668 STRUCTURE OF THE SCALES OF LEPISMA SACCHARINA. 
corrugations of the membrane. In numerous instances, air bub- 
bles have been observed imprisoned between the heavy ribs on one 
or two sides, and by these corrugations on the other sides. There- 
fore the corrugations may safely be said to be on the same surface 
of the scale with the longitudinal ridges, and the branching vein- 
like structure on or near the other surface. Careful focussing is 
corroborative of this idea, making it certain that these two details 
of structure lie in different planes. With monochromatic light, 
the delineation of this structure is eminently satisfactory, and the 
effect of the slightest change in focal adjustment is at once felt. 
When the object is a little out of focus the light is unequally re- 
fracted and broken up in passing through this complicated net- 
work of ridges and corrugations, and produces an appearance of 
fine molecules over the whole surface of the scale. 
The coarse and the fine beads both vanishing under advancing 
definition, together with the behavior of the confined bubbles of 
air, seems to my mind fully to demonstrate the reality of the 
structure above described. Often, when the corrections are not 
perfect, the semblance of beading can be directly traced to a seem- 
ing enlargement of points of linear intersection and branching. 
When the 3, is at its best work the finer transverse markings are 
usually irregular both in strength and direction but always unmis- 
takable. They may be plainly seen on some of the smaller scales 
and in the central parts of the larger, and at almost as good 
advantage as near the edges of the easier scales. Sometimes they 
are continuous across several intercostal spaces and again only 
extending across one, or it may be merely budding, as it were, 
from the ribs. It will be noticed that the “beads” as drawn 
by Mr. Hollich exhibit corresponding irregularities. 
In conclusion the remark of Beck on the scales of Lepidocyrtus 
may well be quoted—‘“and my own belief is that the markings 
upon this and all other varieties of Podura-scales are more or less 
elevations or corrugations upon the surface, which answer ut 
simple purpose of giving strength to very delicate membranes.” 
If this idea is true of the eae it applies with greater force to 
the complicated ridges of Lepism 
The same original structure is pre modified in diverging di- 
rections so as to subserve totally distinct purposes. And as hairs 
are probably modified scales, and a regular gradation may be 
* Transactions R. M. S., 1862, p. 88. 
