Plate 5 



A. Examples of the surface of contact between cells. Figure from two 

 ectodermal cells A and B, in the surface of a 12-day-old chick embryo. 

 O, outer surface; D, desmosome; I, interdigitated membranes. Note 

 the two dense, parallel plasma membranes and the lighter deposit between 

 them revealing the intercellular cement. / is a tuft of fine fibrils (pre- 

 keratin) attached to the desmosome plates. The cytoplasm contains fine 

 dense particles but no particle-covered membranes. Stain: PTA. 



B. Another example of an intercellular contact between two rat pancreas 

 cells A and B. Again the two contacting membranes appear as dense, 

 parallel lines separated by a dark material, the intercellular cement. /// is 

 a mitochondrion, and P are RNP granules attached to the system of 

 cytoplasmic membranes of these granular secreting cells. Stain: lead 

 hydroxide. 



Micrograph kindly supplied by M. S. C. Birbeck. 



