468 



BERTRAM G. SMITH 



age furrows become irregular and broken to an extent never 

 observed in earlier stages. Outside of the region of the micro- 

 meres, the biradial pattern of cleavage is retained. 



In this as in other cleavage stages the most recent furrows, 

 and especially the most recent portions of such furrows, are in 

 general quite noticeably the widest. This fact once established 

 may be made use of in connection with other evidence to iden- 

 tify cleavage furrows. The broadening of the ends of the ver- 

 tical furrows as they invade the lower hemisphere is a fairly con- 

 stant feature of the cleavage; as shown by unpublished drawings 

 from living material by Prof. Bashford Dean, it is also well 

 expressed in the eggs of Necturus. 



Figs 82 to 84 

 allegheniensis. 

 41. 



3 -^ 3 



82 83 ' 



Lower hemispheres of fourth cleavage stages of Cryptobranchus 

 All the figures are camera drawings of preserved material. X 



Fig. 82 Lower hemisphere of the egg shown in figure 208. 



Fig. 83 Lower hemisphere of the egg shown in figure 76. This figure would 

 serve equally well to represent the lower hemisphere of the egg drawn for figure 75. 

 Fig. 84 Lower hemisphere of the egg represented in figure 80. 



In the majority of eggs of this stage* the second cleavage fur- 

 rows have reached the lower pole, and the third furrows have 

 just passed the equator (figs. 82 to 84). The second cleavage 

 furrows intersect the first at right angles at the lower pole. 

 For some distance on each side of the pole the second cleavage 

 furrows are for a time markedly wider than the first. The second 

 furrows are further distinguished by the fact that the third 

 furrows run closer to them than to the first. In the latter part 

 of this stage the third furrows sometimes become complete (fig. 

 84), as a rule joining the first at some distance from the pole. 



