The following interesting account of the development of some of these germs is given by a careful experimental naturalist, M. Pouchet. He steeped darnel in water for one hour, then filtered the water and set it aside. On the next day a number of monads appeared on the surface of the filtered fluid. These were nearly all dead on the following day, and their bodies formed a thin granular scum on the surface. On the third day there began to appear some "œufs spontanées," first as little greenish-yellow clots formed of some of the granules of the scum. The central granules were larger and more compact than the rest, and the outside ones more delicate and exhibiting looseness of cohesion, forming, as the mass gradually assumed a spheroidal form, a kind of zona pellucida. This was more distinct in other specimens, and then the vitellus was seen in gyration. On the fourth day almost all the eggs were perfectly formed, and on the fifth day perfect Paramecia appeared.

In the lowest infusoria, such as the Bacteria, all these changes cannot be followed; but they are observed to appear in clots in a way quite inconsistent with the notion that they had been produced from eggs dropping accidentally from the surrounding air. The surface of a fluid in fermentation is seen to be covered with a delicate mucous film. In this film there appear all at once a number of pale motionless lines, nearly parallel to one another, and of the form and size of bacteria, and in a few hours they have developed into living and active infusoria.1 That eggs do float in the air has, however, been ascertained experimentally, by drawing a column of air through gun-cotton, and then dissolving the gun-cotton, when a number of small,

1 Pouchet: Nouvelles Expériences sur la Génération Spontanée, pp. 111-16; Paris, 1864.

round, or oval bodies, quite indistinguishable from the spores of minute plants and the ova of infusoria, were found.1

The question, therefore, remains as yet undecided, whence these early forms of life arise; but for their development it has been ascertained that three requisites must unite,organic matter, water, and air.

The cell is not the first living organism, however, for the Protozoa exhibit a still more rudimentary condition, consisting of homogeneous jelly-like substance; and the chief modification this undergoes consists in the consolidation of certain parts of it by the deposit of horny, calcareous or silicious matter. This may take place on the outer surface only, so as to form shells, or in the construction of an internal network, as in the sponge.

The Amoeba is an example of an organization at its lowest term, without the distinct differentiation into containing and contained parts necessary to constitute a cell. However inert this creature may seem when first glanced at, its possession of vital activity is soon made apparent by the movements which it executes and the changes of form it undergoes; these being, in fact, parts of one and the same set of actions. For the shapeless mass puts forth one or more finger-like prolongations, which are simply extensions of its gelatinous substance in those particular directions; and a continuation of the same action, just distending the prolongation, and then, as it were, carrying the whole body into it, causes the entire mass to change its place. When, in the course of its progress, it meets with a particle appropriate to its nutriment, its gelatinous body spreads itself over this, so as to envelope it completely; and the substance, sometimes animal, sometimes vegetable, thus taken

1 Pasteur: Mémoires sur les Corpuscules organisés; Paris, 1861.

into this extemporized stomach, undergoes a sort of digestion therein, the nutrient material passing into the substance of the sarcode, and any indigestible portion making its way to the surface, from some part of which it is, as it were, finally squeezed out."

1

Inherent in the primordial cell of every organism, whether it be vegetable or animal, and in all the tissues that are developed out of it, is a governing principle or force which, acting independently of the consciousness of the organism, and whether the latter be endowed with consciousness or not, builds matter into machines of singular complexity for a fixed, manifest, and apparently predetermined object—the preservation and perfection of the individual, and the continuance of the species.

This spontaneous force, for which it is difficult to select. a name, operates through and upon matter in three modes:

1. It moulds and compounds matter into living organisms.

2. It moves and regulates the motions of these organisms.

3. It acts-in those animals endowed with consciousness -through the vesicular neurine contained in the cranium, which it has already accumulated, and we have the phenomenon of thought.

In simple cellular animalcules this force is central. It has gathered the material of which the cell is composed from various parts. It organizes the particles, and marshals them as a general his host.

When a number of cells, each possessing the same properties, are combined into one mass, we have a living 1 Carpenter Animal Physiology, s. 129; London, 1867.

:

being without individuality: such is the yeast plant, and the hydra. They are rather societies of unicellular organisms than compound individuals.

But in higher types of plants, the functions of the cells are diversified. Some secrete colouring matter; others starch, gum, sugar, oil; and another the material for reproduction. In the higher animals, and in some vegetable organisms, the functions are more specialized, and are carried on by special apparatuses constructed for the purpose. Food is assimilated by one class, is carried thus assimilated to the molecular tissues by another; the results of waste and repair are carried off by machinery adapted to the purpose; the germ-cells and sperm-cells are developed also in special tissues-the reproductive organs. There are also apparatuses for the prehension of food, for the supply of the oxidizing material, &c.

All these require to be combined in action for the attainment of the objects of the organism as a unity, and we have therefore a special apparatus formed for this end, in which that unconscious force, previously, and indeed still, present alike in all the cells, is now specially localized: this apparatus is the nervous system.

In the invertebrate sub-kingdom is seen the simplest form of nervous system, which consists of distinct ganglia with commissural cords and nerves, administering to the functions of automatic life.

A nerve consists of two portions, one vascular, the other fibrous. The function of the vascular portion is to convey impressions inwards, that of the fibrous portion is to reflect the impressed force outward, resolving it into muscular action.

The simplest mode of action is when an impression made on the afferent nerve thrills to the ganglionic centre in

which the nerve terminates, when it alters its direction, and is shot down the motor nerve which sets the muscles in operation, and at once discharges the force received.

This action is simply reflex.

Thus a force A acting on the afferent nerve becomes B, which is precisely equivalent in amount to the force A. The nervous system of the lower organisms is simply one of reflex action.

If the ganglion be one through which consciousness is necessarily affected, sensation becomes a necessary link in the circle, and the action is then called consensual.

Sensation is the lowest form of mental action. The next stage is that called ideo-motor action, in which the sensation is resolved into an idea, and the idea sets the muscles in operation, if the will approves, and expends the force received, or else stores it up for future expenditure.

In the lowest organisms that have nervous apparatuses each ganglion has the same function as any other. In the Radiata the nervous system consists of a ring around the mouth, with ganglia at the base of each ray. Each of these ganglia is precisely similar in character to all the others.

In the Mollusca, which inhabit univalve shells, there is no such repetition of parts, but there is a single ganglion, or, if the creature have a foot, there is added a special pedal ganglion, united by a commissure to the main ganglion.

It has reference

In the Conchifera, inhabiting bivalve shells, there are at least two ganglia, generally three or four. Of these one is posterior to the others, and is of large size. to the hinge of the valves. It is the branchial ganglion, the seat of muscular action, whilst the smaller ganglia in the forepart are the seats of sensation. Through these the animal receives impressions, which it communicates to