114 ROSS G. HARRISON 
reversal of direction of growth, regeneration, or differentiation. 
The reversed member may grow and differentiate in the same 
direction as the origmal, another axis than that on which growth 
is taking place being the one that is reversed. Reversal may 
thus occur without axial heteromorphosis and vice versa. 
25. In any system, like that of the Imib bud at the tune of 
transplantation, in which at least one axis is left undifferentiated, 
rotation of the elements of which the system is made up might 
account for reversal. The rotation of cells observed by Hadzi 
and Przibram is, however, concerned prmiarih^ with wound 
healing, and heret is no evidence that it is correlated with the 
occurrence of axial heteromorphosis or reversal of asymnietr5\ 
26. As an alternative to the hypothesis of rotation, we might 
consider reversal as due to reversal of molecular asymmetry 
according to analogy with the behavior of optically active com- 
pounds. 
27. There is an analogy between the production of enantio- 
morphic lunbs and the production of situs inversus viscerum, as 
effected by Spemann. Either the reversal may be due to reversal 
of the intmiate structure, or it may take place in spite of the 
intmiate structure through the direct action of mechanical factors 
on the individual parts of the differentiating sj'stem. 
28. The transplanted limbs show both regulation of form and 
functional adaptation. The two often go hand in hand, but not 
necessarily, for some cases show regulation of form without 
function, and others functional regulation without form regulation. 
29. Functional regulation is largely a matter of innervation, 
and it occurs only in orthotopic grafts or in those approxunately 
in that position (Detwiler). 
30. Form regulation is either primary, as in the case of har- 
monic combmations, or secondary, as in the disharmonic. In 
the latter it takes place in one of two ways, either by rotation of 
the developing limb or by means of reduplication and reduction 
of the disharmonic member. 
31. Form regulation by rotation has been observed to occur 
only in orthotopic grafts; reduplications in disharmonic combi- 
nations are more frequent in orthotopic than in heterotopic 
