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Mitochondria in the intestinal epithelial cells of starved and fed salamanders.

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MITOCHONDRIA IN THE INTESTINAL EPITHELIAL
CELLS O F STARVED AND F E D SALAMANDERS
MYRA A. WILLIAMS
Department of Zoology, Duke University, Durham, North Carolina
TWO PLATES (THIRTEEN FIGURES)
INTRODUCTION
Numerous investigations have been made on the relation of
mitochondria to digestion and absorption. Animals from all
the vertebrate classes have been utilized in these studies, but
the results obtained are divergent and non-conclusive. The
present study of the absorptive cells of the intestinal mucosa
of Triturus pyrrhogaster attempts to throw more light on the
mitochondria1 changes by carefully controlling the nutritional
conditions of the animals. At the same time the fat content
of these cells was studied to determine whether it might be a
factor involved in the changes.
MATERIALS AND METHODS
For this investigation ninety-one specimens of Triturus
pyrrhogaster (Japanese salamander) were used. The animals
were fed earthworms for 3 to 4 weeks before experimentation
began. The well-nourished animals, killed by decapitation at
intervals of 3 to 24 hours following the time of feeding, served
as controls ; twenty-six specimens were killed after starvation
for 2,3,7,10,14,30,60, and 120 days. Sixteen animals starved
for 2 weeks were re-fed f o r 4 days. These animals were killed
at intervals of 4 to 24 hours after feeding. Of the animals
starved for 1 month, 4 were re-fed once, 4 for 4 days, and 4
were fed until the weight lost during starvation had been
regained. This required from 7 t o 15 days.
195
196
MYRA A. WILLIAMS
Each animal, after being slightly dried with a paper towel,
was weighed before being killed; also its total length and tail
length were recorded. Animals which were starved were
weighed a t the beginning and at the end of the fast; those refed were weighed again at the time of killing. The general
condition of the animal, the size of the f a t bodies, and the
degree to which food appeared digested were noted. The
digestive tract was clipped out, its length measured, and pieces
about 10mm. long were immediately fixed in Regaud's solution (Lee, p. 308). F o r mitochondria1 study two pieces of
intestine were taken a t 1.5 em. and at 5 to 7.5 em. posterior
to the pylorus. A n intermediate piece was preserved in
Regaud's solution and stained with Sudan I11 to show fat.
Tissue preserved for mitochondria was cleared in xylol, enibedded in paraffin, and sectioned transversely a t 3 or 4
microns. The material used for study of fat was embedded
in 20% gelatin and sectioned at 12 microns with a freezing
microtome. Regaud's o r Heidenhain's iron hematoxylin stains
were used f o r mitochondria.
F o r determination of the amount of water in the intestine, a
piece was taken from the posterior end of the intestine,
weighed in a dish on analytical balances, dried at 33" to 35" C.,
reweighed, and the percentage of water determined.
OBSERVATIONS
Well-nourished animals (co+ztrols). I n the amphibian intestinal mucosa only two types of cells are recognizable, the
absorptive and the goblet cells. The investigation is concerned
chiefly with the absorptive cells. I n the well-fed animals,
regardless of the length of time after feeding, the mitochondrial picture of the epithelial cells shows no significant variation. The mitochondria a r e present as (1)rings, both round
and oval; (2) granules of all types, many of which a r e connected to form a dumb-bell shaped rod; and (3) filaments and
rods, some of which have thickened regions and occasional
blebs (figs. 1 and 2). If only a few filamentous mitochondria
a r e found present in the cells, the rods, spherules, rings and
MITOCHONDRIA I N SALAMANDER INTESTINE
197
dumb-bell forms are numerous, and the short filaments present
are curved, wavy, or beaded (fig. 1).If long filamentous mitochondria predominate there are fewer rings, dumb-bell forms
and short filaments (fig. 2). The distribution of mitochondria
is similar in the cells of all the well-fed animals. The cells
may, for convenience in description, be divided into zones as
follows: zone 1 extends from the intestinal lumen to about
midway between the lumen and the nucleus; zone 2 extends
from zone 1 to the nucleus; zone 3 is the region around the
nucleus; and zone 4 the region below the nucleus (fig. I).
Zones 1 and 2 comprise the supra-nuclear region, zone 4 the
sub-nuclear region.
