posed a theory of the formation of the universe which was afterwards developed into that well-known nebular hypothesis which till within a few years has been almost universally accepted as a reasonable explanation of the genesis of the stellar world. This theory was strengthened by the study of paleontology in England, and of embryology in Germany. During the first half of the century it was thought by many that life repeats itself, comes and goes in well-defined circles, but this hypothesis was displaced in the second half of the century by a belief in the gradual development of all natural forces toward a certain end. Hence the introduction of the word evolution.
Hutton's opposition to the catastrophic theory in geology prepared the way for Lyell in England who was unwilling to accept the genetic theory without modification. Nor was he content to remain a morphologist. "The Vestiges of Creation," published in 1840, and written by Robert Chambers, of Edinburgh, favored the genetic theory and applied it to the cosmic molar and molecular phenomena. The book, valuable for its suggestions and for the discussions to which it gave rise, met with decided opposition in many circles on the ground of its materialistic views and its tendency to explain nature without any reference to the supernatural. For a similar reason the opinions of many German scientists were unacceptable in Great Britain.
Yet in spite of the weight which the names of Humboldt, Cuvier and Richard Owen carried, it became evident, about the middle of the nineteenth century, that the morphological theory alone would not satisfy the scientific world. Doubts began to be cherished as to the fixity and permanence of species. There was opposition to the catastrophic theories in geology. Sir Charles Lyell in his "Principles of Geology" suggests orderly development, though without breaking with the older theories. Herbert Spencer in his writings in the early fifties sees more clearly than most others the necessity of some such theory as that which was afterwards known as the theory of evolution, or the gradual development of all forms and all life out of a simple original substance. As early as 1759 C. T. Wulff, as a result of his studies on cellular structure and growth, had come to the conclusion that growth is by additions and gave the world his theory of epigenesis. His influence dates from the year 1812 and was made effective through the work of Schleiden, Schwann, Mohl and Pander, who led the way in the study of that scientific embryology of which Pander is accounted the founder. Through these studies and those of Haeckel, which came later, the essential identity of the cell in structure substance and growth in the vegetable and animal world, was established.
As Herbert Spencer had prepared the English mind for the views of Darwin, so Haeckel prepared the way for their favorable consideration in Germany and on the continent. The work of Lamarck and of Von Baer, of Königsberg and St. Petersburg, was also of importance. But