1 62 RE GENERA TION 



In general, it may be stated in regard to these experiments in 

 hydra that when pieces are united in the same direction, that is, by 

 unlike surfaces, a single individual is formed and no regeneration 

 takes place where the union has been made, but when like surfaces 

 are brought together, although perfect union may result, a process of 

 regeneration takes place later, at or near the line of union. Even 

 the presence of cut-surfaces at one or both cut-ends of the united 

 components does not generally affect the result, although, in a few 

 cases, it may change it, in so far that heteromorphic regeneration may 

 take place from one piece. This sometimes leads to a suppression of 

 regeneration at the line of union. The experiments do not show, 

 perhaps, conclusively whether the heteromorphosis of the smaller 

 component is due to the polarity of the larger component effecting a 

 change in the smaller one, or whether the closing of the oral end of 

 the smaller component (by its union with the other) brings about the 

 result. All things considered, it seems to me that the larger compo 

 nent has directly influenced the other. 



King has found that if two posterior pieces of hydra are united 

 by the oral cut-surfaces, and then after they have fused both pieces 

 are cut off near the line of fusion, there develops from the small 

 piece a single hydra, with a foot at one end and tentacles at the other. 

 If only one of the pieces is cut off near the line of fusion, a new 

 head develops from its oral surface, as Peebles had found. If two 

 anterior ends are united by their aboral cut-surfaces, and then later 

 both are cut off near the line of fusion, a single hydra develops from 

 the small, double piece. If one of the components is cut off near 

 the line of union, a foot develops from the oral cut-end. If in any 

 of the cases the cut is made some distance from the line of union, 

 then each cut-surface develops its typical structure. These experi- 

 ments leave no doubt as to the influence of the larger piece on the 

 smaller one. Especially interesting is the formation of one individual 

 from two short pieces united in opposite directions. In this case we 

 must suppose that one piece has the stronger influence on the combi- 

 nation (perhaps because it is a little larger), and determines the polari- 

 zation of the other piece. 



King finds that when two posterior pieces are united by their oral 

 ends, regeneration of one or of two heads often takes place at the 

 line of union (Fig. 47, B, B l , B z \ as Wetzel had found. If a dark 

 green individual is united to a light green one, it can be seen that in 

 many cases the new heads are formed by both components, as shown 

 in Fig. 47, B l . Later one of the posterior ends is absorbed, and 

 the halves may then separate (Fig. 47, B l t B z }. If a number of 

 pieces are united, as indicated in Fig. 47, E, a number of heads may 

 be formed, and one or more of these may have a double origin. No 



