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 l 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. 



FIG. 89. Diagram of ventral 

 view of worker, showing loca- 

 tion of groups of olfactory 

 pores. 



