470 



BERTRAM G. SMITH 



3' I' 3' 



85 



Figs. 85 to 90 Upper hemispheres of eggs of Cryptobranchus allegheniensis 

 in the fifth cleavage stage. All the figures are camera drawings from preserved 

 material. Figure 86 is drawn from the egg photographed for figure 211, and figure 

 87 from the egg photographed for figure 210. X 4f . 



The careful study of a large number of eggs emphasizes 

 irregularity in this cleavage and the absence of a well established 

 type. Two sets of fifth cleavage furrows are often recognizable: 

 an inner, within the former region of micromeres, and an outer, 

 just outside of this region. Either set may be, in whole or in 

 part, vertical, latitudinal or oblique (see especially figure 85 

 for an example of outer, and figure 89 foi an example of inner 

 latitudinal cleavage furrows). A study of the most regular 

 cases of cleavage described under Stage 6 shows that in these 

 eggs the fifth cleavage furrows must have come in with greater 

 regularity than in any eggs directly observed in the fifth cleavage 

 stage : these fifth cleavage furrows are almost uniformly vertical, 

 thus preserving the regular alternation in the direction of the 

 furrows. 



