EPILOGUE 287 



ionically, as though no semipermeable membrane existed, but at 

 least this may tend to clarify somewhat the doubt expressed by 

 Rothschild and others that, under certain circumstances, ATP can 

 penetrate and effectively activate the flagellum. II it is true, as sug- 

 gested by Steinbach and Dunham, that the invertebrate "tails act 

 like so many highly permeable strands of jelly," this could account 

 for the absence of a glycolytic system in these flagella, in contrast to 

 that found in mammalian sperm which are enclosed by a fibrous 

 sheath and, presumably, a physiological membrane as well. It is to 

 be hoped that this approach will be applied to an investigation of 

 ionic balance in mammalian sperm and thereby elucidate the strange 

 situations found there in regard to ionic tolerances (Bishop, 1962). 



Many new ultrastructural details have been visualized in the elegant 

 electron micrographs presented here by Fawcett and in the cyto- 

 chemical localizations demonstrated by Nelson. One is made aware 

 of an increasing structural complexity and optical differentiation of 

 elements within the axial bundle. Additional fibrils and cross con- 

 nections are indicated in the matrix. Although the standard 9 + 2 

 axial fibrillar pattern is universal throughout flagellar and ciliary 

 systems, the more restricted (mammals, birds, and possibly some in- 

 vertebrates), outermost peripheral array of extra fibers has here re- 

 ceived the most attention. Fawcett's interpretation of material from 

 a number of mammalian species credits these electron-dense fibers 

 with a major role in contractile movement, a view supported by 

 Nelson's localization of antimyosin antibodies and ATPase activity 

 in the same sites. One wonders whether similar methods of analysis 

 can be applied to the simplified and more generally distributed type 

 of motile organelle and, if so, where the myosin-like substance might 

 be. In the 9 + 2 cilia of the rotifer, Philodina, Lansing and Lamy 

 (1961) find evidence, by a different technique, of ATPase in two 

 areas outside the circular array of fibrils associated with filaments 

 1 and 5. 



The abundance of cytochrome oxidase and succinic dehydrogenase 

 in both the midpiece and tail of clam and bull sperm, alluded to by 

 Nelson, presents a quandary in the light of the usual distribution of 

 these enzymes and the general localization of the mitochondrial ap- 

 paratus in the sperm midpiece. In some gametes, those of the honey- 

 bee, for example, what appear to be mitochondria extend far down 



