ABSTRACT
The cuticles of four species of isopods, the terrestrial species
rmadillidium vulgare and Porcellio scaber, and the marine species Idotea
montereyensis and Idotea resecata, were examined, focusing attention on whether
or not there is a detectable lipid layer such as occurs in insects which
might aid in water-proofing the integument of these animals. The rates of water
loss over a range of temperatures were compared. A comparison of such rates with
those of animals which had been treated with chloroform, a lipid solvent, is
presented, and the results suggest that similar methods used in the past may
lead to erroneous conclusions. No lipids were detectable in the cuticles with
histochemical techniques. Basic structural similarities and differences in
the cuticles of the four species are given, and the significance of these
results are discussed.
INTRODUCTION
Several researchers have looked at the question of possible
cuticular water proofing in terrestrial isopods, focusing their
attention on the permeability properties of the integuments of the
arthropods (Edney, 1951, 1954, 1968; Warburg, 1968; Bursell, 1955).
Much of their work has been based on earlier studies and methods
used for investigating the same phenomenon in insect cuticles
(Beament, 1945, 1958, 1959; Wigglesworth, 1945, 1948; Holdgate,
1956; Mead-Briggs, 1956). The work on insects typically shows the
presence of a critical transition temperature at which layers of
waxy, lipid material in the cuticle deteriorate and the permeability
of the integument dramatically increases, as evidenced by increasing
rates of water loss from the animals at higher temperature ranges
(Wigglesworth, 1918). Although such waxy layers have been reported
present in the epicuticle of many of the insect species for which it
was tested, the evidence for such layers in isopods is less con¬
vincing and the results have been subject to several conflicting
interpretations (Bursell, 1955; Edney, 1957). Often the approach
utilized has been to note changes in the rates of water loss in
insects and isopods after lipids present have been removed by
treatment with lipid solvents, but such evidence which only shows
the resulting increase in the rate of transpiration does not seem
substantial enough to credit water-retaining properties of the
animals solely to the presence of lipids in their cuticles.
Only a few observations have been reported on the actual
substructure of the isopod cuticle (Bursell, 1955), although many
generalized descriptions of the arthropod cuticle have been given
(Richards, 1951; Dennel, 1961; Lockwood, 1967). A visual examination
of the cuticles of several species may reveal characteristics which
could account for any differences or similarities in the rates
of water loss among these animals The presence of a water proofing
layer could be tested histochemically.
The purpose of this study was to re-examine some of the
water-retaining properties of several species of isopods. To determine
whether or not any such properties are inherent to isopods, suggesting
they might be considered as a form of pre-adaptation for their
invasion of land, species representing quite different habitats
were compared. Armadillidium vulgare Latreille (1804) is a terrestrial
species capable of withstanding dry conditions, and is typically
found where a Mediterranean climate prevails. Porcellio scaber Latreille
(180h) is found in more humid terrestrial environments (Miller, 1938).
Idotea (Pentidotea) montereyensis Maloney (1933) is found on algae
primarily in the intertidal regions, where it may face partially
exposed conditions (Menzies, 1950), and Idotea (Pentidotea) resecata
Stimpson (1857) occurs on Macrocystis and was studied to represent
one of the truly marine species of isopods (North, 1971).
The investigation was conducted in two parts. The rates of
evaporative water loss were examined with each species for a series
of temperatures to get an idea of their relative water retaining
properties. An examination of the structure of the cuticle of each
species was undertaken simultaneously to determine the basic
characteristic of their cuticles and to note any significant differences
between the species. Suspecting that waxy substance, or lipids,
might be in part responsible for any permeability shown by the
cuticles, the effects of a lipid solvent on the rates of transpira¬
tion and on the substructure of the cuticle were examined.
MATERIALS and METHODS
Animals: Specimens of the terrestrial isopods A. vulgare and P. scaber
were collected from Carmel Valley and Pacific Grove, Monterey County,
California. The marine I. montereyensis was obtained from Dillon
Beach, Marin County, California, and from along the Pacific Grove
coastline south of Monterey Bay, while I. resecata was collected from
Monterey Bay in the vicinity of Hopkins Marine Station. Prior to the
experiments, the terrestrial animals were kept in large containers at
a humidity of 90% and fed on leaf litter and carrots. The marine
