Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 63 a, b), or of Fro. 63a.— Head and anterior body segments of a Eunice, viewed from the dorsal sur- f-ace. T, tentacles. Ct, tentacular cirrus. C, parapodial cirrus. Br, parapodial gill. lancet-shaped closely-packed leaves with a large surface extension (fig. 64). FIG. 61. — Transveroe section througn the gill of a Teloostean fish, b, branchial leaf- let with capillaries ; c, 1 ranchial artery con- taining venoua blood; d, branchial vein con- taining
Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 63 a, b), or of Fro. 63a.— Head and anterior body segments of a Eunice, viewed from the dorsal sur- f-ace. T, tentacles. Ct, tentacular cirrus. C, parapodial cirrus. Br, parapodial gill. lancet-shaped closely-packed leaves with a large surface extension (fig. 64). FIG. 61. — Transveroe section througn the gill of a Teloostean fish, b, branchial leaf- let with capillaries ; c, 1 ranchial artery con- taining venoua blood; d, branchial vein con- taining arterial blood. a. branchial bar. FIG. G3i.—Transverse section through the body of Eu- nice. Br, gill; C, cirrus ; P, parapodium with a bundle of seta3; D, alimentary caiial; A', nervous system The organs of aerial respiration, on the contrary, are internal. They present likewise the condi- tion favourable for an exchange of gases between the air and the blood, viz., a large extent of surface. They have the form either of lungs or sir-bearing tubes. In the first case (Spiders, Vertebrates) they consist of spacious sacs with alveolar or spongy
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