122 MARINE BIOLOGICAL LABORATORY. 



comes impossible, and death follows. Thus it would 

 appear that the life of these animals is cyclic. During 

 the period of reproduction, which is the adult life of 

 the animal, a sort of physiological decUne takes place, 

 and this decline can be repaired only by conjugation. 



Now if during these experiments the animals have 

 not been injured or poisoned, it would seem that Maupas 

 had proved that death may occur normally among uni- 

 cellular forms. 



Weismann, however, is not ready to admit this. He 

 claims that conjugation is a necessary condition of the 

 animal's life, just as fertilization is a necessary con- 

 dition for the survival of an ovum, and if conjugation 

 is denied, the death in consequence is accidental and 

 not natural ; further, that the fact that conjugation^ 

 is necessary does not imply that the protoplasm is 

 not potentiaPy immortal. He seems, however, to over- 

 look the fact that a certain physiological decline has 

 taken place, and that if there is any physiological 

 decline the cycle of life is incomplete ; therefore the 

 seeds of death must exist inherent in the life of the 

 animal. It is, then, for the present, impossible to 

 speak of the Infusoria as potentially immortal, and 

 to claim that that portion of the Metazoa which under- 

 goes physiological dechne has no equivalent in these 

 forms. Nevertheless, it is too soon to declare that 

 the idea that death is an adaptation is altogether 

 erroneous. 



In many well-known unicellular forms, neither a physio- 

 logical decline nor a process of rejuvenation has been 

 observed. The Bacteria, the Cyanophyceae, and Yeast 

 increase by budding, spore building, and fission, and 



