492 CM. Child. 



form of the new part in these two pieces corresponds very closely 

 with the differences in its use. 



The last of the points to be considered in connection with these 

 pieces is that which concerns the size and complexity of the char- 

 acteristic organs of the regenerated part, especially the pharynx 

 and the intestine. In the Series Ji, and 82, in which regeneration 

 occurred from a level near the anterior end, the pharynx is much 

 larger and the intestinal branches are much more fully regenerated 

 in the pieces with ganglia (Fig. 11) than in these without (Figs. 

 9 and 10). 



In the second pair of series, in which regeneration occurred 

 from a level near the middle of the body, the regeneration of the 

 posterior end of the pharynx is much more complete in the pieces 

 with ganglia (Figs. 15 and 16) than in those without (Figs. 17 and 

 18), and here again we find a difference in the extent of the 

 intestinal branches similar to that in the preceding sets. 



In the third pair of series, in which regeneration occurred from 

 a level at the posterior end of the pharynx, regeneration of the 

 pharynx does not take place but there is the same difference in the 

 number and extent of the intestinal branches that has been ob- 

 served in the other cases (compare Figs. 24 and 25 with Figs. 

 26 and 27). 



As regards the pharynx the difference in size in the two sets is 

 doubtless an expression of the proportionality characteristic of 

 regenerating parts; the greater the amount of regeneration the 

 larger the pharynx. But why does such a proportionality exist ^ 

 This is a difficult question to answer and Driesch has even as- 

 serted that it cannot be answered in physico-chemical terms. It 

 is true that we are at present unable to analyze the factors con- 

 cerned, but I see no reason for assuming an autonomistic or 

 vitalistic principle. The conditions of the case seem to me to be 

 somewhat as follows : The regenerating part represents a certain 

 region of the body and its relations to the old part determine that 

 it shall function in a characteristic manner, /. e., in the manner of 

 the part which it represents. Consequently the area affected by 

 particular functional stimuli will be more or less nearly propor- 

 tional to the size of the regenerated portion. 



