68 MR. J. WATSON ON CERTAIN SCALES 



In the family Satyridae, the plumules have been found 

 in several genera,, as shown by M. Deschamps; the type 

 is again distinct^ and is well known to microscopists as a 

 scale of our common meadow brown Butterfly (Hippar- 

 chia Janiva), and possesses similar relative varieties. 



The battledore scales of FolyommatuSy long known to 

 microscopists, are of a form differing from any others, 

 again with generic similarity and specific variation. They 

 may perhaps serve the same office as the plumules, but 

 whether or not they have the same mode of attachment 

 requires further investigation. 



Next comes the interesting question concerning the 

 fiinction of these plumules in the economy of the insects, 

 and the purpose they serve beyond that of the ordinary 

 scales, which seem to act as the feathers of birds, in guard- 

 ing the insects from wet, and supporting them in their 

 flight — unless, indeed, they are not more nearly allied to 

 the scales of fish. Reaumur and some other entomo- 

 logists have supposed that the common scales, in addition 

 to these ends, supply the tracheae in the nervures of the 

 wings with air, and that the striae show the channels or 

 air-passages; but after close examination of them with 

 high powers, no external openings have been found fitting 

 them for this purpose. The plumules, on the contrary, 

 appear admirably adapted for air-vessels : they are hollow, 

 and can be inflated like balloons, and have a tuft of ciha 

 at the summit, which, by constant oscillation, may pre- 

 vent hurtful substances from entrance, just as the cilia in 

 the spiracles of many insects act. Through the bulb, 

 which is valve-like- shaped, being divided into two lobes, 

 there may be communication with the tracheae. The 

 plumules may thus perform a double function, conducting 

 a supply of air to the nervures of the wings, and, when 

 inflated, adding considerably to the buoyancy of the in- 

 sect. Besides, from the manner in which they are placed, 



