12 
POPULAR SCIENCE REVIEW. 
to escape notice of their enemies, as when a leaf-like butterfly 
perches on a twig*, and looks as if it had grown there — one of 
many surrounding leaves. 
These remarks may assist the student in looking for right 
analogies and avoiding wrong ones in investigating lepido- 
pterous or other scales. 
The minute markings of such scales have always been 
favourite objects for the microscopist to display, and some of 
them are still regarded as good practical tests for various 
powers. Among the most difficult to show clearly are certain 
markings on the scales of insects to which the name of Podura 
is still popularly given, though entomologists now call them 
by other appellations. The famous test scales of microscopists 
come from an insect now named Lepidocyrtus curvicollis ; 
and since Dr. Pigott affirmed that with sufficiently corrected 
glasses a distinctly beaded structure was to be seen in them, 
fresh discussion as to their real nature has gone on without 
ceasing, and strong feelings, as well as reasonings, have been 
shown by many who had perfectly satisfied themselves with the 
appearance of the well-known note-of-exclamation marks, so 
well shown and so beautifully figured by the late Richard Beck. 
It seems probable that insect scales are essentially composed 
of two membranes more or less corrugated, forming a sort of 
quill at the end where their insertion into the membrane takes 
place, and expanding upwards into a sort of bag, in the so- 
called 66 battledore ” variety, and into a flattened plume in the 
ordinary sort. An intermediate membrane has been described 
by some observers, but this appears only the result of a de- 
posit which in most scales takes a more or less beaded form, 
and may combine into a distinct layer in some kinds. 
Dr. Pigott’s 66 beads ” are by no means inconsistent with the 
existence of corrugations, and the exclamation marks are pro- 
bably true aspects with a particular focussing and illumina- 
tion, though few observers, who have taken much care in the 
investigation, have for many years supposed them to afford an 
accurate and complete idea of structure. 
The extreme delicacy of the Podura or Lepidocyrtus scale gives 
rise to so much difficulty, both of observation and interpretation, 
that it is advisable to be guided by analogy drawn from easier 
scales in its interpretation. This plan was pursued by the writer, 
who traced what seemed to be real beads in ordinary and easy 
butterfly scales, through more difficult ones, up to those of 
Lepidocyrtus curvicollis. 
Mr. R. J. Mclntire took up the question with great skill 
and with an absence of prejudice somewhat remarkable, in a 
discussion that has excited an unusual amount of strong feeling ; 
and whatever ultimate conclusion may be reached, his obser- 
