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decayed leaves. — The fluviatile Mollusca, including many Gasteropoda, and some 

 Conchifera, 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.) 

 All 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 " 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 *i<p*X>?, the head, a scientific term employed for the brain ; used by some, im- 

 properly, for the cerebrum only. 