species were retained in separate tanks with aerated sea water at
ambient temperature, and either Macrocystis or Phyllospadix presented
as food. All were used within a week of being collected.
Water Loss: The rates of water loss over a range of temperatures were
determined for each of the four species. At least ten animals were
used for each data point, except in the experiments on 1. montereyensis
where only eight and five animals were used at each temperature when
determining the rates of dead and live animals. Only intermolt male
animals of approximately the same size were used, with the following
average weights: A. vulgare, 70 mg; P. scaber, 10.1 mg; L. montereyensis,
66.5 mg; and I. resecata, 79.h mg. The animals were first weighed
individually on a Mettler balance and then placed in cylindrical
containers sealed with mesh at both ends. The containers were set
inside a dessicating chamber such that none were stacked on top of
each other. The low humidity of the chambers was achieved by using
Drierite (anhydrous calcium sulfate) and was checked during the experi¬
ment with cobalt chloride indicator papers (Solomon, 1915) to be
less than 10%. The temperature of the dessicating chambers was maintained
by placing them in a regulated temperature cabinet and the temperature
was recorded during each experimental run. The temperatures generally
used were 53 253 293 38, and 50 C. The animals were re-weighed
at the end of an hour's exposure to such conditions, and the weight
loss was recorded.
The surface area of the experimental animals was calculated
for each species by tracing the outline of the outspread animals onto
graph paper using a dissecting microscope with a camera lucida
attachment (Wigglesworth, 1945). The following average figures were
used for each of the given species: A. vulgare, 1.5 cm ; P. scaber
1.38 cm ; I. montereyensis, 1.1 cm; and I. resecata, 1.83 cm".
The rates of water loss were calibrated and expressed as mg/cm/ hr.
To reduce the amount of extraneous surface water initially
clinging to them,,the aquatic animals, both live and dead, were blotted
with paper towel ing and dried slightly with an air stream in a uniform
manner, before the initial weighing. This method was checked for its
accuracy and uniformity by re-wetting and weighing the same animal
several times. For experiments on dead animals, the isopods were
killed by exposure to ammonia vapors for roughly fifteen minutes,
and then used immediately to determine the rates of water loss
(Bursell, 1950).
In order to compare the effects of a lipid solvent on the cuticle
of isopods and to test for the removal of such lipids, the animals
were refluxed in chloroform for 2 hours (Bursell, 1955; Holdgate.
1956; Mead-Briggs, 1956; Shaw, 1955; Beament, 1955). After filtering
off the chloroform while it was still warm, blotting the animals,
and allowing the chloroform to evaporate until almost no odor could
be detected (Mead-Briggs, 1956), the transpiration experiments were
carried out as noted above.
For comparison the rate of evaporation from a free-water surface
was found by exposing a shallow vial,with known diameter and filled
with water, in the same apparatus (Wigglesworth, 1915).
Histochemistry: Thin hand-cut sections were made of the exoskeleton
of each species. Sectioning was best achieved by first killing the
animal, either by exposure to ammonia vapors or by quickly removing
the head. The peraeopods were carefully removed, and the animal was
frozen with dry ice. The sectioning was done quickly, using razor
blades, under a dissecting microscope. Sections cut without first
freezing were examined as well.
Some of the sections were stained with methylene blue, Sudan III,
and Sudan IV, the latter two stains being specific for lipids. The
methods followed were those given by Pantin (1918) and Pearse (1968).
Whole animals and sections were also stained for the presence of
lipids by placing the material in a dessicator and subjecting them
to the vapors of a dilution of a 2% solution of osmium tetroxide.
Untreated animals, both normal and stained, were compared with those
of the same species which had been treated with chloroform. Inter-
specific comparisons of the cuticles were likewise made. Most of the
descriptions and dimensions which are given refer to sections of the
dorsal part of the thoracic segments of the exoskeleton, as those
were the regions easiest to section and carefully examine.
An additional proceedure called for immersing the whole animals
in a 10% Chlorox solution, followed by 5% potassium hydroxide and
a series of alcohol and xylene baths (Becker & Roudabush, 1912).
The hard, calcified components of the exoskeleton were all that
remained after such treatment; these were examined both as whole
mounts and as sections.
RESULT.
Water loss: The rates of water loss from both live and dead animals
of each species are plotted in Figs. 1-h. Note that there seems to be
no significant difference between the live and dead animals of A.vulgare,
