Archive image from page 80 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 OUTLINE OF DEVELOPMENT, CHRONOLOGY 63 into the body-cavity through the umbiUcus, 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 chalazse, which is usually the same thing. If the egg be placed as in Fig. 32 A, w
Archive image from page 80 of The development of the chick. The development of the chick : an introduction to embryology . developmentofchi02lill Year: 1936 OUTLINE OF DEVELOPMENT, CHRONOLOGY 63 into the body-cavity through the umbiUcus, 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 chalazse, 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., Allantois. Am., Amnion, a. v., (in B) Area vitelhna. E., Embryo. S. t., Sinus terminalis. Other Abbreviations as in Fig. 32. found in about 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
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