been observed in mitochondria of the grasshopper kidney, in certain 

 protozoa, and in hepatic cells (Figure 3-7) . Even more complex arrange- 

 ments have been described. 



^ ■o-fvr, 



Figure 3-7. Electron Micrograph Showing Portion of Two Mitochondria 

 in the Cortex of Paramecium multimicronucieatum. The envelope delimiting 

 the mitochondrion is double, consisting of an outer (omm) and inner (imm) 

 mitochondrial membrane. Structures corresponding to the cristae mito- 

 chondriales in mammahan somatic cells are present as extensive finger-like 

 projections or microvilU (mv) protruding into the matrix of the organelle 

 from the inner mitochondrial membrane. The lumen of a microvillus appears 

 continuous with the space separating the inner and outer mitochondrial 

 membranes at the points indicated by arrows. (From Sedar. A. W. and 

 Porter, K. R., 1955. "The Fine Structure of Cortical Components of Para- 

 mecium Multimicronucieatum," /. Biophys. Biochem. CytoL, 1, Fig. 14, 

 Plate 157.) 



Some of the reported changes in mitochondrial shape, distribution, and 

 internal organization appear to be closely correlated with cell differenti- 

 ation (Fawcett, 1959). In rat, guinea pig, and opossum spermatogonia 

 the mitochondria are few in number, but otherwise quite typical. In the 



STRUCTURE AND FUNCTION OF CYTOPLASMIC ORGANELLES / 31 



