282 CELLS, TISSUES, AND ORGANISMS 



outflow. Rose and Hay do not distinguish a reserve of indifferent cells 

 within the epidermis but do describe the internal movement and the 

 transition of epithelium into mesenchymatous cells of regeneration. 



Rose ( 1948a ) stained epidermis supravitally and then observed the 

 appearance of stained mesenchymatous cells. In ordinary histological 

 sections he also could see occasional small streams or tongues of epi- 

 dermis extending into underlying parts, which he cited as morphologi- 

 cal evidence for inward migration and transformation of epidermal 

 cells. We have also seen such irregularities in normal regeneration but 

 attach other significance to them (see also Hellmich, 1930); they may 

 be quite marked under certain experimental circumstances, as various 

 workers have described. We will survey these circumstances below in 

 the description of our experiments. Another reason for Rose's belief 

 emerged from cell counts of the epidermis and mesenchymatous cells 

 at the time the blastema was being formed. He observed a sudden de- 

 crease in epithelial cells which coincided in time with a rapid increase 

 in mesenchymatous cells. Support for the view of an epidermal origin 

 of mesenchymatous tissue was also derived from the fact that regenera- 

 tive powers of a part suppressed by X-rays may be recalled by trans- 

 plantation to the stump of non-irradiated skin taken from another 

 extremity (Luther, 1948; Trampusch, 1951; Rose, Quastler, and Rose, 

 1955). Rose, Quastler, and Rose interpreted the results to mean that 

 non-irradiated epidermal cells were transformed into mesenchymatous 

 cells and in this way initiated regeneration (compare Trampusch, 

 1958, 1959 ) . The evidence of Hay ( 1952 ) in support of Rose was 

 based on the identification of cells from heteroploid skin which had 

 moved into the blastema. Epithelium has also been designated as the 

 source of cells in invertebrate regeneration, in this case by dedifiFeren- 

 tiation and internal migration ( Cresp, 1957 ) . 



The view that epidermis is a source of mesenchymatous tissue in 

 amphibian regeneration has been re-evaluated and discarded by a 

 number of workers (Heath, 1953; Manner, 1953; Chalkley, 1954). The 

 evidence against Rose's view has been weighed carefully by Chalkley 

 ( 1959 ) in a recent survey and need not be gone into here. We wish to 

 comment in passing, however, on the historical fact that the idea of an 

 epithelial origin of subepidermal elements has been previously raised in 

 literature other than that on regeneration. Klaatsch (1894) reported 

 that ectoderm gives rise to skeletal elements, and Maurer (1895) as- 

 serted that it gives off individual cells into the developing dermis ( see 

 also Schuberg, 1908; Saguchi, 1913). Kraus (1906) described the in- 

 ward movement of cells dissociated from the ectoderm to form dermal 

 elements and, indeed, even somatic musculature and axial skeleton. 

 Retterer (1855, 1904) and others (see review by Schaffer, 1927) 

 described leucocytes and connective tissue arising from epithehal cells 



