306 CELLS, TISSUES, AND ORGANISMS 



nerves (Singer, 1952, 1959; Lash, 1956). Perhaps only the rate of 

 repair is affected, since the frequency of mitosis appears to be in- 

 fluenced by the nerve (Inoue, 1957; Overton, 1950). The meaning of 

 the nervous invasion may have to be sought elsewhere. The simplest 

 explanation is that nerve fibers assail the epidermis because there are 

 no physical barriers to the invasion. The undersurface of the epidermis 

 is relatively naked, unguarded by a basal and adepidermal membrane, 

 and the intercellular spaces are open to the ground substance of the 

 blastema. The nerve fibers, whose invasive powers are well known, 

 grow with abandon among the epidermal cells. Whatever other service 

 they may perform in regeneration, their presence in the epithelium 

 does render the epithelium highly irritable, and therefore does serve to 

 protect the delicate growth from mechanical harm ( Singer, 1949a ) . 



References 



Adova, A. N., and Feldt, A. M., 1939. "Biochemical Peculiarities of Various Re- 

 gions of the Axolotl's Body Connected with Form-Building under the Action 

 of Organizers," Compt. Rend. Acad. Sci. 25, 43. 



Amprino, R., and Camosso, M., 1955. "Le role morphogenetique de la crete 

 ectodermique apicale du bourgeon des membres de I'embryon de poulet," 

 Compt. Rend. Assoc. Anat. 42, 197. 



Andreasen, E., 1952. "On the Occurrence of the Lymphocytes in the Normal 

 Epidermis," Acta Dermat .-V enereal ., Suppl. 29, 32, 17. 



Andrew, W., and Andrew, N. V., 1949. "Lymphocytes in the Normal Epidermis 

 of the Rat and Man," Anat. Rec. 104, 217. 



Balinsky, B. I., 1956. "A New Theory of Limb Induction," Proc. Nat. Acad. Sci. 

 U.S. 42, 781. 



Barfurth, C, 1891. "Zur Regeneration der Gewebe," Arch. Microsc. Anat. 37, 406. 



Bell, E., Kaighn, M. E., and Fessenden, L. M., 1959. "The Role of Mesodermal 

 and Ectodermal Components in the Development of the Chick Limb," Dev. 

 Biol. 1, 101. 



Billingham, R. E., and Medawar, P. B., 1950. "Pigment Spread in Mammalian 

 Skin," Heredity 4, 141. 



Bodemer, C. W., 1958. "The Development of Nerve-Induced Supernumerary 

 Limbs in the Adult Newt, Triturus viridescens," J. Morph. 102, 555. 



Bostroem, E., 1928. Der Krebs des Menschen. (Leipzig, G. Thieme Verlag). 



Brunst, V. V., 1959. "Roentgen Regression and Roentgen Stimulation in Axolotl 

 ( Siredon mexicanum) ," Acta Union Inter, contre le Cancer 15, 568. 



Butler, E. C, 1933. "The Effects of X-Radiation on the Regeneration of the Fore- 

 limb of Amhlystoma," J. Exp. Zool. 65, 271. 



Butler, E. C, and Schotte, O. E., 1941. "Histological Alterations in Denervated 

 Non-Regenerating Limbs of Urodele Larvae," /. Exp. Zool. 88, 307. 



Chalkley, D. T., 1954. "A Quantitative Histological Analysis of Forelimb Regen- 

 eration in Triturus viridescens," J. Morph. 94, 21. 



Chalkley, D. T., 1959. "The Cellular Basis of Limb Regeneration," in C. S. Thorn- 

 ton, ed., Regeneration in Vertebrates (Chicago, Chicago U. Press). 



