University of Virginia Library

CHAPTER III.

THE DEVELOPMENT OF THE OYSTER.

The body of an oyster is not a simple, unorganized
lump of flesh, but a complicated organism, made up
of many parts, each one so related to the other parts
that we must study the whole animal before we can
understand the admirable adjustment of each organ to
its use.

The oyster is unintelligible until we have studied
the organs which compose it, and the organs themselves
are unintelligible unless they are studied as
constituent parts of the whole.

The oyster is a unit, a complete individual whole,
made up of units of a lower order, the organs, in
somewhat the same way that a regiment of soldiers is
a unit, made up of units of a lower order, the companies.

A description of the organs of the oyster does not,
however, by any means complete the analysis of its
body, for when any part is studied under a microscope,
after it has been properly prepared, it is found
to be made up of units of a still lower order, just as
each company is made up of individual soldiers, or
as the ten dimes which make a dollar are themselves
made up of cents.

Every part consists of cells, which are united into
organs, in nearly the same way that these are united
to form the oyster; and in order that what I shall say
about its development from the egg may be intelligible,
this fact must be held clearly in mind.

Each cell is a minute portion of living matter, with
an individuality of its own, like the individualities of
the soldiers which form the regiment.

The properties of each organ are due, in part, to the
way in which the cells are arranged, and in part to the
properties of the cells themselves, for the cells which
enter into one organ may be quite different from those
which enter into another.

Each of the cells which form the glandular surface
of the mantle is itself a gland, and is quite different
from a muscle cell, so that, in a certain sense, the
activity of the mantle in forming the shell is the sum
of the activities of its cells, just as the evolutions of a
regiment are the sum of the actions of the soldiers,
but a regiment can do many things which would be
beyond the power of an unorganized mob, and the
formation of the shell is due to the activity of the
mantle as a whole.

In an adult oyster we have gland cells in the mantle,
muscle cells in the muscles, nerve cells in the nervous
system, ciliated cells in the gills, and so on; but if we
study the animal at earlier and earlier stages, we find
that these distinctions disappear, until, in ultimate
analysis, all the cells are alike so far as the microscope
can tell us.

They are simply minute, definitely limited masses of
living matter, with the power to grow when furnished

with food; and after their size has thus increased, they
have the power to multiply by splitting up into smaller
and more numerous cells, which in their turn grow
and multiply in the same way.

They at first exhibit no traces whatever of the uses
to which they are to be put, but as they grow older
they gradually become specialized in various directions
and are built up into the tissues and organs of
the body, losing at the same time their sharp distinctness
and fusing with each other.

Just as certain cells become gland cells, others
muscle cells, and so on, certain cells of the adult
body become set apart as reproductive cells, eggs in
the female and male cells in the male.

The egg cells grow until they become very much
larger than any of the ordinary cells of the body; at
the same time their outlines become sharply defined,
and they become dark-colored and granular. The
granular appearance is due to the fact that as they
approach maturity they become filled with food, which
is stored away in them as a provision for the time
when they are to be cast off from the body of the
oyster, to lead an independent existence.

The male cells are very much smaller than the eggs,
they contain little food, and when they are mature
each of them is furnished with a long cilium or vibrating
hair, by means of which the cell is able to swim
in the water, while the egg is motionless and sinks to
the bottom as soon as it is set free.

When the reproductive elements are fully ripe they
are discharged from the body into the cloacal chamber
of the mantle. The male cells are swept out into the

ocean by the current produced by the gill cilia. As
they contain no food supply, their power to live independently
is very limited, and all soon die except
those which come into contact with eggs.

In the American oyster the eggs are swept out into
the water in the same way. The eggs of the European
oyster are much larger and heavier, and they fall into
the water tubes of the gills and lodge there. Here
they are exposed to the current of water which circulates
through the gills, and this current brings with it
some of the male cells which swim in the water around
the oyster-bed. As soon as one of them comes into
contact with an egg it fuses with it and loses its
individuality and is lost in the substance of the egg,
which is thus fertilized and at once begins its development
into a new oyster.

