ELECTRON MICKOSCOI'Y 



granules. The membranes have a smooth 

 surface and enclose clear spaces. The num- 

 ber and length of the membranes vary, 

 presumablj'^ because of different functional 

 stages of the Golgi apparatus. There are 

 mostly several pairs of membranes arranged 

 in parallel form with each other and one can 

 occasionally see that the clear space which 

 each pair of membranes encloses is distended 

 to a vacuole of varying size (Fig. 3). The 

 small vesicles are quite numerous and 

 bordered by a smooth membrane. Fre- 

 quently, the clear centers of the small 

 vesicles become condensed, thus obtaining 

 the appearance of small granules (Fig. 2). 

 The diameter of the small vesicles and the 

 granules ranges between 200A and lOOOA. 

 The appearance of the Golgi apparatus as a 

 whole varies greatly from cell to cell and 

 from tissue to tissue. It is best developed in 

 secretory cells where its function presimiably 

 is involved in the secretory process. Evi- 



dently the secretion products are prefab- 

 ricated elsewhere in the cell, but the end 

 products appear as small secretory granules 

 within the Golgi zone. Here they enlarge and 

 migrate eventually to the upper part of the 

 cell. In non-secretory cells, the Golgi ap- 

 paratus presumably plays an important role 

 in the metabolism of the cell, either by 

 offering its membranes as surfaces for en- 

 zymatic activity or by being utilized as a 

 system of channels for the intracellular flow 

 of metabolites and fluid. 



Small Vesicles. Vesicles of the same order 

 of magnitude as those found within the Golgi 

 zone may be traced elsewhere in the cell. 

 Their origin is unknown but they could 

 possibly be derived from the Golgi ap- 

 paratus. In some instances, as in non-ciliated 

 cells of the ciliated epithelia of the bronchi 

 and bronchioles (cross reference: ciliated 

 epithelia ultrastructure), in the distal con- 

 voluted tubule cells of the kidney, and in 



Fig. 9. Surface area of a dark, intercalated cell of the collecting tubvile of the 

 mouse kidney. The cytoplasm is pervaded by abundant microvesicles, one in connec- 

 tion with the surface (at 9). Tiny microvilli (Vi) extend into the tubular lumen (Lu). 

 In between the vesicles, which all are bound by a smooth membrane, are abundant 

 granules (arrows) with the size of about 150A, probably corresponding to granules 

 which in other cells have been demonstrated to contain RNA. Magnification 57,000X 



102 



