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and been extended to the feet, and in that case the digit was 
decidedly not a finger but a toe. 
They were then driven to the last cause— 
III. The correlation of organs. This phrase expressed our 
ignorance rather than explained it away. Nevertheless’ some 
distinctions might be drawn as to the nature of the correlation, 
which was exhibited by the extension of the extra part to the 
fore limb. 
1. It was not a teleological correlation, like that which 
associated the carnivorous teeth with the transverse glenoid 
cavity for the reception of the hinge of the lower jaw. 
2. It was not a correlation such as that by which the 
single occipital condyle was found associated with the seg- 
mented jaw in the sauroids. 
3. It was not a physiological correlation, since it affected 
parts containing various structures with various functions—as 
nerves, bones, &e. 
4. It was not an entirely arbitrary (which meant an 
entirely lawless and unexplained) correlation, as that which 
determined that white cats with blue eyes should be deaf. 
5. It was a correlation which obeyed laws and was capable 
of analogical illustration. It would seem to be due to a force 
operating in the organism which is best expressed by calling | 
it “polarity,” and finds its best analogy in the force which 
determines that a erystal shall be built up symmetrically 
around its axes, and that no molecule can be added on one 
side of these axes without a corresponding one attaching itself 
to the other. Or perhaps the polarity exhibited in electrolysis 
affords even a closer analogy. It would be interesting to find 
that there was latent in the system of the highest vertebrates 
a force so masked by other dominant forces and exacting con- 
ditions as only to appear thus suddenly and abnormally, yet 
which was identical with that which determines the shape of 
the simplest forms of inorganic matter. 
