Experiments wn Grafting 293 
When two cut aboral ends are united (Fig. 9), two new foot 
processes are formed (Fig. 10), and the two pieces subsequently 
pinch apart to form each a separate individual. The explana- 
tion is the same as in the last case. 
These results can be somewhat better understood when taken 
in connection with the experiments of hydras partiaily split length- 
wise. If the anterior end is split for only a short distance, each 
half will round up and produce a separate head (Fig. 11). 
Subsequently the two heads may slowly fuse into a single one. 
The result is similar to the fusion of two bodies in the grafted 
hydra with one head. If the split extends farther into the 
hydra, as in Fig. 12, the two parts slowly draw apart until 
they finally pinch off at the foot region and produce two 
hydras. Why in one case the two separated parts unite and 
in the other case separate farther can possibly be ex- 
plained on the view that I have tentatively suggested above. 
It will be noted that in the case of slightly separated heads 
the influence of the single body prevails, and reunites the 
parts from behind forward by drawing them together and es- 
tablishing the normal tension relations; and in the case of the 
more separated anterior ends, these ends prevail and cause 
the single trunk to pinch farther apart, causing, as it were, the 
halves of the single trunk to draw up into their respective 
anterior ends. 
The results of uniting the squarely cut posterior end of one 
individual with a cut surface in the side of another individual 
(Fig. 13) are similar in many ways to the last. The united 
pieces usually adjust themselves in such a way as to share the 
common trunk (Fig. 14). Subsequently the two pieces split 
apart farther and separate in the region of the foot. If the 
grafted piece does not succeed in halving the trunk, z.e. if it 
does not turn anteriorly, a foot develops at the line of union 
(Fig. 15), and the graft pinches off without passing down to the 
base of the stock. What conditions lead to this difference in 
behavior have not been sufficiently made out, but it is probable 
that the kind of union, or the relative sizes of the graft and 
