220 ORTHOPTERA. 



and number of the venae olliquce must thus have been determined by the knots (lines) of 

 the vibrations of the membrane *. 



The two transverse veins (figg. 22, 23, v) must have a different origin, for they are 

 placed at the base of the tympanum, where the membrane is scarcely modified, and 

 therefore does not produce a musical sound. Their direction is precisely the opposite 

 to that of the true venae obliquce, and two suppositions are possible : a. They might be 

 regarded as an extra development of two transverse venulse of the reticulation [vide 

 fig. 18, the venulse at the base of the elytron joining the v. ulnaris (diagonalis) and the 

 v. media] ; b. Or, they might be considered as formed by the last two (inner) venae 

 obliquce (fig. 9, left to v) broken at right angles at their base, and rejected transversely 

 to the v. media. This modification must of course produce a special kind of sound. 



In a general way, it may be said that the tambourine of the male elytra is a musical 

 instrument, each tribe of Gryllidae possessing a different sort of fiddle, and that in each 

 tribe the genera present varieties of their typical fiddle, producing a somewhat different 

 note. It must therefore be admitted that the characters afforded by the musical 

 organ are of great importance in determining the systematic position of the species. 



In the tribe Gryllinse the venae obliquce, 2-6 and more, are obliquely transverse, and 

 the venae post-analis and jpost-axillares are arched. The genus Nemobius presents an 

 exception to these characters, in consequence of the small size of the species : the 

 tambourine is somewhat incomplete, having only one vena obliqua, which is longitudinal 

 and nearly parallel with the speculum, often abbreviated or obsolete. 



Synopsis generum. 



1. Metatarsus posticus superne nee sulcatus, nee serratus. Tibiae anticae in latere externo 

 foramine instructae. — Nemobius, Serv. 

 1, 1. Metatarsus posticus superne sulcatus, biseriatim spinulosus. 



2. Tibiarum posticarum calcar superum quam intermedium distincte longius. Tibiae posticse 

 breviores. (Tibiae anticae in latere externo tympano distincto instructae.) (Stirps 

 Brachytrypus.) 

 3. Ocelli in trigonum dispositi. Ovipositor rudimentarius. — Anurogryllus, Sss. 

 3, 3. Ocelli in lineam transversam dispositi. Ovipositor variabilis. — Brachytrypus, S. 

 2, 2. Tibiarum posticarum calcar superum quam intermedium brevius vel illo aequilongum (vel 

 sublongius). — (Stirps Gryllus.) 

 3. Tibiae anticae in utroque latere foramine instructae ; foramine externo oblongo, interno 

 minore. 

 4. Species majores. Elytra ? in dorso areolis rhomboidalibus reticulata ; $ tympani 

 venis obliquis 3-4 ; vena mediastina $ $ ramosa. — Gryllus, L. 



* Somewhat similar to what occurs when the skin of a tambourine, sprinkled with fine sand, is made 

 to emit a sound by rubbing its frame with a bow : the sand, agitated by the vibration, groups into different 

 lines and figures, formed by the interference of the sonorous waves. 



