LIFE, IN ITS LOWER FORMS.

No. III. (continued.)

POLYPIFERA.

LET us suppose that the buds continually put forth from the sides of the Hydra, instead of falling off to commence a new and isolated existence, remained permanently attached to the parent stock, giving forth in their turn buds, becoming permanent branches. We should then have the essential form of a compound polype; such, for example, as that of the great marine family, Sertulariada. Here we find the germ first developing a single Hydra-like polype, consisting of a slender stem or body of granular flesh, enclosing a stomachal cavity, the orifice of which is surrounded by a circle of sensitive tentacles. Soon, however, a lateral bud projects, which shoots upward and developes a similar head of tentacles, while, from the side of this, another shoot still carries up the rising stem, which assumes a plant-like condition of branching stalks, with many lateral tentacled buds. It is true that in these marine species we commonly find an additional structure, of which no trace appears in the freshwater Hydra:—the whole compound animal is enclosed in a tube of transparent substance, somewhat flexible though firm, resembling horn, an exudation from the gelatinous integument; and this tube, at every bud, takes the form of an open cell or cup (varying much in shape according to the species), into the cavity of which each individual polype-head can withdraw itself on alarm, and from the orifice of which it protrudes and expands when seeking prey.

In the accompanying Plate, the figure a represents one of the most regular of these species; and, therefore, one

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