ANIMALIZATION AND VEGETALIZATION
177
chondria, would reduce the extension of the mitochondria population,
thus entailing the reduction of the animal zone. Iodosobenzoic acid
checking the formation of the mitochondrial inhibitors, would cause an
uniform mitochondrial development, resulting in the extension of the
animal zone.
Shaver (1955, 1956, 1957), studying the distribution of the mitochondria during development, has obtained results very different from
those obtained by Gustafson and Lenique. In Shaver's experiments,
mitochondrial distribution is studied in situ in whole embryos vitally
stained by Janus green or by Nile blue sulphate or in embryos fixed
and stained by Harman's method (1950). The quantitative method of
Shelton et al. (1953) for counting mitochondria in homogenates has been
adapted to study the various developmental stages of sea urchin eggs.
According to Shaver the number of mitochondria remains approximately
constant during the cleavage and blastula stages, then it increases, from
the mesenchyme blastula stage and reaches a peak in the early gastrula.
In the next stages the number of mitochondria abruptly decreases. No
gradient of distribution of the mitochondria is observed in the mesenchyme blastula and gastrula stages. Moreover, the mitochondria show a
great variability in size and shape. This mitochondrial heterogeneity may
indicate differences of structure and function in mitochondria. Shaver
concludes that his results do not support the hypothesis of differentiation based on a gradient of distribution of the mitochondria.
By a study of the distribution of mitochondria with the electron
microscope, Berg et al. (1962) have confirmed the observations of Shaver.
No mitochondrial gradient has been observed in gastrulae of Lytechinus
pictus and Strongylocentrotus
purpuratus.
A connection between mitochondria and the reduction gradient is
suggested from the nature of the cytochemical tests used to demonstrate
the reduction gradients. Differences in size of mitochondria in vegetal
and animal regions of the larvae may offer an explanation for the
existence of the reduction gradients (Berg et al., 1962), as may also
differences in activity of mitochondria.
Indeed, the mitochondria play an important part in the functioning
of cells, but the activity of other cellular inclusions, especially the
microsomes, must be taken into account. This point of view will be made
clear by a short comparison between the chief activities of the mitochondria and of the microsomes. The mitochondria are important in the
metabolism of carbohydrates and of fatty acids. They are the site of
reactions of oxidative phosphorylation generating phosphoric esters
rich in energy (ATP). The mitochondria incorporate amino-acids; they
are also able to synthesize specific proteins (Bates et al., 1960). In this
respect however, they seem less active than the microsomes, In the liver
177
chondria, would reduce the extension of the mitochondria population,
thus entailing the reduction of the animal zone. Iodosobenzoic acid
checking the formation of the mitochondrial inhibitors, would cause an
uniform mitochondrial development, resulting in the extension of the
animal zone.
Shaver (1955, 1956, 1957), studying the distribution of the mitochondria during development, has obtained results very different from
those obtained by Gustafson and Lenique. In Shaver's experiments,
mitochondrial distribution is studied in situ in whole embryos vitally
stained by Janus green or by Nile blue sulphate or in embryos fixed
and stained by Harman's method (1950). The quantitative method of
Shelton et al. (1953) for counting mitochondria in homogenates has been
adapted to study the various developmental stages of sea urchin eggs.
According to Shaver the number of mitochondria remains approximately
constant during the cleavage and blastula stages, then it increases, from
the mesenchyme blastula stage and reaches a peak in the early gastrula.
In the next stages the number of mitochondria abruptly decreases. No
gradient of distribution of the mitochondria is observed in the mesenchyme blastula and gastrula stages. Moreover, the mitochondria show a
great variability in size and shape. This mitochondrial heterogeneity may
indicate differences of structure and function in mitochondria. Shaver
concludes that his results do not support the hypothesis of differentiation based on a gradient of distribution of the mitochondria.
By a study of the distribution of mitochondria with the electron
microscope, Berg et al. (1962) have confirmed the observations of Shaver.
No mitochondrial gradient has been observed in gastrulae of Lytechinus
pictus and Strongylocentrotus
purpuratus.
A connection between mitochondria and the reduction gradient is
suggested from the nature of the cytochemical tests used to demonstrate
the reduction gradients. Differences in size of mitochondria in vegetal
and animal regions of the larvae may offer an explanation for the
existence of the reduction gradients (Berg et al., 1962), as may also
differences in activity of mitochondria.
Indeed, the mitochondria play an important part in the functioning
of cells, but the activity of other cellular inclusions, especially the
microsomes, must be taken into account. This point of view will be made
clear by a short comparison between the chief activities of the mitochondria and of the microsomes. The mitochondria are important in the
metabolism of carbohydrates and of fatty acids. They are the site of
reactions of oxidative phosphorylation generating phosphoric esters
rich in energy (ATP). The mitochondria incorporate amino-acids; they
are also able to synthesize specific proteins (Bates et al., 1960). In this
respect however, they seem less active than the microsomes, In the liver