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Duplicitas anterior in the toad Eleutherodactylus alticola.

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DUPLICITAS ANTERIOR I N T H E TOAD,
ELEUTHERODACTYLUX ALTICOLA
W. GARDNER LYNN
Department of Biology, The Catholic University of America, Washington, D . C.
T W O TEXT FIGURES A N D TWO PLATES (FOURTEEN FIGURES)
The infrequent occurrence of spontaneous twinning in amphibians
has been remarked by many investigators and has been most recently
emphasized by Schwind ('42) who has pointed out that, although double monsters are not uncommon among teleosts, reptiles, birds and
mammals there have been very few reports of such anomalies among
amphibians. The scarcity of such reports is the more significant when
one considers the large numbers of frog and salamander eggs which
are examined each year in biology class-rooms and laboratories all
over the world. Lebedinsky ('23), in describing a case of duplicitas
anterior in Rana fusca, states that there had been only four records
of spontaneously occurring conjoined twins in Anura prior to his paper.
This is in error however, f o r one of the records which Lebedinsky
cites is really a report on twelve cases of such twinning. The present
author's rather brief scrutiny of the early literature has yielded
seventeen accounts of double monsters in frogs and toads. Of these,
twelve were found in Rana esculenta (Born, 1882), four in Rana fusca
(Born, 1881; Loyez, 1897 ; Spemann and Falkenberg, '19 ; Lebedinsky,
'23) and one in the Obstetrical Toad, Alytes obstetricans (HkronRoyer, 1884). I n his recent paper, Schwind ( '42) has described twentynine cases of spontaneous anterior reduplication in Rana sylvatica.
Twenty-seven of these were found in a single bunch of eggs. It is noteworthy that all of the cases thus far reported concern embryos or early
larvae, so that there are no records of conjoined twins in metamorphosed frogs or toads. The case to be recorded in the present paper is
uniqiie in that, although it concerns embryonic stages, the species
involved is one which possesses no aquatic tadpole stage and the double monster to be described has, therefore, the body form and internal
organization of an adult frog.
The genus Eleutherodactylus is a group of leptodactylid toads which
is widespread in tropical America and the West Indies. The embryology of one member of this genus has been described in some detail
345
346
W. GARDNER LYNN
(Lynn, '42) and that account will serve as a basis for discussion of
the double monster. The large-yolked, unpigmented eggs of these animals are laid on land, in hollows beneath stones or logs. From these
eggs, after a period of development which lasts approximately 4 weeks,
tiny frogs having the typical adult body form are hatched. During the
embryonic history neither external nor internal gills are ever formed,
there is no true operculum and the fore and hind limbs appear simnltaneously and grow steadily. There are no tadpole-like mouth parts or
ventral suckers and the development of such structures as the skull,
aortic arches and digestive tract are greatly modified in relation to
this direct development. The embryo has a broad, vascular tail which
apparently serves as the chief respiratory organ during intra-oval
existence. After hatching the lungs become functional and the tail
quickly dwindles away.
The specimen under consideration was collected in Jamaica, €3. W. I.
during the summer of 1941 in the course of an investigation concerning
the results of experimental removal of the pituitary anlage in the
Eleutherodactylus en1bryo.l The species E. alticola is a Jamaican endemic and, as its name indicates, it is a montane form occurring from
about 5,500 feet to the top of the highest mountain in the island, Blue
Mountain Peak, at 7,360 feet. The clump of eggs to which the double
monster belonged was taken from beneath a stone on the southwestern slope of Blue Mountain Peak on July 15, 1941. There were
twenty eggs in the clutch. When the eggs were first examined under
the microscope upon arrival at the laboratory 2 days later, it was
found that the embryos were in an early limb bud stage (stage -22 as
defined by Lynn, '42). Eighteen of the embryos seemed normal and
were later utilized for experimental work, one embryo was abnormal
in that the body was unusually short and thick, the other was the double
monster herein described.
DESCRIPTION O F SPECIMEN
Sketches of the embryo were made when it was first discovered and
these are reproduced in figures 1 and 2. Figure 3 shows a photograph
'The opportunity to work in Jamaica was afforded by a grant from the Brooks F'und of
The Johns Hopkins University. The author is indebted t o hfr. C. Bernard Levis, Curator
of the Museum of the Institute of Jamaica, and to the Natural History Society of Jamaica
f o r the use of the (217-desdale House as laboratory and living quarters f o r our party. Gratitude is also due to Dr. Jolin P. Marbarger who, under difficult conditions, made photographs
of the living animal in our field laboratory; t o Mr. John Spurbeck of The Johns Hopkins
rniversity, who photographed the nnimal after pieserration ; and t o Rev. Henry E. Wncho~vski v ha, a t The Catholic University of America, prepared the specimen f o r microscopic
study.
