48 



"TERRA NOVA " EXPEDITION. 



in length. The apex is 0"24 mm. across, while the lower and broadest part is 0'45 mm. 

 There is no rostellum and there are no hooks. The neck is broadest at its junction 

 with the head and gradually narrows to the first segment. 



Segments. — The following information regarding the segments is derived from 

 stained specimens, from near the head-end and near the tail-end of the worms. 



Maturity is late. The general size and shape of the segments, which are broader 

 than long, does not vary much. Antero-posteriorly they measure 0"32 mm., the 

 cephalad border being 0'5 mm. in width and the caudad border 0'62mm. The staining 

 of the segments is diffuse. The genital openings are on the side and are unilateral : 

 they vary considerably in formation in various parts of the worm. Thus in immature 

 portions there is no projecting ring, while in those which are more mature there is a 

 well-marked ring outside the border of the segment, while at a deeper level there is a 

 second ring containing the openings of the cirrus and vagina. The cirrus is simple, 

 rounded and unarmed. The straight vas deferens which runs from it ends in a slight 

 dilatation. The vagina is below the cirrus-opening. The small and rounded testes 

 are arranged in a circular manner around the dilated end of the vas deferens, and 

 this is a characteristic feature of the species ; they number from twenty-two to twenty- 

 four. In the more mature segments they are displaced to one side by the uterus. In 

 front of them, and some distance from the anterior border, are the ovary and yolk- 

 gland. These are of no great size, but can easily be differentiated by their staining. 

 A single excretory canal runs down each side, externally to the testes. The canal is 

 narrow and is internal to the genital atrium. 



29. Tetrabothriuscylindraceus (Rud.), 1819. (PI. IV, fig. 31.) 



Host. — McCormick's Skua [Megalestris maccormicki) ; intestine. These birds feed 

 largely on blubber, and on the excrement of seals. They also feed on fish. Although 

 a large number of birds were examined only a very few Cestodes were obtained. 



External Appearance. — This is a fairly slender worm. The longest specimen 

 is 8 cm. long, and the segments are at first uniform in size, but gradually lengthen 

 towards the caudal end. The colour is a dirty brown. Unfortunately, all the 

 specimens had lost the scolex. 



Description of Segment. — The segments drawn (PI. IV, fig. 31) are from fairly 

 near the anterior end of the fragment. They are quadrate, and measure 0'64 mm. 

 from side to side, and 0*47 mm. longitudinally. Each segment is slightly narrower at 

 the cephalic end than at the caudal border. In a stained specimen the outer portions 

 remain unstained. 



In the middle, occupying the more cephalic portion of the segment, is a deeply- 

 staining mass composed of the testes (Fig. 31, /). These are numerous — fifteen to 

 thirty — and are generally arranged in a horse-shoe shape, with the concavity caudad. 

 The ovary and yolk-gland (yg) are in front of these, fairly large, and immediately 

 behind the cephalic border. 



