REJUVENESCENCE IN EMBRYO AND LAR\A 427 



than of kind, and that there is much more (Hffercnce in this respect 

 between different forms of agamic reproduction than between 

 agamic reproduction from single cells and small cell masses and 

 gametic reproduction. From the physiological point of view the 

 reproductive process is fundamentally the same wherever it occurs 

 in nature : it is in all cases the reconstitution of a new organism from 

 a part of one previously existing, but the starting-point of the new 

 individual and consequently the degree of reconstitution and the 

 result differ in different forms and with different conditions. 



CONCLUSION 



It is only necessary to point out the close agreement between 

 all the different lines of evidence in indicating that the early stages 

 of development from the egg in both animals and plants constitute 

 a period of rejuvenescence in every sense. Minot ('08) has already 

 advanced this view on the basis of the changes in the nucleoplasmic 

 relation, but has failed to present any of the physiological evidence 

 in support of it. The nucleoplasmic relation is a rather unsafe 

 criterion of physiological age, but it is interesting to see that in the 

 present case it leads to the same conclusion as the physiological 

 evidence. 



From this point of view gametic reproduction differs from 

 agamic only in the greater degree of specialization of the reproduc- 

 tive cells and the special conditions necessary to initiate the pro- 

 cess of dedifferentiation and rejuvenescence. The same periodic 

 changes, the same Ufe cycle and age cycle, occur in both. We 

 can dispense entirely with that remarkable conception, the germ 

 plasm of the Weismannian theory, and say that germ plasm is 

 any protoplasm capable under the proper conditions of undergoing 

 dedifferentiation and reconstitution into a new individual of the 

 species. Reproduction, whether it is the process of reconstitution 

 in a piece experimentally isolated from an animal or plant body, 

 or the process of development from the fertilized egg, is funda- 

 mentally the same physiological process and involves both regressive 

 and progressive changes, both rejuvenescence and senescence. 



A recent attempt by Godlewski ('10) to compare the process of 

 regeneration with gametic reproduction requires mention here. 



