324 PRINCIPLES OF EMBRYOLOGY 



through the boneless region, the regenerate will be provided with the 

 full necessary complement of bones (the rule does not hold for the tail, 

 see page 308). This formation by the regenerate of structures which are 

 more complete than the stump shows clearly that regeneration is not 

 merely a result of the outgrowth of the tissues of the stump, but is a 

 phenomenon m which an mdividuation field arises m the blastema and 

 leads to the development of the complete section of the organ between 

 the level of the cut and the distal tip. However, although the structure 

 of the regenerate is not directly produced by the outgrowth of the tissues 

 exposed at the cut, those tissues are operative in determmmg the character 

 of the individuation field which arises. In most cases, as we have seen, a 

 mere absence of a tissue does not lead to any deficiency m the mdividua- 

 tion field If, however, tissues from two different organs are mixed, com- 

 pound or hybrid individuation fields may appear Thus Liosner and 

 Woronzowa (193?) and Monroy and Oddo (i943 W found that if 

 muscles from the tail are grafted into the urodele limb at the site of ampu- 

 tation the regenerate may be intermediate m structure between a tail and 

 a limb. Similarly intermediate structures were found by Luther 1948) 

 after the transplantation of skin from the foot to the tail (Fig. 14.7}. 



SUGGESTED READING 

 For a full treatment, A. E. Needham 1952. Other recommended reading : Weiss I939. 

 pp. 458-478; Barth 1940. Rose 1948^; Avel 1940 (oligochaetes, not treated m the text). 

 Spiegelman 1945. 



