G. Brown (George Brown) Goode.

The fisheries and fishery industries of the United States (Volume 1:1) online

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heart from the gills before it passes to all parts of the body.

A curious and interesting point which I think it desirable to mention, because I have not
noticed that attention has hitherto been especially called to it, is the metamorphosis of the larval
Oyster into the adult. A. de Quatrefages 1 has alluded to it, but not in explicit terms. I have
shown in my sketch on the growth of the animal that the larval shell was quite different from that
of the adult, in fact, more like a very diminutive pisidium than anything else. The metamorphosis
of the larval shell, or rather its passage into that of the spat, is abrupt. Not so with the soft parts ;
the oldest larva? yet studied by any competent biologist show that the mouth of the larva is
placed on the ventral side of the embryo, and that the hinge is situated on almost exactly the
dorsal or opposite side. The ventral position of the month of the larva? and its anterior or cephalic
position in the adult show that a very important series of changes in the position of the viscera
must take place between the time when the larva loses its principal embryonic features and
acquires the adult arrangement and relations of its hard and soft parts. In other words, we are
made aware, after instituting the foregoing comparison, that the Oyster actually undergoes a
metamorphosis.

If an Oyster be carefully opened it will be found that the animal adheres to the shell at four
points, or at two points on either valve. The principal points of attachment are of course the
insertions of the great compound adductor muscle, made np of two portions which may be
distinguished by the color of the cut ends of the component fibers. The great shield-shaped
purple areas on either valve mark the points of insertion of the great adductor in the American
Oyster, and also in the Portuguese form, which resembles it considerably. In Ontrea eduli*, or the
European species, the insertion of the adductor muscle is very rarely colored, so rarely indeed that
*we may regard this feature as one of the specific marks of this form. But in both the American
and the European species there is a second muscular attachment, as implied above, which appears
to have been very generally overlooked. It is situated nearer to the hinge than to the great
adductor, and is sometimes marked by a slight depression not over an eighth of an inch in its
greatest transverse diameter. It gives attachment to a feeble muscular bundle which springs out
of the mantle on either side of the visceral mass, and when the animal is torn loose a slight
whitish scar on the soft part marks its posit inn on the surface of the mantle. I have been
informed that Mr. W. H. Dall, who has investigated the matter, has identified this muscle with
the pedal muscle of some other acephalous mollusks.

212. SEX, SEXUAL PRODUCTS, AND DIFFERENCE OF THE SEXUAL HABITS OF THE

AMERICAN AND EUROPEAN OYSTERS.

"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. A single ripe egg measures about one five-hundredth of an iiu-h in diameter,
or five hundred laid in a row, touching each other, would make one inch; and a square imli would
contain five hundred such rows, or 500 x 500=250,000 eggs. Nearly all the eggs of a perfectly

1 Metamorphoses of Man and the Lower Animals. Translated by H. Lawson, M. D., pp. 104-109. London, 1864.



720 NATURAL HISTORY OF AQUATIC ANIMALS.

ripe female may be washed out of the ovary into a beaker of sea-water, and, as they are heavier
than the sea-water, they soon sink to the bottom, and the eggs of a medium-sized female will
cover the bottom of a beaker two inches in diameter with a layer of eggs one-twentieth of an inch
deep. The area of the bottom of a beaker two inches in diameter is little more than three square
inches, and a layer of eggs one-twentieth of an inch deep, covering three square inches, is equal to
one three twentieths of an inch deep and two square, and as a single layer of eggs is one five-
hundredth of an inch thick, a layer three-twentieths of an inch thick will contain seventy-five
layers of eggs, with 250,000 eggs in each layer, or 18,750,000 eggs. It is difficult to get the eggs
perfectly pure, and if we allow one-half for foreign matter and errors of measurement, and for
imperfect contact between the eggs, we shall have more than nine millions as the number of eggs
laid by an Oyster of average size, a number which is probably less than the true number.

