NO. lO TROPISMS OF LEPIDOPTERA McINDOO 45 



body hairs act as sound receptors for three reasons : ( i ) Singeing 

 the hairs greatly reduced or abolished the responses ; (2) hairs bearing 

 water droplets or flour did not respond; and (3) during the molting 

 periods when the hairs were disconnected with their nerves there was 

 little or no response. 



Abbott (2) observed that normal Datana larvae gave definite re- 

 sponses to air currents and sudden jars, but to only two notes — C" 

 (512 vibrations) and F sharp (728 vibrations) — by elevating the 

 anterior and posterior parts of the body. These notes were made by 

 using a closed pipe with a movable plunger, a piano, and a mandolin. 

 He assured us that he believed the normal larvae actually responded to 

 the foregoing musical instruments for four reasons : ( i ) They were 

 protected from air currents when tested; (2) they were several feet 

 from the instruments; (3) vil)rations from the substratum were 

 eliminated ; and (4) no responses were observed when the body hairs 

 were covered with water or shellac, or when the body surface was 

 anaesthetized with a 2 per cent solution of procain. Since these 

 caterpillars responded to only two notes, which are not experienced in 

 nature. Abbott believed that these responses were not adaptive, but 

 perhaps secondary, resulting from an " adaptation of certain organs 

 to more significant stimuli." 



IV. THIGMORECEPTORS 



I. TACTILE ORGANS 



It seems that no one has made a thorough stud)- of the tactile organs 

 of Lepidoptera, but those in certain beetles have been carefully studied. 

 The writer (53) found tactile hairs on the cotton boU weevil as fol- 

 lows : Sense hairs (Sensilla trichodea). on the head capsule, antennae, 

 mouth parts, thorax, legs, wings, and abdomen ; sense bristles 

 (S. chaetica), on nearly the same parts; and sense pegs (S. basi- 

 conica), on the head capsule, mouth parts, and genitalia. Besides these 

 three types Lepidoptera have a fourth, the sense scales (S. squami- 

 formia) ; however, it seems that only the small, narrow scales are 

 innervated, while the large, broad ones (fig. 3, B, Sh) have no nerve 

 connection. If the end pegs (S. styloconica) are really innervated, 

 we should add a fifth type of tactile organs. 



Sense scales on the wings of Lepidoptera have been described b>- 

 Guenther (27), Freiling (23), Vogel (88), and Priiflfer {yy). Vogel 

 states that innervated scales are found on the wings of all Lepidoptera, 

 occurring on both sides, mostly on the veins and particularly on the 

 marginal ones, but they may be found also on the basal parts of the 



