REGENERATION IN \TERTEBR\TES 279 



moff, 1931; see also Polezaiev and Faworina, 1935) or of the limb 

 (Taube, 1921), regeneration does not ensue. If the covering is incom- 

 plete, a small regenerate grows from the exposed area. Godlewski 

 showed that the skin flap must be viable to suppress growth. He con- 

 cluded that the dermis was the agent of growth suppression because it 

 constituted a barrier of separation between the epidermis and wound 

 tissues, and not because it mechanically obstructed enlargement of the 

 growing tissues ( compare Goss, 1956b ) . Indeed, regeneration occurred 

 even after chamois was sewed tightly over the fresh wound. Besides, 

 when adult skin was sewed over a wound area which was already cov- 

 ered by a regenerated epithelium of its own, regeneration occurred 

 nevertheless, and the regenerate broke through the overlying skin. It 

 appears, therefore, that a direct contact between epithelium and wound 

 tissues is required for regeneration— a conclusion also reached by 

 Schaxel ( 1921 ) and others. 



JefimoflF ( 1933 ) showed that transplanted skin of certain body 

 regions (for example, belly skin— see Taube, 1921, 1923) but not of 

 others supported limb regeneration. Limb regeneration did not occur 

 when skin of the amputation site was replaced by some taken from the 

 head or back— a result affirmed by Polezaiev and Faworina ( 1935; see 

 also Luther, 1948; Trampusch, 1959). Polezaiev and Faworina at- 

 tributed to the epidermis a specific action during the earliest stages of 

 regeneration, but once growth is initiated, the regenerate epithelium 

 may be replaced by another. 



Lack of intimate association of the epidermis and wound tissues 

 because of too rapid regrowth of dermal connective tissue was blamed 

 by Ross (1944; Gidge and Ross, 1944) for the loss of regenerative 

 capacity in the frog's limb at the time of metamorphosis (see also 

 Komala, 1957). Growth responses of the limb stump were elicited by 

 stripping the skin back from the amputation level to delay the regen- 

 eration of dermis. Still other experiments on the importance of epi- 

 dermis for regeneration have shown that when the regenerate and as- 

 sociated stump are denuded of epithelium and then pushed into a skin 

 pocket in the body wall ( Polezaiev and Faworina, 1935; compare Moro- 

 sow, 1938; Taube, 1921 ) or into the coelom ( Goss, 1956, 1956a; Deck, 

 1955; Pietrzyk-Walknowska, 1959), growth ceases, although differentia- 

 tion may continue whether the regenerate is quite young or very 

 advanced. 



The histology and cytology of the epithelium and of its relations 

 to the underlying blastema also tend to reflect an important role of the 

 epidermis in regenerative events. The epithelium is thin and stretched 

 as it moves over the fresh wound surface, but then later, as its cells 

 divide, it becomes many-layered and thicker than that of normal skin. 

 During the phases of formation of the blastema in which histolysis of 



