MYIASIS AND THE (ESTRID& 31 



moults ; at each moulting the strange creature becomes 

 smaller and smaller, but probably at the same time is 

 provided with a new head well suited for the purpose 

 of that period ; firstly, with a burrowing or grappling 

 head, and in due time with a feeding suctorial mouth, 

 and then only does practical growth begin. No dip- 

 terid flies, at all events, known to be native to Great 

 Britain, possess skin-piercing ovipositors. 



I have been astonished to read in current literature 

 much about cestrid flies which is not in agreement 

 with my long course of personal observation ; for 

 instance, one high authority (F. R. S.) writes that cestrid 

 "flies" appear from May until October, and hints that 

 their egg-laying aggressions upon their victims are not 

 conspicuously observable. I feel confident that the 

 facts are quite otherwise. 



That the bot-flies normally (and a few others abnor- 

 mally, but for short periods only) pass a very long 

 larval stage in the stomach and alimentary canal of 

 herbivorous animals is one of the greatest marvels 

 of insect life. All other growing creatures, which 

 normally breathe in free air, require a certain large 

 amount of breathable oxygen; and they would be 

 stupefied or killed by a much smaller percentage of 

 carbonic dioxide and other fermentive gases of diges- 

 tion than undoubtedly exist in the strange abode 

 wherein the bot-fly maggots dwell during the entire 

 period of their feeding career. It has been stated that 

 fly maggots artificially ingested into the human system 

 have emerged alive in a normal condition, but the 

 repulsive and objectionable experiment is not stated 

 to have procured well nourished and full grown nor- 



