412 



EYCLESHYMER. 



EXPLANATION OF PLATE XIX. 



Figs. 1-15. Cleavage in superior hemisphere of egg of Petromyzon marinu<; 



(X30)- 



Figs. 1-4. Successive stages in cleavage of living egg. 

 Figs. 5, 6, 7. Successive stages in cleavage of second living egg. 

 Figs. 8, 9. Variations in formation of first and second sets of furrows. 

 Figs. 10-13. Variations in formation of third set of furrows. 

 Figs. 14, 15. Later cleavage. 

 Figs. 16-35. Cleavage of Coregonus albus (X 15). 

 Figs. 16, 17, 18, 19. Variations in first cleavage. 

 Figs. 20, 21. Three blastomeres arising from unequal two-cell stage. 

 Figs. 22, 23, 24. Variations in second cleavage. 

 Figs. 25, 26. Conditions derived from unequal two-cell stage. 

 Figs. 27, 28, 29, 30, 31. Variations in third cleavage. 

 Figs. 32, 33. Fourth cleavage. 

 Figs. 34, 35. Later cleavage stages. 



