|Scoliodon (Fish)||Rana (Frog)|
|1. The arterial system consists of a ventral aorta, afferent and efferent branchials, dorsal aorta, and its branches and hypobranchials.||1. The arterial system consists of a truncus arteriosus, three pairs of aortic arches and the dorsal aorta & its branches.|
|2. Five pairs afferent branchial arteries are present.||2. Absent.|
|3. Efferent branchial system is associated with gill-slits along with the respective arteries.||3. Absent.|
|4. The arteries to the head are given off from the first pair of epibranchials and by the branches of dorsal aorta carotid labyrinth is absent.||4.The head is supplied blood by the branches. Carotid arteries arising from the truncus arteriosus. Carotid labyrinth is present.|
|5. Parietal arteries are present.||5. Parietal arteries are absent.|
|6. Hypobranchial plexus is present.||6. It is absent.|
|7. Dorsal aorta is formed by the union of epibranchial arteries of both the right and left sides.||7. The second branches of turncus, the systemic arches of the left and right sides unite to form the dorsal aorta.|
|8. Subclavian arteries arise from the dorsal aorta.||8. Sub clavian artery arises from each systemic arch.|
|9. Absent.||9. Occipito-vertebral artery arises from the systemic arch of each side.|
|10. Coeliaco-mesenteric artery arises from behind the union of the four pairs of epibranchials.||10. Coeliaco-mesenteric artery arises from the junction of the two system¬ic arches.|
|11. Just below the Coeliaco-mesenteric artery, lienogastric artery arises.||11. Lie no gastric artery is absent.|
|12. The parietal artery gives off four pairs renal arteries.||12. Four pairs of renal arteries arise directly from the dorsal aorta.|
|13. Gonadial (Spermatic or ovarian) artery arises from the lieno gastric artery.||13. Gonadial arteries arise directly from the first pair of renal arteries.|
|14. Dorsal aorta terminates into caudal artery.||14. C-iudal artery is absent.|
|15. Pulmo cutaneous arch is absent.||15. The third branch of truncus is the pulmo-cutaneous arch which is divided into pulmonary and cutanecious arteries.|
|Calotes (Lizard)||Columba (Pigeon)||Oryctolagus (Rabbit)|
|1. Heart is situated mid ventrally in the anterior part of the body cavity in the pleuro peritoneal cavity behind the sternum.||1. Same way the heart is located.||1. Heart is situated in the thoracic cavity, between the lungs of two sides (Mediastinum). It is present slightly towards the left side.|
|2. Heart is comparatively smaller in size.||2. Heart is comparatively larger in size.||2. Heart is comparatively larger in size.|
|3. It is enclosed by double walled pericardium.||3. It is also enclosed in the double walled pericardium.||3. Same.|
|4. Heart includes a dorsal sinusvenusus aright auricle, a left auricle and a single incom-pletely divided ventricle.||4. Heart is four chambered, sinus venosus is absent in the adult. Completed divided two auricles and two ventricles by inter auricular septum and inter ventricular septum respectively.||4. Same as in columba.|
|5. The three vena cavae or two precavals and a post caval vein open into the sinus venosus.||5. The three vena cavae or two precavals and a post caval empty the blood directly into the right auricle.||5. Same as in pigeon.|
|6. The left auricle receives two pulmonary veins from the lungs.||6. The left auricle receives four pulmonary veins from the lungs.||6. Left auricle receives two pulmonary veins from the lungs.|
|7. The right auricle possess sinu auricular aperture guarded by valve.||7. Absent.||7. Absent.|
|8. The two auricles are completely separated by inter auricular septum. But the inter ventricular septum in the ventricle is incomplete. Hence oxygenated and deoxygenated types of blood is mixed to some extent in the ventricle.||8. Complete inter auricular and inter ventricular septa are present. There is no possibility of mixing the oxygenated blood with deoxygenated blood.||8. Same as in pigeon.|
|9. The heart of lizard is in a transitional stage approcarhing the double circuit stage But it has not reached it completely due to incomplete division of the encircle.||9. The heart is a double circuit heart because of complete division of ventricle into right and left chambers.||9. Same as in pigeon.|
|10. The auriculo ventricular aperture is guarded by two flap like semilumar valves.||10. The right auriculo ventricular aperture is guarded by two large muscular flap like valve and the left by three valves.||10. The right auriculo-uentricular aperture is guarded by tricuspid valve and the left by bicuspid valve (mytral valve).|
