214 BIOLOGY OF THE PROTOZOA 



the poles of the nuclear spindle which originates within the nucleus. 

 The mitotic figure is thus made up of cytoplasmic elements, kinetic 

 elements derived from the nucleus, and chromatin. A similar 

 combination occurs in dividing Heliozoa. The original description 

 of division of Acanthocystis acukata by Schaudinn, a form possessing 

 the characteristic central granule of the Heliozoa, has been consider- 

 ably modified by later observations. According to Schaudinn the 

 central granule or centroblepharoplast which is the focal point in 

 the cell of the radiating axial filaments, divides to form an amphi- 

 aster (Fig. 100) which becomes the central spindle of a typical 



h^4^< 



_S?V'. 





■h i 



B C 



^,, ', -^ {, , , ; '^ ^v *;;.;. v,>-: A*, w. 'm^ V-^J^ ^ 



D M F (' 



Fig. 100. — Sphcerastrum and Acanlhocyslis. A, Vegetative cell of Sphwrstrum 

 with axial filaments focu.ssed in a central granule (centroblepharoplast); B, C, D, 

 division of central granule and spindle formation in Acanthocystic aculeata; E, F, 

 formation of buds of same; G, exit of central granule from the nucleus of young 

 cells. (After Schaudinn.) 



mitotic figure. The more recent observations of Stern (1924) 

 indicate that, as in the simpler amoeba described above, the central 

 granule of Acanthocystis behaves as a cytoplasmic centrosome, 

 forming poles of a mitotic figure which is derived otherwise entirely 

 from the nucleus. Individuals which have been deprived of their 

 skeletons and membranes which afford resistance to the activities 

 of the enclosed protoplasm, become "sprung," so to speak, and the 

 unusual freedom from restraint results in a separation of the centro- 

 somes from the remainder of the spindle which completes its division 

 without further participation of the centrosomes (Fig. 101). 



