138 DB. J. B. HICKS ON A NEW OBGAN IN INSECTS. 



there are about twenty rows of vesicles, each row separated from 

 the adjoining one by a slight distance. There is a row of hairs 

 between each row of vesicles, the hairs arching over them, and 

 thereby forming a protection from extraneous particles. These 

 hairs are in pairs, one pair being opposite to each vesicle. The 

 rows on the ridge are arranged transversely to the axis of the 

 halteres (fig. 3 a, c) . The vesicles themselves are very trans- 

 parent, and hemispherical or even more nearly spherical projec- 

 tions, apparently cuticular. This is well seen by a profile view, 

 fig. 3 e. Their diameter, in this fly, is about 4-oVo^h of an inch : 

 each vesicle nearly touches its neighbour. 



Beneath these, but on one side only, is a broader, flatter face, 

 on which the vesicles are more distinct, and at a farther distance 

 from each other, the rows arranged parallel to the axis of the hal- 

 teres, and only one hair opposite each vesicle, there being some 

 alternate. The diameter of each of these is about -gy^th of an 

 inch. There is a smaller group of vesicles situated on one side of 

 this latter face, in number about ten ; the individual vesicles are 

 rather larger. 



In the Tdbanidce the arrangement is very similar, with the ad- 

 dition of seven vesicles on the shaft of the halteres, to the upper 

 part of the facet of the ridge, and another group of eight or nine 

 beneath the ridge opposite the broader facet. 



In Tipula the same general arrangement holds, except that in 

 the facets on the ridge the vesicles are arranged in a quincuncial 

 manner, and are larger than those on the broad facet, being about 

 x 9*0 th of an inch, with numerous hairs between each (fig. 4 a). 

 The broader facet too is less extensive relatively to the others, 

 and is also quincuncial in arrangement, of the diameter of 3^- ¥ th 

 of an inch (fig. 4 b). Besides these, in the largest Crane-fly, on 

 the joint, there is a cone, having on its flattened apex a group of 

 about eight or nine vesicles, with numerous very small hairs be- 

 tween them (fig. 4 c). 



The shaft of the halteres is tubular, and through it apparently 

 passes a branch of the nerve, which seems to expand as it reaches 

 the head, and which head contains cellular substance, and has ex- 

 ternally a groove on one side, just below its greatest diameter. 

 The membrane lining the groove is apparently very delicate. A 

 group of hairs is generally found at the end of the groove. 



I have now described the principal features of these curious 

 structures, as found in the halteres of the Diptera ; none that I 

 have examined have been free from them. The number of vesicles 



