SOME ASPECTS OF THE BIOLOGY OF THE CHAETOGNATHS
313
BordAs meant, to iiiclude the accessory fertilization cells, because in
these the quantity of ribonucleoproteins is aIways very small.
As regards the dimensions of oocytes and the general aspect of the
ovaries and testes, several classifications of the maturity stages in
Chaetognatha have been proposed. Alvariiio (1965) has given an
excellent review of them.
Ghirardelli (1951, 1961a,c) has established (in Xagitta injlata and
8. cephaloptera) a connexion between the morphological aspect of the
male and female gonads, as observed with a moderate magnification,
and the cytological condition of the gonad itself: he has distinguished
four stages of maturity plus an initial stage in which the gonads are
not yet perfectly formed. The maturity stages according to Ghirardelli
are sumrnarizcd in Table I. The knowledge and exact evaluation of
the maturity stages has an obvious importance in the determination of
the life cycles of chaetognaths as the researches of several workers have
shown, particularly David (1955, 1965), Fraser (1952), Russell (1932),
Dallot (1967), Alvarifio (1967a), and which we shall discuss shortly
(p. 343).
3. Germ cell determinant
Before leaving the subject of the eggs of chaetognaths, i t is opportune to mention another formation which is present in the eggs, i.e.
the germ cell determinant.
I n 1573 Biitschli discovered that the germinal cells of chaetognaths
can be singled out already in very precocious stages of embryonal
development. He actually described in the gastrula of Xagitta a pluricellular formation situated on the bottom of the archenteron cavity,
and identified it as the primordium of the germinal line. Hertwig (1880)
stated on the contrary that this " anlage " was formed a t first by two
cells only. The segregation of the germinal line is, however, still more
precocious and must be related to the presence in the egg, while still
unsegmented, of a peculiar cytoplasmic inclusion which appears
immediately after the laying of the fertilized eggs, when the two
pronuclei have not yet conjugated. Elpatiewsky (1909) was the first
to describe this structure in the eggs of 8. bipunctata and he called it
" besondere Korper ". At almost the same time this peculiar body
was observed, still in Sagitta, by Buchner (1910) and Stevens (1910);
some years later Vasiljev (1925) stated that it is found also in the eggs
of Xpadella cephaloptera. According to Elpatiewsky the peculiar body
or germinal determinant (Ghirardelli, 1953a-c) is a small neatly
contoured mass, placed in the periphery of the egg, near the vegetative
pole ; it is strongly stained by ferric haematoxylin.
313
BordAs meant, to iiiclude the accessory fertilization cells, because in
these the quantity of ribonucleoproteins is aIways very small.
As regards the dimensions of oocytes and the general aspect of the
ovaries and testes, several classifications of the maturity stages in
Chaetognatha have been proposed. Alvariiio (1965) has given an
excellent review of them.
Ghirardelli (1951, 1961a,c) has established (in Xagitta injlata and
8. cephaloptera) a connexion between the morphological aspect of the
male and female gonads, as observed with a moderate magnification,
and the cytological condition of the gonad itself: he has distinguished
four stages of maturity plus an initial stage in which the gonads are
not yet perfectly formed. The maturity stages according to Ghirardelli
are sumrnarizcd in Table I. The knowledge and exact evaluation of
the maturity stages has an obvious importance in the determination of
the life cycles of chaetognaths as the researches of several workers have
shown, particularly David (1955, 1965), Fraser (1952), Russell (1932),
Dallot (1967), Alvarifio (1967a), and which we shall discuss shortly
(p. 343).
3. Germ cell determinant
Before leaving the subject of the eggs of chaetognaths, i t is opportune to mention another formation which is present in the eggs, i.e.
the germ cell determinant.
I n 1573 Biitschli discovered that the germinal cells of chaetognaths
can be singled out already in very precocious stages of embryonal
development. He actually described in the gastrula of Xagitta a pluricellular formation situated on the bottom of the archenteron cavity,
and identified it as the primordium of the germinal line. Hertwig (1880)
stated on the contrary that this " anlage " was formed a t first by two
cells only. The segregation of the germinal line is, however, still more
precocious and must be related to the presence in the egg, while still
unsegmented, of a peculiar cytoplasmic inclusion which appears
immediately after the laying of the fertilized eggs, when the two
pronuclei have not yet conjugated. Elpatiewsky (1909) was the first
to describe this structure in the eggs of 8. bipunctata and he called it
" besondere Korper ". At almost the same time this peculiar body
was observed, still in Sagitta, by Buchner (1910) and Stevens (1910);
some years later Vasiljev (1925) stated that it is found also in the eggs
of Xpadella cephaloptera. According to Elpatiewsky the peculiar body
or germinal determinant (Ghirardelli, 1953a-c) is a small neatly
contoured mass, placed in the periphery of the egg, near the vegetative
pole ; it is strongly stained by ferric haematoxylin.