484 C. M. Child. 



Is it then possible that certain "formative stimuli" which affect 

 posterior regeneration are connected in some manner with the 

 presence of the cephalic ganglia ? If such exist they certainly do 

 not concern particular organs for regeneration of all the organs 

 characteristic of the part removed takes place in the absence of 

 the ganglia, though these organs are of smaller size or less com- 

 plex in arrangement than when the ganglia are present, as for 

 instance the pharynx and intestinal branches. Moreover, the 

 differences between the two groups differ to a considerable extent 

 with the region from which regeneration takes place. It is clear 

 that we cannot suppose that any particular "formative stimuli" 

 are connected with the presence of the ganglia. We may, how- 

 ever, take the position that all stimuli to growth are more power- 

 ful when the ganglia are present and so bring about a greater 

 amount of regeneration. 



But can we proceed a step further and reach any conclusions 

 as to the character of these stimuli .? I believe that this is 

 possible, and moreover, that these experiments afford valuable 

 data for the interpretation of certain regulative processes in these 

 forms. 



But first it is necessary to recall what was said in an earlier 

 section (pp. 470 and 471) regarding the behavior of the pieces 

 deprived of the cephalic ganglia. The imperfect coordination of 

 movement and the less intense and complex activity are the chief 

 points in which these pieces differ from those in which the ganglia 

 are present. Locomotion is slow and chiefly ciliary, all movements 

 are weaker and there is in general much less movement of all kinds 

 in the absence of the ganglia. These facts are of great impor- 

 tance for the consideration of this problem as the following para- 

 graphs will show. 



The chief points for consideration are as follows: first, what is 

 the reason for the difference in regenerative power between pieces 

 with and those without ganglia ? Second, why is this difference 

 most marked in the anterior regions of the body .? Third, why 

 does it appear chiefly during the later stages of regeneration and 

 only to a slight extent in the earlier .? Fourth, why does the form 

 of the regenerated part as a whole differ in the two cases ^ Fifth, 



