282 



C. M. CHILD. 



and 4) the change in shape may occur in later stages (especially 

 after return to water) without the formation of more new tissue 

 (Figs. 3 and 5)- It follows that the factors determining the 

 change in shape must be in greater or less degree different from 

 those determining the localization andgrowth of new parts. More- 

 over, the change in shape occurs only when the piece is capable 

 of locomotion and it is in general proportional to the locomotor 

 ability of the piece. 



v 



// 



Fir.s. 9-11. 



But pieces which do not possess the old head afford even more 

 positive evidence for these conclusions. Fig. 9 represents a 

 piece corresponding to the region between the lines a and c in 

 Fig. i after fifteen days in 1.5 per cent, alcohol. A new head 

 has appeared, a small new pharynx is present as a mass of undif- 

 ferentiated cells, and some new tissue has formed at the posterior 

 end, but the piece as a whole shows no approach to the normal 

 shape : it has undergone no marked changes in proportion. Inci- 

 dentally it may be noted that the pharynx in such pieces appears 

 much further posteriorly than in similar pieces in water. After 

 seven days more the piece has the shape shown in Fig. 10. It 

 moves about slowly, but its movements are different in character 

 from those of pieces possessing the old head : here the posterior 

 half of the body is very evidently not under complete control, 



