DR. J. BRAXTON HICKS ON UNDESCRIBED SENSORY ORGANS IN INSECTS. 141 



sure about i-roo inch. They are found on the same parts in Acheta and Blatta, of the 

 form of those of the Scorpion-fly, as below. 



In the Scorpion-fly {JPanorpa communis) they are found in a group of ten to twelve on 

 each side of the trochanter (PI. XVIII. fig. I, 1) each one is oval ; and has on one side 

 a ridge running in the direction of the longest diameter (fig. I, 2 a). They are also 

 found in Libellula in the same parts. 



In the genus Gerris (Hemiptera) the organs are foiind in two groups on the trochanter, 

 about four in each group, and their shape is diflTerent from those hitherto described, being 

 oval, with a point at each end and a papilla in the centre (PI. XVIII. fig. K, a). The 

 sam.e organs are found in the Water-Scorpion {Nepa cinerea). 



In the genus Vespa they are found in a group on both the trochanter and femur, near 

 the joint, and a few scattered over the trochanter. I have represented those of Vespa 

 Crabro at PL XVIII. fig. L, 1 ; they are circular at the surface. The tubes leading to 

 the sui'face are curved ; the nerve proceeding to them can be plainly seen, as is shown 

 at fig. L, 2. 



In the Hive-Bee these organs are not so numerous, but are situated in the same part. 



\\i Formica rufa, or the Wood- Ant (PI. XVIII. fig. M, 1), the organs are very numerous, 

 and exist both on the trochanter and femur (fig. M, 1, a a). The nerve can be seen passing 

 to the different groups. On the femoral end also of the tibia are to be found a few small 

 groups, to which the nerve can be traced (fig. M, 2). Their diameter is about g^ro iiich. 



In the various Tenthredines the same organs are to be seen (PI. XVIII. fig. N, 1), 

 larger than the foregoing, and their form, which is shown at fig. N, 2, is somewhat conical. 

 They exist in two groups — one small, on the coxa ; and the other larger, on the trochanter. 



The organs on Grylla viridissima are represented at PI. XVIII. fig. O, 1. They exist 

 on the first and second legs, but not on the third leg ; they are in three groups, two on 

 the trochanter and one on the femur. 



At this place I may mention that I have examined the dilatation on the fore leg of 

 Grylliis and Locusta, considered by Siebold* as the " organ of hearing," and I have arrived 

 at the same conclusion as M.Lespes in the 'Ann. des Sci. Sat.' 1858, namely, that there 

 is no special nerve proceeding to the dilatation, but that within it there is a swelling of 

 the trachese, which principally occupies the space, and that the nerve passes deeper down 

 behind this tracheal swelling, being continued through the joint to the extremity of the 

 leg. I have bleached the integuments, and have been able to see quite through the leg 

 by adjusting the focus suitably. 



The next portions of the Insect to which I wish to direct attention are the palpi, both 

 maxillary and labial. If we examine, with \ to |-inch objective, the palpus of the 

 common Blow- fly {Musca vomitoria), it will be seen to be studded with a number of small 

 transparent dots over more than half its surface, more thickly towards the apex 

 (PI. XVIII. fig. P, 1). Their true nature it is difiicult to teU, but it is probably some- 

 thing similar to that which I shall describe in Vespa Crabro. I have di-awn them 

 enlarged (fig. P, 2), with the minute hair-like cuticular projections between them. Their 

 diameter in this Ply is toVo inch. 



* Wiegm. Archiv, 1844, vol. i. p. 52. 



