FARMERS' INSTITUTES. 163: 



Again, in some the transformations are fav more complete or marked tlian in 

 others. Thus we reco2;nize one of the stronojest arauments in favor of the now 

 generally accepted theory of evolution. It is as if all Dipterouf^ insects had 

 started from some one primal form, and through differences in development, 

 there had resulted the wondrously varied forms that to-day so interest the stu- 

 dent of entomology. 



Kemarlcahle for Variety of Habits. 



A very marked peculiarity of this sub-order is the unparalleled variety of 

 their habits. The mosquito family while larvae feed upon tlie noisome particles- 

 in our stagnant pools, and tlius by consuming the germs of malaria become 

 important sanitary agents. The mosquitoes may hardly be so regarded, since our 

 medical men now look with ill favor upon the practice of phlebotomy or bleeding. 

 Some of the Ilea family, together with many flies, feed as larva? upon decay- 

 ing organic matter, the ordure of our stables and outhouses and other tilth, 

 while as mature flies they attack our domestic and otlier animals, and eveni 

 claim tribute from man himself. One species of the flea family, the jigger of 

 Central America, burrows under the toe-nails of the natives, or of their pale- 

 faced visitors, and thus produce distressing sores, which may become very seri- 

 ous. The Dipterous ticks and bee-lice live by sucking blood from the animals- 

 which they infest. Some of the Bipfera are gall-flies. They lay their egg& 

 upon various plants, — the willow is a favorite, — and the larva? which hatch fronii 

 these, by feeding upon the ])lant, excite excessive growth. Thus the galls arise, 

 which form both house and food for the larvns till they issue as fully developed 

 flies. Some of the Diptera are predaceous, that is, they kill and eat other 

 insects; others, which are closely related to the house-fly, are parasitic. These- 

 lay their eggs on other insects, which are fed upon and destroyed by the larva? 

 which hatch from the eggs. BoWi the predaceous and parasitic Diptera are 

 very valuable to the farmer, as they destroy hosts of his insect enemies which 

 otherwise would bring all his efforts to naught. Others still attack our grains 

 and vegetables and do irreparable damage. h\ fact there are no vwrse insects 

 than the wheat midge and Hessian fly, for these insects usually destroy to the 

 tune of millions. Lastly, some of the Diptera, — the whole family (Edridoi, or 

 bot-flies, — exist while larvae within other animals, either in the natural cavities 

 of the body or else in cavities which by their irritation they form, and it is to- 

 these that I ask your special attention. 



(Estriclae Family. 



The bot-flies are stout, hairy insects, and in a general way much resemble- 

 species of our wild bees, though their bodies posteriorly are more pointed, while 

 the females possess a spy-glass like ovipositor. The mouth is very small, while- 

 the mouth organs are nearly abortive. The antenna? are very small and are 

 inserted in small rounded pits. 



The flies take no food ; in fact, their mouths are too weak and rudimentary 

 to permit of it, their only purpose seeming to be to arrange for the continuance 

 of the species. 



The eggs are usually deposited upon some particular part of the animal 

 infested. These eggs soon hatch ; in same cases, indeed, it is said that they 

 hatch even before deposition, such flies being ovoviviporous. The maggots are- 

 whitish, thick, fleshy, footless, and iiave on their bodies rows of spines, by aid 

 of which they move about. The mouth is small, and sometimes surmounted. 



