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·  Structural, physiological and behavioural modification in an organism, which enables it to survive and reproduce within the limits of a particular environment, is called adaptation. ·  In the words of Huxley , 'adaptation is omnipresent'. ·  It is mainly of three types: aquatic, terrestrial and amphibious. TYPES OF ADAPTATION 1. AQUATIC ADAPTATION ·  Animals living in water are called aquatic animals and their adaptation to the watery medium is called aquatic adaptation. ·  Aquatic animals are of two types: Primary and Secondary. a. Primary Aquatic Adaptation ·  Primary aquatic animals are evolved from aquatic ancestors and have never lived on land such as fishes, sponges, coelenterates, molluscs, echinoderms etc. ·  They are primitive gill-breathing vertebrates. ·  Body is streamlined to minimize water resistance during swimming. ·  Presence of median fins (dorsal, ventral and caudal- unpaired) - dorsal and ventral fins help ...

·  Response or an observable activity of an organism that responds to stimuli in its environment ·  All organisms respond to stimuli like light, heat, chemicals, temperature, pressure, electricity, gravity etc. ·  Ethology:   branch of biology that deals with animal behaviour. ·  Father of ethology:  Khorad Lorenz ·  Stimulus → Sense organs → Brain or Spinal cord → Muscles → Response Types of Behaviour i. Innate or Stereotyped or Instinct or Inborn behaviour ·  Inborn and is genetically controlled, independent of the experience and is determined by heredity. ·  Examples: reflexes, taxes, migration, courtship, mating, leadership, dominance etc. ii. Learned Behaviour ·  Acquired as a result of experiences during the lifetime of an organism to ensure better chances of survival in the changing environment. ·  It is not genetically controlled so never inherited. ·  Examples: dancing, singing, swimming, joking, play...