

 among which they quickly buried themselves, mani- 

 festing the utmost impatience to avoid the light. 

 In about a month, they had undergone their 

 change into pupse, and were bursting their cases 

 and assuming the imago form, at the moment he 



X -2 



