THE CESTODA OF THE SCOTTISH NATIONAL ANTAKCTIC EXPEDITION. 247 



Dibothriocephcdus 



ii-nt. Bainl, 1853. 



About a dozen or more examples of this species were obtained from the stomach of 

 a Ross's Seal, Ommatophoca rossi. These were all smaller than BAIRD'S specimens, 

 which were about 9 inches long. The Scotia examples range from 132 to 29 mm., 

 but most measure about 100 mm. BAIRD'S (2) description is rather brief and confined 

 to externals, but from this, together with his excellent figure, there is no mistaking the 

 identity of the Scotia specimens with his type. 



This species was also found by the /V/M-IMV/V/ Expedition, and the specimens are 

 described by SHIPLEY, to whose account reference is made below. 



Dibothrioc&phalus untm-i-tii'/is, Baird (2), is a slender-bodied worm, with a conical 

 scolex and with fairly sharp tapering point. The two suckers are long and compara- 

 tively deep. According to BAIRD, there are " two small rounded projecting lobes " at 

 their posterior margins, but these in the Scotia examples are only occasionally present, 

 and appear to be dependent upon the state of contraction of the animal. There is no 

 neck; the anterior part of the body for some distance behind the scolex is rounded, 

 resembling an annelid in form ; in the more posterior part the form is thick and 

 flattened, being here elliptical in section. The colour is reddish yellow. The segments, 

 even in the mature part of the; animal, are very short; they are deeply constricted off 

 from each other, and as the free margins are directed backward the segments appear to 

 overlap more than they actually do. The only dimensions given by BAIRD are : " length, 

 about nine inches ; greatest breadth of body, about three lines," and although the 

 Scotia examples are very much smaller, the proportions agree well. The Discovery 

 specimens come much nearer in length to the Scotia, examples, although there is a very 

 distinct discrepancy as regards width. SHIPLKY reports that most of the l>i*cncery 

 examples " were just under 10 cm.," and that "the greatest breadth is 7 mm. in the 

 largest specimen." The longest Scotia worm is 13'2 cm., and its greatest breadth is 

 4'5 mm. ; most of the specimens are about 4 mm. in width. Again, as regards scolex 

 dimensions, SHIPLEY gives "3 mm. in length and -'! nun. in breadth posteriorly." In 

 none of the Scotia specimens is the greatest breadth eijual to the length of the head ; 

 they measure from 3 to 3 '5 mm. long by 2 mm. wide. The actual differences here, 

 however, are slight. 



A general account of the anatomy is given by SHIPLKY (4). He mentions that, 

 besides the two longitudinal canals of the excretory system, " there are also small 

 canals which lie close under the surface at the edges of the proglottides, usually two at 

 each side, but they also break up from time to time into twisting branchlets." These 

 canals appear to be very numerous ; from 42 to 45 may be present in a section, while 

 at each lateral margin a group of four cun usually be made out. 



The testes which occupy the central layer lie mostly towards the dorsal surface. 

 There are from 18 to 20 follicles in a transverse section. 



(ROY. SOC. EDIN. TRANS., VOL. XI.VIII., 445.) 



