G. Brown (George Brown) Goode.

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Convenient.

In the foregoing description wo have described the method of obtaining the spawn only from
the side of the animal exposed in opening the shell. A little exi>erience will enable one to lift up
the head end of the animal and throw it back over the great adductor muscle, expose the opening
of the reproductive organ on the left side, or whatever the case may be, and also express the
spawn from that side, thus as effectually obtaining all of the ripe eggs or milt as is possible in the
process <>t taking the same from fishes.

It is remarkable to note the success attending this method, since almost every egg is perfect
and uninjured, the percentage of ova which are impregnated is much larger than by the old
method, reaching, I should say, quite ninety per cent, of all that are takeii when the products are
perfectly ripe. It is also found that the products are not so readily removed by my process if they
are not perfectly mature, which is also to a certain extent a safeguard against getting poor or
immature spawn. In the course of an hour after the products of the two sexes have beeu mingled
together it will be found that nearly every egg has assumed a globular form, has extruded a polar
cell, lost the distinct germinative vesicle and spot in the center, and begun to develop.

It is noteworthy that our practice as herein described has completely vindicated the state-
ment made by the distinguished French anatomist and embryologist, M. Lacaze-Duthiers, that
there is but a single generative opening on each side of the visceral mass of the Oyster, and that,
as we have stated, it is found to open just below the great adductor muscle.

We have also discovered, since the foregoing was written, that the use of an excessive amount
of milt is of no advantage. The water in which the eggs are to be impregnated only requires to
be rendered slightly milky : a very few drops of good milt is sufficient to make the impregnation
a success. Too much milt causes the eggs to be covered by too large a number of spermatozoa ;
thousands more than are required if too much is used. These superfluous spermatozoa simply
become the cause of a putrescent action which is injurious to the healthy development of the eggs.
A drop of milt to twenty drops of eggs is quite sufficient.

Immediately after the ova have been fertilized it is best to put them into clean sea-water at
once, using water of the same density as that in which the adults grew. If the attempt is made
to impregnate the eggs in water much denser than that in which the adults lived, it is probablo
that the milt will be killed at once. This singular fact, which was accidentally discovered by
Colonel McDonald and myself, shows how very careful we should be to take into consideration
every variation in the conditions affecting a biological experiment. If sufficient water is used no
trouble will be experienced from the pollution of the water by dangerous micro-organisms which
are able to destroy the oyster embryos. From fifty to two hundred volumes of fresh, clean water
may be added to the volume in which the eggs were first fertilized. This may be added gradually
during the first twenty- four hours, so as to assist aeration and prevent the suffocation of the
embryos.

214. RATE OF GROWTH OF OSTREA VIRGHflCA.

SIZE OP THE EGG. The egg of the American Oyster, according to Brooks, is approximately
3^ inch, being very nearly perfectly spherical after the extrusion of the polar or direction cells
(RichtungsbUischen of the German embrvologist*). This accords with what the writer has observed
in our species, and in the Portuguese Oy-ter, probably 0. angulata Lain., the size of the egg
appears to be about the same, judging from specimens of the latter examined by me in March
last. Judging from the figures and the stated amplifications given in the papers of M. Davainc,



726 NATURAL HISTORY OF AQUATIC ANIMALS.

the egg of Ostrea edulis is ^^ inch in diameter. Estimates based on the figures of M. Lacaze-
Dnthiers give dimensions of - 2 -}^ inch. These discrepancies I think are probably too great, and
may be due to imperfect micrometric methods. If they are real it would indicate a specific
difference of some importance between 0. edulia and O. virginica.

