172
R. LALLIER
animalized or vegetalized by other agents appears necessary before
conclusions may be drawn.
The analysis of the incorporation of labelled molecules into the
nitrogenous bases and nucleotides of ribonucleic acid during development has been largely used in the study of the metabolism of ribonucleic
acid. According to Hultin (1953a, d, 1957) the incorporation of
15
N 4 HC1,
14
C-carbonate and
14
C-formate into nucleotides of ribonucleic acid
rapidly increases during the early blastula stage. These observations
indicate that nucleotide metabolism increases during the period of
primary determination simultaneously with the first respiratory
increase. The incorporation of
14
C-adenine increases during development
following a pattern comparable to that of the respiratory curve
(Markman, 1961b). Autoradiographic studies reveal regional differences
in labelling of nuclei by adenine. The incorporation of precursor
predominates in the animal region at the early blastula stage and in the
vegetal region after the mesenchyme blastula stage (Markman, 1961a).
Staining of embryos by pyronine reveals, from the blastula mesenchyme stage onwards, a preferential accumulation of ribonucleic acid in
the cytoplasm of the vegetal part of the embryo. These differences are
also observed in the vegetalized and animalized embryos (Markman,
1957).
Hale's staining procedure reveals some possible difference in the state
of nuclear ribonucleic acid. The observations of Immers (1956), confirmed by Markman (1957), have suggested that the phosphoric groups
of ribonucleic acid exist in a free state in the ectoderm, while in the
entomesoderm they seem to be blocked by proteins.
The relationship between the metabolism of the nucleic acids on the
one hand, and the determination and differentiation of the embryos on
the other has been approached by studying the effects on the development of eggs of diverse antimetabolites, structural analogues of normal
metabolites, able to interfere with the metabolism of nucleic acids.
Hörstadius et al. (1954) have studied the effects of the synthetic
nucleosides, analogues of cytidine and uridine. The synthetic nucleosides
used were, one analogue of uridine, D-ß-galactopyranosyluracyl and four
analogues of cytidine, D-jS-galactopyranosylcytosine, a-arabinopyranosylcytosine, D-xylopyranosylcytosine and D-/?-glucopyranosylcytosine.
Only the three last analogues of cytidine were able to animalize, more
or less, the animal halves. Hörstadius and Gustafson (1954) have also
studied the effects of 8-chloroxanthine, an antimetabolite to purines
and nucleic acids. 8-Chloroxanthine slightly increases the animalization
of animal halves. Whole eggs treated with 8-chloroxanthine develop into
radial larvae. Benzimidazol, a compound structurally related to purines,
enhances the animalization of animal halves but strongly vegetalizes
R. LALLIER
animalized or vegetalized by other agents appears necessary before
conclusions may be drawn.
The analysis of the incorporation of labelled molecules into the
nitrogenous bases and nucleotides of ribonucleic acid during development has been largely used in the study of the metabolism of ribonucleic
acid. According to Hultin (1953a, d, 1957) the incorporation of
15
N 4 HC1,
14
C-carbonate and
14
C-formate into nucleotides of ribonucleic acid
rapidly increases during the early blastula stage. These observations
indicate that nucleotide metabolism increases during the period of
primary determination simultaneously with the first respiratory
increase. The incorporation of
14
C-adenine increases during development
following a pattern comparable to that of the respiratory curve
(Markman, 1961b). Autoradiographic studies reveal regional differences
in labelling of nuclei by adenine. The incorporation of precursor
predominates in the animal region at the early blastula stage and in the
vegetal region after the mesenchyme blastula stage (Markman, 1961a).
Staining of embryos by pyronine reveals, from the blastula mesenchyme stage onwards, a preferential accumulation of ribonucleic acid in
the cytoplasm of the vegetal part of the embryo. These differences are
also observed in the vegetalized and animalized embryos (Markman,
1957).
Hale's staining procedure reveals some possible difference in the state
of nuclear ribonucleic acid. The observations of Immers (1956), confirmed by Markman (1957), have suggested that the phosphoric groups
of ribonucleic acid exist in a free state in the ectoderm, while in the
entomesoderm they seem to be blocked by proteins.
The relationship between the metabolism of the nucleic acids on the
one hand, and the determination and differentiation of the embryos on
the other has been approached by studying the effects on the development of eggs of diverse antimetabolites, structural analogues of normal
metabolites, able to interfere with the metabolism of nucleic acids.
Hörstadius et al. (1954) have studied the effects of the synthetic
nucleosides, analogues of cytidine and uridine. The synthetic nucleosides
used were, one analogue of uridine, D-ß-galactopyranosyluracyl and four
analogues of cytidine, D-jS-galactopyranosylcytosine, a-arabinopyranosylcytosine, D-xylopyranosylcytosine and D-/?-glucopyranosylcytosine.
Only the three last analogues of cytidine were able to animalize, more
or less, the animal halves. Hörstadius and Gustafson (1954) have also
studied the effects of 8-chloroxanthine, an antimetabolite to purines
and nucleic acids. 8-Chloroxanthine slightly increases the animalization
of animal halves. Whole eggs treated with 8-chloroxanthine develop into
radial larvae. Benzimidazol, a compound structurally related to purines,
enhances the animalization of animal halves but strongly vegetalizes