P. scaber, and 1. resecata, suggesting that whatever water-retaining
properties these isopods may have are not due to active mechanisms.
Similar results have been reported by other investigators (Bursell, 1955;
Edney, 1951) working with terrestrial species. The one exception,
that of I. montereyensis, in which the live and dead animals have
slightly different rates, shows the reverse of what might be expected
for the live animals. The deviation is probably due to experimental
error and the size of that particular sample.
The rates of water loss for dead animals of all four species are
shown together in Fig. 5. Note that while there seems to be no difference
between the two terrestrial species and between the two aquatic species,
the differences in the rates between these two groups of animals
are great. The results are simplified and compared with the rates
of evaporative water loss from a free-water surface in Fig. 6. The
differences are what one might expect, since the aquatic forms are
seldom faced with the problems of water shortage. Holdgate (1956)
and Shaw (1955) have reported a similar situation with the rates
for species of aquatic insects being higher than those of the
terrestrial forms.
The rates of water loss by A. vulgare which have been treated
with chloroform are shown in Fig 7 together with the rates of live
and dead animals of that species. Two types of dessication chambers
were set up to determine whether weight loss was truly related to
water loss or whether it might also represent the loss of chloroform -
a heavier and more volatile substance than water. The first set was
identical to those used in the previous experiments; the second set
contained an open vial of chloroform which was used to saturate the
chamber with chloroform vapors and insure that most of the weight
loss recorded was actually due to water loss and not to the evaporation
of chloroform. Note that the rates of the chloroform treated animals
are generally higher and follow the same basic curve when compared
to live and dead animals. The results also show that the rates of
water loss which are recorded from animals following treatment with
such a solvent can greatly be effected by the amounts of the solvent
still remaining in the animals, as evidenced by the discrepency
between the rates figured in which the two different sets of dessicating
chambers were separately used.
Histochemistry: The arthropod cuticle can be seen to have three main
subdivisions. The thin, outer epicuticle is generally quite distinct
from the inner exocuticle and endocuticle, which become very difficult
to correctly distinguish in A. vulgare and P. scaber.
Measurements of the thicknesses of each of these layers were made
for each species, using a compound microscope with a bright field
objective and a calibrated micrometer. The results are given in
Table 1, along with a few values reported for the cuticle thickness
of various insects.
Cross sections of each species are shown simplified in Figs. 8.
and 9. In all four species, the epicuticle is seen to be a very thin,
almost transparent and non chitinous layer. It shows no birefringence
when viewed with polarized light. There is no color reaction of the
epicuticle itself with any of the applied stains. The surface texture
of the species differed. That of P. scaber is notably irregular,
particularily at the posterior region of the thoracic segments, as
is shown in Fig. 10. The surfaces of A. vulgare and P. scaber are
frequently covered with fine setae, which are not birefringent and which
are most easily visible when cross sections are viewed under a
phase contrast microscope. The surface structures of I. montereyensis
and 1. resecata show irregularities as well, particularily on the
epimeral plates. The epicuticle appears to have been laid down in
sheet-like subunits, which are diagrammed in Fig. 11 as they are
seen for a few species viewed under polarized light. Such structures
remain after the treatment of the cuticles with chloroform.
The exocuticle and endocuticle are oftern characterized by
lamellae which run horizontal to the surface of the cuticle. Such
lamellae were visible in all four species, but their thicknesses.
uniformity, and numbers could not be ascertained. Pore and gland
canals could be seen as well, though more easily in the terrestrial
species. Using a phase contrast microscope, the gland canals could
been seen to extend vertically through the entire cuticle, although
they often seemed to be curly rather than extending straight. No
branching of canals was seen in any of the species. With A. vulgare,
small deposits of material were especially visible at the surface
endings of the canals; such endings stained darkly with methylene
blue and osmium tetroxide both before and after treatment of the
animals with chloroform. Such surface deposits are not uniform
throughout the cuticles, but rather are distributed in patches above
regions of darkened material, presumably tanned protein substances.
