CESTODA. 5 



anterior border of the same proglottis, and thus each proglottis has, like the last, the 

 outline of a truncated cone, but it is turned the other way up. 



In the centre of each of the middle proglottides is a dark line caused by the 

 opening of the penis, the oviduct, and the uterus. The penis is most anterior, and is 

 very muscular, it is in many cases exserted. The base of the penis passes into a 

 spherical vesicula seminalis. The testes are scattered through the central tissue. 



The oviduct crosses the duct of the uterus, which is very short and practically hardly 

 exists, and runs backward to the ovary and the shell-gland which lie behind the uterus. 



The uterus is but slightly convoluted and contains few ova, they measure 

 0'042 by 0' 035mm. ; at any rate, that is about the average, for they vary a good deal 

 in their dimensions. They have a single and not very thick egg-shell. 



Like the cells in D. scotti, the epithelial units of D. wilsoni are remarkably 

 well defined and show but little diff'erentiation. The parenchyma again is, at any 

 rate anteriorly, not the vacuolated, spongy-looking tissue which one sees in the 

 older proglottides, but consists of plump cells, well defined, full of protoplasm, with 

 nuclei near the edge. 



Dihotliriocephalus wilsoni. — A small form, length 4 to 5"5mm. ; greatest breadth 

 1mm. ; nine to thirteen proglottides, like truncated cones ; the last is inverted ; no 

 neck ; edges of central proglottides rather crumpled ; posterior edges but slightly 

 overlapping. 



It is a remarkable fact that the only Cestoda brought back by the naturalists on 

 the ' Discovery ' were obtained from one (and that by no means a common one) 

 animal, Oinmatophoca rossi, or Ross's Seal, an animal, in Captain Barrett-Hamilton's 

 words, so little' known that it "might, until a year or two ago, have claimed, and 

 claimed justly,'' along with Weddell's Seal, " to be considered amongst the rarest and 

 most obscurely known of all mammals." * It is also remarkable that the Cestoda 

 should all belong to the same genus. 



If we want to have the history of the Dibothriocephalid species which we find in 

 this animal, the smallest of the Antarctic seals, we must look to its food. Boss's Seal 

 is remarkable for the feebleness and variability of its dentition. " It seems probable 

 that the exact number of its teeth is not of importance to this animal."! Apparently it 

 lives on soft food. Wilson mentions, in the work just quoted, that the " food of this 

 species consists of octopus and vegetable stuff's or seaweeds," and again in " The Voyage 

 of the ' Discovery,' " the "jelly-fish and squids, which apparently form their food." 

 Strictly speaking, I do not think that any cestode larva has been found in a jelly-fish, 

 though Scolex polymorphus is recorded from more than one genus of Ctenophore. On 

 the whole it seems more likely that the plerocercoid stage will be found — if ever it be 

 found — in the tissues of one of the Cephalopods, 



* Eeport on the Collections of Natural History made in the Antarctic Regions during the voyage of the 

 ' Southern Cross,' London, 1902, p. 2. 

 t Op. cit., p. 15. 