" Mobius estimates the number of eggs laid by an average European Oyster at 1,012,925, or only
one-ninth the number laid by an ordinary American Oyster; but the American Oyster is very much
larger than the European, while its eggs are less than one-third as large; so the want of agreement
between these estimates does not indicate that either of them is correct.' Another estimate of
the number of eggs laid by the European Oyster is given by Eyton (' History of the Oyster and
Oyster Fisheries,' by T. 0. Eyton, London, 1858). He says, p. 24, that there are about. 1,800,000,
and therefore agrees pretty closely with Mobius.

"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 500 3 , or 125,000,000. Dividing this, as before, 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 Oyster.

" Although each male contains enough fluid to fertilize the eggs of several females, there does
not seem to be much difference in the number of individuals of the two sexes. When a dozen
Oysters are opened and examined, there may be five or six ripe females and no males, but in
another case a dozen Oysters may furnish several ripe males but no females, and in the long run
the sexes seem to be about equally numerous. Oystermeu believe that the male may be dis-
tinguished from the female by certain characteristics, such as the presence of black pigment
in the mantle, but microscopic examination shows that these marks have no such meaning, and
that there are no differences between the sexes except the microscopic ones. It is not necessary
to use the microscope in every case, however, for a little experience will enable a sharp observer
to recognize a ripe female without the microscope. If a little of the milky fluid from the ovary of
a female with ripe or nearly ripe eggs be taken upon the point of a clean, bright knife-blade and
allowed to flow over it in a thin film, a sharp eye can barely detect the eggs as white dots, while
the male fluid appears perfectly homogeneous under the same circumstances, as do the contents of
the ovary of an immature female, or one which has finished spawning. When the eggs are mixed
with a drop of water they can be diffused through it without difficulty, while the male fluid is
more adhesive and difficult to mix with the water. By these indications I was able in nearly
every case to judge of the sex of the Oyster before I had made use of the microscope. 2

"During my investigations I submitted more than a thousand Oysters to microscopic
examination. My studies were carried on during the breeding season, and I did not find a single

'Miibios' measurement, from .15 to .18 millimeter, is given (Austern und Austernwirthschaft, 1877) as the diameter,
not of the egg, but of the embryo, but his figures show that the European Oyster, like the American, does not grow much
during the early stages of development, but remains of about the same size as the egg.

1 W. K. BROOKS: op. cit., pp. 13-15.



THE CELL STRUCTURE OF THE OYSTER. 721

hermaphrodite. The m;ile cells are so small compared with the eggs that it would be impossible
to state that a mass of egjjs taken from the ovary contained no spermatozoa, although they could
not escape detection it tliey were at all abundant.

"On the other hand, a single egg in the field of the microscope, in a drop of male fluid, would
be very conspicuous and could not escape detection ; and the fact that not a single case of this
kind occurred is sufficient to establish the distinctness of the sexes at the breeding season." 1

Writing about this matter in 1880, I said: "No evidence to show that our Oyster is her-
maphrodite was found during the entire season ; nor were my searches for embryo or eggs in
the mantle or in the gills more successful than those carried on two years before by Professor
Brooks. There is no doubt whatever that the Oyster of Europe nurses its young in its mantle
or gills for some time ; nor can we well question the very high authority of Mobius for saying
that in most cases the sexes are separate, and that only one kind of products, viz, either eggs or
spermatozoa, are at any time found in the generative organs. Lacaze-Duthier's observations seem
to confirm the conclusions of Mobius."

In reference to the structure of the cells which make up the body of the Oyster, as well as
regarding the eggs, Dr. Brooks, on page 19 of his essay, writes as follows:

" 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 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."

Brooks has represented the freshly laid ova of the Oyster with a spherical nucleus and
nncleolus ; the former is large and clear, and is imbedded near the center of the egg, and inside of
it the nucleolus is lodged somewhat to one side. I do not find the latter spherical, as described,
but formed as if composed of a larger and smaller highly refringent pair of spheres, partly fused
with each other, or of the same form as the nncleoli of the eggs of Anodonta as described by
Flemming.

