EXPLANATION OF PLATES. 

 All figures in Plates I-IV are surface views of the early stages of Des- 

 mognathus fusca. All are enlarged about 10 X- 



Plate I. 



Fig. 1. Egg before segmentation, view from above. 



Fig. 2. Egg before segmentation from the side, the slightly lighter animal 

 pole is up. 



Fig. 3. Beginning two-cell stage from above. 



Fig, 4. Four-cell stage from above 



Fig. 5. Same egg as Fig. 4, twenty miiiutes later. 



Fig. G. Another four-cell stage from above. 



Fig. 7. Another four-cell stage. 



Fig. 8. Later four-cell stage from above. 



Fig. 9. Same stage as Fig. 8, turned a little so as to show the extent of the 

 first cleavage plane in the direction of the lower pole. 



Fig. 10. Rather irre- ilar four-cell stage from above. 



Figs. 11 and 12. Later irregular stages of segmentation. 



