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CONTRIBUTIONS OF THE ROYAL ONTARIO MUSEUM
DIVISION OF ZOOLOGY AND gerne perenne

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No. 49 Op Jon “Sip, AR
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SCENT RECEPTORS IN LEPIDOPTERA

By
F. A. Urquhart

100 Queen’s Park
TORONTO, CANADA
April 22, 1958

CONTRIBUTIONS OF THE ROYAL ONTARIO MUSEUM
DIVISION OF ZOOLOGY AND PALAEONTOLOGY

No. 49

SCENT RECEPTORS IN LEPIDOPTERA

By
F. A. Urquhart

100 Queen’s Park
TORONTO, CANADA
April 22, 1958

SCENT RECEPTORS IN LEPIDOPTERA

By F. A. URQUHART

A consideration of the so-called “scent glands” that occur on the wings
of some species of butterflies

In the males of many species of Lepidoptera certain scales of the
wings appear to be different in size and configuration from the majority
of the scales. These have been termed androconia and are believed to
be associated with scent glands. It is further believed that these “scent
scales” produce some sort of aroma which “assists the male butterfly in
locating a mate,” presumably the female being attracted to the male.

Modified scales, or hairs, that are apparently associated with the
production of scent have been described for the Ithomyidi, various
genera of Nymphalinae, a genus of Morphinae, the Hesperidi, and
many others. As far as I have been able to ascertain, no author has
been able to associate such modified hairs or scales with a functional
secretory gland or produce evidence for assuming the production of a
fluid that might be responsible for the odour produced. Further, the
odour produced by the butterfly, or butterflies, in question has been
assumed to emanate from these modified hairs or scales with no evi-
dence to indicate that such is the exact origin of the scent. It would
be most difficult indeed for man’s poorly developed olfactory organs
to locate the pin-point origin of an odour associated with a small patch
of scales or hairs, and even if observations would seem to point to
such an origin, it has never been adequately demonstrated that the
scent arises directly from the scales or hairs rather than being trans-
ported to such areas from some other part of the body. Scudder was
aware of the weakness in assuming that such scales are responsible
for the production of the scent when he wrote in his book, The
Butterflies of the Eastern United States and Canada, “. . . there are
not a few instances known in which the statement regarding the
source of the odor is somewhat vague, a gland being referred to when
the specification of such an organ is a collection of scales of peculiar
character.”

With respect to the odour emitted, most authors agree that it is a
sweet-smelling scent resembling that given off by various species of
flowers, as for example, lilac, violet, syringa, thyme, verbena, orange,
and so on. Miiller refers to it in one species as a “very delicious
perfume.” Of those who have referred to the odour as “disagreeable”
it is more than likely that the scent was not produced by the male
during sexual excitement. That most authors have compared the

3

4 R.O.M., Z. AND P. CONTRIBUTIONS

scent to that produced by flowers is most significant, as we shall see
later in the present discussion.

Concerning the structure and function of the “scent glands” on the
hind wings of the Monarch butterfly, a paper written by S. A.
Housman dealing with this subject was published in The American
Naturalist. The following information was supplied by the author and
the following conclusions rendered:

1. The scent organ of the Monarch butterfly is a slightly elevated
black pouch about three millimetres in length and one and one
half millimetres in width.

bo

The darkly coloured scales which cover it are similar to those
found in the dark areas of the wings.

3. The cavity of the sac is lined with tiny, black, overlapping scales
which are much smaller and more delicate than the surface

scales and more heavily pigmented. These are the “scent scales”
or “androconia.”

4. The inner wall of the sac itself is thin, vellowish, and with regu-
larly arranged circular areas, so-called “scent cups.”

5. Each scent cup is covered with a thin cuticle bearing a minute
central pore from which extends an extremely narrow, hair-like
scale, similar to a seta.

6. Fitted into such pores are the scale stalks or pedicels in contact
with the unicellular gland cells of the epidermis.

7. In areas between the cups are pits in which are located the
pedicels of wide scales.

8. These two types of scales give off characteristic odours and
would account for the term “scent scales” and for reference to
the sac as a “scent gland” or an area of “sensory scales.”

9. Secretion from specialized gland cells escapes in the regions of
the pedicels to coat the surfaces of the scales, and thus these
modified insect hairs serve as outlets for cell secretions.

