264 



THE PROTOZOA 



although two classical objects, Actinosphcerium and Euglypha, have 

 been repeatedly examined. Nuclear division in the former was first 

 described by Gruber ('83), then by Hertwig ('84), by Brauer ('94), 

 and, finally, reexamined in great detail by Hertwig ('98). All agree 

 as to the general features of division, but disagree widely in details. 

 In some stages (before the " primary mitosis," Hertwig) the chromatin 

 is in a single large karyosome which incloses a faintly staining 

 achromatic mass (Gruber, Hertwig). In addition to these there is 



Fig. 140. Nuclear division in Actinosphcerium. [HERTWIG.] 



A, B. Ordinary vegetative nuclei. C. Prophase of division. D. Ordinary mitosis. E. Trans- 

 fusion of intra-nuclear substance (x} to the outside. F, G, H. " Maturation-mitoses." p, pole 

 plates; c, centrosome. 



a conspicuous linin network (Brauer, Hertwig), which Brauer and 

 Hertwig regard as forming the pole-plates during division. During 

 mitosis peculiar and as yet unexplained masses of protoplasm (achro- 

 matic) are formed on the outside of the nucleus (Protoplasmakegel). 

 Brauer and Hertwig agree that these masses are nuclear in origin, 

 but neither gives a satisfactory explanation of their function in divi- 

 sion (Fig. 140). The pole-plates are connected by fibres of "achro- 