DUPLICITAS ANTERIOR I N A TOAD
347
made on the following day.2 It will be noted that, when these illustrations were made, the animal was entirely unpigmented. There were
two heads joined just behind the level of the fore limbs. Both fore and
hind limbs were clearly visible as rounded buds and a similar, but
somewhat larger, bud lying between the two heads apparently represented a fusion of the adjacent fore limbs of the two twins. At this
time there was a difference in the size of the two heads, that of the
left embryo being the smaller, but this difference gradually disappeared at later stages.
Fig. 1 Dorsal view of the double monster when first discovered. J u l y 1 7 , 1941. FL, fused
fore-limbs of the two anterior ends. L, left head. R, right head.
Fig. 2 Ventral view, T, tail.
Observations were made and photographs were taken daily until
August 5th, when our stay in the island ended and it was necessary to
preserve the specimen. From the series of photographs, six have
been chosen for illustration (figs. 3-8). By July 19th (fig. 4) an intense aggregation of pigment cells had appeared along the adjacent
sides of the two embryos while the outer sides had only a few isolated
melanophores. The photographs show the gradual increase in pigmentation and its spread down over the yolk (the future ventral body
wall). It can be seen that the dark streak between the two adjacent
spinal cords persisted through all the embryonic stages observed.
This streak is of course, to be explained by the fact that the melanophores derived from the neural crest material of the two adjacent
sides could not migrate down to furnish the pigmentation of one whole
2 A l l of the p11otogiatihs of the living animal lrave much t o be desired. The? were
taken by the light of a gasoline lantern with a small camera mounted on a compound microscope. Since these embryos continually carry out a slow counter-clockwise rotation within
the egg-membranes it was not possible to give as long exposnres as the available light required. It was necessary t o gacrifiee depth of focus, and even with the lens wide open the
negatives were somewhat underexposed.
348
W. GARDNER LYNN
side of the body as they would have done in a normal embryo, but were
instead densely packed in a very limited area of skin. Although this
deeply pigmented area cannot be distinguished in the photograph of
the s'pecimen after preservation (fig. 9), the sections show the piling
up of melanophores in this area very clearly (fig. 15, M ) .
Comparison of the photographs shows that the fused forelimbs,
which are clearly seen in figure 4, gradually disappeared during later
development; for, as the two heads enlarged. they became fused
further and further anteriorly and the intervening limb tissue appears
to have atrophied. At the time of preservation a small external flap
was still present in this region (fig. 10) but the sections show no
skeletal parts in this structure. The two adjacent scapulae are present,
however, and are fused at their ventral ends with each other and with
the anterior end of the basihyoid cartilage.
During the latter part of the time that the embryo was under observation it was noted that the hind-limbs, although they had differentiated fully, were abnormally small and were somewhat distorted.
This can be seen in figures 9 and 10 which show the embryo after it
had been removed from the egg membranes and preserved. The saclike, highly vascular tail is shown in these photographs and the horny
egg-tooth can be seen at the tip of the upper jaw of each head. On
the basis of its general development at this time one may judge that
the animal would have reached the hatching stage in about 5 days.
The internal anatomy was studied by means of serial sections some
of which are illustrated in figures 11 to 16. At the time of preservation (figs. 9 and 10) the two heads diverged so widely that their anteroposterior axes were almost directly opposed. I n the sections, therefore,
the heads are cut nearly longitudinally although the body is sectioned
transversely.
Study of the sections reveals that there are two complete brains
and four complete internal ears. The two spinal cords join dorsally
at the level of the second spinal nerve and their lumina unite at the
level of the fourth spinal nerve. No spinal nerves are present on the
adjacent sides of the two cords and this is reflected in the pycnotic
ccndition of the cells of the adjacent portions of the paired spinal
cords (fig. 14). The indication is that these cells had differentiated but
had later degenerated. As Schwind has noted in his cases, the two
spinal cords unite by first tilting towards each other dorsally, so that
the roof plates fuse. More posteriorly this tilting continues so that the
dorso-ventral axes of the two cords diverge ventrally and when fusion
of the lumina has occurred, the single tubular structure so formed
DUPLICITAS ANTERIOR I N A TOAD
349
really has a floor plate made up of the medial sides of the originally
separate cords (figs. 14 and 15).
