SKIN TRANSPLANTATION IN FROG TADPOLES 357 



inclusive. Throughout the following pages many of the terms 

 and ideas given by Loeb ('20 a, '21) and his co-workrs are applied 

 in the discussion of my experiments. Other references to the 

 literature are specifically quoted in the text, and a list is appended 

 at the end of the paper. 



I wish to express my grateful acknowledgment to Prof. H. W. 

 Rand for his kindly interest and helpful criticism during the prog- 

 ress of the experiments. The work was begun in the fall of 

 1915 at Harvard University and continued until the following 

 summer. During the next two years it was carried on at the 

 Pennsylvania State College, until interrupted, in the winter of 

 1917, by the war. In October, 1920, the experiments were 

 resumed at Harvard and completed in the spring of 1921. I wish 

 also to thank Prof. E. L. Mark, Director of the Zoological Labora- 

 tories at Harvard, for the privileges of the laboratory and for 

 many courtesies extended to me. 



MATERIAL AND METHODS 



Because of the ease in handling the animals and in making 

 transplantations, frog tadpoles were selected for the experiments. 

 They were of two species, Rana clamitans and R. catesbeiana, 

 and were obtained from three different sources, viz., from ponds 

 either near Cambridge, Massachusetts, or State College, Penn- 

 sylvania, and from Boston dealers in animals, who secured their 

 supply from 'Illinois.' The tadpoles were collected from the 

 ponds during the fall and brought into the laboratory or pur- 

 chased from the dealers during the winter months. In length 

 they varied from 20 to 100 mm., representing different ages and 

 stages of development. No significant differences in the histories 

 of the grafts, excepting white grafts on black regions, could be 

 correlated with differences in species, size, or age. 



A large balanced aquarium with a mud bottom provided the 

 stock animals an almost natural environment. The tadpoles 

 being experimented on were kept singly in small battery-jar 

 aquaria. Attempts to feed the animals were mostly unsuccessful. 

 Earthworms, cooked beef, boiled egg yolk and clam meat, as well as 



