1 76 RE GENERA TION 



when the oral end of a piece is exposed. In order to avoid this diffi- 

 culty I carried out another experiment. Two worms had the first 

 five or six segments cut off and the exposed anterior ends of the 

 worms united, as shown in Fig. 16, D. Then one of the components 

 was cut off, leaving three or four segments attached to the anterior end 

 of the other component. Although regeneration began in one case, it 

 did not go far enough to show what sort of a structure had developed, 

 but Hazen, who took up the same experiment, succeeded in one case 

 in obtaining a definite result. At the exposed aboral end of the 

 small piece a head and not a tail developed (Fig. 16, E). At first 

 sight it may appear that the result shows the influence of the major 

 component on the small piece, causing it to produce a head and not a 

 tail at its aboral end, but I think that this conclusion would be 

 erroneous, because it seems much more probable that we have here a 

 case of heteromorphosis, similar to that in Planaria Ingubris, and that 

 the result depends entirely on the action of the smaller component. 

 It is hardly possible to demonstrate that this is the correct interpre- 

 tation, since if a small piece of this size is isolated it dies before it 

 regenerates. The result is paralleled, however, by the regeneration 

 of a tail at the anterior surface of a posterior piece. 



The process of grafting has long been practised with plants, but 

 the experiments were made more for practical purposes than to study 

 the theoretical problems involved. Vochting has, however, carried out 

 a large number of well-planned experiments. He finds that a stem 

 can be grafted upon a root, and a root upon a stem, a leaf upon 

 a stem or upon a root. Even an entire plant can be grafted upon 

 another. The results show, however, in general, that, whatever the 

 new position may be, the graft retains its morphological characters 

 a shoot remains a shoot, a root is always a root, and a leaf a leaf. 

 Vochting concludes that there is in the plant no principle or organi- 

 zation that conditions an unchangeable arrangement of the main 

 organs. " The inherited order of the parts, acquired apparently on 

 physiological grounds, may be altered by the experimentator ; it is 

 possible for him to change the position of the building blocks within a 

 wide range without endangering the life of the whole." " It is essen- 

 tial, however, for the success of the experiment that the grafted 

 parts, or tissues, retain their normal orientation. If this condition is 

 not fulfilled there may take place, it is true, a union of the parts, but 

 sooner or later disturbances set in." Vochting transplanted pieces in 

 abnormal positions, sometimes reversing the long axis of the grafted 

 piece, sometimes the radial axes, and sometimes both together. In 

 some cases this led to the formation of swellings that interfered with 

 the nourishment but carried with it no further consequences. In 

 other cases the changes went so far that the vital processes were inter- 



