Gametogenesis, Fertilization and Parthenogenesis 



193 



ous invasive bacteria has served to emphasize 

 the relation of the processes of fertilization 

 to those of infection. 



Another type of lytic agent has been ob- 

 tained by Rvmnstrom et al. ('42-'46) in 

 methanol extracts of sea urchin sperm. This 

 agent has a liquefying action on the vitel- 

 line membrane of the unfertilized egg, an 

 effect which can be duplicated by certain 

 detergents. Present evidence (Runnstrom, 

 '49) indicates that it is an unsaturated, 

 eighteen-carbon, fatty acid. 



motility) is also impaired when they are 

 treated with specific antisera that are pre- 

 pared by injection of rabbits with antifertil- 

 izin and that have been rendered non- 

 agglutinating (univalent) so as to avoid the 

 complications that would be introduced by 

 aggkitination (Tyler, '46a). 



Studies of the specificity of the reaction 

 have provided some further information 

 concerning the role of these substances. 

 Lillie's ('19) demonstration that fertilizin 

 was not obtained from other tissues than the 



Table 13. Comparison of Cross-fertilization with Cross-agglutination among Echinoids {from 



Tyler, '49)* 



EGGS OR 

 FERTILIZIN OF 



S. purp. 



SPERMATOZOA OF 



S. fran. 



L. pictus 



D. excent. 



* The upper figures of each pair of rows represent the number of times the sperm suspension is diluted in 

 giving the end point value (2 per cent) of fertilization under certain standard conditions. The lower figures 

 are the agglutination titers in terms of the highest dilution of fertilizin solution that gives visible agglutination. 



Role in Fertilization. Various experiments 

 have been performed to attempt to elucidate 

 the function of fertilizin and antifertilizin 

 in fertilization (see Tyler, '48a; Runnstrom, 

 '49). When sea urchin eggs are deprived of 



X their gelatinous coat they are still fertilizable, 

 but require a higher concentration of sperm 

 to effect fertilization. Whether or not, in 

 addition to facilitating fertilization, the 

 presence of fertilizin is essential for the 

 process cannot, as yet, be readily decided 



7 since upon removal of the gelatinous coat 

 the surface of the egg still evidently possesses 

 a thin layer of fertilizin that cannot be re- 

 moved without damage to the egg. The 

 presence of excess fertilizin in solution 

 around the eggs tends to inhibit rather than 

 promote fertilization. The sperm that have 

 reacted with fertilizin at some distance from 

 the egg are apparently incapable of adhering 

 to the egg, presumably because their com- 

 bining sites are already occupied by fertilizin. 

 When sperm are partially depleted of anti- 

 fertilizin by treatment that does not markedly 

 impair their respiratory activity there is 

 considerable lowering of their fertilizing 

 capacity (Tyler and O'Melveny, '41). The 

 fertilizing capacity of sperm (but not their 



eggs has been amply confirmed and impli- 

 cates this agent as furnishing the basis for 

 the tissue-specificity of fertilization. That 

 the action of fertilizin is predominantly 

 species-specific has also been demonstrated 

 by many workers (see Lillie, '19; Just, '30; 

 Elster, '35; Tyler, '48a, 49), and in several 

 investigations comparison has been made 

 between the degree of cross-agglutination 

 and that of cross-fertilization of various 

 species of animals. The data of Table 13 il- 

 lustrate some of the results that have been 

 obtained in experiments of this type per- 

 formed with four different species of echi- 

 noids. Other species of animals among the 

 asteroids, annelids, and mollusks (not in- 

 cluded in the table) that do not cross- 

 agglutinate with the echinoids, do not give 

 cross-fertilization. 



In general the results show that the degree 

 of cross-agglutination is greater than that of 

 cross-fertilization among the various species. 

 On the other hand, in combinations where 

 cross-reaction of fertilizin and sperm is lack- 

 ing fertilization does not generally occur. 

 There are apparent exceptions to this, such 

 as may be noted in Table 13, where S. 

 franciscanus fertilizin fails to agglutinate 



