When the nematocyst is completely developed, the cnidoblast passes outwards so as to occupy a superficial position in the ectoderm, and a delicate protoplasmic process of sensory nature, termed the cnidocil (cn) projects from the cnidoblast like a fine hair or cilium.
The sensory cells are slender epithelial cells, often with a cilium or stiff protoplasmic process, and should perhaps be regarded as the only ectoderm-cells which retain the primitive ciliation of the larval ectoderm, otherwise lost in all Hydrozoa.
The cell is essentially an individualized mass of protoplasm containing a differentiated protoplasmic body, called a nucleus.
In the Algae such a cell consists essentially of: (1) a mass of protoplasm provided with (2) a nucleus and (3) an assimilating apparatus consisting of a colored protoplasmic body, called a chromatophore, the pigment of which in the pure green forms is chlorophyll, and which may then be called a cliloroplast.
In a second type they are situated at the ends of tracheal strands and consist of groups of richly protoplasmic cells belonging to the epidermis (as in the leaves of many ferns), or to the subjacent tissue (the commonest type in flowering plants); in this last case the cells in question are known as epithem.
The conjoined organism is, in fact, a colony or association of the protoplasmic tinits, though each unit retains its independence.
Every plant is thus found to be composed of a number of these protoplasmic units, or, as they may preferably be termed, proloplasts, all of which are at first exactly alike in appearance and in properties.
Two features which are essentially protoplasmic assume a great importance when we consider these relations.
Communication between the various protoplasts of the colony is, however, carried on by means of fine protoplasmic threads, which are continuous through the cell-walls.
It consists essentially of a number of minute corpuscles or plastids, the protoplasmic substance of which is impregnated with a green coloring matter.
Each is a small protoplasmic body, in the meshes of whose vubstance the green coloring matter chlorophyll is contained in some form of solution.
Again, the degree of differentiation is very slight anatomically, but delicate protoplasmic threads have been shown to extend through all cell-walls, connecting together all the protoplasts of a plant.
But even when inside it does not follow that the Fungus can kill the cell, and many cases are known where the Fungus can break throtigh the cells first lines of defence (cell-wall and protoplasmic lining); but the struggle goes on at close quarters, and various degrees of hypertrophy, accumulation of plastic bodies or secretions, discolorations, &c.,, indicate the suffering of the still living cell.
Protoplasmic Movements.In the cells of many plants the cytoplasm frequently exhibits movements of circulation or rotation.
All directions, numerous protoplasmic threads or bridges.
Chromatophores.The chromatophores or plastids are protoplasmic structures, denser than the cytoplasm, and easily distinguishable from it by their color or greater refractive power.
These layers arc secreted by the protoplasm by the direct apposition of substances on those already in existence; and they may go on increasing in thickness, both by apposition and by the intussusception of particles probably carried in through the protoplasmic fibres, which penetrate the cell-wall as long as the cell lives.
Organs which respond to the mechanical stimulus of contact are found to possess special contrivances in certain of their cells(I) sensitive spots, consisting of places here and there on the epidermal cells where the wall is thin and in close contact with protoplasmic projections.
Tissues.The component parts of the tissues of which plants are composed may consist of but slightly modified cells with copious protoplasmic contents, or of cells which have been modified in various ways to perform their several functions.
In some the protoplasmic contents may persist, in others they disappear.
The walls are pitted, and protoplasmic connections between the laticiferous tubes and neighboring parenchyma-cells have been seen.
The nuclei of the original cells persist in the protoplasmic membrane.
The mode of formation of the sieve plate is not certainly known; but from the fact that delicate connecting threads of protoplasm are present between the cells from their first development it is probable that it is a special case of the normal protoplasmic continuity, the sieve pores being produced by a secondary enla~gement of the minute openings through which these delicate strands pass.
If this is correct it is easy to see that the changes which take place may be initiated by the original delicate protoplasmic strands which pass through the cellwall.
Protoplasmic Continuity.Except in the unicellular plants the cell is not an independent unit.
These protoplasmic strands are, except in the _______ case of sieve tubes, so delicate that special methods have to be employed _______ to make them visible.
The lateral eyes are in Limulus " compound eyes," that is to say, consist of many lenses placed close together; beneath each lens is a complex of protoplasmic cells, in which the optic nerve terminates.
By it a new heredity, free from the limitations of protoplasmic continuity, is established.
Educability, defects or excellences, or peculiarities of mind or body, can be handed on from parent to offspring by protoplasmic continuity in reproduction.
The new matter taken in to make good this constant loss is either a ready-formed protoplasmic material, supplied by some other living being, or it consists of the elements of protoplasm, united together in simpler combinations, which consequently have to be built up into protoplasm by the agency of the living matter itself.
Note that these phagocytic cells are pushing out protoplasmic processes (pseudopodia) by which they grasp their victims. (X woo diam.) FIG.
Hydrocyanic acid is a protoplasmic poison, directly lethal to all living tissues, whether in a plant or an animal.
They are often devoid of hyphae, or put forth fine protoplasmic filaments into the cells of their hosts.
Any one of these soon comes to rest on a host-cell, and either pierces it and empties its contents into its cavity, where the further development occurs (Olpidium), or merely sends in delicate protoplasmic filaments (Rhizophydium) or a short hyphal tube of, at most, two or three cells, which acts as a haustorium, the further development taking place outside the cell-wall of the host (Chytridium).
On the other hand, the uniciliate zoospores of Polyphagus have slightly amoeboid movements, and in this and the pseudopodium-like nature of the protoplasmic processes, such forms suggest resemblances to the Myxomycetes.
The various cells of these organisms are connected by large pits which are traversed by thick protoplasmic threads connecting one cell with the next.
Penicillus is brush-like, example, there is a marked protoplasmic continuity between all the Halimeda and Cymopolia are jointed, Acetabularia has much the same cells of the colony.
Protoplasmic continuity has been observed in the delicate membrane closing the pit.
The attachment of the cell of an ooblastema filament to a cell of the thallus may be effected by means of a minute pore, or the two cells may fuse their contents into one protoplasmic mass.
==Toxicology== Antimony is one of the "protoplasmic" poisons, directly lethal to all living matter.
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.
Hydrocyanic acid is a general protoplasmic poison, all the lower organisms being very susceptible to its action, while in the higher animals it speedily depresses or paralyses all forms of nerve tissue.