The basal bodies contain more internal structures than those described for other organisms. For example, they possess 2 different and separate cartwheel structures. In cilia the 2 central tubules terminate proximally in a different fashion. Three types of cilia have been distinguished. Each type possesses a different array of rootlet fibres. During binary fision one type develops 1 h before all the others while the ciliary shafts, but not the basal bodies, of a second type are being resorbed. These are later reformed when a third variety of cilia develop. Some new basal bodies and cilia are formed at least 30 min before they can be detected using silver staining. Studies of basal body morphogenesis based on this technique are pertinent to the separation of closely adjacent mature basal bodies rather than to their development. The arrangement and spacing of new basal bodies may be partly defined by their rootlet fibres which interconnect basal bodies before they attain their final positions in the cortex. Overlapping microtubules linking basal bodies apparently slide against each other during the final stages of basal body deployment. Heat shocks often inhibit the attachment of new basal bodies to the pellicle but ciliary and rootlet fibres assemble and grow out from the usual sites on these abnormally positioned basal bodies.

The pellicle is highly impermeable to water and the fine structure of its innermost layer resembles that of the waterproofing epicuticle of some insects. A cuff of this pellicular material forms around the distal end of each new basal body and then seals it to the undersurface of the pellicle. The outer wall of the pellicular chamber so formed breaks down when the ciliary shaft is assembled. This ‘cytoplasm-lock’ mechanism may ensure that there is no marked change in the permeability of the pellicle when it is penetrated by outgrowing cilia.

A new type of ciliary membranelle is described. Some of its modified cilia possess flanges attached to their outer fibres. These cilia may have a sensory role. Membranelle basal bodies are linked by fibres exhibiting a non-repeating polarized banding pattern which may be involved in defining the arrangement and spacing of these basal bodies.

A ring of microfilaments encircles the narrow duct joining the contractile vacuole to its outlet pore. This ring may act as a sphincter and be involved in the control of water discharge. During binary fission contractile vacuole pores migrate posteriorly. They are apparently pulled by strands of microtubules and microfilaments attached at one end to a pore and anchored at the the other to more posteriorly situated basal bodies.

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