The actual volume of the egg of the American Oyster would accordingly be a little more
than ^^iroioAot cubic inch, a solid so minute that we are unable to frame any adequate con-
ception of its diminutiveness. Under the best conditions, as seen against a dark back-ground,
it is visible as a grayish-white speck ; almost an optical point. It is from this diminutive spherical
mass of living matter that the young Oyster is developed. The development of the embryo
proceeds, as far as I can make out, according to the accounts given by Uavaiue, Brooks, Horst,
and others, similarly to that of other lamellibrauchs. To Hatschek 1 we are indebted for the most
secure foundation for our future embryological investigations upon this difficult group of mollusks;
and we must not forget to mention the very important researches of Ray Lankester (Phil. Trans.,
1875), principally upon Pisidium. I have not been able to observe the development of the larval
Oyster beyond the size attained by it after the complete segmentation of the egg, the develop-
ment of the shell, the velum, and alimentary tract. In fact, no embryos which I have attempted
to rear from artificially impregnated eggs have ever lived long after the time when they began
to take food, which is immediately after they acquire the velum, permanent mouth, and vent,
and are almost or altogether covered on either side by the very symmetrical larval shells, which
consist of carbonate of lime laid down in a matrix of conchioline. The isolation of the conchioline
is readily effected by the use of acetic acid, the acid dissolving out the lime entirely. I find
that Brooks and Dr. Horst" have tried a similar experiment with similar results. The latter
writer has also been able to watch the development of the naturally impregnated ova of Ostrea
edulia until a pretty advanced stage was reached. He disagrees with Brooks in his interpretation
of the gastrula stage, and thinks that the invagination regarded by the American investigator
as the blastopore must be considered to represent simply the first rudiment of the shell-gland.
In assuming this position, from what I have been able to gather in the course of my own investi-
gation of the development of the American species, I think we are bound to accept Dr. Horst's
determination of the homology of the shell-gland of the Oyster with that of other lamellibrau-
chiate and cephalophorpus mollusks.

EARLY STAGES OF DEVELOPMENT. The oral invagination, according to Dr. Horst, originates
on the opposite or ventral side of the embryo and has no connection with the dorsal pallial
invagination or shell-gland. The early stages of the American and European species, like the
later ones, appear to present no marked differences, except that the latter appears, on the evidence
of Dr. Horst, Mobius, and others, to carry the ova and embryo in the mantle cavity, from which
the first-named author obtained his material for study, by breaking a hole through the shell near
the margin, so as to enable him to introduce a pipette into the pallial chamber. This method of
getting embryos is impossible in our native species, which has wholly different breeding habits, as
is proved by the investigations of Brooks, Winslow, Rice, and myself. How much further than
heretofore Messrs. Brooks and Wiuslow have been enabled to carry the development of our native
Oyster during the past season at Beaufort, North Carolina, I have not been able to learn, nor do I
know anything more definitely as to how much success has been attained in the artificial produc-
tion of Ostrea edulis from artificially-impregnated eggs at the hands of Mr. Littlewood, of England,

'Ueber EntwickelungsResohichte von Teredo. Arbeiten aus dem Zool. Inst. Wien., Bd. iil.

'BijdragetotdeKennisvandeOntwikkelingsgeschiedcnis vau do (Jester (Ostrea edulis L.). door Dr. It. Hoist. Tiidschr.
d. Ned. Dierk. Vereen, Deel, vi, 1882.



LARVAL 0\>TLUS. 727

who h;is d limed that lie li.nl succeeded in rearing them to the age of five months, .specimens uf
which it is said were shown at the Fi.sheiv i:\liibition recently held in Kdinhurgh.

