RECONSTITUTIONAL PATTERNS IN EXPERIMENT 391 



of the host when transplantation is homopleural dorsodorsal or hetero- 

 pleural dorsoventral and is reversed in homopleural dorsoventral and 

 heteropleural dorsodorsal. These relations give four positions of trans- 

 plant with respect to host axes in orthotopic location, as indicated in Fig- 

 ure 133, and four similar positions in lateral heterotopic location. 



Experimental results with Amhly stoma punctatum led Harrison to for- 

 mulate three rules, of which the essential points are as follows: (i) rever- 

 sal in relation to the host of the anteroposterior axis of the limb bud re- 

 sults in a limb with asymmetry of the side opposite that on which the 

 bud was implanted (disharmonic) ; (2) when the anteroposterior axis is 

 not reversed, the asymmetry of the resulting limb is that proper to the 



HOM. 

 D-D 



HOM. 

 D-V 



HET. 

 D-D 



HET. 

 D-V 



Fig. 133. — Diagram of positions of amphibian limb-bud transplants in relation to host 

 axes. A, anterior; P, posterior; D, dorsal; V, ventral, of host outside, of limb bud inside circle; 

 R, right; L, left; Horn. D-D, homopleural dorsidorsal position, etc. (from Harrison, 19210). 



side on which it is located (harmonic) ; (3) the original member (the first 

 to begin development) of limb duplications has an asymmetry according 

 to (i) or (2), and the secondary member is a mirror image. In later ex- 

 periment these rules have been found to hold very generally, few real or 

 apparent exceptions having been observed. 



Duplication, with mirror-imaging of the two limbs, is frequent, and in 

 some cases there is triplication, in which case each limb is usually a mir- 

 ror image of the one next it; that is, there are two planes of mirror-imag- 

 ing, as indicated in Figure 134, but certain cases have been observed in 

 which this relation apparently does not hold (Swett, 1924; Oka, 1934). 

 In orthotopic location duplications are more frequent when axial relations 

 between bud and host are disharmonic; in heterotopic locations they are 

 more frequent when relations are harmonic; but little is known concerning 

 the physiological factors that bring about duplications and triplications. 



As regards the asymmetry relations, Harrison holds that anteropos- 



