Vol. XXVIII. March, 1915. No. 3 



BIOLOGICAL BULLETIN 



NUCLEAR CHANGES IN THE REGENERATING SPINA, 

 CORD OF THE TADPOLE OF RANA CLAMITANS.^ 



GEORGE FRED SUTHERLAND. 



Contents. 



I. Statement of the Problem 1^9 



II. Material and Methods . . .~.^. ^21 



III. Observations ^^'^ 



1. Degenerative Changes after an Operation 123 



2. Enlargement of Nuclei 129 



3. Temporary Partial Closing of the Spinal Cord 129 



4. Cell Division ^31 



IV. Discussion ^^34 



1. Amitosis and Fragmentation ^34 



2. Appearance of Leucocytes ^35 



3. Temporary Closing of the Spinal Cord 136 



4. Rate of Division. Amitosis vs. Mitosis I37 



V. Summary ^3° 



VI. Bibliography • ^39 



I, Statement of the Problem. 



The present paper gives the results of an histological study of 

 the early stages of regeneration in the spinal cord of the frog 

 tadpole, Rana clamitans. It deals especially with the degen- 

 erative nuclear changes immediately following the operation, 

 and the phenomena of nuclear division in the formation of the 

 new organ. 



Fraisse (1885) studied these stages in several vertebrates in 

 order to discover the origin of the regenerated tissues, and pre- 

 sented the following conclusions which may be used as a basis 

 for a further detailed study. 



"i. Sowohl bei Amphibien wie bei Reptilien sind verletzte 

 Gewebe nur im Stande, wiederum gleichartig Gewebe zu erzeugen. 

 Die Leukocyten iibernehmen bei der Gewebsbildung nur die 



1 Contribution from the Zoological Laboratory of the University of Illinois, 



No. 37- 



119 



