5 I 2 DIPTERA CHAP. 



while in the third instar there is a greater diversity in the 

 condition of the lireathing apertures. 



The various forms of Muscidae show considerable distinctions 

 in the details of their natural history, and tliese in certain species 

 vary according to the locality. This subject has been chiefly 

 studied by Portschinsky, a Russian naturalist, and a very interest- 

 ing summary of his results has been given by Osten Sacken,^ 

 to wdiich the student interested in the subject will do well 

 to refer, 



A few years ago a great deal of damage was caused in the 

 Netherlands by Lucilia sericata, a Green-bottle-fly, extremely 

 similar to our common L. caesar, which deposited its eggs in 

 great quantities on sheep amongst their wool. This epidemic 

 wr.s attributed to the importation of sheep from England ; l)ut, 

 according to Karsch, there is reason to suppose that the fly was 

 really introduced from Southern Europe or Asia Minor." 



The larvae of species of the genus Lucilia sometimes attack 

 man and animals in South America, but fortunately not in this 

 country. The larva of Lucilia (Compsowi/ia) macellaria is called 

 the screw-worm, and is the best known of the forms that infest 

 man, the larvae living in the nasal fossae and frontal sinuses, 

 and causing great suffering. The fly is common in North 

 America, but is said never to attack man farther north than 

 in Kansas. A little fly {Stomoxys calci trans), very like the 

 common liouse-fly though rather more distinctly spotted with 

 grey and black, and with a fine, hard, exserted proljoscis, 

 frequently enters our houses and inflicts a bite or prick on us. 

 It is commonly mistaken for an ill-natured house-fly that has 

 taken to luting. It is frequently a source of irritation to cattle. 

 A closely allied ?ij,Haematohia scrrata, is very injurious to cattle 

 in North America, but the same species causes no serious annoy- 

 ance in England. We may mention that the various attacks of 

 Dipterous larvae on man have received the general name 

 " myiasis." 



The Tse-tse fly (Glossina morsitans), another ally of Stomorya, 

 is not very dissimilar in size and shape to the blow -fly." 



^ Berlin, ent. Zeitscltr. xxxi. 18S7, p. 17. 



"^ Biol. Centralhl. vii. 1887, p. 521. 



^ For an account of the habits of this flj', see Kirk, J. Linn. Soc. viii. ISGDj pp. 

 149-156 ; and for a bibliographic list, Wulp, 2'ydscJir. Ent. xxvii. 1884, p. xc-i. and 

 pp. 143-140. 



