The following points highlight the top seven types of system in calotes. The types are: 1. Digestive System 2. Respiratory System 3. Circulatory System 4. Venous System 5. Nervous System 6. Excretory System 7. Reproductive System.
Type # 1. Digestive System:
The digestive system of Calotes is composed of the alimentary canal and digestive glands.
Alimentary canal:
The alimentary canal starts from the mouth. The mouth is a transverse terminal aperture provided with jaws. The jaws are provided with teeth. The teeth are sharp, small, pointed and recurved backwards. They are actually simple cones (haplodont) having an enamel cap and an interior ortho-dentine.
The ortho-dentine encloses a large pulp cavity. The style of attachment of teeth is identified as pleurodont, i.e., the teeth are lodged to the outer wall of the alveolar groove (Fig. 8.8B). All the teeth are similar in size and shape, i.e., they are of homodontous type. But the teeth differ markedly in size in different regions of the jaws.
The mouth leads into the buccal cavity which is large and compressed dorsoventrally. At the posterior part of the roof of buccal cavity, there are two openings for the internal nares. The floor of the cavity houses a median and muscular tongue. The tongue is protrusible and the apex of the tongue is slightly bifurcated. The buccal cavity passes to the stomach through pharynx and oesophagus.
The stomach is elongated, sac-like and placed more or less vertically. The stomach is divisible into a cardiac and a pyloric portion. The pyloric part of the stomach is followed by small intestine which is narrow tubular and coiled.
The small intestine may again be divided into a U-shaped duodenum and a long much coiled ileum. The small intestine is followed by a large intestine (or rectum) which is small, sac-like and opens into the cloaca. At the junction of ileum and rectum a small projection, called coeliac caecum, is present.
The colon is absent. The cloaca opens to the exterior by the anus (or vent). The whole of the alimentary canal is kept in position by folds of peritoneum. The stomach is attached with the body wall by the mesogaster, the ileum by the mesentery and the rectum by the mesorectum.
Digestive glands:
Small unicellular salivary and mucous glands are present in the buccal cavity. These glands are few in number. The most important of the digestive glands is the liver which is massive and situated dorsal to the stomach. The liver is divided into left and right lobes. Both the lobes are united anteriorly (Fig. 8.8C). The upper margin of the liver and the apex of the ventricle are connected by gubernaculum cordis.
The liver secretes bile. The bile remains stored in the gall-bladder. The gall-bladder is a small and roundish sac which is situated on the outer margin of the right lobe of liver. The gall-bladder acts as a reservoir of the bile. The inner wall of the stomach is beset with a large number of unicellular parietal glands and gastric glands which secrete hydrochloric acid and digestive enzymes respectively.
Another important digestive gland in the pancreas. It is a flat and elongated structure. The colour is white. It opens into the beginning of the duodenum. The secretion of pancreas is called pancreatic juice. The juice is alkaline in nature and contains digestive enzymes.
These enzymes are trypsin, amylopsin and lipase. The spleen is a small rounded glandular structure situated in the mesentery below the stomach. It is morphologically connected with the digestive tract, but has got no digestive role. The spleen stores the erythrocytes and also destroys them, when necessary.
Mechanism of food-getting and digestion:
The food of Calotes consists mainly of small living insects. Ingestion is done with the help of the tip of the tongue and the insect is taken inside alive. The sticky mucous secretion helps to catch the prey. True digestion occurs in the stomach where HCI and pepsin react on the food matter.
HCI makes the medium acidic and kills bacteria while pepsin reacts with the protein part of the food and breaks it into peptone and proteoses.
In the next phase, digestion occurs in the duodenum. In the duodenum, bile neutralizes the acidic half-digested chyme and emulsifies the fat part of the food. Now pancreatic juice comes into play. Being alkaline in nature it makes the medium strongly alkaline.
Digestive enzyme, trypsin (present in pancreatic juice) reacts with protein and proteoses and converts them into soluble amino acids. Amylopsin reacts with carbohydrate which transforms into glucose and lipase reacts on fat converting it to fatty acid and glycerol.
The mixture of food containing simpler and soluble products and undigested food materials passes into the intestine. The lining cells of the intestine take up the soluble products while undigested food particles are stored in the rectum from where these are voided periodically.
