vou. u1.] Proceedings of Societies. 85 
this minute powder tell us of the history of butterflies and moths? 
An examination of various species discloses the fact that there is 
considerable diversity both in the structure and distribution of the 
scales. Among some species the scales are in the form of slightly 
flattened hairs, irregularly scattered over the surface of the wings. 
Between this type and the most specialized form of scale every grada- 
tion can be traced; and it is found, moreover, that in species in 
which the structure of the wings, antennz and other parts discloses 
a lowly organization the irregularly disposed hairy form of scale is 
present. Furthermore, itis found that the specialization of the scale 
varies upon different parts of the wing. 
In order to understand the use of these scales it is necessary to 
know something of the structure of the wing. The wing of the 
dragon-fly is cut up by a net work of intersecting veins, but in 
butterflies and moths the veins are fewer in number and cross-vein- 
ing is rare. In the dragon-fly the mesh work of veins strengthens 
the wing, while in the butterflies and moths the scales perform this 
function. The more flat anf regularly disposed the scales are, the 
greater will be their strength. Accordingly any variation in the 
direction of a flattened scale will be preserved by natural selection. 
It is to be expected, moreover, that the greatest change will occur 
in the region of greatest strain. It is found that this is indeed the 
case, for the scales are more flattened on the front than on the hind 
wing, and at the tip more than at the base. Asan additional strength- 
ener, ridges have been developed along the scale. Incidentally, 
these ridges have also been productive of a great variety of iri- 
descent colors, by the interference of light. As soon as these color 
effects began to manifest themselves, sexual selection would be in- 
troduced as a factor in the modification of scales. 
Having followed out one line of development it is necessary to 
correlate this with the evolution of other parts. The classification 
of insects is based largely upon the structure of the wings. In lower 
forms the wings are broad and far apart, while higher forms are dis- 
tinguished by having them closer together and more compact. In 
order to give still greater strength to the stroke of the wings a 
bristle or clump of bristles known as a frenulum, is developed near 
the base of the upper edge of the secondary wing. When consisting | 
of a bundle of bristles each one is a hollow tube, but when formed 
of but one bristle it is composed of a number of tubes joined to- 
