SYMMETRY IN TRANSPLANTED LIMBS 87 
a normal limb usually develops out of two like halves, i.e., two 
dorsal, or two ventral halves, if properly oriented, when the 
opposite half is entirely missing; 4) after inversion of the limb bud 
the material that normally would have formed the radial half of 
the limb gives rise to the ulnar half and vice versa, so that prac- 
tically no part of the bud has the same fate that it would have 
had if it had been left in place; 5) the inoculation of mesoderm 
from the limb bud under the skin of the flank of another embryo 
may result in the formation of a normal limb, although the inoc- 
ulated tissue is badlj^ disarranged by the operation. According 
to all tests that have been applied, the embryonic limb rudiment 
constitutes, therefore, an harmonic equipotential system, though, 
as a whole, it is self-differentiating except for the determination 
of its dorso ventral axis. The term 'harmonic equipotential 
system' is employed here, as defined by Driesch, in the sense that 
the potencies of all parts of the system are the same, the constitu- 
ent cells being totipotent. ^^ Its use does not imply that the 
writer attaches to the existence of such systems the same signifi- 
cance as Driesch, who considers them as constituting a proof of 
the 'autononi}^ of life.' Even without this, however, and even 
though the actual sj^stem may not reach the abstract perfection 
demanded b}^ its definition, it remains as a useful conception in 
experimental morphogenesis. The existence of the equipotential 
system necessitates, in fact, the assumption of some sort of mo- 
lecular hypothesis for the representation of adult form in the 
germ, and herein lies its importance in connection with the pres- 
ent study. ^^ In particular, we must look to the constitution of 
^* The concept 'harmonic equipotential system' is defined by Driesch ('05, p. 
679) as follows: "Bekanntlich nenne ich harmonisch-aquipotentielle Systeme 
solche Formganze, bei denen eine Qifferenzierungs- oder Wachstumsgesamt- 
leistung in ihren Einzelheiten jeweils einzelnen Elementen des Ausgangsganzen 
zufallt, derart, dass jedes Einzelne dieses Ganzen jedes Einzelne jener Leistung 
vermag, alles Einzelne aber derart in Harmonie steht, dass die Leistung selbst 
ein Ganzes ist." The bearing on the question of vitalism is discussed in various 
papers, especially: '99, p. 99; '01, p. 170; '08 b, p. 138. 
'5 Child has expressed skepticism as to the very existence of equipotential 
systems; for instance: "I think we may say that there is at present no valid 
evidence for the belief that any living system which is undergoing regulation or 
development in nature is at any given time an equipotential system" ('11, ]). 
306). Of. also Child, '08. 
