Explanation of Figures, 



Reference Letters. 



Via. 1. Side view of an embryo at tlie stage in wliicli the first rufliuients of append- 

 ages liave appeared. 



Fig. 2. Side view of an embryo at the stage in which all the cephalothoracic 

 appendages have appeared. 



Fio. H. Dorsal view of an embryo at the stage of the maximum ventral fiexnre. 



Fio. 4. Sagittal section of an embryo at the stage of Fig. 3. 



Fig. 5. Cross section of an embryo at the stage of Fig. 3. 



Fig. (!. A portion of the median sagittal section of an embryo at the stage of 

 Fig. 3. 



Fig. 7. Oblique side view of an embryo at the stage of reversion. 



Fig. 8. Oblique sagittal section of an embryo at the stage of Fig. 7. 



Fig. 9. Side view of an embryo at the stage in which the process of reversion lias 

 greatly advanced. 



Fig. 10. Oblique sagittal (about median) section of an embryo at the stage of 

 Fig. 9. 



Fig. 11. Frontal section of the cephalic region of an embryo at the stage of Fig. 9. 



Fi(i. 12. Side view of an embryo at the end of the process of reversion. 



