174 SELECTED NOTES. 



The upper wall of the pulvillus is composed of chitinous semi- or 

 half-tubes directed lengthwise, and joined together at their edges, 

 thus forming a very flexible roof. The lower surface is clothed 

 with fine tapering, unpigmented hairs ; these hairs are commonly 

 said to be hollow, but I have searched in vain to find a lumen in 

 them. In some species the hairs are trumpet-shaped — e.g.^ in 

 those of the Gad-fly and a parasite from an Indian bat. 



Common with the pulvilli of other flies, I find they contain 

 glands, but neither muscle nor nerve. The sections under notice 

 are very rich in glands, which evidently elaborate the viscid fluid 

 by which the fly is enabled to walk in an inverted position on the 

 ceiling or on glass. Here we meet with a difficulty. If the hairs 

 are not hollow, and there are no openings in the lower wall near 

 them, how does this viscid fluid get on to them ? I shall be glad 

 of any suggestions on this matter. 



It has occurred to me that, beyond the circumstance men- 

 tioned above, the viscid fluid may fulfil a much higher purpose to 

 man and other animals. In flies which deposit their eggs upon 

 decomposing and often diseased animal matter, but do not feed 

 upon such matter, the fluid would entomb any disease-germs taken 

 up by their feet — that is, supposing the fluid hardens on exposure 

 to the air like the fluid emitted by the spinnerets of spiders and 

 the larvae of some Lepidoptera. I do not wish to imply that flies 

 do not disseminate disease-germs. This, I believe, is frequently 

 done when they feed on fluids containing such germs, by carrying 

 them on their proboscis to pure fluids, on which they afterwards 

 regale themselves, 



Hilaria pilosa, Longitudinal section of the Tarsus of Male. — 

 In the male insect the first joints of the anterior tarsi are greatly 

 enlarged. In this section the most prominent feature is the 

 numerous large glands with their ducts ; the apodeme, which 

 moves the joints, the nerve, and tracheae, are also shown, whilst 

 no muscle is visible. The ducts penetrate the inner wall of the 

 joint, and the outlet can be seen in one of the sections. 



The purpose of the secretion from these glands is, in all pro- 

 bability, the same as those in Water-Beetles, where the glands 

 have their outlets in both the large and small discs on the anterior 

 feet. 



