dOllinger, baer, and pander. 51 



siderable pecuniary means then necessary to provide a 

 hatching-apparatus, such as would afford uninterrupted 

 observations of the process, or to pay a skilled artist t^ 

 depict in a reliable form the successive stages of develop- 

 ment. They, therefore, confided the execution of the plan 

 to Christian Pander, a wealthy, early friend of Baer's, by 

 whom he had been induced to come to Wurzburg. Dalton, 

 a skilful artist, was engaged to prepare the necessary copper- 

 plates. 



Thus was formed, as Baer says, " that combination, ever 

 memorable in the history of science, in which a veteran, grown 

 gray in physiological researches (Dollinger), a youth glowing 

 with zeal for science (Pander), and an artist without a peer 

 (Dalton), united their powers to lay a firm foundation for 

 the History of the Evolution of the Animal Organism." In 

 a short time the history of the evolution of the Chick, in 

 which Baer took, though indirectly, a most active part, 

 was so far advanced that Pander, in his dissertation ^^ for 

 the degree of doctor, published in 1817, was able to give 

 the first complete sketch of the history of the evolution of 

 the Chick on the basis of Wolff^s theory. He was able to 

 define clearly Wolff"s Theory of Germ-leaves, and to prove 

 from observation the evolution of the complex system of 

 organs from simple leaf-shaped primitive organs, as anti- 

 cipated by Wolff. According to Pander, the leaf-shaped 

 germinal appendage of the hen's egg separates before the 

 twelfth hour of incubation into two distinct layers — an 

 outer serous layer, and an inner mucous layer. Between 

 the two, a third, vascular layer, subsequently develops. 



Baer, who was one of those most active in inducing 

 Pander to make his investigations, and who retained the 



