and a lower, or tail end, where they are bifurcated. "The 

 cephalic end is somewhat curved inside the egg above the 

 spinal cord and forms in this way a very small half-moon 

 fold." 2 ! Describing in detail the structure and situation 

 of this fold, Pander gets to the characteristics of the 

 conditions of the blastoderm. After dividing it by 

 maceration into two layers, he saw under the microscope 

 that under the internal surface of the serous layer, which 

 is lying on the mucous layer, there is a delicate semi- 

 transparent layer of minute granules. This layer is 

 distributed not all over the blastoderm, but occupies only 

 the region of the transparent area and the internal zone of 

 the opaque area, making by itself a division of the opaque 

 area into two zones. Pander especially draws attention 

 to the process of development of this new layer. At about 

 the twelfth hour it is composed of small groups of dispersed 

 granules, forming aggregations in the form of islets; the 

 latter merge in each other but do not form a continuous 

 layer because from them blood islets and blood vessels 

 develop. This layer, the third and middle layer of the 

 blastoderm, Pander called the vascular layer. 



In the German version of Pander's work, it is explained 

 distinctly that the blastoderm, which is composed of the 

 embryonic membranes or layers, is considered the origin of the 

 future embryo. All development is nothing other than "like 

 the metamorphosis of the membrane (blastoderm) . . . and its 

 layers. "22 



To the end of the first days, according to Pander, the 

 primary rudiments of the vertebrae appear, which in his 

 words are as if hung to the primary folds in the form of 

 nearly quadratic spots of a pale-yellowish color, separated 

 by spaces and situated in two parallel lines. The primary 

 folds at first are straight, then become serpent- shaped, 

 curved and wavy. To the tail the folds disperse, and in 

 the spinal cord they form a convex arch. 



21. Ibid . , p. 31. 



22. Pander, BEITRXGE ZUR ENTWICKLUNGSGESCHICHTE 

 DES HUHNCHENS IM EIE, p. 6. 



252 



