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ABSTRACT: A brief description of the foregut inPenœus indicus and a comparative account of the same in the remaining types of Penæidea and Stenopidea examined by me has been given.
The structure of the gastric mill in the Decapoda conforms to a typical plan common to all species, the variations being due
to the coalescence, reduction or disappearance of one or more ossicles; in those forms in which the gastric mill is reduced
the homologies of the principal ossicles can be made out.
The various types of the gastric mills found in the Decapoda can be arranged in a series ranging from simple to complex.
The forms considered as “primitive” for taxonomic and other reasons possess a simple type of gastric mill as compared to the
gastric mills in the more “advanced” forms. The evolution of the gastric mill closely follows the evolution of the Decapoda.
The efficiency of the gastric mill is correlated with the efficiency of the external masticatory apparatus, chiefly the mandibles,
the mandibles being simple in the forms in which the gastric mill is complex andvice versa.
The reason for the presence of the internal masticatory apparatus in one case and of the external masticatory apparatus in
the other can be found in the habit and habitat of the animals. Reptantous habit is associated with the possession of a complex
gastric mill and simple mandibles and the Natantous habit, on the other hand, with the possession of a reduced gastric mill
and complex mandibles.
Proceedings of the Indian Academy of Sciences - Section A Part 3 Mathematical sciences 04/2012; 2(2):155-174.