ERACHIOPODA. 



641 



rents set up by the vibrating cilia with which they are covered. 

 The "arms" are homologous with the tentacular crown ("lopho- 

 phore ") of the Polyzoa, and have the form of lateral tubular pro- 

 longations of the margins of the mouth, usually of great propor- 

 tionate length, coiled up spirally and fringed with ciliated lateral 

 processes or "cirri" (fig. 487). In a few forms the arms can be 

 protruded from between the opened valves of the shell, and in 

 many types they are supported upon a more or less complicated 



Fig. 486. — Morphology of Brachiopoda. A, Lingula (Glottidia) fiy7'amidata{a.fcer Morse) : 

 /, Peduncle ; s, Sand-tube, encasing base of peduncle, b, Lingula anatina (after Cuvier) : p, 

 The peduncle. C, Waldheimia cranium, with adherent young, attached to a stone (after 

 Davidson) : p, Peduncle ; v, Ventral valve ; d, Dorsal valve, d, Crania Ignabergeusis, attached 

 by its ventral valve to a piece of coral (Chalk). 



internal calcareous framework or "loop," the structure of which 

 will be considered in greater detail hereafter. 



On the inner side of the cirri of the arms is a ciliated furrow or 

 "brachial groove," which conducts to the opening of the mouth, 

 and which serves for the conveyance of nutritive particles carried in 

 the water-currents set up by the cilia. The mouth conducts by an 

 oesophagus to a globular stomach, surrounded by a well-developed 

 granular " liver." The intestine is sometimes short, sometimes long 

 and coiled, and it may either terminate in a distinct anal aperture 

 (as in Lingula and the other genera of Inarticulate Brachiopods), or 

 it may end blindly in the middle line (as in Terebrahda and the 

 Articulate genera of Brachiopods generally). A distinct heart is 

 present, in some cases at any rate, and has the form of a contractile 



vol. 1. 2 s 



