THE OLFACTORY ORGANS OF DIPTERA 461 
No. 12, 9 pores, and no. 13, 18 pores. The scattered pores vary 
considerably in number and position and they are located about 
as follows: 1 at a on the base of the humeral vein; 2 always 
present at b on the distal end of the first radial vein; 1 at c on the 
radiomedial vein; 1 at d on the proximal end of the first radial 
vein; and 1 at e on the fourth radial vein. 
Fig. 1 Portions of legs of house fly (Musca domestica co”), showing location of 
groups nos. 1 to 7 of olfactory pores. The drawings at the right represent the 
inner surface and those at the left the outer surface. AntM and PostM stand for 
anterior and posterior margins. X 20. 
c. Pores on halieres. Five groups and 1 isolated pore lie on the. 
base of each halter (fig. 3); nos. 14 to 16 and the isolated pore 
at f being found on the dorsal surface and nos. 17 and 18 on the 
ventral surface. The pores lie on plates whose outlines are simi- 
lar in shape to the contours of the groups of pores themselves; 
