Here, we shall briefly discuw the results of observations on effwts of
temperature within a much more limited range.
Larvae of most of the species cultured at our laboratory were grown
under routine conditions, i.e. at room temperature, which was normally
near 20°C. Because of this no extensive information is available as to
temperature ranges within which larvae of different species may
survive or their optimal growing temperatures. I n a few species,
nevertheless, rather extensive observations on effects of temperature
on development of their eggs and on growth of the larvae were undertaken. Studies of this nature on M . mercenaria and C. virginica have
been the most complete.
M . mercenaria has been grown from egg to metamorphosis at constant temperatures ranging from 18" to 30°C (Loosanoff et al., 1951).
If, within 3 hr after fertilization, eggs of these clams were placed in
water of 15"C, virtually none of them developed normally to straighthinge stage. If eggs were kept a t room temperature from 6 to 9 hr
after fertilization and then subjectod to a temperature of about 15"C,
some developed into straight-hinge larvae. The majority of these
larvae, however, were abnormal and many of them Boon died, although
some continued to grow at a very slow rate.
If eggs and, later, larvae developing from them were kept at room
temperature for the first 2 days after fertilization, until straighthinge stage was well formed, and then placed in water of 15"C, some of
the larvae survived for 12 days or even longer. It is possible that if
given good food, some of the individuals might eventually reach
metamorphosis. However, if larvae grown at room temperature for the
first 2 days of their existence were placed in water of 10°C (Fig. 19),
they would not grow.
Bt the other end of the temperature range, at about 33"C, abnormal
development and heavy mortality usually occurred if recently fertilized
eggs were transferred to water of this temperature. However, if eggs
and, later, larvae developing from them were kept at room temperature
for the first 48 hr after fertilization and then transferred to water of
33"C, rapid normal development, similar to that observed in cultures
kept at 30°C followed. Thus, our observations on development of
eggs and growth of larvae of M . mercenaria a t temperatures from 15"
t o 33°C support the view expressed by Pelseneer (1901) that normal
early cleavage stages of molluscan eggs are limited to a narrower
temperature range than can be tolerated by more advanced stages of
the eggs or larvae.
Larvae of M . mercenaria, developing from eggs within the temperature range of 18" to 30"C, grew to metamorphosis, growth being
temperature within a much more limited range.
Larvae of most of the species cultured at our laboratory were grown
under routine conditions, i.e. at room temperature, which was normally
near 20°C. Because of this no extensive information is available as to
temperature ranges within which larvae of different species may
survive or their optimal growing temperatures. I n a few species,
nevertheless, rather extensive observations on effects of temperature
on development of their eggs and on growth of the larvae were undertaken. Studies of this nature on M . mercenaria and C. virginica have
been the most complete.
M . mercenaria has been grown from egg to metamorphosis at constant temperatures ranging from 18" to 30°C (Loosanoff et al., 1951).
If, within 3 hr after fertilization, eggs of these clams were placed in
water of 15"C, virtually none of them developed normally to straighthinge stage. If eggs were kept a t room temperature from 6 to 9 hr
after fertilization and then subjectod to a temperature of about 15"C,
some developed into straight-hinge larvae. The majority of these
larvae, however, were abnormal and many of them Boon died, although
some continued to grow at a very slow rate.
If eggs and, later, larvae developing from them were kept at room
temperature for the first 2 days after fertilization, until straighthinge stage was well formed, and then placed in water of 15"C, some of
the larvae survived for 12 days or even longer. It is possible that if
given good food, some of the individuals might eventually reach
metamorphosis. However, if larvae grown at room temperature for the
first 2 days of their existence were placed in water of 10°C (Fig. 19),
they would not grow.
Bt the other end of the temperature range, at about 33"C, abnormal
development and heavy mortality usually occurred if recently fertilized
eggs were transferred to water of this temperature. However, if eggs
and, later, larvae developing from them were kept at room temperature
for the first 48 hr after fertilization and then transferred to water of
33"C, rapid normal development, similar to that observed in cultures
kept at 30°C followed. Thus, our observations on development of
eggs and growth of larvae of M . mercenaria a t temperatures from 15"
t o 33°C support the view expressed by Pelseneer (1901) that normal
early cleavage stages of molluscan eggs are limited to a narrower
temperature range than can be tolerated by more advanced stages of
the eggs or larvae.
Larvae of M . mercenaria, developing from eggs within the temperature range of 18" to 30"C, grew to metamorphosis, growth being