BAER, KARL ERNST VON (1792-1876), German biolo gist, was born at Piep, Estonia, on Feb. 29 1792. His father, a small landowner, sent him to school at Reval, which he left in his 18th year to study medicine at Dorpat university. The lec tures of K. F. Burdach (1776-1847) suggested research in the wider field of life-history, and as at that time Germany offered more facilities for and greater encouragement to scientific work, von Baer went to Wirrzburg, where J. I. J. Dellinger (177o-1841), father of the Catholic theologian, was professor of anatomy. He collaborated with C. H. Pander (1794-1865) in researches on the evolution of the chick, the results of which were first published in Burdach's treatise on physiology. Continuing his investigations alone von Baer extended them to the evolution of organisms generally, and after a sojourn at Berlin he was invited by his old teacher Burdach, who had become professor of anatomy at Konigsberg, to join him as prosector and chief of the new zoolog ical museum . Von Baer's discovery of the human ovum is the subject of his Epistola de Ovo Mammalium et Hominis Genesi (Leipzig, 1827), and in the following year he published the first part of his History of the Development of Animals die Entwickelungsgeschichte der Thiere), the second part following in 1837. In this work he demonstrated that the Graafian follicles in the ovary are not the actual eggs, but that they con tain the true ovum. He next showed that in all vertebrates the primary stage of cleavage of the fertilized egg is followed by modification into leaf-like germ-layers (skin, muscular, vascular and mucous) whence arise the several organs of the body by differentiation. He further discovered the gelatinous, cylindrical cord, known as the notochord which passes along the body of the embryo of vertebrates, in the lower types of which it is limited to the entire inner skeleton, while in the higher the backbone and skull are developed round it. In his History of Development he suggests, "Are not all animals in the beginning of their develop ment essentially alike, and is there not a primary form common to all?" (i. p. 223). Notwithstanding this, the "telic" idea, with the archetypal theory which it involved, possessed von Baer to the end of his life, and explains his inability to accept the theory of unbroken descent with modification when it was propounded by Charles Darwin and A. R. Wallace in 1858. The influence of von Baer's discoveries has been far-reaching and abiding. Not only was he the pioneer in that branch of biological science to which Francis Balfour, gathering up the labours of many fellow workers, gave coherence in his Comparative Embryology (1881), but the impetus to T. H. Huxley's researches on the structure of the medusae came from him (Life, i. 163) , and Herbert Spencer found in von Baer's "law of development" the "law of all develop ment" (Essays, i. 30). In 1834 von Baer was appointed librarian of the Academy of Sciences of St. Petersburg (Leningrad). In 1835 he published his Development of Fishes, and as the result of collection of all available information concerning the fauna and flora of the Polar regions of the empire, he was appointed leader of an Arctic expedition in 1837. The remainder of his active life was occupied in divers fields of research, geological as well as biological, an outcome of the latter being his fine monograph on the fishes of the Baltic and Caspian seas. One of the last works from his prolific pen was an interesting auto biography published at the expense of the Estonian nobles on the celebration of the jubilee of his doctorate in 1864. Three years afterwards he received the Copley medal. He died at Dor pat on Nov. 28, 1876.