NO. 10 



TROPISMS OF LEPIDOPTERA — McINDOO 



43 



or " Stift " (Sr) is only slightly different from that pictured in the 

 Lepidoptera examined by Eggers. The writer also saw external marks 

 of these organs in many other Lepidoptera. 



Eggers informs us that their structure is not correlated with that 

 of the tympanic organs. Formerly they were assumed to be auditory 

 in function, but more recently they have been called muscular receptors 



.S^cc'^y Sefm^ff 



Fig. 14. — Johnston organs of codling moth, X 500. A, Semidiagrammatic 

 drawing, showing one olfactory pore (f) and Johnston organ whose distal end 

 is attached to articular membrane (Am). This membrane consists of three con- 

 centric bands of chitin; two tiiin and flexible ones (represented by lines) and a 

 thick, rigid, and much wider one (soHd black) between them. Therefore, it 

 sHghtly resembles a drum head and apparently may be vibrated by jars or by 

 movements of the flagellum. B, Detailed structure of a single chordotonal ele- 

 ment drawn from two sections. All parts, except the nuclei of the enveloping 

 cell (Ec) and cap cell (Cc), were distinctly seen. Other authors have seen these 

 nuclei in other Lepidoptera. The terminal fiber (Tf) of each element is 

 fastened at the bottom of a pit (p) which usually lies in the rigid and thick 

 band of the articular membrane. The other abbreviations are the same as those 

 in figure 13, D. 



or statical-dynamic organs to register the movements of the antennae. 

 Eggers believes that they probably perceive the movements of the 

 articular membrane to which they were attached. These movements 

 are caused by the antennae being used as tactile organs, or by the wind 

 vibrating these appendages. In the males of Culicidae and Chirono- 

 midae, however, they may be special auditory organs. The present 

 writer (52) in 1922 studied the Johnston organs in the honey-bee in 



