572 S. M or gill 



perfectly transparent. If six to seven segments are cut off, so 

 that one or two more stripes of the greenish pigment are left in the 

 old tissue, the head will be perfectly repaired but not a single gran- 

 ule of the old green pigment will be seen in the new segments, 

 though I watched it for four weeks. 



Thus the two adjacent head segments, one from the old worm, 

 filled with pigment, the other produced by the worm anew, pale 

 and pigmentless, lie side by side. 



Heads regenerating from any other level of the worm's body, 

 far away from the pigmented region, are also without pigment. 

 If worms under natural conditions do reproduce themselves by 

 dividing into several pieces (four being the approximate average, 

 calculated from Billow's experiments), should we not expect from 

 this, that the majority of the worms in nature would have heads 

 without pigment ? In fact, such worms with pigmentless heads 

 are not very frequent. 



It is true that after a lapse of a considerable time the pigment is 

 formed anew in the regenerated head, and begins to develop from 

 the distal end of the regenerated head. This delayed development 

 of the pigment in the regenerated head needs however a more 

 complete study. 



REGENERATION AND ADAPTATION 



The tip of the tails in Lumbriculi is almost always missing, or 

 regenerating, which fact indicates that this portion of the worm's 

 body is easily injured and that these injuries are of a very frequent 

 occurrence. On the other hand the power of regeneration is very 

 feeble in this particular region as compared with that in the more 

 anterior and less frequently injured regions. 



If we attempt to find a connection between these facts, we shall, 

 contrary to Weismann's claims, reach the conclusion, already 

 expressed in 1898 by Prof. T. H. Morgan in regard to the frequency 

 of accidental injuries and the power of regeneration in the hermit 

 crab, that "no such relation is found to exist." 



This low capacity of regeneration in a region where regeneration 

 is always going on, seems to contradict the view that the capacity 



