'«i30 THE CAUSES WHICH PROPAGATE 



t rachese^ and according" to my view is not to be confounded with an 

 air-sac. The nerve-system has its greatest swelling in the third 

 gang-lion of the nervous chord (Plate VII., Fig. 1) . The brain (first 

 knot) is smaller than the large ganglia of the chord;, and these 

 are all smaller than the third, which is of a flat shape, and from 

 whose posterior circumference arises a number of nerves to 

 supply the muscles of the sternum, the posterior pair of legs, 

 and ventral parts. The fifth of these nerves {ti) on either side 

 of the third knot of the nervous chord runs to the afore-de- 

 scribed bladder, and attaches itself to its fore upper part, where 

 it lies on the elastic membrane. May this part be the organ of 

 hearing of the grasshopper ? Nothing gainsays it, save that 

 the sensory nerve arises from the third knot of the spinal 

 chord. ""^ Colonel Goureau, independently, it would seem, arrived 

 at this identical conclusion a little later, although he does not 

 mention his reasons. 



Von Siebold and subsequent investigators have directed their 

 attention more especially to the drumskin itself, and its attach- 

 ment to the accredited nerve of hearing. Von Siebold, in 

 Germany and in Istria, carefully examined these parts in various 

 species, and observes the third pair of spiracles, which he con- 

 siders the first abdominal (e) , want the usual horny lips, and thus 

 constantly stand open, performing as he conceives the office of 

 a eustachian tube. They are situated anteriorly and inferiorly 

 to the drumskin, in a triangular enlargement of the horny ring 

 enclosing it. Beneath this the ring itself is discontinuous with 

 a short projection, as noticed by Burmeister. 



Externally, the drumskin is often more or less covered by 

 folds of the integument. There is an anterior (semicircular) 

 projection of the thorax, and a posterior elevation of the horny 

 ring. These in various ways arch over it, so as to reduce the 

 exterior adit to a more or less lunular opening. Von Siebold 

 remarks the drumskin is tolerably exposed in some species, and 

 perfectly so in others, and that the elytra, when closed, cover 

 the adit partially or wholly. Interiorly, the drumskin forms the 

 boundary to a tracheal bladder, comparable to the tympanic cavity. 



The Miillerian ganglion, again, is connected with the drum- 

 skin by means of intermediate horny pieces which Von Siebold 

 considers analogous to the bones of the labyrinth. One (Plate 