There is no such provision for securing the fertilization
of the eggs of the American oyster. They are
thrown out into the water, like the male cells, to be
fertilized by accident, and while many of them meet
with male cells, innumerable multitudes sink to the
bottom and are lost. It is fortunate for other animals
that this is the case, for our oyster is so prolific that
if all the eggs were to be fertilized and were to live
and to grow to maturity, they would fill up the entire
bay in a single season. Far from being an exaggeration,
this statement is much short of the truth. An
average Maryland oyster of good size lays about sixteen
million eggs, and if half of these were to develop
into female oysters, we should have, from a single
female, eight million female descendants in the first
generation, and in the second, eight million times
eight million or 64,000,000,000,000.

In the third generation we should have eight million
times this or 512,000,000,000,000,000,000.

In the fourth, 4,096,000,000,000,000,000,000,000,000.

In the fifth, 33,000,000,000,000,000,000,000,000,000,000,000
female oysters, and as many males, or, in all,
66,000,000,000,000,000,000,000,000,000,000,000.

Now, if each oyster fill eight cubic inches of space,
it would take 8,000,000,000,000,000,000,000,000,000,000,000
to make a mass as large as the earth, and the
fifth generation of descendants from a single female
oyster would make more than eight worlds, even if
each female laid only one brood of eggs. As the,
oyster lives for many years, and lays eggs each year,
the possible rate of increase is very much greater than
that shown by the figures.

The waste of oyster eggs through lack of fertilization
is simply inconceivable, but it is possible to fertilize
them artificially by mixing the eggs and the
male cells in a small quantity of water, where they are
certain to come into contact with each other. In this
way about 98 per cent of the eggs may be saved and
made to produce young oysters, and I have had at
one time in a small tumbler of water a number of
active and healthy oysters, greater, many times, than
the whole human population of Maryland.

If several oysters are opened during the breeding
season, which varies according to locality and climate,
as will hereafter be shown, a few will be found with
the reproductive organ greatly distended and of a
uniform opaque-white color. These are oysters which
are spawning or ready to spawn, that is, to discharge
their eggs. Sometimes the ovaries are so gorged

that the ripe eggs ooze from the openings of the
oviducts before the mass is quite at the point of
being discharged. If the point of a knife be pushed
into the swollen ovary, a milk white fluid will flow
out of the cut. Mixing a little of this with sea water,
and placing it on a slide underneath a cover, a lens of
100 diameters will show, if the specimen is a female,
that the white fluid is almost entirely made up of
irregular, pear-shaped, ovarian eggs, each of which
contains a large, circular, transparent, germinative
vesicle, surrounded by a layer of a granular, slightly
opaque yolk. Perfectly ripe eggs will be seen to be
clean, sharply defined, and separate from each other.
If the specimen be male, a glance through the microscope
shows something quite different from the fluid
of a female. There are no large bodies like the eggs,
but the fluid is filled with innumerable numbers of
minute granules, which are so small that they are
barely visible when magnified 100 diameters. They
are not uniformly distributed, but are much more
numerous at some points than at others, and for this
reason the fluid has a cloudy or curdled appearance.
By selecting a place where the granules are few and
pretty well scattered, very careful watching will show
that each of them has a lively, dancing motion, and
examination with a power of 500 diameters will show
that each of them is tadpole-shaped, and consists of a
small, oval, sharply defined "head," and a long, delicate
"tail," by the lashing of which the dancing is produced.
These are the male cells, whose union with
the eggs or ova of the female is necessary to the fertilization
of the latter, and the consequent hatching of
living oysters.

THE OYSTER   PLATE IV

A.Hoen & Co. Lith

The number of male cells which a single male will
yield is great beyond all power of expression, but the
number of eggs which an average female will furnish
may be estimated with sufficient exactness. An unusually
large American oyster will yield nearly a
cubic inch of eggs, and if these were all in absolute
contact with each other, and there were no portions of
the ovaries or other organs mixed with them, the
cubic inch would contain 5003, or 125,000,000. Dividing
this by two, to allow for foreign matter, interspaces
and errors of measurement, we have about
60,000,000 as the possible number of eggs from a
single very large oyster.

I have shown that, by mixing eggs extracted from
a female with male cells, it is an easy matter to secure
their union in a watch crystal or in a glass beaker.

