134. Miscellaneous. 
In the animals thus placed the first difference that presents itself, 
and that which has most caught the attention of observers, is this: 
the Anodonta has its valves lateral ; the Terebratula has one of them 
dorsal, the other abdominal. 
This difference, which appears very great, has not quite so much 
importance as we should be inclined to attribute to it at first sight ; 
we need only free it from the secondary conditions which surround it, 
so as to see only the fundamental parts. Thus the greatly developed 
and multiplied muscles have become longitudinal and symmetrical, 
in consequence of the arrangement of the valves, and they have at- 
tracted the attention of naturalists perhaps too specially, and led 
them to neglect other more important organs. 
As the Brachiopod lives attached, a special locomotive organ would 
be useless to it; therefore its foot is aborted, and with it the corre- 
sponding portion of the nervous system. Here, morphologically 
speaking, we have a great and fundamental difference, very different 
from that presented by the position of the valves. 
On each side of the mouth of the Terebratula we find two long 
fringed arms, rolled up in a spiral form, and accompanied by a mem- 
branous lip; these are the analogues of the labial vela of the Lamel- 
libranchiata. The investigation of the nervous system justifies this 
notion ; for there exist two small symmetrical ganglia which, with the 
assistance of the long commissure uniting them, surround the ceso- 
phagus like a collar, and furnish nerves to the arms, as in the 
Lamellibranchiata the analogous ganglia furnish the nerves to the 
labial vela. 
These first ganglia, which are difficult to discover, correspond with 
the cesophageal ganglia of the other Mollusca; they are united by 
long connectives with the most highly developed and therefore most 
evident nervous masses, which are found above the mouth, in the 
median line, in the fold of the two lobes of the mantle. We know 
that this last organ performs, in great part, the function of the organ 
of respiration ; and as it receives its nerves from this last ganglionic 
centre, this may be regarded as the analogue of the pallio-branchial 
centre. 
As to the pedal ganglia, they do not exist, as the organ for which 
they are necessary is wanting. 
The organs of Bojanus and those of reproduction open in the 
Terebratula, as in the Anodonta, symmetrically outside and by the 
side of the pallio-branchial nervous centre. Moreover, according to 
the beautiful investigations of Mr. Hancock, the heart in the Brachi- 
opoda is dorsal, which furnishes an additional feature of resemblance 
between the two groups, for im this way the central organ of the 
circulation is separated from the organs of Bojanus and the pallio- 
branchial ganglia by the digestive tube. 
Lastly, in the Brachiopod, as in the Lamellibranchiate Acephalan, 
the organs just referred to are repeated symmetrically on each side 
of the median line of the body. 
Thus if we suppress in the Lamellibranchiate Acephalan the foot 
and the pedal ganglia, there remains an organism having the greatest 
