ItEAltINU OF BIVALVE MOLLUSKS
99
Gutsell (1930) and, more recently, by Costello et al. (1957). The later
development of the larvae, beginning with the formation of the straighthinge stage, however, has never been adequately described because
virtually no one succeeded in growing these larvae to metamorphosis.
The only exception was Wells (1927)) who grew scallop larvae past
setting stage, but gave only a superficial description of them, although
he aupplkd good photographs showing the different stages of
development.
Descriptions of eggs and early stages of several European Pectinidae
were offered by Jmgensen (1946). Efowever, as in the case of the
American bay scallop, virtually nono of the European workers, except
Odhner (1914), gavc photomicrographs of older veliger stages that may
be helpful in identifying the larvae.
The scallops used in our studies were brought, in February, from
Long Island, where they are found in a number of bays, harbors and
inlets. They were placed in running sea water, the temperature of
which was increased within a few days to 20°C. The first spawning
was attempted after 23 days of conditioning. The scallops responded
readily to a temperature stimulus of about 30°C and spawned profusely.
Scallops usually spawn first as males and, later, as females. During
one spawning, fourteen scallops started spawning as males. However,
10 or 15 min later seven of these fourteen individuals began to discharge
eggs, but within a few minutes two of these seven again reverted to
spawning as males, releasing large numbers of spermatozoa. On one
occasion the same scallop was observed releasing sperm and eggs
simultaneously.
Scallop eggs obtained in our experiments measured from 5 5 to 65 p
in diameter, the average size being near 60 p. Belding 11910) and
Gutsell (1930) gave the size of the scallop egg as 63 p. Fullarton (1890)
reported that the egg diameter of a rolntetl European species, Paclen
opercularis, is 68 p. The scallop egg is surrounded by a thin membrane
and is usually of a pale orange color. Brief remarks on fertilization,
cleavage and rate of development of the fertilized ovum were given
by Costello et al. (1957), who based his descriptions on the works of
Belding ( 19 10) and Gutsell ( 1930).
The smallest straight-hinge scallop larvae observed in our cultures
were 80 p long and 65 p wide, and the largest swimming individuals,
approximately 200 x 195 p. Some larvae metamorphosed upon
reaching 175 p in length. Jmgensen (1946) stated that the largest
planktonic stage of the European bcallop, P. opercularis, is approximately 250 to 260 p long, while the larvae of another European scallop,
P ~ c t ~ n
striatus, approaching metamorphosis may be only 200 to 2 10 p
8
99
Gutsell (1930) and, more recently, by Costello et al. (1957). The later
development of the larvae, beginning with the formation of the straighthinge stage, however, has never been adequately described because
virtually no one succeeded in growing these larvae to metamorphosis.
The only exception was Wells (1927)) who grew scallop larvae past
setting stage, but gave only a superficial description of them, although
he aupplkd good photographs showing the different stages of
development.
Descriptions of eggs and early stages of several European Pectinidae
were offered by Jmgensen (1946). Efowever, as in the case of the
American bay scallop, virtually nono of the European workers, except
Odhner (1914), gavc photomicrographs of older veliger stages that may
be helpful in identifying the larvae.
The scallops used in our studies were brought, in February, from
Long Island, where they are found in a number of bays, harbors and
inlets. They were placed in running sea water, the temperature of
which was increased within a few days to 20°C. The first spawning
was attempted after 23 days of conditioning. The scallops responded
readily to a temperature stimulus of about 30°C and spawned profusely.
Scallops usually spawn first as males and, later, as females. During
one spawning, fourteen scallops started spawning as males. However,
10 or 15 min later seven of these fourteen individuals began to discharge
eggs, but within a few minutes two of these seven again reverted to
spawning as males, releasing large numbers of spermatozoa. On one
occasion the same scallop was observed releasing sperm and eggs
simultaneously.
Scallop eggs obtained in our experiments measured from 5 5 to 65 p
in diameter, the average size being near 60 p. Belding 11910) and
Gutsell (1930) gave the size of the scallop egg as 63 p. Fullarton (1890)
reported that the egg diameter of a rolntetl European species, Paclen
opercularis, is 68 p. The scallop egg is surrounded by a thin membrane
and is usually of a pale orange color. Brief remarks on fertilization,
cleavage and rate of development of the fertilized ovum were given
by Costello et al. (1957), who based his descriptions on the works of
Belding ( 19 10) and Gutsell ( 1930).
The smallest straight-hinge scallop larvae observed in our cultures
were 80 p long and 65 p wide, and the largest swimming individuals,
approximately 200 x 195 p. Some larvae metamorphosed upon
reaching 175 p in length. Jmgensen (1946) stated that the largest
planktonic stage of the European bcallop, P. opercularis, is approximately 250 to 260 p long, while the larvae of another European scallop,
P ~ c t ~ n
striatus, approaching metamorphosis may be only 200 to 2 10 p
8