STRUCTURAL ORGANISATION OF ANIMALS
Introduction
·
The variety in nature and habits
of animals in the biosphere are quite amazing and interesting
·
The scientific name of the Indian
cattle leech is Hirudinaria granulosa which belongs
to Phylum Annelida.
·
Annelids are metamerically
segmented worms with well developed organ systems.
·
The scientific name of the common
rabbit is Oryctolagus cuniculus.
·
It represents Phylum Chordata and
Class Mammalia.
·
They are warm blooded and possess
covering of hair on the body.
The Indian
Cattle Leech (Hirudinaria granulosa)
|
Taxonomic Position |
|
|
Phylum |
Phylum Annelida |
|
Class |
Hirudinea |
|
Order |
Gnathobdellida |
|
Genus |
Hirudinaria |
|
Species |
granulosa |
Habit and Habitat
·
Hirudinaria
granulosa (Indian Cattle Leech) is found in India, Bangladesh, Pakistan,
Myanmar and Srilanka.
·
It lives in freshwater ponds,
lakes, swamps and slow stream.
·
They are ectoparasitic
and feed on the blood of fishes, frogs, cattle and human.
·
It is sanguivorous
(blood sucking) in nature.
External Morphology
Divisions of the Body
|
Region |
Segments |
|
Cephalic region |
1st – 5th |
|
Pre-clitellar region |
6th,7th,8th |
|
Clitellar region |
9th,10th,11th |
|
Middle region |
12th – 22nd |
|
Caudal region |
23rd – 26th |
|
Posterior sucker |
27th – 33rd |
Structure
Body wall
Body wall
of leech includes five layers:
·
cuticle
(outermost layer).
·
epidermis
which lies below the cuticle.
·
dermis
which lies below the epidermis formed of connective tissue.
·
muscular
layer formed of circular and longitudinal muscles.
·
botryoidal
tissue lies beneath longitudinal muscles and fills the entire coelom around the
gut.
Locomotion
Looping
or Crawling movement
·
The contraction and relaxation of muscles.
·
Two suckers serve for attachment during
movement on a substratum.
Swimming movement
·
Swim very actively.
·
Perform undulating movements in
water.
Digestive System
·
long alimentary canal
·
the digestive glands
Alimentary
Canal
·
The alimentary canal of leech is
a straight tube running from the mouth to the anus.
·
Mouth is a triradiate
aperture situated in the middle of the anterior sucker that leads into the
small buccal cavity
·
The jaws are provided with
papillae which bear the openings of salivary glands.
·
The buccal cavity leads into
muscular pharynx.
·
The secretion of saliva contains hirudin which prevents the coagulation of blood.
·
Pharynx leads into crop through a
short and narrow oesophagus.
·
Crop is the largest portion of
the alimentary canal. It is divided into a series of 10 chambers.
·
The chambers communicate with one
another through circular apertures surrounded by sphincters
·
A pair of lateral, backwardly
directed caecae arises as blind outgrowth from each
chamber known as caeca or diverticula.
·
The stomach leads into intestine
which is a small straight tube that opens into rectum. The rectum opens to the
exterior by anus.
Food,
Feeding and Digestion
·
The leech feeds by sucking the
blood of cattle and other domestic animals.
·
The leech makes a triradiate or Y shaped incision in the skin of the host by
the jaws protruded through the mouth.
·
The blood is sucked by muscular
pharynx and the salivary secretion is poured.
·
The ingested blood is stored in
crop chambers and its diverticulum.
·
Digestion takes place in stomach
by the action of proteolytic enzyme.
·
The digested blood is then
absorbed slowly by the intestine. Undigested food is stored in rectum and
egested through anus.
·
Leeches prevent blood clotting by
secreting a protein called hirudin. They also inject
an anaesthetic substance that prevents the host from
feeling their bite.
Segmentation of Leech
|
External and Internal features |
Segments in which the structures are present |
|
Body segments |
33 |
|
Anterior Sucker, Mouth, Eyes |
1 - 5 |
|
Posterior sucker |
27 - 33 |
|
Pharynx |
5 - 8 |
|
Crop |
9 - 18 |
|
Stomach |
19 |
|
Intestine |
10 - 22 |
|
Rectum |
23 - 26 |
|
Anus |
26 |
|
Nephridiopores |
6 – 22 |
|
Male genital aperture |
10 |
|
Female genital aperture |
11 |
Respiratory System
·
Respiration takes place through
the skin in leech.
·
Dense network of tiny blood
vessels called as capillaries containing the haemocoelic
fluid extend in between the cells of the epidermis.
·
The exchange of respiratory gases
takes place by diffusion.
·
The skin is kept moist and slimy
due to secretion of mucus which also prevents it from drying.
Circulatory System
·
In leech, circulation is brought
about by haemocoelic system.
