14 Electron micrographs of muscle fibrils. The upper picture is a 

 section across the main direction of the fibril. The larger circles are 

 the myosin filaments and the small points are the actin filaments. The 

 lower picture is a longitudinal section which shows the various bands 

 described in the text. These photographs are reproduced by per- 

 mission of Dr H. E. Huxley 



■P^P^"^ f 



