378 WILLIAM H. COLE 



explain its indifference to any stimuli tending to change its size 

 and shape. 



2. Gi'afts not over eyes (series LB) or over operated eyes {series LO) 



The outcome of the back-skin transplants contributed only 

 negative evidence to the question of a relation between the 

 visual function and the absorption process, because the difference 

 in behavior between the tail-skin and back-skin grafts seemed to 

 be due to the difference in structure. It was then planned to 

 make grafts of tail skin on the back region of tadpoles, not over 

 the eye, to determine whether absorption would ever occur in 

 such cases. These grafts constituted a part of the LB series 

 (table 4). The operation was like that in the other series. The 

 tail skin was fitted to the incision and grafted in place (fig. 15). 

 The orientation was varied and some of the animals were kept 

 in darkness. None of the twenty-two grafts so made were 

 absorbed. They all established complete union along all edges 

 and at the end of two weeks they began to proliferate new tissue. 

 From the anterior end only, growth occurred in three cases ; from 

 the posterior end only, in one case, and from both ends equally, 

 in eight cases. Sixteen cases showed amorphic regeneration. 

 Five weeks after the operation, on an average, these LB grafts 

 had reached the period of equilibrium. Thereafter the tissue 

 remained unchanged. There is no doubt that the tail-skin grafts 

 placed on the body region not over an eye differ entirely in their 

 behavior from those placed over an eye. The former never show 

 absorption; a majority of the latter do. When the operation 

 was varied by using back skin, the results were the same as far 

 as the absence of absorption is concerned. Autotransplants and 

 homoiotransplants of tail or back skin on the back region are 

 never absorbed, and only the tail-skin grafts proliferate. These 

 results indicated definitely that the eye in some way is responsible 

 for the absorption of the tail-skin grafts. Whether the relation 

 between the organ and the adjustment of the graft was due to 

 the function or the structure of the eye was still undetermined. 

 It seemed as though the severance of the optic nerve before the 

 graft was placed over the eye would afford evidence on this ques- 



