Formation of Ciliature in Excystment and Induced Re‐encystment of Oxytricha fallax Stein

Abstract

SYNOPSIS. In excystment the primordium of adoral membranelles (AZM) arises as one granular row stretching meridionally toward the cortical axial poles, growing to several rows. Then the AZM's primordial granules become compactly aggregated with a leaf‐like form. A separate primordium for the undulating membrane also appears as well as cirral primordia, all in arrangement similar to that in dividers and regenerators of the present species. Though it is difficult clearly to decide from where all these primordia are derived, their formation seems to have a morphogenetic relation to the thickening of certain fibrillar structures appearing only in resting cystic stages.Re‐encystment is induced when the excysting cysts after the appearance of a contractile vacuole are transferred to Osterhout's solution from hay infusion employed for excystment induction. Re‐encystment follows after the final step of excystment differentiation is accomplished but with aborted rupture of cyst walls. In the resulting re‐encysted cyst, the secondary cyst walls are enclosed within the original ones. Repeated treatment can produce cysts with further supernumerary cyst walls by additional formation of third walls.Protoplasts in re‐encystment show characteristics similar to animals prior to and after precystic stages. When their original cyst walls are removed, the naked protoplasts obtained take any one of the following courses: 1. recovery of normal form; 2. physiological regeneration; 3. irreversible encystment. Case (1) occurs in naked protoplasts from early stages of re‐encystment; case (2), in those prior to the extrusion of excretory granules seen in the course of re‐encystment; and the case (3), in those after their extrusion. From these results, presumably the removal of an incipient state of physiological regeneration in the course of re‐encystment may be essential for dedifferentiation of the ciliature that redifferentiated fully in the preceding excystment without escapement.