If no solid particles exist in the fluid surrounding the animalcule, the pellets are less consistent, exhibiting the appearance observable in specimens living in colourless water, in which case they are made up of a small number of particles, and seem to be principally composed of mucosity. Sometimes (observes M. Meyen) two of the pellets so formed are, when forcibly pressed together by the contraction of the body of the animalcule, observed to coalesce and become united into one mass, - a circumstance in itself sufficient to prove that they are not enclosed in stomachal walls.

(81). In order to witness the formation of the pellets above described, it is necessary to begin the examination of the animalcule immediately on placing it in coloured fluid, as the deglutition of the coloured particles is very rapid; frequently, in the course of half a minute the pellets may be seen to issue one after the other from the oesophagus, and to be gradually propelled along the internal wall of the cavity of the animalcule. In Paramecium, Kerona, and the Vorticellae, each new pellet pushes the preceding one before it so that they mount up along the opposite wall and are returned down the other side, until, after having accumulated to some extent, they are expelled one after the other from the anal outlet.

* "Quelques Observations sur les Org. digest, deslnfus.," Ann. des Sc. Nat. 1839.

(82). The number of pellets thus formed is frequently so considerable that they fill up the whole abdominal cavity, and so closely united together that they form a mass that revolves slowly upon itself, as may be seen in the Vorticellce. This last kind of movement is the effect of the forcible expulsion of the newly-formed pellets from the gullet into the common cavity, of which fact M. Meyen assures us that he has had convincing proof. In other cases, when the number of pellets is small, they exhibit the kind of circulatory movement already spoken of, the cause of which is not so obvious.

(83). The observations of Dr.Lachmann relative to the mode of feeding of the Acineta (fig. 17) throw considerable light upon this part of their economy. When an Infusorium touches the button-like dilated apex of the ray of an Acineta, it usually remains adhering to it; the apex of the ray becomes still more dilated, so as to form a sucking disk, and the ray becomes thicker and shorter; at the same time other rays make grasping movements, and endeavour to attach their extremities, which are dilated into sucking disks, to the captured prey. If the latter does not soon succeed in making its escape by great exertions,by which the rays of the Acinetae are often much disarranged and injured, the Acineta begins to suck out its contents. Each ray is a sucking proboscis; and it may soon be seen that a current of chyme-particles runs from the alimentary cavity of the captured Infusorium into the body of the Acineta, through the axis of the rays, which, after seizing the prey, have become shortened and thickened. In the body of the Acineta, the chyme-particles still run at first in a single row, but afterwards they collect in a drop, which soon becomes amalgamated with other drops derived from other suckers.

When a considerable quantity of the chyme of the captured animal has passed over into the Acineta, a remarkable change gradually takes place in its appearance: if it was previously pale, nearly transparent, and only very finely granulated, larger, dark globules, resembling fat-drops, now make their appearance here and there, and these soon increase, so that the body acquires a granular aspect and becomes opake. The globules or drops which thus make their appearance can only be formed in the body of the Acineta, as they are far larger than the chyme-particles which are seen flowing through the sucker. The animal whose contents are thus sucked out gradually collapses and dies; many become liquefied when only a little of the chyme is extracted from them, others still live for a long time; in large animalcules, such as Stylonychia mytilus, Paramecium aurelia, etc, the sucking often continues for several hours.

Acineta tuberosa (Ehr.), attached to a stalk of Ceramium diaphanum.

Fig. 17. Acineta tuberosa (Ehr.), attached to a stalk of Ceramium diaphanum. The specimens marked α and s are fully expanded; y, side view of ditto; in δ the tentacula are seen in a partially, and in β in a fully contracted state. The three figures upon the opposite side of the stem of Ceramium represent Acineta mysticina.

(84). A number of roundish corpuscles, sometimes coloured, sometimes colourless, are generally found to occur diffused through the parenchyma of many Infusoria, which were considered by Ehrenberg as ova or spawn. The actual production of young from these corpuscles has, however, never yet been observed; and they are now believed to be nothing more than chyme-globules, which make their appearance after the digestion of food, as in the instance of the Acineta above-mentioned.

(85). A coloured gastric juice has been described by Ehrenberg as existing in the gastric cavities of some Infusoria. The colour has, however, been accounted for by Siebold as produced by refraction and the presence of aggregations of pigment-granules. According to Professor Henfrey the reddish-violet colour is real, and arises from the presence of solution of the chlorophyll of certain Oscillatorice.

(86). Two other organs remain to be mentioned which are common to all the Ciliated Infusoria, namely the "contractile space" and the "nucleus".

(87). The contractile space (seminal vesicle according to Ehrenberg) is regarded by many recent authors, in accordance with Dujardin's example, as a cavity destitute of proper walls (vacuole), which is sometimes supposed to form the analogue of a heart, and sometimes that of an excretory or respiratory water-vascular system. In order to be able to judge of these views, it will be necessary to examine rather closely into the behaviour of this "contractile space;" and for this purpose those Infusoria in which processes or branches derived from it can be detected appear to be particularly worthy of attention.