/. Embryol. exp. Morph. 86, 191-203 (1985)
Printed in Great Britain. © Company of Biologists Limited 1985
Cautery-induced colour patterns in Precis coenia
(Lepidoptera: Nymphalidae)
H. F. NIJHOUT
Department of Zoology, Duke University, Durham, North Carolina 27706,
U.S.A.
SUMMARY
Cautery of the dorsal hind wing in the butterfly, Precis coenia, induces the formation of a
concentric colour pattern around the site of injury. The induced pattern is identical in
pigmentation to the eyespots that normally develop on this wing surface. This response to
cautery also occurs, though much less dramatically, on the ventral forewing. In addition to
the peculiar response to cautery, the dorsal hindwing of Precis also develops a series of unique
pattern aberrations in response to coldshock. These consist of irregular elongation of the
anterior eyespot along the proximodistal axis of the wing. In the most dramatic aberrations
the eyespot field covers the entire anterior half of the wing surface. An analysis is presented
that attempts to reconcile the effects of cautery on the Precis hindwing with the very different
morphological effects of cautery on the colour pattern of Ephestia kiihniella, described by
Kiihn & Von Engelhardt. Computer simulations reveal that thefindingpresented in this paper,
as well as the classical work on Ephestia, can both be explained by assuming that the site of
cautery becomes a sink for one of the morphogens involved in colour pattern determination.
The experimental findings furthermore indicate that minor perturbations of the wing epidermis
can evoke the physiological conditions that attend normal eyespot determination. It is shown
that this interpretation also helps to explain the unusual pattern modifications following
coldshock.
INTRODUCTION
The colour patterns on the wings of Lepidoptera are determined during the
prepupal and early pupal stages (Nijhout, 1978,19846). Microcautery of the wing
epidermis during the period of pattern determination can induce aberrations in the
colour pattern, and from such aberrations it has occasionally been possible to
deduce the characteristics of the processes underlying pattern determination.
Cautery experiments have shown, for instance, that colour pattern determination
occurs independently on each wing surface (Nijhout, 1978, 1980a). In the moth,
Ephestia kiihniella, development of a banding pattern that runs across the forewing
has been shown to depend on the activity of three inducing 'sources', located on the
wing midline (Kiihn & Von Engelhardt, 1933; Nijhout, 1978,19846). These sources
produce a signal that appears to propagate by diffusion. Cauteries of the wing
epidermis, placed between a source and the presumptive location of a cross band,
cause dramatic alterations in the shape and position of that crossband. Kiihn & Von
Key words: Lepidoptera, Precis coenia, pattern formation, cautery, colour.
192
H. F. NIJHOUT
Engelhardt (1933) have proposed that this is due to the fact that dead, cauterized,
cells pose an obstacle to the propagation of the inducing signal. In the butterfly,
Precis coenia, similar sources, dubbed foci (Nijhout, i978,1984ft), are responsible
for inducing circular eyespot-like patterns on the forewing. When the cells of a
focus are killed by cautery before pattern determination begins, the eyespot fails
to develop (Nijhout, 1980a). In both these cases the effect of cautery on the
morphology of the colour pattern can be attributed straightforwardly to an interference with the normal process of pattern determination: in Ephestia, a local
interference with the propagation of an inductive signal, and in the Precis forewing,
an actual elimination of the source of the inductive signal.
In contrast to the Precis forewing, where cautery has no effect on the colour
pattern unless it is placed on or very near a focus, I have found that a cautery placed
almost anywhere on the dorsal hindwing causes the development of a novel colour
pattern, identical in its morphology to the eyespots that normally occur on that wing
surface. This response to cautery appears to be restricted to the dorsal hindwing of
this species. The present paper describes this apparent inductive effect of cautery.
It also proposes a physiological mechanism for this form of pattern induction that
is not only compatible with the other known effects of cautery, but also helps to
explain a peculiar set of pattern aberrations that develop in response to coldshock
on the dorsal hindwing of this butterfly.
