JUGGLING WITH LIFE 



heads when they are decapitated; the reason being, 

 perhaps, that higher organisms have developed a 

 concentration of nerve cells in the head, as ganglia 

 or brain, so that decapitation involves a nervous 

 shock from which the animal does not recover. 



In the case of various worms, however, it is possi- 

 ble to sever the head without destroying the life of 

 the individual. In such case, as Professor T. H. 

 Morgan in particular has shown, a new head may 

 grow closely duplicating the old one, and the indi- 

 vidual may appear to be no worse for the experience. 

 In the case of a certain type of flat fresh water worm 

 known as a planarian, Professor Morgan has cut off 

 both extremities, leaving only an oblong central sec- 

 tion of the body; and has observed a complete 

 restoration of both head and tail. 



Professor Loeb decapitated a marine planarian 

 (Thysanozoon), with the result that the head grew 

 a new body and the body a new head, so that one 

 adult individual had now become two individuals. 

 Indeed this experiment by no means shows the limits 

 of the capacity for rejuvenation of this type of worm. 

 For Professor S. J. Holmes reports that he has cut 

 a planarian into twenty pieces, each of which regen- 

 erated into a complete planarian of reduced size. 

 The' process was repeated over and over until hun- 

 dreds of individuals had been produced, the last 

 "generation" of which comprised individuals less 

 than one-fifteen-hundredth of the bulk of the original 

 individual. 



Reflect that the planarian is a creature having eyes, 

 a nervous system, and a fair equipment of internal 



