REARING O F BIVALVE MOLLUSKS
93
2 or 3 min after the first one. Both individuals discharged eggs in large
numbers for a considerable period. Within 12 hr eight of ten stimulated
mussels spawned, while none of the control group discharged any
sex products.
The experiment was repeated four times involving, altogether,
120 mussels. Of the sixty stimulated mussels, fifty-four responded,
while none of the sixty control animals spawned. All mussels of the
stimulated group remhined alive for at least 2 weeks, after which they
were discarded. Thus, a very simple method for stimulating ripe mussels
to spawn has been developed. To make the method even easier we
filed a small notch at the edge of the shcll through which the needle
was inserted.
According to Jargensen (1946) one of the most remarkable peculiarities of larvae of M . edulis is “ i t s excessive variability both as
regards the color of the shell, its shape, and stage of development as
compared with larval size, in which respects it is not surpassed by any
of our other common Lamellibranch veligers ” (p. 287).
Our cultures of M . edulis were grown during the early period of
our studies of molluscan larvae ; in other words, before the good food
organisms, I . galhana and M . lutheri, became available to us. The
larvae were fed an algal mixture, consisting chiefly of Chbrella and
other green forms, and grew remarkably well. Strangely enough, it was
virtually impossible to injure them by adding to the water large
quantities of food microorganisms, a sitiiation that often arises in
culturing larvae of other species, such as clams Snd oysters.
The smallest normal straight-hinge larvae mcasured approximately
93 x 64 p , and the largest, about 300 x 286 p. Thus, our measurements are very different from those given by Sullivan (1948), who
stated that larvae of M . edulis range in size from 155 x 120 p to
approximately 355 x 320 p. The smallest size given by Sullivan is,
therefore, almost 60 p greater than that of‘ the smallest larvae in our
cultures, and the maximum size is considerably larger than that
which we ever recorded among swimming larvae.
Jargensen also apparently mistook other larvae for advanced
stages of M . edulis because he speaks of individuals which are 400 p
long. Werner (1939), whose length and width measurements of larvae
of M . edulis somewhat resemble ours, still fails to give correct measurements for the smallest straight-hinge stage larvae. In his growth
Curve for these organisms he gives the size of the smallest larvae as
approximately 112 p long and 84 p wide, which is considerably larger
than the size of the smallest larvae ordinarily found in our cultures.
The so-called “ eye ” spot usually begins to appear in larvae when
93
2 or 3 min after the first one. Both individuals discharged eggs in large
numbers for a considerable period. Within 12 hr eight of ten stimulated
mussels spawned, while none of the control group discharged any
sex products.
The experiment was repeated four times involving, altogether,
120 mussels. Of the sixty stimulated mussels, fifty-four responded,
while none of the sixty control animals spawned. All mussels of the
stimulated group remhined alive for at least 2 weeks, after which they
were discarded. Thus, a very simple method for stimulating ripe mussels
to spawn has been developed. To make the method even easier we
filed a small notch at the edge of the shcll through which the needle
was inserted.
According to Jargensen (1946) one of the most remarkable peculiarities of larvae of M . edulis is “ i t s excessive variability both as
regards the color of the shell, its shape, and stage of development as
compared with larval size, in which respects it is not surpassed by any
of our other common Lamellibranch veligers ” (p. 287).
Our cultures of M . edulis were grown during the early period of
our studies of molluscan larvae ; in other words, before the good food
organisms, I . galhana and M . lutheri, became available to us. The
larvae were fed an algal mixture, consisting chiefly of Chbrella and
other green forms, and grew remarkably well. Strangely enough, it was
virtually impossible to injure them by adding to the water large
quantities of food microorganisms, a sitiiation that often arises in
culturing larvae of other species, such as clams Snd oysters.
The smallest normal straight-hinge larvae mcasured approximately
93 x 64 p , and the largest, about 300 x 286 p. Thus, our measurements are very different from those given by Sullivan (1948), who
stated that larvae of M . edulis range in size from 155 x 120 p to
approximately 355 x 320 p. The smallest size given by Sullivan is,
therefore, almost 60 p greater than that of‘ the smallest larvae in our
cultures, and the maximum size is considerably larger than that
which we ever recorded among swimming larvae.
Jargensen also apparently mistook other larvae for advanced
stages of M . edulis because he speaks of individuals which are 400 p
long. Werner (1939), whose length and width measurements of larvae
of M . edulis somewhat resemble ours, still fails to give correct measurements for the smallest straight-hinge stage larvae. In his growth
Curve for these organisms he gives the size of the smallest larvae as
approximately 112 p long and 84 p wide, which is considerably larger
than the size of the smallest larvae ordinarily found in our cultures.
The so-called “ eye ” spot usually begins to appear in larvae when