ItEARINO OF BIVALVE MOLLUSKS
103
The second release of liirger-thari-;ivc.raRc larvae, measuring between
200 and 210 p in length, was also observed in an oyster that was
kept at high temperature for several hours and was probably injured
by this treatment.
Another possibility is that the size upon release may be governed
by the numb of incubating larvae in the mantle cavity, with the
larvae growing faster if the riumber is small.
Swarming or, more correctly, releasf) of larvae by parent oysters
was observed on numerous occasions. 1 t i general, it resembled discharge of eggs by a spawning female of C virginica. The larvae were
expelled in cloud-like masses by a forccful closing motion of the shells.
Discharge of larvae by a single female niay continue for 3 or even
4 days. Usually, during the 1st day only a few larvae are released.
The chief masses of larvae are expelled during the 2nd day and then
the number of newly released larvae sharply decreases. Larvae that
had just been released usually contained in their stomach large quantities of algal cells which had been added to the water during their
incubation.
I n many of our experiments, including the early one when larvae
were fed phytoplankton composed principidly of Chlorella, the veligers
grew and survived well. At temperatures ranging between 18" and
20°C " eyed " larvae measuring approximatrely 270 p, with a prominent
pigmented spot, began to appear about the 9th or 10th day. Setting
usually began on the 15th or 16th day, altltough in several cases. when
fed I . galhana and M . lutheri, the larvae began to set between the
7th and 8th days.
Setting size of the larvae in our cultures was most commonly
between 280 and 300 p. In this respect, (aur o h r v a t i o n s agree with
those of Cole (1!+3$)), who reported t,hat metamorphosing larvae in
his experiments measured from 290 to :rIO p. However, we have
never observed larvar as large ns 350 p which Cole found in some
of his tanks. Imai et 01. (1953) reported that none of thc larvae of
0. edulis in their cultures reached 300 p in width, and most of the
individuals in Walne's ( 1 956) broods also set before reaching 300 p.
Throughout the experiments the rate of growth of individual larvae
of the same troods showed considerahle v
300 p in length and were undergoing mrtamorphosis, other larvae still
measurcd only about 175 p, thus bciiig of approximately the same
size as many larvae at the time of swarming.
When recently released larvae were plac*ed in culture jars many of
them ascended to the surfact. and formed l a ~ g e ,
brown, floating masses,
103
The second release of liirger-thari-;ivc.raRc larvae, measuring between
200 and 210 p in length, was also observed in an oyster that was
kept at high temperature for several hours and was probably injured
by this treatment.
Another possibility is that the size upon release may be governed
by the numb of incubating larvae in the mantle cavity, with the
larvae growing faster if the riumber is small.
Swarming or, more correctly, releasf) of larvae by parent oysters
was observed on numerous occasions. 1 t i general, it resembled discharge of eggs by a spawning female of C virginica. The larvae were
expelled in cloud-like masses by a forccful closing motion of the shells.
Discharge of larvae by a single female niay continue for 3 or even
4 days. Usually, during the 1st day only a few larvae are released.
The chief masses of larvae are expelled during the 2nd day and then
the number of newly released larvae sharply decreases. Larvae that
had just been released usually contained in their stomach large quantities of algal cells which had been added to the water during their
incubation.
I n many of our experiments, including the early one when larvae
were fed phytoplankton composed principidly of Chlorella, the veligers
grew and survived well. At temperatures ranging between 18" and
20°C " eyed " larvae measuring approximatrely 270 p, with a prominent
pigmented spot, began to appear about the 9th or 10th day. Setting
usually began on the 15th or 16th day, altltough in several cases. when
fed I . galhana and M . lutheri, the larvae began to set between the
7th and 8th days.
Setting size of the larvae in our cultures was most commonly
between 280 and 300 p. In this respect, (aur o h r v a t i o n s agree with
those of Cole (1!+3$)), who reported t,hat metamorphosing larvae in
his experiments measured from 290 to :rIO p. However, we have
never observed larvar as large ns 350 p which Cole found in some
of his tanks. Imai et 01. (1953) reported that none of thc larvae of
0. edulis in their cultures reached 300 p in width, and most of the
individuals in Walne's ( 1 956) broods also set before reaching 300 p.
Throughout the experiments the rate of growth of individual larvae
of the same troods showed considerahle v
300 p in length and were undergoing mrtamorphosis, other larvae still
measurcd only about 175 p, thus bciiig of approximately the same
size as many larvae at the time of swarming.
When recently released larvae were plac*ed in culture jars many of
them ascended to the surfact. and formed l a ~ g e ,
brown, floating masses,