GRAFTING AND REGENERATION 165 



plete separation of the two individuals (Fig. 48, B s , B*}. Each may 

 get a part of the original foot, or a new foot may arise on the graft 

 as the division approaches the base. 



In other experiments only a small part of the foot-end was cut 

 from the animal that served as the graft. The long anterior piece 

 was grafted as before upon the side of the stock. After the two had 

 united, the graft was cut in two, leaving a part of the graft attached 

 to the stock. The part regenerated tentacles, and in two cases sub- 

 sequently separated from the stock as in the first experiment. In a 

 third case the graft was absorbed by the stock as far as the circle 

 of new tentacles, but its subsequent fate was not determined. In a 

 fourth case the graft did not regenerate its tentacles, and was com- 

 pletely absorbed into the wall of the stock. The smaller the piece 

 that is grafted on the stock the greater the chance that it will be 

 absorbed, and furthermore short, broad rings are more likely to 

 be absorbed than long, tubular pieces of the same volume. 1 



Rand's results show in general that when hydras are grafted 

 together they regain the typical form in one of two ways, either 

 by separation into two individuals, or by the absorption of the smaller 

 into the larger component. In the former case the result is brought 

 about in the same way as when the anterior end is partially split in 

 two and the halves subsequently separate. When the graft is ab- 

 sorbed it is not clear whether the absorbed piece disappears or, as 

 seems not improbable, forms a part of the wall of the stock. 



It is important to notice the difference between lateral buds and 

 lateral grafts. The buds separate in the course of four or five days 

 by constricting at the base, but this never happens in lateral grafts. 

 Rand has also made some experiments with buds. He cut off the 

 outer oral end of a bud, and grafted it back upon the stock in a new 

 place. It did not separate from the stock as does a bud, but by 

 a slow process of division it was set free in the same way as are 

 lateral grafts. The proximal end of the bud, which was left at- 

 tached, developed tentacles at its free end, constricted at its base, 

 and was set free. The separation was, however, somewhat delayed. 

 In another experiment a bud was split in two lengthwise, and the 

 cut was extended so that the body of the parent was separated into 

 two pieces. Twenty-four hours later it was found that each half-bud 

 had closed in, and was much larger than when first cut. The half- 

 bud, that was attached to the posterior end of the anterior piece, was 

 constricting at its base, and subsequently it separated at its point of 



1 Rand found that when a posterior piece was grafted by its cut, oral end to the side 

 of another hydra that it was absorbed into the stock. In one case it moved down the whole 

 length of the body of the stock and finally disappeared by absorption into the foot of the 

 stock. 