Mitochondria are evenly distributed throughout zones 1and
2, with occasionally a very slight aggregation in zone 1. The
granular forms are usually more numerous in zone 1. Filaments are generally parallel to the long axis of the cell
(fig. 2). I n zone 4 the numerous mitochondria are mostly
rods and granules with fewer rings and filaments than in the
supra-nuclear cytoplasm.
The Sudan I11 tests for fat revealed either light orange
droplets (fig. 3) or a diffuse yellow coloration of the cells. The
quantity of fat is rather small in all these specimens. I n some
specimens #thefat in concentrated in zones 2 and 4 (fig. 3),
in the other specimens it is distributed throughout the cytoplasm of the absorptive cells of both the folds and the crypts of
the intestinal wall (fig. 4). I n addition t o mitochondria and
fat drops other granules occur almost universally in the supranuclear cytoplasm but are seldom observed in the sub-nuclear
cytoplasm. These granules range in size from the diameter
of the spherical mitochondria t o that of large nucleoli; with
iron hematoxylin they are stained black.
Starved animals. During starvation the body weight of an
animal constantly decreases, while at the same time the
per cent of water in the intestine increases; the fat bodies
and liver decreases progressively in size; and the digestive
tract decreases in length and diameter, with a corresponding
reduction in the number of intestinal folds. The liver in addi-
198
MYRA A. WILLIAMS
tion to becoming thinner, grows much darker in color. The
gall bladder is always filled with bile and often bile clots
appear i n the gut lumen. Histologically, there is a n increase
in the number of goblet cells in the mucosa of the intestine,
a thinning and increased homogeneity of the striated border,
and a loss of staining capacity by the epithelial cells. I n
animals starved for 4 months almost every second cell is a
goblet cell.
The absorptive cells of animals starved for 2, 3, and 4
months a r e much smaller than the controls ; the cytoplasm has
shrunk relatively more in volume than has the nucleus (cf.
figs. 2 and 5). The mitochondria have decreased somewhat in
size; the filaments a r e thinner and fainter and the granules
a r e smaller. Filaments with looped ends, blebs, or thickened
places a s well as ring-shaped mitochondria are infrequent.
I n zone 1 of the cytoplasm only granules occur, frequently
associated in chains. The filaments are always short and occur
in zones 2 and 3. Some of the filaments are beaded, others have
a granular enlargement at each end. Scattered among the
filaments a r e granuies. The mitochondria of zones 2 and 3 are
less compact than in zone 1. Zone 4 contains fewer mitochondria than in the controls (fig. 5). I n the cells of animals
starved 7 to 10 days filamentous mitochondria predominate
(fig. 6) ; after 14 to 30 days granules predominate (fig.7).
Some fat appears in the intestinal epithelial cells of
practically all the starved animals. It is in a diffuse condition
in the cells of all the mucosal crypts and folds. The dark granules previously described appear in the cells of nearly all of
the starved animals. However, they are fewer than in the
cells of the well-fed specimens. Animals starved for 1 to 4
nioiitlis show fewer of these than animals starved for a shorter
period of time.
R e - f e d animals. Re-feeding of starved animals results in a
restoration of the mitochondria to the normal (well-fed) condition. The granular mitochondria in the cells of the animals
starved f o r 2 weeks and then fed transform into the varied
forms characteristic of the controls. I n like manner some of
M I T O C H O N D R I A I N S A L A M A N D E R INTESTINE
199
the granules, chains of granules, and thin threads characteristic of the animals starved for 1 month change into other
forms when these animals are re-fed.
One re-feeding. Within 2 hours after a single re-feeding a
change is evident in a few specimens in the morphology and
especially in the distribution of the mitochondria. The normal
distribution (numerous basally, evenly distributed supranuclearly) is restored, and ring-shaped mitochondria reappear, as well a s short beaded filaments, and filaments with
terminal loops (fig. 8). By 24 hours after the first feeding,
animals starved f o r 2 weeks display many filaments in the
supra-nuclear cytoplasm (fig. 9). The epithelial cells of most
of the animals starved f o r 2 weeks and re-fed once contain
more fat than the normal animals. This is generally distributed throughout the cytoplasm either as a diffuse dark
yellow coloration, or as orange droplets (cf. fig. 10).
