108
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
again. Probably because of this condition, which resulted in lmge
quantities of sperm in the spawning dishes, many cases of polyspermy
were seen.
The eggs of L. mrtoni measure from 60 to 65 p in diameter. Lov6n
(1848) reported that eggs of the related species, Cardium exiguum, have
a diameter of 64 p and are deposited in a thick gelatinous mantle
within which development goes on until the shell-bearing veliger hss
attained a length of 90 p. Orton (1924), who performed succeesful
artificial fertilization of a closely related species, Cardium fawidurn,
and Jmgensen (1946) reported that eggs of that bivalve messure
about 80 p in diameter, thus being considerably larger than those of
our species. In still another closely related form, Cardium ed&,
according to Lebour (1938), the egg diameter is only 50 p.
The smallest normal straight-hinge larvae in our cultures measured
about 85 x 70 p. Sullivan (1948) stated that very small larvae of
Cardium pinnulaturn are 90 x 80 p, a size closely corresponding to
our smallest normal larvae. In early stages the margin of the larval
shell is outlined by a dark band, similar to that seen in Teredo larvae,
but not quite as prominent. Usually, one end of the shell is slightly
more pointed than the other.
The umbo begins to appear when larvae are between 135 and
150 p in length and is usually quite prominent when a length of about
160 p is reached.
The larvae were grown at room temperature of about 20°C and fed
a mixture of I . galbana and M . lutheri. The first metamorphosing
individuals were observed 8 to 10 days after fertilization. The smallest
individual, having a definite foot but no velum, measured only 205 p,
while the largest swimming larvae with a still well-developed velum
measured 245 p. Some metamorphosed cockles with well-developed
gills and a siphon were only 220p long. No “eye ” wafi observed in
any of the larvae.
The size of the largest swimming larva ever recorded in our
cultures was 250 x 220 p, but only one such individual was seen. The
maximum size of our larvae, therefore, closely agrees with that
described by Sullivan (1948) for C. pinnulaturn, which measured
250 x 230 p. Jarrgensen (1946) mentioned that Lebour grew larvae
of Cardium echinatum which, at metamorphosis, measured about 480 p
in length. We accept this figure with considerable reservation.
Jmgensen also assumed that the maximum length of larvae of
C. exiguum is about 250p: although he never observed this veliger
with certainty in the Sound, where he carried on his experimenta. His
observation on C. fasciatum indicated that the largest larval stages
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
again. Probably because of this condition, which resulted in lmge
quantities of sperm in the spawning dishes, many cases of polyspermy
were seen.
The eggs of L. mrtoni measure from 60 to 65 p in diameter. Lov6n
(1848) reported that eggs of the related species, Cardium exiguum, have
a diameter of 64 p and are deposited in a thick gelatinous mantle
within which development goes on until the shell-bearing veliger hss
attained a length of 90 p. Orton (1924), who performed succeesful
artificial fertilization of a closely related species, Cardium fawidurn,
and Jmgensen (1946) reported that eggs of that bivalve messure
about 80 p in diameter, thus being considerably larger than those of
our species. In still another closely related form, Cardium ed&,
according to Lebour (1938), the egg diameter is only 50 p.
The smallest normal straight-hinge larvae in our cultures measured
about 85 x 70 p. Sullivan (1948) stated that very small larvae of
Cardium pinnulaturn are 90 x 80 p, a size closely corresponding to
our smallest normal larvae. In early stages the margin of the larval
shell is outlined by a dark band, similar to that seen in Teredo larvae,
but not quite as prominent. Usually, one end of the shell is slightly
more pointed than the other.
The umbo begins to appear when larvae are between 135 and
150 p in length and is usually quite prominent when a length of about
160 p is reached.
The larvae were grown at room temperature of about 20°C and fed
a mixture of I . galbana and M . lutheri. The first metamorphosing
individuals were observed 8 to 10 days after fertilization. The smallest
individual, having a definite foot but no velum, measured only 205 p,
while the largest swimming larvae with a still well-developed velum
measured 245 p. Some metamorphosed cockles with well-developed
gills and a siphon were only 220p long. No “eye ” wafi observed in
any of the larvae.
The size of the largest swimming larva ever recorded in our
cultures was 250 x 220 p, but only one such individual was seen. The
maximum size of our larvae, therefore, closely agrees with that
described by Sullivan (1948) for C. pinnulaturn, which measured
250 x 230 p. Jarrgensen (1946) mentioned that Lebour grew larvae
of Cardium echinatum which, at metamorphosis, measured about 480 p
in length. We accept this figure with considerable reservation.
Jmgensen also assumed that the maximum length of larvae of
C. exiguum is about 250p: although he never observed this veliger
with certainty in the Sound, where he carried on his experimenta. His
observation on C. fasciatum indicated that the largest larval stages