MATERIALS AND METHODS
Larvae of Precis coenia were reared on an artificial diet as described by Nijhout (1980a).
Except as noted, cauteries were done on young pupae, 4 to 6h after pupation. Cauteries were
made with a sharpened tungsten needle, wrapped to within 2mm from its tip with three loops
of nichrome wire and insulated with epoxy glue. Current (DC) was passed through the nichrome
wire to heat the tip of the needle to approximately 100 °C. Since in lepidopteran pupae the
forewing is firmly glued over most of the hindwing, cauteries of any but the dorsal surface of
the forewing must be done blindly by inserting the cautery needle sufficiently deeply to
penetrate the desired epidermal layer. As a rule the needle was inserted so as to cauterize both
surfaces of both fore- and hindwing. Since the forewing is always folded over the hindwing in
the same way, it is possible, after a series of exploratory cauteries, to use landmarks on the
forewing cuticle to locate specific areas of the hindwing with reasonable accuracy. For light
cauteries the needle was held in place for about 1/2 second. More severe cauteries were
accomplished by holding the needle in place for up to 10 seconds. Coldshocks were effected
by placing pupae, 4 to 6h after pupation at a temperature of -2°C for a period of 72 h, as
described by Nijhout (1984a).
Computer simulations of diffusion were done by a finite difference method on a 2dimensional rectangular grid in which any node(s) could be designated as source, sink, or
obstacle for the diffusing substance. The diffusing substance propagated with a diffusion
coefficient of 8 x 10"9cm /sec and decayed with a half life of 12 h. These values were derived
as best fits to experimental data on the dynamics of eyespot determination in Precis (Nijhout,
1980a) and have proven to be useful in simulating the development of a variety of patterns
(Nijhout, 19846 and in preparation). Diffusion was allowed to continue for 48h, which is the
normal period for pattern determination in Precis (Nijhout, 1980a). At that time the gradients
produced were nearly at steady state. Sources were modelled as constant-level sources.
Concentration of the diffusing substances were in arbitrary units, as described in the legend
to the appropriate figures.
Cautery-induced colour patterns
193
RESULTS
Cautery-induced patterns on the dorsal hindwing
Cautery of the dorsal epithelium of the hindwing in pupae of Precis coenia
induces the formation of a concentric colour pattern provided the cautery is placed
in the presumptive brown 'background' area of the wing and provided the age of
the pupa is less than 48 h. Figure 1 illustrates the characteristics of the induced
pattern. Cauteries of short duration which kill few cells induce a circular patch of
black pigment at the site of cautery (Fig. 1A). More severe cauteries induce large
patterns that resemble the smaller of the two eyespots on the dorsal hindwing.
Induced patterns have an outer black ring and a yellow central field, identical in
colour to the black and yellow rings of the normal eyespots. Occasionally the centre
of the induced eyespot also bears a patch of orange and black scales, as does the
central field of a normal eyespot.
When a cautery is placed close to one of the natural eyespots, the black and
yellow rings of the induced patterns fuse with their counterparts in the normal
eyespot (Fig. 1C-E). The confluence of the induced pattern with the rings of the
natural eyespot is always perfectly smooth, which can be taken as an indication that
cautery is somehow either mimicking or evoking the physiological conditions that
are normally associated with determination of the outer (peripheral) portions of the
eyespot pattern.
Cautery can induce eyespots anywhere in the brown background area of the wing
and all points within this area appear to be equally responsive (Fig. IE). Areas of
the hindwing that are overlaid by forewing are no more responsive to cautery than
those that are not, so an interaction of fore- and hindwing in the development of
supernumerary eyespots is unlikely.