10. The secreting substance has a faint, fragrant odour likened to
the sweet milkweed blossoms.

11. It may serve, in function, as a sex stimulant in that it is attractive
to the opposite sex.

As I shall point out later in the discussion, there is no evidence for
the conclusion that the two types of scales give off characteristic
odours and hence there is no reason for terming these scales “scent
scales.” There is no evidence for stating that there are specialized
gland cells and that secretions coat the scales. The flower-like perfume
may not originate from the specialized scales.

URQUHART: SCENT RECEPTORS IN LEPIDOPTERA 5

Longstaff in his excellent book Butterfly Hunting in Many Lands
records translations of Fritz Miiller’s papers dealing with hair tufts,
felted patches, and similar structures on the wings of male Lepi-
doptera. The following statement concerning Danaus gilippus and
D. erippus is significant in the present discussion: “It is not possible
to detect any odour arising from the wings of the males of either of
the two species found in the Province of S. Catharina. . . . If one
strongly compresses the abdomen, there is everted on each side of
the last segment a finger-shaped membranous tube with closed apex,
which is covered with dark hairs, erected as the tube passes out of
the abdomen, and exhaling at the same time a somewhat strong odour
in D. gilippus, and one less strong though still perfectly distinct in
D. erippus.” The author further points out that it “appears extremely
unlikely that such a function (namely the production of scent) would
be exercised by a cavity communicating with the air only by a narrow
slit, and, in addition, having apparently no mechanism on the wing
by means of which it could be opened.” It has been suggested that
these sexual spots may be rudimentary in function resulting from
the development of the abdominal scent glands. Doubleday et al.
pointed out that in some males of D. erippus a small portion of the
wing, close to the orifice of the sexual cavity, is denuded of scales as
if they had been repeatedly rubbed away by introducing something
into the slit. This I have also observed and would add that not only
are the scales absent at the entrance to the sexual cavities but this
particular area is slightly concave, forming a cup-like depression, the
presence of which lends further support to the conclusions set forth
in the discussions that follow. Miiller suggests that the substance
produced by the sexual spots is transferred to the tip of the male
abdomen.

In many species of Lepidoptera there are no sexual pouches, similar
to those found in the danaids, but there are patches of modified scales
or hairs on various parts of the wings or, in some cases, on the thorax.
Epicalias acontius possesses a felt-like patch of scales on the lower
surface of the front wings which, when at rest, lies over a similar
patch on the upper surface of the hind wings. Myscelia orsis males
possess a similar felt-like patch on the upper surface of the hind
wings. In the Ithomyidi a tuft of long hairs is located near the front
margin of the hind wings of the males which apparently emits a
vanilla-like odour. In Prepona, one of the Nymphalinae, there is a
similar tuft of black hairs on the hind wings of the males. The males
of Thaumantis, a genus of Morphinae, have hair tufts of a similar
nature on the upper surface of the hind wings near the base. In
species of Antirrhea, one of the Satyrinae, the males are said ‘to
produce a strong odour from a patch of scales located on the hind
wings at the anterior base of the upper surface, which is covered by

6 R.O.M., Z. AND P. CONTRIBUTIONS

the fore wings and protected by a covering mane of pale buff hairs.
Stichophthalma (Morphinae) has a patch of modified scales and an
erectile wisp of hairs on the hind wings of the male. A species of
Ageronia (Nymphalinae) possesses two large, brown spots situated
between the wings, where they oppose each other, which appear to
be associated with emitting a scent. In Leptalis (Pierinae) there is
a patch of scales associated with production of scent on the portions
of the front and hind wings which conceal each other. In the case of
Melete the odour is most pronounced when the wings are opened—
the odour being retained when the wings are closed. It is interesting
to note that, according to Scudder, Aurivillius “looks askant at the
so-called scent scales described by Fritz Miiller because he could
detect no odour from Mancipium brassicae even though large andro-
conia were present. This is a very interesting observation and one
which will be readily answered in the discussion that follows.

In summary we may conclude that: (1) there are modified hairs
and/or scales on the wings or thorax of male butterflies which are
associated with the emission of a flower-like scent; (2) in most cases
these modified scales are Jocated on the hind wings of the male; (3)
in some instances no detectable odour is associated with such modi-
fied scale areas; (4) abdominal glands producing a flower-like odour
are present in the males of most species which possess modified
scale patches; (5) the degree of modification of scales varies from a
simple, almost unchanged, patch of scales, through those in which
the scales are highly modified and densely clustered, and culminates
in the advanced development of a partly closed pocket as found on
the hind wings of the males of the Monarch butterfly. It should also
be emphasized that many observations indicate that these specialized
patches are often covered by similar patches on the underside of the
front wings, or by a mantle of hair.

