10 JAMES GRAY 



mal elements bend simultaneously in two planes, distal elements 

 might also be excited to bend in corresponding planes. In other 

 words, the bending waves would be comparable with muscular move- 

 ments of "myogenic" origin. The rhythmical activity of sperm 

 "models" when activated by ATP makes it difficult to think that 

 anything comparable with conducted nervous impulses is funda- 

 mentally concerned, but here again the situation would be clarified 

 by more precise information of the extent to which the form and 

 frequency of the waves displayed by such models differ from those 

 seen in a living flagellum (see Bishop, this symposium). 



If the form and frequency of the waves are dependent on external 

 forces, a relatively simple explanation is forthcoming for the fact 

 that when two or more flagella are in close proximity with each other, 

 their waves become synchronized; this phenomenon is, of course, not 

 restricted to flagella, but probably occurs in all undulating organ- 

 isms under comparable conditions. If, during its transverse move- 

 ment an element of one individual came into contact with a more 

 slowly moving element of another individual, its speed would be 

 reduced while that of the latter increased. Sometimes an author uses 

 an unfortunate simile. In discussing the relatively low metabolic 

 level of a dense suspension of sea urchin spermatozoa (1928), I used 

 the expression "They do not make any effort to move." This has been 

 criticized by Rothschild (1961) as implying "some sort of free-will on 

 the part of the spermatozoon." My remark was intended to convey 

 the belief that isometric activity of the contractile elements of the 

 tail did not occur. The evidence presented above supports the view 

 that unless the tail is free to alter its shape, there is no conversion of 

 chemical into mechanical energy along its length, and the metabolic 

 activity may be expected to be correspondingly reduced. 



Not the least interesting aspect of flagellar movement is one touched 

 on by Rothschild (1961), namely, the very small dimensions of the 

 filaments which exhibit it. Can it be that the whole of the essential 

 structures may, one day, be located in a relatively small number of 

 macromolecules each able to exhibit active changes in shape and 

 able to liberate mechanical energy when subjected to external me- 

 chanical deformation? In this respect the work of Astbury's school 

 may be of fundamental significance (Pautard, this symposium). 



