190 Kart WILHELM GENTHE, 
are dark blue, the karyolymph and the protoplasm a kind of dirty 
purple. 
The systems of longitudinal and transverse muscle fibers in the 
mantle are are shown in Fig. 4, 5, and 6. They stop at some 
distance from the edge of the lips, so that the lips themselves do 
not contain muscle fibers. Along the mid-ventral line of the mantle 
(carinal side) shows a streak which in sections proves to be a blood 
lacuna. 
The muscle systems of the body. 
The muscle systems of the body I have tried to bring out in 
Fig. 8 and 16. Fig. 8 is a glycerine mount which showed the 
muscles quite well esp. in dark-ground illumination. Only occasionally 
other preparations esp. stained balsam mounts had to give supple- 
mentary aid. Fig. 16 was drawn from an animal cut sagittally 
. with a razor, stained in paracarmine and mounted in balsam. It 
had to be compared and combined with other like preparations and 
with total mounts and thus to be made a little diagrammatic in 
some portions. The muscles which start from the disk and form 
the above described systems of the mantle are omitted, they can 
be sufficiently seen in Fig. 4—6. Fibres of the transverse system 
converge towards the knob of attachment as seen in Fig. 6. 
There are seven main muscles which connect the body with 
the disk, five of these insert near the horny knob of the disk, the 
point of attachment of the animal to the shell, two farther caudad. 
The region just dorsad of the lips and as far as the attach- 
ment knob is difficult to work out but evidently the most im- 
portant one for the mechanism of the animal’s movements. 
As mentioned before, the animal is firmly attached to the shelf: 
in the region of the horny knob and only there. Sometimes the 
attachment takes in a certain portion of the disk caudad from the 
knob. The whole disk is often tightly pressed against the roof of 
the cavity. By carefully breaking the shell you can easily free 
the ventral side of the animal and usually most of the disk, but 
near the knob the animal will invariably tear. Here it can be freed 
only by dissolving the calcareous shell in acid. Between the knob 
and the dorsal edge of the lips (Fig. 7 and 8) there are two tooth- 
like projections, one on each side, covered with the same spicules 
which over the entire mantle. Between these is a strong brownish 
