Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/272

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The uses ascribed by Von Buch to the lobes of Ammonites in affording attachment to the base of the mantle around the margin of the transverse plates, would in no way interfere with the service we have assigned to the same lobes, in supporting the external shell against the pressure of deep water. The union of two beneficial results from one and the same mechanical expedient, confirms our opinion of the excellence of the workmanship, and increase our admiration of the Wisdom in which it was contrived.

On examining the proofs of Contrivance and Design that pervade the testaceous remains of the family of Ammonites, we find, in every species, abundant evidence of minute and peculiar mechanisms, adapting the shell to the double purpose of acting as a float, and of forming a protection to the body of its inhabitant.

All the lobes, as they dip inward, are subdivided by numerous denotations, which afford points of attachment to the mantle of the animal; thus each lobe is flanked by a series of accessory lobes, and these again are provided with further symmetrical denotations, the extremities of which produce all the beautiful appearances of complicated foliage, which prevail through the family of Ammonites, and of which we have a striking example on the surface of Pl. 38.

The extremities of the denotations are always sharp and pointed, inwards, towards the air-chamber; (Pl. 38, d. 1.); but are smooth and rounded upwards towards the body of the animal, (Pl. 38, S. S.,) and thus the jagged terminations of these lobes may have afforded hold fasts whereby the base of the mantle could fix itself firmly, and as it were take r00t, around the bottom of the external chamber.

No such denotations exist in any species of Nautilus. In the N. Pompilius, Mr. Owen has shown that the base of the mantle adheres to the outer shell, near its junction with the transverse plate by means of a strong horny girdle; a similar contrivance probably existed also in all the fossil species of Nautili. The sides of the mantle also of the N. Pompilius are fixed to the sides of the great external chamber by two strong broad lateral muscles, the impressions of which are visible in most specimens of this shell.