The body of the oyster, like that of all animals,
except the very simplest, is made up of organs, such
as the heart, digestive organs, gills and reproductive
organs, and these organs are at some period in the
life of the oyster made up of microscopic cells. Each
of these consists of a layer of protoplasm around a
central nucleus, which, in the egg, is a large, circular,
transparent body, known as the germinative
vesicle. Each cell of the body is able to absorb food,
to grow, and to multiply by division, and thus to contribute
to the growth of the organ of which it forms a
part. The ovarian eggs are simply the cells of an
organ of the body, the ovary, and, so far as the microscope
shows, they differ from the ordinary cells only
in being much larger and more distinct from each
other; and they have the power, when detached from

the body, of growing and dividing up into cells, which
shall shape themselves into a new organism like that
from whose body the egg came. Most of the steps
in this wonderful process may be watched under the
microscope, and, owing to the ease with which the
eggs of the oyster may be obtained, this is a very
good egg to study.

About fifteen minutes after the eggs are fertilized,
Plate IV, Fig. 1, they will be found to be covered
with male cells. In about an hour the egg will be
found to have changed its shape and appearance. It
is now nearly spherical, and the germinative vesicle is
no longer visible. The male cells may or may not
still be visible upon the outer surface. In a short
time a little transparent point makes its appearance
on the surface of the egg, increases in size, and soon
forms a little, projecting, transparent knob—the polar
globule.

Recent investigations tend to show that while these
changes are taking place, one of the male cells penetrates
the protoplasm of the egg and unites with the
germinative vesicle, which does not disappear, but
divides into two parts, one of which is pushed out of
the egg and becomes the polar globule, while the
other remains behind and becomes the nucleus of the
developing egg, but changes its appearance so that it
is no longer conspicuous. The egg now becomes
pear-shaped, with the polar globule at the broad end
of the pear, and this end soon divides into two parts,
so that the egg is now made of one large mass and
two slightly smaller ones, with the polar globule
between them. Plate IV, Fig. 2.

The later history of the egg shows that at this early
stage it is not perfectly homogeneous, but that the
protoplasm which is to give rise to certain organs
of the body has separated from that which is to give
rise to others.

If the egg were split vertically we should have what
is to become one half of the body in one part and the
other half in the other. The single spherule at the
small end of the pear is to give rise to the cells of
the digestive tract of the adult, and to those organs
which are to be derived from it, while the two spheres
at the large end are to form the cells of the outer wall
of the body and the organs which are derived from it,
such as the gills, the lips and the mantle, and they are
also to give rise to the shell. The upper portion of the
egg soon divides up into smaller and smaller spherules,
Plate IV, Figs. 3, 4, 5, until we have a layer of small
cells wrapped around the greater part of the surface of
a single large spherule. This spherule now divides
up into a layer of cells, and at the same time the egg,
or rather the embryo, becomes flattened from above
downward, and assumes the shape of a flat, oval disk.
In a sectional view it is seen to be made up of two
layers of cells; an upper layer of small transparent
cells, which are to form the outer wall of the body,
and which have been formed by the division of the
spherules which occupy the upper end of the egg, and
a lower layer of much larger, more opaque cells, which
are to become the walls of the stomach, and which have
been formed by the division of the large spherule.

This layer is seen in the section to be pushed in a
little toward the upper layer, so that the lower surface

of the disk-shaped embryo is not flat, but very slightly
concave. This concavity is destined to grow deeper
until its edges almost meet, and it is the rudimentary
digestive cavity. A very short time after this stage
has been reached, and usually within from two to four
hours after the eggs were fertilized, the embryo undergoes
a great change of shape. Plate IV, Fig. 6.

A circular tuft of long hairs, or cilia, now makes
its appearance at what is thus marked as the anterior
end of the body, and as soon as these hairs are formed
they begin to swing backward and forward in such a
way as to constitute a swimming organ, which rows
the little animal up from the bottom to the surface of
the water, where it swims around very actively by the
aid of its cilia. This stage of development, which is
of short duration, is of great importance in rearing the
young oysters, for it is the time when they can best be
siphoned off into a separate vessel and freed from the
danger of being killed by the decay of any eggs which
may fail to develop. On one surface of the body at
this stage there is a well-marked groove, and when a
specimen is found in a proper position for examination,
the opening into the digestive tract is found at the
bottom of this groove. The embryo now consists of
a central cavity, the digestive cavity, which opens
externally by a small orifice, the primitive mouth,
and which is surrounded at all points, except at the
mouth, by a wall which is distinct from the outer
wall of the body. Around the primitive mouth these
two layers are continuous with each other.

