Studies on Regulation. IV. 109 



When the cut is made at any level posterior to the ganglia 

 neither the ganglia themselves nor the head are regenerated (Cf. 

 Lillie, '01). 



Posterior regeneration is qualitatively complete at all levels 

 posterior to the ganglia whether the ganglia are present or absent 

 in the piece, but pieces cut anterior to the ganglia never regenerate 

 the ganglia nor the posterior parts. 



Lateral regeneration is qualitatively complete when the ganglia 

 are present, but when they are absent neither they nor the lateral 

 part of the head removed are regenerated though lateral regen- 

 eration of other parts may be more or less complete in the ab- 

 sence of the ganglia. Removal of the right or left half of the 

 ganglia is followed by complete regeneration from the remaining 

 half. 



In general the amount of tissue regenerated in pieces kept with- 

 out food is much less than that removed, though all the organs 

 may be present. The amount of posterior regeneration varies 

 inversely as the distance of the cut surface from the anterior end. 

 The size of the piece does not affect the quality of regeneration 

 and affects the amount only slightly, except on approach to the 

 minimal size, when a marked decrease in the amount of regenera- 

 tion occurs. The minimal size of pieces capable of qualitatively 

 complete posterior regeneration was not determined with exact- 

 ness, but transverse pieces less than one tenth the length of the 

 body are still capable of qualitatively complete posterior regenera- 

 tion and pieces even smaller than this, but containing the cephalic 

 ganglia, regenerate completely in all directions. 



REGENERATION AND MOVEMENT. 



Considering first one of the simplest cases, viz., posterior re- 

 generation from a transverse cut surface we find that in Lepto- 

 plana, as in Planaria and other Turbellaria, the new tissue which 

 makes its appearance on the cut surface assumes a rounded outline 

 and grows or extends posteriorly in the direction of the longi- 

 tudinal axis, becoming more slender and tapering as regeneration 

 proceeds. Figures 2 — 4, drawn from careful measurements, will 

 serve as an illustration of the course of regeneration in such cases. 



