176
R. LALLIER
period of development. The distribution of the mitochondria seems
uniform throughout segmentation until the blastula stage. At the
mesenchyme blastula stage, the number of mitochondria increases more
quickly in the animal zone. These mitochondria are then distributed
according to an animal-vegetal gradient. This gradient may also be
observed in the young gastrula. A second mitochondrial centre appears
in the intestine of the prismatic larva. In the pluteus, mitochondria are
observed in the oesophagus and the proctodaeum, as well as in the
intestine. In embryos vegetalized with lithium, the number of mitochondria rises more slowly than in normal development. On the other
hand, the zone which is rich in mitochondria is limited to the most
animalized regions of the blastula. In the more advanced stages, a
second mitochondrial centre appears in the entodermal structures. The
formation of this centre occurs earlier in larvae treated with lithium
than in normal larvae.
In embryos animalized by iodozobenzoic acid, the zone rich in
mitochondria is much more extensive than in normal or vegetalized
larvae. This phenomenon may not result from the augmentation of the
number of the mitochondria but from a greater uniformity in their
distribution.
Lenicque et al. (1953) have extended this research to the study of
isolated animal and vegetal halves. They observed that in isolated
animal halves, the mitochondrial pattern agrees with that of a whole
embryo animalized by iodosobenzoic acid. Reciprocally, in the isolated
vegetal halves, the mitochondrial pattern is consistent with that of
lithium-vegetalized larva. Moreover the implantation of vegetative
material, such as the micromeres, has an influence over the distribution
of the mitochondria. Thus, the implantation of micromeres in an animal
half, shifts the mitochondrial pattern into that of a normal or a
vegetalized larva. The strength of the effect is a function of the number
of implanted micromeres. These experiments show that the distribution
pattern of the mitochondria is closely related to the type of larval
development.
From all these results, Gustafson and Lenicque have drawn the
following interpretation. The determination period corresponds to the
development of mitochondrial precursors. During the period of visible
differentiation, the mitochondria are formed from these precursors.
The differentiation of the ectoderm and of the entomesoderm would be
the result of mutual interactions between two antagonistic metabolic
types. One of them, oriented in the animal-vegetal direction, would
favour the development of mitochondria. The other, with an opposite
orientation would produce inhibitors of mitochondrial development.
Lithium ions, favouring the inhibition of the development of the mito-
R. LALLIER
period of development. The distribution of the mitochondria seems
uniform throughout segmentation until the blastula stage. At the
mesenchyme blastula stage, the number of mitochondria increases more
quickly in the animal zone. These mitochondria are then distributed
according to an animal-vegetal gradient. This gradient may also be
observed in the young gastrula. A second mitochondrial centre appears
in the intestine of the prismatic larva. In the pluteus, mitochondria are
observed in the oesophagus and the proctodaeum, as well as in the
intestine. In embryos vegetalized with lithium, the number of mitochondria rises more slowly than in normal development. On the other
hand, the zone which is rich in mitochondria is limited to the most
animalized regions of the blastula. In the more advanced stages, a
second mitochondrial centre appears in the entodermal structures. The
formation of this centre occurs earlier in larvae treated with lithium
than in normal larvae.
In embryos animalized by iodozobenzoic acid, the zone rich in
mitochondria is much more extensive than in normal or vegetalized
larvae. This phenomenon may not result from the augmentation of the
number of the mitochondria but from a greater uniformity in their
distribution.
Lenicque et al. (1953) have extended this research to the study of
isolated animal and vegetal halves. They observed that in isolated
animal halves, the mitochondrial pattern agrees with that of a whole
embryo animalized by iodosobenzoic acid. Reciprocally, in the isolated
vegetal halves, the mitochondrial pattern is consistent with that of
lithium-vegetalized larva. Moreover the implantation of vegetative
material, such as the micromeres, has an influence over the distribution
of the mitochondria. Thus, the implantation of micromeres in an animal
half, shifts the mitochondrial pattern into that of a normal or a
vegetalized larva. The strength of the effect is a function of the number
of implanted micromeres. These experiments show that the distribution
pattern of the mitochondria is closely related to the type of larval
development.
From all these results, Gustafson and Lenicque have drawn the
following interpretation. The determination period corresponds to the
development of mitochondrial precursors. During the period of visible
differentiation, the mitochondria are formed from these precursors.
The differentiation of the ectoderm and of the entomesoderm would be
the result of mutual interactions between two antagonistic metabolic
types. One of them, oriented in the animal-vegetal direction, would
favour the development of mitochondria. The other, with an opposite
orientation would produce inhibitors of mitochondrial development.
Lithium ions, favouring the inhibition of the development of the mito-