94
VICTOR L. LOOSANOFF A N D HARRY C. DAVIS
they reach 215 p in length. This spot is usually located approximably
in the center of the larvae and measures from 6 to 7 p in diameter.
In one individual measuring only 205 p in length a well-defined ‘‘ eye ”
spot was found, but this was the only case of an “ eye ” in such a
small larva recorded after examining thousands of individuals. When
a length of 230 p was reached the “ eye ” spot was present in all larvtle.
The size at which mussel larvae metamorphosed varied by almost
90 p. The smallest metamorphosed individual, attached by a b y m s
to an oyster shell laid in one of our culture jars, was only 215 x 201 p.
Individuals measuring 225 p in length, but fully metamorphosed
and attached by a byssus, were not uncommon. On the other hand,
some larvae continued to swim until they were almost 300 p in length.
Large variations in the size of M. edulis larvae at the time of metamorphosis were also recorded by Jmgensen (1946). He thinks that
variable size at metamorphosis is not entirely due to the fact that
veligers may pass into the bottom stage after attaining a different
stage of organization, but also because of the varying ratio between
the rate of differentiation of the tissues and rate of growth in different
individuals .
The factors which govern appearance of the foot and disappearance
of the velum in larvae of M. edulis are rather baffling. I n some instances
a well-developed foot was observed in animals as small aa 185 p in
length. Such cases, however, were not too common and, usually, the
appearance of a developing foot occurred as the larvae approached
210 p in length. Most larvae possessed a well-developed foot by the
time they reached 230 p in length, but a functional velum has been
observed in larvae as large as 288 p.
The great differences in the state of organization attained at a
certain size by larvae of M . edulis are also emphasized by Jmgensen.
He gives examples of larvae measuring 250 p long and nearing metamorphosis with well-developed gills and foot and with a velum in 8
reduced condition, while in other cases larvae of the same size will
have only a vestige of a foot but a large velum, thus indicating that
they are still far from metamorphosing.
The variation in size of larvae at the time of metamorphosis suggested a more critical analysis of the data on growth of larvae in the
same cultures. Fortunately, among our cultures there was one in which
all larvae originated from eggs of the same female and were fertilized
by sperm of the same male. Regardless of this, 2 days after fertilization the larvae varied in length from 93 to 120 p, with an arithmetic
mean of 106 p. When the culture was 8 days old the length varied
from 107 to 162 p, the average being 130 p. At 14 days some of the
VICTOR L. LOOSANOFF A N D HARRY C. DAVIS
they reach 215 p in length. This spot is usually located approximably
in the center of the larvae and measures from 6 to 7 p in diameter.
In one individual measuring only 205 p in length a well-defined ‘‘ eye ”
spot was found, but this was the only case of an “ eye ” in such a
small larva recorded after examining thousands of individuals. When
a length of 230 p was reached the “ eye ” spot was present in all larvtle.
The size at which mussel larvae metamorphosed varied by almost
90 p. The smallest metamorphosed individual, attached by a b y m s
to an oyster shell laid in one of our culture jars, was only 215 x 201 p.
Individuals measuring 225 p in length, but fully metamorphosed
and attached by a byssus, were not uncommon. On the other hand,
some larvae continued to swim until they were almost 300 p in length.
Large variations in the size of M. edulis larvae at the time of metamorphosis were also recorded by Jmgensen (1946). He thinks that
variable size at metamorphosis is not entirely due to the fact that
veligers may pass into the bottom stage after attaining a different
stage of organization, but also because of the varying ratio between
the rate of differentiation of the tissues and rate of growth in different
individuals .
The factors which govern appearance of the foot and disappearance
of the velum in larvae of M. edulis are rather baffling. I n some instances
a well-developed foot was observed in animals as small aa 185 p in
length. Such cases, however, were not too common and, usually, the
appearance of a developing foot occurred as the larvae approached
210 p in length. Most larvae possessed a well-developed foot by the
time they reached 230 p in length, but a functional velum has been
observed in larvae as large as 288 p.
The great differences in the state of organization attained at a
certain size by larvae of M . edulis are also emphasized by Jmgensen.
He gives examples of larvae measuring 250 p long and nearing metamorphosis with well-developed gills and foot and with a velum in 8
reduced condition, while in other cases larvae of the same size will
have only a vestige of a foot but a large velum, thus indicating that
they are still far from metamorphosing.
The variation in size of larvae at the time of metamorphosis suggested a more critical analysis of the data on growth of larvae in the
same cultures. Fortunately, among our cultures there was one in which
all larvae originated from eggs of the same female and were fertilized
by sperm of the same male. Regardless of this, 2 days after fertilization the larvae varied in length from 93 to 120 p, with an arithmetic
mean of 106 p. When the culture was 8 days old the length varied
from 107 to 162 p, the average being 130 p. At 14 days some of the