Regulation of ciliary pattern in Dileptus (Ciliata). I. Sensory cilia and their conversion into locomotor cilia.

The surface of Dileptus contains three different regions: locomotor, oral and sensory. Each region has cilia with a specific structure and arranged in a characteristic pattern. In the morphogenetic situation when a sensory region transforms into a locomotor one, sensory cilia undergo structural changes converting them into locomotor cilia. The evidence for this is that cilia are found in the transforming region with an inner microtubular pattern intermediate between that of sensory and locomotor cilia. There are also changes in distribution of sensory units leading to a pattern characteristic of locomotor cilia. The conversion of sensory cilia into locomotor ones is also confirmed by a complete lack of evidence for resorption of sensory units within the transforming region, although the resorption is usually very easily observed with the transmission electron microscope. Transformation lasts about 5 h after the operation; afterwards locomotor cilia of normal appearance occupy the transformed region. This way of regulation of ciliary pattern has not been previously described. Its most surprising feature is the regulation of inner structure in an already differentiated ciliary unit. Some aspects of mechanisms which could control this kind of pattern regulation, are discussed.