Comparative morphological and physiological studies of the integumentary tissue and the content of molting hormone in the crayfish Orconectes limosus during a molt cycle

Abstract

The structural changes in the integumentary tissues during a molt cycle of the crayfishOrconectes limosus and the stages of the molt cycle are described. The incorporation of uridine-5-H3 into the nuclei of the epidermis and the tegumental glands during the molt cycle was determined by autoradiography and grain counting. In the epidermal nuclei the incorporation reaches a peak immediately before molt; a first, poorly expressed peak seems to be reached in stageD 1 which is characterized by apolysis and the preparation for secretion of the new epicuticle. In the early premolt stages (D0, D1) the activity of the tegumental gland nuclei compared to that of the epidermal nuclei is higher than in the later premolt stages. A first peak is reached in stage D1, a second one of similar size in stage D4. In stage D2, during and shortly after the secretion of the new epicuticle, heavily labelled hemolymph cells are found in the integumentary tissue beneath the epidermis and between the epidermal cells.Compared toCarcinus maenas only an approximative estimation of the hormone titer could be achieved. This is due to technical difficulties in connection with the very low hormone content of the crayfish. Measurable amounts could be detected between the premolt stages D0 and D3. In this period a rise of the RNA synthesis was observed. The peak of RNA synthesis follows the peak of the molting hormone with a certain delay. This is in accordance with the hypothesis of hormonal control of RNA synthesis during the molt cycle in arthropods. A comparison of the time course of RNA synthesis in the crayfish with the better known time course of the hormone content inCarcinus maenas exhibits a good accordance.