11. There are three aortic arches arising from the ventricle.
11. Only two aortic arches originate from the ventricles.
i.e. Right aortic arch is characteristic of birds.
11. Only two aortic arches arise from the ventricles.
|12. Ductus caroticus is present (connection between carotid & systemic arches)||12. Absent||12. Absent|
|13. Lizard's heart presents a transitional heart, since it approaches the double circuit heart but has not yet completely attained. So the heart is less efficient.||13. Avian heart has at tained maximum com olexity and is a double circuit heart, i.e. venous blood is com pletely separated frorr oxygenated blood.||13. Same as in Pigeon.|
|14. Absent.||14. Sinu-Auricular Node and Auriculo ventricular node are present.||14. SA - node and A.V. node are present. In addition bundle of His muscles are also develop.|
|FISH HEART (SCOLIODON)||FROG HEART (RANA)|
|1. Heart is approximately pear-shaped.||1. Heart is approximately pear-shaped.|
|2. The pericardial cavity is not wide and the pericardium forms double membrane around the heart.||2. The pericardial cavity is not wide and the pericardium forms double membrane around the heart.|
|3. The heart is formed of a dorsally placed sinus venosus and ventrally placed two auricle, a ventricle and truncus arteriosus or conus arteriosus.||3. The heart is formed of a dorsally placed sinus venosus and ventrally placed two auricle, a ventricle and truncus arteriosus or conus arteriosus.|
|4. The atrium or auricle is two-chambered and lies anterior to the ventricle. Auricles are separated by Inter auricular septum.||4. The atrium or auricle is two-chambered and lies anterior to the ventricle. Auricles are separated by Inter auricular septum.|
|5. The auriculo-ventricular valve is membranous.||5. The auriculo-ventricular valve is membranous.|
|6. The conus arteiiosus is incompletely divided by the spiral valve laterally into cavurn aorticum leading to carotid and systemic arches and the cavum pulmocutaneum leading to the pulmocutaneous arch.||6. The conus arteiiosus is incompletely divided by the spiral valve laterally into cavurn aorticum leading to carotid and systemic arches and the cavum pulmocutaneum leading to the pulmocutaneous arch.|
|7. The opening of the truncus with valves are arrenged in two transvarse rows.||7. The opening of the truncus with the ventricle is guarded by three semilunar valves arranged in a single row. They devide rruncus into a proximal pylangium and a distal synangium.|
|8. The walls of the auricle are thick.||8. The muscular walls of the auricle are thin.|
|9. The walls of the ventricle are highly muscular.||9. Same type of ventricle is present.|
|10. The lips of the bilaminate valves are connected to the inner surface of the ventricle is prominent part of the heart.||10. The membranous valves are connected to the inner surface of the ventricle by chordae-tendinae. Both auricles and ventricle are essential parts of the heart.|
|11. The fish heart is venous or branchial heart because it receives deoxygenated blood only.||11. The frog's heart receives both oxygenated and deoxygenated blood. The deoxygenated blood remain separate in the auricles but get mixed in the ventricle.|
|12. Blood passes only once through the heart in a complete circuit.||12. Blood passes through the heart twice in a complete circuit.|
|13. Such type of arrangement is absent.||13. The sinus venosus opens into the right auricle through simi-auricular aperture guarded by simi auricular valve which is also known as pace maker.|
|14. No separate vessel collects oxygenated blood since the heart is venous heart||14. The oxygenated blood is collected by pulmonary vein from lungs and carries into left auricle.|
The typical tetrapod hind limb can be divided into three segments. The thigh, shank and foot (pes) are the three segments. If there are five toes, normally this type of limb is known as pent dactyl limb.
