ANATOMY AND PHYSIOLOGY. 63 
ing of insects, instead of displaying under the micro- 
scope the fibrous texture and the peculiar refractive 
properties of horn, has a wholly different structural 
arrangement. Taking one of the abdominal scales 
of a wasp, we find in this two distinct layers closely 
connected together. First, there is an outer hard 
layer, which bears the beautiful varied colours of the 
insect; beneath this is a thinner and softer layer, 
which, when dry, becomes brittle, and can be sepa- 
rated in the form of small flakes. The smaller hairs, 
which clothe the surface of the body, cannot usually 
be traced deeper than the outer layer, but the larger 
hairs may be followed through it and the inner layer, 
into contact with the soft substance beneath; pro- 
bably supplying the necessary amount of cutaneous 
sensation in this way. By ordinary light it might 
seem that the inner layer was perforated by these 
hairs, giving it what anatomists call a cribriform 
appearance. But this is incorrect; the hairs are a 
part of this layer, growing from it. And polarized 
light shows that these seeming perforations are really 
not holes, but transverse sections of the shafts of 
the hairs, with a concentric laminated structure, which 
refracts the light in crosses, im the same way that 
whalebone or rhinoceros-horn does. 
Within this hard case the soft tissues of the 
wasp are carefully inclosed. To these walls, or to 
ridges springing from them at the junction of the 
several segments, the muscles are attached which 
move the body. And, according to the mode in 
which the edges of the adjoining segments are fitted 
to each other, is the rigidity or flexibility of that 
part of the body secured. Considermg the work 
