288 ' Experimental Zoology 
gan. The principal results are those with Phagocata gracilis 
and Planaria maculata. Owing to the delicacy of the tissues 
and the mobility of the pieces a special method of holding the 
parts together has to be used. By placing the pieces to be united 
between wet sheets of very thin paper, they can be brought into 
close contact and kept in place by means of pieces of glass at the 
sides and needles at the ends. After several hours the pieces 
grow together. It has been found possible to unite cut surface 
from all different levels of the body. If the union is perfect and 
if the pieces are of the same size so that no free edges are left, 
the combination is permanent and regeneration does not take 
place at the cut surface. If the union is not perfect, regeneration 
may take place at the line of union. In this instance also it 
appears that when the cut ends of the nerve cords unite, re- 
generation at the line of graft does not occur; but if one or both 
of the nerve cords is free in either piece, one or two heads may 
appear. Especially interesting in this connection are the cases 
in which one of the pieces is turned upside down. This sort of 
union was made in several cases where the pieces were united 
by their anterior ends. Two heads regenerated at the line of 
graft, one above, the other below. Each was connected with the 
ventral nerve cord of one piece, and the distribution of pigment 
in the new heads showed that each head was made up on one 
surface of the material derived from one worm and on the other 
surface of material from the other worm. 
Trembley first discovered that pieces of hydra could readily be 
grafted by simply bringing the cut surfaces together for a few 
minutes. It has been possible to make practically all kinds of 
unions, including pieces grafted in the side of another individual. 
As these results will be described in some detail in the next sec- 
tion, further description may be omitted here. 
Another hydroid, Tubularia, has also been used for grafting 
experiments. Miss Peebles has shown that cut ends of the stalk 
readily unite if simply held together for a minute or two. In 
some cases no regeneration takes place at the line of graft, espe- 
cially if regeneration takes place elsewhere, or in the vicinity 