Type # 2. Respiratory System:
Calotes is a true lung breather. Structurally the respiratory organs do not show any great improvement over the amphibians but functionally the lungs have become more efficient.
Respiratory structures:
The respiratory structures include a pair of nostrils (or external nares) situated a little ahead of the eyes. The nostrils lead to nasal passages which open into the roof of the buccal cavity. The glottis opens into the larynx which is box-shaped and is made up of a pair of arytenoids and single cricoid (forming the base) cartilages.
The larynx opens into the trachea which is narrow, tubular and beset with complete cartilaginous tracheal rings. The trachea is bifurcated into two and forms a pair of narrow passages, called bronchi. Each bronchus enters into a lung.
The lungs are elongated sac-like structures. The right lung is slightly larger than the left one. Internally each lung is incompletely divided into small chambers by the development of many incomplete septa (Fig. 8.9).
These chambers are called alveoli. The alveoli are the actual areas where exchange of gases occurs. In the distal part of the lung, such chambers are almost absent. This non- partitioned posterior part of the lung is considered as reservoir for the residual air. It constitutes about one-third part of the whole lung. The wall of the lung is made of squamous epithelium.
Mechanism of respiration:
The chemical mechanism of respiration is basically similar in all vertebrates, but the physical mechanism varies in many forms. The physical mechanism is divided into two steps. The steps are: inspiration and expiration.
Inspiration is caused by the movement of the intercostal muscles which raise the ribs and by increasing the volume of thorax reduce lung pressure and cause an inflow of air inside the lungs. Expiration is caused by lowering the ribs through the contraction of intercostal muscles and decreasing thoracic volume. By expiration carbon-dioxide and moisture are removed.
Type # 3. Circulatory System:
Transportation of various substances within an organism is conducted by the circulatory system. The circulatory system consists of cardiovascular system and lymphatic system.
The cardiovascular system includes:
(a) The heart which is an efficient machine to propel,
(b) The fluid vehicle, the blood into the pipelines of (c) arteries and (d) veins.
Structure of Heart:
The heart of Calotes lies in the pleuroperitoneal cavity and occupies a position which is midway between the fore-limbs though the ventricle extends slightly beyond the level of the axillae. Thus the position of the heart is rather forward and such a disposition indicates a lower grade of organisation because such condition is observed in Sphenodon.
The heart is covered by a thin and transparent pericardial membrane. The space between the heart and pericardium is filled with pericardial fluid. The heart is triangular in shape. The auricular region is wider than the ventricular region (Fig. 8.10A).
Sinus venosus:
The heart is made up of five chambers. The sinus venosus is reduced and is disposed transversely and dorsal to the lower half of the auricles. It is thin-walled and is formed by the confluence of the venae cavae. The right half of the sinus venosus is larger than its left counterpart and is formed by the confluence of right anterior vena cava (precaval vein) and posterior vena cava (postcaval vein).
The left portion of the sinus venosus is composed mainly by the left anterior vena cava. A constriction marks off the right and left parts of sinus venosus (Fig. 8.10 B). The sinus venosus opens into the right auricle near the region of the constriction by a semicircular sinuauricular aperture.
The aperture is provided with sinuauricular valves. The valves develop from the upper and lower margins of the aperture and the free end of the valves which is slightly frilled projects into the lumen of the right auricle.
Auricle:
The right auricle is larger than the left auricle and appears darker than the left auricle. The wall of the right auricle is thick and its inner lining is thrown into a number of musculi pectinati which are projected within the lumen.
The left auricle is smaller than the right auricle and it receives a common pulmonary vein. The pulmonary aperture is circular in outline and is located on its dorsal wall close to the inter-auricular septum. The aperture is not provided with valves.
Internally the left and right auricles are separated by a thin, muscular and non-perforated inter-auricular septum. The septum extends posteriorly for a short distance within the ventricle and bears at its posterior tip the auriculoventricular valves.
Ventricle:
The ventricle is muscular, spongy and triangular in appearance. Its apex is directed caudad and bears a thin and white cord of tissue, called gubernaculum cordis. It penetrates the pericardium and reaches the upper margin of liver. The thick-walled ventricle (Fig. 8.10 C) is provided internally with an inter-ventricular septum which divides it incompletely into left and right halves.
