Abstract: The cortical cirral-base-associated fibers (CF) in Euplotes sp.are:anterior longitudinal fibers (AF),posterior longitudinal fibers (PF),and radiating fibers (RF).Among them,the PF of frontoventral cirri (FVC) base are generally longer and thicker;while the AF are smaller;and,the RF are the thinnest and smallestones.The AF of transverse cirri (TC) base almost spread through the whole cortical region of frontoventral and transverse cirri (FVTC);and their RF are thinner- and smaller.Similar fibers,base-associated with different FVC,are different in size and shape.They extend from their cirral-base in various orientations,towards crtical cytoplasm,with apparent polarity and asymmetry.The fibers from FVTC base are heavily entangled,forming a strong net-work of base-associated fibers in their cortical region.During morphogenesis of Euplotes sp.,when the primordia of TC developed a bundle of thick cilia buds,extending towards the cortical fissure,the AF buds of TC primordia,PF buds of FVC primordia,and their RF buds,were developed successively.The fiber buds of left column cirral primordia developed first,then,developed those of the right column.The order of fiber material growth in coincidence with the development and differentiation of new cirri primordia.Also,in the formation of PF of FVC bases and AF of TC bases,polarity and orientation are displayed,I.e.,the directions of fiber material growth are opposite to thar of their corresponding new cirri migration.Old CF are doomed to degenerate during morphogenesis of Euplotes.It is supposed that their degenerating process are related to the gradual lose of old cirris functions during cell differentiation.