Some investigations conducted under the auspices of the Dutch Government indicate that the
structure of the generative organs of the European Oyster is not, as has been supposed, strictly
follicular, but that they may rather be regarded as a mass of anastomosing tubes of irregular caliber.
The complete proof of this has been developed by the writer in the course of investigations carried
out upon oar native Oysters, in which the generative organs were very immature during the
winter season. Both Brooks and myself have spoken of the generative follicles as though they
had been clearly made out ; it now appears that we will be compelled to modify our terminology
somewhat, in the face of the fact that I have sections of the immature generative organ which
exhibit it as a network of germinal cells, as well as sections of the mature organs which show a
more or less distinct tubular structure opening toward the surface into the superficial or surface
outgoing canals. At the same time the tubes show more or less extensive junction or anastomosis
with each other at certain points along their length, with a general tendency to be disposed
vertically to the surface of the visceral mass. This arrangement reminds one somewhat of the

>w. K. BBOOKS: op. fit., p. 35.
46 F



722 NATURAL HISTORY OF AQUATIC ANIMALS.

more or less parallel disposition of the seminal tubules of the testicles or milt of fishes and higher
animals.

In microscopical cross-sections of the adult Oyster, whether it be male or female, the repro-
ductive glands are found to be composed of a great number of minute pouches or follicles. In the
gross arrangement of the follicles no difference between the sexes is discernible when thin sections
are scrutinized with the microscope. Upon making an examination of the contents of the follicles
with the microscope a great difference at once becomes manifest; in the male the spermatic
particles in the follicles appear very finely granular, and if mature the tails or flagella of the
spermatic particles tend to be directed toward the outlet of the follicle; in the female, sections of
the follicles show the eggs in various stages of development attached by their narrow extremity
to the walls of the reproductive saccules. The egg is pyriform in shape while still in the ovary,
but the stalk is not as long as in the eggs of Scrobicularia, as described by von Jhering. As
elsewhere stated, the oyster-egg is not globular when first extruded. It will be readily understood
that the sexes may be very readily distinguished by these and other marks observed in sections.
The immature ova are vastly larger than the spermatozoa, which measure under the ten-thousandth
of an inch at their largest end. The head of the spermatozoon of both the American and European
Oyster is globular; that of the spermatozoon of the Soft Clam (Mya) is ovoidal in form. The tail
or nagellum of the spermatic particle is the locomotive organ which lashes back and forth very
rapidly and propels it through the water and finally brings it into contact with the egg.

213. NEW METHODS OF DISTINGUISHING THE SEXES AND OF TAKING THE EGGS OF

THE OYSTER. 1

DISCRIMINATION OF THE SEXES. One of the first requisites of a practical system of arti-
ficial fertilization of the eggs of the Oyster is a means which, in the hands of unskilled persons,
will enable them, without the aid of a microscope, to infallibly distinguish the sexes apart. Such
a means we now propose to describe. Having tested it practically, and found it possible to
instruct persons of ordinary intelligence in a few minutes, we have no hesitation in offering an
account of the method so as to make it more generally available in the hands of those who may
be interested in this subject.

It is premised that the spawn is squeezed from the reproductive glands by the method to be
described further on. As soon as the spawn is emitted from the generative opening in consequence
of the pressure exerted upon the gland and the ramifications of its ducts, it is drawn up by means
of a small pipette or medicine dropper, provided with a small collapsible bulb at the upper end
which is held between the thumb and forefinger. Pressing the bulb between the fingers, then
immersing the open end of the pipette into the extruded spawn, and then allowing the bulb to
expand by its own elasticity, it will draw or suck up the spawn which has been pressed out very
neatly; and if one is careful, absolutely nothing but the spawn is picked up. One soon becomes
very expert in the use of the pipette.

