ANIMALS

The animals are living objects  with heterotrophy , rapid responsiveness ,very high level of adaptability  and a compact body  that grows only  upto a certain age   and lacks  chlorophyll  and cellulose .They  have definite  shapes and different level of body organization , in habit different parts of the  environment  and form association  with other living organisms.                 Shapes of body  ;Most  animals have definite shape  of their body and each animal is usually  recognised by the shape of its body .The shape of the body is  expressed  in term of symmetry, depending  on which the body shape  is of the following two types ;                                                      [1] Symmetrical .When  parts of the body are  arranged in such a pattern  that it can cut  into two equal halves  through one or more planes   the body is said to be   symmetrical [regular in shape] .                                           [2] Asymmetrical .If  the body parts are arranged  in such a way that the body can not  be cut into two equal halves  through  any plane , the body is said to be asymmetrical[irregular in shape] .Amoeba  and few other animals  have asymmetrical body .                                                                  The  symmetry of  the body  may be spherical  ,bilateral or radial. A ball- shaped body  has spherical  symmetry .It can be cut into two equal halves along the longitudinal  axis ,it is said to be  bilaterally symmetrical .The body of man  bilaterally symmetrical .The earthworm  and frog also show  similar  symmetry .Some animals  have abody  in which  body part radiate  out from the centre  ,it is said to be radially symmetrical .The bodty of star fish is radially symmetrical  and so is the body  of Aurelia  and hydra [both coelenterates].                                                                                                                                                                   The symmetry of the body  is associated with the polarity  and surfaces  of the body .The  distinction of  anterior and posterior  ends in the body  is called polarity  of the body .The  end of the body  that remain  toward the direction  of the movement  is called anterior end  and the end opposite  to this  end   is said to be the posterior end  of the body .The anterior end  is  characterised by the  presence of mouth  and the posterior   end by the  presence  of cloacal  aperture  or anus .Besides , the anterior  and posterior end ,two more ends ,the proximal and distal  ends are also referred  in context of the  description of the body  or an organ .The proximal end  is the end near the point  under reference ,whereas the distal end  is away from the point under reference .The  terms  proximal  and distal  are also  used as prefix to parts .                              Three surfaces  are distinguishable in the body  which remains towards  sky or away from the body  of most animals ;these include dorsal , ventral and lateral .The  surface of the body  which remains  towards sky or  away from the substratum  during the movement is called  dorsal surface  lies between the  dorsal ventral  surfaces on  the sides .It is  represented  by  right and left sides  of the body.In man the head end  is anterior end  and anal end  the posterior end .The  back of the human body  is dorsal surface , whereas the dorsal chest  is the ventral surface .