Cn. XI] EFFECT OF IXJURIXG A ELASTOMERS 



117 



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

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

 sion, the eggs retain their inverted position. 



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

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



FIG. 36. Double embryos. A. Section through segmenting: egg. (After Wetzel.) 

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

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

 embryos united laterally, 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 



