The relationship between metagenesis and polymorphism has raised the question—is metagenesis an outcome of polymorphism or has it lead to the emergence of polymorphism? A discussion on the existence of different grades of metagenesis in cnidarians will help us to find a logical answer. Gradations of Metagenesis: Four different forms of life-histories are seen in the cnidarians which exhibit a [...]
The following points highlight the two main types of polymorphic variabilities in Siphonophora. 1. Modifications of the Polyp: A. Gastrozooids or Trophozooids or Nutritive Zooids: Characters: 1. It is like a typical polyp (Fig. 12.34A,B). 2. Each gastrozooid is a cylindrical and funnel-shaped body with a large mouth. 3. Presence of a well-formed coelenteron. 4. A single long contractile and [...]
In this article we will discuss about Hydra:- 1. Habit and Habitat of Hydra 2. Structure of Hydra 3. Structure and Function of the Different Cellular Units 4. Locomotion 5. Nutrition 6. Respiration and Excretion 7. Reproduction 8. Life History. Contents: Habit and Habitat of Hydra Structure of Hydra Structure and Function of the Different Cellular Units of Hydra Locomotion [...]