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ALBERTO MONROY AND RACHELE MAGGIO
able production of ammonia throughout development and the authors
suggest that oxidation of proteins may contribute a large fraction of the
energy required for early development. This possibility would be worth
exploring. The comparison of the respiratory curve of the Echinoderm
egg with that of the eggs of other animals shows certain interesting
similarities (Tuft, 1953). In fact it can be seen that the first part of the
curve, i.e., that of the exponential increase of 0 2 consumption, is
common to all eggs although varying in degree of steepness. It is also
found that this first increase is followed by a plateau, which, as indicated,
in the sea urchin corresponds to a phase of lowered mitotic rate and the
same is true in the case of the bug Rhodnius prolixus (Tuft, 1953). In
some eggs this phase seems also to correspond to a period during which
the cells of the embryo spread over the yolk ; this, however, does not
apply to the sea urchin egg. It would certainly be most interesting to
investigate the reason for this plateau especially in view of the fact that
the following phase of rapid increase in oxygen consumption marks the
beginning of cell differentiation.
However, the actual significance of the shape of the curve is still
obscure. It may be mentioned here that in the egg of the teleostean fish
Oryzias latipes, the rising parts of the respiratory curve have been found
to correspond to periods of rapid yolk breakdown and utilization of its
products for the synthesis of the embryonic proteins (Monroy et al.,
1961a). Also in the sea urchin, yolk breakdown has been suggested as
proceeding in waves (Kavanau, 1954; see Section V, D) which, however,
do not appear to be correlated with respiratory cycles.
According to the gradient theory of sea urchin development
(Runnström, 1931), two types of metabolism prevail along the animalvegetal axis of the sea urchin egg ; the animal type being most intensive
at the animal pole and gradually degrading towards the vegetal pole,
and the vegetal type running in the opposite direction. The significance
of such gradients, especially in connection with the modifications of
morphogenesis caused by lithium, is discussed by Lallier in this same
volume. The animal-vegetative gradient is directly responsible for the
animal-vegetative organization of the egg and of the ensuing embryo.
However, no quantitative difference has been detected between animal
and vegetal halves either in the respiratory rate or in the distribution of
dipeptidase (Lindahl and Holter, 1940; Holter and Lindahl, 1940). Also
the activity of cytochrome oxidase has been found to be equally
distributed between mesomeres on the one hand and macro- and micro
meres on the other. But when the isolated animal and vegetal cells were
allowed to develop in culture, although they failed to form blastulae and
remained as unorganized cell masses, cytochrome oxidase activity
increased considerably more rapidly in the cells derived from the meso-
ALBERTO MONROY AND RACHELE MAGGIO
able production of ammonia throughout development and the authors
suggest that oxidation of proteins may contribute a large fraction of the
energy required for early development. This possibility would be worth
exploring. The comparison of the respiratory curve of the Echinoderm
egg with that of the eggs of other animals shows certain interesting
similarities (Tuft, 1953). In fact it can be seen that the first part of the
curve, i.e., that of the exponential increase of 0 2 consumption, is
common to all eggs although varying in degree of steepness. It is also
found that this first increase is followed by a plateau, which, as indicated,
in the sea urchin corresponds to a phase of lowered mitotic rate and the
same is true in the case of the bug Rhodnius prolixus (Tuft, 1953). In
some eggs this phase seems also to correspond to a period during which
the cells of the embryo spread over the yolk ; this, however, does not
apply to the sea urchin egg. It would certainly be most interesting to
investigate the reason for this plateau especially in view of the fact that
the following phase of rapid increase in oxygen consumption marks the
beginning of cell differentiation.
However, the actual significance of the shape of the curve is still
obscure. It may be mentioned here that in the egg of the teleostean fish
Oryzias latipes, the rising parts of the respiratory curve have been found
to correspond to periods of rapid yolk breakdown and utilization of its
products for the synthesis of the embryonic proteins (Monroy et al.,
1961a). Also in the sea urchin, yolk breakdown has been suggested as
proceeding in waves (Kavanau, 1954; see Section V, D) which, however,
do not appear to be correlated with respiratory cycles.
According to the gradient theory of sea urchin development
(Runnström, 1931), two types of metabolism prevail along the animalvegetal axis of the sea urchin egg ; the animal type being most intensive
at the animal pole and gradually degrading towards the vegetal pole,
and the vegetal type running in the opposite direction. The significance
of such gradients, especially in connection with the modifications of
morphogenesis caused by lithium, is discussed by Lallier in this same
volume. The animal-vegetative gradient is directly responsible for the
animal-vegetative organization of the egg and of the ensuing embryo.
However, no quantitative difference has been detected between animal
and vegetal halves either in the respiratory rate or in the distribution of
dipeptidase (Lindahl and Holter, 1940; Holter and Lindahl, 1940). Also
the activity of cytochrome oxidase has been found to be equally
distributed between mesomeres on the one hand and macro- and micro
meres on the other. But when the isolated animal and vegetal cells were
allowed to develop in culture, although they failed to form blastulae and
remained as unorganized cell masses, cytochrome oxidase activity
increased considerably more rapidly in the cells derived from the meso-