CHANGE OF SHAPE IN PLANARIA. 



283 



i. e., is not fully coordinated with the anterior region, and when 

 the animal advances it is simply dragged along as a mass of 

 inert material, its posterior end being only very rarely attached 

 to the substratum. The shape of the piece suggests that the 

 anterior part is being stretched by the strain upon it of the pos- 

 terior portion, and I believe that is exactly what is occurring. 



Similar pieces in water attain in the same length of time the 

 shape and structure shown in Fig. II. Pieces in alcohol of 1.5 

 per cent, do not change in shape much beyond the condition 

 shown in Fig. 10, but if they are returned to water they regain 

 their normal locomotor activity and may finally reach a shape 

 like that of Fig. 1 1. 



T r 



12 



14 



15 



FIGS. 1 2-1 6. 



In these cases a new head, a small new pharynx and some 

 new tissue at the posterior end have appeared without any marked 

 change of shape in the piece as a whole (Fig. 9). Evidently the 

 change of shape and the localized formation of new tissue are not 

 necessarily correlated. 



The same thing appears in Fig. 12, which shows a piece from 

 the same region (a to c, Fig. i) after fifteen days in 0.5 per cent, 

 ether. Head, pharynx and posterior end have formed but no 

 change in shape has occurred. This piece was returned to water 

 at this stage and after seven days more had attained the shape 

 shown in Fig. 13. 



