46 NOTES AND MEMORANDA. 



is best made out by treating the fresh antennae with 1 per cent, osmic 

 acid, transferring to absolute alcohol, clarifying with kreosote, and 

 mounting in Canada balsam. 



The supposed otocyst is a brown, thick-walled, chitinous sac, 

 provided with hairs internally, having a diameter of 0-027 mm., and 

 lying free in the cavity of the terminal leaf-like segment of the an- 

 tennfe, towards the inner side of the joint between that segment and 

 tlie preceding one. Under a high magnifying power the chitinous 

 wall of the sac is seen to be covered with rounded or angular areas, 

 the hair-plates, which are about "0044 mm. in diameter, and in tbo 

 centre of each of which is a dei)ression, the Jiair-jnf, giving attach- 

 ment to one of the auditory hairs, which project in a radial direction 

 towards the centre of the sac. These hairs are about two-thirds of the 

 radius of the sac in length and '0009 mm, in diameter at the base, 

 where they are somewhat swollen. They contain a distinct lumen. 

 Running through the wall of the capsule are fine pores corresponding 

 to the hairs. The chitinous capsule is surrounded by a layer of 

 columnar eiiithelial cells, each of which corresponds to one of the 

 hair-plates, and the whole epithelial sac thus constituted is again sur- 

 rounded by a delicate tunica propria. 



The first and second segments of the antennpe bear only isolated, 

 scattered, almost spiny hairs, but the terminal segment has a regular 

 and dense covering of two kinds of appendages — true covering hairs 

 formed by , elevations of the cuticula, and articulated hairs agreeing 

 generally with those of the other segments. The antennary nerve 

 comes direct from the brain, and first branches when within the basal 

 segment. A quantity of fine filaments are given off in the second 

 segment, and go principally to the outer spiny hairs, swelling out at 

 their roots into spindle-shaped ganglia. The other hairs of the first 

 and second segments receive their nerves directly from the principal 

 stem. Between the second and third segments the nerve makes an 

 S-shaped bend, and, passing through the aperture in the joint-mem- 

 brane, divides into filaments as in the second segment. A large braucli 

 is seen to pass direct to the capsule, but the connection of its fibres with 

 the epithelial cells, although very probable, has not been made out. 



An essentially similar structure is met with in the antennte of 

 Sicus ferrugineus, and in that of a species of Helomyza ; in the latter 

 case there is a dark-edged globular structure, which Graber considers 

 to be the sac of the otolith, and suggests that the otolith itself, of which 

 nothing was to be seen, was probably dissolved out by the kreosote. 



Exact physiological observations are, of course, required, before 

 the auditory nature of their structure can be considered as certain ; 

 but Graber mentions Paasch's observations that flies when startled by 

 a sudden noise raise the third joint of the antennre, as if " pricking up 

 their ears." 



It is also requisite to know something of the development of the 

 organ, as to whether it is formed as an invagination of tho inte- 

 gument, and also of its distribution in Tracheata generally. With 

 regard to the latter point, Graber states that he has found it in many 

 members of the sub-order Brachycera, but not in either of the families 

 Muscidoi or Tabanidce. 