Theexocuticle and endocuticle of A. vulgare and P. scaber are
almost transparent, can be seen best with a phase contrast micro¬
scope, and show birefringence under polarized light. The endocuticle
of A, vulgare stained with methylene blue, which Schatz (1952) describes
to be a reaction characteristic of several insect cuticles. Red
pigmentation in the exocuticle, and sometimes a green coloration in
the endocuticle, make the layers more distinguishable in the two
marine species. Such pigmentation could not be effectively removed
priof to staining by up to four days exposure to short ultraviolet
light. There are also frequently packed, crystal-like amber structures
in the region between the red exocuticle and the endocuticle in both
of the aquatic species, as are shown in Fig. 9. Such structures
fail to stain with any of the lipid stains and seem to be
birefringent. I could not determine their structure or function.
The changes in the cuticle after chloroform treatment are most
noticeable in cross sections of A. vulgare. The basic, multi-layered
structure remains, but the pore canals and lamellae are more visible,
and it appears as if the canals may be wider. Of particular note is
the amber or dark colored material which can be seen to fill the canals
in the endocuticle to a line which is uniformly horizontal with the
surface of the cuticle, as is shown in Fig. 12. Such a phenomenon
is never visible in the normal, untreated cuticle, and it seems as
if the material beneath the integument is being drawn up through
the cuticle via the pore canals. Staining with Sudan III and IV
shows no lipids in the cuticle, either before or after treatment
with chloroform. There is considerable staining in areas just beneath
the cuticle, even after chloroform treatment, indicating that
lipids are present there and are not completely removed by the chloroform.
DISCUSSION
Whether or not there is a specific critical temperature at
which the water proofing breaks down in isopod cuticles, such as
those temperatures suggested by Bursell (1955) and others is still
disputable (Edney, 1964, 1968; Lindqvist, 1972; Beament, 1958)
and certainly the presence or suggestion of such points is not
adequate criteria for the presence of a waxy layer which controls
the permeability of the cuticles (Edney, 1957), although investigators
in the past have frequently maintained such conclusions. The increased
rates of water loss in the terrestrial isopods A. vulgare and
P. scaber between the 30 - 50 C temperature range could reflect the
breakdown or activation of some other structural component of the
cuticle, thereby increasing the permeability of the integument. Most
of the evidence points toward such a process as being passive.
although recent experiments by Lindqvist (1972) using different
approaches suggest that temperature effects on other body parts.
such as the ailmentary canal and discharges by it, are perhaps
more accountable for changes in the rates of water loss than are
changes in the permeability of the integument.
Lipids suspected to be active in the water proofing of the
cuticle can be extracted with solvents such as chloroform and ether
(Bursell, 1955; Richards and Korda, 1948). The rates of water loss
after such treatment is usually found to be greater than the rates
of untreated animals, as shown in this study using A. vulgare (Fig 7).
Increases in the transpiration rate after a similar treatment have
been reported by experimenters working with insects as well as isopods
(Beament, 1945, 1955; Wigglesworth, 1945; Holdgate, 1956; Klinge,
1936; Umbach, 1934), but usually the increase in transpiration
is shown for only one temperature point. When one graphs the rate
of water loss versus temperature for a wide range of temperatures, the
results show higher transpiration rates by the chloroform treated
isopods, but the shape of the graph is almost identical with that
which depicts the rates of untreated live and dead animals.
The greater weight losses by chloroform treated animals which have
been reported and interpreted to be due to increased water loss
resulting from removal of lipid waterproofing and the subsequent
greater permeability of the integument may in fact only reflect the
loss of chloroform by these animals. To test this, dessicator chambers
saturated with chloroform vapors were used, and the results indicated
that it is indeed difficult to distinguish in such experiments the
difference between water loss and the loss of the heavier compound,
chloroform. Because of this, and the possibility that chloroform
may have a variety of other effects on the structure of the
whole animal, data which has been reported relative to chloroform
treatment and increased transpiration rates seems questionable.
Such greatly increased transpiration rates following solvent treat-
ment may not be more than an artifact of the methods used.
Cross sections of the cuticles reveal distinct differences
among the four species examined, although there seem to be a few
