II OBSERVATIONS OF PROTOZOA 727 



serological findings indicate synthesis of antigenic material prior to gastrulation. 

 Although it is clear fi^om both amphibian and chick studies that some adult 

 proteins are included in the yolk complement of the egg, it is equally clear that 

 not all adult proteins are represented at least in detectable quantities. This 

 implies synthesis of new proteins by the embryo. This process begins early and 

 may be correlated with the realization of developmental potential of the early 

 blastomeres. However, Berg (1954) seeking a differential peptidase activity in the 

 early blastomeres of Mytilus edulis was unable to find a significant difference. 

 The pursuit of analyses of other details in individual blastomeres of this or other 

 mosaic eggs would, none the less, appear to hold significant possibilities. 



Although the direct application of studies of growth and mitosis of protozoa 

 to the cleavage process has obvious shortcomings, the leads uncovered by such 

 analyses have considerable merit. The mechanics of cell growth in metazoan 

 tissues are by no means understood ; it is reasonable, in the face of inadequate 

 knowledge, to test the critical aspects of the protozoan studies for applicability 

 to the problems of cellular growth and cessation of growth in higher animals 

 as well. 



(rf) Gastrulation 



The period of gastrulation has been recognized as a complex, and therefore, 

 exciting one. The relation of the gastrulation process to inductive capacities has 

 claimed the attention of embryologists since Spemann's definition of the role of 

 the amphibian dorsal lip as "the organizer" (see Chapter 2). The findings of 

 Brachet (1941, 1942) of accumulation of nucleic acid in regions of active differen- 

 tiation and the relation of this accumulation to protein synthesis (Brachet, 1947; 

 Caspersson, 1947; Hultin, 1950a) have provided a measure of integration of 

 apparently diverse findings. Clayton (1953) found for the newt, Triturus alpestris, 

 specific antigens in the gastrular ectoderm and archenteron roof Brachet (1939), 

 however, finds gastrulation "not especially interesting in light of excreted ni- 

 trogen". Brachet (1950) and Boell (1948) provide excellent reviews of respiratory 

 details of the amphibian gastrula. Although much attention has been given to 

 various phases of metabolism, to details of the composition of the organizer and 

 to the process of induction, the relevance of protein to the process has been 

 virtually neglected, except for the possible involvement of nucleoprotein by 

 Brachet and his co-workers; even here the implication of the findings is that the 

 protein moiety is relatively unimportant. 



[e] Organogenesis 



We seek to cover by the term organogenesis the postgastrular phenomena 

 which eventually produce the complete, integrated organism. The processes 

 involved are induction of tissues, differential growth, migration of cells and 

 tissues, and the multitude of changes which may be included under the heading 

 chemodifferentiation, many of which are touched upon by Weiss (1953a). The 

 latter's remarks transcend the significance of intracellular differentiation, for 

 intracellular processes in sum constitute histogenetic changes. 



From the point of view of energy requirements and building requirements the 



Literature p. 744 



