174 



ZOOLOGY 



but the two parts unite to form a single tendon, whicli 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 Zin- 

 gula are shown in Figs. 110 and 113. 



Eunning 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- 



FiG. 111. — View of the inner side of the right half of Waldlieimia australis. 

 Prom a dissection by J. J. Lister. 



1. Mouth. 



2. Lophophore. 



3. Stomach. 



4. Liver tubules. 



5. Median ridge on dorsal shell. 



6. Heart. 



7. Intestine ending blindly. 



8. Peduncular muscle. 



9. Internal funnel-shaped opening of 

 uephridium. 



10. Peduncle. 



11. Body- wall. 



12. Tentacles. 



13. Coil of lip. 



14. Terminal tentacles. 



culated fluid. The vessels composing it are irregularly 

 scattered through the tissue of the body. They are especially 



