406 NOISES OF INSECTS. 
but is supposed to modulate it*. The middle portion is 
occupied by a plate of a horny substance, placed hori- 
zontally and forming the bottom of the cavity. On its 
inner side this plate terminates in a carina or elevated 
ridge, common to both drums®, Between the plate and 
the after-breast (postpectus) another membrane, folded 
transversely, fills an oblique, oblong, or semi-lunar ca~ 
vity®. In some species I have seen this membrane in 
tension—probably the insect can stretch or relax it at its 
pleasure. But even all this apparatus is insufficient to 
produce the sound of these animals;—one still more 
important and curious yet remains to be described, 
This organ can only be discovered by dissection. A 
portion of the first and second segments being removed — 
from that side of the back of the abdomen which answers 
to the drums, two bundles of muscles meeting each 
other in an acute angle, attached to a place opposite to 
the point of the mucro of the first ventral segment of the 
abdomen, will appear¢. In Reaumur’s specimens these 
bundles of muscles seem to have been cylindrical; but 
in one I dissected (Tettigonia capensis) they were tubi- 
form, the end to which the true drum is attached being 
dilated*. ‘These bundles consist of a prodigious number 
of muscular fibres applied to each other, but easily sepa- 
rable. ‘Whilst Reaumur was examining one of these, 
pulling it from its place with a pin, he let it go again, 
and immediately, though the animal had been long dead, 
the usual sound was emitted. On each side of the drum- 
cavities, when the opercula are removed, another cavity 
of a lunulate shape, opening into the interior of the ab- 
* Reaum. ubi supra, f. 3. mm. > Ibid. g. g. ¢. © Ibid. 2 7. 
OTbids One * Ibid. £9. ff. Prare VIII. Fre. 19. bb. 
