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 experiments 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 combination (perhaps because it is a little larger), and determines the polarization 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, B¹, B²_), 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_¹. Later one of the posterior ends is absorbed, and the halves may then separate (Fig. 47, _B¹, B²_). 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 evidences of separation of the pieces was observed in cases of this sort. [Illustration: FIG. 47.--After King. _A._ Hydra split in two, hanging vertically downwards. Later the halves completely separated. _B._ Two posterior ends united by oral surfaces. _B¹._ Same; it regenerated two heads, each composed of parts of both pieces. _B²._ Absorption of one piece leading to a later separation of halves. _C._ Two posterior ends united by oblique surfaces. Later one piece partially cut off, as indicated by line. _C¹._ Later still, two heads developed, one at _N_, the other at _M_. _D._ Similar experiment in which only one head developed, at _M_. _E._ Five pieces united as shown by arrows. Four heads regenerated, one being composed of parts of two pieces.]