SEPARATION OF GROWTH AND DIFFERENTIATION 



159 



OBSERVATIONS AND EXPERIMENTAL DATA: 



Record by a series of drawings and/or photographs, the changes that seem to occur 

 during each day following the embedding of the embryo in the agar. If free of bacteria 

 some of these embryos may survive for 10-12 days, particularly at temperatures 

 slightly below those of the laboratory. 



DISCUSSION: 



Whitaker and Berg (1944) first suggested this method of separating the processes of de- 

 termination, growth, and differentiation, using the Fucus egg. Recently (1945) Holtfreter 

 has made a similar study on the amphibia with very instructive results. He says: "Em- 

 bryonic development is brought about by the integrated cooperation of various chains of 

 biological processes, such as cell multiplication, morphogenetic movements, histological 

 differentiation, differential changes of size and form of the embryo, etc. , each of which 

 has been given ample attention in analytical research while information on the relation- 

 ship of these processes with each other is scarce and has been the by-product rather than 

 the aspired aim of experimental work. " He says, further, that "Instances have been re- 

 corded where cytological differentiation occurred without cleavage, growth without differ- 

 entiation, tissue formation without morphogenetic movements, metabolism without growth 

 or differentiation. " 



The agar medium provides an isotonic but restrictive environment where there may be 

 relatively free exchange of respiratory gases but which prevents expansive growth or the 

 acquisition of body cavities (neurocoel, archenteron, coelom). Such pressure as is ex- 

 erted is due to the forces of expansive growth of the embryo, for it is first exactly fitted 



Figs. 1-4. Embryos of Amblystoirta punctatum of equal age, which have been embedded for 10 days 

 in agar. According to whether they were included completely or partially, they exhibit 

 total or local growth inhibitions respectively. Cytological differentiation has not been 

 affected. Figure 4 shows the agar matrix still present. 



From Holtfreter, 1945: Anat. Rec. 93:59. 