Cauteries placed within the black central disk of one of the natural eyespots on
the hindwing either have no obvious effect or cause a diminution in the size of the
eyespot. Likewise, cautery on the margin of the wing, within the presumptive area
of the submarginal bands and parafocal element (see Nijhout, 1984a,b for nomenclature and homologies of these pattern elements), causes a local distortion of those
patterns but does not induce a novel pattern. When a cautery is placed very near
a parafocal element it induces the formation of an incomplete eyespot that is
truncated where it meets the parafocal element (Fig. IF). The simplest explanation
for this finding is that the physiological events that determine the parafocal
elements and submarginal bands can override pattern induction by cautery. It is
unlikely that determination of the parafocal element occurred before cautery and
therefore precluded redetermination by cautery, because cautery can induce considerable distortions in the shape of the parafocal elements, and evidently interferes
with their proper determination.
Effect of cautery on other wing surfaces
I have demonstrated elsewhere that cautery of the foci on the dorsal forewing can
194
H. F. NIJHOUT
Cautery-induced colour patterns
195
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Fig. 2. Effect of cautery on the ventral surface of the forewing of Precis. (A) Normal
colour pattern. (B, C) Distortions of the outer ring and central disc of the large eyespot
towards and around the site of cautery (open circle).
abolish the development of the large eyespot on that wing surface (Nijhout,
1980a). Cauteries elsewhere on the dorsal forewing as a rule have no effect on the
pattern. Among the nearly 1000 specimens whose forewings have been cauterized
during the past 5 years I have encountered only four cases in which cautery induced
an eyespot-like pattern but these were not nearly as well differentiated as those
illustrated above for the hindwing, or as those that form around transplanted foci
(see Nijhout, 1980a). When cauteries are placed on or near the outer dark ring
of the large eyespot on the forewing, however, the shape of the outer band often
becomes distorted so as to enclose the site of cautery, and the central black disk
of the eyespot occasionally develops a bulge in the direction of the site of cautery.
Both these distortions of the eyespot are more evident and more readily induced
on the ventral surface of the forewing and are illustrated in Fig. 2. Cautery
elsewhere on the dorsal or ventral surface of the forewing has no effect on pattern
development.
Cauteries of the ventral surface of the hindwing induce substantial distortions of
the colour pattern but do not induce eyespot-like patterns. Cautery-induced pattern
Fig. 1. Effect of cautery (arrows) on the pattern of the dorsal hindwing of Precis. (A)
Small black-pigmented spot induced by a cautery of very short duration. (B) Larger
eyespot induced by a more severe cautery. (C, D) When cauteries are placed close to
the normal eyespots the black and pale areas of the induced eyespot fuse smoothly with
those of the normal eyespots. (E) A series of cauteries across the wing shows that
different areas of the wing are equally responsive. (F) Cautery placed near a parafocal
element (pfe; this is a chevron-like pattern that parallels the wing margin and is repeated
in each wing cell), induces an eyespot whose distal portion is truncated by the peak of
the parafocal element, smb, submarginal band.
196
H. F. NIJHOUT
modification on the ventral hindwing can be quite complex and will be described
at a future occasion.
Development of an eyespot-like pattern around the site of cautery thus appears
to be an invariable characteristic of the dorsal hindwing. The cautery-induced
distortions of the eyespots on the forewing may be low-level manifestations of the
same phenomenon, somewhat more readily expressed on the ventral than on the
dorsal surface. The differences in the response of the various wing surfaces to
cautery may simply be due to the fact that their development is asynchronous so that
at any one time they are not in equivalent stages of colour pattern determination.
On this assumption, the forewing would be expected to pass through a stage in
which eyespots could be induced by cautery some time prior to pupation. On the
other hand, the various wing surfaces may simply differ in their threshold to the
'cautery-response', so that cautery only evokes a morphological effect in regions
where this threshold is quite low. This latter view seems at this time to be the most
reasonable, as will be discussed below.
Co Idshock-induced pattern aberrations of the dorsal hindwing
Coldshock-induced pattern modifications in Precis were described by Nijhout
(1984a), who showed that, for a given wing-cell, the modified patterns could be
arranged in a smooth linear morphocline from nearly normal to highly aberrant.
