THE HELIOZOA 



27 



to Hertwig (8) the chromosomes of the second polar division are 

 only half the size of the chromosomes of the first division, and 

 there is, therefore, a reduction in the mass of the 'chromosomes, 

 although there is apparently no reduction in their number. 



The karyokinesis of the nuclei of the ordinary unencysted 

 Adinospliaerium differs from that just described principally in the 

 fact that no centrosomes are present. The first sign of commencing 

 division in these nuclei is the accumulation of a clear mass of 

 nearly homogeneous protoplasm at each pole ; the nucleus becomes 



B. 



C. 



Fio. 6. 



A, Acanthocystis aculeata, H. and L., in the living condition, with expanded pseudopodia. 

 N, the nucleus ; c, the centrosome. B, C, D, B, F, successive stages in the mitoticldivision of 

 the nucleus as seen in preparations. (After Schaudinn.) 



flattened so that the diameter which passes through the proto- 

 plasmic masses is the shortest, and at each end of this diameter an 

 accumulation of achromatic nuclear substance is formed, giving rise 

 to what Hertwig calls the " polar plates." 



In Acanthocystis the nucleus is situated excentrically, and con- 

 sists of a central deeply -staining body, the " pseudonucleolus," 

 surrounded by an area which certainly contains a linin network 

 but much less chromatin. At the exact centre of the endoplasm 

 there is a small body which exhibits radiating lines which 

 appear to extend outwards and be continuous Avith the axes 

 of the pseudopodia (Fig. 6). This body, originally described by 



