73 



, villous membrane, extending vertically across the terminal dllateil 

 part of the animal. Between this ca\'ity and the rest of the body no 

 communication could be detected, on the most minute inspection. 

 Its internal surface is of a yellowish white colour, and smooth. Its 

 function is probably excretory, and it may, therefore, be regarded 

 as exhibiting a rudimentary condition of the respiratory system. On 

 each side of it is a large lateral cavity, internally black and minutely 

 wrinkled, and filled (in the individual examined) with a dark brown 

 fluid, similar in appearance to partly digested blood. This nutriment 

 is conveyed to the lateral cavities by the intervention of the smaller 

 cells anterior to those from the two alimentarjr canals leading from 

 the mouth, and is distributed into the dark-coloured vessels of the 

 muscular tunic : so that the lateral cavities, analogous to those which 

 have been considered as chyle-receptacles in Amphistoma, &c., hold 

 an intermediate position between the alimentary and the sangui- 

 ferous canals. The cells at the smaller end of the body were occu- 

 pied by a yellow fluid, containing numerous ova of the same colour, 

 many of which had thence passed into the tortuous oviduct. 



Distoma is thus seen to possess, in addition to the ce\lula.T paren- 

 chyma of the body, the three systems of canals, digestive, vascular, 

 and generative, which are usually met with in the Trematoda. An 

 analogy to the Leech may be traced, not merely in the external 

 suckers, but also in the form of the cells, wliich at the posterior part 

 of the body communicate with, and form part of, the digestive ap- 

 paratus, especially of the two last cavities, which very closely re- 

 semble the last pair of gastric cceca that occupy, in the Leech, a 

 similar position. 



The reading of the paper was illustrated by the exhibition of the 

 animal described in it, and of drawings of its several parts. 



Mr. Owen subsequently read " Some Remarks on the Entozoa, 

 and on the Structural Differences existing among them ; including 

 Suggestions for their Distribution into other Classes." 



The difiiculty of assigning to the internal parasites of other ani- 

 mals a definite character, by which they may be distinguished as a 

 class, is evident on a mere inspection of the definition proposed for 

 the Entozoa by Cuvier : it rests chiefly on their habitats, and on 

 certain negative properties, and attempts to combine with these a ge- 

 neral resemblance of form. Rudolphi at one time imagined that he 

 had overcome this difficulty, by denying to the Entozoa a nervous 

 system ; but he was subsequently under the necessity of regarding 

 the Nematoidea as excluded from this definition, and he proposed to 

 associate this portion of the Entozoa with the Annelida. But the 

 possession by the red-blooded Worms of a distinct respiratory system 

 would alone be sufficient to forbid this association, even if the essen- 



