42 "TERRA NOVA" EXPEDITION. 



(Fig. 41. <). which is 0*13 mm. in its longest diameter, and 0'07mm. in its broadest. 

 The cirrus was not extruded in any segment, and therefore could not be measured. 



The small uterine opening (<l) is behind and slightly to one side of the cloacal 

 opening. Its longest diameter is ' 05 mm. and its greatest breadth 03 mm. Behind 

 the genital opening the ovarian and other female organs are always grouped very 

 regularly and in a very characteristic manner. The uterus is small and simple, and 

 only contains a few eggs, which measure 0'06 mm. 



The testes are very numerous and are grouped in a definite manner, which is 

 characteristic. They tend to be roughly in paired columns, and there is always, running 

 toward the caudal end of the female organs, a definite row of three or more testes 

 marked off by their direction from the remainder. 



The excretory canals are continuous throughout the segments, and a single one 

 runs down on either side, just outside the junction of the middle and outer thirds. 

 The testes are distributed on their outer side as plentifully as on their inner side. The 

 musculature is not well marked. 



22. Dibothriocephalus <trr//cri, Leip. and Atk. (Text-fig. 7.) 



DibotJiriocepJialus arclterl, Leiper and Atkinson, Pruc. ZooJ. Sm'., 1914, p. 224. 



C to 12 crn. in length. Large square head, 2-04 mm. broad. Lips of the suckers folded inwards. 

 The eggs first appear in the 57th segment and measure O07 mm. Testes scattered diffusely. 



Host. Weddell's Seal (Leptonychotes weddelli); collected in fair quantities from 

 the upper part of the small intestine. 



External Characters. The colour of the worms is a 

 dirty white, and in length they measure from 6 cm. to 

 1 2 cm. They are flattened dorso-ventrally, and attain 

 their greatest breadth as the caudal end of the worm is 

 reached. The anterior segments are more quadrilateral than 

 Fin. 7. - THbofhriocephalus the posterior, which tend to become broadened from side to 

 archer! : Optical _ trans- ^ . U1(] sllorteued from 1)ef()re ] mckwards . T he genital 

 verse section of the head, 



showing the inward fold- pores are in the median line, and at about the middle of 

 ing of the walls of the the segment, 



Head. The head is relatively large, and is somewhat 



square, its greatest breadth (2 '04 mm.) being in the anterior part. Its length is 

 2 mm. 



The central portion, between the two suckers, terminates in a slight cone 

 suggesting a rostellum. There is no true rostellum, and no hooks are present. The 

 suckers run down the head for l'25mm. of its length. The central, interior, portion 

 of the head seems to lie a rod of more solid structure between the two suckers. On 

 looking at the head from the front, the two suckers are seen to be cup-shaped and 

 folded (text-fig. 7) ; the outer lapel of the suckers running out from the head for some 

 distance. The suckers, at their anterior end, measure I '02 mm. from side to side, 



