INTERNAL FACTORS OF REGENERATION IN ANIMALS 67 



several forms that non-nucleated pieces do not produce a new cell 

 wall unless they are connected by protoplasmic threads with nu- 

 cleated pieces. The most delicate connection suffices to enable a 

 non-nucleated piece to make a cell wall, even when the nucleated 

 piece lies in one cell and the non-nucleated in another, the two being 

 connected by a thread of protoplasm that passes through the inter- 

 vening wall. 



If we examine somewhat more in detail some of these cases, we 

 find that when a form like stylonychia is cut into three pieces, the two 

 end-pieces without a nucleus fail to regenerate, while the central 

 piece makes a new entire organism of smaller size. If stentor is cut 

 into three pieces, each piece containing one or more nodes of the 

 macronucleus, each produces a new stentor. If, however, a piece is 

 cut off so that it does not contain a part of the macronucleus, it 

 fails to regenerate. Verworn ('95) succeeded in removing the central 

 capsule with its contained nucleus from the large radiolarian, Thallasi- 

 colla nucleata. The non-nucleated animal remained alive for some 

 time, but eventually died. The nucleated capsule developed a new 

 outer zone with processes like those in the normal animal. If the 

 nucleus is taken from the capsule, the capsule dies, but shows some 

 traces of the formation of an outer zone. If the protoplasm is re- 

 moved as far as possible from around the nucleus, the latter does not 

 regenerate new protoplasm, but dies after a time. Verworn con- 

 cludes that the protoplasm cannot carry on all its normal functions 

 without the nucleus, or the nucleus without the protoplasm. 



These experiments sufficiently demonstrate that non-nucleated 

 pieces are unable to regenerate. If we attempt to examine further 

 into the meaning of the phenomenon, we find a few things that 

 appear to have a bearing on the result. The behavior of the non- 

 nucleated pieces shows that the metabolism of the cell has been 

 changed after the removal of the nucleus. In some cases the 

 protoplasm is not able to carry out the process of digestion of the 

 included food substances. This process may be due to some inter- 

 change that goes on between the nucleus and the protoplasm, 

 which is stopped by the removal of the nucleus, and, in consequence, 

 the metabolism of the cell is changed. The lack of regenerative 

 power may be due to this change in the metabolism. It cannot be 

 claimed, however, that the result is due to a lack of energy in the 

 pieces, for the incessant motion of the cilia in some kinds of pieces, 

 that goes on for several days, shows that a large store of energy is 

 present. Unfortunately, we do not know enough of the relation that 

 subsists between the nucleus and the protoplasm to be able to state to 

 what the lack of regenerative power is due. 



Loeb ('99) has suggested that the lack of power of non-nucleated 



