292 C. M. CHILD. 



As I pointed out concerning Lcptoplana (Child, '04^) move- 

 ment is undoubtedly not a factor of importance in determining the 

 formation of new tissue at a cut surface, but experimental evidence 

 indicates clearly enough that it is a factor in determining the 

 rapidity, amount and direction of growth and to a greater or less 

 extent the character of its differentiation. 



In the experiments on Planaria described above, the head and 

 pharynx, for example, do not attain their " normal " shape and 

 structure when movement is largely inhibited by anaesthetics. 

 By the use of the higher concentrations it is possible to inhibit in 

 almost any desired degree the process of form regulation so far 

 as visible morphogenesis is concerned. Pieces which in water 

 form heads very rapidly may be prevented entirely from forming 

 heads by the proper use of the anaesthetic, or almost any inter- 

 mediate condition between these two extremes may be attained by 

 the formation of incomplete or partial heads. Pieces incapable 

 of forming heads in the anaesthetic, regain their original power 

 when returned to water. But it does not in the least follow from 

 these facts that head formation is entirely the result of actual 

 movement. My position is, and has been, that movement is 

 merely one of the functional activities concerned in development, 

 and which usually concerns later stages to a greater extent than 

 earlier. But in regeneration in the turbellaria and in various, 

 though by no means all, other forms a peculiar condition exists 

 in that new tissue adjoins fully developed parts which may be in 

 active movement. There can be no doubt that movement of these 

 adjoining old parts influences conditions in the new tissue and so 

 affects the result, either quantitatively or qualitatively or both. 

 But movement and functional activity in the stricter sense, in 

 which Driesch uses the word, are certainly far from being univer- 

 sal factors in either form regulation or ontogeny. 



Whatever the importance of movement in a particular case, it 

 is merely one of a great variety of functional factors. In many 

 cases movement and motor use of parts are not concerned at all 

 in regulation and in some other cases it is evident that while 

 movement may affect the later stages this movement is possibly 

 only in consequence of preceding regulation. In Cestoplaua 

 (Child, '05/7), for example, where the posterior portion of an an- 



