426 



Crotfurp af Natural jfai 



which are terrestrial are seen in our gardens, 

 pastures, and plantations ; on the trunks and 

 stems of trees, and in moist and shady 

 places : while multitudes of aquatic species 

 are to be found in the seas of tropical and arc- 

 tic regions, as well as in those which environ 

 our own islands. Others dwell on the 

 margin of fresh-water lakes and ponds, or 

 live at the bottom of rapid streams. In 

 short, they may be said to be universally 

 diffused, and produced in every variety of 

 form and colour. 



The organs of sensation and motion have 

 not the same uniformity in point of number 

 and position as in the vertebrate animals ; 

 and a greater aberration is observable in 

 the position of the heart and organs of re- 

 spiration, as well as in the structure of the 

 latter. The body of the Mollusca is almost 

 entirely occupied by the organs of nutrition; 

 and the organs of sensation and locomotion 

 are entirely subservient to the supply of 

 these. 



The motions of Molluscous animals con- 

 sist of different contractions, varying in their 

 direction, producing inflections and prolon- 

 gations, together with relaxations of their 

 several parts, by means of which they creep, 

 swim, and seize upon such objects as the 

 formation of these parts are adapted to : 

 they are, however, incapable of rapid pro- 

 gress, their limbs not being supported by 

 articulated and solid levers. The name 

 they have received designates them as soft 

 animals ; and this they are pre-eminently. 

 Almost all of them have a peculiar deve- 

 lopment of the skin, which covers their body 

 like a mantle, and has received that appel- 

 lation. This process, however, is sometimes 

 narrowed in a simple disc, or is tubiform, or 

 is hollowed into a sac, and in some cases it 

 is divided and extended in the shape of fins. 



There are two distinct kinds of molluscous 

 animals, namely, cephalous, or such as are 

 provided with a head ; and acephalous, or 

 headless. Those which have heads are usually 

 provided with tentacula, by which they feel 

 their way, and which they have the power 

 of easily retracing when in danger : some 

 have also the organs of sight and hearing ; 

 whilst others, destitute of these, only enjoy 

 the sense of touch. This they possess in 

 the organ of motion, to which the name of 

 foot has been given, and which is a member 

 of considerable importance. Many move 

 along the surface of the ground or bottom 

 of the sea, by means of their foot, which they 

 thrust forward and fix to some solid object, 

 and then by a strong muscular contraction 

 they draw their body to it ; and by a re- 

 petition of this action the animal continues 

 to make progressive motion. Others swim, 

 by using their foot as a fin ; while others, 

 again, permanently attach themselves to a 

 rock or other substance. 



Mollusca are again distinguished into 

 such as are naked, and such as are testaceous, 

 viz. furnished with a shelly covering. The 

 naked Mollusca have a membranous or fleshy 

 mantle (.as before noticed), which, however, 

 has frequently one or more hard laminae in 

 its texture. Shells are formed, like bones, 

 of a combination of earthy and animal 



I matter. The former consists entirely of 

 carbonate of lime ; the latter is composed of 

 layers of membrane, alternating with the 

 mineral matter. The shell is most solid 

 and massive in those species which lead an 

 inactive life. The variety of form, surface, 

 colour, brilliancy, and substance is almost 

 infinite. They are nearly all calcareous, 

 although some are simply of a horny con- 

 sistence ; but in both cases they consist of 

 matter deposited in layers, or exuded from 

 the skin under the epidermis, in the same 

 manner as nails, hairs, horns, scales, &c. 

 The shelly covering differs according as its 

 traiisudation is deposited either in parallel 

 laminse or in close-set veitical filaments. 

 And it is worthy of observation, that the 

 Mollusc always appears inclined to adapt its 

 shell to the form of the body, by reducing 

 its cavity if necessary, as well as by extend- 

 ing it. 



The Mollusca are, for the most part, ex- 

 tremely voracious ; and are not particular 

 in their selection of food. Their digestive 

 apparatus is always highly developed ; in 

 fact, every mode of mastication and degluti- 

 tion is met with : their stomachs are simple, 

 complicated, and frequently provided with 

 a peculiar armature : most species have 

 salivary glands, and always a liver, but 

 neither pancreas nor mesentery ; and the 

 intestinal tube is often of considerable 

 length, and much convoluted. The blood 

 is either colourless, or tinged with a bluish 

 cast ; and circulates, in all Molluscs, in a 

 regular system of arteries and veins, issuing 

 from a heart, which is either muscular or 

 nearly so ; and seems to contain a smaller 

 proportion of fibrin than that of vertebrate 

 animals. Several of the Molhisca are bisexual 

 some produce their young alive, while others 

 are oviparous : the eggs in some are covered 

 by a shelly envelope, and others only by a 

 simple viscosity. Some genera of Mollusca 

 inhabit the sea and fresh waters, while others 

 are entirely terrestrial ; and a few species 

 are amphibious. They feed on all sub- 

 stances, both animal and vegetable. Many 

 of them are taken and used as food for man ; 

 others supply nutritious prey for birds and 

 fishes ; and their shelly coverings are con- 

 verted into many useful articles of com- 

 merce. [See CEPHALOPODA ; PTEROPODA ; 

 GASTEROPODA ; HKTEKOPODA } LAMELLI- 



BKANCHIATA ; PALLIOBKANCH1ATA j TUJVI- 



CATA : also SHELLS.] 



MOLOCH. A singular genus of Reptiles, 

 established by Mr. Gray, and thus described 

 in the Appendix to Capt. Grey's Travels in 

 Australia : " Body depressed, covered with 

 irregular, unequal, small, granular plates, 

 each furnished with a more or less prominent 

 central spine, and with a series of large, 

 conical, convex, acute spines ; head and 

 limbs covered with similar scales and spines ; 

 head small, with very large spines over the 

 eyebrows ; tail with irregular rings of very 

 large acute spines ; femoral and subanal 

 pores none ; teeth small, subequal ; toes 5-5, 

 short, covered above and below with keeled 

 scales ; claws long, acute. The external 

 appearance of this lizard is the most ferocious 



