The pigment present is probably a porphyropsin. The anterior end of spinal cord is enlarged into a complicated brain from which special cranial nerves arise. The larva migrates from river to the sea and starts its adult life. These muscles are helpful in swimming of the fish. Fertilisation is, thus, external. The lumen of the intestine is crescentic due to the presence of a spiral longitudinal fold, the typhlosole. Contraction of muscles of one side bends the body to that side. The ventral aorta swells at its base to form bulbus arteriosus.

Between the optic lobes and the medulla oblongata extends the choroid plexus.

The intestinal mucosa is also made of single-layered epithelium produced into spiral folds.

They are predators on the body of fishes. (vi) An elongated lingual cartilage supports the tongue. The muscle fibres are striated. Marine species have anadromous migratory habit. The pigment present is probably a porphyropsin. At the end of life the endostyle forms a large mass, which is made up of secretory and ciliated cells. The renal portal vein is absent.

(i) Ventral branchial sinus or ventral jugular sinus (ii) Inferior branchial sinus present below the gill pouches (iii) Superior branchial sinus present on the gill pouches. When the gonads become mature the adult again migrates to freshwater for the purpose of spawning. Such teeth are present on the anterior area of the buccal disc. The secretion contains anticoagulant which prevents the coagulation of the blood during feeding. The sexes are separate in the adult while the early developmental stages of ammocoete larvae possess hermaphrodite gonad containing both oocyte and spermatocyte. The anterior funnels together form the pronephros (Fig. Rods of cartilage extend dorsally and ventrally into the fins (Fig. The male has different shape of dorsal fin. The lampreys or lamper eel and hagfishes are the sole existing representative of group ‘Agnatha’, i.e., ‘Jawless fish’. Numerous teeth are present in the buccal funnel which are laminated horny cones. Endocrine Organs 10. The mouth is surrounded by a buccal funnel. In early stages the neural tube does not possess neurocoel and is called a neural rod, later it is transformed into brain and spinal cord. Life history of all lampreys includes two distinct stages, the ammocoete larva lives in fresh water, buried in the mud and is microphagous while the adult lamprey has a sucking mouth, and usually lives in the sea, where it feeds on the fishes and turtles. Both the layers are separated from each other by connective tissue which contains blood capillaries and migratory pigment cells or the chromatophore. The pharynx is continued posteriorly into the oesophagus. A broad infundibulum lies attached beneath the diencephalon and it dorsally gives off a pineal or median eye. Morphologically the pineal eye seems to be placed on the right side while para-pineal organ is on the left side. Special set of muscles operate the buccal funnel and tongue apparatus. The epidermis consists of three or more layers of mucous cells, provided with large intracellular spaces. The water enters into the respiratory pharynx through the 7 pairs of gill-pouches and passes out through the same route. The hepatic portal vein drains blood from the gut and pour into the liver by a contractile portal heart. Metamorphosis is completed within a few weeks. (4) The single dorsal fin is divided into two by a median notch. (5) Velum reduces and surrounds the opening of respiratory tube. (7) The single dorsal fin is divided into two by a median notch. These are very small sized glands and lie diffused in dorsal and ventral parts of pharyngeal pouches. The cartilage is composed of large cells embedded in a matrix of chondrin. The elastic branchial basket is compressed by the contraction of the muscles to throw the water like jets through the gill-openings, while during inspiration the branchial basket expands.
1.6). Marine species have anadromous migratory habit. The skull is of a primitive type. (2) The endostyle is replaced by thyroid gland ventral to the pharynx. The skeleton of lamprey consists of notochord and various cartilaginous structures. In ammocoete larva the paired eyes are buried below the pigmented skin.
This system consists of various tubes opening via coelom to the exterior through which both excretory and genital products are carried away. The blood forming tissue is present in the kidneys and the spinal cord. The red cells of lamprey are nucleated and spherical in shape of about 710 μ in size. Histologically, pineal eye is similar to that of paired eyes.

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