152 MR. R. OWEN ON THE ANATOMY OF THE BRACHIOPODA,. 
The alimentary canal commences by a small puckered transverse mouth', which is 
situated, as before mentioned, immediately behind the folded extremities of the arms, 
and opens opposite the middle line of the perforated valve. The esophagus, after having 
passed through the membrane inclosing the viscera, makes a slight turn upon itself, and 
advances straight towards the opposite valve; it then suddenly expands into a large 
oval stomach, from the sides of which the canals branching out into the hepatic follicles 
are continued. ‘The intestine returns in a direction towards the perforated valve, in- 
clines to the right side, and makes a slight bend forwards before perforating the cir- 
cumscribing membrane, in order to terminate between the mantle-lobes on that side. 
The whole alimentary canal thus forms a loop, whose convexity is turned towards the 
imperforate or upper valve. This description is taken from Ter. psittacea. 
The liver is a bulky gland, of a green colour and minute follicular texture ; it is 
disposed in two principal masses, which lie on each side the alimentary canal, and 
between the two lateral arches of the testaceous loop in those species of Terebratula 
which possess that appendage. In none of the specimens dissected could I perceive 
any trace of a salivary gland; all the glandular structure in connexion with the ali- 
mentary canal bore the green tint characteristic of the liver. In Ter. psittacea the 
ramifications of the hepatic follicles resemble those of Gorgonia flammea ; the ultimate 
sacs, when viewed with a high magnifying power, exhibited plainly the net-work formed 
upon their parietes by the minute hepatic arteries and veins. 
In two of the larger specimens of Ter. Sowerbii, the ova were lodged external to 
the liver, and had also insinuated themselves between the layers of the mantle-lobes, 
in close proximity to, and partly surrounding the branchial vessels. They are pro- 
bably discharged in this way from the mantle, having previously been exposed to the 
influence of the branchial currents. It is their situation, when so far advanced, which 
has tended to prevent the discovery of the organization of the mantle that adapts it to 
the office of respiration ; but if sufficiently young specimens are obtained?, the branchial 
vessels are seen unobscured by the ova. In Ter. psittacea the ova were very distinct, 
and arranged in elongated loops, but did not extend so far along the mantle as in 
Ter. Sowerbii, They projected from the external surface of the mantle. No structure 
that could be supposed to be distinct male or fecundating organs was present ; and 
the generation of Terebratula, therefore, as in the ordinary acephalous Bivalves, must 
be regarded as the simplest kind of hermaphroditism. 
In dissecting a Terebratula I have found it most convenient to cut transversely through 
the perforated valve, so as to leave the orifice and the pedicle connected to the opposite 
valve, by which means the disposition of the muscles is satisfactorily seen, and the 
delicate parts within are less liable to be disturbed than by attempting to separate the 
entire valve. 
1a, Fig, 12. 2 As in Figg. 5 to 9. 
