104
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
often measuring several square millimeters in area. This congregating
tendency apparently did not unfavorably affect larvae. If these m a w s
of larvae were disturbed, the larvae would separate and continue
to swim for some time but, later, would again form floating groups.
Similar floating masses of larvae are frequently observed among older
larvae of other species, including C. virginicu.
I. Ostrea luridu Carpenter
The native oyster of our Pacific coast is the Olympia oysfer,
0. lurida. It is considerably smaller than its close relative, 0. duli8,
or the Atlantic coast oyster, C. virginicu, seldom exceeding a length
of 23 in. Unlike C. wirginica which, when adult, are of separate sexes,
the Olympia oyster is hermaphroditic. Its reproduction is also different
from C. virginicu in that the eggs are not discharged directly in the
water but, as in 0. edulis, they remain within a special brood ohamber
in the mantle cavity of the mother oyster.
Gonad development and spawning of 0. lurida can be induced out
of season by keeping them in water at about room temperature for
several weeks. Spawning can be detected, as in 0. edulis, either by
clouding of the water with discharged sperm or by presence on the
bottom of a few eggs that were lost during spawning. The eggs measure
from 100 to 110 p in diameter.
According to Coe (1931) Olympia oysters begin to spawn when
the temperature reaches 16°C. Hori (1933) indicated the temperature
as 14OC and Hopkins (1937) thought that spawning occurred soon
after the minimum daily water temperature reached 13°C.
In our experiments the incubation period lasted from 7 to 9 days
after which swarms of larvae were discharged in the water. Stafford
(1914) estimated that in 0. lurida the period between spawning and
swarming was 164 days. Coe (1931) reported this period aa 10 to 12
days, and Hopkins (1937), as about 10 days. The difference in time
is probably due to environmental conditions, especially temperature,
under which the different observers conducted their studies.
We were unable to rear successfully recently fertilized cggs that were
occasionally lost by females. However, embryos that were lost after
they had reached the ciliated blastula stage were cultured to straighthinge stage,
In one of our experiments larvae as small as 160 x 149p were
relertsed at swarming, but these larvae appeared immature as they
were too transparent and unable to withdraw the velum completely.
It was possible, nevertheless, to rear even these small larvae to metamorphosis.
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
often measuring several square millimeters in area. This congregating
tendency apparently did not unfavorably affect larvae. If these m a w s
of larvae were disturbed, the larvae would separate and continue
to swim for some time but, later, would again form floating groups.
Similar floating masses of larvae are frequently observed among older
larvae of other species, including C. virginicu.
I. Ostrea luridu Carpenter
The native oyster of our Pacific coast is the Olympia oysfer,
0. lurida. It is considerably smaller than its close relative, 0. duli8,
or the Atlantic coast oyster, C. virginicu, seldom exceeding a length
of 23 in. Unlike C. wirginica which, when adult, are of separate sexes,
the Olympia oyster is hermaphroditic. Its reproduction is also different
from C. virginicu in that the eggs are not discharged directly in the
water but, as in 0. edulis, they remain within a special brood ohamber
in the mantle cavity of the mother oyster.
Gonad development and spawning of 0. lurida can be induced out
of season by keeping them in water at about room temperature for
several weeks. Spawning can be detected, as in 0. edulis, either by
clouding of the water with discharged sperm or by presence on the
bottom of a few eggs that were lost during spawning. The eggs measure
from 100 to 110 p in diameter.
According to Coe (1931) Olympia oysters begin to spawn when
the temperature reaches 16°C. Hori (1933) indicated the temperature
as 14OC and Hopkins (1937) thought that spawning occurred soon
after the minimum daily water temperature reached 13°C.
In our experiments the incubation period lasted from 7 to 9 days
after which swarms of larvae were discharged in the water. Stafford
(1914) estimated that in 0. lurida the period between spawning and
swarming was 164 days. Coe (1931) reported this period aa 10 to 12
days, and Hopkins (1937), as about 10 days. The difference in time
is probably due to environmental conditions, especially temperature,
under which the different observers conducted their studies.
We were unable to rear successfully recently fertilized cggs that were
occasionally lost by females. However, embryos that were lost after
they had reached the ciliated blastula stage were cultured to straighthinge stage,
In one of our experiments larvae as small as 160 x 149p were
relertsed at swarming, but these larvae appeared immature as they
were too transparent and unable to withdraw the velum completely.
It was possible, nevertheless, to rear even these small larvae to metamorphosis.