categorical differences between the marine and terrestrial forms.
That A. vulgare has the thickest cuticle and is also the most terrestrial
of the isopods studied seems significant. The irregularities in the
surface texture and subunits could be an adaptation for the retention
of water. No lipids were detected within the cuticle of any of the
four species examined, although it is certain that there is a fatty
layer beneath the tuticle in A. vulgare, P. scaber, and I. montereyensis.
Perhaps water proofing is provided by only a small amount of lipid,
such as would form a monolayer or be combined with other structural
components of the cuticle, so as to not be detectable by simple
histochemical methods. Perhaps the water-retaining properties of
the cuticle are not at all dependent on the presence of any lipid.
This study has shown several things with regard to the structure
and function of the isopod cuticle. There is no pre-adaptation
apparent in aquatic species when compared to the terrestrial isopods.
It has not been possible to detect lipids in the cuticle using
histochemical methods. Most importantly, the methods used, adopted
from those cited in past insect and isopod literature, cannot separate
a variety of possible explanations for the results which are obtained
from such experiments. The structural effects of chloroform in
of these animals are uncontrollable, as are the increases in the rates of
measured "water loss", as such values are erroneously obtained
and reflect a weight loss due to both water and solvent evaporation.
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Beament, J.W.L. 1945. The cuticular lipoids of insects. J. Exp.
Biol. 21:115-131.
. 1958. The effect of temperature on the water
proofing mechanism of an insect. J. Exp. Biol. 35:194-519.
1959. The water-proofing mechanisms of arthropods.
I. The effect of temperature on cuticle permeability in
terrestrial insects and ticks. J. Exp. Biol. 36:391-122.
Becker, E.R. and R.L. Roudabush. 1942. Brief Directions in Histological
Technique. Lowa State College Press.
Bursell, E. 1955. The transpiration of terrestrial isopods. J. Exp.
Biol. 32:238-255.
Dennel, R. 1961. The integument and exoskeleton, in The Physiology
of Crustacea. T.H. Waterman, editor. Academic Press, New York.
Holdgate, M.W. 1956. Transpiration through the cuticles of some
aquatic insects. J. Exp. Biol. 33:107-118.
Edney, E.B. 1951. The evaporation of water from woodlice and the
millipede Glomeris. J. Exp. Biol. 28:91-115.
1954. Woodlice and the land habitat. Biol. Rev.
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1957. The Water Relations of Terrestrial Arthropods.
Cambridge Univ. Press.
. 1968. The transition from water to land in isopod
Crustaceans. Am. Zocl. 8:309-326.
Edney, E.B. and J.O. Spencer. 1955. Cutaneous respiration in woodlice.
J. Exp. Biol. 32:256-269.
Klinger. 1936. Arb. Phys. angew Ent. Berl. 3:16-69,115-151. (cf.
Wigglesworth, 1915).
Korschelt. 1923. Der Gelbrand, Dytiscus marginalis. I. Leipzig. (cf. Wiggles
worth, 1918).
Lindqvist, O.V., I. Salminen, and P.W. Winston. 1972. Hater content
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J. Exp. Biol. 56:h9-55.
Lockwood, A.P.M. 1967. Aspects of the Physiology of Crustacea.
W.H. Freeman & Co. San Francisco.
Mead-Briggs, A.R. 1956. The effect of temperature upon the permeability
to water of arthropod cuticles. J. Exp. Biol. 33:737-749.
Menzies, R. 1950. The taxonomy, ecology, and distribution of northern
Californian isopods in the genus Idothea with the description
of a new species. Washmann J. Biol. 8(2):55-195.
Miller, M.A. Comparative ecological studies on the terrestrial isopods
of the San Francisco bay region. U.C. Publications in Zool.
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North, W. J. 1771. The Biology of Giant Kelp Beds (lacrocystig) in
California. Verlag Von J. Cramer.
Pantin, C.F.A. 1948. Notes on Microscopial Techniques for Zoologists.
Cambridge Univ. Press.
Pearse, A.G.E. 1968. Histochemistry: Theoretical and Applied. 3rd edition.
Little, Brown, & Co. Boston.
Richards, A.G. 1951. The Integument of Arthropods. Minneapolis: Univ.
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Richards, A.G. and Korda, F.H. 1948. Studies on arthropods. II. Electron
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Schafz L 1952. The development and differentiation of arthropod
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Shaw, J. 1955. The permeability and structure of the cuticle of the
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Solomon, M.E. 1945. The use of cobalt salts as indicators of
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Waloff, N. 1941. The mechanisms of humidity reactions of terrestrial
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Warburg, M.R. 1965. Water relations and internal body temperature of
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Wigglesworth, V.B. 1933. The physiology of the cuticle and of ecdysis in
