EMBRYONIC INDUCTORS AND ORGANIZERS 



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local vital staining by application to the surface of egg or embryo of small 

 pieces of agar impregnated with dye^ is open to the objection only that 

 the dye may be, to some extent, toxic; but results obtained thus far indi- 

 cate that, as the method is used, toxicity is not sufficient to constitute 

 a serious objection to it. 



This method has made it possible to map more or less accurately pro- 

 spective or presumptive embryonic regions and to follow the cell migra- 

 tions that bring them to their definitive positions. Such maps have, in 

 general, little more than formal significance, since isolation and transplan- 



FiG. 149, A , B. — Map of prospective or presumptive urodele embryonic regions at beginning 

 of gastrulation. A , lateral, B, dorsal view. Denser broken lines, neural plate; less dense broken 

 lines, general ectoderm; coarse stippling, notochord; fine stippling, mesoderm; /, beginning of 

 invagination; b, later blastopore; //, limit of invagination; p, basal pole; g, gills; /, lateral meso- 

 derm; pi, pronephros and mesoderm of forelimb; I, caudal region; i-io, somites (after Vogt, 

 1929). 



tation experiments have made it clear that identification of a particular 

 embryonic area, as giving rise in normal development to a particular 

 organ or organ system, gives no information concerning its potentialities 

 or potencies. It shows only that, under the conditions which we call "nor- 

 mal," a certain region of the egg or early developmental stage becomes a 

 certain part.'' 



The accompanying amphibian, teleost, and chick maps indicate formal 

 regional pattern and regional migrations, as determined by local vital 

 staining. The amphibian maps, as given by Vogt (1929), are the most 

 complete. Figure 149 shows the urodele regional map at the beginning 



■•Vogt, 1925; 1926a, b; 1929. 



5 The following papers are concerned with this problem of formal pattern. Fishes: Kopsch, 

 1927; Oppenheimer, 1936c; Vandebroek, 1936a; Pasteels, 1936a. Amphibia: Vogt, 1925, 



