CHAPTER VII 



SEXUAL REPRODUCTION AND 

 REJUVENESCENCE 



t. The Origin of Sexual Reproduction 



The primary organisms in their extremely primitive stages were 

 presumably able to come into contact with other individuals by virtue 

 of the motion of the water in which they were generated. If two 

 different individuals shared some structures in common they would 

 combine with each other and the one having the stronger structure 

 would overcome and assimilize the other. Such a combination might 

 be a struggle for survival, but on the other hand the stronger 

 individual might be able to establish rejuvenescence by this combi- 

 nation. 



When the organisms were evolved to such a degree that some 

 elementary bodies in them were provided with nucleic acid in rich 

 amount and that the structure of such bodies was endowed with a 

 strong reversibility, these bodies would be able to recover their ori- 

 ginal structure when they were liberated from the organisms which 

 had been assimilized or devoured by some stronger individuals. Ac- 

 cordingly, such bodies, if liberated from the defeated, weaker indivi- 

 duals, would be able to assimilize the structure of still weaker 

 individuals if they could enter the latter. The combination of two 

 individuals at such a stage, therefore, may be regarded as a very 

 primitive type of sexual conjugation. It may be said that the primary 

 organisms at this stage had only a pair of genes, and the combination 

 may be comparable to a phenomenon in which weaker bacteria are 

 changed into stronger ones when these two strains are incubated 

 together. 



Thus a strain of bacteria producing phage, /. e., a lysogenic strain 

 can change another strain, which is susceptible to the phage, into 

 the lysogenic strain if these two strains are brought into contact, as 

 was discussed already. Again, R-type of pneumococcus is changed to 

 S-type when comes into contact with S-type. In these instances, 

 nucleic acid-rich particles freed from the stronger strain can substitute 

 the bacterial cell. These particles may be called free genes or viruses, 



