The main currents of zoölogy . FIG. 17.—FRAXCIS M. BALFOUR(1851-1882) FIG. 18.—CLAUDE BERNARD(1813-1878) THE RISE OF EMBRYOLOGY 73 published in 1864, gives an interesting account ofhis mental development. Between von Baer and Balfour (1851-1882) underwhom embryology took on modern aspects, theobservations on the development of animals weregreatly multiplied. Activity was increased after theannouncement of the cell-theory (1839) and em-bryologists began to see more clearly the significanceof the germinal elements and the germ-layers. It was determined that the egg and the sperm aresingle cells,
The main currents of zoölogy . FIG. 17.—FRAXCIS M. BALFOUR(1851-1882) FIG. 18.—CLAUDE BERNARD(1813-1878) THE RISE OF EMBRYOLOGY 73 published in 1864, gives an interesting account ofhis mental development. Between von Baer and Balfour (1851-1882) underwhom embryology took on modern aspects, theobservations on the development of animals weregreatly multiplied. Activity was increased after theannouncement of the cell-theory (1839) and em-bryologists began to see more clearly the significanceof the germinal elements and the germ-layers. It was determined that the egg and the sperm aresingle cells, the final step in reference to all eggsbeing taken by Gegenbaur in 1865. The three germ-layers common to all animals above the Ccelenterates(Hydra, Hydroids, Jelly-fish, etc.) were shown to beessentially alike as to origin and to give rise to thesame kind of tissues in the different animals. In thelight of embryology, all animals were seen to berelated through ancestral lines and to be united on thebroad plane of similari
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