Chapter 28 THE CYCLOSTOMES, OR LAMPREYS

The Lampreys.-Passing upward from the lancelets and setting aside the descending series of Tunicates, we have a long step indeed to the next class of fish-like vertebrates. During the period this great gap represents in time we have the development of brain, skull, heart, and other differentiated organs replacing the simple structures found in the

            
            

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