472 N. E. McINDOO 
arises between each two rows of pores. These rows of hairs are 
only prolongations of the chitin and therefore should be called 
pseudohairs; their only function is probably to protect the rows 
of pores. The apertures (PorAp) of the pores are invariably 
long, narrow slits, while sculptured markings replace the pore 
walls and pore borders in the Hicks’ type. The two halves 
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Figs.4to15 External view of olfactory pores in Musca domestica o’, showing 
variation in size. Fig. 4, groups nos. 1 and 2 (fig. 1); fig. 5, group no. 3; fig. 6, 
group no. 4; fig. 7, group no. 5; fig. 8, group no. 6; fig. 9, group no. 8 (fig. 2); fig. 
10, group no. 9; fig. 11, 10 of 12 pores in group no. 10; fig. 12, 9 of 10 pores in group 
no. 11; fig. 13, group no. 12; fig. 14, 6 of 18 pores in group no. 13; fig. 15, scattered 
pores at b. XX 500. 
(PorR), surrounding the aperture, are similar in position to the 
pore wall, but do not correspond to it; this structure may be 
called the pore ridge. The portion, marked PorL, may be called 
the pore link, because it unites the pore ridges; in position it is 
similar to the pore border, but it is quite different in structure. 
The structure of the basal type of pores is similar to that of the 
Hicks’ type, excepting pore borders are not present and a row of 
