EXPERIMENTAL MORPHOGENESIS 127 



missing part from the wound, but that the new tubularian 

 head was restored by the combined work of many parts of 

 the stern. Further analysis then taught us that Tiibidaria 

 indeed is to be regarded as the perfect type of an 

 harmonious-equipotential system : you may cut the stem at 

 whatever level you like : a certain length of the stem will 

 always restore the new head by the co-operation of its parts. 

 As the point of section is of course absolutely at our choice, 

 it is clear, without any further discussion, that the pro- 

 spective value of each part of the restoring stem is a 

 " function of its position," that it varies with its distance 

 from the end of the stem; and so at once we discover one 

 of the chief characteristics of our systems. But also the 

 second point which enters into our formula can be 

 demonstrated in Tubularia : the dependence of the fate of 

 every element on the actual size of the system. You would 

 not be able to demonstrate this on very long stems, but if 

 you cut out of a Tubularia stem pieces which are less than 

 ten millimetres in length, you will find the absolute size of 

 the head restored to be in close relation to the length of 

 the stem piece, and this dependence, of course, includes the 

 second sort of dependence expressed in our formula. 



The figures will serve to show you a little more con- 

 cretely what has been described. The head of Tubularia 

 consists of a sort of broad base with a thin proboscis upon 

 it, both bearing a large number of tentacles ; these tentacles 

 are the first things to be seen as primordia (" Anlagen ") in 

 the process of restitution. You notice two rings of longitudinal 

 lines inside the stem ; the lines will become walls and then 

 will separate from the stem until they are only connected 

 with it at their basal ends ; the new tentacles are ready as 