Kxi'i:i:iMi:vis \r SUM .1 I.UOMK'S CUKKK. Our experiments m:ide at Saint Jerome's Creek
d u rin t: the pa>t siiiumer gave the most contradictory results, and the interval of development
lietweeii that of our oldest embryo with itw diminutive Pisidium like valves measuring al>out t foj
inch in diameter, and that of the embryo when its valves first begin to lose their embryonic form,
still remains unbridled. The dimensions of the embryo or "fry," as we may more properly call it
when it becomes tixcd, are between vV and -fa inch according as the measurement is made longi-
tudinally or transversely. The difference in magnitude between the oldest artificially incubated
fry seen by me and that of the youngest fixed embryos which I collected is very small, amounting
only to 1 ^,' 1 , 1 inch, or a little more than T fo inch. To determine the relative volumes of these
stages, and consequently the amount of food which has been taken in and converted into the
structure of the more advanced stage in addition to the original bulk of the egg, we need only
take the cubes of their respective diameters and compare them. Taking the diameter of the egg,
or .,,', inch, as the diameter of the most advanced embryo seen by me, which we will consider
unity, and comparing it with ^ inch, or the transverse diameter of the newly fixed fry, we find,
alter having reduced the last quantity to its simplest form as compared with 1, or the diameter of
the egg, that we have 5.1+. The diameters then of the first and last embryonic or truly larval
slaves are to each other as 1 is to 5.1-f, and consequently their volumes will be to each other as
the cubes of these numbers, or as 1 is to 132.651 + . The difference between these two quantities,
or 131.051+ times 1, will give us approximately the amount of food material which has been taken
up by the embryo in passing from the condition when it was first able to feed until it fixed itself,
showing that the process of growth has been going on vigorously in order to augment the volume
of the young creature at the enormous rate indicated by our figures. We have, however, been
Mealing not with absolute but with relative or compared volumes only; if the egg contains
rsotioooo cubic inch of protoplasmic matter approximately, the newly-fixed fry, which we will
assume to be globular, and contains, as shown above, over 132 times as much material, the
absolute bulk of the latter will be ai)oi<nnre cubic inch multiplied by 132, or jjjjMJbiro cubic
inch, which, in its simplest form, is therefore -uriivrs cubic inch, or the absolute volume of the
newly fixed fry. Ninety cubed, or 729,000 young Oysters could therefore be contained in a cubic
inch of space, if taken at the stage at which they begin to be transformed into spat. This large
number is, of course, small when compared with 125,000,000, the number of eggs which might be
contained by the same extent of space.

THE LARVAL, CHARACTER OF THE YOUNG OYSTER. The proof of the larval character of
the youngest fixed stage of the Oyster rests upon the three following well-ascertained facts:
1st. The perfect symmetry and great convexity of the valves; 2d. The entirely different shajM-
of the shell as compared with those of the spat and adult; 3d. Its wholly different micro-
scopic structure when compared with the later and full-grown stages. The form of the shell, at
the time the animal is about to begin to develop the spat shell, is suborbicular, very thin, ven-
tricose, resembling in many respects the shell of Cyclas or Puidium, having the symmetry of
those genera, with umbones of about the same form and prominence. These features mark the
larval shell of the Oyster so unmistakably that its valves may always be very readily recogni/ed
at the tips of the valves of spat under a year old. The larval \alves lie on the tips of the vah.-s
of the spat like small hemispherical caps, but cau usually not be found after the young Oyster
enters upon its second year, as its umbones, together with the larval shells which surmount them.



728 NATURAL HISTORY OF AQUATIC ANIMALS.

have been eroded by the action of the carbonic dioxide in solution in the sea-water. The
presence of the larval shells in an unimpaired condition on the umboues of the valves of Oysters
is therefore an indication that such specimens are young, probably under a year old.

The third character, alluded to above, which distinguishes the larval shell of the Oyster is
the perfect homogeneity of the calcareous matter. Unlike the valves of the spat or translucid
flakes from the shell of the adult, they exhibit no prismatic arrangement of the calcic carbonate
in a matrix of conchioline. In the valves of the adult and spat, on the other hand, the calcic
carbonate tends to assume a prismatic arrangement vertical or at right angles to the plane of
the length and breadth of the shell. This distinction is so marked that in very young individuals
which have only lately become fixed one may very readily determine with the aid of the micro-
scope the line of demarkation along which the formation of the larval shell ceased and where the
prismatic calcareous structure of the valves of the spat began to be developed.

CHAEACTEES OF THE LARVAL SHELL. The only characters of structure which the larval
shell has in common with that of the spat and adult are the lines of growth visible in all three.
This shows that the valves grow in extent at all stages by the addition of lime to the edges of
the valves, each layer of mineral matter and organic matrix extending over successively greater
and greater areas, as in the growth of the shells of mollusks in general, the umbones being
the points from which the valves grow in an eccentric manner in consequence of the gradually
increasing extent of the mantle the shell-secreting organ as the growth of the animal
proceeds. Having clearly denned the nature of the larval shell of the Oyster, up to the time
when it is ready to begin to build or secrete the shell of the spat, we may next discuss the
character of the transition from the one to the other.

