THE PROBLEM 33 



as was first shown by the writer and later confirmed by 

 Jennings. After pairing has occurred an interchange of 

 nuclear substance occurs by a mechanism described and 

 figured in many elementary textbooks of zoology. This 

 process of conjugation, need not further concern us here, 

 for the reason that Woodruff, in the work already referred 

 to, has shown that this phenomenon is not essential to 

 the continued life of the race. Its place may be, and 

 normally very frequently is, taken by the process called 

 endomixis. In this process there occurs a nuclear break- 

 down and reorganization which appears to be the equiva- 

 lent, functionally at least, of that which takes place 

 during conjugation. 



There has been much discussion, particularly among 

 European workers, as for example Dofiein, Jollos, Wede- 

 kind, Slotopowski, and others, about certain philosophi- 

 cal, not to say metaphysical, aspects of immortality in 

 the Protozoa. But all such discussion has in no wise dis- 

 turbed or altered the plain physical fact that there is no 

 place for death in a scheme of reproduction by simple 

 fission, such as is illustrated in Figure 4. Nothing is left 

 at any stage to fulfill the proverbial scheme of "dust to 

 dust and ashes to ashes. ' ' When an individual is through 

 its single individual existence it simply becomes two indi- 

 viduals, which go on playing the fascinating game of 

 living here and now. 



In a few of the simplest and most lowly organized 

 groups of many-celled animals or Metazoa this power of 

 multiplication by simple fission, or budding off a portion 

 of the body which reproduces the whole, is retained as 

 a facultative asset. This process of reproduction in which 

 the somatic or body cells of one generation produce the 

 somatic cells of the next generation has been called 

 agamic reproduction. It occurs as the more usual but not 

 3 



