Recent Tendencies. Experimental Embryology.—Soon after the publication of Balfour's great work on 'Comparative Embryology' a new tendency in research began to appear which led onward to the establishment of experimental embryology. All previous work in this field had been concerned with the structure or architecture of organisms, but now the physiological side began to receive attention. Whitman has stated with great aptness the interdependence of these two lines of work as follows: "Morphology raises the question, How came the
organic mechanism into existence? Has it had a history, reaching its present stage of perfection through a long series of gradations, the first term of which was a relatively simple stage? The embryological history is traced out, and the paleontological records are searched, until the evidence from both sources establishes the fact that the organ or organism under study is but the summation of modifications and elaborations of a relatively simple primordial. This point settled, physiology is called upon to complete the story. Have the functions remained the same through the series? or have they undergone a series of modifications, differentations and improvements more or less parallel with the morphological series?"
