AMPHIBIAN AND INVERTEBRATE DEVELOPMENT 85
(Ranzi, 1941). Furthermore, substances secreted by the adhesive organs
are lost in the water but this entails a negligible loss in weight. A small
amount of nitrogenous matter flows out in the form of hatching enzymes
which hydrolyse the jelly coat of the embryo. In this connection, we
must recall the studies on fish hatching by S. Smith (1957), whose observations are of great general interest.
According to Faure-Fremiet (1925), the dry weight of the embryo of
Rana temporaria decreases by 17% from fertilization to hatching. Needham (1927) reported a 29-1% decrease for the same species after development for ten days at 16° C.
Our data on total nitrogen (TN), total carbohydrates (TC) and total
lipids (TL) of the young larva of Bufo vulgaris, show that the initial
values decrease by as little as 16-18%, carbohydrates and lipids are
the major sources of energy; very little yolk protein is utilized and ultimately it is converted into cell protein (Urbani, 1957).
Let us now examine in greater detail the results of our studies on
the utilization of these three classes of compounds during embryonic
development.
1. Total Nitrogen
Published data on changes in the contents of carbohydrates, proteins
and lipids in amphibian development cannot be interpreted easily, for
several authors have selected as their reference point the 'hatching'
(eclosion, Schlüpfen) of the embryo. Amphibian jelly has a complex
chemical composition, in which carbohydrates, as shown by Minganti
(1954, 1955) vary both quantitatively and qualitatively.
We know nothing of the functional role of this jelly which was studied
exhaustively from the biochemical viewpoint in the echinoderms (Monroy, 1955; Vasseur, 1948). It is known that hatching in the amphibians
does not always occur at a given stage: hatching is the work of enzymes,
produced at a certain stage of embryonic development, which hydrolyse
the jelly. Several factors may retard or accelerate hatching. For this
reason, the definition of the embryonic cycle as the period from fertilization to hatching is not exact, and does not correspond to definite morphological and biochemical characteristics. Therefore in our research, as
in the work of Cotronei, we have considered the embryonic stage as that
period between fertilization and complete yolk resorption; in other
words, the larval stage begins when the animal starts feeding and no
longer behaves like a 'closed box'. Bialaszewicz and Mincovna (1921)
observed that in Rana temporaria and Rana fusca TN decreases by 9%
from fertilization to hatching; Faure-Fremiet (1925) calculated a 12%
decrease in TN during this period. Their results are open to question, for
this loss, expressed on the basis of protein content, is approximately equal
to the loss in dry weight, that is the loss to be expected if only proteins,
D
A.M. 2
(Ranzi, 1941). Furthermore, substances secreted by the adhesive organs
are lost in the water but this entails a negligible loss in weight. A small
amount of nitrogenous matter flows out in the form of hatching enzymes
which hydrolyse the jelly coat of the embryo. In this connection, we
must recall the studies on fish hatching by S. Smith (1957), whose observations are of great general interest.
According to Faure-Fremiet (1925), the dry weight of the embryo of
Rana temporaria decreases by 17% from fertilization to hatching. Needham (1927) reported a 29-1% decrease for the same species after development for ten days at 16° C.
Our data on total nitrogen (TN), total carbohydrates (TC) and total
lipids (TL) of the young larva of Bufo vulgaris, show that the initial
values decrease by as little as 16-18%, carbohydrates and lipids are
the major sources of energy; very little yolk protein is utilized and ultimately it is converted into cell protein (Urbani, 1957).
Let us now examine in greater detail the results of our studies on
the utilization of these three classes of compounds during embryonic
development.
1. Total Nitrogen
Published data on changes in the contents of carbohydrates, proteins
and lipids in amphibian development cannot be interpreted easily, for
several authors have selected as their reference point the 'hatching'
(eclosion, Schlüpfen) of the embryo. Amphibian jelly has a complex
chemical composition, in which carbohydrates, as shown by Minganti
(1954, 1955) vary both quantitatively and qualitatively.
We know nothing of the functional role of this jelly which was studied
exhaustively from the biochemical viewpoint in the echinoderms (Monroy, 1955; Vasseur, 1948). It is known that hatching in the amphibians
does not always occur at a given stage: hatching is the work of enzymes,
produced at a certain stage of embryonic development, which hydrolyse
the jelly. Several factors may retard or accelerate hatching. For this
reason, the definition of the embryonic cycle as the period from fertilization to hatching is not exact, and does not correspond to definite morphological and biochemical characteristics. Therefore in our research, as
in the work of Cotronei, we have considered the embryonic stage as that
period between fertilization and complete yolk resorption; in other
words, the larval stage begins when the animal starts feeding and no
longer behaves like a 'closed box'. Bialaszewicz and Mincovna (1921)
observed that in Rana temporaria and Rana fusca TN decreases by 9%
from fertilization to hatching; Faure-Fremiet (1925) calculated a 12%
decrease in TN during this period. Their results are open to question, for
this loss, expressed on the basis of protein content, is approximately equal
to the loss in dry weight, that is the loss to be expected if only proteins,
D
A.M. 2