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decayed leaves.—The Jiuviatile Mollusca , including many Gasteropoda , and some 
Gonchifera , reside in fresh waters. Some frequent shallow ponds, breathe by 
means of a pulmonary cavity, and come to the surface to respire. Others reside 
in waters of different depths, since they respire by gills, and are less dependent on 
the shallowness of the water.— Marine Mollusca include genera of all the classes. 
Some, termed littoral, burrow in the sand, or adhere to the rocks between high 
and low water mark. Others, named pelagic, dwell in the deep, and are only 
obtained by diving and dredging, or by storms which cast them on shore, (p. 20.) 
Ail the terrestrial conchiferous animals have the power of passing into torpidity, 
or at least they do frequently- enter this state, independently of temperature. This 
is the case with the common Garden Snail ( Helix nemoralis ), when placed in a 
box without food in midsummer; in a day or two they attach themselves to the 
side of their prison, and become torpid, in which state they will remain for years 
if undisturbed. The temperature does not act in this case as with hybernating 
animals; indeed it is in the hottest weather that, in their natural state, they 
most frequently assume the condition alluded to. This circumstance, and the 
fact that the Snail speedily revives if plunged into water, or even slightly 
moistened,leads us to the conclusion that its cause must be sought in the unnatural 
absorption of fluid from the body in long-continued drought. A caged Snail kept 
in succulent herbage would in all probability retain the full use of its powers. 
In the second chapter Dr. Fleming treats of the progress of Molluscology, of 
the various systems propounded by early and recent authors, and of the import¬ 
ance of the characters on which they are severally founded. No one conversant 
with the most celebrated classifications in the different branches of Natural Science, 
or who reflects upon the subject, can doubt that the only way of arriving at 
anything like a natural or rational system, is to take into consideration every 
part of the animal, whether external or internal. Those who have fixed upon 
any one artificial character (Linnaeus, Vieillot, &c., for example) have fre¬ 
quently framed very useful and ingenious arrangements; but these are never to be 
compared, for accuracy, with the 64 natural systems.” The case is strikingly 
analogous to the celebrated physiognomical system of Lavater. This philosopher, 
instead of estimating the moral and intellectual character of Man from the 
development of the brain, the fountain-head, selected the features of the face 
as his index. Now such a mode is productive of some advantage, inasmuch as 
the cerebral development exercises a certain influence over the muscles of the 
face ; but, for obvious reasons, errors must abound even respecting the few pre¬ 
dications which can be made; while the development of the encephalon* affords 
* Ev, in, and the head, a scientific term employed for the brain; used by some, im¬ 
properly, for the cerebrum only. 
