146 THE POPULAR SCIENCE MONTHLY 



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 explana- 

 tion of the genesis of the stellar world. This theory was strengthened 

 by the study of paleontology in England, and of embryology in Ger- 

 many. 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 mor- 

 phologist. " 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 catas- 

 trophic 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 influ- 

 ence 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 Konigsberg and St. Petersburg, was also of importance. But 



