BRACHIOPODA. 699 



number of Brachiopoda. It appears to communicate with the coelome, but 

 is not, as yet, known in its finer details. The heart is usually a contractile 

 vesicle lying in the dorsal mesentery of the stomach : it is connected to a 

 vessel (branchio-systemic vein of Hancock) which runs forwards along the 

 oesophagus, and is only a split in the dorsal mesentery. It appears to be 

 connected with the circum-oesophageal lacunae, and these in their turn 

 with a vessel which runs in the sinus beneath the cirri of the lophophore 

 and gives off a vessel to each cirrus. Genital arteries arising from the 

 heart are also said to be present. Variations are the presence of two hearts 

 in Argiope decollata, and of two large and several small dilatations at the 

 posterior end of the branchio-systemic vein in Crania anomala. Blochmann 

 agrees with van Bemmelen in the opinion that Hancock described as blood- 

 spaces the nervous plexuses of the arms and the branched connective tissue 

 cells of the arms and mantle *. The coelomic fluid contains corpuscles of 

 various kinds in suspension. In Lingula pyramidata there are minute re- 

 fractile globules seen also in the shell : striated spindle-shaped bodies 

 (spermatophores) : small round granular cells or young ova : and the 

 blood corpuscles proper, rounded or oval bodies, homogeneous and 

 nucleated. The blood corpuscles of Argiope Koiualewskii are brown, 

 changing to red, according to Schulgin. There are no special respiratory 

 organs, but the cirri and sinuses of the mantle must serve to aerate the 

 coelomic fluid. 



The nephridia serve the purposes of ovi- and spermi-ducts as well as 

 of renal organs (?). They are two in number, except in the genus 

 Rhynchonella which has four, and open internally into the coelome, and 

 externally into the mantle cavity. The inner aperture is more or less 

 expanded, trumpet-shaped and plicated longitudinally ; it leads into 

 a contracted tube. The lining epithelium of the tube is usually yellow 

 in colour and is ciliated in Argiope Kowalewskii, and probably in other 

 Brachiopoda also. The presence of coloured granules in the cells doubt- 

 less indicates a secretory function. The internal apertures are turned 

 towards the dorsal valve. Those of the pair of organs always present are 

 supported by the ileo-parietal bands. The ducts run in the lateral walls 

 of the body, and they open below the convex or posterior edge of the 

 lophophore by separate slit-like orifices. These orifices are situated in 

 Argiope, each at the bottom of a brood-pouch or sac, invaginated from the 

 lateral walls of the body in which the ova develope. Thecidium has a 

 similar, but single and median brood-pouch. The second pair of nephridia 

 present in Rhynchonella have their internal apertures supported by the 



1 Beyer describes in L. pyramidata two oblong tubular organs, one in each of the lateral 

 oesophageal lacunae, filled with blood-corpuscles. The supporting tissue of the body-walls and 

 mantle contain in the Brachiopod just named channels lined by coelomic epithelium, and containing 

 blood corpuscles. 



