20 LIFE : OUTLINES OF GENERAL BIOLOGY 



be that the basal fact is a state of "auto-katalysis", or self- 

 fermentation, which automatically follows the disproportionate 

 increase of volume and surface, cytoplasm and nucleoplasm, which 

 IxTsistent growth is apt to induce. 



The instability induced by growth may be intracellular, as is 

 familiar in the multiplication of unicellular organisms, or in the 

 ordinary cell-division in many-celled organisms. Hut it may also 

 take the form of localised lines of weakness or low vitality, as is 

 well seen in the fragmentation of some simple multicellular animals, 

 such as Planarian worms. Along these lines of weakness a process 

 of fission may readily occur. 



In cases of sexual reproduction, where germ-cells are separated 

 oft to start a new generation, the relation between growth and 



KiG. 5. 



I'ull grown Oihth (\r Ifinalc of a Trrniito, showinKthc CDormously distcmled 

 alKlomen, containing many thousands of eggs, 



multiplication is not, of course, so direct as in cases of asexual 

 reproduction by fission or fragmentation. This will be discussed 

 later on, but it may Ix^ |X)inted out in the meantime that repro- 

 duction often occurs at the limit of growth, and that there is a 

 familiar s<*esaw Ix^tween feeding and breeding periods, between 

 leahng and flowering, l)etween nutrition and reproduction. 



Turning again to the inorganic world, we see a vortex-ring 

 dividing intf) two, and we know that a molecule often divides 

 into two or more simpler molecules. A nebula may resolve itself 

 into a double star. We must not think of living creatures as though 

 they had no solidarity with Mother ICarth. All the inorganic analogies 

 to organic reproduction are interesting. Yet, when all is said, we 

 arc left with the conviction that nothing is more distinctive of the 

 organism than its |K)wer of multiplying. 



