Ch. XI] EFFECT OF INJURING A BLASTOMERE 



117 



its egg are again rotated through 180 degrees, so that the white 

 >ole is once more turned uppermost. Owing to the compres- 

 sion, the eggs retain their inverted position. 



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

 >egins. The rubber bands are then removed from the slide, 



'"ig. 36.— Double embryos. A. Section through segmenting egg. (After Wetzel.) 

 B. Double embryos united ventrally. C, D. Double embryos united dorsally. 

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

 embryos united laterally, aud 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 



