CESTODA. 4) 
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 ruus 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 ege-shell. 
Like the cells in D. scotti, the epithelial units of D. wilson’ are remarkably 
well defined and show but little differentiation. 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. 
Dibothriocephalus wilsoni—A small form, length 4 to 5°5mm.; greatest breadth 
Imm.; 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, Ommatophoca 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. Ross'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 stuffs 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. 
” 
* Report 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. 
