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



In the palpi of all Diptera formed on the same plan as in Mnsca, I have found these 

 structures existing, varying indeed in number and size. I have also found them in 

 Eristalis tenax. 



In many of the Diptera (Mtisca, Mesemhrinimi, for instance, and Flies of similar con- 

 struction), a group of organs of a somewhat similar character is to be found on the tips 

 of the piercers ; in some there are as many as twenty on each side of the middle line, two 

 large ones generally being situated at the apex. In Tapanus bovinus the tip of the 

 central portion or piercers possesses as many as twenty, apparently having the same 

 structvire as those in the Hymenoptera, to be immediately described. 



I have found similar organs on or about the palpi of some of the Hymenoptera, as 

 Vespa, Odynerus, Apis, Bombus, Megachile, Nomada, &c. I have, in PI. XVIII. fig. Q, 1, 

 figured these in Vespa Crabro. They are situated at the basal joint of the labial palpi, 

 about twelve in number, and in the same joint of the maxillary palpi, but fewer and 

 more scattered. In Vespa vulgaris theu' diameter is rrro iiich. In fig. Q, 2, I have 

 given an enlarged view of one, — (2) showing a section in which the nerve («) is seen 

 expanding on the inner surface of the covering-in membrane, (3) as seen from above. 



In Odynerus muraria and O. Antilope, for instance, they are foimd also on the centre 

 of the base of the labium. 



In Ajns mellijica these organs, instead of being placed on the fii'st joint of the labial and 

 maxillary palpi, are close to the origin of the palpus. I have shown these at PL XVIII. 

 fig. R, 1 a, 2 a. If we examine the apex of the labial palj)i of this Bee, we shall find three 

 or four structures somewhat similar, but having a few papillae at the surface. They are 

 situated among the hairs, and are represented at PL XVIII. fig. R, 3 a. In the Megachile 

 (Leaf-cutting Bee) they are very similarly situated, but on the base of the tongue, and on 

 the basal joint of its palpus, and a few scattered over the second joint (PL XIX. fig. A, 1). 



In Nomada succincta I can find them only on the base of the labial palpi, and one on 

 the distal end of each segment of the same palpi, which latter are of much larger size 

 (PL XIX. fig. B, a). 



This will suffice to point out the kind of structure to be found on or about the palpi ; 

 to aU of them a bundle of nerves can be seen proceeding. 



In Byticiis marginalis I have observed a few organs on the maxillary palpi, situated in 

 an oblique row (PL XIX. fig. E, 1 « & 3), of apparently similar nature to the structures 

 which I have observed on the antennae of that insect (in the second paper read before the 

 Linnean Society, May 1859). They are shown enlarged at fig. E, 3. 



A group of similar structures is to be found in some of the Arachnida, as Arania, 

 Tegenaria, on the under surface of the maxillEe, extending lengthwise along the middle 

 on a space nearly devoid of hairs. They are the only organs which I have been able to 

 meet with in that tribe ; but as the habits of the Arachnida show them to be chiefly 

 dependent on sight for their guidance in obtaining supplies of food, we probably might 

 not expect to find a large development of these organs, or others I am about to mention. 



In the palpi of Lepidoptera I have observed a peculiar structure, which I cannot find 

 noticed by any one, and which differs much from the other I have described. 



The structure in question consists of a depression on the apex of the terminal joint. 



