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Psyche 4:63-70, 1883.

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PSYCHE.
THE SCALES OF COLEOPTERA.
BY GEORGE DIMMOCK, CAMBRIDGE, MASS.
( Confiniced from page 47.)
GENERAL SUMMARY.
After the preceding descriptions of
some forms of scales among coleoptera,
I wish to consider the subject more
generally. First to be considered is the question, in what families of coleoptera have scales been found. Fischer men-
tioned scales as occurring in teredyles, clavicornes, Zanzellicornes and curcu-
lioizia'e.s,-or to use the modern equiv- alents for the families in which he found scale-bearing species,- in the cleridae, ptinidue, dermestidae, byr~hidae,
scarabaeidae and cvrculionidae. To
this list I would add with certainty the elatendue, basing this addition on the
scales of Chalcole$idius and Alaus
described in this paper. According to
my views of what constitutes a scale I
would add further the ceram&ycidae,
and with some doubt the bufrestidae.
The scales of Clytus robiniae de-
scribed in this paper, it seems to me,
can scarcely be called hairs. altho to
the naked eye or to a low-power lens
they appear like hairs. They are too
much flattened and the striae end in the manner in which they do in scales.
The question whether the sword-shaped
appendages of Psiloptera dmmmondi
are really scales or hairs is less easily settled but I should be inclined, from
the arrangement of their striae, to term them scales. The form of scale from
Ahus is readily seen, by the figure of
its transverse section (fig. 7, d), to be too flat to be termed a hair, and this or similar forms are not uncommon among
coleoptera.
The question of the morphological
identity of scales and hairs of insects has been long since settled, so that the ques- tion of whether an appendage is a scale
or hair has little importance. The ex-
tremely minute spines or hairs upon
the wings of diptera, hymenoptera and
other insects are simply another form of scales. It is only in insects where cer- tain kinds of brilliant coloration have
been developed that one finds scales.
This leads to a consideration of how
hairs and scales of insects affect color- ation. They may simply cover a sur-
face of the same color as their own ; in such cases hairs may, according to the
angle in which they stand, their abund-
ance or their length, give rise to ap-
pearances which we designate as pubes-
cent. velvety, pilose, sericeous, etc. ; scales under similar circumstances may
give rise to ~irnilara~pearances, but are Psi& 4 06M1 (pre-1903). http //psyche aitclub 0@#4-006J html



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(14 PS 2THم� [jiily-~iignht i~s.1.
most often imbricated asul usuiillj+ cause hsive other striae and contrivances to more lustre thaii hairs. Hairs or scales act on the colors produced. The nu- may be of a different color from the merous modifications need not be enii- surface on which they are placed. If merated here. I have aliided to special they are numerous and opake they may effects of coloration in describing the entirely conceal the surface on which scales of different insects and shall they are inserted, as the white hairs again refer to some of them when dis- hide the bronze surface of the 'sides of cussing the modes by which the scales the thorax in Cicin-deZa dorsalis, and themselves are colored. I may acid here as the white scales of Aluus oculatus
that the general effect of transparent
hide the black surface beneath the rings scales is to produce metallic coloration. on the thorax ; or they may only partly The kinds of coloration in coleoptera conceal the surface of the insect, giving have been neatly tabulated by Fischer, rise to coarser and finer mixtures and according to the families of these insects. shades of color. Opake scales. or I translate his table, making in it, a few hairs, of more than one color, may cause altereitions based upon my own obser- figuration, whether they imbricate as on vations and indicated bv italics. (See
the wings of lepidoptera, or are separ- nextpage.) ated as on A~~thrcnus sct-ojhnlariae, Next to the consideration of how the The possibilities of varying effects
color and presence of scales and hairs
of color are iiiany with opake scales affect the appearance of surfaces to and hairs, but with transparent ones. which they are attached is the not less especially if they are colored, the effects interesting question of the causes of
of color can be multiplied still farther. coloration in scales themselves. But With hairs the effects are not so re- before considering the causes of color. markable as with scales. The scale, by properly speaking, <ج few words are -
its form, increases the number of layers appropriate on the causes which pro- of the surface of an insect which are duce silvery and milk-white appearan- available for colorational purposes. ces in scales and on insects. Leydig Where the surface of an elytron had was the first, in 1855, to call attention previously a cuticular and hypodermal to the presence of air between or he- layer, by the addition of a scale of the neath their chitin layers as a cause for simplest type there
is an addition of certain silvery spots and scales on in- two cuticislar and, theoretically at least, sects. He speaks of air in the finer
two hypodermal or sub-cuticular layers ; pore-canals of Ixodes iestudinis. giv- in all six layers, without counting over- ing these canals it black appearance, lappings of imbricated scales. Some but causing the whitish grey color of of these surfaces may have pigments,
the skin. So too he mentions silver;'
striae, hairs and pther appliances to scales on a spider, Sulticus, and glis- produce colors, and other surfaces tening hairs on another spider. Ghione



