SPERM TAIL STRUCTURE AND MOVEMENT MECHANISM 149 



ence of a circle but inclined inward a few degrees. He also described 

 small "arms" projecting from one member of each doublet toward 

 the next in the row and observed a spokelike pattern of linear den- 

 sities radiating from the central pair toward the nine fibers of the 

 outer row. These findings have been extended by Gibbons and Grim- 

 stone (1960) in an elegant study of protozoan flagella. The presence 

 of arms was confirmed, and it was established that they are two in 

 number, and are consistently oriented in a clockwise direction from 

 the point of view of an observer looking along the flagellum from the 

 base toward the tip. The subfiber bearing the arms was designated 

 subfiber A and the other, subfiber B. Instead of a spokelike radial 

 pattern in the matrix, these authors observed in heavily stained cross 

 sections of flagella, nine dots situated midway between the central 

 and the outer fibrils (Fig. 1 A). These were interpreted as end-on views 

 of an additional set of slender longitudinal filaments overlooked by 





*•:©• 





».\B 



A 



1 



Fig. 1. A. The structure of the axial filament complex of a flagellum 

 as depicted by Gibbons and Grimstone. The central pair of fibers is en- 

 closed in a central sheath and nine secondary fibers are situated midway 

 between the central pair and the outer double fibers. B. The author's in- 

 terpretation of the axial filament complex of sperm flagella. Instead of a 

 second set of fibers there is a pattern of linear densities in the matrix 

 consisting of two curved lines connecting one member of the central pair 

 to the other, and nine radial lines connecting the central pair with sub- 

 fiber A of each outer fiber. Subfiber A of each doublet bears a pair of short 

 arms and its interior is considerably denser than that of subfiber B. 



