EXPERIMENTAL MORPHOGENESIS 153 



to the typical arrangement of all the cells with respect to 

 each other. But that is certainly not the case. Now, you 

 may ask yourselves if you could imagine any sort of a 

 machine, which consists of many parts, but not even of an 

 absolutely fixed number, all of which are equal in their 

 faculties, but all of which in each single case, in spite of 

 their potential equality, not only produce together a certain 

 typical totality, but also arrange themselves typically in 

 order to produce this totality. "We are indeed familiar 

 with certain occurrences in nature where such curious 

 facts are observed, but I doubt if you would speak of 

 ' machines ' in these cases. The mesenchyme-cells, in 

 fact, behave just as a number of workmen would do who 

 are to construct, say, a bridge. All of them can do every 

 single act, all of them also can assume every single position : 

 the result always is to be a perfect bridge; and it is to 

 be a perfect bridge even if some of the workmen become 

 sick or are killed by an accident. The " prospective values " 

 of the single workman change in such a case. 



I well know that it is only an analogy which I am 

 offering to you. The mesenchyme-cells have not " learned," 

 have no " experience." All that is to occupy us next 

 summer. But in spite of it, there is truth in the analogy ; 

 and perhaps you will prefer it to the merely abstract 

 consideration. 



ON CERTAIN COMBINED TYPES OF MORPHOGENETIC SYSTEMS 



For the sake of completeness it may be remarked, only 

 by the way, that the type of the proper harmonious- 

 equipotential system may go hand in hand with another 



