NOCTUID METATHORAX — TREAT 375 



reinforce this conclusion. There is no suggestion of a "tensor tym- 

 pani" effect nor of a device such as that postulated by Hinton (1955) 

 for the reduction of acoustic sensitivity during some part of the wing- 

 beat cycle. The fact (Roeder and Treat, 1957) that the tympanic 

 membrane can be widely perforated without materially affecting the 

 acoustic response as recorded from the tympanic nerve, suggests that 

 a mechanism for reducing the tension in that membrane would have 

 but little physiological effect upon the sense of hearing. Yet it cannot 

 be stated categorically that no such mechanism exists. The regular 

 pattern of impulses recorded from the Biigel cell, and the modification 

 of this pattern by the stretching of the Biigel sheath must tempt specu- 

 lation in such directions even in the absence of confirmatory evidence. 

 No one can give close attention to the anatomy of the noctuid meta- 

 thorax without realizing the baffling architectural subtlety of the tym- 

 panic organ. It would be rash indeed to attempt conclusions as to func- 

 tion from the morphological consideration of so intricate a structure. 



ABBREVIATIONS USED ON FIGURES 



Segmental structures are those of the metathorax except where otherwise 

 indicated. A roman numeral preceding an abbreviated name refers to a thoracic 

 segment. An arabic number i preceding an abbreviated name refers to the first 

 abdominal segment except for the axillary sclerites of the metathoracic wing 

 which are designed as lAx, 2Ax, and 3Ax respectively. Names of muscles 

 are abbreviated in lower-case letters, those of other structures, with initial capi- 

 tals. Terminology follows mainly that of Niiesch (1953 and 1957). 



AbF, abdominal furca. BF, base of furca. 



AF, anterior furcal arm. Bst, basisternum. 



Al, alula. 



ANP, anterior notal process. CA2-3, connective from abdominal 



ganglion 2 to 3. 

 Cj, conjunctiva. 



Ao, aorta. 



ATP, anterior tendon plate. 



Ax, axillary sclerite (see i, 2, 3Ax). 



Ai + 2, abdominal ganglia i and 2. ^^^' countertympamc cavity. 



CTM, countertympanic membrane. 

 B, Biigel. CTMO, orifice resulting from removal 



Ba, basalare. of countertympanic membrane. 



p. 303. The two structures referred to by Eggers are the scutal phragma 

 (Spannleiste) and the anterior tendon plate (Muskelleiste). To these might 

 be added the dorsomedial sclerotization of the tympanic air sac, to which the 

 fibers of muscle dh^ are attached. The ventral margin of this sclerotization 

 appears in plate 2 as an upcurved line (unlabeled) from near the base of the 

 anterior tendon plate and passing between the labels B and Ep. The structure, 

 which has never been adequately described, seems to be a phragmatal ingrowth 

 from the posterior and medial borders of the countertympanic frame, and 

 would thus be postnotal in origin. 



