HELMINTHOLOGY -HELM I NTIIES THEM ATODES. 471
organization, except an opaque portion situate at tliecephalic extremity, and another part extending through thebody.
Several Distomata from the Acalephae have been madeknown. The Distomum found by Will (Archiv , 1844,Bd. i, p. 343) in the aqueous passages of Beroe rufescenspresented an annulate body, a retractile caudal extremity,and a sessile abdominal acetabulum. Its excretory organ,filled with transparent, round globules, was bifurcate, andsent up the two lateral branches as far as the oral extremity,where they were united at an acute angle; an organization,which the Reporter has met with also in Distomum appen-diculatwn. Another Distomum, of cylindrical figure, andalso furnished with a sessile abdominal acetabulum, wasfound by Philippi (Muller’s Archiv , 1843, p. 66, taf. v, fig.11 and 12) in the stomach of a Physophora. The samenaturalist noticed a Distomum, differing from the above, inthe stomach, and creeping about between the knob-shapedtentacula of Velella spirans. This latter Distomum was fromthree fourths to one line long, was provided with a very large,shortly pedunculate, abdominal acetabulum, and was pro-longed into a thick, rounded, posterior extremity.
From Yarrell (A History of British Fishes, vol. ii,London , 1841, p. 468 : vid. the vignette) we learn that asmany as twenty specimens of the rare parasite Tristomumcoccineum were found on the outer surface of the head of anOrthagoriscus mola, taken on the English coast.
According to J. C. B. Bellamy (Annals Nat. Hist, xiii,1844, p. 78), this discovery has since been repeated on thecoast of England. Rathke (Nova Acta Acad. Leopold.Carol. Nat. Curios, tom. xx, p. 1, 1843, p. 238) has verycorrectly shown that Hirudo hippoglossi or Phylline hippo-glossi, Ok., can in nowise be referred to Tristomum elon-gatum , Nitzsch, as it has been by Diesing, but mustconstitute an independent genus and species, differing as itdoes essentially from Tristomum elongatum, in the presenceof four horny booklets on the but slightly concave surface