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 pupe 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 of 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 
U 
