HOUSE-FLIES 103 



Algonquin reservation in Canada, to remark how similar 

 was their vegetation to that of our own ponds. There 

 were water-lilies just like ours to superficial observation, 

 and these water-lilies were gnawed by insects, which came 

 very near to our China Marks. Of all faunas and floras 

 those of freshwater basins might have been expected to 

 be most narrowly limited in space, because of the great 

 apparent difficulties of transport over land and sea. Yet 

 there is, I believe, no fauna or flora so wide-spread and 

 so constant. Is this due to the long-continued survival 

 of ancient forms in small and disconnected areas, where 

 they are subject only to feeble competition ? Or can it 

 be explained (as Darwin thought) by supposing that fresh- 

 water plants and animals, instead of being at a disadvan- 

 tage, enjoy unusual facilities for dispersal ? 



XIX. HOUSE-FLIES. 



The passage which follows gives all the information 

 respecting house-flies that a well-informed and observant 

 man, who had never occupied himself with insects, was 

 able to furnish. I think it may be taken as representing 

 the average amount of knowledge possessed by intelligent 

 people who are not naturalists. 



" The house-fly is a small insect which buzzes about our 

 rooms in summer. It is often found on the window-pane. 

 Sometimes there are found with it many smaller flies 

 young ones, I suppose. The bluebottle is quite different 

 from the house-fly, much larger and of a blue colour, while 

 the house-fly is black. Some people say that the house- 

 fly stings, but it has never stung me that I can recollect. 

 I do not know where house-flies come from, but bluebottles 

 are bred from maggots, such as anglers use for bait." 



My friend's remarks suggest several comments, and first 

 of all this, that he mixes up under the name of " house- 

 fly " a number of quite different insects. In our houses 



