312 EARLY DETERMINATION IN DEVELOPMENT 



Above-Mentioned Conclusions and Data 

 from Experimental Embryology 



The action of animalizing substances is shown as a demolition 

 of preexisting proteic structures and the action of vegetalizing 

 substances as a resistance to demolition. Does this agree with the 

 findings of experimental embryology? 



All the authors who, in their studies on vertebrates, speak of 

 developmental inhibition induced by LiCl have encountered the 

 resistance to demolition of proteic ultrastructmes at a microscopic 

 level. The delay in synthesis due to Li+ is in agreement with the 

 smaller increase of many enzymes in the LiCl-treated embryos 

 studied by the Stockholm group (Gustafson, 1954), by Lallier 

 (1955) and by others. 



On the other hand, the animalization seems in fact to corre- 

 spond to a demolition of preexisting proteic structures. Proteo- 

 lytic enzymes ( chymotrypsin, ficin, trypsin) are animalizing 

 agents (Horstadius, 1949, 1953; Moore, 1952). The observation 

 made by Lindahl et al. (1951) in this field is highly significant: 

 that from a population of more easily animalizable eggs it is 

 possible to extract in 0.6M KI a greater amount of N; that is, 

 they contain a lower ratio of insoluble N. 



Animalization at times may be induced under the same condi- 

 tions of protein denaturation. Horstadius (1949) found that 

 animalization occurs more easily at a low temperature, Jacobsen 

 et al. ( 1948 ) found that denaturation, induced by urea, is easier 

 to obtain at lower temperatures. Animalization induced by Na- 

 SCN occurs more easily in calcium-free sea water; Ca++ prevents 

 many proteins from undergoing denaturation ( Gorini, 1950 ) . 



From a comparative viewpoint, the regions overdeveloped by 

 the action of animalizing agents and inhibited by vegetalizing 

 agents show a higher oxydoreduction potential. [See the research 

 by Child ( 1936a,b, 1943), by Ranzi (1939), and by Horstadius 

 ( 1955) ]. I think that this may be interpreted as an indication of a 

 much more active protein breakdown. It is possible to follow the 

 formation of the ciliar tuft and of the mitochondria in the cells 

 of the animal pole of the sea urchin embryo (Gustafson, 1954; 



