IDENTIFICATION OF HOUSE-FLIES n 



the transparent tissue of the wing. We are rather 

 compelled to follow something like this plan (simplified) 

 for the purpose of clearly distinguishing the " lesser 

 house-fly" from the common "house-fly." 



In the accompanying illustrations rather similar 

 patterns of wings are shown ; these are typical of 

 the Muscidce and Antkomyidcz, which, taken together, 

 comprise amongst others all the cattle and human pest- 

 ering "sweat-flies" ; only a few really blood-sucking 

 flies are included amongst the Muscidce. 



In critically comparing these four patterns, the chief 

 feature to be observed is the small rib-like nervure 

 called the " discal " " cross-vein," which is situate in the 

 very middle of the wing, and which connects the lowest 

 of a group of longitudinal nerve-lines or veins in the 

 front (or upper) half of the wing to the uppermost of 

 the other group of longitudinal nerve-lines in the hind (or 

 lower) half of the wing. Three " main " longitudinal 

 lines, technically termed "veins," are theoretically 

 recognised as constituting the upper group and four 

 " main " longitudinal lines the lower group ; but these 

 " veins " (numbered 1, 2, 3, 4, 5, 6 and 7) will be found 

 to be varied in different families and genera, each often 

 with characteristic diverging branches, whilst some 

 veins may be rather inconspicuous or quite absent. 

 We will here devote our attention only to two such 

 " veins," those respectively termed "vein 3 " and " vein 

 4," which are connected in the very middle of the 

 wing, as above mentioned, by the small but always 

 distinct "discal" "cross-vein." The illustrated 

 patterns herewith show wings divided into about twelve 

 compartments or cells, to all of which learned entomo- 