Before presenting what I believe to be the true function of ‘the
so-called “scent glands” on the hind wings of the male Monarch
butterfly, I present the following data.

Field Observations

During the past twenty-two years, while engaged in a study of
the migratory habits of the Monarch butterfly, I have made nu-
merous observations on the mating habits of this particular species.
To summarize these observations and to present more clearly an
explanation for the function of the modified scale patches which I
would term the scent receptors of the male, a single case involving
one set of observations is here described dealing with a particular
pasture field during the months of July and August in 1956. This
particular field supported a very rich growth of milkweed (A. syriaca )

URQUHART: SCENT RECEPTORS IN LEPIDOPTERA 7

as well as other flowering plants on one half of it, and a short grass
area supporting small milkweed shoots and seedlings on the other half.
The reason for this difference was that part of the field had been cut
in order to obtain sod for the banks of an adjacent highway and the other
part was left uncut because a small creek meandering through this
particular area made cutting impossible. We had collected and tagged
many Monarch butterflies in this field between 1952 and 1956 and,
from our recorded data, there was a marked difference in sex ratio.
92% being males and 8% females. Although we were well aware of this
peculiar sex ratio we were at the time only interested in tagging and
hence did not study the situation. It was not until the summer of 1956
that this sex ratio became an important factor in our studies of the
migration, because eggs were required for rearing purposes. Many
hours were spent searching for eggs on the leaves of the tall plants and
only a few were found and these were located on the small, slender
leaves associated with the flower clusters. Males were observed resting
upon the broad leaves of the bush-like hawthorn trees, and the
occasional female was seen flying from flower to flower—usually
during the late afternoon. On July 26 it was noticed that a number of
Monarch butterflies were flying close to the ground in the cut-over
area, and on further investigation it was found that all of them were
females and that they were depositing their eggs upon the leaves of
small milkweed seedlings. While awaiting the approach of a female,
the male could be seen resting upon the leaf of the hawthorn tree, his
wings at times out-stretched and at other times partly closed. The
apical half of the abdomen was raised and, when the wings were partly
folded, the abdomen could be seen moving in a somewhat jerky fashion
from side to side. From time to time, the male would leave its chosen
resting place to survey the neighbouring field or to feed upon the
nectar of the flowers, returning again to the hawthorn tree. By waiting
beside the tree it was possible to capture the returning male and
examine it. The abdominal scent glands could be extruded by gently
pressing the tip of the abdomen and in so doing a flower-like perfume
could be immediately detected. The odour was remarkably similar
to that produced by species of flowers belonging to the genus Spiraea.
When a female, having left the part of the field where oviposition took
place, entered that part where the flowering plants were located, she
was immediately pursued by the waiting male. It is interesting to note
that the female was not attracted to the bush where the male lay in
hiding, but, on the contrary, the male pursued the female, even from
some considerable distance (up to 80 feet distance) from his resting
place. On many occasions the male would pursue a chipping sparrow,
a song sparrow, a leaf or a piece of paper blown by the wind. If the
female was overtaken by the male she might elude him by a rapid
zig-zag flight or, with fluttering wings, fly vertically. In the latter case,

8 R.O.M., Z. AND P. CONTRIBUTIONS

the male would circle about the female, thus presenting a vertical
spiral flight. Eventually, but not in every case, the male, now slightly
in front of the female, would fly towards a nearby hawthorn bush
pursued by the female. They would alight upon the leaf, the male
often strutting beside or in front of the female, his wings slightly out-
stretched, the rear wings widely separated from the front wings. Then,
while the female with wings folded or but slightly separated remained
motionless, the male would curve his abdomen sideways so as to reach
the tip of the abdomen of the female and thus grasp her firmly with
his well developed jaw-like claspers. It is interesting to note that
during this performance the proboscis of the female would be slightly
or completely extended as if feeding upon some secretion on the sur-
face of the leaf. I was unable, however, to locate such a fluid on the
surface of the leaf. After resting in this position for a variable period
of time, the male would eventually take to wing carrying the female
suspended beneath him.

It should be noted that copulation took place regardless of the fact
that the female had been ovipositing and hence had previously mated.
From the examination of the bursa it was found that three matings
were not unusual.

Occasionally one male would pursue another. A rapid vertical spiral
flight would ensue, each male trying to get in front of the other. Such
flights were much more rapid than when a male and female were
involved, and eventually they would part, one returning to the nearby
hawthorn bush and the other flying rapidly to a more distant location
across the field.

