Vertebrates 



681 



Table 31. Summary of the Major Histological Changes Occurring in the Adult Urodele Limb 

 During a 28-Day Period of Regeneration (from Manner, '53) 



DAYS OF REGENERATION 



MAJOR HISTOLOGICAL OBSERVATIONS 



1 Day The amputation wound is closed over by the migrating epidermal cells. 



2 Days Numerous phagocyte cells are present in the wound area. The disintegration of 



cartilage begins. The continued migration of the epidermal cells to the distal end 

 of the regenerating limb results in an accumulation of these cells at this point. 



5 Days The disintegration of the striated muscle begins. The epidermal cells continue to 



accumulate at the distal end of the regenerating limb. 



6 Days The connective tissue, with its component cells, migrates between the cut end of the 



bone and the overlying epidermis. The disintegration of the cartilage and bone 

 continues, resulting in cartilage and muscle fragments which presumably are 

 incorporated into the blastema. 



16 Days There is a maximal accumulation of the epidermal cells at the tip of the regenerating 



limb. The disintegration of the cartilage and muscular tissue continues. 



20 Days The first finger makes its appearance. The fibroblasts are beginning to diff"erentiate 



into chondroblasts. The disintegration of the cartilage and muscle ceases. 



28 Days The second finger makes its appearance. The new cartilage continues to differ- 



entiate. 



of a haploid chimaeric limb (Hertwig, '27), 

 or Butler's ('35) transplantations of an un- 

 irradiated limb to an irradiated host which 

 had no capacity for regeneration, or the 

 histological studies showing that any or all 

 of the mesodermal tissues can give rise to 

 the formative elements of the blastema — all 

 of these point to mesenchymal components 

 as the essential elements in blastema for- 

 mation. 



A different line of evidence is secvired in 

 the work of Heath ('53). He replaced the 

 ectoderm of the embryonic limb buds in 

 two slow-growing species of salamander. 

 When A. tigrinum ectoderm (fast-growing) 

 is grafted over Triturus torosus limb bud 

 mesoderm there is first a slight retardation 

 in development, later an acceleration re- 

 sulting in a larger than normal limb. When 

 T. torosus ectoderm (slow-growing) is used 



Fig. 238. /, 48 hours after amputation. E, Epidermis; C, cartilage; M, muscle; C.T., connective tissue. 

 Camera lucida drawing. X 100. 



2, 6 days after amputation. E, Epidermis; C, cartilage; M, muscle; C.T., connective tissue; Bl, blastema. 

 Camera lucida drawing. X 100. 



3, Epidermis at 16 days after amputation. E, Epidermis. Camera lucida drawing. X 100. 



4, 20 days after amputation. E, Epidermis; BL, blastema; C.T., connective tissue; C, cartilage; P.C, 

 precartilaginous tissue. Camera lucida drawing. X 100. (From Manner, '53.) 



