392 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



teriority is definitively established in the primordium or bud at the time 

 of transplantation but that dorsiventrality is not yet established or is re- 

 versible until later stages, the dorsiventrality of the transplant being de- 



np2(u) 



MP,(R) 



P.DU 



Fig. 134, /I -C— Diagrams of limb reduplication. .4, PR, primary limb; P. DU, posterior 

 reduplicating member; A. DU, anterior reduplicating member; MPi{R), primary (radial) 

 mirror plane; MPz{U), secondary (ulnar) mirror plane; 1-4, digits; 5, level of section shown 

 in B and C. B, C, sectional diagrams of reduplication; in B mirror planes radial (MP.) and 

 ulnar (MP.); in C they are radiodorsal (MP.) and ulnopalmar (MP^). D, dorsal; PAL, palmar; 

 R, radial; U, ulnar (from Harrison, 1921a). 



termined by the dorsiventrality of the host. When double or triple limbs 

 develop, the mirror-imaging results, according to Harrison, from develop- 

 ment of more than one growth center within the range of mutual influ- 

 ence. The center developing first, or most advantageously placed, re- 

 verses the asymmetry of the other or others. Localization of growth cen- 