Examination of the Male During Mating and Non-Mating Periods

During the height of the mating season, if a male is held in the
hand a faint perfume may be detected. This odour cannot be detected
out-of-doors, at least I have not been able to detect it under such
conditions, but indoors, away from distracting odours, it is detectable.
If the tip of the abdomen is pressed so as to cause the extrusion of the
abdominal glands then a very decided odour can be detected even
under out-of-doors conditions. It would appear that the odour emana-
ting from the wings is very faint and that from the anal glands very
strong, by contrast.

Before the mating season begins, as for instance during the over-
wintering period, no such perfume can be detected when the butterfly
is held gently in the hand. If the abdomen is squeezed, and the glands
are thus protruded, then the perfume can be detected although it is not
as strong as during the mating season. This would seem to indicate
that there is no perfume emanating from the wings during the non-
mating periods, nor is the odour produced by the anal glands as strong.

URQUHART: SCENT RECEPTORS IN LEPIDOPTERA 9
Scale Examination

The accompanying drawings of the various scale configurations were
made by using a microscope equipped with a camera lucida and hence
represent fairly accurate outlines as well as being of the same magni-
fication. The scales on the membrane of the wing are oval in shape
and they may be smoothly rounded at the apex or with a slight ser-
ration or notch. The scales on the vein of the wing are elongate. The
scales located on the top of the scent receptors are similar in shape to
those found on the wing membrane. These scales are, however, much
more numerous and form a dense mass. Approaching the slit-like
entrance of the scent receptor the scales of the wing membrane become
more elongated and those possessing serrated or notched apices be-
come more numerous. Within the cavity of the scent receptor, the
scales are much smaller, very black in colour and with slight or de-
cidedly serrated apices. These scales have been referred to as “scent
scales” or “androconia.” In addition to these very numerous, closely
packed scales there are a few hair-like scales.

Examination of Scent Receptor

By embedding the portion of the wing bearing the scent receptor
taken from a freshly killed specimen (not one preserved in alcohol or
the like) in paraffin, it is possible to make a transverse section through
the receptor so as to view the parts in relation to each other. This is
shown in the accompanying illustration taken from a camera lucida
drawing. It is seen that the membrane of the wing, located next to
the second cubitus vein (1) is folded in such a manner as to form a
pocket with a narrow slit-like opening (2). There is a small opening
(3) between the cavity of the second cubitus vein and the cavity which
is enclosed by the upper and lower wing membranes (4) and now
forming the roof of the receptor. The chitinous membrane (5) of the
roof of the receptor is of the same thickness as that of the adjacent
vein, and it remains thick until after it has curved into the cavity of
the receptor, at which point (6) it becomes extremely thin—so thin, in
fact, that it is difficult to detect in gross section. I refer to this flap-like
portion of the receptor as a lip. This very thin membrane forms the
wall (7) of the receptor cavity. It will be noted that it becomes thick
again just prior to union with the wing membrane (8).

Attached to this thin membrane and with peg-like bases that pene-
trate into it, are numerous small black scales set into goblet-like
structures, which structures I would term poscula (sing. posculum )
from the latin meaning a goblet. There are also a few hair-like scales
that are set into minute pores located in the centre of saucer-like
structures, which structures I would term patellae (sing. patella) from

10 R.O.M., Z. AND P. CONTRIBUTIONS

the latin meaning a saucer. Many of these patellae do not posses scale-
like hairs. The thin membrane lying between the poscula and patellae
is thrown into shallow irregular folds.

A fluid, originating in the second cubitus vein, passes through the
minute opening (3) and fills the cavity (4) where it becomes trans-
formed into a white, spongy, wax-like substance. If the second cubitus
vein, or the roof of the receptor, is punctured with a fine pin, the fluid
will flow out and, on coming in contact with the air, will form a white,
wax-like covering on the pin identical to that found on the floor of the
receptor.

If the receptor taken from a live male is dissected under the micro-
scope it is quite easy to remove the white, waxy substance from it. If
this substance is placed in chloroform it immediately dissolves, ex-
hibiting no cellular structure.

Anal Scent Glands

As I have pointed out above, if the apex of the abdomen of the male
is squeezed a pair of finger-like, bright yellow glands will appear.
These glands, which I have termed anal scent glands, are covered with
very long, light brown hairs. When first extruded the hairs are clumped
together forming a stiff, brush-like structure, but when fully extended
the hairs stand out at almost right angles to the surface of the gland.
Accompanying the extrusion of the glands there is a decided flower-like
perfume produced. By squeezing the abdomen firmly, a portion of the
rectal tissue is forced out which, like the anal glands, contains a yellow
fluid and yellow tissue. The yellow fluid oozes through the thin mem-
brane producing a large yellow drop. When this liquid is smeared on
the fingers the flower-like odour is very strong.

