382 DISCOVERY REPORTS 



SUMMARY OF DISCUSSION 



To sum up : Specific differences are to be found in the size and the arrangement of testes, in the size 

 and structure of eggs, embryos and embryonic hooks, and in the arrangement and shape of the 

 longitudinal muscles in the fully mature, but not gravid segments. 



SYNONYMY 



The history and the nomenclature of some of the Tetrabothriids occurring in Cetacea have been 

 given by Rees (1953). 



Recently, Baer (1954) has published a list of synonymous names of Tetrabothriids and their specific 

 classification. From the present work it seems, however, that Tetrabothrius zvilsoni, which he considers 

 to be synonymous with T. affinis, actually represents a distinct species (Table 1, p. 387). 



Baer's (1954) criticism of Baylis's (1926) description of T. affinis appears to be justified, as the material 

 examined by Baylis seems to represent another species, described in this paper as T. schaeferi sp.n. 

 The form mentioned by Rees (1953) as Tetrabothrius sp. also appears to represent the same species. 



The two new species described in this paper, namely T. schaeferi and Trigonocotyle prudhoei have 

 been named after Miss F. H. A. Schaefer who, during my recent illness nursed me in hospital, and 

 after my friend Mr S. Prudhoe of the British Museum (Natural History). 



SYSTEMATIC NOTES 

 Genus Tetrabothrius Rudolphi, 1819 

 This genus is represented in the present material by four species. Of these, one seems to be new. 



Tetrabothrius affinis (Loennberg, 1892). (Figs. 1-6, PI. XX, figs. 1-2.) 



Diplobothrium affine Loennberg, in Jagerskiold, 1891. 

 Tetrabothrium {Diplobothrium) affine. Loennberg, 1892. 



Hosts: Blue Whale (Balaenoptera musculus); Sperm Whale (Physeter catodon). 



Localities: Saldanha Bay and Durban (South Africa); South Georgia; and 58 32' S, 34 52' E. 



The specimens examined are about 20 cm. long and about 5 mm. wide. The strobila is cylindrical 

 with very short segments. In some specimens the posterior end of the body is modified into flattened 

 segments, markedly separated from each other (PI. XX, fig. 1). 



This region is the spent part of the body containing the degenerate genital organs. 



The scolex, about 2 mm. long and 2 mm. broad, is variable in shape and bears typical 'epaulettes'. 

 A neck does not seem to be present. 



The musculature is strongly developed in this species. Cross-sections of the body show that the 

 longitudinal muscles form two distinct rings. The internal ring is composed of strongly developed 

 bundles of a very characteristic shape shown in Fig. 4. The circular and dorso-ventral muscles are also 

 very well developed. 



The testes are dorso-ventrally elongate in younger segments and about 90 x 53 ^ in diameter, but in 

 the more developed segments they are irregularly spherical and seem to be arranged in several layers, 

 which are distributed dorso-ventrally. The thick-walled, coiled vas deferens is well developed. The 

 pear-shaped or rounded cirrus-sac possesses thick muscular walls and a strongly developed cirrus. 



The lobate ovary extends transversely in the ventral part of the segment and is composed of dis- 

 tinct egg-cells. The vitelline gland is situated ventrally to the ovary. 



