The domain of single-celled organisms embraces a tremendous diversity of forms and modes of development. It illustrates how varied is the differentiation of which single cells are capable and the great extent to which an organism can establish separate functional structures without dividing itself into cells. The course of development in an individual cell and in a sequence of cell generations can be laid out in a strict sequence and thus lead directly to often highly complicated forms when the organism does not have to cope with a variable environment. This is the case for Radiolarians and Foraminiferans, which hardly ever experience any change in the milieu of the ocean, and for Sporozoans and other organisms placed in a rigidly prescribed series of environmental transitions which determine form and method of reproduction.
KeywordsMating Type Nuclear Division Generative Nucleus Contractile Vacuole Gamete Formation
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