Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 71 cf the body (fig. 66 a, b) (stigmata of Insects, Spiders), or they may 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 larva? of certain Fin. of an Ephemeral fly with seven pairs of ofi'i Cf, slightly magnified ; Tk, isolated tracheal gill strongly magnifi
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 71 cf the body (fig. 66 a, b) (stigmata of Insects, Spiders), or they may 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 larva? of certain Fin. of an Ephemeral fly with seven pairs of ofi'i Cf, 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). Ttt, main tracheal trunk; Et, tracheal gills; Na, the three simple eyes. Insects (Ephemeridse, Libellulidae) 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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