Re-feeding f o r 4 days. Animals starved for only 2 weeks
and re-fed for 4 consecutive days show the normal mitochondrial picture similar to that found in control animals
4 to 4 hours after feeding (fig. 11). I n general, body weight,
cellular dimensions, fat content of the cells, and other gross
and microscopic features have returned to normal.
The mitochondria in the epithelial cells of animals starved
for 1 month and re-fed for 4 days present a similar picture
to those of animals re-fed only once after the month’s fast.
However, the cells have increased somewhat in size. I n some
specimens the cytoplasm is vacuolated, and Sudan I11 tests
reveal far more than the normal quantity of fat (cf. figs. 3
and 10). The cells of the apex of the folds are more heavily
laden with fat droplets than the cells of the crypt regions.
Re-feeding until the pre-fast weight is restored. Animals
starved f o r 2 weeks generally restore their pre-fast body
weight after being fed f o r 4 consecutive days. Seven to 15 days
of feeding were required to restore the body weight of animals
starved for 1 month. A study of all these animals revealed
that usually when the original body weight is restored other
conditions have likewise returned to normal. The mitochondria
200
MYRA 9. WILLIAMS
in the epithelial absorptive cells are normally distributed
and a r e of the normal shapes (cf. figs. 1 and 1 2 ) ; the f a t
content of the cells is normal in quantity and in distribution;
the cellular dimensions are within the normal range ; the cytoplasm has regained its staining capacity; the cellular membrane and striated border a r e of normal thickness and
distinctness; and the percentage of water in the tissue has
decreased. The digestive tract has expanded in diameter and
in length, the number of intestinal folds has returned to normal
(9 to 12), and the number of goblet cells is reduced to normal.
I n some specimens the mitochondria in the cells on the apices
of the folds respond to re-feeding more quickly than do those
in the cells of the crypt zones. This is more evident in re-feeding after a month's fast than after only a 2-week fast.
Mitochondria in t h e posterior intestinal cells. The epithelial
cells of the posterior sections of the intestine of well-fed animals show relatively more filaments, though fewer with looped
ends, and fewer rings than the epithelium of the more anterior
sections (cf. figs. 1 and 13). I n the starved specimens the
condition is the same a s that described for the anterior sections, although the changes occur more slowly. Recovery
during re-feeding is slower than in the anterior part of the
intestine, although when the body weight has returned t o
normal the mitochondria a r e again like those in the cells of
the well-fed specimens.
DISCUSSION
Tlw rnorphology and distribution of initochoizdria characteristic of active and inactive cells. Previous investigators
of mitochondria in the intestinal epithelial cells have believed
that the shape of these cytoplasmic inclusions is an index to
the activity of the cell. Policard ( 'lo), Champy ('ll),P6terfi
( '14)' Corti ( '12, '26)' and Ryozo ( '33) considered filaments
characteristic of inactivity, rods and granules characteristic
of activity. Shun ('20) concluded that the opposite was the
case. Liu ( '30) found supra-nuclearly thin threads, subnuclearly granules during inactivity ; these enlarged and f rag-
MITOCHONDRIA I N SALAMANDER INTESTINE
201
mented during digestion and absorption. Asher ( '08), Demjanenko ( '09) and Zillenberg-Paul ( '09) observed granules
in the cells under all conditions of activity, and noted a change
in the number and distribution of these under different nutritional states. Eklof ('14) found that during starvation the
granular and rod-like mitochondria become aligned into filaments, which tended to converge to an angle just above the
nucleus. I n the cells of the well-nourished animals the mitochondria were more dispersed in the cytoplasm. He found the
mitochondria more numerous and more distinct during activity
than during starvation.
I n contrast to the results of these earlier workers the present
study reveals that during digestion and absorption all forms
of mitochondria are present. They are tmiformly distributed
throughout the supra-nuclear cytoplasm and are typically
more abundant in the sub-nuclear region. This study reveals
that the correlation existing between mitochondria and
digestive and absorptive activities is not merely one of mitochondrial shapes, but it involves chahges in the relative number of forms, as well as the relative distribution of these
forms in the cytoplasn?. During inanition there is never a t
any one time the variety of form among the mitochondria
which is common in well-fed animals (cf. figs. 1 and 2 with
5, 6, and 7). Filaments abound during the first 10 days of
fasting (fig. 6), but 14 to 30 days of fasting produces granular
forms (fig. 7 ) . After 2 to 4 months of starvation both granules
and filaments occur in characteristic positions in the cytoplasm
(fig. 5). I n contrast to the well-nourished animals, zone 1 in
the cells of the specimen starved for 2 to 4 months contains
only granules, more compactly placed than in the well-fed
specimen; zones 2 and 3 show shorter filaments, many of which
are either beaded or have terminal granular enlargements ;
and zone 4 contains fewer mitochondria. Starvation is accompanied by a reduction in the number of filaments with
thickened places, and blebs and usually an elimination of the
rings and terminally looped filaments.