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FTGURE CAPTIONS
Figure 1. Rates of evaporative water loss for Armadillidium vulgare, live
versus dead animals. The rates of evaporative water loss are plotted
against temperature. The temperatures used for the live animals were
50, 38; 28, 21, and 6°C. The temperatures used for the dead animals
were 50, 30, 30, 25, and 5°C. Each point represents the average rate
for a given sample, and the respective standard deviations are shown.
Figure 2. Rates of evaporative water loss for Porcellio scaber, live versus
dead animals. The rates of evaporative water loss are plotted
against temperature. The temperatures used for the live animals were
50; 383 29, 2h, and 6°C. The temperatures used for the dead animals
were 503 38, 293 25; and 6° C. Each point represents the average rate
for a given sample, and the respective standard deviations are shown.
Figure 3. Rates of evaporative water loss for Idotea montereyensis, live versus
dead animals. The rates of evaporative water loss are plotted against
temperature. The temperatures used for the live animals were 38,
293 253 and 6 C. The temperatures used for the dead animals were 50;
383 295 253 and 7°C. Each point represents the average rate for a
given sample, and the respective standard deviations are shown.
Figure l. Rates of evaporative water loss for Idotea resecata, live versus dead
animals. The rates of evaporative water loss are plotted against
temperature. The temperatures used for the live animals were 383
293 21, and 5'C. The temperatures used for the dead animals were
50, 38, 29; 24, and 5°C. Each point represents the average rate for a
given sample, and the respective standard deviations are shown.
Figure 5. Comparative rates of evaporative water loss for A. vulgare, P. scaber
I. montereyensis, and I. resecata, dead animals. The rates of evapora-
tive water loss for dead animals of all four species are plotted
against temperature. Each point represents the average rate for a
given sample, and the respective standard deviations are shown.
Figure 6. Patterns of evaporative water loss for typical aquatic and terrestrial
isopod species. The patterns are derived from Figs. 1-5, and
compared to the pattern of water loss at similar temperatures
from a water surface of known area.
Figure 7. Effects of chloroform treatment on the rates of evaporative water loss.
The rates of evaporative water loss are plotted against temperature.
The dashed line represents animals which were treated with chloroform
and dessicated in chambers which were partially saturated with
chloroform vapors initially. The solid line connecting points from
the other chloroform-treated animals represents animals which were
dessicated under normal experimental conditions. The rates of
evaporative water loss from untreated animals, both live and dead,
and plotted also. Each point represents the average rate for
given sample, and the respective standard deviations are shown.
Relative thicknesses of the cuticles of isopods and insects.
Table I.
Figures are given in microns. The range given represents the variability
found in ten animals of approximately the same size.
Cross section views of the cuticle of two terrestrial species of
Figure 8
isopods, A. yulgare and P. scaber. The following key applies.
epi- epicuticle; exo- exocuticle; endo- endocuticle; p-pore or dermal
canal; 1- lamellae; s-setae.
Figure 9. Cross section views of the cuticle of two aquatic species of isopods,
L. montereyensis and I. resecata. The following key applies:
epi- epicuticle; exo - exocuticle; endo- endocuticle; p-pore or
dermal canal; 1- lamellae; c- crystal-like substruces , identity
uncertain.
Figure 10. Irregularities in the surface and contour of the cuticle of P. scaber
Diagrammed are the irregularities typical of the thoracic segments,
Figure 11. Surface views of A. vulgare and I resecata, as seen with polarized
light. Such substructures in the epicuticle or exocuticle differ
with the terrestrial and aquatic forms.
Figure 12. The effects of chloroform on the substructure of the cuticle of
A. vulgare.
30
28
26
24
22
20
c 18
16
14
0
0 12
10
Armadillidium vulgare
• ive
animals
o dead
animals
o
30
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TEMPERATURE
oC
40
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30
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18
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8
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Porcellio scaber
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30
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TEMPERATURE
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44
40
361
30
28
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16
14
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10
8
6
O
dotea montereyensis
olive animals
odead animals
10
30
20
TEMPERATURE
o
40
50
30
28
26
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22
20
18
16
0
14
0
—
12

