PARTHENOGENESIS 189 



that until we reach the Vertebrata, and even in some of them, 

 the male is nearly always smaller and feebler than the female. 

 In many cases, as in the honey-bee, the male dies the moment 

 after pairing. Having once paired, his functions are at an 

 end, whilst the female has to carry on the race. In some cases, 

 such as in that curious marine worm, Bonellia, the male is 

 reduced to a mere parasite in the body of the female. I used 

 to try to conceal these facts in the time of the suffragette 

 agitation, but sooner or later they were bound to come out. 



The alternation of parthenogenetic eggs with fertilized 

 eggs is another example of the alternation of two different 

 generations; but it is not quite on a level with the cases 

 mentioned above: for here the asexual generation is in reality 

 an unfertilized egg, whereas in the case of the lower animals, 

 such as the Hydrozoa or the flukes, the alternation is 

 between a vegetatively produced sexual generation and a 

 sexually produced vegetative generation. In some cases 

 we have seen that in both kinds of alternation of generation 

 the stages may not be strictly alternate. If S represents the 

 sexual generation and A the asexual, you may have many ^'s 

 before the sexual turns up again, such as S- A A AS- A A AS . 



Parthenogenesis can be induced by artificial means in eggs 

 which are normally sexual. Certain changes in the food or 

 environment or certain stimuli will induce or quicken repro- 

 duction. The members of a pure culture of Paramoecium 

 descended from a single parent may live in many hundreds 

 of generations. A long period of reproduction by simple 

 fission is followed by a period when conjugation is common. 

 This starts a new cycle and is physiologically comparable to 

 the period of fertilization in the higher animals. If such 

 conjugation be prevented the individuals suffer senile decay 

 and die. But artificial stimuli can tide over this period of 

 growing old and of decay. In a certain culture which lasted 

 nearly two years the Paramoecia periodically began to fail 

 every six months, and they would have disappeared entirely 

 had it not been for the application of such stimulants as 

 beef-tea, alcohol, extracts from the brain and pancreas or 

 even a shower of rain. A change of food or environment 

 produced a rejuvenescence, just as conjugation does. 



