20 



THE INVERTEBRATA 



chromosomes but the chromatin merely concentrates as a mass upon 

 the equator of a spindle, whose fibres may not be visible, and divides 

 into two halves which travel to opposite poles. Intermediate cases 

 connect cryptomitoses with eumitoses. Paramitoses occur in cocci- 

 dians, dinoflagellates, and the spore formation of radiolarians, crypto- 

 mitoses for the most part in parasitic and coprozoic forms, as in 

 Haplosporidium and Naegleria. 



In certain cases mitoses repeated several times without dissolution 



Fig. 19. Mitosis (paramitosis) of the sporogony of Aggregata eherthi. 

 After Belar. A, Interphase between divisions. B, Early metaphase. C, Ana- 

 phase beginning. D, Later anaphase. E, Early telophase. F, Later telophase. 

 cen. centriole; chr. chromosomes; nu.me. nuclear membrane; spd. spindle. 



of the nuclear membrane give rise to polyenergid nuclei which possess 

 numerous sets of chromosomes, the sets being finally liberated to 

 form each a daughter nucleus. The polyenergid condition is probably 

 always a provision for spore formation, and may (as in the coccidian 

 Aggregata) occur only as a transient phase before sporulation, but in 

 other cases (radiolarians) it persists for a long time, the nucleus 

 dividing meanwhile as a whole by "giant mitoses" in which all the 

 chromosomes take part. A remarkable process in Amoeba proteus is 



