II. ONTOGENY . 355 



or other substances which may further promote the differentiation. 

 As mentioned already in Part IV, Chapter VI, inorganic salt ions ex- 

 hibit hormone-like function. 



Since the famous researches of Vogt, numerous facts have been 

 found by a number of workers to show the occurrence of considerably 

 rapid movement of component cells in developing embryos (29). 

 Through this movement some proteins with a certain pattern may be 

 able to contact with certain other proteins having other patterns lead- 

 ing to the establishment of "rejuvenescence"; thus the cells may con- 

 tribute to make the development the more complicated. 



As discussed in the previous section, the mechanism of regenera- 

 tion is identical with that of ontogeny, so that phenomena observed in 

 ontogeny are also proved in regeneration. If, for example, the re- 

 generation bud which is replacing the lost leg of a newt is grafted 

 onto the base from which a part of the tail has been removed, the bud 

 becomes tail instead of leg. That is, the bud tissue is in the state of 

 very early gastrular cells which can readily conform themselves to the 

 environments under which they are placed. Such a submission to a 

 new position is based upon the juvenile character of the bud structure, 

 weaker than that of the protoplasm upon v/hich it is transplanted, ac- 

 cordingly it may be said that the bud is subjected to the organizer of 

 the part. 



However, the position effect is, of course, not always attributable 

 to an organizer. Thus, if Tubularia, a simple marihe animal, is de- 

 capitated it will regenerate its head, that is, the portion bearing mouth 

 and tentacles. If, however, the animal is cut off at both ends and 

 that which bore the head is buried in the sand, a new head is regen- 

 erated at the free or foot end and a foot at what was originally the 

 head end. If both ends are buried in the sand none of them regener- 

 ates a head, and if the body is suspended free in the water both ends 

 develop heads (30). Here, evidently, some external condition such as 

 contact, or some other external chemical or physical factors determine 

 w^hether the regenerative cells make a head or a foot. 



In both cases of regeneration and ontogeny, the first direction of 

 differentiation may be determined by external conditions and subse- 

 quently specific structures are developed, which, if developed into a 

 certain extent, will become stabilized so as to be able to act as 

 organizers. 



To sum up, the individual development including regeneration ap- 

 pears to be a phenomenon in which the property of protein capable of 

 changing its structure in conformity with the environment is revealed 

 to the utmost; the changed structure is unstable at first but gradually 

 becomes stronger and capable of exerting its structural influence upon 



