In recent years, antirrietabolites and structural analogs of normal cell coniponents have been used increasingly as tools in the study of morphogenesis. For exaniple, Brachet ('46, '47) has explored the effect of acriflavin, barbituric acid, and beiiziniidazole on the development of aniphibian eggs. More recently Bieber ( '52, '54), in extensive investigations with a large variety of antipnrines and antipyrimidines, has been able to show that particular developmental stages are specifically sensitive to inhibiting agents. Embryological work of this kiiid has come to supplement three earlier lines of esperinieiitation with antimetabolites, all concerned in some fashion with the problem of growth : pathways in nucleic acid metabolism ( e g . , Hitchings, '50) ; tumor growth and its inhibition (c.g., Kidder, '51) ; and iiutrition and population growth in microorganisms (e.g., Lilly, '53).
Regenerating fragments of the ciliate 8te?ztor coericleiis provide test systems in which differeiitiative events have been analyzed to substantial degree (cf. Teisz, '51, '54). Antimetabolite studies on such systems therefore give reasonable promise to be interpretable with some precision, thus adding to an understanding of morphogenesis derived from analogous work on eggs. Inhibition experiments on Stentor fragments are reported in this paper.