This partition has become complete in crocodiles except for an aperture, called foramen of Panizza. The foramen of Panizza is a communicating aperture between the left and right systemic arches just at the point of crossing after their emergence from the ventricle.
The inner cavity of the ventricle has been arbitrarily divided into three regions, namely, cavum pulmonale situated in the right side, cavum arteriosum (or the left hand portion) by a muscular ridge. The ridge arises from the right ventral wall of the ventricle and runs dorsal obliquely. Higher up, it becomes horizontally inclined.
It then runs obliquely again and takes a vertical course. It cuts off the aforesaid cavities. The left and right auriculoventricular apertures lie very close together being separated by the prolongation of the inter-auricular septum. The free lateral edge of the septum bears the auriculoventricular valves.
In the middle of the ventricle and close to the line of demarcation between the auricles and ventricle, there are three apertures from which the aortic arches arise. The inner wall of the ventricle is provided with thick interlacing muscles, called columnae carnae. There are bunches of thread-like muscle fibres, called chordae tendineae, by which the valves remain attached to the columnae carnae.
Valve:
The different compartments of the heart are intercommunicated by apertures having swing door-like flaps, called the valves. These valves control the passage of blood and direct the flow in one direction.
The valves present in the heart of Calotes are:
(a) A pair of leaf-like valves in the sinuauricular aperture.
(b) Sphincter muscle acting as valve in the opening of pulmonary vein into the left auricle,
(c) A pair of leaf-like valves formed by the bifurcation of the inter-auricular septum in the auriculoventricular aperture,
(d) Three semilunar valves in each orifice from which the arterial arches arise.
The walls of the heart are provided with three histological layers common to all blood vessels,, i.e., tunica intima, tunica media and tunica adventitia from inner to the outside. Of these three layers, the tunica media is peculiar in having specialised cardiac muscles showing striations and branching’s. The heart is supplied with the cardiac branch of 10th cranial nerve.
Mechanism of circulation through heart:
In Calotes, the circulatory circuit is double. There are pulmonary or lesser circulation and systemic or greater circulation. Pulmonary circulation is conducted by the pulmonary arteries which carry deoxygenated blood to the lungs. In the lungs, the blood becomes oxygenated and returns to the left auricle by the pulmonary vein.
The left auricle pours its content into the ventricle through the auriculoventricular aperture. In the greater circulation, deoxygenated blood returns to the sinus venosus by two precaval and one postcaval veins. The sinus venosus opens into the right auricle. The right auricle empties its content into the ventricle.
The ventricle sends blood for circulation into the different parts of the body through the systemic and pulmonary arches. The entry and exit of blood in the ventricle are so beautifully arranged that a major quantity of oxygenated blood is always forwarded to the brain region.
As the ventricle is incompletely divided, admixture of oxygenated and deoxygenated blood occurs thrice in Calotes once in the cavum venosum, once in the dorsal aorta and another in the left ductus caroticus.
Thus, though the ventricle in Calotes is morphologically incompletely divided, there is a tendency for the physiological separation of the two types of blood, at least in two auricles completely and in the ventricle partially. From this point, the heart of Calotes is biologically more advanced than that of Bufo.
Blood:
Blood of Calotes is red in colour and is made up of plasma and blood cells. The red blood corpuscles are biconvex, elliptical in outline and each bears an elliptical nucleus. The white blood corpuscles are irregular in outline, non-pigmented and each bears a spherical nucleus.
Arterial System:
Of the six pairs of arterial arches joining the dorsal aorta to the ventral aorta during embryonic development of arteries, the third, fourth and sixth pairs persist in adult Calotes and other reptiles.
As the ventricle in Calotes and other reptiles tends to divide into left and right ventricles by the development of incomplete inter-ventricular septum, the base of the ventral aorta splits into three parts, two of which remain in the right part of the ventricle and the third goes to the left part of the ventricle. Thus from the ventricle of Calotes arise three aortic arches.
These arches are:
(a) One pulmonary aorta and
(b) Two systemic aortae, right and left (Fig. 8.11).
These three aortae are wound around themselves at the source and undergo about one and a half turns round each other. The aortae are covered at the base by a fibrous sheath and thus appear tubular.
