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 to 

 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 20 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 Wolffs 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 



