320
ELVEZIO GHIRARDELLI
indeed a very elastic shell which can be taken off, albeit with some
difficulty, but it is impossible to work on the vitelline membrane
without damaging it. Observations under the electron microscope
have shown that the shell of the egg is made of two clearly defined
layers : the outer one is about 0.1 p thick and has a fibrillous aspect due
to the prescnce of short fibrils clearly oriented, the inner layer is thicker
and looks finely granular (Fig. 21). The vitelline membrane is composed of three layers and intimately connected with the cytoplasm ; it
is very elastic and easy to distort (Ghirardelli, 1963c, 1966b). The
structure of the membrane may perhaps explain the difficulties
experienced when trying to separate the two blastomeres. It also
explains why the eggs change their shape so rapidly when at the
moment of laying they make their way through the two cellular layers
forming the wall of the seminal pouch which, due t o the presence of
the eggs, separate from one another so as to form a “temporary
oviduct ” (Stevens, 1910). The experiments and observations I have
just mentioned, show that the eggs of Xpadella cephnloptera are eggs
with a very precocious determination : there is no reason to doubt that
the eggs of all Chaetognatha may have the same peculiarity in connexion with the existence of the germ cell determinant.
I n the sections of the eggs of 8. cephaloptera stained with ferric
haematoxylin, the germ cell determinant appears as a small roundish
compact mass with a diameter of about l o p . Through opportune
differentiations it is possible to make small granulations evident
within the determinant. This formation stains quite strongly with
pyronin but the pyroninophilia disappears after treatment with warm
HC1 N/1 or the action of the ribonuclease. The determinant is, on the
contrary, completely Feulgen-negative, while the Hotchkiss reaction for
polysaccharides is positive. The determinant is further osmiophil like
the globuli of yolk. On the basis of these data it has been possible t o
conclude that the germ cell determinant of Spadella is a formation rich
in RNA which probably contains a lipid fraction, given by strongly
unsaturated lipids, and a glucide component revealed by the oxidizability with the periodic acid (Ghirardelli, 1953a-c).
Use of the optical microscope does not allow more to be learnt than
has already been said about the morphology of the germ cell determinant, and for this reason it has been deemed useful to study it also
with the electron microscope. For this first research we have used eggs
of Xpadella cephaloptera collected on the Zostera on the bottom of the
Bay of Grignano, near Trieste.
At a small electronic magnification (Ghirardelli, 1966a, 1966b), the
determinant can be normally seen near the periphery of the egg and it
ELVEZIO GHIRARDELLI
indeed a very elastic shell which can be taken off, albeit with some
difficulty, but it is impossible to work on the vitelline membrane
without damaging it. Observations under the electron microscope
have shown that the shell of the egg is made of two clearly defined
layers : the outer one is about 0.1 p thick and has a fibrillous aspect due
to the prescnce of short fibrils clearly oriented, the inner layer is thicker
and looks finely granular (Fig. 21). The vitelline membrane is composed of three layers and intimately connected with the cytoplasm ; it
is very elastic and easy to distort (Ghirardelli, 1963c, 1966b). The
structure of the membrane may perhaps explain the difficulties
experienced when trying to separate the two blastomeres. It also
explains why the eggs change their shape so rapidly when at the
moment of laying they make their way through the two cellular layers
forming the wall of the seminal pouch which, due t o the presence of
the eggs, separate from one another so as to form a “temporary
oviduct ” (Stevens, 1910). The experiments and observations I have
just mentioned, show that the eggs of Xpadella cephnloptera are eggs
with a very precocious determination : there is no reason to doubt that
the eggs of all Chaetognatha may have the same peculiarity in connexion with the existence of the germ cell determinant.
I n the sections of the eggs of 8. cephaloptera stained with ferric
haematoxylin, the germ cell determinant appears as a small roundish
compact mass with a diameter of about l o p . Through opportune
differentiations it is possible to make small granulations evident
within the determinant. This formation stains quite strongly with
pyronin but the pyroninophilia disappears after treatment with warm
HC1 N/1 or the action of the ribonuclease. The determinant is, on the
contrary, completely Feulgen-negative, while the Hotchkiss reaction for
polysaccharides is positive. The determinant is further osmiophil like
the globuli of yolk. On the basis of these data it has been possible t o
conclude that the germ cell determinant of Spadella is a formation rich
in RNA which probably contains a lipid fraction, given by strongly
unsaturated lipids, and a glucide component revealed by the oxidizability with the periodic acid (Ghirardelli, 1953a-c).
Use of the optical microscope does not allow more to be learnt than
has already been said about the morphology of the germ cell determinant, and for this reason it has been deemed useful to study it also
with the electron microscope. For this first research we have used eggs
of Xpadella cephaloptera collected on the Zostera on the bottom of the
Bay of Grignano, near Trieste.
At a small electronic magnification (Ghirardelli, 1966a, 1966b), the
determinant can be normally seen near the periphery of the egg and it