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COLORS
---PA-- 7
Carabici
Hydrocanthari
Brachelytrini
Sternoxi
Malacodermatici
Teredyles
Clavicornes
Palpicornes
Lamellicornes
Melanosomatici
Taxiceratici
Tenebrionini
Helopii
Trachelini
Vesicantes
Stenelytrini
Curculionides
Xylophagi
Longicornes
Chrysomelini
Erotylini
Coccinellin i
Pselaphii
One
Commonly
More rarely
Commonly
More rarely
'I 66
Commonly
6c
< c
More rarely
Always
Commonly
I 6
More rarely
cc 6'
Usually
Commonly
Rarely
Usually
Rarely
C,~mmonly
c c
Rarely
Commonly
Several
More rarely
Commonly
'6
I 6
66
6 6
Very commonly
Rarely
Commonly
Never
More rarely
<I 6'
Commonly
66
Very rarely
More rarely
Usually
Rarely
Usually
More commonly
Commonly
Usually
Commonly
COLORS
-------A -----
7
By special epidermal structures
such as
--- ---L-
7
In the substance Hairs Scales Forming designs Metallic lustre Surface hairy Always Sometimes
Never
Not rarely
Very often Rarely
6 6
Never
6 c
66 66
Very rarely 66
Usually Rarely II Not commonly Not rarely Commonly 66 I6
Sometimes Commonly Commonly
6 c
Always Never Never Not commonly 66 6 6
Sometimes Sometimes Rarely Not rarely Very rarely 6 I Usually Commonly "
Always Never
Never
Usually Rarely Often
- -
Always Never Never
6 c c 6 c c
Almost always Rarely L 6
Always Never 6 c
$6 61 c 6
Very commonly Not commonly c 6
Rarely C6 66 Rarely
Commonly Very many Commonly
Never Never
Rarely Very rarely Rarely
c< cc <c 6 '
66 Rarely Very rarely
Not rarely Never Commonly
Very rarely Usually Rarely
Not rarely Commonly 6<
Rarely 6 Commonly
Very commonly
Very commonly "
Always Never
Never
Not rarely Never
Commonly
I1
Commonly
Commonly Sometimes
Very commonly Very rarely Usually
Usually Rarely
Never
66 61
Very commonly Very rarely
Alwayb
Never
c 6
Rarely Very rarely
Rarely
'6 66 c c Usually
Never 6 6
'6 IL 6 6
$6 Commonly
A ever
1 Without regard to coloration or figuration.



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6 6 P.5- YCHE . [~uly-~vigrist 1883
claustraria, which appendages owe
their silvery whiteness to air within
them.
Again he mentions hairs which
contain air on spiders of the genera
Epeira and Theridium. Then fur-
ther, when considering the insects, Ley- dig writes that it is not difficult to see that the silvery under surface of Hy-
drometra $aludum is due to the pore-
canals being filled with air. He goes
on to say " In a similar way the wings
of Notonecta glauca seem to enclose
air, and I suspect also that the white
color of the hairy powder of many
ajhidae and coccidae is brought about
by like causes." Further on he writes,
'م�I one regards the color of scales it
can inhere as cliffise material in the
substance of the scale itself, or it ap- pears under the form of molecular
pigment, which is deposited in the
cavities of the scales, or finally the
cavities are filled with air which gives a snow-white appearance to the scale.''
Again Leydig writes that when Fischer
says, in speaking of "granulation-scales" (i. e., such scales as those of Hoplia
trifasciata) , "that the 'upper or gran- ulation layer' dissolved visibly in water, but quickly in alcohol or ether, and then only the 'striate basal layer' remained, the words show that he has certainly
seen but incorrectly explained that
change which the scale undergoes upon
the loss of air, in so far as he assumed a 'granulation layer' which dissolves in water !"
Leydig accounted for silvery glisten-
ing scales and surfaces, and for milk-
white coloration among insects, but he
fails to account for the difference between these two kinds of coloration. The
white scales of Pieris Wae and the
silvery scales on the under side of the
posterior wings of Argynnis idalia
both contain no appreciable coloring
matter, and both contain air ; both, too, are simply milk-white by transmitted
light. The difference is that there must be in the silvery scales a polished sur- face towards the observer. Ground
glass does not appear silvery, but what
is the surface of the smoothest polished plate of glass but finely ground glass ? Ground glass differs from polished
glass only in degree ; in ground glass
the scratches are so coarse and so
abundant as to turn most of the
light-waves into the glass again, where
they are lost. In polished glass the
scratches are still present, but have
become so small that even the waves of
light are large in proportion to then],
and so the light-waves reflect as if from a theoretically flat surface.
But some- .
thing more than a polished glass is
needed to reflect much light, for most
of the light passes through the glass ;
something non-transparent must be
behind the glass. In the common
mirror it is a mercury amalgam : in the
butterfly's silvery scale it is a layer of cavities filled with air. This layer of
cavities is not transparent for the same reason that ground glass is not. If we
treat the scale with chloroform it has
an analogous effect to that of treating
the back of a common mirror with
nitric acid, thus dissolving off the
amalgam. In both cases a non-trans-




