CHAPTER TWO 
PHENOMENA WHICH INDICATE A CONTINUOUS FORMA- 
TIVE ACTION WHICH IS EXERTED BY PARTS OF THE 
SOMA UPON THE OTHER PARTS THROUGHOUT THE 
WHOLE OF DEVELOPMENT—-HYPOTHESIS OF THE 
NATURE OF THE FORMATIVE ACTION. 
I. Phenomena Which Indicate a Continued Formative 
Action 
Among the phenomena which seem to indicate indis- 
putably a continuous formative action exercised by a 
more or less great part of the soma upon the other parts 
throughout the whole of development, those of the re- 
generation of amputated organs take a first place. 
It is known that when the antennae of a snail, the 
chelae of a crab, the feet of a salamander or the head of 
a worm are amputated, these organs are reproduced even 
when the amputation is performed during adult life. 
Spallanzani has cut the feet and tail off the same sala- 
mander six successive times, and Bonnett seven times, 
and each time feet were reproduced of exactly the same 
size as the former ones without any increase or decrease 
in any part. These facts show that the formative agent 
whatever it may be is always external to the part formed, 
and that it exercises upon the whole development of that 
part and throughout its entire duration a continuous ac- 
tion, and further that it remains itself unaltered even 
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