SKIN TRANSPLANTATION IN FROG TADPOLES 375 



Proliferation in this case began on the sixteenth day after the 

 operation, continued for ten days, and then ceased. Up to death, 

 over two months after the last recorded change, no further growth 

 took place. In other cases growth continued slowly for a month 

 before stopping. 



The transplants which had shown no absorption did not differ 

 from the others in regard to proliferation. Both kinds of grafts 

 passed through the growth period, and at its close reached the 

 final stage of equilibrium. This behavior was constant in all 

 tail-skin grafts, many of which were kept under observation for 

 as long as five months after the last noticeable change had oc- 

 curred. Morgulis ('09, p. 639) summarized the regeneration of 

 the marine worm, Podarke, as follows: 



There is a lapse of some time, which varies with different individuals, 

 and under different conditions, before new tissue is proliferated; this 

 is followed suddenly by a period of rapid formation of new segments to 

 be in turn followed soon by a period of slower regeneration. Finally the 

 process is brought to a standstill. 



The histories of the proliferation of the tail-skin grafts on frog 

 tadpoles and the regeneration of Podarke are thus seen to be 

 similar. 



In the DN series (table 2) fourteen transplants of tail skin were 

 made, and the animals kept in darkness. Four of them showed 

 absorption, a lower percentage than that found in the LN series. 

 In two cases the eye was one-half exposed; in the others the 

 absorbed area just reached the eyeball. The adjustment went 

 on in a manner similar to that seen in the light grafts. There- 

 fore, it cannot be said that the absence of hght was the direct 

 cause of the smaller percentage of absorption cases. The dif- 

 ference is correlated with the earlier appearance of proliferation. 

 The average number of days at the end of which growth was first 

 observed in the DN series was twelve. In the LN series the 

 average was twenty-one. The adjustment period of the DN 

 grafts was nine days shorter than the same period in the LN 

 grafts. Further, the rate of growth was higher in the DN series, 

 and was indicated by the greater irregularity of the new tissue 

 formed in darkness. It is a well-known fact that in plants the 



