. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. Glass cap S^ Short segments form new heads only at the distal ends; long segments, both at distal and proximal. C. If the distal end of a short segment is prevented from forming o new heod, the proximal end will do D. If the two ends of a short segment are physiologically seporated, both will form a new head. Fig. 22. Regeneration of polyps by stem segments. of moderate length develops a new head at only one cut end, and this is invariably at the distal end. However, if w
. Animal growth and development. Embryology; Growth; Biology; Growth; Embryology; Animals -- growth & development. Glass cap S^ Short segments form new heads only at the distal ends; long segments, both at distal and proximal. C. If the distal end of a short segment is prevented from forming o new heod, the proximal end will do D. If the two ends of a short segment are physiologically seporated, both will form a new head. Fig. 22. Regeneration of polyps by stem segments. of moderate length develops a new head at only one cut end, and this is invariably at the distal end. However, if we prevent the distal end from regenerating by slipping a glass cap over it, then the proximal end will form the head (although slower than the distal end would have done it). This interaction can be relieved in two ways: first, by making the stem segment so long that the two ends are not in close contact; second, by separating the two ends physiologically. The latter can be accomplished by tying a string tightly around the middle of the segment so as to prevent the flow of materials and cells between the ends. When these measures are taken, heads form at both ends without any evidence of competition between them. This type of phenomenon is commonly encountered in develop- mental systems. A case in point is the development of the hind limb in a chick embryo. As described in Chapter 5, the limb originates as a small protuberance from a specific point along the flank of the embryo. Areas surrounding this point can also be shown to be capable of forming the 43. 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 Sussman, Maurice. Englewood Cliffs, N. J. , Prentice-Hall
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