SOME ASPECTS OF THE BIOLOGY O F THE CHAETOGNATHS
349
and the release of the sperm are repeated more than twice at intervals
of several days. The period from spawning t o hatching changes with
water temperature and chlorinity and a minimum of 15 h was recorded
a t the temperature above 27OC. The optimum range of chlorinity for
8. crassa is 17-18%.
It has been remarked in Spadella cephaloptera (Ghirardelli, 1959c,
1960, 1963a) that at the end of spring and the beginning of summer
some specimens can be found whose total length is on average more
than that of the individuals observed in later months. Also the ovaries
of individuals gathered in May are longer than those of the specimens
collected in June, August and September : this can be explained easily
considering that the average number of the eggs found in May in
individuals in the Bay of Villefranclie is sixteen ; this number decreases
to tcn in June, seven in July ; in later months normally from four to
two, or even one, eggs can be seen in the ovaries. On the basis of the
diminution in number of eggs laid, one could presume that the spring
specimens can survive until autumn with several successive spawnings ;
but the progressive reduction in their length excludes this thesis.
The distribution of the stages of maturity in the spring-summer
period, leads one to suppose that maturity can be reached in about 2
months: 1 month from hatching to the beginning of oogenesis and
spermatogenesis, and 1 month for the maturation of the gametes. This
hypothesis is confirmed by observations made on specimens which have
been grown in the laboratory from egg to adult. After spawning, the
ovary shows a state of maturity similar to that of the younger specimens, because one sees only oocytes in the first and second periods of
growth ; these young oocytes will become mature later. I n the laboratory it has been seen that about 1 month separates two successive
layings. The testis, on the contrary, once it has reached maturity does
not show younger stages, but only differences in its activity in connexion with the need to re-fill the seminal vesicles emptied after mating
(Ghirardelli, 1954a).
It still remains to be ascertained whether the spring specimens are
those of the previous autumn which have found refuge on the bottom,
or are a generation born from individuals which have survived the
winter, or are individuals born from eggs laid in autumn and fixed as
usual to submerged objects. The first hypothesis would be valid only
if the individuals which pass the winter are young ones born in autumn
which have not yet reached sexual maturity: they would reach it in
spring, increasing their dimensions at the same time. Observations
made by Furnestin and Brunet (1965) in the port of Marseille, by
Nouvel (1935) at Roscoff and by John (1933) at Plymouth, confirm
349
and the release of the sperm are repeated more than twice at intervals
of several days. The period from spawning t o hatching changes with
water temperature and chlorinity and a minimum of 15 h was recorded
a t the temperature above 27OC. The optimum range of chlorinity for
8. crassa is 17-18%.
It has been remarked in Spadella cephaloptera (Ghirardelli, 1959c,
1960, 1963a) that at the end of spring and the beginning of summer
some specimens can be found whose total length is on average more
than that of the individuals observed in later months. Also the ovaries
of individuals gathered in May are longer than those of the specimens
collected in June, August and September : this can be explained easily
considering that the average number of the eggs found in May in
individuals in the Bay of Villefranclie is sixteen ; this number decreases
to tcn in June, seven in July ; in later months normally from four to
two, or even one, eggs can be seen in the ovaries. On the basis of the
diminution in number of eggs laid, one could presume that the spring
specimens can survive until autumn with several successive spawnings ;
but the progressive reduction in their length excludes this thesis.
The distribution of the stages of maturity in the spring-summer
period, leads one to suppose that maturity can be reached in about 2
months: 1 month from hatching to the beginning of oogenesis and
spermatogenesis, and 1 month for the maturation of the gametes. This
hypothesis is confirmed by observations made on specimens which have
been grown in the laboratory from egg to adult. After spawning, the
ovary shows a state of maturity similar to that of the younger specimens, because one sees only oocytes in the first and second periods of
growth ; these young oocytes will become mature later. I n the laboratory it has been seen that about 1 month separates two successive
layings. The testis, on the contrary, once it has reached maturity does
not show younger stages, but only differences in its activity in connexion with the need to re-fill the seminal vesicles emptied after mating
(Ghirardelli, 1954a).
It still remains to be ascertained whether the spring specimens are
those of the previous autumn which have found refuge on the bottom,
or are a generation born from individuals which have survived the
winter, or are individuals born from eggs laid in autumn and fixed as
usual to submerged objects. The first hypothesis would be valid only
if the individuals which pass the winter are young ones born in autumn
which have not yet reached sexual maturity: they would reach it in
spring, increasing their dimensions at the same time. Observations
made by Furnestin and Brunet (1965) in the port of Marseille, by
Nouvel (1935) at Roscoff and by John (1933) at Plymouth, confirm