THE CELL 



99 



The cells of the metazoa and metaphyta rarely contain 

 more than one nucleus, the striking exception being the 

 bone corpuscles or myeloplaxes found in the red marrow. 



The shape of the nucleus, though usually spheroidal, 

 may vary. In elongate cells it is highly prolate, and in 

 cells subject to much compression may be distinctly 

 oblate. In old cells the nuclei may be irregular in 



FIG. 30. Cells with variously shaped nuclei, a, Vorticella, a ciliated 

 infusorian with a sausage-shaped nucleus, b, Stentor, a ciliated infusorian 

 with a rosary-like nucleus, c, Cells from the silk glands of a caterpillar, with 

 nuclei branched like stag's antlers. (After Korschelt.) 



shape. Rarely in the cells of certain arthropods the 

 nuclei may be branched or even reticular. Diseased 

 cells may also show breaking up or fragmentation of the 

 nucleus karyorrhexis or solution of the nuclear mate- 

 rials karyolysis. 



The cell wall that formed so essential a part of the 

 primitive conception of the cell is an extremely variable 

 structure. The lowest forms of life are commonly with- 

 out it, and the greater number of the cells of the metazoa 

 are without it. 



