Volume 1

Animal and vegetable physiology, considered with reference to natural theology / by Peter Mark Roget.

  • Roget, Peter Mark, 1779-1869.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: Animal and vegetable physiology, considered with reference to natural theology / by Peter Mark Roget. Source: Wellcome Collection.

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    outward form, and in the disposition of their internal organs, preserve the symmetrical arrangement round a common centre so generally exhibited in plants, and especially in flowers, and in the verticillated leaves and branches.* Hence the radiated or star-like forms which predominate in most of the animals composing this class; and hence they have obtained the title of Badiata, by which Cuvier has designated them. Like the animals of the sponge tribe, Polypi are for the most part attached to some shell or base, which may be either of a horny or calcareous nature. The form of this shell admits of almost infinite variety. In some it consti- tutes the external surface of the animal, and encloses the flesh in a general sheath, leaving only openings at the extremities of the tubes for the expansion of each set of tentacula surrounding the respective mouths. Sometimes these tubes are joined together endwise, like the branches of a tree, leaving lateral apertures for the protrusion of the tentacula of each separate potype: this is the case in the Sertularia (Fig. 60). At other times the tubes are placed parallel to each other, like the pipes of an organ, with transverse partitions at regular intervals: such is the structure of the Tiihipora musica, as shown in Fig. 61. In Fig. 62, a portion of the tubes is seen highly magnified, and laid open to show the polypes in their interior. In some species the horny base is fashioned into a num- ber of cells, each of which serves for the protection of its respective polype. These cells are generally placed at the extremity of the branches, presenting the greatest simili- s * See page 69.