PLATE I 



Figure 1. Head of a Muscid fly, seen from the front, with the 

 proboscis removed, pt.s., the ptilinal suture, f., 

 frons. oc.t, the ocellar tubercle (shown enlarged in 

 figure 4). 



Figure 2. The same, seen from behind. 



Figure 3. Diagram showing the segmentation of a primitive 

 insect, after Berlese. The segments are numbered in 

 order. Six are shown in the head, five only being 

 represented in most insects. The last three head 

 segments have appendages, which become a part of 

 the proboscis in the Diptera. The course of the 

 alimentary tract is indicated, s., stomadaeum. ms., 

 mesenteron. p., proctodaeum (page 101). 



Figure 4. The ocellar triangle of Musca, showing the three 

 pigmented ocelli and the ocellar bristles. 



Figure 5. A section through chitin, to show the chitinogenous 

 cells and the laminae, h., a hair, in direct connection 

 with a chitinogenous cell. From Miall and Denny. 



Figure 6. Head of male Tabanus seen from the front. An 

 example of a holoptic fly. Compare Plate III, 

 figure 3, 