·
The blood vessels are replaced by
channels called haemocoelic channels or canals filled
with blood like fluid.
·
The coelomic
fluid contains haemoglobin.
·
There are four longitudinal
channels.
·
One channel lies above (dorsal)
the alimentary canal, one below (ventral) the alimentary canal.
·
The other two channels lie on
either (lateral) side of the alimentary canal which serve as heart and have
inner valves.
·
All the four channels are
connected together posteriorly in the 26th segment.
Nervous System
·
The central nervous system of
leech consists of a nerve ring and a paired ventral nerve cord.
·
The nerve ring surrounds the pharynx
and is formed of suprapharyngeal ganglion (brain), circumpharyngeal connective and subpharyngeal
ganglion.
·
The subpharyngeal
ganglion lies below the pharynx and is formed by the fusion of four pairs of
ganglia.
Excretory System
·
In leech, excretion takes place
by segmentally arranged paired tubules called nephridia.
·
There are 17 pairs of nephridia which open out by nephridiopores
from 6th to 22nd segments.
Reproductive System
·
Leech is hermaphrodite because
both the male and female reproductive organs are present in the same animal.
Male Reproductive System
·
There are eleven pairs of testes,
one pair in each segment from 12 to 22 segments. They are in the form of
spherical sacs called testes sacs.
·
From each testis arises a short
duct called vas efferens, which join with the vas
deferens. The vas deferens becomes convoluted to form the epididymis or sperm
vesicle, to store spermatozoa.
·
The epididymis leads to a short
duct called ejaculatory duct.
·
The ejaculatory ducts on both
sides join to form the genital atrium.
·
The atrium consists of two
regions, the coiled prostate glands and the penial sac consisting of penis that
opens through the male genital pore.
Female Reproductive System
·
It consists of ovaries, oviducts
and vagina.
·
Each ovary is a coiled
ribbon-shaped structure.
·
The ova are budded off from the
ovary. From each ovary runs a short oviduct.
·
The oviducts of the two sides
joins together, to form a common oviduct.
·
The common oviduct opens into a
pear-shaped vagina which lies mid-ventrally in the posterior part of the 11th
segment.
Development
·
Internal fertilization takes
place. This is followed by cocoon formation. Cocoon is also known as egg case
which is formed around the 9th, 10th and 11th segments.
·
Development is direct and
proceeds in cocoon which contain one to 24 embryos.
·
Young leech resembling the adult
emerges.
Parasitic Adaptations of Leech
·
Blood is sucked by pharynx.
·
Anterior and posterior ends of
the body are provided with suckers by which the animal attaches itself to the
body of the host.
·
The three jaws inside the mouth,
causes a painless Y-shaped wound in the skin of the host.
·
. The salivary glands produce hirudin which does not allow the blood to coagulate. Thus,
a continuous supply of the blood is maintained.
·
Parapodia
and setae are completely absent.
·
Blood is stored in the crop. It
gives nourishment to the leech for several months. Due to this reason there is
no elaborate secretion of the digestive juices and enzymes.
Rabbit (Oryctolagus
cuniculus)
|
Taxonomic Position |
|
|
Phylum |
Chordata |
|
Sub-phylum |
Vertebrata |
|
Class |
Mammalia |
|
Order |
Lagomorpha |
|
Genus |
Oryctolagus |
|
Species |
cuniculus |
Habit and Habitat
·
Rabbits are gentle and timid
animals.
·
They are herbivorous animals
feeding on grass and vegetables like turnips, carrots and lettuce.
·
Rabbits are gregarious (moving in
groups) animals.
External Morphology
Coelom (Body cavity)
·
Rabbit is a coelomate animal.
·
The body is divisible into
thoracic cavity and abdominal cavity separated by transverse partition called
diaphragm.
·
Diaphragm is the characteristic
feature of mammals.
·
Lungs and heart lie in the
thoracic cavity, whereas, abdominal cavity encloses digestive and urinogenital system.
Digestive System
·
The digestive system includes the
alimentary canal and the associated digestive gland.
·
The alimentary canal consists of
mouth, buccal cavity, pharynx, oesophagus, stomach,
small intestine, caecum, large intestine and anus.
·
Mouth is a transverse slit
bounded by upper and lower lips.
·
It leads into the buccal cavity.
The floor of the buccal cavity is occupied by a muscular tongue. Jaws bear
teeth.
·
Oesophagus
opens into the stomach followed by small intestine.
·
Caecum is a thin walled sac
present at the junction of small intestine and large intestine.
·
It contains bacteria that helps
in digestion of cellulose.
·
The small intestine opens into
the large intestine which has colon and rectum. The rectum finally opens
outside by the anus.
Digestive glands
·
The digestive glands are salivary
glands, gastric glands, liver, pancreas and intestinal glands.
·
The secretions of digestive
glands help in digestion of food in the alimentary canal.
