EMBRYONIC INDUCTORS AND ORGANIZERS 477 



According to Woerdeman (1933^^, b, d), the glycogen content in the 

 apical hemisphere of the amphibian blastula is high and more or less uni- 

 form but decreases in the dorsal lip region as it invaginates. Similar ob- 

 servations were made by Tanaka (1934)- In transplanted pieces of the 

 dorsal lip the same decrease occurs on invagination (Raven, 1933a, 1935a). 

 On the basis of his observations Woerdeman advanced the view that de- 

 crease in glycogen in the inductor region at the time of gastrulation may 

 be associated with induction, presumably through glycolysis. He found 

 also that implants of malignant tumors known to have high glycolytic 

 activity induce (Woerdeman, 1933c). Fischer and Wehmeier (1933a; 

 Wehmeier, 1934) also suggested, independently of Woerdeman and on 

 other grounds, that glycogen might be an inductor substance and obtained 

 neural-plate inductions with glycogen from liver, but in later experiment 

 they found that inducing power decreased to zero as purification of the 

 glycogen preparations became more complete (Fischer und Wehmeier, 

 1933&). Induction was also obtained with the unsaponifiable material 

 from ethereal extracts of crude glycogen.'^ Both Woerdeman (1933c) and 

 Holtfreter (19346) found glycogen inactive. More recently the conclusion 

 has been drawn from experiments with glycogen from rabbit liver that an 

 agent associated with glycogen is a highly effective inductor (Heatley, 

 Waddington, and Needham, 1937). Pasteels (1936c), using a different 

 method from that of earlier workers for demonstrating intracellular gly- 

 cogen, maintained that the supposed decrease in the region of the dorsal 

 lip does not occur and that, consequently, increased glycolysis cannot be 

 responsible for the inducing power of the chorda-mesoderm. However, 

 with still another method Heatley and Lindahl (1937) found that during 

 gastrulation glycogen decreases in all parts of the embryo but that de- 

 crease is greatest in the invaginating material. The high anaerobic gly- 

 colysis of the inductor region (three times that of other parts) and its high 

 respiratory quotient (about unity), indicating carbohydrate metabolism, 

 have already been noted (pp. 154-55). However, according to Brachet 

 (1939), carbohydrate metaboUsm is not necessary for induction ; induction 

 may take place in the presence of agents inhibiting glycolysis. He sug- 

 gests that proteins may be important factors in induction. Evidently 

 still further investigation along these lines is necessary. Whatever the 

 final conclusion, the glycogen hypothesis is interesting, as pointed out by 

 Weiss (1935, p. 664), in that it suggests that induction is mediated by 



^5 Waddington, Nowinski, Needham, and Needham, 1934; Waddington, Needham, Nowin- 

 ski, Lemberg, and Cohen, 1936. 



