CORNIFIED LAYER-RABBIT

The outer most cells on the skin surface are thin,dead and fully keratinised. They form a horny or cornified layer called stratum corneum. It is especially thick on soles and palms.The outer portion of this layer is constantly being worn away,the dandruff is a familiar .News cells are constantly added from when the granular cells become horny and die. This dead layer is tough ,prevents mechanical injuries and fungal and bacterial attacka,and reduces water loss from the body. The outer surface of epidermis contains minute openings of sweat glands and hair follicles.

TETRODON,DIODON,OSTRACION

Family tetrodontidae,order tetraodontiformes.commonly called globe fish or puffer.shape round or globose when taken out the water,it inflates suddenly with air like a balloon and a sound is emitted by forceful expulsion of air fromoesophagus. scales modified into small spines,especially on ventral side. mouth narrow,teeth fused to form beak.eyes large and protruding pelvic fins lacking.it contain alkaloid poisoncalled tetrodotoxin which is used in lung infection in japan.
DIODON-Family diodontidae,order tetraodontiformes. commonly called porcupine fish. occurs from red sea through indian seas to pacific ocean.Body uniformly covered by large movable spines for defence.
OSTRACION-FAMILYostraciontidae,order tetraodontiformes.Body roughly triangular and encased in a carapace or armour of hexagonal bony plates.commonly called trunk fish or coffer fish.due to presence of two horn like suptaorbitalspines called as cow fish.

STRUCTURE OF SKIN-RABBIT

The skin of rabbit is also built of two main parts -an outer epidermis and an inner dermis.
EPIDERMIS-It is the outer thin stratified epithelium developed from the embryonic ectoderm.The epidermis consist of malpighian layer and the superficial cornified layer.
(a)MALPIGHIAN LAYER-The malpighian layer,or stratum malpighii is divided into (1)SRRATUM GERMINATIVUM-The germinal layer is the innermost layer in contact with the basement membrane secreatedby the underlying dermis.Its cells are columnar,arranged in a single row one cell thick,and continually divide mitotically adding new cells to the epidermis
.

STRATUM SPINOSUM-Its lies above the germinal layer and is also called the transitional layer. It is several layer thick and made of polyhedral cells.these cells are gradually pushed outwards,they become flattened and keratinized due to deposition of a horny scleroprotein known as keratin.
STRARUM GRANULOSUM-The cells in the upper part of stratum spinosum form the granular layer containing keratohyalin granules. It is developed in parts of the body having thick epidermis such nas the palms and the soles.
STRATUM LUCIDUM-Above granular layer in palms ther is non-stainable layer of shiny and refracitle cells.

HEMIRHAMPHUS,ANABAS,REMORA

Family hemirhamphidae, order beloniformes. found in river and ponds of w.bengal and orissa. called as haif-beaked fish.lower dentaries projected beyond the upper jaw,both having pointed teeth.
ANABAS-family Anabantidae ,order perciformes.accessory respiratory organs of thin laminae in supra-branchial chambers,for breathing atmospheric air.travel on land by fins and opercular spines.
REMORA-Family echeneidae, order echeneiformes.size up to 50 cm.scales minute,head depressed and its upper surface bears a large,flat,oval adhesive discor sucker made by two rows of transverse lamillae.scales modified anterior fin. fish usually carried from place to place attached to body of largefish.naive captures sea turtles and fishes with a remora tied with a cord.remora eats smaller fishes.

HIPPOCAMPUS,SYNGNATHUS,FISTULARIA

Belongs to family syngnathidae, order syngnathiformes.Size 5 to 20 cm. Found in tropical and temperate seas including Indian ocean commonly called sea-horse.
BODY- Head large at right angle,tubular snout,mouth toothless and suctorial. Tailed long ,prehensil and coiled around sea-weeds, gills lophobranchs made of several small rounded lobes.On the belly of male is a brood pouch for incubating eggs. On the belly of female is a small anal fin.
SYNGNATHUS- family syngnathidae,order syngnathiformes.45 cm long.structures and habits similar to those of Hippocampus,except that is non-prehensile and carries a small caudal fin,COMMONLY CALLED PIPE FISH.
FISTULARIA-. COMMONLY CALLED FLUTE FISH because of slender elongated eel -like body and long tubular snout.skin naked. mouth small,narrow with minute teeth.caudal fin present with middle caudal ray much elongated and supported by horny rays.

AMIA

The single species of bowfin, amiacalva, is another large,powerful,predatory freaswater fish of north america. The head skeleton and scales are simplifedAND TAIL IS ALMOST HOMOCERCAL. It moves by undulation of body and the long dorsal fin.

POLYODON

Paddle fishes or spoonbills are large bizarre fishes with an intriguing. The great elongation of snout into a flat oar-like rostrum. It is used to strir food from muddy river bottom,paddle fishes are planktivores.

