38 



" TERRA NOVA " EXPEDITION. 



.section. The number varies at different levels. PL III, fig. 16. shows the manner of 

 ending in the front region. In no specimen was the cirrus protruded as in the 

 original description given by Creplin. The dorsal surface is smooth and without 

 spines or hooks. The anterior extremity of the worm is surmounted by the oral 

 sucker (text-fig. 5, e). The wavy margin of the worm separates the oral sucker as by 

 a short intervening lip (text-fig. 5, a') from the corrugated ventral surface on which, 

 at a deeper level, is the common genital pore (PI. Ill, fig. 16, gp). Just within this 

 can be seen two important structures, a large ringed vaginal aperture (text-fig. 5, <l) 

 and a smaller ringed cirrus (text-fig. 5, c). 



This parasite was previously obtained by Dr. Creplin from Balaenoptera acuto- 

 rostrata, in 1821), in Arctic waters, and again by L. A. Jagerskiold from B. acuto- 

 rostrata and B. musculus-, in 1891, on the northern shores of Norway. The seals are, 



e 



Fig. 5. — Ogmogaster plicatus (Creplin.) : Ventral view of the anterior end, showing : a, a', a", the ventral 

 folds of the margin of the body ; b, the genital sinus ; c, the aperture of the male, and d, that of 

 the female genital duct ; e, the oral sucker. 



therefore, new hosts, and are both confined to the Antarctic region. Whales, believed 

 to be of the same species, occur, however, in both Arctic and Antarctic seas, and are 

 known to have similar parasites in each region. 



Internal Anatomy. 



Digest ire Tract. — At the cephalic end is the oral sucker, measuring 0*5 mm., 

 with an internal aperture measuring 0*25 mm. The sucker opens immediately into 

 the oesophagus, and this soon divides into the two gut-branches, which run a 

 tortuous course down either side of the worm to end at a, short distance from the 

 caudal extremity. 



Only a very few points can be added to the excellent and exhaustive description 

 given by L. A. Jagerskiold. 



Genital Organs. — The genital opening is in the middle line on the ventral 



