SYSTEMATIC NOTES 385 



tudinal muscles, the arrangement of the testes, the development of the ovary, and the structure of the 

 eggs. The above-mentioned authors appear to have dealt only with immature specimens, which of 

 course are not satisfactory for comparative purposes. 



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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. 



