The period between Von Baer and Balfour proved to be one of great importance on account of the general advances in knowledge of all organic nature. Observations were moving toward a better and more consistent conception of the structure of animals and plants. A new comparative anatomy, more profound and richer in meaning than Cuvier's, was arising. The edifice on the foundation of Von Baer's work was now emerging into recognizable outlines. The Period of Balfour, with an Indication of Present Tendencies Balfour's Masterly Work.--The workers of this period inherited all the accumulations of previous efforts, and the time was ripe for a new step. Observations on the development of different animals, vertebrates and invertebrates, had accumulated in great number, but they were scattered through technical periodicals, transactions of learned societies, monographs, etc., and there was no compact science of embryology with definite outlines. Balfour reviewed all this mass of information, digested it, and molded it into an organized whole. The results were published in the form of two volumes with the title of _Comparative Embryology_. This book of "almost priceless value" was given to the world in 1880-1881. It was a colossal undertaking, but Balfour was a phenomenal worker. Before his untimely death at the age of thirty-one, he had been able to complete this work and to produce, besides, a large number of technical researches. The period of Balfour is taken arbitrarily in this volume as beginning about 1874, when he published, with Michael Foster, _The Elements of Embryology_. [Illustration: Fig. 69.--Francis M. Balfour, 1851-1882.] His University Career.--Balfour (Fig. 69) was born in 1851. During his days of preparation for the university he was a good student, but did not exhibit in any marked way the powers for which later he became distinguished. At Cambridge, his distinguished teacher, the late Sir Michael Foster, recognized his great talents, and encouraged him to begin work in embryology. His labors in this field once begun, he threw himself into it with great intensity. He rose rapidly to a professorship in Cambridge, and so great was his enthusiasm and earnestness as a lecturer that in seven years "voluntary attendance on his classes advanced from ten to ninety." He was also a stimulator of research, and at the time of his death there were twenty students engaged in his laboratory on problems of development.