Number, shape and size of nucleus

Physical Basis of Heredity 1.  The Nucleus and the Chromosome
The Nucleus 
Significance of nucleus : Hammerling's experiment
Number, shape and size of nucleus
Nucleus in prokaryotes and eukaryotes
Nuclear envelope
Nuclear pore complex and nucleocytoplasmic traffic
Number, size and shape of chromosomes
Morphology of chromosomes
Euchromatin and heterochromatin
Constitutive and facultative heterochromatin
Single-stranded and multi-stranded hypotheses for chromosomes
Chemical composition of chromosomes
Infrastructure of chromosomes
Function of chromosomes
Special types of chromosomes 
Lampbrush chromosomes
Salivary gland chromosomes
Prokaryotic Nucleoids

Generally there is a single nucleus per cell (mononucleate conditions), but more than one nucleus (polynucleate condition) may be found in certain special cases. There may be many nuclei in a syncytium, which is formed due to fusion of cells. A similar multinucleate situation is found in coenocytes commonly found in plants. A coenocyte results by repeated nuclear divisions without cytokinesis.

There are variations with respect to shape of nucleus also. It may be spherical, oval to flattened lobe or irregular in shape. In most cases it has a regular outline, but may also have irregular outline. Shape of nucleus also depends on the cell. In spheroid, cuboid or polyhedral cells, nucleus is usually spheroid. In cylindrical, prismatic or fusiform cells, nucleus is ellipsoid. Irregular nuclei are sometimes found in some neutrophylls or leukocytes and branched nuclei are sometimes found in glandular cells. In still other cases like spermatozoa, pyriform or lanceolate nuclei may be found.

Size of the nucleus would also vary not only depending upon the type of cell involved but also according to activity of cell. The nucleus will be larger in an active cell, but will be smaller in a resting cell.