FIG. 28. 



entrance; in 2 and 3 they have moved up to the equator on 

 the posterior side of the egg; in 4 the egg and sperm nuclei 

 have come together and the sperm centrosome has divided and 

 formed the cleavage spindle; in 5 the egg is dividing into 

 right and left halves; in 6 it is dividing into anterior and 

 posterior halves. 



FIG. 28. CLEAVAGE or THE EGG OF Styela, showing distribu- 

 tion of the yellow protoplasm (stippled) and of the clear and 

 gray protoplasm to the various cells, each of which bears a 

 definite letter and number. 