Pulmonary aorta:
It arises independently from the right portion of the ventricle and soon splits into two branches, each entering into a lung. It carries deoxygenated blood.
Left systemic aorta:
This aorta originates independently from the right (left to pulmonary aorta) portion of the ventricle and moves forward for some distance. Then it curves round the heart and goes downwards to meet the right systemic aorta a little posterior to the apex of ventricle. It carries mostly the deoxygenated blood. From the left systems arch four oesophageal arteries arise.
The first of these arteries arises from near the point of insertion of the left ductus caroticus while the origin of the fourth one is very close to the point of union of the two systemic. Parietal arteries do not originate from the left systemic arch.
Right systemic aorta:
This important aorta emerges independently from the right ventral margin of the base of the ventricle and moves forward. It then curves to the right side of the heart. It meets the left systemic aorta posteriorly to form the dorsal aorta. It carries oxygenated blood.
From the apex of the curvature of the right systemic aorta arises a single and common carotid artery which advances anteriorly and then splits into four arteries. The inner pair of these four branches or the external carotid arteries while the outer pair form the internal carotid arteries.
On both sides prior to its division into left internal and external carotids and right internal and external carotids one thyroid artery is given off from the common carotid.
The main branches from the right and left external carotids are the laryngotracheal artery (one from each) and three buccal arteries (from each). The internal carotids both left and right bifurcate at their tips into inner palatine artery and outer stapedial artery.
The external carotids and their branches supply blood to face and mouth, while the internal carotids and their branches supply blood to the brain. Thus it is to be noted that carotid arteries do not arise independently from the ventricle as they do in amphibians but instead arise from the right systemic aorta.
And as the right systemic arch carries oxygenated blood to anterior organs, specially the brain, this arch is supplied with oxygenated blood. The two internal carotids are connected to the systemic aorta of the corresponding sides by ductus caroticus. The ductus caroticus represents the remnant of embryonic radices between the third and fourth aortic arches.
From the right systemic aorta three oesophageal arteries are given out. The right systemic aorta before its meeting with the left systemic aorta gives rise to a subclavian artery which bifurcates into two and supplies blood to the forelimbs.
From the right systemic aorta a vertebral artery also originates to send blood to the vertebral column. The point of origin of the vertebral artery is situated very close to the subclavian branch. Just before meeting its left counterpart, the right systemic arch gives a pair of parietal arteries.
The right and left systemic aortae unit a little behind the heart and give rise to the dorsal aorta which runs posteriorly and gives branches to visceral organs and posterior parts of the body. The following arteries originate from the dorsal aorta chronologically along the anteroposterior axis.
These are:
(a) Anterior oesophageal artery. It is single and originates from the ventral surface of the dorsal aorta,
(b) First pair of parietal arteries from dorsal aorta which plunge into the parities of third thoracic vertebra.
(c) First and second pairs of gastric arteries which supply the cardiac stomach,
(d) Second pair of parietal arteries,
(e) Third, fourth and fifth pairs of gastric arteries followed by third pair of parietal arteries,
(f) Sixth and seventh pairs of gastric arteries followed by fourth pair of parietal arteries,
(g) Eighth pair of gastric arteries followed by fifth and sixth pair of parietal arteries. It is to be noted that the number of gastric arteries varies from 4-8 pairs.
(h) Anterior mesenteric artery which runs obliquely caudad to supply the intestine,
(i) Coeliac artery which runs obliquely cranial to supply the pyloric stomach. A splenic artery is given off by it to supply the spleen,
(j) Seventh and eighth pairs of parietal arteries.
(k) Posterior mesenteric artery or Hepato- intestinal artery. It arises from the right border of the dorsal aorta. It runs obliquely caudad and on reaching the intestine bifurcates into two—anterior and posterior. The anterior or hepatic supplies the gall-bladder while posterior or intestinal supplies the intestine.
(I) Ninth pair of parietal arteries,
(m) The right and left genital arteries. The point of origin of the right one is a bit up than its counterpart on the left,
(n) Tenth and eleventh pairs of parietal arteries,
(o) Left and right renal arteries. There may be more than one pair,
(p) Twelfth and thirteenth pairs of parietal arteries,
(q) One pair of iliac arteries. Each branch after its origin runs obliquely to the corresponding hind limb. From each a pelvic branch is given off to supply the pelvic girdle. Finally, each branch bifurcates into external and internal iliac. From near the point of bifurcation a slender vesicular artery is given off by each branch,
(r) The dorsal aorta now enters into the tail as caudal artery.
