28 



REGENERATION 



growth. The results show that growth is connected with a structural 

 factor, and is not simply a physiological phenomenon, although no 

 doubt physiological factors are involved. But the physiological factors 

 that are here at work seem to be different from what is ordinarily 

 understood ; for the fact that a tissue that is slowly starving to death 

 should be reduced still further, and at a more rapid rate, in order to 

 supply material to a new part, is certainly a remarkable phenomenon. 



V 



V 



E 



G 



FlG. 134. Planaria lugubris. Dotted line indicates where the worm was cut in two lengthwise. 

 Upper three figures show how a half, that is being fed, regenerates. Lower three figures show 

 other half kept without food. 



At present we are not in a position to offer any explanation that rests 

 on observation, or experiment, as to how the transfer of material takes 

 place, or as to how the new tissue manages to get hold of the mate- 

 rial from other parts. It is possible to protect the old part to a large 

 extent by keeping the regenerating piece well supplied with food. If 

 a well-fed planarian is cut in two along the middle line of the body 

 as indicated in Fig. 13^, A, there develops, in the course of five or six 

 days after the operation, new material along the cut-side of each 



