Monthly Microscopical"! 
Journal, Aug. 1, 1869. J 
Scales of Butterflies, 
75 
and P. Chloris, two West African Butterflies ; and no approach to 
this form has been discovered on any others. The study of the 
actual objects with the binocular microscope and high powers will 
be well rewarded, and give abundant cause for speculation as to the 
absolute form of the plumules. They appear to be hollow mem- 
branous bags of a cylindrical or triangular shape, bound round by 
longitudinal ribs, which are carved inwardly, forming a contraction 
at about one-half or one-third of their length, where they are 
drawn in as by a cord. At the base, the ribs are inflexed towards 
the peduncle and bulb, to which they seem attached by the mem- 
brane. The large double-lobed transparent bulb, besides acting 
as a ball-and-socket joint, seems to serve as a valve to close the bag. 
Above the contraction, the ribs are continued with a curvature 
similar to the lower portion, and terminate in extremely fine and 
delicate points. In different specimens these approach more or 
less closely, and they appear to be free at the upper extremity, 
with a power of contraction or closing to protect the interior of the 
bag from the entrance of injurious matter. Their appearance is 
very much like that of the ciliated tentacula of the Stephanoceros 
or peristomes of some of the Mosses. The length of the bag is 
about l-300th of an inch, without the peduncle and bulb, which, 
when fully drawn out, extend about l-800th of an inch further 
beyond the point of attachment. 
Next comes the interesting question concerning the function 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 guarding the insects from wet, and supporting 
them in their flight — unless, indeed, they are not more nearly 
allied to the scales of fish. Keaumur and some other entomologists 
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 exami- 
nation of them with high powers, no external openings have been 
found fitting them for this purpose. The plumules, on the con- 
trary, 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 prevent hurtful sub- 
stances 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, con- 
ducting a supply of air to the nervures of the wings, and, when 
inflated, adding considerably to the buoyancy of the insect. Besides, 
from the manner in which they are placed, partly between and 
partly under the ordinary scales, the latter must be raised when 
the former are inflated; and when not in use, they probably lie 
