Page:Natural History Review (1861).djvu/482

470 group together the whole aggregate of "imperforate" genera under the three families Gromida, Miliolida, and Lituolida. The family Gromida presents in Lieberkühnia the nearest approach to a naked representative of this Order; the membranous envelope of its sarcode-body being reduced to such extreme tenuity, as only to be distinctly visible where it surrounds the pedicle, from which the pseudopodia are given off; but it is not a little remarkable, and is very significant of the physiological value of the character, that notwithstanding the absence of any shelly wall to limit the extension of the sarcode-body into pseudopodia, these are just as much restricted to one region as if the body had been entirely shut up within an envelope pervious only at one spot. In Gromia, the membranous envelope is of greater firmness, and presents a wide aperture; and the physiological condition of its animal so closely corresponds, except as regards the segmentation of the body, with that of the animal of Miliola, that I cannot see any ground for separating (as M.M. Claparède and Lachmann have done) the Gromida from the Foraminifera proper. Thus I am led to regard Gromia as the unilocular type of the imperforate series; holding the same place in it that Lagena and Orbulina do in the perforated.

The family Miliolida includes an extensive range of generic forms, from the simple undivided Cornuspira (the Spirillina foliacea of Prof. Williamson) to the highly complex and minutely-subdivided Orbitolites. But all these forms are so intimately united with each other, as to constitute an extremely natural assemblage. They all agree in the possession of an imperforate calcareous shell, the substance of which is "porcellanous," being opaque-white by reflected light, and brownish-yellow when sufficiently thin for light to be transmitted through it. The wall of this chamber is simply joined on to that which preceded it, so that the septa between the cavities of adjacent chambers are single, being composed merely of the portions of the walls of the older chambers, which are embraced by the newer. The communications between the successive chambers, and between the last chambers and the exterior (whether formed by a single large aperture as in Miliola, or by the multiplication of smaller pores as in Peneroplis,) are very free; having to give passage not merely to stolons which are subservient to the multiplication of segments, but to bands of sarcode-substance large enough to transmit with facility, to the segments that are furthest removed from the exterior, the nutrient materials obtained by the pseudopodia which issue from the last alone. Neither "intermediate skeleton," nor "canal-system" for its nutrition, presents itself in the Foraminifera of this family; although a sort of representation of it exists in the most complex form of that very aberrant type Dactylopora, which, in addition to the aggregate of separate chambers, has a deposit of solid shell-substance, traversed by a regular system of passages that has no communication with the chambers, but seems to have been in connection with a sarcode-body outside of them.

We occasionally find among the Miliolida that the surface of the shell is formed of arenaceous particles; but these are embedded in a