PLATE XLI. 



Fig. 26. Composite view of head of a female S. viffafimi. (.-^U pho- 

 toKi'aph.s of the fly except the one of the pupae on the stone are greatly 

 enlarged views of the specimens. 



Fig. 27. Hypopharynx and maxilla of S. vittatum. 



Fig. 28. Composite view of mouth parts, showing all the parts intact 

 except the labium, which is entirely removed. The hypopharynx is turned 

 under and upward in the photojrraph. 



Fig. 29. Male S. vittatum mouth parts. Note the tip of the labrum 

 has the two teeth coalesced. Note the difference in the size of the facets 

 of the eye. 



Fig. 30. Labium of female. All mouth parts figured are of the female 

 except figure 28. G, glossa; PG, paraglossa; .1-/, mentum. 



Fig. .31. Ventral view of head of SimuUum larva, showing the fan- 

 like organs spread out. 



Fig. 32. MD, mandible of Siinnliinii larva; AT. antennas of Siiniilivm 

 larva. (According to Johannsen.) 



Fig. 33. Maxilla of Siinnlinin larva, showing the palpus at P. 



Fig. 34. Labium of Simiilhim larva. 



Fig. 3.5. LA, labrum of Siimilimn larva; HI', hypopharynx of Siiiiii- 

 liiini larva; A, anal aperture of Simulium larva. The U-shaped pait lies 

 dorso-cephalad to the rest of it in the larva. Note the rasp-like forma- 

 tion of this organ. The larva uses it to hold onto the stones in the ripples. 



