THE WONDERS OF LIFE 



of development from the simplest repair of plasm in the 

 unicellular protists to the sexual generation of the 

 higher histona. The sperm-cells and ova of the latter 

 are redundant growth-products, which have the power 

 of regenerating the whole multicellular organism. But 

 many of the higher histona have also the capacity to 

 produce new individuals by regeneration from detached 

 pieces of tissue, or even single cells. In the peculiar 

 mode of metabolism and growth which accompanies 

 these processes of regeneration, the memory of the 

 plastidule, or the unconscious retentive power of the 

 biogens, plays the chief part (cf. my Perigenesis of the 

 Plastidule, 1875). In the most primitive kinds of the 

 unicellular protists we find the phenomena of death and 

 regeneration in the simplest form. When an unnu- 

 cleated moneron (a chromaceum or bacterium) divides 

 into two equal halves, the existence of the dividing 

 individual comes to an end. Each half regenerates 

 itself in the simplest conceivable way by assimilation 

 and growth, until it, in turn, reaches the size of the 

 parent organism. In the nucleated cells of most of the 

 protophyta and protozoa it is more complicated, as the 

 nucleus becomes active as the central organ and reg- 

 ulator of the metabolism. If an infusorium is cut 

 into two pieces, only one of which contains the nucleus, 

 this one alone grows into a complete nucleated cell ; the 

 unnucleated portion dies, being unable to regenerate 

 itself. 



In the multicellular body of the tissue-forming or- 

 ganisms we must distinguish between the partial death 

 of the various cells and the total death of the whole 

 organism, or cell-state, which they make up. In many 

 of the lower tissue-plants and tissue-animals the com- 

 munal link is very loose and the centralization slight. 

 Odd cells or groups of cells may be set loose, without any 

 danger to the life of the whole histon, and grow into new 



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