dence of continuit}' between the smooth membranes of the Golgi and 

 certain elements of the endoplasmic reticulum. 



Because the complex is somewhat difficult to isolate from other cellu- 

 lar components, its exact function is not precisely known. The fact that 

 the complex is most readily revealed in cells which have a specialized 

 function in connection with secretion, combined with the observation 

 that there is a general parallel between the morphological changes in 

 the complex and the level of secretory activity, has led to the notion 

 that the Golgi functions as a region for the collection of specialized 

 products. The association between the endoplasmic reticulum and the 

 complex provides a logical means of transport to the cell exterior. It is 

 also tempting to draw an analogy between the proposed function of the 

 Golgi and the contractile vacuole of the protozoa, although some pro- 

 tozoa may have both organelles. 



As in the case of the mitochondria and endoplasmic reticulum, elec- 

 tron microscopy studies have also revealed consistent changes in the 

 Golgi complex which are associated with developmental sequences dur- 

 ing the maturation of mammalian germ cells (Fawcett, 1959). In 

 primary spermatocytes, the Golgi is typical in its fine structure. As 

 development continues, the interior of the complex is altered to produce, 

 finally, a dense body called the acrosome, which is bounded by a single 

 membrane. 



CELL MEMBRANE 



Even cells which appear to be syncitial by ordinary histological 

 methods have in most cases been demonstrated by electron microscopy 

 to be compartmentalized by membranes which are presumably similar 

 in structure and function to those normally forming the outer boundary 

 of free cells. In cross-section, these boundaries appear as osmiophilic 

 lines about 60 A thick, adjacent membranes being separated from each 

 other by a space of the order of 100 A. Current opinion appears to be 

 that the cell membrane is actually a double structure having a lipoidal 

 and protein component. 



A number of interesting modifications or specializations of the cell 

 membrane have been classified by Selby (1959) as follows: (1) narrow 

 evaginations, (2) local thickenings, (3) deep infoldings compartmental- 

 izing the cytoplasm, (4) interlocking of adjacent cells, and (5) narrow 

 invaginations of the cell surface. Adoption of any of these specializations 

 by the cell membrane serves to increase cellular surface area, facilitate 

 transport of materials in and out of the cell, and modify the degree to 

 which adjacent cells are associated with each other. 



64 / CHAPTER 3 



