16 



THE EXTERNAL STRUCTURE OF jMUSCA DOMESTICA 



of pseudo-tracheae traversing each oral lobe is thirty-six, and 

 they are gi'ouped in three sets. One anterior set of twelve 

 pseudo-tracheae run into a single large pseudo-tracheal channel 

 running along the anterior inner margin of the oral lobe, and 

 a posterior set of twenty or twenty-one all run into a common 



t S-- 



Fig. 4. Oral aspect of a pseudo-trachea 

 showing interbifid spaces (i.*.) be- 

 tween bifid ends of the pseudo- 

 tracheal lings. 



Fig. 5. 



Chitinous pseudo-tracheal 

 rings. 



channel running along the posterior inner margin of the lobe; 

 between these two sets a median set of three or four pseudo- 

 tracheae run direct into the oral aperture. 



Graham-Smith (I.e.) has made comparative measurements of 

 the pseudo-tracheae of several species of non-biting flies and 

 of the interbifid .spaces, as he terms the area enclosed between 

 the bifid extremities of the chitinous rings of the pseudo- 

 The average measurements of the various parts are 



tracheae, 

 as follows 



Pseudo-tracheae 



Interbifid spaces 



Diameter 



at 



proximal 



end 



Diameter Diameter near I Diameter near 

 at distal the proximal the distal ends 



end 



ends of the 

 pseudo- 

 tracheae 



Calliphora erythrocepkala 

 Sarcophaga carnaria 

 Lucilia caesar 

 Fannia canicularis 

 Ophyra anthrax 

 Musca domestica 



of the pseudo- 

 tracheae 



•004 iiuu. 



•004 



•004 



•004 



•004 



•003 



The comparatively small size of the interbifid spaces of the 

 house-fly should be noted, as this has some bearing on the 

 feeding habits of the fly. 



