ABSTRACT
The digestive tube is a simple tube made up of an oesophagus, a stomach, an intestine and a rectum. The branched digestive gland or hepatopancreas is situated in the midgut. Only this midgut comes from the embryonic endoderm and is not delimited by a chitin membrane. Glucosamine has a beneficial role, due to the slow speed of the synthesis of the precursor of chitin in crustaceans. The addition of di- or triholosides appears to be more favourable than that of glucose. The addition of starch varies with species, rate of incorporation, the nature of the starch and its method of presentation. Its role as a binder may limit the leaching of certain nutrients and improve the nutritional value of the diet. There are variations in the activity of digestive enzymes during growth, the intermoult cycle and circadian rhythms which allow a study to be made of variations in the diet of the animals.