This stage of development, in which the embryo
consists of two layers, an inner layer surrounding a

cavity which opens externally by a mouth-like opening,
and an outer layer which is continuous with the
inner around the margins of the opening, is of very
frequent occurrence, and it has been found, with modifications,
in the most widely separated groups of animals,
such as the starfish, the oyster, and the frog, and some
representatives of all the larger groups of animals, except
the Protozoa, appear to pass during their development
through a form which may be regarded as a more
or less considerable modification of that presented by
or oyster-embryo. This stage of development is
known as the gastrula stage.

Certain full-grown animals, such as the fresh-water
hydra and some sponges, are little more than modified
gastrulas. The body is a simple vase, with an
opening at one end communicating with a digestive
cavity, the wall of which is formed by a layer of cells,
which is continuous around the opening with a second
layer, which forms the outer wall of the body. This
fact, together with the fact that animals of the most
widely separated groups pass through a gastrula stage
of development, has led certain naturalists to a generalization,
which is known as the "gastrula theory."
This theory or hypothesis is that all animals, except the
Protozoa, are more or less direct descendants of one
common but very remote ancestral form, whose body
consisted of a simple two-walled vase, with a central
digestive cavity opening externally at one end of the
body.

Soon a small, irregular plate makes its appearance
on each side of the body. These little plates are the
two valves of the shell, and in the oyster they are separated

from each other from the first, and make their
appearance independently.

Soon after they make their appearance the embryos
cease to crowd to the surface of the water, and sink to
various depths, although they continue to swim actively
in all directions, and may still be found occasionally
close to the surface. The region of the body which
carries the cilia now becomes sharply defined, as a
circular, projecting pad, the velum, Figs. 7, 8 and 9,
and this is present and is the organ of locomotion, at
a much later stage of development.

The two shells grow rapidly and soon become quite
regular in outline, but for some time they are much
smaller than the body, which projects from between
their edges, around their whole circumference, except
along a short area, the area of the hinge, upon the
dorsal surface, where the two valves are in contact.

The two shells continue to grow at their edges, and
soon become large enough to cover up and project a
little beyond the surface of the body, and at the same
time muscular fibres, Fig. 9, make their appearance.
They are so arranged that they can draw the edge of the
body and the velum in between the edges of the shell.
In this way that surface of the body which lines the
shell becomes converted into the two lobes of the
mantle, and between them a mantle cavity is formed,
into which the velum can be drawn when the animal
is at rest. While these changes have been going on
over the outer surface of the body, other important
internal modifications have taken place.

Soon the outer wall of the body becomes pushed
inward, to form the mouth. The digestive cavity now

becomes greatly enlarged, and cilia make their appearance
upon its walls; the mouth becomes connected
with the chamber which is thus formed, and which
becomes the stomach, and minute particles of food are
drawn in by the cilia, and can now be seen inside the
stomach, where the vibration of the cilia keep them in
constant motion. Up to this time the animal has
developed without growing, and is scarcely larger than
the unfertilized egg, but it now begins to increase in
size.

Soon after the mouth has become connected with
the stomach this becomes united to the body wall at
another point a little behind the mouth, and a second
opening, the anus, is formed. The tract which connects
the anus with the stomach lengthens and forms the
intestine, and, soon after, the sides of the stomach
become folded off to form the two halves of the liver,
and various muscular fibres now make their appearance
within the body.

Such is the scientific history of the oyster-embryo.
The practical utility of the knowledge, however, to
the most of us, is that the American oyster lays a vast
number of eggs, but that they are exposed to dangers
so constant and innumerable, that under ordinary conditions
few ever come to life, or at any rate succeed in
living long enough to anchor themselves and take on
the protection of shells. This is only another example
of a fact well known to naturalists. The number
of eggs laid, or even of individuals born, has very little
to do with the abundance of a species, which is determined,
mainly, by the external conditions to which
it is exposed.

