MITOSIS 113 



tissue-cell in the body. The number may be very large it is 

 said to be one hundred and sixty-eight in a certain crustacean 



Diagrams representing the essential phenomena of mitosis. A, a cell with resting 

 nucleus containing a chromatic reticulum and a single nucleolus. The 

 centrosome is double and surrounded by the centrosphere. , the centrp- 

 somes are separating and each is surrounded by astral rays ; the chromatin 

 forms a convoluted thread or spireme. C, The spireme is broken up into a 

 number of V-shaped chromosomes, the polar spindle is formed between the 

 now widely separate centrosomes. D, The chromosomes attached to the 

 spindle-fibres arc arranged at the equator of the spindle. E, division of the 

 chromosomes, which are viewed end on. /", divergence of the chromosomes. 

 G, chromosomes collecting at the poles of the spindle, the sp^ce between 

 them occupied by interzonal fibres ; commencement of division of the cell- 

 body. //, /, complete division of the cell, and reconstitution of the nuclei. 

 In / the centrosomes are dividing preparatory to a new mitosis. Note 

 ^4-Z> = prophase ; . = metaphase ; P\ (7=anaphase. ff, 7=telophase. 



known as Artemia salina, or it may be very small, as in the 

 thread-worm parasitic in the intestines of the horse (Ascaris 

 megalocephald). Recent researches, however, render it doubt- 

 H 



