Whales and dolphins

Introduction: Whales and dolphins are the animals which are included under the order Cetacea of class mammalia. They come under the phylum chordata.
Habit and habitat : Whales and dolphins are found in all seas. Few of them also live in rivers and lakes. They are carnivorous and predaceous in habit. They are found to be swimming with great strength.
Structure : Body of these animals is fish -like and stream-lined. Scales are lacking. So, the body is naked. But a thick layer of fat is present below the skin in subcutaneous layer. It is also known as blubber . Nasal apertures are found on the top of the head region. Caudal fin or tail fin is expanded horizontally expanded. Their dorsal fin is fatty. They have minute external ear. But pinna are absent. Eyes are very small and are situated at the angle of the mouth. Their body size ranges from small five feet to hundred feet in length and about 150 ton in weight. Whales are the largest animals in the animal kingdom. They are even larger than the dinosaurs. These animals are descended from the land living ancestors and use to breathe air by coming to the surface frequently.

Rhinoceros unicornis

Rhinoceros unicornis is one of the huge animal. It belongs to the order perrisodactyla of class mammalia. This is the huge bodied mammal. Its distribution is in African continent as well as in the Asian continent. In Asia this animal is found in the countries like India, Nepal and Nepal. It is also found to be distributed in the south east countries like Indonesia , Sumatra etc.
Rhinoceros has the huge body with tons of weight. Its body is divisible into head, neck. trunk and tail. Head hinregion consists of special horn which is epidermal in origin. The name Rhinoceros unicornis signifies to the presence off single horn in its head region. Some rhinoceros have two horns in the head region. They are known as Rhinoceros bicornis. Rhinoceros bicornis or two horned Rhino are found to be distributed in a the African continent but not in Asian continent. But single horned Rhino is distributed in Asian continent but not in Africa.
Single horned Rhino which is distributed in Asia is found mainly in the dense forests of the tropical countries like Nepal.

Introduction of amphibian animals

Amphibian animals are those animals which live in the two different types of habitat, the aquatic habitat and the terrestrial habitat or land. These animals need the aquatic habitat at the time of breeding season. Some amphibians are more terrestrial than others. Toads are the amphibians which are more terrestrial. Other amphibians are more aquatic than other amphibians. For example frog is the amphibian which is more aquatic in habitat. There are other amphibians which have tail in their body and which swim in water y and look like the fish or like the larva of frog. Anyway amphibian animals have the important characters like :
- They have stream-lined body shape
- They have thin and moist skin which helps them in cutaneous respiration
- They also respire through the lungs when they are in the adult stage and when they need more oxygen like in breeding season and in the time of high metabolic rate.
- They have the body colour which harmonise them in the surrounding environment-

Introduction of 'Dipnoi'

Dipnoi are also called lung fishes. They have the peculiar character. They first appeared in the mid Devonian deposits, flourished in Permian and Triasic period and became rare. They are actually the  fishes having the skeleton made up of bones . They belong tot he subclass choanichthyes. Actually all the fishes use to respire with  the help of gills but the most interesting and peculiar character of  these fishes is that they have lungs by which they breathe in oxygen during respiration. The living Dipnoans are represented by three genera only. These show the discontinuous distribution. These genera are the following:
1.Protopterus from Africa, 2. Lepidosiren from South America and 3. Neoseratodus from Queensland - Australia.
Dipnoi are so known as lung fishes that they have air filled bladder like structures in their body called air bladder which act as lung. These fishes also possess gills. So, these fishes exhibit the double mode of breathing, i.e. breathing from gills and breathing from lungs or air bladder.

How animals communicate ?

Animals use different methods to communicate with one another. Dogs use to bark and show their communication to their fellow dogs. Mouse vibrates its tail so as to communicate with other mouse. Bee which are the insects use to produce a unique sound to give the signal of presence of some sweet fragrance of flowers in a particular direction. Crows and other birds produce the special sound to give the signal of communiacation with other birds.  Parrots make the sweet call as a method of communication. The communication of animals is for the purpose of giving signal to their own fellow species  and the other purpose is to give signal to the other species and to human beings also. communication of animals is usually nonverbal. Some animals use to communicate just by their body language. They use to make the fast or the slow movement of the body and some times come close to the human beings. Some animals use tom gaze at the other animals and also with human beings. Gazing at a point is also one of the form of communication which is seen usually among the cattles.

Animal behaviour

Definition: Animal behaviour can be defined as the activity of the animals in response to a particular type of environmental stimulus. Animal behaviour is mainly of the two types:
(1) The simple type of animal behaviour and
(2) The complex type of animal behaviour

Simple type of animal behaviour: Simple type of animal behaviour is that behaviour which takes place automatically and without any will. It is also of two types.
 a. Reflexes and b. Taxes
:Reflexes: Reflexes are the animal behaviour which is considered to be of the simple type. It takes place in the higher animals as well as the lower animals. Reflexes can be defined as the automatic activity which occurs without any will. It is also known as the involuntary activity of animals without any will There are different types of reflexes which are- Protective reflexive, anti gravity reflex, righting reflex and the conditioned reflex.
 The protective reflex is that in which the sudden acitivity is shown to protected the stimulated part of the body. For example, sudden withdrawl of one's hand when it touches any hot surface or hot object. In this activity a reflex arc is formed during this type of reflex. This reflex arc involves the different nervous components arranged in a cyclical  pattern. The various nervous components involved in this arc are the receptor organ, sensory neurons, spinal cord, brain, response the motor neuron and the effector organs.