The thirtieth hour of incubation (§ 7) is characterized, 

 according to Pander, by the following: "Primary folds 

 previously were opened with the spinal cord situated between 

 them; now they approach each other mainly at the central 

 distance between the head and tail. The edges of the folds 

 move closer; they cover the spinal cord and after that they 

 accrete. When this approach and accretion of the edges 

 occurs along the whole length, the mentioned folds remain 

 apart, and in the head region they keep the serpent -shaped 

 curves and form a number of three or four chambers of larger 

 sizes. "23 The transverse fold becomes a little widened and 

 stretched to the tail end, forming the head portion, as 

 Wolff called it. Pander does not believe that this fold is 

 duplicated, but suggested that the upper one depends on the 

 bending of the embryonic body, and the lower depends on the 

 bending of the blastoderm. At this stage Pander saw the 

 heart rudiment situated under the head as an elongated, not 

 clearly defined sac. The granulated layer, facing from inside 

 to the serous layer, acquires the shape of a net. 



Within thirty-six hours after the beginning of incubation 

 (§ 8) the anterior ends of the primary folds get together and 

 accrete with each other, forming the forehead and the facial 

 parts of the embryo. "From each side of this rounded area 

 develops one rounded portion. They are situated a little bit 

 backwards, appearing to be the primary rudiment of the eyes 

 and appear as lateral widenings of the primary central rounded 

 area. "24 The heart, according to Pander, becomes a narrowed, 

 straight, cylindrical canal which extends from the heart 

 depression to the head. The granular layer disintegrates 

 into separate islets; these have a yellowish color, while 

 the granules forming the bordering ring are already stained 

 a red color. 



By the forty- second hour of incubation (§9) the end of 

 the head, formerly adjacent to the blastoderm, now is inserted 

 into a small depression formed by the blastoderm, whose fold 

 extends above the head. The fold, forming the border of 

 this depression, represents the rudiment of the amnion. The 

 heart at this stage appeared as an arch curved to the left 



23. pander, DISSERTATED, p. 35. 



24. Ibid., p. 37. 



253 



