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TEXT-BOOK OF ENTOMOLOGY 



trachea passes close to the tympanum, which thus has air on both 

 sides of it : the open air on the outer, the air of the trachea on its 

 inner surface. In fact, as Lubbock states, "the trachea acts like the 



Eustachian tube in our own ear ; it main- 

 tains an equilibrium of pressure on each 

 side of the tympanum, and enables it 

 freely to transmit the atmospheric vibra- 

 tions." 



These tracheae, says Graber, though formed 

 on a similar plan, present many variations, cor- 

 responding to those of the tympana, and showing 

 that the tympana and the tracheae stand in 

 intimate connection with one another. For 

 instance, in those species where the tympana are 

 equal, the tracheae are so likewise ; in Gryllotalpa, 

 where the front tympanum only is developed, 

 though both tracheal branches are present, the 

 front one is much larger than the other ; and 

 where there is no tym- 

 panum, the trachea remains 

 comparatively small, and 

 even in some cases undi- 

 vided (Lubbock,ex Graber). 



lift 

 The acoustic nerve, 



which next to the optic 

 is the thickest in the 

 body, divides soon after 

 entering the tibia into 

 two branches, one al- 

 most immediately 

 forming a ganglion, the 

 supratympanal gangli- 

 on, the other passing rod ^';.,;;;));,; ;)"$"% 

 down to the tympa- * . /</, auditory rod : 



J r ko, terminal piece. 



num, where it expands After Graber, from Lub- 

 Fio.293. The auditory apparatus . A bock. 



in the tibia of a grasshopper, showing into an elongated flat 



the tympanal nerve-endings in situ: ono\ 



EBI, terminal vesicles of Siebold's ganglion, the Organ OI biebold (.b Ig. _".).)). 

 organ ; S.V, nerve of the organ of Sie- . . . , 



bold: <;<\ group ot 'vesicles of same; and closely applied to the anterior 



SO, nerve-endings of the same; vT, 

 front tympanum ; r TV. front branch 

 of the trachea; hT, hinder tympanum; 

 hTr, hinder branch of the trachea; 



.-- ko 



tracheae. 



At the upper part of the ganglion is a 



"'^''"."AV I",:;.??' group terminating below in a single row 



gnpra-tyrnpanal ganglion; r\. con- 

 necting nerve-fibrils between the jran- 

 fMon cells and the terminal vesicles : 



of vesicles, the first few of which are 



gHon cells ana tne terminal vesicles ; "x 



R. upper, u-S, lower, root of the trans- _ T .^.-,_ v - TVlo f ! or ,, 1Q l Vmf i.-liiMi <jnl-isp- 



parent covering membrane. (Other approximately equal, C 



quently diminish regularly in size. Each 



parent covering 



lettering not explained by author.) 



After (Iralx'r. 



