A lamprey is an animal which, though often regarded as a fish, differs from a fish in the absence of paired fins and scales, in the rounded suctorial mouth without supporting jaws, in the presence of gill-pockets in place of the gills of fish, as well as in numerous internal peculiarities. In consequence, the lamprey and the related hag are placed in a distinct class known as cyclostomes, or round mouths. the body is elongated and eel-like, its most conspicuous feature being the seven slits on either side of the neck which communicate with the gill-pockets. The mouth resembles that of the hag in the presence of a muscular rasp known as the tongue. The food consists of all sorts of small animals, as well as of the dead bodies of larger ones, and even of the flesh and blood of living creatures, to which the lampreys attach themselves after the fashion of the hag. They also attach themselves by their mouths to stones, whence the generic name, ‘stone-sucker’. Internally there is much general resemblance to the hag; but the lamprey has well-developed eyes, and has a delicate series of cartilages known as as the branchial basket-work, which supports the pharynx. The adults die soon after spawning near the heads of rivers or creeks; the young, which in many respects differ from their parents, were formerly placed in a separate genus as Ammocoetes. The great sea lamprey (Petromyzon marinus), sometimes 3 feet long, is found on both coasts of the N. Atlantic. Several smaller species inhabit the lakes and rivers of the United States.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 7) (New York, NY: Thomas Nelson and Sons, 1917) 190