E A R L Y D E V E L O P M E N T O F T H E S E A U R C H I N
111
FIG. 9. (b) Disintegration of the cells of the primary mesenchyme in a Paracentrotus
blastula which had been treated with ethionine for 3 hours beginning immediately after
fertilization and then returned to normal sea-water. (From Bosco and Monroy, 1960.)
those present in the unfertilized egg—have been detected until the
gastrula (Perlmann and Gustafson, 1948; Perlmann, 1953) or blastula
stage (Ranzi, 1957).
Finally, a point that should be remembered is that each cleavage
involves the formation of new cell surface. Whatever the mechanism of
its production, there is no doubt that this must involve some kind of
protein synthesis. Therefore a large part of the protein synthesis taking
place during cleavage may possibly be accounted for by the production
of new cell surfaces.
C . Protein Synthesis During the Initial Visible Differentiation Phase
As has already been mentioned, the whole period of the early blastula
is characterized by a plateau both in the curve of oxygen consumption