1. Podocystis Schomburgkii.

Fig. 4. 1. Podocystis Schomburgkii.

2. Rhopalocaniuni ornatum.

* The following table indicates the proportions of genera and species of Forami-niferous shells which have been met with in various geological epochs: -

Carboniferous series..........

1 genus,

1 species;

Jurassic series........

4 genera,

20 „

Cretaceous series..........

30 „

250 „

Tertiary series.........

55 „

460 „

Now existing...............

68 „

900 „

1 Vide Muller, liber die Thalassicollen, Polycystineen und Acanthometren des Mittelmeeres, in Monatsbericht der Konigl. Akademie der Wissenschaften zu Berlin, 13 Nov. 1856.

(28). Actinophrys

Among the most interesting contributions to our knowledge of these simple organisms are those of the distinguished German micrologist Kolliker, whose researches relative to the organization of Actinophrys Sol* are calculated to clear up many doubtful points connected with the physiological history of numerous allied genera of kindred structure. The Actinophrys (fig. 5, l) is a minute animalcule nearly spherical in its shape, having the surface of its body covered with closely-set delicate filaments, the length of which frequently exceeds the diameter of the creature. It does not present a trace of mouth, stomach, intestine, or anus, but consists entirely of a perfectly homogeneous substance of soft and delicate consistence. Examined under a very high power, the whole animalcule appears to be made up of a most regular and delicate tissue of round or polygonal cells, although on closer inspection such is found not to be really the true structure. When the animal is torn or crushed, it becomes evident that it is entirely composed of a semifluid material (sarcode) enclosing vacuoles; for it will be found that the supposed cells may at pleasure, under pressure, be made either to coalesce into larger or be divided into smaller cavities presenting in all respects the character of the normal ones.

Actinophrys Sol.

Fig. 5. Actinophrys Sol. - 1. a, the cortex; b, nucleus of the animalcule; c, homogeneous basal substance; d, vacuoles; e, tentacular filaments. 2. The same, less magnified, at the moment of feeding: - a-e, as above; f, an infusorium which has just entered the substance of the body, while the surrounding filaments enclose it on all sides. 3. Another specimen: - a-e, as in fig. 1; f, a Vau-cheria-syore wholly imbedded in the cortical substance, the opening through which it entered entirely closed, although its situation is indicated by a slight depression; g, another spore already entering the nuclear substance; h, an infusorium lying in a special cavity; i, a spore in the nuclear substance; k, half-digested morsels; I, a swallowed Iiynceus; m, excrementitious matter beginning its exit from the cortical substance. The other figures represent the sarcode highly magnified.

* Siebold and Kolliker's Zeitschr. vol. i. p. 198.

The filamentary appendages to the periphery of this animalcule are essentially tentacular organs, composed of the same substance as the rest of the body, from which they differ only in never having vacuoles in their interior; and if granules are to be detected in their structure, these are very few in number.

(29). The mode in which the Actinophrys is nourished is a subject of the highest interest. Although, as has been stated, the creature has neither mouth nor stomach, yet it lives upon solid nutriment and rejects such parts as are indigestible. The Actinophrys, indeed, feeds upon Infusoria of all kinds, on the lower Algae, such as the Diatomaceae, and even on minute Crustacea, as the young of Lynceus, Cyclops, etc, which it accomplishes in the following manner: - When, in its progress through the water, it comes in contact with fitting food, the object, whether of animal or vegetable nature, as soon as touched by one of the tentacular filaments, usually becomes adherent thereunto. The filament, with prey thus attached, then slowly shortens itself, dragging the object seized towards its devourer, - all the surrounding filaments bending their points together, so that the captive becomes at last enclosed on every side (fig. 5, 2,f).

(30). That the tentacles, however, possess some other power than that of mere prehension appears evident, because nearly every creature of moderate and even immoderate size which strikes against them is at once for a time rendered immoveable. When a Rotifer, in crossing the field with velocity, strikes against any object, the rotatory organ is often seen at once to suspend its operation, more particularly should its cilia strike the cilia of another animalcule; and frequently no notice whatever is taken of the shock; not so, however, with the victim of the Actinophrys Sol, on the instant of contact with whose tentacles it appears to be paralysed.

In some cases the prisoner is held for some seconds on the exact spot where it struck, and then, without any visible means, becomes attracted towards the body of the Actinophrys, gliding slowly down the tentacle until it is jammed between its base and a neighbouring one. In other instances, instead of the prisoner being arrested on or near the extremity of the tentacle on which it strikes, it is shot down to the base with extreme rapidity, to occupy the same position as in the former case. Sometimes it would seem as if the appetite of the Actinophrys were sated, or that the captive was not approved of, for after remaining stunned for a few seconds, ciliary action is feebly recommenced, not sufficient to produce motion, but as if a return to vitality had been effected; shortly it is seen to glide off the tentacle (as if that organ possessed the power both of appropriation and rejection), and frequently, with but little sign of recovered life, it floats out of the field.

(31). But should the Actinophrys be hungry, the spot upon which the captured animalcule is lying slowly retracts, and forms at first a shallow depression, in which the prey, apparently adherent to the surface and following it in its retraction, is finally lodged. The depression, by the continued retraction of the substance, becomes deeper; the imprisoned animalcule, which up to this time had projected from the surface of the Actinophrys, entirely disappears within it, and at the same time the tentacula, which had remained with their extremities applied to each other, again erect themselves and stretch out as before the capture. Finally, the depression assumes a flask-like shape by the drawing-in of its margin, the edges of which coalesce, and thus a cavity closed on all sides is formed wherein the prey is lodged. In this situation it remains a longer or shorter time, gradually, however, approaching the central portion of the body. In the mean time the periphery of the Actinophrys regains in all respects its pristine condition. The engulfed morsel is gradually digested and dissolved, as is readily seen by its change of appearance from time to time.