. The doctrine of descent and Darwinism. Evolution. 2l6 THE DOCTRINE OF DESCENT. from one another. It is extremely interesting to study the development of the Inflata of the upper white Jura, which follow the Ammonites liparus (whose externally visible convolutions display only one row of spines), and carefully break off convolution by convolution. Towards the middle there is a region in which there are always two rows of spines ; nearer the centre the innermost row disappears; soon afterwards the outer one also ; and the nucleus, some millimetres in diameter, now appears for about half a turn
. The doctrine of descent and Darwinism. Evolution. 2l6 THE DOCTRINE OF DESCENT. from one another. It is extremely interesting to study the development of the Inflata of the upper white Jura, which follow the Ammonites liparus (whose externally visible convolutions display only one row of spines), and carefully break off convolution by convolution. Towards the middle there is a region in which there are always two rows of spines ; nearer the centre the innermost row disappears; soon afterwards the outer one also ; and the nucleus, some millimetres in diameter, now appears for about half a turn as a Planulatum, with distinct ribs, which, towards the beginning, likewise disappear. Thus even the Planulate ribs, which prevailed among the Liassic ancestors of these Inflata, and were supplanted by the spines as early as in the brown Jura, still distinguish these later and essentially modified descendants during a short period of their ; WUrtenberger further shows how these relations can be simply ex- plained by the Darwinian theory alone; " without it we should have only an extraordinary ; It was natural to test the applica- bility of the theory of selection also on the forms allied to the Ammonites, such as the Ancyloceras; namely, the genera in which the convolutions do not touch and partially conceal one another, as in genuine Ammonites, and which, as late comers and side shoots of the group, seemed des- tined to decay. Selection and decay.' Wiirtcnbcroer shows how the abandonment of contact. FIG. 20. Anc>Ioi. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Schmidt, Dr. (Eduard Oskar), 1823-1886. New York, D. Appleton and Co.
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