CHARLES B. METZ 



31 



to elevate the fertilization membrane, a high incidence of polyspermy, ab- 

 normal cleavage and complete failure of eggs to respond to insemination. 



It is not yet clear in most cases whether these variations result from sub- 

 optimal activation initiating reactions or from defects in subsequent activation 

 phenomena. However, in certain cases the effects seem to be related rather 

 closely to the initial steps in the activation of the egg. Since these appear to 

 bear upon the nature of the activation initiating mechanism, they will be 

 considered in this section. The most interesting of the recent work concerns the 

 effect of metal binding agents in improving fertilization. A number of studies 

 have shown that proteins, amino acids, Versene and other agents with metal 

 binding or chelating action have a number of effects on echinoderm sperm. 

 These effects include an increase in motihty (57, 64, 69, 93, 118, 120, 131, 133) 

 with or without an appreciable increase in respiration, prolongation of the 

 life span of the sperm (93, 120, 133) and an increase in fertilizin binding capac- 

 ity (57)- Tyler and Rothschild (128) first suggested that certain of these effects 

 may result from a metal binding or chelating action of these agents. Substantial 

 evidence to support this view has been presented by Tyler (118) and Rothschild 

 and Tyler (93). 



One or more of these effects could readily account for the observed (57, 

 93, 120, 133) improvement in the fertilizing capacity of a treated sperm suspen- 

 sion when this is measured quantitatively in terms of the concentration of 

 sperm required to yield a given percentage of fertilized eggs. However, these 

 effects do not so readily account for a qualitative improvement in fertilization 

 in terms of the degree of elevation of the fertilization membrane, etc. Never- 

 theless, such qualitative improvement has been reported by several investiga- 

 tors. 



Runnstrom and his associates have described a number of deviations from 

 the normal fertilization reaction in several sea urchin species (11, 34, 97, 99). 

 These deviations are attributed to variations in the degree of 'cytoplasmic 

 maturity' of eggs that have completed nuclear maturation. 'Underripe' eggs fail 

 to respond to insemination by any manifestation of fertilization, or give low 

 percentages of fertilization and produce poor fertilization membranes (blister- 

 like membranes, tight membranes, incomplete incorporation of cortical granules 

 into the fertilization membrane). Upon attaining cytoplasmic maturity the 

 eggs give the optimal fertilization reaction. 'Overripe' eggs respond to insemi- 

 nation by imperfect or complete failure of membrane formation and abnormal 

 cleavage or complete refractoriness to the inseminating sperm. This cycle of 

 events is reported to be seasonal among individuals of a population (97). Early 

 in the breeding season the sea urchins yield underripe eggs, later ripe eggs 

 appear and finally toward the end of the breeding season the individuals pro- 

 duce overripe eggs. In some cases, at least, underripe sea urchin eggs pass 

 through the ripening cycle on standing in sea water (34, 96). 



