478 CM. Child. 



section. The old parts have continued to decrease in size more 

 rapidly than the new, but otherwise there is little difference be- 

 tween this and the preceding stage. This piece remained alive 

 during another month, the change in relative size of old and new 

 parts continuing, together with reduction in size of the whole. 



The history of this piece is typical for posterior regeneration 

 from this level of the body. Differences in the amount of regen- 

 eration occur in different individuals, but in all cases regeneration 

 may be said to be qualitatively complete in that the characteristic 

 organs of the part removed are regenerated. As the size of the 

 part removed decreases so in general does the amount of regenera- 

 tion. The significance of this fact will be discussed more fully 

 later. When parts of the pharynx or genital ducts are present 

 the regeneration apparently always begins from the old part, but 

 when such organs are wholly removed they are formed anew. In 

 general the level at which regeneration occurs, the presence or 

 absence of food, and individual differences affect the regeneration 

 quantitatively but not qualitatively. 



a. Experiments on the Relation between the Cephalic Ganglia 

 and Posterior Regeneration at Various Levels behind the 

 Head. 

 Mention was made above of thefact that Leptoplana is not cap- 

 able in any case of regenerating a head in the absence of the cephalic 

 ganglia. This apparent dependence of anterior regeneration upon 

 the cephalic ganglia has been established for a number of forms 

 but the question as to the relation between the cephalic ganglia 

 and posterior regeneration in the Turbellaria has received little 

 attention. In order to examine this problem I prepared series of 

 pieces as follows: a certain number of specimens of as nearly as 

 possible the same size were cut at a given level and from half of 

 these the cerebral ganglia were removed by a transverse cut just 

 posterior to them; the regeneration of the two sets was then com- 

 pared at stated intervals with respect to rapidity, amount, and 

 quality of regeneration and the form of the new part. In several 

 cases also series prepared for other purposes proved of value in 

 this connection and could be compared with other pieces cut at 



