INSECT VARIETY. 239 



ORGAN OF HEARING IN THE LOCUSTID^ AND GRYLLIDJ. (PLATE II., 

 FIG. 3; PLATE VI., FIGS. 9 AND 10). 



The auditory org-ans of the leaf-crickets and crickets are 

 commonly on the fore tibias, but in the latter subterranean 

 species these org-ans are found less complex, and often imperfect 

 or absent, and here occur supplementary structures at the 

 abdominal base claiming' analogy with the auditory organs of 

 the g-rasshoppers. Dr. Landois, who appears to have been one 

 of the first to recognise these and describe them as they are found 

 in the mole-cricket, reputes them to be obsolete organs of music 

 of the kind extant in the Cicadidse, in support of which he 

 notices a muscle attached to their anterior edge, which he 

 compares to the motor tympani. 



They are further described by Herr ^^itis Graber, who, never- 

 theless, does not find them to be efticient auditory structures, 

 although he points out their many analogies with the acridiideous 

 organs. He commences by observing the first abdominal ring 

 of the crickets, as in other saltatorial Orthoptera, is little deve- 

 loped, and that the organ in question when present is commonly 

 found between the first and second abdominal spiracles, but the 

 position otherwise does not seem very determinate. Its origin 

 may be traced in the partial modification of one of a row of small 

 plates existing in the lateral membranes connecting the dorsal and 

 ventral arcs, to which cause the encompassing integumental ring 

 owes its peculiar forms (Plate VI., Fig. 10, t). It is also present 

 in various degrees of development in the species. In the mole- 

 crickets (Plate VI., Fig. 9) the tympanum T, seen from within, 

 has an oval shape, truncated anteriorly ; it is excessively thin, 

 talc-white in colour, smooth, and slightly convex. Towards the 

 inferior edge one notices a linear impression and slight ridge, 

 where Landois'' muscle (w) is attached. In other crickets the 

 tympanum is elongate and externally strongly convex, strewn 

 with small callosities ; or it is glassy clear and chitinised at its 

 hinder edge. We likewise find it hairy, or possessing other 

 character of the integument. 



The drumskin generally is covered by a polygonal cellular 

 matrix, and behind it is situated a tracheal bladder. The distri- 

 bution of the nervous system is as follows. The three thoracic 



