REARING OF BIVALVE MOLLUSKS
43
were placed in 5 gal of water, a count of straight-hinge larvae was
made 48 hr later and showed that the culture contained 165 000 normal,
straight-hinge larvae, 11 000 abnormal ones and 2 000 dead individuals.
Therefore, approximately 168000, or about 4,50/, of the eggs placed in
the culture developed into larvae. 111 another culture, whero approximately 7,50000 of those eggs worc plucod in 10 gal of water, t h o count
made 48 hr later gave 424000 normal, 46 000 abnormal and 32 000
dead larvae; therefore, approximately 502000, or 61% of all the eggs
that were originally placed in the culture developed to straight-hinge
stage. From then on, however, larval development was poor, showing
high mortality.
On 19 March, 43 days after the ripe oysters were placed in the icy
water, another group was brought in and, after being kept for 4 days
in running sea water at a temperature ranging between 14" and 1 7 ' C ,
was induced to spawn. Both males and females spawned. One of the
females released 18 million and another, 27 million eggs. Larvae
obtained from eggs of one of the females grew well, increasing approximately 10 p in length per day.
This experiment demonstrated the remarkable fact that oysters
artificially ripened in the middle of winter can be transferred abruptly
from warm to freezing water, retained there for over 40 days, and then
returned to warm water and induced to spawn, producing viable eggs
and sperm that eventually develop into normal straight-hinge larvae.
Even though mortality among larvae obtained in this unusual manner
was relatively high and many larvae were abnormal, the, experiment
demonstrated, nevertheless, the remarkable power of oysters to retain
their ripe sex cells under extremely adverse conditions. Results of
histological studies of gonads of oysters involved in these experiments
will be described later in a special publication.
Regardless of the ability of ovarian eggs of C. virginicu to withstand
exposure to low temperatures for long periods, recently fertilized eggs,
in the polar-body stage of development, do not display the same
tolerance. This was demonstrated by an experiment in which eggs,
within 1 or 2 hr after fertilization, were placed in a refrigerator maintained at a temperature of about 2 ' C , and kept there for 6,24 and 48 hr.
Samples were then returned to room temperature and further development of the eggs subsequently observed. In all samples a few eggs
developed into abnormal ciliated blastulas, but practically all of them
failed to develop further and soon disintegrated.
Healthy shelled larvae of oysters, C. virginim, are, nevertheless,
capable of withstanding sharp changes in temperature of the surrounding water. In a special series of experiments, designed to verify Nelson's
43
were placed in 5 gal of water, a count of straight-hinge larvae was
made 48 hr later and showed that the culture contained 165 000 normal,
straight-hinge larvae, 11 000 abnormal ones and 2 000 dead individuals.
Therefore, approximately 168000, or about 4,50/, of the eggs placed in
the culture developed into larvae. 111 another culture, whero approximately 7,50000 of those eggs worc plucod in 10 gal of water, t h o count
made 48 hr later gave 424000 normal, 46 000 abnormal and 32 000
dead larvae; therefore, approximately 502000, or 61% of all the eggs
that were originally placed in the culture developed to straight-hinge
stage. From then on, however, larval development was poor, showing
high mortality.
On 19 March, 43 days after the ripe oysters were placed in the icy
water, another group was brought in and, after being kept for 4 days
in running sea water at a temperature ranging between 14" and 1 7 ' C ,
was induced to spawn. Both males and females spawned. One of the
females released 18 million and another, 27 million eggs. Larvae
obtained from eggs of one of the females grew well, increasing approximately 10 p in length per day.
This experiment demonstrated the remarkable fact that oysters
artificially ripened in the middle of winter can be transferred abruptly
from warm to freezing water, retained there for over 40 days, and then
returned to warm water and induced to spawn, producing viable eggs
and sperm that eventually develop into normal straight-hinge larvae.
Even though mortality among larvae obtained in this unusual manner
was relatively high and many larvae were abnormal, the, experiment
demonstrated, nevertheless, the remarkable power of oysters to retain
their ripe sex cells under extremely adverse conditions. Results of
histological studies of gonads of oysters involved in these experiments
will be described later in a special publication.
Regardless of the ability of ovarian eggs of C. virginicu to withstand
exposure to low temperatures for long periods, recently fertilized eggs,
in the polar-body stage of development, do not display the same
tolerance. This was demonstrated by an experiment in which eggs,
within 1 or 2 hr after fertilization, were placed in a refrigerator maintained at a temperature of about 2 ' C , and kept there for 6,24 and 48 hr.
Samples were then returned to room temperature and further development of the eggs subsequently observed. In all samples a few eggs
developed into abnormal ciliated blastulas, but practically all of them
failed to develop further and soon disintegrated.
Healthy shelled larvae of oysters, C. virginim, are, nevertheless,
capable of withstanding sharp changes in temperature of the surrounding water. In a special series of experiments, designed to verify Nelson's