Ch. XI] EFFECT OF IXJURIXG A BLASTOMERE 



11' 



its egg are agaiyi rotated through 180 degrees^ so tliat tlie white 

 pole is once more turned uppermost. Owing to the compres- 

 sion, the eggs retain their inverted position. 



After twenty-four hours at 17 degrees C, tlie gastrulation 

 begins. The rubber bands are then removed from the slide, 



Fig. 36. — Double embryos. A. Section through segmentin.o; egg. (After Wetzel.) 

 B. Double embryos uuited veutrally. C, D. Double embryos united dorsally. 

 (After Schultze.) E. Cross-section through C. (After Wetzel.) F. Double 

 embryos united laterallj", and G, cross-section of same. (After Wetzel.) 



the cover-slip carefully cut away from the jelly of the egg, and 

 the slide and egg returned to the water. 



If eggs that have been inverted after the two-cell stage are 



