CYTOCHEMICAL ASPECTS 



181 



enzyme systems, one of which is inactivated or washed out during 

 glycerol extraction. The presence of glycerol-soluble IPPase suggests, 

 as a mechanism of motility, the cyclic interaction of this enzyme with 

 ATPase. The ATP-Mg-ATPase system dominates the contraction 

 phase while something like the NaPP-Mg-IPPase system could par- 

 ticipate in the relaxation phase (Nelson, 1959a). 



With respect to the contraction phase of sperm movement, electron 

 dense "bridges" extending from the peripheral fibers to the axial 

 fibers may tempt one to consider a Huxley-Hanson type of sliding 

 filament mechanism (Fig. 7) in favor of a model based on molecular 

 folding within the peripheral fibers themselves (Nelson, 1958b). The 

 analogy suffers as yet from the lack of evidence for any clear-cut 



Fig. 7. Projections extending between peripheral fibers and axial 

 fibers, indicated by arrows. Note similarity to bridges between actin and 

 myosin filaments of Huxley-Hanson muscle preparations (X 40,000). 



