[Illustration: Fig. 82. Zoanthus socialis (Cuvier), natural size.] MINYADINIANS. [Illustration: Fig. 83. Blue Minyade. Minyas coeulea (Cuvier), natural size.] The Minyadinians seem to represent among the Zoanthairia the form peculiar to the Pennatula among the Alcyonians. In the case of these animals, the base of the body, in place of extending itself in a disk-like form, in order to grapple with the rock and other projections at the bottom of the sea, turns itself inwards, forming a sort of purse, which seems to imprison the air. From this results a sort of hydrostatic apparatus, aided by which the animals can float in the water and transport themselves from one place to another. The Blue Minyade (_Minyas cyanea_--Fig. 83) will serve as a type of this family; its globose, melon-like form is of azure blue, studded with white wart-like excrescences; it is flattened at its two extremities in its state of contraction, and it has three rows of tentacula, which are short, cylindrical, and white. The internal organs are of a delicate rose colour. Cuvier places this species among the Echinodermata, but the observations of Lesueur and Quoy, who were acquainted with the living animal, place it among the Actiniadæ. Many of the species, which are usually fixed, are still capable of swimming and of inflating their suctorial disks; therefore it is by no means certain that the free habit of _Minyas cyanea_ is constant. FOOTNOTES: [Footnote 6: "Cours de Paleontologie Stratigraphique."] [Footnote 7: "On en a vu vivre deux et même trois ans, sans recevoir de nourriture."--_Vie des Animaux_, p. 117.] CHAPTER VIII. ACALEPHÆ, OR SEA NETTLES. "In nova fert animus mutatis dicere formas corpora."--OVID, MET. The class Acalephæ, from ἀκαλήφη, a nettle, so called from the stinging properties which many of them possess, include a great number of radiate animals of which the Medusæ are the type. They form the third class of Cuvier's zoophytes. The Acalephæ, forming the first order, are characterised as floating and swimming in the sea by means of the contraction and dilation of their bodies, their substance being gelatinous, without apparent fibres. The great genus Medusa is characterised by having a disk, more or less convex above, resembling a mushroom or expanded umbrella--the edges of the umbrella, as well as the mouth and suckers, being more or less prolonged into pedicles, which take their place in the middle of the lower surface; they are furnished with tentacula, varying in form and size, which have given rise to many subdivisions, with which we need not concern ourselves.