Secondary Blinding among the Phacopid Trilobites and its Significance

摘要: Secondary blinding occurs in one major group of Phacopid Trilobites (Family Phacopidae). Intermediate stages between the normal condition and total blindness show migration eyes toward antero-lateral cephafic margin reduction visual area. The disappear before reaching cephalic border, but facial suture continues, genus (Ductina) assuming a secondarily hypoparian position. Disappearance eye agrees with Lalicker's observation that first appear on dorsal surface cephalon. This paper is result studies pursued at Museum Comparative Zoology, Cambridge, Mass., other results which have been published previously. writer wishes to express his gratitude Professor Percy E. Raymond for criticism assistance during preparation manuscript.