Fishes . edto the lancelets alone. It refers to those chordate forms whichhave no skull nor brain, as distinguished from the Cranwta,or forms with a distinct brain having a bony or cartilaginouscapsule for its protection. Origin of Lancelets.—It is doubtless true, as Dr. Willey sug-gests, that the Vertebrates became separated from their worm-like ancestry through the concentration of the central along the dorsal side of the body and its conversion i66 The Leptocardii, or Lancelets into a hollow tube. Besides this trait two others are commonto all of them, the presence of the gill
Fishes . edto the lancelets alone. It refers to those chordate forms whichhave no skull nor brain, as distinguished from the Cranwta,or forms with a distinct brain having a bony or cartilaginouscapsule for its protection. Origin of Lancelets.—It is doubtless true, as Dr. Willey sug-gests, that the Vertebrates became separated from their worm-like ancestry through the concentration of the central along the dorsal side of the body and its conversion i66 The Leptocardii, or Lancelets into a hollow tube. Besides this trait two others are commonto all of them, the presence of the gill-slits and that of the noto-chord. The gill-slits may have ser\ed primarily to relieve thestomach of water, as in the lowest forms they enter directly intothe body-cavity. The primitive function of the notochord isstill far from clear, but its ultimate use of its structures inaffording protection and in furnishing a fulcrum for the musclesand limbs is of the greatest importance in the processes of IIG.—Gill-basket of Lamprey.
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