148
R. LALLIER
account recent results. Various aspects of these problems have already
been examined by Hörstadius (1949), Ranzi (1951), Gustafson (1955),
Lallier (1958c), Brächet (1960). Since the first experiments of Lindahl
(1936) on the effects of lithium upon the metabolism of the sea urchin
egg, the analysis of the metabolism of normal and experimentally
modified embryos has been considerably developed. The improvement
in the techniques of biochemical analysis, and the increase in our
knowledge of cellular biochemistry, as well as the discovery of new
chemical agents, capable of modifying embryonic development, are
responsible for these advances. The catabolism of the glucides is at the
present time one of the metabolic processes about which we know most ;
several ways of degrading glucides, already observed in varied organisms,
have been observed again in the sea urchin egg. This explains the
importance of the analysis of the catabolism of glucides in this research.
During the last ten years, the study of the metabolism of nucleic acids
and proteins has developed considerably and much information has
been obtained in this field. Research on metabolism is completed by
the study of cellular structures. In fact, most of the enzymes responsible
for metabolic activity depend upon cellular structures such as, for
instance, the mitochondria and microsomes. The study of the distribution and structure of the cellular inclusions is therefore indispensable to
an analysis of metabolism.
Research on the development of the sea urchin egg has three aspects,
morphological, metabolic and structural. To integrate the diverse
aspects of the observed phenomena in a general concept, the idea of
gradient is used by embryologists. A very important part of this
research is devoted to demonstrating the gradients, to determining their
nature, and to studying the changes they undergo during experimental
modifications of development. The survey of the literature pertaining to
this paper was concluded in April 1962.
II. Normal Development
We will briefly describe the different stages of the development of the
egg up to the pluteus stage (Fig. 1). As an example, we shall take the egg
of the sea urchin, Paracentrotus lividus. The two first cleaving planes,
meridian and perpendicular to each other, together with the third one
which is equatorial, divide the egg into 8 equal blastomeres. The next
cleavage divides the eggs into 16 cells. At this stage, the egg is made up
of 8 cells of medium size called mesomeres, 4 cells of large size called
macromeres and 4 small ones called micromeres. Mesomeres give rise to
the ectoderm of the larva. The macromeres contribute to part of the
ectoderm and produce the whole of the endoderm. The micromeres
R. LALLIER
account recent results. Various aspects of these problems have already
been examined by Hörstadius (1949), Ranzi (1951), Gustafson (1955),
Lallier (1958c), Brächet (1960). Since the first experiments of Lindahl
(1936) on the effects of lithium upon the metabolism of the sea urchin
egg, the analysis of the metabolism of normal and experimentally
modified embryos has been considerably developed. The improvement
in the techniques of biochemical analysis, and the increase in our
knowledge of cellular biochemistry, as well as the discovery of new
chemical agents, capable of modifying embryonic development, are
responsible for these advances. The catabolism of the glucides is at the
present time one of the metabolic processes about which we know most ;
several ways of degrading glucides, already observed in varied organisms,
have been observed again in the sea urchin egg. This explains the
importance of the analysis of the catabolism of glucides in this research.
During the last ten years, the study of the metabolism of nucleic acids
and proteins has developed considerably and much information has
been obtained in this field. Research on metabolism is completed by
the study of cellular structures. In fact, most of the enzymes responsible
for metabolic activity depend upon cellular structures such as, for
instance, the mitochondria and microsomes. The study of the distribution and structure of the cellular inclusions is therefore indispensable to
an analysis of metabolism.
Research on the development of the sea urchin egg has three aspects,
morphological, metabolic and structural. To integrate the diverse
aspects of the observed phenomena in a general concept, the idea of
gradient is used by embryologists. A very important part of this
research is devoted to demonstrating the gradients, to determining their
nature, and to studying the changes they undergo during experimental
modifications of development. The survey of the literature pertaining to
this paper was concluded in April 1962.
II. Normal Development
We will briefly describe the different stages of the development of the
egg up to the pluteus stage (Fig. 1). As an example, we shall take the egg
of the sea urchin, Paracentrotus lividus. The two first cleaving planes,
meridian and perpendicular to each other, together with the third one
which is equatorial, divide the egg into 8 equal blastomeres. The next
cleavage divides the eggs into 16 cells. At this stage, the egg is made up
of 8 cells of medium size called mesomeres, 4 cells of large size called
macromeres and 4 small ones called micromeres. Mesomeres give rise to
the ectoderm of the larva. The macromeres contribute to part of the
ectoderm and produce the whole of the endoderm. The micromeres