. The development of the chick; an introduction to embryology. Birds -- Embryology. OUTLINE OF DEVELOPMENT, CHRONOLOGY 63 into the body-cavity through the uml^iUciis, which thereupon closes. The young chick usually hatches on the twenty-first day. Orientation. It is an interesting and important fact that the embryo appears in a definite relation to the line drawn through the axis of the entire egg, or to the line joining the bases of the two chalazae, which is usually the same thing. If the egg be placed as in Fig. 32 A, with the blunt end to the left, the head of the embryo will be found dire


. The development of the chick; an introduction to embryology. Birds -- Embryology. OUTLINE OF DEVELOPMENT, CHRONOLOGY 63 into the body-cavity through the uml^iUciis, which thereupon closes. The young chick usually hatches on the twenty-first day. Orientation. It is an interesting and important fact that the embryo appears in a definite relation to the line drawn through the axis of the entire egg, or to the line joining the bases of the two chalazae, which is usually the same thing. If the egg be placed as in Fig. 32 A, with the blunt end to the left, the head of the embryo will be found directed away from the observer when the blastoderm is above; the left side of the embryo is therefore towards the broad end, and the right side towards the narrow end of the egg. According to Duval this orientation is. Fig. 33. —A. Yolk of hen's egg incubated 84 hours. (After Duval.) B. Embryo and membranes of the hen's egg on the seventh day of incu- bation. (After Duval.) AL, AUantois. Am., Amnion, a. v., (in B) Area vitelHna. E., Embryo. S. t., Sinus terminaHs. Other Abbreviations as in Fig. 32. found in about 7o of eggs: of 166 eggs observed, in which the embryo was formed, Duval found 124 oriented exactly in this manner, 39 in which the axis of the embryo was slightly oblique, 2 in which the head was towards the broad end, and 1 in which the usual position was completely inverted. In the pigeon's egg the orientation of the embryo is equally definite, but slightly different. The axis of the embryo cuts the axis of the entire egg at an angle of about 45°, the head of the embryo being. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947. New York, Holt


Size: 2029px × 1231px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: ., bookauthorlilliefrankrattray187, bookcentury1900, bookdecade1900