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July-August 1883.1 p-5- ~ c ~ ~ . 67
parent body is converted into a
transparent one, and a mirror, which,
whatever be the materials of which it
is made, if approximately perfect has a
silvery appearance from the amount of
reflected light, is reduced to a slightly reflecting surface. But let the scale dry again from its bath, as Fischer apparently did not do, and the mirror will again
appear. Both silvery and milk-white
colorations are then only optical effects produced by reflected light.
Still another kind of appearance is
seen in the scales of Ho$Zia and of
Entimus. These scales are brilliantly
colored, yet their color is in the one
case entirely lost, in the other case
greatly changed by wetting with almost
any liquid, but when redried the colors
reappear with all their previous brillian- cy. This coloration also resists all
forms of bleaching. It must therefore
be produced by some decomposition of
light. Whatever acts upon the light
must be within the scale, not upon the
outside, for all those scales which
remain perfectly sealed, so that the
liquid does not enter them, retain their color even surrounded by liquid. This
proves that the color is not due to
external striation, where such exists.
The finer striation of the scales of
Entimus is evidently internal, from its
relations to the differently colored
internal cavities of the scales. Besides this striation the interior of the scale is evidently filled with a pith-like
substance into which liquids enter
with equal readiness in all directions ; this- pith-like portion apparently has
some direct influence upon the produc-
tion of the coloration, for wherever
it is injured or has shrunk away from
the basal end of a scale there is no
longer coloration in that place. Perhaps it is a necessary filling to cause the striae to refract the light, the same as air-
cavities are necessary as a backing to
produce the silvery color in the scales
of lepidoptera. The striae themselves
are very fine, but whether they are the
causes of color is hard to determine
without more accurate instruments of
measurement than I have at my com-
mand. As near as I could determine
they are 0.0008 to 0.0009 mm. apart.
The wave length of a ray of light from
Frauenhofer's A line of the spectrum is, according to Willigen, .000760gz mm.,
and the wave length at the HI line is,
according to the same authority,
0.00039713 mm. ; the difference being
0.00036379 mi-n., or the difference of
wave length between violet and red
light. To determine the place in the
spectrum to which the striae of these
scales correspond would require, of
course, much finer measurements.
The kinds of coloration of scales
thus far described are what Hagen has
termed "optical colors."
The second kind of coloration is
what Hagen terms "natural colors," of
which he distinguishes two kinds-der-
mal, where "the pigment is deposited in
the form of very small nuclei in the
cell, or in the product of cells, in the cuticula," and hypodermal, where "the
pigment is a homogeneous fatty sub-
stance, a kind of dye somewhat




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6 8 PSTCHE. [~u~y-~ug-nst ISS.~.
condensed." Hagen further says "To a
certain extent the dermal colors may
have been derived from hypodermal
colors, as the cuticula is secreted by the hypodermis, and the colors may have
been changed by oxidation and air-tight
seclusion." Like organic colors in
general, I have found dermal as well as
hypodermal colors to be subject to the
chlorin bleaching processes, which I
first applied, in 1875, for the purpose
of studying the venation of lepido-
pte~-a,~~-~O the only difference being this, that dermal colors require to be freed,
by long maceration, from their prison
in the chitin.
Thus a distinction between dermal
and hypodermal colors is that the
former bleach only by destruction of
the parts in which they are enclosed,
the latter bleach readily. I do not wish to enter here into a prolonged discussion of the chemical reactions which are
similar or alike in dermal and hypoder-
mal colors, which I hope to discuss
later, after more experiments, but will
add a table which I think will serve for the separation, under the microscope,
of the different kinds of coloration.
By this and other modes of separation
I have studied all the scales of coleo-
ptera which I had at my command, and
Broken scales become colorless but regain original coloration if dried again , . ,
Scales become more
transparent (if injured),
but retain some colora-
tion. Add to the wet
scales some chlorin- <
bleaching solution and
The color remains until
the scales begin to ma-
cerate and lose their
structural peculiarities .
, . , . . .