The femur is the bone of the high and its head articulates with the acetabulum. Its distal end articulates with fibula. The tibia and fibula are the bones of the shank region. They articulate with femur proximally and distally with the tarsal’s of the ankle bones. The fibula bears the most of the body weight.
The foot can be divided into ankle, instep and toes. The ankle is supported by tarsals, which are arranged in rows. The skeleton of ankle or tarsus is the most stable of the regions of the ankle. The instep or metatarsus is supported by the metatarsals. These are elongated bones. The metatarsals are followed by linear series of phalanges of the toes. The phalanges number varies from 1 to 5.
The first toe of the hind limb is called 'hallux or great toe' and the fifth toe is the 'minimus'.
|Calotes (Garden Lizard)||Columba (Pigeon)||Oryctolagus (Rabbit)|
|1. The bones of the hind limb are femur, Tibia, fibula, tarsals, metatarsals and phalanges.||1. The bones of the hind limb are femur, tibia, fibula, tibiotarsus, tarsometatarsals and phalanges.||1. The bones of the hind limb are femur, tibia fibula tarsals, meta tarsals and phalanges.|
|2. The femur is stout bone of the thigh region. It has long, slender and curved shaft in the middle. The shaft enlarges at both the ends.||2. The femur is a stout bone of the thigh region. It has a long, curved shaft in the middle. The shaft has broad ends.||2. Femur consists of long, stout curved shaft. The femur gives support to the thigh region.|
|3. The proximal end of the shaft bears a rounded smooth head which fits info the acetabulum. There are also distinct prominences lesser trochanter and greater trochanter near the head.||3. The proximal end of femur is produced into a rounded head for the articulation with the acetabulum. Opposite to the head a small protuberance greater trochanter is present.||3. The proximal end of femur bears a rounded knob-like head which fits into the acetabulum. There are three rough projections greater, lesser and third trochanters present near the head. Lesser trochanter lies behind the head, greater trochanter in the middle line and the third trochanter opposite to the head are seen.|
|4. It is absent.||4. There is an articular surface is present between the head and trochanter for the antitrochanter of ilium.||4. It is absent.|
|5. Two knob-like condyles are present at the distal end of thefemur. These articulate with the tibia of the shank. Intercondylar groove is present between the two condyles. Patella is absent.||5. The distal end of femu has two prominent condyls with a intercondylar groove. Patella slides in the intercondylar groove on the anterior side. It is a disc-like sesmoid bone.||5. The distal end of femur is pulley-like having two condylesfor tibio-fibule which are separated by a patellar groove. A large sesmoid bone called the patella slides in the patellar groove. It is attached to the tibia by a ligament. Patella is present at the knee-joint.|
|6. The shank consists of two long bones - the tibia and the fibula. They are separate bones.||6. Tibiotarsus fibula is formed of tibiotarsus and fibula. They are separate bones.||6. Tibiofibula is formed of tibia and fibula. They are separate bones.|
|7. Tibia is a stout and curved bone present on the inner side. Its proximal end bears two concave facets for the articulation with the femur. It has also a longitudinal ridge the cnemial crest on the side. Tibiotarsus is absent.||7. Tibiotarsus is a large straight and stout bone and also longer than fibula. It is formed by the fusion of tibia and proximal row of tarsals. The proximal end of it bears a pair of articular surfaces for the condyles of the femur and in between them the cnemial crest for the attachment of tendon of extensor muscles.||7. Tibia is stouter towards the anterior end and narrow towards the posterior end. Its proximal end bears two concave facets for the articulation with the femur and distinct cnemial crest on side.|
