THE OLFACTORY SENSE OF ORTHOPTERA 427 



long, sometimes almost slit-shaped, but the eye-shaped type is 

 the most common. Some of the pore borders are radially stri- 

 ated; this is the first time for striated borders to be found in 

 adult insects. The internal anatomy of these pores is similar 

 to that of those in other orders, but there is one marked differ- 

 ence: in each of these there is an indentation or cavity which 

 encircles the bottom of the chitinous cone. 



Experiments were performed on grasshoppers and crickets to 

 determine whether or not their antennae serve as olfactory re- 

 ceptors. The unmutilated insects were first tested to ascertain 

 their reaction times to the oils of peppermint, thyme, winter- 

 green, and lemon and to the dried leaves of pennyroyal and to 

 bran mash (their food in captivity). Each antenna was then 

 severed through the third segment, and twenty-four hours later 

 these mutilated insects were again tested with the above sources 

 of odors. The average reaction time of the unmutilated grass- 

 hoppers is 8.4 seconds, and of them after being mutilated, 9 

 seconds; of the unmutilated crickets 8.8 seconds, and of the 

 same crickets after being mutilated, 10.2 seconds. In other re- 

 spects the mutilated individuals seemed normal and lived as 

 long as others not mutilated. Since the antennae were cut off 

 just distal to the olfactory pores on the first and second segments, 

 it appears that the remainder of the antennal segments does not 

 bear the olfactory organs as other investigators claim. 



Compared with the so-called olfactory organs on the antennae 

 of Orthoptera, the olfactory pores are better adapted anatomi- 

 cally to receive olfactory stimuli because the peripheral ends 

 of their sense fibers come in direct contact with the external air, 

 while those in the so-called olfactory organs on the antennae are 

 covered with chitin. 



LITERATURE CITED 



McIndoo, N. E. 1918 The olfactory organs of Diptera. Jour. Comp. Neur. 



vol. 29, no. 5, pp. 457-484, 55 figs. 



1919 The olfactory sense of lepidopterous larvae. Ann. Ent. Soc. 



Amer., vol. 12, no. 2, pp. 65-84, 53 figs. 

 Rohler, Ernst 1905 Beitrage zur Kenntnis der Sinnesorgane der Insecten. 



Zool. Jahrb. Anat., Bd. 22, s. 225-288, 1 fig. and 2 pis. 



