Abstract

The molting cycle of Orconectes can be divided into the following stages: Stage A1: begins when the crayfish molts. The animal feels like gelatin. Lasts a few hours. Stage A2: the carapace becomes leathery. Secretion of post exuvial cuticle begins. Lasts about 24 hours. Stage B: the carapace is becoming brittle, but the postorbital ridge and cervical groove can still be bent readily. Lasts 1-3 days. Stage C1: the postorbital ridge and cervical groove are rigid. Chemical changes in the pre-exuvial layers of the cuticle, such as phenolic tanning, are complete. Lasts about 2 days. Stage C2: the carapace has achieved its final state of rigidity except for the gastric region and areola. Lasts about 2 days. Stage C3: the entire carapace has achieved its final state of rigidity. Lasts several days. Stage C4: intermolt. It has been thought that secretion of the cuticle is now complete, but work with a radioactive tracer suggests that secretion continues at a low rate. Length of this stage is variable. Stage D0: beginning of premolt. Separation of the epidermis from the cuticle can be seen at the edge of the uropods and telson. Length of this stage is variable. Stage D1: development of new setae can be seen at the edge of the uropods and telson. Lasts about 10 days. Stage D2: secretion of new cuticle begins. Lasts 1-2 days. Stage D3: enough of the old cuticle has been reabsorbed so that the entire body can readily be compressed between the fingers. Lasts about 3 days. Stage D4: the line of dehiscence opens. Lasts a few hours. Stage E: the animal is in process of molting. Number of days, the gastrolith index, or the regeneration index may also be utilized for molt staging. Injections of ecdysone initiated early premolt and early molt and speeded premolt. The following observations on the crayfish epidermis were reported: Maximum DNA synthesis occurred during stage D1. The cells gained weight during premoIt and lost weight at molt. Protein content and rate of synthesis were correlated with secretion of cuticle. New enzyme synthesis during premolt seemed to be responsible for increasing chitin synthesis at that time. When the crayfish molted, there was a shift in the pathway of chitin synthesis. Before the molt, much of the new chitin was made from old chitin. After the molt, material for chitin synthesis was supplied from the diet.

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