Life of the Young Oyster.—The young American
oyster leads a peculiarly precarious life, since
it is first thrown out an unfertilized egg, and the
chance that it will immediately meet with a male cell
must be very slight; yet if it does not it will perish,
for the sea-water soon destroys unimpregnated eggs.
Having by good chance become fertilized by meeting
a male cell, the next period of great danger is
the short time during which the embryos swarm to
the surface of the water. They are so perfectly defenseless,
and so crowded together close to the surface,
that a small fish, swimming along with open
mouth, might easily swallow, in a few mouthfuls,
a number equal to a year's catch. They are also
exposed to the weather, and a sudden cold wind
or fall in temperature, such as occurred several
times during our experiments, killed every embryo.
The number which are destroyed by cold rains and
winds must be very great indeed. As soon as they
are safely past this stage, and scatter and swim at
various depths, their risks from accidents and enemies
are greatly diminished. Up to this point, which is
reached in from twenty-four hours to six days, there is
no difficulty in rearing them in an aquarium, provided
uniform warm temperature be preserved.

Although I failed to keep the young oysters alive
until they were large enough to handle and plant, my
experiments showed the possibility of rearing them in
unlimited numbers, so soon as some practical method
of preserving them alive during their infancy should
be discovered.

The next great step in this direction is due to Lieut.
Winslow. While I was carrying on my experiments
at Crisfield, in 1879, this officer was engaged in examining
the oyster-beds of Tangier Sound, and he
made frequent visits to the laboratory and learned my
methods. The next year, while stationed at Cadiz,
Spain, on naval duty, he repeated the experiments
with Portuguese oysters, and showed that these, like
the American oysters, have the sexes separate, and
that the eggs are fertilized in the water; that the
young are independent of parental protection, and
that they can be artificially reared like the oysters of
our waters. His results were given in a paper which
was read before the Maryland Academy of Sciences,
in November, 1881, and this paper was afterwards
printed in the American Naturalist.

The next great step was the discovery of a simple
and practical method of rearing the young oysters
which are hatched artificially, and this step, which
completes the solution of the problem, and puts it
within our power to remove forever all danger of the
extermination of the oyster, is the contribution of a
French naturalist, M. Bouchon-Brandeley. This
author, like Winslow, experimented with the Portuguese
oysters, and while he does not seem to have
been acquainted with Winslow's paper, he arrived at
the same conclusion, and showed that the sexes are
separate, that the eggs are fertilized in the water, and
that the young may be hatched artificially; but he
also went one step further, and succeeded in rearing
in this way a very great number of seed-oysters fit for
planting.

His paper was translated and printed April 19, 1883,
in the Bulletin of the U. S. Fish Commission. The
following extracts from this translation show the character
of the methods which are employed, and the results
which were obtained:

"The mollusc, known under the name of the Portuguese
oyster, has not existed upon our coast for more
than thirty years. It is superfluous to here describe
their external form, in that it does not recall that of
O. edulis. In respect to sexuality, the difference between
these two molluscs is very great; most radical.
Ostrea edulis is hermaphrodite; O. angulata is unisexual
or diœcious. We have opened more than
10,000 in all phases of reproductive activity, and we
have not seen a single one of the latter of which the
sex was doubtful. They were all either exclusively
male or exclusively female."

"No less marked is the difference in the mode of
reproduction. The eggs of the common oyster are
fecundated within the valves of the parent, apparently
within the openings of the oviducts; those of the
Portuguese species on the bosom of the waters. The
first cannot develop outside of the incubatory cavity
of the parent; the second undergo their development
in the open currents. The larvæ of O. edulis, in order
to live, develop and attain the errant or pelagic stage
of their existence, are dependent upon the albuminous
liquid secreted by the mother; those of O. angulata,
more vigorous, more independent, and altogether
more active, transport themselves into the living
waters, to there take up the nutritive matters which are
necessary to transform them into spat.

"When after two years we had learned for a certainty
that the sexes of Ostrea angulata were confined
to separate individuals, we immediately conceived that
it was possible to artificially fertilize the eggs of this
mollusc. We were likewise encouraged by the experiments
which Brooks, of the Johns Hopkins University
of Baltimore, had made upon Ostrea virginica,
likewise unisexual, and which had enabled him to follow
the development of the embryos to the formation
of the shell."

"M. Tripota, one of the veteran ostraculturists, and
at the same time one of the most competent, very willingly,
at the request of the commissioner, M. Jouan,
placed at our disposal, with a grace and disinterestedness
for which we are under great obligations, two
beautiful unsubmersible claires, which received fresh
water for several days during the spring tide, and
which were soon arranged for our use by means of
some slight internal alterations. Separated from each
other by a straight, massive wall of earth, these two
ponds, with an area of about 100 meters each, and an
average depth of 80 centimeters to 1 meter (27 inches
to 3 feet), were placed in communication by means of
a pipe, which was closed at either end by a sponge, to
keep out any sediment in suspension in the water. In
this manner all doubt as to the origin of the spat
which was collected was guarded against."

