Fig. 2-3. Living median neurosecretory cells in the protocere- 

 brum of the blowfly, Calliphora, photographed by dark-ground 

 illumination. The secretory granules in the cells are highly refrac- 

 tile and therefore show as bright areas filling the cell bodies ; only 

 the nuclei remain dark. Other brain cells without granules can 

 be seen faintly outlined in the background (from E. Thomsen, 



1954). 



