The Nervous System and the Senses 171 
within a flask ( PorW) which lies in the chitinous body wall. 
These sense organs have protoplasm exposed to the outer 
air, not covered with chitin, while most of the other organs 
which have been supposed to have the olfactory function 
are covered with a chitinous layer. This is especially to be 
noted in the sense organs of the antennae and it is difficult 
to see how odors may be sup¬ 
posed to penetrate such layers. 
The structure of the olfactory 
pores therefore fits them for 
their olfactory function and 
Mclndoo has shown by experi¬ 
mental evidence that this is 
their office. He 1 has also found 
these olfactory organs in spiders 
and in other Hymenoptera. 
Admitting that these olfac¬ 
tory pores are the true organs 
of smell, we are still confronted 
with some difficulty in deciding 
what part responses to odor 
stimuli play in the behavior of 
bees. That bees are attracted 
by odor to honey during a 
dearth of nectar cannot be 
doubted. Similarly it is be¬ 
lieved that the recognition of 
hive-mates, the discovery of 
enemies and the reactions to¬ 
ward the queen are due to re¬ 
sponses to odors. A difficulty encountered in this field of 
investigation is that the human sense of smell is so inefficient 
that it is difficult to comprehend the responses observed, 
1 Mclndoo, N. E., 1911. The lyriform organs and tactile hairs of 
araneads. Proc. acad. nat. sc. Phila., LXIII, pp. 375-418. 
- , 1914. The olfactory sense of Hymenoptera. Ibid., LXVI, pp. 
294-341. 