Type # 4. Venous System:
The deoxygenated blood from the different parts of the body is brought back to heart by means of veins except the pulmonary veins which carry oxygenated blood. The veins run parallel to the arteries, appear dark and in position are superficial to arteries.
The central meeting arena of all veins in the body is the sinus venosus. Sinus venosus is a triangular structure and its two base angles receive left and right Percival’s while the apex receives a single median postcaval (Fig. 8.12).
Each precaval vein has been formed by the union of three veins.
These are:
(a) The external jugular which brings back blood from the floor of mouth and tongue,
(b) The internal jugular which drains blood from the brain and
(c) The subclavian which draws blood from the forelimb.
The right precaval gets an azygos vein. The postcaval is constituted by the large median vein which is formed by the union of right and left efferent renal veins emerging from the two kidneys. Genital veins join the left and right efferent renal veins before their union. A pair of stout but short hepatic veins joins the median postcaval before its entry into the sinus venosus.
A median caudal vein carries blood from the tail region. The caudal vein ultimately bifurcates into two veins which enter into the kidneys. Each vein gives rise to the renal portal vein to the kidney and pelvic vein which receives femoral and sciatic veins from the hind limb.
The pelvic veins unite to form a median epigastric (or anterior abdominal) vein which ultimately opens into the left liver. The anterior abdominal vein and the postcaval are free of each other except through the renal portals in the kidneys. The blood from the visceral organs, i.e., stomach, intestine, pancreas, etc., enters into the left lobe of the liver by a hepatic portal vein.
In Calotes both renal portal and hepatic portal systems are present. These systems have got many advantages and fulfil the demand for a second set of capillaries through which blood must flow. The organisms having such a portal system are always provided with double supplies of blood, arterial and venous.
The pulmonary venous circuit comprises of pulmonary veins. From each lung two pulmonary veins carry blood to the heart. Of these veins, one comes out from the anterior part while the other comes from the posterior part of lung (Fig. 8.13). Near the left auricle all these four branches unite and open into the left auricle. The pulmonary veins bring oxygenated blood to the heart from the lungs.
The lymphatic system is highly developed. The main lymphatic trunk becomes divided and enters into the precaval veins. Lymph hearts are present.
Type # 5. Nervous System:
The nervous system of Calotes consists of:
(a) Central nervous system,
(b) Peripheral nervous system consisting of cranial and spinal nerves which originate from brain and spinal cord respectively and
(c) Autonomic nervous system (or sympathetic nervous system).
Central nervous system:
The brain and the spinal cord constitute the Central Nervous System.
Brain:
The brain is encased in the cranium. The nervous tissues of the brain are protected by two meninges, called piamater and duramater. The piamater remains in close contact with brain and it is highly vascular. The duramater lies just outside the piamater and is mainly fibrous in nature. The two coverings remain separated from each other and the space between them is called subdural space.
Brain of an adult Calotes is differentiated into (a) Forebrain, (b) Midbrain and (c) Hind- brain (Fig. 8.14A).
Forebrain:
The forebrain consists of telencephalon anteriorly and diencephalon posteriorly. From the side wall of telencephalon emerges a pair of sac-like projections, called olfactory lobes. The posterior part of the telencephalon is elongated and is called cerebral hemisphere or cerebrum. The diencephalon bears on the dorsal surface two projections, called parietal organ and pineal body.
The parietal organ is situated anterior to the pineal body (Fig. 8.14 D, E). Another projection called paraphysis, is present in a reduced condition. From the ventral side of the diencephalon hangs a funnel-like structure, called infundibulum, on the apex of which is situated the pituitary body or hypophysis (Fig. 8.14C, D).
Midbrain:
The midbrain consists of a pair of oval optic lobes or corpora bigemina which arise as projections of the dorsolateral walls. Ventral to the optic lobes, there are a pair of longitudinal bands or peduncles, called crura cerebri, which connect the hindbrain to the midbrain.
