NOISES OF INSECTS. 497 



insects in the Cyclopaedia of Anatomy and Physiology, has so admirably 

 illustrated their structure, both internal and external, that this low jarring 

 sound is owing to the shortness of the nervures, and the much greater 

 number of those on the under side of the wing-covers being scored with 

 the same notches as in a file (p. 928.) ; pointed out in the crickets by M. 

 Goureau, who also saw them in the mole- cricket, but seems to have over- 

 looked their extending to so many of the nervures as Mr. Newport has 

 observed to be furnished with them. 



Another tribe of grasshoppers (Acrida, Pterophylla, &c. J ) the females 

 of which are distinguished by their long ensiform ovipositor like the 

 crickets, make their noise by the friction of the bases of their elytra. And 

 the chirping they thus produce is long, and seldom interrupted, which dis- 

 tinguishes it from that of the common grasshoppers (Locusta}. What is 

 remarkable, the grasshopper lark (Sylvia locustella), which preys upon them, 

 makesa similar noise. Professor Lichtenstein, in the Linnean Transac- 

 tions, has called the attention of naturalists to the eye-like area in the 

 right elytrum of the males of this genus 2 ; but he seems not to have been 

 aware that De Geer had noticed it before him as a sexual character ; who 

 also, with good reason, supposes it to assist these animals in the sounds 

 they produce. Speaking of Acrida viridissima common with us he 

 says, " In our male grasshoppers, in that part of the right elytrum which 

 is folded horizontally over the trunk, there is a round plate made of very 

 fine transparent membrane, resembling a little mirror 'or piece of talc, of 

 the tension of a drum. This membrane is surrounded by a strong and 

 prominent nervure, and is concealed under the fold of the left elytrum, 

 which has also several prominent nervures answering to the margin of the 

 membrane or ocellus. There is," he further remarks, " every reason to 

 believe that the brisk movement with which the grasshopper rubs these 

 nervures against each other produces a vibration in the membrane aug- 

 menting the sound. The males in question sing continually in the hedges 

 and trees during the months of July and August, especially towards 

 sunset and part of the night. When any one approaches, they immediately 

 cease their song." 3 In these insects, as in the crickets, M. Goureau has 

 detected in the strong horny ridge immediately behind the mirror or tym- 

 panum, near the base of the upper surface of the left elytrum, the same 

 transverse notches as in Aclieta and Gryllotalpa, while on the under surface 

 of the right elytrum a similar but less strongly notched file-like ridge is 

 found ; and it is obviously by the rubbing of these rasps against the pro- 

 jecting nervures of the borders of the wings, that the sounds resulting 

 from the brisk friction of the elytra proceed. Dr. Burmeister conceives 

 that they are chiefly caused by the forcible expiration of air from the 

 thoracic trachea? and spiracles, first driven against the inflected external 

 margin of the wing, and subsequently against the tympanum, which is thus 

 caused to vibrate and resound ; but Mr. Newport has pointed out that 

 this cannot be the cause, because in Acrida brachelytra the elytra are so ex- 

 ceedingly short and narrow that they do not cover, nor are near, any part 

 of the spiracles, so that the air in passing from these orifices cannot pos- 

 sibly be driven against the tympanum ; which, however, being accom- 

 panied by notched nervures, as in A. viridissima, though differently arranged, 



1 See Kirby in ZooJ. Journ. p. iv. 429. 



Linn. Trans, iv. 51. 3 De Geer, iii. 429. 



K K 



