Pt 



ann 



FIG. 1 8. Tongue of House-fly. Left side of head removed to show 

 internal structure. The empty space is filled with air-sacs not shown 

 in the figure. (With C. Gordon Hewitt's permission, The University, 

 Manchester. ) 



Pt., eversible ' frontal sac' ; /.<:., fat -cells ; C.G., s.o., brain ; P.O., portion of brain 

 supplying nerves to compound eyes ; an.n., oc.n., nerves to antennae and simple eyes ; 

 ph.n., Ib.n., nerves to suction pump and proboscis; r.h., f.h., r.r., r.J., muscles for 

 retraction (or withdrawal) of proboscis ; r./u., r.ds., con.l., muscles opening mouth and 

 controlling the flow of fluid along the 'throat'; af.h., Ex.h., muscles controlling the 

 bending and unbending of the proboscis ; a/., rod concerned in the same process ; 

 P., sheath of 'suction pump,' with its processes a.c., p.c. ; d.pn., muscles working 

 'suction pump'; k, sheath keeping open beginning of 'throat'; oes., 'throat'; 

 l.cp., upper lip ; th., lower lip, also formed by pare of /.A/., d.s., and f, skeletal 

 structures of the oral lobes, one of which is shown ; ps., channels, and^., ' taste pits,' 

 of the oral lobe ; Ip.sr., one of the two saliva glands of the oral lobes ; sal.a., duct of 

 large saliva gland, with ts valve, s.v., and muscles, s.m. t controlling the same ; 

 inxp., maxillary palp. 



