20 SERGIUS MORGULIS 



and the regenerated segments. The results of examinations 

 made 31 and 53 days after the operation are given in table 10. 

 The average number of removed segments was 27, or a little over 

 one-half of the worm's body. The first examination of the regen- 

 erated tails showed that on the average after 31 days only 9.2 

 segments, or practically one-third of the number lost had regen- 

 erated. Fifty-three days after the operation 11 segments on the 

 average (8 to 16 segments) had regenerated, or about 0.4 of the 

 amount removed. The worms were not examined at later peri- 

 ods, but with the knowledge we now possess concerning the phases 

 of regeneration, it ma^^ be said with certainty that the regenera- 

 tive process had alreadj^ reached practically a standstill, and 

 that very few segments were added subsequently. 



The shortening of the tail thus effected by regeneration does 

 not, however, destroy the proportions of the worm, as the whole 

 organism apparently undergoes a corresponding reduction in 

 dimensions. The result of the regeneration of about one-half 

 of the animal is, therefore, to produce smaller worms, but such 

 as are otherwise perfectly normal. 



CONCLUSIONS 



Among numerous perplexing problems with which it is the 

 biologist's lot to deal, the cessation of the growth of an organ- 

 ism when it has attained a certain form is a matter of no small 

 difficulty to understand. Attempts to explain the phenomenon 

 on mechanical principles are conspicuously inadequate. Inves- 

 tigations on regeneration show that, whereas growth may already 

 have been brought to its normal termination, the capacity to 

 grow is still unabated, and that there is sufficient potentiality in 

 reserve to make good a substantial part of any lost portion. Of 

 course, even formative growth on the part of an organism is never 

 reduced to absolute zero, and while the organism maintains itself 

 at a more or less definite status quo, separate parts or organs, as 

 for instance the skin, may still retain the power to grow. 



Experiments have proven conclusively that regeneration may 

 be repeated several, and in some cases even many, times in sue- 



