286 DAVID W. BISHOP 



suspensions can be, there seems to be little harm, and perhaps some 

 advantage, in expressing data in this fashion — so long as conditions 

 are specified — rather than in terms of cell number, protein, nitrogen, 

 wet or dry weights. 



Rothschild's discussion of the form of the propagated wave sug- 

 gests two commentaries. The nonsinusoidal shape of the planar wave 

 as it appears in his slowed-down bull sperm preparation, if taken to 

 mean a difference in amplitude on the two sides of the flagellum, 

 augments other evidence suggesting that the beat is stronger on one 

 side than the other. Assuming the direction of predominant bend- 

 ing bears a constant relation to internal and external structures of 

 the sperm, we are led to the electron micrographic evidence presented 

 by Fawcett for the bat sperm which indicates that a two-dimensional 

 beat in the flagellum, like that of cilia, may be correlated with the 

 position of the individual axial filaments. A more nearly complete 

 picture has been revealed in slowed squid sperm (Bishop, 1958) in 

 which the observed major planar wave corresponds to the position of 

 the prominent spur of the midpiece, which in turn can be seen in 

 electron micrographs to bear a constant relation to the individual 

 axial filaments (Afzelius, personal communication). Another point 

 noted by Rothschild is the variation in amplitude of the propagated 

 wave as it passes down the flagellum of the slowed bull sperm. Wave 

 amplitude normally increases distally in both bull and sea urchin 

 sperm, whereas wavelength decreases in the former and increases in 

 the latter (Gray, 1955; Rikmenspoel, 1957). The question arises 

 whether these variations are to be attributed solely to the physical 

 nature of the tensile and compressible elements of the sperm, or 

 whether, in part at least, they represent differences in the energy 

 supply locally available to the contractile system. Nelson comments 

 on the fact that in rat epididymal sperm the proximal portion, an- 

 terior to the kinoplasmic droplet, can be quiescent while the distal 

 segment undergoes active movement. Comparable wave distributions 

 have been described in living squid sperm and in reactivated sperm 

 model preparations. 



Steinbach and Dunham have taken up a major task and seem to be 

 making considerable, if iconoclastic, headway on a controversial sub- 

 ject — the nature of the permeability of the sperm membranes. It 

 comes as a surprise to learn that the invertebrate sperm tail behaves, 