Hindbrain:
The hindbrain consists of a narrow and non-convoluted metencephalon or cerebellum and a long myelencephalon or medulla oblongata which continues posteriorly with the spinal cord.
Thickenings inside the different brain regions:
The roof of the cerebral hemispheres is thin but the ventrolateral walls are thick. The thick region is called corpus striatum. The roof of the cerebral hemispheres is called neopallium, because the grey matters are situated on the outer margin. The roof of diencephalon is thin, highly vascular and is called roof-plates (see Fig. 8.14D).
The lateral walls are called thalami and the floor is called hypothalamus. Parietal and pineal bodies arise from the roof-plate. The thalamus is thick. From the hypothalamus the infundibulum arises. The roof of the mesencephalon becomes thick to give rise to the optic lobes.
Its floor is also thick and gives rise to the crura cerebri. The roof of the metencephalon is thin and non-nervous but the floor is thick. The myelencephalon is similar to metencephalon in regard to its floor and roof.
Ventricles:
Internally the brain bears cavities which are continuous to one another and to the spinal cord. The cavity is filled with cerebrospinal fluid. The cavities in the cerebral hemispheres are called lateral ventricles or first and second ventricles. The diencephalon contains the third ventricle while the fourth ventricle is situated in the medulla oblongata.
The two lateral ventricles are communicated to the third ventricle or diacoel by a small opening, called foramen of Monro. The third and fourth ventricles or mesocoels are communicated with each other by a narrow passage, called iter or aqueduct of Sylvius.
Commissures in Brain:
Two sides of the brain are connected at places by transverse bands of nerves, called commissures.
The commissures are:
(i) Anterior commissure:
A wide transverse tract of nerve fibres connecting the two corpora striata.
(ii) Habenular commissure:
Anterior to epiphysis and situated between epithalamic ganglia.
(iii) Aberrant commissure:
Runs through the lamina terminalis and joins olfactory lobes. The presence of aberrant commissure in the brain of Calotes is regarded as the most important diagnostic reptilian feature.
(iv) Hippocampal commissure:
Hippocampus is the swollen part of the mid-posterior region of the cerebrum. The two hippocampi are connected by the hippocampal commissure.
(v) Posterior commissure:
It connects the posterior part of the two optic thalami and is situated just at the junction of diencephalon and mesencephalon.
Spinal cord:
It is the posterior prolongation of the brain through the neural canal. Its walls are thick and the roof and the floor bear dorsal and ventral furrows. Externally the spinal cord – is made up of white matter consisting of medullated nerve fibres and internally there.is grey matter containing ganglionic cells and non-medullated fibres.
Peripheral Nervous System:
The peripheral nervous system consists of nerve fibres which are either sensory or motor or mixed. The cranial and spinal nerves constitute this system.
Cranial nerves:
There are 12 pairs of cranial nerves in Calotes (besides the terminal nerve). The origin, distribution and biological nature of the first to tenth pairs of cranial nerves is exactly similar to that of Bufo. Fig. 8.16 will give an idea of the origin and the ramifications of the fifth and seventh cranial nerves in Calotes.
Fig. 8.17 shows the origin and distribution of the ninth and tenth cranial nerves of Calotes. The eleventh and twelfth pairs of cranial nerves are the (a) spinal accessory and (b) hypoglossal respectively.
The spinal accessory (XI) originates from the posterior part of medulla oblongata as efferent fibres and joins with the vagus. Along its course, this nerve receives series of rootlets from the spinal cord. The spinal accessory nerve supplies mostly the striated muscles of the pharynx, larynx and also the autonomic nervous system.
It is a sensory nerve. The hypoglossal nerve (XII) is also a sensory nerve which originates from the medulla oblongata and innervates from the medulla oblongata and innervates the muscles of the tongue and controls its movements during feeding.
Spinal nerves:
There are several pairs of spinal nerves that originate from the spinal cord and emerge out from it between the vertebrae. The spinal nerves are mixed type of nerves. They originate separately and independently but ultimately combine to form a single cord. They originate by a dorsal root which is sensory and a ventral root which is motor in nature.
Each spinal nerve divides into four branches or rami.
