AMPHIBIAN AND INVERTEBRATE DEVELOPMENT 91
individual batchs of eggs. No appreciable decreases in lipids occur up to
the tail bud stage in both Bufo vulgaris and Rana esculenta.
From this stage on, it is possible to detect a slight decrease in the total
lipid content, indicating that lipids are being used as a source of energy.
Increased lipid utilization is noted throughout the subsequent developmental stages until, at the end of yolk resorption, the content is 30-40%
below the initial value. It should be noted that, unlike TN and TC, yolk
lipids are still consumed by the non-feeding young larva for a few days
(Fig. 13).
Di Lernia (1958), working in our laboratory, used an entirely different
and much more sensitive technique. He noted that decrease in lipids
stainable with Sudan Black B begins much earlier, and has already begun
at the gastrula stage. During metamorphosis, there is a marked decrease
in total lipids from the second to the fifth stage; the final values are
approximately 50% below those found at the beginning of metamorphosis (Fig. 15).
Our data on the consumption of proteins, lipids and carbohydrates
agree with those contained in the literature: protein breakdown is very
low in comparison with that of lipids and carbohydrates in the development of amphibian embryos. It appears that there is no strict sequence
in the utilization of these sources of energy (Lovtrup, 1953a, b ; Needham, 1931). They are actually oxidized simultaneously, although in
varying proportions. The only question which remains to be solved is
whether lipid breakdown to supply energy starts before the onset of
gastrulation.
During metamorphosis, these three classes of compounds decrease
fairly steadily but again no definite sequence of utilization can be
established. In this stage of the biological cycle, the animal is supplied
with the necessary energy by combustion of carbohydrates and lipids;
protein utilization is comparatively less, but is greater during metamorphosis than it is during embryogenesis.
III. Biochemical Considerations on the Development
of Some Invertebrates
As mentioned in the Introduction, the biochemical analysis of the
different developmental stages proves especially valuable when it is
extended, on a comparative basis, to species more or less closely related.
It is interesting to compare the results obtained during embryonic
development and metamorphosis of amphibians with those of other
species.
The eggs of Artemia salina Leach and Bornbyx mori L. develop in
cleidoic conditions; the embryo of the former species develops in sea
individual batchs of eggs. No appreciable decreases in lipids occur up to
the tail bud stage in both Bufo vulgaris and Rana esculenta.
From this stage on, it is possible to detect a slight decrease in the total
lipid content, indicating that lipids are being used as a source of energy.
Increased lipid utilization is noted throughout the subsequent developmental stages until, at the end of yolk resorption, the content is 30-40%
below the initial value. It should be noted that, unlike TN and TC, yolk
lipids are still consumed by the non-feeding young larva for a few days
(Fig. 13).
Di Lernia (1958), working in our laboratory, used an entirely different
and much more sensitive technique. He noted that decrease in lipids
stainable with Sudan Black B begins much earlier, and has already begun
at the gastrula stage. During metamorphosis, there is a marked decrease
in total lipids from the second to the fifth stage; the final values are
approximately 50% below those found at the beginning of metamorphosis (Fig. 15).
Our data on the consumption of proteins, lipids and carbohydrates
agree with those contained in the literature: protein breakdown is very
low in comparison with that of lipids and carbohydrates in the development of amphibian embryos. It appears that there is no strict sequence
in the utilization of these sources of energy (Lovtrup, 1953a, b ; Needham, 1931). They are actually oxidized simultaneously, although in
varying proportions. The only question which remains to be solved is
whether lipid breakdown to supply energy starts before the onset of
gastrulation.
During metamorphosis, these three classes of compounds decrease
fairly steadily but again no definite sequence of utilization can be
established. In this stage of the biological cycle, the animal is supplied
with the necessary energy by combustion of carbohydrates and lipids;
protein utilization is comparatively less, but is greater during metamorphosis than it is during embryogenesis.
III. Biochemical Considerations on the Development
of Some Invertebrates
As mentioned in the Introduction, the biochemical analysis of the
different developmental stages proves especially valuable when it is
extended, on a comparative basis, to species more or less closely related.
It is interesting to compare the results obtained during embryonic
development and metamorphosis of amphibians with those of other
species.
The eggs of Artemia salina Leach and Bornbyx mori L. develop in
cleidoic conditions; the embryo of the former species develops in sea