394 W. H. HARRIS ON THE DENTITION OF THE DIPTERA. 



their free ends become fused together, terminating in the form 



of a V. 



Tlie organs in the second row in the illustration number eight, 

 in the third row they are reduced to four ; thus each lobe is 

 furnished with twenty-three organs. The complete set possessed 

 by the fly which furnished this object consisted of forty-six 

 bidentate teeth. 



Figure 2, Polietes lardaria^ furnishes a more robust develop- 

 ment. The stout, primary teeth have lost their V-shaped 

 terminations, indicating the service they have rendered the 

 creature. This group was furnished by a fly taken in late autumn ; 

 recently emerged specimens possess the fully-formed teeth. 



Figures 3 and 4 are examples of the compound type, com- 

 prising four rows. Many of the teeth in the subsidiary rows 

 are beset with very minute projections situate between the two 

 lateral denticles. In Figure 3, Mydaea H7'ba7ia, the primary 

 teeth are tridentate ; but in Figure 4, Spilogaster sp. ?, they are 

 bidentate. 



Figure 5, Jlorellia hortorum. This fly furnishes a compound 

 mouth consisting of two rows. The teeth of the primary row at 

 their free ends are very narrow and tridentate. The basal 

 portions are conspicuously enlarged, and the lateral margins are 

 deeply incurved. The teeth of the subsidiary row are few in 

 number and inconspicuous. 



The illustration is an excellent example of a perfect dissection, 

 showing the entire group of teeth furnished by this fly. 



Figure 6, Musca domestica. The number of teeth possessed by 

 this species is subject to considerable variation ; the normal 

 number is five, but individuals may be found having as few as 

 three, or as many as seven. But, whatever be their number, 

 the teeth are always characterised by saw-like edges. 



Figure 7, Hydrotaea irritans This fly is a common pest in 

 the country, and needs no seeking. Each lobe has seven teeth ; 

 they are long, stoutly and firmly constructed, and considerably 

 curved (see diagram p. 396, N^o. 1 ). Their free ends are tridentate ; 

 the two lateral points, however, are very minute, the central one 

 is prominent. All are exceedingly sharp, rigid, and liable to 

 fracture. They appear to be absolutely solid throughout, and in 

 this respect difler from those of all other known species. 



Figures 8, 9, and 10 represent the dental organs of species of 



