536 CM. Child. 



Since the head, Hke other parts of Leptoplana, is in large degree a 

 complex organ of locomotion, we find that motor activity is an 

 important factor, perhaps the most important in the formation of 

 a characteristic "head." The anterior end does not show the 

 characteristic activity of a "head" in the absence of the ganglia 

 and no head is regenerated. On the other hand, in all cases 

 where a sufficient amount of the ganglionic tissue remains intact 

 to permit the continuance of the characteristic functional activity 

 the regeneration is both qualitatively and quantitatively complete 

 and forms a "head." In short a "head" is regenerated at the 

 anterior end when this part of the body functions in the manner 

 characteristic of a head. The relation between the indeterminate 

 anterior regeneration in the absence of the ganglia and motor 

 activity is indicated by the parallelism between regeneration and 

 motor activity at different levels and from this results the inverse 

 proportion between the amount of material removed and the 

 amount of anterior regeneration from levels posterior to the gan- 

 glia. 



We may conclude then that in the presence of cephalic ganglia 

 a characteristic head must develop since the ganglia determine 

 the functional relations of the various parts and so a characteristic 

 structure results. But why do not the ganglia themselves regen- 

 erate after they are completely removed ? Briefly stated the 

 answer is this: because the other parts of the nervous system do 

 not give rise to the functional conditions necessary for formation 

 of the ganglia. 



The first stage in anterior regeneration is, as in the case of 

 posterior regeneration, the appearance of new tissue at the cut 

 surface (see Child '04b). The appearance of this tissue is doubt- 

 less the result of the altered conditions in this region and is in 

 part a rearrangement of old material in consequence of altered 

 mechanical conditions and in part a proliferation. This material 

 is without doubt capable of forming any region of the body, for if 

 it arose from a posterior cut surface at the same level it would 

 regenerate into a posterior end. Its fate is a function of its 

 position, if we interpret position as not simply space-relation but 

 functional correlation with other parts. In other words the new 



