. The physiology of the Invertebrata. he Amphipoda. Fig. 12 represents the digestivesystem of Oniscus (the wood-louse). It forms a straight tube,the masticatory portion beingstrongly armed. Two ducts,leading from a pair of cellularpancreatic follicles on each sideof the alimentary canal, pour thedigestive fluid into the anteriorportion of the canal. The num-ber of these follicles is variablein other genera of the Isopoda,but in Oniscus there are alwaysfour, two on each side of thealimentary canal. Sometimesthere are one or two tubules which open into the posterior part of the intestine. The fu
. The physiology of the Invertebrata. he Amphipoda. Fig. 12 represents the digestivesystem of Oniscus (the wood-louse). It forms a straight tube,the masticatory portion beingstrongly armed. Two ducts,leading from a pair of cellularpancreatic follicles on each sideof the alimentary canal, pour thedigestive fluid into the anteriorportion of the canal. The num-ber of these follicles is variablein other genera of the Isopoda,but in Oniscus there are alwaysfour, two on each side of thealimentary canal. Sometimesthere are one or two tubules which open into the posterior part of the intestine. The function?of these appendages is of the same nature as the Malpighiantubules of the Insecfa. (30) The Stomapoda are elongated. Cnostacea having ashort, cephalo-thoracic shield which does not entirely coverall the thoracic segments. In the genus Squilla there arefive pairs of maxillipeds, and three pairs of backwardlyturned biramous thoracic feet. The alimentary canal, some-what dilated in its anterior part, is a long cylindrical tube,. Fig. 12. ? -Alimentary CanalOF Oniscus. a = masticatory = pancreatic = intestine. d = anus. * Many new species of the AmpMpoda have been described by Sars inthe V/iristiania Videnak. Sesh. Forliandl., 1882, No. 16, pp. 75-115. 58 PHYSIOLOGY OF THE into which numerous pairs of pancreatic follicles dischargethe digestive fluid. The intestine becomes narrower at theposterior end, and terminates in an anus situated behind somite. (31) The Anovioura form a small order containing thehermit-crabs {Paguridce). They are distinguished from theMacroura in having an uncalcified and soft integument. Theappendages of the body are more or less abortive through disuse,while those of the sixth somite are modified to form means of the claspers the hermit-crabs are capable ofholding on to the columellse of the shells of Molluscs which thePaguridce inhabit. The inner part of the Aiwmoura aresomewhat similar
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectinverte, bookyear1892
