318
ELVEZIO OHIRARDELLI
the next division, when the germinal cell divides for the first time, the
germ cell determinant contained in it also distributes itself into the
two daughter-cells.
Buchner states that each receives an equal share of the determinant ; Elpatiewsky and Stevens, on the other hand, believe that the
determinant splits into unequal portions between the two cells. The
differentiation of the primitive cells is related to this circumstancethe spermatogonia derive from the cell which received a lesser quantity
of determinant, while the oogonia originate from the other one.
Up until now there has not been sufficient evidence t o affirm that
the differentiation of the germinal cells is due to the different quantity
of germ cell determinant they receive, and still less has it been proved
that the primordium of the male line actually is the cell which receives
the lesser quantity of determinant. On the contrary, it cannot be
excluded that, in the same way as in other organisms with balanced
hermaphroditism like Chaetognatha, the differentiation of the germ
cell may be due to the action of a gradient active in a cephalocaudal
direction (Vannini, 1963 ; Ghirardelli, 1965a).
A t the 64-cell stage two cells are already clearly determined as
germinal cells and, although the somatic cells may further divide before
gastrulation, the two primitive cells divide only during or after gastrulation has occurred. This explains why Hertwig (1880) located the
primordium of the germinal line in two cells only, in the very young
gastrula, placed on the wall of the archenteron (opposite the blastopore)
and later four in Sugitta (one only Spadellu in the early gastrula,
according to John, 1933). These four cells do not divide further during
the subsequent phases of embryonic development, which in Spudella,
at a temperature of lS"C, takes about 24 h to complete. Eight hours
are necessary for the gastrulation (Ghirardelli, 1953~). I have also
observed times not greatly differing from those in Sugitta inJlata, while
Kuhl and Kuhl ( 1 965) have seen that gastrulation in Sagitta setosa takes
a somewhat lesser time. It is likely that the differences observed might
be due t o the temperature; Murakami (1959) has actually observed
that the period from spawning t o hatching changes with water temperature and chlorinity. A minimum of 15 h was recorded at a temperature
above 27°C. Murakami supposed that the eggs of Sugitta crassa spawned
in the sea hatch in 1 day in summer and in 2-4 in winter.
At hatching two of the primitive germ cells are situated in front of
the caudal septum and they will give rise to the oogonia; the other
two, situated behind the septum, will originate the male germ line. It
is perhaps opportune t o recall that from the two anterior cells only the
oogonia arise, while all the other cells which take part in the formation
ELVEZIO OHIRARDELLI
the next division, when the germinal cell divides for the first time, the
germ cell determinant contained in it also distributes itself into the
two daughter-cells.
Buchner states that each receives an equal share of the determinant ; Elpatiewsky and Stevens, on the other hand, believe that the
determinant splits into unequal portions between the two cells. The
differentiation of the primitive cells is related to this circumstancethe spermatogonia derive from the cell which received a lesser quantity
of determinant, while the oogonia originate from the other one.
Up until now there has not been sufficient evidence t o affirm that
the differentiation of the germinal cells is due to the different quantity
of germ cell determinant they receive, and still less has it been proved
that the primordium of the male line actually is the cell which receives
the lesser quantity of determinant. On the contrary, it cannot be
excluded that, in the same way as in other organisms with balanced
hermaphroditism like Chaetognatha, the differentiation of the germ
cell may be due to the action of a gradient active in a cephalocaudal
direction (Vannini, 1963 ; Ghirardelli, 1965a).
A t the 64-cell stage two cells are already clearly determined as
germinal cells and, although the somatic cells may further divide before
gastrulation, the two primitive cells divide only during or after gastrulation has occurred. This explains why Hertwig (1880) located the
primordium of the germinal line in two cells only, in the very young
gastrula, placed on the wall of the archenteron (opposite the blastopore)
and later four in Sugitta (one only Spadellu in the early gastrula,
according to John, 1933). These four cells do not divide further during
the subsequent phases of embryonic development, which in Spudella,
at a temperature of lS"C, takes about 24 h to complete. Eight hours
are necessary for the gastrulation (Ghirardelli, 1953~). I have also
observed times not greatly differing from those in Sugitta inJlata, while
Kuhl and Kuhl ( 1 965) have seen that gastrulation in Sagitta setosa takes
a somewhat lesser time. It is likely that the differences observed might
be due t o the temperature; Murakami (1959) has actually observed
that the period from spawning t o hatching changes with water temperature and chlorinity. A minimum of 15 h was recorded at a temperature
above 27°C. Murakami supposed that the eggs of Sugitta crassa spawned
in the sea hatch in 1 day in summer and in 2-4 in winter.
At hatching two of the primitive germ cells are situated in front of
the caudal septum and they will give rise to the oogonia; the other
two, situated behind the septum, will originate the male germ line. It
is perhaps opportune t o recall that from the two anterior cells only the
oogonia arise, while all the other cells which take part in the formation