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angle in the Ischnocera ; and posteriorly where the wing joins the body 
in the Amblyceea. The Akidoproctidae and some species of Tricho- 
decles have these stigmata lateral. 
Fig. 10. Abdominal spiracle of Telrophthalmus titmi. 
Figs. 11-14. Protlioracic stigmata of: (11) Heteroproctus hilli; (12) Apttricolu gadowi; 
(13) TricJiodectes setosus; (14) llelerodoxus longitarsm (11, 13, and 14 in optical 
section). 
The vestibule, which lies below the external aperture, is very variable 
in shape and sculpture. The commonest form has the shape of a 
somewhat flattened sphere, sunk below the surface, with which it is 
