If entirely soluble, as, for instance, an Infusorium, the space in which it is contained contracts as the dissolution of its contents goes on, and finally disappears altogether: should there, however, be an indigestible residue, a passage for its exit is formed, and it is expelled by renewed contractions of the homogeneous substance, and in the same direction, or nearly so, as that which the morsel followed in its introduction. The passage and the opening through which the expulsion was effected disappear again without leaving a trace.

(32). The number as well as the size of the morsels taken at one time, in the manner above described, by an Actinophrys, is very various. Sometimes there may be two, four, or six swallowed simultaneously; occasionally more than ten or twelve.

(33). A remarkable contractile vesicle is always visible in these animalcules, which Mr. Weston* regards as a valvular orifice. It is best distinguished when about the edge of the seeming dish, and is never still night nor day, being slowly but without cessation protruded, occupying from ten to seventy or eighty seconds in its development, and then, like the bursting of a vesicle, rapidly and totally subsiding: for an instant it totally disappears, but only to be as gradually and as certainly reproduced. Should that side of the creature where the valve is placed be turned from the observer, the effects of the contraction are distinctly seen, although the valve itself is not; for at the instant of its bursting and closure, some half a dozen or more of the tentacles situated on or about it, which have been gradually thrust from their normal position by the act of its protrusion, now approach each other with a jerk-like motion caused by the sudden bringing together of their bases.

(34). The valve seems to be formed of a double layer of the external hyaloid membrane, the edges of which appear to adhere to each other tenaciously, notwithstanding the growing distension from within, until the force becomes so great that the lips, as they may be called, suddenly separate, apparently to give vent to some gaseous product.

* Quarterly Journal of Microscopical Science, vol. iv. p. 116.

(35). With regard to the reproduction of the species, Mr. Weston assures us that self-division is one mode. First may be noticed a deep depression above and below, not far from the centre of the body; this, as it increases, throws the tentacles across each other, as a necessary consequence of the depressions in the surface and the position into which the outer membrane (in which the tentacles are inserted) is drawn. As the division proceeds, the two animals steadily, but rather quickly, increase the distance between them, until there is only a long membranous neck, apparently composed first of four, then three, then two irregular lines of cells, which ultimately diminish into a single cord composed of three simple cells, elongated like the links of a chain, and becoming more attenuated till the division is complete. All this latter part of the process is rather rapidly performed; that is, from the first formation of the rows of cells to the time of the final separation occupies only about a quarter of an hour.

(36). The Noctilucae: may perhaps be classed with the Rhizopods. The general shape of the Noctiluca* (fig. 6, l) is that of a minute melon deeply indented at one extremity, at which point is attached a sort of proboscidiform appendage or tail: externally its body seems to consist of two membranes of extreme delicacy, which are apparently filled with a clear fluid. At the bottom of the indentation above-mentioned, close to the insertion of the appendix, there is always found a little mass of mud, or other detritus, which it is very difficult to wash away; but when this is accomplished, it becomes perceptible that this foreign matter is adherent to a semitransparent granular substance, which here protrudes through a little aperture generally called the mouth, and which is continuous with a quantity of the same material situated in the interior of the little globe. No digestive apparatus is visible; but numerous vacuoles of variable size (fig. 6, 2) are discovered in the granular substance within, together with a central nucleus. No rhizopodic expansions are in these organisms protruded externally; but in the interior the microscope reveals a delicate network of irregular filaments that ramify in every direction, and exactly resemble in their character the anastomosing threads of Gromia, represented in a preceding figure.

1. Noctiluca, magnified, and viewed as a transparent object.

Fig. 6. 1. Noctiluca, magnified, and viewed as a transparent object. 2. A portion of its internal tissue magnified 150 diameters, showing vacuoles and rhizopodic expansions.

* M. de Quatrefages, Observations sur les Noctiluqu.es, Ann. des Sc. Nat, 1850.

(37). In the vacuoles it is easy to perceive particles of green matter or other foreign substances, which seem to afford nourishment to the animal; so that these cavities doubtless perform the functions of temporary stomachs, although they are constantly changing their shape and situation in a most remarkable manner.

(38). No reproductive apparatus is apparent in these little beings; yet sometimes individuals are to be seen with double bodies, and, from the observations of Colonel Baddeley as recorded by Mr. Brightwell*, there seems to be little doubt that the Noctiluca multiplies by spontaneous fissure. Colonel Baddeley's researches lead him to infer that this process "begins by the gradual formation of a second nucleus, which after its commencement rapidly arrives at the size and appearance of the other. A second globular substance also (termed by some previous writers on the subject the mouth) is formed, in addition and near to the nucleus; and a constriction, small at first, but gradually increasing, takes place, until the perfect Noctilucae are developed, united at last by a thin band which is speedily ruptured, - the whole process of division not occupying more than twelve hours." The observations of Dr. Busch1, and more particularly those of Mr. Gosse2, clearly demonstrate that the Noctilucae increase also by germs or gemmae.