THEORIES OF DEVELOPMENT 255 



the parts of the archenteron on a smaller scale cannot, Driesch claims, 

 be accounted for on any known chemical or physical principle. 

 There must be, therefore, a different sort of principle involved, and 

 this Driesch calls the vitalistic principle. 



It may be pointed out that this illustration that Driesch has se- 

 lected is only an example of all proportionate development, which 

 many observers have described as taking place in pieces of em- 

 bryos. It is only a striking case of what has been also known in 

 many cases of regeneration, of small pieces producing whole struc- 

 tures, and there is nothing new or startling in this demonstration of 

 a vitalistic principle. The fact may be stated in another way, viz. 

 that the proportionate development of an organ is, within certain 

 limits, self-determining, or is self-determined by its size. The vital- 

 istic principle that Driesch sees demonstrated in these results is 

 the now familiar process of a smaller piece producing the typical 

 structure on a smaller scale ; a phenomenon that a number of other 

 writers had already called attention to as one of the most remark- 

 able phenomena connected with the regeneration of pieces of an adult 

 organism, or of an egg. 



It is something of this same sort that the older zoologists must 

 have had in mind when they spoke of " formative forces " as peculiar 

 to living things. The use of the word "force" in this connection has 

 often been objected to, and not without justification ; since it seems to 

 imply that the action is of the sort for which the physicist uses the 

 word " force." The fundamental question turns upon whether the 

 development of a specific form is the outcome of one or more 

 " forces," or whether it is a phenomenon belonging to an entirely 

 different category from anything known to the chemist and the 

 physicist. If we state that it is the property of each kind of living 

 substance to assume under certain conditions a more or less constant 

 specific form, we only restate the result without referring the process 

 to any better-known group of phenomena. If we attempt to go 

 beyond this, and speculate as to the principles involved, we have 

 very little to guide us. We can, however, state with some assurance 

 that at present we cannot see how any known principles of chemistry 

 or of physics can explain the development of a definite form by the 

 organism or by a piece of the organism. Indeed, we may even go 

 farther and claim that it appears to be a phenomenon entirely beyond 

 the scope of legitimate explanation, just as are many physical and 

 chemical phenomena themselves, even those of the simplest sort. 

 To call this a vitalistic principle is, I think, misleading. We can do 

 nothing more than claim to have discovered something that is present 

 in living things which we cannot explain and perhaps cannot even 

 hope to explain by known physical laws. 



