A reddish-brown body, known as the eyespot, is usually situated near the limits of the hyaline portion, and in the protoplasm contractile vacuoles similar to those of lower animals have been occasionally detected.
Young cells ar full of cytoplasm, old cells generally contain a large vacuole or vacuoles, containing cell-sap, and with only a thin, almost invisible layer of cytoplasm on their walls.
Within the cytoplasm are found manifestations of functional activity, in the form of digestive vacuoles, granules, fat, glycogen, pigment, and foreign bodies.
W.) The substance of the bacterial cell when suitably prepared and stained shows in the larger forms a mass of homogeneous protoplasm containing irregular spaces, the vacuoles, which enclose a watery fluid.
Evidence is not wanting, however, that the cytoplasm must be regarded as, fundamentally, a semifluid, homogeneous substance in which by its own activity, granules, vacuoles, fibrils, &c., can be formed as secondary structures.
It can develop vacuoles, or rather fine bubbles of carbonic acid gas in its cytoplasm, to float up to the surface of the water.
The cells of fungi, in addition to protoplasm, nuclei and sap-vacuoles, like other vegetable cells, contain formed and amorphous bodies of various kinds.
In the first place, the extremely small size and isolation of the vegetative cells place the protoplasmic contents in peculiarly favourable circumstances for action, and we may safely conclude that, weight for weight and molecule for molecule, the protoplasm of bacteria is brought into contact with the environment at far more points and over a far larger surface than is that of higher organisms, whether - as in plants - it is distributed in thin layers round the sap-vacuoles, or - as in animals - is bathed in fluids brought by special mechanisms to irrigate it.
Besides the other spaces are definite rounded or oval vacuoles with a permanent pellicular wall termed by Schutt " pusules "; these open by a duct or ducts into the longitudinal groove.
They enlarge and diminish, and are possibly excretory like the " contractile vacuoles " of other Protista; though it has been suggested that by their communication with the medium they subserve nutrition.