"For the outlet, an apparatus consisting of a wall of
fine sand confined by boards permitted the water to
percolate through it, but prevented the embryos from
escaping with it. The lowermost claire only was
utilized in our experiments. The uppermost claire, in

which we stored the water whenever it was possible,
served as a reservoir from which to decant, the supply
pipe allowing nothing to pass into the experimental
claire except clear water."

"This arrangement completed, the products of artificial
fecundation, impregnated in various ways, were
poured into the experimental reservoir. This took
place in the second week in June."

"According to our belief, we hoped to find some
spat on the collectors placed in the experimental claire
at the end of the same month or by the beginning of
the month of July. M. Tripota, who had taken an active
part in the work, and who took my place in my
absence, continued to supply the claire with fertilized
eggs and mobile embryos."

"The time assigned for experimental proof having
arrived, the collectors were examined, but they did
not bear any apparent trace of spat. This was a deception.
Meanwhile, thinking that the season for the
fry had not yet begun in the Gironde, we expected
happier results from our final experiments. The claire
was emptied, and some modifications were introduced
in the management of the water, and from day to day
mixtures of the generative products were again poured
into the claire."

"On the 24th July the tiles were examined. This
time all had spat attached. It was therefore evident
that the first experiments had not been as unsuccessful
as we had supposed. In fact, each of the tiles immersed
had young oysters attached, to the number of
twenty or thirty, measuring about a centimeter (two-fifths
of an inch) in diameter. This spat was evidently

derived from the spawn put out during the end of
June or the commencement of July; but their small
size had prevented us from seeing them when the inspection
was made at that time. On the 24th July we
had specimens about a month old. This fact was all
the more remarkable, in that, up to that same time, the
collectors placed in the Gironde, in the very center of
the spawning beds, did not show a sign of spat."

"The problem which we had put before ourselves
had accordingly received, from a scientific and practical
point of view, a solution in conformity with our
hopes. It was possible to obtain spat by means of
artificial fecundation, and to capture it in confined
waters. And we no longer had the slightest reason
to doubt the identity of that which had caught on our
tiles, nor to suppose that it came from the waters
without, since there was as yet none apparent in the
Gironde, and the tiles in the upper claire, which served
to feed the experimental claire, were completely
exempt."

"If in forcing nature's processes we arrive at the
same result, that is, provoke the birth of the young
before the time of the normal emission of the spawn,
there is all the more reason for us to suppose that we
have an excellent means to aid and favor her."

Such, briefly sketched, is the early history of the
oyster, and the process of rearing oysters artificially;
but its development is of vastly greater interest than
a mere description would indicate. It contains
enough material for philosophical meditation and for
scientific research to occupy many generations of
students, and the practical importance of a knowledge

of its embryology does not end with the facts, and we
shall find among the purely speculative deductions
which naturalists have drawn from it much which will
help us to appreciate and to utilize the oyster as a
food resource.

When the egg is first laid it is a little globule of
living matter, with no visible indication of the structure
of an oyster, although it is a potential oyster, and
is destined to build up, slowly, but surely, from the
vegetable food in the water, every part of a complicated
adult like that which produced it. It is not, however,
an oyster in miniature. Our utmost means of observation
do not reveal in it anything whatever, at all like
the structure of the adult. Such structure as the
microscope does show is the structure of a cell, like
one of those which make up the oyster's body, and
the process of development is at first simply a process
of cell-multiplication, not the unfolding and enlargement
of a rudimentary oyster. If we compare an
adult oyster to a brick house, then the egg corresponds
to a brick, not to a little house, and development
begins by cell-division or the multiplication of
bricks rather than by the growth of a little house. So
far as the microscope tells us, there is nothing like an
oyster in the egg, yet it must be there in some form,
for an oyster's egg never becomes anything except an
oyster. If we knew only the higher animals we might
suppose that the development of an egg is guided in
some way by the influence of the parent; but there
can be no such directing influence in the case of the
oyster egg, for this is thrown on the world to take
care of itself before its development begins. The

force which causes it to become an oyster cannot come
from parental influence, nor can it be due to anything
in the external world, for hosts of other animals live
in the water with the oyster, and side by side with the
oyster eggs float those of starfishes, annelids and
countless other animals, all exposed to exactly the
same external conditions, and yet each develops after
its own kind, and builds up cell by cell an animal like
its parent.

