64 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[64 



approach to equality in regeneration at this time is probably due to 

 the fact that the new tissue is largely made up of migrating cells and 

 there is not a striking difference in the extent of the migration at the 

 different levels. 



The specific length of material regenerated after the smallest 

 removals is greater than that regenerated after the larger removals not 

 only at four days but also later. It is probable that the factors involved 

 during the first few days of regeneration are quite different from those 

 during later days. Following the injury there is a disintegration of 

 injured cells associated with an active migration of the epidermal cells 



a 

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 o 



a 

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bfl 



m 



.a 



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a 

 a> 



nun. 



1.0 



Figure 6 



1.5 2.8 4.9 8.4 13.1 



— >- Lengths removed in mm. 

 Rana clamitans Second regenerations Four days 



18.1 



T3 

 CD 



a) 



t- 

 <D 



a 



bfi 

 © 



m 



xt 



bo 

 

 o 



o 



s 



o 



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mm. 



0.20 

 0.10 



1.5 2.8 4.9 8.4 



— >- Lengths removed in mm. 



13.1 



18.1 



p, Figure 7 



Rana clamitans Second regenerations Specific lengths Four days 



over the cut surface. There is practically no mitotic cell division. The 

 rapid multiplication of cells comes later. These processes of cell migra- 

 tion apparently are not essentially different at the different levels. They 

 are local responses of the cells at the cut surface. "With the appearance 

 of rapid cell multiplication there is a marked difference at different 

 levels though the shortest removals still show a greater specific length 

 than the others probably because in their case the migrated cells make 

 up a large percent of the total material of the new part. 



Between the end of the fourth and the end of the sixth day after 

 the operation mitotic cell division becomes very rapid and the rate of 

 regeneration for second regenerations reaches its maximum at a majority 

 of the levels on the sixth day. At six days the regeneration for the six 

 levels is respectively 0.62, 0.80, 0.70, 1.1, 1.7 and 2.3 mm., as shown in 



