STRUCTURE OF THE SCALES OF LEPISMA SACCHARINA. 667 
ham’s paraboloid. All these methods point to the same conclu- 
sions. Following up the line of observations described by the 
late Richard Beck, in his most valuable contribution to our knowl- 
edge of this subject, the same results were arrived at in regard to 
the appearance of coarse beading, etc., viz., ‘ that the interrupted 
appearance is produced by two sets of uninterrupted lines on dif- 
ferent surfaces ”* That the longitudinal and the oblique lines are 
on different sides of the scale is also plainly seen by their lying 
in different focal planes under a > objective. And farther, while 
examining a scale in fluid I have repeatedly observed air bubbles 
on one surface of it confined by the longitudinal ribs, and on the 
other side others bounded by the oblique ridges; and on moving 
the slow adjustment up and down, with the movement of the bub- 
bles under control, they never interfere or mix with each other.t 
Nothing further is required to prove that these markings are 
actually ridges and that they project from different surfaces of the 
object. The experiments of Mr. Beck settle this question. 
As microscopical definition advanced the very feeble radiating 
lines were noticed in the spaces between the ribs, formerly thought 
to be smooth. In the central portion of the test these lines are 
parallel with the main ribbing. They in their turn were seen to 
be uneven and pronounced to be “ beaded strie.”{ Must this fine 
beading like its shadowy predecessors be also extinguished by 
intersecting cross lines and so add one more to the long list of 
illusory appearances? To attempt to throw some light upon this 
question is the principal object of the present article. 
In the first place, it is far from being a difficult feat to see this 
beading. Any first class lens, from a 4 upward, when properly 
handled, will display it or something very like it. The writer 
has found it an easy task with Wales’ ; immersion, or even with 
a Beck 1 and deep eye-piece. With Tolles’ = immersion the 
fine transverse structure indicated above is brought out, and it 
becomes at once evident that the small beads are indeed spurious 
like their big brothers, and for a similar reason. 
The fine transverse markings seem to branch from the faint 
radiating ones and have the appearance of a net-work of minute 
Capillaries. Beside these there are coarser transverse waves or 
* The Achromatic Microscope, Beck, p. 50. 
t See Micrographic Dictionary, 2d ed., p. 34, Fig. 3, pl. 27. 
t See M. M. Journal, March, 1873, pl. xi, Figs. 3 and 4. 