There is no escape from the belief that the directing
force is in the egg itself, and when the microscope
was first used to study the early stages of animals,
naturalists thought they could discover in the egg the
little image in miniature of the future animal, and they
taught that this exists in a perfect but dormant and
unexpanded condition in the egg, and that the process
of development is nothing more than the growth and
expansion of this germ.

More careful study with better instruments and improved
methods has failed to verify this supposed discovery,
and so far as our present means of research
go, they reveal nothing whatever in the egg which
resembles the adult in any particular, nor do they
show anything in the oyster egg which should cause
it to become an oyster rather than some other animal.
The testimony of all observers, based upon the study
of all kinds of animals, is that the egg is not comparable
to the adult in miniature, but to one of the constituent
cells of its body; that the development of an
egg is not the unfolding of a germ, but a process of
cell-multiplication. The egg divides into a number of
cells like itself, and these divide and subdivide until

they are very numerous. At first they are alike, but
they soon become specialized in different directions,
and thus gradually build up the tissues and organs of
the body. These gradually acquire their final form,
but they are at first simple cell-aggregates, out of
which the complex whole is finally built up by the
combination and organization of the simple units,
somewhat as a regiment of soldiers is organized from
a mob of men.

The directing influence must be in the egg, although
it has so far eluded all efforts to discover it. The adult
oyster, with its complicated organs, so beautifully and
wonderfully fitted to its needs, and so intricately related
to each other as parts of a complex whole, is a
most interesting subject for study. No one can study
the structure of any animal without admiring the fitness
of all its parts for their work. As we trace out
the use of one part after another, and the oyster becomes
intelligible to us, its completeness impresses us
more and more; but if we are thus impressed by the
study of a complicated mechanism, adapted for bringing
about complicated results, what must be our reflections
when we find in the egg the capacity for producing
the same results without any visible mechanism
whatever! Everything which seems so admirable in
the adult, when it is the result of organization, exists
potentially in the egg, where there is no discoverable
organization; and if the result of the process of development,
the complete oyster, is wonderful and interesting,
how much more wonderful is the process
itself. To those who can picture in imagination its
hidden structure, an egg is one of the most marvellous

bodies in the universe. Elsewhere we have complex
results from complex means, but here we have
the most complex of all things, a living body, arising
without any visible machinery.

Even after the cells which result from the multiplication
of the egg cell become pretty numerous and
begin to shape themselves into a complicated body,
this at first bears no close resemblance to an oyster,
and while the ultimate outcome is an oyster like the
parent, I should give my readers a very incomplete
and erroneous picture of the history of its development
if I did not lay stress upon the very remarkable
fàct that this result is not reached directly.

The mature oyster is a sedentary animal with no
power of locomotion. It lies on its side, soldered to
the bottom by the outside of the deep spoon-shaped
left shell, for which the flat right shell forms a movable
lid. Its gills are very complicated organs, adapted
for drawing into the fixed shell a steady current of
water, and they pour into the open mouth of the animal
a constant stream of food, so that eating goes on as uninterruptedly
as breathing, and is just as much beyond
the control of the animal. The adult oyster makes
no efforts to obtain its food, it has no way to escape
from danger, and after its shell is entered it is perfectly
helpless and at the mercy of the smallest enemy.
So far as active aggressive life goes it is almost as
inert and inanimate as a plant, and its life is purely
vegetative. This is the adult oyster. The young
oyster is very different. It is an active animal, swimming
from place to place. Its gills are not leaf-like,
and they do not divide the mantle-chamber into two

parts. They are nothing but breathing organs, and
are simple finger-like tentacles which hang down into
the water. There is no gill-current as there is in the
adult, and the young oyster must find its own food by
swimming through the water. Its two shells are also
exactly alike, and therefore quite different from those
of the adult.

The egg therefore tends, at first, to build up an
animal which differs greatly from the adult, in structure
as well as in habits, and naturalists believe, as I
have already said, that our modern oysters are the
descendants of an ancient form which was not sedentary,
and the egg at first exhibits a decided tendency
to build up this ancestor rather than an oyster.

