

in ORGANIC ADAPTABILITY 27 



become rearranged, so as to lie in the new direction ot greatest 

 tension and pressure ;. thus they can adapt themselves to changed 

 circumstances." 1 



But it is among the lowest organisms that " Regeneration " 

 performs the most remarkable feats. As long as one 

 condition is maintained, a Protozoon may be not merely 

 injured, but divided into several pieces, and yet each piece 

 will, in a few hours, grow into the entire animal again, 

 dwarfed perhaps, but otherwise, to all appearance, healthy 

 and content. The condition is that each fragment should 

 contain a portion of the " nucleus " of the cell in addition 

 to some of the surrounding protoplasm. If this condition 

 is not observed, if, for example, a portion of the proto- 

 plasm is cut off by itself, it retains for some while activities 

 as similar as may be to those of the entire animal, but it 

 shows no power of reconstruction or recuperation, and in 

 the end it perishes. But a Stentor^ for example, may be 

 divided into twenty-seven parts, and the twenty-seventh 

 fraction may, if containing a fragment of nucleus in its 

 protoplasm, live to become a complete Stentor again. 2 The 

 remarkable nature of this process is best illustrated by the 

 diagram on the following page, which I take from Prof. 

 E. B. Wilson's work, The Cell in Development and 

 Inheritance, p. 250. 



It will be seen that, however much the fragments differ, 

 they end by reproducing the entire organism, the repro- 

 ductive process having in each case the same equilibrium^ 

 point at which waste and repair balance one another and 

 growth ceases. 



Equally remarkable is the tendency of a mutilated 

 embryo to develop into a perfect animal. When the 

 fertilised ovum divides into two distinct cells, it would be 

 natural to suppose that each one of these was destined to 

 develop into one half of the body, and it might be inferred 

 that if one were destroyed, the other must either perish or 

 develop into one half of the embryo only. But it is found, 

 in point of fact, that there are further possibilities. In 



1 Prof. Weismann, Romanes 3 Lecture, p. 15, quoted by Mr. Lloyd 

 Morgan ; Habit and Instinct, p. 313. 



2 Wilson, The Cell in Development and Inheritance, p. 249. 



