470 



RECENT BRACHIOPODA 



mantle of the dorsal valve, as in Cistella and Argiopc ; ^ or they 

 may he outgrowths of the hody wall in the form of long processes, 

 which are coiled and twisted in a very characteristic manner in 

 the various genera. In any case the cross section of the arm 

 shows a groove, one side of which forms a continuous lip, and 

 the other takes the form of a single row of tentacles, whicli are 



Fig. 314. —View of the left half of Cistella 

 (Arffiope) ncapolUana, which has been cut 

 in two by a median loBgitiuliual incision, to 

 show the disposition of the organs. Partlj' 

 diagrammatic. The inorganic part of the 

 shell only is shown. The tubular exten- 

 sions of the mantle and the organic outer 

 layer are not indicated, and hence the pores 

 ajipear open. 



1. Tlie ventral valve. 



2. The dorsal valve. 



3. Tlie stalk. 



4. The mouth. 



5. Lip whicli overhangs the moiith and 

 runs all round the tentacular arms. 



6. Tentacles. 



7. Ovary in dorsal valve. 



8. Liver diverticula. 



9. Occlusor muscle ; its double origin is 

 shown. 



10. Internal opening of left nephridium. 



11. External opening of left nephridium. 



12. Ventral adjustor. The line from 10 

 crosses the dorsal adjustor. 



13. Divaricator muscle. 



richly ciliated and capable of consideralile movement. The whole 

 arm in Bliynchoiiella can l)e protruded from the shell, as was 

 noted years ago by 0. F. MllUer, and although his statement to 

 this effect has often been doulited, its truth was confirmed hj 

 Professor Morse,- who writes : " In the year 1872, while studying 

 living RhynchoneUa in the St. Lawrence, I observed a specimen 



^ Schnlgin, " Argiope Kowalevskii," Zdt. f. vnss. Zool. Bd. 41, LS85. 

 - American Jour, of Sci. and Arts, 3rd series, vol. xvii. 1879. 



