174 ZOOLOGY 
but the two parts unite to form a single tendon, which is in- 
serted into the ventral shell. The divaricators are very small. 
They arise from the ventral shell, and are inserted into the 
dorsal valve in such a relation to the hinge as to cause the 
shell to open when they contract. Additional muscles are found 
in other members of the group, those of Waldheimia and Lin- 
gula are shown in Figs. 110 and 113. 
tunning round the edge of the lophophore, at the base of 
the tentacles, is a canal which is probably continuous with the 
general body-cavity. It gives off a branch into each tentacle, 
and the latter are probably extended by the entrance of the 
coelomic fluid into them (Fig. 109). 
There is a closed vascular system containing a corpus- 
= 
<a) \ 
<a 
SSS | 
yy) 
Frc. 111.—View of the inner side of the right half of Waldhetmia australis. 
From a dissection by J. J. Lister. 
1. Mouth. 9. Internal funnel-shaped opening of 
2. Lophophore. nephridium. 
3. Stomach. 10. Peduncle. 
4. Liver tubules. 11. Body-wall. 
5. Median ridge on dorsal shell. 12. Tentacles. 
6. Heart. 13. Coil of lip. 
7. Intestine ending blindly. 14, Terminal tentacles, 
8. Peduncular muscle. 
culated fluid. The vessels composing it are irregularly 
scattered through the tissue of the body. They are especially 
