150 MOVEMENT OF CILIA AND FLAGELLA 



of these 9 structures into the ciliary bud that the 9 peripheral 

 doublets of the cilium are formed. It is probably not reasonable 

 to assume that all centrioles originated from ciliary basal bodies, 

 so that the number 9 may have its origin in the basic pattern of 

 centriole organiztion rather than in ciliary organization. The 

 answer to this part of the problem may therefore have to be sought 

 elsewhere than in the cilium. It is certainly a most intriguing 

 problem, and may be concerned with requirements of inter- 

 molecular and interfibrillar separation, along similar lines to the 

 suggestions of Serra (1960), although these ideas themselves do 

 not take sufficient account of the known structure of the cilium. 



Haptonemata should fit into this picture somewhere, but, until 

 information is available on their basal structure, any suggestions 

 can be no more than speculation. For example, do the 6, 7 or 8 

 fibrils of the haptonemata that have been described represent a 

 reduction from an original structure with nine contractile fibrils 

 which developed from a typical centriole ? It is interesting to 

 speculate further on the possibility that the haptonema was 

 ancestral to the flagellum, and that an undirected movement and 

 unlocalized contrcation were organized by the addition of a central 

 structure which allowed cross-connexions to localize the con- 

 tractions. It seems that the presence of two central fibrils is 

 cormected in some way with the fact that cilia and flagella normally 

 beat in one plane, and it is interesting that the cross-connexions 

 between the fibrils connect them more or less in two groups, 

 each with four outer fibrils (i.e. 2, 3, 4 and 5 and 6, 7, 8 and 9) 

 and one central fibril and sharing one outer fibril. The beat may 

 be confined to one plane by balanced contractions in these two 

 groups, which are symmetrical about the axis {W-V in Fig. 41b) 

 of the flagellum or cilium that is in the plane of beat. In this 

 arrangement, each group will contain both contracted and 

 non-contracted fibrils at certain phases of the beat, and the two 

 groups will be bound together by the connecting structure 

 between the two central fibrils. 



The functions of the basal body are certainly concerned with 

 morphogenesis, in that they are the centres for the organization 

 of both the ciliary shafts and the ciliary roots. They also form 

 a connexion between the ciliary shaft and the root structures. 

 Ciliary roots are responsible for anchorage in many cases, and 



