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"The lamprey (Petromyzon marinus). I. Then entire animal; note the seven gill-slits of which the first is marked g.s., the nostril n., and the unpaired median fins. II. Ventral aspect of the head; u.t., upper teeth; l.t., lower teeth; p., the piston in the mouth. III. Upper surface of the head; n., the nostril with the pineal groove behind it; e., the eye." -Thomson, 1916

Sea Lamprey

"The lamprey (Petromyzon marinus). I. Then entire animal; note the seven gill-slits of which the first…

An illustration of the median longitudinal section through anterior end of the sea lamprey. "a.v.o, Antrio-ventricular opening; br, Brain; br.o, Internal opening of gill sac; d.a, Dorsal aorta; d.c, Ductus cuvieri; h.v, Hepatic vein; i.j.v, Inferior jugular vein; N, Notochord; oes, Esophagus; olf, Olfactory organ; oc, Pericardium; p.c.v, Left posterior cardinal vein; pit, Pituitary tube; V, Ventricle; v, Velum." (Britannica, 1910)

Cross Section View of a Sea Lamprey

An illustration of the median longitudinal section through anterior end of the sea lamprey. "a.v.o,…