32 THE EEPOET OP THE No. 36 



it is bent up at an angle before reacliing the margin which it joins close to the 

 termination of the third longitudinal vein ; not only is it smaller, but in form and 

 colouration H. canicularis differs from M. domestica. The dorsal surface of the 

 thorax of the male is greyish black with three indistinct longitudinal stripes, the 

 male's abdomen is slender and tapering compared with that of M. domestica; it is 

 bronze black with three or four pairs of translucent yellow lateral areas. The body of 

 the female is coloured a dark ash-grey and the thoracic stripes are more distinct, 

 the abdomen shorter and more robust. 



Musca domestica forms by far the major portion of the fly population. How- 

 ard's, Hamer's and my own observations shov^ that the percentage is usually DO- 

 GS per cent, of the total fly population. 



Another fly that sometimes occurs in houses, especially country houses in the- 

 fall, and also in the spring in England, and whose habits have frequently led to 

 the popular erroneous idea as to the ability of the house-flies to bite, is the blood- 

 sucking Stomoxys calcitrans, known by various popular names such as Storm-fly, 

 Stable-fly, Fall-fly, all of which names are equally inapplicable to one species. 

 ]t can readily be distinguished from M. domestica by the sharp awl-like piercing 

 proboscis which projects forward horizontally from beneath the head. This type of 

 proboscis enables it to pierce the skin of animals and thereby suck the blood of the 

 same. It is interesting to note in passing that S. calcitrans is allied to those 

 tropical blood-sucking Diptera of the different species of Glossinas, which are re- 

 sponsible for the deadly disease of sleeping sickness and Nagana. They carry the 

 Trypanosomes, the organisms which cause the diseases, and by their blood-sucking 

 habits infect man and other animals. The former disease has reduced in a few 

 years the population of Uganda by two-thirds and Nagana has rendered central and 

 sub-tropical Africa practically impassable to horses. 



Musca domestica possesses a proboscis that is quite incapable of piercing the 

 skin. It is only of use in absorbing fluids and this process of absorption is one of 

 great interest. The proboscis is extended in the following manner. The vacant 

 spaces in the head are filled with capacious air-sacs and blood; by the inflation of 

 these air-sacs of the head the blood is driven into the cavity of the proboscis which 

 is thereby extended and the two lobes which form the oral disc are distended by 

 means of the blood. These oral lobes are traversed on their inner sides by a very 

 large number of channels which are kept open by minute rings open at one side — 

 and owing to their tracheal appearance are called pseudotracheae. The oral sur- 

 face is applied to the fluid-moistened surface and by capillary action and the pul- 

 sating movement of the oral lobes the fluid runs along the pseudotracheae into the 

 oval pit and thence into the pumping pharynx — the pumping action of the latter 

 keeping up the constant inward flow of the solution. In the case of such solid food 

 as sugar this is first rendered soluble by the secretion of the lingual or salivary 

 glands. The surface of the oral lobes is kept ir a moist condition by the secretion 

 of a small pair of labial glands. 



If the abdomen of a mature female fly is opened it will be found that it is 

 almost filled by the enormously distended ovaries; the alimentary tract occupying 

 a small trough-like cavity between them and the dorsal region. In the posterior 

 region of the abdomen the ovipositor will be seen usually in a retracted telescopic 

 condition. When exserted the ovipositor is about equal in length to the abdomen 

 and the female fly is thus enabled to deposit her eggs deep down out of the light 

 in the crevices of whatever substance, decaying vegetable or excremental, it may 

 have chosen as a nidus for the larvae. About 120 to 150 eggs become mature at 

 the same time and these are deposited in clumps, as many as sixty or seventy may 



