Koelliker.--Albrecht von Koelliker (1817-1905) was one of the greatest histologists of the nineteenth century. He is a striking figure in the development of biology in a general way, distinguished as an embryologist, as a histologist, and in other connections. During his long life, from 1817 to 1905, he made an astounding number of additions to our knowledge of microscopic anatomy. In the early years of his scientific activity, "he helped in establishing the cell-theory, he traced the origin of tissues from the segmenting ovum through the developing embryo, he demonstrated the continuity between nerve-fibers and nerve-cells of vertebrates (1845), ... and much more." He is mentioned further, in connection with the rise of embryology, in Chapter X. The strong features of this veteran of research are shown in the portrait, Fig. 50, which represents him at the age of seventy. In 1847 he was called to the University of Würzburg, where he remained to the time of his death. From 1850 to 1900, scarcely a year passed without some important contribution from Von Koelliker extending the knowledge of histology. His famous text-book on the structure of the tissues (_Handbuch der Gewebelehre_) passed through six editions from 1852 to 1893, the final edition of it being worked over and brought up to date by this extraordinary man after he had passed the age of seventy-five. By workers in biology this will be recognized as a colossal task. In the second volume of the last edition of this work, which appeared in 1893, he went completely over the ground of the vast accumulation of information regarding the nervous system which an army of gifted and energetic workers had produced. This was all thoroughly digested, and his histological work brought down to date. Schultze.--The fine observations of Max Schultze (1825-1874) may also be grouped with those of the histologists. We shall have occasion to speak of him more particularly in the chapter on Protoplasm. He did memorable service for general biology in establishing the protoplasm doctrine, but many of his scientific memoirs are in the line of normal histology; as, those on the structure of the olfactory membrane, on the retina of the eye, the muscle elements, the nerves, etc., etc. [Illustration: Fig. 50.--Von Koelliker, 1817-1905.]