CILIUM - ORIGIN AND 9-FOLD SYMMETRY

How the cilium appeared is still such a poorly defined question that c urrent hypotheses range from a symbiotic spirochaete to a cellular eye . In this paper, the whole question is subdivided into a list of probl ems which are morphological, physiological and temporal. These problem s are examined one by one, in order to analyse the most popular exogen ous hypothesis of Margulis as well as other recent exogenous and endog enous hypotheses. To overcome fundamental topological and temporal dif ficulties, a new endogenous hypothesis is expounded, according to whic h the cilium derives from a cellular peduncle reinforced with microtub ules. This hypothesis implies a geometrical rationale for the ninefold symmetry. In the last paragraph the consequences of the various hypot heses are compared.