RELATIVE STABILITY OF LIVING MATTER 325 



but it has been assumed to be the cause of the production of 

 such twins as are exceedingly similar. Hypothetical cases of this 

 sort are known as "identical twins," supposedly arising from a 

 single ovum instead of from two. 



Experiments upon a variety of species show different powers 

 of development from part embryos. Wilson found, and Morgan 

 verified the fact, that in Amphioxus each of the first two or four 

 cells could develop an entire embryo, and that the one to eight 

 blastomeres would develop to the blastula stage but no farther. 

 Zoja showed that the isolated blastomeres in a number of jelly- 

 fish developed each a whole embryo but of small size. 1 Driesch 

 studied the matter in ascidians and found the cleavage of iso- 

 lated blastomeres to be neither like that of the whole embryo 

 nor like the development they would each have undergone had 

 they remained in place. They produce symmetrical gastrulae 

 and larvae of small size, but lacking in certain parts? 



No one can avoid the conclusion that the phenomena of re- 

 generation generally show an extreme stability of living mat- 

 ter ; but they also betray, especially in lower organisms and in the 

 developing embryo, an unexpected elasticity. To assign absolute 

 stability or extreme instability to living matter would be to state 

 but half the truth. A fair interpretation of the facts of regen- 

 eration leads to the conviction that living matter has the power 

 of extreme readjustment in its effort to discharge its normal func- 

 tions, and that it will discharge those functions as nearly as may 

 be, even under dire distress, and even though important details 

 of structure are by force omitted. 



Regeneration in plants. This is different from regeneration 

 in animals in that " the piece does not complete itself at the cut 

 end, nor does it change its form into that of a new plant, but 

 the leaf buds that are present on the piece begin to develop, 

 especially those near the distal end of the piece." 3 The processes 

 are similar in the two cases in that a piece may give rise to a 

 whole individual, as when the begonia leaf throws out first roots 

 and then stems, which develop into perfect plants. 



Regeneration in higher animals. It is a somewhat singular fact 

 that the lower animals possess larger powers of regeneration of lost 



1 Morgan, Regeneration, p. 237, 2 Ibid. p. 236. 8 Ibid. p. 15. 



