EXTIRPATION OF ORGAN ANLAGEN 



255 



25 



HEART a4-'v! 

 ARE 



AMBLYSTOMA 



GILL ANLAGE 

 PRONEPHRIC AREA 



MANDiaiLAR ARCH 



4TH BR. CLEFT 



OPTIC VESICLE 



SENSE PLATE 



TRAPEZOID AREA 

 HEART AREA 



RANA PIPIENS ' STAGE 15 



^ 1& 



26 Hrs. 



75 Hrs. 

 B 



84 Hrs 



Hr. 



23 Hrs. 

 C 



50 Hrs. 



Self-differentiation of presumptive heart material cultured in modified Holtfreter's 

 solution. A, Amblystoma punctatum, stage 11. Explant of gastrula wall from out- 

 lined area lateral to the blastopore differentiates as shown in B. Arrows show 

 direction of contraction wave at 84 hours after explantation. C, differentiation of 

 presumptive mesoderm explanted from an embryo of stage 15, late medullary plate 

 stage. (Redrawn after Bacon, '45.) 



(Courtesy W. M. Copenhaver and W. B. Saunders Pub. Co., from 

 Willier, Weiss, Hamburger "Analysis of Development" 1955.) 



