306 



Mr. J. A. Dell on the Structure 



the head are nearer to one another than the openings on 

 the face. The tunnels are not of absolutely uniform 

 diameter, though their variations are nowhere very great. 



The antennary muscles, which are the only important 

 muscles in the head, are attached close to the hinder 

 openings of the chitinous tunnels, which seem to act as 

 struts, and prevent the head from yielding when a strain 



Fig. 12. 



Ventral view of mouth- parts of fly (to left) ; maxilla 

 in side view (to right). 



is put upon it by the contraction of the antennary muscles. 

 Similar structures have been described in Anopheles, 

 where a pair of straight chitinous tunnels perforate the 

 head, and in Chironomus, where a pair of small openings 

 on the face open into a pair of somewhat irregular cham- 

 bers, which in turn open to the exterior by a pair of slit-like 

 apertures on the back of the head.* 



* Miall and Hammond (1900). 



