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A. W. BELLAMY. 



lip region, which has spread apically and now includes the lateral 

 lips. The area then spreads more or less symmetrically from 

 the apical and lateral borders of the disintegrated area until all 

 of the pigmented cells are involved. The yolk cells retain their 

 structure long after the pigmented cells have completely dis- 



C 



FIG. 5. View from animal pole showing stages in the disintegration of eggs in 

 a four-cell stage after ten days' exposure to a temperature of o C. The eggs were 

 in a two-cell stage when placed in the cold chamber. 



integrated, except in the case of alcohol, which attacks the yolk 

 rapidly from the start. Fig. 8 illustrates the general process. 



(d) Later Embryonic Stages. With the beginning of elonga- 

 tion, while two regions of high susceptibility are still present, 

 viz., the apical and the dorsal lip region (now posterior), the 

 posterior growing region, especially during the formation of 

 the neural folds, appears relatively less susceptible than it did 

 earlier. This apparent greater difference is probably due to 

 local differences associated with the formation of the neural plate. 

 In embryos beginning to elongate, disintegration begins first 

 at the apical end in the medial dorsal region and spreads laterally 

 and posteriorly, more rapidly in the posterior direction, to meet 



