256 C. M. Child. 



more frequently the lateral margins are extended laterally and 

 attached, the broader does the body of the worm become. 



When a part of the body of Leptoplana is isolated from the 

 other parts it is necessary to consider the particular conditions in 

 each case before we can understand the changes that occur. The 

 mechanical conditions connected w^ith locomotion will differ 

 according to the region of the body from which the piece is taken, 

 since different regions show different behavior as regards attach- 

 ment and, what is more important, the kind and degree of change 

 in the direction and amount of tension to which the tissues are 

 subjected, will differ greatly according to the regions of the body 

 involved, the amount and kind of movement and various other 

 conditions. Usually observation of the pieces during locomotion 

 is the only satisfactory method, for this is the only way of deter- 

 mining how a particular piece uses a certain part or when it begins 

 to use the regenerated tissues in locomotion. 



All figures are drawn from careful measurements made when 

 the specimens were fully extended, the following measurements 

 being made in each case, w^here the parts mentioned were present: 

 length of animal or piece, distance from anterior end of head to 

 middle of groups of eyes, distance from anterior end of head to 

 anterior end of pharynx, length of pharynx, length of new tissue, 

 width of head at widest part, width of head at level of eyes, width 

 of body at posterior end of pharynx, width of body 1-2 mm. 

 anterior to cut surface, /. e., just anterior to the region which has 

 contracted in consequence of the cut, width of new tissue at cut 

 surface, one or two other measurements of width of new tissue at 

 different levels according to form of this part. While the speci- 

 men w^as under observation figures were draw^n from the measure- 

 ments in order that local curvatures and other special features not 

 indicated by the measurements might be recorded; the extent of 

 the intestinal branches in the new tissue was also indicated in the 

 figures. 



I. Ex pertinents. 



From some twenty-five series of experiments concerning the 

 changes in proportion four have been selected which show the 

 results obtained after section at different levels of the body. In 

 order to permit direct comparison the more important measure- 

 ments of these series are grouped in tabular form. All measure- 



