AUDITORY SENSE OF HONEY-BEE 183 
chitin (represented by broken lines). Consequently, instead of 
this articulation being weak, it is as strong as any other, and when 
broken by a steady pull, the articular membrane remains fastened 
to the third segment, showing that the knobs, although having 
considerable play in their sockets, nevertheless lend considerable 
strength to the articulation. 
. Longitudinal sections through the second antennal segment 
show the following: A large group of sense cells (fig. 12, SC) 
lies on either side of the section; two large antennal nerves (JN), 
called internal and external olfactory nerves by Janet (’11), run 
through the center of the segment and at various places unite 
with the groups of sense cells, as shown in figure 12, and a large 
trachea (7'r) runs near the nerves and sends out branches here 
and there. 
A thorough study of these sections under an oil-immersion 
lens shows the following: The elliptical sense cells (fig. 7, SC) 
have conspicuous nuclei (Nuc), short nerve fibers (fig. 12, NF) 
‘which run into the nerves, and long and comparatively large 
sense fibers (SF) which run in bunches toward the articular mem- 
brane. About half-way between the sense cell and articular 
membrane may be seen small slender nuclei (fig. 7, Nuc), some of 
which seem to lie on the surface of the sense fibers, but it is more 
likely that these are hypodermal nuclei, although the nuclei in 
the hypodermis (fig. 12, Hyp) usually are round and much larger. 
When the bunches of sense fibers reach the flexible strands of 
chitin (Ch) the individual fibers separate, run between these 
strands, then unite singly with the inner ends of the knobs (K). 
Figure 12 is a diagram showing most of the second segment in 
longitudinal section and in perspective, and a small portion of 
the third segment in both cross and longitudinal section and in 
perspective. It is noted that the thin articular membrane 
(ArtM), bearing the chitinous knobs (K), is unprotected and 
fully exposed to the outside air. Two of the knobs are cut length- 
wise, showing the cone-shaped cavity which opens to the exterior. 
The other knobs are heavily shaded, showing that they are buried 
in the articular membrane. 
