It is, moreover, possible that the so-called electric organs, whilst in a condition not highly developed, may have subserved some distinct function: at least, I think, Matteucci could detect no pure electricity in certain fishes provided with the proper organs.

In one of your letters you alluded to nails, claws, hoofs, etc.

From their perfect coadaptation with the whole rest of the organisation, I cannot admit that they would have been formed by the direct action of the conditions of life.

H.Spencer's view that they were first developed from indurated skin, the result of pressure on the extremities, seems to me probable.
In regard to thorns and spines I suppose that stunted and [illegible] hardened processes were primarily left by the abortion of various appendages, but I must believe that their extreme sharpness and hardness is the result of fluctuating variability and "the survival of the fittest." The precise form, curvature and colour of the thorns I freely admit to be the result of the laws of growth of each particular plant, or of their conditions, internal and external.

It would be an astounding fact if any varying plant suddenly produced, without the aid of reversion or selection, perfect thorns.