88 ROSS G. HARRISON 
the elementary units of the Hmb bud, rather than to their ar- 
rangement, for the representation of those relations of symmetry 
that the experiments here described have revealed. ^^ In other 
words, it is the intimate protoplasmic structure that underlies 
symmetry. 
In an equipotential system without axial differentiation, it is 
most natural to assume that the elements themselves are iso- 
tropic." Axial differentiation would then result from the grad- 
ual modification of these units by reaction wdth other elements 
of the system or through external influences. These differentia- 
tions with reference to directions in space may be referred arbi- 
trarily to three axes crossing one another at right angles. They 
are geometrically of four grades, according to the number of 
axes along which polarization has taken place. 
Taking the models used in stereochemistry to show the spatial 
relations of the atom groups in certain carbon compounds, we 
may represent the above four conditions of the elements of the 
organism or system by four figures (fig. 136) in which the groups 
that determine the axial relations are situated at the four angles 
of a tetrahedron. At the center of each tetrahedron we might 
by analogy assume a carbon atom linked to the four groups occu- 
pying the angles of the figure, though this is not necessary for the 
present purpose. By hypothesis the groups at the angles are 
supposed to be at first all alike (fig. 136, 1). If one of them 
should be changed by some reaction, the structure of the molecule 
would become polarized (fig. 136, 2), and if all the molecules 
should assume approximately the same orientation, the system 
which they constitute would show a similar polarity. If two of 
3^ The question whether relations of symmetry of the organism are to be based 
upon symmetrical relations of the intimate protoplasmic structure is answered 
in the affirmative by Driesch ('08 a, p. 144): "Wir miissen also alle Symmetrie 
und auch alle Wirkungen, die von iiusseren iFaktoren ausgehen und sich auf 
Symmetrie beziehen, ani praformierte, gerichtete Elemente des 'Protoplasmas' 
beziehen und konnen in jenen Wirkungen nur richtende und umordnende 
Geschehnisse sehen. 
3' To avoid misunderstanding, it should be stated that when we speak of equi- 
potentialitj' and isotropy, we do not lose sight of the fact that the system in its 
entirety is heterogeneous. 