Position of Scent Repectors on the Wing in Relation to the Tip of the
Male Abdomen

There are many places on the hind wings, as well as on the front
wings, where the so-called “scent glands” might be located. It is in-
teresting to note, however, that they are located on the upper surface
of the hind wings in a position such that they can be readily touched
by the tip of the abdomen, as I have indicated in the accompanying
illustration which was drawn to scale by tracing the outline of the
wings and the abdomen. The fact that these structures are so located
in relation to the tip of the abdomen may be readily demonstrated by
bending the abdomen of the male slightly and moving it to the right
or left.

The scent receptor is a pocket-like structure formed by a folding of
the wing membrane, as outlined above. If the function of this structure

URQUHART: SCENT RECEPTORS IN LEPIDOPTERA Ll
was simply that of producing a secretion that attracted the female, then
the opening could face in any direction. However, the slit-like opening
faces the abdomen and is so located that the tip of the abdomen can
be quite easily pressed against it.

Experimentation

A portion of the wing, bearing a scent receptor, was taken from a
live male and placed under the microscope. The tip of the abdomen
of the male was pressed so as to produce a drop of yellow liquid from
the rectal tissue. Using a fine dissecting pin, the drop was taken from
the tip of the abdomen and placed at the opening to the scent
receptor. Within a few seconds the drop of liquid had been absorbed
by the scent receptor. Dissection of the latter showed that not only
were the scales within the receptor covered with the fluid but the
underlying wax-like material had also absorbed it.

The experiment was repeated, using a drop of water. The drop
remained in a spheroidal shape and was not absorbed.

Summary

From the above discussion the following may be deduced:
1. The female is not attracted to the male.

2. The male pursues the female in areas where flowering plants are
present.

3. Following the nuptial flight the female follows the male.
4. The proboscis of the female is uncoiled as if attempting to feed.

5. A male awaiting a female may be seen to raise the abdomen so
that the tip of it comes into contact with the scent receptors.

6. A fluid, produced by anal glands and the tissue (perhaps from
rectal papillae?) of the rectum, bears a flower-like odour, which
is most noticeable during the mating season.

7. A flower-like odour appears to be present on the wings during the
mating season but is much fainter than that from the anal glands
and rectal tissue.

8. A wax-like substance of a spongy nature, soluble in chloroform, is
present in the scent receptor and is derived from a fluid origi-
nating in the second cubital vein. This fluid is believed to be
derived from the thorax and conveyed to the receptor by the
cubital vein.

9. The odoriferous fluid from the anal glands and rectal tissue is
absorbed by the scent receptors.

12 R.O.M., Z. AND P. CONTRIBUTIONS
Conclusion

It is concluded that the so-called “scent glands” located on the
hind wings of the male Monarch butterfly are actually “scent re-
ceptors’ receiving the odoriferous fluid from the anal glands and
rectal tissue and that the specialized scales become coated with the
fluid and at the same time direct it to the poscula and patellae where
it enters through minute pores in the thin chitin into the absorbent
material beneath.

Purpose of Scent Receptors and Function During Mating

In most species of animals the male is attracted to and pursues the
female. That this has an important function in maintaining a vigorous
species has long been realized. The stronger male of those contending
for a given female usually succeeds in final copulation. The female,
in contrast, shows little or none of this aggressiveness and hence, we
may assume, does not possess a positive urge towards copulation.

Confining our discussion to the Monarch butterfly: The male,
being the aggressor, pursues the female. Since copulation cannot take
place during flight, it is necessary for the male and female to come
to rest together. The female, possessing no inclinations towards copu-
lation, would continue in flight. In order to lure, as it were, the female
to rest, the male produces, from anal glands, a substance that, in so
far as the human olfactory organs are concerned, resembles the odour
of flowers. The female, surrounded by this aroma produced during the
mating flight is attracted to it and hence follows the male to the place
of his choosing. Alighting upon the leaf of a plant, the female
seeks the origin of the aroma, hence the reason for the uncoiling
of the proboscis, and while she is so involved the male is able to
seize the tip of the female’s abdomen with his strong chitinous, jaw-
like claspers. Having thus secured the female, copulation can take
place. It is obvious why the male does possess such powerful clasping
organs, strong enough to bear the weight of the female while he is
in flight.

