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The experimental production of cyclopia in the fish embryo (Fundulus heteroclitus).

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THE EXPERIMENTAL PIlODUCTION O F CYCLOPIA I N
THE FISH EMBRYO (FUNDULUS HETEROCLITUS).
BY
In a series of experiments on localizatioii and regeneration in the
fish embryo it was noted that defects, made in the anterior end of
the embryonic shield, often gave rise to cyclopean forms. With the
renewed interest in the subject since the publication of the papers
by Spemann and Stockard, it seems desirable to indicate this mechanical method by which these forms were produced and to enter somewhat upon the bearing they may have upon the theories of the origin
of Cyclopia. Physicians have been interested in Cyclopean monsters
for centuries and many theories concerning thcir origin have been
advanced. Two groups of theories are to bc recognized, the germinal
and the enriromental. Concerning the germinal origin there is no
direct or indirect proof such as might be obtained were cyclopean
monsters viable and capable of sexual maturity and subsequent re
production with the possibility of transmitting to their offspring
the same peculiarity, through peculiarities in the germplasm. The
very fact that this chance of transmission is eliminated would speak
against the germinal origin. There is considerable evidence in favor
of the second view, that Cyclopia are due to some modification of
the embryo during the early stages of development. The experiments
of Spemann and Stockard and likewise of the ones recorded below
seem to support this view. Spemann's' experiments consisted in
constricting the eggs of triton during the two cell or later stages
by a fine thread about the circumference of the first cleavage plane.
Double headed monsters, exhibiting rarying degrees of fusion of
Weber experimentell erzeugte Doppelbildungen niit cTclopischem Defekt.
2001. Jahrbuch., Supp. VII, 1904.
(175)
176
Warren H. Lewis.
n
FIGS.1, 2.-Showing
embryonic shield at operation stnges. The black area
shows usual amount of tissue lost by the operation.
FIGS.3, 4, 5.-Dorsal, lateral and ventral views of normal head shortly after
hatching.
FIQ.6.-Experiment ha,. Operation on stage 2 (see Fig. 2).
FIGS.
7,8, 9.-Experiment ha,,. Operation on stage 2. Right eye completely
absent.
FIGS.10, 11, 12.-Experiment ha,. Operation on stage 2. Left eye entirely
absent.
The Experimental Production of Cplopia.
1;:
two or more eyes were often produced. This fusion of the eyes was
probably primary before the eye rudiments were recognizable. In
StoCkard’s* experiments on fish embryos (Fundulus heteroclitus) ,
the eggs shortly after fertilization were placed in sea water solution of magnesium chloride with rcsulting production of the cyclopean
condition in a large percentage of the eggs. The cyclopean condition
i? also primary in these experiments, “the earliest indication of
an eye is just as truly cyclopean as it will be later,” S t o ~ k a r d . ~
Neither Spemann’s nor Stockard’s cyclopean monsters can be looked
upon as germinal in origin but are truly due to environmental
conditions. The additional data from the following experiments
extends the possibility of cyclopean monsters depending upon a b
normal influences exerted during early embryonic development.
These experiments were done at the Marine Biological Laboratory,
\Yoodu Hole, Mass., and a few of the typical ones are given below.
Such forms were easily reproduced during two succeeding seasons.
The experiments were made on the eggs of Fundulus heteroclitns
clnriiig the embryonic shield stage. The egg was held with a small
pair of forceps and a very fine needle was thrust through the cpg
niembrane into the anterior end of the shield; as the needle was withdrawn slight pressure on the forceps caused some of the material
of the embryonic shield in the region of the needle prick to be estruded. As the experiments were done under the binocular microscope, it was possible to determine with some degree of accuracy
about how much material had escaped. This is indicated in Figs. 1
and 2 by the solid black patch at the anterior end of the ernbryonic
shield. The amount of material extruded yaried somewhat in each
experiment, the variations becoming more eridcnt during the later
stages of development. After the embryonic shield begins to appear,
there is w r y little or no regeneration of the central nervous system
and defects caused at this time consequently become more and more
apparent as development proceeds.
*The artificial prodiiction of R single niediau cyclopean eye in the fish
enibryo by x~leansof Sea Water Solutions of Magnesinin Chloride. Arch. f.
Ent~~iclrlungsxnechanfkder Organisnieii, Bd. 23, 1907.
”Science, 1’01. XSVIII, p. 455.
178
Warren H. Lewis.
16
21
FIGS.13, 14, 15.-Experiment hm,. Operation on stage 1 (see Fig. 1). E p m
i n contact i n median plane.
FIQS.16, 17, 18.-Experiment
h,. Operation on stage 1. Eyes fused, with
two lenses and two cup cavities.
FIQS.19, 20, 21.-Experiment ha,,. Operation on stage 2. Eyes fused with
two lenses and one large cup cavity.
YIOS. 22, 23, =.-Experiment
hall. Operation on stage 1. Eyes completely
fused with one lens and one cup cavity.
The Experimental Production of Cyclopia.
