BRACHIOPODA 



175 



developed in the mantle and in those parts of the body-wall 

 next to the shell, and send oif numerous caeeal processes into 

 the canals permeating the substance of the latter. The blood is 

 probably aerated as it comes through the vessels of the mantle. 

 The presence of a central heart in Argiope is a matter of dis- 

 pute if it exists, it is a contractile vesicle situated dorsal to 

 the stomach ; a spherical vesicle is found in this position in 

 Waldheimia, but its relation to the blood-vessels is not very 

 definitely known. 



The nephridia, which also function as genital ducts, open 

 internally, with large funnel-shaped mouths, which are directed 

 towards the posterior, end of the dorsal shell. These openings 

 lead to short tubes which run in that part of the body-wall 

 which is pushed in to form the brood pouch ; into this they 



PiQ. 112. — The posterior quarter of a Waldheimia austredis has been removed, in 

 order to show the relations of alimentary canal, nephridia, etc. The coelom is 

 represented black. From a dissection by J. J. Lister. 



1. Dorsal shell. 7. Intestine. 



2. Ventral shell. 8. 



3. Stomach. 9. 



4. Liver. 10. 



5. Gastroparietal bands. 



6. Heart. 



Tendons of adductor muscles. 



Ovary. 



Internal funnel-shaped opening of 

 nephridia with three ova drop- 

 ping in. 



eventually open. The walls of the tube consist of a connect- 

 ive tissue basement membrane lined by glandular cells 

 crowded with brown concretions. Some of these cells are 

 also ciliated. 



