Pi. 





a n. n 



oes- 



m--%~-4 r^ 



Kf 



mxp. 



<JP- 



FlG. l8. — 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 Heivitfs permission, The University, 



Manchester. ) 



Pt., eversible ' frontal sac ' ; J.c, 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 ; 

 f>h.n., td.n., nerves to suction pump and proboscis ; r./z., f.h., ?-.r., r.J., muscles for 

 retraction (or withdrawal) of proboscis ; r.fu., r.ds., con. I., muscles opening mouth and 

 controlling the flow of fluid along the 'throat'; af.k,, Px.k., muscles controlling the 

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

 F. t sheath of 'suction pump,' with its processes a.c, p.c. ; d.pu., muscles workinj 

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

 t.ep., upper lip; ///., lower lip, also formed by pare of t.hp., d.s. t and j, skeletal 

 structures of the oral lobes, one of which is shown ; ps., channels, and £/. , ' taste pit: 

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

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

 ttz.rp., maxillary palp. 



