II.
THE EMBRYOLOGY
OF ASCIDIANS
71
becomes more active as development progresses, (β) Starting at gastrulation, both CO in the light and DECA produce an increasing inhibition
of oxygen consumption. Because of the common property both agents
have of forming complexes with copper ions, the possibility arises of the
presence of a copper containing system active in the terminal respiration.
It is well known that the variations in the respiratory activity of the
egg during development can be considered (Gustafson, 1954) as dependent on variations in the quantity of the cytochrome oxidase. In the
Ascidians, Holter and Zeuthen (1944) have not been able to discover
any difference in the respiration of the anterior and of the posterior
blastomeres (4-cell stage), however, cytochemical (Ries, 1937; Reverberi
and Pitotti, 1939) and microchemical (Berg, 1956) determinations
indicate a higher content of cytochrome oxidase and (Berg, 1957)
succinic dehydrogenase in the posterior blastomeres.
B. Specific Inhibition of Enzymatic Activity
Every organism is the ultimate result of a long sequence of chemical
reactions, which start at fertilization. It can be assumed, at least in
the mosaic eggs, that the very first chemical reactions are diverse in
the different blastomeres. The diversity, of course, becomes gradually
greater, with the progress of development and finally, the morphological
structures appear. The morphological characters of these structures are
certainly dependent on the molecular aggregation of the last-produced
chemical substances, but unfortunately, we know nothing of this
embryonic physics and chemistry. With the latter the enzymes are
certainly concerned. There is no chemical reaction which is not initiated,
or promoted, by the enzymes. Thus, these agents are, in the end,
responsible for the morphological structures themselves, and blocking
of a specific enzymatic activity should result in a disturbance in a
morphological structure. However, this is a simplified way of considering
development, in fact, some enzymes can be 'called into action' only
after the structures have been completed and then they have nothing
to do but assure the function of these structures. Furthermore the
organism does not possess only one way of building its structures.
Finally, no specific agent is so 'specific' as to block solely one enzyme,
and no others; this difficulty can, however, be overcome by the use
of appropriate concentrations of the inhibitors. Indeed, research by
means of enzymatic inhibitors can lead to useful results in embryology.
We shall try now to collect together the results which have been
reached in the Ascidians in this manner.
THE EMBRYOLOGY
OF ASCIDIANS
71
becomes more active as development progresses, (β) Starting at gastrulation, both CO in the light and DECA produce an increasing inhibition
of oxygen consumption. Because of the common property both agents
have of forming complexes with copper ions, the possibility arises of the
presence of a copper containing system active in the terminal respiration.
It is well known that the variations in the respiratory activity of the
egg during development can be considered (Gustafson, 1954) as dependent on variations in the quantity of the cytochrome oxidase. In the
Ascidians, Holter and Zeuthen (1944) have not been able to discover
any difference in the respiration of the anterior and of the posterior
blastomeres (4-cell stage), however, cytochemical (Ries, 1937; Reverberi
and Pitotti, 1939) and microchemical (Berg, 1956) determinations
indicate a higher content of cytochrome oxidase and (Berg, 1957)
succinic dehydrogenase in the posterior blastomeres.
B. Specific Inhibition of Enzymatic Activity
Every organism is the ultimate result of a long sequence of chemical
reactions, which start at fertilization. It can be assumed, at least in
the mosaic eggs, that the very first chemical reactions are diverse in
the different blastomeres. The diversity, of course, becomes gradually
greater, with the progress of development and finally, the morphological
structures appear. The morphological characters of these structures are
certainly dependent on the molecular aggregation of the last-produced
chemical substances, but unfortunately, we know nothing of this
embryonic physics and chemistry. With the latter the enzymes are
certainly concerned. There is no chemical reaction which is not initiated,
or promoted, by the enzymes. Thus, these agents are, in the end,
responsible for the morphological structures themselves, and blocking
of a specific enzymatic activity should result in a disturbance in a
morphological structure. However, this is a simplified way of considering
development, in fact, some enzymes can be 'called into action' only
after the structures have been completed and then they have nothing
to do but assure the function of these structures. Furthermore the
organism does not possess only one way of building its structures.
Finally, no specific agent is so 'specific' as to block solely one enzyme,
and no others; this difficulty can, however, be overcome by the use
of appropriate concentrations of the inhibitors. Indeed, research by
means of enzymatic inhibitors can lead to useful results in embryology.
We shall try now to collect together the results which have been
reached in the Ascidians in this manner.