Illustrations 



Fig. 1 . A typical spermatogonium, seen in optical section. 

 The figure is intended to show the structure of the 

 living cell page 4 



Fig. 2 (plate). Electron-micrographs representing the cyto- 

 plasm of a large phagocytic cell from the blood 

 of the domestic fowl, and of an acinar cell from 

 the pancreas of the rat facing page 10 



Fig. 3. Graph showing the rate of penetration of mercuric 



chloride into gelatine-albumin gel page 23 



Fig. 4. A typical spermatogonium, as seen in a routine 



microscopical preparation page 26 



Fig. 5. Diagram showing the changes in volume imdergone 

 by gelatine-albumin gel when acted upon by 

 fixatives page 11 



Fig. 6. Structural formulae for hydrated aluminium ions 



page 113 



Fig. 7. Diagram of a finished microscopical slide in 

 sectional view, showing adhesives and varnish 



page 1 34 



XHl 



