Plate XI. Electron micrographs of transverse sections of 

 sperm tails. 



(a) Sections of two sperm tails of Bufo. The main axis of 

 the tail contains the 9-plus-2 bundle of fibrils. A fin (undulat- 

 ing membrane) of dense material extends to one side in the plane 

 of the central fibrils and ends at a thickened margin. From 

 Burgos and Fawcett (1956). X 60,000. 



(b) Incomplete section of a sperm tail of Apis. The surface 

 membrane of the cell is missing, but the remaining structure 

 appears to be complete. The two large structures on the right 

 are the longitudinal mitochondrial strands; they are separated 

 from the axial fibre bundle by two additional structures of 

 unknown function. The peripheral fibrils of the axial bundle 

 have outward extensions of dense material, and surround some 

 interesting structures including the central fibrils w'hich are 

 linked bv a semicircular filament. From Rothschild (1955). 



X 110,000. 



(c) Transverse sections through the principal-piece region of 

 three sperm tails of Carta. The 9-plus-2 fibril bundle is clearly 

 seen, and shows many details of fine structure, such as radial 

 links and connexions between the central fibrils. One subfibril 

 of each peripheral doublet appears to have a dense centre, and 

 also bears the arms. Seven outer coarse fibres are prominent 

 in each section, and each bundle is surrounded by a dense 

 fibrous sheath, from which laminae project towards peripheral 

 fibrils 3 and 8. The cell membrane is separated from the 

 fibrous sheath by a less dense region. Micrograph by Fawcett. 



X 100,000. 



