204 BIOLOGICAL LECTURES. 



prevented by the ectodermal covering, and the cord then 

 divides and turns upwards around the digestive tract to form 

 the commissures and brain. Still the most essential point is 

 unaccounted for, viz., that the cord divides at the anterior end, 

 for were the new part a tail and not a head, the division 

 would not take place. These examples will suffice to show that 

 the phenomena are too complicated to be accounted for by the 

 form of the new part ; however, the form of the new part may 

 be one of the factors, but not the only one. The obvious 

 fact that cannot be left out of account is that the new part is a 

 head long before the cells undergo their definitive differentia- 

 tion ; and it seems to be owing to the new substance being 

 from the start a head, that many of the results take place. 

 Nothing is easier at this stage of the analysis than to drop 

 into metaphysical ideas and speak of vital factors or formative 

 forces, etc. I have not escaped this pitfall altogether, for I 

 pointed out on one occasion that the process appeared as 

 though guided by intelligence. "I mean that what we call 

 correlation of the parts seems here to belong rather to the 

 category of phenomena that we call intelligent than to physical 

 or chemical processes as known in the physical sciences. The 

 action seems, however, to be intelligent only so far as concerns 

 the internal relations of the parts, etc." 1 The reactions to 

 stimuli that are amongst the most common phenomena of living 

 things is what I had in mind, and it is true that at present we 

 cannot explain them as the result of known chemical or physical 

 properties of matter, but I do not think that therefore I was 

 justified in calling them intelligent processes, even in the broad- 

 est use of the word, for we thereby fall into the error of attempt- 

 ing, to explain simpler processes by more complicated and less 

 well-understood ones. 



We are confronted, then, with the question : What is it that 

 gives to the new part the structural character or chemical com- 

 position to form a new head ? If we say its form, i.e., its closed 

 dome-shaped figure, we meet with the objection that this same 

 form is almost universally present where the new part is present 

 as a knob. However, since in each such knob of new cells the 



1 " Some Problems of Regeneration," Biol. Lect., 1898. 



