OLFACTORY SENSE OF THE HONEY BEE 323 



it invariably stains less deeply than the surrounding chitin, 

 but with iron hematoxylin there is scarcely any difference in 

 coloration. 



Since the pore apertures are so small only occasionally does 

 the microtome knife pass through the lowest part of the aperture. 

 On account of this it is quite difficult to find a sense fiber that 

 runs into the aperture. Nevertheless, when many sections are 

 critically studied, it is possible to see several such connections 

 (fig. 16, A, I-K). Sometimes the slit is shallow (fig. 16, A) 

 and at other times it is deep (fig. 16, C). 



As a rule the sense cells are conspicuous. In most cases their 

 sense fibers are broken so that it is generally difficult to trace a 

 sense fiber from the sense cell into the pore, although in these 

 sections almost every pore contains at least a small portion of 

 the sense fiber {SF, fig. 16, C, D, H-J). As compared with 

 the hypodermal cells (figs. 17 and 19) the sense cells are large 

 and in most cases lie parallel or oblique to the inner side of the 

 hypodermis. Since most of them lie rather distant from the 

 pores, their sense fibers (fig. 19, SF) are long. Their nerve 

 fibers (fig. 19, NF) also are long. The size of these cells is not 

 necessarily determined by the size of the pores, because in the 

 legs the pores (fig. 16, A and D) are larger than those (fig. 16, 

 I and J) in the wings where the largest sense cells (fig. 16, E-G) 

 are found. 



Many sections, each 6 microns thick, are required to contain 

 all the pores found in group 1 on the front wing. These sections 

 (fig. 19) show that groups 1 and 2 do not lie in the same plane 

 as they appear to lie when observed externally. On the con- 

 trary, they lie in two different planes that are almost perpendicu- 

 lar to each other. In other words, the subcosta (fig. 3, SC) near 

 its distal end bends at righ angles and the radius (fig. 19, R) 

 is connected with the subcosta only on the dorsal side. The 

 great size of group 1 is also shown by the fact that most of its 

 sense cells (fig. 19, SC) are cut transversely while only a few are 

 seen in a longitudinal view. Five sections, each 10 microns 

 thick, include all the sense cells belonging to group 6 on the femur 

 of the third leg. Thus this group is about 50 microns wide. 



