Europ. J. Protisto!' 30, 379-393 (1994) November 25, 1994 European Journal of PROTISTOLOGY Quantitative Regulation of Ciliary Structures in Polymorphic States of the Hypotrichous Ciliate Onychodromus indica, Kamra and Sapra 1993 Kamal Kamra 1 and Gulshan R. Sapra" 1 SGTB Khalsa College, University of Delhi, Delhi, India 2Department of Zoology, University of Delhi, Delhi, India SUMMARY Onychodromus indica depicts several polymorphic states, exhibiting a wide range in the cell size with corresponding changes in the number of ciliary structures. Under different culture conditions cells transform and perpetuate as distinctly different morphs; the trans- formation involves a change in the quantum of cortical structures related to its size. A numerical analysis of the membranelles of the adoral zone of membranelles (AZM) in relation to the cell size shows that morphic transformations occur through a process of unequal cellular divisions wherein controlled adjustment in the AZM size occurs in two different ways prior to the cytokinesis. In a "step-up" situation the opisthe develops a larger than expected oral primordium and subsequently a larger AZM. Conversely, in the "step-down" situation a measured resorption of the membranelles of the parental AZM occurs leading to the formation of a smaller proter. Such unequal cellular divisions occur several times until transformed morphs of characteristic dimensions are formed . This stud y projects morphic transformations as the model system for the anal ysis of quan - titative changes in cortical structures. Introduction The cortex of hypotrich ciliates bears multikinetoso- mal ciliary elements that are asymmetrically positioned in a species-specific manner [9]. Two sets of such struc- tures are formed prior to cell division (one set during reorganization) through an ordered and regulated pro- cess of cortical morphogenesis. The multifaceted regu- lation during division includes the setting up of two metameric maps, correct positioning of ciliary primor- dia (Rev.: [3]), and quantitative regulation of size and number of cortical elements in relation to cell size and shape (Rev.: [44]). Numerical adjustments of cortical attributes related to cell size during starvation [4, 12, 28, 35, 46], giant cell formation [17, 18-23,37,39,46], and in regen- erating fragments [10,11,28,31,43] are well recorded phenomena. However, most of the aforementioned stu- dies do not provide precise quantitative data (except © 1994 by Gustav Fischer Verlag, Stuttgart for [4]) and mostly compare two or more states of a cell thereby revealing little information about the course of events . It is noteworthy that cortical reorga- nization has been stated as the usual pathway to bring about quantitative adjustments (Table 1). The present study throws further light on the devel- opmental strategies that bring about quantitative reg- ulation of the cortical structures in Onychodromus indica. This large polymorphic hypotrich [33] shows considerable plasticity in its cortical attributes. The variability in cell dimensions is accompanied by conco- mitant modifications in the number of ciliary struc- tures. In nature, O. indica feeds on several types of food organisms, including conspecific prey. The corti- cal variability is mainly related to the prey size. To gain an insight into the mechanisms that determine the mor- phometry of morphs we have chosen four laboratory situations where cells were fed exclusively ad libitum on one type of food organism in anyone given situa- 0932-4739-94-0030-0379$3.50-0