179
In a number of instances the material taken out with the needle
point was from one side of the anterior end of the embryonic shield
with the resulting absence at the time of hatching of the eye on that
side. Fig. 6 shows the head of such an embryo, which was operated
on at the stage shown in Fig. 2 and killed a few days, after hatching,
15 days after the operation aiid I f days after fertilization. The
right eye consists merely of a small bit of retina remaining in the
otherwise almost normal brain mall. The left eye is apparently
normal as are also the brain and nasal pits. Figs. 7, 8, 0 are from
another embryo operated on at the same time and stage as the
one shown in Fig. 6, and killed 15 days after the operation. The
sections show complete absence of the right eye, but with an otherwise normal brain and head. Figs. 10, 11, and 12 are from another
embryo operated on at the same time and stage and killed 15 days
later. I n this embryo the left eye is entirely wanting, the forebrain is slightly reduced in size aiid the nasal pits are quite close
together. The right eye lies nearer the median plane than normal.
See Figs. 3, 4, and 5.
Figs. 13, 14 and 15 are from an embryo in which the operation
defect was about medial and done at a stage such as seen in Fig. 1.
Fifteen days after the operation the embryo was pulled out of
the membrane and killed. The two eyes are in contact, but each one
is surrounded even at the place of contact with its own pigment layer.
Two optic nerves are present and two lenses. The two nasal pits are
in contact, but the brain is apparently about normal in size. Figs.
16, 17 and 18, from an embryo operated upon as above, show a
median cyclopean eye in which the pigment layer is wanting between
the two components. The two cup cavities are also slightly reduced
in size. This fusion of the eye rudiments in the median line has
taken place in such a manner as to separate the cranial from the
facial portions at the anterior end of the head, contrast Fig. 17 with
a similar view of the normal head, Fig. 4. Figs. 19, 20 and 21
show a somewhat similar cyclopean eye. The operation was done
at the stage shown in Fig. 2, and the embryo killed 15 days later.
The sections show a common cup cavity, the retinal and pigment
layers forming a continuous wall about the cavity. There are two
180
WTarrcn 11. Lewis.
lenses and two pupils, however. The lenses are in contact. There
are also two distinct optic nerves. The brain is reduced in size and
the eye separates it from the mouth region.
Figs. 22, 23 and 24 are from an embryo operated upon at a stage
shown in Fig. 2 and killed 15 days later. Here is a single median
cyclopean eye with one pupil and one lens and one cup cavity. A
slight median notch on the anterior side of the optic cup indicates
its origin from portions of two eye rudiments. The large optic
cup shows in sections a very beautiful median eye with complete
continuity of the layers of the rctinas of the two components about
a single large cup cavity and a single lens. The two nasal pits
are in contact and lie dorsal to the eye. The brain is somewhat
reduced, and its anterior end separated widely from the mouth region
by the medially placed eye.
The explanation of the formation of these various abnormalities
is in a way a comparatively simple one, if we assume that already
in the early embryonic shield stage the various parts of the central
nervous system and the eyes are, probably, already predetermined,
and secondly that there is very little or no power of regeneration
in this tissue. Numerous experiments on regeneration indicate
very clearly that there is very little or no regeneration of the tissue
(at least that of the central nervous system) extruded during the
operation. Tlic repair, taking place after the operation, consists
merely of a rapid closing together of the parts left behind, and thus,
a healing of the wound occurs without regeneration of lost parts.
This closing of the wound is accomplished in a few minutes, and
rudiments are thus brought into contact that normally are quite
widely separated, those of the two eyes, for example. The subsequent
differentiation adjusts itself to the new relations of these rudiments
with the resulting abnormal forms. Thus as one examines these
developing embryos, from the very first time the eye rudiments are
visible in the living specimen under the binocular microscope, they
appear to have the same amount of fusion or loss of an eye that is
clearly to be found in the same individual at later stages and at the
time of hatching. So we can explain these cyclopean forms through
a fusion of the rudiments of the two eyes immediately after the
operation, even though a t this time no rudiments art! risible. Differentiation of the eye tissue c d e n t l y occurs sometime before it
becomes visible by our crude microscopic methods.
Thus cyclopia in man can be explained through the influence of
esternal factors acting during early stages of development in such
il iiianner as to prodlice a singlc eye ridiment, and we need not
seek for a germinal explanation. I n these experiments on fish
embryos, the eye rudiments wcre brought into contact and fused
soon after the operation determining at this time the end result.
There was not the formation of two eyes and then their subseqnent
fusion into a single median eye. It seems likely that in man similar
early fusion of the eye rudiments must take place to produce cyclopia.
These experiments throw no light, of course, on the cause of the early
defect in man, although Stockard's experiments indicate that chemical factors might be responsible for such defective or altered early
development.
The great similarity betwrwi these cyclopean forms and those
produced by Stockard suggests that the lIgC1, may have i n some
nianner prevented the growth of certain cells at the anterior end of
the embryonic shield during the embryonic shield stage. It is possilde that the 31gC1, solution might have the same effect on eggs
subjected to its influence during and just preceding the formaticxi
of the embryonic shield.
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