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CELLS, TISSUES, AND ORGANISMS 



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'■* • ' * ■ - ' *'--*■- "^ Figure 8. Cell suspension (a) and 



early (b) and differentiated (c) 

 aggregates of chondrogenic cells 

 from the limb-buds of a 4-day chick 

 embryo. 



tially a miniature neural retina; the cells differentiate into sensory 

 elements and into ganglion cells with axons and, upon further cultiva- 

 tion, give rise to masses of neuro-retinal tissue ( see Figure 9 ) . 



An equally striking example of the ability of dispersed cells to re- 

 build tissues derives from studies on kidney cells. The kidney (meso- 

 nephros) in an 8-day chick embryo is a complex structure comprising 

 a variety of cell types which originate in different regions of the em- 

 bryo, develop at different rates, and perform various specific functions. 

 In normal development these diverse cells become structurally and 

 functionally organized by a succession of tightly integrated events and 

 interactions. When such a tissue is broken up into individual cells, all 

 this intricate epigenesis appears voided. Yet not only are the dispersed 



