288 Experimental Zoology 



gan. The principal results are those with Phagocata gracihs 

 and Planaria maculata. Owing to the dehcacy of the tissues 

 and the mobihty 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 Hne of union. In this instance also it 

 appears that when the cut ends of the nerve cords unite, re- 

 generation at the hne 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 



