NUCLEAR CHANGES IN RANA CLAMITANS. 1 23 



zone. At this stage in the development of the tadpole, the cells 

 near the distal end of the spinal cord show little differentiation. 



Fig. 3. Transverse section through the normal spinal cord, showing the nuclei 

 and the outer cytoplasmic zone, cc, central canal. (890 diameters.) 



I. Degenerative Changes after an Operation. 

 When a tadpole's tail is removed the old notocord extends out 

 beyond the other tissues, and the connective tissue between the 

 notocord and spinal cord is usually broken so that the spinal 

 cord bends dorsally as in Figs. 7 and 8. A transverse cut through 

 the tail leaves the various organs at the cut surface in contact 

 with the surrounding medium, the water in which the tadpole 

 lives. Sections of tadpoles killed immediately after the operation 

 show the direct effect of the cutting (Figs. 4 and 5). Many. 



Fig. 4. Transverse section through the end of the spinal cord immediately after 

 the operation, showing deeply-staining nuclei, cc, central canal; nn, normal nuclei; 

 dn, deeply-staining nuclei. (920 diameters.) 



nuclei and cells are broken and irregular in appearance and may 

 be loosened or torn apart from each other. The injured nuclei 

 at the cut edge and extending forward with decreasing frequency, 

 are homogeneous in appearance and take a deep haematoxyliri 

 stain. Undoubtedly some of the nuclei are cut, and this accounts 

 for the irregularity in shape of a good many. But a good many 

 others, also staining deeply, are rounded and smaller than normal 

 nuclei. These may be either normal nuclei which under the 



