SYMMETRY IN TRANSPLANTED LIMBS 5 
ance with rule 1 or 2, while the other is the niin'or image of the 
first. 
Experiments previously reported^ have shown that the limb bud 
is an 'harmonic equipotential system/^ and additional experi- 
ments with inverted buds (p. 87) and with half buds (p. 83) 
confirm this result. We must assume, then, that the potencies 
of the cells of the limb bud to form the fore limb are in the last 
instance represented in their intimate structure and not merely 
in their arrangement. The above rules show, however, that not 
all essential features are stamped upon the constituent elements 
of the rudiment at the time of transplantation. For example, 
the difference between the right bud and the left is not an abso- 
lute one, since a right limb bud upside down behaves like a left 
one right side up and vice versa. From this the conclusion has 
been drawn that the elements making up the limb bud are dif- 
ferentiated in an anteroposterior direction, i,e., along the antero- 
posterior axis, but are not yet differentiated, at least not irre- 
versibly, along the dorsoventral axis at the period of development 
at which the transplantations are made. In this one respect the 
differentiation of the limb is dependent upon its orientation w^ith 
reference to the dorsoventral axis of the embryo; otherwise as 
regards its specific form, the limb bud constitutes a self-differenti- 
ating system. 
These questions will be considered more fully in the concluding 
section (p. 85). 
METHODS AND TERMINOLOGY 
All experiments were made upon embryos of Amblystoma 
punctatum in stages that have been previously defined,^ 
In performing the operations the embryo which is to receive 
the implanted limb bud is first made read}^ If the bud is to be 
placed in normal location, the wound is prepared as in the extir- 
pation experiments referred to above. A circular incision, hav- 
* Harrison, '18. 
^ "Jedes kann Jedes iind alles Einzelne steht in Harmonie zu einander." 
(Driesch, '02, p. 229.) See also: '99, p. 72; '05, p. 679, and '08 b, p. 120. 
^Harrison, '15 and 'IS. 
