344 GENERAL PHYSIOLOGY 



tadpole's tail and the death of which no one will deny, are likewise 

 employed again as material for the construction of other organs. 

 But, if in the conjugation of the Infusoria there are realty dying 

 parts, really partial corpses, the fundamental contrast between 

 unicellular and multicellular organisms, maintained by Weismann, 

 disappears, and the whole difference consists simply in the quanti- 

 tative relation of the surviving and the dying substance ; in 

 multicellular organisms only the body-cells die, while the 

 reproductive cells continue to live. In general, it would be wholly 

 incorrect to say that in multicellular organisms an exceedingly 

 large mass, namely, the whole body, dies, and only tiny masses, 

 the ova or spermatozoa, remain living, while in Infusoria the 

 greater part remains living and the smaller part dies. There are 

 examples among animals where the relation does not differ at all 

 from that in Infusoria. A female frog, e.g., produces in the course 

 of her life a mass of eggs that in relation to her body is even con- 

 siderably greater than the mass of cell-substance that in the in- 

 fusorian body in conjugation remains living in contrast to that 

 which dies. If, therefore, the frog and, in general, the multicellular 

 organism are mortal, the unicellular Infusoria are mortal also ; in 

 both cases it is only a part of the living substance of the individual 

 that is transmitted to the descendants. 



Not only in the life of the Infusoria, but also in that of other 

 unicellular organisms there are periodically recurring events, in 

 which parts of their body perish. Many Protista reproduce by the 

 formation of spores. If this process be followed in a large radio- 

 larian, e.g., Thalassicolla, which has been studied in detail by 

 R. Hertwig and Brandt, it is found that the nucleus in the central 

 capsule breaks up into many small nuclei, which surround themselves 

 each with a protoplasmic mass, and develop into many small swarm- 

 spores ; the large, extracapsular, protoplasmic body and also a 

 part of the intracapsular protoplasm, which is not consumed in the 

 formation of spores, perish completely. Here, likewise and per- 

 haps still more evidently than in the Infusoria, there are really 

 partial corpses. We see, therefore, that with the great majority of 

 unicellular organisms, with all whose course of development has 

 thus far been studied in detail, Weismann's idea does not agree. 



^Finally, the possibility is not to be dismissed that there may be, 

 or may once have been in the course of the phylogeny of living 

 substance, Protista, whose cycle of development is so simple that 

 their living substance simply grows constantly without conjugation 

 and without spore-formation, and, when they have reached a certain 

 volume, divides without any remnant, and continues to grow and 

 divide as long as the external conditions allow. According to Weis- 

 mann's idea, such Protista would be really immortal beings. But at 

 this point the weakness of the doctrine of immortality appears per- 

 haps most distinctly. If Weismann's standpoint be accepted, that 