The scent receptors perform a most interesting function in the
mating role. While engaged in the nuptial flight the anal glands may
be extruded, thus producing a heavy aroma of flowers. The anal
glands may remain extruded while he fans his wings in front of the
female when she is resting upon the surface of the leaf. Once the
male attempts to secure the tip of the female’s abdomen with his
claspers, however, the anal glands must be retracted. When the anal
glands are retracted the aroma of flowers would also dissipate. In
order to continue to surround the female with the aroma, a small
quantity of the fluid is introduced into the scent receptors and these

URQUHART: SCENT RECEPTORS IN LEPIDOPTERA 13

then take over for the brief period when clasping, prior to copulation,
is taking place. The fluid is introduced into the scent receptors most
likely during the strutting and fanning phase just prior to clasping,
although, as pointed out above, it is not unusual to see the operation
in progress while the male is awaiting the arrival of a female.

I have pointed out that in some species there is simply a cluster
of scales or hairs which perform the same function and hence are
scent receptors. The Monarch butterflies, and other genera of the
same family, possess a more specialized structure. Although acting
in a like manner to that of clusters of hairs or scales, these specialized
receptors possess a spongy material which acts like a blotter, and, in
order to retain the fluid producing the odour for a longer period of
time, the receptor is covered with a roof of scales as well as a heavy
chitinous membrane. This arrangement permits a longer period of
time for the male to grasp the female. The liquid applied to exposed
hair or scale clusters would volatilize much more rapidly than that
contained in such a pocket.

We can now more readily understand why specialized hair clusters
and scales are usually located on the hind wings within easy reach
of the tip of the abdomen. We can understand the reason for de
Niceville’s observation, recorded in the Journal and Proceedings of
the Asiatic Society of Bengal, vol. 41: “The males (Euploeinae) may
often be observed patrolling a small aerial space, with the end of the
abdomen curled under the body toward the thorax, and with the two
beautiful yellow anal tufts of long hairs distended to their fullest
extent at right angles to the body.” It also explains the observation
of Miller that in D. erippus “a very small portion of the wing, close
to the orifice of the sexual cavity, was entirely denuded of scales as
if they had been repeatedly rubbed away by introducing something
into the slit.” In this species, the area referred to is slightly concave,
forming a cup-like depression which received the drop of fluid from
the anal glands and hence is a further specialization as compared to
that found on the wing of the Monarch butterfly. It also explains why
in some butterflies a patch of scales on the hind wings may be covered
by a similar patch on the underside of the front wings because this
mechanism would assist in preventing rapid volatilization of the scent-
producing fluid until it was needed, and this interpretation would
account for the presence of a strong odour when the wings were
separated. Finally, the present interpretation will, I feel confident,
explain many of the observations which have been made relative to
the mating flight (as in the case of the graylings) of many species
of butterflies, the presence of hair and scale clusters on parts of the
body, and the presence or absence of odours during certain seasons
of the year and under certain conditions as here outlined.

14 R.O.M., Z. AND P. CONTRIBUTIONS
Bibliography

Many papers have been published concerning the presence and
possible function of the scent receptors on the wings of butterflies.
For a summary of pertinent information and discussions I suggest
the following two publications.

LOnGSTAFF, G. B.

1912. Butterfly hunting in many lands. Longmans, Green and Co., New
York.

SCUDDER, S. H.
1889. Butterflies of the eastern United States and Canada, vol. 1. Published
by the author, Cambridge, Mass.

URQUHART: SCENT RECEPTORS IN LEPIDO?PTERA 15

PLATE I

Scales: 1-6 from wing membrane near opening to scent receptor; 7—8 from exterior
roof covering of scent receptor; 9-11 from central area of wing; 12 from top of wing
vein; 13 — 15 from inside of scent receptor.

16 R.O.M., Z. AND P. CONTRIBUTIONS

dorsal

scent receptor 2nd cubitus vein

lip ventral

__—-patella

Sac. 1S
ae base of scale
Mi
Os
TA :
pore 6 hair-like scale

Yl hairs
tip fo
Li a ee

ZZ

scent gland

E

PLATE II

A: transverse section through scent receptor of right rear wing; explanation of numbers
given in text. B: left, lateral view of male Monarch showing position of tip of abdomen
in relation to scent receptor. C: structures located within the cavity of the scent
receptor. D: anal scent gland partly extruded. E: anal scent glands fully extruded.

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