268 



Fig. 103. 



Embryogenesis: Progressive Differentiation 



Fig. 104. 



Fig. 105. Fig. 106. 



Fig. 103. Induction of symmetrical brain parts and eye by mouse kidney, boiled for 15 minutes and im- 

 planted in the blastocoele of an early gastrula of Triturus (from Chuang, '39) . 



Fig. 104. Induction of tail in posterior trunk region of Triturus, obtained by implantation of mouse kidney 

 which had been killed by dipping briefly in boiled water (from Chuang, '39). 



Fig. 105. Induction of a neural tube by 3,4-benzpyrene, using coagulated egg albumen as a carrier. Axial 

 organs of host above, and induced neural tube adjacent to transplant below. (From Needham, '42, after 

 Waddington.) 



Fig. 106. Heteroplastic induction of balancer, a. Larva of Triturus cristatus. The prospective head epider- 

 mis on the right side had been replaced in the early gastrula by prospective belly epidermis of Triturus 

 taeniatus. The right balancer induced in the transplant by underlying T. cristatus structures is of T. taeniatus 

 type. Notice its size, shape, direction of outgrowth, absence of terminal club, b. Normal larva of Triturus 

 taeniatus, for comparison. (From Rotmann, '35a.) 



ney, thyroid of some mammals) induced 

 preferentially spinocaudal strvictures. Less 

 conspicuous and complex inductions were ob- 

 tained with grafted tissues from various in- 

 vertebrates. Inactive were agar, starch, 

 glycogen, wax, charcoal. 



Similar results were obtained by Need- 

 ham, Waddington and Needham ('34) and 



Wehmeier ('34) on urodeles, and by Rau- 

 nich ('42b) on anurans. The implantation 

 of plant tissues (cambium, root tip) pro- 

 duced merely ectodermal thickenings (Rago- 

 sina, '37; Toivonen, '38); but Brachet ('43, 

 '50) obtained neuralizations by applying 

 nucleoprotein fractions from yeast and wheat 

 embryos. 



