4S() BERTRAM G. SMITH 



In preserved material the nuclei of the niicromeres are often 

 easily distinj»;uishable in surface views, 



In the living egg, the roof of the segmentation cavity has be- 

 come quite opaque, and the cells are compactly arranged. During 

 the latter part of this stage a translucent condition begins to 

 appear at the animal pole, indicating a thinning-out of the cells 

 in this region, as in Stage 6; but this time the cells form a firm 

 tissue, with no spaces between them. 



In Necturus the cleavage furrows in the region of the vegetal 

 pole are fainter than in Cryptobranchus ; this condition is reversed 



107 108 



Figs. 107 and 108 Advanced cleavage stage of Necturus maculosus. . Two 

 views of a single egg, photographed after preservation. X 4. 



in the upper hemisphere, where the micromeres are outlined 

 far more boldly in Necturus (figs. 107 and 108) than in Crypto- 

 branchus (both statements refer to preserved material, fixed by 

 the same method). 



Stage 9: (Jigs. 109, 110 and 218). This stage is reached about 

 nineteen hours later than the preceding stage. Individual micro- 

 meres in the region of the animal pole are barely visible to the 

 naked eye. The zone of transition between micromeres and 

 macromeres has become broader and more marked. An excen- 

 trically situated area of accelerated cell division in the micromeres 

 is only occasionally found in surface views of this stage. 