|8. Tibia distally bears a concavity for the tarsals.||8. Tibio tarsus distally bears a pulley-like articular surface for the tarsals which is surrounded by a pair of distal lateral tubercles.||8. Tibia distally bears articular surface for the tarsals.|
|9. Fibula is a slender bone present on the outerside. It bears facets on either side.||9. Fibula is small, slender bone. It is closely applied to the tibiotarsus.||9. Fibula is a slender and weak bone. It lies on the outer side. The bone is narrower towards the distal end and is closely applied to the tibia.|
|10. Tarsab are five in number which are arranged in two rows. Proximal row has two tarsals the larger compound piece formed by the fusion of a rjbiale, intermedium and centrale and present infront of tibia. A small fibulare present infront of the Sbula. The distal row has three small tarsab called distal tarsab or distalia.||10. The free tarsals are absent. The proximal row of tarsals are fused with tibia and forms tibiotarsus. The distal row of tarsals are fused with the metatarsals and forms tarso metatarsus. It is as long as the femur bone. It is straight and stout.||10. There are six tarsal bones which are arranged in two rows. The proximal row tarsab are two, astragalus and calcaneum. Astragalus is considered to represent two fused tarsals. Calcaneun is produced back wards into a strong calcaneal process which forms the heel. The central row has only one tarsal-centrale or navicular. The distal row contains three tarsab. The first distal tarsal is absent due to the absence of hallux. The second distal tarsal is mesocuneiform which is the smallest distal tarsal. The third distal tarsal is ecto cuneiform which largest one. The fifth distal tarsals are fused to form largest bone in the row - cuboid.|
|11. There are five meta-tarsals corresponding to the five toes.||11. There are four meta tarsals. The first one is free and in the form of a small projection. The second, third and fourth are fused with the distal row of tarsals to form tarso metatarsus. Ankle joint is known as mesotarsal.||11. There are four meta tarsals. There are second, third, fourth and fifth, meta tarsals. The first one is absent|
|12. There are five toes. There are two phalanges in the hallux, three in the second, four in the third, five in the fourth and three in fifth toes. The phalanges formula can be expressed as 2, 3, 4, 5, 3 (same as for the hand). The terminal phalanx of each toe supports a strong, curved, horny & pointed claw.||12. There are four toes. The hallux is directed backwards and contain two phalanges. The second toe with three, third one with four and the fourth one with five phalanges are formed. The phalanges formulae can be ex¬pressed 2, 3, 4, 5. The terminal phalanx of each toe is pointed and curved which supports a strong, pointed horny claw.||12. There are four toes. Each toe has three phalanges. The phalanges formula can be expressed as 3, 3, 3, 3. The terminal part of each phalanx is pointed and curved to support a horny claw.|
A typical tetrapod fore limb can be divided into three segments. The upper arm, fore arm and hand (menus) are the three segments. As there are five fingers normally, this type of limb is known as pentadactyl limb.
The skeletal structures of the fore limb consists of humerus, radius ulna, carpals, Meta carpals and phalanges.
The humerus is the bone of the upper arm and its head articulates with the glenoid cavity .Its distal end articulates with the ulna The Radius and ulna are the bones of the fore arm. They articulate with humerus proximally and distally with the carpals of the mist bones. The radius bears most of the body weight.
The hand can be divided into wrist, palm and digits (fingers). The wrist is supported by carpal bones which are arranged in rows. The palm is supported by the metacarpals. The metacarpals are followed by linear series of phalanges of the fingers The phalanges number vary from 1 to 5.
