86
ENRICO URBANI
and no carbohydrates or lipids had been utilized: this view is not acceptable in the light of new experimental findings.
Görtner (1914), on the other hand, reported a negligible decrease in
TN during the first stage of development in the Urodele Cryptobranchus
allegheniensis; this was confirmed by Gregg and Ballentine (1946) for
Ranapipiens in the period from fertilization to hatching.
The problem was also studied by Wills (1936), whose investigations
covered the period from fertilization to the beginning of feeding (the
true embryonic stage). He found that the TN content decreased from
260 to 210-230 γ in Triturus torosus and from 290 to 260 y in Ambystoma
tigrinum, that is, a decrease of 14-4% in the first species, and of 10-4%
in the second. These results seem very reliable.
L.0vtrup (1953) reported a TN decrease in Ambystoma
mexicanum
from the tail bud stage to the feeding of the young larva.
Summing up these data, it can be concluded that the utilization of
proteins as energy sources in the first stages of development (up to the
tail bud stage) is very doubtful; on the other hand, it seems clear that
there is a decrease in total nitrogen from the tail bud stage to the end of
embryonic development.
However, Boell (1955) is not quite convinced by the experimental data
which would disprove initial protein combustion. He rightly notes that,
considering the high protein content of the egg, any decrease through
combustion would necessarily be very low. In his opinion, 'the question
of protein as an energy source is highly confused.'
In a previous paper on total nitrogen content during the embryonic
development of Bufo vulgar is, our results were essentially in agreement
with those of other authors, for our data indicated a 17% decrease in
total nitrogen from the tail bud stage onwards. However, some of the
published data left us somewhat perplexed. For instance, Brächet (1939),
Boell et al. (1939), and Gregg and Ornstein (1952) showed that urea
and ammonia are eliminated in small quantities during amphibian gastrulation: these compounds must undoubtedly result from protein
metabolism.
We decided therefore to look further into this question, and to detect
whatever TN decrease there was, if any, during the first stages. Two
different techniques were used.
Several analyses were made to determine TN in Bufo vulgaris from
fertilization to the end of yolk resorption, especially during the first
developmental stages. It was established that a small decrease in TN
did in fact occur even before the tail bud stage (Urbani, 1957) (Fig. 13).
The other technique consisted in determining the amounts of urea
and ammonia released into the water from eggs and embryos at different developmental stages (Urbani and De Cesaris Coromaldi, 1957).
ENRICO URBANI
and no carbohydrates or lipids had been utilized: this view is not acceptable in the light of new experimental findings.
Görtner (1914), on the other hand, reported a negligible decrease in
TN during the first stage of development in the Urodele Cryptobranchus
allegheniensis; this was confirmed by Gregg and Ballentine (1946) for
Ranapipiens in the period from fertilization to hatching.
The problem was also studied by Wills (1936), whose investigations
covered the period from fertilization to the beginning of feeding (the
true embryonic stage). He found that the TN content decreased from
260 to 210-230 γ in Triturus torosus and from 290 to 260 y in Ambystoma
tigrinum, that is, a decrease of 14-4% in the first species, and of 10-4%
in the second. These results seem very reliable.
L.0vtrup (1953) reported a TN decrease in Ambystoma
mexicanum
from the tail bud stage to the feeding of the young larva.
Summing up these data, it can be concluded that the utilization of
proteins as energy sources in the first stages of development (up to the
tail bud stage) is very doubtful; on the other hand, it seems clear that
there is a decrease in total nitrogen from the tail bud stage to the end of
embryonic development.
However, Boell (1955) is not quite convinced by the experimental data
which would disprove initial protein combustion. He rightly notes that,
considering the high protein content of the egg, any decrease through
combustion would necessarily be very low. In his opinion, 'the question
of protein as an energy source is highly confused.'
In a previous paper on total nitrogen content during the embryonic
development of Bufo vulgar is, our results were essentially in agreement
with those of other authors, for our data indicated a 17% decrease in
total nitrogen from the tail bud stage onwards. However, some of the
published data left us somewhat perplexed. For instance, Brächet (1939),
Boell et al. (1939), and Gregg and Ornstein (1952) showed that urea
and ammonia are eliminated in small quantities during amphibian gastrulation: these compounds must undoubtedly result from protein
metabolism.
We decided therefore to look further into this question, and to detect
whatever TN decrease there was, if any, during the first stages. Two
different techniques were used.
Several analyses were made to determine TN in Bufo vulgaris from
fertilization to the end of yolk resorption, especially during the first
developmental stages. It was established that a small decrease in TN
did in fact occur even before the tail bud stage (Urbani, 1957) (Fig. 13).
The other technique consisted in determining the amounts of urea
and ammonia released into the water from eggs and embryos at different developmental stages (Urbani and De Cesaris Coromaldi, 1957).