Dentition in Rabbit
·
Teeth are hard bone-like
structures used to cut, tear and grind the food materials.
·
The rabbit has two sets of teeth.
·
The existence of two sets of
teeth in the life of an animal is called diphyodont
dentition.
·
The two types of teeth are milk
teeth (young ones) and permanent teeth (in adults).
·
In rabbit the teeth are of
different types. Hence, the dentition is called heterodont.
·
There are four kinds of teeth in
mammals viz. the incisors (I), canines (C), premolars (PM) and molars (M). This
is expressed in the form of a dental formula.
·
The number of each kind of tooth
in the upper and the lower jaws on one side is counted.
·
The dental formula is 
·
In rabbit it is written as 
·
The gap between the incisors and
premolar is called diastema.
Respiratory System
·
Respiration takes place by a pair
of lungs, which are light spongy tissues enclosed in the thoracic cavity.
·
On the lower side of the thoracic
cavity is the dome shaped diaphragm.
·
Each lung is enclosed by a double
membranous pleura.
·
The anterior part of the wind
pipe is enlarged to form the larynx or voice box with its wall supported by
four cartilaginous plates.
·
Inside the larynx lies the vocal
cord and its vibrations result in the production of sound. The larynx leads
into trachea or wind pipe.
·
The epiglottis prevents the entry
of food into the trachea through the glottis.
·
The trachea divides into two
branches called the bronchi one entering into each lung and dividing into
further branches called bronchioles which end in alveoli.
·
The respiratory events consist of
inspiration (breathing in) and expiration (breathing out) allowing exchange of
gases (oxygen and carbon dioxide).
Circulatory System
·
The circulatory system is formed
of blood, blood vessels and heart.
·
The heart is pear shaped and lies
in the thoracic cavity in between the lungs. It is enclosed by pericardium, a
double layered membrane.
·
The heart is four chambered with
two auricles and two ventricles.
·
The right and left auricles are
separated by interauricular septum, similarly right
and left ventricles are separated by interventricular septum.
·
The right auricle opens into the
right ventricle by right auriculoventricular
aperture, guarded by a tricuspid valve.
·
The left auricle opens into the
left ventricle by left auriculoventricular aperture
guarded by a bicuspid valve or mitral valve.
·
The opening of the pulmonary
artery and aorta are guarded by three semilunar valves.
·
The right auricle receives
deoxygenated blood through two precaval (superior
vena cava) and one postcaval (inferior vena cava)
veins from all parts of the body.
Nervous System
·
The nervous system in rabbit is
formed of the central nervous system (CNS), peripheral nervous system (PNS) and
autonomic nervous system (ANS).
·
CNS consists of brain and spinal
cord. PNS is formed of 12 pairs of cranial nerves and 37 pairs of spinal
nerves. ANS comprises sympathetic and parasympathetic nerves.
·
Brain is situated in the cranial
cavity and covered by three membranes called an outer duramater,
an inner piamater and a middle arachnoid membrane.
·
The brain is divided into
forebrain (prosencephalon), midbrain (mesencephalon)
and hindbrain (rhombencephalon).
·
The right and left cerebral
hemispheres are connected by transverse band of nerve tissue called corpus
callosum.
·
The midbrain includes the optic
lobes.
·
The hindbrain consists of the
cerebellum, pons varolii and medulla oblongata.
Urinogenital System
It
comprises the urinary or excretory system and the genital or reproductive
system. Therefore, they are usually described as urinogenital
system in vertebrates.
Excretory system
·
Each kidney is made of several
nephrons. It separates the nitrogenous wastes from blood and excretes it in the
form of urea.
·
From each kidney arises the
ureters which open posteriorly into the urinary bladder and leads into a thick
walled muscular duct called urethra.
Reproductive System
·
Sexual dimorphism is exhibited in
rabbits. The male and female sexes are separate and are morphologically
different.
Male Reproductive system
·
The male reproductive system of
rabbit consists of a pair of testes which are ovoid in shape.
·
Each testis consists of numerous
fine tubules called seminiferous tubules.
·
This network of tubules lead into
a coiled tubule called epididymis, which lead into the sperm duct called vas
deferens.
·
There are three accessory glands
namely prostate gland, cowper’s
gland and perineal gland. Their secretions are involved in reproduction.
Female reproductive system
·
The female reproductive system of
rabbit consists of a pair of ovaries which are small ovoid structures. They are
located behind the kidneys in the abdominal cavity.
·
The uterus join together to form
a median tube called vagina.
·
The common tube is formed by the
union of urinary bladder and the vagina and is called the urinogenital
canal or vestibule.
·
It runs backwards and opens to
the exterior by a slitlike aperture called vulva.
·
A pair of Cowper’s gland and
perineal gland are the accessory glands present in the female reproductive
system.
Concept Map
