MALACOLOGY. 



87 



Others who subsist upon living objects, in situations 

 where their prey from local habits or necessity are to 

 be found constantly situated, penetrate the shell by 

 drilling a hole with their toothed proboscis, and have 

 consequently but little trouble in seeking a commen- 

 surate supply of nutriment ; and with such as are not 

 permanently located to one spot, the trouble is some- 

 what greater ; but when once attained, a supply of 

 food lasts a considerable time, and other objects are 

 not far distant to replenish the store. Molluscs living 

 upon animal or vegetable decomposition, no doubt dis- 

 cover it by the sense of smell or feeling, and have also but 

 little trouble in finding it. This is the case with those 

 which, like the greater part of the slugs, feed upon 

 vegetation, in a more or less solid state of life ; with 

 these it only requires their being cut into small por- 

 tions and swallowed. In short, for all the species 

 whose nourishment depends upon molecules of mat- 

 ter, or invisible minute animated beings, no necessity 

 exists for the labour of searching after them, the cus- 

 tomary motion of their organs producing a vortex, 

 into which the food is drawn, and probably swallowed 

 with the fluid itself, as it flows through the animal's 

 structure. 



The diseases of molluscs cannot any of them 

 cither be studied or accounted for beyond the 

 general conclusion that a want of proper food or 

 accident has occasioned a disordered state of action. 

 The first must very rarely occur in an element teem- 

 ing with animation, adapted to the immediate supply 

 of that imperative necessity ; the latter, also, is less 

 likely to happen, from the strong defence nature has 

 wisely provided, to secure them from external injury, 

 or the attacks of enemies. Both these events, as we 

 have shown, do nevertheless occur ; and thus, by 

 the laws of nature, one animal becomes the prey of 

 another. 



In some bivalve molluscs, which are the most fre- 

 quently known to us as articles of food in our mar- 

 kets, a visible difference exists in what we term their 

 state of growth and condition of appearance ; they 

 have even some of them their season, but we can in 

 no way satisfactorily explain what peculiar state of 

 disorganisation they labour under, or why indeed any 

 moment of time should render them better than an- 

 other, except that period which in oysters has been 

 ascertained to be the time when the office of repro- 

 duction is in activity ; and they, like all other crea- 

 tures, suffer from its operation. 



In the Sepia, and the first class ot the Cephalopoda, 

 we have shown that they possess a more perfect sys- 

 tem of organisation than any other of the molluscs, not 

 only with regard to the development of animal senses, 

 but also as respects the exercise of them, it being a 

 well established fact that they use occasionally what 

 in the higher orders of creation would be termed cun- 

 ning, in attracting and seizing their prey. The intel- 

 ligence they exhibit decreases, in proportion as the 

 animals of this tribe descend in the scale of organisa- 

 tion, till it arrives ultimately at that point when it 

 cedes to a mere mechanical operation, and is only 

 confined to the opening or shutting of the valves of 

 their shells, as in the oysters and other numerous 

 species of that type. The general sensibility, or 

 rather susceptibility, of the molluscs that is, the 

 sense of touch is strikingly manifest in all of them, 

 every portion of their structure being most delicately 

 formed, so as to receive the slightest impression, 

 externally applied, and different from that state of re- 



laxed or unexcited period of repose they enjo}', when 

 not actively employed in the exercise of their several 

 functions ; but this sensibility is more particularly 

 situated at the edges of the mantle, which are very 

 often furnished with tentacular organs, of exquisite 

 susceptibility ; these are clearly distinguishable in 

 the conchyliferous Paraccpkalvphora, and also in 

 the two lobes of the mantle of all the Acephala, The 

 oyster, for example, may be observed to close its 

 valves, merely by a sudden impulse being given to the 

 water in which it lies. This sense becomes less appa- 

 rent in many species, whose exterior envelope being al- 

 ways exposed, is less tuberculous; and in those whose 

 skin is more or less hardened by exposure, it is scarcely 

 to be observed at all. 



A friend, whose modesty will not allow us to 

 name him, but whose scientific knowledge we have 

 more than once gladly availed ourselves of, well 

 knowing its accuracy and judgment, has favoured 

 us with some facts connected with this subject, 

 founded upon repeated experiments and the most 

 certain data ; with his permission we here insert 

 the result of them : " The form of the mouth, so 

 called, in molluscs, varies extremely in its character, 

 and it requires some experience in these singularly 

 organised creatures to distinguish it at all in many 

 species. Nevertheless, it always exists in some form 

 or another, depending greatly upon the figure of what 

 we may term the lips, or surrounding muscles, these 

 also possessing no given permanently fixed character, 

 except as regards generally each species ; they are, 

 consequently, very different in the distinct classes or 

 groups. In the most perfectly organised, the Sepia 

 for instance, these lips resemble a folded circular 

 membrane, of great delicacy, pierced in "the centre, 

 and symmetrically fringed at the edge. In the Tetltys* 



Tethys leporina lower and upper sides. 



the Doris, and the Patella, the lip forms a thick semi- 

 circular band, and at the centre of its lower side the 

 opening of the mouth is placed ; this is sometimes 

 carried out laterally, and forms a tentacular appendage. 

 In the Triton, the front edge of this thickened band 

 is dilated and fringed, forming a membranous curtain 

 varying in its size ; sometimes these lips are pro- 

 longed into the shape of a cup or glass, at the bottom of 

 which is the tongue, or trunk, this is the case with 

 the Conus. Within these lips, which are contractile 

 in everv part, and closing many of them like the open- 

 ing of a bag drawn together, there are found in 

 some species hard or corneous portions, which the 



