CHAPTER IX 

 GRAFTING AND REGENERATION 



BY uniting parts of the same or different animals, or of plants, 

 there is given an opportunity of studying a number of important 

 problems connected with the regeneration of the grafted parts. 

 Trembley's experiments in grafting pieces of hydra are amongst 

 the earliest recorded cases of uniting portions of different animals, 

 although in plants the process of grafting has been long known. 1 

 Trembley found that if a hydra is cut in two, the pieces can be 

 reunited by their cut-surfaces, and a complete animal results. No 

 regeneration takes place where the union has been made. He also 

 succeeded in uniting the anterior half of one individual with the 

 posterior half of another individual, and again produced a single 

 individual. He failed to obtain a permanent union between different 

 species. 



More recently, Wetzel has carried out a number of different 

 experiments in uniting pieces of hydra. He found that if two 

 hydras are cut in two, the two anterior pieces may be united by the 

 aboral cut-surfaces (Fig. 46, B), and the two posterior pieces may 

 also be united by their oral cut-surfaces (Fig. 46, A). The fusion 

 of these " like-ends " takes place as readily as when unlike ends are 

 brought in contact, as in Trembley's experiments. Subsequently, 

 however, regenerative changes take place. When, for instance, two 

 anterior pieces are united by their aboral ends, there develop after 

 two or three days one or two outgrowths, at or near the line of union, 

 that become new feet, and the two individuals may subsequently 

 separate. When two posterior pieces are united by their oral sur- 

 faces, a double circle of tentacles generally develops, one on each 

 side of the line of union. The pieces then pinch apart and produce 

 two hydras. 2 In another experiment the head and a part of the foot 

 were cut from a hydra, and the head was turned around and grafted 

 by its aboral surface upon the aboral surface of the middle piece. 

 Another animal was cut in two in the middle, and the posterior half 

 was grafted by its oral end to the oral end of the middle piece. In 



1 For references to the literature on grafting in plants see Vochting ('84). 

 3 In one case they separated only after three months. 



