358 MANUAL OF TEE MOLLUSCA. 



food is obtained by means of cujTents created by cilia* 

 Lingida may have the power of slightly extending the arms. 

 The internal skeleton consists of tWo spiral processes in the 

 Spiriftridm (Fig. IGS), whilst in Terehratula and Thecidium it 

 takes the form of a loop, which supports the brachial mem- 

 brane, but does not strictly follow the course of the arms. The 

 mode in which the arms are folded is highly characteristic of 

 the genera of Bracliiopoda ; the extent to which they are sup- 

 ported by a calcareous skeleton is of less importance, and 

 liable to be modified by age. That margin of the oral arms 

 ■which answers to the lower lip of an ordinary bivalve, is 

 fringed with long filaments {cirri), as may be seen even in dry 

 specimens of recent Terebratidce. In some fossil examples the 

 cirri themselves were supported by slender processes of shell ; * 

 they cannot, therefore, be yibratile organs, but are probably 

 themselves covered with microscopic cilia, like the oral ten- 

 tacles of the ascidian polypes {cilio-brachiata of Farre). The 

 anterior lip and inner margin of the oral arms is plain, and 

 forms a narrow gutter along which the particles collected by 

 the ciliary currents may be conveyed to the mouth. The object 

 of the folding of the arms is obviously to give increased surface 

 for the disposition of the cirri. 



The mouth conducts by a narrow oesophagus to a simple 

 stomach, which is surrounded by the large and granulated 

 liver; the intestine of Lingida is reflected dorsally, slightly 

 convoluted, and terminates between the mantle lobes on the" 

 right side (Fig. 202). In OrUcida it is reflected ventrally, and 

 passes straight to the right, ending as in Lingida. In Terehra- 

 tula, Rhynclionella, and j^robably all the articulated Brachiopoda, 

 the intestine is simple and reflected ventrally, passing through 

 a notch or foramen in the hinge-plate, and ending behind the 

 ventral insertion of the adductor muscle (Fig. 145, v.)t 



The circulatory system is far less complex than was formerly 

 supposed, and does not difl'er greatly from the same system in 

 the Tunicata. The heart is placed on the dorsal surface of the 

 stomach, and consists of a simple, unilocular, pyriform vesicle 

 without any auricle. From it the blood is propelled through 



* Spirifera rostrata and Terehratula peduncidoides, in the Biitish Museum. 



t The position at which the intestine terminates in the TcrcbratuJa: and Bhyn- 

 chonellcE, seems to necessitate the escape of tlie faeces by tlie umbonal opening ; in 

 these extinct genera wliich have the foramen closed at an earlj^ age, there is still an 

 opening between tlie valves (e. g. in Uncites) which has been mistaken for a byssal 

 notch. Mr. Hancock has carefully dissected several species of these genera without 

 detecting any anal aperture. Filling the intestines with injections waa tried, but no 

 outlet could be discovered. 



