160 PROBLEMS OF FERTILIZATION 



either of the foregoing senses; but there is apparently 

 no slackening in rate of the processes, which merely 

 occur on a smaller scale or with less energy. Theoret- 

 ically such experiments should enable one to determine 

 how much of the spermatozoon is essential for complete 

 activation, but the practical difficulties have so far 

 prevented such a determination. 



The quantitative side of fertilization furnishes a 

 very interesting problem. It would seem that incom- 

 plete activation of the egg is not compensated in later 

 stages but sooner or later results in a complete arrest 

 of the vital machinery. 



It is possible that we should also include in the 

 conception of partial fertilization cases of fertilization 

 with stale or injured gametes; if either the egg or sper- 

 matozoon be involved development takes a slower 

 tempo and ceases sooner or later with development of 

 various abnormalities. Such conditions may obviously 

 grade all the way up to the normal (see Stockard, 

 Dungay, Hertwig). Such results should not, however, 

 be understood in a purely quantitative sense, but also 

 in the sense of a growing disharmony dependent on 

 variation in the degree of the effect upon different 

 portions of the egg. 



In the case of the artificial induction of partheno- 

 genesis the quantitative aspect of activation has been 

 very accurately measured by R. S. Lillie (1915) in the 

 case of the starfish egg. Under the influence of higher 

 temperatures (about 29-36 C.) or butyric acid (about 

 N/26o concentration) the activation process is started 

 in the egg. If the process is allowed to proceed to a 

 certain optimum stage and the eggs are then returned 



