Elementary text-book of zoology elementarytextbo0101clau Year: 1884 71 of the body (fig. 66 a, b) (stigmata of Insects, Spiders), or they rnay be more restricted in number, and communicate also with cavities of complicated structure which are used for other functions (nasal cavities of Vertebrates). In the aquatic larvse of certain FIG. 67a.—Larva of an Ephemeral fly with seven pairs of tracheal gills A7, slightly magnified ; Tk, isolated tracheal gill strongly magnified. FIG. 67i.—Tracheal sys- tem at the sides of the alimentary canal of an Agrion larva (after L. Dufour). ZV,

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Elementary text-book of zoology elementarytextbo0101clau Year: 1884 71 of the body (fig. 66 a, b) (stigmata of Insects, Spiders), or they rnay be more restricted in number, and communicate also with cavities of complicated structure which are used for other functions (nasal cavities of Vertebrates). In the aquatic larvse of certain FIG. 67a.—Larva of an Ephemeral fly with seven pairs of tracheal gills A7, slightly magnified ; Tk, isolated tracheal gill strongly magnified. FIG. 67i.—Tracheal sys- tem at the sides of the alimentary canal of an Agrion larva (after L. Dufour). ZV, main tracheal trunk ; JT/, tracheal gills; If a, the three simple eyes. Insects (Epherneridfe, Libellulidse) the tracheae may be without any external openings. In such cases processes of the body filled with a close network of tracheae, which take up oxygen from the water, and are known as tracheal gills, are developed (fig. 67 a, b). In rare instances tracheal gills are developed on the wall of the rectum, and

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