u08 MANUAL OF THE MOLLTJSCA. 



food is Obtained by means of cujTents created by cilia* 

 Lingula may have the power of slightly extending the arms. 

 The internal skeleton consists of two spiral processes in the 

 S'piriferidce (Fig. 168), 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 Brachiopoda; 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 biyalve, is 

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

 specimens of recent Terehratidoe. 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-h-achiata 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 inci'eased 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 Lingula is reflected dorsally, slightly 

 convoluted, and terminates between the mantle lobes on the 

 fight side (Fig. 202). In Orhicida it is reflected ventrally, and 

 passes straight to the right, ending as in Lingula. In Terehra^ 

 tula, Bhynchonella, and probably all the articulated Brachiopodaj 

 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 difler 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 rostrdta and Terehratula pectunculoides, in the Sritish Museum. 



t The position at which the intestine terminates in the Terebratulee and JRhyn- 

 chonellcB, seems to necessitate the escape of the feeces by the umbonal opening ; in 

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

 opening between the valves (e. g. in Uncites) which has been mistaken for a bj'ssal 

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

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

 outlet could be discovered. 



