DETAILS OF MITOSIS 



89 



the subject it must be left an open question whether it occurs in all. 

 In some of the gregarines and Heliozoa, the process is of nearly or 

 quite the same type as in the Metazoa. From such mitoses, how- 

 ever, various gradations may be traced toward a much simpler pro- 

 cess, such as occurs in Aviceba and the lower flagellates ; and it is not 

 improbable that we have here representatives of more primitive con- 

 ditions. Among the more interesting of these modifications may be 

 mentioned : — 



I. Even in forms that nearly approach the mitosis of higher types 



B 



D 



Fig. 38.— Mitotic division in Infusoria. [R. Hertwig.] 



A-C. Macronucleus of Spirochona, showing pole-plates. D-H. Successive stages in the 

 division of the micronucleus of /'a/-rt7/zaT///OT. D. The earliest stage, showing reticulum. G. Fol- 

 lowing stage (" sickle-form ") with nucleolus. E. Chromosomes and pole-plates. F. Late ana- 

 phase. H. Final phase. 



the nuclear membrane may persist more or less completely through 

 every stage {^Noctiluca, EiiglypJia, Actifiosp/icsmnn). 



2. Asters may be present (Heliozoa, gregarines) or wanting (In- 

 fusoria, Radiolaria). 



3. In one series of forms the centrosome or sphere is represented 

 by a persistent intranuclear body (nucleolo-centrosome) of consider- 

 able size, which divides to form a kind of central spmdle {Eiiglena 

 Aniceba, Infusoria.?). 



4. In a second series the centrosome or sphere is a persistent 



