insects: their feet. 129 



their eyes, wings, and abdomen ; but I am also inclined 

 to believe that, in general, when this passing of the legs 

 over the back of the head and outer marijin of the 

 wings takes place in connexion with the ordinary rub- 

 bing of the tarsi together, as it usually does, that the 

 object 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 jpulmlli. Here, too, it 

 should be noticed, in proof of the importance of all the 

 ptdvilli being kejjt 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 pulmlli, sometimes between the two fore tarsi, and 

 at other times betw^een the two hind ones 



" Tliough 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 wdiich these pul- 

 villi, and those of insects generally, act in affecting 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 ob- 

 servers to a field evidently, as yet, so imperfectly ex- 

 plored. 



" After waiting the above, intended as the conclu- 

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

 fact which I cannot forbear addino- to it. Observinir a 

 housefly on the w^indow, whose motions seemed very 

 6* 



