EXPERIMENTAL MORPHOGENESIS 123 



Let us put the question in the following way : on what 

 factors does the fate of any element of our system depend 

 in all possible cases of development obtainable by means of 

 operations ? We may express our results in the form of 

 an equation : 



p.*. (X)=f(...) 



i.e. " the prospective value of the element X is a function 

 of ... " of what ? 



We know that we may take off any part of the whole, 

 as to quantity, and that a proportionate embryo will 

 result, unless the part removed is of a very large size. 

 This means that the prospective value of any element 

 certainly depends on, certainly is a function of, the absolute 

 size of the actually existing part of our system in the 

 particular case. Let s be the absolute size of the system 

 in any actual experimental case of morphogenesis : then we 

 may write p.v. (X} =f (s . . . ). But we shall have to add 

 still some other letter to this s. 



The operation of section was without restriction either 

 as to the amount of the material removed from the germ, or 

 as to the direction of the cut. Of course, in almost every 

 actual case there will be both a definite size of the actual 

 system and a definite direction of the cut going hand-in- 

 hand. But in order to study independently the importance 

 of the variable direction alone, let us imagine that we have 

 isolated at one time that part of our system which is 

 bounded by the lines ^ 6 1 , and at another time an equal 

 amount of it which has the lines a 9 Z> as its boundaries. 



** t 



Now since in both cases a typical small organism may result 

 on development, we see that, in spite of their equal size 