With the exception of the dorsal hindwing, progressively more affected patterns in
a morphocline always exhibited a progressive diminution in the diameter of eyespots.
The large eyespot on the dorsal hindwing of Precis, however, undergoes a most
unusual modification of shape that has no counterpart on any of the other wing
surfaces, nor have such modifications been seen in any other species I have studied
so far. Figure 3 illustrates several of these patterns. In the least affected individuals
the outer light ring of the eyespot becomes slightly broader than usual (Fig. 3A).
This effect seems to come about through a diminution in the diameter of the central
dark disk of the eyespot though this cannot be tested objectively because there is
natural individual variability in the diameter of the eyespot, and both wings of an
individual are always affected identically. In slightly more severe pattern modifications the dark and light outer rings of the eyespot become extended proximally or
distally, or in both directions, depending on the individual (Fig. 3B-D). More
dramatic aberrations also affect the central disc of the eyespot, which tends to
Fig. 3. Coldshock-induced pattern aberrations on the dorsal hindwing of Precis. (A)
Least affected pattern consists of a widening of the pale outer ring of the large anterior
eyespot (cf. normal eyespot in Fig. 1A). (B, C, D) Three examples of distortion of the
peripheral portion of the large eyespot. Extension of the outer rings may be proximal
(B), distal (C), or anterior (D), and there is a tendency for elongation of the pattern
along wing veins (D). (E, F) In the most severe aberrations the eyespot becomes
expanded to encompass nearly the entire anterior half of the wing. The morphology of
the small posterior eyespot is seldomly affected by coldshock.
Cautery-induced colour patterns
3A
^.••'.•H";.v.
197
198
H. F. NIJHOUT
become extended proximally, and at least part of the outline of the eyespot
becomes smeared out and indistinct. In the most extreme cases the entire anterior
half of the hindwing is set off from the posterior half by a broad black streak,
homologous to the black outer ring of the eyespot (Fig. 3E, F).
In contrast to the coldshock-induced pattern modifications of the other wing
surfaces (Nijhout, 1984a), those on the dorsal hindwing could not be arranged into
a smooth morphological series. As a general trend, there is a progressive elongation
of the anterior eyespot along the proximodistal wing axis (evident in Fig. 3A—»E),
but out of some 40 moderately to severely affected individuals, no two resembled
each other either in detail or in overall shape of the pattern modification, which
suggests the operation of a pattern generating mechanism with a relatively large
amount of noise. The aberrant patterns on the left and right wings of a given
individual, however, were always identical or nearly so.
DISCUSSION
Cautery-induced eyespots
The simplest interpretation of the findings presented above and illustrated in Fig.
1 is that cautery somehow mimicks a focus and causes the local synthesis of a
morphogen identical to, or equivalent to, the one normally produced by a focus and
responsible for the formation of native eyespots. This interpretation is, however,
inconsistent with all earlier known effects of cautery on colour pattern formation.
Cautery, when placed on presumptive source cells in the dorsal fore wing of Precis,
clearly eliminates those sources and abolishes development of an eyespot (Nijhout,
1980a). Cauteries placed at other sites of the dorsal fore wing of Precis have no
effect on the colour pattern (Nijhout, 1980a). In Ephestia cauteries cause local
distortions of the pattern which have been interpreted as being due to the fact that
cauterized cells form a local obstacle to the propagation of a pattern-determining
signal or morphogen (Kiihn & Von Engelhardt, 1933; Murray, 1981). While it is
possible that these multifarious effects of cautery (elimination of a source [Precis
forewing], apparent induction of a source [Precis hindwing], apparent obstacle to
signal propagation [Ephestia forewing]), are due to fundamental species- and wing
disk-specific differences in the mechanism of pattern development, it is more likely
that these various effects are simply different manifestations of a common response
to cautery. It is, in fact, possible to construct a single model that can account for all
the known effects of cautery.