OSTEICHTHYES-BONY FISH-latimeria

There are 20,000 living species of bony fish.The teleostei comprising about 17,000 species.
LOBE-FINNED FISH
LATIMERIA-They were dominant in devonian times about 280 million years.Dr.j.l.b smith of rhodes university named this "living fossil" Latimeria chalumnae. Latimer is blue-grey with irregular white spots and highly reflective golden eyes. size range 0.75 to slightly over 2 m.In the absence of claspers male latimeria achieve copulation is not know.It discovered in 1938 coast of south africa,crossopterygians are all extinct .
The skeletal elements of paired fins lobes resembled the priximal skeletal elements of tetrapod limbs.
skull was similar to that of earliest amphibians.
Fresh waters forms migrated from one body of water to another because they could use their air bladders like lungs.

OSTEICHTHYES-SCORPAENIFORMES

Enlarged heads and pectoral fins.
Projecting spines from gill covering.
e.g pterois(scorpion fish)
ORDER 12.PLEURONECTIFORMES
Bottom dwellers.
Body flat, lying one side.
Head asymmetrical ,both eyes present on upper or dorsal side.
Dorsal and anal fins fringing body.e.g
flatfish-pleuronectes,synaptura,solea.
ORDER 13. ECHENEIFORMES
Scales cycloid.
No air bladder.
Dorsal fins form a flat oval adhesive disc.
e,g echeneis or remora(sucker fish)
ORDER 14. TETRAODONTIFORMES OR PLECTOGNATHI
Strong jaws with a sharp beak.
Scales often spiny.
e.g diodon(porcupine fish),tetrodon(globe fish),ostracion(trunk fish)
ORDER 15. LOPHIIFORMES
Bulb like tip over head to lure prey into wide mouth.
luminescent organ present.
e,g antennarius(angler fishes)

OSTEICHTHYES- 5. ORDER BELONIFORMES

Scales cycloid.
Pectoral fins large.
e.g
exocoetus ,cypselurus(flying fish)belone(garfish),hemirhamphus(half beak),belone(garfish).
ORDER 6. SYNGNATHIFORMES OR SOLENICHTHYES
Protective scales on body.
snout tubular with suctorial mouth.
swim bladder closed.
e.g hippocampus(sea horse),syngnathus(pipe fish),fistularia(flute fish)
ORDER 7.OPHIOCEPHALIFORMES OR CHANNIFORMES
Head depressed with plate-like scales.
Air bladder long and without duct.
Accessory respiratory organs present.
e.g ophiocephalus or channa.
ORDER 8. SYMBRANCHIFORMES
Body elongated,e,g eel.
Gill slits join to form ventral slit.
Paired fins,air bladder lacking.
e.g amphipnous,symbranchus(eels).
ORDER 9. MASTACEMBELIFORMES
Body eel-like.
nostrils on tubular tentacles at end of snout. e,g mastacembelus,macrognathus.
ORDER 10.PERCIFORMESOR PERCOMORPHI
Fin spines present.
Dorsal fins weberian apparatus absent.
Air bladder with out duct.e,g lates(bhetki)

OSTEICHTHYES-SUPERORDER-TELEOSTEI

Mouth opening terminal,small.
Scales cycloid,ctenoid or absent.
Tail fin homocercal.
 A hydrostatic swim bladder usually present.
Advanced or modern ray-finned fishes.
ORDER 1. CLUPEIFORMES
Scales cycloid.
Head and operculum not scaled.
Fins without spines.
Tail fin homocercal.
Pelvic finsabdominal.
Air bladder withopen duct to pharynx.
No auditory vesicles.
e.g clupea,salmo sardinops esox notopterus.
ORDER 2. SCOPELIFORMES
Deep sea forms with phosphorescent organs.
Mouth wide with minute teeth.Swim bladder absent. Dorsal and anal fins with claspers.
ORDER 3.CYPRINIFORMES
Air bladder with duct to pharynx. ossicles present between airbladderand internalear.
e.g labeorohita clarius wallago electrophorus.
ORDER  4. ANGUILIIFORMES
Body long and slender,snake-like .
Scales absent.
Dorsal and anal fins long .
Pelvic fins present.
Air bladder .
e.g anguilla muraena(moray)

OSTEICHTHYES-HOLOSTEI

Mouth opening small.
Ganoid or cycloid scales.
Tail fin heterocercal.
Ray-finned fish, transitinal between CHONDROSTEI AND TELEOSTEI.
ORDER 1. AMIIFORMES
Thin, overlapping cycloid scales.
Snout normal ,rounded.
Long dorsal fin.
e.g AMIA(BOWFIN)
ORDER 2. SEMIONOTIFORMES
Scales rhomboidal ganoid in oblique rows.
Snout and body elongated. e.g Lepidosteus or lepisosteus(garpike)

