26 



LORD ROTHSCHILD 



(a) (b) 



Fig. 5. (a) Diagram of a transverse section of a flagellum of Trich- 

 onympha. (After Gibbons and Grimstone, 1960.) (b) Diagram of a trans- 

 verse section of the sperm tail of Psammechinus miliaris. (After Afzelius, 

 1959.) 



I wondered, for example, whether the 'arms" which are now being 

 seen on the "clockwise" side of the fibrils in some sperm tails and 

 cilia (Fig. 5) might be devices by which fibrils embrace one another, 

 for some unknown reason, which implies fibrillar movement in a 

 plane at right angles to that normally postulated. Alternatively, the 

 number 9 may not have any particular point in regard to flagellar 

 or ciliary movement and may have been developed for quite different 

 reasons to do, for example, with cell division. The marked difference 

 in the size and mode of anterior attachment of some of the bull 

 sperm tail peripheral fibrils, recently demonstrated by Blom and 

 Birch-Andersen (I960), which I have recently confirmed, may lend 

 some slight support to this possibility. I have a working model of a 

 spermatozoon at Cambridge, unfortunately too big to bring with 

 me, which propagates bending waves from the front to the back end 

 of its tail in an enjoyably spermlike way, with only two contractile 

 fibrils in its tail. Of course — at least I think of course — the waves 

 have to be planar if there are only two fibrils; if the waves were 

 helical, or if their plane varied, one would need more fibrils. 



One way to gain further insight into the mode of action of the fi- 

 brils and, therefore, of their raison d'etre, might be by trying to ob- 

 serve them during activity. Given that in the nineteenth and early 

 twentieth century zoologists were apparently able to see sperm tail 

 fibrils with the light microscope, should we not have another shot 