202
MYRA A. WILLIAMS
Relationship of mitochondria t o physiological activity o f t h e
cells. The intestinal mucosa of amphibians contains only goblet and columnar cells. It has been suggested (Holmes, '28;
Noble, '31) that the columnar cells perform a dual role,
secretion and absorption. The present study reveals that the
initochondria in these columnar cells of animals previously
starved appear normal as early as 4 hours after re-feeding.
It would seem probable that intestinal absorption does not
begin so soon after a meal, since autopsy of the digestive
tract in this study, as well as in that of XcCurdy ('39), revealed that food remains in the stomach froiii 24 to 48 hours.
Thus it appears probable that the immediate mitochondria1
alteration in these intestinal cells may be initiated by enzyme
elaboration. Cowdry. ( '18) considered thickened places and
blebs on filamentous mitochondria as indicative of secretion.
This study substantiates Cowdry's conclusions in that mitochondria of the type indicated a r e more abundant in the cells
of the feeding animals than in the starved ones and are fewer
in the cells of the lower end of the intestine where eiizyiiie
productivity is probably less pronounced. A further evidence
for the fact that mitochondria1 changes a r e correlated at least
in part with enzyme secretory activity is the fact that in the
posterior intestinal cells the changes in the mitochondria
are slower and the differences are never so great as in the
anterior intestinal cells where secretion is probably more
pronounced.
If the secretive and absorptive functions of the intestine
a r e performed by different cells of the intestinal niucosa the
fact has not been clearly demonstrated. To what extent
digestion and absorption a r e intracellular processes is unknown (Starling, '35 ; Best and Taylor, '39 ; RIacleod, '41).
Verzkr and bIcDougal1 ('36) and Rlacleod ( '41, p. 986), state
that fats and pei*haps glucose and proteins are transformed
intracellularly by tlie intestinal epithelial cells before they
a r e passed into tlie circulating fluids of the body. It is believed (Champy, '11; Liu, '30) that mitochondria play a n
active role i n these absorptive processes. The bipolarity in
MIT OCHONDR IA I N SALAMANDER INTESTINE
203
the arrangement of the mitochondria in cells is usually considered indicative of secretion in two directions (Cowdry, '18,
'24, p. 318). I n this study the partial loss of the bipolarity of
the mitochondria in the cells of starved animals suggests a
change in this two-fold secretion (cf. fig. 1with figs. 5 and 7)
and is an evidence that some of the mitochondria1 modifications observed in these cells of normal animals are related
to absorptive phenomena. Further evidence that mitochondria
are associated with absorptive activity is that the restoration
of the mitochondria to normal occurs first in the cells on the
apices of the folds where absorption is believed to be most
abundant. Sudan I11 tests show more fat in the apices of the
folds than in the cells of the crypt regions.
BIcCurdy ( '39) considered rings and terminally looped filaments in the liver cells as indicative of digestive and absorptive
activity. This study of intestinal cells substantiates that
claim. These forms are almost totally absent from the cells
of the starved animals.
The fact that the response of the mitochondria to re-feeding
is more clear-cut than is the response to fasting suggests that
mitochondria are sensitive indices to the physiological state
of the cells. Although in early starvation the amount of niaterial in the digestive tract decreases, a small amount remains
for some time. The depletion of the nutritive material from
the cytoplasm is slow and gradual. The intake of food after
the cells are practically depleted is a well defined event. The
response likewise is clearly defined. Ingestion initiates
throughout the digestive tract a series of changes (secretion of
enzymes and hormones) concerned with digestion and absorption. Almost immediately upon ingestion the entire digestive
tract seems to become sensitized. However, the posterior
portion of the intestine becomes active slightly later than
the anterior portion, which can be correlated with the probability that the lower portion of the intestine is more concerned
with absorption than with the secretion of enzymes. Other
portions of the digestive system become active later as indicated by a comparison of the intestine with the liver of
204
MYRA A. WILLIAMS
h1cCurdy's ( '39) preparations from some of the same specimens used in the present study, which shows that resumption
of the normal state in the liver occurs later than in the
anterior intestine.
