M. Sars on an Intestinal Worm in an Acaleph. 89 
tinal worms. They were affixed to the internal wall of the 
stomach of the Acaleph by one of their extremities, and moved 
but slightly and very slowly the rest of thar bodies. Carefully 
detached from their place of adhesion they became more lively, 
and crept about a glass plate, alternately lengthening and short- 
ening their body (PI.1V.fig. 1’. of the natural size). The form of the 
body is consequently very variable, beng sometimes much elon- 
gated, sometimes ribbon-shaped (fig. 1 to 3) ; sometimes shorter 
and broader anteriorly, or in the centre (fig. 4), but posteriorly 
(5) always acute; further somewhat flattened, so that the two sides 
(fig. 1) are broader than the other two (fig. 2). Not a trace of 
articulation is visible on the smooth, soft body, which even in the 
perfectly contracted state, in which it almost acquires the form of 
a pitcher, indicates no perceptible transverse folds. 
The anterior extremity of the body (a) is circular, and surround- 
ed by four suckers, (ec) of oval form, and whose longitudinal axis 
coincides with the axis of the animal: each of them is divided 
interiorly by a septum into two spaces or cavities, the hindermost 
of which is largest, the front one being a little smaller and nar- 
rower. By means of these organs the worm attaches itself to the 
walls of the ventral cavity of the Acaleph. From between these 
suckers projects the conical anterior extremity of the body, at the 
apex of which is observed a small circular aperture, which is pro- 
bably the mouth. When the worm crawls, the anterior extremity 
is sometimes projected (figs. 1. and 4), sometimes retracted within 
the suckers (figs. 2, 3.) ; this always takes place alternately, the 
entire body expanding and contracting, in which mamner the aui- 
mal each time advances a little distance. 
The worm observed by me may probably be identical with that 
which the British naturalists have described as a new genus with 
the name Tetrastoma. I have for the time placed it in the ge- 
nus Scolex, O. F. Miller, with the specific name Acalepharum. 
EXPLANATION OF PLATE IV. FIGS. 1 To 6. 
Fig. 1'. Two individuals, natural size ; all the other figures are more or less 
magnified. 
Fig. 1. An individual] seen from the broad side, with the anterior extremity 
projected. 
Fig. 2. The same from one of the narrow sides with retracted anterior ex- 
tremity. 
Fig. 3. The same slightly, and fig. 4. greatly contracted. 
Fig. 5. The anterior portion of the body with the suckers highly magnified. 
fig. 6. An individual pressed flat under the compressorium. 
In all these figures, a designates the anterior extremity of the body; 6, the 
posterior ; cc, the suckers. 
Ann. & Mag. N. Hist. Vol. xvi. H 
