688 



Regeneration 



generated are tail-like in appearance. The 

 scales are much more like scales which cover 

 the tail than those ordinarily found on the 

 limb. The character of the scales, their size 

 and location, has frequently been used as 

 species diagnostic, and here the form of the 

 regenerate seems to change the scale pattern; 

 e.g., in Weiss' ('30) case where the tail was 

 transplanted heterotopically to the limb 

 region, the tail was later covered by the 

 scutes which formed from the material which 

 originally would have covered a limb, but 

 the scales were definitely tail scales. Noble 



an observation by H. Miiller (1864) that 

 temperature had a decided effect upon re- 

 generation in lizards. Noble and Clausen 

 found that when the temperature was kept 

 constant the skin of any definite area regen- 

 erated the same type of scale. They found 

 no evidence of reversion to a common type. 

 Moreover, the scales of the head and back are 

 regenerated in a form similar to the original. 

 The size of the regenerate has something to 

 do with form, for small areas of epidermis 

 can be removed even on a regenerating tail 

 and will be restored to the original scalation. 



Fig. 244. Tail regenerate in the gecko (Hemidactylus flaviviridis) . K, Reconstituted cartilaginous tube 

 surrounding central canal with poorly regenerated nervous system. (From Woodland, '21.) 



and Bradley ('33), and later Noble and 

 Clausen ('36), ran a series of experiments 

 to determine what the factors might be 

 which are involved in the pattern, form and 

 color of the scales. 



While it has been known for a long while 

 that the lizard scales in a regenerate may be 

 quite different in arrangement and form, 

 Boulenger (1888) pointed out that the re- 

 generate might be a much less special or 

 individualized type of scale and that there- 

 fore it was closer to the ancestral type. Wer- 

 ner (1896) confirmed this idea and intro- 

 duced the idea of reversion to the ancestral 

 condition. Tomier ('06) pointed out that 

 this type of reasoning was slightly unsafe, 

 but the idea had caught and was extended 

 by Werber ('05) and carried to its logical 

 reductio ad absurdum by Barbour and Stet- 

 son ('29), who compared the scale pattern 

 in an extant regenerating form with that of 

 an "undoubted ally of Jurassic age." 



Marcucci ('26) and Avel and Verrier ('30) 

 gave data which showed that the shape and 

 size of the regenerate determine the scale 

 form. When Noble and Clausen ('36) de- 

 cided to repeat this work they made use of 



The work of Bovet ('30) and Marcucci 

 ('32) seems to indicate that the factors con- 

 trolling scale form lie in the mesoderm of 

 the blastema, but this can be changed by 

 temperature effects (Noble and Clausen, 

 '36). Noble and Clausen have studied the 

 formation of the relatively broader ventral 

 scalation — this type of scale can be caused 

 to form on the dorsal side of the tail by 

 implanting muscle from the ventral half of 

 the tail. The converse experiment also holds. 

 The pigment or shade of the scale is deter- 

 mined by the scale location and is not af- 

 fected by the transplant. Barber ('44) has 

 studied the healing of the wound over the 

 tail and compared this with the healing in 

 the limb region. She concludes that the heal- 

 ing is responsible for the restriction of re- 

 generation in the limb. 



PHYSIOLOGICAL REGENERATION 



We can now turn from the active or acute 

 type of restorative process to the repetitive 

 or physiological process which is character- 

 istic of both the preceding group and the 

 subsequent group of birds and mammals. 



