SYMMETRY IN TRANSPLANTED LIMBS 91 
The point which it is desired to emphasize is that in an oi-ganic 
'equipotential system' there must be some intmiate structural 
basis for adult characters in the units that make up the embryonic 
rudiment. 93 It cannot be in the arrangement of these units; for 
in that case marked disturbances of development would be pro- 
duced by such operations as removing half of the rudiment, fusing 
two buds together, combining two like halves, inverting the 
dorsoventral axis, or inoculating masses of mesoderm cells from 
the limb rudiment under the skin of the flank ; and yet normal 
development may follow any of these procedures. 
These experiments yield, of course, no information concerning 
the localization in the cell of the representatives of the adult form 
characters in question. The system here dealt with is a pluri- 
cellular one, but it is interesting to find that in the most thorough 
and careful studies of polarity and symmetry in the egg, the 
basis of these properties is found to be in the cytoplasm of the egg 
cell. Lillie ('06, '09) shows that the polarity of the Chaetopterus 
egg must be located in the ground-substance, because any amount 
of shifting of visible granulations in the egg, such as yolk, oil 
droplets, pigment, etc., has no effect on the polarity of the result- 
ing embryo. With this conclusion the work of Morgan and his 
collaborators ('08 b, '09, '10) on the centrifuged eggs of various 
animals, more particularly Arbacia and Cumingia, is in substan- 
tial accord. Conklin ('16, '17), in his Study of Crepidula, con- 
cludes that it is the spongioplasmic framework of the egg-cell that 
determines its polarity, though he does not consider how this 
quality is determined in relation to the intimate structure of the 
spongioplasm. To the extent that Conkhn places the seat of 
polarity in the more viscid rather than in the more fluid constit- 
uent of the cytoplasm, he takes issue with Lillie, but in the main, 
there is agreement between these two investigators. Lillie, how- 
ever, goes a step further when he says ('09, p. 77) : ''The existence 
of polarity and bilaterality in an optically homogeneous medium, 
and the persistence of both as to orientation under experimental 
conditions that seriously modify the quantitative relations of 
the oriented medium in different regions (as, for instance, when 
'9 Cf. Driesch, ]. c. 
