Experiments in Grafting 289 



from a free end, but at other times one or two hydranths may 

 develop near the region of union. 



Crampton has carried out the ingenious experiment of uniting 

 halves and portions of the pupae of moths. After bringing the 

 cut surfaces together they are held in place by melted paraffin 

 placed around the line of union. The parts stick together and 

 moths may emerge united in different ways according to the 

 combinations formed at the time of union. The internal organs 

 do not unite, and the union is incomplete in this respect, since, 

 although sticking together, there is no continuity between the 

 internal organs, but the skin and the integumentary organs in 

 general do unite. 



The preceding cases relate to combinations where large parts 

 of the animals have been united. It has been long known in 

 surgery that small pieces of different organs can be transplanted, 

 and it is a regular practice to graft pieces of skin over exposed 

 surfaces. These pieces of skin become attached, and their 

 epithelial cells may spread over the exposed parts. Leo Loeb 

 has found in the case of guinea pigs that black skin can be per- 

 manently established in the midst of a region of white skin, but 

 white skin grafted upon a surface formerly occupied by black 

 skin is slowly thrown off and replaced by black skin. 



Ribbert has carried out many experiments in which pieces of 

 different organs were grafted in foreign parts of the body. If 

 these pieces are very small, they may remain alive for a long time, 

 and even begin to proliferate new material. Subsequently, how- 

 ever, they become absorbed. 



The Influence o] the United Parts on Each Other: Formative 



Factors 



In the cases given in the preceding section, with the exception 

 of hydra and of the planarians, there is no attempt on the part 

 of the united pieces to produce a new whole organism by a re- 

 modeling of the old parts. The case is different with hydra 

 and planarians, especially the former, in which a process of 

 remodeling or morphallaxis takes place in case the union does 



