ORIGIN OF THE INDIVIDUAL 247 



thousand generations, without conjugation and without any 

 signs of degeneration. In other words fertilization is not a 

 necessary antidote for inherent senescence, and this, taken 

 in connection with other data which point in the same direc- 

 tion, such as the fact that in many plants sexual propagation 

 is seldom if ever resorted to, renders it fairly safe to make the 

 general statement that the need of fertilization is not a pri- 

 mary attribute of living matter. Now, reproduction is such 

 an attribute and therefore the evidence at hand indicates 

 that reproduction and fertilization are intrinsically separate 

 processes which, however, have become closely associated, 

 especially in higher forms. 



So far our conclusion is entirely negative fertilization 

 is not reproduction and is not intrinsically necessary for re- 

 production. What then is its significance? Though ferti- 

 lization may not be necessary in the life of simple organisms 

 under favorable conditions, this does not indicate that it 

 may not be a stimulus to protoplasmic activity when it does 

 occur perhaps a very important factor under special en- 

 vironmental conditions. Indeed there is no doubt that con- 

 jugation in certain cases directly results in stimulating all the 

 vital processes of the cell, including reproduction. But it 

 would seem that the essential factor in this stimulation is 

 not the essence of fertilization synkaryon formation. In 

 Paramecium, for example, an internal nuclear reorganization 

 process known as ENDOMIXIS occurs periodically. Although 

 endomixis is carried on by each cell without the cooperation 

 of another cell, and therefore without synkaryon formation, 

 nevertheless it apparently effects a physiological stimulation 

 similar to that which follows synkaryon formation during 

 conjugation. This is the special aspect which the discussion 

 of the ' dynamic ' effect of fertilization in Protista has recently 

 assumed. (Fig. 131.) 



