The nerve-cells are bodies of rounded, oval, or irregular form, varying greatly in size, but always microscopic, and having an average diameter of about 1-2000th of an inch. Each cell contains in its interior a small but important structure, named the " nucleus", lying in a mass of finely fibrillated protoplasm, and itself containing a still smaller particle, named the "nucleolus". The surface of the nerve-cell is sometimes smooth, and gives off one or two fine filamentous processes; in some instances, however, many such processes shoot from it. These divide and subdivide as they recede from the cell, and either join with or enter into very close relation with the processes from other cells. In most, if not in all cases, one of the processes is larger and longer than the rest. If traced for some distance it may be seen to become a true nerve-fibre, which may terminate in a muscle or in a gland, or in one of the organs of sense - ear, eye, nose, etc. - or may serve to bring two nerve-cells into connection with each other.