THE AMERICAN NATURALIST, An Illustrated Magazine OF NATURAL HISTORY. EDITED BY E. D. COPE AND J. S. KINGSLEY, - ASSISTED BY DR. C. O. WHITMAN, DR. C. E. BESSEY, H. C MERCER, PROF. C. M. WEED, VOLUME XXX. PHILADELPHIA, U. S. A. THE EDWARDS & DOCKER CO., 518 & 520 MINOR STREET, 1896. A Comparative Study of the Point of Acute Vision in the Vertebrata The Formulation of the Natural Sciences. E. D. COPE......... ΙΟΙ The History and Principles of Geology, and Its Aim. J. C. HARTZELL, The Constancy of Bacterial Species in Normal Fore Milk. H. L. BOL- 177 285 Life Before Fossils. CHARLES MORRIS............................. Birds of New Guinea (Continued from p. 1065, Vol. XXIX). G. S. The Bearing of the Origin and Differentiation of the Sex Cells in Cymatogaster on the Idea of the Continuity of the Germ Plasm. ...... The Probable Influence of Disturbed Nutrition on the Evolution of 265 372, 451, 554 On the Mississippi Valley Unionidæ Found in the St. Lawrence and Atlantic Drainage Areas. C. T. SIMPSON Extensive Migration of Birds as a Check Upon the Production of Geo- graphical Varieties. T. H. MONTGOMERY... The Oldest Civilized Man (Illustrated). E. D. CopE................... 616 The Bacterial Diseases of Plants: A Critical Review of the Present State of Our Knowledge. E. F. SMITH...............626, 716, 796, The Meaning and Structure of the So-called "Mushroom Bodies" of 643 Prof. Baldwin's "New Factor in Evolution." HERBERT NICHOLS..... 697 |