312 



GEORGE w. TANNREUTHER. 



FIG. 21. Same as preceding figure with pronuclei slightly enlarged. Both 

 macronuclei are spherical. 



FIG. 22. Early stages in the fusion of the pronuclei. 



FIG. 23. Later stages in the fusion of the pronuclei. The macronuclei are in 

 their first stages of disintegration. 



FIG. 24. Early cleavage stage of the fertilization nucleus. The macronucleus 

 has divided into several parts. 



FIG. 25. Later stages in the cleavage of the fertilization nucleus and the begin- 

 ning of size differences in the daughter cleavage nuclei. 



FIG. 26. The two cleavage nuclei remain connected by a delicate fiber in 

 their early differentiation in the formation of the new micronucleus and the new 

 macronucleus. 



FIGS. 27-30. Different stages in the differentiation of the new micronucleus 

 and the new macronucleus. Also the last stages in the disintegration and absorption 

 of the old macronucleus, o. ma., old macronucleus. 



