NO. lO TROPISMS OF LEPIDOPTERA McINDOO 2/ 



quickly through chitinous structures, pit pegs (fig. 3, C, Sco) would 

 be excellent olfactory organs. Styles, usually terminating in end pegs, 

 may be found on all segments except the first and second. A style 

 (fig. 3, B, S) is nothing more than a prolongation of the distal outer 

 edge of the segment and it is supposed to be innervated, but in codling- 

 moth antennae it (fig. 3, D) has no nerve and consequently cannot 

 be a sense organ. The writer has failed to find a drawing by any 

 author showing a nerve connected with this structure. 



The antennae of 21 other species (table 2) examined by the writer 

 varied much in respect to barbs, from typical filiform antennae to 

 fully feathered ones. The sense organs, as a rule, were widely dis- 

 tributed on both the shaft and barbs. In Argynnis cybele the pit pegs 

 lie only on the club part of the antenna. Some of them are large and 

 irregular in shape, and perhaps a pit bears more than one peg. In 

 II of the specimens pit pegs were totally absent and in 12 no end 

 pegs were observed on the comparatively few styles, and even styles 

 were absent in one moth (No. 23) and in all the butterflies (Nos. 31 

 to 34) examined. 



From the preceding it is evident that pore plates (S. placodea), 

 common to three orders of insects (aphids, beetles, and bees and 

 wasps), are totally absent in Lepidoptera, while the pegs (S. basi- 

 conica) are practically wanting. These two types are the ones gen- 

 erally considered as olfactory receptors in most insects. It is said that 

 the end pegs and pit pegs of Lepidoptera replace the pegs and pore 

 plates of other orders, but there is no proof whatever for this assump- 

 tion, and furthermore it is doubtful whether the end pegs are ever 

 innervated. 



Granting that the pit pegs and end pegs are the only olfactory 

 organs of Lepidoptera and drawing conclusions from the observations 

 of Schenk and the present writer, eight individuals (table 2, nos. i to 

 4, 17, 18, 23, 24) of the 34 specimens examined cannot smell at all, 

 while four other individuals (nos. 10, 19, 20, 25) have comparatively 

 few end pegs as olfactory receptors. 



(b) Olfactory pores. — At the suggestion of his reviewers the 

 writer (48) in 1914 called the sense organs herein discussed " olfactory 

 pores." Guenther {2y) in 1901 seems to have been the first to describe 

 the internal structure of these organs in Lepidoptera. He called those 

 in the wings " Sinneskuppeln " and found their structure to be similar 

 to that described by the present writer, although he did not see the 

 pore aperture passing to the exterior. Vogel (88) made a more ex- 

 tended studv of them in the wings of. many Lepidoptera. He con- 



