The doctrine of descent and Darwinism . us, some millimetres in diameter, now appears forabout half a turn as a Planulatum, with distinct ribs,which, tow^ards the beginning, likewise disappear. Thuseven the Planulate ribs, which prevailed among theLiassic ancestors of these Inflata, and were supplanted bythe spines as early as in the brown Jura, still distinguishthese later and essentially modified descendants duringa short period of their youth. Wiirtenberger further shows howthese relations can be simply ex-plained by the Darwinian theoryalone ; without it we should haveonly an extraordinary
The doctrine of descent and Darwinism . us, some millimetres in diameter, now appears forabout half a turn as a Planulatum, with distinct ribs,which, tow^ards the beginning, likewise disappear. Thuseven the Planulate ribs, which prevailed among theLiassic ancestors of these Inflata, and were supplanted bythe spines as early as in the brown Jura, still distinguishthese later and essentially modified descendants duringa short period of their youth. Wiirtenberger further shows howthese relations can be simply ex-plained by the Darwinian theoryalone ; without it we should haveonly an extraordinary problem. It was natural to test the applica-bility of the theory of selection alsoon the forms allied to the Ammonites,such as the Ancyloceras; namely, thegenera in which the convolutions donot touch and partially conceal oneanother, as in genuine Ammonites,and which, as late comers and sideshoots of the group, seemed des-FiG. 20. Ancyloceras. tiucd to dccay. Sclcctlon and dccay .<*Wiirtenberger shows how the abandonment of contact. FORMS ALLIED TO AMMONITES. 217 in the convolutions was to the spinous Ammonites anadvantage which would be established by selection. Ifother palaeontologists consider the fluctuations of formaccompanying the relaxation of the closed spiral asevincing the decline of the group, no contradictionseems to be implied, for what was originally used as anadvantage by natural selection, proved injurious in itsconsequences. As we have seen, the earliest states are obliterated to
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Keywords: ., bookauthorschmidtd, bookcentury1800, bookdecade1880, bookyear1882
