132 PROBLEMS OF FERTILIZATION 



The females of many insects possess seminal receptacles 

 in which spermatozoa received from the male may be 

 stored up for long periods; in the case of ants and bees, 

 for instance, spermatozoa within the seminal receptacles 

 may retain their fertilizing power for years. 



The actual conditions of vitality and fertilizing 

 power can, however, best be studied in forms with 

 external insemination, especially marine forms. Sea 

 urchins furnish ideal material for such a study. In 

 this case it has been shown, especially by the studies of 

 E. J. Cohn (1918), that the vitality and fertilizing 

 power endure in inverse ratio to activity. Concen- 

 trated sperm suspensions retain their vitality longer 

 than more dilute suspensions because they rapidly pro- 

 duce a paralyzing concentration of CO 2 (see p. 101). 

 Similarly, any substance that will paralyze the spermat- 

 ozoa without killing them, such as dilute acids, KCN, 

 etc. , will prolong the period of fertilizing power. Cohn has 

 shown that Fuch's (1915) result on increase in duration 

 of fertilizing power of sperm suspensions in specific egg 

 water as compared with similar suspensions in sea- water 

 is due to the paralyzing effect of the water on the sperm. 



The question may now be raised whether the ferti- 

 lizing power of sperm suspensions is dependent exclu- 

 sively on motility, or whether the presence of a specific 

 substance borne by the sperm is not also necessary? 

 Such a substance must be borne superficially, for the 

 fertilization reaction begins immediately after attach- 

 ment of the spermatozoon to the egg. Loeb (1913, 

 p. 227) at one time postulated the idea that the sperm 

 bears a lysin-like substance producing superficial cy- 

 tolysis of the egg, which he regarded as the first step 



