The Escharæ greatly resemble the Flustræ, for here also the cells are disposed side by side upon the same plane, so as to form a broad leaf-like polyzoary, which, however, is not of a horny or coriaceous texture, as in the latter genus, but completely calcified, so as to present something of the massiveness of the stony corals. The annexed wood-cuts, showing us _Eschara cervicornis_, first A, in its natural size; then B, a few cells magnified twenty diameters, and ultimately C, a single individual so highly magnified as to reveal some of the details of its otherwise invisible structure, give us a good idea of the truly remarkable organisation of the Polyzoa. In the Escharæ and Flustræ the cellular extension of the common stock or polyzoary is unbroken, and opening on both surfaces, while in the Retepores we find the cells opening only on one side, and the leaf-like expansion pierced like network. [Illustration: Eschara cervicornis. (Natural size.)] [Illustration: Portion of a branch of the polypary of Eschara cervicornis, magnified twenty diameters, to show the form and arrangement of cells.] In cabinets of natural history, the species commonly called Neptune's ruffles will rarely be found wanting. It is a native of the Mediterranean, but individuals of a smaller size are also found in the British seas. [Illustration: An individual of Eschara cervicornis, highly magnified. _a._ Tentacula _b._ First digestive cavity. _d._ Stomach. _f._ Anus. ] [Illustration: Retepora cellulosa. (Neptune's Ruffle.)] The Lepraliæ, or Sea-Scurfs, form thin calcareous crusts of a white-yellow or reddish colour on rocks, shells, and sea-weeds. To the naked eye they appear as rude unsightly eruptions, so as to justify their name derived from the hideous leprosy of the East, but, when magnified, their cells, generally disposed in regular concentric rows, exhibit a surprising diversity and elegance of structure. Forty species are found in the North Sea alone; hence we may judge how great the number of still unknown forms must be that spread their microscopic traceries over the algæ and shells of every zone. It would lead me too far were I minutely to describe the Cellulariæ with their cells disposed in alternating rows on narrow bifurcated branches; the Tubulipores, with their mouths at the termination of tubular cells without any movable appendage or lip; the Bowerbankias and Lagunculas, with their creeping stems and separate cells; suffice it to say that a wonderful exuberance of fancy displays itself in the structure of the numerous varieties of the Polyzoa. [Illustration: A. Portion of a Cellularia, magnified. B. A Bird's Head Process, more highly magnified, and seen in the act of grasping another.]