If it is assumed that colour patterns are determined at least in part by chemical
morphogens that emanate from discrete sources (Nijhout, 1978,1980a,ft, 1984ft),
and if the hypothesis that cautery induces a local source of morphogen is rejected
as inconsistent with other findings, then four other potential effects of cautery at the
cell and tissue level are plausible and may be considered in formulating a
hypothesis. 1) Cautery could cause the local destruction of a morphogen as an
incidental response to wounding or wound healing. The site of cautery would then
Cautery-induced colour patterns
199
behave as a sink for morphogen. 2) Cautery could locally alter the sensitivity of cells
to morphogen. Such a local raising or lowering of a threshold could lead to distortions of the colour pattern. 3) Cautery could cause a local delay in development and
determination while would healing takes place. Finally, 4) cautery could simply kill
cells, making them incapable of producing, transmitting or destroying morphogen.
This is the hypothesis Kiihn & Von Engelhardt (1933) used to explain the effects
of cautery on pattern modification in Ephestia.
The first two hypotheses may be different aspects of the same mechanism. In
general, the threshold of sensitivity of cells to a given substance will be set by the
concentration (and binding affinity) of other chemicals in the cell with which the
first reacts. The distribution of such a threshold-determining substance represents
what I have called the interpretation landscape (Nijhout, 1978,1984ft). In order to
produce a circle from a point source, it is necessary that the interpretation landscape be flat, which is to say, that the substance with which the local morphogen
interacts be homogeneously distributed at some finite concentration.
The cautery-induced eyespots on the hindwing (Fig. 1) and the distortions in the
shape of the fore wing eyespot (Fig. 2) can be readily explained by assuming that
cautery causes a local depletion of the substance that makes up the interpretation
landscape. Figure 4 shows the result of a computer simulation based on this
hypothesis which mimicks the morphological effects of cautery reasonably well.
The third hypothesis, that cautery and wound healing cause a local delay in
determination is not, in principle, unreasonable. Such a developmental delay could
result in the formation of an eyespot if it occurred in the presence of a continually
rising level of morphogen, and if the delay was somehow graded from the site of
cautery outwards. Morphological evidence, however, does not provide evidence
for such a delay. Scale development, which begins immediately after the period for
colour pattern determination (Nijhout, 1980ft), is synchronous at the site of cautery
with scale development elsehwere on the wing, as is the initiation of pigment
synthesis. Furthermore, if such a model is also to be used to explain the effect of
cautery on the colour pattern of Ephestia (see below), many of the assumptions
must be reversed (e.g. either the cautery must accelerate determination, or the
sources of Kiihn & Von Engelhardt must be sinks).
The differences in the observed responses to cautery and coldshock on forewing
and hindwing are unlikely to be due to differences in the timing of equivalent
developmental stages on each wing surface. Other developmental events such as
mitosis, which coincides with the period of colour pattern determination, and scale
differentiation and pigment synthesis, which follow shortly thereafter (Nijhout,
1980ft), are synchronous on both wing surfaces and there is no a priori reason for
believing that colour pattern determination would be uniquely asynchronous.
Furthermore, I have done cauteries of the dorsal forewing over a broad time span,
from the moment of pupation to 36 h after the termination of colour pattern determination (Nijhout, 1980a), and I have recently done surgery on imaginal disks in
situ at times from 12 h to 4 days prior to pupation, and at no time have I observed
200
H. F. NIJHOUT
Fig. 4. Computer simulation of cautery-induced pattern formation in Precis. Star marks
position of a constant-level point source for morphogen, the focus, set at an arbitrary
concentration of 1000 units. The interpretation landscape, initially flat, is set at 100
units. Open square marks location of sink in interpretation landscape. Pattern is plotted
where ratio between focal gradient and interpretation landscape is 0-7 ± 0-2.
effects that even remotely resemble the induced eyespots on the dorsal hindwing.
