Volume 2

Rare and remarkable animals of Scotland, represented from living subjects. With practical observations on their nature / By Sir John Graham Dalyell, baronet.

  • Dalyell, John Graham, 1775-1851.
Date:
1847-1848
Catalogue details

Licence: Public Domain Mark

Credit: Rare and remarkable animals of Scotland, represented from living subjects. With practical observations on their nature / By Sir John Graham Dalyell, baronet. Source: Wellcome Collection.

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    seen from the preceding detail, that seven hydrse subsisted in 66 days; that their average duration, including the interval of their absence, scarcely exceeded nine days ;—that a new head might even unfold and occupy the place of one which had been in existence the preceding day. The progressive degeneration of external organs, whether in size or number, is no less remarkable,—as if evincing the gradual exhaustion of the resources or energies of nature. Contrasting the fine, florid, and luxu- riant hydra with 22 tentacula, and some remote successor, pale and di- minutive, with only 6 or 7, proves the difference between feeble and vigo- rous evolution. In probing the embryonic sources, a subject of such profound interest to the philosopher, arguments might be reared against the infinite evolu- tion of germs, from the nature of the reproductions of the two species of Tubularia now described. Some might certainly maintain that were such the primitive order, all the germs would unfold the true complement of organs, distinguishing its peculiar kind, though of diminished size. But if the germ be generated immediately in the parent, it might be said that the production of animals in such rapid succession impairs the quantum of elementary matter to be derived for each, which shall suffice for the nucleus of the offspring,—whence the organization of the successive hydrse degenerates Likewise, some may conclude that the primitive or succes- sive germs are not all reposited in a magazine of vitality, seated amidst the pith or elsewhere deep in the stem, but that the embryo may be gene- rated from the internal surface of the fistulous tube below, or formed in some invisible cell, by the organic energies of the parent. If we admit the universal vascular structure of the elementary parts of animal matter, the theory of primitive germs is supported, because the dilatability and increment of the parts, resulting from the institution of life and consequent nutrition, may adapt them for the benefit of the per- fect being. Perhaps there are varieties of this and the subject of the next chap- ter, which perplex the observer in determining on rejecting identity. The want of absolute uniformity which pervades all animated objects, and of which we become sensible as we are more or less acquainted with them, can-