OSTEICHTHYES-SUBCLASS-ACTINOPTERYGII

Paired fins thin,broad, without fleshy basal lobes, and supported by dermal finrays.
One dorsal fin, may be divided.
Caudal fin without epichordal lobe.
Olfactory sacs not connected to mouth cavity.
Popularly called ray- finned fishes. divided into three infraclasses or super orders CHONDROSTEL HOLOSTEI AND TELEOSTEI.
SUPERORDER A. CHONDROSTEI
Mouth opening large.
Scales ganoid.
Tail heterocercal.
e.g ray-finned fish or cartilaginous ganoid.
ORDER 1. POLYPTERIFORES
Rhomboid ganoid scales and pectrol fins.
Dorsal fin of eight finlets.
Ossified skeleton.
e.g polypterus(bichir)
ORDER 2. ACIPENSERIFORMES
Scales less .
Skleton cartilaginous.
e.g acipenser(sturgeon), polyodon(paddlefish)

OSTEICHTHYES-BONY FISH

SUBCLASS-SARCOPTERYGII
Paired fins leg-like with a fleshy,bony central axis covered by scales.
Dorsal fins.
Caudal fin hreterocercal with an epichordal lobe.
Olfactory sacs usually connected to mouth cavity by internal nostrils or choanae.
Fleshy or lobe-finned or air breathing fish.
Divided into two superorders .ORDER 1. CROSSOPTERYGII
Paired fins lobate.
Caudal fin three lobed.
Premaxillae and maxillae present.
Internal nares present or absent.
Spiracles present.
Air bladder vestigial.
Primitive fleshy-finned extinct fishes. Latimeria. ORDER 2. DIPNOI
Median fins continuous to form diphycercal tail.
Premaxillae and maxillae absent.
Internal nares present and spiracles absent.
Air bladder single or paired,lung like e.gEPICERATODUS,PROTOPTERUS LEPIDOSIREN.

OSTEICHTHYES-CLASSIFICATION

It includes true bony fishes.There include 20,000 living species,both freshwater and marine. Some of the freshwater forms are the carp,perch,bass, trout,catfish,sucker. Where as marine fishes are the tarpon,meckerel,tuna,sailfish,barracula,flyingfish. The classification of class osteichthyes by A.S.ROMER(1966) . The two subclass include sarcopterygii and Actionpterygii.The subclass Teleostei include 17,000 species the singke largest group of living vertebrates.

OSTEICHTHYES-BONY FISH

Cloaca lacking.
Anus absent.
Respiration by four pair of gill on bony gill arches, covered by a common operculum on either side.
Ventral heart
Sinus venosus and conus arteriosus present.
Adult kidneys mesonephric.
Excretion ureotelic.
Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum.
Cranial nerves 10 pairs.
Well developed lateral line system.
Internal ear with three semicircular canals.
Sexes seperate.
Gonads paired.
 Fertilization usually external.
Mostly oviparous,rarely ovoviviparous or viviparous.
Eggs minute to 12 mm.
Cleavage meroblastic.
Development direct, rarely with metamorphosis.
Claspers absent.

OSTEICHTHYES-BONY FISH

GENERAL CHARACTERS
Inhabit all sorts of water-fresh,brackish or salt warm or cold water.
Body spindle-shaped and streamlined.
Fins both median and paired ,supported by fin rays of cartilage or bone.
Tail usually homocercal.
Skin with mucous gland,usually with embedded dermal scales of 3 types ganoid,cycloid or ctenoid.
Placoid abescent.
Endoskeleton chiefly of bone.
Claspers absent.
Mouth terminal or subterminal.

BRANCHIOSTOMA-GAMETES

Mature ovaries or testes can be identified only in sections because of the different structure of spermatozoa and ova they contain. The testes present a streaky appearance due to presence of spermatozoa. The mature sperm of branchiostoma one of the smallest among chordates in length. It consist of the nucleated head with acrosome a middle piece and a long tail. The ovary contain ova which are large and some what rounded cells each 0.i mm in diameter and having a large nucleus. They are microlecithal or poor in yolk content. Gonoducts are abesenr. Mature gametes are discharged into the atrium by rupture or dehiscence of gonadial wall along certain waeker spots called cicatrices which after wards close. The gametes so liberated escape through atriopore with the outgoing water current.

BRANCHIOSTOMA-REPRODUCTIVE SYSTEM

In amphioxus the two sexes are separate but there is no sexual dimorphism as male and female individuals look identical.
GONADS-The adult has 26 to27 pair of similar gonads arranged metamerically in two rows,one pair in each segment from 25 to 51. The gonads are situated ventro-laterally from middle of pharyngeal region up to the atriopore. They are visible through the transparent bodywall arranged in a linear series . Gonads are simple hollow sacs mesodermal in origin and bulginginto atrial cavity. They are covered on the outer side by the bodywall and on the inner side by the atrial epithelium. Gonads contain an outer secondary gonadial cavity around an inner primary gonadial cavity surrounding a group of germ cells which arises from its wall.
DEVELOPMENT-Fertilization and development take place externally in sea water .

