This resuscitation of embryology and development of the epigenesis-theory was chiefly connected with the university of Würtzburg. One of the professors there at that time was Döllinger, an eminent biologist, and father of the famous Catholic historian who later distinguished himself by his opposition to the new dogma of papal infallibility. Döllinger was both a profound thinker and an accurate observer. He took the keenest interest in embryology, and worked at it a good deal. However, he is not himself responsible for any important result in this field. In 1816 a young medical doctor, whom we may at once designate as Wolff’s chief successor, Karl Ernst von Baer, came to Würtzburg. Baer’s conversations with Döllinger on embryology led to a fresh series of most extensive investigations. Döllinger had expressed a wish that some young scientist should begin again under his guidance an independent inquiry into the development of the chick during the hatching of the egg. As neither he nor Baer had money enough to pay for an incubator and the proper control of the experiments, and for a competent artist to illustrate the various stages observed, the lead of the enterprise was given to Christian Pander, a wealthy friend of Baer’s who had been induced by Baer to come to Würtzburg. An able engraver, Dalton, was engaged to do the copper-plates. In a short time the embryology of the chick, in which Baer was taking the greatest indirect interest, was so far advanced that Pander was able to sketch the main features of it on the ground of Wolff’s theory in the dissertation he published in 1817. He clearly enunciated the theory of germinal layers which Wolff had anticipated, and established the truth of Wolff’s idea of a development of the complicated systems of organs out of simple leaf-shaped primitive structures. According to Pander, the leaf-shaped object in the hen’s egg divides, before the incubation has proceeded twelve hours, into two different layers, an external _serous_ layer and an internal _mucous_ layer; between the two there develops later a third layer, the _vascular_ (blood-vessel) layer.[8] [8] The technical terms which are bound to creep into this chapter will be fully understood later on.—Translator.