The next requisite is a shallow glass dish, or even a plain tumbler will answer, into which
say a half gill of clean sea-water has been poured. Taking up the extruded spawn from the
oiening of the duct it is dropped from the pipette into the clear water. This last simple operation
enables us to tell without fail to which sex the products belong. If the creamy white mass consists
of eggs which have been pressed from the generative openings and is dropped into the water, it will
at once break up into a granular cloud as the spawn strikes the latter, the granules themselves

'The observations and experiments discussed in this article were conducted at Saint Jerome's Creek during the
months of July and August, 1882.



AKTIFH'IAL I.KT I.D! NC OK OYSTERS. 723

being very distinctly visible, especially if tin- glass vessel be resting upon a dark ground so as to
bring tlic \\liitisli granules into relief. Tin- granules art- nothing more than the ova or eggs of the
Oyster, and at once indicate that the individual from which they were obtained is a female. In
case the products are male, they break u|t as they mingle with the water into a milky white cloud
in which no granules are visible to the naked eye. It is also very iiii|M>rtaiit to observe that as the
milt is stirred in the water it breaks up at lirst into long, fleecy white clouds which resemble very
strikingly in miniature what are known to meteorologists as cirrus clouds, or, vulgarly, "mare's
tails." reminding one of these in the way in which the flue particles of milt give rise to streaks,
\\ isps. and libers as it breaks up in the water, without giving rise to any visible granular appear-
ance a> o.-eur> in the ease of the female products, but to an opalescent or milky asj>ect. These
distinctions, once learned, are so palpable that the novice may as infallibly discriminate the sexes
of the O\stcr apart by their aid as can be done by the most skilled biologist with a powerful
microscope.

Tin: iMi'KKGNATiON OF THE EGOS. The method formerly used was to first learn the sex of
a number >f adult Oysters with the microscope, then cut out the generative glands with their
products and cuop up those of different sexes separately in small dishes with sea-water. This
system we may now say is barbarous, because it is crude; large numbers of eggs are destroyed
by crushing, or are injured by the rough usage to which they are subjected, and, besides, there is
no assurance that the eggs or milt operated with are quite mature. It is also troublesome to free
the generative gland from fragments of the liver which help to pollute the water in the incubating
vessels with putrescible organic matter, and thus interfere greatly with the life and healthy devel-
opment of the embryos.

By our method the objectionable features of the old plan, as stated above, are overcome. If
possible, select good-sized Oysters ; open them with the greatest possible care so as not to mutilate
the mantle and soft parts. Carefully insert an oyster-knife between the edges of the valves and
cut the great adductor muscle as close as possible to the valve which you intend to remove,
leaving the animal attached to the other valve, which, if possible, should be the left or deepest one.
The soft parts being firmly fixed or held fast by the great adductor muscle to the left valve
jirevents the animal from slipping under the end of the pipette, held flatwise, as it is gently and
tirmly stroked over the generative gland and ducts to force out the generative products.

To prepare the animals to take the spawn from them, after opening, the following precautions
arc to be observed: Note that the reproductive gland in great part envelopes the visceral mass,
and extends from the heart space, just in front of the great adductor, to within a half inch or so of
the bead 01 mouth end of the animal, which lies next to the hinge. Note also that both sides of
the visceral mass which incloses the stomach, liver, and intestine are enveloped on either side by
a membrane which also lies just next the shell and is garnished by a fringe of purplish, sensitive
tentacles along its entire border except at the head end where the mantle of the left side passes
into and is continuous with that of the right side of the animal. The ventral or lowermost side of
the animal, anatomically speaking, is marked by the four closely corrugated gill plates or pouches,
which are preceded in front by the four palps or lips, but both the gills and palps depend
downward between the lower borders of the mantle of the right and left sides. Note, too, that
if the mantle is carefully cut and thrown back on the exposed side of the animal between the
upper edges of the gills and the lower edge of the cut or exposed end of the great adductor
muscle, the lower and hinder blunted end of the visceral mass will be exposed to view. It is on

either side of this blunted end of the visceral mass between the np|H-r edi: the gills and lower

side of the great muscle that the reproductive glands opeu almost evi.-.ly below tin- -..-.it adductor.