The transition is apparently an abrupt one. The excessive convexity of the valves of the fry
contrast strongly with the almost flat lower valve and feebly convex upper one of the spat. At
the free edges of the larval shells where they pass directly into the structure of the valves of the
spat there is a marked offset or angle marking very distinctly the difference of convexity between
the two stages of shell development.

FOOD OF THE YOUNG OYSTER. As already remarked, I have seen food in the intestine
of the young Oyster on the second day of development, but how long it may take before the
young embryo of this stage of growth shall have taken and appropriated one hundred and
thirty-two times its own volume of food material, I am not able to say. This it must do
before it can have attained to the size of the larva which is transformed into spat. The food
is propelled through the alimentary canal by the action of innumerable vibratory filaments
which clothe the inside of the throat, stomach, and intestine as in the adult ; the intestine,
stomach, and liver are not, however, as complex as in the full-grown animal.

Of the method of fixation 1 have as yet learned nothing of value. That this is accomplished
by some sort of byssus I have no doubt. The fact that it is the left valve which is always the
lowermost and attached one would indicate that the method of fixation was not capricious or
haphazard in its nature.

I would infer from what we learn from the study of other animals that it may require quite a
week before an embryo reaches the dimensions of one-eightieth of an inch, but we have no data
upon which to base any conclusions of value. Of the later stage of development we know some-
thing definitely. The main fact which we have so far decided is the size of the larval shell.

RATE OF GROWTH. After fixation the growth of spat is very rapid, as may be inferred
from the fact that I have found spat upon collectors which had not been placed in position



FOOD OF TOE OYSTER. 729

more than a week to ten days, upon which I detected spat one-fourth of an inch across. In
other cases the following were the observed dimensions: On a collector which had been placed
near a bed of spawning Oysters for twenty days I obtained a specimen of spat seven-sixteenths
of an inch across; from another collector immersed for forty-four days I obtained specimens
tliii icon-sixteenths of an inch in diameter; from another out forty-eight days a specimen
measuring about one inch. Another set of collectors which had been out for seventy-nine days
had spat attached which measured one and three-fourths inches across. Some still larger spat
oillri-trd l>y me was not over eighty-two days old, and measured nearly two inches in length
from the hinge to the distal margin of the valves. Still larger specimens have been observed
by the writer, which bore every evidence of having affixed themselves during the same
season.

If we contrast the above measurements with those given by Mobius of the spat of 0. ,<liiti*
of known age, I conclude that the American Oyster prows three or four times as rapidly as the
former. For instance, Mobius figures a European Oyster twelve to fifteen months old, which
measures only one and one-fourth inches in diameter. Contrasting this with the size of the
American at seventy-nine to eighty-two days old, and measuring, from one and three-fourths to
nearly two inches in diameter, we see how greatly our species surpasses that of Europe in vigor
and rapidity of growth.

Of the rate of growth beyond the ages given above I have only a few data, based on the spat
which was caught on collectors put out in Saint Jerome's Creek in July and August, 1880. In the
following autumn the collectors which had been put out into the creek were taken up and the spat
removed from them. This was then put into a box, through wh ; oh the water could circulate
freely, and put back into the creek, in order that we might be enabled to learn how much growth
these young Oysters would make during the winter and next season. I did not have an opportu-
nity to examine them, howerar, until the 10th of July, 1882. From the time of their fixation in
July and August, 1880, to the time when I made my last examination of these specimens, a
period of about twenty-three months had accordingly elapsed. One of the largest specimens
examined by me measured three and three eighths inches in length and two and five-eighths
inches in width. Another smaller specimen measured two and a half inches long and two
and a quarter inches in width. They were about the size of Oysters available for planting, and I
have no doubt that in the course of two or three years more, if placed under favorable conditions,
they would reach a marketable size. The inference, therefore, is that it takes at least four to five
years for an Oyster to grow large enough, starting from the egg, to be available for market.

In order that an Oyster may grow to attain the great size of certain single individuals which
I have seen, it may take even ten years. I should think it would take at least that length of time
for an Oyster to grow until Us valves would measure nine inches in length, a few of which I have
seen of this enormous size. These, it must be remembered, were not " Raccoon Oysters" or "Cat's-
tongues," as the narrow, elongate individuals are called which grow so densely crowded together
upon the banks as to be abnormally lengthened. Under favorable conditions, I do not think
it improbable that an Oyster may live to the age of twenty years, attaining corresponding
dimensions.

