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Organ-Forming Areas in the Early Chick Blastoderm

1935; SAGE Publishing; Volume: 32; Issue: 8 Linguagem: Inglês

10.3181/00379727-32-8066c

1535-3702

B. H. Willier, Mary E. Rawles,

Tissue Engineering and Regenerative Medicine

In attempting to locate the various organ-forming areas of the early blastoderm, a series of transverse and longitudinal cuts has been made at certain measured distances from the primitive pit in such a manner as to divide a single blastoderm of the head-process stage of development into a definite number (either 11 or 18) of median and lateral pieces. The developmental potency of each piece was tested in the chorio-allantoic membrane. Each part of the blastodisc is found thereby to have a certain capacity for development or specific organization, which becomes expressed in the form of specific tissues. Nearly 400 grafts have been examined histologically, a generalized analysis of which follows. 1. Differences in developmental capacity along the antero-posterior axis. The portion of the area pellucida anterior to the head-process and that part of the area containing the posterior half of the primitive streak yield grafts much less frequently and invariably smaller ones than do those portions including either the node or the head-process. Also, the grafts from these portions exhibit a similar difference in the quantity of organ tissues produced, the node and process portions showing by far the greater variety and amount of tissues. Very striking is the demonstration that particular structures develop only from rather definite regions or areas of the blastoderm. So characteristic are some organ tissues of particular regions that we can speak of eye-forming, thyroid-forming, ear-forming, or mesonephros-forming levels or areas. The eye and thyroid-forming areas are associated with the anterior end of the head-process, ear farther posteriorly at the node level, while the center of the mesonephric area lies just posterior to the primitive pit (Fig. 1).