INSECTS: THEIR FEET 135 



ject is rather for the purpose of completing the entire 

 cleansing of the tarsal brushes (for which the row of strong 

 hairs visible under a lens on the exterior margin of the 

 wings seems well adapted), so that they may act more 

 perfectly on the pulvilli. Here, too, it should be noticed, 

 in proof of the importance of all the pulvilli being kept 

 clean, that as the tarsi of the two middle legs cannot be 

 applied to each other, flies are constantly in the habit of 

 rubbing one of these tarsi and its pulvilli, sometimes be- 

 tween the two fore tarsi, and at other times between the 

 two hind ones 



* 4 Though the above observations, hastily made on the 

 spur of the occasion since beginning this note, seem to 

 prove that it is necessary the pulvilli of flies and of some 

 other insects should be kept free from moisture and dust 

 to enable them to ascend vertical polished surfaces, they 

 cannot be considered as wholly settling the question as to 

 the precise way in which these pulvilli, and those of insects 

 generally, act in effecting a similar mode of progression; 

 and my main reason for here giving these slight hints is 

 the hope of directing the attention of entomological and 

 microscopical observers to a field evidently, as yet, so 

 imperfectly explored. 



" After writing the above, intended as the conclusion 

 of this note, I witnessed to-day (July 11, 1842), a fact 

 which I cannot forbear adding to it. Observing a house- 

 fly on the window, whose motions seemed very strange, I 

 approached it, and found that it was making violent con- 

 tortions, as though every leg were affected with St. Vitus 1 

 dance, in order to pull its pulvilli from the surface of the 

 glass, to which they adhered so strongly that, though it 

 could drag them a little way, or sometimes by a violent 



