BRACHIOPODA 173 
ary canal, is ciliated. The alimentary canal is supported by 
a median sheet of connective tissue, the mesentery, which 
passes from it to the ventral shell’ (Fig. 109), and by two lateral 
sheets, termed the gastroparietal bands, which pass out from 
the stomach to the sides of the body-wall. 
Owing to the peculiar relations of the animal to its shell, 
the body-cavity becomes very complicated, it is partly pro- 
duced into the mantles which line the shells, and here the 
reproductive organs partially lie. At the posterior and lateral 
regions the body-wall is pushed in, in such a way as to form 
two lateral brood pouches, which lie behind the level of the 
lophophore, and are enclosed by the shell. The embryos 
undergo the early stages of their developement in these pouches. 
The coelom is traversed by four bundles of muscle fibres, two 
of which open and close the shell, the other two move the shell 
Fic. 110.—Waldheimia flavescens. Diagram showing the muscular system. 
After Hancock, 
1. Ventral valve. 7. Divaricators. 
2. Dorsal valve. 8. Accessory divaricators. 
3. Calcareous loop. 9. Ventral adjustors. 
4. Mouth. 10. Peduncular muscles. 
5. Extremity of intestine 11. Dorsal adjustors. 
6. Adductor. 12. Peduncle. 
on its peduncle. ‘The latter are termed adjustors, and a pair 
arise from each valve of the shell and are inserted into the 
peduncle. By their contraction they raise or depress the shell, 
and by contracting alternately they may also serve to rotate it. 
The occlusor muscles have a double origin from the dorsal shell, 
