THE CESTODA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 249 



loops to each side ; in the mature parts it appears as a rounded mass filled with the 

 shelled ova. The yolk follicles are exceedingly numerous in the mature segments, 

 lying closely over the whole of the inner part of the peripheral layer and visible 

 externally. They form morula-like masses, more or less irregular in shape. In section 

 they are mainly circular, and measure '052 mm. in diameter. The individual yolk cells 

 are large, measuring when fully grown about '016 mm. 



The ovary consists of a pair of flattened circular masses, which in their maximum 

 development measure '174 mm. in diameter, connected by a narrow band in the middle. 

 The shelled ova measure '051 mm. x '034 mm. They are not operculate. 



The testes follicles, which occupy the central area, occur in the planes between those 

 occupied by the yolk follicles. Where the yolk follicles occur the central area is 

 narrowed, and only the extreme ends of the individual testes appear here. The 

 individual cells of the testes are extremely small. The cirrus sac is highly muscular, 

 circular in form ; the short protrusible penis is relatively thick. 



The cuticle is remarkably thick, measuring - 1 4 mm. ; the sub-cuticle consists of 

 fairly large cells of irregular shape, amongst which the small excretory canals occur. 

 These are fairly numerous, viz. between 30 and 40. The rest of the body consists 

 largely of a thin and loosely packed parenchyma. 



This form is clearly differentiated from all the other small Bothriocephalids in the 

 laterally placed suckers and distinctive form of the scolex, size and general shape of 

 the proglottides, nature of the yolk follicles, and characteristics of the ova. 



We propose for it the name of Dibothriocephalus mobilis. 



Dibothriocephalus pygoscel is, n. sp. (PI. II. figs. 11 and 12.) 



A small quantity of Cestode material, undated, and labelled, " Adult tapeworms from 

 some species of Pi/goscelis, probably P. antarctica or P. adelia ; possibly, though not 

 likely, P. papua," was found to consist of a number of extremely brittle fragments of a 

 Dibothriocephalus* Only one or two head pieces could be found, the larger of which 

 measured 29 cm. Fragments up to 21 cm. in length occur in the collection. 



The scolex measures 1'8 mm. in length, is of almost uniform breadth, slightly 

 broader at the posterior border, where it measures '7 mm. in diameter. The suckers 

 are long and shallow, forming a pair of dorso-ventral grooves, extending nearly the 

 whole length of the scolex. 



There is a short neck ; the anterior proglottides are markedly flanged, and at least 

 four times as broad as long. In the broadest part of the worm they reach 9 mm. in 

 breadth and about 1'5 mm. in width. The common genital pore can be seen upon the 

 ventral surface as a rather broad crescentic slit, a little way behind the anterior border, 

 while the uterine pore is placed slightly behind in the middle line. 



* This was found by Dr PIRIE lying on the snow near the baach at Scotia Bay, South Orkneys, where a number of 

 penguins had been congregated chiefly P. antarctica and P. adelia, January 11, 1904. See Zoological Log, 

 p. 95, including footnote. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 447.) 



