BITING APPARATUS : STOMOXYDINAE 53 



which there are developed plates of thin chitin, the extent of the chiti- 

 nization and the distribution of the plates differing in the different 

 genera. At the distal margin, where the two walls are continuous, 

 there is a fringe of more or less conspicuous macrochaetae. The inner 

 wall is of about equal extent, and there is in no case a definite pseudo- 

 tracheal membrane, though in Haematobia and Bdellolarynx there 

 are well marked traces of it ; it is composed of a strong but homoge- 

 nous sheet of tissue, attached internally to the discal sclerite, and 

 continuous with the external wall at the distal margin of the 

 proboscis. The two inner walls of the labella are in contact with one 

 another in the position of rest, the fissure between them being continuous 

 with the groove on the anterior surface of the labium, and extending 

 for some distance on the posterior surface. 



The teeth and the interdental armature (Plate XII, fig. 5) are situated 

 at the proximal limit of the inner surface. The teeth are oblong struct- 

 ures of considerable size, three to four times as long as broad, pointed at 

 the distal end, and with in most cases a secondary cutting point, 

 produced by a deep indentation of the margin of one side. They are 

 from four to six in number, and are firmly united to one another by their 

 bases, the whole set uniting together proximally to form a thick ridge of 

 chitin, the proximal outline of which is curved to correspond with the 

 distal margin of the discal sclerite. The teeth are attached to the 

 margin of the sclerite by a strong band of fibrous tissue, which is con- 

 spicuous in sections on account of its peculiar staining properties. 

 The interdental armature consists of one or more rows of leaf-like 

 blades, arising from slender stalks, which are attached to the membrane 

 of the inner wall between the teeth. The arrangement of the armature 

 differs in the different genera, but all conform to the same general type. 

 In Stomoxys there is a pair of sets of blades, each consisting of four to 

 six, between each pair of teeth, the two sets of each pair diverging from 

 one another as in Philaematomyia. In Lyperosla there are two rows 

 of blades, a proximal and a distal, of which the latter are the larger. 

 The blades are extremely thin, and have a finely granular surface. 



In addition to the blades, there are on the inner wall certain special 

 structures which probably have a sensory function. The most con- 

 spicuous of these are the ' rod-like hairs ' first described by Stephens 

 and Newstead in Stomoxys. These are short but stout and heavily 

 pigmented, and are situated opposite the apices of the teeth, usually two 

 to each largeltooth. They appear to be grooved on one side, though 

 this may be due to the presence of a central channel. 



