10 GENETICS 



even as man is frequently made good, if it is not too 

 extensive and does not involve too highly specialized 

 tissues, as, for example, in the case of a skin wound. 



When the intake of non-living material is in excess 

 of the outgo, growth results, with the consequence 

 that more living substance is built up than existed 

 before. Thus a fragment of a living sponge or a 

 piece of a begonia leaf is each sufficient to restore a 

 duplicate of the original organism. 



A process similar to the repair of the begonia leaf 

 is that employed so effectively in the great groups of 

 the one-celled animals and plants, the Protozoa and 

 Protophyta, by means of which their numbers are 

 maintained. These one-celled organisms usually multi- 

 ply by fission, that is, by division into halves, and 

 each half grows to the size of the parent organism 

 from which it sprang. When two daughter protozoans 

 are thus formed, they are essentially orphans because 

 they have no parents, alive or dead. The parental 

 substance in such a process, along with the regulating 

 power necessary to reorganization, goes over bodily 

 into the next generation in the formation of the 

 daughter-cells, leaving usually no remains whatever 

 behind. In primitive forms of this description, con- 

 tinuous life is the natural order, and death, when it 

 does occur, is, as Weismann has pointed out, acci- 

 dental and quite outside the plan of nature. 



In these cases, it is easy to see the reason for "or- 

 ganic resemblance" between successive generations. 

 Parent and offspring are successive manifestations 

 of the same thmg, just as the begonia plant, restored 