BRANCHIOSTOMA-FREE NERVE ENDINGS

These are sensitive to internal stimuli such as contractions of muscles.The exteroreceptors there are also present some enteroreceptorsin the form of free nerve ending in muscles.

BRANCHIOSTOMA-SENSORY CELLS AND PAPILLAE

Sensory cells scattered all over the epidermis,especially on the dorsal side. Groups of sensory cells or papillae are present on oral cirri and velar tentacles. These are chaemoreceptors and tactile organs.

BRANCHIOSTOMA-INFUNDIBULAR ORGAN

It is located at the floor of cerebral ventricle . It consists of a patch of tall ,columnar and strongly ciliated epitheliar cells. The exact function of infundibular orgain is uncertain. The various function assigned are detection of pressure in the cerebro-spinal fluid perceiving the shadow cast by cephalic pigment spot or neurosecretion.

BRANCHIOSTOMA-KOLLICKER'S PIT

It is a depression of ciliated ectodermal cells on the roof in the anterior region of cerebral vesicle. The area where larval neuropore closes when the adult neural tube is formed. It lacks sensory cells but it is considered anolfacrory chaemoreceptor due to its position corresponding with the single nostril of cyclostomes.

BRANCHIOSTOMA-HATSCHEK'S GROOVE

The pit and groove of  Hatschek present in the roof of oral hood are considered sensory organs of unknown function.

BRANCHIOSTOMA-CEPHALIC PIGMENT SPOT

It is large pigmented spot on the anterior wall of cerebral vesicle. It is act as cerebral eye. but it lacks a lens and is also not photosensitive. It is supposed to shield the ocelli from any frontal stimulation by light and probably acts as a thermoreceptor.

BRANCHIOSTOMA-NERVES, OCELLI

The  Peripheral nervous system includes paired nerves from nerve cord.The two pair arising from cephalic vesicle are called cerebral nerves. They lack ventral roots. They are sensory in nature and convey impulses from receptors of snout, oral hood and buccal cirri to the nerve cord.The nerves arising from nerve cord behind the cerebral vesicle are called spinal nerves. Each pair of spinal nerves actually includes separate dorsal and ventral nerve roots .Dorsal nerve root is both sensory and motor and passes out to skin between myotomes. The ventral nerve root is motor and opposite to the myotome .The dorsal and ventral roots of a pair do not originate at the same level and the dorsal root of one side lies opposite the ventral root. The dorsal root is single the ventral root is made of several branches. Nerves of amphioxusare primitive and non-myelinated is not covered by a sheath of myelin in the vertebrates.
OCELLI-These are photoreceptors or light-sensitive organs on the ventro-lateral sides of nerve cord. They are originated in different directions and help the animal in burrowing in sand or in swimming spirally to perceive light from all directions. The eye spot or ocelli is made up of two cells an outer pigment cell or melanocyte and inner photosensitive cell with a striated apicalborder which serves as a lens. The photosensitive cell sends a fine nerve fibre to the nerve cord.

BRANCHIOSTOMA-NERVE CORD

The central nervous system of Branchiostoma includes a hollow dorsal neural tube or nerve cord lying mid-dorsally . It has no ganglia. Its anterior end terminates in the rostrum. It has slight enlargement brain called cerebral vesicle. The posterior part called the spinal cord. The narrow canal called neurocoel. It dilates within the cerebral vesicle forming its ventricle.At the roof arise pouch -like blind dorsal diverticulum that extends behind the central canal. The cerebral vesicle contains two receptor organ a pigment spot infundibular organs on its floor. It consists of inner grey matter of nerve cells surroundings the central canal and outer white matter of nerve fibres. These enables the animal to contract suddenely and violently in case of danger.

BRANCHIOSTOMA-AUTONOMIC NERVOUS SYSTEM

It consist of two nerve plexes in the gut wall connected to nerve cord plexes in the gut wall connected to nerve cord by visceral .The autonomous system control the involuntary muscles of the gut wall. Sympathetic ganglia are lacking.

BRANCHIOSTOMA-NERVOUS SYSTEM

The nervous system is very simple. The well developed brain, as found in higher chordates is absent.

BRANCHIOSTOMA-BROWN FUNNELS

The two sac like brown funnel are situateddorsally upon the posteroor end of pharynx. The narrow anterior end of each funnel opens into the epibranchial or dorsal coelomic canal of its side.. Most the funnel where the excretory while of to be receptor organs.