120 



FERTILIZATION 



water or molar urea, pH 7, with or without removal of fertilization 

 membranes. Urea was found to be the more effective agent, and 

 some of Sugiyama's results are given in Table 19. If eggs are re- 



TABLE 19 

 Refertilization of sea-urchin eggs (Hemicentrotus pulcherrimus) 

 inseminated in normal sea water after washing in M-urea for 

 2 min. Membranes not removed before application of urea. 

 Polyspermic eggs in cofitrol inseminations, o. T° C, 11. 



fertilized before anaphase, polyspermic divisions take place at the 

 time of first cleavage ; but if they are refertilized after the full growth 

 of the amphiaster, first cleavage proceeds normally and poly- 

 spermy becomes evident at second cleavage. Eggs can even be 

 refertilized after second cleavage. These experiments are of such 

 interest that they deserve to be repeated, when some obscure points 

 in Sugiyama's work could be cleared up. For example, no in- 

 formation is given in Table 19, which is extracted from Sugi- 

 yama's paper (p. 341), about refertilization sperm densities; but 

 from other data in his paper, the final sperm dilutions must have 

 been i/ioo or i/iooo. If the semen of this Japanese sea-urchin is 

 similar to that of British varieties, these dilutions correspond to 

 sperm densities of 2 X 10^ and 2 X 10" per ml. The first of these 

 is a fairly thick soup, and one wonders what would have happened 

 if untreated fertilized eggs had been re-inseminated at this sperm 

 density (cf. Table 17). What, if any, is the effect of supernatants 

 from dense sperm suspensions on fertilized and treated eggs? 

 Doubts may be entertained whether Sugiyama or Rothschild & 

 Swann (1952), in their experiments involving insemination with 

 dense sperm suspensions, have paid sufficient attention to Samp- 

 son's work (1926a, b) on the effects of sperm extracts on fertiliza- 

 tion and development, though the point is discussed in Rothschild 

 and Swann's paper (p. 479). This question certainly requires 

 further investigation in the context of these recent experiments; 



