(13). Rhizopoda

On carefully examining the contents of a marine aquarium, or a glass vessel casually filled with sea-water, the microscopic observer will not unfrequently perceive, adherent to the sides, numerous beings which, from their minute size and transparency, have until a very recent period entirely escaped notice, although the part they are destined to play in the economy of this world is by no means unimportant. The body of one of these remarkable organisms (fig. 1, l) consists of a minute spherical vesicle, something resembling a globular flask provided with a short narrow neck, filled with a fawn-coloured glutinous substance containing numerous minute granules, and apparently unprovided with any external appendages. On placing one of these creatures, however, in a glass of sea-water (its native element), it is found in the course of a few hours to have attached itself to the sides of the vessel by means of numerous long ramified filaments of hyaline transparency, which soon begin to reveal their office to be that of a locomotive appa-ratus, by whose aid the animal can transport itself from place to place, but with such extreme slowness that its movements are hardly perceptible. The locomotive filaments thus displayed are perceptible by the naked eye, their length being, when fully extended, four or five times the transverse diameter of the body; still they exhibit in their interior no appearance of organization, but resemble so many threads of molten glass. When protruded, each of these filaments, at first simple and of equable diameter through its entire length, soon begins to elongate itself in a very mysterious manner, moving in different directions, as though seeking some basis of support.

As the elongation of the filament continues, apparently owing to a constant influx of new material into its substance, it is seen to give off here and there secondary branches, which, in turn dividing dichotomously, give to the whole structure the root-like appearance represented in the figure. The retraction of these singular organs is accomplished by a sort of inversion of the above process, each filament shrinking as it were into itself until it totally disappears. The most remarkable circumstance, however, observable in the economy of these creatures is, that the protruded filaments are able to coalesce and, as it were, to become fused together, forming a gelatinous network that spreads out in all directions (fig. 1, 2).

First.

First.

Animal.

Animal.

1 Vide D'Orbigny, Diet. Univers. d'Hist. Nat. 1845, v., and Foraminiferes Fossiles, 1846: Ehrenberg, Berlin Trans. 1838 and 1839, or Weaver's abstract, Ann. Nat. Hist. 1841, vii. pp. 296, 374: Dujardin, Ann. Sc. Nat. 1835, iv. & v.: Clark, Ann. Nat. Hist. 1849, iii. 380; 1850, v. 161: Williamson, Trans. Micr. Soc. ii. and Micr. Journal, i.: Carpenter, Trans. Geol. Soc. 1849, and Phil. Trans. 1856: Carter, Ann. Nat. Hist. 1852, x.

1. Gromia oviformis, with the rhiziform tentacles displayed.

1. Gromia oviformis, with the rhiziform tentacles displayed.

2. Filaments fused together into a kind of network.

(14). When a Rhizopod, having all its filaments thus extended, wishes to advance in any given direction, those threads which are directed in front become elongated, and those placed behind, on the contrary, are drawn forward, while the intermediate move so as to accommodate themselves to each change of position, thus evidently exhibiting a consentaneity of action.

(15). Internally these creatures present no traces of any special nutritive apparatus; neither are there any organs appropriated to reproduction, their multiplication being apparently accomplished either by gemmation or by simple division, as any portion of the mass separated from the rest seems capable of living and of forming a new centre of organization.

(16). The delicate body of Gromia, above described, is unprovided with anything like a shell; but there are many races presenting an organization in every way analogous (such as the Miliolce, the Cristel-larice, the Vorticialce, and others), that possess the power of secreting shells of very exquisite texture, many of which form extremely beautiful objects when examined under the microscope.

(17). The Foraminifera constitute a very curious and remarkable group, important from the immense numbers in which they occur in a fossil state, and interesting from the peculiarities of structure whereby they are distinguished. The shells of these singular organisms (fig. 2) are divided into distinct compartments*, so as almost exactly to resemble in their form the camerated shells of the Nautili, Ammonites, and other highly-organized mollusca. Examined, however, in a living state, they are found to belong to animals of a very different type, as remarkable for the simplicity of their organization as for their elegance and delicacy. The shell, as represented in the figure, consists of numerous chambers divided from each other by calcareous septa, and perforated by innumerable minute orifices, or foramina, from which circumstance is derived the characteristic name. Internally these chambers are entirely filled with a homogeneous, transparent, glairy substance, which, being soft and diffluent, like the arms of Gromia described above, can be protruded through the numerous apertures in the periphery of the shell in the shape of long contractile filaments (pseudojpodia).

1. Nonionina, exhibiting pseudopodia protruded through the foramina in the walls of the shell.

Fig. 2. 1. Nonionina, exhibiting pseudopodia protruded through the foramina in the walls of the shell.