102
VICTOR L. LOOSANOFF A N D HARRY C. DAVIS
water was changed daily and the oysters were given sufficient quantities
of food to keep them and the larvae alive.
At room temperatures swarmings took place from 6& to 10 days
after spawning. The size of larvae released by a single female in the
same swarming varied considerably. On one occasion samples of
100 larvae were collected from swarms released by each of six females
which had been kept in separate aquaria. Larvae released by female (A)
ranged in length from 142 to 199 p, with a modal size of 186 p ; by
female (B), from 164 to 192 p, with a modal size of 184 p ; by female (C),
from 164 to 203 p, with a modal size of 188 p ; by female (D), from
149 to 203 p, with a modal size of 187 p ; by female (E), from 164 to
192 p, with a modal size of 180 p ; and female (F), from 164 to 195 p,
with a modal size of 183 p. Occasionally, broods of smaller larvae
measuring 175 x 1 6 0 p were released. The average size of such
broods closely resembled those reported by Boury (19281, Voisin (1931)
and Korringa (1941).
In rare cases the modal sizes of larval broods were unusually large,
over 200 p in length. Because all female oysters incubating larvae
were kept at the same temperature, it is improbable that the difference
in size of the liberated larvae of the different broods was governed by
the temperature at which incubation occurred. It seems more reasonable that size of larvae at liberation depends upon how long larvae
are retained in the mantle cavity. This may be governed by the physiological condition of the parent oysters or the conditions in the water in
which oysters are kept, the larvae being retained longer and, hence, are
larger at time of release when these conditions are not at their optimum.
This is supported by observations on liberation of larvae by two females
that appeared sick. The first was used in an experiment where induced
spawning was attempted by quickly raising the temperature to 37°C.
The oyster did not spawn but was apparently injured by this treatment
because it gaped for several hours after its return to sea water at room
temperature. It did spawn the next day, however, but the spawning
was not normal because too many eggs were found on the bottom
of the aquarium near the oyster. The eggs, nevertheless, were fertilized.
Ten days later this oyster discharged, simultaneously, a brood of
larvae and many empty larval shells, indicating that many larvae hacl
died within the mantle cavity during incubation. There was also a
considerable number of abnormal larvae with defective vela. Normal
larvae, which still were in the majority, measured from 199 to 212 p
in length, with a modal size of about 2 0 8 p . Regardless of some
abnormality observed in the development of this brood, the larvae
were reared to metamorphosis.
VICTOR L. LOOSANOFF A N D HARRY C. DAVIS
water was changed daily and the oysters were given sufficient quantities
of food to keep them and the larvae alive.
At room temperatures swarmings took place from 6& to 10 days
after spawning. The size of larvae released by a single female in the
same swarming varied considerably. On one occasion samples of
100 larvae were collected from swarms released by each of six females
which had been kept in separate aquaria. Larvae released by female (A)
ranged in length from 142 to 199 p, with a modal size of 186 p ; by
female (B), from 164 to 192 p, with a modal size of 184 p ; by female (C),
from 164 to 203 p, with a modal size of 188 p ; by female (D), from
149 to 203 p, with a modal size of 187 p ; by female (E), from 164 to
192 p, with a modal size of 180 p ; and female (F), from 164 to 195 p,
with a modal size of 183 p. Occasionally, broods of smaller larvae
measuring 175 x 1 6 0 p were released. The average size of such
broods closely resembled those reported by Boury (19281, Voisin (1931)
and Korringa (1941).
In rare cases the modal sizes of larval broods were unusually large,
over 200 p in length. Because all female oysters incubating larvae
were kept at the same temperature, it is improbable that the difference
in size of the liberated larvae of the different broods was governed by
the temperature at which incubation occurred. It seems more reasonable that size of larvae at liberation depends upon how long larvae
are retained in the mantle cavity. This may be governed by the physiological condition of the parent oysters or the conditions in the water in
which oysters are kept, the larvae being retained longer and, hence, are
larger at time of release when these conditions are not at their optimum.
This is supported by observations on liberation of larvae by two females
that appeared sick. The first was used in an experiment where induced
spawning was attempted by quickly raising the temperature to 37°C.
The oyster did not spawn but was apparently injured by this treatment
because it gaped for several hours after its return to sea water at room
temperature. It did spawn the next day, however, but the spawning
was not normal because too many eggs were found on the bottom
of the aquarium near the oyster. The eggs, nevertheless, were fertilized.
Ten days later this oyster discharged, simultaneously, a brood of
larvae and many empty larval shells, indicating that many larvae hacl
died within the mantle cavity during incubation. There was also a
considerable number of abnormal larvae with defective vela. Normal
larvae, which still were in the majority, measured from 199 to 212 p
in length, with a modal size of about 2 0 8 p . Regardless of some
abnormality observed in the development of this brood, the larvae
were reared to metamorphosis.