Cellular Differentiation, Ontogeny and Molecular Biology

Abstract

There is a vast array of different cell types within the animal kingdom. There are probably more than 200 discinct cell types, and many of these include a number of different varieties (Alberts et al., 1983). In gross visual terms they are recognized in different species, either of Protozoa or Metazoa, at different levels of evolutionary structural and functional complexity. In animals throughout ontogeny, cellular diversity is clearly recognizable at the level of light microscopy. Visualized under the electron microscope, cells contain what would appear to be a multitude of subcellular organelles of infinite complexity, which by virtue of their number, arrangement, and disposition confer upon the cell its distinctive ultrastructural specificity.