i 8 o LOCAL AND GENERAL FACTORS IN THE DEVELOP- MENT OF "PATTERN " IN RHODNIUS PROLIXUS (HEMIPTERA)

MOST studies on morphogenesis have been made upon composite structures, such as eyes or appendages, whose form is controlled by the co-operation of a great number of cells. In insects, however, the tiny fragment of cuticle laid down by a single cell may possess morphological characters controlled by the activities of that cell alone. The cuticle of insects provides, therefore, an unusually simple medium for the study of morphogenesis and the nature of those processes which "determine" the activity of a given cell. As material for the present work the epidermis of the abdomen in the blood-sucking bug Rhodnius has been employed. This consists of a single layer of cells which lays down an extracellular cuticle. The cuticle has a "pattern", since it varies in structure and in coloration in different regions. As we shall see, the individual cells in each region are "determined " for the formation of different elements in this pattern. Certain elements in the pattern, however, are capable of regeneration. In other words, certain of the cells retain potencies which are normally suppressed. The material therefore affords an opportunity of studying the process by which th