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 their 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. IV. fig. 1'. of the natural size) . The form of the 

 body is consequently very variable, being sometimes much elon- 

 gated, sometimes ribbon-shaped (tig. 1 to 3) ; sometimes shorter 

 and broader anteriorly, or in the centre (fig. 4), but posteriorly 

 {b) 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 («) is circular, and surround- 

 ed by four suckers, {cc) 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 manner the ani- 

 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, 0. F. Miiller, 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^^. 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; h, the 



posterior ; c c, the suckers. 



Ann. ^ Mag. N. Hist. Vol. xvi. H 



