II.
THE EMBRYOLOGY
OF ASCIDIANS
59
In the unfertilized Ascidian egg, the different constituents are diffused
uniformly throughout the egg. Thus the Nadi-reaction colours all parts
of the egg, except a small zone at the animal pole and a diffuse coloration
is obtained also with Janus green, which means that mitochondria, and
the enzymes contained in them, are distributed uniformly, that is with
no particular concentration, in the egg.
The cytochemical reaction for RNA leads to the same conclusion;
and, as the RNA granules are mostly connected with the endoplasmic
reticulum one can assume that this reticulum is also spread throughout
the egg.
The same ubiquitous distribution has been shown for the granules of
glycogen (Mancuso, 1956), and for glutathione (Ries, 1937; Urbani and
Urbani-Mistruzzi, 1947; Mancuso, 1952a).
The metachromatic granules, which have been described by Dalcq
(1957a) in Ascidiella aspersa, have, however, a restricted distribution
under the cortex.
The topographical relations of these same components are radically
different in the fertilized egg, as a consequence of the ooplasmic movements which occur at fertilization. These movements were described,
long ago, by Conklin (1905): to the ooplasmic segregations which follow
were attributed specific morphogenetic values.
The movements and segregation of the mitochondria can be followed
in every detail in the transparent egg of Phallusia. With Janus green
the unfertilized egg, as mentioned above, stains lightly and uniformly;
after fertilization the colour migrates and accumulates at the vegetal
pole (Reverberi, 1956). The same result is obtained if the egg is tested
for the Nadi-reaction (Reverberi and Pitotti, 1939). The difference
between the unfertilized and the fertilized egg, which was emphasized
by Reverberi and Pitotti but was not noticed by Ries (1937) has been
more recently confirmed by Child (1951).
Treatment of the egg at intervals after fertilization with benzidine or
tetrazolium salts gives the same result. It is known that these treatments
are indicative of mitochondria.
A similar migration must be assumed also for the metachromatic
granules of Dalcq; in fact after fertilization they are no longer found
under the cortex, but in the 'yellow crescent'; the nature of these
granules has not yet been determined. One can only affirm that they are
not mitochondria; chemically they show as mucopolysaccharide, and
contain acid phosphatases; possibly they correspond to the lysosomes of
de Duve etal (1955).
The granules of glycogen, on the contrary, after fertilization migrate
to the periphery of the egg (Mancuso, 1956). The glutathione can be
found in the centre of the egg.
THE EMBRYOLOGY
OF ASCIDIANS
59
In the unfertilized Ascidian egg, the different constituents are diffused
uniformly throughout the egg. Thus the Nadi-reaction colours all parts
of the egg, except a small zone at the animal pole and a diffuse coloration
is obtained also with Janus green, which means that mitochondria, and
the enzymes contained in them, are distributed uniformly, that is with
no particular concentration, in the egg.
The cytochemical reaction for RNA leads to the same conclusion;
and, as the RNA granules are mostly connected with the endoplasmic
reticulum one can assume that this reticulum is also spread throughout
the egg.
The same ubiquitous distribution has been shown for the granules of
glycogen (Mancuso, 1956), and for glutathione (Ries, 1937; Urbani and
Urbani-Mistruzzi, 1947; Mancuso, 1952a).
The metachromatic granules, which have been described by Dalcq
(1957a) in Ascidiella aspersa, have, however, a restricted distribution
under the cortex.
The topographical relations of these same components are radically
different in the fertilized egg, as a consequence of the ooplasmic movements which occur at fertilization. These movements were described,
long ago, by Conklin (1905): to the ooplasmic segregations which follow
were attributed specific morphogenetic values.
The movements and segregation of the mitochondria can be followed
in every detail in the transparent egg of Phallusia. With Janus green
the unfertilized egg, as mentioned above, stains lightly and uniformly;
after fertilization the colour migrates and accumulates at the vegetal
pole (Reverberi, 1956). The same result is obtained if the egg is tested
for the Nadi-reaction (Reverberi and Pitotti, 1939). The difference
between the unfertilized and the fertilized egg, which was emphasized
by Reverberi and Pitotti but was not noticed by Ries (1937) has been
more recently confirmed by Child (1951).
Treatment of the egg at intervals after fertilization with benzidine or
tetrazolium salts gives the same result. It is known that these treatments
are indicative of mitochondria.
A similar migration must be assumed also for the metachromatic
granules of Dalcq; in fact after fertilization they are no longer found
under the cortex, but in the 'yellow crescent'; the nature of these
granules has not yet been determined. One can only affirm that they are
not mitochondria; chemically they show as mucopolysaccharide, and
contain acid phosphatases; possibly they correspond to the lysosomes of
de Duve etal (1955).
The granules of glycogen, on the contrary, after fertilization migrate
to the periphery of the egg (Mancuso, 1956). The glutathione can be
found in the centre of the egg.