These branches are:
(a) Dorsal branch, thin, short and supplies sense organs, glands and muscles,
(b) Ventral branch, long, thick and supplies hypo-axial organs,
(c) Meningeal branch, small and goes back to supply the neural canal and
(d) Ramus communicants which communicates with autonomic nervous system. Several spinal branches often meet together and form plexus.
Autonomic nervous system:
This system consists of a chain of complicated ganglia with receptor and effector nerves formed mostly by the offshoots from the ventral branches of the spinal nerves.
The branches from these ganglia innervate muscles of heart, lungs, digestive system and glands which work continuously and are not controlled by will. Autonomic nervous system comprises of two divisions of nerves which are structurally similar but functionally antagonistic.
These are:
(a) Sympathetic nerves having activating role and
(b) Parasympathetic nerves which have inhibitory action.
Type # 6. Excretory System:
The excretory system of Calotes consists of a pair of metanephric kidneys situated in the abdominal cavity. These are retroperitoneal in position and lie one on either side of the vertebral column. Each kidney is dark-red in colour and is lobed. The kidneys are free at the anterior end but are united along the inner margins at the posterior part. The posterior ends of the kidneys run over the cloacal chamber.
Histologically each kidney is made up of a central portion, the medulla and a peripheral portion, the cortex. The cortex contains numerous renal or Malpigian corpuscles. Each corpuscle consists of Bowman’s capsule which is a double-walled cup of epithelial cells.
The space between the two layers of the capsule is the beginning of the renal tubule. In the concavity of the Bowman’s capsule lies the glomerulus which is a spherical tuft of arterial capillaries.
The renal tubules open into the collecting tubule which communicates with the ureter. The kidney has a double set of capillary system. One set is formed by the afferent and efferent renal arteries while the other set is formed by renal and renal portal veins.
There are a pair of ureters arising one from each kidney. The ureters are short and open into the cloaca separately. From the lateral wall of the cloaca arises a single urinary bladder which is allantoic in origin. The urine of Calotes is semisolid in consistency and contains uric acid.
Type # 7. Reproductive System:
Sexes in Calotes are separate and it is difficult to distinguish between the male and the female from external morphological features.
Male reproductive system:
This system includes a pair of testes situated in the abdominal cavity which remain suspended by a special dorsal fold of the mesentery, called mesorchium. The testes are white oval bodies. The testis of the right side is larger in size compared to that of the left side and situated slightly higher up in the abdominal cavity.
The testes undergo a drastic change in size. In the breeding time they become larger than they are at the non-breeding period. From the inner surface of each testis runs the epididymis which receives the vasa efferentia. The epididymis proceeds posteriorly as vas deferens (Fig. 8.19A).
Two vasa deferentia open separately by small papillae into the cloaca but before opening into the cloaca each receives the ureter of the corresponding side. So through this common duct both urine and male gametes pass into the cloaca which is designated as the urinogenital duct.
The posterolateral side of the cloaca is provided with a pair of copulatory sacs each of which houses a hemipenis. The hemipenis is reversible. The hemipenes (plural of hemipenis) are actually the bilateral sacculations of the cloaca which extend posteriorly below the skin.
When everted, the hemipenes protrude through the cloacal aperture. The distal end of each hemipenis is large and rounded. The hemipenes are grooved to conduct sperms from the cloacal cavity of the male into that of a female.
Female reproductive system:
This system includes a pair of ovaries which have similar position as that of testes (Fig. 8.19B). Each ovary is fixed to the dorsal side by a special fold of mesentery, called mesovarium. The female gonoduct is called oviduct. The oviduct is attached with the body wall by a special fold of peritoneum, called broad ligament.
The anterior end of the oviduct is wide, funnel-shaped, ciliated and is situated near the corresponding ovary below the level of lungs. The oviducts are not coiled but are folded which run posteriorly to open independently into the cloaca.
The diameter of the oviduct shows gradual increase towards the posterior side in cross-section. The lower part of the oviduct is designated as the uterus where the eggs are stored temporarily prior to laying. In the anterior part of the oviduct there are many albumen glands and the posterior part is provided with shell glands.
In Calotes, the fertilization is internal. Mature eggs are fertilized in the anterior part of the oviduct. The eggs are heavily yolked and are covered by calcareous shell.