It has frequently been noted that in double monsters of this type,
the doubling of the notochord is more extensive than that of any other
structure. I n the present specimen the two notochords do not fuse at
all. They are rather widely separated at most levels of the body (figs.
14 and 15) but approach each other near the root of the tail. Here
the right notochord decreases in diameter (fig. 16) and, although both
continue into the tail, the right soon dwindles away and only the left
notochord continues to the tip of the tail.
Fusion of the two digestive tracts occurs at the posterior end of the
oesophagus so that there is a single stomach. There are two livers and
two gall bladders however, and the liver of the left twin is reversed in
situs, having its gall bladder on its left side instead of on its right.
Two tracheae and two pairs of lungs are present. Because of the wide
divergence of the two heads and the relatively early stage of development of the lungs, the two respiratory tracts do not approach each
other near enough to show any fusion.
In the body region, only the lateral mesonephroi are present. A
curious feature of the internal anatomy however, is an unpaired mass
of cystic mesonephric tissue lying between the two heads, dorsal to the
heart and enclosed by the two adjacent scapulae (fig. 11). This mass is
interpreted as representing the two adjacent mesonephroi which, after
differentiating, lost connection with the body cavity during the growth
and further fusion of the twin anterior ends. The cystic condition of
the structure is explained by the fact that it has no duct.
The pronephroi have normally degenerated to glandular-appearing
masses at this stage. I n this specimen such a picture is presented by
the pronephros of the right side, but that on the left side is enlarged
and cystic (fig. 14, P).
Study of the heart region reveals a normal heart on the left side
and a much modified one on the right. Two postcaval veins emerge from
the two livers and each enters a separate sinus venosus. On the left side
the sinus venosus enters an atrium which is well differentiated and
possesses the beginning of an interatrial septum on its left side. This
in turn enters a muscular ventricle and from the right side of the ventricle the conus arteriosus emerges and gives off three pairs of aortic
arches. The left heart is therefore normal in development and in situs.
On the right side the sinus venosus enters a thin-walled chamber
which doubtless represents the atrium of the right heart but is small and
without a septum. Shortly anterior to this a small muscular structure
350
W. OARDNER LYNN
on the ventral wall of this atrium represents the ventricle and conus,
but its cavity is completely occluded. The atrium then sends a large
connective across to the sinus venoms of the left heart and it is clear
that the blood from the right side was thus sent into the left heart for.
although the atrium of the right twin continues for some distance anterior to this point, it finally ends blindly. The blood supply to both
heads is derived from branches of the conus of the left heart. It is
not unlikely that, at early stages, both hearts were well developed
and that the reduced condition of the right heart at the stage studied
is a result of degenerative changes. Schwind ('42) reports a case in
which two separate hearts could be seen at early stages, but had fused
by the time the specimen was preserved.
Unfortunately, in the present specimen, the heart region was not
visible in life because of the curvature of the animal around the yolk.
DISCUSSION
Since spontaneous twinning seems to occur with greater frequency
in large-yolked eggs like-those of teleosts, reptiles and birds than it
does in smaller-yolked forms, it might be supposed that such twinning
may prove to be common in the group of amphibians which the present
report concerns; for the eggs of Eleutherodactylus are much larger
than those of ordinary amphibians and are indeed larger than man)teleost eggs. The lack of any previous records of twinning in this
group could easily be attributed to the infrequency of observations 011
eggs of this type. Although a considerable number of amphibians is
known to have large-yolked eggs and direct development, most of
them are found in the tropics and the eggs have been seen by relative17
few collectors. The present author finds, upon examining his field
records, that he has observed some 4,500 eggs of the genus Eleutherodactylus in the past 12- years without finding any other cases of
twinning but this is really a very small number, equivalent to what
would be seen in a single large bunch of Rana pipiens eggs.
Twinning has been induced in Fundulus eggs by exposure to ultraviolet light (Hinrichs and Genther, '31) but Schwind's attempts t o
cause twinning in the eggs of Rana by this and other treatments, were
unsuccessful. I n view of its large size and unusual mode of development, similar experiments with the egg of Eleutherodaetylus would be
of great interest.
