60 



GENERAL EMBRYOLOGY 



Probably the most interesting modifications of mitosis among the 

 Protozoa are those connected with the formation and behavior of the 

 centrosome and mitotic spindle, upon the origin of which they may 



FIG. 28. Nuclear division in the Rhizopod, Euglypha. After Schewiakoff. 

 X 800. A. Coarse network of chromatin. B. Contraction of chromatin fibers 

 and beginning of formation of loops (chromosomes). C. Arrangement of chro- 

 mosomes in equatorial plate. Polar view. D. Equatorial plate. Lateral view. 

 Spindle forming. E. Splitting of chromosomes and beginning of divergence. 

 F. Continued divergence of chromosomes. G. Division nearly completed. 



perhaps throw some light. In some species there is no indication of 

 a specialized organ concerned particularly with division. In a few 

 forms, as mentioned above, a division center may be formed, although 



FIG. 29. Nuclear division in the Rhizopod, Centropyxis aculeata. After 

 Schaudinn (Doflein). A. Nucleus in vegetative stage. B. Appearance of 

 centriole. C. Equatorial plate. Spindle with centrosomes; plasma radiations, 

 D. Beginning of reconstruction of daughter nuclei. 



no definite nucleus is present, the distributed chromatin granules 

 collecting into a single group only at the time of cell fission. In some 

 species of Amoeba, and in a few other forms, one of the large chromatin 



