THE GEOGRAPHICAL VARIATION OF EARLY EMBRYONIC 

 PROCESSES IN MARINE EGGS 



By Alexander W'olsky * 



UNESCO Science Cooperation Office for South East Asia 



Djakarta, Indonesia 



A. Introduction 



In a recent paper I have pointed out that the eggs of the marine 

 Polychaete Hydroides norvegica have probably different cleavage pat- 

 terns in the North Sea and in the Mediterranean (Wolsky 1952). 

 Whereas in Kristineberg (near Fiskebackskil), on the west coast of 

 Sweden, the early cleavage was found to be spiral and equal, an earlier 

 observer, working at Cette (Sete) on the Mediterranean coast of France, 

 found it orthoradial and unequal (Soulier 1898, 1902). It was suggested 

 that this difference may be due to a differentiation of physiological 

 races within the species, which occupy different regions and differ from 

 each other in an early embryonic character of their eggs. A further 

 study of the literature has revealed that the occurrence of such egg 

 races, differing from each other in some physiological properties and 

 early developmental processes is a widespread phenomenon. Moreover, 

 these races seem to be well adapted to the environmental conditions of 

 the geographical area in which they occur. This not only corroborates 

 the view about the existence of two t^^ races in Hydroides norvegica, 

 but also provides a basis for a more profound explanation of the pheno- 

 menon and for some generalizations. In the following the relevant facts 

 will be reviewed first, followed by some theoretical considerations and 

 their application to the case of Hydroides. 



B. The Relevant Facts Concerning Physiological Egg Races 



(1) The factor which seems to have the most profound influence on 

 the physiological properties and early developmental processes of eggs 

 is temperature. This is obvious, considering the fundamental correlation 

 between temperature and the properties of living matter, especially the 

 velocity of biochemical reactions which make out the bulk of early em- 

 bryonic processes (cf. Belehradek 1935). In addition, in the case of 

 equatic eggs, salinity (osmotic pressure) of the medium is just as im- 

 portant as temperature, and the two factors act synergetically. Higher 



* Present address: Biological Laboratory, Fordham University, New York 58, U.S.A. 



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