Since the hindwings are susceptible to eyespot induction for at least a 24 h period
it should have been possible to detect an equivalent period for the fore wing, if it
existed. Likewise, coldshocks have been done on animals from 24 h prior to pupation to 48 h after pupation. Both forewing and hindwing were found to have the
same sensitive period for the induction of colour pattern aberrations (0 to 24 h after
pupation), and in hundreds of coldshocked animals I have never found morphological aberrations of the forewing eyespot that resemble those of the eyespot on the
hindwing (Nijhout, 1984a). Differences in the responses of forewing and hindwing
to cautery and temperature shock are thus probably not simply due to asynchronies
in pattern development on these two surfaces. On the model presented above one
would have to assume that the effectiveness of the cautery-induced sink differed on
fore and hindwing.
The case of Ephestia
Cauteries on the wings of Ephestia have an effect on the colour pattern that
appears to be the exact opposite of what I have described above for Precis. Whereas
Cautery-induced
colour patterns
201
Fig. 5. (A) Two drawings of the effect of cautery on the banding pattern of Ephestia
(redrawn from Kiihn & Von Engelhardt, 1933). In both cases there is a ring of light
coloured scales around the site of cautery, connected by a bridge to the nearest crossband . (B, C, D) Attempts at simulating the effects of cautery illustrated in A. In all three
panels the wing is modelled as a rectangle. Stars represent positions of three sources
elucidated by Kiihn & Von Engelhardt (1933; see also Nijhout, 1978, 19846). The
source levels were set at 1500 for the anterior (top) source in each panel, 1250 for the
middle source and 1000 for the posterior source. The interpretation landscape is
modelled as a flat plane at a value of 300 throughout. In B the open rectangle models
a barrier to the diffusion of the morphogen produced by the sources. In C and D the
open squares model sinks for the same morphogen. Pattern (black) is plotted where the
ratio between the focal morphogen and the interpretation landscape is 0-5 ± 0-2.
Modelling cautery as a barrier to diffusion does not induce the formation of a ring
around the site of cautery (B). Smaller barriers have even less effect on the morphology
of the banding pattern than the barrier shown in B, which is three times as wide as the
size of the cauteries modelled in C and D. Modelling a cautery as a sink for morphogen
yields a reasonably accurate reproduction of the experimentally obtained patterns
shown in A.
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H. F. NIJHOUT
in Precis the site of cautery becomes enclosed by a ring of pigment, in Ephestia the
course of pigment bands becomes altered so as to exclude the site of cautery from
the central pattern field (Fig. 5A; see Kiihn & Von Engelhardt, 1933, for numerous
illustrations). The pattern alterations in Ephestia have traditionally been ascribed
to the fact that cautery sets up a barrier to the diffusion of morphogen (Kiihn & Von
Engelhardt, 1933; Murray, 1981).
I have simulated the effect of imposing a barrier to diffusion on the morphology
of the pigment bands in Ephestia. These simulations revealed that while the gross
features of the experimental results illustrated by Kiihn and Von Engelhardt (deviation of bands around the site of cautery) are readily mimicked, there are two
morphological details that proved difficult or impossible to simulate, namely, 1) the
development of a border of light-coloured scales (identical in colour to the pigment
bands) around the site of cautery, and 2) the frequent occurrence of a narrow bridge
of light-coloured scales that connects the border around the site of cautery with the
nearest pigment band (Fig. 5A). A ring of pigment that runs completely around the
site of cautery proved impossible to obtain (Fig. 5B), due to the fact that diffusing
morphogen tends to bank up slightly on the proximal (upstream) side of the barrier.
By contrast, when a cautery was simulated as a sink for morphogen, the bordering
ring of pigment around the cautery site was almost always obtained, and a bridge
between it and one of the simulated pigment bands could easily be made to appear
by an appropriate choice of thresholds (Fig. 5C, D). It appears that the effect of
cautery on the colour pattern of Ephestia can be explained better by assuming that
cautery induces a local sink for morphogen than by assuming that it merely presents
a barrier to its diffusion.
