DEATH 



alternation of sexual and asexual modes 

 of reproduction. 



iv. The asexual mode of reproduction, by 

 fission, is the more primitive one. Con- 

 jugation, or sexual reproduction, gives an 

 advantage in the struggle for existence; 

 and at first a luxury, has through the 

 action of natural selection become a 

 necessity. 



v. The normal duration of life of a given 

 species is that which is most advantage- 

 ous to the species i.e. t an animal dies 

 when it has produced sufficient young to 

 ensure the perpetuation of the species 

 under existing conditions. 



vi. In Metazoa, as in Protozoa, there is direct 

 continuity of living matter by cell division 

 from generation to generation. 



vii. The statement that " no Protozoon has 

 ever lost an ancestor by death" may now 

 be extended thus : There is not a single 

 component cell in the body of a Metazoon 

 that has ever lost an ancestor by death. 

 For each component cell in the body of 

 a Metazoon is descended by direct fission 

 from the egg. The egg was a body cell 

 of the parent, and in its turn was derived 

 by cell division from the egg cell from 

 which the parent was developed ; and so 

 on, generation behind generation, there 

 has been unbroken continuity of living 

 matter. 



