96 



BIOLOGY OF THE PROTOZOA 



for division, the endosome fragments into minute chromomeres, 

 which may be strung out in lines through the nucleus, these strings 

 being divided transversely at division. Or the chromomeres may 

 be aggregated in a fairly homogeneous transverse plate in the center 

 of the dividing nucleus (Fig. 51). The former condition is illustrated 

 by the nucleus during vegetative division of Actinosphaerium eich- 

 hornii according to Hertwig, the latter condition by Sphaerastnnu 

 and Acanthocystis (Fig. 50), Collodictyum (Fig. 51), Paramoeba 

 chaetognathi, or the myxomycete Comatricha obtusata according to 

 Lister. 



Fig. 51. — Nuclear division in Collodictyum tried latum. (After Belaf.) 



A slight modification of this type is shown by nuclei containing 

 multiple endosomes as in Pelomyxa binucleata which fragment at 

 periods of division, giving rise to a granular nuclear plate (?) which 

 presumably divides to form the daughter plates as shown in Schau- 

 dinn's well-known figure or to division figures like that of Centwpyzis 

 aculeata. 



Another widely distributed type of division figure is derived from 

 vesicular nuclei in which the chromatin is not contained in one or 

 more endosomes but is distributed peripherally about the nucleus 

 where it usually forms a distinct chromatin reticulum. Such nuclei 

 usually contain an endosome which may be the most conspicuous 

 structure of the nucleus. In . 1 moeba crystalligera the peripheral 

 chromatin appears to be passively divided without any appreciable 

 change in its make up. In Amoeba vespertilio the peripheral chro- 



