124 MARINE BIOLOGICAL LABORATORY. 



juvenescence by conjugation. In other words, those 

 to which it was an advantage to retain their immortality 

 have retained it, and those which varied in such a 

 manner that immortahty could be advantageously re- 

 placed by rejuvenescence have, by the action of natural 

 selection, undergone this modification. If this is so, 

 Weismann's error is not in claiming that death was 

 an adaptation, but in asserting that all unicellular forms 

 are immortal. 



Still another and earlier opponent of Weismann has 

 urged serious objections to this theory of the origin of 

 death. Professor Charles S. Minot was the first to 

 maintain — and many have taken up his suggestion — 

 that Weismann is fundamentally wrong in comparing 

 the life-history of a Metazoon, which is a complex colony 

 of cells, with that of a Protozoon, which is a single cell. 

 Minot urges that an individual Metazoon is comparable 

 to a colony of Protozoa, not to a single cell. If this 

 be so, then the death of a Metazoon (a colony of cells) 

 has its only homologue in the degeneration and death 

 of a culture of Protozoa. The Metazoon colony is the 

 product of a single germ-cell, as is also the whole 

 culture of Infusoria. 



This comparison seems safe between the Metazoa and 

 those forms of Protozoa which conjugate, and in which 

 senile deo:eneration occurs. But how is it when we 

 bring those which do not conjugate under consideration.'' 

 If this view be correct, then a single Metazoon is equiva- 

 lent to all of a species of Bacterium which may arise 

 through generations of fission. As far as our knowl- 

 ed"-e sfoes, these Bacteria are immortal and their num- 

 bers almost infinite. We know, on the other hand, that 



