Diversity at the Subcellular Level 



and Its Significance 



Keith If. Porter 



Biological Laboratories 

 Harvard University, Cambridge, Massachusetts 



Diversity in the microscopic anatomy of cells requires no exposition; 

 it is illustrated in numerous histological and cytological treatises. 

 There are in nature essentially as many distinct and separate forms 

 of cells as there are tissues they comprise. Some kinds, especially cells 

 performing similar functions, are remarkably alike in different ani- 

 mals or plants, but enough difference is usually apparent to permit 

 their separation. That equal or greater variations would be apparent 

 at the '"subcellular," or "submicroscopic" level, seemed probable but 

 a more thorough investigation of the question was delayed pending 

 the development of modern technics for electron microscopy. Now 

 these procedures have been quite widely applied and results of recent 

 observations have not been surprising in the degree of diversity they 

 have depicted; it is, in other words, not greater than one might have 

 expected. Diversity at submicroscopic levels naturally expands on 

 the diversity evident at the microscopic because compartments of the 

 cells which formerly appeared structureless now are described in 



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