Some of you may ask how we know that the remote
ancestors of the oyster were different from modern
oysters. This is a fair question, and I will try to give
an outline of the reasons for this opinion, and perhaps
an illustration may help us.

When a Baltimorean visits New York or Savannah
or Boston or Chicago, he finds that while the people
of these cities talk the same language, it is with a
difference. They all talk what they call English, but
when an Englishman comes among us he tells us
that it is not English, and it is quite clear to an
American who visits England that the people there do
not know how to talk United States, although the
differences are trivial ones, of accent and idiom, and
do not in the least hinder conversation.

If, however, we cross the narrow strip of water
which separates England from the German empire, we
find a strange language, which at first seems totally

unfamiliar and unintelligible, but as our ears become
more accustomed to the strange sounds we find many
which are not as unintelligible as they seemed at first.

When a German talks of his vater, his mutter, his
bruder, his schwester, when he asks us to share his
brod und butter, or offers us a glas wasser, we need no
dictionary to tell us what he means.

We know that the Americans and the English of
to-day are descended from common ancestors, only a
few generations back, from whom they have inherited
their common language, and we know from literature
that this was not exactly the same as modern English
or modern American, and history also tells us that
still further back, Anglo-Saxon and modern German
had a common starting-point. Philologists therefore
make use of the resemblances between languages to
trace out their origin, and whenever they find that two
or three languages have a common plan, a fundamental
similarity of grammatical structure, they believe
that they are divergent modifications from a
common starting-point. In some cases printed language
has preserved an actual history of the process,
but in other cases, where there is no such history, the
student of comparative grammar forms his conclusions
by comparison; and, even where the primitive language
is lost, he is able to reconstruct it in part, for he
knows that it must have been characterized by all the
features which its derivatives have in common.

Now, animals exhibit resemblances of very much
the same character as those between languages, and
when we find that several representatives of a great
group are constructed upon the same fundamental

plan, we infer, just as the philologist does, that they
are the divergent descendants of a common ancestor,
from whom they have inherited the features which
they have in common.

The philologist is sometimes able to verify his conclusion
by the proofs which have been preserved in
books and inscriptions, and he regards this as evidence
that, in other cases where no such record is preserved,
his results are equally trustworthy.

Occasionally the student of comparative anatomy,
like the student of comparative grammar, finds a fossil
form which unites in itself the characteristics of several
widely separated descendants, and is thus enabled to
test and to verify the conclusions which he has reached
by comparative study.

In this way, through the study of details too numerous
and minute to be described here, it can be shown
that the oyster is descended from a mollusc which
was furnished with locomotor organs and sense organs,
and which wandered about in search of food, and had
altogether a much wider and more varied life than that
of the oyster. Its gills were very simple and were
nothing but breathing organs, and the many uses
which they serve were provided for by distinct organs.

Very long ago, as we measure time, but quite late
in the history of the mollusca, as the continental areas
were elevated and became covered with terrestrial
vegetation, and fringed by bays and sounds of brackish
water, it gradually became modified in such a way as
to fit it for life in these estuaries. Its locomotor organs
and its organs for discovering and capturing food
were gradually lost, as it learned to feed upon the

microscopic life of the mud-flats. The gills then
gradually became modified and fitted for maintaining
the circulation of water, and for filtering out the
minute food particles it contains.

Food is most abundant on the muddy bottom, but
in estuaries this is so deep and soft that a locomotor
animal would sink and smother in it, so the oyster
has gradually become converted into a fixture, and
has learned to fasten itself when young to something
firm enough to keep it out of the soft mud, but near
enough to it to be within easy reach of the vast supply
of food which it affords. As a fixed animal does not
need to have the two sides of its body balanced, the
fixed oyster has become one-sided, and has thus been
still better fitted for its peculiar mode of life.

These changes, while they are on the whole advantageous,
since they enable the oysters to avail
themselves of inexhaustible supplies of food, are not
without disadvantage. The oyster has become so
perfectly adapted for a life on those hard bodies which
occur in the soft mud of estuaries, that it cannot live
anywhere else, and the young oysters which do not
find a proper home soon die. In shallow bays and
sounds hard substances are rare and far apart, and
many young oysters must perish from inability to
find a proper resting place. To meet this danger the
oyster's birth rate has been enormously increased, so
that among its innumerable descendants some few
may be able to find proper homes, and may grow up
to maturity in their turn.