215. THE FOOD OF THE OYSTER.

OBSERVATIONS AT SAINT JEROME'S CREEK. The following extracts, taken mainly from
my report for 1880 to the Fish Commissioner of Maryland, will give some idea of the kinds of
organisms usually encountered on oyster banks and beds. Theae observations were made at



730 NATURAL HISTORY OF AQUATIC ANIMALS.

Saint Jerome's Creek, a few miles north of the mouth of the Potomac, during the months of July,
August, September, and October:

"The food of this mollusk, as is well known, consists entirely of microscopic beings and
fragments of organic matter, which are carried by currents from the palps and gills, which have
been already described, to the large mouth of the animal at the hinge end of the shell. The inside
of the gullet and stomach, like some other parts of the body, are covered with cilia, so that food
once fairly in the mouth will be carried by their action down to the cavity of the stomach, where
it is carried into the folds and deep pouches in its walls, and even into the openings of the bile
ducts, to undergo digestion or solution, so as to be fitted in its passage through the intestine to
be taken into the circulation, and finally disposed of in building up the structures of the body.

"Along with the food which is taken, a very large amount of indigestible dirt, or inorganic
matter, is carried in, which, in a great measure, fills up the intestine, together with the refuse or
waste from the body. This material, when examined, reveals the fact that the Oyster subsists
largely on diatoms, a low type of moving plants which swim about in the water, incased in minute
sandstone cases, or boxes, of the most delicate beauty of workmanship. These, when found in
the intestine, have usually had their living contents dissolved out by the action of the digestive
juices of the stomach. I have found in our own species of Oyster the shells of three different
genera of diatoms, viz: Campylodiscus, Coscinodiscm, and Navicula. The first is a singularly bent
form; the second is discoidal; and the last boat-shaped, and all are beautifully marked. Of
these three types, I saw a number of species, especially of the latter, but as I was not an authority
upon the systematic history of any of them I had to neglect the determination of the species. No
doubt many more forms are taken as food by the Oyster, since I saw other forms in which the
living matter inside the siliceous cases was brown, the same as in most of the preceding forms
which I have indicated. Some of these brown forms were so plentiful as to color a considerable
surface whereon they grew of the same tint as themselves.

"Besides the diatoms and the spores of algse, the larvae or young of many animals, such as
sponges, bryozoa, bydroids, worms, mollusks, are small enough to be taken in as aliment by
the Oyster, though their bodies in most cases being soft and without a skeleton, it is impossible
to find any traces, either in the stomach or intestine, of their remains, to indicate that they have
formed a part of the bill of fare of the animal. What, however, demonstrates that such small
larval organisms do help to feed the Oyster is the fact that at the heads of the small inlets or
creeks along the Chesapeake, where the water is but little affected by the tides and is somewhat
brackish and inclined to be stagnant, there always appears to be a relatively greater development
of a somewhat characteristic surface or shallow water fauna of minute forms.

"In Saint Jerome's Creek the microscopic fauna of its headwaters is entirely different from
that of the body of the creek; two minute forms inhabit in vast numbers the former, while I
sought in vain for them in the more open and changeable waters of the main body of the inlet,
which are brought into active movement twice a day by the action of the tides. One of these
forms, an infusorian, 1 one twenty-fifth of an inch in length, was found covering every available,
surface of attachment, so that countless multitudes of the naked young would be swimming about
in the water previous to building the curious spiral tubes which they inhabit admirably fitted in
this state as food for the Oyster. Besides the type referred to, there were a number of other
infusorians, which in their HO called swarming stages of development would become available
as Oyster food. Of such types I noticed four diftV-rent species, either belonging or very nearly



' On the occurrence of JVcio produda, Wright, in the Chesapeake Buy. Am. A'aluratist, 1880, pp. 810, 811.



LOCATION OF OYSTKK BEDS. 731



related to tin- genus Cotlinniia ; all of the forms built tubes tor themselves. I also nuiK-ed



Online LibraryG. Brown (George Brown) GoodeThe fisheries and fishery industries of the United States (Volume 1:1) → online text (page 121 of 146)