358 MANUAL OF THE MOLLUSCA. 
food is obtained by means of currents « d by cilia, 
Lingula may have the power of slightly e tending the arms, 
The internal skeleton consists of two spiral processes in the 
Spiriferide (Fig. 168), whilst in Terebratula 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 
hable to be modified by age. That margin of the oral arms 
which answers to the lower lp of an ordinary bivalve, is 
fringed with long filaments (cirri), as may be seen eyen in dry 
specimens of recent Terebratule. In some fossil examples the 
cirri themselyes were supported by slender processes of shell ; * 
they cannot, therefore, be vibratile 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 cesophagus to a simple 
stomach, which is surrounded by the large and granulated 
liver; the intestine of ZLingula is reflected dorsally, slightly 
conyoluted, and terminates between the mantle lobes on the 
right side (Fig. 202). In Orbicula it is reflected ventrally, and 
passes straight to the right, ending asin Lingula. In Terebra- 
tula, Rhynchonella, and probably 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. 144, v.)+ 
The circulatory system is far less complex than was formerly 
supposed, and does not differ 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 Terebratula pectunculoides, in the British Museum. 
7 The position at which the intestine terminates in the Terebratule and Ihyn- 
chonella, seems to necessitate the escape of the feces by the umbonal opening; in 
these extinct genera which have the foramen closed at an early age, there is still au 
opening between the 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 was tried, but no 
outlet could be discovered. 
