6 FERTILIZATION 



Schrumpfung (wrinkling), roughening, granulation, or simply 

 cortical change are nearer the facts. Moser (1939a) examined this 

 reaction in the eggs of Arbacia punctulata. He found that a layer of 

 cortical granules immediately below the plasma membrane, 

 diameter o-8/x, disappeared at fertilization, the disappearance start- 

 ing at the point of attachment of the fertilizing spermatozoon and 

 passing progressively over the egg surface, in about 10 seconds at 

 26° C. A breakdown of cortical granules in the eggs of Sahellaria 

 vulgaris Verrill, 5-10 minutes after fertilization, was described in 

 the same year by Novikoff (1939). Moser's studies were followed 

 up by Endo (1952), who observed that at fertilization, the cortical 

 granules, of which there are about o-Sjfjr in the eggs of Clypeaster 

 japoniciis Doderlein, doubled their diameters and then exploded. 

 Just before they disappear, sea-urchin egg cortical granules, which, 

 according to Monne & Harde (1951), contain polysaccharides 

 esterified with sulphuric acid residues, exhibit Brownian move- 

 ment, which suggests that at this time, the cortex becomes more 

 fluid (Allen, 1954). A similar phenomenon occurs when fish eggs 

 and those of the marine worm Nereis succinea (Leuckart) are 

 fertilized, though in these, alveoli in the cortex break down pro- 

 gressively after fertilization (Yamamoto, 1944; Kusa, 1953; 

 F. R. Lillie, 1919). In addition, Kusa (1954) has shown that the 

 cortical alveoli in the egg of the dog salmon, Oncorhyiichus keta 

 (Walbaum), contain mucopolysaccharides esterified with sulphuric 

 acid residues. As regards the cortical response to fertilization, 

 there is, therefore, a marked chemical and morphological re- 

 semblance between fish and echinoderm eggs. But, as we shall see 

 later, it would at present be dangerous to ascribe too important or 

 dominating a role to exploding cortical granules or discharging 

 cortical alveoli in fertilization. 



There has been some misunderstanding (Allen, 1954), perhaps 

 of a verbal nature, about the disappearance of the cortical granules 

 and the change in the light-scattering properties of the egg surface 

 at fertilization, when viewed with dark-ground illumination. There 

 is no doubt that the cortical granules disappear, but at the same 

 time, the cortex becomes more granular, or roughened. Rothschild 

 & Swann (1949) suggested that this granulation, which is associated 

 with an increase in light scattering, might be due to the formation 

 of microscopic or sub-microscopic particles at the egg surface. 

 The appearance of this granulation naturally does not imply that 