In the cells of well-fed animals a variety of mitochondria1
forms exists at all times. Lewis and Lewis ('15) found this
condition to be characteristic of physiologically 'active cells.
The series of changes observed at intervals from 2 to 120 days
of starvation indicates that despite the absence of activity of
the organ in which the cells occur, the mitochondria still a r e
capable of undergoing to a limited extent the same transformations noted i n the controls. I f the size, distribution, and
greater variability in shape of the niitochondria in the cells
of the controls a r e correctly correlated with the greater
physiological activity of the intestine in these animals, then
the reduction in size, and the relative stability, as well as the
change in distribution of mitochondria in the intestinal cells
in animals starved for some length of time furnishes a n index
of their lowered physiological activity. The rapidity with
which the mitochondria return to normal when the starved
animals a r e re-fed shows the extreme sensitivity of these
bodies when the organ again becomes active.
SUMMARY S N D CONCLUSIONS
1. During digestion and absorption all forms of mitochondria a r e present in the intestinal epithelial cells. They
a r e evenly distributed in the supra-nuclear cytoplasm, but
are more abundant in the sub-nuclear zone.
2. During starvation the variation in the form of mitochondria decreases, their size diminishes, and their distribution in the cells is altered.
3. Re-feeding reverses the inanition changes and restores
the mitochondria in size, distribution, and morphology to those
characteristic of the well-nourished state.
4. h'litochondria in the form of rings and looped-end filaments, as well as filaments with blebs and characteristic
MITOCHONDRIA I N SALAMANDER INTESTINE
205
elongated enlargements, seem t o be associated with digestive
and absorptive activity of the cells.
5. Mitochondria are believed to be sensitive indices to the
physiological state of the cells.
LITERATURE CITED
ASHER,L.
1908 Das Verhalten des Darmepithels bei Verschieden funktionellen
Zustanden. Ztscbr. f . Biol., Bd. 51, S. 115-126.
BEST, c. €I., AND N. B. TAYLOR 1939 The physiological basis of medical practice.
Second edition. The Williams and Wilkiils Co., Baltimore. xvi JI1872 pp.
CHAXPY,C. 1911 Recherche8 sur l'absorption intestinale et le r61e des mitochondries dans 1'absorption et la sbcr6tion. Archives D 'Anatomie
Microscopique, Tom. 13, pp. 55-170.
CORTI, A. 1912 Studi sulla Minuta strutta della mucosa intestinale di Vertebrati
i n riguardo a i suoi diversi momenti funzionali. Arch. ital. di anat. e.
d i embriol., Bd. 11, S. 1-89.
____
1926 Le lacunome ravble les premi&res mqdifications structurales des
cellules absorbantes de 1 'intestine a u cours de leur fonctionnement.
Bull. d'histol. (appliq. a les physiol. a la pathologie.), Tom. 111,
pp. 265-270.
COWDRY,E. V. 1918 The mitochondria1 constituents of protoplasm. Contrib.
Embryol. (Carnegie Inst.),. Wash., vol. 8, pp. 41-160.
1924 General cytology. The Univ. of Chicago Press, Chicago.
vii
754 pp.
DENJ A N E N K O , K. 1909 Das Verhalten des Darmepithels bei Vershiedenen funktionelen Zustanden. Ztschr.. f. Biol., Bd. 52, s. 153-188.
ERLOF,H. 1914 Chondriosomenstudien a n den epithel- und Drusenzellen des
Rlagen- Darmkanals und den Oesophagusdrusenzellen bei Saugetieren.
Anatomische Hefte, Bd. 51, S. 1-227.
HOLMES,S. J. 1928 The biology of the frog. 4th revised edition. The Macmillan Co., N. Y . ix
386 pp.
LEE, A. B 1937 The microscopists' vade-mecum. 10th ed. Edited by J. Broiite
Qatenby and T. S. J. Painter and A. Churchill Ltd. xi
784 pp.