The first finger of the fore limb is called 'pollex or thumb' and the fifth finger is the 'minimus'.
|Calotes (Garden Lizard)||Columba (Pigeon)||Oryctolagus (Rabbit)|
|1. The bones of the fore limbs are humerus, radius, ulna, carpals, metacarpals and phalanges.||1. The bones of the fore limb are humerus, radius, ulna, carpals carpometa carpus and phalanges.||1. The bones of the fore limb are humerus, radius, ulna, carpals, metacarpals and phalanges.|
|2. Humerus is in the form of a long bone with proximal and distal ends.||2. Humerus is a long & slightly flattened with a bent shaft associated by proximal and distal ends.||2. Humerus possess a proximal head, shaft and a distal end.|
|3. The proximal end of humerus is round and distal end is pulley like with two articular surfaces for the radius and ulna. Supra trochlear foramen is absent.||3. The proximal end of humerus is highly expanded and form into the head A prominent deitcid ridge and a pneumatic foramen are present near the head. The distal end articulates with the radius and ulna by the articular surfaces. Supra trochlear foramen is absent.||3 The proximal end of hu-merus is divided into two parts by a bicipital groove. One part has head which fits into the glenoid cavity. This part has lesser tuberosity. The greater tuberosity is present on the other part. Shaft is present along with deltoid ridge. The distal end has median and lat¬eral epicondyles. Pulley-like trochlea is formed at the distal end which articulates with ulna. Suprotrochlear foramen is present.|
|4. Two elongated and separate radius and ulna bones are present.||4. Same as in calotes.||4. Same as in columba.|
|5. Radius is a slender bone. It has a styloid process and concavity for the carpalsdistally.||5. Radius is a straight and slender bone. It has a concavity for the articulation with humerus at the proxima end The distal end is convex.||5. Radius is small slender and slightly curved bone With a concavity at the proximal end. The distal end is flat.|
|6 Ulna is rod liket and stoutet than radius, Proximally it has ole cranon process to articulate with humerus. Distally it has a concavity for the articulation with carpals.||6. Ulna is stouter and longer than radius It is slightly curved. A cranon process to blunt olecranon process is present at the proximal end. The distal ends of radius & ulna articulate with carpometacarpus.||6. Ulna is a long and curved bone. Proximally it bears olecranon process and sigmoid notch for the articulation with the trochlear end of humerus. Epiphyses are present at the distal ends of radius & ulna for the articulation with carpals.|
|7. Wrist or carpus has ten (10) small bony carpals arranged in three rows. The proximal row has three carpals - radiale, intermedium and ulnare. A centrale lies in the second row. A pisiform is attached to the distal end of the ulna on its post axial side as an additional bone. The third row has five distal carpals. Except the fourth, the remaining distal carpals are very small.||7. The wrist contains only two proximal carpals. One smaller-radiate and a larger ulnare articulate with radius & ulna respectively. The three distal carpals are fused with the meta carpals to form the carpometa carpus. It is a characteristic feature of aves.||7. Wrist consists of eight small carpal bones arranged in two rows. The proximal row contains three carpals-radiale or scaphoid, intermedium or semilunar and ulnare or unciform. The median row has a single centrale. The distal row comprises four true carpals-trapezium, trapezoid, smallest magnum and largest unciform.|
|8. Carpometa carpus is absent Five slender meta carpals support the palm. These are of unequal size & with expanded ends. The middle or third meta carpal is the longest, the second and fourth are only a little shorter than the third. The first and fifth meta carpals are much shorter.||8. Meta carpals are three in number which are fused with the distal carpals and form an elongated compound bone carpometa carpus.||8. There are five long, slender and of unequal size metacarpals support the palm. The first is the shortest and the third is the longest. Each meta carpal has small epiphysis at their end with a middle slender shaft. Carpometa carpus is absent.|
|9. There are five fingers.||9. There are three fingers.||3. There are five fingers.|
|10. The phalanges are the small bones support the fingers. The number of phalanges differ in the respective fingers. The first finger has two, second has three, third has four, fourth has five and fifth has three phalanges Thus the phalanges formula can be expressed as 2,3, 4, 5, 3.||10. The phalanges are the small bones support the fingers. The first finger has one, second has two and third has one phalanges. Thus the phalanges formula can be expressed as 1, 2, 1.There are no claws on the fingers.||10. The phalanges are small bones and their total number is 14. The first finger has two phalanges & the remaining four fingers have three phalanges each. Thus the phalanges formula can be expressed as 2,3,3,3.3.|
|11. Sesamoid bones are absent. The distai phalanx of each finger supports a strong curved, pointed claw is formed from the epidermis.||11. Sesamoid bones are absent.||11. Sroas nodule-like bones are present on the underside of the fingers. These are seen at the joints between the meta carpals and the first phalanges and also between the second and third phalanges. These provide additional strength to the fingers during burrowing.|
|12. It is a penta dactyl limb.||12. The fore limb supports the wing.||12. it is a penta dactyl limb.|
The hard parts of the animal body are collectively known as skeletal system or simply skeleton. The vertebrates possess the hard parts inside the body. It is known as endo skeleton. The endo skeletal structures are formed with cartilages and bones which are the living tissues. The endo skeleton has been divided into: The hard parts of the animal body are collectively known as skeletal system or simply skeleton. The vertebrates possess the hard parts inside the body. It is known as endo skeleton.