10

8
O
dotea resecata
e live animals
O dead animals
30
10
20
TEMPERATURE
40
50
• Armadillidium vlgare
O Porcellio scaber
A looted montereyensis
30 A dotea resecata
28
26
24
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18
2

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Q 1O
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TEMPERATÜRE
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—
terrestrial species
— aquatt species
— free-water surface


25
TEMPERATURE
50
44
40
32
28
26
24
22
20
18
16
14
12
10

2
0
Armadillidium vulgare
o live
animals
o dead animals
treated animals
ACHC
AC
treated
C
animals

20
30
TEMPERATÜRE
10
40
exposed
50
SPECIES
Armadillidium
Vulgare
Porcellio
scaber
Idotea
montereyensis
Idotea resecata
SPECIES
Periplanta (adult)
Rhodnius
(abdominal tergites
of adult)
(abdominal tergites
of 5th instar
nymph)
Tenebrio (adult)
Dytiscus larva
ISOPODS
EPÉCUTICLE
EXOCUTICLE
2.4-8 u
15-60 n
8-48 u
1-10
8-16 u
21-10
1-8 u
16-18 u
INSECTS
SOURCE
Richards & Anderson
(1912)
Wigglesworth (1933)
Wiggl sworth (1918)
Korschelt (1923)
ENDOCUTICLE
10-176 n
20-50 u
16-80
24-96 u
TOTAL THICKNESS
10 u
30 u
60 u
u
up to 370
20-10 u
TOTAL
THICKNESS
60-215 u
28-116 u
56-104 u
88-10 u
Armadillidiumvulgare
++
tat-








.
.
.
.
.
::
....:.
.



Porcellioscaber

—






.

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...


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. .....
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. . . .












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..







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.
Cted moiterepess


3


MLE
Ltg
P

Tresecata
doteg
ta






-
s.l.. 0.

—
--



erdo
......
—

—
Porcellio scaber


t


...



.




.
.

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......


......
Armadillidium vulgare
*
l
.


3.


*


.
.
..


.








..






.
dotea resecata








.





.. . ..





.

* . .