THE STRUCTURE OF THE SCALES OF LEPISMA 
SACCHARINA. 
BY G. W. MOREHOUSE. 
For many years this test has been subjected to most careful and 
critical examination by the most competent observers and with the 
best microscopes, but, after all, the true character of its markings 
still remains a disputed question. These differences of opinion 
have evidently arisen partly from the complex nature of the mark- 
ings themselves, and partly from the different conditions under 
which they have been seen. In this scale we have coarse ribs 
easily seen with a very ordinary glass, and on the other hand deli- 
cate structures severely taxing the powers of the finest objectives 
in existence. This fact alone is sufficient to account for the want 
of agreement, without accusing any person of being biassed by a 
theory ; while those observers who think their own instruments are 
the best will continue to be satisfied with what they may happen 
to see, and shut their eyes to any advance. 
As the microscope has been improved, our ideas of the structure 
of the Lepisma scale have been gradually modified, and who will 
now claim it to be “ too easy for a test object?” 
In the order of difficulty of resolution we have — 
1. The heavy longitudinal ridges running from end to end of 
the scale and slightly projecting at the point. 
-= 2. Distinct ribs generally radiating from the quill, or curved 
parallel with the outline of the scale, and becoming faint in the 
centre and parts remote from the quill. 
3. Transverse corrugations of the membranes. 
4, Faint irregular veins branching from the diverging ridges 
(No. 2) generally taking a transverse direction, and, together with 
the corrugation, causing the spurious appearance of fine beading 
at their points of intersection with the ridges. 
- To make sure of my work on this scale I have studied it under 
a number of different conditions. The observations have been 
conducted with monochromatic sunlight ; with white cloud and 
lamp ; with central beam and oblique ; with mirror, prisms, achro- 
matic condenser with and without central stops, and with Wen- 
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