NO. 4-] 



PLAXARIA MA CL'LA TA . 



I 97 



terior direction. As a result of the tension caused by the pull- 

 ing, growth took place in the region a (Fig. 8), making the 

 position of the posteriorly directed head a permanent and 

 natural one. 



In the case of Fig. 9 the bud was produced in the same way, 

 but from day to day as the tension increased a slight cut was 

 made at a, and as a result we do not have the head end of the 

 bud directed posteriorly to the main axis of the worm, but 

 nearly at right angles to it. The cutting prevented growth, 

 and hence, when the animal comes to rest, or when relaxed in 



FIG. 6. 



FIG. 7. 



FIG. 8. 



FIG. 9. 



FIG 6. At a is seen the kind of cut which was made to produce buds. 



FIG. 7. A head regenerated from a bud, and a bud, b. 



FIG. 8. Pseudoheteromorphosis. 



FIG. 9. Frequent cutting at a prevented pseudoheteromorphosis in the worm of this figure. 



killing, the bud, instead of remaining in a posteriorly directed 

 position as when in motion, takes a position more nearly the 

 same as that which it originally occupied. 



While the bud was developing, the cut edge of the larger part 

 regenerated enough new tissue to replace that which went to 

 produce the bud. Thus we have a well-formed double-headed 

 planarian in the case of Fig. 8. In Fig. 9 the bud failed to 

 develop a left eye. This may be due to the frequently cutting 

 at a ; otherwise our present knowledge of the case makes it 

 impossible to decide what the cause may be. 



iii. Final Fate of Parts. - - One point was quite noticeable 

 in all the experiments with buds. When the animal had be- 



