144 THE LAW OF BIRTHS AND DEATHS 



only for a short time ; they soon become over-mature. 

 (Hertwig, vol. vi. p. 32). Their normal functions become 

 weakened, as is seen from the fact that, although they 

 can still undergo fertilisation for a time, yet this occurs 

 in an abnormal fashion ; several spermatozoa make 

 their way into the egg, the result being an abnormal 

 process of development. Without doubt, this phenomenon 

 is analogous to the senile degeneration of Ciliata which 

 have been prevented from pairing at a suitable period." l 

 We see again that there is an optimum point for fertilisa- 

 tion, but there seems no reason to suppose that there is 

 any analogy between the effects of over-maturity and 

 the effects of fatigue or lack of nourishment. 



Other similar facts are reported by Hertwig. " The 

 receptive capacity of the large female gamete of the 

 species Cutleria, after it has come to rest, and has become 

 capable of functioning as an egg, lasts only for a compara- 

 tively short time. Falkenberg (vol. vii. p. 10) has per- 

 formed a large number of experiments which show that, 

 whilst on the third day after they have come to rest 

 almost all the eggs are capable of becoming fertilised, on 

 the fourth day only half are in that condition. Further, 

 after this period all the eggs lose their receptive capacity, 

 and although spermatozoids are placed in their neighbour- 

 hood, commence to die off, exhibiting the same changes as 

 those eggs which where completely shut off from the fertilis- 

 ing cells." 2 This is probably what happens in the case of 

 the higher forms of life when the eggs become over-mature. 



Although the evidence showing the operation of the 

 principle among these lowest forms of lives is relatively 

 small in quantity, yet it tells in favour of the hypothesis 

 with remarkable force. The facts are just what might 

 be anticipated, and are precisely parallel with what 

 occurs among the higher forms of life. Highly favourable 



* The Cell, Dr. O. Hertwig. 8 Ibid. 



