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THE PROTOZOA 



that of the intra-nuclear division-centre in Englena (Fig. 142). In 

 Noctiluca the central spindle, which is derived from the extra-nuclear 

 division-centre, takes a similar intra-nuclear position during division 

 of the nucleus, and when the nuclear membrane disappears in the ad- 

 jacent portions of the nucleus, the kinetic substance is again intra- 

 nuclear, although the centres of attraction are outside (Fig. 141, D, E). 

 In Actinosph&rium> both Brauer ('94) and Hertwig ('98) explained the 

 cytoplasmic accumulations (Protoplasmakegel) as coming from the 

 nucleus, and Hertwig pictured the outer mass and the inner achro- 

 matic substance as connected through openings in the membrane 

 (Fig. 140). Confirmatory evidence is also shown in other Heliozoa. 

 In Actinophrys there is no extra-nuclear division-centre, and Schau- 



B C 



Fig. 143. Mitosis in Tetramitus chilomonas. 



A. Ordinary form with distributed chromatin (c) and division-centre (j). B, The chromatin 

 granules are collected prior to division. C. The division-centre has divided. D. Later stage in 

 division ; each daughter-nucleus is surrounded by a group of chromatin granules. 



dinn ('96) interprets the achromatic spindle figure as nuclear in origin 

 (Fig. 130, p. 236). 1 



The flagellate Tetramitus shows an apparently similar division- 

 centre. During the resting phases, the chromatin is distributed 

 throughout the cell, while an indefinite " achromatic mass " appears 

 to be in direct connection with the cytoplasmic reticulum. Imme- 

 diately before division, however, the chromatin granules collect about 

 this body, and then, save for the absence of a membrane, the aggre- 

 gate resembles the nucleus of Euglena. Division takes place as 



1 A significant fact is that in Actinophrys the radiating axial filaments centre in the 

 nucleus, while in other Heliozoa with a "Centralkorn" the radiating axial filaments centre 

 in this extra-nuclear body. This indicates that in Actinophrys the attraction-centre is within 

 the nuclear substance and presumably in. the " achromatic substance." 