LEWIS, M. R., AND W. H. LEWIS 1915 Mitochondria (and other cytoplasmic
structures) in tissue cultures. Am. J. Anat., vol. 17, pp. 339-401.
LIE, A. C. 1930 The mitochondria-Golgi complex of the columnar epithelium
of the small intestine during absorption. Chinese Jour. Physiol., vol. 4,
pp. 359-364.
M ~ U R D YMARY
,
B. D. 1939 Mitochondria in liver cells of fed and starved
salamanders. J. Morph., vol. 64, pp. 9-35.
MACLEOD,
J. J. R. 1941 Macleod's Physiology in modern medicine, edited b y
Philip Bard and others. 9th Ed. The C. V. Mosby Company, St. Louis.
xxvi
1256 pp.
NOBLE,G. I(. 1931 The Biology of the amphibia. 1st Ed. McGraw-Hill Book
Company, Inc., N. Y . and London. xiii
577 pp.
+
+
+
+
+
206
MYRA A. WILLIAMS
PBTERFI,
T. 1914 Histologische Veranderungen der Darmepithellen wdhrend der
Resorption. Anat. A m . Erganzungsheft 1913-1914, Bd. 46, S. 1G8-131.
1910 Faits et hypotheses concernant la physiologie de la cellule
P0LICA4RD,, A.
intestinale. Compt. Rend. de la Societe de Biol., Tom. 68, pp. 8-10.
*RYozO, S. 1933 Study on mitochondria and metachondria of intestinal epithelial cells. Jap. Jour. Exp. Med., vol. 11, pp. 397405. (Biol. Abstr.
vol. 9, no. 5 , pp. 975, no. 8725, 1935).
*SHTX’, 0. 1920 Effect of starvation on re-feeding upon the mitochondria and
other cytoplasmic contents. Anat. and Anthrop. Assn. of China.
(Abstr. from Library of Congress, Washington).
STARLING,
E. H. 1936 Starling’s principles of human physiology. 7th edition.
Edited and revised by C. Lovatt Evans. Lea and Febiger. Philadelphia.
xiii
1096 pp.
F.,
VERZ~R
, AND E. J. MCDOUGALI. 1936 Absorption from the intestine. Jlonographs on physiology. Longmans, Green and Co., Ltd. xii
294 pp.
ZILLENBERG-PAUL,
0. 1909 Fortgesetzte Untersuchungen iiber das Verhalten
des Darniepithels bei verschiedenen funktioiiellen Zustanden. Ztschr. I.
Biol., Bd. 52, S. 327-354.
+
+
* Read abstract only, original not available.
PLATE 1
EXPLANATION O F PLATES
811 figures were niade with the aid of a camera lucida at a magnification of
approximately 750 times.
EXPLANATION OF FIGURES
1 Absorptive cell from
2 Absorptive cell from
3 Absorptive cell froin
4 Absorptive cell from
5 Absorptive cell from
6 Absorptive cell from
control animal killed 2 hours after feeding.
control aniinal killed 6 hours after feeding.
control aninial showing f a t droplets.
control animal showing f a t throughout.
aniinal starved for 3 months.
animal starred for 1 week.
MITOCHOKDRIA I N SALAMANDER INTESTINE
PL.4TE 1
MYRA A . WILLIAMS
3
207
PLATE 2
EXPLANATION OF FIGURES
7
8
9
10
11
12
13
Absorptive cell from animal starved for 2 weeks.
Absorptive cell from animal starved for 2 weeks, and killed 2 hours after
being re-fed only once.
Absorptive cell from animal starved for 2 weeks and re-fed once; killed
24 hours after feeding.
Fat droplets in a n animal starved for 1 month, then re-fed for 4 days.
(Killed 6 hours after feeding.)
Absorptive cell from another animal re-fed for 4 days a f t e r a f a s t of 2
weeks, and killed 12 hours after feeding.
Absorptive cell from animal re-fed a f t e r a month’s fast, uiitil the original
body weight was restored. (Seven consecutive days.)
Posterior intestinal cell from a control animal killed 12 hours after feeding.
208
MITOCHONDRIA I N SALAMANDER INTESTINE
X Y R A A. WILLlAMS
8
7
11
12
209
PLATE 2
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