THE ANATOMY OF THE RIVER-MUSSEL. 
247 
size and constancy after winter.” * The pyloric portion of the 
stomach, or that which communicates with the intestine, is on 
the left side ; and the first curve of the digestive tract, in that 
its concavity looks towards the ganglion of the foot, is termed 
a “ neural” flexure (Huxley). The subsequent course of the 
intestine will be better understood by reference to figs. 2 and 
3, which are diagrammatic drawings from actual specimens, 
than by reading a necessarily elaborate and possibly obscure 
description. The lining membrane of the greater part of the 
intestine is thrown into large and deep transverse folds ; while 
upon the wall of the nearly terminal portion which runs 
beneath and parallel to the first portion of intestine, a longi- 
tudinal ridge begins to be developed, which is continued to the 
end of the intestine. That part of the intestine which, by 
virtue of its straight course, may be truly as well as analogi- 
cally termed “ rectum,” after running through the single ventri- 
cle of the heart f (see figs. 2, 3, 4, and 6), passes over the 
posterior adductor, to terminate in the posterior part of the 
upper of the two pallial chambers. 
In Anodonta , as in all Lamellibranchs, salivary glands are 
absent. There is, however, a well-developed liver, of a pale 
green colour and spongy texture, surrounding the stomach, into 
which it discharges its secretion by numerous ducts, the orifices 
of which may be plainly seen. 
The river-mussel can scarcely be said to select food. Any 
matters, whether animal, vegetable, or inorganic, with which 
the water entering the branchial chamber may be charged, 
are, through the agency of cilia lining the mouth and gills, 
* Various have been the theories respecting the supposed function of this 
body. According to some, it assists, like the sand or stones taken into a 
bird’s gizzard, in grinding the food ; others hold that it aids the foot in its 
resilience after contraction ; while, according to Poli, it probably regulates 
the flow of bile into the stomach, by means of processes which project, 
valve-like, from its upper end into the orifices of the biliary ducts. I have 
recently found in a specimen of Anodonta what I take to be the upper por- 
tion of this organ, in the shape of a small irregular body, gelatinous in 
appearance and substance, and which, as Poli says, u dum arescit est maxime 
friabilis.” Under the microscope it did not present any cellular structure, 
but was in appearance granular and somewhat like roughened ice. Some 
years ago I found this body in a Pholas. It was, according to my notes, 
“ cylindrical, cartilaginous in appearance,” and was, as far as I can remember, 
about ^ inch in length, and of the diameter of a stick of nitrate of silver. 
u Ejus substantia,” says Poli, u refert adamussim cristallum purissimum, 
flint-glass ab Anglis nuncupatum; est autem flexilis, et valde elasticus.” 
This body is said to exist in most Dimyaria, but to be absent (with one ex- 
ception) in the Monomyaria. 
t This happens with all Lamellibranchs, with the exception of the oyster 
( Ostrea ), the ship-worm {Teredo), the u poulette ” (Anomia), and Area. 
