CELL DIVISION 



11 



Chromatic Figure. — The spireme is described for some species as a 

 contimious thread. In other species there is no continuous thread for 



Fig. 45. Fig. 46. 



Fig. 45. — Mitosis involving centrosomes in a cell of the segmenting ovum of Unio. 

 The spireme is irregular and the nuclear membrane is undergoing degeneration. {From 

 Dahlgren and Kepner's Principles of Animal Histology.) 



Fig. 46. — Mitosis involving centrosomes in the egg of the mollusk Diaulula. The 

 equatorial plate is shown in side \'iew. (From Wilson's The Cell, after MacFarland.) 



^ 





Fig. 47. Fig. 48. 



Fig. 47. — Mitosis in the absence of centrosomes in a cell of the root-f ip of the hyacinth. 

 The spireme has recently segmented into chromosomes. {From Dahlgren and Kepner's 

 Principles of Animal Histology.) 



Fig. 48. — Metaphase of cell division in the root-tip of the hyacinth (see also Fig. 47). 

 The centrosomes are absent throughout the process. {From Dahlgren and Kepner's 

 Principles of Animal Histology.) 



the chromatin forms in segments directly at the time of the condensation 

 of the chromatin network. Even so important a feature as the spHtting 



