38 Prof. J. C. Schiodte on the Tunnelling Coleopterous 



ia others it is entirelj^ smootli all over in both sexes; and this 

 is really the appearance presented when the parts are observed 

 through an ordinary pocket magnifier. But whilst, on the one 

 hand, it seems impossible that the friction of the two ridges 

 against one another could produce a sound in those species 

 where they are described as entirely smooth (supposing always 

 the description to be correct), a careful examination shows, on 

 the other hand, that the lateral part of the ridge on the abdo- 

 men, which Erichson evidently looks upon as the source of the 

 sound, cannot by any means be concerned in its production. It 

 lacks two essential conditions, being neither in a favourable po- 

 sition nor furnished with transverse grooves sufficiently fine. 

 The creaking sound produced by many insects depends on a very 

 rapid and powerful friction of a very thin edge against a grooved 

 surface, the fine transverse striae of which catch hold of and again 

 let go the edge. The thinner the edge, the finer the striae, and 

 the greater the velocity of the movement, the higher is the note; 

 and if the velocity and strength of the movement are small and 

 the grooves coarse, no sound, or a mere low rattling noise, can 

 be produced. But that lateral part of the abdominal ridge 

 which, in some species, under a moderate power, shows transverse 

 grooves is placed so far forward that the ridge on the femur 

 could touch it only when the leg is stretched out, moved by its 

 tensors, when the movements would not by any means be strong 

 or quick enough ; and its direction is, moreover, such that the 

 grooves could not alternately catch and let go the ridge on the 

 femur. Besides, these grooves are so distant from each other, 

 so coarse, and so deficient in sharpness, in comparison with the 

 striae on the creaking-apparatus of other Coleoptera, that even 

 on that account they cannot be regarded as sources of sound. 

 Even in animals so large as Necrophori and Ceramhyces, the 

 striae on the surface of the creaking-apparatus are so extremely 

 close and minute that they show interferential colours*, and are 

 distinctly observable only by the assistance of a very strong mag- 

 nifier. The structure does not come out clearly till the parts are 

 examined under the microscope by strong side light and a mag- 

 nifying-power of 50-100 times. If the creaking-apparatus of 

 Hetej'ocerus deserves that appellation, the striae must be expected 

 to be still more minute, and the surface would appear smooth 



part of the ridge is described as grooved in both sexes of H. marffinafus, 

 intermedius, and Icevigatus, grooved in the male but smootli in the female 

 of H. fossor, femoralis, fusculus, and hispidatus, smooth iu both sexes of 

 H. parallelus, obsoletus, and sericans. 



* On the creaking-apparatus of Necropho7-i, v. Naturhistorisk Tids- 

 skrift, ser. 2. vol. i. (184-J), pp. (il, 69; and on that of Cerumbijces, Nat. 

 Tid. ser. 3. vol. ii. p. 494 [Ann. & Mag. Nat. Hist. vol. xv. pp. 191, 192]. 



