DYNAMICS OF REGENERATIVE PROCESSES 



211 



or branch which is situated as much as possible at the foremost end 

 of the regenerating piece of worm. He assumes that through the 

 muscular action the liquids of the body are forced to stream toward 

 this end, and that this fact has some connection with the form- 

 ation of a new head. There can be no doubt that the facts here 

 mentioned agree with Bardeen's suggestion. The obhque pieces in 

 Morgan's experiments, which have at first the heads and tails outside 

 the hne of symmetry of the middle piece, gradually assume afterward 

 a normal position (Figs. 51-54). I am inchned to beheve as Child 



Figs. si-S4- — Afi'er Morgan. 

 Successive stages in the regeneration of the oblique piece adcf of Fig. 50. 



does that this is due to purely mechanical conditions. The head of 

 such an oblique piece is asymmetrical, the one side ah being less stretched 

 than the other side ic. The higher tension of the piece he will have the 

 effect of bringing i nearer c. The reverse is true for the tail de], and 

 the effect will here be that e will be pulled nearer i. In this way purely 

 mechanical conditions are responsible for the fact that the soft tissues 

 of the animal are gradually restored to their true orientation.* 



It was of interest to find out whether heteromorphosis could be pro- 

 duced in Planarians. At my request Dr. Van Duyne undertook experi- 

 ments in this direction and succeeded in a few cases, f Figure 55 shows 

 one of these instances. On the right side of the animal the posterior 

 part had been cut off. A new head which was directed backward was 

 regenerated in place of the amputated part. Morgan was more suc- 

 cessful later on. He obtained a larger number of heteromorphoses by 

 cutting short pieces out of a Planarian than by cutting out long pieces. J 



* Tt is in mv opinion not only unnecessary but directly confusing to introduce for the 

 explanation nf these phenomena of restitution such mystical forces or conceptions as Noll's 

 " MorphEeslhesia," and similar things. 



t Van Duyne, Pfiusrer's Archiv, Vol. 64, p. 560, i8g6. 



} Morgan, Archiv fur Entmickelungsmechanik, Vol. 17, p. 683, 1904. 



