NUCLEAR CHANGES IN RANA CLAMITANS. I39 



4. The new cord is formed by the cells of the old cord near the 

 cut edge, by mitotic division and migration. 



5. The number of mitotic divisions at different periods is 

 proportional to the rate of regeneration at those periods as de- 

 termined by Durbin. Amitotic division, if it occurs, is not 

 important in the formation of the regenerated organ. 



6. There is no observational evidence from this study that 

 amitotic division does occur in normal regenerating spinal cord 

 cells. 



This work was carried on under the direction of Dr. Charles 

 Zeleny. His suggestion of the problem, and constant interest 

 in its progress are sincerely appreciated. 



VI. BIBLIOGRAPHY. 

 Barfurth, D. 



'91 Zur Regeneration der Gewebe. Archiv fiir mikroskopische Anatomie, Bd. 



37. pp. 406-491. 

 '03 Die Erscheinungen der Regeneration bei Wirbeltierembryonen. Handbuch 

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 Boring, A. M. 



'05 Regeneration in Polychoerus caudatus. Part II. Histology. Jour. 

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 Child. C. M. 

 '06 Contributions toward a Theory of Regulation. I. The Significance of the 

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 Durbin, M. L. 

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'85 Die Regeneration von Geweben und Organen bei den Wirbelthieren, 

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 Morgan, T. H, 



'00 Regeneration in Planarians. Arch, f . Entwicklungsm. der Org., Bd. 10, p. 58. 

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 Morgulis, Sergius 



'10 Is Regeneration a Repetition of the Ontogenetic and Phylogenetic Proc- 

 esses? Amer. Nat., Vol. 44, p. 92. 

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'01 Notes on Regeneration in Planaria lugubris. Arch. f. Entwicklungsm. der 



Org., Bd. 13, p. 396. 

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 '07 Histological Study of Regeneration in Planaria simplicissima, Planaria 

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