. Figs. 7-10. Tetrabothrius wihoni from Sei Whale. 7, cross section through mature segment; 8, transverse section of segment showing cirrus-sac and vagina; 9, cross-section through portion of longitudinal muscle; 10, egg. Tetrabothrius ruudi Nybelin, 1928. (Figs. 11-15.) Host: Fin Whale (Balaenoptera physalus). Locality: South Georgia. The length of the specimens examined is about 9 cm. and the width about 2 mm. The scolex, pro- vided with four suckers and ' epaulettes' is about 2 mm. broad. The longitudinal muscles form two more or less distinct rings. The inner one is formed by well accentua
. Figs. 7-10. Tetrabothrius wihoni from Sei Whale. 7, cross section through mature segment; 8, transverse section of segment showing cirrus-sac and vagina; 9, cross-section through portion of longitudinal muscle; 10, egg. Tetrabothrius ruudi Nybelin, 1928. (Figs. 11-15.) Host: Fin Whale (Balaenoptera physalus). Locality: South Georgia. The length of the specimens examined is about 9 cm. and the width about 2 mm. The scolex, pro- vided with four suckers and ' epaulettes' is about 2 mm. broad. The longitudinal muscles form two more or less distinct rings. The inner one is formed by well accentuated bundles, composed of well developed fibres. The circular muscles are not well developed. The testes, situated dorsally, are about 42 X 45^ in transverse section. They are not very numerous. The vas deferens is well developed. The cirrus-sac is pear-shaped, as depicted by Nybelin (1928). The ovary, extending horizontally in the ventral part of the segment is well developed. The vitelline gland lies ventrally to the ovary. The very well developed uterus possesses the same kind of opening as in previous forms and similar modified parenchymatous tissue. The formation of the uterine duct commences in the mature segments where the uterus has not yet reached full development. In the early stages the modified tissue surrounding the duct is markedly visible. The eggs are 40-50^ in diameter, the embryonic membrane 30 x 30/Li and the embryo 17 x i8/l*. In eggs cleared in glycerine, embryonic hooks have not been observed. The excretory system shows the ventral vessel to be relatively greater in diameter than the dorsal one, the latter possessing thick muscular walls.
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