|Calotes (Garden Lizard)||Columba (Pigeon)||Oryctolagus (Rabbit)|
|1. Pelvic girdle is stout and solid. Ifts well suited for walking habits.||1. Pelvic girdle is large and pneumatic. It is well suited for bipedal locomotion.||1. Pelvic girdle is stout and associates with the vertebral column. It is adopted for swift running.|
|2. Each os innominatum is formed by the ilium, ischium and pubis.||2. Same as in calotes.||2. Each os innominatum is formed by ilium, ischium, pubis and cotyloid cartilage bones.|
|3. The bones are structurally united.||3. The bones are compactly fused.||3. Same as in columba.|
|4. Ilium is strong, rod shaped and is directed upwards.||4. Ilium is long, thin and plate-like bone. It is differentiated into preacetabular and postacetabular regions.||4. Ilium is large and broad. The antero-dorsal edge is raised to form iliac crest.|
|5. Ilium articulates with two sacral vertebrae.||5. Ilium articulates with synsacrum.||5. Anteriorly ilium has articular surface for the sacral vertebrae.|
|6. Ischium is flat, slightly curved and axe-shaped. It is directed downwards and backwards.||6. Ischium a flat bone fused with the post acetabulariiium. They are separated by ilio-ischial foramen.||6. Ischium is broad and slightly curved bone lying behind ilium. It is posterodorsal in position.|
|7. Ilio-ischial foramen is present.||7. llio-ischial foramen is large.||7. Ilio-ischial foramen is absent.|
|8. Ischial tuberosity is absent.||8. It is absent is pigeon.||8. Ischium bears an ischial tuberosity.|
|9. Ischial symphysis is present.||9. It is absent.||9. Ischial symphysis is present.|
|10. Hypoischium is present between the ends of the two ischia.||10. Absent.||10. Absent.|
|11. On the ventral side posteriorly the pubis is formed like a flat elongated and slight ly curved bone, pubis.||11. Pubis is long, slender, curved bone. It lies ventral and parallel with ischial, Pubis.||11. Pubis is flat curved bone directed ventrally pubis symphysis is present. Epipubis is absent.|
|Shark (Scoliodon)||Frog (Rana)|
|1. The pelvic girdle is formed with cartilage tissues.||1. The pelvic girdle is formed chiefly with bone tissues.|
|2. It is embeded in the body wall muscles infront of the cloacal aperture.||2. It is present at the hind end of the trunk.|
|3. It is a simple transverse bar known as ischio - pubis bar.||3. It consists of two similar halves which are separated infront and fused behind to form a median vertical disc.|
|4. Each half of the girdle is formed by the fusion of ilium ischium and pubis.||4. Each half of the girdle consists of three bones - ilium, isclium and pubis.|
|5. Acetabulum is absent.||5. Each side of the vertical disc bears a cup-like depression Acetabulum. The head of femur of the thigh bone articulates with the acetabulum. So all the three bones take part in the formation of the acetabulum.|
|6. The ilium possess an iliac process and a foramen.||6. The ilium extends forwards in the form of an arm to articulate with the transverse process of the sacral vertebra. A vertical ridge is formed along with this arm is called iliac crest.|
|7. Ischium and pubis fused together and form Ischio-pubis bar.||7. The ischium forms the posterior part of the disc and acetabulum. Ischium, fuses with the other side ischium and forms ischium symphysis.|
|8. Pubis fuses with ischium. It is not a separate bone.||8. The pubis forms the ventral part of the disc and acetabulum. It fuses with the pubis of the other half and forms pubic symphysis. It is a separate bone.|