Co Ids hock-induced aberrations of the hindwing eyespot
In Precis, cautery of the hindwing usually induces the outer (black and yellow)
rings of the eyespot, and very light cautery induces only a local spot of black
pigment (Fig. 1A), homologous to the black outer ring of the eyespot. Thus fairly
small disturbances in the background field are evidently sufficient to establish the
conditions under which the outer rings of the eyespot are normally induced.
This observation may help explain the erratic development of the outer rings of
the large eyespot after coldshock (Fig. 3). I have previously shown that the development of colour pattern aberrations (phenocopies) after coldshock is due to alteration of a single developmental parameter (Nijhout, 1984a), and that circumstantial
evidence strongly suggests that this parameter is associated with the formation of
the interpretation landscape (Nijhout, 1984!?). If coldshock somehow lowers the
level of the interpretation landscape, and if, as the cautery experiments suggest, the
level of the interpretation landscape in a normal wing is already close to critical for
the determination of the outer bands of an eyespot, then it is possible that after
coldshock the interpretation landscape could fall to a critical level for pattern
induction over wide regions of the wing. The irregular character of coldshockinduced patterns could then be due to irregularities in the normal distribution of the
Cautery-induced colour patterns
203
putative interpretation landscape-morphogen. This interpretation finds circumstantial support in the observation that the size and shape of the eyespots on the
dorsal hindwing of Precis exhibit an uncommon degree of individual variability
(illustrations in Comstock, 1927).
Figure 3 shows that a sector of the wing that contains the smaller of the two
eyespots remains relatively unaffected by coldshock, while cauteries in this area
induce eyespots as effectively as they do elsewhere on the wing (Fig. 1). It is not
clear how this relative stability to coldshock is to be explained. I am unable to detect
a developmental asynchrony between these two regions of the wing, but it is
noteworthy that the demarcation between the affected and unaffected areas,
illustrated in Fig. 3E,F roughly corresponds in position to a compartment boundary
detected by Sibatani (1982) in homeotic transformations of the wings of many
species of Lepidoptera.
I wish to thank Mary Nijhout and Greg Wray for critical comments on the manuscript, Laura
Williams for drawing Figure 5A and for technical assistance with the experimental work, and
Greg Wray for help in writing the interactive features of the computer programs used in this
study. This work was supported in part by the Duke University Research Council and by Grant
PCM-8214535 from the National Science Foundation.
REFERENCES
COMSTOCK, J. A. (1927). Butterflies of California. Los Angeles: Comstock.
KUHN, A. & VON ENGELHARDT, M. (1933). Uber die Determination des Symmetriesystems auf
dem Vorderfliigel von Ephestia kiihniella. Wilhelm Roux' Archiv. EntwMech. Org. 130,
660-703.
MURRAY, J. D. (1981). On pattern formation mechanisms for lepidopteran wing patterns and
mammalian coat markings. Phil. Trans. R. Soc. B 295, 473-496.
NIJHOUT, H. F. (1978). Wing pattern formation in Lepidoptera: A model. /. exp. Zool. 206,
119-136.
NIJHOUT, H. F. (1980a). Pattern formation on lepidopteran wings: Determination of an eyespot.
Devi Biol. 80, 267-274.
NIJHOUT, H. F. (1980b). Ontogeny of the color pattern on the wings of Precis coenia (Lepidoptera: Nymphalidae). Devi Biol. 80, 275-288.
NIJHOUT, H. F. (1984a). Colour pattern modification by coldshock in Lepidoptera. /. Embryol.
exp. Morph. 81, 287-305.
NIJHOUT, H. F. (1984ft). The developmental physiology of colour patterns in Lepidoptera. Adv.
Insect Physiol. (in press).
SIBATANI, A. (1980). Wing homeosis in Lepidoptera: A survey. Devi Biol. 79, 1-18.
{Accepted 9 November, 1984)