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 



■,v 2 



FlQ. 110. — Woddheimia flcmescens. Diagram showing the muscular system. 

 After Hancock. 



1. Ventral valve. 



2. Dorsal valve. 



3. Calcareous loop. 



4. Mouth, 



5. Extremity of intestine. 



6. Adductor. 



7. Divaricators. 



8. Accessory divaricators. 



9. Ventral adjusters. 



10. Peduncular muscles. 



11. Dorsal adjusters. 



12. Peduncle. 



on its peduncle. The latter are termed adjusters, 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 contractiug alternately they may also serve to rotate it. 

 The occlusor muscles have a double origin from the dorsal sheU, 



