3 8o DISCOVERY REPORTS 



GENERAL DISCUSSION 



The cestodes collected represent ten different species belonging to six genera. Of these species, two 

 appear to be new to science and two represent larval stages, the specific identification of which does not 

 seem possible at present, although it can be seen that they belong to two different genera. The list 

 given below shows the names of the cestodes examined and Table 2 (p. 394) their occurrence in 

 particular hosts. 



LIST OF CESTODES EXAMINED 



1. Tetrabothrius affinis (Loennberg, 1891). 



2. T. wilsoni (Leiper & Atkinson, 1914). 



3. T. ruudi Nybelin, 1928. 



4. T. schaeferi sp.n. 



5. Trigonocotyle globicephalae Baer, 1954. 



6. Tr. prudhoei sp.n. 



7. Priapocephalus grandis Nybelin, 1922. 



8. Diplogonoporus balaenopterae Loennberg, 1892. 



9. Phyllobothrium larva. 

 10. Tetraphyllidean larva. 



With the exception of the two larval forms and Diplogonoporus balaenopterae, the rest of the above 

 mentioned cestodes belong to the family Tetrabothriidae, which appears to contain the bulk of the 

 cestodes found in Cetacean hosts. 



Because of their great similarity the identification of certain species presents certain difficulties. 



The scolex in the majority of these cestodes bears four suckers, which are variable in shape and size. 

 These suckers are usually provided with modifications called ' epaulettes ' or with fleshy protuberances 

 such as occur in the Genus Trigonocotyle. The scolex is subject to contraction and consequently its size 

 and shape give no help in specific determination. In the genus Priapocephalus, however, this organ 

 is acorn-like and easy to distinguish, though some variations in its contour do occur, as was mentioned 

 by Nybelin (1928) for P. minor. 



The strobila in the Tetrabothriids is either cylindrical and worm-like, or flattened, as in the other 

 groups of cestodes. The cylindrical strobila appears to be typical of Tetrabothrius affinis, though in some 

 cases, a short portion showing flattened segments occurs in the hind part of the body (PI. XX, fig. 1). 

 In Trigonocotyle globicephalae a short anterior portion of the body is cylindrical, while the remainder 

 of the strobila is flattened. 



Modifications of the anterior part of the body have also been noticed in the only example of the 

 Pseudophyllidea, present in this collection, namely Diplogonoporus balaenopterae, where that portion of 

 the strobila is markedly undulate dorso-ventrally (PI. XXI, fig. 6). It is difficult to prove at the 

 moment whether these modifications represent natural features or are caused by fixation. 



The genital organs in Tetrabothriids are also very similar and uniform in structure. Although there 

 is much variation in the number of the testes in immature proglottids and their size and arrangement 

 in the medullary parenchyma is difficult to determine, in the fully mature segments where egg pro- 

 duction has not yet begun, it is possible to ascertain their number and arrangement. 



In some forms, as in Trigonocotyle globicephalae , the testes, when examined in the cylindrical part of 

 the body, are distributed in many layers. In the flattened portion of the body, however, they are 

 arranged in a single layer. 



