52 



"TERRA NOVA " EXPEDITION. 



and do not extend for any great distance down the sides. They are not deep and 

 have no overhanging border. 



The head measures 0 " 9 mm. in breadth and 0"9 mm. in an antero-posterior direction. 

 The outside measurement of a sucker in its broadest part is 0*42 mm., and in its 

 longest axis 0*62 mm. The greatest inside measurements are 0'2mm. by 0*34 mm. 

 There is no neck, the head being immediately followed by the segments. 



Segments. — The segments described (Fig. 30) are those from the head-end of the 

 worm, and later, segments cut in serial sections from nearer the caudal end. Each 

 segment measures 1*14 mm. from side to side and 0' 42 mm. antero -posteriorly. The 

 hinder border of the preceding segment overlaps it for over a third of its ventral 

 surface, and it in turn overlaps the following segment. The musculature is exceedingly 

 well developed. There is a clear outer space in a stained specimen and a more deeply 

 staining interior containing the generative organs. The testes are numerous, 30 to 45, 



and are found internally to the excretory canals. They 

 are bunched more closely together in the middle of the 

 segment and are there difficult to count. A small ovary and 

 yolk-gland are placed in front of them near the anterior 

 s'b border of the segment. The genital openings are peculiar. 



Fig. 9.~Tcfrnbothrms cather- T/hey are unilateral and open on the side of the segment, 



inae : the terminal organs , . ^ 



of the genital apparatus. but more on tlie central than on the dorsal aspect. There is 

 ec, muscular external a small punctate opening . or depression showing signs of 

 portion of cloaca; ic, in- str i at i on (text-fig. 9, ec). Internally to this there is a well- 



ternal portion ; s, cirrus ; . . . . . . 



sb cirrus-sac marked ring (ic) containing the male and female openings, 



and behind that a very large cirrus (•?) and cirrus-sac (sb). 

 The outer opening has an internal measurement of 0 ' 02 mm. and an external diameter 

 of 0 ' 04 mm. The inner ring has an internal aperture of 0 1 04 mm. and an external 

 opening of 0'06 mm. The cirrus measures 0* 1G mm., and is unarmed. 



In sections of more mature segments the whole of the interior is taken up by a 

 mass of eggs in a sac-like uterus, which is simple and undivided. Well-marked broad 

 bands of muscular fibres are present. Two excretory canals run down either side of 

 the segments. The outer and smaller lies very near the edge. The inner, a far wider 

 canal, runs down at a short distance from it internally. 



34. Tetrabothrius aichesoni, Leip. and Atk. (Text-fig. 10). 



TetrabothriuB aichesoni, Leiper and Atkinson, Proc. Zool. Soc, 1914, p. 225. 



Strobila 3 cm., more slender than in the preceding species. Segments more uniform, only over- 

 lapping slightly. Testes arranged in three distinct sets, very numerous, far in excess of those of the 

 previous forms. 



Host. — Trinidad Petrel (GEstrelata trinitatis) ; intestine. 



External Characters. — This Cestode is of a dirty white colour, and measures 3 cm. 

 to 3 '5 cm. in length. It is a more slender worm than the preceding, and the segments 



