FACE AND ANTENNAE 11 



to be composed of two scleritos for whicli 'I'dwiisenfl, in a letter 

 to me, suggests the term "frontalia." In the male the eyes are 

 only narrowly separated by the frontal stripe. In the female the 

 frontal stripe Avidens out on the vertex. This character provides 

 a ready means of distinguishing the male from the female, as 

 the result of it is that in the male the eyes are close together 

 on the dorsal side, being separated by about one-fifth of the 

 width of the head, whereas in the female the space between 

 the eyes is about one-thirfl the width of the head. The edges 

 of the genae bordering on the frons bear each a row of stout 

 setae — the fi'onto-orbital bristles. 



The antennae are situated below the lower edge of the frons. 

 Each antenna consists of three joints and the arista. The two 

 proximal joints are short and compose the " scape " and arise from 

 a strip representing the antennal segment, situated between the 

 frons and the prefrons. The third joint, the flagellum, is longer, 

 and hangs vertically in front of the clypeus. It is covered with 

 sensory setae, and contains two pits of sensory function (olfactory, 

 I believe). From the upper side the plumose arista arises. This 

 probably represents the terminal three joints of the antenna. The 

 lower edge of the frons represents the anterior margin of the epi- 

 cranium. It is of interest here to note that, whereas the arista 

 of M. domestica is plumose, that is, it bears fine bristles on the 

 upper and lower sides, the arista of the stable-fly, Stomoxys 

 calcitrans, bears bristles on the upper side only, and the arista of 

 the lesser house-fly, Fannia canicularis, is apparently devoid of 

 bristles, in reality it is minutely pilose. 



The rest of the fticial region is composed of the clypeus or, as 

 it is usually called, the face, a convenient term, but one which 

 hides its true morphology. The face is depressed, and is C(n'ered 

 by the flagella of the antennae. Between the upper and lateral 

 edges of the face and the lower edge of the epicranium a crescentic 

 opening, the lunule, marks the invagination of the ptilinum. The 

 epistomium is a narrow strip below the face bounding the anterior 

 edge of the proboscis aperture. 