SUMMARY
1. A case of daplicitas anterior in an embryo of Eleutherodactylus
alticola, a leptodactylid toad having large-yolked terrestrial eggs, is
DTJPLICITAS ANTERIOR. IN A TOAD
351
reported. The monster was discovered in an early limb-bud stage and
was observed until near the end of its period of intra-oval development,
at which time it had nearly attained the body form of the adult toad.
2. The internal morphology is described from serial sections. The
two spinal cords join at the level of the fourth spinal nerve but the
two notochords remain separate throughout their extent. Two livers
are present, that of the left twin being in reversed situs. The heart
of the left twin is normal but that of the right twin is reduced to a tube
connecting with ithe sinus venosus of the left heart.
LITERATURE CITED
BORN,G . 1881 Eine Doppelbildung bei Rana fusca Roes. Zooi. Anz., 1.01. 4. pp. 135-139.
1882 Uber Doppelbildungen beim Frosch und ihre Entstehung. Breslauer
arztl, Zeits., vol. 4, pp. 162-163.
€115~0~-ROYER
1884 Cas t6ratologiquea observes chez quelqnes ti5tards de batraciens anoures
et de la possibilite de prolonger m6thodiquement 1%tat larvaire chez les batraciens.
Bull. SOC. Zool. France, vol. 9, pp. 162-168.
HINRICIIS, M. A., AND I. T. GENTHER 1931 Ultra-violet radiation and the production of
twins and double monsters. Phys. Zool., vol. 4, pp. 461-485.
LEBEDINSKY,
N. G. 1923 Ueber eine Duplicitas anterior von R m a fusca und ueber die
teratogenetische Terminationsperiode der symmetrischen Doppelbildnngen der
Placentalier. Anat. Anz., vol. 56, pp. 257-266.
LOYEZ,M. 1897 Sur un thtard dr Rana temporarin hic6phalc. Bull. Ror. Zool. Frnncr,
v01. 22, pp. 146-148.
LYNN,W. G. 1942 The embryology of Eleutherodactylus nubicola, a n anuran which has
no tadpole stage. Carnegie Contr. to Embryol., vol. 30, pp. 27-62.
SCHWIND,
J. L. 1942 Spontaneous twinning in the amphibia. Am. J. Anat., vol. i l , pp.
117-151.
RPEMANN, H., AND H. FALK~NBERG
1919 Ueber asymmetrische Entwicklung und Situs
inversus viscerum bei Zwillingen nnd Doppelbildungen. Arch. f. Ent.-Mech., vol.
45, pp. 3il-420.
PLATE 1
EXPLANATION
Figs. 3-10
OF FIGURES
Photographs of the speeimen at successive stages of development.
3 July 18. X 10.
4 July 19. X 14.
5 July 23. X 8.
0 July 27. X 8.
r
July 28. X 8.
8 July 30. X i .
9 After preservation, August 5. Dorsal view. X 5.
10 After preservation, August 5. Ventral view. X 5.
352
PLATE 1
1 ) U P L I C I T A S ANTERIOR TN h TOAD
\V. G . fiYiVX
353
PLATE 2
EXPLANATION OF FIGURES
Figs. 11-lti
Photograplis of sections of the double nionster a t different levels. X 30.
11 Section :it the h e 1 of the two adjacent otic capsules t o show unpaired median n l a s
of cystic mesonephi ic tissue.
12 Section a t the level of the upper end of 1ie;irt. The left heart is on tlie reader's left;
tlie right heart, rrimesented by a relatively uiidifl'erentiated tuhe, is on the reader's right.
13 Section a t the level of the lower end of the lieart at the point where the postcaral
vein leaves the left liver.
14 Sectioii a t the level wltere the two spinal cords come into contact.
15 Section at the level of fusion of tlie luniina of the two spinal cords.
16 Section through the base of tlie tail showing the spinal cord and the left notochord
cut twice. The right notoellord is sectioned a t tlie base of the tail but does not extend t o
the tip of the tail.
ABBREVIATIONS
ATR, atrium; C, coniiectiiig vessel between riglit and left hearts; CA, conus arteriosus;
LL, left liver; LN, left notochord ; M, melanophores, densely aggregated ; MES, fused mass
of mesonephric tissue; P, cystic pronephros; RH, right heart; RL, right liver; RN, riglit
notochord ; SC, spinal cord ; SV, sinus venoms; V, ventricle.
354
UL-PI,ICITAS -4NTERIOR IN A TOAD
\T. G . L Y N N
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