152
R. LALLIER
Hörstadius (1935, 1949) has analysed development using operative
methods. From the results obtained, it appears that isolation of the
animal halves induces hyperdevelopment of the ectodermal structures
(animalization). Reciprocally, the isolation of the vegetal halves induces
the extension of the development of the entomesodermal structures
(vegetalization). The animalizing and vegetalizing effects observed in
some groups of isolated blastomeres can be corrected by the recombination of groups of blastomeres from different parts of the egg. For instance,
the animalization of isolated animal halves can be diminished by the
addition of vegetative material, such as the micromeres. It is also
possible to obtain the development of normal larvae from combinations
of animal and vegetative blastomeres.
2. Chemical Methods
Various substances can modify the development of the larvae either
towards vegetalization or animalization.
There are only a few vegetalizing agents. The most commonly used is
lithium, the effects of which were discovered by Herbst (1892). Recently,
a derivative of pyrazolone, phenazone, has been shown to strongly
vegetalize whole eggs (Lallier, 1959c). An inhibitor of protein synthesis,
chloramphenicol, is also an effective vegetalizing agent (Lallier, 1961).
Other substances provoke vegetalization, but it is often not very
pronounced and generally it can only be observed when fragments
rather than whole eggs are treated. This is the case with dinitrophenol
(Hörstadius, 1953) and some amino-acids (Gustafson and Hörstadius,
1957).
Animalizing agents are more numerous. They belong to very different
chemical classes : metallic ions, sulphydryl compounds, reagents of the
sulphydryl groups, proteolytic enzymes, etc. . . . The most active, in
increasing order of activity, are: thiocyanate and iodide (Lindahl, 1936),
iodosobenzoic acid (Runnström and Kriszat, 1952), thiomalic acid
(Lallier, 1952), some sulphonic organic derivatives (Lallier, 1955c) and
zinc ions (Lallier, 1955a). All these agents are able to animalize whole
eggs.
Chemical agents have a different action according to the development
period in which they are used. The development of the sea urchin egg
into the pluteus may be divided into two periods. The first period
extends to the blastula stage when the primary mesenchyme is formed.
This is the determination phase, during which the equilibrium between
the differentiating tendencies of the ectoderm and the endoderm are
progressively stabilized. The second period begins with the formation of
the primary mesenchyme (blastula mesenchyme stage) and is accompanied by visible signs of differentiation, gastrulation and the formation
R. LALLIER
Hörstadius (1935, 1949) has analysed development using operative
methods. From the results obtained, it appears that isolation of the
animal halves induces hyperdevelopment of the ectodermal structures
(animalization). Reciprocally, the isolation of the vegetal halves induces
the extension of the development of the entomesodermal structures
(vegetalization). The animalizing and vegetalizing effects observed in
some groups of isolated blastomeres can be corrected by the recombination of groups of blastomeres from different parts of the egg. For instance,
the animalization of isolated animal halves can be diminished by the
addition of vegetative material, such as the micromeres. It is also
possible to obtain the development of normal larvae from combinations
of animal and vegetative blastomeres.
2. Chemical Methods
Various substances can modify the development of the larvae either
towards vegetalization or animalization.
There are only a few vegetalizing agents. The most commonly used is
lithium, the effects of which were discovered by Herbst (1892). Recently,
a derivative of pyrazolone, phenazone, has been shown to strongly
vegetalize whole eggs (Lallier, 1959c). An inhibitor of protein synthesis,
chloramphenicol, is also an effective vegetalizing agent (Lallier, 1961).
Other substances provoke vegetalization, but it is often not very
pronounced and generally it can only be observed when fragments
rather than whole eggs are treated. This is the case with dinitrophenol
(Hörstadius, 1953) and some amino-acids (Gustafson and Hörstadius,
1957).
Animalizing agents are more numerous. They belong to very different
chemical classes : metallic ions, sulphydryl compounds, reagents of the
sulphydryl groups, proteolytic enzymes, etc. . . . The most active, in
increasing order of activity, are: thiocyanate and iodide (Lindahl, 1936),
iodosobenzoic acid (Runnström and Kriszat, 1952), thiomalic acid
(Lallier, 1952), some sulphonic organic derivatives (Lallier, 1955c) and
zinc ions (Lallier, 1955a). All these agents are able to animalize whole
eggs.
Chemical agents have a different action according to the development
period in which they are used. The development of the sea urchin egg
into the pluteus may be divided into two periods. The first period
extends to the blastula stage when the primary mesenchyme is formed.
This is the determination phase, during which the equilibrium between
the differentiating tendencies of the ectoderm and the endoderm are
progressively stabilized. The second period begins with the formation of
the primary mesenchyme (blastula mesenchyme stage) and is accompanied by visible signs of differentiation, gastrulation and the formation