The following points highlight the top six theories regarding the origin of metazoa. The theories are: 1. Syncytial-Ciliate Theory 2. Colonial Flagellate Theory 3. Colonial Blastea and Planula Theories 4. Gastraea Theory 5. Monophyletic Origin of Metazoans 6. Polyphyletic Origin of Metazoans. 1. Syncytial-Ciliate Theory: The origin of metazoans probably took place through the growth, nuclear division and cellularisation of [...]
The below mentioned article provides a detailed account of Metazoa. Protozoa are acellular animals of small size, they have a permeable limiting membrane which prevents the animals from growing beyond a certain size, and it precludes the formation of structures which will give strength and rigidity necessary for large size. But more important than strength is the factor that the [...]
In this article we will discuss about Coelenterata:- 1. History of Coelenterata 2. General Characters of Coelenterata 3. Classification 4. Tissues 5. Polyp and Medusa 6. Polymorphism 7. Corals. Contents: History of Coelenterata General Characters of Coelenterata Classification of Coelenterata Tissues of Coelenterata Polyp and Medusa of Coelenterata Polymorphism of Coelenterata Corals of Coelenterata 1. History of Coelentrata: Aristotle knew [...]