724 NATURAL HISTORY OF AQUATIC ANIMALS.

From these openings we will afterwards find, if the animal is sexually mature and the operation is
properly conducted, that the spawn will be forced out in a vermicular, creamy white stream. But
in order to fully expose the reproductive organ we should carefully continue to sever the mantle
of one side with a sharp penknife or small scissors, some distance forward of the great muscle
towards the head, cutting through the mantle just above the upper borders of the gills and following
a cavity which lies between the latter and the lower border of the visceral mass. A little
experience will teach one how far it is necessary to carry this incision of the mantle. For some
distance in front of the heart space the mantle is free or detached from the visceral mass and
reproductive organ which lies immediately beneath, and this enables one, if the last described
incision has been properly made, to almost completely expose the one side of the visceral mass
and the richly tinted, yellowish-white reproductive gland which constitutes its superficial portion.
The opening of the gland and its superficial ramifying ducts being laid bare on the exposed side
of the animal we are ready to press out the spawn on that side. Before beginning this, however,
it is important to observe that the principal duct passes down just along the edge of the visceral
mass where the latter bounds the heart space, in which the heart may be observed to slowly
pulsate, and that this great duct ends somewhere on the surface of the ventral blunted end of the
visceral mass. To expose the great or main generative duct it may be necessary to cut through
or remove the pericardial membrane which incloses or covers the heart space on the exposed side.
If the Oyster is sexually mature, the main duct will be observed to be distended with spawn, and
that, originating from it and branching out over almost the entire surface of the visceral mass,
there are minor ducts given off, which again and again subdivide. If these are noted, and it is
observed that they are engorged, giving them the appearance of a simple series of much branched
great veins filled with creamy white contents, it may be certainly presumed that your specimen is
mature and that spawn may be readily pressed from it.

The operation of pressing the spawn out of the ducts requires care. The side of the end of the
pipette may be used, being careful not to crush or break open the ducts as you gently and firmly
stroke the pipette flatwise over the side of the visceral mass backward from the hinge towards
the heart space and over the great duct at the border of the latter diagonally downward and
backward to the opening of the reproductive organ. If this has been properly done it will be
found that the generative products are being pushed forward by the pipette through the ducts,
as the pressure will be seen to distend the latter, the contents of the branches flowing into the
larger and larger trunks until they are forced outward through the main duct and opening below
the great adductor, where they will pour out in a stream one-sixteenth of an inch or more in diameter
if the products are perfectly ripe. The sexes may be discriminated as described at the outset, and
it is well to first find a male by the method already given and proceed to express the milt as
described above into say a gUl of sea-water, adding pipetteful after pipetteful until it acquires a
milky or opalescent white color. As the milt or eggs are pressed out of the opening of the ducts
they are to be sucked up by the pipette and dropped into the water, the mixture of milt being first
prepared, to which the eggs may be added as they are expressed from the females. The judgment
of the operator is to be used in mixing the liquids; in practice I find that one male will supply
enough milt to fertilize the eggs obtained from three or four females, and it does not matter if the
operation takes from twenty to thirty minutes' time, as the male fluid, which it is best to prepare
first, will retain its vitality for that period.

It is always desirable to be as careful as possible not to get fragments of other tissues mixed
with the eggs and milt, and the admixture of dirt of any kind is to be avoided. To separate



BATE OF GROWTH OF OSTREA VIROINIOA. 725

any such 1 raiments nicely, I find n small strainer of coarse bolting or cheese cloth to be very



Online LibraryG. Brown (George Brown) GoodeThe fisheries and fishery industries of the United States (Volume 1:1) → online text (page 120 of 146)