. Animal biology. Zoology; Biology. 258 METAZOAN PHYLA There are two gill chambers, one on each side of the body, lying between the lateral wall of the body and a broad plate extending ven- trally from each side of the dorsal surface. Each gill chamber is open in front, forming a channel in which lies the scaphognathite, or bailer, of the second maxilla. It is also open by a narrow slit along the ventral side and in the lower part of the posterior end. In this chamber, in the cray- fishes of the eastern states, which belong to the genus Cambarus, are two rows of gills. The outer row is attache
. Animal biology. Zoology; Biology. 258 METAZOAN PHYLA There are two gill chambers, one on each side of the body, lying between the lateral wall of the body and a broad plate extending ven- trally from each side of the dorsal surface. Each gill chamber is open in front, forming a channel in which lies the scaphognathite, or bailer, of the second maxilla. It is also open by a narrow slit along the ventral side and in the lower part of the posterior end. In this chamber, in the cray- fishes of the eastern states, which belong to the genus Cambarus, are two rows of gills. The outer row is attached to the first joints of the append- ages from the second maxilliped to the fourth walking leg (Fig. 163). The inner row of gills, double except in the case of the first one, arises InfesHne Digestive S-homach \/as deferens "^^^^'^ \ Heart "Dorsal ab- ~~ \ dominal drferv Supraesophageal gang!I on Anfennule /infenna Anus. Swirnmerets Telson ,, J . - - ,.,„ , Ventral / Wernal nerve cord / artery Opening of vas deterens Walking'. legs Fig. 164.—Partly diagrammatic longitudinal section of the European crayfish, Astacui fluviatilis Fabricius. {From Borradaile and Potts, "The Invertehrata," after Shipley and MacBride, by the courtesy of The Macmillan Comjyany.) The indi\-idual is a male and the first two swimmerets are modified to form copulatory appendages. from the membrane attaching the same appendages to the wall of the body. In the crayfishes of the Pacific coast, which belong to the genus Astacus, there is also a third row attached to the wall of the body itself. In respiration a current of water is maintained in the gill chambers pro- duced by movements of the swimmerets, which direct water into the posterior end of the chamber, while it is being bailed or scooped out from the anterior end by the scaphognathite. 293. Internal Structure.—The various systems in the crayfish are well developed (Fig. 164). Some of the systems, like the muscular and nervou
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