384 MR. R. OWEN ON THE ANATOMY OF DISTOMA CLAVATUM. 
stoma clavatum. The surface of the cavity in Distoma clavatum, of which the small pos- 
terior orifice is the outlet, singularly contrasts with that of the receptacles on either 
side ; being of a yellowish white colour, and smooth. The office of this posterior sac 
being most probably excretory, it may be regarded as exhibiting a rudimentary condi- 
tion of the respiratory system. 
This large species of Distoma exhibits, according to Mr. Menzies, well-marked loco- 
motive powers. ‘‘In moving,” he observes, “‘ it fastens itself alternately by the ven- 
tral aperture and its mouth, raising its slender neck between them into an arched form, 
like a leech, and in this manner drags its body along with a slow motion. It is of a 
whitish colour, somewhat pellucid, discharging at its mouth a black-coloured fluid, 
which can easily be perceived through its body!.”” The superaddition of an excretive 
organ is in just accordance with the muscular energies above observed ; and the ana- 
logy to the Leech is further shown in the form of the cells, which at the posterior part 
of the body communicate with and form part of the digestive apparatus ; especially of 
the last two cavities, which very much resemble the last pair of gastric ceca occu- 
pying a similar position in the Leech. 
PLATE XLI. 
Figg. 17 to 20. Disroma cLavatum. 
Fig. 17. Ventral surface of Distoma clavatum. 
a. Anterior pore, where the true mouth is situated. 
b. Posterior depression, suctorial disc, or holder. 
c. The genital orifice. 
d. The orifice of the posterior sac. 
18. Distoma clavatum, dissected from the dorsal aspect. 
e. The cuticular wrinkled integument. 
f. The muscular integument. 
g. The anal sac, laid open: a bristle is placed through the orifice. 
h. h. Cavities external to the anal sac, with a black minutely wrinkled surface. 
i. Masses of ova. 
k. The oviduct. 
l. The testis. 
m. Vessels. 
19. Posterior view, showing the muscular discs surrounding the oral, a', and pre- 
hensile, 0', fosse, and the termination of the genital tube, c’. 
m. The vascular circle surrounding the oral disc. 
20. The oviduct, k, and testis, J. 
' Loc. cit., p. 188. 
