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Several cases are on record of the same species presenting varieties in the upper and lower parts of the same formation. Thus Trautschold gives a number of instances with Ammonites, and Hilgendorf has described a most curious case of ten graduated forms of Planorbis multiformis in the successive beds of a fresh-water formation in Switzerland.
All the well-known, usually very clear proofs from palæontology, comparative anatomy, &c., which we are accustomed to meet with in evolutionist books are wanting here, the genealogical trees of the Equidæ, with the gradually diminishing number of toes and the varying teeth, of Planorbis multiformis, of the ammonites, the graduated series of stages exhibited by individual organs, for instance, from the ganglion merely sensitive to light up to the intricate eye, or from the rayed skeleton of the paired fins in fishes up to the five-fingered hands and feet of the higher vertebrates, &c.
In the fresh water chalk formation of Steinheim, near Heidenheim, in Würtemberg, scientists have found, on the same place, in an uninterrupted series of strata, the snail valvata or paludina multiformis in all imaginable transitions from the flat winding, showing the form of a chess-board, up to the sharp form of a tower.
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