INTRODUCTION 7 



becomes so very much broader above that the light dustiness 

 of the sides is entirelv obliterated. The abdomen gi-aduallv 

 becoming darker. The shimmering areas on the separate seg- 

 ments generally bro^\^^ish. All the other parts are the same as 

 in the male." 



The mature insects measure from 6 t(j 7 mm. in length and 

 fi'om 13 to 15 mm. across the wings. Frequently dwarfed speci- 

 mens may be found, normal in every respect but size. This is due, 

 as my breeding experiments demonstrated, to advei-se conditions 

 during the larval stage ; starvati<ni especially tends to produce 

 undersized individuals. 



Distribution of Muse a domestic a. 



Musca domestica is undoubtedly the most Avidely distributed 

 insect to be found ; the animal most commonly associated with 

 man, whom it appears to have followed over the entire globe. 

 It extends from the sub-polar regions, where Linnaeus refers to 

 its occuiTence in Lapland and Finmark as " rara avis in Lapponia, 

 at in Finmarchia Nonvegiae integras domos fere replet," to the 

 tropics, where it occurs in enormous numbers. Referring to its 

 abundance in a house near Para in equatorial Brazil, Austen 

 (1904) says : "At the mid-day meal they swarmed on the table 

 in almost inconceivable numbers," and other travellers in dif- 

 ferent tropical countries have related similar experiences to me, 

 how they swarm round each piece of food as it is carried to 

 the mouth. 



In the civilised and populated regions of the world it occurs 

 commonly, and the British Museum (Natural Histor}^) collection 

 and my own contain specimens from the follo-wong localities 

 (certain of the localities have, in addition, been obtained from 

 lists of insect faunas) : 



Asia. Aden; North- We.st Provinces (India); Calcutta; 

 Madras ; Bombay (it probably occurs over the whole of India) ; 

 Ceylon ; Central China ; Hong-Kong ; Shanghai ; Straits Settle- 

 ments; Japan. 



Africa. Port Said ; Suez, Eg}-pt ; Somaliland ; Nyassaland ; 

 Uganda ; British E. Africa : Rhodesia ; Transvaal ; Natal ; Cape 