|9. Pubis is formed with cartilage tissue.||9. Pubis is formed with calcified cartilage tissue.|
|10. The pelvic girdle is straight in the middle but bent at the ends. These are produced dorso-lat-erally into short iliac processes.||10. The pelvic girdle V-shaped associated with a vertical disc formed with the ischium & pubis bones.|
|11. The pelvic fins are attached directly.||11. The hind limb bones are articulating with the pelvic girdle.|
|12. The pelvic girdle provides attachment to the claspers through the muscles of male.||12. Such arrangement is absent. Penis is absent.|
15 Main Theories of Biological Evolution of Man (with Statistics)
Read this essay to learn about the 15 main Theories of Biological Evolution of Man !
1. Theory of Eternity:
2. Theory of Divine Creation:
3. Theory of Spontaneous Origin:
4. Theory of Catachysm or Catastrophism:
5. Theory of Uniformitarianism:
6. Theory of Cosmic Origin of life:
7. Theory of Cynogen:
8. Theory of Chemo-synthesis:
9. Theory of Virus
10. Theory of Organic evolution
11. Theory of Lamarck (Lamarckism):
12. Theory of Darwin (Darwinism):
13. Mutation Theory of Hugo De Vries:
14. Theory of Gregor Mendel:
15. Synthetic Theory of Evolution (Neo-Darwinism):
In neoteny, the physiological (or somatic) development of an animal or organism is slowed or delayed.
Ultimately this process results in the retention, in the adults of a species, of juvenile physical characteristics well into maturity.
In vertebrate biology, neoteny is most easily identified when sexually mature, completely viable juveniles or larva are found.
- The cytoplasm contains one or many nuclei.
- Contractile vacuole is absent.
- Mouth is absent.
- Cytoplasm contains food vacuoles. They take up the process of digestion.
- Megalospheric form: Its proloculum is big in size. A single large nucleus is present in one of the chambers. It takes up sexual reproduction.
- Microspheric form: Its proloculum is small in size. Many nuclei are present in the cytoplasm. This form reproduces by asexual reproduction.
The Protozoans are acellular animals without tissues or organs. They exist singly or in colonies. In these colonies all cells are alike. But in "Proterospongia" a colonial flagellate some degree of differentiation exists among the individuals forming the colony.
- Contractile Vacuole" for water regulation in the body.
- Photoreceptors" as sensory structures.
- Cilia and flagella" for locomotion and food collection.
- Skeletal secretions for protection and to give shape.
- The cristae detect turning movements of the head.
- The maculae in the utriculus and sacculus detect changes in the position of the body at rest and in the forward movement. With a change in the position of the body, the otoliths change their position due to gravity and bring pressure on the underlying sensory hairs and this stimulates the neurosensory cells. The body position is corrected. Thus equilibrium is brought forward.
- The maculae & lagena will detect under water sound vibrations to some extent.
Ten pairs of cranial nerves arise from the brain at different locations to supply the anterior region of the body. In addition to them a pair of terminal or pre olfactory nerves (zero nerves) arises from the ventral surface of the cerebrum.
The ten pairs of cranial nerves are furnished below for detail study.